Basic electroanalytical characterization of lithium insertion into thin, well-crystallized V₂O₅ films

Slow-scan rate cyclic voltammetry (SSCV), potentiostatic intermittent titration (PITT) and electrochemical impedance spectroscopy (EIS) have been applied simultaneously to study Li ion intercalation into V₂O₅ films prepared by evaporative vacuum-deposition on Pt foils. Two different films, 1600 and 3600 angstroms thick, were used to study the influence of the film's thickness on the major electroanalytical characteristics of these intercalation electrodes. Modeling of the impedance spectrum related to the thin V₂O₅ film was performed using an equivalent circuit analog including the following elements: three R||C semicircles (covering the high-frequency domain) and finite-length Warburg in sequence with the intercalation capacity (a straight line of unit slope at intermediate frequencies, and a sloping capacitive line at the very low frequencies). Sharp minima on D versus E plots, which are observed in the vicinity of the cyclic voltammetric peaks, present further evidence of very high, attractive electron-ion interactions during Li ion intercalation into the V₂O₅ electrode, as was already described for similar processes in graphite and some transition metal oxides: Li_xCoO_2, Li_xNiO₂, Li_xCo_yNi_1-yO₂ and Li_xMn₂O₄. The diffusion length in these electrodes related to the V₂O₅ film's thickness.