Charge Transport Mechanism in Solid-State Redox-End Members in Lithium-Sulfur(Li-S) Batteries

Abstract

The insulating nature of solid state redox end members (Li2S and S) in Lithium-Sulfur (Li-S) batteries may result in performance limitations in cells that minimize or eliminate the solubility of polysulfides. For example, the formation of Li2S films on the cathode surface during discharge could give rise to the sudden death of voltage of the cell. To prevent these limitations it is helpful to understand charge transport mechanisms in Li2S and S, which are poorly understood. Here, we characterize these mechanisms using first-principles calculations. In particular, we examine the concentrations and mobilities of intrinsic defects such as vacancies, interstitials, and localized electrons/holes (polarons) in both compounds. We describe how these data can be used to inform a continuum model of transport that allows for estimation of the critical thickness of Li2S and S films, and relate this to a critical cell capacity.