Battery electrode and method for manufacturing the same

Abstract

The present invention relates to an electrode composition comprising PTFE and a crosslinkable fluororesin, a method for preparing the same, and its use for the manufacture of electrochemical cell components.

Description

[Technical Field]

[0001] Cross-reference of related applications This application claims priority under European Patent No. 23181467.4, filed on 26 June 2023, and the entirety of that application is incorporated herein by reference for all purposes.

[0002] The present invention relates to an electrode composition comprising PTFE and a crosslinkable fluororesin, a method for preparing the same, and its use for the manufacture of electrochemical cell components. [Background technology]

[0003] To date, electrodes for lithium secondary batteries have been primarily manufactured by a wet process that involves preparing a slurry in which electrode active materials, additives, and binders are dispersed in a solvent or aqueous medium, and then processing the slurry to form an electrode film.

[0004] The dry electrode process was developed to reduce the time-consuming and costly drying steps required by the wet process described above.

[0005] A typical dry process utilizes the fibrillating properties of a particular polymer to provide a matrix for the conductive material to be embedded. Some polymers in the family of fluoropolymers, such as polytetrafluoroethylene (PTFE), are particularly inert and stable in common electrode solvents used in secondary batteries, even when using organic solvents at high operating or storage temperatures. Therefore, the stability of electrodes fabricated using PTFE can be higher than that of electrodes fabricated using other binders.

[0006] For example, a dry electrode fabrication process may include combining a PTFE binder with an electrode active material in powder form, and then calendering the mixture to form an electrode film. However, while PTFE has good adhesion to the electrode active material, it has difficulty adhering to the current collector.

[0007] Methods for improving the adhesion of PTFE to current collectors and electrode active materials are known in the art by using PTFE in combination with either PVDF or VDF / HFP copolymer as a binder. For example, U.S. Patent No. 11,276,846 discloses a dry process for manufacturing electrodes, comprising rolling a granular powder containing a combination of PTFE and either PVDF or VDF / HFP copolymer onto a metal current collector using rollers heated to a predetermined temperature, thereby enabling the rolled granular powder to adhere to the current collector by the pressure and temperature of the rollers. In the method described in U.S. Patent No. 11,276,846, adhesion can be achieved when at least one of the first binder and the second binder contained in the granular powder is melted.

[0008] International Publication No. 2021 / 023707 discloses that in a process for manufacturing electrodes using a solvent-based slurry, casting the electrode-forming composition onto a current collector allows for thermal crosslinking of a specific crosslinkable vinylidene fluoride copolymer, resulting in electrodes with improved performance, particularly in terms of adhesion to metals.

[0009] The applicant has surprisingly found that when electrodes are fabricated by an efficient dry process that includes a calendering step of dry material onto a substrate, selecting a copolymer based on a specific VDF combined with PTFE significantly improves the adhesion of the electrode film to the current collector. [Overview of the project]

[0010] Therefore, in this specification, a. Polytetrafluoroethylene (PTFE) and; b. Fluoropolymer [polymer (F)], - (i) Repeating units derived from vinylidene fluoride (VDF) monomer, - Repeating units derived from at least one vinyl monomer (HA) of formula (I) R1R2C=CR3-R

[0012] , , , , , , , (I) (wherein R1, R2 and R3 are the same as or different from each other and are independently selected from a hydrogen atom, a halogen atom, and a C1-C5 hydrocarbon group, and R x is an optionally substituted C2-C 20 linear or branched hydrocarbon chain moiety containing at least one aliphatic hydroxyl group), - Repeating units derived from at least one carboxyl group-containing vinyl monomer (CA) (where the monomer (CA) is different from the monomer (HA)), and a fluoropolymer [polymer (F)] containing; A binder composition [binder (B)] for use in the production of an electrode for an electrochemical device, characterized by containing The total amount of the monomer (HA) and the monomer (CA) in the polymer (F) is at most 5.0 mol%, preferably at most 1.5 mol%, based on the total number of moles of the repeating units of the polymer (F), At least 50% of the monomer (CA) is randomly distributed in the polymer (F), A binder composition [binder (B)] is provided.

[0011] In another aspect, the present invention is an electrode-forming composition [composition (C)] for use in the production of an electrode for an electrochemical device, comprising a) at least one electrode active material (AM), b) a binder (B) as defined above, [[ID=3E]]c) an optional at least one conductive agent An electrode-forming composition [composition (C)] is provided.

[0012] The applicant has surprisingly found that due to the processability of the binder (B), it is suitable for the production of electrodes by a dry process in a calendar device with a very short contact time, and as a result, an electrode with very high adhesion to the current collector can be obtained by a very efficient process.

[0013] Thus, in another aspect, the present invention is a method for manufacturing an electrode [electrode (E)] for an electrochemical cell, comprising: -A) obtaining a binder (B) by combining polytetrafluoroethylene (PTFE) and the fluoropolymer [polymer (F)] defined above; -B) dry-grinding at least one electrode active material (AM), a binder (B) as defined above, and optionally at least one conductive agent in the absence of a solvent; -C) feeding the powdered dry mixture obtained in step B) to a compressor to form a self-supporting dry film; and -D) laminating the dry film on a conductive substrate in a calendar to form an electrode. A method including the above steps is provided.

[0014] In another aspect, the present invention provides an electrode (E) for a secondary battery obtainable by the method defined above.

[0015] In a further aspect, the present invention relates to an electrochemical device such as a secondary battery or a capacitor, comprising at least one electrode (E) as defined above.

Embodiments for Carrying Out the Invention

[0016] In relation to the present invention, the term “weight percent” (weight%) refers to the content of a particular component in a mixture, calculated as the ratio between the weight of that particular component and the total weight of the mixture. When referring to repeating units derived from certain monomers in a polymer / copolymer, weight percent (weight%) refers to the ratio between the weight of the repeating units of that monomer and the total weight of the polymer / copolymer. When referring to the total solids content of a liquid composition, weight percent (weight%) refers to the ratio between the weights of all non-volatile components in the liquid.

[0017] As used herein, the terms “adhere” and “bond” refer to two layers being permanently joined to each other through their contact surfaces.

[0018] The term “electrochemical device” is intended herein to mean an electrochemical cell / assembly comprising a positive electrode, a negative electrode, and a liquid electrolyte, wherein a single-layer or multi-layer separator is in contact with at least one surface of one of the electrodes. Non-limiting examples of suitable electrochemical devices include, in particular, secondary batteries, especially alkaline or alkaline earth secondary batteries such as lithium-ion batteries, lead-acid batteries, and capacitors, in particular lithium-ion capacitors and electric double-layer capacitors (supercapacitors). Non-limiting examples of electrochemical cells include, in particular, batteries, preferably secondary batteries and electric double-layer capacitors.

[0019] For the purposes of this invention, "secondary battery" is intended to refer to a rechargeable battery. Non-limiting examples of secondary batteries include, in particular, alkaline or alkaline earth secondary batteries.

[0020] In relation to the present invention, the term "PTFE" refers to a polymer obtained from the polymerization of tetrafluoroethylene (TFE).

[0021] However, the PTFE polymer may also contain small amounts of one or more comonomers, but is not limited to, hexafluoropropylene, perfluoro(methyl vinyl ether), perfluoro(propyl vinyl ether), and perfluoro-(2,2-dimethyl-1,3-dioxole), although it is understood that the latter do not significantly adversely affect the unique properties of the tetrafluoroethylene homopolymer, such as its thermal and chemical stability. Preferably, the amount of such comonomers does not exceed about 3 mol%, more preferably less than about 1 mol%; a comonomer content of less than 0.5 mol% is particularly preferred. If the total comonomer content is greater than 0.5 mol%, the amount of perfluoro(alkyl vinyl ether) comonomer is preferably less than about 0.5 mol%. The PTFE homopolymer is most preferred.

[0022] The PTFE suitable for use in the preparation of binder (B) of the present invention may be in the form of a powder or latex.

[0023] PTFE in powder form is obtained by solidifying a PTFE grid by cryogenic solidification or by electrolytic solidification with the addition of an electrolyte. See, for example, U.S. Patent No. 6,790,932. Preferred examples of electrolytes are as follows: - Based on the amount of water in the solidification container, a concentration of 2 g / l of aluminum sulfate (Al2(SO4)3) is calculated. - Based on the amount of water in the solidification container, calculate 8 g / l of ammonium carbonate ((NH4)2CO3), or - Nitric acid (HNO3), 25 ml of a 65% solution calculated based on the amount of water in the coagulation container.

[0024] Alternatively, the PTFE powder may be obtained from a PTFE grid in the form of a gel by coagulation with the electrolyte described above. The gel may be obtained according to U.S. Patent No. 6,790,932 and U.S. Patent No. 6,780,966.

[0025] After coagulation occurs, the polymer is washed with demineralized water at room temperature. Following coagulation and washing, the resulting PTFE powder is then dried.

[0026] PTFE grids are generally obtained by dispersion or emulsion polymerization.

[0027] PTFE in powder form generally has a particle size of 1 to 1600 microns, preferably 100 to 800 microns, and more preferably 400 to 700 microns.

[0028] Particle size can be expressed relative to D50, which is the corresponding particle size when the cumulative percentage reaches 50%. D50 is also called the medium particle size or medium diameter. For example, in a powder sample with D50 = 5 μm, it means that 50% of the particles are larger than 5 μm and 50% of the particles are smaller than 5 μm.

[0029] A suitable monomer (HA) is given by formula (I): R1R2C=CR3-R x (I) (In the formula, R1, R2 and R3 are either the same as or different from each other, and are independently selected from hydrogen atoms, halogen atoms, and C1-C5 hydrocarbon groups, R x C2-C2 contains at least one aliphatic hydroxyl group. 20 The compound is a linear or branched hydrocarbon chain (which may be optionally substituted with at least an ether group, a ketone group, an epoxy group, a percarbonate group, or an ester group).

[0030] In relation to the present invention, the term "aliphatic hydroxyl group" refers to a hydroxyl group bonded to an aliphatic carbon atom.

[0031] In a preferred embodiment, the monomer (HA) is of formula (Ia): [ka] (wherein R1, R2 and R3 are the same as or different from each other and are independently selected from a hydrogen atom and a C1-C3 hydrocarbon group, and R’ OH is an optionally substituted C1-C5 hydrocarbon moiety containing at least one aliphatic hydroxyl group) is a compound.

[0032] Non-limiting examples of the monomer (HA) of formula (Ia) include, inter alia: - hydroxyethyl (meth) acrylate (HEA), - 2-hydroxypropyl acrylate (HPA), - hydroxyethylhexyl (meth) acrylate, and mixtures thereof.

[0033] Preferably, at least one monomer (HA) is hydroxyethyl (meth) acrylate (HEA) or 2-hydroxypropyl acrylate (HPA).

[0034] Suitable carboxyl group-containing vinyl monomers (CA) are of formula (II):

Chemical formula

[0035] <r In a preferred embodiment, the monomer (CA) is of formula (IIa):

Chemical formula

[0036] R' H The chain may further contain one or more oxygen atoms, carbonyl groups, or ester groups.

[0037] Non-restrictive examples of monomers (CA) in formula (IIa) include, among others: - Acrylic acid (AA) and - (meth)acrylic acid, - 2-carboxyethyl (meth)acrylate, - (meth)acryloyloxyethyl succinate, - (meth)acryloyloxypropyl succinate, And mixtures thereof are also included.

[0038] Preferably, at least one monomer (CA) is acrylic acid (AA).

[0039] In preferred embodiments of the present invention, monomer (CA) is acrylic acid, and monomer (HA) does not contain a carboxyl group.

[0040] The molar ratio between repeating units (ii) and (iii) in polymer (F) is preferably in the range of 20:1 to 1:20, preferably 10:1 to 1:10, and more preferably 1:5 to 5:1.

[0041] In polymer (F), it is essential that at least 50% of the monomers (CA) are randomly distributed within the polymer (F).

[0042] It is known in the art that when VDF comonomers are continuously supplied during the polymerization of VDF, the comonomers are randomly distributed in the polymer chain, where the VDF-(comonomer)-VDF sequence is normally predominantly present.

[0043] Therefore, when polymer (F) is prepared by a polymerization reaction that includes the continuous supply of monomer (CA) during VDF polymerization, a random distribution of monomer (CA) exists in the polymer chain, resulting in a VDF-(CA)-VDF sequence.

[0044] More preferably, in the polymer (F), at least 70% of the monomers (CA) are randomly distributed within the polymer (F).

[0045] The expression "randomly distributed monomers (CA)" is intended to represent the presence of the sequence VDF-(CA)-VDF, and the amount of randomly distributed monomers (CA) is determined as a percentage between the average number of VDF-(CA)-VDF sequences and the total average number of (CA) monomer repeating units.

[0046] When each (CA) repeating unit is isolated, i.e., contained between two repeating units of the VDF monomer, the average number of (CA) sequences is equal to the average total number of (CA) repeating units, and therefore the fraction of randomly distributed units (CA) is 100%: this value corresponds to a completely random distribution of (CA) repeating units. Thus, as stated above, the larger 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 units (CA) will be.

[0047] In a preferred embodiment of the present invention, the monomer (HA) fractions are also randomly distributed in the polymer (F).

[0048] When both monomer (HA) and monomer (CA) are continuously supplied during VDF polymerization, both comonomers (HA) and (CA) are randomly distributed in the polymer chain, resulting in VDF-(HA)-VDF and VDF-(CA)-VDF sequences. The total percentage of randomly distributed monomers (HA) and (CA) is determined as the percentage between the average number of VDF-(CA)-VDF sequences and VDF-(HA)-VDF sequences and the total average number of monomer repeating units of monomer (CA) and monomer (HA).

[0049] According to this preferred embodiment, at least 50%, more preferably at least 70%, of the total monomers (CA) and monomers (HA) are randomly distributed in the polymer (F).

[0050] The determination by analysis of the total amounts of randomly distributed monomers (HA) and (CA) indicates the VDF-(comonomer)-VDF sequence. 19 The total amount of monomers in the polymer is measured by F-NMR. 19 F-NMR, 1 This can be done by measuring using one or more techniques such as 1H-NMR, carboxyl group titration, or FT-IR.

[0051] The polymer (F) preferably contains at least 0.001%, more preferably at least 0.01 mol%, of repeating units derived from the monomer (HA).

[0052] The polymer (F) preferably contains repeating units derived from monomer (HA) in an amount of up to 5.0%, more preferably up to 3.0 mol%, and even more preferably up to 2.0 mol%.

[0053] The polymer (F) preferably contains at least 0.01%, more preferably at least 0.02 mol%, of repeating units derived from the monomer (CA).

[0054] The polymer (F) preferably contains repeating units derived from monomer (CA) in an amount of up to 5.0%, more preferably up to 3.0 mol%, and even more preferably up to 2.0 mol%.

[0055] Excellent results have been obtained using polymer (F) containing repeating units derived from at least 70 mol% VDF.

[0056] Polymer (F) can be an elastomer or a semicrystalline polymer, and is preferably a semicrystalline polymer.

[0057] As used herein, the term “semi-crystalline” means a fluoropolymer having at least one crystalline melting point in addition to a glass transition temperature Tg as determined by DSC analysis. For the purposes of the present invention, semi-crystalline fluoropolymer is intended herein to mean a fluoropolymer having a heat of fusion of 10–90 J / g, preferably 30–80 J / g, and more preferably 35–75 J / g, as measured according to ASTM D3418-08.

[0058] For the purposes of this invention, the term "elastomer" is intended to refer to a true elastomer, or a polymer resin that serves as a basic component for obtaining a true elastomer.

[0059] A true elastomer is defined by ASTM, Special Technical Bulletin, Standard 184 as a material that can be stretched to twice its intrinsic length at room temperature and, when released after being held under tension for 5 minutes, simultaneously returns to within 10% of its initial length.

[0060] Preferably, the intrinsic viscosity of polymer (F), measured in dimethylformamide at 25°C, is 0.05 l / g to 0.80 l / g, more preferably 0.15 l / g to 0.60 l / g, and even more preferably 0.20 l / g to 0.50 l / g.

[0061] The polymer (F) of the present invention typically has a melting temperature (Tm) that falls within the range of 120 to 200°C.

[0062] The polymer (F) of the present invention preferably has a low proportion of insoluble components in standard polar aprotic solvents for VDF, such as NMP. More preferably, a solution of polymer (F) in the standard polar aprotic solvent remains homogeneous and stable for several weeks with substantially no insoluble residue.

[0063] Thanks to the small amount of insoluble components, the GPC and NMR analyses of polymer (F) are unaffected, and there are no issues with reliability or reproducibility.

[0064] The melting temperature can be determined from a DSC curve obtained by scanning differential calorimetry (hereinafter also called DSC). If the DSC curve shows multiple melting peaks (endothermic peaks), the melting temperature (Tm) is determined based on the peak with the largest peak area.

[0065] The polymer (F) may further contain repeating units derived from one or more fluorinated comonomers (CF) different from VDF.

[0066] In this specification, the term "fluorinated comonomer (CF)" is intended to mean an ethylenically unsaturated comonomer containing at least one fluorine atom.

[0067] Some non-limiting examples of suitable fluorinated comonomers (CFs) include, in particular: (a) C2-C8 fluoro- and / or perfluoroolefins such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene, and hexafluoroisobutylene; (b) Vinyl fluoride; C2-C8 hydrogen-containing monofluoroolefins such as 1,2-difluoroethylene and trifluoroethylene; (c)Formula CH2=CH-R f0 (In the formula, R f0(These are perfluoroalkylethylenes, which are C1-C6 perfluoroalkyl groups); (d) Chlorotrifluoroethylene (CTFE) and other chloro- and / or bromo- and / or iodo-C2~C6 fluoroolefins; (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) These are some examples.

[0068] The fluorinated comonomer (CF) is preferably HFP.

[0069] In one preferred embodiment, the polymer (F) is semicrystalline and contains 0.1 to 10.0 mol%, preferably 0.3 to 5.0 mol%, and more preferably 0.5 to 3.0 mol%, of repeating units derived from the fluorinated comonomer (CF).

[0070] It is understood that polymer (F) may contain chain ends, defects, or other impurity types different from those defined above, without impairing its properties.

[0071] Polymer (F) is more preferably, - At least 70 mol%, preferably at least 75 mol%, and more preferably at least 85 mol%, of vinylidene fluoride (VDF), - At least one monomer (FA) in an amount of 0.005 mol% to 1.5 mol%, preferably 0.01 mol% to 1.0 mol%, - 0.01 mol% to 1.5 mol%, preferably 0.01 mol% to 1.0 mol%, of at least one vinyl monomer (CA), - A repeating unit derived from at least one fluorinated comonomer (CF) in an optional amount of 0.5 to 3.0 mol%, Includes repeating units derived from

[0072] The polymer (F) of the present invention can be obtained by polymerization of a VDF monomer, at least one monomer (HA), at least one monomer (CA), and at least one optionally comonomer (CF) in either a suspension in an organic medium or in an aqueous emulsion carried out as typically described in the art (see, for example, U.S. Patent No. 4,016,345, U.S. Patent No. 4,725,644 and U.S. Patent No. 6,479,591), for example, according to the procedure described in International Publication No. 2022 / 223347.

[0073] A preferred method for preparing polymer (F) comprises polymerizing vinylidene fluoride (VDF) monomer, monomer (HA), monomer (CA), and an optional comonomer (CF) in an aqueous medium in the presence of a radical initiator, wherein the method comprises continuously supplying an aqueous solution containing monomer (HA) and monomer (CA).

[0074] Suitable initiators known for polymerization of fluorinated monomers are organic peroxides, such as those selected from the group consisting of dialkyl peroxides, diacyl peroxides, peroxyesters, and peroxydicarbonates.

[0075] Examples of dialkyl peroxides include di-t-butyl peroxides, with peroxyesters including t-butyl peroxypivalate and t-amyl peroxypivalate, and peroxydicarbonates including di(ethyl) peroxydicarbonate, di(n-propyl) peroxydicarbonate, diisopropyl peroxydicarbonate, di(sec-butyl) peroxydicarbonate, di(2-ethylhexyl) peroxydicarbonate and di(4-tert-butylcyclohexyl) peroxydicarbonate.

[0076] The amount of initiator required for polymerization depends on its activity and the temperature used for polymerization. The total amount of initiator used is generally between 100 and 30,000 ppm by weight, based on the total weight of monomers used.

[0077] The initiator may be added in pure form, as a solution, as a suspension, or as an emulsion, depending on the initiator selected.

[0078] Chain transfer agents, or CTAs, can be added to the polymerization. Suitable CTAs for this polymerization are known in the art and are typically short hydrocarbon chains such as ethane and propane, esters such as ethyl acetate or diethyl maleate, diethyl carbonates, etc. When organic peroxides are used as initiators, they can also act as effective CTAs during the progress of free radical polymerization. However, additional CTAs may be added all at once at the start of the reaction, or they may be added in installments or continuously throughout the progress of the reaction. The amount of CTA and the manner of its addition depend on the desired properties.

[0079] In a preferred preparation process, 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 more preferably greater than 100 bar.

[0080] The continuous supply of aqueous solutions containing monomers (HA) and (CA) is usually essential throughout the entire polymerization run.

[0081] Therefore, it is possible to obtain a nearly statistical distribution of both monomers (HA) and monomer (CA) within the VDF monomer polymer backbone of polymer (F).

[0082] The expression "continuous supply" or "continuous feeding" means that during polymerization, a slow, small, and gradually increasing addition of aqueous solutions of monomer (HA) and monomer (CA) is performed.

[0083] An aqueous solution of monomer (HA) and monomer (CA) is continuously supplied during polymerization in an amount of at least 50% by weight of the total amount of monomer (HA) and monomer (CA) supplied during the reaction (i.e., initial charge plus continuous supply). 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 monomer (HA) and monomer (CA) is continuously supplied during polymerization. Even if this requirement is not essential, a gradually increasing addition of VDF monomer can be carried out during polymerization. Generally, the method of the present invention is carried out at a temperature of at least 30°C, preferably at least 35°C.

[0084] According to a preferred embodiment of the present invention, polymer (F) is of formula (III): -(R a ) x -RO-R b (III) (In the formula, RO is a divalent group containing at least one oxygen atom, R a R is a linear or branched hydrocarbon group of C1-C5, b (where x is a hydrogen atom or a linear or branched hydrocarbon group of C1-C5, and x is an integer selected from 1 and zero.) It includes the terminal group, The terminal groups are present in an amount of at least 1 / 10000 VDF units, preferably more than 1.5 / 10000 VDF units, and more preferably more than 2 / 10000 VDF units.

[0085] Non-restrictive examples of divalent RO include, in particular: Ether (-O-), Ester (-O-CO-), Ketone (-CO-), Epoxide, and Percarbonate (-O-CO-O-) group It includes.

[0086] In a further preferred embodiment of the present invention, RO is a divalent radical containing at least two oxygen atoms. More preferably, RO is a percarbonate group.

[0087] Preferably, R a and R b Both are linear or branched alkyl radicals of C2-C3, more preferably linear or branched alkyl radicals of C3.

[0088] Preferably, x is zero.

[0089] When polymerization is carried out in a suspension state, the polymer (F) is typically obtained in the form of a powder.

[0090] When polymer (F) powder particles are prepared by a suspension polymerization process, they have a size distribution with a D50 value of 10 to 1000 μm, preferably 10 to 500 μm.

[0091] When polymerization to obtain polymer (F) is carried out in an emulsion state, polymer (F) is typically provided in the form of an aqueous dispersion (D) and can be used either directly by emulsion polymerization or after a concentration step.

[0092] The polymer (F) obtained by emulsion polymerization can be isolated in solid form from the aqueous dispersion (D) by means known in the art, such as spray drying, freeze-drying, solidification, and drum drying, but is not limited to these methods.

[0093] The dried PVDF powder has an average particle size of 0.2 to 200 microns, preferably 0.3 to 50 μm, and more preferably 0.5 to 1 μm.

[0094] The polymer (F) in powder form may optionally be further extruded to obtain the polymer (F) in pellet form.

[0095] The binder (B) can be obtained by mixing both PTFE and polymer (F) in powder form, or by mixing PTFE latex and polymer (F) latex, followed by co-coagulation and isolation by cryogenic or electrolytic procedures.

[0096] To obtain the desired polymer ratio in the blend, the dry content of PTFE latex and / or polymer(F) latex can be evaluated by drying 50 grams of polymer latex at 200°C in a thermobalance.

[0097] Generally, the weight ratio of PTFE / polymer (F) will range from 95 / 5 wt / kg to 30 / 70 wt / kg. A person skilled in the art will select the most appropriate weight ratio considering the target final properties of the binder (B).

[0098] Surprisingly, the applicant found that the amount of polymer (F) added to PTFE does not affect the ability of PTFE to fibrillate.

[0099] In another embodiment, the present invention relates to an electrode-forming composition [Composition (C)] for use in the fabrication of electrodes for electrochemical devices, a) At least one type of electrode active material (AM), b) A binder (B) as defined above, c) At least one optional conductive agent and The present invention provides an electrode-forming composition [Composition (C)] containing the following:

[0100] The amount of binder (B) that can be used in the electrode-forming composition (C) is influenced by various factors. One such factor is the surface area and amount of the active material, as well as the surface area and amount of the conductivity-imparting additive added to the electrode-forming composition. These factors are considered important because the binder particles provide a bridge between the conductive material particles, keeping them in contact.

[0101] The electrode-forming composition [Composition (C)] of the present invention contains one or more electrode active materials (AM). For the purposes of the present invention, the term "electrode active material" is intended to mean a compound that can incorporate or insert alkali or alkaline earth metal ions into its structure during the charging and discharging stages of an electrochemical cell and then substantially release them. The electrode active material can preferably incorporate or insert lithium ions and release them.

[0102] The properties of the electrode active material in the electrode-forming composition (C) of the present invention differ depending on whether the composition is used for the production of a negative electrode (anode) or a positive electrode (cathode).

[0103] When forming a positive electrode for a lithium-ion secondary battery, the electrode active material can include a composite metal chalcogenide of the formula LiMQ2 (where M is at least one metal selected from transition metals such as Co, Ni, Fe, Mn, Cr, and V, and Q is a chalcogen such as O or S). Among these, it is preferable to use a lithium-based composite metal oxide of the formula LiMO2 (where 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.

[0104] As an alternative, when forming a positive electrode for a lithium-ion secondary battery, further, the electrode active material is of the formula M1M2(JO4) f E 1-fThe formula may include a lithified or partially lithified transition metal oxyanion system electroactive material (wherein M1 is lithium, which may be partially substituted by another alkali metal corresponding to less than 20% of the M1 metal; M2 is a transition metal with an oxidation level of +2 selected from Fe, Mn, Ni or mixtures thereof, which may be partially substituted by one or more further metals with oxidation levels of +1 to +5, corresponding to less than 35% of the M2 metal, including 0; JO4 is any oxyanion; J is any of P, S, V, Si, Nb, Mo or a combination thereof; E is a fluoride, hydroxide, or chloride anion; and f is typically the mole fraction of the JO4 oxyanion contained in 0.75 to 1).

[0105] M1M2(JO4) as defined above f E 1-f The electroactive material is preferably phosphate-based and may have an ordered or modified olivine structure.

[0106] More preferably, the electrode active material when forming the positive electrode is Li 3-x M' y M'' 2-y (JO4)3 (wherein 0≦x≦3 and 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 with another oxyanion, and J is any of S, V, Si, Nb, Mo or a combination thereof). More preferably, the electrode active material is of the formula Li(Fe x Mn 1-x The electroactive material is a phosphate-based material of PO4 (wherein 0 ≤ x ≤ 1, and x is preferably 1) (i.e., lithium iron phosphate of the formula LiFePO4).

[0107] When forming a negative electrode for a lithium-ion secondary battery, the electrode active material may preferably include one or more carbon-based materials and / or one or more silicon-based materials.

[0108] In some embodiments, the carbon-based material may be selected from graphite, graphene, or carbon black, such as natural or artificial graphite. These materials may be used alone or in mixtures of two or more.

[0109] The carbon-based material is preferably graphite.

[0110] 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.

[0111] More specifically, the silicon-based compound may be silicon oxide or silicon carbide.

[0112] When present in the electrode active material, the silicon-based compound is included in an amount ranging from 1 to 60% by weight, preferably 5 to 30% by weight, relative to the total weight of the electroactive compound.

[0113] One or more optionally selected conductivity-imparting additives may be added to improve the conductivity of electrodes produced from the compositions of the present invention. Conductives for batteries are well known in the art.

[0114] Examples include carbon-based materials such as carbon black, graphite powder, carbon nanotubes, graphene, or fibers, or metal powders or fibers 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®.

[0115] If present, the conductive agent is different from the carbon-based material mentioned above.

[0116] The amount of the optional conductive agent is preferably 0 to 30% by weight of the total solids in the electrode-forming composition. In particular, for the cathode-forming composition, the optional conductive agent is typically 0% to 10% by weight, more preferably 0% to 5% by weight, of the total solids in the composition.

[0117] For anode-forming compositions that do not contain silicon-based electroactive compounds, the optional conductive agent is typically 0% to 5% by weight, more preferably 0% to 2% by weight, of the total solid content in the composition. In contrast, for anode-forming compositions that contain silicon-based electroactive compounds, it has been found that it is beneficial to introduce a larger amount of the optional conductive agent, typically 0.5% to 30% by weight, of the total solid content in the composition.

[0118] The electrode-forming composition (C) can be prepared by thoroughly mixing at least one electrode active material (AM), a binder (B), and at least one optionally conductive agent.

[0119] Mixing under high shear force involves fibrillation of binder particles to generate fibrils that ultimately form a matrix or lattice to support the resulting composition. The resulting dough-like material can be calendered multiple times to produce a conductive film of desired thickness and density. High shear force can be provided by subjecting the mixture to an extruder.

[0120] The electrode-forming composition (C) of the present invention can be used in a method for manufacturing an electrode [electrode (E)], and the method is as follows: - A) To obtain a binder (B) by combining polytetrafluoroethylene (PTFE) and the fluoropolymer [polymer (F)] defined above. - B) Dry grinding of at least one electrode active material (AM), a binder (B) as defined above, and at least one optional conductive agent in the absence of a solvent. - C) The powdered dry mixture obtained in step B) is supplied to a compressor to form a self-supporting dry film, and - D) Laminating a dried film onto a conductive substrate in a calender to form an electrode. Includes.

[0121] In step B), the mixing of the electrode active material (AM), the binder (B) as defined above, and at least one optional conductive agent is carried out by dry mixing these components without adding any solvents, liquids, or processing aids to the particle mixture. Dry mixing may be carried out, for example, in a mill, mixer, or blender (such as a V-blender equipped with a high-strength stirring rod or other alternative devices as further described below) until a uniform dry mixture is formed. Those skilled in the art will recognize, after reading this specification, that the mixing time may vary based on batch size, material, particle size, density, and other characteristics, and still remain within the scope of the present invention.

[0122] In step C) of the method of the present invention, the powdered dry mixture obtained in step B) is subjected to a physical compression step to obtain a self-supporting dry film.

[0123] The compression of the dry mixture obtained in step B) may be carried out as physical compression, for example, by a roller press or a tablet press, but it may also be carried out as rolling, build-up, or by any other technique suitable for this purpose.

[0124] The mechanical compression process may be related to the thermal consolidation process. The combination of pressurization and heat treatment allows for thermal consolidation at a lower temperature than if it were performed alone.

[0125] In one embodiment, the mechanical compression step is carried out by compression, preferably by compressing the dry mixture obtained in step B) between two metal foils. Preferably, the mechanical compression step is carried out by applying a compression pressure of 5 to 50 MPa, preferably 10 to 30 MPa.

[0126] The compression process is preferably carried out at a temperature not exceeding 120°C, preferably in the range of 40 to 100°C.

[0127] The compression step C) may be repeated multiple times as appropriate to obtain a homogeneous film having the target thickness.

[0128] In step D), the dried film obtained in step C) is laminated onto a conductive substrate in a calender to form electrodes.

[0129] The substrate material sheet may include metal foil, particularly aluminum foil.

[0130] For improved adhesion of the binder (B), the dried film obtained in step C) can be applied to a conductive substrate without the need for any primer or adhesive layer.

[0131] It has been found that randomly incorporating specific crosslinkable monomers into a vinylidene fluoride backbone yields a crosslinkable vinylidene fluoride copolymer, and when this copolymer is mixed with PTFE and thermally crosslinked during the lamination step (D) of the method of the present invention, an electrode with significantly higher adhesion to the current collector can be obtained compared to electrodes obtained by a dry process using PTFE and PVDF that are not modified to crosslink.

[0132] As used herein, “heat treatment,” “thermally crosslinked,” and “thermally occurring” are understood to mean that the crosslinking process of the present invention is activated solely by temperature.

[0133] The lamination process (D) is carried out in a calender, and the dried film obtained in process (C) has a very short residence time between the calender rolls. This short residence time, combined with the high temperature of the calender process, has the effect of not giving the polymer (F) time to completely melt, but the polymer (F) is exposed for a short time to a temperature at a level at least sufficient to activate crosslinking.

[0134] Those skilled in the art will recognize that the time required to achieve crosslinking is generally temperature-dependent, with crosslinking occurring more rapidly as the temperature rises. The residence time in the calendar can be appropriately varied from 10 seconds to 30 days depending on the temperature and the properties of the polymer (F), which is sufficient to achieve crosslinking but does not completely melt the polymer (F).

[0135] Thermal crosslinking involves a reaction between at least some of the hydroxyl groups of the repeating unit derived from monomer (HA) and at least some of the carboxyl groups of the repeating unit derived from monomer (CA).

[0136] The electrode (E) of the present invention is particularly suitable for use in electrochemical devices, especially in secondary batteries.

[0137] In one embodiment, the present invention provides an electrochemical device which is a secondary battery, and this secondary battery is - Positive electrode and negative electrode A secondary battery that includes, Here, at least one of the positive electrode and the negative electrode is electrode (E) according to the present invention.

[0138] Preferably, the electrochemical device is - Positive electrode and negative electrode It is a secondary battery that includes, Here, the positive electrode is electrode (E) according to the present invention.

[0139] The secondary battery of the present invention is preferably an alkaline secondary battery or an alkaline earth secondary battery.

[0140] The secondary battery of the present invention is more preferably a lithium-ion secondary battery.

[0141] The electrochemical device according to the present invention can be prepared by standard methods known to those skilled in the art.

[0142] If any disclosure of a patent, patent application, or publication incorporated herein by reference conflicts with the description of this application to such an extent that it obscures certain terms, the description herein shall prevail.

[0143] The present invention will be described below in relation to the following embodiments, the object being described is merely illustrative and not intended to limit the scope of the invention. [Examples]

[0144] raw materials PTFE: A PTFE homopolymer powder having a specific gravity of 2.18 as measured according to ASTM D792 and a rheometric pressure of 8.00 MPa as measured according to ASTM D4895.

[0145] Carbon Black, available as SC65 from Imerys SA.

[0146] NMC811 (COSMO Advanced Materials & Technology, D50=10.28μm).

[0147] Preparation of Polymer 1: PVDF homopolymer: In an 80L reactor equipped with an impeller rotating at a speed of 250 rpm, 52.4 kg of demineralized water and 0.4 g of hydroxypropyl methylcellulose (Dow's Methocel®-K100) were sequentially introduced per kg of VDF. Oxygen present in the reactor was removed at a fixed temperature of 20°C using a sequence of vacuum and nitrogen purging. This sequence was repeated three times.

[0148] Next, 41.38 g of a 75% solution of the initiator t-amyl perpivalate (from United Initiators) in isododecane and 250.02 g of diethyl carbonate were introduced into the reactor. Immediately afterward, the stirring speed was increased to 300 rpm, and 22.99 kg of VDF was added to the reactor. The reactor was then gradually heated until the setpoint temperature of 52°C was reached. The pressure was kept constant at 120 bar throughout the entire polymerization experiment using VDF. A total of 11.49 kg of VDF was added, and no further VDF was added. The temperature was then raised to 65°C, and after a total of 169 minutes, the reaction was stopped by degassing the suspension until atmospheric pressure was reached.

[0149] Next, the polymer was collected by filtration and suspended in clean water in a stirred tank. After washing, the polymer was dried overnight in a 65°C oven. 29.94 kg of dried powder was recovered.

[0150] The polymer has an intrinsic viscosity of 1:0.27 l / g and a T of 169.3°C. f2 A polymer having the following characteristics was obtained.

[0151] Preparation of polymer (A-1): A 4L reactor equipped with an impeller rotating at a speed of 650 rpm was sequentially introduced with 2,006 g of demineralized water, 0.5 g of hydroxypropyl methylcellulose (Methocel®-K100GR, from Dow) per 1 kg of VDF monomer, 0.4 g of ethylene oxide homopolymer (Alkox-E45®, from Alkoro) per 1 kg of total VDF monomer, and a solution of 59.91 g of trisodium phosphate (from Sigma Aldrich).

[0152] Oxygen present in the reactor was removed at a fixed temperature of 14°C using a sequence of vacuum and nitrogen purging. This sequence was repeated three times.

[0153] Next, 200 g of desalted water, 11.28 g of hydrogen peroxide (from Brenntag), and 3.53 g of ethyl chloroformate (from Framochem) were introduced into the reactor.

[0154] After 15 minutes, 0.14 g of hydroxyethyl acrylate (HEA), 0.28 g of acrylic acid (AA), and 1.166 g of VDF were added to the mixture at a stirring speed of 880 rpm. The reactor was then gradually heated until a first setpoint temperature of 45°C, corresponding to a reactor pressure of 120 bar, was reached.

[0155] The pressure was kept constant at 120 bar throughout the entire polymerization by supplying aqueous solutions containing 9.40 g of AA and 4.70 g of HEA per liter of solution. After 365 minutes, the polymerization was stopped by degassing the suspension until it reached atmospheric pressure. A total of 721 g of AA and HEA solution was introduced into the reactor.

[0156] Next, the polymer was collected by filtration and suspended in clean water in a stirred tank. After washing, the polymer was dried in an oven at 65°C for 12 hours. 919 g of dried powder was recovered.

[0157] Film formation By mixing all the components in an automatic mortar, a dry mixture containing 2.5% PTFE, 2.5% polymer 1 or polymer (A-1), 90% NMC, and 5% carbon black was obtained.

[0158] The resulting mixture was calendered six times at 40°C, and then four more times at 90°C to obtain a film with a uniform thickness of approximately 0.18 mm.

[0159] Lamination with a metal substrate The lamination process was carried out in a calender at a temperature of 200°C for 10 seconds. The material was passed through the calender six times for a total of 60 seconds.

[0160] Adhesion evaluation and measurement Adhesion was evaluated and measured between the film and aluminum foil obtained as described above, in accordance with ASTM D 1876, in the layered structure (film / metal foil) obtained after lamination. The adhesion values ​​are reported in Table 1.

[0161] [Table 1]

[0162] These data demonstrate that the binder of the present invention has dramatically improved adhesion to metal foils compared to binders containing PVDF homopolymer.

Claims

1. a. Polytetrafluoroethylene (PTFE) and; b. Fluoropolymer [polymer (F)], - (i) Repeating units derived from vinylidene fluoride (VDF) monomer, - (ii) Repeating units derived from at least one vinyl monomer (HA) of formula (I) R １ R ２ C=CR ３ -R ｘ (I) (wherein, R １ , R ２ and R ３ are the same as or different from each other, and are independently selected from a hydrogen atom, a halogen atom, and a C １ -C ５ hydrocarbon group, and R ｘ is a linear or branched hydrocarbon chain moiety of C ３ -C ２０ containing at least one aliphatic hydroxyl group), - (iii) Repeating units derived from at least one carboxyl group-containing vinyl monomer (CA) (where monomer (CA) is different from monomer (HA)), Fluoropolymers [polymers (F)] and A binder composition [binder (B)] for use in the manufacture of electrodes for electrochemical devices, characterized by containing the following: The total amount of monomers (HA) and (CA) in the polymer (F) is a maximum of 5.0 mol%, preferably a maximum of 1.5 mol%, relative to the total number of moles of repeating units of the polymer (F). At least 50% of the monomer (CA) is randomly distributed in the polymer (F), and the amount of randomly distributed monomer (CA) is determined as a percentage between the average number of VDF-(CA)-VDF sequences and the total average number of (CA) monomer repeating units. Binder composition [Binder (B)].

2. The binder (B) according to claim 1, wherein the polymer (F) comprises at least 60 mol%, more preferably at least 70 mol%, of repeating units derived from VDF with respect to all repeating units of the polymer (F).

3. The binder (B) according to claim 1 or 2, wherein the weight ratio of PTFE / polymer (F) is contained in a ratio of 95 / 5 weight / weight to 30 / 70 weight / weight.

4. The monomer (HA) is a compound of formula (I): R １ R ２ C=CR ３ -R ｘ (I) (In the formula, R １ , R ２ and R ３ These are either the same as or different from each other, and include hydrogen atoms, halogen atoms, and C １ ~C ５ Selected independently of hydrocarbon groups, R ｘ C contains at least one aliphatic hydroxyl group. ３ ~C ２０ The binder (B) according to any one of claims 1 to 3, wherein the monomer (HA) is a linear or branched hydrocarbon chain portion, which may optionally contain one or more oxygen atoms, carbonyl groups, or carboxyl groups in the chain, and preferably the monomer (HA) is selected from the group consisting of hydroxyethyl (meth)acrylate (HEA), 2-hydroxypropyl acrylate (HPA), hydroxyethylhexyl (meth)acrylate, and mixtures thereof.

5. The monomer (CA) is a compound of formula (II): 【Chemistry 1】 (In the formula, R １ , R ２ and R ３ They are either the same as or different from each other, and the hydrogen atom and C １ ~C ３ Selected independently of hydrocarbon groups, R Ｈ C contains at least one carboxyl group and does not contain an aliphatic hydroxyl group. ２ ~C １０ The binder (B) according to any one of claims 1 to 4, wherein the monomer (CA) is a hydrocarbon moiety, and preferably the monomer (CA) is selected from the group consisting of acrylic acid (AA), (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, (meth)acryloyloxyethyl succinic acid, (meth)acryloyloxypropyl succinic acid, and mixtures thereof.

6. Polymer (F) has terminal groups of formula (III): () ａ ) ｘ _____ ｂ (_=) (In the formula, RO is a divalent group containing at least one oxygen atom, R ａ C １ ~C ５ A linear or branched hydrocarbon group, R ｂ is hydrogen or C １ ~C ５ (A linear or branched hydrocarbon group, where x is an integer selected from 1 and zero.) Includes, The terminal group is present in an amount of at least 1 / 10000 VDF units, preferably more than 1.5 / 10000 VDF units, and more preferably more than 2 / 10000 VDF units. The binder (B) according to claim 5.

7. An electrode-forming composition [Composition (C)] for use in the fabrication of electrodes for electrochemical devices, a) At least one type of electrode active material (AM), b) A binder (B) according to any one of claims 1 to 6, c) at least one optional conductive agent and An electrode-forming composition [Composition (C)] characterized by containing the following.

8. A method for manufacturing electrodes [electrodes (E)] for electrochemical cells, - A) To obtain a binder (B) by combining polytetrafluoroethylene (PTFE) and a fluoropolymer [polymer (F)], - B) Dry grinding of at least one electrode active material (AM), a binder (B) as defined above, and at least one optional conductive agent in the absence of a solvent. - C) The powdered dry mixture obtained in step B) is supplied to a compressor to form a self-supporting dry film, and - D) Laminating a dried film onto a conductive substrate in a calender to form an electrode. A method that includes this.

9. The method according to claim 8, wherein in step B), the dry mixing is carried out, for example, in a mill, mixer or blender until a uniform dry mixture is formed.

10. The method according to claim 8, wherein step C) is performed at a temperature not exceeding 120°C.

11. An electrode (E) for a secondary battery, which can be obtained by the method described in any one of claims 8 to 10.

12. An electrochemical device, such as a secondary battery, comprising at least one electrode (E) as described in claim 11.

13. The aforementioned electrochemical device - Positive electrode and negative electrode It is a secondary battery that includes, The electrochemical device according to claim 12, wherein at least one of the positive electrode and the negative electrode is the electrode (E) according to claim 11.

14. The aforementioned electrochemical device - Positive electrode and negative electrode It is a secondary battery that includes, The electrochemical device according to claim 13, wherein the positive electrode is the electrode (E) described in claim 11.

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