Improved porous membrane and device including the improved porous membrane

Abstract

A multilayer porous membrane having two outer layers and at least one inner layer, wherein the average pore size of the inner layer is larger than that of either of the two outer layers. The multilayer porous membrane may be used, for example, as a battery separator or as part of a battery separator. Compared to conventional multilayer porous membranes for battery separators, the multilayer porous membrane herein may exhibit at least one of improved thermal properties, improved resistance to metal contamination, improved ease of manufacture, and combinations thereof.

Description

[Technical Field]

[0001] The present application relates to improved multi-layer porous membranes that may be useful as battery separators. In particular, the multi-layer porous membranes described herein may exhibit at least one of the following: improved thermal properties, improved resistance to metal contamination, and improved ease of manufacture. [Background technology]

[0002] Commonly used electrode materials for secondary batteries may contain transition metals, including iron (Fe), manganese (Mn), nickel (Ni), cobalt (Co), aluminum (Al), and others. For example, some exemplary electrode materials may include lithium nickel cobalt manganese oxide (NMC or NCM), lithium iron phosphate (LFP), lithium nickel manganese spinel (LMNO), lithium nickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO), lithium cobalt oxide (LCO), or combinations thereof. Some of these electrode materials come into contact with an electrolyte, resulting in the presence of transition metal ions in the electrolyte. Under appropriate conditions, these metal ions can be reduced to their metallic form. This metal plating results in dendrite growth. If dendrites grow through the separator and the two electrodes come into contact, a short circuit occurs.

[0003] Another source of metal contamination may be metallic equipment used to manufacture battery components and / or batteries, e.g., brushes, rollers, etc. The metallic equipment may be a source of cobalt, copper, or iron ions in the battery. Summary of the Invention [Problem to be solved by the invention]

[0004] In view of the foregoing, methods for reducing, mitigating, or eliminating metallic contamination of batteries may be desirable.

[0005] In one aspect, the present specification describes a multi-layer porous membrane that, when used as a battery separator, can, among other things, reduce or eliminate metal contamination in batteries. The multi-layer porous membrane can be used as a separator with metal mitigation properties. The multi-layer porous membrane can be particularly useful in batteries where metal contamination is a problem. [Means for solving the problem]

[0006] The multi-layer porous membrane may comprise at least three layers: two outer layers each individually comprising, consisting of, or consisting essentially of polypropylene, and at least one inner layer comprising, consisting of, or consisting essentially of polypropylene, such that the average pore size of the inner layer is larger than the average pore size of either or both of the outer layers.

[0007] The pore size ratio of a multilayer porous membrane can be calculated by dividing the average pore size of the inner layer by the average pore size of the outer layer. In some embodiments, the pore size ratio can be greater than 1.0. In some embodiments, the pore size ratio can be 1.2 to 5.0, 1.2 to 4.5, 1.2 to 4.0, 1.2 to 3.5, 1.2 to 3.0, 1.3 to 2.5, 1.4 to 2.5, 1.5 to 2.5, 1.6 to 2.5, 1.7 to 2.5, 1.2 to 2.0, 1.2 to 1.9, 1.2 to 1.8, 1.2 to 1.7, 1.2 to 1.6, 1.2 to 1.5, 1.2 to 1.4, or 1.2 to 1.3.

[0008] With respect to pore size, in some embodiments, the average pore size of the inner layer is 5% or more, 10% or more, 20% or more, 30% or more, 40% or more, or 50% or more of the average pore size of either or both of the outer layers.

[0009] In some embodiments, the two outer layers each have an average pore size of 0.05-0.5 μm (50-500 nm), 0.1-0.4 μm (100-400 nm), 0.11-0.35 μm (110-350 nm), 0.12-0.3 μm (120-300 nm), or 0.15-0.3 μm (150-300 nm), and the average pore sizes of the two outer layers may be the same or different. The average pore size of the inner layer may also be 0.05-0.5 μm (50-500 nm).

[0010] In some embodiments, the two outer layers each have an average pore size of less than 0.25 μm, and the two outer layers may be the same or different. The average pore size of the inner layer may be greater than 0.25 μm.

[0011] In some embodiments, this inner layer may comprise, consist of, or consist essentially of a polypropylene having a melt flow rate (MFR) different (either higher or lower) than the MFR of the polypropylene in one or both outer layers.

[0012] In some embodiments, the inner layer may comprise, consist of, or consist essentially of a polypropylene homopolymer, copolymer, or terpolymer having an MFR of less than 1.0 g / 10 min as measured according to JIS K 7210. In some embodiments, the MFR may be 0.1 to 0.75 g / 10 min.

[0013] In some embodiments, the inner layer may comprise, consist of, or consist essentially of polypropylene and another component. This component may be present in an amount of 1% to 20% by weight, or 5% to 10% by weight. The other component may be one or more selected from elastomers, ethylene / alpha-olefin copolymers, low molecular weight polymers such as polypropylene, low melting point polymers such as polypropylene, and combinations thereof. In some embodiments, the elastomer may be a styrene elastomer. The styrene elastomer may be one or more selected from block copolymers of styrene and isoprene (SIS), styrene-ethylene-butylene-styrene (SEBS), styrene-ethylene-propylene-styrene (SEPS), styrene block copolymers, styrene-ethylene-ethylene-propylene-styrene (SEEPS) block copolymers, styrene-ethylene-propylene (SEP) block copolymers, triblock copolymers having styrene end blocks and a midblock that may or may not be hydrogenated, and combinations thereof.

[0014] In some embodiments, the multi-layer porous membrane may have one inner layer, and in other embodiments, there may be two or more inner layers. In embodiments with two or more inner layers, one of the inner layers may comprise, consist of, or consist essentially of polyethylene, which may provide a shutdown function, and one of the inner layers may comprise, consist of, or consist essentially of polypropylene.

[0015] The multi-layer porous membrane may have a thickness of 5 to 25 μm or 5 to 15 μm.

[0016] In some embodiments, the multi-layer porous membrane may be formed by a coextrusion process. For example, two or more layers of the structure may be coextruded with one another. In embodiments where only one inner layer is present, the inner layer may be coextruded with at least one or both outer layers.

[0017] In some embodiments, two or more layers may be laminated together to form a multi-layer porous membrane. In embodiments where only one inner layer is present, this inner layer may be laminated to at least one or both outer layers.

[0018] The multi-layer porous membrane may have a puncture strength at 16 μm of greater than 300 gf, greater than 310 gf, greater than 320 gf, greater than 330 gf, greater than 340 gf, or greater than 350 gf.

[0019] In another aspect, battery separators are also described that include the multi-layer porous membranes described herein. In some embodiments, the battery separators can include a coated multi-layer porous membrane, with a coating provided on one or both sides of the multi-layer porous membrane. The coating can be, but is not limited to, a ceramic coating, a polymer coating, a shutdown coating, an adhesive / bond coating, or a combination thereof.

[0020] In another aspect, batteries are also described that include the battery separators described herein, which in some embodiments have electrodes that include lithium nickel cobalt manganese oxide (NMC or NCM), lithium iron phosphate (LFP), lithium nickel manganese spinel (LMNO), lithium nickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO), lithium cobalt oxide (LCO), or combinations thereof.

[0021] In another aspect, a vehicle comprising the battery described herein is also described, which may be a hybrid electric vehicle (HEV), a mild hybrid electric vehicle (MHEV), or a plug-in hybrid electric vehicle (PHEV). [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is an SEM of a membrane according to some embodiments described herein. [Figure 2]FIG. 2 is a graph of pore size data according to some invention embodiments disclosed herein. [Figure 3] FIG. 3 is a graph of pore size data from several comparative examples disclosed herein. [Figure 4A] FIG. 4A is a table containing data for Examples 1, 2, and 3 of the invention described herein. [Figure 4B] FIG. 4B is a table containing data for Examples 4, 5, and 6 of the invention described herein. [Figure 4C] FIG. 4C is a table containing data for Examples 7, 8, and 9 of the invention described herein. [Figure 5] FIG. 5 is a table containing data for comparative embodiments described herein. DETAILED DESCRIPTION OF THE INVENTION

[0023] The multilayer porous membrane described herein may exhibit at least one of the following: improved thermal properties, improved resistance to metal contamination, and improved ease of manufacture. These properties result from the unique structure of the multilayer porous membrane, which includes a multilayer structure having two outer layers and at least one inner layer, with the average pore size of the inner layer or layers being larger than that of the outer layer. This microporous membrane may be particularly useful for secondary batteries containing electrode materials with transition metals capable of forming metal dendrites, which may pose a risk of short-circuiting the battery. A short circuit can result in smoke, fire, and / or explosion. Therefore, preventing short circuits enhances battery safety.

[0024] multilayer porous membrane The membrane structure is not particularly limited, but preferably comprises the following: two outer layers and at least one inner layer. In some embodiments, the structure may comprise two or more, three or more, four or more, five or more, six or more, seven or more, eight or more, nine or more, or ten or more inner layers. At least one inner layer has an average pore size larger than the average pore size of the outer layers. The average pore sizes of the outer layers may be the same or different, but both layers have an average pore size smaller than the average pore size of the at least one inner layer.

[0025] In some embodiments, the average pore size of the one or more inner layers is at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50% larger than the pore size of the two outer layers. In some embodiments, the pore size ratio of the membrane, which is the ratio of the average pore size of the one or more inner layers to the average pore size of the outer layers, is at least 1.05, at least 1.10, at least 1.20, at least 1.30, at least 1.40, at least 1.50, at least 1.60, at least 1.70, at least 1.80, at least 1.90, at least 2.00, at least 2.10, at least 2.10, at least 2.20, at least 2.30, at least 2.40, or at least 2.50. In some particularly preferred embodiments, the ratio of the average pore size of the one or more inner layers to the average pore size of the outer layer is 1.20 or greater, 1.50 or greater, or 1.70 or greater. Such membranes exhibit improved metal mitigation.

[0026] In some embodiments, the average pore size of the outer layer may be, independently, 0.05 to 1.0 μm (50 to 1,000 nm), 0.1 to 0.9 μm (100 to 900 nm), 0.1 to 0.8 μm (100 to 800 nm), 0.1 to 0.7 μm (100 to 700 nm), 0.1 to 0.6 μm (100 to 600 nm), 0.05 to 0.5 μm (50 to 500 nm), 0.1 to 0.4 μm (100 to 400 nm), 0.11 to 0.35 μm (110 to 350 nm), or 0.12 to 0.3 μm (120 to 300 nm), or 0.15 to 0.3 μm (150 to 300 nm).

[0027] In some embodiments, the average pore size of the inner layer may be 0.05 to 1.0 μm, 0.1 to 0.9 μm, 0.15 to 0.8 μm, 0.2 to 0.7 μm, 0.3 to 0.6 μm, or 0.3 to 0.5 μm, or 0.3 to 0.4 μm.

[0028] In some preferred embodiments, the average pore size of the inner layer is 0.5 μm or more, 0.4 μm or more, 0.3 μm or more, 0.2 μm or more, or 0.1 μm or more, and the average pore size of the outer layer is 0.5 μm or less, 0.4 μm or less, 0.3 μm or less, 0.2 μm or less, or 0.1 μm or less.

[0029] The composition of the layers of the multilayer porous membrane is not particularly limited, and any thermoplastic resin may be used. Furthermore, the compositions of the layers of the multilayer porous membrane may be the same or different from each other. For example, in a three-layer structure having two outer layers and one inner layer, the compositions of the outer layers may be the same or different, and the composition of the inner layer may be the same or different from the composition of either or both of the outer layers.

[0030] In some preferred embodiments, the two outer layers and at least one inner layer may comprise, consist of, or consist essentially of a polypropylene homopolymer, copolymer, or terpolymer. The polypropylene homopolymers, copolymers, or terpolymers in the outer and inner layers may be the same, e.g., have the same or substantially the same melt flow rate, or may be different, e.g., have different melt flow rates. The polypropylene used may have a melt flow rate of 0.1 to 2, 0.1 to 1.9, 0.1 to 1.8, 0.1 to 1.7, 0.1 to 1.6, 0.1 to 1.5, 0.1 to 1.4, 0.1 to 1.3, 0.1 to 1.2, 0.1 to 1.1, 0.1 to 1.0, 0.1 to 0.95, 0.1 to 0.9, 0.1 to 0.85, or 0.1 to 0.80, as measured according to JIS K7210. , 0.1 to 0.75, 0.1 to 0.70, 0.1 to 0.65, 0.1 to 0.60, 0.1 to 0.55, 0.1 to 0.50, 0.1 to 0.45, 0.1 to 0.40, 0.1 to 0.35, 0.1 to 0.30, 0.1 to 0.25, 0.1 to 0.20, or 0.1 to 0.15.

[0031] In some embodiments, the inner layer may comprise, consist of, or consist essentially of a polypropylene having a low MFR as measured according to JIS K 7210. For example, the inner layer may comprise, consist of, or consist essentially of a polypropylene polymer, copolymer, or terpolymer having an MFR as measured according to JIS K 7210 of less than 1.0, less than 0.95, less than 0.9, less than 0.85, less than 0.8, less than 0.75, less than 0.7, less than 0.65, less than 0.6, less than 0.55, less than 0.5, less than 0.45, less than 0.4, less than 0.35, less than 0.3, less than 0.25, less than 0.2, less than 0.15, less than 0.1, or less than 0.05.

[0032] The method for achieving different average pore sizes in the layers of a multilayer porous membrane is not particularly limited. In some embodiments, an additive may be added to the inner layer that allows the inner layer to form large pores when co-extruded with two outer layers. For example, an inorganic or organic pore-forming or nucleating agent may be added. A polymer or elastomer may also be added for this purpose. For example, different average pore sizes may be achieved between layers by extruding each layer of the structure separately and stretching them to form pores. The stretched layers may then be laminated together to form the final structure.

[0033] In some embodiments, to achieve large pores, the inner layer may comprise polypropylene and another component which may be added in an amount of 1% to 20% by weight, 2% to 20% by weight, 3% to 20% by weight, 4% to 20% by weight, 5% to 20% by weight, 6% to 20% by weight, 7% to 20% by weight, 8% to 20% by weight, 9% to 20% by weight, 10% to 20% by weight, 11% to 20% by weight, 12% to 20% by weight, 13% to 20% by weight, 14% to 20% by weight, 15% to 20% by weight, 19% to 20% by weight.

[0034] For example, the inner layer may include polypropylene and an elastomer, which in some embodiments may be a styrene elastomer. For example, at least one of a block copolymer of styrene and isoprene (SIS), a styrene-ethylene-butylene-styrene (SEBS), a styrene-ethylene-propylene-styrene (SEPS), a styrene block copolymer, a styrene-ethylene-ethylene-propylene-styrene (SEEPS) block copolymer, a styrene-ethylene-propylene (SEP) block copolymer, a triblock copolymer having styrene end blocks and a hydrogenated or non-hydrogenated midblock, and combinations thereof may be used. In some embodiments, at least one inner layer may contain the elastomer in an amount of 1% by weight or more, 3% by weight or more, 5% by weight or more, or 10% by weight or more but not more than about 20% by weight.

[0035] In other preferred embodiments, ethylene / α-olefin copolymers such as ethylene / propylene copolymers, ethylene / 1-butene copolymers, ethylene / 1-hexene copolymers, ethylene / 1-octene copolymers, propylene / 1-butene copolymers, ethylene / propylene / 1-butene copolymers, or combinations thereof may be added to achieve large pores in the inner layer. In some embodiments, such ethylene / α-olefin copolymers may be added to the inner layer in an amount of 1% by weight or more, 3% by weight or more, 5% by weight or more, or 10% by weight or more to about 20% by weight or less.

[0036] In another preferred embodiment, a low melting point polypropylene homopolymer, copolymer, or terpolymer may be added to the inner layer to achieve large pore sizes. A low melting point is a melting point of less than 100°C, less than 95°C, less than 90°C, less than 85°C, less than 80°C, less than 75°C, less than 70°C, less than 65°C, less than 60°C, less than 55°C, less than 50°C, less than 45°C, less than 40°C, less than 35°C, less than 30°C, less than 25°C, less than 20°C, less than 15°C, less than 10°C, or less than 5°C by weight. In some embodiments, the low melting point polypropylene may be added to the inner layer in an amount of 1% by weight or more, 3% by weight or more, 5% by weight or more, or 10% by weight or more to about 20% by weight or less.

[0037] In another preferred embodiment, a low molecular weight polypropylene homopolymer, copolymer, or terpolymer may be added to the inner layer to achieve a large pore size. The low molecular weight polypropylene may have an MFR of 20 or more, 30 or more, 40 or more, 50 or more, 60 or more, 70 or more, 80 or more, 90 or more, 100 or more, 110 or more, 120 or more, 130 or more, 140 or more, 150 or more, 160 or more, 170 or more, 180 or more, or 200 or more, as measured according to JIS K7210. In some embodiments, the low molecular weight polypropylene may be added to the inner layer in an amount of 1 wt% or more, 3 wt% or more, 5 wt% or more, or 10 wt% or more to about 20 wt% or less.

[0038] In some preferred embodiments, the multi-layer porous membrane is a dry-process multi-layer porous membrane, meaning that the membrane is formed without or with minimal use of solvents or oils. The dry process may include, consist of, or consist essentially of extrusion, annealing, and one or more stretching steps to form or shape the pores. In some embodiments, the membrane may be stretched in one direction (uniaxial) or two directions (biaxial), or more.

[0039] In some embodiments, a multilayer porous film may be formed by coextrusion of two or more layers of a structure. In some embodiments, all layers of a structure may be coextruded. For example, if a multilayer porous membrane consists of two outer layers and one inner layer, all three layers may be coextruded. Alternatively, one outer layer and one inner layer may be coextruded, and the structure may then be laminated to another outer layer that has been extruded separately. Layers may be laminated before or after stretching. Another embodiment involves coextrusion of two or more layers separately, and then laminating these coextruded layers with one or more additional sets of coextruded layers.

[0040] In some embodiments, a multi-layer porous membrane may be formed by laminating three or more monoextruded layers, for example, two outer layers and one inner layer may be extruded separately and then laminated together either before or after stretching the separately extruded films.

[0041] The thickness of the multilayer porous membrane is not particularly limited and may be 1 to 50 μm, 1 to 40 μm, 1 to 30 μm, 1 to 25 μm, 1 to 20 μm, 1 to 15 μm, 1 to 10 μm, or 1 to 5 μm.

[0042] Battery separator Battery separators herein are not so limited and may comprise, consist of, or consist essentially of at least one multi-layer porous membrane described herein. In some embodiments, the multi-layer porous membrane may be coated on one or both sides.

[0043] Regarding the coating, the coating is not particularly limited. The coating may be a ceramic coating, a polymer coating, a shutdown coating, an adhesive / bonding coating, or a combination thereof. The thickness of the coating is not particularly limited, but may be 0.1 to 10 μm, 0.2 to 9 μm, 0.3 to 8 μm, 0.4 to 7 μm, 0.5 to 6 μm, 0.6 to 5 μm, 0.7 to 4 μm, 0.8 to 3 μm, 0.9 to 2 μm, or 1 to 5 μm.

[0044] Shutdown coatings can provide this additional safety feature to all polypropylene membranes that do not shut down like typical PP / PE / PP shutdown separators. The application of a ceramic coating can further add to the separator's anti-metal contamination capabilities by helping to prevent dendrite growth that can short-circuit the battery.

[0045] Battery or device The uses of the membranes or battery separators described herein are not particularly limited. The membranes may be used, for example, as part of a battery separator for secondary batteries, capacitors, and the like. The membranes may also be useful in textiles, filters, HVAC applications, fuel cell applications, and the like.

[0046] The types of batteries in which the battery separators may be used are also not particularly limited. In some preferred embodiments, the battery separators may be useful in any battery where metal dendrite growth is a concern. Metal dendrite growth may result from the precipitation and growth of lithium or transition metals described herein. In these devices, the membranes or battery separators described herein can help mitigate metal dendrite growth.

[0047] vehicle The type of vehicle in which the batteries described herein are used is not particularly limited, for example, the vehicle may be a hybrid electric vehicle (HEV), a mild hybrid electric vehicle (MHEV), a plug-in hybrid electric vehicle (PHEV), or the like.

[0048] The products and devices of the appended claims are not limited in scope by the specific products and devices described herein; the specific products and devices described herein are intended to exemplify certain aspects of the claims, and any functionally equivalent products and devices are intended to fall within the scope of the claims. Various modifications of the products and devices in addition to those shown and described herein are intended to fall within the scope of the appended claims. Furthermore, while only certain representative products and devices are specifically described herein, other combinations of products and devices are intended to fall within the scope of the appended claims, even if not specifically recited. Thus, whether or not a combination of steps, elements, ingredients, or components may be expressly recited herein, other combinations of steps, elements, ingredients, and components are included, even if not expressly recited. As used herein, the term "comprising" and variations thereof are used synonymously with the term "including" and variations thereof, and are open, non-limiting terms. Although the terms "comprising" and "including" are used herein to describe various embodiments, the terms "consisting essentially of" and "consisting of" may be substituted for "comprising" and "including" to provide more specific embodiments of the present invention and are disclosed. Other than in the examples, or where otherwise stated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims should be understood as at least and should be construed in light of the number of significant digits and ordinary rounding approaches, rather than as an attempt to limit the application of the doctrine of equivalents to the scope of the claims.

[0049] The present invention may be embodied in other forms without departing from its spirit and essential characteristics, and therefore, reference should be made to the appended claims, rather than the foregoing specification, as indicating the scope of the invention. Components that can be used to practice the disclosed methods and systems are disclosed. These and other components are disclosed herein, and it is understood that combinations, subsets, interactions, groups, etc. of these components are specifically contemplated and described herein for all methods and systems, even though each of their various individual and collective combinations and permutations may not be explicitly disclosed. This applies to all aspects of the present application, including, but not limited to, steps in the disclosed methods. Thus, when there are various additional steps that may be performed, it is understood that these additional steps may each be performed by any specific embodiment or combination of embodiments of the disclosed methods.

[0050] The foregoing detailed descriptions of structures and methods have been presented for illustrative purposes only. Examples have been used to disclose preferred embodiments, including the best mode, and will also enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. These examples are not intended to be exhaustive or to limit the invention to the precise steps and / or forms disclosed, many modifications and variations are possible in light of the above teachings. Features described herein may be combined in any combination. Method steps described herein may be performed in any order that is physically possible. The patentable scope of the invention is defined by the appended claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims when they have structural elements that do not differ from the literal language of the claims, or when they include equivalent structural elements that are not substantially different from the literal language of the claims.

[0051] The products and devices of the appended claims are not limited in scope by the specific products and devices described herein, but rather are intended to exemplify certain aspects of the claims. Any functionally equivalent products and devices are intended to fall within the scope of the claims. Various modifications of the products and devices in addition to those shown and described herein are intended to fall within the scope of the appended claims. Furthermore, while only certain representative products and devices are specifically described herein, other combinations of products and devices are intended to fall within the scope of the appended claims, even if not specifically recited. Thus, whether or not combinations of steps, elements, ingredients, or components may be expressly recited herein, other combinations of steps, elements, ingredients, and components are included, even if not expressly recited.

[0052] As used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from "about" or "approximately" one particular value and / or to "about" or "approximately" another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values ​​are expressed as approximations, by use of the antecedent "about," it is understood that the particular value forms another embodiment. It is further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. "Optional" or "optionally" indicates that the subsequently described event or circumstance may or may not occur, and that the description includes instances when the event or circumstance occurs and instances when the event or circumstance does not occur.

[0053] Throughout the detailed description and claims herein, the term "comprise" and variations of that word, such as "comprising" and "comprises," mean "including but not limited to," and are not intended to exclude, for example, other additives, components, integer values, or steps. The terms "consisting essentially of" and "consisting of" may be used in place of "comprising" and "including" to provide more specific embodiments of the present invention, and are also disclosed. "Exemplary" or "for example" denotes "an example of" and is not intended to convey an indication of a preferred or ideal embodiment. Similarly, "such as" is used in a descriptive or exemplary sense, rather than in a limiting sense.

[0054] Unless otherwise noted, all numbers expressing geometric shapes, dimensions, and the like used in the specification and claims should be understood to be at least as and should be construed in light of the number of significant digits and ordinary rounding approaches, and not as an attempt to limit the application of the doctrine of equivalents to the claims.

[0055] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosed invention belongs. All publications and cited materials cited herein are specifically incorporated by reference.

[0056] Additionally, the invention illustratively disclosed herein may suitably be practiced in the absence of any element not specifically disclosed herein. [Example]

[0057] The inventive and comparative examples were formed by a dry stretching process that involved co-extrusion of polypropylene composition 1 (PP1) and polypropylene composition 2 (PP2) to form a membrane having the following three-layer structure: PP1 / PP2 / PP1. PP1 and PP2 for each of the examples are defined in Figures 4A, 4B, 4C and the table in Figure 5.

[0058] For example, in Example 1, PP1 is polypropylene with MFR 0.8 g / 10 min, and PP2 is a blend of polypropylene with MFR 0.5 g / 10 min and styrene elastomer, the amount of styrene elastomer being 5 wt %.

[0059] In Example 2, PP1 is polypropylene with an MFR of 0.8 g / 10 min, and PP2 is a blend of polypropylene with an MFR of 0.5 g / 10 min and a styrene elastomer, the styrene elastomer being the same as that used in Example 1 at 5 wt %.

[0060] In Example 3, PP1 is polypropylene with an MFR of 0.8 g / 10 min, and PP2 is a blend of polypropylene with an MFR of 0.5 g / 10 min and 8 wt % styrene elastomer, the styrene elastomer being the same as that used in Example 1.

[0061] In Example 4, PP1 is polypropylene with an MFR of 0.5 g / 10 min, and PP2 is a blend of polypropylene with an MFR of 0.5 g / 10 min and 8 wt % styrene elastomer, the styrene elastomer being the same as that used in Example 1.

[0062] For Example 5, PP1 is polypropylene with an MFR of 0.4 g / 10 min, and PP2 is a blend of polypropylene with an MFR of 0.5 g / 10 min and 8 wt. % styrene elastomer, the styrene elastomer being the same as that used in Example 1.

[0063] For Example 6, PP1 is polypropylene with an MFR of 0.4 g / 10 min, and PP2 is a blend of polypropylene with an MFR of 0.5 g / 10 min and 8 wt. % styrene elastomer, the styrene elastomer being the same as that used in Example 1.

[0064] For Example 7, PP1 is polypropylene with a MFR of 0.8 g / 10 min, and PP2 is a blend of polypropylene with a MFR of 0.5 g / 10 min and 5 wt % of a low melting point PP with a melting point below 100°C.

[0065] For Example 8, PP1 is polypropylene with a MFR of 0.8 g / 10 min, and PP2 is a blend of polypropylene with a MFR of 0.5 g / 10 min and 10 wt % low molecular weight PP with a MFR of 100 g / 10 min.

[0066] For Example 9, PP1 comprises polypropylene with a MFR of 0.5 g / 10 min and PP2 comprises polypropylene with a MFR of 0.8 g / 10 min. PP2 is not a blend.

[0067] For Comparative Example 1, PP1 contains polypropylene with an MFR of 0.8 g / 10 min, and PP2 contains polypropylene with an MFR of 0.5 g / 10 min. PP2 is not a blend.

[0068] For Comparative Example 2, PP1 contains polypropylene with an MFR of 0.8 g / 10 min, and PP2 contains polypropylene with an MFR of 0.5 g / 10 min. PP2 is not a blend.

[0069] The membranes of Examples 1 to 9 and Comparative Examples 1 and 2 were analyzed, and the results are shown in Figures 4A, 4B, 4C, and the table in Figure 5. The pore size ratio was obtained by calculating the average pore size of the inner layer and the average pore size of the outer layer and dividing the average pore size of the inner layer by the average pore size of the outer layer. The average pore size was measured as follows.

[0070] Area average major pore diameter The area-average primary pore diameter was measured by image analysis of cross-sectional scanning electron microscope (SEM) images of the membrane. Cross-sectional SEM was measured according to the following procedure. 1) Samples for cross-sectional SEM: Film samples stained with ruthenium (Ru) were processed by freeze-fracturing with the fracture direction parallel to the MD. 2) SEM observation conditions: The sample was placed on a stub with conductive carbon paste, dried, and then plasma-coated with osmium using an osmium coater (Vacuum Device Corporation) under the following conditions: discharge voltage gain 4.5, discharge time 0.5 seconds. 3) SEM observation was performed using an S-4800 (Hitachi High-Technologies Corporation) under the following conditions: accelerating voltage: 1 kV, working distance: 5 mm, magnification: 5,000, detection signal: LA10. Three locations were randomly selected for observation.

[0071] To distinguish the pore area from the resinous region, the acquired SEM images were converted into binary images using the Otsu method in ImageJ software. The area-average primary pore diameter was calculated using the following equation:

number

[0072]

number

[0073] Pores that are partially included in the edge of the image or 0.001 μm of the image 2 Pores smaller than this were excluded from the calculation.

[0074] The membrane of Example 1 had the structure shown in Figure 1. The pore distribution in the layer of the sample of Example 1 was measured and is shown in Figure 2. The pore distribution in the layer of the sample of Comparative Example 2 was also measured and is shown in Figure 3. Comparative Example 2 and Example 1 are identical except that the inner layer of Example 1 contains a blend with a styrene elastomer. The membrane's ability to mitigate metal growth was also evaluated, with Examples 6 and 8 demonstrating the best results, as they exhibited the most metal growth mitigation. While not wishing to be bound by any particular theory, it is believed that a higher pore size ratio corresponds to greater metal growth mitigation. Metal growth mitigation can be replicated by using small coin-cell batteries to examine how the separator in the battery mitigates the growth of specific metals from the cathode to the anode during charging and discharging. For example, ratios greater than 1.2, greater than 1.3, greater than 1.4, greater than 1.5, greater than 1.6, greater than 1.7, greater than 1.8, greater than 1.9, or greater than 2.0 may be preferred. In the examples, the highest pore size ratio was achieved with the blend shown in Example 6.

[0075] Example 1 shows large pores in the middle layer and small pores in the outer layer. While the addition of styrene elastomer to the middle layer is believed to be the cause of this difference, there may be other ways to achieve the same result, i.e., large pores in the middle layer. For example, the addition of a nucleating agent may achieve the same effect. Furthermore, to form a structure with large pores in the middle layer, an example may be used in which the outer and middle layers are separately extruded, laminated together, and stretched. Furthermore, to form a structure with large pores in the middle layer, an example may be used in which the outer and middle layers are separately extruded, stretched, and laminated together. In such a structure, it may not be necessary to add anything to the middle layer to form large pores. Large pores may be formed by further stretching the middle layer.

Claims

1. A dry-process multi-layer porous membrane, comprising: two outer layers, each of said outer layers comprising, consisting of, or consisting essentially of polypropylene; one or more inner layers comprising, consisting of, or consisting essentially of polypropylene; Including, The dry-process multi-layer porous membrane, wherein the average pore size of the inner layer is larger than the average pore size of the outer layer.

2. The pore size ratio of the multilayer porous membrane is 1.2 or more, and the pore size ratio is determined by the following formula: (average pore size of the one or more inner layers) / (average pore size of the outer layer) The multi-layer porous membrane of claim 1.

3. 3. The multilayer porous membrane of claim 2, wherein the pore size ratio is 1.3 or greater, 1.4 or greater, 1.5 or greater, or 1.6 or greater.

4. The multilayer porous membrane according to claim 2, wherein the pore size ratio is 1.7 to 2.

5.

5. A method for producing a multilayer porous membrane as described in claim 1, comprising co-extruding at least one outer layer with the inner layer, or co-extruding both outer layers with one inner layer.

6. A method for producing a multilayer porous membrane as described in claim 1, comprising laminating at least one outer layer to an inner layer, or laminating both outer layers to the inner layer.

7. 5. The multi-layer porous membrane of any one of claims 1 to 4, wherein at least one of the inner layers comprises, consists of, or consists essentially of a blend of polypropylene and another component, the another component being one or more selected from elastomers, ethylene / alpha-olefin copolymers, low molecular weight polymers such as polypropylene, low melting point polymers such as polypropylene, and combinations thereof.

8. The multi-layer porous membrane of claim 7, wherein the other component is added in an amount of 1% to 20% by weight, or 5% to 20% by weight.

9. 8. The multi-layer porous membrane of claim 7, wherein the other component is an elastomer, and the elastomer is a styrene elastomer, which may be one or more selected from a block copolymer of styrene and isoprene (SIS), a styrene-ethylene-butylene-styrene (SEBS), a styrene-ethylene-propylene-styrene (SEPS) styrene block copolymer, a styrene-ethylene-ethylene-propylene-styrene (SEEPS) block copolymer, a styrene-ethylene-propylene (SEP) block copolymer, a triblock copolymer having styrene end blocks and a midblock that may or may not be hydrogenated, and combinations thereof.

10. 5. The multilayer porous membrane according to any one of claims 1 to 4, wherein at least one of the inner layers comprises, consists of, or consists essentially of a polypropylene homopolymer having an MFR of less than 1.0 g / 10 min, or from 0.1 to 0.75 g / 10 min, as measured according to JIS K7210.

11. 5. The multilayer porous membrane of claim 1, wherein the average pore size of the one or more inner layers is at least 5%, at least 10%, at least 20%, at least 30%, or at least 50% larger than the average pore size of either or both of the outer layers.

12. 5. The multilayer porous membrane according to claim 1, wherein the two outer layers each have an average pore size of 0.05 to 0.5 μm (50 to 500 nm), or less than 0.25 μm (250 nm), and the average pore sizes of the two outer layers may be the same or different.

13. 5. The multi-layer porous membrane according to any one of claims 1 to 4, wherein at least one of said inner layers has an average pore size of 0.05 to 0.5 μm (50 to 500 nm), or less than 0.25 μm (250 nm).

14. 5. The multi-layer porous membrane according to claim 1, wherein at least one of said inner layers comprises a polypropylene having a different (lower or higher) MFR than the polypropylene used in at least one of said outer layers.

15. The multilayer porous membrane according to any one of claims 1 to 4, having a thickness of 5 to 25 μm, or 5 to 15 μm.

16. The multi-layer porous membrane according to any one of claims 1 to 4, comprising only one inner layer.

17. 5. The multi-layer porous membrane of any one of claims 1 to 4, comprising two or more inner layers, one of said inner layers comprising, consisting of, or consisting essentially of polyethylene, said polyethylene optionally providing a shutdown function, and one of said inner layers comprising, consisting of, or consisting essentially of polypropylene.

18. The multilayer porous membrane according to any one of claims 1 to 4, having a puncture strength of more than 300 gf at a thickness of 16 μm.

19. 5. A battery separator comprising the multi-layer porous membrane of any one of claims 1 to 4, wherein a coating is provided on one or both sides of the multi-layer porous membrane, the coating being a ceramic coating, a polymer coating, a shutdown coating, an adhesive / adhesive coating, or a combination thereof.

20. 20. A battery comprising the battery separator of claim 19, wherein the electrodes comprise lithium nickel cobalt manganese oxide (NMC or NCM), lithium iron phosphate (LFP), lithium nickel manganese spinel (LMNO), lithium nickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO), lithium cobalt oxide (LCO), or combinations thereof.

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