Effect of Discharge Cutoff Voltage on Reversibility of Lithium/Sulfur Batteries with LiNO₃-Contained Electrolyte

LiNO 3 is unique in suppressing the redox shuttle of lithium polysulfides in Li/S battery. In this paper we evaluate the effect of discharge cutoff voltage on the reversibility of Li/S battery with a LiNO 3 -contained electrolyte. Based on a study of the liquid Li/S cells with a 0.05 m Li 2 S 9 solution as the catholyte, we find that the highly reversible discharge and charge cycling of Li/S cells occurs at higher than 1.8 V vs. Li/Li + , which corresponds to a multistage redox process of the sulfur cathode between elemental sulfur and insoluble Li 2 S 2 . At lower potentials, not only the Li 2 S 2 is reduced into poorly reversible Li 2 S, but also the LiNO 3 is reduced irreversibly. Moreover, the irreversible reduction of LiNO 3 further reduces the reversibility of the poorly reversible Li 2 S, resulting in a significant slowdown in the electrode reaction kinetics and a permanent loss in the reversibility of the Li/S cell. This work suggests that deep discharge must be avoided for a long cycle life Li/S battery when LiNO 3 is used as an additive or a co-salt of the electrolyte.