Aqueous separator slurry composition

Abstract

The present invention relates to an aqueous slurry composition comprising an aqueous polymeric binder and anionic oxide nanoparticles that can be used, for example, to coat electrodes and / or separators of electrochemical devices. After drying, the coating is highly porous, electronically insulating, and exhibits high dimensional stability at elevated temperatures.

Description

[Technical field]

[0001] The present invention relates to an aqueous slurry composition for use in coating separators in electrochemical devices. [Background technology]

[0002] Separators play a critical role in batteries. It has been demonstrated that the use of composite separators compared to traditional polyolefin separators improves the performance of lithium-ion batteries. This invention advances separator technology, improves the safety of lithium-ion batteries, and helps to promote and accelerate the adoption of EV (electric vehicle) batteries and battery energy storage.

[0003] In inorganic particle / polymer matrix or polymer binder coating compositions, the polymer matrix or polymer binder can serve to adhere between inorganic particles, adhere the coating to a free-standing porous separator, and / or adhere the coated separator to an electrode (adjacent or abutting the separator coating) and / or form the separator in situ on the electrode to create an integrated electrode separator for lithium ion batteries. Good contact between the separator and the electrode can be important for optimal cycle life of lithium batteries, because the presence of voids or spaces between the separator and the electrode can adversely affect long term cycle life or battery performance.

[0004] Known inorganic nanoparticle / polyvinylidene fluoride (PVDF) coatings are generally based on non-aqueous slurry, solvent-based systems using solvents such as acetone, tetrahydrofuran (THF), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAC), and combinations thereof. PVDF is used in such coatings because it is inert and stable in, for example, lithium-ion battery systems. However, the non-aqueous solvents used to dissolve PVDF are often hazardous, volatile, environmentally unfriendly, and may generate undesirable emissions if not handled properly, thus requiring careful use, disposal, and / or recycling. Coating processes based on non-aqueous systems can be costly, have adverse environmental impacts, and can be difficult to handle due to safety concerns related to flammability.

[0005] Thus, there is a need for new, optimized, and / or improved free-standing coated or cast separators that are cast directly onto electrodes of electrochemical devices for use having or manufactured using aqueous or water-based slurry systems, which may be preferred compared to non-aqueous or solvent-based coating systems, for example, due to performance, cost, environmental, safety, and / or economic factors. Separators, cathodes, and anodes coated with aqueous slurries of polymer binders and inorganic nanoparticles not only have excellent mechanical strength and excellent wet / dry adhesion, but also provide dimensional stability at high temperatures to the separator or electrodes, thereby reducing the possibility of shorting the battery during use or at elevated temperatures.

[0006] Prior art: http: / / dx.doi.org / 10.1016 / j.jpowsour.2015.11.067 demonstrates the casting of an aluminum oxide-based ceramic paste to form a separator using aluminum oxide particles of a few microns size (Figure 2b). The separator coating produced on the top of the electrode had limited flexibility and was 50 μm thick, which was thicker than commercial PE / PP separators. Furthermore, the SEM images (particularly Figure 2b) show that the separator coating on the top was non-uniform, which is likely due to the use of cationic surface-charged alumina. In contrast, the present invention uses anionic oxide nanoparticles, which form a uniform coating and allow the production of flexible thin separators with thicknesses of less than 25 μm, which are comparable to commercial PE / PP separators.

[0007] http: / / dx.doi.org / 10.1016 / j.memsci.2016.02.047 shows the fabrication of a free-standing separator using micron-sized aluminum oxide and the pore former PEG, which can be seen from the SEM shown in Figure 2(c). The fabricated separator had a thickness of 37 μm, which was thicker than commercially available PE / PP separators. The PEG was removed by a time-consuming process of immersing the separator in DI water and then drying it. In contrast, in this invention, anionic oxide nanoparticles are used to prepare a slurry that can produce highly porous separators without the need for pore formers.

[0008] In DE-FC26-05NT42403 (report: https: / / www.osti.gov / servlets / purl / 1160224), section H-15, "Entek," demonstrates separators made using a combination of UHMWPE gel processing and high loading levels of precipitated silica or fumed alumina as fillers. The resulting filled separators have large pore sizes, greater than 20 microns in thickness, which can compromise battery performance and safety. In contrast, the present invention uses highly loaded anionic oxide nanoparticles, i.e., at least 20 weight percent anionic oxide nanoparticles, to produce highly porous separators without organic solvents or gel processing, which is environmentally sustainable and therefore desirable.

[0009] US Patent Publication No. US20160164060 discloses an aqueous process for coating a separator. The process is for producing a coated separator for a lithium battery, the process includes the steps of (a) providing a porous substrate, (b) applying a coating slurry to at least one surface of the porous substrate, where the coating slurry comprises ceramic particles and a polymer binder in water or an aqueous solution or suspension, and (c) drying the coating slurry to form a coating layer on the porous substrate. The selection of the type of ceramic used was not based on surface charge. As a result, the aqueous slurry coating is expected to be non-uniform as evidenced in the SEM images of 1-5, which may be caused by the use of cationic surface-charged alumina. In contrast, the coating in the SEM image of 8 is uniform because it is solution cast with a muted surface charge. Furthermore, in the example using alumina particles, the particle size is 0.65 μm and the BET surface area is 4.6 m. 2 In contrast to this patent, the present invention uses the surface charge characteristics (anionic) of inorganic particles, the specific surface area (>15 m 2 / g) and compatibility with other ingredients in the slurry to prevent agglomeration and provide a uniform coating.

[0010] US Patent No. 9,954,211 relates to a separator with a porous organic-inorganic coating layer consisting of a mixture of inorganic particles and a polymer binder on a porous substrate, and an electrochemical device including the separator. "The inorganic particles are added to and dispersed in a first polymer binder solution. The solvent preferably has a similar solubility parameter to the first polymer binder and has a low boiling point. This is advantageous for uniform mixing and ease of solvent removal." All of the teachings and examples in this patent are solution-based casting. The present invention uses water-based polymer binders and ingredients, eliminating the use of hazardous and environmentally harmful solvents as mentioned above. Summary of the Invention [Problem to be solved by the invention]

[0011] In aqueous slurries, cationic surface charged fumed alumina, when mixed with conventional water-based polymeric binders including, but not limited to, polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), acrylic latex, or polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), or combinations thereof, reduces colloidal stability and causes severe flocculation, preventing uniform mixing of the slurry and uniform coating. Surface functionality is important in determining interactions with other components in the aqueous slurry composition. [Means for solving the problem]

[0012] Surprisingly, it has been found that by using anionic oxide nanoparticles, preferably aluminum oxide and / or silica, in an aqueous system, the slurry is stable in that it does not form visible aggregates or agglomerates. The cast slurry produces a smooth surface without visible defects (no agglomeration of anionic nanoparticles and binder), thus providing desirable slurry qualities for coating applications.

[0013] The present invention provides a homogenous slurry (anionic particles and binder are uniformly dispersed in the slurry (no visible agglomerations and Hegman fineness less than 5)) that can be used, for example, to coat electrodes and / or separators of electrochemical devices. The separator comprises a porous composite having a microporous substrate and a coating layer formed on at least one surface of the porous substrate, the coating layer being formed from particles and / or mixtures of particles and an aqueous or water-based polymeric binder.

[0014] The present invention further provides a method for manufacturing a separator for a lithium ion battery, the method comprising providing a porous substrate, such as a polyolefin substrate or an electrode, and forming a porous composite by applying a coating layer to at least one surface of the porous substrate or electrode, the coating layer comprising particles and / or a mixture of particles (inorganic) and an aqueous or water-based polymer binder, which may comprise one or more typically water-insoluble polymers (e.g., PVDF, SBR, acrylic, etc.) and one or more typically water-soluble polymers (e.g., PVA, CMC, PAA, etc.).

[0015] The present invention further provides the use of the free-standing coated separator in a lithium ion battery.

[0016] Also provided is the use in a single operation where a slurry of conductive material (electrode-forming slurry) and an aqueous slurry composition of the present invention (to form the separator) are simultaneously cast onto a current collector and dried to form an integrated electrode / separator assembly.

[0017] The present invention discloses a method for preparing an aqueous slurry using an anionic fumed oxide and an aqueous polymer binder, with a low Hegman fineness of less than 5, which indicates good flowability and fineness of grind. Preferably, the Hegman fineness is less than 3. It has been surprisingly found that the surface charge of the nanoparticles plays a key role in the dispersion uniformity and stability of the slurry to achieve a slurry without visible coagulation and / or agglomeration. Otherwise, untreated fumed aluminum oxide will cause severe agglomeration, preventing a uniformly mixed slurry and uniform coating, a quality that is detrimental to achieving a defect-free coating.

[0018] The disclosed invention can be cast alone to produce separators, membranes, or films, or can be co-cast in a multi-layer casting as disclosed in U.S. Pat. No. 11,133,562 to produce a composite separator in situ on an electrode for application in an electrochemical cell.

[0019] The present invention utilizes anionic surface-charged oxides, such as fumed aluminum oxide and fumed silica, to prepare an aqueous homogenous slurry. It has been found that the surface charge of the inorganic particles plays an important role, as the aqueous slurry composition may agglomerate depending on the surface charge of the oxide. Fewer additives and dispersants are required to address the agglomeration challenge, minimizing undesirable chemicals that jeopardize the performance of the battery.

[0020] An aspect of the invention is the preparation of water-based coatings using anionic oxide nanoparticles that provide the requisite slurry qualities for the coating. Using the invention, aqueous deposition by various means can be carried out to achieve the separator and / or separator coating.

[0021] Other applications of the slurry composition include those requiring thin membranes that exhibit high porosity and electronic impedance.

[0022] The final aqueous slurry composition in dilute conditions (0.1-1% solids, preferably 1% solids) should have a negative zeta potential of less than -10 mV, preferably less than -20 mV, and more preferably less than -30 mV.

[0023] Aspects of the invention Aspect 1. An aqueous slurry composition comprising: a) at least one polymeric binder, and b) at least one anionic oxide nanoparticle having a volume average particle size of 5 nm to 500 nm;

[0024] Aspect 2. The aqueous slurry composition of aspect 1, wherein the anionic oxide nanoparticles comprise at least one of zinc oxide, aluminum oxide, zirconia, or silica.

[0025] Aspect 3. The aqueous slurry composition according to Aspect 1 or 2, wherein the anionic oxide nanoparticles comprise anionic fumed aluminum oxide and have a volume average particle size of 5 nm to 200 nm, preferably 20 to 100 nm.

[0026] Aspect 4. The surface area of ​​the anionic oxide nanoparticles is 15 to 600 m 2 / g, preferably 20 to 300m 2 / g of the aqueous slurry composition according to any one of aspects 1 to 3.

[0027] Aspect 5. The aqueous slurry composition according to any one of Aspects 1 to 4, wherein the weight ratio of the anionic oxide nanoparticles to the polymer binder is from 5:95 to 95:5.

[0028] Aspect 6. The aqueous slurry composition according to any one of Aspects 1 to 4, wherein the weight ratio of the anionic oxide nanoparticles to the polymer binder is from 15:85 to 85:15, and preferably from 25:75 to 75:25.

[0029] Aspect 7. The aqueous slurry composition according to any one of Aspects 1 to 6, wherein the aqueous slurry has a solids content of 10% to 70% by weight, based on the total weight of the aqueous slurry composition.

[0030] Aspect 8. The aqueous slurry composition according to any one of Aspects 1 to 7, wherein the aqueous slurry composition has an anionic zeta potential.

[0031] Aspect 9. The aqueous slurry composition according to any one of Aspects 1 to 8, wherein the aqueous slurry composition has a negative zeta potential of less than -10 mV, preferably less than -20 mV, and more preferably less than -30 mV.

[0032] Aspect 10. The aqueous slurry composition of any one of Aspects 1-9, having a viscosity of less than 20,000 cP, preferably less than 10,000 cP.

[0033] Aspect 11. The aqueous slurry composition of any one of Aspects 1-10, wherein the polymeric binder comprises both a water soluble polymeric binder and a water insoluble polymeric binder.

[0034] Example 12. The aqueous slurry composition of any one of Examples 1-11, wherein the polymeric binder comprises at least one of SBR, an acrylic binder, a PVDF binder, or a mixture thereof.

[0035] Example 13. The aqueous slurry composition of any one of Examples 1-12, wherein the polymeric binder comprises at least one water soluble binder selected from the group consisting of PAA, CMC, PVA, HASE, ASE, or a mixture thereof.

[0036] Aspect 14. The aqueous slurry composition of any one of Aspects 1-13, wherein the anionic oxide nanoparticles are fractal in shape.

[0037] Aspect 15. The aqueous slurry composition according to any one of Aspects 1 to 14, further comprising inorganic particles having a particle size of 1 micron or more.

[0038] Aspect 16. A separator for a secondary battery comprising a coating composition, the coating composition comprising: a) at least one polymer binder; and b) at least one anionic oxide nanoparticle having a volume average particle diameter of 5 nm to 500 nm.

[0039] Aspect 17. The separator of aspect 165, wherein the coating has a thickness of 0.5 to 30 microns, preferably 1 to 20 microns, and more preferably 2 to 10 microns.

[0040] Aspect 18. A separator for a secondary battery comprising the composition according to any one of Aspects 1 to 15 in a dried form.

[0041] Aspect 19. A separator formed from the aqueous slurry composition according to any one of aspects 1 to 15.

[0042] Embodiment 20. A method for making a battery separator, comprising: 1) providing an aqueous slurry composition comprising: a) at least 20 weight percent anionic oxide nanoparticles; and b) up to 80 weight percent polymeric binder, the weight percent being based on the total weight of the anionic oxide nanoparticles and polymeric binder; 2) applying the aqueous slurry composition onto a substrate; and 3) drying the aqueous slurry to form a coating on the substrate.

[0043] The method of claim 20, wherein the aqueous slurry is the slurry of any one of claims 1 to 15.

[0044] Aspect 22. The method of aspect 20 or 21, wherein the substrate is an electrode.

[0045] Aspect 23. The method of aspect 20 or 21, wherein the substrate is a free-standing separator.

[0046] Aspect 24. The method of aspect 20, 21, or 22, wherein the aqueous slurry is applied simultaneously with the electrode slurry in a wet-on-wet manner. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] "Copolymer" means a polymer with two or more different monomeric units. "Polymer" is used to include homopolymers and copolymers. Resin and polymer are used interchangeably. Polymers may be homogeneous, heterogeneous, and have a gradient distribution of comonomer units. All cited references are incorporated herein by reference. Percentages used herein mean weight percent unless otherwise specified.

[0048] In the present invention, solids refers to the nanoparticles and the polymer binder. Solids content refers to the weight percent of solids in the aqueous slurry based on the weight of the total slurry.

[0049] By nanoparticles is meant that the particle size of the oxide is less than 500 nm, preferably less than 200 nm. The nanoparticles may be less than 100 nm. The specific surface area of ​​the nanoparticles is less than 15 m. 2 / g or more, preferably 20m 2 / g or more, more preferably 30m 2 / g or more. Particle size is the volume average particle size measured by light scattering, Nicom, or Microtech instruments.

[0050] The slurry must be castable, i.e., it is homogeneous (free of aggregates) and has a viscosity of less than 20,000 cP at room temperature, preferably less than 10,000 cp in a Haake viscometer at a shear rate of 11 sec at 25°C.

[0051] The present invention provides an aqueous slurry composition that can be used, for example, to coat electrodes and / or separators of electrochemical devices. The aqueous slurry composition includes a) at least one polymeric binder and b) at least one anionic oxide nanoparticle. The polymeric binder is water-based. The water-based polymer includes, but is not limited to, PVDF, SBR, or acrylic latex, or water-soluble polymers such as PVA, CMC, and PAA, or mixtures thereof, that bond the anionic charged oxide particles to each other at various contact points.

[0052] When using a water-insoluble polymer latex as the binder component, a water-soluble binder can also be added to the aqueous slurry composition. The water-soluble binder can act as a binder or a thickener. For the purpose of the present invention, any polymer thickener is considered to be part of the water-soluble binder. The polymer thickener can be used alone as a binder or in combination with another water-soluble binder or a water-insoluble binder.

[0053] The present invention also provides a coating made from the aqueous slurry composition on a substrate. The substrate may be a separator, an electrode, or a base substrate from which the coating is removed to provide a film that can be applied onto the desired substrate. The coating functions as an in situ separator between the anode and cathode in a battery as described in U.S. Pat. No. 11,133,562, the contents of which are incorporated herein by reference. The coatings described herein result from the application of the aqueous slurry composition of the present invention.

[0054] Anionic oxide nanoparticles useful in the present invention include, but are not limited to, ceramics, metal oxides, aluminum oxide (Al 2 O 3 ), alumina, titanium oxide (TiO 2 ), silicon oxide, silica (SiO 2 ), zirconium oxide (ZrO 2), zinc oxide (ZnO), silicates, kaolin, talc, and mixtures thereof. Preferably, the anionic oxide nanoparticles are zinc oxide, alumina or silica, most preferably alumina (fumed alumina, fumed aluminum oxide) and silica (fumed silica).

[0055] Anionic oxide nanoparticles in dilute conditions have an anionic charge with a negative zeta potential of less than -10 mV.

[0056] The oxide particles are preferably 15 to 600 μm 2 / g, preferably 30 to 500m 2 / g and has an anionically charged surface. Examples of anionic oxide nanoparticles include anionic fumed alumina and fumed silica.

[0057] Some particles with a large specific surface area have a three-dimensional branched structure, which is called a fractal shape, and can result in particles with a large aspect ratio. A fractal shape is an assembly of primary particles with three-dimensional branching. Preferably, the anionic oxide nanoparticles have a fractal shape.

[0058] Anionic oxide particles suitable for the present invention have a volume average diameter ranging from about 5 nm to about 500 nm, preferably from about 5 nm to about 400 nm, and most preferably from about 15 nm to about 350 nm in size. The particles can have a variety of shapes, including, but not limited to, rectangular, spherical, fractal, elliptical, cylindrical, oval, dogbone, or amorphous.

[0059] Additionally, in some embodiments, the particles purchased from a particle manufacturer may be pre-coated with some material to, for example, increase the compatibility of the particles with the polymer matrix, improve the uniformity of the particles, dissolution of the particles in a portion of the polymer matrix, dispersibility of the particles in the polymer matrix, avoid agglomeration of the particles, and / or stabilize the particles in the aqueous slurry composition.

[0060] Binders used in the present invention The preferred polymer binder provides interconnectivity of the anionic oxide particles and acts as a binding agent (or binder) to provide and promote adhesion between 1) the oxide particles / particles in the polymer coating layer, 2) the coating layer and the base substrate or porous membrane, and / or 3) the coated separator membrane and the battery electrodes. Good adhesion between the particles is important to ensure that the resulting coating layer has physical integrity and does not peel off. Good adhesion between the anionic oxide / polymer coating layer and the base substrate, and between the coated separator membrane and the battery electrodes, is important to ensure sufficient and optimal ion transport during the charge and discharge cycles of the battery and to reduce impedance at interfaces such as boundary layers.

[0061] Polymeric binders useful in the present invention include, but are not limited to, water soluble polymers of polyvinylidene (PVDF), polyethylene tetrafluoride ethylene (PETFE), polyvinyl fluoride (PVF), poly(alkyl)acrylates, poly(alkyl)methacrylates, polystyrene, polyvinyl alcohol (PVOH), polyacrylonitrile, polyacrylamide and copolymers thereof, as well as emulsions of carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polymethacrylic acid (PMAA) homopolymers or copolymers thereof or mixtures thereof.

[0062] By high molecular weight is meant a solution viscosity of at least 100 cp. The binder should have a high solution viscosity, i.e., greater than 100 cp at 5% by weight in organic solvent (NMP) for water-insoluble binders, measured at room temperature (25° C.), and greater than 100 cp at 2% by weight in water for water-soluble binders, measured at room temperature (25° C.). Preferably, the solution viscosity is between 100 cp and 10,000 cp, more preferably between 100 cp and 5000 cp, measured at 5% solids in NMP at room temperature. For water-soluble polymers, the viscosity is between 100 cp and 10000 cp, preferably between 100 cp and 5000 cp, measured at 2% by weight in water and pH 7 at room temperature (25° C.). In this application, the pH can vary from 2 to 12, depending on the type of polymer and the application. Preferably, the Rv of the binder is at least 0.2 dl / g up to 2 dl / g.

[0063] Due to its excellent electrochemical resistance and excellent adhesion between fluoropolymers, PVDF has been identified as a useful polymer binder for coating separators and as an in-situ coating on the electrodes of electrolyzers. The separator forms a barrier between the anode and cathode in the battery, allowing high ionic transport while preventing electronic shorting.

[0064] Polyvinylidene Fluoride In a preferred embodiment, the polymer is a polyvinylidene fluoride homopolymer or copolymer. The term "vinylidene fluoride polymer" (PVDF) as used herein includes homopolymers, copolymers, and terpolymers within its meaning. PVDF homopolymers exhibit high solvent resistance, low swelling (less than 50%) in battery electrolyte, and high melting points (above 150°C), resulting in improved dimensional stability (less than 10% shrinkage) at high temperatures (100°C). PVDF copolymers are particularly preferred because they have lower melting points ("Tm") and less crystalline structure than homopolymers. Such copolymers include vinylidene fluoride copolymerized with at least one comonomer. Most preferred copolymers and terpolymers of the present invention are those in which vinylidene fluoride units comprise at least 50 mole percent, at least 70 mole percent, preferably at least 75 mole percent, more preferably at least 80 mole percent, and even more preferably at least 85 mole percent of the total weight of all monomer units in the polymer.

[0065] The PVDF used in the coating composition is preferably cured at 230° C. for 100 seconds. -1 The melt viscosity measured by ASTM method D-3835 is 10 kpoise or more, preferably 20 kpoise or more.

[0066] Fluoropolymers, such as polyvinylidene-based polymers, may be prepared by any method known in the art. Methods such as emulsion polymerization and suspension polymerization are preferred. These methods are known in the art.

[0067] acrylic Acrylic polymers, as used herein, are meant to include polymers, copolymers and terpolymers formed from methacrylate and acrylate monomers in the acid or ester form, and mixtures thereof. The methacrylate and acrylate monomers may comprise 51-100 percent of the monomer mixture, with 0-49 percent of other ethylenically unsaturated monomers including, but not limited to, styrene, alpha methyl styrene, acrylonitrile, acrylamide. Suitable acrylate and methacrylate monomers and comonomers include, but are not limited to, methyl acrylate, ethyl acrylate and methacrylate, butyl acrylate and methacrylate, isooctyl methacrylate and acrylate, lauryl acrylate and methacrylate, stearyl acrylate and methacrylate, isobornyl acrylate and methacrylate, methoxyethyl acrylate and methacrylate, 2-ethoxyethyl acrylate and methacrylate, dimethylaminoethyl acrylate and methacrylate monomers. (Meth)acrylic acids, such as methacrylic acid and acrylic acid, may be comonomers. Acrylic polymers include multi-layer acrylic polymers such as core-shell structures that are typically prepared by emulsion polymerization.

[0068] styrene Styrenic polymers, as used herein, are meant to include polymers, copolymers and terpolymers formed from styrene and alpha-methylstyrene monomers, and mixtures thereof. Styrene and alpha-methylstyrene monomers comprise 50-100 percent of the monomer mixture, with 0-50 percent of other ethylenically unsaturated monomers being present, including, but not limited to, acrylates, methacrylates, and acrylonitrile. Styrenic polymers include, but are not limited to, polystyrene, acrylonitrile-styrene-acrylate (ASA) copolymers, styrene-acrylonitrile (SAN) copolymers, styrene-butadiene copolymers (such as styrene-butadiene rubber (SBR)), methyl methacrylate-butadiene-styrene (MBS), and styrene-(meth)acrylate copolymers (such as styrene-methyl methacrylate copolymer (S / MMA)).

[0069] Polyolefins, as used herein, are meant to include polyethylene, polypropylene, and copolymers of ethylene and propylene. Ethylene and propylene monomers may comprise 51-100 percent of the monomer mixture, with 0-49 percent of other ethylenically unsaturated monomers including, but not limited to, acrylates, methacrylates, acrylonitrile, and anhydrides. Examples of polyolefins include ethylene ethyl acetate copolymers (EVA), ethylene (meth)acrylate copolymers, ethylene anhydride copolymers and graft polymers, propylene (meth)acrylate copolymers, propylene anhydride copolymers and graft polymers.

[0070] Other additives The aqueous slurry composition of the present invention may further contain inorganic particles (P) having a particle size of about 1 micron or more as measured by SEM. The inorganic particles (P) are not particularly limited as long as they are electrochemically stable. In other words, the inorganic particles (P) that can be used in the present invention are not particularly limited as long as they do not undergo oxidation and / or reduction within the driving voltage range of the applied battery (for example, 0 to 5 V based on Li / Li+). Examples of the inorganic particles (P) include, but are not limited to: BaTiO 3 , Pb(Zr,Ti)O 3 (PZT), Pb 1-x La x Zr l-y Ti y O 3 (PLZT), PB(Mg 3 Nb 2 / 3 )O 3 -PbTiO 3 (PMN-PT), hafnia (HfO 2 ), lithium phosphate (Li 3 PO 4 ), lithium titanium phosphate (Li x Ti y (PO 4 ) 3 , 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO 4 ) 3 , 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y -type glass (0 < x < 4, 0 < y < 13) (14Li 2 O - 9Al 2 O 3 - 38TiO 2 - 39P 2 O 5 etc.), lithium lanthanum titanate (Li x La y TiO 3 , 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w, 0 <x<4、0<y<1、0<z<1、0<w<5)(Li 3.25 Ge 0.25 P 0.75 S 4 etc.), lithium nitride (Li x N y , 0 <x<4、0<y<2)(Li 3 N, etc.), SiS 2 Mold Glass (Li x S y S z , 0 <x<3、0<y<2、0<z<4)(Li 3 PO 4 -Li 2 S-SiS 2 etc.), P 2 S 5 Mold Glass (Li x P y S z , 0 <x<3、0<y<3、0<z<7)(LiI-Li 2 SP 2 S 5 etc.), SrTiO 3 , SnO 2 , CEO 2 , MgO, NiO, CaO, ZnO, ZrO 2 , Y 2 O 3 , Al 2 O 3 , TiO 2 , SiC or a mixture thereof. Preferably, the inorganic particles (P) are BaTiO 3 , Pb(Zr,Ti)O 3 , Pb1-xLaxZryO 3 (0 <x<1、0<y<1)、PBMg 3 Nb 2 / 3 ) 3 , PbTiO 3 , hafnia (HfO(HfO 2 ), SrTiO 3 , SnO 2 , CEO 2 , MgO, NiO, CaO, ZnO, Y 2 O 3 , Al 2 O 3 , TiO 2 , SiC, ZrO 2, boron silicate, BaSO 4 More preferably, the inorganic particles (P) include at least one of SrTiO 3 , SnO 2 , CEO 2 , MgO, NiO, CaO, ZnO, Y 2 O 3 , Al 2 O 3 , TiO 2 , SiC.

[0071] The weight ratio of the inorganic particles (P) to the polymer binder in the aqueous slurry composition is 5:95 to 95:5, preferably 15:85 to 85:15, and more preferably 25:75 to 75:25.

[0072] The aqueous slurry composition of the present invention may further include effective amounts of other additives, including, but not limited to, fillers, leveling agents, defoamers, pH buffers, and other adjuvants typically used in formulations while meeting the desired separator requirements.

[0073] The slurry compositions of the present invention may optionally contain a wetting agent, thickener, or rheology modifier.

[0074] Optionally, a wetting agent can be present in the slurry composition. Surfactants function as wetting agents, but wetting agents can also include non-surfactants. The presence of any wetting agent can allow the anionic oxide nanoparticles to be uniformly dispersed in the slurry. Useful wetting agents include, but are not limited to, ionic and non-ionic surfactants such as TRITON® series (Dow), PLURONIC® series (BASF), BYK-346 (BYK Additives), and organic liquids compatible with the solvent, such as NMP, DMSO, isopropyl alcohol, and acetone.

[0075] The slurry composition may contain a thickener and / or rheology modifier. These may be one or more thickeners or rheology modifiers in amounts of 0-10 parts, preferably 0-5 parts per 100 parts of water (parts by weight). The addition of a thickener or rheology modifier to the above dispersion prevents or slows down the settling of the anionic oxide nanoparticles while providing a suitable slurry viscosity for the casting process. In addition to organic rheology modifiers, inorganic rheology modifiers may also be used alone or in combination. Examples include carboxymethylcellulose (CMC), polyacrylic acid (PAA), alkali swellable rheology modifiers, including alkali swellable emulsions (ASE), hydrophobically modified alkali swellable emulsions (HASE), and other materials that provide pH-induced rheology changes.

[0076] The solids content of the aqueous slurry composition can be from 10 weight percent to 70 weight percent solids, preferably from 10 to 50 weight percent, and more preferably from 10 to 35% (based on the combined weight of the polymer binder and the weight of the nanoparticles).

[0077] Purpose The aqueous slurries of the present invention can be used, for example, to coat electrodes and / or separators of electrochemical devices, and after drying, the coatings exhibit high porosity (20% or more by volume) and high dimensional stability (less than 10% shrinkage at 100° C.).

[0078] One application of the coating made using the aqueous slurry composition of the present invention is to use an aqueous PVDF latex and anionic charged nanoparticles (examples include fumed alumina, fumed silica, or fumed zirconia) and PAA as a rheology modifier. The resulting coating has a porosity of 20-80% by volume, preferably 25-75%, and can be used as a separator in lithium ion batteries or other types of electrochemical devices. This new coating using the aqueous slurry composition of the present invention may provide improved safety, improved performance, and reduced manufacturing costs. Porosity is measured gravimetrically. The resulting coating not only does not shrink at high temperatures, but also expands at hot spots inside the battery, further separating runaway electrodes from each other. The response to temperature can be tuned with the resin composition, for example by varying the amount of HFP comonomer in the PVDF resin. This is because a film composite made with a resin with a higher HFP content (i.e., 20% HFP) will expand at a lower temperature than a resin with a lower HFP content (i.e., 8% HFP), and therefore may require a higher temperature to achieve the same expansion / expansion. The preferred weight percentage of HFP in the PVDF copolymer is 1-25% by weight.

[0079] Another advantage of the aqueous slurry composition is that it can be cast simultaneously with the electrodes. That is, two slurry layers (active electrode and separator layer) are cast simultaneously onto the current collector using a wet-on-wet casting technique using a double slot die casting machine. A drying and calendaring step then forms an integral electrode-separator structure. For multi-layer composite structures such as electrode separators for electrochemical devices, they can be cast wet-on-wet. Using the wet-on-wet technique, the two layers intertwine at the contact points, eliminating abrupt interfaces, improving adhesion. Films or coatings can be cast directly simultaneously with the substrate in a one-step wet-on-wet process.

[0080] Separator In a preferred embodiment, the aqueous slurry composition of the present invention, when dried on a substrate (thereby forming a coating), can withstand the harsh environment in a battery or other electrochemical device. The aqueous slurry composition can be easily processed into a coating. When the aqueous slurry composition is coated on an electrode, the resulting coating functions as a separator without the need for a separate, separate separator. The aqueous slurry composition includes anionic oxide nanoparticles. Preferably, the anionic oxide nanoparticles comprise at least 20% of the weight of the coated separator composition. The anionic oxide nanoparticles provide dimensional stability (minimal shrinkage) to the separator. The particles may be spherical or fractal shaped structures, but are often irregular in shape.

[0081] The anionic oxide nanoparticles in the aqueous slurry composition form a void volume in the coating during drying, form micropores in the coating, and act as spacers to maintain the physical shape. In addition, the anionic oxide particles have the characteristic that their physical properties do not change even at high temperatures of 200°C or higher, so that coated separators using the anionic oxide particles have dimensional stability. Mixtures of anionic oxides are also contemplated.

[0082] In one embodiment, the nanoparticles may be surface treated by chemical (such as etching or functionalization), mechanical, or irradiation (such as plasma treatment).

[0083] The anionic oxide nanoparticles in the aqueous slurry composition are present in an amount from 5 to 95 weight percent, preferably from 15 to 85 weight percent, more preferably from 20 to 85 weight percent, preferably from 30 to 85 weight percent, preferably from 25 to 75 weight percent, based on the total weight of the polymer and the anionic oxide nanoparticles.

[0084] The weight ratio of the anionic oxide nanoparticles to the polymer binder in the aqueous slurry composition is 5:95 to 95:5, preferably 15:85 to 85:15, and more preferably 25:75 to 75:25.

[0085] Coating Method The aqueous slurry composition is applied to at least one surface of a substrate, such as a free-standing separator or electrode, by means known in the art, such as by brush, roller, inkjet, dip, knife, gravure, wire rod, squeegee, foam applicator, curtain coating, vacuum coating, slot die, or spray. The aqueous slurry composition is then dried at room temperature or at elevated temperatures in an oven at temperatures between 40 and 200°C. The drying step may help evaporate much or nearly all of the water originally contained in the aqueous slurry composition. Once the slurry composition is applied to a substrate and dried, a coating is formed on the substrate. The final dry thickness of the coating is between 0.5 and 30 microns, preferably between 1 and 20 microns, and more preferably between 2 and 10 microns.

[0086] The aqueous slurry composition can be cast onto a substrate and then removed from the substrate and placed on the electrode, or cast directly onto the electrode. Non-limiting examples of substrates include porous and / or microporous membranes, including commercially available mono-, bi-, tri-, and / or multi-layer (coextruded or laminated) porous membranes that are well known to those skilled in the art. Substrates are polyolefin-based, including, for example, polyethylene, polypropylene, or combinations thereof, including homopolymers and / or copolymers of such polyolefins. EXAMPLES

[0087] Test Method Fumed oxides (alumina and silica). Fumed silica - average particle size 50-300 nm, surface area 30-450 m 2 / g. The average particle size of fumed alumina is 50-300 nm, and the surface area is 30-450 m 2 / g.

[0088] The zeta potential of the aqueous slurry composition in dilute condition (preferably 1% solids) was measured using a Malvern Zetasizer.

[0089] The BET specific surface area, pore volume, and pore size distribution of the materials can be measured using a QUANTACHROME NOVA-E gas adsorption apparatus. Nitrogen adsorption and desorption isotherms are generated at 77K.

[0090] General Procedure: Aqueous slurry compositions were prepared using a ThinkyARE-310 mixer. Five 6.5 mm zirconium beads are added to a 125 ml Thinky jar. Fumed aluminum oxide dispersion and an aqueous CMC solution (1.5 wt %) (BVH9CMC, provided by Ashland) are added to the jar and mixed in the Thinky at 2000 rpm for 2 minutes. 2008WAL35 acrylic latex (an acid-functionalized copolymer of styrene and 2-ethylhexyl acrylate) is added to the jar and mixed at 2000 rpm for an additional 2 minutes. Kynar® LBG-2200LX ("LBG-2200") PVDF latex (provided by Arkema) is added and mixed at 2000 rpm for 4 minutes. PAA has a molecular weight of 3,000,000 Daltons and was purchased from Aldrich.

[0091] Depending on the application and manufacturing requirements, different slurry qualities (flowability, adhesion, etc.) are required. The composition of the aqueous slurries is summarized in the table below. Additional ingredients may include thickeners and dispersants / surfactants such as Pluronic or IPA.

[0092] 2008WAL35 is a water-based acrylic binder with a MFFT below 25° C. PP06_3 is a water-based acrylic binder with a MFFT below 25° C. Kynar® LBG-2200LX is a PVDF binder available from Arkema Inc.

[0093] In the following examples, various coated separators for use in lithium ion batteries were prepared and tested. The thickness of the separator coating was measured using a Mitutoyo digital indicator. Using the example formulations, a variety of separator thicknesses (0.5 μm to 30 μm) can be produced by adjusting the wet coat thickness.

[0094] The flexibility of the coated separator was measured to ASTM D522 using the TQC cylindrical bend test, in which the coated separator on aluminum foil can withstand mandrel number 2 without cracking.

[0095] Examples of aqueous slurry compositions using anionic and cationic fumed aluminum oxide are shown in the table below. The table shows that slurries can be made with high weight percentages of anionic oxide nanoparticles that exhibit excellent flowability with Hegman particle size values ​​reported as less than 5. Hegman particle size measurements were performed according to ASTM D1210-05. In the comparative examples, varying the surface charge of the aluminum oxide results in significant differences in Hegman particle size values. In particular, cationic fumed aluminum oxide produces large aggregates with a Hegman particle size value reported as 8. In contrast, low Hegman particle size values ​​(less than 5) are measured when anionic aluminum oxide is used. Low Hegman particle size values ​​are necessary to ensure defect-free separator coatings. The viscosity of the formulations was measured using a Haake viscometer at 25°C and a shear rate of 11 seconds. The slurries formulated using cationic oxides exhibit severe coagulation that exceeds the torque limit of the equipment. Weight percentages are based on total solids.

[0096] [Table 1]

[0097] Anionic fumed aluminum (Aerodisp® W-640ZX (Evonik)) was used in Examples 1, 2, and 3. Cationic fumed aluminum (Cab-o-sperse® PG-003 (Cabot)) was used in Examples C-4, C-5, and C-6.

[0098] The volume resistivity of the coated separator was measured by measuring the volume resistivity of two gold-plated electrodes (area 3 cm) under a load of 60 N. 2 ) using a Yokogawa Digital Resistance Meter Model 755601 (100MΩ max). To directly compare the resistivity of the coated separator (used in Example 1) and the Celgard separator (a commercially available separator), the separator was placed on aluminum foil and the resistivity was measured. Both separators are not conductive as their resistivity is above what the instrument can measure.

[0099] In Table 2, the viscosities of the formulations were measured using a Haake viscometer at 25° C. and an 11-sec shear rate. In Examples 7, 8, 9, and 10, Aerodisp W-640ZX (anionic fumed aluminum oxide from Evonik) was used as the fumed oxide. In Examples 11, 12, 13, and 14, Aerodisp W7520 (anionic fumed silica from Evonik) was used as the fumed oxide.

[0100] [Table 2]

[0101] This table shows that various binders work in conjunction with anionic silica or anionic aluminum oxide.

[0102] The viscosity of the formulations was measured using a Haake viscometer at 25° C. and an 11-sec shear rate.

[0103] [Table 3]

[0104] Aerodisp W-640ZX (anionic fumed aluminum oxide manufactured by Evonik) was used as the fumed oxide in Examples 15 and 16. The alumina used in Table 3 is inorganic particles having a particle size of more than 1 micron.

[0105] Various embodiments of the present invention have been described to accomplish various objectives of the present invention. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations will be readily apparent to those skilled in the art without departing from the spirit and scope of the invention.

Claims

1. An aqueous slurry composition comprising: a) at least one polymer binder, and b) at least one anionic oxide nanoparticle having a volume average particle size of 5 nm to 500 nm;

2. 10. The aqueous slurry composition of claim 1, wherein the anionic oxide nanoparticles comprise at least one of zinc oxide, aluminum oxide, zirconia, or silica.

3. 2. The aqueous slurry composition of claim 1, wherein the anionic oxide nanoparticles comprise anionic fumed aluminum oxide and have a volume average particle size of 5 nm to 200 nm, preferably 20 to 100 nm.

4. The surface area of ​​the anionic oxide nanoparticles is 15 to 600 m 2 / g, preferably 20 to 300 m 2 The aqueous slurry composition of claim 1, wherein the % by weight of the aqueous slurry composition is 0.1g.

5. 10. The aqueous slurry composition of claim 1, wherein the weight ratio of the anionic oxide nanoparticles to the polymer binder is from 5:95 to 95:

5.

6. 2. The aqueous slurry composition of claim 1, wherein the weight ratio of the anionic oxide nanoparticles to the polymer binder is from 15:85 to 85:15, preferably from 25:75 to 75:

25.

7. 7. The aqueous slurry composition according to claim 1, wherein the solids content of the aqueous slurry is 10% to 70% by weight based on the total weight of the aqueous slurry composition.

8. The aqueous slurry composition according to any one of claims 1 to 6, wherein the aqueous slurry composition has an anionic zeta potential.

9. The aqueous slurry composition according to any one of claims 1 to 6, wherein the aqueous slurry composition has a negative zeta potential of less than -10 mV, preferably less than -20 mV, more preferably less than -30 mV.

10. The aqueous slurry composition of any one of claims 1 to 6, having a viscosity of less than 20,000 cP, preferably less than 10,000 cP.

11. The aqueous slurry composition according to any one of claims 1 to 6, wherein the polymer binder comprises both a water-soluble polymer binder and a water-insoluble polymer binder.

12. The aqueous slurry composition of any one of claims 1 to 6, wherein the polymer binder comprises at least one of SBR, an acrylic binder, a PVDF binder, or a mixture thereof.

13. 7. The aqueous slurry composition of claim 1, wherein the polymer binder comprises at least one water-soluble binder selected from the group consisting of PAA, CMC, PVA, HASE, ASE, or a mixture thereof.

14. The aqueous slurry composition of any one of claims 1 to 6, wherein the anionic oxide nanoparticles are fractal in shape.

15. The aqueous slurry composition according to any one of claims 1 to 6, further comprising inorganic particles having a particle size of 1 micron or more.

16. A separator for a secondary battery comprising a coating composition, the coating composition comprising: a) at least one polymer binder; and b) at least one anionic oxide nanoparticle having a volume average particle size of 5 nm to 500 nm.

17. The separator of claim 16, wherein the coating has a thickness of 0.5 to 30 microns, preferably 1 to 20 microns, more preferably 2 to 10 microns.

18. A separator for a secondary battery comprising the composition according to any one of claims 1 to 6 in a dried form.

19. A separator formed from the aqueous slurry composition according to any one of claims 1 to 6.

20. 1. A method for manufacturing a battery separator, the method comprising: 1) providing an aqueous slurry composition comprising: a) at least 5 weight percent anionic oxide nanoparticles; b) up to 95 weight percent polymeric binder, wherein the weight percent is based on the total weight of the anionic oxide nanoparticles and the polymeric binder; and c) optionally inorganic particles having a particle size of 1 micron or greater; 2) applying the aqueous slurry composition onto a substrate; and 3) drying the aqueous slurry to form a coating on the substrate.

21. The method of claim 20 wherein the substrate is an electrode.

22. The method of claim 20 , wherein the substrate is a free-standing separator.

23. 21. The method of claim 20, wherein the aqueous slurry is applied simultaneously with the electrode slurry in a wet-on-wet manner.

24. The method according to claim 20, wherein the aqueous slurry is a slurry according to any one of claims 1 to 6.