Stoichiometry Dependence of Physical and Electrochemical Properties of the SnOx Film Anodes Deposited by Pulse DC Magnetron Sputtering

A batch of Sn oxides was fabricated by pulse direct current reactive magnetron sputtering (pDC−RMS) using different Ar/O2flow ratios at 0.3 Pa; the influence of stoichiometry on the physical and electrochemical properties of the films was evaluated by the characterization of scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray reflection (XRR), X-ray photoelectron spectroscopy (XPS) and more. The results were as follows. First, the film surface transitioned from a particle morphology (roughness of 50.0 nm) to a smooth state (roughness of 3.7 nm) when Ar/O2flow ratios changed from 30/0 to 23/7; second, all SnOxfilms were in an amorphous state, some samples deposited with low O2flow ratios (≤2 sccm) still included metallic Sn grains. Therefore, the stoichiometry of SnOxcalculated by XPS spectra increased linearly from SnO0.0.08to SnO1.71as the O2flow ratios increased, and the oxidation degree was further calibrated by the average valence method and SnO2standard material. Finally, the electrochemical performance was confirmed to be improved with the increase in oxidation degree (x) in SnOx, and the SnO1.71film deposited with Ar/O2= 23/7 possessed the best cycle performance, reversible capacity of 396.1 mAh/g and a capacity retention ratio of 75.4% after 50 cycles at a constant current density of 44 μA/cm2.Keywords:tin oxide film;reactive magnetron sputtering;oxygen vacancy;cycle performance