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 Li_2.8 Zr_0.2 In_0.8 Cl₆ 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 Cl₆ after postheating. Moreover, reheated Li_2.8 Zr_0.2 In_0.8 Cl₆ after air exposure is successfully applied in solid-state LiNi_0.8 Co_0.1 Mn_0.1 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.