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Titel:

CFP2022-880

Direct design comparison of Li-ion cells in the formats PHEV1, pouch, 18650, and 21700 built on pilot-scale
Lecture
Cell design advances
Design

The industrially-relevant cell formats PHEV1 (prismatic), multi-layer pouch, 18650 and 21700 (cylindrical) [1] are directly compared by experiments. The direct comparison becomes possible by using the same anode (graphite), cathode (NMC622), separator, and electrolyte. Our experiments show that the main differences between these formats are their capacities, sizes, as well as tab and the jellyroll/stack configurations (flat-wound, stacked, wound). Our comparison involves voltage curves during formation (0.1C), discharge rate capability (0.5C – 3C), cell resistances (1 kHz), heating behavior due to current flow, and tab configurations, as well as comparison with coin half cells with anode and cathode vs. Li counter electrode. The data are put into context with results from commercial cells [2]. Interestingly, we find that the volume/surface ratio of the cells has a strong influence on the heating behavior and therefore on the discharge capacity at high C-rates (see image) [3]. The cell resistance is mainly affected by the cathode area and the tab configuration. While aging at 1C/25°C is very similar in 18650 and 21700 cells, we show that the cycle life can be improved by a special tab design in 21700 cells.

References:
[1] T. Waldmann, R.-G. Scurtu, K. Richter, M. Wohlfahrt-Mehrens, J. Power Sources. 472 (2020)
228614. https://doi.org/10.1016/j.jpowsour.2020.228614
[2] J.B. Quinn, T. Waldmann, K. Richter, M. Kasper, M. Wohlfahrt-Mehrens, J. Electrochem. Soc. 165
(2018) A3284–A3291. https://doi.org/10.1149/2.0281814jes
[3] T. Waldmann, S. Rössler, M. Blessing, R. Schäfer, R.-G. Scurtu, W. Braunwarth,
M. Wohlfahrt-Mehrens, J. Electrochem. Soc. 168 (2021) 090519,
https://doi.org/10.1149/1945-7111/ac208c

Acknowledgment:
Funding of the projects E-QUAL (03XP0252A) and RollBatt (03XP0245A) by the German Federal Ministry of Education and Research (BMBF) are gratefully acknowledged.

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Co-Autoren

Stefan Rössler, Markus Blessing, Rares-George Scurtu, Daniel Brändle, Wolfgang Braunwarth, Margret Wohlfahrt-Mehrens

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