Pseudo-capacitive properties of LiCoO2/AC electrochemical capacitor in various aqueous electrolytes

LiCoO2 particles were synthesized by a sol-gel process. X-ray diffraction analysis reveals that the prepared sample is a single phase with layered structure. A hybrid electrochemical capacitor was fabricated with LiCoO2 as a positive electrode and activated carbon (AC) as a negative electrode in various aqueous electrolytes. Pseudo-capacitive properties of the LiCoO2/AC electrochemical capacitor were determined by cyclic voltammetry, charge–discharge test, and electrochemical impedance measurement. The charge storage mechanism of the LiCoO2-positive electrode in aqueous electrolyte was discussed, too. The results showed that the potential range, scan rate, species of aqueous electrolyte, and current density had great effect on capacitive properties of the hybrid capacitor. In the potential range of 0–1.4 V, it delivered a discharge specific capacitance of 45.9 Fg–1 (based on the active mass of the two electrodes) at a current density of 100 mAg–1 in 1 molL–1 Li2SO4 aqueous electrolyte. The specific capacitance remained 41.7 Fg–1 after 600 cycles.