Water‐Mediated Synthesis of a Superionic Halide Solid Electrolyte

To promote the development of solid-state batteries, polymer-, oxide-, and sulfide-based solid-state electrolytes (SSEs) have been extensively investigated. However, the disadvantages of these SSEs, such as high-temperature sintering of oxides, air instability of sulfides, and narrow electrochemical windows of polymers electrolytes, significantly hinder their practical application. Therefore, developing SSEs that have a high ionic conductivity (> 10@3 S cm@1), good air stability, wide electrochemical window, excellent electrode interface stability, low-cost mass production is required. Herein we report a halide Li superionic conductor, Li3InCl6, that can be synthesized in water. Most importantly, the assynthesized Li3InCl6 shows a high ionic conductivity of 2.04 X 10@3 Scm@1 at 25 8C. Furthermore, the ionic conductivity can be recovered after dissolution in water. Combined with a LiNi0.8Co0.1Mn0.1O2 cathode, the solid-state Li battery shows good cycling stability. All-solid-state lithium batteries (ASSLBs) using solid-state electrolytes (SSEs) are considered as promising next-generation energy-storage systems with improved safety through the elimination of the flammable liquid electrolyte in convention lithium-ion batteries (LIBs). Among the various types of electrolytes, oxide-based and sulfide-based SSEs are considered to be the most promising candidates for use in ASSLBs because of their high ionic conductivity of over 10@3 Scm@1.[1c,2] Despite the recent progress made in these SSEs, several serious obstacles are still hindering their practical applications, especially the manufacturing complexity and sensitivity. For oxide-based SSEs, high sintering temperatures are required both during the synthesis of SSEs and in the subsequent steps to promote intimate contact between electrode materials and SSE, making the manufacturing costly and which also might cause interfacial reactions. For sulfide-based SSEs, their chemical instability in air and moisture inevitably cause deterioration of the structure/ composition, leading to a large decrease in ionic conductivity and the release of noxious H2S gas. [5] Another serious challenge for sulfide SSEs is the unavoidable and detrimental side reactions with high-voltage oxide cathode materials (e.g. LiCoO2 and LiNixMnyCozO2). [6] Direct contact between sulfide SSEs and oxide cathode materials results in the formation of a lithium deficient space-charge layer and the diffusion of transition metals from cathode to sulfide SSE which react with the electrolyte and form metal sulfides. In this context, interfacial protection layers between sulfide SSEs and oxide cathodes are necessary but introduce extra complexity and cost for the fabrication process. 8] To address these issues, halide SSEs, which were developed in the 1970s, have emerged as attractive alternatives. Unfortunately, the development of halide SSEs has been limited due to their relatively low ionic conductivity and the structural instability of some species. 10] For example, the Li3YCl6 synthesized by Lutz and Steiner in 1992 only achieved an ionic conductivity of approximately 10@4 Scm@1 at 200 8C. Although high-temperature phase Li3InBr6 has a high ionic conductivity of 10@3 S cm@1 at 25 8C, the asprepared Li3InBr6 shows quite low ionic conductivity of 10@7 Scm@1 and its structure will be destroyed at @13 8C. In more recent times, the relatively stable Li3YCl6 and Li3YBr6 SSEs with high ionic conductivities of around 10@3 Scm@1 were synthesized by Asano et al. using a high-energy ball milling and high-temperature annealing process. Nevertheless, these Li-conducting halide SSEs are still sensitive to moisture. Achieving high ionic conductivity, high stability toward oxide cathodes, moisture resistance, and a water-based synthesis method would be an ultimate goal for halide SSEs. Herein, we report a halide-based SSE, Li3InCl6, that can be synthesized via a H2O-mediated route (see Equation (1)). The reaction between LiCl and InCl3 can be mediated by H2O at room temperature to form Li3InCl6·xH2O, and the removal of H2O affords pure Li3InCl6 and recovered conductivity (Figure 1). The Li3InCl6 SSE possesses a high ionic conduc[*] Dr. X. Li, Dr. J. Liang, J. Luo, K. R. Adair, C. Wang, Dr. M. N. Banis, Dr. R. Li, Prof. X. Sun Department of Mechanical and Materials Engineering University of Western Ontario 1151 Richmond St, London, Ontario, N6A 3K7 (Canada) E-mail: xsun9@uwo.ca Dr. N. Chen, Dr. M. N. Banis Canadian Light Source 44 Innovation Boulevard, Saskatoon, SK S7N 2V3 (Canada)