On the influence of tab-design in large format lithium-ion pouch cells on cell performance and plating behavior

Summary:

Lithium-ion batteries are the technology of choice for electrochemical energy storage systems, particularly in electromobility. One important research aspect is the tab design and its influence on the cell behavior. Using a model that has been previously verified by Erhard et. al. to accurately simulate the spatial potential distribution across a 500 x 100 mm² single-layered NMC/graphite pouch cell this work takes a more in-depth look at the impact of different tab-designs on the charge and discharge behavior of a large-format lithium-ion pouch cell.

A rectangular (176×175.4 mm²) shaped NMC622/C pouch cell with a standard tab-design is modified through a change in either tab position or tab width for a total of 5 different tab-layouts (“standard”, “in”, “out”, “narrow”, “wide”). Each model is analyzed regarding its temporal current distribution across the electrode surface, temperature variation, dischargeable capacity, plating risk and plating homogeneity in order to find the optimal tab layout for specific user cases.

At low to mid C-Rates (C/10 to 1C) the tab-designs show no significant impact on cell performance, while at 3C a considerable benefit is observable: The potential plating onset during 2C-CC charging can be delayed by up to 4% SOC by using a narrow tab-design and by using a wide tab-design the temperature gradients as well as the current density distribution can be reduced by up to 0.7 °C and up to 0.55% respectively.

To summarize, a homogeneous tab-design (large tab width and centered position) leads to a more evenly distributed current density and temperature across the cross-sectional area, which in turn results in less temperature deviation and thus, in theory, improved ageing. In contrast, a more inhomogeneous tab-design (thinner tabs and more outward position) leads to increased local current densities and higher temperature gradients, but also a slightly better discharge performance (dischargeable capacity) due to the increase in electrochemical performance caused by higher localized temperatures.