Asymmetric porous membrane

Abstract

The present invention provides a porous membrane that can enhance the oxidation resistance of the PE inner layer in thin and ultrathin shutdown separators or other shutdown structures. [Solution] A porous membrane comprising two outer layers and at least one selective inner layer, wherein the thickness ratio of one of the two outer layers to the other of the two outer layers is 1.1:1 to 4:1.

Description

[Technical Field]

[0001] This application relates to improved porous membranes and battery separators, and to liquid electrolyte secondary lithium-ion batteries incorporating them. In particular, the improved porous membranes disclosed herein may be used to form thinner, safer battery separators and batteries. [Background technology]

[0002] In the electric vehicle (EV and HEV) industrial market, the focus is on increasing the energy density of lithium-ion batteries while maintaining safety and lifespan.

[0003] One development aimed at improving safety is the shutdown separator. For example, a three-layer shutdown separator is described in U.S. Patent No. 5,952,120, which is incorporated herein by reference in its entirety. These shutdown separators typically have structures such as PP / PE / PP, PP / PE / PE / PP, or PP / PE / PE / PE / PP, where all layers are the same or substantially the same thickness. This symmetry was preferred because, for example, asymmetry in the separator can cause curling and other problems. Generally, shutdown separators improve safety at high temperatures by stopping ion transport and current flow across the separator. The PE layer, with its lower melting temperature, melts before the PP layer, and the molten PE fills the pores of the separator, blocking ion transport.

[0004] It is generally accepted that thinner separators allow for the formation of batteries with higher energy density, and that more cells can be incorporated into a single battery with nearly the same weight and thickness. Therefore, a promising method for achieving high energy density without sacrificing safety is to reduce the total weight and thickness of the three layers, thereby creating thin or ultrathin shutdown separators, such as three-layer shutdown products. However, simply reducing the symmetrical total thickness to create ultrathin or thin shutdown separators, such as three-layer shutdown separators, still presents application problems. For example, the rough surface of the cathode surface can easily break through and penetrate the outer layer of PP when used in liquid electrolyte lithium secondary batteries. Furthermore, high-voltage electrons can easily oxidize the PE layer, initiating side reactions and generating gases. In this case, energy density and safety are reduced. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Therefore, it is desirable to improve the oxidation resistance of the PE inner layer in thin and ultra-thin shutdown separators, such as three-layer shutdown separators or other shutdown structures. [Means for solving the problem]

[0006] In one embodiment, a porous membrane comprising two outer layers and at least one inner layer is described herein. The ratio of the thickness of one of the two outer layers to the thickness of the other of the two outer layers is, in some preferred embodiments, 1.1:1 to 4:1, 1.1:1 to 3:1, or 1.1:1 to 3:1. The total thickness of the membrane may be 5 to 30 microns, 5 to 20 microns, 5 to 15 microns, or 5 to 10 microns.

[0007] In some embodiments, the porous membrane may be a microporous membrane. In some embodiments, the porous membrane may be a dry process microporous membrane or a microporous membrane produced by a dry stretching process.

[0008] In some embodiments, the porous membrane may include 1 to 10 inner layers. In some embodiments, the porous membrane may include only one inner layer, making the porous membrane a trilayer.

[0009] In some embodiments, the two outer layers may contain, consist of, or essentially consist of polypropylene. At least one of the inner layers may contain, consist of, or essentially consist of polyethylene. In some embodiments, the porous membrane may have a three-layer structure PP / PE / PP, where "PP" is a polypropylene-containing layer and "PE" is a polyethylene-containing layer.

[0010] In some embodiments, the porous membrane may be formed by a method comprising laminating at least one outer layer with at least one inner layer. In some embodiments, the porous membrane may be formed by a method comprising co-extruding at least one outer layer with at least one inner layer.

[0011] In another embodiment, a porous membrane comprising two outer layers, where one layer is thicker than the other, is described herein. The thickness ratio may be 1:1.1 to 4:1. The total thickness of the membrane may be 5 to 30 microns, 5 to 20 microns, 5 to 15 microns, or 5 to 10 microns. In some preferred embodiments, the total thickness of the membrane may be 8 to 12 microns. In some preferred embodiments, calendering may be performed to achieve a thin or thinner separator having, for example, a thickness of 5 to 12 microns. In some embodiments, calendering is not necessary to form a thin or thinner separator. Calendering can also reduce the pore size.

[0012] In some embodiments, the porous membrane may be a microporous membrane. In some embodiments, the porous membrane may be a dry process microporous membrane or a microporous membrane produced by a dry stretching process.

[0013] In some preferred embodiments, the thicker layer may contain, consist of, or essentially consist of polypropylene, and the thinner layer may contain, consist of, or essentially consist of polyethylene.

[0014] In some embodiments, the porous membrane can be formed by a method including co-extruding two layers, a thin layer and a thick layer. In some embodiments, the porous membrane can be formed by a method including laminating one of the two layers onto the other of the two layers. Preferably, the battery separator is Li / Li + For this, 4.2 or higher, Li / Li + For this, 4.5 or higher, or Li / Li + It has an electrochemically stable voltage of 5.0 or higher. Typically, these results are obtained from cyclic voltammetry. In a typical procedure, two blocking electrodes are used. Pt is used as the cathode and metallic Li is used as the anode. A separator is placed between the electrodes in a sandwich structure with the electrolyte in between. The scan is performed using a voltage of 0 to 5 volts. The current changes depending on the voltage. Side reactions can be seen as peaks in the current-voltage plot.

[0015] In some embodiments, the separator comprises one of the porous membranes described herein, having a coating on a thinner outer layer or on the thinner of two layers. In some embodiments, the coating is selected from at least one of ceramic coatings, polymer coatings, shutdown coatings, crosslinked coatings, or a combination thereof. In some embodiments, the coating has a thickness of 1 to 5 microns.

[0016] In another aspect, a secondary battery is disclosed that includes, consists of, or consists essentially of an anode, a cathode, a liquid electrolyte, and any of the battery separators described herein between the anode and the cathode. In a preferred embodiment, the thicker of the two outer layers of the porous membrane faces the cathode. The coated thinner layer, or the uncoated outer layer, faces the anode.

[0017] In one aspect, a porous membrane is described herein that includes two outer layers and at least one inner layer. One of the outer layers has a smaller average pore size, lower porosity, and / or higher tortuosity than the other outer layer.

[0018] In another aspect, a battery separator is described that includes, consists of, or consists essentially of a porous membrane having outer layers with different average pore sizes. In some embodiments, the separator has an electrochemical stability voltage of 4.2 or greater with respect to Li / Li + In some embodiments, the electrochemical stability voltage is 4.5 or greater with respect to Li / Li + or 5.0 or greater with respect to Li / Li +

[0019] In some embodiments, the battery separator has a coating applied to the outer layer having a smaller average pore size, lower porosity, and / or higher tortuosity. The coating can be at least one of a ceramic coating, a polymer coating, and a shutdown coating. The coating layer can have a thickness of 1 to 5 microns.

[0020] In another aspect, a secondary battery is described. The secondary battery may include an anode, a cathode, a liquid electrolyte, and a battery separator including a porous membrane having outer layers with different average pore diameters described herein between the anode and the cathode. In some embodiments, the outer layer having a smaller average pore diameter, a lower porosity, and / or a higher degree of tortuosity may face the anode. In embodiments where the battery separator has a coating applied to the outer layer of the porous membrane having a smaller average pore diameter, a lower porosity, and / or a higher degree of tortuosity, the coating may face the anode.

[0021] In yet another aspect, an asymmetric porous multilayer membrane including at least one polypropylene (PP)-containing layer and at least one polyethylene (PE)-containing layer is described. The ratio of the thickness of the one or more PP-containing layers to the one or more PE-containing layers ranges from 1.1:1 to 25:1, from 1.1:1 to 20:1, or from 4:1 to 10:1.

[0022] In a probably preferred embodiment, the membrane can comprise, consist of, or consist essentially of two PP-containing layers and one PE-containing layer, and the layers are arranged in the order of PE / PP / PP. In some embodiments, the membrane can comprise, consist of, or consist essentially of any one of the structures of PE / PE / PP / PP / PP / PP (where PE is a PE-containing layer and PP is a PP-containing layer), PE / PE / PE / PP / PP / PP / PP / PP / PP (where PE is a PE-containing layer and PP is a PP-containing layer), PE / PE / PE / PE / PP / PP / PP / PP / PP / PP / PP / PP (where PE is a PE-containing layer and PP is a PP-containing layer), or PE / PE / PE / PE / PE / PP / PP / PP / PP / PP / PP / PP / PP / PP / PP (where PE is a PE-containing layer and PP is a PP-containing layer).

[0023] In embodiments comprising two or more PP-containing layers, these layers may comprise, consist of, or essentially consist of identical or different PP-containing materials. The PP-containing materials may be a single polypropylene, a mixture of two or more different polypropylenes, or a single polypropylene. The material may consist of, or essentially consist of, a mixture of polypropylene and an additional component, or a mixture of two or more different polypropylenes and an additional component. In some embodiments, the additional component may be an elastomer. The elastomer may be a styrene-based elastomer.

[0024] In embodiments where two or more PE-containing layers exist, the PE-containing layers may contain, consist of, or essentially consist of the same or different PE-containing materials.

[0025] In a presumably preferred embodiment, the multilayer film is formed by co-extruding two or more or three or more layers, but the film can also be formed by laminating those layers, or by a combination of co-extrusion and lamination. For example, all three layers of a PE / PP / PP structure can be co-extruded. Alternatively, they may all be laminated. In the case of lamination, the laminated layers may be a combination of layers formed by different processes such as wet and dry processes, or a combination of layers formed by the same process. For example, a wet-process PE layer may be laminated onto two PP layers formed by a dry process.

[0026] In some preferred embodiments, the multilayer film may be a dry-process multilayer film. The film may also be formed by a wet process, a beta-nucleation process, or the like.

[0027] In another embodiment, a battery separator comprising, consisting of, or essentially consisting of the asymmetric porous multilayer film described above is described. In some embodiments, the battery separator comprises a film in which only one of the outermost layers of the asymmetric porous multilayer film is a PE-containing layer. In some embodiments, the battery separator may include coatings on both sides of the asymmetric porous multilayer film described herein. The coatings may be any one of the following: a ceramic coating, a shutdown coating, an adhesive coating, a polymer coating, or a combination thereof.

[0028] In another embodiment, a battery comprising a battery separator of this specification is described. The battery comprises, or consists of, an anode, a cathode, a liquid electrolyte, and an asymmetric multilayer porous membrane, or may essentially consist of them. In some embodiments, the PE-containing outermost layer of the separator may face the anode.

[0029] In yet another embodiment, an asymmetric porous multilayer film is described comprising at least one polypropylene (PP)-containing layer and at least one polyethylene (PE)-containing layer. The ratio of the thicknesses of one or more PE-containing layers to one or more PP-containing layers is in the range of 1.1:1 to 25:1, 1.1:1 to 20:1, or 4:1 to 10:1. The details of such a film may be the same as those of the film described above, except that the amount of PP is greater, and the PP-containing layers in the film become PE-containing layers, and the PE-containing layers become PP-containing layers. [Brief explanation of the drawing]

[0030] [Figure 1] Figure 1 is a schematic diagram of an exemplary film described herein. [Figure 2A] Figures 2A and 2B are both FESM images of exemplary membranes described herein. [Figure 2B] Figure 2B is a FESM image of an exemplary membrane described herein. [Figure 3]Figure 3 is a schematic diagram showing the difference between film thickness and pore length. The degree of flexibility is derived from these two measurements. [Figure 4A] Figures 4A, 4B, 4C, 4D, 4E, and 4F are schematic diagrams of exemplary embodiments described herein. [Figure 4B] Figures 4A, 4B, 4C, 4D, 4E, and 4F are schematic diagrams of exemplary embodiments described herein. [Figure 4C] Figures 4A, 4B, 4C, 4D, 4E, and 4F are schematic diagrams of exemplary embodiments described herein. [Figure 4D] Figures 4A, 4B, 4C, 4D, 4E, and 4F are schematic diagrams of exemplary embodiments described herein. [Figure 4E] Figures 4A, 4B, 4C, 4D, 4E, and 4F are schematic diagrams of exemplary embodiments described herein. [Figure 4F] Figures 4A, 4B, 4C, 4D, 4E, and 4F are schematic diagrams of exemplary embodiments described herein. [Figure 5A] Figures 5A and 5B are schematic diagrams of exemplary embodiments described herein. [Figure 5B] Figures 5A and 5B are schematic diagrams of exemplary embodiments described herein. [Figure 6A] Figures 6A, 6B, and 6C are schematic diagrams of exemplary embodiments described herein. [Figure 6B] Figures 6A, 6B, and 6C are schematic diagrams of exemplary embodiments described herein. [Figure 6C] Figures 6A, 6B, and 6C are schematic diagrams of exemplary embodiments described herein. [Figure 7] Figure 7 shows the pore size distribution of an exemplary embodiment described herein. [Modes for carrying out the invention]

[0031] Asymmetric porous membrane Asymmetric porous membranes are described herein. An asymmetric porous membrane may include, consist of, or essentially consist of two outer layers and optionally at least one inner layer. There may be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more inner layers. In some embodiments, the porous membrane may consist of, or essentially consist of, two outer layers, and may have no inner layers. The ratio of the thickness of one of the two outer layers to the thickness of the other of the two outer layers may be 1.1:1 to 10:1, 1.1:1 to 9:1, 1.1:1 to 8:1, 1.1:1 to 7:1, 1.1:1 to 6:1, 1.1:1 to 5:1, 1.1:1 to 4:1, 1.1:1 to 3:1, or 1.1:1 to 2:1. In some preferred embodiments, the total thickness of the porous membrane may be 2-30 microns, 2-25 microns, 2-20 microns, 2-15 microns, or 2-10 microns. In some embodiments, the total thickness of the porous membrane may be 3-12 microns, 4-12 microns, 5-12 microns, or 9-12 microns. In some embodiments, at least one of the outer layers has a thickness of 2-6 microns or 4-5 microns. In some embodiments, when the asymmetric porous membrane is used in a battery, the outer layer having a thickness of 2-6 microns or 4-5 microns is positioned facing the cathode.

[0032] In some embodiments, the outer layers may comprise one outer layer having a larger average pore diameter, higher porosity, and / or higher flexibility, and the other outer layer having a smaller average pore diameter, lower porosity, and / or lower flexibility, thus having different average pore diameters, different porosity, and / or different flexibilitys. In some embodiments, the pore diameter, porosity, and / or flexibility and thickness of both outer layers may differ. In some embodiments, only the thickness of the outer layers, or only the pore diameter, porosity, and / or flexibility may differ.

[0033] In some embodiments, the asymmetric porous membrane may be macroporous, nanoporous, or microporous. In some preferred embodiments, the asymmetric porous membrane is The membrane may be microporous. For example, the pores of a porous membrane may have an average pore diameter of 0.01 to 1.0 microns. In some preferred embodiments, the average pore diameter may be 0.1 to 1.0 microns, 0.1 to 0.9 microns, 0.1 to 0.8 microns, 0.1 to 0.7 microns, 0.1 to 0.6 microns, 0.1 to 0.5 microns, 0.1 to 0.4 microns, 0.1 to 0.3 microns, or 0.1 to 0.2 microns. The pores of a porous membrane may have any shape. For example, they may be slit-shaped, circular, substantially circular, or asymmetrical.

[0034] In some preferred embodiments, the asymmetric porous membrane may be a dry-process asymmetric porous membrane. In some embodiments, the dry process is a method that does not use any pore-forming factors / pore-forming agents or beta-nucleating factors / beta-nucleating agents. In some embodiments, the dry process does not use any solvents, waxes, or oils. In some embodiments, the dry process does not use any pore-forming factors / pore-forming agents or beta-nucleating factors / beta-nucleating agents and does not use any solvents, waxes, or oils.

[0035] Dry-process asymmetric porous membranes may be formed by a dry stretching process. An exemplary dry stretching process, known as the Celgard® dry stretching process, is incorporated herein by reference in whole by Chen et al., Structural Characterization of Celgard (registered trademark) Microporous Membrane Precursors: Melt-Extruded This is described in PolyethyleneFilms, J. of Applied Polymer Sci. 53, 471-483 (1994). The Celgard® dry stretching process refers to one in which pore formation results from stretching a non-porous orientation precursor at least in the mechanical direction. Also, Kesting, Robert E., Synthetic Polymeric Membranes, A Structural Perspective, Second Edition, John Wiley & Sons, New York, NY, (1985), pages 290-297, which is incorporated herein by reference in whole, also discloses a dry stretching process. In some preferred embodiments of the dry stretching process, the process may include a stretching step. The stretching process may include, consist of, or essentially consist of, uniaxial stretching (e.g., stretching in the MD direction only or in the TD direction only), biaxial stretching (e.g., stretching in the MD and TD directions), or multiaxial stretching (e.g., stretching along three or more different axes such as MD, TD, and another axis). In some embodiments, the dry stretching process may include, consist of, or essentially consist of, an extrusion process and a stretching process, in or out of this order. In some embodiments, the dry stretching process may include, consist of, or essentially consist of, an extrusion process, an annealing process, and a stretching process, in or out of this order. In some embodiments, the extrusion process may be an inflation film extrusion process or a cast film extrusion process. In some embodiments, a non-porous precursor is extruded and stretched to form pores. In some embodiments, a non-porous precursor is extruded, annealed, and then stretched to form pores. In other embodiments, porous or non-porous precursors may be formed by methods other than extrusion, such as sintering or printing, and stretching may be performed on the precursor to form pores or to enlarge existing pores.

[0036] In some embodiments, pore-forming factors / pore-forming agents or beta-nucleating factors / beta-nucleating agents may be used, and the process is still considered a dry process. For example, the particle stretching process can be considered a dry process because the oil or solvent forms pores without being extruded with the polymer and without being extracted from the extruded polymer. In the process, particles such as silica or calcium carbonate are added to a polymer mixture, and these particles help in the formation of pores. In such a method, for example, the polymer mixture containing particles and polymer is extruded to form a stretched precursor, and voids are created around the particles. In some embodiments, the particles may be removed after the voids have been created. The particle stretching process may include a stretching step before or after the removal of the particles, but since the principle pore formation mechanism is the use of particles rather than stretching, the particle stretching process is not considered a dry stretching process.

[0037] In some preferred embodiments, the structure of a dry-process porous membrane may have one or more notable features. For example, a dry-process membrane may contain more than 10% polypropylene. Wet processes or other processes using solvents are generally incompatible with polypropylene because the solvent degrades it. Therefore, wet-process porous membranes typically contain less than 10% polypropylene, most typically less than 5%. Another notable feature of some dry-process porous membranes, particularly when used as battery separators, is their ability to have a shutdown function. In some cases, a shutdown function can be imparted by a PP / PE / PP structure in which the PE layer is the shutdown layer. This is unique to dry-process membranes because layers mainly containing polypropylene (PP) cannot generally be formed by wet processes. Dry processes are unparalleled in their suitability for forming PP / PE / PP or other shutdown membrane structures.

[0038] In some embodiments, prominent dry-process porous membranes may be in the presence of lamellae and fibrils. For example, the porous membrane may be as shown in Figures 1, 2A, and 2B. It can have such a structure. Figures 2A and 2B are FESM images showing slit-shaped micropores in a Celgard® microporous membrane containing PE(A) and PP(B). In some embodiments, the pores or micropores of the dry-process porous membrane may be circular, rectangular, semicircular, trapezoidal, etc.

[0039] In some embodiments, a notable feature of dry-process porous membranes is the absence or substantial absence of pinholes. Pinholes are considered defects and, generally, are not intentionally formed features of dry-process porous membranes. In some embodiments, dry-process microporous membranes may be completely free of or substantially free of pinholes larger than 10 nm. In some preferred embodiments, the pores of dry-process porous membranes are bent. In some embodiments, a notable feature of dry-process porous membranes is the degree of bend. In some embodiments, the degree of bend of a dry-process porous membrane is greater than 1, 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. In some embodiments, a formula for roughly calculating the degree of bend is (Formula 1). Curvature=x / t (Formula 1) In the above formula, "x" is the length of the opening or pore of the porous membrane, and "t" is the thickness of the membrane. Since the length of a pinhole is the same as the thickness of the membrane, a pinhole has a degree of curvature of 1. Since the length of a pore is longer than the thickness of the membrane, a bent pore has a degree of curvature greater than 1, as shown in Figure 3.

[0040] In some embodiments, the dry-stretched porous membrane is semi-crystalline. In some embodiments, the dry-stretched porous membrane is semi-crystalline and oriented in a single direction. For example, the membrane may be MD-oriented. Porous films formed by wet processes, such as films formed by a beta nucleation process, may be randomly oriented.

[0041] In some embodiments, an asymmetric porous membrane may be formed by laminating at least one outer layer with at least one inner layer. In embodiments without an inner layer, the asymmetric porous membrane may be formed by laminating at least one outer layer with another outer layer. For example, if the asymmetric porous membrane is formed by a dry process such as a dry stretching process, the membrane may be formed by separately extruding at least one of the outer layers and one of the inner layers, or by separately extruding both outer layers. Then, before or after the stretching process, one of the outer layers may be laminated with the other outer layer or one of the inner layers.

[0042] In some embodiments, an asymmetric porous membrane may be formed by co-extruding at least one outer layer with at least one inner layer. In embodiments without an inner layer, the asymmetric porous membrane may be formed by co-extruding two outer layers. For example, when the asymmetric membrane is formed by a dry process such as a dry stretching process, the two outer layers are co-extruded together, and the non-porous co-extruded material can be stretched to form pores. In another example, when a dry process such as a dry stretching process is used to form an asymmetric porous membrane, at least one outer layer is co-extruded with at least one inner layer, and the non-porous co-extruded material can then be laminated with the inner layer or other outer layers. The lamination process may be performed before or after stretching, which can be used to form pores.

[0043] In some embodiments, the outer layer of the axion membrane may contain, consist of, or essentially consist of polyethylene. In some embodiments, at least one of the inner layers may contain, consist of, or essentially consist of polyethylene. For example, in some embodiments, the axion membrane may have the following structures: PP / PE, PP / PE / PP or PP / PE / PE / PP, or PP / PE / PE / PE / PP, or PP / PE / PE / PE / PE / PE / PP, or PP / PE / PE / PE / PE / PE / PE / PP, or PP / PE / PE / PE / PE / PE / PE / PE / PP, or PP / PE / P The film may be made of E / PE / PE / PE / PE / PE / PE / PE / PE / PE / PP, or PE / PP / PP, or PE / PE / PP / PP / PP / PP, or PE / PE / PE / PP / PP / PP / PP / PP / PP / PP, or PE / PE / PE / PE / PE / PP / PP / PP / PP / PP / PP / PP / PP / PP, or PE / PP / PP / PP, or PE / PP / PP / PP, or PE / PP / PP / PP / PP / PP, or PE / PP / PP / PP / PP / PP / PP, or PE / PP / PP / PP / PP / PP / PP, or PE / PE / PP / PP / PP / PP. In embodiments in which the asymmetric film includes two outer layers and does not include an inner layer, at least one of the outer layers may include, consist of, or be essentially made of polypropylene, and the other may include, consist of, or be essentially made of polyethylene. In a preferred embodiment, the thicker of the two outer layers may contain, consist of, or be essentially made of polypropylene. In a preferred embodiment, if there is no inner layer, the thinner of the two outer layers may contain, consist of, or be essentially made of polyethylene.

[0044] In some embodiments, the asymmetric multilayer porous membrane may include at least one polypropylene (PP)-containing layer and at least one polyethylene (PE)-containing layer, where the thickness ratio of one or more PP-containing layers to one or more PE-containing layers is 1.1:1 to 25:1, 1.1:1 to 20:1, 1.1:1 to 15:1, 1.1:1 to 10:1, 1.1:1 to 9:1, 1.1:1 to 8:1, 1.1:1 to 7:1, 1.1:1 to 6:1, 1.1:1 to 5:1, 1.1:1 to 4:1, 1.1:1 to 3:1, or 1.1:1 to 2:1. For example, the PE / PP / PP structure may include a PE-containing layer (PE) with a thickness of 1 micron and a PE-containing layer with a thickness of 3 microns. It has two 0.5 micron PP-containing layers (PP), which can give a ratio of 7:1.

[0045] In a likely preferred embodiment, the film may include, consist of, or essentially consist of two PP-containing layers and one PE-containing layer, with the layers arranged in the order PE / PP / PP. In some embodiments, the film may include, consist of, or essentially consist of any one of the following structures: PE / PE / PP / PP / PP / PP (where PE is a PE-containing layer and PP is a PP-containing layer), PE / PE / PE / PP / PP / PP / PP / PP / PP / PP / PP / PP (where PE is a PE-containing layer and PP is a PP-containing layer), or PE / PE / PE / PE / PP / PP / PP / PP / PP / PP / PP / PP / PP / PP / PP (where PE is a PE-containing layer and PP is a PP-containing layer). Furthermore, the structure can be PE / PP / PP / PP, PE / PP / PP / PP / PP, and PE / PP / PP / PP / PP / PP, etc.

[0046] In a film comprising two or more, three or more, four or more, five or more, six or more, seven or more, eight or more, nine or more, ten or more, or up to 100 PP-containing layers, each PP-containing layer may contain, consist of, or essentially consist of identical or different PP-containing materials. The PP-containing material may contain, consist of, or essentially consist of at least 50% polypropylene. Some may contain at least 55% PP, at least 60% PP, at least 65% PP, at least 70% PP, at least 75% PP, at least 80% PP, at least 85% PP, at least 90% PP, at least 95% PP, or 100% PP. The polypropylene may contain, consist of, or essentially consist of a single PP homopolymer, copolymer, or terpolymer, or a blend of two or more different homopolymers, copolymers, or terpolymers, or a combination thereof. In some embodiments, the PP-containing material may include, consist of, or essentially consist of, a PP homopolymer, copolymer, or terpolymer, or a blend of two or more PP homopolymers, copolymers, or terpolymers, and additional components. The additional components may be any one of additional polymers, elastomers and the like, or a combination thereof. Elastomers may be added, for example, to improve strength. The elastomer may be a styrene-based elastomer.

[0047] In some embodiments, the film comprises two or more PE-containing layers, the PE-containing layers may comprise identical or different PE-containing materials. The PE-containing material may comprise, consist of, or essentially consist of at least 50% polyethylene. Parts may comprise at least 55% PE, at least 60% PE, at least 65% PE, at least 70% PE, at least 75% PE, at least 80% PE, at least 85% PE, at least 90% PE, at least 95% PE, or 100% PE. The polyethylene may comprise, consist of, or essentially consist of a single PE homopolymer, copolymer, or terpolymer, or a blend of two or more different homopolymers, copolymers, or terpolymers, or a combination thereof. In some embodiments, the PE-containing material may comprise, consist of, or essentially consist of a PE homopolymer, copolymer, or terpolymer, or a blend of two or more PE homopolymers, copolymers, or terpolymers, and additional components. The additional components may be any one of the following: additional polymers, elastomers and / or similar substances, or a combination thereof. Elastomers may be added, for example, to improve strength. The elastomer may be a styrene-based elastomer.

[0048] In some embodiments, two or more or three or more layers can be co-extruded. For example, in a PE / PP / PP structure, all three layers may be co-extruded, or two may be co-extruded and the third layer laminated onto the two co-extruded layers. As another example, in a PE / PE / PE / PP / PP / PP / PP / PP / PP structure, the three PE layers may be co-extruded (PE / PE / PE), or the two sets of three PP layers may be co-extruded separately (PP / PP / PP). The co-extruded PE layers and the two sets of co-extruded PP layers can then be laminated together to form the final structure (PE / PE / PE) / (PP / PP / PP) / (PP / PP / PP). Structures such as (PE / PE / PE / PE) / (PP / PP / PP / PP) / (PP / PP / PP / PP), (PE / PP / PP / PP) / (PP / PP / PP / PP) / (PP / PP / PP / PP), (PE / PE / PP / PP) / (PP / PP / PP / PP) / (PP / PP / PP / PP), (PE / PE / PE / PP) / (PP / PP / PP / PP) / (PP / PP / PP / PP), etc., can be formed. (PP / PP / PP / PP), (PE / PE / PP / PP), etc., represent co-extruded structures, and " / " means the lamination interface. In some embodiments, all layers can be laminated together. For example, in the case of a PE / PP / PP structure, one PE layer and the other two PP layers can be laminated together. Co-extrusion of layers may be preferred over lamination because it can form thinner layers without the film handling problems that occur when laminating thin films of less than 10 microns, especially less than 5 microns, or particularly less than 1 micron.

[0049] In some preferred embodiments, the multilayer asymmetric porous membrane may be the dry process membrane described herein.

[0050] In some embodiments, the asymmetric porous membrane can be macroporous, nanoporous, or microporous. In some preferred embodiments, the asymmetric porous membrane may be a microporous membrane. For example, the pores of the porous membrane can have an average pore diameter of 0.01 to 1.0 microns. In some preferred embodiments, the average pore diameter can be 0.1 to 1.0 microns, 0.1 to 0.9 microns, 0.1 to 0.8 microns, 0.1 to 0.7 microns, 0.1 to 0.6 microns, 0.1 to 0.5 microns, 0.1 to 0.4 microns, 0.1 to 0.3 microns, or 0.1 to 0.2 microns. The pores of the porous membrane can have any shape. For example, they can be slit-shaped, circular, substantially circular, or asymmetric.

[0051] Separator for battery The separator for battery described herein is not so limited. In a preferred embodiment, the separator for battery may comprise, consist of, or consist essentially of at least one of the asymmetric porous membranes described herein. In some preferred embodiments, the asymmetric porous membrane may be a microporous asymmetric membrane.

[0052] The separator for battery is Li / Li + with respect to 4.2 or more, Li / Li + with respect to 4.5 or more, or Li / Li + preferably has an electrochemical stability voltage of 5.0 or more with respect to.

[0053] In some embodiments, the separator is configured to have superior oxidation resistance compared to typical two-layer, three-layer, or multilayer separators where all layers, including the outermost layer, are the same or substantially the same thickness. A typical three-layer separator of PP / PE / PP, where each layer is the same thickness, may have a PE layer on the separator side closest to the cathode that is prone to oxidation. Similarly, typical two-layer separators such as PP / PE and PP / PP / PE may also have a PE layer on the separator side closest to the cathode that is prone to oxidation. A typical multilayer separator, for example, described in U.S. Patent Application Publication 2018 / 0323417, which is incorporated entirely herein by reference, has a structure of (PP / PP / PP) / (PE / PE / PE) / (PP / PP / PP) or (PP / PP) / (PE / PE) / (PP / PP ) may have, for example, (PP / PP / PP) or (PP / PP) represent co-extruded three-layer and two-layer structures, respectively, and (PE / PE / PE) and (PE / PE) represent co-extruded three-layer and two-layer structures, respectively. According to the present invention as described herein, by having a thicker polypropylene outer layer (or, for example, a thicker co-extruded two-layer, three-layer, etc., when forming a multilayer embodiment) and positioning this layer closest to the cathode, the separator described herein has desirable oxidation resistance compared to a typical three-layer, two-layer, or multilayer separator where all layers are the same or substantially the same thickness. In embodiments where one outermost layer is PE and the other outermost layer is PP, the PP layer may face the cathode or be closest to the cathode in order to have oxidation resistance. In embodiments with an inner layer, oxidation resistance is mainly required on one side facing the cathode, and a thinner separator is preferred, so the other outermost layer may be thinner. In embodiments without an inner layer, the other outer layer may be a thin polyethylene layer. The polyethylene layer may have a shutdown function. In that case, the polyethylene layer should be thick enough to provide that function.

[0054] In some embodiments, the separator described herein comprises, consists of, or essentially consists of, at least one asymmetric porous membrane, configured such that the thinner of the two outer layers of the asymmetric porous membrane described herein is positioned closest to the anode of the secondary battery. In some embodiments, this may mean that the thinner of the two outer layers is coated. For example, the thinner of the two outer layers may be coated with a ceramic coating comprising, consisting of, or essentially consisting of inorganic or organic heat-resistant or ceramic particles and a binder. For example, a ceramic coating is disclosed in U.S. Patent No. 6,432,586, which is incorporated herein by reference in its entirety. The ceramic coating generally serves to prevent, inhibit, or slow the growth of lithium dendrites growing from the anode to the cathode of a typical secondary battery, such as a lithium-ion battery. In some embodiments, the thinner of the two outer layers may be coated with a polymer coating or a shutdown coating. Also in some embodiments, the thicker of the two outer layers may be coated.

[0055] battery The batteries described herein are liquid electrolyte batteries or cells, or electrochemical devices such as capacitors or supercapacitors. In some embodiments, the battery may include a battery separator described herein between the anode and the cathode. In a preferred embodiment, the battery separator includes at least one asymmetric porous membrane described herein, wherein the thicker of the two outermost layers of the porous membrane faces the cathode. In a preferred embodiment, the thinner of the two outermost layers faces the anode. When the battery separator described herein is coated, the coating faces the anode to prevent lithium dendrite formation.

[0056] A suitable anode can have an energy capacity of 372 mAh / g or more, preferably 700 mAh / g or more, preferably 3860 mAh / g or more, and preferably 4200 mAh / g or more. The anode may consist of lithium metal foil or lithium alloy foil (e.g., lithium aluminum alloy) or graphite, graphene, carbon nanotubes, and silicon (Si), lithium. The anode is not produced from lithium-containing intercalation compounds or lithium-containing insertion compounds alone.

[0057] A suitable cathode may be any cathode compatible with the anode and may contain an intercalation compound, an insertion compound, or an electrochemically inert binder. Suitable intercalation materials include, for example, LiCoO2, LiNiO2, and LiNi 0.8 Co 0.2 O2, LiLiLi 0.8 Co 0.15 Al 0.05 O2, LiMn 0.5 Ni 0.5 O2, LiMn 1 / 3 Ni 1 / 3 Co 1 / 3 O2, LiMn 0.4 Ni 0.4 Co 0.2 This includes O2, LiFePO4, and LiMn2O4. Suitable polymers include, for example, sodium carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyimide (PI), and acrylic acid esters (polyacetylene, polypyrrole, polyaniline, and polythiopene).

[0058] The nominal voltages of the batteries described herein are 4.0V / cell or higher, 4.2V / cell or higher, 4.5 volts / cell or higher, 5.0 volts / cell or higher, or 5.5 volts / cell or higher. obtain.

[0059] Any of the battery separators described herein may be incorporated into any vehicle, such as an electric vehicle, or device, such as a mobile phone or laptop, that is fully or partially battery-powered.

[0060] Various embodiments of the present invention have been described in relation to the realization of various objectives of the present invention. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Many modifications and adaptations will be readily apparent to those skilled in the art without departing from the spirit and scope of the invention.

[0061] Figures 4A, 4B, 4C, 4D, 4E, and 4F schematically show some arrangements of the battery cells disclosed herein.

[0062] Figures 5A and 5B schematically show some arrangements of battery cells according to other embodiments disclosed herein. These figures schematically show outer layers having different pore sizes, porosity, and / or curvature.

[0063] Several non-exclusive examples are disclosed in Table 1 below.

[0064] [Table 1-1]

[0065] [Table 1-2]

[0066] [Table 1-3]

[0067] [Table 1-4]

[0068] [Table 1-5]

[0069] Examples 1-70 prepared a total of 140 cases, including those with and without a ceramic coating on the thinner of the two outer layers of the film, or on the side intended to face the anode. It was also possible to form the ceramic on the thicker of the two outer layers, or on both outer layers.

[0070] In Examples 1-70, the thinner outer layer was also prepared to have a smaller pore diameter, lower porosity, and / or higher flexibility than the thicker outer layer. In some embodiments, these can be formed by forming a PP layer having a smaller pore diameter, lower porosity, and / or higher flexibility, or by forming a PP layer in which one has a smaller pore diameter, lower porosity, and / or higher flexibility, and the other has a larger pore diameter, higher porosity, and / or lower flexibility, as well as by laminating a PP layer or a PP layer with a PE layer to form the structure shown in the table above. Ta.

[0071] In Examples 71-75, all layers had the same thickness, but one of the outer layers had a smaller pore diameter, lower porosity, and / or higher flexibility than the other, resulting in structures such as PP / PE / PP, PP / PE, PP / PE / PE / PP, PP / PE / PE / PE / PP, (PP / PP) / (PE / PE) / (PP / PP), and (PP / PP / PP) / (PE / PE / PE) / (PP / PP / PP). For example, in the PP / PE structure, the PP layer had a smaller average pore diameter, lower porosity, and / or higher flexibility than the PE layer. Furthermore, in a multilayer embodiment formed by laminating co-extruded (PP / PP) or (PP / PP / PP) with co-extruded (PE / PE) or (PE / PE / PE), one of the outermost PP layers or one of the co-extruded PP two or three layers may have a smaller average pore diameter, lower porosity, and / or higher flexibility than the other outermost PP layer or co-extruded PP two or three layers. Also, in some embodiments, the thicknesses of the outermost PP layers or the co-extruded PP triple or double layers may differ.

[0072] Regarding the two-layer film, it was found that the thicker polypropylene layer provides oxidation resistance, and the polyethylene layer provides shutdown capability. The second polypropylene layer is not necessary (however, there may be one in some embodiments), and therefore, it can be omitted to obtain a thinner separator. It was also found that having a polypropylene layer with a smaller pore diameter, lower porosity, and / or higher flexibility may help in dendrite blocking when the layer having a smaller pore diameter, lower porosity, and / or higher flexibility is positioned facing the anode of the battery. A coating applied on this layer having a smaller pore diameter, lower porosity, and / or higher flexibility may be even better at delaying or stopping lithium dendrite growth. Since lithium dendrite growth can cause short circuits in batteries, batteries that can delay or prevent its growth are safer.

[0073] In the three-layer, four-layer, and five-layer embodiments, the thicker polypropylene layer provides oxidation resistance to the side of the film that is closest to the cathode of the secondary battery cell. A thinner polypropylene layer can be used on the other side where oxidation resistance is less critical, allowing for the formation of a thinner separator. Of the two outer layers, the thinner one, configured to be closest to the anode where oxidation resistance is less critical, may be provided with a ceramic coating. The ceramic coating grows from the anode to the cathode to prevent short circuits and / or heat This can help prevent, inhibit, or slow the growth of lithium dendrites that could cause runaway reactions. Additionally, polypropylene layers with smaller average pore diameters may be used on sides where oxidation resistance is less critical, allowing for the formation of thinner separators. A ceramic coating can be applied over an outer layer with a larger average pore diameter, configured to be closest to the anode where oxidation resistance is less critical. The ceramic coating can help prevent, inhibit, or slow the growth of lithium dendrites that could grow from the anode to the cathode, potentially causing short circuits and / or thermal runaway reactions.

[0074] In other embodiments, an asymmetric structure is formed with a thin PE-containing outer layer. Normally, adding a PE-containing layer to the outside is undesirable because such a layer may oxidize within the battery cell, and because PE melts at a lower temperature than PP, the addition of a PE-containing layer may reduce the heat resistance of the separator. However, the PE-containing layer exhibits improved / reduced pin removal force compared to the PP-containing layer. Reduced pin removal force is a particularly desirable property when the film is used as a battery separator in cylindrical cells. The applicant has developed a thin film to provide reduced pin removal force while maintaining the heat resistance of the battery separator. A PE-containing outer layer is provided. If only one of the outermost layers is a PE-containing layer and this layer faces the cathode, oxidation will occur unless a coating such as a ceramic coating is provided on the PE-containing layer to protect it. Therefore, it is preferable that it faces or is close to the anode of the battery cell. Providing a ceramic coating on the PE-containing layer may not be suitable for the purpose of providing a layer to reduce the pin removal force on the surface. If shutdown characteristics are desired, a thicker PE-containing layer may be provided. Examples including a PE-containing outer layer are shown in Examples 76 to 114 in Table 2 below.

[0075] [Table 2-1]

[0076] [Table 2-2]

[0077] [Table 2-3]

[0078] In Examples 76-88, the structures were formed by co-extruding three layers, but they could also be formed by lamination. In Examples 89-101, the final structure was formed by co-extruding (PP / PP / PP) and (PE / PE / PE) respectively, and then laminating two (PP / PP / PP) composites onto one (PE / PE / PE) composite. In Examples 102-114, the final structure was formed by co-extruding (PE / PP / PP) and (PP / PP / PP) respectively, and then laminating two (PP / PP / PP) composites with one (PE / PP / PP). It is also possible to replace (PE / PP / PP) with (PE / PE / PP) to form a (PE / PE / PP) / (PP / PP / PP) / (PP / PP / PP) structure. The stretching of the composites can be performed before or after lamination. Figures 6A, 6B, and 6C show battery cells containing films according to some embodiments described herein. In some preferred embodiments, the co-extruded PE / PP / PP structure, such as one of Examples 76-88, and the intermediate PP layer are formed from a polypropylene blend comprising polypropylene and at least one other polymer. For example, a styrene-based elastomer can be used as the other polymer. The PE layer consists of polyethylene of these embodiments, and the outer PP layer consists of polypropylene of these embodiments. In any one of Embodiments 76-114, the resulting structure may be provided with a coating on one or both sides. For example, a ceramic coating may be formed on the side facing the anode. In other embodiments, a cross-linked coating may be formed on either one or both sides of the anode-facing and cathode-facing sides.

[0079] Table 3 below shows the advantages of a co-extruded PE / PP blend / PP structure containing polypropylene and approximately 5% styrene-based elastomer compared to a co-extruded PE / PP / PP structure without the blend.

[0080] [Table 3]

[0081] Figure 7 shows the pore size distribution of a co-extruded PE / PP blend / PP product compared to the pore size distribution of a co-extruded PE / PP / PP product. The pore size of the product containing the blend is bimodal. The advantages of these products include high strength due to the high PP content, a PE layer for shutdown, further improved strength of the product containing the PP blend, reduced coefficient due to the outer PE, and a stepped pore size distribution. In the case of the PP blend, where PE > PP blend > PP, the stepped pore size may help mitigate dendrite growth if the PE layer faces the anode. Using PE as the outer layer provides a desirable reduction in the coefficient of friction for use in cylindrical cells where pin removal force may be a problem. Oxidation is not a problem when a single PE is used and the PE layer faces the anode.

Claims

1. A porous membrane comprising two outer layers and at least one selective inner layer, wherein the thickness ratio of one of the two outer layers to the other of the two outer layers is 1.1:1 to 4:

1.

2. The porous membrane according to claim 1, wherein the ratio is 1.1:1 to 3:

1.

3. The porous membrane according to claim 1, wherein the ratio is 1.1:1 to 2:

1.

4. The porous membrane according to any one of claims 1 to 3, wherein the porous membrane is microporous.

5. A porous membrane according to any one of claims 1 to 3, comprising 1 to 10 inner layers.

6. A porous membrane according to any one of claims 1 to 3, comprising one inner layer.

7. The porous membrane according to any one of claims 1 to 3, wherein the porous membrane is formed by a method comprising laminating at least one of the two outer layers and at least one inner layer.

8. The porous membrane according to any one of claims 1 to 3, wherein the porous membrane is formed by a method comprising co-extruding at least one of the two outer layers and at least one inner layer.

9. The porous membrane according to any one of claims 1 to 3, wherein the two outer layers contain polypropylene, are made of polypropylene, or are essentially made of polypropylene, and the at least one inner layer contains polyethylene, is made of polyethylene, or is essentially made of polyethylene.

10. The porous membrane according to any one of claims 1 to 3, wherein the porous membrane is a dry process microporous membrane.

11. The porous membrane according to any one of claims 1 to 3, wherein the porous membrane is a microporous membrane produced by a dry stretching process.

12. The porous membrane according to any one of claims 1 to 3, wherein the total thickness of the porous membrane is 5 to 30 microns.

13. The porous membrane according to claim 12, wherein the thickness is 5 to 20 microns.

14. The porous membrane according to claim 12, wherein the thickness is 5 to 15 microns.

15. The porous membrane according to claim 12, wherein the thickness is 5 to 10 microns.

16. A porous membrane comprising two outer layers but not an inner layer, wherein the ratio of the thickness of one of the two outer layers to the other of the two outer layers is 1.1:1 to 4:

1.

17. The porous membrane according to claim 1, wherein the ratio is 1.1:1 to 3:

1.

18. The porous membrane according to claim 1, wherein the ratio is 1.1:1 to 2:

1.

19. The porous membrane according to any one of claims 16 to 18, wherein the porous membrane is microporous.

20. A porous membrane according to any one of claims 16 to 18, formed by a method comprising laminating at least one of the two outer layers with the other of the two outer layers.

21. The porous membrane according to any one of claims 16 to 18, wherein the porous membrane is formed by a method including co-extrusion of the two outer layers.

22. The porous membrane according to any one of claims 16 to 18, wherein the thicker of the two outer layers contains polypropylene, is made of polypropylene, or is essentially made of polypropylene, and the thinner of the two outer layers contains polyethylene, is made of polyethylene, or is essentially made of polyethylene.

23. The porous membrane according to any one of claims 16 to 18, wherein the porous membrane is a dry process microporous membrane.

24. The porous membrane according to any one of claims 16 to 18, wherein the porous membrane is a microporous membrane produced by a dry stretching process.

25. The porous membrane according to any one of claims 16 to 18, wherein the total thickness of the porous membrane is 5 to 30 microns.

26. The porous membrane according to claim 25, wherein the thickness is 5 to 20 microns.

27. The porous membrane according to claim 25, wherein the thickness is 5 to 15 microns.

28. The porous membrane according to claim 25, wherein the thickness is 5 to 10 microns.

29. A battery separator comprising, consisting of, or essentially consisting of, a porous membrane according to any one of claims 1 to 28 or 57 to 62.

30. The aforementioned battery separator is Li / Li ＋ A battery separator according to claim 29, having an electrochemically stable voltage of 4.2 or higher relative to [the specified value].

31. The aforementioned battery separator is Li / Li ＋ A battery separator according to claim 29, having an electrochemically stable voltage of 4.5 or higher relative to [the specified value].

32. The aforementioned battery separator is Li / Li ＋ A battery separator according to claim 29, having an electrochemically stable voltage of 5.0 or higher relative to [the specified value].

33. The battery separator according to any one of claims 29 to 32, wherein the porous membrane includes a coating layer applied to the thinner of the two outer layers.

34. The battery separator according to claim 33, wherein the coating is at least one of a ceramic coating, a polymer coating, and a shutdown coating.

35. The battery separator according to claim 34, wherein the coating layer has a thickness of 1 to 5 microns.

36. A secondary battery comprising a battery separator according to any one of claims 29 to 32 between an anode and a cathode, and having a liquid electrolyte, wherein the thicker of the two outer layers of the porous membrane faces the cathode and the thinner of the two outer layers faces the anode.

37. A secondary battery comprising a battery separator according to any one of claims 33 to 35 between an anode and a cathode, wherein the coating layer faces the anode, and the battery has a liquid electrolyte.

38. A porous membrane comprising two outer layers and selectively at least one inner layer, A porous membrane comprising at least one of the following: the average pore diameter of one of the two outer layers is smaller than the average pore diameter of the other outer layer; the porosity of one of the two outer layers is lower than the porosity of the other outer layer; and the degree of flexibility of one of the two outer layers is higher than the degree of flexibility of the other outer layer.

39. The porous membrane according to claim 38, wherein the average pore diameter of one of the two outer layers is smaller than the average pore diameter of the other.

40. The porous membrane according to claim 39, wherein the average pore diameter of the smaller of the two outer layers is 0.005 to 0.5, 0.005 to 0.05, 0.025 to 0.05 microns, or 0.025 to 0.04 microns.

41. The porous material according to claim 39, wherein the average pore diameter of the smaller of the two outer layers is 1-30% smaller, 1-25% smaller, 1-20% smaller, 1-15% smaller, 1-10% smaller, or 1-5% smaller.

42. The porous membrane according to claim 38, wherein the porosity of one of the two outer layers is lower than the porosity of the other outer layer.

43. The porous membrane according to claim 42, wherein the lower porosity of one of the two outer layers is 1-30%, 1-25%, 1-20%, 1-15%, 1-10%, or 1-5%, and the lower porosity of one of the two outer layers is 5%-50%, 10%-40%, 15%-30%, or 20%-25%.

44. The porous membrane according to claim 38, wherein the degree of curvature of one of the two outer layers is higher than the degree of curvature of the other outer layer.

45. The porous membrane according to claim 44, wherein the higher degree of curvature of one of the two outer layers is greater than 1, greater than 1.1, 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.

46. A battery separator comprising, or consisting of, or essentially consisting of, a porous membrane according to any one of claims 38 to 45 or 57 to 62.

47. The aforementioned battery separator is Li / Li ＋ A battery separator according to claim 46, having an electrochemically stable voltage of 4.2 or higher relative to [the specified value].

48. The aforementioned battery separator is Li / Li ＋ A battery separator according to claim 46, having an electrochemically stable voltage of 4.5 or higher relative to [the specified value].

49. The aforementioned battery separator is Li / Li ＋ A battery separator according to claim 46, having an electrochemically stable voltage of 5.0 or higher relative to [the specified value].

50. The battery separator according to any one of claims 46 to 49, wherein the porous membrane comprises a coating layer applied to an outer layer having a smaller average pore diameter or a larger average pore diameter, a higher or lower porosity, and / or a higher or lower degree of flexibility.

51. A battery separator according to claim 50, wherein a coating layer is applied to an outer layer having a smaller average pore diameter than described above, a lower porosity than described above, and / or a higher degree of flexibility than described above.

52. The battery separator according to claim 50 or 51, wherein the coating is at least one of a ceramic coating, a polymer coating, and a shutdown coating.

53. The battery separator according to claim 45, wherein the coating layer has a thickness of 1 to 5 microns.

54. A secondary battery comprising a battery separator according to any one of claims 46 to 53 between an anode and a cathode, and having a liquid electrolyte, wherein the outer layer of the porous membrane having a smaller average pore diameter, lower porosity, and / or higher flexibility faces the anode or the cathode.

55. The secondary battery according to claim 54, wherein the outer layer of the porous membrane having a smaller average pore diameter, lower porosity, and / or higher flexibility faces the anode.

56. A secondary battery comprising a battery separator according to any one of claims 50 to 53 between an anode and a cathode, wherein the coating layer faces the anode and the battery has a liquid electrolyte.

57. The porous membrane according to claim 1 or 38, wherein the porous membrane is a multilayer porous membrane.

58. The porous membrane according to claim 57, wherein two or more layers of the porous membrane are co-extruded layers.

59. The porous membrane according to claim 57, wherein the porous membrane comprises four or more layers.

60. The porous membrane according to claim 58, wherein the porous membrane comprises four or more layers.

61. The porous membrane according to claim 1 or 38, wherein the porous membrane does not contain an inner layer.

62. The porous membrane according to claim 61, wherein one of the outer layers contains PE and the other outer layer contains PP.

63. At least one polypropylene (PP)-containing layer, At least one polyethylene (PE)-containing layer, An asymmetric porous multilayer film comprising, The asymmetric porous multilayer film wherein the ratio of the thickness of one or more PP-containing layers to one or more PE-containing layers is in the range of 1.1:1 to 25:

1.

64. The asymmetric porous multilayer film according to claim 63, wherein the ratio is in the range of 1.1:1 to 20:

1.

65. The asymmetric porous multilayer film according to claim 64, wherein the ratio is in the range of 4:1 to 10:

1.

66. The asymmetric porous multilayer film according to any one of claims 63 to 65, comprising two PP-containing layers and one PE-containing layer, wherein the layers are arranged in the order of PE / PP / PP or PE / PP blend / PP.

67. The asymmetric porous multilayer film according to claim 66, wherein the PP-containing layer contains the same or different PP-containing materials.

68. An asymmetric porous multilayer film according to any one of claims 63 to 65, wherein there are two or more PP-containing layers, and the PP-containing layers have the same or different PP-containing materials.

69. The asymmetric porous multilayer film according to any one of claims 63 to 68, wherein the PP-containing material of one or more PP-containing layers comprises a single polypropylene, a mixture of two or more different polypropylenes, a single polypropylene and an additional component, or a mixture of two or more different polypropylenes and an additional component.

70. The asymmetric porous multilayer film according to claim 69, wherein the additional component is at least one of polymers other than polypropylene, elastomers, or combinations thereof.

71. The asymmetric porous multilayer film according to claim 70, wherein the elastomer is a styrene-based elastomer.

72. The asymmetric porous multilayer film according to claim 63, wherein two or more PE-containing layers are present, and the PE-containing layers are made of the same or different PE-containing materials.

73. An asymmetric porous multilayer film having the following structure PE / PE / PP / PP / PP / PP, wherein PE is a PE-containing layer and PP is a PP-containing layer, according to claim 63.

74. An asymmetric porous multilayer film having the following structure PE / PE / PE / PP / PP / PP / PP / PP / PP / PP, wherein PE is a PE-containing layer and PP is a PP-containing layer, according to claim 63.

75. An asymmetric porous multilayer film having the following structure PE / PE / PE / PE / PP / PP / PP / PP / PP / PP / PP / PP / PP, wherein PE is a PE-containing layer and PP is a PP-containing layer, according to claim 63.

76. An asymmetric porous multilayer film having the following structure PE / PE / PE / PE / PE / PP / PP / PP / PP / PP / PP / PP / PP / PP / PP / PP, wherein PE is a PE-containing layer and PP is a PP-containing layer, according to claim 63.

77. The asymmetric porous multilayer film according to any one of claims 63 to 76, wherein the film is formed by co-extruding two or more layers.

78. The asymmetric porous multilayer film according to claim 77, wherein three or more layers are co-extruded.

79. The asymmetric porous multilayer film according to claim 66, wherein all three layers of PE / PP / PP or PE / PP blend / PP are co-extruded.

80. The asymmetric porous multilayer film according to any one of claims 63 to 79, wherein the film is a dry process film.

81. A battery separator comprising an asymmetric porous multilayer film according to any one of claims 63 to 80.

82. The battery separator according to claim 81, wherein only one of the outermost layers of the asymmetric porous multilayer film is a PE-containing layer.

83. The battery separator according to claim 82, further comprising a ceramic coating or a crosslinked coating on the outermost PE-containing layer.

84. A battery comprising an anode, a cathode, a liquid electrolyte, and a battery separator according to claim 81.

85. A battery comprising an anode, a cathode, a liquid electrolyte, and a battery separator according to claim 82 or 83, wherein the outermost layer, which is also a PE-containing layer, faces the anode or is closest to the anode.

86. A battery separator according to claim 81, comprising one or more selected from ceramic coatings and crosslinked coatings on at least one surface.

87. An asymmetric porous multilayer film comprising at least one polypropylene (PP)-containing layer and at least one polyethylene (PE)-containing layer, wherein the ratio of the thickness of one or more PE-containing layers to one or more PP-containing layers is in the range of 1.1:1 to 25:

1.

88. The asymmetric porous multilayer film according to claim 87, wherein the ratio of the plurality of PE-containing layers to the plurality of PP-containing layers is in the range of 1.1:1 to 20:

1.

89. The asymmetric porous multilayer film according to claim 88, wherein the ratio of the plurality of PE-containing layers to the plurality of PP-containing layers is in the range of 4:1 to 10:1.

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