Lithium transition metal mixed oxides coated with pyrogenically produced zirconium-containing oxides

Abstract

The present invention relates to a process for producing coated lithium transition metal mixed oxides, wherein a lithium transition metal mixed oxide and pyrogenically produced zirconium dioxide and / or a pyrogenically produced zirconium-containing mixed oxide are dry-mixed by an electrodynamic mixing unit having a specific electrical power of 0.05-1.5 kW / kg of lithium transition metal mixed oxide; a coated lithium transition metal mixed oxide obtainable by this process; a cathode for a lithium battery and a lithium battery comprising such coated particles.

Description

Technical Field

[0001] The present invention relates to a process for producing a coated lithium transition metal mixed oxide, a coated lithium transition metal mixed oxide obtainable by the process, a cathode for a lithium battery comprising such a coated metal oxide, and a lithium battery. Background Art

[0002] In recent years, various energy storage technologies have attracted widespread public attention and have become the subject of intensive research and development in both industry and academia. As energy storage technologies expand into devices such as mobile phones, video cameras, and laptop computers, and further into electric vehicles, demand is increasing for high-energy-density batteries to serve as power sources for these devices. Secondary lithium batteries are one of the most important types of batteries currently in use.

[0003] Secondary lithium batteries typically consist of an anode made of carbon or a lithium metal alloy, a cathode made of a lithium-metal oxide, and an electrolyte consisting of a lithium salt dissolved in an organic solvent. The separator in a lithium battery provides a pathway for lithium ions to flow between the positive and negative electrodes during the charge and discharge processes.

[0004] One of the common problems with cathode materials is that they age quickly and therefore lose performance during cycling. This phenomenon is particularly relevant to nickel-manganese-cobalt mixed oxides (NMC) with high nickel content. Deactivation of positive electrode materials occurs through several electrochemical degradation mechanisms. Surface transformations (such as due to Ni 4+ The formation of a NiO-like phase caused by the reduction of NMC and oxygen loss and transition metal rearrangement) leads to an unstable crystal structure. This phase transition is associated with the initial cracks that appear at the surface of the cathode particles and the subsequent disintegration of the particles. In addition, the electrolyte decomposes at the reactive surface of the NMC and the electrolyte decomposition products are deposited at the interface of the cathode material, which leads to an increase in resistance. In addition, the conductive salt LiPF6 commonly used in liquid electrolytes reacts with trace amounts of H2O present in all commercially available preparations to form HF. This highly reactive compound causes lattice distortion in the cathode material by dissolving transition metal ions from the surface of the cathode material into the electrolyte. All of these degradation mechanisms lead to a decrease in capacity, performance and cycle life.

[0005] It is known that coating lithium transition metal mixed oxide particles with certain metal oxides can inhibit undesirable reactions of the electrolyte with the electrode materials and thus improve the long-term stability of lithium batteries.

[0006] WO 00 / 70694 discloses mixed transition metal oxide particles coated with oxides or mixed oxides of Zr, Al, Zn, Y, Ce, Sn, Ca, Si, Sr, Mg and Ti. These are obtained by suspending the uncoated particles in an organic solvent, mixing the suspension with a solution of a hydrolyzable metal compound and a hydrolysis solution, and subsequently filtering off, drying and calcining the coated particles.

[0007] US2015 / 0340689A1 discloses a cathode active material (CAM) for lithium batteries comprising a core of a transition metal oxide and a coating comprising zirconium dioxide. Such coated CAMs are typically prepared by mixing a transition metal precursor with zirconium (IV) nitrate having an average particle size of less than 1 μm and calcining the mixture thus obtained at 700°C to form a CAM coated with ZrO2. An alternative embodiment (Example 5) shows the mixing of a transition metal precursor with zirconium (IV) dioxide having an average particle size of less than 1 μm provided by Aldrich Co. and calcining the resulting coated CAM at 700°C. Analysis of these materials by SEM microscopy showed that the average particle size of the ZrO2 particles present in the coating was about 400 nm ( Figure 2 , analysis example 1).

[0008] US 2016 / 0204414 A1 describes a CAM for a battery comprising a non-aqueous electrolyte, comprising a transition metal oxide core with a zirconium compound present on the surface of the core. These examples show the use of zirconium dioxide with an average particle size of 1 μm to coat the CAM.

[0009] CN 105161710 A discloses a CAM comprising a transition metal mixed oxide core and a coating comprising aluminum oxide or zirconium oxide with a particle size of 5-100 nm. Thus, in Example 4, a LiNi 0.5 Co 0.2 Mn 0.3 Mg 0.02 The precursor of O2 was mixed with ZrO2 with a particle size of 20 nm. The resulting coated CAM was calcined at 580°C.

[0010] JP 2013235666 A describes a CAM comprising a transition metal oxide core and a layer comprising ZrO2 particles having a predominantly monoclinic structure. 50 =10μm LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 particles and average particle size D 50 = 27 nm ZrO2 particles were mixed at a rotation speed of 4000 rpm and subsequently calcined at 800°C.

[0011] While the last two references mention nanostructured ZrO2 particles with an average particle size of 20-30 nm, no further details are provided regarding the preparation or source of such particles. Most likely, the given average particle size relates to primary ZrO2 particles. Such small primary particles often aggregate and agglomerate to form larger micron-sized particles.

[0012] In the Journal of the Chinese Institute of Engineers, Vol. 28, No. 7, pp. 1139-1151 (2005), it is disclosed that LiCoO powder can be coated with ZrO having an average particle size of 500-600 nm by spray pyrolysis using either a sol-gel or a mechano-thermal method. In the latter method, the LiCoO powder is ultrasonically treated with a dispersion of ZrO in ethanol for 30 minutes, followed by slow evaporation of the solvent at 50° C. and calcination at 450° C. for 10 hours.

[0013] In addition, some zirconium-containing mixed metal oxides have been reported for use in lithium batteries.

[0014] US2017179544A discloses the preparation of lithium cathode materials doped with mixed metal oxides based on zirconium. Therefore, in Example 1, Li7La3Zr2Al 0.07 O 12.0105 The method is to mix the metal salts and sinter the mixture at 1200 ° C for 10 hours, and then with lithium transition metal mixed oxide Li (Li 10 / 75 Ni 18 / 75 Co 9 / 75 Mn 38 / 75 )O2 dry mix and then heated at 900 ° C for 20 hours to form the lithium positive electrode material. It is obvious from the preparation process that only large-sized Li7La3Zr2Al can be used in this embodiment. 0.07 O 12.0105 Sintered particles.

[0015] It is known to coat cathode materials of lithium batteries with metal oxides such as Al2O3, TiO2 and ZrO2 to improve their cycling performance. However, practical methods for improving battery life are often limited. Thus, in the case of zirconium dioxide, the use of commercially available nano-sized ZrO2 particles often results in uneven distribution and a large number of agglomerated ZrO2 particles on the surface of the core cathode material (such examples are shown in Figure 2 ), therefore, little or no improvement in cycling performance was observed compared to uncoated cathode materials. Summary of the Invention

[0016] The problem addressed by the present invention is to provide modified lithium transition metal mixed oxides as cathode materials (especially high nickel NMC type) for use in lithium batteries. Such modified cathode materials should provide higher cycling stability than unmodified materials.

[0017] During intensive experiments, it was surprisingly found that pyrogenically produced zirconium dioxide or pyrogenically produced zirconium-containing mixed oxides can be successfully used to coat lithium transition metal mixed oxides, which can be used as cathodes for lithium batteries.

[0018] The present invention provides a process for producing coated lithium transition metal mixed oxides, wherein the lithium transition metal mixed oxide and pyrogenically produced zirconium dioxide and / or pyrogenically produced zirconium-containing mixed oxides are dry-mixed by means of an electrodynamic mixing unit having a specific electrical power of 0.05 to 1.5 kW / kg of lithium transition metal mixed oxide.

[0019] The term "electrical hybrid unit" in the context of the present invention relates to any hybrid device which is operated by supplying electrical energy.

[0020] Electrical power is the rate per unit time at which electrical energy is transferred through an electrical circuit. The term "specific electrical power" in the context of the present invention relates to the electrical power provided by the electrodynamic mixing unit during the mixing process per kg of lithium transition metal mixed oxide.

[0021] Dry mixing is understood to mean that no liquid is added or used during the mixing process, i.e., for example, essentially dry powders are mixed together. However, traces of moisture or some non-aqueous liquids may be present in the mixed raw materials, or these may include water of crystallization. Preferably, the mixture of lithium transition metal mixed oxide with pyrogenically produced zirconium dioxide and / or pyrogenically produced zirconium-containing mixed oxide contains less than 5% by weight, more preferably less than 3% by weight, and even more preferably less than 1% by weight of water and / or other liquids.

[0022] The dry mixing process of the present invention has several advantages over mixing processes involving wet coating (e.g., coating with a dispersion containing a metal oxide). Such wet coating processes inevitably involve the use of solvents that must evaporate after the coating process is complete. Therefore, the dry coating process of the present invention is simpler and more economical than the wet coating processes known from the prior art. On the other hand, it has been surprisingly found that the dry coating process of the present invention also provides a better distribution of the zirconium-containing metal oxide particles on the surface of the lithium transition metal mixed oxide.

[0023] If the specific electrical power used is less than 0.05 kW / kg of lithium transition metal mixed oxide, this leads to an inhomogeneous distribution of the zirconium dioxide or zirconium-containing mixed oxide, which may not be firmly bonded to the core material of the lithium transition metal oxide.

[0024] A specific electrical power exceeding 1.5 kW / kg of the lithium transition metal mixed oxide results in poor electrochemical properties. In addition, there is a risk that the coating becomes brittle and easily cracks.

[0025] The nominal electrical power of the mixing unit can vary over a wide range, for example from 0.1 kW to 1000 kW. Thus, a laboratory-scale mixing unit with a nominal power of 0.1-5 kW or a production-scale mixing unit with a nominal power of 10-1000 kW can be used. The nominal electrical power is the absolute maximum electrical power stated on the nameplate of the mixing unit.

[0026] The volume of the mixing unit can also be varied within a wide range, for example from 0.1 to 2.5 m 3 Thus, laboratory-scale mixing units with volumes of 0.1-10 L or mixing units with volumes of 0.1-2.5 m 3 production-scale mixing units.

[0027] The term "volume of the mixing unit" in the context of the present invention refers to the maximum volume of the chamber of the electrokinetic mixing unit into which the substances to be mixed can be placed.

[0028] Preferably, in the process according to the invention, a forced mixer in the form of an intensive mixer with a high-speed mixing tool is used. It has been found that a mixing tool with a speed of 5 to 30 m / s, more preferably 10 to 25 m / s, gives the best results. In the context of the present invention, the term "mixing tool" refers to any object in a mixing unit that can move, for example rotate, shake, etc., and thus mix the contents of the mixing unit. Examples of such mixing tools are various forms of agitators. Commercially available mixing devices that are very suitable for the process according to the invention are, for example, Henschel mixers or Eirich mixers.

[0029] The mixing time is preferably from 0.1 to 120 minutes, more preferably from 0.2 to 60 minutes, very preferably from 0.5 to 10 minutes.

[0030] After mixing, the mixture can be heat-treated. This treatment can improve the adhesion of the coating to the lithium transition metal mixed oxide particles. However, this treatment is not necessary in the method according to the invention, since the pyrogenically produced zirconium dioxide or zirconium-containing mixed oxide adheres to the lithium transition metal mixed oxide with sufficient strength. Therefore, a preferred embodiment of the method according to the invention does not include any heat treatment after mixing.

[0031] It has been found that when the BET surface area of ​​zirconium dioxide and zirconium-containing mixed oxides is 5 m 2 / g-200m 2 / g, more preferably 10m 2 / g-150m 2 / g and most preferably 15-100m 2 The best results with regard to the adhesion of zirconium oxide to lithium transition metal mixed oxides were achieved at 1000 Å / g. The BET surface area can be determined in accordance with DIN 9277:2014 by nitrogen adsorption according to the Brunauer-Emmett-Teller procedure.

[0032] The zirconium dioxide and zirconium-containing mixed oxides used in the process according to the invention are produced pyrogenically, that is to say by a pyrolysis process (also called a “gas phase process”).

[0033] The present invention relates to the invention of the present invention and the invention relates to a kind of metal oxide that can be used for the preparation of the present invention.This " pyrolysis " or " gas phase " method relate to flame hydrolysis or the flame oxidation of the corresponding metal precursor in the oxyhydrogen flame to form metal oxide.This reaction initially forms highly dispersed approximately spherical elementary metal oxide particles, and in further reaction process, these particles coalesce to form aggregation.Then aggregation can be gathered into agglomerate.Contrary to the agglomerate that can be separated into aggregation relatively easily by introducing energy usually, if can, only could aggregation be further decomposed by strongly introducing energy.Can partly destroy and be converted into the particle of nanometer (nm) scope favourable to the present invention by suitable grinding with described metal oxide powder.

[0034] The preparation of pyrogenic zirconium dioxide is further described in EP 717008 A and WO 2009053232 A1.

[0035] WO 2015173114 A1 further describes the preparation of certain pyrogenic mixed oxides comprising zirconium.

[0036] Zirconium dioxide powder and other zirconium-containing mixed metal oxides produced pyrolytically, especially by flame hydrolysis, can be produced starting with a zirconium halide, preferably zirconium chloride, as a Zr precursor. ZrCl and other metal precursors (if applicable) can be evaporated, and the resulting vapors, alone or with a carrier gas such as nitrogen, mixed with other gases (i.e., air, oxygen, nitrogen, and hydrogen) in a mixing unit of a burner. The gases react with each other in a flame in a closed combustion chamber to produce zirconium dioxide (or mixed zirconium oxides) and exhaust gases. The hot exhaust gases and metal oxides are then cooled in a heat exchanger unit, the exhaust gases are separated from the metal oxides, and any halide residues adhering to the resulting metal oxides are removed by heat treatment with moist air.

[0037] A flame spray pyrolysis (FSP) process suitable for preparing zirconium dioxide or zirconium-containing mixed metal oxides may include the following steps:

[0038] 1) atomizing a solution containing a zirconium precursor, for example by means of air or an inert gas, preferably using a multi-substance nozzle, and

[0039] 2) mixed with combustion gases, preferably hydrogen and / or methane, and air, and

[0040] 3) Let the mixture burn in the flame into the reaction chamber surrounded by the shell,

[0041] 4) Cooling the hot gas and solid products and then removing the solid products from the gas.

[0042] Preferred Zr metal precursors for the production of zirconium dioxide and zirconium-containing mixed oxides by flame spray pyrolysis are zirconium carboxylates, in particular zirconium carboxylates of aliphatic carboxylic acids having 6 to 9 carbon atoms, such as zirconium 2-ethylhexanoate.

[0043] Other metal precursors required to produce the zirconium mixed metal oxide may be inorganic, such as nitrates, chlorides, or organic compounds such as carboxylates.

[0044] The metal oxide precursor used can be atomized by dissolving it in water or an organic solvent. Suitable organic solvents include methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, 2-acetone, 2-butanone, ether, tert-butyl methyl ether, tetrahydrofuran, C1-C8-carboxylic acids, ethyl acetate, toluene, petroleum and mixtures thereof.

[0045] Thus, the pyrogenically produced zirconium dioxide and the pyrogenically produced zirconium-containing mixed oxide used in the process according to the invention are preferably in the form of aggregated primary particles, preferably primary particles having a number average diameter of 5 to 100 nm, more preferably 10 to 90 nm, even more preferably 20 to 80 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.

[0046] The average diameter of aggregates of pyrogenically produced zirconium dioxide and pyrogenically produced zirconium-containing mixed oxides is typically about 10 to 1000 nm, and the average diameter of agglomerates is typically 1 to 2 μm. These average values ​​can be determined in a suitable dispersion, for example, an aqueous dispersion, by static light scattering (SLS). Agglomerates and some aggregates can be disrupted, for example, by grinding or ultrasonication of the particles to produce particles with a smaller particle size.

[0047] Preferably, the average particle size d of the zirconium dioxide and / or zirconium-containing mixed oxide is as determined by static light scattering (SLS) after ultrasonication of a mixture consisting of 5 wt. % of the particles and 95 wt. % of a 0.5 g / L aqueous sodium pyrophosphate solution at 25° C. for 60 seconds. 50 It is 10-150 nm, more preferably 20-130 nm, even more preferably 30-120 nm.

[0048] Therefore, the pyrogenically produced zirconium dioxide and pyrogenically produced zirconium-containing mixed oxide used in the process of the present invention are preferably characterized by high dispersibility, i.e., the ability to form relatively small particles under mild ultrasound treatment. Dispersibility under these mild conditions is believed to be related to the conditions during the dry coating process. This means that agglomerates of zirconium oxide are destroyed during the mixing process of the present invention in a manner similar to that under ultrasound treatment, and a uniform coating of the transition metal oxide can be formed.

[0049] The distribution span (d ) of the particles of zirconium dioxide and / or zirconium-containing mixed oxides is determined by static light scattering (SLS) of a mixture consisting of 5 wt % of the particles and 95 wt % of a 0.5 g / L aqueous sodium pyrophosphate solution after ultrasonic treatment at 25° C. for 60 seconds. 90 -d 10 ) / d 50 It is preferably 0.4-1.2, more preferably 0.5-1.1, even more preferably 0.6-1.0.

[0050] Therefore, the pyrogenically produced zirconium dioxide and the pyrogenically produced zirconium-containing mixed oxide used in the process of the invention are preferably characterized by a relatively narrow particle size distribution. This contributes to achieving a high-quality zirconium oxide coating on the surface of the transition metal oxide.

[0051] d value 10 d 50 and d 90 It is usually used to characterize the cumulative particle size distribution of a given sample. For example, d 10 The diameter is 10% of the sample volume by less than d 10 The diameter of the particles, d 50 50% of the sample volume is less than d 50 The diameter of the particles. 50 Also called the "volume median diameter" because it divides the sample equally by volume; d 90 90% of the sample volume is less than d 90 The diameter of the particles.

[0052] Zirconium dioxide and zirconium-containing mixed oxides are preferably hydrophilic in nature, i.e., they are not further treated with any hydrophobic reagents such as silanes after being synthesized by pyrolysis. The particles thus produced generally have a purity of at least 96% by weight, preferably at least 98% by weight, and more preferably at least 99% by weight. The metal oxide containing zirconium may contain a hafnium compound in the form of hafnium dioxide. Based on ZrO2, the proportion of hafnium dioxide can be 1 to 4% by weight. The zirconium dioxide and zirconium-containing mixed oxides used in the method of the present invention preferably contain elements Cd, Ce, Fe, Na, Nb, P, Ti, Zn in a proportion <10ppm and elements Ba, Bi, Cr, K, Mn, Sb in a proportion <5ppm, wherein the sum of the proportions of all these elements is <100ppm. Based on the mass of the metal oxide powder, the content of chloride is preferably less than 0.5% by weight, more preferably 0.01 to 0.3% by weight. The proportion of carbon is preferably less than 0.2% by weight, more preferably 0.005% by weight to 0.2% by weight, even more preferably 0.01% by weight to 0.1% by weight, based on the mass of the metal oxide powder.

[0053] The zirconium-containing mixed oxide may also contain lithium and optionally at least one of lanthanum and / or aluminum. The following zirconium-containing mixed metal oxides are particularly preferred: LiZrO3, and x La3Zr2M y O 8.5+0.5x+z mixed oxides,

[0054] Wherein 6.5≤x≤8, preferably 7.0≤x≤7.5;

[0055] 0≤y≤0.5, preferably 0≤x≤0.2;

[0056] For M = Hf, Ga, Ge, Nb, Si, Sn, Sr, Ta, and Ti, z = 2y;

[0057] For M = Al, Sc, V and Y, z = 1.5y;

[0058] For M = Ba, Ca, Mg and Zn, z = y;

[0059] The most preferred 12 .

[0060] The term "transition metal" in the context of the present invention includes the following elements: Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Ta, W, Re, Os, Ir, Pt, Au. Preferably, the transition metal is selected from nickel, manganese, cobalt and mixtures thereof.

[0061] The lithium transition metal mixed oxides preferably used in the process according to the invention are selected from 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.

[0062] The lithium transition metal mixed oxide preferably has the general formula LiMO2, wherein M is at least one transition metal selected from nickel, cobalt, manganese; more preferably M=Co or Ni x Mn y Co z , where 0.3≤x≤0.9, 0≤y≤0.45, 0≤z≤0.4.

[0063] The lithium transition metal mixed oxide of the general formula LiMO 2 can further be doped with at least one other metal oxide, in particular aluminum oxide and / or zirconium oxide.

[0064] The coated lithium transition metal mixed oxide preferably has a number average particle size of 2 to 20 μm. The number average particle size can be determined by laser diffraction particle size analysis in accordance with ISO 13320:2009.

[0065] The proportion of zirconium dioxide and / or zirconium-containing mixed oxides, relative to the total weight of the mixture of lithium transition metal mixed oxide and zirconium dioxide and / or zirconium-containing mixed oxides used, is preferably 0.05% to 5% by weight, more preferably 0.1% to 2% by weight.

[0066] If the proportion of zirconium dioxide and / or zirconium-containing mixed oxides is less than 0.05% by weight, no beneficial effect of the coating is generally observed. In the case of proportions greater than 5% by weight, no beneficial effect of an additional amount of zirconium coating greater than 5% by weight is generally observed.

[0067] The coated lithium transition metal mixed oxide preferably has a coating thickness of 10 to 200 nm, as determined by TEM analysis.

[0068] The present invention also provides a coated lithium transition metal mixed oxide comprising a number average particle size d on the surface of the lithium transition metal mixed oxide. 50 The number average particle size d of the pyrogenically produced zirconium dioxide and / or the pyrogenically produced zirconium-containing mixed oxide in the coated lithium transition metal mixed oxide is 10 nm to 150 nm, preferably 20 nm to 130 nm, more preferably 30 nm to 120 nm. 50 The average particle size d of the pyrogenically produced zirconium dioxide and / or the pyrogenically produced zirconium-containing mixed oxide used in the process according to the invention can be measured by transmission electron microscopy (TEM) analysis and corresponds to50 The value can be determined by static light scattering (SLS) of a mixture consisting of 5 wt% of the particles and 95 wt% of a 0.5 g / L sodium pyrophosphate aqueous solution after ultrasonic treatment at 25°C for 60 seconds.

[0069] The coated lithium transition metal mixed oxides of the invention are preferably obtainable by the process of the invention.

[0070] In a preferred embodiment of the process according to the invention, further preferred features of the above-mentioned coated lithium transition metal mixed oxide, pyrogenically produced zirconium dioxide and / or pyrogenically produced zirconium-containing mixed oxide are also preferred features of the coated lithium transition metal mixed oxide, pyrogenically produced zirconium dioxide and / or pyrogenically produced zirconium-containing mixed oxide in terms of the coated lithium transition metal mixed oxide according to the invention, regardless of whether it is produced by the process according to the invention.

[0071] The present invention further provides an active cathode material for a lithium battery, comprising the coated lithium transition metal mixed oxide according to the invention or the coated lithium transition metal mixed oxide obtainable by the process according to the invention.

[0072] The positive electrode and cathode of a lithium battery generally include a current collector and an active cathode material layer formed on the current collector.

[0073] 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.

[0074] Active positive electrode materials may include materials capable of reversibly intercalating / deintercalating lithium ions and are 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. Particularly preferred are lithium transition metal mixed oxides (NMCs) comprising nickel, manganese and cobalt.

[0075] The present invention further provides a lithium battery comprising a coated lithium transition metal mixed oxide or a coated lithium transition metal mixed oxide obtainable by the process according to the invention.

[0076] In addition to the cathode, the lithium battery of the invention may also comprise an anode, an optional separator, and an electrolyte comprising a lithium salt or a lithium compound.

[0077] The anode of a lithium battery can include any suitable material commonly used in secondary lithium batteries that can reversibly intercalate and deintercalate lithium ions. Typical examples include carbonaceous materials, including crystalline carbon such as natural or artificial graphite in the form of plate-like, flaky, spherical, or fibrous graphite; amorphous carbon such as soft carbon, hard carbon, mesophase pitch carbide, burnt coke, or mixtures thereof. In addition, lithium metal or conversion materials (such as Si or Sn) can be used as the anode active material.

[0078] The electrolyte of a lithium battery can be in liquid, gel or solid form.

[0079] The liquid electrolyte of the lithium battery may include any suitable organic solvent commonly used in lithium batteries, such as anhydrous ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, dimethoxyethane, fluoroethylene carbonate, vinylethylene carbonate, or a mixture thereof.

[0080] The gel electrolyte includes a gel polymer.

[0081] Solid electrolytes for lithium batteries may comprise oxides, such as lithium metal oxides, sulfides, phosphates, or solid polymers.

[0082] The electrolyte of a lithium battery may contain a lithium salt. Examples of such lithium salts include lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium perchlorate (LiClO 4) , lithium tetrafluoroborate (LiBF4), Li2SiF6, lithium trifluoromethanesulfonate, LiN(SO2CF2CF3)2 and mixtures thereof.

[0083] The present invention also provides use of the coated lithium transition metal mixed oxide according to claim 12 or 13 in an active positive electrode material of a lithium battery. DETAILED DESCRIPTION

[0084] Example

[0085] Starting materials

[0086] According to Example 1 of WO 2009053232 A1, a specific surface area (BET) of 40-60 m 2 / g of vapor phase ZrO2.

[0087] BET surface area ≥ 35m 2 / g of commercially available “nano-ZrO2” powder (particle size 20-30 nm) was provided by ChemPURFeinchemikalien und Forschungsbedarf GmbH.

[0088] BET surface area of ​​0.30-0.60 m 2 / g, median particle size d 50 =10.6±2 μm (determined by static laser scattering method) commercially available lithium nickel manganese cobalt mixed oxide powder NMC (7-1.5-1.5) (PLB-H7 type) was provided by Linyi Gelon LIB Co.

[0089] Particle size distribution of different ZrO2 types

[0090] Samples (5 wt %) of fumed ZrO2 or commercially available "nano ZrO2" powder were dispersed in a solution of sodium pyrophosphate (0.5 g / L) in distilled water and treated in an external ultrasonic bath (160 W) at 25°C for 1 min.

[0091] Figure 1 shows the particle size distribution of vapor phase ZrO2, and Figure 2 The particle size distribution of "nano ZrO2" is shown, and the particle size distribution is analyzed by static laser diffraction (SLS) using a laser diffraction particle size analyzer (HORIBA LA-950). For gas phase ZrO2, a single peak type and very narrow particle size distribution (d 10 =0.06014μm,d 50 =0.07751μm,d 90 =0.11406μm, span=(d 90 -d 10 ) / d 50 = 0.7), while for “nano ZrO2” of ChemPUR, a wide bimodal distribution was detected, indicating large undispersed particles (d 10 =0.10769μm,d 50 =3.16297μm,d 90 =5.80804μm, span=(d 90 -d 10 ) / d 50 =1.8).

[0092] Example 1

[0093] NMC powder (217.8 g) was first mixed with 2.2 g (1.0 wt%) of fumed ZrO2 powder in a high-intensity laboratory mixer (Somakon mixer MP-GL with a 0.5 L mixing unit) at 500 rpm (specific electrical power: 350 W / kg NMC) for 1 minute to homogenize the two powders. The mixing intensity was then increased to 2000 rpm (specific electrical power: 800 W / kg NMC, tip speed of the mixing tool in the mixing unit: 10 m / s) and mixing was continued for 5 minutes to achieve dry coating of the NMC particles with ZrO2.

[0094] As determined by TEM analysis, the coated NMC particles showed a ZrO2 coating with a thickness of 10-200 nm.

[0095] Comparative Example 1

[0096] The procedure of Example 1 was completely repeated, with the only difference being that “nano ZrO 2 ” powder was used instead of gas phase ZrO 2 .

[0097] Analysis of ZrO2-coated lithium transition metal mixed oxides by SEM-EDX

[0098] Figure 3 shows the SEM-EDX image of Zr (white) on the NMC coated with ZrO2 prepared by using the vapor phase method ZrO2 (Example 1), Figure 4 The analysis results of NMC coated with "nano-ZrO2" (Comparative Example 1) are shown. Figure 3 and Figure 4 The axes represent: x-axis = particle diameter; left y-axis = volume percentage, right y-axis = cumulative volume percentage. The NMC mixed oxide dry-coated with fumed ZrO2 showed that all NMC particles were completely and evenly covered with ZrO2. No large ZrO2 agglomerates were detected, indicating that the nanostructured fumed ZrO2 had good dispersion. In addition, no free, unattached ZrO2 particles were found near the NMC particles, indicating strong adhesion between the coating and the substrate (NMC). In contrast, Figure 5 The "nano-ZrO2" shows that only fine ZrO2 particles are attached to the surface of the NMC particles. Larger ZrO2 particles are not dispersed and therefore not attached, and are located near the NMC particles. As a result, the NMC particles are not completely covered with zirconium oxide.

[0099] Electrode preparation

[0100] Electrodes for electrochemical measurements were prepared by blending 90 wt% NMC with 5 wt% polyvinylidene fluoride binder (PVDF5130, manufacturer: Solef) and 5 wt% conductive carbon black (SUPER PLi, manufacturer: TIMCAL) under an inert gas atmosphere. N-methyl-2-pyrrolidone (NMP) was used as a solvent. The slurry was cast on aluminum foil and dried on a hot plate at 120°C in air for 20 minutes. The electrode sheet was then dried in a vacuum oven at 120°C for 2 hours. Circular electrodes with a diameter of 12 mm were punched out of the larger sheet and then flattened between two rollers with a pressure of 90 psi and dried again in a vacuum oven at 120°C for 12 hours to remove any residual water and NMP.

[0101] Lithium battery assembly

[0102] The lithium battery cells used for the cycling tests were assembled as CR2032 coin cells (MTI Corporation) in an argon-filled glove box (GLOVEBOX SYSTEMTECHNIK GmbH). Lithium metal (ROCKWOOD LITHIUM GmbH) was used as the anode material. Celgard 2500 was used as the separator. 25 μL of a 1 M LiPF6 solution in ethylene carbonate and ethyl methyl carbonate (50:50 wt / wt; SIGMA-ALDRICH) was used as the electrolyte. The cells were crimped using a crimping machine (MTI).

[0103] Constant current cycle test

[0104] The constant current cycling performance of the assembled lithium battery was measured at 25°C using a MACCOR battery cycler at a cutoff voltage of 3.0-4.3V. The C-rate (charge / discharge) was increased every four cycles from 0.1C / 0.1C (charge / discharge) to 0.3C / 0.3C, 0.5C / 0.5C, 1.0C / 1.0C, 1.0C / 2.0C, and 1.0C / 4.0C. Afterwards, the battery cell was cycled at 0.5C / 0.5C for long-term stability testing. (0.5C rate corresponds to 0.7mAh / cm 2 For the calculation of capacity and specific current, only the mass of active material is considered. Figure 5 Shown in. Figure 5 The axes show: x-axis = cycle number; y-axis = discharge capacity in mAh / g.

[0105] exist Figure 5 In the figure, the cycling performance of NMC coated with fumed ZrO2 (line with triangles) was compared with that of NMC coated with "nano ZrO2" (line with circles) and with reference to uncoated NMC (line with squares). It is clear from the results that the fumed ZrO2 coating significantly improves the stability and cycle life of NMC. Compared with the other tested materials, the NMC coated with fumed ZrO2 showed the highest discharge capacity in all cycles, both in the initial rate test and in the long-term cycle test. It is worth noting that it also showed a higher initial specific discharge capacity at 0.1C than the other samples. The battery with NMC coated with "nano ZrO2" showed significantly worse cycling performance. For this material, the rate performance at a discharge rate of 4C and the capacity retention in the long-term cycle test were even worse than the results of the uncoated NMC.

Claims

1. A method for producing a coated lithium transition metal mixed oxide, characterized in that: The lithium transition metal mixed oxide and the zirconium dioxide produced in the gas phase process and / or the zirconium-containing mixed oxide produced in the gas phase process are dry-mixed by an electric mixing unit having a specific electrical power of 0.05-1.5 kW per kg of lithium transition metal mixed oxide.

2. The method according to claim 1, characterized in that The specific electrical power of the mixing unit is 0.1-1000kw.

3. The method according to claim 1 or 2, characterized in that The volume of the mixing unit used is 0.0001m 3 Up to 2.5m 3 .

4. The method according to claim 1 or 2, characterized in that The speed of the mixing tools in the mixing unit is 5-30 m / s.

5. The method according to claim 1 or 2, characterized in that The BET surface area of ​​the zirconium dioxide and / or zirconium-containing mixed oxide used for producing the coated lithium transition metal mixed oxide is 5 to 200 m 2 / g.

6. The method according to claim 1 or 2, characterized in that The zirconium dioxide and zirconium-containing mixed oxides used for producing the coated lithium transition metal mixed oxide are in the form of aggregated primary particles, wherein the number average diameter of the primary particles is from 5 to 100 nm, as determined by transmission electron microscopy (TEM).

7. The method according to claim 1 or 2, characterized in that The average particle size d of the particles of zirconium dioxide and / or zirconium-containing mixed oxides used for producing the coated lithium transition metal mixed oxides was determined by static light scattering (SLS) after ultrasonic treatment of a mixture consisting of 5 wt. % of the particles and 95 wt. % of a 0.5 g / L aqueous sodium pyrophosphate solution at 25° C. for 60 seconds. 50 10-150nm.

8. The method according to claim 1 or 2, characterized in that The distribution span (d ) of the particles of zirconium dioxide and / or zirconium-containing mixed oxides for producing coated lithium transition metal mixed oxides was determined by static light scattering (SLS) after ultrasonic treatment of a mixture consisting of 5 wt. % of the particles and 95 wt. % of a 0.5 g / L aqueous sodium pyrophosphate solution at 25° C. for 60 seconds. 90 -d 10 ) / d 50 It is 0.4-1.

2.

9. The method according to claim 1 or 2, characterized in that The zirconium-containing mixed oxide further comprises lithium and, optionally, at least one of lanthanum and / or aluminum.

10. The method according to claim 1 or 2, characterized in that The lithium transition metal mixed oxide is selected from 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 a mixture thereof.

11. The method according to claim 1 or 2, characterized in that The proportion of zirconium dioxide and / or zirconium-containing mixed oxides is 0.05% to 5% by weight, relative to the total weight of the mixture of lithium transition metal mixed oxide and zirconium dioxide and / or zirconium-containing mixed oxides used.

12. A coated lithium transition metal mixed oxide produced by the process of any one of claims 1 to 11.

13. The coated lithium transition metal mixed oxide according to claim 12, comprising a number average particle size d 50 Zirconium dioxide produced by a gas phase process and / or zirconium-containing mixed oxide produced by a gas phase process with a diameter of 10 nm to 150 nm.

14. An active cathode material for a lithium battery, comprising the coated lithium transition metal mixed oxide according to claim 12 or 13.

15. A lithium battery comprising the coated lithium transition metal mixed oxide according to claim 12 or 13.

16. Use of the coated lithium transition metal mixed oxide according to claim 12 or 13 as an active positive electrode material for lithium batteries.

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