Multilayer battery separators

Abstract

A microporous battery separator is provided having a first co-extruded multilayered portion and a second co-extruded multilayered portion. The two portions are bonded together. In a preferred embodiment, the battery separator has two substantially identical multilayered portions bonded together face-to-face. Each of the two multilayered portions has at least one strength layer and at least one shutdown layer. Methods for making the battery separators are also provided. Preferably, a tubular multilayered film is extruded, and collapsed onto itself to form a multilayered battery separator precursor. The precursor is then bonded and annealed before it is stretched to form a microporous multilayer battery separator.

What is claimed is:  
     
         1 . A battery separator comprising: 
 a microporous film having a first co-extruded multilayered portion and a second co-extruded multilayered portion, said first portion and said second portion being substantially identical, being bonded face-to-face.    
     
     
         2 . The battery separator of  claim 1  wherein said film being formed by collapsing a tubular film onto itself.  
     
     
         3 . The battery separator of  claim 1  wherein said co-extruded multilayered portion further comprising at least one strength layer and at least one shutdown layer.  
     
     
         4 . The battery separator of  claim 1  wherein a uniaxial orientation of said first portion being at an angle relative to a uniaxial orientation of said second portion.  
     
     
         5 . The battery separator of  claim 1  wherein said film further comprising four layers, the first and fourth layers consisting essentially of polypropylene, the second and third layers being bonded together and consisting essentially of polyethylene.  
     
     
         6 . The battery separator of  claim 1  wherein said film further comprising six layers, the second and fifth layers consisting essentially of polyethylene, the first, third, fourth and sixth layers consisting essentially of polypropylene, said third and fourth layers being bonded together.  
     
     
         7 . The battery separator of  claim 1  wherein said film having a thickness of from about 0.5 mil to about 1.5 mils.  
     
     
         8 . The battery separator of  claim 1  wherein said film having a peel strength of at least about 5 grams/inch.  
     
     
         9 . The battery separator of  claim 1  wherein said battery separator has a thickness of from about 0.5 mil to about 1.5 mils and a puncture strength of at least about 500 grams.  
     
     
         10 . The battery separator of  claim 3  wherein each said multilayered portion having one said strength layer and one said shutdown layer, wherein said multilayered portions being bonded together such that the uniaxial orientation of each portion is at an angle relative to the other and that said film having two strength layers sandwiching two shutdown layers bonded together, said film having a thickness of from about 0.5 mil to about 1.5 mils and a puncture strength of at least about 500 grams.  
     
     
         11 . The battery separator of  claim 3  wherein each said multilayered portion having two said strength layers sandwiching one said shutdown layer, said strength layers and said shutdown layer, wherein the two multilayered portions being bonded together such that the uniaxial orientation of each portion is at an angle relative to the other and that said film having a six-layer construction, the first, third, fourth and sixth layers being strength layers and the second and fifth layers being shutdown layers, said film having a thickness of from about 0.5 mil to about 1.5 mils and a puncture strength of at least about 500 grams.  
     
     
         12 . A method for making a multilayer battery separator comprising the steps of: 
 extruding a tubular multilayered film;    collapsing the tubular multilayered film onto itself to form a multilayered battery separator precursor having two plies of the multilayered film;    bonding and annealing the precursor; and    stretching the bonded and annealed precursor to form a microporous multilayer battery separator.    
     
     
         13 . The method of  claim 12  wherein said precursor is bonded by thermocompression bonding.  
     
     
         14 . The method of  claim 12  wherein said multilayered tubular film has two layers including a shutdown layer and a strength layer.  
     
     
         15 . The method of  claim 14  wherein said strength layer consists essentially of polypropylene, and said shutdown layer consists essentially of polyethylene.  
     
     
         16 . The method of  claim 12  wherein said multilayered tubular film has three layers including two strength layers sandwiching a shutdown layer.  
     
     
         17 . The method of  claim 16  wherein said strength layer consists essentially of polypropylene, and said shutdown layer consists essentially of polyethylene.  
     
     
         18 . A method for making a multilayer battery separator, comprising the steps of: 
 co-extruding a first multilayered flat sheet;    co-extruding a second multilayered flat sheet;    laminating said first and second flat sheets to form a battery separator precursor;    bonding and annealing said precursor; and    stretching the bonded and annealed precursor to form a multilayer battery separator.    
     
     
         19 . The method of  claim 18  further comprising extracting an extractable material from said precursor.