Microporous membranes, methods for making these membranes, and the use of these membranes as battery separator films

Abstract

A membrane includes a first polyethylene having an Mw<1.0×10 6 , a second polyethylene having an Mw≧1.0×10 6 , and a polypropylene having an Mw≧5.0×10 5 and a ΔHm 80.0 J/g; wherein (a) the sum of the amounts of (i) polypropylene having an Mw≧5.0×10 5 and a ΔHm 80.0 J/g, and (ii) the second polyethylene is≧15.0 wt. %, the weight percents being based on the total weight of the polymer in the membrane; (b) the membrane has a thickness≦12.0 μm; and (c) the membrane is microporous.

1 . A membrane comprising a first polyethylene having an Mw−1.0×10 6 , a second polyethylene having an Mw≧1.0×10 6 , and a polypropylene having an Mw≧5.0×10 5  and a ΔHm 80.0 J/g; wherein (a) the sum of the amounts of (i) polypropylene having an Mw≧5.0×10 5  and a ΔHm 80.0 J/g, and (ii) the second polyethylene is≧15.0 wt. %, the weight percents being based on the total weight of the polymer in the membrane; (b) the membrane has a thickness≦12.0 μm; and (c) the membrane is microporous. 
     
     
         2 . The membrane of  claim 1 , wherein the polypropylene having an Mw≧5.0×10 5  and a ΔHm 80.0 J/g is present in the membrane in an amount in the range of from 1.0 wt. % to 15.0 wt. %, the first polyethylene is present in the membrane in an amount in the range of from 70.0 wt. % to 85.0 wt. %, and the second polyethylene is present in membrane in an amount in the range of from 1.0 wt. % to 19.0 wt. %, all being based on the total weight of the polymer in the membrane. 
     
     
         3 . The membrane of  claim 1 , wherein the membrane has a meltdown temperature≧145.0° C. and an a normalized pin puncture strength≧3.20×10 2  mN/μm, and a TD Tensile strength≧1.4×10 5  kPa. 
     
     
         4 . The membrane of  claim 1 , wherein the membrane has porosity in the range of 20% to 80%, a normalized air permeability≦50.0 seconds/100 cm 3 /μm, and a TD 105° C. Heat Shrinkage≦10.0%. 
     
     
         5 . The membrane of  claim 1 , wherein the polypropylene comprises≧90.0 wt. % isotactic polypropylene having an Mw≧6.0×10 5 , an MWD 8.5 and a ΔHm 90.0 J/g, the weight percent being based on the weight of the polypropylene. 
     
     
         6 . The membrane of  claim 1 , wherein the membrane has a 105° C. TD heat shrinkage≦6.0%. 
     
     
         7 . The membrane of  claim 1 , wherein the first polyethylene has an Mw in the range of from 4×10 5  to 6.0×10 5  and an MWD in the range of from 3.0 to 10.0, and the second polyethylene has an Mw in the range of from 1.0×10 6  to 3.0×10 6  and an MWD≦in the range of from 4.0 to 15.0. 
     
     
         8 . The membrane of  claim 1 , wherein the membrane is a monolayer. 
     
     
         9 . The membrane of  claim 8 , wherein the first polyethylene has a terminal unsaturation amount<0.20 per 1.0×10 4  carbon atoms. 
     
     
         10 . A battery separator film comprising the membrane of  claim 1 . 
     
     
         11 . A process for producing a microporous membrane, comprising:
 (1) extruding a mixture of diluent and polymer to form an extrudate, the polymer comprising a first polyethylene having an Mw<1.0×10 6 , a second polyethylene having an Mw≧1.0×10 6 , and a polypropylene having an Mw≧5×10 5  and a ΔHm≧80.0 J/g; wherein the sum of the amounts of the polypropylene having an Mw≧5.0×10 5  and a ΔHm 80.0 J/g and the second polyethylene is≧15.0 wt. %, all the weight percents being based on the total weight of the polymer in the mixture; and   (2) processing the extrudate into a microporous membrane having a thickness≦12.0 μm.   
     
     
         12 . The method of  claim 11 , wherein said step of processing includes stretching the extrudate in at least one planar direction. 
     
     
         13 . The method of  claim 11 , wherein said step of processing includes removing at least a portion of the diluent from the extrudate. 
     
     
         14 . The method of  claim 13 , wherein said step of processing is devoid of any step of stretching the extrudate after said step of removing the solvent. 
     
     
         15 . The method of  claim 13 , wherein said step of processing optionally includes stretching the extrudate after said step of removing the solvent to a magnification factor of≦1.1 and excludes any stretching of the extrudate after said step of removing the solvent at a magnification factor or>1.1. 
     
     
         16 . The method of  claim 11 , further comprising cooling the extrudate. 
     
     
         17 . The method of  claim 11 , further comprising subjecting the membrane to a thermal treatment. 
     
     
         18 . The method of  claim 12 , wherein the stretching of step is conducted biaxially to a magnification factor in the range of from 9-fold to 49-fold in area, while exposing the extrudate to a temperature in the range of 90.0° C. to 125.0° C. 
     
     
         19 . The method of  claim 11 , further comprising removing any remaining volatile species from the membrane. 
     
     
         20 . The membrane product of  claim 11 . 
     
     
         21 . A battery comprising an anode, a cathode, and electrolyte, and battery separator located between the anode and the cathode, the battery separator being a membrane comprising a first polyethylene having an Mw≦1.0×10 6 , a second polyethylene having an Mw≧1.0×10 6 , and a polypropylene having an Mw≧5.0×10 5  and a ΔHm 80.0 J/g; wherein (a) the sum of the amounts of (i) the polypropylene having an Mw≧5.0×10 5  and a ΔHm 80.0 J/g and (ii) the second polyethylene is≧15.0 wt. %, the weight percents being based on the total weight of the polymer in the membrane; (b) the membrane has a thickness≦12.0 μm; and (c) the membrane is microporous. 
     
     
         22 . The battery of  claim 21 , wherein the battery separator membrane is a monolayer. 
     
     
         23 . The battery of  claim 21 , wherein the polypropylene having an Mw≧5.0×10 5  and a ΔHm 80.0 J/g is present in the membrane in an amount in the range of from 1.0 wt. % to 15.0 wt. %, the first polyethylene is present in the membrane in an amount in the range of from 70.0 wt. % to 85.0 wt. %, and the second polyethylene is present in membrane in an amount in the range of from 1.0 wt. % to 19.0 wt. %, based on the total weight of the polymer in the membrane. 
     
     
         24 . The battery of  claim 21 , wherein the membrane has a meltdown temperature≧145.0° C. and an a normalized pin puncture strength≧3.20×10 2  mN/μm, and a TD Tensile strength≧1.4×10 5  kPa. 
     
     
         25 . An electric vehicle or hybrid electrical vehicle comprising motor means electrically connected to the battery of  claim 24 .