Impeding polysulfide shuttling with a three-dimensional conductive carbon nanotubes/MXene framework modified separator for highly efficient lithium-sulfur batteries

The shuttling of polysulfide is still a major issue which greatly hinders the practical application of lithium-sulfur (Li-S) batteries. Here, we report a multifunctional separator for trapping polysulfide and reusing the active sulfur species in Li-S batteries. The multifunctional separator was fabricated by coating the commercial polypropylene (PP) separator with a three-dimensional (3D) interwoven framework structure composed of 1D carbon nanotubes (CNTs) and 2D Ti3C2Tx MXene nanosheets. Taking advantages of the excellent electrical conductivity and strong chemical interaction with polysulfide of Ti3C2Tx MXene, the ability in immobilizing and reusing of polysulfide for the multifunctional separator was significantly enhanced compared with pure CNTs modified separator. At mean time, the presence of CNTs effectively helps avoid the restacking of MXene nanosheets, resulting in an interfacial layer between separator and cathode with an interconnected conductive network, which can facilitate fast Li ion and electron transport and thus improve the rate capabilities and sulfur utilization. Moreover, the effect of MXene content on the structure and electrochemical performance were systematically investigated. At MXene content of 5% and CNTs/MXene mass loading of 0.16 mg cm−2, the cell with CNTs/MXene-PP (CMP) separator delivered an initial capacity of 1415 mA h g-1 at 0.1 C, a capacity retention of 614 mA h g−1 after 600 cycles at 1 C with a low capacity decay of 0.06% per cycle in the 0.8–2.5 mg cm−2 sulfur-loaded cathode. Such 3D carbon nanotubes/MXene conductive framework provides great potential for developing efficient functional separator for high-performance Li-S batteries and can be easily applied in electrode materials for other electrochemical energy storage systems.