Investigation of oxide (V₂O₅) thin films as electrodes for rechargeable microbatteries using Li

V₂O₅ thin films were prepared by reactive rf sputtering and used in the application as electrodes in rechargeable battery with Li as a counterelectrode. The V₂O₅ films were deposited onto uncoated and SnO₂ coated glass by sputtering a V cathode using Ar+O₂ gas mixtures. The structural properties of the V₂O₅ films were characterized by x-ray diffraction, infrared spectroscopy, and photoelectron spectroscopy (XPS: x-ray induced and UPS: UV induced photoelectron spectroscopy). Microbatteries were constructed using the V₂O₅ thin films as cathode, LiClO₄+propylene carbonate as the electrolyte and Li metal as the anode. The V₂O₅ electrodes were characterized by there electrochemical behavior (current–voltage curves during charging and recharging). X-ray diffraction measurement demonstrated that unannealed V₂O₅ films were amorphous with no sharp reflexes. Annealing to 350 °C was sufficient to produce crystalline β-V₂O₅ (monoclinic) on uncoated glass or orthorhombic V₂O₅ on SnO₂ coated glass. XPS spectra revealed the expected V/O ratio and line positions. However, the O 1s peak was split into two components, one from the - - V₂O₅ component (530.4 eV), the other at 532.9 eV is attributed to the uptake of water from the atmosphere. The charged microbattery resulted in a maximum voltage of 3.4 V for the currentless circuit and a capacity of 34.5 mC/cm². With XPS we could demonstrate the migration of Sn (from the conductive coating of the glass substrate) into the V₂O₅ layer for the Li intercalated electrodes. Further, UPS spectra from charged and uncharged V₂O₅ indicate band-gap changes due to the Li uptake. © 2003 American Vacuum Society.