Battery separator and method of making same

Abstract

A battery separator comprises a multi-layered film, individual layers of said film having been bonded together by heat and pressure, having a peel strength of greater than or equal to 40 grams per inch (1.6 g/mm) and a thickness of ≦25 microns. A method for making a battery separator comprises the steps of: extruding and winding up a first precursor film, extruding and winding up a second precursor film, unwinding the first and second precursor films, stacking up the first and second precursor films to form a single stacked precursor, laminating the single stacked precursor film, winding up the laminated single stacked precursor film, stacking up a plurality of laminated single stacked precursor films, and making microporous the stacked plurality of laminated single stacked precursor films.

1 . A battery separator comprising 
 a multi-layered microporous film, individual layers of said film having been bonded together by heat and pressure, having a peel strength of greater than 40 grams per inch (1.6 g/mm) and a thickness of ≦25 microns.    
     
     
         2 . The battery separator of  claim 1  wherein said multi-layered microporous film being a tri-layered film.  
     
     
         3 . The battery separator of  claim 2  wherein said tri-layered film having a polypropylene-polyethylene-polypropylene structure.  
     
     
         4 . The battery separator of  claim 1  wherein said film having a thickness of less than or equal to 20 microns.  
     
     
         5 . The battery separator of  claim 1  wherein said film having a thickness of less than or equal to 15 microns.  
     
     
         6 . A battery separator comprising: 
 a multi-layered microporous film, individual layers of said film having been bonded together by heat and pressure, having a peel strength of greater than 40 grams per inch (1.6 g/mm) wherein at least one layer being substantially polypropylene, another layer being substantially polyethylene, and the film having a thickness of less than or equal to 15 microns.    
     
     
         7 . A method of making a battery separator comprising the steps of: 
 extruding and winding up a first precursor film;    extruding and winding up a second precursor film;    unwinding the first and second precursor film;    stacking up the first and second precursor films to form a single stacked precursor;    laminating the single stacked precursor film;    winding up the laminated single stacked precursor film;    stacking up a plurality of laminated single stacked precursor films; and    making microporous said plurality of laminated single stacked precursor films.    
     
     
         8 . The method of  claim 7  wherein extruding the first or second precursor further comprises extruding with a slot die, T die, or a blown film die.  
     
     
         9 . The method of  claim 7  wherein the single stacked precursor being a tri-layer precursor.  
     
     
         10 . The method of  claim 9  wherein the tri-layer precursor being a polypropylene-polyethylene-polypropylene precursor.  
     
     
         11 . The method of  claim 7  wherein laminating being at speeds greater than 100 ft/min (30.5 m/min).  
     
     
         12 . The method of  claim 11  wherein laminating being at speeds greater than 125 ft/min (38.1 m/min).  
     
     
         13 . The method of  claim 12  wherein laminating being at speeds greater than 150 ft/min (45.7 m/min).  
     
     
         14 . The method of  claim 13  wherein laminating being at speeds greater than 200 ft/min (61.0 m/min).  
     
     
         15 . The method of  claim 7  wherein laminating being conducted between heated nip rollers.  
     
     
         16 . The method of  claim 15  wherein the nip roller temperature ranging from 145° C. to 170° C.  
     
     
         17 . The method of  claim 16  wherein the nip roller temperature ranges from 155° C. to 165° C.  
     
     
         18 . The method of  claim 15  wherein the nip roller pressure ranges from 100 to 800 pounds per linear inch (pli).  
     
     
         19 . The method of  claim 18  wherein the nip roller pressure ranges from 100 to 300 pli.  
     
     
         20 . The method of  claim 7  wherein a chill roll following the nip rollers.  
     
     
         21 . The method of  claim 20  wherein the chill roll temperature ranges from 20° C. to 45° C.  
     
     
         22 . The method of  claim 21  wherein the chill roll temperature ranges from 25° C. to 40° C.  
     
     
         23 . The method of  claim 20  wherein an air knife being placed between the nip rollers and the chill roll.  
     
     
         24 . The method of  claim 20  wherein edge trim knives follow the chill roll.  
     
     
         25 . The method of  claim 7  wherein the plurality of laminated single stacked precursor films being at least six laminated single stacked precursor films.  
     
     
         26 . The method of  claim 25  wherein the plurality of laminated single stacked precursor films being at least twelve laminated single stacked precursor films.  
     
     
         27 . The method of  claim 26  wherein the plurality of laminated single stacked precursor films being at least sixteen laminated single stacked precursor films.  
     
     
         28 . The method of  claim 7  wherein making microporous said plurality of laminated single stacked precursor films being selected from the group consisting of a dry process and a wet process.  
     
     
         29 . A method of making a battery separator comprising the steps of: 
 extruding a precursor film,    laminating together two or more precursor films to form a multi-layered precursor film,    stacking up at least twelve multi-layered precursor films, and    making microporous the stacked multi-layered precursor films.    
     
     
         30 . The method of  claim 29  wherein at least sixteen multi-layered precursor films are stacked up.  
     
     
         31 . The method of  claim 29  wherein making microporous the stacked multi-layered precursor films being selected from the group consisting of a dry process and a wet process.