Pouch Cell Heat Seal Micro-Void Detection and Transport Leak Resistance
Pouch cell heat seals require precise thermal pressing and non-destructive inline acoustic or helium screening to prevent micro-void leaks during transit.
Solvent Swelling
Meaning
Physical phenomenon occurs when a polymer absorbs organic liquid and increases in volume. In pouch battery packaging, solvent swelling affects the inner polymer layers when they come into contact with the liquid electrolyte. This absorption can weaken the mechanical properties of the sealant layer and lead to delamination.
Material Degradation
Linear carbonate solvents like dimethyl carbonate can penetrate the amorphous regions of the polypropylene film. This penetration reduces the intermolecular forces between polymer chains, leading to a loss of tensile and peel strength. Sourcing specialists select highly crystalline polymers that are less susceptible to this type of volume increase.
Hermetic Failure
Weakened seals are prone to micro-leakage and moisture ingress under thermal cycling conditions. As the polymer expands, the adhesive bond with the neighboring aluminum foil is subjected to constant peel stresses. This continuous tension can cause the seal to fail prematurely during the operating life of the battery.
Prevention Method
Selecting the correct polymer density and copolymer ratio helps to limit this absorption and maintain seal integrity. Testing protocols require submerging sealed film samples in the solvent mixture at high temperatures to measure the percentage change in weight and thickness. This evaluation ensures that the chosen pouch material can survive the cell life cycle without loss of structural strength.
It allows the cell to maintain its structural boundary under all standard charging and discharging schedules.