Production caused variation in capacity aging trend and correlation to initial cell performance

Battery packs usually consist of multiple individual cells in a series connection, thus the worst cell defines the pack's performance. All cells do age individually causing a spread in cell performance. We will show that not only the local operating conditions, but also variances from within the cell manufacturing process influence the variation of aging trends. By an experiment with 48 cells from a mass production line it can be found that the aging spread cannot be neglected. Using data mining algorithms a dependency between initial cell performance and cycle lifetime is identified. The resulting linear regression model can predict the lifetime and can therefore be used to classify cells into different batches before battery pack production.