A high Al-doping ratio halide solid electrolyte with a 3D Li-ion transport framework

Abstract

Rare earth metal-based halide solid electrolytes (HSEs) are among the most promising electrolyte candidates for novel solid-state batteries. However, reducing the content of rare earth metals while still retaining high Li-ion conductivity remains a great challenge. In this work, we report a class of Al-substituted halide solid electrolytes, Li₃Al_xY_1−xCl₆, and explore the impact of Al substitution content on the halide structure and lithium-ion transport. Interestingly, Li₃Al_0.7Y_0.3Cl₆ exhibits a high ionic conductivity of 1.05 × 10⁻⁴ S cm⁻¹ with a high Al substitution ratio of 70% even at 25 °C. Bond valence site energy (BVSE) analysis reveals that the disorderly substitution of a higher proportion of smaller atomic radius Al elements into the structure potentially opens 3D migration pathways and reduces the energy barrier for lithium ion migration, thereby enhancing Li ion conductivity. As a result, the as-prepared Li₃Al_xY_1−xCl₆ demonstrated a stable operation of Li electrochemical stripping and plating at 100 μA cm⁻² over 2500 h.