Study On The Preparation And Electrochemical Properties Of Two-Dimensional Mxene/Nickel-based Composites

As a high-efficiency energy storage and conversion device,supercapacitors exhibit the advantages of fast charge and discharge rate,high power density,safety and environmental protection.However,low energy density limits its widespread development and application.Nickel-based compounds have the advantage of high theoretical capacity.However,the intrinsic conductivity of the nickel-based compound is poor and the structure is unstable during charge and discharge process,resulting in unsatisfactory electrochemical performance such as cycle life and rate capability.In order to overcome the above problems,we have proposed a strategy of constructing composite materials.Composites of nickel-based compound and highly conductive carrier material were prepared by structural design,and make full use of the synergistic effect of binary materials to solve the problem of poor conductivity and stability,thereby obtaining composite electrode material with high specific capacity,high rate and long cycle life.At the same time,the application of composite electrode materials in hybrid supercapacitors is studied to obtain electrochemical energy storage devices with high energy density and stable performance.The research work is mainly focused on the following aspects:1.Ni?OH?₂ nanosheets were grown in situ on nickel foam by hydrothermal method using nickel nitrate aqueous solution as precursor liquid.The effect of precursor concentration on the structure of Ni?OH?₂ nanosheets was investigated.The Ni?OH?₂ nanosheets are interdigitated to form a porous structure,which is beneficial to electrolyte ion diffusion and charge transport.When 0.12 mmol of nickel nitrate is added,the as-prepared 0.12M-NHNF composite exhibits superior electrochemical performance by electrochemical test comparison.The hybrid supercapacitor assembled with 0.12M-NHNF and activated carbon as positive and negative electrodes,respectively,exhibits higher energy density.2.Ni₂CO₃?OH?₂ was supported on the surface and interlayer of two-dimensional Ti₃C₂substrate by hydrothermal method.The effects of precursor mass ratio on the morphology and electrochemical properties of Ti₃C₂/Ni₂CO₃?OH?₂ composites were systematically investigated.The Ti₃C₂/Ni₂CO₃?OH?₂ composites fully exert the synergistic effect between two-dimensional Ti₃C₂ and Ni₂CO₃?OH?₂,and effectively increase the electrochemical active sites.Compared with individual Ni₂CO₃?OH?₂,30-Ti₃C₂/Ni₂CO₃?OH?₂ exhibits a higher specific capacity(173 mAh g^-1)and stability.A hybrid supercapacitor was assembled with30-Ti₃C₂/Ni₂CO₃?OH?₂ and activated carbon as positive and negative electrodes,respectively,showing high energy density.3.Using cetyltrimethylammonium bromide as a bridging agent,the delaminated Ti₃C₂nanosheets?d-Ti₃C₂?were supported on the surface of nickel foam?NF?by self-assembly method to construct a binder-free composite electrode.The composite electrode material can effectively prevent the re-aggregation of d-Ti₃C₂,increase the active area of the d-Ti₃C₂nanosheets,and expose the surface to expose more oxygen-containing functional groups to provide abundant active sites.The binder-free d-Ti₃C₂/NF composite exhibits a high specific capacitance as a positive electrode material(specific capacitance of 654 F g^-11 at 1 A g^-1)and good rate performance.4.The Ni₃S₂/d-Ti₃C₂/NF composite was prepared by in-situ growth of Ni₃S₂ in d-Ti₃C₂/NF composite by solvothermal method.The porous Ni₃S₂ was supported on the surface of d-Ti₃C₂ nanosheet and in close contact with nickel foam,shorten the charge transfer path and reduce contact resistance and electron transfer resistance.The addition of d-Ti₃C₂nanosheets increased the electrochemical active sites and significantly improve conductivity.The hybrid supercapacitor assembled with Ni₃S₂/d-Ti₃C₂/NF and activated carbon as positive and negative electrodes,respectively,exhibits high energy density and long cycle life.