A Comparative study on separators based on non-polyolefin and polyolefin polymers for lithium batteries

Currently, polyolefin-based microporous separators are widely used in lithium batteries because of their good mechanical strength, chemical stability, and reasonable price. But they have some important intrinsic limitations such as: low wettability, low porosity, and great shrinkage at high temperatures. To overcome these drawbacks, new polymers have been introduced like poly(vinylidene fluoride) (PVDF) and its copolymers, polyacrylonitrile (PAN), poly(vinyl alcohol) (PVA), and poly(methyl methacrylate) (PMMA). According to many investigations, these new polymers have better properties than polyolefins. For instance, there have better wettability with electrolyte. Also these kinds of separators are able to create a good adhesion with the surface of the electrodes and this feature will reduce interfacial resistance. Except PMMA, other non-polyolefins have higher melting temperature than polyolefins that this feature will result in better thermal stability of non-polyolefins than polyolefins. Compared with other new polymers, PVDF and its copolymers have the most variety of properties such as: processability by different techniques, chemical inertness, stable at high voltages, excellent mechanical properties, controllable degree of crystallinity, and high dielectric properties that can improve the ionization of lithium salts. In order to further improve the properties of blends or nanocomposites of them have been developed which have excellent wettability, high ionic conductivity and also robust mechanical strength.