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Today's Li-ion battery stringent requirements include high electric currents, large format cells and possibly the use of carbon based current collectors, which would enhance the electrochemical-thermal non-uniformities in the cell. Although a number of models have been implemented in order to study such non-uniformities, no efforts have been made to describe the distribution of side reaction rates and their effect on aging distribution. To fill that gap, we developed a pseudo-3D porous electrode electrochemical model that incorporates via first principles the solid-electrolyte interphase (SEI) growth on the anode, which is thought to be a dominant aging mechanism. The model was used to simulate the cyclic behavior of a large format (40 Ah) Li-ion polymer pouch cell with the assumption of a carbon based positive current collector. It was found that SEI growth localization would form in the electrode thickness and planar dimensions during discharging, but would be destroyed during the subsequent charging, so that the associated aging would be uniform upon cycling. This suggests that computationally efficient lumped models could be used to describe the cell aging process associated with the SEI growth on the graphitic anode, which would be ideal for onboard implementations such as in electric vehicle applications.

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SUMMARY The thermal behavior of a Li‐ion battery module that belongs to the battery system of an actual electric vehicle prototype was numerically investigated. Realistic driving loads and passive cooling conditions were considered. A combination of a vehicle dynamics model, an equivalent electric circuit battery model, and a 3D finite‐element thermal model was used in the analysis. Temperature and electric potential measurements, performed at the cell and module levels, were first used for model calibration. Electric currents, associated with the ARTEMIS driving cycles, were then calculated and applied in the battery model to predict the heat sources for the thermal model. It was found that the temperature increase corresponding to urban transportation requirements in European countries is tolerable. Nevertheless, road and highway applications would result in a temperature increase that accelerates cell ageing, and an active cooling strategy is required. Copyright © 2012 John Wiley & Sons, Ltd.

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To gain insight into the collector-electrode interface in Li-ion batteries, a mesoscale model resolved at the particle scale in a representative volume element domain was developed. The underlying microstructure was first generated using a random packing and a dynamic collision algorithm. A finite element stress analysis was then used to calculate the deformations which are induced by Li-ion concentrations. The collector-electrode mechanical interaction was modeled using an adhesive contact law which was derived from the atomistic Lennard-Jones energy potential considering Van der Waals attractions. A finite element electrical analysis followed to calculate the collector contact resistance considering quantum tunneling currents. As a model application, we elaborated the role of the electrode microstructure by evaluating the damage and contact resistances for 8 various LiFePO 4 based cathodes. We found that optimum interfaces would be achieved using a rough collector, low porosity, small particle sizes with disk like shapes and conductive additives in the interstitial sites. Pressure application was also beneficial. The developed model could be used either separately prior to commonly used porous electrode electrochemical models which require the collector-contact resistance as a parameter, or coupled in a 3D mesoscale electrochemical analysis so that a mechanical-electrochemical interaction would be considered.

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One of the challenges faced when using Li-ion batteries in electric vehicles is to keep the cell temperatures below a given threshold. Mathematical modeling would indeed be an efficient tool to test virtually this requirement and accelerate the battery product lifecycle. Moreover, temperature predicting models could potentially be used on-board to decrease the limitations associated with sensor based temperature feedbacks. Accordingly, we present a complete modeling procedure which was used to calculate the cell temperatures during a given electric vehicle trip. The procedure includes a simple vehicle dynamics model, an equivalent circuit battery model, and a 3D finite element thermal model. Model parameters were identified from measurements taken during constant current and pulse current discharge tests. The cell temperatures corresponding to an actual electric vehicle trip were calculated and compared with measured values. The resulting accuracy was high enough (max error 1.07 K) and suggests that designers could rely largely on similar numerical thermal simulations during the design of Li-ion battery systems for electric vehicles. Additionally, the thermal model could be used on-board in a battery management system control strategy to keep the cell temperatures within a safe window. A model reduction procedure is nevertheless needed to scale down the computational effort to the on-board capabilities.