The formation of Lithium ion batteries (LIBs) is one of the most important steps during battery production, which can affect the batteries lifetime, safety and quality. The initial charge/discharge cycles determine the structure and composition of the solid electrolyte interphase (SEI) and controls a time-consuming production step. Numerous studies focused on the understanding of the SEI build-up and its effect on the battery quality. An Inline-battery-analysis while performing the formation would be a fast quality control and a helpful tool for process optimization.

Without interrupting the current flow of the formation multiple real-time impedance spectra are measured during the formation of a multilayered pouch cell. Therein, information can be gained regarding the different interphase and charge transfer resistances as well as their progression, leading to the determination of the SEI formation completion and potential lithium plating effects. Measuring an impedance spectrum every minute, time, voltage or state of charge dependent effect could be analyzed via an equivalent electrical circuit.

In this study voltage regions with impedance spectra changes in the formation of a multilayered pouch cell with NMC811||C are examined. The voltage ranges from the correlate with the differential capacity test. The online impedance spectroscopy technique is a powerful tool to determine cell quality parameters during cell finalization.