secondary batteries

Abstract

The present invention relates to separators for electrochemical devices comprising vinylidene fluoride copolymers having improved thermal stability, methods for making same, and electrochemical devices containing same.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to European Patent Application Publication No. 19315080.2, filed July 29, 2019, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to separators for electrochemical devices comprising vinylidene fluoride copolymers having improved thermal stability, methods for making same, and electrochemical devices containing same. [Background technology]

[0003] Lithium-ion batteries have become an indispensable part of human daily life. In the context of sustainable development, lithium-ion batteries are expected to play a more important role as they are increasingly being used in electric vehicles and renewable energy storage.

[0004] Separator layers are a key component of a battery. These layers help prevent contact between the battery's anode and cathode while allowing the electrolyte to pass through them.

[0005] The performance of a separator in a lithium-ion battery is determined by several requirements, such as porosity, chemical stability, electrical insulation, wettability, dimensional stability, and resistance to degradation by chemical agents and electrolytes. Furthermore, the separator should have good thermal stability to withstand temperature peaks during long-term operation and battery use.

[0006] Vinylidene fluoride (VDF) polymers are known in the art to be suitable for the manufacture of composite separators and as coatings for porous separators for use in non-aqueous electrochemical devices such as batteries, preferably secondary batteries.

[0007] For example, Lee et al., J. Polym. Sci. Part B Polym. Phys. 2013, 51, 349-357, discloses the coating of a polypropylene microporous separator with electrospun nanoparticles of polyvinylidene fluoride-co-chlorotrifluoroethylene (PVDF-co-CTFE). However, the PVDF-co-CTFE copolymer is characterized by poor thermal stability, which is lower than that of the PVDF homopolymer.

[0008] VDF polymers are also known for the preparation of binders for electrodes. WO 2008 / 129041 (SOLVAY SPECIALTY POLYMERS ITALY SPA) discloses VDF copolymers containing repeating units derived from at least one (meth)acrylic comonomer and at least another fluorinated comonomer different from VDF as binders for electrodes, which impart very good adhesion of the electrodes to the current collector.

[0009] Adhesion between the separator and electrodes is another important feature in battery assembly, which can improve battery performance characteristics and ease of handling during manufacturing.

[0010] EP 2631974 (SAMSUNG SDI) proposes improving the adhesive strength between the negative electrode and the separator in a lithium battery by coating at least one surface of the separator with a PVDF homopolymer layer, where the negative electrode binder comprises a VDF-based copolymer.

[0011] It appears that there is a problem in the art of batteries, and particularly lithium batteries, to provide a coated separator that can provide good, outstanding adhesion to the separator substrate material and at the same time improves the adhesion of the separator to the electrodes, has good lamination strength, electrical conductivity, and thermal stability similar to or better than the electrode polymer binder. Summary of the Invention

[0012] The applicant was therefore faced with the problem of providing a polymer suitable for coating the substrate material of a separator for an electrochemical cell, said polymer being such that it simultaneously provides outstanding adhesion to the separator base material and improved adhesion of the coated separator to the electrodes, thus improving the long-term performance of the battery.

[0013] Surprisingly, applicants have found that the above problems can be solved when a separator for an electrochemical cell is at least partially coated with a vinylidene fluoride-chlorotrifluoroethylene copolymer comprising repeat units derived from hydrophilic (meth)acrylic monomers randomly distributed throughout the entire vinylidene fluoride-chlorotrifluoroethylene copolymer backbone.

[0014] Thus, in a first aspect, the present invention relates to a coated separator for an electrochemical device comprising a substrate layer (P) at least partially coated with a vinylidene fluoride copolymer (polymer (F)) obtained by copolymerizing vinylidene fluoride (VDF), chlorotrifluoroethylene (CTFE) and at least one hydrophilic (meth)acrylic monomer (MA) continuously fed into a reactor during copolymerization.

[0015] Surprisingly, the presence of repeat units derived from hydrophilic (meth)acrylic monomers randomly distributed throughout the vinylidene fluoride-chlorotrifluoroethylene copolymer backbone improves the thermal stability of the vinylidene fluoride-chlorotrifluoroethylene copolymer itself.

[0016] In a second aspect, the present invention relates to a method for the preparation of a coated separator for an electrochemical device as defined above, comprising: i) providing an uncoated substrate layer (P); ii) providing a coating composition (composition (C)) comprising a vinylidene fluoride copolymer (polymer (F)) obtained by copolymerizing vinylidene fluoride (VDF), chlorotrifluoroethylene (CTFE) and at least one hydrophilic (meth)acrylic monomer (MA), the at least one hydrophilic (meth)acrylic monomer (MA) being continuously fed into a reactor during copolymerization; iii) at least partially applying the coating composition (C) of step ii) onto at least one portion of the substrate layer (P); iv) drying the at least partially coated substrate layer (P) of step iii); The present invention relates to a method comprising:

[0017] In a further aspect, the present invention relates to an electrochemical device comprising a coated separator as defined above. DETAILED DESCRIPTION OF THE INVENTION

[0018] In the context of the present invention, the term "weight percent" (wt%) refers to the content of a particular component in a mixture, calculated as the ratio between the weight of the particular component and the total weight of the mixture. When referring to repeating units derived from a certain monomer in a polymer / copolymer, weight percent (wt%) refers to the ratio between the weight of the repeating units of such monomer divided by the total weight of the polymer / copolymer. When referring to the total solids content (TSC) of a liquid composition, weight percent (wt%) refers to the ratio between the weights of all non-volatile components in the liquid.

[0019] The term "separator," as used herein, is intended to mean a porous, single-layer or multi-layer polymeric material that electrically and physically separates electrodes of opposite polarity in an electrochemical cell and permits ion flow therebetween.

[0020] The term "electrochemical cell" is intended herein to mean an electrochemical cell comprising a positive electrode, a negative electrode and a liquid electrolyte, with a single or multi-layer separator adhered to at least one surface of one of the electrodes.

[0021] Non-limiting examples of electrochemical cells include batteries, preferably secondary batteries, and electric double layer capacitors, among others.

[0022] For purposes of the present invention, "secondary battery" is intended to mean a rechargeable battery. Non-limiting examples of secondary batteries include alkaline or alkaline earth secondary batteries, among others.

[0023] In the context of the present invention, the term "substrate layer" is intended herein to mean either a monolayer substrate consisting of a single layer or a multilayer substrate comprising at least two layers adjacent to each other.

[0024] The substrate layer (P) can be made of any porous substrate or fabric commonly used for separators in electrochemical devices, including at least one material selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, polyethylene, and polypropylene, or a mixture thereof. Preferably, the substrate layer (P) is polyethylene or polypropylene.

[0025] The term "(meth)acrylic monomer" as used herein includes acrylic acid and / or methacrylic acid, esters of acrylic acid or methacrylic acid, and derivatives and mixtures thereof.

[0026] The term "at least one hydrophilic (meth)acrylic monomer (MA)" is understood to mean that the polymer (A) may comprise repeat units derived from one or more hydrophilic (meth)acrylic monomers (MA) as described above. In the remainder of the specification, the expressions "hydrophilic (meth)acrylic monomer (MA)" and "monomer (MA)" are understood for the purposes of the present invention both in the plural and in the singular, i.e., they are understood to mean one or more both hydrophilic (meth)acrylic monomers (MA).

[0027] The hydrophilic (meth)acrylic monomer (MA) preferably has the formula (I): [ka] (In the formula, R1, R2 and R3, which are equal to or different from each other, are independently selected from a hydrogen atom and a C1-C3 hydrocarbon group; and R OH is a hydrogen atom or a C1-C5 hydrocarbon moiety containing at least one hydroxyl group and / or at least one carboxylic acid group) Follow.

[0028] More preferably, the hydrophilic (meth)acrylic monomer (MA) is preferably of formula (II): [ka] (In the formula, R1, R2, R OH each of R1, R2, R3 has the meaning as defined above, and R3 is hydrogen; more preferably, each of R1, R2, R3 is hydrogen, while R OH have the same meaning as detailed above) Follow.

[0029] Non-limiting examples of hydrophilic (meth)acrylic monomers (MA) are, inter alia, acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate; hydroxyethylhexyl (meth)acrylate.

[0030] The monomer (MA) is more preferably - Formula: [ka] of hydroxyethyl acrylate (HEA), - Formula: [ka] 2-hydroxypropyl acrylate (HPA) of any one of the following: - Formula: [ka] of acrylic acid (AA), and - A mixture of these is selected among.

[0031] Most preferably, the monomer (MA) is AA and / or HEA.

[0032] The polymer (F) may further comprise other moieties such as defects, end groups, etc., which do not affect or impair its physicochemical properties.

[0033] The polymer (F) is semi-crystalline. The term semi-crystalline is intended to mean a polymer (F) having a detectable melting point. A semi-crystalline polymer (F) is generally understood to advantageously have a heat of fusion, measured according to ASTM D3418, of at least 0.4 J / g, preferably at least 0.5 J / g, more preferably at least 1 J / g.

[0034] Polymer (F) is a linear copolymer, i.e., it is composed of a macromolecule made up of a substantially linear sequence of repeating units from VDF, CTFE and (MA) monomers; polymer (F) is therefore distinguishable from grafted and / or comb polymers.

[0035] Polymer (F) preferably contains at least 0.05 mol %, more preferably at least 0.1 mol %, even more preferably at least 0.5 mol % of repeat units derived from CTFE.

[0036] Polymer (F) preferably comprises at most 10 mol %, more preferably at most 7 mol %, even more preferably at most 5 mol % of repeat units derived from CTFE.

[0037] The polymer (F) preferably comprises at least 0.05 mol %, more preferably at least 0.1 mol %, even more preferably at least 0.2 mol % of repeat units derived from said hydrophilic (meth)acrylic monomer (MA).

[0038] The polymer (F) preferably comprises at most 2 mol %, more preferably at most 1.8 mol %, even more preferably at most 1.5 mol % of repeat units derived from said hydrophilic (meth)acrylic monomer (MA).

[0039] In a more preferred embodiment, the polymer (F) contains repeating units derived from CTFE in an amount ranging from 0.5 to 10 mol % and repeating units derived from the hydrophilic (meth)acrylic monomer (MA) in an amount ranging from 0.2 to 1.5 mol %.

[0040] In a more preferred embodiment of the present invention, the repeating units derived from the hydrophilic (meth)acrylic monomer (MA) of formula (I) are contained in the polymer (F) in an amount of 0.2 to 1 mol % relative to the total number of moles of the repeating units of the polymer (F), and the repeating units derived from the CTFE monomer are contained in the polymer (F) in an amount of 0.5 to 4 mol % relative to the total number of moles of the repeating units of the polymer (F).

[0041] More preferably, the hydrophilic (meth)acrylic monomer (MA) is a hydrophilic (meth)acrylic monomer of formula (II), even more preferably it is acrylic acid (AA) and the polymer (F) is a VDF-AA-CTFE terpolymer.

[0042] The polymer (F) advantageously has an intrinsic viscosity, measured in dimethylformamide at 25° C., greater than 0.15 l / g and at most 0.60 l / g, preferably comprised in the range from 0.20 to 0.50 l / g and more preferably in the range from 0.25 to 0.40 l / g.

[0043] The preparation of polymer (F) is a process for producing a vinylidene fluoride copolymer, comprising the step of copolymerizing vinylidene fluoride (VDF), chlorotrifluoroethylene (CTFE) and at least one hydrophilic (meth)acrylic monomer (MA), the at least one hydrophilic (meth)acrylic monomer (MA) being added continuously to the VDF and CTFE during copolymerization.

[0044] The expressions "continuous feeding", or "continuous addition", or "continuous feeding" mean that slow, small, incremental additions of an aqueous solution of hydrophilic (meth)acrylic monomer (MA) are made until polymerization is complete.

[0045] The polymer (F) thus obtained has a high uniformity of the monomer (MA) in the polymer backbone, which advantageously maximizes the influence of the modifying monomer (MA) on both the adhesive and / or hydrophilic behavior of the resulting copolymer.

[0046] In addition, the Applicant has surprisingly found that the presence of the monomer (MA) uniformly distributed in the polymer (F) has the effect of improving the thermal stability of the VDF-CTFE copolymer, which is otherwise unsatisfactorily low, in particular lower than that of the VDF homopolymer.

[0047] The polymer (F) is typically obtained by emulsion or suspension polymerization of at least one VDF monomer, at least one hydrogen-containing (meth)acrylic monomer (MA) and CTFE, for example according to the procedures described in WO 2008 / 129041.

[0048] In a second aspect, the present invention relates to a method for the preparation of a coated separator for an electrochemical device as defined above.

[0049] In step ii) of the process, a composition (C) is provided comprising a polymer (F) as defined above.

[0050] The composition (C) preferably comprises a polymer (F) as defined above and a solvent (S).

[0051] The choice of solvent (S) is not particularly limited, provided that it is suitable for solubilizing the polymer (F).

[0052] The solvent (S) is typically alcohols such as methyl alcohol, ethyl alcohol and diacetone alcohol, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone and isophorone, linear or cyclic esters such as isopropyl acetate, n-butyl acetate, methyl acetoacetate, dimethyl phthalate and gamma-butyrolactone, linear or cyclic amides such as N,N-diethylacetamide, N,N-dimethylacetamide, dimethylformamide and N-methyl-2-pyrrolidone, and - Dimethyl sulfoxide is selected from the group consisting of:

[0053] Composition (C) may further comprise at least one wetting agent and / or at least one surfactant and one or more additional additives.

[0054] Composition (C) may further comprise at least one non-electroactive inorganic filler material.

[0055] The term "non-electroactive inorganic filler material" is intended herein to mean a non-conductive inorganic filler material that is suitable for the manufacture of electrically insulating separators for electrochemical cells.

[0056] The non-electroactive inorganic filler material in the separator according to the present invention typically has an electrical resistivity (p) of at least 0.1×10 ohm-cm, preferably at least 0.1×10 ohm-cm, measured at 20° C. according to ASTM D 257.

[0057] Non-limiting examples of suitable non-electroactive inorganic filler materials include natural and synthetic silica, zeolites, alumina, titania, metal carbonates, zirconia, silicon phosphates and silicates, among others.

[0058] Composition (C) can be prepared by any method known in the art, such as by a method comprising mixing polymer (F) with solvent (S).

[0059] In step iii) of the method of the present invention, the composition (C) obtained in step ii) is at least partially applied to at least one portion of said substrate layer (P) by a technique selected from casting, spray coating, rotary spray coating, roll coating, doctor blading, slot die coating, gravure coating, inkjet printing, spin coating and screen printing, brush, squeegee, foam applicator, curtain coating, vacuum coating.

[0060] The present invention also relates to an electrochemical device comprising a coated separator as defined above, a positive electrode and a negative electrode.

[0061] Preferably, the electrochemical device is a secondary battery, preferably a lithium secondary battery.

[0062] In a preferred embodiment of the present invention, the lithium secondary battery comprises: - a coated separator as defined above; - a positive electrode; - negative electrode and At least one of the positive electrode and the negative electrode is an electrode containing an electrode active material and a binder, and the binder is a vinylidene fluoride (VDF) copolymer [polymer (A)]; - repeating units derived from vinylidene fluoride (VDF); - repeat units derived from acrylic acid in an amount of 0.05 to 10 mol %; - optionally, repeat units derived from at least one perhalogenated monomer (FM) in an amount of 0.5 mol % to 5.0 mol %, preferably 1.5 to 4.5 mol %, more preferably 1.5 mol % to 3.0 mol %, and even more preferably 2.0 to 3.0 mol %, relative to the total molar amount of repeat units in said polymer (A); The polymer (A) contains a vinylidene fluoride (VDF) copolymer.

[0063] In a more preferred embodiment of the present invention, the lithium secondary battery comprises: - a coated separator as defined above, in which the polymer (F) is a VDF-AA-CTFE terpolymer; - a positive electrode; - negative electrode and At least one of the positive electrode and the negative electrode is an electrode containing an electrode active material and a binder, and the binder is a vinylidene fluoride (VDF) copolymer [polymer (A)]; - repeating units derived from vinylidene fluoride (VDF); - repeat units derived from acrylic acid in an amount of 0.05 to 10 mol %; - optionally, repeat units derived from at least one perhalogenated monomer (FM) in an amount of 0.5 mol % to 5.0 mol %, preferably 1.5 to 4.5 mol %, more preferably 1.5 mol % to 3.0 mol %, and even more preferably 2.0 to 3.0 mol %, relative to the total molar amount of repeat units in said polymer (A); The polymer (A) contains a vinylidene fluoride (VDF) copolymer.

[0064] The polymer (A) is semi-crystalline. The term semi-crystalline is intended to mean a polymer (A) that has a detectable melting point. A semi-crystalline polymer (A) is generally understood to advantageously have a heat of fusion, measured according to ASTM D3418, of at least 0.4 J / g, preferably at least 0.5 J / g, more preferably at least 1 J / g.

[0065] Polymer (A) is composed of a macromolecule made up of a substantially linear sequence of repeating units from VDF monomer, acrylic acid and optionally monomer (FM); polymer (A) is therefore distinguishable from grafted and / or comb polymers.

[0066] Polymer (A) preferably comprises at least 0.05 mol %, more preferably at least 0.1 mol %, even more preferably at least 0.5 mol % of repeat units derived from monomer (FM).

[0067] The polymer (A) preferably contains at most 10 mol %, more preferably at most 7 mol %, even more preferably at most 5 mol % of repeat units derived from the monomer (FM).

[0068] Non-limiting examples of suitable monomers (FM) include, among others: - C2-C8 perfluoroolefins such as tetrafluoroethylene and hexafluoropropylene (HFP); - C2-C8 hydrogen-containing fluoroolefins such as vinyl fluoride, 1,2-difluoroethylene and trifluoroethylene; - Formula CH2=CH-R f0 (In the formula, R f0 is a C1-C6 perfluoroalkyl) perfluoroalkylethylene; - chloro- and / or bromo- and / or iodo-C2-C6 fluoroolefins, such as chlorotrifluoroethylene (CTFE); - Formula CF2=CFOR f1 (In the formula, R f1 is C1-C6 fluoro- or perfluoroalkyl, for example, CF3, C2F5, C3F7), (per)fluoroalkyl vinyl ethers; CF2=CFOX0(per)fluoro-oxyalkyl vinyl ether (wherein X0 is C1-C 12 Alkyl groups, C1-C 12 C1-C with one or more ether groups such as oxyalkyl groups or perfluoro-2-propoxy-propyl groups 12 (per)fluorooxyalkyl groups; - Formula CF2=CFOCF2OR f2 (In the formula, R f2 is a C1-C6 fluoro- or perfluoroalkyl group, for example a C1-C6 (per)fluorooxyalkyl group having one or more ether groups such as CF3, C2F5, C3F7 or -C2F5-O-CF3); Formula CF2 = CFOY0 (wherein Y0 is C1 to C 12 Alkyl group or (per)fluoroalkyl group, C1-C 12 C1-C having an oxyalkyl group or one or more ether groups 12 (per)fluorooxyalkyl groups, Y0 containing a carboxylic or sulfonic acid group in the form of its acid, acid halide or salt); fluorodioxoles, preferably perfluorodioxoles Examples include:

[0069] The fluorinated monomer (FM) is preferably chlorotrifluoroethylene (CTFE) or hexafluoropropylene (HFP).

[0070] The polymer (A) may further comprise other moieties such as defects, end groups, etc., which do not affect or impair its physicochemical properties.

[0071] Suitable polymers (A) are typically prepared as described in the art (see, for example, WO 2008 / 129041 and WO 2019 / 101806).

[0072] In a preferred embodiment of the present invention, the polymer (A) is a VDF-AA copolymer.

[0073] In another preferred embodiment of the present invention, the polymer (A) is a VDF-AA-CTFE terpolymer.

[0074] In a preferred embodiment of the present invention, the lithium secondary battery comprises: - a coated separator comprising a substrate layer (P) at least partially coated with a polymer (F), the polymer (F) being VDF-AA-CTFE, wherein the repeating units derived from AA are contained in an amount of 0.2 to 1 mol % relative to the total moles of the repeating units of the polymer (F), and the repeating units derived from CFTE are contained in an amount of 0.5 to 4 mol % relative to the total moles of the repeating units of the polymer (F); - a positive electrode; - negative electrode and At least one of the positive electrode and the negative electrode is an electrode comprising an electrode active material and a binder, and the binder comprises a VDF-AA copolymer.

[0075] In an even more preferred embodiment of the present invention, the lithium secondary battery comprises: - a coated separator comprising a substrate layer (P) at least partially coated with a polymer (F), the polymer (F) being VDF-AA-CTFE, wherein the repeating units derived from AA are contained in an amount of 0.2 to 1 mol % relative to the total moles of the repeating units of the polymer (F), and the repeating units derived from CTFE are contained in an amount of 0.5 to 4 mol % relative to the total moles of the repeating units of the polymer (F); - a positive electrode; - negative electrode and At least one of the positive electrode and the negative electrode is an electrode containing an electrode active material and a binder, and the binder contains a vinylidene fluoride (VDF) copolymer [polymer (A)] which is a VDF-AA-CTFE terpolymer.

[0076] The applicant has surprisingly found that the adhesion between the at least partially coated separator of the present invention and at least one electrode is greatly enhanced when the binder of at least one of the positive and negative electrodes comprises polymer (A).

[0077] Without being bound by any theory, the inventors believe that the presence of acrylic monomer structures, i.e., polymers comprising hydrophilic (meth)acrylic monomers (MA) and acrylic acid monomers, respectively, both in the separator coating and in the electrode binder, is responsible for the improved compatibility between the separator and the electrode, thus resulting in greatly enhanced adhesion between the at least partially coated separator of the present invention and the electrode.

[0078] The positive and negative electrodes prepared by using a binder comprising the polymer (A) as defined above can be prepared according to any procedure known to those skilled in the art.

[0079] When the polymer (A) is used as a binder for an electrode, a binder solution of the polymer (A) is generally prepared.

[0080] The organic solvent used to dissolve the polymer (A) and provide the binder solution of the present invention is preferably polar, and examples thereof include N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphamide, dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, and trimethyl phosphate. Since the vinylidene fluoride polymer used in the present invention has a degree of polymerization much higher than that of conventional polymers, it is more preferable to use a nitrogen-containing organic solvent with greater dissolving power, such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, or N,N-dimethylacetamide, among the above organic solvents. These organic solvents can be used alone or in a mixture of two or more species.

[0081] To obtain a binder solution of the polymer (A) described above, it is preferable to dissolve 0.1 to 10 parts by weight, particularly 1 to 5 parts by weight, of the copolymer (A) in 100 parts by weight of such an organic solvent. If the amount is less than 0.1 part by weight, the polymer will occupy too little of the solution and will therefore be unable to demonstrate its ability to bind the powdered electrode material. If the amount is more than 10 parts by weight, the solution will have an abnormally high viscosity, which will not only make the preparation of the electrode-forming composition difficult, but also make it difficult to avoid gelation.

[0082] To prepare a polymer (A) binder solution, it is preferable to dissolve the copolymer (A) in an organic solvent at a high temperature of 30 to 200° C., more preferably 40 to 160° C., and even more preferably 50 to 150° C. If the temperature is lower than 30° C., dissolution takes a long time, making it difficult to achieve uniform dissolution.

[0083] An electrode-forming composition can be obtained by adding and dispersing a powdered electrode material (an active material for a battery or an electric double layer capacitor) and optional additives such as a conductivity-imparting additive and / or a viscosity modifier into the polymer (A) binder solution thus obtained.

[0084] When forming a positive electrode for a lithium ion battery, the active material may include a composite metal chalcogenide represented by the general formula LiMY2 (where M represents at least one chemical species of transition metals such as Co, Ni, Fe, Mn, Cr, and V; and Y represents a chalcogen such as O or S). Among these, it is preferable to use a lithium-based composite metal oxide represented by the general formula LiMO2 (where M is the same as above). Preferred examples thereof include LiCoO2, LiNiO2, LiNi x Co 1-x O2 (0 < x < 1) and spinel-structured LiMn2O4 may be mentioned.

[0085] Alternatively, when further forming a positive electrode for a lithium ion battery, the active material has the nominal formula AB(XO4) f [[ID=1十一]]E 1-f (where A is lithium, which may be partially substituted by another alkali metal representing less than 20% of the A metal, B is the main redox transition metal at the +2 oxidation level selected from Fe, Mn, Ni, or a mixture thereof, which may be partially substituted by one or more additional metals representing less than 35% of the main +2 redox metal including at oxidation levels from +1 to +5 and 0, XO4 is any oxyanion where X is any of P, S, V, Si, Nb, Mo, or a combination thereof, E is a fluoride, hydroxide, or chloride anion, and f is the mole fraction of the XO4 oxyanion, generally included in the range of 0.75 to 1 (including extreme values)) of a lithiated or partially lithiated transition metal oxyanion-based electrode material.

[0086] The above AB(XO4) f E[[ID=2十]] 1-f The active material is preferably phosphate-based and may have a regular or modified olivine structure.

[0087] More preferably, the active material as described above has the formula Li 3-x M’ y M’’ 2-y(XO4)3, where 0≦x≦3, 0≦y≦2, and M′ and M″ are the same or different metals, at least one of which is a redox transition metal; XO4 is primarily PO4, which may be partially substituted with another oxyanion, where X is P, S, V, Si, Nb, Mo, or a combination thereof. Even more preferably, the active material has the nominal formula Li(Fe x Mn 1-x )PO4, where 0≦x≦1, where x is preferably 1 (i.e., lithium iron phosphate of formula: LiFePO4).

[0088] When forming a negative electrode for a lithium battery, the active material may preferably include a carbon-based material and / or a silicon-based material.

[0089] In some embodiments, the carbon-based material can be, for example, graphite, such as natural or artificial graphite, graphene, or carbon black.

[0090] These materials may be used alone or as a mixture of two or more of them.

[0091] The carbon-based material is preferably graphite.

[0092] The carbonaceous material may be used preferably in the form of particles having an average diameter of about 0.5 to 100 μm.

[0093] The silicon-based compound may be one or more selected from the group consisting of chlorosilane, alkoxysilane, aminosilane, fluoroalkylsilane, silicon, silicon chloride, silicon carbide, and silicon oxide. More particularly, the silicon-based compound may be silicon oxide or silicon carbide.

[0094] When present, the at least one silicon-based compound is contained in the active material in an amount ranging from 1 to 30% by weight, preferably from 5 to 10% by weight, based on the total weight of the active material.

[0095] In particular, when using active materials such as LiCoO or LiFePO that exhibit limited electrical conductivity, a conductivity-imparting agent may be added to improve the electrical conductivity of the resulting composite electrode layer formed by applying and drying the electrode-forming composition of the present invention. Examples of such agents include carbonaceous materials such as carbon black, graphite fine powder and fiber, and metal fine powders and fibers such as nickel and aluminum.

[0096] The active material for the electric double layer capacitor preferably has an average particle (or fiber) diameter of 0.05 to 100 μm and a fiber diameter of 100 to 3000 μm. 2 / g, i.e., having a relatively small particle (or fiber) diameter and a relatively large specific surface area compared to that of the active material for the battery.

[0097] To the extent that the disclosure of any patents, patent applications, and publications incorporated herein by reference contradicts the statements of this application to the extent that the term may be unclear, the statements of this application shall control.

[0098] The present invention will now be described in more detail with reference to the following examples, which are provided solely for the purpose of illustrating the present invention and are not intended to limit the scope of the present invention. [Example]

[0099] raw materials Polymer A-1: ​​Polymer A-1 obtained as described in WO 2008 / 129041, having an intrinsic viscosity of 0.30 l / g in DMF at 25°C and a T 2f VDF-AA (0.9 mol %) polymer with

[0100] Polymer A-2: Polymer A-2 obtained as described in WO 2008 / 129041, having an intrinsic viscosity of 0.35 l / g in DMF at 25°C and a T 2f VDF-AA (0.2 mol %) polymer with

[0101] Polymer (F-1): Intrinsic viscosity of 0.35 l / g in DMF at 25°C and T 2f VDF-AA (0.9 mol%)-CTFE (0.56 mol%) polymer having

[0102] Polymer (F-2): Intrinsic viscosity of 0.352 l / g in DMF at 25°C and T 2f VDF-AA (0.2 mol%)-CTFE (3.7 mol%) polymer having

[0103] Initiator (TAPPI): t-amyl-perpivalate in isododecane (75 wt % solution of t-amyl perpivalate in isododecane), commercially available from Arkema.

[0104] Suspending agent B1: Alcotex AQ38, a 38 g / l aqueous solution of Alcotex 80 in water: 80% hydrolyzed high molecular weight polyvinyl alcohol, commercially available from SYNTHOMER.

[0105] Suspending agent B2: Bermocoll® E230FQ from AkzoNobel.

[0106] Active material NMC: LiNi 0.6 Co 0.2 Mn 0.2 O2, commercially available from Umicore SA.

[0107] Conductive additive: C-NERGY TM SUPER C65 (SC-65), commercially available from Imerys Graphite & Carbon.

[0108] Measurement of polymer intrinsic viscosity The intrinsic viscosity (η) [dl / g] was calculated using an Ubbelhode viscometer based on the drop time at 25°C of a solution obtained by dissolving the polymer (A) in N,N-dimethylformamide at a concentration of about 0.2 g / dl, according to the following formula:

number

[0109] DSC analysis DSC analysis was performed according to the ASTM D 3418 standard; melting point (T f2 ) was determined at a heating rate of 10°C / min.

[0110] Preparation of Polymer F-1 Into a 4-liter reactor equipped with an impeller operating at a speed of 650 rpm, 1913 g of demineralized water and 1.6 g of suspending agent B1 per kg of Mni (initial monomer added to the reactor before the set-point temperature) were sequentially introduced. The reactor was purged at 20 °C with a series of vacuum (30 mmHg) and nitrogen purges. 4.57 g of TAPPI were then introduced. At a speed of 880 rpm, 0.44 g of acrylic acid (AA), 14 g of chlorotrifluoroethylene (CTFE), and 1348 g of vinylidene fluoride (VDF) were introduced. The reactor was gradually heated to the set-point temperature of 55 °C, and the pressure was fixed at 120 bar. The pressure was constantly kept equal to 120 bar by feeding 1041 g of an aqueous acrylic acid solution during the polymerization, with a concentration of acrylic acid fixed at 10.12 g per kg of water. After this feeding, no more water was introduced, the pressure began to drop, and the polymerization was stopped by degassing the reactor until atmospheric pressure was reached. A total conversion of the monomers at 86% was reached. The polymer thus obtained was then recovered, washed with demineralized water, and dried overnight at 65°C.

[0111] Preparation of Polymer F-2 An 80-liter reactor equipped with an impeller operating at 250 rpm was sequentially charged with 44.8 kg of demineralized water and 1.6 g of Suspending Agent B2 per kg of MnO (initial monomer added to the reactor before the set-point temperature). The reactor was purged with a series of vacuums (30 mmHg) and nitrogen purges at 20°C. Then, 37.47 g of TAPPI and 102.6 g of diethyl carbonate (DCE) were added. The stirring speed was increased to 300 rpm. Finally, 2.81 g of acrylic acid, 1.4 kg of chlorotrifluoroethylene (CTFE), and 26.6 kg of vinylidene fluoride (VDF) were charged to the reactor. The reactor was gradually heated to a set-point temperature of 55°C, and the pressure was fixed at 120 bar. The pressure was kept constant at 120 bar by feeding 20.6 kg g of an aqueous solution of acrylic acid at a concentration of 3.27 g of AA per kg of water. After this feeding, no further aqueous solution was introduced and the pressure began to drop. The polymerization was then stopped by degassing the reactor until atmospheric pressure was reached. A conversion of 87% of the comonomer was obtained. The polymer thus obtained was then recovered, washed with demineralized water and dried at 65 ° C.

[0112] Preparation of Comparative Polymer 1: The polymerization conditions and raw materials were those described in the preparation of polymer F-2, except that all of the acrylic acid was fed at the beginning of the polymerization. The pressure was kept constant at 120 bar by feeding demineralized water (instead of the acrylic acid solution) during the polymerization. After this feeding, no more water was introduced, and the pressure began to drop, and the polymerization was stopped by degassing the reactor until atmospheric pressure was reached. A conversion of 84% of the monomers was reached. The polymer thus obtained was then recovered, washed with demineralized water, and dried overnight at 65°C. 2f Therefore, the inventors have 2f is higher than that of F-2, it can also be concluded that the distribution is less random compared to F-2, which is typical of a non-uniform distribution of comonomer units in the polymer.

[0113] Thermal stability of PVDF homopolymer and VDF-CTFE copolymer TGA dynamics under nitrogen were carried out at a heating rate of 10° C. / min on the following polymers: Polymer a: a PVDF homopolymer having an intrinsic viscosity of about 0.1 l / g in DMF at 25°C; and Polymer b: a VDF-CTFE (8.4 mol %) polymer with an intrinsic viscosity of about 0.10 l / g in DMF at 25°C.

[0114] The temperatures at which the two polymers a and b lost 1%, 2% and 10% of their weight were recorded, and the results are shown in Table 1.

[0115] [Table 1]

[0116] The results show that the VDF-CTFE polymer, polymer b, has lower thermal stability compared to the PVDF homopolymer, polymer a.

[0117] thermal stability TGA analysis under nitrogen at 200° C. with a heating rate of 10° C. / min was carried out on polymers F-1 and F-2 and on polymers A-1 and A-2.

[0118] The results are shown in Table 2.

[0119] [Table 2]

[0120] The results show that polymers F-1 and F-2, for use in the separators of the present invention, have better thermal stability than polymers A-1 and A-2, used in the prior art as binders for electrodes.

[0121] chemical stability The chemical resistance of Polymer F-1 to basic substances was compared with that of Polymer A-1. Tests were performed on a 5 wt% solution of the polymer in NMP to which DEA ​​(diethylamine) was added in an amount to provide a concentration of 0.3 wt% in NMP. Polymer degradation (presence of conjugated double bonds) was observed after 4 hours using a UV-visible detector.

[0122] The results show that, expressed as a relative percentage, the degradation of polymer F-1 was 35% compared to that of polymer A-1.

[0123] General preparation of electrodes To compare the adhesive behavior of polymers F-1 and F-2 for use in the separators of the present invention with those commonly used in the art as electrode binders, i.e., polymers A-1 and A-2, a composition was prepared by premixing 14.9 g of an 8 wt % solution of polymers (F-1, F-2, A-1, and A-2) in NMP, 115.4 g of NMC, 2.4 g of SC-65, and 37.7 g of NMP in a centrifugal mixer for 10 minutes.

[0124] The mixture was then mixed using a high-speed disk impeller at 2000 rpm for 1 hour. The resulting composition was cast onto a 20 μm-thick Al foil using a doctor blade, and the resulting coating was dried in a vacuum oven at 90°C for approximately 70 minutes to obtain a cathode. The dried coating had a thickness of approximately 110 μm.

[0125] The positive electrode so obtained had the following composition: 97% by weight NMC, 1% by weight polymer, 2% by weight conductive additive.

[0126] Adhesion peel force method To evaluate the adhesion of the dried coating layer to the Al foil, a peel test was performed on the electrodes prepared as described above using the setup described in standard ASTM D903 at a speed of 300 mm / min at 20° C. The results are shown in Table 3.

[0127] [Table 3]

[0128] In view of the above, it was found that electrodes prepared by using polymer F-1 (wherein polymer F-1 has repeat units derived from monomer AA uniformly distributed in the polymer backbone) as a binder have much higher adhesion to metal foil than those obtained by using comparative polymer 1, which was prepared by adding AA all together at the start of the polymerization.

Claims

1. A coated separator for an electrochemical device, comprising a substrate layer (P) at least partially coated with a vinylidene fluoride copolymer (polymer (F)) obtained by copolymerizing vinylidene fluoride, chlorotrifluoroethylene and at least one hydrophilic (meth)acrylic monomer (MA), wherein the at least one hydrophilic (meth)acrylic monomer (MA) is continuously fed to a reactor during copolymerization, wherein the hydrophilic (meth)acrylic monomer (MA) is a compound represented by the formula (I): 【Chemical 1】 (In the formula, R 1 , R 2 and R 3 , which are equal to or different from each other, are independently selected from a hydrogen atom and a C 1 -C 3 hydrocarbon group; and R OH is a hydrogen atom or a C 1 -C 5 hydrocarbon moiety containing at least one hydroxyl group and / or at least one carboxylic acid group. Follow the method.

2. 2. The method of claim 1, wherein the substrate layer (P) comprises at least one material selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, polyethylene, and polypropylene, or mixtures thereof.

3. The hydrophilic (meth)acrylic monomer (MA) has the formula (II): 【Chemistry 2】 (wherein R1 and R2, which may be equal to or different from each other, are each a hydrogen atom and C １ ~C ３ are independently selected from hydrocarbon groups; R3 is hydrogen, and R ＯＨ is a C containing a hydrogen atom or at least one hydroxyl group and / or at least a carboxylic acid group １ ~C ５ hydrocarbon portion) The method of claim 1 according to

4. The hydrophilic (meth)acrylic monomer (MA) is - Formula: 【Chemistry 3】 of hydroxyethyl acrylate, - Formula: 【Chemistry 4】 2-hydroxypropyl acrylate of any one of the above - Formula: 【Chemistry 5】 of acrylic acid, and - their mixtures The method of claim 1 or 3, wherein the compound is selected from the group consisting of:

5. The method of claim 4, wherein the hydrophilic (meth)acrylic monomer (MA) is acrylic acid.

6. 6. The method of claim 5, wherein polymer (F) comprises repeat units derived from chlorotrifluoroethylene in an amount ranging from 0.5 to 10 mol % and repeat units derived from acrylic acid in an amount ranging from 0.2 to 1.5 mol %.

7. The method according to any one of claims 1 to 6, i) providing an uncoated substrate layer (P); ii) providing a coating composition (composition (C)) comprising vinylidene fluoride (polymer (F)) obtained by copolymerizing vinylidene fluoride, chlorotrifluoroethylene and at least one hydrophilic (meth)acrylic monomer (MA), the at least one hydrophilic (meth)acrylic monomer (MA) being continuously fed into a reactor during copolymerization; iii) at least partially applying the coating composition (C) of step ii) onto at least one portion of the substrate layer (P); iv) drying the at least partially coated substrate layer (P) of step iii); A method comprising:

8. The method of claim 7 , wherein the composition (C) further comprises a solvent (S).

9. 9. The method of claim 7 or 8, wherein composition (C) further comprises at least one wetting agent and / or at least one surfactant.

10. The method of any one of claims 7 to 9, wherein composition (C) further comprises at least one non-electroactive inorganic filler material.

11. - a coated separator prepared by the method according to any one of claims 1 to 6; - a positive electrode; - negative electrode and an electrochemical device comprising: at least one of a positive electrode and a negative electrode comprising an electrode active material and a binder, the binder being a vinylidene fluoride copolymer [polymer (A)]; - repeating units derived from vinylidene fluoride; - repeat units derived from acrylic acid in an amount of 0.05 to 10 mol %; - repeating units derived from at least one perhalogenated monomer (FM) in an amount of 0.5 mol % to 5.0 mol % relative to the total molar amount of repeating units in said polymer (A); A method for preparing an electrochemical device comprising a vinylidene fluoride copolymer [polymer (A)] comprising:

12. 12. The method of claim 11, wherein the coated separator comprises a substrate layer (P) at least partially coated with a vinylidene fluoride copolymer (polymer (F)) obtained by copolymerizing vinylidene fluoride, chlorotrifluoroethylene, and at least one hydrophilic (meth)acrylic monomer (MA), the at least one hydrophilic (meth)acrylic monomer (MA) being continuously fed into a reactor during copolymerization, wherein the monomer (MA) is acrylic acid.

13. 13. The process according to claim 11 or 12, wherein the monomers (FM) in the polymer (A) are selected from chlorotrifluoroethylene and hexafluoropropylene.

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