Development of 21700 Cell - Change of the cell format for demonstrator cells

The potential of the developed technologies and materials in the CoFBAT project will be displayed by the construction of demonstrator cells. Preferably, the format of these demonstrator cells should meet state of the art standards.

In this context, the project partners have chosen to change the cell format from 30Ah stacked pouch cells to wounded cells of the type 21700 with a foreseen capacity of ~4-5Ah.

This cylindrical 21700 cell format – a cell with 21mm in diameter and 70 mm in height - is well known in various applications, reaching from power tools to automotive applications. Nowadays this cell format is also used by large automotive companies focusing on e-mobility. The increased importance of the cell format is mainly driven by the possibility to reduce costs in cell production. At the Tesla Battery Day 2020 the company even displayed that considering cell size, cell form and costs, the company is intensively working on increasing the 21700 cell format to 46800 (46 mm diameter, 80mm height).

Advantages and Disadvantages of the different cell formats:

Cylindrical cells are well suitable for high-speed automated manufacturing, allow easy thermal management on pack level and provide high mechanical stability. The disadvantages comprise lower packaging density on pack level and a larger required number of contactors and support due to the smaller cell capacity.

A stacked pouch cell allows the lowest weight and highest flexibility in electrode dimensions, it is not comparable processable on automated machinery in terms of speed, costs, and precision.

The new demonstrator format in the context of CoFBAT:

Regarding the CoFBAT project, the change of cell format provides various benefits:

  • The materials can be tested in demonstrator cells produced on the highest level of mass production

  • Commercialisation grade of the cell format allows a qualification of the project´s inventions against commercialized products at a comparable standard

  • From the production perspective the change from stacked to cylindrical format result on the one hand in a higher complexity due to the winding step, but on the other hand, it provides the notable benefit, to assess the potential of the developed gel polymer electrolyte/separator technologies in cylindrical usage.

The novel 21700 concept cell implemented based on Gel polymer electrolyte and cobalt free anode/cathode will provide a breakthrough in thermal stability, cycling and cost.

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