Li vacancy-induced ionic conductivity enhancement in Li 4 B 7 O 12 Cl for all-solid-state Li-ion battery application

Safety concerns associated with lithium batteries suggest the development of solid-state batteries as a promising variant. In this work, we doped a lithium boracite (Li 4 B 7 O 12 Cl) with Mg 2+ to modify the Li + sites and observed significant improvement in ionic conductivity by two orders of magnitude (from 3.03 × 10 −7 S cm −1 to 2.81 × 10 −5 S cm −1 at room temperature). We attribute the enhanced ion conductivity to the artificially induced Li vacancies resulting from Mg doping. The as-fabricated symmetrical battery (Li|Li 3.6 Mg 0.2 B 7 O 12 Cl|Li) exhibited good cycling performance with a stable voltage output even after 60 hours of cycling. The battery showed a coulombic efficiency retention of ∼99.7% after the cycling test. Our work demonstrates that Li 4 B 7 O 12 Cl is a superior solid electrolyte for solid-state batteries and the introduction of Li vacancies can be an efficient approach to greatly improve the ionic conductivity of other electrolytes.