Aluminum oxide dispersion for use as a separator coating in secondary batteries

Abstract

1. An aqueous dispersion containing aluminum oxide powder, wherein the aluminum oxide powder is present in the form of aggregated primary particles having an aggregate size distribution with a median aggregate size (D50) of 220 nm to 500 nm as determined by dynamic light scattering measurements, and wherein the aluminum oxide powder is dispersed in an amount of at least 20 wt. %, preferably 40 to 60 wt. %, more preferably 50 to 60 wt. %, based on the total weight of the dispersion, over a period of 10 minutes. 2 / g~100m 2 / g BET, and the dispersion at least one carboxylic acid from the group consisting of dicarboxylic acids and / or hydroxytricarboxylic acids having 2 to 7 carbon atoms, and - Aqueous dispersions, characterized in that they further comprise at least one amino alcohol having 1 to 6 carbon atoms, preferably DMEA (dimethylethanolamine), 2-amino-2-methyl-1-propanol.

Description

[Technical Field]

[0001] The present invention generally relates to aluminum oxide dispersions, coatings for secondary battery separators using the aluminum oxide dispersions, and methods of making the dispersions and coatings. The present invention further relates to secondary batteries and electrical devices using the separators. [Background technology]

[0002] Secondary batteries, such as lithium-ion batteries, use separators made of polyolefins in membrane form due to their good mechanical properties, chemical stability, and low cost. Polyolefin separators are often coated with inorganic materials to enhance thermal stability and improve the overall safety of the battery cell.

[0003] Moisture inside a lithium-ion battery impairs its performance. Therefore, materials used in lithium-ion battery separators must meet strict moisture requirements. Typically, a residual moisture limit of 2000 ppm is acceptable, but further reductions in moisture content are desirable.

[0004] Dispersions of aluminum oxide in aqueous media are well known. For example, EP 1987095 and US 2008264299 describe aqueous aluminum oxide dispersions and their use as coatings in various applications. However, these dispersions use various hygroscopic materials. For example, the dispersion described in EP 19870951 contains hygroscopic organic phosphonic acid components and sodium hydroxide, and therefore the residual water content after drying is too high for lithium-ion battery separator coatings. Furthermore, sodium ions can also alter the electrical performance of lithium-ion batteries. The aluminum oxide dispersion described in US 2008264299 also uses sodium hydrogen phosphate as an additive, which is hygroscopic and can increase the moisture content in the ceramic separator coating.

[0005] EP 1771518 describes an aqueous dispersion that can be obtained by placing an agglomerated titanium dioxide powder having a specific surface area of ​​20 to 150 m / g in water in an amount such that the desired dispersion contains at least 20% by weight titanium dioxide, at least one amino alcohol having 1 to 6 carbon atoms, and at least one carboxylic acid from the group consisting of dibasic carboxylic acids and / or hydroxycarboxylic acids having 2 to 6 carbon atoms. However, titanium oxide cannot be used as a coating for the separator because it irreversibly binds lithium ions, reducing the capacity of the battery.

[0006] Continuing higher safety and performance requirements for secondary batteries necessitate further improvements in the materials used to coat the separator. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] European Patent No. 1987095 [Patent Document 2] US Patent Application Publication No. 2008264299 [Patent Document 3] European Patent No. 19870951 [Patent Document 4] European Patent No. 1771518 Summary of the Invention [Problem to be solved by the invention]

[0008] It has been found that parameters such as the specific surface area and size of the flame synthetically obtained aluminum oxide agglomerate particles can have a significant effect on the amount of binder used in the aluminum oxide coating formulation, as well as on the coating properties, in particular the residual moisture and air permeability of the coating.

[0009] The objective of this invention is to use nanostructured, flame-synthesized aluminum oxide (Al2O3) with a low BET specific surface area and simultaneously a large aggregate size distribution to form highly packed, stable dispersions particularly suitable for the formation of ceramic coatings for lithium-ion battery separators. A "low" BET specific surface area is defined as 10-100 m 2 / g, preferably 10 to 90m 2 / g, more preferably 30 to 90m 2 / g, more preferably 30 to 55m 2 / g. A "large" aggregate size distribution means an aggregate size distribution having a median particle size (D50) of 220 nm to 500 nm, preferably 230 nm to 400 nm, and more preferably 250 nm to 300 nm, as determined by dynamic light scattering measurements.

[0010] Separators for which this coating is particularly suitable are made of polyolefin materials, such as polyethylene and polypropylene, but the coating can also be used with separators made of other plastic materials, such as those made of nylon, PET (polyethylene terephthalate), PVC (polyvinyl chloride), PI (polyimide), PVDF (polyvinylidene fluoride), and PEEK (polyether ether ketone). [Means for solving the problem]

[0011] The aluminum oxide dispersions according to the present invention exhibit high compatibility with a variety of different lithium-ion battery binders. Thin, homogeneous coatings with thicknesses of less than 5 μm, preferably less than 3 μm, and more preferably less than 2 μm, with a lower limit of 500 nm, can be obtained on separators with low water content of less than 1000 ppm and high air permeability as indicated by low Gurley numbers of less than 100 s.

[0012] According to a first aspect of the present invention, there is provided an aqueous dispersion containing aluminum oxide powder, wherein the aluminum oxide powder is present in the form of aggregated primary particles having an aggregate size distribution with a median aggregate size (D50) of 220 nm to 500 nm, preferably 230 to 400 nm, and more preferably 250 nm to 300 nm, as determined by dynamic light scattering measurements, and the aluminum oxide powder is present in an amount of at least 20 wt. %, preferably 40 to 60 wt. %, more preferably 50 to 60 wt. %, based on the total weight of the dispersion, at a concentration of 10 ml. 2 / g~100m 2 / g BET, and the dispersion at least one carboxylic acid from the group consisting of dicarboxylic acids and / or hydroxytricarboxylic acids having 2 to 7 carbon atoms, and An aqueous dispersion is provided, characterized in that it further comprises at least one amino alcohol having from 1 to 6 carbon atoms, preferably at least one of DMEA (dimethylethanolamine) and 2-amino-2-methyl-1-propanol.

[0013] The aqueous dispersion may have a viscosity of less than 100 mPas (millipascals), preferably between 100 and 10 mPas, more preferably between 60 and 15 mPas. 2 / g, preferably 10 to 90m 2 / g, preferably 30 to 90m 2 / g, more preferably 30 to 55m 2 / g BET surface area.

[0014] The aluminum oxide agglomerated primary particles have a unimodal particle size distribution with Z-avg(v) of less than 500 nm, preferably between 500 nm and 150 nm, more preferably between 350 nm and 180 nm.

[0015] In one embodiment, for example, the at least one carboxylic acid can be at least one of citric acid and oxalic acid, the at least one amino alcohol can be at least one of dimethylethanolamine (DMEA) and 2-amino-2-methyl-1-propanol, and the aluminum oxide powder can be of flame synthetic origin, meaning it is a flame synthesized aluminum oxide powder.

[0016] The aqueous dispersion may be further characterized as being free of sodium dihydrogen phosphate, phosphonic acid, or hygroscopic materials.

[0017] At least one amino alcohol has a specific surface area of ​​2.5 to 8.0 μmol / m of aluminum oxide. 2 may be present in the dispersion in an amount of

[0018] At least one carboxylic acid has a specific surface area of ​​1.0 to 4.0 μmol / m 2 may be present in an amount of

[0019] The aqueous dispersion is stable in the pH range of 5-10 for at least 1 month, preferably at least 6 months.

[0020] According to another aspect of the present invention, there is provided a coating composition for a secondary battery separator, further characterized by being obtained by adding a binder and a wetting agent to the aqueous dispersion.

[0021] The coating composition comprises aluminum oxide particles in an amount of 5 wt. % to 70 wt. %, preferably 10 wt. % to 60 wt. %, more preferably 15 wt. % to 50 wt. %, based on the total weight of the coating composition; a binder in an amount of 1 to 20 wt. %, preferably 2 to 15 wt. %, more preferably 3 to 10 wt. %, based on the total weight of the coating composition; and a wetting agent in an amount of 0.01 to 1.0 wt. %, based on the total weight of the coating composition may include:

[0022] According to yet another aspect of the present invention, the process for preparing an aqueous dispersion comprises: - forming a water slurry of agglomerated aluminum oxide powder, at least one amino alcohol, and at least one carboxylic acid in water in amounts corresponding to the desired amount in the dispersion; - Producing a pre-dispersion by introducing an amount of energy into the water slurry that is less than the energy required to form the dispersion; and producing the dispersion by introducing the pre-dispersion into a high-energy mill and grinding the pre-dispersion using the high-energy mill at a pressure of at least 500 bar.

[0023] The energy introduced into the water slurry to produce the pre-dispersion is 1000 kJ / m 3 It may be less than.

[0024] In one embodiment, the pre-dispersion may be split into at least two partial streams that are introduced into a high energy mill and discharged through a nozzle to collect in a gas or liquid filled reaction space.

[0025] The present invention also relates to the use of an aqueous dispersion for forming a coating layer on at least one surface of a separator of a secondary battery, the separator is a thin film made of at least one of polyolefin, nylon, PET (polyethylene terephthalate), PVC (polyvinyl chloride), PI (polyimide), PVDF (polyvinylidene fluoride) and PEEK (polyether ether ketone); The coating formed on the separator has a moisture content of less than 1000 ppm and an air permeability defined by a Gurley value of at most 100 s, preferably at most 50 s, more preferably at most 30 s.

[0026] The battery may be any secondary battery, such as, for example, a lithium ion battery. In one embodiment, the battery is a lithium ion battery and the separator is made of a polyolefin, for example, including at least one of polypropylene, polyethylene, or any combination thereof.

[0027] The separator is a membrane comprising at least one polyolefin; a coating layer obtained by applying a coating composition using an aluminum oxide dispersion onto at least one surface of the membrane and applying heat to dry the coating layer; and The coating layer formed on the separator has a moisture content of less than 1000 ppm and an air permeability, as defined by a Gurley value, of a maximum of 100 s, preferably a maximum of 50 s, and more preferably a maximum of 30 s, as measured using the coating formed on both sides of the separator.

[0028] In one embodiment, the membrane may be made of polyethylene and may have a thickness of 3 to 20 μm, and the coating layer may be homogeneous and have a thickness of less than 5 μm, preferably less than 3 μm, more preferably less than 2 μm, with a lower limit of 500 nm.

[0029] The present invention further relates to a secondary battery including the separator, and a device including the secondary battery.

[0030] The equipment may comprise an electric or electronic device, such as, for example, a mobile phone, an electronic watch, a key fab, a laptop computer, a desktop computer, a computer pad, a power tool, a vacuum cleaner, an electric lawn mower, an appliance, an electric vehicle, or the like.

[0031] These and other features and advantages of the present invention will be understood by those skilled in the art from the following detailed description taken in conjunction with the following drawings. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1 is a simplified schematic diagram of a method for making an aluminum oxide dispersion according to one embodiment of the present invention. [Figure 2] 1 illustrates a process for making aluminum oxide powder according to one embodiment of the present invention. [Figure 3] FIG. 1 is a simplified schematic diagram of a method for making a coating composition for a lithium ion separator using an aluminum oxide dispersion according to one embodiment of the present invention. [Figure 4] FIG. 1 is a simplified schematic diagram of a lithium-ion battery having a separator coated on both sides with an aluminum oxide coating according to one embodiment of the present invention. [Figure 5A] 1 shows the aggregate particle size distribution of aluminum oxide powder in an aqueous dispersion according to an embodiment of the present invention. [Figure 5B] 1 shows the aggregate particle size distribution of aluminum oxide powder in an aqueous dispersion according to an embodiment of the present invention. [Figure 5C] 1 shows the aggregate particle size distribution of aluminum oxide powder in an aqueous dispersion according to an embodiment of the present invention. [Figure 5D] 1 shows the aggregate particle size distribution of aluminum oxide powder used in aqueous dispersions prepared according to comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0033] 1, a method of making a dispersion containing aluminum oxide according to one embodiment is provided. Accordingly, the method comprises: - according to step 102, placing in water the aggregated aluminum oxide, at least one amino alcohol having 1 to 6 carbon atoms, and at least one carboxylic acid from the group consisting of dicarboxylic acids and / or hydroxytricarboxylic acids having 2 to 7 carbon atoms; - producing a pre-dispersion by introducing an amount of energy less than the energy required to form the dispersion, according to step 104; then, according to step 106, producing a dispersion by introducing the pre-dispersion into a high-energy mill and grinding the pre-dispersion using the high-energy mill at a pressure of at least 500 bar; may include:

[0034] For example, the pre-dispersion may have a viscosity of 1000 kJ / m 3 (kilojoules per cubic meter) of energy into the aqueous slurry. In some embodiments, the pre-dispersion may be formed by introducing less than 200 kJ / m 3 It can be formed by introducing the following energy into the aqueous slurry:

[0035] In some embodiments, the pre-dispersion may be split into at least two partial streams, which may be placed in a high energy mill under a pressure of at least 500 bar, discharged through a nozzle, and allowed to collide with one another in a reaction chamber filled with a gas or liquid.

[0036] The agglomerated aluminum oxide is 10 to 100 m 2 / g, preferably 10 to 90m 2 / g, more preferably 30 to 90m 2 / g, more preferably 30 to 55m 2 / g BET specific surface area.

[0037] Amino alcohols have a specific surface area of ​​2.5 to 8.0 μmol / m of aluminum oxide. 2 The carboxylic acid may be present in the dispersion in an amount of 1.0 to 4.0 μmol / m2 of the specific surface area of ​​the aluminum oxide. 2 may be present in an amount of

[0038] The introduction of energy into the aqueous slurry to produce the pre-dispersion can be carried out by using mechanical means. Suitable mechanical means for producing dispersions, such as the pre-dispersions described herein, are generally known in the art and may include, by way of illustrative but non-limiting examples, stirring, agitation, shaking, and / or grinding. In particular, shear conditions can be applied to introduce energy into the aqueous slurry. Suitable devices for preparing the pre-dispersion can be, for example, rotor / stator machines or toothed disks.

[0039] In a preferred embodiment, the pressure during the high-energy milling process may be at least 2000 bar. It is also noted that it may be advantageous to expose the dispersion to the high-energy milling process several times.

[0040] The present invention provides an aqueous dispersion obtainable by the above process. The dispersion may have a low viscosity of less than 100 mPas, preferably between 100 and 10 mPas, more preferably between 60 and 15 mPas, and may comprise Al2O3 particles in an amount of at least 20 wt% solids by weight of the total dispersion weight, preferably between 40 and 60 wt%, more preferably between 50 and 60 wt% solids by weight of the total dispersion weight, solids as that term is used herein being the weight percentage of aluminum oxide particles in the dispersion.

[0041] The dispersion of aluminum oxide may preferably have a unimodal particle size distribution with Z-avg(v) of less than 500 nm, preferably between 500 nm and 150 nm, more preferably between 350 nm and 180 nm.

[0042] Additionally, the dispersion does not contain any hygroscopic ingredients such as sodium dihydrogen phosphate or phosphonic acids used in some conventional metal oxide dispersions.

[0043] The inventors have discovered that large aggregate particle size of aluminum oxide has an unexpectedly positive effect on the air permeability of coating layers formed as described herein from aluminum oxide dispersions, resulting in coatings with lower total water content that meet and exceed the moisture requirements for ceramic coatings of lithium ion battery separators.

[0044] For separator ceramic coating applications, dispersions having basic conditions as indicated by a basic pH are preferred, with dispersions having a pH of 8 to 10 being more preferred. Aluminum oxide dispersions within the basic pH range, particularly within the preferred range of 8 to 10, have been found to provide improved compatibility with binder systems used in coating slurry formulations.

[0045] Al2O3 powder The agglomerated aluminum oxide powder may be flame-synthetically prepared aluminum oxide, also known as fumed aluminum oxide powder or fumed alumina powder. Flame-synthetically prepared here is understood to mean a powder obtainable by flame hydrolysis or flame oxidation. The powder thus prepared consists of aggregates of sintered primary particles initially formed during the reaction. These aggregates may also be called secondary particles. Multiple aggregates may subsequently form agglomerates. Due to the reaction conditions, flame-synthetically prepared powders exhibit very low surface porosity and surface hydroxyl groups, with a maximum of 10 OH / nm².

[0046] Dispersions using mixed metal oxide powders containing aluminum oxide powder can also be made, however, dispersions using powders containing aluminum oxide as the sole metal oxide component are preferred.

[0047] According to the invention, the aluminum oxide powder used in the dispersion is 10 to 100 m 2 / g, preferably 10 to 90m 2 / g, more preferably 30 to 90 m 2 / g, more preferably 30 to 55m 2 / g BET surface area, and characterized by a D50 of 220 to 500 nm, preferably 230 to 400 nm, more preferably 250 nm to 300 nm, as determined by dynamic light scattering measurements; The aluminum oxide powder preferably has a monomodal distribution of aggregate particle sizes.

[0048] The dispersions provided by the present invention are stable in the pH range of 5 to 10, meaning that they are stable against settling and reagglomeration for a period of at least 1 month, preferably 6 months.

[0049] The volume-related aggregate diameter (Z-avg(v)) is less than 500 nm and no particles greater than 1000 nm are detectable in dispersions according to the invention by conventional light scattering methods for determining particle size distribution in dispersions, such as dynamic (e.g., Malvern Zetasizer or Horiba LA-950).

[0050] Synthesis of aluminum oxide Aluminum oxide powder can be preferably produced by a flame synthesis process. Referring now to FIG. 2, an example of a flame synthesis process for the synthesis of aluminum oxide powder is provided. This process involves evaporating aluminum chloride (AlCl) in an evaporator 7 and supplying aluminum chloride vapor "a" to a mixing chamber 1. The vapor may be transported to the mixing chamber via an inert gas. Separate from the aluminum chloride vapor, combustion gases including hydrogen "b" and primary air "c" are introduced into the mixing chamber 1. Air "c" may optionally be enriched with oxygen. Air "c" may optionally be preheated before being supplied to the mixing chamber 1.

[0051] The aluminum oxide particles produced are in the form of agglomerated primary particles, which are pore-free and have hydroxyl groups on their surfaces. Hydrochloric acid is formed as a by-product in the conversion of aluminum chloride, most of which is removed from the aluminum oxide particles by steam treatment. As a result, only a small amount of chlorine remains on the aluminum oxide particles.

[0052] The hydrogen b is preferably used in slight excess compared to the theoretical amount required for the complete hydrolysis of aluminum chloride according to the following equation:

[0053] 2H2+O2→2H2O 2AlCl3 + 3H2O → Al2O3 + 6HCl The ratio of supplied hydrogen to stoichiometrically required hydrogen is called the "gamma" ratio.

[0054] The ratio of supplied oxygen to stoichiometrically required oxygen is called the "lambda" ratio.

[0055] The "gamma" and "lambda" ratios themselves are commonly known to those skilled in the art, as described, for example, in US Pat. No. 8,197,791.

[0056] The oxygen excess, or lambda ratio, required for this reaction for complete hydrolysis of aluminum chloride is greater than 1 to 5.

[0057] The reaction mixture "d" is fed into a burner (inside the reaction chamber 2) in a central tube and ignited. The exit velocity of the reaction mixture from the burner can range from 10 m / s to 100 m / s. The flame burns in a water-cooled reaction chamber 2. The reaction gases and solids from the reaction chamber are cooled in a cooling coil 3 before entering a gas-solid separation unit 4, e.g., a cyclone and / or a filter.

[0058] The resulting aluminum oxide powder is then separated from the gas in a downstream gas-solid separation unit 4 (e.g., a cyclone) and deposited at the bottom of the gas-solid separation unit 4, where it is collected via the bottom outlet. The powder from 4 is transferred to a deoxidation unit 5 to remove the acid from the powder. The aluminum oxide powder is treated with countercurrent air and steam inside the unit 5 at a high temperature, e.g., about 700 °C. The temperature is not limited to 700 °C and can generally range from 400 °C to 900 °C. The purpose of treating the aluminum oxide powder with air and steam at high temperature is to remove chlorine (e.g., HCl, chlorine gas) and adjust the powder's pH to a value between 2 and 7. Depending on the specific intended use of the aluminum powder, the powder pH can be adjusted to a specific value within the range of 2 to 7. The powder is collected in a silo 6 and can be further processed as needed, e.g., packaged. The discharge velocity of the reaction mixture from the mixing chamber to the reaction chamber can be at least 10 m / s.

[0059] The gamma ratio can be from 0.9 to 1.6, preferably from 1.0 to 1.4, and more preferably from 1.0 to 1.2.

[0060] AlCl3 / m in the range of 0.2-0.6 kg 3 gases may be used.

[0061] In a specific embodiment of the process according to the invention, a secondary gas consisting of air and / or nitrogen can be introduced into the reaction chamber. The ratio of primary air to secondary gas preferably has a value between 10 and 0.5. The introduction of the secondary gas can help to avoid caking in the reaction chamber.

[0062] dispersion The amino alcohols in the dispersions according to the invention are preferably selected from the group comprising monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, N,N-dimethylisopropanolamine, 3-amino-1-propanol, 1-amino-2-propanol, 2-amino-2-methyl-1-propanol and / or N,N-dimethylethanolamine, N,N-dimethylethanolamine and 2-amino-2-methyl-1-propanol being particularly preferred.

[0063] The carboxylic acids in the dispersions according to the invention are preferably selected from the group comprising the dicarboxylic or hydroxytricarboxylic acids oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, lactic acid, malic acid, tartaric acid and / or citric acid, with citric acid and oxalic acid being particularly preferred.

[0064] In the dispersion according to the invention, the content of amino alcohol and at least one dicarboxylic acid or hydroxytricarboxylic acid is such that, for the amino alcohol, the specific surface area of ​​aluminum oxide is 2.5 to 8.0 μmol / m 2 For carboxylic acids, the specific surface area of ​​aluminum oxide is 1.0 to 4.0 μmol / m 2 In a preferred embodiment, the content of the amino alcohol and at least one dicarboxylic acid or hydroxytricarboxylic acid is such that the specific surface area of ​​the aluminum oxide is 3.0 to 6.0 μmol / m 2 For carboxylic acids, the specific surface area of ​​aluminum oxide is 1.5 to 3.0 μmol / m 2 It could be.

[0065] The dispersion according to the invention may optionally contain at least one preservative for long-term stability and to prevent bacterial and algal growth. Suitable preservatives may include: Aqueous formulations of 2-methylisothiazolin-3-one (MIT), benzisothiazolinone (BIT), 2-bromo-2-nitro-propane-1,3-diol, and 3(2H)-5-chloro-2-methyl-isothiazolone, and mixtures thereof, formaldehyde donors based on dimethylol or trimethylol urea, formamidomethylol, paraformaldehyde, bronopol, nitrilodibromopropionamido 1,3-di(hydroxymethyl)-5,5-dimethylhydantoin, or hexahydrotriazine.

[0066] A particularly preferred preservative is ACTICIDE MV, a commercially available mixture of CIT and MIT supplied by the UK company Thor.

[0067] In the dispersion according to the invention, the preservative may be present in an amount of 0.02 to 0.4% by weight, preferably 0.05 to 0.2% by weight, based on the total amount of the dispersion.

[0068] coating The present invention also provides the use of an aluminum oxide dispersion according to the invention for the preparation of a coating for a separator of a secondary battery, such as for example a lithium ion battery.

[0069] The coating composition may comprise a dispersion according to the present invention and at least one binder. The binder may preferably be an acrylate-based compound. Ideally, the binder should be hydrophilic.

[0070] The coating composition may have a content of aluminum oxide particles of 5 wt % to 70 wt %, preferably 10 wt % to 60 wt %, more preferably 15 wt % to 50 wt %, based on the total weight of the coating composition.

[0071] The coating composition may further have a binder content of 1 to 20% by weight, preferably 2 to 15% by weight, more preferably 3 to 10% by weight, based on the aluminum oxide powder.

[0072] The coating composition may further comprise a wetting agent and optionally other auxiliary substances such as pH buffers and viscosity aids.

[0073] 3, a coating composition can be prepared by adding a dispersion according to the present invention to a solution of a binder while stirring, according to step 302. While continuing to stir, a wetting agent and optionally other auxiliary substances such as additives are further added, according to step 304. The preparation of the coating composition further includes diluting the mixture until a desired ratio of aluminum oxide powder to binder and a desired total solids content is established, according to step 306, and obtaining a coating composition comprising aluminum oxide in an amount of 15-50 wt.%.

[0074] As described above, the coating composition may be obtained by forming a mixture of a binder, a wetting agent, an aluminum oxide dispersion, and optionally other additives, preferably with stirring. Figure 3 shows an example of the order in which the various parts of the coating composition may be added. However, it should be noted that the order in which the various parts of the mixture are added may be changed. For example, the binder and wetting agent may be added to the aluminum oxide dispersion with stirring to form a mixture. As another example, the binder and wetting agent may be mixed first, and then the aluminum oxide may be added to the binder and wetting agent mixture with stirring. The mixture may be optionally stirred for a period of time (several minutes to an hour) to ensure homogeneity and then degassed, if necessary. In some embodiments, degassing may be performed under vacuum. It should be understood that other additives include, for example, pH buffers and viscosity enhancers.

[0075] The process may include diluting the dispersion to a desired solids content, based on the total weight of the dispersion before adding the binder and wetting agent, prior to adding the binder and wetting agent to the dispersion. The desired solids content will depend largely on the coating process used. For example, the dispersion dilution may be to a solids content in the range of 15-50% by weight, i.e., aluminum oxide, as shown in step 308.

[0076] The coating composition is particularly suitable for forming a thin coating film on a lithium ion battery separator.

[0077] In some embodiments, the coating composition resulting from the above process may comprise aluminum oxide in an amount of 5 to 50 wt % based on the total weight of the coating composition, a binder in an amount of 1 to 15 wt % based on the weight of the aluminum oxide, and a wetting agent in an amount of 0.01 to 1.0 wt % based on the total weight of the coating composition.

[0078] The binder may be selected from any suitable binder. For example, some preferred binders may include acrylate-based compounds. Some examples of suitable binders may include polyvinyl alcohol, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and modified polyvinylidene fluoride (PVDF).

[0079] A binder is added to the coating composition to adhere the oxide particles to the polymer surface and to adhere the oxide particles to each other.

[0080] Any suitable wetting agent can be used, including, for example, acetylene glycols and their alkoxylates, ethoxylates, or ethylene oxide-propylene oxide copolymers, octyl- or nonylphenols, and fluorosurfactants (also known as fluorinated surfactants), including perfluorocarboxylic acids such as perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). Other suitable wetting agents include eugenol polyethers and eugenol polyether siloxanes, as described in U.S. Patent No. 9,993,786 B2. Still other suitable wetting agents include lithium dodecylbenzenesulfonate, nonionic fluorosurfactants, and lithium stearate.

[0081] The purpose of adding a wetting agent in a coating composition is to reduce the surface tension of the aqueous coating slurry, making the coating compatible with the substrate surface to which it is applied. For example, in some embodiments, the substrate is the surface of a lithium ion battery separator, which may be made of a polyolefin material.

[0082] Applying a coating onto the separator Aluminum oxide-containing coating compositions are used to apply thin, uniform ceramic coatings to polyolefin separators in secondary batteries, such as lithium-ion batteries. Polyolefin separators typically have a thickness of 3 to 20 μm. To apply the coating, according to some embodiments, the separator membrane may be fixed on a vacuum table, and a slot die may be placed over the separator with an appropriate gap between the slot die and the separator. At the start of the coating process, the slot die speed and the coating formulation flow rate are set to desired values ​​to control the thickness of the coating applied to the separator surface. Once the separator surface is covered with a thin film of the coating composition, the wet-coated lithium-ion battery separator is dried at an elevated temperature for a specified time to remove residual moisture. This process can be repeated to apply an additional ceramic layer to the other side of the separator.

[0083] The resulting coating film may have a thickness of 0.2 μm to 10 μm, preferably 0.5 μm to 5 μm, and more preferably 1 μm to 3 μm. The resulting coating exhibits an overall increase in air permeability as indicated by a Gurley number of up to 100 s, preferably up to 50 s, and more preferably up to 30 s.

[0084] By "homogeneous" it is meant that the coating film is easily applied to the surface of the separator and forms a film of uniform thickness with uniform appearance and air permeability over the entire surface area.

[0085] FIG. 4 shows a lithium-ion battery, generally designated 300, including a separator made from a membrane 316 and coated with a coating layer 318. The coating layer 318 is formed on both sides of the membrane 316 using the process described above. The lithium-ion battery 300 can be used in electronic and electrical devices 400, including, for example, mobile phones, computers (laptop computers, desktop computers, computer pads), electronic watches, key fobs, appliances, power tools, vacuum cleaners, electric lawn mowers, and electric vehicles. The lithium-ion battery 300 further includes a cathode active material 312 on a cathode plate 310 and an anode active material 322 on an anode plate 320. An electrolyte 324 is disposed around the separator and between the anode active material 322 and the cathode active material 312. [Example]

[0086] Analysis procedure Size distribution measurement (Malvern) Dynamic light scattering (DLS) is a physics technique that can be used to determine the size distribution profile of small particles in suspension or polymers in solution. This instrument can be used to measure the particle size of dispersed materials (e.g., inorganic nanoparticles or polymer spheres) in the range of 3 nm to approximately 6 μm. The measurement is based on the Brownian motion of particles within a medium and the scattering of incident laser light due to the difference in refractive index between the liquid and solid materials.

[0087] To measure the particle size distribution, a Malvern Zetasizer nano S is used, with the Z-avg(v) value being the mean value of the distribution. In a plastic cuvette, a single drop of the as-produced dispersion is diluted with distilled water to obtain a slightly turbid solution. In automated mode, this has been measured using the aforementioned equipment.

[0088] BET The BET specific surface area of ​​the particles is determined in accordance with DIN 66131.

[0089] Viscosity measurement Dynamic viscosity was measured using a Physica MCR 300 from Anton Paar using rotational viscosimetry and a single gap cylinder CC 27.

[0090] The viscometer's motor drives a bob within a stationary cup. The rotational speed of the bob is preset to produce a specific motor torque required to rotate the measurement bob. This torque must overcome the viscous forces of the test material and is therefore a measure of its viscosity.

[0091] The data are measured at a shear rate of 100 s-1 and 23°C.

[0092] Stability determination The stability of the dispersion is determined by visual inspection and viscosity control after a certain period of time (1 week and 1 month). Good stability is recognized when there are no visible effects such as settling, flocculation, or separation within the dispersion and the viscosity remains below 100 mPas after production. All samples are stored at room temperature.

[0093] Solids The solids content of the dispersions according to the invention is determined using a muffle furnace. A specified amount of dispersion (3 g) is weighed into a crucible. The water is first evaporated by treating the dispersion in a furnace at 105°C for 120 minutes, and then all other components are burned off by treating at 1000°C for 120 minutes. The remaining weight is measured and divided by the original value to obtain the solids content.

[0094] Air permeability Air permeability was measured by the Gurley method, which is the time in seconds it takes for 100 cc (cubic centimeters) of air to pass through a one square inch membrane when a constant pressure of 4.88 inches of water is applied.

[0095] The air permeability of uncoated and coated separators was measured using a Gurley Precision Instruments Model 4110N GURLEY Densometer. 100 cc of air was forced through the separator membrane and the time was recorded. The shorter the time, the higher the air permeability (=lower Gurley number) and the better the Li-ion conductivity.

[0096] Gurley measurements were performed on ceramic coated and related uncoated separators to directly compare the effect of the ceramic coating on air permeation performance.

[0097] water content The water content was determined by Karl Fischer analysis. The water content was measured using a Mettler-Toledo C30S device. For the KF measurements, a temperature of 300°C for 10 minutes was preset. 0.1 g of each sample (oxide powder, dry dispersion, dry coating slurry, and ceramic coated separator) was used for the test series, and multiple measurements were performed. The samples were weighed directly into KF vials.

[0098] Example Preparation of aluminum oxide powder The aggregate size distribution of the powders was determined by DLS (dynamic light scattering).

[0099] The BET specific surface area of ​​the particles was determined in accordance with DIN 66131.

[0100] Gamma ratio = H2 supplied / H2 stoichiometrically required Lambda ratio = O2 supplied / O2 stoichiometrically required Example 1 (present invention): Aluminum chloride (AlCl3) is vaporized and the vapor is transferred to a mixing chamber. Separately from the feedstock, combustion gases containing hydrogen and primary air are introduced into the mixing chamber. The combustion gases have a hydrogen excess of 1.05 compared to the theoretical value required for complete hydrolysis of AlCl3 according to the following equation: 2H2+O2→2H2O 2AlCl3 + 3H2O → Al2O3 + 6HCl The oxygen excess ratio for this reaction to obtain complete hydrolysis of AlCl is 1.04. Therefore, the values ​​of the gamma and lambda ratios were 1.05 and 1.04, respectively.

[0101] The reaction mixture was fed into a burner in the central tube and ignited. The exit velocity of the reaction mixture from the burner was 33.7 m / s. The flame was burned in a water-cooled reaction chamber. The powder formed was deposited in a downstream cyclone and filter and then treated with countercurrent air and steam at approximately 700°C.

[0102] The BET specific surface area of ​​the obtained powder was 44 m 2 The aggregate particle size distribution obtained by dynamic light scattering is shown in Figure 1 and had a D50 value of 260 nm.

[0103] Example 2 (Comparative): Comparative Example 1 was carried out according to the procedure described in Example 1, except that the combustion gas had a hydrogen excess of 2.3 compared to the theoretical value required for the complete hydrolysis of aluminum chloride according to the following equation: 2H2+O2→2H2O 2AlCl3 + 3H2O → Al2O3 + 6HCl The oxygen excess ratio for this reaction to obtain complete hydrolysis of AlCl was 0.95. The gamma and lambda ratio values ​​for Example 2 were 2.3 and 1.04, respectively.

[0104] The reaction mixture was fed into a burner in the central tube and ignited. The exit velocity of the reaction mixture from the burner was 37.6 m / s. The flame was burned in a water-cooled reaction chamber. The powder formed was deposited in a downstream cyclone and filter and then treated with countercurrent air and steam at 700 °C.

[0105] The BET specific surface area of ​​the obtained powder was 48m 2 / g.

[0106] The aggregate particle size distribution obtained by dynamic light scattering is shown in Figure 1 and had a D50 value of 206 nm.

[0107] Measurement of aggregate size distribution: The aggregate size distribution is determined by DLS measurements using a SYMPATEC NANOPHOX instrument. For analysis, a 20g dispersion of 1 wt% aluminum oxide in water is prepared by sonication for 5 min using an ultrasonicator (Hielscher UP400St, amplitude 50%). For accurate measurements using the Nanophox, a single scattering ratio in the range of 20-80% is set by diluting 100-500mg of this as-produced dispersion with distilled water to a total volume of 2.5g.

[0108] Further examples were carried out in the same manner as in Example 1 (key parameters of the reaction conditions and physicochemical values ​​of the produced aluminum oxide powder are included in Table 1). Examples 1 and 3 are examples of the present invention. Examples 2 and 4 are comparative examples.

[0109] [Table 1]

[0110] In Table 1, *v B = exit velocity from the burner. Also, gamma and lambda values ​​are based on a core gas of primary air, hydrogen, and inert gases. Concentration of Al2O3 ("c") in the total gas volume based on the core gas (i.e., AlCl3 (as gas phase) and PH2; primary air), which is all gases passing through the core tube. All other gases (MH2 and secondary air) are not considered in the concentration of Al2O3 core concentration. Concentration of Al2O3 (all) refers to the concentration of Al2O3 based on the entire gas stream, including MH2 and secondary air. Note that MH2 and secondary air do not contribute to product variation; only the core gas contributes to product variation.

[0111] Preparation of Aluminum Oxide Dispersion Example D1: A 0.85 kg quantity of citric acid (2.0 μmol / m per specific surface area of ​​Al2O3) 2 citric acid) and 48.3 kg of demineralized water are placed in the reaction vessel. Then, in order to obtain a fluid pre-dispersion, 0.85 kg of 2-amino-2-methyl-1-propanol (4.2 μmol / m2 per specific surface area of ​​Al2O3) is added. 2 (equivalent to 45 ml of amino alcohol) is added in proportion to the amount of powder added. 2 50.0 kg of the aluminum oxide powder of Example 1 having a BET specific surface area of ​​1 / g is drawn under shear conditions through the suction pipe of the Ystral Conti-TDS 3, and once the drawing is complete, the pre-dispersion is subjected to shearing at 3000 rpm for 30 minutes.

[0112] The resulting dispersion had 50 wt. % Al2O3, a unimodal particle size distribution with a Z-avg(v) value of 217 nm, a viscosity of 58 mPas (at a shear rate of 100 s-1), and good stability. The aggregate size distribution by volume of the aluminum oxide dispersion is shown in Figure 5A. As can be seen in Figure 5A, the aluminum oxide powder has an approximately bell-shaped curve and contains no particles with diameters greater than 1000 nm. The aluminum powder also contains no particles with diameters less than 50 nm.

[0113] Example D2: The pre-dispersion produced as described in Example D1 is fed in one pass through a UHDE high pressure device HPD 4075-nano through a diamond nozzle with a diameter of 0.20 mm at a pressure of 2500 bar.

[0114] The resulting dispersion had 50 wt% Al2O3, exhibited a unimodal particle size distribution with a Z-avg(v) value of 187 nm, a viscosity of 16 mPas (at a shear rate of 100 s-1), and good stability. The aggregate size distribution by volume of the aluminum oxide dispersion is shown in Figure 5B.

[0115] Example D3: The pre-dispersion produced as described in Example D1 is fed twice through a UHDE high pressure device HPD 4075-nano through a diamond nozzle with a diameter of 0.20 mm at a pressure of 2500 bar.

[0116] The resulting dispersion had 50 wt% Al2O3, exhibited a unimodal particle size distribution with a Z-avg(v) value of 187 nm, a viscosity of 13 mPas (at a shear rate of 100 s-1), and good stability. The aggregate size distribution by volume of the aluminum oxide dispersion is shown in Figure 5C.

[0117] Example D4: To a 1-liter batch containment vessel, add 8.5 g of carboxylic acid (citric acid, 2.0 μmol / m 2 Al2O3) and 483 g of demineralized water. To obtain a fluid pre-dispersion, 8.5 g of amino alcohol (N,N-dimethylethanolamine, 4.2 μmol / m 2 To this end, 500 g (45 ml) of aluminum oxide powder from Example 1 is added to the dispersion while an Ultra-Turrax (IKA T 25) is shearing the dispersion at 6000 rpm. 2 / g BET) is added to the containment vessel and then subjected to shear for an additional 30 minutes once addition is complete. The dispersion is then treated with ultrasound (Hielscher UP400St, 24 kHz with Ti-sonotrode) at 100% amplitude for 60 minutes.

[0118] The resulting dispersion has 50 wt% Al2O3, shows a unimodal particle size distribution with a Z-avg(v) value of 502 nm, a viscosity of 18 mPas (at a shear rate of 100 s-1), and has good stability.

[0119] Comparative Example CD1: Preparation of a dispersion showing too high a water content during coating Al2O3 powder (45 m 2A dispersion prepared using AEROXIDE® Alu 65 (BET 65m / g) was produced according to Example 1 of U.S. Patent Application Publication No. 2008264299, the procedure of which is reproduced here. 2 / g), the Al2O3 powder (45 m 2 / g BET was used. Therefore, 34.7 kg of deionized water was placed in a 60 1 stainless steel batch vessel. Next, 7.0 kg (45 ml) of Al2O3 powder from Example 1 was added. 2 / g BET) is sucked under shear conditions using the suction pipe of the Ystral Conti-TDS 3. Furthermore, 13.3 kg of a solution of 1.80 kg anhydrous citric acid, 1.49 kg disodium hydrogen phosphate (NaHPO) dihydrate and 10 kg water is added, as well as 65.0 kg of AlO powder from Example 1 (45 m 2 / g BET) is aspirated. After completion of the aspiration, the aspiration connector is closed and shearing at 3000 RPM is continued for another 10 minutes. After grinding, 108 g of Acticide® MV (THOR Co.) is added as a preservative. This pre-dispersion produced as described is passed twice through a UHDE high-pressure device HPD 4075-nano through a diamond nozzle with a diameter of 0.20 mm at a pressure of 2500 bar. This results in a dispersion with 50 wt. % Al2O3, showing a unimodal particle size distribution with a Z-avg(v) value of 106 nm (see Figure 5D), a viscosity of 16 mPas (at a shear rate of 100 s-1), and good stability.

[0120] Comparative Example CD2: Preparation of a dispersion with higher BET aluminum oxide AEROXIDE Alu 130(130m 2 / g) and 24.6 g of citric acid as the carboxylic acid and 24.6 g of 2-amino-2-methyl-1-propanol as the amino alcohol, it was not possible to prepare a dispersion according to Example D4. After the addition of 40 wt. % Al2O3 material, the dispersion was too viscous for further processing.

[0121] Comparative Example CD3: Preparation of Aluminum Oxide Dispersion Using Carboxylic Acid Only According to Example D4, a dispersion could not be prepared using only citric acid as the carboxylic acid. After the addition of 20 wt. % Al2O3 material, the dispersion was too viscous for further processing.

[0122] Preparation of coating formulation: Dispersions from the inventive and comparative examples were used to prepare respective ceramic coating formulations as follows: First, before adding each binder, the dispersion is diluted to a predetermined solids content of 20 wt% by adding water. The amount of binder is adjusted to 3 wt% based on the weight of the aluminum oxide powder. Finally, a wetting additive (fluorosurfactant) is added in an amount of 0.2 wt% based on the total weight of the formulation. This final coating slurry is homogenized by gentle stirring for 15 minutes and then transferred to a slot die coater.

[0123] Lithium-ion battery separator coating: Using the coating formulation from the above example, a thin, uniform 2 μm ceramic coating was applied to a PE-based separator available from Asahi Kasei Corporation of Japan under the trade name HIPORE AC 1681. The separator was a microporous membrane with high pore uniformity and a thickness of 16 μm. To apply the coating, the separator membrane was fixed on a vacuum table and the slot die was adjusted to create a 15 μm gap with respect to the separator. At the start of the coating process, the slot die speed was set to 0.4 m / min and the coating formulation flow rate was 0.4 ml / min. The wet-coated lithium-ion battery separator was dried at 50°C for 2 hours. This process was repeated to apply an additional 2 μm thin layer to the opposite side of the separator. The same process was repeated for both the inventive example and the comparative example, and the parameters and data are shown in Table 2.

[0124] [Table 2]

[0125] As can be seen in Table 2, the water content of the coating compositions of Dispersions D1-D3 is significantly reduced compared to the coating composition of Comparative Dispersion CD1.

[0126] Additionally, the air permeability of the coating compositions made with Dispersions D1-D3 is higher compared to the coating composition produced with Comparative Dispersion CD1. Thus, the overall performance of ceramic coated separators using the novel aluminum oxide dispersions of the present invention is significantly improved.

[0127] While the present invention has been described with reference to only certain examples, it should be understood that the invention is not limited to only the particular examples described. After reading this disclosure, one skilled in the art will be able to envision several variations of the described examples and other examples that fall within the scope of the invention as defined in the following claims. For example, an element described as used alone or in combination with other features in one example may also be used with a different combination of features in another example without departing from the scope of the disclosed and claimed invention.

[0128] Also, for example, although the present invention has been described primarily with reference to lithium ion batteries, it should be understood that the dispersions and coating compositions using the dispersions may also be used in separators for other secondary batteries, such as, for example, sodium ion type secondary batteries.

Claims

1. 1. An aqueous dispersion containing aluminum oxide powder, wherein the aluminum oxide powder is present in the form of aggregated primary particles having an aggregate size distribution with a median aggregate size (D50) of 220 nm to 500 nm as determined by dynamic light scattering measurements, and wherein the aluminum oxide powder is present in an amount of at least 20 wt. %, based on the total weight of the dispersion, at a concentration of 10 m ２ / g to 100m ２ / g, and the dispersion has a BET of at least one carboxylic acid from the group consisting of dicarboxylic acids and / or hydroxytricarboxylic acids having 2 to 7 carbon atoms, and - An aqueous dispersion, characterized in that it further comprises at least one amino alcohol having from 1 to 6 carbon atoms.

2. the dispersion has a viscosity, measured by rotational viscosimetry, of less than 100 mPas, preferably from 100 to 10 mPas, more preferably from 60 to 15 mPas; The aluminum oxide powder has a particle size of 10 to 100 mm as determined in accordance with DIN 66131 ２ / g, preferably 10 to 90 m ２ / g, preferably 30 to 90 m ２ / g, more preferably 30 to 55 m ２ / g BET surface area, the aluminum oxide agglomerated primary particles have a unimodal particle size distribution with Z-avg(v) of less than 500 nm, preferably from 500 nm to 150 nm, more preferably from 350 nm to 180 nm, as determined by dynamic light scattering measurements; the at least one carboxylic acid is at least one of citric acid and oxalic acid; the at least one amino alcohol is dimethylethanolamine (DMEA) and 2-amino-2-methyl-1-propanol; The aluminum oxide powder is further characterized in that it is a flame-synthesized aluminum oxide powder. The aqueous dispersion of claim 1.

3. the dispersion does not contain sodium dihydrogen phosphate, phosphonic acid, or hygroscopic materials; The at least one amino alcohol has a specific surface area of ​​the aluminum oxide of 2.5 to 8.0 μmol / m ２ is present in the dispersion in an amount of The at least one carboxylic acid has a specific surface area of ​​the aluminum oxide of 1.0 to 4.0 μmol / m ２ is further characterized in that 3. An aqueous dispersion according to claim 1 or 2.

4. 4. An aqueous dispersion according to any one of claims 1 to 3, which is stable in the pH range of 5 to 10 for at least 1 month, preferably at least 6 months, as determined by the method described herein.

5. A coating composition for a secondary battery separator, characterized in that it is obtained by adding a binder and a wetting agent to the aqueous dispersion according to any one of claims 1 to 4.

6. the aluminum oxide particles in an amount of 5 wt. % to 70 wt. %, preferably 10 wt. % to 60 wt. %, more preferably 15 wt. % to 50 wt. %, based on the total weight of the coating composition; the binder in an amount of 1 to 20 wt. %, preferably 2 to 15 wt. %, more preferably 3 to 10 wt. %, based on the total weight of the coating composition; and Wetting agent The coating composition of claim 5 comprising:

7. - forming a water slurry of the agglomerated aluminum oxide powder, the at least one amino alcohol, and the at least one carboxylic acid in water in amounts corresponding to the amount desired in the dispersion; - producing a pre-dispersion by introducing into said water slurry by mechanical means an amount of energy less than the energy required to form said dispersion; - then producing said dispersion by introducing said pre-dispersion into a high energy mill and grinding said pre-dispersion with said high energy mill at a pressure of at least 500 bar. The process for preparing the aqueous dispersion according to claims 1 to 4, characterized in that

8. 8. The process of claim 7, wherein the energy introduced into the water slurry to produce the pre-dispersion is less than 1000 kJ / m.

9. 7. Use of the coating composition according to claim 5 or 6 for forming a coating layer on at least one surface of a separator of a secondary battery, wherein the separator is a thin film made of at least one of polyolefin, nylon, PET (polyethylene terephthalate), PVC (polyvinyl chloride), PI (polyimide), PVDF (polyvinylidene fluoride) and PEEK (polyether ether ketone), and the coating formed on the separator has a moisture content of less than 1000 ppm and an air permeability defined by a Gurley value of a maximum of 100 s, preferably a maximum of 50 s, more preferably a maximum of 30 s, as determined by the method described herein.

10. The use of the coating composition according to claim 9, wherein the separator is made of a polyolefin comprising at least one of polypropylene, polyethylene or any combination thereof.

11. 1. A separator for a lithium ion battery cell, comprising: a membrane comprising at least one polyolefin; A coating layer comprising the dispersion of any one of claims 1 to 4 or a coating layer obtained by applying the coating composition of claims 5-6 onto at least one surface of the film and drying the dispersion by applying heat to form the coating layer; Equipped with the coating layer formed on the separator has a moisture content of less than 1000 ppm and an air permeability, as defined by a Gurley value, of a maximum of 100 s, preferably a maximum of 50 s, and more preferably a maximum of 30 s, as measured using the coating formed on both sides of the separator; Separator.

12. the membrane is made of polyethylene and has a thickness of 3 to 20 μm; The coating layer is homogeneous and has a thickness of less than 5 μm, preferably less than 3 μm, more preferably less than 2 μm, with a lower limit of 500 nm; The separator according to claim 11.

13. A secondary battery comprising the separator according to any one of claims 1 to 12.

14. 14. An apparatus comprising the secondary battery according to claim 13, comprising an electric or electronic device including a mobile phone, an electronic watch, a key fab, a laptop computer, a desktop computer, a computer pad, a power tool, a vacuum cleaner, an electric lawn mower, an electric appliance, and an electric vehicle.

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