Study On Preparation And Supercapacitor Performance Of Ti₃C₂T_x-based Composites Electrode

With the increasing consumption of fossil energy,the development of green renewable energy conversion and storage devices demands promote solutions by scientists around the world.Supercapacitors are prominent among many energy storage devices due to their excellent rate characteristics,long cycle life and wide operating temperature range.As the core part of supercapacitor,the electrochemical activity and conductivity of electrode materials determine the performance of the device.Since Ti₃C₂T_x（MXene）was reported by Professor Yury Gogosti in 2011,it has been widely used in supercapacitors due to its characteristics（e.g.,high conductivity,good flexibility,strong stability,and good hydrophilicity）.However,its layered structure is easy to stack and has a low specific capacitance,which cannot meet the conditions of practical application.MnO₂ and NiFe-LDH are rich in resources and low in cost.They are both electrode materials with high theoretical specific capacitance,but due to their low conductivity,their electrochemical activity is insufficient.Taking advantage of good conductivity and flexibility of Ti₃C₂T_x and high specific capacitance of MnO₂ and NiFe-LDH,two composite electrode materials,MnO₂/Ti₃C₂T_x/CC and NiFe-LDH/Ti₃C₂T_x,were successfully synthesized by one-step hydrothermal method in this paper.The structure,morphology,composition and superelectric properties of the composite electrode materials were characterized and analyzed.The asymmetric supercapacitor was packed with the composite material as the positive electrode,the performance of the asymmetric supercapacitor was detected and the actual application experiment of lighting the LED lamp was successfully completed.The main results are as follows:（1）The Al element layer of Ti₃Al C₂（MAX）was etched by hydrofluoric acid,and the etched products were layered using dimethyl sulfoxide（DMSO）.A single layer or few layers of Ti₃C₂T_x MXene（s-MXene）were successfully prepared.The morphology and composition of s-MXene were detailedly studied.The results showed that the diameter of the prepared s-MXene was between 5-20 um,and the surface had abundant-OH and-F functional groups.（2）The flexible conductive MXene/CC substrate was prepared by coating s-MXene on carbon cloth（CC）substrate.Then,MnO₂ nanorod arrays were grown on the surface of MXene by one-step hydrothermal method.Finally,MnO₂/Ti₃C₂T_x/CC nanocomposites were successfully prepared.TEM results show that the prepared MnO₂nanorods have a diameter of 30-100 nm and a length of 400-800 nm.（3）The electrochemical performance of MnO₂/Ti₃C₂T_x/CC was compared with MnO₂/CC and Ti₃C₂T_x,the results show that the prepared MnO₂/Ti₃C₂T_x/CC composite electrode has a higher specific capacitance（511.2 F/g）,which is better than MnO₂nanorod/CC（302.3 F/g）.Even if the current is increased by 5 times,the composite electrode still has 60.3%Specific capacitance retention rate,showing excellent rate performance.After 10,000 cycles,the capacitance was reduced by only 17%,showing excellent cycle stability.The improvement of electrochemical performance comes from the synergistic effect of Ti₃C₂T_x and MnO₂.In addition,the all-solid flexible supercapacitor based on this composite electrode shows a high energy density of 29.58Wh/kg at a power density of 749.92 W/kg,showing Practical application value.（4）Through a one-step hydrothermal method,using Ti₃C₂T_x nanosheets as the substrate,NiFe-LDH nanosheet arrays were grown in-situ,and NiFe-LDH/Ti₃C₂T_xcomposite electrode materials were successfully prepared.The negatively charged functional groups on the surface of Ti₃C₂T_x attract LDH to nucleate on it,and the grown NiFe-LDH nanosheets have an interconnected network structure with a thickness of10-20 nm and a diameter between 100 nm and 500 nm.（5）The electrochemical performance of NiFe-LDH/Ti₃C₂T_x composite electrode material and pure NiFe-LDH was compared.It was found that the specific capacitance of NiFe-LDH/Ti₃C₂T_x at a current density of 1 A/g is 720.2 F/g,which is better than NiFe-LDH（465 F/g）and still has 84%capacitance after 1000 cycles.The improved electrochemical performance is attributed to the conductive network formed by the sheet-like Ti₃C₂T_x substrate,which accelerates the electron transport in the material,and LDH uses Ti₃C₂T_x as the substrate to nucleate,reducing the structural changes of LDH during charge/discharge.The asymmetric supercapacitor using the composite material as a positive electrode package has a power density of 758.27 W/kg at an energy density of 42.4 Wh/kg,and also exhibits excellent performance.In this paper,the preparation of MnO₂/Ti₃C₂T_x/CC and NiFe-LDH/Ti₃C₂T_xcomposite electrode materials,the electrochemical performance and the application experiment of actually lighting LED lamps are studied.The synthesized Ti₃C₂T_x-based composite material has excellent electrochemical performance and has the potential as a high-performance supercapacitor electrode.These research results are of great value for broadening the practical application of Ti₃C₂T_x.