The future development of electric vehicles is linked with their batteries. In parallel of the actual research focused on the development of new materials and increase of batteries performances in terms of energy, power, cost, durability and weight, it is necessary to develop modeling tools. The simulations are helpful for improving the knowledge of both physical and chemical phenomena, optimize the battery design according with the user requirements, and reduce the test/validation phase. Mathematical models are also of crucial interest in the Battery Management System, in order to improve safety and performance during operation (in particular state of charge and state of health indicators).

In the present study, the sensitivity and accuracy determination of basic parameters of the cell is first discussed. In Li-ion batteries the existence of the SEI layer and the formation of this layer during first cycles leads to unprecise knowledge of the initial insertion state of both electrodes [1] (and the faradaic balance between the two). Our work show that no heavy simulation models are needed to evaluate these parameters, provided that the thermodynamical insertion isotherms of the two electrodes are known. These can be determined at small current in a pouch cell configuration. Importantly, the shape of these isotherms has a strong influence on the accuracy of this strategy to evaluate the initial insertion states of both electrodes.

The second part of this work revisits one of the most used porous electrodes based model to describe the behavior of lithium-ion batteries [2]. Numerous complex derivations [3] of this model are available in the literature, but relatively few works-to the best of our knowledge- analyze in details its predictive capability. To investigate the model, firstly, all the physical quantities are set in a dimensionless form, as commonly used in fluid mechanics: the parameters that act in the same or the opposite ways are regrouped and the total number of simulation parameter is greatly reduced. In a second phase, the influence of the parameter is discussed, and interpreted with the support of the limit cases. This analysis is based on galvanostatic and pulse/relaxation profiles (discharge voltage and concentration gradients) compared with tested commercial NMC/NCA LIB. The simulations are performed with the software Comsol® and the post-processing with MatLab®.

References

[1] M. Ecker, K. Dung, P. Dechent, K. Stefan, A. Warnecke, D. U. Sauer, Parameterization of a Physico-Chemical Model of a Lithium-Ion Battery, I. Determination of Parameters, J. of The Electrochemical Society, 162 (9) A1836-A1848 (2015)

[2] M. Doyle, T. Fuller, J. Newman , Modeling of Galvanostatic Charge and Discharge of the Lithium/Polymer/Insertion Cell, J. Electrochem. Soc. 140 (1993) 1526

[3] J. Li, Y. Cheng, L. Ai, M. Jia, S. Du, B. Yin, S. Woo, H. Zhang, 3D simulation on the internal distributed properties of lithium-ion battery with planar tabbed configuration, J. of Power Sources 293 (2015) 993-1005