A novel resistor-inductor network-based equivalent circuit model of lithium-ion batteries under constant-voltage charging condition

Highlights: • Introduced a novel RL network-based ECM to describe the battery CV charging current. • Developed enhanced ECMs containing multiple parallel-connected RL networks. • Conducted a comparative study to determine the preferred model structure. • Proposed a simplified model with satisfactory current estimation accuracy. • Validated the feasibility and superiority with test data after different cycles. -- Abstract: A constant-current constant-voltage (CCCV) charge protocol is commonly used for lithium-ion batteries. The dynamic characteristic of the constant-voltage (CV) charging current is discovered to be related to battery aging. In order to quantitatively describe the load current during the CV charging period, an equivalent circuit model (ECM) based on the resistor-inductor (RL) network is proposed in this paper. Motivated by the current expression derived based on the conventional resistor–capacitor (RC) network-based ECM, an RL network-based ECM is developed to characterize the CV charging current. Then, the parallel-connected RL networks are employed to improve the model fidelity. The test data of four lithium iron phosphate (LiFePO₄) batteries in different aging states are employed to validate the proposed model. Comparative results show that the proposed 2nd-order ECM is the best choice, considering both the model accuracy and complexity. In addition, a simplified 2nd-order model is proposed, achieving a satisfactory accuracy with only three model parameters to be identified. Therefore, this model can be easily implemented in the battery management system (BMS).