Rare Earth Metal Ion-Doped Halide Solid Electrolytes plus Ta5+ Substitution for Long Cycling All-Solid-State Batteries

Abstract

Li2ZrCl6 (LZC) solid electrolyte has been recognized as a promising candidate for all-solid-state batteries (ASSBs), owing to its remarkable compatibility with high-voltage cathodes and the cost advantage among halide electrolytes. However, the ionic conductivity of LZC (≈0.4 mS cm−1) requires enhancement. Herein, rare earth metal elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Y) have been doped into LZC, resulting in a doubling of the ionic conductivity. Moreover, Ta5+ is utilized to further modulate the concentration of Li+ to enhance the ionic conductivity and reduce the dosage of expensive rare-earth metal. Using the Li-Zr-Dy-Cl component as a case study, 16 types of Dy3+ and Ta5+ co-doped electrolytes have been synthesized and the optimal Li2.1Zr0.8Dy0.15Ta0.05Cl6 (LZDTC) exhibits the ionic conductivity of 1.67 mS cm−1. Three-dimensional Li-ion transport pathways in LZDTC has been revealed. The dual-substitution of Dy and Ta at Zr site changes length of Li-Cl bond and Li occupation, thereby reducing the resistance to Li+ migration. ASSBs of Li-In/LGPS-LZDTC/NCM811 demonstrate a capacity of 117 mA h g−1 after 500 cycle at 0.5 C with a 74% retention rate, highlighting the effectiveness of the dual-doping strategy for creating superionic conductors for ASSBs.