Symposium EN03—Intercalation Energy Storage Materials and Systems for Beyond Li-Ion Batteries

Electronic and automotive industries are strategic towards economic development owing to their substantial participation in the gross domestic product of several countries. Currently, these industries converge on the pursuit of higher energy density batteries for their products, for instance, wearable electronic devices and electric cars. Furthermore, beyond lithium-ion battery systems are also gaining traction given the uncertainty of lithium supply in the future. As a consequence, in order to develop high-performance monovalent-ion batteries further understanding of intercalation process of monovalent ions – such as Li⁺, Na⁺ and K⁺ – in layered materials is desirable, because this process is the stepping-stone towards novel battery technologies. Belonging to transition metal dichalcogenides (TMD) family, tantalum disulfide (TaS₂) is a layered polymorph with superconducting behavior that, unlike several TMD, presents metallic conductivity in its 2H phase. In addition, the interlayer spacing of TaS₂ – approximately 6% larger than TiS₂ – makes it a promising host material for intercalation of alkali metal ions with radii larger than Li⁺. Here we report 2H-TaS₂ as electrode material for lithium- (LIB), sodium- (SIB), and potassium-ion (PIB) batteries in a comprehensive electrochemical study to unveil aspects such as charge storage mechanism, ionic diffusion coefficient calculation, and impedance information obtained in the frequency domain analysis in half-cell configuration. Results indicate that first cycle charge specific capacity of LIB is 344 mAh g^-1. Moreover, long term cycling reveals reasonable stability with capacity decay of 0.23% per cycle within 40 cycles as PIB at 50 mA g^-1. To summarize, this work intends to shed light on the understanding of charge storage mechanism of 2H-TaS₂, and ultimately contribute towards the development of high-performance electrode materials for monovalent-ion batteries.

One of the most important obstacles that make supercapacitors an inappropriate option to replace batteries at this time is self-discharge. Energy loss in supercapacitors is significant, especially when the charging time is short. Reducing the charge redistribution, by enlarging electrodes porosity is a possible solution to minimize the self-discharge. More focus has been given in this work to study the effect of sodium dodecyl benzene sulfonate (SDBS) on the spontaneous voltage drop in electric double-layer capacitors (EDLCs). Different concentrations of SDBS were added to change the porosity of PEDOT:PSS-based electrodes. The lowest voltage drop (ΔV) (-11.3%) was achieved in the PEDOT:PSS-based electrode with 2.0 wt% of SDBS. Also, the experimental results showed that increasing the concentration of SDBS more than 2.0 wt% leads to a reduction in the slope of the self-discharge curve and voltage drop directly. The samples with a high percentage of SDBS showed a sharp initial voltage drop due to high leakage current and high internal resistance. At the high scan rate of 200 mV/s, the highest measured specific capacitance of 11.4 F/g was reached in the electrode with 2.0 wt% of SDBS. Results indicated that the porosity structure of the electrode has an important role in decreasing the self-discharge in EDLCs by reducing the spontaneous voltage drop.

DFT simulations of Na, and K on different carbon motifs (defective graphene basal planes, planar graphitic layers, cylindrical pores, and combinations of these) found in hard carbon anode materials were conducted to investigate their effect on the metal intercalation. We show that both oxygen-, and nitrogen-containing defects are energetically favorable to form on these carbon motifs (in agreement with experimental characterization),^3–5 both at the basal plane, in the graphitic stacks, and on strained edge sites. Assessing the effect of these defects on Na, and K interaction with the carbon structure, we found that these defects improve the initial sodiation and potassiation steps, but that the strong interaction between the metals and the defects can limit their diffusion, leading to irreversible capacity loss. To elucidate the effect of the same defects on divalent ion battery metals (Ca, Mg, and Zn) we expanded our study to also include these. Ca was shown to have the highest affinity towards these anode models, whereas neither Mg or Zn could not be shown to favorably adsorb. Intercalation in expanded graphitic pores showed that the narrow graphitic stacks with interlayer distance of < 3.4 Å for Na, and < 3.8 Å for K is inaccessible for intercalation. Graphitic stacks with interlayer distance < 6 Å were found to be important for metal storage, whereas wider planar pores and cylindrical pores are beneficial for Na and K diffusion. ² These simulations further showed that both these pore shapes and sizes are instrumental in the electrochemical performance of these anodes and need to be considered in computational modelling.

Acknowledgment
The financial support from EPSRC (Engineering and Physical Sciences Council) under the grant number EP/M027066/1, and EP/R021554/2, is acknowledged.


References
¹ A.C.S. Jensen, E. Olsson, H. Au, H. Alptekin, Z. Yang, S. Cottrell, K. Yokoyama, Q. Cai, M.-M. Titirici, and A.J. Drew, J. Mater. Chem. A 8, 743 (2020).
² E. Olsson, J. Cottom, H. Au, Z. Guo, A.C.S. Jensen, H. Alptekin, A.J. Drew, M.-M. Titirici, and Q. Cai, Adv. Funct. Mater. 30, 1908209 (2020).
³ H. Alptekin, H. Au, A.C. Jensen, E. Olsson, M. Goktas, T.F. Headen, P. Adelhelm, Q. Cai, A.J. Drew, M.-M. Titirici, and A.C. Jensen, ACS Appl. Energy Mater. acsaem.0c01614 (2020).
⁴ H. Au, H. Alptekin, A.C.S. Jensen, E. Olsson, C.A. O’keefe, T. Smith, M. Crespo-Ribadeneyra, T.F. Headen, C.P. Grey, Q. Cai, A.J. Drew, and M.M.-M. Titirici, Energy Environ. Sci. (2020).
⁵ E. Olsson, G. Chai, M. Dove, and Q. Cai, Nanoscale 11, 5274 (2019).

Due to the rapid battery market expansion, and the limited and geographically concentrated lithium and cobalt resources, there is significant concern regarding the short-term supply and long-term sustainability of lithium-ion batteries (LIBs). Potassium-ion batteries (KIBs) are emerging as a promising complementary technology to LIBs due to the relative abundance of potassium. KIBs can also use graphite anodes providing a critical advantage over sodium-ion batteries (NIBs).

In my talk, I will provide a brief overview of the most promising cathodes [1], anodes [2] and electrolytes to date and a concise techno-economic model of KIBs. I will then discuss the critical research challenges that need to be addressed for KIBs to become a viable technology [3].

References
1. Fiore M, Wheeler S, Hurlbutt K, Capone I, Fawdon J, Ruffo R, et al. Paving the Way toward Highly Efficient, High-Energy Potassium-Ion Batteries with Ionic Liquid Electrolytes. Chem Mater., 2020.
2. Capone I, Aspinall J. Electrochemo-Mechanical Properties of Red Phosphorus Anodes in Lithium, Sodium, and Potassium Ion Batteries. Matter, 2020.
3. Dhir S, Wheeler S, Capone I, Pasta M. Outlook on K-Ion Batteries. Chem, 2020.

Development of Li metal anodes is critical to the realization of next generation high specific energy batteries. Commercialization of Li metal anodes, however, is plagued by its poor cyclability. This is because Li metal inevitably reacts with electrolytes, forming mechanically vulnerable solid-electrolyte interphase (SEI). With the significant volume fluctuation during Li metal cycling, the SEI easily cracks, leading to dendritic growth and continuous capacity loss. Electrolyte engineering recently arises as one of the most promising approaches to address these issues. Novel electrolyte systems alter the Li-ion solvation structure, enabling much improved Li deposition homogeneity and Coulombic efficiency (CE). However, further studies are still in demand. First, recently developed electrolyte recipes are usually complicated or cost-inefficient (high concentration, multi-solvent, multi-salt, etc.). Second, understandings on the working mechanisms of these Li-compatible electrolytes are still controversial. Here, we design and synthesize a family of fluorinated ether molecules that enables practical Li metal battery cycling performances with optimized electrolyte formulations and study their working mechanisms.
Fluorinated 1,4-dimethoxylbutane (FDMB), 1,5-dimethoxylpentane (FDMP), 1,6-dimethoxylhexane (FDMH) and 1,8-dimethoxyloctane (FDMO) are designed and synthesized for the first time as solvents for Li metal battery electrolytes. When Li salts are dissolved, the O and F atoms on these molecules chelate onto Li-ions simultaneously, leading to a unique brownish electrolyte color and high stability to metallic Li as well as high voltage cathodes. With these molecules, we demonstrate two electrolyte formulations that enables practical Li metal battery cycling performances. In the first formulation, we combine FDMB with 1 M LiFSI salt. It achieves excellent CE (over 99.5%) with a single-salt-single-solvent electrolyte configuration. As a result, a Cu||NMC532 anode-free pouch cell (~250 mAh) runs for 100 cycles before 80% capacity retention under lean electrolyte condition. In the first formulation, we use FDMH as the main solvent. Due to its reduced Li salt solubility, small portion of dimethoxyethane (DME) is added to enable much reduced ionic and interfacial resistance, resulting in the 1 M LiFSI/6FDMH-DME electrolyte. It enables 250 cycles of 20 μm Li||NMC811 cells before 85% capacity retention. Cu||NMC811 anode-free pouch cells also last for 120 cycles before reaching 75% of initial capacity. We show that the molecular design of solvent molecules could serve as one of the most promising strategies enabling practical Li metal batteries. Additionally, with an advanced pouch cell pressure sensing platform, we show that the cycling performances of these electrolytes are weakly affect by the operational pressure.
With characterization tools, we further demonstrate the working mechanism of these electrolytes. XPS shows an FSI^- anion-derived SEI chemistry with LiF nanoparticles accumulating with cycling on the deposited Li metal surface. This inorganic, anion-derived SEI chemistry is further confirmed by Cryo-STEM and AFM characterizations. With electrochemical experiments, we verify that the formation of an anion-derived, LiF rich rSEI (residual SEI, SEI remaining on the electrode after Li stripping) framework is likely the key to homogeneous Li deposition and prolonged cycle life in these electrolytes, as well as other previously reported Li-compatible electrolyte systems with LiFSI. These findings will serve as critical guides to the electrolyte designs of Li metal battery in the future.

Historically, the identification of new Li-ion cathode materials has led to significant advances in the field, and currently, they underpin the overall performance and production costs of batteries. Accurate first-principles calculations, coupled with the database-based big-data approach, has led advances and predictions into new materials in the past¹. The scarcity of data among the underexplored chemical spaces, however, has limited the ability of such approaches for computationally predicting truly new materials. In this work, we apply ab initio random structure searching (AIRSS)^2,3, an unbiased massively parallel structure prediction method, to search for stable phases in the Li-Fe-O-S chemical space. Experimentally, an anti-perovskite phase Li₂FeSO⁴ had been shown to be a promising low-cost earth-abundant cathode material with good rate capacity. Our search was able to re-discover this phase and its low-temperature distortions, along with a range of other previously unknown stable and metastable phases. Their potential for battery applications has been assessed. The use of crystal structure prediction helps us pursue fundamental structure-property relationships in cathodes, and thus will also help the field to explore and find new paradigms in the future.

References:

(1) Hautier, G.; Fischer, C.; Ehrlacher, V.; Jain, A.; Ceder, G. Data Mined Ionic Substitutions for the Discovery of New Compounds. Inorg. Chem. 2011, 50 (2), 656–663. https://doi.org/10.1021/ic102031h.
(2) Pickard, C. J.; Needs, R. J. Ab Initio Random Structure Searching. Journal of physics. Condensed matter : an Institute of Physics journal 2011, 23 (5), 053201–053201. https://doi.org/10.1088/0953-8984/23/5/053201.
(3) Pickard, C. J.; Needs, R. J. High-Pressure Phases of Silane. Phys. Rev. Lett. 2006, 97 (4), 045504. https://doi.org/10.1103/PhysRevLett.97.045504.
(4) Lai, K. T.; Antonyshyn, I.; Prots, Y.; Valldor, M. Anti-Perovskite Li-Battery Cathode Materials. J. Am. Chem. Soc. 2017, 139 (28), 9645–9649. https://doi.org/10.1021/jacs.7b04444.

The low cost and abundance of sodium have driven growing interest in Na-ion batteries (NIBs) as a possible alternative to Li-ion batteries. Nevertheless, fundamental differences between Na and Li, such as ionic radius and reduction potential, make it challenging to develop suitable electrode materials for embedding Na ions. Among the various electrodes explored to date, sodium titanates (Na₂Ti_nO_2n+1) anodes arise as one of the most promising candidates due to its large abundance and nontoxicity ^[1,2].
Early approaches on improving electrochemical performance of sodium titanates revealed that the adjustment of n value of Na₂Ti_nO_2n+1 can change the arrangements of constituent TiO₆ octahedra and thus, affect the capacity and cycle life of the anodes ^[3-5]. In general, sodium titanates with higher Na contents (e.g. Na₂Ti₃O₇) possess layered structures with high capacity, whereas those with lower Na contents (e.g. Na₂Ti₆O₁₃) have tunnel structures with long cycle life ^[6]. Despite these efforts, titanate anodes without any materials modifications commonly suffer from poor rate performance, which mainly results from the intrinsic insulating nature of titanate anodes associated with large band gap of 3.7-3.9 eV ^[3,7].
One of the most effective ways to improve the electrical conductivity is to narrow the band gap of materials. The defect chemistry of sodium titanates, however, has not been fully analyzed, and remains a bottleneck in the design of anodes for high power applications. In this study, using layered Na₂Ti₃O₇ and tunneled Na₂Ti₆O₁₃ as testbed materials, we analyze the intrinsic defects and their effects on electronic structures and fermi level position. Using hybrid Density Functional Theory calculations, we evaluate the dominant native defects, and provides guidelines for defect engineering for anodes with improved performance.

(1) Advanced Functional Materials 26.21 (2016): 3703-3710.
(2) Nano Energy 18 (2015): 20-27
(3) Advanced Energy Materials 3.9 (2013): 1186-1194
(4) Small 12.22 (2016): 2991-2997
(5) ACS applied materials & interfaces 10.1 (2018): 437-447
(6) Physical Chemistry Chemical Physics 14.7 (2012): 2333-2338
(7) ACS applied materials & interfaces 10.44 (2018): 37974-37980

In order to address the ever-increasing demand for better battery materials [1], we present a study exploring the potential of multi-layered heterostructures made from transition-metal dichalcogenides (TMDCs) in order to understand the benefits and drawbacks such layered materials could have as potential device electrodes.

Layered materials of atomically thin sheets have demonstrated promise as electrode materials due to their interlayer spacing allowing for easy lithium intercalation and diffusion. One family of such materials is the transition metal dichalcogenides (TMDCs) [2,3], which have already demonstrated promise in this application [4]. Further, recent advances in CVD [5] have allowed the development of novel materials formed from the heterostructuring of component TMDCs. These ‘designed’ materials allow for tailoring of material properties by utilising the new physics that arises from their combination. In particular, the opportunity to optimise transport, diffusion barriers and maintain the higher capacities that some structures offer, could provide a new generation of electrode materials.

We show how the properties of heterostructures and superlattice systems change compared to the constituents, highlighting the advantages and disadvantages of these materials, and estimate the maximum capacity of these structures. We do this using first principles density functional theory, explaining how the open-circuit voltage profiles and lithium diffusion barriers change for the composites, and the potential such structures have for future battery development.

REFERENCES
[1] Saxena, S et al . IEEE Industrial Electronics Magazine, 2017.
[2] Lin, L et al . Energy Storage Materials, 2019, 19.
[3] Chhowalla, M. et al. Nature Chemistry, 2013, 5.
[4] Zhang, L et al. Nano Letters, 2018, 18, 1466-1475.
[5] Sherrell, P et al. ACS Appl. Energy Mater. 2019, 2, 8, 5877-5882.

In the recent time, sodium-ion batteries (SIBs) has been attracted as a substitute of lithium-ion batteries (LIBs) due to the depletion of Li and the similar physicochemical properties of Na to Li. However, because of the larger ionic radius of Na⁺ (102 pm) than Li⁺ (78 pm), the hard carbon which shows wider interlayer spacing and porous structure compared to graphite has been actively investigated for use as anodes of SIBs. In the current study, spray-dried cellulose nanocrystals (CNCs) carbonized over a wide temperature range (i.e., 800–2500 °C) were prepared for carbon anodes of SIBs. The carbonized CNCs exhibited low surface area of 1.5 m²/g which is required to ensure minimal loss of Na ions for SEI layer formation. The structural variations in the CNC-based carbon anodes are correlated with the sodiation mechanism by investigating the galvanostatic voltage profiles, and it is found that Na ion adsorption takes place in the less-ordered carbonaceous structures followed by intercalation into the more ordered internal carbon structure with an average interlayer spacing of >0.37 nm. Among the various anodes examined, the CNCs carbonized at 1500 °C (C1500) deliver the highest reversible specific capacity of 311 mA h g^-1 at a current density of 10 mA g^-1, and exhibit an outstanding rate capability (273 mA h g^-1 at 400 mA g^-1). In addition, they also possess an excellent specific capacity retention of 92.3% even after 400 cycles at 100 mA g^-1, along with an initial coulombic efficiency of 85%. Density functional theory (DFT) calculation exhibits that the energy barrier for Na ion intercalation of C1500 (0.20 eV) is almost a half that of the CNCs carbonized at 2500 °C (0.39 eV). We therefore believe that our results establish a foundation for the materials and their corresponding electrochemical properties, in addition to providing a novel route for the development of highly effective SIB systems.

Redox mediators (RMs) are considered an effective countermeasure to reduce the large polarization in lithium-oxygen batteries. Nevertheless, achieving sufficient enhancement of the cyclability is limited by the trade-offs of freely mobile RMs, which are beneficial for charge transport but also trigger the detrimental shuttling phenomenon. Here, we successfully decoupled the charge-carrying redox property of RMs and shuttling phenomenon by anchoring the RMs in polymer form, where physical RM migration was replaced by electron self-exchangealong polymer chains. Using a model system of a polymer, PTMA (2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl methacrylate), whose repeating unit containsthe well-known RM tetramethylpiperidinyloxyl (TEMPO), it is demonstrated that PTMA is capable of functioning as a stationary RM, preserving not only the redox activity of TEMPO, but also the charge-carry property enabled by electron exchange along polyemr chain. Anchoring the RM in air electrode as polymer foam successfully prevents the shuttle phenomena. Consquently, the efficiency of RM-mediated Li2O2 decomposition remains remarkably stable without the consumption of oxidized RMs or degradation of the lithium anode, resulting in marked improvement of the performance of the lithium-oxygen cell.

Current advancements in energy technologies rely on combining the high-performance active electrodes with two-dimensional materials such as graphene for enhanced conductivity, mechanical stability and flexibility. Understanding the physical and electrochemical attributes of the formed interfaces can assist in device designing and performance. We utilize Density functional theory (DFT) to present an insightful analysis of selenium(Se) and graphene(Gr) composite cathode for potassium ion batteries. Se is replacing S as a favored cathode choice for being less reactive, free from shuttle effects, and possessing superior electrical conductivity. However, it falls short on electronic conductivity and abundance as per the industrial scale. Thus, Se based electrodes are consistently used with a carbon-based conductive additive to target long product life and weighted efficiency. To this end, the electrochemical performance of the Se-K cathode is determined by open-circuit voltage (OCV) plot and is compared with its counter-part Gr interfaced Se-K cathode. Significant variation in voltage plot and inter-atomic distances is seen due to the presence of Gr additive. To further the interface analysis, the interface strength of the Se/Gr 3D/2D interface has been quantified and correlated to the crystal structure, size, surface chemistry, and surface potential of the interfacing materials. The present analysis covers the chemical, physical and electrochemical contributions of Gr additive to the Se-K cathode for potassium ion battery which can assist the experimentalist and industries in fine-tuning the design of Se/Gr composite cathodes.

Vascular channel structures are ubiquitous in nature. Examples such as roots, blood vessels, and lung alveoli show how vasculatures represent the optimal structures with a perfect balance between surface area and mass transport. For lithium-ion batteries, creating vascular porous channels in the electrodes can potentially enhance the transport and kinetics by ensuring the fresh supply of electrolyte that mitigates the electrode polarization and thereby achieve high power or fast charging without damaging the electrode. However, it is challenging to optimize for the vascular structure from the immense parameter hyperspace. Variables such as radii, angles, and branch numbers constitute millions of possible combinations. In addition, even if the vascular structure could be optimally designed, it is nontrivial to fabricate them at the scale of battery cells. In this talk, I will show our recent research progress that uses deep learning and finite element modeling to quickly predict the battery performance and also to inverse-design the parameters of the most efficient vascular electrode structure. Depending on the model complexity, we can arbitrarily choose the performance criteria among charge capacity, cycle life, maximum local temperature, and maximum local stress. The performance of the predicted vascular electrode is then validated by microfabrication. By connecting artificial intelligence and micromanufacturing, we envision this research will significantly broaden our design parameter hyperspace of high-rate energy storage devices and provide an effective general approach for solving multiscale and multiphysics problems in reactive flow systems.

The electrical breakdown properties of metal-aluminum oxide-metal structures are investigated. The structures are prepared on silicon wafers in vacuum. A bottom electrode consisting of Cu (thickness 600nm) and Al (60nm) is prepared by thermal evaporation first. Then the aluminum oxide film (200nm) is deposited by electron beam evaporation from ceramic powder with a low oxygen support. Au, Cu or Pd (85nm) are evaporated on top using a shadow mask. The diameter of the top electrodes varies between .1mm and 1.9mm. The whole structure is prepared without breaking the vacuum.
Capacitance vs. frequency measurements of the device reveal a relaxational dielectric permittivity caused by fluctuating protons in the amorphous oxide [1]. Then a ramp voltage positive at the top electrode with speed 1V/s is applied. Before the sample finally has an electrical breakdown in fields of up to 4.5MV/cm single partial breakdown spots are visible at the top electrode. They appear in fields above 1MV/cm. At comparable voltages the density of the spots is three to four times higher at the Pd electrode than at the Cu and Au electrodes. A similar observation was published by P. Ball [2]. Pd electrodes can exhibit an electrochemical mechanical damage because of a high H flux and hydrogen evolution.
On the top the breakdown spots have a diameter of about 20 micrometer. Using an AFM it is found that the spots form caves or craters which are as deep as 1.5 micrometer. They penetrate the bottom electrode and reach down into the silicon substrate [3]. Considering the crater’s volume and the specific heats of the different materials the energy necessary to form the craters by thermal energy can be calculated. This energy is compared to the electrostatic energy stored in the capacitance at the voltage where the spot appears. For the smallest capacitance of about 3pF with a diameter of .1mm and a spot voltage of 36V the electrostatic energy available from the structure is 50 times smaller than the energy necessary to melt the materials. If the materials are evaporated, the electrostatic energy is even 350 times smaller than the required evaporation energy [3].
It seems that the electrical breadown with its hot plasma channel triggers another so far unknown process which delivers the energy necessary to form the craters. At the present moment one can only speculate about the physical nature of this effect. It remains an open question if this process is somehow related to the supposed cold fusion reported 31 years ago [4] and recently discussed again in [2].
[1] L. Kankate, C. Nies, W. Possart, H. Kliem, IEEE TDEI, vol. 25, 1508 (2018)
[2] P. Ball, MRS BULLETIN, vol. 44, 833 (2019)
[3] H. Kliem, K. Faliya, IEEE TDEI, vol. 27, 1080 {2020}
[4] M. Fleischmann, S.Pons, J. Electroanal. Chem. Interfacial Electrochem., vol. 261, 301 (1989}

Redox flow batteries offer a reliable solution for future grid-scale energy storage due to its flexible design in decoupling energy and power independently. In comparison with mostly investigated and commercialized all vanadium redox flow batteries, aqueous zinc-iodide flow battery (ZIFB) is a highly promising contender due to its cost-effectiveness, environment friendliness, safety, and high energy density. Currently it is possible to achieve a ZIFB with high energy density based on aqueous ZnI₂ as electrolytes. However, there are still obstacles to overcome before utilizing its full potential. Therefore, various research is under investigation to improve the battery design by optimizing its components towards the development of high-performance batteries. For example, achieving reversible Zn deposition/dissolution is highly challenging in Zn-based batteries. Inhomogeneous growth of metallic Zn on the surface of the anode during charging, can lead the cell to improper discharge. Herein, we have carried out the performance comparisons of different carbon based anodes on the basis of their physical structure, hydrophilic properties and electrical conductivities. We have found that planar, graphitized and highly conductive anode can lead to efficient Zn deposition/dissolution, resulting the cell to achieve high energy efficiencies. On the other hand, electrolyte has a major contribution in scaling up the battery performance. Due to an imbalance of concentration of solutes between the anode and cathode compartments during electrochemical cycling, the differential osmotic pressure results in water migration through the ion-permeable membrane from the compartment with lower ionic strength to the compartment with higher ionic strength, which is usually overlooked by using a static positive compartment, limiting its capacity. The addition of extra solute to the electrolyte solution is a way out to resolve this issue and reach an ionically balanced situation between two compartments. In this work, we have carried out the experimental analysis of a lab-scale Zn-I flow battery as per our theoretical ionic strength calculations to reach an overall balanced system. From the theoretical calculation, it has been proven that by adding extra potassium iodide (KI) to an electrolyte of 1:1 ZnI₂: KI, the ionic balance between the compartments could be achieved. We have performed electrochemical impedance spectroscopic (EIS) as a tool to study the solution resistance and ionic conductivity of the half-cell compartments. Further full cell cycling following post-mortem analysis of the half-cell electrolytes ensured no water migration between compartments during cycling, also excellent cycling efficiencies have been achieved. Overall, the mechanisms of optimizing anode material and electrolyte design, show an promising path to enhance the performance Zn-I flow batteries, which enlighten a step forward to the research in the next-generation aqueous flow batteries.

The work was funded by MINECO/ERDEF through WINCOST (ENE2016-80788-C5-5-R) and CCU+Ox (PID2019-108136RB-C33) projects.
M. Chakraborty received PhD grant from the EU Horizon 2020 research and innovation programme (DOC FAM COFUND 2016) under the Marie Sklodowska–Curie grant agreement No 754397.

Potassium-ion batteries are a promising alternative to conventional lithium-ion batteries. They have the potential to be low cost and sustainable as they can contain only cheap and abundant elements. In potassium-ion batteries lithium is replaced with potassium, the copper current collector is replaced with aluminium, and high-performance cathodes do not require cobalt. They have the crucial advantage over sodium-ion batteries that graphite, the commercial lithium-ion anode, can reversibly intercalate potassium but not sodium.

Potassium manganese hexacyanoferrate (KMnHCFe), a Prussian blue analogue, operates at a high voltage of around 4 V vs. K⁺/K and has a high theoretical specific capacity of 155 mA h g^-1. During a recent analysis of non-aqueous potassium-ion batteries we identified KMnHCFe||graphite as one of the most promising potassium-ion battery chemistries [1]. However, numerous challenges remain such as preventing aluminium current collector corrosion at high voltage and minimising parasitic reactions from water remaining in the KMnHCFe structure, both of which reduce the coulombic efficiency. Additionally, an electrolyte that performs well with both the KMnHCFe cathode and graphite anode must be developed.

In this work we make two key advancements to address the challenges presented by the KMnHCFe||graphite system [2]. Firstly, a systematic optimisation of the citrate-assisted synthesis of KMnHCFe was performed, using high-throughput synthesis and characterisation tools, to reduce the defect and water content whilst controlling for particle size. Secondly, an ionic-liquid based electrolyte, 1 M KFSI in Pyr_1,3FSI (potassium bis(fluorosulfonyl)imide in N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide)), was employed that forms stable passivating layers on both the cathode and anode, leading to highly efficient half-cell cycling. The electrochemical performance of KMnHCFe was observed to be highly dependent on particle size, the larger particles showing lower specific capacity but better cyclability. An optimised KMnHCFe material displayed a specific capacity of 119 mA h g^-1 and a stable coulombic efficiency of 99.3%, a significant improvement over the previous state of the art. In the same electrolyte graphite displays excellent electrochemical performance maintaining 99% of its specific capacity after 400 cycles and a stable coulombic efficiency of 99.94%.

References:

[1] Dhir, S.; Wheeler, S.; Capone, I.; Pasta, M. Chem 2020, 6 (10), 2442–2460.
[2] Fiore, M.; Wheeler, S.; Hurlbutt, K.; Capone, I.; Fawdon, J.; Ruffo, R.; Pasta, M. Chem. Mater. 2020, 32 (18), 7653–7661.

Due to the fast intercalation kinetics and the potential for pseudocapacitance, layered materials are promising for supercapacitor energy storage and understanding the role of ion confinement and transport is critical in enhancing the required properties of high energy and power density. Two-dimensional metal carbides and nitrides of early transition metals (MXenes) are one such class of materials that enable fast surface redox reactions and combine properties of high conductivity with hydrophilicity [1]. High volumetric capacitance of 1500 F cm^-3, has been achieved with the most widely used Ti₃C₂ MXene with aqueous H₂SO₄ electrolyte [2], indicating a dominant role of proton transport and surface protonation reactions contributing to the enhanced energy storage.

Nuclear quantum effects (NQEs), e.g. tunneling, on the structural and dynamical properties might be of significance due to the delocalization of light nuclei such as hydrogen but are often ignored in computational simulations. Here, we explore the NQEs on proton under confinement and under the influence of co-cation intercalation of Li⁺, Na⁺, and K⁺ using ReaxFF Path-Integral Molecular Dynamics (PIMD) simulations. Considering two cases of Ti₃C₂O₂ MXene with sparse intercalation of water and a single layer of water, we use grand-canonical monte carlo to reach equilibrium of intercalated protons for each system with/out co-cation intercalation, followed by thermosetted ring polymer MD method of PIMD to capture NQEs. The difference in the number of protons intercalated show a strong interplay between the protons, co-cation, water and the MXene surface. Benchmarking against equivalent classical MD simulations of bulk water, first we show that the NQEs enable a broadening of the O-H and O-O radial distribution functions (RDFs), indicative of bond stretching due to proton delocalization. Although capturing NQEs in simulations is vital in matching experimentally obtained properties of bulk water [3], we investigate its importance in proton transport mechanism in the MXene configurations considered using RDFs, hydrogen-bonding network and proton/water diffusion coefficients.

These insights into the NQEs may help understand the proton transfer mechanism more accurately and lead towards a rigorous procedure for the associated simulations.

References
[1] B. Anasori, et al., Nat. Rev. Mater. 2, 16098 (2017)
[2] M. R. Lukatskaya, et al., Nat. Energy 2, 17105 (2017).
[3] M. Ceriotti, et al., Chem. Rev. 116, 7529 (2016).

Magnetic tunnel junction (MTJ) can serve as an excellent testbed for connecting molecule between two ferromagnetic electrodes. A paramagnetic molecule covalently bonded to two ferromagnetic electrodes with two thiol functional groups can produce intriguing transport and magnetic properties. We have chemically bonded paramagnetic molecules between two ferromagnetic electrodes of a MTJ along the exposed side edges. In this paper we discussed the observation of molecule induced dramatic changes in the magnetic and transport properties of the conventional magnetic tunnel junctions. Paramagnetic molecules were chemically bonded to ferromagnetic electrodes to bridge them across the insulating spacer along the exposed edges. Paramagnetic molecular channels along the tunnel junction edges decreased the overall current, through tunnel barrier and molecular channels, > 5 orders of magnitude below the leakage current of the bare tunnel junction at room temperature. These molecules caused significant changes in the spin density of states due to potential spin filtering effect. Also, paramagnetic molecules produced antiferromagnetic coupling between the affected magnetic electrodes. In this state spin transport in the magnetic tunnel junction based molecular devices plummeted by several orders. It is also noteworthy that our experimental studies provide a platform to connect a vast variety of ferromagnetic leads to the even broader array of high potential molecules such as single molecular magnets, porphyrin, and single ion molecules. The strength of exchange coupling between ferromagnetic electrodes and molecules can be tailored by utilizing different tethers and terminal functional groups. The MTJMSD can provide an advanced form of logic and memory devices, including a testbed for the molecule-based quantum computation devices. Future studies about the interaction between molecular magnets and ferromagnets and the interaction of thiol ended alkanes with ferromagnets will be of very valuable. This study indicates the potential of magnetic molecules as a means of transforming conventional magnetic tunnel junctions and producing unprecedented magnetic and transport properties.

On the recent research front for the next generation secondary batteries beyond Li, potassium insertion into graphite in non-aqueous cells has brought new insights into the electrochemical K⁺ intercalation behavior and introduced advantageous benefits from potassium. Since potassium resources are much abundant and the standard potential of K⁺/K is 0.13 V below that of Li⁺/Li, potassium-ion batteries can be regarded as an appealing alternative to LIBs to realize high voltage systems with low cost. The crucial issue is the development of cathode materials able to accommodate the large K-ion without displaying detrimental structural changes toward cycle life and rate capability performance. The 4.7 V LiMn_1.5Ni_0.5O₄ spinel is already a promising cathode for the next generation of high voltage LIBs, and its host structure, λ-Mn_0.75Ni_0.25O₂, could be of great interest for K-ion batteries. Here, we investigate for the first time the potassium insertion properties into electrochemically prepared λ-MnO₂ (λ-MO) and λ-Mn_0.75Ni_0.25O₂ (λ-MNO) spinels^1,2. We show the λ-MNO material is capable of reacting with potassium ions along the first discharge in KPF₆/EC/PC electrolyte to convert to a layered phase, K_0.5Mn_0.75Ni_0.25O₂ (KMNO). Then, a highly reversible potassium extraction/insertion is observed, corresponding to the exchange of ≈ 0.3 K⁺ (90 mAh g^-1) during the first cycle at a C/20 rate at an average potential of 3.3 V vs K⁺/K. Excellent cycling stability is observed from the 15^th cycle with 70 mAh g ^-1 still available after 60 cycles. Note also that 65% capacity is retained after 350 cycles at a C/5 rate. A comparative analysis between λ-MO and λ-MNO highlights the even greater performance of λ-MNO as high voltage cathode material for K⁺-ion batteries. Moreover, the origin of the attractive electrochemical performances of λ-MNO is investigated by XRD, Raman, and EDS experiments after discharge and charge cycles.

[1] A. Bhatia, J.P. Pereira-Ramos, N. Emery, B. Laik, Ron I. Smith, R. Baddour-Hadjean*. “An exploratory investigation of spinel LiMn_1.5Ni_0.5O₄ as cathode material for K-ion battery”, 2020, ChemElectroChem, article (DOI: doi.org/10.1002/celc.202000462)
[2] A. Bhatia, J.P. Pereira-Ramos, N. Emery, B. Laik, Ron I. Smith, R. Baddour-Hadjean*. “An exploratory investigation of spinel LiMn_1.5Ni_0.5O₄ as cathode material for K-ion battery”, 2020, ChemElectroChem, front cover(DOI: doi.org/10.1002/celc.202000890)

Today the implementation of renewable energy supply is an important task for society. In this context, efficient energy storage is a key element for the successful realization of the energy turnaround. One of the most promising electrochemical energy storage concepts relies on rechargeable batteries such as Li-ion batteries as a very prominent example. [1]

However, lithium is listed as critical raw material since the production of lithium is only controlled by a few countries (e.g. in South American countries). [2] Therefore, new alternatives for anode-materials have to be found, which offer a higher accessibility combined with a high standard electrode potential. One promising candidate is sodium since it is an abundant resource in the earth crust and offers easy access worldwide. [3][4]

In addition to identifying alternatives for lithium as anode material, suitable cathode materials, which are electrochemical active versus Na⁺-intercalation, have to be found. In this context, layered vanadium oxides like hydrated vanadium oxide (H₂V₃O₈ or V₃O₇*H₂O) offer a flexible platform for cathode materials based on metal ion insertion. [5] H₂V₃O₈ possesses mixed valance states of V⁴⁺ and V⁵⁺ and due to its open framework it allows for reversible intercalation of various ions like Li⁺, Na⁺ or Zn²⁺. By changing its morphology from particles to thin fibers, faster charging and higher charge densities are enabled.

In this contribution, we present structural and morphological properties of H₂V₃O₈ synthesized under hydrothermal conditions with additives (e.g. rGO) in addition to the electrochemical properties. We show that conductive additives lead to higher energy densities combined with higher cycling stabilities for Na-ion batteries. Further modifications such as presodiation of H₂V₃O₈ are explored to compensate the loss of Na⁺-ions due to the formation of the solid electrolyte interface (SEI) in the first cycles.


__________
[1] Arianna Moretti et. al., Adv. Energy Mater. 2016, 6, 1600868
[2] Ashby, Michael F., Butterworth-Heinemann, 2013, 349-413
[3] Xiaoxiao Liu et. al., Adv. Funct. Mater. 2019, 29, 1903795
[4] Iqra Moeez et. al., ACS Appl. Mater. Interfaces 2019, 11, 41394−41401
[5] Aura Tolosa et. al., ACS Appl. Energy Mater. 2018, 1, 3790−3801

NASICON-type Na₃V₂(PO₄)₃ (NVP) is promising as positive electrode material for Na-ion batteries due to its robust crystal structure, providing long cycle life and great rate capability.^[1,2] However, it is able to exchange only two Na⁺ ions per two Vanadium transition metals leading to a moderate specific capacity of 118 mAh/g. Therefore, it has been an important challenge in the research field to improve the specific capacity while keeping the solid framework of NASICON structure. Recently, several new NASICON-type materials such as Na_3+xMg_xV_2-x(PO₄)₃,^[3] Na₄MnV(PO₄)₃,^[4-6] and Na₄MnCr(PO₄)₃,^[7] have been reported attempting to gain higher specific capacity and have better sustainability. Surprisingly, Na₄FeV(PO₄)₃ has not been reported yet in literature. We thus decided to study the Fe/V-mixed system demonstrating possible extraction of three Na⁺ ions per two transition metals. Sol-gel and solid-state methods with various synthesis parameters were investigated to synthesize the target material, Na₄FeV(PO₄)₃. We obtained the NASICON-type phase with small amount of secondary phases (NaFePO₄ and Na₃PO₄). To obtain the pure phase, Na₃FeV(PO₄)₃ has been synthesized and electrochemically sodiated to form Na₄FeV(PO₄)₃. Herein, we present for the first time crystal structures of the NASICON materials, Na₃FeV(PO₄)₃ and Na₄FeV(PO₄)₃, using high resolution Synchrotron X-ray diffraction (SXRD) as well as the electrochemical performances. 2.64 Na⁺ were extracted from the Na₄FeV(PO₄)₃ upon charge process, corresponding to a specific capacity of 146.3 mAh/g. We could clearly observe a superstructure in Na₃FeV(PO₄)₃ due to Na⁺ ordering, which is different from the structure reported in the literature.^[6] Thermal analyses of Na₃FeV(PO₄)₃ were performed combining in situ temperature XRD and differential scanning calorimetry (DSC). An ordered/disordered phase transition is observed at 123°C with an increase symmetry from monoclinic (Space Group: C2/c) to rhombohedral (Space group: R-3c). The superstructure reflections from the ordered phase completely disappear at high temperature, which reversibly appear again as temperature goes down. The fully electrochemically sodiated Na₄FeV(PO₄)₃ crystallizes in a rhombohedral unit cell (R-3c) with all the sodium sites almost fully occupied. Since Vanadium and Iron share the same crystallographic site synchrotron X-ray absorption spectroscopy (XAS) at V and Fe K-edges and Mossbauer spectroscopy were performed. These technics allow to differentiate the local V, and Fe environments, respectively, and their oxidation states in both Na₃FeV(PO₄)₃ and Na₄FeV(PO₄)₃. Extended X-Ray Absorption Fine Structure (EXAFS) analysis shows that average bond distance of Fe – O increases from 1.99 Å in Na₃FeV(PO₄)₃ to 2.06 Å in Na₄FeV(PO₄)₃ while that of V – O remains unchanged as 2.02 Å suggesting the reduction of Fe³⁺ to Fe²⁺ without noticeable distortion of the MO₆ octahedra. The details of the local environments and oxidation states evolution and the electrochemical performances will be discussed.

References
[1] J.-N. Chotard, G. Rousse, R. David, O. Mentré, M. Courty, and C. Masquelier, Chem. Mater., 27, 5982–5987 (2015).
[2] K. Saravanan, C.W. Mason, A. Rudola, K.H. Wong, and P. Balaya, Adv. Energy Mater., 3, 444–450 (2013).
[3] A. Inoishi, Y. Yoshioka, L. Zhao, A. Kitajou, and S. Okada, ChemElectroChem, 4, 2755–2759 (2017).
[4] F. Chen, V.M. Kovrugin, R. David, O. Mentré, F. Fauth, J.-N. Chotard, and C. Masquelier, Small Methods, 1800218, 1800218 (2018).
[5] M. V Zakharkin, O.A. Drozhzhin, I. V Tereshchenko, D. Chernyshov, A.M. Abakumov, E. V Antipov, and K.J. Stevenson, ACS Appl. Energy Mater., 1, 5842–5846 (2018).
[6] W. Zhou, L. Xue, X. Lü, H. Gao, Y. Li, S. Xin, G. Fu, Z. Cui, Y. Zhu, and J.B. Goodenough, Nano Lett., 16, 7836–7841 (2016).
[7] J. Wang, Y. Wang, D.H. Seo, T. Shi, S. Chen, Y. Tian, H. Kim, and G. Ceder, Adv. Energy Mater., 1903968, 1–10 (2020).

In recent years, the increase in demand for lithium-ion batteries (LIBs) has brought attention to the supply of the raw materials used in production of the cathode. Using a direct recycling process to reclaim spent cathodes for second use not only recovers the component elements, but also aims to keep the existing structure in-tact and minimize steps and costs associated with reprocessing the material. Cobalt in particular is a high value material of concern and is a major component of the commonly used Li(Ni_xMn_yCo_z)O₂ (NMC) class of cathodes. While NMC materials have gained marketplace acceptance, their exact composition has evolved. For instance five years ago NMC111 was commonly used, versus NMC622 or NMC811 are more common now. This change in composition over time presents a challenge to directly recycling cathode materials since those coming out of service are no longer in line with current compositions. The goal of this work is to upcycle an NMC111 powder to the more relevant Ni-rich NMC622 target composition. Reactions with different Ni-rich coatings were explored as a method of incorporating nickel into the structure through solid state methods. The challenges of obtaining identifying reaction conditions which avoid the formation of undesired oxides and lead to a more homogeneous material will be discussed. Structural and compositional analysis will be detailed.

We study the electrochemical and structural responses of primary cathode nanoparticles for magnesium ion insertion. By systematically varying the electrolyte, we observe a successful Mg²⁺ insertion and the consistent solid-solution phase transition in the nanoparticles. Further examination by scanning electron nanodiffraction (SEND) in scanning transmission electron microscope (STEM) revealed two distinctive strain and phase distribution patterns in the cathode nanoparticles at nanometer resolution regulated by the electrolyte. One is consist of a uniform, major phase domain distribution due to an elastic strain relaxation mechanism at the atomic level, whereas the other one is consist of a non-uniform, scattered phase domain distribution or “core-shell” structure with a plastic strain relaxation mechanism. The varied chemo-mechanical behaviors are associated with the coherency strain and charge screening effect occurred in the Mg²⁺ insertion revealed at the atomic level by STEM imaging and DFT calculations. Our work shows that electrochemical parameters such as the electrolyte have a direct influence on the cathode structural heterogeneity during Mg ion insertion, which rationally guide the design of battery materials with high stability and capacity.

Classical molecular dynamics (MD) simulations are applied to study the transport of Na-ions in cathode materials for Na-ion batteries (SIB). Two different materials (in Na_xTi₂(PO₄)₃) are studied to access and compare the level of Na-ion diffusion in electrode structure. Sodium constitute a potential alternative of Lithium in alkali metal batteries, since sources of Li are limited, and Na is readily available. titration, impedance measurements etc.) diffusivity estimates specifically from impedance curves are often measured away from the equilibrium and fitting parameters are prone to produce large errors. MD simulations using universal force field have provided a direct assessment of self-diffusion coefficient of Na-ions in the structure of Na_xV₄O₁₀ with varying concentrations of Na-ions (0.33 < x < 1.33), calculating a diffusion coefficient of 5.75 x 10^-8 cm²/s for x=0.66 at 300 K, which is in good agreement with experiments. Mean square displacement (MSD) and Na-ion density plots are further providing a mechanistic insight on the route of Na-ion transport.

As a next generation material, NASICON structured type (NaTi₂(PO₄)) SIB material, are investigated for Na-ion transport. Inter-atomic based partial charge potential model is applied, and concentration of Na-ion is varied (from 0.82 < x < 0.98) in the supercell (total of 9000 atoms) of Na_xTi₂(PO₄)₃ at 323 K. Na⁺ transport of different sets of runs are calculated and MD trajectory are visualized. MSD of Na⁺ as a function of time. Self-diffusion coefficient of Na⁺ is calculated from the slope of MSD vs time plot for the three-dimensional transport, following Einstein’s relation. Calculated diffusivities are in the range of ~10^-8-10^-9 cm²/s and corresponding ionic conductivity is estimated to be (~10^-4 S/cm). These values are in agreement with experimentally measured values of Na-ions in the same structure.

References

Saroha, R., Khan, T.S., Chandra, M., Shukla, R., Panwar, A.K., Gupta, A., Haider, M.A., Basu, S. and Dhaka, R.S., 2019. Electrochemical properties of Na_0.66V₄O₁₀ nanostructures as cathode material in rechargeable batteries for energy storage applications. ACS omega, 4(6), pp.9878-9888.

Wani, M.S., Anjum, U., Khan, T.S., Dhaka, R.S. and Haider, M.A., 2020. Understanding Na-Ion Transport in Na_xV₄O₁₀ Electrode Material for Sodium-Ion Batteries. Journal of Electronic Materials, pp.1-6.

Although lithium-ion batteries are today’s go-to high-energy battery technology, the inherent safety issues of Li-ion remain a persistent challenge, especially when Li-ion battery packs are required, as in electrified vehicles and distributed microgrids. The monolithic three-dimensional (3D) zinc “sponge” developed at the U.S. Naval Research Laboratory (NRL) solves long-standing performance limitations for zinc anodes and paves the way for next generation Ni–Zn batteries competitive with the specific energy of Li-ion systems plus adding improved safety inherent to aqueous, nonflammable electrolytes. However, the current performance of β-Ni(OH)₂ composite electrodes does not provide sufficient performance or energy density to match that of Zn sponge anodes and represents a critical bottleneck to Ni–Zn batteries with high energy density. We are investigating Ni-based cathodes redesigned as architectures to wire the electrode volume in 3D while building on Texas State’s microwave synthesis of multi-substituted α-Ni(OH)₂ to increase the capacity, minimize the parasitic oxygen evolution reaction, and provide stable multi-electron cycling of the active material.

This presentation discusses the application of covalent organic frameworks (COFs) as cathodes in battery chemistries beyond the Li-ion viz. non-aqueous liquid electrolyte-based Li/Na-S and aqueous Zn-ion batteries.

We have designed covalent organic framework nanosheets over end-opened multi-walled carbon nanotubes (CNT-CON) and explored their role as sulfur host in metal sulfur batteries. The carbon nanotubes provide the conductivity and confine the elemental sulfur, whereas the covalent organic nanosheets layer acts as a porous (chemical) trap to prevent polysulfide dissolution electrolyte. Numerous experimental methods investigated the crystallinity, porosity, and framework composition of the cathode material. The molecularly designed covalent organic framework viz. the CNT-CON/S when employed as the cathode in Li-S and Na-S battery exhibited a significant improvement in electrochemical performance (specific capacity and cycling efficiency) as compared to CNT/S and COF/S cathode. All these studies convincingly show that COFs grafted on to conducting carbon structures can serve as alternative (organic) electrodes for high-performance metal-sulfur battery systems (Ruth Gomes et al. ACS Sustainable Chem. Eng. 2020).

The second part of the lecture will discuss a redox-active two-dimensional COF and its graphene oxide composite (COF-GOPH) as a cathode in an aqueous rechargeable Zn-ion battery (ZiB). Zinc metal anode and varying concentrations of Zn²⁺-ion and Li⁺-ion electrolytes were used in the cell with COF-GOPH cathode. The best battery performance was obtained when the composition of the Zn and Li-based electrolytes are 1:1. Combination and X-ray photoelectron spectroscopy and conductivity measurements reveal that optimum concentration of Li⁺ ions in the mixed-ion electrolyte was beneficial for better facilitation of Zn⁺² diffusion into the electrode, providing superior electrochemical performance. The COF-Zn aqueous mixed-ion system offers a better alternative to conventional aqueous organic batteries with a single type of ions. It ensures excellent electrochemical performance in cycling stability reversibility and capacity retention (Akshatha Venkatesh et al. submitted, 2021).

The above examples of employing COF in battery chemistries beyond the Li-ion further broadens the potential of COFs. The work clearly demonstrates that COFs can be used in the development of new and efficient battery systems that are safe, cost-effective, eco-friendly, and, most importantly, providing a sustainable future.

The increasing demand for energy especially from renewable and intermittent resources (e.g. sun and wind) along with the colossal demand for portable electronics and the growing popularity of electric vehicles, push the community to be more dependent on energy storage technologies, especially Lithium-ion battery (LIB)). Concurrent with this booming LIB technology, an emerging topic of research has been dedicated to curtailing the environmental concerns, the Li mining geopolitical issues, as well as providing other cost effective and environmental benign alternatives. Rechargeable zinc and aluminum aqueous batteries hold promise owing to the affordability, high capacity and safety [1, 2]. Eumelanin is the most common form of the pigment melanin in the human body, with diverse functions including photoprotection, antioxidant behavior, metal chelation, and free radical scavenging [3]. Sepia Melanin is a natural eumelanin extracted from the ink sac of cuttlefish. The poor solubility of melanin in most of organic solvent combined with the density of metal-binding catechol groups that reversibly bind mono and multivalent metal ions, constitutes the foundation and stability for its use in energy storage systems [4, 5]. In this work, we report on the use of sepia melanin with reduced graphene oxide (as conductive binder) grafted on carbon paper as a highly stable, biosourced, environmentally benign and biocompatible cathode for Zn⁺² and Al⁺³ aqueous rechargeable batteries. This stable, environmentally benign and bio compatible cathode will enable applications from biomedical devices to grid storage.


[1] Kundu D, Oberholzer P, Glaros C, Bouzid A, Tervoort E, Pasquarello A and Niederberger M 2018 Organic cathode for aqueous Zn-ion batteries: taming a unique phase evolution toward stable electrochemical cycling Chem. Mater. 30 3874-81
[2] Elia G A, Marquardt K, Hoeppner K, Fantini S, Lin R, Knipping E, Peters W, Drillet J F, Passerini S and Hahn R 2016 An overview and future perspectives of aluminum batteries Adv. Mater. 28 7564-79
[3] Di Mauro E, Xu R, Soliveri G and Santato C 2017 Natural melanin pigments and their interfaces with metal ions and oxides: Emerging concepts and technologies MRS Communications 7 141-51
[4] Jo K Y, Wei W, Sang Eun C, F. W J and J. B C 2014 Catechol Mediated Reversible Binding of Multivalent Cations in Eumelanin Half Cells Adv. Mater. 26 6572-9
[5] Kim Y J, Wu W, Chun S E, Whitacre J F and Bettinger C J 2013 Biologically derived melanin electrodes in aqueous sodium ion energy storage devices Proceedings of the National Academy of Sciences 110 20912-7

Zn-ion battery is an increasingly attractive alternative energy storage system compared to traditional Li-ion batteries due to their low cost, high theoretical capacity, and increased safety. However, dendrite formation limits the stability of the Zn metal anode and restricts the practical use of Zn-ion batteries. In our early work, MoS₂ via electrodeposition has been proven to be an effective barrier to Zn dendrite growth, however, the growth of such MoS₂ thin films has not been well studied. For this study, a series of tests on the deposition of MoS₂ on Zn of different grain size proved that Zn grain boundaries are favorable sites for the start of MoS₂ growth. The Zn coated anodes were then tested for their efficiency in symmetrical cell testing. The MoS₂ layer, as thin at 50 nm, increased the anodic diffusion of Zn ions and improved overall battery performance. The structure-property relations of MoS2 coatings on Zn has been studied systematically. The Zn ion conductivity of the MoS₂ coated anode with the variation of the coating thickness and morphology of MoS2 also has been studied. This study further reinforces the possibility of creating practical Zn-ion batteries as next generation energy storage systems.

Today, Lithium ion batteries are often the primary means of providing electrical power to a diverse ecosystem of devices, from mobile phones to electric vehicles. However, while capacity, cost, and reliability of Li-ion chemistries have steadily improved over the past two decades, limitations of the technology have become increasingly apparent. Indeed, despite considerable investment in LIBs, it is not clear the technology will reach optimal energy density and per-cell cost targets, laid out in industry and government-sponsored roadmaps, by the year 2030 at its current rate of progress. Furthermore, cost fluctuations in the price of raw materials used to fabricate LIBs and environmental impacts caused by both production and disposal have yet to be fully addressed.

Given the present and anticipated limitations of LIBs, investigations into alternative divalent metal-ion battery chemistries which utilize magnesium or zinc have continued to gain traction within the scientific and engineering community. Mg-ion cells offer a theoretical volumetric capacity which exceeds that of lithium while utilizing an element more abundant in the earth’s crust. Mg anodes are also dendrite free, allowing greater practical capacitates than what is currently achievable with intercalation-type anodes used for LIBs. However, Mg-ion battery cells consisting of sulfur-containing chalcogenide cathodes and Mg metal anodes must utilize unconventional and often volatile electrolyte solutions to inhibit anode surface passivation.

Here, the electrochemical behavior of WS₂ cathodes and Mg-CNT composite anodes in contact with a conventional EC/PC polymer-gel (PVDF-HPF) electrolyte is investigated within the context of Mg-ion insertion. Indeed, the atomic structure and interlayer spacing of WS₂ is similar to other Mg-insertion cathodes such as TiS₂ and MoS₂, while Mg-CNT composite anodes have demonstrated compatibility with perchlorate-containing electrolytes. Analysis of WS₂ cathodes via cyclic voltammetry shows a reversible redox reaction involving Mg species at the cathode/electrolyte interface, indicating a possible intercalation mechanism. Additional cathode and anode surface data is provided by XPS, Powder XRD, and Raman Spectroscopy. Cell fabrication details and analysis of reacted cathodes and anodes in the context of Mg-ion intercalation will be discussed.

The development of next-generation energy storage demands electrode materials with higher capacity. One potential solution is to charge layered oxides, such as LiCoO₂ and Li(Ni_xCo_yMn_z)O₂ (NCM) cathodes, to a higher electrode potential so that more Li+ ions can be removed. However, this is often impeded by performance degradation arising from following phenomena: 1) phase transition in the bulk electrode, 2) surface reconstructions, and 3) electrolyte oxidation. In this talk I will present our recent studies on using ceramic electrolyte-based coatings to alleviate these issues. With a thin layer of Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) coating, phase transition and surface reconstruction of LiCoO₂ are suppressed. Consequently, LAGP protected LiCoO₂ shows a discharge capacity of 196 mAh g^-1 at 0.1 C when charged to 4.5 V vs. Li⁺/Li. The capacity retention is 88% over 400 cycles . The LAGP coating also suppresses electrolyte oxidation when layered oxides are combined with polyethylene oxide (PEO)-based solid polymer electrolytes. While PEO is easily oxidized above 4 V vs. Li⁺/Li when it is in contact with bare LiCoO₂ and NCM523, it is stable up to 4.3-4.4 V vs. Li⁺/Li with a LAGP coating. When charged to 4.3 V, capacity retention of 89.7% over 200 cycles, and 93.8% over 100 cycles are achieved in LAGP-LiCoO2/PEO/Li cells and NCM523/PEO/Li cells, respectively. The corresponding average coulombic efficiencies are ~99.8%. These studies show that solid electrolyte coating is an effective approach to enhance interfacial stability of 4V layered oxide cathodes with various electrolytes at high electrode potentials.

Beyond lithium-ion battery (LIB) chemistries demand new electrode materials exhibiting unique features to accommodate the larger and/or multivalent active ions. Zeolite-templated carbon (ZTC) is an ordered microporous carbon scaffold that is molecularly thin, electrically conductive, and connected in three dimensions. Its narrow pore size distribution is centered at 1.2 nm, permitting the controlled introduction and ultrafast conduction of a wide range of molecular guests. We report methodological studies of the serviceability of ZTC as a stable cathode material across wide voltage ranges for both bulky, polyatomic anions (as in dual-ion electrochemistries) and divalent cations (as in magnesium-ion electrochemistries) in high energy density and high power density electrochemical cells. Charge storage proceeds by a purely capacitive mechanism at the cathode, mated with the faradaic mechanism of metal plating and stripping at the anode. Solid-state NMR spectroscopy sheds insight into the roles of the ion and solvent in charge/discharge cycling within the microporous framework of ZTC, with intuitive trends revealed based on ion size, solvent size, and solvent viscosity.

The rechargeable seawater battery (SWB) is one of the potential candidates as a large-scale energy storage system due to its low cost and eco-friendliness compared to Li-ion batteries. However, the current seawater battery using a Hong Nasicon (Na₃Zr₂Si₂PO₁₂) [H-NASICON] Na-conducting membrane suffers from high ohmic polarization as a result of its low ionic conductivity. One way to reduce to this polarization is to use a Na-conducting membrane with higher ionic conductivity than H-NASICON. In this regard von-Alpen type NASICON (Na_3.1Zr_1.55Si_2.3P_0.7O₁₁) [VA-NASICON] was investigated as a possible replacement membrane for use in a SWB. The electrical, mechanical, chemical stability and SWB cell testing of VA-NASICON and H-NASICON were evaluated and compared. It was observed that VA-NASICON exhibited both a higher bulk and grain boundary conductivity leading to a total ionic conductivity of 3 times higher than that for H-NASICON. The results will be explained in terms of the difference in structure and microstructure between the two materials. The difference in the mechanical properties; hardness, fracture toughness and fracture stress between the two materials will be explained based on their microstructural differences. The ionic conductivity, structure and microstructure of VA-NASICON were unchanged after testing in seawater, suggesting it is chemically stable in seawater. Testing of VA-NASICON in SWB coin cells revealed it exhibited about 1.5 x the power compared to H-Nasicon. This value is in close agreement the lower ohmic resistance of VA-NASICON compared to H-NASICON. The results of this study suggest that of the two materials evaluated, VA-NASICON is the better choice for a Na-ion conducting electrolyte in a SWB than the current H-NASICON.

All-solid-state batteries hold the potential to transform electrochemical energy storage technologies. Replacing the flammable liquid electrolyte with a solid-state ion conductor can improve battery safety and may further increase battery energy density when paired with lithium metal anodes. However, widespread implementation of all-solid-state batteries is hindered in part by the fact that candidate solid-state electrolytes typically exhibit ionic conductivities that are several orders of magnitude lower than liquid electrolytes, which typically results in slow charge/discharge rates. While there are a multitude of candidate electrolyte materials for all-solid-state batteries, rapid advancements in this field necessitate a fundamental understanding of the relationships between composition and ionic conductivity. These design principles may then be leveraged to identify and target new materials with ionic conductivities that are competitive with existing liquid electrolyte technologies. One such family of materials is the argyrodites of the general formula Li₆PS₅X (X = halide or pseudohalide), as they can achieve ionic conductivities that are nearly competitive with liquid electrolytes. Because the X-site can be occupied by either halides or larger pseudohalides, these materials provide an exciting system to understand the underlying relationships between structure, composition, and ion conduction in candidate solid electrolytes. In this work, I have prepared new argyrodite materials with pseudohalides at the X-site and have determined the structure-property relationships that contribute to low activation barriers and high ionic conductivities in these materials. This work highlights an exciting approach to tuning ionic conductivity in new electrolyte materials for potential applications in all-solid-state batteries.

We present a combined experimental and theoretical investigation of atomic dynamics in the superionic compound Cu₇PSe₆, rationalizing the atomistic diffusion mechanism and the impact of host lattice dynamics. Inelastic neutron scattering (INS) and quasi-elastic neutron scattering (QENS) were performed as a function of temperature and were complemented with ab-initio molecular dynamics extended to long time scales with the use of machine-learned potentials (MLMD). INS data reveal characteristic changes at the onset of superionic behavior, providing insights into the role of the host lattice dynamics, while QENS probes the superionic Cu diffusion via the jump length, residence time, and diffusion constant. The MLMD simulations reveal that the long-range Cu diffusion is limited by an inter-cluster hopping step, which is strongly coupled to the host phonon dynamics. Further, MLMD simulations enable us to capture the ultralow lattice thermal conductivity within the Green-Kubo framework. These results supersede the traditional quasiharmonic phonon picture to capture the strong anharmonicity in this superionic system.

This research was supported by the U.S. DOE.

The anticipated commercialization of all-solid-state lithium batteries highlights the urgent need to develop recycling strategies for solid-state electrolytes. Garnet type, Li₇La₃Zr₂O₁₂ (LLZO), and NASICON-type, Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) electrolytes are particularly promising because of their high conductivity and good chemical stability against lithium metal and air, respectively. Here, we use cold sintering process to recycle degraded electrolytes with poor structural integrity. The low temperature allows co-sintering of composites, which still remains challenging for conventional sintering. Two model systems, LLZO with polypropylene carbonate (PPC) and lithium perchlorate (LiClO₄), and LAGP with bis(trifluoromethanesulfonyl)imide (LiTFSI) salts, are studied. LLZO-PPC-LiClO₄ shows a reprocessibility for eight times with ionic conductivities in excess of 10⁻⁴ Scm⁻¹ at room temperature and relative densities of 76~80%, which are comparable with the values of pristine sample. LAGP-LiTFSI reprocessed composites exhibit high relative densities of around 90% and ionic conductivities above 10⁻⁵ Scm⁻¹ at room temperature. Thus, we demonstrate the use of cold sintering to recycle ceramic-salt and ceramic-salt-polymer integrated electrolytes.

The Olivine lithium iron phosphate cathode provides a very stable and high rate cathode for lithium and lithium-ion intercalation batteries. However, its energy density is much lower than that of the NMC layered oxides. This can be helped by switching to lithium manganese phosphate, which has an 0.5 V higher cell potential. To achieve energy densities approaching those of the layered oxides, it will be necessary to achieve a two-electron reaction per redox center. In principle, the anode can be lithium, sodium, magnesium or calcium. Vanadium is one of few suitable transition metal centers where a two-electron can be achieved, as vanadium can readily undergo between the +5 and +3 oxidation states, and in some cases to the +2 state. The earliest two-electron cathode was vanadium diselenide, VSe2, [1] with relatively low cell potentials as the reaction uses the +4 to +2 oxidation states. VS₂ would be expected to have more attractive potentials. Vanadium phosphates are found to readily and reversibly intercalate both two lithium or two sodium ions [2,3], with the former having cell potnetials around 4 and 2.5 volts. The challenges facing these systems will be discussed [4].

[1] M. S. Whittingham, Mater. Res. Bull., 13, 959-965 (1978)
[2] M. S. Whittingham et al., Accounts of Chemical Research 51, 258-264 (2018). DOI: 10.1021/acs.accounts.7b00527
[3] C. Siu et al., Chem. Commun., 54, 7802-7805 (2018). DOI: 10.1039/c8cc02386g
[4] N. A. Chernova et al, Advanced Energy Materials, in press. DOI: 10.1002/aenm.202002638.

Sodium-ion batteries are important for energy storage because sodium is much more abundant than lithium which is the fundamental element for lithium-ion batteries. From chemical point of view, sodium-ion cathodes open up opportunities for utilizing novel electrochemistries that are not possible in lithium-ion cathodes. For example, Fe³⁺/Fe⁴⁺ and Cu²⁺/Cu³⁺ redox cannot be utilized in lithium-ion cathode because of structural disorder or/and exceedingly high voltage that is incomptabile with currently available electrolyte. In sodium-ion cathodes, structural ordering enabled by the large size of sodium ion, the diversity of structures, and the relatively low voltage make it possible to utilize the Fe³⁺/Fe⁴⁺ and Cu²⁺/Cu³⁺ redox couples. This talk will focus on the latter one. Two kinds of materials with the same stoichiometry (Na_2/3Cu_1/3Mn_2/3O₂) but different structures (P2 and P3) are synthesized and characterized to understand the structure-property relationship in these materials. Synchrotron and neutron scattering as well as DFT calculations are used to understand the bulk structural changes during electrochemical cycling. Synchrotron-based hard and soft x-ray spectroscopies are used to understand the chemistries both in the bulk and at the surface in these two materials. The effect of crystal structure on the activity of Cu will be explained and the possibility of O activity will also be discussed.

Layered transition-metal oxides have been successfully employed as electrode materials for Li-ion batteries, however, intercalating Na or K instead often introduces effects that can diminish reversibility and rate capability. Within these materials, Na and K tend to stabilize additional host crystal structures accessed via topotactic phase transitions and display a stronger preference for ordering within the intercalation layers to minimize electrostatic energy. In some cases, rather than discrete orderings appearing at some particular intercalant concentrations, the stable orderings within a concentration range form a continuum, or a "Devil’s staircase," of hierarchical orderings based on some underlying motifs. Using a first-principles statistical mechanical approach, we have identified several such sets of orderings in common layered oxides intercalated with Na or K, within the O3/P3/O1 structure family. An important set of orderings appears in the P3 structure at intermediate concentrations, in which variants of one particular ordering are separated by periodically spaced antiphase boundaries. The overall density of boundaries in this case determines the average composition. Another notable set of orderings is predicted for K intercalation at high concentrations, where alternating regions of octahedrally and prismatically coordinated K exist in the same intercalation layer. This mixed coordination leads to significant distortions of the host structure. We discuss these sets of orderings in the context of phase stability predictions for several systems and compare our results to experimentally observed voltage profiles and structural evolution during cycling. We also explore ramifications for ion diffusion and electrode performance.

Layered NaNi_xFe_yMn_zO₂ cathode (NFM) is of great interest in sodium ion batteries due to its high theoretical capacity and utilization of abundant, environmentally-friendly elements. However, the evolution of the local bonding of the transition metals (TMs) beyond the first charge/discharge cycle is not well understood. In this work, we investigate the reversibility of TM ions in layered NFMs with varying Fe contents and potential windows after multiple cycles. Utilizing ex situ synchrotron X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) of pre-cycled samples the valence and bonding evolution of the TMs are elucidated. Our results indicate that Fe redox (Fe³⁺/Fe⁴⁺) is active in the first several cycles in these NaNi_xFe_yMn_zO₂ samples, but on the 5^th cycle Fe no longer participates in charge compensation. Manganese was found to be inactive for all cycles. The Ni redox couple contributes most of the charge compensation for NFMs beyond the 1^st cycle. Ni redox is quite reversible in the cathodes with less Fe contents. However, the Ni redox couple shows significant irreversibility with high Fe content of 0.8, suggesting an interaction between Ni and Fe bonds. The electrochemical reversibility of the NFM cathode becomes increasingly enhanced with the decrease of either Fe content or with lower upper charge cutoff potential.

We reported the high working voltage of K-ion battery (KIB) comparable to Li-ion and higher than Na-ion batteries based on the fact that the standard potential of potassium is lower than those of lithium and sodium in nonaqueous electrolyte [1,2]. In 2015, our group reported a graphite negative electrode delivering >250 mAh g^-1 with excellent reversibility [1]. Furthermore, a Prussian blue analogue (PBA) of K₂Mn[Fe(CN)₆] demonstrated highly reversible potassium insertion/extraction and 4 V operation, realizing a 4 V-class K₂Mn[Fe(CN)₆]/graphite full cell [3]. The previous studies revealed that a three-dimensional open framework structure of PBAs is suitable for insertion/extraction of large K⁺ ion. In addition to the PBAs, polyanionic compound and metal organic phosphate open framework (MOPOF) materials are potential positive electrode materials for KIBs due to their open framework structure and inductive effect. In this talk, our recent studies on potassium insertion into various polyanionic compounds and MOPOFs, such as orthorhombic KFeSO₄F (o-KFeSO₄F), KFePO₄F, K₆(VO₂)(V₂O₃)₂(PO₄)₄(P₂O₇) (K6V6P6), and K₂[(VOHPO₄)₂(C₂O₄)] [4,5], will be presented to give a perspective of potassium insertion material design.
We have reported a reversible potassium extraction and insertion into o-KFeSO₄F, which has KTiOPO₄-type structure providing large channels for K⁺ ion diffusion. In this study, potassium insertion mechanism of KFe(III)PO₄F having the same crystal structure was examined and compared with that of o-KFe(II)SO₄F. KFe(III)PO₄F exhibited reversible potassium insertion and extraction based on the Fe³⁺/Fe²⁺ redox couple. In addition to the KTiOPO₄-type structure materials, other open-framework materials of K6V6P6 and K₂[(VOHPO₄)₂(C₂O₄)] were investigated. K6V6P6 delivered a reversible capacity of ca. 60 mAh g^-1 with a plateau at 4.0 V. K₂[(VOHPO₄)₂(C₂O₄)] exhibited a large discharge capacity of >100 mAh g^-1 and excellent rate capability due to the facile migration of K⁺ ions in the framework. From these results, we will present our future insight into electrochemical potassium insertion chemistry for battery applications.

References
[1] S. Komaba et al., Electrochem. Commun., 60, 172 (2015).
[2] T. Hosaka, S. Komaba et al., Chem. Rev., 120, 6358 (2020).
[3] X. Bie, K. Kubota, S. Komaba et al., J. Mater. Chem. A, 5, 4325 (2017).
[4] T. Hosaka, T. Shimamura, S. Komaba et al., Chem. Rec., 19, 735 (2019).
[5] A. S. Hameed, S. Komaba et al., Adv. Energy Mater, 1902528 (2019).

Rechargeable lithium-ion batteries with high energy density that can be safely charged and discharged at high rates are desired for electrified transportation and other applications. In this talk, I will report the discovery of a disordered rocksalt (DRS) Li3V2O5 anode with near-optimal intercalation potentials for safe, fast-charging batteries. In particular, we will demonstrate that the outstanding electrochemical performance of these DRS electrodes can be attributed to a hitherto undiscovered redistributive lithium intercalation reaction with low energy barriers. Beyond the immediate practical applications, the discovery of this novel high-rate intercalation reaction opens a completely new space for the search of metal oxide electrodes for fast-charging, long-life lithium-ion batteries. Further, I will discuss a statistical analysis of the ultimate limits of intercalation into DRS type materials.

Two-dimensional transition-metal carbide MXenes has been known as a promising material of high-performance electrode for energy storage applications with both non-aqueous and aqueous electrolytes because it has electronic conductivity, ion capability in interlayer nanospace, and the redox activity of Ti. Especially, as an electrode of electrochemical capacitors, MXenes have a unique dependence of capacitance on intercalated cation species and a distinctive behavior that is both capacitive and pseudocapacitive depending on the electrolyte. To better understand electrochemical mechanism of these behaviors, we performed a microscopic theoretical analysis of the electric-double layer (EDL) in the interlayer nanospace of the MXene electrode by combining first-principles calculations based on density functional theory (DFT) and classical implicit solvation theory named three dimensional reference-site interaction model (3D-RISM) method [1]. By using the quantum-classical hybrid simulation, solvation effect at the interlayer nanospace of MXene electrode was taken into consideration appropriately with low computational cost comparable with conventional DFT simulation.

For the unique dependence of capacitance on intercalated cation species, our simulation results showed that the capacitance of EDL capacitors can be enhanced by a factor of 1.8, when the water molecules are strongly confined into the two-dimensional nanoslits of titanium carbide MXene electrode. This is because that dipolar polarization of strongly confined water overscreens an external electric field applied on the EDL and enhances capacitance with a characteristically negative dielectric constant of a water molecule [2, 3].

Another investigated feature is the distinctive behavior that is both capacitive and pseudocapacitive depending on the electrolyte. As a result of their electronic states simulated via the quantum-classical hybrid simulation, it was found that the hydration shell of intercalated ions prevents orbital coupling between MXene and the intercalated ions, which leads to the formation of an EDL and capacitive behavior. However, once the cations are partially dehydrated and adsorbed onto the MXene surface directly, because of orbital coupling of the cation states with the MXene states, particularly for surface-termination groups, charge transfer occurs and results in a pseudocapacitive behavior [4].

Research on niobium pentoxide (Nb₂O₅)-based electrodes for electrochemical energy storage devices is gaining traction because of its ability to store charge at high rates despite its wide bandgap and low electronic conductivity—a phenomenon not observed in other widely studied transition metal oxides electrode materials. Crystalline form of Nb₂O₅— orthorhombic and pseudohexagonal phases— also presents superior electrochemical stability and rapid ion transport of alkali-metal ions throughout the a–b plane. This work investigated the effect of different crystalline structures of Nb₂O₅ in micro/nano fibermat geometry as working electrode in sodium half-cells. The micro/nano fibermat geometry promoted Na-ion de/intercalation reactions combined with capacitive reactions. Results show that these materials present excellent cycling stability and specific capacity within 0 to 2.25 V potential window. Orthorhombic Nb₂O₅ outperform amorphous Nb₂O₅ and many other traditional high capacity metal oxide-based electrodes such as birnessite such as MnO₂ and RuO₂.

Currently, pure electric vehicles (EV) are produced from many car makers. And it is becoming more popular with the public. However, an additional increase of driving range with long life and high safety is necessary to make EV popularized completely. Also, aviation service such as air-taxi will be commercialized soon. Therefore, the application of new materials such as Si and Li-metal anode is essential to increase energy density dramatically at this moment. And proper electrode engineering has brought Si-based anode materials closer to commercialization from consumer applications. However, Si technology has not yet been significantly commercialized due to a number of shortcomings. In particular, cycle life and irreversible capacity losses due to side reactions continue to be issues that plague their widespread use. Thus, the addition of only thimbleful silicon is possible right now for practical batteries, and it is difficult for the dramatic increase of energy density of batteries.
In this presentation, we can check the current status of approaches for commercialization of Si anode based batteries. Also, newly developed advanced architecture with offering higher battery capacity and faster rate performance, all while being produced via a low-cost solution chemistry-based manufacturing process will be introduced. This scalable manufacturing procedures of silicon-based anode can lead to significantly improved performance of next-generation batteries, which have high energy density, long-term cycling stability, and fast charging ability.
In the case of Li-metal, the electrode structure is going to be porous rapidly and the growth of Li dendrite is going to be generated rapidly. And those lead short cycle life performance, low safety and poor reliability. Thus, Li-metal anode is not possible to be applied to EV, and it is tested for the application of drones that have low requirement for life and safety.
In this presentation, we are going to introduce hybrid Li-metal battery, having high energy density (-800 Wh/L, -360 Wh/kg), high safety and long cycle life performance, which is applicable to practical EV. We applied hybrid Li-metal anode technologies and additional support from safe materials to retard thermal runaway.

Advanced (scanning) transmission electron microscopy ((S)TEM) techniques have been intensively applied to study the reaction kinetics of electrode materials for secondary ion batteries. With/Combining different TEM techniques, including in-situ TEM and diffraction, HAADF-STEM, and STEM-electron energy-loss spectroscopy, researchers are able to probe local structural and chemical information of electrode materials at atomic resolution. This talk will focus on using in-situ and analytical TEM to characterize the oxide electrode material for lithium ion batteries. After reviewing the recent advances of in-situ TEM investigations on both anode and cathode, we will discuss the dynamical study on the phase evolution, strain effect and passivation layer of conversion-type Fe₃O₄, aiming to understand how reaction pathways affect the batteries performances [1-3]. In addition, this talk will present our investigations on effects of defects on capacity fade of Ni-rich Li(Ni, Mn, Co)O₂ cathode [4].
References:
[1] He K. et al., Visualizing non-equilibrium lithiation of spinel oxide via in situ transmission electron microscopy, Nature Communications, 7,11441 (2016)
[2] Hwang S. et al., Strain coupling of conversion-type Fe3O4 thin film for lithium ion battery, Angewandte Chemie, 56,7813, (2017)
[3] Li J. et al. Phase evolution of conversion-type electrode for lithium ion batteries, Nature Communications, 10,2224 (2019)
[4] Li S. et al., Angewandte Chemie International Edition, (2020) https://doi.org/10.1002/anie.202008144

Low temperature (< -20 °C) operation of conventional Li-based secondary batteries is severely hindered by increased cell polarization, which can be attributed mainly to the low ionic conductivity of electrolytes and sluggish solid-state diffusion in graphite. Additionally, charging of graphite-based Li-ion batteries under low-temperature conditions can cause undesirable Li plating; thus, there is a substantial need for next-generation anodes that can operate over a wide temperature range. In this regard, the Li metal anode has previously shown some promise for ultra-low temperature operation; however, it generally exhibits limited cycling capability and low Coulombic efficiency. Here, we develop advanced electrolyte formulations (which consist of dual salts and/or dual solvents) and show that these formulations can substantially improve the Coulombic efficiency (CE) of both Li and Na metal anodes down to -60 °C.^1-2 For example, we show that pure ether based electrolytes exhibit CE < 50 % for Li cycling at -40 °C, but using FEC additives increases CE to over 90 %. The origins for this improved performance are primarily due to beneficial alterations of the solid-electrolyte interphase (SEI) at low temperatures when these additives are used. We perform cryo-transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy to link SEI chemistry and structure as a function of temperature to cycling performance. Furthermore, we investigate the solvation structure of Li⁺ and Na⁺ in the electrolyte and relate solvation structure to SEI formation. Our results provide important guidance for designing electrolytes and interfaces for efficient operation of high-energy batteries at low temperatures.

References
1. Thenuwara, A. C.; Shetty, P. P.; Kondekar, N.; Sandoval, S. E.; Cavallaro, K.; May, R.; Yang, C.-T.; Marbella, L. E.; Qi, Y.; McDowell, M. T., Efficient Low-Temperature Cycling of Lithium Metal Anodes by Tailoring the Solid-Electrolyte Interphase. ACS Energy Letters 2020, 5 (7), 2411-2420.
2. Thenuwara, A. C.; Shetty, P. P.; McDowell, M. T., Distinct Nanoscale Interphases and Morphology of Lithium Metal Electrodes Operating at Low Temperatures. Nano Letters 2019, 19 (12), 8664-8672.

High-valent redox at the positive electrodes are required to achieve high-energy density in intercalation lithium and sodium-ion batteries. Yet, high-valent redox is usually accompanied by strong structural irreversibility and hysteresis. In this talk, I will present a unified understanding of high valent redox that integrates redox chemistry with point defect chemistry and coulombic interaction. I will draw examples from lithium-ion electrode chemistries based on 3d, 4d and 5d transition metals.

Many layered Li and Na cathode materials deliver additional capacity via lattice oxygen redox reactions. However, its origin is under debate. The irreversibility and hysteresis of lattice oxygen redox limit its practical applications. With combined magnetic resonance spectroscopy and computational studies, we have discovered that layered structures with stacking faults can afford additional removal of lithium accompanied by lattice oxygen redox. The insights gained in this work may inspire materials design which employs structural disorder for achieving high-capacity stable cathode materials.

The discovery of anionic redox chemistry in layered compounds was traced back to ligand-hole chemistry in chalcogenides, in which the redox of S₂^2-, Se₂^2- or Te₂^2- ions in layered structures might be involved. In recent years, investigation of oxygen redox chemistry in cathode materials has attracted a lot of attention based on the potential to increase the energy density of Li-ion batteries. The reversible oxygen redox reactions in layered cathode materials such as Li-rich NMC and Li₂Ru_0.5Mn_0.5O₃ are considered to be responsible for their extraordinary specific capacity. Similarly, the reversible sulfur redox reaction in layered chalcogenides is considered a promising approach to increase the specific capacities in sodium-ion batteries. However, only a limited number of studies on the nature of anionic redox chemistry in layered chalcogenides have been reported in the literature. Issues about whether the redox mechanism is based on reversible formation/decomposition of S-S dimers or formation of electron holes on S are still under debate. We have designed and synthesized a series of layered cathode materials such as NaCrS₂, Ti substituted NaCrS₂ and Se substituted NaCrS₂ for a systematic investigation about the nature of anionic redox chemistry of sulfur, including the formation of localized electron holes, anionic dimers, and disulfide-like species during the charging process. The charge compensation mechanisms and structural evolution of these cathode materials have been investigated using synchrotron-based multi-model characterization techniques such as in situ/ex situ x-ray absorption spectroscopy, x-ray diffraction, x-ray pair distribution function analysis as well as spatially resolved x-ray fluorescence mapping combined with DFT calculation. These results provided valuable information for the development of high energy cathode materials based on the anionic redox reaction for sodium batteries.

Acknowledgment
The work at Brookhaven National Laboratory was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technology Office of the U.S. Department of Energy through the Advanced Battery Materials Research (BMR) Program under contract DE-SC0012704. This research used resources at beamlines 7-BM (QAS), 8-BM (TES) of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704.

Harnessing electrochemical activity exceeding the limit of conventional transition metal redox, observed in Li-excess and Na-excess cathodes, is one of the most promising routes towards dramatically increasing the energy density of battery materials. However, the majority of materials exhibiting such anomalous capacity suffer from substantial voltage hysteresis and structural degradation. Two prominent exceptions are Na₂Mn₃O₇ and Li₂IrO₃, which are model systems for non-hysteretic redox beyond the transition metal limit. Nonetheless, the mechanism of their redox behavior and stability to structural transformation remains controversial, with significant inconsistencies between experimental observations and the "O-redox" theories proposed as explanations of their behavior. We derive the first redox mechanism to consistently explain all experimental observations in Na₂Mn₃O₇ and Li₂IrO₃, based on the oxidation of a delocalized, π-bonded network of metal-d and oxygen-p orbitals. This mechanism, which we term π-redox, leads to a unique behavior wherein the oxidation potential, capacity and structural evolution is dictated by the long-range structure of the π-network rather than local bonding environments. We show that π-redox competes with oxidation-driven transition metal migration, which is dominant in layered Li-excess materials based on Li₂MnO₃ but may be suppressed in layered Na-ion cathodes. The π-redox mechanism establishes the first rigorous framework for engineering non-hysteretic redox beyond the limit of transition metal capacity, which is particularly promising in layered Na-ion materials.

Conventional positive electrode materials for Li-ion batteries utilize a Li⁺ intercalation mechanism charge-balanced by redox on transition metals within an oxide host lattice. Moving forward, multielectron cathodes that exhibit contributions to the redox from structural anions are of interest for the potential to dramatically increase charge storage capacity. Oxidation of Li-rich oxides can achieve >1 electron oxidation per transition metal, but, due to the high-voltage redox, electrolyte degradation and other unwanted side reactions can convolute interpretation of the electrochemistry. Later group chalcogenides, however, operate within the potential window of the electrolyte preventing complications associated with electrolyte decomposition. Capacity beyond that compensated by a one-electron oxidation on a transition metal is often attributed to anion oxidation enabled by covalent interactions with the metal. Here, we report anion redox in a solid solution, Li₂FeS_2-ySe_y, where the metal-anion covalency is tuned through systematic substitution of the anion to further understand the role of covalency on reversible anion redox. Multielectron redox is observed in all materials in the solid solution along with a systematic shift of the high-voltage plateau associated with anion oxidation. Spectroscopic studies indicate concomitant Fe and S/Se oxidation throughout charging contrary to the discrete Fe and S redox observed in Li₂FeS₂. Perselenide bonds are found to form in Li₂FeSe₂ accompanied by the irreversible formation of a new, high-impedance phase, which leads to poor cyclability. Therefore, while tuning metal-chalcogenide covalency provides a handle to control anion redox, the structural changes incurred through anion-anion bonding can be deleterious to material performance. As such, developing holistic understanding of the electronic and structural response to anion redox is necessary to design next-generation multielectron energy storage materials.

Due to their exceptional high energy density, lithium-ion batteries are of central importance in many modern electrical devices. A serious limitation, however, is the slow charging rate used to obtain the full capacity. Thus far, there have been no ways to increase the charging rate without losses in energy density and electrochemical performance. Here we show that the charging rate of a cathode can be dramatically increased via interaction with white light. We find that a direct exposure of light to an operating LiMn₂O₄ 3-D intercalation cathode during charging leads to a remarkable lowering of the battery charging time by a factor of two or more. This enhancement is enabled by the induction of a microsecond long-lived charge separated state, consisting of Mn⁴⁺ (hole) plus electron. This results in more oxidized metal centers and ejected lithium ions are created under light and with voltage bias. We anticipate that this discovery could pave the way to the development of new fast recharging battery technologies.

For energy storage, nowadays, Li-ion and Na-ion batteries are major technologies for mobility applications and also for large-scale storage of energy and their integration in the grid. In the scope of finding new positive electrode materials with improved performances, the deep understanding of the link between their structure, electronic structure and electrochemical behavior is crucial. To that extent, Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) appeared to be a key tool, as for paramagnetic materials, it allows to probe both, the local structure and the local electronic structure thanks to the hyperfine interaction.
Using MAS-NMR we showed that several phosphate materials as Na₃V₂(PO₄)₂F₃, which is a promising materials for positive electrode application Na-ion batteries exhibit some O-defects leading to the formation of V⁴⁺ ions locally. These V⁴⁺ ions are forming a vanadyl-type bond with the defect O, and affect the electrochemical cycling performances. ²³Na, ³¹P MAS (and ¹⁹F) NMR was also used to probe the local structure and electronic structure of the solid solution series Na₃V₂(PO₄)₂F_3-yO_y and other Na₃(V,M)₂(PO₄)₂F_3-yO_y materials with M = Fe or Al. These studies combined with DFT calculations lead to a better understanding of the local arrangement and the local electronic structure.
Layered Na_xMO₂ oxides are also interesting for application in Na-ion batteries. Among them, P2-Na_xCoO₂ appears to be a model material with a very specific phase diagram and unusual physical properties. ²³Na MAS NMR was used to characterize the changes in the electronic structure during Na deintercalation. It was shown that the position of the signal is governed by an interplay between the Fermi contact interaction due to localized electrons and the Knight interaction due to the delocalized ones. Depending on the Na content, the evolution of the ²³Na shift provides then information about the local electronic structure in the material.

Recently, an ion exchange reaction that can stabilize potassium intercalation oxides was proposed as a new approach to develop cathode materials for K-ion batteries (KIBs).^1-4 Such ion exchange method indeed has frequently used for the development of novel Li-layered oxides to attain structural features of Na layered oxides.^5-7 This ion exchange reaction has the potential to discover novel layered cathode materials by accessing the metastable states that cannot be achieved by conventional high-temperature calcination. However, the solid-state ion-exchange mechanism and the resulting phase evolution are not well understood.
In this work, we systematically investigate electrochemical Na⁺/K⁺ ion exchange in layered oxides using O3-type Na₃Ni₂SbO as a model system.⁸ We found intriguing phase transitions according to the relative Na/K content upon K intercalation by in-situ XRD: (i) coexist of K-rich and Na-rich phases during charging and discharging and (ii) phase transformation of Na-rich phase upon K intercalation. Strong electrostatic repulsion between Na and K ions that have radically different bond lengths to coordinating oxygen ions can result in this complex phase evolution. We uncovered that upon Na⁺/K⁺ ion exchange Na ions remaining in the desodiated Na_xNi₂SbO₆ phase are pushed away from the intercalating K ions, thereby separating Na-rich and K-rich phases in a particle. Interestingly, this phenomenon creates complex, three-phase equilibrium during the desodiation and potassiation processes in Na_xK_yNi₂SbO₆: phase equilibrium between one K-rich and two Na-rich phases or two K-rich and one Na-rich phase is observed, as dictated by the Gibbs phase rule. Our computational study further demonstrated that this phase separation originates from the large lattice mismatch along the c-axis between the K-rich and Na-rich phases. Our observations and interpretations demonstrate that “ion-exchanged” systems may be more complex to interpret than the previously understood. Our analysis should be applicable to other ion-exchange systems where the exchanged ions are not well miscible in the host structure.

References
[1] S. Baskar et al. ECS Transactions 2017, 80, 357.
[2] N. Naveen et al. Chem. Mater. 2018, 30, 2049.
[3] J. Y. Hwang et al. Energy Environ. Sci. 2018, 11, 2821.
[4] H. Zhang et al. Chem. Commun. 2019, 55, 7910.
[5] C, Delmas et al. Mater. Res. Bull. 1982, 17, 117.
[6] A. R. Armstrong et al. Nature 1996, 381, 499.
[7] F. Capitaine et al. Solid State Ionc. 1996, 89, 197.
[8] H. Kim et al. Chem. Mater. 2020, 32, 4312.

Ab initio modelling is a useful tool in the study of battery electrodes, able to support experimental findings and predict new phases and behaviours, providing a suitable and accurate method is used. Regular Density Functional Theory (DFT) functionals such as the commonly used PBE, however, are impacted by the ‘self-interaction error’ which severely impacts the accuracy of calculations involving the highly-correlated 3d valence electrons in transition metals (TMs).¹
Historically, the study of battery cathodes using DFT has been improved through the addition of ‘U’ parameters, which correct for the self-interaction error,² however these parameters require tuning to experimental measurements on the specific system in question, while also need to be varied during intercalation (with changes in oxidation state) and can be highly sensitive to changes in transition metal composition. This makes them unideal for the description of complex cathode systems containing multiple transition metals and valencies, weakening them as a predictive tool for new systems.
Additionally, with the increased development behind the theory of anionic redox in cathodes, accurate assessment of the charge transfer transition, which standard DFT tends to underestimate, is crucial.³ Minimally-parameterised hybrid DFT functionals such as HSE06 are routinely used to accurately predict the band gaps of semiconductors, however previous studies have highlighted disagreement between hybrid DFT and band gaps recorded from XPS-BIS for TM cathode materials, as well as overestimation of predicted intercalation voltages.^4,5
In this study, we address this issue, using a combination of HSE06 and high-level quasiparticle self-consistent GW calculations (with the inclusion of additional terms to W from the Bethe-Salpeter equation) to explore the electronic structure of sodium intercalation cathodes such as NaCoO₂ and NaFeO₂, as well as comparisons to their lithium counterparts, at the highest feasible level of ab initio theoretical methods. We demonstrate how the inclusion of additional screening terms to the on-site Coulombic interaction leads to changes in the valence electronic structure of the cathodes not seen in cheaper methods. Secondly, we examine how the inclusion of corrections for the van der Waals forces, crucial to simulation of deintercalation behaviour, varies between hybrid and standard DFT. In doing so, we hope to set out a blueprint for guiding accurate future calculations of cathodes that rely less on parameterisation, and as such demonstrate reliable predictive power.
(1) Urban, A.; Seo, D.-H.; Ceder, G. npj Comput. Mater. 2016, 2 (October 2015), 16002.
(2) Zhou, F.; Cococcioni, M.; Marianetti, C. A.; Morgan, D.; Ceder, G. Phys. Rev. B - Condens. Matter Mater. Phys. 2004, 70 (23), 235121.
(3) Ben Yahia, M.; Vergnet, J.; Saubanère, M.; Doublet, M. L. Nat. Mater. 2019, 18 (5), 496.
(4) Seo, D. H.; Urban, A.; Ceder, G. Phys. Rev. B - Condens. Matter Mater. Phys. 2015, 92 (11), 115118.
(5) Aykol, M.; Kim, S.; Wolverton, C. J. Phys. Chem. C 2015, 119 (33), 19053.

One of the major challenges of the 21st century is our ability to solve energy-related problems caused by ever-higher consumption, demography and standard of living. It is therefore imperative to anticipate this energy demand and this in a context of sustainable development. Storage technologies are highly dependent on the materials used and it is necessary to search for new materials with advanced properties that are also ecological and economical. Despite the high performance of lithium-based materials, its cost is driving scientists to develop alternative systems based on sodium and potassium, which are widely abundant in the earth's crust.

Manganese based oxide materials are promising cathodes for alkaline ion batteries due to their high energy density, low-cost and low-toxicity. Focusing on layered-type structures, one has to cite of course the A_xMnO₂ families showing interesting insertion properties in all the system based on lithium, sodium and even more recently potassium. Moreover, we notice that the system A-Mn-O are extremely rich in term of original structures. For example, we found a new lithium rich composition Li₄Mn₂O₅ with a disordered rock salt structure that was showing an exceptional capacity of about 300mAg/g. Interestingly, the material Na₄Mn₂O₅ has been reported with a layered type structure, different from the lithiated phase and we will discuss the relationship between the structure and insertion properties. Also, we have reported the electrochemical properties of the phase Na₂Mn₃O₇ with a lamellar structure built of [Mn₃O₇]^2-_∞ anionic layers hold by sodium ions; a reversible discharge capacity of 160 mAh/g at 2.1V vs Na⁺/Na through a biphasic process is observed.

In recent years, we can see a growing interest of researchers for K-ion batteries (KIBs). Thus, many compounds have been studied belonging to families already studied for Li-ion and Na-ion batteries (LIBs and NIBs, respectively). So far, only lamellar phases K_xMnO₂ are reported. We will discuss on the possibility to explore and find other composition for this application.

In this presentation, we will discuss and compare the three system Li-Mn-O, Na-Mn-O and K-Mn-O in term of structure and properties towards the insertion of alkaline ions.

State-of-the-art synthesis for layered oxide cathodes for Na ion batteries involves prolonged high temperature (>700^oC) processing for long reaction times (~24 hours) under high oxygen pressure, followed by slurry casting after mixing with binders and additives. Here, we introduce, an intermediate temperature (350^oC), dry molten sodium hydroxide mediated electrodeposition process to grow air and moisture sensitive layered sodium transition metal oxides, Na_xMO₂ (M=Co, Mn, Ni, Fe) as binder-and-additive-free cathode materials for Na ion battery. Despite being synthesized at the lowest reported synthesis temperature and reaction times, our electrodeposited oxide cathodes retain the key structural and electrochemical performance observed in the high temperature bulk synthesized analogues. We demonstrate that tens of microns thick, >80% dense Na_xCoO₂ and Na_xMnO₂ can be deposited at a growth rate of ~5-20 mg/cm²/hr, with near theoretical gravimetric capacity, rate capability and chemical diffusion coefficient of Na⁺ ions. The electrodeposited oxide cathodes can be accessed as both the thermodynamically stable O3 and metastable P2 polytypes. Growth texture, tortuosity and microstructure of the electroplated oxide cathodes are controlled by careful tuning of the deposition parameters and bath chemistry. Fast Na⁺ ion conducting 110, 101 and 104 facets can be vertically oriented, enabling electrodeposited cathodes with ultrahigh loading (30-40 mg/cm²), low tortuosity and reversible high areal capacity (3-4 mAh/cm²) while operating at high current densities (~1 mA/cm²).

Four distinguished panelists will share their vision with the audience on the topic of beyond Li-ion batteries through short presentations that are followed by a panel discussion. Next generation Li, Na, K and Zn ion batteries will be discussed in this 2 hour panel session with a particular focus on advanced cathode, anode and electrolyte concepts and designs. The audience will have the opportunity to directly interact with the panelists.

Schedule:
Introductory Remarks by Anton Van der Ven
Presentation by Stanley M. Whittingham—Li Batteries for Energy Storage to Green the Environment - Is There Another Battery Alternative?
Presentation by Shinichi Kimoba—Sodium and Potassium Chemistry for Batteries
Presentation by Christopher Johnson—Calendar Life of Si Anodes in LIBs: Time is Ticking
Presentation by Debra Rolison—The Case for Zinc
Panel Discussion
Closing Remarks by Anton Van der Ven

This session will be moderated by Anton Van der Ven and Xin Li

The lithium-sulfur (Li-S) battery is a promising next-generation rechargeable battery with high energy density. Given the outstanding capacities of sulfur (1675 mAh g^–1) and lithium metal (3861 mAh g^–1), Li-S battery theoretically delivers an ultrahigh energy density of 2567 Wh kg^–1. However, this energy density cannot be realized due to several factors, particularly the shuttling of polysulfide intermediates between the cathode and anode, which causes serious degradation of capacity and cycling stability of a Li-S battery. In this work, a simple and scalable route was employed to construct freestanding laser-scribed graphene (LSG) interlayer with nano-sized carbon particles, which effectively suppresses the polysulfide shuttling in Li-S batteries. Thus, a high specific capacity (1160 mAh g^–1) with excellent cycling stability (80.4% capacity retention after 100 cycles) has been achieved due to the unique structure of hierarchical three-dimensional pores in the freestanding LSG.

The significant attention toward developing flexible electronic devices and smart textiles have been encouraging the utilization of various flexible current collectors as well as investigating their interface effects on the device performance. Using the traditional fabrication of supercapacitors and batteries onto textile fabrics and polymeric substrates requires additional processes of conductive-layer coatings and non-conductive binder additives. In this work, binder-free flexible electrodes of nickel hydroxide are directly deposited on conductive carbon cloth (CC) using a simple and short-time synthesis assisted by microwaves. The growth of nickel hydroxide nanoflakes is observed using x-ray diffraction and scanning electron microscopy after 10 min and 30 min of the microwave heating time at a fixed temperature. All our samples are tested as supercapacitor electrodes in potassium hydroxide aqueous electrolyte at room temperature. In specific, electrochemical impedance spectroscopy is used to study the electrode/electrolyte interface in terms of ions diffusion and charge transfer resistance. The redox Faradic mechanism of energy storage is confirmed by the cyclic voltammetry and the galvanostatic charging-discharging techniques. Nickel hydroxide nanoflakes that are prepared in 30 min show a conformal coating on all substrate microfibers and a consequently larger electrochemical active area which results in higher capacitance than the electrodes prepared in 10 min. Such optimization in the design and fabrication of binder-free electrodes and current collectors could improve the flexibility of electronic devices and promote their implantation into functional textile applications.

High voltage dual-ion batteries (DIBs) have been reported using a water-in-bisalt electrolyte, metal halides, and graphite electrodes but the full cell energy density is lower than commercialized batteries. Replacing graphite with heteroatom substituted graphite lamellar structures like BC₃, B₃C₁₀N₃ can improve the performance of the dual ion battery. Heteroatom substituted graphite materials have been studied for metal ion intercalation in anodes and show similar electronic conductivity as graphite but remain unexplored for the halogen intercalation process. Halogen intercalation process in cathode host is of significant importance because it is directly related to the capacity and cycling of the battery. Halogen intercalation in graphite has been explored using diffraction and isothermal based studies but a rigorous thermodynamic and kinetic investigation is still missing. From a thermodynamic standpoint, only one study has reported the existence of chlorine intercalated graphite structure but a range of bromine intercalated graphite structures have been reported although there is no consensus about the staging process or the composition of bromine in graphite layers at every stage. Hence, a computation model to understand the halogen intercalation processes in graphite structures is needed to resolve the inconsistencies that can be used to study heteroatom substituted graphite structures. Through this model, our aim is to predict materials that can replace graphite as host structures in dual ion batteries to achieve high energy densities and longer cyclability.

In this paper, we aim to find answers to fundamental questions about the thermodynamics and kinetics of bromine and chlorine intercalated graphite structures: a.) Develop a convex energy hull diagram for bromine-intercalated structures and study the staging at every composition from the most stable structure, b.) Find, if any, thermodynamic stable chlorine-intercalated graphite structures, c.) Develop a convex energy hull diagram for bromine and chlorine co-intercalated structures and study the staging at every composition from the most stable structure, d.) Kinetic investigation of halogen diffusion in graphite using adaptive kinetic Monte Carlo techniques. All the calculations in this work have been performed using Density Functional Theory (DFT) methods in Vienna ab-initio Simulation Package (VASP). For all the structures modeled in this work, we will model structural properties using Raman Spectrum, Extended X-Ray Fine Spectrum, X-Ray Diffraction, and Pair distribution functions that are directly accessible via experiments as well. This will help us guide experiments towards an informed choice of cathode hosts for dual ion batteries using water in the salt electrolytes from our computational results.

With the extensive research of intercalation in layered materials beginning in 1841, these compounds have since found use in battery, optoelectronics, and biomedical wearable devices (Inorg. Chem. Front. 2016, 3, 452; Adv. Mater. 2019, 1808213). With essentially limitless possibilities of intercalation compounds due to combinations of different host lattices and guest species (e.g. donor, acceptor, and neutral compounds), intercalation chemistry creates the unique opportunity to engineer and design future compounds for specific applications such as electrodes. However, this is only feasible if structure-property relationships of intercalated materials are extracted. Due to the large quantity of data on intercalation compounds, machine learning (ML) is an ideal approach (J. Phys. Mater. 2019, 2 032001). Previous ML studies of graphite intercalated compounds have often been limited in scope to alkali metal guests (J. Mater. Chem. A 2019, 7, 19070-19080; ACS Appl. Mater. Interfaces 2019, 11(20), 18494–18503). Here, we employ ML and deep-learning (DL) to elucidate structure-property relationships in bulk graphite intercalation compounds with donor, acceptor, and neutral guests. Furthermore, we explore the application of these structure-property relationships to single and few-layered intercalation compounds where surface adsorption and intercalation of these ultra-thin materials can play significant roles in resulting properties of the intercalation compound as the 2D limit is approached.

We studied tellurium containing oxide Li₂Ni₂TeO₆ using x-ray diffraction, magnetic measurements, and neutron powder diffraction. Li₂Ni₂TeO₆ crystallizes in the orthorhombic crystal structure having Fddd space group. The magnetic susceptibility measurements performed at Ha = 1 kOe exhibits an upturn below ~80 K and maintains its constant value up to lower temperatures. The magnetic hysteresis is seen at lower temperatures below 80 K indicating the development of a ferromagnetic component that get disappears above 80 K revealing a ferromagnetic transition at ~80 K. Both ferromagnetic and antiferromagnetic peaks are revealed in neutron powder diffraction patterns below 80 K.

As the most promising energy storage system (ESS), rechargeable alkali metal-ion batteries have been attracting great attention. The selection of suitable electrode material is a fundamental step in the development of metal-ion batteries to achieve enhanced performance. In the present study, we have explored the feasibility of monolayers of phosphorene analogs, namely, group IV monochalcogenides. The monochalcogenide layers form structures belonging to the same orthorhombic crystal system and possess similar hinge-like structures like phosphorene. Just this unique hinge-like structure and the isolation of 2D forms will introduce strong anisotropic properties endowing them with fascinating properties, such as tunable bandgaps, high carrier mobility, and predominantly anisotropic and optical properties. We present two-dimensional (2D) sheets of germanium and tin sulfides and tellurides as promising high-capacity and stable materials for energy storage. GeS, GeTe, SnS, and SnTe with layered structures are prepared via a simple liquid-phase exfoliation approach. As-synthesized 2D nanosheets can effectively increase the electrolyte-electrode interface area and facilitate metal ion transport. As a result, GeS, GeTe, SnS, and SnTe nanosheets deliver a high areal capacity of 1.76 mAh cm^-2,1.05 mAh cm^-2, 2.66 mAh cm^-2, 1.22 mAh cm^-2 respectively as anodes in lithium-ion batteries (LIBs). Further analysis of these monochalcogenides in sodium-ion batteries (SIBs) and potassium-ion batteries (KIBs) suggest that layered monochalcogenides can be potential anodes in other metal-ion batteries.

Lithium-ion rechargeable batteries have been widely used as a power source for portable devices and are available for applications to electric vehicles, which demand high power, high energy, inexpensive and safe batteries[1]. Their continuous improvement is tightly bound to the understanding of lithium (de)intercalation phenomena in electrode materials. Here we address for the first time the use of Raman spectroscopy to understand the mechanisms involved in high voltage spinels LiNi_xMn_2-xO₄ (x = 0; x = 0.5).

Although the “classical” lithium-containing spinel LiMn₂O₄ (LMO) has been extensively studied, certain points remain unclear. For instance, very little is known on the nature of the intermediate composition Li_0.5Mn₂O₄ postulated halfway during charge/discharge for which attempts to model a lithium/vacancy ordering have been made. On the other hand, compositions within the solid solution LiNi_xMn_2-xO₄ (0 < x ≤ 0.5) are of interest as they exhibit increasing voltage upon lithium extraction. The best compromise is found for LiNi_0.5Mn_1.5O₄ (LNMO): with a high specific capacity of 140 mAh g^-1 available along a wide potential plateau at ≈ 4.7 V vs Li⁺/Li, LNMO is widely studied as a next-generation positive electrode material for Li-ion batteries. LNMO exists as two polymorphs, “disordered” (Fd-3m) where Mn/Ni occupy 16d sites randomly and “ordered” (P4₃32) where Ni and Mn sit on ordered 4a and 12d sites. So far, the disordered form has outperformed the ordered form from an electrochemical point of view [2]. The delithiation/lithiation mechanism of disordered LNMO has been previously investigated using mainly X-ray and neutron diffraction and in situ synchrotron. Although these methods provide a picture of the phase evolution during cycling, we still lack information about the atomic level variations as lithium ions deintercalate/intercalate in the crystal structure of LNMO. Raman spectroscopy on the other hand is a very appropriate tool to enrich the knowledge of the structure of Li intercalation compounds at the scale of the chemical bond. A wealth of structural information including symmetry changes, local disorder, changes in bond lengths, emergence of secondary phases, etc… can be extracted from the Raman study of various Li intercalated host lattices, providing therefore a better insight into the mechanisms governing the electrode performances [3].

In this work, Raman spectroscopy (RS) is used to explore the short-range environment in LMO and LNMO. We provide here for the first time a complete assignment of the LMO and LMNO Raman fingerprint as well as a detailed qualitative and quantitative picture of structural and vibrational changes during the charge-discharge of these cathode materials. A careful RS investigation led on the LMO cathode during the first charge process provides the first detailed experimental evidence of an ordering scheme at the scale of the chemical bond of the intermediate composition Li_0.5Mn₂O₄. A combined approach using XRD and RS allows picturing changes in LNMO crystal structure and in the oxidation states of the nickel during stages of the charge-discharge process. Raman spectra collected between 3.5 and 4.9 V display rich and varying features. Appropriate analysis based upon Raman spectra fittings allow access to a quantitative estimation of the different Ni²⁺, Ni³⁺ and Ni⁴⁺ redox species in the LNMO spinel oxide at different oxidation-reduction states. This makes RS a powerful probe to evaluate the state of charge of the cathode material. Finally, we demonstrate the great efficiency of RS as an efficient and simple diagnostic tool of the self-discharge phenomenon occurring in the LNMO electrode.

References
[1] J. M. Tarascon, M. Armand, Nature 414 (2001) 359.
[2] A. Manthiram, K. Chemelewski, E. S. Lee, Energy Environ. Sci. 7 (2014) 1339.
[3] R. Baddour-Hadjean, J. P. Pereira-Ramos, Chem. Rev. (2010) 110, 1278.

Vanadium dioxide-based materials have promising structural, electrical, and chemical properties that promote it as an essential component in electronics, energy conversion, and storage devices such as supercapacitors. One of the main challenges that may limit the implementation of vanadium dioxides in large-area applications is the vacuum-based synthesis processes such as chemical vapor deposition. In addition, the high-cost and complication of the conventional fabrication of supercapacitor electrodes are considered as other challenges. In this research, our high-quality vanadium dioxide-based ink is synthesized using a solution process [1]. Then, the ink is monolithically printed on flexible substrates. The printing technique is straightforward, scalable, and cost-effective. The electrochemical impedance spectroscopy was used to measure the resistance of the printed supercapacitors, while the cyclic voltammetry was conducted to confirm the energy storage mechanism of our materials. The areal electrode capacitances are calculated from the galvanostatic charging-discharging experiment to be in the range of 650-200 µF/cm² at areal currents of 10-80 µA/cm². Interestingly, the effects of the material properties on the device performance are investigated and deeply correlated to explain the results. Such innovative printed supercapacitors would attract attention as energy storage components that can be fully integrated into systems of flexible electronic devices, the Internet of Things, and smart textiles.

[1] Weiwei Li, Mohammad Vaseem, Shuai Yang, and Atif Shamim, Flexible and reconfigurable radio frequency electronics realized by high-throughput screen printing of vanadium dioxide switches. Nature-Microsystems and Nanoengineering 6, 77 (2020). https://doi.org/10.1038/s41378-020-00194-2.