Intercalation of lithium in r.f.-sputtered niobium oxide film as electrode material for lithium-ion batteries

Vanadium oxide films were prepared by r.f.-sputtering using an argon sputter gas and a V2O5 target. The films were characterized by scanning electron microscopy, atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical techniques. The oxide film as deposited is amorphous; they are heat-treated in the range 300–700°C in oxygen atmosphere and are composed of orthorhombic V2O5 crystals. At higher heat-treatment temperatures (600–700°C) the crystallization of the oxide proceeded significantly with ab-direction parallel to the substrate. The oxide film undergoes a reversible lithium intercalation and deintercalation process. The kinetics of the intercalation process of lithium into amorphous V2O5 film was studied using an a.c. impedance method. Furthermore, a rocking-chair type V2O5 film/LixV2O5 film cell could be charge–discharge cycled over 300 times at a current of 10μA at 25°C.