Interface Modification and Halide Substitution To Achieve High Ionic Conductivity in LiBH₄-Based Electrolytes for all-Solid-State Batteries

Abstract

A fast solid-state Li-ion conductor Li₁₆(BH₄)₁₃I₃@g-C₃N₄ was synthesized using a simple ball-milling process. Because of the combined effect of halide substitution and the formation of an interface between Li₁₆(BH₄)₁₃I₃ and g-C₃N₄, Li₁₆(BH₄)₁₃I₃@g-C₃N₄ delivers a high ionic conductivity of 3.15 × 10^-4 S/cm at 30 °C, which is about 1-2 orders of magnitude higher than that of Li₁₆(BH₄)₁₃I₃. Additionally, Li₁₆(BH₄)₁₃I₃@g-C₃N₄ exhibits good electrochemical stability at a wide potential window of 0-5.0 V (vs Li/Li⁺) and excellent thermal stability. The Li/Li symmetrical cell based on the Li₁₆(BH₄)₁₃I₃@g-C₃N₄ electrolyte achieves long-term cycling with a small increase in overpotential, confirming superior electrochemical stability against Li foil. More importantly, Li₁₆(BH₄)₁₃I₃@g-C₃N₄-based Li batteries are compatible with S-C and FeF₃ cathodes and MgH₂ anodes and can achieve long-term cycling with Li₄Ti₅O₁₂ anodes at a temperature range from 30 to 60 °C. The developed strategy of coupling halide substitution together with interface modifications may open a new avenue toward the development of LiBH₄-based high ionic conductivity electrolytes for room-temperature all-solid-state Li batteries.