ELECTROCHEMICAL LITHIUM INTERCALATION REACTION OF ANODIC VANADIUM-OXIDE FILM

The electrochemical lithium intercalation reaction of anodic vanadium oxide films in 1 M LiClO4 propylene carbonate solution has been investigated by the galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) as a function of electrode potential. Measured impedance spectra were analysed using the complex nonlinear least-squares (CNLS) fitting method. The impedance spectra measured in the potential range from 3.6 to 2.6 V-Li/Li+ showed that the electrochemical intercalation reaction of lithium ions into the anodic vanadium oxide film consists of three consecutive steps of charge transfer at the electrolyte-oxide Nm interface, lithium ion incorporation into the oxide film and diffusion through the oxide film. The charge transfer reaction at the electrolyte-anodic vanadium oxide film interface is mainly affected by the valence change of vanadium ions in the anodic vanadium oxide film. In the electrode potential range from 3.0 to 3.6 V-Li/Li+ i.e., lower lithium content (delta=0-1) of the oxide film, intercalated lithium ions are highly accumulated in the near-surface region of the anodic vanadium oxide film. The component diffusivity of lithium in the oxide film was determined to be 10(-12)-10(-14) cm(2) s(-1) in the lithium content range investigated, owing to the increased interaction between intercalated lithium ions.