Structure Design And Performances Of MXene-based Flexible Electrodes And Their All-in-One Supercapacitors

The rapid development of wearable electronics has increased the demand for flexible supercapacitors with characteristics of high energy storage,fast charge-discharge rate,small thickness,light weight and high flexibility.Recent years,all-in-one flexible supercapacitors have been received extensive attention and have been studied extensively for the purpose of improving the electrochemical performance,mechanical durability and applicability of flexible supercapacitors.In this thesis,the MXene materials with high conductivity,large capacitance,high density and excellent hydrophilicity were used to prepare flexible film electrodes.Embedding the carbon nanotube(CNT)/metal oxide composites into the interspace between the MXene layers can block the restacking of MXene nanosheets,and create porous electrode structure.The unique electrode structure can enlarge the ion accessible surface,construct efficient ion diffusion path and improve the electron transportation,avoiding the negative effects of metal oxides.A vacuum filtration assisted layer-by-layer strategy was also developed to fabricate MXene-based all-in-one supercapacitors.The specific research contents are as follows:(1)The CNT@MnO₂ composite was synthesized by the in situ growth of MnO₂ nanosheets on the outer surface of CNTs under the hydrothermal condition.The MXene/CNT@MnO₂ composite film electrode was constructed by embedding the CNT@MnO₂ composite into the interspace between the MXene layers,forming a three dimensional porous structure.The efficient ion diffusion channel,enhanced ion accessible active surface area and good conductivity facilitate to achieve excellent electrochemical performance.The all-in-one flexible supercapacitor was prepared by vacuum filtrating the MXene/CNT@MnO₂,cellulose nanomicrocrystal(CNC)and MXene/CNT@MnO₂ layers one by one.MXene/CNT@MnO₂ composite film shows high specific capacitance of 221F/g,good cycling stability and flexibility.The maximum energy density of the all-in-one device could reach 24.5m Wh/cm~3 at the power density of 0.5W/cm~3(2)FeOOH nanoparticles were in situ grown on the outer surface of CNTs.After annealing at high temperature,Fe OOH nanoparticles converted to Fe₂O₃ nanoparticles,forming the CNT@Fe₂O₃ composite.The CNT@Fe₂O₃ composite as spacer was embedded into the interlayers of MXene films to construct the MXene/CNT@Fe₂O₃ composite film electrode,which has large the ion accessible active surface area,short ion diffusion path and fast electron transportation.The all-in-one flexible supercapacitor was also prepared by using the vacuum filtration assisted layer-by-layer strategy.The composite film electrode and its corresponding supercapacitor have excellent electrochemical performance and mechanical flexibility.The maximum specific capacitance of MXene/CNT@Fe₂O₃ composite film is 487.5 F/g,and the maximum energy density of the all-in-one device could reach 5.3mwh/cm~3 at the power density of 69.9mW/cm~3...