Study of Vanadium Oxides at Different Oxygen Flows Prepared by Reactive Magnetron Sputtering and its Evaluation as Cathodes for Lithium Batteries

Vanadium pentoxide has intrinsic properties which allow it to obtain electrothermal and thermochemical stability [1]. One of the manufacturing techniques that allow obtaining low thicknesses, homogeneity, and control of the microstructure, is the reactive sputtering magnetron process which also allows to generate different stoichiometries of vanadium oxides and specifically V₂O₅ [1, 2]. The formation of different vanadium oxides mainly depends on the oxygen content of the system [3]. The aim of this work is the study of the effect of oxygen on argon plasma during the process of reactive sputtering and the further influence on the electrochemical performance as electrode. The samples were prepared by DC reactive magnetron sputtering using different oxygen flows and deposited over stainless steel at room temperature. The target was metallic vanadium, while the plasma was argon (15 sccm) combined with oxygen at 1.25, 1.75, 2.25, 2.5, 3.0 and 3.25 sccm. The deposition process was monitored by optical emission spectroscopy (OES), and the samples were characterized by XRD, EDS, Raman confocal spectroscopy, XPS and AFM. In the study of plasma at a constant power of 150W, the OES spectrum exhibited the emission lines of vanadium (458 nm), oxygen (777 nm) and argon (811 nm), showing that the intensity of the V and Ar lines decrease with the increase of oxygen. XRD results demonstrated that the samples were amorphous for all the different oxygen flows. Raman analysis indicated for the sample deposited at 3 sccm, the presence of the V-O-V bonding corresponding to a crystalline structure of the rhombohedral type of V₂O₅, by the vibrational stretching modes (143 cm^-1), and of the V=O bonding by the second flexion vibrational band (995 cm^-1). XPS established a correlation between the oxygen flow and the main V oxidation state: V⁺⁴ at 1.25 O-flow, V⁺⁴/V⁺³ at 1.75 O-flow and V⁺⁵ over 2.5 O-flow. A capacity of 280 mAh/g at 1C is observed in the sample with higher oxygen flow in contrast to the samples with lower oxygen flow.<br/><br/><b>References</b><br/>[1] M. Panagopoulou <i>et al</i>., The Journal of Physical Chemistry C, <b>121</b>(1), 70–79(2016).<br/>[2] D. Wruck, S. Ramamurthi <i>et al</i>., Thin Solid Films, <b>182</b>(1-2), 79–86(1989).<br/>[3] L.-J. Meng, R.A. Silva <i>et al</i>., Thin Solid Films, <b>515</b>(1), 195–200(2006).