Thermal Effect of Cooling the Cathode Grid Tabs of a Lithium-Ion Pouch Cell

Abstract

Infrared thermography shows that the joint between the cathode grid stack and the cell tab is a source of Joule heating within a lithium-ion pouch cell. This can exacerbate thermal gradients within the cell core if the C-rate is sufficiently high. This paper studies the heat generated at the cathode tab joint of a 14Ah lithium iron phosphate (LFP) pouch cell. The heat generation was quantified by using an energy balance equation and the average heat transfer coefficient was calculated by modeling the cell as an isothermal vertical plate in natural convection. The influence of this heat on the cell's thermal gradients was studied during a 3C and 8C rate of discharge. It has been found that removal of this heat at its source can appreciably lower the overall average surface temperature of the cell. However, at a 3C rate discharge, the removal of this heat can induce a greater thermal gradient within the cell core. At an 8C rate of discharge, there is a minimal improvement in the temperature gradient. As a result, a thermal management system which incorporates cathode tab heat removal would most likely be an ineffective design feature