LiV 3 O 8 -based functional separator coating as effective polysulfide mediator for lithium–sulfur batteries

Abstract

The commercial development of high-energy lithium-sulfur (Li-S) batteries is still hampered by the irreversible active material loss and fast capacity decay triggered by the dissolution of polysulfide species and the subsequent polysulfide shuttle effect. Carbon-coated separators can limit the diffusion of polar polysulfide intermediates between electrodes. However, the capacity fading still exists owing to the weak interaction of nonpolar carbons. Herein, a novel lithium vanadium(V) oxide-coated hybrid separator (LiV3O8-HS) is designed for enhancing the performance of Li-S batteries. The results show that the LiV3O8 coating acts as a shield-like redox mediator to physically block the diffusion of polysulfide intermediates and chemically promotes the conversion of soluble higher-order polysulfides to insoluble short-chain polysulfides via internal disproportionation reactions, accelerating the redox reaction kinetics and lessening the active material loss during cycling. As a consequence, Li-S cells with the LiV3O8-HS demonstrated superior electrochemical performance despite using a pure sulfur cathode, with a high initial discharge capacity of 1254 mAh g-1 at 0.2 C and superior long-term cyclability with a low average capacity decline of 0.063% per cycle after 500 cycles at 0.5 C. The coating of the commercial separator, which can be straightforwardly adopted in an industrial process, offers a simple and powerful route for boosting the performance of Li-S batteries toward commercial application.