Modelling and Characterization of Lithium-Ion Battery Cell Using Electrochemical Impedance Spectroscopy (Case Study LiFePO4)

Lithium Ferro Phosphate (LiFePO4) batteries are a primary choice for electric vehicles and energy storage systems due to their superior thermal stability and extended cycle life compared to conventional batteries. However, their performance is influenced by factors such as electrochemical characteristics, temperature, charge/discharge rates, and usage patterns. This study analyzes the LiFePO4 AMP20m1HD-A cell using electrochemical impedance spectroscopy (EIS) at State of Charge (SOC) levels of 20–90% and discharge rates (C-rate) ranging from 0.5C to 3C under ambient conditions. The battery cell modeling is based on the equivalent circuit model (ECM) approach, which consists of a combination of inductance, ohmic resistance, two pairs of R-CPE components, and a Warburg element to represent charge transfer dynamics and ion diffusion. Parameter fitting of the ECM using the non-linear least squares method yielded an average Root Mean Square Error (RMSE) of 3.87×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−6</sup> Ω, indicating high accuracy. Model validation at 80% SOC (0.5C) and 20% SOC (3C) resulted in an RMSE of 5.74×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−6</sup> Ω, demonstrating consistent impedance representation across operating conditions. The results reveal that SOC and C-rate variations significantly impact electrochemical characteristics, particularly resistance and capacitance. These findings emphasize the importance of accounting for operational variability in Battery Management System (BMS) design to optimize battery performance and longevity. This research provides a foundation for precise, application-oriented modeling to advance LiFePO4-based battery management systems.