Enhancing the performance of lithium-sulfur batteries by embedding asymmetric Co-N3S1 single-atom catalysts into hollow SeSPAN nanofibers

Abstract

Sulfurized polyacrylonitrile (SPAN) is a promising cathode material for lithium-sulfur (Li-S) batteries, effectively mitigating the shuttle effect of lithium polysulfides through the formation of covalent S–S bonds. However, conventional SPAN electrodes are limited by an active material loading below 40 % and sluggish reaction kinetics. To address these challenges, a Co-N₃S₁ single-atom catalyst (SAC) with a hollow cubic morphology was designed and synthesized, followed by its integration into SeSPAN nanofibers. By employing a dual-mode loading strategy that integrates covalent bonding with physical confinement, the active material loading is increased upto 63 wt%. The three-dimensionally interconnected fiber network provides abundant reactive interfaces, enhancing the accessibility and utilization of Co active sites. Meanwhile, the carbon shell encapsulating the Co-N₃S₁ SAC improves overall conductivity, thereby accelerating lithium-ion and electron transport. Experimental results and density functional theory calculations collectively validate the superior performance of the Co-N₃S₁/SeSPAN cathode, primarily attributed to sulfur incorporation. The high electronegativity of sulfur induces electronic redistribution around Co single atoms, thereby modulating their asymmetric coordination environment, strengthening metal-polysulfide interactions, and effectively lowering the reaction energy barrier. The synergistic optimization of physical and electronic structures not only promotes the solid-to-solid transition from S₈ to Li₂S but also accelerates interfacial reaction kinetics, ultimately enhancing active material utilization and overall battery performance. As a result, the electrode achieves a capacity of 706.7 mAh/g at 0.2 C, retains 545.8 mAh/g at 1 C, and maintains 99.24 % capacity retention over 1000 cycles. This study providing a promising route for high energy density, long-life Li-S batteries