Lithium-sulfur batteries (LSBs) are promising secondary batteries owing to their substantial energy density of 2600 Wh kg-1, cost-effectiveness, and environmental friendliness.[1] Nevertheless, the commercialization of LSBs is constrained by factors such as the polysulfide shuttle effects, sluggish kinetics of the sulfur reduction reaction (SRR), inadequate conductivity, etc.[2] Slow SRR process constitutes a pivotal impediment hindering LSBs from attaining heightened electrochemical performance. Extensive research endeavors are dedicated to the exploration of tailored catalysts aimed at enhancing SRR kinetics through the manipulation and design of materials, encompassing methodologies such as interface engineering,[3] strain engineering,[4] single-atom engineering,[5] defect engineering,[6] etc. Among these, defect engineering can change the surface structure, electronic configuration, and chemical activity of the catalyst, thereby exerting influence on the rate and selectivity of the catalytic reaction, which aroused great research interest.[7]
    This exposure of unsaturated coordination sites and active sites caused by vacancies enhances adsorption and catalytic ability.[8] At the same time, the missing atomic vacancies leave the electrons on the catalyst surface in an unsaturated state, forming an energy potential well. When electrons or ions pass by, their diffusion barrier is lowered to achieve high reaction kinetics of electrode reactions.[9] Zheng et al. found the presence of sulfur vacancies function as the electrocatalytic center, enhancing the intrinsic adsorption capacity of catalyst.[10] Wang et al further proved the cation Ti vacancy in Ru@Ti3C2Tx-VC optimized H2O adsorption ability and resulted an excellent alkaline HER catalytic activity.[11] Although defect engineering affords a measure of control over catalyst properties, there is still some limitations and drawbacks. The precise manipulation of defect type, spatial distribution, and quantity within catalysts poses a formidable challenge. In actual operations, it is often difficult to achieve precise defect control, making it difficult to accurately locate and control the introduction and distribution of defects. Further research and in-depth mechanism exploration are imperative to surmount these limitations, thereby enhancing the feasibility of the application of defect engineering in the field of SRR.
Among numerous catalyst candidates, 3d transition metal Co-based materials have aroused great research interest due to their higher electron density and larger angular momentum in 3d electron orbit, making cobalt easier to participate in electron transfer and the formation and breakage of chemical bonds in catalytic reactions. Most previous studies have focused on the impact of anion vacancies on the spin state of the catalyst. In this study, we selected Co1-xSe as the subject of cation vacancies to explore its promotion effect on the SRR reaction process. CoSe with cobalt vacancy in it undergoes spatial spin polarization, resulting in parallel alignment of electron spin directions. This arrangement facilitates the separation of electron-hole pairs and hinders subsequent recombination. The Co vacancies readjust the electronic arrangement of the surface structure of the catalytic material. The local electron rearrangement at the vacancies can serve as active sites for chemical adsorption and electron supply, inducing uniform deposition in the initial nucleation stage of polysulfide deposition and enhancing the efficiency of charge separation and surface reactions. Henceforth, this strategy effectively catalyzes the kinetic processes inherent in the SRR. The electrochemical performance of LSBs is substantially enhanced through the implementation of the cation vacancy strategy. This study presents a systematic approach for modulating catalytic functionality by controlling active site structures, providing insights for the systematic design of polysulfide catalysts aimed at enhancing the durability of LSBs.