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

Lithium–sulfur (Li–S) batteries are one of the most prospective high-energy-density secondary batteries with ultrahigh energy density and low cost. Sulfurized polyacrylonitrile (SPAN) with a unique chemical structure and satisfactory electronic conductivity proves to be a promising sulfur cathode material. Nevertheless, the application of Li–SPAN batteries is severely limited by sluggish sulfur kinetics and uncontrollable Li deposition, resulting in poor cycling in ether-based electrolytes. Herein, a dual-functional electrolyte additive, lithium selenide (Li 2 Se), is proposed. For a sulfur cathode, Li 2 Se will continuously attack the S–S bonds of polysulfides, forming more reactive S–Se bonds with lowered reaction energy barriers and accelerating the kinetics. For a lithium anode, Li 2 Se is conducive for Li + transportation and forms a stable selenide-containing organic–inorganic hybrid solid electrolyte interphase (SEI), which lowers the nucleation overpotential and enhances exchange current density for Li deposition. Resultantly, the Li 2 Se-assisted Li–SPAN battery shows ultrahigh discharge capacities, enhanced rate performance, and outstanding cycling stability (an initial capacity of 1516 mAh g –1 at 2C and 600 mAh g –1 after 500 cycles). Noticeably, it delivers an areal capacity of 10.3 mAh cm –2 under a high cathode loading of 12.0 mg cm –2 . This work demonstrates a promising dual-functional additive to advance the performance of Li–SPAN batteries.