Study On The Capacitive Performance Of Nickel Cobalt Sulfide/graphene Aerogel Composite Electrodes For Supercapacitors

Under the current energy situation,the development of new energy and the study of energy-saving technology have become increasingly urgent.Supercapacitor has attracted extensive attention in the field of scientific research due to its characteristics such as fast charging and discharging,high power density,long cycle life,safety and reliability and environmental friendliness as a new energy storage device.Electrode material is the key component which affects the performance of supercapacitors.NiCo₂S₄ has great application prospect in supercapacitor due to its high specific capacitance and high electrochemical activity.NiCo₂S₄ suffers from low electrical conductivity and large volume change in its charge/discharge processes,leading to poor rate capability and cycling stability of its electrodes.In order to solve the above problems,graphene aerogel?GA?with porous structure,large specific surface area,excellent electrical conductivity and stable mechanical properties is compounded with NiCo₂S₄ to improve the electrochemical properties of electrode material.In this paper,graphene hydrogel was prepared by hydrothermal method used graphene oxide as raw material.The NiCo₂S₄/GA composites were prepared by solvothermal method in different solvents.The morphology and composition of the samples were characterized by scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,Fourier transform infrared spectroscopy?FTIR?,Raman spectroscopy?Raman?,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?,and the electrochemical performance of the samples was measured.The main contents are as follows:?1?Graphene aerogel was prepared by hydrothermal method and freeze-drying method.The optimum conditions for preparing graphene aerogel were determined by changing the concentration of graphene oxide,the reaction temperature and the amount of reducing agent.The results showed that the graphene aerogel was prepared with 2 mg mL^-11 of graphene oxide concentration,200 mg of reducing agent ascorbic acid and 180?of reaction temperature had a porous structure with uniform pore distribution.Capacitance performance tests were carried out,when the current density was 0.5 A g^-1,the specific capacitance of graphene aerogel reached 97.8 F g^-11 with good electrochemical performance.?2?NiCo₂S₄/GA composites were prepared by solvothermal method.The effects of reaction solvent,reaction concentration and solution pH on the microstructure of NiCo₂S₄ and its relationship with electrochemical performance were discussed.It is found that NiCo₂S₄ obtained in ethanol was nanoparticles with irregular morphology compared to NiCo₂S₄/GA composite prepared in other solvents,but the particle size distribution was not uniform.When the pH of the solution was adjusted to 8.2 by adding a certain amount of ammonia hydroxide,the size of the prepared NiCo₂S₄ nanoparticles decreased from 53.28nm to 25.94 nm and uniformly distributed on the graphene aerogel as a substrate,resulting in shortening the diffusion path of electrolyte ions to increase the ions transfer rate.Electrochemical test results showed that the composite had a specific capacitance of 354.7 F g^-11 at a current density of 1 A g^-11 without ammonia hydroxide,and capacitance retention was 52.1%at a current density of10 A g^-1.After adding ammonia,its electrochemical performance was better than that of the composite without ammonia hydroxide.When the current density was 1 A g^-1,the specific capacitance reached 704.34 F g^-1.After the current density increased by 10 times,the specific capacitance retention rate was60.1%.At a current density of 2 A g^-1,after 1500 consecutive constant current charge and discharge tests,the initial specific capacitance was still maintained at80.3%.?3?Asymmetric supercapacitors were assembled used NiCo₂S₄/GA composite as positive electrode,activated carbon?AC?as negative electrode,and polyvinyl alcohol?PVA?-KOH gel as electrolyte and separator.At a power density of 800.2 W kg^-1,the energy density of the NiCo₂S₄/GA//AC asymmetric supercapacitor reached 20.9 Wh kg^-1.After 5000 consecutive constant current charge and discharge tests,it still maintained an initial specific capacitance of71.6%.Therefore,NiCo₂S₄/GA composites have broad application prospects in energy storage devices as electrode materials.