Lithium cobalt oxide thin films deposited at low temperature by ionized magnetron sputtering

Abstract

Thin films of lithium cobalt oxides have been deposited by ionized magnetron sputter deposition with and without substrate heating. The technique uses a built-in radio frequency coil to generate an inductively coupled plasma (ICP) confined close to the substrate. The ICP plasma results in ion bombardment on the film surface, which serves as an extra energy input during film growth. Therefore, the film properties can be modified at a relatively lower temperature. The plasma irradiation induces variations of crystallography and morphology, as characterized by X-ray diffraction and scanning electron microscopy. The deposited films were tested as cathodes for lithium batteries, and the discharge curves were measured to compare the electrochemical properties of the deposited films. Applying suitable plasma irradiation, well crystallized LiCoO 2 phase was obtained at 350 °C (substrate temperature), which was much lower than the temperature (700 °C–750 °C) for conventional post anneal process. The LiCoO 2 films, fabricated under in-situ plasma irradiation and a relatively lower substrate temperature (350 °C), showed a discharge potential plateau at 4.3 V–3.8 V with a capacity of ∼ 110 mAh/g as discharged to 1.5 V.