Low-cost rare-earth-oxide-derived Li3TmCl4Br2 halide electrolyte with superior ionic conductivity for all-solid-state batteries

Abstract

Halide solid electrolytes (HSEs) are promising for all-solid-state batteries but are hindered by the high cost and hygroscopicity of rare-earth chloride precursors. This study addresses this challenge by developing a novel, cost-effective synthesis strategy. We utilize rare-earth oxides as starting materials and employ an ammonium salt-assisted liquid-phase method to synthesize Li₃Tm/LuCl₆-based solid electrolytes. Through systematic optimization and strategic Br⁻ doping for partial Cl⁻ substitution, we achieve a superior performer Li₃TmCl₄Br₂. This material exhibits a high room-temperature ionic conductivity of 2.94 mS cm⁻¹. Crucially, this oxide-based route reduces raw material costs by approximately 70%. Furthermore, we resolve the poor interfacial stability with Li metal by applying a Li₆PS₅Cl modification interlayer which enables stable Li stripping/plating for over 1400 h in symmetric cells. All-solid-state batteries using the modified electrolyte demonstrate excellent electrochemical performance. This work provides a rational design strategy and paves a practical path for the scalable production of high-performance and low-cost HSEs.