Electrochemical & Equivalent Circuit Modelling and Validation of Lithium-Ion Cell in GT-AutoLion

High energy and power density Lithium-ion batteries are used as energy storage devices for indispensable applications ranging from cell phones to hybrid electric vehicles, unmanned aerial vehicles and commercial passenger aircrafts. To monitor the health of the battery and its various performances, it is crucial to understand the electrochemical behavior of the battery. The Doyle-Fuller-Newman (DFN) model is a popular electro-chemistry-based model, which characterizes the solid and electrolyte diffusion dynamics in the battery and predicts current/voltage response. However, the DFN model requires many parameters that need to be estimated to obtain an accurate battery model. In this article, an electro-chemistry based cell model is developed using GT-AutoLion to simulate and validate the performance for two different commercially available Lithium Iron Phosphate (LiFePO₄) and Nickel Cobalt Aluminum (NCA) cells. GT-AutoLion is a powerful tool for physics-based modeling to predict variations in material, electrode and cell design that can affect performance and characteristics of cells. Two-step procedure is used to estimate the thermodynamic parameters using low-current discharges and kinetic parameters using high pulse discharge current. A parameter sensitivity analysis is performed to understand the critical parameters like diffusivity, conductivity etc. that can significantly affect the performance of cell. The fidelity of the model is confirmed by the satisfactory fit of the model to the experimental data. The developed electrochemical cell model is used to create an equivalent electrical circuit model using Virtual Hybrid Pulse Power Characterization (HPPC) tests. Various parameters like open circuit voltage, internal resistance, and RC circuit parameters are estimated using HPPC test. The equivalent electrical circuit model also has very good correlation with electrochemical cell model which can be used to integrate in any pack level electrical and thermal models