Low Temperature Deposition of Polycrystalline Lithium Transition Metal Oxide Thin Films for Micro Batteries

Abstract

The choices of substrates for lithium micro batteries or thin film batteries have been limited by the high annealing temperatures, which are generally required in the fabrication of polycrystalline thin film cathodes. In this paper, a plasma assisted technique has been developed for low temperature fabrication of polycrystalline lithium transition metal oxides as thin film cathodes. The thin films were deposited by magnetron sputtering, followed by thermal annealing and plasma treatments. By applying plasma treatments, polycrystalline films of LiCoO2, LiMn2O4 and LiFePO4 have been obtained under relatively lower annealing temperatures (<400 oC). The low temperature prepared films with/without plasma treatments were compared in terms of morphologies, crystal structures and electrochemical performances. It was found that the plasma treatments lifted the discharge voltages and increased the capacity of the low temperature prepared films. The results have demonstrated the feasibility of fabricating thin film batteries on polymers or glass substrates, which generally can only endure temperatures lower than 400 oC.