LiCoPO 4 thin films were deposited on Li 1+x+y Al x Ti 2−x Si y P 3−y O 12 (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/PEO 18 -Li(CF 3 SO 2 ) 2 N/LATSP/LiCoPO 4 /Au cell was fabricated to investigate the electrochemical performance and Li-ion chemical diffusion coefficients, D˜Li, of the LiCoPO 4 thin films. The potential dependence of D˜Li values of the LiCoPO 4 thin film was investigated by potentiostatic intermittent titration technique and was compared with those of the LiFePO 4 thin film. These results showed that the intercalation mechanism of Li-ion in LiCoPO 4 is different from that in LiFePO 4 .