Li vacancy-induced ionic conductivity enhancement in Li4B7O12Cl for all-solid-state Li-ion battery application

Abstract

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 (Li₄B₇O₁₂Cl) with Mg²⁺ 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_3.6Mg_0.2B₇O₁₂Cl|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 Li₄B₇O₁₂Cl 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.