The role of cell geometry when selecting tab or surface cooling to minimise cell degradation

Abstract

Thermal management of lithium ion batteries is critical to maintain cells at their optimum temperature and balance performance with degradation. Previous work has shown tab cooling to be better for performance and lifetime, but only if sufficient heat removal can be achieved, which depends in part on cell geometry. In this paper, a large form-factor pouch cell is shown to suffer from faster degradation when tab-cooled although still benefitting from higher useable energy. This paper introduces the ratio of surface-to-tab cell cooling coefficient, CCC ratio , as a qualitative measure to assess a cell’s suitability for tab cooling. For low CCC ratio cells, tab cooling results in more useable energy and lower degradation rates than surface cooling. However, the large pouch cell used in this study has a high CCC ratio , indicating that it is difficult to remove sufficient heat through tab cooling. At beginning of life, tab cooling allows access to more usable energy in the cell, but the rate of high temperature-induced degradation is greater, compared to the surface cooled cell. As a result, the useable energy from the tab cooled cell diminishes more rapidly, and after a certain cycle count, the useable energy from the surface cooled cell is superior. The optimum cooling approach will therefore be dependent on the desired lifetime of the system. This research should be of particular interest to cell and battery pack designers. • Thermal management approach (tab or surface cooling) is dependent on cell geometry. • The cell cooling coefficient (CCC) can be used to evaluate which approach is preferred. • Cells that give slower degradation through surface cooling still provide more energy when tab cooling. • The choice of tab or surface cooling depends on the target lifetime required.