Preparation And Supercapacitor Properties Of Co₃O₄

Supercapacitor is an excellent energy storage device with high power density, high energy density, high charge-discharge efficiency, excellent reversibility, long cyclic performance and non-pollution. Transition metal oxides, such as MnO₂, NiO and Co₃O₄ have been investigated as supercapacitor material due to their redox pseudocapacitance and excellent electrochemical properties.In this study, Co₃O₄ supercapacitor electrode material was prepared by solid and liquid reaction methods, and was modified by doping with AI or La. The influence of electrolytes on Co₃O₄ electrode was studied. The structure of the sample analyzed by X-rays diffraction(XRD) and differential thermal analysis(DTA). The electrochemical performance was investigated by cyclic voltammetric measurements (CV), constant current charge/discharge measurements.The influence of solid reaction condition, such as calcination temperature and milling time on the electrode capacitance of the resulting cobalt oxide was investigated. The results shows that: cobalt oxides obtained at a milling time of 2h, calcined temperature of 400℃has the largest capacity of 73.25F·g^-1. Tests of the capacitance of Co₃O₄ in lmol/L electrolytes of KOH, LiOH and NaOH revealed that pseudocapacitance and properties of cobalt oxidea are not significiently influenced by cation. The specific capacitance of Co₃O₄ is 35.39F·g^-1, 37.01F·g_-1 and 32.06F·g^-1 in KOH, LiOH and NaOH solution, respectively. Electrochemical tests of Co₃O₄ in different concentration of KOH electrolyte showed that the higher the electrolyte concentration, the greater the specific capacitance, the specific capacitance reached up to 86.67F·g^-1 in the 5mol/L KOH solution.In the preparation of cobalt oxide using liquid phase reaction method, Co₃O₄, Na₂CO₃ and KOH were used as precipitating agent respectively. Capacitance of the resulting Co₃O₄ was studied. It was found that: with Co₃O₄ as precipitating agent, 3hs of reaction time, 50℃of reaction temperature, 400℃of calcined temperature, the resulting electrode material has the largest capacity of 81.72F·g^-1; with Na₂CO₃ as precipitating agent, 3hs of reaction time, 50℃of reaction temperature, 300℃of calcined temperature, the resulting electrode material has the largest capacity of 259.29F·g^-1; with KOH as precipitating agent, 5h of reaction time, 50℃of reaction temperature, 350℃of calcined temperature, the resulting electrode material has the largest capacity of 300.59F·g^-1.Co₃O₄ was doped with aluminum and lanthanum by chemical precipitation method, X-ray diffraction analysis indicated that doping with Al and La changed the crystal structure of Co₃O₄. When the mole ratio of Co(â…¡) with Al(â…¢)was 1:0.05, the specific capacitance was 1.64 times of that of pure Co₃O₄ electrode material; When the mole ratio of Co(â…¡) with La(â…¢)was 1:0.03, the specific capacitance was 1.80 times of that of pure Co₃O₄ electrode material; Clearly, doping Co₃O₄ with aluminum and lanthanum improved the capacitance of electrode material.