Improving the accuracy of voltage estimation in the low charge state range at low temperature: An equivalent circuit model considering the influence of temperature on solid phase diffusion process

Electric vehicles, energy storage systems, ships, unmanned aerial vehicles, etc. often experience changes in battery temperature when working in different environments, especially in low-temperature environments, the battery temperature changes significantly. The robustness of the battery model is particularly important, and the reliability of the model directly affects the accuracy of state estimation such as SOC, SOH, and SOE of the battery, indirectly leading to power outages, sudden drop in range, and insufficient power during vehicle operation, leading to serious accidents. Traditional equivalent circuit models (ECM), such as the Rint model and first-order RC model, do not take the solid-phase diffusion process into account, resulting in low voltage estimation accuracy in the low SOC region. The Electrochemistry Equivalent Circuit Model (E-ECM) adds a simplified solid-phase diffusion module based on the ECM, but due to fixed parameters, the parameters will also change without taking into account changes in battery temperature, especially when the model is at low temperatures, resulting in poor voltage estimation accuracy. To improve the performance of the model in the low temperature and low SOC range, this paper optimizes its simplified solid-phase diffusion module based on E-ECM and proposes a Temperature-Dependent Equivalent Circuit Model (TD-ECM), which greatly improves the voltage simulation accuracy at different temperatures and low SOC ranges. In TD-ECM, a first-order inertial link is used to simulate the solid-state diffusion process, and the severity of this solid-state diffusion process is temperature dependent to reflect the difference between the surface charge state (SOCsurf) and the average charge state (SOCmean), ultimately manifested as the difference in voltage. In addition, to obtain appropriate parameters for the proposed TD-ECM, an iterative parameter extraction method was presented. The final results show that TD-ECM can significantly improve the voltage estimation accuracy at different temperatures especially in the low SOC range where RMSE is significantly lower than ECM and E-ECM.