Dependence of Al2O3 Coating Thickness and Annealing Conditions on Microstructural and Electrochemical Properties of LiCoO2 Film

Abstract

We studied the dependence of Al2O3 coating thickness and annealing conditions on the surface morphology and electrochemical properties of Al2O3 coated LiCoO2 films. The optimum coating thickness allowing for the highest capacity retention was about 24 nm. A sample consisting of Al2O3 coated on annealed LiCoO2 film with additional annealing at 400 degrees C had a uniform coating layer between the coating materials and cathode films. This sample showed the best capacity retention of similar to 91 % with a charge-cut off of 4.5 V after 30 cycles, while the bare cathode film showed a capacity retention of similar to 32 % under the same conditions. The formation of second phases such as Co-Al-O was observed in the coating films by X-ray photoelectron spectroscopy (XPS). The Co-Al-O containing samples showed a higher initial capacity because of their smaller grain size, but less capacity retention than the Al2O3 containing samples.