Atomic Layer Deposition of Alumina-Coated Thin-Film Cathodes for Lithium Microbatteries

This work shows the electrochemical performance of sputter-deposited, binder-free lithium cobalt oxide thin films with an alumina coating deposited via atomic layer deposition for use in lithium-metal-based microbatteries. The Al2O3 coating can improve the charge-discharge kinetics and suppress the phase transition that occurs at higher potential limits where the crystalline structure of the lithium cobalt oxide is damaged due to the formation of Co4+, causing irreversible capacity loss. The electrochemical performance of the thin film is analysed by imposing 4.2, 4.4 and 4.5 V upper potential limits, which deliver improved performances for 3 nm of Al2O3, while also highlighting evidence of Al doping. Al2O3-coated lithium cobalt oxide of 3 nm is cycledam at 147 &A cm(-2) (similar to 2.7 degrees C) to an upper potential limit of 4.4 V with an initial capacity of 132 mAh g(-1) (65.7 mu Ah cm(-2) & m(-1)) and a capacity retention of 87% and 70% at cycle 100 and 400, respectively. This shows the high-rate capability and cycling benefits of a 3 nm Al2O3 coating.