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

Abstract Li 2 ZrCl 6 (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, Ta 5+ 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 Dy 3+ and Ta 5+ co‐doped electrolytes have been synthesized and the optimal Li 2.1 Zr 0.8 Dy 0.15 Ta 0.05 Cl 6 (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.