Stoichiometry dependence of electrochemical performance of thin-film SnOx microbattery anodes deposited by radio frequency magnetron sputtering

Thin-film SnOx microbattery anodes, with various oxygen deficiencies, are deposited from a SnO2 target on to an ambient temperature substrate by radio frequency (RF) magnetron sputtering. The high reversible capacity and cycle performance characteristics of SnOx are described. RF power density and process gas pressure during deposition are fixed at 2.5 W/cm2 and 10 mTorr, respectively. The SnOx films are characterized by energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Constant-current galvanostatic charge–discharge tests of half cells are also performed. The stoichiometric parameter x increases with the increase in oxygen partial pressure, but decreases when the number of Sn chips placed on the target material in an argon atmosphere are increased. It is observed that SnOx transforms to lithium oxide and metallic Sn after an initial Li intercalation reaction. The charge–discharge performance of the tin oxide films is found to be dependent on stoichiometry. In the present work, SnO1.43 is the optimum stoichiometry, exhibiting the highest reversible capacity (498.33 μA h/cm2 μm) and the lowest irreversible capacity (301.79 μA h/cm2 μm).