A nonwoven nanofiber separator, including a composite of a first polymer material and a second polymer material, wherein: the first polymer material may include at least one member selected from the group consisting of poly(vinylidene fluoride), polyimide, polyamide and polyacrylonitrile; the second polymer material may include at least one member selected from the group consisting of polyethylene glycol, polyacrylonitrile, poly(ethylene terephthalate), poly(vinylidene fluoride), poly(vinylidene fluoride-hexafluoropropylene) and poly(vinylidene fluoride-co-chlorotrifluoroethylene); and the second polymer material is different from the first polymer material. A method of improving physical stability of a battery separator with improved performance is also provided.