New State of Health Definition Considering Capacity Fade and Impedance Increase

This paper examines the performance loss of lithium ion (LiIo) batteries as a result of aging effects. For this purpose, the state of merit (SOM) is introduced as a novel parameter. The SOM can be calculated as an inherent quantity considering both the increase in impedance as well as the loss in capacity of a battery cell. This is realized by measuring the time needed for a discharge process with different current rates (CR) within the allowed current range. The discharge times contain all the required performance information for calculating the SOM making it a comprehensive parameter to state the current overall condition of the cell. To validate the SOMapproach, the SOM, the capacity and the impedance are estimated for three cells at different conditions of aging. Finally, the SOM, the impedance increase as well as the capacity decrease are compared and discussed.