Enhancing the interfacial bond strength of aluminum/polymer laminated film of the soft package lithium‐ion battery through polydopamine surface modification

Abstract The aluminum (Al) foil used in Al/polymer laminated film of the soft package lithium‐ion battery (LIB) is widely treated with a hexavalent chromate conversion coating to increase the adhesive strength and durability of the adhesive joint. Given that hexavalent chromate is toxic and carcinogenic, a novel and chromate‐free method was developed in this study for surface modification of the Al foil using polydopamine (PDA) functionalization after titanium (Ti) chemical conversion. Ti conversion favors the deposition of PDA and introduces more functional groups of PDA on the Al surface. A novel polypropylene‐based hot melt adhesive, MAH‐g‐(PP/PBE), was prepared by melt grafting of maleic anhydride on the blend of polypropylene and propylene‐based elastomer for use as the inner adhesive of Al/polymer laminated film. Then, treated Al foil/MAH‐g‐(PP/PBE) composites were prepared and their interfacial adhesive strengths were investigated. The results show that the amine and catechol groups of PDA improve the interfacial adhesion between adhesive and Al foil by improving the wettability and interfacial interaction. The peel strength between MAH‐g‐(PP/PBE) and PDA functionalized Al foil after Ti conversion treatment can reach 3.55 N/mm, which is increased by 322% compared with that between MAH‐g‐PP and untreated Al foil. PDA functionalization after Ti chemical conversion and MAH‐g‐(PP/PBE) have great potential to improve interfacial adhesion of Al/polymer laminated film used in LIB package.