Addressing practical challenges of LiB cells in their pack applications.

ABSTRACT

In a battery pack, several lithium-ion batteries (LiBs) are connected in series and parallel so that sufficient voltage, current and power can be provided for applications. To ensure safe operation, when one of the LiB cells in a pack has its SoH below 80%, the entire pack will have to be discarded. Thus, ensuring all the LiB cells degrade similarly in a pack is crucial to maximize the potential of all the cells in a pack. There are several methods to perform screening on the LiB cells for such purpose, but there exist many practical challenges for estimating and predicting the degradation rate of the cells before they are chosen to be put in a pack which will be described in this work. This work provides solutions to some of these challenges and shows through experiments that one can screen the weak cells from production batch with just the first discharge cycle, and one can also predict the statistical distribution of the degradation rates of LiB cells in a production batch. On-line in-situ determination of the SoH of each cell connected in a pack is also made possible with a solution presented in this work, and this method is verified over many different types of LiB from various manufacturers.