Coated cathode active materials and process for their manufacture

Abstract

Process for coating a cathode active material for lithium-ion batteries, wherein said process comprises the steps of: (a) providing a particulate cathode active material according to the general formula Li1+xTM1-xO2 wherein TM is a combination of metals of which at least 95 mol-% are transition metals, and at least 80 mol-% of TM is nickel, x is in the range of from -0.01 to +0.05, and TM contains at least one of cobalt and manganese, and the average particle diameter (D50) is in the range of from 3 to 6 µm, (b) mixing said cathode active material with nanoparticulate oxide of tungsten in an amount of 0.2 to 1.5 mol-% W referring to TM, (c) treating the resulting mixture thermally at a temperature in the range of from 300 to 450°C under a carbon-free atmosphere that contains at least 25% by volume of oxygen.

Description

[0001] 240774

[0002] 1

[0003] Coated Cathode Active Materials and Process for their Manufacture

[0004] The present invention is directed towards a process for coating a cathode active material for lithium-ion batteries, wherein said process comprises the steps of:

[0005] (a) providing a particulate cathode active material according to the general formula Lii+xTMi-xO2wherein TM is a combination of metals according to formula (I), x is in the range of from -0.01 to +0.05, and TM contains at least one of cobalt and manganese, and the average particle diameter (D50) is in the range of from 3 to 6 pm,

[0006] (b) mixing said cathode active material with nanoparticulate oxide of tungsten in an amount of 0.2 to 1 .5 mol-% W referring to TM,

[0007] (c) treating the resulting mixture thermally at a temperature in the range of from 300 to 450°C under a carbon-free atmosphere that contains at least 25% by volume of oxygen.

[0008] Lithium-ion secondary batteries are modern devices for storing energy. Many application fields have been and are contemplated, from small devices such as mobile phones and laptop computers through car batteries and other batteries for e-mobility. Various components of the batteries have a decisive role with respect to the performance of the battery such as the electrolyte, the electrode materials, and the separator. Particular attention has been paid to the cathode materials. Several materials have been suggested, such as lithium iron phosphates, lithium cobalt oxides, and lithium nickel cobalt manganese oxides. Although extensive research has been performed, the solutions found so far still leave room for improvement.

[0009] Currently, a certain interest in so-called Ni-rich cathode active materials may be observed, for example cathode active materials that contain 60 mol-% or more of Ni, referring to the total content of metals other than lithium.

[0010] The cathode material is of crucial importance for the properties of a lithium-ion battery. Lithium- containing mixed transition metal oxides have gained particular significance, for example spinels and mixed oxides of layered structure, especially lithium-containing mixed oxides of nickel, manganese and cobalt; see, for example, EP 1 189 296. Such lithium-containing mixed oxides of nickel, manganese and cobalt are generally prepared in a two-stage process. In a first stage, a sparingly soluble salt of the transition metal(s) is prepared by precipitating it from a solution, for example a carbonate or a hydroxide. This sparingly soluble compound is in many cases also referred to as a precursor. In a second stage, the precursor is mixed with a lithium compound, for example Li2CO3, LiOH or Li2O2, and calcined at high temperatures, for example at 600 to 1100°C. 240774

[0011] 2

[0012] One problem of lithium-ion batteries is attributed to undesired reactions on the surface of the cathode active materials. Such reactions may be a decomposition of the electrolyte or the solvent or both. It has thus been tried to protect the surface without hindering the lithium exchange during charging and discharging. Examples are attempts to coat the cathode active materials with, e.g., aluminium oxide or calcium oxide, see, e.g., US 8,993,051 . In coatings according to the above patent, one is limited to metals that form volatile compounds. In addition, some of the volatile compounds are difficult in handling, e.g., AI(CH3)3.

[0013] In US 2018 / 0226646, certain tungsten coatings are disclosed.

[0014] It was an objective of the present invention to provide cathode active materials with improved specific capacity and cycling performance, and reduced resistance growth. In addition, it was an objective to reduce or even avoid capacity loss through corrosion effects.

[0015] Accordingly, the process as defined at the outset has been found, hereinafter also referred to as inventive process. The inventive process comprises at least three steps, (a), (b), and (c), in the context of the present invention also referred to as step (a) and step (b) and step (c), respectively. Steps (a) and (b) and (c) are performed subsequently. Steps (a) to (c) are described in more detail below.

[0016] Step (a) includes providing a particulate cathode active material according to the general formula Lii+xTMi.xO2wherein TM is a combination of metals of which at least 95 mol-% are transition metals, and at least 80 mol-% of TM is nickel, x is in the range of from -0.01 to +0.05, preferably +0.01 to +0.04, and TM contains at least one of cobalt and manganese, and the average particle diameter (D50) is in the range of from 3 to 6 pm. Cathode active material provided in step (a) is hereinafter also referred to as starting material.

[0017] In one embodiment of the present invention, cathode active material provided in step (a) has an average particle diameter (D50) in the range of from 3 to 6 pm, preferably from 4 to 6 pm. The average particle diameter may be determined, e. g., by light scattering or LASER diffraction or electroacoustic spectroscopy. The particles are usually composed of agglomerates from primary particles, and the above particle diameter refers to the secondary particle diameter.

[0018] In one embodiment of the present invention, cathode active material provided in step (a) has a monomodal particle diameter distribution. In another embodiment of the present invention, cathode active material according to general formula Lii+xTMi.xO2 has a bimodal particle diameter distribution. 240774

[0019] 3

[0020] In one embodiment of the present invention, cathode active material provided in step (a) has a broad particle diameter distribution as expressed through the span, (D90 - D1) / (D50). D10, D50 and D90 are the respective percentiles. Strictly speaking, D50 is the median but it is frequently also referred to as average particle diameter (D50). The span is preferably in the range of from 2 to 6.

[0021] In one embodiment of the present invention, starting material has a specific surface (BET), hereinafter also referred to as “BET surface”, in the range of from 0.1 to 1.0 m2 / g. The BET surface may be determined by nitrogen adsorption after outgassing of the sample at 200°C for 30 minutes or more and beyond this in accordance with DIN ISO 9277:2010.

[0022] In one embodiment of the present invention, starting material has a moisture content in the range of from 20 to 2,000 ppm, determined by Karl-Fischer titration, preferred are 200 to 1 ,200 ppm.

[0023] TM is a combination of metals according to general formula (I)

[0024] (NiaCobMnc)i-dMd (I) wherein a is in the range of from 0.85 to 0.95, preferably from 0.88 to 0.95, b is in the range of from 0.025 to 0.12, preferably from 0.04 to 0.1 , c is in the range of from 0.025 to 0.2, preferably from 0.04 to 0.1 , d is in the range of from zero to 0.05,

[0025] M is selected from Al, Mg, Ti, Zr, Nb, Ta and W, and combinations of at least two of the foregoing, preferably Al and Al and at least one of the foregoing, and a + b + c = 1. 240774

[0026] 4

[0027] The starting material provided in step (a) is usually free from conductive carbon, that means that the conductive carbon content of starting material is less than 1% by weight, referring to said starting material, preferably 0.001 to 1.0 % by weight.

[0028] Again, some elements are ubiquitous. In the context of the present invention, traces of ubiquitous metals such as sodium, calcium, iron or zinc, as impurities will not be taken into account. Traces in this context will mean amounts of 0.05 mol-% or less, referring to TM in starting material.

[0029] In one embodiment of the present invention, material provided in step (a) is in the form of monoliths or a so-called “single-crystalline material” or “monolithic”. Single-crystalline materials are composed of primary particles that have an average particle diameter of from 1.1 to 5 pm or bigger. The particle shape of single-crystalline materials is preferably irregular.

[0030] In particularly preferred embodiments, material provided in step (a) is mainly monolithic.

[0031] In an alternative embodiment, material provided in step (a) is in the form of a polycrystalline material. Polycrystalline materials are agglomerates of many primary particles with a diameter in the range of from 75 to 150 nm. The particle shape of polycrystalline materials is preferably spherical.

[0032] Step (b) includes mixing said cathode active material with nanoparticulate oxide of tungsten in an amount of 0.2 to 1 .5 mol-% W referring TM.

[0033] Examples of oxides of tungsten are tungstic acid (H2WO4), W2O3, WO2and WO3, especially tungstic acid and WO3.

[0034] Said oxide of tungsten is nanoparticulate. That means that the average particle diameter (D50) is in the range of from 100 nm to 10 pm, preferably 500 nm to 5 pm, preferably determined by PSD using a dry cell and referring to the weight average. Particles of said oxide of tungsten may be in the form of agglomerates. Then, the diameter of such agglomerates is counted as particle diameter.

[0035] Said oxide of tungsten preferably has a broad particle size distribution. The particle size distribution may be expressed as span or span of particle size distribution. The span of particle size distribution is defined as (D90) - (D10), divided by (D50), and preferably in the range of from 2 240774

[0036] 5 to 6. The values of (D10) and (D90) are the respective percentiles. The diameter refers to the diameter of secondary particles.

[0037] The temperature at which step (b) is performed is preferably ambient temperature or higher, for example 20 to 75°C, preferably 20 to 50°C.

[0038] For mixing, high-speed mixers may be used. In experiments on a gram scale (up to 30 g), mortars with a pestle or a spatula may be used as well.

[0039] In one embodiment of the present invention, mixing time is from 1 minute to one hour, preferably from 90 seconds to 10 minutes. The bigger the amount the longer a mixing time is preferred.

[0040] Step (c) includes treating the mixture resulting from step (b) thermally at a temperature in the range of from 300 to 450°C, preferably 300 to 400°C under a carbon-free atmosphere that contains at least 25% by volume of oxygen.

[0041] Carbon-free atmosphere in the context of the present invention means a carbon dioxide content in the range of from zero to 500 ppm by weight, preferred are 0.01 or less up to 50 ppm by weight. The CO2content may be determined by, e.g., optical methods using infrared light. It is even more preferred to perform step (c) under an atmosphere with a carbon dioxide content below detection limit for example with infrared-light based optical methods.

[0042] Said atmosphere contains at least 25% by volume of oxygen, determined at the beginning of step (c). Preferred are at least 50% by volume of oxygen, more preferred is pure oxygen. The rest may by inert, for example nitrogen or a noble gas, e.g., argon.

[0043] Step (c) may be performed in a rotary kiln or roller hearth kiln, rotary kilns being preferred.

[0044] Step (c) may have a duration in the range of from 10 minutes to 12 hours, preferably one to five hours. When determining the duration, the time at a temperature in the range of from 300 to 450°C is contemplated, and heating and cooling times are neglected.

[0045] A heating at a temperature above 450°C should be avoided. It is observed that at temperatures higher than 450°C, the coating quality decreases.

[0046] Cathode active material as obtained from the inventive process may be used for making cathodes for lithium-ion batteries. 240774

[0047] 6

[0048] A further aspect of the present invention relates to coated cathode active materials, hereinafter also referred to as inventive coated cathode active materials. Inventive coated cathode active materials may be obtained in accordance with the inventive process, and they are useful components of cathodes for lithium-ion batteries. Inventive coated cathode active materials comprise a core (1) and a layer (2) on the outer surface of core (1), said layer (2) also referred to as coating (1). Inventive coated cathode active materials are described in more detail below.

[0049] Coated cathode active materials comprise

[0050] (1) a core material according to the general formula Lii+xTMi.xO2wherein TM is a combination of metals according to formula (I), x is in the range of from -0.01 to +0.05, and TM contains at least one of cobalt and manganese,

[0051] (2) a layer on the outer surface comprising a tungsten compound and a lithium compound, wherein said core (1) has an average particle diameter (D50) in the range of from 3 to 6 pm, and wherein the layer (2) is non-homogeneous with respect to thickness and chemical composition and has an average thickness in the range of from 2 to 50 nm. The thickness of layer (2) may be determined by TEM-EDX imaging of cross sections of individual particles, for example at least 10 randomly picked individual particles.

[0052] Non-homogeneous with respect to thickness means that the thickness varies by at least ± 30% in one particle, or at least an island or Swiss cheese structure is detectable in at least 25% of the particles. Island structure refers to coatings where only minor parts of the overall outer surface are coated. Swiss cheese structure implies that major parts are coated but minor are not.

[0053] TM is described in more detail above. TM is a combination of metals according to formula (I)

[0054] (NiaCobMnc)i-dMd (I) wherein a is in the range of from 0.85 to 0.95, preferably from 0.88 to 0.95, b is in the range of from 0.025 to 0.12, preferably from 0.04 to 0.1 , c is in the range of from 0.025 to 0.2, preferably from 0.04 to 0.1 , 240774

[0055] 7 d is in the range of from zero to 0.05,

[0056] M is selected from Al, Mg, Ti, Zr, Nb, Ta and W, and combinations of at least two of the foregoing, preferably Al and Al and at least one of the foregoing, a + b + c = 1.

[0057] In one embodiment of the present invention, inventive coated cathode active material is in the form of monoliths or a so-called “single-crystalline material” or “monolithic”. Single-crystalline materials are composed of primary particles that have an average particle diameter of from 1 .1 to 5 pm or bigger. The particle shape of single-crystalline materials is preferably irregular.

[0058] In particularly preferred embodiments, inventive coated cathode active material is mainly monolithic. That means that at least 60% by volume of inventive coated cathode active material is monolithic.

[0059] In an alternative embodiment, inventive coated cathode active material is in the form of a polycrystalline material. Polycrystalline materials are agglomerates of many primary particles with a diameter in the range of from 75 to 150 nm. The particle shape of polycrystalline materials is preferably spherical.

[0060] In one embodiment of the present invention, inventive coated cathode active material has an average particle diameter (D50) in the range of from 3 to 6 pm, preferably from 4 to 6 pm. The average particle diameter may be determined, e. g., by light scattering or LASER diffraction or electroacoustic spectroscopy. The particles are usually composed of agglomerates from primary particles, and the above particle diameter refers to the secondary particle diameter.

[0061] In one embodiment of the present invention, inventive coated cathode active material has a monomodal particle diameter distribution. In another embodiment of the present invention, cathode active material according to general formula Lii+xTMi.xO2 has a bimodal particle diameter distribution.

[0062] In one embodiment of the present invention, inventive coated cathode active material has a broad particle diameter distribution as expressed through the span, (D90 - D1) / (D50). D10, D50 and D90 are the respective percentiles. Strictly speaking, D50 is the median but it is frequently also referred to as average particle diameter (D50). The span is preferably in the range of from 240774

[0063] 8

[0064] Inventive coated cathode active material may be used for making cathodes as sole cathode active material or preferably as component of a mixture, more preferably as minority component.

[0065] Another aspect of the present invention is thus a mixture of at least two cathode active materials, wherein one is an inventive coated cathode active material according, and a second cathode active material corresponds to the formula Lii+yTM*i-yO2wherein TM* is a combination of metals of which at least 95 mol-% are transition metals, and at least 80 mol-% of TM* is nickel, y is in the range of from -0.01 to +0.05, and TM* contains at least one of cobalt and manganese, and the second cathode active material has an average particle diameter (D50) in the range of from 7 to 15 pm. Such mixtures are hereinafter also referred to as inventive blends or inventive mixtures.

[0066] In one embodiment of the present invention, TM* corresponds is a combination of metals according to formula (I). Preferably, in inventive mixtures, TM* is a combination of metals according to formula (I) but differs in at least one variable from TM, for example in the nickel content by at least 0.05 or in the cobalt content by at least 0.02 or in the manganese content by at least 0..02.

[0067] In a preferred embodiment, the weight ratio of inventive coated cathode active material and second cathode active material in inventive mixtures is in the range of from 10:90 to 35:65.

[0068] A further aspect of the present invention is the use of an inventive coated cathode active material alone or in an inventive mixture for the manufacture of a cathode for a lithium-ion battery and ultimately for the manufacture of a lithium-ion battery.

[0069] A further aspect of the present invention is an electrochemical cell comprising

[0070] (1) a cathode comprising an inventive coated cathode active material alone or in an inventive mixture,

[0071] (2) an anode, and

[0072] (3) an electrolyte comprising a sulfide corresponding to formula (II)

[0073] Li7.r-2SPS6.r-SXr(II), wherein

[0074] X is chlorine, bromine or iodine 240774

[0075] 9

[0076] 0.8 < r < 1 .7 and s 0 < s < (-0.25 r) + 0.5, or l_i3PS4.

[0077] A further aspect of the present invention refers to electrodes comprising at least one inventive coated cathode active material according to the present invention. They are particularly useful for lithium-ion batteries. Lithium-ion batteries comprising at least one electrode according to the present invention exhibit a good cycling behavior / stability. Electrodes comprising at least one inventive coated cathode active material according to the present invention are hereinafter also referred to as inventive cathodes or cathodes according to the present invention.

[0078] Specifically, inventive cathodes contain

[0079] (A) at least one inventive coated cathode active material,

[0080] (B) carbon in electrically conductive form,

[0081] (C) a binder material, also referred to as binders or as binders (C), and, preferably,

[0082] (D) a current collector.

[0083] In a preferred embodiment, inventive cathodes contain

[0084] (A) 80 to 98 % by weight inventive coated cathode active material,

[0085] (B) 1 to 17 % by weight of carbon,

[0086] (C) 1 to 15 % by weight of binder, percentages referring to the sum of (A), (B) and (C).

[0087] Cathodes according to the present invention can comprise further components. They can comprise a current collector, such as, but not limited to, an aluminum foil. They can further comprise conductive carbon and a binder.

[0088] Cathodes according to the present invention contain carbon in electrically conductive modification, in brief also referred to as carbon (B). Carbon (B) can be selected from soot, active carbon, carbon nanotubes, graphene, and graphite, and from combinations of at least two of the foregoing.

[0089] Suitable binders (C) are preferably selected from organic (co)polymers. Suitable (co)polymers, i.e. homopolymers or copolymers, can be selected, for example, from (co)polymers obtainable by anionic, catalytic or free-radical (co)polymerization, especially from polyethylene, polyacrylonitrile, polybutadiene, polystyrene, and copolymers of at least two comonomers selected from 240774

[0090] 10 ethylene, propylene, styrene, (meth)acrylonitrile and 1 ,3-butadiene. Polypropylene is also suitable. Polyisoprene and polyacrylates are additionally suitable. Particular preference is given to polyacrylonitrile.

[0091] In the context of the present invention, polyacrylonitrile is understood to mean not only polyacrylonitrile homopolymers but also copolymers of acrylonitrile with 1 ,3-butadiene or styrene. Preference is given to polyacrylonitrile homopolymers.

[0092] In the context of the present invention, polyethylene is not only understood to mean homopolyethylene, but also copolymers of ethylene which comprise at least 50 mol-% of copolymerized ethylene and up to 50 mo-l% of at least one further comonomer, for example a-olefins such as propylene, butylene (1 -butene), 1 -hexene, 1 -octene, 1 -decene, 1 -dodecene, 1 -pentene, and also isobutene, vinylaromatics, for example styrene, and also (meth)acrylic acid, vinyl acetate, vinyl propionate, Ci-Cio-alkyl esters of (meth)acrylic acid, especially methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl acrylate, 2-ethylhexyl acrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, and also maleic acid, maleic anhydride and itaconic anhydride. Polyethylene may be HDPE or LDPE.

[0093] In the context of the present invention, polypropylene is not only understood to mean homo-pol- ypropylene, but also copolymers of propylene which comprise at least 50 mol-% of copolymerized propylene and up to 50 mol-% of at least one further comonomer, for example ethylene and a-olefins such as butylene, 1 -hexene, 1 -octene, 1 -decene, 1 -dodecene and 1 -pentene. Polypropylene is preferably isotactic or essentially isotactic polypropylene.

[0094] In the context of the present invention, polystyrene is not only understood to mean homopolymers of styrene, but also copolymers with acrylonitrile, 1 ,3-butadiene, (meth)acrylic acid, Ci- Cio-alkyl esters of (meth)acrylic acid, divinylbenzene, especially 1 ,3-divinylbenzene, 1 ,2-diphe- nylethylene and a-methylstyrene.

[0095] Another preferred binder (C) is polybutadiene.

[0096] Other suitable binders (C) are selected from polyethylene oxide (PEO), cellulose, carboxymethylcellulose, polyimides and polyvinyl alcohol.

[0097] In one embodiment of the present invention, binder (C) is selected from those (co)polymers which have an average molecular weight Mwin the range from 50,000 to 1 ,000,000 g / mol, preferably to 500,000 g / mol. 240774

[0098] 11

[0099] Binder (C) may be cross-linked or non-cross-linked (co)polymers.

[0100] In a particularly preferred embodiment of the present invention, binder (C) is selected from halogenated (co)polymers, especially from fluorinated (co)polymers. Halogenated or fluorinated (co)polymers are understood to mean those (co)polymers which comprise at least one (^polymerized (co)monomer which has at least one halogen atom or at least one fluorine atom per molecule, more preferably at least two halogen atoms or at least two fluorine atoms per molecule. Examples are polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene, polyvinylidene fluoride (PVdF), tetrafluoroethylene-hexafluoropropylene copolymers, vinylidene fluoridehexafluoropropylene copolymers (PVdF-HFP), vinylidene fluoride-tetrafluoroethylene copolymers, perfluoroalkyl vinyl ether copolymers, ethylene-tetrafluoroethylene copolymers, vinylidene fluoride-chlorotrifluoroethylene copolymers and ethylene-chlorofluoroethylene copolymers.

[0101] Suitable binders (C) are especially polyvinyl alcohol and halogenated (co)polymers, for example polyvinyl chloride or polyvinylidene chloride, especially fluorinated (co)polymers such as polyvinyl fluoride and especially polyvinylidene fluoride and polytetrafluoroethylene.

[0102] Inventive cathodes may comprise 1 to 15% by weight of binder(s), referring to inventive cathode active material. In other embodiments, inventive cathodes may comprise 0.1 up to less than 1% by weight of binder(s).

[0103] A further aspect of the present invention is a battery, containing at least one cathode comprising inventive cathode active material, carbon, and binder, at least one anode, and at least one electrolyte.

[0104] Embodiments of inventive cathodes have been described above in detail.

[0105] Said anode may contain at least one anode active material, such as carbon (graphite), TiO2, lithium titanium oxide, silicon or tin. Said anode may additionally contain a current collector, for example a metal foil such as a copper foil.

[0106] Said electrolyte may comprise at least one non-aqueous solvent, at least one electrolyte salt and, optionally, additives. 240774

[0107] 12

[0108] Non-aqueous solvents for electrolytes can be liquid or solid at room temperature and is preferably selected from among polymers, cyclic or acyclic ethers, cyclic and acyclic acetals and cyclic or acyclic organic carbonates.

[0109] Examples of suitable polymers are, in particular, polyalkylene glycols, preferably poly-Ci-C4-al- kylene glycols and in particular polyethylene glycols. Polyethylene glycols can here comprise up to 20 mol-% of one or more Ci-C4-alkylene glycols. Polyalkylene glycols are preferably polyalkylene glycols having two methyl or ethyl end caps.

[0110] The molecular weight Mwof suitable polyalkylene glycols and in particular suitable polyethylene glycols can be at least 400 g / mol.

[0111] The molecular weight Mwof suitable polyalkylene glycols and in particular suitable polyethylene glycols can be up to 5,000,000 g / mol, preferably up to 2,000,000 g / mol.

[0112] Examples of suitable acyclic ethers are, for example, diisopropyl ether, di-n-butyl ether, 1 ,2-di- methoxyethane, 1 ,2-diethoxyethane, with preference being given to 1 ,2-dimethoxyethane.

[0113] Examples of suitable cyclic ethers are tetrahydrofuran and 1 ,4-dioxane.

[0114] Examples of suitable acyclic acetals are, for example, dimethoxymethane, diethoxymethane, 1 ,1 -dimethoxyethane and 1 ,1 -diethoxyethane.

[0115] Examples of suitable cyclic acetals are 1 ,3-dioxane and in particular 1 ,3-dioxolane.

[0116] Examples of suitable acyclic organic carbonates are dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.

[0117] Examples of suitable cyclic organic carbonates are compounds according to the general formulae (II) and (III)

[0118] 240774 where R1, R2and R3can be identical or different and are selected from among hydrogen and Ci-C4-alkyl, for example methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tertbutyl, with R2and R3preferably not both being tert-butyl.

[0119] In particularly preferred embodiments, R1is methyl and R2and R3are each hydrogen, or R1, R2and R3are each hydrogen.

[0120] Another preferred cyclic organic carbonate is vinylene carbonate, formula (IV).

[0121] The solvent or solvents is / are preferably used in the water-free state, i.e. with a water content in the range from 1 ppm to 0.1% by weight, which can be determined, for example, by Karl-Fischer titration.

[0122] Electrolyte (C) further comprises at least one electrolyte salt. Suitable electrolyte salts are, in particular, lithium salts. Examples of suitable lithium salts are LiPF6, LiBF4, l_iCIO4, LiAsF6, LiCF3SO3, LiC(CnF2n+iSO2)3, lithium imides such as LiN(CnF2n+iSO2)2, where n is an integer in the range from 1 to 20, LiN(SO2F)2, Li2SiF6, LiSbF6, LiAICI4and salts of the general formula (CnF2n+iSO2)tYLi, where m is defined as follows: t = 1 , when Y is selected from among oxygen and sulfur, t = 2, when Y is selected from among nitrogen and phosphorus, and t = 3, when Y is selected from among carbon and silicon. 240774

[0123] 14

[0124] Preferred electrolyte salts are selected from among LiC(CF3SO2)3, LiN(CF3SO2)2, LiPF6, LiBF4, l_iCIO4, with particular preference being given to LiPF6and LiN(CF3SO2)2.

[0125] In an embodiment of the present invention, batteries according to the invention comprise one or more separators by means of which the electrodes are mechanically separated. Suitable separators are polymer films, in particular porous polymer films, which are unreactive toward metallic lithium. Particularly suitable materials for separators are polyolefins, in particular film-forming porous polyethylene and film-forming porous polypropylene.

[0126] Separators composed of polyolefin, in particular polyethylene or polypropylene, can have a porosity in the range from 35 to 45%. Suitable pore diameters are, for example, in the range from 30 to 500 nm.

[0127] In another embodiment of the present invention, separators can be selected from among PET nonwovens filled with inorganic particles. Such separators can have porosities in the range from 40 to 55%. Suitable pore diameters are, for example, in the range from 80 to 750 nm.

[0128] Batteries according to the invention further comprise a housing which can have any shape, for example cuboidal or the shape of a cylindrical disk or a cylindrical can. In one variant, a metal foil configured as a pouch is used as housing.

[0129] Batteries according to the invention display a good cycling stability and a low capacity fading and a high charge density.

[0130] Batteries according to the invention can comprise two or more electrochemical cells that combined with one another, for example can be connected in series or connected in parallel. Connection in series is preferred. In batteries according to the present invention, at least one of the electrochemical cells contains at least one cathode according to the invention. Preferably, in electrochemical cells according to the present invention, the majority of the electrochemical cells contains a cathode according to the present invention. Even more preferably, in batteries according to the present invention all the electrochemical cells contain cathodes according to the present invention.

[0131] The present invention further provides for the use of batteries according to the invention in appliances, in particular in mobile appliances. Examples of mobile appliances are vehicles, for example automobiles, bicycles, aircraft or water vehicles such as boats or ships. Other examples 240774

[0132] 15 of mobile appliances are those which move manually, for example computers, especially laptops, telephones or electric hand tools, for example in the building sector, especially drills, battery-powered screwdrivers or battery-powered staplers.

[0133] The present invention is further illustrated by the following working examples.

[0134] General remarks: Percentages and ppm are percent or ppm, respectively, by weight unless specifically noted otherwise.

[0135] ICP: inductively coupled plasma

[0136] In the atmosphere for steps C-(c.1) to (c.7), a carbon-free atmosphere was applied, with a level of CO2being below detection level (IR).

[0137] I. Synthesis of inventive and of comparative cathode active materials

[0138] Step (a.1): a cathode active material was provided, B-CAM.1. Average particle diameter (D50): 4.0 pm, composition Lii 04TM0.96O2, TM = Ni0.92Co0.03Mn0.04. B-CAM.1 was essentially composed of monolithic particles with irregular shape.

[0139] 1.1 Synthesis of comparative cathode active material C-CAM.1

[0140] Step (b.1): An amount of 60 g B-CAM.1 was dry-mixed with 0.2 g of WO3(0.2 mol-% of W, referring to TM) in a laboratory mixer LabRam twice over a period of one minute each. A mixture was obtained.

[0141] Step C-(c.1): A ceramic crucible was filled with 20 g of the mixture from step (b.1). The mixture was then heated to 200°C with a heating rate of 2 °C / min and then maintained at 200°C for two hours under an atmosphere of pure oxygen. Then, the resultant cathode active material was allowed to cool naturally. Then, it was sieved with 32 pm mesh. C-CAM.1 was obtained.

[0142] 1.2 Synthesis of comparative cathode active material C-CAM.2

[0143] Step (b.2): An amount of 60 g B-CAM.1 was mixed with 0.2 g of WO3(0.2 mol-% of W, referring to TM) and 13 g of de-ionized water with a spatula in a glass jar. The resultant mixture was dried in a vacuum oven at 50°C for 15 hours. A dry mixture was obtained. 240774

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[0145] Step C-(c.2): A ceramic crucible was filled with 20 g of the dry mixture from step (b.2). The mixture was then heated to 200°C with a heating rate of 2 °C / min and then maintained at 200°C for two hours under an atmosphere of pure oxygen. Then, the resultant cathode active material was allowed to cool naturally. Then, it was sieved with 32 pm mesh. C-CAM.2 was obtained.

[0146] 1.3 Synthesis of comparative cathode active material C-CAM.3

[0147] Step (b.3): An amount of 60 g B-CAM.1 was mixed with 13 g of de-ionized water and then with 1.0 g of WO3(0.9 mol-% of W, referring to TM) with a spatula in a glass jar. The resultant mixture was dried in a vacuum oven at 50°C for 15 hours. A dry mixture was obtained.

[0148] Step C-(c.3): A ceramic crucible was filled with 20 g of the dry mixture from step (b.3). The mixture was then heated to 200°C with a heating rate of 2 °C / min and then maintained at 200°C for two hours under an atmosphere of pure oxygen. Then, the resultant cathode active material was allowed to cool naturally. Then, it was sieved with 32 pm mesh. C-CAM.3 was obtained.

[0149] 1.4 Synthesis of inventive cathode active material CAM.4

[0150] Step (b.4): An amount of 60 g B-CAM.1 was dry-mixed with 0.3 g of H2WO4(0.2 mol-% of W, referring to TM) with a spatula. A dry mixture was obtained.

[0151] Step (c.4): A ceramic crucible was filled with 20 g of the dry mixture from step (b.4). The mixture was then heated to 400°C with a heating rate of 2 °C / min and then maintained at 400°C for two hours under an atmosphere of pure oxygen. Then, the resultant cathode active material was allowed to cool naturally. Then, it was sieved with 32 pm mesh. Inventive CAM.4 was obtained.

[0152] 1.5 Synthesis of inventive cathode active material CAM.5

[0153] Step (b.5): An amount of 60 g B-CAM.1 was mixed with 12.5 g of de-ionized water and then with 0.3 g of H2WO4(0.2 mol-% of W, referring to TM) with a spatula. The resultant mixture was dried in a vacuum oven at 50°C for 15 hours. A dry mixture was obtained.

[0154] Step (c.5): A ceramic crucible was filled with 20 g of the dry mixture from step (b.5). The mixture was then heated to 300°C with a heating rate of 2 °C / min and then maintained at 300°C for two hours under an atmosphere of pure oxygen. Then, the resultant cathode active material was allowed to cool naturally. Then, it was sieved with 32 pm mesh. CAM.5 was obtained. 240774

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[0156] I.6 Synthesis of inventive cathode active material CAM.6

[0157] Step (b.6): An amount of 60 g B-CAM.1 was mixed with 12.5 g of de-ionized water and then with 1 .4 g of H2WO4(0.9 mol-% of W, referring to TM) with a spatula. The resultant mixture was dried in a vacuum oven at 50°C for 15 hours. A dry mixture was obtained.

[0158] Step (c.6): A ceramic crucible was filled with 20 g of the dry mixture from step (b.6). The mixture was then heated to 400°C with a heating rate of 2 °C / min and then maintained at 400°C for two hours under an atmosphere of pure oxygen. Then, the resultant cathode active material was allowed to cool naturally. Then, it was sieved with 32 pm mesh. CAM.6 was obtained.

[0159] Each of the inventive cathode active materials had a core and a coating layer. As assessed by SEM, the coating layers had an average thickness in the range of from 2 to 50 nm and contained a lithium-tungsten compound. The coating layers appeared non-homogeneous with respect to thickness.

[0160] II. Testing of Cathode Active Material

[0161] 11.1 Electrode manufacture, general procedure

[0162] 11.1.1 Cathode Manufacture

[0163] Positive electrode: PVDF binder (Solef® 5130) was dissolved in NMP (Merck) to produce a 7.5 wt.% solution. For electrode preparation, binder solution (3 wt.%), graphite (SFG6L, 2 wt.%), and carbon black (Super C65, 1 wt.-%) were suspended in NMP. After mixing using a planetary centrifugal mixer (ARE-250, Thinky Corp.; Japan), either inventive CAM.1 or CAM.2 (94 wt.%) was added and the suspension was mixed again to obtain a lump-free slurry. The solid content of the slurry was adjusted to 65%. The slurry was coated onto Al foil using a KTF-S roll-to-roll coater (Mathis AG). Prior to use, all electrodes were calendared. The thickness of cathode material was 70 pm, corresponding to 15 mg / cm2. All electrodes were dried at 105°C for 7 hours before battery assembly.

[0164] 11.1.2: Electrolyte Manufacture

[0165] A base electrolyte composition was prepared containing 12.7 wt% of LiPF6, 26.2 wt% of ethylene carbonate (EC), and 61.1 wt% of ethyl methyl carbonate (EMC) (EL base 1), based on the total weight of EL base 1 . To this base electrolyte formulation 2wt.% of vinylene carbonate (VC) was added (EL base 2). 240774

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[0167] 11.2 Test cell Manufacture - coin-type half cells

[0168] Coin-type half cells (20 mm in diameter and 3.2 mm in thickness) comprising a cathode prepared as described under 11.1.1 and lithium metal as working and counter electrode, respectively, were assembled and sealed in an Ar-filled glove box. In addition, the cathode and anode and a separator were superposed in order of cathode / / separator / / Li foil to produce a half coin cell. Thereafter, 0.15 mL of the EL base 1 which is described above (III.2) were introduced into the coin cell.

[0169] 11.3 Evaluation of cell performance

[0170] Evaluation of coin half-cell performance: The initial performance and the cycling performance were measured as follows: Coin half cells according to 11.3 were tested in a voltage range between 4.3 to 2.7 at 25°C. For the two initial cycles, the charging was conducted in the CC- CV mode, i.e., a constant current (CC) of 0.05 C was applied until reaching 4.3 V, followed by the CV step until the current dropped to 0.01 C. After 10 min resting time, discharging was carried out at constant current of 0.05 C to 2.7 V. For the cycling test, the constant current was chosen to be 0.33 C until 56 cycles were reached and discharge capacity retention was calculated by comparing the initial 0.33 C discharge capacity and the 0.33 C discharge capacity at the end of the cycle test. The results are summarized in Table 1.

[0171] Table 1 : Electrochemical performance data of inventive and comparative cathode active materials

Claims

24077419Patent Claims1 . Process for coating a cathode active material for lithium-ion batteries, wherein said process comprises the steps of:(a) providing a particulate cathode active material according to the general formula Lii+xTMi-xO2wherein TM is a combination of metals according to general formula (I)(NiaCObMno)i.dMd (I) wherein a is in the range of from 0.80 to 0.95, b is in the range of from 0.025 to 0.2, c is in the range of from zero to 0.2, and d is in the range of from zero to 0.05,M is selected from Mg, Al, Ca, Si, Ti, Zr, Mo, Nb, and Ta, a + b + c = 1 , x is in the range of from -0.01 to +0.05, and TM contains at least one of cobalt and manganese, and the average particle diameter (D50) is in the range of from 3 to 6 pm,(b) mixing said cathode active material with nanoparticulate oxide of tungsten in an amount of 0.2 to 1 .5 mol-% W referring to TM,(c) treating the resulting mixture thermally at a temperature in the range of from 300 to 450°C under a carbon-free atmosphere that contains at least 25% by volume of oxygen.

2. Process according to claim 1 wherein oxide of tungsten is selected from tungstic acid and WO3.

3. Process according to claim 1 or 2 wherein oxide of tungsten has an average particle diameter (D50) in the range of from 100 nm to 10 pm.

4. Process according to any of the preceding claims wherein the oxide of tungsten has a span of particle size distribution, defined as (D90) - (D10), divided by (D50) in the range of from 2 to 6.240774205. Process according to any of the preceding claims wherein at least 60 % by volume of said particulate cathode active material is in the form of monolithic particles.

6. Process according to any of claims 1 to 4 wherein said particulate cathode active material is polycrystalline, and the average particle diameter refers to the secondary particles.

7. Coated cathode active material comprising(1) a core material according to the general formula Lii+xTMi.xO2wherein TM is a combination of metals according to general formula (I),(NiaCObMno)i.dMd (I) wherein a is in the range of from 0.80 to 0.95, b is in the range of from 0.025 to 0.2, c is in the range of from zero to 0.2, and d is in the range of from zero to 0.05,M is selected from Mg, Al, Ca, Si, Ti, Zr, Mo, Nb, and Ta, a + b + c = 1(2) x is in the range of from -0.01 to +0.05, and TM contains at least one of cobalt and manganese,(3) a layer on the outer surface comprising a tungsten compound and a lithium compound, wherein said core (1) has an average particle diameter (D50) in the range of from 3 to 6 pm, and wherein the layer (2) is non-homogeneous with respect to thickness and chemical composition and has an average thickness in the range of from 2 to 50 nm.

8. Coated cathode active material according to claim 7 wherein at least 60% by volume of inventive coated cathode active material is in the form of monolithic particles.

9. Coated cathode active material according to claim 7 wherein said particulate cathode active material is polycrystalline, and the average particle diameter refers to the secondary particles2407742110. Mixture of at least two cathode active materials, wherein one is a coated cathode active material according to any of the claims 7 to 9, and a second cathode active material corresponds to the formula Lii+yTM*i-yO2wherein TM* is a combination of metals according to formula (I), y is in the range of from -0.01 to +0.05, and TM* contains at least one of cobalt and manganese, and the second cathode active material has an average particle diameter (D50) in the range of from 7 to 15 pm.11 . Mixture according to claim 10 wherein the weight ratio of coated cathode active material according to any of the claims 7 to 9 and second cathode active material is in the range of from 10:90 to 35:65.

12. Use of a coated cathode active material according to claim 7 to 9 or a mixture according to claim 10 or 11 for the manufacture of a lithium-ion battery.

13. Electrochemical cell comprising(1) a cathode comprising a cathode active material according to claim 7 to 9 or a mixture according to claim 10 or 11 ,(2) an anode, and(3) an electrolyte comprising a sulfide corresponding to formula (II)Li7.r-2SPS6.r-SXr(II), whereinX is chlorine, bromine or iodine0.8 < r < 1 .7 and s 0 < s < (-0.25 r) + 0.5, or l_i3PS4.

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