Kono et al. reported bi-axial orientation of gel sheets of high molecular weight polyethylenes, by what is often referred to as the “wet process", to obtain microporous film with a uniform and fine network of micro fibrils, 3 dimensionally interconnected and relatively narrow pore size distribution in 1984. A Tonen Chemical polyethylene separator provides many advantages as separator for lithium ion rechargeable batteries (LIBs) and was used in the world's first commercial LIB by Sony in 1991.
The demand for LIBs has increased rapidly, and now they are used in electrical vehicles and energy storage systems in addition to laptops, cellular phones, smartphones, power tools and cordless cleaners.Toray and Tonen established JV in 2010 and expand the separator business now.
LIB manufacturers desire thinner separators to increase the energy density and power of LIB. Separator manufacturers need to improve heat resistance and mechanical strength of thinner such as 5micron in order to meet safety requirements.
In this paper, we would like to outline the manufacturing processes, roles and features of separators, then to introduce our commercial products and our development activities of co-extruded and coated separators.