It's getting hot in here : temperature gradients in lithium-ion battery packs

Abstract

A 5 channel, 40A battery cycler was constructed for the purpose of carrying out thermal studies on Lithium-ion battery packs. Boston Power Swing Key 442 battery blocks were tested to determine the magnitude of the temperature gradient over the pack. The battery blocks were stacked vertically, similar to how they might be situated on an electric vehicle. They were cycled, discharged then charged, at a current of 40A in stacks of one, two, three and four, with and without unidirectional air-cooling from the top of the pack. The resulting temperature data was analyzed to see if a temperature gradient over the pack was present. A correlation was found between placement in the pack and cell temperature; the lower down in the pack a cell was, and thus the further from the air flow, the warmer the pack became during operation. For the four battery test, a maximum temperature difference of 2.9°C was observed between the hottest and coldest cells.