(Digital Presentation) Effects of Non-Uniform Temperature Distribution on the Degradation of Liquid-Cooled Lithium-Ion Cells

Non-uniform temperature distribution develops inside lithium-ion (Li-ion) cells due to heat generation and low thermal conductivity in the thickness direction. Such non-uniform temperature distribution can cause non-uniform and accelerated degradation of Li-ion cells, as shown in our previous work on an air-cooled stack consisting of five Li-ion cells1, 2. Compared with air cooling, liquid cooling is more widely used for large-size Li-ion cells due to its stronger cooling capability. Liquid cooling would cause larger temperature gradient in Li-ion cells than air-cooling. It was therefore hypothesized that the degradation of liquid-cooled Li-ion cells will be more non-uniform than air-cooled cells. To test the hypothesis, a stack of water-cooled parallel-connected Li-ion cells, as schematically shown in Figure 1, were tested and compared with the air-cooled stack. Each cell has a nominal capacity of 3 Ah. As expected, the temperature distribution in the liquid-cooled stack was very non-uniform (Figure 2) and the cells degraded differently (Figure 3). Unexpected, however, the middle cell in the water-cooled stack degraded slower than the side cells, which is opposite to the trend of the air-cooled stack. Further investigation suggested that the opposite trend can be attributed to the combined effects of temperature rise and temperature gradient. Moreover, capacity drop and recovery was observed for the cells in the liquid-cooled stack after reference performance test, which could be attributed to the anode overhang effects3. References G. M. Cavalheiro, T. Iriyama, G. J. Nelson, S. Huang and G. Zhang, Journal of Electrochemical Energy Conversion and Storage, 17 (2020). H. J. Gonzalez Malabet, G. M. Cavalheiro, T. Iriyama, A. Gabhart, G. J. Nelson and G. Zhang, Journal of The Electrochemical Society, 168, 100507 (2021). B. Gyenes, D. A. Stevens, V. L. Chevrier and J. R. Dahn, Journal of The Electrochemical Society, 162, A278 (2014). Figure 1