Long-Cycling Lithium-Sulfur Batteries Enabled by Reactivating Inactive Lithium

High-energy-density lithium-sulfur (Li-S) batteries are attractive but hindered by short cycle life. The formation and accumulation of inactive Li deteriorate the battery stability. Herein, a phenethylamine (PEA) additive is proposed to reactivate inactive Li in Li-S batteries with encapsulating lithium-polysulfide electrolytes (EPSE) without sacrificing the battery Coulombic efficiency (CE). PEA undergoes reactions with inactive Li to form organic polysulfide R-LiPEA in a reduction state at the anode side and subsequently reacts with the S cathode to generate O-LiPEA in an oxidation state. R-LiPEA and O-LiPEA engage in redox cycles to reactivate inactive Li that accumulates in batteries. Compared with 122 cycles based on EPSE without PEA, Li-S batteries with PEA additive in EPSE achieve 185 cycles under demanding conditions and maintain higher CE of 96% with PEA than 93% without PEA. This work elucidates the ingenious modification of amino-based additives to reactivate inactive Li by an organic polysulfide redox mechanism for advanced Li-S batteries.