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

Superionic halides have aroused interests in field of solid electrolytes such as Li2 ZrCl6 . However, they are still facing challenges including poor air stability which lacks in-depth investigation. Here, moisture instability of Li2 ZrCl6 is demonstrated and decomposition mechanism in air is clearly revealed. Li2 ZrCl6 decomposes into Li2 ZrO3 , ZrOCl2 ·xH2 O and LiCl during initial stage as halides upon moisture exposure. Later, these side products evolve into LiCl(H2 O) and Li6 Zr2 O7 after longer time exposure. More importantly, structure of destroyed halides cannot be recovered after postheating. Later, Indium is doped into Li2 ZrCl6 (9.7 × 10-5 S cm-1 ) to explore its effect on structure and properties. Crystal structure of ball-milled In-doped Li2 ZrCl6 electrolytes is converted from the Li3 YCl6 -like to Li3 InCl6 -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 Li2.8 Zr0.2 In0.8 Cl6 is achieved since halide hydrates are formed after air exposure instead of total decomposition and the hydrates can be restored to Li2.8 Zr0.2 In0.8 Cl6 after postheating. Moreover, reheated Li2.8 Zr0.2 In0.8 Cl6 after air exposure is successfully applied in solid-state LiNi0.8 Co0.1 Mn0.1 O2 /halides/Li6 PS5 Cl/Li-In battery. The results in this work can provide insights into air instability of Li2 ZrCl6 and effective strategy to regulate air stability of halides.