Research On The Fabrication And Supercapacitor Performance Of NiCoZn-Carbonate Hydroxides

With increasing the demand for energy resources,it is crucial to develop supercapacitors electrode materials with high specific capacity and excellent cycling stability.Transition metal-based carbonate hydroxides（M（CO₃）_x（OH）_y）（M=Fe,Zn,Ni,Co,and Mn,etc.）have excellent capacitive properties.Among them,carbonate ions(CO₃^2-)improve the wettability of the electrode surface,which help electrolyte penetration into the electrode material and facilitate ion transfer in the redox reaction.Some Ni Co-carbonate hydroxides（Ni Co-CH）morphologies with high specific capacity have been developed,such as nanoneedles,nanobelts,sea urchin-like,and flower-like morphologies.However,problems such as large volume change,poor cycling stability,and low electrical conductivity affect the energy storage capacity of Ni Co-CH.Compared with the above morphologies,the hollow structure provides a channel for electrolyte diffusion,enhances the contact area between electrolyte and electrode,and releases the stress to reduce the volume change during charging and discharging,ensuring the cycling stability of the electrode.The self-templated method can obtain hollow structures,which can eliminate heterogeneous growth,simplify the procedure,and better control the uniformity of the material.Elemental substitution is an effective method to further improve conductivity.The addition of appropriate amount of Zn element can accelerate electron and ion transfer and improve the electrochemical stability and activity of Ni Co-CH.In this paper,Ni Co Zn-glycerate（Ni Co Zn-G）solid spheres with Zn²⁺different additions of uniform size were prepared by the self-templated method using isopropanol and glycerol as the solvent and PVP as the size control agent.Then Ni Co Zn-glycerate solid spheres and urea were used as raw materials,and ethanol and water were used as mixed solutions to prepare Ni Co Zn carbonate hydroxides（Ni Co Zn-CH）by the solvothermal method.Ni₁Co₁Zn_0.25-G was prepared at 0.25 mmol Zn²⁺addition,and then Ni₁Co₁Zn_0.25-CH has the best electrochemical properties prepared by the solvothermal reaction of Ni₁Co₁Zn_0.25-G and 6 mmol urea.In the three-electrode system test,Ni₁Co₁Zn_0.25-CH shows a high specific capacity of 792.6 C g^-1 at 1 A g^-1 and good cycling stability(87.9%capacitance retention after 10000 cycles at 10 A g^-1).Ni₁Co₁Zn_0.25-CH as the positive electrode and activated carbon（AC）as the negative electrode were used to assemble Ni₁Co₁Zn_0.25-CH//AC asymmetric supercapacitors.Ni₁Co₁Zn_0.25-CH//AC has an excellent cycle stability of 99.9%after 15000 cycles at 10 A g^-1 and a good energy density of 33.7 Wh kg^-1 at a power density of 400 W kg^-1.