A new insight into the molecular rearrangement of sulfurized polyacrylonitrile cathode in ether electrolyte

Abstract

Sulfurized polyacrylonitrile (SPAN) is one of the most promising cathode materials with high energy density. However, irreversible shuttling effect is easily triggered by formation of soluble polysulfides (Li2Sn, 2< n ≤8) in ether electrolytes. The major challenge relies in the control of molecular rearrangement of SPAN to avoid spontaneous generation of Li2Sn. This work reveals the morphological and structural roles that responsible for the compatibility of SPAN with ether electrolytes. Besides the length of the covalently bonded –Sx– chains in the pyrolyzed PAN backbone, the protection of SPAN fragments from robust interactions with solvents enables a stable cycling of electrodes. The freestanding SPAN cathode with a continuous fibrous network exhibits a much higher electrochemical stability than its powder counterparts. The single-phase solid-solid reaction of SPAN with Li+ can be realized with Li2S as the sole discharge product. Nevertheless, the reversible reaction is kinetically dominated by the activation of the produced Li2S. The recharge ability and rate capability can be improved by rationally controlling the molecular rearrangement of SPAN. The trace amount of in-situ generated Li2Sn acting as a chemical mediator can promote the reversible decomposition of Li2S, offering a new insight into cathode design of Li–S batteries.