Microporous Polymeric Membrane, Battery Separator, and Battery
The invention relates to microporous polymeric membrane having a good balance of rupture temperature and air permeability. The invention also relates to a battery separator formed by such a microporous membrane, and a battery comprising such a separator. Another aspect of the invention relates to a method for making the microporous polymeric membrane, a method for making a battery using such a membrane as a separator, and a method for using such a battery.
1 . A multi-layer microporous membrane, comprising:
a first layer material comprising polyethylene and a second layer material comprising polypropylene, the polypropylene having (1) a weight-average molecular weight ≧6×10 5 , (2) a heat of fusion ≧90 J/g, and (3) an MWD in the range of 2 to 6, wherein
(a) the multi-layer microporous membrane has at least a first microporous layer containing the first layer material, a third microporous layer containing the first layer material, and a second microporous layer containing the second layer material, the second microporous layer being located between the first and third microporous layers, and
(b) the total amount of polypropylene in the multi-layer microporous membrane is at least 2.0 wt. % based on the total weight of the multi-layer microporous membrane.
2 . The multi-layer microporous membrane of claim 1 , wherein
(a) the polyethylene of the first layer material is a first polyethylene, the first polyethylene being present in the first layer material in an amount in the range of from 80 wt. % to 100 wt. % based on the weight of the first layer material,
(b) the polypropylene of the second layer material is present in the second layer material in an amount in the range of from 1 wt. % to 100 wt. %, based on the weight of the second layer material, and
(c) the second layer material further comprises a second polyethylene, the second polyethylene being present in the second layer material in an amount in the range of from 0 wt. % to 99 wt. %, based on the weight of the second layer material.
3 . The multi-layer microporous membrane of claim 1 , wherein the first microporous layer material consists essentially of polyethylene.
4 . The multi-layer microporous membrane of claim 1 , wherein the multi-layer microporous membrane is a three-layer membrane and wherein the amount of polypropylene in the second layer material is in the range of 20 wt. % to 50 wt. %.
5 . The multi-layer microporous membrane of claim 1 , wherein the first layer further comprises polypropylene that is optionally the same as the polypropylene of the second layer material, the polypropylene of the first layer material being present in an amount in the range of from 0.5 wt. % to 10 wt. % based on the weight of the first layer material.
6 . The multi-layer microporous membrane of claim 1 , wherein
(a) the first and/or second polyethylene comprises PE1, PE2, or both PE1 and PE2, and wherein
(1) the first polyethylene has a Mw in the range of 1×10 5 to 5×10 6 ;
(2) the second polyethylene has an Mw ranging from 1×10 5 to 5×10 6 ;
(3) PE1 is one or more of a high-density polyethylene, a medium-density polyethylene, a branched low-density polyethylene, or a linear low-density polyethylene;
(4) PE1 is at least one of (i) an ethylene homopolymer or (ii) a copolymer of ethylene and a comonomer selected from propylene, butene-1, hexene-1;
(5) PE2 has an Mw of at least 1×10 6 ;
(6) PE2 is at least one of (i) an ethylene homopolymer or (ii) a copolymer of ethylene and a comonomer selected from propylene, butene-1, hexene-1;
(7) the amount of the PE1 in the first microporous layer material is in the range of from 50 wt. % to 100 wt. %, based on the weight of the first microporous layer material;
(8) the amount of the PE2 in the first microporous layer material is in the range of from 0 wt. % to 50 wt. %, based on the weight of the first microporous layer material;
(9) the amount of the PE1 in the second microporous layer material is in the range of from 40 wt. % to 60 wt. %, based on the weight of the second microporous layer material;
(10) the amount of the PE2 in the second microporous layer material is in the range of from 0 wt. % to 50 wt. %, based on the weight of the second microporous layer material;
(11) the first and/or second polyethylene has Mw/Mn in the range of 5 to 300; and
(b) the second polypropylene has at least one of:
(1) an Mw/Mn in the range of 2 to 6;
(2) an MW in the range of 9×10 5 to 2×10 6 ; and
(3) a heat of fusion is 100 J/g or more.
7 . The multi-layer microporous membrane of claim 1 , wherein the second microporous layer has a thickness in the range of about 4.6% to about 50% of the total thickness of the multi-layer microporous membrane.
8 . The multi-layer microporous membrane of claim 6 , wherein the first microporous layer material further comprises polypropylene.
9 . The multi-layer microporous membrane of claim 6 , wherein PE1 is high-density polyethylene and the PE2 is ultra-high molecular weight polyethylene.
10 . The multi-layer membrane of claim 9 , wherein the first and/or second polyethylene comprises 8 wt. % or less of PE2 and 92 wt. % or more of PE1.
11 . A method for producing a microporous membrane, comprising,
(1) combining a polyethylene resin and a first diluent,
(2) combining a polypropylene resin, and a second diluent; the polypropylene resin having the polypropylene having (a) a weight-average molecular weight of 6×10 5 or more, (b) a heat of fusion of 90 J/g or more, and (c) an MWD in the range of 2 to 6;
(3) extruding at least a portion of the combined first polyethylene resin and first diluent, and extruding at least a portion of the combined first polypropylene resin and second diluent to produce a multi-layer extrudate which comprises
a first layer comprising the combined polyethylene and first diluent, a second layer comprising the polypropylene and the second diluent, and a third layer comprising the combined polyethylene and first diluent, wherein the second layer is located between the first and third layers and wherein the polypropylene is present in the extrudate in an amount ≧2.0 wt. % based on the weight of polymer in the extrudate; and then
(4) cooling the multi-layer extrudate to form a multi-layer sheet,
(5) removing at least a portion of the first and second diluents from the multi-layer sheet to form a diluent-removed sheet, and
(6) removing at least a portion of any volatile species from the sheet to form the microporous membrane.
12 . The method of claim 11 , wherein the combined polyethylene and first diluent is a first polyolefin solution, wherein the combined polypropylene and second diluent is a second polyolefin solution, and wherein
the polyethylene resin is present in the first polyolefin solution in an amount in the range of from about 0.5 wt. % to about 75 wt. % based on the total weight of polyolefin in the first polyolefin solution,
the first polyolefin solution comprises polypropylene resin, the polypropylene resin being present in the first polyolefin solution in an amount in the range of from about 0 wt. % to about 10 wt. % based on the total weight of polyolefin in the first polyolefin solution,
the second polyolefin solution comprises polyethylene resin, the polyethylene resin being present in the second polyolefin solution in an amount in the range of from about 40 wt. % to about 90 wt. % based on the total weight of polyolefin in the second polyolefin solution,
the polypropylene resin is present in the second polyolefin solution in an amount in the range of from about 10 wt. % to about 60 wt. % based on the total weight of polyolefin in the second polyolefin solution;
the first diluent is present in the first polyolefin solution in an amount in the range of from about 25 wt. % to about 99 wt. % based on the weight of the first polyolefin solution; and
the second diluent is present in the second polyolefin solution in an amount in the range of from about 25 wt. % to about 99 wt. % based on the weight of the second polyolefin solution.
13 . The method of claim 12 wherein
(a) the polyethylene of the first, second, and third layer independently comprise a PE1, a PE2, or both PE1 and PE2, wherein
(1) the first polyethylene has a Mw in the range of 1×10 5 to 5×10 6 ;
(2) the second polyethylene has an Mw ranging from 1×10 5 to 5×10 6 ;
(3) PE1 is one or more of a high-density polyethylene, a medium-density polyethylene, a branched low-density polyethylene, or a linear low-density polyethylene;
(4) PE1 is at least one of (i) an ethylene homopolymer or (ii) a copolymer of ethylene and a comonomer selected from propylene, butene-1, hexene-1;
(5) PE2 has an Mw of at least 1×10 6 ;
(6) PE2 is at least one of (i) an ethylene homopolymer or (ii) a copolymer of ethylene and a comonomer selected from propylene, butene-1, hexene-1;
(7) the amount of the PE1 in the first microporous layer material is in the range of from 50 wt. % to 100 wt. %, based on the weight of the first microporous layer material;
(8) the amount of the PE2 in the first microporous layer material is in the range of from 0 wt. % to 50 wt. %, based on the weight of the first microporous layer material;
(9) the amount of the PE1 in the second microporous layer material is in the range of from 40 wt. % to 60 wt. %, based on the weight of the second microporous layer material;
(10) the amount of the PE2 in the second microporous layer material is in the range of from 0 wt. % to 50 wt. %, based on the weight of the second microporous layer material;
(11) the first and/or second polyethylene has Mw/Mn in the range of 5 to 300; and
(b) the second polypropylene has at least one of:
(1) an Mw/Mn in the range of 2 to 6;
(2) an MW in the range of 9×10 5 to 2×10 6 ; and
(3) a heat of fusion is 100 J/g or more.
(b) the polypropylene has at least one characteristic selected from:
(1) a weight-average molecular weight of 9×10 5 to 2×10 6 ,
(2) a heat of fusion of 100 J/g or more, and
(3) a molecular weight distribution (Mw/Mn) in the range of 2 to 6.
14 . A battery comprising an anode, a cathode, an electrolyte, and the multi-layer microporous membrane of claim 1 , wherein the multi-layer microporous membrane separates at least the anode from the cathode.
15 . The battery of claim 14 , wherein the electrolyte contains lithium ions and the battery is a secondary battery.
16 . The battery of claim 14 used as a source or sink of electric charge.
17 . A microporous membrane having Rupture temperature 180° C. or higher and comprising polypropylene wherein the total amount polypropylene in the membrane is ≧2 wt. %, based on the total weight of the membrane.
18 . The microporous membrane of claim 17 , wherein the total amount polypropylene in the membrane having
(a) an Mw≧6×10 5 ,
(b) an MWD in the range of 2 to 6, and
(c) a heat of fusion of 90 J/g or higher
is ≧2 wt. %, based on the total weight of the membrane.
19 . The microporous membrane of claim 17 wherein the membrane has Normalized Air Permeability satisfying the relationship A≦(M*P)−I where A is the microporous membrane's Normalized Air Permeability thickness, P is the microporous membrane's Normalized Pin Puncture Strength, M is a slope in the range of about 0.09 to about 0.1, or about 0.95 to about 0.99, and I is ≧100.
20 . A battery comprising the separator of claim 19 .
21 . A battery separator made by the process of claim 11 .