Insights into Multiphase Reactions during Self-Discharge of Li-S Batteries

Lithium-sulfur (Li-S) batteries are promising next-generation rechargeable energy storage systems due to their high energy density and use of abundant and inexpensive materials. However, rapid self-discharge and poor cycling stability due to the solubility of intermediate polysulfide conversion products have slowed their commercialization. Herein, we provide a detailed account of the multiphasic reactions occurring during the self-discharge of a Li-S battery held at various depth of discharge (DOD) through both simulation and experiment. For the first time, self-discharge of a full Li-S battery is simulated using a 1D model to describe reactions at both the anode and cathode. The model accurately describes experimentally derived results obtained over the longest durations of self-discharge studied to date (140 h). This validated model was used to follow the reversible and irreversible capacity loss caused by shuttling and precipitation of insoluble Li₂S₂ and Li₂S as a function of DOD. While the most rapid self-discharge is observed at low DOD, this also leads to the smallest irreversible loss. The results suggest that resting a Li-S battery near 2.1 V minimizes both reversible and irreversible losses.