Argyrodite- and Halide-Containing All-Solid-State Lithium Batteries

Inorganic All-solid-state batteries (ASSBs) are attracting great interest as next-generation energy storage systems due to their potentially better safety and higher energy density compared to the current lithium-ion batteries with organic liquid electrolytes^1-4. The development of these batteries is based, on the one hand, on exploration of electrolyte conductors with fast ionic conductivity<br/>(10^-3 S.cm^-1) and high voltage stability “windows” and, on the other, on the optimization of the interfaces between electrolyte and active materials at the positive and negative electrodes. Major research efforts have been undertaken to optimize inorganic solid electrolytes (SEs) including sulfides, oxides, polymers and halides. Among them, sulfides, and halides are more promising owing to their high ionic conductivities, their plasticity enabling good contact with electrode materials and suitable integration conditions in All-Solid-State batteries systems conditions, in particular compared to oxide electrolytes.<br/><br/>For sulfides, the <b>Argyrodite-type Li₆PS₅X (X = Cl, Br, and I) family </b>has been extensively investigated ^5-6 and a very high ionic conductivity of over 10 mS.cm⁻¹ at room temperature was recently found in the compound Li_5.3PS_4.3Cl_1.7⁷. Due to the lower cost of chloride-based Argyrodite-type SEs than that of Argyrodite-type SEs with other halide ions, industrial and fundamental battery applications mainly concentrate on this compound. We undertook a detailed investigation on how the anion disordering in the structure influences the global Li⁺ ion transport and we found a new compositional space that allows to build promising All-Solid-State<br/>Batteries ⁸. However, some problems still need to be solved, such as their reactivity with H₂O in air and the production of poisonous H₂S, which requires inert gas atmosphere during synthesis and handling.<br/><br/>That’s why the inorganic <b>metal-halide SEs family</b>, including <b>Li₃MCl₆ (M = In, Er, Sc, Yb, etc.)</b> and <b>Li₂ZrCl₆</b>, has gained increasingly attention in recent years as several of its members exhibit excellent compatibility with high-voltage cathode materials and are suitable as catholytes in SSB. We undertook an exploratory work on halide solid electrolytes, carried out through the prism of two selected samples, Li₃InCl₆ and Li₂ZrCl₆. While much investigation remains to be done to understand all the mechanisms involved in those compounds, this work has shown different ways to synthesize them and successful methods to improve the ionic conductivity.<br/><br/>After a brief description of an ASSB and its requirements, in terms of solid electrolyte and processing, we will present the optimization of two electrolytes, a sulfide and an halide, and their integration in full all-solid state cells.<br/><br/><b>Keyword: </b><i>All-Solid-State Batteries, inorganic solid electrolyte, ionic conductor, Argyrodite-type electrolytes, halide-type electrolytes </i><br/><br/><b>References </b><br/>1. J. Janek, W. G. Zeier, <i>Nat. Energy</i>, 1 <b>(2016)</b> 16141.<br/>2. A. Manthiram, X. Yu, S. Wang, <i>Nat. Rev. Mater</i>, 2 <b>(2017)</b> 16103.<br/>3. C. Z. Ke, F. Liu, Z. M. Zheng, <i>et al</i>., <i>Rare Met</i>., 40 <b>(2021)</b> 1347–1356.<br/>4. Q. Yu, K. Jiang, C. Yu, <i>et al</i>., <i>Chinese Chemical Letters</i>, 32 <b>(2021)</b> 2659–2678.<br/>5. S Boulineau, M Courty, JM Tarascon, V Viallet, <i>Solid State Ionics</i>, 221 <b>(2012)</b> 1-5<br/>6. S Boulineau, JM Tarascon, JB Leriche, V Viallet, <i>Solid State Ionics</i>, 242 <b>(2013)</b> 45-48<br/>7. X. Peng, <i>et al</i>., <i>Energy Storage Materials, 30</i> <b>(2020)</b> 67-73.<br/>8. J. Auvergniot, C. Masquelier, V. Viallet, D. Shanbhag, <i>World Patent</i> WO2023/247531A1 (2023)