Cell manufacturing/Formation

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Production process

• The formation describes the first charging and discharging processes of the battery cell.
• For formation, the cells are put in special good carriers in formation racks and contacted by spring-loaded contact pins.
• The cells are then charged or discharged according to precisely defined current and voltage curves.
• During formation, lithium ions are embedded in the crystal structure of the graphite on the anode side. Here the Solid Electrolyte Interface (SEI) is formed, which creates a interface layer between the electrolyte and the electrode.
• The parameters during formation vary depending on the cell manufacturer and have a high impact on cell performance. They depend on the cell concept and chemistry and represent the core knowledge of a cell manufacturer.
• In some cases, pouch cells in particular are pressurised during formation by special good carriers.

Process parameters & requirements

• First charge: approx. 0.1 C - 0.5 C; State of Charge (SOC) approx. 20 % - 80 %
• Successive increase in C-rates with each charging and discharging cycle
• Duration of formation process: up to 24 h
• Low contact resistances at the spring-loaded contact pins

Technology alternatives

• There are different procedures for the formation depending on the cell manufacturer and cell chemistry.

Quality influences

• Orientation of the cells
• Contact method
• Process temperature
• Pressurisation, especially of pouch cells

Quality features

• Formation of the SEI layer
• Stability of the SEI layer
• Internal resistance of the cell

Source

Heimes, H.H.; Kampker, A.; Lienemann, C.; Locke, M.; Offermanns, C.; Michaelis, S.; Rahimzei, E. (2018) Lithium-Ion Battery Cell Production Process; PEM of RWTH Aachen and VDMA, 3rd Edition, ISBN:978-3-947920-03-7

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Subject	Property	Object
Cell manufacturing/Formation	HasPredecessor	Cell manufacturing/Electrolyte Filling
Cell manufacturing/Formation	HasSuccessor	Cell manufacturing/Degassing

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