Study On Electrode Materials Based On Two-Dimensional Transition Metal Carbide And Electrochemical Properties

The hybrid supercapacitor is a new type of energy storage device between supercapacitors and secondary batteries,capable of maintaining a high energy density at a large current density,combining the characteristics of both supercapacitors and secondary batteries.This thesis focuses on the design of electrode materials based on two-dimensional transition metal carbide?MXene?.By surface modification and preparation of composite materials,the interlayer spacing of MXene is expanded,the self-stacking of nanosheets is prevented,and the electrochemical properties of the electrode materials are improved.Further,hybrid electrochemical capacitors having high energy density and high power density are assembled.The specific research contents are as follows:?1?Using the negatively charged nature of two-dimensional titanium carbide?Ti₃C₂T_x,MXene?surface,an organic base?tetramethylammonium hydroxide,TMAOH?is chosen as an intercalation agent to intercalate organic cations?tetramethylammonium ion,TMA⁺?into the interlayers of Ti₃C₂T_x to effectively enlarge the interlayer spacing and prevent re-stacking of the nanosheets,which is beneficial to the infiltration of the electrolyte and increases the transport rate of the electrolyte ions.The prepared TMA⁺surface modified Ti₃C₂T_x?TMA⁺-Ti₃C₂T_x?exhibits excellent electrochemical performance as a supercapacitor electrode material:showing a specific capacitance of 299.6 F g^-1 at a current density of 0.5 A g^-1;still maintaining 90%of the initial capacity after cycling 4000 times at a current density of 4 A g^–1.?2?Using the negatively charged nature of the delaminated Ti₃C₂T_x nanosheet?d-Ti₃C₂T_x?surface and the positively charged nature of the delaminated cobalt-aluminum double hydroxide?d-LDH?surface,driven by electrostatic interaction,two kinds of oppositely charged nanosheets are self-assembled layer-by-layer to obtain two-dimensional CoAl-LDH/Ti₃C₂T_x composites with heterostructures,which combine the advantages of high electron conductivity of Ti₃C₂T_x and high electrochemical activity of CoAl-LDH to effectively improve the electrochemical reactivity of the electrode material and accelerate the kinetics of the Faraday reaction.Among them,with a mass ratio of 3:1?CoAl-LDH:Ti₃C₂T_x?,the L3T1 composite exhibits the best performance,showing a high specific capacity of 523.6 F g^–1 at a current density of 0.5 A g^–1.While at a current density of 10 A g^–1,it still retains 365.8 F g^–1 with a good rate performance.After cycling 5000 times at a current density of 4 A g^–1,the specific capacitance of L3T1 is only attenuated by 10%,confirming its excellent cycle stability.L3T1 and activated carbon?AC?are assembled into a L3T1//AC asymmetric supercapacitor with a voltage range of 0.0¹.6 V,which exhibits an energy density of 28.6 Wh kg^-1 at a power density of 321.8 W kg^-1.?3?The abundant surface termination groups of Ti₃C₂T_x nanosheets can immobilize the dopamine molecule?DA?,which can be in situ polymerized to a uniform polydopamine?PDA?coating to obtain PDA/Ti₃C₂T_x composite.After heat treatment in an inert atmosphere at 300°C,the prepared PDA300/Ti₃C₂T_x composite electrode material has abundant lithium-incorporating active sites and fast transporting channels for electrons and ions,and exhibits excellent electrochemical performance.The PDA300/Ti₃C₂T_x electrode displays a high specific capacity of 1190 mAh g^–1 at a current density of 50 mA g^–1 and retains 552 mAh g^–1 at a current density of 5 A g^–1 with a good rate performance.The capacity retention rate is 82%after 1000 cycles at a current density of 1 A g^–1.The PDA300/Ti₃C₂T_x and activated graphene?AGN?are assembled into a lithium-ion capacitor with a voltage range of 1.5³.7 V,which exhibits an energy density of 84 Wh kg^-1 at a power density of 390W kg^-1.