Effect of Current Path on Parallel Lithium-ion Cells in Electric Vehicles Battery Packs

In many electric vehicle applications Lithium-ion battery packs are built out of a large numbers of small cells linked in parallel to increase their capacity. So far, parallelized cells have mostly been treated as one large homogeneous cell, assuming equal potentials and currents to all cells and considering the capacity as the sum of the individual capacities. However, this assumptions is false if resistive losses in the interconnecting current collectors and cells' capacity variations are considered. Cell currents were measured on an experimental setup composed of five cells of different capacities linked in parallel. The paper names the two possible electrical configuration (Cis and Trans) and their impact on current distribution. On the basis of total current throughput, Trans configuration appears to be more effective than the Cis to maintain current homogeneity. Slight capacity variations also appear to have an impact on current distribution. Conclusions of this article can help improve battery pack design and manufacturing.