Water-based binder for coating an anode current collector for a secondary li-ion battery, process to make the binder, anode active material slurry and anode comprising the binder, as well as use of the binder

Abstract

The present invention relates to a water-based binder (1) for coating an anode current collector for a secondary Li-ion battery, wherein the binder (1) comprises an emulsion polymerizate (2) being a copolymerizate of a) 35 to 70 wt.% of styrene, b) 20 to 47 wt.% of aliphatic conjugated diene-based monomer, c) 1 to 15 wt.% of (meth)acrylonitrile, d) 0.1 to 5 wt.% of itaconic acid and / or fumaric acid, e) 0 to 20 wt.% of one or more of auxiliary monomer 1, and1 f) 0 to 5 wt.% of one or more of auxiliary monomer 2, wherein the auxiliary monomers 1 and 2 are selected from a specific list, and wherein the weight portions (wt.%) of the components a) to f) are based on the solid content of the emulsion polymerizate (2) and sum up to 100 wt.%. Claimed is also a process to make the water-based binder (1), an anode active material slurry for coating an anode current collector for a secondary Li-ion battery and an anode for the secondary Li-ion battery comprising the water-based binder (1), as well as the use of the water-based binder (1).

Description

[0001] Water-based binder for coating an anode current collector for a secondary Li-ion battery, process to make the binder, anode active material slurry and anode comprising the binder, as well as use of the binder.

[0002] The present invention relates to a water-based binder for coating an anode current collector for a secondary Li-ion battery, a process to make the waterbased binder, an anode active material slurry for coating an anode current collector for a secondary Li-ion battery, an anode for the secondary Li-ion battery comprising the water-based binder, as well as the use of the waterbased binder.

[0003] Rechargeable Li-ion batteries, also called Li-ion accumulators, secondary Li- ion batteries, and in short just Li-ion batteries, have obtained in recent times increased relevance and have become essential parts in many smaller and larger devices of modern life and beyond. Li-ion batteries are - among others - lighter, smaller, recharge faster and have a higher specific energy than conventional lead-acid batteries. Non-limiting devices and uses of today’s rechargeable Li-ion batteries include smartwatches and smartphones, laptops, electric vehicles, including cars and electrical bikes, emergency power backup systems, reliable and lightweight marine performance systems, solar power storage devices, surveillance or alarm systems in remote locations, and external portable power packs.

[0004] Li-ion batteries are composed of one or more power-generating compartments called cells. Each cell is composed of a negative electrode, i.e. , anode, a positive electrode, i.e., cathode, a separator, and an electrolyte.

[0005] The anode and cathode are separated by a separator, which keeps the two electrodes apart to prevent an electrical short circuit, while also allowing the movement of lithium ions between the anode and the cathode, during charge and discharge. The separator has for that reason a porous microstructure, a good mechanical strength, and an excellent chemical resistance to the electrolyte.

[0006] The electrolyte of Li-ion batteries comprises typically lithium salts, e.g., LiPFe, dissolved in organic liquid solvents, e.g., ethylene carbonate and dimethyl carbonate. During discharge of the Li-ion battery, the Li-ions of the electrolyte move from the negative electrode, i.e., anode, through the solvent of the electrolyte to the positive electrode, i.e., cathode, and back when charging.

[0007] Each of the electrodes comprise a current collector, which may be a thin metal film, onto which an active material layer adheres - either on one or both sides of the current collector. The active material layer of the anode comprises typically graphite, a thickener and a binder, and the active material layer of the cathode comprises typically a Li-metal oxide, having the general structure of LiMCh, wherein M stands for one or more transition metals, and a binder, such as polyvinylidene fluoride (PVDF).

[0008] The active material, which forms the active material layer of the anode, i.e., the anode active material, is most typically applied onto the anode current collector by coating and in the form of an anode active material slurry, followed by drying. The binder, preferably in the form of a water-based binder to avoid unwanted organic volatile compounds (VOC’s), provides - among others - adhesion to the anode current collector. It is needless to say that a high adhesion is key to good battery properties, including for electrode slitting, since otherwise delamination of the electrode may occur. Furthermore, superior adhesion is an important element for a long battery life. In addition, the binder affects also the Direct Current Internal Resistance (DCIR) of an electrode. A low DCIR-value is highly favorable for battery performance. Thus, there is a high demand for further improving the performance of batteries, in particular the performance of the anode current collector of a secondary Li-ion battery, and specifically the adhesion of the anode coating to the anode current collector as well as further reduce the Direct Current Internal Resistance (DCIR) of the coated anode.

[0009] Surprisingly, it was found that this demanding problem can be solved with a water-based binder (1 ) for coating an anode current collector for a secondary Li-ion battery, wherein the binder (1 ) comprises an emulsion polymerizate (2) being a copolymerizate of a) 35 to 70 wt.% of styrene, b) 20 to 47 wt.% of aliphatic conjugated diene-based monomer, c) 1 to 15 wt.% of (meth)acrylonitrile, d) 0.1 to 5 wt.% of itaconic acid and / or fumaric acid, e) 0 to 20 wt.% of one or more of auxiliary monomer 1 selected from the group of hydroxy alkyl (meth)acrylate, vinyl acetate, vinyl propionate, and C9-C12 vinyl versatate; and f) 0 to 5 wt.% of one or more of auxiliary monomer 2 selected from the group of (meth)acrylic acid, N-functionalized derivatives of (meth)acrylamides, vinyl trialkoxysilanes, and olefinic crosslinking monomer comprising 2 or more olefinic groups, wherein the weight portions (wt.%) of the components a) to f) are based on the solid content of the emulsion polymerizate (2) and sum up to 100 wt.%.

[0010] Claimed also is a process to make the water-based binder (1 ) according to the invention, wherein the monomers a) to f) are emulsion polymerized in a semi-batch mode in an aqueous environment and in absence of organic solvents. Furthermore, claimed is also the anode active material slurry for coating an anode current collector for a secondary Li-ion battery comprising an anode active material, a conductive material, a thickener, and a water-based binder, wherein the water-based binder is the water-based binder (1 ) according to the invention.

[0011] In addition, claimed is also the anode for the secondary Li-ion battery, wherein the anode comprises an anode active material layer coated on the anode current collector, wherein the anode active material layer is the anode active material slurry according to the invention, when applied onto the anode current collector and dried, and thus comprises the binder (1 ) of the invention.

[0012] Claimed is also the use of the water-based binder (1 ) according to the invention as binder for coating an anode current collector for a secondary Li- ion battery, in paper coating, adhesives, lamination adhesives, open mesh fabrics, board coating, flexible packaging, regenerated leather, cellulose sheet and / or paper impregnation.

[0013] The water-based binder (1 ), i.e., binder (1 ), the process to make the binder (1 ), the anode active material slurry, the anode comprising the binder (1 ), as well as the use of the binder (1 ) according to the invention exhibit numerous advantages.

[0014] The binder (1 ) is stable over months, low in viscosity and volatile organic compounds (VOC’s) and does not sediment. Furthermore, the binder provides an excellent film-formation at drying temperatures of the different applications, or even lower. In addition, the binder is compatible with a broad range of ingredients, in particular with the ingredients used for coating the anode current collector. And most importantly, the binder (1 ) - although employed in low concentrations of e.g., 1 wt.% only - provides improved adhesion, determined as 180° peel adhesion force, i.e., 180° peel adhesion strength, as well as a reduced, i.e., improved, Direct Current Internal Resistance (DCIR) of the coating on the anode current collector for a secondary Li-ion battery.

[0015] The process to make the binder (1 ) is straightforward and can be completed within a - compared to other emulsion polymerization processes - short time at high conversion and low grit formation. Hence, the process parameters are not complex, and the used ingredients are well known in this industry and not difficult to handle. Thus, the process according to the invention results in binder (1 ) having a continuously high quality.

[0016] The claimed anode active material slurry comprising the binder (1 ) does not sediment nor flocculate and its viscosity is stable for several days. It can be easily processed and applied onto the anode current collector and thereupon further processed, e.g., dried.

[0017] The thus obtained and claimed anode for the secondary Li-ion battery, which is coated with the anode active material slurry and dried thereafter, and which comprises - typically in low concentrations as e.g., 1 wt.% - the binder (1 ) according to the invention, exhibits improved adhesion, determined as 180° peel adhesion force, as well as a reduced, i.e., improved, Direct Current Internal Resistance (DCIR).

[0018] In addition, it was surprising to find that the binder (1 ) according to the invention provides superior properties in a number of additional application fields and thus can be used therein.

[0019] The WO-A-2024 / 009866 discloses a binder composition for an electricity storage device comprising 50 to 99 wt.% of a conjugated diene, 1 to 19 wt.% of a,[3-unsaturated nitrile, and e.g., 1 to 30 wt.% of an aromatic vinyl compound. This binder has due to the high content of conjugated diene and low content of aromatic vinyl compound a distinct lower glass transition temperature (Tg) than the binder according to the present invention. Thus, it is particularly suited for slurries to coat the positive electrode, i.e. , cathode, of the secondary Li-ion battery electrode, and not the anode. Slurries to coat the cathode comprise most typically metal oxides, wherein one metal is Lithium. Hence, said slurries are highly ionic, wherein the slurries to coat anodes comprise non-ionic materials such as graphite and carbon black. Therefore, the requirements for binders for cathode coatings differ significantly from binders for anode coatings.

[0020] The WO-A-2023 / 227369 refers to the use of an aqueous dispersion of a polymer P obtainable by radically initiated emulsion polymerization, which comprises polymerizing 40 to 75 wt.% of a vinylaromatic compound, 22.5 to 55 wt.% of a conjugated aliphatic diene, 0.5 to 10 wt.% of an ethylenically unsaturated monomer containing acid groups, 1 to 5 wt.% of a (meth)acryl- amide and 1 to 10 wt.% of a (meth)acrylonitrile. Hence, the presence of a (meth)acrylamide in the aqueous dispersion is essential, wherein the claimed composition does not contain (meth)acrylamide. As a matter of facts, it was found that (meth)acrylamides have a negative effect on 180° peel adhesion forces and should therefore be avoided.

[0021] The water-based binder (1 )

[0022] The water-based binder (1 ), i.e., binder (1 ), according to the invention is particularly suited for coating an anode current collector for a secondary Li- ion battery.

[0023] The binder (1 ) comprises an emulsion polymerizate (2) being a copolymerizate, i.e., consisting, of a) 35 to 70 wt.% of styrene, b) 20 to 47 wt.% of aliphatic conjugated diene-based monomer, such as butadiene, and / or isoprene, c) 1 to 15 wt.% of (meth)acrylonitrile, d) 0.1 to 5 wt.% of itaconic acid and / or fumaric acid, e) 0 to 20 wt.% of one or more of auxiliary monomer 1 selected from the group of hydroxy alkyl (meth)acrylate, vinyl acetate, vinyl propionate, and C9-C12 vinyl versatate; and f) 0 to 5 wt.% of one or more of auxiliary monomer 2 selected from the group of (meth)acrylic acid, N-functionalized derivatives of (meth)acrylamides, vinyltrialkoxysilanes, and olefinic crosslinking monomer comprising 2 or more olefinic groups, wherein the weight portions (wt.%) of the components a) to f) are based on the solid content of the emulsion polymerizate (2) and sum up to 100 wt.%.

[0024] Preferable non-limiting examples of auxiliary monomer 1 being a hydroxy alkyl (meth)acrylate include hydroxy C2- to C6- alkyl (meth)acrylate, in particular hydroxy C2- to C4- alkyl (meth)acrylate, and mixtures thereof, wherein hydroxy ethyl (meth)acrylate and hydroxy propyl (meth)acrylate are particularly preferred.

[0025] Preferable, non-limiting examples of auxiliary monomer 2 being a N- functionalized derivatives of (meth)acrylamides include N-methylol (meth)acrylamide, N-[(3-dialkylamino)alkyl](meth)acrylamide, wherein the alkyl group may be a C1 - to C6- alkyl group, N-[(3-dimethylamino)- propyl]methacrylamide (DMAPMA), N-[(3-dimethylamino)ethyl]methacryl- amide (DMAEMA), 2-Acrylamido-2-methylpropane sulfonic acid and its alkali-salts, N-[3-(Trialkoxysilyl)-alkyl](meth)acrylamide, wherein the alkyl group may be a C1- to C6- alkyl group, N-[3-(Trimethoxysilyl)-propyl]acryl- amide, and mixtures thereof. It is noted that N-functionalized derivatives of (meth)acrylamides differ significantly from the unsubstituted (meth)acrylamide, since the functionalization provides e.g., an ionic character, a steric hindrance, and / or a crosslinking functionality to the emulsion polymerizate (2). Thus, the N- functionalized derivatization contributes to latex stabilization and / or allows the polymer to crosslink, which improves cohesion and peel adhesion forces of the applied and dried anode active material layer comprising the emulsion polymerizate (2). Hence, the benefit of the N-functionalized derivatization overrules the somewhat negative effect of the unsubstituted amide-group of (meth)acrylamide.

[0026] Preferable, non-limiting examples of auxiliary monomer 2 being a vinyl- trialkoxysilanes include vinyltrialkoxysilanes with a C1- to C4-alkoxy group, in particular a C1- to C3-alkoxy group, such as vinyltrimethoxysilane, vinyltriethoxysilane, and tripropoxysilane, and mixtures thereof.

[0027] Preferable, non-limiting examples of auxiliary monomer 2 being an olefinic crosslinking monomer comprising 2 or more olefinic groups include di- or tri- (meth)acrylate, allyl (meth)acrylate, polyalkylene and alkylene glycol di(meth)acrylate, such as polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, tri- and tetraethylene glycol di(meth)acrylate and ethylene glycol (meth)acrylate; 1 ,3-butanediol di(meth)acrylate, 1 ,4-butanediol di(meth)acrylate, glycerol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, diurethane di(meth)acrylate, divinyl benzene, 1 ,6-hexanediol di(meth)acrylate, trimethylolpropane diallyl ether, tetraallyl pentaerythritol, triallyl pentaerythritol, diallyl pentaerythritol, diallyl phthalate, triallyl cyanurate, bisphenol A diallyl ether (meth)acrylamide, methylene bisacrylamide, allyl sucrose, and mixtures thereof.

[0028] Hence, the emulsion polymerizate (2) does not include alkyl (meth)acrylate monomers, such as methyl methacrylate or butyl acrylate; nor alpha-methyl styrene dimer; nor a monomer containing glycidyl groups, such as glycidyl (meth)acrylate. In addition, the emulsion polymerizate (2) does not contain (meth)acrylamide.

[0029] Preferably, the emulsion polymerizate (2) of the water-based binder (1 ) is a copolymerizate, i.e. , is consisting, of a) 40 to 70 wt.%, in particular 45 to 70 wt.%, of styrene, b) 25 to 45 wt.%, preferably 30 to 45 wt.%, of butadiene, and / or isoprene, c) 1 to 12 wt.%, in particular 1 to 10 wt.%, of (meth)acrylonitrile, d) 0.2 to 4 wt.%, in particular 0.5 to 3 wt.%, of itaconic acid and / or fumaric acid, e) 0 to 15 wt.%, in particular 0 to 10 wt.%, of one or more of auxiliary monomer 1 selected from the group of hydroxy alkyl (meth)acrylate, vinyl acetate, vinyl priopionate, and C9-C12 vinyl versatate; and f) 0 to 5 wt.%, in particular 0 to 4 wt.%, of one or more of auxiliary monomer 2 selected from (meth)acrylic acid, N-functionalized derivatives of (meth)acrylamides, vinyltrialkoxysilanes, and olefinic crosslinking monomer comprising 2 or more olefinic groups.

[0030] In one preferred embodiment, the emulsion polymerizate (2) does not include a hydroxy alkyl (meth)acrylate, such as e.g., hydroxy ethyl (meth)acrylate or hydroxy propyl (meth)acrylate.

[0031] In another preferred embodiment, the emulsion polymerizate (2) of the waterbased binder (1 ) is a copolymerizate, i.e., is consisting, of

[0032] - 35 to 70 wt.%, in particular 40 to 70 wt.%, in particular 45 to 70, of styrene,

[0033] - 20 to 47 wt.%, in particular 25 to 45 wt.%, in particular 30 to 45, of butadiene, - 1 to 15 wt.%, in particular 1 to 12 wt.%, in particular 1 to 10 of acrylonitrile,

[0034] - 0.1 to 5 wt.%, in particular 0.2 to 4 wt.%, in particular 0.5 to 3, of itaconic acid, and

[0035] - 0 to 5 wt.%, in particular 0 to 4 wt.%, in particular 0 to 3, of one or more auxiliary monomers 2 selected from (meth)acrylic acid, N- functionalized derivatives of (meth)acrylamides, vinyltrialkoxy- silanes, and olefinic crosslinking monomer comprising 2 or more olefinic groups.

[0036] The water-based binder (1 ) may further comprise 0 to 50 wt.%, preferably 0 to 40 wt.%, based on the solid content of the binder (1 ), of additives (3), wherein the additives (3) include preferably water-soluble polymers, antioxidants, dispersants, surfactants, and / or rheology modifiers, wherein the antioxidants, dispersants, surfactants, and / or rheology modifiers are most preferably added in an amount of up to 10 wt.%, based on the solid content of the binder (1 ). Thus, it is possible to further improve the performance of the binder (1 ), and / or optimize the binder (1 ) for individual applications.

[0037] The emulsion polymerizate (2) of the water-based binder (1 ) may be a phased copolymerizate, i.e. , it may comprise two or more different polymer phases, such as a core-shell polymerizate. The polymerizate (2) is, however, preferably a one-phase copolymerizate, in particular a seeded one-phase copolymerizate. Thus, the emulsion copolymerizate does most typically not exhibit a morphology and therefore has one glass transition temperature (Tg) only. Since a seed, i.e., a seed latex, is added only in small amounts, most typically 5 wt.% or lower, the seed latex does neither contribute to form a morphology nor a separate glass transition temperature (Tg).

[0038] According to the invention, a copolymerizate comprising 2 or more polymer phases reveals two or more glass transition temperatures (Tg), wherein each phase comprises less than 80% of all detected phases. Thus, the phase detected by glass transition temperature measurements of the one-phase copolymerizate according to the invention covers 80% or more of all detected phases.

[0039] It was found that the absence of alkyl (meth)acrylate monomers and / or (meth)acrylamide results in improved peel adhesion forces. Hence, the emulsion polymerizate (2) of the water-based binder (1 ) does not contain, i.e., is free of, alkyl (meth)acrylates such as methyl methacrylate, and / or (meth)acrylamide.

[0040] Preferably,

[0041] - the monomers a) to f) of the emulsion polymerizate (2) are selected to result in a glass transition temperature (Tg) of the emulsion polymerizate (2) of between -20°C and +40°C, preferably between 0°C and +30°C, in particular between +5°C and +25°C, determined according to DIN 51007 using a heating rate of 10°C / min., wherein the midpoint of the segment of the mid-tangent between the extrapolated baselines is reported,

[0042] - the solids content of the emulsion polymerizate (2) is between 35 to 65 wt.%, preferably between 40 to 60 wt.%, in particular between 45 to 55 wt.%, and / or

[0043] - the volume mean of the particle size (MV) of the emulsion polymerizate (2) is between 50 and 300 nm, preferably between 75 and 250 nm, in particular between 100 and 200 nm, determined by dynamic light scattering.

[0044] The skilled person is well able to adapt the ingredients of the emulsion polymerization recipe, such as the monomers, to result in the intended glass transition temperature (Tg), solids content and particle size (MV) of the emulsion polymerizate (2). Most typically, the emulsion polymerizate (2) is stabilized with a stabilizer, wherein the stabilizer may be a surfactant and / or a colloidal stabilizer. The one or more stabilizers may be added prior to the addition of any monomer charge, during the addition of a monomer charge or a combination thereof.

[0045] Non-limiting examples of suitable nonionic surfactants, i.e., emulsifier, include tert-octylphenoxyethylpoly(39)-ethoxyethanol, dodecyl oxypoly (10) ethoxy ethanol, nonyl phenoxyethyl-poly(40)ethoxyethanol, polyethylene glycol 2000 monooleate, ethoxylated castor oil, fluorinated alkyl esters and alkoxylates, polyoxyethylene (20) sorbitan monolaurate, sucrose mono- cocoate, di(2-butyl)phenoxypoly(20)ethoxyethanol, hydroxyethyl cellulosepolybutyl acrylate graft copolymer, dimethyl silicone polyalkylene oxide graft copolymer, poly(ethylene oxide) poly(butyl acrylate) block copolymer, block copolymers of propylene oxide and ethylene oxide, 2,4,7,9-tetramethyl-5- decyne-4,7-diol ethoxylated with 30 moles of ethylene oxide, N-polyoxy ethylene(20)lauramide, N-lauryl-N-polyoxyethylene(3)amine and / or poly(10) ethylene glycol dodecyl thioether.

[0046] Non-limiting examples of suitable anionic surfactants include sodium lauryl sulfate, sodium dodecyl benzene sulfonate, potassium stearate, sodium dioctyl sulfo succinate, sodium dodecyldiphenyloxide disulfonate, nonyl- phenoxyethylpoly(l)ethoxyethyl sulfate ammonium salt, sodium styrene sulfonate, sodium dodecyl allyl sulfosuccinate, linseed oil fatty acid, sodium or ammonium salts of phosphate esters of ethoxylated nonylphenol, sodium octoxynol-3-sulfonate, sodium cocoyl sarcocinate, sodium 1 -alkoxy-2 - hydroxypropyl sulfonate, sodium alpha-olefin (C14-16)sulfonate, sulfates of hydroxyalkanols, tetrasodium N-(1 ,2-dicarboxy ethyl)-N-octadecylsulfo- succinamate, disodium N-octadecylsulfosuccinamate, disodium alkyl amido polyethoxy sulfosuccinate, disodium ethoxylated nonylphenol half ester of sulfo succinic acid and the sodium salt of tert-octylphenoxyethoxy- poly(39)ethoxyethyl sulfate. Non-limiting examples of suitable colloidal stabilizers include one or more of polyvinyl alcohol (PVOH), i.e., partly hydrolyzed polyvinyl acetate with a degree of hydrolysis of e.g., 80 to 95 mole-%, polyvinyl pyrrolidone (PVP), ethylene glycol, EO / PO block polymers, polyacrylic acids (PAA) with a MW up to e.g., 100’000 Da or even higher, polysaccharides and their derivatives, in particular polysaccharide ethers, such as cellulose, starch, guar gum, xanthan gum, agar-agar, and dextrin, as well as their alkyl ether, hydroxy alkyl ether, and carboxy alkyl ether, in particular methyl, ethyl and propyl ether, hydroxy methyl, hydroxy ethyl, and hydroxy propyl ether, as well as carboxymethyl ether. The colloidal stabilizers may be of anionic or non-ionic nature.

[0047] Preferably, the emulsion polymerizate (2) is stabilized with an anionic stabilizer (4) as listed above, preferably in an amount of 0.1 to 3 wt.%, in particular 0.1 to 2 wt.%, based on the sum of the active content of the anionic stabilizer (4) and the solids content of the emulsion polymerizate (2).

[0048] The process to make the water-based binder (1 )

[0049] According to the process according to the invention to make the water-based binder (1 ) according to the invention, the monomers a) to f) are emulsion polymerized in a semi-batch mode in an aqueous environment and in absence of organic solvents. While emulsion polymerization as well as a semi-batch polymerization mode are well known, it was a surprise to obtain the high performing emulsion polymerizate (2), and thus the binder (1 ), at high conversion and low grit formation by using this well-known technique.

[0050] Preferably, the emulsion polymerization is carried out in the presence of the stabilizer (4), and optionally in the presence of a chain transfer agent, and / or seed latex. The stabilizer (4) may be part of the water phase added up front of the polymerization, and / or may be part of a pre-emulsion comprising at least part of the monomers. The chain transfer agent and the seed latex may be added up front, in a separate feed and / or as a mixture with at least one monomer.

[0051] Suitable chain transfer agents are well known and may be added in an amount of 0.01 to 5 wt.%, preferably from 0.05 to 1.5 wt.%, based on 100 parts of added monomers a) to f). Non-limiting examples include iso-octyl- thioglycolate, iso-octylmercaptopropionate, ethylthioethanol, limonene, 2- mercaptoethanol, cyclohexene, alkylmercaptans such as n-octylmercaptan, n-dodecylmercaptan, t-dodecylmercaptan, and tridecylmercaptan, abietic acid, terpilolene, terpinene or any mixture of 2 or more chain transfer agents. Preferred chain transfer agents include n-dodecylmercaptan and t-dodecyl- mercaptan.

[0052] Seeded emulsion polymerization is well known. The seed latex employed is typically a latex with a small particle size to aid nucleation of the emulsion polymerization. Preferably, the seed latex is added in an amount of 0.05 to 5 wt.%, in particular in an amount of 0.1 to 2 wt.%, based on the solids content of the emulsion polymerizate (2).

[0053] The emulsion polymerization during the monomer feed is preferably carried out within a temperature range of 70°C and 95°C, in particular between 73°C and 90°C. Alternatively - or in addition - the monomer feed is preferably carried out within 250 to 420 min., in particular between 280 to 400 min. This leads to an efficient process and a limited occupation period of the polymerization equipment, such as the polymerization reactor. Hence, the process allows the making of a high amount of polymerization batches within a given amount of time. In a preferred embodiment of the process, the monomers a), b), and c) are added continuously and monomer d) is added up front or within the first 30 min., in particular within the first 15 min., of the addition of the monomers a), b) and c), i.e. , from start of the first addition of monomer a), b) or c), in case the start of their addition is different. Hence, the monomer d) monomers, i.e., itaconic acid and / or fumaric acid, which get at least partially deprotonated and thus becoming anionic in the reaction medium, may serve as co-stabilizer of the emulsion polymerizate (2).

[0054] The optional monomer e), i.e., auxiliary monomer 1 , and / or monomer f), i.e., auxiliary monomer 2, may be added at least partially in parallel - or together - with the monomers a), b) and c). Alternatively, monomers e) and / or f) may be added up front or within the first 30 min., in particular within the first 15 min., of the addition of the monomers a), b) and c).

[0055] The thus obtained emulsion polymerizates exhibit an iodine content, measured according to JIS K 6235: 2006, of most typically 125 g iodine per 100 g dry polymer or lower, which is assigned to a certain degree of crosslinking of the butadiene units within the emulsion polymerizate (2).

[0056] The use of the water-based binder (1 )

[0057] The water-based binder (1 ) according to the invention is particularly suited as binder for coating an anode current collector for a secondary Li-ion battery. In addition, it was surprisingly found that it provides excellent properties in paper coating, adhesives, lamination adhesives, open mesh fabrics, board coating, flexible packaging, regenerated leather, cellulose sheet and / or paper impregnation. Thus, one binder (1 ) may be used in a wide range of different applications. In addition, the water-based binder (1 ) can be used to improve peel strength, binding strength of the coating applied to the anode current collector for a secondary Li-ion battery. Alternatively, or in addition, the binder (1 ) can be used to decrease the Direct Current Internal Resistance (DCIR) of the coating applied to the anode current collector for a secondary Li-ion battery. Hence, the performance of secondary Li-ion batteries can be improved significantly, despite the typically low amount of binder (1 ) employed in the applied coatings.

[0058] Anode active material slurry

[0059] The anode active material slurry, according to the invention, for coating an anode current collector for a secondary Li-ion battery, comprises an anode active material, a conductive material, a thickener, and the water-based binder (1 ) and thus emulsion polymerizate (2) according to the invention.

[0060] The anode active material slurry of the present invention is designed and is particularly suitable for coating an anode current collector for a secondary Li- ion battery. As such, the slurry is not suitable for electrodeposition, since the major component of the slurry is the anode active material, which is most typically non-ionic.

[0061] The slurry preferably comprises i) 80 to 98 wt.%, in particular 90 to 98 wt.%, of at least one anode active material, ii) 0 to 5 wt.%, in particular 1 to 4 wt.%, of at least one conductive material, iii) 0.1 to 5 wt.%, in particular 0.2 to 4 wt.%, of at least one thickener, iv) 0.2 to 5 wt.%, in particular 0.5 to 4 wt.%, of the water-based binder (1 ) comprising the emulsion polymerizate (2), v) 0 to 5 wt.%, in particular 0 to 4 wt.%, of at least one further component selected from the group of dispersants, waterborne crosslinking agents, filler, proteins, polysaccharides and their derivatives, and synthetic water-soluble polymers; and vi) at least one solvent, in particular water, wherein the wt.% are based on their solids content in relation to the solids content of the total slurry, determined according to ASTM D3926-05(2019). Thus, the components i) to v) sum up to 100 wt.% of total solids.

[0062] The at least one anode active material i) represents the major component of the slurry and thus of the coated anode. The anode active material i) allows to store and release the lithium ions upon charging and discharging the Li- ion battery. Thus, the Li-ions intercalate in the anode active material i). Preferred, non-limiting examples of anode active materials i) include graphite, in particular natural graphite, artificial graphite, synthesized graphite, curved graphite, activated carbon, non-graphitizable carbon, soft carbon, hard carbon, mesocarbon microbeads (MCMB), silicon particulate, Si-C composite particulate, silicon oxide, such as silicon monoxide (SiO) and silicon dioxide (SiO2), tin oxide (SnO), tin dioxide (SnO2), tin particulate, lithium titanate (e.g., Li4Ti5O12), and mixtures thereof.

[0063] The optional at least one conductive material ii) facilitates intercalation of Li- ions and thus enhances fast charging of Li-ion batteries. A widely used conductive material ii) is carbon black (CB), which is an amorphous carbon with graphite-like crystallites that have more orientations and a larger lattice spacing than graphite. Preferred, non-limiting examples of conductive materials ii) include carbon black, acetylene black, ketjen black, carbon fibers, carbon nanotubes, activated carbon, graphene, petroleum coke, and mixtures and / or combinations thereof. The thickener iii) may be based on a polysaccharide and / or a synthetic thickener. They are commercially available and known to the skilled person.

[0064] Non-limiting, preferred polysaccharide-type thickeners include cellulose, starch, guar gum, xanthan gum, agar-agar, and dextrin, as well as their alkyl ether, hydroxy alkyl ether, and carboxy alkyl ether, in particular methyl, ethyl and propyl ether, hydroxy methyl, hydroxy ethyl, and hydroxy propyl ether, as well as carboxymethyl ether. Non-limiting examples of preferred polysaccharide and their derivatives include polysaccharide fibers, and water-soluble polysaccharide derivatives such as carboxyalkyl cellulose, carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxy methyl cellulose, hydroxy ethyl cellulose, hydroxy propyl cellulose, carboxymethyl starch, carboxymethyl guar, methyl guar, ethyl guar, hydroxy methyl guar, and hydroxy ethyl guar.

[0065] Non-limiting, preferred synthetic-type thickeners include alkali-swellable emulsions (ASE), hydrophobically modified alkali-swellable emulsions (HASE), hydrophobically modified polyurethanes (HELIR), and hydrophobically modified polyethers (HMPE)

[0066] The slurry may comprise at least one further component v) selected from the group of dispersants, waterborne crosslinking agents, filler, proteins, synthetic water-soluble polymers, polysaccharides, and their derivatives. Preferred dispersants include nonionic and anionic surfactants. Preferred waterborne crosslinking agents include carbodiimide. Preferred fillers include clay and silica. Preferred proteins include gelatin and casein. Preferred synthetic water-soluble polymers include polyvinyl alcohol (PVOH), polyvinyl pyrrolidone (PVP), ethylene glycol, EO / PO block polymers, polyacrylic acids (PAA) with a MW up to e.g., 100’000 Da or even higher. The slurry comprises further at least one solvent vi). The preferred solvent is water. Preferably, the slurry comprises less than 0.2 wt.%, preferably less than 0.1 wt.%, and in particular 0 wt.%, of VOC, i.e., of volatile organic compounds having a boiling point of 250°C or below, measured at a pressure of 101 ,3 kPa, wherein the wt.% are based on the total amount of slurry (1 ), measures according to the Directive 2004 / 42 / EG of the European Parliament and of the Council, of April 21 , 2004. Thus, the slurry is environmentally friendly and does not - or only to a tiny amount - comprise unwanted volatile components. As a conclusion thereof, no specific precautions are required when drying the active material slurry applied on the anode current collector.

[0067] The anode

[0068] The anode is - during discharge of the second Li-ion battery - the negative electrode.

[0069] The anode according to the invention comprises an anode active material layer comprising the water-based binder (1 ) and thus emulsion polymerizate (2) according to the invention, wherein the anode active material layer is coated on the anode current collector, wherein the anode active material layer is the anode active material slurry according to the invention when applied onto the anode current collector and dried, and thus comprises the binder (1 ) according to the invention.

[0070] Preferably, the anode current collector of the anode is - due to its excellent electrically conductive properties - based on, and in particular is, a copper foil.

[0071] In another preferred embodiment, the i) anode active material layer, i.e. , the applied and dried anode active material slurry according to the invention, of the anode has a thickness of between 5 pm and 5 mm, preferably between 0.01 mm and 2 mm, and / or a density after calendering between 1 g / cm3and 2 g / cm3, and / or between 1.2 g / cm3and 1.9 g / cm3; and / or ii) anode current collector of the anode has a thickness of between 1 pm and 1 mm, preferably between 2 pm and 0.2 mm; wherein the thickness of the anode active material layer and the anode current collector is determined after calendering according to ISO 2808:2019, preferably with a micrometer gauge, and the density of the anode active material layer is determined by dividing the weight of the coated anode active material layer by its volume, determined by multiplying its thickness, measured according to DIN 862 I Form A1 using a micrometer, with the covered area.

[0072] Thus, the anode is well suited for basically any size for known types of secondary Li-ion batteries and can be optimized to provide best performance.

[0073] The anode is preferably made by coating the anode current collector with the anode active material slurry of the invention, followed by drying the slurry and optionally calendaring the coated anode.

[0074] In a first step a), the at least one anode active material i), the optional at least one conductive material ii), the at least one thickener iii), the water-based binder (1 ) comprising the emulsion polymerizate (2) (iv) according to the invention, and the optional further component v) are - optionally upon addition of solvent vi) - mixed to obtain the anode active material slurry. The solvent vi) can be added beforehand, during the addition of the various compounds - either continuously or batch-wise - and / or after the addition of the components i) to v), e.g., to adjust solids and / or viscosity of the slurry. The mixing of the components i) to vi) is not limited to a specific type of mixer. The skilled person in the art can make the proper selection, which may depend on the scale of mixing. Furthermore, he can select the mixing sequence, as well as the time for mixing. It is possible to use one or more than one mixer. Preferred, non-limiting examples of mixer include ball mixing, ultrasonic mixing, super mixer, Henschel mixer, flash mixer, flow jet mixer, drum mixer, ribbon cone mixer, pug mixer, nauta mixer, ribbon mixer, spartan granulator, Loedige mixer, planetary mixer, hydrodynamic shear mixer, screw-type kneader, defoaming kneader, paint shaker, pressure kneader, and two-roll kneader.

[0075] In a second, optional process step b), the pH, solids and / or viscosity of the slurry are adjusted, if required, by adding a base, an acid, one or more solvents vi). In case there is a need, the skilled person is able to select the type and the amount of said additives and perform this optional step b).

[0076] In a further process step c), the resulting anode active material slurry from step a) and optional step b) is applied, i.e. , coated, on one or both sides of the anode current collector. Preferred coating means include slot-die, doctor blade, comma bar, backing roll or tensioned web.

[0077] In a following process step d), the applied anode active material slurry is subjected to a first drying step to result in the anode active material layer coated on the anode current collector. This drying step may include subjecting the anode active material slurry applied on the anode current collector to warm, e.g., temperatures of 70°C or below, hot, e.g., to temperatures of up to 150°C or above, and / or low-humidity air, wherein drying may be performed at ambient pressure or in a vacuum, e.g., at pressures of 0.1 atm or lower. Alternatively, or in addition, drying may be performed using irradiation with e.g., infrared light, or electron beams. This drying step may be carried out just for some minutes or for an hour or more, depending on the size and thickness of the anode active material slurry which needs to be dried, as well as on the drying capability of the apparatus, the applied slurry is subjected to.

[0078] In a further, optional process step e), the anode active material layer coated on the anode current collector is subjected to at least one further drying step. As such, a total of even 4 or more drying steps may be possible, e.g., i) starting at low temperature of about 60°C, ii) increase the temperature to e.g., 150°C, iii) decrease the temperature to about 60°C, and iv) maintaining the temperature at about 60°C. Said drying steps are known to the skilled person in the art.

[0079] In yet a further, optional process step f), the anode active material layer coated on the anode current collector is optionally calendered after the final drying step, to result in a density of the anode active material layer of between 1 g / cm3to 2 g / cm3, determined by dividing the weight of the coated anode active material layer by its volume, determined by multiplying its thickness, measured according to DIN 862 I Form A1 using a micrometer, with the covered area. Such a calendering step is known to the skilled person in the art.

[0080] Following these steps, the obtained anode is typically subjected to further steps, e.g., by a slitting process, by vacuum drying, and afterwards further processed to obtain the secondary Li-ion battery comprising the anode of the invention. These process steps are known to the skilled person in the art, and he is well able to manufacture the secondary Li-ion battery.

[0081] Preferably, the anode active material slurry is adjusted to

[0082] - a pH of between 4 and 10, in particular a pH of 5 and 9. Adjusting the pH may be performed using a base, e.g., LiOH, NaOH, KOH, NaHCOs, NH4OH, preferably in the form of an aqueous solution; - a Brookfield viscosity between 500 mPa.s and 10’000 mPa.s, preferably between 2’000 mPa.s and 7’000 mPa.s, measured at 15 rpm and 23°C according to ISO 2555:2018, using a disc spindle; and / or

[0083] - a solids content of 30 to 70 wt.%, preferably 40 to 60 wt.%, based on the total amount of anode active material slurry (1 ), and measured according to ASTM D3926-05(2019).

[0084] In addition, or alternatively,

[0085] - the anode active material slurry is applied on one or both sides of the anode current collector with a coat weight per side of about 30 g / m2to about 150 g / m2, preferably of about 60 g / m2to about 120 g / m2, based on the dried slurry, to obtain the anode, wherein the anode active material slurry is applied preferably by means of a slot casting process, doctor blade, comma bar, backing roll or tensioned web; and / or

[0086] - the anode active material layer coated on the anode current collector, is dried in at least one further drying step between 40°C and 350°C, preferably between 60°C and 250°C, and preferably at ambient pressure.

[0087] The proper pH-, viscosity- and / or solids adjustment provides optimal parameter to apply, i.e. , coat, the anode active material slurry onto one or both sides of the anode current collector, including to get the desired coat weight. The latter is demanded by the developer of Li-ion batteries to achieve the targeted performance of the Li-ion battery.

[0088] Examples

[0089] Preparation of latex 1 The experimental latex 1 was made by conventional emulsion polymerization. To a suitably sized polymerization vessel were 74 parts of water, 1.4 parts of itaconic acid, 0.02 parts of a chelating agent and 0.07 parts of sodium hydroxide added. The vessel is then heated to 77 °C. Once the temperature was reached, 0.298 parts of a polystyrene seed latex (seed diameter 23 nm) were added. A first monomer feed stream comprising 60.6 parts styrene, 2 parts acrylonitrile and 0.22 parts tertiary dodecyl mercaptan is added to the stirred aqueous polymerization mixture for a period of about 5 hours. A second monomer stream comprising 36 parts butadiene is started 10 minutes after the start of the first monomer stream and added to the reactor content during 280 minutes. Coincident with the addition of the monomers, an aqueous stream comprising 15 parts of water, 0.5 parts of Dowfax 2A1 , an anionic surfactant and 1.0 part of sodium persulfate is added to the polymerization medium from time 0 to 340 minutes. The temperature of the vessel is maintained at 77°C during the first 260 minutes of the addition of the monomer and polymerization aids and ramped up to 95°C from 260 minutes to 300 minutes and maintained at 95°C for an additional 20 minutes after end of the aqueous stream containing the persulfate. At the end of this period, the vessel is then cooled to ambient temperatures and the pH of subsequent emulsion is adjusted to 5.5 with 20% sodium hydroxide before being subjected to steam distillation to remove the unconverted monomers and being filtered over a 325 mesh filter.

[0090] The final solids content is 48.2%, the particle size 162 nanometers, the Brookfield viscosity 44 mPa.s (spindle 2, 50 rpm), the glass transition temperature (Tg) is 8.0 °C, the gel content 95.1 %. The iodine content, measured according to JIS K 6235: 2006, is 122 g iodine / 100 g dry polymer.

[0091] Preparation of latex 2 The experimental latex was made by conventional emulsion polymerization. To a suitably sized polymerization vessel were 72.67 parts of water, 1 .4 parts of itaconic acid, 0.02 parts of a chelating agent and 0.07 parts of sodium hydroxide added. The vessel is then heated to 90 °C. Once the temperature was reached, 0.275 parts of a polystyrene seed latex (seed diameter 22.4 nm) were added. A first monomer feed stream comprising 50.6 parts styrene, 9 parts acrylonitrile and 0.75 parts tertiary dodecyl mercaptan is added to the stirred aqueous polymerization mixture for a period of about 5 hours. A second monomer stream comprising 39 parts butadiene is started 10 minutes after the start of the first monomer stream and added to the reactor content during 280 minutes. Coincident with the addition of the monomers, an aqueous stream comprising 15 parts of water, 0.5 parts of Dowfax 2A1 , an anionic surfactant and 1.0 part of sodium persulfate is added to the polymerization medium from time 0 to 340 minutes. The temperature of the vessel is maintained at 90°C during the first 260 minutes of the addition of the monomer and polymerization aids and ramped up to 95°C from 260 minutes to 300 minutes and maintained at 95°C for an additional 20 minutes after end of the aqueous stream containing the persulfate. At the end of this period, the vessel is then cooled to ambient temperatures and the pH of subsequent emulsion is adjusted to 5.5 with 20% sodium hydroxide before being subjected to steam distillation to remove the unconverted monomers and being filtered over a 325 mesh filter.

[0092] The final solids content is 48.0%, the particle size 164 nanometers, the Brookfield viscosity 100 mPa.s (spindle 2, 50 rpm), the glass transition temperature (Tg) is 8.8 °C, the gel content 89.9%.

[0093] The reference latex 3 The reference latex 3 relates to a well-known industry standard latex from competition for slurries used for coating an anode current collector for a secondary Li-ion battery. The latex 3 is based on styrene, butadiene, and methyl methacrylate.

[0094] The solids content is 44.9%, the particle size 142 nanometers, the Brookfield viscosity 42 mPa.s (spindle 2, 50 rpm), the glass transition temperature (Tg) is 9.7 °C, and the gel content 92.4%.

[0095] Preparation of latex 4

[0096] The experimental latex was made by conventional emulsion polymerization. To a suitably sized polymerization vessel were 80 parts of water, 1 part of itaconic acid, 0.02 parts of a chelating agent and 0.05 parts of sodium hydroxide added. The vessel is then heated to 77 °C. Once the temperature was reached, 0.275 parts of a polystyrene seed latex (seed diameter 22.4 nm) were added. A first monomer feed stream comprising 59 parts styrene, 2 parts acrylonitrile, 2 parts acrylic acid and 0.25 parts tertiary dodecyl mercaptan is added to the stirred aqueous polymerization mixture for a period of about 5 hours. A second monomer stream comprising 36 parts butadiene is started 10 minutes after the start of the first monomer stream and added to the reactor content during 280 minutes. Coincident with the addition of the monomers, an aqueous stream comprising 15 parts of water, 0.5 parts of Dowfax 2A1 , an anionic surfactant and 1 .0 part of sodium persulfate is added to the polymerization medium from time 0 to 340 minutes. The temperature of the vessel is maintained at 77°C during the first 250 minutes of the addition of the monomer and polymerization aids and ramped up to 95°C from 260 minutes to 300 minutes and maintained at 95°C for an additional 20 minutes after end of the aqueous stream feed. At the end of this period, the vessel is then cooled to ambient temperatures and the pH of subsequent emulsion is adjusted to 5.5 with 20% sodium hydroxide before being subjected to steam distillation to remove the unconverted monomers and being filtered over a 325-mesh filter.

[0097] The final solids content is 50.2% the particle size 155 nanometers, the Brookfield viscosity 94 mPa.s (spindle 2, 50 rpm), the glass transition temperature is 9.9 °C, the gel content 95.5%.

[0098] Preparation of latex 5

[0099] The experimental latex was made by conventional emulsion polymerization. To a suitably sized polymerization vessel were 75.6 parts of water, 1 .4 parts of itaconic acid, 0.02 parts of a chelating agent and 0.07 parts of sodium hydroxide added. The vessel is then heated to 77 °C. Once the temperature was reached, 0.298 parts of a polystyrene seed latex (seed diameter 23 nm) were added. A first monomer feed stream comprising 59.6 parts styrene, 2 parts acrylonitrile and 0.22 parts of tertiary dodecyl mercaptan is added to the stirred aqueous polymerization mixture for a period of about 5 hours. A second monomer stream comprising 36 parts of butadiene is started 10 minutes after the start of the first monomer stream and added to the reactor content during 280 minutes. A third monomer stream comprising 1 parts of 2- hydroxyethylacrylate is being fed to the reactor from time 20 minutes to 280 minutes. Coincident with the addition of the monomers, an aqueous stream comprising 15 parts of water, 0.5 parts of Dowfax 2A1 , an anionic surfactant and 1 .0 part of sodium persulfate is added to the polymerization medium from time 0 to 340 minutes. The temperature of the vessel is maintained at 77°C during the first 260 minutes of the addition of the monomer and polymerization aids and ramped up to 95°C from 260 minutes to 300 minutes and maintained at 95°C for an additional 20 minutes after the end of the feeds. At the end of this period, the vessel is then cooled to ambient temperatures and the pH of subsequent emulsion is adjusted to 6 with 20% sodium hydroxide before being subjected to steam distillation to remove the unconverted monomers and being filtered over a 325-mesh filter.

[0100] The final solids content is 51.2%, the particle size 159 nanometers, the Brookfield viscosity 99 mPa.s (spindle 2, 50 rpm), the glass transition temperature is 7.9 °C, the gel content 95.4%.

[0101] Preparation of reference latex 6

[0102] The experimental latex was made by conventional emulsion polymerization. To a suitably sized polymerization vessel were 53.68 parts of water, 1 .4 parts of itaconic acid, 0.02 parts of a chelating agent and 0.05 parts of Dowfax 2A1 , an anionic surfactant added. The vessel is then heated to 85 °C. Once the temperature was reached, 0.282 parts of a polystyrene seed latex (seed diameter 24 nm) were added. A first monomer feed stream comprising 48.1 parts of styrene, 9 parts of acrylonitrile and 0.70 parts of tertiary dodecyl mercaptan is added to the stirred aqueous polymerization mixture for a period of about 5 hours. A second monomer stream comprising 39.5 parts of butadiene is started 7 minutes after the start of the first monomer stream and added to the reactor content for 270 minutes. A third stream comprising 12 parts of water and 2 parts of acrylamide is started 25 minutes after the start of the first monomer feed and stopped after 4 hours feed time. Coincident with the addition of the monomers, an aqueous stream comprising 14 parts of water, 0.8 parts of Dowfax 2A1 , an anionic surfactant, 1 .0 part of sodium persulfate and 0.15 part of sodium hydroxide is added to the polymerization medium from time 0 to 310 minutes. A stream comprising 5 parts of water and 0.3 parts of sodium metabisulfite in added to the reactor in 2 steps: 50% from 320 minutes to 330 minutes, the remaining fraction is added from 330 minutes to 350 minutes. A stream comprising 2.1 parts of water, 0.3 parts of t-butyl hydroperoxide and 0.05 parts of Dowfax 2A1 is added to the reactor from time 330 minutes to 355 minutes. The temperature of the vessel is maintained at 85°C during the first 270 minutes of the addition of the monomer and polymerization aids and ramped up to 95°C from 270 minutes to 295 minutes and maintained at 95°C for an additional 80 minutes. At the end of this period, the vessel is then cooled to ambient temperatures and the pH of subsequent emulsion is adjusted to 7 with 20% sodium hydroxide before being subjected to steam distillation to remove the unconverted monomers and being filtered over a 325-mesh filter.

[0103] The final solids content is 49.3% the particle size 165 nanometers, the Brookfield viscosity 89 mPa.s (spindle 2, 50 rpm), the glass transition temperature is 9 °C, the gel content 91 .0%.

[0104] Preparation of reference latex 7

[0105] The experimental latex was made by conventional emulsion polymerization. To a suitably sized polymerization vessel were 80 parts of water, 0.02 parts of a chelating agent added. The vessel is then heated to 77 °C. Once the temperature was reached, 0.275 parts of a polystyrene seed latex (seed diameter 22.4 nm) were added. A first monomer feed stream comprising 59 parts of styrene, 2 parts of acrylonitrile, 3 parts of acrylic acid and 0.25 parts of tertiary dodecyl mercaptan is added to the stirred aqueous polymerization mixture for a period of about 5 hours. A second monomer stream comprising 36 parts butadiene is started 10 minutes after the start of the first monomer stream and added to the reactor content during 280 minutes. Coincident with the addition of the monomers, an aqueous stream comprising 15 parts water, 0.5 parts of Dowfax 2A1 , an anionic surfactant, 1 .0 part of sodium persulfate and 0.1 parts of sodium hydroxide is added to the polymerization medium from time 0 to 340 minutes. The temperature of the vessel is maintained at 77°C during the first 250 minutes of the addition of the monomer and polymerization aids and ramped up to 95°C from 250 minutes to 300 minutes and maintained at 95°C for an additional 20 minutes after end of the aqueous stream feed. At the end of this period, the vessel is then cooled to ambient temperatures and the pH of subsequent emulsion is adjusted to 5.5 with 20% sodium hydroxide before being subjected to steam distillation to remove the unconverted monomers and being filtered over a 325 mesh filter.

[0106] The final solids content is 50.1 %, the particle size 161 nanometers, the Brookfield viscosity 81 mPa.s (spindle 2, 50 rpm), the glass transition temperature is 10.0 °C, the gel content 91.7%.

[0107] Preparation of reference latex 8

[0108] The experimental latex was made by conventional emulsion polymerization. To a suitably sized polymerization vessel were 76 parts of water, 2 parts of itaconic acid, 0.02 parts of a chelating agent and 0.07 parts of sodium hydroxide added. The vessel is then heated to 90 °C. Once the temperature was reached, 0.298 parts of a polystyrene seed latex (seed diameter 23 nm) were added. A first monomer feed stream comprising 62 parts of styrene and 0.3 parts of tertiary dodecyl mercaptan is added to the stirred aqueous polymerization mixture for a period of about 4.5 hours. A second monomer stream comprising 36 parts of butadiene is started 10 minutes after the start of the first monomer stream and added to the reactor content during 255 minutes. Coincident with the addition of the monomers, an aqueous stream comprising 15 parts water, 0.5 parts of Dowfax 2A1 , an anionic surfactant and 1 .0 part of sodium persulfate is added to the polymerization medium from time 0 to 330 minutes. The temperature of the vessel is maintained at 90°C during the first 255 minutes of the addition of the monomer and polymerization aids and ramped up to 95°C from 255 minutes to 295 minutes and maintained at 95°C for an additional 20 minutes after end of all feeds. At the end of this period, the vessel is then cooled to ambient temperatures and the pH of subsequent emulsion is adjusted to 6.5 with 20% sodium hydroxide before being subjected to steam distillation to remove the unconverted monomers and being filtered over a 325 mesh filter.

[0109] The final solids content is 49.6%, the particle size 163 nanometers, the Brookfield viscosity 145 mPa.s (spindle 2, 50 rpm), the glass transition temperature is 8.5 °C, the gel content 93.7%.

[0110] Latex characterization

[0111] The solids contents of the latices 1 to 8 were determined according to ASTM D3926-05(2019).

[0112] The particle sizes are recorded as volume mean of the particle size (MV), and determined by dynamic light scattering using a Nanotrac 150.

[0113] The Brookfield viscosities were determined according to ISO 2555:2018 and measured at 50 rpm using spindle 2.

[0114] The glass transition temperatures (Tg) were determined according to DIN 51007 using a heating rate of 10°C / min., wherein the midpoint of the segment of the mid-tangent between the extrapolated baselines is reported.

[0115] The Gel Content was determined by the following procedure: A latex film was casted, dried at room temperature and weighed (dry latex film (A)) using a latex sample adjusted to pH 8 with a 20 wt.% NaOH solution. Said film was allowed to swell in toluene for 26 hrs at room temperature. The resulting toluene-insoluble portion, i.e. , wet gel, was separated from the liquid phase by filtration and weighed, dried in a vented oven at 130°C for 2 hrs, and weighed again to obtain the dry weight of the gel (C). The Gel Content (in %) was determined by the following formula: Gel Content = (weight of dry gel (C) / weight of dry latex film (A))x100.

[0116] Table 1 : Monomer composition of the emulsion polymerizates according to the invention (latex 1 and 2) and of the reference latex 3, which is a well-known industry standard in slurries used for coating an anode current collector for a secondary Li-ion battery. a) Reference latex 3 relates to an industry standard latex from competition. The presented composition is obtained by sample analysis and may differ slightly from the monomer composition from its manufacture. b) ST stands for styrene. c) BD stands for butadiene. d) IA stands for itaconic acid. e) VCN stands for vinyl cyanide, i.e., acrylonitrile. f) MMA stands for methyl methacrylate.

[0117] Table 2: Monomer composition of the emulsion polymerizates according to the invention (latex 4 and 5) and of the reference latices 6, 7 ,8. b) ST stands for styrene. c) BD stands for butadiene. d) IA stands for itaconic acid. e) VCN stands for vinyl cyanide, i.e., acrylonitrile. g) AA stands for acrylic acid. h) HEA stands for hydroxyethyl acrylate i) AAM stands for acrylamide

[0118] Preparation of the dry powder mixture 1 (PM-1)

[0119] Synthetic Graphite (EV7 from Shanghai Shanshan) and carbon black (Super P® Li from Imerys) were dried separately in an oven at 120°C for 8 hrs.

[0120] 95.6 parts of the dried graphite were added into a 5-L. double planetary disperser-type mixer, made by Ross China (model DPD-2R), followed by the addition of 1 part of carbon black. The graphite and the carbon black were mixed at 600 rpm for 15 min. to obtain a homogeneous dry powder mixture, i.e. , PM-1 , which was split up between all subsequent formulations. Preparation of the dry powder mixture 2 (PM-2)

[0121] The dry powder mixture 2 (PM-2) was prepared as the dry powder mixture 1 (PM-1 ), wherein natural graphite (TG8 from Shanghai Shansan) was taken instead. The natural graphite was also dried separately in an oven at 120°C for 8 hrs.

[0122] Preparation of the dry powder mixture 3 (PM-3)

[0123] The dry powder mixture 3 (PM-3) was prepared as the dry powder mixture 1 (PM-1 ), wherein 95.7 parts of the dried graphite and one part of carbon black were mixed.

[0124] Preparation of the dry powder mixture 4 (PM-4)

[0125] The dry powder mixture 4 (PM-4) was prepared as the dry powder mixture 1 (PM-1 ), wherein synthetic graphite (Graphite QG-1 from Shanghai Shansan) was taken instead. The graphite QG-1 was also dried separately in an oven at 120°C for 8 hrs.

[0126] Preparation of carboxymethyl cellulose solution

[0127] Carboxymethyl cellulose (CMC; Sunrose® MAC 350 from Nippon Paper Industries Co., Ltd.) was dried in an oven at 85°C for 8 hrs. prior use.

[0128] A 1 .6% (w / w) aqueous solution of carboxymethyl cellulose was prepared by adding to a 5 L. beaker 98.4 parts of deionized water, followed - while stirring - by slow addition of 1 .6 part of the dried CMC. The mixture was stirred using a Dissolver Stirrer at 700 rpm for 120 min. The obtained solution had a Brookfield viscosity of about 5’000-20’000 mPa.s, determined according to ISO 2555:2018 and measured at 50 rpm using a disc spindle, and a pH of 6.5-8.5. The thus obtained CMC-solution was split up between all subsequent formulations.

[0129] No pH adjustment was made before further use.

[0130] Preparation of anode active material slurries

[0131] In examples 1 , 2 and reference example 3 (see Table 3), 966 g of the dry powder mixture PM-1 and PM-2, respectively, were added into a 5-L. double planetary disperser-type mixer, made by Ross China (model DPD-2R), equipped with a cooling system, followed by adding 437.5 g of CMC-solution while stirring, followed by thorough mixing at 600 rpm for 30 min., addition of further 437.5 g of CMC-solution, mixing at 600 rpm for 5 min, followed by further mixing at 1500 rpm for 140 min. Afterwards, 50 g of latex, which was diluted to a solid content of 40 wt.% prior use, was slowly added while slight stirring, followed by mixing at 600 rpm for 30 min.. Finally, 109 g of deionized water were added while slight mixing to adjust the solids content of the obtained anode active material slurry to 50 wt.%. The slurries obtained is stable over days and does not sediment. Their Brookfield viscosity is between about 4000 to 8000 mPa.s, determined according to ISO 2555:2018 and measured at 15 rpm using a disc spindle.

[0132] In examples 4, 5 and reference example 6 (see Table 4), the anode active material slurries were prepared as cited above for examples 1 , 2, and reference example 3, wherein 966 g of dry powder mixture PM-3, two times 470 g of CMC-solution and 45 g of latex, which was diluted to a solid content of 40 wt.% prior use, were employed. Finally, 109 g of deionized water was added.

[0133] In examples 7, 8, 9 and reference examples 10, 11 , 12 and 13 (see Tables 5 and 6), the anode active material slurries were prepared as above, wherein 966 g of the dry powder mixture PM-4, were added into a 5-L. double planetary disperser-type mixer, made by Ross China (model DPD-2R), equipped with a cooling system, followed by adding 437.5 g of CMC-solution while stirring, followed by thorough mixing at 600 rpm for 30 min., addition of further 437.5 g of CMC-solution, mixing at 600 rpm for 5 min, followed by further mixing at 1500 rpm for 140 min. Afterwards, 50 g of latex, which was diluted to a solid content of 40 wt.% prior use, was slowly added while slight stirring, followed by mixing at 600 rpm for 30 min. Finally, 109 g of deionized water were added while slight mixing to adjust the solids content of the obtained anode active material slurry to 50 wt.%. Their Brookfield viscosity is between about 3400 to 3800 mPa.s, determined according to ISO 2555:2018 and measured at 50 rpm using a disc spindle (spindle 5).

[0134] All obtained anode active material slurries revealed a good dispersibility and stability.

[0135] Anode coating and calendering

[0136] The slurries obtained as described above were each applied on both sides of a 10 pm thick copper foil, i.e. , the anode current collector, using a transfer roll coating machine from Nanjing Mojiesi Energy Technology Limited (Model TB- 300L-1.5M) with a coat weight per side of 120 g / m2: The coating thickness of the slurry was before calendering 120 pm and after calendering 75 pm. The machine speed was 1 m / min. The coated copper foils comprising the applied slurries were dried in an oven at 70 °C for 5 minutes to obtain an anode active material layer having a press density of 1 .6 g / cm3. The press pressure was 8 tons. Thus, the coated anodes, i.e., coated anode current collectors for a secondary Li-ion battery, were obtained.

[0137] Carrying out 180° pee! tests

[0138] The 180° peel adhesion forces were determined after calendering using the peel test according to ASTM D903, with a peel strength tester (Cheminstruments AR-2000) with a speed of 12 inch / min.

[0139] For performing the 180° peel tests, i.e., peel strength tests, i.e., measuring the peel adhesion forces, the coated anodes were cut into 50 x 30 mm strips. One side was adhered with a double side tape onto an aluminum sample having a thickness of 2 mm.

[0140] The reported data are relative to the 180° peel adhesion force of the industry standard latex 3 as reference. Each reported value reflects the mean of 3 measurements.

[0141] Table 3: Ingredients, slurry and 180° peel adhesion forces of the anodes of examples 1 , 2 and reference example 3 comprising the various emulsion polymerizates, i.e., latices. a) The dry powder mixture 1 (PM-1 ) is based on synthetic graphite, see above. b) The dry powder mixture 2 (PM-2) is based on natural graphite, see above. c) The reported data are relative to the 180° peel adhesion force using PM-1 and PM-2, respectively, comprising the industry standard latex 3 as reference (=100%). Each value reflects the mean of 3 measurements.

[0142] The results in Tables 3 and 4 demonstrate impressively that omission of methyl methacrylate in a styrene-butadiene based latex according to the invention, i.e., in the emulsion polymerizate (2), as shown in examples 1 , 2, 4 and 5, improves the 180° peel adhesion forces - after calendering - of an anode current collector for a secondary Li-ion battery, coated with the anode active material slurry according to the invention, by 7 to 35 %, relative to the today’s industry standard, and independent on the type of graphite used. The presence of (meth)acrylonitrile and itaconic acid and / or fumaric acid in the latex further contribute to the beneficial performance characteristics of the slurry, and in particular with respect to the 180° peel adhesion forces of the obtained anodes. The observed 180° peel adhesion forces with the emulsion polymerizates (2) are even more surprising for latex 1 (see examples 1 , 4 and 7), which has a high gel content of 95.1 %, since it is known that gel contents higher than 93% reduce film formation and thus the adhesion of the slurry to a substrate.

[0143] Table 4: Ingredients, slurry, and anode properties of examples 4, 5 and reference example 6 comprising the various emulsion polymerizates, i.e. , latices. For each example, a total of 3 equally prepared anode samples were tested, wherein the mean value is reported. c) The reported data are relative to the 180° peel adhesion force using PM-3 comprising the industry standard latex 3 as reference (=100%). Each value reflects the mean of 3 measurements. d) DCIR stands for Direct Current Internal Resistance, see below. The standard deviation is within ±2 % e) The dry powder mixture 3 (PM-3) is based on synthetic graphite, see above.

[0144] The 180° peel adhesion forces of the anodes of examples 7 to 9 and reference examples 10 to 13 were measured as well (see Tables 5 and 6).

[0145] The results reported in Table 5 confirm that the examples 7 to 9 comprising the latices 1 , 4 and 5, respectively, which are according to the invention, provide superior 180° peel adhesion forces, when compared to reference example 11 , which comprises the industry standard latex 3 as reference. In addition, reference example 10, which comprises the reference latex 6 containing 2 wt.% acrylamide, results in even worse 180° peel adhesion forces.

[0146] In particular, example 8 in Table 5, i.e. , which is based on PM-4 and latex 4 comprising - besides styrene (ST), butadiene (BD), itaconic acid (IA) and acrylonitrile (VCN) - a small amount, i.e., 2 wt.%, of acrylic acid (AA), even further improves the 180° peel adhesion force. Hence, the copolymerization of minor amounts of acrylic acid boosts the performance of the emulsion polymerizate (2), and thus of the binder (1 ).

[0147] Example 9 in Table 5, i.e., when using PM-4 and latex 5 comprising - besides styrene (ST), butadiene (BD), itaconic acid (IA) and acrylonitrile (VCN) - a small amount, i.e., 1 wt.%, of 2-hydroxyethyl acrylate (HEA) provides also an improved 180° peel adhesion force, when compared to the industry standard latex reference. Although the 180° peel adhesion force result from example 9 is somewhat reduced compared to the one of example 7 comprising latex 1 without HEA, it is expected that a latex, i.e., emulsion polymerizate (2), comprising HEA may reveal even better results in other formulations.

[0148] Reference Example 10 (see Tables 5 and 6), which is based on PM-4 comprising reference latex 6, which contains 2 wt.% acrylamide (AAM), results, however, in a reduced 180° peel adhesion force, when compared to both, PM-4 comprising the industry standard latex reference with MMA (Table 5, reference example 11 ), and - even more pronounced - PM-4 comprising latex 1 according to the invention (Table 6), which just contains styrene (ST), butadiene (BD), itaconic acid (IA), and acrylonitrile (VCN).

[0149] Table 5: Ingredients, slurry, and 180° peel adhesion forces of the anodes of examples 7, 8 and 9 and reference examples 10 and 11 comprising the various emulsion polymerizates, i.e., latices. The 180° peel adhesion forces are referenced to example 11 , which is based on PM-4 and the industry standard latex 3 as reference (=100%). c) The reported data are relative to the 180° peel adhesion force using PM-4 comprising the industry standard latex 3 as reference (=100%). Each value reflects the mean of 3 measurements.

[0150] The results reported in Table 6 confirm that the example 7 comprising latex 1 , which are according to the invention, provides superior 180° peel adhesion forces over reference example 10 with reference latex 6 comprising 2 wt.% of acrylamide (AAM), reference example 12 with reference latex 7 comprising 3 wt. % acrylic acid (AA), but no itaconic acid (IA), and reference example 13 with reference latex 8 comprising no acrylonitrile (VCN).

[0151] Table 6: Ingredients, slurry, and 180° peel adhesion forces of the anodes of example 7 and reference examples 10, 12 and 13 comprising the various emulsion polymerizates, i.e., latices. The 180° peel adhesion forces are referenced to example 7 (=100%), which is based on PM-4 and latex 1 , which is according to the invention. c) The reported data are relative to the 180° peel adhesion force using PM-4 comprising as reference (=100%) latex 1 , which is according to the invention. Each value reflects the mean of 3 measurements.

[0152] The results reported in Tables 3 to 6 demonstrate impressively that the examples 1 , 2, 4, 5, 7, 8, and 9, which comprise latex 1 , 2, 4 (+ acrylic acid, AA) or 5 (+ hydroxyethyl acrylate, HEA), i.e. , the emulsion polymerizate (2), and thus the binder (1 ) according to the invention, reveal a superior 180° peel adhesion force, when compared to reference examples 3, 6, and 10 to 13, which comprise a reference latex, i.e., the industry standard latex 3 (+ methyl methacrylate (MMA), latex 6 (+ acrylamide, AAM), latex 7 (+acrylic acid, AA, but no itaconic acid, IA), or latex 8 (no acrylonitrile (VCN). As a conclusion thereof, the presence of itaconic acid (IA) and acrylonitrile (VCN) in a styrene-butadiene base polymer, and the absence of e.g., methyl methacrylate (MMA) and acrylamide (AAM) in said styrene-butadiene based polymers are essential for achieving superior 180° peel adhesion forces.

[0153] Measuring the Direct Current Internal Resistance (DCIR)

[0154] The anodes prepared with examples 4, 5 and reference example 6, i.e. , with PM-3, were also subjected to Direct Current Internal Resistance (DCIR) measurements.

[0155] In a first step, the anodes were charged at ambient temperature, i.e., about 25°C, with a constant current at a rate of 1 C to 4.2V, then charged at the constant voltage with a cut-off current of 0.2A. Afterwards, the anodes were allowed to rest for 30 min., followed by discharging the anodes at a rate of 1 C by a constant current to 2.75V, wherein their actual capacity at a rate of CO was tested, followed by allowing the anodes to rest for another 30m in. Subsequently, the anodes were charged again at constant current at a rate of 1 C for 0.5 hrs. Afterwards, the charge of the anodes was adjusted to a state of charge (SOC) of 50%.

[0156] In a second step, the thus obtained anodes were placed in a temperature adjustable thermal chamber for measuring the DCIR. Thus, the thermal chamber was adjusted to the respective temperature, i.e., to +25°C and to -25°C, respectively, and the anodes were placed therein and allowed to temperature-adjust for 6 hrs. Afterwards, the anodes were discharged at a rate of 1 C for 10 seconds, wherein the Open Circuit Voltage (OCV) was recorded for each anode at the start and the end of the discharge. Hence, the DCR was calculated according to the following formula: DCR — (OCVstart - OCVend) / (discharge wherein the value (discharge stands for the current at a rate of 1 C.

[0157] The DCIR-results reported in Table 4 demonstrate that at the temperature of +25°C the Direct Current Internal Resistance (DCIR) of example 4 is reduced, i.e., improved, by 7.5%, relative to reference example 6 comprising the industry standard latex 3 (Ref.), while the DCIR at the temperature of -25°C remains unchanged. This is, in addition to the 16% higher 180° peel adhesion force, a substantial enhancement over the performance of the today’s industry standard.

[0158] Furthermore, example 5 comprising latex 2 having a higher content of acrylonitrile, results in only a marginally lower DCIR-performance at both, +25°C and -25°C, but revealing a 7% higher 180° peel adhesion force, relative to reference example 6, comprising the today’s industry standard latex 3 (Ref.). While the presented results are only early experiments, they demonstrate impressively the potential of the present invention for improving the anode performance by further optimizing the formulation of and / or the process to make the binder (1 ) and the emulsion polymerizate (2) within the claimed embodiment, and thus in absence of methyl methacrylate.

Claims

Claims1. Water-based binder (1 ) for coating an anode current collector for a secondary Li-ion battery, wherein the binder (1 ) comprises an emulsion polymerizate (2) being a copolymerizate of a) 35 to 70 wt.% of styrene, b) 20 to 47 wt.% of aliphatic conjugated diene-based monomer, c) 1 to 15 wt.% of (meth)acrylonitrile, d) 0.1 to 5 wt.% of itaconic acid and / or fumaric acid, e) 0 to 20 wt.% of one or more of auxiliary monomer 1 selected from the group of hydroxy alkyl (meth)acrylate, vinyl acetate, vinyl priopionate, and C9-C12 vinyl versatate; and f) 0 to 5 wt.% of one or more of auxiliary monomer 2 selected from the group of (meth)acrylic acid, N-functionalized derivatives of (meth)acrylamides, vinyltrialkoxysilanes, and olefinic crosslinking monomer comprising 2 or more olefinic groups, wherein the weight portions (wt.%) of the components a) to f) are based on the solid content of the emulsion polymerizate (2) and sum up to 100 wt.%.

2. Water-based binder (1 ) according to claim 1 , characterized in that the emulsion polymerizate (2) is a copolymerizate of a) 40 to 70 wt.%, preferably 45 to 70 wt.%, of styrene, b) 25 to 45 wt.%, preferably 30 to 45 wt.%, of butadiene, and / or isoprene, c) 1 to 12 wt.%, preferably 1 to 10 wt.%, of (meth)acrylonitrile, d) 0.2 to 4 wt.%, preferably 0.5 to 3 wt.%, of itaconic acid and / or fumaric acid, e) 0 to 15 wt.%, preferably 0 to 10 wt.%, of one or more of auxiliary monomer 1 selected from the group of hydroxy alkyl(meth)acrylate, vinyl acetate, vinyl priopionate, and C9-C12 vinyl versatate; and f) 0 to 5 wt.%, preferably 0 to 4 wt.%, of one or more of auxiliary monomer 2 selected from (meth)acrylic acid, N-functionalized derivatives of (meth)acrylamides, vinyltrialkoxysilanes, and olefinic crosslinking monomer comprising 2 or more olefinic groups.

3. Water-based binder (1 ) according to claim 1 , characterized in that the emulsion polymerizate (2) is a copolymerizate of- 35 to 70 wt.%, preferably 40 to 70 wt.%, in particular 45 to 70, of styrene,- 20 to 47 wt.%, preferably 25 to 45 wt.%, in particular 30 to 45, of butadiene,- 1 to 15 wt.%, preferably 1 to 12 wt.%, in particular 1 to 10 of acrylonitrile,- 0.1 to 5 wt.%, preferably 0.2 to 4 wt.%, in particular 0.5 to 3, of itaconic acid, and- 0 to 5 wt.%, preferably 0 to 4 wt.%, in particular 0 to 3, of one or more auxiliary monomers 2 selected from (meth)acrylic acid, N-functionalized derivatives of (meth)acrylamides, vinyltrialkoxysilanes, and olefinic crosslinking monomer comprising 2 or more olefinic groups.

4. Water-based binder (1 ) according to any one of claims 1 to 3, characterized in that the binder (1 ) further comprises 0 to 50 wt.%, preferably 0 to 40 wt.%, of additives (3), wherein the additives (3) include preferably water-soluble polymers, antioxidants, dispersants, surfactants, and / or rheology modifiers, based on the solid content of the binder (1 ).

5. Water-based binder (1 ) according to any one of claims 1 to 4, characterized in that the emulsion polymerizate (2) is a one-phase copolymerizate, preferably a seeded one-phase copolymerizate.

6. Water-based binder (1 ) according to any one of claims 1 to 5, characterized in that emulsion polymerizate (2) is free of alkyl (meth)acrylates such as methyl methacrylate.

7. Water-based binder (1 ) according to any one of claims 1 to 6, characterized in that- the monomers a) to f) of the emulsion polymerizate (2) are selected to result in a glass transition temperature Tg of the emulsion polymerizate (2) of between -20°C and +40°C, preferably between 0°C and +30°C, in particular between +5°C and +25°C, determined according to DIN 51007 using a heating rate of 10°C / min., wherein the midpoint of the segment of the mid-tangent between the extrapolated baselines is reported,- the solids content of the emulsion polymerizate (2) is between 35 to 65 wt.%, preferably between 40 to 60 wt.%, in particular between 45 to 55 wt.%, and / or- the volume mean of the particle size (MV) of the emulsion polymerizate (2) is between 50 and 300 nm, preferably between 75 and 250 nm, in particular between 100 and 200 nm, determined by dynamic light scattering.

8. Water-based binder (1 ) according to any one of claims 1 to 7, characterized in that the emulsion polymerizate (2) is stabilized with an anionic stabilizer (4), preferably in an amount of 0.1 to 3 wt.%, in particular 0.1 to 2 wt.%, based on the sum of the active content of the anionic stabilizer (4) and the solids content of the emulsion polymerizate9. Process to make the water-based binder (1 ) according to any one of claims 1 to 8, characterized in that the monomers a) to f) are emulsion polymerized in a semi-batch mode in an aqueous environment and in absence of organic solvents.

10. Process of claim 9, characterized in that the emulsion polymerization is carried out in the presence of the stabilizer (4), and optionally in the presence of a chain transfer agent, and / or seed latex.11 . Process of claims 9 or 10, characterized in that the emulsion polymerization during the monomer feed is carried out within a temperature range of 70°C and 95°C, preferably between 73°C and 90°C, and / or that the monomer feed within 250 and 420 min., preferably between 280 and 400 min.

12. Process of any one of claims 9 to 11 , characterized in that the monomers a), b), and c) are added continuously and monomer d) is added up front or within the first 30 min., in particular within the first 15 min., of the addition of the monomers a), b) and c).

13. Anode active material slurry for coating an anode current collector for a secondary Li-ion battery comprising an anode active material, a conductive material, a thickener, and a water-based binder, characterized in that the water-based binder is the water-based binder (1 ) of any one of claims 1 to 8.

14. Anode for the secondary Li-ion battery, wherein the anode comprises an anode active material layer coated on the anode current collector, wherein the anode active material layer is the anode active material slurry according to claim 13 when applied onto the anode current collector and dried, and thus comprises the binder (1 ) of any one of claims 1 to 8.

15. Use of the water-based binder (1 ) of any one of claims 1 to 8 as binder for coating an anode current collector for a secondary Li-ion battery, in paper coating, adhesives, lamination adhesives, open mesh fabrics, board coating, flexible packaging, regenerated leather, cellulose sheet and / or paper impregnation.

16. Use of claim 15 to improve peel strength, binding strength, and / or decrease the Direct Current Internal Resistance (DCIR) of the coating applied to the anode current collector for a secondary Li-ion battery.

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