Evolution of initial cell-to-cell variations during a three-year production cycle
Markus Schindler, Johannes Sturm, Sebastian Ludwig, Julius Schmitt, Andreas Jossen
Abstract
Consistent quality of the battery system in battery electric vehicles (BEVs) is highly dependent on constant quality of the supplied individual cells. Especially for promising, relatively novel material combinations, cell-to-cell parameter variations may vary over years, since cell manufacturers might have not yet found the ideal composite to produce cells with high capacity and cycle stability. This study investigates the development of cells’ capacity, internal resistance and energy density over a time span of nearly three years for three different batches of the same cell. The cell under investigation is commercially available and offers a promising material combination of silicon-graphite and nickel-rich NMC. Differential voltage and differential capacity analysis are used to explain possible reasons for cell-to-cell variations. As a result, we found significant differences in cell-to-cell variations between the batches. For BEV manufacturers, this means in particular that they should consider how they can counter the influence of these cell-to-cell variations through an operating strategy in order to protect themselves in the long term against regress claims by customers.