The Cell Cooling Coefficient as a design tool to optimise thermal management of lithium-ion cells in battery packs

Lithium-ion cells and battery packs are not typically designed for optimised thermal management. As a result, almost every cell in use worldwide is performing below optimum levels and degrading needlessly fast. The root cause of the problem is the lack of information surrounding the thermal performance of cells. Cell Cooling Coefficients (CCCs) have been developed to define a cell's heat rejection capability. Here, CCCs indicate how thermal performance varies with geometric change in five different pouch cells. Surface cooling performance is reduced dramatically by increasing the electrode-stack thickness. Tab cooling performance is unaffected by electrode-stack thickness, but tab cross-sectional area is a significant thermal bottleneck. In this study, increasing tab thickness by 34% yields a tab cooling performance enhancement of 20%, with a specific energy reduction of just 0.7%. The evidence highlights that cell designers have fallen into the ‘sub-system optimisation trap’, whilst trying to optimise cell specific energy. Simple redesign could drastically improve tab cooling capability for most cells. Tab cooling is known to benefit the performance and lifetime of cells, when the thermal bottleneck is not a limiting factor. The battery industry must embrace innovation and implement tab cooling in the automotive market, grid storage and beyond.