Coating compositions for separator membranes used in secondary batteries

Abstract

An aqueous coating composition for a separator in a secondary battery is provided. The coating composition includes: a) at least one polymeric binder, b) at least one alkali metal silicate, c) optionally, at least one alkali metal siliconate, and d) inorganic particles. A coated separator is also provided.

Description

[0001] COATING COMPOSITIONS FOR SEPARATOR MEMBRANES USED IN SECONDARY

[0002] BATTERIES

[0003] FIELD OF THE INVENTION

[0004] The invention relates to coating compositions for separator membranes used in secondary batteries.

[0005] BACKGROUND

[0006] The separator is a key component of secondary batteries, such as lithium-ion batteries (LIB). The separator serves as a physical barrier between the cathode and the anode while allowing the transportation of ions, such as lithium ions, between the cathode and the anode. Microporous polyolefins such as polyethylene and polypropylene - based separators are widely used in the secondary battery industry due to their good mechanical strength and chemical stability to the electrolytes used in secondary batteries, such as LIBs, as well as their ability to allow mass transport of the ions between the cathode and the anode.

[0007] A problem associated with polyolefin-based separator membranes is that the low melting points of polyolefins tend to result in poor thermal stability of these separators, which poses a potential safety hazard, as well as impacting the long-term performance of the secondary batteries. To improve the thermal stability, coatings incorporating inorganic particles, such as ceramic particles, in a polymeric binder are often used to coat polyolefin-based separators.

[0008] Among different polymeric binder technologies for inorganic particulate coatings, waterborne latex polymers are often used.

[0009] CN 108467503B relates to a preparation method of a heat-resistant lithium battery diaphragm. CN 111554858A relates to a high-peel-strength ceramic slurry and a ceramic coating diaphragm which is coated by the disclosed coating.

[0010] US 11,258,133 B2 relates to a binder composition for a non-aqueous secondary battery porous membrane.

[0011] US 2014 / 0147726A1 relates to a porous membrane for a secondary battery including non-conductive particles and a water-soluble polymer.

[0012] US 2016 / 0164060 Al relates to aqueous or water-based polymeric coated separators, membranes, films, or the like.

[0013] WO 2015 / 046191A1 relates to a binder for a coating on a separator for nonaqueous secondary batteries. The coating includes the binder and inorganic particulate fillers.

[0014] Thus, a technical challenge remains in the field of inorganic particulate coatings (also known as ceramic coatings) for separators. Achieving a balance between good thermal resistance, adhesion to separator substrates, and minimal impact on separator porosity is a significant problem to be overcome. Latex polymers enabling ceramic coatings with good film formation are desired for providing thermal stability and adhesion to polyolefin separator substrates. However, their too-thorough film formation negatively affects the permeability (also referred to as porosity) of the ceramic coatings and the ceramic coated separators, thus compromising lithium-ion transportation and leading to decreased LIB performance.

[0015] SUMMARY

[0016] It was surprisingly found that latex-silicate hybrid binders were able to provide inorganic particulate coatings with good balance of thermal stability, permeability, and adhesion to polyolefin separator substrates. The invention relates to an inorganic particle coating composition that is designed to be applied onto the separator membrane used in secondary batteries, such as lithium-ion batteries. The coating composition is formed from a coating slurry comprising at least one inorganic particle, e.g. ceramic particle, at least one latex polymer, and at least one alkali metal silicate. The inorganic particle coated separator membrane shows a good balance of the properties of thermal resistance, porosity, and adhesion force between the coating and the base separator membrane. In addition, the coating composition is especially suitable for polyolefin-based separator membranes because it imparts improved heat resistance to the separator, compared to an uncoated such separator membrane, while at the same time not comprising the mass transfer ability of the membrane, as measured by the Gurley number of the coated membrane.

[0017] An aqueous coating composition for a separator in a secondary battery is provided. The aqueous coating composition comprises, consists of, or consists essentially of the following. a) at least one polymeric binder, b) at least one alkali metal silicate, c) optionally, at least one alkali metal siliconate, and d) inorganic particles.

[0018] A coated separator for a secondary battery is also provided. The coated separator comprises, consists of, or consists essentially of a porous or microporous substrate and a coating layer on at least one surface of the substrate. The coating layer is formed from an aqueous coating composition comprising, consisting of, or consisting essentially of the following components. a) at least one polymeric binder, b) at least one alkali metal silicate, c) optionally, at least one alkali metal siliconate, and d) inorganic particles.

[0019] BRIEF DESCRIPTION OF THE FIGURES

[0020] FIG. 1 shows results of thermal testing at 130°C and

[0021] FIG. 2 shows results of thermal testing at 150°C. DETAILED DESCRIPTION

[0022] When a plurality of lower limits and a plurality of upper limits are provided herein with respect to ranges of a variable or ratio, the invention contemplates all ranges from any disclosed lower limit to any disclosed upper limit.

[0023] The terms “latex” and “emulsified polymeric binder” are used interchangeably.

[0024] “Water soluble” means that the material dissolves into water at 10 mg per liter or greater at 25°C, as opposed to “insoluble” which means less than 10 mg per liter of the substance will dissolve in water at 25°C.

[0025] A basic and novel characteristic of the aqueous coating composition are its ability to mitigate the porosity / permeability impact of the coated separator to mass transport of ions, as measured by the Gurley number, compared to conventional separator coating compositions that only use latex polymer as binders. Another basic and novel characteristic of the coating composition is its ability to impart improved thermal resistance to the coated polyolefin separator membrane, as measured by the thermal shrinkage of the coated membrane upon exposure to 130°C and / or 150°C, compared to an uncoated such separator membrane.

[0026] A basic and novel characteristic of the coated separator is its porosity / permeability to mass transport of ions, as measured by the Gurley number. Another basic and novel characteristic of the coated separator is its improved thermal resistance, as measured by the thermal shrinkage of the coated membrane upon exposure to 130°C and / or 150°C, compared to an uncoated such separator membrane.

[0027] Coating composition

[0028] As discussed above, the coating composition comprises, consists of, or consists essentially of a) at least one polymeric binder; b) at least one alkali metal silicate; c) optionally, at least one alkali metal siliconate, and d) inorganic particles.

[0029] Polymeric binder

[0030] The aqueous coating composition may comprise, consist of, or consist essentially of 0.01-

[0031] 40 wt% of the at least one polymeric binder, based on based on a total dry weight of the

[0032] 4 inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate, and the at least one alkali metal siliconate in the aqueous coating composition. For example, the aqueous coating composition may comprise at least 0.02, 0.05, 0.1, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30 or at least 35 wt% of the at least one polymeric binder, based on based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate, and the at least one alkali metal siliconate in the aqueous coating composition. For example, the aqueous coating composition may comprise at most 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9.5, 9, 8.5, 8, 7.5, 7, 6.5, 6, 5.5, or at most 5 wt% of the at least one polymeric binder, based on based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate, and the at least one alkali metal siliconate in the aqueous coating composition. According to some embodiments, the aqueous coating composition may comprise from 0.01-35, 0.0.01-30, 0.01-25, 0.01-20, 0.01-15, 0.01-10, or from 0.01-5wt% of the at least one polymeric binder, based on based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate, and the at least one alkali metal siliconate in the aqueous coating composition. According to some embodiments, the aqueous coating composition may comprise from 0.02-40, 0.05-40, 0.1-40, 0.5-40, 0.75-40, or from 1-40, 1.25-40, 1.5-40, 1.75-40, 2-40, 2.25-40, 2.5-40, 2.75-40, 3-40, 3.25-40, 3.5-40, 3.75-40, 4-40, 4.25-40, 4.5-40, 4.75-40, 5-40, 6- 40, 7-40, 10-40, 15-40, 20-40, 25-40, or from 30-40wt% of the at least one polymeric binder, based on based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate, and the at least one alkali metal siliconate in the aqueous coating composition. According to some embodiments, the aqueous coating composition may comprise from 0.01-25, 0.02-20, 0.05-15, or from 0.1-10, 0.5-9, 0.75-8, 1-7, 1.25-6.5, 1.5-6, 1.75-5.75, 2-5.5, 2.25-5.25, 2.5-5, 2.75-4.75, 3-4.5, or from 3.25-3.75 wt% of the at least one polymeric binder, based on based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate, and the at least one alkali metal siliconate in the aqueous coating composition.

[0033] The polymeric binder may be in a form of a latex, i.e. an aqueous emulsified polymer. The polymeric binder may comprise, consist of, or consist essentially of, as polymerized monomers, any ethylenically unsaturated monomer. Non-limiting examples are (meth)acrylates, vinyl esters, vinyl aromatic monomers, styrene, and substituted styrene, (meth) acrylamide and derivatives thereof, olefins, and combinations thereof.

[0034] Non-limiting examples of suitable alkyl (meth)acrylates are alkyl esters of (meth) acrylic acid, or (eth)acrylic acid, for example. Such acrylate monomers may be C1-C22 linear, cyclic or branched alkyl esters of (meth) acrylic acid, or (eth)acrylic acid. Non-limiting examples include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, cyclohexyl (meth)acrylate, allyl methacrylate, 2-ethylhexyl acrylate; isooctyl methacrylate and iso-octyl acrylate, lauryl acrylate and lauryl methacrylate, stearyl acrylate and stearyl methacrylate, isobomyl acrylate and isobomyl methacrylate monomers. According to an embodiment, the ethylenically unsaturated monomer comprises at least one of vinyl aromatic monomers, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethyl hexyl acrylate, (meth)acrylic acid, or a combination thereof.

[0035] Other suitable monomers include but are not limited to ethylene, propylene, mono- ethylenically unsaturated carboxylic acid monomer, phosphorous-containing monomer, sulfur- containing monomer, silane co-monomers, and mixtures thereof.

[0036] These other suitable monomers may include various carboxylic acids such as itaconic acid, and esters thereof, various esters of versatic acid, methoxyethyl acrylate and methoxyethyl methacrylate, 2-ethoxy ethyl acrylate and 2-ethoxyethyl methacrylate, and combinations thereof.

[0037] Also suitable as monomers are acrylonitrile; vinyl cyanides; vinylpyrrolidone; polypropylene glycol mono(meth)acrylate or polyethylene glycol mono(meth)acrylate; phosphorous-based monomers including but are not limited to phosphoalkyl (meth)acrylates or acrylates, phosphoalkyl (meth)acrylamides or acrylamides, phosphoalkyl crotonates, phosphoalkyl maleates, phosphoalkyl fumarates, phosphodialkyl (meth)acrylates, phosphodialkyl crotonates, vinyl phosphates and (meth)allyl phosphate, phosphate esters of polypropylene glycol mono(meth)acrylate or polyethylene glycol mono(meth)acrylate, polyoxyethylene allyl ether phosphate, vinyl phosphonic acid. Suitable sulfur-based monomers include, but are not limited to, vinyl- and allyl- sulfonic or sulfuric acids, sulfoethyl (meth)acrylate, aryl- sulfonic or sulfuric acids, (meth)acrylamidoethane- sulfonic or sulfuric acids, methacrylamido-2-methyl propane- sulfonic or sulfuric acids, and the alkali metal salts of sulfonic and sulfuric acids. Suitable optional silane co-monomers include, but are not limited to methacryloxypropyl trimethoxysilane, methacryloxypropyl triethoxysilane, methacryloxypropyl tripropoxysilane, vinyltriacetoxysilane, vinyltrimethoxysilane, and vinyltriethoxysilane.

[0038] Crosslinkable co-monomers may also optionally be present in the polymeric binder. These crosslinkable co-monomers may be of two different types. The first type is crosslinkable co- monomers that include two or more sites of ethylenic unsaturation such that the crosslinks are formed during polymerization of the polymeric binder a). The second type of crosslinkable comonomer is those that include, in addition to an ethylenic unsaturation ((meth)acrylate, allyl or vinyl functional groups), at least one moiety that is capable of reacting with a separate crosslinking compound that may be included in the one-part aqueous composition to form a crosslink.

[0039] Suitable crosslinkable co-monomers with two or more sites of ethylenic unsaturation include, but are not limited to, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, trimethylol propane trimethacrylate, 1,3 -butyleneglycol dimethacrylate, and 1, 4-butyleneglycol dimethacrylate, hexanediol dimethacrylate, divinyl benzene, diallyl phthalate, and the like.

[0040] Crosslinkable co-monomers that are capable of reacting with a separate crosslinking agent that may be included in the aqueous coating composition may be selected from, for example, acetoacetate co-monomers containing (meth)acrylate, allyl or vinyl functional groups including but not limited to acetoacetate moieties such as: 2-acetoacetoxyethyl (meth)acrylate, 3- acetoacetoxypropyl (meth)acrylate, 4-acetoacetoxybutyl (meth)acrylate, 2-cyanoacetoxyethyl (meth)acrylate, 3 -cyanoacetoxypropyl (meth)acrylate, 4-cyanoacetoxybutyl (meth)acrylate, N(2- acetoacetoxyethyl) (meth)acrylamide, allyl acetoacetate, 2,3-di(acetoacetoxy)propyl (meth)acrylate, vinyl acetoacetate and combinations thereof. Also suitable are co-monomers containing a keto group such as diacetone acrylamide. Non-limiting particular examples of such crosslinkable monomers are acetoacetoxyethyl methacrylate and diacetone acrylamide. Watersoluble crosslinking agents that can react with certain moieties of these second type of crosslinkable comonomers may also optionally be included in the aqueous coating composition. These water-soluble crosslinking agents effect post crosslinking during film formation and drying by reacting with the crosslinkable moieties on the second type of crosslinkable co- monomers. For example, such crosslinking agents containing at least two hydrazine and / or hydrazide groups may be included in certain embodiments of the aqueous coating composition. Preferred such separate crosslinking agents are water soluble. Non-limiting examples include oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, sebacic acid dihydrazide, maleic acid dihydrazide, fumaric acid dihydrazide and / or itaconic acid dihydrazide. Adipic acid dihydrazide (ADH) is a particular example of such a water-soluble cross- linking agent for use in the coating compositions herein, especially those produced from monomer compositions containing diacetone acrylamide (DAAM). Other suitable water-soluble crosslinking agents are compounds which contain at least two amine functional moieties such as ethylene diamine and hexamethylene diamine. Such cross-linking agents are especially useful in combination with polymers comprising 1,3- dicarbonyl groups as the crosslinkable moiety, such as acetoacetoxyethyl methacrylate (AAEM).

[0041] The monomers may be selected such that the Tg of the polymeric binder may be from -20 to 120 °C, or from 10 to 80 °C, or from 15 to 50°C.

[0042] Methods of preparing the emulsion polymers and the monomers useful to prepare useful as the binders in the present coating composition are known in the art (see, e.g., “Emulsion Polymerization: Theory and Practice” by D. C. Blackley published by Wiley in 1975, “Emulsion Polymerization” by F. A Bovey et al. published by Interscience Publishers in 1965, and “Emulsion Polymerization and Emulsion Polymers” by P.A. Lovell et al. published by Wiley Science in 1997).

[0043] Alkali metal silicate

[0044] The aqueous coating composition comprises from 0.01-20 wt% of the at least one alkali metal silicate based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate, and the at least one alkali metal siliconate in the aqueous coating composition. For example, the aqueous coating composition may comprise at least 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.9, 0.1, 0.2, 0.3, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or at least 18 wt% of the at least one alkali metal silicate based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate, and the at least one alkali metal siliconate in the aqueous coating composition. For example, the aqueous coating composition may comprise at most 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, or at most 0.05 wt% of the at least one alkali metal silicate based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate, and the at least one alkali metal siliconate in the aqueous coating composition. The aqueous coating composition may comprise 0.01-20, 0.02-20, 0.03-20, 0.04-20, 0.05-20, 0.06- 20, 0.07-20, 0.08-20, 0.920, 0.1-20, 0.2-20, 0.3-20, 0.3-20, 0.4-20, 0.5-20, 0.6-20, 0.7-20, 0.8-20, 0.9-20, 1-20, 2-20, 3-20, 4-20, 5-20, 6-20, 7-20, 8-20, 9-20, 10-20, 11-20, 12-20, 13-20, 14-20, or 15-20 wt% of the at least one alkali metal silicate based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate, and the at least one alkali metal siliconate in the aqueous coating composition. The aqueous coating composition may comprise 0.01-19, 0.01-18, 0.01-17, 0.01-16, 0.01-15, 0.01-14, 0.01-13, 0.01-12, 0.01-11, 0.01-10, 0.01-9, 0.01-8, 0.01-7, 0.01-6, 0.01-5, 0.01-4, 0.01-3, 0.01-2, 0.01-1, or 0.01-0.9 wt% of the at least one alkali metal silicate based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate, and the at least one alkali metal siliconate in the aqueous coating composition. The aqueous coating composition may comprise 0.01-15, 0.02-10, 0.03-8, 0.04-6, 0.05-4, 0.06-3, 0.07-3.75, 0.08-3.5, 0.9-3.25, 0.1-3, 0.2-2.75, 0.3-2.5, 0.3-2.5, 0.4-2, 0.51.75, 0.6-1.25, or 0.7-1 wt% of the at least one alkali metal silicate based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate, and the at least one alkali metal siliconate in the aqueous coating composition.

[0045] The alkali metal silicate may be soluble in water at 10 mg per liter or greater at 25°C. A general formula for the alkali metal silicates is formula (I).

[0046] MiOn S1O2 where M is an alkali metal such for example, Na, K, Li, Rb, or Cs; and n is the molar ratio (MR), defining the number of moles of silica (SiCh) per mole of alkali metal oxide (M2O). A molar ratio of 1 designates the metasilicates, MsSiCL. According to an embodiment, M may be at least one of Na, K, Li, Rb, or Cs.

[0047] The alkali metal silicate may also be expressed as Formula (II). M 2xSiyO2y+x, (II) where M’ may be alkali metal ions such as Li+, Na+, K +, Rb+, Cs+, or ammonium ion NH4+.

[0048] Non-limiting examples of suitable alkali metal silicates are as follows. Sodium silicates Na2On SiCh; disodium metasilicate, anhydrous Na?SiO3; disodium metasilicate pentahydrate Na2SiO3*5H2O; disodium metasilicate nonahydrate NaiSiCb^fTO; potassium silicates KaOn SiCh; lithium silicates LiaO’n SiCh, and combinations thereof. Silicates with alkali cations and small or chain-like anions, such as sodium, or potassium, or lithium ortho- and metasilicates, are also non-limiting examples of suitable alkali metal silicates for use in the coating composition. Polysilicates are also suitable for use in the coating composition. Non-limiting examples of alkali metal silicates include inorganic silicate salts, sodium silicate, potassium silicate, lithium silicate, rubidium silicate, ammonium silicate, orthosilicates, or mixtures thereof. In one embodiment, the at least one silicate b) may comprise, consist of, or consist essentially of at least one of sodium silicate, potassium silicate, lithium silicate, rubidium silicate, ammonium silicate, orthosilicates, inorganic silicate salts, or a mixture thereof. Ina another embodiment, the alkali metal silicate may be potassium silicate, sodium silicate, lithium silicate, or a combination thereof. The alkali metal silicate may be potassium silicate and / or sodium silicate.

[0049] Inorganic particles

[0050] The coating composition may comprise consist of or consist essentially of from 60-99.5 wt% of inorganic particles based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate in the coating composition, and the at least one alkali metal siliconate. For example, the coating composition may comprise at least 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or at least 99 wt% of inorganic particles based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate in the coating composition, and the at least one alkali metal siliconate. The coating composition may comprise at most 99.5, 99, 98, 97, 96, 95, 94, 93, 92, 91, 90, 89, 88, 87, 86, 85, 84, 83, 82, 81, 80 79, 78, 77, 76, 75, 74, 73, 72, 71, 70, 69, 68, 67, 66, 65, 64, 63, 62, or at most 61 wt% of inorganic particles based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate in the coating composition, and the at least one alkali metal siliconate. The coating composition may comprise 60-99, 60-98, 60-97, 60- 96, 60-95, 60-90, 60-85, 60-80, 60-75, or 60-70 wt% of inorganic particles based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate in the coating composition, and the at least one alkali metal siliconate. The coating composition may comprise 65-99.5, 70-99.5, 75-99.5, 80-99.5, 85-99.5, 90-99.5, 91-99.5, 92- 99.5, 93-99.5, 94-99.5, 95-99.5, 96-99.5, 97-99.5, 98-99.5, or 99-99.5 wt% of inorganic particles based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate in the coating composition, and the at least one alkali metal siliconate.

[0051] The inorganic particles may comprise at least one of ceramics, metal oxides or combinations thereof; preferably aluminum oxide (AI2O3), boehmite, titanium oxide (TiO?), silicon oxide (SiCh), zinc oxide (ZnO), metal hydroxides, metal carbonates, water-insoluble silicates, kaolin, talc, minerals, glass, calcium carbonate, barium sulfate and magnesium oxide or mixtures thereof; more preferably aluminum oxide (AI2O3), boehmite, or mixtures thereof. Also suitable are, Gibbsite (Al(OH))), silicon oxide, magnesium hydroxide, calcium oxide, BaTiO, ZrO, alumino-silica complex oxide; nitride particles such as aluminum nitride and boron nitride; particles of covalent crystals such as silicon and diamond; particles of ionic crystals having low water solubility such as barium sulfate, calcium fluoride, and barium fluoride; and microparticles of clays such as montmorillonite.

[0052] Alkali metal siliconates

[0053] The aqueous coating composition may optionally comprise 0.01-5 wt% of at least one alkali metal siliconate based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate in the coating composition, and the at least one alkali metal siliconate. According to an embodiment, the alkali metal siliconate may comprise at least one alkyl siliconate.

[0054] The alkali metal siliconate may conform to Formula (III).

[0055] (XO)3-nSiR(OH)n(III) In Formula (III), X is an alkali metal; n is 0, 1, or 2; and R is an alkyl or aryl group. According to some embodiments, X comprises at least one of sodium, potassium, lithium, rubidium, cesium, or combinations thereof. In Formula (III), R may comprise a C1-C8 alkyl group or an aryl group. According to some embodiments, R may comprise methyl, ethyl, n- propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl, n-pentyl, iso-pentyl, tert-pentyl, neopentyl, phenyl, aryl, or cyclohexyl. According to some embodiments, R may methyl or ethyl and X may be at least one of sodium, potassium, or lithium According to another embodiment, R may be methyl, X may be potassium and n may be 0. According to another embodiment, the alkali metal siliconate may be potassium methyl siliconate.

[0056] Additives

[0057] The coating composition may further include comprise at least one additive. Non-limiting examples of suitable additives are those that are typically included in coating compositions including, for example, ammonium hydroxide, alkali metal hydroxides, or other bases to neutralize latex, leveling agents, emulsifiers, rheology control additives, additional polymers, dispersants or surfactants, defoamers, thickeners, stabilizers, viscosity stabilizers, biocides, solvents, rheology modifiers, wetting or spreading agents, conductive additives, thermal insulating fillers, adhesion promoters, antiblocking agents, anti-cratering agents or anti-crawling agents, anti-static agents, flame retardants, chelating agents, cross-linking agents, flattening agents, insecticides, lubricants, oils, or waxes. According to an embodiment, the coating composition may comprise, consist of, or consist essentially of at least one of a rheology modifier, a wetting agent, a dispersant, or a combination thereof.

[0058] According to some embodiments, the aqueous coating composition may further comprise a rheology modifier. Nonlimiting examples are carboxymethyl cellulose (CMC), carrageenan, hydroxyethylcellulose (HEC), hydrophobically modified HEC (HMHEC); hydrophobically modified alkali-soluble emulsions (HASEs); and nonionic synthetic associative thickeners (NSATs), hydrophobically modified alkali swellable emulsions (HASE), hydrophobically modified ethoxylated urethane resins (HEUR). If present, the aqueous coating composition may comprise from 0.01 to 10 wt% of a rheology modifier, based on a total dry weight (i.e., exclusive of water) of the aqueous coating composition. According to some embodiments, the aqueous coating composition may further comprise a wetting agent, i.e. a surfactant. Non-limiting examples include silicone surfactants such as HYDROPALAT® WE 3220, nonionic surfactants such as tertoctylphenoxyethylpolyethoxyethanol, dodecyloxypolyethoxyethanol, tridecyloxypolyethoxyethanol, nonylphenoxyethyl-polyethoxyethanol, polyethylene glycol 2000 monooleate, ethoxylated castor oil, fluorinated alkyl esters and alkoxylates, polyoxyethylene sorbitan monolaurate, sucrose monococoate, di(2-butyl)phenoxypolyethoxyethanol, hydroxyethylcellulosepolybutyl acrylate graft copolymer, dimethyl silicone polyalkylene oxide graft copolymer, polyethylene oxide)poly(butyl acrylate) block copolymer, block copolymers of propylene oxide and ethylene oxide, 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylated with 30 moles of ethylene oxide, N- polyoxyethylenelauramide, N lauryl-N-polyoxy ethyleneamine and polyethylene glycol dodecyl thioether. Aso suitable are ionic (anionic or cationic) surfactants such as sodium lauryl sulfate, sodium lauryl ether sulfate, sodium dodecylbenzenesulfonate, potassium stearate, sodium dioctyl sulfosuccinate, sodium dodecyldiphenyloxide disulfonate, nonylphenoxyethylpolyethoxyethyl sulfate ammonium salt, sodium styrene sulfonate, sodium dodecyl allyl sulfosuccinate, palmitic acid, palmitoleic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, mixtures of fatty acids (e.g., linseed oil fatty acid), sodium or ammonium salts of phosphate esters of ethoxylated nonylphenol, sodium octoxynol-3 -sulfonate, sodium cocoylsarcocinate, sodium l-alkoxy-2- hydroxypropyl sulfonate, sodium a-olefm (C 14-C 16) sulfonate, sulfates of hydroxyalkanols, tetrasodium N-( 1 ,2-dicarboxy ethyl )-N-octadecylsulfosuccinamate, disodium N- octadecylsulfosuccinamate, disodium alkylamido polyethoxy sulfosuccinate, di sodium ethoxylated nonylphenol half ester of sulfosuccinic acid and the sodium salt of tertoctylphenoxyethoxypolyethoxyethylsulfate, or combinations thereof.

[0059] If present, the coating composition may comprise from 0.01-5wt% of a wetting agent (surfactant) based on the total dry weight (i.e. exclusive of water) of the coating composition.

[0060] According to some embodiments, the aqueous coating composition may further include a dispersant. The purpose of the dispersant is to help disperse the inorganic particles in the coating composition. Non-limiting examples include polyacrylate dispersants, EO / PO block copolymers, acrylic / styrene copolymers, methacrylic copolymers, poly hydroxystearate derivatives, and alkyd PEG resin derivatives. Also suitable are sodium polyaspartate, sodium polyacrylate, butyl PVP, or sodium polynaphthalene sulfonate.

[0061] If present, the coating composition may comprise from 0.01-5 wt% of a dispersant, based on the total dry weight (i.e. exclusive of water) of the coating composition.

[0062] Coating process

[0063] A process for producing a coated separator for a secondary battery, comprising applying the aqueous coating composition of any of claims 1-13 to at least one surface of the substrate, to form a coating layer on the substrate.

[0064] According to an embodiment, the process may further comprise heating the coating layer to at least 20°C. Forced air drying (room temperature or warmer), hot air drying, infrared drying, far infrared ray. or the like can be used.

[0065] Non-limiting examples of coating methods are gravure roll coating, slit coating, anilox roll coating, slot-die coating and spraying. Also suitable are a die coating method, a dip coating method, a roll coating method, a doctor coating method, a knife coating method, a spray coating method, a gravure coating method, a screen-printing method, an electrostatic coating method, and the like.

[0066] Coated separator

[0067] A coated separator for a secondary battery, comprising a porous or microporous substrate and a coating layer on at least one surface of the substrate, wherein the coating layer is formed from an aqueous coating composition comprising, consisting of or consist of the aqueous coating composition. The coating layer thickness may be less than 10 pm on each side, preferably less than 8 pm on each side, more preferably less than 5 pm on each side.

[0068] Porous or microporous substrate

[0069] The porous or microporous substrate may comprise olefinic polymers, such as polyethylene, polypropylene, copolymers of propylene and ethylene, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, and combinations thereof. Certain nonlimiting aspects of the invention may be summarized as follows.

[0070] Aspect 1 : An aqueous coating composition for a separator in a secondary battery comprising: a) at least one polymeric binder, b) at least one alkali metal silicate, c) optionally, at least one alkali metal siliconate, and d) inorganic particles.

[0071] Aspect 2: The aqueous coating composition of Aspect 1, wherein the alkali metal silicate has the formula (I) or (II):

[0072] M2O • n SiO2(I)

[0073] M’2xSiyO2y+x, (II) where M is an alkali metal; and n is the molar ratio (MR), defining the number of moles of silica (SiO2) per mole of alkali metal oxide (M2O); and where M’ is an alkali metal ion such as Li+, Na+, K +, Rb+, Cs+, or ammonium ion NH4+.

[0074] Aspect 3: The aqueous coating composition of Aspect 2, wherein M is at least one of Na, K, Li, Rb, or Cs.

[0075] Aspect 4: The aqueous coating composition of any of Aspects 1-3, wherein the alkali metal siliconate comprises at least one alkyl siliconate.

[0076] Aspect 5: The aqueous coating composition of any of Aspects 1-4, wherein the alkali metal siliconate conforms to Formula (III):

[0077] (XO)3-m SiR(OH)m(III) where: X is alkali metal; m is 0, 1, or 2; and R is an alkyl or aryl group.

[0078] Aspect 6: The aqueous coating composition of Aspect 5, wherein R comprises a C1-C8 alkyl or aryl group. Aspect 7: The aqueous coating composition of Aspect 5 or Aspect 6, wherein R comprises at least one of methyl, ethyl, n-propyl, isopropyl, n-butyl, iso-butyl, tert-butyl, n-pentyl, iso-pentyl, tert-pentyl, neopentyl, phenyl, aryl, or cyclohexyl.

[0079] Aspect 8: The aqueous coating composition of any of Aspects 5-7 wherein R is methyl or ethyl and X is at least one of sodium, potassium, or lithium.

[0080] Aspect 9: The aqueous coating composition of any of Aspects 1-8, wherein the inorganic particles comprise at least one of ceramics, metal oxides or combinations thereof; preferably aluminum oxide (AI2O3), boehmite, titanium oxide (TiCh), silicon oxide (SiC>2), zinc oxide (ZnO), metal hydroxides, metal carbonates, water insoluble silicates, kaolin, talc, minerals, glass, or mixtures thereof; more preferably aluminum oxide (AI2O3), boehmite, or mixtures thereof.

[0081] Aspect 10: The aqueous coating composition of any of Aspects 1-10, wherein the polymeric binder comprises, as polymerized monomer, at least one ethylenically unsaturated monomer.

[0082] Aspect 11 : The aqueous coating composition of Aspect 10 wherein the ethylenically unsaturated monomer comprises at least one of vinyl aromatic monomers, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethyl hexyl acrylate, (meth)acrylic acid, or a combination thereof.

[0083] Aspect 12: The aqueous coating composition of any of Aspects 1-11, further comprising at least one of a rheology modifier, a wetting agent, a dispersant, or a combination thereof.

[0084] Aspect 13: The aqueous coating composition of any of Aspects 1-12, wherein the coating composition comprises:

[0085] 0.01-40 wt% of the at least one polymeric binder,

[0086] 0.01-20 wt% of the at least one alkali metal silicate, optionally, 0.01-5 wt% of the at least one alkali metal siliconate, and

[0087] 60-99.5 wt% of the inorganic particles; based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate in the coating composition, and the at least one alkali metal siliconate. Aspect 14: A process for producing a coated separator for a secondary battery, comprising applying the aqueous coating composition of any of Aspects 1-13 to at least one surface of the substrate, to form a coating layer on the substrate.

[0088] Aspect 15: The process of Aspect 14 wherein the process further comprises heating the coating layer to at least 20°C.

[0089] Aspect 16: A coated separator for a secondary battery, comprising a porous or microporous substrate and a coating layer on at least one surface of the substrate, wherein the coating layer is formed from an aqueous coating composition comprising: a) at least one polymeric binder, b) at least one alkali metal silicate, c) optionally, at least one alkali metal siliconate, and d) inorganic particles.

[0090] Aspect 17: The coated separator of Aspect 16, wherein the alkali metal silicate has the formula (I):

[0091] M2O • n SiO2(I)

[0092] M’2xSiyO2y+x, (II) where M is an alkali metal; and n is the molar ratio (MR), defining the number of moles of silica (SiO2) per mole of alkali metal oxide (M2O); and where M’ is an alkali metal ion such as Li+, Na+, K +, Rb+, Cs+, or ammonium ion NH4+.

[0093] Aspect 18: The coated separator of Aspect 17, wherein M is at least one of Na, K, Li, Rb, or Cs.

[0094] Aspect 19: The aqueous coating composition of any of Aspects 16-18, wherein the alkali metal siliconate comprises at least one alkyl siliconate.

[0095] Aspect 20: The coated separator of any of Aspects 16-17, wherein the alkali metal siliconate conforms to Formula (III):

[0096] (XO)3-mSiR(OH)m (III) where: X is alkali metal; m is 0, 1, or 2; and R is an alkyl or aryl group.

[0097] Aspect 21 : The coated separator of Aspect 20, wherein R comprises a C1-C8 alkyl or aryl group.

[0098] Aspect 22 : The coated separator of Aspect 20 or Aspect 21 , wherein R comprises at least one of methyl, ethyl, n-propyl, isopropyl, n-butyl, iso-butyl, tert-butyl, n-pentyl, iso-pentyl, tert-pentyl, neopentyl, phenyl, aryl, or cyclohexyl.

[0099] Aspect 23: The coated separator of any of Aspects 20-22 wherein R is methyl or ethyl and X is at least one of sodium, potassium, or lithium.

[0100] Aspect 24: The coated separator of any of Aspects 16-23, wherein the inorganic particles comprise at least one of ceramics, metal oxides or combinations thereof; preferably aluminum oxide (AI2O3), boehmite, aluminum oxide (AI2O3), titanium oxide (TiCh), silicon oxide (SiCh), zinc oxide (ZnO), metal hydroxides, metal carbonates, water insoluble silicates, kaolin, talc, minerals, glass, or mixtures thereof; more preferably aluminum oxide (AI2O3), boehmite, or mixtures thereof.

[0101] Aspect 25: The coated separator of any of Aspects 16-24, wherein the polymeric binder comprises, as polymerized monomer, at least one ethylenically unsaturated monomer.

[0102] Aspect 26: The coated separator of Aspect 25 wherein the ethylenically unsaturated monomer comprises at least one of vinyl aromatic monomers, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethyl hexyl acrylate, (meth)acrylic acid, or a combination thereof.

[0103] Aspect 27: The coated separator of any of Aspects 16-26, wherein the coating composition further comprises at least one of a rheology modifier, a wetting agent, a dispersant, or a combination thereof.

[0104] Aspect 28: The coated separator of any of Aspects 16-27, wherein the coating composition comprises:

[0105] 0.01-40 wt% of the at least one polymeric binder,

[0106] 0.01-20 wt% of the at least one alkali metal silicate, optionally, 0.01-5 wt% of the at least one alkali metal siliconate, and 60-99.5 wt% of the inorganic particles; based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate in the coating composition, and the at least one alkali metal siliconate.

[0107] Within this specification, embodiments have been described in a way which enables a clear and concise specification to be written, but it is intended and will be appreciated that embodiments may be variously combined or separated without departing from the invention. For example, it will be appreciated that all preferred features described herein are applicable to all aspects of the invention described herein.

[0108] In some embodiments, the invention herein can be construed as excluding any element or process step that does not materially affect the basic and novel characteristics of the compositions, prepared therefrom and methods for making and using such compositions described herein. Additionally, in some embodiments, the invention can be construed as excluding any element or process step not specified herein. Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.

[0109] EXAMPLES

[0110] Hybrid binder preparation

[0111] A hybrid binder was prepared by mixing 239 parts of Encor® CL36 (a styrene-acrylic latex polymer, 49% solids, Arkema, Inc.), 100 parts of KASIL® 1 (potassium silicate, 29.5% solids, PQ Corporation), 9 parts of SIP6898.0 (potassium methyl siliconate solution, 44-56% in water, Gelest), and 23 parts of water. Inventive Example 1

[0112] A ceramic coating slurry was prepared by mixing aluminum oxide (average particle size of about 0.4 pm), poly aery late dispersant, the above hybrid binder composition, carboxy methyl cellulose (Degree of substitution of the carboxymethyl cellulose was about 0.9-1.05, 1 % solution viscosity of the carboxy methyl cellulose was 2000-4000 cps as measured by Brookfield viscometer, LV type, spindle #4 at 30 rpm), wetting agent, and water to achieve a final solid content of about 30 wt% in water. The composition of the coating composition, by dry weight, is shown in Table 1.

[0113] Table 1 : Inventive Example 1 coating composition, by dry weight

[0114] Comparative Example 1

[0115] Comparative example 1 was prepared the same way as Inventive Example 1, except that 4.5 wt% of Encor® CL 36 (a styrene-acrylic latex polymer) was used to replace the hybrid binder composition.

[0116] Comparative Example 2

[0117] Comparative example 2 was prepared the same way as Inventive Example 1 , except that 4.5 wt% of KASIL® 1 (a water-soluble potassium silicate) was used to replace the hybrid binder composition. Preparation of ceramic coated separator membranes

[0118] A ceramic coated separator membrane was prepared by casting the ceramic coating compositions of Inventive Example 1 , Comparative Example 1 or Comparative Example 2 onto both sides of a polyethylene (PE) separator membrane about 14 pm thick using a wire bar coater, followed by drying in an oven at 60 °C for 5 mins. The final coating thickness was around 3-4 pm on each side.

[0119] Thermal resistance of ceramic coated separator membranes at 130°C

[0120] The ceramic coated separator was cut into an 8.0 cm x 8.0 cm square sample, followed by being placed in an oven at 130°C for 1 hour. Afterwards, the sample was taken out and cooled down to room temperature. The dimensions of the samples after the thermal treatment were then measured and recorded as Ml and M2 in longitudinal direction (MD) and a transverse direction (TD), respectively.

[0121] Thermal shrinkage of the sample in MD direction was reported as:

[0122] MD1 = [(8 - Ml) / 8]xl00%;

[0123] Thermal shrinkage of the sample in TD direction was reported as:

[0124] TD1 = [(8 - M2) / 8]xl00%

[0125] Thermal resistance of ceramic coated separator membranes at 150°C

[0126] The ceramic coated separator was cut into an 8.0 cm x 8.0 cm square sample, followed by being placed in an oven at 150° C for 1 hour. Afterwards, the sample was taken out and cooled down to room temperature. The lengths of the samples after thermal treatment were then measured and recorded as M3 and M4 in longitudinal direction (MD) and a transverse direction (TD), respectively.

[0127] Thermal shrinkage of the sample in MD direction was reported as:

[0128] MD2 = [(8 - M3) / 8]xl00%;

[0129] Thermal shrinkage of the sample in TD direction was reported as:

[0130] TD2 = [(8 - M4)[ / 8xl00% Characterization of the ceramic coated separator membrane porosity

[0131] The permeability (porosity) of the ceramic coated separator membrane was characterized by measuring the Gurley value using a Gurley Standard Densometer 41 ION.

[0132] Peel adhesion:

[0133] The adhesion force between the ceramic coating and the polyethylene separator membrane was characterized by measuring the 180° peel strength using a tensile / compression tester from Chemlnstruments. The ceramic coated separators were cut into 1 inch wide strips. The load cell was 25 lbs obtained from FUTEK, and the peel speed was set at 50 mm / min. The adhesion force was measured in triplicate, and the number was reported by the average value with standard deviation.

[0134] Results

[0135] The results of the thermal testing at 130°C are shown in FIG. 1 and the results of the thermal testing at 150°C are shown in FIG. 2. Thermal resistance is an important feature of separator membranes. As expected, the uncoated polyethylene (PE) separator membranes showed noticeable dimensional change after being exposed to 130 °C for 1 hour, shown in FIG ID. All the ceramic coated separator membranes exhibited improved thermal resistance compared to the uncoated membrane. The separator membrane coated by Inventive Example 1 (FIG 1A) had similar performance to Comparative Example 1 (FIG. IB) and outperformed Comparative Example 2 (FIG. 1C). Under a more challenging testing condition, 150 °C for 1 hour, a significant integrity loss was observed for the uncoated PE separator membrane (FIG. 2D). The separator membranes coated by Comparative Example 1 and Comparative Example 2 both exhibited poor thermal resistance, as evidenced by the significant shrinkage. Only Inventive Example 1 coated separator membrane retained relatively good integrity under 150 °C testing.

[0136] Table 2 shows the results of the thermal resistance, porosity (permeability) and adhesion testing of the coated membranes. Table 2: Thermal resistance, permeability (porosity) and coating adhesion testing results.

[0137] The Gurley value of the uncoated separator was measured to be 214 sec / 100 cc. For the permeability (porosity) of ceramic coated separator membranes, Inventive Example 1 coated separator membrane had better permeability (porosity) than Comparative Example 1 and Comparative Example 2, as evidenced by its lower Gurley value (Table 1). For the adhesion force between the ceramic coating and base PE separator membranes, Inventive Example 1 was similar in performance to Comparative Example 1 and outperformed Comparative Example 2 (Table 1).

[0138] In summary, it is surprising to find that Inventive Example 1 including both latex polymer and silicate as the polymeric binder for ceramic coating showed the best balance of the properties of high thermal resistance, high coating permeability (porosity), and high peel adhesion compared to using latex polymer or silicate alone as the binder. The enhanced ceramic coated separator properties associated with Inventive Example 1 will ultimately lead to improved lithium-ion battery performance.

Claims

What is claimed is:

1. An aqueous coating composition for a separator in a secondary battery comprising: a) at least one polymeric binder, b) at least one alkali metal silicate, c) optionally, at least one alkali metal siliconate, and d) inorganic particles.

2. The aqueous coating composition of claim 1, wherein the alkali metal silicate has the formula(I) or (II):M2O • n SiO2(I)M’2xSiyO2y+x, (II) where M is an alkali metal; and n is the molar ratio (MR) defining the number of moles of silica (SiCh) per mole of alkali metal oxide (M2O); and where M’ is an alkali metal ion such as Li+, Na+, K +, Rb+, Cs+, or ammonium ion NH4+.

3. The aqueous coating composition of claim 2, wherein M is at least one of Na, K, Li, Rb, or Cs.

4. The aqueous coating composition of any of claims 1-3, wherein the alkali metal siliconate comprises at least one alkyl siliconate.

5. The aqueous coating composition of any of claims 1-4, wherein the alkali metal siliconate conforms to Formula (III):(XO)3-m SiR(OH)m(III) where: X is alkali metal; m is 0, 1, or 2; and R is an alkyl or aryl group.

6. The aqueous coating composition of claim 5, wherein R comprises a C1-C8 alkyl or aryl group.

7. The aqueous coating composition of claim 5 or claim 6, wherein R comprises at least one of methyl, ethyl, n-propyl, isopropyl, n-butyl, iso-butyl, tert-butyl, n-pentyl, iso-pentyl, tert-pentyl, neopentyl, phenyl, aryl, or cyclohexyl.

8. The aqueous coating composition of any of claims 5-7, wherein R is methyl or ethyl and X is at least one of sodium, potassium, or lithium.

9. The aqueous coating composition of any of claims 1-8, wherein the inorganic particles comprise at least one of ceramics, metal oxides or combinations thereof; preferably aluminum oxide (AI2O3), boehmite, titanium oxide (TiCh), silicon oxide (SiCh), zinc oxide (ZnO), metal hydroxides, metal carbonates, water insoluble silicates, kaolin, talc, minerals, glass, or mixtures thereof; more preferably aluminum oxide (AI2O3), boehmite, or mixtures thereof.

10. The aqueous coating composition of any of claims 1-10, wherein the polymeric binder comprises, as polymerized monomer, at least one ethylenically unsaturated monomer.

11. The aqueous coating composition of claim 10, wherein the ethylenically unsaturated monomer comprises at least one of vinyl aromatic monomers, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethyl hexyl acrylate, (meth)acrylic acid, or a combination thereof.

12. The aqueous coating composition of any of claims 1-11, further comprising at least one of a rheology modifier, a wetting agent, a dispersant, or a combination thereof.

13. The aqueous coating composition of any of claims 1-12, wherein the coating composition comprises:0.01-40 wt% of the at least one polymeric binder,0.01-20 wt% of the at least one alkali metal silicate, optionally, 0.01-5 wt% of the at least one alkali metal siliconate, and60-99.5 wt% of the inorganic particles; based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate in the coating composition, and the at least one alkali metal siliconate.

14. A process for producing a coated separator for a secondary battery, comprising applying the aqueous coating composition of any of claims 1-13 to at least one surface of the substrate, to form a coating layer on the substrate.

15. The process of claim 14 wherein the process further comprises heating the coating layer to at least 20°C.

16. A coated separator for a secondary battery, comprising a porous or microporous substrate and a coating layer on at least one surface of the substrate, wherein the coating layer is formed from an aqueous coating composition comprising: a) at least one polymeric binder,b) at least one alkali metal silicate, c) optionally, at least one alkali metal siliconate, and d) inorganic particles.

17. The coated separator of claim 16, wherein the alkali metal silicate has the formula (I):M2O • n SiO2(I)M’2xSiyO2y+x, (II) where M is an alkali metal; and n is the molar ratio (MR), defining the number of moles of silica (SiO2) per mole of alkali metal oxide (M2O); and where M’ is an alkali metal ion such as Li+, Na+, K +, Rb+, Cs+, or ammonium ion NH4+.

18. The coated separator of claim 17, wherein M is at least one of Na, K, Li, Rb, or Cs.

19. The aqueous coating composition of any of claims 16-18, wherein the alkali metal siliconate comprises at least one alkyl siliconate.

20. The coated separator of any of claims 16-17, wherein the alkali metal siliconate conforms to Formula (III):(XO)3-mSiR(OH)m(III) where: X is an alkali metal; m is 0, 1, or 2; and R is an alkyl or aryl group.

21. The coated separator of claim 20, wherein R comprises a C1-C8 alkyl or aryl group.T122. The coated separator of claim 20 or claim 21, wherein R comprises at least one of methyl, ethyl, n-propyl, isopropyl, n-butyl, iso-butyl, tert-butyl, n-pentyl, iso-pentyl, tert-pentyl, neopentyl, phenyl, aryl, or cyclohexyl.

23. The coated separator of any of claims 20-22, wherein R is methyl or ethyl and X is at least one of sodium, potassium, or lithium.

24. The coated separator of any of claims 16-23, wherein the inorganic particles comprise at least one of ceramics, metal oxides or combinations thereof; preferably aluminum oxide (AI2O3), boehmite, aluminum oxide (AI2O3), titanium oxide (TiCh), silicon oxide (SiCh), zinc oxide (ZnO), metal hydroxides, metal carbonates, water insoluble silicates, kaolin, talc, minerals, glass, or mixtures thereof; more preferably aluminum oxide (AI2O3), boehmite, or mixtures thereof.

25. The coated separator of any of claims 16-24, wherein the polymeric binder comprises, as polymerized monomer, at least one ethylenically unsaturated monomer.

26. The coated separator of claim 25, wherein the ethylenically unsaturated monomer comprises at least one of vinyl aromatic monomers, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethyl hexyl acrylate, (meth)acrylic acid, or a combination thereof.

27. The coated separator of any of claims 16-26, wherein the coating composition further comprises at least one of a rheology modifier, a wetting agent, a dispersant, or a combination thereof.

28. The coated separator of any of claims 16-27, wherein the coating composition comprises:0.01-40 wt% of the at least one polymeric binder,0.01-20 wt% of the at least one alkali metal silicate, optionally, 0.01-5 wt% of the at least one alkali metal siliconate, and60-99.5 wt% of the inorganic particles; based on a total dry weight of the inorganic particles, the at least one polymeric binder, the at least one alkali metal silicate in the coating composition, and the at least one alkali metal siliconate.

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