Preparation And Electrochemical Properties Of Ni-Co Based Supercapacitor Electrode Materials

With the increase of fossil energy consumption and energy demand,high-performance supercapacitors have attracted the attention of researchers because of their high specific power,rapid charge-discharge ability and excellent stability.In this paper,the preparation and morphology control of supercapacitor electrode materials are studied.In order to improve the electrochemical performance of supercapacitor electrode materials,various kinds of electrodes and composite materials with different binding methods are prepared.In this paper,transition metal nickel/cobalt oxide/sulfide are selected as the basic research object.(1)In the first section,we developed a novel and facile strategy through sacrificing ZnO template,and prepared a self-supporting nanostructure.The introducing of holes increases the contact surface of electrode material and electrolyte,facilitates ionic diffusion,and alleviates the stress generated in reaction.The obtained materials benefitted from the unique hollow structure,good stability and low resistance achieved by the use of the binder-free self-supporting method,exhibited a large electrochemical capacity of 748.1 C g-1 at 1 A g-1,which was higher than that of pure Co3O4 directly grown on the substrate without adding Zn2+as template.Furthermore,a hybrid Zn@Co//activated carbon(AC)supercapacitor device reached a specific energy of 60.91 Wh kg-1 at a specific power of 450 W kg-1.(2)Second,we report the preparation of an effective and novel NiCo2O4 dendritic structure with nanothorn arrays,using a stepwise,bottom-up hydrothermal and self-sacrificial template method.Rod-like ZnO is synthesized on Ni foam as self-sacrificing template,and Ni-Co-based precursor is grown on it through a hydrothermal method.NiCo2O4 dendritic crystals are obtained by alkali etching of the template and calcination,which significantly enhance its performance on electrochemical energy storage.Although the ZnO matrix is removed by alkali etching,it provides a basis for the growth of Ni-Co oxide.The obtained material can be directly used as electrode material without further processing,offering the benefit of unique structural advantages and low electron transmission resistance,as there is no need to use a binder.The as-obtained NiCo2O4 nanothorn electrode exhibits excellent electrochemical performance.It shows ultrahigh specific capacitance of 1534 C g-1 at 1 A g-1 current density,good rate discharge performance(75.8%retention from 0.5 A g-1 to 5 A g-1),values superior to those of nanothorn NiO,Co3O4 and bare NiCo2O4 nanosheet structures and excellent cycling ability(83%retention after 5000 cycles).The as-assembled NiCo2O4//AC hybrid supercapacitor device also exhibits high energy density of 64.1 Wh kg-1 at the power density of 450 W kg-1.(3)In the third section,we report a novel Ni3S2 carbon coated(denoted as NCC)rod-like structure prepared by a facile one-pot hydrothermal method and employ it as a binder free electrode in supercapacitor.We coated carbon with glucose as carbon source on the surface of samples and investigated the suitable glucose concentration.The as-obtained NCC rod-like structure demonstrated great performance with a huge specific capacity of 657 C g-1 at 1 A g-1,preeminent rate capability of 87.7%retention,the current density varying to 10 A g-1,and great cycling stability of 76.7%of its original value through 3500 cycles,which is superior to the properties of bare Ni3S2.The result presents a facile,general,viable strategy to constructing a high-performance material for the supercapacitor applications.