MXene-碳黑/硫复合材料在锂硫电池一体式电极的研究

锂硫电池的实际能量密度不高和多硫化物（LiPSs）的穿梭效应等问题严重影响了该电池的实际应用。本文通过将二维的Ti₃C₂T_x Mxene纳米片与碳黑/硫（CB/S）材料进行混合,制备了Ti₃C₂T_x-CB/S正极材料并将其涂覆在商业隔膜（PP）上,最终获得了Ti₃C₂T_x-CB/S-PP一体式电极并用于锂硫电池。利用Ti₃C₂T_x纳米片对CB/S进行修饰,不仅能提高活性物质硫的导电性,还能对扩散的LiPSs进行物理阻挡和化学吸附。而一体式电极的设计有利于提高电池的能量密度。恒流充放电测试结果表明,Ti₃C₂T_x-CB/S-PP电极在0.1 C电流下的初始放电容量为1028.8 mAh·g^-1,高于不含Ti₃C₂T_x的CB/S-PP电极的896.8 mAh·g^-1。Ti₃C₂T_x-CB/S-PP电极还展示出了比基于传统铝箔集流体的Ti₃C₂T_x-CB/S-Al电极更好的循环稳定性,前者在0.5 C下400圈长循环测试中的每圈衰减率为0.072%,而后者则为更高的0.10%。本文利用Ti₃C₂T_x-CB/S构建一体式电极的策略为实现高性能和高能量密度的锂硫电池提供了新的研究方向。

Study on MXene-Carbon Black/Sulfur Composite in Integrated Electrode of Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are considered as a promising energy storage device due to their ultrahigh theoretical energy density of 2500 Wh·kg^-1 and low cost. However, the practical application of Li-S batteries is seriously limited by their low actual energy density, the shuttle effect of polysulfides (LiPSs), and the insulating nature of sulfur and lithium sulfides. Carbon materials have been developed in the design of sulfur hosts due to their adjustable pore structure and high electrical conductivity, but their non-polar surfaces have weak interactions with LiPSs. Herein, MXene-carbon black/sulfur (Ti₃C₂T_x-CB/S) composites were prepared and applied to the integrated electrodes of Li-S batteries. The CB/S was prepared via a melting-diffusion method and Ti₃C₂T_x MXene nanosheets were synthesized by etching Ti₃AlC₂ MAX with LiF/HCl. After mixing CB/S and Ti₃C₂T_x , Ti₃C₂T_x-CB/S cathode material was obtained and coated on commercial separator (PP) to prepare Ti₃C₂T_x-CB/S-PP integrated electrodes. On the one hand, the two-dimensional Ti₃C₂T_x nanosheets dispersed in the CB/S particles not only serve as multiple physical barriers to inhibit the diffusion of LiPSs, but also have strong chemical interactions with them, effectively alleviating the shuttle effect. Thus, Ti₃C₂T_x improves the conductivity of CB/S composite, which is beneficial to the reaction kinetics of the cathode. Furthermore, the design of Ti₃C₂T_x-CB/S-PP integrated electrode increases the energy density of Li-S batteries. X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to analyze the structures, morphologies, and surface chemical composition of the synthesized materials. The results of constant current charge/discharge tests showed that Ti₃C₂T_x-CB/S-PP electrode achieved superior rate performance and cycling performance than CB/S-PP electrode. The initial discharge capacity of Ti₃C₂T_x-CB/S-PP electrode at 0.1 C current was 1028.8 mAh·g^-1, higher than 896.8 mAh·g^-1 of CB/S-PP electrode. The cycling test at 0.2 C indicated that Ti₃C₂T_x-CB/S-PP maintained a discharge capacity of 726.4 mAh·g^-1 after 80 cycles, better than CB/S-PP (529.2 mAh·g^-1). Moreover, due to the improved utilization of the active material at the interface between the cathode and the separator, Ti₃C₂T_x-CB/S-PP electrode also showed better cycling stability compared to the Ti₃C₂T_x-CB/S-Al electrode based on the traditional aluminum foil current collector. The capacity degradation rate of Ti₃C₂T_x-CB/S-PP was only 0.072% per cycle in a long-term cycling test of 400 cycles at 0.5 C, while that of Ti₃C₂T_x-CB/S-Al was 0.10%. The strategy of using Ti₃C₂T_x-CB/S to construct an integrated electrode provides a new direction for Li-S batteries with high performance and high energy density.