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Kirchheim unter Teck, Germany

Veth C.,Dt. ACCUmotive GmbH and Co KG. | Dragicevic D.,Dt. ACCUmotive GmbH and Co KG. | Pfister R.,Dt. ACCUmotive GmbH and Co KG. | Arakkan S.,MBRDI India | Merten C.,University of Stuttgart
Journal of the Electrochemical Society

This paper presents a 3D electro-thermal model approach for large-format lithium ion cells. The model development is focused on the prediction of 3D behavior of large-format lithium ion cells up to high discharge currents. The distribution and inhomogeneity of internal state values in the cell like temperature, current, power loss, SOC as well as voltage can be predicted reliably with this kind of models. The demand for calculating these state values on battery management systems can be met with a model order reduction introduced in this paper. Moreover, the interdependency of the temperature inhomogeneities and the inhomogeneities of inner state values in the cell can be studied. These dependencies have major influence on lifetime and performance of large-format lithium ion cells during common traction applications. The paper presents the configuration of a 3D equivalent circuit model considering full cell geometry and internal electrical resistances. In order to consider 3D thermal as well as 3D electrical effects, the direct coupling of the 3D electrical model with a 3D thermal FEM model is introduced. Furthermore, in this paper a convergence study on elementary cell resolution is performed. Additionally, the model is comprehensively validated with a thermal characterization over a wide range of temperature and current up to 300 A. © 2014 The Electrochemical Society. Source

Veth C.,Dt. ACCUmotive GmbH and Co KG. | Dragicevic D.,Dt. ACCUmotive GmbH and Co KG. | Merten C.,University of Stuttgart
Journal of Power Sources

The thermal behavior of a large-format lithium ion cell has been investigated during measurements on cell and battery level. High current discharges up to 300 A are the main topic of this study. This paper demonstrates that the temperature response to high current loads provides the possibility to investigate internal cell parameters and their inhomogeneity. In order to identify thermal response caused by internal cell processes, the heat input due to contact resistances has been minimized. The differences between the thermal footprint of a cell during cell and battery measurements are being addressed. The study presented here focuses on the investigation of thermal hot and cold spots as well as temperature gradients in a 50 Ah pouch cell. Furthermore, it is demonstrated that the difference between charge and discharge can have significant influence on the thermal behavior of lithium ion cells. Moreover, the miscellaneous thermal characteristics of differently aged lithium ion cells highlight the possibility of an ex-situ non-destructive post-mortem-analysis, providing the possibility of a qualitative and quantitative characterization of inhomogeneous cell-aging. These investigations also generate excellent data for the validation and parameterization of electro-thermal cell models, predicting the distribution of temperature, current, potential, SOC and SOH inside large-format cells. © 2014 Elsevier B.V. All rights reserved. Source

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