The Effects of Substrate and Annealing on Structural and Electrochemical Properties in LiCoO₂ Thin Films Prepared by DC Magnetron Sputtering

LiCoO₂ thin films were fabricated by direct current magnetron sputtering method on STS304 and Ti substrates. The effects of substrate and annealing on their structural and electrochemical properties of LiCoO₂ thin film cathode were studied. Crystal structures and surface morphologies of the deposited films were investigated by X-ray diffraction and field emission scanning electron microscopy. The as-deposited films on both substrates have amorphous structure. The (104) oriented perfect crystallization was obtained by annealing over 600°C in STS304 substrate. The LiCoO₂ thin film deposited on Ti substrate shows the (003) texture after annealing at 700°C. The electrochemical properties were investigated by the cyclic voltammetry and charge–discharge measurement. The 600°C-annealed LiCoO₂ film deposited on STS304 substrate exhibits the inithial discharge capacity of 22 uAh/cm² and the 96% capacity retention rate at 50th cycles. The electrochemical measurement on annealed films over 600°C was impossible due to the formed TiO₂ insulator layer using Ti substrate. As a result, it was found that the STS304 substrate seems to be more suitable material than the Ti substrate in fabricating LiCoO₂ thin film cathode.