Cu (x) Co3 - x O-4 thin films (with x = 0, 0.1, 0.3, and 0.5) were successfully deposited on glass and indium-doped tin oxide substrates by the sol-gel method. Despite the observed enhancement in crystallinity, a decrease in ion capacity was observed with the increasing of annealing temperature, which was attributed to the suppression of the diffusion of the electrolyte ions into the films. It was also deduced that Cu doping resulted in a significant increase in capacity with a maximum value of 2.92E-02 C/cm(2) which was obtained for x = 0.3. The observed decrease in capacity after raising the x value from 0.3 to 0.5 was due to the formation of mixed spinel structure. The results also showed that the variation of optical absorption coefficient, optical band gap energy, electrical resistance, and doping density with x was consistent with the general characteristics of the formed mixed spinel structure when it exceeded x = 0.3.