Methods of manufacturing thin, high density nonwoven separators for energy storage devices

Abstract

An insulating (nonconductive) microporous nonwoven polymeric battery separator comprised of a single layer of enmeshed microfibers and nanofibers and supercalendered to extremely thin dimensions and high densities is provided. Such a separator accords the ability to not only attune the porosity and pore size to any desired level through a single nonwoven fabric, but provide further benefits in terms of further reduced pore size, reduced electrolyte level requirements, and reduced total volume of the subject battery cell itself. As a result, the inventive separator permits a high strength material with low porosity and low pore size to levels previously unattained. The separator, a battery including such a separator, the method of manufacturing such a separator, and the method of utilizing such a separator within a battery device, are all encompassed within this invention.

What we claim is: 
     
         1 . A method of manufacturing a single-layer polymeric battery separator, said method comprising the steps of:
 providing a plurality of polymeric microfibers having a maximum length of 25 mm and a minimum size of 2 microns;   providing a plurality of polymeric nanofibers having a maximum length of 25 mm and a maximum size of 700 nanometers;   subjecting said plurality of microfibers and plurality of nanofibers simultaneously to a wetlaid nonwoven fabricating method such that said polymeric microfibers enmesh in a non-uniform pattern with interstices between said microfibers and said polymeric nanofibers become entangled with said microfibers and with said other nanofibers such that said nanofibers are introduced within said interstices between said microfibers as well as on the surface of the substrate formed from said plurality of polymeric microfibers; and   subjecting said enmeshed structure to a supercalendering procedure, wherein said procedure entails contact with at least three separate calendering nips, and wherein each calendering nip applies a pressure of at least 500 lbs/inch.   
     
     
         2 . The method of  claim 1  wherein said supercalendered enmeshed structure exhibits a maximum thickness of 25 microns and a maximum porosity of 45%. 
     
     
         3 . The method of  claim 2  wherein said supercalendered enmeshed structure exhibits a maximum mean flow pore size of 0.7 microns. 
     
     
         4 . The method of  claim 1  wherein said supercalendered enmeshed structure exhibits a maximum thickness of 20 microns. 
     
     
         5 . The method of  claim 1  wherein said supercalendered enmeshed structure exhibits a maximum thickness of 15 microns. 
     
     
         6 . The method of  claim 1  wherein said supercalendered enmeshed structure exhibits a maximum thickness of 12 microns.