Estimation of State-of-Charge and State-of-Health for Lithium-Ion Degraded Battery Considering Side Reactions

Abstract

State of charge (SOC) and state of health (SOH) are of critical importance to ensure safety, reliability, and prolong battery life. In this paper, a novel SOC & SOH estimation method considering side reactions over the lifespan of a Li-ion degraded battery is presented. To achieve this, an order-reduced electrochemical model considering side reactions is established first by simplification of the partial differential equations (PDEs) using the Laplace transform, inverse Laplace transform, Pade approximation, etc. The open-circuit-voltage (OCV) versus SOC correlation is utilized as the link between equivalent circuit model (ECM) and electrochemical model. Then the current induced accumulated aging effects of loss of ions and active materials on the electrode stoichiometry could be calculated to obtain a modified OCV- SOC curve. The updated OCV-SOC relationship is applied to an ECM based SOC estimator. The SOH monitoring is achieved by quantifying the capacity fade with the help of equilibrium potentials. Finally, the robustness and effectiveness of the SOC and SOH estimation scheme integrated with the presented OCV curve are validated by simulated and experimental results. The results show that the SOC estimation precision of the presented scheme regarding battery interior properties has been improved compared to the existing method. Future work is also highlighted.