Preparation Of Nickel Hydroxide/Graphene Nanocomposites And Their Application In Supercapacitor

Nickel hydroxide has been widely used in nickel-based secondary batteries?such as nickel-hydrogen batteries,zinc-nickel batteries,cadmium-nickel batteries?,electrochemical supercapacitors,electrochemical sensors,microwave absorbing materials and other fields due to its good electrochemical performance and pollution-free characteristics.As a very important functional material,especially as an electrochemical energy storage material,it has attracted much attention.In this paper,doping,compounding and controllable preparation for nickel hydroxide were invested.The electrochemical performance and its application in supercapacitors were also discussed,and the structure and morphology of the prepared composite materials are characterized.The main research contents are as follows:?1?Using NaOH as precipitant and one-pot hydrothermal prepared pure?-Ni?OH?₂ and?-Ni?OH?₂/reduced graphene oxide?rGO?with different content of rGO.Raman spectra indicated that the GO was partially reduced after hydrothermal reaction in hot alkali environment.FESEM analysis showed that it can effectively inhibit the agglomeration of nickel hydroxide nanoparticles to add graphene and improve the utilization rate of active substances.Electrochemical results indicated that added the graphene into nickel hydroxide can effectively improve the electrical conductivity and enhance the diffusion rate,and also reduce the electrochemical reaction resistance,especially improve the high current charging and discharging performance of the material.Among them,the composite with the best electrochemical properties has a specific capacitance of 1975 F g^-1 at the current density of 1 A g^-1,and it still has 1097F g^-1 at 30 A g^-1,exhibited excellent high-rate capability.?2?In order to increase the potential window and energy density of supercapacitors,an asymmetric supercapacitor was assembled by introducing rGO as the negative electrode and using the above-mentioned composite as the positive electrode.The electrochemical performance of the supercapacitor was tested under the two-electrode system.When the current density is 0.5 A g^-1,the specific capacitance can reach 97 F g^-1,and when the current density is 10 A g^-1,the specific capacitance can keep 64 F g^-1,which has better rate performance.After 3000 cycles at the current density of 3 A g^-1,the specific capacitance retention rate of the device is 74%,which shows good cycle stability.When the power density is 0.39 kW kg^-1,the energy density is 32.4 Wh kg^-1,which shows excellent performance.?3?Using urea as precipitant and a simple and controllable homogeneous precipitation method synthesized Al-doped?-Ni?OH?₂/rGO composites with three-dimensional mesoporous structure.By compounding rGO,the specific surface area of the material was greatly increased,and the contact area between the electrode material and electrolyte was significantly increased,thus the electrochemical performance was significantly improved.It had a specific capacitance of 2558 F g^-1 at the current density of 1 A g^-1 and 1925 F g^-1 even at 30 A g^-1 current density.In addition,when the power density is 0.39 kW kg^-1,the energy density is 46.4 Wh kg^-1,which is excellent in the electrochemical performance test under the two-electrode system.After 3000 cycles(at current density of 3A g^-1),the initial capacity is maintained at 72%.The improvement of the properties of the composites is due to its unique three-dimensional layered mesoporous structure.