Degradation Evolution for Li2ZrCl6 Electrolytes in Humid Air and Enhanced Air Stability via Effective Indium Substitution

Abstract Superionic halides have aroused interests in field of solid electrolytes such as Li 2 ZrCl 6 . However, they are still facing challenges including poor air stability which lacks in‐depth investigation. Here, moisture instability of Li 2 ZrCl 6 is demonstrated and decomposition mechanism in air is clearly revealed. Li 2 ZrCl 6 decomposes into Li 2 ZrO 3 , ZrOCl 2 · x H 2 O and LiCl during initial stage as halides upon moisture exposure. Later, these side products evolve into LiCl(H 2 O) and Li 6 Zr 2 O 7 after longer time exposure. More importantly, structure of destroyed halides cannot be recovered after postheating. Later, Indium is doped into Li 2 ZrCl 6 (9.7 × 10 −5 S cm −1 ) to explore its effect on structure and properties. Crystal structure of ball‐milled In‐doped Li 2 ZrCl 6 electrolytes is converted from the Li 3 YCl 6 ‐like to Li 3 InCl 6 ‐like with increasing In content and ionic conductivity can also be enhanced (0.768–1.13) × 10 −3 S cm −1 ). More importantly, good air stability of optimal Li 2.8 Zr 0.2 In 0.8 Cl 6 is achieved since halide hydrates are formed after air exposure instead of total decomposition and the hydrates can be restored to Li 2.8 Zr 0.2 In 0.8 Cl 6 after postheating. Moreover, reheated Li 2.8 Zr 0.2 In 0.8 Cl 6 after air exposure is successfully applied in solid‐state LiNi 0.8 Co 0.1 Mn 0.1 O 2 /halides/Li 6 PS 5 Cl/Li–In battery. The results in this work can provide insights into air instability of Li 2 ZrCl 6 and effective strategy to regulate air stability of halides.