Symposium EN12—Advanced Materials and Chemistries for Low-Cost and Sustainable Batteries

Polysulfide shuttling is an inevitable trait of metal-sulfur (S)-based batteries. Such shuttling behavior is directly related to the amount of soluble intermediate polysulfide species and is primarily affected by electrolyte constituents. While the sulfur electrode suffers from lower accessible capacity due to the loss of active S species, sodium (Na) metal is also plagued by severe plating/stripping and dendrite growth, leading to cyclable Na loss. However, it is still poorly understood whether Na or S electrode has the most deleterious consequences for overall Na-S chemistry in specific electrolyte combinations. Given the influence of electrolyte in dictating the intermediate reaction steps, electrode-electrolyte interphase formation, and effectiveness of ionic transport, this work carefully investigates the effects of single and multi-solvent electrolyte on the electrochemical signatures of S electrode. Additionally, this work probes the aging process of Na metal, altered by different types of electrolyte-specific morphological evolution, manifesting a dramatic drop-off in cell performance. This complex electrochemical interaction in both the electrodes is further compounded by the limiting ionic transport at low-operating temperatures. Current work explores the electrolyte-mediated changes in decoupled cathode-anode cell signature and impedances and performances using a three-electrode cell configuration in different temperature conditions. By correlating the electrolyte-specific structural-compositional evolution and operational specifications of both the metal and sulfur electrodes, this work aims to lay the ground for thermally versatile and high-performance Na-S batteries.

In this tutorial, I will review the use a Battery Performance and Cost model to undertake a cost analysis of the materials for sodium-ion and lithium-ion cells, as well as complete batteries, and determine the effect of exchanging lithium with sodium, as well as the effect of replacing the material used for the anode current collector foil, on the cost. Moreover, I will compare the calculated production costs of exemplary sodium-ion and lithium-ion batteries and highlight the most relevant parameters for optimization. Finally, the major raw materials for lithium-ion cathodes will be examined in terms of potential supply risks because supply issues may lead to increased costs. Through the use of a scenario-based supply and demand analysis, the risks to the supply of lithium and cobalt will be assessed, and implications for battery research will be discussed.

In the last two decades, Li-ion batteries have proven to offer some of the best performance among the existing electrochemical energy storage technologies, striving to firm variable renewable generation and mass-market full electrification. A Li-ion battery cell exploits the redox activities of the anode and cathode to generate electricity outside the cell while reversibly intercalating Li ions between the two electrodes through an ionic conducting electrolyte. The difference in electrochemical potential between the electrodes is the thermodynamical driving force of the cell, while its rate capability is governed by the kinetics of the ion transport in the electrodes and in the electrolyte. Ab initio techniques, relying on the knowledge of the physical laws without the need of experimental inputs, provide insight onto the materials' electronic and structural properties, and shed light onto the dynamical processes that underlie the battery performance. Calculation of intercalation potentials, pre- diction of electrochemical, chemical and phase stabilities, study of dissolution and diffusion phenomena in the electrolytes and electrodes, and characterization of mechanical properties are a few examples of the various applications of the state-of-the-art ab initio approaches for the modelling of battery materials. In this tutorial, we provide an overview of the ab initio methods to study ionic diffusion in battery materials. First, we discuss the simulation approaches to probe the dynamic evolution of a system of atoms via the quantum mechanical potential, namely the Born-Oppenheimer and the Car-Parrinello first-principles molecular dynamics (FPMD) techniques. Thus, the extraction of the diffusion coefficients from the sampled trajectories according to the Green-Kubo relation is described, together with the role of ionic correlations in these systems (tracer/charge diffusion coefficient), and the use of the Nernst-Einstein equation to compute the ionic conductivity from the diffusion. To conclude, we present few benchmark cases from the recent literature and we discuss intrinsic 1 limitations together with recently proposed solutions, as the use of ab initio molecular dynamics in conjunction with machine learning, to give reliable ambient temperature diffusion coefficients that can be directly compared with the experiments.

Lithium metal battery systems (LMBs) are being sought as an ultimate replacement to LIBs, potentially increasing the cell energy by over fifty percent due to the high capacity and low voltage of the metal anode. Analogous improvement in energy is possible with sodium metal batteries (NMBs) and with potassium metal batteries (KMBs), where existing ion insertion anodes can be replaced by plating/stripping metal. However, in all three cases safety and performance are compromised by an unstable solid electrolyte interphase (SEI) that consumes metal ions and electrolyte, and ultimately leads to dendrites. This presentation provides a series of case studies derived from the group's LMB, NMB and KMB research on the microstructural design principles that provide for long-term cycling and fast-charge stability of metal anodes. The approaches may be categorized as the following: a) design of plating/stripping supports and templates with tuned geometry and functionality; b) design of secondary interlayers placed between the metal anode and the separator; and c) design of multifunctional hybrid separators to replace the conventional polymer separators employed with LIBs. It is demonstrated that despite appearing distinct, the efficacy of each in enabling electrochemical stability originates from three fundamental features that are directly interrelated. The wetting behavior of the electrolyte on the anode must be optimized, the wetting/stripping behavior of the metal anode on the current collector must be controlled, and a geometrically and chemically modified SEI must be established. Simultaneously achieving all three leads to stable plating/stripping, while missing even one leads to rapid dendrite growth. Cryogenic FIB cross sections and cryo-TEM are combined to yield new insight regarding film wetting behavior and early dendrite formation in optimized versus baseline specimens, analyzing growth in several representative electrolytes.

Electrolyte engineering has enabled improved cycling of Li metal batteries and anode-free cells at low current densities; however, fast ionic conduction and high-rate capability are desirable yet less-studied. Meanwhile, the understanding of tuning ionic transport in advanced electrolytes is still lacking. Herein, we iteratively design and synthesize a family of fluorinated-1,2-diethyoxyethanes (fluorinated-DEEs) as electrolyte solvents. The position and amount of fluorine atoms functionalized on the DEE were found to significantly impact Li cyclability, oxidative stability, and ionic conduction. The partially-fluorinated, locally-polar –CHF₂ is identified as the optimal group rather than fully-fluorinated –CF₃ in common designs. Paired with 1.2M LiFSI, these developed single-salt-single-solvent electrolytes simultaneously enable high conductivity, low and stable overpotential, >99.5% Li || Cu efficiency (up to 99.9%), and fast activation (Li || Cu efficiency >99.3% within two cycles). Combined with high-voltage stability, these electrolytes achieve ~200 cycles in thin-Li || high-loading-NMC811 full batteries and >140 cycles in fast-cycling Cu || microparticle-LFP pouch cells under realistic testing conditions, which stand among the state-of-the-art. The correlation of Li ion–solvent coordination, solvation environments, and battery performance is investigated. Our electrolyte design and systematic study point out the path towards practical Li metal batteries.

One of the key challenges in the development of energy storage devices is the ability to operate efficiently under extremely cold environments (i.e. below -20 °C), especially for batteries in temperature-sensitive applications such as portable electronic devices, transportation, and stationary energy storage. As reported, at low temperature, the increased internal resistance and sluggish ion diffusion in batteries lead to declined charge-delivering capability, which deteriorates cell performance and eventually terminates the power output. Although lithium (Li) metal battery (LMB) with ether electrolyte is considered promising in overcoming these issues due to the low viscosity of ether solvent and its distinctive electrode structure, the low-temperature performance of LMBs remains unsatisfactory. A series of problems are observed upon the anode-electrolyte interphase, including aggravated side reactions, abnormal Li deposition, and dramatically increased solid-electrolyte interphase (SEI) resistance. Thus, building a stable SEI layer on the Li metal anode is critical for the development of low-temperature LMBs.
Here, we demonstrate a dioxolane (DOL)-based electrolyte with dimethyl sulfoxide (DMSO) as the low-temperature additive, which helps to construct a robust SEI layer that possesses uniform structure and good composition consistency even under extremely cold condition. In this electrolyte, DOL works as the primary electrolyte component that defines the basic electrochemical properties, while DMSO further tunes the SEI composition to boost the low-temperature performance. To elucidate the modified microstructure and chemical composition of the SEI film, cryogenic transmission electron microscopy, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy are conducted to make a comprehensive investigation. Moreover, a series of electrochemical tests are conducted under extremely cold environments, and results demonstrate that the adjusted SEI is resilient to the stripping and plating cycles of Li metal at temperatures as low as -80 °C. Full cells with lithium iron phosphate as the cathode material are assembled and good electrochemical performance is achieved at -40 °C at 0.2 C. The solvation structure of DMSO added electrolyte is also investigated to fundamentally understand how it affects the SEI formation. Our work establishes fundamental insights into the low-temperature electrolyte additives and paves the road to the further applications of LMBs in harsh environments.

The sluggish electrochemical kinetics of sulfur species has impeded the wide adoption of lithium-sulfur battery, which is one of the most promising candidates for next-generation energy storage system. Here, we present the electronic and geometric structures of all possible sulfur species and construct an electronic energy diagram to unveil their reaction pathways in batteries, as well as the molecular origin of their sluggish kinetics. By decoupling the contradictory requirements of accelerating charging and discharging processes, we select two pseudocapacitive oxides to enable the efficient transport of electron/Li⁺ to and from sulfur intermediates respectively. After incorporating pseudocapacitive oxides, the electrochemical kinetics of sulfur cathode is significantly accelerated by a factor of 5 times and 1.8 times, respectively. This strategy, which couples a fast-electrochemical reaction with a spontaneous chemical reaction to bypass a slow-electrochemical reaction pathway, offers a solution to accelerate an electrochemical reaction, providing new perspectives for the development of high-energy battery systems.

Batteries based on multivalent metals have the potential to meet the future needs of large-scale energy storage. However, the complexity of multivalent metal-ion chemistries has led to technical challenges. Mg²⁺ interacts strongly with electrolyte solutions and cathode materials, leading to sluggish ion dissociation and diffusion, and consequently low power. With better understanding of electrolyte-electrode interactions and recognizing the strong influence of electrolyte solutions on cathode storage mechanism, fast Mg²⁺ storage could be realized by combining a highly performing single salt electrolyte and heterogeneous enolization redox chemistry in a Mg battery that delivers a specific power nearly two orders of magnitude higher than that of state-of-the-art Mg batteries. In a separate work, we studied zinc plating/stripping behavior in the presence of porous and nonporous separators. We find that adoption of porous separators results in directional metal penetration upon plating and “dead zinc” formation upon stripping. Using a nonporous separator, zinc plating/stripping was limited beneath the separator. The uniform ion flux generated by intermolecular solvent channels leads to a dense and uniform metal deposition morphology and reversible stripping. These results emphasize the microstructure of separators can serve to stabilize metal and provide guidelines for developing novel separators for long-cycle-life aqueous zinc batteries.

Sodium (Na) based batteries are the promising alternative to Li-ion batteries due to the similar physical and chemical properties between Na and Li, as well as the natural abundance and therefore low cost of Na resources. Among all possible anodes for Na batteries, Na metal anode exhibits exceptional advantages because of its high theoretical capacity (1166 mAh/g) and low redox potential (-2.71 V vs. SHE). However, highly reactive Na metal anodes suffer from rapid electrode degradation and short-circuit related safety issues caused by the formation of unstable and fragile solid electrolyte interphase (SEI) and dendritic Na growth. Herein, we present a bifunctional and inexpensive electrolyte additive, hexadecyl trimethylammonium bromide (CTAB) that provides a synergistic effect to stabilize Na metal anode from CTA⁺ cation and Br^- anion. Previous study on Li metal anode indicated that cationic surfactant used as an electrolyte additive could suppress Li dendrites growth by the role of lithiophobic surfactant cations, whereas the anions are ineffective on the anode protection. However, in this work, we discovered that the cation CTA⁺ and anion Br^- can work synergistically to enhance the stability and electrochemical performance of Na metal anode. Specifically, sodiophobic CTA⁺ can be absorbed onto the Na protuberant areas of the Na metal surface by electrostatic forces, which promotes preferential deposition of Na to surrounding regions by sodiophobic repulsion mechanism, thereby enabling uniform Na plating. More promisingly, Br^- anions can facilitate the formation of a stable NaBr-rich SEI layer, which has been confirmed by the cryogenic transmission electron microscopy (Cryo-TEM). The NaBr-rich SEI layer exhibit low energy barrier for Na⁺ transport, which restrain the propensity of dendrite nucleation. We show that with the addition of 5 mM CTAB in the electrolyte, a superior electrochemical performance of Na metal anode with high areal capacity (up to 30 mAh/cm²) and high current density (up to 8 mA/cm²) can be achieved over long-term cycling for 800 h. As a proof of concept, the constructed Na-S full cell delivers high performance with a high cathode loading of 4 mg/cm².

Rapidly developing technologies call for sustaining, safe, and cost-efficient rechargeable energy storage devices for portable electronics and electrical vehicles beyond traditional lithium-ion batteries. Alkali metal batteries allowing high battery voltages and high electrode capacities are intensively studied aiming to fulfill this increasing need of efficient energy storage, whereas the dendrite issue as well as interfacial issues are threating the battery safety, limiting the battery performance, and therefore being hindered in commercialization. Low-temperature liquid metals including mainly fusible alloys are considered as promising alternatives of alkali metals as anode materials thanks to their dendrite-free or self-healing features, as well as superior mechanical and electrochemical properties. Beside the dendrite-free feature, liquid metals could also promise coherent electron and ion conduction at the interfaces in a battery. As another one of the competitive high-energy-density battery components, the solid-state electrolytes have been suffering from the poor interfacial contact, which could potentially be solved by the conformal liquid metal electrodes. Since multiple species of elements can be obtained in a liquid alloy, the interfacial charge selection behavior with various interfaces is an interesting and crucial designing principle that needs further study for deeper understandings. With deeper understanding of the interfacial behaviors and rational designs of battery, liquid metals can promise a bright future for next-generation high-energy-density and safe energy storage applications.

Calcium batteries are promising alternatives to lithium batteries owing to their high energy density, comparable redox potential, and Earth abundance. However, to meet practical demands in high-performance applications, suitable electrolytes are required, which, for Calcium batteries remains a challenge. Here, we report the synthesis and characterization of poly(ethylene glycol) diacrylate (PEGDA)–based gel electrolytes using calcium salts in a mixture of ethylene carbonate (EC) and propylene carbonate (PC) solvents. We report room-temperature conductivity between 10⁻⁵ and 10⁻⁴ S/cm, an electrochemical stability window of ∼3.8 V, full dissociation of the salt, and minimal coordination with the PEGDA backbone. Cycling of symmetric Ca metal cells using this gel electrolyte proceeds but with increasing overpotentials, which can be attributed to interfacial impedance between the electrolyte and calcium surface, which inhibits charge transfer. Calcium may still be plated and stripped yielding high-purity deposits and no indication of significant electrolyte breakdown, indicating that high overpotentials are associated with an electrically insulating, yet ion-permeable solid electrolyte interface (SEI). This work provides a contribution to the study and understanding of polymer gel materials toward their improvement and application as electrolytes for calcium batteries¹.
1. Biria, Saeid, Shreyas Pathreeker, Francielli S. Genier, Fu-Hao Chen, Hansheng Li, Cameron V. Burdin, and Ian D. Hosein. "Gel Polymer Electrolytes Based on Cross-Linked Poly (ethylene glycol) Diacrylate for Calcium-Ion Conduction." ACS Omega (2021).

Lithium-ion batteries (LIBs) dominate today’s renewable energy storage market, however increasing energy storage demands will require use of more abundant materials in order to keep cost under control. Sodium-ion batteries (SIBs) are considered a promising route given its vast abundance but they suffer worse reactivity issues than LIBs. Developing all solid state Na ion batteries (SSBs) is not only needed to ensure device safety but may be enabling for market entry. We propose, building on our architecture-based approach successful in solid-state LIBs¹, to solve the problems mentioned above. This approach uses nanoscale area enhanced topographies (i.e. nanopores, trenches, pillars, etc) to dramatically improve both energy and power density (areal and volumetric). Here we present initial steps toward expanding this concept into solid state Na systems.

We recently developed an atomic layer deposition (ALD) process for sodium phosphorus oxynitride (NaPON), analogous to the well-known lithium phosphorus oxynitride (LiPON) solid-state electrolyte (SSE). ALD NaPON exhibited an ionic conductivity of 2.5 × 10^-6 S/cm at 80 °C, comparable to those of ALD fabricated Li⁺ conductors and high enough to use in 3D Na-SSBs.² In this presentation, we will report on the underlying materials chemistry and challenges of fabricating the first thin-film nanoscale Na-SSB using an evaporated Na metal anode and an ALD V₂O₅ (30 nm) cathode, and offer direct comparisons to the analogous lithium-based devices.

V₂O₅ was chosen as the cathode material due to its success in thin-film LIBs and its capability to reversibly intercalate Na⁺ up to a capacity of 235 mAh/g. Initial electrochemical analysis was conducted with NaPON-coated V₂O₅ vs. Na metal in liquid electrolyte cells. The observed redox chemistry suggests that V₂O₅ is sodiated to Na₂V₂O₅ during the NaPON ALD deposition. However, when NaPON-coated V₂O₅ is used with a liquid electrolyte, NaPON acts as a stable solid electrolyte interphase layer, extending cycling lifetime and reducing interfacial resistance. All solid-state device (Na/NaPON/V₂O₅) electrochemical characterization suggests further sodiation of the V₂O₅ cathode during the Na metal evaporation to a fully sodiated Na₃V₂O₅ state. We use TEM, ToF-SIMs, and XPS analysis to infer the underlying processing phenomena and the subsequent electrochemical effects on the Na-SSB. Unlike their sodium analogues, V₂O₅ remains unlithiated during ALD LiPON deposition and subsequent Li evaporation.¹ This finding highlights the nontrivial contrast between a Na/NaPON/V₂O₅ SSB to a Li/LiPON/V₂O₅ SSB, assembled identically except for the Li and LiPON (i.e. same deposition techniques).

1. Pearse, A.; Schmitt, T.; Sahadeo, E.; Stewart, D. M.; Kozen, A.; Gerasopoulos, K.; Talin, A. A.; Lee, S. B.; Rubloff, G. W.; Gregorczyk, K. E., Three-Dimensional Solid-State Lithium-Ion Batteries Fabricated by Conformal Vapor-Phase Chemistry. ACS Nano 2018, 12 (5), 4286-4294.
2. Nuwayhid, R. B.; Jarry, A.; Rubloff, G. W.; Gregorczyk, K. E., Atomic Layer Deposition of Sodium Phosphorus Oxynitride: A Conformal Solid-State Sodium-Ion Conductor. ACS Applied Materials & Interfaces 2020, 12 (19), 21641-21650.

Owing to its low-cost advantage, Na-ion batteries (NIBs) have been widely studied as a promising candidate competitive with conventional Li-ion batteries (LIBs) for large-scale applications. Nevertheless, the current energy-normalized cost of NIBs (0.14$/Wh⁻¹) is more expensive than that of LIBs (0.11$/Wh⁻¹)¹ and the development of high-capacity electrodes for NIBs are essential for future energy storage system. Of electrodes discovered to date, layered Na-Mn-O cathodes have attracted much attention due to its high specific capacity and operating voltage.² These materials commonly accommodate Na ions by the redox reactions between Mn³⁺ and Mn⁴⁺, allowing large theoretical capacity (e.g. 244 mAhg⁻¹ for Na_xMnO₂). However, the Mn³⁺/Mn⁴⁺ redox reaction necessarily accompanies with the Jahn-Teller distortion³ that lowers the capacity retention, which hinders the use of Na-Mn-O-based cathodes.
One effective way to avoid the Jahn-Teller effect is to change the chemical composition; recent studies reported that Na₂Mn₃O₇ layered oxides can accommodate Na⁺ ions without the Mn³⁺/Mn⁴⁺ redox reaction and display improved cyclability.⁴ In addition, introducing Al dopants is also known to be effective in soothing the Jahn-Teller effect.⁵ In this context, the addition of Al dopants on Na₂Mn₃O₇ may enable the further enhancement in cathode performance. Still, the effect of Al dopants on Na₂Mn₃O₇ is yet to be elucidated. In this study, using density functional theory calculations, we performed a comparative study between pristine Na₂Mn₃O₇ and Al-doped Na_2.4Al_0.4Mn_2.6O₇ to analyse the effect of Al dopants on the cathode performance. Calculations suggest that the substitution of Al for Mn makes Na⁺ ions to be inserted in various sites other than those in Na₂Mn₃O₇, resulting in smooth voltage profiles with improved capacity. Furthermore, owing to relatively high electronegativity of Al, the addition of Al dopants alters anionic redox reactions and associated structural changes of Na₂Mn₃O₇ upon charge. Based on above findings, we also discuss potential strategies for finding dopants that enable high performance sodium manganese oxide cathodes.
References
¹ J. W. Choi and D. Aurbach, Nat. Rev. Mater., 2016, 1, 1-16.
² K. Lu, Z. Hu, Z. Xiang, J. Ma, B. Song, J. Zhang, and H. Ma, Angew. Chem., 2016, 128, 10604-10608.
³ C. Stock, L. Chapon, O. Adamopoulos, A. Lappas, M. Giot, J. Taylor, M. Green, C. Brown,and
P. Radaelli, Phys. Rev. Lett., 2009, 103, 077202.
⁴ B. Song, M. Tang, E. Hu,et al., Chem. Mater., 2019, 31, 3756-3765.
⁵ W.-L. Pang, X.-H. Zhang, J.-Z. Guo, et al., J. Power Sources, 2017, 356, 80-88.

Magnesium, calcium and aluminum are promising elements for future low-cost batteries due to the attractive energy density of metals and possible application of metal anodes in battery cells. All three elements are highly abundant in the earth's crust whit homogenous distribution on the globe. They are considered sustainable elements for batteries used in renewal energy storage, contributing to the decrease of cell cost.
Besides the above-mentioned benefits, there are several challenges connected with stripping and deposition of the metals, with the appropriate electrolyte formulation compatible with the metal anode and potential cathode materials, with current collectors, the housing of the cell and with the choice of appropriate cathode materials. A combination of multivalent anodes with classical insertion cathodes typically results in low electrochemical activity, while much better activity can be obtained with cathodes that allow coordination redox reaction or conversion redox reaction. Among those, the highest applicability can be obtained with redox-active polymers and sulfur-based cathodes.
In this presentation, an overview of recent achievements in our group in the field of multivalent batteries will be discussed with a focus on the proper selection of battery components in order to achieve electrochemical properties attractive for commercialization.

Acknowledgement: This work is supported HONDA R&D Europe and by the Slovenian Research Agency (research core funding No. P2-0393 and research project Z2-1864).

References:
J. Bitenc, K. Pirnat, T. Bančič, M. Gaberšček, B. Genorio, A. Randon-Vitanova and R. Dominko, Anthraquinone-Based Polymer as Cathode in Rechargeable Magnesium Batteries, ChemSusChem, 2015, 8, 4128–4132.
A. Vizintin, J. Bitenc, A. Kopač Lautar, K. Pirnat, J. Grdadolnik, J. Stare, A. Radon-Vitanova and R. Dominko, Probing electrochemical reactions in organic cathode materials via in operando infrared spectroscopy, Nat. Commun., 2018, 9, 661.
Jan Bitenc, Alen Vizintin, Joze Grdadolnik, Robert Dominko, Tracking electrochemical reactions inside organic electrodes by operando IR spectroscopy Energy Storage Materials 21 (2019) 347–353
A. Robba, A. Vizintin, J. Bitenc, G. Mali, I. Arčon, M. Kavčič, M. Zitnik, K. Bučar, G. Aquilanti, C. Martineau-Corcos, A. Randon-Vitanova, R. Dominko, Chem. Mater.,2018, 29, 9555-9564.
J. Bitenc, N. Lindahl, A. Vizintin, M. Abdelhami, R. Dominko, P. Johansson, Concept and electrochemical mechanism of an Al metal anode - organic cathode battery. Energy storage materials, Jan. 2020, vol. 24, str. 379-383
J. Bitenc, A. Scafuri, K. Pirnat, M. Lozinskek, I. Jerman, J. Grdadolnik, B. Fraisse, R. Berthelot, L. Stievano, R. Dominko, Electrochemical performance and mechanism of calcium metal-organic battery. Batteries & supercaps, ISSN 2566-6223, [in press] 2020, 14 str.

Lithium sulfur batteries (LSBs) are a promising next generation energy storage technology due to their high theoretical capacity, low cost, and environmental friendliness surpassing that of current lithium ion batteries (LIBs). However, the LSB still has challenges that restricts its practical applications. A major obstacle that limits its performance is the dissolution of long-chain lithium polysulfides into the electrolyte which results in loss of active material and capacity fade during the charge/discharge cycles. Here, we developed a novel sulfur composite with a liquid metal (LM) and graphene oxide dispensed on carbon cloth electrode to achieve a long cycling of lithium sulfur batteries. The liquid nature of the metal results in many advantages. It provides a strong encapsulation of the sulfur particles, which inhibits the polysulfide shuttle effect. In addition, it prevents the detachment of the sulfur particles from the current collector albeit large volume changes and cracking of the sulfur during lithiation and delithiation, maintaining the electron conduction paths. This innovative composite resulted in a high discharge capacity, an outstanding capacity retention over 300 cycles at 0.2 C, and a high coulombic efficiency. Our results demonstrate an effective method to surpass the polysulfide shuttle effect and pave a new way towards practical applications of lithium sulfur batteries by using multifunctional liquid metal composites.

Manganese oxides have been highly studied as cathode materials for Li-ion batteries (LIBs) due to their low cost, environmentally benign nature, high theoretical capacity, and unique morphologies that allow for facile ion intercalation. Demonstrated here, V-substituted alpha-MnO2 was successfully synthesized with no crystalline or amorphous impurities, as evidenced by X-ray diffraction (XRD) and Raman spectroscopy. TEM revealed a morphological evolution from nanorods to nanoplatelets as V-substitution increased, while electron-energy loss spectroscopy (EELS) confirmed uniform distribution of vanadium within the materials. Rietveld refinement of synchrotron XRD described an increase in bond lengths and larger range of bond angles with increasing V-substitution, indicating structural distortion. X-ray absorption spectroscopy (XAS) of the pristine materials revealed the V valence to be above 4+ and the Mn valence to decrease as V content increases. Upon electrochemical lithiation, increasing amounts of V were found to preserve the Mn-Mn relationship at higher depths of discharge, which relates to enhanced structural stability. Electrochemical testing showed the 10%V-substituted sample delivered the highest capacity and capacity retention after 50 cycles and had the lowest polarization resistance according to pulse test results. This enhanced electrochemistry is related to the high level of V-substitution and the nanoplatelet morphology of the 10% V-substituted material. DFT calculations predicted that the high stability of highly oxidized V ions upon lithiation is essential to ensure the structural stability and polarization-resistance by enhancing the stability of the K⁺centered 2 by 2 tunnel and promoting symmetric structural changes, which likely lead to the observed enhancement in structural stability.

New energy storage systems require developments in electrode design and architectures to enable high energy density along with high power and fast charge rates. A balance between active material loading and full utilization of the electrode needs to be made when considering conventional battery electrode fabrication techniques such as slurry-caste electrodes and dense pelletized electrodes. In this work, thick porous electrode fabrication techniques have been developed to obtain a higher active mass loading in an architecture which also enables ion and electron transport. Synchrotron-based operando energy dispersive X-ray diffraction (EDXRD) was used to examine the homogeneity of the phase distribution in a thick porous electrode (TPE) of lithiated LVO over extended high rate cycling. Three locations were probed, while cycling at a fast rate of 1C, revealing a homogeneous phase transition across the thickness of the electrode at the 1^st and 95^th cycles. Continuum modelling results agreed with the EDXRD results, indicating homogenous lithiation across the electrode upon discharge at 1C and ascribed decreasing accessible active material to be the cause of capacity fade between the 1^st and 95^th cycles. The model was supported by the observation of significant particle fracture by ex situ SEM, consistent with loss of electrical contact. The absence of the beta phase peaks in the EDXRD over extended cycling are consistent with electrochemical accessibility of only part of the active material. Overall, through combining operando EDXRD, continuum modeling, and ex situ measurements we gained a deeper understanding of lithium vanadate transport properties and the capacity loss mechanism under high rate extended cycling within a thick highly porous electrode architecture.

Ni-rich NMC, such as NMC622, is an attractive Li-ion battery cathode material due to its balance of energy density, thermal stability, and reversibility. However, a compromise must be struck between higher energy density associated with a more positive upper voltage limit, and better reversibility at lower voltage limits. Improved understanding of structural transformations occurring as a function of voltage window, and their associated impacts on capacity fading, are critically needed to rationalize electrochemical behavior. Through operando X-ray characterization of cells cycled at 3-4.3 V and 3-4.7 V both before and after extensive cycling, this study presents an in-depth investigation into the effects of voltage window on the structural transformations of NMC622 over extended cycling. The utilization of this operando methodology over many cycles enables the collection of data on the structural transformations that can cause capacity fade as the fade occurs in real time. Cycling at 3-4.7 V, initially led to a higher delivered capacity along with greater lithium extraction and greater structural distortion. However, charging at this higher potential led to significantly more capacity fade along with reduced lithium (de)insertion, increased structural distortion, and significant particle cracking. This study provides important insights into the mechanisms of capacity fade in NMC622/Li-ion batteries, which will enable the design of NMC622 electrodes that deliver both higher capacities and exhibit better capacity retention.

High-nickel layered cathode LiNi_xCo_yMn_1-(x+y)O₂ material is the center of attention for high energy density cathode materials and sustainable resources. In this work, cathode material with low or no cobalt (0 <= y <= 0.06) was synthesized successfully by the co-precipitation method followed by the lithiation process. The resulted materials have spherical and uniform size distribution morphology. Coatings and dopings (such as transition metal doping and Li containing glass material coating) on these materials were studied to show a significant improvement in cycling stability. The post-cycling TEM and SEM characterization indicate that the doping and coating can reduce the reconstruction layer of the layer structured, high-Ni and low-Co cathode materials and maintain the spherical morphology in contrast to bare control materials. The procedure for synthesizing single-crystals cathode using these precursors was also explored and promising potential for a long-cycling low-Cobalt material.

The fast charging of lithium-ion batteries (LIBs) is vital for the broad adoption of electric vehicles. However, the poor ionic conductivity of the electrolyte, low electronic conductivity of thick graphite anode electrodes, and increased impedances at electrode/electrolyte interphases upon cycling is the critical barrier to achieving the fast-charging performance of LIBs. The polymer binder of battery electrodes is used to ensure their mechanical integrity. It significantly influences the Li⁺ transport and charge transfer in the electrode materials, particularly for ultrathick electrodes. Herein, a new Li⁺ affinity polymer material is proposed as a binder for graphite anode with a practical level of areal capacity (4 mAh cm⁻²). The functional polymer binder can not only deliver higher ionic conductivity than conventional graphite binder, but it also can facilitate Li⁺ transport in anode by creating additional ion transport pathways through surface conduction when the Li-ion transport rate is limited to a liquid electrolyte at extreme fast charging conditions. As a result, the LiNi_0.8Co_0.1Mn_0.1O₂ || graphite full cell with a high mass loading (3.5 mAh cm⁻²) and high charging rate (6 C) can stably operate over 100 cycles.

Current electrodes for lithium ion technology rely on graphite-based anodes that have a relatively low theoretical capacity (372 mAh g^-1). Alternative materials such as transition metal oxides provide higher specific capacities due to multiple electron transfers. Particularly appealing is magnetite, Fe₃O₄, as it is a low cost, earth abundant and environmentally friendly material with the potential to deliver 924 mAh/g. Despite significant research on the design and synthesis of electrode active materials, the design and composition of the electrodes has also been shown to affect the function of the battery including the rate capability and capacity retention. Herein, is the exploration of electrode factors and binders that aid in electron and ion transport of magnetite (Fe₃O₄) based anodes. Water-soluble polymers in conjunction with polyethylene glycol (PEG) are studied to determine the role of carboxylate functionalities on overall function. Overall, this study compares a series of electrode designs to identify materials that can be manipulated to assist overall electrochemical performance of composite Li-ion battery anodes.

Lithium ion batteries have long been established as the leading technology for energy storage devices due to their high energy density and longevity¹. Common cathode materials for these batteries are layered oxides. LiCoO₂ (LCO) is a popular layered oxide which is commonly used within the electronic industry. Yet, due to increasing environmental impacts tied with the price of the cobalt, there has been a substantial push for cobalt-free cathode materials, especially for the automotive application².

The isostructural compound LiNiO₂ (LNO) has been identified as the ideal replacement for LCO. This is principally due to LNO's comparably high theoretical capacity, however, the material is affected by mechanical and thermodynamical instabilities. Recent work has demonstrated that substitution strategies can cater for the instabilities whilst also minimising the reduction in capacity^3,4. In this study, density functional theory calculations have been carried out in order to fully understand the doped structure with the aim to find a stable nickel-rich cathode with a high theoretical capacity. Experimentally it has been reported that the ground state structure of LNO has the R3m space group. However, computational calculations have demonstrated that it is in fact the P2₁/c structure⁵. Using the true ground state structure, point defects will be investigated in these cathode materials in order to fully understand the doped structure.

References

[1] J. Peres, C. Delmas, A. Rougier, M. Broussely, F. Perton, P. Biensan and P. Willmann, Journal of Physics and Chemistry of Solids, 1996, 57, 1057-1060.
[2] P. Zehetmaier, A. Cornélis, F. Zoller, B. Böller, A. Wisnet, M. Döblinger, D. Böhm, T. Bein and D. Fattakhova-Rohlfing, Chemistry of Materials, 2019, 31, 8685-8694.
[3] U. Kim, D. Jun, K. Park, Q. Zhang, P. Kaghazchi, D. Aurbach, D. Major, G. Goobes, M. Dixit, N. Leifer, C. Wang, P. Yan, D. Ahn, K. Kim, C. Yoon and Y. Sun, Energy & Environmental Science, 2018, 11, 1271-1279.
[4] H. Ryu, G. Park, C. Yoon and Y. Sun, Journal of Materials Chemistry A, 2019, 7, 18580-18588.
[5] S. Sicolo, M. Mock, M. Bianchini, K. Albe, Chem. Mater. 2020, 32, 10096–10103.

The application of secondary batteries for electric propulsion, personal consumer electronics as well as power tools has grown immensely over the last decade and battery chemistries can be tailor made to meet the requirements of the application. Super high charge rates and cycle-life can be achieved employing zero strain anodes based on LTO (Li₄Ti₅O₁₂). With a (de)intercalation potential of 1.55V vs. Li/Li⁺, LTO based batteries are inherently safer as lithium plating at high charge rates is omitted.
However, the high operation potential and the rather low specific capacity of LTO (~170 mAh/g) comes with the cost of a reduced cell potential and hence gravimetric and volumetric energy density. Pairing LTO based anodes with high capacity cathodes such as NCA (LiNi_0.8Co_0.15Al_0.05O₂) or NMC 811 (LiNi_0.8Mn_0.1Co_0.1O₂) increases the energy content of such a battery concept. Yet, these materials rely on cobalt, which is not viable from an ethical nor sustainable perspective. A more pronounced effect with respect to the energy density as well as sustainability is apparent when pairing LTO anodes with high voltage materials such as LNMO (LiNi_0.5Mn_1.5O₄). This spinel cathode has a rather moderate capacity of 147 mAh/g, but an almost 1 V higher intercalation potential compared to layered oxides. This combination could in principle increase the gravimetric energy density of LTO based cells by up to 30% compared to a NMC442‖LTO cell. Unfortunately, the LiPF₆ containing carbonate-based electrolytes are deemed inapplicable at these potentials, and a cobalt free LTO based battery with increased energy is contingent on a high voltage electrolyte that allows for high cycling stability.
This study screens the cyclability of LNMO‖LTO full cells with alternative electrolytes aiming for a high voltage tolerable solution with adequate properties such as conductivity, safety, and operational temperature. Alternative solvents such as sulfones, nitriles and fluorocarbonates and combinations thereof, as well as different high voltage additives, are screened and characterised in this study. The results are benchmarked against a state-of-the-art electrolyte based on LiPF6 in EC/EMC.

Replacement of liquid electrolytes in Li-ion batteries with all solid systems based upon polymers (SPEs), ceramics or composites will enable Li-ion batteries to achieve enhanced safety characteristics by reducing the flammability, removing solvents and providing resistance to lithium metal dendrite formation. To achieve this safety goal, it is critical that these replacements function without plasticiser, or the need for even small amounts of solvent additives. However, the potential benefits of SPEs are tempered by reduced Li⁺ conductivity when contrasted to conventional liquid systems, and the need to run at elevated temperature to ensure the highest possible conductivity.
Much effort has been directed at the replacement of polyethylene oxide (PEO) which, despite significant effort cannot be easily used above 4 V. PEO is vulnerable to oxidation and degradation caused by Li salts and electrode by-products under operating conditions. Replacement for PEO has involved the study of many systems including polyesters, polycarbonates and polynitriles, with more exotic systems looking at co-polymers and composite SPEs. Polyethyleneimine (PEI), is the nitrogen bearing analogue of PEO, and contains NH which allows for Li salts anion sequestration via H-bonding. Theoretically, it should be weakly Li co-ordinating and strongly anion-coordinating, thus promoting Li⁺ transport. However, early studies have shown low conductivity for PEI systems, thought in part to be due to high crystallinity.
This study will look at the preparation of novel, plasticiser free polyethyleneimine (PEI) co-polymers designed with the aim of reducing crystallinity in the SPE. The route from monomer to SPE, and subsequent testing and benchmarking against PEO systems will be shown. Performance data from studies using a flexible cell solution, that allows simultaneous, in operando measurement of SPE thickness under electrochemical characterisation, at a range of temperatures will be shown. This method allows for accurate determination of SPE conductivity and Li⁺ transference number at different temperatures.

Rechargeable lithium–oxygen batteries have high theoretical energy density (~3600 Wh kg^-1). During operation, oxygen undergoes a reduction reaction (ORR) to generate the discharge product of Li₂O₂, which is decomposed during the recharge process with oxygen evolution (OER).¹ However, this recharging process is primarily disturbed by the large overpotential attributed to the sluggish OER kinetics. Very recently, photo-assisted Li–O₂ batteries with semiconductor-containing cathodes have gained attention as a promising approach for enhanced energy storage.² Plasmonic materials (such as Au, Ag, Cu, Pd, and Al) have unique properties interacting with light, known as surface plasmon resonance (SPR).³ Under light illumination, plasmonic effects such as near-field enhancement, FRET, local heat, and hot carriers have found increasing application in catalysis. In this study, we demonstrate plasmonic effect in the Li–O₂ battery system by incorporating gold nanoparticles on the Ketjen Black (KB) cathode with different amounts and sizes. Upon light irradiation, during discharge, the presence of plasmonic Au NPs induce a morphology change to thin and small Li₂O₂ particles, which can be easily decomposed during the charging process. Most importantly, during both discharging and charging processes, the hot carrier from plasmonic Au NPs help to form and decompose the Li₂O₂ with decreasing charge voltage. As a result, the cell with Au NP/KB shows a significant increase in the round-trip efficiency from 75.2 to 80.2%. Our approach, further supported by a meticulous analysis of the near-field enhancement and local heat effects, is the first report individually showcasing the promise of plasmonic metal nanostructures in high-energy storage.

References
[1] Y.-C. Lu, B. M. Gallant, D. G. Kwabi, J. R. Harding, R. R. Mitchell, M. S. Whittingham, Y. Shao-Horn, Energy Environ. Sci. 2013, 6, 750.
[2] P. Tan, X. Xiao, Y. Dai, C. Cheng, M. Ni, Photo-assisted non-aqueous lithium-oxygen batteries: progress and prospects, Renew. Sustain. Energy Rev. 2020, 127, 109877.
[3] S. V. Boriskina, H. Ghasemi, G. Chen, Chem. Rev. 2016, 116(24), 14982-15034.

Organic electrode materials operating in aqueous electrolytes offer the opportunity to avoid toxic, critical and expensive materials but often feature limited cyclability. In this work, we report on a 3D network composite material, based on natural melanin (sepia melanin, extracted from the ink sac of cuttlefish) and nitrogen and sulfur doped graphitic carbon quantum dots (N,S GCQDs). N,S GCQDs not only improve the conductivity of the formed composite but also provide functional groups and active sites, and add faradaic activity for better electrode wettability and electrochemical performance. We also investigated the effect of various undoped and doped CQDs, synthesized from acetic acid and sucrose, on the electrochemical performance of sepia melanin, a quinone macromolecule. The sepia/N,S GCQD (8:2 W/W) composite shows optimum areal capacitance (ca. 180 mF/cm²) that is about 2 times higher than sepia alone (ca. 77 mF/cm²) with enhanced charge transfer resistance (1 ohm for sepia/N,S GCQDs compared to 10 ohms for sepia) evaluated through electrochemical impedance spectroscopy. Sepia/N,S GCQD symmetric supercapacitor in 0.5 M Na₂SO₄ aqueous electrolyte features promising capacitance retention ca. 92% after 10 000 cycles at 5 A g^-1, 100% coulombic efficiency, 11 µW h cm^-2 and 102 mW cm^-2 maximum energy and power densities. This work aims at easy preparation of stable and potentially biodegradable supercapacitor electrode materials from green resources for applications in environmentally benign electrochemical energy storage devices.

Supercapacitors (SCs) are being considered the next-generation power storage devices due to their many favorable properties. In this regard, mesoporous nanostructures are excellent supercapacitor electrodes as they enjoy a large number of active sites and high surface area promising the utilization of the full capacitance of the active materials. In this study, we report on the assembly of electrospun, binder-free mesoporous Mn_0.56V_0.42O@C fibrous electrodes. The morphological and structural analyses of the fabricated Mn_0.56V_0.42O@C electrodes were investigated using field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and glancing angle X-ray diffraction (GAXRD). The X-ray photoelectron spectroscopy (XPS) and GAXRD confirm the formation of Mn_0.56V_0.42O nanofibers and their successful bonding to carbon during crystal growth. Those fibrous composite electrodes showed excellent specific capacitance of 668.5 F g^–1 at 1 A g^–1. The highly obtained capacitance is attributed to the multiple oxidation states of the Mn–V oxides, the binder-free electrodes, surface roughness, and the mesoporous nature of the fabricated nanofibers. The asymmetric supercapacitor composed of the mesoporous Mn_0.56V_0.42O@C nanofibers as the positive electrode and graphene hydrogel as the negative electrode possesses ultrahigh energy density of 37.77 W h kg^–1 and a power density of 900 W kg^–1 with superior Coulombic efficiency over 13000 charge/discharge cycles.

The state-of-the-art manufacture of lithium ion battery (LIB) cathodes is slot-die coating of a high viscosity slurry consisting of active materials, conductive additives, and a polymeric binder in N-methyl-2-pyrrolidone (NMP). The operation of slot-die is costly due to the 2-coat/2-cure electrode processing and the use of NMP solvent, which is an expensive consumable with serious health concerns. An alternative approach is the use of waterborne binder systems applied to metal foils using electrocoat. Electrocoat is a process widely recognized to be a high-throughput, low cost, coating application method that allows simultaneous coating of both sides of metal. This presentation will demonstrate the development of novel binders to enable electrodeposited lithium-ion battery electrode coating system. The novel binders were designed for flexibility, ionic mobility, and compatibility with high-energy density active materials and formulated to result in stable water-based cathode coating systems. Furthermore, electrodeposition process parameters were explored and validated in proof-of-concept, semi-continuous lab scale testing. Compared to the conventional NMP based coatings with slot-die process, the electrocoat process is environmentally friendly and capable of reducing the cell costs by at least 20% while improving battery performance.

Iron fluoride (FeF₃^.0.33H₂O) is a candidate for Lithium Ion Battery (LIB) due to great theoretical capacity and low cost. However, the poor electric conductivity hinders its application to LIB. The electric conductivity of cathode part is factor that influence to battery performance such as capacity and cycle stability. Thus, conductive materials are essential for improve electric conductivity. Generally, composite with carbon material for example Carbon Black (CB) and Multi-Wall Carbon Nano-Tubes (MWCNTs) are applied [1]. Nevertheless, poor cycle stability is an obstacle to become the dominant cathode material in the LIB market. Herein, we suggest that electro-less Nickel plating on FeF₃^.0.33H₂O powder for improving electric conductivity. We carried out X-Ray Diffraction pattern analysis (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Energy Dispersion Spectroscopy (EDS) for material characteristics. Also, we carried out Four-point prove, charge-discharge test and Electrochemical Impedance Spectroscopy (EIS) for electrochemical properties. Ni layer which is coating on iron fluoride powder layer with thicknesses of 10 nm~ 20 nm is observed by SEM and TEM. Respectively, Ni-coated FeF₃^.0.33H₂O powder show 150% increased electric conductivity then FeF₃^.0.33H₂O powder. Also, It shows good capacity up to 150 mAhg^-1 at 0.2C (cut-off voltage 1.0V) and capacity retention ~80% after 50 cycles.

Reference
[1] Liu, Li, et al., Journal of Power Sources 238 (2013), 501-515.

Polymer electrolytes have received increasing attention in battery materials research and development. Their performance can be improved with addition of ionic liquids (ILs), which increases the ionic conductivity and provides enhanced safety. In a recent study, self-healing capability that reduces lithium dendrite formation at the electrolyte/electrolyte interface has been reported, for example, in PVDF-HFP-ILs electrolyte containing Al₂O₃ nanofibers. [1] In this work, a series of PVDF-HFP-ILs with different ratios of Al₂O₃ nanofiber content were prepared through solution cast technique. The dynamics of ions confined within polymer-Al₂O₃ matrix were explored by impedance and pulsed field gradient NMR spectroscopy. The distribution of Al₂O₃ nanofibers in the polymer network was probed through SEM-EDX analysis. Lastly, the local environment of ions and their interaction with polymer and Al₂O₃ nanofibers were established through a detailed solid-state NMR analyses detecting ¹H, ²⁷Al, ¹³C, ¹⁹F, ⁷Li nuclei including 2D ¹³C{¹H} HETCOR experiments. In addition to mechanical reinforcement, enhancement of ionic conductivity was observed with the addition of Al₂O₃ nanofibers.

1. T. Chen, W. Kong, Z. Zhang, L. Wang, Y. Hu, G. Zhu, R. Chen, L. Ma, W. Yan, Y. Wang, J. Liu, and Z. Jin, Nano Energy 54, 17 (2018).

Among the electrochemical energy storage devices, batteries have attracted tremendous attention of scientific society due to its amazing feature of high power, good cycle life, tunable energy density. The development of active and safe organic materials for electrochemical storage devices is another area of interest for electrochemical energy storage system, which can be contained low cost, natural abundance, possibly green compounds (i.e., C, H, O, N or S), and simple synthesis. [1] Until now, many organic materials have been investigated but only conducting polymers are used for energy storage system and others restricted due to their electrical conductivity issue and material loading. Herein, we attempted new material and engineering strategies to resolve the key issues facing the electrochemical energy storage system. Our material with new synthesis approach is able to offer optimistic electrochemical performance and reach unmatched ultra-high rate pseudocapacitive performance.


References
Jouhara, A., Dupré, N., Gaillot, A. C., Guyomard, D., Dolhem, F., & Poizot, P, Nat. Commun. 2018, 9(1), 4401.

A sustainable, carbon-neutral future will be an aspiration, not a reality, without cost-effective energy storage. Batteries will be a critical technology in the suite of choices for energy storage, especially for electrification of vehicles. But shouldn’t batteries themselves be sustainable? We evaluated the supply risk of elements versus their abundance in the earth’s upper crust [1]. A supply risk of 1 or less and an abundance above 0.003 wt% includes such battery-relevant elements as Ni, Zn, S, Mn, Ti, Fe, and Al. Our team has focused on rechargeable zinc-based batteries whose aqueous electrolytes impart a safer battery chemistry over lithium-based batteries as well as competitive gravimetric and volumetric energy at the system-level. Designing electrodes as architectures in which the entire volume of the electrode is electron- and ion-wired in 3D distributes the available electrified interface thereby lowering local current density. Formulating zinc as a sponge creates an alkaline anode that cannot form zinc dendrites. Similarly, formulating layered MnOx as a nanometric coating throughout a carbon nanofoam improves the rate performance of zinc-ion cathodes.

[1] B.J. Hopkins, C.N. Chervin, M.B. Sassin, J.W. Long, D.R. Rolison, J.F. Parker, Sustain. Energy Fuels 2020, 4, 3363–3369.
[2] J.S. Ko, M.B. Sassin, D.R. Rolison, J.W. Long, Sustain. Energy Fuels 2018, 2, 626–636.

The demand for lithium has grown tremendously over the past decades due to Li-ion battery development for electric vehicles, portable electronics, and stationary energy storage. Electrochemical intercalation is a new platform method for separation. It allows selective Li extraction from complex aqueous systems such as brines and seawater. However, the high concentration of Na poses a great challenge to compete (co-intercalate) with Li during extraction. In this talk, I will present the host electrode materials' structural response upon co-intercalation of Li and Na which have big ionic radius differences. I will also discuss strategies to promote Li intercalation during co-intercalation from both aspects of materials design and electrochemical methods development.

Electrochemical energy storage is a keystone to support the rapid transition to a low carbon emission future for grid storage and transportation. While research on electrochemical energy storage devices has mostly dealt with performance improvements (energy density and power density), little attention has been paid to designing devices that can be recycled with low-cost and low environmental impact. Thus, next-generation energy storage devices should also address the integration of recyclability into the device design. In this talk, we present the development of recyclable energy storage devices based on solution processible redox-active conjugated polymers [1]. The high electronic and ionic charge transport in these polymers enables the operation of single-phase electrodes in aqueous electrolytes with C rates >100 with excellent electrochemical stability when charged to 1.2 V. Finally, we demonstrate the recyclability of these devices, achieving >85% capacity retention in each recycling step and recycled devices twice. Our work provides a new direction for developing recyclable devices for sustainable energy storage technologies.
[1] D. Moia, A. Giovannitti, A. A. Szumska, I. P. Maria, E. Rezasoltani, M. Sachs, M. Schnurr, P. R. F. Barnes, I. McCulloch, J. Nelson, Energy Environ. Sci. 2019, 12, 1349.

Sodium-ion conduction is a promising alternative to lithium-ion batteries (LIB). The advantages of sodium include higher natural abundance, similar physicochemical properties to lithium, and lower cost of battery active materials. However, a simple technology transference from LIB to sodium-ion batteries (SIB) is impeded by differences in intercalation mechanisms. Particularly, graphite, an established anode material in LIBs, is unsuitable to SIBs because the interlayer distance between its graphene sheets is too small for effective Na+ insertion. For this reason, some of the preferred anode materials for SBIs are disordered carbons with larger interlayer spacing, such as hard carbons. Hard carbons (HCs) also have the advantage of being predominately produced by the carbonization of biomass and residues, which contributes positively to the environmental and economic impact of SIBs. However, the method of HC production often includes chemical activation steps and high carbonization temperatures. In this work, we produced HC from avocado peels by simply water washing and relatively mild temperatures of carbonization (900 and 1100 °C). We chose avocados due to the considerable waste generated and its constant increase in consumption. Avocados generate waste from their peels, seeds, and parts of the pulp, which can amount to a total of up to 30% of its weight in solid waste. Efficient ways to process and repurpose this waste are especially relevant due to the continuous market growth of avocados. In 2019, they were the 8th most consumed fruit or vegetable in the USA, partially due to lifestyle trends and potential health benefits. To the best of our knowledge, the possibility of producing HC from avocado peels for energy storage has never been explored. HC produced by avocado peels was characterized regarding its crystalline properties (XRD), surface area and porosity (BET and BJH analysis), morphology and atomic composition (SEM-EDX), and degree of graphitization (Raman spectroscopy). The material characterization revealed the conversion of the avocado peels in carbon powders with a carbon content of > 92 at. %, graphene interlayer distances of 3.95 Å (superior to the required for Na+ intercalation), pore size of approximately 4.8 nm, and degree of graphitization of 0.96. After confirming the suitability of the produced HC as anode materials, electrochemical characterization was carried out with coin cells containing HC anodes and sodium metal discs as cathodes. Our samples demonstrated reversible intercalation and deintercalation of sodium ions and excellent cycling performance, namely, a reversible capacity of 352.55 mAh/g at 0.05 A/g, rate capability up to 86 mAh/g at 3.5 A/g, capacity retention of >90%, and 99.9% Coulombic efficiencies after 500 cycles. This study shows for the first time avocado peels as a sustainable source to produce hard carbon that can provide excellent anode performance in sodium-ion batteries.

Tin oxide-based materials have been intensively investigated as alternative anodes for lithium-ion batteries due to their high specific capacity, non-toxicity, and ease of handling.^[1] However, the initial formation of Li₂O upon lithiation is essentially irreversible, which has a severe effect on the first cycle Coulombic efficiency and the reversibly achievable capacity upon cycling.^[2] It has been shown that the incorporation of transition metal dopants can address this issue, as it enables the reversible formation of Li₂O. The choice of the dopant, however, plays a critical role for the long-term cycling stability, rate capability, and eventual energy density of the resulting lithium-ion cells.^[3]
Herein, we show that the incorporation of specific combinations of different dopants allows for further tailoring the electrochemical properties. We also demonstrate the production of such materials using a scalable continuous hydrothermal flow method. The performance of the best performing composition was further improved by applying a carbonaceous coating. The electrochemical investigation of the coated anode material was conducted in half-cells and in high-energy full-cells using high-voltage LiNi_0.5Mn_1.5O₄ as active material for the cathode^[4] – in addition to the realization of some large-scale battery cells to power a remotely controlled model car. Following these first scale-up activities, we conducted a preliminary life cycle assessment to compare the sustainability and suitability of such materials with the state of the art. Simultaneously to these rather application-oriented research, we performed also an in-depth investigation of the synergistic impact of the different dopants via ex situ synchrotron X-ray absorption spectroscopy to elucidate the de-/lithiation mechanism at the atomic scale. This comprehensive and extensive analysis provides additional insights into the potential application of (multi-doped) SnO₂ for lithium-ion batteries.

References
[1] F. Zoller, D. Böhm, T. Bein, D. Fattakhova Rohlfing, ChemSusChem 2019, 12, 4140.
[2] D. Bresser, S. Passerini, B. Scrosati, Energy Environ. Sci. 2016, 9, 3348.
[3] Y. Ma, Y. Ma, G. Giuli, T. Diemant, R. J. Behm, D. Geiger, U. Kaiser, U. Ulissi, S. Passerini, D. Bresser, Sustain. Energy Fuels 2018, 2, 2601.
[4] A. Birrozzi, J. Asenbauer, T. E. Ashton, A. R. Groves, D. Geiger, U. Kaiser, J. A. Darr, D. Bresser, Batter. Supercaps 2020, 3 (3), 284–292.

Vascular structures are ubiquitous in nature. Examples such as roots, blood vessels, and lung alveoli are the outcomes of millions of years of evolution to balance between surface area and mass transport. For lithium-ion batteries, it is anticipated that creating vascular channels in the electrodes also enhances the kinetics by ensuring the fresh electrolyte supply to achieve fast charging. Ideally, such optimal vasculature can help to fully utilize the electrode uniformly and to minimize overpotential. However, it is challenging to find the right parameters out of the immense parameter hyperspace. Herein, we use artificial neural network (ANN) to accelerate the computation of possible structures with high accuracy. An inverse searching library is compiled to find the top-ranked vascular structures under different industrial fabrication criteria. The prototype delivers a customized package containing optimal geometric parameters, and their uncertainty and sensitivity analysis. Finally, the full-vascularized cell shows a 75% improvement of charging capacity than the traditional homogeneous cell under 3.2C current density. This research provides an innovative methodology to solve the fast-charging problem in batteries and broaden the applicability of data-driven deep learning to different scientific or engineering areas.

Lithium-ion batteries have enabled the continuous transition from gasoline-powered to electric vehicles and several “traditional” car-makers have (very) recently announced their “exit” from combustion engines in the near future. The impressive success of this technology, however, raises also an increasing awareness of sustainability issues – not least with regard to critical elements such as cobalt, commonly comprised in the positive electrode active material, and the use of toxic and harmful solvents for the (positive) electrode preparation.^[1–3] Cobalt-free and manganese-rich LiNi_0.5Mn_1.5O₄ (LNMO) would provide a viable solution to overcome these issues, especially in combination with the utilization of water-soluble, bio-derived polymers as binders, but the pronounced water-sensitivity and high de-/lithiation potential of LNMO are still hampering the commercial breakthrough.^[3–5] Apparently, the key towards overcoming these issues relies on the stabilization of the LNMO|water and LNMO|electrolyte interface.
Herein, we will report a comprehensive overview of our activities in this field, covering (i) an in-depth understanding of the processes occurring at the interface with the LNMO particles, (ii) the development of suitable active material and electrode treatments prior to the cell assembly, (iii) the optimization of the electrolyte composition to achieve stable interphases for both the anode and the cathode, as well as (iv) the tailored design of suitable binder compositions that allow for suitable mechanical properties and stable long-term cycling of commercially relevant sized electrodes – in half-cells and high-performance full-cells. We will show that only the combination of these complementary approaches appears capable of overcoming the present challenges and, thus, enabling the commercial application of LNMO-based cathodes in (more) sustainable lithium-ion batteries.

References
[1] E. A. Olivetti, G. Ceder, G. G. Gaustad, X. Fu, Joule 2017, 1, 229.
[2] C. Vaalma, D. Buchholz, M. Weil, S. Passerini, Nature Reviews Materials 2018, 3, 18013.
[3] D. Bresser, D. Buchholz, A. Moretti, A. Varzi, S. Passerini, Energy Environ. Sci. 2018, 11, 3096.
[4] B. Aktekin, M. J. Lacey, T. Nordh, R. Younesi, C. Tengstedt, W. Zipprich, D. Brandell, K. Edström, The Journal of Physical Chemistry C 2018, 122, 11234.
[5] M. Wentker, M. Greenwood, J. Leker, Energies 2019, 12, 504.

Non-uniform lithium intercalation in porous electrodes during charging reduces the capacity of lithium ion batteries at fast charge rates. Recent work highlights the importance of the thermodynamics of cathode materials in dictating charging capacity at high rates. The analogous thermodynamic behavior of negative electrodes and its relationship to Li plating have not been investigated at high charge rates. In this study, we use finite element analysis and simplified numerical and analytical models to study conventional and architectured electrode structures (i.e., layered with varied porosity, patterned with secondary channels, etc.) at high charge rates. While some of these strategies can increase capacity at a given rate, the benefits in reducing lithium plating are generally more striking. For example, layered designs can reduce the overpotential that drives plating even though these structures do not substantially increase capacity. Our modeling results are compared to and validated by experiments. Further, we demonstrate that reaction inhomogeneity is substantially affected by staging behavior in the equilibrium potential in ways that can contribute to Li plating events at high charge rates. The overall results of this study provide guidance for designing both electrode architectures and optimized charging protocols for fast charging applications.

Developing lithium-ion battery electrodes with high energy and power is essential to meet the ever-growing portable electronics and electric vehicle markets, which calls for achieving high utilization of the active material in thick electrode designs and elevating the overall energy density. In this talk, I will present our recent research progress on high-performance electrode architecture design and the impacts of structural parameters on the underlying kinetics. A low-tortuosity design could provide faster ion transport across electrode thickness, enabling thick electrode composed of graphene oxide (GO) supported magnetite (Fe₃O₄) nanoparticles with excellent rate capability, achieving areal capacity of 3.6 mAh cm^–2 under 10 mA cm^–2. In addition, further fine tuning of the lamellar thickness and the pore size in low-tortuosity architecture shows significant impact on the electrochemical kinetics in thick LiNi_1/3Mn_1/3Co_1/3O₂ (NCM111) electrodes, where a better capacity retention with increasing C-rates (70% retention under 2.5 C) is found in electrodes with thinner lamellar thickness (~ 5 μm) and relatively large pore size (~ 20 μm) compared to those with thicker lamellar walls. Providing similar low-tortuosity morphology, this could be ascribed to faster diffusion into thin lamellar walls as opposed to their thick counterparts. Our research reveals more insights into structure-affected electrochemistry and highlights more delicate designs in low-tortuosity electrode architectures.

Microporous separators are critical components in lithium ion batteries (LIBs). Most battery separators serve two key functions: to physically separate the electrodes to avoid electrical shorting, and to allow the transport of ions. Conventional separators are fabricated from low cost, commodity thermoplastics, such as polyethylene and polypropylene, but make up 20% of the total material cost of a cell due to complex, energy-intensive manufacturing process. Moreover, conventional separators are considered passive components, providing adequate electrolyte uptake and ohmic resistance but contributing little other functionality to the cell. Thus, developing low cost, multifunctional separators is a potential strategy to reduce battery costs, while addressing cell cycle/calendar life.
In this presentation, we will introduce a novel separator fabrication process, where microporous separators are coated directly onto electrode foils in a facile, one-step additive process. This process promises to reduce energy consumption and manufacturing steps, and microporous poly(1,4-butanediol diacrylate) (pBDDA) separators fabricated using this approach possess superior performance metrics compared to commercial separators. These separators have a porous morphology with an average pore diameter of 40μm, and a porosity of 38%. In a lab setting, the fabricated separators have a thickness between 40-50μm. We have demonstrated that pBDDA separators hold 30% more electrolyte by mass when compared to Celgard 2500, and have an effective ionic conductivity of 3.32mS/cm – a 66% improvement over the same commercial benchmark. When incorporated into an electrochemical cell, the capacity retention of pBBDA separators is on par with Celgard over long-term cycling, showing the material is stable and effective during use.
In addition to simplifying separator manufacturing and cell fabrication, our approach provides for facile incorporation of novel polymer chemistries without additional processing steps. For example, novel copolymer compositions have been designed to scavenge HF contamination that is intrinsic to LiPF6-based liquid electrolytes. These functional separators mitigate the buildup of HF in the electrolytes, thereby suppressing Mn²⁺ dissolution in LiMnO₂ cathodes and improving capacity retention and lifetime of the lithium ion cells.

Cathode material plays a dominant role in determining the capacity and cost of lithium-ion batteries (LIBs). Reducing the cost and improving the performance of cathode materials is critical for further advancing the application of LIBs in areas such as electric vehicles and grid energy storage. One type of the most promising cathode materials is nickel-rich metal oxides including Li(Ni_0.6Co_0.2Mn_0.2)O₂ (NCM622) and Li(Ni_0.8Co_0.1Mn_0.1)O₂ (NCM811) due to their high capacity and low cobalt content, especially considering the high price and toxicity of cobalt. Nevertheless, current nickel-rich cathode materials are experiencing challenges such as a fast capacity fading and low thermal stability, which are the result of structural degradation, microcracks, and side reactions related to the polycrystalline structure. An efficient way to solve those issues is using single crystal cathodes (SCC) that have better thermal stability and lower capacity fading because of improved structural stability and mechanical strength. However, current synthesis methods of SCC are facing various challenges, inhibiting their application for large-scale low-cost production of high-performance SCC. For instance, the coprecipitation method needs long-time preparation of precursor, whereas the solid-state molten salt method usually introduces impurity phase due to non-uniform mixing and post-treatment. Therefore, a flame spray synthesis (FSS) method is proposed for SCC materials with following features: (1) all needed metal elements are dissolved in the form of salt in precursor solution to guarantee homogeneous mixing and avoid extra steps of solid-state mixing; (2) the droplet-to-particle route allows easy control of the size of particles by adjusting spray properties; (3) the high temperature operating condition allows fast decomposition of raw material. In the current work, nickel-rich NCM811 cathode materials were synthesized with an FSS setup that has two heating sections, with a low-temperature section for evaporation control and a flame section for fast decomposition of precursor. The as-prepared sample was then post-annealed to produce the single crystal material. To obtained materials with optimized performance, we are investigating a wide range of parameters including the precursor concentration, amount of additives, operating temperature and residence time in each heating section, and post-anneal temperature and time. Our current coin cell tests showed that single crystal NCM811 synthesized with FSS had an improved cycling performance when compared with polycrystalline NCM811. We believe that FSS is promising in advancing the production and application of single crystal cathode materials because of its features such as fast production, homogenous mixing, and high scalable potential.

The use of zinc negative electrodes and aqueous electrolytes is an appealing modality for low cost scalable batteries. Further, transition metal oxides are viable options for cathode materials in these systems. Specifically, the electrochemical charge storage of sodium vanadate (NaV₃O₈ or NVO) cathodes in aqueous Zn-ion batteries has been demonstrated and is hypothesized to be influenced by the inclusion of structural water for facilitating ion transfer in the material. Materials properties considered important (morphology, crystallite and particle size, surface area) are systematically studied herein through investigation of two NVO materials, NaV₃O₈. 0.34H₂O [NVO(300)] and NaV₃O₈.0.05H2O [NVO(500)], with different water content, acicular morphologies with different size and surface area achieved via post-synthesis heat treatment. The electrochemistry of the two materials was evaluated in aqueous Zn-ion cells with 2 M ZnSO₄ electrolyte using cyclic voltammetry, galvanostatic cycling, and rate capability testing. The thinner NVO(300) nanobelts demonstrate greater specific capacities and higher effective diffusion coefficients relative to the thicker NVO(500) nanorods. Notably however, while cells containing NVO(500) deliver lower specific capacity, they demonstrate enhanced capacity retention with cycling. The structural changes accompanying oxidation and reduction are elucidated via ex situ X-ray diffraction, transmission electron microscopy, and operando V K-edge X-ray absorption spectroscopy (XAS), where NVO material properties are shown to influence the ion insertion. Operando XAS verified that electron transfer corresponds directly to change in vanadium oxidation state, affirming vanadium redox as the governing electrochemical process.

Modern electrical grids, especially those comprising energy from intermittent, renewable sources, such as wind and solar, require storage.¹ Nonaqueous redox flow batteries (NRFB) are a promising technology to meet this growing need.² Compared to their aqueous counterparts, they have the potential to approach the energy density of lithium-ion batteries, while maintaining the advantages of flow systems, including decoupled scaling of power and energy ratings and thermal stability.

Despite their promise, fundamental technical obstacles have limited the application of NRFB so far. These include low solubility and poor stability of active-materials as well as poor electrochemical performance. To address these issues, we have developed an active-material known as vanadium bis-hydroxyiminodiacetate (VBH), which is based on a family of molecules that is naturally occurring and produced biologically.³ Biosynthesis of this molecule evolved in mushrooms of the Amanita genus, to bind vanadium selectively and with the highest stability ever reported, using a unique, tetradentate, bis-carboxylato-η²-hydroxyimino- motif.⁴ Ligand-substitution is suppressed, shutting down a major mechanism of decomposition. In this way, natural selection serves as a toolkit for molecular design, elucidating a scaffold for optimized NRFB active materials.

In this presentation we provide an overview of some key challenges in NRFB development, along with our recent efforts at addressing them, and some strategies we are pursuing to make further in-roads. We will show that our bioinspired active-material exhibits excellent chemical stability during long durations of electrochemical cycling to high states-of-charge.⁵ Further, we will demonstrate that the thermodyamics of the electrolyte can be tuned to greatly enhance the solubility of the active-material.⁶ Finally, we will report our recent progress on a modular synthetic scheme, whereby the VBH scaffold can be covalently modified to tune its electronics and steric properties.

1. P. Albertus et al., Joule, 2020, 4, 21-32.
2. R. M. Darling et al, Energy Environ. Sci., 2014, 7, 3459-3477.
3. H. Huang et al., J. Mater. Chem. A, 2017, 5, 11586-11591.
4. R. E. Berry et al., Angew Chem Int Ed Engl, 1999, 38, 795-797.
5. Gokoglan et al., J. Electrochem. Soc., 2019, 166, A1745-A1751.
6. Pahari et al., RSC Adv, 2021, 11, 5432-5443.

The establishment of sustainable energy sources highly depends on efficient storage devices to guarantee a consistent power supply. The growing demand for lithium-ion batteries (LIBs) for this purpose combined with concerns about lithium availability has motivated the search for viable storage alternatives. Sodium-ion conduction is a suitable candidate due to sodium’s abundance in the earth’s crust and similar monovalent storage mechanism as Li+. In recent years, the development of components specifically for sodium-ion batteries (SIBs) have inspired much research interest, but fundamental inquiries on ion transport remain unanswered. Notably, solid polymer electrolyte (SPE) studies remain almost solely concentrated on Li-ions, even though revolutionary storage devices could result from the combination of sodium’s natural availability with the possibility of higher energy density in solid-state devices. The challenges associated with SPEs, such as low ionic conductivities, could be further addressed by characterizing the ion-transport properties of the polymer host and the strength of the salt-polymer interactions. In this work, we used atomistic molecular dynamic simulations of sodium SPEs to observe the influence of oxygen density in polymer chains on the resulting electrolyte’s diffusivity, coordination, and cation-anion interactions. For this purpose, we characterize sodium-ion transport in two polymer hosts, namely, polyethylene oxide (PEO) and poly(tetrahydrofuran) (PTHF) that contain two and four carbons in their repeating units, respectively. Sodium perchlorate was added to the systems in a concentration of EO/Na (EO = ethylene oxide) or BO/Na (BO = butylene oxide) equal to 15. The simulation boxes were created using the software MedeA 3.1 from Materials Design, and the molecular dynamics package LAMMPS was used in the equilibration and production runs, with the universal forcefield PCFF+. To mitigate the limitations of our non-polarizable model, we multiplied the charges of Na, Cl, and O by 0.75 to reproduce transport properties without overestimation. Production runs were carried out in NPT at 353 K (80 °C), 1 atm, with timestep of 1 fs, for 100 ns. The radial distribution function (RDF) between Na-O from the polymers PEO and PTHF was calculated to investigate the local solvation environment, which confirmed the stronger coordination of sodium cations with PEO’s polymer backbone, while, in PTHF, the lower oxygen density in its chains resulted in weaker coordination. The differences in oxygen density in the polymer chain also influence the hopping mechanism in each electrolyte. In PTHF, interchain hopping was more prevalent, while in PEO, intrachain hopping happened more often due to the stronger coordination with the polymer chains. Additionally, sodium cations showed a higher probability of coordinating with 2-3 oxygens from PEO while in PTHF, Na+ coordinated with only one polymer oxygen. Consequently, the Na+ decomplexation could easily be achieved in the PTHF electrolytes. This caused the faster motion of Na+ in PTHF, as demonstrated by the sodium ion self-diffusivity 2.3x higher in PTHF than in PEO. However, significant ion cluster formation was seen in the PTHF system. In PTHF, only 8.11% of ions were fully isolated from each other, mostly because Na+ was free to form larger clusters with ClO4-. In PEO, 32.2% of all ions were dissociated due to a greater dispute of coordination between PEO oxygens and perchlorate ones. The significant presence of clusters in the PTHF electrolyte could potentially result in the transport of Na+ ions in the opposite direction from where cations should move during battery cycling, which could be verified by lower transference numbers experimentally. This work’s findings elucidate the fundamental influences and correlations of polymer ether content on ion transport, which can inform on novel syntheses to improve future sodium polymer electrolytes.

Among the candidates competing with lithium ion battery technology for large-scale energy storage applications are aluminum-based systems, which have significant cost and safely advantages. In this work, we investigate aqueous electrolytes containing aluminum trifluoromethanesulfonate (AlTf₃) ranging in concentration from 0.1m to 3.6m. Cation, anion, and water molecular self-diffusion coefficients were determined by pulsed field gradient nuclear magnetic resonance (NMR) measurements of the ²⁷Al, ¹⁹F, and ¹H nuclei, respectively. A special high-gradient probe was used for the ²⁷Al measurements due to short relaxation times associated with nuclear quadrupole interactions characteristic of this spin-5/2 nucleus. Together with ionic conductivity measurements, the NMR results yield information on the degree of salt dissociation and Al ion transference at all concentrations.

Ionic liquids (ILs) have become ubiquitous due to their many attractive characteristics including their task specific tunability. In their application as electrolytes, low viscosity is a necessity to allow fast ion dynamics. One of the ways in which low viscosity can be achieved is by using large asymmetric ions with high conformational flexibility. Towards this, large cations such as 1-butyl-3-methylimidazolium (BMIM⁺) with relatively short and flexible alkyl chains have been successful. Additionally, the use of large weakly interacting anions such as bis(trifluoromethanesulfonyl)imide (TFSI^-) have found similar success. In this study, we performed ¹H and ¹⁹F NMR Fast Field Cycling (FFC) broadband relaxometry measurements on four ILs comprised of the BMIM⁺ cation combined with the tetracyanoborate (BCN₄^-), acetyl(trifluoromethylsulfonyl)imide (TfNAc^-), (methylsulfonyl) 2,2,2 – trifluoroacetyl amide (MsNTFA^-), and bis(trifluoromethanesulfonyl) methane (TFSM^-) anions. The objective of the study is to determine how the anion’s conformational flexibility affects the dynamics of both ions.

Variable temperature ¹H relaxation dispersion (R₁) results followed the anion order: MsNTFA^- > NTfAc^- > TFSM^- > B(CN)₄^-. These results demonstrate that the MsNTFA^- and B(CN)₄^- anions provide the least and most favorable environments, respectively, for the cation’s transport. This result is also supported by solution viscosity (η), ionic conductivity (σ) and cation self-diffusion coefficient (D) measurements.

Metal-organic framework (MOF) derived porous carbon structures have attracted great interest due to their inherently high specific surface area, tunable pores, well-organized structures, and highly heteroatom doped natures. These intriguing physiochemical properties make them a promising material for energy and sensor-related applications. Although various MOF structures with different metal and ligand groups have rapidly emerged as a new platform for the fabrication of diverse carbonaceous materials, it is still highly difficult to fabricate hollow three-dimensional carbon networks. In this study, we present a solution based one-pot synthesis route for the growth of zeolitic imidazolate frameworks (ZIFs) on sacrificial ZnO tetrapod (ZTP) templates and one-step carbonization of the fabricated ZIF-8/ZTP structures to form porous carbon network. We found that the growth of ZIF-8 on ZTP is the key step for fabrication of hollow carbon structures with different morphologies. Structural and morphological characterization details of the resulting carbon structures and the intermediate products will also be presented. These carbon nanostructures have a high potential for use as an electrode active material in energy storage and conversion devices.

We appreciate support from the Institute for Basic Science (IBS-R019-D1), and please note: "Adv. Funct. Mater. 2020, 1909725".

Lithium-ion batteries (LIBs) suffer from volatility, toxicity, high-cost, and flammability due to their organic electrolytes. Aqueous batteries (ABs), a promising alternative, have addressed these issues based on its aqueous nature. However, an intrinsic narrow electrochemical stability window (1.23 volts) of ABs limits their output voltage, energy density and consequently their large-scale applications.

Recent interests and developments have been all focused on expanding the stability window beyond 3.0 volts by introducing highly concentrated “water-in-salt” electrolytes. However, their grid-scale application is restricted due to the use of expensive Li salts and salt precipitation at low temperatures.

Herein, we introduce a hybrid aqueous/non-aqueous solvent with an inexpensive Li salt which expands the stability window to 3.44 volts while being environmentally benign and nonflammable. Our hybrid electrolyte demonstrates the high ionic conductivity, cycling stability and rate capability with TiO₂/LiCoO₂ full cell at both ambient and low temperature conditions. We further explore electrochemical properties and local structure of Li hydration sheath with the aid of ⁷Li and ¹⁷O nuclear magnetic resonance spectroscopy (NMR) as well as classical and ab-initio molecular dynamics (MD).

Silicon/Germanium (Si/Ge) nanostructures are promising materials for energy storage applications due to their high energy density (both volumetric and gravimetric), large lithiation capacity, low toxicity, and high thermal stability. The challenge to utilize these tremendous properties of Si/Ge nanostructures for desired applications is controlled growth over large scale. Here, we report a unique approach to achieve controlled synthesis of Si/Ge nanostructures. We have used a novel photonic curing technique, which uses an intense pulsed light with a broad spectrum (220-1500 nm), to instantaneously prepare these nanoparticles. Unlike conventional methods like rapid thermal annealing where there is enough time to relax to the preferred equilibrium state, quenching during photonic curing occurs much more rapidly (milliseconds), allowing the trapping of metastable states to form unique nanostructures. Si/Ge precursors were spray coated on glass and processed with PulseForge. At capacitor bank voltage of 600V, 10 pulses of light with 8 J/cm² fluence each (total fluence of 80 J/cm²) were used to produce Si/Ge nanoparticles (20 nm – 60 nm). Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) showed presence of Si/Ge nanostructure resulting from instantaneous photonic curing process. 3-Aminopropyltrimethoxysilane was used to improve attachment of the Si/Ge precursors on the substrate, and it was observed through EDS analysis that it increased the carbon content in the synthesized nanomaterial. The present work shows that photonic curing route for Si/Ge nanostructures can be promising way for low-cost large scale-controlled synthesis of energy efficient Si/Ge nanostructures.

Organic batteries are composed of abundant elements (i.e. C, H, O, N and S) and can be produced through eco-friendly procedures. Thereby they provide the possibility for electrochemical energy storage with a –compared to conventional inorganic batteries – smaller environmental footprint and lower cost.^1–3 Despite an increased interest in the scientific community within the last years, there are still unresolved issues with organic battery materials that need to be addressed before commercialization. First, the electric conductivity of organic materials is frequently very low. Thus, large amounts of conductive carbon need to be added and the achievable areal mass loading is too low for practical applications. Second, the processing of the electrode should be without the usage of hazardous solvents and binders to be in line with the general goal of sustainability. And third, the understanding of the reaction mechanism of organic active materials upon cycling is so far still limited, but essential to rationally improve the materials. Herein, we present an in-depth analysis of the (de-)lithiation mechanism of tetra-lithium perylene-3,4,9,10-tetracarboxylate (PTCLi₄) as an exemplary organic active material. Furthermore, we replaced the metallic current collector foil with a carbon current collector (CCC), made of ex cellulose carbon fibers, i.e. from cheap and renewable sources. This in combination with an environmentally friendly aqueous processing allowed us to produce metal-free organic electrodes with good electrochemical performance, a high active material content (80 wt%), an excellent cycling stability (>10,000 cycles), and a very high areal mass loading (>50 mg cm^-2).

References
1. Poizot, P., Dolhem, F. & Gaubicher, J. Progress in all-organic rechargeable batteries using cationic and anionic configurations: Toward low-cost and greener storage solutions? Curr. Opin. Electrochem. 9, 70–80 (2018).
2. Esser, B. et al. A perspective on organic electrode materials and technologies for next generation batteries. J. Power Sources 482, 228814 (2021).
3. Lu, Y. & Chen, J. Prospects of organic electrode materials for practical lithium batteries. Nat. Rev. Chem. 4, 127–142 (2020).

To eliminate power sector emissions, low-cost energy storage of weekly to seasonal duration must accompany renewable generation. Recent analysis suggests that long-duration energy storage systems must cost less than $20/kWh to facilitate the transition.¹ These storage systems must simultaneously be safe, energy-dense, and have long cycle/calendar life to ensure market adoption. One intriguing approach to satisfy all of these criteria is the development of aqueous batteries with electrodes made from cheap, energy-dense materials. Manganese oxides, which are earth-abundant, water-stable, and have rich ion-insertion chemistry, are attractive candidates for aqueous battery cathodes. However, rational design of these batteries demands a better understanding of their ion intercalation mechanisms and the relationships between voltage, electrolyte composition and electrode structure.

In this talk, we will discuss our efforts to predict insertion voltages of protons and alkali ions (H⁺, Li⁺, Na⁺, K⁺) into manganese oxides using first-principles DFT calculations. Despite the success of the SCAN functional in predicting the polymorphic structure of manganese oxides grown during chemical synthesis,² we will show that a DFT+U approach is required for accurate computation of manganese oxide energetics. We will discuss our computed energy referencing scheme that captures the appropriate physics of the manganese oxide system (e.g. magnetic structure, 3d electron energies, zero point energies and entropies) and ensures reasonable predictive accuracy while avoiding overfitting. In doing so, we will highlight some of the tradeoffs associated with this computational approach. We will also analyze how the computed Pourbaix diagrams predict electrode thermodynamic behavior for a specific alkali ion and manganese oxide polymorph. Emphasis will be placed on the implications for the design of aqueous batteries with different alkali intercalant ions. Finally, we will compare our computational results to our own experiments and suggest promising strategies for improved aqueous battery cathodes.

1) Sepulveda, N.A. et al. Nat Energy 6, 506–516 (2021)
2) Kitchaev, D.A. et al. J. Am. Chem. Soc. 2017, 139 (7), 2672–2681

Redox-active conjugated polymers are an interesting class of materials for electrochemical devices since their properties can be tuned by chemical design to enable redox activity in various electrolytes. In our presentation, we will introduce design rules for the development of conjugated polymers with high electronic and ionic charge transport properties to enables fast charging of single-phase electrodes in aqueous electrolytes [1,2]. While the choice of the polymer backbone is important for achieving electrochemical stability of the charged polymer states, it is found that the tuning of the local environment of the polymers is equally important. The tuning of the local environment of the materials is achieved by attaching hydrophilic (polar) side chains to the polymer backbone to enable fast ion transport, swelling, and reversible phase changes. Electrodes fabricated with these polymers can utilize more than 70 % of the available redox-active state in the bulk of the polymer while maintaining high electrochemical stability during continuous cycling. Our work shows the importance of chemical design strategies for achieving high electrochemical stability for conjugated polymers in aqueous electrolytes.
[1] A. Giovannitti, C. B. Nielsen, D.-T. Sbircea, S. Inal, M. Donahue, M. R. Niazi, D. A. Hanifi, A. Amassian, G. G. Malliaras, J. Rivnay, I. McCulloch, Nat. Commun. 2016, 7, 13066.
[2] D. Moia, A. Giovannitti, A. A. Szumska, I. P. Maria, E. Rezasoltani, M. Sachs, M. Schnurr, P. R. F. Barnes, I. McCulloch, J. Nelson, Energy Environ. Sci. 2019, 12, 1349.

Redox flow batteries (RFBs) are considered as a prime candidate for addressing the intermittency problem in renewable energy sources, due to their unique architecture that allows for unparalleled scalability and flexibility required for grid integration. [1]. Among several types of RFBs under development, non-aqueous redox flow batteries (NRFBs) have the potential to approach the energy density of lithium-ion batteries, while maintaining the advantages of flow systems, including ability to decouple power and energy ratings, and thermal stability [2]. Regardless of the active materials used, NRFBs suffer from low energy densities because the energy density is primarily dependent on the electrolyte concentration used [3]. The solubility values of redox active materials in non-aqueous organic solvents are relatively lower compared to aqueous systems, which negatively affects the energy density of the flow cell [4]. One promising approach for drastically improving the energy density of NRFBs is the utilization of solid charge storage materials, which are reversibly oxidized/reduced in the electrolyte tanks upon interaction with the redox active species dissolved in electrolyte [5].

Herein, we aim to demonstrate a redox-mediated flow battery using a highly stable bio-inspired electrolyte and a suitable solid storage material to provide evidence that the addition of a compatible solid material greatly improves the energy density. To accomplish this objective, a highly stable bio-inspired electrolyte, vanadium(IV/V)bis-hydroxyiminodiacetate (VBH) [6], is selected as the redox active material. Implementing VBH as a high-stability testbed (i.e., no interference from side reactions) would allow the detailed analysis required for the elucidation of the indirect redox mediation reactions between the solid storage and redox active materials. For the solid storage material, cobalt hexacyanoferrate (CoHCF), a Prussian blue analog, is selected based on its formal potential, which overlaps well with the formal potential of VBH. After sufficient evidence of improvement in the capacity is established, the solid charge storage material is optimized to further improve the energy density. Optimization of the critical parameters such as the amount of solid storage material, the operating current density, and the electrolyte flow rate is presented. The performance characteristics of the RFBs with and without solid charge storage materials present are reported and compared using a suite of electrochemical methods, including charge/discharge cycling.

References:
[1] G. L. Soloveichik, Chem. Rev., 2015, 115 (20), 11533-11558.
[2] K. Gong, Q. Fang, S. Gu, S. F. Y. Li, Y. Yan, Energy Environ. Sci., 2015, 8 (12), 3515-3530.
[3] S. Gentil, D. Reynard, H. H. Girault, Curr. Opin. Electrochem. 2020, 21, 7-13.
[4] Y. Cao, J. -J. J. Chen, M. A. Barteau, J. Energy Chem. 2020, 50, 115-124.
[5] R. Yan and Q. Wang, Adv. Mater., 2018, 30, 1802406.
[6] H. Huang, R. Howland, E. Agar, M. Nourani, J. A. Golen, P. J. Cappillino, J. Mater. Chem. A., 2017, 5, 11586-11591.

In the context of looking beyond the lithium-ion technology, magnesium batteries appear as promising candidates. Indeed, magnesium is abundant and less reactive than alkali metals, and its low redox potential opens the way to high energy density batteries. However, two major roadblocks slow down the development of magnesium batteries: the strong passivation of the magnesium surface with classical electrolytes and the lack of suitable positive electrode materials.
Alloy-type materials that can react electrochemically with magnesium have been widely evaluated as negative electrode materials, with very high corresponding capacities as well as a good behavior with classical electrolytes. However, their application as bulk electrode materials replacing magnesium metal lowers significantly the total energy density, in some cases below a critical threshold where the system becomes not competitive.
In the ongoing revival of lithium-metal batteries, the protection of lithium metal by alloy-type materials has been proposed. Such coating strongly influences the evolution of the electrode-electrolyte interface and induces long lifespan, with especially less polarization and less dendrite formation.
The purpose of our work is to adapt such coating strategy to protect the magnesium surface, thus enabling the use of classical electrolytes based on the Mg(TFSI)₂ salt. Here, we aim to show our attempts to deposit a thin layer of a p-block element on the surface of a magnesium electrode, through chemical reduction of metallic salt in solution, or via solid-solid and liquid-solid reactions. Coating are characterized by combining X-ray diffraction and electronic microscopy with surface-scale techniques such as X-ray photoemission spectroscopy. The positive impact of the coating is checked by evaluating the behavior of unprotected and protected electrodes in full cells, first with standard Chevrel phase Mo₆S₈, and then with more promising sulfur-based composites as high energy density systems are targeted. In comparison with bare magnesium electrodes, lower capacity decay and long battery lifespan is observed. These preliminary works are very promising and pave the way to the development of magnesium-metal batteries with very simple electrolytes.

The recent interest in microscopic autonomous systems, such as microrobots, colloidal state machines and smart dust has created a need for microscale energy storage and harvesting. However, the incompatibility of material properties used at the macroscale with micro-fabrication techniques creates significant challenges to realizing microscale energy systems. Herein, we use photolithography to create picoliter (10^-12 L) devices that scavenge ambient air for Zn oxidation, achieving the highest recorded energy densities of 760 to 1070 Wh L^-1 at a scale less than 100 μm in lateral size. We have elucidated the critical role of phosphate buffered electrolyte in achieving such high energy densities. Zinc phosphate precipitates contributed to a higher discharge voltage in phosphate buffered saline compared to other neutral electrolytes. More than 10,000 devices per wafer can be released into solution as functional colloids with in-built power supplies. Within a volume of only 2 pL, these batteries can deliver open circuit voltages of 1.16 V with total energies ranging from 5.5 ± 0.3 to 7.7 ± 1.0 μJ and maximal power around 2.7 nW. Such systems can power a memristor providing access to two-state memory, as well as bimorph actuators for colloidal robotic applications. The high energy density, tiny size and simple configuration promise the mass fabrication and adoption of such picoliter Zn-air batteries for micron-scale, colloidal robotics with autonomous functions.

In the past decades, lots of efforts are made by researchers to promote the development of structural lithium ion batteries, which endow energy storage ability to structural parts for vehicle lightweighting. However, the two strategies people normally use nowadays still have major challenges. One method is introducing thick or heavy packaging and mechanically supporting parts to or inside cells, which intrinsically decreases the energy densities of these energy storage devices. The other one is replacing conventional cell parts like electrodes and electrolytes with materials which have strong mechanical properties but poor electrochemical cycling stability, which sacrifice cycling performance of batteries.
By finite element analysis, we find that the reason of unsatisfying flexural behavior of conventional lithium ion batteries is the sliding of separator and electrode layers relative to each other, and it will greatly increase if we can suppress this sliding. The reason is that if layers are bonded together, all components will participate in the resistance of bending rather than slide relatively, which inspires us with a new idea to improve the mechanical behavior of batteries.
Here we propose a bioinspired and scalable interfacial design to make cell parts of lithium ion batteries robust by applying suitable and strong “binders” to each interface inside. With a thin coating layer of porous PVDF-HFP, which is previously shown without detriment to cycling performance, electrodes can be bonded with PVDF-coated separators tightly by hot pressing. With these techniques, all components in cells can contribute to the overall mechanical strength with more efficient load transfer, which dramatically enhances the flexural modulus of pouch cells from 0.28 to 3.1 GPa. On the other side, on account of the chemical simplicity of this strategy, the structural battery in this work can deliver a comparable specific capacity of 148.6 mAh g⁻¹ with conventional cells and show 95.5% capacity retention after 500 cycles. Moreover, the specific energy only decreases by 3%, which is the smallest reduction reported so far in structural batteries. A prototype of “electric wings” is also demonstrated, which allows an aircraft model to fly steadily. This work comes up with a new and straightforward way to design structural batteries, with both mechanical performance and energy density satisfied, and the method can be easily transferred to large-scale production in industry.
In addition, we apply finite element analysis to conduct simulations to compare the contribution of materials' intrinsic mechanical properties and interfacial adhesion strength in flexural behaviors of batteries, which provides a valuable insight into feasible structural batteries with balanced mechanical and electrochemical properties.

Developing sustainable biosourced electrode materials for energy storage applications is an urgent need, to keep pace with the ongoing increase in energy demand combined with the rapid use of electric vehicles and portable electric devices. Growing environmental concerns have spurred investments in renewable but intermittent energies. The need to switch to environmentally friendly, widely available, organic materials is confronted by the low conductivity and stability of most candidates and the difficulties of creating an efficient, metal-free current collector. In this work, we present a sustainable high energy density supercapacitors based on bio-sourced materials grafted on surface treated carbon paper electrode. An acidic and thermal treatment is used to induce O, N, S, and P surface doping and increase the surface area of the carbon paper. This doping improves wettability, conductivity (through the formation of graphene quantum dots), and adds faradaic activity improving the capacitance of the bare electrode. Additional deposition of sepia melanin and catechin (a tannin) with high specific capacitance and energy density shows very promising results for supercapacitors. Up to 2850 mF/cm² (228 F/g) capacitance, with 100% retention after 5 000 cycles at 20 A/g, 100% coulombic efficiency, 0.87 and 1.01 mW h/cm² (69.71, 81.25 W h/kg) and 277.15 and 158.10 mW/cm² (22.20 and 12.66 kW/kg) energy and power densities for sepia melanin and catechin, respectively, were achieved for symmetric supercapacitor devices in 0.5 M Na₂SO₄ (pH 5) electrolyte. This work provides a general guidance to design high-performance supercapacitor electrodes based on bio-sourced and potentially biodegradable materials

The development of the new generation of electrolytes for energy storage, which simultaneously enable substantial improvements in energy and power density, safety and reductions of environmental impacts and cost, is a big challenge at the present time. Deep eutectic solvents (DESs), which sometimes are considered a sub-class of ionic liquids due to their similar properties, have shown to be promising as electrolytes.^1,2 These solvents are defined as a mixture of two or more species, typically a hydrogen bond donor (HBD) species and a hydrogen bond acceptor (HBA) species which may be solid or liquid, and that at a particular composition present a melting point depression usually being liquids at room temperature. Among their most relevant properties, they have low volatility, low flammability and wide electrochemical and thermal stability windows. Unlike typical ionic liquids, DESs can be inexpensive, readily synthesized, and can often be prepared from biodegradable, and nontoxic constituents. In this work, the molecular rotational and translational dynamics of three different DESs based on choline chloride (ChCl) were studied using the fast field-cycling nuclear magnetic resonance relaxometry (FFC-NMR) and pulsed-field gradient (PFG) NMR techniques. Specifically, ChCl was chosen as the HBA at concentrations between 5 and 33mol% and glycerol, ethylene glycol (EG) or phenol were used as the HBDs. It was observed that the translational and rotational motions of all species became slower with increasing ChCl concentration for EG and phenol as the HBDs, but the opposite trend was observed for glycerol. Moreover, the PFG-NMR diffusion measurements identified a slow exchange process between the hydroxyl (OH) groups of choline and the HBDs.


1. Smith, E. L.; Abbott, A. P.; Ryder, K. S. Deep Eutectic Solvents (DESs) and Their Applications. Chemical Reviews 2014, 114, 11060–11082.
2. Tome, L. I. N.; Baiao, V.; da Silva, W.; Brett, C. M. A. Deep eutectic solvents for the production and application of new materials. Applied Materials Today 2018, 10, 30–50.

Lithium-oxygen batteries have higher energy densities than traditional lithium-ion batteries. However, they are not yet commercially viable due to poor efficiency, high charging voltages, and low cycle lifetimes. These issues could be addressed with a deeper fundamental understanding of the atomistic behavior of these batteries, especially how different factors impact lithium transport behavior. We have used classical MD simulations to examine lithium transport behavior in ten different solvents. We have validated our classical force fields by experimentally measuring the densities, viscosities, and ionic conductivities of our solvent–LiTFSI systems for comparison. However, our classical MD simulations have allowed us to go beyond these measurements and investigate properties that can be more difficult to access experimentally, such as the residence time of solvent molecules in the lithium solvation shell.

In last few decades, mounting concerns about the sustainability of fossil fuel-based energy and ever-increasing energy demand around the globe has led to the exploration of clean and renewable energy sources.^1,2 As a result, incorporation of renewable energy sources such as wind and solar into the electrical grid is taking place rapidly. ³ However, the inherent intermittency of these sources results in demand-supply imbalance which impedes efficiency. ⁴ One of the ways to tackle this problem is assuring reliability by integrating energy storage systems into the grid. ⁵ Redox flow batteries (RFBs) are a promising technology for grid level energy storage with a potential to match the performance of state-of-the-art Li-ion batteries with numerous additional advantages including decoupled power and energy rating ⁶, a wide range of working temperatures and a good safety profile.
Despite the numerous benefits of RFBs, the technology is still at its infancy and widescale implementation of them is hindered due to following three fundamental issues namely poor stability (cycling and calendar life), low energy density resulting from poor solubility of active material, and poor performance. In our previous study, we bio-mimicked an octa-coordinated dianionic vanadium complex, vanadium-bis-hydroxyiminodiacetate (VBH), from a naturally occurring biomolecule, amavadin, as a redox active molecule for flow battery application and established its extraordinary stability during exhaustive cycling. ^7,8,9 Herein, we utilize the VBH scaffold to tune thermodynamic parameters including solvation free energy and lattice enthalpy by designing molecules with varying counter cations and provide the clear pathway to further solubilize the VBH based active materials. In particular, we present evidences that increasing alkyl chain length of quaternary ammonium counter-cations, despite less favorable solvation energy, increases the solubility by facilitating the weakening of the crystal lattice. We further report electrochemical cycling of this material at moderate concentration in both symmetric and full-cells, in conjunction with an anthraquinone negolyte.

References
1. Höök, M., & Tang, X. (2013). Depletion of fossil fuels and anthropogenic climate change—A review. Energy Policy, 52, 797-809.
2. IEA (2015), Energy Statistics of OECD Countries 2015, OECD Publishing, Paris, https://doi.org/10.1787/energy_stats_oecd-2015-en.
3. IEA (2021), Renewable Energy Market Update 2021, IEA, Paris https://www.iea.org/reports/renewable-energy-market-update-2021
4. Yang, Z., Zhang, J., Kintner-Meyer, M. C. W., Lu, X., Choi, D., Lemmon, J. P., & Liu, J. (2011). Electrochemical Energy Storage for Green Grid. Chemical Reviews, 111(5), 3577–3613.
5. Grid energy storage, US Department of Energy (2013)
6. Dunn, B., Kamath, H., & Tarascon, J.-M. (2011). Electrical Energy Storage for the Grid: A Battery of Choices. Science, 334(6058), 928–935.
7. Huang, H., Howland, R., Agar, E., Nourani, M., Golen, J. A., & Cappillino, P. J. (2017). Bioinspired, high-stability, nonaqueous redox flow battery electrolytes. Journal of Materials Chemistry A, 5(23), 11586–11591.
8. Gokoglan, T. C., Pahari, S. K., Hamel, A., Howland, R., Cappillino, P. J., & Agar, E. (2019). Operando Spectroelectrochemical Characterization of a Highly Stable Bioinspired Redox Flow Battery Active Material. Journal of The Electrochemical Society, 166(10), A1745–A1751.
9. Pahari, S. K., Gokoglan, T. C., Visayas, B. R. B., Woehl, J., Golen, J. A., Howland, R., Mayes, M. L., Agar, E., & Cappillino, P. J. (2021). Designing high energy density flow batteries by tuning active-material thermodynamics. RSC Advances, 11(10), 5432–5443.

Electrolytes control battery recharge time and efficiency, anode/cathode stability, and ultimately safety, thus their optimization is crucial for the design of modern energy storage devices. In this work, we focus on ionic liquid-based electrolytes. This promising class of electrolytes possesses superior chemical stability compared to standard organic solvents, however, poor and anomalous transport properties are hindering their applicability [1]. Unfortunately, classical energy models struggle to provide the level of accuracy needed to reliably predict and investigate ionic conductivity.

Here we study the applicability to such systems of state-of-the-art equivariant graph neural networks (NequIP [2]). Ionic liquid-based electrolytes provide a unique challenge due to their strong ionic interactions and liquid nature. Additionally, substantially diverse inter-atomic environments are expected as a function of lithium-salt doping [3], raising the question of model transferability. Our promising results show that we can circumnavigate the ad-hoc and system-dependent tweaks to the classical energy models (for instance charge rescaling or polarizability), while retaining computational speed and near-DFT accuracy for large-scale ionic transport molecular dynamics investigations.

[1] N Molinari, JP Mailoa, N Craig, J Christensen, and B Kozinsky. Transport anomalies emerging from strong correlation in ionic liquid electrolytes. (2019)
[2] S Batzner, TE Smidt, L Sun, JP Mailoa, M Kornbluth, N Molinari, and B Kozinsky. SE(3)-Equivariant Graph Neural Networks for Data-Efficient and Accurate Interatomic Potentials. (2021)
[3] N Molinari, JP Mailoa, and B Kozinsky. General trend of a negative Li effective charge in ionic liquid electrolytes. (2019)

The shuttle effect of soluble lithium polysulfide (LiPS), which results in the gravest capacity degradation, is one of the critical issues to hinder the commercialization of lithium–sulfur batteries (LSBs). Here, we report mutually exclusive Ti₃C₂T_x MXene and graphene oxide multilayer composite to suppress the shuttle effect by both physical inhibition of micro/mesoporous and chemical absorption of surface functional groups. The abundant surface functional groups of GO and MXene attract the positively charged lithium ion (Li⁺) and eject the negatively charged polysulfides (S_n^2-) through electrostatic affinity and repulsion. A simple approach using vacuum filtration was utilized to encapsulate elemental sulfur (S₈) between GO and MXene film (GSM), playing role in a permselective separator and functionalized current collector, respectively. The functionally antagonistic GSM is directly utilized as cathode for LSBs and exhibits a specific capacity of 1,425 mAh g^-1 at 0.1C in the initial cycle. The abundant functional groups, which can chemisorb the LiPSs, result in a high cyclic retention of approximately 85.1% after 500 cycles. Furthermore, we demonstrate a flexible LSB with a PEO-LiTFSI electrolyte based on the flexibility of the exceptionally thin GSM due to the 2D nanomaterials, MXene and graphene oxide.

By virtue of their chemical and mechanical resiliency, carbon cathodes have shown excellent electrochemical behavior in aluminum batteries. Oppositely, this was possible only with expensive ionic liquid electrolytes, whose biodegradability, corrosivity and moisture sensitivity is an issue. By contrast, their use in Al systems operating in the aqueous electrolytes has scarcely been explored and the reported results were consistently poor. In this work, we assemble an Al-C battery with an aqueous electrolyte (aluminum trifluoromethanesulfonate) and study the electrode-electrolyte interactions. On the anode side, we find that both the electrode pretreatment and the electrolyte concentration play essential roles in solid-electrolyte interface (SEI) formation. While on the cathode side, we find pore size and hydrophilicity as important parameters in enabling superior performances. Consequently, employing a hydrophilic reduced graphene oxide (rGO) as the active cathode material enables an aqueous Al-C battery with a high energy density (136 Wh kg^-1 per cathode mass) and one of the best capacity retentions reported (>60% across a range of current densities and constant Coulombic efficiency close to unit). Furthermore, our rGO cathode more than doubles the benchmark for life cycles (to +200 cycles) and can be charged rapidly (<5 minutes). To explain this response, we propose a charge storage mechanism wherein the [Al(H₂O)₆]³⁺ ions do not get desolvated when inserted into the cathode. The guest Al ions (surface adsorbed or intercalated) act as proton donors and may get anchored on the oxygen moieties of the rGO, further promoting the formation of an electrochemical double layer. A mixed charge-storage regime follows that stabilizes the carbon cathode and enables unprecedented response.

Polyanionic materials are intensively studied as promising positive electrode materials for Na-ion batteries thanks to high stability and fast ionic mobility within their structural framework.^1-3 Among those polyanionic materials, Na₃V₂(PO₄)₂F₃ and Na₃(VO)₂(PO₄)₂F are the two most attractive ones due to their high voltage for two Na⁺ ions extraction and their high theoretical energy densities of ~ 500 mAh.g^-1. These two compositions are indeed the two end members of a family of compounds described with the general formula Na₃V₂(PO₄)₂F_3-yO_y where 0 ≤ y ≤ 2. We will first discuss the stability of these active compounds in aqueous media, and at different states of charge and discharge.⁴ Then, we will compare the performance of optimized carbon-coated stoichiometric Na₃V₂(PO₄)₂F₃ in a large panel of cycling conditions, at different rates and temperatures.^5-6 Finally, we will show how cationic and anionic substitution have been widely explored with the target to reversibly de-intercalate and re-intercalate the third Na⁺ ion from/in the structure.

Acknowledgements: This study is performed in the frame of the French RS2E and European Alistore-ERI networks on battery research. The authors thank Région Nouvelle Aquitaine, the French National Research Agency (STORE-EX Labex Project ANR-10-LABX-76-01) and the European Union’s Horizon 2020 research and innovation program under grant agreement No 875629 (NAIMA) for their financial support.

References
1. Masquelier et al., Chem. Rev. 2013, 113, 6552
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5. Broux et al., Small Methods 2018, 1800215
6. Nguyen et al., J. Phys. Chem. C 2020, 124, 23511

Lithium ion batteries are the state of the art electrochemical storage systems in many mobile applications. The further development of high-performance, cost-efficient and sustainable energy storage systems continues to be a key technology both for the full transition from combustion engines to full electric vehicles and for the intermediate storage of renewable energies. The rapidly increasing market for lithium-ion batteries in the transport and energy sectors is leading to a rapidly growing need for materials for these cells, whose supply security and environmental compatibility must be ensured – especially for critical raw materials such as cobalt, which is a component in state of the art cathode materials. The high costs of cobalt have led to the development of nickel rich layered materials with reduced cobalt content and the next generation of cathode material will contain less than 5 percent cobalt by weight (NCM811).

The development of cobalt free, manganese rich cathode materials with reduced nickel content such as LiNi_0.5Mn_1.5O₄ (LNMO) or Li_1+xNi_0.5Mn_1.5O₄ (0<x<1) can contribute significantly to further reduction of cost, high electrochemical performance and higher safety compared to lithium ion batteries with nickel-rich layered oxides. The lithium‐nickel‐manganese oxide compounds can be tailored with respect to composition and crystal structure in order to reach high capacities up to 250 mAh g^-1 [1-3] The presentation will give an overview on synthesis routes and electrochemical performance of LNMO and a series of Li_1+xNi_0.5Mn_1.5O₄ (0<x<1) cathode materials. Strategies to increase the electrochemical performance and the long life stability include i) development of tailored crystallite and particle design, ii) a profound understanding of the reaction mechanisms during lithium insertion and extraction, iii) the analysis of underlying ageing mechanisms in half and full cells, iv) development of protective surface coatings and v) the optimization of electrode/electrolyte interfaces. We will present full cell data with LNMO and Li_1+xNi_0.5Mn_1.5O₄ (0<x<1) cathode materials using various electrolytes and will discuss strategies for further optimization.

1 P. Axmann, G. Gabrielli, M. Wohlfahrt-Mehrens, J. Power Sources 301, 2016, 151-159
2 G. Gabrielli, M. Marinaro, M. Mancini, P. Axmann, M. Wohlfahrt-Mehrens, J. Power Sources
351, 2017, 35-44
3 M. Mancini, P. Axmann, G. Gabrielli, M. Kinyanjui, U. Kaiser, M. Wohlfahrt-Mehrens,
ChemSusChem 9, 2016, 1-8

Sodium-ion batteries (SIBs) have rapidly gained interest for their potential usage in large-scale grid energy storage, due to the higher abundance of sodium over lithium [1-2]. Inspired by electrodes common in lithium-ion batteries (LIBs), analogous materials are often considered in the development of SIBs [3]. However, while graphite anodes (~360 mA h g⁻¹) are most frequently used for LIBs, it is hard carbon (~300 mA h g⁻¹) which are one of the most promising for SIBs. The electrode binder, which connects particles of the electrode to one another as well as to the current collector, is regularly found to be polyvinylidene fluoride (PVDF). To improve sustainability of batteries, PVDF should be replaced with non-fluorinated, environmentally friendly binders. Lignin is an abundant natural polymer, and Kraft lignin, a by-product from pulp mills, has previously been reported as an inexpensive and environmentally-friendly NMP (N-methyl pyrrolidone)-soluble binder for LIBs [4].
Here, sodium lignosulfonate, a sulfonated lignin derivative, is introduced as a non-toxic, water-soluble binder for hard carbon electrodes. Its electrochemical performance in half- and full-cells against Prussian White is compared with other water-soluble binders, sodium carboxymethyl cellulose (CMC) and sodium alginate, as well as the NMP-soluble lignin. Furthermore, the impact of the lignosulfonate and CMC binders on the composition of the solid electrolyte interphase (SEI) layer is determined by X-ray photoelectron spectroscopy (XPS).

[1] Larcher, D. & Tarascon, J. M. Towards greener and more sustainable batteries for electrical energy storage. Nat. Chem. 7, 19–29 (2015).
[2] Yabuuchi, N., Kubota, K., Dahbi, M. & Komaba, S. Research development on sodium-ion batteries. Chem. Rev. 114, 11636–11682 (2014).
[3] Luo, W., Shen, F., Bommier, C., Zhu, H., Ji, X. & Hu, L. Na-Ion Battery Anodes: Materials and Electrochemistry. Acc. Chem. Res. 49, 231–240 (2016).
[4] Domínguez-Robles, J., Sánchez, R. Díaz-Carrasco, P., Espinosa, E., García-Domínguez, M. T. & Rodríguez, A. Isolation and characterization of lignins from wheat straw: Application as binder in lithium batteries. Int. J. Biol. Macromol. 104, 909–918 (2017).

Magnesium-ion batteries (MIBs) have received great attention in recent years as an alternative battery chemistry to Li-ion technologies thanks to the intrinsic advantages of Mg over Li. Mg has a significantly larger volumetric capacity (3832 mAh cm⁻³ vs 2061 mAh cm⁻³ for Li), higher natural abundance and lower cost than Li [1]; Mg also has a relatively low standard redox potential (-2.37 V vs. SHE [1]). Furthermore, due to the divalent nature of the Mg²⁺ cation, for the same amount of ions stored in a host material (usually the cathode), the specific capacity is doubled in comparison with a monovalent cation. Thanks to these key advantages MIBs can theoretically achieve higher energy densities at a lower cost than LIBs [2] making MIBs a very attractive battery technology. However, one of the main fundamental challenges in MIBs is the slow Mg²⁺ ion solid state diffusion into the cathode active material’s lattice. This is generally attributed to the high charge/radius ratio of the Mg²⁺ ion, which results in strong interactions between the anions and cations of the host structures [3]. As consequence, cathode materials for MIBs usually show very poor electrochemical performance (low specific capacities, high overpotentials and poor rate capability).
Vanadium-based oxides cathodes have been the object of intense study over the past few years due to their relatively high potential of 2.5 V vs Mg²⁺/Mg, and the possibility to explore multiple oxidation states of vanadium, i.e. V⁵⁺/V⁴⁺ and V⁴⁺/V³⁺, resulting in higher theoretically achievable specific capacities [4]. Within this family, the H₂V₃O₈ (HVO) phase shows promising structural and morphological characteristics which could favour Mg²⁺ intercalation. Specifically, H₂V₃O₈ has a relatively large interlayer distance of 8.4 Å and can crystallize in a nanowire morphology. However, H₂V₃O₈ has only recently been tested in a MIB for the first time, showing a specific capacity of around 80 mAh g^-1 at room temperature, even though its theoretical specific capacity is 190 mAh g^-1, for the intercalation of 1 eq. of Mg²⁺ [5].
In our study, a post-mortem analysis of HVO electrodes upon charge and discharge at specific cycle numbers was carried out to investigate the intercalation mechanism of Mg²⁺ into HVO. For the first time, we demonstrate the electrochemical performance of HVO in TFSI-based electrolytes with a specific capacity approaching 200 mAh g^-1 at room temperature. Furthermore, by combining bulk and surface characterization techniques, changes in the HVO crystal structure, morphology and surface chemistry were analysed in-depth. Depending on the cycle number, Mg²⁺ intercalation upon discharge resulted in a 0.5% to 4% change in the unit cell parameters compared to the pristine electrode. The intercalation caused a change in the V⁵⁺/V⁴⁺ ratio, with a lower ratio (i.e. higher amount of V⁴⁺) associated with cycle numbers showing the highest capacity values. However, Mg²⁺ ions could not be completely extracted upon charge, resulting in lattice parameters which do not return to their original values. Although the nanostructured morphology of HVO did not change over cycling, surface roughening of the nanowires was observed at high cycles numbers, indicating formation of a TFSI-containing surface layer. Evidence of V dissolution could also be confirmed, resulting in capacity fading after about 35 cycles.


[1] C. Kuang, W. Zeng, and Y. Li, J. Nanosci. Nanotechnol., vol. 19, no. 1, pp. 12–25, 2019.
[2] Y. Tian et al., Chem. Rev., vol. 121, no. 3, pp. 1623–1669, Feb. 2021.
[3] E. Levi, YGofer, and D. Aurbach, Chem. Mater., vol. 22, no. 3, pp. 860–868, 2010.
[4] H. Tang et al., Electrochem. Energy Rev., vol. 1, no. 2, pp. 169–199, Jun. 2018.
[5] M. Rastgoo-Deylami, M. S. Chae, and S.-T. Hong, Chem. Mater., vol. 30, no. 21, pp. 7464–7472, Nov. 2018.

Research into new energy storage technologies, for both portable and stationary applications, has become imperative in order to meet present and future energy requirements. Recently, rechargeable sodium oxygen batteries are receiving a great deal of interest as possible alternatives to lithium ion batteries, because of their potentially higher gravimetric energy densities (1605 or 1108 Wh/kg based on Na₂O₂ or NaO₂ discharge products, respectively)¹.

In order to facilitate the advancement of this technology, the development of targeted approaches to dealing with the technology’s unique chemistry are required. The vast majority of the work reported on sodium oxygen batteries has been devoted to the development of suitable air cathodes² (primarily focused on carbon), catalysts, and - to a lesser extent - redox mediators, neglecting electrolytes despite their importance. Electrolytes, consisting of a salt and a non-aqueous solvent, are a key component of any optimized system. The parameters affecting electrolyte physiochemistry (solvent-salt structure and dynamics) are, therefore, critical to battery performance, lifetime and safety. The composition of the electrolyte (solvent and salt) has been identified as key parameter which controls the crystal growth during the discharge process, and subsequently the dissolution of discharge products during charge. Glyme-based solvents have been widely – but arbitrarily – used, and to date no clear correlation between solvent/electrolyte properties and battery performance have been outlined.
In this work, we will discuss and clarify the relationship between glyme chain length and cell chemistry and performance. We will, moreover, demonstrate how solvent selection helps define cell chemistry and performance, by linking salt-solvent interactions to solvation energies - and subsequently to sodium battery electrolyte properties - through the combination of both experimental and computational methodologies. In addition, we will unravel how careful combination of different solvents such as ionic liquids can modify the speciation and solvation of the discharge products, so as to obtain the desired deposition mechanism and crystal growth.


References

¹ I. Landa-Medrano, C. Li, N. Ortiz-Vitoriano, I. Ruiz de Larramendi, J. Carrasco and T. Rojo J. Phys. Chem. Lett. 2016 ,7(7), 1161–1166.
² M. Enterría, C. Botas, J.L. Gómez-Urbano, B. Acebedo, J.M. López del Amo, D. Carriazo, T. Rojo, and N. Ortiz-Vitoriano. J Mater. Chem. A 2018, 6 (42), 20778-20787.

Molten sodium batteries are a grid-scale energy storage technology with over 500 MW/4 GWh deployed worldwide that utilize inexpensive sodium and sulfur or aluminum-containing materials. Despite their legacy of reliably and safely providing large capacity energy storage for decades, they do not enjoy widespread popularity as an alternative to grid-scale lithium-ion batteries. This can largely be attributed to the high temperatures necessary to operate these systems (270 – 350 °C), which greatly increases the capital cost to install them ($600-700/kWh) despite their use of low-cost active materials. Lowering the temperature to near the melting temperature of sodium (97.8°C) can create dramatic savings by reducing the cost of inactive materials such as the insulation, wiring, and seals, while increasing battery longevity by slowing aging of all system components. Traditional battery chemistries such as sulfur/polysulfides and nickel/nickel chloride, while effective for high temperatures, simply do not work at low temperatures (< 150 °C) as materials solidify. To lower the temperature by nearly 200 °C, complete re-engineering of the cathode is necessary. Here we describe the development of a low temperature catholyte utilizing low-cost and earth-abundant materials to create a high performance, low temperature molten sodium battery. This was achieved by first identifying redox-active molten salts composed of sodium iodide and a metal halide salt that are liquid at 100 °C. The effect of sodium iodide content and choice of metal halide salt on battery voltage and power performance was studied to identify compositions capable of near-commercially relevant levels of power and energy density. The long-term cyclability of catholyte compositions was evaluated in batteries at 110 °C, with some catholyte compositions capable of cycling in some cases for up to 8 months. Electrochemical performance was weighed against constraints in molten salt cost to create a low-cost, high performance catholyte.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

As the energy-storage market is accelerating and expanding globally with lithium-ion batteries, cost and sustainability of the technology for electric vehicles and grid-storage are becoming a serious concern. This has prompted immense interest on battery chemistries based on earth-abundant, low-cost materials. In this regard, batteries based on multivalent ions, such as magnesium, calcium, zinc, aluminum, etc. have generated much interest, as they occur at much higher terrestrial concentrations, diminishing the issues associated with sustainability and supply chain. Also, multivalent ions can theoretically store more charge than monovalent lithium or sodium, although with a lower operating voltage. However, multivalent-ion batteries are faced with a few scientific and technological challenges.

First, nonaqueous multivalent-ion batteries suffer from a lack of appropriate electrolytes, which makes a true assessment of their performance difficult. Second, except for zinc, the lack of appropriate anode/electrolyte combinations also makes the reversible plating and stripping of the multivalent metallic anodes challenging. Without proper assessment of the electrochemical cells, it will be hard to understand the true behavior of the cathode. Therefore, this presentation will focus first on the use of chemical insertion/extraction reactions of multivalent ions with appropriate reagents to assess the potential of various hosts.

Among the various multivalent-ion batteries, much of the fundamental research has focused on aqueous zinc-ion batteries, and attractive performances have been reported with high capacity and rates with oxide-based cathodes. Despite the apparent success with zinc-ion batteries in aqueous electrolytes, the concept of multivalent-ion batteries remains elusive, as witnessed by a lack of sensible progress in other multivalent-ion chemistries, such as magnesium-ion and aluminum-ion batteries. This mismatch points to a fundamental gap in the knowledge surrounding aqueous zinc-ion batteries, especially the hidden role of protons originating from aqueous electrolyte or from any water present in the cathode.

To delineate the actual solid-state diffusion behavior of zinc ions, the presentation will provide a series of studies to assess the relative extent of zinc-ion versus proton insertion in common solid-state hosts. The use of a microwave-assisted insertion technique for chemical insertion of zinc ions into hosts and elevated-temperature electrochemical zinc-ion insertion will be discussed. Our results indicate that in general and as expected, the diffusion of zinc ions in oxidic hosts is an energy-demanding process that prohibits its efficient utilization in rechargeable batteries. On the contrary, the inclusion of aqueous electrolytes allows the introduction of charge-compensating protons that can readily diffuse into the solid-state hosts, with the release of an equivalent amount of zinc ions into the electrolyte. Therefore, the utilization of aqueous electrolytes with zinc anode is conceptually similar to other systems in which protons are the actual working ions.

Overall, our study reveals that attempts to insert zinc ions strictly in non-aqueous electrolytes are accompanied by severe thermodynamic and kinetic limitations, often encountering significant host-guest electrostatic repulsions due to the higher charge on Zn²⁺ and subsequent capacity loss. This issue can be suppressed by employing more covalent chalcogenide-based hosts, but at the cost of lower cell capacity and voltage. Even in the chalcogenides, zinc-ion diffusion tends to be slow compared to that in other rechargeable batteries. Given the slow native diffusivity of multivalent ions in solid-state hosts, it appears that the possibility of multivalent-ion batteries hinges on the development of alternative cathode architectures that do not rely on the long-range solid-state diffusion of guest ions.

Mechanically stable and foldable air cathodes with exceptional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities are key components of wearable metal-air batteries. Herein, we report a directional freeze-casting and annealing approach for the construction of 3D honeycomb nanostructured, N, P-doped carbon aerogel incorporating in situ grown FeP/Fe₂O₃ nanoparticles as the cathode for flexible Zn-air battery. The aqueous rechargeable Zn-air batteries assembled with this carbon aerogel exhibit a remarkable specific capacity of 648 mAh g^-1 at current density of 20 mA cm^-2 with good long-term durability, outperforming those assembled with commercial Pt/C+RuO₂ catalyst. Furthermore, such foldable carbon aerogel with directional channels can serve as freestanding air cathode for flexible solid state Zn-air battery without the use of carbon paper/cloth and additives, giving a specific capacity of 676 mA h g^-1 and an energy density of 517 W h kg^-1 at 5 mA cm^-2 together with good cycling stability. This work offers a new strategy to design and synthesize highly effective bifunctional air cathode applied in electrochemical energy devices.

Rechargeable aqueous Ni–Zn batteries can provide an energy-dense, safer alternative to Li-ion batteries for a wide range of applications including electric vehicles, portable electronic devices, and grid-level energy storage. We investigate approaches to obtain high-capacity cathodes that can support the performance of dendrite-suppressing Zn sponge anodes pioneered at the U.S. Naval Research Laboratory. We substitute metal ions (aluminum, cobalt, manganese, or zinc) into α-Ni(OH)₂, a phase that stores greater than one-electron per Ni, but requires stabilization to avoid transformation to the lower capacity β-phase. We use a microwave-assisted process that expresses α-Ni(OH)₂ in a high surface-area nanosheet morphology, and show that this morphology is retained for all metal-ion substituents.¹ The substituents do, however, influence aggregate growth, interlayer spacing, and Raman vibrational frequencies. The metal-ion-substituted materials are fabricated into powder-composite cathodes and tested versus zinc sponge anodes in alkaline electrolyte. We find that of the substituents evaluated, only Al³⁺-substitution favorably increases the discharge capacity, discharge voltage, and oxygen evolution reaction onset voltage and improves the cycling stability of the α-phase. The enhanced electrochemical performance and phase stability of Al³⁺-substituted α-Ni(OH)₂ nanosheets correlate to the presence of interlayer ordered nitrates and changes to the environment of intralayer Ni. The rational selection of substituents and rethinking the electronic wiring within the cathode structure provide a pathway to realize energy dense, safe, rechargeable Ni–Zn batteries.

References
1. Kimmel, S.W.; Hopkins, B.J.; Chervin, C.N.; Skeele, N. L.; Ko, J.S.; DeBlock, R.H.; Long, J.W.; Parker, J.F.; Hudak, B.M.; Stroud, R.M.; Rolison, D.R.; Rhodes, C.P. Capacity and Phase Stability of Metal-Substituted α-Ni(OH)₂ Nanosheets in Aqueous Ni–Zn Batteries. Materials Advances 2021, 2, 3060–3074.

A layered MoO₃ material with large interlayer spacing represents a promising cathode for aqueous rechargeable Zn-ion batteries (ARZIBs), but the implementation of this material is limited due to the intrinsically low conductivity and poor structural stability. A 30 m ZnCl₂ water-in-salt electrolyte (WISE) was introduced to a MoO₃ nanobelt cathode for the first time, significantly increasing the stability of MoO₃ cathodes compared to those in 3 M ZnSO₄ and 3 M ZnCl₂ electrolyte. The Zn/MoO₃ cell in WISE unambiguously demonstrated significantly improved rate performance delivering 349, 253, and 222 mAh/g at 100, 500, and 1000 mA/g, denoting a 2x, and 12x capacity increase of those achieved in 3 M electrolytes at 500 and 1000 mA/g, respectively. A capacity retention rate of 73% was achieved after (dis)charging at 100 mA/g for 100 cycles, and no obvious capacity fading was observed at higher current densities of 500 mA/g and 2A/g. A compilation of structural and morphological characterization was systematically performed to provide insight into the mechanisms of the improved performance in ZnCl₂ WISE for the MoO₃ cathode materials. Specifically, our data collectively suggested that the drastic fading in 3M electrolytes can be attributed to the parasitic surface deposits on Zn originated from Mo dissolution and H₂ formation due to Zn corrosion and hydrogen evolution reaction (HER), which were significantly suppressed in the ZnCl₂ WISE. The direct visualization of these side reactions was achieved for the first time in the Zn-MoO₃ system, using an in situ optoelectrochemical measurement.

All-solid-state battery technologies point toward a sustainable energy future, aiming to replace the ammable liquid organic electrolytes currently used with safer solid-state inorganic electrolytes. Oxides generally show better electrochemical properties but weaker ionic conductivity when compared to their sulfide counterparts. Here we use first-principles molecular dynamics simulations to extensively simulate LGPO, the oxide analogue of LGPS, one among the best conducting solid-state electrolytes. From canonical simulations we predict that a hypothetical tetragonal phase mirroring that of LGPS would be highly conductive. We thus explore the dynamical stability of this phase and of an existing orthorhombic phase of LGPO via isobaric-isothermal simulations, while extracting from the trajectories the relevant elastic moduli.

Grid scale stationary energy storage is critical for integration of renewable electricity such as solar and wind into electric grid, and also enable the new opportunity for resilient and smart grid. The cost, life and temperature range of batteries need to be significantly improved for this purpose. My lab we developed a breakthrough metal-H₂ battery chemistry to meet the needs of grid scale storage, in which hydrogen gas electrodes is anodes and transition metal oxides are cathodes. This battery chemistry is low-cost, with long life over 30,000 cycles and 30 years. It can be operated in a wide range of temperature of -40 to +60 °C and is maintenance-free. The fast charging/discharge up to 10min is possible in this chemistry. The spinout company EnerVenue has realized very exciting commercial prototypes based on this technology. The metal-H₂ battery affords an ideal storage solution to integrate solar and wind electricity into the grid.

Sodium-ion batteries (NIBs) are the closest of the “Beyond Lithium-Ion” batteries to commercialization. Their benefits include reduced cost and potentially better safety compared to lithium-ion analogs as well as sustainability, due to the greater earth abundance of sodium compared to lithium. Layered titanate anodes are proposed as alternatives to the more commonly used hard carbons, and have advantages such as greater density and higher first cycle coulombic efficiencies. For this talk, we will discuss several examples of this materials.

Batteries based on the magnesium-ion chemistry are considered as promising alternatives to lithium ion technologies due to the high theoretical volumetric capacity (3833 mAhcm⁻³ for the Mg-anode), low toxicity and natural abundance of magnesium, as well as the di-valent character of the Mg²⁺ cations. Furthermore, since magnesium deposition takes place without dendrite formation on the Mg-metal anode surface, the Mg-cell is expected to be considerably safer than comparable cells based on Li metal.¹

Despite these positive attributes, the development of Mg secondary batteries is hindered by the slow solid-state diffusion of Mg²⁺ ions into the cathode lattice, which lead to relatively low practical capacities, irreversible capacity losses and poor cyclic stability. In this work, this issue is explored by synthesising and characterising a phosphate-based system with olivine-related structure to investigate its suitability as cathode materials for Mg-ion batteries, with phosphates building-blocks chosen due to their open three-dimensional framework, structural stability and safety under oxidizing conditions.² Therefore, in this work the novel olivine-related (Mg_0.5Ni_0.5)₃(PO₄)₂ compound was synthesised by the solid-state method and investigated as a potential electrode active material.

(Mg_0.5Ni_0.5)₃(PO₄)₂ was subjected to a comprehensive physico-chemical characterization in order to optimize the synthesis conditions, determine the phase purities and assess the particle morphologies. Furthermore, the reaction mechanisms and electrochemical behaviour of the orthophosphate-based material with monovalent Li⁺ and divalent Mg²⁺ ions were investigated using post-mortem analysis (XRD, FTIR and XPS) in order to establish the nature of the charge storage reaction mechanisms.

In addition to the challenges associated with the development of novel electrode materials, it is well known that Mg-based electrolytes, which consist of ionic salts (i.e. Mg(ClO₄)₂) dissolved in aprotic organic solvents (i.e. acetonitrile), form passivating layers on the surface of the Mg metal anode, leading to poor performance of the overall cell. In order to address this problem, activated carbon was used as the counter electrode to replace the metallic magnesium Our results show that (Mg_0.5Ni_0.5)₃(PO₄)₂ has a first cycle discharge capacity of 90 mAhg^-1 when a 0.5 M Mg(ClO₄)₂ in acetonitrile solution is used as the electrolyte. Post mortem XRD, FTIR and XPS analysis of the electrode after cycling suggest that a conversion reaction takes place during discharge due to the extrusion of Ni²⁺ cations from the host material lattice. In a similar fashion, Cu-Ni alloys and amorphous Li₃PO₄ form during the electrochemical reaction between (Mg_0.5Ni_0.5)₃(PO₄)₂ and lithium metal using a LiPF₆-based electrolyte, achieving a practical capacity of 600 mAhg^-1. Based on the electrochemical data, it is possible to conclude that the conversion reaction of (Mg_0.5Ni_0.5)₃(PO₄)₂ with Mg metal as the counter electrode should occur as observed for lithium, if an electrolyte is found which does not passivate the Mg surface. However, since the Mg-electrode is passivated, our findings show that the use of a carbon-based counter electrode significantly improves the practical capacity of (Mg_0.5Ni_0.5)₃(PO₄)₂ when a Mg-electrolyte is used.

References
1. H. D. Yoo, I. Shterenberg, Y. Gofer, G. Gershinsky, N. Pour, D. Aurbach, Energy Environ. Sci., 2013, 6, 2265–2279;
2. P. Canepa, G. Sai Gautam, D. C. Hannah, R. Malik, M. Liu, K. G. Gallagher, K. A. Persson, G. Ceder, Chem. Rev., 2017, 117, 4287–4341.

Aqueous organic redox flow batteries (RFBs) are promising for grid-scale energy storage, but identifying stable and inexpensive organic redox couples suitable for practical applications has been challenging. Here we report a new, inexpensive, and robust anolyte, Dextrosil-Viologen (Dex-Vi), that demonstrates a record overall RFB performance for viologen redox species in neutral aqueous media, including reduced anion-exchange membrane permeability, increased volumetric capacity capability, and improved chemical stability. At 0.1 M, the first redox state of Dex-Vi demonstrates no distinguishable capacity decay over two weeks of cycling (1,200+ cycles) when paired with BTMAP-Fc catholyte in an anolyte-limiting cell configuration. Even at a high concentration of 1.5 M in a practical capacity-balanced RFB, Dex-Vi demonstrates extremely stable cycling performance for one-electron utilization as well as flowable and soluble behavior when it is doubly reduced. Furthermore, by rationalizing a high-yield hydrothermal synthetic approach that has never been applied to viologen RFB molecules along with a low-cost precursor, the predicted mass production cost of Dex-Vi is below $10/kAh. These results not only establish a new benchmark organic anolyte promising for practical RFB applications but also shows that the properties of organic redox species for RFB can be enhanced with minute performance tradeoffs through rationalized structural and synthetic design.

Disordered rock-salt Li-rich transition metal (TM) oxides, especially those based on Mn, are exciting prospective high-energy-density cathode materials for the next generation of LIBs due to their potential to replace Co-based cathodes [1]. Recently it has been shown that F substitution can reduce oxygen redox by lowering the average anion valence and increasing the amount of redox-active TM [2] as well as improve energy density, average voltage, and rate performance [3]. The substituting F tends to be incorporated in Li-rich environments due to its preference to bond with Li rather than TM [2]. We have investigated how both F substitution and Li excess affect the migration energy for Li diffusion in various local atomic configurations using first-principles calculations in combination with the nudged elastic band (NEB) method [4]. We use orthorhombic-LiMnO₂as a model case to investigate the effects of F substitution and Li excess. Based on our results, we demonstrate that F has only a small effect on Li migration barriers while Li excess has a strong positive effect and actually decreases Li migration barriers. Hence, we do not expect any detrimental impact on Li transport when fluorination is used as a design strategy to increase the TM redox [4].

[1] Lee, J., Kitchaev, D. A., Kwon, D. H., Lee, C. W., Papp, J. K., Liu, Y. S., ... & Guo, J. (2018). Reversible Mn 2+/Mn 4+ double redox in lithium-excess cathode materials. Nature, 556(7700), 185.
[2] Kitchaev, D. A., Lun, Z., Richards, W. D., Ji, H., Clément, R. J., Balasubramanian, M., ... & McCloskey, B. D. (2018). Design principles for high transition metal capacity in disordered rocksalt Li-ion cathodes. Energy & Environmental Science, 11(8), 2159-2171 [2].
[3] Lee, J., Papp, J. K., Clément, R. J., Sallis, S., Kwon, D. H., Shi, T., ... & Ceder, G. (2017). Mitigating oxygen loss to improve the cycling performance of high capacity cation-disordered cathode materials. Nature communications, 8(1), 981 [3].
[4] Jadidi, Z., Chen, T., Xiao, P., Urban, A., & Ceder, G. (2020). Effect of fluorination and Li-excess on the Li migration barrier in Mn-based cathode materials. Journal of Materials Chemistry A, 8(38), 19965-19974.

The importance of long-duration energy storage (LDES) in the emerging sustainable, carbon-free global energy infrastructure continues to become increasingly clear. While several different types of storage are likely needed to meet growing LDES demands, new or adapted battery technologies are expected to play key roles in the future LDES technology space. Here, we describe how emerging low temperature, high voltage molten sodium batteries offer promise as one of these batteries. LDES can refer to storage from several different perspectives and application sets: 1) long discharge duration (e.g., >6-10 hours), 2) long storage duration between charge and discharge, or 3) long battery lifetime (>10-15 years). We will describe here the structure and chemistry of a developing low temperature (near 100°C) molten sodium-halide battery and discuss why it may be especially well-suited for LDES applications. These batteries comprise a molten sodium anode, a fully inorganic, molten sodium iodide-based metal halide salt catholyte, and an efficient solid state sodium ion-conducting separator. The specific composition of the molten salt catholyte and the engineering of the solid-state separator allow for the operation of these batteries at the low temperature of 110°C with a stable cycling voltage of 3.65V. We will discuss recent extended battery cycling behavior and the stability of battery performance during extended “frozen” storage experiments. Connecting our findings to LDES applications including extended discharge duration, extended storage duration, and long-lifetime storage, we outline the potential impact of low temperature molten sodium batteries to the rapidly evolving LDES technical landscape.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Aqueous soluble organic (ASO) redox-active materials have recently shown great promise as alternatives to transition metal ions to be employed as energy-bearing active materials in redox flow batteries for large-scale energy storage because of their structural tunability, cost-effectiveness, availability, and safety features. Development so far however has been limited to a small palette of organics that are aqueous soluble and tend to display the necessary redox reversibility within the water stability window. There is however noticeably much larger number of organic molecules that exhibit some degree of irreversible redox activities. In this presentation, we show how the molecular engineering of fluorenone enables the alcohol electro-oxidation needed for reversible ketone hydrogenation and dehydrogenation at room temperature without the use of a catalyst. Flow batteries based on these fluorenone derivative anolytes operate efficiently and exhibit stable long-term cycling at ambient and mildly increased temperatures in a non-demanding environment. These results suggest the potential for identifying other atypical organic redox molecules for energy storage.

Reference: Feng et al., Science 372, 836–840 (2021)

Nonmetal ammonium ( NH4+) ions have recently been explored as effective charge carriers in battery systems due to their abundancy, light weight, small hydration shells in water. The research concerning the use of redox chemistry in ammonium ion batteries, particularly in flexible ammonium ion batteries, is still in its infancy. For the first time, we report a flexible full ammonium ion battery (AIB) composed of a concentrated hydrogel electrolyte sandwiched between nanosized hydrated ammonium vandate cathode and polyaniline (PANI) anode, for enhanced performance. The hydrogel electrolyte is simply synthesized by using ammonium sulfate, xanthan gum and water. As a reference, the AIB based on the liquid aqueous electrolyte is prepared first, which exhibits a capacity of 121 mAh g^-1 and a capacity retention of 95% after 400 cycles at a specific current of 0.1 A g^-1. The simple synthesis of the hydrogel electrolyte allows us to facilely tune and optimize the salt contents in the electrolyte, to maximize the ionic conductivity, transport kinetics, mechanical characteristics, and consequently the battery performance. It is found that the flexible battery based on the hydrogel electrolyte prepared from 3 M ammonium sulfate solution shows the best electrochemical performance, i.e., a capacity of 60 mAh g^-1 while maintaining a capacity retention of 88% after 250 cycles at a specific current of 0.1 A g^-1, which are better than the few results reported for flexible AIBs in literature. Moreover, the flexible AIB retains excellent electrochemical performance when bent by 90 and 180 degrees, demonstrating remarkable mechanical strength and flexibility. Therefore, this study sheds new light on the utilization of concentrated hydrogel electrolyte in the AIB chemistry, for future developments of new electrochemical energy storage technology with high safety and low cost.

Relegated to the annals of history, Zn/CuO batteries have long thought to be solely a primary battery system. Surpassed by Zn/MnO₂ in both the commercialization as a primary cell and focus on fundamental investigations into generating secondary versions of the battery, very little research has been performed on CuO alkaline cells. However we have recently demonstrated that by including a bismuth additive into the CuO cathode formulation, Zn/CuO cells are capable of cycling over 100 times at > 124 Wh/L, with capacities from 674 mAh/g (cycle 1) to 362 mAh/g (cycle 150).¹ To mitigate the capacity losses of long-term cycling CuO cells, we demonstrate two limited depth of discharge (DOD) strategies capable of cycling at 202 mAh/g for over 250 cycles or for ~ 40 mAh/cm² and unprecedented energy densities of ~ 260 Wh/L for up to 80 cycles. Using a suite of electrochemical and spectroscopic techniques, including rotating ring disk electrochemistry, impedance, and energy dispersive x-ray diffraction the role of the bismuth additive in enabling the CuO cycling is elucidated. This work serves as a steppingstone for the development of low-cost, safe, and energy dense secondary batteries based on often overlooked conversion chemistries.

This work was Supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525. The views expressed herein do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

Ref 1 Schorr, N.B.; Arnot, D.J.; Bruck, A.M.; Duay, J.; Kelly, M. Habing, R.L.; Ricketts, L.S.; Vigil, J.A.; Gallaway, J.W.; Lambert, T.N. ACS Applied Energy Materials, 2021, Accepted

Aqueous rechargeable zinc-iodine batteries (ZIBs) are promising candidates for grid energy storage because they are safe and low-cost and have high energy density. However, the shuttling of highly soluble triiodide ions severely limits the device’s Coulombic efficiency. Herein, we demonstrate for the first time a double-layered cathode configuration with a conductive layer (CL) coupled with an adsorptive layer (AL) for ZIBs. This unique cathode structure enables the formation and reduction of adsorbed I₃^- ions at the CL/AL interface, successfully suppressing triiodide ion shuttling. A prototypical ZIB using a carbon cloth as the CL and a polypyrrole layer as the AL simultaneously achieves outstanding Coulombic efficiency (up to 95.6%) and voltage efficiency (up to 91.3%) in the aqueous ZnI₂ electrolyte even at high-rate intermittent charging/discharging, without the need of ion selective membranes. These findings provide new insights to the design and fabrication of ZIBs and other batteries based on conversion reactions.

Ionogels are pseudo-solid state electrolytes in which an ionic liquid electrolyte is confined in an organic or inorganic matrix. One well established ionogel synthesis route is based on sol-gel chemistry where silica precursors dissolved in an ionic liquid electrolyte (ILE) undergo hydrolysis and condensation polymerization. By using an ionic liquid as the solvent, no evaporation occurs and the resulting material is a macroscopically rigid, nonporous material in which the ionic liquid is trapped by capillary forces in the nanometer sized pores in the silica network. Using this approach, it is possible to develop pseudo-solid state materials that possess the electrochemical, thermal and chemical properties of the ionic liquid. Moreover, sol-gel synthesis enables the precursor sol to penetrate porous electrodes before solidifying, a feature which is especially attractive for solid-state batteries.

In this presentation, we review our recent work on synthesizing Li-ion and Na-ion conducting ionogels and their incorporation in solid-state battery structures. We developed Li-ion conducting ionogels based on using an ILE comprised of 0.5M LiTFSI in [BMIM] [TFSI] that exhibited conductivity and electrochemical properties comparable to those of the parent ILE. These pseudo-solid state materials were also incorporated in ‘2.5D’ batteries comprised of a LiFePO₄ cathode array with a lithium anode. More recently we have focused on Na-ion conducting ionogels. One approach was based on using an ionic liquid electrolyte consisting of 0.5M NaFSI in [PYR14][TFSI]. The resulting material exhibited good ionic conductivity (0.7 mS cm^–1) and a nearly 5V electrochemical stability window. Sodium-ion solid-state batteries with excellent reversibility were demonstrated using this Na-ion conducting ionogel in conjunction with two Na-ion intercalation materials which served as positive and negative electrodes. We have also begun to investigate the synthesis and properties of ionogels that incorporate glyme-based electrolytes as such electrolytes have shown excellent stability in contact with sodium metal. We have successfully developed tetraglyme-based ionogels and incorporated them in sodium metal batteries using Na₃(VO)₂(PO₄)₂F as the cathode. Capacities in excess of 400 Wh kg^-1 were achieved at 0.5C. In summary, the ability to design the ion transport properties of ionogels coupled with their thermal and electrochemical stability makes these materials a very promising direction for use in solid-state energy storage devices.

Electrically conducting polymers may have broad application in electrical energy storage. A conductive and adhesive Poly(9,9-dioctylfluorene-co-fluorenone-comethylbenzoic ester) (PFM) polymer was recently developed as a multifunctional electrode binder for rechargeable battery applications. Pure Sn nanoparticles electrode with PFM conductive polymer adhesive binder are prepared and tested in sodium ion battery. It shows high specific capacity and high cycling stability without any conductive additive compared with Sn/CMC (carboxy methylated cellulose) and Sn/PVDF (polyvinylidene fluoride) electrode. The Sn in Sn/PFM electrodes delivers 806 mAh g^-1 at C/50 and 610 mAh g^-1 at C/10. After 10 cycles at C/10, the capacity of Sn has no decay. SEM and TEM images show that the Sn particles in Sn/PFM electrode are still fully coated by PFM polymer after huge expansion during sodiation and shrinkage during desodiation.

K-ion battery (KIB) has recently attracted much attention as a potential high-voltage and high-power battery due to low standard electrode potential of K⁺/K and fast ionic diffusion of K⁺ ion in electrolyte solutions, respectively [1]. In 2015, our group reported graphite negative electrode, which delivered a reversible capacity of more than 250 mAh g^-1 with excellent reversibility and rate performance [2]. We also confirmed that a K-graphite intercalation compound of KC₈ was electrochemically formed with several stage transformations [3]. Furthermore, a Prussian blue analog (PBA) of K₂Mn[Fe(CN)₆] (KMnHCF) showed highly reversible potassium insertion/extraction and ca. 4 V vs. K⁺/K operation to realize a 4 V-class graphite // K₂Mn[Fe(CN)₆] full cell [4]. The cycle performance of the full cells drastically improved using the proper electrolytes, such as KPF₆-KN(SO₂F)₂ binary salt electrolytes [5]. In contrast, the bulk properties that affect the electrochemical properties of graphite and PBA have not been fully understood. Thus, we investigated the predominant bulk properties affecting the potassium insertion reaction into graphite and PBA electrodes.
Potassium insertion properties of several types of graphite were investigated, and we found that the crystallinity significantly affects the reversibility of K⁺ ion intercalation. Although the high reversible capacity and Coulombic efficiency of graphite electrodes in K cells were achieved during initial cycles regardless of the crystallinity, high crystallinity graphite demonstrated less potential-hysteresis and superior capacity retention to low crystallinity graphite. Operando XRD measurement confirmed a similar staging process of K-GICs for both graphite samples. However, high crystallinity graphite was transformed into higher crystallinity K-GIC as well as higher reversibility of potassium de-/intercalation than low crystallinity graphite. A turbostratic disorder in low crystallinity graphite led to the redox-potential split and lower crystalline K-GIC and potassium-extracted graphite. Thus, we concluded that high crystallinity is important for applying graphite to long-life potassium-ion batteries.
In addition to the graphite electrodes, we investigated the K⁺ insertion reaction into KMnHCF. Although the particle size and the number of [Fe(CN)₆]^n– anion vacancies may affect the electrochemical performance of PBAs, the difficulty of independently controlling the particle size and number of anion vacancies has hindered understanding the impact of each factor [6]. We successfully synthesized KMnHCFs through a precipitation route, and the particle size and number of the anion vacancies were varied by employing a proper chelate agent and Na/K ionic exchange route. When nearly stoichiometric KMnHCF was synthesized and tested, smaller particle sizes were important for achieving superior electrochemical performance in capacity and rate capability. However, even in larger particles, introducing a suitable number of anion vacancies enabled KMnHCF to exhibit comparable electrode performance, which would be due to the enhancement of K⁺ ion diffusion. From these results, we will present future insight into electrochemical potassium insertion chemistry.
References:
[1] T. Hosaka, S. Komaba et al., Chem. Rev., 2020, 120, 6358–6466.
[2] S. Komaba, K. Kubota et al., Electrochem. Commun., 2015, 60, 172-175.
[3] K. Kubota, S. Komaba et al., Chem. Rec., 2018, 18, 459-479.
[4] X. Bie, S. Komaba et al., J. Mater. Chem. A, 2017, 5, 4325-4330.
[5] T. Hosaka, S. Komaba et al., ACS Appl. Mater. Interfaces, 2020, 12, 34873-34881.
[6] T. Hosaka, S. Komaba, ChemSusChem, 2021, 14, 1166-1175.

Development of energy storage system in the past year focus on improvement of energy density. While the progress is remarkable, safety problems of lithium ion batteries (LIB) have been intensively exposed. On one hand, LIB is not intrinsically safe with very active anode, flammable electrolyte and oxygen-releasing cathode; on the other hand, many application scenarios actually don’t require very high energy density.
We work on aqueous electrolyte batteries to achieve both high energy density and superior safety performance. we show how to activate the desired reversible I⁰/I⁺ redox at a potential of 0.99 V vs. SHE by electrolyte tailoring via F^-, Cl^- ions-containing salts. The electronegative F^- and Cl^- ions can stabilize the I⁺ during charging. In an aqueous Zn ion battery based on an optimized ZnCl₂ + KCl electrolyte with abundant Cl^-, I-terminated halogenated Ti₃C₂I₂ MXene cathode delivers two well-defined discharge plateaus at 1.65 V and 1.30 V, superior to all reported aqueous I₂-metal (Zn, Fe, Cu) counterparts. Together with the 108% capacity enhancement, the high voltage output results in a significant 231% energy density enhancement.
In addition, we also develop various approaches to stabilize the Zn anode. We accurately quantifying the hydrogen evolution in Zn metal battery by in-situ battery-gas chromatography-mass analysis. Then, we propose an vapor-solid method for an highly electronically insulating (0.11 mS×cm^-1) but high Zn²⁺ ion conductive (80.2 mS×cm^-1) ZnF₂ solid ion conductor with high Zn²⁺ transfer number (0.65) to isolate Zn metal from liquid electrolyte, which can not only prohibit over 99.2 % parasitic hydrogen evolution reaction during cycling but also guide uniform Zn electrodeposition. Meanwhile, Zn@ZnF₂//Zn@ZnF₂ symmetric cell exhibits excellent stability over 2500 h (over 6250 cycles) with 1 mAh×cm^-2 of Zn reversibly cycled at 5 mA×cm^-2, and stable cycling under ultrahigh current density and areal capacity (10 mA×cm^-2, 10 mAh×cm^-2) over 590 h (285 cycles), which far outperforms all reported Zn metal anode in aqueous system. In light of the superior Zn@ZnF₂ anode, the practical-level aqueous Zn@ZnF₂//MnO₂ batteries (~3.2 mAh×cm^-2) shows remarkable cycling stability over 1000 cycles with 93.63 % capacity retained at ~100 % coulombic efficiency.

Recently, a variety of approaches have been proposed to address the key challenges of Zn anodes for Zn batteries, i.e., Zn dendrites, low reversibility, hydrogen generations and limited cycle life. Fundamentally, the electrolyte and electrode-electrolyte interface play a vital role in the electrochemical performance of Zn anodes. Nevertheless, the principles of stabilizing the Zn anode interface are not well developed so far.

In this talk, we will systematically discuss the fundamental principles of developing high-performance Zn anodes in low-cost dilute aqueous electrolytes with a trace amount of functional polymer additives. The correlation between the reaction kinetics and the stability of Zn anodes and polarity of the polymer additive in dilute 1 M ZnSO₄ aqueous electrolytes was revealed. The polymer additive tailors the electrochemical performance by rearranging the“Zn²⁺-H₂O-SO₄^2--polymer” bonding network and the space charge region of Zn anodes. PAM polymer with moderate polarity exhibits synergic enhancement as the “smoother” and “thruster” for the diffusion of Zn²⁺ towards the Zn anodes, showing uniform Zn deposition with minimal impact on reaction kinetics in both half and full cells. This work significantly provides useful insight on designing low-cost and high-performance aqueous electrolytes through functional electrolyte additives.

Reference:
1. Y. Jin, K.S. Han, Y. Shao, M.L. Sushko, J. Xiao, H. Pan, J. Liu, Advanced Functional Materials 2020, 30, 2003932.
2. M. Yan, H. Ni, H. Pan, Rechargeable Mild Aqueous Zinc Batteries for Grid Storage. Advanced Energy and Sustainability Research 2020, 1, 2000026.
3. M. Yan, C. Xu, Y. Sun, H. Pan, H. Li, Nano Energy 2021, 82, 105739.
4. M. Yan, H. Pan et al., Tailoring the stability and kinetics of Zn anodes through trace organic polymer additives in dilute aqueous electrolytes, under review.

Considering the natural abundance and low cost of sodium resources, sodium ion batteries (SIBs) have received much attention for large scale electrochemical energy storage. However, rational electrode materials design and good mechanistic understanding are required to enable advanced SIBs with high energy density. On the cathode side, P2 type and O3 type layered oxides are promising cathode materials due to their high specific capacity. However, they both suffer from rapid capacity degradation during high-voltage operation, and yet the mechanism remained poorly understood. On the anode side, phosphorus delivers the highest theoretical capacity (ca. 2600 mAh/g) among various anode materials, but undergo huge volume changes during sodiation/de-sodiation and severe capacity degradation. In this work, we will present our mechanistic understanding on the degradation of layered oxide cathodes during high-voltage charge and how intergrowth structure can mitigate these problem. We will also introduce our strategies to stabilize and improve the rate performance of high-capacity phosphorus anode through structure design and Sb doping. We expect our findings could promote the development of high-energy and low-cost SIBs based on layered oxides cathode and phosphorus anode chemistry.

The needed massive deployment of lithium ion batteries (LIBs), in particular to satisfy the demand from the Electric Vehicle (EV) sector, encourage battery manufacturers to multiply the number of giga-factories to reduce the cost of production. Such a production consists of a complex process involving multiple steps, such as the slurry preparation, its coating, drying, calendering, electrolyte infiltration and formation. The choice of the manufacturing parameters along the process strongly impacts the overall LIB cell performance. However, the optimization of the manufacturing parameters to obtain the desired characteristics of LIB cells is currently based on a forward "trial and error" approach. This approach is inefficient in terms of time and cost due to the infinite number of possibilities for adjusting the manufacturing parameters. The integration of digitalization into giga-factories such as Artificial Intelligence (AI) and multiscale modeling is essential to accelerate the manufacturing process optimization and significantly raise the work efficiency of scientists, engineers and production line operators. Here I present our efforts in developing a digital twin of battery manufacturing within the context of the ERC-funded ARTISTIC project [1,2], supported on a combination of physical and AI/machine learning models trained with data arising from in house high throughput characterizations. This digital twin allows simulating the different steps along the manufacturing process, predicting in three dimensions the resulting electrode properties and evaluating the associated electrochemical performance upon battery cell cycling. The predictive capabilities of this digital twin are illustrated with results for different electrode materials (graphite, Silicon/graphite, NMC, LFP) and formulations, paving the way towards manufacturing digital optimization. I also present the online free services that the project is offering, such as a tool for battery manufacturing simulation from an internet browser and a tool for stochastic generation and meshing of lithium ion battery electrodes and separators [3]. Finally, I conclude with our recent work by us (extending our work published in Ref. [4]) on the implementation of our computational models in novel Augmented Reality interfaces to assist the battery manufacturing work.

References
[1] https://www.erc-artistic.eu/
[2] https://www.erc-artistic.eu/scientific-production/publications
[3] https://www.erc-artistic.eu/computational-portal
[4] Franco, A.A., Chotard, J.N., Loup Escande, E., Yin, Y., Zhao, R., Rucci, A., Ngandjong, A.C., Herbulot, S., Beye, B., Ciger, J. and Lelong, R., 2020. Entering the Augmented Era: Immersive and Interactive Virtual Reality for Battery Education and Research. Batteries & Supercaps, 3(11), pp.1147-1164.

A molecular scale insight into ion transport and compatibility with electrodes is important for understanding deficiencies of the currently used aqueous and non-aqueous electrolytes. In this presentation I will summarize recent progress made towards improving molecular scale understanding of the structure and electrochemistry for a wide range of aqueous and non-aqueous electrolytes for lithium and divalent batteries. Accurate molecular dynamics (MD) simulations of these electrolytes using polarizable force field will be used to establish a correlation between the ion transport mechanisms, electrolyte structure and transference number. Reactive modeling will focus on the competitive solvent and salt reduction and oxidation at the passivated electrochemical interfaces using Born Oppenheimer Molecular Dynamics (BOMD) simulations using DFT functionals. These BOMD simulations included critical factors needed to realistically represent electrolyte reactivity at electrodes such as explicit description of the substrate – electrolyte interactions; accurate representation of electrolyte structure, ion pairing and aggregation near an electrode.

Lithium metal polymer (LMP^Ò) solid-state batteries based on the use of dry PEO-based electrolytes have been developed since the early 2000’s by the Bolloré’s group and its subsidiary BlueSolutions company. The reliability of this technology which derives from polymer electrolyte (SPE) membrane Li batteries proposed by M. Armand in the late 70’s[1]^,[2] has been demonstrated in different applications with the first practical deployment in the world in full electric vehicles in 2011. This technology is now widely utilized not only in multiple e-mobility scenarios but also in stationary storage applications all over the world (Europe, North America, Asia and Africa). Like many other electrochemical storage technologies, the search for efficient, cheaper but also earth-abundant insertion electroactive materials remains an ongoing challenge to mitigate environmental issues. In this respect, the potential interest of electroactive organic materials to build eco-friendlier batteries has been the subject of intense research[3]. However, little is known about their behavior when implemented in the LMP^Ò technology. We therefore embarked in the investigation of the electrochemical and physicochemical behaviors of neutral molecule and salt compounds as positive electrode material of LMP^Ò cells.


[1]Armand, M.B.; Chabagno, J.M.; Duclot, M. Second International Meeting on Solid Electrolytes Extended Abstracts; St Andrews, Scotland, 1978.

[2] Armand, M.B.; Chabagno, J.M.; Duclot, M. Fast Ion Transport in Solids; Vashishta, P., Mundy, J.N., Shenoy, J.K., Eds.; North Holland Publishers: Amsterdam, The Netherlands, 1979; p. 131

[3]Poizot, P.; Gaubicher, J.; Renault, S.; Dubois, L.; Liang, Y.; Yao, Y. Chem. Rev. 2020, 120, 6490.

Electrode structures of commercial lithium-ion cells are isotropic at the macro-scale, comprising a homogenous mixture of constituents including active materials, carbon conductive additives, polymetric binders, and randomly distributed inter-connected porosity. Due to restricted ion mobility in the tortuous pore channels and anisotropic electric-field distribution when in operation, the Li-ion concentration and activation overpotential are inevitably inhomogenous through the electrode thickness, especially at fast charge-discharge rates when the concentration and overpotential gradients become steeper. As a result, the electrochemically active material is inhomogeneously utilized and the reaction rate is spatially varying, which have detrimental effects on battery performance and lifetime, local capacity degradation, overheating and stress concentration. This is an electrode-scale problem, regardless of the specific electrode materials.
We design, manufacture and assess the performance of carefully controlled heterogeneous, graded electrode structures with the aim of promoting greater uniformity in overpotential distribution, and reaction rates across the electrode thickness. We investigate the arising polarization, and impedance behavior, as well as side reactions such as SEI formation. We demonstrate that micro-scale composition-graded electrodes provide enhanced capacity retention at fast charge-discharge rates to mitigate the long-lasting challenge of energy-power trade-off of lithium-ion batteries, and reduce battery degradation rate in both half-cell and full-cell lithium-ion batteries.

References
C. Cheng, R. Drummond, S. R. Duncan, and P. S. Grant, J. Power Sources 413, 59 (2019)
C. Cheng, R. Drummond, S. R. Duncan, and P. S. Grant, J. Power Sources 448, 227376 (2020)

Electrical energy storage (EES) devices have staged important technological revolutions in the past years, with special attention given to Li-ion batteries (LIBs). However, novel socioeconomical paradigms¹ have urged for environmentally friendly and sustainable alternatives regarding these technologies. In this context, organic materials have attracted attention as potential candidates to pave the way toward the achievement of truly green batteries. They offer several advantages like cost efficiency, sustainability, synthesis from renewable or feedstock and tunable properties.² Nonetheless, hindrances related to cyclability and energy density need to be solved before the achievement of such alternative technologies. In this study, we report the development of a novel Artificial Intelligence (AI) methodology to accelerate the discovery of organic electroactive materials, with special focus given to LIBs positive electrodes. This framework has rendered an AI-kernel that enabled us to tap into the almost limitless organic library in a fast and accurate fashion. Requiring only the molecular SMILES representation as input, the kernel is divided in three levels, each composed by an independent learning scheme. The first level is based on Graph Neural Networks (GNN) and is responsible to identify if a given molecule is redox stable. The second level predicts the oxidation and reduction potentials (P_Ox and P_Red) of the redox-stable molecules by using a combination of Natural Language Processing (NLP) to analyze the SMILES and Recurrent Neural Networks (RNN). Finally, the third level is composed by a least squares multi-regression model that connects the molecular redox potentials (P_Ox and P_Red) predicted in the previous level to the battery open circuit voltage (OCV) (V vs. Li/Li⁺). To fuel the AI, two different databases have been developed: a small set of predicted molecular crystals following an interplay between DFT and an evolutionary algorithm^3,4; and a larger set of more than 30000 unique molecules with redox properties extracted from DFT. We demonstrate the AI-kernel efficiency by performing a high-throughput screening in 20 million molecules following a capacity (mAh/g) → OCV (V vs Li/Li⁺) selection to find suitable electrode candidates. As the final part of this screening, new DFT calculations were performed for the selected molecules with a two-fold goal: to validate the AI-kernel performance and to further filter the candidates list. This process led to the discovery of about 500 promising molecules for cathode compounds, with some exhibiting theoretical energy densities superior to 2000 Wh/kg. Moreover, the AI-kernel accurately identified common molecular characteristics that lead to such higher-voltage electrodes and pointed out an interesting donor-accepter-like effect that may drive the future design of cathode-active materials.

References:
1 P. T. Brown and K. Caldeira, Nature, 2017, 552, 45–50.
2 S. E. Burkhardt, J. Bois, J. M. Tarascon, R. G. Hennig and H. D. Abruña, Chemistry of Materials, 2013, 25, 132–141.
3 R. P. Carvalho, C. F. N. Marchiori, D. Brandell and C. M. Araujo, ChemSusChem, 2020, 13, 2402–2409.
4 R. P. Carvalho, C. F. N. Marchiori, V.-A. Oltean, S. Renault, T. Willhammar, C. Pay Gómez, C. M. Araujo and D. Brandell, Materials Advances, 2021, 2, 1024–1034.

Potassium-ion batteries (KIBs) are emerging as a promising complementary technology to lithium-ion batteries due to their potential low cost and high rate capability¹.

In my talk, I will discuss the progress we have made in understanding the crystal structure-electrochemistry relationship in Prussian Blue Analogue cathodes², the electro-chemo-mechanical properties of red phosphorous (RP) upon alloying with potassium³ and its application in RP-graphite composite anodes⁴ and, lastly, in identifying and characterising electrolytes and interfaces compatible with both electrodes.

I will then discuss the critical research challenges that need to be addressed for KIBs to become a viable technology.

References
1 S. Dhir, S. Wheeler, I. Capone and M. Pasta, Chem, 2020, 6, 2442–2460.
2 M. Fiore, S. Wheeler, K. Hurlbutt, I. Capone, J. Fawdon, R. Ruffo and M. Pasta, Chemistry of Materials, 2020, 32, 7653–7661.
3 I. Capone and J. Aspinall, Matter, 2020, 1–17.
4 I. Capone, J. Aspinall, H. J. Lee, A. Xiao, J. Ihli and M. Pasta, ChemRxiv, 2020.

Implementation of intermittent renewable energy sources derived from wind and solar power motivates development of safe, sustainable, low cost energy storage devices, specifically batteries based on aqueous electrolytes. As a negative electrode material, Zn has a high theoretical capacity (820 mAh/g), low redox potential (-0.76 V vs. SHE), and low toxicity such that aqueous electrolyte zinc based batteries may prove to be a desirable alternative for Li-ion batteries for some applications. Recent studies on aqueous Zn ion batteries using mildly acidic electrolytes have demonstrated the possibility of zinc anodes with high cycle life. Several classes of cathode materials have been explored as possible candidates including metal-inserted vanadates and manganese oxides.
Vanadium based materials are appealing for aqueous electrochemical energy storage due to the multiple accessible redox states for the vanadium center. Layered vanadates, supported by cation pillars, are of interest for Zn-ion batteries as the vanadium redox center allows for high capacity and the layered structure promotes facile ion transfer. In particular, sodium vanadium oxides (NVO) show promise as cathode materials for Zn-ion aqueous batteries.
Manganese oxides are also of interest due to their low cost and low environmental impact. Manganese oxide structural chemistry is synthetically rich and a number of polymorphs have been considered. Tunnel-type materials such as α-MnO₂ are particularly noteworthy owing to their facile synthesis and high energy density. Despite its appealing electrochemistry, however, the exact reaction mechanism of α-MnO₂ in zinc batteries has remained unclear where zinc insertion, proton insertion, and/or structural changes have been proposed.
Understanding the key parameters that govern the charge storage mechanisms of the Zn aqueous systems remains a critical challenge in order to advance these systems to next generation products. Thus, investigations that probe mechanisms can provide a pathway for ultimately controlling electrochemical outcomes. This presentation will discuss the influence of material properties on the electrochemistry of NVO in Zn-ion aqueous cells and operando studies clarifying the dominant redox mechanism of α-MnO₂ in zinc batteries.

In recent years, rechargeable lithium-oxygen (Li-O₂) batteries have been studied as a future battery system mainly due to their ultrahigh theoretical capacity, low cost, and environmental friendliness. However, the further development of Li-O₂ batteries into commercial applications is hindered by issues such as low energy efficiency, short cycle life, parasitic reactions, and poor rate capability. These issues are mainly the result of the voltage hysteresis and high overpotential in the cathode side. The voltage hysteresis during cycling is large, giving rise to low energy efficiencies and high overpotentials, which in turn, cause significant electrode and electrolyte decomposition. Thus, it is necessary to develop high-performance catalysts for the cathode to address the challenges raised by the overpotential and to boost the performance of Li-O₂ batteries. Three groups of positive-electrode catalysts for Li-O₂ batteries were studied by researchers: carbon materials, noble metal-based materials, and transition metal-based materials.
Considering that the cathodic process is a complicated redox reaction taking place in the triple-phase of gas, liquid, and solid, the structural design of cathode electrodes is critical to achieving high-performance Li-O₂ batteries. Indeed, the catalysts used in cathodes generally have a high surface area to provide transport pathways for oxygen, lithium ions, and electrons and thus increase the reaction sites for the Oxygen reduction reaction (ORR).
Among the transition metal-based materials, Co₃O₄ can reduce the charge overpotential and improve the cycling performance of Li-O₂ batteries. Co₃O₄ crystallizes in the spinel structure (Co^IICo^III₂O₄), with edge-sharing CoO₆ octahedra (Co³⁺ centered) interconnected by corner-sharing CoO₄ tetrahedra (Co²⁺ centered), this structure can accommodate vacancies and lattice defects, that potentially act as active sites to promote electrochemical reactions. Cu/Ni substitution of Co in the structure would ensure a more sustainable material development as well as the improved electrical conductivity of the material to increase the electron supply to reaction sites. Furthermore, using ordered mesoporous Co-based oxides is beneficial due to their high surface area.
In this context, a series of ordered mesoporous Cu/Ni/Co oxides are prepared via nanocasting with varied Cu/Ni ratios to establish their impact on the electrochemical performance of the catalysts. The performance of non-aqueous Li-O₂ batteries is directly determined by the reversible formation mechanism of the discharge products, being either Li₂O₂ or LiOH [1]. Therefore, the nature and evolution of the discharge products, in different voltage steps for the first discharge cycle was investigated by ex situ XRD tests. These tests show the formation of LiOH as a discharge product in presence of mesoporous Cu/Ni/Co oxides in the cathode. A lower overpotential was observed both in ORR and oxygen evolution reaction (OER) with a discharge capacity in the range of 4000-6000 mAh/g_carbon based on different Cu/Ni ratios. During discharge, O₂ reduction was detected along with the LiOH formation with a voltage plateau at 2.8V (≈ 0.1V discharge overpotential). During charge, O₂ evolution was detected along with LiOH decomposition up to 3.55 V, and at higher voltages, products from parasitic reactions can be detected. These results show promising properties of the mesoporous Cu/Ni/Co oxides as catalysts that can effectively promote the OER at a low overpotential. This lower overpotential is a key step in the development of reversible Li-O₂, particularly in LiOH-based Li-O₂ due to the increased stability of LiOH over other discharge products.

[1] Li Z. et al. Understanding the electrochemical formation and decomposition of Li₂O₂ and LiOH with operando X-ray diffraction. Chemistry of Materials. 2017, 29, 1577-1586.

Electron microscopy techniques and their canonical tools are providing an unprecedented opportunity to probe the evolution of structure, chemical composition, and electronic state of the battery-electrode materials and surfaces following their electrochemical activity at the micro and nanoscale. Although other powerful analytical techniques for structural characterization exist, such as X-ray and neutron diffraction, these techniques analyze the bulk material yielding an average crystallographic and spectroscopic information. Electron microscopy allows the direct viewing of individual particles at an ultra-high spatial (e.g. sub-Å) and energy (∼3 meV) resolution. Furthermore, the STEM-based methods enable direct imaging of both heavy and light elements, and simultaneous energy-dispersive X-ray (EDX) and electron energy loss (EEL) spectroscopies. Thus, STEM remains the ideal tool to explore the chemical reactions and their consequences, i.e., structural mechanisms, which occur in the electrode materials during electrochemical activity.

In this contribution, we will provide insights into the atomic-level structure and spectroscopy of potential multivalent cathodes after discharge, which are mostly undetectable during bulk characterization. In particular, structural changes in MgCrMnO₄ after Mg discharge, and CaCo₂O₄ and FePO₄ after Ca discharge are explored by employing atomic-resolution imaging and electron energy loss spectroscopy. All the electron-microscopy studies were performed in an aberration-corrected JEOL JEM-ARM200CF, equipped with a cold field emission gun, operated at 200 kV. Furthermore, battery cathode samples were prepared inside an Ar-filled glovebox to avoid any chance of sample degradation by air exposure. Results show that Mg intercalation into TM spinels results in the formation of a rocksalt surface layer whereas Ca (de)intercalation into layered CaCo₂O₄ develops an amorphous surface layer. On the other hand, Ca intercalation into polyanionic compounds proceeds via a core-shell process. These results guide battery scientists to better select and design the components of the battery to optimize the performance of the system.

Sodium-ion batteries (NIBs) are attractive alternatives to lithium-ion batteries (LIBs) due to the high earth abundance and low cost of Na, the cathodes do not require cobalt, and their device architectures can be similar to those of LIBs, thereby streamlining production. One challenge associated with the development of NIBs is that the cost reduction must make up for the lower energy densities relative to LIBs, and as a result there is a strong drive towards development of alloying anodes for NIBs due to their high storage capacity and favorable redox potentials. Sn nanoparticles appear as an attractive option to increase the capacity of NIB anodes. This is because of a desirable redox potential of around 0.2 V vs. Na⁺/Na combined with a very high theoretical capacity of 847 mAh/g and high rate capability.^1,2 Nanosizing can further help prevent cracking and pulverization of the electrodes arising from volume expansion during alloying. The combination of chemical and mechanical resilience during electrochemical cycling ultimately enhances both the maximum capacity and lifetime of devices employing these materials.
Bottom-up synthesis methods rely on chemical pathways utilizing different precursor materials and chemical reducing agents for the production of nanomaterials. These methods have been successfully employed at the lab scale for the production of nanomaterials with good control over their dimensions, dispersity, morphology, and composition, but are severely lacking in the ability to scale up to industrial levels. Mechanochemistry is a technique that has been widely used on the industrial scale for the production of materials for battery anodes, but almost exclusively via top-down approaches relying on comminution of bulk materials that does not allow for control over the resulting morphology or composition. In this work we demonstrate a new method for the bottom-up mechanochemical synthesis of Sn nanoparticles with controlled dimensions for use in NIBs. The synthesis itself is entirely solid-state, employing only a metal halide precursor and a reducing agent during ball milling, and does not necessitate any capping agents for size control or solvents until the workup of the synthesized materials. The sizes of the particles are controlled by adjusting the milling time, and the influence of particle size on the electrochemical performance was investigated in proof of concept NIBs. The milling time does not have a direct relationship with the particle size because once the particles grow for long enough, they will begin to experience comminution and not continuously grow. The product from the shortest milling time demonstrated capacities of 475 mAh/g at 0.1C alongside the highest current rates in the series, which can be attributed to the fast diffusion of Na⁺ in the nano-sized particles. The samples milled the longest showed the highest capacity of 594 mAh/g at 0.1C. Rate capability studies demonstrated stable CE values close to 100%, indicating high reversibility and structural resilience. Overall these results demonstrate proof of concept for Sn nanoparticles in NIBs synthesized via a new scalable synthesis method based on solid-state bottom-up mechanochemistry.
References:
(1) Palaniselvam, T.; Goktas, M.; Anothumakkool, B.; Sun, Y.; Schmuch, R.; Zhao, L.; Han, B.; Winter, M.; Adelhelm, P. Adv. Funct. Mater. 2019, 29 (18), 1900790.
(2) Palaniselvam, T.; Babu, B.; Moon, H.; Hasa, I.; Santhosha, A. L.; Goktas, M.; Sun, Y.; Zhao, L.; Han, B.; Passerini, S.; Balducci, A.; Adelhelm, P. Batter. Supercaps 2021, 4 (1), 173–182.

The European Strategic Energy Technology Plan established the transformation to climate neutrality by 2050 since energy production is responsible for 75% of the greenhouse gas emission in the EU.¹ For this transformation, the use of renewable energy sources and clean energy carriers should be drastically increased. In parallel, the mobility should implement sustainable and smart technologies in transportation. In this scenario, energy storage devices, especially batteries, are a key technology towards a low-carbon energy system, as large-scale stationary energy storage and electric vehicle applications. Lithium-ion batteries (LIBs) are excellent candidates due to their high energy and high-power density. In fact, LIBs dominate the market for portable electronics and electric vehicles. However, the demand of LIBs is increasing, and the future supply of the raw materials (cobalt and lithium) makes uncertain their feasibility for massive renewables’ energy storage.² Therefore, there is an urgent need to develop alternative energy storage devices that meet the cost, raw material availability and good performance requirements.

In this context, Sodium-ion batteries (SIBs) have been postulated as potential low-cost energy storage devices for large-scale stationary applications and light electromobility due to the almost infinite and widely distributed sodium resources and a 30% cost reduction respect with LIBs.^3,4 In fact, SIBs employing non-aqueous liquid electrolyte are rather close to commercialization.^5,6 Among cathode chemistries, different positive materials have been selected, being the main used one layered oxides while as negative electrode Hard Carbon (HC) is considered the anode of choice.⁷

With regards to large-scale stationary energy storage, sodium-based battery systems appear to be promising even for seasonal/annual storage systems. In particular, Na-seawater batteries, making use of multiple electrolytes, i.e., seawater as the catholyte (as well as the cathode material), a solid electrolyte physically separating the two electrode compartments, and a non-aqueous anolyte, appear very promising.⁸ Because natural seawater is also the active material in the open-structured cathode, the Na seawater battery can be supplied infinitely with Na⁺ cations, which are transferred to the anode side during charging. The generated sodium can be stored inside (for daily/weekly storage) and/or outside (for seasonal/annual storage) the cell. The process can be reversed during discharge, delivering electricity on demand.
As additional benefits, Na-seawater batteries upon charge produce desalinized water (for industrial and residential uses), and chlorine (for bleach, disinfectant, and polymer chemistries) while during discharge generates NaOH, which can be used for CO₂ capture.

References
1) https://setis.ec.europa.eu/implementing-set-plan-2020-report-2020-11-23_en
2) C. Vaalma, D. Buchholz, M. Weil, S. Passerini, Nature Rev. Mat. 3, 18013 (2018).
3) M. A. Muñoz-Márquez, D. Saurel, J.L. Gómez-Cámer, M. Casas-Cabanas, E. Castillo-Martínez, T. Rojo. Adv. Energy Mater. 7, 1700463 (2017).
4) I. Hasa, S. Mariyappan, D. Saurel, P. Adelhelm, A.Y. Koposov, C. Masquelier, L. Croguennec, M. Casas- Cabanas, J. Power Souces 482, 228872 (2021).
5)https://www.greencarreports.com/news/1098434_faradion-electric-bike-prototype-powered-by-sodium-ion-batteries
6) X.H. Rong, Y.X. Lu, X.G. Qi, Q. Zhou, W.H. Kong, K. Tang, L.Q. Chem, Y.-H. Hu, Energy Storage Sci. Techn. 9, 515 (2020).
7) H. Moon, M. Zarrabeitia, E. Frank, O. Böse, M. Enterría, D. Saurel, I. Hasa, S. Passerini, Batteries & Supercaps 4, 960 (2021).
8) Y. Kim et al, Sodium Biphenyl as Anolyte for Sodium–Seawater Batteries, Adv. Funct. Mater. 2001249 (2020)

The state-of the-art rechargeable Lithium-ion batteries (LIBs) use liquid electrolytes and are the major choice for current EVs and portable electronic applications. However, these LIBs still suffer from many issues related to safety, lifespan and energy density. Accordingly, solid-state lithium batteries (SSLBs) have recently emerged as a promising alternative energy storage device due to their ability to overcome the intrinsic disadvantages of liquid-electrolyte LIBs and possess a greater volumetric energy density due to the use of solid-state electrolytes (SSEs). However, the interfacial issues between SSEs and electrodes (both cathode and anode) have a significant impact on the stability and lifetime of SSLBs [1-3]. The origin of these interfacial phenomena is the unstable contact and chemical reactions between electrodes and electrolytes to form an interlayer with extremely low electronic and/or ionic conductivities, which restricts the performance of the SSLBs. An artificial, uniform and ultrathin interfacial layer is critical to address these challenges [2, 3]. Atomic layer deposition (ALD) and molecular layer deposition (MLD) are unique coating techniques that can realize excellent coverage and conformal deposition with precisely controllable at the nanoscale level due to its self-limiting nature, which are ideal for addressing the challenges of interface in SSLBs [2, 3]. In addition, design of SEI in SSLBs is very important for obtaining high performance of SSLBs.
In this talk, we will report to addresses the interfacial challenges in SSLBs via two strategies: (i) develop ALD/MLD to rationally design novel coatings for sulfide-based interface design [4-7]; and (ii) SEI design of solid-state Li-S batteries [8-10]. The goal is to prevent capacity degradation of SSLBs caused by high interfacial resistance and chemical/electrochemical reactions between electrodes and electrolytes.

Lithium (Li) anode has been actively investigated in the battery R&D in order to achieve advanced batteries with higher energy density. Among various studies, Li protection strategies have been a crucial topic of interest since the evolution of a thick solid electrolyte interface (SEI) layer on the reactive lithium metal anode and dendrite growth caused by irregular lithium deposition result in poor cyclic performance and low coulombic efficiency of lithium-metal batteries. In this study, to reduce the undesirable side reactions on the surface of metallic Li anode, Li⁺ conducting polymer coatings have been investigated for the application of a lithium-halide battery. The Li anode protected by a crosslinked PEG-POSS polymer coating demonstrated enhanced specific capacity, rate performance, and cyclability compared to the battery with bare Li anode. In addition, we confirmed that Li deposits with a round shaped-granular morphology are uniformly formed underneath the polymer layer, which indicates that this polymer layer is successfully functioning as a Li⁺ conducting protective layer on the lithium anode. Detailed experimental data and the working mechanism for the performance enhancement will be addressed in the presentation.

Moving beyond Li-ion/intercalation cathode batteries to Li and other alkali metal batteries paired with high capacity metal fluoride conversion cathodes like FeF_x (x = 2 or 3) represents a promising route to high capacity secondary batteries. Fe is considerably more earth abundant and environmentally friendly than elements like Co, and Fe-based conversion cathodes have significantly higher capacities than intercalation cathodes like FePO₄. However, the pairing of a Li metal anode with an FeF_x cathode presents new challenges for battery design. While studies on Li have long emphasized the importance of a protective solid-electrolyte interphase (SEI) on anode performance, recent work has shown that the cathode-electrolyte interphase (CEI) is likewise important to FeF_x cathode performance. Therefore, it is important to find an electrolyte that is compatible with, and creates a protective layer on, both the Li metal anode and the FeF_x cathode.

Here, we present a series of electrolytes optimized for either Li metal or FeF₃ and identify an electrolyte that enables a system-level solution for a Li metal/FeF₃ full cell battery. We show that while an electrolyte with high Li(T)FSI concentration results in high coulombic efficiency (CE) at the Li anode, it produces a poorly performing organic-rich CEI on the FeF₃ surface. Conversely, the FeF₃ cathode shows excellent performance in a pyrrolidinium-based ionic liquid electrolyte, but the Li anode appears to exhibit parasitic side reactions and very poor CE. Bridging the gap between these two results, we will report on our work that demonstrates using an electrolyte that forms an inorganic-rich CEI and a Li2O-rich SEI, stabilizing the cathode and the anode, respectively leads to high overall coulombic efficiencies. Using this electrolyte, we demonstrate a coin cell-scale full cell battery that retains 80% of its post-formation cycle capacity over 50 cycles. Additional characterization including STEM, XPS, and other techniques is also presented. These initial results using well-studied Li metal provide a launching point for the further development of such system-level approaches, as well as the investigation of Na metal as an anode. While more reactive and possessing a lower theoretical capacity than Li, Na is more earth-abundant and its system-level compatibility with conversion cathodes is of great interest.

This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525. The views expressed herein do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

Calcium anodes are attractive for use in beyond lithium-ion batteries due to their high theoretical energy densities (1337 mAh g^-1, 2073 mAh mL^-1), high natural abundance, and reported low propensity for dendrite formation [1, 2]. To achieve high (> 99.9%) coulombic efficiencies (CE), calcium anodes require a robust solid-electrolyte interphase (SEI) that suppresses parasitic reduction of electrolyte components while permitting cationic transport at appreciable rates. While high CEs for long cycling life have not yet been achieved in calcium-based electrolyte systems, the Ca(BH₄)₂-THF system (≤ 99% CE) can serve as a model for identifying surface components responsible for protective and transport functions. Several research groups have explored the native SEIs that form on Ca(BH₄)₂-THF electrodeposits. Wang et al. used X-ray diffraction and chemical digestion (i.e. bulk techniques) to suggest that CaH₂ is the primary surface interphase component [3], while Jie et al. used X-ray photoelectron spectroscopy (i.e. a surface-sensitive technique) to identify CaCO₃ and CaO as interphase constituents [4]. These contrasting experimental results, coupled with reports of significant nonuniformity during plating and stripping of calcium [5, 6], underscore a critical need to clarify the chemical identity of the species in calcium interphases and to spatially map their chemistry and microstructure.

In this contribution, we present detailed characterization of interphases of calcium electrodeposits generated from high concentration Ca(BH₄)₂-THF electrolytes. Central to our work is the use of cryogenic transmission electron microscopy (cryo-TEM), which enables analysis of calcium deposits with the liquid electrolyte vitrified in place, thereby preserving the native interphase generated upon electrodeposition. By applying techniques such as electron energy loss spectroscopy (EELS) mapping, selected-area diffraction (SAD), and high-resolution transmission electron microscopy (HRTEM) imaging to cryogenic samples, we demonstrate that the native interphase is a nanometric calcium oxide with a heterogeneous distribution of secondary phases, including borates. Furthermore, we find that CaH₂ exists as segregates in the bulk calcium deposit rather than at the surface. Further cryo-TEM studies, supplemented with electrochemical measurements, elucidate the protective function of the evolving oxide interphase during open-circuit holds. Finally, we leverage our findings to manipulate the heterogeneity and chemistry of the oxide interphase; by employing mixed solvents and mixed anions, the cationic transport properties are significantly enhanced.

Our results are a critical step towards the design and realization of an ideal solid-electrolyte interphase for high-efficiency rechargeable calcium metal batteries.

This work was performed, in part, at the Center for Integrated Nanotechnologies (CINT), an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. DOE’s National Nuclear Security Administration under contract DE-NA-0003525. The views expressed in the article do not necessarily represent the views of the U.S. DOE or the United States Government.

References:
[1] M. E. Arroyo-de Dompablo et al. Chem. Rev. 2020, 120(14), 6331-6357.
[2] B. Ji et al. Adv. Mater. 2020, 33(2), 2005501.
[3] D. Wang et al. Nat. Mater. 2018, 17(1), 16-20.
[4] Y. Jie et al. Angew. Chem. Int. Ed. 2020, 59(21), 12689-12693.
[5] A. M. Melemed and B. M. Gallant. J. Electrochem. Soc. 2020, 167(14), 140543.
[6] S. D. Pu et al. ACS Energy Letters 2020, 5(7), 2283-2290.

In recent years, tremendous researches have been conducted to achieve high-energy-density lithium (Li)-ion batteries. Among various candidates, cobalt (Co)-free/nickel (Ni)-rich layered cathode materials are considered as one of the promising candidates that can provide practical battery use and cost reduction. However, the Co-free/Ni-rich layered cathode materials have a highly reactive surface that can easily lead to inevitable contaminations in air by forming residual Li compounds such as LiOH and Li₂CO₃ which cause capacity decay and poor cell performance. Here, we demonstrate the effectiveness of a thin polyimide/polyvinyl pyrrolidone (PI/PVP, as referred to as PP) layer to protect LiNi_0.96Mg_0.02Ti_0.02O₂ (NMT) cathode particles under storage in an atmosphere with ~30% humidity for two weeks. Compared to the fresh bare NMT, the stored bare NMT shows visible contaminated surface, Li consumption and decreased lattice O due to exposure to limited moisture and CO₂ in the air. On the other hand, the PP coated NMT (PP@NMT) has practically the same surface and structure before and after exposure to air. In the cycling performance test using a conventional LiPF₆/carbonate electrolyte at the current density of C/3 (1C = 1.5 mA cm^–2) under 25 °C, the graphite (Gr)-based Li-ion battery of Gr||NMT system with stored bare NMT shows a continuous capacity decay, resulting in the capacity retention of merely 49.5% after 100 cycles, while the Gr||NMT cell with stored PP@NMT has the capacity retention of 84.7% after 100 cycles. In addition, after cycling, not only the stored bare NMT cathode material has more cracks inside the particle with NiF byproducts and structural degradation than stored PP@NMT but also the Gr anode pared with stored bare NMT has more generation of byproducts on the surface than Gr anode pared with PP@NMT. Furthermore, an advanced localized high-concentration electrolyte can enable the cell with stored PP@NMT cathode to achieve capacity retention of 89% over 400 cycles at 25 °C. This work offers a promising facile approach to protection of Co-free/Ni-rich layered cathodes for practical applications.

I will start by giving an overview of our work on assembly and functionalization strategies of nanocellulose aimed at specific properties, with an eye toward high impact applications including energy, electronics, building materials. Examples include transparent nanopaper for optoelectronics (as a replacement of plastics), super strong and tough wood (replacement of steel, Nature 2018), and radiative cooling wood (Science, 2019). I will then focus on our work on applying nanocellulose/wood as building blocks for advanced energy devices, including flexible, thick battery electrodes with nanocellulose binder, three-dimensional carbon derived from wood for advanced batteries (replacement of metal current collectors for beyond Li-ion batteries), and all solid-state Li metal batteries using nanocellulose ion conductors (Nature, 2021).

Lithium ion batteries are ubiquitous in our society with uses extending from personal electronics to EVs and stationary storage. However, due to the environmental and ethical issues of raw materials (i.e., lithium, high purity graphite and cobalt) and increasing demands for lower cost and high safety, emerging battery technologies such as those based on sodium chemistries are becoming more attractive. Sodium metal provides the opportunity for higher energy density devices while the possibility of carbonising waste biomass to produce hard carbons for Na ion batteries offers a more sustainable energy solution. Ionic liquid electrolytes have been investigated for over two decades as a safe alternative to traditional organic solvents, in particular for higher energy density, metal anodes. IL electrolytes based on fluorosulfonimide (FSI) anions have particularly favourable properties with respect to enhanced ion transport, high sodium salt solubility and the stable SEI formation. Even within this family of IL electrolytes, the salt concentration, IL cation chemistry and molecular additives have a dramatic effect on the electrochemical performance of both Na metal and carbon anodes. Using solid state NMR, SEM and XPS, we show that this is related to the SEI composition on the anode surface. The effect of anode pre-conditioning on cycling stability is also discussed. MD simulations provide some insights into the influence of chemistry and preconditioning on stability. Finally, we also demonstrate significant stability enhancement at high rate and high capacity cycling of Na metal when a phosphonium IL cation is present in contrast to the pyrrolidinium IL cation.

Hexacyanometallates have gained great attention due to their interesting properties originating from their flexibility in synthetic methods, allowing a large degree of chemical tunability. Hexacyanometallates can be prepared by bottom-up assembly of molecular precursors via the formation of continuous chemical bonding between transition metal ions and ligand molecules. These cyanide ligands can enable the long-range charge transport with abundant CN triple bonds that can provide free electrons for electrical conduction. Due to such flexibility in their design and resultant properties, they can have a wide variety of applications including energy storage, harvesting, catalysis, and magnetic applications. In this talk, I will introduce diverse applications of hexacyanometallates for electrode, coating, and redox mediator materials. First, a new Cr-based negolyte coordinated with strong-field ligands will be introduced. The complex of [Cr(CN)₆]⁴⁻ prefers low-spin states, facilitating a stable and fast redox reaction, capable of mitigating strong Jahn–Teller effects, thereby facilitating low redox potential, high stability, and rapid kinetics. The prototype full-cell configuration features a high-energy density of 11.4 Wh L⁻¹ and a stable lifetime of 250 cycles. Second, manganese hexacyanometallates (MnHCMn) shows a monoclinic crystal structure composed of nonlinear Mn–N≡C–Mn bonds and containing eight large interstitial sites occupied by Na⁺ ions. The experiments demonstrate a high specific capacity of 210 mAh g^-1 and excellent capacity retention at high rates. Here, we discover a novel mechanism wherein small lattice distortions allow for the unprecedented storage of 50% more sodium cations than in the undistorted case. These results represent a step forward in the development of high-performance redox flow and sodium-ion batteries.

Rechargeable sodium and potassium metal batteries are considered to be important to various energy applications in modern society. The pursuit of higher energy density should ideally come with high safety, a goal difficult for electrolytes based on organic solvents. Room temperature ionic liquids have been widely explored as promising candidates due to their non-flammable nature¹. Among them, ionic liquids comprised of AlCl₃ and 1-ethyl-3-methylimidazolium chloride are a classical chloroaluminate based electrolyte system with many desired properties including non-flammability, non-volatility, low viscosity, high conductivity, and high thermal stability and chemical inertness². However, it remains challenging to realize ideal battery performances on the basis of chloroaluminate ionic liquids, due to the severe corrosion of chloroaluminate based compounds to alkali metal.

Here we report chloroaluminate ionic liquid electrolytes comprised of aluminium chloride/1-methyl-3-ethylimidazolium chloride/sodium chloride ionic liquid spiked with important additives, e.g., ethylaluminum dichloride and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide. This leads to the first chloroaluminate ionic liquid electrolyte for rechargeable sodium metal battery³. The obtained batteries reached voltages up to ~ 4 V, high Coulombic efficiency (up to 99.9%), and high energy and power density of ~ 420 Wh kg^-1 and ~ 1766 W kg^-1, respectively. More than 90% of the original capacity can be retained after 700 cycles. In addition, stable and high-energy-density potassium metal batteries were obtained on the basis of chloroaluminate ionic liquid electrolyte⁴, which could stably work at high temperature up to 60 °C. These results provide a new approach to advanced alkali metal batteries with high energy/high power densities, long cycle life and high safety⁵.

References
1. Yang, Q. et al. Ionic liquids and derived materials for lithium and sodium batteries. Chem. Soc. Rev. 2018, 47, 2020–2064.
2. Pickup, P. G. & Osteryoung, R. A. Charging and discharging rate studies of polypyrrole films in AlCl₃: 1-methyl-(3-ethyl)-imidazolium chloride molten salts and in CH₃CN. J . Electroanal. Chem. Interfacial Electrochem. 1985, 195, 271–288.
3. Sun, H., Zhu, G., Xu, X., Liao M., Li, Y., Angell, M., Gu, M., Zhu, Y., Hung, W., Li, J., Kuang, Y., Meng, Y., Lin, M., Peng, H., Dai, H. A safe and non-flammable sodium metal battery based on an ionic liquid electrolyte. Nat. Commun. 2019, 10, 3302.
4. Sun, H., Liang, P., Zhu, G., Hung, W., Li, Y., Tai, H., Huang, C., Li, J., Meng, Y., Angell. M., Wang, C., Dai, H. A high-performance potassium metal battery using safe ionic liquid electrolyte. PNAS. 2020, 117, 27847–27853.
5. Sun, H., Zhu, G., Zhu, Y., Lin, M., Chen, H., Li, Y. Hung, W., Zhou, B., Wang, X., Bai, Y., Gu, M., Huang, C., Tai, H., Xu, X., Angell. M., Shyue, J., Dai, H. High safety and high energy density lithium metal batteries in a novel ionic liquid electrolyte. Adv. Mater. 2020, 2001741.

The oxygen redox is expected to offer a new route to attain an unprecedentedly high energy density for lithium-rich layered oxides, thus regarded as an alternative cathode chemistry beyond the high-nickel layered materials. However, the complexity from the dynamic changes in the structure, e.g. cation migrations/disorders and local oxygen bond alternations, and the corresponding redox activity change prohibits the full understanding of this class of materials, making it difficult to achieve the highly reversible oxygen redox. Herein, we present a consistent theoretical framework for the triptych of structural disorder, subsequent oxygen bonding rearrangement and redox chemistry, encompassing a wide range of layered oxides both in Charge-Transfer and Mott-Hubbard systems. It is unraveled that cation disorders stabilize oxygen redox by promoting strong oxygen-oxygen and/or metal-oxygen π hybridization, which hinges on the occupancy of oxygen non-bonding states and metal-oxygen covalency. On the other hand, anion disorders compensate for the electron deficiency of oxygen network without significantly regulating bonding arrangements. More importantly, we address how the formation of short covalent bonds affects electrochemical and structural reversibility, and report oxygen dimers that freely move in the structure as a key catalyst of the poor structural resilience. Our findings rationalize long-reported phenomenological correlations between structural disorders and oxygen redox, and offer a fundamental basis for optimizing the reversibility of oxygen redox taking into account of inevitable formation of structural disorders.

Because of its high reversible capacity, environmentally favorable characteristic, and cheap cost, nickel-rich ternary layered oxide LiNi0.8Co0.1Mn0.1O2 (NCM811) is regarded as one of the most promising cathode materials for next-generation lithium-ion batteries. However, this type of cathode material has low thermal stability, a phase change during the charge-discharge process, and a safety concern, all of which limit its applicability. On the other hand, the electrochemical characteristics of NCM811 have improved considerably due to increased research and development of manufacturing processes. In this work, the progress of carbon growth on the nickel-rich layered oxide NCM811 cathode material has been prepared and performed as a positive electrode for Li-ion batteries. Compared to the pristine NCM811, the capacity retention of the NCM811-carbon grown cathodes improved to 85.0% after 100 cycles at 1C under elevated temperature. In addition, the initial coulombic efficiency and cycle stability of the NCM811-carbon grown materials were enhanced as a result of this structure-reconstructed layer's capacity to inhibit side reactions at the interface and stabilize the bulk structure over cycles.

As the demand for healthcare increases, various types of wearable devices have been developed for monitoring physiological information and biomarkers. Among these, smart contact lenses are attracting attention due to their huge applications ranging from health monitoring to digital entertainment. Inserting batteries inside contact lenses is still a challenge due to the need for miniaturization and the high safety requirements of placing batteries in the ocular system. Conventional batteries are not suitable to contact lenses because it can cause serious damage to the eyes if they break due to the release of toxic substances. We introduced a safe aqueous battery that utilizes tears as an electrolyte and supplies electric power to a microprocessor. Prussian blue analogues (PBAs), known as biocompatible host materials for Na- or K- ions, have been used as cathode and anode materials for electrochemical cell operation in the tears solution containing low concentrations of ions. The ultraviolet (UV) polymerized hydrogel was utilized as an ion-permeable separator as well as soft contact lens with embedding the electrodes which consist of carbon nanotubes and PBA. The battery embedded in the contact lens showed a discharge capacity of 155 µAh at potentials between 0.2 V and 0.9 V in an artificial tears solution. Bending tests and cytotoxicity tests while charging and discharging the battery were conducted to verify the mechanical stability and biocompatibility of the battery, respectively. For practical application, stable charge and discharge cycles of the battery in commercial contact lens cleaning solutions have demonstrated. The battery can supply high enough power to operate the low-power static random access memory. It could supply electric power to smart contact lenses without worrying about damage to eyes due to leakage of harmful substances from mechanical failure of the battery.
Acknowledgment
The content of this abstract has been published in J. Yun et al., Nano Lett., Vol 21, page 1659–1665.

Two-dimensional (2D) layered materials have been an important part of rechargeable battery research and development. Graphite and inorganic layered compounds such as transition metal dichalcogenides found application in low-capacity Li-ion batteries as electrode components. On the other hand, the commercialization of high-capacity rechargeable batteries such as metal-air batteries for electric vehicles is hampered by poor kinetics of oxygen redox chemistry. In order to efficiently harvest the energy density of metal-air batteries (theoretical specific energy of Li-O₂ is 13 kWh/kg [1]), a bifunctional catalyst is needed to catalyze oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Here, we propose to use an organic 2D-layered coordination polymer of transition metals (Ni, Fe, Cu) as a precursor of a highly efficient bifunctional catalyst [2, 3].
In this presentation, we will introduce our work on Ni(II) dithiooxamide (dto) coordination polymer and discuss OER and ORR electrochemistry in alkaline solutions on a nanocomposite derived from Ni(dto). Ni(dto) forms a coordination polymer with a layered structure composed of sheets of four Ni(II) atoms in planar configuration with five dto ligands. The interlayer distance is 3.6 Å [4]. Electrochemical cycling of Ni(dto), dispersed in a carbon matrix, in the potential range of 0.4 to 1.6 V vs. RHE, resulted in the formation of g-NiOOH which was found active towards OER and ORR in 1 M KOH solutions. The nanocomposite showed an enhanced ORR activity with the onset potential of 0.78 V and the half-wave potential of 0.72 V vs. RHE in O₂-saturated 1 M KOH solutions. The overpotential, h, for OER on NiOOH/C was 390 mV at I =12 mA/cm² [5]. At the same current density, the h_OER for Fe-doped NiOOH was 308 mV. Fe doping was found to improve OER kinetics. In this presentation, we will discuss the effect of Fe doping on OER and ORR performance with the help of in-situ Raman spectroscopy.


References:

[1] M. A. Rahman, X. Wang and C. Wen, J. Electrochem.Soc.,160, A1759 (2013).
[2] R.P. Putra, H. Horino, I.I. Rzeznicka, Catalysts, 10, 233 (2020).
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[5] R. P. Putra, I. Rachman, H. Horino and I. Rzeznicka, Catal. Today, under review (2021).

Water-in-Salt Electrolyte (WiSE) which is highly concentrated aqueous solution is a promising electrolyte for energy storage devices such as battery and supercapacitor. WiSE shows three surprising features; a) very stable SEI formation during the first few charging/discharging cycles; b) more than 3 V electrochemical stability window; c) fast ion transfer in a highly viscous solution. Despite such superior electrochemical properties, however, there exist no research suggesting a theoretical boundary between dilute solution and WiSE. In this research, we propose a new approach to understand WiSE based on an eutectic mixture. Although potassium acetate (KOAc) WiSE is an aqueous solution, liquid state was observed at sub-zero temperature. As salt is added in water, the number of strongly bound water molecules to a point charge is increased in the solution. This non-freezing water renders aqueous solution difficult to crystalize. Eventually the freezing temperature (T_f) of the aqueous solution dropped to below -60 ^oC near the critical point. After the lowest or critical point is reached, T_f increases again. Therefore, we suggest that before the critical point, the solution is sufficiently dilute where colligative properties are observed, and after the critical point, the solution is called WiSE. Finally, we demonstrated the sub-zero operation of WiSE based supercapacitor. The capacitance of a symmetric cell using activated carbon electrodes is measured approximately 50 F/g at -20 ^oC.

An initial crystalline phase transforms into another phases as cations are electrochemically inserted into its lattice. Precise identification of phase evolution at an atomic level during transformation is thus the very first step to comprehensively understand the cation insertion behavior. By using atomic-column-resolved scanning transmission electron microscopy, we directly visualize the simultaneous intercalation of both H₂O and Zn during discharge of Zn into V₂O₅ with an aqueous electrolyte. In particular, when further Zn insertion proceeds, multiple intermediate phases, which are not identified by a macroscopic powder diffraction method, are clearly imaged, showing structurally topotactic correlation between the phases. These findings suggest that smooth multiphase evolution with a low transition barrier is significantly related to the high reversible capacity of oxide cathodes for aqueous rechargeable cells.

Sodium (Na) ion battery (NIB) is an attractive alternative solution for stational energy storage and electrical vehicles because of its low cost and abundant availability. Although rapid progress has been made on electrode materials, the stable electrolyte that is compatible with both cathode and anode is still limited, which hinders large-scale application of NIBs. Here, we report a low flammable electrolyte for highly reversible and high voltage sodium ion batteries. The high capacity retention (>80% for 300 cycles) and high columbic efficiency can be achieved for high voltage (4.2 V) full cells because of the stable interphases on both cathode and anode sides. These interphase layers can minimize undesirable reactions between the electrode and the electrolyte, and block the dissolution of transition metals from cathode. The interphase analysis, including XPS, TEM and EIS, has been used to identify the correlation between electrochemical performance and electrolyte properties. The insights obtained in this work can be used to guide the further development of stable electrolyte to enable safe and long cycle life of rechargeable batteries.

Electrolytes play a crucial role in lithium-ion batteries (LIBs) by strongly affecting longevity and safety. Lithium hexafluorophosphate (LiPF₆) salt in carbonate-based solvents has been widely used as an electrolyte in commercial LIBs for over three decades. However, its insufficient thermal stability limits the cycle-life of LIBs. Studies have shown that the PF₆^– decomposition at elevated temperature is initiated by the reaction: LiPF₆ → LiF + PF₅. Nevertheless, the underlying process that triggers thermal decomposition of PF₆^– at elevated temperatures is still unknown and impedes our ability to design optimal electrolytes. We report that the presence of urea (2 wt %) suppresses the decomposition reaction in 1 M LiPF₆ dissolved in propylene carbonate (PC) at elevated temperatures. A combined study of nuclear magnetic resonance (NMR) and ab initio molecular dynamics (AIMD) simulations elucidate the structure and dynamic properties of the LiPF₆/PC electrolytes in the absence and presence of urea additive, which are correlated with the stability of the electrolyte at elevated temperatures. Spin-lattice (T₁) relaxation time measurement and pulsed-field gradient (PFG) NMR reveal that (i) rotational motion of PF₆^- and PC changes from small-angle libration to reorientation with elevated temperatures, and (ii) the hopping motion of Li⁺ at elevated temperature (≥ 80 °C) seen in the electrolyte is suppressed when urea additive is present. The latter is inferred due to preferential solvation with urea leading to capture of Li⁺ within a solvation cage. To attain atomic understanding of the observations, we performed AIMD simulations at room temperature and 100 °C with and without urea. AIMD simulation at 100 °C reveals an elongated P-F bond and a shortened Li⁺-F when PF₆ binds to Li⁺ which are not seen at room temperature, which may prompt the PF₆^– decomposition. In the presence of urea, a shorter Li⁺- O_urea bond length is observed relative to Li⁺-F_PF6 and Li⁺-O_PC bond lengths, indicating a stronger interaction of urea with Li⁺ than PF₆ and PC. Based on these observations, we infer that thermally activated dynamics of PF₆^– accelerate the first decomposition reaction to form LiF and PF₅. In this presentation, we will discuss the correlation between macroscopic thermal stability and molecular level ion/solvent dynamics of the LiPF₆-based carbonate electrolytes.

Molten sodium batteries offer a promising technology for grid scale energy storage. Typical molten sodium battery chemistries such as Na-S and Na-NiCl₂ (ZEBRA) require temperatures near 300 and 200 °C, respectively, to operate. Driving operating temperatures down to near 100 °C would decrease operating costs, minimize materials aging effects, and minimize system-level materials costs through use of polymeric seals, thinner wires, and less insulation. To enable battery operation at such low temperatures, we have developed a suite of redox-active molten salt catholytes based on metal halide-sodium iodide chemistries that melt at <100 °C. While each metal halide-sodium iodide system provides a unique phase stability, conductivity, and redox potential, they all share the same underlying I^-/I₃^- redox used to store energy in the molten sodium battery. Nevertheless, each system shows distinct electrochemical performance. We couple idealized electrochemical measurements in a three-electrode cell with electrochemical modeling to better understand the electrochemical reactions and chemical equilibrium present during the deceptively simple oxidation of iodide. This modeling effort provides insights as to the factors which limit electrochemical performance, enabling targeted improvements to catholyte composition that significantly improve overall electrochemical kinetics. Leveraging this understanding, we identify cost-competitive metal halide-sodium iodide catholyte compositions for use in a molten sodium battery.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Lithium metals for anode of secondary batteries are drawing great attentions due to high theoretical capacity, high potential, and low density for next-generation high-energy storage systems. However, dendritic growth of lithium (Li) metal during repetitive charge and discharge cycles can cause severe problems such as low lifespan and risks of explosions raised from short circuits. In this study, we synthesized highly porous aramid nanofiber film (PANF) separators by sequential solvent-substitution methods to suppress Li dendritic growth. Porosities and pore sizes of PANF were controlled by self-assembly processes of aramid nanofibers during solvent-substitutions. Highly porous nanostructures enabled to improve wettability to electrolytes and ionic conductivities for PANF. Symmetric cell tests showed stable cycle operations up to 3000 cycles at currunt density of 50 mA/cm² with cycling capacity of 1 mAh/cm² , that could be attributed to effective suppressions of Li dendrite formations. For the full cell tests with LiFePO₄ (LFP) cathodes, PANF samples showed higher capacity than commercialized separator samples from 1 C to 30 C rates. The PANF separators are expected to one of most promising candidates for advanced separators for the Li metal batteries.

In the past decades, Zn-ion batteries witness massive success in the primary battery sector. However, Li-ion battery technology emerged with a simple operating principle and became ubiquitous. The escalating concerns over the safety of non-aqueous Li-ion electrochemistry and the use of expensive Co and Ni transition metal redox centers brought the attention back to the aqueous rechargeable Zn-ion batteries. Now, Zn-ion batteries are a frontline contender for large and gride storage applications. These are gained significant consideration with high safety, eco-friendliness, economical and easy fabrication of devices. Zn-MnO₂ is a magic composition and successfully investigated for primary battery application. Here, we tried to shed light on the uncertain intercalation mechanism of rechargeable Zn-Mn chemistry. We studied the electrochemical activity of cryptomelane with high potassium doping, the specific composition of K_1.33Mn₈O₁₆ as a cathode for Zn-ion batteries. The phase-pure end product was synthesized by employing the ultrasonic sonochemical method. Rietveld refinement (GSAS, EXPGUI interface) confirmed the occurrence of the I4/m (#87) space group. The electrochemical properties were examined using ZnSO₄ based electrolyte in a potential window of 1.0 to 1.8V. It delivered a high capacity of 312 mA h g^-1 at the current rate of C/10 and exhibited robust cycling stability over 650 cycles (retaining 80% capacity of the initial cycle). We used different cell configurations to understand the role of H⁺ and K-ions in the Zn-ion (de)intercalation. The detailed mechanistic studies were demonstrated using electrochemical and spectroscopy tools (K. Sada, B. Senthilkumar, P. Barpanda, J. Mater. Chem. A, 2019, 7, 23981-23988).

High-voltage spinel LiMn_1.5Ni_0.5O₄ (LMNO) is an attractive cobalt-free cathode material which can deliver high energy density (650 W h kg^-1) due to its high operating voltage ^~4.7 V (vs Li⁺/Li) arising from the Ni²⁺/Ni⁴⁺couple.¹ The spinel framework offers a 3D diffusion channel for Li⁺, leading to high ionic conductivity. Another unique characteristic of the material arises from the potential to tune performance through harnessing cation disorder.² Introducing cation disorder during synthesis inevitably brings additional complexity (e.g. oxygen vacancies), making it challenging to rationalise the most significant factors towards designing LMNO with optimum electrochemical performance.^3–5

In this study we used quantum chemistry techniques^6,7 to predict the defect landscapes of LMNO under various synthesis conditions. Analysis of the formation energy of all intrinsic defects in the ordered phase P4₃32 LMNO using the supercell approach, can provide logical explanations for experimental observations and reveal insights on the charge compensation mechanisms and changes to local cation-ordering associated with those defects, which cannot be obtained easily through experiments and characterisations.

References
[1] G. Liang, V. K. Peterson, K. W. See, Z. Guo and W. K. Pang, J. Mater. Chem. A, 2020, 8, 15373–15398.
[2] J. H. Kim, S. T. Myung, C. S. Yoon, S. G. Kang and Y. K. Sun, Chem. Mater., 2004, 16, 906–914.
[3] B. Aktekin, M. Valvo, R. I. Smith, M. H. Sørby, F. Lodi Marzano, W. Zipprich, D. Brandell, K. Edström and W. R. Brant, ACS Appl. Energy Mater., 2019, 2, 3323–3335.
[4] Y. Chen, Y. Sun and X. Huang, Comput. Mater. Sci., 2016, 115, 109–116.
[5] B. Aktekin, F. Massel, M. Ahmadi, M. Valvo, M. Hahlin, W. Zipprich, F. Marzano, L. Duda, R. Younesi, K. Edström and D. Brandell, ACS Appl. Energy Mater., 2020, 3, 6001–6013.
[6] C. Freysoldt, B. Grabowski, T. Hickel, J. Neugebauer, G. Kresse, A. Janotti and C. G. Van de Walle, Rev. Mod. Phys., 2014, 86, 253–305.
[7] S. Kim, S. N. Hood, J. S. Park, L. D. Whalley and A. Walsh, J. Phys.: Energy, 2020, 2, 036001.

The magnesium ion secondary battery (MIB) has attracted much attention because magnesium (Mg) metal has high theoretical capacity (3,755 mAh/cm³), high electrochemical stability, and high abundance in the earth. However, developing anode and cathode materials with superior capacity for conventional electrolytes has required considerable study. Bismuth (Bi) has high capacity as an anode and also resists oxidation in Mg-containing electrolyte, so is a promising candidate material. However, experimental studies suggest that the available capacity has not yet reached the theoretical limit, and that the cycle life is short. This is due to sluggish diffusion of Mg²⁺ into the anode material and the slow interfacial charge transfer. We aimed to improve the electrochemical properties by atomizing the internal and surface structure of the Bi anode and enhancing the diffusion of Mg²⁺. In this study, we prepared Bi films by an electrodeposition method, in which the structure of the Bi electrodes could be controlled by changing electrodeposition conditions. We also evaluated the electrochemical properties of Bi anode materials deposited with different deposition times and current densities, to elucidate the relationships between the structure of the Bi anode and its capacity and cycle life.
We prepared an electrolytic bath by dissolving H₂SO₄, Na₂SO₄ and polyethylene glycol in pure water, and subsequently added H₂SO₄ to the electrolytic bath to control the pH at 1.2. Before electrodeposition, we removed organic species and native oxide from the Cu foil surface with NaOH and HCl. We employed a Cu plate with an exposed foil area of 2 × 2 cm² and a carbon plate as the cathode and anode, respectively. The Bi electrodeposition was carried out, while changing the deposition time and current density (from 10 to 50 mA/cm²). The film thickness was controlled by the deposition time (from 1.5 to 3.0 μm), and was calculated based on the weight increase under the assumption that the film was uniform. The surface morphology and crystal structure of the Bi films were evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. In addition, the characteristics were compared before and after discharge/charge. The cycle characteristics of the Bi anodes were studied in PhMgCl/THF electrolyte. The bipolar half-cells were assembled with Mg plate as the anode and Bi electrode as the cathode. We established representative galvanostatic charge/discharge profiles of the Bi electrodes, at a current density of 50 mA/g within 0–0.6 V, versus Mg²⁺/Mg. We evaluated the cyclic stability of the Bi electrodes under the same conditions until the 50^th cycle. The elemental composition and chemical bonding state of the Bi films after charge/discharge were evaluated by energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS).
The cycling performance of Bi films with thicknesses of 1.5, 2.0, and 3.0 μm until the 50^th cycle. Each film showed a capacity of about 300 mAh/g at the early stage of cycling, which is the maximum capacity. The capacities were about 1.5 times those of the Bi anodes which Niu et al. prepared by powder metallurgy. The cycle performance differed among Bi films differing in thickness, and the 1.5-µm Bi film maintained the maximum capacity until the 25th cycle. Thus, film thickness had an impact on the cycle performance. The surface morphology of Bi films with different thicknesses before and after the charge/discharge reaction shows agglomerates involving a large number of particles with increasing film thickness, which consists of particles from 1 to 3 µm. after charging/discharging, and also consists of Mg dendrites with thicknesses of 2 and 3 µm. The localized formation of Mg dendrites on the Bi surface could explain the decreased cycle performance of the Bi films prepared in this study.

Metal-air batteries happen to be more viable and sustainable energy storage systems due to high safety, low cost and less environmental repercussions. Li-air battery despite of having the highest theoretical energy density lags behind Zn-air battery in terms of resource availability and operation safety. Also, the electrode potential of such metals like Li, Na, Al is very negative, thus making them more susceptible to anodic corrosion in aqueous environment by evolution of hydrogen, further compromising the safety of the battery. Zinc being the most promising candidate for metal-air batteries is extensively being studied to improve the short-comings of by-product saturation and precipitation, dendritic growth during Zn plating and hydrogen evolution. In this work, conductive substrate modified with carbon nanotube is deposited with zinc to be utilized for the improvement of life-cycle and durablity of the anode for zinc-air battery. To construct a flexible rechargeable battery, CNT can provide larger surface area for Zn deposition and improves its performance by allowing better flow of electrolyte as well as prohibits the dendritic growth by anchoring strongly. On the other hand, multi-principal 2-D metal chalcogenides have been used a bifunctional oxygen electrocatalyst for the cathode of ZAB giving maximum charge-discharge cyclic stability and constant discharge voltage (close to 1.65 V). These high-entropy materials comprising of quasi-equimolar quinary or higher principal metals, provide numerous combinations of surface structure and therefore, adsorption sites and electronic environments. The tunable properties influence the catalytic behavior through charge transfer, adsorption, etc. The high-entropy metal sulfides, as in this study, stabilized by configurational entropy are ideal to explore the structure-property relationship.

Covalent organic frameworks (COFs) are potentially promising electrode materials for electrochemical charge storage applications thanks to their pre-designable reticular chemistry with atomic precision, allowing precise control of pore size, redox-active functional moieties, and stable covalent frameworks. However, studies on the mechanistic and practical aspects of their zinc-ion storage behavior are still limited. In this study, we report a strategy to enhance the electrochemical performance of COF cathodes in zinc-ion batteries (ZIBs) by introducing the quinone group into 1,4,5,8,9,12-hexaazatriphenylene-based COFs. Electrochemical characterization demonstrates that the introduction of the quinone groups in COF significantly pushes up Zn²⁺ storage capability against H⁺ and elevates the average (dis-)charge potential in aqueous ZIBs. The computational and experimental analysis further reveals the favorable redox-active sites that host Zn²⁺/H⁺ in COF electrodes and the root cause for the enhanced electrochemical performance. This work demonstrates that molecular engineering of COF structure is an effective approach to achieve practical charge storage performance.

Anode-free metal batteries feature appealing advantage in boosting the energy density, however, demanding extraordinary Coulombic efficiency (> 99.7%). Although Zn-based metal batteries are promising for stationary storage and micropower systems, the parasitic side reactions make the anode-free devices are hardly achievable. In this work, a salting-in effect induced hybrid electrolyte is proposed as an effective strategy that enables both high reversibility of Zn anode and good compatibility with various cathodes. It is demonstrated that in the presence of propylene carbonate, triflate anions are involved in the Zn²⁺ solvation sheath structure, even at a low salt concentration (2.14 M). The unique solvation structure results in the reduction of anions, thus forming a hydrophobic solid electrolyte interphase. The waterproof interphase along with the decreased water content in the hybrid electrolyte efficiently prohibit side reactions and dendrite growth, thus ensuring stable Zn anode with an unprecedented Coulombic efficiency (99.93% over 500 cycles at 1 mA cm^-2). More importantly, we design an anode-free Zn metal battery, which exhibits excellent cycling stability (80% capacity retention after 275 cycles at 0.5 mA cm^-2). This work provides an efficient strategy to design hybrid electrolytes for aqueous anode-free Zn metal batteries.

Carbon-containing materials are a promising alternative to develop novel technologies applicable in supercapacitors and energy storage devices. Among these materials, Carbon Fibers (CF) are base electrodes of wide use in electrochemical cells mainly because of their good flexibility and high mechanical resistance. Carbon nanotubes (CNT) films have high electrical conductivity, high resistance to acid electrolytes, and high specific surface area. This work aims to develop CNT/CF electrodes and study the electrochemical behavior of both separated materials, CF and CNT, and in the composite. A viscose fabric pyrolysis produced the CF, using a temperature ramp-up to 850 °C at a 5 °C/min heating rate. The CNT was deposited over two different substrates: the CF and silica fabric. The latter was used to evaluate only the contribution of the CNT since the silica fiber presents no electrochemical response. Thermal Assisted Chemical Vapor Deposition (TA-CVD) at atmospheric pressure was the CNT film growth technique. The precursors for floating catalyst growth were the mixture of 84% camphor and 16% ferrocene, in which 12.5 g was dissolved in 50 mL of n-hexane. It was evaporated while inserted dropwise in a chamber at a temperature of 220 °C. An argon gas flow (200 sccm) carried this vapor into the reactor at 850 °C. The process lasted for 15 minutes, promoting the CNT growth. To increase the CNT samples' hydrophilicity, we performed a surface activation process using steam and CO₂ simultaneously. The electrochemical behavior of the CF, CNT, and CNT/CF samples was measured using a three-electrode cell setup with an Ag/AgCl saturated reference electrode and a platinum grid counter electrode. The electrolyte was an aqueous sulfuric acid solution of 1.0 M. Electrochemical characterization of the samples involved electrochemical impedance spectroscopy (EIS) technique, cyclic voltammetry (CV), and galvanostatic charge and discharge (GCD) routines. In addition, the samples were morphologically and structurally characterized by scanning electron microscopy (SEM), and Raman spectroscopy, respectively. The results got by electrochemical measurements showed a distinct behavior for the samples. The FC acts as a double-layer electrochemical capacitor (EDLC) while CNT exhibited typical Faradaic behavior. The CNT/FC composite showed an intermediate behavior between EDLC and battery, characterized as a supercapacitor. Electrochemical purification to remove electrochemically available iron residues shows that the Faradaic behavior was because of these residues. The combination of FC and CNT properties provides a composite with high specific capacitance (150F/g) and high conductivity and presents a prospective application as supercapacitors and energy storage devices.

Magnesium secondary batteries have been regarded as promising candidates for large-scale storage systems with high safety, high energy density, and low production costs. Magnesium batteries profit from the use of a metal anode due to the dendrite-free deposition of magnesium ions. In addition to the challenge of finding suitable liquid or solid-state electrolytes, the hunt for viable cathode materials is a key success factor for battery fabrication. Copper sulfide can be reversible converted into magnesium sulfide and delivers high capacity (560 mAh g^-1). Interestingly, the charged and discharged products (CuS/Cu₂S and Cu) are electrically conductive, which is profitable for the positive electrode. Copper (0.01 %) and sulfur (0.05 %) as well as magnesium (2.4 %) are highly earth-abundant and are therefore sustainable raw materials.
Conventional battery cell production makes use of common current collectors like Al and Cu foil, which is on the one hand side non-active material and on the other side not feasible because of undesirable side reactions with sulfur and the electrolyte. This makes the battery heavier and less efficient.
Therefore, we designed electrospun cathode material of copper sulfide and carbon nanofibers with flexible network architecture and promising properties as the positive electrode for magnesium batteries. These copper sulfide loaded fibers have been analyzed using XPS, SEM, and Raman spectroscopy.
The advantages of the composite material are large surface area, high porosity, large liquid permeability, and good electrical conductivity, making these prepared fibers ideal candidates for application as electrode material in Mg-based secondary batteries for large-scalable, sustainable, and low-cost energy storage devices.

An efficient, scalable method to produce high quality hybrid nanocomposites remains an unmet challenge, limiting the applications of hybrid materials for batteries, biosensors, supercapacitors, drug delivery agents, and electro-catalysis. Herein, we report a facile single-step method facilitated by a protein mediated for the preparation of MoS₂/graphene hybrid (MoS₂/Gr) nanoplatelets, achieving as high as 10 mg mL^-1 concentrations of MoS₂ nanosheets. The hybrid was characterized by various biophysical methods including Raman spectroscopy, powder X-ray diffraction, UV-Visible spectroscopy, electron microscopy and energy-dispersive X-ray spectroscopy, establishing the presence of both exfoliated MoS₂ and graphene as a hybrid. The nanocomposites showed functional electrocatalytic activity and stability toward the hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction. A Zn-air battery constructed with this hybrid material exhibited an excellent cathode with a high open circuit voltage of 1.126 V. The battery characteristics of the hybrid were superior to those made from either MoS₂ nanosheets or Gr nanosheets or a mixture of unexfoliated MoS₂ and graphite. Thus, hybridization of a highly conducting nanosheet with that of a catalytic nanosheet showed particular advantages of the hybrid and the entire process was facilitated by protein-based exfoliation by simply stirring on the benchtop.

Energy storage technologies play a crucial role in the endeavor of solving the climate change, intermittency of renewable sources and air pollution puzzle. These sustainable energy storage devices demand new materials for energy storage systems, which alleviate their cost and increase longevity ^[1]. Lithium-ion batteries (LIBs) have emerged as the most well-known and efficient rechargeable electrochemical energy storage devices, and thus forms the biggest share in today’s electrical vehicles and portable consumer electronic markets. Sodium (SIBs)-and Potassium (KIBs)- ion batteries are next to the lithium-ion batteries towards the commercialization, from the viewpoint of both cost and raw material abundance in comparison with the existing LIBs ^[2,3]. Whilst hard carbon remains as the primary choice of anode for post-lithium battery application due to its stable cycling performance and structural integrity over few hundreds to thousands of cycles. Nevertheless, it suffers from lower energy density, inferior rate performances, serious risk of alkali metal plating under high current discharge. On the other hand, where alloy anodes are promising due to their larger uptake of alkali-ions in comparison with their intercalation-type counterparts. In this line, antimony- based anode materials are appealing for alkali-ion battery applications due to their high theoretical capacity and lower insertion voltage ^[4,5].
In this work, we have fabricated Sb/ hard carbon composites as anodes for alkali-ion (Li⁺, Na⁺ and K⁺) batteries ^[6]. We have utilized simple, practical, and scalable high-energy ball-milling approach to prepare these Sb/hard carbon composites and explored its electrochemical performances methodically. The structural and morphological studies reveal that Sb nanoparticles are embedded into carbon matrix, which provide mechanical buffer and conductive network to alleviate particle detachment and agglomeration to improve alkali-ion insertion kinetics. Amongst all the composites, the anode with 50:50 ratio showed an optimal sodium-ion storage performance in terms of capacity, rate capability and excellent cycle life up to 800 cycles compared to other composite anodes. Remarkably, the optimized HS5050 also provides higher capacities of 572 and 380 mAh g^-1 in lithium and potassium cells, respectively with impressive cycle life. From these studies, it was observed that the energy storage behaviors are different for diverse alkali-ion systems and the overall synergistic effect has a significant influence on their electrochemical charge storage process. The detailed insights and such coherent approach to develop such antimony-based anodes in sustainable rechargeable batteries will be discussed thoroughly.

References:
[1] D. Larcher, J.M. Tarascon, Towards greener and more sustainable batteries for electrical energy storage, Nat. Chem. 7 (2015) 19–29.
[2] M. Walter, M. V. Kovalenko, K. V. Kravchyk, Challenges and benefits of post-lithium-ion batteries, New J. Chem. 44 (2020) 1677–1683.
[3] T. Hosaka, K. Kubota, A.S. Hameed, S. Komaba, Research Development on K-Ion Batteries, Chem. Rev. 120 (2020) 6358–6466.
[4] M.Á. Muñoz-Márquez, D. Saurel, J.L. Gómez-Cámer, M. Casas-Cabanas, E. Castillo-Martínez, T. Rojo, Na-Ion Batteries for Large Scale Applications: A Review on Anode Materials and Solid Electrolyte Interphase Formation, Adv. Energy Mater. 7 (2017) 1700463.
[5] H. Tan, D. Chen, X. Rui, Y. Yu, Peering into Alloy Anodes for Sodium-Ion Batteries: Current Trends, Challenges, and Opportunities, Adv. Funct. Mater. 29 (2019) 1808745.
[6] V. Ahuja, B. Senthilkumar, P. Senguttuvan, Mater. Res. Bull. (2021) Under submission

Olivine NaFePO₄ is a promising cathode material for Na-ion batteries, but aspects of the phase diagram for Na_xFePO₄ (0<x<1) remain poorly understood. Reports using x-ray diffraction have found the NaFePO₄ phase diagram to be quite distinct from LiFePO₄ with both a solid solution forming at x>2/3 and an intermediate ordered phase at x=2/3. The larger differential in unit cell size for Na_xFePO₄ with x=1 and x=0 compared to LiFePO₄ is thought to allow for more structural relaxation in the sodium material. In this work, the phase diagram of Na_xFePO₄ is investigated for x=0, x=2/3, and x=1 using neutron powder diffraction. We find new insight into the lattice volume expansion as a function of temperature for the intermediate phase. Our measurements extend to higher temperatures than previously reported and the reversibility of high-temperature structural transformations are examined.

The development of feasible, scalable, and environmentally safe electrode materials that provide stable cycling performance is critical for the success of beyond lithium-ion batteries. With respect to the sodium- and potassium-ion battery anodes fabricated using transition metal monochalcogenides such as germanium and tin sulfides and tellurides show poor cycle stability and fast capacity degradation, due to low electronic conductivity and dissolution of chemical species in the electrolyte. Herein we report chemical functionalization of monochalcogenide nanosheets with polymer-derived silicon oxycarbide (SiOC) with the aim to preserve the electrodes from dissolution in the organic electrolyte, without compromising its role in charge/discharge processes. The high performances of electrodes are attributed to the high electric conductivity and structural stability of the SiOC fibers with unique structure, which not only buffers the volume change of monochalcogenides with the internal space but also acts as high-efficient transport pathways for ions and electrons Our results suggest that monochalcogenides–SiOC composite electrode are effective in bringing improved cycle stability over neat monochalcogenides.

Gallium has always been an intriguing metal, especially because of its low melting temperature (30°C). This melting temperature can even be lower when alloying Gallium with elements such as Indium and Tin. The Ga₈₆In₁₄, Ga₉₂Sn₈ and Ga₇₇In₁₅Sn₈ alloys have melting temperatures of 16 °C, 25 °C and 11 °C, respectively. These alloys are extensively studied to design stretchable and self-healing electronic circuits.¹ In the recent years, they have been also studied in the field of Li-ion batteries as self-healing electrode materials with prolonged cycle-life.² Indeed, after delithiation, the liquid alloys recover their initial shape due to the transition from the solid lithiated phases back to the pure liquid delithiated phase. However, as they are being tested in Li-ion batteries, almost no study has been performed for their use in beyond Li-based technologies such as Na-ion batteries.

In this presentation, our results on using Gallium, Ga₈₆In₁₄, Ga₉₂Sn₈ and Ga₇₇In₁₅Sn₈ as electrodes in Na-ion batteries will be presented.³ The electrochemical reactions of these compounds with Na were carefully studied. Electrochemical measurements were coupled with ex-situ PXRD and SEM analyses to have a complete overview of the involved reactions, their potentials, their capacities and the self-healing properties of the alloys. Finally, the possible applications of these liquid alloys in Na-ion batteries will be discussed.

References
1. Tang, S.-Y., Tabor, C., Kalantar-Zadeh, K. & Dickey, M. D. Gallium Liquid Metal: The Devil’s Elixir. Annu. Rev. Mater. Res. 51 (2021).
2. Guo, X., Zhang, L., Ding, Y., Goodenough, J. B. & Yu, G. Room-temperature liquid metal and alloy systems for energy storage applications. Energy Environ. Sci. 12 (2019).
3. Le Ruyet, R., Mohimont, F., Naylor A. & Younesi, R. Gallium-based liquid alloys as electrodes for Na-ion batteries. In preparation.

The growing energy demand met by fossil fuels for decades, leading to pollution and global warming. Therefore, the shift to clean and renewable energy sources is a must to achieve carbon neutrality. However, the alternating nature of wind and solar energy necessitates the development of energy storage technologies for frequency balancing and grid stability. Batteries are thought to be the optimal solution. Among all types of batteries, all-vanadium redox flow batteries (VRFBs) have independent modularity of energy and power ratings, flexible design, and provide large-scale energy storage at a reasonable cost. However, the energy efficiency of VRFBs is still not satisfactory for widespread applications.
Commercial VRFBs use graphitized carbon-based electrodes due to their high chemical and electrochemical stability and conductivity. However, their electrochemical activity towards vanadium ions is poor. For improved electrochemical activity, the thermal treatment and its role in introducing the necessary surface functional groups and the increase of the electrode wettability were thoroughly investigated. However, to further reduce polarization losses, interest in carbon nanostructures, such as graphene¹, reduced graphene oxide², carbon nanotubes³, carbon nanowalls⁴, carbon nanofibers⁵, and carbon nanoplatelets⁶, is growing owing to their excellent conductivity, stability, and large surface area.
The fullerene family has not yet been explored in the VRFBs application. Fullerenes have a very unique cage-like structure with high surface area and conductivity, which would allow fast electron transfer. The electronic cloud surrounding the fullerene molecule could also enhance the adsorption of ions onto its surface. In this work, we, therefore, report, for the first time, the electrochemical activity of fullerene C₇₆ towards VO²⁺/VO₂⁺ redox reaction in G1 and G3 VRFBs. C₇₆ showed superior electrocatalytic activity in both versions of VRFBs, as evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), while also inhibited the chlorine evolution in G3 VRFB when compared to thermally treated carbon cloth (TCC) electrode. It is noteworthy to point out that treatment is, thus, unnecessary and undesirable in G3 VRFBs.⁷

References
1 Z. González, C. Flox, C. Blanco, M. Granda, J. R. Morante, R. Menéndez and R. Santamaría, J. Power Sources, 2017, 338, 155–162.
2 M. Jing, C. Zhang, X. Qi, Y. Yang, J. Liu, X. Fan, C. Yan, and D. Fang, Int. J. Hydrogen Energy, 2020, 45, 916–923.
3 G. Wei, C. Jia, J. Liu, and C. Yan, J. Power Sources, 2012, 220, 185–192.
4 Z. González, S. Vizireanu, G. Dinescu, C. Blanco and R. Santamaría, Nano Energy, 2012, 1, 833–839.
5 G. Wei, X. Fan, J. Liu, and C. Yan, J. Power Sources, 2014, 270, 634–645.
6 P. Han, H. Wang, Z. Liu, X. Chen, W. Ma, J. Yao, Y. Zhu, and G. Cui, Carbon N. Y., 2011, 49, 693–700.
7 F. A. El Diwany, B. A. Ali, E. N. El Sawy and N. K. Allam, Chem. Commun., 2020, 56, 7569–7572.

The penetration of clean and renewable wind and solar energies is expected to reach up to 75% of the total electrical energy by 2050. However, the electrical grid becomes unstable when the power from renewable energy sources exceeds 20% of the total generated power. Developing efficient energy storage systems is crucial for such a transition since they are required to store surplus electricity and balance supply and demand. Among all energy storage systems, vanadium redox flow batteries (VRFBs) are thought to be an optimal solution for long-term energy storage (~30 years) due to the decoupling of power and energy densities, fast response, and long cycle life, and low annualized cost.¹ However, their relatively high system capital cost, primarily due to the cell stack needs to be reduced. Increasing the kinetics of both half-cell reactions can reduce the size of the stack and, consequently, the cost. Even though carbon-based electrodes have good chemical and electrochemical stability and good conductivity, with no treatment they suffer from sluggish kinetics due to the lack of oxygen functional groups and hydrophilicity.^2,3 Therefore, different electrocatalysts were incorporated with the carbon-based electrodes, specifically carbon nanostructures^4,5 and metal oxides^6,7, to enhance the kinetics at both electrodes to increase the kinetics at the VRFB electrodes.
Herein, novel hydrated tungsten oxide (HWO) nanoparticles were synthesized via facile hydrothermal methods and deposited on carbon cloth electrodes for both half-cell reactions. The superior electrocatalytic activity was observed for the V²⁺/V³⁺ reaction, in addition to suppressed HER. As for the VO²⁺/VO₂⁺ reaction, the incorporation of C₇₆ was necessary to enhance the conductivity and kinetics, while the HWO inhibited chlorine evolution. Experiments were also done in the mixed acid electrolyte (H₂SO₄/HCl) to imitate the 3^rd Generation (G3) VRFB for more practicality and to study the effect of HWO on the chlorine evolution parasitic reaction.

References
1 2020 Grid Energy Storage Technology Cost and Performance Assessment | Department of Energy, https://www.energy.gov/energy-storage-grand-challenge/downloads/2020-grid-energy-storage-technology-cost-and-performance, (accessed 22 June 2021).
2 Y. Gao, H. Wang, Q. Ma, A. Wu, W. Zhang, C. Zhang, Z. Chen, X. X. Zeng, X. Wu and Y. Wu, Carbon N. Y., 2019, 148, 9–15.
3 R. Wang and Y. Li, J. Power Sources, 2019, 421, 139–146.
4 Z. González, C. Flox, C. Blanco, M. Granda, J. R. Morante, R. Menéndez and R. Santamaría, J. Power Sources, 2017, 338, 155–162.
5 D. O. Opar, R. Nankya, J. Lee and H. Jung, Electrochim. Acta, 2020, 330, 135276.
6 M. G. Hosseini, S. Mousavihashemi, S. Murcia-López, C. Flox, T. Andreu and J. R. Morante, Carbon N. Y., 2018, 136, 444–453.
7 M. Faraji, R. Khalilzadeh Soltanahmadi, S. Seyfi, B. Mostafavi Bavani, and H. Mohammadzadeh Aydisheh, J. Solid State Electrochem., 2020, 24, 2315–2324.

Sodium ion-based devices have been intensively investigated as a promising alternative to lithium-ion devices for large scale energy storage due to their similar electrochemical properties and sodium low-cost thanks to its abundance resources. However, many challenges remain sodium ion devices to become commercially competitive as lithium-ion devices. One of them concerns the ionic size of sodium, larger than that of lithium, resulting in slower electrochemical kinetics and significant restrictions in the intercalation process reducing performance and device lifetime. Despite these drawbacks, extensive efforts are focused on the rational design of nanostructured and novel electrodes to improve the Na⁺ transport kinetics. Niobium pentoxide is promising as it presents electrochemical stability and rapid ion transport throughout the a–b plane, suitable for a wide array of electrochemical energy applications. This work reports the preparation of a flexible and freestanding film of multiwalled carbon nanotube decorated with Nb₂O₅ nanoparticles through vacuum filtration and investigate the effect of Nb₂O₅ as sodium-ion symmetric supercapacitor (SIC) and anode battery (SIB). In both cases, the results show a peseudocapacitance contribution. In a SIB half-cell configuration, the electrode delivers a reversible sodium-ion storage capacity of ~ 163 mA h g^-1 at 25 mA g^-1 and present a retention of capacity of ~ 68 mA h g^-1 after 100 cycles at 25 mA g^-1. The SIC full cell shows a long cycling stability after 10,000 cycles and delivers a high energy density of 64.11 W h kg^-1 with a power density of 74.98 W kg^-1. Even with a power density of 14,766 W kg^-1, it delivers a high energy density of 55 W h kg^-1.

Sodium ion batteries have attracted attention because sodium is an abundant metal in the Earth's crust, which facilitates its obtaining and processing and, consequently, offers sustainability and low cost. Although sodium-ion batteries have a similar function to lithium-ion batteries, due to the greater atomic radius of sodium, they have poor diffusion and restrictions of the intercalation process in the interstices of the electrode. To address these deficiencies, Sn a promising anode candidate to construct viable, stable, and low-cost sodium-ion batteries for energy storage systems because it alloys high theoretical capacities, high conductivity and safe reaction potential. In this work, we related a Sn-based anode material by synthesizing a composite of Sn nanoparticles on nitrogen-doped carbon nanofibers via electrospinning technique for sodium ion batteries. The composite shows a high reversible capacity of ~1100 mA g^-1 at 25 mA g^-1. Even with a current density of 1 A g^-1, the material delivers a capacity of ~120 mA g^-1. Results show a long cycling stability within 0 to 2.5 V potential window.

Si-Li batteries are promising in many ways, e.g. they have high theoretical specific capacity (4200 mAh/g). However, the volume expansion upon lithiation may lead to high internal strain/stresses and fracture phenomena. We associate this phenomenon to the fact that an electrochemical insertion of Li leads to multi-phase particles with significant changes in specific volumes of phases. We introduce a thermodynamic formulation of the phase transformation including the role of charged lattice point defects, the internal stress/strain field, and the deviation from perfect stoichiometry of the compounds.

From our ab initio calculations, we obtain: the formation energies (Ef) of Si-Li compounds; the Ef of defects (both charged and neutral vacancies/interstitials) in pure and lithiated Si; the dielectric constants (needed for charged defect); and the elastic constants of Si and several compounds. The DFT calculations are performed with PBE and HSE06 functionals. The hybrid functional HSE06 allows us to reproduce the semi-conductor nature of the solid solution Si(Li) and the Li-poor compounds, by providing a closer-to-reality band gap and therefore, permitting us to investigate realistic properties of the charged point defects. From the formation energies of the Si-Li compounds, the neutral and charged defects in Si and its lithiated compounds, the phonon frequencies and the elastic constants, we compute the free Gibbs energies of the particle with respect to the composition, temperature, and the particle size. The increment of the Gibbs free energy with the number of Li yields the open circuit voltage (OCV).

Our results are in good agreement with measured OCV at high temperature (415°C), with respect to the off-stoichiometric composition of the stable compounds [1]. From the investigation of the metastable Si-Li phases that are only formed under electrochemical insertion of Li, we simulate the charging-discharging OCV cycles.

References:
[1] C.J. Wen and R.A. Huggins, Journal of Solid State Chemistry 37, 271 (1981).

New electrolytes with enhanced anodic stability have enabled electrochemical synthesis of anion-intercalated graphite (or p-doped graphite) compounds at voltages > 4.5 V vs Li⁺/Li. The p-doped GICs form the basis of an emerging battery concept called dual-ion battery (DIB) in which both cations and anions from the electrolyte participate in the energy storage process. With the current state-of-the-art electrolytes and electrode materials, DIBs have been demonstrated to offer specific energy densities close to 200 Wh kg^-1, and are potentially attractive for stationary applicaitons. In this contribution, we will explore the design of hybrid DIB cells based on composite electrodes consisting of high voltage positive active materials such as LNMO and natural graphite, which doubles as a conductive additive and an anion intercalation host. Since it contributes ( ~100-120 mAh g^-1) to the overall capacity, natural graphite can be used in much higher proportions without affecting the specific capacity of the composite electrode, while enhancing the rate capability by virtue of its metallic conductivity. The ratios of both active materials are varied to achieve optimal combinations.
Similar to ordinary DIBs, this battery concept is, however, affected by challenges associated with instability of electrolytes within the high operating voltage required for anion intercalation (typically ranging from 4.5 to 5.2 V Li⁺/Li), corrosion of Al current collector and graphite exfoliation. Highly concentrated-salt electrolytes and ionic liquids are often used as they have wider kinetic stability windows than conventional battery electrolytes. These limitations give rise poor coulombic efficiency (typically < 90 %), aggravated self-discharge and poor capacity retention over extended cycles. Efforts are geared towards understanding and mitigating the parsitic reactions by creating stable cathode-electrolyte interface (CEI) layer and generating passivated Al current collectors with the help of various electrolyte additives (salt additives and co-solvents). Using a range of surface and bulk characterizations tools, and operando gas pressure measurements we strive to understand the nature and resilience of the CEI layer forming at different states-of-charge in such electrodes. In addition, works on the design of new current collectors with improved anodic stability will be introduced.

In the large-scale storage of renewable energy, sustainability and cost-effectiveness are of utmost importance. Lithium-ion batteries (LIBs) are a common energy storage technology for portable electronics and electric vehicles. However, reserves of lithium are limited and therefore, the increasing use of LIBs on larger scales could result in a significantly higher price in future. Next to lithium, sodium is the smallest and lightest alkali metal and therefore, sodium-ion batteries (SIBs) are a potential alternative technology to LIBs. Sodium is the 6^th most abundant element in the Earth’s crust and is widely available, which positively influences the sustainability of SIBs.
Conventional liquid electrolytes for SIBs consist of a sodium salt dissolved in (an) organic solvent(s). However, the latter cause a safety hazard because of their high flammability. At temperatures of 55 °C or higher, the solubility of the solid electrolyte interphase (SEI) components derived from such electrolytes is higher than at ambient temperature. This can have a negative influence on the electrochemical performance. Ionic liquids can be used as alternatives for organic solvents. They consist entirely out of ions, are liquid in a wide temperature range, are non-flammable, and offer a high electrochemical stability. They have a high conductivity and can also dissolve high amounts of salt. However, their main drawback is their high cost.
Deep eutectic solvents (DESs) are mixtures of Lewis/Brönsted acids and bases. The melting point of a DES is below that of the individual components. Their use as electrolyte in batteries may offer substantial benefits over conventional electrolytes and ionic liquids. They can significantly improve safety because they have a low vapor pressure and can be non-flammable, and they can be cost-effective. Thus far, DESs have not yet been reported as electrolytes for SIBs. In LIBs, however, a DES (LiTFSI dissolved in N-methyl acetamide (NMA)) allowed stable electrochemical cycling of full cells, even at 60 °C.¹ The low solubility of sodium salts (compared to lithium salts) and sodium’s milder Lewis acidity imply that it is more difficult to create a DES based on a sodium salt than a similar DES based on a lithium salt. In the example described above, changing LiTFSI to NaTFSI might not lead to the formation of a DES at all, or will at least have a large impact on the physico- and electrochemical properties.
In this presentation, we will report non-flammable DESs, based on the dissolution of NaTFSI in NMA, that can be used as electrolyte in SIBs. Increasing the NaTFSI concentration increased the DESs’ reductive and oxidative stability. First-principles modelling revealed that the increased anodic stability was related to the strong ionic interactions between NMA molecules and TFSI^- with Na⁺. The hydrogen bonds between individual NMA molecules are progressively disrupted with increasing NaTFSI concentration. When cycled at 55 °C, (Na₃V₂(PO₄)₂F₃)/(Na_2+xTi₄O₉/C) full cells showed an improved electrochemical stability when a DES was used in comparison to when a conventional electrolyte was used, with 74.8% capacity retention after 1000 cycles at 1 C and 97.0% capacity retention after 250 cycles at 0.2 C. This shows that DESs can be viable electrolytes for SIBs, as they can offer a high durability and safety.
The authors acknowledge the Research Foundation Flanders (FWO Vlaanderen) for financial support under the project number G053519N. This work is further supported by Hasselt University and Research Foundation Flanders via the Hercules project AUHL/15/2 - GOH3816N). The computational resources and services used in this work were provided by the VSC (Flemish Supercomputer Center), funded by Research Foundation Flanders and the Flemish Government – department EWI.
(1) Boisset, A. et al. Phys. Chem. Chem. Phys. 2013, 15, 20054–20063.

The demand for generating clean and sustainable sources of energy has lead to a huge leap in the research of efficient, high-performance electrochemical systems for energy storage and harvesting. In terms of resource availability, manufacturing expense and safety, Na ion batteries (SIBs) are now evolving as contenders for the highly successful Lithium ion battery (LIB) technology.
Layered oxide materials are promising candidates for cathode systems, because of their high capacities arising from fast ionic conduction. However, there still exist pitfalls of irreversible structural transition during electrochemical cycles, the most prominent one being the gliding of (MO₂)_n layers, O3 to P3 phase or P2 to O2 phase, which eventually leads to degradation and capacity loss.
The Na_xMO₂ (M=3d transition metal) class of compounds, with 3d transition elements have been extensively researched on as cathodes. The 4d transition series is relatively newer, and sodium (de)-intercalation has been proved to occur in Nb, Mo and Rh systems ^[1,2]. As reported by Delmas et al^[3], NaRhO₂ can be synthesised in O3 and P2 type structures with Na ions occupying octahedral and trigonal prismatic sites respectively. It is interesting to note that these systems preserve the O3 type stacking upto a high temperature (300°C).
Thus, a nearly reversible (de)-intercalation of Na in the 0.33 < x < 1 composition range, makes it a superior cathodic system.
In this work, we have theoretically studied the electrochemistry in O3 and P2 type NaRhO₂, using Density Functional Theory for detailed insights into the electronic structures of the intermediates Na_xRhO_2. We have also delineated the Minimum Energy Pathways for Na diffusion with low activation barriers of ~210meV and compared it with previously reported Na_xMO₂ systems.
In addition to this, we have employed a Cluster Expansion (CE) technique followed by Grand Canonical Monte Carlo (GCMC) simulations, to reproduce the trends in the voltage profiles of O3 and P2 systems, as a function of composition x. The computed voltage profile from MC simulations corroborate well with the experimental observation ^[3], with voltage steps at ~x=0.3 and x=0.5. This cumulative approach involving First Principles theory and stochastic simulations provides a clear understanding of the (de)-intercalation mechanism, from the associated Na/vacancy orderings within the voltage window of 2.4V to 4.2V.

References :
1. Chang, S. O.; Park, H.-H.; Maazaz, A.; Delmas, C. Sur l′Obtention des Oxydes Lamellaires LiNbO2 et NaNbO2 par Voie Chimique et Electrochimique. Preparationpar Desintercalationdes Solutions Solides Correspondantes. C.R. Acad.Sc.Paris, SerieII (1989), 308, 475−478.
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