High-efficiency metal selenide as an electrocatalyst in a separator for lithium–sulfur batteries†

The construction of a modified separator with excellent catalytic ability and the ability to adsorb lithium polysulfides (LiPSs) is crucial for properly solving the challenges associated with lithium–sulfur batteries (LSBs). Herein, a metal–organic framework (MOF) substrate with a porous polyhedron structure is initially designed, then a mixture of ZIF-67 and melamine is carbonized into N-doped carbon (NC) covered with cobalt nanoparticles that are surrounded with carbon nanotubes to obtain Co/NCC. Finally, Co/NCC is selenized in situ to form CoSe/NCC which has good adsorption properties and accelerated polysulfide conversion ability. The CoSe/NCC material is coated onto a polypropylene (PP) separator (CoSe/NCC/PP) to inhibit LiPSs passing through the separator. Multi-walled carbon nanotubes (MWCNTs) are fused with sulfur to give MWCNTs/S which is used as the positive electrode. CoSe, derived from a MOF, has sulfurophilic properties and acts synergistically on the separator with the highly conductive NC and carbon nanotubes (CNTs) that originate from the melamine. CoSe/NCC possesses many active sites and uses Lewis acid–base interactions to anchor the LiPSs, thus promoting multi-stage redox reaction kinetics. Electrochemical tests show that the initial discharge capacity of a lithium–sulfur battery with a CoSe/NCC/PP separator and a MWCNTs/S cathode is 1270 mAh g⁻¹ at 0.5 C, and the discharge capacity is still 932 mAh g⁻¹ after 100 cycles, with a capacity retention rate of 73%. In addition, the battery also has good cycling performance under high current densities of 1 and 5 C. This work provides ideas and methods for the application of metal selenides as separator modification materials in LSBs and would be expected to be applied to other rechargeable batteries.