State of charge estimation of lithium batteries: Review for equivalent circuit model methods

Lithium batteries play a crucial role in powering modern technology due to their high energy density, long life span, low self-discharge rate, making them indispensable for numerous applications. Accurate information on the state of charge (SOC) is crucial, as it not only enhances battery management but also mitigates range anxiety. Previous research has proposed various SOC estimation methods, focused on principles, model evaluation, and verification. Several reviews have summarized these methods, but little has specifically focused on discussing the equivalent circuit model (ECM) methods, which are renowned for their physical relevance and accuracy. This review examines various commercial lithium battery models, analyzing the rationale behind the ECM methods' selection and the associated evaluation techniques. It offers a thorough overview of lithium battery characteristics, modeling, and parameter identification methods. Moreover, this review identifies existing limitations and challenges, and proposes future directions in testing setups and evaluation methodologies to improve SOC estimation.