Lean Cell Finalization in Lithium‐Ion Battery Production: Determining the Required Electrolyte Wetting Degree to Begin the Formation

In order to make electric transportation more accessible, the cost of lithium‐ion batteries must decrease. One way to achieve this is by increasing the production rates, especially in the time‐consuming steps of electrolyte filling and cell formation. Within this work, lithium‐ion pouch and hardcase cells are filled with electrolyte and the formation is started at varying wetting degrees. Data from the formation, stabilization, and life cycle testing are analyzed to determine the effect of an incomplete wetting degree on the cell quality. Additionally, postmortem analysis is performed to help understand the mechanisms induced when a cell with incomplete wetting is subjected to a current. The pouch cells demonstrate a linear capacity fade, regardless of the wetting degree, but feature strong lithium plating which becomes visible during postmortem analysis. In contrast, the hardcase cells display a clear correlation between the cell quality and the wetting degree in both the life cycle test and the postmortem analysis. It is shown that a wetting degree of 98% is required before starting the formation to avoid lithium plating in the cell. Within this work, lithium‐ion pouch and hardcase cells are filled with electrolyte and the formation is started at varying wetting degrees. The effect of beginning the formation with a partial wetting degree is studied based on cell testing data and postmortem analysis, which shows pronounced lithium plating in cells with insufficient wetting.