The cell designs by Fraunhofer FFB

Level of development of the round cell, prismatic cell and pouch cell

The design of a battery cell plays a crucial role in determining its characteristics, such as energy and power density, aging, and safety behavior. Three common cell formats include the round cell, prismatic cell, and pouch cell, which are utilized across industries, not just in automotive applications. Power tools often use round cells, while smart devices rely on pouch cells. The prismatic cell, with its sturdy housing, is often the preferred choice in commercial vehicles.

Lecture »Cell designs from Fraunhofer FFB - flexible and adaptable« 

Presentation by our Head of Product and Production Technology Saskia Wessel at the online conference for electromobility live on 29. March 2023. It was held in german, but auto-subtitles are available in many languages.

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The structure of prismatic cells resembles that of a pouch cell, except for the hard case that serves as its outer housing. These cells can hold one or more stacks of cells or flat coils, with arrester flags connected to terminals embedded in the cover. This design can be more complex than that of a pouch cell, as it can accommodate multiple cell composites. Additionally, electrodes can be stacked or wound, similar to round cells. Once the cell stack is packed into the housing, it is filled with electrolytes and sealed. Advantages and disadvantages of the pouch cell

  • (+) Safety and thermal management
  • (-) Power and energy density

FFB PrismCell medium and FFB PrismCell Large

Fraunhofer FFB will produce two models of the prismatic cell, which differ in dimensions: The FFB PrismCell medium will measure 100mm shorter and also a few millimeters less in width than the FFB PrismCell Large. With these two sizes, we cover the most important application areas of prismatic cells.

  • FFB PrismCell medium: stationary storage systems
  • FFB PrismCell large: E-mobility

For each model, there will be a "high power" and a "high energy" variant, which differ from each other in the cell chemistries used.

We anticipate creating the initial prototypes by the summer of 2023. The Large model should be ready for production by 2025 at the "FFB PreFab," while the "FFB Fab" will be responsible for the Medium cells. By combining the pouch cell and prismatic cell, we can take advantage of their synergy and use cell stacks created on the pouch line for prismatic cell production at the "FFB PreFab."Research focuses on the prismatic cell the contacting system, safety elements, lid assemblies, production optimization, and the usability of the results obtained here for new cell chemistries (e.g. sodium ions and ASSB). 

Der Zelldummie der prismatischen Zelle

The basis of the cylindrical cell provides a coil (or jellyroll). This is made of long strips, consisting of the anode, the separator, and the cathode, which are wound up. The coil is placed in a cylindrical metal housing, filled with electrolytes, and sealed.

Advantages and disadvantages of the cylindrical cell

  • (+) Energy density and manufacturing costs
  • (-) Flexibility and thermal management

The FFB round cells

Two different round cells with a height of 70mm and a diameter of 21mm (Format21700) are currently under development. One variant is being developed with a high energy density (HE) and another is optimized in terms of performance (HP).

In pouch cells, several anodes and cathodes are alternately stacked on top of each other (e.g. via single sheet stacking or the Z-fold process), separated by a separator. At each electrode, there are so-called arrester flags for contacting. A distinction is made between the so-called counter-tab (arrester flags opposite each other) and the one-sided-tab (arrester flags on the same side) design. The electrode stack is sealed in a flexible pouch foil, filled with electrolyte, and sealed.

3D-Explosionsgrafik einer OST-Pouchzelle