Experimental and density functional theory study of the effect of polar groups on interaction at the polyolefin-aluminum laminated film interface

Abstract

Good adhesive strength and joint durability are necessary for aluminum (Al)/polymer laminated film for lithium-ion battery packages. A modified propylene-based elastomer (mPBE) was prepared as the inner adhesive in this study. The polar group was grafted onto the PBE molecular chain via melt grafting with the assistance of styrene. The adhesive performance of PBE modified with glycidyl methacrylate is significantly higher than that of commercially available inner adhesives, Mitsui A and Dupont 739. Moreover, environmentally friendly trivalent chromium [Cr(III)] chemical conversion was used to treat Al foil and improve the adhesive joint. The wettability behavior of adhesive melt on the surface of Al foil was studied using high-temperature contact angle testing. The results indicate that wettability is not the sole factor impacting interfacial strength, surface energy of the adhesive melt also plays a role. To further study the effect of polar groups on the mPBE adhesion, a solvent casting-evaporation method was developed to prepare an ultra-thin mPBE coating on the Al foil surface. The morphology of mPBE-coated Al foils and the thickness of the coating were studied by atomic force microscope. The bonding mechanism at the interface was studied through time-of-flight secondary ion mass spectroscopy, and it was shown that the Cr(III) conversion coating could react with polar groups via acid-base interaction. Moreover, quantum chemical calculations based on density functional theory were used to reveal the bonding mechanism at the molecular level, and it is found that the adhesive strength is related to the electron-donor abilities and reactivity of the adhesive molecules.