The Electrochemical Performance of Bias-Sputter-Deposited Nanocrystalline Nickel Oxide Thin Films Toward Lithium

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Abstract
Nickel oxide (NiO) thin films have been deposited by reactive rf sputter deposition under O2∕ArO2∕Ar flow ratios of 1∕31∕3 and 3∕13∕1 . Negative electric bias was applied on the substrates during film deposition. The current-voltage characteristics measured on the copper substrate holder showed that the ions in the O2∕ArO2∕Ar mixture gas plasma can be effectively drawn to the substrate by negative bias. As the substrate bias increased, the films developed different crystallographic preferred orientation and surface morphology, as characterized by X-ray diffraction and scanning electron microscopy. The electrochemical properties of the nickel oxide thin-film anodes were tested and compared. The discharge cutoff voltage was set at 0.5 V to avoid film peeling due to stress accumulated in the NiO+Li∕∕Ni+Li2ONiO+Li∕∕Ni+Li2O redox process. Thin films with individualized nanoparticles (∼20nm)(∼20nm) on the surface showed a relatively lower first cycle capacity loss of 29%. For films with smooth and dense surface, a reversible capacity of ∼720mAh∕g∼720mAh∕g with near 100% capacity retention up to 30 cycles can be achieved.