State of Health Estimation of LiFePO4/Graphite Cells

LiFePO4 / graphite batteries degrade in electric vehicle applications. The end of battery life is usually considered at 80% of initial capacity. State of health (SoH) of the batteries must be estimated for efficient and safe battery usage in vehicles, but the SoH estimation is complex, involving operational and environmental conditions (e.g., state of charge, terminal voltage, current rate, internal resistance, ambient temperature, and thermal effect) as well as cell degradation mechanisms. This work studies the degradation mechanisms of LiFePO4 / graphite cells and attempts to estimate the SoH using partial charge capacity instead of internal resistance, coulomb counting method, and model-based approaches usually used in the literature [1-5].