Optimized Heat Dissipation of Energy Storage Systems
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Optimized Heat Dissipation of Energy Storage Systems The quality of the heat dissipation from batteries towards the outer casing has a strong impact on the performance and life of an electric vehicle. The heat conduction path between battery module and cooling system is realized in series production electric vehicles by means of paste-like materials. These so-called gap fillers exhibit high thermal conductivity and specific mechanical properties. The aim of an ongoing BMWi research project is to develop a new generation of gap fillers with improved thermal conductivity and reduced density and to qualify them for use in series production.
Michael Frauenhofer, Marc Gormanns, Martin Simon, Martin Rütters, Holger Fricke
The Audi E-tron convinces with the performance of its electric drive. While other electric vehicles electronically throttle down after short intervals with maximum power output to prevent the battery from overheating, the battery of the E-tron maintains its specific operating temperature thanks to a sophisticated cooling system. To make this possible, Audi has designed and implemented a comprehensive thermal management system.
Significance of the gap filler The gap filler takes over the function of heat conduction and tolerance compensation between battery module and battery housing. During the assembly of the battery, the gap filler is applied into the compartments of the battery tray by a robot (Figure 1). The battery modules are then inserted. During this movement, the gap filler is effectively pressed against the surface to be wetted, and great care must be taken not to damage the pressure-sensitive battery cells. The flow properties of the gap filler are therefore formulated in such a way that resulting pressing forces prevent any damage to the battery. At the 12
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same time, the gap between the battery and the casing ground must be completely filled without air bubbles. This concept has already been in series production since 2018, and to date, over 50,000 vehicles have been produced and sold. Like the combustion engine in conventional cars, the battery is a core component of electric vehicles that significantly determines its price. Due to the operational reliability, all current concepts assume that the individual battery cells can be integrated into a lightweight battery housing. The battery housing is advantageously completely integrated into the vehicle body shell lower as much as possible the center of gravity of the vehicle. For safety reasons, the water- cooling system is placed underneath the battery modules to ensure that the lithiumion cells are not exposed to water, even during a crash. Pure polymer-based resins or pastes have an intrinsically low thermal conductivity, so they must be filled with particles of higher thermal conductivity for efficient heat dissipation. At present, ceramic particles, e.g. made of aluminum oxide, are used in particular, whereby high degrees
of filling is aimed at to achieve maximum thermal conductivity. Furthermore, pastes available to
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