Catalytic Disproportionation for Suppressing Polysulfide Shuttle in Li-S Pouch Cells: Beyond Adsorption Interactions

Addressing the lithium polysulfide shuttle is critical for the high-energy-density lithium-sulfur pouch cells in practical applications, especially under high sulfur loading and lean electrolyte conditions. In contrast to previously reported heterogeneous adsorption catalysis within cathode or separator with slow catalytic kinetics and limited adsorption area, herein, lithium difluorophosphate (LiPO2F2) is demonstrated as a homogeneous catalyst in electrolyte which mitigates polysulfide diffusion. The Li-S pouch cell with LiPO2F2 in the electrolyte has record-breaking shelving stability of two months, significantly improved capacity retention from 37.0% to 81.4% after long cycling, and electrical-car-level energy density over 400 Wh kg(-1). A minimal amount of 1 wt% LiPO2F2 tends to facilitate lithium polysulfide disproportionation on the S/C cathode instead of in the electrolyte, which initiates the fast transformation of soluble lithium polysulfide to insoluble solid S-8 and Li2S2/Li2S. The reliable mechanism of polysulfide disproportionation via biradicals is further proposed by both density functional theory calculation and experiments. To best of the authors' knowledge, this is the first report on mechanism of polysulfide disproportionation via biradical intermediates. It is believed that this new insight into homogeneous catalytic mechanisms in electrolytes may pave the way for the commercialization of high-energy-density Li-S batteries.