Evaluation of Internal Resistance Methods for Tracking Battery State of Health

The industrial 18650 li-ion cells have been extensively used in portable devices, electric vehicles (EVs), military applications etc. Especially the state of health (SOH) parameter of the li-ion cells is quite important for these devices or systems in terms of durability and safety. On this matter, the change of internal resistance is used as a feature to track battery SOH. Thus, we comparatively observed both AC and DC internal resistance methods to see which method has strong relationship individually. The results have shown that AC impedance measurement is highly dependent to internal and external status of cell while DC resistance measurements give us more precise results under the limited test abilities such as control of cell internal temperature. This could give advantage for basic battery management modules which cannot be able to handle complex analysis and reach internal status of the cell.