Current distribution within parallel-connected battery cells

Parallel connections can be found in many battery applications. Therefore, it is of high interest to understand how the current distributes within parallel battery cells. However, the number of publications on this topic is comparably low. Furthermore, the measurement set-ups are often not clearly defined in existing publications and it is likely that additional impedances distorted the measured current distributions. In this work, the principles of current distributions within parallel-connected battery cells are investigated theoretically, with an equivalent electric circuit model, and by measurements. A measurement set-up is developed that does not significantly influence the measurements, as proven by impedance spectroscopy. On this basis, two parameter scenarios are analyzed: the Delta R scenario stands for battery cells with differing impedances but similar capacities and the Delta C scenario for differing capacities and similar impedances. Out of 172 brand-new lithium-ion battery cells, pairs are built to practically represent the Delta R and Delta C scenarios. If a charging pulse is applied to the Delta R scenario, currents initially divide according to the current divider but equalize in constant current phases. The current divider has no effect on Delta C pairs but, as a rule of thumb for long-term loads, currents divide according to the battery cell capacities. (C) 2016 Elsevier B.V. All rights reserved.