Influence of Terminal Tabs/Busbar Ohmic Heat on Maximum Cell Temperature of a Li-ion Battery System for PHEV Applications

The battery packs for plug-in hybrid electrical vehicle (PHEV) applications are relatively small in the charge depleting (CD) mode but fairly large in the charge sustaining (CS) mode for their duties in comparison to the battery packs for hybrid electrical vehicle (HEV) applications. Thus, the heaviest battery thermal load for a PHEV pack is encountered at the end of the CD mode. Because the cells in PHEV battery packs are generally larger than those in the HEV packs in both capacity and size, control of the maximum cell temperature and the maximum differential cell temperature for the cells in a PHEV pack with high packing efficiency is a challenge for the cooling system design. The maximum cell temperatures locate in the areas near the terminal tabs where the current densities are highest. During a continuous discharge process with a high cell current in the CD mode operation, the Ohmic heat generated in the terminal tabs and busbars can have significant impact on the local cell temperatures near the terminals. Cooling of a PHEV pack involves not only dissipating the heat generated in the cells but also managing the Ohmic heat generated in the terminal tabs and busbars. A finite element analysis is conducted in this study on thermal behavior of a Li-ion battery system with indirect liquid cooling. Cell temperature distributions are simulated under the cell thermal load equivalent to those in PHEV applications. Influence of the busbar Ohmic heat on the maximum cell temperature and the maximum differential cell temperature through different busbar designs and tab-busbar connections are analyzed. In addition, the impact of the pack configurations on the cell temperature distributions under the same pack load is also evaluated.