PNNL

Abstract

The cycle life of high-energy Li-S cells is largely constrained by quick electrolyte depletion. LiNO3 has been a well-established additive known for protecting the Li metal anode and stabilizing the battery from polysulfides "shuttling”. However, it can be depleted prematurely and can pose safety risks when exposed to carbon, sulfur, or Li metal under harsh conditions. In this study, LiPO2F2 was explored as a safe and durable alternative additive in ether-based electrolytes. LiPO2F2 demonstrates superior performance in Li/S batteries, especially under high sulfur loading (~ 4 mg/cm2) and lean electrolyte conditions (E/S = 4), achieving long-term cycling stability of 40%, compared to 14.7% with LiNO3. This additive facilitates the disproportionation of polysulfides, reducing their dissolution and mitigating the shuttle effect. Additionally, LiPO2F2 promotes the formation of a stable SEI composed of inorganic anion-derived species, improving the battery’s overall stability and functionality. These findings blaze a trail in the design of safer and more durable electrolytes for Li-S batteries.