Preparation And Electrochemical Performance Of Nickel-cobalt Double Hydroxide Composite

Transition metal layered double hydroxide（LDH）with high theoretical specific capacity and abundant redox active centers are considered as ideal cathode materials for asymmetric supercapacitors,but limited specific surface area and low conductivity hinder the improvement of electrochemical performance.Metal Organic Frameworks（MOFs）are porous materials containing metal ions and organic ligands,and their high porosity and large surface area provide pseudocapacitive active centers,which are perfect precursors for the fabrication of various derivatives such as nano porous carbon,metal oxides,metal hydroxides and mixed metal oxides.Therefore,in order to improve the specific capacitance,rate performance and electrical conductivity of NiCo-LDH electrode material,this paper prepared nickel-cobalt hydroxide using Zeolite-like imidazole frameworks（ZIFs）precursors,and constructed heterojunction composite material by vulcanization to improve the electrochemical performance of electrode material.The effects of the ratio of precursors to nickel source and the amount of thioacetamide on the structure and electrochemical properties of electrode materials were studied.（1）Co-ZIF-L was prepared by hydrothermal method as a metal precursor,and NiCo-LDH nanosheets were prepared by one-step ion exchange and coprecipitated method at room temperature.Then NiCo-LDH/Co₃S₄ composites with heterogeneous structures were constructed by controlling the amount of sulfur source.The large surface area of the composite material provides more active sites for the pseudocapacitance reaction,so that NiCo-LDH/Co₃S₄ can obtain high specific capacitance and good magnification performance.The specific capacitance of NiCo-LDH/Co₃S₄ is 1456.2 F g^-1 at a current density of 1 A g^-1 and 1240.4 F g^-1 at a high current density of 10 A g^-1,giving a specific capacitance retention of 85.2%.In addition,the assembled asymmetric supercapacitor（NiCo-LDH/S-100//AC）has an energy density of 35.21Wh kg^-1 when the power density is 749.98 W kg^-1,which has good potential for practical application.（2）Nano-scale three-dimensional polyhedral ZIF-67 precursor was prepared by room temperature precipitation method.With ZIF-67 as precursor,interleaved NiCo-LDH nanosheets were prepared by solvothermal method and ion exchange reaction.Then,NiCo-LDH nanosheets were used as the base.NiCo-LDH/NiS₂ composites with reinforced specific capacitance were prepared by vulcanization.The composite has a rich mesoporous structure,which can expose more reaction sites and facilitate the accelerated electrochemical reaction process,and the large specific surface area and pore capacity enable it to exhibit high specific capacitance and excellent multiplicative performance.NiCo-LDH/NiS₂ electrode material obtained a high specific capacitance of 1713.2 F g^-1 at a current density of 1 A g^-1 and a specific capacity of 1331.4 F g^-1 at a high current density of 30 A g^-1,with a retention rate of77.7%.The asymmetric supercapacitor（NiCo-LDH/NiS₂//AC）assembled with activated carbon as the negative electrode obtained energy density of 52.6 Wh kg^-1 at a power density of 750 W kg^-1 and 12.94 Wh kg^-1 at a high-power density of 15000 W kg^-1.