Li-ion battery is an integral part for the electric or hybrid electric vehicles, as they provide high energy density and power density with extended cycle-life compared to their closest rivals, Ni-MH batteries [1]. Electric vehicles (EVs) require an advanced real-time based battery management system (BMS) that ensure a safe and efficient energy utilization, estimate state-of-charge (SOC) and state-of-health (SOH), and cell balancing [1]. A high performing BMS needs an accurate cell model that can precisely capture the cell dynamics in EVs. Due to the inherent complexity of the physics-based model, BMS are often based on equivalent circuit models [2-4] that are relatively easy to implement but lack the important underlying physico-chemical processes. In order to predicts an accurate cell response, a physico-chemical model based on fundamental governing equations of migration and diffusion processes as well as the kinetics of intercalation require precisely evaluated model parameters for the material under consideration [5].

In this work, a commercial 18650 cell is analyzed in order to parameterize a physico-chemical model. The parameters are estimated by the results of experiments performed on the cell material under investigation. For this, the fully discharged cell was opened in a glove box under inert environment with both moisture and oxygen level below 0.5 ppm. The material samples were collected in an air tight desiccator and analyzed using different methodology.

The results obtained based on the proposed methodology are presented as: electrodes, electrolyte, and separator composition; kinetic, transport, and thermodynamics parameters; electrodes and separator physical properties, e.g., porosity, microstructure, particle size distribution etc.; cell internal configuration, e.g., jelly roll dimension, electrode tab location and their dimension etc.; and full-cell electrode balancing determination. A range of electrochemical techniques were used to determine the kinetic and thermodynamic properties of the electrode materials, e.g., galvanostatic intermittent titration technique (GITT) was used to estimate the diffusion coefficient of Li-ion in anode and cathode at different state of charge (SOC) also, to ascertain the open circuit voltage (OCV) of the respective electrodes. In order to estimate the exchange current density, electrochemical impedance spectroscopy (EIS) was employed. The SEM images to illustrate the microstructures of cathode, anode and separator and the particle size distribution of cathode and anode are shown in Figure.

References:

1. D. Rahn, and C. Y. Wang, Battery Systems Engineering, Wiley, State College, PA (2013).
2. L. Plett, J. Power Sources, 134, 252 (2004).
3. W. Verbrugge, and R. S. Conell, J. Electrochem. Soc., 149, A45 (2002).
4. L. Moss, G. Au, E. J. Plichta, and J. P. Zheng, J. Electrochem. Soc., 155, A986 (2008).
5. S. Ahamad, and A. Gupta, Electrochim. Acta, 297, 916 (2019).