Dispersion and coating compositions comprising lithium metal phosphates

Abstract

The present invention relates to dispersions and coating compositions comprising lithium metal phosphates. The present invention relates to a dispersion comprising 1 to 50 wt.-% of a lithium metal phosphate having the general formula Li 1+a M 2‑b N c (PO4) 3+d with M = Ti, Zr or Hf; N = a metal other than Li other than M; 0 < a < 0.6, 0 < b < 0.6, 0 < c < 0.6, 0 < d < 0.8 and 50 to 99 wt.-% of a trialkyl phosphate. The present invention further relates to coating compositions comprising such dispersions and their use in lithium ion batteries.

Description

Invention Field

[0001] This invention relates to dispersions and coating compositions comprising lithium metal phosphates, methods for producing such dispersions, and their use in lithium-ion batteries. Existing technology

[0002] Rechargeable lithium-ion batteries are one of the most important types of batteries currently in use. A typical rechargeable lithium-ion battery consists of an anode made of carbon material or a lithium metal alloy, a cathode made of lithium-metal oxide, an electrolyte in which lithium salt is dissolved in an organic solvent, and a separator that provides a channel for lithium ions between the positive and negative electrodes during charging and discharging.

[0003] Typical components of such liquid lithium-ion batteries, such as the cathode, anode, and separator, can be coated with layers made of metal oxides or compounds that provide lithium-ion conductivity. This results in the formation of a defined solid electrolyte interface (SEI) that conducts lithium ions and is resistant to possible electrolyte breakdown products.

[0004] In efforts to develop rechargeable batteries with improved inherent safety and energy density, significant progress has recently been made in replacing liquid electrolytes with solid electrolytes. Among these systems, rechargeable lithium-ion batteries with electrodes made of lithium metal or lithium metal alloys are considered to offer high energy density and are particularly suitable. Such all-solid-state rechargeable lithium-ion batteries should possess good ion conductivity at the interface between the electrode active material and the electrolyte to achieve the desired loading characteristics.

[0005] H. Xiea et al., in the Journal of Power Sources 2011, Vol. 196, pp. 7760-7762, described the preparation of Li by solid-state reaction of ZrO2 with Li2CO3, NH4H2PO4 and CaCO3. 1.2 Zr 1.9 Ca 0.1 (PO4)3. The lithium-ion conductivity of this zirconium lithium phosphate was found to be similar to that of Li-3, which was used as a solid lithium-ion separator in a lithium-ion battery test cell. 1.3 Ti 1.7 Al 0.3 (PO4)3 is equivalent.

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

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

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

[0009] Therefore, as described in US2009081554A1, high ionic conductivity can be achieved by coating the surface of the active electrode material with lithium-containing compounds such as LiTi2(PO4)3. In US2009081554A1, an ethanol solution of the precursor lithium ethoxide, phosphorus pentoxide, and tetraisopropoxide titanium was used to coat the electrode directly on the electrode surface to prepare a lithium titanium phosphate coating. Summary of the Invention

[0010] Problems and Solutions

[0011] Preparing a coating of lithium metal phosphate from a solution of the corresponding precursor on the electrode surface is not so convenient because it requires very careful selection of reaction conditions that are compatible with both the precursor used and the substrate to be coated.

[0012] Therefore, it is desirable to find a method for the direct application of pre-prepared lithium metal phosphates.

[0013] One possibility for doing this is to use a dispersion containing fine particles of lithium metal phosphate.

[0014] However, the preparation of such ready-to-use dispersions has proven to be quite problematic. Using common solvents such as alcohols or dimethoxyethane (DME) results in unstable dispersions that tend to form large agglomerates of lithium metal phosphates and high-viscosity pastes, rather than the desired fine-particle dispersions.

[0015] This dispersion is not suitable for obtaining a uniform coating of high-quality lithium metal phosphate required for lithium-ion batteries.

[0016] The problem addressed by this invention is to provide a dispersion of lithium metal phosphate that is substantially free of large agglomerates. Such a dispersion preferably has a relatively low viscosity and is stable for at least several days, preferably several weeks, during which time it does not lead to a significant increase in viscosity or the formation of precipitation or agglomerates.

[0017] Such dispersions should be well-suited for preparing coating compositions for coating lithium-ion battery components, particularly anodes, cathodes, and separators.

[0018] Another problem solved by the present invention is to provide a method for producing such dispersions.

[0019] The present invention provides a dispersion comprising 1% to 50% by weight of a compound having the general formula Li 1+a M 2-b N c (PO4) 3+d Lithium metal phosphate and 50% to 99% by weight of trialkyl phosphate, wherein

[0020] M = Ti, Zr, or Hf;

[0021] N = a metal that is neither Li nor M;

[0022] 0≤a≤0.6, 0≤b≤0.6, 0≤c≤0.6, 0≤d≤0.8.

[0023] Even with the presence of very small lithium metal phosphate particles, this dispersion surprisingly proved to be low-viscosity and long-term stable. Furthermore, coating compositions containing this dispersion were found to be highly suitable for coating lithium-ion battery components.

[0024] Lithium metal phosphate

[0025] The lithium metal phosphate used in the dispersion of the present invention has the general formula Li 1+a M 2-b N c (PO4) 3+d ,in

[0026] M = Ti, Zr, or Hf, with M = Zr being preferred;

[0027] N = a metal that is neither Li nor M;

[0028] 0≤a≤0.6, 0≤b≤0.6, 0≤c≤0.6, 0≤d≤0.8,

[0029] The preferred values ​​are 0≤a≤0.3, 0≤b≤0.3, 0≤c≤0.3, and 0≤d≤0.4.

[0030] The non-Li, non-M metallic 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 the context of this invention, silicon dioxide and boron are considered metals, and their compounds are referred to as "metal precursors." Preferably, the lithium metal phosphate of this invention comprises calcium (Ca), aluminum (Al), iron (Fe), and / or yttrium (Y).

[0031] The lithium metal phosphate used in the dispersion of this invention can have a 5m 2 / g-100m 2 / g, preferably 7m 2 / g-80m 2 / g, more preferably 15m 2 / g-60m 2 / g of BET surface area.

[0032] The surface area of ​​BET can be determined according to DIN 9277:2014 by nitrogen adsorption according to the Brunauer-Emmett-Teller procedure.

[0033] 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 average diameter of typically 1-100 nm, more preferably 3-70 nm, and more preferably 5-50 nm, as determined by transmission electron microscopy (TEM). This number average diameter can be determined by calculating the average size of at least 500 particles analyzed by TEM.

[0034] Dynamic light scattering (DLS) is a technique in physics used to determine the size distribution profiles of small particles in suspensions. 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 within the medium and the scattering of incident laser light due to the difference in refractive indices between liquid and solid materials.

[0035] The resulting value is the hydrodynamic diameter of the corresponding sphere of the particle. d 50 d 90 and d 99 These values ​​are commonly used standards of discussion because they describe the hydrodynamic diameter of particles at or below 50%, 90%, or 99% of the particle size distribution. The lower these values, the better the particle dispersion. Monitoring these values ​​can provide clues about the stability of the particle dispersion. If these values ​​increase significantly, the particles are not stable enough and may agglomerate and precipitate over time, resulting in a lack of stability. Depending on the viscosity of the medium, it can be said that dm is less than 1000 nm (1 μm).99 The value is an indicator of a stable dispersion because the particles are in a state of rest (abeyance) over time.

[0036] The number-average particle size d of the lithium metal phosphate in the dispersion of the present invention, as determined by dynamic light scattering (DLS) at 25°C in a dispersion diluted with a trialkyl phosphate containing approximately 1% by weight of lithium metal phosphate, is... 50 Preferably, it is about 0.03μm-2μm, more preferably 0.04μm-1μm, and even more preferably 0.05μm-0.5μm.

[0037] The number-average particle size d of the lithium metal phosphate in the dispersion of the present invention, as determined by dynamic light scattering (DLS) at 25°C in a dispersion diluted with a trialkyl phosphate containing approximately 1% by weight of lithium metal phosphate, is... 99 Preferably less than 1 μm, more preferably about 0.05 μm-1 μm, more preferably 0.1 μm-0.8 μm, and even more preferably 0.15 μm-0.5 μm.

[0038] Therefore, compared to dispersions using similar but different dispersants, such as those using trialkyl phosphate, the dispersions of the present invention are substantially free of large particles, i.e., those with a particle size greater than 1 μm. This makes the dispersions of the present invention particularly suitable for producing coating compositions with small, finely distributed lithium phosphate particles, especially suitable for coating lithium-ion battery elements.

[0039] The agglomerates and some aggregates of lithium metal phosphate can be further broken down, for example by grinding or ultrasonic treatment of the particles to obtain particles with smaller particle size and narrower particle size distribution.

[0040] The lithium metal phosphate used in the dispersion according to the invention preferably has a compaction density of 20 g / L-200 g / L, more preferably 25 g / L-150 g / L, even more preferably 30 g / L-100 g / L, and still more preferably 40 g / L-80 g / L.

[0041] The compacted density of powdery 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 involves measuring the apparent density of the bed after mixing and compaction.

[0042] The lithium metal phosphate used in the dispersions of this invention is preferably obtained by pyrolysis (also known as the “gas-phase method”). The terms “pyrolysis-generated,” “pyrolytic,” and “gas-phase” are used interchangeably in the context of this invention. This “pyrolysis” or “gas-phase” method involves the flame hydrolysis or flame oxidation of the corresponding metal precursor in an oxyhydrogen flame to form a compound produced by pyrolysis. The reaction initially forms highly dispersed, nearly spherical primary particles, which aggregate to form aggregates during further reaction. These aggregates can then coalesce into agglomerates. In contrast to agglomerates, which can typically be separated into aggregates relatively easily by introducing energy, the aggregates can only be further broken down, if possible, by strongly introducing energy. The particles can be partially broken down and converted into nanometer (nm) particles by appropriate grinding. However, such grinding is not necessary because the “freshly prepared” gas-phase particles have a sufficiently small particle size.

[0043] Lithium metal phosphates are preferably produced by flame spray pyrolysis, and preferably by using a solution of metal carboxylates and organophosphates as precursors.

[0044] In this flame spray pyrolysis process, a solution of metal compound (metal precursor) and phosphorus source is typically introduced into the flame in the form of fine droplets. The flame is formed by igniting fuel gas and oxygen-containing gas. The metal precursor used in the flame is oxidized and / or hydrolyzed together with the phosphorus source to obtain the corresponding lithium metal phosphate.

[0045] The flame spray pyrolysis process preferably includes the following steps:

[0046] a) The metal precursor solution is atomized using atomizer gas to provide an aerosol.

[0047] b) To obtain a reaction stream by reacting the aerosol with a flame obtained by igniting a mixture of fuel gas and oxygen-containing gas in the reaction space of the reactor.

[0048] c) Cool the reaction stream and

[0049] d) The solid lithium metal phosphate was then removed from the reaction stream.

[0050] Examples of fuel gases are hydrogen, methane, ethane, natural gas, and / or carbon monoxide. Hydrogen is particularly preferred. Fuel gases are especially suitable for embodiments where a high degree of crystallinity of the produced lithium metal phosphate is desired.

[0051] Oxygen-containing gas is typically air or oxygen-enriched air. It is particularly useful in embodiments where, for example, it is desirable to produce lithium metal phosphates with a high BET surface area. The total amount of oxygen is usually chosen to be sufficient to completely convert the fuel gas and the metal precursor.

[0052] To obtain an aerosol, a vaporized solution containing a metal precursor can be mixed with an atomizer gas such as nitrogen, air, and / or other gases. The resulting aerosol consists of fine droplets, preferably with an average droplet size of 1-120 μm, particularly preferably 30-100 μm. Droplets are typically generated using single-material or multi-material nozzles. To increase the solubility of the metal precursor and obtain a suitable viscosity for easy solution atomization, the solution can be heated.

[0053] The metal carboxylates used as precursors in flame spray pyrolysis can be, independently, straight-chain, branched, or cyclic valerates (C5), hexanoates (C6), heptanoates (C7), octanoates (C8), nonanoates (C9), decanoates (D10), undecanoates (C11), dodecanoates (C12), tridecanoates (C13), tetradecanoates (C14), pentadecanoates (C15), hexadecanoates (C16), heptadecanates (C17), octadecanoates (C18), nonadecanates (C19), icosanoates (C20), and mixtures thereof, of the metal used.

[0054] Metal precursors can also be inorganic metal compounds, such as nitrates, carbonates, chlorides, bromides, or other organometallic compounds, such as alkoxides, for example, ethanol, n-propoxide, isopropoxide, n-butoxide, and / or tert-butoxide.

[0055] The organophosphate esters used in the flame spray pyrolysis process are preferably selected from phosphonic acid (H3PO3), orthophosphoric acid (H3PO4), metaphosphoric acid (HPO3), pyrophosphoric acid (H4P2O7), polyphosphoric acid esters and mixtures thereof.

[0056] Organophosphates can be selected from alkyl (such as methyl, ethyl, propyl, butyl, hexyl) esters, aryl (such as phenyl) esters, mixed alkyl / aryl esters and mixtures thereof.

[0057] If small lithium metal phosphate particles with high BET surface area and low compaction density are required, it is preferable to use organophosphates as phosphorus sources during flame spray pyrolysis.

[0058] The solvent used for the metal precursor can be selected from linear or cyclic, saturated or unsaturated, aliphatic or aromatic hydrocarbons, carboxylic acid esters, ethers, alcohols, carboxylic acids and mixtures thereof.

[0059] Lithium metal phosphates known in the art, typically prepared via solid-state synthesis, possess relatively high material density and low BET surface area, making them suitable for use as core materials in solid-state electrolytes for lithium-ion batteries. However, if such compounds are to be used as additives capable of distributing well within or on the surface of core materials, smaller particle size, lower material density, and higher BET surface area are crucial. Therefore, lithium metal phosphates prepared via pyrolysis, as described above, are particularly suitable for providing the dispersions of the present invention and their use in lithium-ion batteries.

[0060] Lithium metal phosphates obtained by pyrolysis can be further heat-treated. This further heat treatment is preferably carried out at a temperature of 600°C-1300°C, more preferably 650°C-1250°C, even more preferably 700°C-1200°C, and still more preferably 750°C-1150°C. Heat treatment allows for the acquisition of lithium metal phosphates with optimized properties, particularly the desired crystal structure.

[0061] The lithium metal phosphate obtained by pyrolysis can be further ground, preferably using a ball mill. Ball milling is preferably carried out with ZrO2 balls, for example with ZrO2 balls having a diameter of about 0.5 mm, in a suitable solvent (e.g., ethanol or isopropanol).

[0062] Dispersions containing lithium metal phosphate

[0063] The dispersion of the present invention comprises 1% to 50% by weight, preferably 5% to 45% by weight, more preferably 10% to 40% by weight, more preferably 15% to 35% by weight of lithium metal phosphate, and 50% to 99% by weight, preferably 55% to 95% by weight, more preferably 60% to 90% by weight, more preferably 65% ​​to 85% by weight of trialkyl phosphate.

[0064] Trialkyl phosphate is preferably selected from trimethyl phosphate, triethyl phosphate, tri-n-propyl phosphate, triisopropyl phosphate, methyl diethyl phosphate, and mixtures thereof.

[0065] The selected trialkyl phosphate has the advantage of being water-soluble, thus simplifying the cleaning process.

[0066] The dispersion of the present invention may also contain components other than lithium metal phosphate and trialkyl phosphate components, such as solvents, dispersants or other additives.

[0067] Therefore, solvents selected from water, dimethyl sulfoxide, tetramethylurea, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, and acetone can be present in the dispersions of the present invention as other components of this class.

[0068] Suitable dispersants can be polymers or salts of such functional groups, such as alkylammonium salts or alkanolammonium salts, having acid and / or amine functional groups. The acid groups can be phosphate or sulfonic acid groups. The number average molecular weight of such dispersants is preferably at least 500 g / mol, particularly preferably from 500 g / mol to 1000 g / mol. Dispersants can be polymers and copolymers, such as block copolymers or copolymers with statistically significant structures. Suitable dispersants are available from Byk Chemie under the trade name... For obtaining suitable dispersants, also refer to, for example, WO2010 / 025889 and EP-A-893155.

[0069] The total amount of such other components in the dispersion of the present invention may be up to 20% by weight, more preferably up to 10% by weight, and even more preferably up to 5% by weight.

[0070] However, preferably, the dispersion of the present invention is substantially free of such other components, i.e., its amount is less than 0.5% by weight.

[0071] Based on the total weight of the dispersion, all components of the dispersion of the present invention total 100% by weight.

[0072] In 10s -1 The shear rate and the dynamic viscosity of the dispersion of the present invention, determined at 22°C, are preferably less than 60 mPas, more preferably less than 50 mPas, more preferably in the range of 1 mPas to 50 mPas, more preferably 2 mPas to 40 mPas, and more preferably 3 mPas to 30 mPas.

[0073] The dynamic viscosity of the dispersion of the present invention can be within 10s. -1 The shear rate and dynamic viscosity at 22°C are measured using any suitable device for determining the dynamic viscosity.

[0074] Method for producing dispersions containing lithium metal phosphate

[0075] The invention also includes a method for producing a dispersion according to the invention, comprising mixing a lithium metal phosphate and a trialkyl phosphate and optionally grinding or milling the resulting dispersion. Using these milling techniques can significantly reduce the particle size of agglomerates.

[0076] The preparation of the dispersion of the present invention is preferably carried out at 10°C-50°C, more preferably at 15°C-40°C.

[0077] To avoid unwanted heating of the dispersion during grinding or milling, the dispersion can be cooled using a heat exchanger.

[0078] If you want to produce dispersions with particularly small particle sizes, you can grind or mill them, for example, by using a high-energy mill such as a wet-jet mill.

[0079] For this purpose, a pre-dispersion comprising lithium metal phosphate particles and trialkyl phosphate, such as a dispersion obtained by a rotor / stator system or a dissolver apparatus, is split into at least two sub-streams, and these sub-streams are released through nozzles in a high-energy mill at a pressure of at least 500 bar, allowing some of the streams to meet in a reaction chamber filled with gas or liquid. This high-energy milling can be repeated multiple times. A suitable high-energy mill is, for example, the UltimaizerSystem HJP-25050 mill from Sugino Machine Ltd.

[0080] 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.

[0081] ZrO2 beads with a diameter of about 0.8 mm can be ball-milled using a conventional laboratory or production-scale ball mill. Preferably, the ball milling process provides the dispersion with 0.1 to 10 kWh / kg, more preferably 0.2 to 5 kWh / kg, and more preferably 0.5 to 3 kWh / kg of energy.

[0082] Wet coating compositions comprising the dispersions of the present invention and dry coating compositions obtained therefrom

[0083] The present invention also provides a wet coating composition comprising the dispersion according to the invention, an organic binder, and an optionally present solvent.

[0084] This wet coating composition preferably comprises 50 wt%-99 wt%, more preferably 55 wt%-95 wt%, 60 wt%-90 wt%, 65 wt%-85 wt% of the dispersion of the present invention, 1 wt%-50 wt%, more preferably 5 wt%-45 wt%, more preferably 10 wt%-40 wt%, more preferably 15 wt%-35 wt% of an organic binder, and optionally 1 wt%-50 wt%, more preferably 5 wt%-45 wt%, more preferably 10 wt%-40 wt%, more preferably 15 wt%-35 wt% of a solvent.

[0085] Based on the total weight of the composition, all components of the wet-coating composition total 100% by weight.

[0086] The organic binder can be selected from polyethylene oxide, polyvinylidene fluoride, polyvinylidene chloride, polytetrafluoroethylene, polyacrylonitrile, polyamide, polyimide, polyetheretherketone, polymethyl methacrylate, polytetraethylene glycol diacrylate, polyvinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride / trifluorochloro copolymer, polysulfone, polyethersulfone and mixtures thereof.

[0087] The solvent optionally used in the wet coating composition of the present invention may be selected from water, alcohols, 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 below 300°C at 1 atm, and more preferably below 200°C. During the curing of the wet coating composition according to the present invention, this relatively volatile solvent can readily evaporate or vaporize. Most preferably, the wet coating composition of the present invention comprises trialkyl phosphate selected from trimethyl phosphate, triethyl triphosphate, tri-n-propyl phosphate, triisopropyl phosphate, methyl diethyl phosphate, and mixtures thereof as the sole solvent.

[0088] 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 those mentioned above) and optionally with other additives (such as solvents, dispersants, etc., preferably those mentioned above).

[0089] The present invention also provides the use of the wet coating composition according to the invention for coating components of lithium-ion batteries, such as the positive and negative electrodes or separators of lithium-ion batteries.

[0090] A method for coating using the wet coating composition of the present invention may include the following steps:

[0091] a) Applying the coating composition of the present invention to the surface of components of a lithium-ion battery, such as its electrodes or membranes.

[0092] b) Curing the organic binder and / or removing the solvent.

[0093] In step a) of the coating method, the wet coating composition of the present invention preferably forms a layer with a thickness of less than 100 μm, more preferably 10 μm to 100 μm, and particularly preferably 20 μm to 80 μm on the coated substrate.

[0094] In step b), curing of the composition can be achieved by at least partial polymerization and / or solvent removal. Depending on the system used, this step is preferably carried out at a temperature of 0 to 500°C, particularly preferably 5 to 400°C, and very particularly preferably 10 to 300°C. Curing can be carried out in the presence of air or under oxygen-free conditions, such as in a protective atmosphere of nitrogen or carbon dioxide. The step can be carried out under standard pressure or under reduced pressure (e.g., under vacuum).

[0095] The present invention also provides a dry coating composition obtained by evaporating a trialkyl phosphate and optionally a solvent from a wet composition according to the invention. 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 a solvent from the wet coating composition.

[0096] The dry coating composition of the present invention preferably forms a layer with a thickness of less than 30 μm, more preferably less than 20 μm, and particularly preferably 1 μm to 10 μm on a coated substrate.

[0097] The present invention also provides the use of the wet coating composition of the present invention or the dry coating composition of the present invention for coating electrodes or separators of lithium-ion batteries.

[0098] Lithium-ion batteries containing the dispersion of the present invention

[0099] The present invention also provides a lithium-ion battery comprising a dry-coating composition according to the present invention.

[0100] The lithium-ion battery of the present invention may include a positive electrode (cathode), a negative electrode (anode), a separator, and an electrolyte containing a lithium compound.

[0101] The positive electrode (cathode) of a lithium-ion battery typically includes a current collector and an active cathode material layer formed on the current collector.

[0102] The current collector can be aluminum foil, copper foil, nickel foil, stainless steel foil, titanium foil, polymer substrate coated with conductive metal, or a combination thereof.

[0103] The active cathode material may include materials capable of reversibly inserting / deintercalating lithium ions and is well known in the art. Such active cathode materials may include transition metal oxides, such as mixed oxides comprising Ni, Co, Mn, V or other transition metals and optionally lithium. Preferred mixed lithium transition metal oxides used as active cathode materials are selected from lithium-cobalt oxides, lithium-manganese oxides, lithium-nickel-cobalt oxides, lithium-nickel-manganese-cobalt oxides, lithium-nickel-cobalt-aluminum oxides, lithium-nickel-manganese oxides, or mixtures thereof.

[0104] The anode of a lithium-ion battery can comprise any suitable material capable of reversibly inserting / deintercalating lithium ions, typically used in secondary lithium-ion batteries. Typical examples are carbonaceous materials, including crystalline carbon such as natural or artificial graphite in the form of plate-like, flake-like, spherical, or fibrous graphite; and amorphous carbon such as soft carbon, hard carbon, mesophase pitch carbides, coke, or mixtures thereof. Additionally, lithium metal or conversion materials (e.g., Si or Sn) can be used as the anode active material.

[0105] The electrolyte in a lithium-ion battery can be in liquid, gel, or solid form.

[0106] The liquid electrolyte of a lithium-ion battery may include any suitable organic solvent commonly used in lithium-ion batteries, such as anhydrous ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, dimethoxyethane, fluoroethylene carbonate, vinyl ethylene carbonate, or mixtures thereof.

[0107] Gel electrolytes include gel polymers.

[0108] The solid electrolyte of a lithium-ion battery may contain oxides, such as lithium metal oxides, sulfides, phosphates, or solid polymers.

[0109] The liquid or polymer gel electrolyte of lithium-ion batteries typically contains lithium salts. Examples of such lithium salts include lithium hexafluorophosphate (LiPF6), lithium bis-2-(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), Li2SiF6, lithium trifluoromethanesulfonate, 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.

[0110] Lithium-ion batteries, especially those with liquid or gel electrolytes, may also include a separator to prevent direct contact between the two electrodes (which would result in an internal short circuit).

[0111] The diaphragm material may include polyolefin resins, fluorinated polyolefin resins, polyester resins, polyacrylonitrile resins, cellulose resins, nonwoven fabrics, or mixtures thereof. Preferably, the material includes polyolefin resins such as polyethylene or polypropylene-based polymers, fluorinated resins such as polyvinylidene fluoride polymers or polytetrafluoroethylene, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polyacrylonitrile resins, cellulose resins, nonwoven fabrics, or mixtures thereof.

[0112] The lithium-ion battery according to the present invention may comprise a liquid electrolyte, a gel electrolyte, or a solid electrolyte. In the context of the present invention, a liquid mixture of an uncured, unpolymerized, or uncrosslinked lithium salt and an organic solvent is referred to as a "liquid electrolyte." A gel or solid mixture comprising a cured, polymerized, or crosslinked compound or a mixture thereof, optionally a solvent, and a lithium salt is referred to as a "gel electrolyte." Such a gel electrolyte can be prepared by polymerization or crosslinking of a mixture comprising at least one reactive (i.e., polymerizable or crosslinkable) compound and a lithium salt.

[0113] One special type of lithium-ion battery is the lithium polymer battery, in which a polymer electrolyte is used instead of a liquid electrolyte. Similar solid-state batteries may also use other types of solid electrolytes, such as sulfided, oxidized solid electrolytes, or mixtures thereof.

[0114] The battery of the present invention can be a lithium metal battery, such as lithium-air, lithium-sulfur (Li-S) and other types of lithium metal batteries.

[0115] Lithium-air batteries typically consist of a porous carbon cathode and an organic glass-ceramic or polymer-ceramic electrolyte.

[0116] Lithium-sulfur (Li-S) batteries typically contain iron disulfide (FeS2), iron sulfide (FeS), copper sulfide (CuS), or lead sulfide plus copper sulfide (PbS+CuS) cathodes.

[0117] There are 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-monofluoride (Li-(CF)). x Lithium-thionyl chloride (Li-SOCl2), lithium-thionyl chloride (Li-SO2Cl2), lithium-sulfur dioxide (Li-SO2), lithium-iodine (Li-I2), lithium-silver chromate (LiAg2CrO4), lithium-vanadium pentoxide (Li-V2O5 or Li / Al-V2O5), lithium-copper chloride (Li-CuCl2), lithium copper oxide (II) (Li-CuO), lithium-copper oxyphosphate (Li-Cu4O(PO4)2) and other types. Detailed Implementation

[0118] Example

[0119] Example 1: Preparation of lithium zirconium phosphate

[0120] 23.75 kg of a commercially available solution containing 3370 g of lithium in the form of lithium neodecanoate dissolved in naphtha, comprising 2 wt%. Deca Lithium 2), 15 kg of a commercially available solution containing 11.86 wt% zirconium ethylhexanoate dissolved in a white solvent oil (Octa Zirconium 12) and 5384 g of a commercially available solution (Alfa Aesar) containing 16.83 wt% triethyl phosphate were mixed to obtain a clear solution. This solution corresponds to the composition LiZr2(PO4)3.

[0121] This dispersion consists of 1.5 kg / h and 15 Nm 3 / h of air is atomized into an aerosol via a two-component nozzle and sprayed into the tubular reactor under combustion flame conditions. The combustion gases of the flame are 8.5 Nm³. 3 / h of hydrogen and 30Nm 3 The air composition is / h. In addition, 25Nm was used. 3 / h of secondary air. After the reactor, the reaction gas is cooled and filtered.

[0122] The BET surface area of ​​the obtained lithium zirconium phosphate powder is 44 m². 2 / g, compacted density is 52g / L, as measured by static light scattering method d 50 The value is 76 nm. XRD analysis shows that the main phase of the product is rhombohedral lithium zirconium phosphate.

[0123] Measurement of dynamic viscosity

[0124] The dynamic viscosity of the dispersion was measured using the rotational viscometry method with a Physica MCR 301 from Anton Paar and a PP25 measuring plate with a distance set to 0.5 mm.

[0125] The viscometer's motor drives a bob within a fixed cup. The bob's rotation speed is preset and generates a specific motor torque necessary to rotate the bob. This torque must overcome the viscous forces of the substance being measured, thus serving as a measure of its viscosity. Data is obtained in 10s. -1 The shear rate was measured at 22°C.

[0126] Example 2: Preparation of LZP dispersion

[0127] The lithium zirconium phosphate (LZP, 6 g) prepared in Example 1 was added to triethyl phosphate (TEP, 14 g), and the mixture was sonicated for 30 minutes using an ultrasonic processor UP400S (400 W, 24 kHz) equipped with a Ti-sonotrode. After dilution with TEP to obtain an LZP concentration of approximately 1 wt%, the particle size distribution was measured using dynamic light scattering (DLS) via an LB-500 apparatus (Horiba Ltd., Japan).

[0128] D was obtained immediately after the preparation of the dispersion by the DLS method. 50 d 90 and d 99 Values ​​and d after the dispersion was stored at room temperature for 1 week and 4 weeks. 99 Value and in 10s after production -1 The dynamic viscosity of the dispersion, measured at 22°C, is shown in Table 1.

[0129] Example 3: Preparation of LZP dispersion

[0130] The ball mill (Netzsch Laboratory Mill Micro Series) was pre-loaded with triethyl phosphate (TEP, 315 g), the peristaltic pump was set to 90 rpm, and the ball mill speed was set to 1000 rpm. Lithium zirconium phosphate (LZP, 135 g) was added to the TEP. The peristaltic pump speed was then adjusted to 120 rpm and the ball mill speed was set to 2500 rpm. The dispersion was treated for 120 minutes (introducing 0.4 kWh of energy). Particle size distribution was measured as described in Example 2.

[0131] D was obtained immediately after the preparation of the dispersion by the DLS method. 50 d 90 and d 99 Values ​​and d after the dispersion was stored at room temperature for 1 week and 4 weeks. 99 Value and in 10s after production -1 The dynamic viscosity of the dispersion, measured at 22°C, is shown in Table 1.

[0132] Comparative Example 1

[0133] A dispersion of 30 wt% LZP in ethanol (EtOH) was prepared in the same manner as in Example 2, the only difference being that EtOH was used instead of TEP.

[0134] D was obtained immediately after the preparation of the dispersion by the DLS method. 50 d 90 and d 99 Values ​​and d after the dispersion was stored at room temperature for 1 week and 4 weeks. 99 Value and in 10s after production -1 The dynamic viscosity of the dispersion, measured at 22°C, is shown in Table 1.

[0135] Comparative Example 2

[0136] A dispersion of 30 wt% LZP in isopropanol (iPrOH) was prepared in the same manner as in Example 2, the only difference being that isopropanol (iPrOH) was used instead of TEP.

[0137] However, the dispersion becomes very viscous during preparation, making it impossible to measure particle size distribution or viscosity.

[0138] Comparative Example 3

[0139] The dispersion of 30 wt% LZP in dimethoxyethane (DME) was prepared in the same manner as in Example 2, except that DME was used instead of TEP.

[0140] However, the dispersion becomes very viscous during preparation, making it impossible to measure particle size distribution or viscosity.

[0141] A comparison of Examples 2-3 with Comparative Examples 1-3 shows that using TEP as a solvent can yield samples with considerably small di. 99 The LZP dispersions with particle sizes (Table 1) are dispersions that are essentially free of large particles >1 μm. Importantly, these dispersions using TEP solvent exhibit low viscosity and remain stable without any particle agglomeration after storage at room temperature for 1 and 4 weeks, in contrast to the dispersions from Comparative Example 1 using EtOH as the solvent (Table 1).

[0142] Example 4: Preparation of coating composition

[0143] Slurry A: The dispersion of 30 wt% LZP prepared in Example 3 in TEP was diluted with TEP under stirring to a solid content of 20 wt% LZP.

[0144] Slurry B: Poly(vinylidene fluoride-co-hexafluoropropylene, PVDF-HFP) organic binder with a MW of 400,000 g / mol from Sigma Aldrich, Germany, was completely dissolved and stirred overnight in TEP at 35°C to form a 10 wt% PVDF-HFP solution in TEP.

[0145] Slurries A and B were mixed together to achieve a final LZP to binder ratio of 6:1 (LZP:PVDF). (The resulting coating composition consisted of 75 wt% of the dispersion of Example 3, i.e., slurry A, and 25 wt% of slurry B, and contained 15 wt% LZP, 2.5 wt% PVDF-HFP, and 82.5 wt% TEP).

[0146] Example 5: Coating copper foil with the coating composition of Example 4

[0147] Five ml of the coating composition obtained in Example 4 was placed into a doctor blade device (doctor blade: Quadruple Film Applicator, Model 360, Erichsen, Germany, slit width 50 μm). The coating speed was set to 0.4 m / min, and coating of an 18 μm thick copper foil (Hohsen, Japan) was started. A stable and uniform wet film of approximately 50 μm thickness was obtained on the copper foil surface.

[0148] The wet coating was dried at 100°C for 2 hours to obtain a 5 μm thick LZP dry coating. This layer exhibited excellent adhesion to copper foil.

[0149] Table 1: Dispersions of lithium zirconium phosphate in various solvents

[0150]

[0151] (1) and (2) the dispersions become very viscous during the preparation process, making it impossible to measure the particle size or viscosity.

Claims

1. A dispersion comprising 1 to 50 weight percent of a lithium metal phosphate having the general formula Li 1+a M 2-b N c (PO4) 3+d and 50 to 99 weight percent of a trialkyl phosphate, wherein M = Ti, Zr or Hf; N = metal other than Li other than M; 0 < a < 0.6, 0 < b < 0.6, 0 < c < 0.6, 0 < d < 0.8, wherein the lithium metal phosphate has a particle size d 99 .

2. Dispersion according to claim 1, wherein the lithium metal phosphate is in the form of agglomerated primary particles.

3. Dispersion according to claim 1 or 2, wherein the lithium metal phosphate is obtained by pyroprocessing.

4. The dispersion of claim 1 or 2, wherein the lithium metal phosphate has a BET surface area of 5 m 2 / g to 100 m 2 / g.

5. Dispersion according to claim 1 or 2, wherein the lithium metal phosphate has a tap density of 20 g / L to 200 g / L.

6. Dispersion according to claim 1 or 2, wherein the trialkyl phosphate is selected from trimethyl phosphate, triethyl phosphate, tri-n-propyl phosphate, tri-iso-propyl phosphate, methyldiethyl phosphate and mixtures thereof.

7. Process for the preparation of a dispersion according to any one of claims 1 to 6, comprising mixing a lithium metal phosphate and a trialkyl phosphate and optionally milling or grinding the resulting dispersion.

8. Process according to claim 7, wherein the milling or grinding is carried out by ultrasonication or by a wet jet mill or a ball mill.

9. Wet coating composition comprising a dispersion according to any one of claims 1 to 6, an organic binder and optionally a solvent.

10. Wet coating composition according to claim 9, comprising 50 wt.% to 99 wt.% of a dispersion according to any one of claims 1 to 6, 1 wt.% to 50 wt.% of an organic binder and optionally 1 wt.% to 50 wt.% of a solvent.

11. Wet coating composition according to any one of claims 9 to 10, wherein the organic binder is selected from polyethylene oxide, polyvinylidene fluoride, polyvinylidene chloride, polytetrafluoroethylene, polyacrylonitrile, polyamide, polyimide, polyether ether ketone, polymethyl methacrylate, polytetraethylene glycol diacrylate, polyvinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride / chlorotrifluoroethylene copolymer, polysulfone, polyether sulfone and mixtures thereof.

12. Dry coating composition obtained by evaporating the trialkyl phosphate and optionally the solvent from a wet coating composition according to any one of claims 9 to 11.

13. Use of a wet coating composition according to any one of claims 9 to 11 or a dry coating composition according to claim 12 for coating an electrode or a separator of a lithium ion battery.

14. Lithium ion battery comprising a dry coating composition according to claim 12.

Images