Fluorine-containing polymer powder, electrode mixture, electrode, and secondary battery

Abstract

A fluorine-containing polymer powder according to the present invention is for a binding agent for a secondary battery electrode and includes a fluorine-containing polymer that includes a unit based on tetrafluoroethylene. The compressive elastic modulus of the fluorine-containing polymer as found from formula 1 is 0.10–1.20 MPa.　Formula 1: compressive elastic modulus=(compressive stress at 50% deformation-compressive stress at 10% deformation) / 0.4. An electrode mixture according to the present invention may include the fluorine-containing polymer powder and an electrode active material. The electrode mixture may also contain a conductive auxiliary agent, the fluorine-containing polymer powder content being 0.5–19.5 mass%, the electrode active material content being 80–99 mass%, and the conductive auxiliary agent content being 0.5–19.5 mass% relative to the total mass of the electrode mixture.

Description

Fluorine-containing polymer powder, electrode mixture, electrode, and secondary battery

[0001] This disclosure relates to fluorine-containing polymer powders, electrode mixtures, electrodes, and secondary batteries. This application claims priority to Japanese Patent Application No. 2025-055435, filed in Japan on March 28, 2025, the contents of which are incorporated herein by reference.

[0002] Lithium-ion secondary batteries and other secondary batteries are used in small, portable electrical and electronic devices such as notebook computers, mobile phones, smartphones, tablet computers, and ultrabooks due to their high voltage and energy density, low self-discharge, minimal memory effect, and the possibility of ultra-lightweight design. They are also used in automotive power supplies and large stationary power supplies.

[0003] Electrodes for non-aqueous electrolyte secondary batteries such as lithium-ion batteries are generally manufactured by coating a current collector with an electrode mixture containing electrode active material and binders. Conventionally, electrodes have been manufactured using a wet method with solvents such as N-methyl-2-pyrrolidone, but the environmental harmfulness of N-methyl-2-pyrrolidone has been suggested. On the other hand, in recent years, a dry method has been investigated in which the electrode mixture is stretched and formed into a sheet to create an electrode mixture sheet, which is then attached to a current collector to manufacture the electrode.

[0004] Patent Document 1 discloses a method for producing an electrode mixture by using a fluorine-containing polymer powder as an electrode binder, and kneading the electrode binder together with an electrode active material and a conductive additive in an extruder.

[0005] Patent No. 7303470

[0006] It has been found that there are challenges in achieving uniformity of the mixed state in the mixing process of an electrode mixture containing a fluorine-containing polymer powder and an electrode active material, as described in Patent Document 1, and also in thinning the sheet obtained using the electrode mixture. When the uniformity of the mixed state decreases, the internal resistance of the battery increases, and the capacity retention rate of the secondary battery decreases. When it is difficult to thin the sheet, the manufacturing efficiency of the secondary battery decreases.

[0007] The present disclosure aims to provide a fluorine-containing polymer powder used to prepare an electrode mixture, which is excellent in the uniformity of the resulting electrode mixture and in the thinning of the sheet obtained using the electrode mixture; an electrode mixture containing the fluorine-containing polymer powder; an electrode containing the electrode mixture; and a secondary battery containing the electrode.

[0008] The Disclosers, after diligent study, have found that the above problems can be solved by the following configurations: [1] A fluorine-containing polymer powder containing a fluorine-containing polymer for use as a binder for secondary battery electrodes, wherein the fluorine-containing polymer has units based on tetrafluoroethylene and the compressive modulus calculated from the following formula 1 is 0.10 to 1.20 MPa. Compressive modulus = (compressive stress at 50% deformation - compressive stress at 10% deformation) / 0.4 Formula 1 [2] The fluorine-containing polymer powder according to [1], wherein the volume-based median diameter D50 of the fluorine-containing polymer powder is 280 to 1000 μm. [3] An electrode mixture comprising the fluorine-containing polymer powder according to [1] or [2] and an electrode active material. [4] The electrode mixture according to [3], further comprising a conductive additive, wherein the content of the fluorine-containing polymer powder is 0.5 to 19.5% by mass relative to the total mass of the electrode mixture, the content of the electrode active material is 80 to 99% by mass, and the content of the conductive additive is 0.5 to 19.5% by mass. [5] An electrode comprising a current collector and an electrode layer comprising the electrode mixture according to [3] or [4] disposed on the current collector. [6] A secondary battery comprising the electrode according to [5].

[0009] According to this disclosure, it is possible to provide a fluorine-containing polymer powder used for preparing an electrode mixture, which is excellent in the uniformity of the resulting electrode mixture and in the thinning of the sheet obtained using the electrode mixture, an electrode mixture containing the fluorine-containing polymer powder, an electrode containing the electrode mixture, and a secondary battery containing the electrode.

[0010] This is a schematic diagram showing the compression section of a device for measuring the compressive modulus of fluorine-containing polymer powders in accordance with JIS Z8844:2019.

[0011] The meanings of terms used herein are as follows: A numerical range expressed using "~" means a range that includes the numbers written before and after "~" as the lower and upper limits. In numerical ranges described stepwise in this specification, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Also, in numerical ranges described in this specification, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples. In this specification, each component may be made using one substance alone or two or more substances in combination. Here, when two or more substances are used in combination for each component, the content for that component refers to the total content of the substances used in combination, unless otherwise specified. "Unit" is a general term for an atomic group derived from one monomer molecule that is directly formed by the polymerization of monomers, and an atomic group obtained by chemically transforming a part of the above atomic group. "Monomer-based unit" will also be simply called "monomer unit" below. The content (mass %) of each monomer unit relative to the total units contained in a fluorine-containing polymer is determined by analyzing the fluorine-containing polymer using solid-state nuclear magnetic resonance (NMR) spectroscopy and infrared absorption spectroscopy (IR). However, the content of each monomer unit calculated from the amount of each monomer added is approximately in agreement with the actual content of each monomer unit. "Fibrillation" is a phenomenon in which small fibers (fibrils) are subdivided due to shearing of fibers caused by friction, etc.

[0012] [Fluorine-containing polymer powder] The fluorine-containing polymer powder of this disclosure is a fluorine-containing polymer powder having a compressive modulus of 0.10 to 1.20 MPa, which can be calculated from the following formula 1. Compressive modulus = (Compressive stress at 50% deformation - Compressive stress at 10% deformation) / 0.4 Formula 1

[0013] The compressive stress at 50% deformation is preferably 0.080 to 0.550 MPa, more preferably 0.100 to 0.500 MPa, and even more preferably 0.150 to 0.450 MPa. If the compressive stress at 50% deformation is above the lower limit of the above range, it is possible to suppress particle collapse and excessive fibrillation when mixing the fluorine-containing polymer powder with the electrode active material, etc. If it is below the upper limit of the above range, sufficient fibrillation of the fluorine-containing polymer powder can proceed in the calender roll, promoting the thinning of the sheet. The compressive stress at 10% deformation is preferably 0.010 to 0.040 MPa, more preferably 0.015 to 0.035 MPa, and even more preferably 0.020 to 0.030 MPa. If the compressive stress at 10% deformation is above the lower limit of the above range, it is possible to suppress particle collapse and excessive fibrillation when mixing the fluorine-containing polymer powder with the electrode active material, etc. If the value is below the upper limit of the above range, the fibrillation of the fluorine-containing polymer powder in the calender roll will proceed sufficiently, promoting the thinning of the sheet.

[0014] The compressive modulus is 0.10 to 1.20 MPa, preferably 0.20 to 1.10 MPa, and more preferably 0.30 to 1.00 MPa. If the compressive modulus is above the lower limit of the above range, it is possible to suppress the breakdown of particles and excessive fibrillation when mixing the fluorine-containing polymer powder with the electrode active material, etc., thereby improving the uniformity of the mixing. In addition, it is possible to suppress the formation of streaks (hereinafter also referred to as "white streaks") that occur when the electrode mixture sheet ruptures. If it is below the upper limit of the above range, the fibrillation of the fluorine-containing polymer powder proceeds sufficiently, and the thinning of the sheet can be promoted.

[0015] (Method for measuring the compressive modulus of fluorine-containing polymer powder) Figure 1 is a schematic diagram showing the compression section of a device for measuring the compressive modulus of fluorine-containing polymer powder in accordance with JIS Z8844:2019. The compression section of the device comprises a deformation and load sensor 1, a flat indenter 2, and a measurement stage 3. Specifically, the measurement method involves passing the fluorine-containing polymer powder through a sieve with a mesh size of 4000 μm. Then, particles 4 with a particle diameter L of 300 to 700 μm are placed one by one on the measurement stage 3 and compressed by the flat indenter 2 at a measurement compression speed of 19 μm / second and at room temperature (25°C). The compression stress when the particle 4 is deformed by 10% from the original state (hereinafter also referred to as "compressive stress at 10% deformation") and the compression stress when the particle 4 is deformed by 50% from the original state (hereinafter also referred to as "compressive stress at 50% deformation") are measured by the deformation and load sensor 1 attached to the flat indenter 2. The compressive modulus of a total of 10 particles is calculated according to Equation 1 below. The average value is taken from the 8 points excluding the maximum and minimum values, and this average value is used as the compressive modulus. Compressive modulus = (Compressive stress at 50% deformation - Compressive stress at 10% deformation) / 0.4 Equation 1

[0016] The above measurements may be performed using known measuring devices, with the fine particle crushing force measuring device (NS-A series, manufactured by NanoSeeds Co., Ltd.) and the microcompression tester (MCT-510, manufactured by Shimadzu Corporation) being preferred, and the fine particle crushing force measuring device (NS-A series, manufactured by NanoSeeds Co., Ltd.) being more preferred.

[0017] The standard specific gravity (SSG) of the fluorinated polymer powder is preferably 2.120 to 2.190, more preferably 2.125 to 2.185, and even more preferably 2.130 to 2.180. A particularly preferred value is 2.130 to 2.160. SSG is used as a measure of the relative average molecular weight of the fluorinated polymers constituting the fluorinated polymer powder. A lower SSG value suggests that the fluorinated polymers constituting the powder are not regularly arranged between molecules. Generally, the higher the average molecular weight of the fluorinated polymer, the less likely it is that the fluorinated polymers will be regularly arranged between molecules. Therefore, a lower SSG value means that the average molecular weight of the fluorinated polymers constituting the fluorinated polymer powder is high. Furthermore, if a large amount of units other than tetrafluoroethylene-based units are introduced into the fluorinated polymer, the resulting fluorinated polymer structure becomes more diverse, making regular arrangement less likely. This tends to increase the amount of amorphous structures, lower the density, and decrease the SSG value. The SSG is measured in accordance with ASTM D4895-10. Specifically, 12.0 g of the sample (fluorine-containing polymer powder) is weighed and molded into a cylindrical mold with an inner diameter of 28.6 mm at 34.5 MPa for 2 minutes. This is placed in a 290°C oven and heated at 120°C / hour, held at 380°C for 30 minutes, then cooled at 60°C / hour and held at 294°C for 24 minutes. After being held in a 23°C desiccator for 12 hours, the specific gravity of the molded sample and water at 23°C is measured and this is defined as the SSG. If the SSG is below the upper limit of this range, the average molecular weight is sufficiently large, which tends to improve the repeated durability during charge and discharge when used as an electrode mixture sheet.

[0018] The moisture content of the fluorine-containing polymer powder is preferably 0.040% by mass or less, more preferably 0.020% by mass or less, even more preferably 0.010% by mass or less, particularly preferably 0.005% by mass or less, and most preferably 0.002% by mass or less, relative to the total mass of the fluorine-containing polymer powder. The above moisture content is measured by the following method: The mass of the fluorine-containing polymer powder is measured before and after heating at 150°C for 2 hours, and the moisture content is calculated according to the following formula: Three samples are taken, the calculation is performed for each, and the average value is taken and the average value is adopted. Moisture content (by mass) = 100 × [(Mass of fluorine-containing polymer powder before heating (g)) - (Mass of fluorine-containing polymer powder after heating (g))] / (Mass of fluorine-containing polymer powder before heating (g))

[0019] The bulk density of the fluorine-containing polymer powder is preferably 350 to 600 g / L, and more preferably 400 to 550 g / L. The bulk density is measured in accordance with the method for measuring apparent density specified in JIS K6892:1995.

[0020] The angle of repose of the fluorine-containing polymer powder is preferably 32 to 44°, and more preferably 33 to 40°. If the angle of repose is within the above range, the progress of fibrous formation of the fluorine-containing polymer powder during mixing with electrode active materials, etc., can be suppressed while reducing the average particle size of the fluorine-containing polymer powder. The angle of repose of the fluorine-containing polymer powder can be measured, for example, by known measurement methods. Examples include the fixed funnel method, the inclined plate method, and the rotating cylinder method, but the fixed funnel method is more preferred. In the specific measurement method of the fixed funnel method, the fluorine-containing polymer powder to be measured is dropped from a funnel of a certain height onto a horizontal measurement table, and the base angle is calculated from the diameter and height of the resulting conical deposit, and this base angle can be taken as the angle of repose. For example, it can be measured based on JIS-R9301-2-2:1999 (corresponding international standard: ISO 920:1976).

[0021] The pore volume of fluorine-containing polymer powders is 0.2 to 15.0 cm³. ３ Preferably, the amount is 0.5 to 10.0 cm / g. ３ A value of / g is more preferable. If the pore volume is within the above range, the miscibility between the electrode active material and the conductive additive is promoted.

[0022] The average pore size of the fluorine-containing polymer powder is preferably 0.05 to 2.0 μm, and more preferably 0.1 to 1.5 μm.

[0023] The pore volume and average pore diameter of fluorine-containing polymer powder can be measured by the mercury intrusion method using a known analytical instrument (e.g., AutoPore IV 9520, Micromeritics). Specifically, the fluorine-containing polymer powder is placed in the measuring cell of the measuring instrument, and mercury is introduced into the measuring cell. Next, the mercury introduced into the measuring cell is pressurized, and the volume of mercury pushed into the pores present in the fluorine-containing polymer powder is measured during pressurization. In this process, as the pressure applied to the mercury increases, the mercury is sequentially pushed from the larger pores to the smaller pores. Therefore, the relationship between the pore diameter of the pores formed in the fluorine-containing polymer powder and the cumulative pore volume can be determined from the relationship between the pressure applied to the mercury and the volume of mercury pushed into the pores. As pressure is further increased, the pressurized mercury penetrates sequentially from the larger pores to the smaller pores of the sample. From the pressure and the amount of mercury injected at that time, the pore diameter and volume of the pores in the fluorine-containing polymer powder can be calculated. By dividing the total pore diameter by the total number of pores, the average pore diameter can be calculated.

[0024] In aqueous dispersions, the average primary particle size (PPS) of the fluorine-containing polymer is preferably 500 nm or less, more preferably 450 nm or less, and even more preferably 400 nm or less. Below the above upper limit improves binding strength and electrode flexibility. The lower limit is preferably 100 nm or more, more preferably 180 nm or more, and even more preferably 200 nm or more. The range is preferably 100 to 500 nm, more preferably 180 to 450 nm, and even more preferably 200 to 400 nm. PPS is the volume-based median diameter measured by a known laser diffraction / scattering particle size distribution analyzer. A HORIBA LA-920 or similar can be used.

[0025] The volume-based median diameter D50 of the fluorine-containing polymer powder is preferably 280 μm or more, more preferably 300 μm or more, and even more preferably 320 μm or more. The upper limit is preferably 1000 μm or less, and more preferably 800 μm or less. The range is preferably 280 to 1000 μm, more preferably 300 to 1000 μm, and even more preferably 320 to 800 μm.

[0026] The median diameter D50 is measured using a known laser diffraction / scattering particle size distribution analyzer. When using the HORIBA LA-920 as the particle size distribution analyzer, 5 mL of fluorine-containing polymer powder is placed in a dry flow cell and measured in transmittance mode.

[0027] Fluorine-containing polymer powder is used as a binder for secondary batteries. For example, fluorine-containing polymer powder is used in electrode mixtures for forming components or layers that constitute a secondary battery. It is more preferable to use it in electrode mixtures obtained by mixing fluorine-containing polymer powder with electrode active material, etc. Examples of components or layers that constitute a secondary battery include the electrode layer in the electrode described later. Furthermore, the secondary battery is not particularly limited as long as it is a known secondary battery. Preferred embodiments of the secondary battery are as described later.

[0028] The following details the various components that fluorine-containing polymer powders may contain.

[0029] ≪Fluorine-containing polymer≫ The fluorine-containing polymer powder contains a fluorine-containing polymer. The fluorine-containing polymer of this embodiment is clearly distinguished from an elastomer. An elastomer is an elastic polymer with no melting point that exhibits a storage modulus G' of 80 kPa or more at 100°C and 50 cpm. The melting point can be determined as the temperature corresponding to the maximum value of the melting peak measured by differential scanning calorimetry (DSC). The storage modulus G' is a value measured under conditions of 100°C and 50 cpm in accordance with ASTM D6204. The fluorine-containing polymer includes either or both of the fluorine-containing polymer 1 and fluorine-containing polymer 2 described below.

[0030] <Fluorine-containing polymer 1> Fluorine-containing polymer 1 contains units based on tetrafluoroethylene (hereinafter referred to as "TFE units"). Alternatively, fluorine-containing polymer 1 may consist only of TFE units.

[0031] (TFE units) The content of TFE units relative to the total units of the fluorine-containing polymer 1 is 99% by mass or more, preferably 99.5% by mass or more, and more preferably 99.9% by mass or more. The content of TFE units relative to the total units of the fluorine-containing polymer 1 is preferably 99 mol% or more, more preferably 99.5 mol% or more, and even more preferably 99.9 mol% or more.

[0032] (Units based on other monomers) The fluorine-containing polymer 1 may contain units based on monomers other than TFE units. Examples of other monomers include perfluoroolefins such as hexafluoropropylene (HFP); hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride (VdF); perhaloolefins such as chlorotrifluoroethylene; perfluorovinyl ethers such as perfluoro(alkyl vinyl ether) (PAVE); perfluoroallyl ethers; (fluoroalkyl)ethylene (FAE); and ethylene. Among these, HFP, VdF, FAE, or PAVE are preferred as other monomers, with FAE being particularly preferred. Furthermore, the other monomers may be monomers used in the method for producing the fluorine-containing polymer powder described later.

[0033] As PAVE, a monomer represented by formula (PA) is preferred. CF ２ =CF-O-Rf １ Formula (PA) In formula (PA), Rf １ Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms. １ The number of carbon atoms in the perfluoroalkyl group represented by is preferably 1 to 8, more preferably 1 to 6, even more preferably 1 to 5, and particularly preferably 1 to 3, from the viewpoint of superior polymerization reactivity. The perfluoroalkyl group may be linear or branched.

[0034] A concrete example of PAVE is CF ２ = CFOCF３ (PMVE), CF ２ =CFOCF ２ CF ３ (PEVE), CF ２ =CFOCF ２ CF ２ CF ３ (PPVE), CF ２ =CFOCF ２ CF ２ CF ２ CF ３ and CF ２ =CFO(CF ２ ) ８ F, with PMVE or PPVE being preferred.

[0035] As the FAE, a monomer represented by formula (FA) is preferred. CZ ２ =CX(CF ２ ) ｍ Y Formula (FA) In formula (FA), X, Y and Z each independently represent a hydrogen atom or a fluorine atom, and m represents an integer of 2 to 6. Specific examples of FAE include CH ２ =CH(CF ２ ) ２ F, CH ２ =CH(CF ２ ) ３ F, CH ２ =CH(CF ２ ) ４ F (PFBE), CH ２ =CF(CF ２ ) ３ H, CH ２ =CF(CF ２ ) ４ H, with PFBE or CH ２ =CH(CF ２ ) ２ F being preferred, and PFBE being more preferred.

[0036] The content of units based on other monomers (preferably units based on PFBE) is preferably 1 mol% or less, more preferably 0.5 mol% or less, and even more preferably 0.1 mol% or less, relative to the total units of the fluorine-containing polymer 1. The content of units based on other monomers is preferably 1% by mass or less, more preferably 0.5% by mass or less, and more preferably 0.1% by mass or less, relative to the total units of the fluorine-containing polymer 1. If the fluorine-containing polymer 1 contains units based on other monomers, the content of units based on other monomers (preferably units based on PFBE) is preferably 0.001% by mass or more, and more preferably 0.002% by mass or more, relative to the total units of the fluorine-containing polymer.

[0037] The content of fluorine-containing polymer 1 is preferably 90% by mass or more, more preferably 93% by mass or more, and even more preferably 96% by mass or more, based on the total mass of the fluorine-containing polymer.

[0038] The fluorine-containing polymer 1 may have a core-shell structure. A core-shell structure is a structure in which one chemical species acts as a core, and the other chemical species form a shell surrounding the core. Examples of fluorine-containing polymer 1 having a core-shell structure include a particle containing a core of fluorine-containing polymer 1 with a high average molecular weight and a shell of fluorine-containing polymer 1 with a lower average molecular weight, or containing other units.

[0039] The content of fluorine-containing polymer 1 is preferably 90 to 100% by mass, more preferably 99 to 100% by mass, and even more preferably 99.9 to 100% by mass, based on the total mass of the fluorine-containing polymer powder.

[0040] <Fluorine-containing polymer 2> Fluorine-containing polymer 2 contains TFE units.

[0041] (TFE units) The content of TFE units relative to the total units of the fluorine-containing polymer 2 is less than 99% by mass, preferably 30% by mass or more and less than 99% by mass, and more preferably 40% by mass or more and less than 99% by mass. The content of TFE units relative to the total units of the fluorine-containing polymer 2 is less than 99 mol%, preferably 20 mol% or more and less than 99 mol%, and more preferably 30 mol% or more and less than 99 mol%.

[0042] Fluorine-containing polymer 2 may contain units based on monomers other than the TFE units described in fluorine-containing polymer 1.

[0043] <Other Impurities> The fluorine-containing polymer powder may contain other impurities. Other impurities are not particularly limited, but include water, water-soluble organic solvents (described later), emulsifiers, polymerization initiators, nucleating agents, chain transfer agents, pH adjusters, stabilizing aids, dispersion stabilizers, radical scavengers, polymerization initiator decomposition agents, and dicarboxylic acids. The amount of other impurities is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, and even more preferably 0.01% by mass or less, based on the total mass of the fluorine-containing polymer powder.

[0044] [Method for producing fluorine-containing polymer powder] A preferred method for producing fluorine-containing polymer powder includes step A of obtaining an aqueous dispersion containing a fluorine-containing polymer, step B of obtaining a wet fluorine-containing polymer powder from the aqueous dispersion, and step C of obtaining a fluorine-containing polymer powder from the wet fluorine-containing polymer powder.

[0045] <Step A> Step A is a step to obtain an aqueous dispersion containing a fluorine-containing polymer.

[0046] The process of preparing the above aqueous dispersion includes polymerizing monomers that constitute the fluorine-containing polymer in an aqueous medium. The type and amount of monomers used can be appropriately selected according to the desired composition of the fluorine-containing polymer. Examples of polymerization methods include known polymerization methods.

[0047] Step A is preferably a step in which a first monomer containing TFE is polymerized in the presence of an aqueous medium to obtain an aqueous dispersion containing a fluorine-containing polymer.

[0048] (Aqueous medium) Specific examples of aqueous mediums include water and mixed solvents of water and water-soluble organic solvents. Specific examples of water-soluble organic solvents include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol. In the case of a mixture of water and a water-soluble organic solvent, the concentration of the water-soluble organic solvent relative to the total mass of the mixture is preferably 10% by mass or less. It is preferable that the aqueous medium be water only.

[0049] (First Monomer) The first monomer contains TFE. The first monomer may consist of TFE alone. The first monomer may also contain other monomers other than TFE as described above. The TFE content is preferably 99 mol% or more of the total number of moles of the first monomer. It may also be 100 mol%. In the case of the second fluorine-containing polymer, it may be less than 99 mol%.

[0050] Examples of polymerization methods for the first monomer include emulsion polymerization, solution polymerization, and suspension polymerization. Emulsion polymerization is a method of polymerization in which a monomer that is poorly soluble in water is emulsion-dispersed in water under stirring. Solution polymerization is a method in which the polymerization reaction is carried out in a solvent. Suspension polymerization is a polymerization method in which the monomer and solvent are stirred and suspended. This can be carried out by heating the monomer in the presence of an aqueous medium. The aqueous medium may or may not contain an emulsifier.

[0051] Examples of emulsifiers include one or more fluorine-containing emulsifiers selected from the group consisting of fluorine-containing carboxylic acids and salts thereof, having 4 to 7 carbon atoms and 1 to 4 etheric oxygen atoms in the main chain, as described in Example C ２ F ５ OC ２ F ４ OCF ２ COONH ４ (Ammonium perfluoro-3,6-dioxaoctanoate) is preferred. The amount of emulsifier is preferably 1,500 to 20,000 ppm by mass relative to the yield of the fluorine-containing polymer. The emulsifier may be used alone or in combination of two or more types.

[0052] (Polymerization Initiator) A polymerization initiator may be used to promote polymerization. Known polymerization initiators can be used. Examples of polymerization initiators include oil-soluble radical polymerization initiators and water-soluble radical polymerization initiators. A single polymerization initiator may be used, or two or more may be used in combination. The polymerization initiator may be supplied in its entirety to the polymerization system before the polymerization reaction starts, or it may be added to the polymerization system continuously or intermittently.

[0053] Examples of oil-soluble radical polymerization initiators include dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and disec-butyl peroxydicarbonate; peroxyesters such as t-butyl peroxyisobutyrate and t-butyl peroxypivalate; dialkyl peroxides such as di-t-butyl peroxide; di(ω-hydro-dodecafluoroheptanoyl) peroxide, di(ω-hydro-tetradecafluoroheptanoyl) peroxide, di(ω-hydro-hexadecafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleryl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide, di(perfluorononanoyl) peroxide, di(ω-chloro-hexafluoro Examples include di[perfluoro(or fluorochloro)acyl]peroxides such as olobutyryl peroxide, di(ω-chloro-decafluorohexanoyl) peroxide, di(ω-chloro-tetradecafluorooctanoyl) peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl-peroxide, di(dichloropentafluorobutanoyl) peroxide, di(trichlorooctafluorohexanoyl) peroxide, di(tetrachloroundafluorooctanoyl) peroxide, di(pentachlorotetradecafluorodecanoyl) peroxide, and di(undachlorodotriacontafluorodocosanoyl) peroxide.

[0054] Examples of water-soluble radical polymerization initiators include persulfates such as ammonium persulfate and potassium persulfate, water-soluble organic peroxides such as disuccinic acid peroxide, bisglutaric acid peroxide, and tert-butyl hydroperoxide, and water-soluble redox catalysts. Examples of water-soluble redox catalysts include oxidizing agents such as bromate or its salts, chloric acid or its salts, persulfate or its salts, permanganate or its salts, and hydrogen peroxide. Examples of reducing agents include sulfurous acid or its salts, bisulfite or its salts, thiosulfate or its salts, and organic acids.

[0055] As polymerization initiators, water-soluble radical polymerization initiators are preferred, a combination of a persulfate and disuccinic acid peroxide is more preferred, and ammonium persulfate alone or a combination of ammonium persulfate and disuccinic acid peroxide is even more preferred. Water-soluble redox catalysts are also preferred, a combination of the oxidizing agent and the reducing agent is more preferred, a combination of bromate or its salt and sulfurous acid or its salt (e.g., ammonium sulfite), and a combination of permanganate or its salt (e.g., potassium permanganate) and oxalic acid are even more preferred. Polymerization initiators may be used individually or in combination of two or more.

[0056] The amount of polymerization initiator used is preferably 0.01 to 5 parts by mass, more preferably 0.01 to 3 parts by mass, and even more preferably 0.01 to 2 parts by mass, per 100 parts by mass of the first monomer used.

[0057] (Other components) In step A, other components such as nucleating agents, chain transfer agents, pH adjusters, stabilizing aids, dispersion stabilizers, radical scavengers, polymerization initiator decomposition agents, and dicarboxylic acids may be used. Each component may be used alone or in combination of two or more. The above other components may be used as needed before, during, and after polymerization.

[0058] A nucleating agent may be used to promote the crystallization of monomers or polymers. Known nucleating agents can be used. Examples of nucleating agents include fluoropolyethers such as perfluoropolyether acids and nonionic surfactants. Examples of perfluoropolyether acids include those described in J. Appl. Polymer Sci. 57, 797 (1995).

[0059] A chain transfer agent may be used to adjust the average molecular weight of the fluorine-containing polymer. Known chain transfer agents can be used. Examples of chain transfer agents include compounds containing carbon tetrachloride and thiol groups. Examples of compounds containing thiol groups include 3-mercaptopropionic acid, 2-ethylhexyl-3-mercaptopropionate, and methoxybutyl-β-mercaptopropionate.

[0060] To suppress rapid changes in pH during polymerization, a pH adjusting agent may be used. Known pH adjusting agents can be used. Specific examples of pH adjusting agents include inorganic salts. Specific examples of inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate, and carbonates such as sodium bicarbonate and sodium carbonate. More preferred examples of phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate.

[0061] Stabilizing agents may be used to suppress spoilage and discoloration during polymerization. Known stabilizing agents can be used. Preferred stabilizing agents are paraffin wax, fluorinated solvents, or silicone oil, with paraffin wax being more preferred. Paraffin wax may be liquid, semi-solid, or solid at room temperature. Among these, saturated hydrocarbons with 12 or more carbon atoms are preferred. The melting point of paraffin wax is preferably 40 to 65°C, and more preferably 50 to 65°C. When using a stabilizing agent, the amount used is preferably 0.1 to 12% by mass, and more preferably 0.1 to 8% by mass, based on the mass of the aqueous medium used.

[0062] Dispersion stabilizers may be used to stabilize dispersion during polymerization. Known dispersion stabilizers can be used. Examples of dispersion stabilizers include polymeric dispersants, surfactant-type dispersants, and inorganic dispersants.

[0063] Radical scavengers may be used to suppress polymerization that generates by-products. Known radical scavengers can be used. Examples of radical scavengers include aromatic hydroxy compounds, aromatic amines, N,N-diethylhydroxylamine, quinone compounds, terpenes, thiocyanates, and cupric chloride. Examples of aromatic hydroxy compounds include unsubstituted phenols, polyhydric phenols, salicylic acid, m- or p-salicylic acid, gallic acid, and naphthol. Examples of unsubstituted phenols include o-, m- or p-nitrophenols, o-, m- or p-aminophenols, and p-nitrosophenols. Examples of polyhydric phenols include catechol, resorcinol, hydroquinone, pyrogallol, phloroglucin, and naphthresorcinol. Examples of aromatic amines include o-, m- or p-phenylenediamine and benzidine. Examples of quinone compounds include o-, m- or p-benzoquinone, 1,4-naphthoquinone, and alizarin. Examples of thiocyanates include ammonium thiocyanate (NH₃). ４ Examples include SCN, potassium thiocyanate (KSCN), and sodium thiocyanate (NaSCN).

[0064] A polymerization initiator decomposer may be used to decompose the polymerization initiator used. Known polymerization initiator decomposers can be used. Examples of polymerization initiator decomposers include sulfites, bisulfites, bromates, diimines, diimines, oxalic acid, oxalates, copper salts, and iron salts.

[0065] As the dicarboxylic acid, any known dicarboxylic acid can be used. Preferably, the dicarboxylic acid is a compound represented by the general formula: HOOC-R-COOH (wherein R represents an alkylene group having 1 to 5 carbon atoms), more preferably succinic acid, malonic acid, glutaric acid, adipic acid, or pimelic acid, and even more preferably succinic acid.

[0066] The polymerization temperature and polymerization pressure in the polymerization of the first monomer can be appropriately determined depending on the type of monomer used, the average molecular weight of the target fluorine-containing polymer, and the reaction rate. The polymerization temperature is preferably 5°C or higher, more preferably 10°C or higher, even more preferably 30°C or higher, and particularly preferably 50°C or higher. Polymerization can be promoted if the polymerization temperature is above the above temperature. The upper limit is preferably 150°C or lower, more preferably 120°C or lower, and even more preferably 100°C or lower. Reactions that produce by-products can be suppressed if the polymerization temperature is below the above temperature. The range is preferably 5 to 150°C, more preferably 10 to 120°C, even more preferably 30 to 100°C, and particularly preferably 50 to 100°C. The polymerization pressure is preferably 0.05 MPaG or higher, more preferably 0.3 MPaG or higher, and even more preferably 0.5 MPaG or higher. Polymerization can be promoted if the polymerization pressure is above the above pressure. The upper limit is preferably 5.0 MPaG or lower, and more preferably 3.0 MPaG or lower. If the polymerization pressure is below the above-mentioned level, the reaction that produces by-products can be suppressed. The range is preferably 0.05 to 5.0 MPaG, more preferably 0.3 to 3.0 MPaG, and even more preferably 0.5 to 3.0 MPaG.

[0067] The content of the fluorine-containing polymer is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, and even more preferably 10 to 30% by mass, relative to the total mass of the aqueous dispersion. The solid content concentration of the aqueous dispersion is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, and even more preferably 10 to 30% by mass. The solid content concentration of the aqueous dispersion can be measured, for example, by the following method: The solid content concentration of the aqueous dispersion is calculated by heating 2.0 g of the aqueous dispersion at 170°C for 20 minutes, weighing the mass of the residue, and then determining the solid content concentration using the following formula: "Solid content concentration (mass%) = 100 × heated residue of aqueous dispersion (g) / mass of aqueous dispersion (2.0 g)"

[0068] <Step B> Step B is a step to obtain a fluorine-containing polymer wet powder from the aqueous dispersion obtained in Step A. As a method for obtaining a fluorine-containing polymer wet powder from an aqueous dispersion, for example, known methods can be used, and it is preferable to obtain the fluorine-containing polymer wet powder by agglutination treatment from the aqueous dispersion. It is even more preferable to obtain the fluorine-containing polymer wet powder by diluting the aqueous dispersion before agglutination treatment and then performing solid-liquid separation after agglutination treatment.

[0069] Dilution of the aqueous dispersion is preferably done with pure water, and the solid content concentration relative to the aqueous dispersion is preferably 5 to 30% by mass, and more preferably 8 to 20% by mass. It is best to dilute it to a concentration within the above range.

[0070] (Agglutination Treatment) Agglutination treatments include freeze agglutination, acid agglutination, base agglutination, mechanical agglutination, and agglutination using a coagulant, with mechanical agglutination being preferred. In the case of freeze agglutination, the agglutination temperature is preferably -20 to 0°C. The agglutination time is preferably 1 hour or more, and more preferably 2 hours or more. In the case of acid agglutination, a method of adding an acid-containing solution to an aqueous dispersion is preferred. Examples of acids to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, and hydrofluoric acid, with hydrochloric acid or nitric acid being preferred. The concentration of the acid relative to the total mass of the acid-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. In the case of base agglutination, a method of adding a base-containing solution to an aqueous dispersion is preferred. Examples of bases to be added include sodium hydroxide, potassium hydroxide, and ammonium carbonate, with sodium hydroxide being preferred. The concentration of the base relative to the total mass of the base-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. In the case of aggregation using a coagulant, known coagulants can be used. Known coagulants include aluminum salts, calcium salts, and magnesium salts. Specifically, aluminum sulfate, with the general formula M'Al(SO) ４ ) ２ 12H ２Examples include alum, calcium nitrate, and magnesium sulfate represented by O [wherein M' is a monovalent cation other than lithium], with alum being preferred, and potassium alum being more preferred, where M is potassium.

[0071] - Mechanical Agglomeration Treatment - Mechanical agglomeration may be performed using known stirring devices, such as motor stirring and magnetic stirring, with motor stirring being preferred. The stirring device is preferably equipped with stirring blades. The number of blades is preferably 2 to 10, and more preferably 2 to 8. Examples of stirring blades include paddle-type stirring blades, inclined paddle-type stirring blades, turbine-type stirring blades, receding stirring blades, and anchor-type stirring blades, with inclined paddle-type stirring blades being preferred. The stirring rotation speed is preferably 10 to 3000 rpm, more preferably 50 to 2000 rpm, and even more preferably 100 to 1500 rpm. If the stirring rotation speed is above the lower limit of the above range, the compressive modulus of the fluorine-containing polymer powder obtained by the heat treatment described later is likely to be above the lower limit of the above range. If the stirring rotation speed is below the upper limit of the above range, the compressive modulus is likely to be below the upper limit of the above range.

[0072] The mechanical coagulation treatment temperature is preferably 5 to 50°C, and more preferably 10 to 40°C. The mechanical coagulation treatment time is preferably 0.1 to 2 hours, and more preferably 0.1 to 1 hour.

[0073] The solid-liquid separation method is not particularly limited as long as it can separate the separation liquid from the fluorine-containing polymer wet powder, for example, a centrifuge.

[0074] <Step C> Step C is a step in which fluorine-containing polymer powder is obtained from the fluorine-containing polymer wet powder obtained in Step B. As a method for obtaining fluorine-containing polymer powder from fluorine-containing polymer wet powder, for example, known methods can be used, and it is preferable to obtain fluorine-containing polymer powder by drying the fluorine-containing polymer wet powder and then heat-treating it.

[0075] The drying process can be carried out using an electric furnace or a steam furnace. For example, it can be carried out using an electric furnace such as a parallel flow box electric furnace, a ventilated box electric furnace, a ventilated conveyor electric furnace, a band electric furnace, a radiant conveyor electric furnace, a fluidized bed electric furnace, a vacuum electric furnace, agitated electric furnace, an airflow electric furnace, and a hot air circulation electric furnace, or a steam furnace corresponding to the above (an apparatus in which "electric furnace" in the apparatus name of each electric furnace is read as "steam furnace"). A parallel flow box electric furnace, a ventilated box electric furnace, a ventilated conveyor electric furnace, a band electric furnace, a fluidized bed electric furnace, a hot air circulation electric furnace, or a steam furnace corresponding to the above (an apparatus in which "electric furnace" in the apparatus name of each electric furnace is read as "steam furnace") is preferred in that it can remove moisture and unreacted monomers more efficiently.

[0076] The drying temperature is preferably 100°C or higher, more preferably 150°C or higher, and even more preferably 170°C or higher. The upper limit is less than 280°C, preferably 260°C or lower, and more preferably 240°C or lower. The range is preferably 100°C or higher and less than 280°C, more preferably 150 to 260°C, and even more preferably 170 to 240°C. The drying time is preferably 1 hour or more, and preferably 3 hours or more. The upper limit is preferably 100 hours or less, more preferably 50 hours or less, and even more preferably 30 hours or less. The range is preferably 1 to 100 hours, more preferably 3 to 50 hours, and even more preferably 3 to 30 hours.

[0077] A preferred heat treatment method involves arranging the dried fluorine-containing polymer powder in a metal container so that it has a uniform thickness, placing the entire metal container into a preheated oven, and performing heat treatment in air to produce the fluorine-containing polymer powder.

[0078] The heat treatment temperature is 280°C or higher, preferably 280 to 315°C, more preferably 285 to 310°C, and even more preferably 290 to 305°C. If the temperature is above the lower limit of the above range, the compressive modulus can be improved. If the heat treatment temperature is above the lower limit of the above range, the compressive modulus can be improved. If the heat treatment temperature is below the upper limit of the above range, it is possible to prevent the compressive modulus from becoming excessive.

[0079] The heat treatment time is preferably 2 to 48 hours, more preferably 3 to 36 hours, and even more preferably 3 to 24 hours. If the heat treatment time is above the lower limit of the above range, the compressive modulus can be improved. If the heat treatment time is below the upper limit of the above range, it is possible to prevent the compressive modulus from becoming excessive.

[0080] Since the heat treatment is performed at 280°C or higher, and the drying treatment described above is performed at below 280°C, the heat treatment and drying treatment can be distinguished by the treatment temperature.

[0081] [Variations of the Method for Producing Fluorine-Containing Polymer Powder] The first and second embodiments of the method for producing fluorine-containing polymer powder will be described below as variations of the method for producing fluorine-containing polymer powder.

[0082] <First Embodiment> The first embodiment of the method for producing fluorine-containing polymer powder is to perform steps D and E instead of step A above. After step E, steps B and C above are performed. In the first embodiment, "aqueous dispersion" in step B is read as "aqueous emulsion". Step D: A step of polymerizing non-fluorine monomers in an aqueous medium to obtain a solution 1 containing a polymer (hereinafter also referred to as "specific polymer C") that contains units based on non-fluorine monomers. Step E: A step of polymerizing TFE in solution 1 without substantially adding a surfactant to solution 1 to obtain an aqueous emulsion containing a fluorine-containing polymer.

[0083] (Step D) Step D is a step in which a non-fluorinated monomer is polymerized in an aqueous medium to obtain a solution 1 containing a specific polymer C. Below, the materials used in Step D will be described in detail first, and then the procedure of Step D will be described in detail.

[0084] -Non-fluorinated monomers- Non-fluorinated monomers are monomers that do not contain fluorine atoms. Non-fluorinated monomers usually have polymerizable groups, and the number of polymerizable groups is preferably 1 to 3, and more preferably 1. As polymerizable groups, ethylenically unsaturated groups are preferred. More specifically, examples include acryloyl groups, methacryloyl groups, vinyl ether groups, vinyl ester groups, vinyl groups, and allyl groups, with acryloyl groups, methacryloyl groups, vinyl ester groups, or vinyl ether groups being preferred.

[0085] As a non-fluorinated monomer, the monomer represented by formula (NF) is preferred. Formula (NF) CH ２ =CR １１ -L １ -R １２ R １１ L represents a hydrogen atom or an alkyl group. The alkyl group preferably has 1 to 3 carbon atoms, more preferably 1. The alkyl group may be linear or cyclic. If the alkyl group is cyclic, it corresponds to a cycloalkyl group. If it is linear, it may be a straight chain or a branched chain. １ The symbol represents a single bond, -C(=O)-O-*, -O-C(=O)-*, or -O-. * is R １２ It represents the connection position with L. １ If is -C(=O)-O-*, then equation (1) is CH ２ =CR １１ -C(=O)-OR １２ Represents R １２ L represents a hydrogen atom, alkyl group, alkenyl group, or nitrile group. １ If it is a single bond, R １２ is a nitrile group. The number of carbon atoms in the alkyl group is preferably 1 to 10, more preferably 1 to 6, and even more preferably 1 to 4. The number of carbon atoms in the alkenyl group is preferably 2 to 10, more preferably 2 to 6, and even more preferably 2 to 4. The alkyl group may be linear or cyclic. If the alkyl group is cyclic, it corresponds to a cycloalkyl group. Also, if it is linear, it may be linear or branched. The alkenyl group may be linear or cyclic. Also, if it is linear, it may be linear or branched.

[0086] The monomer represented by formula (NF) is more preferably selected from the group consisting of the monomer represented by formula (NF-1), the monomer represented by formula (NF-2), the monomer represented by formula (NF-3), and the monomer represented by formula (NF-4). Formula (NF-1) CH ２ =CR １１ - (= O) - O - R １３ Formula (NF-2) CH ２ =CR １１-O-(=O)-R １４ Formula (NF-3) CH ２ =CR １１ -O-R １５ Formula (NF-4) CH ２ =CR １１ -R １６ R １１ The definition is as stated above. R １３ R represents a hydrogen atom, an alkyl group, or an alkenyl group, preferably an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms. The alkyl group may be linear or cyclic. Furthermore, if linear, it may be linear or branched. １４ R represents an alkyl group, preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group. It may also be linear or cyclic. Furthermore, if linear, it may be linear or branched. １５ R represents an alkyl group, preferably a linear alkyl group or a cyclic alkyl group. １６ This represents a nitrile group.

[0087] Examples of non-fluorinated monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, vinyl methacrylate, vinyl acetate, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, ethyl vinyl ether, and cyclohexyl vinyl ether. Non-fluorinated monomers may be used individually or in combination of two or more. Preferably, the non-fluorinated monomer is the monomer represented by formula (NF-1) or the monomer represented by formula (NF-2), R １３A monomer represented by formula (NF-1), in which the alkyl group is more preferred. Since the monomer represented by formula (NF-1) and the monomer represented by formula (NF-2) have ester groups and carboxyl groups, which are water-affinity groups, the monomer and its polymer are water-affinity. Therefore, especially at low concentrations, the monomer and its polymer are considered to be stably dispersed in an aqueous medium without the need for a surfactant.

[0088] -Specific Polymer C- Specific polymer C is a polymer that contains units based on non-fluorinated monomers. Specific polymer C usually contains only units based on non-fluorinated monomers, but may also contain units based on fluorinated monomers. In other words, in addition to non-fluorinated monomers, fluorinated monomers may also be used in step C. Fluorinated monomers are monomers having fluorine atoms, such as TFE. The content of units based on non-fluorinated monomers in specific polymer C is preferably 90% by mass or more, and more preferably 95% by mass or more, relative to the total units of specific polymer C. It may also be 100% by mass.

[0089] -Aqueous media- Examples of aqueous media include the aqueous media used in step A described above.

[0090] -Polymerization Initiator- A polymerization initiator may be used in step D. In other words, a polymerization initiator may be used during the polymerization of the non-fluorinated monomer. An example of a polymerization initiator is the water-soluble radical polymerization initiator used in step A described above. -Procedure for Step E- In step E, the polymerization of the non-fluorinated monomer is carried out in an aqueous medium. Specifically, it is preferable to mix the non-fluorinated monomer with the aqueous medium and carry out the polymerization of the non-fluorinated monomer in the resulting mixture. As mentioned above, a fluorinated monomer may be used in combination as needed.

[0091] The amount of non-fluorinated monomer used is preferably 200 ppm by mass or less, more preferably 1 to 150 ppm by mass, even more preferably 5 to 100 ppm by mass, and particularly preferably 5 to 50 ppm by mass, relative to the amount of TFE supplied (amount of TFE used) in step F described later. As for the method of supplying the non-fluorinated monomer, it is preferable to supply the entire amount to the polymerization system at the beginning of the polymerization reaction.

[0092] The content of the non-fluorinated monomer in the dispersion obtained by mixing the non-fluorinated monomer with an aqueous medium is preferably 0.000015 to 0.0030% by mass, and more preferably 0.000075 to 0.0023% by mass, based on the total mass of the dispersion. Since the non-fluorinated monomer usually polymerizes entirely to form a specific polymer C, the concentration of the specific polymer C in the obtained solution 1 is within the above numerical range. The above concentrations of the non-fluorinated monomer and the specific polymer C are the concentrations when the obtained solution 1 is used in step E without diluting it with an aqueous medium. When the obtained solution 1 is diluted with an aqueous medium to obtain the above specific polymer C concentration, and the diluted solution is used in step E, a high-concentration solution corresponding to the dilution ratio is produced in step D. The dilution ratio is not particularly limited, but 10 times or less is preferred.

[0093] The amount of polymerization initiator used is preferably 0.2 to 1000% by mass, and more preferably 0.2 to 500% by mass, relative to the total amount of non-fluorinated monomers.

[0094] The amount of polymerization initiator used is preferably 0.1 to 1000 mol%, and more preferably 0.1 to 300 mol%, relative to the total amount of non-fluorinated monomers.

[0095] The polymerization temperature for non-fluorinated monomers is preferably 10 to 95°C, more preferably 50 to 90°C. The polymerization time is preferably 5 to 400 minutes, more preferably 5 to 300 minutes, and even more preferably 5 to 200 minutes. The pressure conditions during polymerization are preferably reduced pressure or atmospheric pressure. Among these, 0 to 2.0 MPa is preferred, more preferably 0 to 1.0 MPa, and even more preferably 0 to 0.5 MPa. Polymerization may also be carried out in a TFE atmosphere. Generally, polymerization of non-fluorinated monomers in an aqueous medium proceeds preferentially over TFE polymerization.

[0096] The above step D yields solution 1 containing specific polymer C. Specific polymer C may be dissolved in solution 1 or dispersed in particulate matter in an aqueous medium. During the polymerization of TFE in step E, described later, although specific polymer C is not an emulsifier, it is presumed that the balance of interfacial tension between the aqueous medium and the fluorine-containing polymer causes specific polymer C to be present at the boundary between them, contributing to the stabilization of the dispersion of the fluorine-containing polymer in the aqueous medium. The average particle size of the specific polymer C particles is preferably 0.1 to 100 nm, and more preferably 0.1 to 50 nm. The average particle size can be measured using a laser diffraction / scattering particle size distribution analyzer (manufactured by Horiba, Ltd., product name "LA-920"). Note that the average particle size is the median diameter in the volume-based particle size distribution.

[0097] Furthermore, the solution 1 obtained in step D may contain unreacted non-fluorinated monomers. In addition, the polymerization atmosphere in step D may be carried out under a TFE-containing atmosphere, taking step E into consideration. In such a case, it is thought that a portion of the specific polymer C in step E may become a polymer containing TFE units. Alternatively, from another perspective, the fluorinated polymer particles obtained in step E are not limited to particles consisting of a physical mixture of the specific polymer C and the fluorinated polymer, but can also be considered to be particles containing a TFE copolymer having units based on non-fluorinated monomers.

[0098] (Step E) Step E is a step in which TFE is polymerized in solution 1 obtained in Step E without substantially adding a surfactant to solution 1, thereby obtaining an aqueous emulsion containing a fluorine-containing polymer. Below, the materials used in Step E will be described in detail first, and then the procedure of Step E will be described in detail.

[0099] -TFE- In process E, TFE is used.

[0100] —Other Monomers— In Step E, other monomers other than TFE may be further used within a range that does not impair the effects of the present disclosure. Examples of other monomers include a monomer having a polar group (hereinafter sometimes referred to as "specific monomer D"). Since the polar group in the specific monomer D interacts with an aqueous medium, it is presumed that the polar group is located between TFE and the aqueous medium during polymerization of TFE and exhibits a surfactant-like function. As a result, polymerization of TFE proceeds favorably and the occurrence of chain transfer is also suppressed.

[0101] Examples of the polar group contained in the specific monomer D include sulfonic acid groups, sulfonic acid salt groups, carboxylic acid groups, carboxylic acid salt groups, phosphonic acid groups, and phosphonic acid salt groups. Among these, a group represented by formula (A) or a group represented by formula (B) is preferable, and a group represented by formula (A) is more preferable, from the viewpoint of further suppressing the formation of fluorine-based oligomers. Formula (A) -SO ３ M Formula (B) -COOM In formula (A) and formula (B), M represents a hydrogen atom, NH ４ , or an alkali metal atom. Examples of the alkali metal atom include a lithium atom, a sodium atom, and a potassium atom.

[0102] The specific monomer D usually has a polymerizable group, and the number of polymerizable groups is preferably 1 to 3, more preferably 1. An ethylenically unsaturated group is preferable as the polymerizable group. More specifically, examples include acryloyl groups, methacryloyl groups, vinyl ether groups, vinyl ester groups, vinyl groups, and allyl groups, with acryloyl groups, methacryloyl groups, vinyl ester groups, or vinyl ether groups being preferable.

[0103] As the specific monomer D, a monomer represented by formula (3) is preferable from the viewpoint of further suppressing the formation of fluorine-based oligomers. Formula (3) CR ３１ R ３２ =CR ３３ -L ３ -R ３４ In formula (3), R ３１ and R ３２ each independently represent a hydrogen atom or a fluorine atom.

[0104] R３３ represents a hydrogen atom, a fluorine atom, or an alkyl group which may be substituted with a fluorine atom. Among these, a hydrogen atom or a fluorine atom is preferred from the viewpoint of better copolymerizability with TFE. The term "alkyl group which may be substituted with a fluorine atom" means an alkyl group in which at least one hydrogen atom in the alkyl group may be substituted with a fluorine atom. The alkyl group which may be substituted with a fluorine atom preferably has 1 to 3 carbon atoms, and more preferably has 1 carbon atom.

[0105] L ３ represents a single bond or a divalent linking group. Among these, a single bond is preferred from the viewpoint of better copolymerizability with TFE. Examples of the divalent linking group include divalent hydrocarbon groups (which may be divalent saturated hydrocarbon groups, divalent aromatic hydrocarbon groups, alkenylene groups, or alkynylene groups. The divalent saturated hydrocarbon group may be linear, branched or cyclic, and examples thereof include alkylene groups, which preferably have 1 to 20 carbon atoms. The divalent aromatic hydrocarbon group preferably has 5 to 20 carbon atoms, and examples thereof include phenylene groups. In addition, it may be an alkenylene group having 2 to 20 carbon atoms or an alkynylene group having 2 to 20 carbon atoms.), divalent heterocyclic groups, -O-, -S-, -SO ２ -, -C(=O)-, -Si(R ａ ) ２ -, -N(R ｂ )-, and groups formed by combining two or more of these. Here, R ａ represents an alkyl group (preferably having 1 to 10 carbon atoms) or a phenyl group. R ｂ represents a hydrogen atom or an alkyl group (preferably having 1 to 10 carbon atoms). Examples of the group formed by combining two or more of these groups include -OC(=O)-, -C(=O)N(R ｂ )-, alkylene group-O-alkylene group, alkylene group-OC(=O)-alkylene group, and alkylene group-Si(R ａ ) ２ -phenylene group-Si(R ａ ) ２Examples include the above. The above divalent hydrocarbon group may have substituents. Examples of substituents include halogen atoms (e.g., fluorine atoms, chlorine atoms). In other words, the hydrogen atoms in the above divalent hydrocarbon group may be substituted with halogen atoms.

[0106] R ３４ This represents the group represented by formula (A) or the group represented by formula (B) above.

[0107] The monomer represented by formula (3) is preferably selected from the group consisting of the monomer represented by formula (3-1), the monomer represented by formula (3-2), the monomer represented by formula (3-3), the monomer represented by formula (3-4), the monomer represented by formula (3-5), and the monomer represented by formula (3-6), with the monomer represented by formula (3-1) being more preferred. Formula (3-1) CR ３１ R ３２ =CR ３３ -R ３４ Formula (3-2) CR ３１ R ３２ =CR ３３ - (CF ２ ) ｍ１ -R ３４ Formula (3-3) CR ３１ R ３２ =CR ３３ - (CF ２ C (CF ３ ) F) ｍ２ -R ３４ Formula (3-4) CR ３１ R ３２ =CR ３３ -O-(CFR) ３５ ) ｍ３ -R ３４ Formula (3-5) CR ３１ R ３２ =CR ３３ -O-(CF ２ CFR ３５ O) ｍ４ -CF ２ CF ２ -R ３４ Formula (3-6) CR ３１ R ３２ =CR ３３ -CF ２ -O-(CF(CF３ ) CF ２ O) ｍ５ -CF (CF ３ )-R ３４

[0108] In formulas (3-1) to (3-6), R ３１ ~R ３４ The definition is as described above. In equation (3-2), m1 represents an integer from 1 to 10. In equation (3-3), m2 represents an integer from 1 to 5. In equation (3-4), m3 represents an integer from 1 to 10. R ３５ is a fluorine atom or CF ３ This represents... In equation (3-5), m4 represents an integer from 1 to 10. ３５ The definition is as described above. In equation (3-6), m5 represents 0 or an integer from 1 to 10.

[0109] A specific example of specific monomer D is ammonium vinylsulfonate. Specific monomer D may be used alone or in combination of two or more types.

[0110] -Polymerization Initiator- A polymerization initiator may be used in step E. In other words, a polymerization initiator may be used during the polymerization of TFE. Examples of polymerization initiators that can be used include those described in step D. A mixture of persulfate and disuccinic acid peroxide is preferred as the polymerization initiator, and a mixture of ammonium persulfate and disuccinic acid peroxide is more preferred. The amount of polymerization initiator used is preferably 0.10% by mass or more, more preferably 0.10 to 1.5% by mass, and even more preferably 0.20 to 1.0% by mass, based on the total amount of TFE supplied to the polymerization system.

[0111] - Stabilizing Agents - Stabilizing agents may be used in step E. Preferred stabilizing agents are paraffin wax, fluorinated solvents, or silicone oil, with paraffin wax being more preferred. Paraffin wax may be liquid, semi-solid, or solid at room temperature. Among these, saturated hydrocarbons with 12 or more carbon atoms are preferred. The melting point of paraffin wax is preferably 40 to 65°C, and more preferably 50 to 65°C. Stabilizing agents may be used individually or in combination of two or more.

[0112] -Other- In addition, in step E, monomers other than TFE and specific monomer D may be used as long as they do not impair the effects of this disclosure. However, in terms of superior various properties of the fluorine-containing polymer, the amount of TFE used is preferably 99.5% by mass or more, and more preferably 99.8% by mass or more, relative to the total amount of monomers used in step E.

[0113] -Procedure for Step E- During Step E, no surfactant is substantially added to Solution 1. In other words, in Step E, TFE polymerization is carried out in Solution 1 without substantially adding any new surfactant to Solution 1. A surfactant is a compound having a hydrophilic group (e.g., a polar group) and a hydrophobic group (e.g., a hydrocarbon group). The definition of a polar group is the same as the definition of a polar group contained in specific monomer D. Examples of surfactants include known surfactants, nonionic surfactants and ionic surfactants, and more specifically, hydrocarbon-containing surfactants and fluorinated surfactants. The definition of a hydrocarbon-containing surfactant is as described later. In Step E, it is preferable not to substantially add at least one selected from the group consisting of hydrocarbon-containing surfactants and fluorinated surfactants to Solution 1. "Substantially not added" means that no surfactant is added, or if added, the amount of surfactant added is 200 ppm by mass or less relative to the total mass of Solution 1. The lower limit is not particularly limited, but 0 ppm by mass is preferred. In other words, it is preferable not to add a surfactant to Solution 1 in Step E.

[0114] TFE is added to the polymerization system (i.e., the polymerization reaction vessel) by conventional methods. For example, TFE is added to the polymerization system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. When a polymerization initiator is used, the polymerization initiator may be added to the polymerization system all at once or in stages.

[0115] When using specific monomer D, the amount of specific monomer D used relative to the total amount of TFE is preferably 0.150% by mass or less. In other words, the amount of specific monomer D added relative to the total amount of TFE is preferably 0.150% by mass or less. From the viewpoint of the stability of the aqueous emulsion during polymerization, the amount of specific monomer D used relative to the total amount of TFE is preferably 0.100% by mass or less, and more preferably 0.090% by mass or less. Furthermore, from the viewpoint of improving the average molecular weight, the amount of specific monomer D used relative to the total amount of TFE is preferably 0.005% by mass or more, and more preferably 0.010% by mass or more. The range is preferably 0.005 to 0.100% by mass, and more preferably 0.010 to 0.090% by mass. When using two or more types of specific monomer D, the total amount of specific monomer D used should be within the above range.

[0116] When using specific monomer D, the amount of specific monomer D used relative to the total amount of TFE is preferably 0.150 mol% or less. In other words, the amount of specific monomer D added relative to the total amount of TFE is preferably 0.150 mol% or less. From the viewpoint of the stability of the aqueous emulsion during polymerization, the amount of specific monomer D used relative to the total amount of TFE is preferably 0.100 mol% or less, and more preferably 0.090 mol% or less. Furthermore, from the viewpoint of improving the average molecular weight, the amount of specific monomer D used relative to the total amount of TFE is preferably 0.001 mol% or more, and more preferably 0.005 mol% or more. The range is preferably 0.001 to 0.100 mol%, and more preferably 0.005 to 0.090 mol%. When using two or more types of specific monomer D, the total amount of specific monomer D used should be within the above range.

[0117] The polymerization temperature is preferably 10 to 95°C, and more preferably 15 to 90°C. The polymerization pressure is preferably 0.5 to 4.0 MPa, and more preferably 0.6 to 3.5 MPa. The polymerization time is preferably 50 to 520 minutes, more preferably 50 to 450 minutes, and even more preferably 50 to 300 minutes.

[0118] Furthermore, steps D and E may be carried out continuously in the same polymerization reaction vessel. In addition, in the manufacturing method of this disclosure, it is sufficient that the specific polymer C is formed in step D, and step E may be carried out before the non-fluorinated monomer is completely consumed in step D.

[0119] The above procedure yields an aqueous emulsion in which the fluorine-containing polymer is dispersed in particulate form (an aqueous emulsion containing a fluorine-containing polymer). The concentration of the fluorine-containing polymer in the aqueous emulsion is preferably 10 to 45% by mass, more preferably 10 to 30% by mass, and even more preferably 10 to 25% by mass, based on the total volume of the aqueous emulsion. Within this range, the fluorine-containing polymer in the aqueous emulsion can be more easily coagulated, and the turbidity of the coagulated liquid can be suppressed. The PPS of the fluorine-containing polymer in the aqueous dispersion is preferably 100 to 500 nm, and more preferably 150 to 350 nm. The PPS of the fluorine-containing polymer is the volume-based particle size D50 (median diameter) measured by a laser scattering particle size distribution analyzer.

[0120] <Second Embodiment> The second embodiment of the method for producing fluorine-containing polymer powder is to perform step F instead of step A above. After step F, steps B and C above are performed. Step F: A step of polymerizing a monomer containing tetrafluoroethylene (hereinafter also referred to as "specific monomer F") in an aqueous dispersion containing a first fluorine-containing polymer and an aqueous medium to obtain an aqueous dispersion containing a fluorine-containing polymer different from the first fluorine-containing polymer (hereinafter also referred to as "second fluorine-containing polymer").

[0121] (Step F) Step F is a step in which a monomer containing TFE is polymerized in an aqueous dispersion containing a first fluorine-containing polymer and an aqueous medium to obtain an aqueous dispersion containing a second fluorine-containing polymer different from the first fluorine-containing polymer.

[0122] -Aqueous dispersion- In the second embodiment, an aqueous dispersion containing the first fluorine-containing polymer and an aqueous medium is used.

[0123] -First Fluorine-Containing Polymer- The first fluorine-containing polymer is presumed to solubilize a specific monomer F by adsorbing and incorporating it in its hydrophobic region during polymerization. Adding a polymerization initiator then causes the specific monomer F to polymerize within the particles of the first fluorine-containing polymer. Furthermore, the first fluorine-containing polymer is presumed to contribute to dispersion stabilization in aqueous media.

[0124] The Tg of the first fluorine-containing polymer is preferably 10°C or lower, more preferably 5°C or lower, even more preferably 3°C or lower, and particularly preferably 0°C or lower, from the viewpoint of efficiently adsorbing the specific monomer F. From the viewpoint of thermal stability after molding, the Tg of the first fluorine-containing polymer is preferably -50°C or higher, more preferably -45°C or higher, and even more preferably -40°C or higher. The range of the Tg of the first fluorine-containing polymer is preferably -50 to 10°C, more preferably -45 to 5°C, even more preferably -40 to 3°C, and particularly preferably -40 to 0°C. The Tg of the first fluorine-containing polymer is measured by differential scanning calorimetry (DSC). As a method for bringing the Tg of the first fluorine-containing polymer within the above range, for example, a method of adjusting the type and amount of monomer used in the production of the first fluorine-containing polymer can be mentioned.

[0125] The first fluorine-containing polymer preferably contains TFE units and PAVE-based units (hereinafter also referred to as "PAVE units"), as this makes it easier to adjust the Tg to the above range.

[0126] PAVE is preferred as the monomer represented by the above formula (PA) because it exhibits excellent polymerization reactivity when producing the first fluorine-containing polymer and because it allows for more efficient production of the fluorine-containing polymer. The monomer represented by formula (PA) is synonymous with the monomer represented by formula (PA) in the above-mentioned fluorine-containing polymer, and the preferred embodiment is also the same.

[0127] When the first fluorine-containing polymer contains TFE units and PAVE units, the amount of PAVE units relative to the total of TFE units in the first fluorine-containing polymer is preferably 20 to 60 mol%, more preferably 25 to 60 mol%, and even more preferably 30 to 55 mol%, in terms of ease of adjusting Tg to the above range and enabling more efficient production of the fluorine-containing polymer.

[0128] The first fluorine-containing polymer may contain units based on monomers other than TFE and PAVE, but it is preferable that it substantially contains units based on other monomers in order to produce the fluorine-containing polymer more efficiently. Substantially containing units based on other monomers means that the content of units based on other monomers is 0.01 mol% or less relative to the total units of the first fluorine-containing polymer, and 0 mol% is more preferable. If units based on other monomers are included, hexafluoropropylene is preferred as the other monomer.

[0129] Before initiating the polymerization of the monomer used for the polymerization of the first fluorine-containing polymer, the content of the first fluorine-containing polymer is 0.01 to 4.0% by mass relative to the total mass of the aqueous medium in the aqueous dispersion. From the viewpoint of producing the second fluorine-containing polymer more efficiently, 0.01 to 0.6% by mass is preferred, and 0.01 to 0.5% by mass is more preferred.

[0130] In this specification, "before starting the polymerization of the monomer used in the polymerization of a fluorine-containing polymer" means immediately before the start of polymerization. Here, "the start of polymerization" refers to the point in time when the monomer and polymerization initiator are brought into the reactor after the reactor temperature has been raised to above the polymerization temperature, and the point in time when the reactor temperature is raised to above the polymerization temperature after the monomer and polymerization initiator have been brought into the reactor.

[0131] Before initiating the polymerization of the monomers used in the polymerization of the fluorine-containing polymer, the concentration of sulfate ions is preferably 10 ppm by mass or less, and more preferably 5 ppm by mass or less, relative to the total mass of the aqueous medium in the aqueous dispersion, in order to suppress discoloration of the fluorine-containing polymer. It may also be 0 ppm by mass. One example of a method for achieving the above-mentioned sulfate ion concentration is to remove sulfate ions using an anion exchange resin during the production of the first fluorine-containing polymer. Here, sulfate ions originate, for example, from the polymerization initiator (particularly ammonium persulfate) used during the production of the first fluorine-containing polymer, and may be present in the aqueous dispersion containing the first fluorine-containing polymer. It is presumed that the discoloration of the fluorine-containing polymer is suppressed as a result of suppressing the formation of low heat-resistant end groups in the fluorine-containing polymer by having a sulfate ion content of 10 ppm by mass or less (particularly 5 ppm by mass or less).

[0132] Before initiating the polymerization of the monomer used in the polymerization of the first fluorine-containing polymer, the concentration of sulfate ions is preferably 10 ppm by mass or less, and more preferably 5 ppm by mass or less, relative to the total mass of the aqueous medium in the aqueous dispersion, in order to suppress the discoloration of the first fluorine-containing polymer. It may also be 0 ppm by mass. One example of a method for achieving the above-mentioned concentration of ammonium ions is to remove ammonium ions using a cation exchange resin during the production of the first fluorine-containing polymer. Here, the ammonium ions originate, for example, from the initiator (particularly ammonium persulfate) used during the production of the first fluorine-containing polymer, and may be present in the aqueous dispersion containing the first fluorine-containing polymer. It is presumed that the production efficiency of the fluorine-containing polymer is improved as a result of the ammonium ion content being 20 ppm by mass or less, which reduces the ionic strength in the aqueous medium.

[0133] The first fluorine-containing polymer is preferably dispersed in an aqueous medium in the form of particles. In this case, the average particle size of the first fluorine-containing polymer is preferably 1 to 150 nm, more preferably 10 to 120 nm, and even more preferably 50 to 120 nm, from the viewpoint of being able to produce the fluorine-containing polymer more efficiently. The average particle size of the first fluorine-containing polymer is the particle size at the point where the cumulative volume is 50% on the cumulative curve, determined by measuring the particle size distribution by laser diffraction / scattering, with the total volume of the particle collection set to 100%, and the median diameter D50.

[0134] A preferred method for producing the first fluorine-containing polymer is to polymerize monomers (preferably a monomer mixture containing TFE and PAVE) in an aqueous medium in the presence of a polymerization initiator. This yields the first fluorine-containing polymer dispersed in particulate matter in the aqueous medium. The aqueous medium in which the particles of the first fluorine-containing polymer thus obtained are dispersed may be used as the aqueous dispersion as is, or another aqueous medium may be added and used as the aqueous dispersion. Alternatively, the first fluorine-containing polymer may be dispersed in another aqueous medium by solvent substitution and used as the aqueous dispersion.

[0135] As polymerization initiators used in the production of the first fluorine-containing polymer, water-soluble polymerization initiators are preferred, persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate, organic polymerization initiators such as disuccinic acid peroxide and azobisisobutylamidine dihydrochloride are more preferred, persulfates are even more preferred, and ammonium persulfate is particularly preferred.

[0136] Examples of aqueous media used in the production of the first fluorine-containing polymer include the aqueous media used in step A described above. The aqueous media contained in the aqueous dispersion may be the polymerization solvent used in the production of the first fluorine-containing polymer. Before starting the polymerization of the monomers used for the polymerization of the fluorine-containing polymer, the content of the aqueous media is preferably 60 to 99.9% by mass, more preferably 96 to 99.9% by mass, and even more preferably 98 to 99.9% by mass, relative to the total mass of the aqueous dispersion.

[0137] The method for producing the first fluorine-containing polymer preferably includes a heating step in which an aqueous medium in which the first fluorine-containing polymer is dispersed is heated. This deactivates the polymerization initiator present in the system, making the polymerization of the fluorine-containing polymer less susceptible to the influence of the polymerization initiator used in the production of the first fluorine-containing polymer. As a result, a fluorine-containing polymer with a high average molecular weight is more easily obtained. The heating temperature in the heating step is preferably 70 to 100°C, more preferably 80 to 98°C, and even more preferably 85 to 95°C, from the viewpoint of further promoting the deactivation of the polymerization initiator in the aqueous medium.

[0138] -Other Components- The aqueous dispersion used in this manufacturing method may contain other components besides the first fluorine-containing polymer and the aqueous medium. Specific examples of other components that the aqueous dispersion may contain include chain transfer agents, emulsifiers other than fluorine-based emulsifiers, pH adjusters, and waxes.

[0139] Specific examples of chain transfer agents include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane.

[0140] Specific examples of emulsifiers other than fluorine-based emulsifiers include sodium lauryl sulfate, Perex SS-H manufactured by Kao Chemical Corporation, and Newcol 1305-SN manufactured by Nippon Emulsifier Co., Ltd.

[0141] Examples of pH adjusting agents include the pH adjusting agent used in step A described above.

[0142] Specific examples of waxes include Paraffin Wax-155 and Paraffin Wax-150 (both manufactured by Nippon Seiro).

[0143] If the aqueous dispersion contains a chain transfer agent, the content of the chain transfer agent is preferably 0.1 to 5 parts by mass per 100 parts by mass of the aqueous medium. Furthermore, the amount of chain transfer agent used is preferably 0.1 to 20 parts by mass, more preferably 0.1 to 15 parts by mass, and even more preferably 0.1 to 10 parts by mass, per 100 parts by mass of the amount of the specific monomer F described later. If the aqueous dispersion contains an emulsifier other than a fluorine-based emulsifier, the content of the emulsifier other than a fluorine-based emulsifier is preferably 0.01 to 5 parts by mass per 100 parts by mass of the aqueous medium. If the aqueous dispersion contains a pH adjuster, the content of the pH adjuster is preferably 0.01 to 3.0 parts by mass per 100 parts by mass of the aqueous medium. If the aqueous dispersion contains wax, the content of wax is preferably 1 to 10 parts by mass per 100 parts by mass of the aqueous medium.

[0144] Before initiating the polymerization of the monomer used for the polymerization of the second fluorine-containing polymer, the concentration of the fluorine-based emulsifier is 100 ppm by mass or less relative to the total mass of the first fluorine-containing polymer in the aqueous dispersion. From the viewpoint of achieving superior effects in this disclosure, it is preferably 50 ppm by mass or less, more preferably 25 ppm by mass, and even more preferably 5 ppm by mass or less. It may also be 0 ppm by mass. A fluorine-based emulsifier refers to an emulsifier in which the hydrophobic portion of the hydrophilic and hydrophobic portions of the emulsifier contains fluorine atoms. Specific examples of fluorine-based emulsifiers include fluorine-containing alkanates and fluorine-containing ether carboxylic acid compounds. An example of a method for adjusting the concentration of the fluorine-based emulsifier within the above range is a method of producing an aqueous dispersion without using a fluorine-based emulsifier.

[0145] Before initiating the polymerization of the monomer used in the polymerization of the second fluorine-containing polymer, the concentration of fluoride ions is preferably 100 ppm by mass or less, and more preferably 50 ppm by mass or less, relative to the total mass of the aqueous dispersion, from the viewpoint of polymerization stability. It may also be 0 ppm by mass. One example of a method for achieving the above-mentioned concentration of fluoride ions is to remove sulfate ions using an anion exchange resin during the production of the first fluorine-containing polymer. Here, fluoride ions may be produced by the reaction between the polymerization initiator (e.g., ammonium persulfate) and the monomer used in the production of the first fluorine-containing polymer, and may be present in the aqueous dispersion.

[0146] -Specific Monomer F- Specific monomer F contains TFE. The amount of TFE used is preferably 97 to 100% by mass, more preferably 98 to 100% by mass, and even more preferably 99 to 100% by mass, relative to the amount of specific monomer F used.

[0147] The specified monomer F may contain fluorine-containing monomers other than TFE, but may not substantially contain fluorine-containing monomers other than TFE. "Substantially not containing fluorine-containing monomers other than TFE" means that the amount of fluorine-containing monomers other than TFE used is 0.0001% by mass or less relative to the amount of specified monomer F used, and may even be 0% by mass. Examples of fluorine-containing monomers other than TFE include chlorotrifluoroethylene (hereinafter also referred to as "CTFE"), VdF, fluoroalkylethylene, PAVE, and hexafluoropropylene. Two or more fluorine-containing monomers other than TFE may be used in combination.

[0148] The specified monomer F may contain other monomers besides the fluorine-containing monomer, but it is preferable that it does not contain other monomers. Substantially free of other monomers means that the amount of other monomers used is 0.0001% by mass or less relative to the amount of the specified monomer F, and 0% by mass is more preferable. Specific examples of other monomers include ethylene, propylene, vinyl chloride, and vinylidene chloride. Two or more other monomers may be used in combination.

[0149] The amount of specific monomer F used is preferably 1 to 50 parts by mass, more preferably 1 to 40 parts by mass, and even more preferably 1 to 30 parts by mass, based on 100 parts by mass of the aqueous medium contained in the aqueous dispersion.

[0150] -Polymerization Initiator- In the second embodiment, it is preferable that the specific monomer F is polymerized in the presence of a polymerization initiator. An example of a polymerization initiator is the water-soluble radical polymerization initiator used in step A described above.

[0151] The amount of polymerization initiator used is preferably 1 to 1000 ppm by mass, more preferably 5 to 750 ppm by mass, and even more preferably 10 to 500 ppm by mass, based on 100% by mass of the amount of specific monomer F used. Examples of polymerization initiators include the water-soluble radical polymerization initiator used in step A described above.

[0152] -Other Components- Other components (hereinafter also referred to as "other components") may be used during the polymerization of the specific monomer F. A specific example of other components is a reducing agent. The amount of other components used is preferably 1 to 2000 ppm by mass per 100% by mass of the amount of specific monomer F used.

[0153] -Procedure for Step F- In this manufacturing method, the specific monomer F is polymerized in the aqueous dispersion to produce a second fluorine-containing polymer.

[0154] The fluorine-containing polymer obtained by this manufacturing method is as described above. The first fluorine-containing polymer and the second fluorine-containing polymer may be copolymerized.

[0155] The specific monomer F is introduced into the reaction system (i.e., the polymerization reaction vessel) by a conventional method. For example, the specific monomer F may be introduced into the reaction system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, the specific monomer F may be dissolved in an aqueous medium, and the resulting solution may be introduced into the reaction system continuously or intermittently. When a polymerization initiator is used, the polymerization initiator may be added to the reaction system all at once or in portions.

[0156] The polymerization temperature is preferably 10 to 95°C, and more preferably 15 to 90°C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, and more preferably 0.6 to 3.5 MPaG. The polymerization time, in the case of batch processing, is preferably 90 to 1000 minutes, and more preferably 90 to 700 minutes.

[0157] Polymerization of the specific monomer F is preferably carried out in the absence of a substantial emulsifier. Examples of emulsifiers include known emulsifiers and general surfactants. The absence of a substantial emulsifier means an environment in which the emulsifier content is 0.03 ppm by mass or less relative to the total mass of the aqueous medium contained in the aqueous dispersion, preferably 0.02 ppm by mass or less, and more preferably 0 ppm by mass.

[0158] As described above, it is presumed that during the polymerization of the specific monomer F, the specific monomer F polymerizes within the particles of the first fluorine-containing polymer. Therefore, it is thought that this manufacturing method produces particles containing both the first fluorine-containing polymer and the second fluorine-containing polymer. In other words, it is presumed that this manufacturing method yields the fluorine-containing polymer in the form of particles containing both the first fluorine-containing polymer and the second fluorine-containing polymer. In this case, this manufacturing method yields an aqueous dispersion in which particles containing the first fluorine-containing polymer and the second fluorine-containing polymer are dispersed in the aqueous medium.

[0159] [Electrode mixture] The electrode mixture of this disclosure comprises the above-mentioned fluorine-containing polymer powder and an electrode active material. Furthermore, when the electrode mixture is a negative electrode mixture, it is preferable that the negative electrode mixture comprises the fluorine-containing polymer powder and the negative electrode active material. When the electrode mixture is a positive electrode mixture, it is preferable that the positive electrode mixture comprises the fluorine-containing polymer powder and the positive electrode active material.

[0160] The content of fluorine-containing polymer powder is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1.0% by mass or more, relative to the total mass of the electrode mixture. The upper limit is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 19.5% by mass or less, and particularly preferably 10% by mass or less. The range is preferably 0.1 to 50% by mass, more preferably 0.5 to 30% by mass, even more preferably 0.5 to 19.5% by mass, and particularly preferably 1.0 to 10% by mass. Within the above range, the retention of the electrode active material and the mechanical strength of the electrode mixture sheet are sufficient, battery performance such as cycle characteristics is also good, and the decrease in battery capacity or conductivity can be further suppressed. Because fluorine-containing polymer powder has excellent binding strength, even a small amount can sufficiently retain the electrode active material within the electrode mixture.

[0161] <Electrode Active Material> The electrode mixture contains an electrode active material. Examples of electrode active materials include a positive electrode active material and a negative electrode active material, which can be appropriately selected according to the desired electrode.

[0162] (Positive Electrode Active Material) When the electrode mixture is a positive electrode mixture, the positive electrode mixture contains a positive electrode active material. As the positive electrode active material, a material that electrochemically intercepts and releases lithium ions is used. Examples of such materials include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides, with lithium cobaltate, lithium nickelate, lithium manganeseate, lithium nickel-manganate, composite metal oxides, or polyanion-olivine type positive electrode materials being preferred. From the viewpoint of having a high average discharge voltage and being cost-advantageous, the positive electrode active material may also be a lithium-containing transition metal oxide. Examples of composite metal oxides include nickel-manganese-cobalt oxide. As for nickel-manganese-cobalt oxide, LiNi ｘ Mn ｙ Co ｚ O ２ A compound represented by the formula (x + y + z ≤ 1) is preferred, and LiNi ０．６ Mn ０．２ Co ０．２ O ２ (Hereafter also referred to as "NMC622") or LiNi ０．３３Co ０．３３ Mn ０．３３ O ２ This is preferable.

[0163] A surface deposit material with a different composition from the positive electrode active material may be attached to the surface of the positive electrode active material. Examples of surface deposit materials include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0164] The positive electrode active material particles can take the form of lumps, polyhedrons, spheres, ellipsoids, plates, needles, and columns. Furthermore, the positive electrode active material may consist of either primary or secondary particles.

[0165] The volume-based median diameter D50 of the positive electrode active material particles (primary or secondary particles) is preferably 0.3 μm or more, more preferably 0.5 μm or more, and even more preferably 1.0 μm or more. The upper limit is preferably 30 μm or less, and more preferably 25 μm or less. The range is preferably 0.3 to 30 μm, more preferably 0.5 to 25 μm, and even more preferably 1.0 to 25 μm. When within the above range, high tap density products are more easily obtained, or the diffusion time of lithium within the particles becomes appropriate, which can further suppress the deterioration of battery performance. In terms of improving the packing performance during positive electrode manufacturing, two or more positive electrode active materials with different median diameters D50 may be mixed as the positive electrode active material.

[0166] The volume-based median diameter D50 of the positive electrode active material is measured using a known laser diffraction / scattering particle size distribution analyzer. When using the HORIBA LA-920 as the particle size distribution analyzer, a 0.1% by mass aqueous solution of sodium hexametaphosphate is used as the dispersion medium during measurement, and the measurement is performed after ultrasonic dispersion for 5 minutes with the measurement refractive index set to 1.24.

[0167] The BET specific surface area of ​​the positive electrode active material is 0.1 m². ２ Preferably 0.3 m ２A value of 1 / g or higher is more preferable. The upper limit is 50mg. ２ Preferably less than / g, and 30m ２ Less than / g is preferable. The range is 0.1 to 50m ２ / g is preferred, and 0.3 to 30 m ２ / g is more preferable. The above BET specific surface area is defined as the value measured by the nitrogen adsorption BET single-point method using the gas flow method, after pre-drying the sample at 150°C for 30 minutes under nitrogen flow using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.), and then using a nitrogen-helium mixed gas that has been precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3.

[0168] The positive electrode active material may be used alone or in combination of two or more types. When using two or more positive electrode active materials, a suitable combination is LiCoO ２ And, LiNi ０．３３ Co ０．３３ Mn ０．３３ O ２ Combinations with ternary systems such as LiCoO ２ And LiMN ２ O ４ Or a combination in which part of this Mn is replaced with other transition metals, etc.; LiFePO ４ And LiCoO ２ Alternatively, this could be a combination in which a portion of the Co is replaced with other transition metals, etc.

[0169] The content of the positive electrode active material is preferably 50 to 99.5% by mass, and more preferably 80 to 99% by mass, relative to the total mass of the electrode mixture, in order to achieve a high battery capacity.

[0170] (Negative electrode active material) The negative electrode active material is not particularly limited as long as it can reversibly perform intercalation (intercalation) of lithium ions, or doping and dedoping of lithium ions with counteranions. Specifically, examples include lithium metal, carbon-based materials such as graphite, hard carbon, and soft carbon, metals that can form alloys with lithium such as aluminum, silicon, and tin, amorphous oxides such as silicon oxide and tin oxide, and lithium titanate.

[0171] As a negative electrode active material, a silicon-containing negative electrode active material is preferred because it allows for the production of high-capacity batteries. Preferred silicon-containing negative electrode active materials include silicon particles, particles having a structure in which silicon fine particles are dispersed in a silicon-based compound, silicon oxide particles represented by the general formula SiOx (0.5 ≤ x ≤ 1.6), or mixtures thereof. Silicon oxide is a general term for amorphous silicon oxides, and silicon oxide is represented, for example, by the general formula SiOx (0.5 ≤ x ≤ 1.6). x is preferably 0.8 ≤ x < 1.6, and more preferably 0.8 ≤ x < 1.3. This silicon oxide can be obtained, for example, by heating a mixture of silicon dioxide and metallic silicon to produce silicon monoxide gas, which is then cooled and precipitated.

[0172] The silicon-containing negative electrode active material may be coated with carbon. Coating with carbon imparts conductivity, which can improve battery characteristics. Methods for imparting conductivity include, for example, mixing with conductive particles such as graphite, coating the surface of the silicon-containing negative electrode active material with a carbon film, and combining both methods. However, coating with a carbon film is preferred, and chemical vapor deposition (CVD) is more preferred.

[0173] The particle shapes of the negative electrode active material can include lumpy, polyhedral, spherical, ellipsoidal, plate-like, needle-like, and columnar shapes. Furthermore, the negative electrode active material may consist of either primary or secondary particles.

[0174] The average particle diameter of the negative electrode active material particles (primary or secondary particles) is preferably 0.1 to 50 μm, more preferably 0.2 to 30 μm, and even more preferably 0.5 to 20 μm. The average particle diameter is the mass-average particle diameter (median diameter) measured by the particle size distribution method using laser diffraction.

[0175] The BET specific surface area of ​​the negative electrode active material is 0.5 to 100 m². ２ / g is preferred, and 1 to 20 m ２ / g is more preferable. The BET specific surface area can be measured in the same way as the BET specific surface area of ​​the positive electrode active material described above.

[0176] The content of the negative electrode active material is preferably 50 to 99.5% by mass, and more preferably 80 to 99% by mass, relative to the total mass of the electrode mixture.

[0177] <Conductive Additives> The electrode mixture may contain conductive additives. Examples of conductive additives include metallic materials such as copper and nickel; graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; and amorphous carbon such as needle coke, carbon nanotubes, fullerenes and vapor-phase carbon fibers.

[0178] The content of the conductive additive is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, and particularly preferably 1% by mass or more, based on the total mass of the electrode mixture. The upper limit is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, even more preferably 19.5% by mass, even more preferably 15% by mass or less, and particularly preferably 10% by mass or less. The range is preferably 0.01 to 50% by mass, more preferably 0.1 to 30% by mass, even more preferably 0.5 to 20% by mass, even more preferably 0.5 to 19.5% by mass, even more preferably 1 to 15% by mass, and particularly preferably 1 to 10% by mass.

[0179] The electrode mixture comprises a fluorine-containing polymer, an electrode active material, and a conductive additive, wherein the content of the fluorine-containing polymer is preferably 0.5 to 19.5% by mass of the total mass of the electrode mixture, the content of the electrode active material is preferably 80 to 99% by mass of the total mass of the electrode mixture, and the content of the conductive additive is preferably 0.5 to 19.5% by mass of the total mass of the electrode mixture. More preferably, the content of the fluorine-containing polymer is preferably 0.5 to 10% by mass of the total mass of the electrode mixture, the content of the electrode active material is preferably 88 to 99% by mass of the total mass of the electrode mixture, and the content of the conductive additive is preferably 0.5 to 10% by mass of the total mass of the electrode mixture. It is even more preferable that the content of the fluorine-containing polymer is 0.5 to 5% by mass relative to the total mass of the electrode mixture, the content of the electrode active material is 90 to 99% by mass relative to the total mass of the electrode mixture, and the content of the conductive additive is 0.5 to 5% by mass relative to the total mass of the electrode mixture. It is particularly preferable that the content of the fluorine-containing polymer is 0.5 to 3% by mass relative to the total mass of the electrode mixture, the content of the electrode active material is 94 to 99% by mass relative to the total mass of the electrode mixture, and the content of the conductive additive is 0.5 to 3% by mass relative to the total mass of the electrode mixture.

[0180] <Thermoplastic Resin> The electrode mixture may contain a thermoplastic resin. Examples of thermoplastic resins include polyvinylidene fluoride, polypropylene, polyethylene, polystyrene, polyethylene terephthalate, and polyethylene oxide.

[0181] When a thermoplastic resin is included, the ratio of the thermoplastic resin content to the electrode active material content in the electrode mixture (thermoplastic resin content / electrode active material content) is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.10% by mass or more. The upper limit is preferably 3.0% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2.0% by mass or less. The range is preferably 0.01 to 3.0% by mass, more preferably 0.05 to 2.5% by mass, and even more preferably 0.10 to 2.0% by mass. In this embodiment, it is preferable not to include a thermoplastic resin.

[0182] <Other Components> The electrode mixture may contain other components besides those described above. Examples of other components include solid electrolytes, binders other than the fluorine-containing polymer powder of this embodiment, thickeners, and additives. Examples of solid electrolytes include sulfide solid electrolytes having an argyrodite-type crystal structure, oxide solid electrolytes, and halogenated solid electrolytes.

[0183] The electrode mixture is preferably substantially free of organic solvents. Specifically, the organic solvent content is preferably 1.0% by mass or less, more preferably 0.1% by mass or less, based on the total mass of the electrode mixture. It may also be 0% by mass.

[0184] Examples of binders other than fluorine-containing polymer powders include elastomer components such as styrene-butadiene rubber, acrylic rubber, and styrene-ethylene-butadiene-styrene; and fibrous components such as cellulose, carboxymethylcellulose, cellulose nanofibers, and aramid fibers. It is preferable to mix the fibrous components as powders, and it is even preferable if they are finely ground (microfibrillated) beforehand using various grinding methods, as this improves their mixability with the fluorine-containing polymer powder. Furthermore, adding fibrous components to the electrode mixture tends to increase the strength of the resulting sheet.

[0185] The electrode mixture is preferably in sheet form.

[0186] The electrode mixture can be suitably used as an electrode mixture for secondary batteries. It is particularly suitable for lithium-ion secondary batteries. When used in secondary batteries, the electrode mixture is usually used in sheet form.

[0187] [Method for Manufacturing Electrode Mixture] A preferred method for manufacturing the electrode mixture includes a step X1 in which a raw material composition containing a binder containing a fluorine-containing polymer powder, an electrode active material, and, if necessary, a conductive additive is pulverized and mixed. With the above method for manufacturing the electrode mixture, the electrode mixture can be obtained in a relatively short number of steps. It is also preferable that the method for manufacturing the electrode mixture further includes a step X2 in which the raw material composition pulverized and mixed in step X1 is rolled into a sheet. When step X2 is included, a sheet-like electrode mixture can be obtained.

[0188] (Step X1) Step X1 is a step of grinding and mixing a raw material composition containing a binder containing fluorine-containing polymer powder, an electrode active material, and a conductive additive as needed. As a mixing method, a method using a mixing device is preferred. Examples of mixing devices include jet mills, pin mills, blenders, twin-screw extruders, and mixers. Jet mills, mixers, or twin-screw extruders are preferred because they can achieve both crushing of the fluorine-containing polymer powder and suppression of fiber formation. Examples of jet mills include impact type, which grinds by colliding particles with each other or with a collision body (target); swirling airflow type and loop type, which grinds by mutual collision of particles in a grinding zone formed by multiple grinding nozzles arranged in a circulating airflow; fluidized bed type, which grinds by collision or friction between particles in a fluidized bed; and supersonic type. Details of impact type, swirling airflow type, loop type, and fluidized bed type jet mills are described in "Advanced Grinding Technology and Applications," edited by the Japan Powder Industry Technology Association, NGT Co., Ltd., p. 162. Examples of impact-type jet mills include pulverizers that discharge a fluid such as compressed air from a nozzle and pulverize particles by causing them to collide with each other in a high-speed turbulent airflow formed within the jet mill, and pulverizers that transport resin particles with a high-speed airflow and pulverize them by causing them to collide with an impactor.

[0189] (Process X2) Process X2 is a process of rolling the raw material composition crushed and mixed in process X1 into a sheet. The rolling method in process X2 can be a roll press, a flat plate press, or a calender roll. The rolling conditions are not particularly limited and can be appropriately selected according to the desired thickness and density of the electrode mixture. When a roll press device (HSARP-60150-2HL, manufactured by Hosen Co., Ltd.) is used as the roll press, the roll temperature during rolling is preferably 60 to 150°C, and more preferably 80 to 120°C. The roll speed during rolling is preferably 1 to 150 m / min, and more preferably 1 to 100 m / min. The ratio of the low-speed roll peripheral speed to the high-speed roll peripheral speed during rolling (hereinafter also referred to as the "roll peripheral speed ratio") is preferably 1 / 1.5 to 1 / 20, and more preferably 1 / 3 to 1 / 15. The rolling load is preferably 1 ton to 20 tons, and more preferably 2 to 10 tons. The roll gap during rolling is preferably 10 to 500 μm, and more preferably 20 to 300 μm.

[0190] -Method for evaluating mixing uniformity- Mixing uniformity can be evaluated by visual inspection of the electrode mixture obtained by step X1 in the above-described method for manufacturing the electrode mixture. It is preferable that no aggregates with a major diameter of 5 mm or more are observed in the electrode mixture by visual inspection, and it is more preferable that no aggregates with a major diameter of 2 mm or more are observed in the electrode mixture.

[0191] -Method for evaluating the appearance of the sheet- The appearance of the sheet can be evaluated by visual inspection of the electrode mixture sheet obtained by step X2 in the electrode mixture manufacturing method described above. It is preferable that there are three or fewer white streaks with a width of 1 mm and a length of 1 cm or more, and it is more preferable that none are observed.

[0192] -Method for Calculating Sheet Thickness- The sheet thickness can be calculated by randomly selecting 10 points from the electrode mixture sheet obtained by step X2 in the electrode mixture manufacturing method described above, measuring the film thickness at each point with a measuring force of 0.01 N using a Lightmatic VL-50 series (manufactured by Mitsutoyo Co., Ltd.) and a carbide spherical surface measuring probe, and taking the average value of the 10 points. The thickness of the electrode mixture sheet is preferably 300 μm or less, and more preferably 200 μm or less.

[0193] [Electrode] The electrode of this disclosure includes a current collector and an electrode layer containing an electrode mixture located on at least one surface of the current collector. The electrode layer may be located on both surfaces of the current collector. A conductive carbonaceous material may be placed between the current collector and the electrode layer as needed.

[0194] <Current Collector> The electrode includes a current collector. When the electrode is the positive electrode, the current collector may be a metallic material such as aluminum, titanium, tantalum, stainless steel, and nickel, or an alloy thereof; or a carbon material such as carbon cloth and carbon paper. A metallic material is preferred, and aluminum or an alloy thereof is more preferred. When the electrode is the negative electrode, the current collector may be a metallic material such as copper, nickel, titanium, tantalum, and stainless steel, or an alloy thereof; or a carbon material such as carbon cloth and carbon paper. A metallic material is preferred, and copper, nickel, or an alloy thereof is more preferred.

[0195] Examples of current collector shapes include metal foil, metal cylinders, metal coils, metal plates, expanded metal, punched metal, and foamed metal in the case of metal materials, and carbon plates, carbon thin films, and carbon cylinders in the case of carbon materials. Among these, metal foil is preferred as the shape of the current collector. The metal foil may be formed in a mesh shape as appropriate. The thickness of the current collector is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. The upper limit is preferably 1 mm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. Within the above range, excellent handling and strength can be obtained. The range is preferably 1 μm or more and 1 mm or less, more preferably 3 to 100 μm, and even more preferably 5 to 50 μm.

[0196] Furthermore, it is preferable that a conductive additive is applied to the surface of the current collector, as this reduces the electrical contact resistance between the current collector and the positive electrode active material layer. Examples of conductive additives include precious metals such as carbon, gold, platinum, and silver.

[0197] <Electrode Layer> The electrode includes an electrode layer. The electrode layer is placed on a current collector and contains the electrode mixture described above. The content of the electrode mixture is 30 to 99% by mass, preferably 40 to 98% by mass, and more preferably 50 to 98% by mass, based on the total mass of the electrode layer. The electrode layer may be either a positive electrode layer or a negative electrode layer, and can be appropriately selected depending on the electrode active material contained in the electrode mixture.

[0198] The density of the positive electrode layer is 3.00 g / cm³. ３ The above is preferable, and 3.10 g / cm³ ３ The above is more preferable, at 3.20 g / cm³. ３ The above is even more preferable. The upper limit is 4.50 g / cm³. ３ The following is preferable: 4.40 g / cm³ ３ The following is more preferable: 4.30 g / cm³ ３ The following is even more preferable: The range is 3.00 to 3.80 g / cm³. ３ Preferably, 3.10 to 3.75 g / cm³ ３ More preferably, 3.20 to 3.70 g / cm³ ３ This is even more preferable. The density of the negative electrode layer is 1.3 g / cm³. ３ The above is preferable, 1.4 g / cm³ ３ The above is more preferable, 1.5 g / cm³ ３ The above is even more preferable. The upper limit is 2.0 g / cm³. ３ The following is preferable: 1.9 g / cm³ ３ The following is more preferable: 1.8 g / cm³ ３ The following is even more preferable: The range is 1.30 to 2.00 g / cm³. ３ Preferably, 1.40 to 1.90 g / cm³ ３ More preferably, 1.50 to 1.80 g / cm³ ３ This is even more preferable. Within the above range, the penetration of the electrolyte near the current collector / electrode active material interface is excellent, and the charge / discharge characteristics at high current densities can be particularly excellent. Furthermore, the conductivity between the electrode active materials can also be excellent.

[0199] The thickness of the electrode layers (positive electrode layer and negative electrode layer) is preferably 10 μm or more, and more preferably 20 μm or more, in terms of high capacity and high output. The upper limit is preferably 500 μm or less, and more preferably 450 μm or less. The range is preferably 10 to 500 μm, and more preferably 20 to 450 μm.

[0200] [Secondary Battery] The secondary battery of this disclosure includes the electrodes described above. The secondary battery may be a secondary battery using an electrolyte, or it may be a solid-state secondary battery. Examples of secondary batteries include non-aqueous secondary batteries such as non-aqueous electrolyte secondary batteries, all-solid-state batteries, and fuel cells. Specifically, examples include nickel-cadmium batteries, nickel-metal hydride batteries, lithium secondary batteries, sodium-ion secondary batteries, zinc-ion secondary batteries, fluoride-ion secondary batteries, alkali metal secondary batteries, halide secondary batteries, and lithium-air secondary batteries.

[0201] A secondary battery preferably includes a positive electrode, a negative electrode, an electrolyte, and a separator. The secondary battery may have either a laminated structure in which the positive electrode, separator, and negative electrode are included in that order, or a wound structure in which the positive electrode, separator, and negative electrode are wound in a spiral shape. When the secondary battery has a laminated structure, it is preferable that the laminated structure is formed by bundling the metal core portions of each electrode layer and welding them to the terminals. When the secondary battery has a wound structure, the internal resistance can be reduced by providing multiple lead structures on the positive electrode and negative electrode, respectively, and bundling them to the terminals.

[0202] Rechargeable batteries can take various shapes, such as cylindrical, prismatic, laminated, coin-type, and large. The shapes and configurations of the positive electrode, negative electrode, and separator can be modified according to the specific shape of the rechargeable battery.

[0203] Examples of the above-mentioned separators include porous membranes such as polyethylene and polypropylene; and nonwoven fabrics such as resin nonwoven fabrics such as polypropylene and glass fiber nonwoven fabrics. The material or shape of the separator is not particularly limited as long as it is stable in the electrolyte and has excellent liquid retention properties. Among these, resin, glass fiber, or inorganic material is preferred for the separator material. The shape of the separator is preferably a porous sheet or nonwoven fabric. The thickness of the separator is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 8 μm or more. The upper limit is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. The range is preferably 1 to 50 μm, more preferably 5 to 40 μm, and even more preferably 8 to 30 μm.

[0204] A non-aqueous electrolyte is preferred as the electrolyte. Examples of non-aqueous electrolytes include those obtained by dissolving a known electrolyte salt in a known organic solvent for dissolving electrolyte salts. Examples of organic solvents for dissolving electrolyte salts include known hydrocarbon solvents such as vinylene carbonate, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; and fluorine-based solvents such as fluoroethylene carbonate, fluoroether, and fluorinated carbonate. An example of an electrolyte salt is LiClO ４ LiAsF ６ LiBF ４ LiPF ６ , LiN (SO ２ CF ３ ) ２ , and LiFSI(LiN(SO ２ F) ２ ), LiBOB(LiB(C ２ O ４ ) ２ ), LiDFOB (LiBF ２ (C ２ O ４ )), LiPF ２ (C ２ O ４ ) ２ LiPF ４(C ２ O ４ ), and LiN (SO ２ C ２ F ５ ) ２ One example is LiPF, which has good cycle characteristics. ６ LiBF ４ , LiN (SO ２ CF ３ ) ２ , LiN (SO ２ C ２ F ５ ) ２ Alternatively, a combination of these is preferable.

[0205] The solid-state secondary battery is preferably an all-solid-state secondary battery. The solid-state secondary battery is also preferably a lithium-ion battery or a sulfide-based all-solid-state secondary battery. The solid-state secondary battery preferably includes a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode.

[0206] The solid electrolyte used in the compound for solid-state secondary batteries may be either a sulfide-based solid electrolyte or an oxide-based solid electrolyte. Of these, sulfide-based solid electrolytes are preferred.

[0207] The above sulfide-based solid electrolyte is not particularly limited, 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-Li ２S-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 ４－ｘ Ge １－ｘ P ｘ S ４ (X=0.6~0.8), Li ４＋ｙ Ge １－ｙ Ga ｙ S ４ (y=0.2-0.3), LiPSCl, LiCl, Li ７－ｘ－２ｙ PS ６－ｘ－ｙ Cl ｘ Any of the following can be used: (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5), or a mixture of two or more. Furthermore, the sulfide-based solid electrolyte preferably contains lithium. A lithium-containing sulfide-based solid electrolyte is used in solid-state batteries that use lithium ions as carriers and is preferred in that it is an electrochemical device with high energy density.

[0208] The average particle size of the sulfide-based solid electrolyte can be adjusted as appropriate depending on the application and desired battery characteristics. For example, from the viewpoint of improving battery characteristics, the average particle size by volume is preferably 4 μm or less, more preferably 3 μm or less, even more preferably 2 μm or less, and particularly preferably 1 μm or less. The average particle size is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more. In other words, the average particle size is preferably 0.1 to 4 μm, more preferably 0.3 to 3 μm, even more preferably 0.5 to 2 μm, and particularly preferably 0.5 to 1 μm.

[0209] The specific surface area of ​​sulfide-based solid electrolytes, like the average particle size, can be adjusted as appropriate depending on the application and desired battery characteristics. For example, from the viewpoint of improving battery characteristics, the specific surface area can be set to 3 m². ２ Preferably 5 m ２ More preferably 10 m ２ A value of 100 m² or more is even more preferable. On the other hand, from the viewpoint of long-term storage, the specific surface area should be 100 m². ２ Preferably less than / g, and 50m ２ More preferably less than / g, and 30m ２ A value of less than or equal to / g is even more preferable. The specific surface area should be 3 to 100 m². ２ / g is preferred, and 5 to 50m ２ / g is more preferable, 10 to 30 m ２ A value of / g is even more preferable. The specific surface area can be measured by BET specific surface area measurement, for example, using the high-performance specific surface area and pore distribution analyzer ASAP-2020 manufactured by Micromeritics.

[0210] The content of the fluorine-containing polymer powder is preferably 1 to 20 parts by mass, more preferably 1 to 10 parts by mass, even more preferably 1.5 to 9 parts by mass, and particularly preferably 2 to 8 parts by mass, per 100 parts by mass of the above sulfide-based solid electrolyte.

[0211] The oxide-based solid electrolyte described above is preferably a compound that contains oxygen atoms, has ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and is also electronically insulating.

[0212] Examples of oxide-based solid electrolytes include Li ｘａ La ｙａ TiO ３ [xa=0.3~0.7, ya=0.3~0.7] (LLT), Li ｘｂ La ｙｂ Zr ｚｂ M ｂｂ ｍｂ O ｎｂ (M ｂｂ(The elements are Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, and xb satisfies 5 ≤ ​​xb ≤ 10, yb satisfies 1 ≤ yb ≤ 4, zb satisfies 1 ≤ zb ≤ 4, mb satisfies 0 ≤ mb ≤ 2, and nb satisfies 5 ≤ ​​nb ≤ 20.) Li ｘｃ B ｙｃ M ｍＬ ｚｃ O ｎｃ (M ｍＬ (The element is C, S, Al, Si, Ga, Ge, In, Sn, and xc satisfies 0 ≤ xc ≤ 5, yc satisfies 0 ≤ yc ≤ 1, zc satisfies 0 ≤ zc ≤ 1, and nc satisfies 0 ≤ nc ≤ 6.) Li ｘｄ (Al, Ga) ｙｄ (Ti, Ge) ｚｄ Si ａｄ P ｍｄ O ｎｄ (wherein 1≦xd≦3, 0≦yd≦2, 0≦zd≦2, 0≦ad≦2, 1≦md≦7, 3≦nd≦15), Li （３－２ｘｅ） M ｅｅ ｘｅ D ｅｅ O(xe represents a number between 0 and 0.1, M ｅｅ D represents a divalent metal atom. ｅｅ ) Li ｘｆ Si ｙｆ O ｚｆ (1≦xf≦5, 0<yf≦3, 1≦zf≦10), Li ｘｇ S ｙｇ O ｚｇ (1≦xg≦3, 0<yg≦2, 1≦zg≦10), Li ３ BO ３ -Li ２ SO ４ Li ２ O-B ２ O ３ -P ２ O ５ Li ２ O-SiO ２ Li ６ BaLa ２ Ta ２ O １２ Li ３ PO （４－３／２ｗ） Nｗ (where w < 1), Li has a LISICON (Lithium super ionimLonductor) type crystal structure. ３．５ Zn ０．２５ GeO ４ La having a perovskite-type crystal structure ０．５１ Li ０．３４ TiO ２．９４ La ０．５５ Li ０．３５ TiO ３ LiTi having a NASICON (Natrium super ionimLonductor) type crystal structure ２ P ３ O １２ Li １＋ｘｈ＋ｙｈ (Al, Ga) ｘｈ (Ti, Ge) ２－ｘｈ Si ｙｈ P ３－ｙｈ O １２ (wherein 0 ≤ xh ≤ 1, 0 ≤ yh ≤ 1), and Li having a garnet-type crystal structure ７ La ３ Zr ２ O １２ (LLZ) is one example. Furthermore, ceramic materials in which elemental substitutions have been made to LLZ are also known. For example, LLZ-based ceramic materials in which at least one element of Mg (magnesium) and A (A is at least one element selected from the group consisting of Ca (calcium), Sr (strontium), and Ba (barium)) has been substituted for LLZ are also mentioned. Phosphorus compounds containing Li, P, and O are also desirable. For example, lithium phosphate (Li ３ PO ４ ), LiPON and LiPOD, which are lithium phosphates in which some of the oxygen is replaced with nitrogen. １ (D １ Examples include at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc. Also, LiA １ ON (A １ (This also includes at least one selected from Si, B, Ge, Al, C, Ga, etc.) For example, Li ２ O-Al ２ O３ -SiO ２ -P ２ O ５ -TiO ２ -GeO ２ , and Li ２ O-Al ２ O ３ -SiO ２ -P ２ O ５ -TiO ２ These are some examples.

[0213] The above oxide-based solid electrolyte preferably contains lithium. Oxide-based solid electrolytes containing lithium are used in solid-state batteries that use lithium ions as carriers and are preferred in that they are electrochemical devices with high energy density.

[0214] The above oxide-based solid electrolyte is preferably an oxide having a crystalline structure. Oxides having a crystalline structure are preferred in terms of good Li ion conductivity. Examples of oxides having a crystalline structure include perovskite type (La ０．５１ Li ０．３４ TiO ２．９４ etc.), NASICON type (Li １．３ Al ０．３ Ti １．７ (PO ４ ) ３ (etc.), Garnet type (Li ７ La ３ Zr ２ O １２ Examples include (LLZ, etc.). Among these, the NASICON type is preferred.

[0215] The present disclosure will be explained in detail below with reference to examples. Examples 1 to 8 are embodiments, and Examples 9 to 13 are comparative examples. However, the present disclosure is not limited to these examples.

[0216] [Measurement and Evaluation Methods] The various measurement and evaluation methods are as follows.

[0217] <Compressive Modulus of Fluorine-Containing Polymer Powder> The compressive modulus of fluorine-containing polymer powder was measured using the NS-A series fine particle crushing force measuring device (manufactured by NanoSeeds Co., Ltd.) in accordance with the measurement method described above. The fluorine-containing polymer powder obtained in each of the examples described below was sieved through a 4000 μm mesh. Then, particles with a measurement particle diameter of 300 to 700 μm were placed one by one on the measurement stage and compressed with a flat indenter at a measurement compression speed of 19 μm / second and room temperature (25°C). The compressive stress at 10% deformation and the compressive stress at 50% deformation were measured using deformation and load sensors attached to the flat indenter. The compressive modulus of a total of 10 particles was calculated according to Equation 1 below. Of the calculated compressive moduli, the average value was taken for 8 points excluding the maximum and minimum values, and this average value was used as the compressive modulus. Compressive Modulus of Compression = (Compressive Stress at 50% Deformation - Compressive Stress at 10% Deformation) / 0.4 Equation 1

[0218] <Volume-based median diameter D50 and mean primary particle size (PPS) of fluorine-containing polymer powder> The volume-based median diameter D50 of fluorine-containing polymer powder was measured using the fluorine-containing polymer powder obtained in each example described below (fluorine-containing polymer powder used in the electrode mixture of each example), and the PPS was measured using the aqueous dispersion obtained in each example described below as the sample, with the measurement performed using a laser diffraction / scattering particle size distribution analyzer LA-920 (manufactured by Horiba, Ltd.). The median diameter D50 was measured by placing 5 mL of fluorine-containing polymer powder into a dry flow cell and performing the measurement in transmittance mode.

[0219] <Proportion of each unit in fluorine-containing polymer powder> The proportion of each unit in the fluorine-containing polymer powder obtained in each of the examples described below is: １９ The CTFE content was determined from F-NMR analysis and infrared absorption spectroscopy. Regarding the CTFE content, a thin film disc was created by press-molding a fluorine-containing polymer powder, and the infrared absorbance of the thin film disc was measured using FT-IR, resulting in 957 cm⁻¹. －１ Absorbance / 2360 cm －１ It was calculated by multiplying the ratio of absorbances by 0.58.

[0220] <Solid Content Concentration of Aqueous Dispersion> The solid content concentration of the aqueous dispersions obtained in the examples described below is calculated by heating 2.0 g of the aqueous dispersion at 170°C for 20 minutes, weighing the mass of the residue, and then using the following formula: "Solid Content Concentration (mass%) = 100 × Heating Residue of Aqueous Dispersion (g) / Mass of Aqueous Dispersion (2.0 g)"

[0221] <Mixing Uniformity> The electrode mixtures obtained in each of the examples described below were visually observed, and their mixing uniformity was evaluated according to the evaluation criteria below. A and B were considered acceptable. A: No aggregates with a long diameter of 2 mm or more were observed. B: Aggregates with a long diameter of 2 mm or more were observed, but no aggregates with a long diameter of 5 mm or more were observed. C: Aggregates with a long diameter of 5 mm or more were observed.

[0222] <Sheet Appearance Evaluation> The electrode mixture sheets obtained in each of the examples described below were visually inspected, and the aggregation state of the fluorine-containing polymer powder was judged according to the following criteria. A and B were considered acceptable. A: 0 white streaks with a width of 1 mm and a length of 1 cm or more B: 1 to 3 white streaks with a width of 1 mm and a length of 1 cm or more C: 4 or more white streaks with a width of 1 mm and a length of 1 cm or more

[0223] <Sheet Thickness Evaluation> Ten sheets were randomly selected from each electrode mixture sheet obtained in the examples described below. The film thickness at each point was measured using a Lightmatic VL-50 series (manufactured by Mitsutoyo Co., Ltd.) and a carbide spherical probe with a measuring force of 0.01 N. The thickness of each electrode mixture sheet was determined by taking the average value of the ten points. The following criteria were used for evaluation. A and B were considered acceptable. A: Less than 120 μm B: 120 μm or more and less than 130 μm C: 130 μm or more

[0224] [Example 1] <Method for producing fluorine-containing polymer powder> A 100 L stainless steel autoclave equipped with baffles and a stirrer is used to produce C ２ F ５ OC ２ F ４ OCF ２ COONH ４63 g of Ammonium perfluoro-3,6-dioxaoctanoate (hereinafter also referred to as "APFDO"), 670 g of paraffin wax, and 60 L of deionized water were charged into the autoclave. After purging the autoclave with nitrogen and reducing the pressure, it was pressurized with a TFE and heated to 70°C while stirring. Next, the pressure was increased to 1.765 MPa with the TFE, and 5.0 g of dissolved disuccinate peroxide (concentration 80% by mass, the remainder being water) was injected. After about 3 minutes, the internal pressure dropped to 1.78 MPa. Polymerization proceeded while adding TFE to maintain the autoclave internal pressure at 1.80 MPa. A total of 125 g of APFDO dissolved in warm water was added during polymerization. In addition, a total of 4 g of ammonium sulfite dissolved in water was added during polymerization. The temperature was lowered to 64°C during the polymerization process, and then raised to 80°C during the latter half of the polymerization. The reaction was terminated when the amount of TFE added reached 26 kg. After that, the TFE in the autoclave was released into the atmosphere to obtain an aqueous dispersion. The polymerization time was 183 minutes. The obtained aqueous dispersion was cooled, and the paraffin wax of the supernatant was removed to obtain aqueous dispersion A containing the fluorine-containing polymer. The solid content concentration of the obtained aqueous dispersion A was 28% by mass, and the PPS of the fluorine-containing polymer was 0.33 μm.

[0225] Next, aqueous dispersion A was diluted with pure water to a concentration of 10% by mass, and 40 g of it was introduced into a cylindrical coagulation tank having a baffle with a diameter of 90 mm, a height of 170 mm, a width of 18 mm, and a height of 140 mm. Then, coagulation treatment was performed using a four-blade inclined paddle-type stirring blade with a blade diameter of 70 mm at 20°C and a stirring speed of 600 rpm, and solid-liquid separation was performed to obtain a fluorine-containing polymer wet powder. The fluorine-containing polymer wet powder was dried at 150°C for 6 hours, and then heat-treated at 260°C for 3 hours in an atmospheric atmosphere to obtain the fluorine-containing polymer powder of Example 1. The volume-based median diameter D50 of the fluorine-containing polymer powder was 428 μm.

[0226] Furthermore, when the proportion of each unit in the fluorine-containing polymer powders of Example 1 and Examples 2 to 13 described later was measured using the method described above, the TFE unit content in the fluorine-containing polymer powder of each example was 99% by mass or more relative to the total units of the fluorine-containing polymer powder of each example.

[0227] <Preparation of Electrode Mixture> NMC622 (manufactured by Hosen Co., Ltd., average particle size 10 μm, positive electrode active material), the fluorine-containing polymer powder of Example 1, and acetylene black (manufactured by Sigma-Aldrich) were mixed in a mass ratio of 96:3:1 using a V-type mixer VK-1 (manufactured by Irie Shokai Co., Ltd.) at 60 rpm for 10 minutes to obtain a mixture. Subsequently, the above mixture was pulverized and mixed using an Ex-Mini Jet Mill (manufactured by M-Tech Chemical Co., Ltd.) with a feed rate of 3 g / min and an air pressure of 0.4 MPa to obtain the electrode mixture (positive electrode mixture) of Example 1.

[0228] <Preparation of Electrode Mixture Sheet> The obtained electrode mixture (100g) was pressed using a roll press device (HSARP-60150-2HL, manufactured by Hosen Co., Ltd.) under the following conditions: roll temperature 120°C, roll speed 1 m / min, roll peripheral speed difference 1:10, load 2t, and roll gap 100 μm, to obtain an electrode mixture sheet (electrode layer) of Example 1 with a thickness of 104 μm.

[0229] <Fabrication of Lithium-ion Secondary Battery> The electrode mixture sheet prepared above was tabbed to form the positive electrode. A metallic lithium foil (manufactured by Honjo Chemical Co., Ltd.) was used as the negative electrode and was placed opposite the negative electrode via a 20 μm thick microporous polyethylene film (separator). Next, the non-aqueous electrolyte described later was injected and allowed to sufficiently permeate the separator, etc., then sealed, pre-charged, and aged to fabricate a lithium-ion secondary battery. As the organic solvent for the non-aqueous electrolyte, a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC = 30:70 (volume ratio)) was weighed into a sample bottle and the mixture was prepared. LiPF was added to this mixture so that the concentration in the electrolyte was 1.0 mol / L. ６ A non-aqueous electrolyte was obtained by mixing salts at 23°C.

[0230] [Examples 2-7, 9-13] For the fluorine-containing polymer powders, electrode mixtures, electrode mixture sheets, and lithium-ion secondary batteries in Examples 2-7 and 9-13, the fluorine-containing polymer powders and electrode mixture sheets were prepared in accordance with the manufacturing procedure of Example 1, except that the manufacturing conditions shown in Table 1 below were changed. Specifically, the stirring speed during the agglomeration process, the heat treatment temperature, and the heat treatment time were changed. In Example 9, no heat treatment was performed.

[0231] The thickness of the electrode mixture sheets in Examples 2 to 7 and Examples 9 to 13 was 109 μm in Example 2, 111 μm in Example 3, 117 μm in Example 4, 119 μm in Example 5, 124 μm in Example 6, 108 μm in Example 7, 102 μm in Example 9, 103 μm in Example 10, 103 μm in Example 11, 133 μm in Example 12, and 132 μm in Example 13.

[0232] [Example 8] A 100 L stainless steel autoclave equipped with baffles and a stirrer was charged with 63 g of APFDO, 670 g of paraffin wax, and 60 L of deionized water. After purging the autoclave with nitrogen and reducing the pressure, 34.1 g of chlorotrifluoroethylene (CTFE) was injected under pressure using a TFE, and the temperature was raised to 70°C while stirring. The pressure was then increased to 1.80 MPa using the TFE, and 5.0 g of dissolved disuccinic acid peroxide (concentration 80% by mass, the remainder being water) was injected. The internal pressure dropped to 1.78 MPa in about 3 minutes. Polymerization was carried out while adding TFE to maintain the autoclave internal pressure at 1.80 MPa. A total of 125 g of APFDO was added during polymerization by dissolving it in warm water. In addition, a total of 4 g of ammonium sulfite was added during polymerization by dissolving it in water. The temperature was lowered to 64°C during the polymerization process, and then raised to 80°C during the latter half of the polymerization. The reaction was terminated when the amount of TFE added reached 26 kg, and the TFE in the autoclave was released into the atmosphere. The polymerization time was 205 minutes. The obtained aqueous dispersion was cooled, and the paraffin wax of the supernatant was removed to obtain aqueous dispersion B containing the fluorine-containing polymer. The solid content concentration of the obtained aqueous dispersion B was 26% by mass, and the PPS of the fluorine-containing polymer was 0.29 μm.

[0233] The test was carried out in the same manner as in Example 1, except that aqueous dispersion B was used, and the fluorine-containing polymer powder of Example 8 (volume-based median diameter D50 of the fluorine-containing polymer powder: 450 μm), the electrode mixture of Example 8, the electrode mixture sheet of Example 8, and the lithium-ion secondary battery of Example 8 were obtained. The thickness of the electrode mixture sheet of Example 8 was 111 μm.

[0234]

[0235] As shown in Examples 1 to 8, when a fluorine-containing polymer powder with a compressive modulus of 0.10 to 1.20 MPa was used as a binder, the mixing uniformity evaluation was A, indicating excellent mixing uniformity of the electrode mixture. Furthermore, the sheet thickness was A or B, making it easier to create thin films. In addition, the sheet appearance evaluation was A, indicating that the formation of white streaks could be suppressed. On the other hand, in Examples 9 to 11, where the compressive modulus was less than 0.10 MPa, the mixing uniformity of the electrode mixture was poor. This is thought to be because the particles broke down and fibrillation became excessive during mixing of the fluorine-containing polymer powder with the electrode active material. Also, in Examples 12 and 13, where the compressive modulus was greater than 1.20 MPa, it was difficult to create thin films of the electrode mixture sheets. This is thought to be because the fibrillation of the fluorine-containing polymer powder did not proceed sufficiently.

[0236] According to this disclosure, it is possible to provide a fluorine-containing polymer powder used for preparing an electrode mixture, which is excellent in the uniformity of the resulting electrode mixture and in the thinning of the sheet obtained using the electrode mixture, an electrode mixture containing the fluorine-containing polymer powder, an electrode containing the electrode mixture, and a secondary battery containing the electrode.

[0237] 1...Deformation and load sensor, 2...Planar indenter, 3...Measurement stage, 4...Particle, L...Measured particle diameter

Claims

1. A fluorine-containing polymer powder containing a fluorine-containing polymer for use as a binder for secondary battery electrodes, wherein the fluorine-containing polymer has units based on tetrafluoroethylene and the compressive modulus calculated from the following formula 1 is 0.10 to 1.20 MPa. Compressive modulus = (Compressive stress at 50% deformation - Compressive stress at 10% deformation) / 0.4 Formula 1 2. The fluorine-containing polymer powder according to claim 1, wherein the volume-based median diameter D50 of the fluorine-containing polymer powder is 280 to 1000 μm.

3. An electrode mixture comprising the fluorine-containing polymer powder described in claim 1 or claim 2 and an electrode active material.

4. The electrode mixture according to claim 3, further comprising a conductive additive, wherein the content of the fluorine-containing polymer powder is 0.5 to 19.5% by mass relative to the total mass of the electrode mixture, the content of the electrode active material is 80 to 99% by mass, and the content of the conductive additive is 0.5 to 19.5% by mass.

5. An electrode comprising a current collector and an electrode layer comprising the electrode mixture according to claim 3, disposed on the current collector.

6. A secondary battery comprising the electrode described in claim 5.

Images