Secondary battery electrode binder

Abstract

The present invention pertains to binder compositions comprising hydrogenated nitrile butadiene rubber and certain acrylic polymers, and to the use of the same in the preparation of electrodes for secondary batteries.

Description

1 SPOP 2024 / 047Secondary battery electrode binderCross reference to previous applications

[0001] This application claims priority to European application No. 24315545.4 filed on 02 December 2024, the whole content of this application being incorporated herein by reference for all purposesTechnical Field

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

[0003] The quest for more efficient, durable, and cost-effective materials for electrode binders in energy storage devices, such as batteries and supercapacitors, has been a focal point of research and development in the field of electrochemistry and materials science. Among the various materials explored, hydrogenated nitrile butadiene rubber (HNBR) resin stands out due to its unique properties, which include excellent thermal stability, chemical resistance, and mechanical strength. These characteristics make HNBR resin a promising candidate for use in electrode binders, which play a crucial role in maintaining the structural integrity of electrodes and ensuring efficient electron and ion transport within energy storage devices.

[0004] Moreover, the chemical resistance of HNBR resin ensures that the binder remains intact in the aggressive chemical environments typically encountered within batteries and supercapacitors. This resistance is crucial for preventing binder degradation, which can lead to electrode delamination and, ultimately, device failure. The mechanical strength of HNBR also contributes to the durability of the electrode, enabling it to withstand the physical stresses encountered during device assembly and operation.

[0005] The use of HNBR in electrodes is for example disclosed in US2013183577, wherein a LiFePO4(LFP) cathode is prepared, and in EP3316360, which discloses binder compositions for Nickel-rich positive electrodes comprising HNBR.

[0006] However, while HNBR is imparting good rheology and gelation resistance to electrode binders, it is suffering from scarce adhesion level, thus preventing the use of low binder amounts.

[0007] Moreover, the interaction of HNBR resin with specific electrode materials and electrolytes has been identified as an area requiring further investigation. Certain2 SPOP 2024 / 047compositions of HNBR may exhibit less than optimal compatibility with common electrode materials or electrolytes, potentially affecting the electrochemical performance and stability of the energy storage device. This compatibility issue underscores the need for tailored formulations of HNBR resin to ensure optimal performance across a wide range of electrode and electrolyte systems.

[0008] To this aim, Journal of Power Sources, Volume 440, 15 November 2019, suggests that to ensure insolubility in the electrolyte, HNBR is previously crosslinked.

[0009] JP 2012-256541 discloses the use of 0.3 parts of HNBR in combination with 1.2 parts of a block copolymer comprising (meth)acrylic acid ester monomers in positive electrode binders in order to achieve good slurry stability and good peel strength.Summary of invention

[0010] An object of the present invention is to provide an electrode slurry composition containing a binder having excellent processing and no gelation, while showing very high adhesion level to metal collectors. This excellent mechanical adhesion paves the way to binder amount reduction with advantage in terms of battery energy density and durability.

[0011] Thus, the invention provides a polymer composition (P) comprising:a) at least one hydrogenated nitrile rubber (R) comprising recurring units derived from at least one conjugated diene monomer and recurring units derived from at least one α,β-ethylenically unsaturated nitrile monomer, in which the degree of hydrogenation of the diene units incorporated into the rubber is in the range from 98 to 100%; andb) at least one copolymer (A) comprising recurring units derived from a vinyl monomer (I) having an acid component and recurring units derived from a (meth) acrylic acid alkyl ester monomer (II),wherein the amount of hydrogenated nitrile rubber (R) in composition (P) is comprised between 50 and 90% by weight, based on the total amount of 100% by weight of composition (P).

[0012] A second object of the present invention pertains to a positive electrode-forming composition (C) comprising:i) at least one positive electrode active material (AM);ii) at least one polymer composition (P) as above defined;iii) optionally, at least one solvent (S), andiv) optionally, at least one conductive agent.3 SPOP 2024 / 047

[0013] In another object, the present invention pertains to the use of the positive electrodeforming composition (C) 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 a positive 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) optionally, drying the assembly provided in step (III);(V) submitting the assembly obtained in step (III) or the dried assembly obtained in step (IV) to a compression step to obtain a positive electrode (E).

[0014] In a further object, the present invention pertains to a positive electrode (E) obtainable by the process of the invention.

[0015] In still a further object, the present invention pertains to an electrochemical device comprising at least one electrode (E) of the present invention.Detailed description

[0016] The α,β-ethylenically unsaturated nitrile monomer may be any α,β-ethylenically unsaturated compound having a nitrile group. Examples thereof include acrylonitrile, α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile, α-alkylacrylonitriles such as methacrylonitrile and ethacrylonitrile, and the like. Among these, acrylonitrile and methacrylonitrile are preferable, and acrylonitrile is particularly preferable.

[0017] The amount of α, β-ethylenically unsaturated nitrile units is typically in the range from 15% to 60% by weight, preferably 20% to 50% by weight, more preferably from 30% to 45% by weight, based on the total amount of 100% by weight of all the monomer units in polymer rubber (R).

[0018] The conjugated diene monomer may be of any type, especially conjugated C4-C12 dienes. Particular preference is given to 1,3-butadiene, isoprene, 2,3- dimethylbutadiene, 1,3-pentadiene (piperylene) or mixtures thereof. Especially preferred is 1,3-butadiene.

[0019] The amount of conjugated diene is typically in the range from 40% to 90% by weight, preferably 50% to 85% by weight, more preferably 55% to 75% by weight, based on the total amount of 100% by weight of all the monomer units in polymer rubber (R).4 SPOP 2024 / 047

[0020] In addition, the hydrogenated nitrile rubber (R) may optionally contain one or more further copolymerizable monomers in an amount of 0% to 20% by weight, preferably 0.1 %to 15% by weight, more preferably 3% to 10% by weight based on the total amount of 100% by weight of all monomer units in the hydrogenated nitrile butadiene rubber.

[0021] The preparation of hydrogenated nitrile rubbers suitable for use in the present invention is very familiar to the person skilled in the art.

[0022] The initial preparation of the nitrile rubbers via polymerization of the abovementioned monomers is extensively described in the literature (e.g. Houben- Weyl, Methoden der Organischen Chemie [Methods of organic chemistry], Vol.14 / 1, Georg Thieme Verlag Stuttgart 1961).

[0023] The subsequent hydrogenation of the nitrile rubbers to give hydrogenated nitrile rubber can take place in the manner known to the person skilled in the art. By way of example, a suitable method is reaction with hydrogen with use of homogeneous catalysts, e.g. the catalyst known as “Wilkinson” catalyst (((PPh3)3RhCl)) or others. Processes for the hydrogenation of nitrile rubber are known. Rhodium or titanium are usually used as catalysts, but platinum, iridium, palladium, rhenium, ruthenium, osmium, cobalt or copper can also be used either in the form of metal or else preferably in the form of metal compounds (see, for example, US 3700637, EP 134023, US 4464515).

[0024] Hydrogenated nitrile rubbers suitable for use in the present invention are commercially available.

[0025] Preferably, said at least one hydrogenated nitrile rubber (R) is a hydrogenated acrylonitrile-butadiene copolymer (HNBR).

[0026] In a more preferred embodiment, the at least one hydrogenated nitrile rubber (R) is HNBR comprising from 30% to 45% by weight, based on the total amount of 100% by weight of all the monomer units in polymer rubber (R), of acrylonitrile (ACN).

[0027] The at least one hydrogenated nitrile rubber (R) has a degree of hydrogenation of the diene units incorporated into the rubber in the range from 98 to 100%, which means that it comprises residual double bonds in an amount of more than 0% and not more than 2% based on the total amount of the HNBR.

[0028] The at least one copolymer (A) is a copolymer that comprises recurring units derived from a vinyl monomer (I) having an acid component and recurring units derived from a (meth) acrylic acid alkyl ester monomer (II).

[0029] The term “copolymer” encompasses polymers having more than one monomer unit. In one embodiment of the invention, copolymer (A) is a copolymer that is5 SPOP 2024 / 047derived exclusively, for example, from the two monomer types (I) and (II) as described below. The term "copolymer" likewise encompasses, for example, additionally terpolymers and quaterpolymers, derived from the two monomer types (I) and (II) and one or more further monomer units (III).

[0030] As the vinyl monomer (I) having an acid component, a vinyl monomer having a carboxylic acid group, a vinyl monomer having a sulfonic acid group, and a combination thereof can be used. Preferably, a vinyl monomer having a carboxylic acid group can be used.

[0031] Examples of the vinyl monomer having a carboxylic acid group include monocarboxylic acids and derivatives thereof, dicarboxylic acids and acid anhydrides thereof, derivatives thereof, and combinations thereof. Of these, monocarboxylic acids are preferred.

[0032] Examples of monocarboxylic acids include acrylic acid, methacrylic acid, cratonic acid and the like. Examples of monocarboxylic acid derivatives include 2- ethylacrylic acid, isocrotonic acid, a-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, β-diaminoacrylic. An acid etc. are mentioned. Among these, acrylic acid and methacrylic acid are particularly preferable.

[0033] Examples of dicarboxylic acids include maleic acid, fumaric acid, itaconic acid and the like. Examples of acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, and the like. Examples of dicarboxylic acid derivatives include methyl maleate such as methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid; diphenyl maleate, nonyl maleate, decyl maleate, Examples thereof include maleate esters such as dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate. Of these, itaconic acid is preferred.

[0034] As the vinyl monomer (I) having a carboxylic acid group, any one of the aboveexemplified compounds can be used alone, or two or more kinds can be used in combination.

[0035] Examples of the vinyl monomer having a sulfonic acid group include, for example, a sulfonic acid group-containing monomer having a sulfonic acid group and a polymerizable group and having no other functional group, or a salt thereof, an amide group, a sulfonic acid group, and a polymerizable monomer containing a group or a salt thereof, a monomer containing a hydroxyl group, a sulfonic acid group and a polymerizable group or a salt thereof, and a combination thereof.

[0036] Among the above various monomers (I), acrylic acid, methacrylic acid, itaconic acid, with acrylic acid and methacrylic acid are even more preferable.6 SPOP 2024 / 047

[0037] Examples of the (meth) acrylic acid alkyl ester monomer (II) include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate. Among these, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and pentyl acrylate are preferable, butyl acrylate and ethyl acrylate are more preferable, and butyl acrylate is particularly more preferable.

[0038] In the present invention, the copolymer (A) preferably further contains recurring units derived from at least an additional vinyl monomer (III).

[0039] Examples of monomer (III) include styrene, a-methyl styrene, vinyl toluene, t-butyl styrene and acrylonitrile. Among these, styrene and acrylonitrile are preferable, and styrene is particularly preferable.

[0040] The amount of the monomer (I) in the copolymer (A) is preferably 0.5 to 5 parts by weight per 100 parts by weight of the total of the monomers (I) and (II) (the total of the monomers (I), (II) and (III), when monomer (III) is included).

[0041] The amount of the monomer (II) in copolymer (A) is preferably 60 to 90 parts by weight, more preferably 70 to 85 parts by weight in 100 parts by weight of the sum of the monomers (I) and (II) (the sum of the monomers (I), (II) and (III) when monomer (III) is included).

[0042] The amount of the monomer (III) in copolymer (A) is preferably 10 to 30 parts by weight, more preferably 15 to 20 parts by weight, in the total 100 parts by weight of the monomers (I), (II) and (III).

[0043] In one embodiment of the present invention, copolymer (A) is a polymer comprising recurring units derived from methacrylic acid (MAA), recurring units derived from n-butyl acrylate (BA) and recurring units derived from styrene (STY).

[0044] In another embodiment of the present invention, copolymer (A) is a polymer comprising recurring units derived from methacrylic acid (MAA), recurring units derived from n-butyl acrylate (BA) and recurring units derived from methyl methacrylate (MMA).

[0045] Monomers (I), (II) and (III) can be arranged in blocks or they can be randomly distributed in copolymer (A).

[0046] According to an embodiment of the invention, copolymer (A) is a block copolymer obtained by controlled radical polymerization using RAFT / MADIX agents.

[0047] By "block copolymer" as used herein it is intended any controlled-architecture copolymer, including but not limited to true block polymers, which could be diblocks, tri-blocks, or multi-blocks; branched block copolymers, also known as linear star polymers; comb; and gradient polymers. Gradient polymers are linear polymers whose composition changes gradually along the polymer chains,7 SPOP 2024 / 047potentially ranging from a random to a block-like structure. Each block of the block copolymers may itself be a homopolymer, a random copolymer, a random terpolymer, or a gradient polymer.

[0048] The amount of hydrogenated nitrile rubber (R) in composition (P) is comprised between 50 and 90% by weight, preferably between 60 and 80% by weight, based on the total amount of 100% by weight of composition (P).

[0049] The applicant has surprisingly found that when copolymer (A) in the composition (P) is included in amounts higher than 40 % by weight, the slurry viscosity of binder compositions comprising said composition (P) is too high to be suitably used in the preparation of electrodes for secondary batteries. This tendency to gelation is prevented when electrode-forming compositions comprising a composition (P) comprising the rubber (R) in amount of at least 50 % by weight is used while, at the same time, the manufacturing of electrodes having enhanced flexibility, adhesion and electrochemical stability is enabled.

[0050] Polymer composition (P) is particularly suitable for use in the preparation of electrode-forming compositions, more particularly positive electrode-forming compositions.

[0051] According to a preferred embodiment, the positive electrode-forming composition (C) of the present invention comprises, preferably consists of:i) at least one positive electrode active material (AM);ii) at least one polymer composition (P) as above defined;iii) at least one solvent (S), andiv) optionally, at least one conductive agent.

[0052] The electrode active material (AM) for positive electrodes is preferably a compound capable of intercalating lithium ions or sodium ions.

[0053] 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.

[0054] 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.

[0055] 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□0.21,8 SPOP 2024 / 047NaFe2(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.

[0056] 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, Na0.7FePO4or NaMnPO4; 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, Na2CoP207, Na4-xFe2+x / 2(P2O7)2 with 2 / 3 < x < 7 / 8 e.g. Na3.12Fe2.44(P2O7)2or 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).

[0057] In some preferred embodiments the active materials are fluorophosphates preferably selected from the list consisting of NaVPO4F, Na2CoPO4F, Na2FePO4F, Na2MnPO4F, Na3(VOi-xPO4)2Fi+2x (with 0 < x < 1) e.g. Na3(VOPO4)2F or Na3V2(PO4)2F3(NVPF).

[0058] The conventional active materials (AM) at the positive electrode of lithium-ion batteries may comprise a composite metal chalcogenide of formula LiMQ2, 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 LiMO2, wherein M is the same as defined above. Preferred examples thereof may include LiCoO2, LiNiO2, LiNixCo1-xO2(0 < x < 1) and spinel-structured LiMn2O4.

[0059] 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)9 SPOP 2024 / 047LiNixM1yM2zQ2(II)wherein M1and M2are the same or different from each other and are transition metals selected from Co, Fe, Mn, Cr and V,wherein 0.5 < x < 1,wherein y+z = 1-x, andQ denotes a chalcogen, preferably selected from O and S.

[0060] 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, M2is 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 M2metals, including 0, JO4is 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 JO4oxyanion, generally comprised between 0.75 and 1.

[0061] The MiM2(JO4)fEi-f electro-active material as defined above is preferably phosphate-based and may have an ordered or modified olivine structure.

[0062] More preferably, the electrode active material has formula Li3.xM’yM”2.y(JO4)3wherein 0<x<3, 0<y<2, M’ and M” are the same or different metals, at least one of which being a transition metal, JO4is preferably PO4which 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 formulaLixAyDzPO4,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, 0 I z <1.5.

[0063] The A component is preferably Fe, Mn, and Ni, and particularly preferably Fe.

[0064] The D component is preferably Mg or Ca.

[0065] Examples of the phosphate-based compounds having an olivine structure include lithium iron phosphate (LFP), lithium iron manganese phosphate (LMFP) and lithium manganese phosphate.

[0066] 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.10 SPOP 2024 / 047

[0067] 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.

[0068] 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 a mixture of two or more species.

[0069] The positive electro-forming composition (C) of the invention may further optionally include at least one conductive agent.

[0070] 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®.

[0071] The preferred positive electrode-forming composition (C) according to this embodiment comprises, preferably consists of:i) at least one 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 i) + ii) + iii) + iv);ii) at least one composition (P) in an amount from 0.5 to 10 % by weight, preferably from 1 to 5 % by weight, with respect to the total weight of i) + ii) + iii) + iv); iii) at least one a solvent (S); andiv) at least one conductive agent selected from carbon black and carbon nanotubes, in an amount from 1 to 10 % by weight, preferably from 2 to 5 % by weight with respect to the total weight of i) + ii) + iii) + iv).

[0072] In a further instance, the present invention provides a process for preparing the composition (C) according to this first embodiment as above defined, said process comprising the following steps:- adding the rubber (R) dissolved in a portion of the solvent (S);- adding the polymer (A) dissolved in a portion of the solvent (S);- adding the positive active material (AM), optionally the conductive agent and the residual solvent (S);- mixing the resulting suspension.

[0073] Rubber (R) and polymer (A) are each dissolved in solvent (S) to obtain solutions of 5 to 15 % by weight.11 SPOP 2024 / 047

[0074] The positive electrode-forming composition (C) according to the invention has a total solid content that preferably ranges from 50 and 70% by weight, more preferably the total solid content ranges from 50 to 60% by weight.

[0075] The total solid content of the composition (C) is understood to be cumulative of all non-volatile ingredients thereof, notably including rubber (R), polymer (A), active material (AM) and conductive agent.

[0076] The Applicant has found that the addition of an amount of the (meth)acrylate copolymer (A) to rubber (R) facilitates the handling of composition (C) during the manufacture of the electrode, as a result of the decrease in the viscosity of the mixture. The Applicant has demonstrated that the presence of both a rubber (R) and a copolymer (A) in the binder of the present invention has a synergistic effect on limiting the increase of the slurry viscosity, thus being able to provide excellent processing and no gelation while showing very high adhesion level.

[0077] Without wishing to be bound by theory, at least a partial crosslinking is believed to take place after mixing rubber (R) and copolymer (A), resulting in a binder composition having good compatibility with active materials and limited tendency to gelation.

[0078] One aim of the present invention is thus to provide a composition 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.

[0079] Composition (C) is also particularly suitable for use in the preparation of electrodes for solid state batteries, which further comprise at least one sulfide- based solid electrolyte. The composition (C) further comprising at least one sulfide- based solid electrolyte will be identified hereinafter as composition (C1).

[0080] In a further embodiment of the present invention, it is thus provided a positive electrode-forming composition (C1) suitable for use in the preparation of positive electrodes for solid state batteries, said composition (C1) comprising:a) at least one positive electrode active material (AM);b) a composition (P) as above defined;c) at least one solvent (S);d) optionally, at least one conductive agent; ande) at least one sulfide-based solid electrolyte.

[0081] As used here, the phrase “sulfide-based solid electrolyte,” refers to an inorganic solid state material that conducts Li+ions but is substantially electronically insulating.12 SPOP 2024 / 047

[0082] In the present invention, the term “sulfide-based solid ionic conducting inorganic particle” is not particularly limited as long as it is a solid electrolyte material containing sulfur atom(s) in the molecular structure or in the composition.

[0083] The sulfide-based solid ionic conducting inorganic particle preferably contains Li, X (with X being P, Si, Sn, Ge, Al, As, or B) and S, to increase Li-ion conductivity.

[0084] The sulfide-based solid electrolyte according to the present invention is more preferably selected from the group consisting of:- lithium tin phosphorus sulfide (“LSPS”) materials, such as Li10SnP2S12;- lithium phosphorus sulfide (“LPS”) materials, such as glasses, crystalline or glass-ceramic of those of formula (Li2S)x-(P2S5)y, wherein x+y=1 and 0<x<1, Li7P3S11, Li7PS6, Li4P2S8, Li9.6P3S12and Li3PS4;- doped LPS, such as Li2CuPS4, Li Li1+2xZn1-xPS4, wherein 0<x<1, Li3.33Mg0.33P2S6, and Li4.3xScxP2S6, wherein 0<x<1;- lithium phosphorus sulfide oxygen (“LPSO”) materials of formula LixPySzO, where 0.33<x<0.67, 0.07<y<0.2, 0.4<z<0.55, 0<w<0.15;- lithium phosphorus sulfide materials including X (“LXPS”), wherein X is Si, Ge, Sn, As, Al, such as Li10GeP2S12and Li10SiP2S12;- lithium phosphorus sulfide oxygen including X (“LXPSO”), wherein X is Si, Ge, Sn, As, Al;- lithium silicon sulfide (“LSS”) materials;- lithium boron sulfide materials, such as Li3BS3and Li2S- B2S3-Lil;- lithium tin sulfide materials and lithium arsenide materials, such as Li0.8Sn0.8S2, Li4SnS4, Li3.833Sn0.833As0.166S4, Li3AsS4-Li4SnS4, Ge-substituted Li3AsS4; and- Argyrodite-type sulfide materials of general formula Li7-xPS6.xXxwherein:- Y represents at least one halogen element selected in the group of Cl, Br and I or a combination thereof; and x represents a positive number from 0.8 to 2.0, such asthe compounds being possibly deficient in sulfur, lithium or halogen, for instance Li6-xPS5-xCl1+xwith 0<x<0.5, or doped with a heteroatom.

[0085] Particularly preferred sulfide solid electrolytes are LPS materials, LSPS materials and Argyrodite-type sulfide materials.

[0086] In another object, the present invention pertains to the use of the positive electrodeforming composition (C) for the manufacture of a positive electrode (E), said process comprising:(I) providing a metal substrate having at least one surface;13 SPOP 2024 / 047(II) providing a positive 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) optionally drying the assembly provided in step (III);(V) submitting the dried assembly obtained in step (IV) to a compression step to obtain a positive electrode (E).

[0087] 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).

[0088] The drying temperature will be selected so as to effect removal by evaporation of one or more solvents (S) from the positive electrode (E) of the invention.

[0089] When the composition (C) used in the manufacturing of a positive electrode is composition (C1), the present invention provides an electrode for solid-state batteries obtainable by the process as above defined.

[0090] The applicant has surprisingly found that the processability of the polymer composition (P) make it suitable for the preparation of positive electrodes by dry processes or extrusion at low temperatures, thus providing electrodes by a very efficient process.

[0091] The composition (C) which does not include any solvent (S) will be identified hereinafter as composition (C2).

[0092] In another embodiment of the present invention it is thus provided a positive electrode-forming composition [composition (C2)] for use in the preparation of electrodes for electrochemical devices, characterized by comprising:a) at least one positive electrode active material (AM);b) a polymer composition (P) as above defined; andc) optionally, at least one conductive agent.

[0093] In one embodiment, the composition (C2) is suitably in the form of a dry mixture.

[0094] Composition (C2) according to this embodiment can be prepared by dry mixing the at least one positive electrode active material (AM), the polymer composition (P) as above defined, and optionally, at least one conductive agent in the absence of solvent.

[0095] In an alternative embodiment, the composition (C2) as above defined can be obtained in the form of a self-supporting dry film. According to this embodiment, the14 SPOP 2024 / 047composition (C2) in the form of dry mixture is fed to a compactor to form a self- supporting dry film.

[0096] The compacting of the composition (C2) dry mixture can take place as a mechanical compaction, for example by means of a roller compactor or a tablet press, but it can also take place as rolling, build-up or by any other technique suitable for this purpose.

[0097] The mechanical compaction step may be associated to a thermal consolidation step. The combination of an applied pressure and a heat treatment makes thermal consolidation possible at lower temperatures than if it were done alone.

[0098] In one embodiment, the mechanical compaction step is carried out by compression, suitably by compressing the composition (C2) dry mixture between two metal foils. Preferably, the mechanical compaction step is done by application of a compression pressure between 5 and 50 MPa, and preferably between 10 and 30 MPa.

[0099] The compaction step is conveniently carried out at a temperature not exceeding 200 °C, preferably at a temperature lower than 180 °C.

[0100] When composition (C2) is used in the preparation of a positive electrode by a process in the absence of solvent, the process for manufacturing a positive electrode [electrode (E)] for electrochemical cell comprises the following steps: (la) providing a positive metal substrate having at least one surface;(Ila) providing an electrode-forming composition (C2) as above defined;(Illa) applying the composition (C2) provided in step (Ila) onto the at least one surface of the metal substrate provided in step (la), thereby providing an assembly comprising a metal substrate coated with said composition (C) onto the at least one surface;(IVa) submitting the assembly obtained in step (Illa) to a compression step to obtain the positive electrode (E) of the invention.

[0101] In step (Illa), when the composition (C2) is provided in step (Ila) in the form of a self-supporting film, the self-supporting film of composition (C2) is applied onto the at least one surface of the metal substrate provided in step (la) by lamination, in order to obtain the positive electrode (E).

[0102] Thanks to the improved adhesion of the composition (C2), the dry self-supporting film obtained can be applied onto the metal substrate without the need for any primer or adhesive layer.

[0103] In a further object, the present invention pertains to the positive electrode (E) obtainable by the processes of the invention.15 SPOP 2024 / 047

[0104] The positive electrode (E) of the invention is thus particularly suitable for use in electrochemical devices, in particular in secondary batteries.

[0105] For the purpose of the present invention, the term “secondary battery” is intended to denote a rechargeable battery.

[0106] The secondary battery of the invention is preferably an alkaline or an alkaline-earth metal secondary battery.

[0107] The secondary battery of the invention is more preferably a Lithium-ion secondary battery.

[0108] In still a further object, the present invention pertains to an electrochemical device comprising a positive electrode (E) of the present invention.

[0109] 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.

[0110] An electrochemical device according to the present invention can be prepared by standard methods known to a person skilled in the art.

[0111] 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.

[0112]

[0113] 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.

[0114] EXPERIMENTAL PART

[0115] Raw materials

[0116] LFP: LFP active material commercially available from Dynanonic Co. Ltd. DY-3, having d50 = 0.6-1.8 pm.

[0117] Carbon nanotubes: C-nano 4% weight multiwall carbon nanotube (MWCNT) in N- Methyl-2-pyrrolidone (NMP) solvent.

[0118] NMP: N-Methyl-2-pyrrolidone, available from Sigma Aldrich.

[0119] HNBR: acrylonitrile / butadiene rubber comprising 34% of acrylonitrile, <0.9% residual double bonds, commercially available from Arlanxeo.

[0120] Preparation of polymer (A-1)

[0121] In a 2L double-jacketed reactor equipped with a mechanical stirring system, baffles, a condenser, and a cryostat bath, 180 g of water and 4.011 g of an aqueous solution of Rhodapex AB / 20 surfactant at 28.41% were added. Separately, 561.89 g of a16 SPOP 2024 / 047pre-emulsion containing butyl acrylate (301.72 g), styrene (74.00 g), methacrylic acid (3.86 g), Rhodapex AB / 20 at 28.41% (17.31 g), and water (165 g) was prepared. The pre-emulsion was prepared using an Ultra-Turrax® T25 for 1 minute. At room temperature, 30 g of this pre-emulsion was added to the reaction mixture. The temperature of the reaction mixture was then programmed to reach 80°C within 1 hour. During the heating process, the mixture was degassed by nitrogen bubbling. Once the temperature reaches 76°C, 1.9 g of a 50% aqueous solution of acrylamide and 4.05 g of a 4.7% aqueous solution of ammonium persulfate were added to the reaction mixture. After 20 minutes at 80°C, the remaining pre-emulsion solution, 531.89 g, was added to the reaction mixture under stirring over 6 hours and 30 minutes. In parallel with the addition of the pre-emulsion, a 6% aqueous solution of ammonium persulfate (25.32 g) was also added over a period of 7 hours. At the end of the initiator addition, an additional cooking step of 1 hour at 80°C was performed. The mixture was then cooled to room temperature before being collected. The particle size was measured by light scattering using a Zetasizer. A value of 106.6 nm was obtained with a dispersity of 0.011. A final dry extract for the latex of 50.08% was experimentally measured by thermogravimetry. The product was then purified by dropwise precipitation into a solution composed of 650 g of dihydrated CaCl2(65 g of salt dissolved in 585 g of water) and 650 g of ethanol. The precipitated latex was washed several times before being moderately dried at 50°C.

[0122] Preparation of polymer (A-2)

[0123] In a 2L double-jacketed reactor equipped with a mechanical stirring system, baffles, a condenser, and a cryothermostatic bath, 180 g of water and 5.6 g of an aqueous solution of Rhodapex AB / 20 surfactant at 28.41% were added. Separately, a pre- emulsion of 561.89 g was prepared, containing butyl acrylate (301.72 g), methyl methacrylate (74.00 g), methacrylic acid (3.86 g), Rhodapex AB / 20 at 28.41% (17.31 g), and water (165 g). The pre-emulsion was prepared using an Ultra- Turrax® T25 for 1 minute. At room temperature, 43.6 g of this pre-emulsion was added to the reaction mixture. The temperature of the reaction mixture was then programmed to reach 80°C within 1 hour. During the heating process, the mixture was degassed by nitrogen bubbling. Once the temperature reaches 76°C, 1.9 g of a 50% aqueous acrylamide solution and 4.05 g of a 4.7% aqueous ammonium persulfate solution were added to the reaction mixture. After 20 minutes at 80°C, the remaining pre-emulsion, 518.29 g, was added to the reaction mixture under stirring for 6 hours and 30 minutes. After 50 minutes of reaction, a 2.4% aqueous ammonium persulfate solution (24.4 g) was added in parallel over a period of 617 SPOP 2024 / 047hours. At the end of the initiator addition, an additional cooking step of 1 hour at 80°C was performed. The mixture was then cooled to room temperature before being collected. The particle size was then measured by light scattering using a zetasizer. A value of 109.9 nm was obtained with a dispersity of 0.003. A final dry extract for the latex of 48.92% was measured experimentally by thermogravimetry. The product was then purified by dropwise precipitation into a solution composed of 650 g of dihydrated CaCl2(65 g of salt dissolved in 585 g of water) and 650 g of ethanol. The precipitated latex was washed several times before being moderately dried at 50°C.

[0124] Examples 1-3: Slurry Preparation

[0125] The slurry components, detailed in Table 1, were added to the mixing cup in the following order: i) multi-walled carbon nanotubes pre-dispersed in NMP; ii) HNBR in solution (8% weight in NMP) and either Polymer (A-1) or Polymer (A-2) (8% weight in NMP) in a ratio by weight of 7:3; iii) LFP; and, iv) NMP step 1. The mixture was then mixed using a high-speed disk impeller at 500 rpm for 5 minutes, followed by 75 minutes at 1900 rpm. Then the slurry was diluted to a total solid content of 54% (with the addition of NMP step 2) and mixed again with a Kurabo mixer (KURABO MAZERUSTAR KK-400WE-G2) for 12 minutes.

[0126] Slurry composition comprising 3.5% of composition (P) in the composition (C) are obtained in Examples 1 and 2, while a composition comprising 2% of composition (P) in the composition (C) is obtained in Example 3.

[0127] Comparative Example 1

[0128] The same procedure detailed above for Examples 1 to 3 was followed, but without adding anyone of polymers (A-1) or (A-2).

[0129] A composition comprising 3.5% of HNBR in the composition (C) is obtained.

[0130] Comparative Example 2

[0131] The same procedure detailed above for Examples 1 to 3 was followed, with polymer (A-1) but without adding HNBR.

[0132] A composition comprising 3.5% of polymer (A-1) is obtained.

[0133] Comparative Example 3

[0134] The same procedure detailed above for Examples 1 to 3 was followed, with polymers (A-2) but without adding HNBR.

[0135] A composition comprising 3.5% of polymer (A-2) is obtained.

[0136] Comparative Example 4

[0137] The same procedure detailed above for Examples 1 to 3 was followed, but with HNBR and Polymer (A-2) in a ratio by weight of 3:7.18 SPOP 2024 / 047

[0138] A composition comprising 3.5% of composition (P) in the composition (C) is obtained.Table 1Comp. Comp. Comp. Ex. Ex. Ex. 3 Comp.1 2 (g) 3 (g) 1 (g) 2 (g)- 4 (g)(g) (g)HNBR 38.0 - - 27.1 27.1 15.5 10.8(A-1) - 38.0 - 10.8 6.2(A-2) - - 38.0 - 10.8 - 27.1 LFP 83.1 83.1 83.1 83.1 83.1 84.4 83.1 CNT 16.0 16.0 16.0 16.0 16.0 16.0 16.0 solutionNMP 2.9 2.9 2.9 2.9 2.9 2.9 2.9 step 1NMP 20.6 20.6 20.6 20.6 20.6 33.6 20.6 step 2

[0139] General Preparation of the Electrode comprising active material (LFP):

[0140] Positive electrodes were obtained by casting the as-obtained dispersions of Table 1 herein above on 15 pm thick aluminum foil with a doctor blade and drying the as- coated layers in a vacuum oven at temperature of 90°C for about 50 minutes. The thickness of the dried coating layers was about 150 pm.

[0141] Comparative Electrodes CE1, CE2, CE3 and CE4 and Electrodes E1 and E2, containing 3.5% binder, 95.75% LFP and 0.75% CNTs were obtained, respectively, from slurry compositions Comp. 1, Comp. 2, Comp.3, Comp 4, Ex. 1 and Ex. 2.

[0142] The electrode E3, obtained starting from slurry composition of Ex.3, contains 2% binder content, 97.25% LFP and 0.75% CNTs.

[0143] Peel strength:

[0144] Peel strength of the electrodes obtained as above detailed was measured as follows in accordance with ASTM Standard D903. Each aluminium foil adhesive member (15 pm thickness) was cut into a 25 mm × 150 mm strip which was then laminated onto the electrode adhered by rolling a 2 kg roller back and forth for 3 strokes at a rate of 10 mm / s. The resultant laminate was left standing for a predetermined time at 20°C. The adhesive film was peeled off the surface of the19 SPOP 2024 / 047adhered at a defined speed of 300 mm / min in a 180-degree direction. The force (peel force) required for such peeling was measured and recorded as the bond strength (MPa).

[0145] The results of the aforementioned tests are shown in Table 2 herein below.

[0146] Slurry Viscosity Measurement:

[0147] Slurry viscosity of the slurry compositions as above detailed was 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 (mPas) from shear rate of 0.1 to 1000 1 / s.

[0148] The results of the aforementioned tests are shown in Table 2 herein below.Table 2Example Slurry Peel StrengthViscosity at 10 (%)s-1 (%) Normalized* Normalized*Comp. 1 1 1Comp. 2 2.6 3Comp. 3 gelled n.a.Ex.1 0.5 9Ex. 2 0.9 3Ex. 3 0.3 4Comp. 4 gelled n.a.‘Values normalized to Comp. 1

[0149] The data shown in Table 2 demonstrate that compositions (P) according to the invention, comprising both a rubber (R) and a polymer (A), with rubber (R) representing at least 50 % by weight of the compositon (P), can be used in the prepartion of slurry compositions that are characterized by low slurry viscosity; on the contrary, slurry compositions comprising only HNBR or only a polymer (A) have higher slurry viscosities, or even they gelled, thus preventing their use in the preparation of electrodes.

[0150] At the same time, the electrodes prepared by the use of the compositions (P) of the present invention show good or even very good peel strength.

Claims

20 SPOP 2024 / 047ClaimsClaim 1. A polymer composition (P) comprising:a. at least one hydrogenated nitrile rubber (R) comprising recurring units derived from at least one conjugated diene monomer and recurring units derived from at least one a,p-ethylenically unsaturated nitrile monomer, in which the degree of hydrogenation of the diene units incorporated into the rubber (R) is in the range from 98 to 100%; andb. at least one copolymer (A) comprising recurring units derived from a vinyl monomer (I) having an acid component and recurring units derived from a (meth) acrylic acid alkyl ester monomer (II),wherein the amount of hydrogenated nitrile rubber (R) in composition (P) is comprised between 50 and 90% by weight, preferably between 60 and 80% by weight, based on the total amount of 100% by weight of composition (P).Claim 2. The composition (P) according to claim 1, wherein the a,|3-ethylenically unsaturated nitrile monomer is selected from the group consisting of: a- halogenoacrylonitriles such as a-chloroacrylonitrile and a-bromoacrylonitrile, a- alkylacrylonitriles such as methacrylonitrile and ethacrylonitrileClaim 3. The composition (P) according to claim 1, wherein the conjugated diene is selected from the group consisting of 1,3-butadiene, isoprene, 2,3-dimethylbutadiene, 1,3-pentadiene (piperylene) or mixtures thereof.Claim 4. The composition (P) according to claim 1, wherein the vinyl monomer (I) is selected from acrylic acid, methacrylic acid, itaconic acid.Claim 5. The composition (P) according to claim 1, wherein the (meth) acrylic acid alkyl ester monomer (II) is selected from the group consisting of: methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate.Claim 6. The composition (P) according to claim 1, wherein the copolymer (A) further contains recurring units derived from at least an additional vinyl monomer (III), wherein the additional vinyl monomer (III) is selected from the group consisting of styrene, a- methyl styrene, vinyl toluene, t-butyl styrene and acrylonitrile.Claim 7. A positive electrode-forming composition (C) comprising:i) at least one positive electrode active material (AM);ii) at least one polymer composition (P) according to anyone of claims 1 to 6;iii) optionally, at least one solvent (S), andiv) optionally, at least one conductive agent.21 SPOP 2024 / 047Claim 8. The composition (C) according to claim 7, which comprises, preferably consists of:i) at least one 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 i) + ii) + iii) + iv);ii) at least one composition (P) in an amount from 0.5 to 10 % by weight, preferably from 1 to 5 % by weight, with respect to the total weight of i) + ii) + iii) + iv);iii) at least one solvent (S); andiv) at least one conductive agent selected from carbon black and carbon nanotubes, in an amount from 1 to 10 % by weight, preferably from 2 to 5 % by weight with respect to the total weight of i) + ii) + iii) + iv).Claim 9. The composition (C) according to claim 7, which comprises, preferably consists of:a. at least one positive electrode active material (AM);b. a composition (P) according to anyone of claims 1 to 6;c. at least one solvent (S);d. optionally, at least one conductive agent; ande. at least one sulfide-based solid electrolyte.Claim 10. The composition (C) according to claim 7, which consists of:a. at least one electrode active material (AM);b. a composition (P) according to anyone of claims 1 to 6; andc. at least one conductive agent.Claim 11. The composition (C) according to claim 10, wherein composition (C) is either in the form of dry mixture or in the form of a self-supporting film.Claim 12. 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 a positive electrode-forming composition (C) according to anyone of claims 7 to 11;(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) optionally, drying the assembly provided in step (III);(V) submitting the assembly obtained in step (III) to a compression step to obtain a positive electrode (E).Claim 13. A positive electrode (E) obtainable by the process according to claim 12.22 SPOP 2024 / 047Claim 14. An electrochemical device comprising at least one positive electrode (E) of claim 13.

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