The electrical properties of lithium-ion batteries (LIBs) are highly dependent on the production process. Process variations during production lead to a variation of physical product parameters, inhomogeneities, and defects. While defects should be avoided due to their significant impact on the cell’s performance and safety, inhomogeneities are usually acceptable in tolerances [1]. As a result, LIBs of the same batch often show a distribution of electrical properties. Depending on the application scenario, a production-related deviation of specific electrical parameters can be crucial. For high-energy applications, a capacity variation can lead to an overall reduction of capacity utilization in battery packs [3]. For high-power applications, the impact of manufacturing-induced variation on the cell’s electrical performance should also be considered.

In this work, we investigate the criticality of the variation of electrical parameters based on an electrical-equivalent-circuit (EEC) approach. An EEC model of a high-power lithium-iron phosphate/graphite cell is created and parametrized with comprehensive measurements, including electrochemical impedance spectroscopy and pulse measurements of a single cell. In addition, reduced measurements of a batch of the same cell type are used to determine the statistical variation of the EEC-model parameters. Based on the statistical analysis of the cell batch, a virtual set of cells is created. To investigate the impact of variation in an automotive 12V scenario, the voltage response of the virtual cells is simulated and analyzed at several operating temperatures.

The results indicate that the variation of EEC parameters can significantly impact the overall dynamic voltage drop, depending on the application scenario and the operating temperature. At high temperatures, the variation of serial resistance has the largest impact on the overall voltage drop for the investigated scenarios. However, the total voltage drop induced by the EEC elements is comparably low. At lower temperatures, the variation of EEC parameters can have a critical impact because of the increase in overall voltage drop. Nevertheless, due to its reduced contribution to the total voltage drop at these temperatures, the effect of variation in serial resistance becomes less critical. At the same time, the contribution of other EEC elements, and therefore the impact of variation, increases.

[1] Evans, D., Luc, P. M., Tebruegge, C., & Kowal, J. (2023). Detection of Manufacturing Defects in Lithium-Ion Batteries-Analysis of the Potential of Computed Tomography Imaging. Energies, 16(19), 6958.
[2] Wildfeuer, L., & Lienkamp, M. (2021). Quantifiability of inherent cell-to-cell variations of commercial lithium-ion batteries. ETransportation, 9, 100129.
[3] Dubarry, M., Pastor-Fernández, C., Baure, G., Yu, T. F., Widanage, W. D., & Marco, J. (2019). Battery energy storage system modeling: Investigation of intrinsic cell-to-cell variations. Journal of Energy Storage, 23, 19-28.