Electrode State of Health Estimation for Lithium Ion Batteries Considering Half-cell Potential Change Due to Aging

Estimation of electrode state of health (eSOH) is essential to understanding battery degradation status in detail. This is accomplished by considering electrode capacity and a utilization range as eSOH parameters. In this paper, we propose a novel combination of two eSOH estimation approaches (i.e. voltage fitting and differential voltage analysis). By utilizing peak information in the differential voltage curve, the proposed method can separate individual electrode's contributions from the full-cell voltage. This separation allows the proposed method to identify changes in the positive electrode half-cell potential curve and to calibrate the aged half-cell potential function by refitting the coefficient of the basis functions. A comparison between the conventional voltage fitting method and the proposed method for an aged NMC/graphite cell shows that the proposed method can significantly reduce the voltage fit error while matching the location of distinct peaks in the differential voltage curve that the conventional method fails to do.