Influence of cell parameter differences and dynamic current stresses on the current distribution within parallel-connected lithium-ion cells

To satisfy energy and power requirements of electric vehicles, traction batteries contain a high number of parallel- as well as serial-connected lithium-ion cells. Due to cell manufacturing and battery architecture tolerances, inhomogeneous electrical and thermal stresses on the individual cells arise during operation. To guarantee the service life of the battery, the power output of the battery has to be limited depending on the most loaded cells. This article investigates the influences of cell parameter variances and dynamic current stresses on the current distribution within parallel cells. A series of measurements considering two consecutive pulses with varied dynamic current conditions, continuous alternating charge and discharge pulses, as well as a typical drive cycle are conducted. Correlations of cell parameter variances and the current conditions to the current distribution are provided and validated using experimental data. This knowledge helps predicting the cell currents onboard and optimizing the operating window of the battery while guaranteeing the service life.