Polytetrafluoroethylene resin powder, electrode mixture, electrode layer, electrode, and secondary battery

Abstract

The present invention pertains to a polytetrafluoroethylene resin powder that can be used as a binder for a secondary battery. In an aspect ratio distribution based on the cumulative number of particles constituting the polytetrafluoroethylene resin powder, the cumulative 50% aspect ratio is 0.65-0.85, and the cumulative ratio of particles having an aspect ratio of less than 0.30 is 10% or less.

Description

Polytetrafluoroethylene resin powder, electrode mixture, electrode layer, electrode, secondary battery

[0001] The present invention relates to a polytetrafluoroethylene resin powder, an electrode mixture, an electrode layer, an electrode, and a secondary battery. This application claims priority to Japanese Patent Application No. 2024-188454, filed in Japan on October 25, 2024, the contents of which are incorporated herein by reference.

[0002] Lithium-ion secondary batteries and other secondary batteries offer high voltage and high energy density, low self-discharge, minimal memory effect, and the ability to be made extremely lightweight. Therefore, they are used in small, portable electrical and electronic devices such as notebook computers, mobile phones, smartphones, tablet computers, and ultrabooks. They are also used in automotive power supplies and large-scale stationary power supplies.

[0003] Furthermore, electrodes for non-aqueous electrolyte secondary batteries, such as lithium-ion secondary batteries, are generally manufactured using a wet method, in which an electrode mixture containing active material and binders is applied to a current collector to produce the electrodes. On the other hand, in recent years, a dry method has been considered in which the electrode mixture is stretched and formed into a sheet, and this sheet is then bonded to a current collector to produce the electrodes, in order to reduce the environmental impact during manufacturing and improve oxidation resistance.

[0004] Patent Document 1 discloses a polytetrafluoroethylene-based resin powder used as a binder for secondary batteries.

[0005] Japanese Patent Publication No. 2023-051887

[0006] We evaluated polytetrafluoroethylene resin powders as described in Patent Document 1. As a result, we found that it is difficult to reconcile the following three conditions: excellent storage stability of polytetrafluoroethylene resin powders, ease of thinning when using electrode mixtures obtained by mixing with active materials, etc., with resistance to breakage when producing sheets.

[0007] The present invention aims to provide a polytetrafluoroethylene resin powder that has excellent storage stability and is used to prepare an electrode mixture by mixing it with an active material, and which is easy to thin and difficult to break when a sheet is made using the resulting electrode mixture. The present invention also aims to provide an electrode mixture, an electrode layer, an electrode, and a secondary battery.

[0008] As a result of diligent research, the inventors have found that the above problem can be solved by the following configuration.

[0009] [1] A polytetrafluoroethylene resin powder used as a binder for secondary batteries, wherein, in the aspect ratio distribution based on the cumulative number of particles constituting the polytetrafluoroethylene resin powder, the aspect ratio at 50% cumulative is 0.65 to 0.85, and the cumulative proportion of particles with an aspect ratio of less than 0.30 is 10% or less. [2] The polytetrafluoroethylene resin powder according to [1], wherein the aspect ratio at 50% cumulative is 0.68 to 0.80. [3] An electrode mixture comprising the polytetrafluoroethylene resin powder according to [1] or [2] and an active material. [4] The electrode mixture according to [3], further comprising a conductive additive, wherein the content of the polytetrafluoroethylene resin powder is 1 to 20% by mass relative to the total mass of the electrode mixture, the content of the active material is 70 to 96% by mass relative to the total mass of the electrode mixture, and the content of the conductive additive is 1 to 20% by mass relative to the total mass of the electrode mixture. [5] The electrode mixture according to [3], further comprising a sulfide-based solid electrolyte, wherein the content of the polytetrafluoroethylene resin powder is 1 to 20% by mass relative to the total mass of the sulfide-based solid electrolyte. [6] The electrode mixture according to any one of [3] to [5], which is in the form of a sheet. [7] An electrode layer comprising the electrode mixture according to any one of [3] to [6]. [8] An electrode comprising a current collector and the electrode layer according to [7] disposed on the current collector. [9] A secondary battery comprising the electrode according to [8].

[0010] According to the present invention, a polytetrafluoroethylene-based resin powder is available that has excellent storage stability and is used to prepare an electrode mixture by mixing it with an active material, and which is easily formed into a thin film and is resistant to breakage when a sheet is made using the resulting electrode mixture. Furthermore, according to the present invention, an electrode mixture, an electrode layer, an electrode, and a secondary battery can be provided.

[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. 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. A combination of two or more preferred embodiments is a more preferred embodiment. "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 referred to as "unit" below. The content (mass %) or molar %) of each unit relative to the total units contained in a resin or polymer is determined by analyzing the resin or polymer using solid-state nuclear magnetic resonance (solid-state NMR) spectroscopy. Furthermore, the content of each unit calculated from the amount of each monomer added usually closely matches the actual content of each unit.

[0012] [Polytetrafluoroethylene-based resin powder (polytetrafluoroethylene-based resin powder)] The polytetrafluoroethylene-based resin powder of this embodiment (hereinafter also simply referred to as "PTFE-based resin powder") is a PTFE-based resin powder used as a binder for secondary batteries, wherein in the aspect ratio distribution based on the cumulative number of particles constituting the PTFE-based resin powder, the aspect ratio at 50% cumulative is 0.65 to 0.85, and the cumulative proportion of particles with an aspect ratio of less than 0.30 is 10% or less.

[0013] The PTFE-based resin powder of this embodiment exhibits excellent storage stability. When a sheet is made using the electrode mixture obtained by mixing with an active material, it is easy to thin the film and difficult to break. Although the mechanism of action is not entirely clear, the inventors speculate as follows: When the cumulative 50% aspect ratio of the particles constituting the PTFE-based resin powder is less than 0.65, the particles have a relatively long fibrous shape, and after storage over time, the particles tend to entangle with each other, resulting in poor storage stability. In contrast, if the cumulative 50% aspect ratio is 0.65 or higher, the particles are less likely to entangle with each other even after storage over time, thus it is presumed that storage stability is excellent. Furthermore, when the cumulative 50% aspect ratio is greater than 0.85, the particles constituting the PTFE-based resin powder have a relatively spherical shape close to a perfect circle. Therefore, when making a sheet using manufacturing equipment such as a roll press, the spherical particles tend to slip. As a result, the electrode mixture cannot be sufficiently pressurized, making it difficult to thin the sheet. In contrast, if the cumulative aspect ratio at 50% is 0.85 or less, the particles constituting the PTFE resin powder have an appropriate shape, not becoming too spherical. As a result, the electrode mixture can be sufficiently pressurized, making it easier to thin the sheet. In the aspect ratio distribution based on the cumulative number of particles constituting the PTFE resin powder, if the cumulative ratio of particles with an aspect ratio of less than 0.30 exceeds 10%, the proportion of the above-mentioned particles, which are relatively prone to fiberization, increases. Therefore, excessive fiberization progresses during the sheet manufacturing process. As a result, the sheet becomes more prone to breakage. In contrast, if the cumulative ratio of the above-mentioned particles is 10% or less, excessive fiberization is suppressed, and it is presumed that the sheet will be less prone to breakage. As described above, the inventors have found that the problem of this invention can be solved mainly by adjusting the cumulative aspect ratio at 50% and the cumulative ratio of particles with an aspect ratio of less than 0.30. Hereinafter, "the effects of the present invention are superior" refers to the superior storage stability of the PTFE-based resin powder, the ease of forming thin sheets, and the resistance of the sheets to breakage being at least one of these effects being superior.

[0014] <Cumulative 50% Aspect Ratio> The cumulative 50% aspect ratio is 0.65 to 0.85, preferably 0.68 to 0.83, and more preferably 0.68 to 0.80 in that the effects of the present invention are superior.

[0015] The cumulative 50% aspect ratio is the aspect ratio when the cumulative number of particles in a PTFE resin powder reaches 50%, with the total number of measured particles being set to 100%. The aspect ratio is the ratio of the minor axis diameter of a particle to the major axis diameter (minor axis / major axis), and the closer the aspect ratio is to 1, the closer the particle shape is to a perfect circle. The minor axis diameter of a particle indicates the diameter of the longest part perpendicular to the major axis diameter of the particle.

[0016] A preferred method for measuring the cumulative 50% aspect ratio is to use a known measuring device and measure it using a static image analysis method. An example of such a measuring device is the Morphologi 4 (manufactured by Malvern Panalogical). More specifically, the measurement method described in the Examples section is relevant.

[0017] Methods for adjusting the cumulative 50% aspect ratio include, for example, the freezing and mechanical processing and classification processes described later, and the cumulative 50% aspect ratio can be adjusted by adjusting the processing conditions.

[0018] <Cumulative Ratio> The cumulative ratio of particles with an aspect ratio of less than 0.30 is 10% or less, preferably 8% or less. The lower limit is often 0% or more. The lower limit may be 1% or 2%. The range is preferably 0 to 10%, and more preferably 0 to 8%.

[0019] The above cumulative ratio is the cumulative ratio of particles with an aspect ratio of less than 0.30 in an aspect ratio distribution based on the same cumulative number criterion as the 50% cumulative aspect ratio. In other words, the above cumulative ratio is the proportion of the total number of particles with an aspect ratio of less than 0.30 when the total number of measured particles is set to 100%.

[0020] As a method for measuring the cumulative ratio described above, a method using static image analysis with a known measuring device is preferred. Specifically, the PTFE resin powder is first sieved through a sieve with a mesh size of 2360 μm. Then, the PTFE resin powder is placed on a sample stage, and the particles of the PTFE resin powder are observed and images are acquired at a microscope magnification of 2.5x. More than 10,000 particles are observed, and the aspect ratio distribution based on the cumulative number of particles constituting the PTFE resin powder is obtained, and the aspect ratio at 50% cumulative is calculated. In addition, the cumulative ratio of particles with an aspect ratio of less than 0.30 is calculated. Note that PTFE resin powder with particle diameters that are too small to observe may be excluded from measurement. For example, by setting the trash size to 25, particles of 25 pixels or less can be excluded from measurement. Also, PTFE resin powder with particle shapes that are too complex may be excluded from measurement. For example, by setting the filter envelope to 0.9, particles with an envelope of less than 0.9 are excluded from measurement. The envelope is calculated as (envelope circumference of the particle / actual circumference of the particle). The envelope circumference of the particle indicates the length of the circumference that smoothly encloses the outermost part of the particle. The actual circumference of the particle indicates the actual circumference including the fine irregularities of the particle. An example of a measuring device is the Morphologi 4 (manufactured by Malvern Panalogical). More detailed information can be found in the measurement method described in the Examples section.

[0021] Methods for adjusting the above cumulative ratio include, for example, the freezing and mechanical processing and classification processes described later, and the above cumulative ratio can be adjusted by adjusting the processing conditions.

[0022] <Units> The PTFE resin that constitutes the PTFE resin powder contains units based on tetrafluoroethylene (hereinafter also referred to as "TFE units").

[0023] (TFE Units) PTFE-based resins are resins containing TFE units. The resins of this embodiment are clearly distinguished from elastomers. Elastomers are elastic polymers with no melting point that exhibit 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 TFE unit content is preferably 99% by mass or more, more preferably 99.5% by mass or more, and even more preferably 99.9% by mass or more, relative to the total units of the PTFE-based resin. The upper limit is preferably 100% by mass or less. Furthermore, the TFE unit content is preferably 99 mol% or more, more preferably 99.5 mol% or more, and even more preferably 99.9 mol% or more, relative to the total units of the PTFE resin. The upper limit is preferably 100 mol% or less.

[0024] (Units based on other monomers) PTFE resins may contain units based on other monomers in addition to 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, PAVE, or FAE are preferred as other monomers. Furthermore, the other monomers may be monomers used in the method for producing PTFE resins described later.

[0025] PAVE is preferably a monomer represented by formula (PA).

[0026] CF ２ =CF-O-Rf １ (PA)

[0027] In formula (PA), Rf １ Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms. １The number of carbon atoms in the perfluoroalkyl group represented by is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3 in terms of better polymerization reactivity. The perfluoroalkyl group may be either linear or branched.

[0028] As the PAVE, for example, CF ２ =CFOCF ３ (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 =CF0(CF ２ ) ８ F are mentioned, and PMVE or PPVE is preferred.

[0029] As the FAE, a monomer represented by the formula (FA) is preferred.

[0030] CZ ２ =CX(CF ２ ) ｍ Y (FA)

[0031] In the formula (FA), X, Y and Z each independently represent a hydrogen atom or a fluorine atom. m represents an integer of 2 to 6. As the FAE, for example, CH ２ =CH(CF ２ [[ID=5)]] ) ２ F, CH ２ =CH(CF ２ ) <0000)]] F, CH ２ =CH(CF ２ ) ４ [[ID=7)] F (PFBE), CH ２ =CF(CF ２ ) ３ H, and CH ２ =CF(CF ２ ) ４ H are mentioned, and PFBE or CH ２ =CH(CF２ ) ２ F is preferred.

[0032] 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 PTFE resin. The lower limit is preferably 0 mol% or more. The content of units based on other monomers is preferably 1 mass% or less, more preferably 0.5 mass% or less, and even more preferably 0.1 mass% or less, relative to the total units of the PTFE resin. The lower limit is preferably 0 mass% or more.

[0033] The total content of TFE units and PFBE-based units is preferably 95% by mass or more, more preferably 99% by mass or more, and even more preferably 99.9% by mass or more, relative to the total mass of the PTFE resin. The upper limit is preferably 100% by mass or less.

[0034] The content of each unit in PTFE resin is: １ H-NMR and １９ It can be measured by known methods such as F-NMR.

[0035] <Other> The form of the PTFE resin powder is not particularly limited as long as it is a powder containing particles. For example, granular and particulate forms are included. The particles constituting the PTFE resin powder may be either primary particles or secondary particles. It is preferable that the particles constituting the PTFE resin powder include secondary particles.

[0036] PTFE-based resin powder may contain particles having a core-shell structure. Examples of particles having a core-shell structure include particles comprising a core of high molecular weight resin containing TFE units and a shell of resin containing low molecular weight resin or units based on other monomers containing TFE units.

[0037] The particle size D50 of the PTFE resin powder is preferably 450 to 750 μm, and more preferably 500 to 700 μm. The particle size D50 is the so-called median size, and in the cumulative particle size distribution measured by static image analysis, it is the particle size when the cumulative number of particles is 50% when the total number of measured particles is set to 100%. As a method for measuring the particle size D50, a method using static image analysis with a known measuring device is preferred. An example of a measuring device is the Morphologi 4 (manufactured by Malvern Panalogical).

[0038] The standard specific gravity (SSG) of PTFE-based resin powder is preferably 2.120 to 2.190, more preferably 2.125 to 2.190, and even more preferably 2.130 to 2.180. SSG is used as a relative measure of molecular weight, and a lower value indicates a higher molecular weight. Furthermore, if the amount of comonomer introduced into the PTFE-based resin powder is high, the amorphous structure increases further, the density decreases, and the SSG value tends to decrease. SSG can be measured in accordance with ASTM D4895-10.

[0039] The moisture content of the PTFE resin 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 PTFE resin powder. The lower limit is preferably 0% by mass or more, and more preferably 0.0001% by mass or more. The moisture content is calculated by measuring the mass of the PTFE resin powder before and after heating it at 150°C for 2 hours, and using the following formula. Three samples are taken, the moisture content is calculated for each, and the average is taken and the arithmetic mean is adopted.

[0040] Moisture content (mass%) = 100 × [(Mass of PTFE resin powder before heating (g)) - (Mass of PTFE resin powder after heating (g))] / (Mass of PTFE resin powder before heating (g))

[0041] PTFE-based resin powder is used as a binder for secondary batteries. It is preferable that the PTFE-based resin powder be used in compositions for forming components or layers that constitute a secondary battery, and more preferably in electrode mixtures obtained by mixing the PTFE-based resin powder with an active material. The term "binder" here is synonymous with general binders and refers to so-called binders, dispersants, and adhesives. Examples of components or layers constituting a secondary battery include the electrode layer described later. Furthermore, the secondary battery itself is not particularly limited as long as it is a known secondary battery. Preferred embodiments of the secondary battery will be described later.

[0042] [Method for producing PTFE resin powder] The method for producing PTFE resin powder is not particularly limited as long as it is a method that can produce PTFE resin powder. A preferred method for producing PTFE resin powder is one that includes step A of obtaining an aqueous dispersion containing PTFE resin and step B of obtaining PTFE resin powder from the aqueous dispersion.

[0043] <Process A> Process A is a process to obtain an aqueous dispersion containing a PTFE-based resin.

[0044] Step A, for example, is a step of polymerizing monomers that constitute the PTFE resin in an aqueous medium. The monomers can be appropriately selected according to the desired PTFE resin powder. As for the polymerization method, for example, a known polymerization method can be used.

[0045] As step A, it is preferable to polymerize a first monomer containing TFE in the presence of an aqueous medium to obtain an aqueous dispersion containing a PTFE-based resin.

[0046] (Aqueous medium) Examples of aqueous media include water and mixed solvents of water and water-soluble organic solvents, with water being preferred. 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 mixed solvent of water and water-soluble organic solvent, the concentration of the water-soluble organic solvent is preferably 10% by mass or less.

[0047] (First Monomer) The first monomer contains TFE. The first monomer may also contain other monomers besides TFE. The TFE content is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, even more preferably 99 mol% or more, even more preferably 99.5 mol%, and especially preferably 99.9 mol% based on the total number of moles of the first monomer. The upper limit is preferably 100 mol% or less.

[0048] Examples of polymerization methods for the first monomer include emulsion polymerization, solution polymerization, and suspension polymerization. This can be carried out by heating the monomer in the presence of an aqueous medium and a polymerization initiator. The aqueous medium may or may not contain an emulsifier.

[0049] (Polymerization initiators) Examples of polymerization initiators include oil-soluble radical polymerization initiators and water-soluble radical polymerization initiators.

[0050] 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, and di(ω-chloro-hexafluoro Examples include di[perfluoro(or fluorochloro)acyl]peroxides such as butyryl 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.

[0051] As a water-soluble radical polymerization initiator, a water-soluble thermal radical initiator or a water-soluble redox catalyst is preferred, more preferably ammonium persulfate or a mixture of persulfate and disuccinic acid peroxide, and even more preferably ammonium persulfate or a mixture of ammonium persulfate and disuccinic acid peroxide. As a water-soluble thermal radical initiator, persulfates such as ammonium persulfate and potassium persulfate, or water-soluble organic peroxides such as disuccinic acid peroxide, bisglutaric acid peroxide, and tert-butyl hydroperoxide are preferred. As a water-soluble redox catalyst, a combination of an oxidizing agent such as bromate, chloric acid, persulfate, permanganate and its salts, and hydrogen peroxide, and a reducing agent such as sulfurous acid, bisulfite, thiosulfate and its salts, and organic acids is preferred.

[0052] 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.

[0053] (Other components) In polymerization of the first monomer, other components such as nucleating agents, chain transfer agents, buffers, pH adjusters, stabilizing aids, dispersion stabilizers, radical scavengers, polymerization initiator decomposition agents, and dicarboxylic acids may be used.

[0054] Examples of nucleating agents include fluoropolyethers such as perfluoropolyether acids, nonionic surfactants, and chain transfer agents. Examples of perfluoropolyether acids include those described in J. Appl. Polymer Sci. 57,797 (1995).

[0055] As stabilizing agents, paraffin wax, fluorinated solvents, or silicone oils are preferred. The paraffin wax may be liquid, semi-solid, or solid at room temperature. The melting point of the paraffin wax is preferably 40 to 65°C, and more preferably 50 to 65°C. As stabilizing agents, saturated hydrocarbons with 12 or more carbon atoms are preferred.

[0056] 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 (NH4). ４ Examples include SCN, potassium thiocyanate (KSCN), and sodium thiocyanate (NaSCN).

[0057] Any compound capable of decomposing the polymerization initiator can be used as a decomposition agent for the polymerization initiator, such as sulfites, bisulfites, bromates, diimines, diimines, oxalic acid, oxalates, copper salts, and iron salts.

[0058] As the dicarboxylic acid, compounds represented by HOOC-R-COOH (where R represents an alkylene group having 1 to 5 carbon atoms) are preferred, and succinic acid, malonic acid, glutaric acid, adipic acid, or pimelic acid are more preferred.

[0059] The polymerization temperature and polymerization pressure in the polymerization of the first monomer can be appropriately adjusted depending on the type of monomer used, the molecular weight of the target PTFE resin, 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. The upper limit is preferably 150°C or lower, more preferably 120°C or lower, and even more preferably 100°C or lower. 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. The upper limit is preferably 5.0 MPaG or lower, and even more preferably 3.0 MPaG or lower. 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.

[0060] The PTFE resin content is preferably 5.0 to 50.0% by mass, more preferably 10.0 to 45.0% by mass, and even more preferably 10.0 to 30.0% by mass, relative to the total mass of the aqueous dispersion. The solid content concentration of the aqueous dispersion is preferably 5.0 to 50.0% by mass, more preferably 10.0 to 45.0% by mass, and even more preferably 10.0 to 30.0% by mass. The solid content concentration of the aqueous dispersion is determined by weighing the mass of the residue after heating the aqueous dispersion (2.0 g) at 170°C for 20 minutes, and using the following formula.

[0061] The solid content concentration (mass%) of the aqueous dispersion = 100 × mass of residue after heating (g) / mass of aqueous dispersion before heating (2.0 g). The average primary particle size of the PTFE resin in the aqueous dispersion is preferably 100 to 500 nm, and more preferably 150 to 300 nm. The average primary particle size of the PTFE resin is the volume-based particle size D50 (median diameter) measured by a laser scattering particle size distribution analyzer.

[0062] <Step B> Step B is a step in which PTFE-based resin powder is obtained from the aqueous dispersion obtained in Step A. Examples of methods for obtaining PTFE-based resin powder from an aqueous dispersion include known methods, and it is preferable to obtain PTFE-based resin powder by performing coagulation treatment and drying treatment from the aqueous dispersion, and it is more preferable to obtain a PTFE-based wet resin by performing coagulation treatment from the aqueous dispersion, and then drying the PTFE-based wet resin to obtain PTFE-based resin powder.

[0063] Examples of coagulation treatments include freeze coagulation, acid coagulation, base coagulation, mechanical coagulation, and coagulation using a coagulant, with acid coagulation or freeze coagulation being preferred. The coagulation temperature for freeze coagulation is preferably -20 to 0°C. The coagulation time is preferably 1 hour or more, and more preferably 2 hours or more. For acid coagulation, 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 in 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. For base coagulation, 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 in 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. Examples of agglutination using a coagulant include a method using a known coagulant. Examples of known coagulants include aluminum salts, calcium salts, and magnesium salts. Specifically, aluminum sulfate, M'Al(SO4) ４ ) ２ 12H ２ Examples include alum, calcium nitrate, and magnesium sulfate, represented by O [where M' represents a monovalent cation other than lithium], with alum being preferred and potassium alum being more preferred, where M' is potassium.

[0064] Furthermore, pH adjusters or flocculation aids may be used during the flocculation treatment. Examples of pH adjusters include sodium carbonate and sodium bicarbonate. Examples of flocculation aids include inorganic salts such as potassium nitrate, sodium nitrate, sodium carbonate, and sodium bicarbonate, as well as organic solvents such as alcohol-based solvents and acetone. It is also preferable to carry out the flocculation treatment in the presence of at least one compound selected from the group consisting of ammonia, ammonium salts, and urea.

[0065] As for the drying treatment, a treatment to dry the PTFE-based wet resin obtained by the agglomeration treatment is preferred. The drying temperature is preferably 100°C or higher, more preferably 110°C or higher, even more preferably 120°C or higher, and particularly preferably 170°C or higher. The upper limit is preferably 280°C or lower, more preferably 250°C or lower, and even more preferably 230°C or lower. The range is preferably 100 to 280°C, more preferably 110 to 250°C, even more preferably 120 to 230°C, and particularly preferably 170 to 230°C. The drying time is preferably 1 hour or more, more 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. Furthermore, the water content in the PTFE-based wet resin, which is the material to be dried, is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, per 100 parts by mass of the PTFE-based wet resin. The upper limit is preferably 150 parts by mass or less, and more preferably 100 parts by mass or less. The range is preferably 10 to 150 parts by mass, more preferably 20 to 100 parts by mass, and even more preferably 30 to 100 parts by mass.

[0066] Furthermore, the drying process is preferably carried out in an atmosphere containing ammonia. An atmosphere containing ammonia means an atmosphere in which ammonia gas can come into contact with the PTFE-based wet resin. For example, this may be an atmosphere in which ammonia gas is present, or an atmosphere in which ammonia gas is generated by heating or other means in the presence of ammonia or a compound that generates ammonia gas. Examples of compounds that generate ammonia gas include ammonium salts and urea, with ammonium carbonate being preferred.

[0067] Furthermore, the drying process may be carried out using an electric furnace or a steam furnace. Examples of electric furnaces and steam furnaces include parallel flow box-type electric furnaces, ventilated box-type electric furnaces, ventilated conveyor-type electric furnaces, band electric furnaces, radiant conveyor-type electric furnaces, fluidized bed electric furnaces, vacuum electric furnaces, agitated electric furnaces, airflow electric furnaces, and hot air circulation electric furnaces, as well as steam furnaces corresponding to these (devices in which "electric furnace" is read as "steam furnace" in the device names of each electric furnace listed above).

[0068] After the agglomeration treatment and before the drying treatment, known granulation treatments and known particle sizing treatments may be performed. Granulation treatment is a treatment that increases the average particle size of the PTFE-based resin powder (particles) (for example, to several hundred μm), and particle sizing treatment is a treatment that adjusts the properties and particle size distribution of the particles by stirring, etc.

[0069] <Other Processes> The method for producing PTFE-based resin powder may further include other processes. Examples of other processes include freeze-machining and classification. It is preferable to carry out the other processes after process B, and it is more preferable to carry out the freeze-machining and classification processes in the order of process B. It is preferable to carry out freeze-machining and classification as other processes in the method for producing PTFE-based resin powder. The other processes make it easier to adjust the cumulative aspect ratio of 50% and the cumulative ratio of particles with an aspect ratio of less than 0.30.

[0070] (Freeze-Machining Treatment) Freeze-machining treatment is a process in which mechanical impact is applied to PTFE-based resin powder in the presence of a cold material such as liquid nitrogen. By performing freeze-machining treatment, excessive deformation and excessive fiber formation of the particles constituting the PTFE-based resin powder are suppressed, while the aspect ratio of the particles (especially the cumulative 50% aspect ratio) can be easily adjusted.

[0071] Examples of equipment for frozen machining include the Rotor Speed ​​Mill P-14 (manufactured by Fritsch) and the ZM300 (manufactured by Lechtsch).

[0072] The method for freeze-machining involves, for example, setting an impact rotor blade in the above-mentioned apparatus and rotating it. Then, a coolant such as liquid nitrogen is added. After that, PTFE-based resin powder is introduced and mechanical impact is applied to the PTFE-based resin powder. The rotor rotation speed for freeze-machining is preferably 4000 rpm or more, and more preferably 6000 rpm or more. The upper limit is preferably less than 10000 rpm, and more preferably 9000 rpm or less, as this makes it easier to adjust the aspect ratio of the particles (especially the cumulative 50% aspect ratio). The range is preferably 4000 rpm or more and less than 10000 rpm, and more preferably 6000 to 9000 rpm. The processing temperature for freeze-machining is preferably 0°C or less, more preferably -20°C or less, and even more preferably -50°C or less. The lower limit is preferably -200°C or higher. The range is preferably -200 to 0°C, more preferably -200 to -20°C, and even more preferably -20 to 50°C.

[0073] (Classification process) Classification is a process that classifies PTFE-based resin powder to adjust the particle size distribution.

[0074] Classification methods include, for example, sieving and centrifugal classification, with centrifugal classification being preferred due to its high accuracy. Sieving methods include, for example, sieving PTFE resin powder using a sieve of any size and obtaining the sieved material. Centrifugal classification methods include, for example, using a centrifugal classifier that uses both air and centrifugal force for classification. In the method using a centrifugal classifier, for example, PTFE resin powder may be introduced into the classification section by primary air, and the coarse powder may be separated to the outside of the classification section by centrifugal force, while the fine powder may be separated to the inside of the classification section by suction force. Furthermore, if the powder particles are agglomerated, a secondary air blowing process may be performed to break up the agglomeration. Examples of centrifugal classifiers include the Turboplex ATP (manufactured by Hosokawa Micron Corporation), the Micron Classifier (manufactured by Seishin Corporation), and the Eddy Classifier (manufactured by Nisshin Engineering Co., Ltd.).

[0075] The classification conditions can be appropriately adjusted to match the target cumulative aspect ratio of 50% and the cumulative ratio of particles with an aspect ratio of less than 0.3. When centrifugal classification is performed in the classification process, the rotor speed is preferably 5000 rpm or less, more preferably 3500 rpm or less, and even more preferably 2500 rpm or less. The lower limit is often 1000 rpm or more. The range is preferably 1000 to 5000 rpm, more preferably 1000 to 3500 rpm, and even more preferably 1000 to 2500 rpm. When centrifugal classification is performed in the classification process, the processing temperature is preferably 10°C or less, more preferably 5°C or less. The lower limit is often -20°C or higher. The range is preferably -20 to 10°C, and more preferably -20 to 5°C.

[0076] <First Embodiment> The method for producing PTFE-based resin powder may be the first embodiment. The first embodiment is a method for producing PTFE-based resin powder, comprising steps C, D, and E described below. Step C: A step of polymerizing a non-fluorinated monomer in an aqueous medium to obtain a solution C containing a polymer (hereinafter also referred to as "specific polymer C") that includes units based on a non-fluorinated monomer. Step D: A step of polymerizing TFE in solution C without substantially adding a surfactant to solution C to obtain an aqueous emulsion containing PTFE-based resin. Step E: A step of obtaining PTFE-based resin powder from the aqueous emulsion obtained in step D. Furthermore, the first embodiment may include the above-mentioned other steps after step E, as it is easier to adjust the cumulative aspect ratio of 50% and the cumulative ratio of particles with an aspect ratio of less than 0.30. As described above, examples of other steps include freezing mechanical processing and classification. Other processes are preferably carried out after process E, and more preferably, the freezing and mechanical processing and classification processes are carried out in that order after process E.

[0077] (Step C) Step C is a step in which a non-fluorinated monomer is polymerized in an aqueous medium to obtain a solution C containing a specific polymer C.

[0078] -Aqueous media- Examples of aqueous media include the aqueous media used in process A.

[0079] -Non-fluorinated monomers- Non-fluorinated monomers are monomers that do not contain fluorine atoms. Non-fluorinated monomers preferably have polymerizable groups. The number of polymerizable groups is preferably 1 to 3, and more preferably 1. Examples of polymerizable groups include ethylenically unsaturated groups, with acryloyl groups, methacryloyl groups, vinyl ester groups, vinyl ether groups, vinyl groups, or allyl groups being preferred, and acryloyl groups, methacryloyl groups, vinyl ester groups, or vinyl ether groups being more preferred.

[0080] As a non-fluorinated monomer, the monomer represented by formula (NF) is preferred.

[0081] CH ２ =CR １１ -L １ -R １２ (NF)

[0082] R １１ L represents a hydrogen atom or an alkyl group, preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group. １ * represents a single bond, -CO-O-*, -O-CO-*, or -O-. * represents R １２ It represents the connection position with L. １ If the monomer is -CO-O-*, the monomer represented by formula (NF) is CH ２ =CR １１ -CO-O-R １２ That is. R １２ L represents a hydrogen atom, alkyl group, alkenyl group, or nitrile group. １ If it is a single bond, R １２ The group represents 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 and alkenyl group may be linear or cyclic.

[0083] The monomer represented by formula (NF) is preferably one of the monomers represented by formulas (NF-1) to (NF-4).

[0084] CH ２ =CR １１ -CO-O-R １３ (NF-1) CH ２ =CR １１ -O-CO-R １４ (NF-2) CH ２ =CR １１ -O-R １５ (NF-3) CH ２ =CR １１ -R １６ (NF-4)

[0085] 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. １４R represents an alkyl group, preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group. １５ R represents an alkyl group, preferably a linear alkyl group or a cyclic alkyl group. １６ This represents a nitrile group.

[0086] 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. The monomer represented by formula (NF-1) or formula (NF-2) is preferred, with the monomer represented by formula (NF-1) being more preferred. Since the monomers represented by formula (NF-1) and (NF-2) have hydrophilic groups, such as ester groups or carboxyl groups, the monomers and their polymers are hydrophilic. Therefore, it is presumed that the monomers and their polymers can be stably dispersed in an aqueous medium (especially at low concentrations) without the need for a surfactant.

[0087] -Fluorine-based monomers- Step C may also use fluorine-based monomers. Fluorine-based monomers are monomers containing fluorine atoms, such as TFE.

[0088] -Polymerization Initiator- A polymerization initiator may be used in step C. Examples of polymerization initiators include the water-soluble radical polymerization initiator used in step A.

[0089] -Procedure for Step C- Step C is a step in which a non-fluorinated monomer is polymerized in an aqueous medium. Preferably, Step C is a step in which the non-fluorinated monomer is polymerized in a mixture obtained by mixing the aqueous medium and the non-fluorinated monomer. As described above, a fluorinated monomer or a polymerization initiator may be used.

[0090] The amount of non-fluorinated monomer used is preferably 200 ppm by mass or less, more preferably 1 to 150 ppm by mass, and even more preferably 5 to 50 ppm by mass, relative to the amount of TFE supplied in step D (amount of TFE used). As for the method of adding the non-fluorinated monomer, it is preferable to add the entire amount to the polymerization system at the beginning of the polymerization reaction.

[0091] The content of the non-fluorinated monomer in the mixture 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, relative to the total mass of the mixture. Since the non-fluorinated monomer usually polymerizes entirely to form a specific polymer C, the concentration of the specific polymer C in the resulting solution C will be within the above numerical range. Furthermore, the above concentrations of the non-fluorinated monomer and the specific polymer C are the concentrations when the resulting solution C is used in step D without dilution with an aqueous medium. Alternatively, solution C may be diluted with an aqueous medium to obtain a diluted solution, which will have the same concentration as the specific polymer C, and this diluted solution may be used in step D. A dilution ratio of 10 times or less is preferred.

[0092] 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. 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.

[0093] 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.

[0094] Step C yields a solution C containing a specific polymer C. The specific polymer C may be dissolved in solution C or dispersed in particulate matter in an aqueous medium. During the polymerization of TFE in step D, although the specific polymer C is not an emulsifier, it is presumed that due to the balance of interfacial tension between the aqueous medium and the PTFE resin, the specific polymer C exists at the boundary between the two and contributes to the stabilization of the dispersion of the PTFE resin in the aqueous medium. The average particle size of the specific polymer C 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"). The average particle size is the median diameter in the volume-based particle size distribution.

[0095] Solution C may contain unreacted nonfluorine monomers. Furthermore, the atmosphere within the polymerization system in step C may be a TFE-containing atmosphere, taking step D into consideration. In this case, a portion of the specific polymer C in step D may be a polymer containing TFE units. Also, the PTFE-based resin obtained in step D may be either particles of a physical mixture of the specific polymer C and a polymer containing TFE units, or particles of a polymer containing TFE units based on nonfluorine monomers.

[0096] -Specific Polymer C- Specific polymer C is a polymer containing units based on non-fluorinated monomers. Specific polymer C may contain only units based on non-fluorinated monomers, or it may contain units based on fluorinated monomers and units based on fluorinated monomers. 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. The upper limit is preferably 100% by mass or less.

[0097] (Step D) Step D is a step in which TFE is polymerized in solution C without substantially adding a surfactant to solution C, in order to obtain an aqueous emulsion containing a PTFE-based resin.

[0098] -Other Monomers- Step D may also use other monomers besides TFE. Examples of other monomers include monomers having polar groups (hereinafter also referred to as "specific monomer D"). Since the polar groups of specific monomer D interact with aqueous media, specific monomer D can be positioned between TFE and the aqueous media during TFE polymerization and exhibit surfactant-like function. As a result, TFE polymerization proceeds smoothly and the occurrence of chain transfer is suppressed.

[0099] Examples of polar groups that specific monomer D may possess include sulfonic acid groups, sulfonic acid bases, carboxylic acid groups, carboxylic acid bases, phosphonic acid groups, and phosphonic acid bases. The group represented by formula (A) or formula (B) is preferred because it further suppresses the formation of fluorine-based oligomers.

[0100] -SO ３ M (A) - COOM (B)

[0101] In formulas (A) and (B), M is independently a hydrogen atom, NH, etc. ４ Alternatively, it represents an alkali metal atom. Examples of alkali metal atoms include lithium, sodium, and potassium atoms.

[0102] The specific monomer D preferably has polymerizable groups. The number of polymerizable groups is preferably 1 to 3, and more preferably 1. Examples of polymerizable groups include ethylenically unsaturated groups, and are preferably acryloyl groups, methacryloyl groups, vinyl ester groups, vinyl ether groups, vinyl groups, or allyl groups, and more preferably acryloyl groups, methacryloyl groups, vinyl ester groups, or vinyl ether groups.

[0103] In terms of further suppressing the formation of fluorine-based oligomers, the monomer represented by formula (P) is preferred as the specific monomer D.

[0104] CR ３１ R ３２ =CR ３３ -L ３ -R ３４ (P)

[0105] In formula (P), R ３１ and R３２ Each independently represents a hydrogen atom or a fluorine atom.

[0106] R ３３ represents a hydrogen atom, a fluorine atom or an alkyl group which may be substituted by a fluorine atom. A hydrogen atom or a fluorine atom is preferable in that the polymerizability with TFE is better. The alkyl group which may be substituted by a fluorine atom means an alkyl group in which at least one hydrogen atom in the alkyl group may be substituted by a fluorine atom. The number of carbon atoms of the alkyl group which may be substituted by a fluorine atom is preferably 1 to 3, more preferably 1.

[0107] L ３ represents a single bond or a divalent linking group. A single bond is preferable in that the polymerizability with TFE is better. Examples of the divalent linking group include a divalent hydrocarbon group, a divalent heterocyclic group, -O-, -S-, -SO ２ -, -CO-, -Si(R ａ ) ２ -, -N(R ｂ )- and groups formed by combining two or more of these. R ａ represents an alkyl group (preferably an alkyl group having 1 to 10 carbon atoms) or a phenyl group. R ｂ represents a hydrogen atom or an alkyl group (preferably an alkyl group having 1 to 10 carbon atoms). Examples of the divalent hydrocarbon group include a divalent saturated hydrocarbon group, a divalent aromatic hydrocarbon group, an alkenylene group and an alkynylene group. The divalent saturated hydrocarbon group may be linear, branched or cyclic. Examples of the divalent saturated hydrocarbon group include an alkylene group, and an alkylene group having 1 to 20 carbon atoms is preferable. The divalent aromatic hydrocarbon group preferably has 6 to 20 carbon atoms, and a phenylene group is more preferable. The alkenylene group preferably has 2 to 20 carbon atoms. The alkynylene group preferably has 2 to 20 carbon atoms. Examples of the group formed by combining two or more of these include -OC(O)-, -C(O)N(R ｂ )-, an alkylene group -O- alkylene group, an alkylene group -OC(O)- alkylene group, and an alkylene group -Si(Rａ ) ２ - Phenylene group - Si (R ａ ) ２ Examples include the divalent hydrocarbon group. Furthermore, the divalent hydrocarbon group may have substituents. Examples of substituents include halogen atoms such as fluorine atoms and chlorine atoms.

[0108] R ３４ This represents the group represented by formula (A) or the group represented by formula (B) above.

[0109] The monomer represented by formula (P) is preferably one of the monomers represented by formulas (P-1) to (P-6), and more preferably the monomer represented by formula (P-1).

[0110] CR ３１ R ３２ =CR ３３ -R ３４ (P-1) CR ３１ R ３２ =CR ３３ - (CF ２ ) ｍ１ -R ３４ (P-2) CR ３１ R ３２ =CR ３３ - (CF ２ C (CF ３ ) F) ｍ２ -R ３４ (P-3) CR ３１ R ３２ =CR ３３ -O-(CFR) ３５ ) ｍ３ -R ３４ (P-4) CR ３１ R ３２ =CR ３３ -O-(CF ２ CFR ３５ O) ｍ４ -CF ２ CF ２ -R ３４ (P-5) CR ３１ R ３２ =CR ３３ -CF ２ -O-(CF(CF ３ ) CF ２ O) ｍ５-CF (CF ３ )-R ３４ (P-6)

[0111] In formulas (P-1) to (P-6), R ３１ ~R ３４ The definition is as described above. In equation (P-2), m1 represents an integer from 1 to 10. In equation (P-3), m2 represents an integer from 1 to 5. In equation (P-4), m3 represents an integer from 1 to 10. R ３５ is a fluorine atom or CF ３ This represents... In equation (P-5), m4 represents an integer from 1 to 10. ３５ The definition is as stated above. In equation (P-6), m5 represents an integer between 0 and 10.

[0112] An example of specific monomer D is ammonium vinylsulfonate.

[0113] -Polymerization Initiator- A polymerization initiator may be used in step D. In other words, a polymerization initiator may be used during the polymerization of TFE. An example of a polymerization initiator is the polymerization initiator used in step C. 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 1.50% by mass, and even more preferably 0.20 to 1.00% by mass, based on the total mass of TFE supplied to the polymerization system.

[0114] - Stabilizing agent - Step D may use a stabilizing agent. Examples of stabilizing agents include the stabilizing agent used in step A.

[0115] -Other Monomers- Step D may use monomers other than TFE and specific monomer D. In terms of superior properties of the PTFE-based resin powder, 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 D. The upper limit is preferably 100% by mass or less.

[0116] -Procedure for Step D- During Step D, no surfactant is substantially added to Solution C. In other words, in Step D, TFE polymerization is carried out in Solution C without substantially adding any new surfactant to Solution C. A surfactant is a compound having hydrophilic groups (e.g., polar groups) and hydrophobic groups (e.g., hydrocarbon groups). The definition of a polar group is the same as the definition of a polar group possessed by specific monomer D. Examples of surfactants include known surfactants, nonionic surfactants and ionic surfactants, and hydrocarbon-containing surfactants or fluorinated surfactants are preferred. In Step D, it is preferable not to substantially add at least one selected from the group consisting of hydrocarbon-containing surfactants and fluorinated surfactants to Solution C. The above "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 C. There is no particular lower limit, but 0 ppm by mass or more is preferred. In other words, it is preferable not to add a surfactant to Solution C in Step D.

[0117] TFE is introduced into the polymerization system (e.g., polymerization reaction vessel, etc.) by conventional methods. For example, TFE may be introduced into the polymerization system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. The polymerization initiator may be added to the reaction system all at once or in portions.

[0118] When using specific monomer D, the amount of specific monomer D used is preferably 0.150% by mass or less relative to the total mass of TFE. 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. In terms of the stability of the emulsion during polymerization, the amount of specific monomer D used is preferably 0.100% by mass or less, and more preferably 0.090% by mass or less, relative to the total mass of TFE. Furthermore, in terms of improving molecular weight, the lower limit 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.

[0119] When using specific monomer D, the amount of specific monomer D used is preferably 0.150 mol% or less relative to the total number of moles of TFE. In other words, the amount of specific monomer D added relative to the total amount of TFE is preferably 0.150 mol% or less. In terms of the stability of the emulsion during polymerization, the amount of specific monomer D used is preferably 0.100 mol% or less, and more preferably 0.090 mol% or less, relative to the total number of moles of TFE. Furthermore, in terms of improving molecular weight, the lower limit 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.

[0120] 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.

[0121] Furthermore, steps C and D may be carried out continuously in the same polymerization reaction vessel. In addition, in the first embodiment, it is sufficient that the specific polymer C is formed in step C, and step D may be carried out before the non-fluorinated monomer is completely consumed in step C.

[0122] The above procedure yields an aqueous emulsion in which PTFE resin is dispersed in particulate form (an aqueous emulsion containing PTFE resin). The concentration of PTFE resin 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 PTFE resin in the aqueous emulsion can be more easily coagulated, and turbidity of the coagulated liquid can be suppressed. The average primary particle size of the PTFE resin in the aqueous dispersion is preferably 100 to 500 nm, and more preferably 150 to 300 nm. The average primary particle size of the PTFE resin is the volume-based particle size D50 (median diameter) measured by a laser scattering particle size distribution analyzer.

[0123] (Process E) Process E is a process to obtain PTFE-based resin powder from the aqueous emulsion obtained in process D. Process E can be carried out using the procedure and conditions of process B.

[0124] <Second Embodiment> The method for producing PTFE-based resin powder may also be the second embodiment. The second embodiment is a method for producing PTFE-based resin powder, comprising the following steps F and G. Step F: A step of polymerizing a monomer containing TFE (hereinafter also referred to as "specific monomer F") in an aqueous dispersion containing an aqueous medium and a first fluorine-containing polymer to obtain an aqueous dispersion containing a PTFE-based resin different from the first fluorine-containing polymer. Step G: A step of obtaining PTFE-based resin powder from the aqueous dispersion obtained in step F. Furthermore, the second embodiment may include the above-mentioned other steps after step G, as it is easier to adjust the cumulative aspect ratio of 50% and the cumulative ratio of particles with an aspect ratio of less than 0.30. As described above, examples of other steps include freeze-machining and classification. The other steps are preferably carried out after step G, and it is more preferable to carry out the freeze-machining and classification in that order after step G.

[0125] (Step F) Step F is a step in which a specific monomer F is polymerized in an aqueous dispersion containing an aqueous medium and a first fluorine-containing polymer to obtain an aqueous dispersion containing a PTFE-based resin different from the first fluorine-containing polymer.

[0126] -Aqueous media- Examples of aqueous media include the aqueous media used in process A.

[0127] -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.

[0128] The glass transition temperature 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, in terms of efficient adsorption of the specific monomer F. The lower limit is preferably -50°C or higher, more preferably -45°C or higher, and even more preferably -40°C or higher, in terms of thermal stability after molding. The glass transition temperature range 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 glass transition temperature of the first fluorine-containing polymer is measured by differential scanning calorimetry (DSC). A method for bringing the glass transition temperature of the first fluorine-containing polymer within the above range is, for example, by adjusting the type and amount of monomer used in the production of the first fluorine-containing polymer.

[0129] 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 glass transition temperature to the above range.

[0130] PAVE is preferred as a 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 PTFE-based resins.

[0131] When the first fluorine-containing polymer contains TFE units and PAVE units, the amount of PAVE units is preferably 20 to 60 mol%, more preferably 25 to 60 mol%, and even more preferably 30 to 55 mol%, relative to the total number of moles of TFE units and PAVE units, in order to easily adjust the glass transition temperature within the first fluorine-containing polymer and to produce PTFE-based resins more efficiently.

[0132] 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 PTFE-based resins 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 of the total units of the first fluorine-containing polymer, and 0 mol% is more preferable. HFP is preferred as the other monomer.

[0133] Before initiating the polymerization of the monomer used in the polymerization of the PTFE resin, the content of the first fluorine-containing polymer is preferably 0.01 to 4.0% by mass, more preferably 0.01 to 0.6% by mass, and even more preferably 0.01 to 0.5% by mass, based on the total mass of the aqueous medium in the aqueous dispersion.

[0134] In this specification, "before starting the polymerization of the monomer used for polymerization of PTFE-based resins" means immediately before the start of polymerization. Here, "the start of polymerization" refers to the time when the monomer and polymerization initiator are brought into the reactor after the reactor has been heated to or above the polymerization temperature, and the time when the reactor is heated to or above the polymerization temperature after the monomer and polymerization initiator have been brought into the reactor.

[0135] The first fluorine-containing polymer is preferably dispersed in an aqueous medium in the form of particles. 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, in order to produce PTFE-based resin more efficiently. The average particle size of the first fluorine-containing polymer is determined by measuring the particle size distribution by laser diffraction / scattering, calculating the cumulative curve with the total volume of the particle collection set to 100%, and finding the particle size at the point on the cumulative curve where the cumulative volume is 50% (median diameter D50).

[0136] 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 to it 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.

[0137] 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, or 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.

[0138] Examples of aqueous media used in the production of the first fluorine-containing polymer include the aqueous media used in step A. 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 monomer used for the polymerization of the PTFE resin, 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.

[0139] 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 PTFE resin less susceptible to the influence of the polymerization initiator used in the production of the first fluorine-containing polymer. As a result, a PTFE resin with a high 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, as this further promotes the deactivation of the polymerization initiator in the aqueous medium.

[0140] -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.

[0141] The specified monomer F may contain fluorine-containing monomers other than TFE, or it may not contain substantially any 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 the specified monomer F used, and may even be 0% by mass. Examples of fluorine-containing monomers other than TFE include chlorotrifluoroethylene, VdF, fluoroalkylethylene, PAVE, and HFP.

[0142] The specific 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 specific monomer F used, and 0% by mass is preferable. Examples of other monomers include ethylene, propylene, vinyl chloride, and vinylidene chloride.

[0143] 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.

[0144] -Polymerization Initiator- In step F, it is preferable to polymerize a specific monomer F in the presence of a polymerization initiator. Examples of polymerization initiators include the water-soluble radical polymerization initiator used in step A.

[0145] 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, per 100 parts by mass of the specific monomer F used.

[0146] -Other Components- The aqueous dispersion may contain other components besides the aqueous medium and the first fluorine-containing polymer. Examples of other components include chain transfer agents, emulsifiers other than fluorine-based emulsifiers, pH adjusters, waxes, and reducing agents.

[0147] Examples of chain transfer agents include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane.

[0148] Examples of emulsifiers other than fluorine-based emulsifiers include sodium lauryl sulfate, Perex SS-H (manufactured by Kao Chemical Co., Ltd.), and Newcol 1305-SN (manufactured by Nippon Emulsifier Co., Ltd.).

[0149] Examples of pH adjusting agents include inorganic salts. Examples of inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate, and carbonates such as sodium bicarbonate and sodium carbonate, with disodium hydrogen phosphate dihydrate or disodium hydrogen phosphate dodecahydrate being preferred.

[0150] Examples of waxes include Paraffin Wax-155 and Paraffin Wax-150 (both manufactured by Nippon Seiro).

[0151] Before initiating the polymerization of monomers used in the polymerization of PTFE resins, the concentration of the fluorine-based emulsifier is preferably 100 ppm by mass or less, more preferably 50 ppm by mass or less, even more preferably 25 ppm by mass, and particularly preferably 5 ppm by mass or less, relative to the total mass of the first fluorine-containing polymer in the aqueous dispersion. The lower limit is preferably 0 ppm by mass or more. 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. 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, for example, a method of producing an aqueous dispersion without using a fluorine-based emulsifier.

[0152] Before initiating the polymerization of the monomer used to obtain the PTFE resin, 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, in terms of polymerization stability. The lower limit is preferably 0 ppm by mass or more. An example of a method for achieving the above-mentioned concentration of fluoride ions is, for example, a method of removing fluoride ions using an anion exchange resin during the production of the first fluorine-containing polymer.

[0153] -Procedure for Step F- Step F involves polymerizing the specific monomer F in the aqueous dispersion to produce a PTFE-based resin.

[0154] The PTFE-based resin obtained by step F is as described above. The first fluorine-containing polymer and the PTFE-based resin may be copolymerized.

[0155] The specific monomer F is introduced into the polymerization system (e.g., a polymerization reaction vessel) by a conventional method. For example, the specific monomer F may be introduced into the polymerization 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. 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 under conditions where emulsifiers are substantially absent. Examples of emulsifiers include known emulsifiers (surfactants). Conditions where emulsifiers are substantially absent mean 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, and in the second embodiment, it is considered that particles containing the first fluorine-containing polymer and the PTFE-based resin are produced. That is, according to the second embodiment, it is presumed that the PTFE-based resin powder is obtained in the form of particles containing the first fluorine-containing polymer and the PTFE-based resin. In this case, according to the second embodiment, an aqueous dispersion is obtained in which particles containing the first fluorine-containing polymer and the PTFE-based resin are dispersed. In the aqueous dispersion, the average primary particle diameter of the PTFE-based resin is preferably 100 to 500 nm, and more preferably 150 to 300 nm. The average primary particle diameter of the PTFE-based resin is the volume-based particle diameter D50 (median diameter) measured by a laser scattering particle size distribution analyzer.

[0159] (Process G) Process G is a process for obtaining PTFE-based resin powder from the aqueous dispersion obtained in process F. Process G can be carried out using the procedures and conditions of process B.

[0160] [Electrode Mixture] The electrode mixture of the present invention comprises a PTFE-based resin powder and an active material. Furthermore, when the electrode mixture is a negative electrode mixture, it is preferable that the negative electrode mixture comprises a PTFE-based resin powder and a negative electrode active material. When the electrode mixture is a positive electrode mixture, it is preferable that the positive electrode mixture comprises a PTFE-based resin powder and a positive electrode active material.

[0161] <PTFE-based resin powder> The electrode mixture contains PTFE-based resin powder. The PTFE-based resin powder is the same as the PTFE-based resin powder of the present invention, and the preferred embodiments are also the same.

[0162] The content of PTFE-based resin powder is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% 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 20% by mass or less, and particularly preferably 10% by mass or less. The range is preferably 0.1 to 50% by mass, more preferably 0.1 to 30% by mass, even more preferably 0.5 to 20% by mass, even more preferably 1 to 20% by mass, and particularly preferably 1 to 10% by mass. Within the above range, the retention of the 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 PTFE-based resin powder has excellent binding strength, even a small amount can sufficiently retain the active material in the electrode mixture.

[0163] <Active Material> The electrode mixture contains an active material. Examples of active materials include a positive electrode active material and a negative electrode active material, which can be appropriately selected according to the desired electrode.

[0164] The active material content is preferably 50 to 99.5% by mass, more preferably 60 to 99.0% by mass, and even more preferably 70 to 96.0% by mass, relative to the total mass of the electrode mixture, in order to increase the battery capacity. In another embodiment, 80 to 99.9% by mass is preferred, and 88 to 96.0% by mass is more preferred.

[0165] (Positive Electrode Active Material) When the electrode mixture is a positive electrode mixture, the positive electrode mixture contains a positive electrode active material. The positive electrode active material is not particularly limited as long as it can reversibly perform intercalation of lithium ions, intercalation of lithium ions, or doping and dedoping of lithium ions with counteranions. Examples of positive electrode active 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 nickelmanganate, composite metal oxides, or polyanion olivine type positive electrode materials being preferred. Due to its high average discharge voltage and low cost, the positive electrode active material may also be a lithium-containing transition metal oxide. Examples of composite metal oxides include nickel-manganese-cobalt oxide. Examples of nickel-manganese-cobalt oxide include 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 ０．３３ Co ０．３３ Mn ０．３３ O ２ (Hereinafter also referred to as "NMC111") is more preferable.

[0166] 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.

[0167] Examples of positive electrode active material shapes include lumpy, polyhedral, spherical, ellipsoidal, plate-like, needle-like, and columnar shapes. Furthermore, the positive electrode active material may be either primary or secondary particles.

[0168] The volume-based particle size D50 (median diameter) of the positive electrode active material is preferably 0.3 μm or larger, more preferably 0.5 μm or larger, and even more preferably 1.0 μm or larger. The upper limit is preferably 30 μm or smaller, and more preferably 25 μm or smaller. 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. 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. Two or more positive electrode active materials with different particle sizes D50 may be mixed as the positive electrode active material in terms of improving packing performance during positive electrode fabrication. The particle size D50 is measured by a known laser diffraction / scattering particle size distribution analyzer.

[0169] The BET specific surface area of ​​the positive electrode active material is 0.1 m². ２ Preferably 0.3 m ２ A 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 30m ２ / g is more preferable.

[0170] 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.

[0171] (Negative Electrode Active Material) When the electrode mixture is a negative electrode mixture, the negative electrode mixture includes a negative electrode active material. The negative electrode active material is not particularly limited as long as it can reversibly carry out, for example, intercalation of lithium ions, desorption and insertion of lithium ions, or doping and dedoping of lithium ions with counteranions. Examples of negative electrode active materials include 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; lithium titanate; and lithium metal.

[0172] 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 SiOx, or mixtures thereof. Silicon oxide is a general term for amorphous silicon oxides. x is 0.5 ≤ x ≤ 1.6, preferably 0.8 ≤ x < 1.6, and more preferably 0.8 ≤ x < 1.3. 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.

[0173] 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. Coating with a carbon film is preferred, and coating with a carbon film using chemical vapor deposition (CVD) is more preferred.

[0174] Examples of the negative electrode active material's shape include lumpy, polyhedral, spherical, ellipsoidal, plate-like, needle-like, and columnar shapes. Furthermore, the negative electrode active material may be either primary or secondary particles.

[0175] The volume-based particle size D50 (median diameter) of the negative electrode active material is preferably 0.1 to 50 μm, more preferably 0.2 to 30 μm, and even more preferably 0.5 to 20 μm. The particle size D50 can be measured using the same method as for the positive electrode active material.

[0176] 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 using the same method as for the positive electrode active material.

[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, and even more preferably 1% 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 20% by mass or less, 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 1 to 20% by mass, even more preferably 1 to 15% by mass, and particularly preferably 1 to 10% by mass.

[0179] <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.

[0180] <Other Components> The electrode mixture may contain other components besides the above-mentioned components. Examples of other components include solid electrolytes, binders other than PTFE-based resin powders, conductive materials, thickeners, and additives. The electrode mixture preferably contains a solid electrolyte, and more preferably a sulfide-based solid electrolyte. Examples of solid electrolytes include sulfide-based solid electrolytes having an argyrodite-type crystal structure, oxide-based solid electrolytes, and halogenated solid electrolytes. Examples of solid electrolytes include solid electrolytes that constitute secondary batteries as described later. When the electrode mixture contains a solid electrolyte (preferably a sulfide-based solid electrolyte), the content of PTFE-based resin powder is preferably 1 to 20% by mass, more preferably 1 to 15% by mass, and particularly preferably 1 to 10% by mass, relative to the total mass of the solid electrolyte (preferably a sulfide-based solid electrolyte). Furthermore, if the electrode mixture contains a solid electrolyte (preferably a sulfide-based solid electrolyte), the content of the solid electrolyte (preferably a sulfide-based solid electrolyte) is preferably 1 to 30% by mass, and more preferably 1 to 20% by mass, relative to the total mass of the electrode mixture.

[0181] Examples of binders other than PTFE-based resin 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 PTFE-based resin powder. Furthermore, adding fibrous components to the electrode mixture tends to increase the strength of the resulting sheet.

[0182] The electrode mixture is preferably substantially free of organic solvents. Specifically, the organic solvent content is preferably 1.0% by mass or less, and more preferably 0.1% by mass or less, relative to the total mass of the electrode mixture. The lower limit is preferably 0% by mass or more.

[0183] In the case where the electrode mixture contains PTFE-based resin powder, an active material, and a conductive additive, the content of the PTFE-based resin powder is preferably 1 to 20% by mass of the total mass of the electrode mixture, the content of the active material is preferably 70 to 96% by mass of the total mass of the electrode mixture, and the content of the conductive additive is preferably 1 to 20% by mass of the total mass of the electrode mixture. In another embodiment, the content of the PTFE-based resin powder is preferably 1 to 10% by mass of the total mass of the electrode mixture, the content of the active material is preferably 88 to 96% by mass of the total mass of the electrode mixture, and the content of the conductive additive is preferably 1 to 10% by mass of the total mass of the electrode mixture.

[0184] The electrode mixture is preferably in sheet form.

[0185] The electrode mixture can be suitably used as an electrode mixture for secondary batteries. In particular, the electrode mixture is suitable for lithium-ion secondary batteries. When used in secondary batteries, the electrode mixture is used, for example, in a sheet-like form (electrode layer).

[0186] [Method for Manufacturing Electrode Mixture] The method for manufacturing the electrode mixture is not particularly limited as long as it is a method that can manufacture the above-mentioned electrode mixture. A preferred method for manufacturing the electrode mixture includes a step X1 of grinding and mixing a raw material composition containing a binder containing PTFE-based resin powder, an active material, and, if necessary, a conductive additive. With the above method for manufacturing the electrode mixture, the electrode mixture can be obtained in a relatively short number of steps. Furthermore, it is also preferable that the method for manufacturing the electrode mixture further includes a step X2 of rolling the raw material composition ground and mixed in step X1 into a sheet. When step X2 is included, a sheet-like electrode mixture (electrode layer) can be obtained.

[0187] <Step X1> Step X1 is a step of grinding and mixing a raw material composition containing a binder containing PTFE resin powder, an active material, and a conductive additive as needed. A mixing method using a mixing device is preferred. Examples of mixing devices include a jet mill, pin mill, blender, twin-screw extruder, and mixer. The mixing conditions are not particularly limited and can be adjusted as appropriate according to the target electrode mixture.

[0188] A jet mill is generally a device that uses high-pressure air or gas to pulverize powders by causing them to collide with each other or with the inner wall of the mill at high speed. Examples of jet mills include the impact type, which pulverizes by colliding particles with each other or with a target; the swirling airflow type and loop type, which pulverize by mutual collision of particles in a pulverizing zone formed by multiple pulverizing nozzles arranged in a circulating airflow; the fluidized bed type, which pulverizes by collision and friction between particles in a fluidized bed; and the supersonic type. Examples of impact type, swirling airflow type, loop type, and fluidized bed type jet mills include those described on page 162 of "Advanced Pulverizing Technology and Applications," edited by the Japan Powder Industry Technology Association, published by NGT Co., Ltd.

[0189] The grinding pressure of the jet mill is preferably 0.1 to 2.0 MPaG, and more preferably 0.2 to 0.9 MPaG, in order to achieve both crushing efficiency and suppression of fiber formation.

[0190] <Process X2> Process X2 is a process in which the raw material composition crushed and mixed in process X1 is rolled into a sheet. The rolling method in process X2 can be a roll press, a flat plate press, or a calender roll machine. The rolling conditions are not particularly limited and can be appropriately selected according to the desired thickness and density of the electrode mixture.

[0191] <Other Processes> The method for producing the electrode mixture may include other processes besides the above-described steps X1 and X2. Examples of other processes include a pre-mixing process. It is preferable to perform the pre-mixing process before step X1. Examples of pre-mixing processes include mixing the raw material composition using a V-blender. Pre-mixing means a process in which the raw material composition containing PTFE-based resin powder and active material, etc., is uniformly mixed without causing the PTFE-based resin powder to become fibrous.

[0192] [Electrode Layer] The electrode layer of the present invention is a layer containing the above-mentioned electrode mixture. The electrode layer may be either a positive electrode layer or a negative electrode layer, and can be appropriately selected depending on the active material contained in the electrode mixture.

[0193] The density of the positive electrode layer is 3.00 g / cm³. ３The 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 3.80 g / cm³. ３ The following is preferable: 3.75 g / cm³ ３ The following is more preferable: 3.70 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 1.30 g / cm³. ３ The above is preferable, specifically 1.40 g / cm³. ３ The above is more preferable, specifically 1.50 g / cm³. ３ The above is even more preferable. The upper limit is 2.00 g / cm³. ３ The following is preferable: 1.90 g / cm³ ３ The following is more preferable: 1.80 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 interface between the current collector and the active material is excellent, and the charge-discharge characteristics at high current densities can be particularly excellent. Furthermore, the conductivity between the active materials can also be excellent.

[0194] The thickness of the electrode layer (positive electrode layer or 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.

[0195] [Electrode] The electrode of the present invention includes a current collector and an electrode layer containing an electrode mixture disposed on the current collector. A conductive carbonaceous material may be placed between the current collector and the electrode layer as needed. The electrode layer is as described above.

[0196] <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, as well as their alloys; or a carbon material such as carbon cloth and carbon paper. A metallic material is preferred, and aluminum or its alloy 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, as well as their alloys; or a carbon material such as carbon cloth and carbon paper. A metallic material is preferred, and copper, nickel, or its alloy is more preferred.

[0197] Examples of current collector shapes include metal foil, metal cylinder, metal coil, metal plate, 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, with metal foil being preferred. 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. 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. Within the above range, excellent handling and strength can be obtained.

[0198] Furthermore, it is preferable that a conductive additive is applied to the surface of the current collector in order to reduce 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.

[0199] [Secondary Battery] The secondary battery of the present invention includes the electrodes described above. The secondary battery may be a secondary battery that uses 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.

[0200] 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.

[0201] Rechargeable batteries can take various shapes, such as cylindrical, prismatic, laminated, coin-type, and large. Furthermore, the shapes and configurations of the positive electrode, negative electrode, and separator can be modified according to the specific battery shape.

[0202] Examples of separators include porous membranes such as polyethylene and polypropylene; nonwoven fabrics made of resins such as polypropylene; and nonwoven fabrics such as 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. Resins, glass fibers, or inorganic materials are preferred as the material of the separator. The shape of the separator is preferably a porous sheet or a 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.

[0203] 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.

[0204] The solid-state secondary battery is preferably an all-solid-state secondary battery, and more preferably a lithium-ion all-solid-state 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 and negative electrodes.

[0205] The solid electrolyte used in the mixture for solid-state secondary batteries may be either a sulfide-based solid electrolyte or an oxide-based solid electrolyte.

[0206] Examples of sulfide-based solid electrolytes include Li ２ S-P ２ S ５ Li ２ S-P ２ S ３ Li ２ S-P ２ S ３ -P ２ S ５ Li ２ S-SiS ２ LiI-Li ２ S-SiS ２ LiI-Li ２ S-P ２ S ５ LiI-Li ２ S-P ２ O ５ LiI-Li ３ PO ４ -P ２ S ５ LiI-Li ２ S-SiS ２ -P ２ S ５ Li ２ S-SiS ２ -Li ４ SiO ４ Li ２ S-SiS ２ -Li ３ PO ４ Li ３ PS ４ -Li ４ GeS ４ Li ３．４ P ０．６ Si ０．４ S ４ Li ３．２５ P ０．２５ Ge０．７６ 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 Examples include (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5), and mixtures of two or more of these. 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.

[0207] As an oxide-based solid electrolyte, a compound containing an oxygen atom, possessing ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and having electronic insulating properties is preferred. For example, 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 ｃｃ ｚｃ O ｎｃ (M ｃｃ (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.) Liｘｄ (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） N ｗ (where w < 1), Li has a LISICON (Lithium superionic conductor) 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 superionic conductor) type crystal structure ２ P ３ O１２ 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. Also, ceramic materials in which elemental substitution has been performed on LLZ are also examples. For example, an LLZ-based ceramic material is one 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 on LLZ. Also, phosphorus compounds containing Li, P and O are preferred. 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 the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, and Au. Also, LiA １ ON (A １ This also includes at least one selected from the group consisting of Si, B, Ge, Al, C, and Ga. For example, Li ２ O-Al ２ O ３ -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.

[0208] Oxide-based solid electrolytes preferably contain 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.

[0209] The present invention will be described in detail below with reference to examples. Examples 1 to 4 and 9 are examples, and Examples 5 to 8 and 10 are comparative examples. However, the present invention is not limited to these examples.

[0210] [Measurement and Evaluation Methods] The various measurement and evaluation methods are as follows.

[0211] <Cumulative 50% Aspect Ratio, Cumulative Ratio of Particles with an Aspect Ratio Less Than 0.3, and Particle Size D50> The PTFE resin powders obtained in each of the examples described below (PTFE resin powders used in the electrode mixtures of each example) were first sieved through a mesh opening of 2360 μm, and then the aspect ratio distribution based on the cumulative number of particles constituting the PTFE resin powder was obtained using Morphologie 4 (Malvern Panarytic) under the following conditions. The cumulative 50% aspect ratio, the cumulative ratio of particles with an aspect ratio less than 0.3, and the particle size D50 were calculated.

[0212] (Measurement conditions) Microscope magnification: 2.5x Trash size: 25 Segmentation type: fs sharp edge Number of measured particles: 10,000 or more Filter: Envelopment degree 0.9

[0213] <Average Primary Particle Size (PPS) of PTFE Resin Powder> The aqueous dispersions obtained in each of the examples described below were used as measurement samples, and the PPS was measured using a laser diffraction / scattering particle size distribution analyzer LA-920 (manufactured by Horiba, Ltd.).

[0214] <Proportion of each unit in PTFE resin powder> The proportion of each unit in the PTFE resin that constitutes the PTFE resin powder obtained in the examples described below is: １９ The results were obtained using F-NMR analysis and infrared absorption spectroscopy.

[0215] <Solid content concentration of aqueous dispersions> The solid content concentration of the aqueous dispersions obtained in each of the examples described below was determined by weighing the mass of the residue after heating the aqueous dispersion (2.0 g) at 170°C for 20 minutes and using the following formula.

[0216] Solid content concentration (mass%) of aqueous dispersion = 100 × mass of residue after heating (g) / mass of aqueous dispersion before heating (2.0g)

[0217] <Storage Stability> The PTFE resin powder obtained in each of the following examples (50 g of the PTFE resin powder used in the electrode mixture in each example) was placed in a plastic container and stored at 5°C for one month. The state of the PTFE resin powder thereafter was observed, and the storage stability was evaluated according to the following evaluation criteria. "A": No aggregates were observed in the PTFE resin powder after storage. "B": Aggregates were observed in the PTFE resin powder after storage, but they were easily dissolved. "C": The entire PTFE resin powder after storage became a loose mass and could not be easily dissolved.

[0218] <Sheet Thinning> The thickness of the sheets obtained in each of the examples described below was measured, and the thinning of the sheets was evaluated according to the evaluation criteria below. In cases where the sheet thickness was non-uniform, the thickest part was measured.

[0219] "A": The sheet thickness was 250 μm or less. "B": The sheet thickness was between 250 μm and 350 μm. "C": The sheet thickness was greater than 350 μm.

[0220] <Sheet Breakage> We checked for breakage in the sheet fabrication process for each example described below.

[0221] "A": The sheet did not rupture. "B": The sheet did rupture.

[0222] [Example 1] <Preparation of PTFE resin powder> In a 100L stainless steel autoclave equipped with baffles and a stirrer, C ２ F ５ OC ２ F ４ OCF ２ COONH ４(Ammonia perfluoro-3,6-dioxaoctanoate, hereafter also called "APFDO") (70g), paraffin wax (872g), and deionized water (59L) were added. After purging the autoclave with nitrogen and reducing the pressure, CH4 was used. ２ = CH - (CF ２ ) ４ F (PFBE, 2g) and deionized water (300g) were added by suction. Next, the mixture was pressurized with TFE and heated to 70°C while stirring. Then, the pressure was increased to 1.765 MPa with TFE, and 5.0g of disuccinic acid peroxide (80% by mass, the remainder being water) dissolved in approximately 70°C warm water (1L) was added. The internal pressure dropped to 1.746 MPa in 453 seconds. Polymerization was then carried out while adding TFE to maintain the autoclave internal pressure at 1.765 MPa. A total of 125g of APFDO dissolved in warm water was added during polymerization. In addition, a total of 4g of ammonium sulfite dissolved in water was added during polymerization. The temperature was lowered to 65°C during the process and then raised to 90°C in the latter half of polymerization. The reaction was terminated when the amount of TFE added reached 23 kg, and 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 on the supernatant was removed to obtain aqueous dispersion A containing PTFE resin. The solid content concentration of the obtained aqueous dispersion A was 26% by mass, and the average primary particle size of the PTFE resin was 0.25 μm.

[0223] Next, aqueous dispersion A was diluted with pure water to a concentration of 10% by mass, the temperature was adjusted to 20°C, and the mixture was stirred to cause coagulation to obtain a PTFE-based wet resin. The PTFE-based wet resin was then dried at 180°C to obtain PTFE-based resin powder 1A.

[0224] <Freezing and Machining Process> A rotor speed mill P-14 (manufactured by Fritsch) was fitted with six impact rotor blades and rotated at 6000 rpm. Liquid nitrogen was added to PTFE resin powder 1A and mixed, and the mixture was left to stand for 2 minutes before being introduced into the mill. Freezing and machining was performed in one pass, and the mixture was recovered from the bag filter to obtain PTFE resin powder 1B.

[0225] <Classification Process> The obtained PTFE-based resin powder 1B was subjected to a standing experiment with LabClassil N-01 (manufactured by Seishin Corporation) at 5°C for at least one day. After that, an air volume of 1 m³ was added. ３ Classification (centrifugal classification) was performed at a rate of 1 kg / min under the conditions of 1 kg / min and a rotor rotation speed of 2000 rpm. Fine powder was removed, and coarse powder was collected to obtain PTFE-based resin powder 1C.

[0226] Furthermore, when the proportion of each unit in the PTFE resin constituting the PTFE resin powders 1A, 1B, and 1C was measured using the method described above, the TFE unit content in each PTFE resin was 99% by mass or more relative to the total units of each PTFE resin.

[0227] <Preparation of Electrode Mixture> 400 g each of NMC622 (manufactured by Hosen Co., Ltd., average particle size 10 μm, positive electrode active material), PTFE-based resin powder 1C, and acetylene black (manufactured by Sigma-Aldrich) were placed in a V-type mixer VK-1 (manufactured by Irie Shoji Co., Ltd.) in a mass ratio of 96:3:1 and mixed at 60 rpm for 10 minutes to obtain the mixture. Subsequently, the above mixture was crushed 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). Using a roll press device, the obtained electrode mixture (50 g) was processed under the following conditions: metal roll diameter φ60 mm, roll temperature 120°C, roll gap 200 μm, roll speed 1 m / min, roll peripheral speed difference 1:10, and load 3 t, to obtain a sheet (electrode layer) with a width of 150 mm and a length of 3 m.

[0228] [Examples 2-4, 6-8] Examples 2-4 and 6-8 were obtained using the same procedure as in Example 1, except that the classification and freeze-machining conditions shown in the table below were changed for the PTFE resin powder 1A obtained in Example 1. When the proportion of each unit in the PTFE resin constituting each PTFE resin powder was measured using the method described above, the TFE unit content in all PTFE resins was 99% by mass or more of the total units in each PTFE resin.

[0229] [Example 5] In Example 5, a sheet was obtained using the same procedure as in Example 1, except that the PTFE-based resin powder Z obtained by the method described below was used without undergoing classification or freeze-machining treatment. A stainless steel autoclave with a capacity of 6 L, equipped with a stainless steel stirring blade and a temperature control jacket, contained deionized water (3480 g), paraffin wax (100 g), and CF. ３ CF ２ OCF ２ CF ２ OCF ２ COONH ４ (15.75 g), and hydrophilic monomer D (Ammonium 2,3,3,3-tetrafluoro-2-[(1,1,2-trifluoro-2-propenyl)oxy]-Propanoate, structural formula: CH ２ = CFCF ２ OCF (CF ３ ) COONH ４ 35 mg of ammonium persulfate was added, and the autoclave was heated to 70°C while the inside was replaced with nitrogen gas to remove oxygen. TFE was injected under pressure to set the system pressure to 0.78 MPaG, and the system temperature was maintained at 70°C while stirring. Next, an aqueous solution of ammonium persulfate (14.0 mg) dissolved in water (20 g) was injected under pressure with TFE to start the polymerization reaction. As the polymerization reaction progressed, the system pressure decreased, but TFE was added to maintain the system temperature at 70°C and the system pressure at 0.78 MPaG. When 433 g of TFE had been consumed since the start of polymerization, an aqueous solution of hydroquinone (17.0 mg) dissolved in water (20 g) was injected under pressure with TFE as a radical scavenger. Polymerization continued thereafter, and when the amount of TFE polymerized reached 1273 g from the start of polymerization, stirring and TFE supply were stopped, the gas in the system was immediately released to return to atmospheric pressure, the polymerization reaction was terminated, and an aqueous dispersion was obtained. The obtained aqueous dispersion was taken out, cooled, and the paraffin wax was separated to obtain an aqueous dispersion Z containing PTFE resin. The average primary particle size of the PTFE resin in the obtained aqueous dispersion Z containing PTFE resin was 295 nm, and the solid content concentration was 26.5% by mass.

[0230] Next, aqueous dispersion Z was diluted with water to a solid content concentration of 13% by mass, and the PTFE resin was solidified while stirring in a container. The mixture was then filtered to separate the water and obtain a PTFE-based wet resin. The water content of the PTFE-based wet resin was 40% by mass. The obtained PTFE-based wet resin was placed in a stainless steel mesh tray (distribution amount: 2.0 g / cm²). ２ The mesh tray was heat-treated in a hot air circulating electric furnace at 180°C. After 5 hours, the mesh tray was removed and air-cooled to obtain PTFE resin powder Z. The proportion of each unit in the PTFE resin constituting the PTFE resin powder Z was measured using the method described above, and the TFE unit content was 99% by mass or more of the total units of the PTFE resin.

[0231] Furthermore, in Example 8, the evaluation of sheet thinning and sheet rupture was not performed because aggregates formed and the effects of the invention were not achieved.

[0232]

[0233] The evaluation results shown in the table above indicate that the PTFE-based resin powder of the present invention exhibits excellent storage stability. Furthermore, it was confirmed that when a sheet is made using the electrode mixture obtained by mixing with an active material, it is easy to form a thin film and is resistant to breakage. From a comparison of Examples 1 to 4, it was confirmed that the effects of the present invention are superior when the cumulative 50% aspect ratio is between 0.68 and 0.80.

[0234] [Example 9] In an environment with a dew point of -60°C or lower, the mass ratio of sulfide-based solid electrolyte (Fine LPSCl, manufactured by NEI Corporation) with an average particle size of 1 μm, lithium niobate-coated NMC111 particles (positive electrode active material) with an average particle size of 7 μm, a conductive additive (acetylene black, manufactured by Sigma-Aldrich), and PTFE-based resin powder 1C was changed to 20:75:2:3. Otherwise, the mixture and then the electrode mixture (positive electrode mixture) were prepared using the same procedure as in Example 1, and a sheet (electrode layer) was obtained. The obtained sheet was evaluated in the same way as in Example 1, and it was confirmed that it was easy to thin and difficult to break, similar to Example 1.

[0235] [Example 10] A sheet (electrode layer) was obtained using the same procedure as in Example 9, except that PTFE-based resin powder Z from Example 5 was used instead of PTFE-based resin powder 1C from Example 9. The obtained sheet was evaluated in the same way as in Example 1, and it was confirmed that the evaluation for thinning of the sheet was "C" and the evaluation for sheet fracture was "B", similar to Example 5.

Claims

1. A polytetrafluoroethylene resin powder used as a binder for secondary batteries, wherein, in the aspect ratio distribution based on the cumulative number of particles constituting the polytetrafluoroethylene resin powder, the aspect ratio at 50% cumulative is 0.65 to 0.85, and the cumulative proportion of particles with an aspect ratio of less than 0.30 is 10% or less.

2. The polytetrafluoroethylene resin powder according to claim 1, wherein the cumulative 50% aspect ratio is 0.68 to 0.

80.

3. An electrode mixture comprising the polytetrafluoroethylene resin powder described in claim 1 or 2 and an active material.

4. The electrode mixture according to claim 3, further comprising a conductive additive, wherein the content of the polytetrafluoroethylene resin powder is 1 to 20% by mass with respect to the total mass of the electrode mixture, the content of the active material is 70 to 96% by mass with respect to the total mass of the electrode mixture, and the content of the conductive additive is 1 to 20% by mass with respect to the total mass of the electrode mixture.

5. The electrode mixture according to claim 3, further comprising a sulfide-based solid electrolyte, wherein the content of the polytetrafluoroethylene-based resin powder is 1 to 20% by mass relative to the total mass of the sulfide-based solid electrolyte.

6. The electrode mixture according to claim 3, which is in the form of a sheet.

7. An electrode layer comprising the electrode mixture according to claim 3.

8. An electrode comprising a current collector and an electrode layer according to claim 7 disposed on the current collector.

9. A secondary battery comprising the electrode described in claim 8.

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