Low Frequency Impedance Spectroscopy – Modeling Study on the Transferability of Solid Diffusion Coefficients

This work elaborates the transferability of electrode diffusion coefficients gained from fitting procedures in frequency domain to an electrochemical battery model run in time domain. An electrochemical battery model of an NMC622 half-cell electrode is simulated with sinusoidal current excitations at different frequencies. The current and voltage signals are analyzed in frequency domain via Nyquist and Bode plots. The frequency domain analysis of time domain simulations is applied to assess the numerical convergence of the simulation and the sensitivity on particle diameter, electrode and electrolyte diffusion coefficients. The simulated frequency spectra are used to fit the electrode diffusion coefficient by means of different electrical equivalent circuit models and the electrochemical battery model itself. The fitted diffusion coefficients from the different electrical equivalent circuit models deviate by one order of magnitude from the a priori known reference data. The fitting results from the electrochemical battery model show a perfect match and the corresponding simulation times underline the feasibility of this fitting approach. The impact of different electrode diffusion coefficients is further assessed by constant current discharge and pulse discharge simulations at different C-rates. The voltage responses deviate in the range of 20 mV for the 2C discharge pulse.