Symposium EN02—Solid-State Batteries—Electrodes, Electrolytes and Interphases

The main challenge that hinders the use of lithium (Li)-ion batteries in space applications is their low performance at low temperatures from -30 to 20 °C. Such low performance is mostly due to the low ionic conductivity and freezing of the non-solid electrolyte leading to a significant loss in the battery’s capacity. In this research, the behavior of Li-ion batteries is investigated by employing electrochemical characterization techniques to study their performance at low temperatures. The findings of this research indicate that the capacity of Li-ion batteries is decreased greatly at subzero temperature. Cyclic voltammetry profiles show that the peak separation increases with decreasing the temperature while the current decreases. The charge transfer resistance increases due to the freezing of the non-solid electrolyte, which leads to unstable Solid Electrolyte Interphase (SEI) film formation and weak permeation of electrolyte into the active material. The capacity decreases due to a significant decrease in the diffusivity of lithium ions and substantially increased charge-transfer resistance. The cell retains nearly 50% of its room-temperature capacity at 0 °C. This can be ascribed to the low diffusivity of lithium ions which affects the interface stability between the cathode and the electrolyte. Material characterization methods such as x-ray photoelectron spectroscopy (XPS) and X-ray diffractions (XRD) are used to examine the change in the material of the electrodes and the electrolyte to determine the reasons behind the performance degradation. This study contributes to the development of Li-ion batteries for low temperature and space applications by understanding the electrochemical behavior of Li-ion batteries.

The solid-state lithium metal battery (SSLMB) has been considered as a promising candidate for safe high-energy-density storage systems as it can deliver superior safety, cycling life, energy density and cell design. Despite considerable advantages, the advance of SSLMB-technology is still hindered by a highly resistive and unstable interface between the Li-metal anode and the solid electrolyte leading to decreased practical capacity and continuous side reactions [1, 2].

To achieve good interface compatibility between the solid electrolyte and Li anode, interlayers have been proposed to stabilize the interface through improved physical contact between the solid electrolyte and Li anode and increased chemical/electrochemical stability. During the past decades several years, several strategies have been considered which can be summarized as top-down approaches (magnetron sputtering, spark plasma sintering, electron-beam evaporation, pulsed laser deposition, solvent casting, spin coating), and bottom-up approaches (sol–gel derived synthesis, atomic layer deposition, chemical vapor deposition, electrochemical-assisted synthesis)[3-5]. However, most of those strategies are not capable of building an interface that can fulfil the demands of high conductivity, good physical contact, and chemical stability at the same time.

In this contribution we demonstrate an approach, based on a tailored multifunctional interlayer between the NASICON solid electrolyte (Li_1.5Al_0.5Ge_1.5(PO₄)₃, LAGP) and Li anode, that successfully addresses the interfacial issues[6]. This interlayer is designed by creating a quasi-solid-state paste in which the functionalities of LAGP nanoparticles and an ionic liquid electrolyte (IL) are combined. In the solid-sate cell, the LAGP-IL interlayer separates the Li metal from bulk LAGP electrolyte and creates a chemically stable interface with low resistance (~5 Ohm cm²) and efficiently prevents thermal runaway at elevated temperatures (300 ^oC). We show that solid-state cells designed with this interlayer can operate at high current densities, 2 mA cm^-2 (an order of magnitude higher than that previously reported) and deliver high energy density, high-rate capability, and increased safety. The same strategy can also be applied to the SSLMB based on other classes of solid electrolytes for future energy storage technologies to meet the demand of high energy density.

Reference
[1] J. Janek, W. G. Zeier, Nat. Energy 2016, 1, 16141.
[2] Y. Xiao, Y. Wang, S.-H. Bo, J. C. Kim, L. J. Miara, G. Ceder, Nat. Rev. Mater. 2019, 5, 105.
[3] S. Lobe, A. Bauer, S. Uhlenbruck, D. Fattakhova-Rohlfing, Adv. Sci. 2021, n/a, 2002044.
[4] A. Banerjee, X. Wang, C. Fang, E. A. Wu, Y. S. Meng, Chem. Rev. 2020, 120, 6878.
[5] Q. Liu, Y. Liu, X. Jiao, Z. Song, M. Sadd, X. Xu, A. Matic, S. Xiong, J. Song, Energy Storage Mater. 2019, 23, 105.
[6] S. Xiong, Y. Liu, P. Jankowski, Q. Liu, F. Nitze, K. Xie, J. Song, A. Matic, Adv. Funct. Mater. 2020, 30, 2001444.

The electrical double layer (EDL) is a key feature of all electrochemical interfaces, controlling the kinetics and thermodynamics of both electron transfer and ion transfer reactions, and therefore the performance of solid-state batteries (SSB). Unlike in a liquid electrolyte with an EDL made of solvated ions, the EDL in a solid electrolyte is made up of charged point defects. Thus, the well-known Poisson-Boltzmann equation at electrode/liquid-electrolyte interfaces no longer holds in SSBs. This problem is even more challenging, as ion insertion and/or reaction with the electrode alters the material and thus band alignments at the electrode/solid-electrolyte interfaces.
In this talk, a density functional theory (DFT)-informed theoretical framework was established to predict the interface potential profiles. We first assumed the electrochemical potential for Li⁺ ions reached a constant at the open circuit equilibrium condition, then derived the relationship among the electrostatic potential, the lithium chemical potential, Fermi level, ionization potential, and the work function. This relationship yielded quantitative profiles of the electrostatic potential and electronic energy level alignments across the entire solid-state batteries. It was predicted the electrostatic potential inside the solid electrolyte can be either flat or sloped due to the point defect chemistry in the different solid electrolyte materials. The electrostatic potential jump at the electrode/electrolyte interface creates intrinsic barriers for Li⁺ transport across the interface. The model prediction over a range of solid-state battery systems can be used to explain multiple experimental impedance observations at solid-electrolyte/cathode interfaces. To obtain the electrostatic potential variation as a function of the distance to the interface, a more general model for the EDL at a solid-state electrochemical interface based on the Poisson-Fermi-Dirac equation was developed. The EDL structure is presented in various materials that are thermodynamically stable in contact with a lithium metal anode. The model further allows designing the optimum interlayer thicknesses to stabilize the interface without introducing additional electrostatic barriers for lithium ion transport at relevant solid-state battery interfaces.

Cracks and Fracture in solid state electrolytes such as LLZO enables Li dendrites to penetrate in the form of dendrites. These dendrites pierce through the solid-state electrolyte and eventually cause an electrical short between the anode and the cathode. One method to slow down this process is to increase the fracture resistance of the glass / ceramic type solid electrolyte via ion exchange, where, for example, large iso-valent cation exchanges with a primary cation in the glass thus increasing the residual compressive stress, and hence increasing its toughness. This technique is used commercially, for example, to make crack-resistant glass for cell phones (Gorilla Glass) where Na+ ions in the glass are exchanged with larger iso-valent K+ ions. In this work we use quantum calculations combined with molecular dynamics modelling to explore the residual stress situation for the case when Li+ ions are exchanged with the larger K+ ions in LLZO. Increasing the fraction of Li+ ions exchanged increases the residual compressive stress. Unfortunately, if too many Li+ are exchanged, the Li+ conductivity is reduced. Another concern is the diffusion of K should be negligible compared to Li, thus ensuring that the compressive zone remains stable. We explore how to optimize these tradeoffs in order to make a solid-state electrolyte that has both high resistance to fracture and high Li+ ion conductivity.

The Li metal is a good candidate for the anode in the solid-state batteries due to its high specific capacity (3860 mAh/g), but the Li dendrites formed due to nonuniform Li deposition usually cause short-circuiting, impeding the commercial application of the Li metal-based solid-state batteries. The non-uniform Li deposition is the result of an uneven distribution of current density on the inhomogeneous Li surface, where Li atoms tend to deposit on the surface protrusions and further promote the dendrite growth. Since the stripping process generates vacancies when removing Li, which may accumulate as voids and lead to uneven distribution of current density and dendrite growth, understanding how vacancies evolve near the Li/solid electrolyte (SE) interface is critical to help maintain a smooth Li surface during the stripping process and contribute to a uniform Li deposition in subsequent cycling.
In this work, a density functional theory (DFT) - kinetic Monte Carlo (KMC) multiscale simulation scheme is developed to simulate the Li vacancy evolution at two representative interfaces: Li/LiF (lithiophobic) and Li/Li₂O (lithiophilic). As the compressive stress is usually applied during the battery operation, the stress induced Li creep effects are considered given the low melting point of Li. Specifically, the DFT calculations are utilized to get the optimized atomic interface structure, calculate the Li vacancy formation energy and the Li forward (towards the interface) and backward (towards the bulk) hopping barriers. The KMC simulation is then used to simulate the evolution of Li vacancies near the interface by taking various Li hopping rates based on the DFT as inputs. To incorporate the creep behavior under a mechanical bias (E_p) into the hopping events, the DFT-calculated forward (backward) hopping barrier is decreased (increased) by half of E_p, which leads to a net Li flux rate corresponding to the creep strain rate imposed by the compressive stress (σ) on a given Li foil thickness (L).
It was found that at room temperature, without the creep effects, few vacancies at the Li/LiF interface migrate to the bulk Li, while at the Li/Li₂O interface, vacancies submerge into the bulk quickly. When the creep effect is considered, although vacancies at the Li/Li₂O interface more readily travel into deeper regions in the bulk Li, a large portion of vacancies at the Li/LiF interface migrate into the bulk as well. Thus, the interfacial properties (lithiophilic or lithiophobic) determine the vacancy hopping behavior with no creep effects but have weaker impacts on the vacancy evolution under compressive stress. Over the typical range of the product of L and strain rate in Li metal batteries spanning over 6 orders of magnitude, vacancies in Li/LiF can always form a uniform distribution in the Li metal and show little dependence on L×strain rate values, suggesting the importance of applying the compressive stress during Li stripping.

Solids with high lithium-ion conductivity are of great importance for the realization of solid-state batteries. So far thiophosphates have been reported to exhibit the highest lithium ionic conductivity. However, they pose several intrinsic problems such as their narrow thermodynamic window[2] and H₂S gas evolution from the oxidation of the sulfide solid electrolyte.[3] This has led to a shift of interest towards oxide superionic conductors. The discovery of novel fast Li-ion conductors within an oxide anion framework has been challenging due to the less effective screening of cation interactions by the oxygen anions.[4] Most of the work so far has been limited to the compositional and structural modification within the frameworks of the known superionic conductors such as garnet[5] or the lithium analogue of the Na-superionic conductors (NASICON).[6]

In this talk, we will discuss our recent findings on the relation between the topology of the crystal structure and fast Li-ion transport by utilizing first principles modeling based on density functional theory. We find that there are well-defined features of crystal structures that promote fast Li-ion conduction. In some cases, these crystallographic features provide a highly distorted lithium environment which reduces the barrier for Li hopping by several hundreds of meVs. Using these features we performed high-throughput ab-initio molecular dynamics on the Materials Project database to search for novel oxide superionic conductors and discover 10 novel oxide frameworks that are predicted to exhibit high ionic conductivity exceeding 0.1 mS/cm at room temperature. This study provides new insights on the structural origin of fast diffusion in oxide superionic conductors and can be applied as a general guideline to discover novel frameworks that can be designed to enable fast lithium diffusion.


References:
[1] A. Manthiram, X. Yu, S. Wang, Nat. Rev. Mater. 2:16103 (2017)
[2] W. Richards, L. Miara, Y. Wang, J. Kim, G. Ceder, Chem. Mater. 27:266-273 (2016)
[3] H. Murumatsu, A. Hayashi, T. Ohtomo, S. Hama, M. Tatsumisago, Solid State Ionics 182:116-119 (2011)
[4] S. Ong, Y. Mo, W. Richards, L. Miara, H. Lee, G. Ceder, Energ. Environ. Sci. 6:148-156 (2012)
[5] R. Murugan, V. Thangadurai, W. Weppner, Angew. Chem. Int. Ed. 46:7778-7781 (2007)
[6] H. Aono, E. Sugimoto, Y. Sadaoka, N. Imanaka, G. Adachi, Solid State Ionics 40:38-42 (1990)

One of the obstacles hindering the development of lithium-ion battery of high quality is the cycling-induced structural damage/degradation, which contributes to the capacity fade. In this work, we bring out the important role of the structural damage/degradation in the deformation analysis of active material in lithium-ion battery during charging and discharging. Following the approach in damage mechanics, we introduce a scalar state variable in thermodynamic potentials to describe the evolution of the structural damage/degradation. The scalar state variable is dependent on chemical reaction, enthalpy change, dilatation and strain energy during electrochemical cycling. A constitutive relation is developed, in which the elastic properties and the molar volume of the active material are implicit functions of the scalar state variable. Using the constitutive relation, we incorporate the lithiation-induced damage in the analysis of the lithiation-induced deflection of an electrode beam. The numerical results show the relaxation of the lithiation-bending moment induced by the lithiation-induced damage. The method developed in this work provides an approach to incorporate cycling-induced structural damage/damage in the deformation analysis of lithium-ion battery.

Solid-state batteries have attracted tremendous academic and industrial attention as the likely successor to lithium ion batteries. The key component of solid-state batteries is the solid-state electrolytes with high ionic conductivity [1] and great interfacial stability against battery electrodes [2]. While many sulfide and halide ionic conductors are reported with high conductivity, the chemical instability in the air of these materials inhibits their practical usage in batteries. Due to their stability and non-toxicity, oxides are the preferred choice for solid-electrolyte materials, but only a handful of oxide Li-ion conductors have been experimentally discovered with high conductivity.

Computational modeling based on density-functional-theory methods has been used to accurately predict the intrinsic properties of solid electrolyte materials. Such predictive power has made computational modeling a critical tool to efficiently design and discover new materials with desired properties, such as low cost, high ionic conductivity, great phase and electrochemical stability, accelerating the development of all-solid-state batteries [3].

In this talk, I will present our new discoveries in the physical and chemical design principles for solid-state electrolyte materials using computational modeling. More specifically, I will discuss crystallographic descriptors in solid-state ionic conductors which would enable fast ionic transport. I will report our recent progress in using high-throughput screening for computational design and experimental discovery of novel lithium and sodium solid-state electrolytes.

[1] Yan Wang et al., “Design principles for solid-state lithium superionic conductors,” Nat. Mater., 14, 1026-1031, (2015).
[2] Y. Xiao, Y. Wang, S.-H. Bo, J. C. Kim, L. Miara, G. Ceder, “Understanding interface stability in solid-state batteries”, Nature Review Materials, 5, 105-126 (2020).
[3] G. Ceder, S. Ong, Y. Wang, “Predictive modeling and design rules for solid electrolytes.” MRS Bulletin, 43(10), 746-751 (2018).

Amorphous sulfide electrolytes exhibit exceptionally high Li-ion conductivity near room temperature. A key concern, however, is their mechanical stability in the presence of strains in the adjacent electrode materials accompanying reversible Li storage. Detailed understanding of elastoplastic and fracture properties is lacking, mainly due to the difficulties associated with characterizing such highly moist-sensitive materials. In this talk, we will present our experimental results showing that the mechanical behavior of amorphous sulfide electrolytes is rate-dependent, i.e., they exhibit viscous characteristics when undergoing deformation. We will further demonstrate through careful instrumented indentation experiments, that the material behaves in a viscoplastic manner at short timescales of ~ 1 min. Finally, we will discuss the implications of these findings for understanding and improving the contact of the sulfide electrolytes with Li-metal anodes.

As fast-ion conductors, cluster-ion anti-perovskites (APs) are attractive for potential new mechanisms of conduction whereby cation and anion motion is highly correlated [1, 2]. Cluster-ion APs, like perovskites, have a framework that accommodates diverse atomic substitutions. Furthermore, the potential for cluster-ion substitution onto one or both anion sites (A and B in X₃AB) provides additional compositional degrees of freedom. We have synthesized and characterized a series of compositions Na_3-x(NH₂)_xO_1-x(BH₄), a unique sodium ion conductor with two chemically distinct cluster anions, in order to further understand the correlation between anion rotation and cation translation. We are particularly interested in the x = 1 composition which shows a significant positive deviation from conductivity trends as predicted by a vacancy diffusion model. This presentation will discuss the synthesis and characterization of Na₂(NH₂)(BH₄) via XRD, neutron diffraction, NMR, and AIMD, aimed at understanding the temperature dependent rotational dynamics of the cluster anions and their effects on cation transport.

This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.

References:
[1] Hong Fang and Puru Jena. Li-rich antiperovskite superionic conductors based on cluster ions. Proceedings of the National Academy of Sciences, 2017, 114, 110461.
[2] Hong Fang and Puru Jena. Sodium Superionic Conductors Based on Clusters. ACS Appl. Mater. Interfaces. 2019, 11, 963-972.

The search for fast new sodium-ion solid electrolytes remains intense to eventually realize all-solid-state sodium batteries for scalable energy storage solutions in the future. In the pursuit of extraordinary performing electrolytes, candidate materials are currently often designed from scratch while drawing on chemical intuition to improve the ionic conductivity.
For the sodium hexathiohypodiphosphate Na₄P₂S₆ a complementary strategy will be showcased, namely, how synthetic control and post-synthetic treatment impact this material's properties, even though structural differences are minute.¹ Two different synthesis methods are compared: a solid-state reaction² and a precipitation route from aqueous solution³. Combined investigations using powder X-ray diffraction (PXRD), precession electron diffraction (PED), differential scanning calorimetry (DSC), solid-state nuclear magnetic resonance spectroscopy (ssNMR), and Raman spectroscopy reveal that the solid-state synthesized material is characterized by a Na⁺ and vacancy disorder-driven enantiotropic phase transition at 160 °C (α- to β-Na₄P₂S₆), which is accompanied by a symmetry change of the P₂S₆^4– anion. Precipitated Na₄P₂S₆ already crystallizes in a β-like polymorph at room temperature, likely assisted by inter- and intralayer defects. Bond-valence and nudged elastic band (NEB) calculations are employed to identify a low energy, 2D conduction network in β-Na₄P₂S₆, suggesting facile 2D long-range Na⁺ diffusion. Electrochemical impedance spectroscopy reveals a higher ionic conductivity at room temperature in precipitated β-like Na₄P₂S₆ (2×10^–6 S cm^–1) compared to the solid-state α polymorph (7×10^–7 S cm^–1). The activation energy is around 0.4 eV for both materials.
Independent of the synthetic protocol, Na₄P₂S₆ exhibits another high-temperature polymorph (γ). A structural analysis spanning local and long-range length scales enables the elucidation of the complex structure. The anion and cation arrangement facilitates 3D superionic Na⁺ conduction, which we confirm with ab initio molecular dynamic (MD) simulations.

¹ Scholz, T.; Schneider, C.; Eger, R.; Duppel, V.; Moudrakovski, I.; Schulz, A.; Nuss, J.; Lotsch, B. V. J. Mater. Chem. A, 2021, 9, 8692–8703.
² Kuhn, A.; Eger, R.; Nuss, J.; Lotsch, B. V. Z. Anorg. Allg. Chem., 2014, 640, 689–692.
³ Fincher, T.; LeBret, G.; Cleary, D. A. J. Solid State Chem., 1998, 141, 274–281.

The substitution of liquid electrolytes with solid ionic conductors is a promising strategy for a new generation of safer batteries with higher energy densities. In terms of developing components for All Solid-State Batteries, plenty of research focused on optimization of solid electrolyte properties. Garnet materials, especially doped Li₇La₃Zr₂O₁₂ (LLZO), are considered a very promising class of solid electrolytes due to their high lithium-ion conductivity in the range of 10^–4 S/cm^1,2, as well as their compatibility with metallic lithium as anode. Recently, the combination of inorganic electrolytes with conducting polymers to form hybrid materials has also come into focus.^3,4

Scientific research mainly addresses material properties and characterization, but less manufacturing methods and cell assembly. Fraunhofer IKTS is investigating different scalable manufacturing processes for All Solid-State Batteries⁵ in several projects. We have developed a process chain for freestanding LLZO separator sheets with high ion conductivity, and we have started the processing of LLZO inks for rapid printing of electrolytes or as conductive additives. This talk will give an overview about the material’s synthesis, slurry preparation, tape casting, lamination, and sintering, as well as ink development and printing. Some of the challenges encountered during the development will be included, too.

The properties of the obtained LLZO were evaluated using XRD, scanning electron microscopy and electrochemical methods, especially impedance spectroscopy. The morphological and electrochemical properties of the cast and sintered LLZO sheets or printed LLZO were compared to sintered pellets of the same powder.

1. Ohta, S.; Kobayashi, T.; Asaoka, T., J. Power Sources 2011, 196 (6), 3342–3345.
2. Li, Y.; Han, J.-T.; Wang, C. an; Xie, H.; Goodenough, J. B., J. Mater. Chem. 2012, 22 (30), 15357–15361.
3. Zhang, X.; Liu, T.; Zhang, S.; Huang, X.; Xu, B.; Lin, Y.; Xu, B.; Li, L.; Nan, C.-W.; Shen, Y., J. Amer. Chem. Soc. 2017, 139 (39), 13779–13785.
4. Zhang, W.; Nie, J.; Li, F.; Wang, Z. L.; Sun, C., Nano Energy 2018, 45, 413–419.
5. Hüttl, J.; Seidl, C.; Auer, H.; Nikolowski, K.; Görne, A. L.; Arnold, M.; Heubner, C.; Wolter, M.; Michaelis, A. Energy Storage Mater. 2021, 40, 259–267.

All-solid-state Lithium-Sulfur battery technology is the most promising candidate for next-generation batteries due to its high energy density, long cycle life, and superior safety. However, it faces many challenges, such as unstable lithium/solid-state electrolyte (SSE) interface, lithium dendrite penetration, and poor sulfur utilization of the cathode, which hinder its practical application. In this talk, first, I will present a novel approach based on the use of organic-inorganic nanocomposite interphase to construct stable lithium/Li₁₀GePS₁₂ (LGPS) interface. The nanocomposite is formed in situ on Li by the electrochemical decomposition of a liquid electrolyte, thus having excellent chemical and electrochemical stability, an affinity for Li and LGPS, and limited interfacial resistance. And stable Li electrodeposition over 200 cycles for a full cell was achieved. Second, a sulfur vapor deposition (SVD) method for fabricating sulfur-carbon composite with a high sulfur content of 71.4-83.3 wt% will be present for all-solid-state lithium-sulfur batteries. By creating better interfacial contact at the carbon-sulfur interface and confining sulfur within porous carbon, the electronic transport within the sulfur cathode is improved. Enhanced discharge specific capacities, rate performance, and cycling stability of sulfur cathode were demonstrated using the SVD method compared with conventional sulfur-carbon preparation approaches. Last, I will present the development of solid-state-electrolyte with high conductivity to significantly enhance sulfur utilization to enable solid-state Li-S to achieve high energy density.

Room-temperature operation of high-voltage all-solid-state batteries requires solid electrolytes that combine high cation conductivity (≥1 mS cm⁻¹), compatibility with lithium or sodium metal anodes and high-voltage cathodes, and intimate electrode/solid electrolyte interfaces. However, none of the solid electrolytes has fulfilled these material properties so far. Hydroborates, a yet underexplored class of solid electrolytes,^1,2 are highly conductive at room temperature and compatible with lithium and sodium metal anodes. However, the cell voltage was limited up to 3 V in previous reports,^3–6 mainly due to the limited electrochemical oxidative stability of the solid electrolytes.⁷
Here we show that a hydroborate solid electrolyte, consisting of two kinds of hydroborate anions with different oxidative stability limits, can be effectively stabilized in contact with a 4 V-class cathode.⁸ At high voltage, the less stable anions tend to form a passivating interphase layer upon electrochemical oxidation at the cathode/solid electrolyte interface, while the more stable anions remain intact in the interphase layer, maintaining cation conduction. The self-passivating interphase enables the first stable cycling of a 4 V-class hydroborate-based all-solid-state battery employing a sodium metal anode and a cobalt-free, high-voltage cathode. The cells exhibit a discharge capacity of 100 mAh g⁻¹ at C/5 and an excellent capacity (78 %) and energy (76 %) retention after >800 cycles at room temperature. Applying external pressure enables a discharge capacity of >110 mAh g⁻¹ at C/10 with a high areal capacity close to 1.0 mAh cm⁻². This work records the highest discharge cell voltage and specific energy at the active material level among all reported all-solid-state sodium batteries, demonstrating the attractive material properties and potential of hydroborates that surpass intensively investigated oxides and sulfides as solid electrolytes for high-voltage all-solid-state batteries.

References:
1. L. Duchêne, A. Remhof, H. Hagemann, and C. Battaglia, Energy Storage Mater. 2020, 25, 782.
2. M. Brighi, F. Murgia, R. Černý, Cell Rep. Phys. Sci. 2020, 1, 100217.
3. L. Duchêne, R.-S. Kuehnel, E. Stilp, E. Cuervo Reyes, A. Remhof, H. Hagemann, C. Battaglia, Energy Environ. Sci. 2017, 10, 2609.
4. L. Duchêne, D. H. Kim, Y. B. Song, S. Jun, R. Moury, A. Remhof, H. Hagemann, Y. S. Jung, and C. Battaglia, Energy Storage Mater. 2020, 26, 543.
5. F. Murgia, M. Brighi, R. Černý, Electrochem. Commun. 2019, 106, 106534.
6. S. Kim, H. Oguchi, N. Toyama, T. Sato, S. Takagi, T. Otomo, D. Arunkumar, N. Kuwata, J. Kawamura, and S. Orimo, Nat. Commun. 2019, 10, 1081.
7. R. Asakura, L. Duchêne, R.-S. Kuehnel, A. Remhof, H. Hagemann, and C. Battaglia, ACS Appl. Energy Mater. 2019, 2, 6924.
8. R. Asakura, D. Reber, L. Duchêne, S. Payandeh, A. Remhof, H. Hagemann, and C. Battaglia, Energy Environ. Sci. 2020, 13, 5048.

Lithium (Li) metal has been considered as an ideal anode for high-energy rechargeable Li batteries while Li nucleation and growth at the nano scale remains mysterious as to achieving reversible stripping and deposition. A few decades of research have been dedicated to this topic and we have seen breakthroughs in novel electrolytes in the last few years, where the efficiency of lithium deposition is exceeding 99%. Here, cryogenic-transmission electron microscopy (Cryo-TEM/Cryo-FIB) was used to reveal the evolving nanostructure of Li deposits at various transient states in the nucleation and growth process, in which a disorder-order phase transition was observed as a function of current density and deposition time. More importantly, the complementary techniques such as titration gas chromatography (TGC) reveals the important insights about the phase fraction of solid electrolyte interphases (SEI) and electrochemical deposited Li (EDLi). While cryo-EM has made significant contributions to enabling lithium metal anodes for batteries, its applications in the area of solid state electrolytes, thick cathodes are still in its infancy, I hope to showcase how innovative characterization for solid state batteries can be designed to probe buried interphases. Last but not least, I will discuss a few new perspectives about how future cryogenic imaging and spectroscopic techniques can accelerate the innovation of novel energy storage materials and architectures.

As the demand for lithium-ion batteries with improved safety and energy density increases, all-solid-state batteries (ASSBs) have become a promising option for a wide variety of applications due to the elimination of the flammable liquid electrolyte. In particular, oxide-based solid electrolytes are advantageous because of their exceptional chemical stability against many high voltage cathode materials and lithium metal. However, oxide-based solid electrolytes generally have a lower ionic conductivity than that of liquid electrolytes and sulfide-based solid electrolytes, thereby necessitating the use of a thin, dense film to shorten the ionic diffusion path and ensure a good rate performance. Many current methods used to synthesize oxides produce aggregated powders with wide size distributions and therefore cannot be used to make thin, dense, defect-free films. Furthermore, gas-phase deposition techniques, such as atomic layer deposition, can produce high quality thin films, but are severely limited by their high cost and low production rate. We investigated using flame assisted spray pyrolysis, an inexpensive, scalable method that produces loosely agglomerated nanoparticles with controlled morphology, combined with conventional tape casting to produce thin film solid-state electrolytes. LiAlO₂ was specifically chosen as the solid-state electrolyte due to its impressive chemical stability that has recently made it a promising choice for electrode coatings in both conventional batteries and ASSBs. The morphology and ionic conductivity of the as-synthesized LiAlO₂ films as well as the cycling performance of a battery with LiAlO₂ films, a lithium metal anode, and a Li(Ni_0.8Co_0.1Mn_0.1)O₂ cathode were characterized and discussed.

Solid-state electrolytes (SSEs) are promising candidates to circumvent flammability concerns of liquid-based batteries. However, attaining high energy densities requires thinning down SSE layers remains challenging as scalable coating processes are needed. Manufacturing parameters, including binder type, binder ratio, liquid to solid ratio, and cosolvent among others, have a significant influence on the performance of SSE films. While previous studies have reported the fabrication of thin and flexible SSEs, only ionic conductivity was considered for performance evaluation, and no systematic research on the effects of manufacturing conditions on the quality of the SSE films was performed. Here, both uniformity and ionic conductivity are considered for evaluating the SSE films under the guidance of machine learning (ML). Unsupervised ML algorithms, Principal Component Analysis and k-Means clustering, associated to Support Vector Machine, are employed to decipher the interdependencies between manufacturing conditions and film performance. Guided by ML models, an SSE film with a thickness of 40 µm was fabricated and used to construct a LiNi_0.8Co_0.1Mn_0.1O₂ || Li₆PS₅Cl || LiIn cell, leveraging its high ionic conductivity and good uniformity to achieve stable cycling performance. This study presents a ML-assisted experimental approach as an efficient strategy to optimize SSE films, paving the way towards mass production of all-solid-state batteries.

In high energy density batteries, solid electrolytes (SEs) are a safe and promising alternative to liquid electrolytes, but challenges such as low ionic conductivity and dendrite formation, remain. Recent work by others has determined that dendrite formation within Li₇La₃Zr₂O₁₂ and Li₃PS₄ SEs is due to their non-negligible electronic conductivity. Thus, research must re-focus its efforts to keep electronic conductivity low. Notably, solid LiI has negligible electronic conductivity, making LiI a good candidate for SE development. In our previous work, we utilized LiI SE with a conductive additive to create a composite SE capable of forming a Li/I₂ rechargeable battery in situ. Additional work demonstrated interfacial modification with either lithium or gold contacts, can effectively lower the cell impedance and improve coulombic efficiency (CE).
In this work, a LiI SE was improved by reducing particle size via processing. Several processing methods were examined; grinding (G), sonicating (C-S), and grinding with sonicating (G-S), and compared to a control (C) sample of LiI that underwent no processing. To control for LiI hydration effects, which results in increased conductivity via increased defect density, LiI monohydrate content was controlled among samples. With further processing, particle size was reduced from 5 ± 1 µm to 2.0 ± 0.2 µm for the C and G-S samples. Each sample was utilized with a 1:2 lithium iodide:3-hydroxypropionitrile (LiI(HPN)₂)) conductive additive, creating a 80/20 LiI/LiI(HPN)₂ SE composites. Reducing particle size resulted in a significant increase in ionic conductivity, from 7.7 x 10^-8 to 6.1 x 10^-7 S cm^-1, at room temperature. This improvement is attributed to an increase in the number of grain boundaries and defects, enabling better mixing with the electrolyte additive, LiI(HPN)₂ and an overall improvement in ion transport. 3D confocal Raman spectroscopy with non-negative matrix factorization (NMF) analysis determined aggregation of HPN within the composites was lessened in the sample with smallest particle size. When utilized in a self-forming Li/I₂ battery, reduced particle size (improved conductivity) led to significantly reduced overpotential, enabling the coulombic efficiency to reach 100% in the first cycle. Additionally, the cells with G-S composite electrolyte (smallest LiI particle size) exhibited improved electrochemical function at higher cycling rates compared with the other electrolyte types. This work demonstrates the effect(s) of decreasing solid electrolyte particle size in a self-forming, self-healing, all solid-state battery.

All solid-state Li-ion batteries hold the promise of safety, lower cost, and improvements concerning specific energy, specific power, and cycle performance compared to traditional liquid Li-ion batteries. However, there has been little work done on the fabrication of solid electrolyte via plasma vapor deposition (PVD) technique. Our goal is to deposit and characterize solid electrolyte thin film using a NASICON-like, lithium aluminum titanium, phosphate (Li_1+xAl_xTi_2-x(PO₄)₃, (LATP)) solid compound and fabricate microbatteries using lithography. LATP is the interest in this study due to its high ionic conductivity of ~3x10^-3S cm^-1 and reported stability. They are deposited through RF-magnetron sputtering of a 99.9% pure single LATP target onto a thermal silicon oxide substrate. The films’ structural and compositional properties were characterized using multiple techniques such as scanning electron microscopy (SEM) and X-ray diffraction while the lithium depth profile on pristine and cycled devised was measured by secondary ion mass spectroscopy (SIMS) and nuclear reaction analysis (NRA). SIMS and NRA data were combined to depict a lithium depth profile of 0.1 atomic % ⁷Li in the electrolyte. SIMS and NRA will also be used to correlated the atomic % of ⁷Li in the electrolyte and quantify the Li trapped in the electrodes after cycling to the battery performance.

All solid-state lithium batteries (ASSBs) offer higher power and energy density than traditional lithium-ion batteries and are inherently safer due to solid-state electrolytes (SSEs) replacing flammable organic liquid electrolytes. Due to their high room temperature ionic conductivity and malleability allowing for good contact at the electrodes, sulfide-based SSEs are promising candidates for ASSBs. However, thiophosphate based SSEs face two main challenges for commercialization: the narrow voltage window where the electrolyte is electrochemically stable, and its reactivity with NMC and Li metal active materials. Pairing sulfide SSEs with compatible cathodes is crucial to designing high energy dense ASSBs.

An FeS₂ metal sulfide cathode offers a high theoretical capacity (894 mAh/g) and excellent compatibility with sulfide SSEs without additional interface engineering. ASSBs based on Li_6.6Ge_0.6Sb_0.4S₅I (LGSSI) and FeS₂ exhibit an initial capacity of 715 mAh/g at C/10 and are stable for 220 cycles with a capacity retention of 84.5% at room temperature. The structural stabilities of Li_6.6Ge_0.6Sb_0.4S₅I (LGSSI) during cycling are characterized by operando energy dispersive X-ray diffraction (EDXRD), which allows rapid collection of spatially-resolved structural data without redesigning or disassembling the sealed cells and risking contamination by air (Figure 1a). The electrochemical stability is assessed, and an operating voltage window from 0.7-2.4 V (vs. In–Li) is confirmed. Initial EDXRD of a carbon/In-Li half cell is shown in Figure 1b, with the primary reflection of LGSSI observed near a photon energy of 86 keV. During a negative potential sweep (shown in Figure 1c) LGSSI reflections located in the carbon cathode shifted to lower energy, indicating a locally higher d-spacing. This demonstrated that contact with conductive carbon caused a structural instability in the LGSSI.

Layered Li-Ni _1/3Mn_1/3Co_1/3O₂ (NMC111) is a widely used cathode material due to its high working potential (>3.6V), and high capacity of 160 mAh/g. However it is proposed that sulfide SSE decomposes where it contacts the NMC cathode particles, causing ionically insulating interfaces to form and hindering the transport of lithium ions. This decomposition of active materials causes a large capacity loss in the first cycle, and the reactivity of NMC and the SSE has prevented this battery from achieving high energy density. A 120 µm thick NMC111 cathode was paired with electrolyte Li₆PS₅Cl as the SSE and operando EDXRD was utilized to determine the time-dependent lithiation gradient during the first two cycles. This structural analysis of the cathode reveals information about the current distribution and its time evolution; vital information to increasing the energy density of sulfide based ASSBs.

With the use of energy storage devices rather than generators in larger and harsher environments, the demand for new energy storage devices with superior performance and reliability is increasing. The ideal structure proposed to meet this requirement is in the form of using lithium metal for the positive electrode, sulfur for the negative electrode, and placing a solid electrolyte between the two electrodes. The sulfur electrode has a theoretical capacity of at least five times higher than that of the conventional cathode, so it is expected to improve the performance of energy storage devices. However, the actual capacity of sulfur electrode varies depending on the state of the solid electrolyte. If a solid electrolyte with high crystallinity and high rigidity is used, the interfacial compatibility with sulfur is low, so that only a small part of the theoretical capacity of sulfur can be utilized. Therefore, for high capacity, a gel-type solid electrolyte with low crystallinity should be used to increase the interfacial properties of sulfur and electrolyte. However, in a gel-type solid electrolyte with a low crystallinity that sulfur exhibits theoretical performance, the sulfur electrode is combined with lithium and causes a shuttle effect that can't be easily controlled and reversed, just like a liquid electrolyte, and the sulfur diffuses to all parts of the battery. When lithium is removed from sulfur, sulfur with low conductivity is irregularly precipitated in the cell, seriously impeding repeated charge/discharge and stable operation. In this study, nano-additives were used to increase the stability when using a gel-type solid electrolyte and a sulfur electrode. The use of nano-additives significantly improved the performance of the sulfur electrode while maintaining the properties of the solid electrolyte. Nanoadditives have been materials with highly controlled internal structures and high surface areas, such as graphene pomegranate pockets and nitrogen-rich carbon nanotubes. For example, graphene pomegranate sacs provide conductivity to the sulfur electrode and make the sulfur stable around it because of its low interfacial energy with sulfur. In addition, when lithium is removed from the sulfur electrode, sulfur is precipitated around the graphene pomegranate bag, leading to a stable reaction. In addition, in the case of nitrogen-rich carbon nanotubes, excellent conductivity was provided by uniformly stacking structures extending in one direction, and sulfur was accommodated in a large internal space. In addition, the low interfacial energy with sulfur allowed sulfur to stay near the nanotubes with sufficient nitrogen, leading to structurally reversible reactions during charging and discharging. We accurately revealed the interfacial energy between nano-additives, sulfur electrodes, and electrolytes based on experiments, and through electrochemical tests, stability was verified through more than 3,000 charge/discharge reactions, and close to theoretical capacity were achieved. As a result, nano additives with similar surface energy to sulfur stabilize the unstable behavior of sulfur through low interfacial energy and control the irreversible reaction of sulfur in solid electrolytes.

Solid electrolytes with a fast ion conduction are crucial for all solid batteries. The perovskite type lithium lanthanum titanate (LLTO) solid electrolytes have been known as one of promising next-generation lithium-ion batteries because they provide high-energy density and superior cyclic stability. However, in spite of these advantages, their practical application is plagued by low ionic conductivity at room temperature.
Here, the LLTO solid electrolyte optimized at the temperature of 1380°C are found to exhibit high lithium ion conductivity of 2.55 x 10^-4 S/cm, which was more than 100 times higher than that of the solid electrolyte stabilized at 1200°C. In addition, periodic lattice shrink/expansion was observed in the LLTO optimized at 1380°C. Using the first-principles density functional theory calculations, we find that the oxygen vacancies play critical rules in expanding the lattice parameter normal to the lithium migration path, which greatly enhance lithium ion conductivity. Relevant structure reconstructions and underlying mechanism will be discussed in detail at the atomic scale.

Lithium dicyanamide (LiN(CN)₂) reacts with phosphorus cyanide (P(CN)₃) in a 2:1 or greater mole ratio in any anhydrous non-protic mutual solvent to form a resin. The resin solution is used to coat metal coupons or to impregnate silica fiber paper, which are then cured at temperatures of 200-300 °C, forming adherent, ion conducting films. When fully cured, those films have a low ionic conductivity, probably due to rigid crosslinking of the thermoset. We will report our efforts to increase that ionic conductivity by introducing various additives to the system. We have explored (1) adding cations of different sizes, (2) increasing the Li concentration by adding lithium cyanide, (3) introducing RP(CN)₂ components to reduce the crosslink density, (4) adding non-volatile, Li-coordinating organic plasticizers to increase ion mobility. The ionic conductivity and chain motions of these films were characterized by impedance and dielectric relaxation spectroscopy. Additionally, reactions in solution were followed by NMR and bulk thermoset material was analyzed by solid state NMR. We evaluated how the composition and conductivities of these materials depends on conditions of preparation.

To recognize the autonomous driving of electric vehicles in real-time, large-capacity batteries should be installed in the vehicle. Liquid electrolyte-based lithium-ion batteries (LIBs) have limited battery capacity expansion due to their liquid electrolytes and have an explosion risk during driving. To resolve the LIB's limitations, solid-state electrolytes (SEs) are promising to considerable research attention. However, SEs are low ion conductivity than liquid electrolytes and make the dendrite during the working process. Garnet structure solid electrolytes were known that have high ion conductivity at room temperature, among solid electrolytes.
In this study, we studied the characteristics of the garnet structure-based Li-La-Zr-Ta-O (LLZTO) according to atmospheric exposure time after the solid-state synthesis method. LLZTO's morphology characteristic according to the synthetic environment was analyzed using the XRD (X-ray Diffraction) and SEM (Scanning electron microscopy). To analysis electrochemistry properties such as ion conductivity and activation energy, impedance analysis was performed. LLZTO's impedance data is comparing was compared the commercial LLZTO's ion conductivity. To compare the LLZTO's ionic conductivity reduction ratio according to the atmospheric exposure time, we compared synthetic LLZTO and commercial LLZTO with atmospheric exposure time. As a result, we found that the ionic conductivity reduction ratio of synthetic solid electrolytes is smaller than commercial LLZTO.

Lithium metal batteries are more energy-dense than commercial lithium-ion batteries; however, unstable and non-uniform plating and stripping at the lithium metal anode can lead to short circuiting if the structures, known as dendrites, breach the gap between anode and cathode. To mitigate this problem, inorganic-organic hybrid films have been placed at the lithium metal anode to encourage uniform deposition arguably through the robust mechanics and diffusion mechanisms of the composite. This study aims to optimize the design of these films by focusing on poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) composite films, quantifying the relationship between concentration of LiF and Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (Ta-doped LLZO) ceramic fillers to mechanics and conductivity of the separator as well as to plating and stripping uniformity at the lithium metal anode after cycling. The hybrid separators demonstrate high modulus, yield stress, and ductility in uniaxial tension experiments as both pristine and swollen with electrolyte. Additionally, long term cycling validates the composite as electrochemically compatible in a lithium metal system through postmortem surface analysis of the lithium metal electrodes.

All-Solid-state Lithium-Ion batteries(ASSLIBs) are considered as more efficient and safer alternatives to traditional lithium-ion batteries with liquid electrolytes. Among the candidate solid electrolyte materials, Lithium Phosphorus Sulfide (LPS) has attracted the attention of researchers due to its high Lithium ion conductivity. However, major challenges arise due to LPS having complicated porous geometries and multiple phases with different ion transport abilities. Additionally, suppressing dendrite growth at the anode surface is needed for high energy density solid state batteries using Li metal as anode. Our goal is to identify the electrolyte that best promotes ion transport and the interface morphology that best suppresses dendrite growth.

In this study, we used the Lattice Boltzmann Method (LBM) to simulate half-cells with a Li working electrode, virtual Li counter electrode, and LPS solid electrolyte. In order to investigate the ion transport process, we tested the electrolyte with various porosities, diffusivities, and phases with different ion conductivities. In our ion-transport simulations, we simulated Li-ion transport through solid-state electrolytes by measuring flux at the electrolyte-electrode interface . The results show that flux at the electrolyte-electrode interface increases as porosity decreases or diffusivity increases. Our multiphase simulations were conducted with a single porous electrolyte with less conductive secondary phases. The simulation indicated that lower percentage of the second phase resulted in higher Li-ion flux. To investigate dendrite formation, we studied three interface morphologies: rough with no micropattern, rough with micropattern, and smooth with micropattern. For each system, we varied charge current, surface roughness, and micropattern hole size. Our results reveal that dendrite formation at the anode/electrolyte interface is favored in the rough systems and is inhibited in micropattern systems. Our study demonstrates the effects of factors on the performances of ASSLIBs in order to provide information for finding high-performing and commercially-viable candidate systems.

Nickle-rich LiNi0.8Co0.1Mn0.1O2 (NMC 811) exhibits outstanding properties in high energy density and low cost, making it promising as the cathode material in all-solid-state lithium batteries (ASSLBs). In various solid-state electrolytes (SEs), thiophosphate-based eletrolyes own superior ionic conductivity and processbility. However, NMC 811 suffers from severe surface electrochemical, chemical, and voltage incompatibility towards thiophosphate-based electrolytes. Diverse interface engineerings have been reported to solve this issue, whereas they are typically cumbersome and expensive. Therefore, finding a coating strategy that satisfied all the requirements of cost-efficiency, stability, uniformity, scalability, and easy-achieving is necessary. In this work, we fabricated a highly stable NMC 811 coated with a ~10 nm of LiOH-based layer through a time-and cost-effective one-step sintering process. Compared with conventional coating strategies, this method made a conformally coating in the NMC 811 lithiation process without extra processes. Meanwhile, LiOH interfacial coating layer only conducts ions but not electrons resulting suppressed decomposition of sulfide electrolyte. As a result, the ASLBs exhibited remarkable cycling stability for 600 cycles with a capacity of 130 mAh g^-1 on average at C/10 at a wide electrochemical window of 2.50−4.20 V (vs. Li-In) and satisfactory rate capability (119.4 mAh g–1 at 1C).

Recently, there has been a great attention toward stretchable and flexible lithium-ion batteries (LIBs) that are safe, leakage-proof, low cost, and electrochemically and mechanically stable. These stretchable batteries must provide long cycle life and show high electrochemical and mechanical performance for a wide variety of applications such as wearable electronics, biomedical sensors and portable devices.
Due to this accelerated demand, in this study, a thin-film stretchable lithium-ion battery has been fabricated, tested and optimized. The lithium-ion cell is fabricated in a spiral configuration with the thickness of less than 0.8 mm and provides out-of-plane stretchability. In addition, comprehensive tests including electrochemical and mechanical cycling, and electrochemical impedance spectroscopy (EIS) has been conducted to evaluate and optimize the performance of the stretchable batteries. Results show that high areal discharge capacity of 1 mAh/cm² after 100 electrochemical cycles is achieved for spiral stretchable batteries. Moreover, electrochemical performance, EIS and voltage of the stretchable batteries have been measured simultaneously in both flat and stretched states. Results reveal that the spiral battery can be stretched up to 500% without any significant change in its electrochemical performance. Furthermore, scanning electron microscopy (SEM) images of the battery confirm stable interfaces and structural integrity throughout cycling and stable specific capacity up to 200 cycles has been demonstrated. In comparison with the previous work on stretchable batteries, a significant enhancement has been achieved with respect to specific capacity, energy density, performance stability in stretched state and during long cycles.

Solid-state batteries (SSBs) have seen a dramatic increase in research in recent years because of their ability to address safety challenges associated with flammable liquid electrolytes, and the potential to enable Li metal anodes. Recently there has been an increase in attention paid to anode-free SSB configurations, where all of the lithium inventory in the battery is supplied from the cathode. Accordingly, Li metal is plated out at the interface between a solid electrolyte and a metallic current collector. This enables a N:P ratio of 1, representing a significant increase in the theoretical energy density compared to cells with excess Li metal in the anode. The anode-free configuration results in unique physical phenomena with regards to chemo-mechanics at the interface, and also represents a valuable platform to quantify the stability and reversibility of Li plating and stripping at solid-solid interfaces.

To probe the dynamic evolution of anode-free solid-state batteries, in this talk, I will present results using a complimentary set of in situ/operando methodologies. First, we will explore quantify the impacts of electrochemical cycling conditions and external variables on the voltage signatures and reversibility of anode formation. Comparisons will be made between anode-free cells using state-of-the-art metal oxide and sulfide solid electrolytes. Operando video microscopy will be used to study the morphological evolution of the interface, including 3-dimensional analysis using focus variation microscopy. The chemical evolution of SEI formation during the initial anode formation cycle will be explored using operando x-ray photoelectron spectroscopy (XPS). The results of these investigations point towards unique processes that occur in anode-free SSBs, including transitions in reaction pathways between SEI formation and Li plating, as well as mechanical evolution of both the Li metal and current collector during nucleation and growth.

The increasing demand for safe and dense energy storage has shifted research focus from liquid electrolyte-based Li-ion batteries towards solid-state batteries (SSBs). However, the application of SSBs is impeded by uncontrollable Li dendrite growth and short circuiting, whose mechanism remains elusive. Herein we conceptualize a scheme to visualize Li deposition in the confined space inside carbon nanotubules (CNTs) to mimic Li deposition dynamics inside solid electrolyte (SE) cracks, where the high-strength CNT walls mimic the mechanically strong SEs. We observed that the deposited Li propagates as a creeping solid in the CNTs, presenting an effective pathway for stress relaxation. When the stress-relaxation pathway is blocked, Li deposition-induced stress reaches GPa level and causes CNT fracture. Mechanics analysis suggests that interfacial lithiophilicity critically governs Li deposition dynamics and stress relaxation. Our study offers critical strategies for suppressing Li dendritic growth and constructing high energy density, electrochemically and mechanically robust SSBs.

The need for higher energy density rechargeable batteries has generated interest in metallic electrodes paired with solid electrolytes. However, impedance growth at the Li metal-solid electrolytes interface due to void formation during cycling at practical current densities and areal capacities, e.g., greater than 0.5 mA cm^-2 and 1.5 mAh cm^-2 respectively, remains a significant barrier. Here, we show that introducing a wetting interfacial film of Na-K liquid between Li metal and Li_6.75La₃Zr_1.75Ta_0.25O₁₂ (LLZTO) solid electrolyte permits reversible stripping and plating of up to 150μm of Li (30 mAhcm^-2), approximately ten times the areal capacity of today’s lithium-ion batteries, at current densities above 0.5 mA cm^-2 and stack pressures below 75 kPa, all with minimal changes in cell impedance. We further show that this increase in the accessible areal capacity at high stripping current densities is due to the presence of Na-K liquid at the Li stripping interface; this performance improvement is not enabled in the absence of the Na-K liquid. This design approach holds promise for overcoming interfacial stability issues that have heretofore limited performance of solid-state metal batteries.

Lithium metal penetration through garnet based LLZO solid electrolytes (SEs) have been identified as a critical failure process. At critical current density, LLZO SE has been known to short-circuiting, and can even result in fracturing of the SE. The combined chemo-mechanical phenomena- which can significantly affect the performance in all solid-state batteries, requires detailed investigation of several related phenomena. Characterizing the dynamical mechanical evolution that occurs in the electrode-SE is challenging. Investigation of the mechanical driving forces of lithium metal penetration through the SE is a particularly important challenge. To probe the chemo-mechanical phenomena that occur during lithium plating, this study reports in-situ curvature measurements that were designed to evaluate the stresses that evolve in LLZO during lithium plating. The experimental configuration created for this work provides data which was analyzed with a detailed Finite Element Model (FEM) to quantitatively evaluate stress evolution in the solid electrolyte. The results show that Li metal plating within a surface flaw can produce stress build-up prior to short-circuiting. The combined results from both the experiments and the FEM suggest that it is critical to minimize surface defects and flaws during manufacturing processes.

Pure metals (i.e., Li, Na, K) are attractive battery anodes because they possess large theoretical capacities for their respective systems. However, pairing metal anodes with solid electrolytes produces a rigid interface with fundamental mechanical issues: stress buildup can lead to electrolyte fracture and metal penetration, while a lack of sufficient pressure leads to a loss of anode-electrolyte contact. The anode’s mechanical properties govern both stress buildup and relaxation, but such properties (e.g., the yield stress) are highly sensitive, varying by orders of magnitude with temperature, rate, and size. In this work, we systematically survey the mechanical behavior of lithium, sodium, and potassium at bulk scales for temperatures from 0 C to 45 C and strain rates from 10^-2 to 10^-4 s^-1, while using micro- and nano-indentation measurements to delineate the size-dependence of mechanical behavior. Temperature dependent and (separately) size dependent deformation mechanism maps emerge from these measurements, allowing the prediction of flow stress for alkali metals under a broad variety of conditions. Towards illustrating the utility of the deformation mechanism maps, we outline the implications for stress buildup within metallic protrusions at the solid-state electrolyte / anode interface. Furthermore, both deformation maps and mechanical measurements demonstrate that Na and K metal are far softer than Li metal under equivalent conditions, and may provide more conformal interfaces than Li metal during operation of fast-charging solid-state batteries. Overall, the results presented herein will provide important guidance in designing solid-state batteries with persistent interfacial contact

Garnet solid-state electrolyte Li₇La₃Zr₂O₁₂ (LLZO) are promising candidates for the development of all solid-state batteries, owing to their high ionic conductivity and chemical stability in contact with Lithium metal. However, insufficient interfacial contacts in LLZO-based solid-state batteries leads to high area-specific resistance (ASR), gradual void formation and dendrite-induced shorting during electrochemical cycling². By applying external pressure to symmetric / full cells, proper interfacial contact can be achieved. However, excessive stack pressure can be detrimental to Li-LLZO kinetics and stability, which affects the overall cell performance³. In this study, we systematically evaluated the combined effect of stack pressure (5-30 MPa) and temperature (25-70C) in Li stripping/plating behavior (symmetric cells).The morphological changes at Li-LLZO interfaces under pressure and temperature are complex in nature. Improper contact points lead to void formation and inhomogeneous plating, which result to rise in constriction resistance. The contact issues can be eliminated completely under extreme confinement. But stress-induced Li dissolution along grain boundaries or surface flaws of LLZO can still cause shorting. Through critical current density (CCD) and long-term Li-stripping measurements on Li\LLZO\Li cells, an optimum pressure range of 10-20 MPa is observed for stable operation at room temperature up to 0.5 mA/cm². The cell shorting scenarios at high current densities are different. At low pressure (5 MPa) cells encounter a void-induced shorting, whereas at high pressure (20 MPa), stress-induced shorting is evident. Increasing the temperature at the optimum pressure range shows a significant increment of current density (> 1.3 mA/cm²). Combined effect of pressure and temperature in full cell performance and stability was also investigated by employing composite LiFePO₄ electrodes.

We develop a real-time framework for computing the concentration and electric fields in one dimensional battery cell. Subsequently we calculate the kinetics of dendritic growth using asynchronous evolution in the concentration of anions and cations and the cell voltage. Consequently, we develop a phase field model for the initiation and growth process of the dendritic microstructures which is highly dependent to the computed three variables. The main focus in the phase field model is the variation in the charge density ρ and the value of the computed electric potential V for determining the ultimate energy functional ΔG . The results are useful for determining the design strategy for controlling the microstructures particularly for the effect of the original concentration C₀, the potential difference V₀ and the inter-electrode separation l.

The successful integration of Li metal anode with solid electrolytes seems to be a must for a high-energy-density solid-state battery. However, Li dendrites tend to form in solid electrolytes during plating and eventually lead to the short circuit of the cell. The formation of dendrites has been observed in solid electrolytes with various crystal structures from glass, glass-ceramic, poly-crystalline to single-crystalline, but the mechanism of such an unexpected dendrite growth remains elusive. In this presentation, I will introduce our recent understandings of lithium dendrite formation in solid electrolytes based on neutron depth profiling characterizations and electrochemical measurements on typical solid electrolytes. We highlight the important role of the electronic conductivity of solid electrolytes in the formation of isolating dendrites inside solid electrolytes. We will also discuss corresponding dendrite prevention strategies.

The ever-growing demand for robust, long-duration energy storage has driven research into emerging technologies, such as sodium-based batteries. Solid sodium electrolytes are a key component to the successful implementation of molten sodium, solid-state, and sodium-ion batteries for large-scale and long-duration energy storage. The sodium (Na) Super Ion CONductor (NaSICON) is a promising candidate solid electrolyte, due to its high conductivity and chemical stability against molten sodium. At high current densities or after extended use, however, potential changes in the material properties of NaSICON may lead to various forms of degradation. In-situ deterioration of NaSICON stands to potentially decrease the performance, lifetime, and safety of sodium batteries. Characterizing potential degradation mechanisms is critical to widespread NaSICON utilization, but these processes have not been studied extensively. In this presentation, the microstructural, mechanical, and electrochemical properties of NaSICON before and after exposure to sodium battery environments are investigated. Structural characterization by x-ray diffraction, atomic force microscopy, and scanning electron microscopy is combined with mechanical and electrochemical measurements, such as nanoindentation and electrochemical impedance spectroscopy. We have found that critical properties, such as elastic modulus, of NaSICON are altered after exposure to electrochemical cycling. These changes, coupled with high current density, can lead to localized failure in the form of microcracking or dendrite formation and propagation. The degradation and failure of these electrolytes may be further exacerbated by the presence of microstructural ceramic defects, such as porosity, from the fabrication process. Understanding these mechanisms will be used to guide improved design and formulation of NaSICON for use in sodium batteries.

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

Commercialization of energy-dense lithium metal batteries relies on stable and uniform plating and stripping on the lithium metal anode. In electrochemical-mechanical modeling of solid-state batteries, there is a lack of consideration of specific mechanical properties of battery-grade lithium metal. Defining these characteristics is crucial for understanding how lithium ions plate on the lithium metal anode, how plating and stripping affect deformation of the anode and its interfacing material, and whether dendrites are suppressed. Recent experiments show that the dominant mode of deformation of lithium metal is creep. This study measures the time and temperature-dependent mechanics of two thicknesses of commercial lithium anodes inside an industrial dry room, where battery cells are manufactured at high volume. Furthermore, a directional study examines the anisotropic microstructure of 100 μm thick lithium anodes and its effect on bulk creep mechanics. It is shown that these lithium anodes undergo plastic creep as soon as a coin cell is manufactured at a pressure of 0.30 MPa, and achieving thinner lithium foils, a critical goal for solid-state lithium batteries, is correlated to anisotropy in both lithium’s microstructure and mechanical properties.

Dendrite formation is one major cause of battery failure and associated safety hazards. The emergent solid-state batteries using lithium anodes remain victim to dendrite growth, which hinders its commercial viability. The mechanism of dendrite formation and propagation in solid electrolytes is largely different from that in liquid systems, yet the challenges in non-invasively and directly tracking the process in real-time leave the exact mechanism elusive. Herein, we demonstrate for the first time to track the kinetics of lithium dendrite growth at both the interface and bulk of different depths in Li/ Li₇La₃Zr₂O₁₂ (LLZO) /Li solid cells using three-dimensional in-situ and ex-situ nuclear magnetic resonance imaging (MRI) non-invasively. We show that the accumulation of Li microstructure kicks off from the surface of LLZO before hard shorting the Li/LLZO/Li cell. More importantly, we identified Li evolution originated both from the interface and from the bulk LLZO electrolyte. The techniques developed and demonstrated herein can also be applied to other related fields in materials research.

Recent demands for very small electronic devices generated a need for miniaturized energy-storage devices that can provide the power and energy needed for various applications such as wearable gadgets, medical devices and wireless sensor networks. Rechargeable micro-batteries have been investigated as a reliable route for achieving this target. However, in order to reach reliable performance of such micro-batteries while reducing the size and minimizing the fabrication cost, more sophisticated architectures need to be developed. Here, we introduce a novel approach to fabricate an all solid-state Li metal micro-battery based on directed fluidic assembly-based printing. This unique approach facilitated the assembly of all battery components including cathode, anode, and electrolyte at micro-scale dimensions, without the need of implementing costly fabrication techniques or utilizing complicated sacrificial templates as in the case of traditional micro-battery fabrication methods. Moreover, the porous cathode framework attained using this approach provided enough space for the polymer electrolyte to infiltrate the porous cathode leading to a cathode-supported electrolyte membrane. This drastically enhanced the battery performance through combining superior ionic transport and low interfacial resistance between the electrolyte and the cathode, as well as providing excellent electronic pathways through the cathode scaffoldings. Results shows that the as-printed LiFePO₄/Li solid state battery has an outstanding performance with discharge capacity of 157 mA h g^-1 at 0.1C, and a long-term cycling stability of 99.6% coulombic efficiency with a capacity retention of 89 .5 % after 200 cycles. The EIS measurements also showed a lower interfacial resistance of the cathode-supported electrolyte micro-battery compared to its separated membrane counterpart. We believe that this unique approach will pave the way for mass production of high performance all solid-state micro batteries based on Li metal anodes as miniaturized energy devices.

Rational design and synthesis of solid electrolytes using cost-effective precursors for fast ion conduction is an effective approach for producing solid electrolytes for mass production at a low-cost. In this study, we demonstrate how the ionic conductivity in a poor Li⁺-ion conductor-Li₃PO₄-can be tuned to a fast Li⁺-ion conductor by interrupting the PO₄^3- anion sublattice via diversifying the anion species. This is achieved by first introducing a highly polarizable I^- anion in the vicinity of PO₄^-3 which results in a frustrated Li-anion interaction, thereby encouraging fast hopping around the interrupted anion framework. An ionic conductivity of 0.15 mS/cm at room temperature was achieved for the composition 1.4Li₃PO₄ – LiI, a 10¹⁰-fold enhancement compared with the ionic conductivity of Li3PO4, 10^-14 mS/cm. Phase analysis from multinuclear solid-state NMR revealed a large fraction of amorphous phases Li_3+yPO₄I_y and Li₄PO₄I, in addition to the residual crystalline LiI and LiI^.H₂O phases. The formation of Li_3+yPO₄I_y and Li₄PO₄I phases was determined to be the reason for achieving high Li⁺-ion conduction which was confirmed by AIMD. ⁷Li NMR relaxometry revealed fast-Li⁺-ion mobility because of the incorporation of iodide anions that resulted in the interruption of the PO₄^3- sublattice. ⁶Li tracer-exchange NMR showed Li₄PO₄I to be more conductive than the Li_3+yPO₄I_y. Overall, this study demonstrates that interruption of anion frameworks by introducing large polarizable anion in an amorphous matrix is powerful strategy to enhance Li⁺-ion conduction.

Fast ion conductors with high conductivity and stability are key to realizing high-performance all-solid-state batteries for next-generation energy storage. Lithium argyrodites have demonstrated tunable conductivity via anion doping. However, Li deficiency and anion mixing coexist in previously studied halogen-doped argyrodite compounds, and both of them impact Li⁺ conduction.^1-3 To investigate the effects of anion mixing, we synthesized novel argyrodites Li_5.3PS_4.3Cl_1.7-xBr_x (0 ≤ x ≤ 1.7) with fixed Li content. The highest room-temperature conductivity around 26 mS/cm is achieved in Li_5.3PS_4.3Cl_0.7Br, with an exceptionally low activation energy of 0.16 eV for Li⁺ transport. To characterize the long- and short-range structural order and to discover the origin of fast Li⁺ conduction, X-ray diffraction and nuclear magnetic resonance are utilized. It shows that a diversified anion sublattice is formed via S/Cl/Br mixing at Wyckoff 4d sites. While the long-range structure is maintained, the introduction of Br^- in the structure displaces Cl to off-center positions from 4a/4d sites. The effects of the observed anion disorder on the mobility of Li⁺ and anions are investigated using NMR relaxometry. It reveals that Br^- incorporation slows down Li⁺ motion but increases PS₄^3- rotation, and overall leads to lower energy barriers for Li⁺ transport.

References:
1. Pengbo Wang, Haoyu Liu, Sawankumar Patel, Xuyong Feng, Po-Hsiu Chien, Yan Wang, and Yan-Yan Hu. Chemistry of Materials, 2020, 32, 9, 3833-3840.
2. Xuyong Feng, Po-Hsiu Chien, Yan Wang, Sawankumar Patel, Pengbo Wang, Haoyu Liu, Marcello Immediato-Scuotto, and Yan-Yan Hu. Energy Storage Materials, 30 (2020) 67–7368.
3. Sawankumar Patel, Swastika Banerjee, Haoyu Liu, Pengbo Wang, Po-Hsiu Chien, Xuyong Feng, Jue Liu, Shyue Ping Ong, Yan-Yan Hu. Chemistry of Materials, 2021, 33, 1435−1443.

The complex origins of solid-state battery failure call for multidimensional diagnostics utilizing not one but a combination of tools that can quantify the void and dendrite formation, identify the chemical and mechanical natures of the Li dendrites and electrolyte decomposition products, and in situ monitor the evolution of the processes. However, there is lack of tools that connect multiple techniques with desirable length scale, resolution and sensitivity for characterizing solid-state batteries. The objective of this work is to develop an air-free vessel with an in-situ cell test platform connecting FIB-SEM tomography, ToF-SIMS, and in-SEM nanoindentation for structural, chemical, and mechanical characterizations of solid-state Li batteries. We fabricated solid-state thin-cells (less than 100 μm) and micro-cells with electrochemical performance on par with their bulk-type counterparts. Electrochemical tests with precise temperature control, external pressure, and pressure monitoring of thin solid-state cells were demonstrated with structural, chemical and mechanical characterizations. We hope the consolidated diagnostic platform presented here will allow us to effectively predict and optimize the physical and chemical changes of components within solid-state Li batteries during charge and discharge.

Acknowledgement: This work was supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Vehicle Technologies Program under Contract DE-EE0008864.

To date, a primary challenge for the further development of all-solid-state batteries is resolving and controlling the Li-ion distribution within their interfaces and interphases. Therefore, spatially determining where Li⁺ favorably accumulates upon device cycling can reveal how to mitigate the chemical reactions that lead to capacity fade. Here, we implement nanoscale-resolved secondary ion mass spectroscopy (SIMS) in an oxygen-free environment to elucidate the spatial distribution of Li⁺ ions in energy-storage devices composed by Si/LiPON/LiCoO₂ in a thin film configuration, an ideal model system with >90% capacity retention after 100 cycles and 98% of Coulombic efficiency. We acquire the ionic depth profile and 3D map of Li⁺ for both pristine and cycled devices, revealing a Li⁺ enrichment at the electrolyte layer upon cycling. This 3D tomography of Li⁺ spatial distribution indicates enrichment of Li⁺ at the LiPON electrolyte. As an independent technique to tomographical studies, we will also discuss the surface potential distribution in both in-plane and cross-section modes, from nanoscale maps acquired with environmental Kelvin-probe force microscopy (KPFM), performed under Ar and with no air exposure. Our KPFM measurements enable access to all relevant interfaces in full devices under various environmental conditions, such as temperature and humidity. The complementary imaging methods employed in our work represent a useful platform for screening Li-ions and can be extended to 3D designs and to other types of batteries, such as Na-ion devices.

Solid-state batteries with lithium metal anodes are attractive for next-generation energy-storage systems with high energy density and safety. But the realization of these promises largely depends on the development of superior ion conductors for the solid-state electrolyte as well as ion-conducting additives for the cathode materials. A research group led by Prof. Liangbing Hu at the University of Maryland, College Park demonstrated that molecule-engineered cellulose nanofibrils through the insertion of copper and lithium ions can be used as a high-performance solid polymer electrolyte that presents record-high ionic conductivity, wide electrochemical stability window, low activation energy, and scalability. The new system, namely Li-Cu-CNF, has the benefit of low cost since the main material sources are wood fibers. In addition, the one-dimensional structure of Li-Cu-CNF also makes it an effective ion-conducting binder for the cathode, and its effective ionic percolation allowed us to fabricate the thickest LiFePO₄ solid-state cathode ever reported, suggesting the material’s potential for increasing battery energy density.
Despite the experimental discovery, the origin of the high Li-ion conductivity in the Li-Cu-CNF system remained a mystery. We have developed both quantum and atomistic models to uncover the accurate atomic structures of the Li-Cu-CNF system and the lithium-ion conduction mechanism therein. These understandings cannot be obtained by any currently available experimental techniques. We have unveiled the atomic structures of Li-Cu-CNF very quickly with input from experiments. Through comprehensive density functional theory calculations, classical molecular dynamics simulations, and x-ray absorption spectroscopy modeling, we clearly showed how copper ions connect the cellulose chains and open the channels, which are preconditions for insertion and effective transport of lithium ions in Li-Cu-CNF. More than that, we have proposed that the abundant oxygen-containing functional groups and bound water in the cellulose molecular channels lead to a lithium-ion hopping mechanism that is decoupled from the polymer segmental motion, which is the most fundamental reason that Li-Cu-CNF can deliver the highest lithium-ion conductivity among all the solid polymer electrolytes ever reported during the last four decades. Using molecular dynamics simulations, we have pointed out that the conduction mechanism can also be generalized to cellulose-based sodium-ion and potassium-ion batteries.

Reference:
[1] Chunpeng Yang,^# Qisheng Wu,^# Weiqi Xie,^#, …, Yue Qi,* Liangbing Hu,*. Nature, in press. (^#Equal contribution; *Corresponding authors)

Traditional solid polymer electrolytes (SPEs) aiming at lithium battery application are made by simply dissolving a Li-salt in a suitable polymer matrix, rendering both Li⁺ cations and anions mobile. As a result, since most of the lithium batteries chemistries involve the intercalation/deintercalation of the Li⁺ cation, concentration gradients and cell polarization develop, causing premature cell failures. Another polymer electrolyte design is to graft the anion onto the polymer backbone, whereby single-ion conductors (SICs) with the Li⁺ cation as the sole mobile species can be created. SICs both provide the safety, the mechanical stability, and the flexibility of SPEs, and circumvent the problematic issues connected with cycling, but their ionic conductivities remain low at room temperature, due to the rigidity of the polymer matrix and the dense electrostatic interactions from the attached ionic group.^1,2
Herein we suggest and explore an intermediate and synergetic design; by using a SIC, LiPSTFSI (poly[(4-styrenesulfonyl) (trifluoromethanesulfonyl) imide]), doped with the LiTFSI salt. The aim is to improve the ion transport mechanism by both increasing the Li⁺ concentration and the flexibility of the polymer matrix – as TFSI is a plasticizing anion.^3,4
We have explored different doping degrees, from 1 to 90 wt%, and how they induce changes in the glass transition temperatures, the mechanical properties, and the charge carrier speciation. With a rather high doping degree, 50-70 wt% LiTFSI, we find considerable improvements in the Li⁺ dynamics and the ionic conductivity. A deeper analysis of the conduction mechanism reveals an Arrhenius behavior, with possibilities for strong trade-offs/synergies between ion transport by hopping between ionic clusters, a different speciation, an increased charge carrier concentration, and an increased free volume.

1. H. Zhang, C. Li, M. Piszcz, E. Coya, T. Rojo, L. M. Rodriguez-Martinez, M. Armand and Z. Zhou. Chem. Soc. Rev. 46 (3), 797–815 (2017).
2. J. Liu, P. D. Pickett, B. Park, S. P. Upadhyay, S. V. Orski and J. L. Schaefer. Polym. Chem. 11 (2), 461–471 (2020).
3. S. Sylla, J. Y. Sanchez and M. Armand. Electrochim. Acta 37 (9), 1699–1701 (1992).
4. Q. Ma, Y. Xia, W. Feng, J. Nie, Y. S. Hu, H. Li, X. Huang, L. Chen, M. Armand and Z. Zhou. RSC Adv. 6 (39), 32454–32461 (2016).

Lithium-ion batteries (LIBs) are the primary candidates for advancing energy storage needs, but their function is hampered by the liquid, organic-solvent-based electrolytes that shuttle lithium cations between electrodes during charging and discharging. These electrolytes, e.g. LiPF₆ in EC:DEC, can combust if a battery’s operating constraints are exceeded. Solid polymer electrolytes (SPEs) offer a promising alternative: they are more thermodynamically stable than their liquid counterparts, and are stable when in contact with Li metal, which could substantially increase a battery’s capacity. Polyethylene oxide (PEO), noted for its ability to dissolve lithium salts and conduct lithium ions, has been the focus of SPE research since the 70’s. Its primary drawback is the strong coordination of Li⁺ relative to loosely coordinated anions, which translates into a low cationic transference number. In addition, ionic conduction occurs only in amorphous domains of the bulk polymer matrix, which renders ionic conductivity suboptimal at ambient conditions, approaching the benchmark of 10^-3 S/cm only at 80°C.

The persistent issues with PEO and PEO-based architectures are low ionic conductivity and transference number. Recent computational work by Savoie et al.¹ suggests that using Lewis-acidic boron moieties in the polymer backbone, as opposed to the Lewis-basic ether oxygen, can invert the solvation mechanism and increase Li⁺ cation mobility relative to that of the anion. It has been experimentally demonstrated that including boron-containing moieties in polymer electrolyte materials provides an anion trapping site which improves Li⁺ transference.^2,3

We present the synthesis of a novel, single-ion conducting, polymer electrolyte and its preliminary electrochemical and material characterization. The electrolyte is accessible through the modification of a simple and abundant polyolefin, polybutadiene, by the introduction of dialkylborane moieties to the backbone through hydroboration. We create an ionically conductive polymer film by first drop casting the synthesized polyborane onto stainless steel discs, and then adding butyllithium to it. This electrolyte exhibits geometry-normalized conductivities approaching 10^-7 S/cm at 50°C. Further electrochemical and material characterization, in addition to molecular dynamics simulations, provide insight into the mechanism of ionic conduction in these polymer films and allow for further optimization.

1. Savoie, B. M., Webb, M. A. & Miller, T. F. Enhancing Cation Diffusion and Suppressing Anion Diffusion via Lewis-Acidic Polymer Electrolytes. J. Phys. Chem. Lett. 8, 641–646 (2017).
2. Matsumi, N., Sugai, K. & Ohno, H. Ion conductive characteristics of alkylborane type and boric ester type polymer electrolytes derived from mesithylborane. Macromolecules 36, 2321–2326 (2003).
3. Mizumo, T., Sakamoto, K., Matsumi, N. & Ohno, H. Simple introduction of anion trapping site to polymer electrolytes through dehydrocoupling or hydroboration reaction using 9-borabicyclo[3.3.1]nonane. Electrochim. Acta 50, 3928–3933 (2005).

Solid state lithium ion batteries have the potential to meet increasingly stringent safety and power density requirements in the transportation and consumer electronics sectors. Realizing the promise of solid state lithium ion batteries will require development of composite solid electrolytes that combine the compliance and processability of polymers with the ruggedness, temperature flexibility, and ionic conductivity of ceramics. In this work, we present a simple one-pot method for preparation of a high inorganics composite comprised of lithium aluminum germanium phosphate (LAGP) and polyethylene oxide (PEO). This is the first step toward development of composite materials more readily compatible with a broad range of battery fabrication techniques. Fourier transform infrared (FTIR) analysis of the polymer/ceramic product shows perturbations in the P-O stretching region (800 cm^-1 to 1250 cm^-1) of the LAGP spectrum, consistent with specific surface interaction between the LAGP and the PEO. Solid state multinuclear magnetic resonance (⁷Li, ²⁷Al, ³¹P), which is sensitive to even small changes in short-range structure of the bulk phase, reveals little difference between LAGP and the LAGP/PEO composite, suggesting that the polymer-ceramic interaction is confined to a thin surface region. Results obtained for other composite preparation schemes, including sheer vs. impact milling and pre-treatment activation of the LAGP surface will be presented.

Solid-state battery (SSB) technology is racing toward commercialization due to its perceived inherent safety and high energy density, both key metrics for the electric vehicle market. To that end, high interfacial resistance between solid electrolyte (SE) and cathode is a critical challenge that must be overcome. The addition of liquid electrolyte (LE) at the SE and cathode interface has been shown to substantially reduce interfacial resistance. However, the inclusion of LE has also led to safety concerns and an emphasis on all-solid-state batteries (ASSBs). In this presentation we quantify the potential thermal consequences of various failure modes, to inform the safety-performance trade-off associated with the potential inclusion of LE in SSBs.

Thermodynamic modeling of a SSB allowing for addition of LE will be presented for the first time, alongside analysis of an ASSB and Li-ion battery (LIB). Three failure scenarios were considered; thermal runaway from external heating, internal short circuit, and catastrophic mechanical failure of the SE. Thermal runaway from external heating included cathode decomposition, LE reaction with the resulting O₂, and LE reaction with the lithiated anode. Internal short circuit considered the complete conversion of stored electrochemical energy to heat, without other reactions. Catastrophic mechanical failure allowed for thermal runaway combined with cathode-generated O₂ reacting with the Li anode through a broken SE. The volume of LE in SSB and LIB was varied, and the resulting potential heat release compared. Heat release and potential temperature rise was analyzed for different ASSB, SSB, and LIB formats of increasing energy density. The results show that the addition of small quantities of LE at the cathode in SSBs has modest safety consequences and may be a relevant pathway to commercialization. For small quantities of LE, the potential temperature rise of the typical thermal runaway reactions are small relative to the release of stored energy, highlighting the importance of the overall energy density in assessing safety. The results allow safety concerns to be integrated with interfacial resistance performance challenges to better inform SSB designs.

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

Solid-state lithium thin-film batteries (TFBs) offer exceptional energy storage performance with high energy density, long cycle life, and enhanced safety. Fabrication of thin film cathodes typically involves high temperature depositions or a thermal annealing step to crystallize the thin film cathodes into the desired crystallographic phases. For example, state-of-the-art sputter deposited LiCoO₂ (LCO) must be annealed at >500°C to achieve a maximum charge storage capacity of 67 µAh cm^-2 µm^-1 (equivalent to 135 mAh g^-1). These high temperatures place significant constraints on the materials of construction and processing of solid-state thin film batteries. In this talk, our efforts to develop low temperature cathode fabrication approaches to mitigate these constraints and expand the potential applications of thin film batteries will be discussed.

The first project utilizes polymeric charge-transfer complexes. These complexes are formed through vapor phase infiltration of I₂ or ICl into poly(4-vinylpyridine) (P4VP) films prepared by initiated chemical vapor deposition (iCVD). iCVD enables room-temperature synthesis of well-defined films directly on the surface of Pt current collectors. After infiltration with I₂ or ICl, the cathodes are coated nominally with 1 mm of lithium phosphorous oxynitride (LiPON) electrolyte and an evaporated Li metal anode. Discharging at 70°C, the P4VP-I₂ and P4VP-ICl deliver capacities of 8.7 and 36.2 µAh cm^-2 µm^-1, respectively, with an average voltage of 2.2V and 3.15V. The cathodes appear to be irreversible under normal operating conditions, limiting their application to primary electrochemical cells. However, it has been shown that these cathodes are readily prepared on flexible, temperature sensitive substrates, as well as complex, three dimensional architectures, which should allow them to be readily integrated into wearable, low cost devices and enable additional energy-intensive applications.

In the second project, a class of lithium metal oxide cathode materials are prepared by RF magnetron sputtering and incorporated into solid state thin film batteries consisting of LiPON electrolyte and Li metal anode. Charged to 4V vs. Li/Li⁺, specific capacities in excess of 110 mAh cm^-2 mm^-1 have been achieved, which is 64% larger than state-of-the-art LCO cathodes. When cycled at a rate of 0.6C (100 minutes for charge/discharge), 83% of the maximum capacity is retained. Moreover, the cathodes are highly reversible with coulombic efficiencies in excess of 99.8%, resulting in greater than 94.7% capacity retention over 100 galvanostatic charge/discharge cycles. Efforts to further enhance rate performance and cycle lives will be discussed, in addition to demonstrations of these cathodes on flexible, polymeric (temperature sensitive) substrates.

All-solid-state lithium battery technology is one of the most promising candidates for next-generation batteries due to the high energy density, long cycle life and superior safety. To realize the technology in practical application, solid electrolyte (SE) is the key. The family of thiophosphate SEs is receiving much attention due to the high ionic conductivity at room temperature (> 1 mS cm^-1) which could even exceed conventional liquid electrolytes. However, most of the thiophosphate SEs were prepared through solid-state-reaction route by high-energy ball milling and post high-temperature treatment at above 300 ^oC which is energy consuming and not suitable for large-scale production. Here, we will demonstrate the synthesis of argyrodite-type SEs through facile solution-based method with low annealing temperature below 200 ^oC. The synthesized SE demonstrated a high ionic conductivity of ~ 4.01 mS cm^-1 at room temperature and superior stability against lithium metal anode. At room temperature, Li|SE|Li symmetric cell demonstrated a high critical current density of 1 mA cm^-2 and low areal interfacial resistance of 6 ~ 7 Ω cm². The demonstration of the synthesis of argyrodite-type SEs extend the family of solution-synthesized sulfide-based SEs.

Solid-state batteries have significant advantages over conventional liquid batteries, providing improved safety, design freedom, and potentially reaching higher power and energy densities. One of the major obstacle in the commercial realization of solid-state batteries is the high resistance at the interfaces. Essential for overcoming this bottleneck is to achieve in-depth fundamental understanding of the crucial electrochemical processes at the interface. Conventional electrochemical stability calculations for solid electrolytes, determining the formation energy towards the energetically favourable decomposition products, often underestimate the stability window because kinetics are not included. Here we discuss a computational scheme that takes the redox-activity of the solid electrolytes into account in calculating the electrochemical stability, which in many cases appears to dictate decomposition route and thus the electrochemical stability. This methodology is applied to different chemical and structural classes of solid electrolytes, exhibiting goodagreement with experimentally observed electrochemical stability. Several examples will be discussed, and compared to experimental observations. These results suggest that the electrochemical stability of solid electrolytes is not always determined by the stability of the decomposition products but often originates from the intrinsic stability of the material itself. The processes occurring outside the stability window can lead towards phase separation or solid-solution depending on the reaction mechanism of the material. These newly gained insights provide better predictions of the practical voltage ranges and structural stabilities of solid electrolytes, which may be valuable for material and interface design of solid-state batteries.

The advent of solid-state batteries has spawned a recent increase in interest in lithium conducting solid electrolytes, especially in the lithium thiophosphates. However, many open questions remain when trying to optimize electrolytes and understand solid state battery chemistries.

In this presentation, we will show how an understanding of the structure-transport properties of the lithium argyrodites Li₆PS₅X can help tailor the ionic conductivity. We show that an anion site-disorder and anionic charge inhomogeneities are important and that and that tailoring dis disorder leads to improvements of the conductivity.

Further, we will show that it is not only important to find fast ionic conductors, but that fast ionic conduction is paramount within solid state battery composites. Measuring the effective ionic transport in cathode composites provides an avenue to explore transport and stability limitations that in turn provide better criteria for solid state battery performance.

Lastly, we will show how tailoring particle size distributions can help create solid-state battery cells with conversion-type active materials.

Solid-state batteries enable safer energy storage than common liquid ion batteries due to the use of a solid electrolyte. To compete with liquid ion batteries the solid electrolytes need to be structurally tailored to provide comparable conductivities.^[1,2] In recent years, the ternary halides Li₃MX₆ (M = Y, Er, In; X = Cl, Br, I) have garnered the interest of researchers due to their high ionic conductivities. Iso- or aliovalent substitutions within this material class are scarce preventing a deeper understanding of structure-property relationships. In this work, we investigate the impact of Zr substitution on the structure and ionic conductivity of Li₃InCl₆ (Li_3-xIn_1-xZr_xCl₆ with 0 ≤ x ≤ 0.5) using a combination of neutron diffraction, nuclear magnetic resonance and impedance spectroscopy. Analysis of high-resolution neutron diffraction data suggests a cation site-disorder and a tetrahedrally coordinated Li⁺ site, which has not been reported in Li₃InCl₆ yet. In combination, all here-found Li⁺ positions form a three-dimensional polyhedral network enabling 3D diffusion. The Zr⁴⁺ substitution in Li₃InCl₆ induces non-uniform volume changes and increases the number of vacancies in the structure, all of which lead to an increasing ionic conductivity in this series of solid solutions. This investigation highlights the importance of understanding the solid electrolyte structure-property relationships to further improve not just the materials themselves but also for the utilization in solid-state batteries.

References.
(1) Ohno S., Rosenbach C., Dewald G.F., Janek J., Zeier W.G. "Linking Solid Electrolyte Degradation to Charge Carrier Transport in the Thiophosphate-Based Composite Cathode toward Solid-State Lithium-Sulfur Batteries" Adv. Funct. Mater. 2021, 31, 2010620.
(2) Ohno S., Koerver R., Dewald G., Rosenbach C., Titscher P., Steckermeier D., Kwade A., Janek J., Zeier W.G., "Observation of chemo-mechanical failure and influence of cut-off potentials in all-solid-state Li-S batteries” Chem. Mater. 2019, 31, 2930-2940.
(3) Helm B., Schlem R., Wankmiller B., Banik A., Gautam A., Ruhl J., Li C., Hansen M.R., Zeier W.G. "Exploring Aliovalent Substitutions in the Lithium Halide Superionic Conductor Li_3-xIn_1-xZr_xCl₆ (0 < x < 0.5)" Chem Mater. 2021. doi.org/10.1021/acs.chemmater.1c01348.

Li6PS5Br argyrodites have been identified as promising solid electrolytes due to high ionic conductivities. Although it is known that the material can be synthesized with anion site-disorder among Br and S the exact effect on its properties has not been clear so far. In line with experimental investigations we show in this contribution how systematic density functional theory calculations have been applied to understand the intricate interplay between the underlying Br/S site-exchange and the materials properties.
The lattice constant of Li6PS5Br was found to depend on the degree of Br/S site-exchange and shows a minimum at 50% site-exchange. Also energetically a relationship is found and the most stable structures are obtained for the ordered material, i.e., at 0% site-exchange. At 50% the least stable structures are found and the energy difference amounts to 125 meV/f.u. on average. The assessment of the configurational entropy due to Br/S site-exchange itself and the vibrational entropy cannot explain the experimentally observed dependence between temperature and equilibrium site-exchange. We therefore conclude that a substantial part of the entropy needs to stem from the highly mobile Li ions.
Indeed, the Br/S site-exchange is key for favorable transport properties of Li6PS5Br. In the absence of any site-exchange only local Li motion within Li "cages" around the S ions is observed. Even at 700 K such intracage jumps dominate the simulations. Temperatures of 800 K or higher are need to initiate intercage jumps that are needed for true long range transport within reasonable simulation times. The introduction of Br/S site-exchange changes the situation drastically: At 50% site-exchange long-range transport is observed already at 500 K. In order to understand the diffusion mechanism we analyzed the individual anion exchanges. According to our simulations the main reason for improved transport properties is due to Br ions on S sites. These defects mainly cause for the generation of Li Frenkel pairs whose interstitial is rather mobile and travels among the neighboring Li cages via interstitial and interstitialcy mechanisms. The Li vacancy, on the other hand, seems to be strongly bound to the anion defect.
At last we focused on grain boundaries in Li6PS5Br. Admittedly, their resistances to the ionic conductivity seem to be of little concern experimentally but the reasons for this circumstance have not been elucidated, yet. To this end we prepared simple tilt and twist grain boundaries and analyzed their influence on the Li diffusion. We find that again the Br/S site-exchange plays a delicate role in this context: At 0% site-exchange grain boundaries seem to improve the transport properties because they locally disrupt the strict cage ordering. At 50%, however, Li transport is slightly deteriorated compared to the bulk phase.

Lithium thiophosphates (LPS), with the general composition (Li₂S)_x(P₂S₅)_1-x, are one of the most promising classes of prospective electrolyte materials in solid-state batteries (SSBs), owing to their superionic conductivity at room temperature (>10^–3 S cm^–1), soft mechanical properties, and low grain boundary resistance. So far, several glass-ceramic (gc) LPS compositions have been synthesized and characterized experimentally. The ionic conductivity of the gc-LPS materials is significantly influenced by the glassy phases, and the relationship between structures and conductivity remains unclear due to the limitation of experimental techniques in characterizing amorphous phases. To resolve the atomic structures of gc-LPS with varying compositions, we mapped the phase diagram by integrating density functional theory (DFT), artificial neural network (ANN) potentials as implemented in the atomic energy network package (ænet), genetic-algorithm (GA) sampling, and ab initio molecular dynamics (AIMD) simulations. The thermodynamic stability and ionic conductivity of glassy/ceramic phases was correlated with the local structural motifs in the known LPS crystal structures. Structure-composition-conductivity relationships of gc-LPS were demonstrated. With machine learning accelerated sampling and AIMD simulations, a candidate solid-state electrolyte composition with high ionic conductivity (>10^–2 S cm^–1) was identified, which could provide a design strategy for optimized LPS materials with enhanced conductivity and stability.

References
[1] Haoyue Guo, Qian Wang, Alexander Urban, Nongnuch Artrith. “Structure-Composition-Conductivity Relationships of Glass-Ceramic Lithium Thiophosphates Electrolytes.” in preparation.

The development of solid-state batteries has been slowed by limited understanding of the features that control ion mobility in solid electrolytes (SE). In the case of anti-perovskite (AP) SE, lattice distortions have been proposed as one such controlling factor: APs that exhibit distortions of the octahedral building blocks are predicted to exhibit enhanced ionic mobility. Nevertheless, large distortions come at a cost to stability, implying a tradeoff between stability and ionic mobility. The present study combines theory and experiments to explore the synthesizability of several marginally-stable APs predicted to exhibit high mobility for Li⁺, Na⁺, and K⁺. Density functional theory calculations, in combination with the quasi-harmonic approximation, were used to predict the free energy change, ΔG_r(T), for synthesis reactions involving 36 alkali-metal-based APs, X₃AZ (X = Li, Na, or K; A = O, S, or Se; Z = F, Cl, Br, or I). A linear correlation is observed between the degree of lattice distortion and the stabilization temperature, at which ΔG_r(T) = 0. Hence, APs with the highest ionic mobility generally require the highest synthesis temperatures. These data were used to guide experimental synthesis efforts of APs by estimating the temperatures above which a given AP is expected to be thermodynamically stable. Attempts were made to synthesize several AP compositions; overall, good agreement is obtained with the computational predictions. These data suggest that a compound’s zero Kelvin decomposition energy is an efficient descriptor for predicting the ease and likelihood of synthesizing new SEs.

All-state-state lithium batteries (ASSLBs) have gained worldwide attention because of intrinsic safety and increased energy density. Compared with other types of solid-state electrolytes including oxide-based, polymer-based and sulfide-based electrolytes, recently-developed halide-based solid-state electrolytes (SSEs) have garnered considerable attention for all-solid-state lithium batteries (ASSLBs) due to the high ionic conductivity, high oxidation voltage and good stability toward oxide cathode materials [1]. However, there are still many challenges in halide-based solid-state electrolytes for ASSLBs including controllable and mass-production synthesis, achieving high humidity tolerance and demonstrate high-performance of ASSLBs; in particular, increased understanding of mechanisms during synthesis and tuning their properties of the electrolytes as well as interface with electrode materials[1].

In this talk, (i) I will demonstrate synthesis strategy [2-3], in particular, new and salable water-mediated synthesis method [2]. (ii) I will report a systematic study on the correlations among structural evolution, Li⁺ migration properties, and humidity stability resulting of the halide-based electrolytes, along with in-situ characterization for understanding of the mechanisms [4], (iii) Full cell battery performance will be optimized [5], and (iv) humidity ability [6]. In the end, energy densities of ASSLBs using different solid-state electrolytes in ASSLBs will be discussed [7].


References:
X. Li, J. Liang, X. Yang, K. Adair, C. Wang, F. Zhao, X. Sun. Progress and Perspectives of Halide-based Lithium Conductors for All-Solid-State Batteries. Energy Environ. Sci., 13, 1429-1461 (2020).
X. Li, J. Liang, X. Sun, et al., H2O-Mediated Synthesis of Superionic Halide Solid Electrolyte. Angewandte Chemie International Edition, 58, 16427-16432 (2019).
X. Li, J. Liang, X. Sun, et al.,. Air-Stable Li3InCl6 Electrolyte with High Voltage Compatibility for All-Solid-State Batteries. Energy Environ. Sci., 12, 2665 - 267 (2019).
X. Li, J. Liang, X. Sun, et al.,. Origin of Superionic Halide Solid Electrolytes with High Humidity Tolerance, J. Am. Chem. Soc. 142, 7012-7022 (2020).
C. Wang, X. Li, J. Liang, X. Sun, et al., Eliminating Interfacial Resistance in All-Inorganic Batteries by In-situ Interfacial Growth of Halide-based Electrolyte. Nano Energy, 2020, in press.
X. Li, J. Liang, X. Sun, et al., Origin of Superionic Li₃Y_1-xIn_xCl₆ Halide Solid Electrolytes with High
Humidity Tolerance, Nano Letters, 20, 6, 4384–4392 (2020).
J. Liang, X. Li, K. Adair, X. Sun, Metal Halide Superionic Conductor for All-Solid-State Batteries, Acc. Chem. Res. 54, 1023-1033(2021).

Rechargeable lithium (Li) metal batteries are regarded as the next-generation power sources due to their high energy density that can potentially reach 500 Wh kg^-1 at cell level. The success of high energy-density Li metal batteries largely depends on the development of electrolytes because the electrolyte should be chemically and electrochemically stable on both Li metal anode and high-voltage cathode, suppress the growth of mossy/dendritic Li morphology and prevent the penetration of Li dendrites. Currently, the liquid electrolytes have achieved much progress, reaching a high Li Coulombic efficiency (CE) about 99.5% and a high voltage stability up to 4.5 V. However, the Li CE is still not high enough to ensure the long cycle life and the mossy/dendritic Li formation during repeated cycling would cause safety concerns. The solid-state inorganic electrolytes face more challenges, in either low ionic conductivity, high interfacial resistance with electrodes, poor stability with Li metal or high voltage cathode, unable to prevent Li penetration, or low mechanical strength, etc. The third approach is to use polymer or polymer composite electrolytes, which may mitigate the above issues related to liquid electrolytes and solid-state inorganic electrolytes. Polyethylene oxide (PEO) is the most widely studied polymer in polymer electrolytes and batteries. However, the conventional PEO-based electrolytes have low room-temperature ionic conductivity and low oxidative stability (< 4 V vs. Li/Li⁺), thus their applications must be set at high temperatures and limited to 4 V-class cathode materials, resulting in a low energy density of the batteries. Therefore, to develop high-voltage PEO-based electrolytes for Li metal batteries is of high significance. In this talk, we will report the efforts at PNNL to develop PEO-based polymer-in-salt electrolytes that are stable up to 4.3 V. More details will be discussed during the presentation at the meeting.

Anti-perovskites materials have recently attracted great interest as a family of solid state electrolytes with high ionic conduction.[1] Typical solid-state ionic conductors have temperature-dependent ionic conductivity following Arrhenius behavior over a substantial range of temperature, corresponding to a constant activation energy E_a. In the Na₃OCl antiperovskite, there are regimes of Arrhenius behavior separated by broad transitions, all while the structure remains cubic . Such non-Arrhenius ionic conductivity of Na₃OCl has been observed in previous literature. [2][3] However, there is no clear explanation for this non-Arrhenius transition. Differential scanning calorimetry shows thermal transitions in the vicinity of these conductivity transitions. Reitveld refinement on temperature dependent synchrotron XRD of Na₃OCl suggests changes in the B_eq and anisotropic U₃₃ of Na around 305^oC, which is consistent with the conductivity jump temperature. Meanwhile, the octahedral tilts observed at low temperature becomes much less above the transition temperature. We explain this as the activation of octahedra fluctuation[1] above the transition temperature as the time-averaged synchrotron fitted structure becomes closer to cubics . In this work, we use multiple temperature-resolved characterization methods including synchrotron XRD, transport measurements, and calorimetry, and modeling by AIMD and DFT, to understand this behavior and to gain insight into tuning antiperovskites for high ionic conductivity.

This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.

References:
1. Kim, K., & Siegel, D. J. (2019). Correlating lattice distortions, ion migration barriers, and stability in solid electrolytes. Journal of materials chemistry A, 7(7), 3216-3227.
2. Ahiavi, Ernest, et al. "Mechanochemical synthesis and ion transport properties of Na3OX (X= Cl, Br, I and BH4) antiperovskite solid electrolytes." Journal of Power Sources 471 (2020): 228489.
3. Wang, Yonggang, et al. "Structural manipulation approaches towards enhanced sodium ionic conductivity in Na-rich antiperovskites." Journal of Power Sources 293 (2015): 735-740.

Solid state batteries (SSBs), especially those utilizing conversion-type active materials (C-AMs), are one of the most promising future energy storage devices.¹ However, the volume variation of C-AMs upon electrochemical cycling are a great challenge for the mechanical stability of SSBs. The periodic volume variation is known to deteriorate the physical contact between the AMs and solid electrolytes (SEs), and emphasizes the necessity of achieving robust mechanical properties.² Although considerable progress already made by choice of materials, modulation of their interfaces, or even adopting new battery concepts,³ there is still a long way to go in order to realize practical SSBs.

Obtaining a better understanding of SSBs is highly desirable, but appropriate methods are often limited by their shallow penetration depth alongside design aspects of the cells. Compared with other technologies, 3D tomography is able to penetrate solid-state samples and detect details of the bulk by virtue of utilizing high energy X-Rays, making 3D tomography a powerful technology for visualizing SSBs during operation.⁴ CuS is a well-studied conversion material with high electronic and ionic conductivity that exhibits a volume expansion of 75% after being fully lithiated. It also shows good cycling stability and is known to react with lithium in a manner that produces a macro-scale displacement of Cu in SSBs.⁵ While known to occur in standard cells, this type of displacement reaction in metal sulfides has not yet been studied in SSBs.

Herein, a model SSB with Li/β-Li₃PS₄/µm-CuS structure was investigated by 3D tomography to study the macro-scale displacement reaction and its accompanying morphological and volume variations. We found that the applied mechanical field can seriously affect the reaction, where the reduced Cu particles and cracks clearly demonstrate growth in preferred orientations. While Cu reduction is reversible, nearly 50% of cracks are maintained within the electrodes after the 1^st delithiation. This results in disruption of the ionic and electronic transport pathways, as supported by a higher transfer resistance and the observation of more “dead” materials produced in the electrodes.

References:
(1) Randau, S.; Weber, D. A.; Kötz, O.; Koerver, R.; Braun, P.; Weber, A.; Ivers-Tiffée, E.; Adermann, T.; Kulisch, J.; Zeier, W. G.; Richter, F. H.; Janek, J. Nat. Energy 2020, 5 (3), 259–270.
(2) Wu, X.; Billaud, J.; Jerjen, I.; Marone, F.; Ishihara, Y.; Adachi, M.; Adachi, Y.; Villevieille, C.; Kato, Y. Adv. Energy Mater. 2019, 9 (34), 1–10.
(3) Baggetto, L.; Niessen, R. A. H.; Roozehoom, F.; Notten, P. H. L. Adv. Funct. Mater. 2008, 18 (7), 1057–1066.
(4) Ning, Z.; Jolly, D. S.; Li, G.; De Meyere, R.; Pu, S. D.; Chen, Y.; Kasemchainan, J.; Ihli, J.; Gong, C.; Liu, B.; Melvin, D. L. R.; Bonnin, A.; Magdysyuk, O.; Adamson, P.; Hartley, G. O.; Monroe, C. W.; Marrow, T. J.; Bruce, P. G. Nat. Mater. 2021.
(5) Santhosha, A. L.; Nazer, N.; Koerver, R.; Randau, S.; Richter, F. H.; Weber, D. A.; Kulisch, J.; Adermann, T.; Janek, J.; Adelhelm, P. Adv. Energy Mater. 2020, 10 (41), 1–9.

Solid electrolyte is the key component for all-solid-state batteries. Extensive research attentions are being attracted to the design and development of high performance solid electrolytes with high ionic conductivity and low diffusion energy barriers. Recently halides with general formula Li₃MX₆ (M=metals such as Y, In and Sc; X=Cl or Br) have attracted a lot of attention from both industry and academia because the halide Li-ion conductors are potentially more all-around candidates for all-solid-state batteries than existing sulfides and oxides. They showed higher ionic conductivities than those of oxides (such as LLZO and variants) and better chemical and electrochemical stabilities than sulfides (such as LGPS and argyrodite materials). However, many detailed features in their crystal structure are yet to be clearly described and the key factors that govern the ionic conductivity are yet to be revealed. Here we report our recent findings in design, synthesis, electrochemical testing and particularly crystal structure characterizations of novel halide compounds. The long range structure and the thermodynamic stability are investigated with using ex situ and in situ synchrotron X-ray diffraction. The Li sublattice, local ordering and stacking faults are characterized with using neutron diffraction and pair distribution function analysis. The relation between these structural features and the ionic conductivity and diffusion energy barriers are revealed and discussed.

Solid-state Li-batteries (SSLiBs) have the potential to be a transformational and intrinsically safe energy storage solution. However, their progress has been limited by high solid-solid interfacial impedance and numerous reports of Li-dendrites and a corresponding “critical current density”. By first modifying the garnet surface to enable Li-metal to wet it and then fabricating garnet-electrolytes into tailored tri-layer microstructures to form electrode supported dense thin-film (~10μm) solid-state electrolytes we have been able to overcome these limitations. The microstrucurally tailored porous garnet scaffold support increases electrode/electrolyte interfacial area, overcoming the high impedance typical of planar geometry SSLiBs resulting in an area specific resistance (ASR) of only ~2 to 7 Ωcm^-2 at room temperature. The unique garnet scaffold/electrolyte/scaffold structure further allows for charge/discharge of the Li-metal anode and cathode scaffolds by pore-filling, thus providing high depth of discharge ability without mechanical cycling fatigue seen with typical electrodes. Moreover, these scalable multilayer ceramic fabrication techniques, without need for dry rooms or vacuum equipment, provide for dramatically reduced manufacturing cost.

The fabrication of supported dense thin-film garnet electrolytes, their ability to cycle Li-metal at high current densities with no dendrite formation, and results for Li-metal anode/garnet-electrolyte based batteries with a number of different cathode chemistries will be presented.

Room temperature lithium ion conductors have been intensively studied in an attempt to develop solid state batteries that can be deployed for high energy applications. In recent years, promising solid lithium ion conductors with competitive ionic conductivity to those of liquid electrolytes have been demonstrated. The integration of highly conductive solid electrolytes into the battery system is, however, still very challenging mainly due to the high impedance existing at different interfaces throughout the battery structure.

In this talk, I will highlight our recent work on the understanding of interfaces between the solid electrolytes and anode & cathode, providing new insights into enabling future all solid-state batteries. I will also show that high energy and long cycle life can be achieved in solid state batteries via optimizing the interfacial thermodynamics.

All-solid-state sodium (Na) batteries (ASSSBs) attract increasing attention due to the use of high-capacity Na metal anode and solid electrolytes (SEs) with high safety. Recently, significant research achievements have been made in developing Na-ion conductors. In particular, sulfide SEs generally offer higher ionic conductivity (10⁻⁴−10⁻³ S cm⁻¹ at room temperature) and lower grain boundary resistance. However, the practical applications of sulfide-based ASSSBs are significantly hampered by the challenges originating from (1) significant reactions at SE/Na interface; (2) poor solid-solid contact between SE and electrodes. To solve these issues and enhance the electrochemical performance of sulfide-based ASSSBs, here, we design and demonstrate several strategies including elements doping in sulfide SEs and interface modifications between sulfide SEs and electrodes. As a result, long-term cycling stability was achieved due to 1) the formation of stable interface to prevent the sever interfacial reactions; 2) the creation of intimate contact between sulfide SEs and electrodes. These methods provide effective strategies to address the challenges between sulfide SEs and Na metal, enabling the successful utilization of Na metal and sulfide SEs in ASSSBs towards next-generation safe and high-energy density energy storage systems.

Sodium all solid-state batteries (Na-ASSBs) offer a combination of improved safety and lowered costs due to the use of non-flammable solid-state electrolytes (SSEs) and naturally abundant Na-based raw materials. However, a fundamentally different approach is necessary to achieve a simultaneous leap in multiple SSE properties – ionic conductivity, (electro) chemical stability and processibility. Our recent work has demonstrated long cycle performance of a Na-ASSB enabled by a new class of halide-based SSE, achieving a capacity retention of approximately 90% after 1000 cycles at a rate of 1C, representing one of the best Na-based battery performances in the literature till date. This was made possible through a joint computational and experimental exploration of novel halide-based Na SSEs. In this talk, I will discuss computational strategies based on ab initio and the machine learning interatomic potential, that has proven to be highly effective to report the discovery of moderate ionic conductivity of 6.6 x 10^-5 S cm^-1 at ambient temperature for Na_3-xY_1-xZr_xCl₆ (NYZC) several orders of magnitude higher than oxide coatings. Enhanced Na-conductivity in NYZC is attributed to abundant Na vacancies and cooperative MCl₆ rotation resulting non-Arrhenius behavior.

Solid-state batteries (SSBs) have been recognized as promising next-generation rechargeable batteries because of their potential to push energy density limits and ensure safety. Sulfide-based solid electrolytes (SEs) are promising candidates for solid-state batteries (SSBs) because of their high ionic conductivity and good malleability. Like conventional liquid electrolytes, SE decomposes at the electrode-electrolyte interface when the potential is outside its electrochemical stability window, forming a solid-solid interphase (SSI) layer. SSI’s properties and the dynamic evolution of its structure are crucial for the stability and performance of SSBs. For example, some decomposition products may have high ionic resistance, which is detrimental to the cell performance; some redox processes are reversible and participate in the electrochemical cycle with the active electrode materials. Understanding the dynamic structure of the SSI and its impact to transport properties is essential for incorporating sulfide SE into commercial batteries.

Modelling the inherent complexity and the dynamic evolution of the SSIs is very challenging with first-principles methods, such as density functional theory, because of the computational hurdle associated with the large system size (e.g., more than one thousand atoms) and time scale. Herein, we develop an integrated approach that combines high-performance computing and machine learning tools with state-of-the-art synchrotron X-ray absorption spectroscopy (XAS)/electron energy-loss spectroscopy (EELS), to tackle the complex SSIs. Ex situ and in situ XAS/EELS are applied to characterize SSIs’ chemical structure and dynamic evolutions upon formation and during electrochemical cycling. We focus on two types of sulfide SEs, the baseline glass/ceramic Li₂S-P₂S₅ (LPS), and the more advanced argyrodite Li₆PS₅Cl (LPSCl) which has higher ionic conductivity and is promising for commercial use. Our results reveal the reaction mechanism at the interface of sulfide-based SEs and provide a fundamental understanding of the current material limitations. This study can help identify key material parameters to optimize cell performance, thus providing a basis for the design and optimization of SEs for SSBs.

Inorganic all-solid-state lithium-ion batteries (ASSLIBs) are considered as a promising candidate for next-generation energy storage devices that can meet the safety requirements of electric vehicles by utilizing nonflammable solid-state electrolytes (SSEs).[1, 2] However, the poor interfacial compatibility in composite cathodes (SSE/cathode/carbon/current collector) is challenging the stable delivery of electrochemical performance.[3, 4] Our research mainly focuses on the development of interfacial engineering strategies to address the challenges at the internal and external interfaces in the composite cathodes targeting high-performance ASSLIBs. [5-7] In this talk, three parts will be included. Firstly, I will review our previous studies. For example, at the SE/cathode interface, we designed a dual-functional Li3PO4 (LPO) modification to suppress both the side-reactions and contact loss at the SSE/cathode interface.[8] We also developed a surface-cleaning strategy to investigate the underlying degradation mechanism at SSE/cathode interface.[9] At the SSE/carbon interface, a poly(3,4-ethylenedioxythiophene) (PEDOT) modification is designed as a semiconductive additive for composite cathodes.[10] The modified ASSLIB demonstrates a competitive rate capacity, which is 10 times greater than that of the bare cathode. Secondly, I will introduce our recent work, focusing on the current collector interface. Our study found that the interfacial stability at the current collector interface is highly dependent on the temperatures. At the end of this talk, I will introduce our work on low-temperature inorganic ASSLIBs. Our study revealed that manipulating the electronic conductivity in the composite cathodes is the key factor that determines the electrochemical performance at low temperatures.

References
[1] F. Zhao, J. Liang, C. Yu, Q. Sun, X. Li, K. Adair, C. Wang, Y. Zhao, S. Zhang, W. Li, S. Deng,
R. Li, Y. Huang, H. Huang, L. Zhang, S. Zhao, S. Lu, X. Sun, Advanced Energy Materials, 10
(2020) 1903422.
[2] X. Li, J. Liang, J. Luo, M. Norouzi Banis, C. Wang, W. Li, S. Deng, C. Yu, F. Zhao, Y. Hu,
T.-K. Sham, L. Zhang, S. Zhao, S. Lu, H. Huang, R. Li, K.R. Adair, X. Sun, Energy &
Environmental Science, 2019, 12, 2665.
[3] C. Yu, Y. Li, M. Willans, Y. Zhao, K.R. Adair, F. Zhao, W. Li, S. Deng, J. Liang, M.N. Banis,
R. Li, H. Huang, L. Zhang, R. Yang, S. Lu, Y. Huang, X. Sun, Nano Energy, 2020, 69, 104396.
[4] C. Yu, Y. Li, K.R. Adair, W. Li, K. Goubitz, Y. Zhao, M.J. Willans, M.A. Thijs, C. Wang, F.
Zhao, Q. Sun, S. Deng, J. Liang, X. Li, R. Li, T.-K. Sham, H. Huang, S. Lu, S. Zhao, L. Zhang, L.
van Eijck, Y. Huang, X. Sun, Nano Energy, 2020, 77, 105097.
[5] X. Li, Z. Ren, M. Norouzi Banis, S. Deng, Y. Zhao, Q. Sun, C. Wang, X. Yang, W. Li, J. Liang,
X. Li, Y. Sun, K. Adair, R. Li, Y. Hu, T.-K. Sham, H. Huang, L. Zhang, S. Lu, J. Luo, X. Sun,
ACS Energy Letters, 2019, 4, 2480.
[6] C. Wang, J. Liang, S. Hwang, X. Li, Y. Zhao, K. Adair, C. Zhao, X. Li, S. Deng, X. Lin, X.
Yang, R. Li, H. Huang, L. Zhang, S. Lu, D. Su, X. Sun, Nano Energy, 2020, 72, 104686.
[7] C. Wang, X. Li, Y. Zhao, M.N. Banis, J. Liang, X. Li, Y. Sun, K.R. Adair, Q. Sun, Y. Liu, F.
Zhao, S. Deng, X. Lin, R. Li, Y. Hu, T.-K. Sham, H. Huang, L. Zhang, R. Yang, S. Lu, X. Sun,
Small Methods, 2019, 3, 1900261.
[8] S. Deng, X. Li, Z. Ren, W. Li, J. Luo, J. Liang, J. Liang, M.N. Banis, M. Li, Y. Zhao, X. Li,
C. Wang, Y. Sun, Q. Sun, R. Li, Y. Hu, H. Huang, L. Zhang, S. Lu, J. Luo, X. Sun, Energy Storage
Materials, 2020, 27 117.
[9] S. Deng, Q. Sun, M. Li, K. Adair, C. Yu, J. Li, W. Li, J. Fu, X. Li, R. Li, Y. Hu, N. Chen, H.
Huang, L. Zhang, S. Zhao, S. Lu, X. Sun, Energy Storage Materials, 2021, 35, 661.
[10] S. Deng, Y. Sun, X. Li, Z. Ren, J. Liang, K. Doyle-Davis, J. Liang, W. Li, M. Norouzi Banis,
Q. Sun, R. Li, Y. Hu, H. Huang, L. Zhang, S. Lu, J. Luo, X. Sun, ACS Energy Letters, 2020, 5,
1243.

Thermal runaway of nonaqueous Li-ion batteries starts from decomposition of the solid electrolyte interphase (SEI). Introduction of solid electrolyte has been considered as a promising solution to improve the safety and achieving high energy density. However, it is quite challenging for the construction well-conducted and thermal stable interfaces. Our previous research indicates the thermal stability between metallic lithium and inorganic solid-state electrolytes is not always under controlled. Herein, we proposed that the in-situ solidification strategy is a comprehensive methodology for the pathway toward practical solid state batteries. For example, the in-situ solidification strategy is applied to generate artificial solid electrolyte interface (SEI) between electrodes (both cathode and anode) and electrolytes. The in-situ built SEI not only promotes the electrochemical stability, but also shows great potential for the promotion on the thermal stability of SSBs. Thus, the in-situ solidification could make the thermal property of SEI well-designed and controllable, which means the thermal stability of the battery could be improved significantly.

Sulfide electrolytes have been considered as one of the most promising ion conductors for all-solid-state lithium batteries due to the breakthrough in ionic conductivity, low particle-boundary resistance and excellent ductility.^[1] Different type sulfide electrolytes with room temperature ionic conductivity of 10^-3 ~ 10^-2 S/cm have been successfully synthesized. The electrochemical stability and compatibility with lithium can be improved with oxide or halogen doping^[2] as well as densified solid electrolyte with flat surface^[3]. Based on the high ionic conductive sulfide electrolyte powder, thin film were obtained by wet chemical surface modification method^[4] or dry film approach^[5]. The obtained Li_5.4PS_4.4Cl_1.6 sulfide electrolyte membrane possesses a high ionic conductivity of 8.4 mS cm^-1 with a thin thickness of 30 μm, which is crucial to realize high energy density all-solid-state rechargeable batteries.^[5]
Compared with lithium transition metal oxide cathodes, sulfur based materials, especially transition metal sufides, show much better interface compatibility with sulfide electrolytes. A series of transition metal sulfides or sulfur-based materials are employed as electrodes for all-solid-state rechargeable batteries, such as MoS₃^[6] FeS₂^[7], VS₄^[8] or sulfur^[9]. The intimate contact interface can be realized by coating sulfide electrolytes evenly on the surface of active materials, which enables the battery to withstand the large stresses/strains during repeated charging/discharging, leading to significant improvements in energy density and cycle life.^[10] Besides, in order to improve electronic conductions, highly conductive carbonaceous materials were employed as hosts for nanosized sulfur based materials to form active material/electrom additive nanocomposites. Although different reaction mechanisms, all these nanocomposites employed as cathodes in all-solid-state ltihum batteris show enhanced electrochemical performances^{[6, 9]}. Furthermore, coating sulfide electrolyte on active material/electron additive nanocomposites can simultaneously realize three-dimensional electronic/ionic conduction networks at the triple solid-solid contact interface^{[8, 11]}. For example, 10%rGO-VS₄@Li₇P₃S₁₁ nanocomposites with multi-channel continuous electronic/ionic conductive network can be prepared by a facile liquid-phase deposition reaction and further employed as an alternative material for sulfur cathode in all-solid-state room temperature lithium batteries, exhibiting improved rate capability and cycling stability. ^[8]
Clearly, all-solid-state lithium batteries with sulfur-based cathodes and sulfide electrolytes are promising next generation high energy density batteries. More attentions should be concerned in the dendrite formation, interfacial contact, reducing the electrolyte thickness as well as high specific areal capacity with high current density.

References:
[1] J. Wu, L. Shen, Z. Zhang, et al., Electrochemical Energy Reviews 2021, 4, 101.
[2] G. Liu, D. Xie, X. Wang, et al., Energy Storage Materials 2019, 17, 266.
[3] G. Liu, W. Weng, Z. Zhang, et al., Nano Letters 2020, 20, 6660.
[4] G. Liu, J. Shi, M. Zhu, et al., Energy Storage Materials 2021, 38, 249.
[5] Z. Zhang, L. Wu, D. Zhou, et al., Nano Letters 2021, doi:10.1021/acs.nanolett.1c01344.
[6] Q. Zhang, Z. Ding, G. Liu, et al., Energy Storage Materials 2019, 23, 168.
[7] H. Wan, G. Liu, Y. Li, et al., ACS Nano 2019, 13, 9551.
[8] Q. Zhang, H. Wan, G. Liu, et al., Nano Energy 2019, 57, 771.
[9] X. Yao, N. Huang, F. Han, et al., Advanced Energy Materials 2017, 7, 1602923.
[10] X. Yao, D. Liu, C. Wang, et al., Nano Letters 2016, 16, 7148.
[11] H. Wan, L. Cai, F. Han, et al., Small 2019, 15, 1905849.
[12] J. Wu, S. Liu, F. Han, et al., Advanced Materials 2021, 33, 2000751.

The all-solid-state Li-ion battery (Li-ASSB) is expected as one of the next-generation energy conversion and storage devices that could potentially become widespread in use owing to a number of its promising features such as high energy density (with the use of Li metal/alloy as anode), high working capacity (with the use of high-voltage cathodes), and high safety in contrast to conventional batteries with organic and liquid components (i.e., organic/liquid electrolytes). These aforementioned features are closely linked to the inorganic solid electrolyte (SE) component in Li-ASSB. Thus, novel high-performance SE design and optimization has become one of the the highly active areas in battery research.
Recently, electronically-inverted Li-rich perovskites have attracted great interest for SE use. In here, using density functional theory (DFT) calculations, an in-silico-generated chemical space of more than 500 inorganic compounds with an inverse Ruddlesden-Popper-type structure (Li₄(X_1-aX’_a)(Z_1-bZ’_b)₂, where X, X’ = {O^2-, S^2-, Se^2-, Te^2-} and Z, Z’ = {F^-, Cl^-, Br^-, I^-}, 0 ≤ a, b ≤1) was explored in order to find novel solid electrolyte candidates. Based from DFT thermodynamic convex hull results, about 167 compounds were determined to be (meta)stable, at least 20 novel compounds were found to belong to the Li₄O(Cl_1-bBr_b)₂ series and O/S/I-bearing compositions. Representative compounds were further evaluated using: i) phase diagram approach for (electro)chemical stability analysis, ii) slab modelling for surface properties and ii) DFT molecular dynamics method for characterizing Li⁺ ion conductivity and transport mechanism. Computationally cheap, yet useful, material descriptors were also determined based from correlation analysis of the accumulated DFT dataset. These descriptors can be useful in future solid electrolyte design/screening, such as for thermodynamic phase stability, electronic property, and Li⁺ ion conduction properties.

R.J. is thankful for the Japan Science and Technology Agency (JST) Precursory Research for Embryonic Science and Technology (PRESTO) program for the financial support. This research was also supported in part by JST through “Materials research by Information Integration” Initiative (MI2I)” and Advanced Low Carbon Technology-Specially Promoted Research for Innovative Next Generation Batteries Program (ALCA-SPRING Grant Number JPMJAL1301), JSPS KAKENHI Grant Number JP19H05815, JSPS KAKENHI Grant Number JP21K14729, and MEXT as Elements Strategy Initiative, Grant Number JPMXP0112101003, Materials Processing Science project ("Materealize"), Grant Number JPMXP0219207397 and “Program for Promoting Researches on the Supercomputer Fugaku (Fugaku Battery & Fuel Cell Project).

Reference:
Randy Jalem, Yoshitaka Tateyama,Kazunori Takada, and Masanobu Nakayama, Chem. Mater. 2021 (https://doi.org/10.1021/acs.chemmater.1c00124)

Sulfide solid electrolytes (SEs) have attracted much attention because of their high ionic conductivity and deformability. However, sulfide SEs have an issue of low air-stability. They generate H₂S gas when exposed to air. Sahu et al reported that stability of sulfide SEs against moisture in air can be explained by hard and soft acids and bases theory.^[1] Based on the theory, Sn-based SEs such as Li₄SnS₄ show higher air-stability than argyrodite type SEs and Li₂S–P₂S₅ type SEs, which have P–S bonds.^[2,3] However, Li₄SnS₄ showed lower ionic conductivity of ~10⁻⁵ S cm⁻¹ 25 °C than the conventional SEs (10⁻³–10⁻⁴ S cm⁻¹). Kanazawa et al reported that the hexagonal Li₄SnS₄ prepared by mechanochemical treatment showed higher ionic conductivity than orthorhombic Li₄SnS₄ prepared by solid phase synthesis.^[3] In this study, LiI and Li₃PS₄ were added to hexagonal Li₄SnS₄ to increase ionic conductivity of Li₄SnS₄-based SEs. Furthermore, air-stability of them was compared.
The XRD patterns of LiI-added Li₄SnS₄ showed the diffraction peaks of hexagonal Li₄SnS₄ shifted to the lower angle, suggesting that the lattice volume increased due to the I⁻ ion with large ionic radius. The sample with x = 0.43 in xLiI●(1−x)Li₄SnS₄ showed the higher ionic conductivity of 1.6 × 10⁻⁴ S cm⁻¹ at 25 °C than that with x = 0 (4.5 × 10⁻⁵ S cm⁻¹). Furthermore, XRD patterns of as-milled samples of LiI–Li₄SnS₄–Li₃PS₄ systems exhibited halo patterns, indicating that they became amorphous state due to the multicomponent. The sample of 37LiI●38Li₄SnS₄●25Li₃PS₄ (mol%) showed the ionic conductivity of 4.5 × 10⁻⁴ S cm⁻¹ at 25 °C. These samples are decomposed by heat-treatment at more than 240 °C, suggesting that they are thermally metastable. The prepared Li₄SnS₄-based SEs showed similar air-stability to hexagonal Li₄SnS₄ and generated smaller amount of H₂S gas than the argyrodite type SEs.

References
[1] G. Sahu et al., Energy Environ. Sci., 7 (2014) 1053.
[2] H. Kwak et al., J. Power Sources, 446 (2020) 227338.
[3] K. Kanazawa et al., Inorg. Chem., 57 (2018) 9925.

Acknowledgement
This work was supported by JSPS KAKENHI Grant Number JP20K22558.

All-solid-state battery (ASSB) has attracted great attention for future energy storage with safety and high-energy density. The practical application of ASSBs requires solid-state electrolytes (SSEs) which are not only highly conductive but also flexible for good interfacial contant between SSEs and electrodes. Recently, Li{N(SO₂F)₂}(NCCH₂CH₂CN)₂ (Li(FSA)(SN)₂) organic flexible molecular crystal has been experimentally reported as a promising SSE with high Li-ion conductivity of ca. 10^–4 S cm^-1 at room temperature and exceptionally low activation energy (E_a) of 28 kJ mol^-1 [K. Tanaka et al., Nano Lett., 2020, 20, 8200-8204]. However, the fast conduction mechanism remains unexplained because all the Li-ions are held in the crystal framework, and the distances between the constituent Li-ions are too long for hopping. Herein, molecular dynamics (MD) simulations were performed to clarify the mechanism of the extraordinarily fast Li-ion conduction in the succinonitrile (SN)-based molecular crystal. Atomistic MD revealed that Li-ion vacancies can exist stably in Li(FSA)(SN)₂ crystal and give rise to the one-dimensional Li-ion hopping pathway contrary to the conventional scenario in which the fast conduction is attributed to the three-dimensional pathway. The calculated E_a of 34 kJ mol^-1 is in good agreement with the experimental value, which substantially supports the one-dimensional conduction. The low E_a is intimately connected with the motion of the SN molecules. Two SN molecules at the vacancy site change their conformation, following which one of the SN molecules creates an electronegative region, while the other one carries the adjacent Li-ion to the electronegative region by the swing motion. The insights on the behavior of organic moieties and Li-ion conduction obtained from this study enable to propose a novel design principle for the fast ion-conductive molecular crystals.

For addressing the requirements of better safety and higher energy density of lithium-ion batteries targeting for the electric vehicle application, solidification of electrolytes using nonflammable superionic conductors has been rigorously investigated. Owing to their high ionic conductivities reaching maximum 10^-2 S cm^-1 at room temperature and the mechanically-sinterable property, sulfide solid electrolyte (SE) materials are considered as the key to the success of all-solid-state batteries. Moreover, wet-chemical syntheses and/or processes of sulfide SEs have been developed. The wet-chemical synthesis, such as using tetrahydrofuran, proceeds in a suspension, and provides opportunities in multiple aspects including particle size control and the reduction of mixing energy. For several compositions of sulfide materials, it has been shown that SEs could be fully dissolved into specific solvents, such as ethanol and methanol, and then the original SEs could be precipitated via the removal of solvent and subsequent heat treatment. This is referred to as the solution process. The solution processability of sulfide SEs offers direct SE coatings on active materials and infiltration of the conventional electrodes used for lithium-ion batteries. Both of which allow for intimate ionic contacts between active materials and SEs.
In this presentation, we report on a new universal liquid-phase synthesis of sulfide solid electrolytes, which takes the combined advantages of the wet-chemical synthesis and the solution process. It is demonstrated that SE precursors including not only conventional Li₂S, P₂S₅, and LiX but also metal sulfides are fully dissolved in a solvent, forming a homogeneous solution. Via the universal liquid-phase synthesis, promising electrochemical performances are demonstrated for Li- and Na-ion all-solid-state batteries.

References
[1] Dae Yang Oh, A. Reum Ha, Ji Eun Lee, Sung Hoo Jung, Goojin Jeong, Woosuk Cho, Kyung Su Kim, Yoon Seok Jung, ChemSusChem 2020, 13, 146.
[2] Yong Bae Song, Dong Hyeon Kim, Hiram Kwak, Daseul Han, Sujin Kang, Jong Hoon Lee, Seongmin Bak, Kyung-Wan Nam, Hyun-Wook Lee, Yoon Seok Jung, Nano Lett. 2020, 6, 4337.
[2] Kern Ho Park, Dae Yang Oh, Young Eun Choi, Young Jin Nam, Lili Han, Ju-Young Kim, Huolin Xin, Feng Lin, Seung M. Oh, Yoon Seok Jung, Adv. Mater. 2016, 28, 1874.

All-solid-state Li or Li-ion batteries (ASLBs) using inorganic solid electrolytes (SEs) have promising opportunities in terms of better safety and higher energy density. The cut-off score of Li⁺ conductivities of 10^-3 S cm^-1 for room-temperature operable ASLBs severely narrows the SE materials to several classes of materials, including sulfides, closo-borates, and halides. Thanks to mechanical sinterability, cost, and density, sulfide SEs are highly competitive, however, they suffer from poor chemical stability when preparing wet-slurries. They are dissolved in conventional polar organic solvents and conventional polymers such as PVDF are thus not available. Furthermore, the polymeric binders impedes Li⁺ ion transport. This could be relieved by employing liquid electrolytes or gel polymer electrolyte binders but at the expense of the ASLB's thermal stability.^[1]
In this study, we reports on our recent development of dry polymer electrolyte (DPE) binders for practical ASLBs.^[2] Furthermore, the use of cosolvents and Li salt offers the engineering ability to control ionic contacts and Li⁺-conductivity, respectively. Remarkable enhancements in utilizing electrode active materials and their outstanding thermal stability, enabled by the contact and Li⁺-conductivity engineerable DPE-based binders, will be presented.

References
[1] D. Y. Oh, Y. J. Nam, K. H. Park, S. H. Jung, K. T. Kim, A. R. Ha, Y. S. Jung, Adv. Energy Mater., 2019, 9, 1802927.
[2] K. T. Kim, D. Y. Oh, S. Jun, Y. B. Song, T. Y. Kwon, Y. Han, Y. S. Jung, Adv. Energy Mater., 2021, 11, 2003766.

Organic ionic plastic crystals (OIPCs) have shown increasing promise as solid state electrolytes for energy devices such as lithium or sodium batteries, DSSCs and fuel cells. OIPCs are crystalline phases found in many of the same organic salt families as ionic liquids but these materials have elevated melting points and exhibit various forms of disorder, which is the origin of their plastic mechanical properties. This intrinsic disorder is fundamentally responsible for the fast ion conduction of introduced target ions, such as lithium or sodium, and core to their efficient performance as solid-state electrolytes. However, how different cation, anion and molecular structures impact the phase behaviour, disorder and ion transport in the electrolytes is still not well understood.
Key to the development of plastic crystal electrolytes is expanding the range of cations and anions available, and understanding the resulting structure and dynamics. Here we discuss our development of new plastic crystal-based materials for energy applications, in particular lithium metal batteries. We also discuss our recent research into novel zwitterion-based electrolytes. Insights into the relationships between the different cations, anions and zwitterionic structures and the physical, thermal and electrochemical properties of the resultant solid electrolytes are presented.

Solid-state Li batteries have the potential for the increased power density. For this aim, it is crucial to understand the structural, chemical, and mechanical properties of interfaces between electrolyte and electrode. A molecular crystalline solid electrolyte is a candidate for better mechanical contact with the electrode due to its physical flexibility [1]. Among a variety of molecular crystals, we selected Li(FSA)(SN)₂ composed of lithium bis(fluorosulfonyl)amide (FSA: Li{N(SO₂F)₂}) and succinonitrile (SN: NCCH₂CH₂CN) [2]. Although Li(FSA)(SN)₂ exhibits a high Li-ion conductivity of ~10^-4 S cm^-1 at 30 ^oC, the battery operation using this electrolyte has yet been tested. In this study, we fabricated solid-state batteries using Li(FSA)(SN)₂ molecular crystals and LiCoO₂ thin-film electrodes. The cyclic voltammogram showed redox current peaks at around 3.9 V vs. Li/Li⁺, being in good agreement with the redox voltages of Co³⁺/⁴⁺ for LiCoO₂ positive electrode. When the battery was charged and discharged at the current density of 1 µA cm^-2 in 3.0–4.0 V vs. Li/Li⁺, the discharge capacity after 100 cycles maintained 90% of the 1st discharge capacity (50 mAh g^-1) and the Coulombic efficiency in each cycle was approximately 95%. These results indicate the high cycle stability and efficiency in solid-state Li batteries using Li(FSA)(SN)₂ molecular crystals [2].

[1] Moriya, Sci. Technol. Adv. Mater., 18 (2017) 634.
[2] Tanaka, Watanabe et al., Nano Lett., 20 (2020) 8200.

Despite the increased demand of high-energy density lithium-ion batteries (LIBs), safety issues caused by the use of flammable organic electrolytes hinder their market expansion. In this regard, all-solid-state lithium batteries (ASLBs) using nonflammable inorganic solid electrolytes (SEs) are considered a promising alternative to conventional LIBs.^[1] In particular, high Li-ion conductivity and deformable property of sulfide SEs are important advantages for high-performance practical ASLBs. However, there has been much room for improvement of performances of ASLBs using sulfide SEs. Specifically, the chemo-mechanical issues of crack propagation occurring at electrode active materials and interfaces are attributed to the severe deterioration of the performance.^[2,3] Thus, the adhesion property of polymeric binders that provides the mechanical integrity of ASLBs is important.
In this presentation, we report on our recent development of polymeric binders whose mechanical strength are improved via chemical method during slurry fabrication process. Promising electrochemical performances of ASLBs using the chemically-modified binders will be presented

References
[1] D. Y. Oh, Y. J. Nam, K. H. Park, S. H. Jung, K. T. Kim, A. R. Ha, Y. S. Jung, Adv. Energy Mater. 2019, 1802927
[2] D. Y. Oh, K. T. Kim, S. H. Jung, D. H. Kim, S. Jun, S. Jeoung, H. R Moon, Y. S. Jung, Mater. Today, 2021 (in press)
[3] K. T. Kim, D. Y. Oh, S. Jun, Y. B. Song, T. Y. Kwon, Y. Han, Y. S. Jung, Adv. Energy Mater., 2021, 2003766

Understanding electronic and ionic transport across interfaces is critical for designing high-performance electronic and ionic devices. However, the electronic structures at the interfaces of metals and mixed conductors, which conduct both electrons and ions, remain poorly understood. To quantitatively address the issue, we fabricated thin-film batteries using epitaxial thin films through an in-vacuo process [1]. This study reveals that a Schottky barrier is present at the interface of a Nb-doped SrTiO₃ metal (current collector) and a LiCoO₂ mixed conductor (positive electrode) and that the interfacial resistance can be tuned by inserting an electric dipole layer. Furthermore, the interfacial resistance significantly decreased by more than 5 orders of magnitude upon the insertion of a 1 nm-thick insulating LaAlO₃ layer at the interface [2]. We apply these techniques to solid-state lithium batteries and demonstrate that tuning the electronic energy band alignment by interfacial engineering is applicable to the interface of metals and mixed conductors. These results highlight the importance of designing positive electrode and current collector interfaces for solid-state lithium batteries with high power density.

[1] M. Haruta, T. Hitosugi et al., Solid State Ion. 2016, 285, 118-121.
[2] K. Nishio, T. Hitosugi et al., ACS Appl. Mater. Interfaces 2021, 13, 15746-15754.

Lithium-ion batteries (LIBs) are the most common energy storage technology for portable electronics and electric vehicles. Their performance may be further improved by the synthesis of core-shell particles, where an active material core is coated with a shell consisting of a material with high conductivity. As such, the shell may enhance the energy and power density of batteries containing a liquid electrolyte by creating a network for electron and ion transport. The shell materials may also act as protective coatings for an improved electrochemical stability, e.g. by preventing the dissolution of transition metals, particularly manganese.
This presentation will provide an overview of our recent research on the preparation of core-shell particles for use as positive electrode materials in LIBs. The synthesis of these materials relied on chemical solution deposition (CSD) as coating technique, where the shell material is formed from a solution.
By careful control of the hydrolysis and condensation of a titanium precursor dissolved in ethanol, an amorphous TiO_x layer was formed on the surface of LiNi_0.5Mn_1.5O₄ (LNMO) particles.¹ Subsequent annealing caused the diffusion of Ti ions into the LNMO surface and the formation of a 2-4 nm thick Ti-rich spinel surface. Ti surface doping suppressed the dissolution of Ni and Mn and thereby increased LNMO’s electrochemical stability and rate capability. In another instance, LNMO core particles were coated with amorphous Li₄Ti₅O₁₂ (LTO) using a solution-gel synthesis route.² In this technique, aqueous precursor solutions containing the metal ions are made and mixed in stoichiometric ratios. The LNMO particles are dispersed in the precursor mixture, after which the water is dried off and the resulting material is annealed. The amorphous LTO coating improved LNMO’s rate capability and acted as a HF scavenger, increasing the electrochemical stability.
Similar coating techniques were also employed for the coating of titanium oxide layers on LiNi_0.6Mn_0.2Co_0.2O₂ (NMC-622) particles.³ NMC-622 can offer a high energy density owing to its high theoretical capacity. However, increasing the upper cut-off potential to further increase the energy density has a negative impact on its electrochemical stability. Applying a TiO_x coating on the NMC-622 surface was found to have a positive influence on the electrochemical stability of NMC-622/Li₄Ti₅O₁₂ full cells. In half cells, TiO_x coated NMC-622 showcased an improved rate capability compared to the uncoated material. The rate capability of NMC-622 could also be improved by coating it with LiNbO₃ using a solution-gel coating technique.
In summary, CSD routes were developed for the synthesis of core-shell materials, consisting of a core of an active material for LIBs, and a shell that provides conductivity and electrochemical stability. The CSD routes are versatile and may be extended to numerous shell and core materials, providing exciting opportunities to improve the latter’s performance in various applications.
The authors acknowledge the Research Foundation Flanders (FWO Vlaanderen) for financial support under the project number S005017N (SBO XL-Lion).
(1) Ulu Okudur, F. et al. RSC Adv. 2018, 8 (13).
(2) Ulu Okudur, F. et al. Manuscript in preparation.
(3) Mylavarapu, S. K. et al. Submitted.

In the critical area of sustainable energy storage, solid-state batteries are attracting considerable attention due to their potential safety, energy-density and cycle-life benefits [1]. A complete understanding of solid electrolyte materials for lithium- and sodium-ion batteries requires greater fundamental knowledge of their structural, ion transport and interface properties. For example, the impact of aliovalent doping, defect clustering and grain boundaries on Li- and Na-ion conduction properties are often not fully understood on the atomic-scale. This talk will highlight recent studies [2-4] on ion conduction mechanisms, doping effects and grain boundary structures in oxide and oxyhalide anti-perovskite based solid electrolyte materials.

[1] T. Famprikis et al., Nature Mater., 18, 1278 (2019).
[2] M.J. Clarke et al, ACS Appl. Energy Mater. 4, 5094 (2021).
[2] J.A. Dawson et al., Chem. Mater., 31, 5296 (2019)
[3] J. A. Dawson et al., J. Am. Chem. Soc., 140, 362 (2018).

Garnet Li₇La₃Zr₂O₁₂ is a promising solid electrolyte candidate for solid-state Li-ion batteries. However, sufficiently fast Li-ion mobility required for battery applications only emerges at high temperatures, upon a phase transition to cubic structure. A well-known strategy to stabilize the cubic phase at room temperature relies on aliovalent substitution; in particular, the partial replacement of Li⁺ by Al³⁺ and Ga³⁺ ions. Yet, fundamental aspects regarding this aliovalent substitution remain poorly understood. Here we present some exciting examples of our most recent theoretical work in this area [1-2] and, with the aid of experiments, also expand our simulation capabilities towards understanding interfacial Li-ion transport in composite materials comprising a conductive, flexible polymer matrix embedding Li₇La₃Zr₂O₁₂ filler particles [3].

We first examine why, despite having the same formal charge, Ga³⁺ substitution yields higher conductivities (10⁻³ S/cm) than Al³⁺ (10⁻⁴ S/cm). To answer this long-standing question, we combined for the first time molecular dynamic simulations and advanced hybrid Monte Carlo sampling techniques to precisely unveil the atomistic origin of this phenomenon explicitly performing simulations at room temperature [1]. Our results show that Li⁺ vacancies generated by Al³⁺ and Ga³⁺ substitution remain adjacent to Ga³⁺ and Al³⁺ ions, without contributing to the promotion of Li⁺ mobility. However, while Ga³⁺ ions tend to allow limited Li⁺ diffusion within their immediate surroundings, the less repulsive interactions associated with Al³⁺ ions lead to a complete blockage of neighboring Li⁺ diffusion paths. This effect is magnified at lower temperatures and explains the higher conductivities observed for Ga-substituted systems.

In addition, we thoroughly compared the room temperature Li-ion diffusion in tetragonal and cubic Al-substituted Li₇La₃Zr₂O₁₂ [2]. Combining the conductivities of individual phases through an effective medium approximation allowed us to estimate the conductivities of cubic/tetragonal phase mixtures that are in good agreement with those reported in several experimental works. This suggests that phase coexistence (due to phase equilibrium or gradients in Al content within a sample) could have a significant impact on the conductivity of Al-substituted Li₇La₃Zr₂O₁₂, particularly at low Al contents.

Finally, we investigate interfacial Li-ion transport in a composite solid-state electrolyte integrating polyethylene oxide (PEO) plus lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) and Ga-doped Li₇La₃Zr₂O₁₂ fillers [3]. Our simulations automatically produce the interfacial Li-ion distribution assumed in previous space-charge models and, for the first time, a long-range impact of the garnet surface on the Li-ion diffusivity is unveiled. Based on our calculations and tensile strength and conductivity experimental measurements, we are also able to explain a previously reported drop in conductivity at a critical filler fraction well below the theoretical percolation threshold.

Overall, by making a thorough comparison with reported experimental data, our theoretical studies and simulations advance the current understanding of Li-ion mobility in Li₇La₃Zr₂O₁₂ garnets and their interfaces with polymer matrices in composite electrolytes. These fundamental insights might guide future in-depth characterization experiments of these relevant energy storage materials.

References
[1] ACS Appl. Mater. Interfaces 2019, 11, 753.
[2] Acta Materialia 2019, 175, 426.
[3] ACS Appl. Mater. Interfaces 2021, accepted.

Measuring and predicting potential distributions within solid-state batteries is key to understanding and controlling the mechanisms that limit their performance. We combine Kelvin probe force microscopy (KPFM) and neutron depth profiling (NDP) to map the contact electric potential difference and the corresponding Li distributions within operating Si-LiPON-LiCoO2 solid-state batteries under open circuit, low current and high current conditions. We observe the largest drop in potential at the anode-electrolyte interface with a smaller drop at the cathode electrolyte interface and a shallow gradient within the bulk of the electrolyte. Cycling at high current irreversibly increases the potential drop at the electrolyte/anode interface, a change that is also observed in impedance spectra collected in situ. We deconvolve the contributions from ions, electrons, and interfaces to the measured potential distributions by correlating KPFM and NDP profiles and by comparisons with a first principles-informed energy 'band' model for ions and electrons.

Poly(ethylene oxide) based solid polymer electrolytes (SPEs) have been increasingly popular due to its fast segmental dynamics, high conductivity, and the ability of solving a wide range of different lithium salts. However, downsides of using PEO are its semi-crystalline nature and poor mechanical performance. The primary challenge for this electrolyte system is to increase the mechanical strength without decreasing ionic conductivity. To achieve this, one technique is to blend PEO with another polymer that can provide mechanical rigidity and eliminate crystallinity. In this sense, a high (T_g) polymer poly(methyl methacrylate) (PMMA) is commonly used. Incorporation of PMMA into PEO significantly increased the mechanical strength and efficiently decreased PEO crystallization. However, there was a major drawback: PEO segmental dynamics decreased dramatically. To overcome this, using various PEO architectures as linear and non-linear ones including stars, hyper-branched and bottlebrushes could be a promising way. Neat non-linear PEOs were reported to have less crystallization and more free volume due to branching compared to linear counterparts. Moreover, there would be fewer contact sites and interpenetration between PEO and PMMA due to topological constraints, which will suppress the decrease in PEO segmental dynamics. To these hypotheses, we used PMMA in blends with varying PEO architectures (linear, stars, hyper-branched and bottlebrushes) and then doped with lithium bis(trifluoromethane-sulfonyl)-imide (LiTFSI) salt to form novel SPEs. XRD results revealed that room temperature miscibility of these polymers can be strikingly expanded over 50 % using non-linear PEO (PEO:PMMA). Temperature modulated DSC results showed two distinct effective glass transition temperatures which could be tuned from linear to non-linear structures with increased number of branching. Broadband dielectric spectroscopy (BDS) measurements have unveiled PMMA segmental dynamics known as α relaxation have increased less for the non-linear PEO/PMMA blends in comparison to their linear counterparts because of less contact sites and interpenetration between PMMA and PEO introduced by the topological changes, suggesting that faster PEO segmental dynamics would be possible and promote ionic conductivity in these systems. The PEO/PMMA blend based electrolytes consisting of 20%wt PEO showed that the ionic conductivity for the bottlebrush PEO architecture was five times greater than the linear counterpart at around room temperature while other non-linear topologies have similar ionic conductivities when compared to linear PEO architecture. Furthermore, extending PEO content over 50wt% PEO in these linear and non-linear PEO/PMMA based solid polymer electrolytes resulted in a significant increase reaching up to 3.6*10^-4 S/cm , as high as one order of magnitude at room temperature and three times higher at higher temperatures up to in the ionic conductivities when compared to ionic conductivities of pure PEO based electrolytes usually ranged between 10^-5-10^-4 S/cm. Thus, this study indicates promising results such that non-linear PEO/PMMA based solid polymer electrolytes with faster segmental dynamics and higher PEO content could potentially lead higher ionic conductivities required for the application standpoint of the PEO based solid polymer electrolytes. Eventually, room temperature mechanical characteristics for PEO/PMMA blends will be also discussed.

All-solid-state Li-ion batteries require Li-ion conductors as solid electrolytes (SEs). Li-containing halides are emerging as a promising class of lithium-ion conductors with good electrochemical stability and other properties needed for SEs in all-solid-state batteries. Compared to oxides and sulfides, Li-ion diffusion mechanisms in Li-containing halides are less well understood, in particular regarding the effects of Li content and cation sublattices, which can be tailored for improving Li-ion conduction. Using first-principles computation, a systematic study is performed on the Li-ion conduction of known Li-containing chlorides with close-packed anion frameworks and a wide range of their doped compounds. A dozen potential chloride Li-ion conductors are predicted with increased Li-ion conductivities, and it is revealed that the Li-ion migration is greatly impacted by the cation configuration and concentrations. By analyzing a large set of materials data, it is proposed that low Li content, low cation concentration, and sparse cation distribution increase Li-ion conduction in chlorides, and these principles are demonstrated in designing new chloride Li-ion conductors. This study provides insights into the effects of the cation sublattice on Li-ion diffusion, highlights potential chloride Li superionic conductors, and proposes design principles to further develop halide Li-ion conductors.
Paper reference:
Liu, Y., Wang, S., Nolan, A. M., Ling, C., Mo, Y., Tailoring the Cation Lattice for Chloride Lithium-Ion Conductors. Adv. Energy Mater. 2020, 10, 2002356. https://doi.org/10.1002/aenm.202002356

Solid-state batteries (SSBs) that pair an inflammable solid electrolyte with a lithium metal anode can potentially improve the energy density, power density and safety of current lithium-ion batteries. Designing a composite cathode with sufficient ionic/electronic transport pathways and active interfacial area is pivotal to achieve optimal rate performance in SSBs. Electrode microstructure-coupled transport and kinetic interactions affect the evolution of internal resistive pathways, utilization of active material and the electrochemical reaction distribution within these systems. In this work, we analyze the mesoscale underpinnings of electrode microstructure on the underlying kinetic-transport mechanisms, thermo-electrochemical interplay, and the resulting influence on cell performance. Design criteria including the fraction of conductive additives and particle sizes required to achieve fast charge/discharge rates in SSBs are discussed.

Li₇La₃Zr₂O₁₂ (LLZO) garnet ceramics are promising electrolytes for all-solid-state lithium-metal batteries with high energy density. However, these electrolytes are prone to Li⁺/H⁺ exchange, that is, protonation, resulting in degradation of their Li-ion conductivity. Here, we identify how common processing steps, such as surface cleaning in alcohol or acetone, trigger LLZO partial protonation¹. We deconvolute the contributions to the electrochemical impedance spectra of both the protonated LLZO phase (HLLZO) and its decomposition products forming upon annealing. While the mixed conduction of H⁺/Li⁺ ions in HLLZO decreases the contribution of the electrolyte to the overall impedance, it deteriorates the transport of Li⁺ ions across the LLZO/Li interface. This is also the case after thermal decomposition of HLLZO, which occurs at significantly lower temperature than that for pristine LLZO. As a result, symmetric Li/LLZO/Li cells suffer from inhomogeneous lithium electrodeposition within the first three cycles when stripping and plating a capacity of 1 mAh/cm² per half-cycle at 0.1 mA/cm². We demonstrate that LLZO protonation is avoided when applying solvents with very low acidity, such as hexane. Such Li/LLZO/Li cells provide stable cycling over more than 300 h, demonstrating the importance of selecting an appropriate solvent for LLZO processing to prevent dendrites formation.
Reference:
1. Grissa, R., Payandeh, S., Heinz, M. & Battaglia, C. Impact of Protonation on the Electrochemical Performance of Li₇La₃Zr₂O₁₂ Garnets. ACS Appl. Mater. Interfaces 13, 14700–1409 (2021).

Many factors affect the conduction of ions through polyelectrolyte membranes including: water and ion content, glass transition (Tg) of the polymer, dielectric constant of the medium, and microstructure (e.g. aggregation, microphase separation). Determining the effects that chemical changes to a polymer will have on the conductivity of the resulting ion exchange materials requires characterizing and deconvoluting the many different properties that depend upon polymer chemistry. Molecular dynamics (MD) simulations can be applied to rapidly screen whether candidate changes to a polyelectrolyte’s structure will have the desired effect on ion transport.
Poly(dimethylaminomethyl styrene) (pDMAMS) is a structurally simple polymer capable of hydroxide conduction after quaternization with CH¬3I and OH- exchange. The effects of changing ion content on OH- ion diffusivity in anhydrous, quaternized pDMAMS are studied using MD simulations on linear co-polymers of 4-dimethylaminomethylstyrene (4-DMAMS) and 4-butylstyrene, selected for its similar Tg to pDMAMS. Molecular dynamics is utilized to characterize truly anhydrous systems, whereas most experimental materials would contain a non-negligible amount of tightly bound water. Increasing content of neutral 4-butylstyrene over methylated 4-DMAMS results in a tradeoff between increased polymer flexibility and decreased dielectric strength and ion content. MD simulations are performed on co-polymers with 4-butylstyrene content from 0% to 75%. At 300 K, MD simulations yield an OH- self-diffusion coefficient of ~ 0.05 μm2/s in pure methylated pDMAMS (0% 4-butylstrene). As the 4-butylstyrene content of co-polymers increases up to 50%, OH- diffusivity decreases by a factor of two, but at 75% 4-butylstyrene content, the OH- diffusion constant increases by a factor of two compared to that of 100% methylated pDMAMS. The glass transition temperature of the co-polymers decreases as the 4-butylstyrene content increases, from ~800 K at 0% 4-butylstyrene to ~500 K at 75%, thus providing a more mobile platform for OH- at high 4-butylstyrene content. The dramatic decrease in Tg with increasing 4-butylstyrene but minimum OH- diffusivity at ~50% 4-butylstyrene shows that there are competing factors affecting hydroxide conduction in these materials. Simulations of alternating and random co-polymers show that the patterning of co-polymers has little effect on the OH- diffusivity. This study presents a computational framework to understand fundamental principles regarding hydroxide conduction in polymer electrolytes.

A low Li plating/stripping Coulombic efficiency and continuous lithium dendrite growth are two critical challenges for all-solid-state batteries. Here, we address both challenges by inserting a mix-conductive interlayer between electrolyte and Li anode. The lithiophilic side of interlayer promotes the uniform deposition of lithium, while lithiophobic layer inhibits the Li plating on electrolyte surface and prevents the lithium dendrite growth. The mixed ionic/electronic conductive interlayer enable enables Li anode to achieve a high Coulombic efficiency (CE) of 99.6%, which is the highest CE reported. The electrochemical performance of solid state Li/LiCoO2 full cells weas also investigated.

Solid-state batteries offer the promise of improved energy density and safety characteristics compared to lithium-ion batteries, but electro-chemo-mechanical evolution and degradation of materials and interfaces can play an outsized role in limiting their performance due to the all-solid nature of these systems. Here, I will present my group’s recent work using in situ and operando experiments to understand interfacial evolution and stress changes in solid-state batteries with lithium metal and alloy anodes. Operando X-ray tomography is used to reveal interfacial dynamics in solid-state batteries with Li metal anodes. Segmentation and detailed image analysis enable correlation of interfacial contact loss to electrochemical behavior of symmetric cells, and the loss of interfacial contact area at the Li metal interface is found to cause current constriction and cell failure. The effects of interphase formation on mechanical degradation, stress evolution, and contact area loss are also discussed. Finally, stack pressure evolution during cycling of full solid-state batteries is measured in situ and correlated with fundamental processes within electrode materials and the properties of composite electrode structures. Cells with alloy-based anodes are found to exhibit large (megapascal-level) changes in stack pressure during cycling in a constant volume cell casing, with stable capacity and stress changes over long-term cycling. Together, these findings show the importance of controlling chemo-mechanics and interfaces in solid-state batteries.

Solid electrolytes (SEs) containing metal ions such as Li₃InCl₆ or Li₇SiPS₈ have gained interest for applications in solid-state batteries (SSBs) in recent years due to their high ionic conductivities. However, there are still some challenges to overcome, such as their inherent reduction instability, which impedes the application with a lithium metal anode (LMA) [1].
If the decomposition layer formed upon contact of a SE with lithium metal contains electronically conducting compounds like metals, the decomposition layer can form a mixed conducting interphase (MCI) that continues to grow until either lithium is depleted or the SE is completely reduced. As a result of the metal dispersed in the MCI, the electronic conductivity of the cell should increase, which in turn decreases the internal cell resistance and leads to short circuits [2]. However, this is not the case for all metal ion containing SEs. The resistance of a Li|Li₃InCl₆|Li cell, for example, constantly increases during the decomposition. Despite the fact that indium metal is among the formed decomposition products the interphase behaves like a Solid Electrolyte Interphase with a low interphase conductivity [3]. Therefore, knowledge about the composition of the interphase between lithium metal and SEs as well as the temporal evolution of the cell resistance is crucial.

Here, we report our latest findings on the stability of a variety of metal ion containing SEs in contact with lithium metal. We further cover the kinetics of the heterogeneous solid-state reaction and the chemical composition of the resulting interphase. Impedance spectroscopy measurements were conducted to investigate the temporal evolution of the interphase resistance between the lithium metal anode and the SE. In situ-sputter-deposition of lithium metal onto the surface of the SE pellets and subsequent X-ray photoelectron spectroscopy measurements were performed to study the chemical composition upon contact. Multiple repetitions of these steps allow a detailed characterization and identification of the decomposition products within the forming interphase. By additionally employing time-of-flight secondary ion mass spectrometry, we were able to categorize the interphase and estimate its spatial extension.
Combining the results allows a detailed distinction between possible interphases of metal ion containing electrolytes and thereby promotes the understanding of the SE stability toward LMAs.



References:
[1] X. Li, J. Liang, X. Yang, K. Adair, C. Wang, F. Zhao, X. Sun, Energy Environ. Sci. (2020) 10.1039/C9EE03828K
[2] S. Wenzel, T. Leichtweiss, D. Krüger, J. Sann, J. Janek, Solid State Ion. 278 (2015) 10.1016/j.ssi.2015.06.001
[3] L. Riegger, R. Schlem, J. Sann, W. Zier, J. Janek, Angew. Chem. (2020) 10.1002/ange.202015238

Solid state batteries (SSB) offer potential advantages over traditional lithium ion batteries in energy density, safety and battery packing. Much of the prior work has focused on the development of solid electrolytes but the anodes and cathodes are also key to delivering the potential benefits of a SSB. The anode of a SSB could use several different choices of active material, such as graphite, silicon, graphite/silicon, and Li metal, which is generally considered as the ultimate choice for a SSB due to its high specific capacity. However, since in principle the cathode provides all Li needed in the battery operation, there is technically no need to put extra Li in the anode to achieve an operating cell.

Various concepts for a Li-free anode have been studied, but there are many challenges to implement this concept. Particularly when the anode only consists of current collector, inducing Li to plate and strip at the interface between LLZO and current collector has proven difficult. We start with approaches to directly reduce the interfacial resistance between LLZO and the current collector by sputtering a thin film of metal directly onto the LLZO separator. A simple test cell is used with a Li metal foil on one side of a LLZO separator which has a metal film and current collector on other side. At the beginning of performance testing, the cell requires an “initialization” by plating a small amount of Li onto the current collector. This initial charging conditions the interface between the metallized LLZO and the current collector and the quality of new interface affects the performance of cell in terms of the critical current density and cycling behavior. In this work, two type of metallization(Au or Cu) are used to explore this approach. The impact of initial Li plating for various values of current and total deposited capacity is described. In addition, the impact of operating temperature is investigated.

Pore formation at the lithium metal anode (LMA) | solid electrolyte (SE) interface is a key obstacle in the path to utilizing LMAs in solid state batteries (SSB) at the industrial level.
Oftentimes it is theorized that this pore formation would occur due to an insufficient vacancy diffusion within the LMA. Recently, however, it has been shown that the interfacial work of adhesion between the LMA and the SE is a key factor in determining if vacancy agglomeration at the LMA | SE interface is thermodynamically favored. [1]
In order to computationally address the kinetics of this system at finite temperature, kinetic Monte Carlo (KMC) simulations based on a nearest neighbour bond counting approach are applied in this work. As SE, differently treated garnet Li7La3Zr2O12 (LLZO) were considered [2].
It was found that neither the formation, nor the annihilation of pores are a result of slow vacancy diffusion. The pore formation, on the one hand, is mainly influenced by the interface thermodynamics between the LMA and the SE. The pore annihilation, on the other hand, is limited by the stripping of vacancies from the pore surface.
Within the implemented setup, an analytical expression for the anodic critical current density, beyond whichthe interface becomes morphologically unstable, was defined. The results are in accordance with values determined experimentally by electrochemical impedance spectroscopy (EIS) measurements and reveal an order of magnitude variation depending on the interface thermodynamics. Likewise, the time until full contact loss, t0, strongly depends on the interaction strength between the LMA and the SE. For a given LMA|SE interaction energy, the experimentally observed square root dependence between t0 and the applied stripping current density was reproduced [3].
The analysis of pore dissolution in a lithium metal bulk cell showed that the healing time (until a pore is completely dissolved) can be described by an analytical model of precipitate shrinkage if the curvature of the pore surface is taken into account. Moreover, it was concluded that the transfer of vacancies into the bulk is the limiting step of pore dissolution, which is in accordance with activation barriers determined by Density Functional Theory (DFT) calculations.
Finally, a proposed method to attenuate and/or compensate pore formation at the LMA | SE interface, namely the introduction of a thin ionic liquid interlayer (IL) [4], is incorporated within the KMC model. The experimentally observed increase in the time until contact loss is reproduced and attributed to a suppression of vacancy kinetics at the interface due to an instantaneous adjustment of the IL until its maximal volume expansion is reached.

[1] Seymour, I., & Aguadero, A. (2021). Suppressing Void Formation in All-Solid-State Batteries: The Role of Interfacial Adhesion on Alkali Metal Vacancy Transport. Journal of Materials Chemistry A
[2] Sharafi, A., Kazyak, E., Davis, A. L., Yu, S., Thompson, T., Siegel, D. J., ... & Sakamoto, J. (2017). Surface chemistry mechanism of ultra-low interfacial resistance in the solid-state electrolyte Li7La3Zr2O12. Chemistry of Materials, 29(18), 7961-7968.
[3] Krauskopf, T., Mogwitz, B., Hartmann, H., Singh, D. K., Zeier, W. G., & Janek, J. (2020). The Fast Charge Transfer Kinetics of the Lithium Metal Anode on the Garnet Type Solid Electrolyte Li6.25Al0.25La3Zr2O12. Advanced Energy Materials, 10(27), 2000945
[4] Fuchs, T., Mogwitz, B., Otto, S. K., Passerini, S., Richter, F. H., & Janek, J. (2021). Working Principle of an Ionic Liquid Interlayer During Pressureless Lithium Stripping on Li6. 25Al0.25La3Zr2O12 (LLZO) Garnet Type Solid Electrolyte. Batteries & Supercaps.

The solid-state battery has drawn a huge interest with its motive to overcome the issues and challenges faced by batteries using conventional liquid electrolytes. The novel idea of using green approaches or bio-based sources for lithium batteries excites many researchers due to their eco-friendly, less carbon footprint in its synthesis and recycling at the end. In this work, we report a full bio-based solid-state electrolyte based on functionalized carbonated soybean oil (CSBO) obtained from the naturally occurring epoxidised soybean oil (ESBO) using CO₂ and biomass. CSBO shows remarkable adhesive properties as characterized by rheological measurements owing to its bigger chains bearing multifunctional cyclic carbonates. LiTFSI salt reinforced CSBO was characterized following standard electrochemical measurements exhibiting ionic conductivity to ~10^-3 S cm^-1 at 100 ^oC and 10^-5 S cm^–1 at room temperature. The electrochemical window for this electrolyte was obtained to be 4.8 V (vs. Li/Li⁺) and transference number up to 0.31, allowing it to be explored for high voltage cathodes. CBSO shows stable stripping and plating behaviour for longer cycles making it a good candidate for higher coloumbic efficiency electrolyte batteries. We also demonstrated the galvanostatic charge-discharge of LiFePO₄ (Lithium Ferrrophosphate, LFP) with CSBO electrolytes delivering the gravimetric capacity of 124 mAhg^-1 and 150 mAhg^-1 appx. at ambient room and higher temperature respectively. Therefore, our study provides a promising direction of developing bio-based solid electrolytes to facilitate progress in sustainability, cost-effective and safe manner to create a solid-state lithium-ion battery for global utilization.

The dramatic possible effects of climate change are becoming clearer day by day. Batteries are a key technology to reach the UN Sustainable Development Goals, by accelerating the shift to zero-emission transportation and providing energy storage to allow for an increased proportion of intermittent renewable energy sources. However, today's conventional lithium-ion batteries with a liquid electrolyte are steadily reaching the limit of their physiochemical energy density, while safety issues related to the flammable liquid electrolyte remain a challenge. Solid state batteries, on the other hand, offers the potential of high safety, high energy density and high power density. There are many classes of solid electrolytes, each with their own advantages and disadvantages. Hybrid composite electrolytes, with ceramic fillers in a solid polymer electrolyte, offers the potential to overcome the disadvantages related to both ceramic and polymeric electrolytes alone.

Here, we present a detailed investigation of the fabrication and performance of solid poly (ethylene oxide) (PEO) - Li_6.25Al_0.25La₃Zr₂O₁₂ (Al-doped LLZO) composite electrolytes. LLZO powder and fibres were prepared, by solid state reaction and needleless electrospinning, respectively. Both fabrication routes were chosen due to their scalability. For the powder, the effect of the calcination temperature and ball milling on the phase purity and particle size of the LLZO powder was investigated. The preparation of solutions for needleless electrospinning is more challenging than for conventional electrospinning. Here, the conductivity and viscosity to prepare spinnable solutions for needleless electrospinning was investigated, as well as the effect of the calcination temperature on the phase purity. The solid electrolytes were prepared by casting composites of the ceramic fillers in PEO with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The effect of ceramic filler content, particle size and morphology and dopamine functionalization on the solid electrolyte performance was investigated. While there are several reports of these effects studied individually, a detailed understanding of their combined effects appears to still be lacking, which is necessary for composite electrolytes to successfully reach their potential.

Li-S batteries promise high energy density, low cost, and free of resource constraints of transition metals. Solid state Li-S also in principle circumvents the soluble sulfur species involved in its liquid electrolyte counterpart, resulting in longer cycle life. However, the volume change of both Li and S cathode, the insulating nature of S, and the tendency of Li dendrite-related cell shorting have continued to plague the technology. In this talk, we will report our recent effort towards building a long-life solid state Li-S cell. To stabilize the Li anode, we employ porous carbon as a mixed-conducting 3D host for Li metal. This reduces the effective current density acting on the electrolyte layer, increases the apparent critical current and mitigates cell shorting. To reduce the thickness and enhance the mechanical stability of the electrolyte, we use in-situ polymerization to form nanoscopic composites of sulfide-based solid electrolytes. Finally, we engineer sulfur cathodes with intrinsic electronic conductivities and limited volume changes to extend cycle life. With advancements on all components of the cell, we will fully realize a long-life, low-cost solid state Li-S technology.

Fast ion conducting glasses have long been considered as alternatives to flammable liquid electrolytes in Li and Na batteries. However, for such glassy solid electrolytes (GSEs) studied so far, they have lacked the unique combination of required electrochemical properties for use as a solid electrolyte with the equally important requirements of viscoelastic behavior to form them into thin films suitable for high ion conductivity separators. Indeed, to date, most GSEs are considered as “invert” glasses where the high viscosity promoting glass formers in the compositions, such as SiO₂, B₂O₃, or P₂O₅ are not the dominant component, but rather are the minor component and the alkali salt, such as Li₂O or Na₂O is the majority component. This has led to the general observation that such high alkali content invert glasses are rather poor glasses formers that crystallize rapidly upon heating above their glass transition temperature into the viscoelastic supercooled liquid regime. This has forced most workers in this field to consider only fully crystallized polycrystalline ceramic versions of these compositions or at most glass ceramics where the crystalline phase is dominant, > 90 v/v%. In this first ever report of thin film fast ion conducting glasses made by viscoelastic deformation processing of redrawing glass preforms, we report new compositions where we have broken this long standing paradigm of high conductivity combined with high alkali salt concentration but poor glass formability and will summarize our efforts to produce thin films of Li and Na ion conducting glasses and test in them in symmetric and asymmetric cells.

Flexible solid-state batteries are designed to be conformal, lightweight, and can be rolled without any loss of energy. They are needed for powering wearable electronics, smart packaging, and medical devices, etc. Most of them target at room temperature applications, as the sluggish ionic transport in the solid-state electrolytes degrades even faster at lower temperature. Though organic electrolytes allow for a wide working temperature window, most organic electrolytes require expensive, tedious, and toxic synthesis processes. Recently, rechargeable batteries based on aqueous electrolytes have shown high potential attributed to their low cost and intrinsic safety. For instance, the zinc ion battery (ZIB) is attractive owing to its stable zinc anode from abundant sources, features of multivalent charge transfer, a superb theoretical capacity and low redox potential of the zinc anode. Another appealing choice is an aqueous battery using non-metal ions as charge carriers, such as NH₄⁺ with a lighter molecular weight (18 g mol^-1) than metal ions above and a small hydrated ionic size of 3.31 Å, leading to faster ion diffusion in the electrolyte. However, the use of aqueous electrolytes poses a challenge due to its freezing at sub-zero temperature.
In this work, concentrated hydrogel electrolytes are employed to construct flexible zinc ion batteries and ammonium ion batteries that can operate at subzero temperature with better safety and lower cost, while maintaining high energy/power and long cycling life. The quasi-solid-state electrolyte is simply synthesized via using respective salt, water, and hydrophilic polymer (e.g., biodegradable edible xanthan gum). The composition of the electrolyte is optimized to maximize the battery performance. A flexible ZIB is assembled using the hydrogel electrolyte sandwiched between a vanadate cathode and a zinc anode, while a flexible ammonium ion battery consists of the electrolyte between a vanadate cathode and a polyaniline anode. For example, the flexible ZIB exhibits a very high capacity of 239 and 83 mAh g^-1 under 0.2 A g^-1 at -20 degreeC and -40 degreeC, respectively. Additionally, chemically self-charging flexible batteries are fabricated, which are different from conventional self-charging systems relying on energy sources. Notably, the ZIB can be chemically self-charged by the oxidation reaction between the cathode and the oxygen in air. The flexible ZIB delivers a specific discharge capacity of 179 mAh g^-1 after the cathode is exposed to air and oxidized for 12 hours at room temperature, exhibiting a decent self-recharging ability. As such, this study sheds new light on the utilization of concentrated hydrogel electrolytes in flexible batteries with new capabilities, for developments of next-generation electrochemical energy storage technology with high safety and low cost.

In situ biasing Transmission Electron Microscopy technique is a powerful tool to reveal morphological and structural changes in solid state battery samples at the nanoscale during charge and discharge cycles. It has an advantage over other methods like X-ray or Neutron Diffration as it provides a direct observation on the dynamic evolution of crystal and electronic structures and can uncover intrinsic mechanisms behind it. The former one is especailly important as it accounts for the performance of batteries.

One of the main limitations in the application of in situ biasing TEM to study solid state batteries is FIB lamella sample preparation process. It’s not only complicated, but it also possess a very low success rate and as a result, very time consuming. In general, preparing a clean and electrically connected biasing sample without electrical short circuit is a challenging task. There are a lot of pitfalls when preparing FIB lamellas for electrical experiments. Often the preparation process needs to be repeated several times after unsuccessful TEM experiments due to sample’s bad electrical quality. These repetitions cost additional FIB and TEM time.

In this work we would like to present a new method of preparing and preliminary characterizing sold state battery samples in a dual beam microscope - an in situ FIB. This method is based on MEMS Nano-Chips designed for biasing and heating and biasing TEM experiments. The method uses a modified SEM stub, e.g. FIB stub with electrical connections to the outside world. The stub is specifically designed to prepare the FIB lamella on the MEMS chip in one go (without breaking the vacuum). During the preparation, the sample can be biased to check for short circuits and for proper electrical connection to the sample, ensuring the good quality of the lamella. We will also discuss how the tool can be employed to do further characterization of the sample inside FIB/SEM and its correlation with the in situ TEM technique.

Polymer electrolytes can provide several advantages over liquid electrolytes in alkaline battery architectures. Mechanically robust polymer separators such as Celgard membranes inhibit dendrite growth and can be made exceptionally thin, which increases current density by minimizing IR losses. However, preparing ionically conductive, submicron-thick polyelectrolyte films on nonplanar electrode geometries remains a challenge for solution and melt polymer processing methods.
We use free radical–initiated chemical vapor deposition (iCVD) of styrenic monomers to grow 100 nm – 1 μm thick films on a variety of metallic and insulating substrates and then convert the polymer into anion-conductive polyelectrolytes. By judicious choice of quaternization and ion-exchange conditions, the thin-film polymer survives conversion from hydrophobic insulator to high ion-exchange capacity (IEC up to 3 mEq g^–1) polyelectrolyte without delamination or pinhole formation. The single-ion conductivity of bicarbonate (HCO₃^–), the equilibrium anionic species, is measured by impedance spectroscopy of the films on interdigitated electrodes as a function of relative humidity; the films exhibit modest conductivity even when equilibrated at low relative humidity.
The chemical structure of these thin films is characterized using surface overlayer enhanced ATR-IR spectroscopy and X-ray photoelectron spectroscopy to determine their similarity to previously reported iCVD-grown polymer and bulk materials polymerized using the same monomer and initiator. Solid-state magic-angle spinning ¹H and ¹³C NMR spectroscopy performed on films grown on high surface–area substrates allows us to contrast chemical structure in the supported thin-film expression with their bulk-polymerized counterparts.

Solid-state batteries (SSBs) are emerging as the next devices to substitute conventional lithium-ion batteries. Besides improved safety and reliability, the capability of thin film processing to design devices in novel form factors creates new opportunities in energy storage. Nevertheless, the most common cathode material used in thin film batteries is lithium cobalt oxide (LCO), which is only electrochemically active in a particular phase formed at 500 °C, and there are many reports of Li deficiency in the films after annealing. In pursuit of a low temperature alternative which will also address the Li deficiency, we have studied a new process to deposit lithiated vanadium oxide (LVO) thin films as a promising cathode material for application in SSBs. Vanadium oxide (V₂O₅) has a layered structure that can be preserved with the insertion of up to 2 lithium ions, giving it a higher theoretical capacity when compared to LCO. Herein, the lithium content of the cathode is controlled simultaneously with the deposition of the vanadium oxide host on a silicon wafer substrate using a co-sputtering process, where two targets – vanadium oxide (V₂O₅) and lithium oxide (Li₂O) – are run at the same time to produce the films.
The LVO co-sputtering process was studied and analyzed, including structural characterization and electrochemical evaluation using a conventional liquid cell. A SSB employing the LVO as a cathode was successfully fabricated, and presented electrochemical activity with good reversibility at different electrochemical conditions, which proves that the LVO is a good candidate as a cathode material for SSBs. The power of the V₂O₅ target was fixed at ~150 W while the Li₂O target power was varied to change the amount of lithium in the LVO films to have a desirable capacity during charge and discharge. The effect of a post-deposition annealing at 300 °C was also studied in comparison to LVO samples produced at ambient temperature. To the best of our knowledge, this is the first time that a successful co-sputtered lithiated vanadium oxide material is fabricated and tested in a SSB.
Raman spectroscopy indicates that some peaks correspond to vibrations which are found in crystalline V₂O₅ films, but it suggests that the LVO has its own characteristic peaks. A post-deposition annealing step did not dramatically alter the Raman spectrum, but the vibrational modes were better preserved after electrochemically cycling when the LVO is post-annealed at 300 °C under a nitrogen atmosphere. Surface analysis obtained from XPS confirmed a lithiated V₂O₅ composition up to 3 lithium ions per vanadium oxide. The best LVO film held ~70 % of the theoretical capacity (1 lithium per V₂O₅) as calibrated by liquid cell testing, and less when used in a SSB, but showed excellent reversibility in early cycling and a higher voltage than bulk V₂O₅. The use of co-sputtered LVO in SSBs will still be further investigated, but the preliminary results indicate the developed LVO is an excellent candidate for a cathode material. The use of a relatively low post-annealing temperature to produce an electrochemically active material, and the possibility to apply the developed co-sputtering process with different ion species, like magnesium or sodium, reveal the potential use of this work for a broader range of solid-state devices.

A primary hazard associated with lithium ion batteries is the combustibility of the liquid electrolyte, which is a key component for conduction of Li⁺ between anode and cathode. Polymer electrolytes can nominally improve safety by reducing the quantity and volatility of organic species. However, their poor room-temperature conductivity (10–100× lower in plasticized PEO than in pure propylene carbonate) and propensity to pyrolyze into volatile, flammable species at sufficiently elevated temperature makes them less-than-ideal electrolytes for lithium-ion batteries.
Lithium dicyanamide – LiN(CN)₂, itself a lithium salt explored for battery electrolytes – is shown to react with cyanophosphines (e.g. P(CN)₃, RP(CN)₂ where R is an aromatic moiety) in up to a 2:1 mole ratio, resulting in cross-linked sol-gel networks that fully incorporate both monomers. The high phosphorus and low hydrocarbon content of the resulting lithium cyanophosphine yields a material that is thermo-oxidatively stable, while simultaneously providing a high density of labile Li⁺ (up to 5 mEq g^-1).
Pulsed field gradient (PFG) ¹H, ⁷Li, and ¹³C NMR spectroscopies were utilized to demonstrate that: a) Oligomerization of both dicyanamide and cyanophosphine definitively occurs prior to gelation; b) Negligible amounts of either monomer remain unreacted; and c) Lithium remains effectively coordinated by the solvent, diffusing in concert with solvent instead of the oligomeric cyanophosphine polyanions. The resulting sol-gels exhibit a Li⁺ transference number near unity when used as an electrolyte between lithium foils, in accordance with NMR data showing negligible polyanion diffusivity under these conditions. Application of the measured Li⁺–solvent complex diffusion coefficients as the reaction mixture approaches gelation also allows estimation of Li⁺ mobility and, by proxy, the fraction of mobile Li⁺ in the system.

Lithium dicyanamide (LiN(CN)₂) can trimerize, oligomerize, or polymerize through thermal treatment, and the product of this polymerization is dependent on both impurities and conditions of heating. We have thermally treated LiC₂N₃ containing small amounts of various additives such as halide, NaC₂N₃, LiCN, and other materials as pressed pellets under vacuum, and characterized the products by both solution and solid state NMR, and by dielectric relaxation spectroscopy. Direct detection of ¹³C NMR spectra for the solid products was used to the relative amounts triazine and C≡N. The relative intensities and widths of the triazine peaks reflected variations in the reaction completion. Variable temperature ⁷Li NMR was particularly useful for determining the correlation times and activation energies of the lithium ion motion in these materials as a function of preparation conditions and thermal history.

All solid-state batteries (ASSB) are receiving increased attention for a variety of reasons that include elimination of the volatile solvents and support of faster battery charging compared with typical liquid-type systems [1]. One of most important components in the ASSB is the solid state electrolyte. To enable fast battery charging, it is necessary that the electrolytes have high ionic conductivities. Several families of solid state electrolytes currently exit and include sulfides, halides, oxides and boron-hydrogen salts. Closo borate materials are promising candidates owing to their high ionic conductivity (> 6 mS cm^-1 in Li system [2] and > 30 mS cm^-1 in Na system [3,4] and wide electrochemical window. Our group has demonstrated that these anions have high compatibility with active metals such as magnesium making these salts highly attractive for utilization as solid state electrolytes [4,5,6] . Herein, we will assess the potential of these solid state electrolytes and discuss our recent efforts towards understanding and improving the Li⁺ and Na⁺ ionic mobilities in these electrolytes.

Reference
[1] Y. Kato, et al, Nature Energy, 1, 16030 (2019).
[2] S. Kim, et al, Nature commun., 10, 1081 (2019).
[3] W. S. Tang, et al, ACS Energy Lett., 1, 659-664 (2016).
[4] R. Mohtadi, et al., Nature Reviews, 2, 16091 (2016).
[5] M. Kar, et al., Energy Environ. Sci., 12, 566-571 (2019).
[6] R. Mohtadi, et al, Molecules 25, 1791 (2020).

Solid-electrolyte interphase (SEI), a layer formed on the electrode surface, is essential for electrochemical reactions in batteries and critically governs the battery stability. Active materials, especially those with extremely high energy density, such as silicon (Si), often inevitably undergo large volume swing upon ion insertion and extraction, raising a critical question as how the SEI interactively responds to and evolves with the material and consequently controls the cycling stability of the battery. Here, by integrating sensitive elemental tomography, advanced algorithm and cryogenic scanning transmission electron microscopy, we unveil, in three-dimension, a correlated structural and chemical evolution of Si and SEI. Corroborated with a chemomechanical model, we demonstrate progressive electrolyte permeation and SEI growth along the percolation channel of the nanovoids due to vacancy injection and condensation during the delithiation process. Consequently, the Si-SEI spatial configuration evolves from the classic “core-shell” structure in the first few cycles to a “plum-pudding” structure following extended cycling, featuring the engulfing of Si domains by the SEI, which leads to the disruption of electron conduction pathways and formation of dead Si, contributing to capacity loss. The spatially coupled interactive evolution model of SEI and active materials, in principle, applies to a broad class of high-capacity electrode materials, leading to a critical insight for remedying the fading of high-capacity electrodes.

Lithium containing materials have been of great interest for coating development, due to the rapid development of lithium-ion batteries. Among these materials, lithium nitride has received much attention recently due to its high lithium-ion conductivity and low electric conductivity, which together are beneficial for coating layers at the interface between lithium metal anodes and sulfide electrolytes in solid-state lithium batteries. Previously reported lithium nitride coatings were prepared by the reaction between lithium metal and nitrogen atmosphere at elevated temperature, which makes it challenging to precisely control the thickness of the resulting lithium nitride layer. The thickness of the coating layer is important for the performance of the obtained batteries, because too thick coating introduces unnecessary interfacial impedance, and too thin coating does not improve the stability.
In this study, we prepared lithium nitride via magnetron sputtering for the first time, using Li metal target in Ar/N₂ gas atmosphere, with deliberate preparation of the Li target surface to avoid oxide contamination, and careful control of the sputtering power to avoid melting of the Li target. The polycrystalline Li₃N formed on the target surface and the amorphous coating on the glass substrate were measured by x-ray diffraction and other characterization methods. The thickness of the obtained lithium nitride coating can be controlled by varying the sputtering time. We applied the resulting lithium nitride coating on the sulfide electrolyte as an interfacial layer to stabilize the sulfide electrolyte in contact with Li metal. After cell assembly protocol was systematically optimized, the obtained coated sulfide solid-state electrolyte showed a slightly increased impedance and a significantly improved cycling performance in a spring-loaded lithium metal symmetric cell. These results demonstrate the feasibility of sputtering Li₃N binary and related ternary lithium nitride coatings as interfacial layers in solid-state batteries.

Polycrystalline solids can exhibit material properties that differ significantly from those of equivalent single-crystal samples, in part, because of a spontaneous redistribution of mobile point defects into so-called space-charge regions adjacent to grain boundaries. The general analytical form of these space-charge regions is known only in the dilute limit, where defect-defect correlations can be neglected. Using kinetic Monte Carlo simulations of a three-dimensional Coulomb lattice gas, we show that grain-boundary space-charge regions in non-dilute solid electrolytes exhibit overscreening -- damped oscillatory space-charge profiles -- and underscreening -- decay lengths that are longer than the corresponding Debye length and that increase with increasing defect-defect interaction strength. Overscreening and underscreening are known phenomena in concentrated liquid electrolytes, and the observation of functionally analogous behaviour in solid electrolyte space-charge regions suggests that the same underlying physics drives behaviour in both classes of systems. We therefore expect theoretical approaches developed to study non-dilute liquid electrolytes to be equally applicable to future studies of solid electrolytes.

Glassy-type solid state electrolytes such as state-of-the-art LiPON avoid grain boundaries and prevent Li-dendrite propagation leading to extremely good cyclability and the commercialization of planar thin-film LiPON-based microbatteries. However, its reduced ionic conductivity (~1 μS/cm) limits its performance at high/discharge rates and the severe degradation of its electrochemical and structural properties upon their exposure to ambient conditions and high temperatures (> 300 °C) hinders scalability and manufacturability. Among the next generation solid-state electrolytes, NASICON superionic solid electrolyte Li_(1+x)Al_xTi_(2-x)(PO₄)₃ (LATP) with 0.3 ≤ x ≤ 0.5 remains one of the most promising solid electrolytes thanks to its good ionic conductivity (~0.5 - 1 mS●cm^-1) and outstanding stability in ambient air. Despite the intensive research for bulk systems, there are only very few studies of LATP in thin film form. In particular, the only successful reports of relatively high ionic conduction (~10^-5 S●cm^-1) have been achieved through amorphous sputtered films.

In this talk, we will explore the properties of high performance LATP thin films fabricated by Large-Area Pulsed Laser Deposition. The as-deposited thin films exhibit an ionic conductivity around 0.5 μS●cm^-1 at room temperature (comparable to the state-of-the-art of LiPON) which increases to remarkably high values of 0.1 mS●cm^-1 after an additional annealing at 800 °C. We will discuss the formation of a glassy, intergranular phase connecting highly conducting LATP grains as a possible cause for the significant enhancement in ionic conductivity by two orders of magnitude. The performance of both as-deposited and annealed LATP films makes them suitable as solid electrolytes, which opens the path to a new family of stable and highly performing thin solid-electrolytes. We will discuss its integration with other battery components, with special attention to interfacial coatings matching the electrochemical window at low potentials.

LiMn_1.5Ni_0.5O₄ (LNMO) spinel material, is being thoroughly studied as a cathode candidate for lithium ion battery. LNMO can crystallize either with an ordered structure (P4₃32 space group), where the manganese and the nickel atoms are located in specific sites, or with a disordered structure (Fd-3m space group), where the manganese and the nickel are randomly distributed. Synthesis parameters are key to control the degree of ordering in LNMO and the electrochemical performance is highly affected by it. In particular, the disordered structure is found to have better performances, especially at high rates. The ordering can be studied using several techniques such as neutron powder diffraction (NPD), Raman or solid state magic angle spinning nuclear magnetic resonance (NMR). In particular, ⁷Li NMR spectra shows a single peak for the fully ordered structure, while a larger number of signals is found for the disordered one. In the first part of this study, we propose a signal assignment of the NMR signals using DFT calculations, which has helped to understand how each different lithium local environment modifies the Fermi contact shift.
Some of the main advantages of LNMO are that they have good performance at high rates due to their 3D structure, and their ability to store large energy density as their work at high voltage. However, cycling at high voltage has as well some drawbacks, especially in terms of structural and chemical stability. Electrolyte degradation and manganese dissolution in the electrolyte are two of the main problems this material faces. Coating the LNMO with a protective layer is regarded as an effective approach to stabilize the electrode/electrolyte interface. Li₃PO₄ was calculated to have a good compatibility [1] and it has been experimentally found to avoid chemical attacks from the electrolyte [2]. One of the main issues in the study of the coating refers to their characterization. This is often challenging and can cast doubts on their goodness. By instance, HRTEM images can only provide local information, so the combination of different techniques is required. In this work, ⁷Li and ³¹P MAS NMR is used, in combination with X-ray diffraction (XRD) and scanning and transition electron microscopies (SEM and TEM), to provide a trustworthy characterization of Li₃PO₄-coated LNMO prepared by different routes. In particular, the closeness of diamagnetic compounds (such as Li₃PO₄) to paramagnetic ones (such as LNMO) have strong influence on the NMR spectra, [3] so NMR can be a useful technique to have an overall idea on the goodness of the coating. In addition, ⁷Li MAS NMR allows to characterize as well, whether the coating process does modify the Ni/Mn distribution in the spinel phase.

Bibliography:

[1] Xiao, Y. et al. Joule 2019, 3 (5), 1252–1275.
[2] Chong, J. et al. Chem. - A Eur. J. 2014, 20 (24), 7479–7485.
[3] Dupré, N. et al. J. Mater. Chem. 2008, 18 (36), 4266–4273.

Among the alternatives to conventional Li-ion batteries, solid-state batteries (SSBs) have the potential for high energy density as they may enable the use of a metal anode. However, the penetration of metal filaments into a solid electrolyte (SE) and resulting shorting is an obstacle to the commercialization of metal-anode SSBs. This work utilizes continuum modeling to study the mechanism of metal deposition within the SE due to the electronic conductivity of the SE. We show that metal deposition can happen in isolated micro-size voids within the SE and we specify the conditions under which it causes failure due to SE fracture. The vulnerability to metal deposition in the SE is investigated by controllable parameters (such as the cell voltage, applied current density, and etc.), and suppression strategies of metal deposition are proposed. These findings provide a deeper understanding of the Li penetration in the SE in order to eventually overcome the challenge in solid-state batteries. In addition, our work shows that metal propagation through the electronic can be overcome with a few focused strategies.

All-solid-state lithium battery is attracting attention as one of the promising candidates for a next generation energy storage technology. The solid electrolyte (SE) with much higher modulus than lithium is expected to prevent lithium dendrite penetrations and contributes to improved safety while increasing the energy density. However, there are many cases where lithium dendrite penetrates the solid electrolyte leading to a short circuit and premature failure of the battery. The interaction between the growing lithium dendrites and the solid electrolyte involves complex interplay of electrochemistry and mechanics. This can become even more complicated when the size-scale of the dendrites are in nano-scale, particularly at the initial state of the nucleation and growth, since the mechanical properties deviates from the bulk. Here in situ transmission electron microscopy (TEM) plays an important role in directly observing the growth behavior of the dendrites and how it is affected by the mechanical stress at the SE/Li interface. We developed a quantitative in situ TEM technique that can measure the force imposed on the lithium dendrite as it grows from the solid electrolyte.
The method was applied to evaluate the critical force that changes growth direction of the dendrite from vertical to horizontal with respect to the SE surface. Since the size of the dendrite was in nano-scale it sustained much higher stress than the bulk yield stress. Furthermore, the method successfully captured the change in the mechanical behavior of the dendrite at different growth rate indicating higher stress can be imposed to the SE at faster growth rate. In addition to the mechanical response of the dendrite growth, the crack propagation of the SE was characterized. It revealed that the lithium dendrite, during it growth process, can cause the crack to propagate in the SE from the surface defect. The in situ TEM observation clearly showed the crack growth and opening behavior, and the force associated with the process was precisely evaluated. The in situ TEM provides fundamental insights to the electro-chemo-mechanics of the lithium dendrite and solid electrolytes, and the information obtained in this work can be used as essential parameters to design all-solid-state lithium batteries with improved performance.

Zinc (Zn) anode has good promise for energy storage application due to its excellent intrinsic properties such as high stability, high volumetric capacity, abundance, and low cost. Its relatively high electrode potential of -0.76 V vs. standard hydrogen electrode is ideal for neutral or mildly acidic aqueous electrolytes. Further, its polarization is much lower than other multivalent metal anodes such as magnesium and aluminum. However, its significantly high self-corrosion, hydrogen evolution reaction during the charging process, dendrite growth, and nonuniform stripping/plating of the Zn over long-term cycling restrict its practical application. These issues can lead to the migration of Zn during the plating/stripping processes and even cause battery failure. Artificial solid electrolyte interface (ASEI) applied on the surface of Zn anode has been suggested as a promising approach to address these issues. ASEI regulates the initial nucleation and manipulates Zn ion distribution in the surroundings of the anode surface. Nonetheless, only a few studies have investigated ASEI prepared using anionic polyelectrolyte.
In this study, we report the observation of ASEI on a Zn-carbon composite anode, based on ultra-thin layers of carboxymethyl cellulose (CMC), which is an anionic polyelectrolyte. The Zn anode having ASEI enables reversible and dendrite-free zinc plating/stripping even at high current densities, endowed by the fast ion migration coupled with cationic modulation. The ASEI is highly permeable for Zn ions and avoids excessive Zn utilization by hindering the access of water molecules and electrons. The ASEI can effectively suppress corrosion and regulate Zn plating/stripping behavior as confirmed via electrochemical characterization. Electrochemical impedance spectroscopy studies confirm that the anode having ASEI exhibits reduced charge transfer resistance and enhanced Zn ions absorption/desorption. As confirmed by X-ray tomography, during the charging and discharging cycle, no evidence for dendrite growth and zinc migration are observed. A mechanistic investigation of the role of CMC as ASEI is presented, along with data showing that the CMC coating layer can enhance the cycling stability of the Zn anode in aqueous Zn-ion batteries. This technique can be also applied in other Zn-based batteries having aqueous electrolytes.

The interfacial impedance between lithium metal and garnet solid electrolytes (e.g. LLZO) is usually dominated by poor solid-solid contact. This can lead to current constriction spots at the interface and to the rapid growth of lithium filaments through the LLZO, eventually short-circuiting the cell at small nominal current densities. Different approaches have proven effective to decrease such interfacial impedance, for example the removal of the lithio-phobic Li₂CO₃ layer which can form on the LLZO surface during glovebox storage. Alternatively, lithio-philic thin films like amorphous Al₂O₃ can be deposited at the Li|LLZO interface. Both approaches show similar interfacial impedances before cycling, but the difference in the long-term effect on the interface stability is unclear. Also, whether lithio-philic thin films can provide a mechanical and/or electronic-insulating barrier hindering the propagation of lithium filaments, or whether their role is simply to improve the lithium wettability on the LLZO surface to avoid current constrictions, remains an open question. In this study, we deposit amorphous Al₂O₃ and LiPON thin films via magnetron sputtering on Li₂CO₃-free LLZO solid electrolytes obtained via a rapid acid treatment. We assess the performance of such thin films through potential step chronoamperometry and in-operando impedance spectroscopy, and we use scanning electron microscopy to investigate the morphological stability of the modified Li|LLZO interface. Our findings provide a better understanding of the effect of interfacial ceramic thin films on improving the cycle life of a lithium metal cell. We also assess the most useful properties of the interfacial thin films which prevent the propagation of lithium filaments through the solid electrolyte.

A novel water based in-situ precipitation method is devised for the fabrication of polymer matrix composite solid electrolytes, achieving effective spatial dispersion of Li_1.3Al _0.3Ti_1.7(PO₄)₃ (LATP) nanoparticles up to particle loadings of 30 wt% (15 vol%). Amorphous LATP nanoparticles precipitate in ostensibly random locations within the poly(ethylene) oxide (PEO) matrix. The highest 20^○C ionic conductivity of 3.8 × 10^-4 S/cm, observed at 13 vol% LATP and EO/Li = 10, which exceeds that of the polymer matrix by 2 orders of magnitude. This result is consistent with earlier predictions based on our tri-phase model, both in composition and magnitude. Accordingly, the most highly conductive region is the interphase into which the polymer surrounding the LATP particles is transformed. Minimizing particle agglomeration permits expansion of the interphase into a larger fraction of the bulk polymer. Detailed analyses of our data provide new insights into the nature of the interphase and the transport mechanisms in these systems.(NSF-DMR 1610742)