Helium Leak Rate Conversion for Pouch Cell Seals
Convert helium leak rates to air and moisture ingress rates by identifying the microchannel flow regime using Knudsen numbers to calculate 10-year cell degradation.
Tab Seal Voids
Meaning
Unfilled gaps or pockets of trapped gas within the thermoplastic seal around the metal terminal tabs of a pouch cell compromise the hermetic barrier. Operators monitor for tab seal voids because they create potential leak paths for electrolyte and allow external moisture to enter the cell. The mismatch in thermal conductivity between the metal tab and the surrounding polymer laminate often causes these defects during heat sealing.
Void Formation
Surface contamination on the metal tab or insufficient seal pressure prevents the thermoplastic adhesive from wet-out on the metal surface. The presence of tab seal voids is particularly common at the transitions where the tab enters the pouch, where the polymer must deform around a sharp metal edge. Pre-treating the metal tabs with a polymer primer layer helps to minimize the occurrence of these defects.
Inspection Method
Acoustic microscopy and high-resolution thermography are used to detect internal air pockets without destroying the cell. Cells exhibiting tab seal voids of a size exceeding the quality threshold are rejected before the electrolyte filling step to prevent future leakage. Standardized vacuum leak tests confirm the physical integrity of the terminal area.
Failure Consequence
Ingress of moisture through these microscopic paths leads to the formation of gaseous reaction products and cell swelling. Over time, the electrolyte degradation caused by tab seal voids reduces the capacity of the cell and increases its internal resistance. Robust sealing protocols are therefore critical to ensuring the long-term reliability of pouch batteries.