TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Method: The electrochemical cells are formed by stacking (i) full cells having positive electrode (7), separator layer (15) and negative electrode (8) as a basic unit with separator film interposed between each stacked cell; or (ii) bicells having positive electrode, separator layer, negative electrode, another separator layer and another positive electrode, or bicells having negative electrode, separator layer, positive electrode, another separator layer and another negative electrode as basic unit with separator film between each stacked cell. The separator film is prepared by providing a polymeric support layer, dissolving a gellable polymer in solvent to form a gellable polymer solution, coating the support layer with gellable polymer solution to form a multi-layer film, and stretching and heat-setting the multi-layer film. Heat-setting is performed under tension at 50degreesC or at polymer melting point for 10 seconds - 1 hour. The support layer is prepared by injecting the polymer into an extruder equipped with T-die or tubular die, and annealing the extruded polymer in dry oven at room temperature to polymer melting point.    TECHNOLOGY FOCUS - POLYMERS - Preferred Materials: The support layer is made of high-density polyethylene, low-density polyethylene, linear low-density polyethylene, polypropylene, high-crystalline polypropylene, polyethylene-propylene copolymer, polyethylene-butylene copolymer, polyethylene-hexene copolymer, polyethylene-octene copolymer, polystyrene-butylene-styrene copolymer, polystyrene-ethylene-butylene-styrene copolymer, polystyrene, polyphenylene oxide, polysulfone, polycarbonate, polyester, polyamide, polyurethane, polyacrylate, polyvinylidene chloride, polyvinylidene fluoride (PVDF), polysiloxane, polyolefin ionomer, polymethyl pentene, hydrogenated oligocyclopentadiene, and/or its copolymer or derivative. The gellable polymer layer is made of PVDF, PVDF-chlorotrifluoroethylene copolymer, PVDF-hexafluoropropylene copolymer, polyethylene oxide, polypropylene oxide, polybutylene oxide, polyurethane, polyacrylonitrile, polyacrylate, polymethyl methacrylate, polyacrylic acid, polyamide, polyacrylamide, polyvinyl acetate, polyvinylpyrrolidone, polytetraethylene glycol diacrylate, polysulfone, polyphenylene oxide, polycarbonate, polyester, polyvinylidene chloride, polysiloxane, polyolefin ionomer, and/or its copolymer or derivative. Preferred Composition: The gellable polymer layer comprises lithium salt(s) (i.e. lithium thiocyanate, lithium perchlorate, LiCF3SO3, lithium hexafluoroarsenate, LiN(CF3SO2)2, or lithium tetrafluoroborate), and porous inorganic particle(s) (i.e. silicon dioxide, titanium dioxide, aluminum oxide, magnesium oxide, or boron oxide).Preferred Dimensions: The support layer has a pore size of 0.001-10 microns and a thickness of 1-50 microns. The gellable polymer layer has a pore size of at most 10 microns and a thickness of 0.01-25 microns.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Solvent: The solvent is 1-methyl-2-pyrrolidone, acetone, ethanol, n-propanol, n-butanol, n-hexane, cyclohexanol, acetic acid, ethyl acetate, diethyl ether, dimethyl formamide, dimethyl acetamide, dioxane, tetrahydrofuran, dimethyl sulfoxide, cyclohexane, benzene, toluene, xylene, water, or derivative this solvent.