Estimation of Battery Separator Area, Cell Thickness and Diffusion Coefficient Based on Non-Ideal Liquid-Phase Diffusion Modeling

Abstract

The aim of this work is to present a fast and in situ diffusion modeling technique to extract essential electrochemical parameters from liquid-phase diffusion which can be used to implement a realistic battery in a pseudo-2D finite element modeling environment. A generalized Warburg element was used within an extended Randles equivalent circuit to obtain an appropriate fit on non-ideal diffusion impedance. Based on the calculation method presented in this paper, the values of diffusion-related parameters such as the cross-sectional area of the separator Asep, cell thickness Lcell as well as liquid-phase and solid-phase diffusion coefficients Dl and Ds were derived, successfully. A characteristic cell which allowed the exchange current density i0 and reaction rate constant k0 to be calculated was also established. The experimental data was measured by electrochemical impedance spectroscopy (EIS), resistivity measurement and the galvanostatic intermittent titration technique (GITT). The results show that our hypothesis to extract essential electrochemical parameters from the tail part of diffusion impedance is correct. The applicability of our concept is confirmed by the prosperous validation results produced by computed tomography (CT) and battery dynamics simulation in finite-element environment. Due to the inherent limitations of the pseudo-2D Doyle-Fuller-Newman (DFN) model, our technique is accordingly valid within the current range of 0–1 C.

Keywords

• li-ion battery
• diffusion
• warburg
• geometrical parameters
• electrochemical impedance spectroscopy
• parameter estimation