Intercalation−deintercalation design in MXenes for high-performance supercapacitors

MXene is a new intercalation pseudocapacitive electrode material for supercapacitor application. Intensifying fast ion diffusion is significantly essential for MXene to achieve excellent electrochemical performance. The expansion of interlayer void by traditional spontaneous species intercalation always leads to a slight increase in capacitance due to the existence of species sacrificing the smooth diffusion of electrolyte ions. Herein, an effective intercalation−deintercalation interlayer design strategy is proposed to help MXene achieve higher capacitance. Electrochemical cation intercalation leads to the expansion of interlayer space. After electrochemical cation extraction, intercalated cations are deintercalated mostly, leaving a small number of cations trapped in the interlayer silt and serving as pillars to maintain the interlayer space, offering an open, unobstructed interlayer space for better ion migration and storage. Also, a preferred surface with more −O terminations for redox reaction is created due to the reaction between cations and −OH terminations. As a result, the processed MXene delivers a much improved capacitance compared to that of the original Ti₃C₂T_x electrode (T stands for the surface termination groups, such as −OH, −F, and −O). This study demonstrates an improvement of electrochemical performance of MXene electrodes by controlling the interlayer structure and surface chemistry.