Asymmetric porous membrane

Abstract

The proposed porous membrane (multiple options) asymmetric porous multilayer membrane (multiple options) comprises two outer layers and optionally at least one inner layer. The outer layers can be asymmetric in thickness, pore size, porosity, tortuosity, or a combination thereof. The thickness ratio of one outer layer to the other is 1.1 to 25:1. In some embodiments, both outer layers are PP-containing layers; in some embodiments, one outermost layer can be a PE-containing layer, while the other can be a PP-containing layer. Also proposed are battery separators (multiple options), one option of which comprises or consists of a porous membrane, or comprises or consists of an asymmetric multilayer membrane. Also proposed are batteries (multiple variants) comprising an anode, a cathode, a liquid electrolyte, and a battery separator. The battery separators described herein can have an electrochemical stability voltage equal to or higher than 4.2 v. s. Li / Li + ​

Description

[0001] field

[0002] This application focuses on improved porous membranes, and battery separators and liquid electrolyte secondary lithium-ion batteries incorporating such membranes. In particular, the improved porous membranes disclosed herein can be used to form thinner and safer battery separators and batteries.

[0003] background

[0004] The electric vehicle (EV or HEV) industry is highly focused on increasing the energy density of lithium-ion batteries while maintaining safety and lifespan.

[0005] One advancement in improving safety is the use of closure septa. For example, a three-layer closure septa is described in U.S. Patent No. 5,952,120 (incorporated herein by reference in its entirety). These closure septa typically have structures such as PP / PE / PP, PP / PE / PE / PP, PP / PE / PE / PE / PP, etc., where all layers have the same or substantially the same thickness. This symmetry is preferred because, for example, asymmetry in the septa can lead to curling or other problems. Generally, closure septa improve safety at high temperatures by stopping ion transport and current flow across the septa. The lower-melting-point PE layer melts before the PP layer; the molten PE fills the pores of the septa, thereby impeding ion transport.

[0006] It is generally believed that thinner separators allow for higher energy density batteries—more cell cells can be contained within a single cell of roughly the same weight and thickness. Therefore, a promising approach to achieving high energy density without sacrificing safety appears to be to manufacture thin and ultra-thin separators, such as three-layer separators, by reducing the overall weight and thickness of the three-layer separator. However, simply symmetrically reducing the overall thickness to manufacture ultra-thin or thin separators, such as three-layer separators, still presents application challenges. For example, when used in liquid electrolyte lithium secondary batteries, the rough surface of the positive electrode can easily break and penetrate the PP outer layer. Furthermore, under high voltage, electrons readily oxidize the PE layer, initiating side reactions and generating gas. In such cases, both energy density and safety are reduced. Therefore, there is a need to increase the oxidation resistance of the inner PE layer in thin and ultra-thin separators (e.g., three-layer separators or other separator structures).

[0007] Overview

[0008] On one hand, this document describes a porous membrane comprising two outer layers and at least one inner layer. In some preferred embodiments, the thickness ratio of one of the two outer layers to the other can be 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 can be 5 to 30 micrometers, 5 to 20 micrometers, 5 to 15 micrometers, or 5 to 10 micrometers.

[0009] In some embodiments, the porous membrane may be a microporous membrane. In some embodiments, the porous membrane may be a dry-processed microporous membrane or a microporous membrane produced by a dry stretching process.

[0010] In some embodiments, the porous membrane may comprise 1 to 10 inner layers. In some embodiments, the porous membrane may comprise only one inner layer, making the porous membrane a three-layer membrane.

[0011] In some embodiments, the two outer layers may comprise, be made of, or be substantially composed of polypropylene. At least one of the inner layers may comprise, be made of, or be substantially composed of polyethylene. In some embodiments, the porous membrane may have a PP / PE / PP three-layer structure, wherein "PP" is a polypropylene-containing layer and "PE" is a polyethylene-containing layer.

[0012] In some embodiments, a porous membrane can be formed by a method comprising laminating at least one outer layer with at least one inner layer. In some embodiments, a porous membrane can be formed by a method comprising co-extruding at least one outer layer with at least one inner layer.

[0013] On the other hand, this document describes a porous membrane comprising two outer layers, one layer being thicker than the other. The thickness ratio can range from 1:1.1 to 4:1. The total thickness of the membrane can be 5 to 30 micrometers, 5 to 20 micrometers, 5 to 15 micrometers, or 5 to 10 micrometers. In some preferred embodiments, the total thickness of the membrane can be 8 to 12 micrometers. In some preferred embodiments, calendering can be performed to obtain thinner or thinner separators having a thickness of, for example, 5 to 12 micrometers. In some embodiments, calendering is not necessary for forming thinner or thinner separators. Calendering can also reduce the pore size.

[0014] In some embodiments, the porous membrane may be a microporous membrane. In some embodiments, the porous membrane may be a dry-processed microporous membrane or a microporous membrane produced by a dry stretching process.

[0015] In some preferred embodiments, the thicker layer may comprise, be made of or substantially composed of polypropylene, while the thinner layer may comprise, be made of or substantially composed of polyethylene.

[0016] In some embodiments, the porous membrane can be formed by a method comprising a step of co-extruding two layers—a thinner layer and a thicker layer. In some embodiments, the porous membrane can be formed by a method comprising a step of laminating one of the two layers to the other. Preferably, the battery separator has a Li / Li ratio greater than or equal to 4.2. + 4.5 vsLi / Li +Or equal to or greater than 5.0 vsLi / Li + The electrochemically stable voltage is determined. Typically, these results are derived from cyclic voltammetry. In a typical process, two blocking electrodes are used; Pt is used as the cathode, and Li metal as the anode. A separator is placed between the electrodes in a sandwich structure, with the electrolyte in between. Voltage scans are performed using voltages from 0 to 5 volts. Current varies with voltage. Peaks in the current-voltage plot indicate the presence of side reactions.

[0017] In some embodiments, the separator comprises any of the porous membranes described herein, having a coating on a thinner outer layer or one of two layers. In some embodiments, the coating is selected from at least one of ceramic coatings, polymer coatings, shut-off coatings, crosslinked coatings, or combinations thereof. In some embodiments, the coating has a thickness of 1 to 5 micrometers.

[0018] On the other hand, a secondary battery is disclosed, comprising, or substantially comprising, the following: an anode, a cathode, a liquid electrolyte, and any battery separator described herein between the anode and cathode. In a preferred embodiment, the thicker of the two outer layers of the porous membrane faces the cathode. The thinner, coated or uncoated outer layer faces the anode.

[0019] On the other hand, a porous membrane comprising two outer layers and at least one inner layer is described. One of the outer layers has a smaller average pore size, lower porosity, and / or higher tortuosity than the other.

[0020] On the other hand, a battery separator is also described, comprising, or substantially composed of, a porous membrane with an outer layer having a different average pore size. In some embodiments, the separator has a Li / Li ratio equal to or greater than 4.2 vs. + The electrochemically stable voltage. In some embodiments, the electrochemically stable voltage is equal to or greater than 4.5 vsLi / Li + Or equal to or greater than 5.0 vsLi / Li + .

[0021] In some embodiments, the battery separator has a coating applied to an outer layer having a smaller average pore size, lower porosity, and / or higher tortuosity. The coating can be at least one of the following: a ceramic coating, a polymer coating, and a shut-off coating. The coating can have a thickness of 1 to 5 micrometers.

[0022] In another aspect, a secondary battery is described. This secondary battery may include an anode, a cathode, a liquid electrolyte, and a battery separator between the anode and cathode. The separator includes a porous membrane having an outer layer with different average pore sizes as described herein. In some embodiments, the outer layer having a smaller average pore size, lower porosity, and / or higher 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 size, lower porosity, and / or higher tortuosity, this coating may face the anode.

[0023] In another aspect, an asymmetric porous multilayer membrane is described, comprising at least one polypropylene (PP) layer and at least one polyethylene (PE) layer. The thickness ratio of the PP layer to the PE layer is from 1.1:1 to 25:1, 1.1:1 to 20:1, or 4:1 to 10:1.

[0024] In a potentially preferred embodiment, the membrane may comprise, be composed of, or substantially comprise essentially the following: two PP-containing layers and one PE-containing layer, wherein these layers are arranged in the order PE / PP / PP. In some embodiments, the membrane may comprise, be composed of, or substantially comprise at least one of the following structures: 73.

[0025] PE / PE / PP / PP / PP / PP, where PE is a layer containing PE and PP is a layer containing PP;

[0026] PE / PE / PE / PP / PP / PP / PP / PP / PP, where PE is a layer containing PE and PP is a layer containing PP;

[0027] PE / PE / PE / PE / PP / PP / PP / PP / PP / PP / PP / PP, where PE is a layer containing PE, and PP is a layer containing PP; or

[0028] PE / PE / PE / PE / PE / PP / PP / PP / PP / PP / PP / PP / PP / PP, where PE is a layer containing PE and PP is a layer containing PP.

[0029] In embodiments comprising two or more PP-containing layers, these layers may comprise the same or different PP-containing materials, or be composed of, or substantially composed of, the same or different PP-containing materials. The PP-containing materials may comprise, or be composed of, the following: a single polypropylene, a mixture of two or more different polypropylenes, a single polypropylene and other components, or a mixture of two or more different polypropylenes and other components. In some embodiments, the other component may be an elastomer. This elastomer may be a styrene elastomer.

[0030] In embodiments that include two or more PE-containing layers, the PE-containing layers may contain the same or different PE-containing materials, or be composed of or substantially composed of the same or different PE-containing materials.

[0031] In a potentially preferred embodiment, a multilayer film is formed by co-extruding two or more, or three or more, layers; however, the film can also be formed by laminating these 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 can all be laminated. For lamination, the laminated layers can be a combination of multiple layers formed by different processes (e.g., wet processes, dry processes, etc.) or a combination of multiple layers formed by the same process. For example, a wet-process PE layer can be laminated onto two PP layers formed by a dry process.

[0032] In some preferred embodiments, the multilayer membrane can be a dry-process multilayer membrane. It can also be formed using wet processes, β-nucleation processes, etc.

[0033] On the other hand, a battery separator comprising the aforementioned asymmetric porous multilayer membrane, or composed of or substantially composed of the aforementioned asymmetric porous multilayer membrane, is described. In some embodiments, the battery separator comprises a membrane wherein only one of the outermost layers of the asymmetric porous multilayer membrane is a PE-containing layer. In some embodiments, the battery separator may comprise a coating on either side of the asymmetric porous multilayer membrane described herein. The coating may be any one of a ceramic coating, a shut-off coating, an adhesive coating, a polymer coating, or a combination thereof.

[0034] On the other hand, a battery incorporating the battery separator described herein is described. The battery may comprise, or be substantially comprised of, the following: an anode, a cathode, a liquid electrolyte, and an asymmetric multilayer porous membrane. In some embodiments, the outermost PE-containing layer of the separator may face the anode.

[0035] In another aspect, an asymmetric porous multilayer membrane is described, comprising at least one polypropylene (PP) layer and at least one polyethylene (PE) layer. The thickness ratio of the PE-containing layer to the PP-containing layer is 1.1:1 to 25:1, 1.1:1 to 20:1, or 4:1 to 10:1. Furthermore, this membrane may also be similar in detail to the membrane described above, wherein the amount of PP is larger, and the PP-containing layer in this membrane becomes a PE-containing layer, and the PE-containing layer becomes a PP-containing layer. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of an exemplary membrane described herein.

[0037] Figure 2A and Figure 2BThese are all FESM images of the exemplary membranes described in this article.

[0038] Figure 3 This is a schematic diagram illustrating the difference between film thickness and pore length. The curvature is derived from these two measurements.

[0039] Figure 4A , Figure 4B , Figure 4C , Figure 4D , Figure 4E and Figure 4F This is a schematic diagram of an exemplary embodiment described herein.

[0040] Figure 5A and Figure 5B This is a schematic diagram of an exemplary embodiment described herein.

[0041] Figure 6A , Figure 6B and Figure 6C This is a schematic diagram of an exemplary embodiment described herein.

[0042] Figure 7 The aperture distribution of the exemplary embodiments described herein is shown.

[0043] Detailed description

[0044] Asymmetric porous membranes

[0045] This document describes asymmetric porous membranes. Asymmetric porous membranes may comprise two outer layers and optionally at least one inner layer, and may be composed of or substantially composed 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 be composed of or substantially composed of two outer layers without any inner layers. The thickness ratio of one of the two outer layers to the other 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 to 30 micrometers, 2 to 25 micrometers, 2 to 20 micrometers, 2 to 15 micrometers, or 2 to 10 micrometers. In some embodiments, the total thickness of the porous membrane may be 3 to 12 micrometers, 4 to 12 micrometers, 5 to 12 micrometers, or 9 to 12 micrometers. In some embodiments, at least one of the outer layers has a thickness of 2 to 6 micrometers or 4 to 5 micrometers. In some embodiments, when the asymmetric porous membrane is used in a battery, the outer layer having a thickness of 2 to 6 micrometers or 4 to 5 micrometers is positioned facing the cathode.

[0046] In some embodiments, the outer layers may have different average pore sizes, different porosities, and / or different tortuosities, with one outer layer having a larger average pore size, higher porosity, and / or higher tortuosity, and the other having a smaller average pore size, lower porosity, and / or lower tortuosity. In some embodiments, the pore size, porosity, and / or tortuosity, as well as the thickness, of the two outer layers may all be different. In some embodiments, only the thickness of the outer layers or only the pore size, porosity, and / or tortuosity may be different.

[0047] In some embodiments, the asymmetric porous membrane can be macroporous, nanoporous, or microporous. In some preferred embodiments, the asymmetric porous membrane can be a microporous membrane. For example, the pores of the porous membrane can have an average pore size of 0.01 to 1.0 micrometers. In some preferred embodiments, the average pore size can be 0.1 to 1.0 micrometers, 0.1 to 0.9 micrometers, 0.1 to 0.8 micrometers, 0.1 to 0.7 micrometers, 0.1 to 0.6 micrometers, 0.1 to 0.5 micrometers, 0.1 to 0.4 micrometers, 0.1 to 0.3 micrometers, or 0.1 to 0.2 micrometers. The pores of the porous membrane can have any shape. For example, they can be slit-shaped, circular, substantially circular, or asymmetric.

[0048] In some preferred embodiments, the asymmetric porous membrane may be a dry-process asymmetric porous membrane. In some embodiments, the dry process is a process that does not use any pore-forming reagents / agents or β-nucleating reagents / agents. In some embodiments, the dry process is a process that does not use any solvents, waxes, or oils. In some embodiments, the dry process is a process that does not use any pore-forming reagents / agents or β-nucleating reagents / agents, and also does not use any solvents, waxes, or oils.

[0049] Dry-process asymmetric porous membranes can be formed using a dry stretching process. (In Chen et al.) Structural characterization of microporous membrane precursors: Melt-extruded polyethylene films (J. of Applied Polymer Sci., vol. 53, 471-483 (1994, the full text of which is incorporated herein by reference) describes what is known as microporous membrane precursors. An exemplary dry stretching process. Dry stretching is a process in which a non-pore-oriented precursor is stretched at least in the processing direction to form a hole. Kesting and Robert E.'s *Synthetic Polymeric Membranes, A Structural Perspective* (Second Edition, John Wiley & Sons, New York, NY, (1985), pp. 290-297, the entire text of which is incorporated herein by reference) also discloses a dry stretching process. In a dry stretching process according to some preferred embodiments, the process may include a stretching step. The stretching step may consist of, or substantially consist of, the following: uniaxial stretching (e.g., stretching only in the MD direction or only in the TD direction), biaxial stretching (e.g., stretching in both 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 consist of an extrusion step and a stretching step, or substantially consist of an extrusion step and a stretching step, performed in this order or not. In some embodiments, the dry stretching process may comprise an extrusion step, an annealing step, and a stretching step, consisting of or substantially consisting of extrusion, annealing, and stretching steps, performed in this order or not. In some embodiments, the extrusion step may be a blown film extrusion step 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 can be formed by methods other than extrusion, such as by sintering or printing, and the precursor can be stretched to form pores or to enlarge existing pores.

[0050] In some embodiments, pore-forming agents / particles or β-nucleating agents / particles can be used, and the process is still considered a dry process. For example, a particle stretching process can be considered a dry process because the oil or solvent is not extruded with the polymer and extracted from the extruded polymer to form pores. In a particle stretching process, particles such as silica or calcium carbonate are added to the polymer mixture, and these particles contribute to pore formation. In such methods, for example, a polymer mixture containing particles and polymer is extruded to form a precursor, which is stretched and creates voids around the particles. In some embodiments, the particles can be removed after void formation. Although a particle stretching process may include a stretching step before or after particle removal, a particle stretching process is not considered a dry stretching process because the primary pore-forming mechanism is the use of particles rather than stretching.

[0051] In some preferred embodiments, the structure of dry-process porous membranes can have one or more distinctive features. For example, dry-process membranes can contain more than 10% polypropylene. Wet processes or other processes using solvents are generally incompatible with polypropylene because the solvents degrade the polypropylene. Therefore, wet-process porous membranes typically contain no more than 10% polypropylene, most typically 5% or less. Another distinctive feature of some dry-process porous membranes (particularly those used as battery separators) is their ability to shut off. In some cases, this shut-off function can be imparted by a PP / PE / PP structure, where the PE layer is the shut-off layer. This is unique to dry-process membranes because layers primarily composed of polypropylene (PP) cannot typically be formed in wet processes. Dry processes are particularly suitable for forming PP / PE / PP or other shut-off membrane structures.

[0052] In some implementations, the presence of sheets and fibrils can distinguish the porous membrane from the dry process. For example, the porous membrane can have a similar structure to... Figure 2A and 2B of Figure 1 The structure shown. Figure 2A and 2B This is a FESM image showing PE(A) and PP(B). The slit-like micropores in the microporous membrane. In some embodiments, the pores or micropores of the dry process porous membrane can be circular, elliptical, semi-circular, trapezoidal, etc.

[0053] In some embodiments, a significant feature of dry-process porous membranes is that they contain no or are substantially free of pinholes. Pinholes are considered a defect and are generally not a characteristic intentionally formed in dry-process porous membranes. In some embodiments, dry-process microporous membranes may contain no or are substantially free of pinholes larger than 10 nm. In some preferred embodiments, the pores of the dry-process porous membrane are tortuous. In some embodiments, a significant feature of dry-process porous membranes is their tortuosity. In some embodiments, the tortuosity of the 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, the formula used to roughly calculate the tortuosity is formula (1):

[0054] Curvature = x / t (1)

[0055] Where "x" represents the length of the opening or pore in the porous membrane, and "t" represents the membrane thickness. The tortuosity of a pinhole is 1 because the length of the pinhole is the same as the membrane thickness. For example... Figure 3 As shown, the curvature of the curved hole is greater than 1 because the length of the hole is longer than the thickness of the membrane.

[0056] 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 thin films formed by wet processes, such as those formed by β-nucleation processes, may be randomly oriented.

[0057] In some embodiments, an asymmetric porous membrane can be formed by laminating at least one outer layer with at least one inner layer. In embodiments that do not include an inner layer, an asymmetric porous membrane can 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 can be formed by extruding at least one of the outer layers and at least one of the inner layers separately, or by extruding two outer layers separately. Then, one of the outer layers can be laminated with another outer layer or one of the inner layers before or after the stretching step.

[0058] In some embodiments, an asymmetric porous membrane can be formed by co-extruding at least one of the outer layers with at least one of the inner layers. In embodiments without an inner layer, an asymmetric porous membrane can be formed by co-extruding two outer layers. For example, if the asymmetric membrane is formed by a dry process such as a dry stretching process, the two outer layers can be co-extruded together, and the non-porous co-extruded material can be stretched to form pores. In another example, if a dry process, such as a dry stretching process, is used to form the asymmetric porous membrane, at least one of the outer layers is co-extruded with at least one of the inner layers, and then the non-porous co-extruded material can be laminated with an inner layer or another outer layer. Lamination can be performed before or after stretching that can be used to form pores.

[0059] In some embodiments, the outer layer of the asymmetric membrane may comprise polyethylene, be composed of, or be substantially composed of polyethylene. In some embodiments, at least one of the inner layers may comprise polyethylene, be composed of, or be substantially composed of polyethylene. For example, in some embodiments, the asymmetric membrane may be a membrane having the following structures: PP / PE, PP / PE / PP, PP / PE / PE / PP, PP / PE / PE / PE / PP, PP / PE / PE / PE / PE / PE / PP, PP / PE / PE / PE / PE / PE / PE / PP, PP / PE / PE / PE / PE / PE / PE / PE / PP, PP / PE / PE / PE / PE / PE / PE / PE / PE / PP, PP / PE / PE / PE / PE / PE / PE / PE / PE / PE / PP, PP / PE / PE / PE / PE / PE / PE / PE / PE / PE / PE / PP, PP / PE / PE / PE / PE / PE / PE / PE / PE / PE / PE / PE / PP, PE / PP / PP PE / PE / PP / PP / PP / PP, PE / PE / PP / PP / PP / PP / PP / PP, PE / PE / PE / PP / PP / PP / PP / PP / PP / PP / PP / PP / PP, PE / PE / PE / PE / PE / PE / PP / PP / PP / PP / PP / PP / PP / PP / PP / PP / PP, PE / PP / PP / PP, PE / PP / PP / PP / PP / PP, PE / PP / PP / PP / PP / PP / PP, PE / PE / PP / PP / PP / PP / PP. In embodiments where the asymmetric film comprises two outer layers and no inner layer, at least one of the outer layers may comprise polypropylene, or be composed of or substantially composed of polypropylene, while the other may comprise polyethylene, or be composed of or substantially composed of polyethylene. In a preferred embodiment, the thicker of the two outer layers may comprise polypropylene, or be composed of or substantially composed of polypropylene. In a preferred embodiment, the thinner of the two outer layers, when no inner layer is provided, may comprise polyethylene, or be composed of or substantially composed of polyethylene.

[0060] In some embodiments, the asymmetric multilayer porous membrane may comprise at least one polypropylene (PP) layer and at least one polyethylene (PE) layer, wherein the thickness ratio of the PP layer to the PE layer 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, a PE / PP / PP structure may have a 1-micrometer-thick PE layer (PE) and two 3.5-micrometer-thick PP layers (PP), with a thickness ratio of 7:1.

[0061] In a potentially preferred embodiment, the membrane may comprise, be composed of, or substantially comprise: two PP-containing layers and one PE-containing layer, wherein these layers are arranged in a PE / PP / PP order. In some embodiments, the membrane may comprise, be composed of, or substantially comprise any of the following structures:

[0062] PE / PE / PP / PP / PP / PP, where PE is a layer containing PE and PP is a layer containing PP;

[0063] PE / PE / PE / PP / PP / PP / PP / PP / PP, where PE is a layer containing PE and PP is a layer containing PP;

[0064] PE / PE / PE / PE / PP / PP / PP / PP / PP / PP / PP / PP, where PE is a layer containing PE, and PP is a layer containing PP; or

[0065] PE / PE / PE / PE / PE / PP / PP / PP / PP / PP / PP / PP / PP / PP, where PE is a layer containing PE and PP is a layer containing PP.

[0066] The structure can also be PE / PP / PP / PP, PE / PP / PP / PP / PP, PE / PP / PP / PP / PP / PP, etc.

[0067] 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 the same or different PP-containing materials, or be composed of or substantially composed of the same or different PP-containing materials. The PP-containing material may contain at least 50% polypropylene, or be composed of or substantially composed 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, be composed of, or substantially composed of: homopolymers, copolymers, or terpolymers of a single PP, or blends of homopolymers, copolymers, or terpolymers of two or more different PPs, or combinations thereof. In some embodiments, the PP-containing material may comprise, be composed of, or substantially comprise of: homopolymers, copolymers, or terpolymers of single PP molecules, or blends of two or more homopolymers, copolymers, or terpolymers of PP with other components. Other components may be any of other polymers, elastomers, or combinations thereof. Elastomers may be added to, for example, increase strength. The elastomer, for example, may be a styrene elastomer.

[0068] In some embodiments where the membrane comprises two or more PE-containing layers, the PE-containing layers may comprise the same or different PE-containing materials. The PE-containing material may comprise at least 50% polyethylene, or be composed of or substantially composed of at least 50% polyethylene. Some may contain 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, or be composed of or substantially composed of: homopolymers, copolymers, or terpolymers of a single PE, or blends of two or more homopolymers, copolymers, or terpolymers of different PEs, or combinations thereof. In some embodiments, the PE-containing material may comprise, or be composed of: homopolymers, copolymers, or terpolymers of a single PE, or blends of two or more homopolymers, copolymers, or terpolymers of different PEs, and other components. Other components may be any of other polymers, elastomers, and the like, or combinations thereof. Elastomers can be added to, for example, increase strength. The elastomer, for example, can be a styrene elastomer.

[0069] In some implementations, two or more, or three or more, layers can be co-extruded. For example, for a PE / PP / PP structure, all three layers can be co-extruded, or two layers can be co-extruded and the third layer can be laminated onto the two co-extruded layers. As another example, in a PE / PE / PE / PP / PP / PP / PP / PP / PP structure, three PE layers (PE / PE / PE) can be co-extruded, and two sets of three PP layers (PP / PP / PP) can be co-extruded separately. Then, the PE co-extruded material can be laminated with the two sets of PP co-extruded layers 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) can be formed. (PP / PP / PP / PP) and (PE / PE / PP / PP) represent co-extrusion structures, and " / " indicates the lamination interface. In some embodiments, all layers can be laminated together. For example, for a PE / PP / PP structure, the PE layer can be laminated with two other PP layers. Co-extrusion of layers may be superior to lamination because it allows the formation of thinner layers without the film handling problems that occur when laminating films smaller than 10 micrometers, especially smaller than 5 micrometers, and particularly smaller than 1 micrometer.

[0070] In some preferred embodiments, the multilayer asymmetric porous membrane can be a dry process membrane as described above.

[0071] In some embodiments, the asymmetric porous membrane can be macroporous, nanoporous, or microporous. In some preferred embodiments, the asymmetric porous membrane can be a microporous membrane. For example, the pores of the porous membrane can have an average pore size of 0.01 to 1.0 micrometers. In some preferred embodiments, the average pore size can be 0.1 to 1.0 micrometers, 0.1 to 0.9 micrometers, 0.1 to 0.8 micrometers, 0.1 to 0.7 micrometers, 0.1 to 0.6 micrometers, 0.1 to 0.5 micrometers, 0.1 to 0.5 micrometers, 0.1 to 0.4 micrometers, 0.1 to 0.3 micrometers, or 0.1 to 0.2 micrometers. The pores of the porous membrane can have any shape. For example, they can be slit-shaped, circular, substantially circular, or asymmetric.

[0072] Battery separator

[0073] There are few limitations on the battery separator described herein. In a preferred embodiment, the battery separator may comprise at least one of the asymmetric porous membranes described herein, or be composed of or substantially composed 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.

[0074] Preferably, the battery separator has a Li / Li ratio greater than or equal to 4.2. + 4.5 vsLi / Li + Or equal to or greater than 5.0 vsLi / Li + The electrochemically stable voltage.

[0075] In some preferred embodiments, this separator is configured to provide superior oxidation resistance compared to typical double, triple, or multi-layer separators (where all layers, including the outermost layer, have the same or substantially the same thickness). A typical triple separator—PP / PE / PP—where each layer has the same thickness, may readily oxidize the PE layer from the side of the separator closest to the cathode. Typical double separators—PP / PE, PP / PP / PE, etc.—may also readily oxidize the PE layer from the side of the separator closest to the cathode. Typical multilayer separators, such as those described in US2018 / 0323417 (the entire contents of which are incorporated herein by reference), may have structures such as (PP / PP / PP) / (PE / PE / PE) / (PP / PP / PP) or (PP / PP) / (PE / PE) / (PP / PP), where (PP / PP / PP) or (PP / PP) represents 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 invention described herein, by providing a thicker polypropylene outer layer (or, for example, a thicker co-extruded two-layer, three-layer, etc., when forming a multilayer embodiment), and by placing this layer closest to the cathode, the separators described herein exhibit better oxidation resistance compared to typical three-layer, two-layer, or multilayer separators (where all layers have the same or substantially the same thickness). In embodiments where one outermost layer is PE and the other is PP, the PP layer may face or be closest to the cathode to provide oxidation resistance. In embodiments with an inner layer, the outermost layer can be thinner because oxidation resistance is primarily required on the cathode-facing side, and because a thinner separator is preferred. In embodiments without an inner layer, the outer layer can be a thin polyethylene layer. The polyethylene layer can provide a shut-off function. In this case, the polyethylene layer should be thick enough to provide this function.

[0076] In some embodiments, the separator described herein may comprise at least one asymmetric porous membrane as described herein, or be composed of or substantially composed of at least one asymmetric porous membrane as described herein, wherein the thinner of the two outer layers of the asymmetric porous membrane is configured to be 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 inorganic or organic heat-resistant or ceramic particles and a binder, or be composed of or substantially composed of inorganic or organic heat-resistant or ceramic particles and a binder. For example, the ceramic coating may be one as described in US 6,432,586 (which is incorporated herein by reference in its entirety). Among other functions, the ceramic coating also helps to prevent, inhibit, or slow the growth of lithium dendrites, which typically grow from the anode to the cathode in a 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 shut-off coating. In some embodiments, the thicker of the two outer layers may also be coated.

[0077] Battery

[0078] The battery described herein is a liquid electrolyte battery or battery cell, or an electrochemical device such as a capacitor or supercapacitor. In some embodiments, the battery may include a battery separator as described herein between the anode and cathode. In a preferred embodiment, the battery separator comprises at least one asymmetric porous membrane as described herein, with the thicker outermost layer of the porous membrane facing the cathode. In a preferred embodiment, the thinner layers of the two outermost layers face the anode. When the battery separator described herein is coated, the coating faces the anode to prevent lithium dendrite formation.

[0079] A suitable anode may have an energy capacity greater than or equal to 372 mAh / g, preferably ≥700 mAh / g, more preferably ≥3860 mAh / g, and even more preferably ≥4200 mAh / g. The anode is composed of lithium metal foil or lithium alloy foil (e.g., lithium-aluminum alloy) or graphite, graphene, carbon nanotubes, and silicon (Si) or Li. The anode is not necessarily made solely of lithium-containing intercalation or lithium-containing insertion compounds.

[0080] A suitable cathode can be any cathode compatible with the anode and can contain intercalation compounds, insertion compounds, or electrochemically inert binders. Suitable intercalation materials include, for example, LiCoO2, LiNiO2, and LiNi. 0.8 Co 0.2 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiMn 0.5 Ni 0.5O2, LiMn 1 / 3 Ni 1 / 3 Co 1 / 3 O2, LiMn 0.4 Ni 0.4 CO 0.2 O2, LiFePO4, LiMn2O4. Suitable polymers include, for example, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), poly(vinylidene fluoride) (PVDF), polyimide (PI) and acrylates (polyacetylene, polypyrrole, polyaniline and polythiophene).

[0081] The nominal voltage of the battery described in this article may be equal to or higher than 4.0V / cell, equal to or higher than 4.2V / cell, equal to or higher than 4.5V / cell, equal to or higher than 5.0V / cell, or equal to or higher than 5.5V / cell.

[0082] Any battery separator described above can be incorporated into any vehicle (e.g., an electric vehicle) or device (e.g., a cell phone or laptop) that is fully or partially powered by a battery.

[0083] Various embodiments of the invention have been described to achieve its various objectives. It should be understood that these embodiments are merely illustrative of the principles of the invention. Many variations and modifications will be apparent to those skilled in the art without departing from the spirit and scope of the invention.

[0084] Figure 4A , 4B Figures 4C, 4D, 4E, and 4F schematically illustrate some arrangements of the battery cells as disclosed herein.

[0085] Figure 5A and 5B Some arrangements of battery cells according to other embodiments disclosed herein are schematically illustrated. These figures schematically show outer layers with different pore sizes, porosities, and / or curvatures.

[0086] Table 1 below discloses some non-limiting embodiments:

[0087] Table 1

[0088]

[0089]

[0090]

[0091] *Multilayer implementations are 6- or 9-layer structures formed by bonding co-extruded PP and PE in two or three layers. Structures with 12, 15, 18, or 21 layers can also be formed.

[0092] A total of 140 embodiments, from Examples 1 to 70, were prepared by coating or not coating a ceramic coating on the thinner of the two outer layers of the membrane or on the side facing the anode. Alternatively, the ceramic can be formed on the thicker of the two outer layers or on both outer layers.

[0093] Examples 1 to 70 are also prepared in such a way that the thinner outer layer has a smaller pore size, lower porosity, and / or higher tortuosity than the thicker outer layer. In some embodiments, these features can be formed by: forming a PP layer with a smaller pore size, lower porosity, and / or higher tortuosity; or forming multiple PP layers, one of which has a smaller pore size, lower porosity, and / or higher tortuosity, and another has a larger pore size, higher porosity, and / or lower tortuosity, and laminating one or more PP layers with a PE layer to form the structure in the table above.

[0094] Examples 71 to 75 describe preparations of structures 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), wherein each layer has the same thickness, but one of the outer layers has a smaller pore size, lower porosity, and / or higher tortuosity than the other. For example, in a PP / PE structure, the PP layer has a smaller average pore size, lower porosity, and / or higher tortuosity than the PE layer. Similarly, for example, 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 bilayers or ternary layers may have a smaller average pore size, lower porosity, and / or higher tortuosity than the other outermost PP layer or co-extruded PP bilayer or ternary layer. In some implementations, the thickness of the outermost PP layer or the co-extruded PP three-layer or two-layer layer may also be different.

[0095] Regarding the two-layer membrane, it was found that the thicker polypropylene layer provides oxidation resistance, while the polyethylene layer provides shut-off capability. A second polypropylene layer is not necessary (although it may be present in some embodiments), thus allowing for a thinner separator without it. It was also found that providing smaller pore sizes, lower porosity, and / or higher tortuosity in the polypropylene layer can help prevent dendrite formation when the layer with smaller pore size, lower porosity, and / or higher tortuosity is positioned facing the anode in the battery. Applying a coating to this layer with smaller pore size, lower porosity, and / or higher tortuosity may be even better in delaying or stopping lithium dendrite growth. Lithium dendrite growth can cause short circuits in the battery, therefore batteries where its growth can be delayed or prevented are safer.

[0096] Regarding three-, four-, and five-layer implementations, a thicker polypropylene layer provides oxidation resistance to the side of the membrane placed closest to the cathode in the secondary battery cell. A thinner polypropylene layer can be used on the other side, where oxidation resistance is less critical, thus forming a thinner separator. A ceramic coating can be applied to the thinner of the two outer layers, configured closest to the anode, where oxidation resistance is less of an issue. The ceramic coating helps prevent, inhibit, or slow the growth of lithium dendrites from the anode to the cathode, which can lead to short circuits and / or thermal runaway. Alternatively, a polypropylene layer with a smaller average pore size can be used on the side where oxidation resistance is less critical, thus forming a thinner separator. A ceramic coating can be applied to the outer layer with a larger average pore size, configured closest to the anode, where oxidation resistance is less of an issue. The ceramic coating helps prevent, inhibit, or slow the growth of lithium dendrites from the anode to the cathode, which can lead to short circuits and / or thermal runaway.

[0097] In other embodiments, an asymmetric structure is formed with a thin PE-containing outer layer. Generally, providing a PE-containing layer as the outermost layer is not preferred because such a layer may oxidize within the battery cell, and adding a PE-containing layer may reduce the heat resistance of the separator, as PE melts at a lower temperature compared to PP. However, PE-containing layers do exhibit improved / reduced needle removal forces compared to PP-containing layers. Reduced needle removal forces are a particularly desirable characteristic if the membrane is used as a battery separator in a cylindrical battery. The applicant has provided a thin PE-containing outer layer to provide reduced needle removal forces while maintaining the heat resistance of the battery separator. Only one layer in the outermost layer is a PE-containing layer, and preferably, this layer faces or is closest to the anode in the battery cell, because if it faces the cathode, it will oxidize unless a coating (such as a ceramic coating) is provided on the PE-containing layer to protect it. Providing a ceramic coating on the PE-containing layer may defeat the purpose of providing the layer to reduce needle removal forces on the surface. If shut-off performance is required, a thicker PE-containing layer can be provided. Examples that include a PE outer layer are Examples 76 to 114 in Table 2 below.

[0098] Table 2

[0099]

[0100]

[0101] Examples 76-88 are formed by co-extruding three layers, but they can also be formed by laminating them. Examples 89-101 are formed by co-extruding individual (PP / PP / PP) and (PE / PE / PE) composites, and then laminating two (PP / PP / PP) composites with one (PE / PE / PE) composite to form the final structure. Examples 102-114 are formed by co-extruding individual (PE / PP / PP) and (PP / PP / PP) composites, and then laminating two (PP / PP / PP) composites with one (PE / PP / PP) composite to form the final structure. Alternatively, (PE / PE / PP) can be used instead of (PE / PP / PP) to form a (PE / PE / PP) / (PP / PP / PP) / (PP / PP / PP) structure. The composites can be stretched before or after lamination. Figure 6A , 6BExamples 6C and 6C show a battery cell comprising a membrane according to some embodiments described above. In some preferred embodiments, the co-extruded PE / PP / PP structure and the intermediate PP layer, as in any of Examples 76-88, are formed from a polypropylene blend comprising polypropylene and at least one other polymer. For example, a styrene elastomer can be used as the other polymer. In these embodiments, the PE layer is composed of polyethylene, and in these embodiments, the outer PP layer is composed of polypropylene. In any of Embodiments 76 to 114, a coating may be provided on one or both sides of the resulting structure. For example, a ceramic coating may be formed on the anode-facing side. In other embodiments, a crosslinked coating may be formed on either or both of the anode-facing side and the cathode-facing side.

[0102] Table 3 below shows the advantages of co-extruded PE / PP blend / PP structures compared to co-extruded PE / PP / PP structures without blends, wherein the blends contain polypropylene and approximately 5% styrene elastomer.

[0103] Table 3

[0104] performance unit Co-extruded PP / PP / PE Co-extruded PP / PP blends / PE thickness μm 10.6 10.2 Gurley JIS (Japanese Standard Value) s 198 183 Puncture strength gf 188 203 Normalized puncture intensity gf / μm 17.7 19.9 Porosity ％ 45.1 43.2 MD shrinkage at 105℃ for 1 hour ％ 5.5 4.4 resistance <![CDATA[Ωcm 2 ]]> 1.0 0.9 MD elongation ％ 85 80 TD elongation ％ 838 789 MD tensile strength <![CDATA[Kgf / cm 2 ]]> 1591 1585 TD tensile strength <![CDATA[Kgf / cm 2 ]]> 169 137 Average dielectric breakdown V 1377 1390 Shut-off temperature ℃ 136 135 PP surface static COF - 0.35 0.34 PE surface static COF - 0.28 0.22 PP surface dynamic COF - 0.38 0.37 PE surface dynamic COF - 0.27 0.17

[0105] Figure 7 The comparison shows the pore size distribution of co-extruded PE / PP blends / PP products with that of co-extruded PE / PP / PP products. The pore size distribution of the products with blends is bimodal. The advantages of these products include high strength due to the high PP content, a PE layer for closure, even higher strength in products containing PP blends, a reduced coefficient of friction due to the PE in the outer layer, a hierarchical pore size distribution, and so on. If the PE layer faces the anode, the hierarchical pore size in the PP blend examples (PE > PP blend > PP) may help slow dendrite growth. Using PE in the outer layer reduces the coefficient of friction required for use in cylindrical cells where needle removal force can be a problem. If single PE is used and the PE layer faces the anode, oxidation is not an issue.

Claims

1. An uncoated, asymmetric multilayer porous membrane comprising two outer layers and at least one inner layer, wherein, The thickness ratio of one of the two outer layers to the other of the two outer layers is from 1.1:1 to 4:1; The thicker of the two outer layers is a polypropylene layer facing or closest to the cathode, the thinner of the two outer layers is facing or closest to the anode, and at least one inner layer is a polyethylene layer; and The porous membrane is prepared by a dry stretching process.

2. The porous membrane as described in claim 1, wherein, The thickness ratio is from 1.1:1 to 3:

1.

3. The porous membrane as described in claim 1, wherein, The thickness ratio is 1.1:1 to 2:

1.

4. The porous membrane according to any one of claims 1 to 3, wherein, Porous membranes are microporous.

5. The porous membrane according to any one of claims 1 to 3, wherein, Including an inner layer of 1 to 10.

6. The porous membrane according to any one of claims 1 to 3, wherein, It contains one inner layer.

7. The porous membrane according to any one of claims 1 to 3, wherein, At least one of the two outer layers is laminated with at least one inner layer.

8. The porous membrane according to any one of claims 1 to 3, wherein, At least one of the two outer layers is co-extruded with at least one inner layer.

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

10. The porous membrane according to any one of claims 1 to 3, wherein, Porous membranes include dry-process microporous membranes.

11. The porous membrane according to any one of claims 1 to 3, wherein, Porous membranes are microporous membranes 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 micrometers.

13. The porous membrane of claim 12, wherein, The total thickness of the porous membrane is 5 to 20 micrometers.

14. The porous membrane of claim 12, wherein, The total thickness of the porous membrane is 5 to 15 micrometers.

15. The porous membrane of claim 12, wherein, The total thickness of the porous membrane is 5 to 10 micrometers.

16. An uncoated, asymmetric bilayer porous membrane, wherein, It contains two outer layers containing PP and no inner layer. The PP in one outer layer is different from the PP' in the other outer layer. The thickness ratio of the PP layer in the two outer layers to the PP' layer in the two outer layers is 1.1:1 to 25:1; The thicker of the two outer layers faces or is closest to the cathode, and the thinner of the two outer layers faces or is closest to the anode; and The porous membrane is prepared by a dry stretching process.

17. The porous membrane of claim 16, wherein, The thickness ratio is 1.1:1 to 3:1, or the thickness ratio is 1.1:1 to 4:

1.

18. The porous membrane of claim 16, wherein, The thickness ratio is 1.1:1 to 2:

1.

19. The porous membrane according to any one of claims 16 to 18, wherein, Porous membranes are microporous.

20. The porous membrane according to any one of claims 16 to 18, wherein, The two outer layers are stacked together.

21. The porous membrane according to any one of claims 16 to 18, wherein, The two outer layers are co-extruded.

22. The porous membrane according to any one of claims 16 to 18, wherein, Porous membranes include dry-process microporous membranes.

23. The porous membrane according to any one of claims 16 to 18, wherein, Porous membranes are microporous membranes produced by a dry stretching process.

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

25. The porous membrane of claim 24, wherein, The total thickness of the porous membrane is 5 to 20 micrometers.

26. The porous membrane of claim 24, wherein, The total thickness of the porous membrane is 5 to 15 micrometers.

27. The porous membrane of claim 24, wherein, The total thickness of the porous membrane is 5 to 10 micrometers.

28. A battery separator comprising, or composed of, the porous membrane as described in claim 1 or 16.

29. The battery separator as claimed in claim 28, wherein, The battery separator has a voltage relative to Li / Li of 4.2 volts or higher. + The electrochemically stable voltage.

30. The battery separator as claimed in claim 28, wherein, The battery separator has a voltage relative to Li / Li of 4.5 volts or higher. + The electrochemically stable voltage.

31. The battery separator as claimed in claim 28, wherein, The battery separator has a voltage relative to Li / Li of 5.0 volts or higher. + The electrochemically stable voltage.

32. The battery separator as claimed in claim 28, wherein, Of the two outer layers of the porous membrane, the thickness of the coated outer layer is less than the thickness of the uncoated outer layer.

33. The battery separator as described in claim 32, wherein, The coating is at least one of the following: a ceramic coating, a polymer coating, and a shut-off coating.

34. The battery separator as claimed in claim 33, wherein, The coating has a thickness of 1 to 5 micrometers.

35. A secondary battery comprising a battery separator as described in claim 28 between an anode and a cathode, and having a liquid electrolyte, wherein, In the porous membrane, the outer layer facing the cathode is thicker than the outer layer facing the anode.

36. A secondary battery comprising a battery separator as described in any one of claims 32 to 34, between an anode and a cathode, wherein, The coating faces the anode and has a liquid electrolyte.

37. An uncoated porous membrane comprising two polypropylene-containing outer layers and at least one inner layer, wherein, The thickness ratio of one of the two outer layers to the other of the two outer layers is from 1.1:1 to 4:1; The thicker of the two outer layers is a polypropylene layer facing or closest to the cathode, the thinner of the two outer layers is facing or closest to the anode, and at least one inner layer is a polyethylene layer. The porous membrane is prepared by a dry stretching process; and The porous membrane has at least one of the following: The average pore size of one of the two outer layers is smaller than the average pore size of the other outer layer; The porosity of one of the two outer layers is less than the porosity of the other outer layer; and One of the two outer layers has a higher degree of curvature than the other.

38. The porous membrane of claim 37, wherein, The outer layer has a small average pore size, ranging from 0.01 to 1.0 micrometers.

39. The porous membrane of claim 37, wherein, The outer layer has a high degree of curvature, which is greater than 1.

40. A battery separator comprising, or composed of, any one of claims 37 to 39, a porous membrane.

41. The battery separator as claimed in claim 40, wherein, The battery separator has a voltage relative to Li / Li of 4.2 volts or higher. + The electrochemically stable voltage.

42. The battery separator as claimed in claim 40, wherein, The battery separator has a voltage relative to Li / Li of 4.5 volts or higher. + The electrochemically stable voltage.

43. The battery separator as claimed in claim 40, wherein, The battery separator has a voltage relative to Li / Li of 5.0 volts or higher. + The electrochemically stable voltage.

44. The battery separator as claimed in claim 40, wherein, The porous membrane also includes a coating applied to one of the two outer layers, which has a larger average pore size, a larger porosity, and / or a smaller tortuosity.

45. The battery separator as claimed in claim 40, wherein, The porous membrane also includes a coating applied to one of the two outer layers, which has a smaller average pore size, smaller porosity, and / or greater tortuosity.

46. ​​The battery separator as claimed in claim 44, wherein, The coating is at least one of the following: a ceramic coating, a polymer coating, and a shut-off coating.

47. The battery separator as claimed in claim 44, wherein, The coating has a thickness of 1 to 5 micrometers.

48. A secondary battery comprising a battery separator as described in claim 40 between an anode and a cathode, and having a liquid electrolyte, wherein, An outer-faced anode or cathode with a smaller average pore size, smaller porosity, and / or greater tortuosity.

49. The secondary battery as claimed in claim 48, wherein, Outer surface-facing anode with smaller average pore size, smaller porosity and / or larger tortuosity.

50. A secondary battery comprising a battery separator as described in claim 46 or 47 between an anode and a cathode, wherein, The coating faces the anode and contains a liquid electrolyte.

51. An uncoated, asymmetric porous multilayer membrane comprising at least one polypropylene (PP) layer and at least one polyethylene (PE) layer, wherein, The ratio of the total thickness of one or more PP layers to the total thickness of one or more PE layers is in the range of 1.1:1 to 25:1; At least one PP layer is oriented or closest to the cathode, and at least one PE layer is oriented or closest to the anode; and The asymmetric porous multilayer membrane is prepared by a dry stretching process.

52. The asymmetric porous multilayer membrane as described in claim 51, wherein, The ratio is in the range of 1.1:1 to 20:

1.

53. The asymmetric porous multilayer membrane as described in claim 52, wherein, The ratio is in the range of 4:1 to 10:

1.

54. The asymmetric porous multilayer membrane according to any one of claims 51 to 53, 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.

55. The asymmetric porous multilayer membrane as described in claim 54, wherein, The PP-containing layers contain the same or different PP-containing materials.

56. The asymmetric porous multilayer membrane according to any one of claims 51 to 53, wherein, There are two or more PP-containing layers, and the PP-containing layers have the same or different PP-containing materials.

57. The asymmetric porous multilayer membrane according to any one of claims 51 to 53, wherein, One or more PP-containing layers of PP-containing material comprise a single polypropylene, a mixture of two or more different polypropylenes, a single polypropylene and other components, or a mixture of two or more different polypropylenes and other components.

58. The asymmetric porous multilayer membrane as described in claim 57, wherein, Other components are at least one of polymers other than polypropylene, elastomers, or combinations thereof.

59. The asymmetric porous multilayer membrane as described in claim 58, wherein, The elastomer is a styrene elastomer.

60. The asymmetric porous multilayer membrane as described in claim 51, wherein, There are two or more PE-containing layers, and the PE-containing layers have the same or different PE-containing materials.

61. The asymmetric porous multilayer membrane as described in claim 51, wherein, It has a PE / PE / PP / PP / PP / PP structure, where PE is a layer containing PE and PP is a layer containing PP.

62. The asymmetric porous multilayer membrane as described in claim 51, wherein, It has a PE / PE / PE / PP / PP / PP / PP / PP / PP structure, where PE is a layer containing PE and PP is a layer containing PP.

63. The asymmetric porous multilayer membrane as described in claim 51, wherein, It has a PE / PE / PE / PE / PP / PP / PP / PP / PP / PP / PP / PP structure, where PE is a layer containing PE and PP is a layer containing PP.

64. The asymmetric porous multilayer membrane as described in claim 51, having a PE / PE / PE / PE / PE / PP / PP / PP / PP / PP / PP / PP / PP / PP / PP structure, wherein, PE is a layer containing PE, and PP is a layer containing PP.

65. The asymmetric porous multilayer membrane according to any one of claims 51 to 53, wherein, A film is formed by co-extruding two or more layers.

66. The asymmetric porous multilayer membrane as described in claim 65, wherein, Three or more layers are co-extruded.

67. The asymmetric porous multilayer membrane as described in claim 54, wherein, All three-layer PE / PP / PP or PE / PP-blend / PP are co-extruded.

68. A battery separator comprising an asymmetric porous multilayer membrane as described in any one of claims 51 to 53.

69. The battery separator as claimed in claim 68, wherein, In asymmetric porous multilayer membranes, only one outermost layer is a PE-containing layer.

70. The battery separator as claimed in claim 69, wherein, A ceramic coating or cross-linked coating is included on the outermost layer containing PE.

71. The battery separator as claimed in claim 68, wherein, It comprises a ceramic coating and / or a cross-linked coating on at least one side.

72. A battery comprising an anode, a cathode, a liquid electrolyte, and a battery separator as claimed in claim 68.

73. A battery comprising an anode, a cathode, a liquid electrolyte, and a battery separator as described in claim 69 or 70, wherein, The outermost layer, i.e. the layer containing PE, faces or is closest to the anode.

Images