Hole Polaron Diffusion in the Final Discharge Product of Lithium–Sulfur Batteries

Abstract

Poor electronic conductivity of bulk lithium sulfide (Li2S) is a critical challenge for the debilitating performance of the lithium–sulfur battery. This study focuses on investigating the thermodynamic and kinetic properties of native defects in Li2S based on a first-principles approach. It is found that the hole polaron p+ can form in Li2S by removing a 3p electron from an S2– anion. The p+ diffusion barrier is only 90 meV, which is much lower than the Li vacancy (VLi–) diffusion barrier. Hence p+ has the potential to serve as a charge carrier in the discharge product. Once the vacancy–polaron complex (VLi––2p+) forms, the charge transport will be hindered due to the relatively higher diffusion barrier of the complex. Heteroatom dopants, which can decrease the p+ formation energy and increase VLi– formation energy, are expected to be introduced to the discharge product to improve the electronic conductivity.