LiCoPO4 thin films were deposited on Li1+x+y Al x Ti2−x Si y P3−y O12 (LATSP) solid electrolyte by radio frequency magnetron sputtering and were characterized by X-ray diffraction and scanning electron microscope. The films show a (111) preferred orientation upon annealing and are chemically stable with LATSP up to 600°C in air. An all-solid-state Li/PEO18-Li(CF3SO2)2N/LATSP/LiCoPO4/Au cell was fabricated to investigate the electrochemical performance and Li-ion chemical diffusion coefficients, D ˜ Li , of the LiCoPO4 thin films. The potential dependence of D ˜ Li values of the LiCoPO4 thin film was investigated by potentiostatic intermittent titration technique and was compared with those of the LiFePO4 thin film. These results showed that the intercalation mechanism of Li-ion in LiCoPO4 is different from that in LiFePO4.