Positive electrode binder for lithium ion batteries

Abstract

The invention relates to a binder for a positive electrode of a Li-ion battery, to a method for producing said electrode and to the use thereof in a Li-ion battery. The invention also relates to a Li-ion battery manufactured by incorporating said electrode.

Description

TECHNICAL FIELD

[0001] The present invention relates to a binder for Li-ion battery positive electrodes, a method for preparing said electrodes and their use in Li-ion batteries.

[0002] The present invention also relates to Li-ion batteries manufactured by incorporating said electrodes. BACKGROUND

[0003] Electrochemical devices such as secondary batteries typically comprise a positive electrode, a negative electrode and an electrolyte.

[0004] Electrodes for lithium batteries are generally produced by mixing a binder with a powdery electrode active material.

[0005] Fluororesins such as polyvinylidene-based polymers have been used as binders for forming positive electrodes. In particular, polyvinylidene fluoride (PVDF) provides good electrochemical stability and high adhesion to electrode materials. Therefore, PVDF is the preferred binder material for electrode slurries.

[0006] US 2018 / 0355206 discloses the use of copolymers of methyl methacrylate and methacrylic acid mixed with PVDF for the preparation of LiNMC electrode slurries which have good adhesion to current collectors; said mixture has a viscosity that allows easy spreading of the active material on the metal current collector, thus facilitating the manufacture of electrodes for lithium-ion batteries.

[0007] US 2015 / 0280238 discloses a stable electrode binder dispersion for the preparation of LFP cathodes of lithium-ion batteries, said dispersion comprising PVDF and a (meth)acrylic polymer dispersant dispersed in an organic diluent.

[0008] The solutions currently available in this field rely on the use of PVDF homopolymer-based binders, which however have poor adhesion to current collectors.

[0009] Modified PVDF polymers, such as those comprising repeating units derived from hydrophilic (meth)acrylic monomers (e.g. acrylic acid), are well known in the art. Such copolymers have been developed with the aim of adding suitable adhesion to metals (e.g. aluminium or copper) to the mechanical properties and chemical inertness of PVDF.

[0010] However, modified PVDF polymers are problematic when used to prepare slurries for forming positive electrodes with certain active materials. In particular, in lithium-ion batteries, a significant drawback when using LiFePO4 (LFP) active materials is that the slurries often experience a rapid increase in viscosity, leading to gel formation and thus preventing them from being used as binders for LPF cathodes.

[0011] The time-dependent rheological properties of composite electrode slurries have also been observed in sodium-ion secondary batteries; in fact, the presence of NaOH on the material when exposed to air can induce gelation of the slurry, followed by defluorination of hydrogen and crosslinking of PVDF. This gelation results in an uneven coating.

[0012] Both in research and from an industrial perspective, there remains a demand for polymers with higher performance, particularly those that offer better mechanical properties and greater adhesion to current collectors.

[0013] One approach is to find a polymer blend that avoids the drawbacks of contact between PVDF homopolymers and modified PVDF polymers and certain active materials (such as LFP), while simultaneously ensuring the feasibility of wet casting of the electrode and the high adhesion of the final product.

[0014] In addition, there is a need in industry for polymers that have improved tolerance when in contact with battery electrolytes, especially in the case of carbonate-based electrolytes, particularly in terms of swelling resistance.

[0015] The present invention provides a positive electrode forming composition that prevents gelation and enables the manufacture of an electrode with enhanced adhesion, reduced polymer swelling upon contact with electrolyte, lower resistivity, electrochemical stability, and longer battery life. Summary of the Invention

[0016] Therefore, the object of the present invention is a positive electrode forming composition (C) comprising...

[0017] - At least one positive electrode active material (AM), and

[0018] - At least one adhesive (B), wherein adhesive (B) comprises:

[0019] a) At least one vinylidene fluoride (VDF) polymer [polymer (F)], comprising:

[0020] (i) Repeating units derived from VDF;

[0021] (ii) Optionally, a repeating unit derived from at least one monomer (MA) having formula (I):

[0022] (I)

[0023] wherein:

[0024] - R1, R2and R3, equal to or different from each other, are independently selected from a hydrogen atom and a C1-C3hydrocarbon group, and

[0025] - R X is a C1-C 20 hydrocarbon moiety comprising at least one functional group selected from a hydroxyl group, a carboxyl group, an epoxy group, an ester group, a phosphate group and an ether group,

[0026] the amount of these recurring units being from 0.05% to 10% by moles with respect to the total number of moles of recurring units of the polymer (F);

[0027] b) at least one branched (meth)acrylic polymer [polymer (A)] obtained from the polymerization of at least one (meth)acryloyl monomer [monomer (MAM)] with at least one molecule comprising at least two vinyl groups [monomer (BM)], wherein monomer (BM) is selected from the group consisting of divinyl aryl monomers such as divinylbenzene; (meth)acrylate diesters, such as alkylene di(meth)acrylates, such as ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate; oligomeric alkylene glycol di(meth)acrylates, for example like tetraethylene glycol di(meth)acrylate, poly(ethylene glycol) di(meth)acrylate, poly(propylene glycol) di(meth)acrylate; divinyl (meth)acrylamides, such as methylene bisacrylamide; divinyl ethers, such as poly(ethylene glycol) divinyl ether; and tetra- or tri-(meth)acrylates such as pentaerythritol tetra(meth)acrylate, trimethylolpropane tri(meth)acrylate or glucose di- to penta(meth)acrylate, and

[0028] wherein polymer (A) contains less than 1% by moles of monomer (BM);

[0029] - at least one solvent (S); and

[0030] - optionally at least one additive imparting electrical conductivity.

[0031] In a second example, the present application relates to the use of the electrode-forming composition (C) of the present application in a process for manufacturing a positive electrode [electrode (E)] for an electrochemical device, said process comprising:

[0032] (i) providing a metal substrate having at least one surface;

[0033] (ii) providing an electrode-forming composition (C) as defined above;

[0034] (iii) applying the composition (C) to the at least one surface of the metal substrate, thereby providing an assembly comprising a metal substrate having said composition (C) coated on the at least one surface;

[0035] (iv) drying the assembly provided in step (iii).

[0036] In a third example, the present application relates to a positive electrode (E) obtainable by the method of the present application.

[0037] In a fourth example, the present application relates to an electrochemical device comprising a positive electrode (E) of the present application. DETAILED DESCRIPTION

[0038] In the context of the present application, the use of round brackets “(…)” before and after a symbol or number of a part of an identification or formula has the sole purpose of better distinguishing the symbol or number with respect to the rest of the text; therefore, said round brackets can also be omitted.

[0039] The terms “acrylic” and “acrylate” are used interchangeably (unless doing so would change the intended meaning) and include acrylic acid and its derivatives. The term “(meth)acrylic” or “(meth)acrylate” is intended to cover both acrylic / acrylate and methacrylic / methacrylate forms of the indicated material, for example (meth)acrylate monomers.

[0040] The electrode active material (AM) of the positive electrode is preferably a compound capable of intercalating lithium ions or sodium ions.

[0041] Conventional active materials (AM) at the positive electrode of sodium-ion batteries are usually selected from Na-based layered transition metal oxides, Prussian blue analogues and polyanionic materials.

[0042] In some embodiments, the active material is a Na-based layered transition metal oxide, which is classified according to the stacking order of the oxygen layers as O3-, P2- and P3-type. P2-type structures generally correspond to the general formula NaxMO2, wherein M represents a transition metal ion such as Co, Mn, and x is 2 / 3.

[0043] In some embodiments, the active material is a polyanionic material having the general formula A x P[R(CN)6] 1-y .Prussian blue analogues (PBAs) of mH20, where A is an alkali metal ion, P is a N-coordinated transition metal ion, R is a C-coordinated transition metal ion, y is a [R(CN)6] vacancy, where 0 ≤ x ≤ 2 and 0 ≤ y < 1, such as Na 0.81 Fe[Fe(CN)6] 0.79 , NaFe2(CN)6, Na 1.63 Fe 1.89 (CN)6, Na 1.72 MnFe(CN)6, Na 1.76 Ni 0.12 Mn 0.88 [Fe(CN)6] 0.98 , Na2Ni x Co 1-x Fe(CN)6(where 0 ≤ x ≤ 1, such as Na2CoFe(CN)6).

[0044] In some other embodiments, the active material is a polyanionic material of general formula Na x M y (XO4) n (where X = S, P, Si, As, Mo and W, and M is a transition metal) with a series of tetrahedral anionic units (XO4) n- and derivatives (X m O 3m+1 ) n- Among them, phosphates NaMPO4 such as NaFePO4, Na 0.7 FePO4or NaMnPO4; sodium (natrium / sodium) superionic conductors of NASICON type structure of general formula Na x M2(XO4)3(where 1 ≤ x ≤ 4, M = V, Fe, Ni, Mn, Ti, Cr, Zr; X = P, S, Si, Se, Mo) - with a single transition metal type such as Na3V2(PO4)3(NVP), Na3Cr2(PO4)3, Na3Fe2(PO4)3; - binary transition metal types 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, Na 4-x Fe 2+x / 2 (P2O7)2(where 2 / 3 ≤ x ≤ 7 / 8, such as Na 3.12 Fe 2.44(P2O7)2 or Na 3.32 Fe 2.34 (P2O7)2), Na2(VO)P2O7, Na7V3(P2O7)4; fluorophosphates NaVPO4F, Na2CoPO4F, Na2FePO4F, Na2MnPO4F, Na3(VO 1-x PO4)2F 1+2x (wherein 0 < x < 1, for example Na3(VOPO4)2F or Na3V2(PO4)2F3 (NVPF)); fluorosulfates such as NaMSO4F (wherein M = Fe, Co, Ni); mixed phosphate / pyrophosphates with general formula Na4M3(PO4)2(P2O7) (wherein M represents a transition metal) 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, Na 2+2x Fe 2-x (SO4)3, Na 2+2x Co 2-x (SO4)3, Na 2+2x Mn 2-x (SO4)3 (wherein 0 < x < 1); silicates with general formula Na2MSiO4 (wherein M = Mn, Fe, Co and Ni).

[0045] In some preferred embodiments, the active material is a fluorophosphate preferably selected from the list consisting of: NaVPO4F, Na2CoPO4F, Na2FePO4F, Na2MnPO4F, Na3(VO 1-x PO4)2F 1+2x (wherein 0 < x < 1, for example Na3(VOPO4)2F or Na3V2(PO4)2F3 (NVPF)).

[0046] The conventional active material (AM) at the positive electrode of a lithium-ion battery can comprise a complex metal chalcogenide with 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, the use of lithium-based complex metal oxides with formula LiMO2 is preferred, wherein M is the same as defined above. Preferred examples thereof can include LiCoO2, LiNiO2, LiNi x Co 1-x O2 (0 < x < 1) and spinel-structured LiMn2O4.

[0047] Alternatively, the electrode active material may contain materials having the formula M1M2(JO4). f E 1-f Electroactive materials based on lithiated or partially lithiated transition metal oxygen anions, wherein M1 is lithium, which may be partially substituted by another alkali metal comprising less than 20% of the metal M1; M2 is a transition metal selected from Fe, Mn, Ni or mixtures thereof at an oxidation level of +2, which may be partially substituted by one or more other metals at an oxidation level between +1 and +5 and comprising less than 35% of the metal M2, including 0; JO4 is any oxygen anion, wherein J is P, S, V, Si, Nb, Mo or combinations thereof; E is a fluoride anion, hydroxide anion or chloride anion; f is the mole fraction of JO4 oxygen anion, typically included between 0.75 and 1.

[0048] As defined above, M1M2(JO4) f E 1-f The electroactive material is preferably phosphate-based and may have an ordered or modified olivine structure.

[0049] More preferably, the electrode active material has the formula Li 3-x M' y M'' 2-y (JO4)3, where 0 ≤ x ≤ 3, 0 ≤ y ≤ 2, M' and M'' are the same or different metals, at least one of which is a transition metal, JO4 is preferably PO4, which may be partially substituted by another oxygen anion, wherein J is S, V, Si, Nb, Mo or a combination thereof. More preferably, the electrode active material (AM) is a phosphate-based electroactive material having the following formula.

[0050] Li x A y D z PO4,

[0051] Where A is selected from the following groups: Mn, Fe, Co, Ni and Cu; D is selected from the following groups: Mg, Ca, Sr and Ba; x, y and z are numbers that satisfy the following relationships: 0 < x < 2, 0 < y < 1.5, 0 ≦ z < 1.5.

[0052] Component A is preferably Fe, Mn and Ni, and particularly preferably Fe.

[0053] Component D is preferably Mg or Ca.

[0054] Examples of compounds with an olivine structure include lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), and lithium manganese phosphate.

[0055] In addition, as a positive electrode active material (AM), materials with partial or complete carbon coverage on the surface can be used to supplement conductivity.

[0056] Based on 100 parts by weight of the positive electrode active material, the amount of carbon coated is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, and even more preferably 5 parts by weight or less.

[0057] The compound having an olivine structure is present in the composition (C) in an amount of 70% or more by mass relative to 100% of the entire positive electrode active material (AM).

[0058] More preferably, the amount is 90% or more by mass, and most preferably, the positive electrode active material (AM) consists only of compounds having an olivine structure.

[0059] Most preferably, the positive electrode active material (AM) consists only of lithium iron phosphate (LFP).

[0060] In the positive electrode composition of the present invention, the active material (AM) has an average particle size of 3 µm or less.

[0061] The average particle size (D50) of compounds with an olivine structure is more preferably in the range of 0.01 to 1.8 µm.

[0062] The average particle size of the positive electrode active material can be measured using a particle size analyzer for dynamic light scattering.

[0063] As the average particle size becomes smaller, the surface area becomes larger, and the adhesive must be bonded with a small amount of adhesive, thus requiring the adhesive to be flexible.

[0064] By using positive electrode active materials containing compounds with an olivine structure and an average particle size of 3 µm or smaller, the electrical characteristics (such as output characteristics) are excellent when the positive electrode composition of a secondary battery is used as the positive electrode of the battery.

[0065] The composition (C) of the present invention further comprises an adhesive (B), which comprises:

[0066] a) At least one vinylidene fluoride (VDF) copolymer [polymer (F)]

[0067] b) At least one branched (meth)acrylic acid polymer [polymer (A)];

[0068] c) at least one solvent (S); and

[0069] d) Optionally, at least one additive imparting conductivity.

[0070] The polymer (F) comprises repeating units derived from vinylidene fluoride (VDF) and optionally repeating units derived from at least one monomer (MA) having formula (I):

[0071] (I)

[0072] in:

[0073] R1, R2, and R3 may be the same as or different from each other, and are independently selected from hydrogen atoms and C1-C3 hydrocarbon groups, and

[0074] - R X It is a C1-C containing at least one functional group 20 The hydrocarbon portion, wherein the functional group is selected from hydroxyl, carboxyl, epoxy, ester, phosphate ester, and ether groups.

[0075] The amount of these repeating units is 0.05% to 10% of the total number of moles of repeating units in the polymer (F).

[0076] More preferably, the monomer (MA) preferably conforms to formula (II):

[0077] (II)

[0078] Each of R1 and R2 has the meaning as defined above, R3 is hydrogen, and R OH It is a hydrogen or a C1-C5 hydrocarbon moiety containing at least one hydroxyl group and / or at least one carboxyl group; more preferably, each of R1, R2, and R3 is hydrogen, while R OH It has the same meaning as described above.

[0079] Non-limiting examples of monomers (MA) include acrylic acid, methacrylic acid, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxyethylhexyl methacrylate.

[0080] The monomer (MA) is more preferably selected from:

[0081] - Hydroxyethyl acrylate (HEA) having the following formula:

[0082]

[0083] - 2-Hydroxypropyl acrylate (HPA) having any of the following formulas:

[0084]

[0085] - Acrylic acid (AA) with the following formula:

[0086]

[0087] - and its mixtures.

[0088] Most preferably, the monomer (MA) is AA or HEA.

[0089] Polymers (F) may also contain other parts that neither affect nor impair their physicochemical properties, such as defects, end groups, etc.

[0090] The polymer (F) is semi-crystalline. The term semi-crystalline is intended to refer to a polymer (F) having a detectable melting point. It is generally understood that a semi-crystalline polymer (F) has an advantageous heat of fusion of at least 0.4 J / g, preferably at least 0.5 J / g, more preferably at least 1 J / g, as determined according to ASTM D 3418.

[0091] The polymer (F) is preferably a linear copolymer, i.e., it is composed of macromolecules made up of a substantially linear sequence of repeating units from VDF monomers and (MA) monomers; the polymer (F) can therefore be distinguished from grafted and / or comb polymers.

[0092] The polymer (F) contains at least 0.05%, more preferably at least 0.1%, and even more preferably at least 0.2% of repeating units derived from the monomer (MA) on a molar basis.

[0093] The polymer (F) contains preferably up to 2% by molar, more preferably up to 1.8% by molar, and even more preferably up to 1.5% by molar, repeating units derived from the monomer (MA).

[0094] In a preferred embodiment of the invention, the polymer (F) contains repeating units derived from the monomer (MA) having formula (I) in an amount of 0.2% to 1% in moles relative to the total number of repeating units in the polymer (F).

[0095] The polymer (F) advantageously has an intrinsic viscosity in dimethylformamide that is greater than 0.15 l / g and at most 0.60 l / g, preferably in the range of 0.20-0.50 l / g, and more preferably in the range of 0.25-0.40 l / g, as measured at 25°C.

[0096] The polymer (F) may further comprise repeating units derived from one or more fluorinated comonomers (CF) other than VDF.

[0097] The term “fluorinated comonomer (CF)” is intended to refer to an olefinic unsaturated comonomer containing at least one fluorine atom.

[0098] Non-limiting examples of suitable fluorinated comonomers (CF) include, in particular, the following:

[0099] (a) C2-C8 fluoroolefins and / or perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene and hexafluoroisobutylene;

[0100] (b) C2-C8 hydrogenated monofluoroolefins, such as fluoroethylene; 1,2-difluoroethylene and trifluoroethylene;

[0101] (c) Having the formula CH2=CH-R f0 Perfluoroalkyl ethylene, wherein R f0 It is a C1-C6 perfluoroalkyl group;

[0102] (d) Chlorinated and / or brominated and / or iodinated C2-C6 fluoroolefins, such as trifluorochloroethylene (CTFE).

[0103] In one embodiment of the invention, the polymer (F) comprises 0.1% to 10.0% (molar), preferably 0.3% to 5.0% (molar), and more preferably 0.5% to 3.0% (molar) repeating units derived from the fluorinated comonomer (CF).

[0104] The polymer (F) more preferably comprises repeating units derived from:

[0105] - Vinylidene fluoride (VDF) of at least 70%, preferably at least 75%, and more preferably at least 85% by molar weight.

[0106] - 0.2% to 1% by molar amount of monomer (MA) having formula (I);

[0107] - Optionally, 0.5% to 3.0% of repeating units derived from at least one fluorinated comonomer (CF) on a molar basis.

[0108] The polymer (F) can be obtained by polymerizing a VDF monomer, at least one monomer (MA), and optionally at least one comonomer (CF) in a suspension in an organic medium according to a procedure described, for example, in WO 2008 / 129041, or in an aqueous emulsion, typically as described in the art (see, for example, US 4,016,345, US 4,725,644 and US 6,479,591).

[0109] A procedure for preparing polymer (F) in suspension includes polymerizing vinylidene fluoride (VDF) monomer, monomer (MA), and optionally comonomer (CF) in an aqueous medium in the presence of a free radical initiator in a reaction vessel. The method includes...

[0110] - Continuous feed containing an aqueous solution of monomer (MA); and

[0111] - Maintain the pressure in the reactor vessel above the critical pressure of vinylidene fluoride.

[0112] Throughout the suspension polymerization operation, the pressure is maintained above the critical pressure of vinylidene fluoride. Generally, the pressure is maintained at a value greater than 50 bar, preferably greater than 75 bar, and even more preferably greater than 100 bar.

[0113] The terms "continuous feed," "continuous addition," or "continuous feeding" refer to the slow, small-volume, incremental addition of the aqueous solution of monomer (MA) until polymerization is complete.

[0114] The resulting polymer (F) exhibits high monomer (MA) uniformity in its polymer backbone, which advantageously maximizes the influence of the modified monomer (MA) on both the adhesive and / or hydrophilic behavior of the resulting copolymer.

[0115] In addition, the applicant has unexpectedly discovered that the presence of monomers (MA) uniformly distributed in the polymer (F) has the effect of improving the thermal stability of VDF copolymers, which are otherwise unsatisfactorily low, particularly lower than the thermal stability of VDF homopolymers.

[0116] At least one branched (meth)acrylic polymer (A) different from polymer (F) is a polymer comprising repeating units derived from at least one (meth)acryloyl monomer [monomer (MAM)] and at least one branched monomer [monomer (BM)] (which is a molecule containing at least two vinyl groups).

[0117] Polymer (A) is a copolymer. As used herein, “copolymer” is intended to mean a polymer having two or more distinct monomer units. The copolymer may be a ternary copolymer having three or more distinct monomer units, or four or more distinct monomer units. The copolymer may be a random copolymer, gradient copolymer, or block copolymer formed by a controlled polymerization method. Preferably, the copolymer is formed by a free radical polymerization method or anionic polymerization method, and the method may be any polymerization method known in the art, including but not limited to emulsion, solution, and suspension polymerization, and may be carried out in bulk and semi-bulk batches.

[0118] The term (meth)acryloyl monomer (MAM) refers to a monomer that has a (meth)acryloyl group in its molecule.

[0119] Suitable (meth)acryloyl monomers (MAMs) are hydrophobic (meth)acryloyl monomers, which may be selected, for example, from (meth)acrylamides having the formula CH2=C(R)-C(=O)-NH-Rh, or (meth)acrylates having the formula CH2=C(R)-C(=O)-O-Rh, wherein R means hydrogen or an alkyl group having 1 to 3 carbon atoms, and Rh means a straight-chain or branched alkyl residue having 1 to 30 carbon atoms, preferably 1 to 15 carbons, more preferably 1 to 5 carbons.

[0120] Non-limiting examples of such monomers are methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, heptyl methacrylate, 2-tert-butylheptyl methacrylate, octyl methacrylate, isooctyl methacrylate, nonyl methacrylate, decyl methacrylate, undecyl methacrylate, 5-methylundecyl methacrylate, dodecyl methacrylate, isoborneol methacrylate, norborneol methacrylate, cycloalkyl methacrylates such as cyclohexyl methacrylate and phenyl methacrylate.

[0121] Polymer (A) may also contain repeating units derived from other α,β-olefinic unsaturated monomers with functional groups (such as carboxyl groups or substituted alkyl esters).

[0122] Suitable α,β-olefinically unsaturated monomers with functional groups can be selected from hydrophilic (meth)acryloyl monomers, such as monoolefinically unsaturated monocarboxylic acids and their derivatives. This particularly includes acrylic acid, methacrylic acid (MAA), hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxyethylhexyl (meth)acrylate, crotonic acid, and 2-carboxyethyl acrylate oligomers such as Sipomer® B-CEA.

[0123] The term "methyl methacrylate polymer" is used within the framework of this invention to refer to a polymer composed of repeating units, wherein more than 50% of the repeating units, on a molar basis, are derived from methyl methacrylate (MMA).

[0124] The preferred (meth)acrylic polymer (A) used in the composition (C) of the present invention is a methyl methacrylate polymer.

[0125] In a preferred embodiment of the present invention, polymer (A) is a methyl methacrylate polymer containing at least 50% methyl methacrylate monomer units on a molar basis, and preferably at least 70% methyl methacrylate monomer units on a molar basis.

[0126] According to the preferred embodiment, polymer (A) may contain 1% to 45%, preferably 3% to 30%, and more preferably 5% to 20% on a molar basis at least one comonomer that can be copolymerized with methyl methacrylate, including but not limited to monomers (MAM) as defined above, or other α,β-olefinic unsaturated monomers with functional groups (such as carboxyl groups or substituted alkyl esters).

[0127] Polymer (A) contains at least one branched monomer (BM).

[0128] According to the present invention, a branched monomer is a monomer that can react at least at two different sites during polymerization, resulting in the growth of branched chains.

[0129] During the preparation of polymer (A), (meth)acryloyl monomer (MAM) can grow in two directions during the polymerization reaction, reacting with another (meth)acryloyl monomer or with a branched monomer.

[0130] According to the present invention, a branched monomer (BM) is a molecule containing at least two vinyl groups. A branched monomer (BM) may also contain more than two vinyl groups. These vinyl groups are suitable for polymerization in addition polymerization reactions. Many such molecules are readily available or can be prepared by reacting any difunctional or polyfunctional molecule with a suitable reactive vinyl group. Examples include divinyl or polyvinyl esters, divinyl or polyvinyl amides, divinyl or polyvinyl aryl compounds (including those having heterocyclic aryl groups), and divinyl or polyvinyl alkyl / aryl ethers.

[0131] Branched monomers (BM) are selected from the group consisting of: divinyl aryl monomers, such as divinylbenzene; (meth)acrylate diesters, such as alkylene di(meth)acrylates, such as ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate; oligoalkylene glycol di(meth)acrylates, such as tetraethylene glycol di(meth)acrylate, poly(ethylene glycol) di(meth)acrylate, poly(propylene glycol) di(meth)acrylate; divinyl (meth)acrylamide, such as methylene bisacrylamide; divinyl ethers, such as poly(ethylene glycol) divinyl ether; and tetra- or tri-(meth)acrylates such as pentaerythritol tetra(meth)acrylate, trimethylolpropane tri(meth)acrylate, or glucose di- to penta(meth)acrylates.

[0132] Preferred branching monomers are divinylbenzene, α,ω-alkylene di(meth)acrylates, or divinyl(meth)acrylamide. Most preferred branching monomers may be α,ω-alkylene di(meth)acrylates, such as ethylene glycol di(meth)acrylate and 1,4-butanediol di(meth)acrylate, or divinyl(meth)acrylamides, such as methylenebisacrylamide.

[0133] More preferably, the branched monomer (BM) is divinylbenzene (DVB).

[0134] The polymer (A) contains less than 1% of at least one branched monomer (BM) on a molar basis, preferably 0.2% to less than 1% on a molar basis.

[0135] The applicant has unexpectedly discovered that the presence of at least one branched monomer (BM) in polymer (A) at less than 1% (molar) allows for a solution of polymer (A) in solvent (S). When the amount of monomer (BM) in polymer (A) is high, the solubility of said polymer (A) in solvent (S) may be problematic.

[0136] Branched (meth)acrylic polymers (A) are prepared by polymerizing a mixture of at least one hydrophilic (meth)acryloyl monomer (MAM) and at least one monomer (BM) in the presence of other α,β-olefinic unsaturated monomers with functional groups such as carboxyl groups or substituted alkyl esters.

[0137] When a branched (meth)acrylic polymer (A) contains a hydrophilic (meth)acryloyl monomer (such as a monoolefinic unsaturated monocarboxylic acid), the polymer (A) may be further at least partially salted to obtain at least a portion of the acidic portion in salt form.

[0138] In embodiments of the present invention, a branched (meth)acrylic polymer (A) that is at least partially salted is therefore provided.

[0139] Therefore, the preparation of branched (meth)acrylic polymers (A) may further include the step of neutralizing at least a portion of the acid groups in a suitable solvent with a salt containing a monovalent cation [salt (SA)].

[0140] The salt (SA) can be any salt capable of neutralizing acid groups, and it is preferably selected from salts capable of providing alkali metal cations, tertiary ammonium cations, or quaternary ammonium cations, more preferably capable of providing Na. + K + Li + Salts of quaternary ammonium cations.

[0141] The polymer (A) 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.

[0142] The polymer (A) in the composition (C) used in the present invention preferably has a weight-average molecular weight (Mw) of about 1 kDa to 150 kDa, preferably 5 kDa to 100 kDa.

[0143] In one embodiment of the invention, polymer (A) is a methyl methacrylate polymer (methyl methacrylate homopolymer) comprising 100% methyl methacrylate monomer units on a molar basis.

[0144] According to another preferred embodiment, polymer (A) is a methyl methacrylate copolymer comprising at least 70% methyl methacrylate monomer units, up to 20% methyl methacrylate monomer units, and less than 1% branched monomer (BM) on a molar basis.

[0145] The choice of solvent (S) is not particularly restricted, provided that the solvent is suitable for dissolving polymer (F) and polymer (A).

[0146] Solvents (S) are typically selected from the following groups:

[0147] - Alcohols, such as methanol, ethanol, and diacetone alcohol.

[0148] - Ketones, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, and isophorone.

[0149] - Straight-chain or cyclic esters, such as isopropyl acetate, n-butyl acetate, methyl acetoacetate, dimethyl phthalate, and γ-butyrolactone.

[0150] - Straight-chain or cyclic amides, such as N,N-diethylacetamide, N,N-dimethylacetamide, dimethylformamide, and N-methyl-2-pyrrolidone, and

[0151] - Dimethyl sulfoxide.

[0152] The electrode forming compositions of the present invention may further include one or more optional conductivity-imparting additives to improve the conductivity of electrodes made from the compositions of the present invention. Conductivity-imparting additives for batteries are known in the art.

[0153] Examples of such conductive agents may include: carbonaceous materials, such as carbon black, finely powdered graphite, carbon nanotubes, graphene, or fibers, or fine powders or fibers of metals such as nickel or aluminum. The preferred conductive agent is preferably carbon black or carbon nanotubes.

[0154] The amount of the optional conductive agent is preferably 0% to 30% by weight relative to the total solids in the electrode forming composition. In particular, for the positive electrode forming composition, the optional conductive agent is typically 0% to 10% by weight, more preferably 0% to 5% by weight, relative to the total solids in the composition (C).

[0155] Composition (C) may further comprise at least one wetting agent and / or at least one surfactant and one or more additional additives.

[0156] Composition (C) may further comprise at least one non-electroactive inorganic filler material.

[0157] The term “non-electroactive inorganic filler material” is intended to refer to a non-conductive inorganic filler material suitable for manufacturing electrically insulating membranes for electrochemical battery cells.

[0158] The non-electroactive inorganic filler material in the diaphragm according to the invention typically has a resistivity (p) of at least 0.1 × 10¹⁰ ohm cm, preferably at least 0.1 × 10¹² ohm cm, as measured according to ASTM D 257 at 20°C.

[0159] Non-limiting examples of suitable non-electroactive inorganic filler materials include, in particular, natural and synthetic silica, zeolites, alumina, titanium dioxide, metal carbonates, zirconium oxide, silicon phosphate, and silicates.

[0160] The adhesive (B) used in the composition (C) according to the invention can be prepared by any method known in the art. Suitable methods include:

[0161] - Dissolve the polymer (F) in a solvent (S).

[0162] - Dissolve the polymer (A) using a solvent (S), preferably a solvent used to dissolve the polymer (F), and

[0163] - Mix the two solutions to provide adhesive solution (B).

[0164] The weight ratio of polymer (F) to polymer (A) in adhesive (B) is conveniently in the range of 95:5 to 70:30. In a preferred embodiment of the invention, the weight ratio of polymer (F) to polymer (A) in adhesive (B) is 90:10.

[0165] The electrode forming composition (C) can be obtained by adding and dispersing powdered electrode material and optional additives (such as conductive additives and / or viscosity modifiers) into a binder solution (B) thus obtained to obtain a uniform slurry.

[0166] The solution of polymer (F) in solvent (S) particularly contains 5% to 20% by weight, preferably about 7% to 10% by weight of polymer (F).

[0167] The solution of polymer (A) in solvent (S) particularly contains 5% to 10% by weight of polymer (A) in 100 parts by weight of such solvent.

[0168] In order to obtain an adhesive solution (B) comprising polymer (F) and polymer (A) as detailed above, it is preferable to dissolve polymer (F) in solvent (S) and dissolve 5% to 10% by weight of polymer (A) in 100 parts by weight of such solvent.

[0169] To prepare the adhesive solution (B), it is preferable to dissolve the polymer (F) and polymer (A) in the solvent (S) at a temperature of 20°C-50°C.

[0170] Alternatively, the adhesive solution (B) can be prepared by first dissolving the polymer (F) in a solvent (S) and then adding the solid polymer (A) to the mixture in which it is prepared.

[0171] The total solids content (TSC) of the composition (C) of the present invention typically includes between 15% and 70% by weight, and preferably between 40% and 60% by weight, relative to the total weight of the composition (C). The total solids content of the composition (C) should be understood as the accumulation of all its non-volatile components, including in particular the polymer (F), polymer (A), electrode active materials, and any other solid non-volatile additives.

[0172] When preparing solutions of polymer (F) and polymer (A) separately and subsequently combining them with electrode active materials, optional conductive materials, and other additives to prepare composition (C), an amount of solvent sufficient to produce a stable solution is used. The amount of solvent used ranges from the minimum required to produce a stable solution to the amount required to achieve the desired total solids content in the electrode mixture after adding the active electrode material, optional conductive material, and other solid additives.

[0173] The two solutions are mixed by any method known in the art, such as by planetary mixing followed by a dispersion stage.

[0174] The presence of polymer (A) in composition (C) allows for the acquisition of a homogeneous slurry composition without any signs of gelation throughout the preparation process. Therefore, polymers (F) with polar groups can be used in electrode-forming compositions containing olivine-type active material electrodes, taking advantage of the properties of such polymers in the electrode, such as greater adhesion to current collectors, improved flexibility, and good mechanical properties.

[0175] In addition, polymer (A) acts as a dispersant in the adhesive composition and reduces the slurry viscosity compared to compositions with the same TSC but containing only polymer (F), active materials, and conductive additives.

[0176] Another advantage of the composition (C) of the present invention is that it can provide an electrode comprising a relatively low amount of binder by weight and makes it possible to increase the amount of active material in the positive electrode in order to maximize the capacity of the battery.

[0177] The electrode forming composition (C) of the present invention can be used in a method for manufacturing a positive electrode [electrode (E)], the method comprising:

[0178] (i) A metal substrate having at least one surface is provided;

[0179] (ii) Provide an electrode forming composition as defined above [Composition (C)];

[0180] (iii) Applying composition (C) to at least one surface of a metal substrate to provide an assembly comprising a metal substrate having the composition (C) coated on the at least one surface;

[0181] (iv) The component provided in the drying step (iii).

[0182] Metal substrates are typically foils, screens, or meshes made of metals such as aluminum, nickel, titanium, and their alloys.

[0183] In step (iii) of the method of the present invention, the electrode forming composition (C) is typically applied to at least one surface of a metal substrate by any suitable procedure such as casting, printing and roll coating.

[0184] Optionally, step (iii) can typically be repeated once or multiple times by applying the electrode forming composition (C) provided in step (ii) to the component provided in step (iv).

[0185] In step (iv) of the method of the present invention, drying can be carried out at atmospheric pressure or under vacuum. Alternatively, drying can be carried out in a modified atmosphere, for example, in an inert gas (with a water vapor content of less than 0.001% v / v) that has been typically and especially dehydrated.

[0186] A drying temperature will be selected so that removal can be carried out by evaporating the aqueous medium from the electrode (E) of the present invention.

[0187] The dried component obtained in step (iv) can be further subjected to a compression step (such as a calendering process) to achieve the target porosity and density of the electrode (E) of the present invention.

[0188] Preferably, the dried component obtained in step (iv) is hot-pressed, and the temperature during the compression step includes 25°C to 130°C, preferably about 60°C.

[0189] The preferred target density of the electrode (E) is between 2 and 3 g / cc, preferably at least 2.1 g / cc. The density of the electrode (E) is calculated as the sum of the products of the densities of the electrode components and their mass ratios in the electrode formulation.

[0190] In another aspect, the present invention relates to electrodes [electrodes (E)] that can be obtained by the method of the present invention.

[0191] Therefore, the present invention relates to an electrode (E) comprising:

[0192] - A metal substrate having at least one surface, and

[0193] - At least one layer directly adhered to at least one surface of the metal substrate, the layer comprising a composition [composition (C')] containing the following:

[0194] a) At least one positive electrode active material (AM);

[0195] b) An adhesive composition [adhesive (B')] comprising:

[0196] b') At least one polymer (F) as defined above,

[0197] b'') At least one polymer (A) as defined above;

[0198] c) Optionally, at least one additive imparts conductivity.

[0199] The composition (C') that adheres directly to at least one surface of the metal substrate corresponds to the electrode forming composition (C) of the present invention, wherein the solvent has been at least partially removed during the electrode manufacturing process, for example in step (iv) (drying) and / or a further compression step. Therefore, all the preferred embodiments described with respect to the electrode forming composition (C) of the present invention also apply to the composition (C') that adheres directly to at least one surface of the metal substrate in the electrode of the present invention, except for the aqueous medium removed during the manufacturing process.

[0200] Preferred positive electrode (E) includes:

[0201] - A metal substrate having at least one surface, and

[0202] - At least one layer directly adhered to at least one surface of the metal substrate, the at least one layer comprising:

[0203] j) Positive electrode active material (AM) having an olivine structure, comprising 90% to 98% by weight;

[0204] (jj) Adhesive (B'), wherein the amount is 0.5% to 10% by weight, preferably 1% to 5% by weight; and

[0205] JJJ imparts conductivity with additives in an amount of 0.5% to 5% by weight.

[0206] The percentage by weight mentioned above is relative to the total weight of j) + jj) + jjj).

[0207] Preferably, the positive electrode (E) comprises at least 95% active material (AM) by weight, and the electrode loading is between 8 and 20 mg / cm2, preferably about 15 mg / cm2.

[0208] Advantageously, the electrode (E) according to the invention is excellent in terms of resistance to electrolyte swelling.

[0209] The electrode (E) of the present invention is particularly suitable for use in electrochemical devices, especially for secondary batteries, exhibiting reduced polymer swelling, lower resistivity, and longer battery life upon contact with electrolyte.

[0210] The secondary battery of the present invention is preferably an alkali metal or alkaline earth metal secondary battery.

[0211] More preferably, the secondary battery of the present invention is a lithium-ion secondary battery.

[0212] The electrochemical device according to the present invention can be prepared by standard methods known to those skilled in the art.

[0213] The invention will now be described with reference to the following examples, which are merely illustrative and not intended to limit the scope of the invention.

[0214] Experimental Section

[0215] raw material

[0216] Polymer (F-1): VDF-AA (1.0% by molar) polymer with an intrinsic viscosity of 0.30 l / g in DMF at 25°C.

[0217] MMA: Methyl methacrylate, commercially available from Sigma-Aldrich;

[0218] MAA: Methacrylic acid, available commercially from Sigma-Aldrich.

[0219] DVB: Divinylbenzene, available commercially from Sigma-Aldrich.

[0220] AMBN: 2,2′-azobis(2-methylbutyronitrile), commercially available from Sigma-Aldrich.

[0221] Nano LFP: LFP DY-3, density: 3.53 g / cm³ 3 Actual specific capacity: 153 mAh / g, commercially available from Shenzhen Dynanonic Co., Ltd.

[0222] Carbon nanotubes: Orgacyl NMP0402. 4% thin multi-walled carbon nanotubes (MWCNTs) in N-methyl-2-pyrrolidone (NMP) solvent.

[0223] Preparation 1: Polymer (A-1): Poly(MMA-MAA-DVB) in NMP (79.8 / 20 / 0.2 mol%)

[0224] In a 2 L jacketed reactor equipped with multi-stage lighting A320 stirring blades, counter-stirring blades, a condenser connected to a microcooler, and a cryostat bath, MMA (24.864 g, 0.246 mol), MAA (5.358 g, 0.061 mol), DVB (0.100 g, 0.616 mmol, 80% purity), AMBN (2.821 g, 0.014 mol), and 414.583 g of NMP were introduced at room temperature. The mixture was purged with nitrogen for 20 minutes at room temperature with stirring. After the nitrogen flow was left in the air, the cryostat bath was programmed to reach 75°C within a 1-hour temperature ramp. Simultaneously, solutions of monomers MMA (140.89 g, 1.393 mol), MAA (30.36 g, 0.349 mol), and DVB (0.568 g, 3.492 mmol, 80% purity) were prepared. Once the temperature in the reactor reached 75°C, the previously prepared monomer solutions were introduced over 1 hour. After the addition was complete, the reaction was aged at 75°C for another 6 hours. Finally, the reaction mixture was diluted with NMP to a maximum concentration of 25.40 wt%, cooled to room temperature, and the reactor was discharged. 1 H NMR (performed in CDCl3) revealed that the conversion rates to monomers MMA, MAA, and DVB were almost quantitative (> 99%).

[0225] Preparation 2: Polymer (A-2): Poly(MMA-MAA-DVB) in NMP (79.5 / 20 / 0.5 mol%)

[0226] In a 2 L jacketed reactor equipped with multi-stage illuminated A320 stirring blades, counter-stirring blades, a condenser connected to a microcooler, and a cryostat bath, MMA (27.747 g, 0.245 mol), MAA (5.353 g, 0.062 mol), DVB (0.250 g, 1.539 mmol, 80% purity), AMBN (2.818 g, 0.014 mol), and 599.089 g of NMP were introduced at room temperature. The mixture was purged with nitrogen for 20 min at room temperature with stirring. After the nitrogen flow was left in the air, the cryostat bath was programmed to reach 75°C in a 1-hour temperature ramp. Simultaneously, solutions of monomers MMA (140.235 g, 1.387 mol), MAA (30.33 g, 0.349 mol), and DVB (1.419 g, 8.721 mmol, 80% purity) were prepared. Once the temperature in the reactor reached 75°C, the previously prepared monomer solution was introduced over 1 hour. After the addition was complete, the reaction was aged at 75°C for another 6 hours. Finally, the reaction was diluted with NMP to a maximum of 10.7 wt%, cooled to room temperature, and the reactor was discharged. 1 H NMR (performed in CDCl3) revealed that the conversion rates to monomers MMA, MAA, and DVB were almost quantitative (> 99%).

[0227] Preparation 3: Polymer (A-3): Poly(MMA-MAA-DVB) in NMP (79.65 / 20 / 0.35 mol%)

[0228] In a 2 L jacketed reactor equipped with multi-stage illuminated A320 stirring blades, counter-stirring blades, a condenser connected to a microcooler, and a cryostat bath, MMA (14.734 g, 0.147 mol), MAA (3.181 g, 0.037 mol), DVB (0.105 g, 0.647 mmol, 80% purity), AMBN (1.658 g, 8.623 mmol), and 658.175 g of NMP were introduced at room temperature. The mixture was purged with nitrogen at room temperature with stirring for 20 min. After the nitrogen flow was left in the air, the cryostat bath was programmed to reach 75°C in a 1-hour temperature ramp. Simultaneously, solutions of monomers MMA (83.495 g, 0.834 mol), MAA (18.028 g, 0.209 mol), and DVB (0.596 g, 3.665 mmol, 80% purity) were prepared. Once the temperature in the reactor reaches 75°C, the previously prepared monomer solution is introduced over 1 hour. After the addition is complete, the reaction is aged at 75°C for another 6 hours. Finally, the reaction is cooled to room temperature, and the reactor is discharged. 1 ¹H NMR (performed in CDCl₃) revealed that the conversion to monomers MMA, MAA, and DVB was almost quantitative (> 99%). The measured solids content was 14.54 wt%.

[0229] Preparation 4: Polymer (A-4): Poly(MMA-MAA-DVB) in NMP (79.5 / 20 / 0.5 mol%)

[0230] In a 2 L jacketed reactor equipped with multi-stage illuminated A320 stirring blades, counter-stirring blades, a condenser connected to a microcooler, and a cryostat bath, MMA (14.700 g, 0.147 mol), MAA (3.180 g, 0.037 mol), DVB (0.150 g, 0.923 mmol, 80% purity), AMBN (1.657 g, 8.618 mmol), and 658.141 g of NMP were introduced at room temperature. The mixture was purged with nitrogen for 20 min at room temperature with stirring. After the nitrogen flow was left in the air, the cryostat bath was programmed to reach 75°C in a 1-hour temperature ramp. Simultaneously, solutions of monomers MMA (83.299 g, 0.832 mol), MAA (18.019 g, 0.209 mol), and DVB (0.852 g, 5.233 mmol, 80% purity) were prepared. Once the temperature in the reactor reaches 75°C, the previously prepared monomer solution is introduced over 1 hour. After the addition is complete, the reaction is aged at 75°C for another 6 hours. Finally, the reaction is cooled to room temperature, and the reactor is discharged. 1 ¹H NMR (performed in CDCl₃) revealed that the conversion to monomers MMA, MAA, and DVB was almost quantitative (> 99%). The measured solids content was 14.58 wt%.

[0231] Preparation 5: Polymer (A-5): Poly(MMA-MAA-DVB) in NMP (79.25 / 20 / 0.75 mol%)

[0232] In a 2 L jacketed reactor equipped with multi-stage illuminated A320 stirring blades, counter-stirring blades, a condenser connected to a microcooler, and a cryostat bath, MMA (14.642 g, 0.146 mol), MAA (3.177 g, 0.037 mol), DVB (0.225 g, 1.384 mmol, 80% purity), AMBN (1.656 g, 8.612 mmol), and 658.083 g of NMP were introduced at room temperature. The mixture was purged with nitrogen for 20 min at room temperature with stirring. After the nitrogen flow was left in the air, the cryostat bath was programmed to reach 75°C in a 1-hour temperature ramp. Simultaneously, solutions of monomers MMA (82.974 g, 0.829 mol), MAA (18.005 g, 0.209 mol), and DVB (1.276 g, 7.843 mmol, 80% purity) were prepared. Once the temperature in the reactor reaches 75°C, the previously prepared monomer solution is introduced over 1 hour. After the addition is complete, the reaction is aged at 75°C for another 6 hours. Finally, the reaction is cooled to room temperature, and the reactor is discharged. 1 ¹H NMR (performed in CDCl₃) revealed that the conversion to monomers MMA, MAA, and DVB was almost quantitative (> 99%). The solids content was measured to be 14.00 wt%.

[0233] Preparation 6: PMMA polymer: MMA homopolymer solution in DMF solution

[0234] In a 500 mL three-necked round-bottom flask equipped with a reflux condenser and mechanical stirrer, 15.15 g (0.15 mol) of MMA, 1.37 g (7.12 mmol) of AMBN, and 123.63 g of DMF were introduced at room temperature. The mixture was purged with nitrogen at room temperature for 15 minutes and then immersed in an oil bath preheated at 80°C. After the temperature was stabilized at 75°C, 85.86 g (0.86 mol) of MMA was added to the reaction mixture over 1 hour using a syringe pump. After the addition was complete, the reaction was stirred for another 6 hours. Following this final aging step, the mixture was cooled to ambient temperature. Finally, dilution was performed to obtain a solution with a solids content of 34.61%.

[0235] Sampling 1 H NMR analysis was used to determine the conversion rate of MMA monomers ( 1 H NMR (in CDCl3): > 99%.

[0236] Example 1:

[0237] Prepare an 8% by weight solution of polymer (F-1) in NMP.

[0238] The polymer (A-1) obtained from preparation 1 above is used to prepare an 8% (by weight) solution of polymer (A-1) in NMP.

[0239] The solutions of polymer (F-1) in NMP and polymer (A-1) in NMP were mixed at a ratio of 9:1 (30.87 g of polymer (F-1) solution and 3.43 g of polymer (A-1) solution).

[0240] Nano-LFP (75.07 g), carbon nanotubes (14.7 g in a solution at 4% wt in NMP) and an additional 15.94 g of NMP were added to a solution containing polymers (F-1) and (A-1) under planetary mixing, followed by a dispersion stage to provide composition 1, which is a cathode paste with a total solids content (TSC) of 56% (95.75% LFP, 0.75% carbon nanotubes and 3.5% binder).

[0241] A homogeneous slurry was obtained, with no signs of gelation during any of the preparation steps. The visual assessment results of the slurry quality are summarized in Table 1.

[0242] Comparison Example 1:

[0243] Prepare an 8% (by weight) solution of HSV900 in NMP.

[0244] Nano-LFP (75.07 g), carbon nanotubes (14.7 g in a solution of 4% wt in NMP) and an additional 15.94 g of NMP were added to a solution containing HSV900 under planetary mixing, followed by a dispersion stage to provide composition (C-1), which is a cathode paste with a total solids content (TSC) of 56% and a binder amount of 3.5%.

[0245] Comparison Example 2:

[0246] Prepare an 8% by weight solution of polymer (F-1) in NMP.

[0247] The PMMA polymer solution obtained in preparation 6 above is used to prepare an 8% (by weight) PMMA polymer solution in NMP:

[0248] The solutions of polymer (F-1) in NMP and PMMA polymer in NMP were mixed at a ratio of 9:1 (30.87 g of polymer (F-1) solution and 3.43 g of PMMA polymer solution).

[0249] Nano-LFP (75.07 g), carbon nanotubes (14.7 g in a solution at 4% wt in NMP) and an additional 15.94 g of NMP were added to a solution containing polymer (F-1) and PMMA polymer under planetary mixing, followed by a dispersion stage to provide composition (C-2), which is a cathode paste with a total solids content (TSC) of 56% (95.75% LFP, 0.75% carbon nanotubes and 3.5% binder).

[0250] The results of the visual assessment of the slurry quality are summarized in Table 1.

[0251] Table 1

[0252]

[0253] A = Good: Visually uniform when still and with manual stirring. No agglomerates, phase separation, or signs of sediment on the container walls.

[0254] B = Medium: The slurry appears homogeneous. There are signs of small agglomerates, such as incompletely dispersed solid particles, small gels, or thin deposits on the bottom or walls of the beaker. It does not prevent the slurry from running.

[0255] C = Poor: The slurry is uneven, with visible signs. Gel or solid agglomerates are present. The slurry viscosity may be too high to allow for casting and may prevent / limit further mixing due to the formation of solid clumps (gel-like). If phase separation occurs, the viscosity of the upper and solid bottom layers is too low.

[0256] Example 4: Evaluation of gelling of electrode-forming compositions

[0257] Immediately after the preparation of compositions 1, C-1, and C-2, their viscosity (t0 viscosity) was measured, and the viscosity of the composition obtained in Example 1 was found to be -50% relative to those compositions from Comparative Example 1 and Comparative Example 2 (the last two compositions showed comparable values).

[0258] The results are reported in Table 2.

[0259] Table 2

[0260]

[0261] Normalized t0 viscosity relative to C-1

[0262] Qualitative monitoring of viscosity changes over time revealed no significant gelling issues and made slurry flowability feasible after several hours / days.

[0263] Example 5: Preparation of electrodes

[0264] A 15 mg / cm² concentration was obtained by applying the electrode forming composition as described above onto a 15 µm thick aluminum foil. 2 The positive electrode is obtained by loading a dry positive electrode mass. The solvent is completely evaporated by drying in an oven at 90°C to produce a strip-shaped positive electrode.

[0265] The obtained positive electrodes (electrodes (E1), (EC-1), (EC-2)) were visually evaluated. The results are reported in Table 3.

[0266] Table 3

[0267]

[0268] A = Good: The appearance is smooth, with no agglomerates on the dry electrode, and no signs of inhomogeneity due to bubble formation and evaporation. It is easy to handle manually, exhibiting good flexibility when slightly bent and folded, with no signs of cracking or detachment of active material.

[0269] B = Medium: The electrode has a uniform appearance. Small aggregates were detected by precise visual observation or optical microscopy. No material flakes off or breaks when gently bent.

[0270] C = Poor: Non-uniformity on the electrode surface is visible to the naked eye (e.g., solid particles dragged during casting). The material may crack or detach from the current collector without treatment. Stamping / cutting for further characterization is not possible.

[0271] Positive electrode adhesion assessment

[0272] The positive electrodes (E1), (EC-1), and (EC-2) were cut into strips (10 cm long and 2.5 cm wide) and applied to a 2 mm thick rigid aluminum foil using a 2.5 × 8 cm double adhesive tape, with the coated side of the electrodes facing the aluminum plate. To prevent any part of the electrode from adhering to the tape, one end of each strip was kept off the double adhesive tape, allowing it to be pulled out of the foil.

[0273] Each sample was pulled from the foil at a 180° angle using a force gauge, which allows for the measurement of the force required to peel the sample from the dual-layer tape. The peeling speed was 300 mm / min, and the temperature was T = 25°C. The results are summarized in Table 4.

[0274] Table 4

[0275]

[0276] Normalized to EC-1

[0277] It has been demonstrated that the electrodes of the present invention exhibit improved adhesion to metal foils compared to standard electrodes of the prior art that contain PVDF.

Claims

1. A positive electrode forming composition (C), the composition comprising: - At least one positive electrode active material (AM), and - At least one adhesive (B), wherein adhesive (B) comprises: a) At least one vinylidene fluoride (VDF) polymer [polymer (F)], comprising: (i) Repeating units derived from VDF; (ii) Optionally, a repeating unit derived from at least one monomer (MA) having formula (I): (I) in: R1, R2, and R3 may be the same as or different from each other, and are independently selected from hydrogen atoms and C1-C3 hydrocarbon groups, and - R X It is a C1-C containing at least one functional group 20 The hydrocarbon portion, wherein the functional group is selected from hydroxyl, carboxyl, epoxy, ester, phosphate ester, and ether groups. The amount of these repeating units is 0.05% to 10% of the total molar number of repeating units in the polymer (F); b) At least one branched (meth)acrylic polymer [polymer (A)] obtained by polymerization of at least one (meth)acryloyl monomer [monomer (MAM)] with at least one molecule comprising at least two vinyl groups [monomer (BM)], wherein monomer (BM) The group consisting of: divinyl aryl monomers such as divinylbenzene; (meth)acrylate diesters, such as alkylene di(meth)acrylates, such as ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate; oligomeric alkylene glycol di(meth)acrylates, such as tetraethylene glycol di(meth)acrylate, poly(ethylene glycol) di(meth)acrylate, poly(propylene glycol) di(meth)acrylate; divinyl (meth)acrylamide, such as methylenebisacrylamide; divinyl ethers, such as poly(ethylene glycol) divinyl ether; and tetra- or tri-(meth)acrylates such as pentaerythritol tetra(meth)acrylate, trimethylolpropane tri(meth)acrylate, or glucose di- to penta(meth)acrylates, and The polymer (A) contains less than 1% monomer (BM) on a molar basis; - At least one solvent (S); and - Optionally, at least one additive imparts conductivity.

2. The composition (C) according to claim 1, wherein, The monomer (MA) is selected from the group consisting of: acrylic acid, methacrylic acid, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxyethylhexyl methacrylate.

3. The composition (C) according to claim 1 or 2, wherein, The active material (AM) has the following formula: Li x A y D z PO4, Where A is selected from the following groups: Mn, Fe, Co, Ni and Cu; D is selected from the following groups: Mg, Ca, Sr and Ba; x, y and z are numbers that satisfy the following relationships: 0 < x < 2, 0 < y < 1.5, 0 ≦ z < 1.

5.

4. The composition according to any one of the preceding claims, wherein, The active material (AM) is selected from lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), and lithium manganese phosphate.

5. The composition (C) according to any one of the preceding claims, wherein, Polymer (A) comprises a repeating unit derived from at least one (meth)acryloyl monomer (MAM), the (meth)acryloyl monomer being selected from the group consisting of: (meth)acrylamidates having the formula CH2=C(R)-C(=O)-NH-Rh, or (meth)acrylates having the formula CH2=C(R)-C(=O)-O-Rh, wherein R means hydrogen or an alkyl group having 1 to 3 carbon atoms, and Rh means a straight-chain or branched alkyl residue having 1 to 30 carbon atoms, preferably 1 to 15 carbons, more preferably 1 to 5 carbons.

6. The composition according to claim 5, wherein, The at least one (meth)acryloyl monomer (MAM) is selected from the group consisting of: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, heptyl methacrylate, 2-tert-butylheptyl methacrylate, octyl methacrylate, isooctyl methacrylate, nonyl methacrylate, decyl methacrylate, undecyl methacrylate, 5-methylundecyl methacrylate, dodecyl methacrylate, isoborneol methacrylate, norborneol methacrylate, cycloalkyl methacrylates such as cyclohexyl methacrylate, and phenyl methacrylate.

7. The composition (C) according to any one of the preceding claims, wherein, Polymer (A) further comprises a repeating unit of at least one hydrophilic (meth)acryloyl monomer selected from the group consisting of: acrylic acid, methacrylic acid (MAA), hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxyethylhexyl (meth)acrylate, crotonic acid, 2-carboxyethyl acrylate oligomers such as Sipomer® B-CEA.

8. The composition (C) according to any one of the preceding claims, wherein, Polymer (A) is a methyl methacrylate polymer containing at least 70% methyl methacrylate monomer units, up to 20% methyl methacrylate monomer units, and less than 1% monomer (BM) on a molar basis.

9. The composition (C) according to any one of claims 1 to 8, wherein, Polymer (A) is at least partially salted.

10. The composition (C) according to any one of the preceding claims, wherein, The weight ratio of polymer (F) to polymer (A) in adhesive (B) is in the range of 95:5 to 70:30, preferably 90:

10.

11. A method for manufacturing a positive electrode [electrode (E)], the method comprising: (i) A metal substrate having at least one surface is provided; (ii) Providing an electrode forming composition according to any one of claims 1 to 10 [Composition (C)]; (iii) Applying the composition (C) provided in step (ii) to at least one surface of the metal substrate provided in step (i) to provide an assembly comprising a metal substrate having the composition (C) coated on the at least one surface; (iv) The component provided in the drying step (iii).

12. A positive electrode (E) which can be obtained by the method according to claim 11.

13. A positive electrode (E) comprising: - A metal substrate having at least one surface, and - At least one layer directly adhered to at least one surface of the metal substrate, the at least one layer comprising: j) Positive electrode active material (AM), comprising 90% to 98% by weight; jj) Adhesive (B'), which contains b') At least one vinylidene fluoride (VDF) copolymer [polymer (F)], comprising: (i) Repeating units derived from VDF; (ii) A repeating unit derived from at least one monomer (MA) having formula (I): (I) in: R1, R2, and R3 may be the same as or different from each other, and are independently selected from hydrogen atoms and C1-C3 hydrocarbon groups, and - R X It is a C1-C containing at least one functional group 20 The hydrocarbon portion, wherein the functional group is selected from hydroxyl, carboxyl, epoxy, ester, and ether groups. The amount of these repeating units is 0.05% to 10% of the total molar number of repeating units in the polymer (F); b'') At least one branched (meth)acrylic acid polymer [polymer (A)]; and Optionally, at least one additive imparts conductivity. The amount of the adhesive (B') is 0.5% to 10% by weight, preferably 1% to 5% by weight; and (jjj) An additive that imparts conductivity, in an amount of 0.5% to 5% by weight. The percentage by weight mentioned above is relative to the total weight of j)+jj)+jjj).

14. An electrochemical device comprising the electrode (E) according to claim 13.

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