Preparation,characterization And Electrochemical Performance Of Ni/Co Based Electrode Materials

With the development of society,people's demand for renewable energy and efficient energy storage equipment is increasing due to severe environmental problems and fossil energy crisis.As a new type of energy storage device,supercapacitors have very important scientific significance and application prospects in the future energy storage and conversion process.Due to the low cost,high theoretical specific capacity,and low environmental impact of nickel-cobalt oxides,nickel-cobalt oxides was selected as the research focus.With using different solvents,different raw materials,a series of experiments were conducted to prepare nickel-cobalt oxides with different morphologies.And by changing the holding time,sintering atmosphere,various samples for comparison were prepared.The specific research content is as follows:?1?The thorn-flower-like precursor was synthesized by a simple solvothermal method.The spinel structure of Ni_1.5Co_1.5O₄ electrode material was obtained by annealing in air atmosphere.The SEM test showed that the morphology of the precursor was thorn on the sheet.After annealing,the thorn in the thorn-flower-like shape of the precursor turned into many small particles.The electrochemical performance of the three-electrode system was tested.The specific capacity of Ni_1.5Co_1.5O₄ was 299.2,284.4,272,263.2,252,208 F g^-1 at current densities of 2,3,5,7,10,and 20 A g^-1,respectively.And when the current density increases from 2 A g^-1 to 20 A g^-1,the specific capacity still maintains 69%,indicating that it has better rate.By changing the synthetic raw materials,single-element electrode materials Ni_xO_y and Co_xO_y were prepared.By comparing the electrochemical properties of the three electrode materials,it can be clearly seen that Ni_1.5Co_1.5O₄ has more excellent electrochemical performance than Ni-O and Co-O.After assembling it into an asymmetric capacitor,it can still maintain 63%of the specific capacity at a high current density,exhibiting excellent rate performance.Excellent cycling charge and discharge performance,with a specific capacity of27.7 F g^-1 after 5000 cycles of charge and discharge.?2?In this chapter,the NiCoO₂ electrode material of thorn-flower-like was prepared by annealing the precursor in the previous chapter at 400°C for 2 h in nitrogen atmosphere.Comparing NiCoO₂ with Ni_1.5Co_1.5O₄,it is found that the electrochemical performance of the product annealed in nitrogen are much larger than that of Ni_1.5Co_1.5O₄.Different precursors of Ni₂?OH?₂CO₃·4H₂O and Co?CO₃?_0.5?OH?·0.11H₂O were prepared by changing the precursor holding time.At the same time,through the single metal components of NiO_x and CoO_x,the formation of the thorn-flower-like morphology was explored.It was found that with the increase of the holding time,the thorns gradually increased,which proved that the relative content of phase Co?CO₃?_0.5?OH?·0.11H₂O gradually increased.Electrochemical performance of the electrode material after annealing was tested.The test results showed that the specific capacity of the NiCoO₂ electrode material was significantly higher than that of Ni-Co-1 h,Ni-Co-5 h,Ni-Co-14 h in the three-electrode system.By comparing the CV and CP curves of the three-electrode systems of NiCoO₂,NiO_x and CoO_x,it was found that the mass specific capacitance of NiCoO₂ is larger than that of NiO_x and CoO_x.The voltage window of the double metal oxide NiCoO₂ is 0.5 V,which is also greater than the 0.4 V of the single metal.NiCoO₂with higher mass specific capacity and better rate performance was selected as the electrode material.For the asymmetrical capacitors test,the specific capacities of NiCoO₂ were 106.5 and70.7 F g^-1 at current densities of 0.5 and 10 A g^-1,respectively.In order to test the stability of the sample,the sample was subjected to a cycle charge-discharge performance test,after 5000cycles at a current density of 2 A g^-1,the specific capacity of the sample still had 77%of the initial specific capacity,which may also prove its excellent electrochemical performance.?3?Due to the good electrochemical properties of NiCoO₂,using isopropanol and 1,3-propanediol as the solvent,a flower-spherical precursor was prepared by heating in an air atmosphere with a heating rate of 1°C min^-1 at first.When heated to 200°C,nitrogen was passed through.Then heated to 300°C,and the temperature was maintained 300°C to obtain a sheet-spherical NiCoO₂.Its large specific surface area and mesoporous pore size can improve the electrochemical performance of the electrode material.By changing the synthetic raw materials,single-element electrode materials Ni_xO_y and Co_xO_y were prepared.By comparing the electrochemical properties of the three electrode materials,it can be clearly seen that NiCoO₂ has more excellent electrochemical performance than Ni_xO_y and Co_xO_y.In the three-electrode system,when the current density of 1 A g^-1,the mass specific capacity of NiCoO₂ is 1026 F g^-1.When the current density increases from 1 A g^-1 to 10 A g^-1,the specific capacity still maintain 73%of the original specific capacity,the specific capacities of Ni_xO_y and Co_xO_y remain 70%and 61%,indicating that NiCoO₂ has a good rate performance.After assembly into asymmetrical capacitors,the cycle performance of NiCoO₂ is superior,and the89 F g^-1 specific capacity can still be maintained after 5000 cycles of charge and discharge.Its maximum specific power density and maximum specific energy density are 4000 W kg^-1 and50.1 Wh kg^-1,respectively.In summary,electrochemical test results show that the flower-spherical NiCoO₂ electrode material has good electrochemical performance.