Superionic halide solid electrolyte Li1.7Zr0.7Ta0.3Cl6 for durable all-solid-state lithium batteries

Zirconium-based halide solid electrolyte, Li 2 ZrCl 6 , with low raw-material cost and high oxidative stability is a promising candidate for next-generation energy storage devices. However, the low ionic conductivity hinders its practical applicability. Herein, we report a new zirconium-based superionic conductor based on high-valence Ta 5+ doping strategy. The optimized Li 1.7 Zr 0.7 Ta 0.3 Cl 6 (LZTC) exhibits excellent ionic conductivity of 1.42 mS cm -1 at 25°C. Moreover, it can be further increased up to 1.68 mS cm -1 with a low activation energy of 0.28 eV by slightly tuning Li + concentration. In addition, LZTC possesses a big compact density of 2.67 g cm -3 under 250 MPa and is compatible with 4V-class cathodes. Density function theory (DFT) and bond valence site energy (BVSE) calculations reveal Ta 5+ substitution significantly reduces the migration energy barrier of lithium ions due to the distortions and defects of local structural environment. The assembled all-solid-state batteries with Li 1.7 Zr 0.7 Ta 0.3 Cl 6 as electrolyte and scNCM811 as cathode show excellent cycling performance for 600 cycles at 1C with a high-capacity retention of 85.7%.