Tensile Testing on Battery Thin Films

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.