Impact of Cell to Cell Variances on the Current Distribution among two parallel Lithium-Ion Cells at constant Current Conditions

Batteries of electric vehicles contain a high number of serial- and parallel-connected cells in order to fulfill the power and energy requirements. Due to Cell to Cell Variances (CtCV), induced by manufacturing tolerances, and the impact of the cell packaging, a heterogeneous electrical and thermal stress arise, among the single cells of a battery. This inhomogeneity can lead to an accelerated degradation of individual cells, reducing the lifetime of the whole battery. One essential factor of this effect is the current distribution within parallel-connected cells. This paper experimentally investigates the influence of the Crate, Depth of Discharge (DoD) and CtCV on the current distribution within two parallel cells at constant current stress. Therefore measurements with three cell groups, which consist of two parallel cells, having different CtCV, are conducted. The measurements show a correlation of the current distribution to the Differential Voltage Analysis (DVA) and increasing current differences with increasing CtCV. The findings help to understand the dynamic of the current distribution and contributes to an optimization of the battery design and operation strategy.