Preparation And Electrochemical Performance Of Flexible Asymmetric Supercapacitor Based On Carbon Cloth

As an energy storage device,supercapacitors possess high power density,long cycle life,and low theoretical heat during the charging and discharging process,attracting extensive attention of researchers in the application of various electronic devices.The development of various miniature or wearable electronic devices has put forward higher requirements for the flexibility and portability of supercapacitors.However,the energy density of current flexible supercapacitors is slightly insufficient compared to other energy storage devices,and the proportion of active materials that play the role of electrochemical energy storage in the general supercapacitor structure is relatively low.To resolve this problem,this work mainly uses lightweight carbon cloth as the matrix and uses electrodeposition to prepare the positive and negative electrodes of a binder-free supercapacitor,and assemble them into an asymmetric all-solid-state flexible supercapacitor.The energy density of as-assembled flexible capacitors is improved by reducing the use of non-electrochemically active materials and increasing the operating voltage of the capacitor.The main work content and research results are as follows:（1）The new two-dimensional material Ti₃C₂T_x（MXene）,employed as the active material of the electrode,was dispersed in an organic solvent to form an electrophoresis deposition solution for synthesis.The binder-free Ti₃C₂T_x/CC electrode by electrophoretic deposition with carbon cloth（CC）as substrate.Because of no components of non-electrochemically active materials such as binders in the electrodes,the as-prepared electrode presents higher electrochemical performance.The electrophoretic deposition method is simple and more efficient to prepare the electrode,and the deposition time can be adjusted to control the loading mass of the active material.In addition,an asymmetric all-solid flexible supercapacitor was assembled,basing on the positive electrode of the binder-free Mn O₂/CC electrode prepared by electrochemical deposition and the negative electrode of the Ti₃C₂T_x/CC electrode.Compared with symmetrical capacitors,this resulting asymmetric capacitor achieves a higher voltage window of 1.7 V and a higher energy density of 19 Wh kg^-1,indicating that the asymmetric structure supercapacitor has a good prospect and value.（2）To further improve the electrochemical performance of MnO₂ cathode,a simple and effective two-step electrodeposition method was developed to prepare Mn O₂/Ti₃C₂T_x/CC composite electrode.Due to the unique multilayer structure of the composite electrode and the good synergy of the active materials,the prepared Mn O₂/Ti₃C₂T_x/CC electrode achieves a high specific capacitance of 411.5 F g^-1.The Mn O₂/Ti₃C₂T_x/CC and Ti₃C₂T_x/CC electrodes employed as electrodes for assembling a flexible asymmetric supercapacitor can further improve the energy density of the supercapacitor.The assembled asymmetric supercapacitor achieves a high voltage window of 1.7 W,a high energy density of 24.3 Wh Kg^-1,and a high-power density of 7630 W Kg^-1,and has good flexibility and cycle stability,indicating that the supercapacitor has high practical value.（3）The PPy@Ti₃C₂T_x/CC composite electrode was prepared by a one-step electrodeposition method to improve the electrochemical performance of PPy.The concentration ratio of pyrrole versus Ti₃C₂T_x in the deposition solution is an important factor affecting the performance of the composite electrode,and a suitable ratio relationship can enable the active material to achieve a good synergistic effect.Due to the good conductivity of Ti₃C₂T_x and the excellent pseudocapacitance performance of PPy,the composite electrode presents a mass-specific capacitance of 375 F g^-1 and can achieve a larger loading mass of active material.The asymmetric flexible supercapacitor consisting of PPy@Ti₃C₂T_x/CC positive electrode and Ti₃C₂T_x/CC negative electrode realizes a 1.2 V high voltage window.The improvement of the voltage window significantly improves the energy density and power density of the capacitor,with an energy density of 15.7 Wh Kg^-1 and a power density of 8855.9W Kg^-1.