Thin-film lithium batteries with 0.3–30 μm thick LiCoO₂ films fabricated by high-rate pulsed laser deposition

High-rate pulsed laser deposition was applied to the preparation of thick LiCoO₂ cathode films, which were then used in the fabrication of thin-film batteries. The deposition rate of the LiCoO₂ films was 2–3 μm/h. The thin-film batteries showed an increase in capacity up to 470 μAh/cm² with increasing cathode film thickness. The rate dependence of discharge capacity was analyzed using a diffusion model in which the chemical diffusion coefficient of lithium in the cathode determines the dynamic capacity. For the initial stage of discharge, the chemical diffusion coefficient was estimated to be 10⁻¹⁰ cm²/s. Conversely, the chemical diffusion coefficient decreases to ~10⁻¹² cm²/s at the end of discharge. From the diffusion model, the available capacity was estimated as a function of cathode thickness. Crack formation inside the LiCoO₂ film is also suggested as a cause of capacity limitation.