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 as‐synthesized Li3InCl6 shows a high ionic conductivity of 2.04×10−3 S cm−1 at 25 °C. 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. A superionic conductor, Li3InCl6, with room‐temperature Li+ conductivity of 2.04×10−3 S cm−1, is prepared by a facile and scalable water‐mediated synthesis route. The reversible conversion between Li3InCl6 and Li3InCl6⋅2 H2O makes it stable against air and humidity, thus ensuring the high ionic conductivity is recovered after conversion.