This case study explores the mechanical behavior of ultra-thin battery separator films and aluminum current collectors used in lithium-ion batteries. Using ASTM-compliant tensile testing with an Instron 68SC-5 and high-precision Instron AVE3 non-contact video extensometer, Covalent evaluated the tensile properties of a 25 µm multilayer PP–PE–PP separator film alongside a 12 µm aluminum current collector foil. The study demonstrates how ultra-thin battery materials experience fundamentally different mechanical demands during winding, calendaring, slitting, and assembly operations. Stress–strain analysis revealed the separator film exhibited high ductility and flexibility, reaching approximately 56.6% strain at break, while the aluminum foil demonstrated significantly higher stiffness and strength but fractured at only ~0.85% strain. The results highlight the importance of accurately characterizing elastic modulus, yield stress, tensile strength, and strain-to-failure in advanced battery materials as manufacturers continue pushing toward thinner, lighter, and higher-energy-density cell designs. The study also demonstrates the exceptional repeatability and precision achievable using modern non-contact strain measurement techniques for delicate thin-film battery materials.
Tensile Testing of Lithium-Ion Battery Separator Films and Aluminum Current Collectors
Lithium-ion battery separators and current collector foils keep getting thinner, and every micron they lose makes them easier to tear, wrinkle or crack during winding, calendering and slitting. In this case study, we ran tensile tests on a 25 µm PP–PE–PP separator and a 12 µm aluminum foil, using a non-contact video extensometer to measure strain accurately on films this delicate. The two materials failed in very different ways: the separator stretched past 56% strain before breaking, while the foil fractured at under 1%.