An estimation model of the state of health of lithium-ion batteries based on the voltage data in the constant current charging stage

This paper addresses the application requirements for Lithium Iron Phosphate (LiFePO?) batteries State of Health (SOH) estimation algorithms in energy storage systems, which demand both high accuracy and model simplicity. A Local Voltage Fitting (LVF) model is proposed and validated. First, combining a second-order equivalent circuit model, the basic mathematical expression for SOH estimation is derived based on the relationship between terminal voltage and charging time during the constant-current charging phase of the battery; To enhance the model's applicability for fitting lithium iron phosphate batteries, this study selected segmented voltage data within the State of Charge (SOC) range 0.30, 0.90 from the constant-current charging curves of each cycle, excluding the difficult-to-fit regions at the ends of the curves, thereby establishing the local fitting framework for the LVF model.