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

Abstract

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 (Li2Se), is proposed. For a sulfur cathode, Li2Se 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, Li2Se 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 Li2Se-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.