V₄C₃T_X MXene: First-principles computational and separator modification study on immobilization and catalytic...

Many attempts have recently used rationally-designed Ti₃C₂T_x MXene-based materials to increase sulfur utilization and tackle the detrimental shuttle effect in Li-S batteries (LSBs) due to their merits of high electronic conductivity, considerable catalytic activity, and sulfur immobilization. Nevertheless, the investigation of applying other two-dimensional (2D) transition metal carbides in LSBs is comparatively rare. In this work, the first-principles computations predicted that V₄C₃T_x could boost the "adsorption-diffusion-conversion" process of lithium polysulfides (LiPSs) over that of most other metal carbides of the MXene family. Inspired by this, we prepared the V₄C₃T_x MXene by hydrofluoric acid (HF) etching and then used it as a functional material coating on a polypropylene (PP) separator for LSB. As expected, the V₄C₃T_x modified PP separator (V₄C₃T_x-PP) can effectively prevent the shuttle effect of LiPSs via physical blocking, chemical adsorption, and catalytic conversion, as confirmed by visual polysulfide adsorption and diffusion tests, XPS analysis, and a series of electrochemical evaluations. As a result, the LSB with a V₄C₃T_x-PP enabled a high capacity and enhanced cycling performance (927 mAh g^-1 at 1 C and 516 mAh g^-1 retained for over 800 cycles, 1 C = 1675 mA g^-1). More encouragingly, the cell achieves a superior rate capability of 725 mAh g^-1 at 2 C and 586 mAh g^-1 at 4 C, respectively. In addition, the V₄C₃T_x-PP-based LSB shows a high areal capacity of 4.3 mAh cm^-2, even with the sulfur loading up to 4 mg cm^-2. This work expands the application types and scope of MXenes from theoretical and experimental points of view. The first use of the V₄C₃T_x MXene modified separator in Li-S batteries creates high potential for practical application.