Polytetrafluoroethylene powder, electrode mixture, electrode, and secondary battery

Abstract

Provided is a polytetrafluoroethylene powder which is mixed with an active material or the like to prepare an electrode mixture, and demonstrates excellent toughness in a sheet obtained by using the electrode mixture. The polytetrafluoroethylene powder is used as a binder for a secondary battery, and contains a polytetrafluoroethylene-based resin and a transition metal element. The content of the transition metal element is 100-1500 ppb by mass with respect to the total mass of the polytetrafluoroethylene powder.

Description

Polytetrafluoroethylene powder, electrode mixture, electrode, and secondary battery

[0001] The present invention relates to a polytetrafluoroethylene powder, an electrode mixture, an electrode, and a secondary battery.

[0002] Secondary batteries such as lithium-ion secondary batteries are used in small, portable electrical and electronic devices such as notebook computers, mobile phones, smartphones, tablet computers, and ultrabooks because of their high voltage, high energy density, low self-discharge and memory effect, and the possibility of ultra-lightweight design. They are also used as on-board power sources for driving automobiles and large stationary power sources.

[0003] Electrodes for nonaqueous electrolyte secondary batteries such as lithium ion batteries are generally produced by applying an electrode mixture containing an active material, a binder, etc., to a current collector. However, in recent years, with the aim of reducing the environmental impact during production and improving oxidation resistance, a dry method has been investigated in which the electrode mixture is stretched and formed into a sheet, which is then attached to a current collector to produce an electrode. The dry method does not require the use of an organic solvent such as N-methyl-2-pyrrolidone.

[0004] Patent Document 1 discloses polytetrafluoroethylene powder used as a binder for electrodes.

[0005] Japanese Patent Application Publication No. 2023-051888

[0006] When the characteristics of a sheet obtained using an electrode mixture containing polytetrafluoroethylene powder and an active material described in Patent Document 1 were evaluated, it was found that there was room for improvement in toughness.

[0007] An object of the present invention is to provide a polytetrafluoroethylene powder that can be mixed with an active material or the like to prepare an electrode mixture, and that can provide a sheet that has excellent toughness using the electrode mixture. Another object of the present invention is to provide an electrode mixture, an electrode, and a secondary battery.

[0008] As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved by the following configurations. [1] Polytetrafluoroethylene powder used as a binder for secondary batteries, comprising a polytetrafluoroethylene resin and a transition metal element, wherein the content of the transition metal element is 100 to 1500 ppb by mass relative to the total mass of the polytetrafluoroethylene powder. [2] The polytetrafluoroethylene powder according to [1], having a charging voltage of -200 to -3000 V. [3] The polytetrafluoroethylene powder according to [1] or [2], having a content of the transition metal element of 200 to 1000 ppb by mass relative to the total mass of the polytetrafluoroethylene powder. [4] The polytetrafluoroethylene powder according to any one of [1] to [3], wherein a hollow cylindrical molded product having an outer diameter of 5 mm and an inner diameter of 4 mm has a withstand voltage of 5 kV or more. [5] The polytetrafluoroethylene powder according to any one of [1] to [4], wherein the content of units based on tetrafluoroethylene relative to the total units of the polytetrafluoroethylene resin is 99% by mass or more. [6] The polytetrafluoroethylene powder according to any one of [1] to [5], wherein the transition metal element is at least one selected from the group consisting of metal elements of Groups 4 to 12 of the long period periodic table excluding technetium, scandium, and yttrium. [7] An electrode mixture comprising the polytetrafluoroethylene powder according to any one of [1] to [6] and an active material. [8] The electrode mixture according to [7], further comprising a sulfide-based solid electrolyte, wherein the content of the polytetrafluoroethylene powder is 1 to 10 parts by mass per 100 parts by mass of the sulfide-based solid electrolyte. [9] The electrode mixture according to [7] or [8], which is in a sheet form.

[10] The electrode mixture according to any one of [7] to [9], further comprising a conductive auxiliary agent, wherein the content of the polytetrafluoroethylene powder is 0.5 to 10 mass% relative to the total mass of the electrode mixture, the content of the active material is 88 to 99 mass% relative to the total mass of the electrode mixture, and the content of the conductive auxiliary agent is 0.5 to 10 mass% relative to the total mass of the electrode mixture.

[11] An electrode comprising a current collector and an electrode layer disposed on the current collector and comprising the electrode mixture according to any one of [7] to

[10] .

[12] A secondary battery comprising the electrode according to

[11] .

[0009] According to the present invention, there can be provided a polytetrafluoroethylene powder that can be mixed with an active material or the like to prepare an electrode mixture, and that has excellent toughness when used to obtain a sheet. Furthermore, according to the present invention, there can be provided an electrode mixture, an electrode, and a secondary battery.

[0010] The meanings of terms used in the present invention are as follows. A numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the upper and lower limits. In numerical ranges described in this specification in stages, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another staged numerical range. Furthermore, in numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the Examples. In this specification, each component may be used alone or in combination with two or more substances corresponding to the component. Herein, when two or more substances are used in combination for each component, the content of that component refers to the total content of the substances used in combination, unless otherwise specified. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. A "unit" is a collective term for an atomic group derived from one molecule of the above-mentioned monomer, formed directly by polymerization of the monomer, and an atomic group obtained by chemically converting a portion of the above-mentioned atomic group. Hereinafter, a "unit based on a monomer" will also be simply referred to as a "unit." The content (mass % or mol %) of each unit relative to all units contained in a polymer (polytetrafluoroethylene-based resin) is determined by analyzing the polymer by solid-state nuclear magnetic resonance spectroscopy (NMR), and usually, the content of each unit calculated from the amount of each monomer added substantially coincides with the actual content of each unit.

[0011] [Polytetrafluoroethylene Powder] The polytetrafluoroethylene powder (hereinafter also referred to simply as "PTFE powder") of this embodiment is a PTFE powder used as a binder for secondary batteries. The PTFE powder contains a polytetrafluoroethylene-based resin (hereinafter also referred to as "PTFE-based resin") and a transition metal element, and the content of the transition metal element is 100 to 1500 ppb by mass relative to the total mass of the PTFE powder. Another aspect of the present invention is the use of a PTFE powder containing a PTFE-based resin and a transition metal element, the content of the transition metal element being 100 to 1500 ppb by mass relative to the total mass of the PTFE powder, as a binder for secondary batteries. Another aspect of the present invention is a binder for a secondary battery, comprising PTFE powder containing a PTFE-based resin and a transition metal element, wherein the content of the transition metal element is 100 to 1500 ppb by mass relative to the total mass of the PTFE powder.

[0012] The inventors have found that, since sheet-shaped electrodes are generally wound with a small radius of curvature in the subsequent winding process, if the electrode layer is brittle, it will crack during winding, and conversely, if the electrode layer is high-strength, it will become brittle and more likely to crack. According to the inventors' studies, by adjusting the content of transition metal elements in the PTFE powder within a predetermined range, the degree of fibrillation of the PTFE powder can be appropriately adjusted. Furthermore, it is presumed that, in a sheet obtained using an electrode mixture containing an active material, if the content of transition metal elements is within a predetermined range, the interactions between the PTFE resin and the transition metal elements, and the interactions between the transition metal elements themselves, etc., are appropriately strong, resulting in excellent sheet toughness. In addition, another effect of the PTFE powder of this embodiment is that the active material mixed with the PTFE powder tends to adhere to the container wall during mixing, tends to be unevenly mixed, and may reduce the recovery amount and reduce yield. In this regard, the PTFE powder of this embodiment can suppress adhesion to a container, particularly because the degree of progress of fibrillation of the PTFE powder can be appropriately adjusted.

[0013] The form of the PTFE powder is not particularly limited, but examples thereof include granular and particulate forms, with particulate forms being preferred. Alternatively, the PTFE powder may be in the form of a powder consisting of aggregates of granular and particulate forms. When the PTFE powder is particulate, the PTFE powder may be either primary particles or secondary particles.

[0014] The standard specific gravity (SSG) of the PTFE powder (PTFE-based resin) 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; a lower value indicates a higher molecular weight. Furthermore, when a large amount of monomers other than tetrafluoroethylene is introduced into the PTFE-based resin, the amorphous structure tends to increase, the density decreases, and the SSG value tends to decrease. SSG is measured in accordance with ASTM D4895-10. Specifically, a 12.0 g sample is weighed and placed in a cylindrical mold with an inner diameter of 28.6 mm at 34.5 MPa for 2 minutes to obtain a molded sample. This is placed in an oven at 290°C, heated at 120°C / hr, held at 380°C for 30 minutes, then cooled at 60°C / hr and held at 294°C for 24 minutes. After holding for 12 hours in a desiccator at 23°C, the specific gravity of the molded product and water at 23°C is measured and this is taken as the SSG.

[0015] The extrusion pressure in the extrusion test of PTFE powder is preferably 5 to 60 MPa, more preferably 10 to 40 MPa, and even more preferably 15 to 25 MPa. The extrusion pressure is measured using the following method. 100 g of PTFE powder left at room temperature for at least 2 hours is placed in a 500 mL glass bottle, and 21.7 g of lubricating oil (Isopar H (registered trademark), manufactured by Exxon Corporation) is added and mixed for 3 minutes to obtain a mixture. The resulting mixture is then left in a 25°C thermostatic chamber for 2 hours, after which the paste is extruded at 25°C through an orifice with a diameter of 2.5 cm, a land length of 1.1 cm, and an entrance angle of 30° under the conditions of a reduction ratio (ratio of the cross-sectional area of ​​the die entrance to the cross-sectional area of ​​the exit) of 100 and an extrusion rate of 51 cm / min to obtain an extrusion bead (string-like material). The pressure required for extrusion at this time is measured and recorded as the extrusion pressure (unit: MPa).

[0016] The withstand voltage of a PTFE powder compact is preferably 4 kV or more, more preferably 5 kV or more, and even more preferably 6 kV or more. When the withstand voltage is equal to or greater than the lower limit, the electrochemical resistance of the PTFE powder is increased, improving durability when the PTFE powder is used as a negative electrode binder. The upper limit of the withstand voltage is not particularly limited, but may be 40 kV or less, or may be 30 kV or less. The withstand voltage is preferably 4 to 40 kV, more preferably 5 to 30 kV, and even more preferably 6 to 30 kV. The withstand voltage is measured in accordance with JIS K6892:1995. Detailed measurement methods are described in the Examples. The withstand voltage varies depending on the impurities contained, as well as the crystallinity, the presence or absence of monomer units other than tetrafluoroethylene, and the molecular weight distribution of the polytetrafluoroethylene resin. Furthermore, by not using nitric acid during aggregation of the PTFE aqueous dispersion, impurities are reduced, and the withstand voltage tends to increase.

[0017] The moisture content of the PTFE 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 powder. The moisture content is measured by the following method. The mass of the PTFE powder is measured before and after heating at 150°C for 2 hours, and the moisture content is calculated according to the following formula. Three samples are taken, and the moisture content is calculated for each sample, and the average is calculated and used. Moisture content (mass%) = 100 x [(mass (g) of PTFE powder before heating) - (mass (g) of PTFE powder after heating)] / (mass (g) of PTFE powder before heating)

[0018] The bulk density of the PTFE powder is preferably 350 to 600 g / L, more preferably 400 to 550 g / L, and is measured in accordance with JIS K6892:1995.

[0019] The angle of repose of the PTFE powder is preferably 32 to 44°, more preferably 33 to 40°. If the angle of repose is within the above range, the average particle size of the PTFE powder can be reduced while suppressing the progression of fibrous formation of the PTFE powder during mixing with an active material, etc. The angle of repose of the PTFE powder can be measured, for example, by a known measurement method. For example, the PTFE-based resin powder to be measured is dropped from a funnel of a certain height onto a horizontal measurement table, and the base angle is calculated from the diameter and height of the resulting conical deposit, and this base angle is taken as the angle of repose. For example, the angle of repose can be measured based on JIS-R9301-2-2:1999 (corresponding international standard: ISO 902:1976).

[0020] The pore volume of the PTFE powder is 0.2 to 15.0 cm ３ / g is preferred, and 0.5 to 10.0 cm ３ / g is more preferable. If the pore volume is within the above range, the mixing property with the active material and the conductive additive is promoted. The pore volume of the PTFE powder can be measured by mercury intrusion porosimetry using a known analytical device (e.g., AutoPoreIV 9520 manufactured by Micromeritics).

[0021] The average pore diameter of the PTFE powder is preferably 0.05 to 2.0 μm, more preferably 0.1 to 1.5 μm. The average pore diameter of the PTFE powder can be measured, for example, by mercury intrusion porosimetry using a known analytical device. Specifically, the pore volume is expressed as V (cm ３ / g), and the specific surface area is A (m ２ / g), the average pore diameter (μm) is calculated as 4V / A. The specific surface area is a BET specific surface area. The BET specific surface area is defined as a value measured by a nitrogen adsorption BET single-point method using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Ohkura Riken Co., Ltd.) after pre-drying a sample at 150°C for 30 minutes under a nitrogen flow, using a nitrogen-helium mixed gas accurately adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3.

[0022] The PTFE powder preferably has a median pore diameter of 10 to 100 μm, which is the pore diameter at which the cumulative value accounts for 50% by volume of the pore volume in a pore distribution profile obtained by mercury intrusion porosimetry using a known analytical device.

[0023] The electrostatic potential of the PTFE powder is preferably -2000 to -14000 V, more preferably -5000 to -12000 V, and even more preferably -200 to -3000 V in terms of superior wall adhesion. When the electrostatic potential is within the above range, the PTFE powder particles repel each other due to electrostatic repulsion during the mixing process with the active material, etc., resulting in improved dispersibility. Furthermore, excellent wall adhesion can also be achieved. The electrostatic potential can be measured using a digital electrostatic potential meter, Model KSD-1000 (manufactured by Kasuga Electric Co., Ltd.). The electrostatic potential can be adjusted using various ionizers and mechanical friction. When charging by mechanical friction, efficient charging can be achieved by applying vibration while in contact with a nylon material due to the triboelectric series. In particular, the electrostatic potential can be easily adjusted by adding dried PTFE powder to a pot mill and rotating it at a speed of 10 to 50% of the critical rotation speed. The critical rotation speed means the rotation speed at which the contents rotate together with the container due to centrifugal force, and is expressed by the following formula: N (critical rotation speed, unit: rpm) = 42.4 / √D (inner diameter of container, unit: m).

[0024] In terms of improving the binding strength and flexibility of the electrode, the average primary particle diameter of the PTFE powder is preferably 500 nm or less, more preferably 450 nm or less, and even more preferably 400 nm or less. The lower limit is preferably 100 nm or more, more preferably 180 nm or more, and even more preferably 200 nm or more. The average primary particle diameter of the PTFE powder is preferably 100 to 500 nm, more preferably 180 to 450 nm, and even more preferably 200 to 400 nm. The average primary particle diameter is the volume-based median diameter obtained by a laser scattering particle size distribution analyzer.

[0025] The average secondary particle diameter of the PTFE powder is preferably 280 μm or more, more preferably 300 μm or more, and even more preferably 320 μm or more. The upper limit is preferably 1000 μm or less, more preferably 800 μm or less, and even more preferably 700 μm or less. The average secondary particle diameter of the PTFE powder is preferably 280 to 1000 μm, more preferably 300 to 800 μm, and even more preferably 320 to 700 μm. The average secondary particle diameter of the PTFE powder can be measured, for example, in accordance with JIS K 6891:1995.

[0026] PTFE powder is used as a binder for secondary batteries. PTFE powder is preferably used, for example, in a composition for forming a member or layer constituting a secondary battery. It is more preferably used in an electrode mixture obtained by mixing PTFE powder with an active material or the like. The term "binder" has the same meaning as a general binder, and includes so-called binding agents, dispersants, and adhesives. Examples of members or layers constituting a secondary battery include the electrode layer in the electrode described below. The secondary battery is not particularly limited as long as it is a known secondary battery. Preferred embodiments of the secondary battery are described below.

[0027] PTFE powder can also be used suitably for other applications. Examples of other applications include ceramic capacitors made of low-temperature sintered barium titanate. To produce capacitors, barium titanate and PTFE powder are mixed and formed into a sheet. A small amount of water is added, and the mixture is densified at a temperature of 100 to 200°C and a pressure of several hundred MPa. The use of the PTFE powder of the present invention can increase the strength of the densified product.

[0028] Various components that the PTFE powder may contain will be described in detail below.

[0029] <PTFE-Based Resin> The PTFE powder contains a PTFE-based resin. PTFE-based resin refers to a resin containing units based on tetrafluoroethylene (hereinafter referred to as "TFE units"). The resin of this embodiment is clearly distinguished from an elastomer. An elastomer is an elastic polymer that has no melting point and exhibits a storage modulus G' of 80 kPa or more at 100°C and 50 cpm. The melting point can be determined as the temperature corresponding to the maximum value of the melting peak measured by differential scanning calorimetry (DSC). The storage modulus G' is a value measured in accordance with ASTM D6204 at 100°C and 50 cpm.

[0030] (TFE unit) PTFE resin is a resin that contains TFE unit, and the content of TFE unit 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, based on the total units of PTFE resin.The upper limit can be 100% by mass.In addition, the content of TFE unit is preferably 99 mol% or more, more preferably 99.5 mol% or more, and even more preferably 99.9 mol% or more, based on the total units of PTFE resin.The upper limit can be 100 mol%.

[0031] (Unit based on other monomer) PTFE resin may comprise unit based on other monomer other than TFE unit.As other monomer, for example, perfluoroolefin such as hexafluoropropylene (HFP); hydrogen-containing fluoroolefin such as trifluoroethylene and vinylidene fluoride (VdF); perhaloolefin such as chlorotrifluoroethylene; perfluorovinyl ether such as perfluoro(alkyl vinyl ether) (PAVE); perfluoroallyl ether; (fluoroalkyl)ethylene (FAE); ethylene.Among them, as other monomer, HFP, VdF, FAE or PAVE are preferred, and FAE is more preferred.In addition, other monomer may be the monomer used in the manufacturing method of PTFE powder described later.

[0032] As the PAVE, a monomer represented by the formula (PA) is preferred. CF ２ ═CF—O—Rf １(PA) In formula (PA), Rf １ represents a perfluoroalkyl group having 1 to 10 carbon atoms. １ From the viewpoint of superior polymerization reactivity, the number of carbon atoms in the perfluoroalkyl group represented by the formula (I) is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3. The perfluoroalkyl group may be linear or branched.

[0033] Specific examples of PAVE include 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 = CFO (CF ２ ) ８ F, and PMVE or PPVE is preferred.

[0034] The FAE is preferably a monomer represented by formula (FA): ２ =CX(CF ２ ) ｍ Y (FA) In formula (FA), X, Y and Z each independently represent a hydrogen atom or a fluorine atom, and m represents an integer of 2 to 6. Specific examples of FAE include CH ２ =CH(CF ２ ) ２ F, CH ２ =CH(CF ２ ) ３ F, CH ２ =CH(CF ２ ) ４ F (PFBE), CH ２ =CF(CF ２ ) ３ H, CH ２ =CF(CF ２ ) ４ H, PFBE or CH２ =CH(CF ２ ) ２ F is preferred, more so than PFBE.

[0035] 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, based on the total units of the PTFE-based 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, based on the total units of the PTFE-based resin.

[0036] The content of the 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-based resin. The upper limit can be 100% by mass.

[0037] The content of each of the various units in the PTFE-based resin is as follows: １９ It can be measured by a known method such as F-NMR (nuclear magnetic resonance analysis).

[0038] The PTFE-based resin may have a core-shell structure. Examples of the PTFE-based resin having a core-shell structure include PTFE-based resins containing a core of a high-molecular-weight PTFE-based resin in particles and a shell of a lower-molecular-weight PTFE-based resin or a PTFE-based resin containing other units.

[0039] The content of the PTFE-based resin is preferably 90% by mass or more and less than 100% by mass, more preferably 99% by mass or more and less than 100% by mass, and even more preferably 99.9% by mass or more and less than 100% by mass, based on the total mass of the PTFE powder.

[0040] <Transition metal element> The PTFE powder contains a transition metal element. The type of transition metal element is preferably a metal element from Group 4 to Group 12 of the long periodic table excluding technetium, scandium, and yttrium, more preferably a metal element from Group 4 to Group 12 of the long periodic table excluding technetium, even more preferably a metal element from Group 7 to Group 12 of the long periodic table excluding technetium, particularly preferably a metal element from Group 7 of the long periodic table excluding technetium, a metal element from Group 8 of the long periodic table, a metal element from Group 10 of the long periodic table, or a metal element from Group 12 of the long periodic table, and most preferably iron, zinc, nickel, and manganese. The transition metal element contained in the PTFE powder may be one type or two or more types.

[0041] The transition metal element content is 100 to 1500 ppb by mass, preferably 200 to 1500 ppb by mass, based on the total mass of the PTFE powder. 200 to 1000 ppb by mass is more preferred, as it provides better wall adhesion. When the transition metal element content is within the above range, the resulting sheet has excellent toughness. The transition metal element content can be measured, for example, using ICP-MS (inductively coupled plasma mass spectrometry). Specifically, 0.1 g of PTFE powder is weighed into a platinum boat and incinerated under an oxygen atmosphere (600°C, 10 minutes) to obtain an ash product. The ash product is then dissolved in dilute nitric acid to obtain a 20 mL solution. The resulting solution is introduced into an ICP-MS analyzer (e.g., 7700x, manufactured by Agilent) to determine whether or not peaks of each transition metal element are detected. The concentrations of detected transition metal elements are measured by comparing them with a standard solution. The concentrations of the transition metal elements that can be analyzed by the above-mentioned device are summed up to obtain the content of the transition metal element.

[0042] As a method for adjusting the content of the transition metal element, a method of wetting the PTFE powder with a solution containing the transition metal element can be mentioned. Specifically, the method shown in the Examples section can be mentioned. Another adjustment method can be, for example, a method of using a material containing the transition metal element in a polymerization reaction to obtain a PTFE-based resin, or adjusting the amount of the material used.

[0043] [Method for producing PTFE powder] The method for producing PTFE powder is not particularly limited as long as it can produce the above-mentioned PTFE powder. For example, the method for producing PTFE powder is preferably a method for producing PTFE powder that includes step A of obtaining an aqueous dispersion containing a PTFE resin, and step B of obtaining PTFE powder from the aqueous dispersion.

[0044] <Step A> Step A is a step of preparing an aqueous dispersion containing a PTFE-based resin.

[0045] The process of preparing the aqueous dispersion can be exemplified by a process of polymerizing the monomer that becomes the unit that constitutes the PTFE-based resin in an aqueous medium.The monomer can be appropriately selected according to the desired PTFE-based resin.The polymerization method can be exemplified by known polymerization methods, for example.

[0046] Step A is preferably a step of polymerizing a first monomer containing TFE in the presence of an aqueous medium to obtain an aqueous dispersion containing a PTFE-based resin.

[0047] (Aqueous Medium) Specific examples of the aqueous medium include water and a mixed solvent of water and a water-soluble organic solvent. Specific examples of the water-soluble organic solvent include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol. In the case of a mixture of water and a water-soluble organic solvent, the concentration of the water-soluble organic solvent is preferably 10% by mass or less. The aqueous medium is preferably water alone.

[0048] (First Monomer) The first monomer includes TFE. The first monomer may include other monomers other than TFE. The content of TFE is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 99 mol% or more, based on the total mole number of the first monomer. The upper limit is preferably 100 mol% or less.

[0049] Polymerization of the first monomer can be carried out by, for example, emulsion polymerization, solution polymerization, or suspension polymerization. The polymerization 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.

[0050] (Polymerization Initiator) Examples of the polymerization initiator include an oil-soluble radical polymerization initiator and a water-soluble radical polymerization initiator.

[0051] Examples of the oil-soluble radical polymerization initiator include dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and disec-butyl peroxydicarbonate; peroxy esters 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 di[perfluoro(or fluorochloro)acyl]peroxides such as di(ω-chloropentafluorobutanoyl)peroxide, di(ω-chlorodecafluorohexanoyl)peroxide, di(ω-chlorotetradecafluorooctanoyl)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(tetrachloroundecafluorooctanoyl)peroxide, di(pentachlorotetradecafluorodecanoyl)peroxide, and di(undecachlorodotriacontafluorodocosanoyl)peroxide.

[0052] The water-soluble radical polymerization initiator is preferably a water-soluble radical initiator or a water-soluble redox catalyst. Examples of the water-soluble radical initiator include persulfates such as ammonium persulfate and potassium persulfate, and water-soluble organic peroxides such as disuccinic acid peroxide, bisglutaric acid peroxide, and tert-butyl hydroperoxide. Examples of the water-soluble redox catalyst include a combination of an oxidizing agent such as bromic acid or a salt thereof, chloric acid or a salt thereof, persulfuric acid or a salt thereof, permanganic acid or a salt thereof, or hydrogen peroxide, with a reducing agent such as sulfurous acid or a salt thereof, hydrogen sulfite or a salt thereof, thiosulfuric acid or a salt thereof, or an organic acid. Among these, a combination of bromic acid or a salt thereof and sulfurous acid or a salt thereof (e.g., ammonium sulfite), and a combination of permanganic acid or a salt thereof (e.g., potassium permanganate) and oxalic acid are more preferred. As the polymerization initiator, ammonium persulfate alone or a mixture of a persulfate and disuccinic acid peroxide is preferred, and ammonium persulfate alone or a mixture of ammonium persulfate and disuccinic acid peroxide is more preferred. The polymerization initiator may be used alone or in combination of two or more. The polymerization initiator may be charged in its entirety into the polymerization system before the start of the polymerization reaction, or may be added to the polymerization system continuously or intermittently.

[0053] The amount of the 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.

[0054] (Other Components) In the polymerization of the first monomer, other components such as a nucleating agent, a chain transfer agent, a buffer, a pH adjuster, a stabilizing aid, a dispersion stabilizer, a radical scavenger, a decomposing agent for the polymerization initiator, and a dicarboxylic acid may be used.

[0055] Examples of the nucleating agent include fluoropolyethers such as perfluoropolyether acids, nonionic surfactants, and chain transfer agents. Examples of the perfluoropolyether acids include the perfluoropolyether acids described in J. Appl. Polymer Sci. 57, 797 (1995).

[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 phenol, polyhydric phenols, salicylic acid, m- or p-salicylic acid, gallic acid, and naphthol. Examples of unsubstituted phenols include o-, m-, or p-nitrophenol, o-, m-, or p-aminophenol, and p-nitrosophenol. Examples of polyhydric phenols include catechol, resorcinol, hydroquinone, pyrogallol, phloroglucinol, 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 (NH ４ Examples include potassium thiocyanate (KSCN), potassium thiocyanate (KSCN), and sodium thiocyanate (NaSCN).

[0057] The decomposer for the polymerization initiator may be any compound capable of decomposing the polymerization initiator used, and examples thereof include sulfites, bisulfites, bromates, diimines, diimine salts, oxalic acid, oxalates, copper salts, and iron salts.

[0058] As the dicarboxylic acid, for example, a compound represented by the general formula: HOOC-R-COOH (wherein R represents an alkylene group having 1 to 5 carbon atoms) is preferable, succinic acid, malonic acid, glutaric acid, adipic acid or pimelic acid is more preferable, and succinic acid is even more preferable.

[0059] The polymerization temperature and polymerization pressure in the polymerization of the first monomer can be appropriately determined depending on the type of monomer used, the molecular weight of the target PTFE-based 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 polymerization temperature is preferably 5 to 150°C, more preferably 10 to 120°C, even more preferably 30 to 120°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 more preferably 3.0 MPaG or lower. The polymerization pressure is preferably 0.05 to 5.0 MPaG, more preferably 0.3 to 5.0 MPaG, and even more preferably 0.5 to 3.0 MPaG, where G indicates gauge pressure.

[0060] A stabilizing aid may be used in the polymerization of the first monomer. As the stabilizing aid, paraffin wax, a fluorine-based solvent, or silicone oil is preferred, and paraffin wax is more preferred. The paraffin wax may be liquid, semi-solid, or solid at room temperature. Among these, saturated hydrocarbons having 12 or more carbon atoms are preferred. The melting point of the paraffin wax is preferably 40 to 65°C, and more preferably 50 to 65°C. One type of stabilizing aid may be used alone, or two or more types may be used in combination.

[0061] The content of the PTFE-based resin is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, and even more preferably 10 to 30% by mass, relative to the total mass of the aqueous dispersion. The solid content concentration of the aqueous dispersion is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, and even more preferably 10 to 30% by mass. The solid content concentration of the aqueous dispersion can be measured, for example, by the following method. The solid content concentration of the aqueous dispersion is calculated by heating 2.0 g of the aqueous dispersion at 170°C for 20 minutes, weighing the mass of the residue, and calculating the solid content concentration using the following formula: "Solid content concentration (mass%) = 100 × heating residue of aqueous dispersion (g) / mass of aqueous dispersion (2.0 g)"

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

[0063] Examples of aggregation treatments include freeze aggregation, acid aggregation, base aggregation, mechanical aggregation, and aggregation using a coagulation agent. In the case of freeze aggregation, the aggregation temperature is preferably -20 to 0°C. The aggregation time is preferably 1 hour or more, more preferably 2 hours or more. In the case of acid aggregation, a method in which an acid-containing solution is added 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 acid concentration 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. In the case of base aggregation, a method in which a base-containing solution is added 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 base concentration 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. For aggregation using a coagulation agent, known coagulation agents can be used. Known coagulants include aluminum salts, calcium salts, and magnesium salts. Specifically, aluminum sulfate, a compound of the general formula M'Al(SO ４ ) ２ ・12H ２ O (wherein M' is a monovalent cation other than lithium), calcium nitrate, and magnesium sulfate are examples of the coagulation method. Alum is preferred, and potassium alum, where M is potassium, is more preferred. Acid coagulation or freeze coagulation is preferred as the coagulation method.

[0064] The drying treatment is preferably a treatment in which the PTFE wet powder obtained by the aggregation treatment is dried. The drying temperature is preferably 100°C or higher, more preferably 150°C or higher, and even more preferably 170°C or higher. The upper limit is preferably 280°C or lower, and more preferably 250°C or lower. The drying temperature is preferably 100 to 280°C, more preferably 150 to 280°C, and even more preferably 170 to 250°C. The drying time is preferably 1 hour or longer, and preferably 3 hours or longer. The upper limit is preferably 100 hours or shorter, more preferably 50 hours or shorter, and even more preferably 30 hours or shorter. The drying time is preferably 1 to 100 hours, more preferably 1 to 50 hours, and even more preferably 3 to 30 hours. The water content of the PTFE wet powder to be dried is preferably 10 parts by mass or higher, more preferably 20 parts by mass or higher, and even more preferably 30 parts by mass or higher, per 100 parts by mass of the PTFE wet powder. The upper limit is preferably 150 parts by mass or less, more preferably 100 parts by mass or less. The water content of the PTFE wet powder to be dried is preferably 10 to 150 parts by mass, more preferably 20 to 150 parts by mass, and even more preferably 30 to 100 parts by mass, per 100 parts by mass of the PTFE wet powder.

[0065] The drying treatment can be carried out using an electric furnace or a steam furnace. For example, it can be carried out using an electric furnace such as a parallel-flow box-type electric furnace, a ventilated box-type electric furnace, a ventilated conveyor-type electric furnace, a band furnace, a radiant conveyor-type electric furnace, a fluidized-bed electric furnace, a vacuum electric furnace, a stirring electric furnace, an airflow electric furnace, or a hot-air circulation electric furnace, or a steam furnace corresponding to the above (an apparatus obtained by substituting "steam furnace" for "electric furnace" in the apparatus name of each electric furnace). In terms of being able to more efficiently remove moisture, unreacted monomers, etc., a parallel-flow box-type electric furnace, a ventilated box-type electric furnace, a ventilated conveyor-type electric furnace, a band furnace, a fluidized-bed electric furnace, a hot-air circulation electric furnace, or a steam furnace corresponding to the above (an apparatus obtained by substituting "steam furnace" for "electric furnace" in the apparatus name of each electric furnace) is preferred.

[0066] <First Aspect> The method for producing PTFE powder may be a first aspect. The first aspect of the method for producing PTFE powder is a method for producing PTFE powder comprising steps C, D, and E. Step C: a step of polymerizing a non-fluorinated monomer in an aqueous medium to obtain solution 1 containing a polymer containing units based on the non-fluorinated monomer (hereinafter also referred to as "specific polymer C"). Step D: a step of polymerizing TFE in solution 1 without adding substantially any surfactant to solution 1 to obtain an aqueous emulsion containing a PTFE resin. Step E: a step of obtaining PTFE powder from the aqueous emulsion obtained in step D.

[0067] (Step C) Step C is a step of polymerizing a non-fluorinated monomer in an aqueous medium to obtain a solution 1 containing a specific polymer C. First, the materials used in Step C will be described in detail below, and then the procedure of Step C will be described in detail.

[0068] - Fluorine-free Monomer - A fluorine-free monomer is a monomer that does not contain a fluorine atom. The fluorine-free monomer usually has a polymerizable group, and the number of polymerizable groups is preferably 1 to 3, and more preferably 1. The polymerizable group is preferably an ethylenically unsaturated group. More specific examples include an acryloyl group, a methacryloyl group, a vinyl ether group, a vinyl ester group, a vinyl group, and an allyl group, and an acryloyl group, a methacryloyl group, a vinyl ester group, or a vinyl ether group is preferred.

[0069] The non-fluorine-containing monomer is preferably a monomer represented by formula (NF): ２ =CR １１ -L １ -R １２ R １１ represents a hydrogen atom or an alkyl group. The alkyl group preferably has 1 to 3 carbon atoms, and more preferably 1. １ represents a single bond, -C(=O)-O-*, -O-C(=O)-* or -O-. * represents R １２ For example, L １ is -C(=O)-O-*, formula (1) is CH ２ =CR １１ -C(=O)-OR １２Represents R １２ represents a hydrogen atom, an alkyl group, an alkenyl group, or a nitrile group. １ When is a single bond, R １２ is a nitrile group. The number of carbon atoms in the alkyl group and alkenyl group is preferably 1 to 10, more preferably 1 to 6, and even more preferably 1 to 4. The alkyl group may be linear or cyclic. When the alkyl group is cyclic, it corresponds to a cycloalkyl group. The alkenyl group may be linear or cyclic.

[0070] The monomer represented by the formula (NF) is preferably a monomer selected from the group consisting of a monomer represented by the formula (NF-1), a monomer represented by the formula (NF-2), a monomer represented by the formula (NF-3), and a monomer represented by the formula (NF-4). ２ =CR １１ -C(=O)-OR １３ Formula (NF-2) CH ２ =CR １１ -OC(=O)-R １４ Formula (NF-3) CH ２ =CR １１ -O-R １５ Formula (NF-4) CH ２ =CR １１ -R １６ R １１ The definition of R is as described above. １３ represents a hydrogen atom, an alkyl group, or an alkenyl group, and preferably an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms. １４ represents an alkyl group, preferably an alkyl group having 1 to 3 carbon atoms, more preferably a methyl group. １５ represents an alkyl group, and is preferably a linear alkyl group or a cyclic alkyl group. １６ represents a nitrile group.

[0071] Examples of non-fluorine-based 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 non-fluorine-based monomers may be used alone or in combination of two or more. The non-fluorine-based monomer is preferably a monomer represented by formula (NF-1) or a monomer represented by formula (NF-2), and R １３ is an alkyl group. The monomers represented by formula (NF-1) and formula (NF-2) have an ester group or a carboxy group, which are hydrophilic groups, and therefore the monomers and polymers thereof have hydrophilicity. Therefore, it is believed that the monomers and polymers thereof can be stably dispersed in an aqueous medium without the need for a surfactant, particularly at low concentrations.

[0072] -Specific Polymer C- The specific polymer C is a polymer containing units based on a non-fluorine-based monomer. The specific polymer C usually contains only units based on a non-fluorine-based monomer, but may also contain units based on a fluorine-based monomer. That is, in addition to the non-fluorine-based monomer, a fluorine-based monomer may be used in step C. The fluorine-based monomer is a monomer having a fluorine atom, and an example of such a monomer is TFE. The content of the units based on a non-fluorine-based monomer in the specific polymer C is preferably 90% by mass or more, more preferably 95% by mass or more, based on the total units of the specific polymer C. The upper limit can be 100% by mass.

[0073] -Aqueous Medium- Examples of the aqueous medium include the aqueous medium in step A described above.

[0074] -Polymerization initiator- A polymerization initiator may be used in step C. That is, a polymerization initiator may be used when polymerizing the non-fluorinated monomer. Examples of the polymerization initiator include the water-soluble radical polymerization initiator used in step A.

[0075] -Procedure of Step C- In Step C, the non-fluorine-based monomer is polymerized in an aqueous medium. Specifically, it is preferable to mix the non-fluorine-based monomer with the aqueous medium and polymerize the non-fluorine-based monomer in the resulting mixed liquid. As described above, a fluorine-based monomer may be used in combination, if necessary.

[0076] The amount of the non-fluorine-based monomer used is preferably 200 ppm by mass or less, more preferably from 1 to 150 ppm by mass or less, still more preferably from 5 to 100 ppm by mass, and particularly preferably from 5 to 50 ppm by mass, relative to the amount of TFE supplied (amount of TFE used) used in the step D described below. Note that the method for charging the non-fluorine-based monomer is preferably initial lump addition, in which the entire amount is charged into the polymerization system before the start of the polymerization reaction.

[0077] The content of the non-fluorinated monomer in the dispersion obtained by mixing the non-fluorinated monomer with the 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 dispersion. Since the entire amount of the non-fluorinated monomer is usually polymerized to form the specific polymer C, the concentration of the specific polymer C in the obtained solution 1 falls within the above-mentioned numerical range. The above-mentioned non-fluorinated monomer concentration and specific polymer C concentration are concentrations when the obtained solution 1 is used in step D without diluting with an aqueous medium. When the obtained solution 1 is diluted with an aqueous medium to achieve the concentration of the specific polymer C and the diluted solution is used in step D, a high-concentration solution corresponding to the dilution ratio is produced in step C. The dilution ratio is not particularly limited, but is preferably 10 times or less.

[0078] The amount of the polymerization initiator used is preferably from 0.2 to 1000% by mass, more preferably from 0.2 to 500% by mass, based on the total amount of non-fluorinated monomers.

[0079] The amount of the polymerization initiator used is preferably 0.1 to 1000 mol %, more preferably 0.1 to 300 mol %, based on the total amount of non-fluorinated monomers.

[0080] The polymerization temperature of the non-fluorine-based monomer 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 conditions or normal pressure conditions. Among these, 0 to 2.0 MPa is preferred, 0 to 1.0 MPa is more preferred, and 0 to 0.5 MPa is even more preferred. The polymerization may also be carried out in a TFE atmosphere. Note that, usually, the polymerization of the non-fluorine-based monomer in an aqueous medium proceeds preferentially over the polymerization of TFE.

[0081] By the above step C, a solution 1 containing the specific polymer C is obtained. The specific polymer C may be dissolved in the solution 1, or may be dispersed in particulate form in the aqueous medium. During the polymerization of TFE in step D described below, the specific polymer C is not an emulsifier, but it is presumed that due to the balance of interfacial tensions with both the aqueous medium and the PTFE-based resin, the specific polymer C exists at the boundary between the two, contributing to the dispersion stabilization of the PTFE-based resin in the aqueous medium. The average particle size of the particles of the specific polymer C is preferably 0.1 to 100 nm, more preferably 0.1 to 50 nm.

[0082] In addition, the solution 1 obtained in step C may contain unreacted non-fluorine-based monomer. Also, the atmosphere in the polymerization system of step C may be carried out under a TFE-containing atmosphere in consideration of step D. In such a case, it is considered that a part of the specific polymer C in step D may become a polymer containing TFE units. From another point of view, the PTFE particles obtained in step D are not limited to particles made of a physical mixture of specific polymer C and PTFE, but may also be particles containing a TFE copolymer having units based on a non-fluorine-based monomer.

[0083] (Step D) Step D is a step of obtaining an aqueous emulsion containing a PTFE resin by polymerizing TFE in the solution 1 obtained in Step D without substantially adding a surfactant to the solution 1. Hereinafter, first, the materials used in Step D will be described in detail, and then the procedure of Step D will be described in detail.

[0084] -TFE- In step D, TFE is used.

[0085] -Other Monomer- In step D, a monomer other than TFE may be further used within a range that does not impair the effects of the present invention. Examples of such other monomers include a monomer having a polar group (hereinafter also referred to as "specific monomer D"). Since the polar group in specific monomer D exhibits an interaction with the aqueous medium, it is presumed that it is located between TFE and the aqueous medium during the polymerization of TFE, thereby exhibiting a surfactant-like function. As a result, the polymerization of TFE proceeds well, and the occurrence of chain transfer is also suppressed.

[0086] Examples of the polar group contained in the specific monomer D include a sulfonic acid group, a sulfonate group, a carboxylic acid group, a carboxylate group, a phosphonic acid group, and a phosphonate group. Among them, the group represented by formula (A) or the group represented by formula (B) is preferred, and the group represented by formula (A) is more preferred, in terms of further suppressing the formation of fluorine-based oligomers. Formula (A) -SO ３ M Formula (B) -COOM In formulas (A) and (B), M is a hydrogen atom, NH ４ or an alkali metal atom. Examples of alkali metal atoms include a lithium atom, a sodium atom, and a potassium atom.

[0087] The specific monomer D usually has a polymerizable group, and the number of polymerizable groups is preferably 1 to 3, and more preferably 1. The polymerizable group is preferably an ethylenically unsaturated group. More specifically, examples of the polymerizable group include an acryloyl group, a methacryloyl group, a vinyl ether group, a vinyl ester group, a vinyl group, and an allyl group, and an acryloyl group, a methacryloyl group, a vinyl ester group, or a vinyl ether group is preferred.

[0088] The specific monomer D is preferably a monomer represented by formula (3) in that the formation of fluorine-based oligomers is further suppressed. ３１ R ３２ =CR ３３ -L ３ -R ３４ In formula (3), R ３１ and R ３２ each independently represents a hydrogen atom or a fluorine atom.

[0089] R ３３ represents a hydrogen atom, a fluorine atom, or an alkyl group which may be substituted with a fluorine atom. Among these, a hydrogen atom or a fluorine atom is preferred in that it has better copolymerizability with TFE. The "alkyl group which may be substituted with a fluorine atom" means an alkyl group in which at least one hydrogen atom in the alkyl group may be substituted with a fluorine atom. The number of carbon atoms in the alkyl group which may be substituted with a fluorine atom is preferably 1 to 3, and more preferably 1.

[0090] L ３ represents a single bond or a divalent linking group. Among these, a single bond is preferred in that it has better copolymerizability with TFE. Examples of the divalent linking group include a divalent hydrocarbon group, a divalent heterocyclic group, -O-, -S-, and -SO ２ -, -C(O)-, -Si(R ａ ) ２ -, -N(R ｂ )-, and groups formed by combining two or more of these. ａ represents an alkyl group (preferably having 1 to 10 carbon atoms) or a phenyl group. ｂ represents a hydrogen atom or an alkyl group (preferably having 1 to 10 carbon atoms). The divalent hydrocarbon group may be a divalent saturated hydrocarbon group, a divalent aromatic hydrocarbon group, an alkenylene group, or an alkynylene group. The divalent saturated hydrocarbon group may be linear, branched, or cyclic, and examples thereof include alkylene groups. The number of carbon atoms is preferably 1 to 20. The divalent aromatic hydrocarbon group preferably has 5 to 20 carbon atoms, and examples thereof include phenylene groups. In addition, the group may be an alkenylene group having 2 to 20 carbon atoms, or an alkynylene group having 2 to 20 carbon atoms. Examples of groups that combine two or more of these groups include -OC(O)-, -C(O)N(R ｂ )-, alkylene group -O-alkylene group, alkylene group -OC(O)-alkylene group, and alkylene group -Si(R ａ ) ２ -phenylene group -Si(R ａ ) ２The divalent hydrocarbon group may have a substituent. Examples of the substituent include a halogen atom (e.g., a fluorine atom, a chlorine atom). In other words, a hydrogen atom in the divalent hydrocarbon group may be substituted with a halogen atom.

[0091] R ３４ represents a group represented by the above formula (A) or a group represented by the above formula (B).

[0092] The monomer represented by formula (3) is preferably a monomer selected from the group consisting of a monomer represented by formula (3-1), a monomer represented by formula (3-2), a monomer represented by formula (3-3), a monomer represented by formula (3-4), a monomer represented by formula (3-5), and a monomer represented by formula (3-6), and more preferably a monomer represented by formula (3-1). ３１ R ３２ =CR ３３ -R ３４ Formula (3-2) CR ３１ R ３２ =CR ３３ -(CF ２ ) ｍ１ -R ３４ Formula (3-3) CR ３１ R ３２ =CR ３３ -(CF ２ C (CF ３ ) F) ｍ２ -R ３４ Formula (3-4) CR ３１ R ３２ =CR ３３ -O-(CFR ３５ ) ｍ３ -R ３４ Formula (3-5) CR ３１ R ３２ =CR ３３ -O-(CF ２ CFR ３５ O) ｍ４ -CF ２ CF ２ -R ３４ Formula (3-6) CR ３１ R ３２ =CR ３３ -CF ２ -O-(CF(CF３ )CF ２ O) ｍ５ -CF (CF ３ )-R ３４

[0093] In formulas (3-1) to (3-6), R ３１ ~R ３４ The definitions of are as described above. In formula (3-2), m1 represents an integer of 1 to 10. In formula (3-3), m2 represents an integer of 1 to 5. In formula (3-4), m3 represents an integer of 1 to 10. R ３５ is a fluorine atom or CF ３ In formula (3-5), m4 represents an integer of 1 to 10. ３５ In formula (3-6), m5 represents 0 or an integer of 1 to 10.

[0094] Ammonium vinyl sulfonate can be mentioned as a specific example of the specific monomer D. The specific monomer D may be used alone or in combination of two or more.

[0095] -Polymerization initiator- In step D, a polymerization initiator may be used. That is, a polymerization initiator may be used when polymerizing TFE. Examples of the polymerization initiator used include the polymerization initiators described in step C. As the polymerization initiator, a mixed system of persulfate and disuccinic acid peroxide is preferred, and a mixed system of ammonium persulfate and disuccinic acid peroxide is more preferred. The amount of the polymerization initiator used is preferably 0.10% by mass or more, more preferably 0.10 to 1.5% by mass, and even more preferably 0.20 to 1.0% by mass, based on the total amount of TFE supplied to the polymerization system.

[0096] -Stabilizing Aid- In step D, a stabilizing aid may be used. As the stabilizing aid, paraffin wax, a fluorine-based solvent, or silicone oil is preferred, and paraffin wax is more preferred. The paraffin wax may be liquid, semi-solid, or solid at room temperature. Of these, saturated hydrocarbons having 12 or more carbon atoms are preferred. The melting point of the paraffin wax is preferably 40 to 65°C, and more preferably 50 to 65°C. One stabilizing aid may be used alone, or two or more stabilizing aids may be used in combination.

[0097] -Other- Furthermore, in step D, a monomer other than TFE and specific monomer D may be used within a range that does not impair the effects of the present invention. However, in terms of improving various properties of the PTFE-based resin, the amount of TFE used is preferably 99.5 mass % or more, and more preferably 99.8 mass % or more, based on the total amount of the monomers used in step D.

[0098] -Procedure for Step D- In Step D, substantially no surfactant is added to Solution 1. That is, in Step D, TFE is polymerized in Solution 1 without substantially adding any new surfactant to Solution 1. A surfactant is a compound having a hydrophilic group (e.g., a polar group) and a hydrophobic group (e.g., a hydrocarbon group). The definition of the polar group is the same as that of the polar group contained in Specific Monomer D. Examples of surfactants include known surfactants, such as nonionic surfactants and ionic surfactants, and more specifically, hydrocarbon-containing surfactants and fluorosurfactants. The definition of the hydrocarbon-containing surfactant is as described below. In Step D, it is preferable that at least one surfactant selected from the group consisting of hydrocarbon-containing surfactants and fluorosurfactants is not substantially added to Solution 1. The phrase "substantially not added" means that no surfactant is added, or, if added, the amount of surfactant added is 200 ppm by mass or less relative to the total mass of Solution 1. The lower limit is not particularly limited, but 0 ppm by mass is preferred. That is, it is preferable that no surfactant is added to Solution 1 in Step D.

[0099] TFE is introduced into a polymerization system (i.e., a polymerization reaction vessel) by a conventional method. For example, TFE is introduced into the polymerization system continuously or intermittently so that the polymerization pressure becomes a predetermined pressure. When a polymerization initiator is used, the polymerization initiator may be added to the polymerization system all at once or in portions.

[0100] When the specific monomer D is used, the amount of the specific monomer D used relative to the total amount of TFE is preferably 0.150% by mass or less. In other words, the amount of the specific monomer D used relative to the total amount of TFE is preferably 0.150% by mass or less. From the viewpoint of the stability of the emulsion during polymerization, the amount of the specific monomer D used relative to the total amount of TFE is preferably 0.100% by mass or less, more preferably 0.090% by mass or less. Furthermore, from the viewpoint of improving the molecular weight, the amount of the specific monomer D used relative to the total amount of TFE is preferably 0.005% by mass or more, more preferably 0.010% by mass or more. When the specific monomer D is used, the amount of the specific monomer D used relative to the total amount of TFE is preferably 0.005 to 0.150% by mass, more preferably 0.005 to 0.100% by mass, and even more preferably 0.010 to 0.090% by mass. When two or more specific monomers D are used, the total amount of the specific monomers D used may be within the above range.

[0101] When the specific monomer D is used, the amount of the specific monomer D used relative to the total amount of TFE is preferably 0.150 mol% or less. In other words, the amount of the specific monomer D used relative to the total amount of TFE is preferably 0.150 mol% or less. From the viewpoint of the stability of the emulsion during polymerization, the amount of the specific monomer D used relative to the total amount of TFE is preferably 0.100 mol% or less, more preferably 0.090 mol% or less. Furthermore, from the viewpoint of improving the molecular weight, the amount of the specific monomer D used relative to the total amount of TFE is preferably 0.001 mol% or more, more preferably 0.005 mol% or more. When the specific monomer D is used, the amount of the specific monomer D used relative to the total amount of TFE is preferably 0.100 to 0.150 mol%, more preferably 0.100 to 0.100 mol%, and even more preferably 0.005 to 0.090 mol%. When two or more specific monomers D are used, the total amount of the specific monomers D used may be within the above range.

[0102] The polymerization temperature is preferably 10 to 95° C., more preferably 15 to 90° C. The polymerization pressure is preferably 0.5 to 4.0 MPa, 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.

[0103] Step C and Step D may be carried out continuously in the same polymerization reaction vessel. In the production method of the present invention, 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.

[0104] The above procedure results in an aqueous emulsion in which the PTFE-based resin is dispersed in particulate form (aqueous emulsion containing a PTFE-based resin). The concentration of the PTFE-based 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, relative to the total amount of the aqueous emulsion. Within the above range, the PTFE-based resin in the aqueous emulsion can be more easily coagulated, and cloudiness of the coagulated liquid can be suppressed. The average primary particle diameter of the PTFE-based resin is preferably 100 to 500 nm, more preferably 150 to 300 nm. The average primary particle diameter of the PTFE-based resin corresponds to D50, measured using a laser scattering particle size distribution analyzer.

[0105] (Step E) Step E is a step of obtaining PTFE powder from the aqueous emulsion obtained in step D. Step E can be carried out using the same procedure and conditions as in step B above.

[0106] <Second Aspect> The method for producing PTFE powder may be in the following second aspect. The second aspect of the method for producing PTFE powder is a method for producing PTFE powder comprising steps F and G. Step F: a step of polymerizing a monomer containing tetrafluoroethylene (hereinafter also referred to as "specific monomer F") in an aqueous dispersion containing a first fluoropolymer and an aqueous medium to obtain an aqueous dispersion containing a PTFE-based resin different from the first fluoropolymer. Step G: a step of obtaining PTFE powder from the aqueous dispersion obtained in step F.

[0107] (Step F) Step F is a step of polymerizing a monomer containing TFE in an aqueous dispersion containing a first fluoropolymer and an aqueous medium to obtain an aqueous dispersion containing a PTFE-based resin different from the first fluoropolymer.

[0108] -Aqueous Dispersion- In the second embodiment, an aqueous dispersion containing the first fluorine-containing polymer and an aqueous medium is used.

[0109] -First Fluorine-Containing Polymer- It is presumed that the first fluorine-containing polymer solubilizes the specific monomer F by adsorbing and incorporating the specific monomer F at the hydrophobic portion during polymerization of the specific monomer F, and that by adding a polymerization initiator to this, the specific monomer F is polymerized within the particles of the first fluorine-containing polymer. It is also presumed that the first fluorine-containing polymer contributes to dispersion stabilization in an aqueous medium.

[0110] The glass transition temperature (hereinafter also referred to as "Tg") of the first fluoropolymer is preferably 10°C or lower, and from the viewpoint of efficient adsorption of the specific monomer F, more preferably 5°C or lower, even more preferably 3°C or lower, and particularly preferably 0°C or lower. From the viewpoint of thermal stability after molding, the Tg of the first fluoropolymer is preferably -50°C or higher, more preferably -45°C or higher, and even more preferably -40°C or higher. The Tg of the first fluoropolymer is preferably -50 to 10°C, more preferably -45 to 5°C, even more preferably -40 to 3°C, and particularly preferably -40 to 0°C. The Tg of the first fluoropolymer is measured by differential scanning calorimetry (DSC). Examples of methods for adjusting the Tg of the first fluoropolymer within the above range include methods of adjusting the type and amount of monomer used in producing the first fluoropolymer.

[0111] The first fluorine-containing polymer preferably contains TFE units and units based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE units") (hereinafter also referred to as "PAVE units"), in that it is easy to adjust the Tg within the above range.

[0112] The PAVE is preferably a monomer represented by the above formula (PA) from the viewpoint of excellent polymerization reactivity in producing the first fluoropolymer and of enabling more efficient production of the PTFE-based resin. The monomer represented by formula (PA) has the same meaning as the monomer represented by formula (PA) in the above PTFE-based resin, and preferred embodiments are also the same.

[0113] When the first fluorine-containing polymer contains TFE units and PAVE units, the content of PAVE units in the first fluorine-containing polymer relative to the total of TFE units and PAVE units is preferably 20 to 60 mol %, more preferably 25 to 60 mol %, and even more preferably 30 to 55 mol %, from the viewpoints that Tg can be easily adjusted to within the above range and that a PTFE-based resin can be produced more efficiently.

[0114] The first fluorine-containing polymer may contain units based on other monomers other than TFE and PAVE, but preferably does not substantially contain units based on other monomers, in order to be able to produce PTFE-based resin more efficiently.The term "does not substantially contain units based on other monomers" means that the content of units based on other monomers is 0.01 mol% or less, more preferably 0 mol%, based on the total units of the first fluorine-containing polymer.When it contains units based on other monomers, the other monomer is preferably hexafluoropropylene.

[0115] Before the start of polymerization of the monomers to be used in polymerization of the PTFE-based resin, the content of the first fluorine-containing polymer is 0.01 to 4.0 mass% relative to the total mass of the aqueous medium in the aqueous dispersion, and from the viewpoint of enabling more efficient production of the second fluorine-containing polymer, it is preferably 0.01 to 0.6 mass%, more preferably 0.01 to 0.5 mass%.

[0116] In this specification, "before starting polymerization of the monomers used in the polymerization of the PTFE-based resin" means immediately before the start of polymerization. Here, "the start of polymerization" includes the time when the monomers and the polymerization initiator are made to coexist in the reactor after the temperature inside the reactor is raised to the polymerization temperature or higher, and the time when the temperature inside the reactor is raised to the polymerization temperature or higher after the monomers and the polymerization initiator are made to coexist in the reactor.

[0117] Before starting polymerization of the monomers used in the polymerization of the PTFE-based resin, the concentration of sulfate ions is preferably 10 mass ppm or less, more preferably 5 mass ppm or less, relative to the total mass of the aqueous medium in the aqueous dispersion, from the viewpoint of suppressing coloration of the PTFE-based resin.The lower limit can be 0 mass ppm.An example of a method for adjusting the concentration of sulfate ions to the above value can be a method of removing sulfate ions using an anion exchange resin during the production of the first fluorine-containing polymer.Here, sulfate ions are derived from, for example, the polymerization initiator (particularly ammonium persulfate) used during the production of the first fluorine-containing polymer, and may be contained in the aqueous dispersion containing the first fluorine-containing polymer.It is presumed that by making the content of sulfate ions 10 mass ppm or less (particularly 5 mass ppm or less), it is possible to suppress the formation of end groups with low heat resistance in the PTFE-based resin, thereby suppressing coloration of the PTFE-based resin.

[0118] Before starting polymerization of the monomer used for polymerization of PTFE-based resin, the concentration of ammonium ion is preferably 20 mass ppm or less, more preferably 10 mass ppm or less, relative to the total mass of the aqueous medium in the aqueous dispersion, from the viewpoint of suppressing aggregation of PTFE-based resin.The lower limit can be 0 mass ppm.An example of a method for adjusting the concentration of ammonium ion to the above value can be a method of removing ammonium ion using a cation exchange resin during the production of the first fluorine-containing polymer.Here, ammonium ion is, for example, derived from the initiator (particularly ammonium persulfate) used during the production of the first fluorine-containing polymer, and may be contained in the aqueous dispersion containing the first fluorine-containing polymer.It is presumed that the content of ammonium ion is 20 mass ppm or less, and as a result, the ionic strength in the aqueous medium is reduced, thereby improving the production efficiency of the PTFE-based resin.

[0119] The first fluoropolymer is preferably dispersed in the aqueous medium in the form of particles. In this case, the average particle size of the first fluoropolymer is preferably 1 to 150 nm, more preferably 10 to 120 nm, and even more preferably 50 to 120 nm, from the viewpoint of more efficient production of the PTFE-based resin. The average particle size of the first fluoropolymer is determined by measuring the particle size distribution by a laser diffraction / scattering method, determining a cumulative curve with the total volume of the particle population as 100%, and measuring the particle size (D50) at the point on the cumulative curve where the cumulative volume is 50%, with detailed measurement conditions as described in the Examples section.

[0120] The method for producing the first fluorine-containing polymer is preferably a method of polymerizing a monomer (preferably a monomer mixture containing TFE and PAVE) in an aqueous medium in the presence of a polymerization initiator.This gives the first fluorine-containing polymer dispersed in the form of particles in the aqueous medium.The aqueous medium thus obtained in which the particles of the first fluorine-containing polymer are dispersed may be used as the aqueous dispersion as is, or another aqueous medium may be added and used as the aqueous dispersion.Furthermore, the first fluorine-containing polymer may be dispersed in another aqueous medium by solvent substitution, and this may be used as the aqueous dispersion.

[0121] The polymerization initiator used in the production of the first fluorine-containing polymer is preferably a water-soluble polymerization initiator, more preferably a persulfate such as ammonium persulfate, sodium persulfate or potassium persulfate, or an organic polymerization initiator such as disuccinic acid peroxide or azobisisobutylamidine dihydrochloride, further preferably a persulfate, and particularly preferably ammonium persulfate.

[0122] The aqueous medium used in producing the first fluoropolymer may be the aqueous medium used in the above-mentioned step A. The aqueous medium contained in the aqueous dispersion may be the polymerization solvent used in producing the first fluoropolymer. Before starting polymerization of the monomers used in polymerizing the PTFE resin, the content of the aqueous medium is preferably 60 to 99.9 mass%, more preferably 96 to 99.9 mass%, and even more preferably 98 to 99.9 mass%, based on the total mass of the aqueous dispersion.

[0123] The method for producing the first fluoropolymer preferably includes a heating step of heating the aqueous medium having the first fluoropolymer dispersed therein after the aqueous medium is obtained. This deactivates the polymerization initiator present in the system, making it less susceptible to the influence of the polymerization initiator used in producing the first fluoropolymer during polymerization of the PTFE-based resin. As a result, a PTFE-based resin with a high molecular weight is more likely to be obtained. The heating temperature in the heating step is preferably 70 to 100°C, more preferably 80 to 98°C, and even more preferably 85 to 95°C, from the viewpoint of further accelerating the deactivation of the polymerization initiator in the aqueous medium.

[0124] -Other Components- The aqueous dispersion used in the present production method may contain other components in addition to the first fluorinated polymer and the aqueous medium. Specific examples of other components that the aqueous dispersion may contain include a chain transfer agent, an emulsifier other than a fluorinated emulsifier, a pH adjuster, and a wax.

[0125] Specific examples of chain transfer agents include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane.

[0126] Specific examples of emulsifiers other than fluorine-based emulsifiers include sodium lauryl sulfate, Pelex SS-H manufactured by Kao Chemical Co., Ltd., and Newcol 1305-SN manufactured by Nippon Nyukazai Co., Ltd.

[0127] Specific examples of pH adjusters include inorganic salts. Specific examples of inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate, and carbonates such as sodium bicarbonate and sodium carbonate. More preferred specific examples of phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate.

[0128] Specific examples of wax include Paraffin Wax-155 and Paraffin Wax-150 (both manufactured by Nippon Seiro).

[0129] When the aqueous dispersion contains a chain transfer agent, the content of the chain transfer agent is preferably 0.1 to 5 parts by mass per 100 parts by mass of the aqueous medium. Furthermore, the amount of the chain transfer agent used is preferably 0.1 to 20 parts by mass, more preferably 0.1 to 15 parts by mass, and even more preferably 0.1 to 10 parts by mass per 100 parts by mass of the specific monomer F described below. When the aqueous dispersion contains an emulsifier other than a fluorine-based emulsifier, the content of the emulsifier other than a fluorine-based emulsifier is preferably 0.01 to 5 parts by mass per 100 parts by mass of the aqueous medium. When the aqueous dispersion contains a pH adjuster, the content of the pH adjuster is preferably 0.01 to 3.0 parts by mass per 100 parts by mass of the aqueous medium. When the aqueous dispersion contains a wax, the content of the wax is preferably 1 to 10 parts by mass per 100 parts by mass of the aqueous medium.

[0130] Before starting polymerization of the monomer used for polymerization of PTFE-based resin, the concentration of fluorine-based emulsifier is 100 mass ppm or less relative to the total mass of the first fluorine-containing polymer in the aqueous dispersion, and from the viewpoint of more excellent effects of the present invention, it is preferably 50 mass ppm or less, more preferably 25 mass ppm or less, and even more preferably 5 mass ppm or less.The lower limit can be 0 mass ppm.The fluorine-based emulsifier means an emulsifier in which the hydrophobic part contains fluorine atoms in the hydrophilic part and the hydrophobic part of the emulsifier.Specific examples of fluorine-based emulsifier include fluorine-containing alkanoic acid salts and fluorine-containing ether carboxylic acid compounds.As an example of a method for making the concentration of fluorine-based emulsifier within the above-mentioned range, a method for producing an aqueous dispersion without using a fluorine-based emulsifier can be mentioned.

[0131] Before starting polymerization of the monomers used in the polymerization of the second fluorine-containing polymer, the concentration of fluoride ions is preferably 100 mass ppm or less, more preferably 50 mass ppm or less, based on the total mass of the aqueous dispersion, from the viewpoint of polymerization stability.The lower limit can be 0 mass ppm.An example of a method for adjusting the fluoride ion concentration to the above value can be a method of removing sulfate ions using an anion exchange resin during the production of the first fluorine-containing polymer.Here, fluoride ions may be generated by the reaction between a polymerization initiator (e.g., ammonium persulfate) and the monomers used in the production of the first fluorine-containing polymer, and may be contained in the aqueous dispersion.

[0132] -Specific Monomer F-Specific monomer F includes TFE. The amount of TFE used is preferably 97 to 100 mass %, more preferably 98 to 100 mass %, and even more preferably 99 to 100 mass %, based on the amount of specific monomer F used.

[0133] The specific monomer F may contain a fluorine-containing monomer other than TFE, but may not substantially contain a fluorine-containing monomer other than TFE. "Substantially not containing a fluorine-containing monomer other than TFE" means that the amount of the fluorine-containing monomer other than TFE used is 0.0001 mass% or less, or may be 0 mass%, relative to the amount of the specific monomer F used. Examples of the fluorine-containing monomer other than TFE include chlorotrifluoroethylene (hereinafter also referred to as "CTFE"), vinylidene fluoride (hereinafter also referred to as "VdF"), fluoroalkylethylene, PAVE, and hexafluoropropylene. Two or more types of fluorine-containing monomers other than TFE may be used in combination.

[0134] The specific monomer F may contain other monomers other than the fluorine-containing monomer, but preferably 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, more preferably 0% by mass, relative to the amount of the specific monomer F used. Specific examples of other monomers include ethylene, propylene, vinyl chloride, and vinylidene chloride. Two or more of the other monomers may be used in combination.

[0135] The amount of the 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, per 100 parts by mass of the aqueous medium contained in the aqueous dispersion.

[0136] -Polymerization initiator- In the second embodiment, the specific monomer F is preferably polymerized in the presence of a polymerization initiator. Examples of the polymerization initiator include the water-soluble radical polymerization initiator used in the step A described above.

[0137] The amount of the polymerization initiator used is preferably 1 to 1,000 ppm by mass, more preferably 5 to 750 ppm by mass, and even more preferably 10 to 500 ppm by mass, relative to 100 parts by mass of the specific monomer F used.

[0138] -Other Components- When polymerizing the specific monomer F, components other than those described above (hereinafter also referred to as "other components") may be further used. A specific example of the other component is a reducing agent. The amount of the other component used is preferably 1 to 2000 ppm by mass relative to 100 parts by mass of the specific monomer F used.

[0139] -Procedure of Step F- In this production method, the specific monomer F is polymerized in the aqueous dispersion to produce a PTFE-based resin.

[0140] The PTFE-based resin obtained by the present production method is as described above. The first fluorine-containing polymer and the PTFE-based resin may be copolymerized.

[0141] The specific monomer F is added to the reaction system (i.e., polymerization reaction vessel) by a conventional method. For example, the specific monomer F may be added to the reaction system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, the specific monomer F may be dissolved in an aqueous medium, and the resulting solution may be added to the reaction system continuously or intermittently. When a polymerization initiator is used, the polymerization initiator may be added to the reaction system all at once or in portions.

[0142] The polymerization temperature is preferably 10 to 95° C., more preferably 15 to 90° C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG. In the case of batch processing, the polymerization time is preferably 90 to 1,000 minutes, more preferably 90 to 700 minutes.

[0143] The polymerization of the specific monomer F is preferably carried out in the substantial absence of an emulsifier. Examples of the emulsifier include known emulsifiers, such as common surfactants. "In the substantial absence of an emulsifier" refers to an environment in which the content of the emulsifier is 0.03 mass ppm or less, preferably 0.02 mass ppm or less, and more preferably 0 mass ppm, relative to the total mass of the aqueous medium contained in the aqueous dispersion.

[0144] As mentioned above, it is presumed that the specific monomer F is polymerized in the particles of the first fluorine-containing polymer during polymerization of the specific monomer F, and therefore it is considered that particles containing the first fluorine-containing polymer and the PTFE-based resin are produced in this production method. That is, it is presumed that the PTFE-based resin is obtained in the form of particles containing the first fluorine-containing polymer and the PTFE-based resin according to this production method. In this case, an aqueous dispersion in which particles containing the first fluorine-containing polymer and the PTFE-based resin are dispersed in the aqueous medium is obtained according to this production method.

[0145] (Step G) Step G is a step of obtaining PTFE powder from the aqueous dispersion obtained in step F. Step G can be carried out using the same procedure and conditions as in step B above.

[0146] [Electrode Mix] The electrode mix of the present invention contains the above-mentioned PTFE powder and an active material. When the electrode mix is ​​a negative electrode mix, the negative electrode mix preferably contains PTFE powder and a negative electrode active material. When the electrode mix is ​​a positive electrode mix, the positive electrode mix preferably contains PTFE powder and a positive electrode active material.

[0147] <PTFE Powder> The electrode mixture contains PTFE powder. The PTFE powder has the same meaning as the PTFE powder of the present embodiment described above, and preferred embodiments are also the same.

[0148] The content of the PTFE powder is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1.0% by mass or more, relative to the total mass of the electrode mixture. The upper limit is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 10% by mass or less. The content of the PTFE powder is preferably 0.1 to 50% by mass, more preferably 0.1 to 30% by mass, even more preferably 0.5 to 30% by mass, and particularly preferably 1.0 to 10% by mass, relative to the total mass of the electrode mixture. Within the above ranges, 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 improved, and a decrease in battery capacity or conductivity can be further suppressed. PTFE powder has excellent binding strength, so even a small content can sufficiently retain the active material within the electrode mixture.

[0149] <Active Material> The electrode mixture contains an active material. Examples of the active material include a positive electrode active material and a negative electrode active material, and the active material can be appropriately selected depending on the intended electrode.

[0150] (Positive Electrode Active Material) When the electrode mixture is a positive electrode mixture, the positive electrode mixture contains a positive electrode active material. In addition to the PTFE powder and the positive electrode active material, the positive electrode mixture may contain at least one selected from the group consisting of a binder other than the PTFE powder, a conductive material, a thickener, and an additive. As the positive electrode active material, a material that electrochemically absorbs and releases lithium ions is used. Examples of such materials include at least one selected from the group consisting of lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides. From the viewpoint of high average discharge voltage and cost advantage, the positive electrode active material may be a lithium-containing transition metal oxide.

[0151] A surface-attaching substance having a different composition from that of the positive electrode active material may be attached to the surface of the positive electrode active material, for example, 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.

[0152] The shape of the particles of the positive electrode active material may be blocky, polyhedral, spherical, oval sphere, plate-like, needle-like, columnar, etc. The positive electrode active material may be either primary particles or secondary particles.

[0153] The volume-based median diameter d50 of the particles (primary particles or secondary particles) of the positive electrode active material is preferably 0.3 μm or more, more preferably 0.5 μm or more, and even more preferably 1.0 μm or more. The upper limit is preferably 30 μm or less, more preferably 25 μm or less. d50 is preferably 0.3 to 30 μm, more preferably 0.5 to 30 μm, and even more preferably 1.0 to 25 μm. Within the above range, a high tap density product is easily obtained, or the diffusion time of lithium within the particles becomes appropriate, thereby further suppressing deterioration of battery performance. In order to improve packing properties during positive electrode preparation, two or more positive electrode active materials with different median diameters d50 may be mixed as the positive electrode active material.

[0154] The median diameter d50 is measured using a known laser diffraction / scattering particle size distribution analyzer. When using a HORIBA LA-920 particle size distribution analyzer, the measurement is performed using a 0.1% by mass aqueous solution of sodium hexametaphosphate as the dispersion medium, and after ultrasonic dispersion for 5 minutes, the measurement is performed with a refractive index set to 1.24.

[0155] The BET specific surface area of ​​the positive electrode active material is 0.1 m ２ / g or more is preferable, and 0.3m ２ / g or more is more preferable. ２ / g or less is preferable, and 30m ２ The BET specific surface area of ​​the positive electrode active material is preferably 0.1 to 50 m / g.２ / g is preferred, and 0.3 to 30m ２ The BET specific surface area is defined as a value measured by a surface area meter (for example, a fully automatic surface area measuring device manufactured by Ohkura Riken Co., Ltd.) using a nitrogen-helium mixed gas precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3, after pre-drying the sample at 150°C for 30 minutes under nitrogen flow, by a nitrogen adsorption BET single-point method based on a gas flow method.

[0156] The positive electrode active material may be used alone or in combination of two or more. When two or more positive electrode active materials are used, a preferred 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 of this with a material in which part of the Mn has been replaced with another transition metal, etc.; LiFePO ４ and LiCoO ２ Alternatively, a combination of Co with other transition metals or the like may be used.

[0157] The content of the positive electrode active material is preferably 50 to 99.5 mass %, more preferably 80 to 99 mass %, based on the total mass of the electrode mixture, in terms of high battery capacity.

[0158] (Negative Electrode Active Material) The negative electrode active material is not particularly limited as long as it can reversibly absorb and release lithium ions, desorb and insert (intercalate) lithium ions, or dope and dedope counter anions of lithium ions. Specific examples include lithium metal, carbonaceous materials such as graphite, hard carbon, and soft carbon, metals that can form alloys with lithium such as aluminum, silicon, and tin, amorphous oxides such as silicon oxide and tin oxide, and lithium titanate.

[0159] As the negative electrode active material, a silicon-containing negative electrode active material is preferable because it allows the production of a high-capacity battery. Examples of the silicon-containing negative electrode active material include silicon particles, particles having a structure in which silicon fine particles are dispersed in a silicon-based compound, and silicon-based compounds represented by the general formula SiO ｘ (0.5≦x≦1.6) or a mixture thereof. Silicon oxide is a general term for amorphous silicon oxide, and silicon oxide is, for example, a silicon dioxide particle represented by the general formula SiO ｘ (0.5≦x≦1.6). Preferably, x satisfies 0.8≦x<1.6, and more preferably 0.8≦x<1.3. This silicon oxide can be obtained, for example, by heating a mixture of silicon dioxide and metallic silicon to produce silicon monoxide gas, followed by cooling and precipitation.

[0160] The silicon-containing negative electrode active material may be coated with carbon. By being coated with carbon, electrical conductivity can be imparted, and battery characteristics can be improved. Methods for imparting electrical conductivity include, for example, a method of mixing with conductive particles such as graphite, a method of coating the surface of the silicon-containing negative electrode active material with a carbon coating, and a method of combining both. The carbon coating method is preferred, and chemical vapor deposition (CVD) is more preferred.

[0161] The shape of the particles of the negative electrode active material may be blocky, polyhedral, spherical, oval sphere, plate-like, needle-like, columnar, etc. The negative electrode active material may be either primary particles or secondary particles.

[0162] The average particle size of the particles (primary particles or secondary particles) 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 average particle size is the weight average particle size measured by particle size distribution measurement using a laser diffraction method.

[0163] The BET specific surface area of ​​the negative electrode active material is 0.5 to 100 m ２ / g is preferred, and 1 to 20m ２ / g is more preferred.

[0164] The content of the negative electrode active material is preferably 50 to 99.5 mass %, more preferably 80 to 99 mass %, based on the total mass of the electrode mixture.

[0165] <Conductive Aid> The electrode mixture may contain a conductive aid. Examples of the conductive aid include metal 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, fullerene, and vapor-grown carbon fiber.

[0166] 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 15% by mass or less, and particularly preferably 10% by mass or less. The content of the conductive additive is preferably 0.01 to 50% by mass, more preferably 0.1 to 30% by mass, and even more preferably 1 to 15% by mass, relative to the total mass of the electrode mixture.

[0167] The electrode mixture contains a PTFE-based powder, an active material, and a conductive aid, and the content of the PTFE-based powder is preferably 0.5 to 10 mass% relative to the total mass of the electrode mixture, the content of the active material is 88 to 99 mass% relative to the total mass of the electrode mixture, and the content of the conductive aid is preferably 0.5 to 10 mass% relative to the total mass of the electrode mixture, and more preferably the content of the PTFE-based powder is 1 to 10 mass% relative to the total mass of the electrode mixture, the content of the active material is 88 to 96 mass% relative to the total mass of the electrode mixture, and the content of the conductive aid is 1 to 10 mass% relative to the total mass of the electrode mixture.

[0168] <Thermoplastic Resin> The electrode mixture may contain a thermoplastic resin, such as polyvinylidene fluoride, polypropylene, polyethylene, polystyrene, polyethylene terephthalate, and polyethylene oxide.

[0169] In the electrode mixture, the ratio of the thermoplastic resin content to the active material content (thermoplastic resin content / active material content × 100) is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.10% by mass or more. The upper limit is preferably 3.0% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2.0% by mass or less. The ratio of the thermoplastic resin content to the active material content is preferably 0.01 to 3.0% by mass, more preferably 0.05 to 2.5% by mass, and even more preferably 0.10 to 2.0% by mass.

[0170] <Other Components> The electrode mixture may contain other components in addition to the various components described above. Examples of the other components include at least one selected from the group consisting of solid electrolytes, binders other than those described above, conductive materials, thickeners, and additives. Examples of solid electrolytes include sulfide solid electrolytes with an argyrodite-type crystal structure, oxide solid electrolytes, and halogenated solid electrolytes. Examples of binders include elastomers such as styrene-butadiene rubber, acrylic rubber, and styrene-ethylene-butadiene-styrene. Examples of fiber components include cellulose, carboxymethyl cellulose, cellulose nanofibers, and aramid fibers. Fiber components are preferably mixed as powders, and are preferably finely pulverized (microfibrillated) by various pulverization methods in advance to improve their mixability with the PTFE powder. Adding fiber components tends to increase the strength of the molded sheet.

[0171] The electrode mixture preferably does not substantially contain an organic solvent. Specifically, the content of the organic solvent is preferably 1.0 mass% or less, more preferably 0.1 mass% or less, based on the total mass of the electrode mixture. The lower limit may be 0 mass%.

[0172] The electrode mixture is preferably in the form of a sheet.

[0173] The electrode mixture can be suitably used as an electrode mixture for secondary batteries. The electrode mixture is particularly suitable for lithium ion secondary batteries. When used in secondary batteries, the electrode mixture is usually used in the form of a sheet.

[0174] [Method for producing electrode mixture] The method for producing the electrode mixture is not particularly limited as long as it can produce the above-mentioned electrode mixture. Among these, a method for producing an electrode mixture including a step X1 of pulverizing and mixing a raw material composition including a binder containing PTFE powder, an active material, and, if necessary, a conductive additive is preferred. The above-mentioned method for producing an electrode mixture can produce an electrode mixture in a relatively short process. It is also preferred that the method for producing an electrode mixture further includes a step X2 of rolling the raw material composition pulverized and mixed in the step X1 into a sheet. When the step X2 is included, a sheet-like electrode mixture is obtained.

[0175] (Step X1) Step X1 is a step of mixing a raw material composition containing a binder containing PTFE powder, an active material, and, optionally, a conductive additive. Mixing using a mixing device is preferred. Examples of mixing devices include a jet mill, a pin mill, a blender, a twin-screw extruder, and a mixer. Jet mills, mixers, and twin-screw extruders are preferred because they can simultaneously crush the PTFE powder and suppress fiberization. Jet mills include collision-type jet mills, which crush particles by colliding with each other or with a collision body (target); swirling airflow-type and loop-type jet mills, which crush particles by mutual collision in a crushing zone formed by multiple crushing nozzles arranged in a circulating airflow; fluidized bed-type jet mills, which crush particles by collision or friction in a fluidized bed; and supersonic jet mills. Details of collision-type, swirling airflow-type, loop-type, and fluidized bed-type jet mills are described in detail in "Advanced Crushing Technology and Applications," edited by the Japan Powder Industry and Engineering Association, NGT Co., Ltd., page 162. Collision-type jet mills include pulverizers that discharge a fluid such as compressed air from a nozzle and crush particles by causing them to collide with each other in the high-speed turbulent airflow formed in the jet mill, and pulverizers that transport resin particles in a high-speed airflow and crush them by causing them to collide with a collision body.

[0176] Commercially available jet mills include Cross Jet Mill (manufactured by Kurimoto Iron Works Co., Ltd.); Jet-O-Mill, A-O Jet Mill, Sanitary AOM, Cojet, Single Track Jet Mill, and Super STJ Mill (all manufactured by Seishin Enterprise Co., Ltd.); Current Jet Mill (manufactured by Nisshin Engineering Co., Ltd.); Urmax (manufactured by Nisso Engineering Co., Ltd.); Supersonic Jet Mill PJM Type, Supersonic Jet Mill CPY Type, Supersonic Jet Mill LJ-3 Type, and Supersonic Jet Mill I Type (all manufactured by Nippon Pneumatic Mfg. Co., Ltd.); Counter Jet Mill, Micro Jet T Type, Spiral Jet Mill, and Micron Jet MJQ (all manufactured by Hosokawa Micron Corporation); Fluidized Bed Jet Mill (manufactured by Nippon Coke & Engineering Co., Ltd.); Nano Grinding Mill (manufactured by Tokuju Kogyosho Co., Ltd.), and EX-Mini Jet Mill (M-Tech Chemical Co., Ltd.). As the jet mill, a single track jet mill is preferred due to its excellent productivity.

[0177] The grinding pressure in the jet mill is preferably 0.1 to 2 MPa, more preferably 0.2 to 0.9 MPa, from the viewpoint of achieving both crushability and suppression of fiber formation.

[0178] (Step X2) Step X2 is a step of rolling the raw material composition pulverized and mixed in step X1 into a sheet. Examples of the rolling method in step X2 include rolling using a roll press, a plate press, a calendar roll, etc. The rolling conditions are not particularly limited and can be appropriately selected according to the thickness and density of the target electrode mixture.

[0179] [Electrode] The electrode of the present invention includes a current collector and an electrode layer containing an electrode mixture disposed on the current collector. If necessary, a conductive carbonaceous material may be disposed between the current collector and the electrode layer.

[0180] <Current Collector> The electrode includes a current collector. When the electrode is a positive electrode, examples of the current collector include metals such as aluminum, titanium, tantalum, stainless steel, and nickel, or metal materials such as alloys thereof; and carbon materials such as carbon cloth and carbon paper, with metal materials being preferred, and aluminum or its alloys being more preferred. When the electrode is a negative electrode, examples of the current collector include metals such as copper, nickel, titanium, tantalum, and stainless steel, or metal materials such as alloys thereof; and carbon materials such as carbon cloth and carbon paper, with metal materials being preferred, and copper, nickel, or its alloys being more preferred.

[0181] Examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, expanded metal, punched metal, and foamed metal in the case of a metal material, and carbon plate, carbon thin film, and carbon cylinder in the case of a carbon material. Among these, metal foil is preferred as the shape of the current collector. The metal foil may be appropriately formed into a mesh. 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 thickness of the current collector is preferably 1 μm to 1 mm, more preferably 3 to 100 μm, and even more preferably 5 to 50 μm. Within the above range, excellent handleability and strength can be achieved.

[0182] In addition, it is also preferable that the surface of the current collector is coated with a conductive additive, which can reduce the electrical contact resistance between the current collector and the positive electrode active material layer. Examples of the conductive additive include carbon and precious metals such as gold, platinum, and silver.

[0183] <Electrode Layer> The electrode includes an electrode layer. The electrode layer is disposed on a current collector and includes the above-described 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, etc.

[0184] The density of the positive electrode layer is 3.00 g / cm ３ More preferably, 3.10 g / cm ３ More preferably, 3.20 g / cm ３ More preferably, the upper limit is 3.80 g / cm３ Preferably, 3.75 g / cm or less ３ More preferably, 3.70 g / cm or less ３ The density of the positive electrode layer is more preferably 3.00 to 3.80 g / cm ３ is preferred, and 3.10 to 3.75 g / cm ３ More preferably, 3.20 to 3.70 g / cm ３ The density of the negative electrode layer is more preferably 1.3 g / cm ３ More preferably, 1.4 g / cm ３ More preferably, 1.5 g / cm ３ More preferably, the upper limit is 2.0 g / cm ３ Preferably, 1.9 g / cm or less ３ More preferably, 1.8 g / cm or less ３ The density of the negative electrode layer is more preferably 1.3 to 2.0 g / cm ３ is preferred, and 1.4 to 1.9 g / cm ３ More preferably, 1.5 to 1.8 g / cm ３ Within the above range, the electrolyte solution can be easily permeated into the vicinity of the current collector / active material interface, and the charge / discharge characteristics at high current densities can be excellent. In addition, the conductivity between the active materials can be excellent.

[0185] The thickness of the electrode layers (positive electrode layer and negative electrode layer) is preferably 10 μm or more, more preferably 20 μm or more, from the viewpoint of high capacity and high output. The upper limit is preferably 500 μm or less, more preferably 450 μm or less. The thickness of the electrode layer is preferably 10 to 500 μm, more preferably 20 to 450 μm.

[0186] [Secondary Battery] The secondary battery of the present invention includes the electrode described above. The secondary battery may be a secondary battery using an electrolyte solution or a solid 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. Specific 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.

[0187] The secondary battery preferably includes a positive electrode, a negative electrode, an electrolyte, and a separator. The secondary battery may have either a laminated structure including a positive electrode, a separator, and a negative electrode in this order, or a wound structure in which the positive electrode, the separator, and the negative electrode are wound in a spiral shape. When the secondary battery has a laminated structure, the laminated structure is preferably a structure formed by bundling metal core portions of each electrode layer and welding them to a terminal. When the secondary battery has a wound structure, the internal resistance can be reduced by providing multiple lead structures on each of the positive electrode and the negative electrode and bundling them to a terminal.

[0188] The shape of the secondary battery may be, for example, cylindrical, square, laminated, coin-shaped, or large. The shapes and configurations of the positive electrode, negative electrode, and separator can be changed according to the shape of each battery.

[0189] Examples of the separator include porous membranes such as polyethylene and polypropylene; and nonwoven fabrics such as nonwoven fabrics made of resins such as polypropylene and glass fiber nonwoven fabrics. The material or shape of the separator is not particularly limited as long as it is stable to the electrolyte and has excellent liquid retention. Among these, the separator material is preferably resin, glass fiber, or an inorganic material. The separator is preferably in the form of a porous sheet or nonwoven fabric. The thickness of the separator is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 8 μm or more. The upper limit is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. The thickness of the separator is preferably 1 to 50 μm, more preferably 5 to 40 μm, and even more preferably 8 to 30 μm.

[0190] The electrolyte solution is preferably a non-aqueous electrolyte solution. Examples of the non-aqueous electrolyte solution include those obtained by dissolving a known electrolyte salt in a known organic solvent for dissolving the electrolyte salt. Examples of the organic solvent for dissolving the electrolyte salt 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. Examples of the electrolyte salt include 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 LiPF is preferred because of its excellent cycle characteristics. ６ , LiBF ４ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ Or a combination of these is preferred.

[0191] The solid-state secondary battery is preferably an all-solid-state secondary battery. The solid-state secondary battery is also preferably a lithium-ion battery or a sulfide-based all-solid-state secondary battery. The solid-state secondary battery preferably includes a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode.

[0192] The solid electrolyte used in the solid secondary battery mixture may be a sulfide-based solid electrolyte or an oxide-based solid electrolyte.

[0193] The sulfide-based solid electrolyte is not particularly limited, and may be 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 P.O. 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 P.O. ４ , Li ３ P.S. ４ -Li ４ GeS ４ , Li ３．４ P ０．６ Si ０．４ S ４ , Li ３．２５ P０．２５ Ge ０．７６ S ４ , Li ４－ｘ Ge １－ｘ P ｘ S ４ (X=0.6~0.8), Li ４＋ｙ Ge １－ｙ Ga ｙ S ４ (y=0.2-0.3), LiPSCl, LiCl, Li ７－ｘ－２ｙ P.S. ６－ｘ－ｙ Cl ｘ (0.8≦x≦1.7, 0<y≦−0.25x+0.5), or a mixture of two or more thereof. The sulfide-based solid electrolyte preferably contains lithium. Sulfide-based solid electrolytes containing lithium are used in solid-state batteries that use lithium ions as a carrier, and are preferred in terms of electrochemical devices having high energy density.

[0194] The oxide-based solid electrolyte is preferably a compound that contains oxygen atoms, has the ionic conductivity of a metal belonging to Group 1 or 2 of the periodic table, and has electronic insulation properties.

[0195] Examples of oxide-based solid electrolytes include Li ｘａ La ｙａ TiO ３ [xa=0.3~0.7, ya=0.3~0.7] (LLT), Li ｘｂ La ｙｂ Zr ｚｂ M ｂｂ ｍｂ O ｎｂ (M ｂｂ is at least one element selected from Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, where 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 ｃｃis at least one element selected from C, S, Al, Si, Ga, Ge, In, and Sn, where xc satisfies 0≦xc≦5, yc satisfies 0≦yc≦1, zc satisfies 0≦zc≦1, and nc satisfies 0≦nc≦6.), Li ｘｄ (Al, Ga) ｙｄ (Ti, Ge) ｚｄ Si ａｄ P ｍｄ O ｎｄ (where 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, and M ｅｅ represents a divalent metal atom. ｅｅ represents a halogen atom or a combination of two or more halogen atoms.), 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 Alumni ２ O ３ -P ２ O ５ , Li ２ O—SiO ２ , Li ６ BaLa ２ Ta ２ O １２ , Li ３ P.O. （４－３／２ｗ） N ｗ (w is w<1), Li having a LISICON (Lithium super ionic conductor) type crystal structure ３．５ Zn ０．２５ GeO ４ , La having a perovskite crystal structure ０．５１ Li ０．３４ TiO ２．９４ , La ０．５５ Li ０．３５ TiO３ , LiTi having a NASICON (sodium super ionic conductor) type crystal structure ２ P ３ O １２ , Li １＋ｘｈ＋ｙｈ (Al, Ga) ｘｈ (Ti, Ge) ２－ｘｈ Si ｙｈ P ３－ｙｈ O １２ (where 0≦xh≦1, 0≦yh≦1), and Li having a garnet-type crystal structure ７ La ３ Zr ２ O １２ (LLZ). Ceramic materials in which element substitution has been performed on LLZ are also known. For example, LLZ-based ceramic materials in which element substitution has been performed on LLZ with at least one of Mg (magnesium) and A (A is at least one element selected from the group consisting of Ca (calcium), Sr (strontium), and Ba (barium)) can be mentioned. Phosphorus compounds containing Li, P, and O are also desirable. For example, lithium phosphate (Li ３ P.O. ４ ), LiPON, LiPOD, in which some of the oxygen in lithium phosphate is replaced with nitrogen １ (D １ is at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc. １ ON (A １ is at least one selected from Si, B, Ge, Al, C, Ga, etc. Specific examples include 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 Examples include:

[0196] The oxide-based solid electrolyte preferably contains lithium. The oxide-based solid electrolyte containing lithium is used in a solid-state battery that uses lithium ions as a carrier, and is preferred in terms of electrochemical devices having a high energy density.

[0197] The oxide-based solid electrolyte is preferably an oxide having a crystalline structure. Oxides having a crystalline structure are preferred in terms of good Li ion conductivity. Examples of oxides having a crystalline structure include perovskite-type (La ０．５１ Li ０．３４ TiO ２．９４ ), NASICON type (Li １．３ Al ０．３ Ti １．７ (P.O. ４ ) ３ etc.), garnet type (Li ７ La ３ Zr ２ O １２ (LLZ), etc.) are listed. Among them, NASICON type is preferred.

[0198] The content of the polytetrafluoroethylene powder is preferably 1 to 10 parts by mass, more preferably 1.5 to 9 parts by mass, and even more preferably 2 to 8 parts by mass, per 100 parts by mass of the sulfide-based solid electrolyte.

[0199] The present invention will be described in detail below with reference to examples. Examples 1 to 9 and 12 to 14 are working examples, and Examples 10 to 11 and 15 are comparative examples. However, the present invention is not limited to these examples.

[0200] [Measurement and Evaluation Methods] Various measurement and evaluation methods are as follows.

[0201] <Transition Metal Element Content> 0.1 g of the PTFE powder obtained in each example described below was weighed into a platinum boat and incinerated under an oxygen atmosphere (600°C, 10 minutes) to obtain an ash product. The obtained ash product was dissolved in dilute nitric acid and adjusted to a constant volume of 20 mL to obtain a solution. The obtained solution was introduced into an ICP-MS analyzer 7700x (manufactured by Agilent) to check for the presence or absence of peaks of each transition metal element. The concentrations of the detected transition metal elements were measured by comparing them with a standard solution. The concentrations of the transition metal elements that could be analyzed by the above analyzer were summed to obtain the transition metal element content (mass ppb). Note that in this measurement method, the transition metal elements are metal elements from Groups 4 to 12 of the long period periodic table excluding technetium, scandium, and yttrium. Furthermore, the transition metal element content shown in the table below was approximately consistent with the transition metal element content derived from the additive.

[0202] <Average primary particle diameter of PTFE-based resin (PPS)> The aqueous dispersions obtained in each example described below were used as samples, and were measured using a laser scattering particle size distribution analyzer (manufactured by Horiba, Ltd., product name "LA-920"). The average primary particle diameter is a median diameter based on volume.

[0203] <Proportion of each unit in PTFE-based resin> The proportion of each unit in the PTFE-based resin obtained in each example described below is １９ It was determined by F-NMR analysis and infrared absorption spectrum analysis.

[0204] <Solid content concentration of aqueous dispersion> The solid content concentration of the aqueous dispersion obtained in each example described below was calculated by heating 2.0 g of the aqueous dispersion at 170°C for 20 minutes, weighing the mass of the residue, and calculating the solid content concentration using the following formula: "Solid content concentration (mass %) = 100 × heating residue of aqueous dispersion (g) / mass of aqueous dispersion (2.0 g)"

[0205] <SSG> The SSG was measured in accordance with ASTM D4895-10. Specifically, 12.0 g of a sample was weighed and held in a cylindrical mold with an inner diameter of 28.6 mm at 34.5 MPa for 2 minutes to obtain a molded sample. This was placed in a 290°C oven, heated at 120°C / hr, held at 380°C for 30 minutes, then cooled at 60°C / hr and held at 294°C for 24 minutes. After holding for 12 hours in a desiccator at 23°C, the specific gravity value of the molded product and water at 23°C was measured, and this was taken as the SSG.

[0206] <Electrification Voltage> The electrification voltage of the PTFE powder obtained in each example described below was measured using a digital electrostatic potential measuring instrument Model KSD-1000 (manufactured by Kasuga Electric Co., Ltd.).

[0207] <Dielectric Strength> Dielectric strength was measured in accordance with JIS K6892:1995. The specific procedure was as follows. The PTFE powder obtained in each example was left at a temperature of 25±2°C for at least 1 hour, then thoroughly sieved through a 1.7 mm mesh sieve at the same temperature. 100±0.1 g of the sieve that passed through was weighed out and used as the sample. The sample was placed in a 500 mL wide-mouth glass bottle, and 25±0.1 g of toluene was added little by little, taking care not to wet the walls of the bottle. The bottle was then stoppered and shaken vigorously for 3 minutes to mix the sample and toluene. The resulting mixture was placed in a preforming mold, and gently pressurized so that the push rod movement speed did not exceed 50 mm / min. The molding pressure was maintained at 0.98 MPa for 1 minute to perform preforming. The preforming product was removed from the preforming mold and immediately transferred to an extrusion molding tester. The lower part of the mold of the extrusion molding tester was maintained at a temperature of 60±5°C. Next, the extrusion molding tester with the preform set in place was attached to a 3-ton hydraulic press, and the ram was moved at a speed of 5-10 mm / min to perform extrusion molding. The dimensions were 5 mm outer diameter and 4 mm inner diameter. Approximately 1 m of the molded product was cut off after it began to emerge. From the remaining molded products, 15 pieces of 25 ± 1 cm length were cut with a sharp blade and inserted into rods on a sample holder and left at room temperature for 12-24 hours. The sample holder was then placed in an electric furnace maintained at 365 ± 5 °C. After the temperature inside the furnace reached 365 ± 5 °C again, the product was heated and baked for 30 ± 3 minutes, then removed and allowed to cool at room temperature. The resulting molded product was used as a test specimen. A metal rod was inserted into the test specimen to serve as the internal electrode, and metal foil was wrapped around the center to serve as the external electrode. A high-voltage lead wire was connected to the external electrode, and the internal electrode was grounded. The applied voltage was quickly increased to a predetermined voltage, and the specimen's ability to withstand this voltage for 1 minute was examined. The predetermined voltage was increased by 1 kV at a time, and the maximum voltage that could be endured for 1 minute was taken as the withstand voltage.

[0208] <Preparation of positive electrode mixture> NMC622 (manufactured by Hosen Co., Ltd., average particle size 10 μm, positive electrode active material), PTFE powder of each example, and acetylene black (manufactured by Sigma-Aldrich) were mixed in a mass ratio of 96: 3: 1, and then pulverized and mixed using an Ex-Mini Jet Mill (manufactured by M-Tech Chemical Co., Ltd.) at a feed rate of 3 g / min and an air pressure of 0.4 MPa to obtain a positive electrode mixture. After mixing, adhesion to the piping was visually confirmed during disassembly and cleaning. 50 g of the obtained electrode mixture was passed through a 3 t roll press at a temperature of 90 ° C. only once to form a sheet, and a positive electrode mixture sheet with a thickness of 200 μm was obtained.

[0209] <Wall Adhesion> After preparing the electrode mixture by powder mixing using a jet mill in <Preparation of Positive Electrode Mixture>, the presence or absence of adhesion to the piping and container walls was visually confirmed, and the wall adhesion was evaluated according to the following evaluation criteria. The lower the wall adhesion, the better. "A": No adhesion was observed. "B": Adhesion was observed.

[0210] <Sheet toughness> The positive electrode mixture sheet obtained in <Preparation of positive electrode mixture> was repeatedly bent 20 times at a radius of 4 mm using a cylindrical mandrel bending tester (Allgood Co., Ltd.), and the toughness was evaluated according to the following evaluation criteria. A and B were evaluated as passing. "A": No cracks were observed. "B": Cracks were observed at the edge of the sheet. "C": The sheet was cracked.

[0211] <Capacity Retention Rate> Graphite QC-6 (manufactured by Hosen Co., Ltd.) and the PTFE powder of each example (Examples 1, 12, and 13) were premixed in a V blender at a mass ratio of 96:4, and then pulverized and mixed in an Ex-mini jet mill (manufactured by M-Tech Chemical Co., Ltd.) at a feed rate of 3 g / min and an air pressure of 0.4 MPa to obtain a negative electrode mixture. After mixing, the obtained negative electrode mixture was passed through a 3 ton roll press at a temperature of 100°C, with the roll gap changed three times in the order of 1 mm → 0.5 mm → 0.2 mm, to form a sheet with an average thickness of 180 μm (average basis weight: 15.5 mg / cm ２) to obtain a negative electrode mixture sheet. During this process, the above-mentioned <Wall adhesion> and <Sheet toughness> were evaluated. This negative electrode mixture sheet was laminated with a 12 μm thick copper foil by pressing at 100° C. and 1 MPa, and then punched out to a diameter of 16 mm. The sheet was then incorporated into an HS flat cell (manufactured by Hosensha) with the following configuration to form a half cell. (Configuration) Working electrode: negative electrode mixture sheet Counter electrode: metallic lithium (manufactured by Honjo Chemical Co., Ltd., 100 μm) Separator: GA55 (glass separator manufactured by Advantec) Electrolyte: 1M LiPF ６ / Ethylene carbonate:dimethylene carbonate = 1:1 Impregnation conditions: -60 kPa, 3 min x 6 times (Evaluation) Using a charge / discharge evaluation device TOSCAT (manufactured by Toyo Systems Co., Ltd.), the capacity mAh / g was measured after 5 cycles of charge / discharge at 0.05 C at 2.0-0.0 V vs. Li electrode, and this was taken as the initial capacity. After evaluating the initial capacity as described above, the charge / discharge rate was increased to 0.5 C and 20 charge / discharge cycles were performed. Then, the rate was returned to 0.05 C and 5 charge / discharge cycles were performed. The capacity at the final cycle was confirmed as the post-cycle capacity, and the capacity retention rate was calculated using the following formula: Capacity retention rate = post-cycle capacity / initial capacity x 100 The evaluation criteria are as follows: A: 98% or more. B: Less than 98%.

[0212] Example 1 Preparation of PTFE Powder In a 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature-controlling jacket, 3600 g of deionized water, 180 g of paraffin wax, and perfluoroether carboxylic acid B (CF ３ CF ２ OCF ２ CF ２ OCF ２ COONH ４5.4 g of the ammonium salt of perfluoroethercarboxylic acid B, 0.108 g of succinic acid, and 0.0252 g of oxalic acid were charged, and the polymerization vessel was heated to 70 ° C. while being purged with nitrogen gas to remove oxygen. After maintaining the temperature in the vessel at 70 ° C. with stirring, TFE was introduced and the pressure was adjusted to 2.7 MPaG. While stirring the contents, deionized water in which 3.5 mg of potassium permanganate was dissolved was continuously added at a constant rate, and TFE was continuously supplied so that the pressure in the polymerization vessel was constant at 2.7 MPaG. When the TFE consumption amount reached 184 g, 3.8 g of the ammonium salt of perfluoroethercarboxylic acid B was added, and when the TFE consumption amount reached 900 g, the entire amount of deionized water in which 3.5 mg of potassium permanganate was dissolved was added. When the TFE consumption reached 1,543 g, stirring and TFE supply were stopped, and the TFE in the polymerization tank was purged to terminate the polymerization reaction, yielding a dispersion. The resulting dispersion was removed and cooled, and the paraffin wax was separated to yield an aqueous dispersion containing a PTFE-based resin. The resulting aqueous dispersion containing a PTFE-based resin had an average primary particle size of 310 nm and a solids concentration of 30.6% by mass. The resulting aqueous dispersion was diluted to a solids concentration of 13% by mass, and nitric acid was added to the mixture while stirring in a container to coagulate the PTFE-based resin, followed by filtering to separate the water, yielding a wet PTFE powder. The water content of the wet PTFE powder was 40% by mass relative to the total mass of the wet PTFE powder. The resulting wet PTFE powder was placed on a stainless steel mesh tray (placement amount: 2.0 g / cm). ２ ), and 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 Powder 1. 100 g of the obtained Powder 1 was wetted with 10 g of 30 mass % ethanol water at room temperature in which 0.3 mg of iron acetate had been dissolved, for 1 hour, and then air-dried and dried at 150°C to obtain PTFE Powder 1 before the electrostatic charge adjustment.

[0213] <Adjustment of Charging Voltage> Next, the obtained PTFE powder 1 before the charging voltage adjustment was placed in a nylon pot with an inner diameter of 150 mm so that the internal volume was 30% by volume, and the pot was rotated for 10 minutes at 20% of the critical rotation speed to charge, thereby obtaining the PTFE powder of Example 1. The PTFE powder of Example 1 had an SSG of 2.16 and a withstand voltage of 4 kV. The obtained PTFE powder was used for the above evaluations. The results are shown in Tables 1 and 2 (hereinafter, similarly shown in Tables 1 to 3).

[0214] [Example 2] 100 g of powder 1 obtained in the same manner as in Example 1 was wetted with 10 g of 30 mass % ethanol water at room temperature containing 0.06 mg of iron acetate dissolved therein for 1 hour, and then air-dried and dried at 150° C. to obtain PTFE powder of Example 2. The charging voltage was also adjusted using the same procedure as in Example 1.

[0215] [Example 3] A PTFE powder of Example 3 was obtained in the same manner as in Example 1, except that 100 g of powder 1 obtained in the same manner as in Example 1 was wetted for 1 hour with 10 g of 30 mass % ethanol water at room temperature in which 0.45 mg of iron acetate had been dissolved.

[0216] [Example 4] PTFE powder 1 before adjustment of the charging voltage, obtained in the same manner as in Example 1, was placed in a nylon pot having an inner diameter of φ150 mm so that the content was 30% by volume in terms of the internal volume, and the pot was rotated for 10 minutes at a rotation speed that was 10% of the critical rotation speed to charge it, thereby obtaining the PTFE powder of Example 4.

[0217] [Example 5] PTFE powder 1 before the adjustment of the charging voltage, obtained in the same manner as in Example 1, was placed in a nylon pot mill, and then charged in the same manner as in Example 1, except that dry nitrogen was sealed in, to obtain the PTFE powder of Example 5.

[0218] [Example 6] A PTFE powder of Example 6 was obtained in the same manner as in Example 1, except that 1,100 g of the powder obtained in the same manner as in Example 1 was wetted for 1 hour with 10 g of 30 mass % ethanol water at room temperature in which 0.33 mg of zinc acetate dihydrate had been dissolved.

[0219] [Example 7] The PTFE powder of Example 6 was obtained in the same manner as in Example 1, except that 100 g of the powder obtained in the same manner as in Example 1 was wetted with 10 g of 30 mass % ethanol water at room temperature in which 0.42 mg of nickel acetate tetrahydrate had been dissolved, for 1 hour.

[0220] [Example 8] The PTFE powder of Example 8 was obtained in the same manner as in Example 1, except that 100 g of powder 1 obtained in the same manner as in Example 1 was wetted for 1 hour with 10 g of 30 mass % ethanol water at room temperature (25°C) in which 0.45 mg of manganese acetate tetrahydrate had been dissolved.

[0221] [Example 9] A PTFE powder of Example 9 was obtained in the same manner as in Example 1, except that 100 g of powder 1 obtained in the same manner as in Example 1 was wetted for 1 hour with 10 g of 30 mass % ethanol water at room temperature in which 0.15 mg of iron acetate and 0.21 mg of nickel acetate tetrahydrate had been dissolved.

[0222] [Example 10] After adjusting the charging voltage in the same manner as in Example 1, an electrode mixture sheet of Example 10 was obtained. That is, powder 1 was used as the PTFE powder of Example 10.

[0223] [Example 11] A PTFE powder of Example 11 was obtained in the same manner as in Example 1, except that 100 g of powder 1 obtained in the same manner as in Example 1 was wetted for 1 hour with 10 g of 30 mass % ethanol water at room temperature in which 0.6 mg of iron acetate had been dissolved.

[0224] Example 12: A 100 L stainless steel autoclave equipped with a baffle and a stirrer was charged with C ２ F ５ O.C. ２ F ４ OCF ２ COONH ４ 70 g of ammonium perfluoro-3,6-dioxaoctanoate (hereinafter referred to as "APFDO"), 872 g of paraffin wax, and 59 liters of deionized water were charged into the autoclave. After replacing the air in the autoclave with nitrogen, the pressure was reduced and the autoclave was filled with CH ２ =CH-(CF ２ ) ４2 g of PFBE (hereinafter referred to as "PFBE") and 300 g of deionized water were suctioned and charged. Next, the autoclave was pressurized with TFE and heated to 70°C with stirring. Next, the pressure was increased to 1.765 MPa with TFE, and 5.0 g of disuccinic acid peroxide (concentration 80% by mass, the remainder being water) was dissolved in 1 liter of warm water at approximately 70°C and injected. Polymerization was then allowed to proceed while adding TFE so as to maintain the internal pressure of the autoclave at 1.765 MPa. APFDO was dissolved in warm water and a total of 125 g of APFDO was added during the polymerization. Furthermore, ammonium sulfite was dissolved in water and a total of 4 g of ammonium sulfite was added during the polymerization. The temperature was lowered to 65°C during the polymerization and then raised to 90°C in the latter half of the polymerization. When the amount of TFE added reached 23 kg, the reaction was terminated, and the TFE in the autoclave was released into the atmosphere. The resulting aqueous PTFE emulsion was cooled, and the supernatant paraffin wax was removed. The solids concentration of the aqueous PTFE emulsion was approximately 26% by mass. The amount of APFDO used was 8,478 ppm by mass relative to the final PTFE yield. The amount of PFBE added was 0.0087% by mass relative to the final PTFE yield. The amount of coagulated material in the reactor was only traces. The average primary particle diameter of the PTFE microparticles was 250 nm. This aqueous PTFE emulsion was diluted with pure water to a concentration of 10% by mass, adjusted to 20°C, and stirred and coagulated to produce a PTFE fine powder. The PTFE fine powder was then dried at 180°C. 100 g of the obtained powder 12 was wetted with 10 g of 30 mass % ethanol water at room temperature containing 0.3 mg of iron acetate dissolved therein for 1 hour, then air-dried and dried at 150 ° C to obtain PTFE powder 12 before adjustment of charging voltage. Next, the obtained PTFE powder 12 before adjustment of charging voltage was placed in a nylon pot with an inner diameter of φ150 mm so that the internal volume was 30 volume %, and the pot was rotated at 20% of the critical rotation speed for 10 minutes to charge, obtaining the PTFE powder of Example 12. The PTFE powder of Example 12 had an SSG of 2.14 and a withstand voltage of 10 kV.

[0225] Example 13: A 100 L stainless steel autoclave equipped with a baffle and a stirrer was charged with 70 g of APFDO, 872 g of paraffin wax, and 59 L of deionized water. The autoclave was purged with nitrogen, then reduced in pressure, pressurized with TFE, and heated to 70°C with stirring. The pressure was then increased to 1.765 MPa with TFE, and 5.0 g of disuccinic acid peroxide (80% by mass, remainder water) dissolved in 1 L of warm water at approximately 70°C was added. The internal pressure dropped to 1.746 MPa in approximately 3 minutes. Polymerization was allowed to proceed while adding TFE to maintain the internal pressure of the autoclave at 1.765 MPa. APFDO was dissolved in warm water and added in total to 125 g of APFDO during the polymerization. Ammonium sulfite was also dissolved in water and added in total to 4 g of ammonium sulfite during the polymerization. The temperature was lowered to 64°C during the polymerization and increased to 80°C in the latter half of the 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. The polymerization time was 155 minutes. The resulting aqueous PTFE emulsion was cooled, and the supernatant paraffin wax was removed. The solids concentration of the aqueous emulsion was approximately 26% by mass. The amount of APFDO used was 8,555 ppm by mass relative to the final PTFE yield. The average primary particle diameter was 275 nm. Only traces of coagulated material remained in the reactor. This aqueous emulsion was diluted to a concentration of 10% by mass with pure water, adjusted to 20°C, and stirred and coagulated to obtain a PTFE fine powder. The PTFE fine powder was then dried at 180°C. 100 g of the obtained powder 13 was wetted with 10 g of 30 mass % ethanol water at room temperature containing 0.3 mg of iron acetate dissolved therein for 1 hour, then air-dried and dried at 150 ° C. to obtain PTFE powder 13 before adjustment of charging voltage. Next, the obtained PTFE powder 12 before adjustment of charging voltage was placed in a nylon pot with an inner diameter of φ150 mm so that the internal volume was 30 volume %, and the pot was rotated at 20% of the critical rotation speed for 10 minutes to charge, obtaining the PTFE powder of Example 13. The PTFE powder of Example 13 had an SSG of 2.15 and a withstand voltage of 6 kV.

[0226] [Example 14] In an environment with a dew point of -60 ° C. or less, a sulfide solid electrolyte (Fine LPSCl manufactured by NEI) having an average particle size of 1 μm, lithium niobate-coated NCM111 particles (cathode active material) having an average particle size of 7 μm, a conductive additive, and the PTFE powder 12 of Example 12 were mixed in a ratio of 20 parts by mass: 75 parts by mass: 2 parts by mass: 3 parts by mass in the same manner as in <Preparation of Cathode Mix> and formed into a sheet. The obtained cathode mix sheet was evaluated for its <wall adhesion> and <sheet toughness>.

[0227] Example 15 The charging voltage was adjusted in the same manner as in Example 12, except that the sample was not wetted for 1 hour with 10 g of 30 mass % ethanol water at room temperature having 0.3 mg of iron acetate dissolved therein, to obtain PTFE powder 15. A positive electrode mixture sheet was produced using PTFE powder 15 in the same manner as in Example 14, and the <wall surface adhesion> and <sheet toughness> were evaluated.

[0228] In Tables 1 to 3, the column "Additive" indicates the compound dissolved in 30% by mass ethanol water when the obtained powder was wetted with 10 g of 30% by mass ethanol water at room temperature for 1 hour. The column "Transition metal element content" indicates the content of the transition metal element relative to the total mass of the PTFE powder of each example.

[0229]

[0230]

[0231]

[0232] As shown in Tables 1 to 3, it was confirmed that the use of the PTFE powder of the present invention resulted in excellent toughness of the sheets obtained by mixing active materials, etc. (Examples 1 to 9, 12, 13, and 14). Furthermore, as shown in Tables 1 and 3, it is presumed that Examples 10 and 15 had low transition metal element contents, resulting in insufficient cohesive force between the PTFE-based resins, and therefore poor sheet toughness. Furthermore, it is presumed that Example 11 had an excessively high transition metal element content, which acted as a foreign substance, thereby resulting in poor sheet toughness. It is believed that interaction with the metal on the wall occurred during grinding in the jet mill, strengthening wall adhesion. Furthermore, as shown in Table 1, a comparison of Examples 1 to 3 and 6 to 9 with Examples 4 and 5 confirmed that when the charging voltage was -200 to -3000 V, both wall adhesion and sheet toughness were superior. Furthermore, as shown in Table 1, a comparison of Examples 1 to 3 confirmed that when the content of the transition metal element was 200 to 1000 mass ppb relative to the total mass of the polytetrafluoroethylene powder, the wall surface adhesion was weakened (excellent wall surface adhesion). Furthermore, as shown in Table 2, Examples 12 and 13, which had withstand voltages of 10 kV and 6 kV, respectively, had higher capacity retention rates than Example 1, which had a withstand voltage of 4 kV.

[0233] According to the present invention, polytetrafluoroethylene powder can be provided that is mixed with an active material or the like to prepare an electrode mixture, and the sheet obtained using the electrode mixture has excellent toughness. Furthermore, according to the present invention, an electrode mixture, an electrode, and a secondary battery can be provided. The entire contents of the specifications, claims, and abstracts of Japanese Patent Application No. 2024-114655 filed on July 18, 2024, and Japanese Patent Application No. 2025-004882 filed on January 14, 2025 are incorporated herein by reference.

Claims

1. A polytetrafluoroethylene powder used as a binder for a secondary battery, comprising a polytetrafluoroethylene resin and a transition metal element, the content of the transition metal element being 100 to 1500 ppb by mass relative to the total mass of the polytetrafluoroethylene powder.

2. The polytetrafluoroethylene powder according to claim 1, having a charging voltage of -200 to -3000V.

3. The polytetrafluoroethylene powder according to claim 1 or 2, wherein the content of the transition metal element is 200 to 1000 ppb by mass relative to the total mass of the polytetrafluoroethylene powder.

4. Polytetrafluoroethylene powder according to claim 1 or 2, wherein the withstand voltage of a hollow cylindrical molded article of 5 mm in outer diameter and 4 mm in inner diameter is 5 kV or more.

5. A polytetrafluoroethylene powder according to claim 1 or 2, wherein the content of units based on tetrafluoroethylene relative to the total units of the polytetrafluoroethylene resin is 99 mass% or more.

6. The polytetrafluoroethylene powder according to claim 1 or 2, wherein the transition metal element is at least one selected from the group consisting of metal elements of Groups 4 to 12 of the long-form periodic table excluding technetium, scandium, and yttrium.

7. An electrode mixture comprising the polytetrafluoroethylene powder according to claim 1 or 2 and an active material.

8. The electrode mixture according to claim 7, further comprising a sulfide-based solid electrolyte, wherein the content of the polytetrafluoroethylene powder is 1 to 10 parts by mass per 100 parts by mass of the sulfide-based solid electrolyte.

9. The electrode mixture according to claim 7, which is in the form of a sheet.

10. The electrode mixture according to claim 7, further comprising a conductive additive, wherein the content of the polytetrafluoroethylene powder is 0.5 to 10 mass% relative to the total mass of the electrode mixture, the content of the active material is 88 to 99 mass% relative to the total mass of the electrode mixture, and the content of the conductive additive is 0.5 to 10 mass% relative to the total mass of the electrode mixture.

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

12. A secondary battery comprising the electrode according to claim 11.

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