Enhanced electronic conductivity and ionic conductivity of Li₂S by doping strategy

Benefitting from its high theoretical capacity, lithium sulfide (Li₂S) holds promise as a cathode material in lithium-ion sulfur batteries and as a prelithiation agent in traditional lithium-ion batteries. However, its poor electronic and ionic conductivity results in a high activation potential and sluggish electrochemical reaction kinetics. This challenge intensifies during fast charging and high mass loading. Doping is versatile in promoting the intrinsic electronic/ionic conductivity of Li₂S by tuning the band gap, lattice structure, crystallinity, defects, and interphase between particles, but there is a lack of a timely summary in this flourishing field. This review addresses the origin of the low electronic/ionic conductivity of Li₂S and then explains the mechanism of how doping promotes electron transfer and ion diffusion. Subsequently, recent research progress about the promoted electronic/ionic conductivity of Li₂S by doping is retrospected. Finally, future perspectives are discussed, aiming at preparing an advanced Li₂S cathode material or prelithiation agent with high energy density and high safety.