Moisture Control from Electrolyte Fill to Export Container
Electrode vacuum baking below 15 ppm residual water prevents hydrofluoric acid formation during electrolyte filling, preserving cell cycle life and landed margin.
Aluminum Laminate Foil
Meaning
This multilayer composite material protects the sensitive internal elements of pouch style lithium batteries from the external environment. A typical aluminum laminate foil consists of an outer polymer layer, a central metal foil, and an inner thermally sealable polymer layer. It acts as an absolute barrier against moisture and oxygen ingress while preventing electrolyte leakage.
Sourcing agents buy this material based on its thickness and formability during the deep drawing process. If the barrier is breached, moisture reacts with the lithium salts to form hydrofluoric acid.
Material Composition
Sourcing specifications define the exact polymers and adhesives used to bind the layers together. Polyethylene terephthalate or polyamide usually forms the outer protective layer to resist mechanical wear and impact. The middle layer of aluminum foil provides the main moisture barrier and must be free of pinholes to ensure pack longevity.
Polypropylene serves as the innermost layer, providing chemical resistance against the aggressive solvents present in the organic electrolyte. This inner layer enables secure thermal sealing under heat and pressure during the final assembly of the cell. Quality controls test the adhesion strength between these layers to prevent delamination during thermal cycling.
Forming Capability
The behavior of this foil during the cold forming process determines the maximum depth of the pouch compartment. Specifiers measure the limiting draw ratio and the elongation at break of the material to ensure that deep pockets can be formed without tearing or microcracking. When the foil is stretched too thin, its barrier properties degrade rapidly, which increases the moisture transmission rate.
Engineers select the thickness of the aluminum core based on the required pouch depth and the mechanical forces the cell will encounter. Heavy duty designs use thicker cores to withstand high internal pressures.
Sealing Reliability
The hermetic seal formed along the edges determines the operational lifespan of the pouch cell. Thermal welding parameters must be carefully optimized to melt the inner polymer layer without damaging the metal core or the outer coatings. This weld must withstand the chemical attack of the electrolyte and the mechanical stresses of cell swelling during charge cycles.
If the seal fails, moisture entering the cell leads to gas generation and capacity fade. Sourcing contracts define the minimum acceptable seal strength and the resistance to electrolyte degradation over the specified storage period.