Dispersion and coating composition containing lithium metal phosphate

Abstract

To provide a dispersion, a coating composition comprising such a dispersion, and the use thereof in lithium ion batteries.SOLUTION: A dispersion in the present invention comprises: 1 mass% to 50 mass% of lithium metal phosphate of a general formula Li1+aM2-bNc(PO4)3+d, where M is Ti, Zr or Hf, N is a metal other than Li and M, and 0≤a≤0.6, 0≤b≤0.6, 0≤c≤0.6, and 0≤d≤0.8; and 50 mass% to 99 mass% of trialkyl phosphate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to dispersions and coating compositions containing lithium metal phosphates, methods for producing such dispersions, and their use in lithium-ion batteries. [Background technology]

[0002] Secondary lithium-ion batteries are one of the most important types of batteries currently in use. These batteries typically consist of an anode made of carbon material or a lithium-metal alloy, a cathode made of lithium-metal oxide, an electrolyte in which a lithium salt is dissolved in an organic solvent, and a separator that allows lithium ions to pass between the positive and negative electrodes during the charging and discharging process.

[0003] Typical components of such a liquid lithium-ion battery, such as the cathode, anode, and separator, can be coated with a layer of metal oxide or compound that provides lithium-ion conductivity. This results in the formation of a distinct solid electrolyte interface (SEI) that conducts Li ions and is resistant to potential electrolyte decomposition products.

[0004] In attempts to develop secondary batteries with improved intrinsically safe explosion-proof structures and energy density, the use of solid electrolytes instead of liquid electrolytes has made considerable progress recently. Among such systems, secondary lithium batteries with electrodes made of lithium metal or lithium metal alloy are considered particularly suitable for providing high energy density. Such all-solid-state secondary lithium-ion batteries should have good ionic conductivity at the interface between the electrode active material and the electrolyte in order to have the required load characteristics.

[0005] H. Xiea, et al., Journal of Power Sources 2011, vol. 196, pp. 7760-7762 describes the solid-phase reaction of ZrO2 with Li2CO3, NH4H2PO4, and CaCO3. 1.2 Zr1.9 Ca 0.1 (PO4)3 is described. The Li-ion conductivity of this lithium zirconium phosphate is Li used as a solid Li-ion separator in a test cell of a Li-ion battery 1.3 Ti 1.7 Al 0.3 It was found to be comparable to the Li-ion conductivity of (PO4)3.

[0006] I. Hanghofer, et al., Dalton Trans., 2019, vol. 48, pp. 9376 - 9387 describes a rhombohedral Ca-stabilized Li suitable as a solid electrolyte for use in all-solid-state lithium-ion batteries by a solid-state reaction of Li2CO3, (NH4)2HPO4 and CaCO3 with either ZrO2 or zirconium acetate 1.4 Ca 0.2 Zr 1.8 (PO4)3 is described.

[0007] Y. Li, et al., PNAS, 2016, vol. 113 (47), pp. 13313 - 13317 describes the preparation of rhombohedral LiZr2(PO4)3 by a solid-state reaction of (NH4)2HPO4 with Li2CO3 and zirconium acetate and its use as a solid electrolyte in all-solid-state lithium-ion batteries. Cells containing LiZr2(PO4)3 were prepared by placing lithium foil on both sides of a LiZr2(PO4)3 pellet.

[0008] In addition to being used as a solid electrolyte or a solid Li-ion separator in a Li-ion battery, lithium metal phosphate can also be applied as a thin coating layer for modifying the active electrode or separator of the battery.

[0009] Thus, high ionic conductivity can be achieved by coating the surface of an electrode active material having some compounds containing lithium, such as LiTi2(PO4)3, as described in US Patent Application Publication No. 2009 / 081554 (US2009081554A1). In US Patent Application Publication No. 2009 / 081554, the coating layer of lithium titanium phosphate is directly prepared by using an ethanol solution of a precursor lithium ethoxide, phosphorus pentoxide and titanium tetraisopropoxide to coat the electrode on the surface of the electrode.

[0010] Preparing a coating layer made of lithium metal phosphate from a solution of the corresponding precursor on the surface of an electrode is not very convenient because it requires a very careful selection of reaction conditions that should be compatible with both the precursor used and the substrate that can be coated.

[0011] Therefore, it is desirable to find a method of directly applying a pre-prepared lithium metal phosphate.

[0012] One possibility would be to use a dispersion containing fine particles of lithium metal phosphate.

[0013] However, it has been found that the preparation of such ready-to-use dispersions is quite problematic. Using common solvents, such as alcohols or dimethoxyethane (DME), tends to induce unstable dispersions, in which large agglomerates of lithium metal phosphate and highly viscous pastes are formed instead of the desired fine particle-like dispersions.

[0014] Such dispersions are not suitable for obtaining a high-quality and homogeneous coating layer of lithium metal phosphate required for lithium-ion batteries.

Prior Art Documents

Patent Documents

[0015] [Patent Document 1] U.S. Patent Application Publication No. 2009 / 081554 [Patent Document 2] International Publication No. 2010 / 025889 [Patent Document 3] European Patent Application Publication No. 893155 [Non-patent literature]

[0016] [Non-Patent Document 1] H. Xiea, et al., Journal of Power Sources 2011, vol. 196, pp. 7760-7762 [Non-Patent Document 2] I. Hanghofer, et al., Dalton Trans., 2019, vol. 48, pp. 9376-9387 [Non-Patent Document 3] Y. Li, et al., PNAS, 2016, vol. 113 (47), pp. 13313-13317 [Overview of the project] [Problems that the invention aims to solve]

[0017] The problem addressed by the present invention is to provide a dispersion of lithium metal phosphate that is substantially free of large agglomerates. Such a dispersion should preferably have a relatively low viscosity and be stable for at least several days, preferably several weeks, that is, it should not cause substantial viscosity increases and precipitation or agglomerate formation during this period.

[0018] Such dispersions should be suitable for preparing coating compositions for coating components of lithium-ion batteries, particularly the anode, cathode, and separator.

[0019] A further challenge addressed by the present invention is to provide a method for producing such a dispersion. [Means for solving the problem]

[0020] The present invention relates to the general formula Li 1+a M 2-b N c (PO4) 3+d [In the formula, M = Ti, Zr, or Hf; N is a metal other than Li and M; [0≦a≦0.6, 0≦b≦0.6, 0≦c≦0.6, 0≦d≦0.8] Lithium metal phosphate 1% to 50% by mass, The present invention provides a dispersion containing 50% to 99% by mass of a trialkyl phosphate.

[0021] Surprisingly, such dispersions were found to be low-viscosity and stable over long periods, even in the presence of extremely small lithium metal phosphate particles. Furthermore, coating compositions containing such dispersions were found to be suitable for coating components of lithium-ion batteries.

[0022] Lithium metal phosphate The lithium metal phosphate used in the dispersion of the present invention is of the general formula Li 1+a M 2-b N c (PO4) 3+d [In the formula, M = Ti, Zr, or Hf, preferably M = Zr; N is a metal other than Li and M; 0≦a≦0.6, 0≦b≦0.6, 0≦c≦0.6, 0≦d≦0.8, Preferably, the following conditions apply: 0 ≤ a ≤ 0.3, 0 ≤ b ≤ 0.3, 0 ≤ c ≤ 0.3, and 0 ≤ d ≤ 0.4.

[0023] Metals other than Li and M, such as N, can preferably be selected from Na, K; Be, Mg, Ca, Sr, Ba, Zn, Co, Ni, Cu, Mn, B, Al, Ga, In, Fe, Sc, Y, La, Ce, Si, Ge, Sn, Pb, V, Nb, Ta, Mo, W, and combinations thereof. In relation to the present invention, silicon and boron should be considered metals, and their compounds are called "metal precursors." Preferably, the lithium metal phosphate of the present invention contains calcium (Ca), aluminum (Al), iron (Fe), and / or yttrium (Y).

[0024] The lithium metal phosphate used in the dispersion of the present invention is 5m 2 / g~100m 2 / g, preferably 7m 2 / g~80m 2 / g, comfortable 15m 2 / g~60m 2 It may have a BET surface area of ​​ / g.

[0025] The BET surface area can be determined by nitrogen adsorption using the Brunauer-Emmett-Teller method in accordance with DIN 9277:2014.

[0026] The lithium metal phosphate used in the dispersion of the present invention is preferably in the form of aggregated primary particles, which preferably have a number-mean diameter of typically 1 to 100 nm, preferably 3 to 70 nm, and more preferably 5 to 50 nm, as determined by transmission electron microscopy (TEM). This number-mean diameter can be determined by calculating the average size of at least 500 particles analyzed by TEM.

[0027] Dynamic light scattering (DLS) is a technique in physics that can be used to determine the size distribution profile of small particles in a suspension. This technique can be used to measure the particle size of dispersed materials in the range of 3 nm to 6 μm. The measurement is based on the Brownian motion of particles in the medium and the scattering of incident laser light due to the difference in refractive index between the liquid and solid materials.

[0028] The resulting value is the hydrodynamic diameter of the corresponding sphere of the particle. Value d 50 d 90 and d 99 These are common criteria for consideration, as they describe the hydrodynamic diameter of particles below 50%, 90%, or 99% of the particles in the particle size distribution. The lower these values, the better the particle dispersion. Monitoring these values ​​can provide clues about the particle dispersion stability. If these values ​​increase significantly, the particles may not be sufficiently stabilized and may tend to agglomerate and settle over time, resulting in a lack of stability. Depending on the viscosity of the medium, <1000 nm (1 μm) d 99 The value indicates that the particles remain stationary over time, and therefore can be considered an indicator of a stable dispersion.

[0029] The number-average particle size of the lithium metal phosphate in the dispersion of the present invention d 50 The particle size is determined by dynamic light scattering (DLS) at a temperature of 25°C in a dispersion diluted with a trialkyl phosphate containing approximately 1% by mass of the lithium metal phosphate, and is preferably about 0.03 μm to 2 μm, more preferably 0.04 μm to 1 μm, and even more preferably 0.05 μm to 0.5 μm.

[0030] The number-average particle size of the lithium metal phosphate in the dispersion of the present invention d 99The particle size is determined by dynamic light scattering (DLS) at a temperature of 25°C in a dispersion diluted with a trialkyl phosphate containing approximately 1% by mass of the lithium metal phosphate, and is preferably less than 1 μm, more preferably about 0.05 μm to 1 μm, more preferably 0.1 μm to 0.8 μm, and even more preferably 0.15 μm to 0.5 μm.

[0031] Thus, compared to dispersions that are similar but use, for example, dispersants other than trialkyl phosphate dispersants, the dispersion of the present invention substantially contains no large particles, i.e., particles with a size greater than 1 μm. This makes the dispersion of the present invention particularly useful for producing coating compositions having finely dispersed small lithium phosphate particles, which are particularly suitable for coating elements of lithium-ion batteries.

[0032] Lithium metal phosphate agglomerates and partially aggregates can be further broken down, for example, by grinding or sonication, to produce particles with smaller particle sizes and a narrower particle size distribution.

[0033] The lithium metal phosphate used in the dispersion according to the present invention preferably has a tamp density of 20 g / L to 200 g / L, more preferably 25 g / L to 150 g / L, even more preferably 30 g / L to 100 g / L, and even more preferably 40 g / L to 80 g / L.

[0034] The tamped density of powdered or coarse-grained granular materials can be determined according to DIN ISO 787-11:1995 “General methods of test for pigments and extenders -- Part 11: Determination of tamped volume and apparent density after tamping”. This includes measuring the apparent density of the bed after stirring and tamping.

[0035] The lithium metal phosphate used in the dispersion of the present invention is preferably obtained by a pyrolysis method, also known as the “fumed” method. The terms “produced by pyrolysis,” “by pyrolysis,” and “fumed” are used synonymously in relation to the present invention. Such a “by pyrolysis” or “fumed” method involves reacting a corresponding metal precursor in flame hydrolysis or flame oxidation in an oxyhydrogen flame to form a compound produced by pyrolysis. This reaction first forms highly dispersed, substantially spherical primary particles, which then aggregate in a further step of the reaction to form an aggregate. The aggregate can then accumulate to form an agglomerate. In contrast to agglomerates, which can usually be separated into aggregates relatively easily by the introduction of energy, the aggregate can only be further broken down by a strong introduction of energy, if any. The particles can be partially broken down and converted into particles in the nanometer (nm) range by suitable grinding. However, such grinding is not necessary because the "as-prepared" fumed particles have a sufficiently small particle size.

[0036] Lithium metal phosphates are preferably produced by flame spray pyrolysis, preferably using a solution of a metal carboxylate and an organic phosphate as a precursor.

[0037] In such a flame spray pyrolysis method, a solution of a metal compound (metal precursor) in the form of microdroplets and a phosphorus source is typically introduced into a flame formed by ignition of a fuel gas and an oxygen-containing gas, where the metal precursor used with the phosphorus source is oxidized and / or hydrolyzed to obtain the corresponding lithium metal phosphate.

[0038] The flame spray pyrolysis method preferably comprises the following steps: a) A step of atomizing a solution of a metal precursor to obtain an aerosol using an atomizer gas, b) A step of introducing the aerosol into a reaction in the reaction space of a reactor having a flame obtained by igniting a mixture of fuel gas and oxygen-containing gas, in order to obtain a reaction flow. c) A step of cooling the reaction flow and d) A step of subsequently removing the solid lithium metal phosphate from the reaction stream. Includes.

[0039] Examples of fuel gases include hydrogen, methane, ethane, natural gas, and / or carbon monoxide. Hydrogen is particularly preferred. The fuel gas is especially used in embodiments where a high degree of crystallinity of the lithium metal phosphate that can be produced is desirable.

[0040] The oxygen-containing gas is generally air or oxygen-enriched air. The oxygen-containing gas is particularly used in embodiments where a high BET surface area of, for example, a lithium metal phosphate that can be manufactured is desirable. The total amount of oxygen is generally selected to be sufficient for the complete conversion of at least the fuel gas and the metal precursor.

[0041] To obtain the aerosol, the vaporized solution containing the metal precursor can be mixed with an atomizer gas, such as nitrogen, air, and / or other gases. The resulting droplets of the aerosol preferably have an average droplet size of 1 to 120 μm, and particularly preferably 30 to 100 μm. The droplets are typically produced using a single-component or multi-component nozzle. The solution may be heated to increase the solubility of the metal precursor and to obtain a viscosity suitable for atomization of the solution.

[0042] The metal carboxylates used as precursors in the flame spray pyrolysis method may be, independently of each other, linear, branched, or cyclic pentanoates (C5), hexanoates (C6), heptanoates (C7), octanoates (C8), nonanoates (C9), decanoates (D10), undecanoates (C11), dodecanoates (C12), tridecanoates (C13), tetradecanoates (C14), pentadecanoates (C15), hexadecanoates (C16), heptadecanoates (C17), octadecanoates (C18), nonadecanoates (C19), eicosanoates (C20), and mixtures thereof of the metal used.

[0043] The metal precursor may be an inorganic metal compound, such as a nitrate, carbonate, chloride, bromide, or another organometallic compound, such as an alkoxide, such as ethoxide, n-propoxide, isopropoxide, n-butoxide, and / or tert-butoxide.

[0044] The organic phosphate used in the flame spray pyrolysis method is preferably selected from phosphonic acid (H3PO3), orthophosphoric acid (H3PO4), metaphosphoric acid (HPO3), pyrophosphoric acid (H4P2O7), polyphosphoric acid esters, and mixtures thereof.

[0045] The organic phosphate can be selected from alkyl esters, such as methyl, ethyl, propyl, butyl, and hexyl; aryl esters, such as phenyl; mixed alkyl / aryl esters; and mixtures thereof.

[0046] The use of organic phosphates as a phosphorus source in this flame spray pyrolysis method is preferred when small particles of lithium metal phosphate with a high BET surface area and low tamp density are required.

[0047] The solvent used with the metal precursor may be selected from the group consisting of linear or cyclic, saturated or unsaturated, aliphatic or aromatic hydrocarbons, carboxylic acid esters, ethers, alcohols, carboxylic acids, and mixtures thereof.

[0048] Lithium metal phosphates known from the prior art, typically prepared by solid-phase synthesis, have relatively high material density and low BET surface area, making them suitable for use, for example, as core materials in the solid electrolyte of lithium-ion batteries. However, when such compounds are intended to be used as additives that can be well distributed in or on the surface of the core material, their smaller particle size, lower material density, and higher BET surface area are critically important. Therefore, lithium metal phosphates prepared by methods such as the pyrolysis method described above are particularly suitable for providing the dispersions and lithium-ion batteries of the present invention.

[0049] Lithium metal phosphates obtained by the pyrolysis method can be further heat-treated. This further heat treatment is preferably carried out at a temperature of 600°C to 1300°C, more preferably 650°C to 1250°C, even more preferably 700°C to 1200°C, and even more preferably 750°C to 1150°C. This heat treatment makes it possible to obtain lithium metal phosphates with optimized properties, in particular, a desired crystalline structure.

[0050] Lithium metal phosphates obtained by the pyrolysis method can be further milled, preferably using a ball mill. This ball milling is preferably carried out in a suitable solvent, such as ethanol or isopropanol, using ZrO2 balls having, for example, a diameter of about 0.5 mm.

[0051] Dispersion containing lithium metal phosphate The dispersion of the present invention contains 1% to 50% by mass of the lithium metal phosphate, preferably 5% to 45% by mass, more preferably 10% to 40% by mass, more preferably 15% to 35% by mass, and 50% to 99% by mass of the trialkyl phosphate, preferably 55% to 95% by mass, more preferably 60% to 90% by mass, and more preferably 65% ​​to 85% by mass.

[0052] The trialkyl phosphate is preferably selected from the group consisting of trimethyl phosphate, triethyl phosphate, tri-n-propyl phosphate, triisopropyl phosphate, methyldiethyl phosphate, and mixtures thereof.

[0053] The selected trialkyl phosphates have the advantage of being water-soluble, which in turn simplifies the cleaning process.

[0054] The dispersion of the present invention may contain, in addition to the lithium metal phosphate and the trialkyl phosphate component, for example, a solvent, a dispersant, or other additives.

[0055] Thus, a solvent selected from the group consisting of water, dimethyl sulfoxide, tetramethylurea, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, and acetone can be present in the dispersion of the present invention as such other components.

[0056] Suitable dispersants may be polymers having acidic functional groups and / or amine functional groups or salts of such functional groups, such as alkylammonium salts or alkanolammonium salts. The acidic groups may be phosphate groups or sulfonic acid groups. The number-average molecular weight of such dispersants is preferably at least 500 g / mol, and particularly preferably 500 g / mol to 1000 g / mol. The dispersant may be both a polymer and a copolymer, such as a block copolymer or a copolymer having a statistical structure. Suitable dispersants are available from Byk Chemie under the trade name Disperbyk®. For the preparation of suitable dispersants, see also International Publication No. 2010 / 025889 (WO2010 / 025889) and European Patent Application Publication No. 893155 (EP-A-893155).

[0057] The total amount of such other components in the dispersion of the present invention may be up to 20% by mass, more preferably 10% by mass, and more preferably 5% by mass.

[0058] However, preferably, such other components are substantially absent in the dispersion of the present invention, i.e., their amount is less than 0.5% by mass.

[0059] All components of the dispersion of the present invention total 100% by mass, based on the total mass of the dispersion.

[0060] 10s -1 The dynamic viscosity of the dispersion of the present invention, determined by the shear rate and 22°C, is preferably in the range of less than 60 mPas, more preferably less than 50 mPas, more preferably 1 mPas to 50 mPas, more preferably 2 mPas to 40 mPas, and more preferably 3 mPas to 30 mPas.

[0061] The dynamic viscosity of the dispersion of the present invention is determined using any apparatus suitable for determining the dynamic viscosity, in 10 seconds. -1 The shear rate and temperature can be measured at 22°C.

[0062] Method for producing a dispersion containing lithium metal phosphate The present invention further includes a method for producing a dispersion according to the present invention, comprising mixing the lithium metal phosphate and the trialkyl phosphate, and optionally grinding or milling the resulting dispersion. The particle size of the agglomerate can be significantly reduced using these milling techniques.

[0063] The dispersion of the present invention is preferably prepared at 10°C to 50°C, more preferably at 15°C to 40°C.

[0064] To avoid undesirable heating of the dispersion during its pulverization or milling, the dispersion can be cooled by a heat exchanger.

[0065] When a dispersion with particularly small particle sizes is to be produced, it can be ground or milled, for example, by a high-energy mill, such as a wet jet mill.

[0066] To achieve this, a preliminary dispersion containing lithium metal phosphate particles and trialkyl phosphate, for example, obtained by a rotor / stator system or dissolver device, is divided into at least two substreams, and these substreams are released into a high-energy mill through nozzles under a pressure of at least 500 bar, allowing these substreams to come into contact in a reaction chamber filled with gas or liquid. Such high-energy grinding can be repeated several times. A suitable high-energy mill is, for example, the Ultimaizer System, model HJP-25050, from Sugino Machine Ltd.

[0067] The grinding or milling in the method of the present invention can also be carried out by a rotor-stator system, homogenization, ultrasonic treatment, or ball mill.

[0068] The ball milling can be carried out using a conventional laboratory-scale or production-scale ball mill having ZrO2 beads having a diameter of approximately 0.8 mm. Preferably, the ball milling process delivers 0.1 to 10 kWh / kg, preferably 0.2 to 5 kWh / kg, and more preferably 0.5 to 3 kWh / kg of energy to the dispersion.

[0069] Wet coating composition containing the dispersion of the present invention and dry coating composition obtained therefrom The present invention further provides a wet coating composition comprising the dispersion according to the present invention, an organic binder, and optionally a solvent.

[0070] Such wet coating compositions preferably contain 50% to 99% by mass, more preferably 55% to 95% by mass, 60% to 90% by mass, or 65% to 85% by mass of the dispersion of the present invention, and 1% to 50% by mass, more preferably 5% to 45% by mass, more preferably 10% to 40% by mass, more preferably 15% to 35% by mass of an organic binder, and optionally 1% to 50% by mass, more preferably 5% to 45% by mass, more preferably 10% to 40% by mass, or more preferably 15% to 35% by mass of a solvent.

[0071] All components of the wet composition are combined to make up 100% by mass, based on the total mass of the composition.

[0072] The organic binder can be selected from the group consisting of polyethylene oxide, polyvinylidene fluoride, polyvinylidene chloride, polytetrafluoroethylene, polyacrylonitrile, polyamide, polyimide, polyetheretherketone, polymethyl methacrylate, polytetraethylene glycol diacrylate, polyvinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride / chlorotrifluoroethylene copolymer, polysulfone, polyethersulfone, and mixtures thereof.

[0073] The solvent optionally used in the wet coating composition of the present invention can be selected from the group consisting of water, alcohol, aliphatic and aromatic hydrocarbons, ethers, esters, aldehydes, ketones, and mixtures thereof. For example, the solvent used may be water, methanol, ethanol, propanol, butanol, pentane, hexane, benzene, toluene, xylene, diethyl ether, methyl tert-butyl ether, ethyl acetate, acetone, dimethylformamide, dimethoxyethane, or trialkyl phosphate. Particularly preferably, the solvent used in the wet coating composition has a boiling point of less than 300°C at 1 atm, and especially preferably less than 200°C. Such relatively volatile solvents can be easily evaporated or vaporized during the curing of the wet coating composition according to the present invention. Most preferably, the wet coating composition of the present invention contains a trialkyl phosphate as a single solvent, selected from the group consisting of trimethyl phosphate, triethyl phosphate, tri-n-propyl phosphate, triisopropyl phosphate, methyl diethyl phosphate, and mixtures thereof.

[0074] The coating composition of the present invention can be prepared by mixing the dispersion of the present invention with at least one organic binder, preferably one of those described above, and optionally other additives, such as solvents, dispersants, etc., preferably those listed above.

[0075] The present invention further provides the use of the wet coating composition according to the present invention for coating components of lithium-ion batteries, such as the positive and negative electrodes or separators of lithium-ion batteries.

[0076] The method of coating using the wet coating composition of the present invention involves the following steps: a) A step of applying the coating composition of the present invention to the surface of a component of a lithium-ion battery, such as its electrode or membrane. b) A step of curing the organic binder and / or removing the solvent. It can include...

[0077] In step a) of the coating method described above, the wet coating composition of the present invention preferably forms a layer on the substrate to be coated having a thickness of less than 100 μm, more preferably 10 μm to 100 μm, and particularly preferably 20 μm to 80 μm.

[0078] The curing of the composition in step b) can be achieved by at least partial polymerization and / or removal of the solvent. Depending on the system used, this step can be carried out at a temperature preferably 0 to 500°C, particularly preferably 5 to 400°C, and most particularly preferably 10 to 300°C. The curing can be carried out in the presence of air or in the absence of oxygen, for example, in a protective gas atmosphere of nitrogen or carbon dioxide. The step can be carried out under standard pressure or under reduced pressure, for example, under vacuum.

[0079] The present invention further provides a dry coating composition obtained by evaporation of a trialkyl phosphate from the wet composition according to the present invention and optionally a solvent.

[0080] The organic binder present in the wet coating composition of the present invention can be cured before, during, or after the evaporation of the trialkyl phosphate and optionally the solvent from the wet coating composition.

[0081] The dry coating composition of the present invention preferably forms a layer on the substrate to be coated having a thickness of less than 30 μm, more preferably less than 20 μm, and particularly preferably 1 μm to 10 μm.

[0082] The present invention further provides the use of a wet coating composition or a dry coating composition according to the present invention for coating electrodes or separators of lithium-ion batteries.

[0083] Lithium-ion battery containing the dispersion of the present invention The present invention further provides a lithium-ion battery comprising the dry coating composition according to the present invention.

[0084] The lithium-ion battery of the present invention may contain a positive electrode (cathode), a negative electrode (anode), a separator, and an electrolyte containing a lithium-containing compound.

[0085] The positive electrode (cathode) of the lithium-ion battery typically includes a current collector and a cathode active material layer formed on the current collector.

[0086] The current collector may be aluminum foil, copper foil, nickel foil, stainless steel foil, titanium foil, a polymer substrate coated with a conductive metal, or a combination thereof.

[0087] The positive electrode active material may contain a material capable of reversibly intercalating / deintercalating lithium ions, and such materials are well known in the art. Such a positive electrode active material may contain a mixed oxide comprising a transition metal oxide, such as Ni, Co, Mn, V, or other transition metals and optionally lithium. A mixed lithium transition metal oxide preferably used as a positive electrode active material is selected from the group consisting of lithium-cobalt oxide, lithium-manganese oxide, lithium-nickel-cobalt oxide, lithium-nickel-manganese-cobalt oxide, lithium-nickel-cobalt-aluminum oxide, lithium-nickel-manganese oxide, or mixtures thereof.

[0088] The anode of the lithium-ion battery may contain any suitable material commonly used in secondary lithium-ion batteries that can reversibly intercalate / deintercalate lithium ions. Typical examples include crystalline carbon, such as natural or artificial graphite in the form of plates, flakes, spheres, or fibrous types; amorphous carbon, such as soft carbon, hard carbon, mesophase pitch carbide, calcined coke, etc., or carbonaceous materials including mixtures thereof. Furthermore, lithium metal or conversion material (e.g., Si or Sn) can be used as the anode active material.

[0089] The electrolyte of the lithium-ion battery may be in the form of a liquid, gel, or solid.

[0090] The liquid electrolyte of the lithium-ion battery may contain any suitable organic solvent commonly used in lithium-ion batteries, such as anhydrous ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate, methyl ethyl carbonate, diethyl carbonate, γ-butyrolactone, dimethoxyethane, fluoroethylene carbonate, vinyl ethylene carbonate, or a mixture thereof.

[0091] The gel electrolyte contains a gelled polymer.

[0092] The solid electrolyte of the lithium-ion battery may contain oxides, such as lithium metal oxides, sulfides, phosphates, or solid polymers.

[0093] The liquid or polymer gel electrolyte of the lithium-ion battery typically contains lithium salts. Examples of such lithium salts include lithium hexafluorophosphate (LiPF6), lithium bis-2-(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), Li2SiF6, lithium triflate, LiN(SO2CF2CF3)2, lithium nitrate, lithium bis(oxalate)borate, lithium-cyclo-difluoromethane-1,1-bis(sulfonyl)imide, lithium-cyclo-hexafluoropropane-1,1-bis(sulfonyl)imide, and mixtures thereof.

[0094] The lithium-ion battery, particularly one having a liquid or gel electrolyte, may also include a separator to prevent direct contact between two electrodes, which would lead to an internal short circuit.

[0095] The separator material may include polyolefin resin, fluorinated polyolefin resin, polyester resin, polyacrylonitrile resin, cellulose resin, nonwoven fabric, or a mixture thereof. Preferably, this material includes polyolefin resin, for example polyethylene or polypropylene polymer, fluorinated resin, for example polyvinylidene fluoride polymer or polytetrafluoroethylene, polyester resin, for example polyethylene terephthalate and polybutylene terephthalate, polyacrylonitrile resin, cellulose resin, nonwoven fabric, or a mixture thereof.

[0096] The lithium-ion battery according to the present invention may contain a liquid electrolyte, a gel electrolyte, or a solid electrolyte. A liquid mixture of the lithium salt and the organic solvent that has not been cured, polymerized, or crosslinked is referred to as a “liquid electrolyte” in relation to the present invention. A gel or solid mixture containing a cured, polymerized, or crosslinked compound or a mixture thereof, optionally a solvent, and the lithium salt is referred to as a “gel electrolyte.” Such a gel electrolyte can be prepared by polymerization or crosslinking of a mixture containing at least one reactive, i.e., polymerizable or crosslinkable compound and lithium salt.

[0097] A special type of lithium-ion battery is a lithium-polymer battery, in which a polymer electrolyte is used instead of a liquid electrolyte. The electrolytes in similar solid-state batteries may also include other types of solid electrolytes, such as sulfide-based, oxide-based solid electrolytes, or mixtures thereof.

[0098] The battery of the present invention may be a lithium metal battery, such as Li-air, lithium-sulfur (Li-S), and other types of lithium metal batteries.

[0099] Lithium-air batteries typically contain a porous carbon cathode and an organic, glass-ceramic, or polymer-ceramic electrolyte.

[0100] Li-sulfur (Li-S) batteries typically contain iron disulfide (FeS2), iron sulfide (FeS), copper sulfide (CuS), lead sulfide, and copper sulfide (PbS+CuS) cathodes.

[0101] Many other known types of lithium metal batteries, such as lithium-selenium (Li-Se), lithium-manganese dioxide (Li-MnO2 or Li / Al-MnO2), and lithium-(CF) monofluoride (Li-(CF)) xOther types include lithium-thionyl chloride (Li-SOCl2), lithium-sulfuryl chloride (Li-SO2Cl2), lithium-sulfur dioxide (Li-SO2), lithium-iodine (Li-I2), lithium-silver chromate (Li-Ag2CrO4), lithium-vanadium pentoxide (Li-V2O5 or Li / Al-V2O5), lithium-copper chloride (Li-CuCl2), lithium-copper(II) oxide (Li-CuO), lithium-copper oxyphosphate (Li-Cu4O(PO4)2), and others. [Examples]

[0102] Example 1: Preparation of lithium zirconium phosphate A clear solution was obtained by mixing 23.75 kg of a solution containing 3370 g of a commercially available solution (Borchers® Deca Lithium 2) containing 2% by mass of lithium in the form of lithium neodecanoate dissolved in naphtha, 15 kg of a commercially available solution (Octa Solingen® Zirconium 12) containing 11.86% by mass of Zr in the form of zirconium ethylhexanoate dissolved in white spirit, and 5384 g of a commercially available solution (Alfa Aesar) containing 16.83% by mass of phosphorus in the form of triethyl phosphate. This solution corresponds to the composition of LiZr2(PO4)3.

[0103] This dispersion is mixed with 1.5 kg / h of air and 15 Nm of air. 3 An aerosol of 8.5 Nm³ of hydrogen was formed through a two-component nozzle and sprayed into a tubular reactor having a combustion flame. The combustion gas of the flame was 8.5 Nm³ of hydrogen. 3 / h and air 30Nm 3 It consisted of / h. Additionally, secondary air 25Nm 3 / h was used. After the reaction, the reaction gas was cooled and filtered.

[0104] The obtained lithium zirconium phosphate powder was 44m 2 The BET surface area of ​​1 / g, the tamp density of 52 g / L, and the 76 nm d, determined by static light scattering. 50It had a value. XRD analysis showed that the main phase of the product was rhombohedral lithium zirconium phosphate.

[0105] Measurement of dynamic viscosity The dynamic viscosity of the dispersion was measured using the rotational viscosity method and a Physica MCR 301 from Anton Paar, with a measuring plate PP25 having a distance set to 0.5 mm.

[0106] The motor of the viscometer drives a bob in a fixed cup. The rotation speed of the bob is preset, generating a specific motor torque required to rotate the measuring bob. This torque must overcome the viscous force of the substance being tested and is therefore a measure of its viscosity. Data is collected in 10 seconds. -1 The shear rate and temperature are measured at 22°C.

[0107] Example 2: Preparation of LZP dispersion In Example 1, lithium zirconium phosphate (LZP, 6 g) was prepared and added to triethyl phosphate (TEP, 14 g) while treating the mixture with ultrasound generated by an ultrasonic processor UP400S equipped with a Ti sonotrode, 400 W, 24 kHz, for 30 minutes. The particle size distribution was measured using dynamic light scattering (DLS) with an LB-500 instrument (Horiba Ltd., Japan) after diluting with TEP to obtain an LZP concentration of approximately 1 mass%.

[0108] The d immediately after preparation of the dispersion obtained by the DLS method 50 d 90 and d 99 The value and the d after 1 week and 4 weeks of storage of the dispersion at room temperature. 99 Value and 10s after manufacturing -1 The dynamic viscosity of the dispersion, measured at 22°C, is shown in Table 1.

[0109] Example 3: Preparation of LZP dispersion Triethyl phosphate (TEP, 315 g) was pre-loaded into a ball mill apparatus (Netzsch Laboratory Mill Micro Series), the peristaltic pump was set to a rotation speed of 90 rpm, and the ball mill was set to 1000 rpm. Lithium zirconium phosphate (LZP, 135 g) was added to the TEP. The peristaltic pump was then adjusted to a rotation speed of 120 rpm, and the ball mill was set to a rotation speed of 2500 rpm. The dispersion was treated for 120 minutes (0.4 kWh of energy was introduced). The particle size distribution was measured as in Example 2.

[0110] The d immediately after preparation of the dispersion obtained by the DLS method 50 d 90 and d 99 The value and the d after 1 week and 4 weeks of storage of the dispersion at room temperature. 99 Value and 10s after manufacturing -1 The dynamic viscosity of the dispersion, measured at 22°C, is shown in Table 1.

[0111] Comparative Example 1 A 30% by mass dispersion of LZP in ethanol (EtOH) was prepared in the same manner as in Example 2, except that EtOH was used instead of TEP.

[0112] The d immediately after preparation of the dispersion obtained by the DLS method 50 d 90 and d 99 The value and the d after 1 week and 4 weeks of storage of the dispersion at room temperature. 99 Value and 10s after manufacturing -1 The dynamic viscosity of the dispersion, measured at 22°C, is shown in Table 1.

[0113] Comparative Example 2 An attempt was made to prepare a 30% by mass dispersion of LZP in isopropanol (iPrOH) in the same manner as in Example 2, except that iPrOH was used instead of TEP.

[0114] However, the dispersion became extremely viscous during its preparation, making it impossible to measure the particle size distribution or viscosity.

[0115] Comparative Example 3 An attempt was made to prepare a 30% by mass dispersion of LZP in dimethoxyethane (DME) in the same manner as in Example 2, except that DME was used instead of TEP.

[0116] However, the dispersion became extremely viscous during its preparation, making it impossible to measure the particle size distribution or viscosity.

[0117] The comparison between Examples 2-3 and Comparative Examples 1-3 shows that using TEP as the solvent results in a considerably lower d 99 We demonstrate that it is possible to obtain LZP dispersions with a particle size (Table 1), i.e., those substantially free of large particles >1 μm. Importantly, such dispersions with a TEP solvent had low viscosity and remained stable with no agglomeration after 1 and 4 weeks of storage at room temperature, the opposite of the dispersion from Comparative Example 1 using EtOH as the solvent (Table 1).

[0118] Example 4: Preparation of coating composition Slurry A: The 30% by mass dispersion of LZP in TEP prepared in Example 3 was diluted with TEP while stirring to a solid content of 20% by mass of LZP.

[0119] Slurry B: A poly(vinylidene fluoride-co-hexafluoropropylene, PVDF-HFP) organic binder from Sigma Aldrich, Germany, with a MW of 400,000 g / mol, was completely dissolved in TEP while stirring overnight at 35°C to form a 10% by mass solution of PVDF-HFP in TEP.

[0120] Slurries A and B were mixed together to obtain a final LZP to binder ratio of 6:1 LZP:PVDF (the resulting coating composition consisted of the dispersion of Example 3, 75% by mass of slurry A and 25% by mass of slurry B, and contained 15% by mass of LZP, 2.5% by mass of PVDF-HFP, and 82.5% by mass of TEP).

[0121] Example 5: Coating of copper foil with the coating composition of Example 4 5 ml of the coating composition obtained in Example 4 was placed in a doctor blade device (doctor blade: Quadruple Film Applicator, Model 360, from Erichsen, Germany, with a 50 μm slit). The coating speed was set to 0.4 m / min, and coating of copper foil (Hohsen, Japan) with a thickness of 18 μm was started. A stable and homogeneous wet film with a thickness of approximately 50 μm was obtained on the surface of the copper foil.

[0122] This wet coating was dried at 100°C for 2 hours to obtain an LZP dry coating layer with a thickness of 5 μm. The adhesion of this layer to the copper foil was excellent.

[0123] [Table 1]

[0124] Preferred embodiments of the present invention are as follows: 1. General formula Li 1+a M 2-b N c (PO4) 3+d [In the formula, M = Ti, Zr, or Hf; N is a metal other than Li and M; [0≦a≦0.6, 0≦b≦0.6, 0≦c≦0.6, 0≦d≦0.8] Lithium metal phosphate 1% to 50% by mass, A dispersion containing 50% to 99% by mass of trialkyl phosphate. 2. The dispersion according to 1., wherein the lithium metal phosphate is in the form of aggregated primary particles. 3. The dispersion according to 1. or 2. above, wherein the lithium metal phosphate is obtained by a thermal decomposition method. 4. The lithium metal phosphate is 5m 2 / g~100m 2A dispersion according to any one of 1. to 3. above, having a BET surface area of ​​ / g. 5. The lithium metal phosphate was determined by dynamic light scattering (DLS) at a temperature of 25°C in a dispersion diluted with a trialkyl phosphate containing approximately 1% by mass of the lithium metal phosphate to have a particle size of less than 1 μm d 99 A dispersion according to any one of the above 1. to 4., having the following properties. 6. The dispersion according to any one of 1 to 5, wherein the lithium metal phosphate has a tamping density of 20 g / L to 200 g / L. 7. The dispersion according to any one of 1 to 6 above, wherein the trialkyl phosphate is selected from the group consisting of trimethyl phosphate, triethyl phosphate, tri-n-propyl phosphate, triisopropyl phosphate, methyl diethyl phosphate, and mixtures thereof. 8. A method for producing the dispersion according to any one of 1 to 7, comprising mixing the lithium metal phosphate and the trialkyl phosphate, and optionally grinding or milling the resulting dispersion. 9. The method according to 8., wherein grinding or milling is carried out by ultrasonic treatment, a wet jet mill, or a ball mill. 10. A wet coating composition comprising a dispersion according to any one of items 1 to 7 above, an organic binder, and optionally a solvent. 11. The wet coating composition according to 10, comprising 50% to 99% by mass of the dispersion according to any one of 1 to 7, 1% to 50% by mass of an organic binder, and optionally 1% to 50% by mass of a solvent. 12. The wet coating composition according to 10. or 11., wherein the organic binder is selected from the group consisting of polyethylene oxide, polyvinylidene fluoride, polyvinylidene chloride, polytetrafluoroethylene, polyacrylonitrile, polyamide, polyimide, polyetheretherketone, polymethyl methacrylate, polytetraethylene glycol diacrylate, polyvinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride / chlorotrifluoroethylene copolymer, polysulfone, polyethersulfone, and mixtures thereof. 13. A dry coating composition obtained by evaporation of a trialkyl phosphate and optionally a solvent from the wet composition described in any of items 10 to 12 above. 14. Use of a wet coating composition according to any of items 10 to 12 above or a dry coating composition according to item 13 above for coating electrodes or separators of a lithium-ion battery. 15. A lithium-ion battery comprising the dry coating composition described in 13. above.

Claims

1. General Li １＋ａ M ２－ｂ N ｃ (PO) ４ ) ３＋ｄ [In the formula, M = Ti, Zr, or Hf; N is a metal other than Li and M; [0 ≤ a ≤ 0.6, 0 ≤ b ≤ 0.6, 0 ≤ c ≤ 0.6, 0 ≤ d ≤ 0.8] Lithium metal phosphate 1% to 50% by mass, A dispersion containing 50% to 99% by mass of trialkyl phosphate.

2. The dispersion according to claim 1, wherein the lithium metal phosphate is in the form of aggregated primary particles.

3. The dispersion according to claim 1 or 2, wherein the lithium metal phosphate is obtained by a method of thermal decomposition.

4. The aforementioned lithium metal phosphate, 5m ２ / g to 100m ２ A dispersion according to any one of claims 1 to 3, having a BET surface area of ​​1 / g.

5. The lithium metal phosphate was determined by dynamic light scattering (DLS) at a temperature of 25°C to have a particle size d of less than 1 μm in a dispersion diluted with a trialkyl phosphate containing 1% by mass of the lithium metal phosphate. ９９ A dispersion according to any one of claims 1 to 4, having the following characteristics.

6. The dispersion according to any one of claims 1 to 5, wherein the lithium metal phosphate has a tamp density of 20 g / L to 200 g / L.

7. The dispersion according to any one of claims 1 to 6, wherein the trialkyl phosphate is selected from the group consisting of trimethyl phosphate, triethyl phosphate, tri-n-propyl phosphate, triisopropyl phosphate, methyl diethyl phosphate, and mixtures thereof.

8. A method for producing the dispersion according to any one of claims 1 to 7, comprising mixing the lithium metal phosphate and the trialkyl phosphate, and optionally grinding or milling the resulting dispersion.

9. The method according to claim 8, wherein grinding or milling is carried out by ultrasonic treatment, a wet jet mill, or a ball mill.

10. A wet coating composition comprising a dispersion according to any one of claims 1 to 7, an organic binder, and optionally a solvent.

11. The wet coating composition according to claim 10, comprising 50% to 99% by mass of the dispersion according to any one of claims 1 to 7, 1% to 50% by mass of an organic binder, and optionally 1% to 50% by mass of a solvent.

12. The wet coating composition according to claim 10 or 11, wherein the organic binder is selected from the group consisting of polyethylene oxide, polyvinylidene fluoride, polyvinylidene chloride, polytetrafluoroethylene, polyacrylonitrile, polyamide, polyimide, polyetheretherketone, polymethyl methacrylate, polytetraethylene glycol diacrylate, polyvinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride / chlorotrifluoroethylene copolymer, polysulfone, polyethersulfone, and mixtures thereof.

13. A dry coating composition obtained by evaporation of a trialkyl phosphate and optionally a solvent from the wet composition according to any one of claims 10 to 12.

14. Use of a wet coating composition according to any one of claims 10 to 12 or a dry coating composition according to claim 13 for coating electrodes or separators of a lithium-ion battery.

15. A lithium-ion battery comprising the dry coating composition described in claim 13.

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