High-efficiency metal selenide as electrocatalyst in separator for lithium-sulfur batteries

The well-framed construction of separator modifier with exquisite catalytic ability and adsorption effect for lithium polysulfides (LiPSs) is crucial for solving properly the challenges encountered by lithium-sulfur batteries (LSBs). Herein, a metal-organic framework (MOF) substrate with porous polyhedron is firstly designed, then the mixture of ZIF-67 and melamine is carbonized into N-doped carbon (NC) covered with cobalt nanoparticles that are surrounded by carbon nanotubes to obtain Co/NCC, which is finally selenized in situ to form CoSe/NCC with high adsorption effect and accelerated polysulfide conversion ability. The CoSe/NCC is coated onto the polypropylene (PP) separator (CoSe/NCC/PP) to inhibit the LiPSs shuttle passing through the separator. Multi-walled carbon nanotubes (MWCNTs) are accustomed to fusing sulfur as a positive electrode (MWCNTs/S). The CoSe/NCC with high conductivity and sulfiphilic property possesses many active sites and anchors LiPSs, thus promoting multistage redox reaction kinetics. The 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 kept at 932 mAh g−1 after 100 cycles, with a capacity retention rate of 73%. In addition, it has also good cyclic 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, which would be expected to be applied to other rechargeable batteries.