Meaning
Structural imperfections describe tiny gaps or air pockets within the fused layers of a pouch cell’s edge closure. These heat seal micro-voids form during the vacuum sealing process when thermal parameters or pressure application are inconsistent. They create potential leak paths for electrolyte vapors and points of entry for atmospheric moisture.
Formation Process
Thermal bonding requires precise control over the temperature, time, and pressure applied to the polymer layers. When the molten plastic fails to wet the metallic foil completely, heat seal micro-voids remain at the interface. These defects are often too small for visual inspection but appear under scanning electron microscopy.
Degradation Risk
Internal pressure fluctuations cause these small gaps to expand over the life of the battery. The presence of heat seal micro-voids leads to a slow loss of solvent and a corresponding rise in internal resistance. Contamination by water vapor through these channels causes hydrofluoric acid formation which corrodes the internal components.
Quality Control
Helium leak testing or vacuum decay methods identify the presence of these flaws in finished cells. Reducing the occurrence of heat seal micro-voids involves optimizing the polymer blend and the sealing jaw geometry. This ensures the long term reliability of the energy storage system.
