Vinylidene fluoride copolymers for lithium battery electrodes

Abstract

The present invention relates to vinylidene fluoride copolymers containing repeat units derived from hydrophilic monomers and their use as binders for electrodes in Li-ion batteries.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to European Patent Application No. 22202256.8, filed October 18, 2022, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to vinylidene fluoride copolymers containing repeat units derived from hydrophilic monomers and to their use as binders for electrodes in Li-ion batteries. [Background technology]

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

[0004] In particular, WO 2008 / 129041 (SOLVAY SPECIALTY POLYMERS ITALY SPA) discloses linear semi-crystalline vinylidene fluoride (VDF) copolymers containing 0.05% to 10 mol % of repeat units derived from (meth)acrylic monomers and their use as binders in electrodes for lithium-ion batteries.

[0005] In general, increasing the molecular weight of fluoropolymers is known to improve the performance of articles made from these materials, particularly in terms of mechanical properties and adhesion of the electrode to the current collector.

[0006] However, increasing the molecular weight of the fluoropolymer increases the viscosity of the electrode-forming formulation containing it, also called the electrode slurry, making the handling and coating process in the manufacture of the electrode much more difficult.

[0007] In the technical field of batteries, and in particular of lithium batteries, the problem is felt to provide electrode binders characterized by very good adhesion without at the same time having adverse effects on the manufacturing process of the electrodes, such as by an increase in the viscosity of the slurry for their manufacture.

[0008] The present invention provides a solution to this problem by combining the ease in the electrode manufacturing process by working with an electrode-forming formulation that has low viscosity at low shear rates with the provision of an electrode that has very high adhesion to the current collector. Summary of the Invention

[0009] It has been discovered that certain vinylidene fluoride copolymers containing certain randomly selected carboxyl-containing vinyl monomers have very good adhesion to metal substrates and can be used to prepare electrode-forming compositions that have low viscosity at low shear rates.

[0010] Therefore, the object of the present invention is to (i) repeat units derived from vinylidene fluoride (VDF) monomers; (ii) Formula (I): [ka] (In the formula: R1, R2 and R3, which are equal to or different from each other, are independently selected from a hydrogen atom and a C1-C3 hydrocarbon group; R H is a C2-C alkyl group containing at least one carboxyl group and no aliphatic hydroxyl group. 10 hydrocarbon moiety) and a repeating unit derived from at least one carboxyl group-containing vinyl monomer (CA) of A fluoropolymer [polymer (F)] comprising: the content of the monomer (CA) in the polymer (F) is at most 5.0 mol % relative to the total number of moles of repeating units of the polymer (F); At least 50% of the monomers (CA) are randomly distributed in the polymer (F), The polymer (F) is represented by the formula (I): -(Ra) x -O-CO-O-CH2-CH3(I) (In the formula, R a is a C1 to C5 linear or branched hydrocarbon group, and x is an integer selected from 1 and zero. and wherein the terminal group of The end groups of formula (I) are present in an amount of at least 20% relative to the total amount of end groups of polymer (F); The polymer (F)

[0011] The second object of the present invention is to a) at least one electrode active material (AM); b) at least one binder (B) comprising at least one polymer (F) as defined above; c) at least one solvent (S); The present invention relates to an electrode-forming composition (C) comprising:

[0012] In another aspect, the present invention relates to the use of an electrode-forming composition (C) in a method for producing an electrode [electrode (E)], said method comprising: (I) providing a metal substrate having at least one surface; (II) providing an electrode-forming composition (C) as defined above; (III) applying the composition (C) prepared in step (II) onto at least one surface of the metal substrate prepared in step (I), thereby preparing an assembly including a metal substrate coated with the composition (C) on at least one surface; (IV) drying the assembly prepared in step (III); (V) subjecting the dried assembly obtained in step (IV) to a compression step to obtain the electrode (E) of the present invention. Regarding use, including

[0013] In a further object, the present invention relates to an electrode (E) obtainable by the method of the present invention.

[0014] In a still further object, the present invention relates to an electrochemical device comprising at least one electrode (E) of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The term "repeating unit derived from vinylidene fluoride" (commonly also designated vinylidene difluoride, 1,1-difluoroethylene, VDF) is intended to mean a repeating unit of formula CF2=CH2.

[0016] In a preferred embodiment, the carboxyl group-containing vinyl monomer (CA) is represented by formula (Ia): [ka] (In the formula, R1, R2 and R3, which are equal to or different from each other, are independently selected from a hydrogen atom and a C1-C3 hydrocarbon group; R' H is hydrogen or a C1-C group containing at least one carboxyl group and no aliphatic hydroxyl group 15 It is a hydrocarbon moiety, R' H may further contain one or more oxygen atoms, carbonyl groups or ester groups in the chain. is a compound of

[0017] The expression "aliphatic hydroxyl group" is intended to mean a hydroxyl group that is directly attached to an aliphatic carbon.

[0018] Non-limiting examples of monomers (CA) of formula (I) include, inter alia: - acrylic acid (AA), (meth)acrylic acid, - 2-carboxyethyl (meth)acrylate, - 3-butenoic acid, - (meth)acryloyloxyethyl succinate, (meth)acryloyloxypropyl succinic acid, - 3-(allyloxy)propanoic acid, and mixtures thereof Examples include:

[0019] Preferably, at least one monomer (CA) is acrylic acid (AA).

[0020] In polymer (F), it is essential that at least 50% of the monomers (CA) are randomly distributed in said polymer (F).

[0021] It is known in the art that continuous feeding of VDF comonomers during the polymerization of VDF results in random distribution of said comonomers in the polymer chain, where the sequence VDF-(comonomer)-VDF is usually present in the majority.

[0022] Thus, when polymer (F) is prepared by a polymerization reaction involving continuous feeding of monomer (CA) during VDF polymerization, there is a random distribution of monomer (CA) in the polymer chain, resulting in a sequence of VDF-(CA)-VDF.

[0023] More preferably, in polymer (F), at least 70% of the monomers (CA) are randomly distributed in said polymer (F).

[0024] The expression "randomly distributed monomers (CA)" is intended to indicate the presence of the sequence VDF-(CA)-VDF, the amount of randomly distributed monomers (CA) being determined as the percentage ratio between the average number of said VDF-(CA)-VDF sequences and the total average number of (CA) monomer repeat units.

[0025] If each (CA) repeat unit is isolated, i.e., contained between two repeat units of a VDF monomer, the average number of (CA) sequences is equal to the average total number of (CA) repeat units, and therefore the fraction of randomly distributed (CA) units is 100%: this value corresponds to a completely random distribution of the (CA) repeat units. Thus, as mentioned above, the greater the number of isolated (CA) units relative to the total number of (CA) units, the higher the percentage value of the fraction of randomly distributed (CA) units will be.

[0026] The analytical determination of the total amount of randomly distributed monomers (CA) was performed by determining the sequence VDF-(comonomer)-VDF. 19 The total amount of monomers in the polymer was measured by F-NMR. 19 F-NMR, 1 This can be done by measuring by one or more of the following techniques: 1 H-NMR, carboxyl titration, FT-IR, etc.

[0027] The polymer (F) preferably contains at least 0.01%, more preferably at least 0.02 mol % of repeat units derived from said monomer (CA).

[0028] Polymer (F) preferably contains at most 5.0% moles of repeating units derived from monomer (CA), more preferably at most 3.0% moles, even more preferably at most 2.0% moles, and even more preferably at most 1.5% moles, based on the total number of moles of repeating units of polymer (F).

[0029] Excellent results have been obtained using polymers (F) containing at least 70 mol % of repeat units derived from VDF.

[0030] The polymer (F) can be an elastomeric or semi-crystalline polymer, preferably a semi-crystalline polymer.

[0031] As used herein, the term "semi-crystalline" means a fluoropolymer that has at least one crystalline melting point in addition to a glass transition temperature Tg by DSC analysis. For the purposes of the present invention, semi-crystalline fluoropolymer is intended herein to mean a fluoropolymer that has a heat of fusion of 10 to 90 J / g, preferably 30 to 80 J / g, more preferably 35 to 75 J / g, measured according to ASTM D3418-08.

[0032] For purposes of the present invention, the term "elastomer" is intended to denote a true elastomer or a polymer resin that serves as a building block to obtain a true elastomer.

[0033] True elastomers are defined by ASTM, Special Technical Bulletin, No. 184 Standard as materials that can be stretched to twice their inherent length at room temperature and that, when released after being held under tension for 5 minutes, simultaneously return to within 10% of their original length.

[0034] Preferably, the intrinsic viscosity of the polymer (F), measured in dimethylformamide (DMF) at 25°C, is 0.05 l / g to 1.0 l / g, more preferably 0.10 l / g to 0.70 l / g, and even more preferably 0.20 l / g to 0.50 l / g.

[0035] The polymer (F) of the present invention generally has a melting temperature (T m )

[0036] The polymer (F) of the present invention has a pseudo-linear structure with very few branches, so that the insoluble portion caused by long branched chains is so small that it can be practically ignored.

[0037] The polymer (F) of the present invention preferably has a low proportion of insoluble components in standard polar aprotic solvents for VDF polymers, such as NMP. More preferably, solutions of polymer (F) in said standard polar aprotic solvents remain homogeneous and stable for several weeks, substantially free of insoluble residues.

[0038] Due to the small amount of insoluble components, the GPC and NMR analysis of polymer (F) is not affected and there are no problems with reliability and reproducibility.

[0039] The melting temperature can be determined from a DSC curve obtained by differential scanning calorimetry (hereinafter also referred to as DSC). When a DSC curve shows multiple melting peaks (endothermic peaks), the melting temperature (Tm) is determined based on the peak with the largest peak area.

[0040] The polymer (F) may further comprise repeat units derived from one or more fluorinated comonomers (CF) different from VDF.

[0041] The term "fluorinated comonomer (CF)" is intended herein to mean an ethylenically unsaturated comonomer containing at least one fluorine atom.

[0042] Non-limiting examples of suitable fluorinated comonomers (CF) include, among others: (a) C2-C8 fluoro and / or perfluoroolefins such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene and hexafluoroisobutylene; (b) C2-C8 hydrogen-containing monofluoroolefins such as vinyl fluoride, 1,2-difluoroethylene, and trifluoroethylene; (c)Formula CH2=CH-R f0 (In the formula, R f0 is a C1-C6 perfluoroalkyl group), (d) chloro-, and / or bromo-, and / or iodo-C2-C6 fluoroolefins such as chlorotrifluoroethylene (CTFE); (e) perfluoro(alkyl) vinyl ethers such as perfluoro(methyl) vinyl ether (PMVE), perfluoro(ethyl) vinyl ether (PEVE), and perfluoro(propyl) vinyl ether (PPVE); (f) Perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD).

[0043] In a preferred embodiment, the polymer (F) is semi-crystalline and contains repeating units derived from the fluorinated comonomer (CF) in an amount of 0.1 to 10.0 mol %, preferably 0.3 to 5.0 mol %, more preferably 0.5 to 3.0 mol %, based on the total number of moles of repeating units of the polymer (F).

[0044] It is understood that moieties of chain ends, defects or other impurity types different from those defined above can be contained in polymer (F) without these impairing its properties.

[0045] The polymer (F) is more preferably - at least 70 mol %, preferably at least 75 mol %, more preferably at least 85 mol % of repeat units derived from vinylidene fluoride (VDF); - 0.01% to 2% by mole, preferably 0.05% to 1.5% by mole, of repeat units derived from at least one vinyl monomer (CA), - optionally 0.5 to 10 mol % of repeat units derived from at least one fluorinated comonomer (CF), It consists of All amounts are relative to the total number of moles of repeating units of polymer (F).

[0046] According to a particular embodiment of the invention, polymer (F) is characterized in that it comprises an end group of formula (I) as defined above, in which x is zero.

[0047] According to another embodiment of the present invention, the polymer (F) has the structure: x is 1 and R a is a C2-C3 linear or branched alkyl radical,

[0048] According to another embodiment of the present invention, polymer (F) comprises end groups of formula (I) as defined above, where x is zero, and end groups of formula (I) where x is 1, and R a is a C2-C3 linear or branched alkyl radical.

[0049] The polymer (F) is - polymerizing, in an aqueous medium, vinylidene fluoride (VDF) monomer, an initial charge of monomer (CA), and optional comonomer (CF) in the presence of a radical initiator system that introduces polymer chain end groups of formula (I); - continuously supplying an aqueous solution containing a monomer (CA); - Maintaining the pressure in the reaction vessel above the critical pressure of vinylidene fluoride It can be obtained by a method comprising:

[0050] Suitable radical initiator systems include radical initiators such as di(ethyl)peroxydicarbonate and hydroethylperoxydicarbonate.

[0051] The amount of radical initiator required for polymerization depends on its activity and the temperature used for polymerization. The total amount of radical initiator used is generally 100 to 30,000 ppm by weight based on the total weight of the monomers used.

[0052] The radical initiator may be added in pure form, in solution, in suspension, or in emulsion, depending on the initiator selected.

[0053] The radical initiator system may include a chain transfer agent (CTA).

[0054] Suitable CTAs for the polymerization process to prepare the polymer (F) according to the invention are known in the art and are typically selected from the group consisting of short hydrocarbon chains such as ethane and propane, esters such as ethyl acetate and diethyl maleate, and diethyl carbonate. When an organic peroxide is used as an initiator, it could also serve as an effective CTA during the free radical polymerization.

[0055] When used, the CTA may be added all at once at the beginning of the reaction, or in portions, or continuously throughout the course of the reaction. The amount of CTA and its mode of addition depend on the desired properties of the resulting polymer (F).

[0056] A preferred CTA for use in the method of the present invention is diethyl carbonate.

[0057] In the process for preparing polymer (F), 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.

[0058] The monomer (CA) is preferably added to the reaction vessel as an aqueous solution.

[0059] It is essential that a continuous supply of aqueous solution containing the monomer (CA) is carried out for the entire duration of the polymerization run.

[0060] As a result, it is possible to obtain an approximately statistical distribution of the monomers (CA) within the main chain of the polymer (F).

[0061] The expressions "continuous feed" or "continuous feeding" mean that during the polymerization, a slow, small amount, incremental addition of an aqueous solution of the monomer (CA) is carried out.

[0062] The aqueous solution of the monomer (CA) is continuously fed during the polymerization in an amount of at least 50% by weight of the total amount of the monomer (CA) fed during the reaction (i.e., the initial addition amount plus the continuously fed amount). Preferably, at least 60% by weight, more preferably at least 70% by weight, and most preferably at least 80% by weight of the total amount of the monomer (CA) is continuously fed during the polymerization. Gradually increasing addition of the VDF monomer can be carried out during the polymerization.

[0063] Preferably, the process of the present invention is carried out at a temperature above the critical temperature of the VDF monomer, ie at a temperature of at least 31°C.

[0064] The polymer (F) is typically provided in powder form according to the methods described above.

[0065] The polymer (F) in the form of a powder can optionally be further extruded to obtain the polymer (F) in the form of pellets.

[0066] The polymer (F) as detailed above can be used as a binder for electrodes of Li-ion batteries.

[0067] The second object of the present invention is to a) at least one electrode active material (AM); b) at least one binder (B) comprising at least one polymer (F) as defined above; c) at least one solvent (S); The present invention relates to an electrode-forming composition (C) comprising:

[0068] For the purposes of the present invention, the term "electrode active material (AM)" is intended to denote a compound that can incorporate or intercalate into its structure and subsequently release alkali or alkaline earth metal ions therefrom during the charge and discharge phases of an electrochemical device. The compound (AM) is preferably capable of incorporating or intercalating and releasing lithium ions.

[0069] The nature of the compound (AM) in the composition (C) depends on whether said composition is used to manufacture a positive electrode (electrode (Ep)) or a negative electrode (electrode (En)).

[0070] When forming a positive electrode (Ep) for a lithium ion secondary battery, the compound (AM) may include a complex metal chalcogenide of the formula LiMQ2 (wherein M is at least one metal selected from transition metals such as Co, Ni, Fe, Mn, Cr, and V, or metals such as Al, and mixtures thereof, and Q is a chalcogen such as O or S). Among these, it is preferable to use a lithium-based complex metal oxide of the formula LiMO2 (wherein M is the same as defined above). Preferred examples thereof include LiCoO2, LiNiO2, LiNi x Co 1-x O2(0 <x<1)、LiNi a Co b Al c O2 (a+b+c=1) and spinel structured LiMn2O4 may be included.

[0071] Alternatively, when forming a positive electrode for a lithium ion secondary battery, the compound (AM) may further be a compound of the formula M1M2(JO4) f E 1-f (wherein M1 is lithium, optionally partially substituted by another alkali metal corresponding to less than 20% of the M1 metal; M2 is a transition metal having an oxidation level of +2 selected from Fe, Mn, Ni or mixtures thereof, optionally partially substituted by one or more additional metals having an oxidation level of +1 to +5, inclusive, corresponding to less than 35% of the M2 metal; JO4 is any oxyanion; J is any of P, S, V, Si, Nb, Mo or combinations thereof; E is a fluoride, hydroxide or chloride anion; and f is the mole fraction of the JO4 oxyanion, typically comprised between 0.75 and 1.

[0072] M1M2(JO4) defined above f E1-f The electroactive material is preferably phosphate-based and may have an ordered or modified olivine structure.

[0073] More preferably, the compound (AM) when forming the positive electrode (Ep) is of 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, and JO4 is preferably PO4, which may be partially substituted with another oxyanion, where J is any of S, V, Si, Nb, Mo or a combination thereof. Even more preferably, compound (AM) has the formula Li(Fe x Mn 1-x )PO4, where 0≦x≦1, and x is preferably 1 (i.e., lithium iron phosphate (LFP) of the formula LiFePO4). LFP active materials suitable for use in the electrodes of the invention can have nanometer particle sizes, meaning less than 1 micrometer in size, or micrometer particle sizes, meaning having a size between 1 micrometer and 1 millimeter.

[0074] When forming a composite negative electrode (En) for a lithium ion secondary battery, the compound (AM) may preferably include a carbon-based material and / or a silicon-based material.

[0075] In some embodiments, the carbon-based material can be graphite, graphene, or carbon black, such as, for example, natural or artificial graphite.

[0076] These materials may be used alone or as a mixture of two or more of them.

[0077] The carbon-based material is preferably graphite.

[0078] The silicon-based compound may be one or more selected from the group consisting of chlorosilane, alkoxysilane, aminosilane, fluoroalkylsilane, silicon, silicon chloride, silicon carbide, and silicon oxide. More specifically, the silicon-based compound may be silicon oxide or silicon carbide.

[0079] When present in compound (AM), the at least one silicon-based compound is contained in compound (AM) in an amount ranging from 1 to 30% by weight, preferably from 5 to 20% by weight, relative to the total weight of compound (AM).

[0080] The solvent (S) may preferably be an organic polar solvent, examples of which may include N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphamide, dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, and trimethyl phosphate. These solvents may be used alone or in a mixture of two or more species.

[0081] An optional conductive agent may be added to improve the conductivity of the resulting electrode (AM).

[0082] Examples may include carbon black, graphite fine powder, carbon nanotubes, graphene or fibers, or other carbonaceous materials, or fine powders 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®.

[0083] The electrode-forming composition (C) of the present invention may optionally further comprise at least one conductive agent.

[0084] If present, the conductive agent is different from the carbon-based material described above.

[0085] In a preferred embodiment of the present invention, an electrode-forming composition (C) for use in preparing a positive electrode (Ep) is provided, said composition comprising: a) at least one electrode active material (AM); b) at least one binder (B) comprising at least one polymer (F) as defined above; c) at least one solvent (S); d) at least one conductive agent, preferably selected from carbon black or graphite fine powder and carbon nanotubes; Includes.

[0086] As mentioned above, the polymer (F) of the present invention has a pseudo-linear structure and a very small insoluble fraction when dissolved in a standard polar aprotic solvent such as NMP.

[0087] Due to the small amount of insoluble components, polymer (F) provides a solution in organic solvents that is not adversely affected by the presence of insoluble residue, commonly referred to as "gel," and is therefore more suitable for use in formulating electrode-forming compositions.

[0088] In another object, the present invention relates to the use of an electrode-forming composition (C) for the manufacture of an electrode (E), said process comprising: (I) providing a metal substrate having at least one surface; (II) providing an electrode-forming composition (C) as defined above; (III) applying the composition (C) prepared in step (II) onto at least one surface of the metal substrate prepared in step (I), thereby preparing an assembly including a metal substrate coated with the composition (C) on at least one surface; (IV) drying the assembly prepared in step (III); (V) subjecting the dried assembly obtained in step (III) to a compression step to obtain the electrode (E) of the present invention. Includes.

[0089] In a further object, the present invention relates to an electrode (E) obtainable by the method of the present invention.

[0090] The applicant has surprisingly found that the electrode (E) of the present invention exhibits outstanding adhesion of the binder to the current collector.

[0091] Therefore, the electrode (E) of the present invention is particularly suitable for use in electrochemical devices, in particular in secondary batteries.

[0092] For the purposes of the present invention, the term "secondary battery" is intended to mean a rechargeable battery.

[0093] The secondary battery of the present invention is preferably an alkali metal secondary battery or an alkaline earth metal secondary battery.

[0094] The secondary battery of the present invention is more preferably a lithium ion secondary battery.

[0095] In a still further object, the present invention relates to an electrochemical device comprising at least one electrode (E) of the present invention.

[0096] The electrochemical device according to the present invention is preferably a secondary battery, and includes a positive electrode and a negative electrode, at least one of which is the electrode (E) of the present invention.

[0097] In one preferred embodiment of the present invention, there is provided an electrochemical device which is a secondary battery including a positive electrode and a negative electrode, wherein the negative electrode is the electrode (E) according to the present invention.

[0098] Electrochemical devices according to the present invention can be prepared by standard methods known to those skilled in the art.

[0099] The present invention will now be described with reference to the following examples, the purposes of which are merely illustrative and are not intended to limit the scope of the invention. [Example]

[0100] Determination of the intrinsic viscosity of the polymer (F) The intrinsic viscosity (η) [dl / g] was calculated based on the drop time at 25°C of a solution obtained by dissolving the polymer (F) in N,N-dimethylformamide at a concentration of about 0.2 g / dl using an Ubbelhode viscometer, according to the following formula:

number

[0101] DSC analysis DSC analysis was performed according to the ASTM D 3418 standard to determine the melting point (T 2f ) was determined at a heating rate of 10°C / min.

[0102] Determination of polar end groups The amount of polar end groups of polymer (F) resulting from the ethyl chloroformate initiator precursor used in the polymerization process is determined by measuring the intensity of the H atom of the CH2 group (in bold in the following formula) relative to the total intensity of the CH2 sites of the VDF monomer units that are the backbone of polymer (F): 1 Determined by H-NMR: CH3-CH2-OCOO-CH2-CF2-

[0103] The content of the terminal group is determined by the following formula: [EG]=(I EG / I VDF ) x 10000 (In the formula, - [EG] is the overall end group content expressed as moles per 10,000 VDF units, -I EG is the intensity of the integral of the end group [EG], normalized to one hydrogen; -I VDF is the intensity, normalized to one hydrogen, of the integrals of the normal and reversed VDF repeat units) was calculated by applying

[0104] Approximately 20 mg of polymer was dissolved in 0.7 ml of hexadeuteroacetone. 1 The H-NMR spectrum showed the aforementioned CH2 at 4.47 ppm, while the CH2 signals from the normal and reverse repeat units of VDF resonated as broad peaks centered at 2.93 and 2.36 ppm, respectively.

[0105] Similar NMR methods were applied to determine the end groups derived from the use of diethyl carbonate chain transfer agent (CH-CH-OCOO-CH-CH-, CH-CH-OCOO-CH(CH)-) as well as to determine -CFH and -CFCH end groups, as known to those skilled in the art.

[0106] Determination of the amount of monomer AA in polymer (F) by NMR The content of alternating AA in polymer (F) is 19 F-NMR spectroscopy. The signal associated with the CF2 site (bold in the formula below) of the VDF unit adjacent to the isolated hydrogenated comonomer is 19 It was found to resonate at approximately -94 ppm in F-NMR. -CH2CF2-CH2CH(COOH)-CH2CF2-CH2

[0107] From the ratio between the normalized intensity of this signal and the normalized intensity of all VDF peaks in the spectrum, it is possible to determine the average number of comonomers statistically inserted between two VDF units.

[0108] Example 1: Preparation of Polymer F-1 In a 4 L reactor equipped with an impeller rotating at a speed of 650 rpm, 2370 g of demineralized water and a solution of 0.4 g of PEO (Alkox®-E45 from Alkorox) per kg of total monomers, 0.5 g of hydroxypropyl methylcellulose (Methocel®-K100 from Dow) per kg of total monomers, and 20.6 g of trisodium phosphate dodecahydrate were successively introduced. The oxygen present in the reactor was removed by a sequence of vacuum and nitrogen purges at a fixed temperature of 14° C. This sequence was repeated three times.

[0109] Then 16.93 g of hydrogen peroxide solution (from Brenntag), 5.9 g of ethyl chloroformate (from Framochem), and 5.9 g of diethyl carbonate were introduced into the reactor.

[0110] After 15 minutes, 0.18 g of acrylic acid (AA) was introduced into the reactor at a stirring speed of 880 rpm. Shortly thereafter, 1174 g of VDF was added to the mixture. The reactor was then gradually heated until a set point temperature of 35° C. was reached.

[0111] The pressure was kept constant throughout the polymerization at 120 bar by feeding an aqueous solution containing 4.15 g of AA per liter of solution. A total of 666 g of solution was introduced into the reactor. After 269 minutes, the polymerization was stopped by degassing the suspension until atmospheric pressure was reached.

[0112] The resulting polymer was then collected by filtration and suspended in clean water in a stirred tank. After washing, the polymer was dried overnight in an oven at 65°C. 837g of dry powder was recovered.

[0113] A polymer containing VDF-AA (0.2 mol %) was obtained with an intrinsic viscosity of 0.299 l / g in DMF at 25°C and a T2f of 170.3°C.

[0114] This polymer contained 2.0 / 10000 VDF units of the end group CH3CH2-OCOO-: 1.3 / 10000 VDF units of units derived from the ethyl chloroformate initiator precursor and 0.7 / 10000 VDF units of units derived from diethyl carbonate.

[0115] In addition, the presence of -CF2H end groups at 2.7 / 10000 VDF units and -CF2CH3 end groups at 1.5 / 10000 VDF units was determined.

[0116] The amount of the end group -CH3CH2-OCOO- is 32.3% relative to the total amount of the end groups of the polymer (F).

[0117] Example 2: Preparation of Polymer F-2 In a 4 L reactor equipped with an impeller rotating at a speed of 650 rpm, 2383 g of demineralized water and a solution of 0.4 g of PEO (Alkox®-E45 from Alkorox) per kg of total monomers, 0.5 g of hydroxypropyl methylcellulose (Methocel®-K100 from Dow) per kg of total monomers, and 20.6 g of trisodium phosphate dodecahydrate were successively introduced. The oxygen present in the reactor was removed by a sequence of vacuum and nitrogen purges at a fixed temperature of 14° C. This sequence was repeated three times.

[0118] Then 16.93 g of hydrogen peroxide solution (from Brenntag) and 5.9 g of ethyl chloroformate (from Framochem) were introduced into the reactor.

[0119] After 15 minutes, 0.77 g of acrylic acid (AA) was introduced into the reactor at a stirring speed of 880 rpm. Shortly thereafter, 1162 g of VDF was added to the mixture. The reactor was then gradually heated until a set point temperature of 35° C. was reached.

[0120] The pressure was kept constant throughout the polymerization at 120 bar by feeding an aqueous solution containing 18.27 g of AA per liter of solution. A total of 659 g of solution was introduced into the reactor. After 624 minutes, the polymerization was stopped by degassing the suspension until atmospheric pressure was reached.

[0121] The polymer was then collected by filtration and suspended in clean water in a stirred tank. After washing, the polymer was dried overnight in an oven at 65° C. 861 g of dry powder was recovered.

[0122] A polymer containing VDF-AA (0.9 mol%) was obtained with an intrinsic viscosity of 0.294 l / g in DMF at 25°C and a T2f of 164.8°C.

[0123] The polymer contained 2.5 / 10000 VDF units with the end group CH3CH2-OCOO- derived from the ethyl chloroformate initiator precursor.

[0124] In addition, the presence of -CF2H end groups at 4.6 / 10000 VDF units and -CF2CH3 end groups at 2.2 / 10000 VDF units was determined.

[0125] The amount of the end group -CH3CH2-OCOO- is 26.9% relative to the total amount of the end groups of the polymer (F).

[0126] Example 3 Comparison: Preparation of Polymer A In a 4 L reactor equipped with an impeller rotating at a speed of 650 rpm, 2205 g of demineralized water and 0.4 g of PEO (Alkox®-E45 from Alkorox) per kg of total monomers and 0.5 g of hydroxypropyl methylcellulose (Methocel®-K100 from Dow) per kg of total monomers were successively introduced. The oxygen present in the reactor was removed by a vacuum and nitrogen purge sequence at a fixed temperature of 11° C. This sequence was repeated three times.

[0127] Then 4.62 g of a solution (75%) of the initiator t-amyl perpivalate (TAPPI, from United Initiators) in isododecane and 6.17 g of diethyl carbonate were introduced into the reactor.

[0128] The reactor was then brought to an agitation speed of 880 rpm. Immediately thereafter, 0.18 g of acrylic acid (AA) and 1176 g of VDF were added to the reactor. The reactor was then gradually heated until a set point temperature of 50° C. was reached.

[0129] The pressure was kept constant throughout the polymerization at 120 bar by feeding an aqueous solution containing 3.33 g of AA per liter of solution. A total of 830 g of solution was introduced into the reactor. After 354 minutes, the polymerization was stopped by degassing the suspension until atmospheric pressure was reached.

[0130] The polymer was then collected by filtration and suspended in clean water in a stirred tank. After washing, the polymer was dried overnight in an oven at 65° C. 987 g of dry powder was recovered.

[0131] A polymer containing VDF-AA (0.2 mol %) was obtained with an intrinsic viscosity of 0.286 l / g in DMF at 25°C and a T2f of 169.6°C.

[0132] The polymer contained end groups from TAPPI addition at 1.1 / 10000 VDF units, -CF2H at 3.2 / 10000 VDF units, and -CF2CH3 end groups at 2.1 / 10000 VDF units.

[0133] The polymer contained 1.1 / 10000 VDF units with the end group CH3CH2-OCOO- derived from diethyl carbonate.

[0134] The amount of the end group -CH3CH2-OCOO- is 14.7% relative to the total amount of the end groups of the polymer (F).

[0135] Example 4 Comparison: Preparation of Polymer B Polymer B was synthesized according to the teachings of WO 2008 / 129041 (Solvay Specialty polymers Italy SPA). The polymer's characteristics are as follows:

[0136] Composition: VDF-AA (0.9 mol %) polymer with an intrinsic viscosity of 0.274 l / g in DMF at 25°C and a T2f of 162.6°C.

[0137] End groups: 2.3 / 10000VDF units of end groups from TAPPI addition, 6.8 / 10000VDF units of CF2H, and 3.1 / 10000VDF units of -CF2CH3 end groups from TAPPI addition.

[0138] The end groups of the formula CH3CH2-OCOO- were not determined.

[0139] General preparation of electrodes using NMC622 active material Positive electrodes having a final composition of 96.5 wt. % NMC622 (Umicore, d50 11.6 μm), 1.5 wt. % of any of polymers (F-1), (F-2), A, and B, and 2 wt. % of a conductive additive were prepared as follows.

[0140] An initial dispersion was prepared by premixing 34.7 g of a 6 wt % solution of polymer in NMP, 133.8 g of NMC622, 2.8 g of SC-65, and 8.8 g of NMP in a centrifugal mixer for 10 minutes.

[0141] An additional 7.2 g of NMP was added and the dispersion was mixed again in the centrifugal mixer for 10 minutes.

[0142] The final slurry was obtained by further stirring with a high speed disc impeller at 1900 rpm for 70 minutes.

[0143] The resulting composition was cast onto an aluminum foil having a thickness of 15 μm using a doctor blade, and the coated layer was dried in a vacuum oven at a temperature of 90° C. for about 50 minutes to obtain a positive electrode. The thickness of the dried coating layer was about 110 μm.

[0144] Example 5: Adhesion and Slurry Viscosity Using the polymers of Examples 1-3 as binders, electrode compositions were prepared according to the procedures set forth above.

[0145] The slurry viscosity of the above-defined compositions was measured on an AntonPaar Rheolab QC using a concentric cylinder apparatus (measuring cup: C-CC27 / QC-LTD Bob: CC27 / P6) equipped with Peltier temperature control at 25° C. The steady-state viscosity was measured from shear rates of 0.1 to 200 1 / s.

[0146] The adhesive peel force between the aluminum foil and the electrode was measured as follows: To evaluate the adhesion of the dried coating layer defined above to aluminum foil, a 180° peel test was carried out according to the configuration described in standard ASTM D903 at 20° C. and a speed of 300 mm / min.

[0147] The slurry viscosity and adhesive strength values ​​are shown in Table 1.

[0148] [Table 1]

[0149] The results show that the polymers of the present invention have lower slurry viscosity and higher adhesion to the current collector than prior art polymers, resulting in better performance and easier handling in the electrode manufacturing process. It has been demonstrated that the presence of certain amounts of specific end groups has a surprising effect on both the slurry viscosity of the electrode-forming composition and the adhesion of the electrode to the current collector.

Claims

1. (i) repeat units derived from vinylidene fluoride (VDF) monomers; (ii) Formula (I): 【Chemistry 1】 (In the formula: R are equal to or different from each other １ , R ２ and R ３ represents a hydrogen atom and C １ ~C ３ R is independently selected from hydrocarbon groups; Ｈ C contains at least one carboxyl group and no aliphatic hydroxyl groups ２ ~C １０ hydrocarbon moiety) and a repeating unit derived from at least one carboxyl group-containing vinyl monomer (CA) of A fluoropolymer [polymer (F)] comprising: the content of the monomer (CA) in the polymer (F) is at most 5.0 mol % based on the total number of moles of repeating units of the polymer (F); At least 50% of the monomers (CA) are randomly distributed in the polymer (F), The polymer (F) has the formula (I): -(Ra) ｘ -O-CO-O-CH ２ -CH ３ (I) (In the formula, R ａ is C １ ~C ５ and x is an integer selected from 1 and zero. and wherein the terminal group of The end groups of formula (I) are present in an amount of at least 20% based on the total amount of end groups of polymer (F); Polymer (F).

2. The carboxyl group-containing vinyl monomer (CA) is represented by the formula (Ia): 【Chemistry 2】 (In the formula, R are equal to or different from each other １ , R ２ and R ３ represents a hydrogen atom and C １ ~C ３ R' is independently selected from hydrocarbon groups; Ｈ is hydrogen or a C having at least one carboxyl group and no aliphatic hydroxyl group １ ~C １５ hydrocarbon moiety) The polymer (F) according to claim 1, which is a compound of the formula:

3. The carboxyl group-containing vinyl monomer (CA) is acrylic acid (AA), (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, 3-butenoic acid, - (meth)acryloyloxyethyl succinate, (meth)acryloyloxypropyl succinic acid, 3-(allyloxy)propanoic acid, and mixtures thereof The polymer (F) according to claim 1 or 2, selected from the group consisting of:

4. 4. Polymer (F) according to any one of claims 1 to 3, further comprising repeat units derived from one or more fluorinated comonomers (CF) different from VDF.

5. at least 70 mol %, preferably at least 75 mol %, more preferably at least 85 mol % of repeat units derived from vinylidene fluoride (VDF); - 0.01% to 1.5% by mole, preferably 0.01% to 1.0% by mole, of repeat units derived from at least one vinyl monomer (CA), - optionally 0.5 to 3.0 mol % of repeat units derived from at least one fluorinated comonomer (CF); The polymer (F) according to any one of claims 1 to 4, consisting of Polymer (F), where all amounts are relative to the total number of moles of repeat units of polymer (F).

6. containing an end group of formula (I) where x is zero and / or an end group of formula (I) where x is 1, R ａ is C ２ ~C ３ The polymer (F) according to any one of claims 1 to 5, wherein the alkyl radical is a linear or branched alkyl radical of the formula:

7. A process for preparing the polymer (F) according to any one of claims 1 to 6, comprising the steps of: polymerizing, in an aqueous medium, vinylidene fluoride (VDF) monomer, an initial charge of monomer (CA), and optional comonomer (CF), in the presence of a radical initiator system that introduces said polymer chain end groups of formula (I); - continuously feeding an aqueous solution containing the monomer (CA), and - maintaining the pressure in the reaction vessel above the critical pressure of the vinylidene fluoride. A method comprising:

8. 8. The method of claim 7, wherein the radical initiator system comprises radical initiators such as di(ethyl)peroxydicarbonate and hydroethylperoxydicarbonate.

9. 9. The method of claim 8, wherein the radical initiator system comprises a chain transfer agent (CTA).

10. a) at least one electrode active material (AM); b) at least one binder (B) comprising at least one polymer (F) according to any one of claims 1 to 6; c) at least one solvent (S); An electrode-forming composition (C) comprising:

11. The electrode-forming composition (C) of claim 10, wherein the at least one electrode active material (AM) is an LFP.

12. A method for producing an electrode [electrode (E)], comprising the steps of: (I) providing a metal substrate having at least one surface; (II) preparing the electrode-forming composition (C) according to claim 10 or 11; (III) applying the composition (C) prepared in step (II) onto at least one surface of the metal substrate prepared in step (I), thereby preparing an assembly including a metal substrate coated with the composition (C) on at least one surface; (IV) drying the assembly prepared in step (III); (V) subjecting the dried assembly obtained in step (IV) to a compression step to obtain the electrode (E) of the present invention. A method comprising:

13. Electrode (E) obtainable by the method according to claim 12.

14. Electrochemical device comprising at least one electrode (E) according to claim 13.

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