Battery separator coating

Abstract

The present invention relates to a coating composition comprising an aqueous dispersion of vinylidene fluoride polymer and its use for the manufacture of electrochemical cell components such as separators.

Description

[Technical Field]

[0001] Cross-reference of related applications This application claims priority from European Patent Application Publication No. 20216012.3, filed on 21 December 2020, and the entire contents of this application are incorporated herein by reference for any purpose.

[0002] The present invention relates to a coating composition containing a vinylidene fluoride polymer, and its use for the manufacture of electrochemical cell components such as separators. [Background technology]

[0003] Lithium-ion batteries have become indispensable to human daily life. In relation to sustainable development, lithium-ion batteries are expected to play an even more important role as their use in electric vehicles and renewable energy storage gains increasing attention.

[0004] The separator layer is a crucial component of a battery. These layers help prevent contact between the anode and cathode of the battery while allowing the electrolyte to pass through. Furthermore, battery performance attributes such as cycle life and power can be significantly influenced by the choice of separator.

[0005] It is known in the art that vinylidene fluoride (VDF) polymers are suitable as binders for manufacturing electrodes and / or composite separators and / or as coatings for porous separators for use in non-aqueous electrochemical devices such as batteries, preferably secondary batteries and electric double-layer capacitors.

[0006] However, some VDF polymers used in separator coating compositions have high solubility in electrolyte solutions, and once dissolved in the electrolyte solution, they move freely around the battery. This can cause problems in terms of higher electrolyte viscosity, increased resistance to lithium ion flow, reduced capacity, and cell assembly.

[0007] Lamination is a crucial process in battery cell assembly that has the effect of forming a uniform interface between the electrodes and the separator, reducing defects before and during the cycle, making assembly easier, and improving battery performance characteristics. The lamination process includes the step of bringing the separator into contact with the electrodes in a face-to-face relationship under specific pressure and temperature conditions.

[0008] Properly stacked interfaces often have lower impedance (resistance) than unstacked interfaces, which improves the power characteristics of the cell.

[0009] The volume change of a polymer after immersion in an electrolyte due to electrolyte-binding interactions, or the incorporation of an organic electrolyte, is called physical swelling. Polymers that exhibit a certain degree of swelling are typically polymers that allow for better lamination.

[0010] In the field of battery technology, particularly lithium batteries, there is a need to provide a coated separator that offers excellent adhesion to the separator substrate material and electrodes, and that does not dissolve in the electrolyte. [Overview of the project]

[0011] Accordingly, the applicant addresses the aforementioned problem by providing a composition suitable for coating substrate materials of separators for electrochemical cells, the coating composition being such that it provides remarkable adhesion to the separator substrate and electrodes, particularly the cathode after immersion in the electrolyte.

[0012] Surprisingly, the applicant has found that the aforementioned problem can be solved by at least partially coating a separator for an electrochemical cell with a composition comprising at least one vinylidene fluoride (VDF) polymer having a high proportion of insoluble components in a standard polar aprotic solvent.

[0013] At the same time, the coating composition exhibits reduced solubility in the electrolyte solution, thus reducing its impact on ionic conductivity and improving the long-term performance of the battery.

[0014] Therefore, in a first aspect, the present invention relates to an aqueous composition [Composition (C)] for use in the manufacture of a separator for an electrochemical apparatus, wherein the composition is A polyvinylidene fluoride (VDF) polymer [polymer (A)] comprising at least one polyvinylidene fluoride (VDF) polymer [polymer (A)] wherein polymer (A) contains more than 75.0 mol% repeating units derived from polyvinylidene fluoride (VDF) monomer, The aforementioned polymer (A) has the following requirements: The proportion of insoluble components in N,N-dimethylacetamide (DMA) at 45°C is more than 60% by weight; and (II) The degree of crystallinity determined by DSC measurement is less than 48%. It satisfies the condition.

[0015] In a second aspect, the present invention relates to the use of composition (C) of the present invention in a process for manufacturing a separator for an electrochemical cell, wherein the process comprises the following steps: i) A step of preparing an uncoated substrate layer [layer (P)]; ii) A step of preparing the composition (C) as defined above; iii) A step of applying the composition (C) obtained in step (ii) to at least a portion of the substrate layer (P) to obtain a separator that is at least partially coated; and iv) A step of drying the at least partially coated separator obtained in step (iii). Includes.

[0016] In a further embodiment, the present invention relates to a separator for an electrochemical cell comprising a substrate layer [layer (P)] at least partially coated with the composition (C) defined above.

[0017] In a further aspect, the present invention relates to an electrochemical cell, such as a secondary battery or a capacitor, comprising a separator at least partially coated as defined above.

BRIEF DESCRIPTION OF THE INVENTION

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

[0019] As used herein, the term "separator" is intended to mean a porous single or multiple layer polymeric material that electrically and physically separates the electrodes of opposite polarity in an electrochemical cell and is permeable to the ions flowing therebetween.

[0020] As used herein, the term "electrochemical cell" is intended to mean an electrochemical cell comprising a positive electrode, a negative electrode and a liquid electrolyte, wherein a single or multiple layer separator is attached to at least one surface of one of the electrodes.

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

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

[0023] The electrochemical cell separator of the present invention may, advantageously, be an electrically insulating composite separator suitable for use in an electrochemical cell. When used in an electrochemical cell, the composite separator is generally, advantageously, filled with an electrolyte that allows ion conduction within the electrochemical cell.

[0024] In this specification, the term "aqueous" is intended to mean a medium containing pure water and water combined with other components that do not substantially alter the physical and chemical properties of water.

[0025] At least one vinylidene fluoride (VDF) polymer [polymer (A)] contains more than 75.0 mol% of repeating units derived from vinylidene fluoride (VDF) monomer.

[0026] Polymer (A) is given by the following formula: [ka] (In the formula, each of R1, R2, and R3 is either equal to or different from each other, and independently is a hydrogen atom or a C1-C3 hydrocarbon group, R OH The repeating unit may further comprise a hydroxyl group or a repeating unit derived from at least one hydrophilic (meth)acrylic monomer (MA) of a C1-C5 hydrocarbon moiety containing at least one hydroxyl group.

[0027] The term “at least one hydrophilic (meth)acrylic monomer (MA)” is understood to mean that polymer (A) may contain repeating units derived from one or more hydrophilic (meth)acrylic monomers (MA) as described above. For the remainder of this specification, the expressions “hydrophilic (meth)acrylic monomer (MA)” and “monomer (MA)” are understood in both plural and singular forms for the purposes of the present invention, i.e., they are understood to mean both one and two or more hydrophilic (meth)acrylic monomers (MA).

[0028] Hydrophilic (meth)acrylic monomers (MA) are preferably of the formula: [ka] (In the formula, R1, R2, R OH Each of them has the meaning as defined above, and R3 is hydrogen; more preferably, each of R1, R2, and R3 is hydrogen, while R OH (This has the same meaning as detailed above.) Follow the rules.

[0029] Non-limiting examples of hydrophilic (meth)acrylic monomers (MA) include, among others, acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate; and hydroxyethylhexyl (meth)acrylate.

[0030] The monomer (MA) is more preferably: - Hydroxyethyl acrylate (HEA) in the following formula: [ka] - Any of the following 2-hydroxypropyl acrylates (HPA): [ka] - Acrylic acid (AA) in the following formula: [ka] - Selected from a mixture thereof.

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

[0032] The amount of (MA) monomer repeating units in polymer (A) can be determined by any suitable method. In particular, acid-base titration, which is well suited for determining the acrylic acid content, NMR, which is suitable for determining (MA) monomers containing aliphatic hydrogen in the side chain (e.g., HPA, HEA), the weight difference based on the total of supplied (MA) monomers and unreacted residue (MA) monomers during the production of polymer (A), and IR can be mentioned.

[0033] If at least one hydrophilic (meth)acrylic monomer (MA) is present, polymer (A) typically contains 0.05 to 10.0 mol% of the total moles of repeating units of polymer (A).

[0034] Polymer (A), as detailed above, may further comprise repeating units derived from at least one other comonomer (CM) distinct from VDF and monomer (MA).

[0035] The comonomer (CM) may be either a hydrogenated comonomer [comonomer(H)] or a fluorinated comonomer [comonomer(F)].

[0036] The term "hydrogenated comonomer [commonomer(H)]" is intended herein to mean an ethylenically unsaturated comonomer that does not contain a fluorine atom.

[0037] Non-limiting examples of suitable hydrogenated comonomers (H) include, in particular, vinyl monomers such as ethylene, propylene, and vinyl acetate, as well as styrene monomers such as styrene and p-methylstyrene.

[0038] The term "fluorinated comonomer [comonomer (F)]" is intended herein to mean an ethylenically unsaturated comonomer containing at least one fluorine atom.

[0039] The comonomer (CM) is preferably a fluorinated comonomer [comonomer (F)].

[0040] Non-limiting examples of suitable fluorinated comonomers (F) include, in particular, the following: (a) C2-C8 fluoro and / or perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), pentafluoropropylene, and hexafluoroisobutylene, (b) C2-C8 hydrogenated monofluoroolefins, such as vinyl fluoride, 1,2-difluoroethylene, and trifluoroethylene; (c) Perfluoroalkyl ethylene of the formula CH2=CH-R f0 (wherein R f0 is a C1-C6 perfluoroalkyl group); (d) Chloro-, and / or bromo-, and / or iodo-C2-C6 fluoroolefins such as chlorotrifluoroethylene (CTFE); (e) (Per)fluoroalkyl vinyl ether of the formula CF2=CFOR f1 (wherein R f1 is a C1-C6 fluoro- or perfluoroalkyl group, such as -CF3, -C2F5, -C3F7); (f) (Per)fluoro-oxyalkyl vinyl ether of the formula CF2=CFOX0 (wherein X0 is a C1-C 12 oxyalkyl group having one or more ether groups or a C1-C 12 (per)fluorooxyalkyl group, such as perfluoro-2-propoxy-propyl group); (g) Fluoroalkyl-methoxy-vinyl ether of the formula CF2=CFOCF2OR f2 (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); (h) Formula:

Chemical formula

[0041] The most preferred fluorinated comonomers (F) are tetrafluoroethylene (TFE), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), perfluoromethyl vinyl ether (PMVE), perfluoropropyl vinyl ether (PPVE), and vinyl fluoride, with HFP being the most preferred among these.

[0042] If at least one comonomer (CM) (preferably HFP) is present, it is typically present in polymer (A) in an amount of 0.05 mol% to 25.0 mol%, preferably 0.5 mol% to 5 mol%, relative to the total moles of repeating units of polymer (A).

[0043] However, the amount of repeating units derived from vinylidene fluoride in polymer (A) must be at least 75.0 mol%, preferably at least 90.0 mol%, and more preferably at least 95.0 mol%, so as not to impair the excellent properties of vinylidene fluoride resin, such as chemical resistance, weather resistance, and heat resistance.

[0044] According to a particular embodiment, polymer (A) consists of repeating units essentially derived from VDF and comonomer (F).

[0045] According to other embodiments, polymer (A) consists essentially of repeating units derived from VDF and HFP.

[0046] Polymer (A) may further contain other parts such as defects, end groups, etc., which do not affect or impair its physicochemical properties.

[0047] Composition (C) may further contain one or more additional additives.

[0048] Any additives in composition (C) include, in particular, the viscosity modifiers, defoamers, dispersants, and non-fluorinated surfactants described in detail above.

[0049] Among non-fluorinated surfactants, examples include nonionic emulsifiers such as alkoxylated alcohols, e.g., ethoxylated alcohols, propoxylated alcohols, and mixed ethoxylated / propoxylated alcohols; anionic surfactants, especially fatty acid salts, alkyl sulfonates (e.g., sodium dodecyl sulfate), alkylaryl sulfonates, and arylalkyl sulfonates; and organically modified siloxanes such as polyethers and siloxanes modified with side chains having primary hydroxyl groups or double bonds.

[0050] Among dispersants, acrylate copolymers are a good example.

[0051] Composition (C) may further contain a co-binding agent. The term “co-binding agent” is used herein to refer to a substance that improves the strength of a dry coating and affects the rheology of a wet coating. Suitable examples of co-binding agents that can be added to composition (C) are polymers or modified polymers of acrylic acid, acrylic acid esters, styrene-acrylic acid esters, vinyl alcohol (PVA), or acrylonitrile (PAN).

[0052] Typically, the total solids content of composition (C) is in the range of 5 to 50% by weight relative to the total weight of composition (C).

[0053] The total solids content of composition (C) is understood to be the sum of all its non-volatile components.

[0054] The amount of polymer (A) used in the aqueous composition (C) of the present invention varies from about 2.0 to 97.0% by weight, where the above weight percentage is based on the total solids weight of composition (C).

[0055] Composition (C) is particularly suitable for coating porous surfaces, especially those such as separators for electrochemical cells.

[0056] The aqueous compositions according to the present invention are particularly advantageous for the production of coated or semi-coated separators suitable for use in lithium-based secondary batteries such as lithium-ion secondary batteries and lithium metal secondary batteries.

[0057] Therefore, in one embodiment, the present invention relates to the use of an aqueous composition (C) in a process for manufacturing a separator for an electrochemical cell, wherein the process comprises the following steps: i) A step of preparing an uncoated substrate layer [layer (P)]; ii) A step of preparing the composition (C) as defined above; iii) A step of applying the composition (C) obtained in step (ii) to at least a portion of the substrate layer (P) to obtain a separator that is at least partially coated; and iv) A step of drying the at least partially coated separator obtained in step (iii). Includes.

[0058] In relation to the present invention, the term "substrate layer" is intended herein to mean either a single-layer substrate consisting of a single layer or a multilayer substrate comprising at least two adjacent layers.

[0059] The substrate layer (P) may be a non-porous substrate layer or a porous substrate layer. If the substrate layer is a multi-layer substrate, the outer layer of the aforementioned substrate may be a non-porous substrate layer or a porous substrate layer. In this specification, the term "porous substrate layer" is intended to mean a substrate layer containing finite-size pores.

[0060] In a preferred embodiment of the present invention, the substrate layer (P) is a multilayer substrate comprising a porous layer containing a ceramic material and a fabric layer.

[0061] Preferred ceramic materials include Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT, x and y are independently 0 to 1), PB(Mg3Nb 2 / 3 Examples include, but are not limited to, O3-PbTiO3 (PMN-PT), BaTiO3, HfO2 (hafnia), SrTiO3, TiO2 (titania), SiO2 (silica), Al2O3 (alumina), ZrO2 (zirconia), SnO2, CeO2, MgO, CaO, Y2O3, and any combination thereof.

[0062] The fabric layer can be made from any fabric commonly used in separators for electrochemical apparatuses, comprising at least one material selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, polyethylene, and polypropylene, or mixtures thereof. Preferably, the base material (P) is polyethylene or polypropylene.

[0063] The layer (P) typically has a porosity of at least 5%, preferably at least 10%, more preferably at least 20%, or at least 40%, and at most 90%, preferably at most 80%.

[0064] The thickness of the layer (P) is not particularly limited, but is typically 3 to 100 micrometers, preferably 5 to 50 micrometers.

[0065] In step iii) of the process of the present invention, composition (C) is typically applied to at least one surface of layer (P) by a technique selected from casting, spray coating, rotary spray coating, roll coating, doctor blade, dipping coating, slot die coating, gravure coating, inkjet printing, spin coating and screen printing, brush, squeegee, foam applicator, curtain coating and vacuum coating.

[0066] The ratio of the weight of the coating to the weight of the support layer in the at least partially coated separator according to the present invention is typically 3:1 to 0.5:1, for example, 2:1, 1.5:1, 1:1, or 0.75:1.

[0067] In step iv) of the method of the present invention, the coating composition layer is dried at a temperature preferably within 25°C to 200°C, and preferably within 60°C to 180°C.

[0068] In a further embodiment, the present invention relates to a separator for an electrochemical cell comprising a substrate layer [layer (P)] at least partially coated with the composition (C) defined above.

[0069] The applicant has surprisingly found that, when used in the aqueous composition (C) of the present invention, polymer (A), which is characterized by a certain degree of crystallinity and a high proportion of insoluble components in a standard polar aprotic solvent, results in the formation of a high gel fraction upon contact with an electrolyte.

[0070] Due to the formation of the aforementioned high gel fraction, the aqueous composition (C) containing polymer (A) has reduced solubility in the electrolyte solution, thereby preventing polymer (A) from freely moving within the battery, and thus the viscosity of the electrolyte does not change. This reduces the impact on ionic conductivity and improves the long-term performance of the battery.

[0071] In particular, polymer (A) has very limited solubility in alkyl carbonates.

[0072] Simultaneously, polymer (A) exhibits appropriate swelling upon contact with the electrolyte, which enables significant adhesion to both the substrate material and the electrode, resulting in good lamination strength.

[0073] Therefore, composition (C) containing polymer (A) is particularly suitable for use in compositions for coating substrate materials of separators for electrochemical cells due to outstanding adhesion to the separator substrate and electrodes, especially the cathode.

[0074] If any disclosure of a patent, patent application, or publication incorporated herein by reference conflicts with the description of this application to such an extent that it obscures certain terms, the description herein shall prevail.

[0075] The present invention will be described in more detail below in relation to the following embodiments, which are provided merely for illustrative purposes and are not intended to limit the scope of the invention. [Examples]

[0076] raw materials Kynar Flex® LBG (LBG), a commercially available product from Arkema.

[0077] Example 1 - Preparation of aqueous VDF-HFP-polymer latex-polymer A1 13.5 liters of deionized water were introduced into a 21-liter horizontal reactor autoclave equipped with baffles and a stirrer operating at 50 rpm. After raising the temperature to 110°C, the pressure was maintained at a constant 42 Bar Ass throughout the trial by supplying VDF / HFP gaseous mixture monomers in a molar ratio of 98:2. 10.8 g / L of 60 mL of ammonium persulfate (APS) and sodium acetate (NaOAc) aqueous solution was added over 4 minutes (900 mL / h).

[0078] Thirty minutes after ignition, the addition of the APS / NaOAc 1:1 solution was resumed at a flow rate of 60 mL / h throughout the entire trial. When 4000 g of the mixture was supplied, the supply was interrupted, and then the pressure was reduced for 30 minutes while maintaining a constant reaction temperature. The final reaction time was 185 minutes.

[0079] The reactor was cooled to room temperature, and aqueous latex with a solid content of 23.8% by weight was recovered.

[0080] The VDF-HFP polymer obtained in this manner was found to contain 1.6 mol% HFP, have a melting point (Tm2) of 149°C, a crystallinity of 40.4 J / g (measured according to ASTM D3418), a Mw of 814 kDalton, and a 76% insoluble fraction.

[0081] Example 2 - Preparation of aqueous VDF-HFP-polymer latex-polymer A2 13.5 liters of deionized water were introduced into a 21-liter horizontal reactor autoclave equipped with baffles and a stirrer operating at 50 rpm. After raising the temperature to 110°C, the pressure was maintained at a constant 42 Bar Ass throughout the trial by supplying VDF / HFP gaseous mixture monomers in a molar ratio of 99.5:0.5. 10.8 g / L of 60 mL of ammonium persulfate (APS) and sodium acetate (NaOAc) aqueous solutions was added over 4 minutes (900 mL / h).

[0082] Thirty minutes after ignition, the addition of the APS / NaOAc 1:1 solution was resumed at a flow rate of 60 mL / h throughout the entire trial. When 4000 g of the mixture was supplied, the supply was interrupted, and then the pressure was reduced for 30 minutes while maintaining a constant reaction temperature. The final reaction time was 155 minutes.

[0083] The reactor was cooled to room temperature and the latex was recovered.

[0084] The aqueous latex obtained in this manner had a solids content of 23.5% by weight. The VDF-HFP polymer obtained in this manner was found to contain 0.4 mol% HFP, have a melting point (Tm2) of 155°C, a crystallinity of 46.2 J / g (measured according to ASTM D3418), a Mw of 832 kDalton, and a 78% insoluble fraction.

[0085] Example 3 - Preparation of aqueous VDF-HFP-polymer latex-polymer A3 13.5 liters of deionized water were introduced into a 21-liter horizontal reactor autoclave equipped with baffles and a stirrer operating at 50 rpm. After raising the temperature to 110°C, the pressure was maintained at a constant 42 Bar Ass throughout the trial by supplying VDF / HFP gaseous mixture monomers in a molar ratio of 99:1. 10.8 g / L of a 1:1 aqueous solution of 60 mL of ammonium persulfate (APS) and sodium acetate (NaOAc) was added over 4 minutes (900 mL / h).

[0086] Thirty minutes after ignition, the addition of the APS / NaOAc 1:1 solution was resumed at a flow rate of 60 mL / h throughout the entire trial. When 4000 g of the mixture was supplied, the supply was interrupted, and then the pressure was reduced for 30 minutes while maintaining a constant reaction temperature. The final reaction time was 163 minutes.

[0087] The reactor was cooled to room temperature and the latex was recovered.

[0088] The aqueous latex obtained in this manner had a solids content of 24.1% by weight. The VDF-HFP polymer obtained in this manner was found to contain less than 1 mol% HFP, have a melting point (Tm2) of 152°C, a crystallinity of 43.5 J / g (measured according to ASTM D3418), a Mw of 849 kDalton, and an insoluble fraction of 80%.

[0089] Example 4 - Preparation of aqueous VDF polymer latex-polymer A4 13.5 liters of deionized water were introduced into a 21-liter horizontal reactor autoclave equipped with baffles and a stirrer operating at 50 rpm. After raising the temperature to 110°C, the pressure was maintained at a constant 50 Bar Ass throughout the trial by supplying VDF gaseous monomer. 10.8 g / L of a 1:1 aqueous solution of 60 mL of ammonium persulfate (APS) and sodium acetate (NaOAc) was added over 10 minutes (360 mL / h).

[0090] Thirty minutes after ignition, the addition of ammonium persulfate (APS) solution was resumed at a flow rate of 60 ml / hour for the entire duration of the trial. When 4000 g of VDF was supplied, the supply was interrupted, and then the pressure was reduced for 30 minutes while maintaining a constant reaction temperature. The final reaction time was 162 minutes.

[0091] The reactor was cooled to room temperature and the latex was recovered.

[0092] The aqueous latex obtained in this manner had a solids content of 23.5% by weight. The VDF polymer obtained in this way was found to have a melting point (Tm2) of 157°C, a crystallinity of 47.5 J / g (measured according to ASTM D3418), a Mw of 773 kDalton, and an insoluble fraction of 64%.

[0093] Comparative Example 1 - Preparation of Aqueous VDF Polymer Latex-Polymer C1 13.5 liters of deionized water were introduced into a 21-liter horizontal reactor autoclave equipped with baffles and a stirrer operating at 50 rpm. After raising the temperature to 122.5°C, the pressure was maintained at a constant 46 Bar Ass throughout the trial by supplying VDF gaseous monomer. 70 mL of pure di-ter-butyl peroxide (DTBP) solution and 300 mL of 0.9 g / L aqueous solution of ammonium persulfate (APS) were added.

[0094] When 200 g of VDF was supplied, a flux rate of 40 mL was supplied to a 3.26 g / L aqueous solution of sodium dodecyl sulfate (SDS) for every 200 g of VDF supplied throughout the entire duration of the trial. The total volume of SDS at the end of the reaction was 760 mL.

[0095] When 4000g of VDF was supplied, the supply was interrupted, and then the pressure was reduced for 30 minutes while maintaining a constant reaction temperature. The final reaction time was 216 minutes.

[0096] The reactor was cooled to room temperature and the latex was recovered.

[0097] The aqueous latex obtained in this manner had a solids content of 21.2% by weight. The VDF polymer obtained in this way was found to have a melting point (Tm2) of 149°C, a crystallinity of 40.4 J / g (measured according to ASTM D3418), a Mw of 508 kDaltons, and an insoluble fraction of less than 3%.

[0098] Comparative Example 2 - Preparation of Polymer C2 using aqueous VDF-HFP polymer latex 13.5 liters of deionized water were introduced into a 21-liter horizontal reactor autoclave equipped with baffles and a stirrer operating at 50 rpm. After raising the temperature to 125°C, the pressure was maintained at a constant 50 Bar Ass throughout the trial by supplying VDF / HFP gaseous mixture monomers in a molar ratio of 98:2. 70 mL of pure di-ter-butyl peroxide (DTBP) solution and 120 mL of 6.75 g / L aqueous solution of ammonium persulfate (APS) were added.

[0099] When 200g of VDF was supplied, the reaction temperature dropped to 115°C, and a flux rate of 40 mL was supplied to an aqueous solution of 3.26 g / L sodium dodecyl sulfate (SDS) for every 200 g of VDF supplied throughout the entire duration of the trial. The total volume of SDS at the end of the reaction was 760 mL.

[0100] When 4000g of VDF was supplied, the supply was interrupted, and then the pressure was reduced for 30 minutes while maintaining a constant reaction temperature. The final reaction time was 263 minutes.

[0101] The reactor was cooled to room temperature and the latex was recovered.

[0102] The aqueous latex obtained in this manner had a solids content of 22.0% by weight. The VDF-HFP polymer obtained in this manner was found to contain 1.5 mol% HFP, have a melting point (Tm2) of 155°C, a crystallinity of 44.9 J / g (measured according to ASTM D3418), a Mw of 632 kDalton, and a 6% insoluble fraction.

[0103] General procedure for determining the insoluble fraction in DMA The latex samples from Examples A1-A4 or Comparative Examples C1 or C2 were dried by shear solidification technique, and the latex was subjected to centrifugation; the resulting powder at a weight ratio (0.25% wt / vol concentration) was dissolved in a solution of N,N-dimethylacetamide (DMA) + LiBr 0.01N at a weight ratio of 1:375 for 4 hours at 45°C with magnetic stirring. After cooling to room temperature, the mixture was centrifuged at 20,000 rpm for 1 hour using a Sorvall RC-6 Plus centrifuge (rotor model: F21S-8X50Y).

[0104] After drying at 150°C for 48 hours, the insoluble fraction was separated and quantified, and its weight was determined by dividing it by the total weight of the solidified powder sample.

[0105] General procedure for determining the weight-average molecular weight (Mw) in DMA The obtained latex samples were dried by shear solidification technique, and the latex was subjected to centrifugation; the resulting powder at a weight ratio (0.25% wt / vol concentration) was dissolved in a solution of N,N-dimethylacetamide (DMA) + LiBr 0.01N at a weight ratio of 1:375 for 4 hours at 45°C with magnetic stirring. After cooling to room temperature, the mixture was centrifuged at 20,000 rpm for 1 hour using a Sorvall RC-6 Plus centrifuge (rotor model: F21S-8X50Y).

[0106] The supernatant of each sample was analyzed using the equipment and conditions detailed below. Mobile phase: DMA Flow rate: 1mL / min Temperature: 45℃ Injection system: Waters 717plus Autosampler Injection volume: 200 μL Pump: Waters Isocratic Pump model 1515 Column: Four Water Styragel HT (300 x 7.5 mm), 10 μm particle size: Styragel HT-6, HT-5, HT-4, HT-3 with guard. Detector: Waters refractive index model 2414 Software for data acquisition and processing: Waters Empower

[0107] General procedure for determining the solubility of VDF-based polymers in propylene carbonate Pour propylene carbonate (PC) into a glass container equipped with a stirring rod. Dry one of the latexes from Examples A1-A4 or Comparative Example C1 or C2 by shear solidification technique, and add the polymer powder obtained by centrifuging the latex to the PC while stirring on a magnetic plate at 90°C. A commonly used concentration is 2.5% by weight (i.e., 0.5 g of polymer and 19.5 g of PC). Maintain the solution / dispersion at 90°C for 2 hours while stirring.

[0108] After 2 hours, the solution / dispersion is centrifuged at 20,000 rpm for 1 hour. The solid is separated from the liquid portion (supernatant). The supernatant is further analyzed to determine the total solids content (using a thermobalance) and viscosity.

[0109] Total solids content measurement: Spread approximately 4g of liquid onto an aluminum pan topped with a fiberglass filter. Cover the solution with another fiberglass filter to avoid mass loss due to boiling. Heat the material to 155°C for 3 minutes and maintain the temperature until the weight change over 50 seconds is less than 1mg.

[0110] The remainder indicates the percentage of solid residue in the solution.

[0111] The dissolved polymer is calculated using the following formula:

number

[0112] General procedure for determining the degree of swelling of VDF-based polymers in alkyl carbonates The degree of swelling of test specimens of polymers A1-A4 and comparative VDF-based polymer C1 or C2 (polymer discs with a thickness of 1.5 mm and a diameter of 25 mm obtained from the compression-molded powder obtained as described above) after immersion was determined by EC:DMC:DEC (1:1:1 volume) at 45°C was determined as the change in mass according to ASTM D471.

[0113] The results are shown in Table 1.

[0114] [Table 1]

[0115] Polymers A1-A4 exhibit a better compromise between swelling and solubility in propylene carbonate, making them particularly suitable for coating substrate materials for separators in electrochemical cells.

[0116] Viscosity measurement: Viscosity was measured using a Brookfield viscometer equipped with an SC-21 spindle.

[0117] The viscosity of PC is 2.6 cP.

[0118] The viscosity should be measured before the gelation of the dissolved polymer begins.

[0119] These results are shown in Table 2.

[0120] [Table 2]

[0121] The data shows that polymer A1 according to the present invention, due to its low solubility in the electrolyte solution, cannot move freely within the battery and does not change the viscosity of the electrolyte. This is confirmed by the fact that the viscosity increase over 24 hours is negligible. Conversely, the polymers of LBG and Comparative Example 2 have high solubility in the electrolyte solution, and once dissolved in the electrolyte solution, they move freely around the battery, causing problems with higher electrolyte viscosity and corresponding increased resistance to lithium ion flow and capacity degradation.

Claims

1. An aqueous composition [Composition (C)] for use in the manufacture of separators for electrochemical apparatus, A polyvinylidene fluoride (VDF) polymer [polymer (A)] comprising at least one polyvinylidene fluoride (VDF) polymer [polymer (A)] wherein polymer (A) contains more than 75.0 mol% of repeating units derived from polyvinylidene fluoride (VDF) monomer, The polymer (A) has the following requirements: (I) The proportion of insoluble components in N,N-dimethylacetamide (DMA) at 45°C is greater than 60% by weight; and (II) The degree of crystallinity obtained by DSC measurement is less than 48%. An aqueous composition [Composition (C)] that satisfies the following conditions.

2. Polymer (A) is given by formula: 【Chemistry 1】 (In the formula, each of R1, R2, and R3 is either equal to or different from one another, and independently represents a hydrogen atom or C) １ ~C ３ It is a hydrocarbon group, R ＯＨ is a C containing a hydroxyl group, or at least one hydroxyl group. １ ~C ５ The composition (C) according to claim 1, further comprising a repeating unit derived from at least one hydrophilic (meth)acrylic monomer (MA) of which is a hydrocarbon moiety.

3. The composition (C) according to claim 1 or 2, wherein the polymer (A) further comprises repeating units derived from at least one comonomer (CM) selected from hydrogenated comonomers [comonomer (H)] or fluorinated comonomers [comonomer (F)].

4. Comonomers (CM) (a) C ２ ~C ８ Fluorofluoroolefins and / or perfluoroolefins; (b) C ２ ~C ８ Hydrogenated monofluoroolefin; (c) Formula CH ２ =CH-R ｆ０ (In the formula, R ｆ０ C １ ~C ６ Perfluoroalkylethylene (which is a perfluoroalkyl group); (d) Chloro, and / or bromo, and / or iodo-C ２ ~C ６ Fluoroolefin; (e) Formula CF ２ = CFOR ｆ１ (In the formula, R ｆ１ C １ ~C ６ (Per)fluoroalkyl vinyl ethers (which are fluoro- or perfluoroalkyl groups); (f) Formula CF ２ =CFOX ０ (In the formula, X ０ C has one or more ether groups. １ ~C １２ Oxyalkyl group or C １ ~C １２ (Per)fluoro-oxyalkyl vinyl ethers (which are per)fluorooxyalkyl groups; (g) Formula CF ２ = CFOCF ２ OR ｆ２ (In the formula, R ｆ２ C １ ~C ６ C having a fluoro- or perfluoroalkyl group, or one or more ether groups. １ ~C ６ Fluoroalkyl-methoxy-vinyl ethers (which are per)fluorooxyalkyl groups; (h) Formula: 【Chemistry 2】 (In the formula, R ｆ３ , R ｆ４ , R ｆ５ , and R ｆ６ Each of them is equal to or different from one another and independently contains a fluorine atom and, optionally, one or more oxygen atoms. １ ~C ６ Fluorodioxole (which is a fluoro- or per(halo)fluoroalkyl group) The composition (C) according to claim 3, which is a fluorinated comonomer [comonomer (F)] selected from the group consisting of the following.

5. The composition (C) according to claim 4, wherein the comonomer (CM) is selected from the group consisting of tetrafluoroethylene (TFE), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), perfluoromethyl vinyl ether (PMVE), perfluoropropyl vinyl ether (PPVE), and vinyl fluoride.

6. The composition (C) according to any one of claims 3 to 5, wherein the at least one comonomer (CM) is present in an amount of 0.05 mol% to 25.0 mol% with respect to the total moles of repeating units of the polymer (A).

7. The composition (C) according to any one of claims 1 to 6, further comprising one or more further additives selected from the group consisting of viscosity modifiers, defoamers, dispersants, and non-fluorinated surfactants as described above.

8. The composition (C) according to any one of claims 1 to 7, further comprising a co-binding agent.

9. A process for manufacturing separators for electrochemical cells: i) A step of preparing an uncoated substrate layer [layer (P)]; ii) A step of preparing the composition (C) according to any one of claims 1 to 8; iii) A step of applying the composition (C) obtained in step (ii) to at least a portion of the substrate layer (P) to obtain a separator that is at least partially coated; and iv) A step of drying the at least partially coated separator obtained in step (iii). A process that includes this.

10. The process according to claim 9, wherein layer (P) is a multilayer substrate comprising a porous layer containing a ceramic material and a fabric layer.

11. The process according to claim 9, wherein in step iii), the composition (C) is applied to at least one surface of the layer (P) by a technique selected from casting, spray coating, rotary spray coating, roll coating, dipping coating, doctor blade, slot die coating, gravure coating, inkjet printing, spin coating and screen printing, brush, squeegee, foaming device, curtain coating and vacuum coating.

12. A separator for an electrochemical cell comprising a substrate layer [layer (P)] at least partially coated with the composition (C) according to any one of claims 1 to 8.

13. An electrochemical cell comprising at least a partially coated separator as described in claim 12.

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