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.