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.