(METH)acrylate polymers as additives in battery electrodes

Abstract

The present invention pertains to a binder for a secondary battery positive electrode, to a method of preparation of said electrode and to its use in a secondary battery. The invention also relates to the secondary batteries manufactured by incorporating said electrode.

Description

(METH)ACRYLATE POLYMERS AS ADDITIVES IN BATTERY ELECTRODESCross reference to previous applications

[0001] This application claims priority to European application No. 23182277.6 filed on 29 June 2023, the whole content of this application being incorporated herein by reference for all purposes.Technical Field

[0002] The present invention pertains to a binder for a secondary battery positive electrode, to a method of preparation of said electrode and to its use in a secondary battery.

[0003] The invention also relates to the secondary batteries manufactured by incorporating said electrode.Background Art

[0004] Electrochemical devices such as secondary batteries typically comprise a positive electrode, a negative electrode and an electrolyte.

[0005] The electrodes for secondary batteries are usually produced by mixing a binder with a powdery electrode active material.

[0006] It is known in the art that polyvinylidene fluoride (PVDF) is the preferred polymer to be used as binder for forming electrodes, in particular as binder in Nickel-rich cathodes production. Considering specific current cell production processes (eg. winding or lamination after winding) with pressures and stresses reached by the components, the use of more flexible additives becomes a need or, at least, a point of attention in materials choice.

[0007] Electrodes flexibility is indeed of primary importance for battery makers because it allows to increase electrode density and / or loading without cracking during the standard cell production process i.e. avoiding fracture of electrode (of either the coating or the collector) during winding or during lamination after winding. Moreover, flexible electrodes allow to reach higher electrode density in the standard pressing conditions or same density with milder pressing conditions.

[0008] When electrodes cannot stand bending, there is the risk of mechanical failure, cracking of the electrodes, eventual materials detachment from current collector and / or battery failure during cycling.

[0009] EP 2953193 discloses that flexibility performances of Nickel-rich cathodes using PVDF homopolymer binders are improved when a nitrile group- containing acrylic polymer is added.

[0010] JP2005-123047 discloses a sheet-like positive electrode binder based on polyvinylidene fluoride containing acrylonitrile-butadiene rubber, which provides improved flexibility to a lithium nickel oxide cathode.

[0011] The solutions currently available in this field rely on the use of PVDF homopolymers-based binders, which however suffer from poor adhesion to current collectors.

[0012] Modified polar PVDF polymers, such as those comprising recurring units derived from hydrophilic (meth)acrylic monomers (e.g. acrylic acid), are well known in the art. Such copolymers have been developed aiming at adding to the mechanical properties and chemical inertness of PVDF suitable adhesion towards metals, e.g. aluminium or copper.

[0013] However, when modified polar PVDF polymers are used in the preparation of a slurry for forming positive electrodes with certain active materials, an important drawback is that the slurry often undergoes to a rapid viscosity increase, leading to the formation of a gel, thus preventing their use as binder for cathodes.

[0014] A time dependency in the rheological properties of the composite electrode slurries is observed also in sodium-ion secondary batteries; in fact, gelation of the slurry can be initiated by the NaOH present on the material when exposed to air, with consequent dehydrofluorination with crosslinking of PVDF. Said gelation leads to inhomogeneous coatings being produced.

[0015] The need for more performing polymers, which guarantee in particular better flexibility and higher adhesion to current collectors, is still felt both in research and from industrial perspectives.

[0016] One way is to find a blend of polymers which therefore avoids the drawbacks of modified polar PVDF polymers in contact with certain active materials such as Nickel-rich active materials, but which at the same time guaranteesthe feasibility of electrodes through wet casting and high adhesions of the final product.Summary of invention

[0017] It is thus an object of the invention a positive electrode-forming composition (C) for use in the preparation of electrodes for electrochemical devices, said composition (C) comprising: a) at least one positive electrode active material (AM); b) one binder (B), wherein binder (B) comprises: bi) at least one vinylidene fluoride (VDF) copolymer [polymer (F)] that comprises:(i) recurring units derived from VDF; and(ii) recurring units derived from at least one hydrophilic vinyl monomer (MA) of formula (I):wherein:- Ri , R2 and R3, 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 comprising at least one functional group selected from a hydroxyl, a carboxyl, an epoxide, an ester, a phosphate and an ether group, in an amount of from 0.05 to 10 % by moles of with respect to the total moles of recurring units of polymer (F); b2) at least one polymer [polymer (A)] derived from the polymerization of at least one monomer (I) and of at least one monomer (II), the said monomers corresponding to the following:- monomer (I): (meth)acrylic acid ester of formula CR1R2=C(R)-C(=O)-O-Rh wherein R means hydrogen or an alkyl group with 1 to 3 carbon atoms, R1and R2are independently selected from the group consisting of H and optionally substituted alkyl group with 1 to 5 carbon atoms, and Rh means a linear or branched alkyl residue with 1 to 30 carbon atoms, preferably with 1 to 15 carbons, more preferably with 1 to 5 carbons, optionally substituted byone or more nitrogen atom or by one or more hydroxyl, thiol or amino functional group;- monomer (II): nitrile group-containing monomer; wherein the content of monomer (II) in the polymer (A) is lower than20 % by moles, preferably lower than 15 % by moles, over the total molar content of polymer (A); c) at least one solvent (S); and d) optionally at least one electroconductivity-imparting additive.

[0018] In a second instance, the present invention pertains to the use of the electrode-forming composition (C) of the invention in a process for the manufacture of a positive electrode for electrochemical devices [electrode (E)], said process comprising:(i) providing a metal substrate having at least one surface;(ii) providing an electrode-forming composition (C) as defined above;(iii) applying the composition (C) onto the at least one surface of the metal substrate, thereby providing an assembly comprising a metal substrate coated with said composition (C) onto the at least one surface;(iv) drying the assembly provided in step (iii).

[0019] In a third instance, the present invention pertains to the positive electrode (E) obtainable by the process of the invention.

[0020] In a fourth instance, the present invention pertains to an electrochemical device comprising a positive electrode (E) of the present invention.Description of embodiments

[0021] In the context of the present invention, the use of parentheses “(...)” before and after symbols or numbers identifying formulae or parts of formulae has the mere purpose of better distinguishing that symbol or number with respect to the rest of the text; thus, said parentheses could also be omitted.

[0022] The terms “(meth)acrylic” or “(meth)acrylate” are intended to cover both the acrylic / acrylate and methacrylic / methacrylate forms of the indicated material, e.g., a (meth)acrylate monomer.

[0023] The electrode active material (AM) of the positive electrode is preferably a compound capable of intercalating lithium ions or sodium ions.

[0024] The conventional active materials (AM) at the positive electrode of sodium- ion batteries are generally selected from Na-based layered transition-metal oxides, Prussian blue analogs and polyanion-type materials.

[0025] In some embodiments the active materials are Na-based layered transitionmetal oxides classified as O3-, P2-, and P3-types depending on the stacking sequence of oxygen layers. P2-type structures generally respond to the general formula NaxMC wherein M stands for a transition metal ion such as Co, Mn and x is 2 / 3.

[0026] In some embodiments the active materials are Prussian blue analogs (PBA) of general formula AxP[R(CN)6]i-yny.mH2O with A and alkali metal ion, P a N-coordinated transition metal ion, R a C-coordinated transition metal ion, □ a [R(CN)e] vacancy, with 0 < x < 2 and 0 < y < 1 such as Nao.8i Fe[Fe(CN)6]o.79no.2i , NaFe2(CN)e, Na1 63Fei.89(CN)6, Nai.72MnFe(CN)e, Nai.76Nio.i2Mno.88[Fe(CN)6]o.98, Na2NixCoi-xFe(CN)e with 0 < x < 1 e.g. Na2CoFe(CN)e.

[0027] In some other embodiments the active materials are polyanion-type materials of general formula NaxMy(XO4)n (where X = S, P, Si, As, Mo and W and M is transition metal), which possess a series of tetrahedron anion units (XO4)n- and their derivatives (Xm03m+i)n’. Among them, phosphates NaMPCk such as NaFePCk, NaojFePCk or NaMnPCk; natrium (sodium) superionic conductor of NASICON-type structures of general formula NaxM2(XO4)3 (where 1 < x < 4 andM = V, Fe, Ni, Mn, Ti, Cr, Zr...; X = P, S, Si, Se, Mo ... ) - with single transition metal type such as Na3V2(PO4)3 (NVP), Na3Cr2(PO4)3, Na3Fe2(PO4)3; - with binary transition metal type such as Na2VTi(PO4)3, Na3FeV(PO4)3, Na4MnV(PO4)3, Na3MnZr(PO4)3, Na3MnTi(PO4)3, Na4Fe3(PO4)2(P2O7) (NFPP); pyrophosphates Na2FeP2O7, Na2MnP2O7, Na2CoP2O7, Na4- xFe2+x / 2(P2O7)2 with 2 / 3 < x < 7 / 8 e.g. Na3.i2Fe2.44(P2O7)2 or Na3.32Fe2.34(P2O7)2, Na2(VO)P2O7, Na7V3(P2O7)4; fluorophosphates NaVPO4F, Na2CoPO4F, Na2FePO4F, Na2MnPO4F, Na3(VOi-xPO4)2Fi+2x (with 0 < x < 1 ) e.g. Na3(VOPO4)2F or Na3V2(PO4)2F3 (NVPF); fluoro sulfates such as NaMSO4F (with M = Fe, Co, Ni); mixed phosphates / pyrophosphates of general formula Na4M3(PO4)2(P2O7) (with M representing transition metals) such as Na4Mn3(PO4)2(P2O7),Na4C03(P04)2(P207), Na4Ni3(PO4)2(P2O7), Na4Fe3(PO4)2(P2O7) (NFPP), Na7V4(P2O7)4(PO4); sulfates such as Na2Fe2(SO4)3, Na2+2xFe2-x(SO4)3, Na2+2xCo2-x(SO4)3, Na2+2xMri2-x(SO4)3 (where 0 < x < 1 ) ; silicates of general formula Na2MSiO4 (with M = Mn, Fe, Co and Ni).

[0028] In some preferred embodiments the active materials are fluorophosphates preferably selected from the list consisting of NaVPCMF, Na2CoPO4F, Na2FePO4F, Na2MnPO4F, Na3(VOi-xPO4)2Fi+2x (with 0 < x < 1 ) e.g. Na3(VOPO4)2F or Na3V2(PO4)2F3 (NVPF).

[0029] The conventional active materials (AM) at the positive electrode of lithium- ion batteries may comprise a composite metal chalcogenide of formula UMQ2, 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 0 or S. Among these, it is preferred to use a lithium-based composite metal oxide of formula LiMO2, wherein M is the same as defined above. Preferred examples thereof may include LiCoC , LiNiC>2, LiNixCoi-xO2 (0 < x < 1 ) and spinel- structured LiMn2O4.

[0030] According to another preferred embodiment, the at least one positive electrode active material (AM) is selected from lithium-containing complex metal oxides of general formula (II)LiNixM1yM2zQ2(II) wherein M1and M2are the same or different from each other and are transition metals selected from Co, Fe, Mn, Cr and V, 0.5 < x < 1 , wherein y+z = 1 -x, andQ is the same as defined above.

[0031] As an alternative, still, the electrode active material may comprise a lithiated or partially lithiated transition metal oxyanion-based electro-active material of formula MiM2(JO4)fEi-f, wherein Mi is lithium, which may be partially substituted by another alkali metal representing less than 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, JO4is any oxyanion wherein J is either P, S, V, Si, Nb, Mo or a combination thereof, Eis a fluoride, hydroxide or chloride anion, f is the molar fraction of the JO4 oxyanion, generally comprised between 0.75 and 1.

[0032] The MiM2(JO4)fEi-f electro-active material as defined above is preferably phosphate-based and may have an ordered or modified olivine structure.

[0033] More preferably, the electrode active material 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 electrode active material (AM) is a phosphate-based electro-active material of formula LixAyDzPO4, wherein A is selected from the group consisting of Mn, Fe, Co, Ni and Cu; D is selected from the group consisting of Mg, Ca, Sr, Ba; x, y and z are numbers that satisfy the following relationships: 0 <x <2, 0 <y <1.5, 0z <1.5.

[0034] The A component is preferably Fe, Mn, and Ni, and particularly preferably Fe.

[0035] The D component is preferably Mg or Ca.

[0036] Examples of the compound having an olivine structure include lithium iron phosphate (LFP), lithium iron manganese phosphate (LMFP) and lithium manganese phosphate.

[0037] Further, as the positive electrode active material (AM), it is possible to use a material whose surface is partially or wholly covered with carbon in order to supplement the conductivity.

[0038] The amount of carbon coated is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, still more preferably 5 parts by weight or less, based on 100 parts by weight of the positive electrode active material.

[0039] Composition (C) of the invention further comprises a binder (B) that comprises: bi) at least one vinylidene fluoride (VDF) copolymer [polymer (F)], as above defined, and b2) at least one polymer [polymer (A)] as above defined.

[0040] The polymer (F) comprises recurring units derived from vinylidene fluoride (VDF) and recurring units derived from at least one hydrophilic vinyl monomer (MA) of formula (I):wherein:- R1 , R2 and R3, 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 comprising at least one functional group selected from a hydroxyl, a carboxyl, an epoxide, an ester, a phosphate and an ether group, in an amount of from 0.05 to 10 % by moles of with respect to the total moles of recurring units of polymer (F).

[0041] The term "hydrophilic vinyl monomer" as employed herein may comprise recurring units derived from one or more than one hydrophilic vinyl monomer (MA) as above described. In the rest of the text, the expressions "hydrophilic vinyl monomer (MA)" is to be intended, both in the plural and the singular, that is to say that they denote both one or more than one hydrophilic vinyl monomer (MA).

[0042] More preferably, the hydrophilic vinyl monomer (MA) preferably complies with formula (III):wherein each of Ri and R2 have the meanings as above defined, R3 is hydrogen, and ROH is a hydrogen or a C1-C5 hydrocarbon moiety comprising at least one hydroxyl group and / or at least a carboxylic group; more preferably, each of R1 , R2, R3 are hydrogen, while ROH has the same meaning as above detailed.

[0043] Non limitative examples of hydrophilic vinyl monomers (MA) are notably acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate; hydroxyethylhexyl(meth)acrylates.

[0044] The monomer (MA) is more preferably selected among:- hydroxyethylacrylate (HEA) of formula:- 2-hydroxypropyl acrylate (HPA) of either of formulae:- and mixtures thereof.

[0045] Most preferably, the monomer (MA) is AA and / or HEA.

[0046] Polymer (F) may still comprise other moieties such as defects, end-groups and the like, which do not affect nor impair its physico-chemical properties.

[0047] Polymer (F) is semi-crystalline. The term semi-crystalline is intended to denote a polymer (F) which possesses a detectable melting point. It is generally understood that a semi-crystalline polymer (F) possesses a heat of fusion determined according to ASTM D 3418 of advantageously at least 0.4 J / g, preferably of at least 0.5 J / g, more preferably of at least 1 J / g.

[0048] Polymer (F) is preferably a linear copolymer, that is to say, it is composed of macromolecules made of substantially linear sequences of recurring units from VDF monomer and (MA) monomer; polymer (F) is thus distinguishable from grafted and / or comb-like polymers.

[0049] Polymer (F) comprises at least 0.05 % by moles, more preferably at least 0.1 % by moles, even more preferably at least 0.2 % by moles of recurring units derived from said hydrophilic vinyl monomer (MA).

[0050] Polymer (F) comprises preferably at most 2 % by moles, more preferably at most 1.8 % by moles, even more preferably at most 1.5% by moles of recurring units derived from said hydrophilic vinyl monomer (MA).

[0051] In a preferred embodiment of the invention, in polymer (F) the recurring units derived from hydrophilic vinyl monomer (MA) of formula (I) are comprised in an amount of from 0.2 to 1 % by moles with respect to the total moles of recurring units of polymer (F).

[0052] The polymer (F) has advantageously an intrinsic viscosity, measured in dimethylformamide at 25 °C, of above 0.15 l / g and at most 0.60 l / g, preferably in the range of 0.20 - 0.50 l / g, more preferably comprised in the range of 0.25 - 0.40 l / g.

[0053] The polymer (F) may further comprise recurring units derived from one or more fluorinated comonomers (CF) different from VDF.

[0054] By the term “fluorinated comonomer (CF)”, it is hereby intended to denote an ethylenically unsaturated comonomer comprising at least one fluorine atoms.

[0055] Non-limitative examples of suitable fluorinated comonomers (CF) include, notably, the followings:(a) C2-C8 fluoro- and / or perfluoroolefins such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene and hexafluoroisobutylene;(b) C2-C8 hydrogenated monofluoroolefins, such as vinyl fluoride; 1 ,2- difluoroethylene and trifluoroethylene;(c) perfluoroalkylethylenes of formula CH2=CH-Rro, wherein Rro is a Ci-Ce perfluoroalkyl group;(d) chloro- and / or bromo- and / or iodo-C2-Ce fluoroolefins such as chlorotrifluoroethylene (CTFE).

[0056] In one embodiment of the invention, polymer (F) comprises from 0.1 to 10.0% by moles, preferably from 0.3 to 5.0% by moles, more preferably from 0.5 to 3.0% by moles of recurring units derived from said fluorinated comonomer (CF).

[0057] The polymer (F) more preferably comprises recurring units derived from:- at least 70% by moles, preferably at least 75% by moles, more preferably at least 85% by moles of vinylidene fluoride (VDF), - from 0.2% to 1 % by moles, of a hydrophilic vinyl monomer (MA) of formula (i);- optionally from 0.5 to 3.0% by moles of recurring units derived from at least one fluorinated comonomer (CF).

[0058] The polymer (F) may be obtained by polymerization of a VDF monomer, at least one monomer (MA) and optionally at least one comonomer (CF), either in suspension in organic medium, according to the procedures described, for example, in WO 2008 / 129041 , or in aqueous emulsion, typically carried out as described in the art (see e.g. US 4,016,345, US 4,725,644 and US 6,479,591).

[0059] The procedure for preparing the polymer (F) in suspension comprises polymerizing in an aqueous medium in the presence of a radical initiator the vinylidene fluoride (VDF) monomer, monomer (MA) and optionally comonomer (CF), in a reaction vessel, said process comprising- continuously feeding an aqueous solution comprising monomer (MA); and- maintaining the pressure in said reactor vessel exceeding the critical pressure of the vinylidene fluoride.

[0060] During the whole suspension polymerization run, pressure is maintained above critical pressure of vinylidene fluoride. Generally, the pressure is maintained at a value of more than 50 bars, preferably of more than 75 bars, even more preferably of more than 100 bars.

[0061] The expressions "continuous feeding", “adding continuously” or "continuously feeding" means that slow, small, incremental additions the aqueous solution of hydrophilic vinyl monomer (MA) take place until polymerization has concluded.

[0062] The polymer (F) thus obtained has a high uniformity of monomer (MA) distribution in the polymer backbone, which advantageously maximizes the effects of the modifying monomer (MA) on both adhesiveness and / or hydrophilic behaviour of the resulting copolymer.

[0063] In addition, the Applicant has surprisingly found that the presence of the monomer (MA) uniformly distributed in the polymer (F) has the effect ofimproving the thermal stability of VDF copolymers, which otherwise is unsatisfactorily low, in particular lower than that of VDF homopolymers.

[0064] The amount of polymer (F) in composition (C) is suitably in the range of from 0.5 to 5 % by weight.

[0065] Polymer (A) is a copolymer derived from the polymerization of at least one monomer (I) and of at least one monomer (II), wherein- monomer (I) is a (meth)acrylic acid ester of CR1R2=C(R)-C(=O)-O-Rh wherein R means hydrogen or an alkyl group with 1 to 3 carbon atoms, R1and R2are independently selected from the group consisting of H and optionally substituted alkyl group with 1 to 5 carbon atoms, and Rh means a linear or branched alkyl residue with 1 to 30 carbon atoms, preferably with 1 to 15 carbons, more preferably with 1 to 5 carbons, optionally substituted by one or more nitrogen atom or by one or more hydroxyl, thiol or amino functional group;- monomer (II) is a nitrile group-containing monomer;

[0066] By "copolymer" as used herein it is intended to denote a polymer having two or more different monomer units. The copolymer could be a terpolymer with three or more different monomer units, or have four or more different monomer units. The copolymer may be a random copolymer, a gradient copolymer, or a block copolymer formed by a controlled polymerization process. Preferably, the copolymer is formed by a free radical polymerization process or an anionic polymerization process, and the process can be any polymerization method known in the art, including but not limited to solution, suspension polymerization, and can be done in bulk, and semi-bulk.

[0067] According to a preferred embodiment of the invention, the monomer (I) is selected from the group consisting of: acrylic acid ester or anhydride, methacrylic acid ester or anhydride, citraconic acid ester or anhydride, maleic acid ester or anhydride, fumaric acid ester or anhydride, itaconic acid ester or anhydride, crotonic acid ester or anhydride, ethacrylic acid ester or anhydride, methyl (meth)acrylic acid ester or anhydride, ethyl (meth)acrylic acid ester or anhydride, propyl (meth)acrylic acid ester or anhydride, isopropyl (meth)acrylic acid ester or anhydride, n-butyl (meth)acrylic acid ester or anhydride, 2-ethylhexyl (meth)acrylic acid ester or anhydride, n-hexyl (meth)acrylic acid ester or anhydride, n-octyl (meth)acrylic acid ester or anhydride; hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate, hydroxyethylhexyl(meth)acrylate; Sipomer® I3.CEA (sold by Solvay), Sipomer® WAM (sold by Solvay), Sipomer® WAM II (sold by Solvay) and other urido-containing monomers; ethylene glycol alkyl ether acrylates such as di(ethylene glycol) ethyl ether acrylate (DEGEEA); glycidyl methacrylate; glycerol methacrylate; (meth) acryloyloxyalkyl succinic acid, such as (meth) acryloyloxyethyl succinic acid and (meth) acryloyloxypropyl succinic acid.

[0068] More preferably, monomer (I) is selected from methyl methacrylic acid ester (MMA) and n-butyl (meth)acrylic acid ester.

[0069] The nitrile group-containing monomer (II) is preferably selected from acrylonitrile and methacrylonitrile.

[0070] The content of nitrile group-containing monomer (II) units in polymer (A) is lower than 20 % by moles, preferably lower than 15 % by moles.

[0071] When the content of the nitrile group-containing monomer (II) units is lower than 20 % by moles, the flexibility of the electrode obtained by using composition (C) is excellent, and the performance of the resulting electrode is improved.

[0072] More preferably, polymer (A) is a copolymer derived from the polymerization of methyl methacrylic acid ester (MMA), n-butyl acrylic acid ester (BA) and acrylonitrile (AN).

[0073] In a particularly preferred embodiment, polymer (A) comprises recurring units derived from methyl methacrylic acid ester (MMA) in an amount of from 10 to 45 % by moles, n-butyl acrylic acid ester (BA) in an amount of from 45 to 80 % by moles and acrylonitrile (AN) in an amount of from 5 to less than 20 % by moles.

[0074] The weight average molecular weight Mw of the polymer (A) is generally between 15 000 and 500 000, preferably between 20 000 and 75 000.

[0075] The polymer (A) is prepared by polymerizing a mixture of at least one monomer (I) and at least one monomer (II) according to any known method in the art.

[0076] The amount of polymer (A) in composition (C) is suitably in the range of from 0.1 to 0.5 % by weight.

[0077] The choice of the solvent (S) is not particularly limited, provided that it is suitable for solubilising polymer (F) and dispersing / dissolving polymer (A).

[0078] Solvent (S) is typically selected from the group consisting of:- alcohols such as methyl alcohol, ethyl alcohol and diacetone alcohol,- ketones such as acetone, methylethylketone, methylisobutyl ketone, diisobutylketone, cyclohexanone and isophorone,- linear or cyclic esters such as isopropyl acetate, n-butyl acetate, methyl acetoacetate, dimethyl phthalate and y-butyrolactone,- linear or cyclic amides such as N,N-diethylacetamide, N,N- dimethylacetamide, dimethylformamide and N-methyl-2-pyrrolidone, and- dimethyl sulfoxide.

[0079] The electrode forming compositions of the present invention may further include one or more optional electroconductivity-imparting additives in order to improve the conductivity of an electrode made from the composition of the present invention. Electroconductivity-imparting additives for batteries are known in the art.

[0080] Examples thereof may include: carbonaceous materials, such as carbon black, graphite fine powder carbon nanotubes, graphene, or fiber, or fine powder or fibers of metals such as nickel or aluminum. The optional conductive agents are preferably carbon black or carbon nanotubes.

[0081] The amount of optional conductive agent is preferably from 0 to 30 % by weight with respect to the total solids in the electrode forming composition. In particular, for positive electrode forming compositions the optional conductive agent is typically from 0 % by weight to 10 % by weight, more preferably from 0 % by weight to 5 % by weight of the total amount of the solids within the composition (C).

[0082] Composition (C) may further comprise at least one wetting agent and / or at least one surfactant and one or more than one additional additives.

[0083] Composition (C) may further comprise at least one non-electroactive inorganic filler material.

[0084] By the term "non-electroactive inorganic filler material", it is hereby intended to denote an electrically non-conducting inorganic filler material, which is suitable for the manufacture of an electrically insulating separator for electrochemical cells.

[0085] The non-electroactive inorganic filler material in the separator according to the invention typically has an electrical resistivity (p) of at least 0.1 x 1010 ohm cm, preferably of at least 0.1 x 1012 ohm cm, as measured at 20°C according to ASTM D 257.

[0086] Non-limitative examples of suitable non-electroactive inorganic filler materials include, notably, natural and synthetic silicas, zeolites, aluminas, titanias, metal carbonates, zirconias, silicon phosphates and silicates and the like.

[0087] Binder (B) for use in the composition (C) according to the present invention can be prepared by any known method in the art.

[0088] A suitable method comprises:- dissolving polymer (F) with a solvent (S),- dissolving polymer (A) with a solvent (S),- mixing to provide a binder mixture (B).

[0089] The weight ratio of polymer (F) to polymer (A) in binder (B) is conveniently in the range of from 95:5 to 70:30. In a preferred embodiment of the invention, the weight ratio of polymer (F) to polymer (A) in binder (B) is 90:10.

[0090] The electrode-forming composition (C) may be obtained by adding and dispersing a powdery electrode material, and optional additives, such as an electroconductivity-imparting additive and / or a viscosity modifying agent, into the thus-obtained binder mixture (B), to obtain a homogeneous slurry.

[0091] The solution of polymer (F) in solvent (S) is notably comprising the polymer (F) in an amount of from 5 to 20 % by weight, preferably about 7 to 10 % by weight.

[0092] The solution of polymer (A) in solvent (S) is notably comprising the polymer (A) in an amount of from 0.1 to 15% by weight in 100 parts by weight of such a solvent.

[0093] The total solid content (TSC) of the composition (C) of the present invention is typically comprised between 50 and 85 % by weight, preferably from 60 and 80 % by weight, over the total weight of the composition (C). The total solid content of the composition (C) is understood to be cumulative of all non-volatile ingredients thereof, notably including polymer (F), polymer (A), the electrode active material and any solid, non-volatile additional additive.

[0094] When the solution of polymer (F) is combined with polymer (A), with an electrode active material and with the optional conductive material and other additives to prepare composition (C), an amount of solvent sufficient to create a stable solution of polymer (F) is employed. The amount of solvent used may range from the minimum amount needed to create a stable solution of polymer (F) to an amount needed to achieve a desired total solid content in an electrode mixture after the polymer (A), the active electrode material, the optional conductive material, and the other solid additives have been added.

[0095] The presence of polymer (A) in the composition (C) makes it possible to obtain high quality homogenous slurry compositions with neither gelation evidence nor inhomogeneity in all the preparation steps. Said composition is suitable for use in the preparation of electrodes.

[0096] The most relevant aspect detected with the addition of polymer (A) to the composition (C) is a huge flexibility enhancement of the electrodes, wherein flexibility is evaluated as cracking diameter of the electrodes.

[0097] The lower the cracking diameter the more flexible is the electrode: it is strictly dependent on binder / additive type

[0098] Applicative flexibility performances are therefore enhanced by the use of the polymer (A) as additive to the VDF polymer, not affecting or even improving other parameters such as adhesion to current collector.

[0099] This effect of flexibility improvement is particularly evident when polymer (A) is a copolymer derived from the polymerization of methyl methacrylic acid ester (MMA), n-butyl acrylic acid ester (BA) and acrylonitrile (AN), with an AN content lower than 20 wt% in polymer (A).

[0100] Another advantage of the composition (C) of the present invention is that it is possible to provide an electrode which comprises a relatively low content by weight of binder and to make it possible to increase the content of active material in the positive electrode, in order to maximise the capacity of the battery.

[0101] The electrode-forming composition (C) of the invention can be used in a process for the manufacture of a positive electrode [electrode (E)], said process comprising:(i) providing a metal substrate having at least one surface;(ii) providing an electrode-forming composition [composition (C)] as above defined;(iii) applying the composition (C) onto the at least one surface of the metal substrate, thereby providing an assembly comprising a metal substrate coated with said composition (C) onto the at least one surface;(iv) drying the assembly provided in step (iii).

[0102] The metal substrate is generally a foil, mesh or net made from a metal, such as from aluminium, nickel, titanium, and alloys thereof.

[0103] In step (iii) of the process of the invention, the electrode forming composition (C) is applied onto at least one surface of the metal substrate typically by any suitable procedures such as casting, printing and roll coating.

[0104] Optionally, step (iii) may be repeated, typically one or more times, by applying the electrode forming composition (C) provided in step (ii) onto the assembly provided in step (iv).

[0105] In step (iv) of the process of the invention, drying may be performed either under atmospheric pressure or under vacuum. Alternatively, drying 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).

[0106] The drying temperature will be selected so as to effect removal by evaporation of the aqueous medium from the electrode (E) of the invention.

[0107] The dried assembly obtained in step (iv) may further be submitted to a compression step such as a calendaring process, to achieve the target porosity and density of the electrode (E) of the invention.

[0108] Preferably, the dried assembly obtained at step (iv) is hot pressed, the temperature during the compression step being comprised from 25°C and 130°C, preferably being of about 60°C.

[0109] Preferred target density for electrode (E) is comprised between 2 and 3 g / cc, preferably at least 2.1 g / cc. The density of electrode (E) is calculated as the sum of the product of the densities of the components of the electrode multiplied by their mass ratio in the electrode formulation.

[0110] In a further aspect, the present invention pertains to the positive electrode [electrode (E)] obtainable by the process of the invention.

[0111] Therefore the present invention relates to a positive electrode (E) comprising:- a metal substrate having at least one surface, and- directly adhered onto at least one surface of said metal substrate, at least one layer consisting of a composition [composition (C’)] comprising: a) at least one positive electrode active material (AM); b) a binder composition [binder (B’)] comprising: b’) at least one polymer (F) as above defined, b”) at least one polymer (A) as above defined; c) optionally, at least one electroconductivity-imparting additive.

[0112] The composition (C’) directly adhered onto at least one surface of said metal substrate corresponds to the electrode forming composition (C) of the invention wherein the solvent has been at least partially removed during the manufacturing process of the electrode, for example in step (iv) (drying) and / or in the further compression step.

[0113] Therefore all the preferred embodiments described in relation to the electrode forming compositions (C) of the invention are also applicable to the composition (C’) directly adhered onto at least one surface of said metal substrate, in electrodes of the invention, except for the aqueous medium removed during the manufacturing process.

[0114] The preferred positive electrode (E) comprises:- a metal substrate having at least one surface, and- directly adhered onto at least one surface of said metal substrate, at least one layer consisting of: j) a positive electrode active material (AM) in an amount from 90 to 98 % by weight; jj) the binder (B’) in an amount from 0.5 to 10 % by weight, preferably from 1 to 5 % by weight; and jjj an electroconductivity-imparting additive in an amount from 0.5 to 5 % by weight, wherein the above mentioned % by weight are in respect to the total weight of j)+jj)+jjj).

[0115] Preferably, the positive electrode (E) comprises of at least 95% by weight of active material (AM) and an electrode loading comprised between 8 and 20 mg / cm2, preferably of about 15 mg / cm2.

[0116] The positive electrode (E) of the invention is particularly suitable for use in electrochemical devices.

[0117] Non-limitative examples of suitable electrochemical devices include, notably, secondary batteries, especially, alkaline or an alkaline- earth secondary batteries such as lithium ion batteries, solid state batteries, lithium-metal batteries, lead-acid batteries, and capacitors, especially lithium ion-based capacitors and electric double layer capacitors (supercapacitors).

[0118] The secondary battery of the invention is more preferably a lithium-ion secondary battery.

[0119] An electrochemical device according to the present invention can be prepared by standard methods known to a person skilled in the art.

[0120] 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.

[0121] The invention will be now described with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the invention.Experimental section

[0122] Raw materials

[0123] Polymer (F-1 ): VDF-AA (1.0% by moles) polymer having an intrinsic viscosity of 0.30 l / g in DMF at 25°C.

[0124] Polymer 1 : Acrylonitrile / butadiene rubber commercialized as BM-720H by ZEON Corporation.

[0125] NMC622 (Cellcore®NMC KHX12): cathode electroactive material.

[0126] Preparation of Polymer A-1

[0127] In a two liter reactor equipped with a mechanical stirrer, a condenser, a thermal probe, and a double jacket, 245.80 g of NMP and 1.01 of AMBNwere introduced. The reactor was closed and the solution was stirred at 100 rpm and purged with nitrogen for 30 minutes.

[0128] A solution of MMA (35.09 g), BA (155.68 g), and AN (9.22 g) was prepared separately. After purging with nitrogen, 15 wt% of the solution was introduced in the reactor.

[0129] The mixture in the reactor was heated to 75 °C, and when the temperature reached 75 °C, the remaining 95 wt% of the monomer solution was introduced into the reactor over a period of 2 hours.

[0130] Then the mixture in the reactor was kept at 75 °C for 6 hours and finally cooled down to 25 °C. The reactor was discharged.

[0131] Polymer MMA-BA-AN 20:70:10 mol% was obtained.

[0132] Preparation of Polymer A-2

[0133] In a two-liter reactor equipped with a mechanical stirrer, a condenser, a thermal probe, and a double jacket, 245.90 g of NMP and 1.00 of AMBN were introduced. The reactor was closed and the solution was stirred at 100 rpm and purged with nitrogen for 30 minutes

[0134] A solution of MMA (37.54 g), BA (142.73 g), and AN (19.73 g) was prepared separately. After purging with nitrogen, 15 wt% of the solution was introduced in the reactor.

[0135] The mixture in the reactor was heated to 75 °C, and when the temperature reached 75 °C, the remaining 95 wt% of the monomer solution was introduced into the reactor over a period of 2 hours.

[0136] Then the mixture in the reactor was kept at 75 °C for 6 hours and finally cooled down to 25 °C. The reactor was discharged.

[0137] Polymer MMA-BA-AN 23:57:20 mol% was obtained.

[0138] EXAMPLE 1 :

[0139] A 8% by weight solution of polymer (F-1 ) in NMP was prepared.

[0140] Polymer (A-1 ) was dissolved in NMP to obtain a 8% by weight solution.

[0141] The solution of polymer (A-1 ) was mixed with the solution of polymer (F-1 ) in NMP in a 1 .2:8.8 ratio (24.908 g of solution of polymer (F-1 ) and 3.397 g of polymer (A-1 )).

[0142] NMC622 and Carbon black “SC65” were added simultaneously to the NMP solution of polymer (A-1 ) and polymer (F-1 ) with planetary mixing followed by dispersion phase to provide Composition 1 , a cathode slurry having aTotal Solid Content (TSC) of 74% (96.3% NMC622, 2% carbon black, 1 .5% polymer (F-1 ) and 0.2% polymer (A-1 )).

[0143] A homogenous slurry was obtained, with no gelation evidence in all the preparation steps. The viscosity of Composition 1 is shown in Table 1 .

[0144] COMPARATIVE EXAMPLE 2:

[0145] A 8% by weight solution of polymer (F-1 ) in NMP was prepared.

[0146] Polymer (A-2) was dissolved in NMP to obtain a 8% by weight solution.

[0147] The solution of polymer (A-2) was mixed with the solution of polymer (F-1 ) in NMP in a 1 .2:8.8 ratio (24.908 g of solution of polymer (F-1 ) and 3.397 g of polymer (A-1 )).

[0148] NMC622 and carbon black were added simultaneously to the NMP solution of polymer (A-2) and polymer (F-1 ) with planetary mixing followed by dispersion phase to provide Composition 2, a cathode slurry having a Total Solid Content (TSC) of 74% (96.3% NMC622, 2% carbon black, 1.5% polymer (F-1 ) and 0.2% polymer (A-2)).

[0149] A homogenous slurry was obtained, with no gelation evidence in all the preparation steps. The viscosity of Composition 2 is shown in Table 1 .

[0150] COMPARATIVE EXAMPLE 3:

[0151] A 8% by weight solution of polymer (F-1 ) in NMP was prepared.

[0152] NMC622 and carbon black were added to the NMP solution of polymer (F- 1 ) with planetary mixing followed by dispersion phase to provide Composition 3, a cathode slurry having a Total Solid Content (TSC) of 74% (96.5% NMC622, 2% carbon black, 1.5% polymer (F-1 )).

[0153] A homogenous slurry was obtained, with no gelation evidence in all the preparation steps. The viscosity of Composition 3 was evaluated.

[0154] COMPARATIVE EXAMPLE 4:

[0155] A 8% by weight solution of polymer (F-1 ) in NMP was prepared.

[0156] Polymer 1 (BM-720H) was dissolved in NMP to obtain a 8% by weight solution.

[0157] The solution of polymerl was mixed with the solution of polymer (F-1 ) in NMP in a 1 .2:8.8 ratio (24.908 g of solution of polymer (F-1 ) and 3.397 g of polymer 1 ).

[0158] NMC622 and carbon black were added simultaneously to the NMP solution of Polymer 1 and polymer (F-1 ) with planetary mixing followed by dispersionphase to provide Composition 4, a cathode slurry having a Total Solid Content (TSC) of 74% (96.3% NMC622, 2% carbon black, 1.5% polymer (F-1 ) and 0.2% Polymer 1 ).

[0159] A homogenous slurry was obtained, with no gelation evidence in all the preparation steps. The viscosity of Composition 4 is shown in Table 1 .Table 1*Values normalized to Composition 3, which comprises polymer (F-1 ) only.

[0160] EXAMPLE 5: Preparation of electrodes

[0161] Positive electrodes were obtained by applying the electrode-forming compositions 1 -4 as above described to both sides of a 15 pm thick aluminium foils so as to obtain a mass of dry positive electrode loading of 40 mg / cm2for each side. The solvent was completely evaporated by drying in an oven at temperature of 90°C to fabricate a strip-shaped positive electrodes.

[0162] Flexibility and adhesion of the positive electrodes so obtained (electrode (E1 ) and (EC-2), (EC-3) and (EC-4), respectively) were evaluated.

[0163] Positive Electrodes Flexibility Evaluation

[0164] Flexibility was measured by a U-bending test, using the coating cracking diameter as parameter to assess and determine flexibility. Double-sided electrodes are cut in stripes (2x10cm) and fixed at the two ends between two horizontal parallel plates of a dynamometer, placed at a distance of 20mm, having a bended shape. During the test, the plates are approached one to the other with the automated crossbeam movement with a speed of 10mm / min. The diameter of the bended electrode is progressively reduced, till a cracking in the electrode coating is observed.

[0165] Lower the cracking diameter, more flexible are the electrodes and therefore more prone to bare the stresses during winding or lamination after winding. Higher flexibility implies also the possibility to reach higher electrode densityin the standard pressing conditions or same density with milder pressing conditions.

[0166] The results are reported in Table 2.

[0167] Positive Electrodes Adhesion Evaluation

[0168] Positive electrodes (E1 ), (EC-2), (EC-3) and (EC-4) were cut in stripes (10 cm long and 2.5 cm wide) and applied onto rigid aluminium foils having thickness of 2 mm, using a biadhesive tape of dimensions 2.5 x 8 cm, with the coated side of the electrode facing the aluminium plate. A portion of the electrode was kept from adhering to the tape, thus leaving one end of each stripe not in contact with the biadhesive tape, allowing for its pulling from the foil.

[0169] Each specimen was pulled from the foil at an angle of 180° by a dynamometer that allowed the measurement of the force needed to peel off the sample from the biadhesive tape. Peeling speed is 300 mm / min, with T=25°C. The results are summarized in Table 2.Table 2*Values normalized to EC-3, obtained from Composition 3, which comprises polymer (F-1 ) only.

[0170] It has been demonstrated that the electrodes of the invention have an improved adhesion to metal foil in comparison with standard electrodes of the prior art comprising polymer (F) only. At the same, the electrodes of the invention show a huge improvement in the flexibility over electrodes prepared by using binders comprising polymer (F) only, but also over electrodes obtained by using binders comprising polymer (F) and an acrylate copolymer including less than 20% by moles of acrylonitrile.

Claims

Claims1. A positive electrode-forming composition (C) for use in the preparation of electrodes for electrochemical devices, said composition (C) comprising: a) at least one positive electrode active material (AM); b) one binder (B), wherein binder (B) comprises: bi) at least one vinylidene fluoride (VDF) copolymer [polymer (F)] that comprises:(i) recurring units derived from VDF; and(ii) recurring units derived from at least one hydrophilic vinyl monomer (MA) of formula (I):- Ri , R2 and R3, 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 comprising at least one functional group selected from a hydroxyl, a carboxyl, an epoxide, an ester, a phosphate and an ether group, in an amount of from 0.05 to 10 % by moles of with respect to the total moles of recurring units of polymer (F); b2) at least one polymer [polymer (A)] derived from the polymerization of at least one monomer (I) and of at least one monomer (II), the said monomers corresponding to the following:- monomer (I): (meth)acrylic acid ester of formula CR1R2=C(R)-C(=O)-O-Rh wherein R means hydrogen or an alkyl group with 1 to 3 carbon atoms, R1and R2are independently selected from the group consisting of H and optionally substituted alkyl group with 1 to 5 carbon atoms, and Rh means a linear or branched alkyl residue with 1 to 30 carbon atoms, preferably with 1 to 15 carbons, more preferably with 1 to 5 carbons, optionally substituted by one or more nitrogen atom or by one or more hydroxyl, thiol or amino functional group;- monomer (II): nitrile group-containing monomer;wherein the content of monomer (II) in the polymer (A) is lower than 20 % by moles, preferably lower than 15 % by moles, over the total molar content of polymer (A); c) at least one solvent (S); and d) optionally at least one electroconductivity-imparting additive.

2. The composition (C) according to claim 1 , wherein the hydrophilic vinyl monomer (MA) is selected from the group consisting of acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate; hydroxyethylhexyl(meth)acrylate.

3. The composition according to any one of claims 1 or 2, wherein the active material (AM) is 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 0 or S.

4. The composition according to any one of claims 1 or 2 wherein the active material (AM) is selected from lithium-containing complex metal oxides of general formula (II)LiNixM1yM2zQ2(II) wherein M1and M2are the same or different from each other and are transition metals selected from Co, Fe, Mn, Cr and V, 0.5 < x < 1 , wherein y+z = 1-x, andQ is a chalcogen such as 0 or S.

5. The composition (C) according to any one of the preceding claims, wherein monomer (I) is selected from the group consisting of: acrylic acid ester or anhydride, methacrylic acid ester or anhydride, citraconic acid ester or anhydride, maleic acid ester or anhydride, fumaric acid ester or anhydride, itaconic acid ester or anhydride, crotonic acid ester or anhydride, ethacrylic acid ester or anhydride, methyl (meth)acrylic acid ester or anhydride, ethyl (meth)acrylic acid ester or anhydride, propyl (meth)acrylic acid ester or anhydride, isopropyl (meth)acrylic acid ester or anhydride, n-butyl (meth)acrylic acid ester or anhydride, 2-ethylhexyl (meth)acrylic acid ester or anhydride, n- hexyl (meth)acrylic acid ester or anhydride, n-octyl (meth)acrylic acid ester or anhydride; hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate, hydroxyethylhexyl(meth)acrylate; Sipomer® I3.CEA (sold by Solvay),Sipomer® WAM (sold by Solvay), Sipomer® WAM II (sold by Solvay) and other urido-containing monomers;ethylene glycol alkyl ether acrylates such as di(ethylene glycol) ethyl ether acrylate (DEGEEA); glycidyl methacrylate; glycerol methacrylate; (meth) acryloyloxyalkyl succinic acid, such as (meth) acryloyloxyethyl succinic acid and (meth) acryloyloxypropyl succinic acid.

6. The composition (C) according to any one of the preceding claims, wherein monomer (I) is selected from methyl methacrylic acid ester (MMA) and n-butyl (meth)acrylic acid ester.

7. The composition (C) according to any one of the preceding claims, wherein monomer (II) is selected from acrylonitrile and methacrylonitrile.

8. The composition (C) according to any one of the preceding claims, wherein polymer (A) is a copolymer derived from the polymerization of methyl methacrylic acid ester (MMA), n-butyl acrylic acid ester (BA) and acrylonitrile (AN).

9. The composition (C) according to any one of the preceding claims, wherein polymer (A) comprises recurring units derived from methyl methacrylic acid ester (MMA) in an amount of from 10 to 45 wt%, n-butyl acrylic acid ester (BA) in an amount of from 45 to 80 wt% and acrylonitrile (AN) in an amount of from 5 to less than 20 wt%.

10. The composition (C) according to any one of the preceding claims, wherein the weight ratio of polymer (F) to polymer (A) in binder (B) is in the range of from 95:5 to 70:30, preferably 90:10.11 . A process for the manufacture of a positive electrode [electrode (E)], said process comprising:(i) providing a metal substrate having at least one surface;(ii) providing an electrode-forming composition [composition (C)] according to any one of claims 1 to 10;(iii) applying the composition (C) provided in step (ii) onto the at least one surface of the metal substrate provided in step (i), thereby providing an assembly comprising a metal substrate coated with said composition (C) onto the at least one surface;(iv) drying the assembly provided in step (iii).

2. A positive electrode (E), which comprises:- a metal substrate having at least one surface, and- directly adhered onto at least one surface of said metal substrate, at least one layer consisting of a composition [composition (C’)] comprising: a) at least one positive electrode active material (AM); b) one binder (B), wherein binder (B) comprises: bi) at least one vinylidene fluoride (VDF) copolymer [polymer (F)] that comprises:(i) recurring units derived from VDF; and(ii) recurring units derived from at least one hydrophilic vinyl monomer (MA) of formula (I):wherein:- Ri , R2 and R3, 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 comprising at least one functional group selected from a hydroxyl, a carboxyl, an epoxide, an ester, a phosphate and an ether group, in an amount of from 0.05 to 10 % by moles of with respect to the total moles of recurring units of polymer (F); b2) at least one polymer [polymer (A)] derived from the polymerization of at least one monomer (I) and of at least one monomer (II), the said monomers corresponding to the following:- monomer (I): (meth)acrylic acid ester of formula CR1R2=C(R)-C(=O)-O-Rh wherein R means hydrogen or an alkyl group with 1 to 3 carbon atoms, R1and R2are independently selected from the group consisting of H and optionally substituted alkyl group with 1 to 5 carbon atoms, and Rh means a linear or branched alkyl residue with 1 to 30 carbon atoms, preferably with 1 to 15 carbons, more preferably with 1 to 5 carbons, optionally substituted by one or more nitrogen atom or by one or more hydroxyl, thiol or amino functional group;- monomer (II): nitrile group-containing monomer; wherein the content of monomer (II) in the polymer (A) is lower than 20 wt%, preferably lower than 15 wt%; c) at least one solvent (S); and d) optionally at least one electroconductivity-imparting additive.

13. An electrochemical device comprising the positive electrode (E) according to any one of claims 11 or 12.

14. The electrochemical device according claim 13 that is a lithium-ion secondary battery.

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