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Validation of a Thermal-Electric Li-Ion Battery Model
Abstract:
Commercial vehicle manufacturers are investing substantial resources into the development and testing of advanced battery systems for the next generation of hybrid and electric vehicles. Likewise the US army is investing in lithium ion battery research for power and energy applications including SLI (starter, lights, and ignition), silent watch, unmanned vehicles, and directed energy weapons. A major design constraint is the management of the heat generated by Li-Ion battery systems. Extreme battery temperatures impact both the performance and reliability of the battery system as well as the overall operation of the vehicle. Analysis tools that can address vehicle and battery thermal management issues are needed to accelerate this development. To meet that need, a coupled thermal-electric model for battery cells and packs has been developed and implemented into the existing thermal modeling software RadTherm. This paper documents the comparison of physical test results with a computer model of the thermal response for an actual vehicle Li-Ion battery cell.
The thermo-electrical battery model described in this paper predicts an effective driving potential and internal conductance for a cell based on the cell environmental temperature and measure of state of charge. From these parameters a local current density is computed and applied to an electrical model of the voltage distribution on the electrodes. Heat generation is derived from the local voltage difference across the electrodes and the current density between electrodes and then applied to a thermal model to predict local temperature rise over the cell.
When applied to a cell, the battery model is useful for predicting the effects of cell size, tab location, and current collector thickness on voltage distribution and local heat generation. The model can also be applied to a multi-cell pack to study the effects of various thermal management strategies. In either application, battery loads corresponding to pre-determined drive cycles can be applied to the model to evaluate the ability of a particular cell or pack design to supply vehicle power in a given operating scenario. In this paper we describe the implementation of the model, compare model predictions to electrical and thermal measurements taken on a test cell, demonstrate the effects of different cell configurations on voltage and temperature distributions, and the show the relative effectiveness of various cooling schemes (natural and forced air convection and edge cooling) applied to a pack.