Two different models were used to obtain transport and kinetic parameters using nonlinear regression from experimental charge/discharge curves of a lithium-ion cell measured at 35°C under four rates, C/5, C/2, 1C, and 2C, where the C rate is
1.656A
. The Levenberg-Marquardt method was used to estimate parameters in the models such as the diffusion of lithium ions in the positive electrode. A confidence interval for each parameter was also presented. The parameter values lie within their confidence intervals. The use of statistical weights to correct for the scatter in experimental data as well as to treat one set of data in preference to other is illustrated. An F-test was performed to discriminate between the goodness of fit obtained from the two models.
A model for the simulation of the steady-state impedance response of a polymer electrolyte membrane fuel cell ͑PEMFC͒ cathode is presented. The catalyst layer of the electrode is assumed to consist of many flooded spherical agglomerate particles surrounded by a small volume fraction of gas pores. Stefan-Maxwell equations are used to describe the multicomponent gas-phase transport occurring in both the gas diffusion layer and the catalyst layer of the electrode. Liquid-phase diffusion of O 2 is assumed to take place in the flooded agglomerate particles. Newman's porous electrode theory is applied to determine over-potential distributions.
The validity of estimating the solid phase diffusion coefficient, D s , of a lithium intercalation electrode from impedance measurement by a modified electrochemical impedance spectroscopy ͑EIS͒ method is studied. A macroscopic porous electrode model and concentrated electrolyte theory are used to simulate the synthetic impedance data. The modified EIS method is applied for estimating D s . The influence of parameters such as the exchange current density, radius of active material particle, solid phase conductivity, porosity, volume fraction of inert material, and thickness of the porous carbon intercalation electrode, the solution phase diffusion coefficient, and transference number, on the validity of D s estimation, is evaluated. A simple dimensionless group is developed to correlate all the results. It shows that the accurate estimation of D s requires large particle size, small electrode thickness, large solution diffusion coefficient, and low active material loading. Finally, a ''full model'' method is developed for the cases where the modified EIS method does not work well.
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