Strategy for High-Energy Li-S Battery Coupling with a Li Metal Anode and a Sulfurized Polyacrylonitrile Cathode

Among lithium-sulfur (Li-S) battery materials, sulfurized polyacrylonitrile (SPAN) has attracted substantial attention as a cathode material owing to its potential to bypass the problematic polysulfide formation and shuttling effect. Carbonate-based electrolytes have been eschewed compared with ether-based electrolytes because of their poor compatibility with Li metal anodes. In this work, we design and study an electrolyte comprising 0.8 M of lithium bis(trifluoromethanesulfonyl)imide, 0.2 M of lithium difluoro(oxalate)borate, and 0.05 M of lithium hexafluorophosphate in ethyl methyl carbonate/fluoroethylene carbonate = 3:1 v/v solution in the Li-S battery coupled with a Li metal anode and SPAN cathode. The well-designed carbonate-based electrolyte effectively stabilizes both electrodes, delivering high Coulombic efficiencies with stable cyclability. Studies using operando optical microscopy and atomic force microscopy demonstrate that dense, uniform Li deposition is promoted to suppress dendrite growth even at a high current density. Operando Raman spectroscopy reveals a reversible Li+ storage behavior in the SPAN structure through the cleavage of disulfide bonds and their redimerization during lithiation and delithiation. As a result, the proposed Li-S battery delivers an overall capacity retention of 73.5% over 1000 cycles, with high Coulombic efficiencies over 99.9%.

Automated summary

In this study, a carbonate-based electrolyte was designed to effectively stabilize both electrodes of the Li-S battery, resulting in high Coulombic efficiencies and stable cyclability. Optical and atomic force microscopy revealed that dense and uniform Li deposition helped suppress dendrite growth at high current densities. Operando Raman spectroscopy confirmed the reversible Li+ storage behavior in the SPAN structure.