Low-Cost Mass Manufacturing Technique for the Shutdown-Functionalized Lithium-Ion Battery Separator Based on Al₂O₃ Coating Online Construction during the β-iPP Cavitation Process

A shutdown-functionalized lithium-ion battery separator plays a pivotal role in preventing thermal runaway as cells experience electrical abuse, overcharge, and external short circuit. In this article, the trilayer separator endowed with shutdown function was fabricated by ingenious co-extrusion and bidirectional drawing based on the nano-Al₂O₃ coating online construction during the β-iPP cavitation process. The middle layer composed of nano-Al₂O₃, polyethylene, and polypropylene offers a shutdown temperature of 130 °C, and skin polypropylene layers with nano-Al₂O₃ coating hold optimized dimensional stability below the meltdown temperature. Crystal structure measurement and pore structure diagnosis disclose that nano-Al₂O₃ thins coarse fibrils and makes the porous structure uniform. De-bonding of nano-Al₂O₃/β-iPP interfaces retains nano-Al₂O₃ not only on the top surface of the separator but also on the pore intine to realize nano-Al₂O₃ coating online construction, consequently strengthening tensile capacity, dimensional stability to heating, and electrolyte affinity. Electrochemical tests further disclose that nano-Al₂O₃ coating stabilizes solid electrolyte interphase germination and heightens lithium-ion migration numbers, confining cell resistances and granting optimal high-rate performance and cycling ability. The proposed approach features simple technics, environment-friendly, continuous fabrication, and coating online construction, which can offer new ideas for the mass fabricating of the high-end separator.