Impact of the tabless electrode design on future cylindrical lithium-ion battery packs

Summary:

Cylindrical lithium ion cell with a tabless electrode experience less current and temperature inhomogenities during cycling compared to cells with a single tab. The enhanced thermal connection between jellyroll and cell can enables effective cooling from the cell top and bottom. As temperature gradients spread in axial direction, the diameter has only minor influence on the temperature profile. This enables using cylindrical cells with larger diameters and opens up new possibilities for future battery pack design. To investigate the influence of the tabless electrode design and the cell diameter on energy density and safety a geometric model was developed. The cell model is based on a real prototype tabless cell. The cell geometry is influenced by a variety of different factors, like the production process, especially winding and welding, mechanical properties during thermal runaway, crash und crush as well as the thickness change of the electrode layers. On module level the cells are placed onto a cooling plate and are arranged in honeycomb structure for maximum packing density. The space between the cells remains variable and is primarily a function of the active material decomposition reactions and the thermal properties of the filling material between the cells to avoid thermal propagation. The model is first applied to arbitrary representative battery dimensions to gain a general understanding of packing density, safety and cell diameter. No spacing between the cells leads to high area usage but very high risk of thermal propagation. Instead increasing the space as a function of cell diameter according to thermal propagation simulations leads to less cell area usage but safe batteries. Inactive components like the cell casing and the hollow core left from the winding process further lower the area usage for energy storing material. Then, the model is applied to solve a real-world case study. The tesla model s plaid battery dimensions of the 5 modules are combined to a single large module and filled with tabless cells with 80 mm cell height, varying cell diameter and sufficient space between the cells to avoid thermal propagation. Small and large diameter lead to less active material volume while there is an optimum inbetween. In this case, cells with 30 mm to 46 mm diameter lead to roughly equal active material volume. For a final decision on the diameter however, additional criteria needs to be taken into account.To sum up, the tabless electrode enables more efficient cooling and larger diameter, that lead to more active material volume inside the battery and more flexibility to choose an optimal diameter for a portfolio of multiple batteries.