From Cell to Battery System - Different Cell Formats and their System Integration
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From Cell to Battery System – Different Cell Formats and their System Integration
© APL | 2dmolier | stock.adobe.com
APL accompanies the battery development process from the selection of the cell format to the integration into the overall system. The company takes a holistic approach combining battery tests, laboratory analyses and extensive simulations that enables targeted optimization of the conflicting priorities for functionality, safety and costs.
STARTING POINT
With a share of up to 60 %, the battery is a significant cost factor in the manufacture of battery-electric powertrains, FIGURE 1. In this context, the selection
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of the optimal cell geometry from the three predominant battery formats – cylindrical, prismatic and pouch – is controversially discussed. While many vehicle manufacturers in recent years have focused on large-format prismatic
or pouch cells, individual companies are pursuing the consistent approach of round cell technology. The battery system is made up of hundreds to thousands of individual cells, which are usually divided into
A U T H O RS
Dipl.-Ing. Christian Lensch-Franzen is CTO at APL GmbH in Landau (Germany).
Dr.-Ing. Marcus Gohl is Head of Basic Development at APL GmbH in Landau (Germany).
Mareike Schmalz, M. Sc. is Project Coordinator in the Department Basic Development at APL GmbH in Landau (Germany).
Dr.-Ing. Tahsin Doguer is Project Engineer in the Department Basic Development at APL GmbH in Landau (Germany).
FIGURE 1 Cost share of battery system and cells in the powertrain and market penetration of cell formats (schematic) (© APL)
additional sub-units, the battery mod ules. The question of the optimal cell cannot be answered solely taking into account the factors of cost and energy density. It is rather an optimization in a complex framework of electrical, thermal and mechanical boundary conditions in the context of the overall system. At the same time, the necessary safety requirements must be guaranteed. APL meets these challenges with a holistic engineering concept. The development work extends from the basic characterization of the battery cells on the material level to the complete system. DIFFERENT BATTERY CELL FORMATS
Cylindrical and prismatic cells have a similar basic structure. In production, electrode layers and separator layers are rolled up into a coil and placed in a fixed housing, FIGURE 2. The pouch cell differs from the other two formats in that it does not have a rigid outer skeleton. With this design, the inner electrode layers are enclosed by a special composite aluminum foil. The cell layers are not MTZ worldwide 11|2020
FIGURE 2 Structure and properties of the battery formats (© APL)
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DE VELO PMENT Batteries
FIGURE 3 Topology of the cell surface (top right), SoC dependency of the expansion (bottom left), local changes in cell thickness (bottom right) (© APL)
rolled but inserted in a stack. This ensures good space utilization and thus a high energy density. MECHANICAL CHALLENGES
The use of pouch cells leads to increased chal
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