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+O-2 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 degreesC was sufficient to produce crystalline beta-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 0 Is 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 2 3.4 V for the currentless circuit and a capacity of 34.5 mC/cm(2). 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. (C) 2003 American Vacuum Society.