Shortening sulfur redox pathway via coupled LiO and CS bonds in LiS batteries

Abstract

The “shuttle effect,” slow sulfur redox kinetics, and low utilization of active materials have become challenges that lithium‑sulfur (LiS) batteries must currently address. To tackle these issues, this study employs 2-chloro-1,4-benzoquinone (MCBQ) as an electrolyte additive. MCBQ, with its carbonyl oxygen structure and halogen substituents, can react with polysulfides to form a cyclic insoluble organic sulfur intermediate that contains LiO bonds and CS bonds. During discharge, it alters the conversion pathway of sulfur species. Taking Li₂S₆ as an example, the original path “Li₂S₆ → Li₂S₄ → Li₂S₂ → Li₂S” is optimized into a new pathway “MCBQ- Li₂S₆ → MCBQ-2Li₂S₃ → MCBQ-2Li₂S” simplifying the route to enhance sulfur redox kinetic efficiency. Moreover, MCBQ also forms an organic-inorganic hybrid interfacial protective layer on the lithium anode side, effectively mitigating the corrosion of the lithium anode by polysulfides. The battery with the MCBQ additive maintains a Coulombic efficiency of 100 % at a current density of 0.2C, with an initial discharge capacity reaching 812 mAh g⁻¹; even after 120 cycles, the capacity decay rate per cycle is only 0.42 %. The introduction of MCBQ not only accelerates sulfur redox kinetics but also enhances the utilization of active materials and overall battery stability.