Study On The Microstructure Control And Electrochemical Properties Of Nickel/Cobalt-based Electrode Materials

Supercapacitor is a new type of energy storage device between traditional capacitor and batteries.It has much higher power density than batteries,widely used in application requiring extremely fast charge and discharge.In order to improve the energy density of supercapacitors,the use of battery-type electrode materials with high theoretical specific capacity has been considered as an effective strategy.However,its poor rate-performance and extremely low cycle stability are the main obstacles to its research.In this paper,nickel-based battery-type electrode materials with high theoretical specific capacity are studied.Electrode materials with high cycle stability and high rate performance are obtained by adjusting the microstructure of materials,optimizing the composition of materials and doping ions.The main research contents and results of this paper are as follows:(1)Preparation and properties of PVP/G Ni-Co LDH nanosheets:high shear mixer was used to prepare graphene,which was stabilized in aqueous solution through the hydrophobic chain in polyvinylpyrrolidone surfactant.High shear mixer was used to strengthen the role of micromixing,and Ni-Co LDH with different Ni/Co ratios was uniformly compounded with graphene to form a rigid staggered nanosheet structure,The structure increases the specific surface area of the material,improves the stability of the structure,alleviates the volume expansion and contraction effect,improves the conductivity of graphene and improves the rate performance of the material.The specific capacity of the material remains66%of its initial value at current density of 62.5 A g^-1.(2)Preparation and properties of NiCo₂S₄ hollow spheres hierarchical nanostructure:The Ni S/Ni S₂ with hollow structure was prepared following the Oswald ripening mechanism and using nickel citrate as precursor.The pores in the hollow structure of NiCo₂S₄ are beneficial to the entry of electrolyte.The dense particle layer in the shell alleviates the electrochemical stress of the electrode material during the charge discharge cycle due to enhanced mechanical strength.At the same time,the doping of Co ions adjusts the energy band structure and accelerate the transfer of electrolyte ions.Therefore,the excellent rate performance and cycle stability are obtained.After 10000 charge-discharge cycles at 5.0 A g^-1 current density,NiCo₂S₄ keeps 92.3%of its initial capacity.(3)Preparation and electrochemical properties of Co(OH)₂ pseudocapacitor material:hollow structured Co₃O₄ was prepared by calcining the cobalt citrate precursor.The Co₃O₄containing oxygen vacancy was prepared by reducing Co₃O₄ with Na BH₄.The Co₃O₄containing oxygen vacancy was vulcanized at room temperature to S^2-doped Co(OH)₂.The electrochemical behavior of Co(OH)₂ is tranformed from battery type to pseudocapacitive behavior.