Investigating wetting and formation behavior of consumer format pouch cells utilizing ultrasound

Methods to detect electrolyte wetting in lithium-ion batteries (LiBs) are limited, but ultrasound (US) techniques have emerged as a promising solution. In this study, wetting behavior in consumer-format pouch cells (5 × 3 cm) was examined using US transmission, electrochemical impedance spectroscopy (EIS), and dyed electrolyte. The results indicate that wetting is almost immediately completed to a sufficient degree. Residual gas pockets, detectable using ultrasound, seem to take a long time to dissolve in the electrolyte or to migrate out to the sides of the pouch on their own. US measurements imply that these remaining gas pockets are expelled during the formation process due to expansion of the graphite anode during lithiation. The gas pockets initially present are not harmful to cell performance, as shown by aging measurements and the absence of plating after formation. Consequently, the formation process can be initiated almost immediately after filling in this cell format.