Vinylidene fluoride copolymer composition, production method thereof, polymer dispersion liquid, electrode for non-aqueous electrolyte secondary battery, electrolyte layer for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery

Abstract

The technical problem of the present invention is to provide a vinylidene fluoride copolymer composition having long-term stable dispersibility in a dispersion medium. The vinylidene fluoride copolymer composition for solving the above technical problem contains a vinylidene fluoride copolymer. The melting point of the vinylidene fluoride copolymer composition is 140 °C or lower, and the reversible heat flow of the vinylidene fluoride copolymer composition has an endothermic peak with a melting enthalpy of 2 J / g or more, and the absolute value of the difference between the temperature of the largest endothermic peak in the endothermic peak and the melting point of the vinylidene fluoride copolymer composition is 10 °C or lower. When a dispersion liquid (the vinylidene fluoride content is 10% by mass) containing butyl butyrate and the vinylidene fluoride copolymer composition is allowed to stand for 20 hours, the content of the vinylidene fluoride copolymer composition in the upper 20% by volume of the dispersion liquid after standing is 4.0% by mass or more and 10% by mass or less.

Description

Technical Field

[0001] The present invention relates to a vinylidene fluoride copolymer composition and a method for producing the same, a polymer dispersion,

[0002] Electrode for nonaqueous electrolyte secondary battery, electrolyte layer for nonaqueous electrolyte secondary battery, and nonaqueous

[0003] Electrolyte secondary battery. Background Art

[0004] Conventionally, as binders for the various layers of non-aqueous electrolyte secondary batteries, vinylidene fluoride

[0005] Vinylidene fluoride polymers are widely used. In particular, vinylidene fluoride and fluorinated alkyl vinyl

[0006] The copolymer of the compound (hereinafter also referred to as "vinylidene fluoride copolymer") is used as a current collector and

[0007] Binders for binding electrode active materials and the like are widely known.

[0008] Here, Patent Document 1 describes an example in which a vinylidene fluoride copolymer is used as

[0009] A binder for electrode layers and electrolyte layers of all-solid batteries, a type of non-aqueous electrolyte secondary batteries.

[0010] In this case, the above-mentioned vinylidene fluoride copolymer is usually mixed with an electrode active material, a solid electrolyte, a solvent,

[0011] In addition, in order to suppress the

[0012] For the dissolution of lithium from the solid electrolyte, a solvent having a small dielectric constant is used.

[0013] However, vinylidene fluoride copolymer is an insulator, so in the above mixture, ion conduction

[0014] The path is cut off, and sometimes the performance of the all-solid-state battery cannot be fully obtained. Patent document 3 records the following

[0015] Summary: When a binder is mixed into a solid electrolyte layer, ion conductivity decreases.

[0016] Therefore, the method of forming an electrode layer or an electrode by dispersing the vinylidene fluoride copolymer instead of dissolving it has been studied.

[0017] For example, Patent Documents 4 and 5 describe techniques for making vinylidene fluoride-hexafluoroethylene

[0018] A slurry in which a fluoropropylene copolymer is dispersed in butyl butyrate or the like.

[0019] Furthermore, Patent Document 6 discloses that: If particulate binder polymers are uniformly dispersed in a dispersion medium, solid electrolytes can be adhered in such a manner that they do not coat the solid electrolyte locally or over the entire surface.

[0020] Then, it is shown that if such a binder dispersion is used, an increase in interfacial resistance between solid electrolyte particles, between solid electrolyte particles and current collectors, etc. can be suppressed, and the binder dispersion can be mixed with solid electrolyte particles for coating and the like.

[0021]

[0022] Prior Art Documents

[0023] Patent Documents

[0024] Patent Document 1: Japanese Patent No. 6257698

[0025] Patent Document 2: International Publication No. WO2012 / 063827

[0026] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2008-103284

[0027] Patent Document 4: Japanese Unexamined Patent Application Publication No. 2016-025025

[0028] Patent Document 5: Japanese Unexamined Patent Application Publication No. 2016-025027

[0029] Patent Document 6: Japanese Unexamined Patent Application Publication No. 2015-159067 Summary of the Invention

[0030] Problems to be Solved by the Invention

[0031] As described in Patent Document 3 above, since vinylidene fluoride copolymers are insulators, when used as binders for electrode layers and electrolyte layers, ion conductivity may sometimes be reduced. Therefore, as in Patent Documents 4 to 6, studies have been made to form electrode layers and solid electrolyte layers by dispersing vinylidene fluoride copolymers without dissolving them.

[0032] Then, in order to further improve the performance of all-solid-state batteries, methods for more uniformly dispersing an adhesive (a vinylidene fluoride copolymer) in polymer dispersions used to form electrode layers and electrolyte layers were explored. Here, it is preferable that the vinylidene fluoride copolymer does not easily settle over a long period in the polymer dispersions used to form electrode layers and electrolyte layers. Therefore, an object of the present invention is to provide a vinylidene fluoride copolymer composition having long-term stable dispersibility in a dispersion medium with a low relative dielectric constant, and to provide a method for manufacturing the vinylidene fluoride copolymer composition. Another object of the present invention is to provide a polymer dispersion, an electrode for a non-aqueous electrolyte secondary battery, an electrolyte layer for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, etc., each containing the above vinylidene fluoride copolymer composition.

[0033] Technical Solution

[0034] The present invention provides the following vinylidene fluoride copolymer compositions.

[0035] That is, the present invention provides a vinylidene fluoride copolymer composition which is a vinylidene fluoride copolymer composition containing a vinylidene fluoride copolymer. The above vinylidene fluoride copolymer contains a structural unit derived from vinylidene fluoride and a structural unit derived from a fluoroalkyl vinyl compound. The melting point of the above vinylidene fluoride copolymer composition is 140 °C or lower. When measuring the reversing heat flow of the above vinylidene fluoride copolymer composition using a temperature-modulated differential scanning calorimeter, the above vinylidene fluoride copolymer composition has an endothermic peak with a melting enthalpy (ΔHm) of 2 J / g or more. The absolute value of the difference between the peak temperature of the largest endothermic peak in the above endothermic peak and the melting point of the above vinylidene fluoride copolymer composition is 10 °C or lower. The content rate of the above vinylidene fluoride copolymer composition in the upper 20% by volume of the dispersion liquid, which contains butyl butyrate and the above vinylidene fluoride copolymer composition and has a content rate of the above vinylidene fluoride copolymer composition of 10% by mass, after stirring at 25 °C for 30 minutes and standing for 20 hours, is 4.0% by mass or more and 10% by mass or less.

[0036] In addition, the present invention also provides a polymer dispersion which contains the above vinylidene fluoride copolymer composition and a dispersion medium with a relative dielectric constant of 15 or lower.

[0037] The present invention also provides an electrode for a non-aqueous electrolyte secondary battery which contains the above vinylidene fluoride copolymer composition. Further provided is an electrolyte layer for a non-aqueous electrolyte secondary battery which contains the above vinylidene fluoride copolymer composition. In addition, a non-aqueous electrolyte secondary battery which contains the above vinylidene fluoride copolymer composition is also provided.

[0038] The present invention also provides a method for manufacturing the following vinylidene fluoride copolymer composition.

[0039] The present invention provides a method for manufacturing a vinylidene fluoride copolymer composition, the vinylidene fluoride copolymer composition containing a vinylidene fluoride copolymer including a structural unit derived from vinylidene fluoride and a structural unit derived from a fluoroalkyl vinyl compound. The method includes: a step of preparing an emulsion in which an untreated vinylidene fluoride copolymer is dispersed in an aqueous medium; and a step of adding a surfactant to the emulsion and stirring to obtain a surfactant-containing emulsion having a surface tension at 25°C of 40 mN / m or less, the melting point of the vinylidene fluoride copolymer composition being 140°C or less.

[0040] Furthermore, the present invention also provides a method for manufacturing a vinylidene fluoride copolymer composition, the vinylidene fluoride copolymer composition containing a vinylidene fluoride copolymer including a structural unit derived from vinylidene fluoride and a structural unit derived from a fluoroalkyl vinyl compound. The method includes: a step of preparing an emulsion in which an untreated vinylidene fluoride copolymer is dispersed in an aqueous medium; and a step of heating the emulsion at a temperature lower than the end point of the peak having the highest temperature among the endothermic peaks observed at 185°C or lower and at a temperature of 40°C or higher when measuring the heat flow of the untreated vinylidene fluoride copolymer with a differential scanning calorimeter, the melting point of the vinylidene fluoride copolymer composition being 140°C or less.

[0041] Advantageous Effects

[0042] The vinylidene fluoride copolymer composition of the present invention has extremely excellent dispersibility in a dispersion medium having a low relative dielectric constant. Therefore, according to the above vinylidene fluoride copolymer composition, an electrode layer and an electrolyte layer uniformly containing the vinylidene fluoride copolymer composition can be formed. Description of the Drawings

[0043] Figure 1 It is a diagram for explaining a method for determining the end point of the endothermic peak of a vinylidene fluoride copolymer. Detailed Description

[0044] 1. Vinylidene Fluoride Copolymer Composition

[0045] The vinylidene fluoride copolymer composition of the present invention is a composition containing a vinylidene fluoride copolymer having specified physical properties. The vinylidene fluoride copolymer composition may be composed only of a vinylidene fluoride copolymer, or may contain a vinylidene fluoride copolymer and other components such as a surfactant.

[0046] The vinylidene fluoride copolymer composition of the present invention only needs to have a melting point of 140°C or less, and is usually in a solid state at 25°C. It should be noted that in this specification, the composition being in a solid state at 25°C means that the main constituent components of the composition are in a solid state at 25°C, and within the range not impairing the object and effects of the present invention, it may also contain liquid components in part.

[0047] As described above, when forming the electrode layer and the electrolyte layer of the non-aqueous electrolyte secondary battery, the vinylidene fluoride copolymer is preferably dispersed in a dispersion medium (a dispersion medium having a low relative dielectric constant), and it is preferable to maintain its dispersibility for a long time. According to the in-depth research of the present inventors, it has been clarified that: when the vinylidene fluoride copolymer composition has specific physical properties, it is easily dispersed in a dispersion medium having a low relative dielectric constant, and the dispersion stability when the dispersion liquid of the vinylidene fluoride copolymer composition is allowed to stand is very high.

[0048] Specifically, it has been clarified that: when the melting point of the vinylidene fluoride copolymer composition is 140 °C or lower, and when measuring the reversible heat flow of the above-mentioned vinylidene fluoride copolymer composition with a temperature-modulated differential scanning calorimeter, the vinylidene fluoride copolymer composition has an endothermic peak with a melting enthalpy (ΔHm) of 2 J / g or more, and the absolute value of the difference between the peak temperature of the largest endothermic peak and the melting point of the vinylidene fluoride copolymer composition is 10 °C or lower. In this case, in a dispersion medium having a relative dielectric constant of 15 or lower, the dispersibility of the vinylidene fluoride copolymer composition becomes good.

[0049] The melting point of the vinylidene fluoride copolymer composition being 140 °C or lower means that the vinylidene fluoride copolymer contains a certain amount or more of structural units derived from a fluoroalkyl vinyl compound. Moreover, it is considered that when the vinylidene fluoride copolymer composition contains structural units derived from a fluoroalkyl vinyl compound, the affinity with a dispersion medium having a low relative dielectric constant is likely to become good.

[0050] In addition, in a vinylidene fluoride copolymer composition of a vinylidene fluoride copolymer containing structural units derived from vinylidene fluoride and structural units derived from a fluoroalkyl vinyl compound having a certain composition ratio, the peak temperature of the largest endothermic peak in its reversible heat flow varies according to the state of the crystalline region of the vinylidene fluoride copolymer in the vinylidene fluoride copolymer composition. The state of the crystalline region of the vinylidene fluoride copolymer varies according to polymerization conditions such as thermal history (temperature, time), reaction rate of monomers, and equipment. Therefore, this peak temperature becomes a value reflecting the manufacturing history. On the other hand, in the above-mentioned vinylidene fluoride copolymer composition, the melting point measured by the method described later is not easily affected by the state of the crystalline region formed during manufacturing. And when the vinylidene fluoride copolymer is appropriately crystallized in a manner that does not impair the affinity with a dispersion medium having a low relative dielectric constant, the absolute value of the difference between this peak temperature and the melting point of the vinylidene fluoride copolymer composition is 10 °C or lower. That is, it can be said that when the above absolute value is 10 °C or lower, the vinylidene fluoride copolymer composition is easily dispersed in a dispersion medium having a low relative dielectric constant.

[0051] In addition, in the present invention, when preparing a dispersion containing butyl butyrate and the above-mentioned vinylidene fluoride copolymer composition and the content rate of the above-mentioned vinylidene fluoride copolymer composition is 10% by mass, the dispersion is stirred at 25 °C for 30 minutes and left standing for 20 hours, and the content rate of the vinylidene fluoride copolymer composition in the upper 20% by volume of the dispersion is 4.0% by mass or more and 10% by mass or less. If the content rate of the vinylidene fluoride copolymer composition in the above-mentioned dispersion is within the above range, the vinylidene fluoride copolymer composition is not likely to settle in a dispersion medium with a low relative dielectric constant, and the dispersibility can be maintained well for a long time.

[0052] Hereinafter, the components, physical properties, manufacturing method, etc. of the vinylidene fluoride copolymer composition will be described in detail.

[0053] · Vinylidene fluoride copolymer

[0054] The vinylidene fluoride copolymer contained in the vinylidene fluoride copolymer composition of the present invention includes a structural unit derived from vinylidene fluoride and a constituent unit derived from a fluoroalkyl vinyl compound. The amount of the constituent unit derived from vinylidene fluoride in the vinylidene fluoride copolymer is preferably 30% by mass or more and 85% by mass or less, more preferably 40% by mass or more and 80% by mass or less, relative to 100% by mass of the constituent units of the vinylidene fluoride copolymer. If the mass fraction of the structural unit derived from vinylidene fluoride is within the above range, the melting point of the vinylidene fluoride copolymer composition is likely to converge to a desired range. The mass fraction of the above-mentioned structural unit derived from vinylidene fluoride can be determined by 19 analyzing the vinylidene fluoride copolymer by F-NMR.

[0055] On the other hand, the fluoroalkyl vinyl compound may be a compound having one vinyl and an alkyl in which one or more hydrogens are substituted with fluorine, or a compound having one vinyl and fluorine bonded to the vinyl (except vinylidene fluoride). Examples thereof include: vinyl fluoride, trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, hexafluoroethylene, fluoroalkyl vinyl ether, and perfluoromethyl vinyl ether, etc. Among these, from the viewpoint of easily improving the affinity with a dispersion medium having a low relative dielectric constant, tetrafluoroethylene and hexafluoropropylene are preferred, and hexafluoropropylene is particularly preferred. In the vinylidene fluoride copolymer, it may contain only one kind of structural unit derived from a fluoroalkyl vinyl compound, or may contain two or more kinds of structural units derived from a fluoroalkyl vinyl compound.

[0056] The amount of the structural unit derived from the fluoroalkyl vinyl compound in the vinylidene fluoride copolymer is not particularly limited as long as the melting point of the vinylidene fluoride copolymer composition described below can be set to 140°C or lower. Although it also depends on the type of the fluoroalkyl vinyl compound, the amount of the structural unit derived from the fluoroalkyl vinyl compound is preferably 15% by mass or more and 70% by mass or less, more preferably 20% by mass or more and 60% by mass or less, relative to 100% by mass of the structural units of the vinylidene fluoride copolymer. If the amount of the fluoroalkyl vinyl compound in the vinylidene fluoride copolymer is within the above range, the melting point of the vinylidene fluoride copolymer composition is likely to converge to the desired range. The mass fraction of the above structural unit derived from the fluoroalkyl vinyl compound can be determined by analyzing the vinylidene fluoride copolymer using 19 F-NMR.

[0057] In addition, within the range that does not impair the object and effect of the present invention, the vinylidene fluoride copolymer may also contain, in part, structural units derived from other monomers that can copolymerize with vinylidene fluoride and the fluoroalkyl vinyl compound.

[0058] Examples of other monomers that can copolymerize with vinylidene fluoride and the like include crosslinkable alkyl vinyl compounds having one vinyl group and a crosslinkable group. Examples of the crosslinkable group also include a vinyl group. That is, the crosslinkable alkyl vinyl compound may be a compound having two or more vinyl groups. In addition, the crosslinkable alkyl vinyl compound may contain a fluorine atom. Examples of the crosslinkable alkyl vinyl compound include perfluorodivinyl ether and perfluoroalkylenedivinyl ether. It should be noted that examples of the perfluoroalkylenedivinyl ether include compounds having the following structure: two vinyl ether groups in which all hydrogen atoms are replaced by fluorine atoms are bonded through a linear or branched divalent perfluoroalkylene having 1 or more and 6 or less carbon atoms.

[0059] In addition, examples of other monomers also include unsaturated dibasic acids or unsaturated dibasic acid monoesters. The unsaturated dibasic acid is an unsaturated dicarboxylic acid or a derivative thereof, and examples thereof include compounds in which two carboxyl groups are bonded through a linear or branched unsaturated alkylene having 1 or more and 6 or less carbon atoms. More specific examples of the above unsaturated dibasic acid include maleic acid, fumaric acid, itaconic acid, and citraconic acid. On the other hand, the unsaturated dibasic acid monoester is a monoester compound derived from the above unsaturated dibasic acid. Examples of the above unsaturated dibasic acid monoester include monomethyl maleate, monoethyl maleate, monomethyl citraconate, and monoethyl citraconate.

[0060] In addition, among examples of other monomers, there are also included compounds containing a vinyl group and a polar group (hereinafter also referred to as "compounds containing a polar group"). Examples of such compounds containing a polar group include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, succinic acid (meth)acryloyloxyethyl ester, succinic acid (meth)acryloyloxypropyl ester, and glycidyl (meth)acrylate, etc.

[0061] The mass fraction of the structural unit derived from the above crosslinkable alkyl vinyl compound, unsaturated dibasic acid, unsaturated dibasic acid monoester, or compound containing a polar group in the vinylidene fluoride copolymer can be arbitrarily set within a range that does not impair the object and effect of the present invention. For example, the introduction amount of the structural unit derived from an unsaturated dibasic acid, an unsaturated dibasic acid monoester, or a compound containing a polar group can be determined by performing FT-IR analysis on the vinylidene fluoride copolymer.

[0062] Herein, the weight-average molecular weight of the vinylidene fluoride copolymer is preferably from 100,000 to 10,000,000, more preferably from 200,000 to 5,000,000, and still more preferably from 300,000 to 2,000,000. If the weight-average molecular weight of the vinylidene fluoride copolymer is within the above range, the dispersibility of the vinylidene fluoride copolymer composition in the dispersion medium is likely to become good. In addition, when the vinylidene fluoride copolymer composition is used as a binder for an electrode layer or an electrolyte layer of an all-solid battery, it is easy to bond the active material and the solid electrolyte. It should be noted that the above weight-average molecular weight is a polystyrene conversion value measured by gel permeation chromatography (GPC).

[0063] · Surfactant

[0064] As described above, the vinylidene fluoride copolymer composition may contain not only the vinylidene fluoride copolymer but also a surfactant.

[0065] Herein, the surfactant contained in the vinylidene fluoride copolymer composition may be an ionic surfactant having an anionic group or a cationic group, or a nonionic surfactant. In addition, the surfactant may be a non-fluorinated surfactant without fluorine or a fluorinated surfactant containing fluorine (such as a perfluorinated surfactant and a partially fluorinated surfactant, etc.).

[0066] The anionic surfactant that can be used is not particularly limited, and known surfactants can be used. The hydrophilic group of the anionic surfactant preferably contains carboxylate, sulfate, sulfonate, phosphate, etc., and may also contain an ester bond, an acid amide bond, or an ether bond. In addition, the hydrophobic group preferably contains an alkyl chain, an alkyl ether chain, a perfluoroalkyl chain, a perfluoroalkyl ether chain, a fluorocarbon chain, or a fluoropolyether chain, and they may have a straight-chain structure or a branched-chain structure.

[0067] The cationic surfactant that can be used is not particularly limited, and surfactants known in the art can be used. The hydrophilic group of the cationic surfactant preferably includes aliphatic quaternary ammonium salts, aliphatic amine salts, cyclic quaternary ammonium salts, and amine acetates. In addition, the hydrophobic group preferably includes an alkyl chain, an alkyl ether chain, a perfluoroalkyl chain, a perfluoroalkyl ether chain, a fluorocarbon chain, or a fluoropolyether chain, which may have a linear structure or a branched structure.

[0068] Furthermore, the nonionic surfactant that can be used is not particularly limited, and surfactants known in the art can be used. The hydrophilic group of the nonionic surfactant preferably has a hydroxyl group, an ether bond, an acid amide bond, an ester bond, etc. in the molecule. In addition, the hydrophobic group preferably includes an alkyl chain, an alkyl ether chain, a perfluoroalkyl chain, a perfluoroalkyl ether chain, a fluorocarbon chain, or a fluoropolyether chain, which may have a linear structure or a branched structure.

[0069] As the surfactant, a surfactant dissolved or mixed in the aqueous medium in the emulsion prepared in the method for producing the vinylidene fluoride copolymer composition described below is preferred.

[0070] The amount of the surfactant contained in the vinylidene fluoride copolymer composition is preferably 0.01% by mass or more and 20% by mass or less, more preferably 0.02% by mass or more and 15% by mass or less, based on the total amount of the vinylidene fluoride copolymer and the surfactant. If the amount of the surfactant is too large, when the obtained vinylidene fluoride copolymer composition is used as an adhesive for the electrode layer and the electrolyte layer, the adhesiveness between the vinylidene fluoride copolymer composition and the active material, the electrolyte, etc. may decrease. However, if the amount of the surfactant is 20% by mass or less, the adhesiveness is not easily reduced. On the other hand, if the amount of the surfactant is 0.01% by mass or more based on the total amount of the vinylidene fluoride copolymer composition, the dispersion stability when the vinylidene fluoride copolymer composition is dispersed in the dispersion medium is improved.

[0071] <Physical properties of the vinylidene fluoride copolymer composition>

[0072] As described above, the vinylidene fluoride copolymer composition of the present invention only needs to have a melting point of 140°C or lower, preferably 135°C or lower, and more preferably 130°C or lower. The melting point of the vinylidene fluoride copolymer composition can be adjusted by the amount of the constituent unit derived from the fluoroalkyl vinyl compound in the above-mentioned vinylidene fluoride copolymer. In addition, in the present specification, the melting point of the vinylidene fluoride copolymer composition is measured by the following method. First, the powdery vinylidene fluoride copolymer composition is pressed at 200°C to form a film with a thickness of 150 μm. Using a differential scanning calorimeter, the melting point of the pressed vinylidene fluoride copolymer composition film is measured in accordance with ASTM D3418. The melting point of the vinylidene fluoride copolymer composition measured by the above method is the value measured after melting the vinylidene fluoride copolymer composition once. Therefore, it is not easily affected by the manufacturing history during the polymerization reaction process of the vinylidene fluoride copolymer described later and the manufacturing method of the vinylidene fluoride copolymer composition.

[0073] On the other hand, when measuring the reversible heat flow of the vinylidene fluoride copolymer composition using a temperature-modulated differential scanning calorimeter, the vinylidene fluoride copolymer composition of the present invention has an endothermic peak with a melting enthalpy (ΔHm) of 2 J / g or more. It should be noted that the literature value (the value described in M Neidhofer: Polymer volume 45, Issue 5, 2004, 1679-1688) of the standard melting enthalpy (ΔHm 0 ) of the vinylidene fluoride polymer is 104.5 J / g. Therefore, the upper limit of the melting enthalpy (ΔHm) of the vinylidene fluoride copolymer is set to 104.5 J / g. Here, the melting enthalpy (ΔHm), the number of peaks at the top of the endothermic peak, and the peak temperature of the vinylidene fluoride copolymer composition vary depending on the state of the crystalline region of the vinylidene fluoride copolymer composition (especially the vinylidene fluoride copolymer), that is, the manufacturing method described later. For example, if a surfactant is arbitrarily added to an emulsion of a vinylidene fluoride copolymer having one peak at the top of the endothermic peak and heated at a specified temperature, the number of peaks at the top of the endothermic peak of the vinylidene fluoride copolymer becomes two or more. The reason is that by heating the emulsion, the crystal structure of the vinylidene fluoride copolymer changes, showing a peak different from the melting peak of the vinylidene fluoride copolymer before heating. It should be noted that in the present specification, the endothermic peak with a melting enthalpy (ΔHm) of 2 J / g or more refers to the peak observed at a temperature of 0°C or higher, and the endothermic peak does not include the peak observed in the temperature region below 0°C.

[0074] Herein, the reversible heat flow of the vinylidene fluoride copolymer composition is determined by a temperature-modulated differential scanning calorimeter. Specifically, a powdery vinylidene fluoride copolymer composition obtained by freeze-drying an emulsion containing the vinylidene fluoride copolymer composition is used as a sample for measurement. Then, it is heated at an average heating rate of 5 °C / minute, a modulation period of 40 seconds, and a modulation amplitude of ±0.531 °C in such a manner as to be in the heat only condition, and a reversible heat flow having a downwardly convex endothermic peak is obtained. In the obtained reversible heat flow, a baseline is linearly drawn in such a manner as to overlap with a linear heat flow on the high-temperature side relative to the end point. Then, in the downwardly convex endothermic peak of the reversible heat flow, when a line is perpendicularly drawn from this baseline to the reversible heat flow, the point having the farthest distance from the baseline to the reversible heat flow is taken as the peak top of the maximum endothermic peak, and the temperature at which this peak top is formed is determined. Herein, the number of minima in the downwardly convex endothermic peak of the reversible heat flow is taken as the number of peak tops of the endothermic peak. On the other hand, the region surrounded by this baseline and the reversible heat flow is taken as the melting enthalpy (ΔHm).

[0075] Furthermore, in the vinylidene fluoride copolymer composition of the present invention, in the endothermic peak of the vinylidene fluoride copolymer having a melting enthalpy (ΔHm) of 2 J / g or more, the absolute value of the difference between the peak top temperature of the maximum endothermic peak and the melting point of the vinylidene fluoride copolymer composition is 10 °C or less. Herein, the "peak top temperature of the maximum endothermic peak" means the temperature (point on the reversible heat flow) at which the distance from the baseline drawn by the above method to the reversible heat flow becomes the maximum in the endothermic peak of the vinylidene fluoride copolymer having a melting enthalpy (ΔHm) of 2 J / g or more. The above absolute value is more preferably 9.5 °C or less, and further preferably 9 °C or less. If the above absolute value is within the above range, the vinylidene fluoride copolymer composition having affinity and dispersibility in a dispersion medium having a low relative dielectric constant is obtained as described above. It should be noted that if the above absolute value exceeds 10 °C, the crystallinity of the vinylidene fluoride copolymer composition is too high, and there is a tendency for the dispersibility to decrease. The above absolute value can be adjusted by the production method of the vinylidene fluoride copolymer composition described later. For example, if the vinylidene fluoride copolymer is made into a solid state (powder state) and then heated, the above absolute value is likely to exceed 10 °C.

[0076] In addition, regarding the vinylidene fluoride copolymer composition of the present invention, when preparing a dispersion liquid containing butyl butyrate and the above-mentioned vinylidene fluoride copolymer composition and the content rate of the above-mentioned vinylidene fluoride copolymer composition is 10% by mass, the content rate of the vinylidene fluoride copolymer composition in the upper 20% by volume of the dispersion liquid after standing for 20 hours is 4.0% by mass or more and 10% by mass or less. The content rate of the vinylidene fluoride copolymer composition in the upper 20% by volume is more preferably 7.0% by mass or more and 10% by mass or less. If the vinylidene fluoride copolymer composition has such dispersion stability in butyl butyrate, in a polymer dispersion liquid or the like used for forming an electrode layer, an electrolyte layer, etc., the vinylidene fluoride copolymer composition is not likely to settle, and it is easy to obtain an electrode layer and an electrolyte layer having desired properties. It should be noted that the content rate of the vinylidene fluoride copolymer composition in the dispersion liquid after standing can be adjusted by the manufacturing method of the vinylidene fluoride copolymer composition described later. For example, it can be adjusted by the amount, type, and whether the emulsion is heated of the surfactant mixed with the vinylidene fluoride copolymer.

[0077] Here, the measurement of the content rate of the vinylidene fluoride copolymer composition after standing is carried out as follows. Prepare a dispersion liquid (the content rate of the vinylidene fluoride copolymer composition is 10% by mass) by adding the vinylidene fluoride copolymer composition to butyl butyrate. Add 20 mL of this dispersion liquid to a 20 mL graduated cylinder, cover it with a sealing film, and let it stand for 20 hours. Then, collect 4 mL from the supernatant of the graduated cylinder, dry it at 135 °C for 1 hour, and let it cool in a desiccator for 1 hour. Then, measure the weight before and after drying, and thereby calculate the content rate of the vinylidene fluoride copolymer composition in the upper 20% by volume of the dispersion liquid.

[0078] In addition, the turbidity of the above-mentioned dispersion liquid is preferably 5% or more. When the turbidity of the above-mentioned dispersion liquid is less than 5%, the vinylidene fluoride copolymer composition dissolves in the dispersion medium. When the turbidity of the above-mentioned dispersion liquid is 5% or more, at least a part of the vinylidene fluoride copolymer composition does not dissolve in the dispersion medium and is dispersed. The above-mentioned turbidity can be adjusted by the type of surfactant used when preparing the vinylidene fluoride copolymer composition, whether it is heated, etc. The turbidity of the above-mentioned dispersion liquid is measured by the following method. Prepare a butyl butyrate dispersion liquid of the vinylidene fluoride copolymer composition (the content rate of the vinylidene fluoride copolymer composition is 10% by mass), and stir it after standing for 20 hours. Measure the turbidity of the above-mentioned dispersion liquid just after stirring according to JIS K 7136.

[0079] It should be noted that the shape of the vinylidene fluoride copolymer composition of the present invention is not particularly limited, but is usually preferably in the form of particles (powder form). In addition, the average secondary particle diameter of the above-mentioned vinylidene fluoride copolymer composition is not particularly limited, and is preferably 1 μm or more and 5000 μm or less, more preferably 2 μm or more and 3000 μm or less. If the average secondary particle diameter of the vinylidene fluoride copolymer composition is within the above range, the treatment of the vinylidene fluoride copolymer is likely to become easier. The above average secondary particle diameter is the cumulative average diameter (D50) of the particle size distribution measured by the laser diffraction / scattering method based on volume.

[0080] <Manufacturing method of vinylidene fluoride copolymer composition>

[0081] The vinylidene fluoride copolymer composition satisfying the above physical properties can be manufactured, for example, by the following three methods. However, the manufacturing method of the above-mentioned vinylidene fluoride copolymer composition is not limited to the following three methods.

[0082] ·First method

[0083] In the first method of the manufacturing method of the vinylidene fluoride copolymer composition, the following steps are carried out: a step of preparing an emulsion in which an untreated vinylidene fluoride copolymer is dispersed in an aqueous medium (hereinafter also referred to as "emulsion preparation step"); and a step of adding an ionic surfactant to the above emulsion and stirring to obtain a surfactant-containing emulsion having a surface tension of 40 mN / m or less at 25°C (hereinafter also referred to as "surfactant addition step").

[0084] In addition, after the surfactant addition step, by carrying out a step of drying the surfactant-containing emulsion to remove the vinylidene fluoride copolymer (hereinafter also referred to as "drying step"), the above-mentioned vinylidene fluoride copolymer composition can be obtained in a solid state. It should be noted that in this method, after obtaining the vinylidene fluoride copolymer composition in a solid state, heating at a temperature above the melting point of the vinylidene fluoride copolymer composition is not carried out. Hereinafter, each step will be described.

[0085] (Emulsion preparation step)

[0086] In the emulsion preparation step, an emulsion in which an untreated vinylidene fluoride copolymer is dispersed in an aqueous medium is prepared. It should be noted that the above emulsion may be a commercially available product. In the present specification, the untreated vinylidene fluoride copolymer refers to a copolymer of vinylidene fluoride and a fluoroalkyl vinyl compound prepared by a usual method, and refers to a copolymer that does not undergo heat treatment, mixing with a surfactant, etc. other than for the purpose of decomposing residual monomers and residual initiators after the polymerization of the vinylidene fluoride copolymer. The above untreated vinylidene fluoride copolymer has substantially the same composition as the above vinylidene fluoride copolymer. Among them, by performing the surfactant addition step described later on the emulsion in which the untreated vinylidene fluoride copolymer is dispersed in an aqueous medium, the dispersibility of the above untreated vinylidene fluoride copolymer in a dispersion medium having a relative dielectric constant of 15 or less changes.

[0087] In this step, the emulsion in which the untreated vinylidene fluoride copolymer is dispersed in an aqueous medium can be prepared by suspension polymerization, emulsion polymerization, solution polymerization, micro suspension polymerization, or the like. In addition, a commercially available product of the emulsion in which the untreated vinylidene fluoride copolymer is dispersed in an aqueous medium can also be used. Among them, a method of obtaining an emulsion in which the untreated vinylidene fluoride copolymer is dispersed in water by emulsion polymerization is preferred.

[0088] As a specific emulsion polymerization method, vinylidene fluoride, a fluoroalkyl vinyl compound, other monomers as required, an aqueous medium, and an emulsifier are mixed in an autoclave. Then, a polymerization initiator soluble in the aqueous medium is added to the above mixture to polymerize vinylidene fluoride, a fluoroalkyl vinyl compound, and other monomers as required.

[0089] The pressure in the autoclave during polymerization is preferably set to 0 MPa to 20 MPa, more preferably set to 0.5 MPa to 15 MPa, and further preferably set to 1 MPa to 10 MPa. By adjusting the pressure during polymerization to the above range, an untreated vinylidene fluoride copolymer can be stably obtained in production.

[0090] The aqueous medium used for emulsion polymerization is not particularly limited as long as it is a liquid in which the above vinylidene fluoride and fluoroalkyl vinyl compound are poorly soluble, and as long as it is a liquid mainly composed of water, it may contain a solvent miscible with water in addition to water. The aqueous medium is preferably water.

[0091] On the other hand, there is no particular limitation on the emulsifier as long as it can form micelles in an aqueous medium and can stably disperse the synthesized untreated vinylidene fluoride copolymer in the aqueous medium. For example, known surfactants can be used. As the emulsifier, any one of nonionic surfactants, cationic surfactants, anionic surfactants, and amphoteric surfactants can be used, or they can be used in combination. Examples of emulsifiers include perfluorinated surfactants, partially fluorinated surfactants, and non-fluorinated surfactants that have been used in the polymerization of polyvinylidene fluoride in the past. Among these surfactants, perfluoroalkyl sulfonic acids and their salts, perfluoroalkyl carboxylic acids and their salts, and fluorine-based surfactants having a fluorocarbon chain or a fluoropolyether chain are preferred. As the emulsifier, one selected from the above can be used alone, or two or more selected from the above can be used. When the total amount of all monomers used for polymerization is set to 100 parts by mass, the addition amount of the emulsifier is preferably 0.0001 to 22 parts by mass.

[0092] There is no particular limitation on the polymerization initiator as long as it can dissolve in an aqueous medium and can polymerize monomers. Examples of polymerization initiators include known water-soluble peroxides, water-soluble azo compounds, and redox initiators. Examples of water-soluble peroxides include ammonium persulfate and potassium persulfate. Examples of water-soluble azo compounds include 2,2'-azobis-isobutyronitrile (AIBN) and 2,2'-azobis-2-methylbutyronitrile (AMBN). Examples of redox initiators include ascorbic acid-hydrogen peroxide. Among them, water-soluble peroxides are preferred from the viewpoints of reactivity and the like. These polymerization initiators can be used alone or in combination of two or more. When the total amount of all monomers used for polymerization is set to 100 parts by mass, the addition amount of the polymerization initiator is preferably 0.01 to 5 parts by mass.

[0093] On the other hand, the above emulsion polymerization method can be a soap-free emulsion polymerization method, a mini-emulsion polymerization method, a seed emulsion polymerization method, etc. The soap-free emulsion polymerization method refers to a method of performing emulsion polymerization without using a conventional emulsifier as described above. In addition, in the soap-free emulsion polymerization method, as the above emulsifier, a reactive emulsifier having a polymerizable double bond in the molecule can also be used. The reactive emulsifier forms micelles in the system at the initial stage of polymerization, but as the polymerization proceeds, it is consumed as a monomer in the polymerization reaction. Therefore, in the finally obtained reaction system, the reactive emulsifier hardly exists in a free state. Therefore, it has the advantage that the reactive emulsifier is not easily exuded to the particle surface of the obtained untreated vinylidene fluoride copolymer.

[0094] Examples of reactive emulsifiers include polyoxyalkylene vinyl ether, sodium alkyl allyl sulfosuccinate, sodium methacryloyloxy polyoxypropylene sulfate, and alkoxy polyethylene glycol methacrylate.

[0095] In addition, in the microemulsion polymerization method, a strong shearing force is applied using an ultrasonic oscillator or the like to make the oil droplets of monomers such as vinylidene fluoride and fluoroalkyl vinyl compounds as fine as submicron size and then polymerization is carried out. At this time, in order to stabilize the fine oil droplets of the monomers, a known hydrophobe is added to the mixed solution. In the microemulsion polymerization method, it is desirable that the polymerization reaction occurs only in each monomer oil droplet and each oil droplet becomes an untreated vinylidene fluoride copolymer (fine particle). Therefore, it is easy to control the particle diameter and particle size distribution of the obtained untreated vinylidene fluoride copolymer and the like.

[0096] Seed emulsion polymerization refers to the polymerization in which the fine particles obtained by the above polymerization method are coated with a polymer composed of other monomers. Monomers are further added to the emulsion of the fine particles, and if necessary, an aqueous medium, a surfactant, a polymerization initiator, etc. are added and they are polymerized.

[0097] Here, in any of the above emulsion polymerization methods, in order to adjust the degree of polymerization of the obtained untreated vinylidene fluoride copolymer, a chain transfer agent can also be used. Examples of the chain transfer agent include ethyl acetate, methyl acetate, diethyl carbonate, acetone, ethanol, n-propanol, acetaldehyde, propionaldehyde, ethyl propionate, and carbon tetrachloride.

[0098] In addition, a pH adjuster can also be used as needed. Examples of the pH adjuster include electrolyte substances having a buffering ability such as sodium dihydrogen phosphate, disodium hydrogen phosphate, and potassium dihydrogen phosphate; and basic substances such as sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, and ammonia.

[0099] In addition, any other components such as an anti-settling agent, a dispersion stabilizer, an anti-corrosion agent, a mildew-proof agent, and a wetting agent can also be used as needed. The addition amount of these optional components is preferably 5 ppm or more and 10 parts by mass or less, more preferably 10 ppm or more and 7 parts by mass or less, based on 100 parts by mass of the total amount of all monomers used for polymerization.

[0100] In the polymerization of the untreated vinylidene fluoride copolymer, the polymerization temperature can be appropriately selected according to the type of the polymerization initiator and the like. For example, it can be set to 0°C to 120°C, preferably set to 20°C to 110°C, and more preferably set to 40°C to 100°C. The polymerization time is not particularly limited, but considering productivity and the like, it is preferably 1 to 24 hours.

[0101] According to the manufacturing method of the present invention, when the aqueous medium is water, an emulsion in which untreated vinylidene fluoride copolymer particles are uniformly dispersed in water can be obtained. The emulsion of commercially available products and the emulsion thus obtained can be used directly, or can be diluted with an aqueous medium to any concentration for use. The above emulsion can be pulverized by at least one method selected from salting out, cryogenic milling, spray drying, freeze drying, etc., and then physically or chemically redispersed in a desired aqueous medium, and then the surfactant addition step described below is carried out. In addition, at this time, any other arbitrary components (except surfactants) can be mixed at any timing, or impurities can be removed from the untreated emulsion through a dialysis membrane or an ion exchange resin, etc. Furthermore, the untreated vinylidene fluoride copolymer can be micronized by cryogenic milling, classification, etc., and then mixed with an aqueous medium, and the surfactant addition step described below is carried out. The method for dispersing the untreated vinylidene fluoride copolymer in the aqueous medium is not particularly limited, and known dispersion methods can be applied.

[0102] Here, the content of the untreated vinylidene fluoride copolymer in the emulsion is preferably 5% by mass or more and 70% by mass or less, more preferably 10% by mass or more and 60% by mass or less. The emulsion prepared or purchased by the above method can be used directly, or can be diluted with an aqueous medium for use. If the content of the untreated vinylidene fluoride copolymer is 5% by mass or more, the vinylidene fluoride copolymer composition can be efficiently prepared. On the other hand, if the content of the untreated vinylidene fluoride copolymer is 70% by mass or less, the dispersibility of the emulsion is likely to be stable.

[0103] The average primary particle size of the untreated vinylidene fluoride copolymer in the emulsion determined by dynamic light scattering is preferably 5 μm or less, more preferably 3 μm or less, and further preferably 1 μm or less. On the other hand, the above average primary particle size is preferably 0.01 μm or more, more preferably 0.05 μm or more, and further preferably 0.1 μm or more. The average primary particle size of the untreated vinylidene fluoride copolymer in the emulsion is calculated by the regularization analysis of dynamic light scattering. For example, DelsaMaxCORE manufactured by BECKMAN COULTER can be used, and according to JIS Z8828, the measurement medium is set as water and the measurement temperature is set as 25 °C for measurement. In addition, the maximum peak obtained by the regularization analysis is taken as the average primary particle size.

[0104] (Surfactant addition step)

[0105] In the surfactant addition step, an ionic surfactant is added to the emulsion prepared in the above emulsion preparation step and stirred to obtain a surfactant-containing emulsion having a surface tension of 40 mN / m or less at 25°C. The ionic surfactant added in this step is not particularly limited as long as the surface tension of the emulsion after addition (surfactant-containing emulsion) is 40 mN / m or less. Here, the surface tension of the emulsion after adding the ionic surfactant (surfactant-containing emulsion) at 25°C is preferably 5 mN / m or more and 40 mN / m or less, more preferably 10 mN / m or more and 40 mN / m or less.

[0106] The above surface tension of the surfactant-containing emulsion is measured by a tensiometer (Sigma701 / 700, manufactured by KSV instruments) using the Wilhelmy method. A platinum plate is used in the measurement, and the average value of the surface tension measured three times at 25°C is used as the value of the surface tension.

[0107] As the ionic surfactant added in this step, an ionic surfactant that is soluble or miscible in the aqueous medium contained in the emulsion is selected, and it can be either an anionic surfactant or a cationic surfactant, and an anionic surfactant is particularly preferred. One of them can be added alone, or two or more of them can be added in combination. By adding an ionic surfactant, it can be adsorbed on the surface of the untreated vinylidene fluoride copolymer contained in the above emulsion, and the dispersibility in a dispersion medium having a relative dielectric constant of 15 or less is improved.

[0108] The anionic and cationic surfactants that can be used are the same as the surfactants exemplified in the surfactant contained in the above vinylidene fluoride copolymer composition.

[0109] The addition amount of the ionic surfactant is appropriately selected according to the surface tension of the surfactant-containing emulsion. Usually, it is preferably 0.01 part by mass or more and 20 parts by mass or less, more preferably 0.02 part by mass or more and 15 parts by mass or less, relative to the total amount of the untreated vinylidene fluoride copolymer in the emulsion. If the amount of the ionic surfactant is too large, when the obtained vinylidene fluoride copolymer composition is used as an adhesive for an electrode layer or an electrolyte layer, the adhesiveness between the vinylidene fluoride copolymer composition and the active material, electrolyte, etc. may sometimes decrease. Therefore, it is preferably 20 parts by mass or less relative to 100 parts by mass of the total amount of the untreated vinylidene fluoride copolymer. On the other hand, if the amount of the ionic surfactant is 0.01 part by mass or more relative to the total amount of the untreated vinylidene fluoride copolymer, the dispersion stability when the vinylidene fluoride copolymer composition is dispersed in the dispersion medium is improved. It should be noted that the remaining components in the surfactant added in this step can be removed as needed by a dialysis membrane, an ion exchange resin, etc.

[0110] (Drying process)

[0111] In the drying process, the aqueous medium is removed from the above surfactant-containing emulsion. The method for removing the aqueous medium is not particularly limited, and it is preferably dried at a temperature that does not affect the physical properties of the vinylidene fluoride copolymer composition in the surfactant-containing emulsion. The drying process can be carried out at atmospheric pressure or under reduced pressure. Through the above drying, the above solid (powder-like) vinylidene fluoride copolymer composition can be obtained. In addition, the device for removing the aqueous medium is not particularly limited, and a tray dryer, a conical dryer, a fluidized bed dryer, a pneumatic dryer, a spray dryer, a freeze dryer, etc. can be used.

[0112] ·Second method

[0113] In the second method of the method for producing a vinylidene fluoride copolymer composition, at least the following steps are carried out: a step of preparing an emulsion in which an untreated vinylidene fluoride copolymer is dispersed in an aqueous medium (hereinafter also referred to as "emulsion preparation step"); and a step of heating the emulsion at a temperature lower than the end point of the highest temperature peak among the endothermic peaks of the above untreated vinylidene fluoride copolymer observed at 185 °C or lower when measuring the heat flow of the above untreated vinylidene fluoride copolymer with a differential scanning calorimeter (hereinafter also referred to as "heating step"). It should be noted that after the above emulsion heating step, by carrying out a step of drying the emulsion to take out the vinylidene fluoride copolymer (hereinafter also referred to as "drying step"), the above solid (powder-like) vinylidene fluoride copolymer composition can be obtained. It should be noted that in this method, after obtaining the solid vinylidene fluoride copolymer composition, heating at a temperature above the melting point of the vinylidene fluoride copolymer composition is not carried out. Hereinafter, each step will be described.

[0114] (Emulsion preparation step)

[0115] In the emulsion preparation step, an emulsion in which an untreated vinylidene fluoride copolymer is dispersed in an aqueous medium is prepared. The above emulsion preparation step can be the same as the emulsion preparation step of the above first method. As described above, a commercially available emulsion can be used.

[0116] (Heating step)

[0117] In the heating step, the emulsion is heated after the emulsion preparation step. When polymerization is carried out in the above emulsion preparation step, the heating step can be continuously carried out directly after polymerization, or the heating step can be carried out separately from polymerization. When heating the emulsion obtained by polymerization, it is preferable that, before the heating step after polymerization, at least unreacted vinylidene fluoride and fluoroalkyl vinyl compound are removed out of the system. By carrying out this operation, the polymerization reaction for forming the vinylidene fluoride copolymer will not start again in the heating step. In addition, it is easy to adjust the state of the crystalline region of the untreated vinylidene fluoride copolymer through the heating step.

[0118] The temperature for heating the emulsion is determined as follows. First, a part of the above untreated vinylidene fluoride copolymer is pulverized and then formed into a film. Using a differential scanning calorimeter, the heat flow of the above film-shaped untreated vinylidene fluoride copolymer is measured by the method according to ASTM D3418. Then, the temperature lower than the end point of the peak with the highest temperature among the endothermic peaks of the vinylidene fluoride copolymer observed below 185 °C is taken as the heating temperature. By carrying out the heating step, the dispersibility in a dispersion medium with a relative dielectric constant of 15 or less is improved.

[0119] The method for determining the temperature for heating the emulsion is more specifically described as follows. First, the emulsion is freeze-dried to make the untreated vinylidene fluoride copolymer into a powder form. Then, a mold with a length of 5 cm × a width of 5 cm × a thickness of 150 μm and about 1 g of the powder-shaped untreated vinylidene fluoride copolymer are sandwiched between two pieces of aluminum foil spray-misted with a release agent and pressed at 200 °C to form a film. Then, using a differential scanning calorimeter (manufactured by METTLER, "DSC-1"), the heat flow of the film-shaped untreated vinylidene fluoride copolymer is obtained by the method according to ASTM D3418. Then, the end point of the peak with the highest temperature among the endothermic peaks of the untreated vinylidene fluoride copolymer observed below 185 °C in this heat flow is determined, and the temperature lower than this end point is taken as the temperature for heating the emulsion.

[0120] It should be noted that this end point is determined in the following manner. A baseline is linearly drawn so as to overlap with the linear heat flow on the high-temperature side (for example, exceeding 185 °C) of the endothermic peak. Among the endothermic peaks of the vinylidene fluoride copolymer observed below 185 °C in this heat flow, in the temperature region on the high-temperature side of the peak with the highest temperature and on the low-temperature side of the lowest temperature where the heat flow overlaps with the baseline, as Figure 1 shown, a tangent line is drawn on the heat flow. Then, the intersection point of this tangent line and the above baseline is taken as the end point of the vinylidene fluoride copolymer.

[0121] From the viewpoint of appropriately changing the crystal structure of the untreated vinylidene fluoride copolymer in the emulsion, the temperature for heating the emulsion is preferably 40 °C or higher, more preferably 60 °C or higher, and further preferably 80 °C or higher.

[0122] If heated at a temperature lower than the end point of the peak with the highest temperature among the endothermic peaks of the vinylidene fluoride copolymer observed below 185°C, the crystal structure of the vinylidene fluoride copolymer in the emulsion changes appropriately, and it is easy to obtain a vinylidene fluoride copolymer composition that satisfies the above physical properties. On the other hand, if heated at a temperature higher than this end point, the crystal structure of the vinylidene fluoride copolymer in the emulsion changes significantly, the dispersion stability of the emulsion decreases, and it is difficult to take out the vinylidene fluoride copolymer composition in powder form.

[0123] When polymerization is carried out in the emulsion preparation step, the heating step can be continuously carried out directly after polymerization. In this case, it is preferable that, after polymerization and before the heating step, at least unreacted vinylidene fluoride and fluoroalkyl vinyl compounds are removed out of the system, and then heating is carried out at the above temperature.

[0124] When polymerization is carried out in the emulsion preparation step, the polymerization and heating steps can also be carried out separately. In this case, it is preferable that, before the heating step, after cooling to a temperature lower than the polymerization temperature, heating is carried out. Specifically, it is preferably cooled to a temperature more than 5°C lower than the polymerization temperature. In addition, the cooling method at this time is not particularly limited. By cooling to the above temperature, it is easy to obtain a heating effect (change in the state of the crystalline region of the untreated vinylidene fluoride copolymer), and it is easy to obtain a vinylidene fluoride copolymer composition having the desired physical properties.

[0125] On the other hand, when polymerization is not carried out in the above emulsion preparation step, for example, when using a commercially available emulsion, it can be directly heated to the above temperature.

[0126] It should be noted that in this specification, heating at the heating temperature means maintaining the emulsion at the above heating temperature for a certain period of time. The heating time is not for the purpose of removing the initiator remaining in the emulsion through the heating step, so there is no particular limitation as long as it is within the range where the state of the crystalline region of the above untreated vinylidene fluoride copolymer changes. As an example, it is preferably 10 seconds or more and 24 hours or less, more preferably 20 seconds or more and 12 hours or less, and still more preferably 30 seconds or more and 6 hours or less. By maintaining the above time at the above heating temperature, the state of the crystalline region formed during the polymerization of the untreated vinylidene fluoride copolymer easily changes, and it is easy to obtain a vinylidene fluoride copolymer composition having the desired physical properties.

[0127] The heating method is not particularly limited and can be carried out without stirring the above emulsion or while stirring. From the viewpoint of the dispersion stability of the above emulsion, it is preferably carried out while stirring. The heating device is also not particularly limited. An autoclave or the like can be used to heat the above emulsion under pressure, under saturated vapor pressure, or under atmospheric pressure.

[0128] (Drying process)

[0129] In the drying process, the aqueous medium is removed from the above emulsion. The method for removing the aqueous medium is not particularly limited, and it is preferably dried at a temperature that does not affect the physical properties of the vinylidene fluoride copolymer composition in the emulsion. The drying process can be carried out under atmospheric pressure or under reduced pressure. Through the above drying, the above solid (powder-like) vinylidene fluoride copolymer composition can be obtained. The drying method can be the same as the drying process in the first method.

[0130] ·Third method

[0131] In the third method of the method for producing a vinylidene fluoride copolymer composition, at least the following processes are carried out: a process of adding a surfactant to the emulsion after the emulsion preparation process and before the heating process in the second method (hereinafter, the emulsion to which the surfactant has been added is also referred to as "surfactant-containing emulsion") (hereinafter, also referred to as "surfactant addition process"). That is, the emulsion preparation process, the surfactant addition process, and the heating process are carried out in sequence. It should be noted that after the above heating process, by carrying out a process of drying the emulsion to take out the vinylidene fluoride copolymer (hereinafter, also referred to as "drying process"), the above solid vinylidene fluoride copolymer composition can be obtained. It should be noted that in this method, after obtaining the solid vinylidene fluoride copolymer composition, heating at a temperature above the melting point of the vinylidene fluoride copolymer composition is not carried out. Hereinafter, each process will be described.

[0132] (Emulsion preparation process)

[0133] In the emulsion preparation process, an emulsion in which an untreated vinylidene fluoride copolymer is dispersed in an aqueous medium is prepared. The above emulsion preparation process can be the same as the emulsion preparation process of the above first method.

[0134] (Surfactant addition process)

[0135] In the surfactant addition process, a surfactant is added to the emulsion prepared in the above emulsion preparation process to prepare a surfactant-containing emulsion. In addition, when polymerization is carried out in the emulsion preparation process, the emulsion (or surfactant-containing emulsion) can be cooled before, after, or during the addition of the surfactant.

[0136] When polymerization is carried out in the above emulsion preparation step, it is preferable to cool the emulsion or the surfactant-containing emulsion after adding the surfactant to a temperature lower than the polymerization temperature in the emulsion preparation step. Specifically, it is preferably cooled to a temperature 5°C or more lower than the polymerization temperature. In addition, the cooling method at this time is not particularly limited. By cooling, it is easy to obtain the effect of the heating step (change in the state of the crystalline region of the untreated vinylidene fluoride copolymer), and it is easy to obtain a vinylidene fluoride copolymer composition having the desired physical properties.

[0137] In this step, if a surfactant is added to the emulsion, the stability of the emulsion in the heating step is improved, so it is preferable. Through the above surfactant addition step, as long as the emulsion in the heating step is stable, therefore, in the above surfactant addition step, the surface tension and the addition amount of the emulsion (surfactant-containing emulsion) after addition are not limited. In addition, it can be carried out in the same manner as the surfactant addition step of the above first method.

[0138] In the surfactant addition step, a surfactant is added to the emulsion prepared in the above emulsion preparation step and stirred. At this time, the surface tension of the emulsion (surfactant-containing emulsion) after addition is not particularly limited, and the surface tension at 25°C is preferably 40 mN / m or less, more preferably 35 mN / m or less.

[0139] As the surfactant added in this step, as long as it is a surfactant that is soluble or miscible in the aqueous medium contained in the above emulsion, there is no particular limitation. For example, in addition to the surfactant added in the above first method, a nonionic surfactant can also be used. The nonionic surfactant that can be used is the same as the surfactant contained in the above vinylidene fluoride copolymer composition.

[0140] In this step, only one surfactant can be added, or two or more surfactants can be added. It should be noted that the remaining components in the surfactant added in this step can be removed by dialysis, ion exchange resin, etc. as needed.

[0141] (Heating step)

[0142] In the heating step, the surfactant-containing emulsion obtained in the above surfactant addition step is heated. The above heating step can be the same as the heating step of the above second method.

[0143] In addition, after the heat treatment, the remaining surfactant contained in the surfactant-containing emulsion can also be removed by dialysis, ion exchange resin, etc. For example, dialysis can be carried out as follows: Inject the surfactant-containing emulsion after heat treatment into a dialysis membrane made of cellulose, and immerse it together with the dialysis membrane in a water tank filled with pure water, and replace the pure water in the water tank at regular intervals.

[0144] (Drying step)

[0145] In the drying step, the aqueous medium is removed from the above surfactant-containing emulsion. The drying method can be the same as the drying step in the first method.

[0146] 2. Polymer dispersion

[0147] The above-mentioned vinylidene fluoride copolymer composition can be used in the form of a polymer dispersion obtained by mixing the above-mentioned vinylidene fluoride copolymer composition and a dispersion medium for the electrode binder or electrolyte binder described later. The above electrode binder is used to form an electrode layer, and the above electrolyte binder is used to form an electrolyte layer.

[0148] In particular, as described above, the vinylidene fluoride copolymer composition has very good dispersibility in a dispersion medium with a low relative dielectric constant and can maintain a stable state for a long time. As the dispersion medium that can be used, a medium that can be removed by drying and has a relative dielectric constant of 15 or less is preferred.

[0149] Here, the dispersion medium with a relative dielectric constant of 15 or less is not particularly limited. For example, it includes non-polar solvents and low-polar solvents. Specifically, examples include: hydrocarbon compounds, ether compounds having an ether bond, ketone compounds having a ketone group, ester compounds having an ester bond, etc. From the viewpoint of easy dehydration treatment, an ester compound is preferred.

[0150] The hydrocarbon compound only needs to be a compound composed of carbon atoms and hydrogen atoms, and can have a chain structure, a branched structure, or a cyclic structure. The number of carbon atoms is not particularly limited, and it can have multiple bonds such as double bonds and triple bonds, and an aromatic structure. Specific examples include: pentane, hexane, heptane, octane, nonane, decane, dodecane, hexene, heptene, cyclohexane, cycloheptane, toluene, xylene, mesitylene, tetralin, etc.

[0151] As specific examples of the ether compound, the following can be cited: alkylene glycol alkyl ethers (ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol, dipropylene glycol, triethylene glycol, polyethylene glycol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether, etc.), dialkyl ethers (dimethyl ether, diethyl ether, diisopropyl ether, dibutyl ether, etc.), cyclic ethers (tetrahydrofuran, dioxane (including 1,2-, 1,3- and 1,4-isomers), morpholine, etc.).

[0152] As specific examples of the ketone compound, the following can be cited: methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, diisopropyl ketone, cyclohexanone, phorone, acetophenone, isophorone, etc.

[0153] As specific examples of the ester compound, the following can be cited: ethyl acetate, butyl acetate, propyl acetate, isopropyl acetate, isoamyl acetate, benzyl acetate, ethyl butyrate, propyl butyrate, butyl butyrate, isoamyl butyrate, ethyl propionate, butyl valerate, methyl lactate, ethyl lactate, butyl lactate, ethylene glycol monoalkyl ether acetate, etc.

[0154] From the viewpoint of easy dehydration treatment, butyl butyrate is preferred.

[0155] In addition, the amount of the dispersion medium in the above polymer dispersion is appropriately selected according to the use of the polymer dispersion, the type of the vinylidene fluoride copolymer composition, etc., and is preferably 50% by mass or more and 99.9% by mass or less, more preferably 75% by mass or more and 99.9% by mass or less, based on 100% by mass of the polymer dispersion. If the amount of the dispersion medium is within the above range, the dispersibility of the vinylidene fluoride copolymer composition in the polymer dispersion is likely to be good.

[0156] In addition, the above polymer dispersion may further contain a solvent in addition to the dispersion medium and the vinylidene fluoride copolymer composition. The type of the solvent is preferably a medium that can be removed by drying, and includes polar solvents and ionic liquids in addition to nonpolar solvents and low-polarity solvents.

[0157] Examples of the solvent can be cited as follows: amide compounds such as dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone; alcohols such as methanol, ethanol, isopropyl alcohol, 2-ethyl-1-hexanol, 1-nonanol, lauryl alcohol, tripropylene glycol; amine compounds such as o-methylaniline, m-methylaniline, p-methylaniline; 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; lactones such as γ-butyrolactone, δ-butyrolactone; sulfoxide / sulfone compounds such as dimethyl sulfoxide, sulfolane; ionic liquids such as ethylmethylimidazolium salt, butylmethylimidazolium salt, etc.

[0158] The amount of the solvent in the above polymer dispersion is not particularly limited as long as it maintains the dispersibility of the vinylidene fluoride copolymer composition in the polymer dispersion. In one example, it is preferably 10% by mass or less.

[0159] 3. Electrodes for non-aqueous electrolyte secondary batteries

[0160] The above polymer dispersion can be used to form an electrode layer of electrodes for various non-aqueous electrolyte secondary batteries and the like. Electrodes of non-aqueous electrolyte secondary batteries include, for example, a current collector and an electrode layer disposed on the current collector. At this time, the above polymer dispersion can be used to form the electrode layer. It should be noted that the electrode can be used for the positive electrode or the negative electrode.

[0161] (1) Current collector

[0162] Current collectors for negative electrodes and positive electrodes are terminals for taking out electricity. The material of the current collector is not particularly limited, and metal foils or metal meshes such as aluminum, copper, iron, stainless steel, steel, nickel, and titanium can be used. In addition, it can also be a material formed by applying the above metal foil or metal mesh on the surface of other media.

[0163] (2) Electrode layer

[0164] The electrode layer can adopt the following layer: mixing the above vinylidene fluoride copolymer composition or polymer dispersion, active material, and, if necessary, a dispersion medium to prepare an electrode mixture, and coating the electrode mixture on the current collector and drying it. The electrode layer can be formed only on one side of the above current collector or can be disposed on both sides. The dispersion medium in the electrode mixture is the same as the dispersion medium described in the above polymer dispersion.

[0165] The components in the electrode layer are appropriately selected according to the type of non-aqueous electrolyte secondary battery. For example, a layer containing the above vinylidene fluoride copolymer composition and active material can be adopted. In addition, in the electrode layer of an electrode for an all-solid-state battery, a layer containing the above vinylidene fluoride copolymer composition, active material, and solid electrolyte is preferred. In addition, the electrode layer can also contain components other than these as needed. Examples of other components include various additives such as conductive aids, pigment dispersants, adhesion aids, and thickeners.

[0166] The amount of the vinylidene fluoride copolymer composition is preferably 0.1% by mass or more and 50% by mass or less, more preferably 0.2% by mass or more and 40% by mass or less, and further preferably 0.3% by mass or more and 30% by mass or less with respect to the total amount of the electrode layer. If the amount of the vinylidene fluoride copolymer composition is within the above range, the adhesiveness of the active material, solid electrolyte, and other components in the electrode layer to the current collector is likely to be good.

[0167] The active material contained in the electrode layer is not particularly limited. For example, known active materials for negative electrodes (negative electrode active materials) or active materials for positive electrodes (positive electrode active materials) can be used.

[0168] Examples of the above negative electrode active materials include: carbon materials such as artificial graphite, natural graphite, hardly graphitizable carbon, easily graphitizable carbon, activated carbon, or materials obtained by firing and carbonizing phenolic resins and pitch; metal / alloy materials such as Cu, Li, Mg, B, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, Cd, Ag, Zn, Hf, Zr, and Y; and metal oxides such as GeO, GeO 2 , SnO, SnO 2 , PbO, and PbO 2 etc. In addition, active materials with coatings applied to the surfaces of these active materials are also included. It should be noted that the negative electrode active material can be a commercially available product.

[0169] On the other hand, examples of the positive electrode active material include lithium-based positive electrode active materials containing lithium. Examples of lithium-based positive electrode active materials include: LiCoO 2 , LiNi x Co 1-x O 2 (0 < x ≤ 1) and other composite metal chalcogenides represented by the general formula LiMY 2 (M is one or more of transition metals such as Co, Ni, Fe, Mn, Cr, and V, and Y is a chalcogen element such as O and S); composite metal oxides with a spinel structure such as LiMn 2 O 4 etc.; and olivine-type lithium compounds such as LiFePO 4 etc. In addition, active materials with coatings applied to the surfaces of these active materials are also included. It should be noted that the positive electrode active material can be a commercially available product.

[0170] The amount of the active material contained in the electrode layer is appropriately selected according to its type, the function of the electrode, the type of the battery, etc., and there is no particular limitation. In one example, it is preferably 50% by mass or more and 99.9% by mass or less relative to the total amount of the active material, the vinylidene fluoride copolymer composition, and the conductive additive. If the amount of the active material is within the above range, for example, a sufficient charge-discharge capacity can be obtained, and the battery performance is likely to be good.

[0171] In addition, there are no particular limitations on the conductive additive as long as it is a compound that can further improve the conductivity between active materials or between an active material and a current collector. In addition, when a solid electrolyte is included as another component in the electrode layer, there are no particular limitations as long as it is a compound that can further improve the conductivity between an active material and a solid electrolyte, between a solid electrolyte and a current collector, or between solid electrolytes, in addition to the above. Examples of the conductive additive include acetylene black, Ketjen black, carbon black, graphite powder, carbon nanofibers, carbon nanotubes, and carbon fibers, etc.

[0172] The amount of the conductive additive contained in the electrode layer is appropriately selected according to its type, the function of the electrode, the type of the battery, etc., and there are no particular limitations, and it can be arbitrarily set according to its type and the type of the battery. From the viewpoint of improving both conductivity and the dispersibility of the conductive additive, in one example, the amount of the conductive additive is preferably 0.1% by mass or more and 15% by mass or less, more preferably 0.1% by mass or more and 7% by mass or less, and still more preferably 0.1% by mass or more and 5% by mass or less, relative to the total amount of the active material, the vinylidene fluoride copolymer composition, and the conductive additive.

[0173] In addition, there are no particular limitations on the solid electrolyte contained in the electrode composite layer as long as it is a solid compound having ionic conductivity, and known inorganic solid electrolytes and polymer solid electrolytes can be used. Examples of the inorganic solid electrolyte include oxide-based solid electrolytes, sulfide-based solid electrolytes, nitride-based solid electrolytes, complex hydride solid electrolytes, etc. In addition, examples of the polymer solid electrolyte include gel-based electrolytes, intrinsic polymer electrolytes, etc.

[0174] As for the oxide-based solid electrolyte, although not limited thereto, examples include perovskite-type LLTO, garnet-type LLZ, NASICON-type compounds, LISICON-type compounds, LIPON-type compounds, β-alumina-type compounds, etc. Specific examples include Li 3 PO 4 、Li 0.34 La 0.51 TiO 3 、Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 、Li 7 La 3 Zr 2 O 12 、Li 6 BaLa 2 Ta2 O 12 、Li 2.9 PO 3.3 N 0.46 、Li 4.3 Al 0.3 Si 0.7 O 4 、50Li 4 SiO 4 -50Li 3 BO 3 、Li 2 O-Al 2 O 3 -SiO 2 -P 2 O 5 -TiO 2 、Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 -0.05Li 2 O etc.

[0175] As a sulfide - based solid electrolyte, it includes a solid electrolyte containing Li, A (where A is at least one of P, Si, Ge, Al, and B), and S. The above - mentioned sulfide - based solid electrolyte may also contain a halogen element. In addition, the following can be cited: compounds of the LGPS (Li - Ge - P - S) type, argyrodite - type compounds, amorphous - based compounds, Li - P - S - based compounds, etc. Specific examples of the sulfide - based solid electrolyte include: Li 2 S - P 2 S 5 、Li 2 S - P 2 S 3 、Li 2 S - P 2 S 3 -P 2 S 5 、Li 2 S - SiS 2 、LiI - Li 2 S - SiS 2 、LiI - Li 2 S - P 2 S 5 、LiI - Li 2 S - P 2 O 5 、LiI - Li 3 PO 4 -P 2 S 5 、LiI - Li2 S-SiS 2 -P 2 S 5 、Li 2 S-SiS 2 -Li 4 SiO 4 、Li 2 S-SiS 2 -Li 3 PO 4 、Li 3 PS 4 -Li 4 GeS 4 、Li 3.4 P 0.6 Si 0.4 S 4 、Li 3.25 P 0.25 Ge 0.76 S 4 、Li 3.25 P 0.75 Ge 0.25 S 4 、Li 10 GeP 2 S 12 、Li 4-x Ge 1-x P x S 4 、Li 6 PS 5 Cl, Li 6 PS 5 Br, Li 6 PS 5 I, etc.

[0176] As a nitride-based solid electrolyte, it is not limited thereto, but specifically, LiN 3 , etc.

[0177] As a complex hydride solid electrolyte, it is not limited thereto, but specifically, LiBH 4 , etc.

[0178] As a gel-based electrolyte, it is not limited thereto. Specific examples include: Poly(ethylene oxide) 8 (Poly(ethyleneoxide) 8 )-LiClO 4 (ethylene carbonate (EC) + propylene carbonate (PC)), Poly(ethylene oxide) 8 (Poly(ethyleneoxide) 8 )-LiClO 4(PC), Poly(vinylidene fluoride)-LiN(CF 3 SO 2 ) 2 (EC+PC), Poly(vinylidene fluoride-co-hexafluoropropylene)-LiPF 6 (EC + Diethyl carbonate (DEC) + Dimethyl carbonate (DMC)), Poly(ethyleneglycol acrylate)-LiClO 4 (PC), Poly(acrylonitrile)-LiClO 4 (EC+PC), Poly(methyl methacrylate)-LiClO 4 (PC), etc.

[0179] As an intrinsic polymer electrolyte, there is no limitation on it. Specific examples include: Poly(ethylene oxide) 8 (Poly(ethylene oxide) 8 )-LiClO 4 , Poly(oxymethylene)-LiClO 4 , Poly(propylene oxide) 8 (Poly(propylene oxide) 8 )-LiClO 4 , Poly(dimethyl siloxane)-LiClO 4 , Poly(vinylidene fluoride-co-hexafluoropropylene)-LiTFSI, Poly(2,2-dimethoxypropylene carbonate)-LiFSI, Poly[(2-methoxy)ethylglycidyl ether] 8 (Poly[(2-methoxy)ethylglycidyl ether] 8 )-LiClO 4 , etc.

[0180] The electrode layer can contain only one of the above solid electrolytes or two or more of the above solid electrolytes.

[0181] In the case where the electrode layer contains a solid electrolyte, the amount of the solid electrolyte is appropriately selected according to its type, the function of the electrode, the type of the battery, etc., and there is no particular limitation. In one example, it is preferably 1% by mass or more and 99.9% by mass or less relative to the total amount of the active material, the vinylidene fluoride copolymer composition, and the solid electrolyte. If the amount of the solid electrolyte is within the above range, sufficient ionic conductivity can be obtained, and the battery performance is likely to be good.

[0182] As described above, the electrode layer may contain a pigment dispersant, a bonding aid, a thickener, etc., and for these, known compounds can be used. Their amounts are not particularly limited as long as they are within the range that does not impair the object and effect of the present invention. In one example, it is preferably 15% by mass or less relative to the total amount of the active material, the vinylidene fluoride copolymer composition, and them.

[0183] The electrode layer may further contain: nitrogen compounds such as phosphorus compounds, sulfur compounds, organic acids, amine compounds, and ammonium compounds; organic esters, various coupling agents of the silane series, titanium series, and aluminum series; resins such as vinylidene fluoride polymers other than the above vinylidene fluoride copolymer, polytetrafluoroethylene (PTFE), styrene / butadiene rubber (SBR), and polyacrylonitrile (PAN); and other additives. Their amounts are not particularly limited as long as they are within the range that does not impair the object and effect of the present invention. In one example, it is preferably 15% by mass or less relative to the total amount of the active material, the vinylidene fluoride copolymer composition, and the additives.

[0184] Here, the thickness of the electrode layer is not particularly limited. In one example, it is preferably 1 μm or more and 1000 μm or less. In addition, the weight per unit area of the active material contained in the electrode layer is not particularly limited and can be set to any weight per unit area. In one example, it is preferably 50 g / m 2 ~1000 g / m 2 and more preferably 100 g / m 2 ~500 g / m 2 .

[0185] (Method for forming the electrode layer)

[0186] The above electrode layer can be formed by performing the following steps: a step of preparing an electrode mixture obtained by mixing the above vinylidene fluoride copolymer composition or polymer dispersion, active material, solid electrolyte as required, dispersion medium, solvent, conductive aid, various additives, etc.; a step of coating the above electrode mixture on a current collector; and a step of drying it.

[0187] The above electrode mixture can be prepared by mixing all components together, or by first mixing a part of the components and then mixing the remaining components. At this time, in order to prevent the temperature of the binder for the electrode layer from rising excessively, it is preferably mixed using a mixer equipped with a temperature control device.

[0188] In addition, the dispersion medium and solvent in the above electrode mixture only need to be able to uniformly disperse the vinylidene fluoride copolymer composition, active material, solid electrolyte, conductive additive, etc. The type of the added dispersion medium is not particularly limited, and it is preferably the same as the dispersion medium contained in the above polymer dispersion. In addition, when a solvent is added, it is preferably the same as the solvent contained in the above polymer dispersion. The total amount of the dispersion medium in the polymer dispersion and the dispersion medium added thereto is not particularly limited, and from a manufacturing perspective, it can be set to any amount. In one example, relative to 100 parts by mass of the above active material, it is preferably 10 parts by mass or more and 20,000 parts by mass or less. The total amount of the solvent in the polymer dispersion and the solvent added thereto is not particularly limited, and from a manufacturing perspective, it can be set to any amount. In one example, relative to 100 parts by mass of the above active material, it is preferably 2,000 parts by mass or less.

[0189] The viscosity of the electrode mixture is not particularly limited as long as it can prevent liquid dripping during the application of the electrode mixture to obtain an electrode, uneven coating of the electrode, drying delay after coating, good workability of electrode production, and good coatability of the electrode. In one example, it is preferably 0.1 Pa·s or more and 100 Pa·s or less. The viscosity of the electrode mixture is measured using an E-type viscometer or the like.

[0190] In addition, the coating method of the electrode mixture is not particularly limited, and methods such as the doctor blade method, reverse roll method, comma bar method, gravure printing method, air knife method, die coating method, and dip coating method can be applied.

[0191] In addition, after the application of the electrode mixture, it is heated at an arbitrary temperature to dry the solvent (dispersion medium). The drying temperature is preferably 30°C or more and 500°C or less in one example. Drying can be carried out multiple times at different temperatures. At this time, drying can be carried out under atmospheric pressure, under pressure, or under reduced pressure. Heat treatment can also be further carried out after drying.

[0192] After the application and drying of the above electrode mixture, pressing treatment can also be further carried out. By carrying out the pressing treatment, the electrode density can be increased. The pressing pressure is preferably 1 kPa or more and 10 GPa or less in one example.

[0193] 4. Electrolyte Layer for Non-aqueous Electrolyte Secondary Battery

[0194] The above-mentioned vinylidene fluoride copolymer composition or polymer dispersion can also be used, for example, in the production of an electrolyte layer for a non-aqueous electrolyte secondary battery. The electrolyte layer for a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "electrolyte layer") may, for example, consist only of the electrolyte layer. The above-mentioned polymer dispersion (vinylidene fluoride copolymer) can be used as the material for the above-mentioned electrolyte layer.

[0195] The electrolyte layer only needs to contain at least the above-mentioned vinylidene fluoride copolymer composition and an electrolyte, and may further contain other components as needed. The electrolyte layer can be a layer for bonding an electrode and an electrolyte, a layer for allowing various ions to conduct, or a layer that undertakes these functions simultaneously. In the above-mentioned electrolyte layer, the above-mentioned vinylidene fluoride copolymer composition can be in the form of particles, a film (including a porous film), or a gel.

[0196] A all-solid-state battery has, for example, a structure in which an electrolyte layer is sandwiched between a pair of electrodes (both having a current collector and an electrode layer). The above-mentioned polymer dispersion can also be used to form the electrolyte layer of such an all-solid-state battery.

[0197] The electrolyte layer can be a layer prepared by coating a substrate with an electrolyte mixture containing, for example, a vinylidene fluoride copolymer composition or a polymer dispersion, a solid electrolyte, a dispersion medium as needed, and any other components, and then drying it. At this time, it can be a layer obtained by peeling the dried layer from the substrate. In addition, it can also be a layer formed by directly coating the above-mentioned electrolyte mixture on the above-mentioned electrode and then drying it.

[0198] It should be noted that the solid electrolyte contained in the electrolyte layer can be the same compound as the solid electrolyte described in the above description of the electrode layer of the electrode. The amount of the solid electrolyte relative to the total amount of the electrolyte layer is appropriately selected according to its type, the function of the electrolyte layer, the type of the battery, etc., and there is no particular limitation. In one example, it is preferably 10% by mass or more and 99.9% by mass or less relative to the total amount of the electrolyte layer.

[0199] Furthermore, the electrolyte layer may also contain components other than the above-mentioned vinylidene fluoride copolymer and the above-mentioned solid electrolyte. Examples thereof include a pigment dispersant, an adhesion aid, a thickener, a filler, various additives, etc. It should be noted that the pigment dispersant, the adhesion aid, and the thickener can be known compounds, or the same as the additives contained in the electrode layer. In addition, their amounts are not particularly limited as long as they do not impair the object and effect of the present invention. In one example, they are preferably 0.1% by mass or more and 90% by mass or less relative to the total amount of the electrolyte layer.

[0200] The filler contained in the electrolyte layer can be an inorganic filler or an organic filler. Examples of the inorganic filler include oxides such as silicon dioxide (SiO 2 ), aluminum oxide (Al 2 O 3 ), titanium dioxide (TiO 2 ), calcium oxide (CaO), strontium oxide (SrO), barium oxide (BaO), magnesium oxide (MgO), zinc oxide (ZnO), barium titanate oxide (BaTiO 3 ); hydroxides such as magnesium hydroxide (Mg(OH) 2 ), calcium hydroxide (Ca(OH) 2 ), zinc hydroxide (Zn(OH) 2 ), aluminum hydroxide (Al(OH) 3 ), meta-aluminum hydroxide (AlO(OH)); carbonates such as calcium carbonate (CaCO 3 ); sulfates such as barium sulfate; nitrides; clay minerals; and boehmite. The filler can contain only one kind or two or more kinds. In addition, their amounts are not particularly limited as long as they do not impair the object and effect of the present invention. In one example, it is preferably 0.1% by mass or more and 90% by mass or less relative to the total amount of the electrolyte layer.

[0201] The thickness of the electrolyte layer is appropriately selected according to the function of the electrolyte layer and is not particularly limited. In one example, it is preferably 1 μm or more and 1000 μm or less.

[0202] The amount of the vinylidene fluoride copolymer composition relative to the total amount of the electrolyte layer is appropriately selected according to its type, the function of the electrolyte layer, the type of the battery, etc. and is not particularly limited. In one example, it is preferably 0.1% by mass or more and 10% by mass or less.

[0203] It should be noted that the method for forming the electrolyte layer is not particularly limited. As described above, it can be formed by coating an electrolyte mixture and drying it. The coating method and drying method of the electrolyte mixture are the same as those of the electrode layer. In addition, as the electrolyte mixture, the above polymer dispersion can be directly mixed in the solid electrolyte, or a dispersion medium and a solvent can be further added as needed. The dispersion medium used for forming the electrolyte layer is not particularly limited and is preferably the same as the dispersion medium contained in the above polymer dispersion.

[0204] 5. Non-aqueous electrolyte secondary battery

[0205] As described above, the above vinylidene fluoride copolymer composition or polymer dispersion can be used for electrodes and electrolyte layers of various non-aqueous electrolyte secondary batteries including all-solid batteries, and can also be used for forming other layers of non-aqueous electrolyte secondary batteries.

[0206] Example

[0207] Hereinafter, the present invention will be described in more detail with reference to examples. The scope of the present invention is not limited or construed by these examples.

[0208] <Preparation of Emulsion>

[0209] (1) Preparation of Emulsion 1

[0210] 280 parts by mass of ion-exchanged water was added to an autoclave and degassed by nitrogen bubbling for 30 minutes. Subsequently, 0.2 part by mass of disodium hydrogen phosphate and 1.0 part by mass of ammonium perfluorooctanoate (PFOA) were charged, pressurized to 4.5 MPa, and subjected to three nitrogen replacements. Thereafter, 0.1 part by mass of ethyl acetate, 11 parts by mass of vinylidene fluoride (VDF), and 24 parts by mass of hexafluoropropylene (HFP) were added to the autoclave. The temperature was raised to 80 °C while stirring. Then, an aqueous solution of 5% by mass ammonium persulfate (APS) was added such that the amount of APS became 0.06 part by mass to initiate polymerization. 65 parts by mass of VDF was continuously added immediately after the start of polymerization so that the pressure inside the autoclave was maintained at 2.5 MPa. After the addition was completed, polymerization was completed when the pressure dropped to 1.5 MPa. After cooling to 40 °C or lower, the residual monomers were removed from the autoclave to obtain Emulsion 1 in which the untreated vinylidene fluoride copolymer was dispersed in water. The solid content concentration (concentration of the vinylidene fluoride copolymer) of the above Emulsion 1 was 21.0% by mass. In addition, the untreated vinylidene fluoride copolymer was taken out by freeze-drying, and based on the method described below, the end point of the endothermic peak observed below 185 °C of the above vinylidene fluoride copolymer was measured, and the result was 132 °C.

[0211] (Method for Determining the End Point)

[0212] First, the emulsion was freeze-dried to obtain a powdery vinylidene fluoride copolymer. Next, a mold measuring 5 cm in length × 5 cm in width × 150 μm in thickness and about 1 g of the powdery vinylidene fluoride copolymer were sandwiched between two pieces of aluminum foil sprayed with a release agent in a mist form and pressed at 200 °C to produce a film. Then, measurement was performed using a differential scanning calorimeter ("DSC-1" manufactured by METTLER) in accordance with ASTM D3418 to obtain the heat flow of the vinylidene fluoride copolymer. In the obtained heat flow, in the endothermic peak of the vinylidene fluoride copolymer observed below 185 °C, in the temperature region on the high-temperature side of the peak of the highest temperature, a baseline was linearly drawn so as to overlap with the linear heat flow. Then, in the endothermic peak of the vinylidene fluoride copolymer observed below 185 °C, in the temperature region on the high-temperature side of the peak of the highest temperature and on the low-temperature side of the minimum temperature at which the heat flow overlaps with the baseline, a tangent line was drawn on the heat flow, and the intersection point of this tangent line and the baseline was taken as the end point of the vinylidene fluoride copolymer.

[0213] (2) Preparation of Emulsion 2

[0214] Before the start of polymerization, the amount of VDF added to the autoclave together was changed from 11 parts by mass to 15 parts by mass, and the amount of HFP was changed from 24 parts by mass to 20 parts by mass. Except for this, polymerization was carried out in the same manner as in the preparation of Emulsion 1, and Emulsion 2 in which the untreated vinylidene fluoride copolymer was dispersed in water was obtained. The solid content concentration (concentration of the vinylidene fluoride copolymer) of the above Emulsion 2 was 20.8% by mass. In addition, the end point of the peak with the highest temperature in the endothermic peak of the untreated vinylidene fluoride copolymer observed below 185 °C determined by the same method as Emulsion 1 was 134 °C.

[0215] (3) Preparation of Emulsion 3

[0216] Before the start of polymerization, the amount of VDF added to the autoclave together was changed from 11 parts by mass to 25 parts by mass, and the amount of HFP was changed from 24 parts by mass to 10 parts by mass. Except for this, polymerization was carried out in the same manner as in the preparation of Emulsion 1, and Emulsion 3 in which the untreated vinylidene fluoride copolymer was dispersed in water was obtained. The solid content concentration (concentration of the vinylidene fluoride copolymer) of the above Emulsion 3 was 21.3% by mass. In addition, the end point of the peak with the highest temperature in the endothermic peak of the untreated vinylidene fluoride copolymer determined by the same method as Emulsion 1 was 152 °C.

[0217] <Example 1>

[0218] Emulsion 1 was added to the autoclave, and further SDS was added so that the concentration of sodium dodecyl sulfate (SDS) relative to the water in the emulsion became 1% by mass, and an emulsion containing a surfactant was obtained. At this time, the surface tension of the emulsion containing the surfactant at 25 °C was measured. The results are shown in Table 1.

[0219] Then, while stirring at 500 rpm, it was heated at a temperature lower than the above end point, i.e., 125 °C, for 1 hour. After that, while continuously stirring, it was air-cooled at room temperature (24 °C) until the temperature in the autoclave became 40 °C or lower. In addition, the above emulsion was freeze-dried to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle size of the above powdery vinylidene fluoride copolymer composition was 174 μm. At this time, the freeze-dried product was obtained by freezing the emulsion after polymerization in liquid nitrogen and drying it under reduced pressure at room temperature.

[0220] <Example 2>

[0221] The concentration of SDS relative to the water in Emulsion 1 was changed from 1% by mass to 0.5% by mass, and heat treatment and freeze-drying were carried out in the same manner as in Example 1, to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle diameter of this powdery vinylidene fluoride copolymer composition was 141 μm.

[0222] <Example 3>

[0223] The surfactant added to Emulsion 1 was changed from SDS to EMULGEN LS-110 (manufactured by Kao Corporation, polyoxyalkylene alkyl ether), and heat treatment and freeze-drying were carried out in the same manner as in Example 2, to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle diameter of this powdery vinylidene fluoride copolymer composition was 197 μm.

[0224] <Example 4>

[0225] The surfactant added to Emulsion 1 was changed from SDS to PFOA (perfluorooctanoic acid), and heat treatment and freeze-drying were carried out in the same manner as in Example 2, to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle diameter of this powdery vinylidene fluoride copolymer composition was 163 μm.

[0226] <Example 5>

[0227] The heating temperature of Emulsion 1 was changed from 125 °C to 95 °C, and heat treatment and freeze-drying were carried out in the same manner as in Example 2, to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle diameter of this powdery vinylidene fluoride copolymer composition was 391 μm.

[0228] <Example 6>

[0229] The heating temperature of Emulsion 1 was changed from 125 °C to 75 °C, and heat treatment and freeze-drying were carried out in the same manner as in Example 2, to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle diameter of this powdery vinylidene fluoride copolymer composition was 364 μm.

[0230] <Example 7>

[0231] The concentration of SDS relative to the water in Emulsion 1 was changed from 0.5% by mass to 0% by mass, and heat treatment and freeze-drying were carried out in the same manner as in Example 2, to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle diameter of this powdery vinylidene fluoride copolymer composition was 173 μm.

[0232] <Example 8>

[0233] The concentration of SDS in water in Emulsion 1 was changed from 0.5% by mass to 0% by mass, and heat treatment and freeze-drying were carried out in the same manner as in Example 6, to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle diameter of the powdery vinylidene fluoride copolymer composition was 424 μm.

[0234] <Example 9>

[0235] The emulsion added to the autoclave was changed from Emulsion 1 to Emulsion 2, and the heating temperature of the emulsion after adding the surfactant (emulsion containing surfactant) was changed from 125 °C to 130 °C, and heat treatment and freeze-drying were carried out in the same manner as in Example 2, to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle diameter of the powdery vinylidene fluoride copolymer composition was 52 μm.

[0236] <Example 10>

[0237] Emulsion 1 was added to the autoclave, and PFOA was further added so that the concentration of PFOA relative to the water in the emulsion became 0.5% by mass. Then, stirring was carried out at 500 rpm at room temperature (24 °C) to dissolve PFOA in the emulsion. The above emulsion was freeze-dried to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle diameter of the powdery vinylidene fluoride copolymer composition was 160 μm.

[0238] <Example 11>

[0239] Emulsion 1 was added to the autoclave, and SDS was further added so that the concentration of SDS relative to the water in the emulsion became 1% by mass. Stirring was carried out at 500 rpm at room temperature (24 °C) to dissolve SDS in the emulsion. The above emulsion was freeze-dried to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle diameter of the powdery vinylidene fluoride copolymer composition was 148 μm.

[0240] <Example 12>

[0241] The concentration of SDS relative to the water in the emulsion was changed from 1% by mass to 0.5% by mass, and dissolution and freeze-drying were carried out in the same manner as in Example 11, to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle diameter of the powdery vinylidene fluoride copolymer composition was 126 μm.

[0242] <Example 13>

[0243] The concentration of PFOA relative to water in the emulsion was changed from 0.5% by mass to 1% by mass, and dissolution and freeze-drying were carried out in the same manner as in Example 10, to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle diameter of the powdery vinylidene fluoride copolymer composition was 219 μm.

[0244] <Example 14>

[0245] The concentration of PFOA relative to water in the emulsion was changed from 0.5% by mass to 0.1% by mass, and dissolution and freeze-drying were carried out in the same manner as in Example 10, to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle diameter of the powdery vinylidene fluoride copolymer composition was 178 μm.

[0246] <Example 15>

[0247] Emulsion 1 was added to an autoclave, and further Acetamin 86 (manufactured by Kao Corporation, stearylamine acetate) was added such that the concentration of Acetamin 86 relative to water in the emulsion became 0.05% by mass, and stirring was carried out at 500 rpm at room temperature (24°C), whereby Acetamin 86 was dissolved in the emulsion. The above emulsion was freeze-dried to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle diameter of the powdery vinylidene fluoride copolymer composition was 821 μm.

[0248] <Comparative Example 1>

[0249] Emulsion 1 was freeze-dried to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle diameter of the powdery vinylidene fluoride copolymer composition was 215 μm.

[0250] <Comparative Example 2>

[0251] The powdery vinylidene fluoride copolymer composition obtained in Example 11 was heat-treated at 125°C for 1 hour to obtain a powdery vinylidene fluoride copolymer composition. The aggregation of the vinylidene fluoride copolymer composition was intense, and thus the average secondary particle diameter could not be measured.

[0252] <Comparative Example 3>

[0253] The powdery vinylidene fluoride copolymer composition obtained in Comparative Example 1 was heat-treated at 125°C for 1 hour to obtain a powdery vinylidene fluoride copolymer composition. The aggregation of the vinylidene fluoride copolymer composition was intense, and thus the average secondary particle diameter could not be measured.

[0254] <Comparative Example 4>

[0255] The surfactant added to the emulsion was changed from PFOA to EMULGEN LS-110, and dissolution and freeze-drying were carried out in the same manner as in Example 10, to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle size of the powdery vinylidene fluoride copolymer composition was 127 μm.

[0256] <Comparative Example 5>

[0257] The emulsion added to the autoclave was changed from Emulsion 1 to Emulsion 3, and the heating temperature of the emulsion was changed from 125 °C to 150 °C. Heat treatment and freeze-drying were carried out in the same manner as in Example 2, to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle size of the powdery vinylidene fluoride copolymer composition was 39 μm.

[0258] <Comparative Example 6>

[0259] To the powdery vinylidene fluoride copolymer composition obtained in Comparative Example 1, sodium dodecyl sulfate (SDS) in an amount of 1% by mass based on the water in the emulsion before freeze-drying was added, to obtain a powdery vinylidene fluoride copolymer composition. The average secondary particle size of the powdery vinylidene fluoride copolymer composition was 215 μm.

[0260] <Comparative Example 7>

[0261] The heating temperature of Emulsion 1 was changed from 125 °C to 180 °C, and heat treatment was carried out in the same manner as in Example 2. Through the above heating process, it could not be recovered in the form of an emulsion having dispersion stability, and thus a powdery vinylidene fluoride copolymer composition could not be obtained.

[0262] <Comparative Example 8>

[0263] The heating temperature of Emulsion 1 was changed from 125 °C to 180 °C, and heat treatment was carried out in the same manner as in Example 7. Through the above heating process, it could not be recovered in the form of an emulsion having dispersion stability, and thus a powdery vinylidene fluoride copolymer composition could not be obtained.

[0264] <Measurement methods for various physical properties>

[0265] The physical properties of the above vinylidene fluoride copolymer composition, emulsion, etc. were measured as follows, respectively.

[0266] · Determination of the solid content concentration of each emulsion

[0267] Approximately 5 g of the obtained emulsion was added to an aluminum cup and dried at 80 °C for 3 hours. Then, the weights before and after drying were measured, and from this, the concentration of the vinylidene fluoride copolymer in the emulsion (solid content concentration) was calculated.

[0268] ·Measurement of the average secondary particle diameter of the vinylidene fluoride copolymer composition

[0269] Regarding the average secondary particle diameter of the vinylidene fluoride copolymer composition, the powdery vinylidene fluoride copolymer composition was measured by the laser diffraction / scattering method on a volume basis, and the cumulative average diameter (D50) of its particle size distribution was calculated. Specifically, using Microtrac MT3300EXII manufactured by MICROTRACBEL, approximately 0.5 mg of the powdery vinylidene fluoride copolymer composition was dispersed in water by stirring to prepare a measurement sample. Water was used as the measurement medium, the refractive index of the medium was set to 1.333, the particle shape was set to non-spherical, the refractive index of the particles was set to 1.42, the measurement time was set to 30 seconds, and the average value of D50 measured 5 times in the transmission mode was used as the average secondary particle diameter.

[0270] ·Measurement of the melting point of the vinylidene fluoride copolymer composition

[0271] The melting point of the vinylidene fluoride copolymer composition was measured in the form of a film prepared by the following method. First, a mold with a length of 5 cm × width of 5 cm × thickness of 150 μm and approximately 1 g of the powdery vinylidene fluoride copolymer composition were sandwiched between two aluminum foils sprayed with a release agent in a mist form and pressed at 200 °C to obtain a pressed film. Then, the melting point was measured using a differential scanning calorimeter ("DSC-1" manufactured by METTLER) in accordance with ASTM D3418.

[0272] ·Temperature-modulated differential scanning calorimetry

[0273] The peak of the reversible heat flow (RHF) and the melting enthalpy of the vinylidene fluoride copolymer composition were measured using a temperature-modulated differential scanning calorimeter (Q-100, manufactured by TA INSTRUMENTS). Specifically, approximately 5 mg of the vinylidene fluoride copolymer composition pulverized by freeze-drying was filled into an aluminum pan as a measurement sample. The measurement conditions were set so as to be only heating conditions, with an average heating rate of 5 °C / min, a modulation period of 40 seconds, and a modulation amplitude of ±0.531 °C. The obtained reversible heat flow had a downwardly convex endothermic peak. In the obtained reversible heat flow, a baseline was linearly drawn so as to overlap with the linear heat flow on the high-temperature side relative to the end point. Then, when a line was perpendicularly drawn from this baseline to the reversible heat flow in the downwardly convex endothermic peak of the reversible heat flow, the point on the reversible heat flow that was the farthest from this baseline was taken as the peak of the endothermic peak, and the temperature of this peak was determined. In addition, the number of minima of the downwardly convex endothermic peak of the reversible heat flow was taken as the number of peaks of the endothermic peak. On the other hand, the area surrounded by this baseline and the reversible heat flow was taken as the melting enthalpy (ΔHm).

[0274] ·Measurement of the surface tension of the emulsion

[0275] The surface tension of the emulsion (in the case of adding a surfactant to the emulsion, the emulsion after adding the surfactant) was measured using the Wilhelmy method with a tensiometer (Sigma701 / 700, manufactured by KSV instruments). A platinum plate was used for the measurement, and the average value of the surface tension measured three times at 25°C was taken as the value of the surface tension.

[0276] · Determination of the content of the vinylidene fluoride copolymer composition in the supernatant of the butyl butyrate dispersion of the vinylidene fluoride copolymer composition

[0277] First, 2 g of the powdery vinylidene fluoride copolymer composition was added to 18 g of butyl butyrate and stirred on a stirrer at 25°C for 30 minutes to prepare a butyl butyrate dispersion of the vinylidene fluoride copolymer composition (the content of the vinylidene fluoride copolymer composition was 10% by mass). 20 mL of this dispersion was added to a 20 mL graduated cylinder, covered with a sealing film, and allowed to stand for 20 hours. 4 mL was collected from the supernatant of the graduated cylinder with a pipette, added to an aluminum cup, dried at 135°C for 1 hour, and cooled in a desiccator for 1 hour. Then, the weight before and after drying was measured, and thus the content of the vinylidene fluoride copolymer composition in the supernatant of the butyl butyrate dispersion of the vinylidene fluoride copolymer composition was determined.

[0278] · Turbidity

[0279] The turbidity of the dispersion obtained by dispersing the vinylidene fluoride copolymer composition in butyl butyrate was measured by the following method. First, 2 g of the powdery vinylidene fluoride copolymer composition was added to 18 g of butyl butyrate and stirred on a stirrer at 25°C for 30 minutes to prepare a butyl butyrate dispersion of the vinylidene fluoride copolymer composition (the content of the vinylidene fluoride copolymer composition was 10% by mass). Then, the turbidity of this dispersion after standing for 20 hours and then stirring was measured using NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. (in accordance with JIS K 7136). It should be noted that the sample was added to a quartz cuvette. In addition, the turbidity of butyl butyrate was set to 0%, and the turbidity of the sample was calculated.

[0280] [Table 1]

[0281]

[0282]

[0283] [Table 2]

[0284]

[0285]

[0286] ※1The vinylidene fluoride copolymer composition precipitated in butyl butyrate and therefore could not be measured.

[0287] ※2 Since the vinylidene fluoride copolymers aggregated strongly, the measurement could not be performed.

[0288] ※3 After the heating step, the emulsion could not be recovered in the form of a stable emulsion, and a particulate (powdered) vinylidene fluoride copolymer composition could not be obtained in the subsequent drying step, so measurement was not possible.

[0289] As shown in Table 2, the melting point of the vinylidene fluoride copolymer composition is below 140°C.

[0290] The ethylene copolymer composition has an endothermic peak with a melting enthalpy (ΔHm) of 2 mJ / g in a reversing heat flow,

[0291] and the difference between the maximum endothermic peak temperature (the peak top temperature of the maximum endothermic peak) and the melting point of the composition

[0292] The absolute value is 10°C or less, and the vinylidene fluoride copolymer composition is dispersed in butyl butyrate.

[0293] The dispersion (containing 10% by mass of the vinylidene fluoride copolymer composition) was allowed to stand for 20 hours.

[0294] The content of the vinylidene fluoride copolymer composition in the upper part is 4.0 mass % or more and 10 mass % or less

[0295] In this case, the dispersibility of the vinylidene fluoride copolymer composition becomes good (Examples 1 to

[0296] 15).

[0297] On the other hand, when the melting point of the vinylidene fluoride copolymer composition exceeds 140°C,

[0298] It is easy to precipitate in butyl butyrate (Comparative Example 5).

[0299] The maximum endothermic peak temperature (maximum absorption) of the reversible heat flow with a melting enthalpy (ΔHm) of 2 mJ / g

[0300] When the absolute value of the difference between the peak temperature of the thermal peak and the melting point of the composition exceeds 10°C, the condensation

[0301] The concentration was intense (Comparative Examples 2 and 3). Furthermore, the vinylidene fluoride copolymer composition was dispersed in butyrate.

[0302] The dispersion (content of the vinylidene fluoride copolymer composition: 10 mass%) was allowed to stand for 1 h.

[0303] The content of the vinylidene fluoride copolymer composition in the upper part after 20 hours is 4.0% by mass or more and exceeds

[0304] 10% by mass, the dispersibility is low in both cases (Comparative Examples 1 to 8).

[0305] In addition, as shown in Table 1, by adding a certain amount of surfactant to the emulsion of vinylidene fluoride copolymer (copolymer dispersion)

[0306] or heating the emulsion, a vinylidene fluoride copolymer composition having desired physical properties can be obtained (Examples 1 to 15). In contrast, when no surfactant is added to the emulsion of vinylidene fluoride copolymer and the emulsion is not heated, the vinylidene fluoride copolymer

[0307] composition easily settles in butyl butyrate (Comparative Example 1).

[0308] Moreover, regardless of whether a surfactant is added to the emulsion, when the vinylidene fluoride copolymer composition is made into a powder form and then heated, the vinylidene fluoride copolymer composition easily settles in butyl butyrate (Comparative Examples 2 and 3).

[0309] Furthermore, when a non-ionic surfactant (non-ionic surfactant) is added to the emulsion and the emulsion is not heated, the vinylidene fluoride copolymer composition also easily settles in butyl butyrate (Comparative Example 4).

[0310] Moreover, when a surfactant is added after the vinylidene fluoride copolymer composition is made into a powder form, the vinylidene fluoride copolymer composition easily settles in butyl butyrate (Comparative Example 6).

[0311] Moreover, if the melting point of the vinylidene fluoride copolymer composition exceeds 140 °C, even if a surfactant is added to the emulsion or the surfactant-containing emulsion is heated, a vinylidene fluoride copolymer composition having desired physical properties cannot be obtained (Comparative Example 5).

[0312] In addition, when measuring the heat flow of the vinylidene fluoride copolymer in the emulsion with a differential scanning calorimeter for the emulsion of vinylidene fluoride copolymer, if heating is performed at a temperature higher than the end point of the highest temperature peak among the endothermic peaks of the vinylidene fluoride copolymer observed at 185 °C or lower, a vinylidene fluoride copolymer composition having desired physical properties cannot be obtained regardless of whether a surfactant is added to the emulsion (Comparative Examples 7, 8).

[0313] This application claims the priority based on Japanese Patent Application No. 2020-198148 filed on November 30, 2020. All the contents described in the specification of the said application are incorporated herein by reference.

[0314] This application claims the priority based on Japanese Patent Application No. 2020-198148 filed on November 30, 2020. All the contents described in the specification of the said application are incorporated herein by reference.

[0315] Industrial availability

[0316] The vinylidene fluoride copolymer composition of the present invention is easily dispersed in a dispersion medium having a low relative dielectric constant, and the dispersion liquid is not likely to settle even when stored for a long time. Therefore, it is very useful in the production of electrode layers and electrolyte layers for non-aqueous electrolyte secondary batteries, etc.

Claims

1. A method for manufacturing a vinylidene fluoride copolymer composition, the vinylidene fluoride copolymer composition containing a vinylidene fluoride copolymer comprising a structural unit derived from vinylidene fluoride and a structural unit derived from a fluoroalkyl vinyl compound, The method comprises: a step of preparing an emulsion in which an untreated vinylidene fluoride copolymer is dispersed in an aqueous medium by an emulsion polymerization method; and a step of heating the emulsion at a temperature lower than the end point of the highest-temperature peak among the endothermic peaks observed at 185°C or lower and at a temperature of 40°C or higher when measuring the heat flow of the untreated vinylidene fluoride copolymer with a differential scanning calorimeter, the melting point of the vinylidene fluoride copolymer composition being 140°C or lower, after the step of preparing the emulsion and before the step of heating the emulsion, further comprising a step of adding a surfactant to the emulsion.

2. The method for manufacturing a vinylidene fluoride copolymer composition according to claim 1, wherein the fluoroalkyl vinyl compound is hexafluoropropylene.

3. The method for manufacturing a vinylidene fluoride copolymer composition according to claim 2, wherein the vinylidene fluoride copolymer composition contains 15% by mass or more and 70% by mass or less of the structural unit derived from the hexafluoropropylene based on 100% by mass of the structural units of the vinylidene fluoride copolymer.

4. The method for manufacturing a vinylidene fluoride copolymer composition according to claim 1, wherein the surfactant contains an anionic surfactant.

Images