Interface Modification and Halide Substitution To Achieve High Ionic Conductivity in LiBH 4 -Based Electrolytes for all-Solid-State Batteries.

A fast solid-state Li-ion conductor Li 16 (BH 4 ) 13 I 3 @g-C 3 N 4 was synthesized using a simple ball-milling process. Because of the combined effect of halide substitution and the formation of an interface between Li 16 (BH 4 ) 13 I 3 and g-C 3 N 4 , Li 16 (BH 4 ) 13 I 3 @g-C 3 N 4 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 Li 16 (BH 4 ) 13 I 3 . Additionally, Li 16 (BH 4 ) 13 I 3 @g-C 3 N 4 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 Li 16 (BH 4 ) 13 I 3 @g-C 3 N 4 electrolyte achieves long-term cycling with a small increase in overpotential, confirming superior electrochemical stability against Li foil. More importantly, Li 16 (BH 4 ) 13 I 3 @g-C 3 N 4 -based Li batteries are compatible with S-C and FeF 3 cathodes and MgH 2 anodes and can achieve long-term cycling with Li 4 Ti 5 O 12 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 LiBH 4 -based high ionic conductivity electrolytes for room-temperature all-solid-state Li batteries.