| Since the 21 st century,environmental problems and energy shortages have become more and more serious.People are eager to find safe,environmentally friendly and renewable alternative energy.Although wind and solar energy are abundant and inexhaustible,they cannot guarantee the continuity of energy due to external factors in energy supply.Energy storage devices such as lithium-ion batteries,fuel cells and supercapacitors are booming.Among them,supercapacitors（SCs）have attracted much attention due to their low cost,fast charge and discharge,long service life and high power density.Electrode materials play deterning roles on the performance of supercapacitors.Electrode materials with excellent performance must have good conductivity,high electrochemical activity and low cost.The widely studied electrode materials contain carbon materials,metal compounds and conductive polymers.Different materials have inherent advantages and disadvantages,so the composite materials can not only make up for the shortcomings of a single material,but also improve the electrode performance through the synergistic effect of the two materials.Among many electrode materials,Ni-Al double hydroxide has been widely used in supercapacitors because of its high theoretical specific capacity and low price,but its poor conductivity and low rate performance affect the practical application.The main work of this paper is to combine two-dimensional metal carbides（Ti3C2Tx）with nickel aluminum double hydroxide（NiAl-LDH）materials on different conductive carriers.Composite materials with unique morphology were synthesized and investigated by electrochemical analysis.The main experiments are as follows:MXene/NiAl-LDH layered nanoflower composite on Ni foam was prepared and used in supercapacitors.NiAl-LDH was successfully grown on the nickel foam coated with MXene nanosheets htrough safe and environmentally friendly immersion process and hydrothermal method.The NiAl-LDH/NF(1203 F g-1)composite exhibits excellent conductivity with a specific capacitance of 1600 F g-1 at a low current density of 1 A g-1.At high current density(10 A g-1),the initial capacitance can still be maintained at 78 % after 3000 cycles of continuous charge and discharge,which shows the good cycle stability.The MXene/NiAl-LDH//AC device with MXene/NiAl-LDH as positive electrode and activated carbon（AC）as negative electrode can provide 27.6Wh kg-1 energy density at 260 W kg-1 power density.Asymmetric supercapacitor device still maintains 89.1 % of the initial capacitance after 5000 cycles at 3 A g-1,indicating that the device has good stability and may have practical application.MXene-PAN nanofibers were prepared by high-voltage electrospinning.MXeneC nanofibers were obtained htrough pre-oxidation and carbonization process.After coating AlOOH layer as aluminum source,NiAl-LDH was hydrothermally grown on MXene-C nanofibers as composite electrode material.The introduction of MXene improves the electrical conductivity of the carbon nanofibers,and the NiAl-LDH nanosheets grow uniformly on the carbon nanofiber substrate,which alleviates the stacking phenomenon of the nanosheets.In the electrochemical test,the specific capacitance of one-dimensional composite material is 550 F g-1 at low current density of 1 A g-1,which is significantly better than that of C@NiAl-LDH without MXene.In addition,the capacitance retention is 75 % at a high current density of 10 A g-1,which shows that the composite electrode material owns good cycle stability. |
