Polytetrafluoroethylene powder, electrode mixture, electrode, and secondary battery

Abstract

To provide a polytetrafluoroethylene powder excellent in toughness of a sheet obtained by using an electrode mixture prepared by mixing the polytetrafluoroethylene powder with an active material or the like.SOLUTION: A polytetrafluoroethylene powder used as a binder for a secondary battery, comprising: a polytetrafluoroethylene-based resin; and a transition metal element, wherein a content of the transition metal element is from 100 to 1500 ppb by mass with respect to a total mass of the polytetrafluoroethylene powder.SELECTED DRAWING: None

Description

[Technical Field]

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

[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, and the like to a current collector. However, in recent years, with the aim of reducing the environmental impact during production and improving oxidation resistance, dry methods have 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 organic solvents such as N-methyl-2-pyrrolidone.

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

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-051888 Summary of the Invention [Problem to be solved by the invention]

[0006] When the properties of a sheet obtained using an electrode mixture containing the polytetrafluoroethylene powder described in Patent Document 1 and an active material 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 provides a sheet having excellent toughness when used with the electrode mixture. Another object of the present invention is to provide an electrode mixture, an electrode, and a secondary battery. [Means for solving the problem]

[0008] As a result of extensive research, the present inventors have found that the above problems can be solved by the following configuration. [1] A polytetrafluoroethylene powder used as a binder for a secondary battery, Contains a polytetrafluoroethylene resin and a transition metal element, Polytetrafluoroethylene powder, 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], 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] The polytetrafluoroethylene powder according to any one of [1] to [3], which has a withstand voltage of 5 kV or more. [5] An electrode mixture comprising the polytetrafluoroethylene powder according to any one of [1] to [4] and an active material. [6] Further, the battery contains a sulfide-based solid electrolyte, The electrode mixture according to [5], 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. [7] The electrode mixture according to [5] or [6], which is in a sheet form. [8] Further containing a conductive additive, 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% by mass relative to the total mass of the electrode mixture, The electrode mixture according to any one of [5] to [7], wherein the content of the conductive assistant is 0.5 to 10 mass % relative to the total mass of the electrode mixture. [9] An electrode comprising: a current collector; and an electrode layer disposed on the current collector and containing the electrode mixture according to any one of [5] to [8].

[10] A secondary battery comprising the electrode according to [9]. [Effects of the Invention]

[0009] According to the present invention, polytetrafluoroethylene powder can be provided which can be mixed with an active material or the like to prepare an electrode mixture, and which provides a sheet having excellent toughness when used with the electrode mixture. Furthermore, the present invention can provide an electrode mixture, an electrode, and a secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0010] The terms used in the present invention have the following meanings. A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the upper and lower limits. In the numerical ranges described in stages in this specification, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the 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 a single substance corresponding to the component, or two or more substances may be used in combination. When two or more substances are used in combination for each component, the content of the component refers to the total content of the substances used in combination, unless otherwise specified. As used herein, a combination of two or more preferred embodiments is a more preferred embodiment. The term "unit" refers collectively to an atomic group derived from one molecule of a monomer, which is formed directly by polymerizing the monomer, and an atomic group obtained by chemically converting a part of the 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 the total 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 is approximately the same as the actual content of each unit.

[0011] [Polytetrafluoroethylene powder] The polytetrafluoroethylene powder (hereinafter also simply referred to 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.

[0012] The present inventors have found that, because sheet-like 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, the degree of progress of fibrillation of the PTFE powder can be appropriately adjusted by adjusting the content of transition metal elements in the PTFE powder within a predetermined range, and it is presumed that, in a sheet obtained using an electrode mixture containing an active material, etc., if the content of transition metal elements is within a predetermined range, the interactions between the PTFE-based resin and the transition metal elements, and the interactions between the transition metal elements themselves, will be of appropriate strength, resulting in excellent sheet toughness. Another effect of the PTFE powder of this embodiment is that active materials mixed with the PTFE powder tend to adhere to the wall of a container during mixing, tend to be unevenly mixed, and may result in a reduced recovery amount and a lower yield, etc. 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 comprising an aggregate of granular and particulate forms. When the PTFE powder is in a particulate form, 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 further preferably 2.130 to 2.180. SSG is used as a relative measure of molecular weight, and the lower the value, the higher the molecular weight. Also, if a large amount of monomers other than tetrafluoroethylene is introduced into a PTFE-based resin, the amorphous structure increases further, 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 molded into a cylindrical mold with an inner diameter of 28.6 mm at 34.5 MPa for 2 minutes. This is placed in a 290°C oven, 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 the sample in a desiccator at 23°C for 12 hours, the specific gravity of the molded product relative to water is measured at 23°C, and this is the SSG.

[0015] The extrusion pressure of the PTFE powder in the extrusion test 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 as follows. 100 g of PTFE powder that had been left at room temperature for at least two hours was placed in a 500 mL glass bottle, 21.7 g of lubricating oil (Isopar H (registered trademark), manufactured by Exxon Chemical) was added, and the mixture was mixed for three minutes to obtain a mixture. The resulting mixture was then left in a 25°C thermostatic chamber for two hours, and then extruded through an orifice with a diameter of 2.5 cm, a land length of 1.1 cm, and an entrance angle of 30° at 25°C 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 speed of 51 cm / min to obtain an extrusion bead (string-like material). The pressure required for extrusion at this time was measured and recorded as the extrusion pressure (unit: MPa).

[0016] The withstand voltage of the PTFE powder molded article 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 binder for a negative electrode. 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, based on 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 value is calculated and used. Moisture content (mass%) = 100 × [(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. The bulk density 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 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. For example, the angle of repose can be measured based on JIS-R931-2-2:1999 (corresponding international standard: ISO 920:1976).

[0020] The pore volume of PTFE powder is 0.2 to 15.0 cm 3 / g is preferred, and 0.5 to 10.0 cm 3 When 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, for example, mercury intrusion porosimetry using a known analytical device (for example, AutoPoreIV 9520 manufactured by Micromeritics).

[0021] The average pore size of the PTFE powder is preferably 0.05 to 2.0 μm, more preferably 0.1 to 1.5 μm. The average pore size 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 When the average pore diameter (μm) is calculated as 4V / A, the average pore diameter (μm) is calculated as 4V / A. The specific surface area is the BET specific surface area. The BET specific surface area is defined as the value measured by the nitrogen adsorption BET single-point method using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.) after pre-drying the sample at 150°C for 30 minutes under a nitrogen flow, using a nitrogen-helium mixed gas precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3.

[0022] The median pore diameter of the PTFE powder is preferably 10 to 100 μm. The median pore diameter of the PTFE powder is the pore diameter when the cumulative value is 50% by volume of the pore volume in a pore distribution profile obtained by mercury intrusion porosimetry using a known analyzer.

[0023] The electrostatic potential of the PTFE powder (secondary particles) 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 surface adhesion. If 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., and dispersibility can be improved. In addition, wall surface adhesion can also be excellent. The electrostatic potential can be measured using a digital electrostatic potential meter, Model KSD-1000 (manufactured by Kasuga Electric Co., Ltd.). Charging voltage can be adjusted using various ionizers and mechanical friction. When charging by mechanical friction, due to the triboelectric series, charging can be done efficiently by vibrating the material while it is in contact with nylon material. In particular, charging voltage can be easily adjusted by putting dried PTFE powder into a pot mill and rotating it at a speed of 10 to 50% of the critical rotation speed. The critical rotation speed is the rotation speed at which the contents rotate along 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 order to improve the binding strength and the 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 size is a 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] The PTFE powder is used as a binder for secondary batteries. The PTFE powder is preferably used, for example, in a composition for forming a member or layer constituting a secondary battery. More preferably, it is used in an electrode binder obtained by mixing the PTFE powder and an active material or the like. Note that the binder has the same meaning as a general binder, and examples include so-called binders, dispersants, and adhesives. Examples of the member or layer constituting the secondary battery include the electrode layer in the electrode described below. Further, the secondary battery is not particularly limited as long as it is a known secondary battery. Preferred embodiments of the secondary battery are as described below.

[0027] The PTFE powder can also be suitably used for other applications. Examples of other applications include ceramic capacitors such as low-temperature sintering type barium titanate. In the capacitor, barium titanate and the PTFE powder are mixed, sheeted, then a small amount of water is added, and a temperature of 100 to 200 °C and a pressure of several hundred MPa are applied to densify. By using the PTFE powder of the present invention, the strength after densification can be increased.

[0028] Hereinafter, various components that the PTFE powder may contain will be described in detail.

[0029] <PTFE-based resin> The PTFE powder contains a PTFE-based resin. The PTFE-based resin refers to a resin containing units based on tetrafluoroethylene (hereinafter referred to as "TFE units").

[0030] (TFE units) The PTFE resin is a resin containing TFE units, and the content of TFE units relative to the total units of the resin 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. The upper limit can be 100% by mass. The content of TFE units is preferably 99 mol % or more, more preferably 99.5 mol % or more, and even more preferably 99.9 mol % or more, relative to all units in the PTFE resin. The upper limit can be 100 mol %.

[0031] (units based on other monomers) The PTFE-based resin may contain units based on other monomers than the TFE units. Other monomers include, for example, perfluoroolefins such as hexafluoropropylene (HFP); hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride (VdF); perhaloolefins such as chlorotrifluoroethylene; perfluorovinyl ethers such as perfluoro(alkyl vinyl ether) (PAVE); perfluoroallyl ethers; (fluoroalkyl)ethylenes (FAE); and ethylene. Among these, the other monomer is preferably HFP, VdF, FAE or PAVE, and more preferably FAE. The other monomer may be a monomer used in the method for producing PTFE powder described below.

[0032] As the PAVE, a monomer represented by formula (PA) is preferred. CF2=CF-O-Rf 1 (PA) In formula (PA), Rf 1 represents a perfluoroalkyl group having 1 to 10 carbon atoms. 1The number of carbon atoms in the perfluoroalkyl group represented by the following formula is preferably 1 to 8, more preferably 1 to 6, even more preferably 1 to 5, and particularly preferably 1 to 3, in terms of better polymerization reactivity. The perfluoroalkyl group may be linear or branched.

[0033] Specific examples of PAVE include CF2=CFOCF3 (PMVE), CF2=CFOCF2CF3 (PEVE), CF2=CFOCF2CF2CF3 (PPVE), CF2=CFOCF2CF2CF2CF3, and CF2=CFO(CF2)8F, with PMVE or PPVE being preferred.

[0034] The FAE is preferably a monomer represented by formula (FA). CZ2=CX(CF2) 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 CH2=CH(CF2)2F, CH2=CH(CF2)3F, CH2=CH(CF2)4F(PFBE), CH2=CF(CF2)3H, and CH2=CF(CF2)4H, with PFBE or CH2=CH(CF2)2F being preferred, and PFBE being more preferred.

[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% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, based on the total units of the PTFE-based resin.

[0036] The content of TFE units and PFBE-based units is preferably 95% by mass or more, more preferably 99% by mass or more, and even more preferably 99.9% by mass or more, relative to the total mass of the PTFE-based resin. The upper limit can be 100% by mass.

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

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

[0039] The content of the PTFE 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 elements> The PTFE powder contains a transition metal element. As the type of transition metal element, metal elements from Groups 4 to 12 of the long periodic table excluding technetium, scandium and yttrium are preferred, and iron, zinc, nickel and manganese are more preferred.

[0041] The content of the transition metal element is 100 to 1500 mass ppb, preferably 200 to 1500 mass ppb, and more preferably 200 to 1000 mass ppb, relative to the total mass of the PTFE powder, and the toughness of the resulting sheet is excellent when the content of the transition metal element is within the above range. The content of transition metal elements 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 ashed under an oxygen atmosphere (600°C, 10 minutes) to obtain an ashed product. The ashed 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 check whether or not peaks of each transition metal element are detected, and the concentrations of the detected transition metal elements are measured by comparing them with a standard solution. The concentrations of each transition metal element that can be analyzed by the above-mentioned analyzer are summed to obtain the content of the transition metal element.

[0042] The content of the transition metal element can be adjusted by wetting the PTFE powder with a solution containing the transition metal element, specifically by the method shown in the Examples section. Another method for adjusting the content is, for example, to use a material containing a transition metal element in the polymerization reaction for obtaining the PTFE-based resin, or to adjust the amount of the material used.

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

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

[0045] The step of preparing the aqueous dispersion includes a step of polymerizing a monomer that will become a unit constituting 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, for example, a known polymerization method.

[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 comprises TFE. The first monomer may include the above-mentioned 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, and particularly preferably 99 mol% or more, based on the total number of moles of the first monomer. The upper limit is preferably 100 mol% or less.

[0049] Methods for polymerizing the first monomer include, for example, emulsion polymerization, solution polymerization, and suspension polymerization. The polymerization can be carried out by heating the monomers 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 di-sec-butyl peroxydicarbonate; peroxyesters such as t-butyl peroxyisobutyrate and t-butyl peroxypivalate; dialkyl peroxides such as di-t-butyl peroxide; di(ω-hydro-dodecafluoroheptanoyl) peroxide, di(ω-hydro-tetradecafluoroheptanoyl) peroxide, di(ω-hydro-hexadecafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleryl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide, di(perfluorononanoyl) peroxide, and di(ω-chloro-hexafluoro). di[perfluoro(or fluorochloro)acyl]peroxides such as di(ω-chlorohexanoyl)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 oxidation-reduction catalyst. The water-soluble radical initiator is preferably a persulfate such as ammonium persulfate or potassium persulfate, or a water-soluble organic peroxide such as disuccinic acid peroxide, bisglutaric acid peroxide, or tert-butyl hydroperoxide. As the water-soluble oxidation-reduction catalyst, 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, and 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, is preferred. 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. The polymerization initiator is preferably ammonium persulfate alone or a mixture of a persulfate and disuccinic acid peroxide, more preferably ammonium persulfate alone or a mixture of ammonium persulfate and disuccinic acid peroxide. 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, relative to 100 parts by mass of the amount of the first monomer used.

[0054] (Other ingredients) 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. Thiocyanates include ammonium thiocyanate (NH4SCN), 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 preferred, succinic acid, malonic acid, glutaric acid, adipic acid or pimelic acid is more preferred, and succinic acid is even more preferred.

[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 desired 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., and even more preferably 50 to 100° C. The polymerization pressure is preferably 0.05 MPaG or more, more preferably 0.3 MPaG or more, and even more preferably 0.5 MPaG or more. The upper limit is preferably 5.0 MPaG or less, and more preferably 3.0 MPaG or less. 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.

[0060] In the polymerization of the first monomer, a stabilizing aid may be used. The stabilizing aid is preferably paraffin wax, a fluorine-based solvent, or silicone oil, and more preferably paraffin wax. Paraffin wax may be liquid, semi-solid, or solid at room temperature. Among them, 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. The stabilizing aids may be used alone or in combination of two or more.

[0061] The content of the PTFE resin is preferably 5 to 50 mass %, more preferably 10 to 45 mass %, and even more preferably 10 to 30 mass %, based on the total mass of the aqueous dispersion. The solid content concentration of the aqueous dispersion is preferably from 5 to 50 mass %, more preferably from 10 to 45 mass %, and even more preferably from 10 to 30 mass %. The solids concentration of the aqueous dispersion can be measured, for example, by the following method. The solids 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 solids concentration using the following formula. "Solid content concentration (mass%) = 100 × heating residue of aqueous dispersion (g) / mass of aqueous dispersion (2.0 g)"

[0062] <Process 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. It is preferable to obtain PTFE powder from an aqueous dispersion by subjecting the aqueous dispersion to an agglomeration treatment and a drying treatment, and it is more preferable to obtain PTFE powder by subjecting the aqueous dispersion to an agglomeration treatment to obtain wet PTFE powder and then drying the wet PTFE powder.

[0063] Examples of the flocculation treatment include freeze flocculation, acid flocculation, base flocculation, mechanical flocculation, and flocculation using a coagulant. 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 coagulation, a method in which an acid-containing solution is added to an aqueous dispersion is preferred. Examples of the acid to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, and hydrofluoric acid, with hydrochloric acid or nitric acid being preferred. The concentration of the acid in the acid-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. A preferred method for base coagulation is to add a solution containing a base to the aqueous dispersion. Examples of the base to be added include sodium hydroxide, potassium hydroxide, and ammonium carbonate, with sodium hydroxide being preferred. The concentration of the base in the solution containing the base 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 coagulant, known coagulants can be used. Known coagulants include aluminum salts, calcium salts, and magnesium salts. Specific examples include aluminum sulfate, alum represented by the general formula M'Al(SO4)2·12H2O (where M' is a monovalent cation other than lithium), calcium nitrate, and magnesium sulfate. Alum is preferred, and potassium alum, where M is potassium, is more preferred. The aggregation method is preferably acid aggregation or freeze aggregation.

[0064] As the drying treatment, a treatment of drying the PTFE wet powder obtained by the agglomeration treatment is preferred. 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 more, and more preferably 3 hours or more. The upper limit is preferably 100 hours or less, more preferably 50 hours or less, and even more preferably 30 hours or less. The 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 more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, per 100 parts by mass of the PTFE 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-type electric furnace, an airflow-type 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 above). 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 above) is preferred.

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

[0067] (Process 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. In the following, first, the materials used in step C will be described in detail, and then the procedure for step C will be described in detail.

[0068] -Non-fluorinated monomers- The non-fluorine-based monomer is a monomer that does not contain a fluorine atom. The non-fluorine-containing 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 specifically, an acryloyl group, a methacryloyl group, a vinyl ether group, a vinyl ester group, a vinyl group, or 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). Formula (NF) CH2=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 carbon atom. L 1represents a single bond, -C(=O)-O-*, -OC(=O)-* or -O-. * represents R 12 For example, L 1 is -C(=O)-O-*, then formula (1) is CH2=CR 11 -C(=O)-OR 12 Represents. R 12 represents a hydrogen atom, an alkyl group, an alkenyl group, or a nitrile group, provided that L 1 If is a single bond, R 12 is a nitrile group. The alkyl group and alkenyl group preferably have 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, and even more preferably 1 to 4 carbon atoms. 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). Formula (NF-1) CH2=CR 11 -C(=O)-OR 13 Formula (NF-2) CH2=CR 11 -OC(=O)-R 14 Formula (NF-3) CH2=CR 11 -OR 15 Formula (NF-4) CH2=CR 11 -R 16 R 11 The definition of is as described above. R 13 represents a hydrogen atom, an alkyl group, or an alkenyl group, and is preferably an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms. R 14represents an alkyl group, preferably an alkyl group having 1 to 3 carbon atoms, more preferably a methyl group. R 15 represents an alkyl group, preferably a linear alkyl group or a cyclic alkyl group. R 16 represents a nitrile group.

[0071] Examples of non-fluorine-containing 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-containing monomers may be used alone or in combination of two or more. As the non-fluorine-containing monomer, a monomer represented by formula (NF-1) or a monomer represented by formula (NF-2) is preferred, and R 13 is an alkyl group. The monomers represented by formula (NF-1) and formula (NF-2) have a hydrophilic group such as an ester group or a carboxy group, and therefore the monomers and their polymers have hydrophilicity. Therefore, it is believed that the monomers and their polymers 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-containing 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 the fluorine-based monomer is TFE. The content of units based on a non-fluorine-containing 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 may be 100% by mass.

[0073] -Aqueous medium- The aqueous medium may be the aqueous medium used in step A above.

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

[0075] -Step C Procedure- In the 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-containing monomer may be used in combination, if necessary.

[0076] The amount of the non-fluorinated monomer used is preferably 200 ppm by mass or less, more preferably 1 to 150 ppm by mass or less, still more preferably 5 to 100 ppm by mass, and particularly preferably 5 to 50 ppm by mass, relative to the amount of TFE supplied (amount of TFE used) used in step D described below. The non-fluorine-containing monomer is preferably added all at once in the initial stage, that is, the entire amount is added to the polymerization system before the polymerization reaction is started.

[0077] The content of the non-fluorine-based monomer in the dispersion obtained by mixing the non-fluorine-based monomer with the aqueous medium is preferably 0.000015 to 0.0030 mass %, more preferably 0.000075 to 0.0023 mass %, relative to the total mass of the dispersion. Since the entire amount of the non-fluorinated monomer is usually polymerized to become the specific polymer C, the concentration of the specific polymer C in the obtained solution 1 falls within the above-mentioned numerical range. The non-fluorinated monomer concentration and the specific polymer C concentration are concentrations when the obtained solution 1 is used in step D without diluting it with an aqueous medium. When the obtained solution 1 is diluted with an aqueous medium to achieve the above-mentioned specific polymer C concentration and the diluted solution is used in step D, a high-concentration solution is produced in step C according to the dilution ratio. 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 mass %, more preferably from 0.2 to 500 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 for 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, and 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. Alternatively, the polymerization may be carried out in a TFE atmosphere. Note that the polymerization of the non-fluorinated monomer in an aqueous medium usually proceeds preferentially over the polymerization of TFE.

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

[0082] The solution 1 obtained in step C may contain unreacted non-fluorinated monomers. In addition, the polymerization atmosphere in step C may be set to 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 perspective, the PTFE particles obtained in step D are not limited to particles consisting of a physical mixture of specific polymer C and PTFE, but can also be considered to be particles containing a TFE copolymer having units based on a non-fluorinated monomer.

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

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

[0085] -Other monomers- In step D, a monomer other than TFE may be further used within the range that does not impair the effects of the present invention. The other monomer may be a monomer having a polar group (hereinafter also referred to as "specific monomer D"). The polar group in specific monomer D interacts with the aqueous medium, and is therefore presumed to function as a surfactant by being located between TFE and the aqueous medium during TFE polymerization. As a result, TFE polymerization proceeds smoothly and chain transfer is 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) -SO3M Formula (B) -COOM In formula (A) and formula (B), M represents a hydrogen atom, NH4, 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 the polymerizable groups is preferably 1 to 3, and more preferably 1. The polymerizable group is preferably an ethylenically unsaturated group, more specifically, an acryloyl group, a methacryloyl group, a vinyl ether group, a vinyl ester group, a vinyl group, or 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. Formula (3) CR 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 optionally substituted with a fluorine atom. Among these, a hydrogen atom or a fluorine atom is preferred in terms of better copolymerizability with TFE. The term "alkyl group which may be substituted with a fluorine atom" refers to an alkyl group in which at least one hydrogen atom may be substituted with a fluorine atom. The alkyl group which may be substituted with a fluorine atom preferably has 1 to 3 carbon atoms, and more preferably 1 carbon atom.

[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-, -SO2-, -C(O)-, and -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 a phenylene group. Alternatively, 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 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 )2 are listed. The 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). Formula (3-1) CR 31 R 32 =CR 33 -R 34 Formula (3-2) CR 31 R 32 =CR 33 -(CF2) m1 -R 34 Formula (3-3) CR 31 R 32 =CR 33 -(CF2C(CF3)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-(CF2CFR 35 O) m4 -CF2CF2-R 34 Formula (3-6) CR 31 R 32 =CR 33 -CF2-O-(CF(CF3)CF2O) m5 -CF(CF3)-R 34

[0093] In formulas (3-1) to (3-6), R 31 ~R 34 The definition of is as described above. In formula (3-2), m1 represents an integer of 1 to 10. In the formula (3-3), m2 represents an integer of 1 to 5. In formula (3-4), m3 represents an integer of 1 to 10. 35 represents a fluorine atom or CF3. In formula (3-5), m4 represents an integer of 1 to 10. 35 The definition of is as described above. In formula (3-6), m5 represents 0 or an integer of 1 to 10.

[0094] A specific example of the specific monomer D is ammonium vinyl sulfonate. The specific monomer D may be used alone or in combination of two or more.

[0095] -Polymerization initiator- A polymerization initiator may be used in step D. That is, a polymerization initiator may be used during polymerization of TFE. The polymerization initiator used may be the polymerization initiator described in step C. As the polymerization initiator, a mixture of persulfate and disuccinic acid peroxide is preferred, and a mixture 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 agent- In step D, a stabilizing aid may be used. The stabilizing aid is preferably paraffin wax, a fluorine-based solvent, or silicone oil, and more preferably paraffin wax. Paraffin wax may be liquid, semi-solid, or solid at room temperature. Among them, 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. The stabilizing aids may be used alone or in combination of two or more.

[0097] -others- 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 order to improve 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 Process D- In step D, substantially no surfactant is added to solution 1. That is, in step D, polymerization of TFE is carried out in solution 1 without substantially adding a 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 the specific monomer D. Examples of surfactants include known surfactants, such as nonionic surfactants and ionic surfactants, and more specifically, hydrocarbon-containing surfactants and fluorine-containing surfactants. The definition of hydrocarbon-containing surfactants is as described below. In step D, it is preferable that at least one selected from the group consisting of hydrocarbon-containing surfactants and fluorine-containing surfactants is not substantially added to solution 1. The above phrase "substantially no surfactant is added" means that no surfactant is added, or if a surfactant is added, the amount of surfactant added is 200 mass ppm or less relative to the total mass of Solution 1. There is no particular lower limit, but 0 mass ppm is preferred. In other words, it is preferred that no surfactant is added to Solution 1 in Step D.

[0099] TFE is added to the polymerization system (i.e., polymerization reaction vessel) by a conventional method. For example, TFE is added to 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 charged relative to the total amount of TFE charged is preferably 0.150% by mass or less. From the viewpoint of emulsion stability during polymerization, the amount of 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. Also, from the viewpoint of improving molecular weight, the amount of 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 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 charged relative to the total amount of TFE charged is preferably 0.150 mol % or less. From the viewpoint of emulsion stability during polymerization, the amount of 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 molecular weight, the amount of 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 specific monomer D is used, the amount of specific monomer D used relative to the total amount of TFE is preferably 0.100 to 0.100 mol%, 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 consecutively 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 the step C, and the step D may be carried out before the non-fluorinated monomer is completely consumed in the step C.

[0104] The above procedure results in an aqueous emulsion in which the PTFE resin is dispersed in particulate form (aqueous emulsion containing the PTFE resin). The concentration of the PTFE resin in the aqueous emulsion is preferably 10 to 45% by mass, more preferably 10 to 30% by mass, and even more preferably 10 to 25% by mass, based on the total amount of the aqueous emulsion. Within the above range, the PTFE resin in the aqueous emulsion can be more easily coagulated, and clouding of the coagulated liquid can be suppressed. The average primary particle size of the PTFE resin is preferably 100 to 500 nm, more preferably 150 to 300 nm. The average primary particle size of the PTFE-based resin corresponds to D50 measured by a laser scattering particle size distribution analyzer.

[0105] (Process 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 procedures and conditions as in Step B above.

[0106] <Second mode> The method for producing the PTFE powder may be the second embodiment described below. The second embodiment of the method for producing PTFE powder is a method for producing PTFE powder, which comprises 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] (Process 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 fluoropolymer- It is presumed that the first fluoropolymer solubilizes 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 fluoropolymer. It is also presumed that the first fluoropolymer contributes to dispersion stabilization in an aqueous medium.

[0110] The glass transition temperature (hereinafter also referred to as "Tg") of the first fluorine-containing polymer is preferably 10°C or lower, and from the viewpoint of efficiently adsorbing 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 glass transition temperature of the first fluoropolymer is preferably −50 to 10° C., more preferably −45 to 5° C., and even more preferably −40 to 3° C. The Tg of the first fluorine-containing polymer is measured by differential scanning calorimetry (DSC). As a method for adjusting the Tg of the first fluoropolymer within the above range, for example, a method of adjusting the type and amount of the monomer used in producing the first fluoropolymer may be mentioned.

[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"), since this makes it easier to adjust the Tg within the above range.

[0112] The PAVE is preferably a monomer represented by the above formula (PA) from the viewpoints of excellent polymerization reactivity in producing the first fluorine-containing polymer and of enabling more efficient production of a 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 monomers other than TFE and PAVE, but preferably does not substantially contain units based on other monomers, in order to more efficiently produce a PTFE-based resin. Substantially free of units derived from other monomers means that the content of units derived from other monomers is 0.01 mol % or less, more preferably 0 mol %, based on the total units of the first fluorine-containing polymer. When units based on another monomer are contained, the other monomer is preferably hexafluoropropylene.

[0115] Before the start of polymerization of the monomers used in the 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 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 ppm by mass or less, more preferably 5 ppm by mass or less, relative to the total mass of the aqueous medium in the aqueous dispersion, in order to suppress coloration of the PTFE-based resin.The lower limit can be 0 ppm by mass. An example of a method for adjusting the sulfate ion concentration to the above range is to remove sulfate ions using an anion exchange resin during production of the first fluorine-containing polymer. Here, the sulfate ions are derived, for example, from the polymerization initiator (particularly ammonium persulfate) used in producing the first fluoropolymer, and may be contained in the aqueous dispersion containing the first fluoropolymer. It is presumed that by keeping the content of sulfate ions at 10 ppm by mass or less (particularly 5 ppm by mass or less), it is possible to prevent the formation of terminal groups with low heat resistance in the PTFE-based resin, thereby suppressing coloration of the PTFE-based resin.

[0118] Before starting polymerization of the monomers used in the polymerization of the PTFE-based resin, the concentration of ammonium ions is preferably 20 ppm by mass or less, more preferably 10 ppm by mass or less, relative to the total mass of the aqueous medium in the aqueous dispersion, in order to suppress aggregation of the PTFE-based resin.The lower limit can be 0 ppm by mass. An example of a method for adjusting the ammonium ion concentration to the above range is to remove ammonium ions using a cation exchange resin during the production of the first fluorinated polymer. Here, the ammonium ions are derived, for example, from the initiator (particularly ammonium persulfate) used in producing the first fluoropolymer, and may be contained in the aqueous dispersion containing the first fluoropolymer. It is presumed that the ammonium ion content of 20 ppm by mass or less reduces the ionic strength in the aqueous medium, thereby improving the production efficiency of the PTFE-based resin.

[0119] The first fluorine-containing polymer 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 from 1 to 150 nm, more preferably from 10 to 120 nm, and even more preferably from 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 set to 100%, and measuring the particle size (D50) at the point on the cumulative curve where the cumulative volume is 50%; detailed measurement conditions are as described in the Examples section.

[0120] The method for producing the first fluorine-containing polymer is preferably a method in which a monomer (preferably a monomer mixture containing TFE and PAVE) is polymerized in an aqueous medium in the presence of a polymerization initiator, thereby obtaining the first fluorine-containing polymer dispersed in the aqueous medium in the form of particles. 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 it is, or another aqueous medium may be added thereto and the resulting mixture may be used as the aqueous dispersion. Alternatively, the first fluorine-containing polymer may be dispersed in another aqueous medium by solvent substitution and the resulting mixture 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 for producing the first fluorine-containing polymer includes the aqueous medium in step A described above. The aqueous medium contained in the aqueous dispersion may be the polymerization solvent used in producing the first fluorine-containing polymer. Before starting polymerization of the monomers used in the polymerization of the PTFE-based 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, since this can further promote the deactivation of the polymerization initiator in the aqueous medium.

[0124] -Other ingredients- The aqueous dispersion used in the present production method may contain other components in addition to the first fluorine-containing polymer and the aqueous medium. Specific examples of other components that may be contained in the aqueous dispersion include a chain transfer agent, an emulsifier other than a fluorine-based 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 Corporation, 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 Parafffin Wax-155 and Parafffin Wax-150 (both manufactured by Nippon Seiro Co., Ltd.).

[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 relative to 100 parts by mass of the aqueous medium. 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, relative to 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 relative to 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 relative to 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 monomers used in polymerization of the PTFE-based resin, the concentration of the fluorine-containing emulsifier is 100 ppm by mass or less, based on the total mass of the first fluorine-containing polymer in the aqueous dispersion, and from the viewpoint of achieving better effects of the present invention, it is preferably 50 ppm by mass or less, more preferably 25 ppm by mass or less, and even more preferably 5 ppm by mass or less. The lower limit is 0 ppm by mass. The fluorine-containing emulsifier refers to an emulsifier in which the hydrophobic moiety contains a fluorine atom, and specific examples of the fluorine-containing emulsifier include fluorine-containing alkanoates and fluorine-containing ether carboxylic acid compounds. One example of a method for adjusting the concentration of the fluorine-containing emulsifier to fall within the above range is to produce an aqueous dispersion without using a fluorine-containing emulsifier.

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

[0132] -Specific monomer F- The specific monomer F includes TFE. The amount of TFE used is preferably from 97 to 100% by mass, more preferably from 98 to 100% by mass, and even more preferably from 99 to 100% by 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 free of fluorine-containing monomers other than TFE" means that the amount of fluorine-containing monomers other than TFE used is 0.0001% by mass or less, and may be 0% by mass, relative to the amount of 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 the fluorine-containing monomer other than TFE may be used in combination.

[0134] The specific monomer F may contain other monomers in addition to the fluorine-containing monomer, but it is preferable that it does not contain any 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 specific monomer F used. Specific examples of the other monomer 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, relative to 100 parts by mass of the aqueous medium used 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 step A above.

[0137] The amount of the polymerization initiator used is preferably 1 to 1000 ppm by mass, more preferably 5 to 750 ppm by mass, and even more preferably 10 to 500 ppm by mass, relative to 100 parts by mass of the specific monomer F used.

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

[0139] -Step F Procedure- 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 this 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 from 10 to 95°C, more preferably from 15 to 90°C. The polymerization pressure is preferably from 0.5 to 4.0 MPaG, more preferably from 0.6 to 3.5 MPaG. In the case of batch processing, the polymerization time is preferably from 90 to 1000 minutes, more preferably from 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" means 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 described above, since it is presumed that the specific monomer F polymerizes within the particles of the first fluorine-containing polymer during the polymerization of the specific monomer F, in this production method, it is considered that particles containing the first fluorine-containing polymer and the PTFE-based resin are formed. That is, according to this production method, it is estimated that the PTFE-based resin is obtained in the form of particles containing the first fluorine-containing polymer and the PTFE-based resin. In this case, an aqueous dispersion in which particles containing the first fluorine-containing polymer and the PTFE-based resin are dispersed in the above aqueous medium is obtained by this production method.

[0145] (Step G) Step G is a step of obtaining PTFE powder from the aqueous dispersion obtained in Step F. As Step G, it can be carried out under the procedures and conditions in Step B described above.

[0146] [Electrode binder] The electrode binder of the present invention contains the above-described PTFE powder and an active material. When the electrode binder is a negative electrode binder, it is preferable that the negative electrode binder contains the PTFE powder and a negative electrode active material. When the electrode binder is a positive electrode binder, it is preferable that the positive electrode binder contains the PTFE powder and a positive electrode active material.

[0147] [PTFE powder] The electrode binder contains the PTFE powder. The PTFE powder has the same meaning as the PTFE powder of the present embodiment described above, and the 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 with respect to the total mass of the electrode binder. 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 30% by mass, more preferably 0.5 to 30% by mass, and even more preferably 1.0 to 10% by mass with respect to the total mass of the electrode binder. Within the above range, the retention of the active material and the mechanical strength of the electrode binder sheet are sufficient, the battery performance such as cycle characteristics is also good, and the decrease in battery capacity or conductivity can be further suppressed. PTFE powder has excellent binding power, so even if the content is small, the active material can be sufficiently held within the electrode mixture.

[0149] <Active material> The electrode mixture includes an active material. Examples of the active material include a positive electrode active material and a negative electrode active material, and can be appropriately selected according to the intended electrode.

[0150] (Cathode active material) When the electrode mixture is a positive electrode mixture, the positive electrode mixture contains a positive electrode active material. The positive electrode mixture may contain, in addition to the PTFE powder and the positive electrode active material, at least one selected from the group consisting of a binder other than the PTFE powder, a conductive material, a thickener, and an additive. The positive electrode active material is a material that electrochemically absorbs and releases lithium ions. 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 viewpoints of high average discharge voltage and cost advantage, the positive electrode active material may be a lithium-containing transition metal oxide.

[0151] A surface-adhering substance having a different composition from the positive electrode active material may be adhered to the surface of the positive electrode active material. Examples of surface-adhering substances include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[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, which can further suppress deterioration of battery performance. In order to improve the filling property when preparing the positive electrode, two or more types of positive electrode active materials having 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 as the 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. The upper limit is 50m 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 / g is more preferred. 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 Okura 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 which the sample is pre-dried at 150°C for 30 minutes under a nitrogen flow, by a nitrogen adsorption BET single-point method using a gas flow method.

[0156] The positive electrode active materials may be used alone or in combination of two or more. When two or more positive electrode active materials are used, a suitable combination is LiCoO2 and LiNi 0.33 Co 0.33 Mn 0.33 combinations of LiCoO2 with ternary systems such as O2; combinations of LiCoO2 with LiMn2O4 or with LiFePO4 with LiCoO2 or with LiFePO4 in which part of the Co has been substituted with other transition metals;

[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 negative electrode active material containing silicon 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 particles are dispersed in a silicon-based compound, and silicon-based compounds represented by the general formula SiO x Silicon oxide particles represented by (0.5≦x≦1.6) or a mixture thereof are preferred. Silicon oxide is a general term for amorphous silicon oxide, and silicon oxide is, for example, a silicon dioxide having the general formula SiO x (0.5≦x≦1.6), where x is preferably 0.8≦x<1.6, and more preferably 0.8≦x<1.3. This silicon oxide can be obtained, for example, by heating a mixture of silicon dioxide and metallic silicon to produce silicon monoxide gas, followed by cooling and precipitation.

[0160] The silicon-containing negative electrode active material may be coated with carbon. The carbon coating can provide electrical conductivity, improving battery performance. Methods for providing electrical conductivity include, for example, mixing with electrically conductive particles such as graphite, coating the surface of the silicon-containing negative electrode active material with a carbon coating, and combining both methods. 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 a 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 additive> The electrode mixture may contain a conductive assistant. Examples of conductive additives 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. Examples of thermoplastic resins include 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 ingredients> The electrode mixture may contain other components in addition to the various components described above. The other components may include, for example, at least one selected from the group consisting of a solid electrolyte, a binder other than those mentioned above, a conductive material, a thickener, and an additive. Examples of the solid electrolyte include sulfide solid electrolytes having 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. Fiber components include cellulose, carboxymethyl cellulose, cellulose nanofiber, and aramid fiber. Fiber components are preferably mixed as powders, and are preferably finely ground (microfibrillated) in advance by various grinding methods, as this improves the 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 is a method that can produce the above-mentioned electrode mixture. Among these, the method for producing an electrode mixture is preferably a method for producing an electrode mixture including a step X1 of pulverizing and mixing a raw material composition containing a binder containing PTFE powder, an active material, and, if necessary, a conductive additive. The above-mentioned method for producing an electrode mixture can obtain an electrode mixture in a relatively short number of steps. The method for producing an electrode mixture preferably further includes step X2 of rolling the raw material composition pulverized and mixed in step X1 into a sheet shape. When step X2 is included, a sheet-shaped electrode mixture is obtained.

[0175] (Process X1) Step X1 is a step of mixing a raw material composition containing a binder containing PTFE powder, an active material, and, if necessary, a conductive additive. The mixing method is preferably a method in which a mixing device is used. Examples of mixing devices include a jet mill, a pin mill, a blender, a twin-screw extruder, and a mixer. A jet mill, a mixer, or a twin-screw extruder is preferred because it can simultaneously crush the PTFE powder and suppress the formation of fibers. Jet mills include collision types that crush particles by colliding them with each other or with a collision body (target), swirling airflow types and loop types that crush particles by collision of particles with each other in a crushing zone formed by multiple crushing nozzles arranged in a circulating airflow, fluidized bed types that crush particles by collision or friction of particles with each other in a fluidized bed, and supersonic types. Collision type, swirling air current type, loop type and fluidized bed type jet mills are described in detail in "Advanced Pulverization Technology and Applications" edited by the Japan Powder Industry and Technology Association, NGT Ltd., p. 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 the Cross Jet Mill (manufactured by Kurimoto Iron Works); Jet-O-Mill, AO Jet Mill, Sanitary AOM, Cojet, Single Track Jet Mill, and Super STJ Mill (all manufactured by Seishin Enterprises); Current Jet Mill (manufactured by Nisshin Engineering); Urmax (manufactured by Nisso Engineering); 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 and Engineering Co., Ltd.); Nano Grinding Mill (manufactured by Tokuju Kogyosho Co., Ltd.), and EX-Mini Jet Mill (M-Tech Chemical). As the jet mill, a single track jet mill is preferred in terms of excellent productivity.

[0177] The pulverization pressure in the jet mill is preferably 0.1 to 2 MPa, more preferably 0.2 to 0.9 MPa, in order to achieve both disintegration properties and suppression of fiber formation.

[0178] (Process X2) Step X2 is a step of rolling the raw material composition pulverized and mixed in step X1 into a sheet shape. Examples of the rolling method in the step X2 include rolling methods using a roll press, a plate press, a calender roll, and the like. 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. The electrode may have a conductive carbonaceous material disposed between the current collector and the electrode layer, if necessary.

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

[0181] The shape of the current collector may be, for example, a metal foil, a metal cylinder, a metal coil, a metal plate, an expanded metal, a punched metal, or a foamed metal, for example, a carbon plate, a carbon thin film, or a carbon cylinder, for example, when made of a carbon material. Of these, a metal foil is preferred as the shape of the current collector. The metal foil may also be formed into a mesh, as appropriate. The thickness of the current collector is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. The upper limit is preferably 1 mm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. Within the above range, excellent handleability and strength can be achieved.

[0182] It is also preferable that the surface of the current collector is coated with a conductive additive in order to reduce the electrical contact resistance between the current collector and the positive electrode active material layer. Examples of the conductive additive include carbon and noble metals such as gold, platinum, and silver.

[0183] <Electrode layer> The electrode includes an electrode layer. The electrode layer is disposed on the current collector and contains the above-mentioned electrode mixture. The electrode layer may be either a positive electrode layer or a negative electrode layer, and can be appropriately selected depending on the active material contained in the electrode mixture, etc.

[0184] The density of the positive electrode layer is 3.00 g / cm 3 More than 3.10 g / cm is preferable. 3More preferably, 3.20 g / cm or more 3 More preferably, the upper limit is 3.80 g / cm 3 Preferably less than 3.75 g / cm 3 Less than 3.70 g / cm is more preferable. 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 is more preferable. The density of the negative electrode layer is 1.3 g / cm 3 More than 1.4 g / cm is preferable. 3 More preferably, 1.5 g / cm 3 More preferably, the upper limit is 2.0 g / cm 3 Preferably less than 1.9 g / cm 3 Less than 1.8 g / cm is more preferable. 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 is more preferable. Within the above range, the permeability of the electrolyte to the vicinity of the current collector / active material interface is excellent, and the charge / discharge characteristics, particularly at high current densities, can be excellent. Also, 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 layers is preferably 10 to 500 μm, more preferably 20 to 450 μm.

[0186] [Secondary battery] The secondary battery of the present invention includes the above-described electrode. The secondary battery may be a secondary battery that uses an electrolyte solution or a solid-state secondary battery. Examples of secondary batteries include non-aqueous secondary batteries such as non-aqueous electrolyte secondary batteries, all-solid-state batteries, and fuel cells. 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 a positive electrode, a separator, and a negative electrode are wound in a spiral shape. When the secondary battery has a laminated structure, the laminated structure is preferably formed by bundling metal core portions of the electrode layers and welding them to terminals. When the secondary battery has a wound structure, the internal resistance can be reduced by providing a plurality of lead structures on each of the positive electrode and the negative electrode and bundling them into 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 properties. Among these, the separator is preferably made of a resin, glass fiber, or inorganic material, and 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 is preferably a non-aqueous electrolyte, such as one obtained by dissolving a known electrolyte salt in a known organic solvent for dissolving electrolyte salts. 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, fluoroethers, and fluorinated carbonates. Examples of electrolyte salts include LiClO4, LiAsF6, LiBF4, LiPF6, LiN(SO2CF3)2, and LiFSI(LiN(SO2F)2), LiBOB(LiB(C2O4)2), LiDFOB(LiBF2(C2O4)), LiPF2(C2O4)2, LiPF4(C2O4), and LiN(SO2C2F5)2, and LiPF6, LiBF4, LiN(SO2CF3)2, LiN(SO2C2F5)2, or combinations thereof are preferred in terms of good cycle characteristics.

[0191] The solid state secondary battery is preferably an all-solid state secondary battery. The solid-state secondary battery is preferably a lithium-ion battery or a sulfide-based all-solid-state secondary battery. The solid 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 examples include Li2S-P2S5, Li2S-P2S3, Li2S-P2S3-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, LiI-Li2S-SiS2-P2S5, Li2S-SiS2-Li4SiO4, Li2S-SiS2-Li3PO4, Li3PS4-Li4GeS4, Li 3.4 P 0.6 Si 0.4 S4, Li 3.25 P 0.25 Ge 0.76 S4, Li 4-x Ge 1-x P x S4 (X = 0.6 to 0.8), Li 4+y Ge 1-y Ga y S4 (y = 0.2 to 0.3), LiPSCl, LiCl, Li 7-x-2y PS 6-x-y Cl x (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5), etc., or a mixture of two or more thereof can be used. Further, the sulfide-based solid electrolyte preferably contains lithium. The sulfide-based solid electrolyte containing lithium is used in a solid battery that uses lithium ions as carriers, and is preferable in terms of an electrochemical device having a high energy density.

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

[0195] Examples of the oxide-based solid electrolyte include, for example, Li xa La ya TiO3 [xa = 0.3 to 0.7, ya = 0.3 to 0.7] (LLT), Li xb La yb Zr zb M bb mb O nb (Mbb 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 cc is 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)、Li3BO3-Li2SO4、Li2O-B2O3-P2O5、Li2O-SiO2、Li6BaLa2Ta2O 12 , LiPO (4-3 / 2w) N w (w<1), Li with LISICON (Lithium super ionic conductor) type crystal structure 3.5 Zn 0.25 GeO4, La with perovskite crystal structure 0.51 Li 0.34 TiO 2.94 , La0.55 Li 0.35 TiO3, LiTi2P3O with NASICON (sodium super ionic conductor) type crystal structure 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 Li7La3Zr2O with a garnet-type crystal structure 12 (LLZ). Ceramic materials in which element substitution has been performed on LLZ are also known. For example, LLZ-based ceramic materials in which 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)) has been substituted for LLZ are also known. Phosphorus compounds containing Li, P, and O are also desirable. For example, lithium phosphate (Li3PO4), LiPON, LiPOD, in which part of the oxygen in lithium phosphate has been substituted with nitrogen, are also desirable. 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 Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2 and Li2O-Al2O3-SiO2-P2O5-TiO2.

[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 etc.), NASICON type (Li 1.3 Al 0.3 Ti 1.7 (PO4)3, etc.), garnet type (Li7La3Zr2O 12 Among them, the 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, relative to 100 parts by mass of the sulfide-based solid electrolyte. [Example]

[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] The 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 in an oxygen atmosphere (600°C, 10 minutes) to obtain an ash product. The resulting ash product was dissolved in dilute nitric acid and adjusted to a constant volume of 20 mL to obtain a solution. The resulting solution was introduced into an ICP-MS analyzer 7700x (Agilent) to check whether or not peaks of each transition metal element were detected. 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). In this measurement method, the transition metal elements are metal elements from Group 4 to Group 12 of the long-period type periodic table excluding technetium, scandium, and yttrium. Also, the content of the transition metal elements shown in the following table was substantially consistent with the content of the transition metal elements derived from the additive.

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

[0203] <Ratio of each unit in PTFE-based resin> The ratio of each unit in the PTFE-based resin obtained in each of the examples described below was 19 determined from F-NMR analysis and infrared absorption spectrum analysis.

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

[0205] <ssg> The SSG was measured in accordance with ASTM D4895-10. Specifically, a 12.0 g sample was weighed and placed in a cylindrical mold with an inner diameter of 28.6 mm at 34.5 MPa for 2 minutes to form a molded sample. This sample 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 to 294°C for 24 minutes. After holding the sample in a desiccator at 23°C for 12 hours, the specific gravity of the molded product relative to water was measured at 23°C, and this was used as the SSG.

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

[0207] <Voltage resistance> The 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 sieved material 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. A molding pressure of 0.98 MPa was maintained 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 extrusion was removed from the extrusion, and 15 pieces of the extrusion were cut with a sharp blade into lengths of 25 ± 1 cm. These pieces were then 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 returned to 365 ± 5°C, the extrusion was baked for 30 ± 3 minutes, then removed and allowed to cool at room temperature. The resulting molded product was used as a test piece. A metal rod was inserted into the test piece to form the internal electrode, and metal foil was wrapped around the center to form 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 specified voltage, and it was determined whether the specimen could withstand this voltage for one minute. The specified voltage was increased in 1 kV increments, and the maximum voltage that could be withstood for one minute was taken as the withstand voltage.

[0208] <Preparation of positive electrode mixture> NMC622 (Hosen Co., Ltd., average particle size 10 μm, positive electrode active material), the PTFE powder of each example, and acetylene black (Sigma-Aldrich) were mixed in a mass ratio of 96:3:1, and pulverized and mixed in an Ex-Mini Jet Mill (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 ton roll press at a temperature of 90° C. only once to form a sheet, to obtain a positive electrode mixture sheet having a thickness of 200 μm.

[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": Deposits were 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 considered acceptable. "A": No cracks were observed. "B": Cracks were observed on the edge of the sheet. "C": The seat cracked.

[0211] <Capacity maintenance rate> Graphite QC-6 (manufactured by Hosensha) 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 resulting negative electrode mixture was passed through a 3-ton roll press at a temperature of 100°C, with roll gaps of 1 mm, 0.5 mm, and 0.2 mm three times to form a sheet with an average thickness of 180 μm (average basis weight: 15.5 mg / cm). 2 During this process, the above-mentioned "wall surface adhesion" and "sheet toughness" were evaluated. This negative electrode mixture sheet was laminated with 12 μm thick copper foil by pressing at 100° C. and 1 MPa, and then punched out to φ16 mm. The sheet was then incorporated into an HS flat cell (manufactured by Hosen Co., Ltd.) in the following configuration to form a half cell. (composition) Working electrode: negative electrode mixture sheet Counter electrode: metallic lithium (Honjo Chemical Co., Ltd., 100 μm) Separator: GA55 (Advantec glass separator) Electrolyte: 1M LiPF6 / ethylene carbonate:dimethylene carbonate = 1:1 Impregnation conditions: -60kPa, 3min x 6 times (evaluation) Using a charge-discharge evaluation device TOSCAT (manufactured by Toyo Systems Co., Ltd.), the capacity mAh / g was measured after five cycles of charge-discharge at 0.05 C between 2.0 and 0.0 V vs. the 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. The rate was then 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: Over 98%. B: Less than 98%.

[0212] 〔Example 1〕 <Production of PTFE Powder> Into a 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature control jacket, 3600 g of deionized water, 180 g of paraffin wax, 5.4 g of ammonium salt of perfluoroether carboxylic acid B (CF3CF2OCF2CF2OCF2COONH4), 0.108 g of succinic acid, and 0.0252 g of oxalic acid were charged. While heating to 70°C, the inside of the polymerization tank was purged with nitrogen gas to remove oxygen. After maintaining the temperature inside the tank at 70°C while stirring, TFE was introduced and the pressure was set 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 inside the polymerization tank became constant at 2.7 MPaG. When the TFE consumption reached 184 g, 3.8 g of ammonium salt of perfluoroether carboxylic acid B was added. When the TFE consumption reached 900 g, the total amount of deionized water in which 3.5 mg of the above potassium permanganate was dissolved was added. When the TFE consumption reached 1543 g, stirring and TFE supply were stopped, the TFE inside the polymerization tank was purged, the polymerization reaction was terminated, and a dispersion was obtained. The obtained dispersion was taken out, cooled, and the paraffin wax was separated to obtain an aqueous dispersion containing a PTFE-based resin. The average primary particle diameter of the aqueous dispersion containing the obtained PTFE-based resin was 310 nm, and the solid content concentration of the aqueous dispersion was 30.6% by mass. Further, the obtained aqueous dispersion was diluted to a solid content concentration of 13% by mass, nitric acid was added while stirring in a container to coagulate the PTFE-based resin, and then separated from water by filtration to obtain a PTFE wet powder. The water content of the PTFE wet powder was 40% by mass based on the total mass of the PTFE wet powder. The obtained PTFE wet powder was placed on a stainless steel mesh tray (placement amount: 2.0 g / cm 2 The mesh tray was heat-treated in a hot air circulation 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] <Adjusting the charging voltage> Next, the obtained PTFE powder 1 before the charge 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 to perform 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 for 1 hour with 10 g of 30 mass % ethanol water at room temperature in which 0.06 mg of iron acetate had been dissolved, and then air-dried and dried at 150° C. to obtain the PTFE powder of Example 2. The charging voltage was also adjusted using the same procedure as in Example 1.

[0215] [Example 3] The 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 internal volume was 30% by 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] The 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 for 1 hour with 10 g of 30 mass % ethanol water at room temperature in which 0.42 mg of nickel acetate tetrahydrate had been dissolved.

[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] The 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] Except for not wetting 100 g of powder 1 obtained in the same manner as in Example 1 with 30 mass % ethanol water containing an additive dissolved therein, the charging voltage was adjusted in the same manner as in Example 1, and then 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] The 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 70 g of C2F5OC2F4OCF2COONH4 (Ammonium perfluoro-3,6-dioxaoctanoate, hereinafter referred to as "APFDO"), 872 g of paraffin wax, and 59 L of deionized water. The autoclave was purged with nitrogen and then reduced in pressure. 2 g of CH2=CH-(CF2)4F (hereinafter referred to as "PFBE") and 300 g of deionized water were then added by suction. The autoclave was then 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. Polymerization was then 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 as APFDO, 125 g in total, during the polymerization. Ammonium sulfite was also dissolved in water and added in total as ammonium sulfite, 4 g in total, during the polymerization. The temperature was lowered to 65°C during the polymerization and raised to 90°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 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 8478 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 trace. 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, stirred, and agglomerated to produce a PTFE fine powder. This PTFE fine powder was then dried at 180°C. 100 g of the obtained powder 12 was wetted for 1 hour with 10 g of 30% by mass ethanol water at room temperature in which 0.3 mg of iron acetate had been dissolved, and then air-dried and dried at 150°C to obtain PTFE powder 12 before adjustment of the charging voltage. Next, the obtained PTFE powder 12 before the charge voltage adjustment was placed in a nylon pot with an inner diameter of φ150 mm so that the internal volume was 30% by volume, and the pot was rotated for 10 minutes at a rotation speed that was 20% of the critical rotation speed to charge it, thereby 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. After replacing the air in the autoclave with nitrogen, the autoclave was depressurized, 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 (concentration 80% by mass, remainder water) dissolved in 1 L of warm water at approximately 70°C was injected. The internal pressure dropped to 1.746 MPa in approximately 3 minutes. The polymerization was carried out while adding TFE to maintain the internal pressure of the autoclave at 1.765 MPa. APFDO was dissolved in warm water and added in a total of 125 g of APFDO during the polymerization. Ammonium sulfite was also dissolved in water and added in a total of 4 g of ammonium sulfite during the polymerization. The temperature was lowered to 64°C during the polymerization and then raised to 80°C in the latter half of the polymerization. The reaction was terminated when 23 kg of TFE had been added, 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 8555 ppm by mass relative to the final PTFE yield. The average primary particle diameter was 275 nm. Only traces of coagulation remained in the reactor. This aqueous emulsion was diluted with pure water to a concentration of 10% by mass, adjusted to 20°C, stirred and agglomerated to obtain a PTFE fine powder. This PTFE fine powder was then dried at 180°C. 100 g of the obtained powder 13 was wetted for 1 hour with 10 g of 30% by mass ethanol water at room temperature in which 0.3 mg of iron acetate had been dissolved, and then air-dried and dried at 150°C to obtain PTFE powder 13 before adjustment of the charging voltage. Next, the obtained PTFE powder 12 before the charge voltage adjustment was placed in a nylon pot having an inner diameter of φ150 mm so that the internal volume was 30% by volume, and the pot was rotated for 10 minutes at a rotation speed that was 20% of the critical rotation speed to charge it, thereby 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 below, a sulfide solid electrolyte (Fine LPSCl manufactured by NEI) with an average particle size of 1 μm, lithium niobate-coated NCM111 particles (cathode active material) with an average particle size of 7 μm, a conductive additive, and PTFE powder 12 from Example 12 were mixed in a ratio of 20 parts by mass:75 parts by mass:2 parts by mass:3 parts by mass and formed into a sheet in the same manner as in <Preparation of Cathode Mix>. The obtained cathode mix sheet was evaluated for <wall adhesion> and <sheet toughness>.

[0227] [Example 15] In Example 12, the charging voltage was adjusted in the same manner as in Example 12, except that the powder 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 "additive" column indicates the compound dissolved in 30 mass % ethanol water when the obtained powder was wetted with 10 g of 30 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] [Table 1]

[0230] [Table 2]

[0231] [Table 3]

[0232] As shown in Tables 1 to 3, it was confirmed that if the PTFE powder of the present invention is used, the sheets obtained by mixing an active material and the like have excellent toughness (Examples 1 to 9, 12, 13, and 14). Furthermore, as shown in Tables 1 and 3, it is believed that Examples 10 and 15 had low transition metal element contents, which resulted in insufficient cohesive force between the PTFE-based resins, and therefore poor sheet toughness. Furthermore, it is believed that Example 11 had too much 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, which strengthened adhesion to the wall. 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 the wall surface adhesion and the sheet toughness were superior. Furthermore, as shown in Table 1, a comparison of Examples 1 to 3 confirmed that when the content of transition metal elements is 200 to 1000 mass ppb relative to the total mass of the polytetrafluoroethylene powder, the wall adhesion is weakened (excellent wall 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.< / ssg>

Claims

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

2. 2. The polytetrafluoroethylene powder according to claim 1, wherein the electrostatic voltage is −200 to −3000 V.

3. 3. The polytetrafluoroethylene powder according to claim 1, 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. 3. The polytetrafluoroethylene powder according to claim 1, which has a withstand voltage of 5 kV or more.

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

6. Further, the battery contains a sulfide-based solid electrolyte, 6. The electrode mixture according to claim 5, 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.

7. The electrode mixture according to claim 5 , which is in the form of a sheet.

8. Further containing a conductive additive, The content of the polytetrafluoroethylene powder is 0.5 to 10 mass% with respect to the total mass of the electrode mixture, The content of the active material is 88 to 99% by mass relative to the total mass of the electrode mixture, The electrode mixture according to claim 5, wherein the content of the conductive assistant is 0.5 to 10 mass% with respect to the total mass of the electrode mixture.

9. An electrode comprising: a current collector; and an electrode layer disposed on the current collector and containing the electrode mixture according to claim 5 .

10. A secondary battery comprising the electrode according to claim 9.

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