PREPARATION OF NANOSTRUCTURED MIXED LITHIUM-ZIRCONIUM OXIDES BY SPRAY PYROLYSIS

Abstract

The invention relates to a process for producing mixed oxides comprising lithium, zirconium and optionally at least one non-metal of Li and Zr, by flame spray pyrolysis, mixed oxides obtainable by this process and their use in lithium-ion batteries.

Description

PREPARATION OF NANOSTRUCTURED MIXED LITHIUM-ZIRCONIUM OXIDES BY SPRAY PYROLYSIS Field of invention The invention relates to a process for producing mixed oxides comprising lithium and zirconium and optionally at least one metal other than Li and Zr, by flame spray pyrolysis, to mixed oxides that can be obtained by this process and for their use as active positive electrode materials in lithium-ion batteries. State of the art Secondary lithium-ion batteries are one of the most important types of batteries in use today. They typically consist of an anode made of carbon 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 flow between the positive and negative electrodes during charging and discharging. In an effort to develop secondary batteries with greater intrinsic safety and energy density, the use of solid electrolytes instead of liquids has progressed considerably in recent times. Among such systems, lithium-ion secondary batteries with electrodes made of lithium metal or lithium-metal alloys are considered to provide high energy density and are particularly suitable. Such solid-state lithium-ion secondary batteries must have good ionic conductivity at the interface between an active electrode material and an electrolyte to achieve the required charging characteristics. This high ionic conductivity can be achieved by coating the surface of an active electrode material with certain lithium-containing compounds, such as LiTi₂(PO₄)₃, as described in JP 4982866 B2. Mixed oxides comprising lithium find diverse applications in lithium-ion batteries in both solid and liquid states. Therefore, in Agnew. Chem. Int., Ed. 2007, 46, pp. 1-5, it has been indicated that a mixed oxide with a composition LÍ7LasZr20i2 (LLZ) and a garnet-type structure has excellent lithium resistance and can be used as a solid electrolyte in a solid-state lithium secondary battery. EP 2159867 A1 describes the preparation of an aluminum-doped enhanced LLZ material for use in solid-state electrolytes. Lithium carbonate, lanthanum hydroxide, and zirconium oxide are mixed and calcined at 900–1125 °C. Al₂O₃ is then added to the calcined LLZ material, followed by a second calcination at 1180 °C to obtain an Al-doped LLZ oxide with a density of approximately 4 g / cm³. Similar mixed oxides are also indicated for use as coating materials for secondary lithium battery electrodes. One of the general problems with lithium battery cathode materials is their rapid aging and, consequently, the loss of performance during cycling. It is known that coating or doping lithium transition metal oxide particles with certain metal oxides can inhibit unwanted electrolyte reactions with the electrode materials, thus improving the long-term stability of lithium batteries. Among other metal oxides, mixed oxides comprising zirconium have been indicated for this purpose. US2017179544A discloses the preparation of lithium positive electrode materials doped with zirconium-based mixed metal oxides. In Example 1, L17La3Zr2Al0,o70i2,oio5 was prepared by mixing the metal salts and sintering the mixture at 1200 °C for 10 hours, followed by dry mixing with a lithium transition metal oxide mixture Li(Li10 / 75Ni118 / 75Co9 / 75Mn38 / 75)02 and subsequent heating at 900 °C for 20 hours to form a lithium positive electrode material. It is evident from this preparation procedure that only large synthesized particles of L17La3Zr2Al0,o70i2,oio5 could be used in this example. The use of relatively large metal oxide particles containing zirconium often leads to a non-homogeneous distribution and large agglomerated metal oxide particles on the surface of the core cathode material and, as a result, minimal or no improvements in cycling performance are observed compared to undoped or uncoated cathode materials. Spray pyrolysis is a known procedure for producing relatively small metal oxide particles. Spray pyrolysis and flame spray pyrolysis are established processes for producing simple metal oxides as well as complex mixed metal oxides. In spray pyrolysis, metal compounds in the form of fine droplets are introduced into a high-temperature zone where they are oxidized and / or hydrolyzed to yield metal oxides. A special form of this process is flame spray pyrolysis, in which the droplets are fed into a flame formed by the ignition of a fuel gas and an oxygen-containing gas. Document WO 2015173114 A1 describes a flame spray pyrolysis process for producing a mixed oxide powder comprising lithium, lanthanum, zirconium, and optionally other metals, using corresponding solutions comprising precursor compounds of lithium, lanthanum, zirconium, and optionally other metal compounds MX as starting materials. Inorganic compounds such as nitrates, chlorides, bromides, or organic compounds such as alkoxides or carboxylates are suggested as metal precursor compounds. The preferred embodiment of this patent application includes nitrates of lithium, lanthanum, zirconium, and other metals. Water, C5-C20 alkanes, C1-C15 alkanecarboxylic acids, and / or C1-C15 alkandes are suggested as solvents for the metal precursors, with water and solvent mixtures containing water being preferred. In all examples, water was used as the sole solvent for the metal nitrate precursors.The BET surface area of ​​the resulting mixed oxides varies in the range of 0.19-5.1 m2 / g with a mean particle size (dso) of approximately 2-3 pm. J. Mater. Chem. A, 2016, vol. 4, pp. 12947-12954 discloses the preparation of a powder with the composition L¡6,25Alo,25La3Zr20i2 having a BET surface area of ​​16 m2 / g, a primary particle size of 90 nm and an agglomerated particle size of approximately 5 pm, by flame spray pyrolysis from ethanolic solutions of lithium propionate (C3 carboxylate), alumatrane [Al(OCH2CH2)3N], lanthanum isobutyrate (C4 carboxylate) and zirconium isobutyrate (C4 carboxylate). Problem and solution The cited prior art documents describe the manufacture of mixed lithium and zirconium metal oxides by spray pyrolysis. However, the resulting products are reported to have a relatively large particle size, low BET surface area, and generally relatively high densities. The problem addressed by the present invention is to provide an improved process for the manufacture of mixed metal oxides of lithium and zirconium usable in secondary lithium-ion batteries, for example, as components of solid-state electrolytes or constituents of electrode materials. Specifically, this procedure should provide metal oxide particles with a relatively small particle size, high BET surface area, and low compressibility density. In the course of exhaustive experimentation, it was surprisingly discovered that mixed oxides of lithium and zirconium with the desired particle properties can be prepared by the flame spray pyrolysis procedure when using a special combination of metal precursors and solvents. The procedure for producing mixed oxide The invention provides a process for producing a mixed oxide comprising lithium, zirconium, and optionally at least one non-metal, L1 and Zr, by flame spray pyrolysis and optional additional heat treatment, characterized in that at least one metal precursor solution, comprising a lithium carboxylate and / or a zirconium carboxylate, wherein each of these metal carboxylates contains from 5 to 20 carbon atoms, and a solvent mixture comprising an alcohol and a carboxylic acid containing from 5 to 20 carbon atoms, wherein the solvent mixture contains less than 10% by weight of water and wherein the molar ratio of the alcohol to the carboxylic acid is between 1:20 and 20:1, is used in the process. During a flame spray pyrolysis procedure, the solution of metallic compounds (metal precursors) in the form of fine droplets is introduced into a flame, which is formed by ignition of a combustible gas and a gas containing oxygen, where the metallic precursors used are oxidized and / or hydrolyzed to give the corresponding metal oxides. This reaction initially forms highly dispersed, approximately spherical primary particles of metal oxides, which subsequently fuse to form aggregates. The aggregates can then accumulate into agglomerates. Unlike agglomerates, which can generally be separated into aggregates relatively easily by the application of energy, aggregates decompose further, if at all, only through the intensive application of energy. The metal oxides produced are called pyrogenic or pyrogenically produced metal oxides. The flame spray pyrolysis procedure is generally described in WO 2015173114 A1 and elsewhere. Flame spray pyrolysis preferably comprises the following steps: a) at least one solution of metallic precursors is atomized to produce an aerosol by means of an atomizing gas, b) the aerosol is reacted in the reactor reaction space with a flame obtained by igniting a mixture of a combustible gas and a gas containing oxygen to obtain a reaction stream, c) the reaction stream is cooled and d) The solid metal oxide is subsequently removed from the reaction stream. Examples of combustible gases are hydrogen, methane, ethane, natural gas, and / or carbon monoxide. Hydrogen is particularly preferred. A specific combustible gas is used for embodiments where high crystallinity of the metal oxides to be produced is desired. The oxygen-containing gas is generally air or oxygen-enriched air. A particular oxygen-containing gas is used for embodiments where, for example, a high BET surface area of ​​the metal oxide is desired. The total amount of oxygen is generally chosen to be sufficient at least for the complete conversion of the fuel gas and metal precursors. To obtain the aerosol, the vaporized solution containing metallic precursors can be mixed with an atomizing gas, such as nitrogen, air, and / or other gases. The resulting fine droplets from the aerosol preferably have an average droplet size of 1–120 µm, more preferably 30–100 µm. The droplets are typically produced using nozzles made of one or more materials. To increase the solubility of the metallic precursors and achieve a viscosity suitable for atomizing the solution, the solution can be heated. The metallic precursors employed in the process of the invention include at least one lithium carboxylate and at least one zirconium carboxylate, each containing from 5 to 20 carbon atoms. The lithium and zirconium carboxylates used in the process according to the invention may be, independently of each other, pentanoate (C5), hexanoate (C6), heptanoate (C7), octanoate (C8), nonanoate (C9), decanoate (C10), undecanoate (C11), dodecanoate (C12), tridecanoate (C13), tetradecanoate (C14), pentadecanoate (C15), hexadecanoate (C16), heptadecanoate (C17), octadecanoate (C18), nonadecanoate (C19), icosanoate (C20) of lithium and / or zirconium, linear, branched or cyclic and mixtures thereof. Most preferably, zirconium 2-ethylhexanoate (C8) and lithium neodecanoate (C10) are used. The metal precursors used may contain carboxylates of metals other than lithium and zirconium. In addition to the metallic precursors of lithium and zirconium, they can also be inorganic metal compounds, such as nitrates, chlorides, bromides or other organic metal compounds, such as alkoxides, for example, ethoxides, n-propoxides, isopropoxides, n-butoxides and / or erc-butoxides. At least one metal other than Li and Zr, optionally contained in the mixed oxide, may preferably be selected from Na, K, Be, Mg, Ca, Sr, Ba, Zn, Co, Ni, Cu, Mn, B, Al, Ga, In, Fe, Se, Y, La, Ti, Zr, Hf, Ce, Si, Ge, Sn, Pb, V, Nb, Ta, Mo, W, and a combination thereof. In the context of the present invention, silica and boron shall be considered metals, and their compounds may also be used as metallic precursors in the process of the invention. Preferably, the mixed oxide of the invention contains lanthanum (La) and aluminum (Al). The solvent mixture used in the process of the invention to dissolve the metal precursors comprises an alcohol and a carboxylic acid containing 5 to 20 carbon atoms. The alcohol is preferably selected from the group consisting of methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol, n-pentanol, n-hexanol, cyclohexanol, n-octanol, 2-ethylhexanol, n-decanol, neodecanol and mixtures thereof. The carboxylic acid is preferably selected from the group consisting of linear, branched or cyclic pentanoic acid (C5), hexanoic acid (C6), heptanoic acid (C7), octanoic acid (C8), nonanoic acid (C9), decanoic acid (D10), undecanoic acid (C11), dodecanoic acid (C12), tridecanoic acid (C13), tetradecanoic acid (C14), pentadecanoic acid (C15), hexadecanoic acid (C16), heptadecanoic acid (C17), octadecanoic acid (C18), nonadecanoic acid (C19), icosanoic acid (C20), and mixtures thereof. The molar ratio of alcohol to carboxylic acid in the solvent mixture used in the present invention is between 1:20 and 20:1, preferably between 1:15 and 15:1, more preferably between 1:10 and 10:1, most preferably between 1:6 and 6:1. The solvent mixture used in the present invention contains less than 10% by weight of water, preferably less than 5% by weight of water, more preferably less than 3% by weight of water, even more preferably less than 2% by weight of water, and even more preferably less than 1% by weight of water. The total metal content in the metal precursor solution is preferably 1-30% by weight, more preferably 2-20% by weight, and even more preferably 3-15% by weight. Total metal content means the total weight proportion of all metals contained in the metal precursors in the metal precursor solution used. The solvent mixture used for the process of the invention may further comprise a chelating agent, i.e., a compound capable of forming two or more coordination bonds with metal ions. Examples of such chelating agents are, for example, diamines such as ethylenediamine, ethylenediaminetetraacetic acid (EDTA), and 1,3-dicarbonyl compounds such as acetylacetone and alkylacetyl acetate. Most preferably, acetylacetone is used as such a chelating agent. It was observed that in the presence of such chelating agents, some metallic precursors, for example, zirconium compounds, show better solubility and no precipitation after a relatively long storage time. The use of the special combination of metal precursors and solvent mixture according to the invention makes it possible to ensure good solubility of all metal precursors and to achieve the desired metal oxide particle properties, such as small particle size, high BET surface area and low compressibility density. The process of the invention may comprise a heat treatment step of the mixed oxide comprising lithium, zirconium and optionally at least one non-metal L1 and Zr, produced by means of flame spray pyrolysis. This additional heat treatment is preferably carried out at a temperature of 600 °C-1300 °C, more preferably at 650 °C-1250 °C, even more preferably at 700 °C-1200 °C, even more preferably at 750 °C-1150 °C. Heat treatment according to the invention yields a heat-treated metal oxide with desirable properties, particularly the desired crystalline structure. For example, heat treatment of LizLasZrsOis at approximately 800–1200°C allows the formation of a mixed metal oxide with a cubic garnet crystalline structure, particularly suitable for use in solid-state electrolytes for lithium-ion batteries. The process of the invention may comprise an additional grinding step, preferably ball grinding of the mixed oxide comprising lithium, zirconium and optionally at least one non-metal L1 and Zr, produced by means of flame spray pyrolysis. Ball milling is preferably carried out using ZrO2 balls, for example, with a diameter of approximately 0.5 mm in a suitable solvent, such as ethanol or isopropane. Most preferably, the process of the invention comprises both heat treatment and ball milling of the heat-treated metal oxide. The ball milling process according to the invention yields a ball-milled metal oxide with desirable properties, particularly the desired crystalline structure and particle size, which is especially suitable for use in lithium-ion batteries. Therefore, heat-treated, ball-milled L¡7La3Zr2Oi2 with a cubic garnet crystalline structure and a desired particle size is particularly suitable for use in solid-state electrolytes for lithium-ion batteries. The mixed oxide The mixed oxide prepared by the procedure according to the present invention preferably has a BET surface area of ​​0.1 m2 / g-100 m2 / g. The untreated mixed oxide, i.e., the product of the process of the invention in which no additional heat treatment has been employed, preferably has a BET surface area of ​​5 m2 / g-100 m2 / g, more preferably 7 m2 / g-70 m2 / g, most preferably 15-50 m2 / g. The heat-treated mixed oxide, i.e., the product of the process of the invention, in which an additional heat treatment has been employed, preferably has a BET surface area of ​​less than 10m2 / g, more preferably 0.1 m2 / g - 10 m2 / g, more preferably 0.2 m2 / g - 5 m2 / g, or more preferably 0.3-3 m2 / g. The heat-treated and ball-ground mixed oxide, i.e., the product of the process of the invention, in which an additional heat treatment and a ball-grinding process have been employed, preferably has a BET surface area of ​​3 m2 / g-30 m2 / g, more preferably 4 m2 / g - 25 m2 / g, more preferably 5 m2 / g - 20 m2 / g. The BET surface can be determined according to DIN 9277:2014 by nitrogen adsorption according to the Brunauer-Emmett-Teller procedure. The mixed oxide prepared by the process according to the invention is generally in the form of aggregated primary particles with an arithmetic mean primary particle diameter of 5–100 nm, preferably 7–70 nm, more preferably 10–50 nm, as determined by transition electron microscopy (TEM). This mean diameter can be determined by calculating the average size of at least 500 particles analyzed by TEM. The arithmetic mean of the particle diameter of the mixed dso oxide (aggregate and agglomerate) is usually approximately 0.05 µm–3 µm, more preferably 0.1 µm–2 µm, and even more preferably 0.15 µm–1.0 µm. This arithmetic mean diameter can be determined in a suitable dispersion, for example, an aqueous dispersion, by the static light scattering (SLS) procedure. Agglomerates and, to some extent, aggregates can be destroyed, for example, by crushing or ultrasonic treatment of the particles to result in particles with a smaller particle size and a narrower particle size distribution. Preferably, the mean particle diameter dso of the mixed oxide is 10-150 nm, more preferably 20-130 nm, even more preferably 30-120 nm, determined by static light scattering (SLS) after 300 seconds of ultrasonic treatment at 25 °C of a mixture composed of 5 wt% particles and 95 wt% of a 0.5 g / l solution of sodium pyrophosphate in water. The (dgo-dio) / dso range of zirconium dioxide particles and / or the mixed oxide comprising zirconium is preferably 0.4-1.2, more preferably 0.5-1.1, even more preferably 0.6-1.0, determined by static light scattering (SLS) after 300 seconds of ultrasonic treatment at 25 °C of a mixture composed of 5% by weight of particles and 95% by weight of a 0.5 g / l solution of sodium pyrophosphate in water. Therefore, the mixed oxide prepared by the process of the present invention is preferably characterized by a relatively small particle size and a narrow particle size distribution. This facilitates high-quality metal oxide doping and / or coating of active electrode materials for lithium-ion batteries. The values ​​d dio, dso, and dgo are commonly used to characterize the cumulative particle diameter distribution of a given sample. For example, the dio diameter is the diameter at which 10% of the sample volume consists of particles smaller than dio; dso is the diameter at which 50% of the sample volume consists of particles smaller than dso. dso is also known as the volume median diameter, as it divides the sample equally by volume; dso is the diameter at which 90% of the sample volume consists of particles smaller than dgo. The mixed oxide prepared by the procedure according to the invention preferably has a compacted density of 20 g / l - 1000 g / l. The untreated mixed oxide prepared by the process according to the invention preferably has a compacted density of 20 g / l-200 g / l, more preferably 30 g / l-150 g / l, even more preferably 40 g / l-130 g / l, and even more preferably 50 g / l-120 g / l. The heat-treated mixed oxide prepared by the process according to the invention preferably has a compacted density of 400 g / l-1000 g / l, more preferably 450 g / l-800 g / l, even more preferably 500 g / l-700 g / l. The compacted density of a powdery or coarse-grained granular material can be determined according to DIN ISO 787-11: 1995 General test procedures for pigments and extenders - Part 11: Determination of compacted volume and bulk density after compaction. This involves measuring the bulk density of a bed after stirring and compaction. The mixed oxide prepared by the process of the invention is preferably hydrophilic in nature and is not further treated with any hydrophobic reagents, such as silanes, after its synthesis by a flame spray pyrolysis process. The particles thus produced typically have a purity of at least 96% by weight, preferably at least 98% by weight, and more preferably at least 99% by weight, where 100% purity means that the mixed oxide contains only the specified metals and oxygen. The mixed oxide may comprise hafnium compounds in the form of hafnium dioxide. The proportion of hafnium dioxide may be from 1 to 4% by weight, based on ZrO2. The chloride content is preferably less than 0.5% by weight, and more preferably less than 0.1% by weight, based on the mass of the mixed oxide powder.The proportion of carbon is preferably less than 2.0% by weight, more preferably 0.005%-1.0% by weight, even more preferably 0.01%-0.5% by weight, depending on the mass of the mixed oxide powder. A mixed oxide is, preferably, a compound with the general formula L¡aZrbMcOo,5a+2b+d (I), where .5 < a < 15, preferably 1.8 < a < 12; 0.5 < b < 3.0, preferably 0.8 < b < 3.0; < c < 5, preferably 1.5 < c < 4 d = 0.5c for M = Na, K; d = c for M = Be, Mg, Ca, Sr, Ba, Zn, Co, Ni, Cu, Mn; d = 1.5c for Μ = B, Al, Ga, In, Fe, Se, Y, La; d = 2c for M = Ti, Zr, Hf, Ce, Si, Ge, Sn, Pb; d = 2.5c for M = V, Nb, Ta; d = 3c for M = Mo, W. In the general formula (I), M may be one or more elements selected from the group consisting of Na, K, Be, Mg, Ca, Sr, Ba, Zn, Co, Ni, Cu, Μη, B, Al, Ga, In, Fe, Se, Y, La, Ti, Zr, Hf, Ce, Si, Ge, Sn, Pb, V, Nb, Ta, Mo, W. Preferably, M = La and Al. οηΛζηη / ζζηζ / Ε / γίΛΐ The invention further provides a mixed oxide comprising lithium, zirconium and optionally at least one non-metal L1 and Zr, wherein - the mixed oxide is in the form of aggregated primary particles, - has a BET surface area of ​​15-50 m2 / g, - an arithmetic mean particle diameter of dso = 0.1-2 pm, as determined by static light scattering (SLS), and - a compacted density of 50-200 g / l. Said mixed oxide can be prepared by the procedure of the invention, in which no additional heat treatment is applied. The invention further provides a mixed oxide comprising lithium, zirconium and optionally at least one non-metal L and Zr, wherein - the mixed oxide is in the form of aggregated primary particles, - has a BET surface area of ​​less than 10m2 / g, preferably 0.110 m2 / g, - an arithmetic mean particle diameter of dso = 1-50 pm, as determined by static light scattering (SLS), and - a compacted density of 400-1000 g / l. Said mixed oxide can be prepared by the procedure of the invention, in which an additional heat treatment is applied and, optionally, a ball milling procedure. The invention further provides mixed oxides that can be obtained by the process according to the present invention. Use of mixed oxide in lithium-ion batteries The invention further provides for the use of the mixed oxide according to the invention or mixed oxide obtainable by the process of the invention in lithium-ion batteries, particularly as a component of a lithium-ion battery solid-state electrolyte, as an additive in liquid electrolyte or gel, or as a component of a lithium-ion battery electrode. οη«ζηη / 77ηζ / Ε / γΐΛΐ The invention further provides a lithium-ion battery comprising the mixed oxide according to the invention or mixed oxide that can be obtained by the process of the invention. The lithium-ion battery of the invention, in addition to the active positive electrode (cathode), may contain an anode, a separator, and an electrolyte containing a compound comprising lithium. The positive electrode (cathode) of the lithium-ion battery generally includes a current collector and a layer of active cathode material formed on the current collector. The current collector can be an aluminum sheet, a copper sheet, a nickel sheet, a stainless steel sheet, a titanium sheet, a polymeric substrate coated with a conductive metal, or a combination thereof. Active positive electrode materials may include materials capable of reversible intercalation / disintercalation of lithium ions and are well known in the art. Such active positive electrode materials may include transition metal oxides, such as mixed oxides comprising Ni, Co, Mi, V, or other transition metals and optionally lithium. The mixed lithium transition metal oxides preferably used as active positive electrode materials are selected from the group consisting of lithium-cobalt oxide, lithium-manganese oxide, lithium-nickel-cobalt oxides, lithium-nickel-manganese-cobalt oxides, lithium-nickel-cobalt-aluminum oxides, lithium-nickel-manganese oxides, or a mixture thereof.The mixed transition metal oxide of lithium preferably has a general formula LiMCte, wherein M is at least one transition metal selected from nickel, cobalt, manganese; more preferably M = Co or NixMnyCoz, wherein 0.3 < x < 0.9, 0 < y < 0.45, 0 < z < 0.4. The anode of a lithium-ion battery can comprise any suitable material, commonly used in secondary lithium-ion batteries, capable of reversible intercalation / disintercalation of lithium ions. Typical examples include carbonaceous materials such as crystalline carbon, like natural or artificial graphite in plate, flake, spherical, or fibrous form; amorphous carbon, such as soft carbon, hard carbon, mesophase pitch carbide, derivatives of heated coke, and the like, or mixtures thereof. Additionally, lithium metal or conversion materials (e.g., Si or Sn) can be used as active anode materials. The electrolyte in a lithium-ion battery can be in liquid, gel, or solid form. The liquid electrolyte of the lithium-ion battery may comprise any suitable organic solvent commonly used in lithium-ion batteries, such as anhydrous ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate, methylethyl carbonate, diethyl carbonate, gamma butyrolactone, dimethoxyethane, fluoroethylene carbonate, vinylethylene carbonate, or a mixture thereof. Gel electrolytes include gelled polymers. The solid electrolyte of a lithium-ion battery may comprise oxides, for example, lithium metal oxides, sulfides, phosphates, or solid polymers. The polymer gel or liquid electrolyte of a lithium-ion battery typically contains a lithium salt. Examples of such lithium salts include lithium hexafluorophosphate (LiPFe), 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(oxalato)borate, lithium cyclodifluoromethane-1,1-bis(sulfonyl)imide, lithium cyclohexafluoropropane-1,1-bis(sulfonyl)imide, and mixtures thereof. The lithium-ion battery, especially one with liquid or gel electrolyte, may also include a separator, which prevents direct contact between the two electrodes, which would lead to an internal short circuit. The spacer material may comprise a polyolefin resin, a fluorinated polyolefin resin, a polyester resin, a polyacrylonitrile resin, a cellulose resin, a nonwoven fabric, or a mixture thereof. Preferably, this material comprises a polyolefin resin, such as a polyethylene or polypropylene-based polymer, a fluorinated resin, such as polyvinylidene fluoride polymer or polytetrafluoroethylene, a polyester resin, such as polyethylene terephthalate and polybutylene terephthalate, a polyacrylonitrile resin, a οηΛζηη / ζζηζ / Ε / γίΛΐ cellulose resin, a nonwoven fabric or a mixture thereof. Brief description of the drawings Figures 1A and 1B are TEM images of Li-LaZr-Al mixed oxide particles prepared as described in comparative example 1. Figures 2A and 2B are TEM images of Li-LaZr-Al (LLZO) mixed oxide particles prepared as described in comparative example 2. Figures 3A and 3B are TEM images of Li-LaZr-Al (LLZO) mixed oxide particles of the invention prepared as described in Example 1. Figure 4 shows XRD patterns of the Li-La-Zr-Al (LLZO) mixed oxide of the invention prepared as described in Examples 1-3. Figure 5 shows the SEM-EDX mapping image of La (target) on NMC coated with LLZO prepared using LLZO prepared as described in Example 1. Figure 6 shows the SEM-EDX mapping image of La (target) on NMC coated with LLZO prepared using LLZO prepared as described in comparative example 1. Figure 7 shows the statistical analyses of the La area distribution in LLZO-coated NMC SEM-EDX mapping images prepared using LLZO prepared as described in comparative example 1 and example 1. Figure 8 shows the results of the initial impedance tests of solid-state lithium metal batteries with LLZO prepared as described in Examples 2 and 3 and without LLZO (PEO), measured by electrochemical impedance spectroscopy (EIS). Figure 9 shows the initial formation results between 3.0 V and 4.3 V at 60 °C and 0.1 C of solid-state lithium metal batteries with LLZO prepared as described in Examples 2 and 3 and without LLZO (PEO). Examples Commercial mixed NMC (7-1.5-1.5) (Type PLB-H7) manganese nickel lithium cobalt oxide powder with a BET surface area of ​​0.30-0.60 m2 / g, a mean particle diameter dso = 10.6 ± 2 pm (determined by the static laser scattering procedure), was supplied by Linyi Gelon LIB Co. οη«ζηη / 77ηζ / Ε / γΐΛΐ Commercial polyethylene oxide (PEO, from Sigma-Aldrich) with an average molecular weight of 4 x 10⁵ g / mol was used for the electrolyte formulation. The PEO was used as received. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) from Kishida with a purity >99% (battery grade) was used as received in the glove compartment. The copper sheet deposited with commercial lithium was purchased from Honjo Metal; the copper layer thickness is 10 pm and the lithium layer thickness is 20 pm. Comparative example 1 (Li-La-Zr-Al mixed oxide from aqueous nitrate precursors) 18.63 kg of an aqueous solution containing 1142 g of LiNOs, 2839 g of La(NO3)3*6H2O, 1670 g of Zr(NO3)4 (metal content: 24% by weight) and 212 g of Al(NO3)3*9H2O were prepared with constant stirring until a clear solution was obtained. This solution corresponds to a composition LÍ7,54La3Zr2Alo,260l2,66. A 2.5 kg / h aerosol of this solution and 15 Nm³ / h of air was formed using a two-component nozzle and sprayed into a tubular reaction chamber with a burning flame. The combustion gases from the flame consisted of 20 Nm³ / h of hydrogen and 75 Nm³ / h of air, resulting in a control temperature of 900 °C at the measuring point one meter below the spray nozzle. An additional 25 Nm³ / h of secondary air was used. After the reactor, the reaction gases were cooled and filtered. The particle properties are shown in Table 1, and the TEM images of the particles are shown in Figure 1A and 1B. Preparation of an NMC powder coated with Li-La-Zr-Al mixed oxide from comparative example 1: The NMC powder (99 g) was mixed with 1.0 g (1 wt%) of the pyrogenic powder from comparative example 1 in a high-intensity laboratory mixer (Somakon MP-GL mixer with a 0.5 L mixing unit) initially for 1 minute at 500 rpm (specific electrical power: 350 W / kg of NMC) to homogeneously mix the two powders. Subsequently, the mixing intensity was increased to 2000 rpm (specific electrical power: 800 W / kg of NMC, peak speed of the mixing tool in the mixing unit: 10 m / s) and mixing continued for 5 minutes to achieve dry coating of the NMC particles by the smoke powder from comparative example 1. Comparative Example 2 (Li-La-Zr-AI mixed oxide of ethanolic nitrate precursors) 18.3 kg of an ethanolic solution containing 779 g of LiNOs, 1930 g of La(NO3)3*6H2O, 1139 g of Zr(NO3)4 (metal content: 24% by weight) and 146 g of Al(NO3)3*9H2O were prepared with constant stirring until a clear solution was obtained. This solution corresponds to a composition L17.54La3Zr2Al2.66. A 2.5 kg / h aerosol of this solution and 15 Nm³ / h of air was formed using a two-component nozzle and sprayed into a tubular reaction chamber with a burning flame. The combustion gases from the flame consisted of 13.7 Nm³ / h of hydrogen and 75 Nm³ / h of air, resulting in a control temperature of 900 °C at the measuring point one meter below the spray nozzle. An additional 25 Nm³ / h of secondary air was used. After the reactor, the reaction gases were cooled and filtered. The particle properties are shown in Table 1, the TEM images of the particles are shown in Figure 2A and 2B. Example 1 (Li-La-Zr-Al mixed oxide) 1320 g of a commercial solution (Octa Solingen® Zirconium 12), containing 12 wt% Zr as zirconium ethylhexanoate, was mixed with 173 g of acetylacetone. This solution was then mixed with constant stirring with 2273 g of a commercial solution (Borchers® Deca Lithium 2), containing 2 wt% Li as lithium neodecanoate. A further solution containing 1125 g of La(NO3)3*6H2O, 83.3 g of Al(NO3)3*9H2O, 2660 g of ethanol, and 2660 g of ethylhexanoic acid (ethanol:ethylhexanoic acid molar ratio = 3.1:1, water content in the solvent mixture: 2.7 wt%) was added with constant stirring until a clear solution was obtained. This solution corresponds to a composition L¡7,54La3Zr2AÍ0,26Ol2,66. A 2.5 kg / h aerosol stream of this solution and a 15 Nm³ / h air stream was formed using a two-component nozzle and sprayed into a tubular reaction chamber with a burning flame. The combustion gases from the flame consisted of 12.9 Nm³ / h of hydrogen and 75 Nm³ / h of air, resulting in a control temperature of 900 °C at the measuring point one meter below the spray nozzle. An additional 25 Nm³ / h of secondary air was used. After the reactor, the reaction gases were cooled and filtered. The particle properties are shown in Table 1, and the TEM images of the particles are shown in Figure 3A and 3B. Preparation of an NMC powder coated with Li-La-Zr-Al mixed oxide of example 1: The NMC powder (99 g) was mixed with 1.0 g (1 wt%) of the pyrogenic powder from Example 1 in a high-intensity laboratory mixer (Somakon MP-GL mixer with a 0.5 L mixing unit) initially for 1 minute at 500 rpm (specific electrical power: 350 W / kg of NMC) to homogeneously mix the two powders. Subsequently, the mixing intensity was increased to 2000 rpm (specific electrical power: 800 W / kg of NMC, peak speed of the mixing tool in the mixing unit: 10 m / s) and mixing continued for 5 minutes to achieve dry coating of the NMC particles by the pyrogenic powder from Example 1. Example 2 (Calcined Li-La-Zr-Al mixed oxide) The mixed oxide obtained in Example 1 was calcined at 950 °C for 6 hours in a rotary kiln. XRD analysis (Figure 4) showed that the main phase of the product was the cubic garnet structure. Example 3 (Calcined and ball-ground Li-La-Zr-Al mixed oxide) The mixed oxide obtained in example 2 was re-milled with 0.5 mm diameter ZrO2 balls in ethanol. XRD analysis (Figure 4) showed that the main phase of the product was still the cubic garnet structure. Table 1: Properties of the mixed oxides οηΛζηη / ζζηζ / Ε / γίΛΐ Example BET [m² / g] D10 [pm] D50 [pm] D90 [pm] Compacted density [g / U] Comparative example 1 19 0.20 1.55 5.34 195 Comparative example 2 21 0.19 1.46 4.67 226 Example 1 25 0.09 0.97 4.70 98 Example 2 < 1 8.31 19.13 42.36 788 Example 3 10 0.41 0.93 5.78 680 SEM-EDX analysis of LLZO-coated mixed lithium transition metal oxides Figure 5 shows the SEM-EDX mapping of La (target) on NMC coated with LLZO prepared using pyrogenic nano LLZO (Example 1). Figure 6 shows the results of the analysis of NMC coated with coarse pyrogenic LLZO (Comparative Example 1). The axes in Figures 5 and 6 represent: x-axis = particle diameter; left y-axis = volume in %, right y-axis = cumulative volume in %. The mixed oxide of NMC coated dry with pyrogenic nano LLZO (Example 1) shows complete and homogeneous coverage of all NMC particles with LLZO (Figure 5). No larger LLZO agglomerates were detected, indicating good dispersibility of the nanostructured pyrogenic nano LLZO. Additionally, no free LTO particles were found alongside the NMC particles, indicating strong adhesion between the coating and the substrate (NMC).Conversely, Figure 6 shows that only the fine LLZO particles of coarse pyrogenic LLZO adhere to the surface of the NMC particles. The larger LLZO particles are not dispersed and therefore not bonded, remaining adjacent to the NMC particles. As a result, the NMC particles are not completely coated with zirconium oxide. Figure 7 shows the statistical analyses of Example 1 and Comparative Example 1. The distribution of the La (target) pm2 area in the SEM-EDX mapping is further analyzed using a normal box plot and shows a clear difference in the dispersibility of La (target) between Example 1 and Comparative Example 1. Hybrid solid electrolyte (HSE) membrane preparation The mixture of LLZO ceramic powder with polyethylene oxide (PEO) and LiTFSI resulted in a solvent-free hot-pressing procedure, producing flexible, self-contained membranes. Two sets of LLZO composite membranes from Example 2 and Example 3 were prepared according to Table 2. The heavy LLZO HSE membrane was shredded, ground with PEO and heavy LLZO to obtain a paste-like material, which was then annealed at 100 °C overnight and subsequently hot-pressed at 100 °C between Teflon substrates to a desired thickness of approximately 110 µm. Table 2: Hybrid solid electrolyte recipe οηΛζηη / ζζηζ / Ε / γίΛΐ EO / Li PEO+LiTFSI (g) LLZO (g) LLZO % by weight type of LLZO 15 0.697+0.303 0.42 30% Example 2 15 0.697+0.303 0.42 30% Example 3 Assembly and characterizations of solid-state lithium metal batteries Three sets of NMC_HSE_L solid-state metal batteries were assembled using (a) PEO without LLZO filler, (b) PEO using calcined LLZO filler (Example 2), and (c) PEO using ball-ground LLZO filler (Example 3). The initial impedance was analyzed by electrochemical impedance spectroscopy (EIS), and the results are shown in Figure 8. Figure 9 shows the initial formation of these three cells between 3.0 V and 4.3 V at 60 °C and 0.1 C. The cell using LLZO from Example 3 showed the highest capacity of 140 mAh / ga ​​at a 0.1 C discharge and the lowest impedance among the three examples.

Claims

1. A process for producing a mixed oxide comprising lithium, zirconium and optionally at least one non-metal of L and Zr, by flame spray pyrolysis, characterized in that at least one solution of metal precursors, comprising a lithium carboxylate and / or a zirconium carboxylate, wherein each of these metal carboxylates contains from 5 to 20 carbon atoms, and a solvent mixture comprising an alcohol and a carboxylic acid containing from 5 to 20 carbon atoms, wherein the solvent mixture contains less than 10% by weight of water and wherein the molar ratio of the alcohol to the carboxylic acid is between 1:20 and 20:1, is used in the process.

2. A process according to claim 1, characterized in that the flame spray pyrolysis comprises the following steps: a) at least one solution of metal precursors is atomized to produce an aerosol by means of an atomizing gas, b) the aerosol is reacted in the reaction space of the reactor with a flame obtained by ignition of a mixture of fuel gas and an oxygen-containing gas to obtain a reaction stream, c) the reaction stream is cooled and d) the solid metal oxide is subsequently removed from the reaction stream.

3. Process according to claim 1 or 2, characterized in that the mixed oxide is a compound of general formula L¡aZrbMcOo,5a+2b+d (I), in which 1.5 < a < 15, οη«ζηη / 77ηζ / Ε / γΐΛΐ 0.5 < b < 3.0, 0 < c < 5, d = 0.5c for M = Na, K; d = c for M = Be, Mg, Ca, Sr, Ba, Zn, Co, Ni, Cu, Mn; d = 1.5c for Μ = B, Al, Ga, In, Fe, Se, Y, La; d = 2c for M = Ti, Zr, Hf, Ce, Si, Ge, Sn, Pb; d = 2.5c for Μ = V, Nb, Ta; d = 3c for M = Mo, W.

4. Process according to claims 1 to 3, characterized in that the mixed oxide has a BET surface area of ​​0.1-100 m2 / g.

5. A process according to claims 1 to 4, characterized in that the lithium and zirconium carboxylates are, independently of each other, carboxylates selected from the group consisting of linear, branched or cyclic lithium and / or zirconium pentanoate (C5), hexanoate (C6), heptanoate (C7), octanoate (C8), nonanoate (C9), decanoate (D10), undecanoate (C11), dodecanoate (C12), tridecanoate (C13), tetradecanoate (C14), pentadecanoate (C15), hexadecanoate (C16), heptadecanoate (C17), octadecanoate (C18), nonadecanoate (C19), icosanoate (C20) and mixtures thereof.

6. A process according to claims 1 to 5, characterized in that the alcohol is selected from the group consisting of methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol, n-pentanol, n-hexanol, cyclohexanol, n-octanol, 2-ethylhexanol, n-decanol, neodecanol and mixtures thereof.

7. A process according to claims 1 to 6, characterized in that the metal precursor solution comprises a chelating agent selected from the group consisting of diamines and 1,3-dicarbonyl compounds.

8. A process according to claims 1 to 7, characterized in that the mixed oxide has an arithmetic mean particle diameter of dso = 0.052 pm, as determined by static light scattering (SLS).

9. Process according to claims 1 to 8, characterized in that the mixed oxide has a compacted density of 20-1000 g / l.

10. A process according to claims 1 to 9, further comprising the heat treatment of the mixed oxide comprising lithium, zirconium and optionally at least one non-metal of L and Zr, produced by flame spray pyrolysis.

11. Process according to claim 10, wherein the heat treatment is carried out at a temperature of 600 °C-1300 °C.

12. A process according to claims 1 to 11, further comprising grinding the mixed oxide comprising lithium, zirconium and optionally at least one non-metal of L and Zr, produced by flame spray pyrolysis.

13. Method according to claim 12, wherein the grinding is ball milling.

14. Mixed oxide comprising lithium, zirconium and optionally at least one non-metal of L and Zr, characterized in that the mixed oxide is in the form of aggregated primary particles, has a BET surface area of ​​15-50 m2 / g, an arithmetic mean particle diameter of dso = 0.1-2 pm, as determined by static light scattering (SLS), and a packed density of 30-150 g / L 15. Mixed oxide comprising lithium, zirconium and optionally at least one non-metal of Li and Zr, characterized in that the mixed oxide is in the form of aggregated primary particles, has a BET surface area of ​​less than 10 m2 / g, an arithmetic mean particle diameter of dso = 1-50 pm, as determined by static light scattering (SLS), and a packed density of 400-1000 g / L 16. Use of the mixed oxide according to claim 14 or 15 as a component of a solid electrolyte, as an additive in a liquid electrolyte or gel, or as a component of an electrode of a lithium-ion battery.

17. Lithium-ion battery comprising the mixed oxide according to claim 14 or 15.