Meaning
Molecules travel through a non-porous polymer matrix by a combination of dissolution and diffusion processes. In battery cell design, polymer permeation dictates how quickly gaseous species and moisture can penetrate the polymeric gaskets or adhesive seal layers. It directly influences the rate of moisture ingress over years of field operation.
Mass Transport
Solvent molecules from the liquid electrolyte dissolve into the polymer seal and slowly diffuse to the dry exterior. At the same time, ambient moisture enters through the opposite surface, utilizing the same polymer permeation mechanism. The speed of this transport is governed by the chemical concentration gradient and the free volume within the polymer chain structure.
Highly crystalline polymers generally offer better resistance to this type of gas migration.
Sourcing Selection
Material selection for pouch cell sealants and cylindrical cell gaskets requires polymers with low diffusion rates. Sourcing managers evaluate polymer permeation rates when selecting materials such as polypropylene or fluoroelastomers for the seals. Procurement contracts for long-life batteries require validation of the permeation coefficient under varied humidity levels.
This ensures that the chosen elastomer will protect the cell throughout its expected service life.
Material Limitation
Temperature increases accelerate the rate of molecule movement through the polymeric material. High operating temperatures increase the polymer chain mobility, which raises the polymer permeation rate and speeds up the ingress of moisture. Sourcing engineers must therefore specify polymers that maintain their barrier properties at high temperature.
This prevents premature degradation of the electrolyte in heavy-duty or industrial applications.
