Effect of Li_0.5La_0.5TiO₃ solid electrolyte films on electrochemical properties of LiCoO₂ thin film cathodes with different rapid-thermal annealing conditions

The structural and electrochemical properties of LiCoO₂ (LCO) cathode films grown at 500 °C and Li_0.5La_0.5TiO₃ (LLTO) solid electrolyte films at room temperature by pulsed laser deposition were investigated by a rapid-thermal annealing (RTA) treatment. The LCO films annealed for 1 min at 700 °C showed the most superior crystallinity and the LLTO films grown on LCO at room temperature maintained an amorphous phase after RTA treatment for 5 min up to 700 °C. The highest initial discharge capacity and capacity retention were obtained in Li/LiCoO₂ cells annealed for 1 min at 700 °C. The RTA treatment is effective in improvement of an interface property and surface morphology of the LLTO films grown at room temperature on LCO. The LCO/Pt cells exhibit an initial discharge capacity of approximately 53 μA h cm^-2 μm and a capacity retention of 73% at 100 cycles. The LLTO/LCO/Pt cells treated at 700 °C for 5 min in an oxygen ambient by RTA exhibited an improvement of a capacity retention as high as 96.1% at 100 cycles.