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

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 Li_2.1Zr_0.8Dy_0.15Ta_0.05Cl₆ (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.