Electrochemical Characterization and 2-RC Equivalent Circuit Modeling of Lithium-Ion Batteries at Low Temperatures

This study systematically investigates the low-temperature electrochemical degradation, transient open-circuit voltage (OCV) characteristics, and impedance dynamics of commercial NMC pouch cells to establish a robust control foundation for hybrid fuel cell/battery energy management systems. Comprehensive time-domain Pulse tests and frequency-domain Electrochemical Impedance Spectroscopy (EIS) were conducted across a broad thermal spectrum (-10°C, 0°C, and 25°C). The experimental results demonstrate a critical vulnerability to sub-zero environments, characterized by a capacity contraction from 7.5Ah at room temperature to 7.1Ah at -10°C, accompanied by an order-of-magnitude escalation in internal resistance (R0 surging to 0.082Ω). Crucially, cross-domain OCV tracking revealed a highly stable thermodynamic equilibrium at 0°C with localized deviations restricted to under -0.5%, revealing that low-temperature environments effectively damp high-frequency voltage fluctuations during specific relaxation intervals. Using these multi-temperature datasets, a non-linear 2-RC equivalent circuit model was parameterized and validated within MATLAB/Simulink. The model successfully replicated physical voltage transients and localized Joule heating profiles (1.8°C rise at extreme cold). These high-fidelity parameter maps provide critical boundary constraints for predicting high-frequency electrochemical transients, contributing to the development of predictive energy management and state-of-health diagnostics in demanding hybrid electric aerospace applications.