V4C3TX MXene: First-principles computational and separator modification study on immobilization and catalytic conversion of polysulfide in Li-S batteries

Many attempts have recently used rationally-designed Ti3C2Tx 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 V4C3Tx 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 V4C3Tx 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 V4C3Tx modified PP separator (V4C3Tx-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 V4C3Tx-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 V4C3Tx-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 V4C3Tx MXene modified separator in Li-S batteries creates high potential for practical application.