Battery electrode and method for manufacturing the same

Abstract

The present invention relates to an electrode composition containing PTFE and a crosslinkable fluororesin composition, 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. 23181469.0, 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 containing PTFE and a crosslinkable fluororesin composition, 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 produced using PTFE can be higher than that of electrodes produced using other binders.

[0006] For example, a dry electrode manufacturing process may include combining a PTFE binder with an active electrode 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] In the art, methods are known for improving the adhesion of PTFE to current collectors and electrode active materials by using a combination of PTFE and 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 on a metal current collector using rollers heated to a predetermined temperature, and adhering the rolled granular powder to the current collector by the pressure and temperature of the rollers. In the method described in U.S. Patent No. 11,276,846, at least one of the first binder and the second binder contained in the granular powder can be attached when it melts.

[0008] International Publication No. 2021 / 023709 discloses that a specific blend of a first VDF-based polymer having a side chain containing a hydroxyl group and a second VDF-based polymer containing repeating units derived from acrylic acid can be thermally crosslinked after the electrode-forming composition is cast onto a current collector in a solvent-based slurry electrode manufacturing process, resulting in an electrode with improved performance, particularly in terms of adhesion to metals.

[0009] Surprisingly, the applicant has found that when manufacturing electrodes by an efficient dry process that includes a calendering step on a substrate, selecting a specific blend of crosslinkable VDF copolymer with PTFE significantly improves the adhesion of the electrode film to the current collector. [Overview of the project]

[0010] Therefore, in this specification, a binder composition [binder (B)] for use in the manufacture of electrodes for electrochemical devices, I. Polytetrafluoroethylene (PTFE) and II. Fluoropolymer composition [Composition (F)], (a) - (ai) Repeating units derived from vinylidene fluoride (VDF) monomer, - (aii) Repeating units derived from at least one hydroxyl group-containing vinyl monomer (HA) of formula (I): R1R2C=CR3-R x (I) (In the formula, R1, R2, and R3 are either the same as or different from each other, independently selected from a hydrogen atom, a halogen atom, and a C1-C5 hydrocarbon group, and Rx is a C2-C5 hydrocarbon group containing at least one aliphatic hydroxyl group) 20 (A linear or branched hydrocarbon chain moiety which may be optionally substituted), A first fluoropolymer [polymer (FA)] comprising at least one such polymer, wherein the total amount of repeating units derived from monomer (HA) in the polymer (FA) is at most 10.0 mol%, preferably at most 5.0 mol%, and more preferably at most 1.5 mol%, relative to the total number of moles of repeating units in the polymer (FA), and is characterized by at least 40% of randomly distributed monomer (HA) fractions, and (b) - (bi) Repeating units derived from vinylidene fluoride (VDF) monomer, - (bii) Repeating units derived from at least one carboxyl group-containing acrylic monomer (CA) of formula (II): [ka] (In the formula, R1, R2, and R3 are either the same as or different from each other, and are independently selected from hydrogen atoms and C1-C3 hydrocarbon groups. H C1-C12 contains at least one carboxyl group. 10 (The hydrocarbon chain portion) A second fluoropolymer [polymer (FB)] different from polymer (FA), which includes, Unlike monomer (HA), The total amount of repeating units derived from the monomer (CA) in the polymer (FB) is at most 10.0 mol%, preferably at most 5.0 mol%, more preferably at most 1.5 mol% with respect to the total molar number of repeating units of the polymer (FB), a polymer (FB) characterized by a fraction of at least 40% of randomly distributed monomer (CA) a fluoropolymer composition [composition (F)] containing A binder composition [binder (B)] is provided, which is characterized by containing

[0011] In another aspect, the present invention is an electrode forming composition [composition (C)] for use in the preparation of an electrode for an electrochemical device, a) at least one electrode active material (AM), b) a binder (B) as defined above, c) optionally, at least one conductive agent An electrode forming composition [composition (C)] containing is provided.

[0012] The applicant has surprisingly found that the processability of the binder (B) is suitable for the production of electrodes by a dry process in a calender 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] Therefore, in another aspect, the present invention is a method for manufacturing an electrode [electrode (E)] for an electrochemical cell, - A) combining polytetrafluoroethylene (PTFE) and the fluoropolymer [polymer (F)] defined above to obtain a binder (B); - 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 powdery dry mixture obtained in step B) 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 electrodes; This provides a method that includes [something].

[0014] In another embodiment, the present invention provides an electrode (E) for a secondary battery, which can be obtained by the method defined above.

[0015] In a further embodiment, the present invention relates to an electrochemical device such as a secondary battery or capacitor, comprising at least one electrode (E) as defined above. [Modes 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 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 is a compound containing at least one aliphatic hydroxyl group which may be optionally substituted with at least ethers, ketones, epoxys, percarboxylates, and esters. 20 (The linear or branched hydrocarbon chain portion) It is a compound of [the compound].

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

[0031] In a preferred embodiment, the monomer (HA) has the formula (Ia):

Chemical formula

[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 are included.

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

[0034] A suitable carboxyl group-containing vinyl monomer (CA) has the formula (II):

Chemical formula

[0035] In a preferred embodiment, the monomer (CA) is of formula (IIa): [ka] (In the formula, R1, R2, and R3 are either the same as or different from each other, and are independently selected from hydrogen atoms and C1-C3 hydrocarbon groups, and R' H This is a C1-C5 hydrocarbon moiety containing hydrogen or at least one carboxyl group and not an aliphatic hydroxyl group. R' H (The chain may further contain one or more oxygen atoms, carbonyl groups, or ester groups.) It is a compound of [the compound].

[0036] 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, These mixtures These are some examples.

[0037] Preferably, at least one monomer (CA) is acrylic acid (AA).

[0038] In preferred embodiments of the present invention, monomer (CA) is acrylic acid, and monomer (HA) does not contain a carboxyl group.

[0039] The weight ratio of polymer (FA) to polymer (FB) in composition (C) may be 5:95 to 95:5, and preferably 20:80 to 80:20.

[0040] The weight ratio between polymer (FA) and polymer (FB) in composition (C) is preferably such that the molar ratio between repeating units (aii) and repeating units (bii) in composition (C) falls within the range of 20:1 to 1:20, preferably 10:1 to 1:10.

[0041] In polymers (FA), it is essential that at least 40% of the fraction consists of randomly distributed units (HA), and in polymers (FB), it is essential that at least 40% of the fraction consists of randomly distributed units (CA).

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

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

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

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

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

[0047] Similarly, when a polymer (FB) is prepared by a polymerization reaction that involves the continuous supply of monomers (CA) during VDF polymerization, a random distribution of monomers (CA) exists in the polymer chain, resulting in a VDF-(CA)-VDF sequence.

[0048] More preferably, in the polymer (FB), at least 70% of the monomers (CA) are randomly distributed within the polymer (FB).

[0049] 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.

[0050] 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.

[0051] The determination by analysis of the total amount of monomers (HA) in randomly distributed polymers (FA) and monomers (CA) in polymers (FB) 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.

[0052] The fractions of units (HA) and (CA) randomly distributed in polymer (FA) and polymer (FB), respectively, are preferably at least 50%, and more preferably at least 60%.

[0053] The polymer (FA) preferably contains at least 0.05 mol%, more preferably at least 0.2 mol%, of repeating units derived from the monomer (HA).

[0054] The polymer (FA) preferably contains up to 5.0 mol%, more preferably up to 5.0 mol%, and even more preferably up to 3.0 mol%, of repeating units derived from the monomer (HA).

[0055] The polymer (FB) preferably contains at least 0.05 mol%, more preferably at least 0.2 mol%, of repeating units derived from the monomer (CA).

[0056] The polymer (FB) preferably contains up to 7.0 mol%, more preferably up to 5.0 mol%, and even more preferably up to 3.0 mol%, repeating units derived from the monomer (CA).

[0057] Both polymers (FA) and (FB) may independently be elastomers or semi-crystalline polymers.

[0058] Preferably, both polymer (FA) and polymer (FB) are semicrystalline polymers.

[0059] As used herein, the term “semicrystalline” 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, semicrystalline fluoropolymer is intended herein to mean a fluoropolymer having a heat of fusion of at least 0.4 J / g, preferably at least 0.5 J / g, and more preferably at least 1 J / g, as determined according to ASTM D3418.

[0060] 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.

[0061] 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.

[0062] Preferably, the intrinsic viscosity of both polymer (FA) and polymer (FB) is measured in dimethylformamide at 25°C. Preferably, polymer (FA) has an intrinsic viscosity of 0.05 l / g to 0.50 l / g, more preferably 0.10 l / g to 0.40 l / g, and polymer (FB) has an intrinsic viscosity of 0.15 l / g to 0.55 l / g, even more preferably 0.20 l / g to 0.50 l / g.

[0063] Both polymer (FA) and polymer (FB) may further contain repeating units derived from one or more fluorinated comonomers (CF) different from VDF.

[0064] The term "fluorinated comonomer (CF)" is intended herein to mean an ethylenically unsaturated comonomer containing at least one fluorine atom.

[0065] 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) C2-C8 hydrogenated monofluoroolefins such as vinyl fluoride, 1,2-difluoroethylene and trifluoroethylene; (c) Perfluoroalkylethylene of formula CH2=CH-RRf0 (wherein RRf0 is a C1-C6 perfluoroalkyl group); (d) Chloro- and / or bromo- and / or iodo-C2~C6 fluoroolefins, e.g., chlorotrifluoroethylene (CTFE).

[0066] The fluorinated comonomer (CF) in polymer (FA) and polymer (FB) is preferably HFP.

[0067] In one preferred embodiment, polymer (FA) and polymer (FB) are semicrystalline.

[0068] In embodiments of the present invention, at least one of the polymer (FA) or polymer (FB) may contain 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).

[0069] It is understood that chain ends, defects, or other impurity types may be present in the polymer (FA) or polymer (FB), but these do not impair its properties.

[0070] The polymer (FA) is more preferably: - At least 70 mol%, preferably at least 75 mol%, more preferably at least 85 mol%, vinylidene fluoride (VDF), - 0.05 mol% to 3.0 mol%, preferably 0.05 mol% to 1.5 mol%, more preferably 0.15% to 1.0 mol%, of at least one hydroxyl group-containing vinyl monomer (HA) Includes repeating units derived from, - Optionally, repeating units derived from at least one fluorinated comonomer (CF) in an amount of 0.5 to 3.0 mol% are also included.

[0071] The polymer (FB) is more preferably: - At least 70 mol%, preferably at least 75 mol%, more preferably at least 85 mol%, vinylidene fluoride (VDF), - 0.05 mol% to 3.0 mol%, preferably 0.05 mol% to 1.5 mol%, more preferably 0.15 mol% to 1.0 mol%, of at least one hydroxyl group-containing vinyl monomer (CA), Includes repeating units derived from, - Optionally, it also includes 0.5 to 3.0 mol% of repeating units derived from at least one fluorinated comonomer (CF).

[0072] Polymers (FA) and polymers (FB) can be obtained by polymerization of a VDF monomer with at least one optionally comonomer (CF) and at least one monomer (HA) and at least one monomer (CA), respectively, in a suspension in an organic medium or in an aqueous emulsion typically carried out as 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, in accordance with the procedure described in International Publication No. 2008129041.

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

[0074] A procedure for preparing a polymer (FB) comprises polymerizing vinylidene fluoride (VDF) monomer, monomer (CA), and an optional comonomer (CF) in an aqueous medium in the presence of a radical initiator in a reaction vessel, wherein the method comprises continuously supplying an aqueous solution containing monomer (CA).

[0075] 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.

[0076] 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.

[0077] 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.

[0078] The initiator may be added in pure form, as a solution, as a suspension, or as an emulsion, depending on the initiator selected.

[0079] 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.

[0080] 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.

[0081] During polymerization to prepare polymer (FA) or polymer (FB), it is essential to maintain a continuous supply of an aqueous solution containing either monomer (HA) or monomer (CA).

[0082] In this format, it is possible to obtain a nearly statistical distribution of monomers (HA) in polymer (FA) and monomers (CA) in polymer (FB) within the polymer backbone of the VDF monomer polymer.

[0083] The expression "continuous supply" or "continuously supplied" means that the slow, small, and gradually increasing addition of aqueous solution of monomer (HA) or monomer (CA) is carried out over most of the polymerization time until at least 70 mol% of VDF monomer is converted.

[0084] The aqueous solution of monomer (HA) or monomer (CA) continuously supplied during polymerization is at least 50% by weight of the total amount of monomer supplied during the reaction for the preparation of polymer (FA) or polymer (FB) (i.e., the initial amount plus the 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) or monomer (CA) is supplied continuously during polymerization. Even if this requirement is not essential, the gradual increase in the addition of VDF monomer can be carried out during polymerization.

[0085] Typically, the process for preparing the polymer (FA) and polymer (FB) of the present invention is carried out at a temperature of at least 35°C, preferably at least 40°C, and more preferably at least 45°C.

[0086] When polymerization to obtain either polymer (FA) or polymer (FB) is carried out in a suspension, polymer (FA) and polymer (FB) are typically supplied in powder form.

[0087] When polymerization to obtain either polymer (FA) or polymer (FB) is carried out in an emulsion, polymer (FA) and polymer (FB) are typically supplied in the form of aqueous dispersions, aqueous dispersion (DA), and aqueous dispersion (DB), respectively, which can be used directly after emulsion polymerization or after a concentration step. Preferably, the solid content of polymer (FA) and polymer (FB) in dispersion (DA) and dispersion (DB) is in the range of 20 to 50% by weight, respectively.

[0088] The polymers (FA) and (FB) obtained by emulsion polymerization can be isolated from the aqueous dispersion (DA) and dispersion (DB), respectively, by concentration and / or coagulation of the dispersion, and can then be obtained in powder form by drying.

[0089] By selectively further extruding the polymer (FA) and polymer (FB), pellet-shaped polymers (FA) and polymer (FB) can be obtained.

[0090] Extrusion is performed appropriately in the extruder. The duration of extrusion is appropriately in the range of a few seconds to 3 minutes.

[0091] According to a preferred embodiment of the present invention, at least one of polymer (FA) or polymer (FB) 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.

[0092] 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.

[0093] In a more preferred embodiment of the present invention, RO is a divalent radical containing at least two oxygen atoms. More preferably, RO is a percarbonate group.

[0094] Preferably, R a and R bBoth are linear or branched alkyl radicals of C2-C3, more preferably linear or branched alkyl radicals of C3.

[0095] Preferably, x is zero.

[0096] When polymerization is carried out in a suspension state, polymer (FA) and polymer (FB) are typically supplied in powder form.

[0097] When polymer (FA) and polymer (FB) 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.

[0098] When polymerization to obtain polymer (FA) or polymer (FB) is carried out in an emulsion state, the polymer is typically supplied in the form of an aqueous dispersion (D), which can be used directly from the emulsion polymerization or after a concentration step.

[0099] The polymer (FA) or polymer (FB) 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, although this does not limit the polymers obtained by emulsion polymerization.

[0100] When polymer (FA) and polymer (FB) powder particles are prepared by a suspension polymerization process, they have a size distribution with a D50 value of 0.25 to 200 microns, preferably 0.3 to 20 microns, and more preferably 0.5 to 1 micron.

[0101] By selectively further extruding the polymer (FA) and polymer (FB) in powder form, pellet-form polymer (FA) and polymer (FB) can be obtained.

[0102] Polymers (FA) and (FB) are typically supplied in powder form according to the process described above.

[0103] 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 and then co-coagulating and isolating them by cryogenic or electrolytic procedures.

[0104] To obtain the desired polymer ratio in the blend, the dry content of PTFE latex and / or composition (F) latex can be evaluated by drying 50 grams of polymer latex at 200°C in a thermobalance.

[0105] Typically, the weight ratio of PTFE / polymer (F) will fall within the range of 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).

[0106] Surprisingly, the applicant found that the amount of composition (F) added to PTFE does not affect the ability of PTFE to fibrillate.

[0107] In another embodiment, the present invention provides an electrode-forming composition [Composition (C)] for use in the manufacture of electrodes for electrochemical devices, a) At least one type of electrode active material (AM), b) A binder (B) as defined above, c) Optionally, at least one conductive agent and The present invention provides an electrode-forming composition [Composition (C)] containing the following:

[0108] 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.

[0109] 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 and then substantially release them during the charging and discharging stages of an electrochemical cell. The electrode active material can preferably incorporate or insert lithium ions and release them.

[0110] 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).

[0111] 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.

[0112] As an alternative form, 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).

[0113] 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.

[0114] 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).

[0115] 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.

[0116] In some embodiments, the carbon-based material may be selected from graphite, graphene, or carbon black, such as natural or artificial graphite. These materials can be used individually or as a mixture of two or more of them.

[0117] The carbon-based material is preferably graphite.

[0118] 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.

[0119] More specifically, the silicon-based compound may be silicon oxide or silicon carbide.

[0120] 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.

[0121] One or more optional conductivity-imparting additives may be added to improve the conductivity of electrodes produced from the compositions of the present invention. Conductives for batteries are known in the art.

[0122] 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®.

[0123] If present, the conductive agent is different from the carbon-based material mentioned above.

[0124] 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.

[0125] 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.

[0126] The electrode-forming composition (C) can be prepared by thoroughly mixing at least one electrode active material (AM), a binder (B), and optionally at least one conductive agent.

[0127] Mixing under high shear force involves fibrillation of binder particles to produce 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.

[0128] 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) Combining polytetrafluoroethylene (PTFE) with the fluoropolymer [polymer (F)] defined above to obtain a binder (B); - 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) Supply the powdered dry mixture obtained in step B) 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 electrodes; Includes.

[0129] In step B), the mixing of the electrode active material (AM), the binder (B) as defined above, and optionally at least one 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.

[0130] 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.

[0131] The compression of the dry mixture obtained in step B) may be carried out as physical compression, for example, by a roller compressor or tablet press, but it may also be carried out as rolling, build-up, or by any other technique suitable for this purpose.

[0132] 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.

[0133] 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.

[0134] The compression process is conveniently carried out at a temperature above 120°C, preferably in the range of 40°C to 100°C.

[0135] Compression step C) can be repeated multiple times, if appropriate, to obtain a homogeneous film of the desired thickness.

[0136] In step D), the dried film obtained in step C) is laminated onto a conductive substrate in a calender to form electrodes.

[0137] The base material sheet may include metal foil, particularly aluminum foil.

[0138] 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.

[0139] By blending specific VDF copolymers in which specific crosslinkable monomers are randomly incorporated into the backbone, a blend of crosslinkable vinylidene fluoride copolymers is obtained, which is miscible with PTFE, and it has been found that thermal crosslinking during the lamination step (D) of the method of the present invention yields electrodes with significantly higher adhesion to the current collector compared to electrodes obtained by a dry process using PVDF that has not been modified to crosslink with PTFE.

[0140] 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.

[0141] 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 calendering process, has the effect of exposing the composition (F) to a temperature level that is not long enough for it to completely melt, but at least sufficient to activate crosslinking.

[0142] 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 composition (F), which is sufficient to achieve crosslinking but not sufficient for composition (F) to completely melt.

[0143] Thermal crosslinking involves a reaction between at least a portion of the hydroxyl groups of the repeating units derived from the monomer (HA) of the polymer (FA) and at least a portion of the carboxyl groups of the repeating units derived from the monomer (CA) in the polymer (FB).

[0144] The electrode (E) of the present invention is particularly suitable for use in electrochemical devices, especially in secondary batteries.

[0145] 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.

[0146] 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.

[0147] The secondary battery of the present invention is preferably an alkaline secondary battery or an alkaline earth secondary battery.

[0148] The secondary battery of the present invention is more preferably a lithium-ion secondary battery.

[0149] The electrochemical device according to the present invention can be prepared by standard methods known to those skilled in the art.

[0150] 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.

Claims

1. A binder composition [binder (B)] for use in the manufacture of electrodes for electrochemical devices, I. Polytetrafluoroethylene (PTFE) and II. Fluoropolymer composition [Composition (F)], (a) - (ai) Repeating units derived from vinylidene fluoride (VDF) monomer, - (aii) Repeating unit derived from at least one hydroxyl group-containing 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 selected from a hydrogen atom, a halogen atom, and a C １ -C 5 hydrocarbon group, and Rx is a linear or branched, optionally substituted C ２ -C ２０ hydrocarbon chain moiety containing at least one aliphatic hydroxyl group), and A first fluoropolymer [polymer (FA)] comprising at least one such polymer (FA), wherein the total amount of repeating units derived from monomer (HA) in the polymer (FA) is at most 10.0 mol%, preferably at most 5.0 mol%, and more preferably at most 1.5 mol%, relative to the total number of moles of repeating units in the polymer (FA). A polymer (FA) characterized in that the fraction of randomly distributed monomer (HA), determined as a percentage between the average number of the VDF-(HA)-VDF sequence and the total average number of (HA) monomer repeating units, is at least 40%, and (b) - (bi) Repeating units derived from vinylidene fluoride (VDF) monomer, - (biii) Repeating units derived from at least one carboxyl group-containing acrylic monomer (CA) 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 is a C containing at least one carboxyl group. １ ~C １０ (This is the hydrocarbon chain portion) A second fluoropolymer [polymer (FB)] different from polymer (FA), which includes, Unlike monomer (HA), The total amount of repeating units derived from monomers (CA) in the polymer (FB) is a maximum of 10.0 mol%, preferably a maximum of 5.0 mol%, and more preferably a maximum of 1.5 mol%, relative to the total number of moles of repeating units in the polymer (FB). A polymer (FB) characterized in that the fraction of randomly distributed monomers (CA), determined as a percentage between the average number of sequences in the VDF-(CA)-VDF and the total average number of repeating (CA) monomer units, is at least 40%. A fluoropolymer composition [Composition (F)] containing, A binder composition [binder (B)] characterized by containing the following.

2. The binder (B) according to claim 1, wherein the weight ratio of PTFE / composition (F) is contained in an amount of 95 / 5 weight / weight to 30 / 70 weight / weight.

3. The monomer (HA) is 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 independently, hydrogen atoms, halogen atoms, and C １ ~C ５ Selected from hydrocarbon groups, R ｘ C comprises at least one aliphatic hydroxyl group and may optionally contain one or more oxygen atoms, carbonyl groups, or carboxyl groups in the chain. ３ ~C ２０ The binder (B) according to claim 1 or 2, which is a compound of the linear or branched hydrocarbon chain portion of , 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.

4. The monomer (CA) is of formula (II): 【Chemistry 2】 (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 3, wherein the monomer (CA) is a compound of the 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.

5. At least one of polymers (FA) or polymers (FB) is 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.) It includes the terminal group, 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 4.

6. The binder (B) according to any one of claims 1 to 5, wherein the molar ratio of polymer (FA) to polymer (FB) in composition (F) is within 5:95 to 95:5, preferably within 20:80 to 80:

20.

7. An electrode-forming composition [Composition (C)] for use in preparing 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) Optionally, at least one 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 composition (F); - B) Dry grinding at least one electrode active material (AM), the binder (B) as defined above, and optionally at least one conductive agent in the absence of a solvent; - C) Supplying the powdered dry mixture obtained in step B) to a compressor to form a self-supporting dry film; and - D) Laminating the dried film onto a conductive substrate in a calender to form the 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 9, wherein step C) is carried out 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. - 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) according to claim 11.

Images