Synthesis Of Ni-Co Oxide And Sulfide Electrode Materials And Their Application In Supercapacitors

With the depletion of primary energy such as oil and coal and the utilization of new renewable resources such as solar energy,biomass energy and tidal energy,researchers will give priority to exploring efficient,clean and sustainable energy storage and power supply technologies.Supercapacitors(also known as electrochemical capacitors)have broad development and application prospects because of their high energy density,fast charging and discharging speed,good cycle performance and wide temperature range.Electrode materials with core-shell structure and high mass loading show great potential in various important energy storage systems,and the actual capacitance of pseudocapacitor materials has become closer to its theoretical value.However,it is always a difficult problem to prepare electrode materials with high mass loading and excellent specific capacitance.In order to improve the energy density and energy storage capacity of the pseudocapacitor electrode material,according to the formula E=1/2CV~2(where C is the specific capacitance and V is the working voltage window),people can improve the energy density(E)of the electrode material by increasing the specific capacitance of the electrode.Many methods of preparing electrode materials for supercapacitors have been reported in the past,such as chemical vapor deposition,electrodeposition and template method.However,these methods need not only a lot of time,but also a lot of manpower and financial resources.In this paper,the core-shell structures were prepared by a convenient hydrothermal synthesis method NiCo₂O₄@Ni O nanoneedle three-dimensional array composite electrode material and composite electrode with core-shell structure NiCo₂S₄@MoS₂ heterogeneous nanorod array composite electrode material.By changing various experimental conditions,the factors affecting the morphology,structure and electrochemical properties of the materials were explored.In this paper,the following results have been obtained.(1)By means of a simple two step hydrothermal reaction,the pine needle like structure was successfully prepared on the foam nickel substrate.NiCo₂O₄@Ni O core-shell nanoneedle modified nanoneedle three-dimensional arrays structure composite electrode material.The electrochemical properties of the synthesized electrode materials were studied under the condition of current density of 1 m A cm^-2 by using three electrode system and KOH solution with concentration of 2 M as electrolyte.The results show that the area specific capacitance of the electrode material NNN-10 can reach 4.65 F cm^-2 when the second step hydrothermal reaction time is 10 h.With the synthesized core-shell structure NiCo₂O₄@Ni O nanoneedle composites and activated carbon(AC)were assembled as positive and negative electrode materials NiCo₂O₄@Ni O//AC supercapacitor and its electrochemical properties were studied.The results show that the supercapacitor has an ultra-high energy density of 48.63 Wh kg^-1 and a power density of 250.1 W kg^-1,and has excellent cycle stability(the specific capacity retention rate is 98.6%after 10000 cycles under the condition of current density of 40 m A cm^-2).The above test results show that the NNN-10 electrode material with large mass load(10.3 mg cm^-2)prepared by two-step hydrothermal method has excellent electrochemical properties and can be applied to supercapacitors with excellent electrochemical properties,which is worthy of further exploration.The research results provide a simple and effective method for the preparation of electrode materials with high mass loading and new morphology core-shell heterostructure,and provide ideas for the preparation of other electrode materials with high-mass loading and high electrochemical properties in the future.(2)The core-shell NiCo₂S₄@MoS₂nanorod arrays were successfully synthesized on the surface of nickel foam by three step hydrothermal method.The mass loading reached 11 mg cm^-2.The effects of the reaction time and reaction temperature on the structure,morphology and electrochemical properties of the core-shell electrode materials were investigated.The experimental results show that the reaction time and temperature will have different effects on the structure and morphology of the composite electrode materials,and cause differences in various properties.Combining various factors,it can be determined that the electrode material with the best electrochemical performance is sample NNM-5.The electrochemical test results show that when the current density is 3 m A cm^-2,the area specific capacitance of the electrode material is as high as 8.86 F cm^-2 After 6000 cycles under the condition of current density of 40 m A cm^-2,the capacitance retention of NNM-5 electrode material can reach88.9%.The above results show that the prepared electrode material has excellent high mass loading,large charge storage capacity and excellent cycle stability.With the synthesized core-shell structure NiCo₂S₄@MoS₂ nanorod composites and activated carbon(AC)were assembled as positive and negative electrode materials NiCo₂S₄@MoS₂//AC supercapacitor,and its electrochemical properties were studied.The results show that the maximum energy density of the supercapacitor is 48.63 Wh kg^-1 at the power density of 250.1 W kg^-1.After 6000 cycles,the capacitance retention is about 75.8%,showing good cycle stability.