Separator for electrochemical cell with overcharge protection and method of making same

Abstract

A separator for a rechargeable electrochemical cell that has a conductive first layer and a non-conductive second layer. The non-conductive second layer and the conductive first layer are adhered to one another, wherein the separator has a higher threshold voltage than a threshold voltage of the conductive first layer alone. At a predetermined voltage, the separator becomes conductive and stops further ionic transfers.

1 - 19 . (canceled) 
     
     
         20 . A separator for use in a rechargeable electrochemical cell comprising:
 an electrically conductive first layer with a first threshold voltage, the electrically conductive first layer includes a fibrous web; and   an electrically non-conductive second layer, the electrically non-conductive second layer and the electrically conductive first layer are adhered to one another and have a second threshold voltage, the second threshold voltage being greater than the first threshold voltage. and wherein the electrically non-conductive second layer includes polymers selected from the group consisting of chlorinated polypropylene, polypropylene-maleic anhydride copolymer, polyvinylideneflouride, and polyvinylideneflouride copolymers.   
     
     
         21 . The separator according to  claim 20 , wherein the separator becomes conductive at between about 4 V and about 5 V. 
     
     
         22 . The separator according to  claim 20 , wherein the first layer includes a chlorinated polypropylene. 
     
     
         23 . The separator according to  claim 20 , further comprising an adhesive incorporated into the electrically non-conductive second layer. 
     
     
         24 . The separator according to  claim 20 , further comprising an adhesive, wherein the adhesive has an adhesion temperature below a first temperature and the second layer includes a resin having a melting temperature, and the first temperature being lower than the melting temperature of the resin. 
     
     
         25 . The separator according to  claim 20 , wherein the electrically conductive first layer is encapsulated by the electrically non-conductive second layer. 
     
     
         26 . The separator according to  claim 20 , wherein the separator is laminated to an anode of the rechargeable electrochemical cell. 
     
     
         27 . A separator for use in a rechargeable electrochemical cell comprising:
 an electrically conductive first layer made of fibrous web; and   an electrically non-conductive second layer, the electrically non-conductive second layer made of a polymeric material in a polyolefin resin, the first layer and the second layer adhered to one another and the polymeric material selected from the group consisting of chlorinated polypropylene, polypropylene-maleic anhydride copolymer, polyvinylideneflouride, and polyvinylideneflouride copolymers.   
     
     
         28 . The separator according to  claim 27 , further comprising a pore former to make distributed micropores in at least one of the first and second layers, the pore former being ethylene carbonate. 
     
     
         29 . The separator according to  claim 27 , wherein the first and second layers are formed independently. 
     
     
         30 . The separator according to  claim 27 , wherein one layer is formed on top of the other layer. 
     
     
         31 . The separator according to  claim 28 , wherein the fibrous web is a polymeric material. 
     
     
         32 . A rechargeable electrochemical cell containing the separator according to  claim 20 .