Polytetrafluoroethylene-based resin, electrode mixture, electrode layer, electrode, and secondary battery

Abstract

The present invention relates to a polytetrafluoroethylene-based resin used as a binder for a secondary battery, wherein the ratio of the endothermic peak height at 338°C to the endothermic peak height at 343°C is 0.10 to 0.95 for the polytetrafluoroethylene-based resin when a straight line including a heat flow value at 320°C and a heat flow value at 350°C is used as a baseline in a differential scanning calorimetry curve obtained by performing differential scanning calorimetry measurement under measurement condition A.

Description

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

[0001] The present invention relates to a polytetrafluoroethylene resin, an electrode mixture, an electrode layer, an electrode, and a secondary battery. This application claims priority to Japanese Patent Application No. 2024-168796, filed in Japan on September 27, 2024, the contents of which are incorporated herein by reference.

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

[0003] Electrodes for non-aqueous electrolyte secondary batteries such as lithium-ion batteries are generally manufactured by coating a current collector with an electrode mixture containing an active material and a binder. On the other hand, in recent years, a dry method has been investigated in which the electrode mixture is stretched and formed into a sheet, and then this sheet is bonded to a current collector to manufacture the electrodes, with the aim of reducing the environmental burden during manufacturing and improving oxidation resistance.

[0004] Patent Document 1 discloses a polytetrafluoroethylene resin used as an electrode binder.

[0005] Japanese Patent Publication No. 2023-051888

[0006] The properties of a sheet obtained using an electrode mixture containing a polytetrafluoroethylene resin and an active material, as described in Patent Document 1, were evaluated. As a result, it was found that at least one of the sheet's breaking strength and the uniformity of the sheet's thickness after storage of the electrode mixture was inferior, indicating room for improvement.

[0007] The present invention aims to provide a polytetrafluoroethylene resin used for preparing an electrode mixture by mixing it with an active material, etc., which exhibits excellent tensile strength of the sheet obtained using the electrode mixture and excellent uniformity of sheet thickness after storage of the electrode mixture over time. The present invention also aims to provide an electrode mixture, an electrode layer, an electrode, and a secondary battery.

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

[0009] [1] A polytetrafluoroethylene resin used as a binder for secondary batteries, wherein, in the differential scanning calorimetry curve obtained by differential scanning calorimetry under measurement condition A, when a straight line including the heat flow value at 320°C and the heat flow value at 350°C is used as the baseline, the ratio of the endothermic peak height at 338°C to the endothermic peak height at 343°C is 0.10 to 0.95. Measurement condition A: Under a nitrogen atmosphere, the temperature is raised from 40°C to 300°C at a heating rate of 10°C / min, held at 300°C for 5 minutes, and then raised from 300°C to 400°C at a heating rate of 2°C / min. [2] Specific surface area is 3 to 15 m². ２[1] A polytetrafluoroethylene resin in the form of [1] / g. [3] An electrode mixture comprising the polytetrafluoroethylene resin described in [1] or [2] and an active material. [4] An electrode mixture according to [3], further comprising a solid electrolyte. [5] An electrode mixture according to [4], wherein the solid electrolyte comprises a sulfide-based solid electrolyte. [6] An electrode layer comprising the electrode mixture according to any one of [3] to [5]. [7] An electrode comprising a current collector and the electrode layer according to [6] disposed on the current collector. [8] A secondary battery comprising the electrode according to [7]. [9] An electrode mixture comprising a polytetrafluoroethylene resin and an active material, wherein, in a differential scanning calorimetry curve obtained by differential scanning calorimetry under measurement condition A, when a straight line including the heat flow value at 320°C and the heat flow value at 350°C is used as the baseline, the ratio of the endothermic peak height at 338°C to the endothermic peak height at 343°C is 0.10 to 0.95. Measurement condition A: Under a nitrogen atmosphere, the temperature is raised from 40°C to 300°C at a heating rate of 10°C / min, held at 300°C for 5 minutes, and then raised from 300°C to 400°C at a heating rate of 2°C / min.

[10] The electrode mixture according to [9], further comprising a solid electrolyte.

[11] The electrode mixture according to

[10] , wherein the solid electrolyte comprises a sulfide-based solid electrolyte.

[0010] According to the present invention, a polytetrafluoroethylene resin can be provided that is used to prepare an electrode mixture by mixing it with an active material, and which exhibits excellent tensile strength of the sheet obtained using the electrode mixture, as well as excellent uniformity of sheet thickness after storage of the electrode mixture over time. Furthermore, according to the present invention, an electrode mixture, an electrode layer, an electrode, and a secondary battery can be provided.

[0011] This is a schematic diagram illustrating a method for measuring the ratio of the endothermic peak height at 338°C to the endothermic peak height at 343°C.

[0012] The meanings of terms used in this invention are as follows: A numerical range expressed using "~" means a range that includes the numerical values ​​written before and after "~" as the lower and upper limits. In numerical ranges described stepwise in this specification, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Also, in numerical ranges described in this specification, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples. In this specification, each component may be made using one substance alone or two or more substances in combination. Here, when two or more substances are used in combination for each component, the content for that component refers to the total content of the substances used in combination, unless otherwise specified. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. "Unit" is a general term for an atomic group derived from one monomer molecule that is directly formed by the polymerization of monomers, and an atomic group obtained by chemically transforming a part of the above atomic group. "Unit based on monomer" will also be simply referred to as "unit" below. The content (mass %) or molar %) of each unit relative to the total units contained in a resin or polymer is determined by analyzing the resin or polymer using solid-state nuclear magnetic resonance spectroscopy (NMR). Typically, the content of each unit calculated from the amount of each monomer added closely matches the actual content of each unit.

[0013] [Polytetrafluoroethylene Resin] The polytetrafluoroethylene resin of the present invention (hereinafter also simply referred to as "PTFE resin") is a PTFE resin used as a binder for secondary batteries. In the differential scanning calorimetry curve obtained by performing differential scanning calorimetry on the PTFE resin under the measurement conditions A described below, when a straight line including the heat flow value at 320°C and the heat flow value at 350°C (a straight line connecting the heat flow value at 320°C and the heat flow value at 350°C) is used as the baseline, the endothermic peak height at 343°C (hereinafter referred to as "h ３４３ｘ It is also called "h". The endothermic peak height at 338°C for the above (hereinafter referred to as "h ３３８ｘ It is also called the ratio of h ３３８ｘ / h ３４３ｘ(hereinafter also referred to as "specific ratio X") is from 0.10 to 0.95.

[0014] In the PTFE-based resin of the present invention, it is excellent in breaking strength and also excellent in the thickness uniformity of the sheet obtained after the electrode binder is stored over time (hereinafter also simply referred to as "thickness uniformity after storage over time"). The mechanism by which the sheet can be produced is not necessarily clear, but the present inventors speculate as follows. As described later, h ３３８ｘ is a value related to the abundance ratio of folded-chain crystals (FCC) in the PTFE-based resin, and h ３４３ｘ was found to be a value related to the abundance ratio of extended-chain crystals (ECC) in the PTFE-based resin. Folded-chain crystals and extended-chain crystals are likely to have differences in the degree of fibrillation in the process of producing the PTFE-based resin (for example, the jet mill treatment described later), etc. When the same treatment is applied under the same conditions. In particular, extended-chain crystals are more likely to be fibrillated compared to folded-chain crystals. Utilizing the above findings, the present inventors have found that when the specific ratio X of the PTFE-based resin is 0.95 or less, extended-chain crystals are moderately present in the PTFE-based resin, and fibrillation of the entire PTFE-based resin is sufficiently promoted. As a result, it is speculated that even when the number of rolling passes is small, the breaking strength of the obtained sheet is excellent. Further, when the specific ratio X of the PTFE-based resin is 0.10 or more, folded-chain crystals are moderately present in the PTFE-based resin, and since fibrillation of the entire PTFE-based resin does not progress too much, it is speculated that a sheet with a uniform thickness can be produced even after the electrode binder is stored over time. Hereinafter, when at least one of the effects of the breaking strength of the sheet and the thickness uniformity after storage over time is more excellent, it is also referred to as "the effect of the present invention is more excellent".

[0015] <Specific ratio X> The specific ratio X (h ３３８ｘ / h ３４３ｘ ) of the PTFE-based resin is from 0.10 to 0.95, preferably from 0.15 to 0.80, more preferably from 0.15 to 0.70, and still more preferably from 0.15 to 0.40 in terms of the more excellent effect of the present invention. h ３３８ｘ is preferably from -0.30 to -0.02 W / g, and more preferably from -0.25 to -0.05 W / g. h ３４３ｘThe preferred value is -0.50 to -0.10 W / g, and more preferably -0.45 to -0.15 W / g.

[0016] The method for measuring the specific ratio X will be described in detail. Figure 1 is a schematic diagram illustrating the method for measuring the specific ratio X. First, differential scanning calorimetry is performed on an object that has not been heated to a temperature of 300°C or higher under the following measurement condition A to obtain a differential scanning calorimetry curve (for example, Figure 1). For differential scanning calorimetry, for example, a differential scanning calorimeter (such as the DSC-Q20 manufactured by TA Instruments Corporation) is used. Measurement condition A: Under a nitrogen atmosphere, the temperature is raised from 40°C to 300°C at a heating rate of 10°C / min, held at 300°C for 5 minutes, and then raised from 300°C to 400°C at a heating rate of 2°C / min.

[0017] Next, in the obtained differential scanning calorimetry curve, the straight line containing the heat flow value at 320°C and the heat flow value at 350°C is set as the baseline (dashed line in Figure 1). In other words, the straight line containing two predetermined points is set as h ３３８ｘ and h ３４３ｘ This will be used as the baseline for the endothermic peak height when calculating h. ３３８ｘ This is the endothermic peak height at 338°C from the baseline mentioned above, and h ３４３ｘ This is the endothermic peak height at 343°C from the baseline mentioned above, and h ３３８ｘ and h ３４３ｘ From this, the specific ratio X can be calculated.

[0018] One method for adjusting the specific ratio X is the pulverization process described later in the method for manufacturing PTFE-based resins.

[0019] Furthermore, it is preferable that the specific ratio X in the same type of PTFE resin is 0.10 to 0.95. In other words, it is preferable that a PTFE resin of the same type (single type) satisfies the predetermined specific ratio X, rather than a mixture obtained using two or more types of PTFE resins satisfying the predetermined specific ratio X. If the above conditions are met, it becomes easier to control the fibrillation of the PTFE resin during sheet production compared to the case where two or more types of PTFE resins exhibiting different properties are used, and the breaking strength of the sheet may be superior.

[0020] <Units> PTFE resins contain units based on tetrafluoroethylene (hereinafter also referred to as "TFE units").

[0021] (TFE Units) PTFE-based resins are resins containing TFE units. The resins of this embodiment are clearly distinguished from elastomers. Elastomers are elastic polymers with no melting point that exhibit a storage modulus G' of 80 kPa or more at 100°C and 50 cpm. The melting point can be determined as the temperature corresponding to the maximum value of the melting peak measured by differential scanning calorimetry (DSC). The storage modulus G' is a value measured under conditions of 100°C and 50 cpm in accordance with ASTM D6204. The TFE unit content is preferably 99% by mass or more, more preferably 99.5% by mass or more, and even more preferably 99.9% by mass or more, relative to the total units of the PTFE-based resin. The upper limit is preferably 100% by mass or less. Furthermore, the TFE unit content is preferably 99 mol% or more, more preferably 99.5 mol% or more, and even more preferably 99.9 mol% or more, relative to the total units of the PTFE resin. The upper limit is preferably 100 mol% or less.

[0022] (Units based on other monomers) PTFE resins may contain units based on monomers other than TFE units. Examples of other monomers include perfluoroolefins such as hexafluoropropylene (HFP); hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride (VdF); perhaloolefins such as chlorotrifluoroethylene; perfluorovinyl ethers such as perfluoro(alkyl vinyl ether) (PAVE); perfluoroallyl ethers; (fluoroalkyl)ethylene (FAE); and ethylene. Among these, HFP, VdF, FAE, or PAVE are preferred as other monomers. Furthermore, the other monomers may be monomers used in the method for producing PTFE resins described later.

[0023] As PAVE, a monomer represented by formula (PA) is preferred. CF ２ =CF-O-Rf １ (PA) In formula (PA), Rf １Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms. １ The number of carbon atoms in the perfluoroalkyl group represented by is preferably 1 to 8, more preferably 1 to 6, even more preferably 1 to 5, and particularly preferably 1 to 3, in terms of superior polymerization reactivity. The perfluoroalkyl group may be linear or branched.

[0024] For example, PAVE is CF ２ = CFOCF ３ (PMVE), CF ２ = CFOCF ２ CF ３ (PEVE), CF ２ = CFOCF ２ CF ２ CF ３ (PPVE), CF ２ = CFOCF ２ CF ２ CF ２ CF ３ , and CF ２ = CFO (CF ２ ) ８ F is one example, with PMVE or PPVE being preferred.

[0025] As the FAE, a monomer represented by formula (FA) is preferred. CZ ２ =CX(CF ２ ) ｍ Y (FA) In formula (FA), X, Y, and Z each independently represent a hydrogen atom or a fluorine atom. m represents an integer from 2 to 6. For FAE, for example, CH ２ =CH(CF ２ ) ２ F, CH ２ =CH(CF ２ ) ３ F, CH ２ =CH(CF ２ ) ４ F (PFBE), CH ２ = CF (CF ２ ) ３ H and CH ２ = CF (CF ２ ) ４ H is an example, and PFBE or CH ２ =CH(CF ２) ２ F is preferred, and PFBE is more preferred.

[0026] The content of units based on other monomers (preferably units based on PFBE) is preferably 1 mol% or less, more preferably 0.5 mol% or less, and even more preferably 0.1 mol% or less, relative to the total units of the PTFE resin. The lower limit is preferably 0 mol% or more. The content of units based on other monomers is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, relative to the total units of the PTFE resin. The lower limit is preferably 0% by mass or more.

[0027] The total content of TFE units and PFBE-based units is preferably 95% by mass or more, more preferably 99% by mass or more, and even more preferably 99.9% by mass or more, relative to the total mass of the PTFE resin. The upper limit is preferably 100% by mass or less.

[0028] The respective content of each unit in PTFE resin is: １ H-NMR and １９ It can be measured by known methods such as F-NMR (nuclear magnetic resonance analysis).

[0029] PTFE resins may have a core-shell structure. Examples of PTFE resins having a core-shell structure include PTFE resins (particles) that contain a core of high molecular weight PTFE resin and a shell of PTFE resin containing units based on lower molecular weight PTFE resin or other monomers.

[0030] The form of the PTFE resin is not particularly limited, but examples include powder, granules, and particulate matter, with particulate matter being preferred. When the PTFE resin is in particulate matter, it may consist of either primary or secondary particles.

[0031] The specific surface area of ​​PTFE resins is 1 to 20 m². ２ A value of / g is preferable, and in terms of achieving better effects of the present invention, 3 to 15 m is preferred. ２ / g is more preferable, 4 to 14 m ２A value of / g is even more preferable. If the specific surface area is within the above range, it can be uniformly dispersed during mixing with the active material, and it is easy to obtain a sheet with excellent thickness uniformity after storage in a single rolling process. Also, if the specific surface area is 3 m² ２ When the concentration is 15 m² or higher, fusion between PTFE primary particles is more suppressed, and dispersibility with the active material is improved, resulting in superior uniformity of thickness after storage over time. ２ When the value is less than / g, it is easier to adjust the frequency of entanglement between primary particles to an appropriate range, and fibrillation is also promoted, which can result in superior sheet strength.

[0032] One method for adjusting the specific surface area of ​​PTFE resin is to perform a solution immersion treatment as described later in the manufacturing method of PTFE resin. Specifically, increasing the processing time of the solution immersion treatment tends to decrease the specific surface area of ​​the PTFE resin. The specific surface area of ​​PTFE resin can be measured using a measurement method compliant with JIS Z8830:2013. For example, the amount of gas adsorbed is measured using the flow method, and the adsorption data is analyzed using the BET one-point method. Specifically, after filling a sample container with PTFE resin, the sample container filled with PTFE resin is degassed by heating it at 200°C for 20 minutes under vacuum. Then, the sample container is allowed to cool to room temperature while maintaining the vacuum. Next, in a gas mixer, helium, which is the carrier gas, and nitrogen, which is the adsorbate, are prepared so that the nitrogen concentration is 30% by volume. The prepared mixed gas is flowed through the PTFE resin of the sample container at a temperature of 25°C, a flow rate of 25 mL / min, and a total pressure of 0.1 MPa. When the sample container is cooled with liquid nitrogen, only nitrogen begins to adsorb onto the surface of the PTFE resin. As adsorption occurs, the nitrogen concentration in the mixed gas decreases, causing an adsorption peak A to appear in the gas concentration detector signal. When the adsorption of nitrogen gas onto the PTFE resin surface is saturated, the mixed gas converges to its initial mixing ratio, and the gas concentration detector signal returns to the baseline. Subsequently, when the sample container is returned to room temperature, the nitrogen adsorbed on the surface of the PTFE resin begins to desorb. As desorption occurs, the nitrogen concentration in the mixed gas increases, causing a desorption peak B to appear in the gas concentration detector signal. Once all nitrogen has desorbed, the detector signal returns to the baseline. The multilayer adsorption amount V (mL / g) of nitrogen is calculated from the area enclosed by the baseline and the curves constituting desorption peak B. The above calculation method allows for the calculation of nitrogen adsorption capacity by a known powder, using the area ratio of the area obtained by the above operation. The monolayer adsorption capacity A is calculated by applying the BET formula in the single-point method shown in Equation 1 below. Monolayer adsorption capacity A (mL / g) = Multilayer adsorption capacity V (mL / g) × P (Pa) / P ０ (Pa) Formula 1 P in Formula 1 ０P represents the total pressure of the gas mixture, and P represents the partial pressure of nitrogen gas in the gas mixture. Since the concentration of nitrogen gas in the gas mixture is 30% by volume, P / P ０ The value is 0.3. Using the calculated monolayer adsorption amount A (mL / g), the specific surface area is calculated using the following formula 2. Specific surface area (m²) ２ / g) = 4.53 (m ２ Equation 2: (mL / mL) × Monolayer adsorption amount A (mL / g) The above measurement can be performed using a fully automated specific surface area analyzer (Macthorpe HM Model-1208, manufactured by Mountec Co., Ltd.), an automated specific surface area analyzer (Gemini VII2390, manufactured by Micromeritics, Inc.), etc.

[0033] The angle of repose of PTFE resin is preferably 32 to 44°, and more preferably 33 to 40°. If the angle of repose is within the above range, the progress of fibrillation of the PTFE resin during mixing with active materials can be suppressed while reducing the average particle size of the PTFE resin. The angle of repose can be measured by known measurement methods. For example, the PTFE resin to be measured can be dropped from a funnel of a certain height onto a horizontal measurement table, and the base angle can be calculated from the diameter and height of the resulting conical deposit, and this base angle can be taken as the angle of repose. For example, it can be measured based on JIS-R9301-2-2:1999 (corresponding international standard: ISO 902:1976).

[0034] The pore volume of PTFE resins is 0.2 to 15.0 cm³. ３ Preferably, the amount is 0.5 to 10.0 cm / g. ３ A value of / g is more preferable. If the pore volume is within the above range, the miscibility with the active material and conductive additives is promoted. The pore volume can be measured, for example, by the mercury intrusion method using a known analytical instrument (e.g., AutoPore IV 9520 manufactured by Micromeritics).

[0035] The average pore size of the PTFE resin is preferably 0.05 to 2.0 μm, and more preferably 0.1 to 1.5 μm. The average pore size can be measured, for example, by the mercury intrusion method using a known analytical instrument. Specifically, the pore volume is V (cm²). ３ Let the specific surface area be A(m²) ( / g), and the specific surface area be A(m²). ２When expressed as ( / g), the average pore size (μm) can be calculated as 4V / A.

[0036] The pore median diameter of the PTFE resin is preferably 1 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more, in terms of excellent wall adhesion. The upper limit is preferably 100 μm or less, and more preferably 90 μm or less. The pore median diameter is the pore diameter at which the cumulative value in the pore distribution profile obtained by the mercury intrusion method using a known analytical instrument becomes 50 volume% of the pore volume.

[0037] The electrostatic charge of the PTFE resin is preferably -14000 to 0V, more preferably -5000 to -100V, and even more preferably -3000 to -200V for superior wall adhesion. When the electrostatic charge is within the above range, the PTFE resins repel each other due to electrostatic repulsion during the mixing process with the active material, etc., which can improve dispersibility. Wall adhesion can also be improved. The electrostatic charge can be adjusted by various ionizers and mechanical friction.

[0038] In terms of improving binding strength and electrode flexibility, the average primary particle size of the PTFE resin in the aqueous dispersion 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 150 nm or more, and even more preferably 180 nm or more. The range is preferably 100 to 500 nm, more preferably 150 to 450 nm, and even more preferably 180 to 400 nm. The average primary particle size is the volume-based median diameter D50 obtained by a laser scattering particle size distribution analyzer.

[0039] The average particle size of the PTFE resin 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 range is preferably 280 to 1000 nm, more preferably 300 to 800 nm, and even more preferably 320 to 700 nm. The average particle size is, for example, the median diameter in the volume-based particle size distribution measured in accordance with JIS K 6891:1995.

[0040] The standard specific gravity (SSG) of PTFE resins is preferably 2.120 to 2.190, more preferably 2.125 to 2.190, and even more preferably 2.130 to 2.180. SSG is used as a relative measure of molecular weight, with lower values ​​indicating higher molecular weight. Furthermore, a higher amount of comonomers introduced into the PTFE resin tends to increase the amorphous structure, lower the density, and decrease the SSG value. SSG can be measured in accordance with ASTM D4895-10.

[0041] In the extrusion test of PTFE resin, the extrusion pressure 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 by the following method: 100 g of PTFE resin, which has been left at room temperature for at least 2 hours, is placed in a 500 mL glass bottle, 21.7 g of lubricating oil (Isopar H®, manufactured by Exxon Corporation) is added, and the mixture is mixed for 3 minutes to obtain a mixture. The obtained mixture is left in a 25°C constant temperature bath for 2 hours, and then paste-extruded at 25°C under conditions of a reduction ratio (ratio of the cross-sectional area of ​​the die inlet to the cross-sectional area of ​​the die outlet) of 100 and an extrusion speed of 51 cm / min, through an orifice with a diameter of 2.5 cm, a land length of 1.1 cm, and an introduction angle of 30° to obtain an extrusion bead (string-like material). The pressure required for extrusion at this time is measured and defined as the extrusion pressure (unit: MPa).

[0042] The moisture content of the PTFE resin is preferably 0.040% by mass or less, more preferably 0.020% by mass or less, even more preferably 0.010% by mass or less, particularly preferably 0.005% by mass or less, and most preferably 0.002% by mass or less, relative to the total mass of the PTFE resin. The lower limit is preferably 0% by mass or more, and more preferably 0.0001% by mass or more. The above moisture content is measured by the following method: The mass of the PTFE resin is measured before and after heating at 150°C for 2 hours, and the moisture content is calculated according to the following formula: Three samples are taken, the calculation is performed for each, and the average value is obtained and adopted. Moisture content (by mass) = 100 × [(Mass of PTFE resin before heating (g)) - (Mass of PTFE resin after heating (g))] / (Mass of PTFE resin before heating (g))

[0043] The bulk density of the PTFE resin is preferably 350 to 600 g / L, and more preferably 400 to 550 g / L. The bulk density is measured in accordance with JIS K6892:1995.

[0044] PTFE resins are used as binders for secondary batteries. PTFE resins are preferably used, for example, in compositions for forming components or layers that constitute a secondary battery. More preferably, they are used in electrode mixtures obtained by mixing PTFE resin with active material, etc. The term "binder" here has the same meaning as the general term "binder," and includes so-called binders, dispersants, and adhesives. Examples of components or layers that constitute a secondary battery include the electrode layer described later. Furthermore, the secondary battery itself is not particularly limited as long as it is a known secondary battery. Preferred embodiments of the secondary battery are described later.

[0045] PTFE resins can be suitably used for other applications as well. Other applications include, for example, low-temperature sintered barium titanate ceramic capacitors. When using PTFE resins in ceramic capacitors, methods include mixing barium titanate and the PTFE resin, forming it into a sheet, adding a small amount of water, and densifying it by applying a temperature of 100 to 200°C and a pressure of several hundred MPa.

[0046] [Method for producing PTFE resin] The method for producing PTFE resin is not particularly limited as long as it is a method capable of producing the PTFE resin described above. A preferred method for producing PTFE resin is one that includes, for example, step A of obtaining an aqueous dispersion containing PTFE resin, and step B of obtaining PTFE resin from the aqueous dispersion.

[0047] <Process A> Process A is a process to obtain an aqueous dispersion containing a PTFE-based resin.

[0048] The process for obtaining the above aqueous dispersion includes polymerizing monomers that constitute the PTFE resin in an aqueous medium. The monomers can be appropriately selected according to the desired PTFE resin. Examples of polymerization methods include known polymerization methods.

[0049] Step A is preferably a step in which a first monomer containing TFE is polymerized in the presence of an aqueous medium to obtain an aqueous dispersion containing a PTFE-based resin.

[0050] (Aqueous medium) Examples of aqueous mediums include water and mixed solvents of water and water-soluble organic solvents. Examples of water-soluble organic solvents include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol. In the case of a mixture of water and water-soluble organic solvent, the concentration of the water-soluble organic solvent is preferably 10% by mass or less. It is preferable that the aqueous medium be water only.

[0051] (First Monomer) The first monomer contains TFE. In addition to TFE, the first monomer may also contain other monomers as described above. The TFE content is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, even more preferably 99 mol% or more, even more preferably 99.5 mol% or more, and especially preferably 99.9 mol% or more, based on the total number of moles of the first monomer. The upper limit is preferably 100 mol% or less.

[0052] Examples of polymerization methods for the first monomer include emulsion polymerization, solution polymerization, and suspension polymerization. This can be carried out by heating the monomer in the presence of an aqueous medium and a polymerization initiator. The aqueous medium may or may not contain an emulsifier.

[0053] (Polymerization initiators) Examples of polymerization initiators include oil-soluble radical polymerization initiators and water-soluble radical polymerization initiators.

[0054] Examples of oil-soluble radical polymerization initiators include dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and disec-butyl peroxydicarbonate; peroxyesters such as t-butyl peroxyisobutyrate and t-butyl peroxypivalate; dialkyl peroxides such as di-t-butyl peroxide; di(ω-hydro-dodecafluoroheptanoyl) peroxide, di(ω-hydro-tetradecafluoroheptanoyl) peroxide, di(ω-hydro-hexadecafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleryl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide, di(perfluorononanoyl) peroxide, di(ω-chloro-hexafluoro Examples include di[perfluoro(or fluorochloro)acyl]peroxides such as olobutyryl peroxide, di(ω-chloro-decafluorohexanoyl) peroxide, di(ω-chloro-tetradecafluorooctanoyl) peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl-peroxide, di(dichloropentafluorobutanoyl) peroxide, di(trichlorooctafluorohexanoyl) peroxide, di(tetrachloroundafluorooctanoyl) peroxide, di(pentachlorotetradecafluorodecanoyl) peroxide, and di(undachlorodotriacontafluorodocosanoyl) peroxide.

[0055] As a water-soluble radical polymerization initiator, a water-soluble radical initiator or a water-soluble redox catalyst is preferred, with ammonium persulfate alone or a mixture of persulfate and disuccinate peroxide being more preferred, and ammonium persulfate alone or a mixture of ammonium persulfate and disuccinate peroxide being even more preferred. As a water-soluble radical initiator, persulfates such as ammonium persulfate and potassium persulfate, or water-soluble organic peroxides such as disuccinate peroxide, bisglutaric acid peroxide, and tert-butyl hydroperoxide are preferred. As a water-soluble redox catalyst, a combination of an oxidizing agent such as bromate or its salt, chloric acid or its salt, persulfate or its salt, permanganate or its salt, or hydrogen peroxide, and a reducing agent such as sulfurous acid or its salt, bisulfite or its salt, thiosulfate or its salt, or organic acid is preferred.

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

[0057] (Other components) In polymerization of the first monomer, other components such as nucleating agents, chain transfer agents, buffers, pH adjusters, stabilizing aids, dispersion stabilizers, radical scavengers, decomposing agents for polymerization initiators, and dicarboxylic acids may be used.

[0058] Examples of nucleating agents include fluoropolyethers such as perfluoropolyether acids, nonionic surfactants, and chain transfer agents. Examples of perfluoropolyether acids include those described in J. Appl. Polymer Sci. 57,797 (1995).

[0059] Examples of radical scavengers include aromatic hydroxy compounds, aromatic amines, N,N-diethylhydroxylamine, quinone compounds, terpenes, thiocyanates, and cupric chloride. Examples of aromatic hydroxy compounds include unsubstituted phenols, polyhydric phenols, salicylic acid, m- or p-salicylic acid, gallic acid, and naphthol. Examples of unsubstituted phenols include o-, m- or p-nitrophenols, o-, m- or p-aminophenols, and p-nitrosophenols. Examples of polyhydric phenols include catechol, resorcinol, hydroquinone, pyrogallol, phloroglucin, and naphthresorcinol. Examples of aromatic amines include o-, m- or p-phenylenediamine and benzidine. Examples of quinone compounds include o-, m- or p-benzoquinone, 1,4-naphthoquinone, and alizarin. Examples of thiocyanates include ammonium thiocyanate (NH4). ４ Examples include SCN, potassium thiocyanate (KSCN), and sodium thiocyanate (NaSCN).

[0060] Any compound capable of decomposing the polymerization initiator can be used as a decomposition agent for the polymerization initiator, such as sulfites, bisulfites, bromates, diimines, diimines, oxalic acid, oxalates, copper salts, and iron salts.

[0061] As the dicarboxylic acid, for example, compounds represented by the general formula: HOOC-R-COOH (wherein R represents an alkylene group having 1 to 5 carbon atoms) are preferred, and succinic acid, malonic acid, glutaric acid, adipic acid, or pimelic acid are more preferred.

[0062] In the polymerization of the first monomer, a stabilizing agent may be used. Preferred stabilizing agents are paraffin wax, fluorinated solvents, or silicone oil. The paraffin wax may be liquid, semi-solid, or solid at room temperature. Among these, saturated hydrocarbons with 12 or more carbon atoms are preferred. The melting point of the paraffin wax is preferably 40 to 65°C, and more preferably 50 to 65°C. The stabilizing agent may be used alone or in combination of two or more.

[0063] The polymerization temperature and polymerization pressure in the polymerization of the first monomer can be appropriately determined depending on the type of monomer used, the molecular weight of the target PTFE resin, and the reaction rate. The polymerization temperature is preferably 5°C or higher, more preferably 10°C or higher, even more preferably 30°C or higher, and particularly preferably 50°C or higher. The upper limit is preferably 150°C or lower, more preferably 120°C or lower, and even more preferably 100°C or lower. The range is preferably 5 to 150°C, more preferably 10 to 120°C, even more preferably 30 to 100°C, and particularly preferably 50 to 100°C. The polymerization pressure is preferably 0.05 MPaG or higher, more preferably 0.3 MPaG or higher, and even more preferably 0.5 MPaG or higher. The upper limit is preferably 5.0 MPaG or lower, and even more preferably 3.0 MPaG or lower. The range is preferably 0.05 to 5.0 MPaG, more preferably 0.3 to 3.0 MPaG, and even more preferably 0.5 to 3.0 MPaG.

[0064] The PTFE resin content is preferably 5.0 to 50.0% by mass, more preferably 10.0 to 45.0% by mass, and even more preferably 10.0 to 30.0% by mass, relative to the total mass of the aqueous dispersion. The solid content concentration of the aqueous dispersion is preferably 5.0 to 50.0% by mass, more preferably 10.0 to 45.0% by mass, and even more preferably 10.0 to 30.0% by mass. The solid content concentration of the aqueous dispersion can be measured, for example, by the following method: The solid content concentration of the aqueous dispersion is calculated by heating 2.0 g of the aqueous dispersion at 170°C for 20 minutes, weighing the mass of the residue, and then determining the solid content concentration using the following formula: "Solid content concentration (mass%) = 100 × heated residue of aqueous dispersion (g) / mass of aqueous dispersion (2.0 g)"

[0065] <Step B> Step B is a step to obtain a PTFE-based resin from the aqueous dispersion obtained in Step A. Examples of methods for obtaining a PTFE-based resin from an aqueous dispersion include known methods, and it is preferable to obtain a PTFE-based resin by performing a coagulation treatment and drying treatment on the aqueous dispersion, and it is more preferable to obtain a PTFE-based wet resin by performing a coagulation treatment on the aqueous dispersion, and then to obtain a PTFE-based resin by drying the above PTFE-based wet resin.

[0066] Examples of coagulation treatments include freeze coagulation, acid coagulation, base coagulation, mechanical coagulation, and coagulation using a coagulant, with acid coagulation or freeze coagulation being preferred. In the case of freeze coagulation, the coagulation temperature is preferably -20 to 0°C. The coagulation time is preferably 1 hour or more, and more preferably 2 hours or more. In the case of acid coagulation, a method of adding an acid-containing solution to an aqueous dispersion is preferred. Examples of acids to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, and hydrofluoric acid, with hydrochloric acid or nitric acid being preferred. The concentration of the acid in the acid-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. For base coagulation, a method of adding a base-containing solution to an aqueous dispersion is preferred. Examples of bases to be added include sodium hydroxide, potassium hydroxide, and ammonium carbonate, with sodium hydroxide being preferred. The concentration of the base in the base-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. For aggregation using a coagulant, known coagulants can be used. Examples of known coagulants include aluminum salts, calcium salts, and magnesium salts. Specifically, aluminum sulfate, with the general formula M'Al(SO4), can be used. ４ ) ２ 12H ２ Examples include alum, calcium nitrate, and magnesium sulfate represented by O [wherein M' is a monovalent cation other than lithium], with alum being preferred, and potassium alum being more preferred, where M is potassium.

[0067] Furthermore, pH adjusters or flocculation aids may be used during the flocculation treatment. Examples of pH adjusters include sodium carbonate and sodium bicarbonate. Examples of flocculation aids include inorganic salts such as potassium nitrate, sodium nitrate, sodium carbonate, and sodium bicarbonate, as well as organic solvents such as alcohol-based solvents and acetone. It is also preferable to carry out the flocculation treatment in the presence of at least one compound selected from the group consisting of ammonia, ammonium salts, and urea.

[0068] As a drying treatment, a treatment to dry the PTFE-based wet resin obtained by the agglomeration treatment is preferred. The drying temperature is preferably 100°C or higher, more preferably 110°C or higher, even more preferably 120°C or higher, and particularly preferably 170°C or higher. The upper limit is preferably 280°C or lower, more preferably 250°C or lower, and even more preferably 230°C or lower. The range is preferably 100 to 280°C, more preferably 110 to 250°C, even more preferably 120 to 230°C, and particularly preferably 170 to 230°C. In particular, when the drying temperature is 110°C or higher, the drying treatment is sufficiently promoted, and when the drying temperature is 250°C or lower, the increase in the extrusion pressure of the PTFE-based wet resin is more easily suppressed. The drying time is preferably 1 hour or more, and preferably 3 hours or more. The upper limit is preferably 100 hours or less, more preferably 50 hours or less, and even more preferably 30 hours or less. The drying time range is preferably 1 to 100 hours, more preferably 3 to 50 hours, and even more preferably 3 to 30 hours. The water content of the PTFE-based wet resin, which is the material to be dried, is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, relative to the total mass of the PTFE-based wet resin. The upper limit is preferably 150% by mass or less, and more preferably 100% by mass or less. The range is preferably 10 to 100% by mass, more preferably 20 to 50% by mass, and even more preferably 30 to 50% by mass.

[0069] Furthermore, the drying process is preferably carried out in an atmosphere containing ammonia, as this enhances the effects of the present invention. An atmosphere containing ammonia means an atmosphere in which ammonia gas can come into contact with the PTFE-based wet resin. For example, this means an atmosphere in which ammonia gas is present, and an atmosphere in which ammonia gas is generated by heating or the like in the presence of ammonia or a compound that generates ammonia gas. Examples of compounds that generate ammonia include ammonium salts and urea, with ammonium carbonate being preferred.

[0070] The drying process can be carried out using an electric furnace or a steam furnace. For example, it can be carried out using an electric furnace such as a parallel flow box electric furnace, a ventilated box electric furnace, a ventilated conveyor electric furnace, a band electric furnace, a radiant conveyor electric furnace, a fluidized bed electric furnace, a vacuum electric furnace, agitated electric furnace, an airflow electric furnace, and a hot air circulation electric furnace, or a steam furnace corresponding to the above (an apparatus in which "electric furnace" in the apparatus name of each electric furnace is read as "steam furnace").

[0071] After the agglomeration treatment and before the drying treatment, known granulation treatments and known particle sizing treatments may be performed. Granulation treatment is a treatment that increases the average particle size of the PTFE resin (particles) (for example, to several hundred μm), and particle sizing treatment is a treatment that adjusts the particle properties and particle size distribution by stirring, etc.

[0072] <Other Processes> The method for producing PTFE resin may further include other processes. Examples of other processes include grinding and immersion in solution. It is preferable to carry out the other processes after process B, and it is more preferable to carry out the grinding and immersion in solution in the order of process B. The other processes make it easier to adjust the specific ratio X or specific ratio Y.

[0073] (Crushing process) The crushing process is a process of crushing PTFE resin.

[0074] Any known grinding process is acceptable, for example, a grinding process using a jet mill. Generally, a jet mill is a device that grinds powders by causing them to collide at high speed with each other or with the inner wall of the mill using high-pressure air or gas. In the present invention, it is preferable to supply the powder while cooling and to adjust the compressed gas to an appropriate flow rate. The cooling temperature is preferably below the glass transition temperature of the PTFE resin, more preferably above -200°C and below 15°C, even more preferably above -200°C and below 10°C, and particularly preferably between -100°C and 0°C, as this makes it easier to adjust the specific ratio X. Examples of cooling methods include using liquid nitrogen and dry ice. By processing the PTFE resin at the above temperature, fibrillation of the PTFE resin is suppressed, and the energy provided by the collision loosens the folded chain crystals of the PTFE resin, which can increase the proportion of fully extended chain crystals, that is, the specific ratio X can decrease. As a result, fibrillation is more likely to occur even with low shear forces during sheet molding, and sheets with excellent strength, such as fracture strength, can be obtained even with fewer passes through the rolls. Furthermore, it is preferable to perform the crushing treatment on PTFE resin alone.

[0075] In a jet mill, the grinding pressure is preferably 0.1 to 2.0 MPaG, which is advantageous in that it allows for both increasing the proportion of extended chain crystals and suppressing fibrillation, and is more preferably 0.2 to 0.9 MPaG, which is advantageous in that it allows for easy adjustment of the specific ratio X.

[0076] Examples of jet mills include the impact type, which grinds particles by colliding them with each other or with a collision body (target); the swirling airflow type and loop type, which grind particles by mutual collision in a grinding zone formed by multiple grinding nozzles arranged in a circulating airflow; the fluidized bed type, which grinds particles by collision and friction within a fluidized bed; and the supersonic type. Details of the impact type, swirling airflow type, loop type, and fluidized bed type jet mills are described in "Advanced Grinding Technology and Applications," edited by the Japan Powder Industry Technology Association, NGT Co., Ltd., page 162. Examples of impact type jet mills include grinders that discharge a fluid such as compressed air from a nozzle and grind particles by mutual collision in a high-speed turbulent airflow formed in the jet mill; and grinders that transport resin particles with a high-speed airflow and grind them by colliding them with a collision body. Commercially available jet mills include the Cross Jet Mill (manufactured by Kurimoto Iron Works Co., Ltd.); Jet-O-Mill, A-O Jet Mill, Sanitary AOM, Cojet, Single Track Jet Mill, Super STJ Mill (all manufactured by Seishin Enterprise Co., Ltd.); Current Jet Mill (manufactured by Nisshin Engineering Co., Ltd.); Ulmax (manufactured by Nisso Engineering Co., Ltd.); Supersonic Jet Grinder PJM type, Supersonic Jet Grinder CPY type, Supersonic Jet Grinder LJ-3 type, Supersonic Jet Grinder I type (all manufactured by Nippon Pneumatic Industry Co., Ltd.); Counter Jet Mill, Micro Jet T type, Spiral Jet Mill, Micron Jet MJQ (all manufactured by Hosokawa Micron Co., Ltd.); Fluidized Bed Jet Mill (manufactured by Nippon Coke Industries Co., Ltd.); Nano Grinding Mill (manufactured by Tokuju Kogyo Co., Ltd.); and EX-Mini Jet Mill (M-Tech Chemical Co., Ltd.). Among jet mills, the Single Track Jet Mill is preferred due to its superior productivity.

[0077] (Solution Immersion Treatment) Solution immersion treatment is a process in which PTFE resin is immersed in a solution. By performing solution immersion treatment, the surface energy of the PTFE resin is adjusted, and the specific surface area tends to decrease. As a result, the PTFE resin tends to disperse uniformly even in the electrode mixture state where a large amount of other components such as active material are present.

[0078] The solution immersion treatment is preferably performed on the PTFE resin after the pulverization treatment described above. It is also preferable to perform a drying treatment after the solution immersion treatment. In particular, it is preferable to process the PTFE resin into powder (preferably by jet milling), immerse it in a solution containing an organic solvent, and then dry it.

[0079] Examples of solutions include hydrophilic organic solvents and mixed solvents of water and hydrophilic organic solvents. Examples of hydrophilic organic solvents include alcohol-based solvents such as methanol and ethanol; ketone-based solvents such as acetone and methyl ethyl ketone; and ester-based solvents such as ethyl acetate and butyl acetate.

[0080] <First Embodiment> The method for producing PTFE resin may be the first embodiment. The first embodiment of the method for producing PTFE resin is a method for producing PTFE resin comprising steps C, D, and E. Step C: A step of polymerizing a nonfluorine monomer in an aqueous medium to obtain a solution 1 containing a polymer (hereinafter also referred to as "specific polymer C") that includes units based on a nonfluorine monomer. Step D: A step of polymerizing TFE in solution 1 without substantially adding a surfactant to solution 1 to obtain an aqueous emulsion containing PTFE resin. Step E: A step of obtaining PTFE resin from the aqueous emulsion obtained in step D. Furthermore, in terms of making it easier to adjust the specific ratio X or specific ratio Y, the first embodiment may further include the above-mentioned other steps after step E. As described above, examples of other steps include grinding and solution immersion. It is preferable to carry out the other steps after step E, and it is more preferable to carry out the grinding and solution immersion after step E.

[0081] (Step C) Step C is a process in which a non-fluorinated monomer is polymerized in an aqueous medium to obtain a solution 1 containing a specific polymer C. Below, the materials used in Step C will be described in detail, followed by a detailed description of the procedure for Step C.

[0082] - Non-fluorine monomer - A non-fluorine monomer is a monomer that does not contain a fluorine atom. The non-fluorine monomer preferably has a polymerizable group. The number of polymerizable groups is preferably 1 to 3, more preferably 1. As the polymerizable group, an ethylenically unsaturated group is preferable. More specifically, an acryloyl group, a methacryloyl group, a vinyl ether group, a vinyl ester group, a vinyl group, and an allyl group are mentioned, and an acryloyl group, a methacryloyl group, a vinyl ester group, or a vinyl ether group is preferable.

[0083] As the non-fluorine monomer, a monomer represented by the formula (NF) is preferable. Formula (NF) CH ２ =CR １１ -L １ -R １２ R １１ represents a hydrogen atom or an alkyl group. The number of carbon atoms of the alkyl group is preferably 1 to 3, more preferably 1. L １ represents a single bond, -CO-O-*, -O-CO-*, or -O-. * represents the bonding position with R １２ . For example, when L １ is -CO-O-*, the formula (NF) is CH ２ =CR １１ -CO-O-R １２ represents. R １２ represents a hydrogen atom, an alkyl group, an alkenyl group, or a nitrile group. However, when L １ is a single bond, R １２ is a nitrile group. The number of carbon atoms of the alkyl group is preferably 1 to 10, more preferably 1 to 6, and still more preferably 1 to 4. The number of carbon atoms of the alkenyl group is preferably 2 to 10, more preferably 2 to 6, and still more preferably 2 to 4. The alkyl group may be either linear or cyclic. When the alkyl group is cyclic, it corresponds to a cycloalkyl group. The alkenyl group may be either linear or cyclic.

[0084] As the monomer represented by the formula (NF), 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) is preferable. Formula (NF-1) CH２ =CR １１ -CO-O-R １３ Formula (NF-2) CH ２ =CR １１ -O-CO-R １４ Formula (NF-3) CH ２ =CR １１ -O-R １５ Formula (NF-4) CH ２ =CR １１ -R １６ R １１ is defined as described above. R １３ represents a hydrogen atom, an alkyl group or an alkenyl group. Among them, an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms is preferable. R １４ represents an alkyl group. Among them, an alkyl group having 1 to 3 carbon atoms is preferable, and a methyl group is more preferable. R １５ represents an alkyl group. Among them, a linear alkyl group or a cyclic alkyl group is preferable. R １６ represents a nitrile group.

[0085] Examples of the non-fluorine monomer 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 monomer may be used alone or in combination of two or more. As the non-fluorine monomer, a monomer represented by the formula (NF-1) or a monomer represented by the formula (NF-2) is preferable, and R １３ A monomer represented by the formula (NF-1) in which is an alkyl group is more preferable. The monomer represented by the formula (NF-1) and the monomer represented by the formula (NF-2) have an ester group or a carboxy group which is a hydrophilic group, and thus the monomer and its polymer have hydrophilicity. Therefore, particularly at a low concentration, the monomer and its polymer are considered to be stably dispersed in an aqueous medium without requiring a surfactant.

[0086] -Specific Polymer C- Specific polymer C is a polymer that contains units based on non-fluorinated monomers. Specific polymer C may contain only units based on non-fluorinated monomers, or it may contain units based on fluorinated monomers. In other words, in addition to non-fluorinated monomers, fluorinated monomers may also be used in step C. A fluorinated monomer is a monomer having a fluorine atom, for example, TFE. The content of units based on non-fluorinated monomers in specific polymer C is preferably 90% by mass or more, and more preferably 95% by mass or more, relative to the total units of specific polymer C. The upper limit is preferably 100% by mass or less.

[0087] -Aqueous media- Examples of aqueous media include the aqueous media used in step A described above.

[0088] -Polymerization Initiator- A polymerization initiator may be used in step C. An example of a polymerization initiator is the water-soluble radical polymerization initiator used in step A described above.

[0089] -Procedure for Step C- In Step C, polymerization of the non-fluorinated monomer is carried out in an aqueous medium. Specifically, it is preferable to mix the non-fluorinated monomer with the aqueous medium and carry out polymerization of the non-fluorinated monomer in the resulting mixture. As mentioned above, a fluorinated monomer may be used in combination as needed.

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

[0091] The content of the non-fluorinated monomer in the dispersion obtained by mixing the non-fluorinated monomer with an aqueous medium is preferably 0.000015 to 0.0030% by mass, and more preferably 0.000075 to 0.0023% by mass, relative to the total mass of the dispersion. Since the entire amount of the non-fluorinated monomer usually polymerizes to form a specific polymer C, the concentration of the specific polymer C in the obtained solution 1 is within the above numerical range. The above concentrations of the non-fluorinated monomer and the specific polymer C are the concentrations when the obtained solution 1 is used in step D without diluting it with an aqueous medium. When the obtained solution 1 is diluted with an aqueous medium to obtain the concentration of the specific polymer C, and the diluted solution is used in step D, a high-concentration solution corresponding to the dilution ratio is produced in step C. The dilution ratio is not particularly limited, but 10 times or less is preferred.

[0092] The amount of polymerization initiator used is preferably 0.2 to 1000% by mass, and more preferably 0.2 to 500% by mass, relative to the total amount of non-fluorinated monomers.

[0093] The amount of polymerization initiator used is preferably 0.1 to 1000 mol%, and more preferably 0.1 to 300 mol%, relative to the total amount of non-fluorinated monomers.

[0094] The polymerization temperature for non-fluorinated monomers is preferably 10 to 95°C, more preferably 50 to 90°C. The polymerization time is preferably 5 to 400 minutes, more preferably 5 to 300 minutes, and even more preferably 5 to 200 minutes. The pressure conditions during polymerization are preferably reduced pressure or atmospheric pressure. Among these, 0 to 2.0 MPa is preferred, more preferably 0 to 1.0 MPa, and even more preferably 0 to 0.5 MPa. Polymerization may also be carried out in a TFE atmosphere. Generally, polymerization of non-fluorinated monomers in an aqueous medium proceeds preferentially over TFE polymerization.

[0095] The above step C yields solution 1 containing specific polymer C. Specific polymer C may be dissolved in solution 1 or dispersed in particulate matter in an aqueous medium. During the polymerization of TFE in step D, described later, although specific polymer C is not an emulsifier, it is presumed that the balance of interfacial tension between the aqueous medium and the PTFE resin causes specific polymer C to be present at the boundary between them, contributing to the stabilization of the dispersion of the PTFE resin in the aqueous medium. The average particle size of the specific polymer C particles is preferably 0.1 to 100 nm, and more preferably 0.1 to 50 nm. The average particle size can be measured using a laser diffraction / scattering particle size distribution analyzer (manufactured by Horiba, Ltd., product name "LA-920"). Note that the average particle size is the median diameter in the volume-based particle size distribution.

[0096] Furthermore, the solution 1 obtained in step C may contain unreacted non-fluorinated monomers. In addition, the atmosphere in the polymerization system in step C may be a TFE-containing atmosphere, taking step D into consideration. In such a case, it is thought that a portion of the specific polymer C in step D may become a polymer containing TFE units. Alternatively, from another perspective, the PTFE particles obtained in step D are not limited to particles consisting of a physical mixture of the specific polymer C and PTFE, but can also be considered to be particles containing a TFE copolymer having units based on non-fluorinated monomers.

[0097] (Step D) Step D is a step in which TFE is polymerized in solution 1 obtained in step D without substantially adding a surfactant to solution 1, in order to obtain an aqueous emulsion containing a PTFE-based resin.

[0098] -TFE- In process D, TFE is used.

[0099] -Other Monomers- In step D, other monomers other than TFE may be used, to the extent that they do not impair the effects of the present invention. Examples of other monomers include monomers having polar groups (hereinafter also referred to as "specific monomer D"). The polar groups in specific monomer D interact with aqueous media and are presumed to be positioned between TFE and the aqueous media during TFE polymerization, exhibiting surfactant-like function. As a result, TFE polymerization proceeds smoothly, and the occurrence of chain transfer is suppressed.

[0100] Examples of polar groups contained in specific monomer D include sulfonic acid groups, sulfonic acid bases, carboxylic acid groups, carboxylic acid bases, phosphonic acid groups, and phosphonic acid bases. Among these, the group represented by formula (A) or the group represented by formula (B) is preferred, with the group represented by formula (A) being more preferred, as it further suppresses the formation of fluorine-based oligomers. Formula (A) -SO ３ M Formula (B) - COOM In formulas (A) and (B), M is a hydrogen atom, NH ４ Alternatively, it represents an alkali metal atom. Examples of alkali metal atoms include lithium, sodium, and potassium atoms.

[0101] The specific monomer D preferably has polymerizable groups. The number of polymerizable groups is preferably 1 to 3, and more preferably 1. The polymerizable group is preferably an ethylenically unsaturated group. More specifically, examples include acryloyl groups, methacryloyl groups, vinyl ether groups, vinyl ester groups, vinyl groups, and allyl groups, with acryloyl groups, methacryloyl groups, vinyl ester groups, or vinyl ether groups being preferred.

[0102] In terms of further suppressing the formation of fluorine-based oligomers, the monomer represented by formula (P) is preferred as the specific monomer D. CR ３１ R ３２ =CR ３３ -L ３ -R ３４ (P) In formula (P), R ３１ and R ３２ Each of these independently represents either a hydrogen atom or a fluorine atom.

[0103] R ３３ This represents a hydrogen atom, a fluorine atom, or an alkyl group which may be substituted with a fluorine atom. Among these, a hydrogen atom or a fluorine atom is preferred because it exhibits better copolymerization with TFE. Note that "alkyl group which may be substituted with a fluorine atom" means an alkyl group in which at least one hydrogen atom in the alkyl group may be substituted with a fluorine atom. The number of carbon atoms in the alkyl group which may be substituted with a fluorine atom is preferably 1 to 3, and more preferably 1.

[0104] L ３ represents a single bond or a divalent linking group. Among these, a single bond is preferred because it exhibits better copolymerization with TFE. Examples of divalent linking groups include divalent hydrocarbon groups (which may be divalent saturated hydrocarbon groups, divalent aromatic hydrocarbon groups, alkenylene groups, or alkylene groups. Divalent saturated hydrocarbon groups may be linear, branched, or cyclic, for example, alkylene groups. The number of carbon atoms is preferably 1 to 20. Divalent aromatic hydrocarbon groups are preferably 6 to 20 carbon atoms, for example, phenylene groups. Other options include alkenylene groups with 2 to 20 carbon atoms, or alkylene groups with 2 to 20 carbon atoms), divalent heterocyclic groups, -O-, -S-, -SO ２ -, -C(O)-, -Si(R ａ ) ２ -, -N(R ｂ ) - and groups formed by combining two or more of these. Here, R ａ R 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). Examples of groups formed by combining two or more of the above include -OC(O)-, -C(O)N(R ｂ )-, alkylene group-O-alkylene group, alkylene group-OC(O)-alkylene group, and alkylene group-Si(R ａ ) ２ - Phenylene group - Si (R ａ ) ２Examples include the above. The above divalent hydrocarbon group may have substituents. Examples of substituents include halogen atoms (e.g., fluorine atoms and chlorine atoms). In other words, the hydrogen atoms in the above divalent hydrocarbon group may be substituted with halogen atoms.

[0105] R ３４ This represents the group represented by formula (A) or the group represented by formula (B) above.

[0106] The monomer represented by formula (P) is preferably selected from the group consisting of the monomer represented by formula (P-1), the monomer represented by formula (P-2), the monomer represented by formula (P-3), the monomer represented by formula (P-4), the monomer represented by formula (P-5), and the monomer represented by formula (P-6), and more preferably the monomer represented by formula (3-1). Formula (P-1) CR ３１ R ３２ =CR ３３ -R ３４ Formula (P-2) CR ３１ R ３２ =CR ３３ - (CF ２ ) ｍ１ -R ３４ Formula (P-3) CR ３１ R ３２ =CR ３３ - (CF ２ C (CF ３ ) F) ｍ２ -R ３４ Formula (P-4) CR ３１ R ３２ =CR ３３ -O-(CFR) ３５ ) ｍ３ -R ３４ Formula (P-5) CR ３１ R ３２ =CR ３３ -O-(CF ２ CFR ３５ O) ｍ４ -CF ２ CF ２ -R ３４ Formula (P-6) CR ３１ R ３２ =CR ３３ -CF ２ -O-(CF(CF３ ) CF ２ O) ｍ５ -CF (CF ３ )-R ３４

[0107] In formulas (P-1) to (P-6), R ３１ ~R ３４ The definition is as described above. In equation (P-2), m1 represents an integer from 1 to 10. In equation (P-3), m2 represents an integer from 1 to 5. In equation (P-4), m3 represents an integer from 1 to 10. R ３５ is a fluorine atom or CF ３ This represents... In equation (P-5), m4 represents an integer from 1 to 10. ３５ The definition is as described above. In equation (P-6), m5 represents an integer between 0 and 10.

[0108] Examples of specific monomer D include ammonium vinylsulfonate. Specific monomer D may be used alone or in combination of two or more types.

[0109] -Polymerization Initiator- A polymerization initiator may be used in step D. In other words, a polymerization initiator may be used during the polymerization of TFE. Examples of polymerization initiators that can be used include those described in step C. A mixture of persulfate and disuccinic acid peroxide is preferred as the polymerization initiator, and a mixture of ammonium persulfate and disuccinic acid peroxide is more preferred. The amount of polymerization initiator used is preferably 0.10% by mass or more, more preferably 0.10 to 1.5% by mass, and even more preferably 0.20 to 1.0% by mass, based on the total mass of TFE supplied to the polymerization system.

[0110] - Stabilizing agent - A stabilizing agent may be used in step D. Examples of stabilizing agents include the stabilizing agent used in step A described above.

[0111] -Other- In addition, in step D, monomers other than TFE and specific monomer D may be used as long as they do not impair the effects of the present invention. In terms of having superior various properties of the PTFE-based resin, the amount of TFE used is preferably 99.5% by mass or more, and more preferably 99.8% by mass or more, relative to the total amount of monomers used in step D. The upper limit is preferably 100% by mass or less.

[0112] -Procedure for Step D- During Step D, no surfactant is substantially added to Solution 1. In other words, in Step D, TFE polymerization is carried out in Solution 1 without substantially adding any new surfactant to Solution 1. A surfactant is a compound having hydrophilic groups (e.g., polar groups) and hydrophobic groups (e.g., hydrocarbon groups). The definition of a polar group is the same as the definition of a polar group contained in specific monomer D. Examples of surfactants include known surfactants, nonionic surfactants and ionic surfactants, and more specifically, hydrocarbon-containing surfactants and fluorinated surfactants. In Step D, it is preferable not to substantially add at least one selected from the group consisting of hydrocarbon-containing surfactants and fluorinated surfactants to Solution 1. The above "substantially not added" means that no surfactant is added, or if added, the amount of surfactant added is 200 ppm by mass or less relative to the total mass of Solution 1. There is no particular lower limit, but 0 ppm by mass or more is preferred. In other words, it is preferable not to add a surfactant to Solution 1 in Step D.

[0113] TFE is added to the polymerization system (i.e., the polymerization reaction vessel) by conventional methods. For example, TFE is added to the polymerization system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. When a polymerization initiator is used, the polymerization initiator may be added to the polymerization system all at once or in stages.

[0114] When using specific monomer D, the amount of specific monomer D used is preferably 0.150% by mass or less relative to the total mass of TFE. In other words, the amount of specific monomer D added relative to the total amount of TFE is preferably 0.150% by mass or less. In terms of the stability of the emulsion during polymerization, the amount of specific monomer D used is preferably 0.100% by mass or less, and more preferably 0.090% by mass or less, relative to the total mass of TFE. Furthermore, in terms of improving molecular weight, the lower limit is preferably 0.005% by mass or more, and more preferably 0.010% by mass or more. The range is preferably 0.001 to 0.100 mol%, and more preferably 0.005 to 0.090 mol%. When using two or more types of specific monomer D, the total amount of specific monomer D used should be within the above range.

[0115] When using specific monomer D, the amount of specific monomer D used is preferably 0.150 mol% or less relative to the total number of moles of TFE. In other words, the amount of specific monomer D added relative to the total amount of TFE is preferably 0.150 mol% or less. In terms of the stability of the emulsion during polymerization, the amount of specific monomer D used is preferably 0.100 mol% or less, and more preferably 0.090 mol% or less, relative to the total number of moles of TFE. Furthermore, in terms of improving molecular weight, the lower limit is preferably 0.001 mol% or more, and more preferably 0.005 mol% or more. When using two or more types of specific monomer D, the total amount of specific monomer D used should be within the above range.

[0116] The polymerization temperature is preferably 10 to 95°C, and more preferably 15 to 90°C. The polymerization pressure is preferably 0.5 to 4.0 MPa, and more preferably 0.6 to 3.5 MPa. The polymerization time is preferably 50 to 520 minutes, more preferably 50 to 450 minutes, and even more preferably 50 to 300 minutes.

[0117] Furthermore, steps C and D may be carried out continuously in the same polymerization reaction vessel. In addition, in the production method of the present invention, it is sufficient that the specific polymer C is formed in step C, and step D may be carried out before the non-fluorine monomer is completely consumed in step C.

[0118] The above procedure yields an aqueous emulsion in which PTFE resin is dispersed in particulate form (an aqueous emulsion containing PTFE resin). The concentration of PTFE resin in the aqueous emulsion is preferably 10 to 45% by mass, more preferably 10 to 30% by mass, and even more preferably 10 to 25% by mass, based on the total volume of the aqueous emulsion. Within this range, the PTFE resin in the aqueous emulsion can be coagulated more easily, and turbidity of the coagulated liquid can be suppressed. The average primary particle size of the PTFE resin is preferably 100 to 500 nm, and more preferably 150 to 300 nm. The average primary particle size of the PTFE resin is the volume-based median diameter D50 measured by a laser scattering particle size distribution analyzer.

[0119] (Process E) Process E is a process to obtain a PTFE-based resin from the aqueous emulsion obtained in process D. Process E can be carried out using the procedure and conditions described in process B above.

[0120] <Second Embodiment> The method for producing PTFE resin may also be the second embodiment described below. The second embodiment of the method for producing PTFE resin is a method for producing PTFE resin comprising step F and step 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 fluorine-containing polymer and an aqueous medium to obtain an aqueous dispersion containing a PTFE resin different from the first fluorine-containing polymer. Step G: A step of obtaining a PTFE resin from the aqueous dispersion obtained in step F. Furthermore, in terms of making it easier to adjust the specific ratio X or specific ratio Y, the second embodiment may further include the above-mentioned other steps after step G. As described above, examples of other steps include grinding and solution immersion. It is preferable to carry out the other steps after step G, and it is more preferable to carry out the grinding and solution immersion after step G.

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

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

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

[0124] The glass transition temperature of the first fluorine-containing polymer is preferably 10°C or lower, more preferably 5°C or lower, even more preferably 3°C or lower, and particularly preferably 0°C or lower, in terms of efficient adsorption of the specific monomer F. The glass transition temperature of the first fluorine-containing polymer is preferably -50°C or higher, more preferably -45°C or higher, and even more preferably -40°C or higher, in terms of thermal stability after molding. The glass transition temperature range of the first fluorine-containing polymer is preferably -50 to 10°C, more preferably -45 to 5°C, and even more preferably -40 to 0°C. The glass transition temperature of the first fluorine-containing polymer is measured by differential scanning calorimetry (DSC). A method for adjusting the glass transition temperature of the first fluorine-containing polymer to be within the above range is, for example, by adjusting the type and amount of monomer used in the production of the first fluorine-containing polymer.

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

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

[0127] When the first fluorine-containing polymer contains TFE units and PAVE units, the amount of PAVE units is preferably 20 to 60 mol%, more preferably 25 to 60 mol%, and even more preferably 30 to 55 mol%, relative to the total number of moles of TFE units and PAVE units, in order to easily adjust the glass transition temperature within the first fluorine-containing polymer and to produce PTFE-based resins more efficiently.

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

[0129] Before initiating the polymerization of the monomer used in the polymerization of the PTFE resin, the content of the first fluorine-containing polymer is preferably 0.01 to 4.0% by mass, more preferably 0.01 to 0.6% by mass, and even more preferably 0.01 to 0.5% by mass, based on the total mass of the aqueous medium in the aqueous dispersion.

[0130] In this specification, "before starting the polymerization of the monomer used for polymerization of PTFE-based resins" means immediately before the start of polymerization. Here, "the start of polymerization" refers to the time when the monomer and polymerization initiator are brought into the reactor after the reactor has been heated to or above the polymerization temperature, and the time when the reactor is heated to or above the polymerization temperature after the monomer and polymerization initiator have been brought into the reactor.

[0131] The first fluorine-containing polymer is preferably dispersed in an aqueous medium in the form of particles. In this case, the average particle size of the first fluorine-containing polymer is preferably 1 to 150 nm, more preferably 10 to 120 nm, and even more preferably 50 to 120 nm, in order to produce PTFE-based resin more efficiently. The average particle size of the first fluorine-containing polymer is determined by measuring the particle size distribution by laser diffraction / scattering, calculating the cumulative curve with the total volume of the particle collection set to 100%, and finding the particle size (D50) at the point on the cumulative curve where the cumulative volume is 50%.

[0132] A preferred method for producing the first fluorine-containing polymer is to polymerize monomers (preferably a monomer mixture containing TFE and PAVE) in an aqueous medium in the presence of a polymerization initiator. This yields the first fluorine-containing polymer dispersed in particulate matter in the aqueous medium. The aqueous medium in which the particles of the first fluorine-containing polymer thus obtained are dispersed may be used as the aqueous dispersion as is, or another aqueous medium may be added to it and used as the aqueous dispersion. Alternatively, the first fluorine-containing polymer may be dispersed in another aqueous medium by solvent substitution and used as the aqueous dispersion.

[0133] For the production of the first fluorine-containing polymer, water-soluble polymerization initiators are preferred, persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate, organic polymerization initiators such as disuccinic acid peroxide and azobisisobutylamidine dihydrochloride are more preferred, persulfates are even more preferred, and ammonium persulfate is particularly preferred.

[0134] Examples of aqueous media used in the production of the first fluorine-containing polymer include the aqueous media used in step A described above. The aqueous media contained in the aqueous dispersion may be the polymerization solvent used in the production of the first fluorine-containing polymer. Before starting the polymerization of the monomer used for the polymerization of the PTFE resin, the content of the aqueous media is preferably 60 to 99.9% by mass, more preferably 96 to 99.9% by mass, and even more preferably 98 to 99.9% by mass, relative to the total mass of the aqueous dispersion.

[0135] The method for producing the first fluorine-containing polymer preferably includes a heating step in which an aqueous medium in which the first fluorine-containing polymer is dispersed is heated. This deactivates the polymerization initiator present in the system, making the polymerization of the PTFE resin less susceptible to the influence of the polymerization initiator used in the production of the first fluorine-containing polymer. As a result, a PTFE resin with a high molecular weight is more easily obtained. The heating temperature in the heating step is preferably 70 to 100°C, more preferably 80 to 98°C, and even more preferably 85 to 95°C, as this further promotes the deactivation of the polymerization initiator in the aqueous medium.

[0136] -Other Components- The aqueous dispersion used in this manufacturing method may contain other components besides the first fluorine-containing polymer and the aqueous medium. Examples of other components that the aqueous dispersion may contain include chain transfer agents, emulsifiers other than fluorine-based emulsifiers, pH adjusters, and waxes.

[0137] Examples of chain transfer agents include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane.

[0138] Examples of emulsifiers other than fluorine-based emulsifiers include sodium lauryl sulfate, Perex SS-H manufactured by Kao Chemical Corporation, and Newcol 1305-SN manufactured by Nippon Emulsifier Co., Ltd.

[0139] Examples of pH adjusting agents include inorganic salts. Examples of inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate, and carbonates such as sodium bicarbonate and sodium carbonate, with disodium hydrogen phosphate dihydrate or disodium hydrogen phosphate dodecahydrate being preferred.

[0140] Examples of waxes include Paraffin Wax-155 and Paraffin Wax-150 (both manufactured by Nippon Seiro).

[0141] Before initiating the polymerization of monomers used in the polymerization of PTFE resins, the concentration of the fluorine-based emulsifier is preferably 100 ppm by mass or less, more preferably 50 ppm by mass or less, even more preferably 25 ppm by mass, and particularly preferably 5 ppm by mass or less, relative to the total mass of the first fluorine-containing polymer in the aqueous dispersion. The lower limit is preferably 0 ppm by mass or more. A fluorine-based emulsifier refers to an emulsifier in which the hydrophobic portion of the hydrophilic and hydrophobic portions of the emulsifier contains fluorine atoms. Examples of fluorine-based emulsifiers include fluorine-containing alkanates and fluorine-containing ether carboxylic acid compounds. An example of a method for adjusting the concentration of the fluorine-based emulsifier within the above range is a method of producing an aqueous dispersion without using a fluorine-based emulsifier.

[0142] Before initiating the polymerization of the monomer used to obtain the PTFE resin, the concentration of fluoride ions is preferably 100 ppm by mass or less, and more preferably 50 ppm by mass or less, relative to the total mass of the aqueous dispersion, in terms of polymerization stability. The lower limit is preferably 0 ppm by mass or more. One example of a method for achieving the above-mentioned concentration of fluoride ions is to remove the fluoride ions using an anion exchange resin during the production of the first fluorine-containing polymer.

[0143] -Specific Monomer F- Specific monomer F contains TFE. The amount of TFE used is preferably 97 to 100% by mass, more preferably 98 to 100% by mass, and even more preferably 99 to 100% by mass, relative to the amount of specific monomer F used.

[0144] The specified monomer F may contain fluorine-containing monomers other than TFE, or it may not contain substantially any fluorine-containing monomers other than TFE. "Substantially not containing fluorine-containing monomers other than TFE" means that the amount of fluorine-containing monomers other than TFE used is 0.0001% by mass or less relative to the amount of specified monomer F used, and may even be 0% by mass. Examples of fluorine-containing monomers other than TFE include chlorotrifluoroethylene (hereinafter also referred to as "CTFE"), vinylidene fluoride (hereinafter also referred to as "VdF"), fluoroalkylethylene, PAVE, and hexafluoropropylene. Two or more fluorine-containing monomers other than TFE may be used in combination.

[0145] The specific monomer F may contain other monomers besides fluorine-containing monomers, but it is preferable that it does not contain other monomers. Substantially free of other monomers means that the amount of other monomers used is 0.0001% by mass or less relative to the amount of the specific monomer F used, and 0% by mass is more preferable. Examples of other monomers include ethylene, propylene, vinyl chloride, and vinylidene chloride.

[0146] The amount of specific monomer F used is preferably 1 to 50 parts by mass, more preferably 1 to 40 parts by mass, and even more preferably 1 to 30 parts by mass, based on 100 parts by mass of the aqueous medium used in the aqueous dispersion.

[0147] -Polymerization Initiator- In the second embodiment, it is preferable that the specific monomer F is polymerized in the presence of a polymerization initiator. An example of a polymerization initiator is the water-soluble radical polymerization initiator used in step A described above.

[0148] The amount of polymerization initiator used is preferably 1 to 1000 ppm by mass, more preferably 5 to 750 ppm by mass, and even more preferably 10 to 500 ppm by mass, per 100 parts by mass of the specific monomer F used.

[0149] -Other Components- Other components other than those listed above may be used during the polymerization of the specific monomer F. Examples of other components include reducing agents. The amount of other components used is preferably 1 to 2000 ppm by mass per 100 parts by mass of the specific monomer F.

[0150] -Procedure for Step F- In this manufacturing method, the specific monomer F is polymerized in the aqueous dispersion to produce a PTFE-based resin.

[0151] The PTFE-based resin obtained by this manufacturing method is as described above. The first fluorine-containing polymer and the PTFE-based resin may be copolymerized.

[0152] The specific monomer F is introduced into the reaction system (i.e., the polymerization reaction vessel) by a conventional method. For example, the specific monomer F may be introduced into the reaction system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, the specific monomer F may be dissolved in an aqueous medium, and the resulting solution may be introduced into the reaction system continuously or intermittently. When a polymerization initiator is used, the polymerization initiator may be added to the reaction system all at once or in portions.

[0153] The polymerization temperature is preferably 10 to 95°C, and more preferably 15 to 90°C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, and more preferably 0.6 to 3.5 MPaG. The polymerization time, in the case of batch processing, is preferably 90 to 1000 minutes, and more preferably 90 to 700 minutes.

[0154] Polymerization of the specific monomer F is preferably carried out in the absence of a substantial emulsifier. Examples of emulsifiers include known emulsifiers and general surfactants. The absence of a substantial emulsifier means an environment in which the emulsifier content is 0.03 ppm by mass or less relative to the total mass of the aqueous medium contained in the aqueous dispersion, preferably 0.02 ppm by mass or less, and more preferably 0 ppm by mass.

[0155] As described above, 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. Therefore, it is thought that this manufacturing method produces particles containing the first fluorine-containing polymer and the PTFE-based resin. In other words, it is presumed that this manufacturing method yields the PTFE-based resin in the form of particles containing the first fluorine-containing polymer and the PTFE-based resin. In this case, this manufacturing method yields an aqueous dispersion in which particles containing the first fluorine-containing polymer and the PTFE-based resin are dispersed in the aqueous medium.

[0156] (Process G) Process G is a process for obtaining a PTFE-based resin from the aqueous dispersion obtained in process F. Process G can be carried out using the procedure and conditions described in process B above.

[0157] [Electrode mixture] The electrode mixture of the present invention may be either the first embodiment or the second embodiment.

[0158] <<First Embodiment>> The electrode mixture of the first embodiment includes the PTFE resin described above and an active material. The PTFE resin in the first embodiment is the PTFE resin of the present invention described above, and is a PTFE resin having a specific ratio X of 0.10 to 0.95. Furthermore, when the electrode mixture is a negative electrode mixture, it is preferable that the negative electrode mixture includes the PTFE resin and a negative electrode active material. When the electrode mixture is a positive electrode mixture, it is preferable that the positive electrode mixture includes the PTFE resin and a positive electrode active material. It is also preferable that the electrode mixture of the first embodiment satisfies the specific ratio Y described later in the second embodiment.

[0159] <PTFE Resin> The electrode mixture of the first embodiment contains a PTFE resin. The PTFE resin is the same as the PTFE resin of the present invention described above, and the preferred embodiment is also the same.

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

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

[0162] In terms of increasing battery capacity, the active material content is preferably 50 to 99.0% by mass, more preferably 80 to 99.0% by mass, and even more preferably 88 to 96.0% by mass, relative to the total mass of the electrode mixture of the first embodiment.

[0163] (Positive Electrode Active Material) When the electrode mixture of the first embodiment is a positive electrode mixture, the positive electrode mixture includes a positive electrode active material. The positive electrode active material is not particularly limited as long as it can reversibly perform intercalation of lithium ions, intercalation of lithium ions, or doping and dedoping of lithium ions with counteranions. Examples include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides, with lithium cobaltate, lithium nickelate, lithium manganeseate, lithium nickelmanganate, composite metal oxides, or polyanion olivine type positive electrode materials being preferred. Examples of composite metal oxides include nickel-manganese-cobalt oxide. Examples of nickel-manganese-cobalt oxides include LiNi ｘ Mn ｙ Co ｚ O ２ A compound represented by the formula (x + y + z ≤ 1) is preferred, and LiNi ０．６ Mn ０．２ Co ０．２ O ２ (Hereafter also referred to as "NMC622") or LiNi ０．３３ Co ０．３３ Mn ０．３３ O ２ (Hereinafter also referred to as "NMC111") is more preferred. The positive electrode active material may be a lithium-containing transition metal oxide, as it has a high average discharge voltage and low cost.

[0164] A surface deposit material with a different composition from the positive electrode active material may be attached to the surface of the positive electrode active material. Examples of surface deposit materials include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0165] The particle shapes of the positive electrode active material can be lumpy, polyhedral, spherical, ellipsoidal, plate-like, needle-like, and columnar. Furthermore, the positive electrode active material may consist of either primary or secondary particles.

[0166] The volume-based median diameter D50 of the positive electrode active material particles (primary or secondary particles) is preferably 0.3 μm or more, more preferably 0.5 μm or more, and even more preferably 1.0 μm or more. The upper limit is preferably 30 μm or less, and more preferably 25 μm or less. The range is preferably 0.3 to 30 μm, more preferably 0.5 to 25 μm, and even more preferably 1.0 to 25 μm. When within the above range, high tap density products are more easily obtained, or the diffusion time of lithium within the particles becomes appropriate, which can further suppress the deterioration of battery performance. In terms of improving the packing performance during positive electrode fabrication, two or more positive electrode active materials with different median diameters D50 may be mixed as the positive electrode active material.

[0167] The median diameter D50 is measured using a known laser diffraction / scattering particle size distribution analyzer. When using the LA-920 manufactured by Horiba, Ltd. as the particle size distribution analyzer, a 0.1% by mass aqueous solution of sodium hexametaphosphate is used as the dispersion medium during measurement, and the measurement is performed after ultrasonic dispersion for 5 minutes with the measurement refractive index set to 1.24.

[0168] The BET specific surface area of ​​the positive electrode active material is 0.1 m². ２ Preferably 0.3 m ２ A value of 1 / g or higher is more preferable. The upper limit is 50mg. ２ Preferably less than / g, and 30m ２ Less than / g is preferable. The range is 0.1 to 50m ２ / g is preferred, and 0.3 to 30m ２ / g is more preferable. The BET specific surface area is defined by pre-drying the sample at 150°C for 30 minutes under nitrogen flow using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.). Thereafter, the value is measured by the nitrogen adsorption BET single-point method using the gas flow method, with a nitrogen-helium mixed gas precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3.

[0169] The positive electrode active material may be used alone or in combination of two or more types. When using two or more positive electrode active materials, a suitable combination is LiCoO ２ And, LiNi ０．３３ Co ０．３３ Mn ０．３３ O ２ Combinations with ternary systems such as LiCoO ２ And, LiMn ２ O ４ Or a combination in which part of this Mn is replaced with other transition metals, etc.; LiFePO ４ And LiCoO ２ Alternatively, this could be a combination in which a portion of the Co is replaced with other transition metals, etc.

[0170] (Negative electrode active material) When the electrode mixture of the first embodiment is a negative electrode mixture, the negative electrode mixture includes a negative electrode active material. The negative electrode active material is not particularly limited as long as it can reversibly carry out, for example, intercalation of lithium ions, desorption and insertion of lithium ions, or doping and dedoping of lithium ions with counteranions. Specifically, examples include carbon-based materials such as graphite, hard carbon and soft carbon; metals that can form alloys with lithium such as aluminum, silicon and tin; amorphous oxides such as silicon oxide and tin oxide; lithium titanate; and lithium metal.

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

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

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

[0174] The volume-based median diameter D50 of the negative electrode active material particles (primary or secondary particles) is preferably 0.1 to 50 μm, more preferably 0.2 to 30 μm, and even more preferably 0.5 to 20 μm. The median diameter D50 can be measured using the same method as described above for the positive electrode active material.

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

[0176] <Conductive Additives> The electrode mixture of the first embodiment may contain conductive additives. Examples of conductive additives include metallic materials such as copper and nickel; graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; and amorphous carbon such as needle coke, carbon nanotubes, fullerenes and vapor-phase carbon fibers.

[0177] 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 of the first embodiment. 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 range is preferably 0.01 to 50% by mass, more preferably 0.1 to 30% by mass, and even more preferably 0.1 to 15% by mass.

[0178] <Thermoplastic Resin> The electrode mixture of the first embodiment may also contain a thermoplastic resin. Examples of thermoplastic resins include polyvinylidene fluoride, polypropylene, polyethylene, polystyrene, polyethylene terephthalate, and polyethylene oxide.

[0179] <Other Components> The electrode mixture of the first embodiment may contain other components in addition to the various components described above. Examples of other components include solid electrolytes, binders other than PTFE resins, conductive materials, thickeners, and additives. The electrode mixture of the first embodiment preferably contains a solid electrolyte, and more preferably contains a sulfide-based solid electrolyte. Examples of solid electrolytes include sulfide-based solid electrolytes having an argyrodite-type crystal structure, oxide-based solid electrolytes, and halogenated solid electrolytes. Examples of solid electrolytes include solid electrolytes that constitute secondary batteries as described later. When the electrode mixture of the first embodiment contains a solid electrolyte (preferably a sulfide-based solid electrolyte), the content of PTFE resin is preferably 1 to 20% by mass, and more preferably 1 to 10% by mass, relative to the total mass of the solid electrolyte (preferably a sulfide-based solid electrolyte).

[0180] Other binders besides PTFE resins that may be included in the electrode mixture include, for example, elastomers such as styrene-butadiene rubber, acrylic rubber, and styrene-ethylene-butadiene-styrene. Fiber components include cellulose, carboxymethylcellulose, cellulose nanofiber, and aramid fiber. In the case of fiber components, it is preferable to mix them as powders, and it is preferable that they are finely ground (microfibrillated) beforehand using various grinding methods, as this improves their mixability with the PTFE powder. Adding fiber components tends to increase the sheet strength after molding.

[0181] The electrode mixture of the first embodiment is preferably substantially free of organic solvents. Specifically, the organic solvent content is preferably 1.0% by mass or less, and more preferably 0.1% by mass or less, relative to the total mass of the electrode mixture of the first embodiment. The lower limit is preferably 0% by mass or more.

[0182] The electrode mixture of the first embodiment is preferably in sheet form.

[0183] The electrode mixture of the first embodiment can be suitably used as an electrode mixture for secondary batteries. In particular, the electrode mixture is suitable for lithium-ion secondary batteries. When used in secondary batteries, the electrode mixture is used, for example, in the form of a sheet (electrode layer).

[0184] <<Second Embodiment>> The electrode mixture of the second embodiment is an electrode mixture comprising a PTFE resin and an active material, wherein in the differential scanning calorimetry curve obtained by differential scanning calorimetry performed under the following measurement condition A, when a straight line including the heat flow value at 320°C and the heat flow value at 350°C is used as the baseline, the endothermic peak height at 343°C (hereinafter referred to as "h ３４３ｙ It is also called "h". The endothermic peak height at 338°C for the above (hereinafter referred to as "h ３３８ｙ It is also called the ratio of h ３３８ｙ / h ３４３ｙ、 The following is also referred to as "specific ratio Y"), which is between 0.10 and 0.95. Measurement conditions A: Under a nitrogen atmosphere, the temperature is raised from 40°C to 300°C at a heating rate of 10°C / min, held at 300°C for 5 minutes, and then raised from 300°C to 400°C at a heating rate of 2°C / min.

[0185] It is estimated that, in the case of electrode mixtures as well, sheets with excellent fracture strength and excellent uniformity of thickness after storage over time can be produced based on a mechanism similar to the estimated mechanism at the specific ratio X described above.

[0186] In the electrode mixture of the second embodiment, the PTFE resin included may not have a specific ratio X outside the predetermined range as long as the specific ratio Y is within the predetermined range; in other words, it may not be the PTFE resin of the present invention described above. The preferred embodiment of the PTFE resin included in the electrode mixture of the second embodiment is the same as the preferred embodiment of the PTFE resin of the present invention described above, except that it may satisfy the specific ratio X. It is preferable that the PTFE resin included in the electrode mixture of the second embodiment is the PTFE resin of the present invention described above. Furthermore, it is preferable that the PTFE resin included in the electrode mixture of the second embodiment is only the PTFE resin of the present invention (a PTFE resin that satisfies the predetermined specific ratio X). As described above, compared to the case in which two or more PTFE resins exhibiting different properties are used, it becomes easier to control the fibrillation of the PTFE resin during sheet production, and the breaking strength of the sheet can be improved.

[0187] The active material is the same as the active material in the first embodiment, and the preferred embodiment is also the same.

[0188] The electrode mixture of the second embodiment may contain components other than the PTFE resin and the active material. Examples of such components include the conductive additive, thermoplastic resin, and other components in the electrode mixture of the first embodiment described above. The electrode mixture of the second embodiment preferably contains a solid electrolyte, and more preferably contains a sulfide-based solid electrolyte. Furthermore, the electrode mixture of the second embodiment may be a preferred embodiment of the electrode mixture of the first embodiment described above.

[0189] <Specific Ratio Y> Specific ratio Y of the electrode mixture in the second embodiment (h ３３８ｙ / h ３４３ｙ The value is 0.10 to 0.95, preferably 0.15 to 0.80, more preferably 0.15 to 0.70, and even more preferably 0.15 to 0.40, in terms of superior effects of the present invention.

[0190] The method for measuring specific ratio Y is the same as the method for measuring specific ratio X described above, except that the object to be measured is replaced with an electrode mixture instead of a PTFE-based resin.

[0191] One method for adjusting the specific ratio Y is the pulverization process described later in the method for manufacturing PTFE-based resins.

[0192] [Method for Manufacturing Electrode Mixture] The method for manufacturing the electrode mixture of the first and second embodiments (hereinafter also simply referred to as "method for manufacturing electrode mixture") is not particularly limited as long as it is a method that can manufacture the electrode mixture of the first and second embodiments described above. In particular, the method for manufacturing the electrode mixture is preferably one that includes a step X1 of grinding and mixing a raw material composition containing a binder containing a PTFE resin, an active material, and a conductive additive if necessary. With the above method for manufacturing the electrode mixture, the electrode mixture can be obtained in a relatively short number of steps. Furthermore, the method for manufacturing the electrode mixture is also preferably to further include a step X2 of rolling the raw material composition ground and mixed in step X1 into a sheet. When step X2 is included, a sheet-like electrode mixture (electrode layer) can be obtained.

[0193] <Step X1> Step X1 is a step of mixing a raw material composition containing a binder containing a PTFE resin, an active material, and, if necessary, a conductive additive. The mixing method is preferably a method using a mixing device. Examples of mixing devices include the jet mill, pin mill, blender, twin-screw extruder, and mixer mentioned above. The mixing conditions are not particularly limited and can be adjusted as appropriate according to the target electrode mixture.

[0194] <Process X2> Process X2 is a process in which the raw material composition crushed and mixed in process X1 is rolled into a sheet. The rolling method in process X2 can be a roll press, a flat plate press, or a calender roll machine. The rolling conditions are not particularly limited and can be appropriately selected according to the desired thickness and density of the electrode mixture.

[0195] [Electrode Layer] The electrode layer of the present invention is a layer containing the electrode mixture of the first embodiment described above or the electrode mixture of the second embodiment described above. 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.

[0196] The density of the positive electrode layer is 3.00 g / cm³. ３ The above is preferable, and 3.10 g / cm³ ３ The above is more preferable, at 3.20 g / cm³. ３ The above is even more preferable. The upper limit is 3.80 g / cm³. ３ The following is preferable: 3.75 g / cm³ ３ The following is more preferable: 3.70 g / cm³ ３ The following is even more preferable: The range is 3.00 to 3.80 g / cm³. ３ Preferably, 3.10 to 3.75 g / cm³ ３ More preferably, 3.20 to 3.70 g / cm³ ３ This is even more preferable. The density of the negative electrode layer is 1.3 g / cm³. ３ The above is preferable, 1.4 g / cm³ ３ The above is more preferable, 1.5 g / cm³ ３ The above is even more preferable. The upper limit is 2.0 g / cm³. ３ The following is preferable: 1.9 g / cm³ ３ The following is more preferable: 1.8 g / cm³ ３ The following is even more preferable: The range is 1.3 to 2.0 g / cm³. ３ Preferably, 1.4 to 1.9 g / cm³ ３ More preferably, 1.5 to 1.8 g / cm³ ３ This is even more preferable. Within the above range, the penetration of the electrolyte near the interface between the current collector and the active material is excellent, and the charge-discharge characteristics at high current densities can be particularly excellent. Furthermore, the conductivity between the active materials can also be excellent.

[0197] The thickness of the electrode layer (positive electrode layer or negative electrode layer) is preferably 10 μm or more, and more preferably 20 μm or more, in terms of high capacity and high output. The upper limit is preferably 500 μm or less, and more preferably 450 μm or less. The range is preferably 10 to 500 μm, and more preferably 20 to 450 μm.

[0198] [Electrode] The electrode of the present invention includes a current collector and an electrode layer containing the electrode mixture of the first embodiment or the electrode mixture of the second embodiment described above, which is disposed on the current collector. A conductive carbonaceous material may be placed between the current collector and the electrode layer as needed. The electrode layer is as described above.

[0199] <Current Collector> The electrode includes a current collector. When the electrode is the positive electrode, the current collector may be a metallic material such as aluminum, titanium, tantalum, stainless steel, and nickel, as well as their alloys; or a carbon material such as carbon cloth and carbon paper. A metallic material is preferred, and aluminum or its alloy is more preferred. When the electrode is the negative electrode, the current collector may be a metallic material such as copper, nickel, titanium, tantalum, and stainless steel, as well as their alloys; or a carbon material such as carbon cloth and carbon paper. A metallic material is preferred, and copper, nickel, or its alloy is more preferred.

[0200] The shape of the current collector can be metal foil, metal cylinder, metal coil, metal plate, expanded metal, punched metal, or foamed metal if it is made of metal, or carbon plate, carbon thin film, or carbon cylinder if it is made of carbon, with metal foil being preferred. The metal foil may be formed into a mesh shape as appropriate. The thickness of the current collector is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. The upper limit is preferably 1 mm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. The range is preferably 1 μm or more and 1 mm or less, more preferably 3 to 100 μm, and even more preferably 5 to 50 μm. Within the above range, excellent handling and strength can be obtained.

[0201] Furthermore, it is preferable that a conductive additive is applied to the surface of the current collector, as this reduces the electrical contact resistance between the current collector and the positive electrode active material layer. Examples of conductive additives include precious metals such as carbon, gold, platinum, and silver.

[0202] [Secondary Battery] The secondary battery of the present invention includes the electrodes described above. The secondary battery may be a secondary battery that uses an electrolyte, or it may be a solid-state secondary battery. Examples of secondary batteries include non-aqueous secondary batteries such as non-aqueous electrolyte secondary batteries, all-solid-state batteries, and fuel cells. Specifically, examples include nickel-cadmium batteries, nickel-metal hydride batteries, lithium secondary batteries, sodium-ion secondary batteries, zinc-ion secondary batteries, fluoride-ion secondary batteries, alkali metal secondary batteries, halide secondary batteries, and lithium-air secondary batteries.

[0203] A secondary battery preferably includes a positive electrode, a negative electrode, an electrolyte, and a separator. The secondary battery may have either a laminated structure in which the positive electrode, separator, and negative electrode are included in that order, or a wound structure in which the positive electrode, separator, and negative electrode are wound in a spiral shape. When the secondary battery has a laminated structure, it is preferable that the laminated structure is formed by bundling the metal core portions of each electrode layer and welding them to the terminals. When the secondary battery has a wound structure, the internal resistance can be reduced by providing multiple lead structures on the positive electrode and negative electrode, respectively, and bundling them to the terminals.

[0204] Rechargeable batteries can take various shapes, such as cylindrical, prismatic, laminated, coin-type, and large. The shapes and configurations of the positive electrode, negative electrode, and separator can be modified according to the specific battery shape.

[0205] Examples of the above-mentioned separators include porous membranes such as polyethylene and polypropylene; nonwoven fabrics made of resins such as polypropylene; and nonwoven fabrics such as glass fiber nonwoven fabrics. The material or shape of the separator is not particularly limited as long as it is stable in the electrolyte and has excellent liquid retention properties. Among these, resin, glass fiber, or inorganic material is preferred for the separator material. The shape of the separator is preferably a porous sheet or nonwoven fabric. The thickness of the separator is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 8 μm or more. The upper limit is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. The range is preferably 1 to 50 μm, more preferably 5 to 40 μm, and even more preferably 8 to 30 μm.

[0206] A non-aqueous electrolyte is preferred as the electrolyte. Examples of non-aqueous electrolytes include those obtained by dissolving a known electrolyte salt in a known organic solvent for dissolving electrolyte salts. Examples of organic solvents for dissolving electrolyte salts include known hydrocarbon solvents such as vinylene carbonate, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; and fluorine-based solvents such as fluoroethylene carbonate, fluoroether, and fluorinated carbonate. An example of an electrolyte salt is LiClO ４ LiAsF ６ LiBF ４ LiPF ６ , LiN (SO ２ CF ３ ) ２ , and LiFSI(LiN(SO ２ F) ２ ), LiBOB(LiB(C ２ O ４ ) ２ ), LiDFOB (LiBF ２ (C ２ O ４ )), LiPF ２ (C ２ O ４ ) ２ LiPF ４ (C ２ O ４ ), and LiN (SO ２ C ２ F ５ ) ２ One example is LiPF, which has good cycle characteristics. ６ LiBF ４ , LiN (SO ２ CF ３ ) ２ , LiN (SO ２ C ２ F ５ ) ２ Alternatively, a combination of these is preferable.

[0207] The solid-state secondary battery is preferably an all-solid-state secondary battery. The solid-state secondary battery is also preferably a lithium-ion battery or a sulfide-based all-solid-state secondary battery. The solid-state secondary battery preferably includes a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode.

[0208] The solid electrolyte used in the mixture for solid-state secondary batteries may be either a sulfide-based solid electrolyte or an oxide-based solid electrolyte.

[0209] Examples of sulfide-based solid electrolytes include Li ２ S-P ２ S ５ Li ２ S-P ２ S ３ Li ２ S-P ２ S ３ -P ２ S ５ Li ２ S-SiS ２ LiI-Li ２ S-SiS ２ LiI-Li ２ S-P ２ S ５ LiI-Li ２ S-P ２ O ５ LiI-Li ３ PO ４ -P ２ S ５ LiI-Li ２ S-SiS ２ -P ２ S ５ Li ２ S-SiS ２ -Li ４ SiO ４ Li ２ S-SiS ２ -Li ３ PO ４ Li ３ PS ４ -Li ４ GeS ４ Li ３．４ P ０．６ Si ０．４ S ４ Li ３．２５ P０．２５ Ge ０．７６ S ４ Li ４－ｘ Ge １－ｘ P ｘ S ４ (X=0.6~0.8), Li ４＋ｙ Ge １－ｙ Ga ｙ S ４ (y=0.2-0.3), LiPSCl, LiCl, Li ７－ｘ－２ｙ PS ６－ｘ－ｙ Cl ｘ Examples include (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5), and mixtures of two or more of these. Furthermore, the sulfide-based solid electrolyte preferably contains lithium. A lithium-containing sulfide-based solid electrolyte is used in solid-state batteries that use lithium ions as carriers and is preferred in that it is an electrochemical device with high energy density.

[0210] As an oxide-based solid electrolyte, a compound containing an oxygen atom, possessing the ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and having electronic insulating properties is preferred.

[0211] Examples of oxide-based solid electrolytes include Li ｘａ La ｙａ TiO ３ [xa=0.3~0.7, ya=0.3~0.7] (LLT), Li ｘｂ La ｙｂ Zr ｚｂ M ｂｂ ｍｂ O ｎｂ (M ｂｂ (The elements are Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, and xb satisfies 5 ≤ ​​xb ≤ 10, yb satisfies 1 ≤ yb ≤ 4, zb satisfies 1 ≤ zb ≤ 4, mb satisfies 0 ≤ mb ≤ 2, and nb satisfies 5 ≤ ​​nb ≤ 20.) Li ｘｃ B ｙｃ M ｃｃ ｚｃ O ｎｃ (M ｃｃ(The element is C, S, Al, Si, Ga, Ge, In, Sn, and xc satisfies 0 ≤ xc ≤ 5, yc satisfies 0 ≤ yc ≤ 1, zc satisfies 0 ≤ zc ≤ 1, and nc satisfies 0 ≤ nc ≤ 6.) Li ｘｄ (Al, Ga) ｙｄ (Ti, Ge) ｚｄ Si ａｄ P ｍｄ O ｎｄ (wherein 1≦xd≦3, 0≦yd≦2, 0≦zd≦2, 0≦ad≦2, 1≦md≦7, 3≦nd≦15), Li （３－２ｘｅ） M ｅｅ ｘｅ D ｅｅ O(xe represents a number between 0 and 0.1, M ｅｅ D represents a divalent metal atom. ｅｅ ) Li ｘｆ Si ｙｆ O ｚｆ (1≦xf≦5, 0<yf≦3, 1≦zf≦10), Li ｘｇ S ｙｇ O ｚｇ (1≦xg≦3, 0<yg≦2, 1≦zg≦10), Li ３ BO ３ -Li ２ SO ４ Li ２ O-B ２ O ３ -P ２ O ５ Li ２ O-SiO ２ Li ６ BaLa ２ Ta ２ O １２ Li ３ PO （４－３／２ｗ） N ｗ (where w < 1), Li has a LISICON (Lithium superionic conductor) type crystal structure. ３．５ Zn ０．２５ GeO ４ La having a perovskite-type crystal structure ０．５１ Li ０．３４ TiO ２．９４ La ０．５５ Li ０．３５ TiO３ LiTi having a NASICON (Natrium superionic conductor) type crystal structure ２ P ３ O １２ Li １＋ｘｈ＋ｙｈ (Al, Ga) ｘｈ (Ti, Ge) ２－ｘｈ Si ｙｈ P ３－ｙｈ O １２ (wherein 0 ≤ xh ≤ 1, 0 ≤ yh ≤ 1), and Li having a garnet-type crystal structure ７ La ３ Zr ２ O １２ (LLZ) is one example. Ceramic materials in which elemental substitution has been performed on LLZ are also known. For example, an LLZ-based ceramic material is one in which at least one element of Mg (magnesium) and A (A is at least one element selected from the group consisting of Ca (calcium), Sr (strontium), and Ba (barium)) has been substituted on LLZ. Phosphorus compounds containing Li, P, and O are also preferred. For example, lithium phosphate (Li ３ PO ４ ), LiPON and LiPOD, which are lithium phosphates in which some of the oxygen is replaced with nitrogen. １ (D １ Examples include at least one selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, and Au. Also, LiA １ ON (A １ (This also includes at least one selected from the group consisting of Si, B, Ge, Al, C, and Ga). For example, Li ２ O-Al ２ O ３ -SiO ２ -P ２ O ５ -TiO ２ -GeO ２ , and Li ２ O-Al ２ O ３ -SiO ２ -P ２ O ５ -TiO２ These are some examples.

[0212] The above oxide-based solid electrolyte preferably contains lithium. Oxide-based solid electrolytes containing lithium are used in solid-state batteries that use lithium ions as carriers and are preferred in that they are electrochemical devices with high energy density.

[0213] The above oxide-based solid electrolyte is preferably an oxide having a crystalline structure. Oxides having a crystalline structure are preferred in terms of good Li ion conductivity. Examples of oxides having a crystalline structure include perovskite type (La ０．５１ Li ０．３４ TiO ２．９４ ), NASICON type (Li １．３ Al ０．３ Ti １．７ (PO ４ ) ３ (e.g.), Garnet type (Li ７ La ３ Zr ２ O １２ Examples include (LLZ, etc.), and the NASICON type is preferred.

[0214] The present invention will be described in detail below with reference to examples. Examples 1 to 5 and 9 are examples, and Examples 6 to 8 and 10 are comparative examples. However, the present invention is not limited to these examples.

[0215] [Measurement and Evaluation Methods] The various measurement and evaluation methods are as follows.

[0216] <Specific Ratio X or Specific Ratio Y> For the PTFE-based resin or electrode binder obtained in each of the examples described below, differential scanning calorimetry (manufactured by TA Instruments, DSC-Q20) was used to measure the differential scanning heat quantity in a nitrogen atmosphere, and a differential scanning heat quantity curve was obtained. As for the temperature rising program (corresponding to Measurement Condition A), in a nitrogen atmosphere, the temperature was raised from 40°C to 300°C at a rate of 10°C / min, held at 300°C for 5 minutes, and then raised from 300°C to 400°C at a rate of 2°C / min. In the obtained differential scanning heat quantity curve, a straight line including the heat flow value at 320°C and the heat flow value at 350°C was used as the baseline of the endothermic peak height. Next, based on the above baseline, the ratio (Specific Ratio X or Specific Ratio Y) of the endothermic peak height at 338°C (h ３４３ｘ or h ３４３ｙ ) to the endothermic peak height at 343°C (h ３３８ｘ or h ３３８ｙ ) was calculated.

[0217] <Method for Measuring Specific Surface Area> For the PTFE-based resin obtained in each of the examples described below, the specific surface area was measured using a BET specific surface area measuring device (manufactured by Mountech, device name: Macsorb HM model-1201). The measurement conditions were as follows: adsorbate: nitrogen, carrier gas: helium, measurement method: flow method (BET one-point method), degassing temperature: 200°C, degassing time: 20 minutes, degassing pressure: N ２ gas flow / atmospheric pressure, and cooling was performed using liquid nitrogen.

[0218] <Average Primary Particle Diameter (PPS) of PTFE-Based Resin and Average Particle Diameter of PTFE-Based Resin> Using the aqueous dispersion obtained in each of the examples described below as a sample, the PPS was measured using a laser scattering particle size distribution analyzer (manufactured by Horiba, Ltd., product name "LA-920"). Similarly, for the PTFE-based resin obtained in each example, the average particle diameter was measured using a laser diffraction / scattering particle size distribution measuring device (manufactured by Horiba, Ltd., product name "LA-920"). However, 5 mL of the PTFE-based resin was put into a dry flow cell, and the measurement was performed in the transmittance mode. The average primary particle diameter and the average particle diameter are the volume-based median diameters.

[0219] <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 was１９ It was determined using F-NMR analysis and infrared absorption spectrum analysis.

[0220] <Solid content concentration of the aqueous dispersion> The solid content concentration of the aqueous dispersion 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 according to the following formula. "Solid content concentration (mass%) = 100 × (residue of the heated aqueous dispersion (g)) / (mass of the aqueous dispersion (2.0 g))"

[0221] <Sheet breaking strength> A strip with a width of 10 mm and a length of 40 mm was cut out from a sheet with an average thickness of 200 μm obtained in each of the examples described below, and the breaking strength was measured using a tensile tester (Tensilon universal material tester RTI series RTI-1225 manufactured by A&D). The distance between chucks was set to 10 mm, and displacement was applied at a constant speed of 10 mm / min in the longitudinal direction (MD direction) of the machine until it broke at room temperature, and the sheet breaking strength was calculated from the maximum load of the measurement result.

[0222] "AA": The breaking strength is 0.30 N / mm ２ or more "A": The breaking strength is 0.15 N / mm ２ or more and less than 0.30 N / mm ２ less than "B": The breaking strength is 0.05 N / mm ２ or more and less than 0.15 N / mm ２ less than "C": The breaking strength is 0.05 N / mm ２ less than or unmeasurable

[0223] <Thickness uniformity after storage over time> The electrode mixture obtained in each of the examples described below was stored for 30 days under storage conditions of normal temperature (25 °C) and normal humidity (65% RH). Using the electrode mixture after the above storage, each sheet for uniformity evaluation was produced in the same procedure as the sheet production procedure of Example 1. The thicknesses at 25 points for each 1 cm × 1 cm grid in each sheet for uniformity evaluation were measured, and the maximum value, minimum value, and arithmetic mean value were calculated from each measured value of the obtained thickness, and the X value was calculated according to the following formula. The thickness uniformity after storage over time was evaluated according to the following evaluation criteria for the X value. X value (%) = 100 × (maximum value - minimum value) / arithmetic mean value

[0224] "AA": X value is 10% or less. "A": X value is greater than 10% and 15% or less. "B": X value is greater than 15% and 20% or less. "C": X value is greater than 20%, cannot be formed into a sheet, or the sheet has at least one hole.

[0225] [Example 1] <Preparation of PTFE resin> In a 6-liter stainless steel autoclave equipped with stainless steel stirring blades and a temperature control jacket, add deionized water (3480g), paraffin wax (100g), CF ３ CF ２ OCF ２ CF ２ OCF ２ COONH ４ (15.75 g), and hydrophilic monomer D (Ammonia 2,3,3,3-tetrafluoro-2-[(1,1,2-trifluoro-2-propenyl)oxy]-Propanoate, structural formula: CH ２ = CFCF ２ OCF (CF ３ ) COONH ４ 35 mg of ammonium persulfate was added, and the autoclave was heated to 70°C while the inside was replaced with nitrogen gas to remove oxygen. TFE was injected under pressure to set the system pressure to 0.78 MPaG, and the system temperature was maintained at 70°C while stirring. Next, an aqueous solution of ammonium persulfate (14.0 mg) dissolved in water (20 g) was injected under pressure with TFE to start the polymerization reaction. As the polymerization reaction progressed, the system pressure decreased, but TFE was added to maintain the system temperature at 70°C and the system pressure at 0.78 MPaG. When 433 g of TFE had been consumed since the start of polymerization, an aqueous solution of hydroquinone (17.0 mg) dissolved in water (20 g) was injected under pressure with TFE as a radical scavenger. Polymerization continued thereafter, and when the amount of TFE polymerized reached 1273 g from the start of polymerization, stirring and TFE supply were stopped, the gas in the system was immediately released to return to atmospheric pressure, the polymerization reaction was terminated, and an aqueous dispersion was obtained. The obtained aqueous dispersion was taken out, cooled, and the paraffin wax was separated to obtain aqueous dispersion A containing PTFE resin. The average primary particle size of the PTFE resin in the obtained aqueous dispersion A containing PTFE resin was 295 nm, and the solid content concentration was 26.5% by mass.

[0226] Next, aqueous dispersion A was diluted with water to a solid content concentration of 13% by mass, and the PTFE resin was solidified while stirring in a container. After that, the water was filtered off to obtain a wet PTFE resin. The water content of the wet PTFE resin was 40% by mass. The obtained wet PTFE resin was placed in a stainless steel mesh tray (distribution amount: 2.0 g / cm²). ２ The mesh tray was heat-treated in a hot air circulating electric furnace at 180°C. After 5 hours, the mesh tray was removed and air-cooled to obtain PTFE resin 1A. The average particle size of PTFE resin 1A was 520 μm, the specific ratio X was 1.00, and the specific surface area was 2 m². ２ The value was / g. The average particle size was measured using the method described above.

[0227] <Jet Milling Treatment> The obtained PTFE resin 1A was subjected to jet milling treatment according to the following procedure. The PTFE resin 1A was immersed in liquid nitrogen and cooled sufficiently. The sufficiently cooled PTFE resin 1A was treated with a jet mill (EX-Mini Jet Mill, manufactured by M-Tech Chemical Co., Ltd.). Nitrogen gas was used as the compressed fluid, and the treatment was performed at a supply pressure of 0.3 MPaG, a grinding pressure of 0.3 MPaG, and a powder supply rate of 3 g / min to obtain PTFE resin 1B. The specific ratio X of PTFE resin 1B was 0.79, and the specific surface area was 5 m². ２ It was / g.

[0228] Furthermore, when the proportion of each unit in PTFE resins 1A and 1B was measured using the method described above, the TFE unit content in each PTFE resin was 99% by mass or more relative to the total units of each PTFE resin.

[0229] <Preparation of Electrode Mixture> NMC622 (manufactured by Hosen Co., Ltd., average particle size 10 μm, positive electrode active material), PTFE resin 1B, and acetylene black (manufactured by Sigma-Aldrich) were mixed in a mass ratio of 96:3:1. Then, the mixture was crushed and mixed using an Ex-Mini Jet Mill (manufactured by M-Tech Chemical Co., Ltd.) with a feed rate of 3 g / min and an air pressure of 0.4 MPa to obtain electrode mixture 1 (positive electrode mixture). The specific ratio Y of the obtained electrode mixture 1 was 0.79.

[0230] The obtained electrode mixture 1 (50 g) was passed through a roll press at 90°C and 3t only once to form a sheet, and a sheet (electrode layer) of Example 1 with an average thickness of 200 μm was obtained.

[0231] [Example 2] For the sheet in Example 2, the conditions were changed as shown in the table below, and the following solution immersion treatment was performed. Otherwise, a sheet was obtained using PTFE resin 2C in the same procedure as in Example 1.

[0232] <Solution Immersion Treatment> The obtained PTFE resin 1B was further subjected to a solution immersion treatment according to the following procedure. PTFE resin 1B was moistened in ethanol adjusted to 14°C for 18 hours, and then air-dried and dried at 150°C to obtain PTFE resin 2C. The specific ratio X of PTFE resin 2C was 0.79, and the specific surface area was 2 m². ２ The result was / g. When the proportion of each unit in PTFE resin 2C was measured using the method described above, the TFE unit content was 99% by mass or more of the total units of the PTFE resin.

[0233] [Examples 3 to 8] For the sheets in Examples 3, 6, and 7, the procedure was the same as in Example 1, except that PTFE resin 1A was used and the conditions shown in the table below were changed. For the sheets in Examples 4, 5, and 8, the procedure was the same as in Example 2, except that PTFE resin 1A was used and the conditions shown in the table below were changed. When the proportion of each unit in each PTFE resin was measured using the method described above, the TFE unit content in all PTFE resins was 99% by mass or more relative to the total units of each PTFE resin. Note that in Example 6, neither jet milling nor solution immersion treatment was performed.

[0234] [Example 9] In an environment with a dew point of -60°C or lower, a sulfide-based solid electrolyte (NEI Fine LPSCl) with an average particle size of 1 μm, lithium niobate-coated NCM111 particles (positive electrode active material) with an average particle size of 7 μm, a conductive additive (acetylene black, manufactured by Sigma-Aldrich), and PTFE-based resin 1B were mixed in a mass ratio of 20:75:2:3. Subsequently, as in Example 1, the mixture was formed into a sheet, and the sheet breaking strength and uniformity of thickness after storage over time were evaluated.

[0235] [Example 10] Except for using PTFE resin 1A, the process was carried out in the same manner as in Example 9, and the sheet breaking strength and uniformity of thickness after storage over time were evaluated.

[0236]

[0237] • EtOH: Ethanol • EtOAc: Ethyl acetate

[0238] From the evaluation results shown in the table above, it was confirmed that using the PTFE-based resin of the present invention results in sheets with excellent breaking strength and excellent uniformity of thickness after storage over time. Furthermore, from a comparison of Examples 1 to 5, the specific surface area of ​​the PTFE-based resin ranged from 3 to 15 m². ２ It was confirmed that the effects of the present invention are superior when the ratio is / g. Furthermore, from a comparison of Examples 1, 4, 5, and 9, it was confirmed that the effects of the present invention are superior when the specific ratio X or specific ratio Y is 0.15 to 0.70 (preferably 0.15 to 0.40).

Claims

A polytetrafluoroethylene resin used as a binder for secondary batteries, In the differential scanning calorimetry curve obtained by performing differential scanning calorimetry under measurement condition A, when a straight line including the heat flow value at 320°C and the heat flow value at 350°C is used as the baseline, A polytetrafluoroethylene resin having a ratio of the endothermic peak height at 338°C to the endothermic peak height at 343°C of 0.10 to 0.

95. Measurement condition A: Under a nitrogen atmosphere, the temperature is raised from 40°C to 300°C at a heating rate of 10°C / min, held at 300°C for 5 minutes, and then raised from 300°C to 400°C at a heating rate of 2°C / min. Specific surface area is 3 to 15 m² ２ The polytetrafluoroethylene resin according to claim 1, wherein the amount is / g. 　 An electrode mixture comprising a polytetrafluoroethylene resin according to claim 1 or 2 and an active material. 　 Furthermore, the electrode mixture according to claim 3, further comprising a solid electrolyte. 　 The electrode mixture according to claim 4, wherein the solid electrolyte includes a sulfide-based solid electrolyte. 　 An electrode layer comprising the electrode mixture according to claim 3. 　 An electrode comprising a current collector and an electrode layer according to claim 6 disposed on the current collector. 　 A secondary battery comprising the electrode described in claim 7. 　 An electrode mixture comprising a polytetrafluoroethylene resin and an active material, In the differential scanning calorimetry curve obtained by performing differential scanning calorimetry under measurement condition A, when a straight line including the heat flow value at 320°C and the heat flow value at 350°C is used as the baseline, An electrode mixture having a ratio of the endothermic peak height at 338°C to the endothermic peak height at 343°C of 0.10 to 0.

95. Measurement condition A: Under a nitrogen atmosphere, the temperature is raised from 40°C to 300°C at a heating rate of 10°C / min, held at 300°C for 5 minutes, and then raised from 300°C to 400°C at a heating rate of 2°C / min. Furthermore, the electrode mixture according to claim 9, further comprising a solid electrolyte. 　 The electrode mixture according to claim 10, wherein the solid electrolyte includes a sulfide-based solid electrolyte.

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