Incorporating Heterogeneous Metal Ions in CoSe₂ Nanosheets for Lithium–Sulfur Batteries

Although lithium–sulfur (Li–S) batteries have the significant advantage of high energy density, their practical application is still hampered by the capacity attenuation caused by the shuttle effect of the intermediate product lithium polysulfides (LiPSs). Designing metal-based catalysts is an effective strategy to improve the reaction kinetics by adsorbing and catalyzing the conversion of LiPSs during charge–discharge. Furthermore, considering that metal ions are the main catalytically active sites, further modification of the electronic structure of metal ions and optimization of their adsorption-catalytic effects on LiPSs are the key to promoting the electrochemical properties of Li–S batteries. In this work, Mn, Mo, and Cr are incorporated into CoSe2 nanosheets to optimize the adsorption–catalysis–desorption process, accelerating the reaction kinetics of Li–S batteries. As a result, the Li–S batteries with Cr-CoSe2 nanosheet modified separator deliver the best cycle performance and rate performance in comparison to that of the other catalysts. This can be ascribed to the superior catalytic capacity of Cr-CoSe2 with an optimized electron structure. To be specific, Cr-CoSe2 possesses the relatively low d band center of Co and proper adsorption strength, in the meanwhile, the shortest Co–S and Li–Se bonds formed between Cr-CoSe2 and Li2S4 can effectively anchor Li2S4 and stretch the Li–S bonds longest to break for further conversion. This work provides the selection of the basis of doping ions for promoting the catalytic effect of metal compounds with optimized electron structure.