Conventional polymer separators for Li-ion batteries (LIBs) suffer from limited mechanical strength and low thermal stability, which may lead to thermal runaway and cell explosion. We produced flexible, binder-free, nonwoven fabric composed of gamma-Al2O3 nanowires, using a simple tape casting technique followed by a heat treatment in air. The overall morphology of the produced fabric is somewhat similar to that of a paper, where the cellulose fibers are replaced with stronger and stiffer Al2O3 nanowires. Owing to the fibrous nature of thus-produced free-standing films and the small diameter of the Al2O3 nanowires, they exhibit good flexibility. This is in contrast to anodized Al2O3 membranes of comparable thickness that are known to be extremely brittle and difficult to handle. Results of electrolyte wetting tests revealed significantly superior performance of Al2O3 paper compared to commonly used commercial olefin (polypropylene) separator or a cellulose fiber separator. The wetting rate of the Al2O3 separator is significantly higher owing to its polar nature, as determined by both the final wetting area and the speed of etting. Thermal stability tests demonstrate the advantage of having a flexible porous ceramic separator with operating temperatures above 800°C, which is important because of rapid heating to high temperatures that may occur in failing LIBs. In contrast, the most commonly used olefin separators typically start melting at around 120°C and oxidize at around 300°C. Finally, the strength of ceramic fibers is known to exceed that of the olefins, which should allow formation of thinner separators in automotive LIBs without sacrifice of their mechanical properties.
. D Lei, J Benson, A Magasinski, G Berdichevsky, G Yushin, Transformation of bulk alloys to oxide nanowires, Science 2017, 355 (6322), 267-271.