In Situ Measurement of Temperature Distribution in Cylindrical Li-Ion Cells

Temperature is critical to the performance, durability and safety of Li-ion batteries [1-5], which are the major challenges for wide application of Li-ion batteries in electric vehicles [1,6]. While surface temperature of Li-ion battery is commonly monitored for proper thermal management, our recent experimental study [7] of internal temperature in cylindrical Li-ion cells shows that the surface temperature can be very different from internal temperature during operations at high C rate, low ambient temperature, or with strong surface cooling.

Due to the sensitivity of Li-ion battery to temperature, measuring internal temperatures can provide more insights about thermal behaviors of Li-ion batteries than measuring only surface temperature. Experimental data of internal temperatures are also valuable for validation of electrochemical-thermal coupled (ECT) battery models that are increasingly used to improve the performance, durability and safety of Li-ion batteries [1,3,8-10]. 

In this study, experimental cylindrical cells (size 18650) with multiple embedded micro thermocouples are manufactured in the Battery Manufacturing Lab at The Pennsylvania State University. Spatial-temporal temperature distribution of the experimental cells is measured experimentally and compared with the surface temperature.

Figure 1 shows schematically the locations of micro thermocouples inside an experimental cylindrical cell. One micro thermocouple (T₁) is located in the hollow core of jelly roll where no heat is generated and local temperature is expected to be lower than that in electrode areas. Three micro thermocouples (T₂, T₃ and T₄) are located between electrode and separator where reaction occurs and heat is generated. Another thermocouple (T₅) is placed on the cell surface to measure surface temperature as a reference.

Figure 2 compares the performance of an experimental Li-ion cell with embedded micro thermocouples and a control Li-ion cell without embedded micro thermocouples. The good agreement of their performance shows that the micro thermocouples have negligible effects on the performance of experimental cell.

Using the experimental cylindrical Li-ion cell, spatial-temporal temperature distributions under various conditions are obtained. The effects of critical parameters on temperature distribution, including C rate, ambient temperature, cooling condition, are investigated.

References

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6. DOE, Fiscal Year 2012 Progress Report for Energy Storage R&D, DOE/EE-0844, (2013).

7. G. Zhang, L. Cao, S. Ge, C.Y. Wang, C. E. Shaffer, and C. D. Rahn, 224^th ECS Meeting, MA2013-02, B3, #538 (2013).

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9. G. Luo and C. Y. Wang, Chap. 7 in Lithium-Ion Batteries: Advanced Materials and Technologies, X. Yuan, H. Liu and J. Zhang Editors, CRC Press (2012).

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