Method for making heat-treated PVDF

Abstract

The present invention relates to a method for producing heat-treated vinylidene fluoride polymer particles, which exhibit excellent dispersibility and solubility in aprotic polar solvents, improved color and are less prone to aggregation, and uses of the vinylidene fluoride polymer particles in electrodes or diaphragms in electrochemical devices and filtration membranes. The method comprises providing an aqueous dispersion of VDF-based polymer particles, heat-treating the same under stirring, and separating the heat-treated polymer particles.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority from European Patent Application No. 18306544.0 filed on November 22, 2018, the entire contents of which are incorporated by reference into this application for all purposes. Technical Field

[0003] The present invention relates to a method for producing heat-treated vinylidene fluoride polymer particles, which exhibit excellent dispersibility and solubility in aprotic polar solvents, improved color and are less prone to aggregation, and uses of the same in various applications. Background Art

[0004] Fluoropolymers are known in the art to be excellent materials for a variety of applications and environments due to their inherent chemical resistance and good mechanical properties.

[0005] In particular, fluorine-containing polymers are known in the art to be suitable for manufacturing parts for electrochemical devices, such as electrodes or separators for secondary batteries.

[0006] Furthermore, fluoropolymers are known in the art to be suitable for making filtration membranes.

[0007] Generally, a technique for manufacturing an electrode or a separator or a filtration membrane for a secondary battery involves using an organic solvent such as N-methyl-2-pyrrolidone for dissolving a fluorine-containing polymer.

[0008] In particular, fluoropolymers are suitable as binders in a process for making electrodes, wherein the fluoropolymer binder is dissolved in an organic solvent such as N-methyl-2-pyrrolidone and then homogenized with the electroactive material and all other suitable components to produce a paste to be applied to the current collector.

[0009] The function of the organic solvent is typically to dissolve the fluoropolymer so as to bind the electroactive material particles to each other and to the current collector when the organic solvent evaporates.

[0010] The fluoropolymer binder should suitably bind the electroactive material particles together and suitably bind the particles to the current collector so that the particles can chemically withstand large volume expansion and contraction during charge and discharge cycles.

[0011] In particular, vinylidene fluoride polymers, especially those having a high molecular weight, are suitable as binders for electrodes in view of their good adhesion properties to a current collector.

[0012] Furthermore, vinylidene fluoride polymers having a high molecular weight are suitable for manufacturing filtration membranes having good mechanical strength.

[0013] Typically, a "good" solvent having sufficient solubility relative to the vinylidene fluoride polymer is selected, and the mixture is stirred under heating, if necessary, to prepare a uniform solution. However, since the vinylidene fluoride polymer powder tends to aggregate during stirring, it takes a long time for the solvent to penetrate into the aggregates to completely dissolve the powder to obtain a uniform solution.

[0014] This tendency is stronger in a vinylidene fluoride polymer having a higher molecular weight, which requires a longer time to be dissolved in an organic solvent such as NMP or acetone, thereby deteriorating productivity.

[0015] It is known that heat treating vinylidene fluoride polymer particles at a temperature somewhat below the melting temperature of the polymer makes the vinylidene fluoride polymer particles more easily soluble in a given solvent.

[0016] EP 2495273, 05 / 09 / 2012 discloses a method for producing a heat-treated vinylidene fluoride polymer powder, which comprises heat-treating the powder at a temperature of not less than 125°C to below the crystalline melting temperature (Tm) of the polymer, in order to improve the dispersibility and solubility of the powder in an aprotic polar solvent (such as NMP).

[0017] Suitable thermal processing equipment known in the art include, for example, furnaces (such as static, continuous, batch, convection), fluidized bed heaters, and the like.

[0018] However, heat treating the powdered material may affect the color of the material.

[0019] Furthermore, in the heat treatment of materials in powder form, agglomeration of said powder material is very likely to occur. Therefore, in addition to the uneven heat treatment, a grinding step is usually required after the heat treatment to restore the appropriate particle size. In addition to the fact that the additional step requires higher costs and longer time in the industrial process, the grinding step may also cause some local heating of the polymer composition and, if this temperature exceeds the melting point of the polymer, may affect the crystallinity of the polymer and therefore the solubility of the polymer.

[0020] Furthermore, the vinylidene fluoride polymer in powder form may be burned when processed at high temperatures.

[0021] Therefore, there remains a need in the art to produce vinylidene fluoride polymer particles having a high molecular weight that can be easily dissolved in an organic solvent, thereby providing a uniform organic solvent solution, while overcoming the above-mentioned productivity, safety and color issues. Summary of the invention

[0022] The applicant has surprisingly found that heat treatment of an aqueous dispersion of a vinylidene fluoride polymer can be easily and conveniently performed as a step in a process for producing (semi)-crystalline vinylidene fluoride polymer particles that can be easily dissolved in an organic solvent.

[0023] It has also been found that homogeneous solutions of these (semi)-crystalline vinylidene fluoride polymer particles in various organic solvents can be readily obtained and can be advantageously processed into articles having uniform properties.

[0024] In a first embodiment, the present invention relates to a method for producing (semi)-crystalline vinylidene fluoride (VDF) polymer particles [polymer (F f ) particles], the method comprising:

[0025] (i) providing an aqueous dispersion [dispersion (D)] consisting of an aqueous medium and particles of at least one (semi-)crystalline VDF-based polymer [polymer (F) particles];

[0026] (ii) heat treating the dispersion (D) provided in step (i) at a temperature comprised in the range from 100° C. to 180° C., preferably from 110° C. to 160° C., under stirring; and

[0027] (iii) the polymer (F f ) particles are separated from the heat-treated dispersion obtained in step (ii).

[0028] In a second embodiment, the present invention relates to one or more (semi)-crystalline vinylidene fluoride (VDF) polymer particles [polymer (F f )particle].

[0029] In a third example, the present invention relates to a composition [composition (C)] comprising:

[0030] - one or more polymers of the invention (F f ) particles, and

[0031] - a liquid medium comprising one or more organic solvents. DETAILED DESCRIPTION

[0032] As used in this specification and the following claims:

[0033] - the expression "(semi)-crystalline polymer" is intended to indicate a polymer having a heat of fusion greater than 1 J / g, more preferably from 35 J / g to 1 J / g, even more preferably from 15 J / g to 5 J / g, when measured by differential scanning calorimetry (DSC) according to ASTM D-3418 at a heating rate of 10° / min;

[0034] The term "dispersion (D)" is intended to indicate an aqueous dispersion of particles comprising at least one polymer (F), said particles having a size distribution with a D50 value from 10 to 1000 μm, preferably from 50 to 500 μm.

[0035] The term "aqueous medium" in dispersion (D) is used to include water and water in combination with other ingredients such as wetting agents and surfactants. As wetting agents, polyols may be mentioned. As surfactants, any of cationic surfactants, anionic surfactants, amphoteric surfactants and nonionic surfactants may be used.

[0036] Preferably, the aqueous medium in the dispersion (D) contains essentially water.

[0037] In one embodiment of the present invention, the polymer (F) particles in the dispersion (D) are wet polymer (F) particles [polymer (WF) particles].

[0038] The polymer (WF) particles are obtained by polymerization, typically by suspension polymerization or by supercritical suspension polymerization, in a polymerization medium comprising vinylidene fluoride (VDF), optionally at least one fluorinated monomer different from vinylidene fluoride (VDF), and optionally at least one hydrogenated monomer.

[0039] The polymerization for producing the polymer (WF) particles is typically carried out at a temperature of at least 10° C., preferably at least 25° C., more preferably at least 45° C. The polymerization is typically carried out at a temperature of at most 140° C., preferably at most 100° C., more preferably at most 80° C. and at a pressure of at least 25 bar, preferably at least 50 bar, more preferably at least 75 bar.

[0040] The polymerization is typically carried out in the presence of a free radical initiator. The free radical initiator may be an organic free radical initiator or an inorganic free radical initiator.

[0041] The free radical initiator is typically selected from the group consisting of:

[0042] -Formula (R f -CO-O)2 bis-acyl peroxide (where R f It is C1-C 10(per)haloalkyl or perfluoropolyoxyalkylene), particularly preferably bis-trichloroacetyl peroxide and bis-dichlorofluoroacetyl peroxide;

[0043] -Formula (R H -O)2 dialkyl peroxide (where R H It is C1-C 10 Alkyl), particularly preferably di-tert-butyl peroxide (DTBP);

[0044] - water-soluble inorganic peroxides, such as ammonium or alkali metal persulfates or perphosphates, particularly preferably sodium and potassium persulfate;

[0045] - dialkyl peroxydicarbonates in which the alkyl group has from 1 to 8 carbon atoms, such as di-n-propyl peroxydicarbonate and diisopropyl peroxydicarbonate;

[0046] - alkyl peroxyesters, such as tert-amyl peroxypivalate and tert-butyl peroxyisobutyrate; and

[0047] - Organic or inorganic redox systems, such as ammonium persulfate / sodium sulfite, hydrogen peroxide / aminoimidomethanesulfinic acid, tert-butyl hydroperoxide / metabisulfite.

[0048] The polymerization medium in the polymerization for making polymer (WF) particles typically comprises an organic phase to which water is usually added in order to facilitate the development of heat dispersion during the reaction. The organic phase can be formed from the monomers themselves without adding solvent, or from the monomers dissolved in a suitable organic solvent.

[0049] At the end of the polymerization, the solid particles are generally separated from the polymerization medium by filtration and subjected to repeated washings with clean water so as to obtain an almost complete replacement of the residual polymerization medium with clean water, thereby providing particles of polymer (WF).

[0050] In another embodiment of the present invention, the polymer (F) particles in the dispersion (D) are dry polymer (F) particles [polymer (DF) particles].

[0051] The polymer (DF) particles are obtained by drying the polymer (WF) particles, preferably at a temperature comprised between 30 and 120°C, preferably between 50 and 90°C, to provide the polymer (DF) particles in the form of powder particles.

[0052] In this embodiment, dispersion (D) can be obtained by dispersing the dried polymer (DF) particles in an aqueous medium that suitably contains a wetting agent to facilitate the dispersion of the powder. The wetting agent can be selected from at least one alcohol, at least one ionic surfactant, at least one nonionic surfactant, or a mixture thereof.

[0053] Preferably, the polymer (F) particles contained in the dispersion (D) are polymer (WF) particles as defined above, ie wet particles of at least one (semi)-crystalline VDF-based polymer which has not been subjected to drying at the end of the polymerization for its manufacture.

[0054] Therefore, the dispersion (D) can be conveniently obtained without any energy- and time-consuming drying process.

[0055] Preferably, the dispersion (D) used in step (i) of the process of the present invention has a solids content of polymer (F) dispersed in an aqueous medium, preferably in water, ranging from 5 to 50% by weight.

[0056] The solids content of the polymer (F) in the dispersion (D) can be conveniently adjusted by adding or removing water to achieve the desired weight percentage.

[0057] Said solids content of polymer (F) dispersed in the aqueous medium allows very effective stirring of the dispersion (D) during step (ii) of the process, which keeps the particles (F) well dispersed in the aqueous medium during the thermal treatment.

[0058] Effective stirring of the dispersion (D) in step (ii) of the process allows a very uniform thermal treatment of the polymer (F) to be achieved.

[0059] For the manufacture of polymers (F f ) particles is typically carried out at a temperature of at least 100°C, preferably at least 110°C, more preferably at least 120°C.

[0060] For the manufacture of polymers (F f ) particles is typically carried out at a temperature of at most 180°C, preferably at most 160°C, more preferably at most 150°C.

[0061] For the manufacture of polymers (F f ) Step (ii) of the process of the invention for producing the particles is typically carried out at a pressure above atmospheric pressure.

[0062] The pressure above atmospheric pressure may be established by carrying out the heat treatment of step (ii) in a container which may be pressurized by the internal pressure generated by water contained in the dispersion (D) heated to above 100°C.

[0063] Optionally, when the intention is to increase the internal pressure within the container, the higher pressure within the container may be obtained by pressurizing with at least one additional non-condensable gas, such as air or nitrogen.

[0064] For the manufacture of polymers (F f ) particles is typically carried out over a period of time ranging from 5 minutes to 6000 minutes, preferably from 10 minutes to 200 minutes, more preferably from 30 minutes to 90 minutes.

[0065] In step (iii) of the process of the present invention, the polymer (F f ) particles are separated from the heat-treated dispersion (D).

[0066] In step (iii), the polymer (F f ) The separation of particles is typically carried out by filtration.

[0067] The polymer (F) obtained in step (iii) of the process may be treated with an aqueous medium. f ) The particles are subjected to a washing step in order to remove possible residual impurities.

[0068] In a preferred embodiment of the present invention, there is provided a method for producing one or more (semi)-crystalline vinylidene fluoride (VDF) polymer particles [polymer (F f ) particles], the method comprising:

[0069] (i) providing an aqueous dispersion [dispersion (D)] consisting of an aqueous medium and particles of at least one (semi-)-crystalline VDF-based polymer [polymer (F)];

[0070] (ii) heat treating the dispersion (D) provided in step (i) in a closed container at a temperature comprised in the range from 100° C. to 180° C., preferably from 110° C. to 160° C., under stirring;

[0071] (iii) the polymer (F f ) separating particles from the heat-treated dispersion obtained in step (ii); and

[0072] (iv) using an aqueous medium to allow the polymer (F) obtained in step (iii) to f ) The particles are subjected to a washing step.

[0073] Preferably, the aqueous medium in washing step (iv) contains essentially water.

[0074] Typically, the polymer (F) separated from the heat-treated dispersion (D) is f ) particles are subjected to drying.

[0075] At a temperature above 50°C, preferably above 80°C, the polymer (F f ) The drying of the particles is conveniently carried out in a fluidized bed.

[0076] The Applicant has surprisingly found that, compared to dry polymer (F) particles which have not been subjected to the heat treatment of the process according to the invention, dry polymer (F f ) particles are more efficient in terms of the energy required and in terms of time setting. Furthermore, the heat-treated polymer (F) particles make the fluidization of the powder obtained therefrom more efficient.

[0077] Without limiting the scope of the present invention, the applicant believes that the polymer (F) obtained by the process of the present invention is due to the change in the conformation of the polymer during the process of the present invention. f ) particles advantageously exhibit higher solubility.

[0078] In a second embodiment, the present invention relates to one or more (semi)-crystalline vinylidene fluoride (VDF) polymer particles [polymer (F f )particle].

[0079] The polymer (F f ) particles typically have an intrinsic viscosity of at least 0.13 l / g, preferably at least 0.15 l / g, more preferably at least 0.20 l / g.

[0080] Polymer (F f ) The intrinsic viscosity of the particles is typically measured in N,N-dimethylformamide at 25°C.

[0081] The polymer (F f ) particles are typically in the form of powder particles.

[0082] Polymer (F f ) The particles are typically in the form of powder particles, which typically have a size distribution with a D50 value of at least 10 μm, preferably at least 30 μm, more preferably at least 60 μm.

[0083] In this document, the D50 value is used according to its ordinary meaning and thus indicates the diameter at which 50% of the particles in a sample are smaller than the D50 value and the remaining 50% of the particles are larger than said D50 value.

[0084] The particle size distribution is determined by laser diffraction by measuring the angular variation in the intensity of light scattered when a laser beam passes through a dispersed sample of particles. The particle size is reported as a volume equivalent sphere diameter.

[0085] The polymer (F f ) particles typically do not contain one or more (semi)-crystalline VDF polymer particles in the form of fine powder particles having an average size of less than 3 μm, preferably less than 5 μm.

[0086] Polymer (F) and polymer (Ff ) each typically further comprises repeating units derived from at least one fluorinated monomer different from vinylidene fluoride (VDF), and optionally repeating units derived from at least one hydrogenated monomer.

[0087] However, it is preferred that polymer (F) and polymer (F f ) each contain at least 70% by mole of repeating units derived from vinylidene fluoride (VDF), wherein the molar amount of the repeating units is relative to the polymer (F) and the polymer (F f ) is the total number of moles of repeating units in the mixture.

[0088] For the purposes of the present invention, the term "fluorinated monomer" is intended to mean an ethylenically unsaturated monomer comprising at least one fluorine atom.

[0089] For the purposes of the present invention, the term "hydrogenated monomer" is intended to mean an ethylenically unsaturated monomer containing at least one hydrogen atom and no fluorine atoms.

[0090] If the fluorinated monomer contains at least one hydrogen atom, it is designated as a hydrogen-containing fluorinated monomer.

[0091] If the fluorinated monomer contains no hydrogen atoms, it is designated as a per(halo)fluorinated monomer.

[0092] The fluorinated monomer may further comprise one or more other halogen atoms (Cl, Br, I).

[0093] Non-limiting examples of suitable fluorinated monomers include notably the following:

[0094] - C2-C8 perfluoroolefins, such as tetrafluoroethylene and hexafluoropropylene (HFP);

[0095] - C2-C8 hydrogenated fluoroolefins, such as vinyl fluoride, 1,2-difluoroethylene and trifluoroethylene;

[0096] -Formula CH2=CH-R f0 Perfluoroalkylethylene, where R f0 is a C1-C6 perfluoroalkyl group;

[0097] - chloro- and / or bromo- and / or iodo-C2-C6-fluoroolefins, such as chlorotrifluoroethylene;

[0098] - Formula CF2=CFOR f1 (per)fluoroalkyl vinyl ether, wherein R f1 is C1-C6 fluoro- or perfluoroalkyl, such as CF3, C2F5, C3F7;

[0099] -CF2=CFOX0 (per)fluoro-oxyalkyl vinyl ether, wherein X0 is C1-C 12 Alkyl, C1-C 12 Oxyalkyl or C1-C 12 (Per)fluorooxyalkyl, such as perfluoro-2-propoxy-propyl;

[0100] - Formula CF2=CFOCF2OR f2 (per)fluoroalkyl vinyl ether, wherein R f2 is a C1-C6 fluoro- or perfluoroalkyl group, such as CF3, C2F5, C3F7, or a C1-C6 (per)fluorooxyalkyl group having one or more ether groups, such as -C2F5-O-CF3;

[0101] - a functional (per)fluoro-oxyalkyl vinyl ether of the formula CF2=CFOY0, wherein Y0 is C1-C 12 Alkyl or (per) fluoroalkyl, C1-C 12 Oxyalkyl or C1-C 12 (per)fluorooxyalkyl, and Y0 comprises a carboxylic acid or sulfonic acid group in the form of its acid, acyl halide or salt; and

[0102] - fluorodioxole, preferably perfluorodioxole.

[0103] Polymer (F) and polymer (F f ) each preferably comprises:

[0104] (a) at least 60% by mole, preferably at least 75% by mole, more preferably at least 85% by mole of repeating units derived from vinylidene fluoride (VDF),

[0105] (b) optionally, from 0.1 to 15 % by mole, preferably from 0.1 to 12 % by mole, more preferably from 0.1 to 10 % by mole of repeating units derived from at least one fluorinated monomer (F), and

[0106] (c) optionally, repeating units derived from at least one hydrogenated monomer,

[0107] The molar amount of the repeating unit is relative to the polymer (F) and the polymer (F f ) is the total number of moles of repeating units in the mixture.

[0108] The hydrogenated monomer may be a functional hydrogenated monomer.

[0109] For the purposes of the present invention, the term "functional hydrogenated monomer" is intended to mean a hydrogenated monomer comprising at least one functional end group.

[0110] Polymer (F) and polymer (F f ) each contain preferably at least 0.01% by mole, more preferably at least 0.05% by mole, even more preferably at least 0.1% by mole of repeating units derived from at least one functional hydrogenated monomer, wherein the molar amount of said repeating units is relative to said polymer (F) and said polymer (F f ) is the total number of moles of repeating units in the mixture.

[0111] Polymer (F) and polymer (F f ) each contain preferably at most 20% by mole, more preferably at most 15% by mole, even more preferably at most 10% by mole, most preferably at most 3% by mole of repeating units derived from at least one functional hydrogenated monomer, wherein the molar amount of said repeating units is relative to said polymer (F) and said polymer (F f ) is the total number of moles of repeating units in the mixture.

[0112] The determination of the average molar percentage of recurring units derived from at least one functional hydrogenated monomer in the (semi)-crystalline vinylidene fluoride polymer can be carried out by any suitable method. Mention may notably be made of the acid-base titration method or the NMR method.

[0113] The functional hydrogenated monomer typically comprises at least one functional end group selected from hydroxyl end groups and carboxylic acid end groups.

[0114] The functional hydrogenated monomer is preferably selected from the group consisting of (meth)acrylic acid monomers of formula (I) and vinyl ether monomers of formula (II):

[0115]

[0116] wherein R1, R2 and R3 are the same or different from each other and are independently a hydrogen atom or a C1-C3 hydrocarbon group, R X is a hydrogen atom or a C1-C5 hydrocarbon group containing at least one hydroxyl group, and R' x It is a C1-C5 hydrocarbon group containing at least one hydroxyl group.

[0117] The functional hydrogenated monomer more preferably has formula (I) as defined above.

[0118] Even more preferably the functional hydrogenated monomer has formula (IA):

[0119]

[0120] wherein R'1, R'2 and R'3 are hydrogen atoms, and R" X is a hydrogen atom or a C1-C5 hydrocarbon group containing at least one hydroxyl group.

[0121] Non-limiting examples of (meth)acrylic monomers of formula (I) include notably acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxyethylhexyl (meth)acrylate.

[0122] The (meth)acrylic monomer of formula (I) is more preferably selected from the following:

[0123] - acrylic acid (AA) of the formula:

[0124]

[0125] - Hydroxyethyl acrylate (HEA) of the formula:

[0126]

[0127] - 2-Hydroxypropyl acrylate (HPA) of any of the following formulas:

[0128]

[0129] - and mixtures thereof.

[0130] In a third example, the present invention relates to a composition [composition (C)] comprising:

[0131] - one or more polymers of the invention (F f ) particles, and

[0132] - a liquid medium comprising one or more organic solvents.

[0133] The composition (C) of the present invention typically comprises:

[0134] - from 0.5% to 50% by weight, preferably from 1% to 30% by weight, more preferably from 5% to 20% by weight, of one or more polymers of the invention (F f ) particles, and

[0135] - from 99.5% to 50% by weight, preferably from 99% to 70% by weight, more preferably from 95% to 80% by weight, of a liquid medium comprising one or more organic solvents, relative to the total weight of composition (C).

[0136] The composition (C) of the present invention can typically be prepared by combining one or more polymers (F f ) particles are dispersed in a liquid medium comprising one or more organic solvents.

[0137] The composition (C) of the invention is advantageously a homogeneous solution.

[0138] The term "solution" is herein intended to mean a clear homogeneous solution of (semi)-crystalline VDF polymer particles as defined above in a liquid medium comprising one or more organic solvents.

[0139] The choice of organic solvent is not particularly limited, provided that it is suitable for dissolving the polymer (F) of the present invention. f )particle.

[0140] Non-limiting examples of organic solvents suitable for use in the composition (C) of the present invention are typically selected from the group consisting of:

[0141] - alcohols, such as methanol, ethanol and diacetone alcohol,

[0142] - ketones, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone and isophorone,

[0143] - linear or cyclic esters, such as isopropyl acetate, n-butyl acetate, methyl acetoacetate, dimethyl phthalate and gamma-butyrolactone,

[0144] - linear or cyclic amides, such as N,N-diethylacetamide, N,N-dimethylacetamide, dimethylformamide and N-methyl-2-pyrrolidone, and

[0145] -Dimethyl sulfoxide.

[0146] The composition (C) of the present invention can be easily processed into various products.

[0147] The composition (C) of the present invention is particularly suitable for use in a process for manufacturing an article, which process comprises processing the composition (C), typically by casting.

[0148] Casting generally involves solution casting, wherein a uniform film of composition (C) is spread onto a suitable substrate, typically using a casting knife, draw bar or slot die.

[0149] According to a first embodiment of the invention, the invention relates to a method for manufacturing a membrane, the method comprising:

[0150] (1a) providing the composition (C) of the present invention, and

[0151] (2a) The composition (C) provided in step (1a) is typically processed into a film by casting.

[0152] Under step (2a) of the method for making a membrane, casting generally involves solution casting, wherein a uniform film of composition (C) is spread onto a suitable substrate typically using a casting knife, a stretching rod or a slot die. The substrate may be a porous substrate or a non-porous substrate.

[0153] The films of the present invention typically comprise at least one layer comprising one or more polymers of the present invention (F f )particle.

[0154] The membrane of the invention is advantageously obtainable by the method according to this first embodiment of the invention.

[0155] The membranes of the present invention are particularly suitable for use in a variety of applications.

[0156] The membrane of the present invention is particularly suitable for use in a separator for an electrochemical device.

[0157] The separator for an electrochemical device of the present invention typically comprises:

[0158] - at least one membrane according to the invention, and

[0159] - Optionally, adhered to said membrane (F) a substrate comprising one or more layers, preferably a porous substrate comprising one or more layers, such as a porous substrate comprising at least one layer comprising at least one polyolefin.

[0160] Therefore, the present invention also relates to a method for producing a separator for an electrochemical device, the method comprising:

[0161] (1b) providing the composition (C) of the present invention, and

[0162] (2b) The composition (C) provided in step (1b) is typically processed by casting onto a substrate.

[0163] In step (2b) of the method for manufacturing a separator for an electrochemical device, casting generally involves solution casting, wherein a uniform film of the composition (C) is spread onto a suitable substrate using a casting knife, a stretching rod or a slot die. The substrate may be a porous substrate or a non-porous substrate.

[0164] The substrate is preferably a porous substrate comprising one or more layers, such as a porous substrate comprising at least one layer comprising at least one polyolefin.

[0165] Non-limiting examples of electrochemical devices include secondary batteries, such as lithium-ion secondary batteries.

[0166] According to a second embodiment of the present invention, the present invention relates to a method for manufacturing a filtration membrane, the method comprising:

[0167] (1c) providing the composition (C) of the present invention,

[0168] (2c) processing the composition (C) provided in step (1c) into a film, typically by casting, and (3c) precipitating the film provided in step (2c) in a non-solvent medium.

[0169] Under step (3c) of the method for making a filtration membrane, casting generally involves solution casting, wherein a uniform film of composition (C) is spread onto a suitable substrate typically using a casting knife, a stretching rod or a slot die. The substrate may be a porous substrate or a non-porous substrate.

[0170] Depending on the final form of the film to be produced, different casting techniques are used.

[0171] When the final product is a flat film, the film can typically be obtained by casting the film onto a flat support substrate (typically a plate, belt or fabric), or onto another microporous support membrane, typically with the aid of a casting knife, a stretching bar or a slot die.

[0172] The term "membrane" is used herein in its ordinary sense, ie, it refers to a discrete, generally thin interface that restricts the permeation of chemical species in contact with it, the membrane containing pores of finite size.

[0173] Membranes containing pores uniformly distributed throughout their thickness are generally referred to as symmetric (or isotropic) membranes; membranes containing pores non-uniformly distributed throughout their thickness are generally referred to as asymmetric (or anisotropic) membranes.

[0174] For the purposes of the present invention, the term "non-solvent medium" means a medium consisting of one or more solvents that are not capable of dissolving the polymer of the present invention at a given temperature. f ) is a medium composed of liquid substances with particles.

[0175] The non-solvent medium typically comprises water and, optionally, at least one organic solvent selected from alcohols or polyols, preferably aliphatic alcohols having a short chain (eg from 1 to 6 carbon atoms), more preferably methanol, ethanol, isopropanol and ethylene glycol.

[0176] The non-solvent medium is generally chosen among those which are miscible with the liquid medium used to prepare composition (C).

[0177] The filtration membrane of the present invention typically comprises at least one layer comprising one or more polymers (F f )particle.

[0178] The filtration membrane of the invention is advantageously obtainable by the method according to this second embodiment of the invention.

[0179] The filtration membrane of the present invention is particularly suitable for filtering various liquid phases and / or gas phases.

[0180] In a fourth embodiment, the present invention relates to a composition for forming an electrode [composition (E)] comprising:

[0181] - one or more polymers of the invention (F f )particle,

[0182] - at least one electroactive compound [compound (EA)],

[0183] - a liquid medium comprising one or more organic solvents,

[0184] - optionally, at least one electrically conductive compound [compound (C)], and

[0185] - Optionally, one or more additives.

[0186] The composition (E) of the present invention preferably comprises:

[0187] - from 0.5% to 50% by weight, preferably from 1% to 30% by weight, more preferably from 5% to 20% by weight, relative to the total weight of the composition (E), of one or more polymers (F f )particle,

[0188] - at least one electroactive compound [compound (EA)],

[0189] - a liquid medium comprising one or more organic solvents,

[0190] - optionally, at least one electrically conductive compound [compound (C)], and

[0191] - Optionally, one or more additives.

[0192] The composition (E) of the present invention can typically be obtained by adding at least one electroactive compound [compound (EA)], optionally at least one conductive compound [compound (C)], and optionally one or more additives to the composition (C) of the present invention.

[0193] The composition (E) of the present invention is particularly suitable for use in a method for producing an electrode for an electrochemical device, the method comprising:

[0194] (1d) providing a composition (E) of the present invention,

[0195] (2d) applying the composition (E) provided in step (1d) to one surface of a metal substrate, thereby providing a surface-coated electrode, and

[0196] (3d) Drying the surface-coated electrode provided in step (2d).

[0197] The metal substrate typically serves as the metal current collector.

[0198] The metal substrate is typically a foil, screen, or mesh made of a metal such as copper, aluminum, iron, stainless steel, nickel, titanium, or silver.

[0199] The electrode of the invention is typically dried at a temperature comprised between 25°C and 200°C.

[0200] Under step (3d) of the method for manufacturing an electrode for an electrochemical device, drying can be carried out at atmospheric pressure or under vacuum. Alternatively, drying can be carried out under a modified atmosphere, for example in an inert gas, typically notably with the removal of moisture (water vapor content less than 0.001% v / v). The drying temperature will be selected so as to remove by evaporation one or more solvents (S) from the electrode of the present invention.

[0201] Therefore, the present invention also relates to an electrode for an electrochemical device, the electrode comprising:

[0202] - one or more polymers of the invention (F f )particle,

[0203] - at least one electroactive compound [compound (EA)],

[0204] - optionally, at least one electrically conductive compound [compound (C)], and

[0205] - Optionally, one or more additives.

[0206] The electrode for an electrochemical device of the present invention can be advantageously obtained by the method of the present invention.

[0207] The electrode for an electrochemical device of the present invention preferably comprises:

[0208] - from 0.1% to 15% by weight, preferably from 0.3% to 10% by weight, of one or more polymers of the invention (F f )particle,

[0209] - from 99.9% to 85% by weight, preferably from 99.7% to 90% by weight, of at least one electroactive compound [compound (EA)], relative to the total weight of the electrode,

[0210] - optionally, at least one electrically conductive compound [compound (C)], and

[0211] - Optionally, one or more additives.

[0212] The electrodes of the present invention are preferably free of one or more organic solvents.

[0213] Non-limiting examples of electrochemical devices include secondary batteries, such as lithium-ion secondary batteries.

[0214] For the purposes of the present invention, the term "electroactive compound [compound (EA)]" is intended to denote a compound that is capable of incorporating or intercalating an alkali metal or alkaline earth metal ion into its structure and substantially releasing an alkali metal or alkaline earth metal ion therefrom during the charging and discharging phases of an electrochemical device. The compound (EA) is preferably capable of incorporating or intercalating and releasing lithium ions.

[0215] The properties of the compound (EA) depend on whether the electrode is a positive electrode or a negative electrode.

[0216] In the case of forming a positive electrode for a lithium ion secondary battery, the compound (EA) may comprise a complex metal chalcogenide of the formula LiMQ2, where M is at least one metal selected from transition metals such as Co, Ni, Fe, Mn, Cr and V, and Q is a chalcogen element such as O or S. Among these, lithium-based complex metal oxides of the formula LiMO2, where M is as defined above, are preferably used. Preferred examples thereof may include: LiCoO2, LiNiO2, LiNi x Co 1-x O2 (0 < x < 1) and spinel-structured LiMn2O4.

[0217] As an alternative, still in the case of forming a positive electrode for a lithium ion secondary battery, the compound (EA) may comprise a lithiated or partially lithiated transition metal oxyanion-based electroactive material of the formula M1M2(JO4) f E 1-f where M1 is lithium, which may be partially replaced by another alkali metal that occupies less than 20% of the M1 metal; M2 is a transition metal at an oxidation level of +2 selected from Fe, Mn, Ni, Al or a mixture thereof or at an oxidation level of +3 selected from V, Co or a mixture thereof, which may be partially replaced by one or more additional metals, the additional metal being at an oxidation level between +1 and +5 and occupying less than 35% of the M2 metal, including 0; JO4 is any oxyanion, where J is P, S, V, Si, Nb, Mo or a combination thereof; E is a fluoride anion, a hydroxide anion or a chloride anion; and f is the mole fraction of the JO4 oxyanion, generally included between 0.75 and 1.

[0218] The M1M2(JO4) f E 1-f electroactive material is preferably phosphate-based and may have an ordered or modified olivine structure.

[0219] More preferably, the compound (EA) has the formula Li 3-x M’ y M” 2-y(JO4)3, wherein 0≤x≤3, 0≤y≤2; M' and M" are the same or different metals, at least one of which is a transition metal; JO4 is preferably PO4, which may be partially substituted with another oxygen anion, wherein J is S, V, Si, Nb, Mo or a combination thereof. Still more preferably, the compound (EA) is of the formula Li(Fe x Mn 1-x )PO4, wherein 0≤x≤1, wherein x is preferably 1 (ie, lithium iron phosphate of formula LiFePO4).

[0220] In the case of forming a negative electrode for a lithium ion secondary battery, the compound (EA) may preferably contain:

[0221] - graphitic carbon capable of intercalating lithium, typically in the form of powders, flakes, fibers, or spheres (e.g., mesocarbon microbeads) loaded with lithium;

[0222] - lithium metal;

[0223] - lithium alloy compositions, notably including those described in US 6203944 (3M INNOVATIVE PROPERTIES CO.) 3 / 20 / 2001 and / or WO 00 / 03444 (MINNESOTA MINING AND MANUFACTURING CO.) 1 / 20 / 2000;

[0224] -Lithium titanates, generally of the formula Li4Ti5O 12 These compounds are generally considered to be “zero strain” intercalation materials that, upon absorbing mobile ions (i.e., Li + ) has a low level of physical expansion;

[0225] - Lithium-silicon alloys, generally referred to as lithium silicides with a high Li / Si ratio, especially those of the formula Li 4.4 Lithium silicide of Si;

[0226] - Lithium-germanium alloys, including Li 4.4 Crystalline phase of Ge;

[0227] -Lithium-tin alloys and lithium-antimony alloys.

[0228] For the purposes of the present invention, the term "conductive compound [compound (C)]" is intended to mean a compound capable of imparting electronic conductivity to an electrode.

[0229] Compound (C) is typically selected from the group consisting of carbonaceous materials, such as carbon black, carbon nanotubes, graphite powder, graphite fibers, and metal powders or fibers (such as powders or fibers of nickel and aluminum).

[0230] The composition (E) of the present invention may further contain one or more additives such as vinylene carbonate, vinyl ethylene carbonate, allyl ethyl carbonate, vinyl acetate, divinyl adipate, acrylic nitrile, 2-vinylpyridine, maleic anhydride, methyl cinnamate, phosphonic acid alkyl esters, and vinyl-containing silane-based compounds.

[0231] Should the disclosure of any patents, patent applications, and publications incorporated by reference into this application conflict with the description of the present application to the extent that it renders a term unclear, the present description shall take precedence.

[0232] The present invention will now be described in more detail with reference to the following examples, the purpose of which is merely illustrative and not limiting the scope of the present invention.

[0233] Experimental Section

[0234] Determination of the intrinsic viscosity of vinylidene fluoride polymer powder particles

[0235] The intrinsic viscosity (η) [dl / g] is measured using an Ubbelhode viscometer on the basis of the falling time of a solution at a concentration of about 0.2 g / dl obtained by dissolving vinylidene fluoride polymer powder particles in N,N-dimethylformamide at 25° C. using the following equation:

[0236]

[0237] where c is the polymer concentration [g / dl], η r is the relative viscosity, i.e. the ratio between the falling time of the sample solution and the falling time of the solvent, η sp is the specific viscosity, η r -1, and Γ is an experimental factor, which corresponds to 3 for vinylidene fluoride polymers.

[0238] Determination of Particle Size Distribution (PSD) of Vinylidene Fluoride Polymer Powders

[0239] The particle size distribution was measured using a Mastersizer 2000 apparatus from Malvern Instruments Ltd equipped with a Hydro 2000G sample dispersion unit using a He-Ne laser with a power source of 2 mW. Particle size distribution was measured on aqueous solutions prepared with a solution of X-100 nonionic surfactant.

[0240] Dissolution time of vinylidene fluoride polymer powder particles

[0241] At room temperature, 3 g of the vinylidene fluoride polymer powder particles were poured into a beaker containing 47 g of N-methyl 2-pyrrolidone (NMP) under stirring using a magnetic stirrer maintained at 500 rpm, thereby obtaining a 6% w / w solution of the vinylidene fluoride polymer in NMP.

[0242] After 15 seconds, the stirrer was stopped and a first visual inspection was carried out: depending on the type of powder, the presence of agglomerates of vinylidene fluoride polymer could be detected at this stage.

[0243] The beaker containing the solution of vinylidene fluoride polymer in NMP is then moved onto a second magnetic stirrer, this time introducing a magnetic stirrer maintained at a higher temperature T. 浴 The beaker was placed in a heating bath at 45° C. The magnetic stirrer was maintained at 500 rpm. The time between the introduction of the beaker into the heating bath and complete dissolution (when the solution appeared clear without any visible particles of the vinylidene fluoride polymer or any visible aggregates thereof) was recorded.

[0244] The dissolution time according to this procedure is then given by the sum of the following two steps: 15 s at room temperature and 15 s at T 浴 The time until dissolution is measured. The test is stopped after a total dissolution time of 30 minutes. If the dissolution time exceeds 30 minutes, the test fails.

[0245] Example 1: Preparation of polymer 1 and dispersion 1 of polymer 1

[0246] 2103 g of desalted water and 1.76 g of 80 polyvinyl alcohol as a suspending agent. The reactor is equipped with an impeller running at a speed of 880rpm. The reactor is vented three times and pressurized to 1 bar twice with nitrogen at 20°C. Then, 4.1g of a solution of 75% by weight of tert-amyl perpivalate initiator in isododecane and 0.5g of acrylic acid (AA) monomer are introduced into the reactor, followed by 1164g of vinylidene fluoride (VDF) monomer. The reactor is then gradually heated to 55°C until a final pressure of 110 bar. During the entire experiment, the temperature is maintained constant at 55°C and the pressure is maintained constant at 110 bar by feeding an aqueous solution of 14.4g / l of AA monomer to a total of 857g. The pressure is reduced to 90 bar, and the polymerization operation is stopped by degassing the suspension until atmospheric pressure is reached. The polymer thus obtained is then recovered and washed several times with desalted water.

[0247] A portion of the wet polymer obtained after washing with water was dried in an oven at 65° C. to yield a polymer 1 powder, ie VDF-acrylic acid (AA) (0.8% by mole) with an intrinsic viscosity of 0.29 l / g in DMF at 25° C. The D50 of the powder was 111.9 μm.

[0248] The remaining wet polymer was added via clean water to give a 15% by weight aqueous dispersion: Dispersion 1.

[0249] Example 2: Heat treatment of dispersion 1

[0250] The preparation of dispersion 1 obtained as in Example 1 was repeated several times to produce 15 Kg of dispersion 1, wherein the concentration of polymer 1 in water was 15% by weight. Dispersion 1 was loaded into a 22 liter stirred reactor under vacuum. The temperature was fixed at 135°C and the stirring rate was at 300RPM. The final pressure in the reactor was 3.7 bar (absolute pressure), which was essentially given by the water pressure. The dispersion was kept under these conditions for 60 minutes. After this, when the slurry was discharged, the reactor was cooled to 40°C under stirring. The dispersion was then filtered and placed in a fluidized bed of air at a temperature between 90°C and 95°C to obtain a polymer (FT-A). The filter cake was well fluidized and was superior to the untreated filter cake.

[0251] In the polymer particles of the polymer (FT-A) after heat treatment and drying, no aggregation or color change from the initial white color of the polymer 1 obtained after polymerization in Example 1 was observed.

[0252] Comparative Example 3: Heat Treatment of Polymer 1 Powder in a Fluidized Bed

[0253] The polymer 1 powder was treated in a fluidized bed at 135°C for a total of 60 minutes.

[0254] The operating conditions of the fluidized bed are as follows:

[0255] Fluidized bed (two configurations with and without fines recirculation were tested)

[0256] Volume: 30L

[0257] Product retention: minimum 1kg - maximum 10kg

[0258] Air flow speed: minimum 20cm / s-maximum 70cm / s (referring to the empty section of the bed)

[0259] Operating temperature: 125℃-135℃

[0260] Dwell time: 60 minutes after reaching the set point temperature

[0261] Heating medium: hot air (preheating is electric heating or steam heating)

[0262] Operating parameters under monitoring: inlet temperature of air, temperature of the bulk, pressure drop in the bed.

[0263] The powder became colored after 10 minutes in the fluidized bed. At the end of the treatment, polymer 1TA was obtained as a brown powder.

[0264] Heat is supplied only by the inlet air. To minimize the heating time, the equipment is preheated before feeding the powder at ambient temperature. To minimize the heating time without the risk of melting or softening of the powder, the inlet temperature of the air is the best compromise. The inlet temperature of the air is up to 10°C higher than the temperature of the powder bulk. Contact of the powder with hot surfaces (especially the distribution grid) must be avoided.

[0265] During the treatment, aggregation of polymer 1 particles was observed. Aggregation of particles increased with increasing residence time in the bed. Due to this trend, it was difficult to maintain particle motion and good fluidization during the entire test. In particular, part of the product aggregated and thus fell onto the distribution plate. At the end of the treatment, partially softened or pre-melted product was found on the distribution plate.

[0266] The same treatment was carried out in a fluidized bed under nitrogen atmosphere. No improvement in color was seen, and the process was made more complicated by the use of bulky equipment.

[0267] Comparative Example 4: Heat treatment of polymer 1 powder with circulating air

[0268] Polymer 1 powder was treated in an oven under the following operating conditions:

[0269] Equipment: Oven

[0270] Powder retention: 1kg

[0271] Operating temperature: 135℃

[0272] Residence time: 60min

[0273] Heating medium: Electric heating and air circulation

[0274] Treatment in an oven resulted in polymer 1TB: colored polymer particles characterized by the formation of aggregates. Even the shape of the polymer particles that were not in the form of aggregates (spherical) was modified by the heat treatment and became very irregular.

[0275] A slight improvement in color can be achieved by treating under a nitrogen atmosphere, resulting in particles of lighter color.

[0276] Example 5: Dissolution time of polymer 1, polymer (FT-A), polymer 1TA and polymer 1TB

[0277] The dissolution test of the polymer powders obtained in Example 2, Comparative Example 3 and Comparative Example 4 was performed as defined above.

[0278] The results are shown in Table 1.

[0279] Table 1

[0280]

[0281] The powders of the polymers treated according to the process of the invention show faster dissolution in NMP than powders obtained by thermal treatment of the polymers in powder form.

[0282] Overall, the process of the invention shows several advantages in terms of the color and solubility of the polymer particles obtained, and in terms of the operating procedures and equipment required compared to the thermal treatment of dry polymer powders by several methods available in the art. The thermal treatment of the process of the invention can be sequenced after the washing required after the polymerization reaction, without the need for intermediate drying. The temperature of the final drying is then the same as for the untreated powder, but the drying is more efficient in terms of time and therefore in terms of the energy required to complete it.

Claims

1. A method for producing a semi-crystalline vinylidene fluoride VDF polymer F f A method for particles, the method comprising: (i) providing an aqueous dispersion D consisting of an aqueous medium and particles of at least one semi-crystalline VDF-based polymer F, and (ii) heat treating the dispersion D provided in step (i) at a temperature comprised between 100° C. and 180° C. under stirring, and (iii) polymer F f separating particles from the heat-treated dispersion obtained in step (ii), wherein the polymer F comprises at least 0.01% by mole of repeating units derived from at least one functional hydrogenated monomer, wherein the molar amount of the repeating units is relative to the total moles of repeating units in the polymer F, wherein the functional hydrogenated monomer has formula (I): wherein R1, R2 and R3 are the same or different from each other and are independently a hydrogen atom or a C1-C3 hydrocarbon group, and R X is a hydrogen atom or a C1-C5 hydrocarbon group containing at least one hydroxyl group.

2. The process according to claim 1, wherein the dispersion D has a solids content of polymer F particles dispersed in an aqueous medium ranging from 5 to 50% by weight. The method according to claim 1 , wherein the temperature ranges from 110° C. to 160° C.

4. The method according to claim 1, wherein the polymer F comprises at least 0.05% by mole of repeating units derived from at least one functional hydrogenated monomer, wherein the molar amount of the repeating units is relative to the total moles of repeating units in the polymer F.

5. The method according to claim 1, wherein the polymer F comprises at least 0.1% by mole of repeating units derived from at least one functional hydrogenated monomer, wherein the molar amount of the repeating units is relative to the total moles of repeating units in the polymer F.

6. The process according to claim 1 or 2, wherein the polymer F comprises up to 20% by mole of repeating units derived from at least one functional hydrogenated monomer, wherein the molar amount of the repeating units is relative to the total moles of repeating units in the polymer F, wherein the functional hydrogenated monomer has formula (I): in, R1, R2 and R3 are each the same or different from each other and are independently a hydrogen atom or a C1-C3 hydrocarbon group, and R X is a hydrogen atom or a C1-C5 hydrocarbon group containing at least one hydroxyl group.

7. The process according to claim 6, wherein the polymer F comprises at most 15% by mole of recurring units derived from at least one functional hydrogenated monomer, wherein the molar amount of the recurring units is relative to the total number of moles of recurring units in the polymer F.

8. The process according to claim 6, wherein the polymer F comprises up to 10% by mole of repeating units derived from at least one functional hydrogenated monomer, wherein the molar amount of the repeating units is relative to the total number of moles of repeating units in the polymer F.

9. The process according to claim 6, wherein the polymer F comprises at most 3 % by mole of repeating units derived from at least one functional hydrogenated monomer, wherein the molar amount of the repeating units is relative to the total number of moles of repeating units in the polymer F.

10. The method according to claim 1 or 2, wherein the polymer F particles are wet polymer WF particles.

11. A semi-crystalline vinylidene fluoride VDF polymer F obtained by the method according to any one of claims 1 to 10 f particle.

12. The polymer F according to claim 11 f Particles, which are in the form of powder particles.

13. A composition C comprising: - one or more polymers F according to any one of claims 11 or 12 f Particles, and - a liquid medium comprising one or more organic solvents.

14. Composition C according to claim 13, wherein the organic solvent is selected from the group consisting of: -alcohol, -ketone, - linear or cyclic esters, - linear or cyclic amides, and -Dimethyl sulfoxide.

15. Composition C according to claim 14, wherein the alcohol is selected from methanol, ethanol and diacetone alcohol.

16. Composition C according to claim 14, wherein the ketone is selected from acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone and isophorone.

17. Composition C according to claim 14, wherein the ester is selected from isopropyl acetate, n-butyl acetate, methyl acetoacetate, dimethyl phthalate and γ-butyrolactone.

18. Composition C according to claim 14, wherein the amide is selected from N,N-diethylacetamide, N,N-dimethylacetamide, dimethylformamide and N-methyl-2-pyrrolidone. The composition C according to claim 13 or 14, which is a homogeneous solution.

20. A film comprising at least one layer comprising one or more polymers F according to any one of claims 11 or 12 f particle.

21. A method for manufacturing a separator for an electrochemical device, the method comprising: (1b) providing a composition C according to any one of claims 13 to 19, and (2b) The composition C provided in step (1b) is typically processed onto a substrate by casting.

22. A method for manufacturing a filtration membrane, the method comprising: (1c) providing a composition C according to any one of claims 13 to 19, (2c) processing the composition C provided in step (1c) into a film, typically by casting, and (3c) precipitating the membrane provided in step (2c) in a non-solvent medium.

23. A composition E for forming an electrode, comprising: - one or more polymers F according to any one of claims 11 or 12 f particle, - at least one electroactive compound EA, - a liquid medium comprising one or more organic solvents, - optionally, at least one electrically conductive compound C, and - Optionally, one or more additives.

24. A method for manufacturing an electrode for an electrochemical device, the method comprising: (1d) providing a composition E according to claim 23, (2d) applying the composition E provided in step (1d) to one surface of a metal substrate, thereby providing a surface-coated electrode, and (3d) Drying the surface-coated electrode provided in step (2d).

Images