Preparation And Electrochemical Performance Of Nickel-based Electrode Materials

Nickel-based compounds become one of the important research objects as supercapacitor electrode materials owing to their low cost,simple synthesis method,high electrochemical redox activity and various crystal morphologies.However,it’s difficult for pure nickel-based compounds to achieve the theoretical capacitances in practical applications for their low electrical conductivity and large resistance.Therefore,in this paper,cobalt and manganese are doped in nickel-based compounds to improve their electrochemical performance.The specific research contents and conclusions are as follows:First of all,nickel-cobalt hydroxides ofαandβcrystal forms were prepared respectively by one-pot hydrothermal method under the action of four different additives such as NH₄F,KF,（NH₄）₂SO₄and NH₄Cl.The effects of their crystal form and morphology on the electrochemical performance were studied.It is found that Ni Co-LDH under the action of KF is assembled into a nano-flower shape from a thin sheet,which provides a rich active site for Faraday charge transfer reactions and exhibits excellent electrochemical performance.The prepared Ni Co-LDH electrode exhibits a maximum specific capacitance of 1624 F g^-1at a current density of 1 A g^-1,a excellent capacitance retention rate of 75.7%at a current density of 10 A g^-1and a good cycle stability.In addition,the supercapacitor assembled with Ni Co-LDH material as the positive electrode and activated carbon（AC）as the negative electrode shows a high energy density of 25.08 W h kg^-1at a power density of 150.5 W kg^-1,suggesting that Ni Co-LDH material is expected to be a candidate material for energy storage device electrodes.Then,the bimetal Ni Mn phosphomolybdate(Ni/Mn-PMo₁₂)nanosheets were grown in situ on a nickel foam substrate by a solvothermal method,and used as a positive electrode material for asymmetric supercapacitors.Under the condition of no binder and the synergistic effect of heteropoly acid and bimetal,the prepared Ni/Mn-PMo₁₂electrode material exhibits excellent electrochemical performance.When the Ni/Mn ratio is 2:1,the composite electrode shows a maximum specific capacitance of 1950.5 F g^-1at a current density of 1 A g^-1,a excellent retentive capability of 1473.8 F g^-1at 20 A g^-1,and good cycling stability with96.9%retention at 5 A g^-1after 2000 charge/discharge cycles.Moreover,an asymmetric ASC device with Ni/Mn-PMo₁₂nanosheets as the positive electrode and activated carbon as the negative electrode exhibits a high energy density of 28.3 W h kg^-1at a power density of 375W kg^-1and excellent cycling stability of 90.3%after 5000 cycles.