Structural Design Of Two-Dimensional Layered Titanium Carbide And Its Electrochemical Performance

Supercapacitors have been attracting considerable attention because of their high power densities,fast charging rate and long cycle lives,and have great application prospects in backup power supply and high power output.However,the currently commercialized supercapacitors suffer from low energy density(?10 Wh kg^-1)because they mainly use low-capacitance carbon materials electrode,which restricts the application of supercapacitors in high energy density demand.In recent years,MXene,a new family of two-dimensional transition metal carbides and nitrides,has become a research hotspot in the field of electrochemical energy storage due to its metal conductivity,hydrophilicity,rich chemical surface.Nevertheless,the research on MXene and its application potential are still in its infancy.In this dissertation,starting from the two-dimensional layered Ti₃C₂,which is a representation in MXene materials.The electrochemical properties were discussed through the design and preparation of Ti₃C₂ based electrode materials with novel structure.The kinetic process of electrochemical energy storage was analyzed,and the application potential of Ti₃C₂ based supercapacitors were explored.Some progresses have been obtained:In this paper,the mixed solution of HCl and LiF was used as the etchant to realize the“corrosion-intercalation-exfoliation”of Ti₃AlC₂ in one step.By optimizing the preparation conditions,two-dimensional few-layered Ti₃C₂nanosheets were successfully prepared and the morphology,crystal structure and composition were investigated.The Ti₃C₂ nanosheets exhibits large interlayer spacing which can be attributed to the embedding of lithium ions hydrate or water molecules during the preparation process and put up a specific surface area of 16.2m² g^-1.The surface of Ti₃C₂ nanosheets contains a large number of oxygen-containing functional groups and a small number of-F and-Cl functional groups.The electrochemical properties of freestanding Ti₃C₂ film electrode was tested which exhibited an areal capacitance of 190 mF cm^-22 and showed excellent cyclic stability.Two-dimensional Ti₃C₂ nanosheets decorated with Ag nanoparticles has been rationally designed and successfully fabricated according to the wedging“pillar”strategy.The Ti₃C₂/Ag hybrid films were prepared through filtering the mixture of Ti₃C₂ nanosheets and Ag nanoparticles aqueous dispersion solution.The restacking of Ti₃C₂ sheets is inhibited effectively and the specific surface area is improved to107 m² g^-1.By adjusting the content of Ag nanoparticles in the hybrid,the Ti₃C₂/Ag?1:2?electrode exhibits the highest area capacitance of 332.2 mF cm^-2,and the mass loading of the electrode material could be increased to 15 mg cm^-2.An asymmetric supercapacitor?ASC?using Ti₃C₂/Ag?1:2?electrode as negative electrode was assembled,which exhibits a maximum energy density of 121.4 Wh cm^-2,a maximum power density of 17395 W cm^-2,and a capacitance retention rate of 82%after 10,000 cycles.Besides,the ASC is capable of supplying power to a single red LED.Sandwich structured Ti₃C₂/PEDOT:PSS hybrid films were designed and prepared with electrostatic self-assembly method.The introduction of PEDOT:PSS can increase the layer spacing of Ti₃C₂ nanosheets and inhibit the restacking phenomenon.The amount of PEDOT:PSS was adjusted to optimize the proportion of composite materials,and the optimal volume capacitance is 1065 F cm^-33 with a80%capacitance retention after 10,000 cycles.The electrode exhibits good flexibility.And the Ti₃C₂/PEDOT:PSS film negative electrode and rGO film potential electrode were used to assemble the flexible asymmetric supercapacitor.The flexible ASC showed no significant change on the electrochemical performance under bending,and it can be applied to the luminous bracelet.Novel porous Ti₃C₂ aerogel structure material was first constructed and its electrochemical performance was investigated systemically.The porous Ti₃C₂aerogel has been synthesized by a simple EDA-assisted self-assembly process.Its inside are channels and pores structure.The interconnected aerogel structure could efficiently restrain restacking of Ti₃C₂ nanosheets.Thus,it exhibits a large specific surface area as high as 176.3 m² g^-1.The unique pore structure of Ti₃C₂ aerogel endow the electrode with high rate performance.As the scan rate increases by 50times,the capacitance retention rate is 76.6%,indicating that Ti₃C₂ aerogel electrode has more important application value at high current density.The ASC based on the Ti₃C₂ aerogel negative electrode and carbon nanofiber film synthesized by electrospinning exhibits the maximum energy density of 120 Wh cm^-22 and the maximum power density of 26123 W cm^-2.After 5000 charges and discharges,the capacitance retention rate is still 82%.Furthermore,the ASC can supply power to a lamp board composed of 19 LEDs in parallel,which indicates its excellent application prospect.