Investigating stacking variations in Li3InCl6 crystal structure and their influence on solid electrolyte properties

Li ₃InCl ₆ (LIC) has recently emerged as a promising halide-based solid electrolyte for all-solid-state Li batteries. This study investigates the structural characteristics of LIC, with a specific focus on potential stacking faults and their impact on the properties of the solid electrolyte. A thermodynamic assessment of crystallographic stacking structures, conducted via first-principles calculations, reveals that certain variations in stacking sequences in the [010] direction relative to the previously reported reference LIC structure result in reduced crystal energy, which implies a thermodynamically more favorable new crystal structure for LIC than the extant reference structure. The efficacy of this novel crystal structure, referred to as #7–8, is evaluated against the reference structure concerning Li-ion mobility and electrochemical stability. The results demonstrate a notable enhancement in ionic conductivity while preserving a comparable electrochemical stability window. Modifications in specific stacking configurations within LIC crystals are shown to enhance Li-ion conductivity by establishing low-energy barrier pathways for Li ions in particular directions. While the mobility in other directions may decrease, this result in an overall improvement in Li-ion conductivity. The proposed crystal structure demonstrates superior thermodynamic stability compared to the conventional reference structure and is consistent with experimentally obtained X-ray diffraction data, underscoring its potential as a novel benchmark for future analyses of LIC crystal structures. Furthermore, this study suggests that two-dimensional defects, such as stacking faults, may play a crucial role in influencing the performance of halide-based solid electrolytes.