TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Component: The fibrous layer further comprises inorganic additives comprising titanium dioxide, barium titanate, dilithium oxide, lithium fluoride, lithium hydroxide, trilithium nitride, barium oxide, disodium oxide, lithium carbonate, calcium carbonate, lithium aluminate, silicon dioxide, and/or aluminum oxide.    TECHNOLOGY FOCUS - POLYMERS - Preferred Component: The heat-resistant polymeric material may comprise aromatic polyesters comprising polyamide, polyimide, polyamideimide, poly(meta-phenylene isophthalamide), polysulfone, polyether ketone, polyether imide, polyethylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate; a polyphosphazene group, i.e. polytetrafluoroethylene, poly diphenoxyphosphazene, poly(bis(2-(2-methoxyethoxy)phosphazene)); polyurethane copolymer including polyurethane and polyetherurethane; cellulose acetate; cellulose acetate butylate; and/or cellulose acetate propionate. The fibrous layer comprises fibers having a fibrous phase of the heat-resistant polymeric material and a fibrous phase of the swelling polymeric material. The swelling material comprises polyvinylidene fluoride, poly(vinylidene fluoride-co-hexafluoropropylene), perfluoropolymer, polyvinylchloride or polyvinylidene chloride and their copolymers, polyethylene glycol derivatives including polyethylene glycol dialkylene ether, polyethylene glycol dialkylene ester, poly-oxide including poly(oxymethylene-oligo-oxyethylene), poly(ethylene oxide), polypropylene oxide, polyvinyl acetate, poly(vinylpyrrolidone-vinyl acetate), polystyrene and polystyrene acrylonitrile copolymers, polyacrylonitrile copolymers including polyacrylonitrile, polyacrylonitrile methylmethacrylate copolymers, polymethylmethacrylate, and/or polymethylmethacrylate copolymers. The porous film comprises a polyolefin-based resin. Preferred Composition: The content of the fibrous phase of the swelling polymeric material is 0-95 wt.% with respect to the polymeric contents of the separator. Preferred Method: Electrospinning comprises electro-blowing, melt blowing, or flash spinning. Preferred Condition: The porous film has a melting point of 100-180degrees C, a porosity of 30-80%, and a pore size of 1-5000 nm. The fibrous phase comprising the fibrous layer has an average fiber diameter of 1-3000 nm. The fibrous layer has a porosity of 30-95%, and a thickness of 1-20 microns.