Color coded ceramic coated battery separator

Abstract

Disclosed herein are ceramic coated microporous polyolefin membranes having a contrast agent incorporated into a polyolefin membrane or ceramic coating. The contrast agent may include dyes, pigments, inorganic oxides, and / or other materials that impart color to the film or coating. The contrast agent makes it possible to easily determine which side of the membrane includes the ceramic coating. Such ceramic coated polyolefin membranes can be used as separator membranes to improve manufacturability, performance, and safety of energy storage devices, such as lithium ion batteries.

Description

Related applications

[0001] This application claims priority to U.S. Provisional Application No. 63 / 621,852, filed January 17, 2024, entitled "Color-Coded, Ceramic-Coated Battery Separator," which is incorporated herein by reference in its entirety. Copyright Notice

[0002] © 2025 Amtek Research International LLC. This patent document contains copyrighted material. The copyright holder does not object to any reproduction of this patent document or its disclosure as presented in the patent files or records of the Patent and Trademark Office, but otherwise reserves all copyright rights. 37 CFR 1.71(d). Technical Field

[0003] This invention relates to the formation of ceramic-coated microporous polyolefin membranes, wherein a contrast agent is incorporated into the polyolefin membrane or ceramic coating to highlight which side is coated. The contrast agent can be a dye, pigment, inorganic oxide, or other material that imparts color to the membrane or coating. Such ceramic-coated polyolefin membranes can be used as separators to improve the manufacturability, performance, and safety of energy storage devices such as lithium-ion batteries. Background Technology

[0004] The separator is an indispensable component affecting the performance, safety, and cost of lithium-ion batteries. During normal operation, the separator's primary function is to prevent electronic conduction (i.e., short circuits or direct contact) between the anode and cathode, while allowing ion conduction via the electrolyte. Under abuse conditions (such as external short circuits or overcharging), the separator is required to shut down at temperatures well below where thermal runaway could occur. Shutdown occurs due to the collapse of pores in the separator caused by the melting and viscous flow of the polymer, thus slowing or stopping ion flow between the electrodes. Almost all Li-ion battery separators contain polyethylene as part of a single-layer or multi-layer structure, causing shunt to begin at approximately 130°C (the melting point of polyethylene).

[0005] Separators for the lithium-ion market are currently manufactured using either a "dry" or "wet" process. In the dry process, polypropylene (PP) or polyethylene (PE) is extruded into thin sheets and subjected to rapid stretching. The sheet is then annealed at 10°C–25°C below the polymer's melting point to control crystallite size and orientation. Next, the sheet is rapidly stretched in the machine orientation (MD) to create slit-like pores or voids. Three-layer PP / PE / PP separators produced via the dry process are commonly used in lithium-ion rechargeable batteries.

[0006] Wet-process separators made of high molecular weight polyethylene are produced by extruding an oil / polymer mixture at elevated temperatures, followed by phase separation, biaxial stretching, and extraction of the process oil (i.e., plasticizer). The resulting separator has elliptical or spherical pores with good mechanical properties in both the machine direction and transverse direction. PE-based separators manufactured in this way using casting or blown film techniques are already widely used in Li-ion batteries.

[0007] The benefits of membrane pore closure in the design of large-scale Li-ion battery cells for hybrid, plug-in hybrid, or electric vehicle applications (HEV, PHEV, EV) have been publicly questioned because it is difficult to guarantee sufficient rate and uniformity of pore closure throughout the entire battery cell. The main reason is that after pore closure, residual stress above the polymer melting point and reduced mechanical properties can lead to shrinkage, tearing, or pinhole formation. The exposed electrodes may then come into contact and create internal short circuits, resulting in increased heat generation, thermal runaway, and even explosion.

[0008] Therefore, battery manufacturers are focusing on using separators with excellent high-temperature in-plane stability. U.S. Patent Application Publication No. 20190097196 A1 describes a method for preparing an aromatic polyamide membrane (e.g., poly(m-phenylene isophthalamide)) for use as a separator in Li-ion batteries. Such polymers have glass transition temperatures above 300°C and thermal decomposition temperatures exceeding 500°C.

[0009] In alternative methods, microporous polyolefin membranes are coated with ceramic particles and an adhesive (e.g., a polymeric adhesive) on one or both sides. Under sufficient load levels, the ceramic imparts high-temperature dimensional stability, defined as an area shrinkage of <5% at temperatures above the polyolefin's melting point. The ceramic layer also protects the polyolefin from oxidation upon contact with a high-voltage cathode (e.g., NMC 622), and its tortuous porous structure mitigates dendrite growth.

[0010] In the case of cylindrical battery cells, the ceramic coating is typically applied only to one side of the polyolefin film because it is easier to extract the jellyroll from the winding needle when the polyolefin surface is in contact with it. Therefore, it is important to know which side of the polyolefin film is coated with ceramic particles, but this is difficult to discern because both the uncoated and ceramic-coated polyolefin surfaces appear white upon visual inspection.

[0011] To date, color coding of the polyolefin membrane or ceramic coating of the diaphragm has not been considered to facilitate easy differentiation of each surface. In this invention, a contrast agent is added to the polyolefin or ceramic coating to allow differentiation between coated and uncoated surfaces to achieve the aforementioned objective. Summary of the Invention

[0012] The purpose of this disclosure is to achieve thin, freestanding, ceramic-coated microporous polyolefin membranes that possess good heat resistance above the melting point of polyolefins and a coated surface easily distinguishable from the uncoated surface of the membrane. The pore size of the microporous membranes typically ranges from about 10 nanometers to several micrometers, with an average pore size of less than about 1 micrometer. Such membranes are typically opaque because the pore size and the size of the polymer matrix are sufficient to scatter visible light. The term "membrane" as used includes other descriptions used in scientific and patent literature, such as "thin film," "sheet," and "mesh." Microporous membranes can also exhibit freestanding characteristics and have interconnected pores throughout the membrane's extension. "Freestanding" means that the membrane possesses sufficient mechanical properties to allow for operations such as winding and unwinding in sheet form for use in energy storage device components.

[0013] In a first preferred embodiment, one or more contrast agents (e.g., pigments) are combined with inorganic particles (e.g., boehmite) in an aqueous solution (e.g., deionized water) and bead-milled to form an aqueous dispersion. A small amount of binder (e.g., carboxymethyl cellulose, polyvinylpyrrolidone, acrylic acid) is added to the dispersion. The dispersion is then coated onto one side of a microporous polyolefin membrane using a Mayer rod and subsequently dried in an oven at 100°C.

[0014] In a second preferred embodiment, one or more contrast agents (e.g., water-soluble dyes) are added to an aqueous dispersion of inorganic particles (e.g., fumed alumina and nanoboehmite), and a small amount of binder is added to the aqueous dispersion. The aqueous dispersion is then coated onto one side of a microporous polyolefin membrane. The coated membrane is then dried in an oven at 100°C.

[0015] In a third preferred embodiment, one or more contrast agents (e.g., blue pigment) are combined with polyethylene and process oil in a twin-screw extruder to form an oil-extended sheet, which is then biaxially oriented. Next, the biaxially oriented sheet is passed through a solvent extraction bath to remove the oil, and then the solvent-loaded sheet is conveyed at an elevated temperature through a dryer to remove the solvent and produce a microporous polyethylene film in which the pigment imparts a color other than white.

[0016] A colored microporous polyethylene membrane is then coated on one side with an aqueous dispersion of inorganic particles (e.g., boehmite) and an adhesive (e.g., acrylate adhesive). The coated side of the membrane is easily distinguishable from the uncoated side.

[0017] The resulting color-coded polyolefin films can be wound or stacked in packaging to separate electrodes in energy storage devices such as batteries, capacitors, supercapacitors, or fuel cell units. Such films are advantageous for the manufacture of energy storage devices, particularly because they combine easily distinguishable coated surfaces with excellent in-plane dimensional stability at temperatures above the melting point of the polymer matrix.

[0018] Additional objects and advantages of the invention will become apparent from the following detailed description of its preferred embodiments with reference to the accompanying drawings. Attached Figure Description

[0019] The accompanying drawings illustrate several embodiments of this disclosure.

[0020] Figure 1 This is a schematic diagram of a bilayer microporous polyolefin membrane with a ceramic coating and a polyethylene substrate film.

[0021] Figure 2 Images depict ceramic-coated microporous polyolefin membranes with pigments and dyes incorporated into the ceramic coating to show a clear contrast between the coated and uncoated surfaces.

[0022] Figure 3 Images depict ceramic-coated microporous polyolefin membranes with dyes incorporated into the ceramic coating to show a clear contrast between the coated and uncoated surfaces.

[0023] Figure 4 Images depict a ceramic-coated microporous polyolefin membrane with pigments incorporated into a polyethylene substrate film, showing a contrast with the side having a ceramic coating.

[0024] Figure 5Images depict the electrolyte compatibility test of AOH 70 boehmite (Nabaltec), Blue 3J pigment (Shepard Color), and Blue 30C59 pigment (Shepard Color) in 1 M LiPF6 at 60°C in a 1:1 EC: EMC (ethylene carbonate: methyl ethyl carbonate) electrolyte. Detailed Implementation

[0025] Wet-process separators made of high molecular weight polyethylene are produced by extruding an oil / polymer mixture at elevated temperatures, followed by phase separation, biaxial stretching, and extraction of the process oil (i.e., plasticizer). The resulting separator has elliptical or spherical pores with good mechanical properties in both the machine direction and transverse direction. PE-based separators manufactured in this way using casting or blown film techniques are already widely used in Li-ion batteries.

[0026] The polyethylene used to manufacture such diaphragms can be of various types. For example, in some embodiments, the polyethylene includes ultra-high molecular weight polyethylene (UHMWPE), very high molecular weight polyethylene (VHMWPE), high-density polyethylene (HDPE), or mixtures thereof. In one embodiment, the polyethylene comprises UHMWPE that typically corresponds to a molecular weight range between about 310 and about 10 million g / mol. In another embodiment, the polyethylene used contains a molecular weight between 500,000 g / mol and 3.1 million g / mol. In yet another embodiment, the polyethylene used contains a molecular weight between 500,000 g / mol and 10 million g / mol. Representative polymers include 150 U and VH035 from KPIC Corporation (Korea), GUR 4120 and 4012 from Celanese Corporation (USA), and UH650 from Asahi Kasei Corporation (Japan).

[0027] The plasticizer used in this invention is a non-evaporative solvent for the polymer and is preferably liquid at room temperature. The plasticizer has little or no solvation effect on the polymer at room temperature; it exerts its solvation effect at or above the softening temperature of the polymer. For polyethylene homopolymers, the solvation temperature will be above about 180°C, and preferably in the range of about 200°C to about 225°C. Process oils, such as paraffin oils, naphthenic oils, aromatic oils, or mixtures of two or more such oils, are preferred. Examples of suitable process oils include Risella 430X from Shell Oil Company and Hydrocal from Calumet Specialty Products. TM 800; and Nytex 820 from Nynas Inc.

[0028] The polymer / oil mixture is extruded through a sheet die or annular die and then biaxially oriented to form a thin, oil-filled sheet. Any solvent compatible with the oil can be used in the extraction step, provided that the solvent's boiling point makes it practical to separate the solvent from the plasticizer by distillation. Such solvents include 1,1,2-trichloroethylene, perchloroethylene, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2-trichloroethane, dichloromethane, 1,1,2-trichloro-1,2,2-trifluoroethane, various trans-dichloroethylene azeotropes (e.g., Tergo MCF – MicroCare LLC), isoPar-G, hexane, heptane, decane, and toluene. In some cases, it is desirable to select a process oil such that any residual oil in the polymer sheet after extraction is electrochemically inactive. The resulting membrane after extraction is microporous with a porosity of approximately 35%–65%. The pore size typically ranges from about 10 nanometers to several micrometers, with an average pore size of less than about 1 micrometer. The membrane thickness can range from about 3 to 25 µm. Other thicknesses have also been envisioned.

[0029] The ceramic coating can then be applied to the membrane and dried. It should be understood that the ceramic coating can contain various types of inorganic particles, including inorganic oxides, carbonates, or hydroxides, such as at least one of alumina, silica, zirconium oxide, titanium dioxide, mica, boehmite, magnesium hydroxide, calcium carbonate, or mixtures thereof. One or more hydrotalcites can also be used alone or in combination with another type of inorganic particles. The coating formulation may further contain inorganic particles dispersed in an aqueous mixture containing a binder. Polymer dispersions or water-soluble polymers are typically used as binders. Exemplary binders may include acrylates, polyvinylpyrrolidone, polyvinyl alcohol, carboxymethyl cellulose, and copolymers or derivatives thereof. The coating thickness can be in the range of about 0.5-6 µm. Other thicknesses are also contemplated. In another embodiment, the coating may contain about 0.3 g / m³. 2 Approximately 12 g / m 2 As agreed 3 g / m 2 Approximately 6 g / m 2 The coating weight. Other coating weights have also been envisioned.

[0030] As previously discussed, contrast agents can be added to polyolefin-based films or ceramic coatings. Various types of contrast agents can be used, including pigments, dyes, inorganic oxides, and combinations thereof. Exemplary pigments can be one or more of metal oxides, carbon, carbides, or mixtures thereof. Exemplary dyes include water-soluble dyes. Other types of contrast agents may also be used.

[0031] The following examples are illustrative in nature and are not intended to be limiting in any way. Example 1

[0032] A 9 µm thick microporous membrane containing ultra-high molecular weight polyethylene, namely ENTEK ® EPH (ENTEK Membrane LLC, Oregon) uses an aqueous dispersion for coating, which contains the following: 337.5 g – DI water 124 g – Boehmite 8.2 g – Acrylic emulsion adhesive 2.5 g – Rheology modifier 0.5 g – Dispersant 3 g – Pigment: Schott Pigment Company, Blue 3J 3 g – Dye: Blue McCormick Assorted Food Color

[0033] A coating dispersion was prepared by mixing boehmite, a dispersant, an acrylic emulsion binder, a rheology modifier, and Sherter Pigment Company Blue 3J in water using agitation. The resulting mixture was milled using a ball mill for three hours. Blue Viagra mixed food coloring was added to the milled solution under low-shear mixing conditions. The coating dispersion contained 26 wt% solids. A diaphragm was coated on one side via a dip-coating line. The wetted diaphragm was then dried using a Heraeus IR heater and forced air through a horizontal oven and wound onto a core before testing. Figure 2 Table 1 shows the physical properties of the coated diaphragm prepared in Example 1. Table 1 Example 2

[0034] A 9 µm thick microporous membrane containing ultra-high molecular weight polyethylene, namely ENTEK ® EPX (ENTEK Membrane LLC, Oregon) uses an aqueous dispersion for coating, which contains the following: 337.5 g – DI water 124 g – Boehmite 8.2 g – Acrylic emulsion adhesive 2.5 g – Rheology modifier 0.5 g – Dispersant 3 g – Dye: Blue Mixed Food Coloring

[0035] A coating dispersion was prepared by mixing boehmite, a dispersant, an acrylic emulsion binder, a rheology modifier, and a blue micranthin mixed food coloring in water using agitation. The coating dispersion contained 26 wt% solids. A diaphragm was coated on one side via a dip-coating line. The wetted diaphragm was then dried using a Heraeus IR heater and forced air through a horizontal oven and wound onto a core before testing. Figure 3 Table 2 shows the physical properties of the coated diaphragm prepared in Example 2. Table 2 Example 3

[0036] A 9 µm thick microporous membrane containing ultra-high molecular weight polyethylene and containing blue pigment was coated with an aqueous dispersion containing the following: 337.5 g – DI water 124 g – Boehmite 8.2 g – Acrylic emulsion adhesive 2.5 g – Rheology modifier 0.5 g – Dispersant

[0037] A coating dispersion was prepared by mixing boehmite, dispersant, acrylic emulsion binder, and rheology modifier in water using agitation. The coating dispersion contained 26 wt% solids. A diaphragm was coated on one side using a doctor blade via an automatic coating machine. The wetted diaphragm was then dried in an oven at 130°C for five minutes before testing. Figure 4 Table 3 shows the physical properties of the coated diaphragm prepared in Example 3. Table 3 Example 4

[0038] Electrolyte aging tests were prepared by adding 0.5 g of AOH 70 boehmite (Nabot), Blue 3J (Schett Pigment Company), and Blue30C59 (Schett Pigment Company) to individual 20 ml scintillation vials and drying them at 120°C for 1 hour. After drying, the scintillation vials were transferred to a glove box, and 5 ml of 1 M LiPF6 in a 1:1 EC:EMC (ethylene carbonate: methyl ethyl carbonate) electrolyte (Aldrich) was added to each vial. The vials were then sealed and placed in an oven at 60°C for 7 days. Figure 5 Comparative images are shown after electrolyte aging at 60°C; electrolytes containing AOH 70 boehmite, Blue 3J, and Blue 30C59 showed similar discoloration after 168 hours of exposure at 60°C. Therefore, the contrast agents do not appear to have an adverse effect on the electrolytes.

[0039] It will be apparent to those skilled in the art that many changes can be made to the details of the above embodiments without departing from the basic principles of this disclosure. Therefore, the scope of this disclosure should be determined only by the following claims.

Claims

1. A freestanding microporous polyolefin membrane, comprising: Microporous polyolefin substrate membrane having a coated side and an uncoated side; and A ceramic coating is disposed on the first main surface of the microporous polyolefin substrate membrane, the ceramic coating comprising inorganic particles and forming the coated side of the microporous polyolefin substrate membrane; The microporous polyolefin base film or the ceramic coating contains a contrast agent that allows the coated side and the uncoated side of the microporous polyolefin base film to be visually distinguishable.

2. The freestanding microporous polyolefin membrane as described in claim 1, wherein, The ceramic coating contains sufficient coating weight to impart high-temperature dimensional stability, which is defined by an area shrinkage rate of < 5% at temperatures above the melting point of the polyolefin.

3. The freestanding microporous polyolefin membrane as described in claim 1 or 2, wherein, The contrast agent contains at least one of pigments or dyes.

4. The freestanding microporous polyolefin membrane as described in claim 3, wherein, The contrast agent contains a water-soluble dye.

5. The freestanding microporous polyolefin membrane as described in claim 3, wherein, The contrast agent contains a pigment, which includes at least one of a metal oxide, carbon, a carbide, or a mixture thereof.

6. The freestanding microporous polyolefin membrane according to any one of claims 1 to 5, wherein, The microporous polyolefin base membrane contains the contrast agent.

7. The freestanding microporous polyolefin membrane according to any one of claims 1 to 6, wherein, The ceramic coating contains this contrast agent.

8. An energy storage device comprising a freestanding microporous polyolefin membrane as described in any one of claims 1 to 7.

9. A method for forming a freestanding microporous polyolefin membrane, the method comprising: A microporous polyolefin substrate film having a first main surface and a second main surface was obtained; as well as A ceramic coating is applied to the first main surface of the microporous polyolefin substrate membrane, the ceramic coating comprising inorganic particles and forming the coated side of the microporous polyolefin substrate membrane; The microporous polyolefin base film or the ceramic coating contains a contrast agent that allows the coated side of the microporous polyolefin base film to be visually distinguishable from the uncoated side of the microporous polyolefin base film.

10. The method of claim 9, wherein, The ceramic coating contains sufficient coating weight to impart high-temperature dimensional stability, which is defined by an area shrinkage rate of < 5% at temperatures above the melting point of the polyolefin.

11. The method of claim 9 or 10, wherein, The contrast agent contains at least one of pigments or dyes.

12. The method of claim 11, wherein, The contrast agent contains a water-soluble dye.

13. The method of claim 11, wherein, The contrast agent contains a pigment, which includes at least one of a metal oxide, carbon, a carbide, or a mixture thereof.

14. The method according to any one of claims 9 to 13, wherein, The microporous polyolefin base membrane contains the contrast agent.

15. The method according to any one of claims 9 to 13, wherein, The ceramic coating contains this contrast agent.

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