Preparation And Supercapacitor Properties Of Nickel Cobalt Matrix Composites

Supercapacitors are used to make up for the shortcomings of batteries because of their advantages:ultra-high power density,shorter charging and discharging time,and wide applicable temperature range.Among them,electrode material is the key component that affects the function index of supercapacitor,so seeking high performance electrode material can greatly improve the performance of supercapacitor.Transition metal compounds are mainly studied as high performance pseudocapacitors because of their high theoretical specific capacity and abundant valence states.However,the low conductivity and poor circulation of this kind of material restrict its performance to be further improved.As is well known,the structure of a material determines its performance,and the electrochemical performance of the material can be optimized by designing its morphology and structure,increasing its specific surface area.Therefore,this paper explores the supercapacitor performance of nickel cobalt based transition metal compounds by selecting appropriate matrix materials and designing their morphology and structure.The specific content is as follows:（1）Through a simple two-step hydrothermal method,the three-dimensional flower ball structure is formed by the interconnection of two-dimensional nano sheets,and a large specific surface area is constructed.Three-dimensional nanoflower structure is composed of layered two-dimensional nanosheets,which act as a supporting skeleton and play a key role in the integrity and stability of the material.NiCo₂S₄nanosheets were loaded uniformly with graphene as the skeleton,and then layered NiMo-LDH nanosheets were grown in situ on ultra-thin NiCo₂S₄.The layered structure effectively prevents the nanosheets from agglomerating,thus improving the charging and discharging efficiency of the whole structure.The resulting RGO@NiCo₂S₄@NiMo-LDH has excellent performance,and the constructed three-dimensional nanoflower structure provides excellent specific capacitance(1 A·g^-1,1346 F·g^-1).In addition,the assembled asymmetric supercapacitor（ASC）provides a power density of 808.19 W·kg^-1and an energy density of 59.38Wh·kg^-1.The device can undergo 10000 charge discharge cycles at 10 A·g^-1,and the capacitance retention rate is stable at 80%.（2）The energy storage performance of MOF mainly comes from the redox reaction of the central metal ions and the large surface area of the active site.The combination of the two central metal ions into the MOFs structure can further improve the conductivity,while the enhanced oxidation state and synergies of the polymetallic components also contribute to improved electrochemical performance.In this paper,by growing NiCo-MOF and directionally fixing it on LDHs,a simple hydrothermal method was used to synthesize 3D interconnected layered structures NiMo-LDH@NiCo-MOF.The prepared NiMo-LDH@NiCo-MOF electrode not only provides enhanced conductivity and cyclic stability,but also obtains excellent specific capacitance,achieving excellent performance of 1536F·g^-1at 1 A·g^-1.In addition,NiMo-LDH@NiCo-MOF asymmetric supercapacitors have a corresponding power density of 797 W·kg^-1at a maximum energy density of 60.2Wh·kg^-1.（3）Using NiCo-MOF hollow spheres synthesized by solvothermal method as matrix material,NiMn-LDH nanosheets have successfully synthesized NiCo-MOF@NiMn-LDH with hollow core-shell structure under the support and guidance of matrix material.Thanks to its unique three-dimensional layered structure and electrochemical synergies between multiple metals,NiCo-MOF@NiMn-LDH has an abundance of active sites and ion diffusion channels,enhancing charge transfer capability.This composite material shows good electrochemical properties of 1692 F·g^-1at 1 A·g^-1in a three-electrode system.