Structure And Electrochemical Properties Of Cobalt-Nickel Phosphate By Hydrothermal Method And Bismuth Phosphate By Solvothermal Method

In recent years,the utilization technology of renewable energy such as wind energy,solar energy,and nuclear energy has been rapidly developed.In order to transfer these energy to the smart grid and improve the reliability of the grid,it is urgent to develope safe and stable energy storage equipment.As an electrochemical energy storage device which is inexpensive,flexible,high energy conversion efficiency,high power density,and low maintenance cost,the supercapacitor has received more and more attention.In this paper,nickel-cobalt phosphate composites were prepared by hydrothermal method,and further optimize its structure.Nanocrystalline bismuth phosphate was synthesized by solvothermal method.In order to further verify the superiorcapacitive performance of the as prepared electrode material,an asymmetric supercapacitor device was assembled employing as-prepared Nickel-cobalt phosphates as the positive electrode,activated carbon(AC)and bismuth phosphate as the negative electrode.The main contents are as follows:1.A hexagonal prismatic micro-rod structure with different nickel-cobalt ratio was prepared by a hydrothermal method.Using XRD,SEM,XPS and other testing methods to study the changes in the structure of the sample prepared under different conditions.Electrochemical workstations and blue electrical test system were used to investigate the changes of electrochemical performance.After a series of tests,it was found that sample with Ni/Co ratio of 0.8:0.2 showed the best electrochemical performance.In three-electrode system,using the electrode material as a working electrode,the specific capacity reached 1905 F/g at a current density of 0.5 A/g,and the capacity maintained 52.9%at a large current density of 10 A/g.The capacity maintained 62.3%even after 3000 cycles at a current density of 5A/g.In two-electrode system,using the electrode material as the positive electrode and the activated carbon as the negative electrode,at the voltage window of 0-1.6 V,the specific capacitance of the device at the current density of 0.5 A/g was 63.9F/g.After 5000 cycles at a current density of 1A/g,the specific capacitance of the device was maintained 98.6%of the initial capacitance,demonstrating excellent cycle performance.The aqueous device showed a high energy density of 22.7 Wh/kg at the power density of 410 W/kg.2.In order to improve the electrochemical performance of the sample,the samples were reacted at different concentrations of NaOH solution.The growth mechanism of the sample was studied by means of XRD,SEM,XPS,etc.Electrochemical workstations and blue electrical test systems were used to study the changes in their electrochemical performance.In three-electrode test system,using the material as a working electrode,the specific capacity reached 2113 F/g at a current density of 0.5 A/g,and the capacity maintained 52.9%at a large current of 10 g-1.In two-electrode test system,the specific capacitances at the current densities of 0.5A/g reached 90.6F/g.After 5000 cycles at a current density of 1 A/g,the device's specific capacitance was maintained 100%of the initial capacitance.Moreover,the maximum energy density up to 32.2 Wh/kg at a power density of 430 W/kg.3.In order to further improve the performance of the devices,bismuth phosphate was synthesized by solvothermal method.Electrochemical workstations and blue electrical test systems were used to study the changes in their electrochemical performance.After a series of tests,it was found that the sample Bi-20-30 had the best electrochemical performance.In three-electrode test system,using this material as working electrode,the specific capacity was 1230 F/g at a current density of 0.1 A/g,what's more the specific capacity was also 800 F/g at a current density of 5A/g.In two-electrode test system,the electrode material used as the negetative electrode,and NNCP-3 used as positive electrode.Under the voltage window of 0-1.5V,the specific capacitance achieve 240.6F/g at a current densities of 0.5 A/g.The maximum energy density is 75.18Wh/kg when the power density is 370W/kg,what's more the energy density is still 41.56Wh/kg when the power density is 7.87KW/kg.Compared with activated carbon,the specific capacity,energy density,and power density had a significant increase.