Microporous membranes and methods for producing and using such membranes

Abstract

The invention relates to microporous polymeric membranes suitable for use as battery separator film. The invention also relates to a method for producing such membranes, batteries containing such membranes as battery separators, methods for making such batteries, and methods for using such batteries.

1 . A monolayer microporous membrane comprising a polyolefin having an Mw>1.0×10 6 , the membrane having a normalized air permeability ≦4.0×10 2  seconds/100 cm 3 /20 μm, and a heat shrinkage at 130° C. of ≦15% in at least one planar direction. 
     
     
         2 . The microporous membrane of  claim 1 , wherein the planar direction is TD and the membrane has heat shrinkage at 105° C. in at least one planar direction of ≦2.5%. 
     
     
         3 . The membrane of  claim 1 , wherein the membrane has a maximum shrinkage in the molten state in at least one planar direction of ≦10.0%. 
     
     
         4 . The microporous membrane of  claim 1 , wherein the polyolefin comprises (a) a first polyethylene, and further comprises at least one of (b) polypropylene having an Mw>1.0×10 6  or (c) a second polyethylene having an Mw>1.0×10 6 . 
     
     
         5 . The microporous membrane of  claim 4 , wherein the first polyethylene has an Mw in the range of 1.0×10 5  to 9.0×10 5  and an MWD in the range of from 3.0 to 15, the second polyethylene has an Mw in the range of 1.1×10 6  to 5.0×10 6  and an MWD in the range of 4.0 to 20.0, and the polypropylene has an Mw in the range of from 1.05×10 6  to about 2.0×10 6 , an MWD in the range of 2.0 to 6.0, and a ΔHm≧100.0 J/g. 
     
     
         6 . The microporous membrane of  claim 5 , wherein the polyolefin comprises from 60.0 wt. % to 99.0 wt. % of the first polyethylene and from 1.0 wt. % to 40.0 wt. % of the second polyethylene. 
     
     
         7 . The microporous membrane of  claim 6 , wherein the membrane has one or more of (1) a thickness in the range of 1.0 μm to 50.0 μm, (2) a porosity in the range of from 25.0% to 80.0%, (3) a normalized pin puncture strength ≧3.0×10 3  mN/20 μm, (4) a tensile strength ≧4.0×10 4  kPa, (5) a TD tensile elongation ≧100%, (6) a meltdown temperature ≧145° C., (7) a shutdown temperature ≦140.0° C., (8) a thickness variation after heat compression ≦20%, (9) an air permeability after heat compression ≦7.0×10 2  sec/100 cm 3 , or (10) TD heat shrinkage at 105° C. in the range of 0.25% to 1.5%. 
     
     
         8 . The microporous membrane of  claim 4 , wherein the polyolefin comprises (a) from 1.0 wt. % to 50.0 wt. % of the polypropylene, (b) from 25.0 wt. % to 99.0 wt. % of the first polyethylene, and (c) from 0.0 wt. % to 50.0 wt. % of the second polyethylene. 
     
     
         9 . The microporous membrane of  claim 8 , wherein the polypropylene is an isotactic polypropylene having an Mw in the range of 1.1×10 6  to 1.5×10 6 , and a ΔHm in the range of 110 J/g to 120 J/g. 
     
     
         10 . The microporous membrane of  claim 9 , wherein the membrane has one or more of (1) a thickness in the range of 1.0 μm to 50.0 μm, (2) a porosity in the range of from 25% to 80.0%, (3) a normalized pin puncture strength ≧3.5×10 3  mN/20 μm, (4) a tensile strength ≧4.0×10 4  kPa, (5) a tensile elongation ≧100%, (6) a meltdown temperature ≧170.0° C., (7) a shutdown temperature ≦140.0° C., (8) a thickness variation after heat compression ≦20%, (9) an air permeability after heat compression ≦7.0×10 2  sec/100 cm 3 , or (10) a TD heat shrinkage at 105° C. in the range of 1.0% to 2.3%. 
     
     
         11 . A method for manufacturing a microporous membrane, comprising:
 (a) stretching an extrudate in at least one of MD or TD, the extrudate comprising diluent and a polyolefin having an Mw>1.0×10 6 , and then removing at least a portion of the diluent from stretched extrudate to form a membrane having a first length along MD and a first width along TD;   (b) stretching the membrane in MD from the first length to a second length larger than the first length by a first magnification factor in the range of from about 1.1 to about 1.5 and stretching the membrane in TD from the first width to a second width that is larger than the first width by a second magnification factor in the range of from about 1.1 to about 1.3; and then   (c) reducing the second width to a third width, the third width being in the range of from the first width to about 1.1 times larger than the first width.   
     
     
         12 . The method of  claim 11 , wherein the MD and TD stretching of step (a) are each conducted to a magnification factor in the range of 3 fold to 9 fold while the extrudate is exposed to a temperature during stretching in the range of Tcd to Tm. 
     
     
         13 . The method of  claim 11 , further comprising heat setting the membrane following steps (b) and/or (c). 
     
     
         14 . The method of  claim 11 , wherein during step (b) the MD stretching is conducted before the TD stretching, wherein the first magnification factor is >the second magnification factor, and wherein
 (i) the MD stretching is conducted while the membrane is exposed to a first temperature in the range of Tcd−30° C. to about Tm−10° C. and   (ii) the TD stretching is conducted while the membrane is exposed to a second temperature that is higher than the first temperature but lower than Tm; and   wherein the reducing of step (c) is conducted while the membrane is exposed to a temperature ≧the second temperature.   
     
     
         15 . The method of  claim 11 , wherein the polyolefin comprises (a) a first polyethylene, and further comprises at least one of (b) polypropylene having an Mw>1.0×10 6  or (c) a second polyethylene having an Mw>1.0×10 6 . 
     
     
         16 . The method of  claim 15 , wherein the second polyethylene has an Mw in the range of 1.1×10 6  to about 5.0×10 6  and an MWD in the range of 4.0 to 20.0, the first polyethylene has an Mw in the range of 1.0×10 5  to 9.0×10 5  and an MWD in the range of from 3.0 to 15.0, and the polypropylene has an Mw in the range of from 1.05×10 6  to about 2.0×10 6 , an MWD in the range of 2.0 to 6.0, and a ΔHm≧100.0 J/g 
     
     
         17 . The method of  claim 16 , wherein the polyolefin comprises from 60.0 wt. % to 99.0 wt. % of the first polyethylene and from 1.0 wt. % to 40.0 wt. % of the second polyethylene. 
     
     
         18 . The method of  claim 15 , wherein the polyolefin comprises (a) from 1.0 wt. % to 50.0 wt. % of the polypropylene, (b) from 25.0 wt. % to 99.0 wt. % of the first polyethylene, and (c) from 0.0 wt. % to 50.0 wt. % of the second polyethylene. 
     
     
         19 . The method of  claim 18 , wherein the polypropylene is an isotactic polypropylene having an Mw in the range of 1.1×10 6  to 1.5×10 6 , and a ΔHm in the range of 110 J/g to 120 J/g. 
     
     
         20 . (canceled) 
     
     
         21 . A battery comprising an anode, a cathode, an electrolyte, and a monolayer microporous membrane comprising polypropylene having an Mw>1.0×10 6 , the membrane having a normalized air permeability ≦4.0×10 2  seconds/100 cm 3 /20 μm, and a heat shrinkage at 105° C. in at least one planar direction ≦2.5%; wherein the microporous membrane separates at least the anode from the cathode. 
     
     
         22 - 23 . (canceled)