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Electrochemical Impedance Response of Lithium Intercalated V2O5 Thin Films
M. Benmoussa, A. Outzourhit and A. Bennouna

200 nm thick V2O5 films are deposited using the sol-gel spin coating technique. The obtained films are nanocristalline as confirmed by XRD measurements. Electrochemical impedance spectroscopy (EIS) is used in the study of the dynamic process intervening while colouring V2O5 films by lithium insertion. Impedance spectra obtained at different potentials showed the characteristic shape of a diffusion process with a Warburg regime at high frequencies and a capacitive branch at low frequencies arising from the charge storage associated with the intercalation of Li+. It was found that a suitable interpretation of the experimental results is provided by modelling the impedance spectra using an equivalent circuit analogue including three R//C semicircles covering the high-frequency domain and a finite-length Warburg in sequence with the intercalation capacity at low frequency domain for moderate lithium insertion V2O5 thin films. SEM micrographs have been taken before and after insertion of lithium in V2O5 thin films and have shown the adsorption of chemical species at the film’s surface. Reliable values of diffusion coefficient, intercalation capacity and charge transfer resistance were obtained using this model. The anomalous increase of the charge transfer resistance, the Warburg resistance and the diffusion time constant for high insertion level is due to the fact that this model is inappropriate to simulate EIS spectra at high insertion levels, since, in this case, the film/substrate interface can not be considered as an absorbing one.

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