Coating composition, application of coating composition and lithium ion battery

Abstract

The present invention relates to a coating composition for a cathode of a lithium ion battery, said coating composition comprising polarity-modified polyvinylidene fluoride as an electrode binder and being substantially free of N-methyl-2-pyrrolidone and / or N-ethyl-2-pyrrolidone. In addition, suitable carbon dispersants are used in composite cathodes. In addition, the invention relates to the use of the coating composition for producing a cathode for a battery and to a battery with the cathode.

Description

Technical Field

[0001] The present invention relates to a coating composition for a cathode of a lithium-ion battery, to the use of the coating composition for preparing the cathode, and to a lithium-ion battery obtainable by using the coating composition. Background Art

[0002] Hereinafter, the term "lithium-ion battery (Batterie)" is used as a synonym for all names commonly used in the prior art for galvanic elements and cells (Zellen) containing lithium, such as lithium-ion cells, lithium-ion battery cells, lithium-ion battery electrodes, lithium polymer cells, lithium-ion polymer cells, lithium batteries, lithium battery electrodes, and lithium-ion accumulators. In particular, rechargeable batteries (secondary batteries) are included. The terms "battery" and "electrochemical cell" are also used as synonyms for the term "lithium-ion battery".

[0003] A lithium-ion battery includes a positive electrode (cathode) and a negative electrode (anode). The cathode has a cathode active material capable of reversibly releasing or accepting lithium ions. In order to assist in the acceptance and release of lithium ions in the cathode active material and to further improve the characteristics of the assembled cathode, additives such as an electrode binder, a conductive additive such as carbon black (English: Carbon Black), and its dispersant are generally incorporated into the cathode. The cathode active material and the additives exist as a composite material, i.e., in the form of a mixture, and the mixture is applied to a cathode current collector made of aluminum. Such cathodes are also described as composite cathodes in the prior art.

[0004] The composition of the composite cathode is an important aspect of the cell chemistry of a lithium-ion battery. By selecting and composing the composite material, certain electrochemical characteristics such as the high-current load capacity or cycle stability of a lithium-ion battery can be adjusted.

[0005] To prepare a composite cathode, a coating composition must first be prepared. The coating composition is also referred to as a cathode slurry or coating material.

[0006] The coating composition is a homogeneous mixture formed by a cathode active material, an electrode binder, conductive carbon, and optionally other additives such as a dispersant, a wetting agent, and a solvent.

[0007] After mixing the above components, the obtained coating composition is applied to a cathode current collector and dried. During the drying process, the existing solvent is removed, and a dried composite material is produced on the surface of the current collector. The composite cathode thus obtained can be installed in a lithium-ion battery.

[0008] The electrochemical properties of a lithium-ion battery can be significantly affected by the properties of the coating composition. A uniform distribution of the constituents of the coating composition is particularly advantageous, since this also ensures a uniform distribution of the solid components in the dried composite material and cathodes with defined properties (such as service life and performance) can be obtained.

[0009] To achieve a uniform distribution of the constituents of the coating composition, N-methyl-2-pyrrolidone (NMP) and / or N-ethyl-2-pyrrolidone (NEP) are commonly used as solvents in the prior art. N-methyl-2-pyrrolidone has a series of advantageous properties for preparing coating compositions for cathodes, such as a vapor pressure suitable for preparing slurries, compatibility with electrode binders, and favorable wetting and dispersion of conductive carbon black.

[0010] However, N-methyl-2-pyrrolidone (NMP) is a CMR substance, whereby it is labeled as a carcinogenic, mutagenic or reprotoxic substance and should fall under the control of the REACH regulation in the future. Therefore, the use of N-methyl-2-pyrrolidone (NMP) in the field of battery production, especially in Europe, is associated with a relatively high technical effort. To work with NMP, government approval is currently required, and strict regulations must be complied with to achieve strict workplace safety. For example, when evaporating on a current collector, N-methyl-2-pyrrolidone (NMP) needs to be recaptured, concentrated and then purified again by special equipment. In addition, personal protective equipment needs to be worn when handling N-methyl-2-pyrrolidone and the production equipment needs to be encapsulated.

[0011] All of the above disadvantages require resource-intensive and capital-intensive technical protection measures, which must be compulsorily taken when handling coating compositions based on N-methyl-2-pyrrolidone (NMP) during battery production.

[0012] For this reason, there is a desire to replace N-methyl-2-pyrrolidone (NMP) as a solvent for cathode coating compositions with alternative solvents having comparable properties.

[0013] A NMP-free coating composition is known from US2020 / 176 777A1. This coating composition comprises a fluoropolymer dispersed in an organic solvent as an electrode binder. This fluoropolymer is in particular polyvinylidene fluoride (PVDF). In addition to the fluoropolymer, an additive polymer consisting of monomers containing at least one heterocycle is proposed. A copolymer formed from polyvinylpyrrolidone and (meth)acrylic acid methyl ester is preferably used. In addition, the proposed coating composition is free of N-methyl-2-pyrrolidone (NMP) and is based on the selection of alternative solvents (such as triethyl phosphate (TEP) and ethyl acetoacetate (EAA)) as co-solvents.

[0014] Other coating compositions without N-methyl-2-pyrrolidone (NMP) are known from the following publications: US2020 136146A1, US2020 176 777A1, US2015 280 238A1, US 2020 295 373A1, US2020 365 873A1, US2020 227 752A1 and US2015280 239A1.

[0015] The above-mentioned publications disclose compositions based on fluoropolymers (such as PVDF) dispersed in solvents without N-methyl-2-pyrrolidone (NMP), respectively. Since N-methyl-2-pyrrolidone (NMP) is removed, an additional additive polymer is added to the known coating composition, which acts as a co-solvent or dispersant for the fluoropolymer and should ensure uniform wetting or distribution of the components even in the NMP-free coating material. Using a fluoropolymer as an electrode binder also requires the addition of an adhesion improver, thereby ensuring sufficient adhesion of the coating composition to the cathode current collector.

[0016] The known coating compositions consist of multiple components that are coordinated with each other and are chemically and electrochemically compatible with each other in order to be able to prepare a cathode with defined mechanical and electrochemical properties. Summary of the Invention

[0017] In this regard, the object of the present invention is to provide a coating composition without NMP, by means of which the above-mentioned disadvantages can be avoided and a cathode can be prepared that meets the electrochemical performance requirements (such as service life) imposed on lithium-ion batteries.

[0018] According to the present invention, the object is achieved by a coating composition for a lithium-ion battery according to claim 1.

[0019] Advantageous embodiments of the coating composition according to the present invention are given in the dependent claims, which can optionally be combined with each other.

[0020] According to the present invention, the object is achieved by a coating composition for a cathode of a lithium-ion battery, wherein the coating composition comprises the following components:

[0021] (A) at least one organic solvent;

[0022] (B) at least one cathode active material;

[0023] (C) at least one conductive carbon;

[0024] (D) At least one carbon dispersant selected from the group consisting of polyvinylpyrrolidone (PVP), polyacrylate, styrene-maleic anhydride copolymer, and copolymers formed from vinylpyrrolidone monomers and (meth)acrylate methyl esters and combinations thereof; and

[0025] (E) At least one fluoropolymer modified with polar groups as an electrode binder;

[0026] Wherein the coating composition does not contain unmodified polyvinylidene fluoride, and wherein the coating composition is substantially free of N-methyl-2-pyrrolidone and / or N-ethyl-2-pyrrolidone.

[0027] The present invention is based on the recognition that in a coating composition free of N-methyl-2-pyrrolidone and / or N-ethyl-2-pyrrolidone, unmodified polyvinylidene fluoride, which is used as an electrode binder in the prior art, can be completely replaced by a fluoropolymer modified with polar groups without adversely affecting the uniformity of the coating composition and the mechanical integrity of the composite cathode. By excluding unmodified polyvinylidene fluoride, a homogeneous material can also be prepared because, in contrast to unmodified polyvinylidene fluoride, a fluoropolymer modified with polar groups can be completely dissolved in the solvent. The reason for this is that the modified fluoropolymer has improved solubility characteristics in a solvent free of NMP compared to unmodified polyvinylidene fluoride. This enables better and more homogeneous mixing with the remaining components of the coating composition. In addition, the polar groups of the modified fluoropolymer can also achieve better adhesion of the composite material obtained from the coating composition to the cathode current collector.

[0028] The polar groups of the modified fluoropolymer also advantageously reduce the fluorine content in the cathode. In addition, the polar anchoring groups of the fluoropolymer improve the adhesion to the metal current collector and can therefore further reduce the binder ratio of the formulation. Suitable polar-modified electrode binders are described, for example, in EP 2 147 029 B1 or EP 3 724 140 B1.

[0029] A homogeneous coating composition in particular has no agglomerates of solid particles.

[0030] In addition, omitting N-methyl-2-pyrrolidone and / or N-ethyl-2-pyrrolidone eliminates a series of the above-mentioned disadvantages from the prior art. The coating composition according to the invention can in particular be handled more simply and is advantageously free of CMR substances, which improves work safety.

[0031] "Unmodified polyvinylidene fluoride" is understood to mean a fluoropolymer consisting only of repeating units selected from the group consisting of vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene and combinations thereof.

[0032] According to a first aspect of the present invention, except for the at least one fluoropolymer modified with a polar group, the coating composition does not contain other fluoropolymers. That is, the fluoropolymer modified with a polar group is the only fluorine-containing polymer in the coating composition.

[0033] Unmodified fluoropolymers especially have insufficient dissolution characteristics and adhesion characteristics, whereby they cannot be satisfactorily dissolved in solvents without NMP. Excluding these compounds thus also improves the uniformity of the coating composition and the adhesion to the metal current collector, which advantageously affects the electrochemical characteristics, service life, cycle stability, reliability, and high current load capacity of the cathode prepared therefrom.

[0034] According to another aspect of the present invention, the fluoropolymer modified with a polar group is completely dissolved in the organic solvent. Additionally, the carbon dispersant preferably exists in a form completely dissolved in the organic solvent. In this way, a particularly uniform coating composition can be achieved. Additionally, the carbon dispersant and / or the fluoropolymer modified with a polar group can interact particularly well with the remaining components dispersed in the solvent of the coating composition, because they can deposit on the solid particles when the solvent evaporates and can prevent the agglomeration of the particles. Additionally, the polar group can anchor itself to the metal current collector.

[0035] In principle, the organic solvent used in the coating composition according to the present invention is not limited, and any solvent known in the prior art that does not contain N-methyl-2-pyrrolidone and / or N-ethyl-2-pyrrolidone and is used for the coating composition of the cathode can be used, as long as the modified fluoropolymer used as the electrode binder can be completely dissolved therein.

[0036] Preferably, the organic solvent is selected from the group consisting of: N-methylpyrrolidone, trialkyl phosphates, dimethyl sulfoxide, tetramethylurea, dimethylacetamide, and dimethylformamide and combinations thereof. That is, multiple solvents among the solvents mentioned can also be used.

[0037] In addition to the above organic solvents, it is advantageously possible to use at least one co-solvent. A co-solvent is understood as a solvent that alone cannot completely dissolve the modified fluoropolymer. However, when combined with one of the above solvents, the co-solvent can assist in achieving good wettability of the conductive carbon.

[0038] Suitable examples of co-solvents are ethyl acetoacetate, γ-butyrolactone, acetone, tetrahydrofuran, n-butyl acetate, propylene carbonate, triacetin, isophorone, and cyclohexanone and combinations thereof.

[0039] In principle, a mixture formed from at least one organic solvent and at least one co-solvent can be conceived.

[0040] The organic solvent particularly preferably includes trialkyl phosphates. The organic solvent very particularly preferably includes triethyl phosphate.

[0041] Triethyl phosphate (TEP) has a series of advantageous properties. On the one hand, triethyl phosphate (TEP) has a higher ignition temperature (480 °C) compared to N-methyl-2-pyrrolidone (NMP) (265 °C), whereby it can be processed more simply. Additionally, triethyl phosphate (TEP) also has a lower enthalpy of evaporation (84.9 Wh·kg) compared to N-methyl-2-pyrrolidone (NMP) (173.5 Wh·kg), whereby the energy consumption during the preparation of the cathode composite material is reduced compared to N-methyl-2-pyrrolidone (NMP). Additionally, in contrast to N-methyl-2-pyrrolidone (NMP), triethyl phosphate (TEP) does not contain CMR substances, whereby its handling during battery production is simplified.

[0042] In a particularly preferred embodiment, the trialkyl phosphate, preferably triethyl phosphate (TEP), is the sole solvent of the coating composition. This embodiment is based on the inventors' recognition that no other solvents need to be added in addition to the trialkyl phosphate, especially triethyl phosphate (TEP), to dissolve the fluoropolymer modified with polar groups and obtain a homogeneous coating composition.

[0043] Additionally, the coating composition according to the invention includes at least one cathode active material as component (B). In principle, the cathode active material is not limited, and any cathode active material known in the prior art that can form a cathode of a lithium-ion battery can be used.

[0044] Therefore, the cathode active materials suitable for use in the cathode can be all cathode active materials known in the prior art that can reversibly absorb or release lithium ions. In particular, the cathode active materials listed below can be used.

[0045] According to one aspect, the cathode active material is preferably selected from the group consisting of: lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium nickel cobalt aluminum oxide (NCA), lithium nickel manganese cobalt oxide (NMC), lithium nickel manganese oxide (NM X ), lithium-rich and manganese-rich lithium nickel manganese cobalt oxide or lithium nickel manganese oxide (LMR), lithium manganese oxide (LMO), lithium manganese spinel (LiMn2O4), LiNi 0.5 Mn 1.5O4 (“high-voltage spinel”), lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium nickel manganese oxide spinel (LNMO) and their derivatives and combinations.

[0046] Lithium nickel manganese cobalt oxide compounds are also known by the abbreviation NMC and sometimes the technical abbreviation NCM is alternatively used. Cathode active materials based on NMC are used in particular in the lithium-ion batteries of electric vehicles. NMC as a cathode active material has a favorable combination of desired properties, such as high specific capacity, reduced cobalt ratio, high high-current capability and high inherent safety, which is manifested, for example, in sufficient stability during overcharge.

[0047] NMC can be described by the chemical formula unit Li α Ni x Mn y Co z O2, where x + y + z = 1, where α represents the numerical value of the stoichiometric ratio of lithium and is usually between 0.8 and 1.15. In the literature, specific stoichiometric ratios are given as three digits, such as NMC-811, NMC-622, NMC-532 and NMC-111. These three digits give the relative contents of nickel:manganese: cobalt, respectively. In other words: for example, NMC 811 is a cathode active material having the general formula unit LiNi 0.8 Mn 0.1 Co 0.1 O2, i.e., where α = 1. Additionally, so-called lithium-rich and manganese-rich NMC with the general formula unit Li 1+E (Ni x Mn y Co z ) 1-E O2 can also be used, where ε is especially between 0.1 and 0.6, preferably between 0.2 and 0.4. Such lithium-rich layered oxides are also referred to as over-lithiated (layered) oxides (OLO).

[0048] According to another aspect, the at least one electrically conductive carbon is selected from the group consisting of: electrically conductive carbon black (carbon black), carbon nanotubes (CNT), graphene, fine-grained synthetic electrically conductive graphite, expanded graphite and carbon nanofibers, especially vapor-grown carbon nanofibers (VGCF) and their combinations.

[0049] Suitable electrically conductive carbon can be obtained under the trade names Super C65 (Imerys), KS6L (Imerys), SFG6L (Imerys), DENKA Black Li-435, HP carbon black (Cabot) and Ketjenblack ECP600JD.

[0050] The coating composition according to the invention comprises at least one electrically conductive carbon. However, it is also conceivable to use a plurality of the above-mentioned electrically conductive carbons in the coating composition.

[0051] The coating composition further comprises at least one carbon dispersant selected from the group consisting of polyvinylpyrrolidone, polyacrylate, styrene-maleic anhydride copolymer, and a copolymer formed from vinylpyrrolidone monomer and (meth)acrylate and combinations thereof.

[0052] The carbon dispersant resists the formation of aggregates of the subdivided electrically conductive carbon. The carbon dispersant is preferably completely soluble in the organic solvent.

[0053] The at least one carbon dispersant is more preferably polyvinylpyrrolidone.

[0054] It is very particularly preferably polyvinylpyrrolidone having an average molecular weight in the range of 30,000 - 1,500,000 g / mol, more preferably in the range of 900,000 - 1,200,000 g / mol.

[0055] By adding the above carbon dispersant to the coating composition according to the invention, the uniformity in terms of the distribution of the electrically conductive carbon in the coating composition is significantly improved. Compared with the coating composition without the carbon dispersant, a significantly improved uniformity of the material and the electrode itself can be found. In particular, the formation of aggregates can be avoided when drying the material on the cathode current collector. Thereby, the cathode or the lithium-ion battery prepared from the coating composition according to the invention has a high surface quality and improved mechanical and electrochemical properties.

[0056] The coating composition according to the invention further comprises at least one fluoropolymer modified with a polar group as an electrode binder.

[0057] The fluoropolymer modified with a polar group is preferably a copolymer comprising at least one repeating unit selected from the group consisting of vinylidene fluoride (-CH2CF2-), tetrafluoroethylene (-CF2-CF2-), and hexafluoropropylene (-CF2CF(CF3)-), and wherein the copolymer comprises at least one repeating unit derived from a monomer of the following formula (I)

[0058]

[0059] In formula (I), R1, R2, and R3 are the same or different and are each independently selected from the group consisting of a hydrogen atom and a C1-C3 hydrocarbon group. R 极性 represents a group with a carbonyl group, a group containing a hydroxyl group, a group with a maleic anhydride group, or -COOROH group, where R OH represents hydrogen or a C1-C5 hydrocarbon group having at least one hydroxyl group.

[0060] In the case of the -COOR OH group, the copolymer comprises at least one repeating unit derived from a (meth)acrylic monomer of the following formula (II)

[0061]

[0062] where R1, R2 and R3 are the same or different and each independently of one another represents a hydrogen atom or a C1-C3 hydrocarbon group, and where R OH represents hydrogen or a C1-C5 hydrocarbon group having at least one hydroxyl group.

[0063] Such copolymers are known in particular from the patent document EP 2 147 029 B1, to which reference is made.

[0064] The monomers are very particularly preferably selected from the group consisting of: hydroxyethyl acrylate (HEA), 2-hydroxypropyl acrylate (HPA) and acrylic acid and combinations thereof.

[0065] Suitable copolymers modified with polar groups are, for example, the compounds known under the trade name Solef from Solvay Speciality Polymers TM company.

[0066] According to another aspect, the coating composition has a solids content in the range from 45 to 80% by weight, preferably from 60 to 77% by weight, particularly preferably from 68 to 77% by weight, based in each case on the total weight of the coating composition. The solids content in particular refers to the solid constituents of the coating composition remaining on the current collector after evaporation of the solvent.

[0067] A coating composition having the above solids content forms a particularly uniform material which can be further processed in a simple manner and dried without agglomerates.

[0068] According to another embodiment, the coating composition comprises the following components, based in each case on the total solids content:

[0069] (A) 90 to 99% by weight, preferably 94 to 98% by weight, of at least one cathode active material, wherein the cathode active material is preferably selected from the group consisting of: lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium nickel cobalt aluminum oxide (NCA), lithium nickel manganese cobalt oxide (NMC), lithium nickel manganese oxide (NMx), lithium-rich and manganese-rich lithium nickel manganese cobalt oxide or lithium nickel manganese oxide (LMR), lithium manganese oxide (LMO), lithium manganese spinel (LiMn2O4), LiNi 0.5 Mn 1.5 O4 (high-voltage spinel), lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium nickel manganese oxide spinel (LNMO) and their derivatives and combinations,

[0070] (B) 0.1 to 5% by weight, preferably 1 to 3% by weight, of at least one electrically conductive carbon, wherein the electrically conductive carbon is preferably selected from the group consisting of: electrically conductive carbon black (carbon black), carbon nanotubes (CNT), graphene, fine-grained synthetic electrically conductive graphite, expanded graphite and carbon nanofibers, especially vapor-grown carbon nanofibers (VGCF) and their combinations;

[0071] (C) 0.1 - 5% by weight, preferably 1 to 2.5% by weight, of at least one fluoropolymer modified with polar groups as an electrode binder; and

[0072] (D) 0.01 - 2% by weight, preferably 0.1 to 0.5% by weight, of at least one carbon dispersant selected from the group consisting of: polyvinylpyrrolidone, polyacrylate, styrene-maleic anhydride copolymer and their combinations;

[0073] wherein the proportions of components (A) to (D) add up to 100%.

[0074] The coating composition having the above solid component proportions has particularly advantageous properties for further processing into a cathode having the mechanical and electrochemical properties desired for use in a lithium-ion battery.

[0075] In another advantageous embodiment of the present invention, the coating composition has a viscosity in the range of 0.1 to 60 Pa s, preferably 5 to 50 Pa s, particularly preferably 15 to 25 Pa s at a shear rate of 0.5 s -1 .

[0076] Viscosity is understood as part of the rheological properties of the coating composition, in particular how a viscous fluid of the material behaves under mechanical loading under specific boundary conditions.

[0077] It can be measured by rotational viscosity measurement method. Using a rheometer of type MCR 302 from Anton Paar company, the viscosity is measured at room temperature (20 °C) in the "dy_auto" state and starting with a plurality of shear rates in the range of, for example, 0.1 to 1000 1 / s.

[0078] According to another aspect, the coating composition has a viscosity in the range of 4 to 20 Pa s, preferably 4 to 10 Pa s, particularly preferably 4 to 6 Pa s, at a shear rate of 50 s -1 .

[0079] In addition, the coating composition can have a viscosity in the range of 2 to 15 Pa s, preferably 5 to 10 Pa s, particularly preferably 8 to 10 Pa s, at a shear rate of 10 s -1 .

[0080] A coating composition having a viscosity distribution characteristic that satisfies at least one of the above sub-ranges is particularly advantageous because such a coating composition can be further processed into a uniform composite material in a simple manner. The viscosity distribution characteristic of the coating composition preferably satisfies at least two, preferably all three, of the above sub-ranges.

[0081] In addition, the present invention also relates to the use of the above coating composition for preparing a battery cathode.

[0082] The proposed coating composition is particularly suitable for preparing the cathode of a lithium-ion battery having defined electrochemical properties because the electrode binder and the carbon dispersant can be completely dissolved in the organic solvent and the remaining solid components of the coating composition are uniformly distributed in the organic solvent and do not tend to agglomerate. In addition, the coating composition does not contain unmodified fluoropolymers such as polyvinylidene fluoride and does not contain N-methyl-2-pyrrolidone, whereby the coating composition can also be processed simply and without cost. Omitting the unmodified fluoropolymer can achieve the preparation of a particularly uniform coating material that does not have agglomerates and adheres well to the cathode current collector. The composite cathode prepared therefrom has high surface quality, good mechanical properties and low roughness, and is particularly suitable for use in lithium-ion batteries.

[0083] In addition, the present invention also relates to a battery having a cathode, an anode and a separator between the cathode and the anode, wherein the cathode is prepared using the above coating composition.

[0084] The separator is arranged between the cathode and the anode and spatially separates them from each other. In addition, the separator is not chemically restricted and any separator known in the prior art can be used. For example, a polyolefin-based separator can be used.

[0085] Suitable polyolefin-based separators are, for example, 2325 three-layer microporous membranes (PP / PE / PP).

[0086] The lithium-ion battery can have a conventional configuration in which the electrodes are connected in parallel. However, it is also conceivable that the electrodes are connected in series. Such a configuration is also referred to as a bipolar configuration. This is preferred because higher voltages and energy densities can thereby be achieved.

[0087] In principle, in the configurations discussed here, the number of electrodes and the separators separating the electrodes is arbitrary. In the sense of the present invention, there is provided at least one anode, at least one cathode, and a separator.

[0088] According to one aspect of the present invention, the anode comprises an anode current collector and at least one anode active material applied to the anode current collector.

[0089] The anode current collector is for electrical contact of the anode active material and is preferably made of a metallic material. For example, the anode current collector can be made of copper, for example in the form of a rolled foil.

[0090] The anode active material can be selected from the group consisting of: carbon-containing materials, silicon, lower oxides of silicon, silicon alloys, metallic lithium, lithium alloys, silicon-carbon composites, aluminum alloys, indium, indium alloys, tin, tin alloys, cobalt alloys, niobium pentoxide, titanium dioxide, titanates (such as lithium titanate (Li4Ti5O 12 )), tin dioxide, and mixtures thereof.

[0091] In addition to the anode active material, the anode can also have additional components and additives, such as an electrode binder for the anode and / or a conductivity improver (such as conductive carbon black, conductive graphite, so-called carbon nanotubes (CNT), carbon fibers, and / or graphene). All common compounds and materials known in the prior art can be used as additional components and additives.

[0092] The electrode binder for the anode is understood hereinafter as a filler having adhesion-promoting properties such that the filler holds the remaining constituents of the anode together and binds to the current collector foil. In this regard, the electrode binder for the anode is not limited, and in principle, any electrode binder known in the prior art that can be used as an electrode binder in the anode of a lithium-ion battery can be used.

[0093] The electrode binder for the anode can in particular be a polymer.

[0094] The electrode binder of the anode can be, for example, a fluorine-containing or fluorine-free polymer, and the polymer is selected from the group consisting of: hydrogenated acrylonitrile butadiene rubber (ANBR), carboxymethyl cellulose (CMC), polyacrylate (PAA), polyvinylpyrrolidone (PVP), polyvinyl acetate (PVAC), polyethylene glycol (PEG), polyethylene oxide (PEO), polymethacrylic acid, polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinylidene fluoride - hexafluoropropylene (PVDF-HFP), polymethacrylate, polyacrylic acid, and styrene-butadiene rubber (SBR), especially vulcanized styrene-butadiene rubber, and combinations thereof.

[0095] According to another aspect, the battery has an electrolyte composition that connects the cathode and the anode to each other in a manner that conducts lithium ions.

[0096] The electrolyte composition can, for example, have a dialkyl carbonate, especially a dialkyl carbonate selected from the group consisting of: diethyl carbonate (DEC), dimethyl carbonate (DMC), or ethyl methyl carbonate (EMC), and combinations thereof.

[0097] The electrolyte composition preferably includes at least one lithium salt (conductive salt) as an additional component, and the lithium salt is preferably selected from the group consisting of: lithium hexafluorophosphate (LiPF6), lithium bis-(fluoromethanesulfonyl)imide (LiFSI), and lithium bis-(trifluoromethanesulfonyl)imide (LiTFSI), and combinations thereof.

[0098] The cathode of the battery is prepared in the case of using the coating composition as described above. Therefore, the cathode is a composite cathode. The composite cathode includes a cathode current collector and a composite material formed by at least one cathode active material, at least one conductive carbon, at least one fluorine-containing polymer modified with a polar group, at least one carbon dispersant, and optionally other additives.

[0099] The cathode current collector is used for electrical contact of the composite material and can be made of aluminum, for example.

[0100] Regarding the composition components of the composite cathode, refer to the above description. Description of the Drawings

[0101] The present invention will be described in detail below with the aid of the drawings. In the drawings:

[0102] - Figure 1 Showing a viscosity comparison between a coating composition with N-methyl-2-pyrrolidone (NMP) based on the prior art and a coating composition with polar-modified polyvinylidene fluoride according to the present invention in a diagram;

[0103] - Figure 2 Graphically show the capacity comparison between two different cells constructed on the cathode side from the coating composition according to the present invention and a coating composition based on N-methyl-2-pyrrolidone (NMP);

[0104] - Figure 3 Graphically show the comparison of energy efficiency between Figure 2 these two cells;

[0105] - Figure 4 Show the comparison of the capacity of these two different cells from Figure 2 on 25 charge-discharge cycles, respectively graphing the average value and standard deviation of three cells for each variant; and

[0106] - Figure 5 Graphically show the capacity comparison between these two different cells from Figure 2 on 200 charge-discharge cycles. Detailed Description of the Invention

[0107] Description of Preferred Embodiments

[0108] The following describes various exemplary coating compositions and cathodes and lithium-ion batteries made from the coating compositions.

[0109] The compositions given are merely exemplary and should not be construed in a limiting sense.

[0110] To prepare the coating composition according to the present invention, in a first step, a fluoropolymer modified with a polar group is mixed with an organic solvent as an electrode binder until the electrode binder has completely dissolved in the solvent. The formation of the binder solution can be optically checked by means of transmitted light illumination.

[0111] In the next step, a carbon dispersant is added to the solution thus obtained and also mixed until a clear solution is produced.

[0112] Subsequently, conductive carbon is added to the obtained solution formed by the electrode binder and the carbon dispersant in the solvent and mixed with the solution to form a homogeneous dispersion. Optionally, the obtained dispersion can also be diluted with a solvent.

[0113] To disperse the conductive carbon in the solution formed by the electrode binder and the carbon dispersant in the solvent, a cathode active material is added in the next step.

[0114] Optionally, the obtained dispersion can be adjusted to a predetermined solid content with an additional solvent.

[0115] Then the components of the coating composition are mixed to form a homogeneous dispersion.

[0116] After mixing, rheological measurements of the viscosity of the coating composition are carried out. If the measured viscosity of the coating composition differs from a predetermined value, the viscosity can be adjusted by evaporation or by adding additional solvent.

[0117] Composition of the coating composition:

[0118] The following components are used to prepare the coating composition according to the invention and the comparative examples:

[0119] TEP: Triethyl phosphate

[0120] NMP: N-Methyl-2-pyrrolidone

[0121] NMC811: Cathode active material of the general formula LiNi 0.8 Mn 0.1 Co 0.1 O2

[0122] Conductive carbon black: Carbon black Super C65

[0123] K30: Polyvinylpyrrolidone

[0124] Zeon BM-730H: Dispersant from Zeon Corporation for use with NMP

[0125] Solef 5140: Polar-modified fluoropolymer from Solvay Speciality Polymers

[0126] The coating composition according to the invention was prepared according to the above method. The preparation of the composition according to the comparative example was carried out according to a similar method, but in which only a dispersion formed from an electrode binder and an organic solvent was obtained.

[0127] The composition of the coating composition according to the invention and the comparative examples is shown in Table 1.

[0128] Table 1 - Coating composition

[0129]

[0130] The data in weight % relate to the solids content.

[0131] A composition identical to the coating composition according to the invention was selected as Comparative Example 1, except that N-methyl-2-pyrrolidone (NMP) was used as the solvent. The dispersant recommended for NMP was used herein and had been dissolved in NMP.

[0132] The solid content of the coating composition of Example 1 is about 70% by weight. The composition according to Comparative Example 1 has a solid content of about 68% by weight.

[0133] The viscosity of the coating composition is determined by rheological measurements. The results can be obtained from Figure 1 the graph in. Example 1 is abbreviated as Bsp.1 and Comparative Example 1 is labeled as Vbsp.1.

[0134] It can be seen that the coating composition according to the invention has the following viscosity distribution characteristics:

[0135] - A viscosity in the range of 0.1 to 60 Pa s, preferably 5 to 50 Pa s, particularly preferably 15 to 25 Pa s, at a shear rate of 0.5 s -1 ;

[0136] - A viscosity in the range of 4 to 20 Pa s, preferably 4 to 10 Pa s, particularly preferably 4 to 6 Pa s, at a shear rate of 50 s -1 ; and

[0137] - A viscosity in the range of 2 to 15 Pa s, preferably 5 to 10 Pa s, particularly preferably 8 to 10 Pa s, at a shear rate of 10 s -1 ;

[0138] Preparation of a battery from the coating composition:

[0139] The batteries prepared using the coating composition according to the invention are compared below with batteries not according to the invention.

[0140] The anodes of the batteries are each composed of a 10 μm thick copper foil, which is coated with an anode composition formed from anode graphite (87.4% by weight), silicon graphite (7.6% by weight), conductive carbon black (1.0% by weight), a polymeric electrode binder (3.5% by weight), and NaCMC (0.5% by weight).

[0141] The cathode composition of the battery is given in Table 2.

[0142] Table 2 - Composition of the cathode

[0143]

[0144] Example 2 is a battery according to the invention, having a cathode obtained using the above coating composition according to the invention. Comparative Example 2 (using NMP based on the prior art) is a battery with a cathode prepared using the coating composition according to Comparative Example 1. Comparative Example 1 in Table 1 thus corresponds to Comparative Example 2 in Table 2.

[0145] The preparation of the cathode and anode will be explained in detail below.

[0146] Preparation of a cathode using the coating composition:

[0147] Prepare to prepare a cathode from the coating composition prepared according to the above method.

[0148] The corresponding coating composition can be applied to the current collector using a doctor blade or a wide slot nozzle. For the preparation of the cathode, the current collector typically consists of aluminum foil.

[0149] Subsequently, the current collector with the applied coating material is dried. During drying, the wet coating material is converted into a dry composite material. The cathode is obtained after drying and optionally calendering (pressing).

[0150] The cathode preferably has a basis weight in the range of 16 to 20 mg / cm 2 and an electrode density of 3 to 5 g / cm 3 .

[0151] Preparation of an anode:

[0152] To prepare the anode of the battery, the anode active material with conductive carbon black and other additives is weighed out and suspended in a solvent formed by water. Subsequently, an electrode binder is added to the suspension.

[0153] The suspension is stirred until a homogeneous anode coating material is present. Preferably, the viscosity of the anode coating material is adjusted to a target viscosity of 5 to 20 Pa s. The viscosity can be changed by adding a solvent or by evaporating the solvent.

[0154] The anode coating material thus obtained can be applied to the current collector foil using a doctor blade or a wide slot nozzle. For the preparation of the anode, the current collector foil typically consists of copper. Subsequently, the anode coating material applied to the current collector foil is dried. During drying, the wet coating material is converted into a dry composite material. The anode is obtained after drying and optionally calendering.

[0155] The anode preferably has a basis weight in the range of 9 to 11 mg / cm 2 and an electrode density of 1 to 2 g / cm 3 .

[0156] Preparation of a battery:

[0157] Mount the above cathode and anode into a single-layer soft-pack battery cell.

[0158] Use Celgard 2325 as the polyolefin separator between the cathode and the anode.

[0159] The electrolyte is a 1 M LiPF6 solution in an organic carbonate, where fluoroethylene carbonate (FEC) serves as a film-forming agent.

[0160] Electrochemical study of the battery

[0161] The cells according to Table 2 undergo various electrochemical measurements. The experimental results of these electrochemical measurements are presented graphically in Figures 2 to 5 as curves.

[0162] Each measurement is carried out as described below.

[0163] The cell is charged at a constant current until the upper cut-off voltage (4.2 V) and then charged at a constant voltage until the current intensity reaches the cut-off criterion or the time for potentiostatic subsequent charging (CCCV charging). Discharge is carried out at a constant current until the lower cut-off voltage (2.8 V) is reached. Figure 2 and Figure 3 The C-rates in the charging and discharging directions are 0.1 C, respectively. Figure 4 The C-rates in the "rate test" in the discharging direction are given in the table (similarly corresponding in the charging direction). In Figure 5 the C-rate is 1 C in both directions.

[0164] In the figure, Example 2 is abbreviated as Bsp.1 and Comparative Example 2 is given as Vbsp.2.

[0165] For all parameters, the cells according to the invention exhibit electrochemical performance comparable to that of the cells prepared from a coating composition based on N-methyl-2-pyrrolidone (NMP) according to Comparative Example 2. Thus, the coating composition according to the invention meets the performance requirements for lithium-ion batteries without relying on carrier solvents such as N-methyl-2-pyrrolidone (NMP) and / or N-ethyl-2-pyrrolidone (NMP).

Claims

1. A coating composition for a cathode of a lithium-ion battery, wherein the coating composition comprises the following components: (A) At least one organic solvent; (B) At least one cathode active material; (C) At least one electrically conductive carbon; (D) At least one carbon dispersant selected from the group consisting of polyvinylpyrrolidone, polyacrylate, styrene-maleic anhydride copolymer, and copolymers formed from vinylpyrrolidone monomers and (meth)acrylic acid methyl esters and combinations thereof; and (E) At least one fluoropolymer modified with a polar group as an electrode binder; wherein the coating composition does not contain unmodified polyvinylidene fluoride, and wherein the coating composition is substantially free of N-methyl-2-pyrrolidone and / or N-ethyl-2-pyrrolidone.

2. The coating composition according to claim 1, wherein Except for the at least one fluoropolymer modified with a polar group, the coating composition does not contain other fluoropolymers.

3. The coating composition according to claim 1 or 2, characterized in that, The fluoropolymer modified with a polar group and optionally the carbon dispersant are completely dissolved in the organic solvent.

4. The coating composition according to any one of the preceding claims, characterized in that The organic solvent is selected from the group consisting of methylpyrrolidone, trialkyl phosphates, dimethyl sulfoxide, tetramethylurea, dimethylacetamide, and dimethylformamide and combinations thereof.

5. The coating composition according to any one of the preceding claims, characterized in that, The organic solvent is a trialkyl phosphate, preferably triethyl phosphate.

6. The coating composition according to any one of the preceding claims, characterized in that, The electrically conductive carbon is selected from the group consisting of conductive carbon black (carbon black), carbon nanotubes (CNT), graphene, fine particulate synthetic conductive graphite, expanded graphite, and carbon nanofibers, especially vapor-grown carbon nanofibers (VGCF) and combinations thereof.

7. The coating composition according to any one of the preceding claims, characterized in that, The carbon dispersant is polyvinylpyrrolidone, preferably polyvinylpyrrolidone having an average molecular weight in the range of 30,000 - 1,500,000 g / mol, more preferably in the range of 900,000 - 1,200,000 g / mol.

8. The coating composition according to any one of the preceding claims, characterized in that, The fluoropolymer modified with a polar group is a copolymer comprising at least one repeating unit selected from the group consisting of vinylidene fluoride (-CH2CF2-), tetrafluoroethylene (-CF2-CF2-), and hexafluoropropylene (-CF2CF(CF3)-), and wherein the copolymer comprises at least one repeating unit derived from a (meth)acrylic monomer of formula (I) wherein R1, R2 and R3 are the same or different and each independently of one another represents a hydrogen atom or a C1-C3 hydrocarbon group, R 极性 represents a group having a carbonyl group, a group having a hydroxyl group, a group having a maleic anhydride group or a -COOR OH - group, and wherein R OH represents hydrogen or a C1-C5 hydrocarbon group having at least one hydroxyl group.

9. The coating composition according to any one of the preceding claims, characterized in that, Respectively based on the total weight of the coating composition, the coating composition has a solids content in the range of 45 to 80% by weight, preferably 60 to 77% by weight, particularly preferably 68 to 77% by weight.

10. The coating composition according to any one of the preceding claims, characterized in that, Respectively based on the total solids content, the coating composition comprises the following components: (A) 90 to 99% by weight, preferably 94 to 98% by weight, of at least one cathode active material, wherein the cathode active material is preferably selected from the group consisting of: lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium nickel cobalt aluminum oxide (NCA), lithium nickel manganese cobalt oxide (NMC), lithium nickel manganese oxide (NMx), lithium-rich and manganese-rich lithium nickel manganese cobalt oxide or lithium nickel manganese oxide (LMR), lithium manganese oxide (LMO), lithium manganese spinel (LiMn2O0), LiNi 0.5 Mn 1.5 O2 (high voltage spinel), lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium nickel manganese oxide spinel (LNMO) and their derivatives and combinations, (B) 0.1 - 5% by weight, preferably 1 to 3% by weight of at least one electrically conductive carbon, which is preferably selected from the group consisting of conductive carbon black (carbon black), carbon nanotubes (CNT), graphene, fine particulate synthetic conductive graphite, expanded graphite, and carbon nanofibers, especially vapor-grown carbon nanofibers (VGCF) and combinations thereof; (C) 0.1 - 5% by weight, preferably 1 to 2.5% by weight of at least one fluoropolymer modified with a polar group as an electrode binder; and (D) 0.01 to 2% by weight, preferably 0.1 to 0.5% by weight, of at least one carbon dispersant, which is preferably selected from the group consisting of polyvinylpyrrolidone, polyacrylate, styrene-maleic anhydride copolymer, and combinations thereof; wherein the proportions of components (A) to (D) add up to one hundred percent.

11. The coating composition according to any one of the preceding claims, characterized in that, The coating composition has a viscosity in the range of 0.1 to 60 Pa s, preferably 5 to 50 Pa s, particularly preferably 15 to 25 Pa s at a shear rate of 0.5 s -1 .

12. The coating composition according to any one of the preceding claims, characterized in that, The coating composition has a viscosity in the range of 4 to 20 Pa s, preferably 4 to 10 Pa s, particularly preferably 4 to 6 Pa s, at a shear rate of 50 s -1 .

13. The coating composition according to any one of the preceding claims, characterized in that, The coating composition has a viscosity in the range of 2 to 15 Pa s, preferably 5 to 10 Pa s, particularly preferably 8 to 10 Pa s at a shear rate of 10 s -1 .

14. Use of the coating composition according to any one of claims 1 to 13 for the preparation of a battery cathode.

15. A battery having a cathode, an anode, and a separator between the cathode and the anode, wherein the cathode is prepared using the coating composition according to any one of claims 1 to 13.

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