Application of finite-diffusion models for the interpretation of chronoamperometric and electrochemical impedance responses of thin lithium insertion V₂O₅ electrodes

The present paper provides modeling of the simultaneously measured electroanalytical responses obtained from a thin vacuum-deposited V₂O₅ film electrode, namely the current vs. time (potentiostatic intermittent titration, PITT) and the complex-plane impedance (electrochemical impedance spectroscopy, EIS). Reliable values of diffusion time constant were obtained from the short-time domain of the chronoamperometric response and the medium-frequency region of the Nyquist plot using the finite-space diffusion models. Narrowness of the semi-infinite Warburg portion of the impedance spectra and the Cottrell region with respect to the frequency and time, respectively, is discussed in terms of possible involvement of the interfering responses such as the Ohmic potential drop, slow Li-ion migration through the surface layer (formed on the electrode surface when in contact with solution electrolyte), retarded Li-ion transfer across the surface layer/electrode's bulk interface, and non-homogeneous distribution of the film's thickness. The properties of the two alternative models, namely the finite-space Warburg (FSW) and in-series combination of the finite-length Warburg (FLW), and the intercalation capacitance were discussed, and the resulted simulated spectra were compared with the experimental one. Taking into account the experimental responses obtained from two V₂O₅ films of different thickness, the FSW model was found to be the most relevant to the experimental data.