The rapid thermal annealing (RTA) process was employed to obtain crystalline LiCoO2 thin films. XRD analyses of the LiCoO2 thin film show increased crystallinity with an increase in the RTA time. The Auger electron spectroscopic analysis of the LiCoO2 film strongly suggests that the RTA process is more advantageous to obtain a stable inter layer between the substrate and the deposited film and between each deposited layer than the conventional annealing process. All-solid-state thin film cells composed of Li/lithium phosphorous oxynitride (Lipon)/LiCoO2 systems were fabricated using the LiCoO2 cathode treated with RTA. The optimum condition of RTA would be 900s at 650°C, which exhibited a good rate capability for high power applications. Two cells were connected in parallel to obtain a higher discharge current, and they showed a specific capacity of 38.4μAhcm−2 μm−1 even at a 25C rate (current density: 7.96mAcm−2).