Experimental and Numerical Electro-Thermal Characterization of Lithium-Ion Cells for Vehicle Battery Pack Applications

Batteries are the key elements for the massive electrification of the transport sector. With the rapidly growing popularity of electric vehicles, it is becoming increasingly important to characterize the behavior of battery packs through fast and accurate numerical models, in order to support experimental activities. A coupled electro-thermal simulation framework is required, as it is the only way to realistically represent the interactions between real world battery pack performances and the vehicle-level thermal management strategies. The purpose of this work is to pave the way for a comprehensive methodology for the development of a supporting modeling framework, to efficiently complement experiments in the optimal design and integration of battery packs. The full methodology consists of the following steps: i) an experimental analysis of the temperature and current dependence on various internal parameters of selected lithium-ion cells based on their electrochemical properties, ii) development and implementation of a battery cell electric model that takes into account the aforementioned dynamics and their dependencies; the electrical model is based on the Equivalent Circuit Model (ECM) and can be used to calculate the electrical output and losses of Li-ion cells as a function of state of charge and current; iii) development of a cell-level multi-domain computational framework for coupled electro-thermal simulations, based on state-of-the art CFD software tools; iv) validation and tuning of the multi-domain framework through ad-hoc designed experiments with controlled cell charge-discharge profiles and temperature measurement; v) extension of both the ECM and multi-domain approaches to full-scale battery packs, to be adopted for electric vehicle characterization under realistic driving conditions, with detailed battery thermal management. Results shown in the present paper cover steps i) to iv) and include a series of static and dynamic experimental tests with voltage response and temperature measurements performed on the selected Li-ion cells. It is shown that the proposed modeling tools can accurately predict the electro-thermal behavior of the cells under static and dynamic current conditions. Most of the average relative errors between predicted values and test values obtained do not exceed 10%.