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

Niobium oxide films have been prepared by r.f. sputtering using an argon sputter gas and a Nb2O5 target; the oxide films have been characterized by scanning electron microscopy, X-ray diffraction method and electrochemical techniques. The oxide film heat-treated at 500 to 700 °C in argon atmosphere is a monoclinic Nb2O5 highly oriented along the c-axis perpendicular to the substrate. The oxide film undergoes a reversible lithium intercalation and de-intercalation process. The kinetics of the intercalation process of lithium into the highly oriented Nb2O5 film was studied using an a.c. impedance method. Furthermore, a rocking-chair-type V2O5 film/Li2Nb2O5 film cell could be charge/discharged over 50 times at a current of 10 μA at 25 °C.