Process for coating a cathode active material, and coated cathode active materials

Abstract

Process for coating a cathode active material for lithium-ion batteries wherein said cathode active material comprises at least 50 mol-% nickel, referring to metals other than lithium, wherein said process comprises the steps of: (a) providing a cathode active material according to the general formula Li1+xTM1-xO2 wherein x is in the range of from zero to 0.2, TM is a combination of metals of which at least 95 mol-% are transition metals, and at least 50 mol-% of TM is nickel, and TM contains at least one of cobalt and manganese, (b) combining said cathode active material with an anhydrous solution of Zr(OR1)4, wherein R1 are same or differ- ent and selected from C2-C4-alkyl, straight chain or branched, (c) adding LiOH∙y H2O, wherein y is in the range of from 0.5 to 3.0, (d) removing the solvent(s), (e) treating the residue thermally at a temperature in the range of from 300 to 450°C.

Description

[0001] Process for coating a cathode active material, and coated cathode active materials

[0002] The present invention is directed towards a process for coating a cathode active material for lithium-ion batteries wherein said cathode active material comprises at least 50 mol-% nickel, referring to metals other than lithium, wherein said process comprises the steps of:

[0003] (a) providing a cathode active material according to the general formula Li i+xTM i-xO2 wherein x is in the range of from zero to 0.2, TM is a combination of metals of which at least 95 mol-% are transition metals, and at least 50 mol-% of TM is nickel, and TM contains at least one of cobalt and manganese,

[0004] (b) combining said cathode active material with an anhydrous solution of Zr(OR1)4, wherein R1are same or different and selected from C2-C4-alkyl, straight chain or branched, and the water content is 650 ppm or less, determined by Karl-Fischer titration,

[0005] (c) adding LiO H y H2O, wherein y is in the range of from 0.5 to 3.0,

[0006] (d) removing the solvent(s),

[0007] (e) treating the residue thermally at a temperature in the range of from 300 to 450°C.

[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 75 mole-% or more of Ni, referring to the total TM content.

[0010] One problem of lithium ion batteries - especially of Ni-rich cathode active materials - 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.

[0011] Other theories assign undesired reactions to free LiOH or Li2COa on the surface. Attempts have been made to remove such free LiOH or Li2COa by washing the cathode active material with water, see, e.g., JP 4,789,066 B, JP 5,139,024 B, and US2015 / 0372300. However, in some instances it was observed that the properties of the resultant cathode active materials did not improve. Some other coating processes have been tried, for example precipitations of a coating material by a sol-gel precipitation process and a subsequent drying. However, it has been found that after such drying, agglomerates may form that remain as sieving residue.

[0012] It was an objective of the present invention to provide a process for making Ni-rich cathode active materials with excellent electrochemical properties and with low loss after sieving. It was also an objective to provide Ni-rich cathode active materials with excellent electrochemical properties, especially a low resistance growth upon cycling and high- temperature storage.

[0013] Accordingly, the process defined at the outset has been found, hereinafter also referred to as "inventive process”.

[0014] The inventive process comprises the following steps:

[0015] (a) providing a cathode active material according to the general formula Li i+xTM i-xO2 wherein x is in the range of from zero to 0.2, TM is a combination of metals of which at least 95 mol-% are transition metals, and at least 50 mol-% of TM is nickel, and TM contains at least one of cobalt and manganese,

[0016] (b) combining said cathode active material with an anhydrous solution of Zr(OR1)4, wherein R1are same or different and selected from C2-C4-alkyl, straight chain or branched,

[0017] (c) adding LiO H y H2O, wherein y is in the range of from 0.5 to 3.0,

[0018] (d) removing the solvent(s),

[0019] (e) treating the residue thermally at a temperature in the range of from 300 to 450°C.

[0020] The inventive process comprises at least five steps, (a), (b), (c), (d) and (e), in the context of the present invention also referred to as step (a) and step (b) and step (c) and step (d) and step (e), respectively. Steps (a) to (e) are performed subsequently.

[0021] In step (a), the inventive process starts off from a cathode active material based on a lithiated oxide of TM wherein TM is a combination of metals of which at least 95 mol-% are transition metals, and at least 50 mol-% of TM is nickel, preferably at least 60 mol-%. Furthermore, TM contains at least one of Co and Mn, preferably TM contains Co and Al or Co and Mn and, optionally, Al. Said material is hereinafter also referred to as starting material. Preferably, said cathode active material is a lithiated oxide of TM. Said lithiated oxide of TM may contain impurities stemming from its manufacture, for example residual lithium hydroxide, residual lithium carbonate and / or lithium sulfate, each less than 1 % by weight, preferably less than 0.5 % by weight.

[0022] In one embodiment of the present invention, said cathode active material provided in step (a) is a material according to general formula Lii+xTMi.xO2, wherein TM is a combination of metals of which at least 95 mol-% are transition metals, and at least 50 mol-% of TM is nickel and, and TM contains at least one transition metal selected from Co and Mn, and, optionally, at least one element selected from Al and Mg-%, and x is in the range of from zero to 0.2. Preferably, at least 75 mole-% of TM is Ni.

[0023] In one embodiment of the present invention the starting material has an average particle diameter (D50) in the range of from 1 to 10 pm, preferably from 2 to 7 m. The average particle diameter can 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.

[0024] In one embodiment, the cathode active material provided in step (a) is in the form of monoliths. In such an embodiment, no primary particles are distinguishable. Such monoliths may be of irregular shape, for example in the form of potatoes or of drops. In a preferred embodiment of the present invention, the cathode active material provided in step (a) is in the form of secondary particles that are agglomerates from primary particles. They are sometimes also referred to as polycrystalline. Secondary particles are preferably spherical or spheroidal in nature.

[0025] In one embodiment of the present invention, the secondary particles of cathode active material provided in step (a) are agglomerates from primary particles that are essentially radially oriented.

[0026] "Essentially radially oriented” does not require a perfect radial orientation but includes that in an SEM analysis, a deviation to a perfectly radial orientation is at most 5 degrees. The portion of radially oriented primary particles may be determined, e.g., by SEM (Scanning Electron Microscopy) of a cross-section of at least 5 secondary particles.

[0027] In one embodiment of the present invention, the starting material has a specific surface (BET), hereinafter also referred to as "BET surface”, in the range of from 0.1 to 2.0 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 accordance with DIN ISO 9277:2010.

[0028] In one embodiment of the present invention, the particulate material provided in step (a) has a moisture content in the range of from 20 to 2,000 ppm, determined by Karl-Fischer titration, preferred are 50 to 1,200 ppm.

[0029] In one embodiment of the present invention, TM corresponds to 50 to 99.9 mol-% nickel, zero to 50 mol-% cobalt and zero to 50 mol-% manganese, wherein at least one of cobalt and manganese is present.

[0030] In one embodiment of the present invention, the variable TM corresponds to general formula

[0031] (I)

[0032] (NiaCObMnc)i.dM1d (I) with a + b + c = 1 and a is in the range of from 0.6 to 0.99, preferably from 0.75 to 0.95, more preferably from 0.85 to 0.95, b is zero or in the range of from 0.01 to 0.2, preferably from 0.025 to 0.2, more preferably from 0.025 to 0.1, c is in the range of from zero to 0.2, preferably from 0.025 to 0.2, more preferably from 0.05 to 0.1 , d is in the range of from zero to 0.1 , preferably from zero to 0.04,

[0033] M1is at least one of Al, Mg, Ti, Nb, Mo, W and Zr, preferably at least one of Al, Ti, Zr and W.

[0034] In one embodiment of the present invention, the variable c is zero, M1is Al, and d is in the range of from 0.01 to 0.05.

[0035] In one embodiment of the present invention TM corresponds to general formula (I) and x is in the range from zero to 0.2, preferably from zero to 0.1 and even more preferably 0.01 to 0.05.

[0036] In one embodiment of the present invention, TM is selected from Nio6Coo 2Mno 2, Nio.7Coo.2Mno.i, NiosCoo i Mno.i, Ni083Co012Mn005, Ni089Co0055AI0055, Ni091Co0045AI0045 and Nio85Coo 1Mno05-

[0037] The cathode active 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.

[0038] 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 in the description of the present invention. Traces in this context will mean amounts of 0.02 mol-% or less, referring to the total metal content of the starting material.

[0039] Traces of sulfate stemming from the synthesis of particulate cathode active material will be neglected as well.

[0040] In step (b), the starting material is combined with an anhydrous solution of Zr(OR1)4, wherein R1are same or different and selected from C2-C4-alkyl, straight chain or branched, for example ethyl, n-propyl, n-butyl, isopropyl, iso-butyl, or sec.-butyl. Specific examples are Zr(OC2H5)4, Zr(O-n-C3H / )4, Zr(O-iso-C3H7)4, Zr(O-n-C4Hg)4, Zr(O-iso-C4Hg)4or Zr(O- tert-C4Hg)4. The term anhydrous in the context of step (b) refers to a solvent that has a water content of 650 ppm or less, determined by Karl-Fischer titration, preferably 75 ppm or less. Ethanol with a water content in the range of from 350 to 650 ppm is feasible as well. The term ppm refers to ppm by mass unless specified otherwise.

[0041] Examples of suitable solvents are C2-C4-alkanols like ethanol, isopropanol, n-butanol, sec. -butanol, THF (tetrahydrofuran), N-methyl-pyrrolidone (“NMP”), dimethyl sulfoxide (“DMSO”). Preferred are the respective alkanol R1-OH, especially ethanol, n-propanol and n-butanol. Mixtures from at least two of the aforementioned solvents are feasible as well, for example of ethanol and R1-OH.

[0042] In one embodiment of the present invention, the concentration of Zr(OR1)4 in said non-aqueous solution is in the range of from 0.8 to 2.5 mol / l.

[0043] In one embodiment of the present invention, the weight ratio of non-aqueous solution of Zr(OR1)4 to cathode active material as provided in step (a) is in the range of from 1 : 1 to 1 : 10, preferably 1 :3 to 1 :6.

[0044] In one embodiment of the present invention, step (b) is performed in a mixer or in rotary kiln, or in a dryer, for example a vacuum dryer, a flash dryer, a rotary dryer, a high shear dryer, a ring dryer, a thin film dryer, a screw conveyor dryer, or a paddle dryer. Preferably, step (b) is performed in a paddle dryer, for example a vacuum paddle dryer or a conical paddle dryer.

[0045] In one embodiment of the present invention, the time between step (b) and step (c) is in the range of from zero to 60 minutes, preferably 2 to 30 minutes.

[0046] In one embodiment of the present invention, step (b) is performed at a temperature in the range of from 15 to 40°C.

[0047] A sludge or mud-like phase is obtained.

[0048] In step (c), LIOfTy H2O, wherein y is in the range of from 0.5 to 3.0, preferably 1 .0 to 2.5, is added to the mud-like phase or sludge resulting from step (b). In the formula of LIOfTy H2O, y denotes an average value. Such LiO H y H2O may be added in bulk or in solution, bulk being preferred. As solvent, alcohol R1-OH is most suitable.

[0049] The molar amount of LiOH y H2O may be in the range of from 1 :1 to 4: 1 , preferably 1.5:1 to 2.5: 1 with respect to Zr added in step (b).

[0050] After or during step (b) or (c), one or more mixing operations are started, for example stirring or shaking. During such mixing operation(s), the temperature may be ambient temperature or higher, for example up to the boiling point of the non-aqueous solvent. In step (d), the solvent(s) are removed, preferably by evaporation. Step (d) may be performed under reduced pressure ("in vacuo”) or at ambient pressure. In embodiments wherein step (d) is performed at ambient pressure, it may be performed under an atmosphere of air, nitrogen or oxygen-enriched air.

[0051] In one embodiment of the present invention, step (d) is performed at a temperature in the range of from 65 to 165°C. The temperature is determined at the set point of the respective vessel.

[0052] In one embodiment of the present invention, step (d) has a duration in the range of from 5 minutes to 12 hours, preferred are 60 minutes to 5 hours.

[0053] In one embodiment of the present invention, step (d) is performed in a rotary kiln, in a mixer or in a dryer as disclosed above. In laboratory scale experiments, for example with samples of 10 g or less, step (d) may be performed in a drying cabinet or a rotary evaporator as well.

[0054] A residue is obtained from step (d). Said residue may have the appearance of a free flowing powder or form layers and require de-agglomeration. Depending on the nature of the solvent(s) used in step (b) and (c), if applicable, the residue may contain some residual solvent(s), for example up to 5% by weight.

[0055] In step (e), the residue from step (d) is treated thermally at a temperature in the range of from 300 to 450°C. Said treatment may be carried out in a rotary kiln, in a roller kiln, in a fluidized or a moving bed. In laboratory scale experiments, for example with samples of 10 g or less, step (e) may be performed in a muffle oven as well.

[0056] In one embodiment of the present invention, the temperature is ramped up before reaching the desired temperature of from 300 to 450°C. For example, residue the mixture of step (d) is heated to a temperature to 250 to 300°C and then held constant for a time of 10 min to 4 hours, and then it is raised to 325 to 450°C.

[0057] In one embodiment of the present invention, the heating rate in step (e) is in the range of from 0.1 to 10 °C / min.

[0058] In one embodiment of the present invention, step (e) has a duration in the range of from thirty minutes to 24 hours, preferred are 45 to 120 minutes. The time required for reaching the desired temperature is neglected when measuring the duration of step (e).

[0059] In one embodiment of the present invention, step (e) is performed under oxidizing conditions, for example an atmosphere of oxygen-enriched air or pure oxygen. In one embodiment of the present invention, steps (b) to (d) and especially step (e) are carried out under an atmosphere with reduced CO2 content, e.g., a carbon dioxide content in the range of from 0.01 to 500 ppm by weight, preferred are 0.1 to 50 ppm by weight. The CO2 content may be determined by, e.g., optical methods using infrared light. It is even more preferred to perform step (d) under an atmosphere with a carbon dioxide content below detection limit for example with infrared light-based optical methods.

[0060] In one embodiment of the present invention, the heat treatment step (e) is performed in a roller hearth kiln, a pusher kiln or a rotary kiln or a combination of at least two of the foregoing. Rotary kilns have the advantage of a very good homogenization of the material made therein. In roller hearth kilns and in pusher kilns, different reaction conditions with respect to different steps may be set quite easily. In lab scale trials, box-type and tubular furnaces and split tube furnaces are feasible as well.

[0061] By performing the inventive process, cathode active materials may be obtained that show excellent electrochemical performance, especially high-temperature storage stability.

[0062] A further aspect of the present invention is a coated cathode active material, hereinafter also referred to as inventive cathode active material. It is advantageously synthesized according to the inventive process.

[0063] Inventive cathode active materials comprise

[0064] (1) a core material according to the general formula Li i+xTM i-xO2 wherein TM is a combination of metals of which at least 95 mol-% are transition metals, and at least 50 mol-% of TM is nickel, and TM contains at least one of cobalt and manganese, and core (1) is a polycrystalline material,

[0065] (2) a layer on the outer surface comprising a lithiated zirconium compound and lithium carbonate, wherein said core (1) has an average particle diameter (D50) in the range of from 1 to 10 pm, and wherein the layer (2) is homogeneous and has a thickness in the range of from 2 to 10 nm.

[0066] The thickness of the layer may be determined by transmission electron microscopy (“TEM”). The homogeneity of the layer may be determined by X-ray photoelectron spectroscopy (“XPS”).

[0067] TM has been defined above in more detail.

[0068] In one embodiment of the present invention inventive cathode active materials have an average particle diameter (D50) in the range of from 1 to 10 pm, preferably from 2 to 7 pm, more preferably from 3 to 5 pm. The average particle diameter (50) 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. In one embodiment of the present invention inventive cathode active materials have a surface (BET) in the range of from 0.1 to 2.0 m2 / g, determined according to DIN-ISO 9277:2003-05.

[0069] A further aspect of the present invention refers to electrodes comprising at least one 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 discharge behavior. Electrodes comprising at least one cathode active material according to the present invention are hereinafter also referred to as inventive cathodes or cathodes according to the present invention.

[0070] Specifically, inventive cathodes contain

[0071] (A) at least one inventive cathode active material,

[0072] (B) carbon in electrically conductive form,

[0073] (C) a binder material, also referred to as binders or binders (C), and, preferably,

[0074] (D) a current collector.

[0075] In a preferred embodiment, inventive cathodes contain

[0076] (A) 80 to 98 % by weight inventive cathode active material,

[0077] (B) 1 to 17 % by weight of carbon,

[0078] (C) 1 to 15 % by weight of binder material, percentages referring to the sum of (A), (B) and (C).

[0079] 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.

[0080] 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.

[0081] 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 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. 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.

[0082] 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 mol% of at least one further comonomer, for example o-olefins such as propylene, butylene (1 -butene), 1 -hexene, 1 -octene, 1 -decene, 1- dodecene, 1 -pentene, and also isobutene, vinyl aromatics, 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.

[0083] In the context of the present invention, polypropylene is not only understood to mean homopolypropylene, 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 o-olefins such as butylene, 1 -hexene, 1 -octene, 1 -decene, 1 -dodecene and 1 -pentene. Polypropylene is preferably isotactic or essentially isotactic polypropylene.

[0084] 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, divi- nylbenzene, especially 1,3-divinylbenzene, 1 ,2-diphenylethylene and o-methylstyrene.

[0085] Another preferred binder (C) is polybutadiene.

[0086] Other suitable binders (C) are selected from polyethylene oxide (PEO), cellulose, carboxymethylcellulose, polyimides and polyvinyl alcohol.

[0087] 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.

[0088] Binder (C) may be cross-linked or non-cross-linked (co)polymers.

[0089] In a particularly preferred embodiment of the present invention, binder (C) is selected from halogenated (copolymers, especially from fluorinated (copolymers. Halogenated or fluorinated (copolymers are understood to mean those (copolymers which comprise at least one (copolymerized (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), tetrafl uoroethylene-hexafluoropropylene copolymers, vinylidene fluoride-hexafluoropropylene copolymers (PVdF-HFP), vinylidene fluoride-tetrafluoroethylene copolymers, perfluoroalkyl vinyl ether copolymers, ethylene-tetrafluoroethylene copolymers, vinylidene fluoride-chlorotrifluoroethylene copolymers and ethylene-chloro- fluoroethylene copolymers.

[0090] 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.

[0091] Inventive cathodes may comprise 1 to 15% by weight of binder(s), referring to cathode active material. In other embodiments, inventive cathodes may comprise 0.1 up to less than 1% by weight of binder(s).

[0092] 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.

[0093] Embodiments of inventive cathodes have been described above in detail.

[0094] Said anode may contain at least one anode active material, such as carbon (graphite), TO2, lithium titanium oxide, silicon or tin. Said anode may additionally contain a current collector, for example a metal foil such as a copper foil.

[0095] Said electrolyte may comprise at least one non-aqueous solvent, at least one electrolyte salt and, optionally, additives.

[0096] 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.

[0097] Examples of suitable polymers are, in particular, polyalkylene glycols, preferably poly-Ci-C4-alkylene glycols and in particular polyethylene glycols. Polyethylene glycols can here comprise up to 20 mol% of one or more Ci-C4-al ky lene glycols. Polyalkylene glycols are preferably polyalkylene glycols having two methyl or ethyl end caps.

[0098] The molecular weight Mwof suitable polyalkylene glycols and in particular suitable polyethylene glycols can be at least 400 g / mol.

[0099] 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.

[0100] Examples of suitable acyclic ethers are, for example, diisopropyl ether, di-n-butyl ether, 1,2-dimethoxyethane, 1,2- diethoxyethane, with preference being given to 1,2-dimethoxyethane. Examples of suitable cyclic ethers are tetrahydrofuran and 1,4-dioxane.

[0101] Examples of suitable acyclic acetals are, for example, dimethoxymethane, diethoxymethane, 1 ,1 -dimethoxyethane and 1 ,1 -diethoxyethane.

[0102] Examples of suitable cyclic acetals are 1 ,3-dioxane and in particular 1 ,3-dioxolane.

[0103] Examples of suitable acyclic organic carbonates are dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.

[0104] Examples of suitable cyclic organic carbonates are compounds according to the general formulae (II) and (III) 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 tert-butyl, with R2and R3preferably not both being tert-butyl.

[0105] In particularly preferred embodiments, R1is methyl and R2and R3are each hydrogen, or R1, R2and R3are each hydrogen.

[0106] Another preferred cyclic organic carbonate is vinylene carbonate, formula (IV). 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.

[0107] Electrolyte (C) further comprises at least one electrolyte salt. Suitable electrolyte salts are, in particular, lithium salts. Examples of suitable lithium salts are LiPFe, UBF4, LiCICh, LIAsFe, LiCFsSOs, LiC(CnF2n+i 802)3, lithium imides such as LIN(CnF2n+iSO2)2, where n is an integer in the range from 1 to 20, LiN(SO2F)2, Li2SiFe, LiSbFe, Li AICI4 and 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.

[0108] Preferred electrolyte salts are selected from among LiC(CF3SO2)3, LIN(CF3SO2)2, LIPFe, LIBF4, UCIO4, with particular preference being given to LIPFe and LIN(CF3SO2)2.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] Batteries according to the invention display a good discharge behavior, for example at low temperatures (zero °C or below, for example down to -10°C or even less), and a very good cycling behavior as well as a good high-tempera- ture storage behavior.

[0114] 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.

[0115] 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 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.

[0116] A further aspect of the present invention is directed to the use of inventive cathode active materials in or for the manufacture of a lithium ion battery, preferably in or for the manufacture of an all-solid-state lithium ion battery. In particular, inventive cathode active materials may be incorporated into a cathode (A) for an all-solid-state lithium ion battery. Cathodes comprising at least one cathode active material according to the present invention are hereinafter also referred to as inventive cathodes or cathodes according to the present invention.

[0117] Inventive electrochemical cells that are all-solid-state batteries further comprise

[0118] (C) a solid electrolyte comprising lithium, sulfur and phosphorus, hereinafter also referred to as electrolyte (C) or solid electrolyte (C).

[0119] In this context, the term "solid” refers to the state of matter at ambient temperature.

[0120] In one embodiment of the present invention, solid electrolyte (C) has a lithium-ion conductivity at 25 °C of > 0.1 mS / cm, preferably in the range of from 0.1 to 30 mS / cm, measurable by, e.g., by impedance spectroscopy.

[0121] In one embodiment of the present invention, solid electrolyte (C) comprises U3PS4, yet more preferably orthorhombic P-I 3PS4.

[0122] In one embodiment of the present invention, solid electrolyte (C) is selected from the group consisting of LI2S-P2S5, LI2S-P2S5-LII, U2S-P2S5-U2O, Ll2S-P2S5-Li2O-LII, Li2S-SiS2-P2S5-Lil, Li2S-P2S5-ZmSnwherein m and n are positive numbers and Z is a member selected from the group consisting of germanium, gallium and zinc, LI2S-SI S2-U3PO4, Ll2S-SIS2-LiyPOz, wherein y and z are positive numbers, U7P3S11, U3PS4, U11S2PS12, LI7P2S8I, and LI7.r-2sPS6-r.sXr wherein X is chlorine, bromine or iodine, and the variables are defined as follows:

[0123] 0.8 < r < 1.7

[0124] 0 < s < (-0.25 r) + 0.5. A particularly preferred example of solid electrolytes (C) is LiePSsCI, thus, r = 1 .0 and s = zero.

[0125] In one embodiment of the present invention, electrolyte (C) is doped with at least one of Si, Sb, Sn. Si is preferably provided as element. Sb and Sn are preferably provided as sulfides.

[0126] In one embodiment of the present invention, inventive electrochemical cells comprise solid electrolyte (C) in a total amount of from 1 to 50 % by weight, preferably of from 3 to 30 % by weight, relative to the total mass of the cathode (A).

[0127] The invention is further illustrated by working examples.

[0128] General remarks:

[0129] Rpm: revolutions per minute

[0130] Anhydrous ethanol was manufactured under a standard laboratory drying method. It contained 53.9 ppm water (Karl Fischer-titration).

[0131] Anhydrous 1 -propanol was manufactured under a standard laboratory drying method. It contained 57.4 ppm water (Karl Fischer-titration). The amount of ppm refers to ppm by weight unless specified otherwise.

[0132] TEM (transmission electron microscopy):

[0133] For Transmission Electron Microscopy (TEM), particles of the respective cathode active material were embedded in Epofix epoxy resin (Struers). Thin sections were prepared by Ultra-Micotomy at ambient temperature (Leica).

[0134] The surface of the particles was imaged by bright-field high-resolution TEM (Thermo-Fisher Themis Z3.1 operated at 300kV) to identify secondary phases segregating at the surface. The chemical composition of the material in crosssection was analyzed by High-Angle Annular Dark-Field Scanning TEM (HAADF-STEM) in combination with Energy Dispersive X-ray spectroscopy (EDS) (Thermo-Fisher SuperX EDS analysis system). Micrographs and elemental mappings were analyzed using the Thermo-Fisher Velox 3 software.

[0135] The XPS analyses were carried out with a Phi Versa Probe 5000 spectrometer (Ulvac PHI, Ml) using monochromatic Al Ko radiation (49.9 W). The XPS system was calibrated according to ISO 15472.2001. The BE (Binding Energy) of Au 4f7 / 2 is 84.00 eV and that of Cu2p3 / 2 is 932.62 eV.

[0136] All samples were mounted in an argon-fi lied glove box and have been transferred via the vendors transfer vessel under argon to the load lock to prevent any contact with air and moisture.

[0137] All samples were mounted insulated against ground and neutralized in the course of the measurements with the built- in charge neutralizer and measured on three non-overlapping sample positions using a spot size of 200pm x 200 pm with a pass energy of 117 eV and an energy step size of 0.5 eV. High resolution analyses were carried out on the same analysis area with a pass energy of 23.5 eV and an energy step size of 0.1 eV. Total dwell time per energy step was 3000 ms for Ni 2p, 600 ms for O 1s, 600 ms for C 1s, 1800 ms for Zr 3d+P2s,

[0138] 3000 ms for Li 1s, 600 ms for the survey spectrum.

[0139] Spectra have been charge corrected to the position of the Hydrocarbon Peak in C1s being at 284.8 eV for all samples. All Spectra were analyzed using standard XPS-analysis software, namely CasaXPS version 2.3.26rev1 .1 using background subtraction with a background averaging of 5 in the survey spectra and 20 in the detail spectra (Av. Width). Relative sensitivity factors and transmission function as provided by the instrument manufacturer were used for quantification.

[0140] The integration areas and background types for the quantification of the survey spectra are given in the following table:

[0141] Table 1 : overview of signals

[0142] Elemental Quantification was done from the survey spectra and the Zr-to-Ni-ratio was calculated by dividing the two values afterwards.

[0143] Lithium carbonate-concentration was calculated based on the amount of Carbonate-Carbon from a fit of the C1s-Detail spectrum:

[0144] The C 1s signals were fitted with five lines.

[0145] The resulting ratio in % was then renormalized to the atomic concentration of total carbon as quantified from the survey spectrum and the total amount of U2CO3 was then calculated by multiplying this value by a factor of 6 based on the nominal stoichiometry of LI2CO3:

[0146] CcO3(total) = (Cc(surv)*CcO3(detail)) / 100

[0147] C|_i2C*O3 = Cc03(total)*6

[0148] I. Syntheses of cathode active materials

[0149] 1.1 Synthesis of a base cathode active material, step (a.1)

[0150] A base cathode active material was synthesized from a hydroxide precursor, stoichiometry by mixing the dried precursor with LiOH*xH2O, 0.1 mol-% WO3, referring to the sum of Ni+Mn+Co, in a molar ratio Li:(Ni+Co+Mn+W) of 1.04:1. The resulting mixture was then filled into a crucible and heated up with 3 °C / min to 760 °C and held at this temperature for 6 h. The calcined material so obtained was cooled down to ambient temperature and was sieved using a 32 pm sieve. B-CAM.1 was obtained with a D50 of 4.0 m (D90: 7.3 pm).

[0151] 1.2 Coating steps

[0152] 1.2.1 Synthesis of inventive CAM.2

[0153] Step (b.2):

[0154] An amount of 4.8 g zirconium(IV) butoxide solution (80 wt.% in 1 -butanol) was diluted with 44 ml dry ethanol, and then added to B-CAM.1 so that the molar ratio of Zr to TM was 0.5 %. The weight ratio of diluted solution : B-CAM.1 was 1 :5. A muddy mixture was obtained.

[0155] Step (c.2): Solid LiOH-2.46 H2O was added to the muddy mixture from step (b.2). The molar ratio of Zr : Li was 1 :2.

[0156] Steps (d.2) and (e.2): The resultant mixture was dried at 70°C under vacuum for 15 hours and subsequently calcined at 375°C for one hour in pure oxygen atmosphere. The resultant CAM.2 was sieved with a 32 pm mesh size with a sieving loss <0.8%.

[0157] 1.2.2 Synthesis of inventive CAM.3

[0158] Step (b.3) An amount of 4.8 g zirconium(IV) butoxide solution (80 wt.% in 1 -butanol) was diluted with 44 ml dry ethanol and then added to B-CAM.1 so that the molar ratio of Zr to TM was 0.5%. The weight ratio of diluted solution to B-CAM.1 was 1 :5. A muddy mixture was obtained.

[0159] Step (c.3): LiOH 2.46 H2O powder was added to the muddy mixture from step (b.3). The molar ratio of Zr : Li was 1 :2.

[0160] Steps (d.3) and (e.3): The resultant mixture was dried at 70°C under vacuum for 15 hours and subsequently calcined at 375°C for one hour in synthetic air atmosphere. The resultant CAM.3 was sieved with a 32 pm mesh size with a sieving loss of 0.8%.

[0161] 1.2.3: Synthesis of inventive CAM.4

[0162] Step (b.4): In accordance with Table 1, zirconium(IV) propoxide solution (70 wt.% in 1 -propanol) was diluted with 1- propanol and then added to B-CAM.1. The weight ratio of diluted solution : B-CAM.1 was 1 :5. A muddy mixture was obtained.

[0163] Step (c.4): Then, LiOH -2.46 H2O was added to the muddy mixture from step (b.4). The molar ratio of Zr : Li was 1 :2.

[0164] Steps (d.4) and (e.4): The resultant mixture was dried at 80°C under vacuum for 15 hours and subsequently calcined at 375°C for one hour in synthetic air atmosphere. The resultant CAM.4 was sieved with a 32pm mesh size with a sieving loss <0.45%. A TEM-EDX image is shown as Figure 1 .

[0165] 1.2.4: Sol-gel coating, Comparative

[0166] In accordance with Table 2, zirconium(IV) butoxide solution (80 wt.% in 1 -butanol) and lithium ethoxide (95%) were dissolved in dry ethanol with a molar ratio of Zr : Li of 1 :2. For complete dissolution the solution was stirred for 17 hours at 45°C. B-CAM.1 was added to the solution and stirred at 45°C. The weight ratio of solution : B-CAM.1 was 5:1 . After 30 minutes of stirring, water (0.27 wt% vs. B-CAM.1) was added for gelation. After stirring for 1 .5 hours at 45°C, the resultant mixture was dried in a rotary evaporator at 50°C under vacuum and subsequently calcined at 375°C for one hour in synthetic air atmosphere. The resultant C-CAM.5 was sieved with a 32 pm mesh size with a sieving loss of 5.5%. A TEM EDX image is shown as Figure 2.

[0167] 1.2.5: Synthesis of C-CAM.6, comparative

[0168] Step (b.4): In accordance with Table 1, zirconium(IV) propoxide solution (70 wt.% in 1 -propanol) was diluted with 1- propanol and then added to B-CAM.1. The weight ratio of diluted solution : B-CAM.1 was 1 :5. A muddy mixture was obtained.

[0169] Step C-(c.4): Then, dry LiOH powder was added to the muddy mixture from step (b.4). The molar ratio of Zr : Li was 1 :2. Steps C-(d.4) and C-(e.4): The resultant mixture was dried at 80°C under vacuum for 15 hours and subsequently calcined at 375°C for one hour in synthetic air atmosphere. The resultant C-CAM.6 was sieved with a 32 m mesh size with a sieving loss of 15%.

[0170] Table 2: Analytical properties of inventive cathode active materials and of C-CAM.5 and C-CAM.6 n.d.: not determined

[0171] The XPS measurements refer to the outer secondary particle surface

[0172] II. Test cell manufacture and electrochemical performance tests

[0173] 11.1 Test cell manufacture

[0174] In a zirconia ball mill, 690 mg of respective cathode active material, 10 mg of amorphous carbon (C65) and 300 mg of p-LiePSsCI and 10 zirconia balls (10 mm diameter) were mixed at 140 rpm for 30 min to yield a cathode composite. The electrochemical cells used for electrochemical testing use an anode composite containing Li isO^, conductive carbon (C65) and U6PS5CI (30:10:60 wt.-%), separator and the cathode as described above. A custom setup was used for testing of the SSB cells (0 10 mm). In the assembling procedure, p-LiePSsCI (100 mg) was compressed at 62 MPa to yield a solid electrolyte pellet. Then, the anode composite (65 mg, ~4.0 mA h cm-2) was pressed to the solid electrolyte pellet, and finally the cathode composite (10 to 12 mg, 1.7 to 2.0 mA h cm-2) was pressed onto the other side of the solid electrolyte pellet at 437 MPa. During electrochemical testing, a pressure of 81 MPa was maintained. Electrochemical testing was performed in the range between 1 .4 and 2.8 V (1 C = 190 mA / g CAM) versus Li4TisOi2 (equivalent to 3-4.4 V vs Li), charged state: LizTisO^. Initially the tests started with a 2 h open circuit voltage (OCV) period. Then, three cycles of galvanostatic intermittent titration technique (GITT) at C / 3 and 25°C were conducted. Thereafter, the cells were charged in constant current / constant voltage (CCCV) mode (with CV step at 2.8V for 1 hour) and an extended 168 h OCV period at 60°C followed. Subsequently, a GITT discharge step was done. Finally, three more cycles of GITT at 25°C were performed. The tests were done using a MACCOR battery test system. The Area-Specific Resistance (ASR) measurement was conducted at a temperature of 25°C and calculated using the current interruption method as outlined below: ASR = S * (V1 - V2) 1 1, where V1 is the voltage at the end of the current interruption, V2 is the initial voltage value after the continuation of the charge process in galvanostatic mode, I is the charge current employed during the galvanostatic mode and S is the electrode surface area, measured in square centimeters (cm2). The ASR growth (%) was determined before and after the high temperature (60°C) OCV period as follows: ASR growth = ASR(after OCV)-ASR(before OCV). The ASR growth was used for evaluation of the materials.

[0175] Table 3: Electrochemical testing and particle size distributions of inventive cathode active materials and of comparative materials, similar to WO 2023 / 121838

Claims

Patent Claims1 . Process for coating a cathode active material for lithium-ion batteries wherein said cathode active material comprises at least 50 mol-% nickel, referring to metals other than lithium, wherein said process comprises the steps of:(a) providing a cathode active material according to the general formula Li i+xTM i-xO2 wherein x is in the range of from zero to 0.2, TM is a combination of metals of which at least 95 mol-% are transition metals, and at least 50 mol-% of TM is nickel, and TM contains at least one of cobalt and manganese,(b) combining said cathode active material with an anhydrous solution of Zr(OR1)4, wherein R1are same or different and selected from C2-C4-alkyl, straight chain or branched,(c) adding LiO H y H2O, wherein y is in the range of from 0.5 to 3.0,(d) removing the solvent(s),(e) treating the residue thermally at a temperature in the range of from 300 to 450°C.

2. Process according to claim 1 wherein step (d) is performed by evaporation.

3. Process according to claim 1 or 2 wherein the solvent in step (b) is selected from C2-C4-alkanols.

4. Process according to any of the preceding claims wherein TM is a combination of metals according to formula(I)(NiaCobMnc)i-dMd (I) with a being in the range of from 0.6 to 0.95, b being in the range of from 0.025 to 0.2, c being in the range of from zero to 0.2, and d being in the range of from 0.02 to 0.1,M is selected from Mg, Al, Ca, Si, Ti, Zr, Mo, W, Nb, and Ta, a + b + c = 1.

5. Process according to any of the preceding claims wherein TM contains of from 0.5 to 2 mol-% W.

6. Process according to any of the preceding claims wherein the molar ratio of TM to Zr is in the range of from 120:1 to 500:1.

7. Process according to any of the preceding claims wherein the water content of the anhydrous solvent used in step (b) is in the range of from 1 to 500 ppm, determined by Karl-Fischer titration.

8. Process according to any of the preceding claims wherein the molar ratio of Li added in step (d) to Zr added in step (b) is in the range of from 1 : 1 to 3: 1 .

9. Process according to any of the preceding claims wherein cathode active material provided in step (a) has an average particle diameter (D50) in the range of from 2 to 7 pm.

10. Process according to any of the preceding claims wherein cathode active material provided in step (a) is in the form secondary particles that are composed of agglomerates from primary particles.11 . Coated cathode active material comprising(1) a core material according to the general formula Lii+xTMi-xO2 wherein x is in the range of from zero to 0.2, TM is a combination of metals of which at least 95 mol-% are transition metals, and at least 50 mol- % of TM is nickel, and TM contains at least one of cobalt and manganese, and core (1) is a polycrystalline material,(2) a layer on the outer surface comprising a lithiated zirconium compound and lithium carbonate, wherein said core (1) has an average particle diameter (D50) in the range of from 1 to 10 pm, and wherein the layer (2) is homogeneous and has a thickness in the range of from 2 to 10 nm.

12. Coated cathode active material according to claim 11 wherein TM is a combination of metals according to formula (I)(NiaCobMnc)i-dMd (I) with a being in the range of from 0.6 to 0.95, b being in the range of from 0.025 to 0.2, c being in the range of from zero to 0.2, and d being in the range of from 0.02 to 0.1,M is selected from Mg, Al, Ca, Si, Ti, Zr, Mo, W, Nb, and Ta, a + b + c = 1.

13. Use of a coated cathode active material according to claim 11 or 12 for the manufacture of an all-solid state battery.

14. Cathode comprising(A) at least one cathode active material according to claim 11 or 12,(B) carbon in electrically conductive form,(C) a binder material, and,(D) a current collector.

15. Electrochemical cell comprising(1) a cathode comprising a coated cathode active material according to claim 11 or 12,(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, orLi3PS4.

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