Meaning
Flexible multilayer foils are used to construct the protective outer housing of pouch-type electrochemical cells. This composite material, known as pouch cell laminate, typically consists of polymer layers bonded to an aluminum barrier foil. It must provide excellent moisture and chemical resistance while remaining light and thin.
Layered Architecture
The external nylon layer provides mechanical and puncture resistance during handling and assembly. Underneath, the aluminum layer serves as a barrier against moisture and gas ingress, which is vital for maintaining the cell chemistry. The innermost layer is made of cast polypropylene, which melt-seals when heated to create a hermetic closure.
This layered structure allows the pouch cell laminate to remain flexible while offering superior protection.
Sourcing Specification
Procurement specifications must detail the thickness of both the aluminum core and the inner polymer layer. Sourcing managers select the pouch cell laminate based on the required form factor and the expected life of the battery. A thicker aluminum layer provides better protection but increases weight and reduces energy density.
Buyers negotiate with laminate manufacturers to balance these trade-offs, ensuring that the material meets the requirements of the specific application.
Failure Vulnerability
Corrosion of the laminate foil occurs if the inner polymer layer is breached by electrolyte. The hydrofluoric acid formed by the reaction of moisture and electrolyte salts can eat through the cast polypropylene and attack the aluminum layer. This leads to delamination and eventual cell leakage, which poses a safety risk.
Sourcing contracts should require the laminate to pass chemical resistance tests to ensure that the material can withstand these chemical attacks.
