Study of lithium diffusion in RF sputtered nickel-vanadium mixed oxides thin films

The kinetics of electrochemical lithium insertion inside RF sputtered Ni/V mixed oxides thin films have been investigated employing different electrochemical techniques. The AC electrochemical impedance spectra, recorded after 10 cycles, showed three steps clearly involved in the intercalation mechanism of lithium in the oxide films: (i) a charge transfer process to the electrolyte/electrode interface, (ii) a solid-state diffusion of Li; and (iii) a space limited diffusion due to the finite volume of the film. This latter portion of the impedance spectra was used to calculate the Li chemical diffusion coefficients (D-Li). D-Li values show an initial increase up to an injected charge of 30 mC cm(-2) and then, upon further intercalation, a decay probably due to the limited Li motion through a decreased number of available sites. These results are in good agreement with the ones obtained by potentiostatic intermittent titration technique applied to the same electrodes. Both techniques agree in giving the same trend for D-Li upon Li intercalation. The same sets of measurements were carried out after 100 and 1000 Li insertion/deinsertion cycles in order to analyze the effect of prolonged cycling on the mechanism of lithium diffusion. (C) 2002 Elsevier Science Ltd. All rights reserved.