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 a membrane, batteries containing such membranes as battery separators, methods for making such batteries, and methods for using such batteries.

1 . A microporous membrane comprising polypropylene having an Mw>0.9×10 6 , the membrane having a 130° C. heat shrinkage ≦8.0% in at least one planar direction and a normalized air permeability ≦4.0×10 2  second/100 cm 3 /20 μm. 
     
     
         2 . The membrane of  claim 1 , wherein the membrane's TD 105° C. heat shrinkage is 0.5% or less. 
     
     
         3 . The membrane of  claim 1 , wherein the membrane's TD 105° C. heat shrinkage is 0.25% or less. 
     
     
         4 . The membrane of  claim 1 , wherein the membrane has an MD maximum shrinkage in the molten state ≦25.0% and a TD maximum shrinkage in the molten state ≦11.0%. 
     
     
         5 . The membrane of  claim 1 , wherein the membrane comprises first and third layers and a second layer located between the first and third layers, and wherein
 (a) the first layer comprises from 1.0 wt. % to 10.0 wt. %, based on the weight of the first layer, of polyethylene having an Mw>1.0×10 6 ;   (b) the third layer comprises from 1.0 wt. % to 10.0 wt. %, based on the weight of the third layer, of polyethylene having an Mw>1.0×10 6 ; and   (c) the second layer comprises ≦40 wt. % of the polypropylene, based on the weight of the second layer.   
     
     
         6 . The membrane of  claim 5 , wherein the first layer further comprises polyethylene having an Mw≦1.0×10 6  in an amount in the range of 90.0 wt. % to 99.0 wt. %, based on the weight of the first layer; the third layer further comprises polyethylene having an Mw≦1.0×10 6  in an amount in the range of 90.0 wt. % to 99.0 wt. %, based on the weight of the third layer; and the second layer further comprises polyethylene. 
     
     
         7 . The membrane of  claim 5 , wherein the second layer comprises 5.0 wt. % to 40.0 wt. % of the polypropylene, 0 wt. % to 10.0 wt. % of polyethylene having an Mw>1.0×10 6 , and 60.0 wt. % to 95.0 wt % of polyethylene having an Mw≦1.0×10 6 , the weight percents being based on the weight of the second layer. 
     
     
         8 . The membrane of  claim 5 , wherein
 (a) the second layer is in planar contact with the first layer and the third layer;   (b) the membrane's total thickness is in the range of 3.0 μm to 200.0 μm;   (c) the first and third layers comprise substantially the same polyethylenes, the amounts of the polyethylenes in the first layer being the same as the amounts of the polyethylenes in the third layer;   (d) the second layer has a thickness of 5.0% to 15.0% of the membrane's total thickness; and   (e) the first and third layers have substantially the same thickness, the thickness of the first and third layers each being in the range of 42.5% to 47.5% of the membrane's total thickness.   
     
     
         9 . The membrane of  claim 1 , wherein the membrane has one or more of (1) a normalized permeability in the range of 150.0 seconds/100 cm 3 /20 um to 390.0 seconds/100 cm 3 /20 μm, (2) porosity ≧25%, (3) a normalized pin puncture strength ≧2.0×10 3  mN/20 μm, (4) an MD tensile strength ≧9.0×10 4  kPa, (5) an TD tensile strength ≧7.5×10 4  kPa (6) MD tensile elongation ≧50%, (7) TD tensile elongation ≧100%, (8) a meltdown temperature ≧170.0° C., (9) a shutdown temperature ≦140.0° C., (10) a thickness variation ratio after heat compression ≦20.0%, and (11) an air permeability after heat compression ≦1.0×10 3  sec/100 cm 3 . 
     
     
         10 . The membrane of  claim 1 , wherein the polypropylene's ΔHm is in the range of from 113 J/g to 119 J/g. 
     
     
         11 . A method for producing a microporous membrane, comprising,
 (a) stretching a multi-layer layer extrudate in at least one of MD or TD, the extrudate comprising at least first and second layers, the first layer comprising a first polyolefin and at least a first diluent, and the second layer comprising a second polyolefin and at least a second diluent, the second polyolefin comprising polypropylene in an amount in the range of from 1.0 wt. % to 40.0 wt. % based on the weight of the second polyolefin, the polypropylene having an Mw>0.9×10 6  and a ΔHm≧100.0 J/g;   (b) removing at least a portion of the first and second diluents from stretched extrudate to produce a dried membrane having a first length along MD and a first width along TD;   (c) 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   (d) 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 , further comprising removing at least a portion of any volatile species from the extrudate after step (b). 
     
     
         13 . The method of  claim 11 , wherein
 (i) the first polyolefin comprises a first polyethylene in an amount in the range of from 90.0 wt. % to 99.0 wt. % and a second polyethylene in an amount in the range of from about 1.0 wt. % to 10.0 wt. %, the weight percents being based on the weight of the first polyolefin, the first polyethylene having an Mw≦1.0×10 6  and the second polyethylene having a weight average molecular weight >1.0×10 6 ;   (ii) the second polyolefin comprises the polypropylene in an amount in the range of 5 wt. % to 40 wt. %, and further comprises (i) a first polyethylene having an Mw≦1.0×10 6  in an amount in the range of 60.0 wt. % to 90.0 wt. % and (ii) a second polyethylene having an Mw>1.0×10 6  in an amount in the range of from 0.0 wt. % to 10.0 wt. %, the weight percents being based on the weight of the second polyolefin;   (ii) the first diluent is present in the first layer of the extrudate in an amount in the range of from about 25.0 wt. % to about 99.0 wt. % based on the weight of the combined weight of the first polyolefin and the first diluent; and   (iv) the second diluent is present in the second layer of the extrudate in an amount in the range of from about 25.0 wt. % to about 99.0 wt. % based on the combined weight of second polyolefin and second diluent.   
     
     
         14 . The method of  claim 11 , wherein the extrudate further comprises a third layer comprising a third polyolefin, the third polyolefin comprising a first polyethylene in an amount in the range of from 90.0 wt. % to 99.0 wt. % and a second polyethylene in an amount in the range of from about 1.0 wt. % to 10.0 wt. %, the weight percents being based on the weight of the third polyolefin, the first polyethylene having an Mw≦1.0×10 6  and the second polyethylene having an Mw>1.0×10 6 . 
     
     
         15 . The method of  claim 11 , wherein
 (i) the extrudate is a three-layer extrudate;   (ii) the second layer is located between the first and third layers and is in planar contact with the first and third layers;   (iii) the first polyolefin and the second polyolefin are the same polyolefin;   (iv) the second layer has a thickness of 5.0% to 15.0% of the extrudate's total thickness; and   (v) the first and third layers have the same thickness, the thickness of the first and third layers each being in the range of 42.5% to 47.5% of the extrudate's total thickness.   
     
     
         16 . The method of  claim 11 , wherein the first, second, and third diluents are independently selected from one or more of nonane, decane, decalin, and liquid paraffin. 
     
     
         17 . The method of  claim 11 , wherein the stretching of step (a) is conducted by simultaneously stretching the extrudate in MD and TD. 
     
     
         18 . The method of  claim 17 , wherein during step (c) the MD stretching is conducted before the TD stretching, wherein the TD stretching is conducted to a second magnification factor in the range of from 1.15 to 1.25, 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-30.0° C. to about Tm-10.0° 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 (d) is conducted while the membrane is exposed to a temperature ≧ the second temperature. 
 
     
     
         19 . The method of  claim 18 , wherein the third width is in the range of 1.0 to 1.05 times the first width. 
     
     
         20 . The method of  claim 18 , wherein the first magnification factor is in the range of 1.1 to 1.4. 
     
     
         21 . A battery comprising an anode, a cathode, an electrolyte, and a multi-layer microporous membrane comprising polypropylene having an Mw>0.9×10 6 , wherein the membrane has a 130° C. heat shrinkage ≦8.0% in at least one planar direction and a normalized air permeability ≦4.0×10 2  second/100 cm 3 /20 μm, and wherein the multi-layer microporous membrane separates at least the anode from the cathode. 
     
     
         22 . The battery of  claim 21 , wherein the electrolyte contains lithium ions and the battery is a secondary battery. 
     
     
         23 . The battery of  claim 22 , further comprising one or more resistive and/or reactive components electrically, electrochemically, and/or electromechanically connected to the battery to form a battery system, wherein the battery is a source or sink of power to the component(s). 
     
     
         24 . The battery system of  claim 23 , wherein at least one component comprises means for moving an electric vehicle or hybrid electric vehicle. 
     
     
         25 . The battery system of  claim 23 , wherein the means comprise an electric motor and/or an electric motor, and the battery is electrically connected to the motor.