| Supercapacitor is a new type of energy storage device seems like traditional capacitors and rechargeable batteries.It has the advantages of excellent cycle performance,wide operating temperature range and environmental protection.In addition,supercapacitor has greater energy density than conventional capacitors and greater power density than rechargeable batteries.Therefore,it has a very broad application prospect in the fields of electric vehicles,aerospace,and electronic products.For supercapacitors.,the choice of electrode materials is the most important factor in determining their performance.At present,transition metal oxides are attracting attention due to their ultra-high electrochemical storage performance,such as NiFe2O4.NiFe2O4 is a transition metal oxide composed of three elements of Ni,Fe and O.It has good specific capacitance.However,the inherent low conductivity properties of metal oxides make them ineffective for use at high currents.To solve this problem,researchers are often compounded with carbon materials.Among all carbon materials,graphene nanosheets(GNSs)have excellent stability,electrical conductivity and large specific surface area,which can greatly improve the disadvantage of poor conductivity of NiFe2O4.In addition,when combined with NiFe2O4,graphene nanosheets can prevent aggregation and are a very excellent composite matrix.Transition metal sulfides are also an excellent candidate for supercapacitor electrode materials,such as WS2.As a matrix with NiFe2O4 composites,WS2 has superior stability and large electrochemical capacity.However,WS2 nanosheets are very easy to stack together to form a bulky structure,so stripping of WS2 nanosheets is an important step before using them as supercapacitor materials.The purpose of this paper is to prepare excellent electrochemical performance electrode materials of NiFe2O4,NiFe2O4/GNSs and NiFe2O4/WS2.The main contents are as follows:(1)NiFe2O4 nanomaterials were prepared by hydrothermal synthesis.The type of precipitant,the concentration of precipitant,the reaction temperature and the reaction time all play an important role on the morphology and properties of the sample.Results show that NiFe204 prepared using 0.2 M urea as the precipitant with reaction temperature of 180℃ and reaction time of 10 h forms nanosheet morphology,showing the best electrochemical performance.At a current density of 1 A/g,the specific capacitance of the sample reaches 240.9 F/g.At a current density of 8 A/g,the specific capacitance can still maintain about 95%,and the energy density can reach 10.15 Wh/kg at a power density of 140 W/kg.(2)NiFe2O4/GNSs composite nanomaterials were synthesized by hydrothermal method.Reaction temperature and reaction time affect the morphology and properties of the sample.When the reaction temperature is 180℃ and the reaction time is 10 h,NiFe2O4 grows into nanosheet,covering the surface of GNSs,interpenetrating to form a network structure,showing the best electrochemical performance.The specific capacitance of the sample arrives at 464.15 F/g at a current density of 1 A/g.Energy density can reach 14.04 Wh/kg at a power density of 70 W/kg,and it maintaines 7.39 Wh/kg at a high power density of 7000 W/kg.In addition,the specific capacitance of the sample increased to 140%after 5000 charge and discharge tests.(3)WS2 was treated by chemical method and liquid phase stripping method.WS2 was obviously thinned and the morphology of nanosheets was well preserved.NiFe2O4/WS2 composite nanomaterials were prepared by hydrothermal synthesis.NiFe2O4 prepared at 180℃ for 9 h grew into nanosheet morphology on the surface of WS2,showing the best electrochemical performance.Specific capacitance can reach 878.04 F/g at current density of 1 A/g.Energy density can reach 25.47 Wh/kg at a power density of 70 W/kg,and it maintaines 13.42 Wh/kg at a high power density of 7000 W/kg.Besides,the sample exhibits excellent cycle performance. |
