Surface And Interface Modification Of Two-dimensional Ti₃C₂T_x And Its Electrochemical Energy Storage Performance

Two-dimensional transition metal carbides/carbonitrides(MXenes)have broad application prospects in the field of energy storage due to their abundant surface functional groups,tunable interlayer spacing,and excellent electrical conductivity.However,the kinetics of alkali metal ions during intercalation/deintercalation is slow,and the stacking between nanosheets due to long cycling reduces the structural stability and battery safety.In this thesis,from the perspective of material defect engineering,the structures of MXenes electrode materials are modified and optimized through the defect regulation strategy of surface and interface modification,as well as the modification of polymer electrolytes through the unique structural advantages of MXenes.The structure-performance relationship between the microstructure and electrochemical performance is further explored.The results obtained are summarized as follows:(1)To solve the problem of slow electrochemical kinetics of Ti₃C₂T_x anode for alkali metal ion batteries,we prepare and control the end capping groups of Ti₃C₂T_x by chemical exfoliation and low-temperature annealing methods.The types of functional groups on the surface of the material are optimized by the substitution of oxygen to some-F functional groups on the surface.The increase of-O functional groups can increase the diffusion rate of Li⁺,promote the transport of electrons,and accelerate the kinetics of the electrode reaction,thereby improving the performance of lithium storage.The optimized Ti₃C₂T_x material exhibits a reversible lithium storage specific capacity of 444.1 m Ah g^-1 after 200 cycles at a current density of 0.1 A g^-1.(2)To solve the problems of unstable structure and slow electrochemical kinetics of Ti₃C₂T_x anode for alkali metal ion batteries,we prepare defect-rich PM-Ti₃C₂T_xanode materials by plasma-assisted mechanochemical route(PM).Defect-rich Ti₃C₂T_xlayer structure is achieved by the activation of plasma and the high-energy ball milling of splitting force.Due to the increased specific surface area and defect density,the active sites of the Ti₃C₂T_x material are increased,thereby optimizing the lithium storage performance.The optimized PM-Ti₃C₂T_x anode exhibits a reversible specific capacity of 242.0 m Ah g^-1 after 400 cycles at 0.1 A g^-1.(3)To solve the problems of poor safety and stability of the electrolyte of alkali metal ion batteries,we adopt the blending method to add layered Ti₃C₂T_x as filler in the PVDF-HFP/PMMA-based polymer electrolyte.The Ti₃C₂T_x filler affects the morphology of the polymer matrix and increases the porosity of the polymer membrane,thereby increasing the contact sites of sodium ions.In addition,the unique layered structure of Ti₃C₂T_x can promote the uniform nucleation and growth of sodium on the surface of the sodium electrode,hinder the growth of sodium dendrites during the sodium deposition process,and improve the safety and stability of the battery.The optimized symmetric cell maintains the Na deposition/stripping overpotential within 50m V after stable cycling at 0.5 m A cm^-2 for 300 hours.(4)Extended exploration:To solve the problem of low capacity of commercial graphite anode,we prepare graphite-derived disordered carbon materials by mechanochemical method.Amorphous sp~3-C and sp~2-C structures are constructed on the graphite surface by the splitting force of high-energy ball milling.The increase of surface defects can further promote Li⁺adsorption and accelerate the electrode reaction kinetics,thereby optimizing the lithium storage performance.The optimized disordered carbon anode exhibits a reversible specific lithium storage capacity of 629.8 m Ah g^-1after 200 cycles at 0.2 A g^-1.