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

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.