Design,Preparation And Electrochemical Performance Of MXene Nanocomposites

Supercapacitor,as an energy storage device,can quickly supply high-power electricity,and maintain stable performance in long cycle.The electrode materials play an important part in the practical application of supercapacitors.Layered Double Hydroxide(LDH),as a common pseudocapacitive electrode material,has unique layered structure,large specific surface area and high electrochemical activity.The poor rate and cycle performance affect the practical application of supercapacitors.Constructing micro-nano composite structures by introducing conductive materials can solve the above problems.The new transition metal carbon,nitrogen or carbon-nitrogen compound MXene,with rich surface functional groups,stable physical and chemical properties,and high conductivity,can improve the electrochemical performance of pseudocapacitive electrode material as conductive composite.In this paper,we designed layered micro-nano structure to enhance the electrochemical performance of LDH electrode materials.MXene@Ni-Mn LDH and Ni-Co LDH@MQDs composites were designed and prepared by introducing two-dimensional Ti₃C₂T_x MXene and zero-dimensional Ti₃C₂T_xMXene quantum dots(MQDs).The main research is as follows:(1)MXene@Ni-Mn LDH composite:MXene@Ni-Mn LDH layered micro-nano structure was designed by introducing two-dimensional Ti₃C₂T_x MXene sheets in order to improve inherent performance defects of LDH.The density functional theory was used to study the electron transmission efficiency and stability of composite.The relevant composite was prepared by a one-step co-precipitation method.In a three-electrode electrochemical test,the composite product obtained at 4 h had the best electrochemical performance.The specific capacitor was 179 m Ah g^-1 at 1 A g^-1 and can maintain 62.5%at 10 A g^-1.The power density of assembled asymmetric supercapacitor was 800 W kg^-1 at an energy density of 44.7 W h kg^-1.The retention rate of initial capacitor was still 90.3%after 5000 cycles of charge and discharge at a current density of 6 A g^-1.The three-dimensional porous micro-nano structure can effectively solve the stacking of LDH.The synergy between MXene and LDH can effectively improve capacity,rate and cycle performance of composites.(2)Ni-Co LDH@MQDs composite:Ni-Co LDH@MQDs micro-nano structure was designed by introducing zero-dimensional Ti₃C₂T_x MQDs in order to enhance rate and cycle performance of LDH.MQDs were prepared by hydrothermal method.The Ni-Co LDH@MQDs composites inlaid with MQDs were grown on the surface of nickel foam with hydrothermal method.In three-electrode cell,the specific capacitor can maintain 72.1%at 10A g^-1.The initial capacitor can still maintain 98.6%after 10000 cycles in two electrode systems.The device exhibited a high energy density of 60.7 W h kg^-1 at power density of 698 W kg^-1.MQDs can adjust the size of LDH sheets.MQDs can improve the rate performance of LDH by constructing surface electron transmission networks and shortening electron transmission paths.The interfacial effect between MQDs and LDH can significantly improve the cyclic stability of composites.