Impedance based loss calculation and thermal modeling of electrochemical energy storage devices for design considerations of automotive power systems

Growing concern about the environmental impact of automotive vehicles contributing to the green house effect and thus global warming, associated with the perspective of a growing world population desiring for more individual transportation, lead to the development of new automotive vehicle concepts such as hybrid electrical vehicles. Since electrochemical energy storage devices are major components of such systems, they play a dominant role. However, to find optimal design solutions regarding environmental as well as ecological aspects adequate models are necessary. Especially, modeling of the internal temperature is a critical issue, since it has an significant influence on the performance and the life expectancy of the batteries and double-layer capacitors. Beside this, robustness, durability and reliability as well as cost and safety are further issues which are either directly or indirectly linked to the temperature of these devices. Hence, in this work, a simulation tool which enables engineers to design energy storage stacks with respect to critical temperatures is developed. The model itself consists of several components, such as an impedance-based lass model, a model to represent reversible temperature effects and a three-dimensional heat transfer model with lumped thermal parameters which allows to model anisotropic heat effects. The proposed model considers all relevant heat transfer mechanisms such as conduction, convection and radiation. Due to the structure of the heat transfer model it is very flexible and thus allows to analyze the thermal behavior of single cells as well as cell stacks.