WO2010048395A2

WO2010048395A2 - Multilayer microporous membranes, methods of making such membranes and the use of such membranes on battery separator film

Info

Publication number: WO2010048395A2
Application number: PCT/US2009/061671
Authority: WO
Inventors: Patrick Brant
Original assignee: Tonen Chemical Corporation
Priority date: 2008-10-24
Filing date: 2009-10-22
Publication date: 2010-04-29
Also published as: WO2010048392A1; US20110206973A1; JP2012506792A; KR20110112276A; WO2010048397A1; WO2010048395A3; KR101678479B1; CN102196900A; CN102196900B; JP5519682B2

Abstract

The invention generally relates to polymeric microporous membranes, and more particularly relates to liquid-permeable multilayer polymeric membranes having one or more filled microlayers, methods for producing these membranes, and the use of these membranes as battery separator film.

Description

MULTILAYER MICROPOROUS MEMBRANES, METHODS OF MAKING SUCH MEMBRANES, AND THE USE OF SUCH MEMBRANES ON BATTERY

SEPARATOR FILM

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. Prov. App. Ser. No. 61/108243, filed

24 Oct 2008; U.S. Prov. App. Ser. No. 61/171686, filed 22 Apr 2009; U.S. Prov. App. Ser. No. 61/226442, filed 17 JuI 2009; U.S. Prov. App. Ser. No. 61/226481, filed 17 JuI 2009, U.S. Prov. App. Ser. No. 61/232671, filed 10 Aug 2009, EP081725073.9 filed 22 December 2008, EP09160968.5 filed 25 May 2009, the contents of each of which are incorporated by reference in their entirety. FIELD OF THE INVENTION

[0002] The invention generally relates to polymeric microporous membranes, and more particularly relates to liquid-permeable multilayer polymeric membranes having one or more filled microlayers, methods for producing these membranes, and the use of these membranes as battery separator film. BACKGROUND OF THE INVENTION

[0003] Liquid-permeable polymeric membranes such as multilayer polymeric membranes can be used as battery separator film in primary and secondary batteries such as lithium ion primary and secondary batteries. For example, PCT Pat. Publ. WO2008016174A1 discloses a multilayer microporous polymeric membrane and the use of such a membrane as a battery separator film. According to the disclosure, the membrane is produced by co- extruding a mixture of polymer and diluent, stretching the extrudate in at least one planar direction, and then removing the diluent. [0004] Liquid-permeable, multilayer membranes are desirable because the layered structures allow improved control over the balance of membrane properties such as meltdown temperature, shutdown temperature, mechanical strength, porosity, permeability, etc. [0005] U.S. Pat. No. 5,336,573 teaches that filler material, such as inorganic filler, has been added to one or more layers of liquid-permeable multilayer membranes. The filler loading is limited, however, to 1 :2 to 1 :3, and when increased beyond these limits, loss of strength, flexibility, and friability becomes a problem. U.S. Publ. No. 2008/0193833 suggests that filler can improve shutdown temperature and heat resistance, but that the inclusion of filler can inhibit the ability to create thin membranes with desirable permeability and mechanical strength. U.S. Publ. No. 2007/0116944 teaches the use of inorganic powder to initiate pore formation during stretching, although it is acknowledged that it is difficult to disperse the inorganic material into the polyolefm.

[0006] A liquid-permeable, multilayer membrane having one or more filled microlayers and an overall balance of desirable properties as well as a process for producing this membrane at relatively high yield, are therefore desired. SUMMARY OF THE INVENTION

[0007] In an embodiment, the invention relates to a micro-porous membrane comprising: i. first and third layers comprising a first polymer; ii. a second layer comprising a second polymer and > 1.0 wt.% of a filler based on the weight of the layer; iii. first and second interfacial regions each comprising the first and second polymer; the first interfacial region being located between the first and second layers and having a thickness Tl; the second interfacial region being located between the second and third layers and having a thickness T2, wherein the absolute value of [(T1-T2)/T1] > 0.05; the first and second interfacial regions each containing < 1.0 wt.% of the filler, based on the weight of the interfacial region.

[0008] In another embodiment, the intention relates to a multilayer microporous membrane comprising: i. a first series of layers including at least two layers having distinct polymeric compositions, where the layers form a sequence based upon the composition of each layer; ii. an interfacial region between the at least two layers having distinct polymeric compositions within the first series, where the interfacial region has a thickness Tl; iii. a second series of layers having the same sequence of layers as the first series; and iv. an interfacial region between said first series and said second series having a thickness T2, wherein the absolute value of [(T1-T2)/T1] > 0.05, and where at least one layer within each series of layers includes > 1.0 wt.% of a filler based on the total weight of the at least one layer.

[0009] In another embodiment, the invention relates to a multilayer micro-porous polymeric membrane comprising: i. at least two internal layers including a first polymer and a filler, and ii. at least two interfacial regions between said internal layers, where the thicknesses of the two interfacial regions vary by at least 5 percent.

[0010] In another embodiment, the invention relates to a battery separator film comprising the microporous membrane of any of the preceding embodiments.

[0011] In another embodiment, the invention relates to a method for making a liquid- permeable membrane comprising: manipulating a first layered article comprising first and second layers to produce a second layered article having an increased number of layers, the first layer comprising a first polymer and a first diluent miscible with the first polymer and the second layer comprising a second polymer and a second diluent miscible with the second polymer; reducing the first layered article's thickness and increasing the first layered article's width before producing the second layered article, and/or reducing the second layered article's thickness and increasing the second layered article's width; and removing at least a portion of the first and second diluents from the second layered article; wherein at least one of the first or second layer further comprises a filler.

BRIEF DESCRIPTION OF DRAWINGS

[0012] Fig. 1 is a schematic illustration of a portion of a multilayer membrane according to the invention. [0013] Fig. 2 is a schematic illustration of an interfacial region and bordering layers of a multilayer membrane according to the invention.

[0014] Figs. 3(a)-3(c) are schematic illustration of a portion of three distinct multilayer membranes according to the invention.

[0015] Fig. 4 schematically illustrates an extrusion system for making a liquid- permeable microlayer membrane.

[0016] Fig. 5 schematically illustrates a multiplying die element and the multiplying process used in the system illustrated in Fig. 1.

[0017] Fig. 6 schematically illustrates an alternative extrusion system for making the liquid-permeable microlayer membrane. [0018] Fig. 7 schematically illustrates layer-multiplication stages that can be used to produce microlayer extrudates.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0019] The invention is based on the discovery of liquid-permeable multilayer membranes having at least one layer comprising polymer and filler, the membrane having an improved meltdown temperature. Such membranes can be produced in a layer multiplication process. It has been observed that subjecting certain layered extrudates as hereinafter described to layer multiplication results in the formation of an interfacial region between a pair of extrudate layers. While not wishing to be bound by any theory or model, it is believed that that polymer diffuses into the interfacial region under layer multiplication conditions at a rate much larger than the filler diffusion rate, and that this difference in diffusion rates results in an increased filler concentration within the layer and a decrease in the variation of filler concentration within the layer. OVERVIEW OF MEMBRANE STRUCTURE [0020] In an embodiment, the invention relates to multilayer microporous membranes comprising microlayers, at least two of the microlayers comprising polymer and filler. In another embodiment, the invention relates to multilayer microporous membranes comprising (a) at least one layer comprising polymer and filler and (b) at least two interfacial regions, the two interfacial regions each comprising polymer and having substantially different thicknesses. The interfacial regions are disposed between the membrane's layers, and a plurality of the membrane's layers include filler. The membranes are liquid-permeable, e.g., to battery electrolyte, at atmospheric pressure and ambient temperature. While the invention is described in terms of these embodiments, it is not limited thereto, and the description of these embodiments is not meant to foreclose other embodiments within the broader scope of the invention.

[0021] For the purpose of this description and the appended claims, the term "layer" means a region of the membrane comprising polymer and substantially parallel to the membrane's skins, the region having average concentration of the polymer (on a weight basis) varying by < 10.0 wt.% in the thickness direction. The term "microlayer" means a layer having a thickness < 1.0 μm. The term "filler" means one or more materials or species added to the polymer used for producing at least one layer of the multilayer microporous membrane, the filler forming a heterogeneous blend with the polymer. The term "polymer" means a composition including a plurality of macromolecules, the macromolecules containing recurring units derived from one or more monomers. The macromolecules can have different size, molecular architecture, atomic content, etc. The term "polymer" includes macromolecules such as copolymer, terpolymer, etc.

[0022] An embodiment of the present invention may be described with reference to Fig. 1, which schematically shows membrane 10 including first external layer L12 and second external layer L 14 (not to scale). External layers include those layers that have one planar surface in contact with the environment and therefore may also be referred to as skin or surface layers. Membrane 10 also includes internal layers L16, L18, L20, and L22, which include those layers having both planar surfaces in contact with adjacent interfacial regions. An interfacial region 124 is disposed between internal layers L20 and L 16, an interfacial region 126 is disposed between internal layers L22 and L 18, and an interfacial region 128 is disposed between internal layers L16 and L22. The layers can be microlayers. [0023] Internal layers Ll 6 and Ll 8 are at least distinct from layers L20 and L22 based upon polymer composition. Internal layers Ll 6 and Ll 8 include filler and therefore may be referred to as filled layers. Internal layers L20 and L22 may optionally include filler, but in this embodiment, they are substantially free of filler.

[0024] Interfacial regions 124 and 126 have a thickness T24 and T26 respectively, and interfacial layer L28 has a thickness T28. T24 equals or is substantially the same as T26, and T24 and T26 are each individually greater than T28. In one or more embodiments, T24 or T26 is at least 5% greater, in other embodiments at least 10% greater, and in other embodiments at least 15% greater than T28. Stated another way, the absolute value of [(T26- T28)/T26] is > 0.05, or in other embodiments > 0.10, or in other embodiments > 0.15. For the purpose of this description and appended claims, the term "absolute value" is understood in this relationship so that the quotient can be represented as a positive number. [0025] With reference still to Fig. 1, internal filled layer L16 has a filler concentration C16 and internal filled layer Ll 8 has a filler concentration C 18; C16 and Cl 8 being in weight percent, based on the total weight of the particular layer. C18 is > C 16. In one or more embodiments, Cl 8 is at least 5.0% greater, in other embodiments at least 10.0% greater, and in other embodiments at least 15% greater than C 16. Stated another way, [(C18-C16)/C18] > 0.05, or in other embodiments > 0.10, or in other embodiments > 0.15. [0026] Thus, while layers Ll 6 and Ll 8 include the same polymer composition and both include filler, they do not have the same filler concentration. Also, Tl 6 is greater than T 18. In one or more embodiments, T16 is at least 0.5% greater, in other embodiments at least 1.0% greater, and in other embodiments at least 1.5% greater than T18. Stated another way, [(T16- T18/T16)] > 0.005, or in other embodiments > 0.010, or in other embodiments > 0.015. [0027] As can be seen from Fig. 1, two distinct interfacial regions of differing thickness

(e.g., 126 and 128) are disposed between filled layer L16 and filled layer L 18. Where internal layer L22 includes filler, two distinct interfacial regions of differing thickness and a filled layer (e.g. L22) are disposed between filled layer L16 and filled layer L 18. [0028] The layers and the interfacial regions of a membrane according embodiments of this invention include regions containing polymer and regions that are substantially free of polymer, which polymer-free regions being also referred to as voids, pores, micropores, or interstices. In other words, the layers or interfacial regions include a polymer region and a pore region. With this understanding, reference may be made to the polymer of a layer or interfacial region and it will understood that this refers to the polymer of the polymer region of the layer or interfacial region. In one or more embodiments, the pores allow for the movement or passage of matter (e.g., electrolyte when the membrane is used as a battery separator film) through the membrane depending on pore size. The layers and interfacial regions may also include residual diluents as will be better understood in further description herein. And, as noted above, the layers may include filler dispersed in the polymer, which means the filler is primarily dispersed in the polymer region.

[0029] In an embodiment, the multilayer membranes include one or more layers that border a common interfacial region. For example, as seen in Fig. 1, layers Ll 6 and L22 border a common interfacial region 128. Generally, the polymer compositions of layers bordering a common interfacial region are different, which may refer to differences in size, molecular architecture, and/or chemical composition. With this understanding, reference may simply be made to the fact that the polymers are different or are characterized by distinct polymeric compositions. For example, reference may be made to first and second polymers, with each being different in one or more of size, molecular architecture, and/chemical composition. The first and second polymers can be polymer compositions, e.g., mixtures of polymers. It should be understood that the multilayer membranes of this invention may include more than two distinct layers and therefore the membrane may include more than two distinct layers each with distinct polymer. Thus, reference to first and second polymers should not limit the scope of the invention. INTERFACIAL REGIONS

[0030] In one or more embodiments, such as the embodiment shown in Fig. 1, the polymer region of the interfacial regions include polymer from each of the two layers disposed on either side of the interfacial region (i.e. layers bordering either side of the region), and the concentration of respective polymers are not distributed homogeneously throughout the interfacial region (i.e. throughout the polymer region of the interfacial region). For example, the average concentration of any given polymer within an interfacial region increases from a minimum near one surface of the region to a maximum near the opposite surface of the region proximate to the layer containing the polymer. Optionally, these surfaces or portions thereof can be planar surfaces as when, e.g., the membrane is flat. For example, as shown in Fig. 2, membrane 30 includes first layer L32, second layer L34, and an interfacial region 136 disposed between the layers. First layer L32 includes a planar surface 33 that borders interfacial region 136, and second layer L34 includes a planar surface 35 that borders interfacial region 136. In other words, both layers L32 and L34 border the same interfacial region 136 at their respective surfaces 33 and 35.

[0031] Layer L32 includes a first polymer Pl, and layer L34 includes a second polymer

P2, and the first polymer is not the same polymer as the second polymer. Interfacial region 136 includes both first polymer and second polymer, and the concentration of the first and second polymers are not homogeneously distributed across the thickness of interfacial region 136. In one or more embodiments, the first polymer decreases from a maximum concentration at or near surface 33 to a minimum concentration at or near surface 35, and the second polymer decreases from maximum concentration at or near surface 35 to a minimum concentration at near surface 33. In particular embodiments, the relative amounts of first and second polymer change at the same rates (but in opposite directions parallel to the thickness of the film) between adjacent layers containing first and second polymer, respectively. In other words, the rate of increase in the concentration of the first polymer in the interfacial region can be the same as the rate of decrease in the concentration of the second polymer, or vice versa. The amount of concentration change in the thickness direction of the first or second polymer (the "concentration profile") is not critical, and can have the profile of, for example, a line, a quadratic, a sine or cosine, an error function, a Gaussian, etc., including segments thereof and combinations of segments thereof.

[0032] The thickness of the interfacial regions is defined as the distance in the thickness direction of the membrane over which the concentration of the first polymer decreases from 90 wt. % to 10 wt. %, based on the weight of first polymer in a layer comprising the first polymer that is in face-to-face contact with the interfacial region. Optionally, the most interior or centermost interfacial region (e.g. the second interfacial region in a four-layer membrane) has the smallest thickness. The thickness of an interfacial region is generally > 25 nm, e.g., in the range of 25 nm to 5.0 μm, or 35 nm to 1.0 μm. LAYERS

[0033] In one or more embodiments, such as the embodiment shown in Fig. 1, the layers, including internal and external layers, as well as filled and unfilled layers, are characterized by having a relatively constant polymer concentration throughout the layer. In other words, the average concentration of any given polymer in the polymer region of the layer does not substantially change. Relative to the interfacial region described above, the average concentration of polymer (in weight percent) within a layer varies by < 10.0 wt.% over the thickness of the layer, based on the weight of polymer in the layer. For example, where a first layer includes a first polymer, the average concentration of the first polymer can increase or decrease over the thickness of the first layer (within the polymer regions of the layer) by ≤IO.O wt.%. Or, where a second layer includes a second polymer, the average concentration of the second polymer can increase or decrease over the thickness of the second layer by < 10.0 wt.%. [0034] The surface between any given layer and an interfacial region that is in contact with the layer may be approximated by a plane where the average concentration variance in polymer concentration between distinct polymers is 10.0% by weight. As those skilled in the art will appreciate, this plane has no thickness and lies between the interface of the interfacial region and the layer. [0035] Optionally, a layer can be characterized by a layer thickness, a relative thickness compared to other layers in the film or the extrudate from which the film was produced, or some combination thereof. In one or more embodiments, the film layers are microlayers. In an embodiment, the microporous membrane includes at least one layer (which can be an internal layer) having a thickness < 25.0 μm, e.g., < 10.0 μm such as < 5.0 μm. In another embodiment, the microporous membrane comprises at least one microlayer, e.g., an internal microlayer, having a thickness < 1.0 μm, e.g., < 0.5 μm or < 0.1 μm, such as in the range of 25.0 nm to 0.75 μm.

[0036] In one or more embodiments, the thickness of at least one layer of the film (e.g., a microlayer), or in other embodiments each layer (e.g., each of a plurality of microlayers), is greater than about two times the radius of gyration of the polymer ("Rg") in the microlayer, e.g., in the range of 25.0 nm to 1.0 μm, e.g., 100 nm to 0.75 μm, or 250 nm to 0.5 μm. Rg

can be determined from the equation Rg = where "a" is the polymer's statistical

6 segment length and N is the number of segments in the polymer based on a four-carbon repeat unit. The value of Rg can be determined by methods described in U.S. Pat. No. 5,710,219, for example. Microlayers and interfacial regions can be imaged (e.g., for the purpose of measuring thickness) using, e.g., TEM, as described in Chaffrn, et al., Science 288, 2197- 2190. REPEATING SEQUENCE OF LAYERS

[0037] In one or more embodiments, the membranes of the present invention include a series of layers, and this series repeats two or more times across the thickness of the membrane. Each series includes at least two layers and an interfacial region disposed between each layer. Each layer sharing a common interfacial region has distinct polymeric composition. The polymeric composition of each layer within the series provides a sequence for the layers within the series, and the sequence repeats in each repeating series of layers. In other words, if a first layer in a two-layered series includes a first polymer, and the second layer includes a second polymer, then the sequence that repeats in each series is a first layer characterized by a first polymer followed by a second layer characterized by a second polymer.

[0038] A transitional interfacial region, which has a thickness different than the thickness of interfacial regions between layers within a series, serves to define the beginning or end of any particular series of layers. In other words, the first layer in a series borders a transitional interfacial region, and the last layer in a series borders a transitional interfacial region. In one or more embodiments, a series is the smallest sequence of layers within a membrane and therefore the interfacial regions between layers within a series are non- transitional interfacial regions. [0039] For example, Fig. 3A shows a membrane having two layers in a series. As will become evident hereinafter, this series may derive from constructing the membrane from an initial co-extrusion of two layers. Membrane 40 includes internal layers 42 A and 44 A with interfacial region 43A disposed therebetween, and it includes internal layers 42B and 44B with interfacial region 43B disposed therebetween. Layers 42A and 44A form first series A, and layers 42B and 44B form second series B. Internal layers 42 A and 44 A comprise substantially different polymers (or mixtures of polymers). For example, in an embodiment layer 42A comprises a first polymer and internal layer 44A comprises a second polymer that is not the same as the first polymer. Likewise, internal layer 42B comprises the first polymer, and internal layer 44B comprises the second polymer. Thus, layers 42A and 44A create a sequence within the first series that is repeated in the second series with layers 42B and 44B. Transitional interfacial region 49 is disposed between first series A and second series B, and the thickness of transitional interfacial region 49 is at least 5% smaller, or in other embodiments at least 10% smaller, or in other embodiments at least 15% smaller than interfacial regions 43A or 43B within the respective series. [0040] Another example can be seen in Fig. 3b, which shows a membrane having three layers in series. Optionally, this series derives from producing the membrane from an extrudate having three layers. Membrane 50 includes internal layers 52A, 54A, and 56A with interfacial region 53A disposed between layers 52A and 54A and interfacial region 55A disposed between layers 54A and 56A. Membrane 50 also includes internal layers 52B, 54B, and 56B with interfacial region 43B disposed between layers 52B and 54B and interfacial region 55B disposed between layers 54B and 56B. Layers 52A, 54A, and 56A form first series A, and layers 52B, 54B, and 56B form second series B. In one or more embodiments, internal layer 52A includes a first polymer, internal layer 54A includes a second polymer that is substantially different from the first polymer, internal layer 56A includes a third polymer that is different from the first and second polymers, internal layer 52B includes the first polymer, internal layer 54B includes the second polymer, and internal layer 56B includes the third polymer. Thus, layers 52A, 54A, and 56A create a sequence within the first series that is repeated in the second series with layers 52B, 54B, and 56B. Transitional interfacial region 59 is disposed between first series A and second series B, and the thickness of transitional interfacial region 59 is at least 5% smaller, or in other embodiments at least 10% smaller, or in other embodiments at least 15% smaller than interfacial regions 53 A, 55 A, 53B or 55B within the respective series. [0041] Yet another example can be seen in Fig. 3c, which shows a membrane having four layers in series. As will become evident hereinafter, this series may derive from constructing the membrane from an initial co-extrusion of four layers. Membrane 60 includes internal layers 62A, 64A, 66A, and 68A with interfacial region 63A disposed between layers 62A and 64A, interfacial region 65A disposed between layers 64A and 66A, and interfacial region 67A disposed between layers 66A and 68A. Membrane 60 also includes internal layers 62B, 64B, 66B, and 68B with interfacial region 63B disposed between layers 62B and 64B, interfacial region 65B disposed between layers 64B and 66B, and interfacial region 67B disposed between layers 66B and 68B. Layers 62A, 64A, 66A, and 68A form first series A, and layers 62B, 64B, 66B, and 68B form second series B. In one or more embodiments, internal layer 62A includes a first polymer; internal layer 64A includes a second polymer that is not the same as the first polymer; internal layer 66A includes a third polymer that is different from both the first and second polymers; internal layer 68A includes a fourth polymer that is different from the first, second, and third polymers; internal layer 62B includes the first polymer; internal layer 64B includes the second polymer; internal layer 66B includes the third polymer; and internal layer 68B includes the fourth polymer. In an embodiment, the third polymer is substantially different from the second and fourth polymer, and is optionally substantially different from the first polymer. The fourth polymer is substantially different from the first and third polymer, and optionally is substantially different from the second polymer. Thus, layers 62A, 64A, 66A, and 68A create a sequence within the first series that is repeated in the second series with layers 62B, 64B, 66B, and 68B. Transitional interfacial region 69 is disposed between first series A and second series B, and the thickness of transitional interfacial region 69 (T69) is at

763 - 769 least 5.0% smaller (e.g., ≤ 0.05 ), or in other embodiments at least 10.0%

763 smaller, or in other embodiments at least 15.0% smaller than the thicknesses of interfacial regions 63A, 65A, 67A, 63B, 65B or 67B within the respective series (T63A, T65A, T67A, T63BG, T65B, or T67B).

[0042] In one or more embodiments, each series of layers includes a first and last layer within the series. The first layer in the series begins the sequence and the last layer in the series ends the sequence. The first and last layers in the series border transitional interfacial regions, although it should be understood that where the first or last layers in the series are external layers they cannot border an interfacial region. FILLER WITHIN FIRST OR LAST LAYERS OF SERIES

[0043] In one or more embodiments, at least one layer in the series comprises filler, e.g., the first layer in a series, the last layer in a series, or both the first and last layers in a series of layers includes filler. When the filled layers are first or last layers in a series, it should be understood that these filled layers border a transitional interfacial region, except for the case where the filled layer includes an external layer. The filler concentration (in weight %, based on the weight of the layer) of the first layer within the first series may be defined by ClA and the filler concentration of the first layer within the second series may be defined by ClB. In one or more embodiments, ClA > ClB; in particular embodiments ClA is at least 5.0% greater, in other embodiments at least 10.0% greater, and in other embodiments at least 15% greater than ClB. In one or more embodiments, [(C1A-C1B/C1A)] > 0.05, or in other embodiments > 0.10, or in other embodiments > 0.15. [0044] In one or more embodiments, the innermost transitional interfacial region bisects the thickness of the membrane. In these embodiments, the membrane includes the same number of layers on either side its innermost transitional interfacial region, and the membrane includes the same number of transitional interfacial regions on either side of this transitional interfacial region. OVERVIEW OF MEMBRANE COMPOSITION

[0045] In an embodiment, the membrane comprises a plurality of layers comprising a first polymer and a plurality of layers comprising a second polymer, wherein the second polymer is different from the first polymer and wherein at least one of the first or second layers contain a filler. For example, in a particular embodiment, the membrane comprises (a) a first plurality of layers comprising a filler and a first polymer and (b) a second plurality of layers comprising a second polymer. Optionally, at least a portion of the layers are microlayers. [0046] The first and/or second polymer can be polyolefin, including mixtures of polyolefms. For example, the multilayer microporous membrane can comprise (a) a first plurality of layers produced from (i) a filler and (ii) a first polymer comprising polyethylene, polypropylene, or both polyethylene and polypropylene and (b) a second plurality of layers produced from (i) an optional filler and (ii) a second polymer is not the same as the first polymer, and optionally is not miscible in the first polymer. [0047] In a particular embodiment where the first polymer is polyethylene, the second polymer can be polyethylene, provided the second polymer's polyethylene is not the same polyethylene (e.g., a different Mw and/or MWD) as the first polymer's polyethylene. When the first polymer is a combination of polymers, e.g., polyethylene and polypropylene, the second polymer can be (i) polyethylene, (ii) polypropylene, or (iii) a different combination of polypropylene and polyethylene (different polyethylene type and/or amount, different polypropylene type and/or amount, or some combination thereof) than that of the first polymer. Although the following embodiments of the invention describe a first plurality of layers comprising filler and polymer and a second plurality of layers comprising polymer without filler, the invention is not limited thereto, and other embodiments where both the first and second plurality of layers comprise fillers are within the broader scope of the invention. [0048] Optionally, the total amount of first polymer (the "first amount") and the total amount of second polymer (the "second amount") in the membrane are each > 1.0 wt.% based on the weight of the membrane. For example, the first and second amounts can each be in the range of from about 10.0 wt.% to about 90.0 wt.%, or from about 30.0 wt.% to about 70.0 wt.%, based on the weight of the liquid-permeable microlayer membrane, with the remaining weight of the membrane being the first or second polymer and, optionally, other species. The first amount can be independently selected from the second amount, and the relative amount of first and second polymer is not critical. Optionally, the membrane contains substantially equal amounts of first and second polymer, e.g., both about 50 wt.%, based on the weight of the membrane.

[0049] In an embodiment, the first polymer comprises polyethylene and the second polymer comprises polypropylene. Since for homopolymer of approximately the same Mw, polyethylene's melting peak ("Tm") is generally < polypropylene's Tm, it is believed that the first polymer improves (i.e., lowers) the membrane's shutdown temperature and the second polymer improves (i.e., increases) the membrane's meltdown temperature. Adding filler having a Tm (or glass transition) > the greater of the first or second polymer's Tm provides a further meltdown temperature increase. [0050] In an embodiment, the total amount of polyethylene in the first polymer is > 50.0 wt.%, e.g., in the range of 60.0 wt.% to 100.0 wt.%, e.g., 75 wt.% to 95.0 wt.%, based on the weight of the first polymer. Optionally, the total amount of polypropylene in the second polymer is > 50.0 wt.%, e.g., in the range of 60.0 wt.% to 100.0 wt.%, e.g., 75.0 wt.% to 95.0 wt.%, based on the weight of the second polymer. [0051] Optionally, the total amount of polyethylene in the membrane is in the range of from about 10.0 wt.% to about 90.0 wt.%, for example from about 25.0 wt.% to about 75.0 wt.%, based on the weight of the membrane. Optionally, the total amount of polypropylene in the liquid-permeable membrane is in the range of 10.0 wt.% to 90.0 wt.%, for example from about 25.0 wt.% to about 75.0 wt.%, based on the weight of the membrane. [0052] The first and second polymers will now be described in terms of embodiments where the first polymer comprises polyethylene and the second polymer comprises polypropylene. While the invention is described in terms of these embodiments, it is not limited thereto, and the description of these embodiments is not meant to foreclose other embodiments within the broader scope of the invention. The first polymer [0053] In an embodiment, the first polymer comprises polyethylene, e.g., polyolefin

(including homopolymer, copolymer, etc.) containing recurring ethylene units. Optionally, the first polymer comprises polyethylene homopolymer and/or polyethylene copolymer wherein at least 85% (by number) of the recurring units are ethylene units. The first polymer can be a mixture of individual polymer components or a reactor blend. Optionally, the polyethylene comprises a mixture or reactor blend of polyethylene, such as a mixture of two or more polyethylenes ("PEl", "PE2", "PE3", etc.). PEl

[0054] In an embodiment, the first polymer comprises PEl. PEl comprises polyethylene having a Tm > 130.0⁰C, e.g., > 131.0⁰C (such as in the range of 131.0⁰C to 135.0⁰C) and an Mw < 1.0 x 10⁶, e.g., in the range of from 1.0 x 10⁵ to 9.0 x 10⁵, for example from about 4.0 x 10⁵ to about 8.0 x 10⁵. Optionally, the PEl has a molecular weight distribution ("MWD") < 1.0 x 10², e.g., in the range of from 1 to 50.0, such as from about 3.0 to about 20.0. For example, the PEl can be one or more of a high density polyethylene ("HPDE"), a medium density polyethylene, a branched low density polyethylene, or a linear low density polyethylene. In an embodiment, the PEl is HDPE. Optionally, the PEl has terminal unsaturation. For example, the PEl can have an amount of terminal unsaturation > 0.20 per 10,000 carbon atoms, e.g., > 5.0 per 10,000 carbon atoms, such as > 10.0 per 10,000 carbon atoms. The amount of terminal unsaturation can be measured in accordance with the procedures described in PCT Publ. WO 1997/23554, for example. Optionally, the amount of PEl is ≤ 99.0 wt.%, e.g., in the range of from 25.0 wt.% to 99.0 wt.%, e.g., from 50.0 wt.% to 95.0 wt.%, or 60.0 wt.% to 85.0 wt.%, based on the weight of the first polymer. [0055] In an embodiment, PEl is at least one of (i) an ethylene homopolymer or (ii) a copolymer of ethylene and ≤ 10 mol.% of a comonomer, such as α-olefm. Such a polymer or copolymer can be produced by any convenient polymerization process, such as those using a Ziegler-Natta or a single-site catalyst. Optionally, the comonomer is one or more of propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-l, octene-1, vinyl acetate, methyl methacrylate, styrene, or other monomer. PE2 [0056] In an embodiment, the first polymer comprises PE2. PE2 comprises polyethylene having an Mw > 1.0 x 10⁶, e.g., in the range of 1.1 x 10⁶ to about 5 x 10⁶, for example from about 1.2 x 10⁶to about 3 x 10⁶, such as about 2 x 10⁶. Optionally, the PE2 has an MWD < 1.0 x 10², e.g., from about 2.0 to about 50.0, such as from about 4 to about 20 or about 4.5 to about 10.0. For example, PE2 can be an ultra-high molecular weight polyethylene ("UHMWPE"). Optionally, the amount of the PE2 is ≤ 99.0 wt.%, e.g., in the range of from 0 wt.% to 74.0 wt.%, e.g., 1.0 wt.% to 46.0 wt.%, or 7.0 wt.% to 32.0 wt.%, based on the weight of the first polymer.

[0057] In an embodiment, PE2 is at least one of (i) an ethylene homopolymer or (ii) a copolymer of ethylene and ≤ 10.0 mol.% of a comonomer such as α-olefm. Optionally, the comonomer is one or more of propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-l, octene-1, vinyl acetate, methyl methacrylate, styrene, or other comonomer. Such a polymer or copolymer can be produced using any convenient polymerization process, such as those using a Ziegler-Natta or a single-site catalyst. PE3

[0058] In an embodiment, the first polymer comprises PE3. PE3 comprises polyethylene having a Tm < 130.0⁰C. Using PE3 having a Tm < 130.0⁰C can provide the finished liquid-permeable membrane with a desirably low shutdown temperature, e.g., a shutdown temperature < 130.5⁰C. Optionally, the amount of PE3 in the first polymer is > 1.0 wt.%, e.g., in the range of 1.0 wt.% to 30.0 wt.%, such as 4.0 wt.% to 17.0 wt.%, or 8.0 wt.% to 13.0 wt.%, based on the weight of the first polymer.

[0059] Optionally, PE3 has a Tm > 85.0⁰C, e.g., in the range of from 105.0⁰C to

130.0⁰C, such as 115.0⁰C to 126.0⁰C, or 120.0⁰C to 125.0⁰C, or 121.0⁰C to 124.0⁰C. Optionally, the PE3 has an Mw < 5.0 x 10⁵, e.g., in the range of from 1.0 x 10³ to 2.0 x 10⁵, such as in the range of from 1.5 x 10³ to about 1.0 x 10⁵. Optionally, the PE3 has an MWD in the range of from 2.0 to 5.0, e.g., 1.8 to 3.5. Optionally, PE3 has a mass density in the range of 0.905 g/cm to 0.935 g/cm . Polyethylene mass density is determined in accordance with A.S.T.M. D1505. [0060] In an embodiment, PE3 is a copolymer of ethylene and < 10.0 mol.% of a comonomer such as α-olefin. The comonomer can be, e.g., one or more of propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-l, octene-1, vinyl acetate, methyl methacrylate, styrene, or other monomer. Optionally, the comonomer amount is in the range of 1.0 mol.% to 5.0 mol.%. In an embodiment, the comonomer is hexene-1 and/or or octene- 1.

[0061] When PE3 is a copolymer, the copolymer optionally has a Composition

Distribution Breadth Index ("CDBI" as hereinafter defined) > 50%, e.g., > 75%, such as > 90%. Optionally, the PE3 copolymer has a relatively narrow compositional distribution, as hereinafter defined. [0062] PE3 can be produced in any convenient process, such as those using a Ziegler-

Natta or single-site polymerization catalyst. Optionally, PE3 is one or more of a low density polyethylene ("LDPE"), a medium density polyethylene, a branched low density polyethylene, or a linear low density polyethylene, such as a polyethylene produced by metallocene catalyst. PE3 can be produced according to the methods disclosed in U.S. Pat. No. 5,084,534 (such as the methods disclosed therein in examples 27 and 41), which is incorporated by reference herein in its entirety.

[0063] In one embodiment, the first polymer has one or more of the following independently-selected features: iv. The first polymer comprises PEl and optionally PE3. v. The first polymer consists essentially of, or consists of, PEl and optionally PE2 and/or PE3. vi. The first polymer comprises PE2 and optionally PE3. vii. The first polymer consists essentially of, or consists of, PE2. viii. The first polymer comprises PEl, PE2, and PE3. ix. PE3 has an Mw < 1.0 x 10⁵. x. PE2 is UHMWPE. xi. PEl is HDPE. xii. PEl has an Mw in the range of from 4 x 10⁵ to about 8 x 10⁵ and an MWD in the range of from 3.0 to 20.0. x. PE2 has an Mw in the range of from 1.2 x 10⁶to 3 x 10⁶ and an

MWD in the range of 4.5 to 10.0. The second polymer

[0064] In an embodiment, the second polymer comprises polypropylene, e.g., polyolefin (homopolymer or copolymer) containing recurring propylene units. Optionally, the second polymer comprises polypropylene homopolymer and/or polypropylene copolymer wherein at least 85% (by number) of the recurring units are propylene units. The second polymer can comprise mixture of individual polymer components or a reactor blend. Optionally, the polypropylene comprises a mixture or reactor blend of polymer. Optionally, the second polymer comprises polypropylene (e.g., PPl) and one or more of PEl, PE2, or PE3. For example, the second polymer can comprise < 99.0 wt.% polypropylene, e.g., in the range of

30.0 wt.% to 90.0 wt.%, such as 40.0 wt.% to 80.0 wt.% polypropylene; < 99.0 wt.% PEl, e.g., in the range of from 5.0 wt.% to 70.0 wt.%, such as 10.0 wt.% to 60.0 wt.%; < 99.0 wt.% PE2, e.g., in the range of from 5.0 wt.% to 70.0 wt.%, such as 10.0 wt.% to 60.0 wt.%; and < 30.0 wt.% PE3, e.g., in the range of from 0 wt.% to 20.0 wt.%, such as 1.0 wt.% to

15.0 wt.%; the weight percents being based on the weight of the second polymer.

PPl

[0065] In an embodiment, the second polymer comprises PPl. PPl comprises one or more of polypropylene homopolymer or copolymer (random or block) of propylene and a comonomer such as α-olefm. PPl has an Mw > 1.0 x 10⁵, for example from about 5.0 x 10⁵ to about 5.0 x 10⁶, such as from about 1.1 x 10⁶ to about 1.5 x 10⁶. Optionally, the polypropylene has an MWD < 1.0 x l0², e.g., from about 1 to about 50, or 2.0 to 6.0; and/or a heat of fusion ("ΔHm") > 80.0 J/g, e.g., in the range of 100.0 J/g to 120.0 J/g, such as from about 110.0 J/g to about 115.0 J/g. [0066] Optionally, the polypropylene comprises a copolymer of propylene and < 10.0 mol.% of a comonomer (such as one or more of α-olefϊns), e.g., ethylene, butene-1, pentene- 1, hexene-1, 4-methylpentene-l, octene-1, vinyl acetate, methyl methacrylate, and styrene, etc.; and diolefms such as butadiene, 1,5-hexadiene, 1,7-octadiene, 1,9-decadiene, etc.; and other comonomer.

[0067] Optionally, the polypropylene has one or more of the following properties: (i) the tacticity is isotactic; (ii) an elongational viscosity of at least about 5.0 x 10⁵ Pa sec at a temperature of 230⁰C and a strain rate of 25 sec^"1; (iii) a Tm (second melt) > about 160.0⁰C, e.g., ≥ 166.0⁰C, or even > about 168.0⁰C, or even > about 170.0⁰C; (iv) a Trouton's ratio of at least about 15 when measured at a temperature of about 230⁰C and a strain rate of 25 sec^"1; (v); an Mw in the range of 5.0 x 10⁵ to 2.0 x 10⁶; (vi) a Melt Flow Rate ("MFR" as defined in ASTM D 1238-95 Condition L) at 23O⁰C and 2.16 kg weight < 0.01 dg/min (e.g., a value low enough that the MFR is essentially not measurable); (vii) exhibits stereo defects < about 50 per 10,000 carbon atoms, or < about 40, or < about 30, or even < about 20 per 10,000 carbon atoms; (viii) a meso pentad fraction of greater than about 96 mol.% mmmm pentads; and/or (ix) an amount extractable species (extractable by contacting the polypropylene with boiling xylene) < 0.5 wt.%, or < 0.2 wt.%, or < 0.1 wt.% based on the weight of the polypropylene.

[0068] In one embodiment, the second polymer has one or more of the following independently-selected features: xiii. The second polymer comprises PPl and optionally at least one of PEl,

PE2, or PE3. xiv. The second polymer consists essentially of, or consists of, PPl and optionally PEl and/or PE2. xv. The second polymer comprises PPl and PEl. xvi. The second polymer consists essentially of, or consists of, PPl. xvii. The second polymer comprises PPl, PEl, and PE2. xviii. PPl has an Mw in the range of from 1.1 x 10⁶ to about 1.5 x 10⁶, an MWD in the range of from 2.0 to 6.0, and a ΔHm in the range of from 110.0 J/g to 120.0 J/g. xix. PE2 is UHMWPE. xx. PEl is HDPE. xxi. PEl has an Mw in the range of from 4.0 x 10⁵ to about 8.0 x 10⁵ and an MWD in the range of from 3.0 to 20.0. x. PE2 has an Mw in the range of from 1.2 x 10⁶to 3 x 10⁶ and an MWD in the range of 4.5 to 10.0. METHODS FOR CHARACTERIZING THE FIRST AND SECOND POLYMERS

[0069] T_m is measured in accordance with JIS K7122. A polymer sample (0.5-mm- thick molding melt-pressed at 210⁰C) is placed at ambient temperature in a sample holder of a differential scanning calorimeter (Pyris Diamond DSC available from Perkin Elmer, Inc.), heat-treated at 230⁰C for 1 minute in a nitrogen atmosphere, cooled to 30⁰C at 10°C/minute, kept at 30⁰C for 1 minute, and heated to 230⁰C at a speed of 10°C/minute. Tm is defined as the temperature of the greatest heat absorption within the range of melting as determined from the DSC curve. Polymers may show secondary melting peaks adjacent to the principal peak, and or the end-of-melt transition, but for purposes herein, such secondary melting peaks are considered together as a single melting point, with the highest of these peaks being considered the Tm. [0070] Mw and MWD are determined using a High Temperature Size Exclusion Chromatograph, or "SEC", (GPC PL 220, Polymer Laboratories), equipped with a differential refractive index detector (DRI). The measurement is made in accordance with the procedure disclosed in Macromolecules, Vol. 34, No. 19, pp. 6812-6820 (2001). Three PLgel Mixed-B columns available from (available from Polymer Laboratories) are used for the Mw and MWD determination. For polyethylene, the nominal flow rate is 0.5 cm³/min; the nominal injection volume is 300 μL; and the transfer lines, columns, and the DRI detector are contained in an oven maintained at 145⁰C. For polypropylene, the nominal flow rate is 1.0 cm³/min; the nominal injection volume is 300 μL; and the transfer lines, columns, and the DRI detector are contained in an oven maintained at 16O⁰C. [0071] The GPC solvent used is filtered Aldrich reagent grade 1,2,4-Trichlorobenzene (TCB) containing approximately 1000 ppm of butylated hydroxy toluene (BHT). The TCB is degassed with an online degasser prior to introduction into the SEC. The same solvent is used as the SEC eluent. Polymer solutions are prepared by placing dry polymer in a glass container, adding the desired amount of the TCB solvent, and then heating the mixture at 16O⁰C with continuous agitation for about 2 hours. The concentration of polymer solution is 0.25 to 0.75mg/ml. Sample solution are filtered off-line before injecting to GPC with 2μm filter using a model SP260 Sample Prep Station (available from Polymer Laboratories). [0072] The separation efficiency of the column set is calibrated with a calibration curve generated using a seventeen individual polystyrene standards ranging in Mp ("Mp" being defined as the peak in Mw) from about 580 to about 10,000,000. The polystyrene standards are obtained from Polymer Laboratories (Amherst, MA). A calibration curve (logMp vs. retention volume) is generated by recording the retention volume at the peak in the DRI signal for each PS standard and fitting this data set to a 2nd-order polynomial. Samples are analyzed using IGOR Pro, available from Wave Metrics, Inc. [0073] CDBI is defined as the percent of copolymer whose composition is within 50% of the median comonomer composition in the copolymer's composition distribution. The "composition distribution" can be measured according to the following procedure. About 30 g of the copolymer is cut into small cubes about 1/8 inch per side. These cubes are introduced into a thick walled glass bottle closed with screw cap along with 50 mg of Irganox 1076, an antioxidant commercially available from Ciba-Geigy Corporation. Then, 425 ml of hexane (a principle mixture of normal and isohexane) is added to the contents of the bottle and the sealed bottle is maintained at about 23°C for about 24 hours. At the end of this period, the solution is decanted and the residue is treated with additional hexane for an additional 24 hours. At the end of this period, the two hexane solutions are combined and evaporated to yield a residue of the copolymer soluble at 23°C. To the residue is added sufficient hexane to bring the volume to 425 mL and the bottle is maintained at about 31⁰C for 24 hours in a covered circulating water bath. The soluble copolymer is decanted and the additional amount of hexane is added for another 24 hours at about 31⁰C prior to decanting. In this manner, fractions of the copolymer component soluble at 40⁰C, 48°C, 55°C, and 62°C are obtained at temperature increases of approximately 8°C between stages. Increases in temperature to 95°C can be accommodated if heptane instead of hexane is used as the solvent for all temperatures about 60⁰C. The soluble copolymer fractions are dried, weighed and analyzed for composition, as for example by weight percent ethylene content. Soluble fractions obtained from samples in the adjacent temperature ranges are the "adjacent fractions". A copolymer is said to have a "narrow compositional distribution" when at least 75 wt.% of the copolymer is isolated in two adjacent fractions, each fraction having a composition difference of no greater than 20% of the copolymer's average wt.% monomer content.

[0074] The polypropylene's ΔHm, is determined by the methods disclosed in PCT Pat.

Publ. WO2007/132942, which is incorporated by reference herein in its entirety. [0075] Meso pentad fraction can be determined from 1^C NMR data obtained at 100

MHz at 125°C on a Varian VXR 400 NMR spectrometer. A 90⁰C pulse, an acquisition time of 3.0 seconds, and a pulse delay of 20 seconds are employed. The spectra are broad band decoupled and acquired without gated decoupling. Similar relaxation times and nuclear Overhauser effects are expected for the methyl resonances of polypropylenes, which are generally the only homopolymer resonances used for quantitative purposes. A typical number of transients collected is 2500. The sample is dissolved in tetrachlorethane-d₂ at a concentration of 15% by weight. All spectral frequencies are recorded with respect to an internal tetramethylsilane standard. In the case of polypropylene homopolymer, the methyl resonances are recorded with respect to 21.81 ppm for mmmm, which is close to the reported literature value of 21.855 ppm for an internal tetramethylsilane standard. The pentad assignments used are well established.

[0076] The amount of extractable species (such as relatively low molecular weight and/or amorphous material, e.g., amorphous polyethylene) is determined by solubility in xylene at 135⁰C, according to the following procedure. Weigh out 2 grams of sample (either in pellet or ground pellet form) into 300 ml conical flask. Pour 200 ml of xylene into the conical flask with stir bar and secure the flask on a heating oil bath. Turn on the heating oil bath and allow melting of the polymer by leaving the flask in oil bath at 135⁰C for about 15 minutes. When melted, discontinue heating, but continue stirring through the cooling process. Allow the dissolved polymer to cool spontaneously overnight. The precipitate is filtered with Teflon filter paper and then dried under vacuum at 9O⁰C. The quantity of xylene soluble is determined by calculating the percent by weight of total polymer sample ("A") less precipitate ("B") at room temperature [soluble content = ((A-B )/A) x 100]. FILLER [0077] In an embodiment, the membrane comprises a plurality of layers, wherein at least one of the layers comprises filler, including mixtures of fillers.

[0078] In an embodiment, the filler comprises one or more materials or species added to the polymer used for producing at least one layer of the microporous membrane, the filler forming a heterogeneous blend with the polymer. For example, the filler can form a discrete phase apart from the polymeric phase of the layer. In one or more embodiments, the discrete phase formed by the filler is discontinuous and dispersed within a polymeric matrix forming the layer. It has been observed that when a battery separator film comprises filler-containing layers (e.g., filler-containing microlayers), the battery separator film exhibits a desirable increase in meltdown temperature compared to an equivalent battery separator film that does not have filler-containing layers. The filler can be, e.g., and inorganic or organic species, and is distinct from species such as catalyst fines, antioxidants, etc. that are generally present in polymer resins used for producing microporous membranes.

[0079] In an embodiment, the filler is an inert particulate filler. The term "inert particulate filler" means any material that when combined with the layer's polymer does not interact (e.g., chemically react) with the polymer. This can be any non-interacting, thermally stable material that maintains or substantially maintains its physical shape at temperatures > 200⁰C for example. In another embodiment, the filler interacts with the layer's polymer, e.g., via Van der Waals, hydrogen, or covalent bonds. [0080] Otionally, the fillers has a melting point or glass transistion > the melting peak or glass transitition of the layer's polymer. Optionally, the filler is substantially non- hygroscopic and is not readily dissovled or dispered in water at temperatures < 100⁰C. The term "non-hygroscopic" means that the filler does not abord a significant amount of moisture when exposed to air at temperatures < 100⁰C. Fillers may be any inorganic or organic material. Preferably the filler should be a rigid material having a non-smooth surface.

[0081] The filler can have a particulate morpololgy, e.g., the form of particles such as a small bead or grain, or the form of a flat or planar object or a rod-like or fiber-like object, etc. Optionally, the particles are nano-sized particles or micro-sized particles. In an embodiment, the filler comprises nano-sized particles having an average size in the particle's largest dimension (e.g., averge diameter for spherical particles) that is < the thickenss of the layer, such as < 75% or < 50% or < 25% or < 10% of the thickness of the layer. Optionally, the particles have an average size < 1.0 μm, in other embodiments < 8.0 x 10² nm, and in other embodiments < 5.0 xlO² nm. In these or other embodiments, the nano-sized particles may have a minimum diameter > 10.0 nm, in other embodiments > 50.0 nm, and in other embodiments 1.0 x 10² nm. In a particular embodiment, the filler is a substantially spherical particle having a diameter in the range of 50.0 nm to 9.0 x 10² nm.

[0082] Optionally, > 90.0 wt.% of the filler particles in the layer have an particle sizes

(measured in thier largest dimension) in the range of from 50 nm to 900 nm, e.g., in the range of 100 nm to 800 nm, or 150 nm to 700 nm. Particle size can be measured by electron microscopy, for example.

[0083] In one or more embodiments, the filler may be present within the layer or layers of the membrane in the form of particulate agglomerates (including aggregates) of smaller particles called '"primary" or "ultimate" particles. Such agglomerates can be used, e.g., when the sizes of filler agglomerates are readily reduced during processing of the ingredients producing the layer. In such cases, agglomerates having much larger gross particle sizes than those ultimately present in the microporous material may be employed, e.g., > 10 μm, > 150 μm, or even > 300 μm.

[0084] In one or more embodiments, the filler can be an inorganic material, such as one or more of metal oxides and hydroxides, metal nitrides, metal carbonates, minerals, synthetic and natural zeolites, cements, silicates, glass particles, salts, and the like. For example, the filler can be, e.g., oxides, hydroxides, or nitrides of iron, silicon, aluminum, titanium, barium magnesium, zinc, copper, tin, antimony, or zirconium, and mixtures of such nitrides and/or oxides. Specific examples of useful oxides include one or more of silica, alumina, zirconia, and magnesia, such as TiO₂, MgO, SiO₂, Al₂O 3, SiS₂, SiPO₄, etc. Suitable nitrides include aluminum nitride and/or silicon nitride. Suitable metal carbonates include calcium carbonate and magnesium carbonate, e.g., CaCO₃. When the filler is obtained from a mineral, the mineral can be, e.g., one or more of mica, montmorillonite, kaolinite, attapulgite, asbestos, talc, diatomaceous earth, vermiculite, boehmite, apatite, mullite, spinel, and olivine. Suitable cements include portland cement. Suitable silicates include one or more of fumed silica, precipitated silica, precipitated metal silicates (e.g., calcium silicate and aluminum polysilicate), silica gel, alumina silica gels, etc. Suitable fillers also include one or more of molybdenum disulfide, zinc sulfide, barium sulfate, calcium fluoride, etc. [0085] In other embodiments, the filler may include a carbonaceous material such as carbon black, coal dust, and graphite.

[0086] In one or more embodiments, the filler includes organic materials such as polymers that form a heterogeneous blend with the polymer of the layer. In particular embodiments, the filler includes crosslinked polymer, which is insoluble in the polymeric phase of the layer. In these or other embodiments, filler includes heat-resistant polymers such as those described in PCT Publ. WO 2008/016174. Suitable polymeric fillers include one or more of polytetrafluoro ethylene, polyimide, polyesters (e.g., polyethylene terephtalate), poly(hexamethylene adipamide), poly(styrene divinyl benzene), and elastomeric particles such as styrene-butadiene rubber, nitrile-butadiene rubber, and/or polyisoprene that have been crosslinked or otherwise cured. FILLER AMOUNT

[0087] In an embodiment, at least a portion of the membranes layers include an appreciable amount of filler ("filled layers"), e.g., the filled layers include > 1.0 wt.% of filler based on the weight of the layer, in other embodiments > 5.0 wt.%, in other embodiments at > 10.0 wt.%, and in other embodiments at least > 25 wt.% of filler. In these or other embodiments, the filler layers may include < 50.0 wt.% filler based on the weight of the layer, or < 40.0 wt.% of filler, or < 30.0 wt.% of filler.

[0088] In an embodiment, at least a portion of the membrane's layers are non-filled layers, where the term "non-filled layers" means that the layer does not contain a significant amount of filler, e.g., are substantially devoid of filler. A layer that is substantially devoid of filler contains an amount of filler that is less than the filler amount needed to cause a > 1.0⁰C increase in the layer's meltdown temperature. In one or more embodiments, the non-filled layers include < 1.0 wt.% of filler based on the weight of the layer, in other embodiments < 0.5 wt.%, in other embodiments < 0.1 wt.% of filler. [0089] In an embodiment, at least a portion of the membrane's interfacial regions (e.g., one or more of the transitional regions) are substantially devoid of filler, e.g., the interfacial region contains < 1.0 wt.% of filler based on the weight of the interfacial region, in other embodiments < 0.5 wt.%, in other embodiments < 0.1 wt.% of filler. METHODS FOR PRODUCING THE MICROLAYER MEMBRANE [0090] In an embodiment, the membrane is produced from a layered polymeric article, e.g., a layered extrudate. The methods for producing the layered extrudate will be described in terms of a first and second embodiment. While the invention is described in terms of these embodiments, it is not limited thereto, and the description of these embodiments is not meant to foreclose other embodiments within the broader scope of the invention. [0091] In the first and second embodiments, the layered polymeric extrudate comprises

(a) at least one layer comprising (i) filler and (ii) a first polymer and (b) a second layer comprising (i) a second polymer that is not the same as the first polymer. The first and second polymers can be selected from among those described in the preceding embodiments. Such first and second polymers can be produced from, e.g., the polymer resins previously described, such as resins of PEl, PE2, PE3 and/or PPl. The first polymer is combined with a first diluent and a filler to form a first mixture and the second polymer is combined with a second diluent to form a second mixture. The invention is not limited to any particular mixing order between the filler, polymer, and diluents. The diluent used to produce a mixture is selected from among those diluents capable of dispersing, dissolving, or forming a slurry with the polymer used to produce the mixture. For examples, the first and second diluents can be solvents for the first and second polymers respectively. In this case, the diluents may be referred to as "membrane-forming" solvents. Optionally, the first and second diluents are mixtures of diluents. [0092] In one or more embodiments, the first and second diluents are miscible with each other. Optionally, the first and second diluents are substantially the same diluent. In an embodiment both the first and second diluents are solvents for polyethylene and/or polypropylene, such as liquid paraffin. The first and second diluents can be selected from among those described in PCT Publ. WO2008/016174, which is incorporated by reference herein in its entirety. The diluents can also be selected from among those described in U.S. Publ. No. 2006/0103055, i.e., diluents that undergo a thermally-induced liquid-liquid phase separation at a temperature not lower than the polymer's crystallization temperature [0093] A first layered article having at least two layers is formed from the first and second mixtures, e.g., by extrusion, coextrusion, or lamination, wherein the layered article comprises at least one layer containing the first mixture and a second layer containing the second mixture.

[0094] In an embodiment, the layered article is produced by coextruding first and second mixtures, the first mixture comprising a filler, a first polymer, and a first diluent and the second mixture comprising a second polymer and second diluent, wherein (i) the first polymer is incompatible with the second polymer, (ii) the first polymer is compatible with the second diluent, (iii) the second polymer is compatible with the first diluent, and (iv) the first and second diluents are compatible. This embodiment is provided as an example, and the description thereof is not meant to foreclose other embodiments within the broader scope of the invention, such as embodiments where the first and second diluents are incompatible, embodiments where the second mixture contains filler but the first mixture does not, embodiments where both the first and second mixture contain filler, and embodiments where the layered article is produced by methods such as casting and/or lamination. First Embodiment [0095] In the first embodiment, the layered extrudate is produced by: (1) combining a first polymer, filler, and a first diluent to form a first mixture, and combining a second polymer, optional filler, and a second diluent to form a second mixture;

(2) coextruding the first and second mixtures through a die to form a first layered extrudate having a first thickness;

(3) manipulating the first layered extrudate to form a second layered extrudate having a second thickness greater than the first thickness and an increased number of layers compared to the first layered extrudate; and

(4) reducing the second thickness, e.g., to about the first thickness or less.

[0096] In addition to these steps, one or more optional cooling steps (2a) can be conducted at one or more points following step (2), an optional step (4a) for stretching the extrudate can be conducted after step (4). The order of the optional steps is not critical.

[0097] Increasing the thickness of the first extrudate and the number of layers thereof to produce the second extrudate can be called "layer multiplication". It is believed that subjecting the layered extrudate to a layer multiplication process results in the polymer regions of the filler-containing layers having (a) a more uniform dispersal of the filler and/or (b) a greater filler concentration. It is believed that that this effect is carried through the process to provide a microporous membrane having filled layers, where the filled layers have a more uniform dispersal of the filler and/or a greater filler concentration compared to membranes that are not produced in a layer multiplication process or an equivalent process. 1. Preparation of the first and second mixtures

(A) Preparation of first mixture

[0098] In an embodiment, the first mixture comprises filler, a first diluent, and a first polymer, the first polymer comprising PEl and PE3; and optionally PE2. These polymers may be combined, for example, by dry mixing or melt blending with a first diluent and filler to produce the first mixture. The first mixture can contain other additives such as, for example, one or more antioxidants. In an embodiment, the amount of any other additives does not exceed about 1.0 wt.% based on the weight of the first mixture. The choice of first diluent, mixing conditions, extrusion conditions, etc. can be the same as those disclosed in PCT Publ. WO 2008/016174, for example. [0099] Optionally, the amount of first polymer in the first mixture is in the range of from 25 wt.% to about 99 wt.% , e.g., about 5 wt.% to about 40 wt.%, or 15 wt.% to about 35 wt.%, based on the combined weight of the first polymer and diluent in the first mixture. Optionally, the amount of filler in the first mixture is > 1.0 wt.% of filler based on the weight of the first polymer and filler in the first mixture, in other embodiments > 5.0 wt.%, in other embodiments at > 10.0 wt.%, and in other embodiments at least > 25 wt.% filler. Optionally, the amount of filler in the first mixture is < 50.0 wt.% filler based on the weight of the filler and first polymer in the first mixture, in other embodiments < 40.0 wt.%, and in other embodiments < 30.0 wt.%.

(B) Preparation of second mixtures [00100] In an embodiment, the second polymer comprises PPl and PEl, and optionally PE2. The second mixture can be prepared by the same method used to prepare the first mixture. For example, the second mixture can be prepared by melt-blending the polymer resins with filler and a second diluent. The second diluent can be selected from among the same diluents as the first diluent. [00101] The amount of second polymer in the second mixture can be in the range of from 25 wt.% to about 99 wt.%, e.g., about 5 wt.% to about 40 wt.%, or 15 wt.% to about 35 wt.%, based on the combined weight of the second polymer and diluent. The first polymer can be combined with the first diluent and the second polymer can be combined with the second diluent at any convenient point in the process, e.g., before or during extrusion. 2. Extrusion

[00102] In an embodiment, the first mixture is coextruded with the second mixture to make a first layered extrudate having a first thickness and comprising a first extrudate layer (formed from the first mixture) and a second extrudate layer (formed from the second mixture). Optionally, the extrudate further comprises a planar surface of the first extrudate layer separated from a planar surface of the second extrudate layer by an interfacial region comprising the first polymer, the second polymer, the first diluent, and the second diluent. The choice of die and extrusion conditions can be the same as those disclosed in PCT Publ. WO 2008/016174, for example. The first and second mixtures are generally exposed to an elevated temperature during extrusion (the "extrusion temperature"). For example, the extrusion temperature is > the melting point ("Tm") of the polymer in the extrudate (first polymer or second polymer) having the higher melting point. In an embodiment, the extrusion temperature is in the range of Tm + 10⁰C to Tm + 120⁰C, e.g., in the range of about 170⁰C to about 230⁰C. [00103] In continuous and semi-continuous processing, the direction of extrusion (and subsequent processing of the extrudates and membrane) is called the machine direction, or "MD". The direction perpendicular to both the machine direction and the thickness of the extrudate (and membrane) is called the transverse direction, or "TD". The planar surfaces of the extrudate (e.g., the top and bottom surfaces) are defined by planes containing MD and TD.

[00104] While the extrusion can be used to make extrudates having two layers, the extrusion step is not limited thereto. For example, a plurality of dies and/or die assemblies can be used to produce a first layered extrudate having four or more layers using the extrusion methods of the preceding embodiments. In such a first layered extrudate, each outer or interior layer can be produced using either the first mixture and/or the second mixture.

[00105] One embodiment for making the first layered extrudate is illustrated schematically in Fig. 4. First and second mixtures (100 and 102) are conducted to a multilayer feedblock 104. Typically, melting and initial feeding is accomplished using an extruder for each mixture. For example, first mixture 100 can be conducted to an extruder 101 and second mixture 102 can be independently conducted to a second extruder 103. The multilayer extrudate 105 is conducted away from feedblock 104. Multilayer feedb locks are conventional, and are described, for example, in U.S. Patents No. 6,827,886; 3,773,882; and 3,884,606, which are incorporated herein by reference in their entirety. 3. Forming the second layered extrudate

[00106] A second layered extrudate having a second thickness greater than the thickness of the first layered extrudate (the first thickness) and a greater number of layers than the first layered extrudate can be produced by any convenient method. For example, the first extrudate can be divided into two or more sections (e.g., along MD), with the sections then stacked in planar (e.g., face-to face) contact. In this context, face-to-face contact means a planar surface of the first section is placed in contact with a planar surface of the second section, e.g., as when the first section's bottom (planar) surface is placed in contact with the second section's top (planar) surface. Fig. 5(A) illustrates this in cross section for an embodiment where polymer-solvent compatibility among the layers results in the growth of an interfacial region Il between the first and second sections after the sections are placed in planar contact. In another embodiment, the first extrudate is folded (e.g., along MD) one or more times to produce adjacent folds in planar contact. Conventional layer multiplication equipment is suitable for the layer multiplication step of the invention, such as that described in U.S. Patents No. 5,202,074 and 5,628,950, which are incorporated by reference herein in their entirety. Unlike the conventional layer multiplication process, the layer multiplication step of the invention involves producing extrudates containing polymer and a significant amount of first and/or second diluent, e.g., > 1.0 wt.% or > 5.0 wt.%, based on the combined weight of the polymers and the diluents. When each diluent is compatible with (e.g., a good solvent for) both the first and second polymers, combining the first section of the first extrudate with the second section of the first extrudate can result in an interfacial region located between the stacked first and second sections.

[00107] In an embodiment, the first extrudate is exposed to an elevated temperature during layer multiplication (the "layer multiplication temperature"). For example, the layer multiplication temperature is > Tm of the polymer in the extrudate having the highest melting point. In an embodiment, the layer multiplication temperature is in the range of Tm + 10⁰C to Tm + 120⁰C. In an embodiment, the extrudate is exposed to a temperature that is the same as (+/- 5°C) as the extrusion temperature. [00108] Referring again to Fig. 4, a conventional layer multiplier 106 can be used to separate first and second sections of the first layered extrudate along the machine direction on a line perpendicular to the planar surface of the extrudate. The layer multiplier redirects and "stacks" one section aside or atop the second section to multiply the number of layers extruded and produce the second layered extrudate. Optionally, an asymmetric multiplier can be used to introduce layer thickness deviations throughout the stack of layers in the second layered extrudate, and provide a layer thickness gradient. Optionally, one or more skin layers 111 can be applied to the outer layers of the second layered extrudate by conducting a third mixture of polymer and diluent 108 (for skin layers) to a skin layer feedblock 110. Optionally, the skin layers are produced from the same polymers and diluents used to produce the first and second mixtures, e.g., PEl, PE2, PE3, and/or PPl.

[00109] Additional layer multiplication steps (not shown) can be conducted, if desired, to increase the number of layers in the second layered extrudate. The additional layer multiplication steps can be conducted at any point in the process after the first layer multiplication step (e.g., before or after the molding of step 4). [00110] When the first and second polymers are each compatible with the first and second diluents, interdiffusion can occur during layer multiplication under appropriate thermodynamic conditions, resulting in a new interfacial region during each successive layer multiplication. The thickness and the relative amounts of first and second polymers (and the gradients thereof in the thickness direction) in the interfacial regions largely depends on the layer contact times, the polymer species selected for the first and second polymer, the diluent, and the extrudate temperature during layer multiplication and molding, etc. [00111] For a first layered extrudate having two layers and an interfacial region situated therebetween, layer multiplication can result in a total of 2^⁺²-*- 1 distinct regions (layers plus interfacial regions) in the second layered extrudate, where "n" is an integer > 1 representing the number of layer multiplications. This is the case even when the first and second polymers would be immiscible (Flory parameter χ > 0; e.g., polyethylene and polypropylene) or poorly compatible in the absence of the diluent. For example, the boundary between layers of polyethylene and isotactic polypropylene has a thickness of approximately 4 nm in blends and co-extruded films of these polymers. Conventional layer multiplication processes using immiscible polymers and without compatible diluent produce 2ⁿ⁺¹ distinct regions. Films produced by such conventional processes have no interfacial regions (i.e., no layer-layer boundary has a thickness > 25.0 nm), and are not liquid-permeable.

[00112] In an embodiment, extrusion (or, e.g., casting) of the first and second mixtures produces a first extrudate having two layers and one interfacial region as shown in cross section in Fig. 5(A), where Layer 1 (Ll) is produced from the first mixture and L2 is produced from the second mixture. A first layer multiplication results in a four-layer extrudate as shown in Fig. 5(B), where Ll and L3 are produced from the first mixture and L2 and L4 are produced from the second mixture. A second layer multiplication results in an eight-layer extrudate where Ll, L3, L5, and L7 are produced from the first mixture and L2, L4, L6, and L8 are produced from the second mixture.

[00113] The interfacial region Il between Ll and L2 produced during extrusion increases in thickness as layer contact time increases as shown in Fig. 5 (A) through (C). During the first layer multiplication, Il is divided into a pair of interfacial regions Il and 13 having approximately equal thickness and located equidistant from the symmetry plane of the second extrudate. The symmetry plane bisects a new interfacial region 12 (a transitional interfacial region) created during the second layer multiplication by the contact of L2 and L3. Like Il and 13, 12 will increase in thickness as the contact time between L2 and L3 increases. A second layer multiplication results in an eight layer extrudate as shown in Fig. 5(C). During the second layer multiplication, layers L5 through L8 are separated (e.g., by cutting along MD) from layers Ll through L4, and stacked in face-to face contact with layers Ll through L4 as shown. Thus, layers Ll, L3, L5, and L7 are produced from the first mixture and layers L2, L4, L6, and L8 are produced from the second mixture. Interfacial region 17 is obtained from original interfacial region II. 16 is obtained from 12, and 15 is obtained from 13. A new interfacial region, 14 (a transitional interfacial region) is created during the second layer multiplication. Additional layer multiplications can be conducted, if desired, either alone of in combination with the molding of step (4).

[00114] In this embodiment, the number of layers in the extrudate following n layer multiplications is equal to 2ⁿ⁺¹. The number of interfacial regions in the extrudate is equal to 2ⁿ⁺¹-l . The total number of distinct regions in the extrudate (layers plus interfacial regions) is equal to 2ⁿ⁺²-l, even when the first and second polymers are immiscible polymers, e.g., not compatible with each other.

[00115] The thickness of an interfacial region of the extrudate depends on the inter- layer contact time "t". When the multilayer extrudate comprises layers of first and second polymer Ll and L2, a sharp interface is formed between Ll and L2 when they are brought together at time t = 0. At t > 0, Ll containing the first mixture and L2 containing the second mixture inter-diffuse into each other, and the sharp interface thus becomes an interfacial region having a thickness T. The thickness T is a function of contact time and diffusion coefficient, and can be estimated using a simplified one-dimensional diffusion model for interfacial regions formed between layers containing the first mixture and layers containing the second mixture (e.g., between Ll and L2), assuming the layer thickness is much thicker than the interfacial region. A parameter φ is defined as the volume concentration of the first mixture in the interfacial region, with φ being in the range of 0 (L2) to 1 in (Ll). In other words, φ = 1 indicates the presence of a homogeneous first mixture and φ = 0 indicates a homogeneous second mixture. The thickness of the interfacial regions "T" is defined by the equation

T = x φ=0 9 — X φ=0 l

[00116] At a constant diffusion coefficient D for the first and second mixture, the diffusion equation can be used to determine the value of φ as a function of thickness ("x") in the interfacial region, given the initial conditions ("LC." that φ is zero at t = 0 in L2 and φ = 1 at t = 0 in Ll . The spatial boundary conditions are φ(-∞,t)=O; and φ(+∞,t)=l . \ d φ ( x , t ) _{= D} d ² φ ( x , t )

{ d t d x ²

I .C . φ (x, t = 0) = 1, x > 0, φ (x, t = 0) = 0, x < 0

The analytical solution for φ is:

[00117] Since Ll and L2 (and L7 and L8 in the case of an eight-layer extrudate) have a greater contact time, Il (and also 13, 15, and 17) is generally thicker than 12 and 16, which in turn are thicker than 14. The interfacial thicknesses continue to increase in thickness according to the equation for φ so long as there is compatible solvent in the extrudate. The diffusion constant D can be determined by conventional methods. The diffusion of the first polymer into the second region is believed to be driven by a concentration gradient, since the first polymer is not the same polymer or mixture of polymers as the second polymer. For example, when a compatible solvent such as liquid paraffin is present, the value of D at the layer multiplication temperature for mixtures of common polyolefms is generally in the range of 10^~π m²/sec to 10^~15 m²/sec. For a D of 1.3 x 10^~13 m²/sec for both polyethylene and polypropylene, for example when Ll contains polyethylene and L2 contains polypropylene and the diluent is liquid paraffin, a contact time of 10 seconds results in an interfacial region having a thickness T = 4.5 μm. The thickness of an interfacial region of the extrudate is optionally > 0.25 μm, e.g., in the range of 0.3 μm to 100 μm or 0.5 μm to 10.0 μm. In one embodiment, the extrudate comprises four layers and three interfacial regions (see, e.g., Fig. 5(B). The second interfacial region of the extrudate (having thickness T2) can be located between the extrudate's first and third interfacial regions (having thicknesses "Tl" and "T3" respectively). The first and third interfacial regions can have approximately equal thickness (Tl approximately equal to T3). In one embodiment, T2 is < Tl and T2 is < T3. In another embodiment, [(T1-T2)/T1] > about 0.05 and [(T3-T2)/T3] > about 0.05, for example [(Tl- T2)/T1] can be in the range of about 0.05 to about 0.95 and [(T3-T2)/T3] can be in the range of about 0.05 to about 0.95, such as [(T1-T2)/T1] in the range of about 0.1 to about 0.75 and [(T3-T2)/T3] in the range of about 0.1 to about 0.75.

[00118] When there is no compatibilizing diluent, the immiscibility of polyethylene and polypropylene leads to the formation of sharp inter-layer boundaries having no little or no inter-diffusion (less than 2*Rg). In this case, the boundary between the layers, should they exist at all, would have constant, or limiting, thicknesses in the range of IOA to 2OθA. 4. Molding the second layered extrudate

[00119] In an embodiment, the second layered extrudate is molded to reduce its thickness. Optionally, the second layered extrudate's layered structure, i.e., layers substantially parallel (e.g., within about 1°) to each other and the planar face of the extrudate, is preserved during molding. The amount of thickness reduction is not critical, and can be in the range, e.g., of from 125% to about 75%, e.g., 105% to 95% of the thickness of the first layered extrudate. In an embodiment, the molding reduces the thickness of the second layered extrudate until it is approximately equal to thickness of the first layered extrudate. Reducing the thickness of the second layered extrudate is generally conducted without a loss in weight per unit length of greater than about 10% based on the weight of the second layered extrudate. Accordingly, the molding generally results in a proportionate increase in the second layered extrudate's width (measured in TD). As an example, the molding can be accomplished using a die or dies 112. The molding can be conducted while exposing the extrudate to a temperature (the "molding temperature") > Tm of the polymer in the extrudate (first or second polymer) having the highest melting peak. Optionally, the molding temperature is > Tm of the polymer in the extrudate having the lowest (coolest) melting peak. In an embodiment, the molding temperature is in the range of Tm + 10⁰C to Tm + 140⁰C. In an embodiment, the extrudate is exposed to a temperature that is the same as (+/- 5°C) as the extrusion temperature. In another embodiment, the second layered extrudate (or third, fourth, etc. layered extrudate) is subjected to additional layer multiplications before molding. [00120] In an embodiment where a skin layer is applied during (or following) layer multiplication, the skin layers optionally can be applied onto the upper and/or lower surfaces of the film as it is conducted through the skin layer feedblock 110 and die(s) 112. When no skin layer is applied, the outer layers of the extrudate become the skin layers. An extrudate leaving the die(s) is typically in molten form.

[00121] Conducting the second layered extrudate through a die is believed to apply sufficient compressive shear to produce a polymeric fibrous morphology in the layers of the second layered extrudate, i.e., a morphology different than the homogeneous morphology of the first extrudate. The fibrous structure is desirable, and is produced in conventional "wet" processes for producing microporous films by stretching the extrudate, e.g., in a tenter machine. Since the molding of the first extrudate creates the desirable fibrous structure, the molding obviates at least a portion (if not all) of the stretching that would otherwise be needed in the conventional wet process. Second Embodiment

[00122] The second embodiment for producing the liquid-permeable microlayer membrane also begins with extruding mixtures comprising the first and second polymer to produce a multilayer extrudate, as in the description of the first embodiment. Fig. 6 illustrates a coextrusion apparatus 10 for forming the multilayer extrudate according to the second embodiment. The apparatus comprises a pair of opposed screw extruders 12 and 14 connected through respective metering pumps 16 and 18 to a coextrusion block 20. A plurality of multiplying elements 22α-g extend in series from the coextrusion block, and are optionally oriented approximately perpendicular to the screw extruders 12 and 14. Each of the multiplying elements comprise a die element 24 disposed in the polymer-diluent mixture passageway of the coextrusion device, as shown in Fig. 7. The last multiplying element 22g is attached to a discharge nozzle 25 through which a layered extrudate extrudes. [00123] A schematic diagram of the layer-multiplication process carried out by the apparatus 10 is illustrated in Fig. 7, which also illustrates the structure of the die element 24 disposed in each of the multiplying elements 22α-g. Each die element 24 divides the polymer-diluent mixture passage into two passages 26 and 28 with adjacent blocks 31 and 32 separated by a dividing wall 33. Each of the blocks 31 and 32 includes a ramp 34 and an expansion platform 36. The ramps 34 of the respective die element blocks 31 and 32 slope from opposite sides of the melt flow passage toward the center of the melt flow passage. The expansion platforms 36 extend from the ramps 34.

[00124] In the second embodiment, the liquid-permeable microlayer membrane is produced using apparatus 10 by extruding a first mixture comprising the first polymer and first diluent and a second mixture comprising the second polymer and second diluent. The first mixture is extruded through the first single screw extruder 12 into the coextrusion block 20, and the second mixtures is extruded through the second single screw extruder 14 into the same coextrusion block 20. In the coextrusion block 20, a two-layer extrudate 38 such as that illustrated at stage A in Fig. 7 is formed with the layer 42 comprising the first mixture on top of the layer 40 comprising the second mixture. The layered extrudate is then extruded through the series of multiplying elements 22α-g to form a 256 microlayer extrudate with microlayers comprising the first mixture alternating with microlayers comprising the second mixture, with interfacial regions situated between the alternating microlayers. As the layered extrudate 38 is extruded through the first multiplying element 22a, the dividing wall 33 of the die element 24 separates the layered extrudate 38 into two sections (optionally in half) 44 and 46 each having a layer comprising the first polymer 40 and a layer comprising the second polymer 42, as shown in Fig. 7, stage B. As the layered extrudate 38 is divided, each of the halves 44 and 46 are conducted along the respective ramps 34 and out of the die element 24 along the respective expansion platforms 36. This reconfiguration (a manipulation to reduce extrudate thickness) of the layered extrudate is illustrated at stage C in Fig. 7. When the divided sections of layered extrudate 38 exit from the die element 24, the expansion platform 36 positions the divided sections 44 and 46 on top of one another to form a four-layer extrudate 50 having, in a substantially parallel stacking arrangement, a layer comprising the first mixture, a layer comprising the second mixture, a layer comprising the first mixture, and a layer comprising the second mixture with interfacial regions optionally situated between the alternating layers of first and second mixture. See, e.g., Fig. 5(B). This process is repeated as the layered extrudate proceeds through each of the multiplying elements 22b-g. When the extrudate is discharged through the discharge nozzle 25, the extrudate comprises 256 microlayers layers. [00125] The second embodiment thus differs from the first embodiment in that the layered extrudate sections are molded (extrudate thickness is decreased and surface area is increased) before the sections are stacked to form a layered extrudate having a greater number of layers. The process parameters in the second embodiment, e.g., selection and amounts of polymer and diluent, molding parameters, process temperatures, etc., can be the same as those described in the analogous part of the first embodiment. The microlayer apparatus of the second embodiment is described in more detail in an article Mueller et al, entitled Novel Structures By Microlayer Extrusion-Talc-Filled PP, PC/SAN, and HDPE- LLDPE. A similar process is described in U.S. Patents No. 3,576,707, 3,051,453, and 6,261,674, the disclosures of which are incorporated herein by reference herein in there entirety. [00126] Optional cooling and stretching steps can be used in the first and second embodiment. For example, extrudate can be cooled following molding. Cooling rate and cooling temperature are not particularly critical. For example, the layered extrudate can be cooled at a cooling rate of at least about 50°C/minute until its temperature (the cooling temperature) is approximately equal to the extrudate's gelation temperature (or lower). Process conditions for cooling can be the same as those disclosed in PCT Publ. WO 2008/016174, for example. The layered extrudate can be stretched, if desired. Stretching (also called "Orientation"), when used, can be conducted before and/or after extrudate molding. Stretching can be used even when a fibrous structure is produced in the layered extrudate during the molding. Optionally, the extrudate is exposed to an elevated temperature (the stretching temperature), e.g., at the start of stretching or in a relatively early stage of stretching (for example, before 50% of the stretching has been completed), aid the uniformity of stretching. In an embodiment, the stretching temperature is < the Tm of the polymer in the extrudate having the lowest (coolest) melting peak. Neither the choice of stretching method nor the degree of stretching magnification is particularly critical stretching can be symmetric or asymmetric, and the order of stretching can be sequential or simultaneous. Stretching conditions can be the same as those disclosed in PCT Publ. WO 2008/016174, for example. [00127] The relative thickness of the first and second layers of the extrudate made by the foregoing embodiments can be controlled, e.g., by one or more of (i) regulating the relative feed ratio of the first and second mixtures into the extruders, (ii) regulating the relative amount of polymer and diluent in the first and second mixtures, etc. In addition, one or more extruders can be added to the apparatus to increase the number of different polymers in the microlayer membrane. For example, a third extruder can be added to add a tie layer to the extrudate.

PRODUCING THE LIQUID-PERMEABLE MICROLAYER MEMBRANE FROM THE MULTILAYER EXTRUDATE

[00128] In an embodiment, at least a portion of the first and second diluents (e.g., membrane-forming solvents) are removed (or displaced) from the layered extrudate in order to form a liquid-permeable, multilayer membrane. A displacing (or "washing") solvent can be used to remove (wash away, or displace) the first and second diluents. Process conditions for removing first and second diluents can be the same as those disclosed in PCT Publ. WO 2008/016174, for example. Removing the diluent (and cooling the extrudate as described below) reduces the value of the diffusion coefficient D, resulting in little or no further increase in the thicknesses of the interfacial regions. Optional membrane drying

[00129] In an embodiment, at least a portion of any remaining volatile species is removed from the membrane (membrane "drying") following diluent removal. For example, the membrane can be dried by removing at least a portion of the washing solvent. Any method capable of removing the washing solvent can be used, including conventional methods such as heat-drying, wind-drying (moving air), etc. Process conditions for removing volatile species such as washing solvent can be the same as those disclosed in PCT Publ. WO 2008/016174, for example. Optional membrane stretching

[00130] In an embodiment, the membrane is stretched at any time after diluent removal. The stretching method selected is not critical, and conventional stretching methods can be used such as by tenter methods, etc. Optionally, the membrane is heated during stretching. The stretching can be, e.g., monoaxial or biaxial. When biaxial stretching is used, the stretching can be conducted simultaneously in, e.g., the MD and TD directions, or, alternatively, the multilayer microporous polyolefϊn membrane can be stretched sequentially, for example, first in MD and then in TD. In an embodiment, simultaneous biaxial stretching is used. [00131] The membrane can be exposed to an elevated temperature during dry stretching (the "dry stretching temperature"). The dry stretching temperature is not critical. In an embodiment, the dry stretching temperature is approximately equal to Tm or lower, for example in the range of from about the crystal dispersion temperature ("Ted") to about Tm, where Tm is the melting point of the polymer in the membrane having the lowest melting peak among the polymers in the membrane. In an embodiment, the dry stretching temperature ranges from about 90⁰C to about 135°C, for example from about 95°C to about 130⁰C.

[00132] When dry-stretching is used, the stretching magnification is not critical. For example, the stretching magnification of the multilayer membrane can range from about 1.1 fold to about 1.8 fold in at least one planar (e.g., lateral) direction. Thus, in the case of monoaxial stretching, the stretching magnification can range from about 1.1 fold to about 1.8 fold in MD or TD. Monoaxial stretching can also be accomplished along a planar axis between MD and TD.

[00133] In an embodiment, biaxial stretching is used (i.e., stretching along two planar axes) with a stretching magnification of about 1.1 fold to about 1.8 fold along both stretching axes, e.g., along both the longitudinal and transverse directions. The stretching magnification in the longitudinal direction need not be the same as the stretching magnification in the transverse direction. In other words, in biaxial stretching, the stretching magnifications can be selected independently. In an embodiment, the dry-stretching magnification is the same in both stretching directions. [00134] In an embodiment, dry stretching involves stretching the membrane to an intermediate size as described above (generally to a magnification that is from about 1.1 fold to about 1.8 fold larger than the membrane's size in the stretching direction at the start of dry- stretching) and then subjecting the membrane to a controlled size reduction in the stretching direction to achieve a final membrane size in the stretching direction that is smaller than the intermediate size but larger than the size of the membrane in the stretching direction at the start of dry stretching. Generally, during relaxation, the film is exposed to the same temperature as is the case during the dry-stretching to the intermediate size. In another embodiment, the membrane is stretched to an intermediate size that is larger than about 1.8 fold the size of the membrane at the start of dry-stretching, as long as the final size of the membrane (e.g., the width measured along TD when the stretching is along TD) in either or both planar directions (MD and/or TD) is in the range of 1.1 to 1.8 fold the size of the film at the start of the dry-stretching step. As a non-limiting example, the membrane is stretched to an initial magnification of about 1.4 to 1.7 fold in MD and/or TD to an intermediate size, and then relaxed to a final size at a magnification of about 1.2 to 1.4 fold, the magnifications being based on the size of the film in the direction of stretching at the start of the dry- stretching step. In another embodiment, the membrane is dry-stretched in TD at an initial magnification to provide a membrane having an intermediate size in TD (an intermediate width) and then relaxed to a final size in TD that is in the range of about 1% to about 30%, for example from about 5% to about 20%, of the intermediate size in TD. Optionally, the size reduction (e.g., a thermal relaxation) is accomplished by moving the tenter clips gripping the edges of the membrane toward the center line of MD.

[00135] The stretching rate is preferably 3 %/second or more in a stretching direction. In the case of monoaxial stretching, stretching rate is 3 %/second or more in a longitudinal or transverse direction. In the case of biaxial stretching, stretching rate is 3 %/second or more in both longitudinal and transverse directions. It is observed that a stretching rate of less than 3 %/second decreases the membrane's permeability, and provides the membrane with large variation in measured properties across the membrane along TD (particularly air permeability). Optionally, the stretching rate is > 5 %/second, such as in the range of 10 %/second to 50 %/second.

[00136] Further optional processing such as heat treatment, cross-linking, and hydrophilizing treatment can be conducted, if desired, under the conditions disclosed in PCT Publ. WO 2008/016174, for example. PROPERTIES OF THE LIQUID-PERMEABLE MICROLAYER MEMBRANE

[00137] In an embodiment, the membrane is liquid-permeable film comprising liquid- permeable microlayers. The membrane has a thickness > 1.0 μm, e.g., a thickness in the range of from about 3.0 μm to about 250.0 μm, for example from about 5.0 μm to about 50.0 μm. Thickness meters such as the Litematic available from Mitsutoyo Corporation are suitable for measuring membrane thickness. Non-contact thickness measurement methods are also suitable, e.g. optical thickness measurement methods. In an embodiment, the membrane further comprises an interfacial region located between at least two of the microlayers. In this case, the sum of the number of distinct compositional regions in the membrane (layers containing the first polymer, layers containing the second polymer, and interfacial regions containing both the first and second polymer) is an odd number equal to 2ⁿ⁺²-l, where "n" is an integer > 1 which can be equal to the number of layer multiplications. A "beta factor" ("β") can be used to describe the liquid-permeable microlayer membrane, where β is equal to the thickness of the thickest interfacial region divided by the thickness of the thinnest interfacial region. Generally, for the membranes of the invention, β > 1.0, e.g., in the range of about 1.05 to 10, or 1.2 to 5, or 1.5 to 4. [00138] Optionally, the membrane can have one or more of the following properties:

A. Porosity > 20.0%

[00139] The membrane's porosity is measured conventionally by comparing the membrane's actual weight to the weight of an equivalent non-porous membrane of 100% polyethylene (equivalent in the sense of having the same length, width, and thickness).

Porosity is then determined using the formula: Porosity % = 100 x (w2-wl)/w2, "wl" is the actual weight of the liquid-permeable microlayer membrane and "w2" is the weight of an equivalent non-porous membrane (of the same polymers) having the same size and thickness. In an embodiment, the membrane's porosity is in the range of 25.0% to 85.0%.

B. Normalized air permeability < 1.0 x 10³ seconds/100 cm³/20 μm

[00140] In an embodiment, the liquid-permeable microlayer membrane has a normalized air permeability < 1.0 x 10³ seconds/100 cm³/20 μm (as measured according to JIS P8117). Since the air permeability value is normalized to the value for an equivalent membrane having a film thickness of 20 μm, the membrane's air permeability value is expressed in units of "seconds/100 cm³/20μm". Optionally, the membrane's normalized air permeability is in the range of from about 20.0 seconds/100 cm³/20 μm to about 500.0 seconds/100 cm³/20 μm, or from about 100.0 seconds/100 cm /20 μm to about 400.0 seconds/100 cm /20 μm. Normalized air permeability is measured according to JIS P8117, and the results are normalized to the permeability value of an equivalent membrane having a thickness of 20 μm using the equation A = 20 μm * (XyT₁, where X is the measured air permeability of a membrane having an actual thickness Ti and A is the normalized air permeability of an equivalent membrane having a thickness of 20μm. C. Normalized pin puncture strength > 2.0 x 10³ niN/ 20 μm

[00141] The membrane's pin puncture strength is expressed as the pin puncture strength of an equivalent membrane having a thickness of 20 μm and a porosity of 50% [gf/20μm]. Pin puncture strength is defined as the maximum load measured at ambient temperature when the liquid-permeable microlayer membrane having a thickness of Ti is pricked with a needle of 1 mm in diameter with a spherical end surface (radius R of curvature: 0.5 mm) at a speed of 2mm/second. The pin puncture strength ("S") is normalized to the pin puncture strength value of an equivalent membrane having a thickness of 20μm and a porosity of 50% using the equation S₂ = [50%*20μm *(Si)]/[Ti*(100% - P)], where Si is the measured pin puncture strength, S₂ is the normalized pin puncture strength, P is the membrane's measured porosity, and Ti is the average thickness of the membrane.

[00142] Optionally, the membrane's normalized pin puncture strength is > 3.0 x 10 mN/20 μm, e.g., > 5.0 x 10⁴ mN/20 μm, such as in the range of 3.0 x 10³3.0 x 10³ mN/20 μm to 8.0 x 10³ mN/20 μm.

D. Tensile strength > 1.2 x 10³ Kg/cm² [00143] Tensile strength is measured in MD and TD according to ASTM D-882A. In an embodiment, the membrane's MD tensile strength is in the range of 1000 Kg/cm² to 2,000 Kg/cm², and TD tensile strength is in the range of 1200 Kg/cm² to 2300 Kg/cm².

E. Shutdown temperature < 140.0 ⁰C

[00144] The shutdown temperature of the liquid-permeable microlayer membrane is measured by a thermomechanical analyzer (TMA/SS6000 available from Seiko Instruments, Inc.) as follows: A rectangular sample of 3 mm x 50 mm is cut out of the liquid-permeable microlayer membrane such that the long axis of the sample is aligned with the membrane's TD and the short axis is aligned MD. The sample is set in the thermomechanical analyzer at a chuck distance of 10 mm, i.e., the distance from the upper chuck to the lower chuck is 10 mm. The lower chuck is fixed and a load of 19.6 mN applied to the sample at the upper chuck. The chucks and sample are enclosed in a tube which can be heated. Starting at 30⁰C, the temperature inside the tube is elevated at a rate of 5°C/minute, and sample length change under the 19.6 mN load is measured at intervals of 0.5 second and recorded as temperature is increased. The temperature is increased to 200⁰C. "Shutdown temperature" is defined as the temperature of the inflection point observed at approximately the melting point of the polymer having the lowest melting point among the polymers used to produce the membrane. In an embodiment, the membrane has a shutdown temperature < 130.5⁰C, e.g., in the range of 120.0°C to 130.0⁰C, e.g., from 124.0⁰C to 129.0⁰C. F. Meltdown temperature > 180.0 ⁰C

[00145] Meltdown temperature is measured by the following procedure: A rectangular sample of 3 mm x 50 mm is cut out of the liquid-permeable microlayer membrane such that the long axis of the sample is aligned with TD and the short axis is aligned with MD. The sample is set in the thermomechanical analyzer (TMA/SS6000 available from Seiko Instruments, Inc.) at a chuck distance of 10 mm, i.e., the distance from the upper chuck to the lower chuck is 10mm. The lower chuck is fixed and a load of 19.6mN applied to the sample at the upper chuck. The chucks and sample are enclosed in a tube which can be heated. Starting at 30⁰C, the temperature inside the tube is elevated at a rate of 5°C/minute, and sample length change under the 19.6 mN load is measured at intervals of 0.5 second and recorded as temperature is increased. The temperature is increased to > 200⁰C. The meltdown temperature of the sample is defined as the temperature at which the sample breaks. In an embodiment, the meltdown temperature is > 180⁰C, e.g., > 200⁰C, or > 220⁰C, > 250⁰C; such as in the range of from 180⁰C to 300⁰C, e.g., 185°C to about 250 ⁰C. Battery [00146] The liquid-permeable microlayer membranes of the invention are useful as battery separators in e.g., lithium ion primary and secondary batteries. Such batteries are described in PCT Publ. WO 2008/016174.

[00147] The battery is useful for powering one or more electrical or electronic components. Such components include passive components such as resistors, capacitors, inductors, including, e.g., transformers, electromotive devices such as electric motors and electric generators, and electronic devices such as diodes, transistors, and integrated circuits. The components can be connected to the battery in series and/or parallel electrical circuits to form a battery system. The circuits can be connected to the battery directly or indirectly. For example, electricity flowing from the battery can be converted electrochemically (e.g., by a second battery or fuel cell) and/or electromechanically (e.g., by an electric motor operating an electric generator) before the electricity is dissipated or stored in a one or more of the components. The battery system can be used as a power source for powering relatively high power devices such as electric motors in power tools and electric or hybrid electric vehicles. [00148] The present invention will be explained in more detail referring to Examples below without intention of restricting the scope of the present invention. Examples

[00149] The present invention will be explained in more detail referring to examples below without intention of restricting the scope of the present invention. (1) Preparation of the first mixture

[00150] A first polymer comprising 18 wt.% of polyethylene having an Mw of 1.95 x 10⁶; 74 wt.% of HDPE having an Mw of 5.6 x 10⁵, a Tm = 134.9°C and 8 wt.% of a polyethylene having Mw of 3.8 x 10⁴, and a Tm = 126.1°C are dry-blended with 0.5 wt.% of tetrakis [methylene-3- (3,5-ditertiary-butyl-4-hydroxyphenyl)-propionate] methane is prepared by dry-blending, the weight percents being based on the weight of the first polymer. [00151] Twenty-five wt.% of first polymer is charged into a strong-blending double- screw extruder having an inner diameter of 58 mm and L/D of 42; 65 wt.% of liquid paraffin (50 cSt at 40⁰C) is supplied to the double-screw extruder via a side feeder; 30.0 wt.% silica, based on the weight of polymer and filler in the first mixture is supplied to the double-screw extruder via a side feeder; the weight percents being based on the weight of the first mixture. These ingredients are mixed to produce the first mixture. (2) Preparation of the second mixture

[00152] A second polymer is prepared in the same manner as above except as follows. The second polymer comprises 100 wt.% of a polypropylene having an Mw of 1.1 x 10⁶, an MWD of 5, a Tm of 164°C, and a ΔHm of 114.0 J/g, based on the weight of the second polymer. Thirty wt.% of the second polymer is charged into a strong-blending double-screw extruder having an inner diameter of 58 mm and L/D of 42 and 70 wt.% of the liquid paraffin is supplied to the double-screw extruder via a side feeder to produce a second mixture. Extrusion [00153] The first and second mixtures are combined to produce a two-layer extrudate having a total thickness of 1.0 mm that is then conducted to a sequence of 9 layer- multiplication stages. Each stage, shown schematically in Fig. 7, layer-multiply the extrudate while exposing the extrudate to a temperature of 210⁰C. [00154] Accordingly, the first mixture is extruded through the first single screw extruder 12 into the coextrusion block 20, and the second mixtures is extruded through the second single screw extruder 14 into the same coextrusion block 20. In the coextrusion block 20, a two-layer extrudate 38 such as that illustrated at stage A in Fig. 7 is formed with the layer 42 comprising the first mixture on top of the layer 40 comprising the second mixture. The layered extrudate is then extruded through the series of 9 multiplying elements 22α-g to produce a 1024-microlayer extrudate with microlayers comprising the first mixture alternating with microlayers comprising the second mixture, with interfacial regions situated between the alternating microlayers. The extrudate residence time in each layer- multiplication stage is approximately 2.5 seconds. The microlayer extrudate has a thickness of 1.0 mm and a width of 0.1 m.

[00155] The microlayer extrudate is then cooled while passing through cooling rollers controlled at 20⁰C, to form a cooled microlayer extrudate, which is simultaneously biaxially stretched at 115°C to a magnification of 5 fold in both MD and TD by a tenter stretching machine. The stretched extrudate is fixed to an aluminum frame of 20 cm x 20 cm, immersed in a bath of methylene chloride controlled at 25°C to remove liquid paraffin with vibration of 100 rpm for 3 minutes, and dried by air flow at room temperature. The membrane is then heat-set at 115°C for 10 minutes to produce the finished liquid-permeable microlayer membrane having a width of 2.5 m and a thickness of 40.0 μm. The membrane's properties are shown in Table 1.

Table 1

[00156] As can be seen in the Table, the liquid-permeable microlayer membrane has both a desirable shutdown temperature (obtained from microlayers containing the first polymer) and a desirable meltdown temperature (obtained from microlayers containing the second polymer), even though the first and second polymers are incompatible. Moreover, the membrane also has desirable air permeability, porosity, and strength values. [00157] All patents, test procedures, and other documents cited herein, including priority documents, are fully incorporated by reference to the extent such disclosure is not inconsistent and for all jurisdictions in which such incorporation is permitted. [00158] While the illustrative forms disclosed herein have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside herein, including all features which would be treated as equivalents thereof by those skilled in the art to which this disclosure pertains. [00159] When numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated. Various modifications and alterations that do not depart from the scope and spirit of this invention will become apparent to those skilled in the art. This invention is not to be duly limited to the illustrative embodiments set forth herein.

Claims

CLAIMSWhat is claimed is:

1. A micro-porous membrane comprising: i. first and third layers comprising a first polymer; ii. a second layer comprising a second polymer and > 1.0 wt.% of a filler based on the weight of the layer; iii. first and second interfacial regions each comprising the first and second polymer; the first interfacial region being located between the first and second layers and having a thickness Tl; the second interfacial region being located between the second and third layers and having a thickness T2, wherein the absolute value of [(T1-T2)/T1] > 0.05; the first and second interfacial regions each containing < 1.0 wt.% of the filler, based on the weight of the interfacial region.

2. The membrane of claim 1, wherein Tl and T2, are each in the range of 15 nm to 10 μm, and wherein the each of the first, second, and third layers has a thickness in the range of 25 nm to 50 μm.

3. The membrane of claims 1-2, wherein the filler is within the first and second polymers.

4. The membrane of claims 1-2, wherein the first and second polymers are incompatible polymers.

5. The membrane of claims 1-4, where the second layer comprises > 5.0 wt.% filler, based on the weight of the layer.

6. The membrane of claims 1-5, where the second layer comprises > 10.0 wt.% filler, based on the weight of the layer.

7. The membrane of claims 1-6, where the second layer comprises > 15.0 wt.% filler, based on the weight of the layer.

8. The membrane of claims 1-7, where the filler includes a species added to the second polymer.

9. The membrane of claims 1-8, where the filler forms a heterogeneous blend with the second polymer, a discrete phase apart from the second polymer, or a combination of a heterogeneous blend and discreet phase.

10. The membrane of claims 1-9, where the filler is an inert particulate filler that is substantially non-hygroscopic.

11. The membrane of claims 1-10, where the filler is a nano-sized particle having an average size in the particle's largest dimension that is < the thickness of the layer.

12. The membrane of claims 1-11, where the filler is a nano-sized particle having an average size in the particle's largest diameter that is 1.0 μm.

13. The membrane of claims 1-12, where the filler is an oxide, hydroxide, or nitride of iron, silicon, aluminum, titanium, barium magnesium, zinc, copper, tin, antimony, or zirconium, and mixtures of such nitrides and/or oxides.

14. A battery separator film comprising the membrane of any of claims 1-13.

15. A battery comprising the battery separator film of claim 14.

16. A multilayer microporous membrane comprising: i. a first series of layers including at least two layers having distinct polymeric compositions, where the layers form a sequence based upon the composition of each layer; ii. an interfacial region between the at least two layers having distinct polymeric compositions within the first series, where the interfacial region has a thickness Tl; iii. a second series of layers having the same sequence of layers as the first series; and iv. an interfacial region between said first series and said second series having a thickness T2, wherein the absolute value of [(T1-T2)/T1] > 0.05, and where at least one layer within each series of layers includes > 1.0 wt.% of a filler based on the total weight of the at least one layer.

17. The membrane of claim 16, where the innerfacial region between the at least two layers having distinct polymeric compositions includes < 1.0 wt.% of filler based on the total weight of the interfacial region.

18. The membrane of claims 16 or 17, where at least one layer within each series of layers includes > 5.0 wt.% of a filler based on the total weight of the at least one layer.

19. The membrane of claims 16 - 18, where at least one layer within each series of layers includes > 10.0 wt.% of a filler based on the total weight of the at least one layer.

20. A method for making a liquid-permeable membrane comprising: manipulating a first layered article comprising first and second layers to produce a second layered article having an increased number of layers, the first layer comprising a first polymer and a first diluent miscible with the first polymer and the second layer comprising a second polymer and a second diluent miscible with the second polymer; reducing the first layered article's thickness and increasing the first layered article's width before producing the second layered article, and/or reducing the second layered article's thickness and increasing the second layered article's width; and removing at least a portion of the first and second diluents from the second layered article; wherein at least one of the first or second or second layer further comprises a filler.

21. The membrane product of claim 20.

22. A battery separator film comprising the membrane of claim 21

23. A battery comprising the battery separator film of claim 22.

24. The battery of claim 23, further comprising an anode, a cathode, and an electrolyte containing lithium ions.

25. The battery of claim 23, wherein the battery is a secondary battery.