Lithium battery electrode binders

Abstract

The present invention pertains to binder compositions comprising vinylidene fluoride polymers and certain acrylic polymers and to their use in the preparation of electrodes for secondary batteries.

Description

1 SPOP 2024 / 031 Lithium battery electrode binders Cross reference to previous applications

[0001] This application claims priority filed on 2024-07-26 in EUROPE with Nr 24315358.2, the whole content of this application being incorporated herein by reference for all purposes. Technical Field

[0002] The present invention pertains to binder compositions comprising vinylidene fluoride polymers and certain acrylic polymers, and to the use of the same in the preparation of electrodes for secondary batteries. Background Art

[0003] Fluoropolymers are known in the art to be suitable as binders for the manufacture of electrodes for use in electrochemical devices such as secondary batteries.

[0004] In particular, WO 2008 / 129041 discloses linear semi-crystalline vinylidene fluoride (PVDF) copolymers comprising from 0.05% to 10% by moles of recurring units derived from (meth)acrylic monomers and uses thereof as binder in electrodes for lithium-ion batteries.

[0005] In general, increasing the fluoropolymers molecular weight is known to increase the performances of articles made from these materials, in particular in terms of mechanical properties and in terms of adhesion of the electrodes to the current collector.

[0006] However, increasing the fluoropolymers molecular weight will increase the viscosity of the electrode-forming formulation including the same, also called electrode slurry, making much more difficult the handling and the coating process in the fabrication of electrodes.

[0007] Hence, the mixing of other polymers with PVDF has been attempted in order to overcome this disadvantage, but there are few polymers having adhesion properties or compatibility in respect of PVDF; moreover, because of adverse effects on the physical properties of the PVDF, the application range is extremely restricted. For example, polymethyl methacrylate resin (hereinafter abbreviated to PMMA) is known to be a material with good compatibility for PVDF (JPH03213336), but the glass transition temperature of PMMA is very high when compared to that of PVDF, so mixtures of these polymers lack flexibility and they have poor adhesion to metals.3 SPOP 2024 / 031 and RX is a C1-C20 hydrocarbon moiety comprising at least one functional group selected from the group consisting of hydroxyl, carboxyl, epoxy, ether (- O-), ketone (-C=O-), epoxy, per-carbonate (-O-CO-O-), ester (-OCO-), ester phosphate, ether group, nitrile and anhydride; in an amount of from 0.05 to 2 % by moles of with respect to the total moles of recurring units of polymer (F); and b) at least one a (meth)acrylate polymer [polymer (A)] that comprises: (I) recurring units derived from methyl methacrylate (MMA); (II) recurring units derived from at least one C4-C18 (meth)acrylate monomer; c) at least one solvent (S); and d) optionally at least one electroconductivity-imparting additive.

[0014] In a second instance, the present invention pertains to the use of the positive 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 the following steps: (I) providing a metal substrate having at least one surface; (II) providing an electrode-forming composition (C) as above defined; (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); (V) submitting the dried assembly obtained in step (IV) to a compression step to obtain the electrode (E) of the invention.

[0015] In a third instance, the present invention pertains to the positive electrode (E) obtainable by the process of the invention.

[0016] In a fourth instance, the present invention pertains to an electrochemical device comprising a positive electrode (E) of the present invention. Detailed description

[0017] 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.

[0018] By the term “recurring unit derived from vinylidene fluoride” (also generally indicated as vinylidene difluoride 1,1-difluoroethylene, VDF), it is intended to denote a recurring unit of formula -CF2-CH2-.6 SPOP 2024 / 031 - (meth)acrylonitrile, - succinic anhydride, - vinyl laurate (VL), - vinyl neodecanoate (VnD), - succinic acid vinyl ester, and mixtures thereof.

[0025] The term "vinyl monomer" as employed herein may comprise recurring units derived from one or more than one vinyl monomer (MA) as above described. In the rest of the text, the expressions "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 vinyl monomer (MA).

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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 vinyl monomer (MA).

[0030] 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 vinyl monomer (MA).

[0031] In a preferred embodiment of the invention, in polymer (F) the recurring units derived from vinyl monomer (MA) of formula (I) are comprised in an amount of from 0.1 to 1 % by moles with respect to the total moles of recurring units of polymer (F).

[0032] 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 - 0.50 l / g.7 SPOP 2024 / 031

[0033] The polymer (F) may further comprise recurring units derived from one or more fluorinated comonomers (CF) different from VDF.

[0034] By the term “fluorinated comonomer (CF)”, it is hereby intended to denote an ethylenically unsaturated comonomer comprising at least one fluorine atoms.

[0035] 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-Rf0, wherein Rf0is a C1-C6perfluoroalkyl group; (d) chloro- and / or bromo- and / or iodo-C2-C6 fluoroolefins such as chlorotrifluoroethylene (CTFE).

[0036] 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).

[0037] In one preferred embodiment of the invention, the polymer (F) 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 vinyl monomer (MA) of formula (I); - optionally 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 at least one fluorinated comonomer (CF).

[0038] 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).

[0039] 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.8 SPOP 2024 / 031

[0040] 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.

[0041] The expressions "continuous feeding", “adding continuously” or "continuously feeding" means that slow, small, incremental additions the aqueous solution of vinyl monomer (MA) take place until polymerization has concluded.

[0042] 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.

[0043] When the recurring units derived from monomer (MA) in polymer (F) comprise functional groups that can be hydrolysed, polymer (F) can be further subjected to a step of hydrolysis. In particular, a polymer (F) comprising recurring units (MA) of formula (I) wherein RX is a C1-C20 hydrocarbon moiety comprising at least one functional group selected from nitrile and anhydride can be subjected to hydrolysis to provide a polymer (F’) wherein the nitrile or anhydride groups are at least partially hydrolyzed to the corresponding carboxylic acid groups.

[0044] The at least one (meth)acrylate polymer (A), different from polymer (F), is a polymer comprising recurring units derived from methyl methacrylate (MMA) and recurring units derived from at least one C4-C18 (meth)acrylate monomer.

[0045] The C4-C18(meth)acrylate monomer may optionally include substituted by one or more functional group(s) selected from the group consisting of double bonds, hydroxyl, carboxyl, epoxy, ether (-O-), ketone (-C=O-), epoxy, per-carbonate (-O- CO-O-) and ester (-OCO-); or a five- to six-membered heterocycle.

[0046] Non-limited examples of C4-C18 (meth)acrylate monomers are n-butyl (meth)acrylate, 2-ethoxy ethyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate), lauryl (meth)acrylate, cycloalkyl (meth)acrylate, like cyclohexyl(meth)acrylate, phenyl (meth)acrylate, polyalkylene glycol acrylate.

[0047] In a preferred embodiment of the present invention, polymer (A) is a polymer comprising recurring units derived from methyl methacrylate and recurring units derived from n-butyl acrylate (BA).

[0048] In another preferred embodiment of the present invention, polymer (A) is a polymer comprising recurring units derived from methyl methacrylate, recurring units derived from n-butyl acrylate (BA) and recurring units derived from octyl acrylate (OA).9 SPOP 2024 / 031

[0049] In still another preferred embodiment of the present invention, polymer (A) is a polymer comprising recurring units derived from methyl methacrylate, recurring units derived from n-butyl acrylate (BA) and recurring units derived from lauryl acrylate.

[0050] The recurring units derived from methyl methacrylate (MMA) and the recurring units derived from at least one C4-C8 (meth)acrylate monomer are present in polymer (A) in an amount ratio between 50:50 to 70:40, preferably in a 60:40 ratio.

[0051] Polymer (A) may further include up to 15 % by moles of additional recurring units derived from at least one one vinyl monomer (MA) of formula (II) as above defined.

[0052] In one embodiment of the present invention, polymer (A) is a polymer comprising recurring units derived from methyl methacrylate, recurring units derived from n- butyl acrylate (BA) and recurring units derived from (meth)acrylic acid.

[0053] The (meth)acrylic polymer (A) is prepared by polymerizing a mixture of methyl methacrylate (MMA), at least one C4-C18(meth)acrylate monomer, and optionally at least one vinyl monomer (MA) of formula (II) as above defined.

[0054] The polymer (A) for use in the composition (C) of the present invention preferably has a number average molecular weight (Mn) of at least 1 kDa, for example between 1 and 150 kDa. More preferably, the polymer (A) has a number average molecular weight (Mn) between 15 and 100 kDa.

[0055] The polymer (A) for use in the composition (C) of the present invention preferably has a ratio between weight average molecular weight (Mw) and number average molecular weight (Mn) of about 1 to 4.

[0056] Polymer (A) may suitably contain from 1 to 50, preferably 3 to 40, and more preferably 10 to 30 % by weight of at least one C4-C18 (meth)acrylate monomer.

[0057] For the purpose of the present invention, the term “Nickel-rich active material” is intended to denote an active material is selected from lithium-containing complex metal oxides of general formula (II) LiNixM1yM2zY2 (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, and Y denotes a chalcogen, preferably selected from O and S.10 SPOP 2024 / 031

[0058] The positive electrode active material (AM) is preferably a compound of formula (II) wherein Y is O.

[0059] In a preferred embodiment, M1is Mn and M2is Co.

[0060] In another preferred embodiment, M1is Co and M2is Al.

[0061] Examples of such active materials include LiNixMnyCozO2 , herein after referred to as NMC, and LiNixCoyAlzO2, herein after referred to as NCA.

[0062] Specifically with respect to LiNixMnyCozO2, varying the content ratio of manganese, nickel, and cobalt can tune the power and energy performance of a battery.

[0063] In a preferred embodiment of the present invention, the active material (AM) is a compound of formula (II) as above defined, wherein 0.5 ≤ x ≤ 1, 0.1 ≤ y ≤ 0.5, and 0 ≤ z ≤ 0.5.

[0064] Non limitative examples of suitable positive electrode active materials (AM) of formula (II) include, notably: LiNi0.5Mn0.3Co0.2O2 , ,

[0065] have been found particularly advantageous are and LiNi0.8Mn0.1Co0.1O2.

[0066] For the purpose of the present invention, the term “compound capable of intercalating sodium ions” is intended to denote a conventional active material suitable for use at the positive electrode of sodium-ion batteries, which is generally selected from Na-based layered transition-metal oxides, Prussian blue analogs and polyanion-type materials.

[0067] In some embodiments the active materials are Na-based layered transition-metal 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 NaxMO2wherein M stands for a transition metal ion such as Co, Mn and x is 2 / 3.

[0068] In some embodiments the active materials are Prussian blue analogs (PBA) of general formula AxP[R(CN)6]1-y□y.mH2O with A and alkali metal ion, P a N- coordinated transition metal ion, R a C-coordinated transition metal ion, □ a [R(CN)6] vacancy, with 0 ≤ x ≤ 2 and 0 ≤ y < 1 such as Na0.81Fe[Fe(CN)6]0.79□0.21,11 SPOP 2024 / 031 NaFe2(CN)6, Na1.63Fe1.89(CN)6, Na1.72MnFe(CN)6, Na1.76Ni0.12Mn0.88[Fe(CN)6]0.98, Na2NixCo1-xFe(CN)6with 0 ≤ x ≤ 1 e.g. Na2CoFe(CN)6.

[0069] 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 (XmO3m+1)n-. Among them, phosphates NaMPO4such as NaFePO4, Na0.7FePO4 or NaMnPO4; natrium (sodium) superionic conductor of NASICON-type structures of general formula NaxM2(XO4)3(where 1 ≤ x ≤ 4 and M = 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. Na3.12Fe2.44(P2O7)2 or Na3.32Fe2.34(P2O7)2, Na2(VO)P2O7, Na7V3(P2O7)4; fluorophosphates NaVPO4F, Na2CoPO4F, Na2FePO4F, Na2MnPO4F, Na3(VO1-xPO4)2F1+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), Na4Co3(PO4)2(P2O7), 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+2xMn2-x(SO4)3 (where 0 ≤ x ≤ 1) ; silicates of general formula Na2MSiO4 (with M = Mn, Fe, Co and Ni).

[0070] In some preferred embodiments the active materials are fluorophosphates preferably selected from the list consisting of NaVPO4F, Na2CoPO4F, Na2FePO4F, Na2MnPO4F, Na3(VO1-xPO4)2F1+2x (with 0 ≤ x ≤ 1) e.g. Na3(VOPO4)2F or Na3V2(PO4)2F3 (NVPF).

[0071] The solvent (S) may preferably be an organic polar one, examples of which may include: N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N- dimethylacetamide, dimethylsulfoxide, hexamethylphosphamide, dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, and trimethyl phosphate. These solvents may be used singly or in mixture of two or more species.12 SPOP 2024 / 031

[0072] The electro-forming composition (C) of the invention may further optionally include at least one conductive agent.

[0073] 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 agent is preferably carbon black. Carbon black is available, for example, under the brand names, Super P® or Ketjenblack®.

[0074] The preferred positive electrode-forming composition (C) comprises: a) positive electrode active material (AM) in an amount from 80 to 98% by weight, preferably from 90 to 97 % by weight, with respect to the total weight of (a)+(b)+(c); b) binder (B) in an amount from 0.5 to 10 % by weight, preferably from 1 to 5 % by weight, with respect to the total weight of (a)+(b)+(c); c) a solvent (S); and carbon black or carbon nanotubes as electroconductivity-imparting additive, in an amount from 1 to 10 % by weight, preferably from 2 to 5 % by weight with respect to the total weight of (a)+(b)+(c).

[0075] The amount of polymer (A) in the binder (B) is preferably comprised between 5 and 40 % by weight, more preferably between 5 and 20% by weight.

[0076] In a further instance, the present invention provides a process for preparing the composition (C) as above defined which comprises: - mixing the polymer (F) with a portion of the solvent (S); - mixing the polymer (A) with a portion of the solvent (S); - mixing the two mixtures obtained above to obtain a mixture of binder (B) in solvent (S); - adding the active material (AM), optionally the electroconductivity-imparting additive and the residual solvent (S); - mixing the resulting suspension.

[0077] The electrode-forming composition (C) according to the invention has a total solid content that preferably ranges from 50 and 90% by weight, more preferably the total solid content ranges from 65 to 80% by weight.

[0078] The Applicant has found that the addition of an amount of the (meth)acrylate polymer (A) to polymer (F) facilitates the handling of composition (C) during the manufacture of the electrode, as a result of the decrease in the viscosity of the binder / active material mixture.13 SPOP 2024 / 031

[0079] One aim of the present invention is thus to provide a binder which makes it possible to easily spread the active material over the metal collector and thus facilitates the manufacture of an electrode for a lithium-ion or sodium-ion battery.

[0080] In another object, the present invention pertains to the use of the electrode- forming composition (C) for the manufacture of a positive electrode (E), said process comprising: (I) providing a metal substrate having at least one surface; (II) providing an electrode-forming composition (C) as above defined; (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); (V) submitting the dried assembly obtained in step (IV) to a compression step to obtain the electrode (E) of the invention.

[0081] Under 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).

[0082] The drying temperature will be selected so as to effect removal by evaporation of one or more solvents (S) from the electrode (E) of the invention.

[0083] In a further object, the present invention pertains to the electrode (E) obtainable by the process of the invention.

[0084] The electrode (E) of the invention is thus particularly suitable for use in electrochemical devices, in particular in secondary batteries.

[0085] For the purpose of the present invention, the term “secondary battery” is intended to denote a rechargeable battery.

[0086] The secondary battery of the invention is preferably an alkaline or an alkaline- earth metal secondary battery.

[0087] The secondary battery of the invention is more preferably a Lithium-ion secondary battery.

[0088] In still a further object, the present invention pertains to an electrochemical device comprising at least one electrode (E) of the present invention.

[0089] The electrochemical device according to the present invention, being preferably a secondary battery, comprises: - a positive electrode and a negative electrode, wherein the positive electrode is the electrode (E) of the present invention.14 SPOP 2024 / 031

[0090] An electrochemical device according to the present invention can be prepared by standard methods known to a person skilled in the art.

[0091] 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.

[0092] 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.

[0093] EXPERIMENTAL PART

[0094] Raw materials

[0095] Polymer (A-1): Plastistrength® L1000, copolymer of MMA / BA commercially available from Arkema.

[0096] Polymer (F-1): VDF-AA (0.6% by moles) polymer having an intrinsic viscosity of 0.40 l / g in DMF at 25°C.

[0097] Carbon nanotubes: Orgacyl NMP0402. 4% thin multiwall carbon nanotube (MWCNT) in N-Methyl-2-pyrrolidone (NMP) solvent.

[0098] NMC811, commercially available from Cosmo Advanced Materials & Technology (d50 = 10.28 μm).

[0099] Determination of intrinsic viscosity of polymer (F)

[0100] Intrinsic viscosity (η) [dl / g] was measured using the following equation on the basis of dropping time, at 25°C, of a solution obtained by dissolving the polymer (F) in N,N-dimethylformamide at a concentration of about 0.2 g / dl using a Ubbelhode viscosimeter: where c is polymerrelative viscosity, i.e. the ratio between the dropping time of sample solution and the dropping time of solvent, ηsp is the specific viscosity, i.e. ηr -1, and Γ is an experimental factor, which for polymer (F) corresponds to 3.

[0101] DSC analysis

[0102] DSC analyses were carried out according to ASTM D4591 standard; the melting point relating to the second heating run (Tf2) was determined at a heating rate of 10°C / min.

[0103] EXAMPLE 1:

[0104] A 8% by weight solution of polymer (F-1) in NMP was prepared.15 SPOP 2024 / 031

[0105] Polymer (A-1) was dissolved in NMP to obtain a 8% by weight solution.

[0106] The solution of polymer (A-1) was mixed with the solution of polymer (F-1) in NMP in a 80:20 ratio.

[0107] NMC811 and MWCNT 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 a final composition of 98% by weight of NMC811, 1.1% by weight of mixture of polymer (F-1) and polymer (A-1) 80:20 and 0.9% by weight of CNT.

[0108] The viscosity of Composition 1 is shown in Table 1.

[0109] COMPARATIVE EXAMPLE 2:

[0110] The same procedure of Example 1 was followed, but no polymer (A-1) was added. Comparative Composition 2 was obtained. The viscosity of Comparative Composition 2 is shown in Table 1.

[0111] Viscosity Measurement

[0112] The slurry viscosity of Composition 1 and or Comparative Composition 2 were measured with an AntonPaar Rheolab QC using a Concentric cylinder setup (Measuring Cup: C-CC27 / QC-LTD Bob: CC27 / P6) with Peltier temperature control at 25°C. Steady state viscosities were measured from shear rate of 0.1 to 10001 / s.

[0113] EXAMPLE 3: Preparation of electrodes

[0114] Positive electrodes were obtained by applying the Composition 1 and Comparative Composition 2 as above described to both sides of a 15 µm 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.

[0115] Flexibility and adhesion of the positive electrodes so obtained (electrode (E1) and (EC-2), respectively), were evaluated.

[0116] Positive Electrodes Flexibility Evaluation

[0117] 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.16 SPOP 2024 / 031

[0118] 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 density in the standard pressing conditions or same density with milder pressing conditions.

[0119] The results are reported in Table 1.

[0120] Positive Electrodes Adhesion Evaluation

[0121] Positive electrodes (E1) and (EC-2) 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.

[0122] 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 1. Table 1 er Normalized slurry Normalized Normalized electrode Polym viscosity / a.u. electrode cracking adhesion / a.u. diameter / a.u. F-1 1.00 ± 0.01 1.00 ± 0.04 1.00 ± 0.08 F-1 / A-1 = 80:20 0.73 ± 0.06 0.73 ± 0.05 0.92 ± 0.05

[0123] The data clearly demonstrate that the composition of the present invention is characterized by improved slurry viscosity and flexibility in comparison with compositions comprising the fluoropolymer alone, while at the same time keeping good adhesion onto metals.

Claims

18 SPOP 2024 / 031 wherein each of R1 and R2 have the meanings as above defined, R3 is hydrogen, and ROH is a hydrogen or a C1-C18 hydrocarbon moiety comprising at least one functional group selected from the group consisting of hydroxyl, carboxyl, epoxy, ether (-O-), ketone (-C=O-), epoxy, per-carbonate (-O-CO-O-), ester (-OCO-), ester phosphate, ether group, nitrile and anhydride. Claim 3. The composition (C) according to claim 1, wherein the vinyl monomer (MA) is a compound of formula (III): R1R2C=CR3-O-C(O)-R4(III) wherein R1, R2and R3, equal to or different from each other, are independently selected from a hydrogen atom, a halogen atom, and a C1-C5 hydrocarbon group, and wherein R4is a C3-C20 linear or branched hydrocarbon chain moiety, optionally comprising at least one functional group selected from a hydroxyl, a carboxyl, an epoxide, an ester phosphate and an ether group. Claim 4. The composition (C) according to anyone of claims 1 to 3, wherein the vinyl monomers (MA) is selected from the group consisting of: - acrylic acid (AA), - (meth)acrylic acid, - 2-carboxyethyl (meth) acrylate, - 3-butenoic acid, - (meth) acryloyloxyethyl succinate, - (meth) acryloyloxypropyl succinate, - 3-(allyloxy)propanoic acid, - hydroxyethyl (meth)acrylate, - hydroxypropyl(meth)acrylate, - hydroxyethylhexyl(meth)acrylate, - (meth)acrylonitrile, - succinic anhydride, - vinyl laurate (VL), - vinyl neodecanoate (VnD), - succinic acid vinyl ester, and mixtures thereof. Claim 5. The composition (C) according to claim 1 wherein polymer (F) further comprises recurring units derived from one or more fluorinated comonomers (CF) different from VDF, wherein said comonomer (CF) is selected from the group consisting of:19 SPOP 2024 / 031 (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-Rf0, wherein Rf0 is a C1-C6 perfluoroalkyl group; (d) chloro- and / or bromo- and / or iodo-C2-C6 fluoroolefins such as chlorotrifluoroethylene (CTFE). Claim 6. The composition (C) according to any one of the preceding claims, wherein polymer (F) 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 0.1% to 1% by moles, of a vinyl monomer (MA) of formula (I); - optionally 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 at least one fluorinated comonomer (CF). Claim 7. The composition (C) according to any one of the preceding claims, wherein the C4-C18(meth)acrylate monomer in polymer (A) is selected from the group consisting of n-butyl (meth)acrylate, 2-ethoxy ethyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate), lauryl (meth)acrylate, cycloalkyl (meth)acrylate, like cyclohexyl(meth)acrylate, phenyl (meth)acrylate, polyalkylene glycol acrylate. Claim 8. The composition (C) according to any one of the preceding claims, wherein polymer (A) is a polymer comprising recurring units derived from methyl methacrylate and recurring units derived from n-butyl acrylate (BA). Claim 9. The composition (C) according to any one of the preceding claims, wherein the recurring units derived from methyl methacrylate (MMA) and the recurring units derived from at least one C4-C18 (meth)acrylate monomer are present in polymer (A) in an amount ratio between 50:50 to 70:40, preferably in a 60:40 ratio. Claim 10. The composition (C) according to any one of the preceding claims, wherein polymer (A) further includes up to 15 % by moles of additional recurring units derived from at least one vinyl monomer (MA) as above defined.20 SPOP 2024 / 031 Claim 11. The composition (C) according to any one of the preceding claims, wherein the polymer (A) is comprised in the binder (B) in an amount between 5 and 40 % by weight, more preferably between 5 and 20% by weight. Claim 12. The composition (C) according to anyone of the preceding claims, wherein the solvent (S) is an organic polar solvent, preferably selected from the group consisting of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N- dimethylacetamide, dimethylsulfoxide, hexamethylphosphamide, dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, and trimethyl phosphate, or mixtures thereof. Claim 13. A process for the manufacture of a positive electrode for electrochemical devices [electrode (E)], said process comprising the following steps: (I) providing a metal substrate having at least one surface; (II) providing an electrode-forming composition (C) according to any one of claims 1 to 12; (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); (V) submitting the dried assembly obtained in step (IV) to a compression step to obtain the electrode (E) of the invention. Claim 14. A positive electrode (E) obtainable by the process according to claim 13. Claim 15. An electrochemical device comprising a positive electrode (E) according to claim 14.

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