Bimetallic (Ti1−xVx)3C2Tx MXene as electrodes for antifreezing flexible all-solid-state micro-supercapacitors with fast ion diffusion and charge transfer

Two-dimensional (2D) MXene Ti₃C₂T_x has been widely investigated as pseudocapacitive electrode materials for supercapacitors, yet their charge storage capability is often hindered by the influences of ion diffusion and charge transfer rates. Therefore, how to explore excellent electrode materials with great specific capacitance, high rate performance and long cycle life has always been a challenge. Herein, high electrochemical activity vanadium atoms are introduced into Ti₃AlC₂ to construct bimetallic (Ti_1−xV_x)₃C₂T_x MXene, and the influence of vanadium doping concentration on the electrochemical performance of microsupercapacitors (MSCs) is systematically researched. Firstly, it was demonstrated by exploring the sample preparation that the strategy of using Ti₃C₂T_x MXene as a template to prepare V₃C₂T_x cannot be achieved. Moreover, the appropriate doping amount of vanadium atoms can significantly improve the charge transfer and enable rapid ion diffusion in the electrode. Therefore, the bimetallic (Ti_1−xV_x)₃C₂T_x MXene constructed by the vanadium doping strategy can increase its charge storage capacity by 30%, and possesses excellent long-term cycling stability (85.93% capacity retention after 20,000 cycles). With the assistance of the modified gel-electrolyte, V-doped MXene-based MSCs still retain 74.15% of the capacitance at −35 °C, indicating that the device has brilliant anti-freezing performance. The corresponding density functional theory (DFT) calculations further elucidate the mechanism of V atom doping to improve charge storage capacity through structural stability and H ion adsorption energy. This work demonstrates the enormous potential of micro-scale flexible supercapacitors through the modification of MXene-based electrode materials and electrolytes, providing new insights for the design of high-performance micro-scale flexible power sources that can operate in complex environments.