Effect of Ti-Doped Al2O3 coating thickness and annealed condition on microstructure and electrochemical properties of LiCoO2 thin-film cathode

Abstract

We investigated the dependence of the various annealing conditions and thickness (6-45 nm) of the Ti-doped Al2O3 coating on the electrochemical properties and the capacity fading of Ti-doped Al2O3 coated LiCoO2 films. The Ti-doped-Al2O3-coating layer and the cathode films were deposited on Al2O3 plate substrates by RF-magnetron sputter. Microstructural and electrochemical properties of Ti-doped-Al2O3-coated LiCoO2 films were investigated by transmission electron microscopy (TEM) and a dc four-point probe method, respectively. The cycling performance of Ti-doped Al2O3 coated LiCoO2 film was improved at higher cut-off voltage. But it has different electrochemical properties with various annealing conditions. They were related on the microstructure, surface morphology and the interface condition. Suppression of Li-ion migration is dominant at the coating thickness >24 nm during charge/discharge processes. It is due to the electrochemically passive nature of the Ti-doped Al2O3 films. The sample be made up of Ti-doped Al2O3 coated on annealed LiCoO2 film with additional annealing at 400°C had good adhesion between coating layer and cathode films. This sample showed the best capacity retention of ∼92% with a charge cut off of 4.5 V after 50 cycles. The Ti-doped Al2O3 film was an amorphous phase and it has a higher electrical conductivity than that of the Al2O3 film. Therefore, the Ti-doped Al2O3 coated improved the cycle performance and the capacity retention at high voltage (4.5 V) of LiCoO2 films.