Study On The Preparation And Electrochemical Performances Of Zinc Cobaltite Electrode Materials

Supercapacitors?SCs?possess some distinctive virtues including high power density,fast charge-discharge rate,long-term cycling life,and environmental friendliness,and are widely applied in both hybrid electric vehicles and backup sources.Therefore,the synthesis of electrode materials with superior electrochemical properties is one of the hot research directions.ZnCo₂O₄ is regarded as a promising electrode material used in SCs field due to its high theoretical specific capacitance(2604 F g^-1).However,the further practical application of ZnCo₂O₄ electrode material will be impeded because of the disadvantage of lower conductivity.To solve this problem,synthesizing the materials in micro-/nanoscale and combinating with other materials are very effective methods.?1?Porous ZnCo₂O₄ nanosheets and microspheres were successfully synthesized in water-ethylene glycol?EG?mixed solvent via a simple solvothermal method,and their specific surface areas were 54.4 and 7.7 m² g^-1,respectively.The effects of experimental parameters such as reaction temperatures and reaction times on the morphologies and sizes of the samples were also investigated.Electrochemical tests showed that ZnCo₂O₄ nanosheets electrode possessed a specific capacitance of 1016 F g^-1 at 1 A g^-1 and a good rate capability(81.4%at 15 A g^-1).The specific capacitance of ZnCo₂O₄ nanosheets electrode remained73.2%of its initial value after 2900 cycles at 5 A g^-1.ZnCo₂O₄ microspheres electrode delivered a specific capacitance of 588 F g^-1 at 1 A g^-1 and favorable rate capability of 84%at15 F g^-1.After 5000 cycles at 8 A g^-1,68.4%capacitance retention could be obtained.?2?We successfully prepared urchin-like ZnCo₂O₄ microspheres by solvothermal method,and also discussed the the influence of solvent ratios on the morphology and size of the final products.The electrochemical performances of urchin-like ZnCo₂O₄ microspheres?S1?and ZnCo₂O₄ layered quasi-microcubes?S2?electrodes synthesized at different H₂O/ethanol solvent ratios?1:3 and 3:1?were studied to further demonstrate the effect of the morphology of electrode material on the electrochemical performance.The specific capacitances of the S1 and S2 electrode materials were 677 and 612 F g^-1 at 1 A g^-1,respectively.The rate capabilities of the S1 and S2 electrode materials were 77.5%and 76.5%at 15 A g^-1.The S1 electrode material illustrated a better cycling performance?107.3%capacitance retention?than S2 electrode material?88.1%?after 5000 cycles at 5 A g^-1.Electrochemical tests indicated that the hierarchical structure of electrode material improved the electrolyte penetration and ion diffusion,and then enhanced the electrochemical properties.?3?The snowflake-like ZnCo₂O₄/ZnO microstructures with a BET specific surface area of32.3 m² g^-1 were rapidly synthesized through a simple hydrothermal method at low temperature.The influences of urea dosages,reaction temperatures and calcination temperatures on the morphology and size of the product were investigated.The snowflake-like ZnCo₂O₄/ZnO composite possessed a high specific capacitance(827 F g^-1 at 1A g^-1),outstanding rate capability(69.6%at 15 A g^-1),and good long-term cycling stability(68.7%capacitance retention during a 5000 charge/discharge cycling process at 5 A g^-1),indicating an outstanding electrochemical performance of ZnCo₂O₄/ZnO composite.