Interfacial Characterization, Electrochemical Evolution and Kinetics in Argyrodite Solid Electrolytes with Li Metal Anode for High Energy Density Solid-State Batteries
Authors: Narayanan Sudarshan , Ulissi Ulderico , Pasta Mauro 
Published: July 2021

An all-solid-state battery (SSB), comprising Li/solid electrolyte (SE)/composite cathode, is of great interest due to its potential for improved safety, higher specific energy, energy density and power density, compared with Li-ion cells, enabling widespread use in portable electronics and electric vehicle applications. A variety of material systems are being considered in this regard that largely meet the criteria expected out of the cells they would be part of, namely, oxides, anti-perovskites, garnets, sulfides, and polymers. However, despite the extensive interest, a major limitation impeding progress in large-scale adoption of these SE materials is the instability in interfaces formed with Li metal, that are detrimental to the performance of the electrochemical cell. Among these SE material systems, ceramic solid electrolytes, and in particular, a class of sulfides called argyrodites (Li6PS5X, X = Cl, Br, I), are capable of delivering sufficient ionic conductivity for SSBs to achieve parity in performance with state-of-the-art Li-ion cells based on liquid electrolytes. The barriers lie within the interfaces between the electrolyte and the two electrodes, in the mechanical properties throughout the device and in processing scalability[1]. The chemistry at such interfaces of Li metal and argyrodite SE surface and their dynamic evolution through surface-sensitive techniques like X-ray photoelectron spectroscopy (XPS) will be probed in our study. Owing to the dependence of cell performance on several factors such as electro-chemo-mechanical properties and on kinetics of the process, an integral part of this study would be characterization under ex-situ, in-situ and in-operando conditions. Prior work by Wenzel et al., Schlenker et al. and Wood et al.[2-4] have reported interfacial characteristics in related cell materials, considering some of these aspects, but contrasting chemistries and a lack of consensus on electrode-electrolyte interphase products underscores the complexity of such a system. In my talk, I will compare and contrast the effect of depositing/plating Li metal on the SE surface using various methods while investigating the evolution of interphasial products formed. I will also present a characterization of the evolution of the interface as a function of electrochemical kinetics, in order to better understand the interplay of these effects in determining cell performance.
References:
[1] Pasta, M., Armstrong, D., Brown, Z.L., Bu, J., Castell, M.R., Chen, P., Cocks, A., Corr, S.A., Cussen, E.J., Darnbrough, E., et al. “2020 roadmap on solid-state batteries”. Journal of Physics: Energy 2 (2020), p 032008
[2] Wenzel, S., Sedlmaier, S.J., Dietrich, C., Zeier, W.G., and Janek, J. (2018), “Interfacial reactivity and interphase growth of argyrodite solid electrolytes at lithium metal electrodes”. Solid State Ionics 318 pp 102–111
[3] Schlenker, R., Stȩpień, D., Koch, P., Hupfer, T., Indris, S., Roling, B., Miß, V., Fuchs, A., Wilhelmi, M., and Ehrenberg, H. (2020). Understanding the Lifetime of Battery Cells Based on Solid-State Li6PS5Cl Electrolyte Paired with Lithium Metal Electrode. ACS Applied Materials and Interfaces 12, 20012–20025
[4] Wood, K.N., Steirer, K.X., Hafner, S.E., Ban, C., Santhanagopalan, S., Lee, S.H., and Teeter, G. (2018). Operando X-ray photoelectron spectroscopy of solid electrolyte interphase formation and evolution in Li2S-P2S5 solid-state electrolytes. Nature Communications 9.