Explicit analysis of impedance spectra related to thin films of spinel LiMn₂O₄

A uniform, dense film of spinel LiMn₂O₄ (0.1 μm thick) has been prepared by the electrostatic spray deposition (ESD) technique. The electroanalytical behavior of this electrode is elucidated by application of electrochemical impedance spectroscopy (EIS). The data have been modeled using an equivalent circuit approach. An excellent fit was found between measured data and an equivalent circuit, comprising Li⁺ migration through surface film, potential-dependent charge transfer resistance, semiinfinite Warburg-type element, reflecting solid state Li⁺ ion diffusion and a finite space Warburg-type element, describing both diffusion and accumulation of lithium at the very low frequency. The apparent chemical diffusion coefficient of lithium in the spinel phase was found within 10^-12<D_Li<10^-9 cm² s^-1 as a function of electrode potential with minima at the potentials corresponding to the voltammetric peaks. The intercalation capacitance was found 0.7<C_L<47 mF cm^-2 exhibiting maxima at the potentials corresponding to the voltammetric peaks.