New Flame Retardant Composite Separators Based on Metal Hydroxide for Lithium-Ion Batteries (LIBs)

From the viewpoint of lithium-ion battery safety, the separator has been considered as a key component, because its primary function is to prevent internal short-circuit between the cathode and the anode. In general, separators in lithium-ion batteries (LIBs) are made mostly of polyolefin, predominantly polyethylene (PE) or polypropylene (PP). These polyolefin-based separators are widely used and offer many advantages but exhibits poor thermal stability at high temperature, and thus result thermal runaway threatening safety issue of LIBs. To improve thermal properties of LIBs, many researches have been reported using ceramic nanoparticles (Al2O3 and SiO2) coated separators. Along with this line, in this study, as a new approach to exciting the thermal stability of a separator, we developed a new composite separator. We tried to improve the thermal stability and flame retardancy of a microporous polyethylene (PE) membrane by coating both sides of the membrane with nano-sized metal hydroxide (Al(OH)3 and Mg(OH)2) ceramic powders and poly(vinylidene fluoride-co-hexafluoropropylene) PVdF-HFP binder. The composite separator exhibited equivalent thermal stability compared to metal oxide ceramic-coated separator and flame retardancy for combustion condition. Also, Using these composite separator, we assembled lithium-ion cells composed of a graphite anode and a LiCoO2 cathode, and showed their electrochemical performances compared to those employing oxide (Al2O3 and SiO2) ceramic-coated separators. Reference [1] J.-K. Park, M.-H. Ryou, G.-B. Han, J.-N. Lee, D.J. Lee, J. Song, J.Y. Lee, South Korea. Patent, 10-1122159, 2012 [2] Y. Lee, M.-H. Ryou, M. Seo, J.W. Choi, Y.M. Lee, Electrochimica Acta 113 (2013) 433– 438 Acknowledgement This research was financially supported by the Basic Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0025738).