Fabrication of Nano-Al2O3 in-Situ Coating Lithium-Ion Battery Separator Based on Synchronous Biaxial Stretching Mechanism of beta-Crystal Polypropylene

The heterogeneous porous construction and inferior electrolyte affinity of separators elevate the lithium-ion transference obstacle and restrict lithium-ion battery performance. In this article, high-performance nano-Al2O3 in situ coating separators with homogenized micropores are fabricated skillfully based on the biaxial stretching cavitation mechanism of beta-crystal polypropylene (beta-iPP). Crystal structure characterizations and porous construction diagnosis reveal that nano-Al2O3 acts as a pore size homogenizing accelerator during biaxial stretching by refining coarse fibril and narrowing pore size distribution availably. Also, nano-Al2O3 in situ remained on the separator surface and intine intensifies the thermal stability and wettability, which overcomes the traditional off-line coating method and uneven aperture distribution of traditional bidirectional tensile beta-iPP separator. Synchro-draw further homogenizes weak interface de-bonding manner and optimizes porous construction by improving the loading mode of beta-iPP lamellae. Therefore, separators experiencing synchro-draw feature superior puncture strength and safety capability, which shuns latent safety peril contributed by excess thermal shrinkage in a single direction. Electrochemical tests further disclose that the Al2O3 in situ coating and uniform porous structure synergistically stabilize the solid electrolyte interface layer and reduce lithium-ion migration obstruction, which gives optimized C-rate capacity and cycle durability of LIBs.