WO2025056565A1 - Adhesion promoter for secondary batteries - Google Patents

Abstract

The present invention relates to a binder solution for a secondary battery comprising a) at least one polymer blend and b) at least one non-aqueous solvent, wherein a) the polymer blend comprises at least one vinylidene fluoride (VDF) (co)polymer and at least one second copolymer comprising i) recurring units derived from at least one ethylenically unsaturated (meth)acrylic monomer and ii) recurring units derived from at least two different ethylenically unsaturated monomers having a nitrogen-containing heterocycle respectively. The present invention also relates to use of said second copolymer as an adhesion promoter towards a current collector of an electrode in a secondary battery.

Description

ADHESION PROMOTER FOR SECONDARY BATTERIES

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to European patent application No.

23306523.4 filed on September 15, 2023, the whole content of this application being incorporated herein by reference for all purposes.

TECHNICAL FIELD

[0002] The present invention relates to a binder solution for a secondary battery comprising a) at least one polymer blend and b) at least one non-aqueous solvent, wherein a) the polymer blend comprises at least one vinylidene fluoride (VDF) (co)polymer and at least one second copolymer comprising i) recurring units derived from at least one ethylen ically unsaturated (meth)acrylic monomer and ii) recurring units derived from at least two different ethylenically unsaturated monomers having a nitrogen-containing heterocycle respectively. The present invention also relates to use of said second copolymer as an adhesion promoter towards a current collector of an electrode in a secondary battery.

BACKGROUND OF THE INVENTION

[0003] An electrochemical cell (also referred to as a “battery”) typically comprises a cathode and an anode, collectively referred to as electrodes. To manufacture such an electrode, electroactive materials are deposited onto a conductive support, acting as a current collector for the electrode. Maintaining an efficient electrical contact between the electroactive materials and the conductive support is necessary for the proper functioning of the electrochemical cell.

[0004] There have been efforts to optimize the electrical contact, for instance, by using a primer which is deposited between the electroactive materials and the conductive support. WO 2009/054987 (Sion Power Corporation), for instance, discloses a primer suitable for the manufacture of an electrode exhibiting good adhesion and electrical contact between the electroactive materials and the conductive support that brings about high discharge capacities in an electrochemical cell. EP 2639863 (Zeon Corporation) discloses a positive electrode for a secondary cell comprising a current collector (in aluminum or aluminum alloy) and a positive electroactive material layer, wherein the positive electroactive material layer contains a positive electroactive material, a water-based binder, an organic phosphonic acid compound, and a polyvalent metal compound, which results in suppressing corrosion of the current collector.

[0005] Fluorinated polymers such as vinylidene difluoride (VDF) (co)polymers have been widely used as binders in conventional lithium-ion batteries. Thanks to their good oxidative resistance, they are mostly applied in the cathode formulations of lithium-ion batteries.

[0006] EP 3649687 A1 (PPG INDUSTRIES OHIO, INC.) relates to a stable VDF polymer dispersion using alternatives to N-methyl-2-pyrrolidone (NMP), for use as a binder in preparing an electrode-forming composition. The electrode-forming composition comprises an electroactive material and a binder, wherein the binder comprises i) a polymer comprising a fluoropolymer dispersed in a liquid medium and ii) a polymer comprising an addition polymer comprising constitutional units comprising the residue of a heterocyclic group-containing ethylenically unsaturated monomer. It is understood that said addition polymer having heterocyclic functionality better disperses carbon by reducing the viscosity of carbon dispersions, resulting in excellent peel strength.

[0007] There still remains however a continuous need in this field for a binder solution for a secondary battery, which exhibits superior adhesion properties towards a current collector, while maintaining high ionic conductivity and good mechanical properties.

SUMMARY OF THE INVENTION

A first object of the invention is a binder solution comprising: a) at least one polymer blend that comprises at least one vinylidene difluoride (VDF) (co)polymer; and at least one second copolymer comprising i) recurring units derived from at least one ethylenically unsaturated (meth)acrylic monomer [monomer (MA)] and ii) recurring units derived from at least two ethylenically unsaturated monomers having a nitrogen-containing heterocycle respectively [monomers (NMs)]; and b) at least one non-aqueous solvent, wherein said at least two monomers (NMs) are different from each other and are represented respectively by Formula (I):

wherein:

R¹, R², R³, R⁴, R⁵ and R⁶, being the same or different from each other, are selected from the group consisting of a hydrogen atom, a linear or branched C1-C6 alkyl group, and a 5- to 6-membered cyclic group;

A is a linkage selected from the group consisting of: a single covalent bond; and a spacer selected from the group consisting of -CO-NH-(CH2)n-, -CO-O- (CH2)n- and -CO-O-(CH2)n-O-CO-, n being an integer from 1 to 5, typically 3 or 4;

X is selected from the group consisting of a carbon atom, a nitrogen atom and a carbonyl group;

Y and Z, independently from each other, are a carbon atom or a nitrogen atom; a, b and c, independently from each other, are an integer 1 or 2; and each dashed-dotted line represents an optional double bond.

[0008] A second object of the invention is a slurry for manufacturing an electrode, comprising a binder solution according to the present invention, c) at least one electroactive material and d) optionally at least one conductive agent.

[0009] A third object of the invention is a process for preparing an electrode, comprising the steps of: providing a current collector having at least one surface; applying a slurry of the present invention onto the surface of said current collector, thereby providing an assembly comprising a metal substrate surface-coated with said slurry; subsequently drying the assembly; and optionally compacting the dried assembly to obtain an electrode.

[0010] A fourth object of the invention is an electrode obtainable by the process according to the present invention.

[0011] A fifth object of the invention is a secondary battery comprising a positive electrode, a negative electrode, and a membrane that is positioned between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is an electrode obtainable by the process according to the present invention.

[0012] Another object of the invention is use of a copolymer comprising i) recurring units derived from at least one ethylenically unsaturated (meth)acrylic monomer [monomer (MA)] and ii) recurring units derived from at least two ethylenically unsaturated (meth)acrylic monomers having a nitrogen-containing heterocycle respectively [monomers (NMs)], wherein said at least two monomers (NMs) are different from each other, as an adhesion promoter towards a current collector of an electrode in a secondary battery.

[0013] It was surprisingly found by the inventors that a copolymer comprising i) recurring units derived from at least one ethylenically unsaturated (meth)acrylic monomer [monomer (MA)] and ii) recurring units derived from at least two different ethylenically unsaturated (meth)acrylic monomers having a nitrogen-containing heterocycle [monomers (NMs)] may deliver a particularly advantageous adhesion properties toward a current collector in an electrode, notably when blended with a VDF (co)polymer.

DETAILED DESCRIPTION OF THE INVENTION

[0014] Ratios, concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. In the context of the present invention, the term ‘percent by weight’ (wt%) indicates the content of a specific component in a mixture, calculated as the ratio between the weight of the component and the total weight of the mixture.

[0015] It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention as claimed. Accordingly, various changes and modifications described herein will be apparent to those skilled in the art. Moreover, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

[0016] For the purpose of the present invention, by the term “a secondary battery” it is intended to denote a rechargeable battery.

[0017] The present invention provides a binder solution for a secondary battery comprising: a) at least one polymer blend that comprises at least one vinylidene difluoride (VDF) (co)polymer; and at least one second copolymer comprising i) recurring units derived from at least one ethylenically unsaturated (meth)acrylic monomer [monomer (MA)] and ii) recurring units derived from at least two ethylenically unsaturated monomers having a nitrogen-containing heterocycle respectively [monomers (NMs)]; and b) at least one non-aqueous solvent, wherein said at least two monomers (NMs) are different from each other and are represented respectively by Formula (I):

wherein:

R¹, R², R³, R⁴, R⁵ and R⁶, being the same or different from each other, are selected from the group consisting of a hydrogen atom, a linear or branched C1-C6 alkyl group, and a 5- to 6-membered cyclic group;

A is a linkage selected from the group consisting of: a single covalent bond; and a spacer selected from the group consisting of -CO-NH-(CH2)n-, -CO-O- (CH2)n- and -CO-O-(CH2)n-O-CO-, n being an integer from 1 to 5, typically 3 or 4;

X is selected from the group consisting of a carbon atom, a nitrogen atom and a carbonyl group;

Y and Z, independently from each other, are a carbon atom ora nitrogen atom; a, b and c, independently from each other, are an integer 1 or 2; and each dashed-dotted line represents an optional double bond.

[0018] VDF (co)polymer

[0019] Vinylidenefluoride polymer (PVDF or VDF polymer) is one of the most widely used fluoropolymers in battery components, thanks to its high cathodic stability, binding strength and adhesion with current collectors.

[0020] In the present invention, a VDF (co)polymer is intended to denote a homopolymer or copolymer comprising recurring units derived from VDF.

[0021] The VDF copolymer typically comprises additional recurring units derived from a second monomer different from VDF, selected from the group consisting of:

C2-C8 partially or fully fluorinated olefins, such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene and hexafluoroisobutylene;

C2-C8 hydrogenated olefins different from VDF, such as vinyl fluoride (VF), trifluoroethylene (TrFE);

(per)fluoroalkyl ethylenes of formula CH2 = CH-Rf, wherein Rf is a Ci-Ce perfluoroalkyl group;

C2-C8 chloro and/or bromo and/or iodo-fluoroolefins such as chlorotrifluoroethylene (CTFE); (per)fluoroalkylvinylethers (PAVE) of formula CF2=CFORf, wherein Rf is a C1-C6 (per)fluoroalkyl group, e.g. CF3, C2F5, C3F7;

(per)fluoroalkylvinylethers of formula CF2=CFORfi, wherein R fi is a Ci-Ce fluoro- or perfluoroalkyl, e.g. CF3, C2F5, C3F7;

CF2=CFOXO (per)fluoro-oxyalkylvinylethers, wherein Xo is a C1-C12 alkyl group, a C1-C12 oxyalkyl group or a C1-C12 (per)fluorooxyalkyl group having one or more ether groups, such as perfluoro-2-propoxy-propyl group; (per)fluoroalkylvinylethers of formula CF2=CFOCF2ORf2, wherein Rf2 is a Ci-Ce fluoro- or perfluoroalkyl group, e.g. CF3, C2F5, C3F7 or a Ci-Ce (per)fluorooxyalkyl group having one or more ether groups such as -C2F5- O-CF3;

- functional (per)fluoro-oxyalkylvinylethers of formula CF2=CFOYo, wherein Yo is a C1-C12 alkyl group or (per)fluoroalkyl group, a C1-C12 oxyalkyl group or a C1-C12 (per)fluorooxyalkyl group having one or more ether groups and Yo comprising a carboxylic or sulfonic acid group, in its acid, acid halide or salt form;

- fluorodioxoles, preferably perfluorodioxoles;

(alkyl) acrylate, e.g., acrylate, methacrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxyethylhexyl (meth)acrylate, methyl methacrylate, butyl acrylate; and hydrogenated monomers denoting an ethylenically unsaturated monomers free of fluorine atom, e.g., ethylene, propylene, vinyl monomers such as vinyl acetate, including styrene and p-methylstyrene.

[0022] Preferably, the second monomer is advantageously selected from the group consisting of vinyl fluoride (VF), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), 1 ,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), (per)fluoroalkylvinylethers (PAVE), such as perfluoro(methyl)vinyl ether (PMVE), perfluoro(ethyl) vinyl ether (PEVE) and perfluoro(propyl)vinyl ether (PPVE), perfluoro-1 ,3-dioxole, and perfluoro(2,2-dimethyl-1 ,3-dioxole) (PDD).

[0023] The VDF copolymer may further comprise third recurring units derived from a third monomer different from VDF and also different from a second monomer. [0024] In order to further improve the performance, various VDF copolymers have been studied and as non-limitative examples of the VDF (co)polymers useful in the present invention, mention can be notably made of VDF homopolymers, VDF/TFE copolymers, VDF/TFE/HFP copolymers, VDF/TFE/CTFE copolymers, VDF/TFE/TrFE copolymers, VDF/CTFE copolymers, VDF/HFP copolymers, VDF/CTFE/HFP copolymer, VDF/TFE/HFP/CTFE copolymers, and the like.

[0025] Second copolymer

[0026] In the present invention, a second copolymer comprises i) recurring units derived from at least one ethylenically unsaturated (meth)acrylic monomer [monomer (MA)] and ii) recurring units derived from at least two different ethylenically unsaturated monomers having a nitrogen-containing heterocycle respectively [monomers (NMs)].

[0027] The second polymer can be polymerized by radical copolymerization of a mixture of at least one monomer (MA) and at least two monomers (NMs) as above defined.

[0028] Any source of free radicals can be used. It is possible in particular to generate free radicals spontaneously, for example by increasing the temperature, with appropriate monomers, such as styrene. It is possible to generate free radicals by irradiation, in particular by UV irradiation, preferably in the presence of appropriate UV-sensitive initiators. It is also possible to use initiators or initiator systems of radical or redox type. The source of free radicals may or may not be water-soluble. It may be preferable to use water-soluble initiators or at least partially water-soluble initiators.

[0029] In the present invention, the ethylenically unsaturated (meth)acrylic monomer [monomer (MA)] is hydrophobic.

[0030] In one embodiment, the ethylenically unsaturated (meth)acrylic monomer [monomer (MA)] is an alkyl ester of (meth)acrylic acid.

[0031] In a particular embodiment, the monomer (MA) is represented by Formula (II)

wherein:

R⁷, R⁸ and R⁹, equal to or different from each other, are independently selected from a hydrogen atom and a C1-C3 hydrocarbon group; and Rx is a C1-C20 hydrocarbon moiety.

[0032] Non-limitative examples of the monomer (MA) include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-hexyl (meth)acrylate, and n-octyl (meth)acrylate.

[0033] Preferably, the monomer (MA) is selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, lauryl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and mixtures thereof.

[0034] More preferably, the monomer (MA) is selected from the group consisting of methyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and mixtures thereof.

[0035] The ethylenically unsaturated (meth)acrylic monomer [monomer (MA)] may be an alkyl ester of maleic anhydride, and as non-limitative examples of the monomer (MA), mention can be notably made of monomethyl maleic anhydride ester, dimethyl maleic anhydride ester, monoethyl maleic anhydride ester, and diethyl maleic anhydride ester.

[0036] In one embodiment, the ethylenically unsaturated monomer having a nitrogen-containing heterocycle [monomer (NM)] of Formula (I) includes a 5- to 6-membered cyclic group having at least one nitrogen in the ring.

[0037] The 5- to 6-membered cyclic group having at least one nitrogen in the ring may be aromatic. Non-limitative examples of the 5- to 6-membered aromatic cyclic group include pyrroles, pyrrolines (a.k.a. dihydropyrroles), imidazoles, pyrazoles, 1 ,2,3-triazoles, 1 ,2,4-triazoles, pyridines, pyridazines (a.k.a. 1 ,2-diazines), pyrimidines (a.k.a. 1 ,3-diazines), pyrazines (a.k.a. 1 ,4-diazines), and triazines. Preferred embodiments are imidazoles. [0038] The 5- to 6-membered cyclic group having at least one nitrogen in the ring may be non-aromatic. Non-limitative examples of the 5- to 6-membered non-aromatic cyclic group include pyrrolidines, pyrrolidones, and piperidines. Preferred embodiments are pyrrolidones.

[0039] The linkage A and the residues R⁴, R⁵ and R⁶ may be attached to the heterocyclic group at any position, either on carbon or nitrogen atom.

[0040] The divalent spacer group A in Formula (I) may typically be -CO-NH- (CH2)n- group, -CO-O-(CH₂)n group or -CO-O-(CH2)n-O-CO- group, n being an integer from 1 to 5, but any other covalent linker group may be contemplated, for example resulting from the reaction of a compound of Formula (l-X):

wherein R¹, R² and R³ are as above defined, with a compound of Formula (l-Y):

(l-Y) wherein R⁴, R⁵ and R⁶ are as above defined, A¹ and A² are two groups reacting together to form a covalent bond.

[0041] For example, A² may be a -(CH2)m-NH2 group wherein m is from 1 to 4, preferably 2 or 3. In that case, A¹ may be for example a carboxylic acid, an acid chloride, an anhydride, an epoxy or an isocyanate group.

[0042] According to another variant, A² may be a -(CH2)m-OH group wherein m is from 1 to 4, preferably 2 or 3. In that case, A¹ may be for example a carboxylic acid, an acid chloride, an anhydride, an ester or an isocyanate group. [0043] In one embodiment, the monomers (NMs) are selected from the group consisting of N-vinylimidazole, 2-vinylimidazole, 4-vinylimidazole, 2- methyl-1-vinylimidazole, N-vinylpyrazole, 3-vinylpyrazole, 4-vinylpyrazole, N-vinyl-1 ,2,3-triazole, N-vinyl-1 ,2,4-triazole, 5-vinyl-1 H-tetrazole, 2-vinyl-2- oxazoline, 4-vinyl-isoxazole, vinyl-1 , 2, 4-oxadiazole, vinyl-1 , 3, 4-oxadiazole, 5-vinyl-1 ,2-thiazole, 4-vinyl-1 ,2,3-thiadiazole, 4-vinyl-1 ,2,5-thiadiazole, N- vinylpyrrole, 2-vinyl-1 H-pyrrole, N-vinyl-1 -pyrroline, 2-vinylpyridine, 4- vinylpyridine, N-vinylpyrrolidine, N-vinyl-2-pyrrolidone, 4-vinylpiperidine, 2- vinylpiperidine, 5-vinylpyrimidine, 2-vinylpyrazine, 4-vinylpyrazine, 2-vinyl- 4,6-diamino-1 ,3,5-triazine, 6-vinyl-2,4-diamine-1 ,3,5-triazine, and mixtures thereof.

[0044] In one embodiment, the weight ratio between the VDF (co)polymer and the second copolymer in the polymer blend of the present invention is from 40: 1 to 3: 1 , preferably from 20: 1 to 6: 1 .

[0045] The second copolymer typically comprises from 1 .0 to 50.0% by moles (mol%), preferably from 5.0 to 40.0 mol%, more preferably from 5.0 to 30.0 mol% of ii) recurring units derived from at least two different monomers having a nitrogen-containing heterocycle [monomers (NMs)], with respect to the total moles of recurring units of the second copolymer.

[0046] Preferably, the second copolymer comprises ii) recurring units derived from N-vinylimidazole and N-vinyl-2-pyrrolidone.

[0047] More preferably, the second copolymer comprises ii) recurring units derived from N-vinylimidazole and N-vinyl-2-pyrrolidone, the mol% of N- vinyl-2-pyrrolidone being greater than the mol% of N-vinylimidazole, with respect to the total moles of recurring units of the second copolymer.

[0048] In one embodiment, the second copolymer comprises from 5.0 to 40.0 mol% of ii) recurring units derived from N-vinylimidazole and N- vinylpyrrolidone, wherein the mol% of N-vinylpyrrolidone is higher than the mol% of N-vinylimidazole, with respect to the total moles of recurring units of the second copolymer.

[0049] Preferably, the second copolymer comprises from 5.0 to 30.0 mol% of ii) recurring units derived from N-vinylimidazole and N-vinyl-2-pyrrolidone, wherein the mol% of N-vinyl-2-pyrrolidone is greater than the mol% of N- vinylim idazole, with respect to the total moles of recurring units of the second copolymer.

[0050] More preferably, the second copolymer comprises from 20.0 to 30.0 mol% of ii) recurring units derived from N-vinylimidazole and N-vinyl-2- pyrrolidone, wherein the mol% of N-vinyl-2-pyrrolidone is greater than the mol% of N-vinylimidazole, with respect to the total moles of recurring units of the second copolymer.

[0051] In a particular embodiment, the second copolymer comprises from 70.0 to 95.0 mol% of i) recurring units derived from at least one ethylenically unsaturated (meth)acrylic monomer [monomer (MA)] and from 5.0 to 30.0 mol% of ii) recurring units derived from at least two ethylenically unsaturated monomers having a nitrogen-containing heterocycle [monomers (NMs)], with respect to the total moles of recurring units of the second copolymer, wherein said at least two monomers (NMs) are different from each other.

[0052] In a more particular embodiment, the second copolymer comprises from 70.0 to 95.0 mol% of i) recurring units derived from methyl methacrylate and butyl acrylate and from 5.0 to 30.0 mol% of ii) recurring units derived from N-vinylimidazole and N-vinyl-2-pyrrolidone, wherein the mol% of N- vinyl-2-pyrrolidone is greater than the mol% of N-vinylimidazole, with respect to the total moles of recurring units of the second copolymer.

[0053] The second copolymer is typically amorphous, exhibits a low degree of crystallinity, i.e. having crystalline phase less than 20 vol%, and has a glass transition temperature (T_g) below room temperature. In most cases, the second copolymer has advantageously a T_g below 10°C, preferably below 5°C, more preferably below 0°C, even more preferably below -5°C.

[0054] The term “amorphous” is hereby intended to denote a polymer having a heat of fusion of less than 5.0 J/g, preferably of less than 3.0 J/g, and more preferably of less than 2.0 J/g as measured by Differential Scanning Calorimetry (DSC) at a heating rate of 10 °C/min according to ASTM D3418.

[0055] The present invention also relates to a slurry for manufacturing an electrode, comprising a binder solution according to the present invention, c) at least one electroactive material, and optionally d) at least one conductive agent.

[0056] Regarding the non-aqueous solvent, there is no specific restriction imposed, as long as the non-aqueous solvent is able to dissolve a fluoropolymer of the present invention.

[0057] Suitable non-aqueous solvents are typically selected from the group consisting of carboxylic acid esters, such as alkyl propionate, dialkyl malonato and alkyl acetate; cyclic esters, such as y-butyrolactone; cyclic sulfonates such as propanesulfone; alkyl sulfonate; alkyl phosphate; and mixtures thereof.

[0058] In some embodiments, the non-aqueous solvent is selected from the group consisting of nitrile-containing solvents, ethers, esters, thiols, thioethers, ketones, and tertiary amines.

[0059] The non-aqueous solvent may be a nitrile-containing solvent with general formula of R-CN, where R represents an alkyl group. Non-limiting examples of nitrile-containing solvents are acetonitrile, butyronitrile, valeronitrile, isobutylnitrile and the like.

[0060] The non-aqueous solvent may be an ether with general formula of R1-O-R2, where R1 and R2 represent independently an alkyl group. Included in the ether solvents are cyclic ethers based on 3, 5 or 6-membered rings. The cyclic ethers can be substituted with alkyl groups, can have unsaturation and can have additional functional elements such as nitrogen or oxygen atoms inside the ring. Non-limiting examples of (cyclic) ether solvents are diethylether, 1 ,2-dimethoxyether, cyclopentyl methyl ether, diethyl ether, dibutyl ether, 1 ,3-dioxolane, 1 ,3-dioxane, anisole, tetrahydrofuran, methyl tetrahydrofuran, tetrahydropyran and the like.

[0061 ] The non-aqueous solvent may be an ester with general formula of R3-COO- R4, where R3 and R4 represent independently an alkyl group. Non-limiting examples of ester solvents are butyl butyrate, ethyl benzoate and the like.

[0062] The non-aqueous solvent may be a thiol with general formula of Rs-S-H or thioether with general formula of R6-S-R7, where Rs, Re and R7 are independently an alkyl group. Included in the thioether solvents are cyclic thioethers based on 3, 5 or 6 membered rings. The cyclic thioethers can be substituted with alkyl groups, can have unsaturation and can have additional functional elements such as nitrogen or oxygen atoms inside the ring. Nonlimiting examples of thiol solvents are ethanethiol, tert-dodecyl mercaptan, thiophenol, tert-butyl mercaptan, octanethiol, dimethylsulfide, ethylmethylsulfide, methyl benzylsulfide and the like.

[0063] The non-aqueous solvent may be a ketone with general formula of RSR9C=O, where Rs and R9 represent independently an alkyl group. Nonlimiting examples of ketone solvents are methyl ethyl ketone, methyl isobutyl ketone, di-isobutyl ketone, acetophenone, benzophenone and the like.

[0064] In a particular embodiment, the non-aqueous solvent is a tertiary amine with general formula of R10R11R12N, where R10, R11 and R12 represent independently an alkyl group. The N atom of the tertiary amine can be buried inside a 3, 5 or 6 membered ring. Non-limiting examples of tertiary amine solvents are triethylamine, dimethylbutylamine, tributylamine, cyclohexyldimethylamine, N-ethylpiperidine and the like.

[0065] In the present invention, the alkyl groups of R1 to R12 respectively refer to “alkyl groups” including saturated hydrocarbons having one or more carbon atoms, including straight-chain alkyl groups, such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, cyclic alkyl groups (or "cycloalkyl" or "alicyclic" or "carbocyclic" groups), such as cyclopropyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl, branched-chain alkyl groups, such as isopropyl, tert-butyl, sec-butyl, and isobutyl, and alkylsubstituted alkyl groups, such as alkyl-substituted cycloalkyl groups and cycloalkyl-substituted alkyl groups as defined above. Additionally, the alkyl groups may include functional groups such as 1 or more unsaturation, ether, carbonyl, carboxyl, hydroxyl, thio, thiol, thioxy, sulfo, nitrile, nitro, nitroso, azo, amide, imide, amino, imino or halogen.

[0066] In another particular embodiment, the non-aqueous solvent is an organic carbonate, which may be partially or fully fluorinated. In the present invention, the organic carbonate may be either cyclic or acyclic. Non-limiting examples of the organic carbonate include, notably, ethylene carbonate (1 ,3-dioxolan-2-one), propylene carbonate, 4-methylene-1 ,3-dioxolan-2- one, 4,5-dimethylene-1 ,3-dioxolan-2-one, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, methyl propyl carbonate, methyl butyl carbonate, ethyl butyl carbonate, propyl butyl carbonate, dibutyl carbonate, di-tert-butyl carbonate, butylene carbonate, mono- and difluorinated ethylene carbonate, mono- and difluorinated propylene carbonate, mono- and difluorinated butylene carbonate, 3,3,3- trifluoropropylene carbonate, fluorinated dimethyl carbonate, fluorinated diethyl carbonate, fluorinated ethyl methyl carbonate, fluorinated dipropyl carbonate, fluorinated dibutyl carbonate, fluorinated methyl propyl carbonate, and fluorinated ethyl propyl carbonate.

[0067] In the other particular embodiment, the non-aqueous solvent is selected from the group consisting of acyclic amides, lactams, lactones, cyclic sulfones, sulfoxides, and tertiary phosphines. Non-limiting examples of the non-aqueous solvent include, notably, dimethyl formamide, /V,/V- dimethylacetamide, N-methyl-2-pyrrolidone, /V-ethyl pyrrolidone, y- butyrolactone, Y-^val^er°l^actone. sulfolane, dimethyl sulfoxide, and hexamethylphosphoramide. In a more preferred embodiment, the nonaqueous solvent is /\/-methyl-2-pyrrolidone (NMP).

[0068] In the present invention, the term “electroactive material” is intended to denote a material that is able to incorporate or insert into its structure and substantially release therefrom metal ions during the charging and discharging phases in a battery.

[0069] The electroactive material is either for a positive electrode or for a negative electrode.

[0070] An electrode in an electrochemical cell is referred to as either an anode or cathode. The anode is defined as the electrode where electrons leave the cell and oxidation occurs, and the cathode as the electrode where electrons enter the cell and reduction occurs. Each electrode may become either an anode or a cathode depending on the direction of electric current through a cell. A bipolar electrode is an electrode that functions as the anode of one cell and the cathode of another cell. When a cell is being charged, the anode becomes the positive electrode and the cathode becomes the negative electrode, while when a cell is being discharged, the anode becomes the negative electrode and the cathode becomes the positive electrode.

[0071] In the present invention, the term “positive electrode” is intended to denote, in particular, the electrode of an electrochemical cell, where reduction occurs during discharging, while the term “negative electrode” is intended to denote, in particular, the electrode of an electrochemical cell, where oxidation occurs during discharging.

[0072] In the case of forming a positive electrode for a secondary battery, the positive electroactive material is not particularly limited. It may comprise a composite metal chalcogenide of formula LiMCh, wherein M is at least one metal selected from transition metals such as Co, Ni, Fe, Mn, Cr, and V and Q is a chalcogen such as O or S. Among these, it is preferred to use a lithium-based composite metal oxide of formula UMO2, wherein M is the same as defined above. Preferred examples thereof may include LiCoCb, LiNiO2, LiNixCoi-xO2 (0 < x < 1 ), and spinel-structured LiMn2O4.

[0073] Another preferred examples thereof may include lithium-nickel- manganese-cobalt-based metal oxide of formula LiNixMn_yCo_zO2 (x+y+z=1 , referred to as NMC), for instance LiNii/sMni/sCoi/sCk, LiNi0.6Mn0.2Co0.2O2, lithium-nickel-cobalt-aluminum-based metal oxide of formula LiNi_xCo_yAlzO2 (x+y+z=1 , referred to as NCA), for instance LiNi0.8Co0.15AI0.05O2, lithium- cobalt-based metal oxide, or lithium-nickel-manganese-based metal oxide (LNMO).

[0074] Alternatively, the positive electroactive material may comprise a lithiated or partially lithiated transition metal oxyanion-based electroactive material of formula Mi M2(JO4)fEi-f, wherein Mi is lithium, which may be partially substituted by another alkali metal representing less that 20% of the Mi metals, M2 is a transition metal at the oxidation level of +2 selected from Fe, Mn, Ni or mixtures thereof, which may be partially substituted by one or more additional metals at oxidation levels between +1 and +5 and representing less than 35% of the M2 metals, including 0, JO4 is any oxyanion wherein J is either P, S, V, Si, Nb, Mo or a combination thereof, E is a fluoride, hydroxide or chloride anion, f is the molar fraction of the JO4 oxyanion, generally comprised between 0.75 and 1. [0075] The Mi M2(JO4)fEi-f electroactive material as defined above is preferably phosphate-based and may have an ordered or modified olivine structure.

[0076] More preferably, the electroactive material of a positive electrode has formula Li3-xM’_yM”2-_y(JO4)3 wherein 0<x<3, 0<y<2, M’ and M” are the same or different metals, at least one of which being a transition metal, JO4 is preferably PO4 which may be partially substituted with another oxyanion, wherein J is either S, V, Si, Nb, Mo or a combination thereof. Still more preferably, the electroactive material is a phosphate-based electroactive material of formula Li(Fe_xMni-_x)PO4 wherein 0<x<1 , preferably x=1 , i.e. lithium iron phosphate of formula LiFePCU.

[0077] Preferably, the electroactive material of a positive electrode is selected from the group consisting of UMQ2, wherein M is at least one metal selected from Co, Ni, Fe, Mn, Cr and V and Q is O or S; LiNi_xCoi-_xO2 (0<x<1 ); spinel-structured LiMn2O4; lithium-nickel-manganese-cobalt- based metal oxide of formula LiNi_xMn_yCo_zO2 (x+y+z=1 ), lithium-nickel- cobalt-aluminum-based metal oxide of formula LiNi_xCo_yAl_zO2 (x+y+z=1 ), and LiFePC

[0078] Preferably, the electroactive material of a positive electrode is selected from the group consisting of UMQ2, wherein M is at least one metal selected from Co, Ni, Fe, Mn, Cr and V and Q is O or S; LiNi_xCoi-_xO2 (0 < x < 1 ); spinel-structured LiMn2O4; lithium-nickel-manganese-cobalt-based metal oxide of formula LiNi_xMn_yCo_zO2 (x+y+z = 1 ) (NMC), lithium-nickel- cobalt-aluminum-based metal oxide of formula LiNi_xCo_yAl_zO2 (x+y+z = 1 ) (NCA), lithium-cobalt-based metal oxide (LCO), lithium-nickel-manganese- based metal oxide (LNMO) and LiFePO4.

[0079] More preferably, the electroactive material of a positive electrode is selected from the group consisting of NMC, NCA, LCO, LNMO and LiFePO₄.

[0080] The amount of c) the electroactive material is typically at least 80.0 wt%, preferably at least 90.0 wt%, more preferably at least 95.0 wt%, and/or at most 99.0 wt%, preferably at most 98.0 wt%, based on the total weight of the electrode-forming composition. [0081] Preferably, the amount of c) the electroactive material is from 80.0 to 99.0 wt%, preferably from 90.0 to 98.0 wt%, more preferably from 95.0 to 98.0 wt%, based on the total weight of the electrode-forming composition.

[0082] In the present invention, the term “conductive agent” is intended to denote, in particular, a material which is used to ensure electrodes to have good charging and discharging performance and to provide additional electrical conductivity. Non-limiting examples of the conductive agent known in the art are carbonaceous materials and metal powders or fibers, for instance carbon black, carbon nanotube (CNT, single wall or multiwall), vapor- grown carbon fiber (VGCF), graphite, graphene, graphite fiber, and fine powder or fibers of metals such as nickel or aluminum. Examples of carbon blacks include Ketjen black and acetylene black. The optional conductive agent is preferably carbon black. Carbon black is available, for example, under the brand names, Super P® or Ketjenblack®.

[0083] The amount of optional conductive agent is preferably from 0 to 10.0 wt% of the total solids in the electrode-forming composition. For instance, for a positive electrode-forming composition the optional conductive agent is typically from 0 to 10.0 wt%, more preferably from 0 to 5.0 wt% of the total amount of the solids within the composition. In a particular embodiment, the amount of conductive agent is from 0.1 to 10.0 wt%, preferably from 0.5 to 8.0 wt%, more preferably from 0.5 to 5.0 wt% of the total amount of the solids within the electrode-forming composition.

[0084] The slurry of the present invention can be used in a process for preparing an electrode comprising the steps of: providing a current collector having at least one surface; applying a slurry of the present invention onto the surface of said current collector, thereby providing an assembly comprising a metal substrate surface-coated with said electrode-forming composition; subsequently drying the assembly; and optionally compacting the dried assembly to obtain an electrode.

[0085] In the present invention, the nature of the “current collector” depends on whether the electrode thereby provided is either a positive electrode or a negative electrode. Should the electrode of the invention be a positive electrode, the current collector typically comprises, preferably consists of at least one metal selected from the group consisting of Aluminum (Al), Nickel (Ni), Titanium (Ti), and alloys thereof, preferably Al. Should the electrode of the invention be a negative electrode, the current collector typically comprises, preferably consists of at least one metal selected from the group consisting of Lithium (Li), Sodium (Na), Zinc (Zn), Magnesium (Mg), Copper (Cu) and alloys thereof, preferably Cu.

[0086] The slurry is typically applied onto at least one surface of the current collector typically by any suitable procedures such as casting, printing and roll coating, which may be repeated, typically one or more times.

[0087] The drying step may be performed either under atmospheric pressure or under vacuum. Alternatively, the drying step may be performed under modified atmosphere, e.g. under an inert gas, typically exempt notably from moisture (water vapour content of less than 0.001 % v/v).

[0088] The drying temperature will be selected so as to effectively remove the non-aqueous solvent from the electrode of the invention by evaporation.

[0089] As an optional step, the dried assembly may be submitted to a compaction step such as a calendaring process, an uniaxial compression process, a isostatic compression process or a combination thereof to achieve the target porosity of the electrode of the invention.

[0090] In a further aspect, the present invention pertains to an electrode obtainable by the process of the invention.

[0091] A fourth object of the present invention is a secondary battery comprising a positive electrode, a negative electrode, and a membrane that is positioned between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is an electrode according to the present invention.

[0092] In the present invention, the term “membrane” is intended to denote, in particular, an ionically permeable membrane placed between a positive electrode and a negative electrode. Its function is to be permeable to the lithium ions while blocking electrons and assuring the physical separation between the electrodes. [0093] The membrane is typically a porous substrate commonly used for a membrane in a secondary battery.

[0094] In one embodiment, the membrane is a porous polymeric material comprising at least one material selected from the group consisting of polyester such as polyethylene terephthalate and polybutylene terephthalate, polyphenylene sulphide, polyacetal, polyamide, polycarbonate, polyimide, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, polyethylene oxide, polyacrylonitrile, polyolefin such as polyethylene and polypropylene, or mixtures thereof, optionally coated with inorganic nanoparticles.

[0095] Non-limitative examples of the inorganic nanoparticles comprise SiCh, TiO2, AI2O3, and ZrO2.

[0096] In a particular embodiment, the membrane is a polyester film coated with either SiO2 or AI2O3.

[0097] A fifth object of the present invention is use of at least one copolymer comprising i) recurring units derived from at least one ethylenically unsaturated (meth)acrylic monomer [monomer (MA)] and ii) recurring units derived from at least two ethylenically unsaturated monomers having a nitrogen-containing heterocycle respectively [monomers (NMs)] as above defined, as an adhesion promoter towards a current collector of an electrode in a solid-state battery, wherein said at least two monomers (NMs) are different from each other.

[0098] In one embodiment, the copolymer is blended with a VDF (co)polymer.

[0099] In a particular embodiment, the copolymer blended with a VDF (co)polymer is dissolved in at least one non-aqueous solvent as above defined.

[00100] In a more particular embodiment, the copolymer blended with a VDF (co)polymer is dissolved in dimethyl formamide, /V,/V-dimethylacetamide, N-methyl-2-pyrrolidone, /V-ethyl pyrrolidone, y-butyrolactone, y- valerolactone, sulfolane, dimethyl sulfoxide, and hexamethylphosphoramide.

[00101] In a preferred embodiment, the copolymer blended with a VDF (co)polymer is dissolved in /V-methyl-2-pyrrolidone (NMP). [00102] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[00103] The invention will be now explained in more detail with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the invention.

[00104] EXAMPLES

[00105] Raw Materials

- LFP (DY3): cathode electroactive material, commercially available from Dyanonic;

- CNT: carbon nanotube as a conductive agent, commercially available from Cnano;

- Butyl butyrate (BB, 99%); Methyl methacrylate (MMA, 99%); N- vinylpyrrolidone (NVP, 99%); N-vinylimidazole (NVI, 99%); 2,2'-azobis(2- methylbutyronitrile) (98%); Xylene (100%), respectively, commercially available from Sigma Aldrich;

- VDF polymer: SOLEF® 6020 commercially available from Solvay Specialty Polymers Italy S.p.A.;

[00106] Synthesis of Second copolymer: BA-MMA-NVP-NVI (56.25/18.75/20/5 in mol%)

[00107] Into a 2 L double-jacketed reactor equipped with mechanical agitator and reflux condenser were added 18.546 g (0.143 mol) of BA, 4.829 g (0.048 mol) of MMA, 57.178 g (0.509 mol) of NVP, 1.211 g (0.013 mol) of NVI, 6.495 g (0.033 mol) of 2,2'-azobis(2-methylbutyronitrile) and 321.709 g of xylene. The reaction mixture was then degassed by bubbling nitrogen and the reactor content was heated to 75°C under agitation. Once the temperature reached at 75°C, a solution of BA (165.241 g, 1.289 mol), MMA (43.027 g, 0.430 mol) and NVI (10.786 g, 0.115 mol) was then introduced continuously over 5 hours via a syringe pump. Once the feed of monomers was completed, the reaction mixture was aged at 75°C for additional 2 hours and one more hour at 80°C whereupon it was cooled to ambient temperature and discharged. The solid content as measured was 47.54% (130°C, 30 min). Monomer conversions were as follows: BA > 98.2%; MMA > 99.5%; NVP > 99.5%; NVI > 92.0%.

[00108] Preparation of a polymer blend solution of VDF polymer and a second copolymer in a non-aqueous solvent according to the present invention

[00109] A 10.0 wt% of a VDF polymer solution was prepared by weighing 1 g of VDF polymer (dried at 120°C overnight) and 9 g of BB (dried over molecular sieves 4 A). The solution was then stirred for a night at 500 rpm. The correct amount of a second copolymer was added to the above 10.0 wt% VDF polymer solution in order to obtain a solution comprising a VDF polymer and a second copolymer in a weight ratio of 3.8:0.2, and mixed together for a night at 500 rpm to obtain a polymer blend solution in a nonaqueous solvent. The second copolymer was used as obtained from its synthesis.

[00110] Preparation of a VDF polymer solution in a non-aqueous solvent

[00111] A 10.0 wt% of a VDF polymer solution was prepared by weighing 1 g of VDF polymer (dried at 120°C overnight) and 9 g of BB (dried over molecular sieves 4 A). The solution was then stirred for a night at 500 rpm to obtain a polymer solution in a non-aqueous solvent.

[00112] Preparation of Positive Electrodes

[00113] A positive electrode composed of 95.75 pbw of LFP, 3.5 pbw of the Polymer blend according to the present invention, and 0.75 pbw of CNTs was produced as the following:

[00114] 24.01 g of the polymer blend solution, 14.48 g of CNTs, 75.07 g of LFP and 8.08 g of NMP were mixed for 3 minutes in a rotational mixer from Kurabo. Subsequently, 10.29 g of the polymer blend solution was added together with 8.07 g of NMP. The slurry as obtained was again mixed for additional 7 minutes, and then kept in the disperser (Dispermat®) with a butterfly impeller for 50 minutes.

[00115] The total solid content (TSC) was measured as being 56%, and then the TSC was adjusted to 54% by dilution with NMP. [00116] Prior to casting, the slurry was kept in the Kurabo mixer for 7 minutes and then the casting was made on aluminum (Al) current collector, with the loading of 30 mg/cm2 (deviation below 5%).

[00117] The wet film was dried at 90°C for 50 minutes under vacuum. All the materials, the preparation and further testing were performed in a dry room with dew point of -10°C.

[00118] Another positive electrode as a comparative example was prepared in the same manner as above described, except that a VDF polymer solution, i.e. without the second copolymer, was used instead the polymer blend solution according to the present invention.

[00119] Measurement of Adhesion property of Positive electrodes toward Al current collector (Peel-off test):

[00120] The adhesion strength of the positive electrode to the Al current collector was evaluated using a 180° peel test. An electrode strip (2 cm*10 cm) of the dried electrode was fixed with the electrode facing down and the current collector facing up on a rigid Al plate (2.6 cm*10 cm) using a double sided tape (width 25mm; thickness 0.24mm). The Al current collector was peeled off from the electrode using a motorized tension/compression force test stand (ESM303 from Mark-10 Corporation), maintaining an angle of 180° and at a constant speed of 300 mm/min.

[00121] The force needed to remove the Al current collector from the electrode was measured as an average value of 3 independent strips, generated from 3 independent electrodes using 3 independent slurries with the identical composition. Peel-off tests were performed in a dry room with dew point of -40°C.

[00122] The positive electrode prepared with a binder solution according to the present invention exhibited higher adhesion property, i.e. 3.47 N/m than the comparative positive electrode, i.e. 3.16 N/m. This proves that the binder solution comprising a polymer blend of a VDF polymer and a second copolymer in a non-aqueous solvent according to the present invention contributes to enhancing the adhesion property towards a current collector of an electrode in a secondary battery.

Claims

Claims

Claim 1 . A binder solution for a secondary battery, comprising: a) at least one polymer blend that comprises at least one vinylidene difluoride (VDF) (co)polymer; and at least one second copolymer comprising i) recurring units derived from at least one ethylenically unsaturated (meth)acrylic monomer [monomer (MA)] and ii) recurring units derived from at least two ethylenically unsaturated monomers having a nitrogen-containing heterocycle respectively [monomers (NMs)]; and b) at least one non-aqueous solvent, wherein said at least two monomers (NMs) are different from each other and are represented respectively by Formula (I):

wherein:

R¹, R², R³, R⁴, R⁵ and R⁶, being the same or different from each other, are selected from the group consisting of a hydrogen atom, a linear or branched Ci- Ce alkyl group, and a 5- to 6-membered cyclic group;

A is a linkage selected from the group consisting of: a single covalent bond; and a spacer selected from the group consisting of -CO-NH-(CH2)n-, -CO-O- (CH2)n- and -CO-O-(CH2)n-O-CO-, n being an integer from 1 to 5, typically 3 or 4;

X is selected from the group consisting of a carbon atom, a nitrogen atom and a carbonyl group;

Y and Z, independently from each other, are a carbon atom or a nitrogen atom; a, b and c, independently from each other, are an integer 1 or 2; and each dashed-dotted line represents an optional double bond.

Claim 2. The binder solution according to claim 1 , wherein the VDF copolymer comprises additional recurring units derived from at least one (per)fluorinated monomer different from VDF, selected from the group consisting of:

- C2-C8 partially or fully fluorinated olefins, such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene and hexafluoroisobutylene;

- C2-C8 hydrogenated olefins different from VDF, such as vinyl fluoride (VF), trifluoroethylene (TrFE), perfluoroalkyl ethylenes of formula CH2 = CH-Rf, wherein Rf is a Ci-Ce perfluoroalkyl group;

- C2-C8 chloro and/or bromo and/or iodo-fluoroolefins such as chlorotrifluoroethylene (CTFE); and

- (per)fluoroalkylvinylethers (PAVE) of formula CF2=CFORf, wherein Rf is a C1- Ce (per)fluoroalkyl group, e.g. CF3, C2F5, C3F7.

Claim 3. The binder solution according to claim 1 or 2, wherein the ethylenically unsaturated (meth)acrylic monomer [monomer (MA)] is represented by Formula (II)

wherein:

R⁷, R⁸ and R⁹, equal to or different from each other, are independently selected from a hydrogen atom and a C1-C3 hydrocarbon group; and Rx is a C1-C20 hydrocarbon moiety.

Claim 4. The binder solution according to any one of claims 1 to 3, wherein the ethylenically unsaturated (meth)acrylic monomer [monomer (MA)] is selected from the group consisting of methyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and mixtures thereof.

Claim 5. The binder solution according to any one of claims 1 to 4, wherein the ethylenically unsaturated monomers having a nitrogen-containing heterocycle [monomers (NMs)] are selected from the group consisting of N- vinylimidazole, 2-vinylimidazole, 4-vinylimidazole, 2-methyl-1-vinylimidazole, N-vinylpyrazole, 3-vinylpyrazole, 4-vinylpyrazole, N-vinyl-1 ,2,3-triazole, N-vinyl-

1.2.4-triazole, 5-vinyl-1 H-tetrazole, 2-vinyl-2-oxazoline, 4-vinyl-isoxazole, vinyl-

1.2.4-oxadiazole, vinyl-1 , 3, 4-oxadiazole, 5-vinyl-1 ,2-thiazole, 4-vinyl-1 ,2,3- thiadiazole, 4-vinyl-1 ,2,5-thiadiazole, N-vinylpyrrole, 2-vinyl-1 H-pyrrole, N-vinyl- 1 -pyrroline, 2-vinylpyridine, 4-vinylpyridine, N-vinylpyrrolidine, N-vinyl-2- pyrrolidone, 4-vinylpiperidine, 2-vinylpiperidine, 5-vinylpyrimidine, 2- vinylpyrazine, 4-vinylpyrazine, 2-vinyl-4,6-diamino-1 ,3,5-triazine, 6-vinyl-2,4- diamine-1 ,3,5-triazine, and mixtures thereof.

Claim 6. The binder solution according to any one of claims 1 to 5, wherein the weight ratio between the VDF copolymer and the second copolymer in the polymer blend is from 40: 1 to 3: 1 , preferably from 20: 1 to 6: 1 .

Claim 7. The binder solution according to any one of claims 1 to 6, wherein the second copolymer comprises from 1.0 to 50.0% by moles (mol%), preferably from 5.0 to 40.0 mol%, more preferably from 5.0 to 30.0 mol% of ii) recurring units derived from at least two ethylenically unsaturated monomers having a nitrogen-containing heterocycle respectively [monomers (NMs)], with respect to the total moles of recurring units of the second copolymer.

Claim 8. The binder solution according to claim 7, wherein the second copolymer comprises ii) recurring units derived from N-vinylimidazole and N- vinyl-2-pyrrolidone, the mol% of N-vinyl-2-pyrrolidone being greater than the mol% of N-vinylimidazole, with respect to the total moles of recurring units of the second copolymer.

Claim 9. The binder solution according to any one of claims 1 to 8, wherein b) the non-aqueous solvent is selected from the group consisting of dimethyl formamide, /V,/V-dimethylacetamide, /V-methyl pyrrolidone, /V-ethyl pyrrolidone, y-butyrolactone, y-valerolactone, sulfolane, dimethyl sulfoxide, and hexamethylphosphoramide.

Claim 10. A slurry for manufacturing an electrode, comprising a binder solution according to any one of claims 1 to 9, c) at least one electroactive material, and optionally d) at least one conducive agent.

Claim 11 . The slurry according to claim 10, wherein c) the electroactive material is for a positive electrode, selected from the group consisting of lithium-nickel-manganese-cobalt-based metal oxide of formula LiNixMn_yCo_zO2 (x+y+z=1), lithium-nickel-cobalt-aluminum-based metal oxide of formula LiNixCo_yAlzO2 (x+y+z=1), lithium-cobalt-based metal oxide, lithium-nickel- manganese-based metal oxide, and LiFePO4..

Claim 12. A process for preparing an electrode, comprising the steps of: providing a current collector having at least one surface; applying a slurry according to claim 10 or 11 onto the surface of said current collector, thereby providing an assembly comprising a metal substrate surface-coated with said slurry; subsequently drying the assembly; and optionally compacting the dried assembly to obtain an electrode.

Claim 13. An electrode comprising obtainable by the process according to claim 12.

Claim 14. A secondary battery comprising a positive electrode, a negative electrode, and a membrane that is positioned between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is an electrode according to claim 13.

Claim 15. Use of at least one copolymer comprising i) recurring units derived from at least one ethylenically unsaturated (meth)acrylic monomer [monomer (MA)] and ii) recurring units derived from at least two ethylenically unsaturated monomers having a nitrogen-containing heterocycle respectively [monomers (NMs)], as an adhesion promoter towards a current collector of an electrode in a secondary battery, wherein said at least two monomers (NMs) are different from each other.

Claim 16. Use according to claim 15, wherein the copolymer is blended with at least one VDF (co)polymer.