Study of Amorphous Vanadium Oxide Cathodes for Li-Ion Batteries Prepared by Reactive Magnetron Sputtering

Within the technological development focused on lithium-ion batteries, vanadium pentoxide (V₂O₅) thin films have been a good candidate to be used as cathodic material due to their high-capacity charge, allowing to increase in the efficiency of lithium-ion batteries [1]. The technique of reactive magnetron sputtering allows the manufacture of homogenous thin films with low thicknesses and specific microstructure. In addition, with this technique we can generate different stoichiometries of vanadium oxides and specifically of V₂O₅ [2-3]. The formation of different vanadium oxides mainly depends on the oxygen content of the system [4]. The aim of this work is based on the preparation of thin films of vanadium oxides on steel substrate by reactive sputtering at different oxygen flows followed by reduction with hydrogen <i>in situ</i>, and their electrochemical evaluation as a potential cathode material. 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 samples were characterized by XRD, EDS, Raman confocal spectroscopy, XPS and AFM. Cyclic voltammograms, the charge/discharge processes and cyclability of batteries were studied. XRD results demonstrated that the samples were amorphous for all the different oxygen flows. Raman analysis indicated 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) for the sample deposited at 3.0 sccm of oxygen. XPS established a correlation between the oxygen flow and the main V oxidation state: V⁺⁴at 1.25 O-flow, V⁺⁴/V⁺³at 1.75 O-flow, and V⁺⁵ over 2.5 O-flow. The sample of 3.0 sccm of oxygen at 1 hour of deposition has a capacity of 295 mAh/g with a charge retention percentage of 96.5% at 50 charge/discharge cycles at 1C. The electrochemical behavior of the samples in reduction with hydrogen, shows a better retention percentage of 99.9% at 50 charge/discharge cycles at 1C, but not an improvement in the charge and discharge capacity, which is 213 mAh/g for the sample of 3.0 sccm of oxygen at 8% pf H₂.<br/><br/>We acknowledge the financial support of the national fellowship sponsored by ANID.<br/><br/><b>References</b><br/>[1] R. Marom, S.F. Amalraj, N. Leifer, D. Jacob, D. Aurbach, J. Mater. Chem. 21 (2011) 9938-9954.<br/>[2] H. Song, C. Liu, C. Zhang, G. Cao, Self-doped V4+-V2O5 nanoflake for 2 Li-ion intercalation with enhanced rate and cycling performance. Nano Energy. 22, 1–10 (2016).<br/>[3]Kim TA, Kim JH, Kim MG, Oh SM (2003) Li + storage sites in amorphous V2O5 prepared by precipitation method. J Electrochem Soc 150(7): A985–A9A9.<br/>[4] L.-J. Meng, R.A. Silva <i>et al</i>., Thin Solid Films, 515(1), 195–200(2006).