| The electrochemical properties of amorphous vanadium pentoxide films fabricated by reactive r.f.-sputtering have been investigated by galvanostatic charge/discharge cycling experiment, AC impedance spectroscopy, and galvanostatic intermittent titration technique (GITT). As x in Li_xV₂O_(5-y) increased (x=0∼2.0), the electromotive force of Li｜1 M LiClO₄-propylene carbonate｜V₂O_(5-y) cells decreased gradually without potential plateau or potential step, demonstrating that an abrupt structural change did not occur in the whole lithium content. Impedance spectra of the cells consisted of a high frequency arc, a low frequency straight line, and a middle frequency Warburg impedance line. Equivalent circuit deduced from Nyquist plot suggests that lithium intercalation reaction consists of three consecutive steps of charge transfer at the electrolyte/cathode interface, diffusion into the film and charge saturation. Chemical diffusivity of Li^+ in Li_xV₂O_(5-y) film, measured using GITT was determined to be 4×10^(-13) to 7×10^(-14)㎠/sec in the lithium content range investigated. The component diffusivity of lithium decreased linearly with lithium content from 9×10^(-14) to 5×10^(-15) ㎠/sec, owing to the decrease in the number of vacant sites available for jumping of lithium atom. |
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