Synthesis And Capacitor Performance Of MXenes Composites

MAX phase is a kind of ternary ceramics materials where M represents a transition metal elements?such as Ti, Ta?, A usually represents III A or IVA element?such as Al, Ga, Si, or Ge?; and X represents C or N. It has good electrical conductivity and structural stability. The layered compound labeled as “MXenes,” obtained by HF etching has a large specific surface area. After testing, MXenes is the very suitable electrode materials for supercapacitor because of the good capacitance performance, conductivity, excellent cycle stability and rapid charge and discharge performance. But the drawback is the lower specific capacitance and the energy storage mechanism is given priority to with electric double layer capacitor, hence the modification to increase its specific capacity appears very promising. Currently the modification of such layered compound can be made into sheet structure similar to graphene by layer separation. The specific surface area can be greatly improved while the material can be used as a substrate material to load other active material. In recent years, the use of composites can solve or improve the performance of a single material, such as poor conductivity, low specific capacity, and cycle performance instability. Manganese dioxide is a kind of metal oxide-based electrode material with the higher theoretical specific capacity, better rapid charge-discharge performance, poor conductivity and cycling stability. Polyaniline as a conductive polymer has a good conductivity, chemical stability and reversibility of charging/discharging, which is suitable for used as electrode material. This thesis successfully use Ti₃AlC₂ as MAX raw material to prepared the composite's precursor Ti₃C₂T_x?MXenes?, where T represents surface termination?O2-, OH-, and/or F-?, D-Ti₃C₂T_x/MnO₂, Ti₃C₂T_x/PANI composite. After testing, the specific capacity and cycling performance are improved.1. Ti₃C₂T_x: Ti₃AlC₂ was etched with hydrofluoric acid to obtain Ti₃C₂T_x, SEM image show that the Ti₃C₂T_x formed layered structure. The electrochemical test results show that the material has a good conductivity and its specific capacitance reached 90 F/g without significant attenuation after 500 cycles.2. D-Ti₃C₂T_x/MnO₂: Ti₃C₂T_x was treated by DMSO to give a sheet MXenes?DTi₃C₂T_x?. The product further reacted with potassium permanganate to give the DTi₃C₂T_x/MnO₂. SEM, TEM and XRD was used to characterize the morphology and structure of this material. Results show that spherical MnO₂ and porous network MnO₂ film grown on surface of the D-Ti₃C₂T_x. After a series of electrochemical test, specific capacitance reached 256 F/g, which increase by 184% relative to Ti₃C₂T_x. After 1000 cycles test, retention rate reached 92% and this result exhibited excellent cycle stability of D-Ti₃C₂T_x/MnO₂. Maximum power density can be achieved 1599.6 W kg-1 and energy density reached 22.82 Wh kg-1. Nyquist plots display that the addition of MnO₂ give a negative effect on the conductivity.3. Ti₃C₂T_x/PANI: Polyaniline was obtained by chemical oxidation method under acidic conditions. The product was mixed and dissolved with Ti₃C₂T_x according to certain proportion to obtain Ti₃C₂T_x/PANI composites by adsorption. In this research, SEM and XRD was used to characterize the morphology and structure of this material. After a series of electrochemical tests, the specific capacity of the material reached 138F/g and increased by 56% respect to MXenes. After 500 cycles, specific capacity still reached 122 F/g and retention rate was 88.4%. The highest power density reached 1603.8W kg^-1 and the highest energy density reached 12.35 Wh kg^-1.