Scaling from cell to system: Comparing Lithium-ion and Sodium-ion technologies regarding inhomogeneous resistance and temperature in parallel configuration by sensitivity factors

Understanding the strengths and limitations of different cell technologies is vital for effectively scaling from cell to system level. In any group of cells connected in parallel, inhomogeneous current flow can occur. To better understand the factors influencing current distribution, we conducted a sensitivity analysis focusing on the effects of inhomogeneous contact resistances and unequal cell temperatures. This analysis was carried out on several state-of-the-art battery chemistries, with Sodium-Ion Batteries and Lithium-Ion Batteries using both NCA and LFP as cathode materials. Our study reveals that both investigated inhomogeneities result in unique outcomes for different cell technologies, such as fluctuations in maximum currents and differences in SoC. By introducing sensitivity factors, LIB_LFP show the highest deviations due to its flat open-circuit-voltage characteristics. This leads to maximum SoC differences of up 14.8 %/R_AC and 7.46 ‰/K between the cells. In contrast, the SIB current distribution shows significantly lower sensitivity to resistance but higher sensitivity to temperature inhomogeneities. The LIB_NCA technology demonstrates comparatively low sensitivity to both investigated inhomogeneities. Our results show that, when selecting a cell type for a particular application, it is crucial to consider the effect of contact resistance and temperature inequalities on current distribution.