Enhanced Rate Performance of Li-S Batteries Enabled By Polysulfide Reactions

Abstract

Lithium-sulfur (Li-S) battery is a promising rechargeable battery system that has both high theoretical capacity and energy density. Moreover, sulfur (S) is inexpensive and nontoxic, making Li-S suitable for large-scale energy storage applications. Sulfur (S8) lithiation during the operation of Li-S battery is a multi-step electrochemical process that involves different lithium polysulfide (Li2Sn, 1…n…8) intermediates. The long-chain polysulfides (PSs) are highly soluble in the aprotic organic electrolyte. There has been a broad consensus that PS dissolution is directly linked to the deterioration of several key performance indexes, such as cycle life, self-discharge and coulombic efficiency, of the battery. However, it is demonstrated in this presentation that the PS dissolution process could have a profound effect on the rate capability of the Li-S battery. It is shown that solution reactions among the PSs take place concurrently with the electrochemical reactions occurring at the solid surfaces. Surprisingly, with properly designing the electrode structure, one can take advantage of the PS solution reaction pathways to substantially enhance the rate capability of a Li-S battery. The following figure compares the rate performance of two Li-S cells that contain the same S-C composite particles having 45% S content but different electrode design. The two electrodes showed dramatically different rate performance. Figure 1