LaCl₃-based sodium halide solid electrolytes with high ionic conductivity for all-solid-state batteries

To enable high performance of all solid-state batteries, a catholyte should demonstrate high ionic conductivity, good compressibility and oxidative stability. Here, a LaCl₃-based Na⁺ superionic conductor (Na_1-xZr_xLa_1-xCl₄) with high ionic conductivity of 2.9 × 10^-4S cm^-1 (30 °C), good compressibility and high oxidative potential (3.80 V vs. Na₂Sn) is prepared via solid state reaction combining mechanochemical method. X-ray diffraction reveals a hexagonal structure (P6₃/m) of Na_1-xZr_xLa_1-xCl₄, with Na⁺ ions forming a one-dimensional diffusion channel along the c-axis. First-principle calculations combining with X-ray absorption fine structure characterization etc. reveal that the ionic conductivity of Na_1-xZr_xLa_1-xCl₄ is mainly determined by the size of Na⁺-channels and the Na⁺/La³⁺ mixing in the one-dimensional diffusion channels. When applied as a catholyte, the NaCrO₂||Na_0.7Zr_0.3La_0.7Cl₄||Na₃PS₄||Na₂Sn all-solid-state batteries demonstrate an initial capacity of 114 mA h g^-1 and 88% retention after 70 cycles at 0.3 C. In addition, a high capacity of 94 mA h g^-1 can be maintained at 1 C current density.