Heterovalent Cation Substitution to Enhance the Ionic Conductivity of Halide Electrolytes

Application of halide electrolytes including Li₃InCl₆ in all-solid-state lithium-metal batteries is still challenging due to the instability with lithium metal and limited ionic conductivity compared with liquid electrolytes and some sulfides. Here, through Zr substitution, a novel Li_2.9In_0.9Zr_0.1Cl₆ electrolyte is synthesized through the ball milling and subsequent annealing process. The ionic conductivity of Li_2.9In_0.9Zr_0.1Cl₆ (1.54 mS cm^–1 at 20 °C) is nearly double that of original Li₃InCl₆ (0.88 mS cm^–1 at 20 °C). Such conductivity enhancement is mainly attributed to the enlarged interplanar spacing and lattice volume, improved concentration of lithium-ion vacancies created by introducing higher-valence Zr⁴⁺, and the change of the preferred orientation from the (001) plane to the (131) plane. As a result, the all-solid-state lithium-metal batteries (ASSLMBs) assembled with the Li_2.9In_0.9Zr_0.1Cl₆ electrolyte also demonstrate a higher charge/discharge capacity, better cycle stability, and rate performance during cycling without an extra lithium source at the anode side.