Simplified Electrochemical Approaches for Quality Determination of the Wetting Process in Lithium‐Ion Cell Production

Electrolyte filling and wetting are safety‐relevant and time‐ and cost‐intensive processes in lithium‐ion cell production, and are hence critical process steps. Currently, only limited measurement technologies are available that would be suitable for inline monitoring and quality assurance of these process sequences. Herein, two promising electrochemical approaches for monitoring electrolyte wetting are presented, which can be utilized in low‐cost measurement devices. Starting from the introduction of a simplified impedance approach with a straightforward data evaluation, a direct current‐based method is introduced that does not require impedance equipment, and can thus be performed with standard battery cyclers. First, the extended applicability of the simplified impedance measurement is demonstrated by examining the dependence of experimental impedance results on varying electrolyte volumes, also including insufficient amounts. Subsequently, the impedance approach is transferred into the direct current method. The latter mimics impedance signals by utilizing repetitive direct current charge and discharge pulses, which are used to determine the batteries’ internal resistance during the electrolyte wetting. Both introduced approaches yield comparable results and allow the inline monitoring of the electrolyte wetting with basic equipment and with no need for demanding data evaluation.