A microcontroller-based state-of-health estimator for lithium-ion batteries

Despite the many advantages of rechargeable batteries, their capacity degradation and state-of-health (SoH - ability of a battery to provide its nameplate discharge capacity over its lifetime) remains an issue in most power applications. The SoH is a qualitative measure of the battery´s charge storage capability, which is a key factor in determining the battery´s end-of-service-life, thus preventing unintended power shortages. This paper presents the design and implementation of an inexpensive microcontroller-based cell cycler, capable of charging and discharging lithium-ion (Li-ion) battery cells whilst accurately measuring the charge being injected or removed from them. An online SoH estimation technique is then developed based on the linear approximation of the relationship between the cell terminal voltage and removed ampere-hour charge. The experimental results on two lithium iron phosphate (LiFePO₄) battery cells give confidence to both the SoH estimation model and the proposed cell cycler.