Separator film, its fabrication method, supercapacitor, battery and capacitor provided with said film

A method for fabricating a separator film for a device used for storing electrical energy, the film being porous and oriented, the film containing a mixture comprising:

• a polypropylene homopolymer,
• at least 10% by weight of at least one copolymer of monomers comprising at least propylene and ethylene,
• at least one beta-nucleating agent,
• wherein the copolymer has an ethylene content greater than or equal to 1% and less than 10% by weight of the copolymer and a propylene content of at least 90% by weight of the copolymer and a propylene content of at least 90% by weight of the copolymer for a micrometric thickness of the film greater than or equal to 8 microns and less than or equal to 30 microns, corresponding to a space factor determined according to the IEC-60674-3-1 standard greater than or equal to 145% and a density of the film stretched in both directions greater than or equal to 0.18 g/cm3 and less than or equal to 0.41 g/cm3,
• and wherein, during a first step said mixture being melt is passed on a chill roll (CR, 13), which rotates and which has a temperature less than the temperature of the mixture being melt to obtain a primary film (F), the primary film (F) is stretched in its longitudinal conveying direction (MD) during a second step after the first step, the film (F) is stretched in the direction transverse (TD) to the longitudinal direction (MD), the method being characterized in that during the first step, said mixture being melt has a time in contact with the chill roll (CR, 13) greater than or equal to 30 seconds.