Non-linear vinylidene fluoride copolymer

Abstract

The present invention relates to a non-linear copolymer containing vinylidene fluoride (VDF) monomer, at least one functional comonomer, and optionally repeating units derived from at least one fluorinated ethylene comonomer. The non-linear fluorinated copolymer contains 0.01 to 3.0 mol% of repeating units derived from the functional comonomer. The non-linear fluorinated copolymer can be used as an electrode binder for a battery.

Description

Technical Field

[0001] The present invention relates to a novel non-linear functional vinylidene fluoride copolymer comprising vinylidene fluoride, one or more functional comonomers and one or more fluorinated ethylene-based comonomers, a production method, and its use as an electrode binder for a battery.

Background Art

[0002] Vinylidene fluoride copolymers have conventionally been used in applications that require special properties such as low surface energy, high chemical resistance, weather resistance, and electrochemical stability. There is a need for fluorinated polymers having modified properties imparted by functional groups, and which can increase those properties, particularly the adhesion to metal foils, especially the adhesion to foils used as current collectors in lithium ion secondary batteries.

[0003] However, due to the aggressive nature of fluorine-containing polymerization free radicals, it is difficult to directly add functional comonomer units into vinylidene fluoride copolymers during polymerization. In one example of a method for producing functionalized vinylidene fluoride copolymers, a functional comonomer (e.g., (meth)acrylic acid) is grafted onto a pre-formed vinylidene fluoride copolymer chain using methods known in the art. Such materials are developed for the purpose of improving the adhesion to metals, such as aluminum or copper, or hydrophilicity, while taking advantage of the mechanical properties and chemical inertness of poly(vinylidene fluoride) (PVDF) copolymer-based materials. As outlined in Heng, T., et.al., “Graft Modification of PVDF-Based Fluoropolymers”, Progress in Chemistry, 33(4), 2021, 596-609, in many cases, these materials are produced by surface functionalization of pre-formed PVDF materials to obtain graft copolymers. Such graft copolymers suffer from the drawback that grafting is generally limited to surface functionalization only. These types of materials are non-uniformly functionalized, their manufacturing process is limited to being carried out on already formed articles, and the stringent processes used may lead to chain scission, resulting in a decrease in the mechanical properties of the final material.

[0004] US8337725 discloses the copolymerization of at least one hydrophilic (meth)acrylic monomer of the following formula: [Chemical Formula] with vinylidene fluoride. Here, each of R1, R2, and R3 may be the same as or different from each other and is independently a hydrogen atom or a C1-C3 hydrocarbon group, and R OH is a C1-C5 hydrocarbon moiety containing hydrogen or at least one hydroxyl group. In this method, although a linear functional copolymer product is produced, the reaction time is quite long and the final productivity is low, resulting in an increase in cost.

[0005] US9434837 discloses an emulsion process in which an acid group-containing comonomer is added to polymerization at a temperature of 20 to 130 °C and a pressure of 280 to 20,000 kPa in an amount of up to 1.0% by weight based on the total monomers.

[0006] US9441054 discloses an emulsion polymerization of vinylidene fluoride containing a methacrylic monomer and having end groups of formula -CF2H and / or CH3 in an amount of at least 30 millimoles per kilogram of vinylidene fluoride repeating units.

[0007] US10079388 discloses an aqueous latex containing at least one vinylidene fluoride polymer containing repeating units derived from vinylidene fluoride and at least one (meth)acrylic monomer, produced by emulsion polymerization.

[0008] WO2018 / 092675 discloses a copolymer of vinylidene fluoride, chlorotrifluoroethylene and an acrylic acid derivative. The polymerization reaction time is described as 100 hours or less, and in representative examples, 32 hours and 19 hours at 28 °C are shown.

[0009] WO2018092677 (US2019 / 0326602) discloses an electrode mixture for a lithium-ion battery having a binder, wherein the binder composition includes a first copolymer of vinylidene fluoride and a polar group-containing compound and a second copolymer of vinylidene fluoride and chlorotrifluoroethylene.

[0010] WO2019 / 167338 (US20210047448) discloses a vinylidene fluoride polymer containing a first structural unit derived from vinylidene fluoride and a second structural unit derived from a monomer other than vinylidene fluoride. The monomer serving as the second structural unit is a primary amine, secondary amine, or tertiary amine having at least one of a hydroxyl group and a carboxyl group, and the content of the second structural unit is 0.05 to 20.0 mol%.

[0011] JP2019160651 discloses a vinylidene fluoride copolymer with an ethoxylated acrylate comonomer, having an intrinsic viscosity of 0.1 to 5.0 dL / g, produced by suspension polymerization.

[0012] The electrode is used in an energy storage device. The energy storage device is not particularly limited, and examples include batteries, capacitors, ultracapacitors, non-aqueous secondary batteries, and the like.

[0013] In this technology, nothing is mentioned about the functional vinylidene fluoride copolymers that result in a non-linear branched structure obtained by copolymerizing vinylidene fluoride and a functional comonomer, and their performance as binders for battery electrode compositions. In fact, US8337725 specifically teaches that linear vinylidene fluoride copolymers are highly desirable in this application.

[0014] Regarding the commercially available product (Solef® 5130) from Solvay, which is considered to be manufactured according to US8337725, it was revealed by detailed size exclusion chromatography (SEC) analysis to have a branched structure of 7% by weight. The branched structure is expressed as the weight percentage of the molar mass distribution and indicates a branch having a slope (α) of ≦0.5 in the log-intrinsic viscosity vs. molar mass Mark-Houwink plot (see Striegel, Yau, Kirkland, Bly, Modern Size-Exclusion Liquid Chromatography, 2nd ed. (2009)). The test method is described in the following Examples section. This product does not seem to be linear (defined as having less than 10% by weight of a branched structure).

[0015] Vinylidene fluoride copolymers are applied as binders for electrode products used in lithium-ion batteries. As the demand for higher battery performance increases, the need to reduce the binder content in the electrodes is also growing. To reduce the binder content, it is most important to improve the performance of the binder material. This performance can be measured by an adhesion test in which the devised electrode is subjected to a peel test. An increase in the peel value obtained from this test leads to an improvement in the binding performance, which may reduce the overall binder addition amount, increase the active material addition amount, and improve the battery capacity. Here, we present the use of non-linear vinylidene fluoride copolymers for this application, which exhibit excellent peel adhesion performance.

[0016] The present invention solves the above problems by providing a non-linear fluorinated copolymer comprising vinylidene fluoride, optionally a fluorinated ethylene comonomer, and a functional comonomer. We have found that copolymers of vinylidene fluoride / functional comonomers containing a branched structure (branches meaning ≧ 10 wt%) exhibit excellent adhesion to metal foils (measured as electrode peel strength). These copolymers are produced using a low-temperature initiator with a half-life temperature of 53 °C or less for 10 hours.

Summary of the Invention

[0017] The present invention relates to non-linear vinylidene fluoride copolymers comprising VDF, any fluorinated ethylene comonomer, and a functional comonomer. The present invention also relates to a suspension method for forming copolymers of vinylidene fluoride and one or more comonomers.

[0018] The present invention further contemplates a method for preparing a fluorinated copolymer in an aqueous reaction medium comprising the following: a) at least one low-temperature initiator, a stabilizer, at least vinylidene fluoride, and a functional comonomer, optionally a fluorinated comonomer b) starting the copolymerization of vinylidene fluoride and the aforementioned functional comonomer with stirring, heating, and superatmospheric pressure.

[0019] The present invention further relates to articles formed from fluorinated copolymers. These articles are used in applications such as electrodes or separators of batteries.

[0020] The present invention further relates to a formulation comprising a vinylidene fluoride copolymer in a solvent, and further comprising activated carbon and metal chalcogenide particles selected from the group consisting of lithium iron phosphate (LFP), lithium nickel manganese cobalt oxide (NMC), lithium manganese cobalt oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, and lithium nickel manganese oxide.

[0021] Aspects of the present invention Aspect 1. A non-linear fluorinated copolymer, comprising at least 87.0 mol% of vinylidene fluoride, 0.01 to 3.0 mol% of a formula 1:

Chemical formula

[0022] Aspect 2. A non-linear fluorinated copolymer of Aspect 1, wherein the fluorinated ethylenic comonomer is selected from the group consisting of tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE), and hexafluoropropene (HFP).

[0023] Aspect 3. A non-linear fluorinated copolymer of Aspect 1 or 2, wherein at least one functional comonomer comprises Formula 1 where R4 is hydrogen.

[0024] Aspect 4. A non-linear fluorinated copolymer of any one of Aspects 1 to 3, wherein at least one functional comonomer comprises acrylic acid.

[0025] Aspect 5. A non-linear fluorinated copolymer of any one of Aspects 1 to 4, wherein the functional comonomer content incorporated in the polymer is 0.01 to 2.0 mol% of the entire non-linear fluorinated copolymer.

[0026] Aspect 6. A non-linear fluorinated copolymer of any one of Aspects 1 to 5, wherein the fluorinated ethylenic comonomer constitutes up to 10.0 mol%, preferably up to 5.0 mol% of the total monomer units of the non-linear fluorinated copolymer.

[0027] Aspect 7. A non-linear fluorinated copolymer of any one of Aspects 1 to 6, wherein the fluorinated ethylenic comonomer comprises HFP.

[0028] Aspect 8. A non-linear fluorinated copolymer of any one of Aspects 1 to 7, wherein the fluorinated ethylenic comonomer comprises at least 90.0 mol% of VDF and 0.1 to 9.99 mol% of HFP.

[0029] Aspect 9. A non-linear fluorinated copolymer according to any one of Aspects 1 to 8, wherein the viscosity of a solution of N-methyl-2-pyrrolidone containing 9.0% by weight of the aforementioned non-linear vinylidene fluoride polymer is measured at 23 °C at a controlled shear rate of 3.36 revolutions per second and is 4000 mPa·s or more and less than 45000 mPa·s, preferably 5000 mPa·s or more and less than 30000 mPa·s, and most preferably 5000 mPa·s or more and less than 20000 mPa·s.

[0030] Aspect 10. A non-linear fluorinated copolymer according to any one of Aspects 1 to 9, wherein the proportion of randomly distributed functional comonomer is less than 37%.

[0031] Aspect 11. A method for producing a non-linear fluorinated copolymer according to any one of Aspects 1 to 10, wherein the method comprises, in a suspension polymerization process, vinylidene fluoride and 0.01 to 3.0 mol% based on the total monomer feed of at least one functional comonomer of Formula 1: [Chemical Formula] (wherein each of R1, R2, and R3 may be the same as or different from each other and is independently a hydrogen atom or a C1-C3 hydrocarbon group, and R4 is hydrogen or a C1-C hydrocarbon moiety containing at least one hydroxyl group) 16 [Hydrocarbon moiety] and optionally at least one fluorinated ethylenic comonomer are polymerized at a temperature of 20 to 70 °C, preferably 35 to 60 °C, in the presence of a low-temperature initiator, where the low-temperature initiator has a half-life temperature of 53 °C or less, preferably 51 °C or less, in 10 hours.

[0032] Aspect 12. The method of Aspect 11, wherein the low-temperature initiator comprises at least one of n-propyl peroxydicarbonate (NPP), isopropyl peroxydicarbonate (IPP), acetyl cyclohexane sulfonyl peroxide, or diisobutyryl peroxide.

[0033] Aspect 13. The method of Aspect 11 or 12, wherein the low-temperature initiator is added to the reaction mixture in an amount of about 0.01 to about 5.0% by weight, preferably about 0.05 to about 2.5% by weight, based on the total monomer weight.

[0034] Aspect 14. The method of any one of Aspects 11 to 13, wherein the pressure during polymerization is 280 to 40,000 kPa, preferably 2,000 to 20,000 kPa.

[0035] Aspect 15. The method of any one of Aspects 11 to 14, wherein the functional comonomer is continuously added to the polymerization.

[0036] Aspect 16. The method of any one of Aspects 11 to 14, wherein the functional comonomer is discontinuously added to the polymerization.

[0037] Aspect 17. A composition for a lithium-ion battery comprising any one of Aspects 1 to 10 of a non-linear fluorinated copolymer, an active material, a non-aqueous solvent, and a conductive material, and optionally a viscosity modifier.

[0038] Aspect 18. The composition of Aspect 17, comprising (a) a non-linear fluorinated copolymer in an amount of 0.5 to 5.0% by weight, preferably 0.5 to 3.0% by weight, based on the total weight (a)+(b)+(c); (b) a conductive material in an amount of 0.5 to 5.0% by weight, preferably 0.5 to 3.0% by weight, based on the total weight (a)+(b)+(c); and (c) an active material, preferably a composite metal, in an amount of 90 to 99% by weight, preferably 94 to 99% by weight.

[0039] Aspect 19. An electrode for a lithium-ion battery obtained by applying the composition of Aspect 18 to a metal film and drying the coating.

[0040] Aspect 20. A lithium-ion battery having the electrode of Aspect 19.

[0041] Aspect 21. An article comprising any one of Aspects 1 to 10 of a non-linear fluorinated copolymer.

BEST MODE FOR CARRYING OUT THE INVENTION

[0042] The term "copolymer" is used to mean a polymer having two or more different monomer units.

[0043] The term "polymer" is used to mean both homopolymers and copolymers.

[0044] The term "linear" is used according to the definition well understood in the art of a polymer chain having a single chain structure and only two end groups. (Page 3 of R.J. Young and P.A. Lovell, Introduction to Polymers, Second Ed., London, 1991.) In this case, the polymer chain contains only the specified (co)monomer units and has no other structural changes such as any additional linking chains ("branches") of any length or number.

[0045] The term "non-linear" is used according to the definition well understood in the art of a polymer chain having one or more additional polymer chains attached at "branch points" to the main linear polymer chain. (Pages 3 and 4 of R.J. Young and P.A. Lovell, Introduction to Polymers, Second Ed., London, 1991.) The one or more additional polymer chains can be of any length from two monomer units to many monomer units. The monomer units containing branches may be the same as or different from those of the linear main chain, but are generally derived from the same monomer units present in the main chain. The branches themselves may have additional branches, and these additional branches are as described above with respect to the number and composition of monomer units.

[0046] The term "branch point" is used according to the definition well understood in the art of a polymer backbone atom unit to which a first monomer unit containing a branch is attached. In the case of fluorinated ethylene-type polymers, this branch point is often a backbone carbon atom.

[0047] As special cases of “branches” with “branch points”, “stars”, “grafts”, “combs”, “brushes”, “chimeras”, “hyperbranches” and “dendrimer” structures, etc. are known. (N. Hadjichristidis, et.al, Chem. Rev. 2001, 101, 3747-3792) All of these structural variations are considered and included in the definition of “non-linear” related to variations of the “branch” structure. As described above, the composition of the branched chains in these special cases may be the same or different monomer compositions, and may also include monomer units in block, random or gradient arrangements.

[0048] For the purposes of the present invention, the terms “non-linear” and “branched” mean the same thing and are used interchangeably.

[0049] “Ethylene-based comonomer” means a comonomer having a polymerizable carbon-carbon double bond. An ethylene-based polymer is a polymer made from ethylene-based monomers.

[0050] The term “initiator”, as well as the expressions “radical initiator” and “free radical initiator”, refer to a chemical substance that can provide a source of free radicals that are generated naturally under ambient conditions through decomposition or by being exposed to additional external stimuli such as heat or light. The term “radical” and the expression “free radical” refer to chemical species containing at least one unpaired electron.

[0051] The "low-temperature initiator" refers to an organic radical initiator with a 10-hour half-life of 53 °C or lower. The "half-life" is used to represent the rate at which this reaction occurs for molecules that thermally decompose into radical species. The half-life value is the time it takes for half of the total of a unit sample of a substance to decompose at a specific temperature. The "10-hour half-life" is the temperature at which any compound reaches its half-life in 10 hours. The initiator used in the present invention is an organic initiator with a 10-hour half-life temperature of 53 °C or lower, preferably 51 °C or lower (for related examples of low-temperature initiators, see Polymer Synthesis, Volume 1, 1992, Part 2 - Free Radical Initiators, Table 2; or "Initiators for High Polymers" Technical Product Brochure, Akzo-Nobel; or Organic Peroxides , Volume 1, D. Swern ed., Wiley-Interscience, 1970, Table 20.).

[0052] All cited documents are incorporated herein by reference. As used herein, unless otherwise specified, percentages shall mean weight percentages.

[0053] The present invention discloses a branched fluorinated copolymer comprising vinylidene fluoride, a functional comonomer, and optionally a fluorinated ethylene comonomer.

[0054] Any fluorinated ethylene comonomer is preferably selected from the group consisting of tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE), and hexafluoropropene (HFP).

[0055] The functional comonomer is preferably acrylic acid.

[0056] According to one embodiment, the fluorinated copolymer comprises vinylidene fluoride and 0.01 to 3.0 mol% of at least one ( "one or more") functional comonomer.

[0057] According to one embodiment, the functional comonomer is randomly incorporated into the copolymer at a rate of less than 40% of the total hydrophilic monomer supplied to the reaction, as determined by nuclear magnetic resonance spectroscopy ( 19 F NMR), and calculated by the following Equation 1 and Equation 2. Equation 1: (Total moles of dry solids produced * mol% of comonomer incorporated) = Moles of comonomer incorporated Equation 2: (Equation 1) / (Total moles of comonomer supplied) = Percentage of separated incorporated functionalized comonomer

[0058] Proton decoupled 19 F NMR spectra of the polymer powder were recorded under the following conditions. Instrument: Bruker AVANCE AC 400 FT NMR SPECTROMETER Measurement conditions: Frequency: 376 MHz Measurement solvent: DMSO-d Measurement temperature: 25 °C Number of scans: 2048

[0059] 19 The F NMR spectra were analyzed to determine the hydrophilic comonomer content in the polymer. Specifically, the area integral (integrated value) of one or more peaks at -94 ppm corresponding to the four fluorine atoms present in the structural unit derived from vinylidene fluoride adjacent to the incorporated hydrophilic comonomer unit was divided by the intensity of all the peaks assigned to fluorine atoms in the spectrum.

[0060] Another object of the present invention is a novel method for producing the above-mentioned non-linear copolymer. The method of the present invention advantageously comprises polymerizing vinylidene fluoride (VDF) monomer and a functional comonomer in an aqueous medium in the presence of a low-temperature initiator in a reaction vessel, the aforementioned method comprising supplying an aqueous solution containing the functional comonomer, and maintaining the pressure in the aforementioned reaction vessel above the critical pressure of vinylidene fluoride.

[0061] The present invention further contemplates a process for preparing a vinylidene fluoride copolymer in an aqueous reaction medium, comprising: a) at least one low-temperature initiator, a stabilizer, vinylidene fluoride, optionally at least one fluorinated ethylenic comonomer, and a functional comonomer, b) initiating the copolymerization of the aforementioned vinylidene fluoride, optional fluorinated ethylenic comonomer and the aforementioned functional comonomer under heating and superatmospheric pressure with stirring.

[0062] In a preferred embodiment, the present invention comprises a non-linear copolymer containing vinylidene fluoride and having more than 87 mole percent vinylidene fluoride monomer units, preferably more than 90 mole percent, and most preferably more than 95 mole percent vinylidene fluoride monomer units.

[0063] Fluorinated ethylenic comonomer The present invention is a vinylidene fluoride copolymer that can optionally have a fluorinated ethylene comonomer. Examples of the fluorinated ethylene comonomer "fluoromonomer" include tetrafluoroethylene (TFE), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, perfluorobutylethylene (PFBE), hexafluoropropene (HFP), vinyl fluoride (VF), pentafluoropropene, 2,3,3,3-tetrafluoropropene, trifluoropropene, fluorinated (alkyl) vinyl ether, for example, perfluoroethyl vinyl ether (PEVE), and perfluoro-2-propoxypropyl vinyl ether, perfluoromethyl vinyl ether (PMVE), perfluoropropyl vinyl ether (PPVE), perfluorobutyl vinyl ether (PBVE), longer-chain perfluorinated vinyl ether, etc., one or more partially or fully fluorinated α-olefins, for example, 3,3,3-trifluoro-1-propene, 2-trifluoromethyl-3,3,3-trifluoropropene, 1,2,3,3,3-pentafluoropropene, 3,3,3,4,4-pentafluoro-1-butene, hexafluoroisobutylene (HFIB), etc., fluorinated dioxoles, for example, perfluoro(1,3-dioxole) and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD), etc., C4 or higher partially fluorinated or perfluorinated α-olefins, C3 or higher partially fluorinated or perfluorinated cyclic alkenes, allyl monomers, partially fluorinated allyl monomers, or fluorinated allyl monomers, for example, 2-hydroxyethyl allyl ether or 3-allyloxypropanediol, etc., and combinations thereof.

[0064] Preferably, any fluorinated ethylene comonomer is selected from the group consisting of tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE), and hexafluoropropene (HFP).

[0065] Functional comonomer The copolymer of the present invention contains functional comonomer units. The functional comonomer is defined by Formula 1. [Chemical Formula] Here, each of R1, R2, and R3 may be the same as or different from each other, and independently is a hydrogen atom or a C1-C3 hydrocarbon group, and R4 is hydrogen or a C1-C hydrocarbon moiety containing at least one hydroxyl group. 16 hydrocarbon moiety.

[0066] In some embodiments, only one of R1, R2, and R3 is hydrogen.

[0067] In some embodiments, two of R1, R2, and R3 are hydrogen.

[0068] One or more functional comonomers can be used in combination with VDF and any one or more fluorinated ethylene comonomers to form the copolymer of the present invention.

[0069] Non-limiting examples of the functional comonomer include acids such as acrylic acid and methacrylic acid.

[0070] The functional comonomer can be used, for example, in an amount of about 0.01 to about 3.0 mol% based on the total monomers. Preferably, they are used in an amount of about 0.01 to about 2.0 mol% based on the total monomers. In various embodiments, the total amount of one or more functional comonomers is at least 0.01 mol%, at least 0.05 mol%, at least 0.10 mol% based on the total monomers. In other embodiments, the total amount of the functional monomer does not exceed 3.0 mol% or preferably does not exceed 2.0 mol% based on the total monomers. The functional comonomer can be used in a solution such as an aqueous solution for ease of handling.

[0071] Process The vinylidene fluoride copolymer of the present invention can be obtained by copolymerizing vinylidene fluoride, one or more functional comonomers represented by Formula 1, and optionally additional fluorinated ethylene comonomers in a suspension polymerization process.

[0072] In that process, a suspending agent is used to impart stability to the copolymer particles during the suspension polymerization reaction. In suspension polymerization, water is used as the dispersion medium, and the suspending agent can be added in the range of 0.005 to 1.0 part by weight, preferably in the range of 0.01 to 0.4 part by weight, based on 100 parts by weight of the total monomers used in the copolymerization.

[0073] The suspending agent is not particularly limited, and examples include methylcellulose, methoxylated methylcellulose, propoxylated methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, polyvinyl alcohol, polyethylene oxide, and gelatin. Preferred suspending agents include functionalized cellulose, fully and partially hydrolyzed poly(vinyl alcohol), and inorganic clay, as described in Chapter 5, Free Radical Polymerization: Suspension, of HANDBOOK of Polymer Reaction Engineering, B.W. Brooks, Dr. T. Meyer, Prof. J. Keurentjes, eds., Wiley, 2005, which is hereby incorporated by reference.

[0074] Initiator The low-temperature initiator is added to the reaction mixture in an amount sufficient to initiate the polymerization reaction and maintain the desired reaction rate. The order of addition can be varied according to the desired process characteristics. In one embodiment, all of the low-temperature initiator is added before the start of the polymerization process. The low-temperature initiator can be added to the reaction mixture in an amount of about 0.01 to about 5.0% by weight based on the total monomers (the total monomers mean vinylidene fluoride, one or more compounds represented by Formula 1, and optionally other fluorinated ethylene comonomers selected as needed), preferably in an amount of about 0.05 to about 2.5% by weight based on the total monomers.

[0075] Examples of suitable low-temperature initiators include peroxides, peroxy esters, peroxydicarbonates, and azo compounds. The low-temperature initiator can include organic peroxides such as alkyl peroxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, peroxy esters, etc., or mixtures thereof. Preferred peroxydicarbonate initiators include acetylcyclohexanesulfonyl peroxide, diisobutyryl peroxide, di-n-propyl peroxydicarbonate, and diisopropyl peroxydicarbonate.

[0076] In the case of low-temperature initiators that are hardly soluble in water, it is advantageous to disperse them in water beforehand. The method used to disperse the low-temperature initiator in water is the method of generating a water-in-oil type emulsion, which is typically known in the art, where water and immiscible components (here the initiator) are subjected to high-shear mixing, and in many cases, surfactants or other stabilizers are added, as described in "Encyclopedic Handbook of Emulsion Technology, 1st Edition, ed. Johan Sjoblom, Marcel-Dekker, New York, 2001", which is incorporated herein by reference. Handling the starting species in this way is particularly advantageous when the thermal stability of the starting species is low, as is apparent from the fact that the 10-hour half-life temperature is less than 53°C. The presence of water in the low-temperature initiator dispersion or emulsion provides a heat sink for the heat of decomposition, reduces the possibility of a thermal runaway reaction of the low-temperature initiator itself, and greatly improves the safety of the process. It is further advantageous that the surfactant or dispersant used to stabilize the low-temperature initiator / water dispersion or emulsion is compatible with the copolymerization reaction, and most advantageously, the surfactant or dispersant used to stabilize the low-temperature initiator / water dispersion is the same as that used to stabilize the reaction emulsion or suspension.

[0077] Chain transfer agent Chain transfer agents are optionally added to the polymerization to control the molecular weight of the product. They may be added to the polymerization all at once at the start of the reaction, or gradually or continuously throughout the reaction. The amount and method of addition of the chain transfer agent are determined by the activity of the particular chain transfer agent being used and the desired molecular weight of the polymer product. The amount of chain transfer agent added to the polymerization reaction is preferably from about 0.0 to about 5.0 weight percent, more preferably from about 0.05 to about 3.0 weight percent, based on the total weight of the monomers added to the reaction mixture.

[0078] Oxygen-containing compounds such as alcohols, carbonates, ketones, esters, and ethers can function as chain transfer agents. Examples of oxygen-containing compounds used as chain transfer agents include isopropyl alcohol, ethyl acetate, methyl acetate, diethyl carbonate, acetone, ethanol, n-propanol, acetaldehyde, propionaldehyde, and ethyl propionate, as described in U.S. Patent 4,360,652. Other classes of compounds that can function as chain transfer agents in the polymerization of halogen-containing monomers include, for example, halocarbons and hydrohalocarbons, and chlorocarbons such as carbon tetrachloride. Simple alkanes or branched alkanes such as ethane, propane, or 2-ethylhexane can also function as chain transfer agents.

[0079] Buffer The polymerization reaction mixture may optionally contain a buffer to maintain a controlled pH throughout the polymerization reaction. It is preferred to control the pH in the range of about 2.0 to about 8.0 to minimize the formation of undesirable colors in the product.

[0080] The buffer has at least one pK in the range of about 4.0 to about 10.0, preferably about 4.5 to about 9.5 a value and / or pK bIt can contain an organic acid or an inorganic acid or an alkali metal salt thereof, or a base or salt of such an organic acid or inorganic acid having a value. Preferred buffers in the practice of the present invention include, for example, phosphate buffers and acetate buffers. A "phosphate buffer" is a salt or mixture of salts of phosphoric acid. An "acetate buffer" is a salt of acetic acid.

[0081] Linear copolymers of vinylidene fluoride with a functional comonomer and optionally with other fluorinated ethylene-based monomers are used in the industry. However, conventional methods for producing such linear polymers have suffered from low reaction productivity and have been difficult to supply sufficient amounts of material to a rapidly growing market. In some embodiments, the present invention provides high productivity in the polymerization of vinylidene fluoride copolymers while maintaining or improving the adhesion performance to metal films. High productivity means that the execution time of the polymerization reaction is less than 12 hours. It is very interesting to shorten the polymerization time and thereby make the process more efficient (faster) and reduce the energy used. In some embodiments of the present invention, the polymerization execution time is less than 12 hours, with high certainty less than 10 hours, and most preferably less than 8 hours. The more efficient the process, the higher the productivity.

[0082] Conditions for copolymerization The temperature used for polymerization can vary, for example, in the range of 20 to 100 °C depending on the selected low-temperature initiator system. The polymerization temperature is preferably 35 to 75 °C, and most preferably 35 to 60 °C.

[0083] Generally, the method of the present invention is carried out at a temperature of 20 to 70 °C, preferably with an upper limit of 60 °C, at least 35 °C, preferably at least 40 °C, more preferably at least 45 °C. The temperature used during the polymerization process can be varied or maintained at a constant temperature.

[0084] The pressure used for the polymerization can be varied in the range of 280 to 40,000 kilopascals (kPa) depending on the capacity of the reactor, the selected low-temperature initiator system, and the choice of monomers. The polymerization pressure is preferably 2,000 to 20,000 kPa.

[0085] Optionally, the functional comonomer can be supplied continuously throughout the polymerization. If a discontinuous supply is used, the supply profile can be varied with respect to rate and / or provided to the reactor in a discontinuous manner. Thus, the supply of the functional comonomer may be carried out in multiple aliquots throughout the polymerization process.

[0086] It is also possible to gradually add VDF or a fluorinated ethylene comonomer during the polymerization. In one embodiment, all of the required VDF monomer is introduced before the start of the polymerization.

[0087] By carrying out aqueous suspension polymerization under the above-mentioned conditions, vinylidene fluoride, the compound represented by Formula 1, and any one or more other fluorinated ethylene comonomers are copolymerized to obtain the vinylidene fluoride copolymer of the present invention.

[0088] In the polymerization process, the compound represented by Formula 1 is supplied at a maximum of 10.0% by weight based on the total monomer supply amount, preferably less than 4% by weight, more preferably 3% by weight or less based on the total monomer supply amount to the polymerization reaction.

[0089] The polymerization is carried out under stirring or other agitation. The stirring / agitation may be constant or the rate may be varied to optimize the process conditions during the polymerization. In one embodiment, multiple stirring speeds and multiple temperatures are considered to control the reaction.

[0090] The polymerization reaction according to the present invention can be carried out by introducing water (preferably deionized water), a suspending agent, vinylidene fluoride, any at least one fluorinated ethylene comonomer, at least one functional comonomer represented by Formula 1, and optionally a chain transfer agent and / or a buffer into a reactor. Before introducing the monomers, air is purged from the reactor. Water is added to the reactor before bringing the reactor to the desired starting temperature, but the other materials can be added before or after bringing the reactor to that temperature. To initiate and maintain the polymerization reaction, at least one low-temperature initiator is added. Additional monomers can optionally be added to replenish the consumed monomers, and other materials, such as a buffer or a chain transfer agent, etc., can optionally be added during the polymerization process to maintain the reaction and adjust the properties of the final product.

[0091] Although the order of combining the polymerization components can be changed, generally, it is preferred that at least a part of the functional comonomer is present in the aqueous reaction medium before the polymerization of the fluorinated ethylene comonomer is initiated. An additional amount of the functional comonomer can be supplied to the reactor during the reaction in the manner described above.

[0092] Alternatively, without supplying an additional fluorinated ethylene comonomer to the reactor, the pressure is maintained only by supplying the functional comonomer and / or additional components, such as a low-temperature initiator or a buffer or simply deoxygenated water, etc., in bulk or in solution.

[0093] When the desired weight of the monomers has been supplied to the reactor, the supply of the monomers is stopped. An additional low-temperature initiator is optionally added and the reaction is allowed to reduce the pressure for an appropriate time. As the monomers in the reactor are consumed, the reactor pressure decreases. At this point, the supply of the functional comonomer can be continued or stopped. When the supply of the functional comonomer is stopped, the copolymer produced in this part of the reaction has a low functional comonomer content or lacks the functional comonomer.

[0094] Once the copolymerization reaction is complete, the reactor is returned to ambient temperature and the remaining unreacted monomer is vented to atmospheric pressure. Next, the aqueous reaction medium containing the copolymer is recovered from the reactor. The product consists of a mixture of the reaction components, namely water, residual functional comonomer, low temperature initiator (and / or decomposition products of the initiator), and copolymer solids.

[0095] Handling of the Product The product of the copolymerization is a solid and can be separated from the aqueous components and dried by conventional methods known in the art including filtration or other suitable solid / liquid separation techniques such as centrifugation etc. Once isolated, the solid product can be purified by washing with deionized water or other techniques and dried for use as a powder and further processed into granules, pellets etc.

[0096] Properties of the Nonlinear Copolymer of the Invention The fluorinated copolymer of the invention is non-linear. The fluorinated copolymer contains at least 10 wt% of a branched structure, preferably at least 15 wt% of a branched structure, most preferably at least 20 wt% of a branched structure, which is measured by size exclusion chromatography using a Mark-Houwink plot as described in Striegel, Yau, Kirkland, Bly, Modern Size-Exclusion Liquid Chromatography, 2nd ed. (2009), which is incorporated herein by reference. The test method is described below.

[0097] The primary particle size of the copolymer of the invention is 10 microns or more. This can be measured by optical microscopy using an eyepiece reticle and a stage micrometer in combination.

[0098] Preferably, the functional comonomer has less than 40% of the separated functionalized comonomer in the backbone on a mole percent basis. The copolymer of the invention may have a proportion of separated functional comonomer of less than 37%, preferably less than 36%.19 It is measured by 19F NMR.

[0099] Preferably, the solution viscosity of the fluorinated copolymer is such that when the viscosity of a solution of N-methyl-2-pyrrolidone containing 9.0% by weight of the aforementioned vinylidene fluoride copolymer is measured at 23°C at a controlled shear rate of 3.36 revolutions per second, it is 2000 mPa·s or more, preferably 5000 mPa·s or more, most preferably 6000 mPa·s or more, and less than 30000 mPa·s, less than 20000 mPa·s, preferably less than 15000 mPa·s. The solution viscosity is measured using a Brookfield DV3 rotational viscometer equipped with an SC4-34 type spindle, a circulating constant temperature bath set at 23°C, and a rotational speed corresponding to a shear rate of 3.36 s -1 and is measured using a rotational speed corresponding to the shear rate.

[0100] Electrodes and Batteries The present invention also relates to components of a lithium-ion battery containing a non-linear fluorinated copolymer, such as electrodes or separators, etc. The non-linear fluorinated copolymer can be used as a binder in a formulation for an electrode that is a cathode or an anode. The present invention encompasses batteries containing the fluorinated copolymer described herein.

[0101] The present invention further relates to a formulation containing a non-linear fluorinated copolymer in a solvent. A further object of the present invention is the use of a non-linear fluorinated copolymer composition as a binder, particularly for forming electrodes of lithium batteries and / or electric double layer capacitors. Also, an object of the present invention is an electrode-forming composition containing a solvent, a non-linear fluorinated copolymer, an active material (powder electrode material), and optionally a conductive material and / or a viscosity modifier.

[0102] Formulation of Electrode Slurry When the electrode to be manufactured is a cathode, the formulation slurry required to form the cathode contains a solvent, a polymer binder, an active material, and a conductive material. The active material and the conductive material are preferably in the form of dry powders. When the electrode is an anode, the slurry for forming the anode contains a solvent, a polymer binder, and a conductive material. The conductive material may be one or more kinds, and may be one or more of coke, carbon black, graphite, activated carbon, carbon fiber, silicon, graphene, graphene oxide, and carbon nanotubes.

[0103] When using the non-linear fluorinated copolymer of the present invention as a binder, generally, a binder solution of the non-linear fluorinated copolymer is prepared. To obtain the binder solution of the non-linear fluorinated copolymer, it is preferable to dissolve 0.1 to 10.0 parts by weight, particularly 1.0 to 5.0 parts by weight of the non-linear fluorinated copolymer in 100 parts by weight of an organic solvent. Any suitable organic solvent for dissolving the polymer binder can be used.

[0104] The organic solvent used to dissolve the non-linear fluorinated copolymer binder to provide the non-linear fluorinated copolymer binder solution according to the present invention may preferably be a polar solvent. Examples thereof include N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), triethyl phosphate (TEP), acetone, tetrahydrofuran, methyl ethyl ketone (MEK), methyl isobutyl ketone (MiBK), ethyl acetate (EA), butyl acetate (BA), dimethyl carbonate (DMC), diethyl carbonate (DEC), or methyl ethyl carbonate (MEC), N-ethyl-2-pyrrolidone, N,N-dimethylacetamide, hexamethylphosphoramide, dioxane, tetramethylurea, (1R)-7,8-dioxabicyclo[3.2.1]octan-2-one (Cyrene manufactured by MilliporeSigma TM) and trimethyl phosphate (TMP) can be mentioned. These solvents may be used alone or as a mixture of two or more. The polymer binder composition is dissolved in the solvent while stirring or heating to make a polymer binder solution.

[0105] The active material includes lithium metal compounds well known in the art. For example, refer to US2018 / 0076444 and US2020373560. The active material for the cathode generally includes lithium transition metal alloy chalcogenide compounds, such as lithium iron phosphate (LFP), lithium nickel manganese cobalt oxide (NMC), lithium manganese cobalt oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, and lithium nickel manganese spinel, etc.

[0106] In order to improve the conductivity of the composite electrode layer formed by coating and drying the electrode-forming composition of the present invention, a conductive material can be added. Examples of the conductive material include, but are not limited to, carbonaceous materials, such as graphite fine powder and fibers, carbon black, Super P (registered trademark) carbon black, C-NERGY TM carbon black, KETJENBLACK, DENKA BLACK, thermal black, channel black, carbon fiber, carbon nanotube, and acetylene black, etc., and metals, such as fine powder and fibers of nickel and aluminum, etc. The preferred conductive material is carbon black.

[0107] In one embodiment, the non-linear fluoropolymer binder material can be used as a component of an electric double layer capacitor. The active material for the electric double layer capacitor preferably includes fine particles or fibers with an average particle diameter (or fiber diameter) of 0.05 to 100 μm and a specific surface area of 100 to 3000 m / g, that is, fine particles or fibers with a relatively small particle diameter (or fiber diameter) and a relatively large specific surface area compared to the active material for the battery, such as activated carbon, activated carbon fiber, silica, or alumina particles, etc.

[0108] The solid content (by weight %) of the electrode slurry containing a fluorinated copolymer binder, an active material, and a conductive material is preferably in the range of 71 to 87% by weight, more preferably about 75 to 85% by weight. The solid content (by weight %) of the electrode slurry may be 80% to 87% by weight.

[0109] The content of the solid component of the cathode formulation having an active material, a conductive material, and a polymer binder may vary in amount compared to each component. Preferably, the amount of the active material is about 90 to 99% by weight based on the total solid content, the amount of the conductive material is about 0.5 to 5.0% by weight based on the total solid content, and the amount of the fluorinated copolymer binder is about 0.5 to 5.0% by weight based on the total weight of the active material, the conductive material, and the fluorinated copolymer binder. The electrode slurry can optionally contain other additives such as a viscosity modifier. Preferably, the electrode slurry does not contain additives.

[0110] Formation of the Electrode The fluorinated copolymer binder in the form of a solvent solution or dispersion is blended with one or more active powder electrode-forming materials to form a slurry dispersion or paste. Next, this dispersion or paste is applied to one or both sides of a conductive substrate using a uniform wet coating application technique known in the art and dried to form a dried composite electrode layer. Next, the electrode layer is compressed by any method known in the art including calendaring as shown in US5776637 and US6200703. In the calendaring, the fluoropolymer binder is dissolved in NMP and processed into the electrode. In another method, the polymer binder in powder form is blended with one or more active powder electrode-forming materials and then a solvent is added to form a slurry dispersion or paste. The subsequent coating, drying, and calendaring steps are the same as above.

[0111] The electrode slurry composition can be applied to at least one side, preferably both sides, of a metal current collector, and for example, can be dried at a high temperature of 50 to 170 °C to form a dried composite electrode layer. As the metal current collector to which the composite electrode layer is firmly attached, any metal having high conductivity and no reactivity in the voltage range of the battery to be constructed can be used. Examples of such substrates include metal foils or wire meshes, and non-limiting examples include iron, stainless steel, steel, copper, lithium, aluminum, nickel, silver, or titanium, or combinations thereof.

[0112] Other applications The non-linear functional polyvinylidene fluoride of the present invention can be used as a component of a film / antifouling, sizing for fibers (carbon fibers), tie layer for multilayer sheets, adhesives (general), water or proton permeable membranes, battery separator coatings, (fluoro)polymer blend compatibilizers, paints, or industrial coatings.

[0113] The present invention, its features, and the various advantages provided by the present invention will be more clearly understood by reading the following examples provided as non-limiting examples for illustration.

Examples

[0114] The particle size of the polymer powder is measured using a laser diffraction method and a Microtrac S3500 particle size analyzer. The data is the volume average particle size (diameter).

[0115] The mole percent of vinylidene fluoride in the copolymer is 19 measurable using F-NMR.

[0116] The weight percent (wt%) of the branched structure contained in the non-linear fluoropolymer is determined using the following method.

[0117] Multi-detector size-exclusion chromatography was used to measure the absolute molar mass and intrinsic viscosity of the samples. The absolute molar mass obtained by multi-detector light scattering and the intrinsic viscosity obtained by differential viscosity measurement were combined in the form of a Mark-Houwink plot to determine the molecular structure defined by the Mark-Houwink slope (α) at each molar mass value. The branched molar mass was determined based on the molar mass corresponding to the change in the slope of the Mark-Houwink plot from (α) > 0.5 to (α) ≤ 0.5. When (α) > 0.5, the material is considered linear. When (α) ≤ 0.5, the material is considered branched (non-linear). The weight % branched structure was determined by integrating the area of the molar mass distribution of the sample having a molar mass corresponding to Mark-Houwink slope (α) ≤ 0.5.

[0118] Sample preparation: 1.0 mg / mL of the polymer was dissolved in DMSO containing 0.1% LiCl while gently shaking and heating at 90 °C for 72 hours. The sample solution was analyzed without additional filtration. Mobile phase: DMSO containing 0.1% LiCl Flow rate: 0.50 mL / min Temperature: 50 °C Separation unit: Agilent 1200 Injection volume: 100 μL Columns: Two PSS PFG analysis linear XL columns and a guard column (7.8 mm I.D. × 30 cm, 7 μm) Detectors: Wyatt HELEOS 8+ light scattering detector, ViscoStar III differential viscometer, and Wyatt T-rEX refractometer. Software for data collection and processing: ASTRA 7

[0119] Example 1: Synthesis A cylindrical jacketed high-pressure autoclave with an internal volume of 17.5 L is fitted with an overhead stirrer, a stirring shaft with three 45 degree angled blade stirrers, a thermocouple and a pressure sensor. A 1.0 wt% solution of acrylic acid ("AA") in deionized water is made by adding 40.0 g of AA to 3960 g of deionized water. This solution is added to a charge pot connected to a high-pressure reciprocating diaphragm pump connected to the autoclave. 4.13 g of Methocel® K100LV (DuPont) (hydroxypropyl methylcellulose (HPMC)) is dissolved in 8717 mL of deionized water and charged to the autoclave. A 650 g emulsion of 3.0 wt% n-propyl peroxydicarbonate (NPP) in deionized water is made by adding 19.5 g NPP, 1.0 g Methocel K100LV, and 629.5 g H2O pre-cooled to 5°C to a 1.0 L plastic bottle and stirring the mixture under high shear for 10 minutes. The entire contents of this emulsion (650 g) is then charged to an autoclave. The stirrer is started at 400 rpm and the autoclave is pressurized to 88 bar(g) (8800 kPa) with vinylidene fluoride (VDF), then the temperature is increased to 50°C and the autogenous pressure rises to 100-105 bar(g) (10,000-10,500 kPa). The AA solution feed is started at a slow rate (approximately 50-100 mL / hr). Additional (VDF) is then added to raise the pressure to 115 bar(g) (11,500 kPa). The start of polymerization is confirmed by a drop in reactor pressure, at which point the feed of AA solution is increased and continuously adjusted (300-700 g / hr) to maintain the reactor pressure at 115 bar(g) (11,500 kPa). The reaction is continued in this manner for 447 minutes, at which point the AA feed pump is stopped and the autoclave pressure is allowed to drop for 60 minutes. At this point, the autoclave is cooled to 25° C., vented, and the product discharged as a foamy aqueous dispersion. A total of 3661 g of AA solution was added over the reaction time. The solid product is separated from the water by gravity filtration using a porous cloth. The wet solid product is then dried to constant weight in a ventilated convection oven. 1676 g of dried product is recovered as a white powder.

[0120] Example 2 A cylindrical high-pressure autoclave with a jacket and an internal volume of 17.5 L is equipped with an overhead stirrer, a stirring shaft with three 45-degree inclined blade agitators, a thermocouple, and a pressure sensor. A 1.5 wt% solution of acrylic acid (AA) in deionized water is prepared by adding 60.0 g of AA to 3940 g of deionized water. This solution is added to a charge pot connected to a high-pressure reciprocating diaphragm pump that is internally connected to the autoclave. 4.13 g of Methocel K100LV is dissolved in 8717 mL of deionized water and charged into the autoclave. 650 g of an emulsion of 3.0 wt% n-propyl peroxydicarbonate (NPP) in deionized water is prepared by adding 19.5 g of NPP, 1.0 g of Methocel K100LV, and 629.5 g of H2O pre-cooled to 5°C to a 1.0 L plastic bottle and stirring the mixture under high shear for 10 minutes. Then, the entire content (650 g) of this emulsion is charged into the autoclave. The stirrer is started at 400 rpm, and the autoclave is pressurized to 88 bar(g) (8800 kPa) with vinylidene fluoride (VDF), and then the temperature is raised to 50°C, at which point the self-generated pressure rises to 100 - 105 bar(g) (10,000 - 10,500 kPa). The supply of the AA solution is started at a low rate (about 50 - 100 mL / hour). Then, additional (VDF) is added to raise the pressure to 115 bar(g) (11,500 kPa). The start of polymerization is confirmed by the natural drop in the reactor pressure, at which point the supply of the AA solution is increased and continuously adjusted (300 - 700 g / hour) to maintain the reactor pressure at 115 bar(g) (11,500 kPa). The reaction is continued in this manner for 459 minutes, at which point the AA supply pump is stopped and the autoclave pressure is allowed to drop naturally for 60 minutes. At this point, the autoclave is cooled to 25°C, vented, and the product is discharged as a foamy aqueous dispersion. A total of 3603 g of the AA solution is added over the reaction time. The solid product is separated from the water by gravity filtration using a porous cloth. The wet solid product is then dried in a ventilated convection oven until it reaches a constant weight. 2825 g of the dry product is recovered as a white powder.

[0121] The divergence, randomness, and solution viscosity were measured.

[0122]

Table 1

[0123] S5130 is Solef® 5130 manufactured by Solvay and is believed to be manufactured according to US8337725. The reaction time and randomness reflect the data of the patent examples.

[0124] Electrode The formulation is prepared using a Thinky ARE-310 mixer. After adding the non-linear fluoropolymer binder solution to the carbon black, seven 6.5 mm zirconium beads are added to the Thinky cup. The mixture is mixed three times for 2 minutes each at 2000 RPM to produce a conductive material slurry by a total of 6 minutes of mixing. The active material is also added together with the first addition of NMP. The active material slurry is mixed twice for 1 minute each at 2000 RPM. NMP is added and the active material slurry is mixed twice for 1 minute each at 2000 RPM. The remaining aliquots of NMP are added and mixed for 1 minute each at 2000 RPM each time to obtain an electrode slurry. The total mixing time for the entire formulation is 13 minutes.

[0125] The resulting slurry is cast onto an aluminum substrate using a doctor blade. The gap setting of the doctor blade is set to a wet thickness of 135 micrometers, and the resulting wet electrode is placed in an oven at 120 °C for 30 minutes.

[0126] The film thickness of the dried electrode is 70 - 75 micrometers, and the mass loading is 18 - 20 mg / cm 2 is. The electrodes are cut into 1-inch (25.4 mm) strips and fed into a calendaring machine with air pressure control. The electrodes are compressed to a target thickness of 55 micrometers. The calendered electrodes are used in the peel test process.

[0127] The electrode peel strength was measured by a 180° peel test according to ASTM D903.

[0128]

Table 2

[0129] (1) *Average value from 3 separate manufacturing processes.

[0130] Examples 1 and 2 show exemplary performance as a battery electrode binder.

Claims

1. At least 87.0 mol% of vinylidene fluoride, and 0.01 to 3.0 mol% of at least one functional comonomer of Formula 1: 【Chemical Formula 1】 (wherein each of R 1 , R 2 , R 3 may be the same as or different from each other, and each independently represents a hydrogen atom or a C 1 -C 3 hydrocarbon group, and R 4 represents hydrogen or a C 1 -C 16 hydrocarbon moiety containing at least one hydroxyl group) and at least one fluorinated ethylenic comonomer optionally comprising a non-linear fluorinated copolymer, wherein the non-linear fluorinated copolymer contains at least 10% by weight of a branched structure, preferably at least 15% by weight of a branched structure, more preferably at least 20% by weight of a branched structure, and the average primary particle diameter of the non-linear fluorinated copolymer is greater than 10 microns.

2. The non-linear fluorinated copolymer according to claim 1, wherein the fluorinated ethylenic comonomer is selected from the group consisting of tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE), hexafluoropropene (HFP), and combinations thereof.

3.

4. wherein the at least one functional comonomer is R 4 The non-linear fluorinated copolymer according to claim 1, comprising Formula 1 wherein R is hydrogen. The non-linear fluorinated copolymer according to claim 1, wherein the at least one functional comonomer contains acrylic acid.

5. The non-linear fluorinated copolymer according to any one of claims 1 to 4, wherein the content of the functional comonomer incorporated in the polymer is 0.01 to 2.0 mol% of the entire non-linear fluorinated copolymer.

6. The non-linear fluorinated copolymer according to any one of claims 1 to 4, wherein the fluorinated ethylenic comonomer constitutes at most 10.0 mol%, preferably at most 5.0 mol% of the total monomer units of the non-linear fluorinated copolymer.

7. The non-linear fluorinated copolymer according to any one of claims 1 to 4, wherein the fluorinated ethylenic comonomer contains HFP.

8. The non-linear fluorinated copolymer according to any one of claims 1 to 4, wherein the fluorinated ethylenic comonomer contains at least 90.0 mol% of VDF and 0.1 to 9.99 mol% of HFP.

9. The viscosity of a solution of N-methyl-2-pyrrolidone containing 9.0% by weight of a vinylidene fluoride polymer, measured at 23°C at a controlled shear rate of 3.36 revolutions per second, is 4000 mPa·s or more and less than 45000 mPa·s, preferably 5000 mPa·s or more and less than 30000 mPa·s, most preferably 5000 mPa·s or more and less than 20000 mPa·s.

10. ​ The proportion of the randomly distributed functional comonomer is less than 37%, and the non-linear fluorinated copolymer according to any one of claims 1 to 4.

11. A method for producing a non-linear fluorinated copolymer, the method comprising, in a suspension polymerization process, vinylidene fluoride and 0.01 to 3.0 mol% based on the total monomer feed of a compound of formula 1: 【Chemical Formula 2】 (wherein each of R 1 , R 2 , R 3 may be the same as or different from each other and are independently a hydrogen atom or a C 1 -C 3 hydrocarbon group, and R 4 is a C 1 -C 16 hydrocarbon moiety containing hydrogen or at least one hydroxyl group) at least one functional comonomer of and optionally at least one fluorinated ethylenic comonomer are polymerized in the presence of a low-temperature initiator at a temperature of 20 to 70 °C, preferably 35 to 60 °C, wherein the low-temperature initiator has a half-life temperature of 53 °C or less, preferably 51 °C or less, for 10 hours, a method for producing a non-linear fluorinated copolymer.

12. The method according to claim 11, wherein the low-temperature initiator comprises at least one of n-propyl peroxydicarbonate (NPP), isopropyl peroxydicarbonate (IPP), acetyl cyclohexane sulfonyl peroxide, or diisobutyryl peroxide.

13. The method according to claim 11 or 12, wherein the low-temperature initiator is added to the reaction mixture in an amount of about 0.01 to about 5.0% by weight, preferably about 0.05 to about 2.5% by weight, based on the total monomer weight.

14. The method according to claim 11, wherein the pressure during polymerization is 280 to 40,000 kPa, preferably 2,000 to 20,000 kPa.

15. The method according to claim 11 or 12, wherein the functional comonomer is added continuously to the polymerization.

16. The method according to claim 11 or 12, wherein the functional comonomer is added discontinuously to the polymerization.

17. A composition for a lithium-ion battery comprising the non-linear fluorinated copolymer according to claim 1, an active material, a non-aqueous solvent, and a conductive material, and optionally a viscosity modifier.

18. (a) comprising the non-linear fluorinated copolymer in an amount of 0.5 to 5.0% by weight, preferably 0.5 to 3.0% by weight, based on the total weight (a)+(b)+(c), (b) the conductive material in an amount of 0.5 to 5.0% by weight, preferably 0.5 to 3.0% by weight, based on the total weight (a)+(b)+(c), and (c) the active material, preferably a composite metal, in an amount of 90 to 99% by weight, preferably 94 to 99% by weight, the composition according to claim 17.

19. An electrode for a lithium-ion battery obtained by applying the composition according to claim 18 to a metal film and drying the coating.

20. A lithium-ion battery having the electrode according to claim 19.

21. An article comprising a non-linear fluorinated copolymer according to any one of claims 1 to 4.

Images