Preparation Of Cobalt-based Nanomaterials For Hybrid Supercapacitor Application

With the increasing population and the depletion of energy,people are eager to develop many renewable energy sources to meet their needs for life.As one of the new energy storage components,supercapacitor has wide prospects in practical applications due to their excellent performance.As one of the types of supercapacitor,hybrid supercapacitor stands out due to its advantages such as high energy density and fast charge and discharge rate.So,hybrid supercapacitor has become a research focus in energy storage.Hybrid supercapacitor is mainly composed of a battery-type positive electrode material,a capacitive negative electrode material,and an electrolyte.Among them,the electrode material has a great impact on the performance of supercapacitors.Battery-type electrode materials reduce the stability of their supercapacitors due to volume expansion during the charge and discharge process,thereby reducing their energy storage performance.In order to solve the problem of battery-type positive electrode materials,this master thesis is mainly based on cobalt-based nanomaterials with high theoretical specific capacitance,and various aspects of improvement are used to prepare positive electrode materials with high electrochemical performance,thereby improving hybrid supercapacitors performance.The specific research content mainly includes the following three aspects:（1）cobalt nickel hexacyanoferrate with Prussian blue structure was synthesized on nickel foam by co-precipitation method（named as Ni₂CoHCF/NF）.Because of its porosity and unique structure with large specific surface area,it facilitates the rapid migration of alkali metal ions and can be used as an intercalation type material for alkali metal ions.It was subjected to a series of electrochemical tests in a 2 M KOH solution.The results show that the specific capacitance of cobalt nickel hexacyanoferrate can reach 585.0 C g^-1(1300.0 F g^-1)at the current density of 0.5 A g^-1.Its specific capacitance can maintain the initial specific capacitance of 85.57%at a current density of 10 A g^-11 after 2000 cycles.Ni₂CoHCF/NF//AC/NF hybrid supercapacitor was assembled with cobalt nickel hexacyanoferrate as the positive electrode material.After 2000 cycles,the specific capacitance still retains the initial specific capacitance of 94.32%at the current density of2 A g^-1,indicating that the hybrid supercapacitor has excellent cycle stability.（2）The zinc-cobalt flower-shaped nanosphere precursor was grown on nickel foam by hydrothermal method,and then the Zn-Co-S-P electrode material（ZnCoSP/NF）with porous network structure composed of nanosheets was synthesized by sulfurization and phosphating treatment.Compared with ZnCoS/NF and ZnCoP/NF,ZnCoSP/NF has a highest specific capacity.The specific capacitance of ZnCoSP/NF is 835.8 C g^-1(1857.6 F g^-1)at the current density of 1 A g^-1.ZnCoSP/NF has been tested for 3000 charge and discharge cycles,the specific capacitance of the electrode material can still maintain the initial specific capacitance of 82.18%at the current density of 10 A g^-1.The ZnCoSP/NF//AC/NF hybrid supercapacitor can maintain 91.64%of the initial specific capacitance after 5000 cycles at a current density of 2 A g^-1,indicating that it has good cyclic stability.At the power density of 387.0 W kg^-1,the energy density of the hybrid supercapacitor can reach 32.78 Wh kg^-1,indicating that the hybrid supercapacitor has excellent electrochemical performance.（3）Co₂Mn nanoneedle were synthesized on nickel foam by hydrothermal method,and then Co₂Al layered double hydroxide nanosheets was supported on Co₂Mn nanoneedle by hydrothermal method to prepare Co₂Al/Co₂Mn nanocomposites,which avoids the addition of conductive agent and binder during subsequent assembly of hybrid capacitors.Co₂Al/Co₂Mn nanocomposite reduces the electrode internal resistance,and enhances charge transport capabilities,which in turn improves the electrochemical performance of the nanocomposite.When the current density is 1 A g^-1,the specific capacitance of the nanocomposite can reach 1125.9 C g^-1(2502.0 F g^-1).The specific capacitance of the Co₂Al/Co₂Mn/NF electrode material still maintains the initial specific capacitance of82.53%at a current density of 20 A g^-1after 6000 cycles.The constructed Co₂Al/Co₂Mn/NF//AC/NF hybrid supercapacitor has excellent cycle stability.Its specific capacitance could maintain the initial of 92.21%after 7000 cycles at a current density of 4A g^-1.When the power density is 412.73 W kg^-1,the energy density of the hybrid supercapacitor can reach 64.58 Wh kg^-1.It shows that the material has excellent electrochemical properties and has certain prospects in practical applications.