Bifunctional Li₂Se Mediator to Accelerate Sulfur Conversion and Lithium Deposition Kinetics in Lithium-Sulfurized Polyacrylonitrile Batteries

Lithium-sulfur (Li-S) batteries are oneof the mostprospective high-energy-density secondary batteries with ultrahighenergy density and low cost. Sulfurized polyacrylonitrile (SPAN) witha unique chemical structure and satisfactory electronic conductivityproves to be a promising sulfur cathode material. Nevertheless, theapplication of Li-SPAN batteries is severely limited by sluggishsulfur kinetics and uncontrollable Li deposition, resulting in poorcycling in ether-based electrolytes. Herein, a dual-functional electrolyteadditive, lithium selenide (Li2Se), is proposed. For asulfur cathode, Li2Se will continuously attack the S-Sbonds of polysulfides, forming more reactive S-Se bonds withlowered reaction energy barriers and accelerating the kinetics. Fora lithium anode, Li2Se is conducive for Li+ transportationand forms a stable selenide-containing organic-inorganic hybridsolid electrolyte interphase (SEI), which lowers the nucleation overpotentialand enhances exchange current density for Li deposition. Resultantly,the Li2Se-assisted Li-SPAN battery shows ultrahighdischarge capacities, enhanced rate performance, and outstanding cyclingstability (an initial capacity of 1516 mAh g(-1) at2C and 600 mAh g(-1) after 500 cycles). Noticeably,it delivers an areal capacity of 10.3 mAh cm(-2) undera high cathode loading of 12.0 mg cm(-2). This workdemonstrates a promising dual-functional additive to advance the performanceof Li-SPAN batteries.