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.