A new finding on the role of LiNO3 in lithium-sulfur battery

Lithium nitrate (LiNO3) is the most studied additive and co-salt for the electrolyte of lithium-sulfur (Li–S) batteries, its known function is to suppress the redox shuttle of soluble lithium polysulfide (PS, Li2Sn), which reflects as an increase in the battery’s coulombic efficiency and cycling stability, as well as a reduced self-discharge rate. The current understanding on this function is that LiNO3 reacts with Li to form a robust surface layer that consequently protects the Li anode from reacting with the dissolved PS. However, little is known on the sulfur cathode except that LiNO3 reduces and adversely affects the battery’s performance when the battery is discharged to lower than 1.7 V. In this paper we report a new finding on the role of LiNO3 in enabling the stable cycling of the sulfur cathode. We show that LiNO3 is capable of catalyzing the conversion of high soluble PS to slightly soluble elemental sulfur near the end of charging process, and that the combination of a soluble nitrate in the electrolyte and an insoluble nitrate in the sulfur cathode leads to synergetic improvement. In addition, a possible mechanism is proposed for the catalysis of LiNO3 on the conversion of PS to elemental sulfur.