High Ionic Conductivity in Li₂ZrCl₆ via La³⁺ Doping for All-Solid-State Lithium Metal Batteries

Halides not only possess high ionic conductivity but also exhibit excellent electrochemical stability against high-voltage cathodes, making them promising candidates for solid-state electrolytes in all-solid-state lithium metal batteries (ASSLMBs). Compared with rare-earth halide electrolytes, Li₂ZrCl₆ electrolytes are less costly. However, they face challenges relating to relatively lower ionic conductivity. Herein, Li_2+xZr_1−xLa_xCl₆ is synthesized through La³⁺ doping in Li₂ZrCl₆. The introduction of La³⁺ increases the concentration of lithium ions in the crystal and expands the lattice volume, leading to ionic conductivity as high as 8.22 × 10⁻⁴ S cm⁻¹. When Li_2.1Zr_0.9La_0.1Cl₆ is applied in ASSLMBs (with a LiNi_0.8Mn_0.1Co_0.1O₂ cathode and a Li-In anode), it exhibits superior electrochemical performance, with high initial capacity of 132.5 mA h g⁻¹, and after 100 cycles at 0.5 C, the battery still maintains a capacity of 72.4 mA h g⁻¹ and high coulombic efficiency of 99.7%.