JP2024101797A - Polytetrafluoroethylene composition, binder for battery, electrode mixture, electrode, and secondary battery - Google Patents

Abstract

To provide a polytetrafluoroethylene composition for a binder for a battery which can be evenly mixed with the powdery component of a battery and can suppress generation of gas in a battery cell and degradation of battery characteristics and can obtain a mixture sheet with an excellent strength and an excellent flexibility, and a binder for a battery, an electrode mixture, an electrode, and a secondary battery which use the polytetrafluoroethylene composition.SOLUTION: The polytetrafluoroethylene composition is used for a binder for a battery, and has an endothermic peak in a region (A) at a temperature of at least 324°C and lower than 333°C and in a region (B) at a temperature of at least 333°C and 350°C at highest in a differential scanning calorimetry.SELECTED DRAWING: None

Description

The present disclosure relates to polytetrafluoroethylene compositions, battery binders, electrode mixtures, electrodes, and secondary batteries.

Secondary batteries such as lithium-ion secondary batteries are used in small, portable electrical and electronic devices such as notebook computers, mobile phones, smartphones, tablet computers, and ultrabooks because of their high voltage, high energy density, low self-discharge, low memory effect, and the ability to be made extremely lightweight. They are also being put into practical use as a wide range of power sources, including on-board power sources for driving automobiles and large stationary power sources. There is a demand for even higher energy density in secondary batteries, and further improvements in their battery characteristics are required.

Patent Document 1 describes an energy storage device in which at least one of the cathode and anode contains a polytetrafluoroethylene mixed binder material.

Patent documents 2 to 6 describe the use of polytetrafluoroethylene as a binder for batteries.

Patent document 7 describes the use of a mixture of polytetrafluoroethylene and polyvinylidene fluoride as a binder for batteries.

Special table 2017-517862 publication International Publication No. 2021/181887 International Publication No. 2021/181888 International Publication No. 2021/192541 International Publication No. 2022/138942 International Publication No. 2022/138939 International Publication No. 2022/234227

The present disclosure aims to provide a polytetrafluoroethylene composition for battery binders that can be mixed uniformly with the powder components of a battery, suppress gas generation inside a battery cell and deterioration of battery characteristics, and produce a composite sheet with excellent strength and flexibility, as well as a battery binder, an electrode composite, an electrode, and a secondary battery that use the same.

The present disclosure (1) provides a polytetrafluoroethylene composition for use in a binder for a battery,
The polytetrafluoroethylene composition has endothermic peaks in a region (A) of 324° C. or higher and lower than 333° C., and in a region (B) of 333° C. or higher and 350° C. or lower, in differential scanning calorimetry.

The present disclosure (2) is a binder for a battery consisting essentially of a polytetrafluoroethylene composition,
The polytetrafluoroethylene composition is a binder for batteries that has endothermic peaks in a region (A) of 324° C. or higher and lower than 333° C. and in a region (B) of 333° C. or higher and 350° C. or lower in differential scanning calorimetry.

The present disclosure (3) is a binder for batteries according to the present disclosure (2), in which the polytetrafluoroethylene composition has an intensity ratio of the endothermic peak intensity in the region (A) to the endothermic peak intensity in the region (B) of 0.05 or more and 3.50 or less.

The present disclosure (4) is a binder for batteries according to the present disclosure (2) or (3), in which the polytetrafluoroethylene composition is paste extrudable.

The present disclosure (5) is a battery binder in any combination with any of the present disclosures (2) to (4), in which the polytetrafluoroethylene composition is stretchable.

The present disclosure (6) is a battery binder in any combination with any of the present disclosures (2) to (5) in which the polytetrafluoroethylene composition has a standard specific gravity of 2.250 or less.

The present disclosure (7) provides a polytetrafluoroethylene composition for use in a binder for a battery,
The polytetrafluoroethylene composition essentially consists of polytetrafluoroethylene (A) exhibiting melt flowability and polytetrafluoroethylene (B) not exhibiting melt flowability.

The present disclosure (8) provides a binder for a battery consisting essentially of a polytetrafluoroethylene composition,
The polytetrafluoroethylene composition is a binder for batteries consisting essentially of polytetrafluoroethylene (A) exhibiting melt flowability and polytetrafluoroethylene (B) not exhibiting melt flowability.

The present disclosure (9) is a binder for a battery according to the present disclosure (8), in which the content of the polytetrafluoroethylene (A) in the polytetrafluoroethylene composition is 1% by mass or more and 50% by mass or less with respect to the polytetrafluoroethylene composition.

The present disclosure (10) is a battery binder in any combination with any of the present disclosures (2) to (6), (8), and (9), in which the polytetrafluoroethylene composition is a powder.

The present disclosure (11) is a battery binder in any combination with any of the present disclosures (2) to (6) and (8) to (10), in which the polytetrafluoroethylene composition is substantially free of moisture.

The present disclosure (12) is a battery binder in any combination with any of the present disclosures (2) to (6) and (8) to (11), in which the polytetrafluoroethylene composition is substantially free of a fluorine-containing compound having a molecular weight of 1,000 or less.

The present disclosure (13) is an electrode mixture comprising a battery binder in any combination with the polytetrafluoroethylene composition described in the present disclosure (1) or (7), or any of the present disclosures (2) to (6), (8) to (12), and an electrode active material.

The present disclosure (14) is an electrode mixture according to the present disclosure (13) that is a sheet.

The present disclosure (15) is an electrode comprising a battery binder in any combination with the polytetrafluoroethylene composition described in the present disclosure (1) or (7), or any of the present disclosures (2) to (6), (8) to (12), an electrode active material, and a current collector.

The present disclosure (16) is a secondary battery having the electrode described in the present disclosure (15).

The present disclosure provides a polytetrafluoroethylene composition for battery binders that can be mixed uniformly with the powder components of a battery, suppresses gas generation inside the battery cell and deterioration of battery characteristics, and can provide a composite sheet with excellent strength and flexibility, as well as a battery binder, an electrode composite, an electrode, and a secondary battery that use the same.

FIG. 2 is a schematic diagram of a cross section of a pressure cell used for measuring the ionic conductivity of a solid electrolyte mixture sheet in the examples.

This disclosure is explained in detail below.

The present disclosure provides a polytetrafluoroethylene (PTFE) composition for use in a battery binder, which has endothermic peaks in a region (A) of 324°C or higher and lower than 333°C and a region (B) of 333°C or higher and 350°C or lower in differential scanning calorimetry (hereinafter also referred to as the PTFE composition (1) of the present disclosure).

In this specification, unless otherwise specified, PTFE composition (1) of the present disclosure and PTFE composition (2) of the present disclosure described below are collectively referred to as the "PTFE composition of the present disclosure."

The PTFE composition (1) of the present disclosure has endothermic peaks in the above regions (A) and (B), so that even if it is kneaded for a long time with the powder components of the battery such as the electrode active material and the solid electrolyte, it is difficult to generate agglomerates, and it can be mixed uniformly with the powder components. In addition, it is also possible to obtain a mixture sheet having excellent strength and flexibility.
The PTFE composition (1) of the present disclosure does not require a large amount of dispersion medium such as water or organic solvent, and can be combined with a wide range of electrode active materials and solid electrolytes, which is advantageous in terms of production process. Also, the process and cost due to the use of dispersion medium can be reduced.
Furthermore, since the PTFE composition (1) of the present disclosure has excellent binding strength with active materials and electrolytes, the amount of use can be reduced.

The PTFE composition (1) of the present disclosure has endothermic peaks in the above region (A) and the above region (B) in differential scanning calorimetry (DSC). The PTFE composition (1) of the present disclosure may have at least one endothermic peak in each of the above regions (A) and (B).
The endothermic peak in region (A) indicates the presence of low molecular weight PTFE, and the endothermic peak in region (B) indicates the presence of high molecular weight PTFE.
Since low molecular weight PTFE has low fibrillation properties, the presence of low molecular weight PTFE reduces the fibrillation of the PTFE composition, and makes it difficult for agglomerates to form even when kneaded with the powder components of the battery for a long time. Therefore, it can be uniformly mixed with the powder components, and the strength and flexibility of the composite sheet can be improved.

The temperature range of region (A) is 324°C or higher and lower than 333°C, but is preferably 326°C or higher and lower than 330°C.
The temperature range of region (B) is 333° C. or higher and 350° C. or lower, but is preferably 336° C. or higher and is preferably 348° C. or lower, and more preferably 346° C. or lower.

The endothermic peak temperatures are the temperatures corresponding to the respective minimum points in region (A) and region (B) of the heat of fusion curve when a PTFE composition that has not been heated to a temperature of 300°C or higher is heated at a rate of 10°C/min using a differential scanning calorimeter [DSC].

The PTFE composition (1) of the present disclosure preferably has an intensity ratio of the endothermic peak intensity in the region (A) to the endothermic peak intensity in the region (B) of 0.05 or more and 3.50 or less, in terms of being able to mix more uniformly with the powder components of the battery and being able to obtain a composite sheet having better strength and flexibility.
The intensity ratio is more preferably 0.08 or more, even more preferably 0.10 or more, even more preferably 0.15 or more, and particularly preferably 0.20 or more, and is more preferably 3.0 or less, even more preferably 2.5 or less, even more preferably 2.0 or less, even more preferably 1.5 or less, and particularly preferably 1.0 or less.

The intensity of the endothermic peak is calculated as the distance between the minimum point (a) and the intersection point (b) of a line passing through the minimum point (a) and perpendicular to the horizontal axis (temperature) with a line connecting the points 300°C and 360°C on the heat of fusion curve. The minimum point (a) of the heat of fusion curve in the measurement of the endothermic peak temperature is taken as (a), and the intersection point (b) of the line passing through the minimum point (a) and perpendicular to the horizontal axis (temperature) is taken as (b).

The above strength ratio can be adjusted by adjusting the mixing ratio of the low molecular weight PTFE and high molecular weight PTFE described above.

The PTFE composition (1) of the present disclosure includes PTFE. The PTFE may be a homopolymer of tetrafluoroethylene (TFE), or may be a modified PTFE that includes a polymerization unit based on TFE (TFE unit) and a polymerization unit based on a modified monomer (hereinafter also referred to as "modified monomer unit"). The modified PTFE may include 99.0 mass% or more of TFE unit and 1.0 mass% or less of modified monomer unit. The modified PTFE may be composed of only TFE unit and modified monomer unit.
The PTFE is preferably the modified PTFE, since it can be mixed more uniformly with the powder components of the battery and it can provide a mixture sheet having greater strength and flexibility.

The modified PTFE can be mixed more uniformly with the powder components of the battery, and a composite sheet having better strength and flexibility can be obtained. Therefore, the content of the modified monomer unit is preferably in the range of 0.0001 to 1.0% by mass relative to the total polymerized units. The lower limit of the content of the modified monomer unit is more preferably 0.001% by mass, more preferably 0.002% by mass, even more preferably 0.005% by mass, even more preferably 0.010% by mass, even more preferably 0.015% by mass, and particularly preferably 0.020% by mass. The upper limit of the content of the modified monomer unit is preferably 0.80% by mass, more preferably 0.60% by mass, even more preferably 0.50% by mass, even more preferably 0.40% by mass, and particularly preferably 0.30% by mass.
In this specification, the modified monomer unit means a portion of the molecular structure of PTFE that is derived from a modified monomer.

The content of each of the above-mentioned polymerized units can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

The modified monomer is not particularly limited as long as it can be copolymerized with TFE, and examples thereof include perfluoroolefins such as hexafluoropropylene [HFP]; hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride [VDF]; perhaloolefins such as chlorotrifluoroethylene [CTFE]; perfluorovinyl ethers; perfluoroallyl ethers; (perfluoroalkyl)ethylenes, ethylenes, etc. The modified monomers used may be one type or multiple types.

The perfluorovinyl ether is not particularly limited, and examples thereof include perfluorovinyl ethers represented by the following general formula (A):
CF ₂ =CF-ORf ¹ (A)
(wherein ^Rf1 represents a perfluoro organic group). In this specification, the "perfluoro organic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are replaced with fluorine atoms. The perfluoro organic group may have an ether oxygen.

An example of the perfluorovinyl ether is perfluoro(alkyl vinyl ether) [PAVE], where Rf ¹ in the general formula (A) is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5.

Examples of the perfluoroalkyl group in the PAVE include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group.

The perfluorovinyl ether further includes those represented by the above general formula (A), in which Rf ¹ is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, and ^those represented by the following formula:

(wherein m represents 0 or an integer of 1 to 4), Rf ¹ is a group represented by the following formula:

(wherein n is an integer from 1 to 4)

The (perfluoroalkyl)ethylene [PFAE] is not particularly limited, and examples include (perfluorobutyl)ethylene [PFBE] and (perfluorohexyl)ethylene.

The perfluoroallyl ether may, for example, be a compound represented by the general formula (B):
CF ₂ =CF-CF ₂ -ORf ² (B)
(wherein ^Rf2 represents a perfluoro organic group).

The above ^Rf2 is preferably a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms. The above-mentioned perfluoroallyl ether is preferably at least one selected from the group consisting of CF ₂ ═CF-CF ₂ -O-CF ₃ , CF ₂ ═CF-CF ₂ -O-C ₂ F ₅ , CF ₂ ═CF-CF ₂ -O-C ₃ F ₇ , and CF ₂ ═CF-CF ₂ -O-C ₄ F ₉ , more preferably at least one selected from the group consisting of CF ₂ ═CF-CF ₂ -O-C ₂ F ₅ , CF ₂ ═CF-CF ₂ -O-C ₃ F ₇ , and CF ₂ ═CF-CF ₂ -O-C ₄ F ₉ , and even more preferably CF ₂ ═CF-CF ₂ -O-CF ₂ CF ₂ CF ₃ .

The modified monomer is represented by the following general formula (I):
CX ¹ X ² = CX ³ X ⁴ (I)
(wherein X ¹ to X ³ are each independently H or F; X ⁴ is F, Cl, Rf or O—Rf; Rf is a perfluoro organic group).

In general formula (I), Rf is preferably a perfluoroalkyl group having 1 to 10 carbon atoms, more preferably a perfluoroalkyl group having 1 to 5 carbon atoms, and even more preferably a perfluoroalkyl group having 1 to 4 carbon atoms.

The modified monomer is preferably at least one selected from the group consisting of CTFE, HFP, perfluoro(methyl vinyl ether) [PMVE], perfluoro(propyl vinyl ether) [PPVE], PFBE, and VDF, more preferably at least one selected from the group consisting of CTFE, HFP, PMVE, and VDF, even more preferably at least one selected from the group consisting of CTFE, HFP, and PMVE, particularly preferably at least one selected from the group consisting of PMVE and HFP, and most preferably HFP, in terms of being able to mix more uniformly with the powder components of the battery and being able to obtain a composite sheet with even greater strength and flexibility.

The PTFE in the PTFE composition (1) of the present disclosure may have a core-shell structure. Examples of PTFE having a core-shell structure include modified PTFE, which contains a core of high molecular weight PTFE and a shell of lower molecular weight PTFE or modified PTFE in the particles. Examples of such modified PTFE include the PTFE described in JP-A-2005-527652.

The PTFE composition (1) of the present disclosure is preferably substantially composed of the PTFE. This allows the effects of the PTFE to be significantly exhibited. The term "substantially composed of PTFE" means that the content of the PTFE is 95.0% by mass or more relative to the PTFE composition.
The content of the PTFE is preferably 98.0% by mass or more, more preferably 99.0% by mass or more, even more preferably 99.5% by mass or more, particularly preferably 99.9% by mass or more, and most preferably 99.95% by mass or more, relative to the PTFE composition.

The PTFE composition (1) of the present disclosure is preferably paste extrudable, since it can be mixed more uniformly with the powder components of the battery and can provide a mixture sheet having better strength and flexibility.
Whether or not a PTFE composition can be paste-extruded is determined by the following method.
60 g of the PTFE composition and 12.3 g of a hydrocarbon oil (trade name: Isopar G (registered trademark), manufactured by ExxonMobil Corporation) as an extrusion aid are mixed in a polyethylene container for 3 minutes. The above mixture is filled into the cylinder of an extruder at room temperature (25±2°C), and a load of 0.47 MPa is applied to the piston inserted into the cylinder and held for 1 minute. Next, the mixture is extruded from the orifice at a ram speed of 20 mm/min. The ratio of the cross-sectional area of the cylinder to the cross-sectional area of the orifice is 200. If the bead breaks and cannot be extruded continuously, it is judged as not extrudable, and if the bead does not break and can be extruded continuously, it is judged as extrudable.

The PTFE composition (1) of the present disclosure is preferably extensible, since it can be mixed more uniformly with the powder components of the battery and can provide a mixture sheet having even greater strength and flexibility.
Whether or not the PTFE composition is expandable is determined by the following method.
50 g of the PTFE composition and 10.25 g of a hydrocarbon oil (trade name: Isopar E (registered trademark), manufactured by ExxonMobil Corporation) as an extrusion aid are mixed in a polyethylene container for 3 minutes. The mixture is filled into the cylinder of an extruder at room temperature (25±2° C.), and a load of 0.47 MPa is applied to the piston inserted in the cylinder and held for 1 minute. The mixture is then extruded through an orifice at a ram speed of 18 mm/min. The ratio of the cross-sectional area of the cylinder to the cross-sectional area of the orifice is 100.
The bead obtained by the above paste extrusion is dried at 230°C for 30 minutes to remove the lubricant. The dried bead is cut to an appropriate length and placed in an oven heated to 300°C. In the oven, it is stretched at a stretching speed of 100%/sec until it is 25 times the bead length before the stretching test. If it does not break during stretching, it is judged to be stretchable, and if it breaks, it is judged to be unstretchable.

The PTFE composition (1) of the present disclosure can be mixed more uniformly with the powder components of a battery, and a composite sheet having even greater strength and flexibility can be obtained. In this respect, the standard specific gravity (SSG) is preferably 2.250 or less, more preferably 2.240 or less, and even more preferably 2.230 or less.
The SSG is also preferably 2.170 or more, more preferably greater than 2.170, and even more preferably 2.175 or more.
The SSG is measured by a water displacement method according to ASTM D 792 using a sample molded according to ASTM D 4895.

The PTFE composition (1) of the present disclosure preferably contains PTFE that exhibits melt flowability and PTFE that does not exhibit melt flowability.

The present disclosure also provides a PTFE composition for use in a battery binder, which is essentially composed of PTFE (A) that exhibits melt flowability and PTFE (B) that does not exhibit melt flowability (hereinafter also referred to as PTFE composition (2) of the present disclosure).

The PTFE composition (2) of the present disclosure contains the above PTFE (A) and (B), so that even if it is kneaded for a long time with the powder components of the battery such as the electrode active material and the solid electrolyte, it is difficult to generate agglomerates, and it can be mixed uniformly with the powder components. In addition, it is possible to obtain a mixture sheet having excellent strength and flexibility.
The PTFE composition (2) of the present disclosure does not require a large amount of dispersion medium such as water or organic solvent, and can be combined with a wide range of electrode active materials and solid electrolytes, which is advantageous in terms of production process. Also, the process and cost due to the use of dispersion medium can be reduced.
Furthermore, since the PTFE composition (2) of the present disclosure has excellent binding strength with active materials and electrolytes, the amount of the composition used can be reduced.

The PTFE (A) exhibits melt flowability.
Since PTFE exhibiting melt flowability has low fibrillation properties, the presence of the above PTFE (A) reduces the fibrillation of PTFE, and makes it difficult for agglomerates to form even when kneaded with the powder components of the battery for a long time. Therefore, it can be uniformly mixed with the powder components, and the strength and flexibility of the mixture sheet can be improved.
In this specification, "exhibiting melt fluidity" means that the melt flow rate (MFR) is 0.25 g/10 min or more, preferably 0.50 g/10 min or more, more preferably 1.00 g/10 min or more. The MFR may be 100 g/10 min or less, and is preferably 80 g/10 min or less.
The MFR is a value obtained in accordance with ASTM D1238 using a melt indexer, and is expressed as the mass (g/10 min) of a polymer flowing out per 10 min from a nozzle having an inner diameter of 2.095 mm and a length of 8 mm at 372° C. and a load of 5 kg.

The above PTFE (A) may be a low molecular weight PTFE.

The PTFE (A) preferably has a melt viscosity (complex viscosity) at 380° C. of 1.0×10 ¹ to 1.0×10 ⁷ Pa·s.
The melt viscosity is more preferably 1.0×10 ² Pa·s or more, even more preferably 1.5×10 ³ Pa·s or more, and particularly preferably 7.0×10 ³ Pa·s or more, and more preferably 7.0×10 ⁵ Pa·s or less, even more preferably 3.0×10 ⁵ Pa·s or less, and particularly preferably 1.0×10 ⁵ Pa·s or less.
In this specification, "low molecular weight PTFE" means PTFE having the melt viscosity within the above range.

The melt viscosity was measured in accordance with ASTM D 1238 using a flow tester (manufactured by Shimadzu Corporation) and a 2φ-8L die, with a 2g sample that had been preheated to 380°C for 5 minutes and held at the above temperature under a load of 0.7 MPa.

The PTFE (A) preferably has an endothermic peak temperature of 324°C or higher and lower than 333°C, more preferably 326°C or higher, and more preferably lower than 330°C.
The endothermic peak temperature is the temperature corresponding to the minimum point on the heat of fusion curve when PTFE that has not been heated to a temperature of 300° C. or higher is heated at a rate of 10° C./min using a differential scanning calorimeter [DSC].

The PTFE (A) may be a homopolymer of TFE, or may be a modified PTFE containing polymerization units based on TFE (TFE units) and polymerization units based on a modified monomer (modified monomer units). The type of modified monomer and the content of the modified monomer units may be the same as those of the PTFE in the PTFE composition (1) of the present disclosure.

In the PTFE composition (2) of the present disclosure, the content of the PTFE (A) may be 1% by mass or more and 90% by mass or less, preferably 1% by mass or more and 50% by mass or less, and also preferably 5% by mass or more, more preferably 45% by mass or less, even more preferably 40% by mass or less, even more preferably 35% by mass or less, and even more preferably 30% by mass or less, relative to the PTFE composition (2).

The PTFE (B) does not exhibit melt flowability.
In this specification, not exhibiting melt flowability means that the melt flow rate (MFR) is less than 0.25 g/10 min, preferably less than 0.10 g/10 min, more preferably 0.05 g/10 min or less.
The MFR is a value obtained in accordance with ASTM D1238 using a melt indexer, and is expressed as the mass (g/10 min) of a polymer flowing out per 10 min from a nozzle having an inner diameter of 2.095 mm and a length of 8 mm at 372° C. and a load of 5 kg.

The above PTFE (B) may be high molecular weight PTFE.

The standard specific gravity (SSG) of the PTFE (B) is preferably 2.200 or less, more preferably 2.180 or less, more preferably 2.170 or less, even more preferably 2.160 or less, and even more preferably 2.155 or less.
The SSG is also preferably 2.130 or more, and more preferably 2.140 or more.
The SSG is measured by a water displacement method according to ASTM D 792 using a sample molded according to ASTM D 4895.

The endothermic peak temperature of the above PTFE (B) is preferably 333°C or higher and 350°C or lower, more preferably 336°C or higher, more preferably 348°C or lower, and even more preferably 346°C or lower.

The above PTFE (B) may be a homopolymer of TFE, or may be a modified PTFE containing polymerization units based on TFE (TFE units) and polymerization units based on a modified monomer (modified monomer units). The type of modified monomer and the content of the modified monomer units may be the same as those of the PTFE in the PTFE composition (1) of the present disclosure.

The PTFE (B) may have a core-shell structure. Examples of PTFE with a core-shell structure include modified PTFE, which contains a core of high molecular weight PTFE and a shell of lower molecular weight PTFE or modified PTFE in the particles. Examples of such modified PTFE include the PTFE described in JP-A-2005-527652.

The PTFE composition (2) of the present disclosure is substantially composed of only the PTFE (A) and (B). This allows the effects of the PTFE (A) and (B) to be significantly exhibited. "Substantially composed of only the PTFE (A) and (B)" means that the total amount of the PTFE (A) and (B) is 95.0 mass% or more relative to the PTFE composition (2).
The total amount of the PTFE (A) and (B) is preferably 98.0% by mass or more, more preferably 99.0% by mass or more, even more preferably 99.5% by mass or more, particularly preferably 99.9% by mass or more, and most preferably 99.95% by mass or more, relative to the PTFE composition (2).
It is also preferable that the PTFE composition (2) of the present disclosure consists only of the above PTFE (A) and (B).

The PTFE composition (2) of the present disclosure is preferably paste extrudable and stretchable, since it can be mixed more uniformly with the powder components of the battery and can produce a composite sheet with superior strength and flexibility.

The PTFE composition (2) of the present disclosure can be mixed more uniformly with the powder components of the battery, and a composite sheet having even greater strength and flexibility can be obtained. Therefore, the standard specific gravity (SSG) is preferably 2.250 or less, more preferably 2.240 or less, and even more preferably 2.230 or less, and is preferably 2.170 or more, more preferably greater than 2.170, and even more preferably 2.175 or more.

The PTFE composition of the present disclosure is preferably substantially free of moisture. This can further suppress gas generation and deterioration of battery characteristics, and can also improve the strength of the composite sheet. In addition, it is advantageous in terms of production process because it is possible to widely select the electrode active material and solid electrolyte to be combined. Substantially free of moisture means that the moisture content of the PTFE composition is 0.010 mass% or less.
The water content is preferably 0.005% by mass or less, more preferably 0.003% by mass or less, even more preferably 0.002% by mass or less, and even more preferably 0.001% by mass or less.
The water content is measured by the following method.
The mass of the PTFE composition is measured before and after heating at 150° C. for 2 hours, and calculated according to the following formula. A sample is taken three times, and the values are calculated respectively, and the average value is determined.
Moisture content (mass%)=[(mass (g) of PTFE composition before heating)−(mass (g) of PTFE composition after heating)]/(mass (g) of PTFE composition before heating)×100

The PTFE composition of the present disclosure preferably does not substantially contain fluorine-containing compounds having a molecular weight of not more than 1000. "Substantially free of fluorine-containing compounds" means that the amount of the fluorine-containing compounds is not more than 25 ppb by mass relative to the PTFE composition.
The amount of the fluorine-containing compound is preferably 20 mass ppb or less, more preferably 15 mass ppb or less, even more preferably 10 mass ppb or less, even more preferably less than 10 mass ppb, even more preferably 1 mass ppb or less, even more preferably less than 1 mass ppb, and particularly preferably less than the lower limit of quantification. The lower limit is not particularly limited, and may be an amount less than the lower limit of quantification.

The amount of the fluorine-containing compound having a molecular weight of 1,000 or less is measured by the following method.
Weigh out 1 g of the sample, add 10 g (12.6 ml) of methanol, and perform ultrasonic treatment for 60 minutes to obtain an extract. The obtained extract is appropriately concentrated with nitrogen purge, and the fluorine-containing compounds in the concentrated extract are measured by LC/MS/MS. Molecular weight information is extracted from the obtained LC/MS spectrum, and the agreement with the structural formula of the candidate fluorine-containing compound is confirmed. Prepare aqueous solutions with 5 or more levels of content of the standard substance, perform LC/MS analysis of the aqueous solutions with each content, plot the relationship between the content and the area area for that content, and draw a calibration curve. Using the above calibration curve, the area area of the LC/MS chromatogram of the fluorine-containing compound in the extract is converted to the content of the fluorine-containing compound.
The lower limit of quantification in this measurement method is 10 ppb by mass.

Examples of the fluorine-containing compound having a molecular weight of 1000 or less include a fluorine-containing compound having a hydrophilic group with a molecular weight of 1000 g/mol or less. The molecular weight of the fluorine-containing compound is preferably 800 or less, and more preferably 500 or less.
Polymer particles obtained by polymerization in the presence of a fluorine-containing surfactant usually contain a fluorine-containing surfactant in addition to PTFE. In this specification, the fluorine-containing surfactant is one that is used during polymerization.
The fluorine-containing compound having a molecular weight of 1,000 or less may be a compound that has not been added during polymerization, for example, a compound that is generated as a by-product during polymerization.
In addition, when the fluorine-containing compound having a molecular weight of 1000 or less contains an anionic moiety and a cationic moiety, it means a compound containing fluorine in which the molecular weight of the anionic moiety is 1000 or less. The fluorine-containing compound having a molecular weight of 1000 or less does not include PTFE.

The hydrophilic group may be, for example, -COOM, -SO ₂ M, or -SO ₃ M, and examples of such anionic groups include -COOM and -SO ₃ M (in each formula, M is H, a metal atom, NR ¹ ₄ , an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent, and R ¹ is H or an organic group).

As the fluorine-containing surfactant, a surfactant containing fluorine (anionic fluorine-containing surfactant) in which the molecular weight of the anionic portion is 1000 or less can also be used. The "anionic portion" refers to the portion of the fluorine-containing surfactant excluding the cation. For example, in the case of F(CF ₂ ) _n1 COOM, it is the portion "F(CF ₂ ) _n1 COO".
The anionic fluorine-containing surfactant may be a compound represented by the following general formula (N ⁰ ):
X ⁿ⁰ - Rf ⁿ⁰ - Y ⁰ (N ⁰ )
(In the formula, X ⁿ⁰ is H, Cl or F. ^{Rf n0} is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms in which some or all of the H's are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H's may be substituted with Cl. Y ⁰ is an anionic group.
The anionic group of Y ⁰ may be -COOM, -SO ₂ M or -SO ₃ M, and may be -COOM or -SO ₃ M.
M is H, a metal atom, NR ¹ ₄ , an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent, and R ¹ is H or an organic group.
The metal atom includes alkali metals (Group 1) and alkaline earth metals (Group 2), such as Na, K, or Li.
R ¹ may be H or a C _1-10 organic group, may be H or a C _1-4 organic group, or may be H or a C _1-4 alkyl group.
M may be H, a metal atom or NR ¹ ₄ , which may be H, an alkali metal (group 1), an alkaline earth metal (group 2) or NR ¹ ₄ , which may be H, Na, K, Li or NH ₄ .
The above Rf ⁿ⁰ may be one in which 50% or more of H is substituted with fluorine.

The above-mentioned fluorine-containing surfactant may be one type of fluorine-containing surfactant or a mixture containing two or more types of fluorine-containing surfactants.

（各式中、Ｍは、Ｈ、金属原子、ＮＲ^１ _４、置換基を有していてもよいイミダゾリウム、置換基を有していてもよいピリジニウム又は置換基を有していてもよいホスホニウムである。Ｒ^１は、Ｈ又は有機基である。）。
本開示のＰＴＦＥ組成物は、上記式で表される含フッ素化合物のいずれをも実質的に含まないことが好ましい。 Examples of the fluorine-containing surfactant include compounds represented by the following formula: The fluorine-containing surfactant may be a mixture of these compounds.
F( _CF2 ) ₇ COOM,
F(CF ₂ ) ₅ COOM,
H(CF ₂ ) ₆ COOM,
H(CF ₂ ) ₇ COOM,
_CF3O ( _{CF2 ) 3OCHFCF2COOM} ,
_C3F7OCF ( _{CF3 ) CF2OCF} ( _CF3 )COOM,
CF ₃ CF ₂ CF ₂ OCF (CF ₃ ) COOM,
CF ₃ CF ₂ OCF ₂ CF ₂ OCF ₂ COOM,
_C2F5OCF ( _{CF3 ) CF2OCF} ( _CF3 )COOM,
_CF3OCF ( _CF3 ) _CF2OCF ( _CF3 )COOM,
_{CF2ClCF2CF2OCF ( CF3 ) CF2OCF2COOM ,
CF2ClCF2CF2OCF2CF ( CF3 ) OCF2COOM ,
CF2ClCF} ( _CF3 )OCF( _CF3 ) _{CF2OCF2COOM ,
CF2ClCF} ( _CF3 ) _OCF2CF ( _CF3 ) _OCF2COOM , and

(In each formula, M is H, a metal atom, NR ¹ ₄ , an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. R ¹ is H or an organic group.)
The PTFE compositions of the present disclosure are preferably substantially free of any of the fluorine-containing compounds represented by the above formulas.

In each of the above formulas, M may be H, a metal atom or NR ¹ ₄ , which may be H, an alkali metal (group 1), an alkaline earth metal (group 2) or NR ¹ ₄ , which may be H, Na, K, Li or NH ₄ .
R ¹ may be H or a C _1-10 organic group, may be H or a C _1-4 organic group, may be H or a C _1-4 alkyl group.

When the PTFE composition of the present disclosure is substantially free of any of the fluorine-containing compounds represented by the above formulas, it can be mixed more uniformly with the powder components of the battery, and a composite sheet having even greater strength and flexibility can be obtained.
"Substantially free of any of the fluorine-containing compounds represented by the above formulas" means that the amount of the fluorine-containing compounds is 25 ppb by mass or less based on the PTFE composition.
The amount of the fluorine-containing compound is preferably 20 mass ppb or less, more preferably 15 mass ppb or less, even more preferably 10 mass ppb or less, even more preferably less than 10 mass ppb, even more preferably 1 mass ppb or less, even more preferably less than 1 mass ppb, and particularly preferably less than the lower limit of quantification. The lower limit is not particularly limited, and may be an amount less than the lower limit of quantification.

The PTFE composition of the present disclosure has the following general formula:
[C _n-1 F _2n-1 COO ^- ]M ⁺
(wherein n is an integer of 9 to 14, preferably an integer of 9 to 12, and M ⁺ represents a cation.) This allows the powder components of the battery to be mixed more uniformly, and a mixture sheet having even greater strength and flexibility can be obtained.
In the above formula, M constituting the cation M ⁺ is the same as M described above.
"Substantially free of the fluorine-containing compound represented by the above formula" means that the amount of the fluorine-containing compound is 25 ppb by mass or less based on the PTFE composition.
The amount of the fluorine-containing compound is preferably 20 mass ppb or less, more preferably 15 mass ppb or less, even more preferably 10 mass ppb or less, even more preferably less than 10 mass ppb, even more preferably 1 mass ppb or less, even more preferably less than 1 mass ppb, and particularly preferably less than the lower limit of quantification. The lower limit is not particularly limited, and may be an amount less than the lower limit of quantification.

The PTFE composition of the present disclosure preferably has non-melt secondary processability. The above-mentioned non-melt secondary processability means that the melt flow rate cannot be measured at a temperature higher than the melting point in accordance with ASTM D-1238 and D-2116, in other words, that the composition does not flow easily even in the melting temperature range.

The form of the PTFE composition of the present disclosure is not limited, but it is preferably a powder, since it can be mixed with the electrode active material and the solid electrolyte without using a large amount of a dispersion medium. The PTFE composition may be in a form other than a powder, for example, a dispersion liquid.

The PTFE composition of the present disclosure may have an average secondary particle size of 350 μm or more, preferably 400 μm or more, more preferably 450 μm or more, and even more preferably 500 μm or more, and preferably 1000 μm or less, more preferably 900 μm or less, even more preferably 800 μm or less, and even more preferably 700 μm or less.
The average secondary particle size is measured in accordance with JIS K 6891.

In terms of excellent handleability, the PTFE composition of the present disclosure has an apparent density of preferably 0.40 g/ml or more, more preferably 0.43 g/ml or more, and even more preferably 0.45 g/ml or more. The upper limit is not particularly limited, but may be 0.70 g/ml.
The apparent density is measured in accordance with JIS K6892.

The PTFE composition of the present disclosure can be produced by mixing low molecular weight PTFE (PTFE (A) that exhibits melt flowability) and high molecular weight PTFE (PTFE (B) that does not exhibit melt flowability). The mixing method is not limited, and the above PTFE may be mixed all in the form of a powder, all in the form of an aqueous dispersion, or mixed in the form of an aqueous dispersion and in the form of a powder. It is preferable to mix all in the form of an aqueous dispersion, as this allows for more uniform mixing.

The PTFE composition of the present disclosure can be suitably manufactured, for example, by a manufacturing method including a step (A) of mixing an aqueous dispersion of low molecular weight PTFE (PTFE (A) exhibiting melt flowability) with an aqueous dispersion of high molecular weight PTFE (PTFE (B) not exhibiting melt flowability), a step (B) of coagulating the aqueous dispersion after mixing to obtain a wet powder, and a step (C) of drying the wet powder.

The aqueous dispersion of low molecular weight PTFE (PTFE (A) exhibiting melt flowability) in step (A) can be produced by a known method, and can be produced by direct polymerization using a method such as emulsion polymerization or suspension polymerization, or can be produced by thermal decomposition or radiation decomposition of high molecular weight PTFE. The above low molecular weight PTFE (PTFE (A) exhibiting melt flowability) is preferably produced by direct polymerization, and more preferably produced by emulsion polymerization.

The aqueous dispersion of high molecular weight PTFE (PTFE (B) that does not exhibit melt flowability) in step (A) can be produced, for example, by emulsion polymerization.

The emulsion polymerization can be carried out by a known method. For example, an aqueous dispersion containing particles (primary particles) of the PTFE can be obtained by carrying out emulsion polymerization of monomers (TFE and, if necessary, modified monomers) necessary for constituting the PTFE in an aqueous medium in the presence of an anionic fluorine-containing surfactant and a polymerization initiator. In the emulsion polymerization, a chain transfer agent, a buffer, a pH adjuster, a stabilizing aid, a dispersion stabilizer, a radical scavenger, etc. may be used as necessary.

The aqueous dispersion may contain at least one of the above-mentioned fluorine-containing compounds.

The above emulsion polymerization can be carried out, for example, in an aqueous medium in the presence of an anionic fluorine-containing surfactant and a polymerization initiator.
The emulsion polymerization can be carried out by charging an aqueous medium, the anionic fluorine-containing surfactant, monomers and, if necessary, other additives into a polymerization reactor, stirring the contents of the reactor, maintaining the reactor at a predetermined polymerization temperature, and then adding a predetermined amount of polymerization initiator to initiate the polymerization reaction. After the start of the polymerization reaction, monomers, polymerization initiators, chain transfer agents, the surfactants and the like may be additionally added depending on the purpose.

The polymerization initiator is not particularly limited as long as it can generate radicals within the polymerization temperature range, and known oil-soluble and/or water-soluble polymerization initiators can be used. Furthermore, it can also be combined with a reducing agent or the like to initiate polymerization as a redox. The concentration of the polymerization initiator is appropriately determined depending on the type of monomer, the molecular weight of the desired PTFE, and the reaction rate.

As the polymerization initiator, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator can be used.

The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, for example, 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, and also 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 Representative examples include di[perfluoro(or fluorochloro)acyl]peroxides such as di(ω-chlorohexafluorobutyryl) peroxide, di(ω-chlorotetradecafluorooctanoyl) peroxide, ω-hydrododecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl-peroxide, ω-chlorohexafluorobutyryl-ω-chlorodecafluorohexanoyl-peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl-peroxide, di(dichloropentafluorobutanoyl) peroxide, di(trichlorooctafluorohexanoyl) peroxide, di(tetrachloroundecafluorooctanoyl) peroxide, di(pentachlorotetradecafluorodecanoyl) peroxide, and di(undecachlorodotriacontafluorodocosanoyl) peroxide.

The water-soluble radical polymerization initiator may be a known water-soluble peroxide, such as ammonium salts, potassium salts, or sodium salts of persulfuric acid, perboric acid, perchloric acid, perphosphoric acid, or percarbonic acid, t-butyl permaleate, t-butyl hydroperoxide, or disuccinic acid peroxide. Among these, ammonium persulfate and disuccinic acid peroxide are preferred. A reducing agent such as sulfites or sulfites may also be included, and the amount used may be 0.1 to 20 times that of the peroxide.

The amount of the water-soluble radical polymerization initiator to be added is not particularly limited, but may be added all at once, stepwise, or continuously in an amount (e.g., several ppm relative to water concentration) at least to the extent that the polymerization rate does not decrease significantly. The upper limit is a range in which the reaction temperature may be increased while removing heat from the equipment side by the polymerization reaction heat, and a more preferable upper limit is a range in which the polymerization reaction heat can be removed from the equipment side.
In terms of easily obtaining the above-mentioned physical properties, the amount of the polymerization initiator added is preferably an amount corresponding to 0.1 ppm or more, more preferably an amount corresponding to 1.0 ppm or more, and is preferably an amount corresponding to 100 ppm or less, more preferably an amount corresponding to 10 ppm or less, relative to the aqueous medium.

For example, when polymerization is carried out at a low temperature of 30°C or less, it is preferable to use a redox initiator that combines an oxidizing agent and a reducing agent as the polymerization initiator. Examples of the oxidizing agent include persulfates, organic peroxides, potassium permanganate, manganese triacetate, cerium ammonium nitrate, and bromates. Examples of the reducing agent include sulfites, bisulfites, bromates, diimines, and oxalic acid. Examples of the persulfates include ammonium persulfate and potassium persulfate. Examples of the sulfites include sodium sulfite and ammonium sulfite. In order to increase the decomposition rate of the initiator, it is also preferable to add a copper salt or an iron salt to the combination of redox initiators. Examples of the copper salt include copper (II) sulfate, and examples of the iron salt include iron (II) sulfate.

As the redox initiator, it is preferable that the oxidizing agent is permanganic acid or a salt thereof, a persulfate, manganese triacetate, a cerium (IV) salt, or bromic acid or a salt thereof, and the reducing agent is a dicarboxylic acid or a salt thereof, or a diimine.
More preferably, the oxidizing agent is permanganic acid or a salt thereof, a persulfate, or bromic acid or a salt thereof, and the reducing agent is a dicarboxylic acid or a salt thereof.

Examples of the redox initiator include combinations of potassium permanganate/oxalic acid, potassium permanganate/ammonium oxalate, manganese triacetate/oxalic acid, manganese triacetate/ammonium oxalate, cerium ammonium nitrate/oxalic acid, and cerium ammonium nitrate/ammonium oxalate.
When a redox initiator is used, either the oxidizing agent or the reducing agent may be charged in advance in a polymerization tank, and then the other may be added continuously or intermittently to initiate polymerization. For example, when potassium permanganate/ammonium oxalate is used, it is preferable to charge ammonium oxalate in a polymerization tank and continuously add potassium permanganate thereto.
In this specification, when the redox initiator is described as "potassium permanganate/ammonium oxalate," it means a combination of potassium permanganate and ammonium oxalate. The same applies to other compounds.

The redox initiator is particularly preferably a combination of an oxidizing agent that is a salt and a reducing agent that is a salt.
For example, the oxidizing agent which is the salt is more preferably at least one selected from the group consisting of persulfates, permanganates, cerium (IV) salts, and bromates, still more preferably permanganates, and particularly preferably potassium permanganate.
The reducing agent which is the salt is more preferably at least one selected from the group consisting of oxalates, malonates, succinates, glutarates and bromates, further preferably oxalates, and particularly preferably ammonium oxalate.

Specific examples of the redox initiator include at least one selected from the group consisting of potassium permanganate/oxalic acid, potassium permanganate/ammonium oxalate, potassium bromate/ammonium sulfite, manganese triacetate/ammonium oxalate, and cerium ammonium nitrate/ammonium oxalate, more preferably at least one selected from the group consisting of potassium permanganate/oxalic acid, potassium permanganate/ammonium oxalate, potassium bromate/ammonium sulfite, and cerium ammonium nitrate/ammonium oxalate, and even more preferably potassium permanganate/oxalic acid.

When using a redox initiator, the oxidizing agent and reducing agent may be added all at once at the beginning of the polymerization, the reducing agent may be added all at once at the beginning of the polymerization and the oxidizing agent may be added continuously, the oxidizing agent may be added all at once at the beginning of the polymerization and the reducing agent may be added continuously, or both the oxidizing agent and reducing agent may be added continuously.

When one of the above redox polymerization initiators is added at the beginning of the polymerization and the other is added continuously, it is preferable to gradually slow down the addition rate in order to obtain PTFE with a low SSG, and it is also preferable to stop the addition midway through the polymerization, preferably before 20 to 40 mass% of the total TFE consumed in the polymerization reaction has been consumed.

When using a redox initiator as a polymerization initiator, the amount of oxidizing agent added to the aqueous medium is preferably 0.1 ppm or more, more preferably 0.3 ppm or more, more preferably 0.5 ppm or more, even more preferably 1 ppm or more, particularly preferably 5 ppm or more, and especially preferably 10 ppm or more, and also preferably 10000 ppm or less, more preferably 1000 ppm or less, more preferably 100 ppm or less, and even more preferably 10 ppm or less. The amount of reducing agent added is preferably 0.1 ppm or more, more preferably 1.0 ppm or more, more preferably 3 ppm or more, even more preferably 5 ppm or more, particularly preferably 10 ppm or more, and also preferably 10000 ppm or less, more preferably 1000 ppm or less, more preferably 100 ppm or less, and even more preferably 10 ppm or less.
When a redox initiator is used in the emulsion polymerization, the polymerization temperature is preferably 100° C. or lower, more preferably 95° C. or lower, and even more preferably 90° C. or lower. The polymerization temperature is preferably 10° C. or higher, more preferably 20° C. or higher, and even more preferably 30° C. or higher.

As the polymerization initiator, a water-soluble radical polymerization initiator and a redox initiator are preferred because the above-mentioned properties can be easily obtained.

The aqueous medium is a reaction medium in which polymerization is carried out, and refers to a liquid containing water. The aqueous medium is not particularly limited as long as it contains water, and may contain water and, for example, a fluorine-free organic solvent such as an alcohol, ether, or ketone, and/or a fluorine-containing organic solvent having a boiling point of 40° C. or less.

In the above emulsion polymerization, nucleating agents, chain transfer agents, buffers, pH adjusters, stabilizing aids, dispersion stabilizers, radical scavengers, polymerization initiator decomposers, dicarboxylic acids, etc. may be used as necessary.

The emulsion polymerization is preferably carried out with the addition of a nucleating agent for the purpose of adjusting the particle size. The nucleating agent is preferably added before the start of the polymerization reaction.
As the nucleating agent, a known agent can be used. For example, it is preferably at least one selected from the group consisting of fluoropolyethers, nonionic surfactants, and chain transfer agents, and more preferably a nonionic surfactant.

The fluoropolyether may, for example, be a perfluoropolyether (PFPE) acid or a salt thereof.
The perfluoropolyether (PFPE) acid or salt thereof may have any chain structure in which the oxygen atoms in the backbone of the molecule are separated by saturated fluorocarbon groups having 1 to 3 carbon atoms. Also, more than one type of fluorocarbon group may be present in the molecule. A representative structure has a repeat unit represented by the following formula:
(-CFCF ₃ -CF ₂ -O-) _n
(-CF ₂ -CF ₂ -CF ₂ -O-) _n
(-CF ₂ -CF ₂ -O-) _n -(-CF ₂ -O-) _m
(-CF ₂ -CFCF ₃ -O-) _n -(-CF ₂ -O-) _m

These structures are described by Kasai in J. Appl. Polymer Sci. 57,797 (1995). As disclosed therein, the PFPE acid or its salt may have a carboxylic acid group or its salt at one or both ends. The PFPE acid or its salt may also have a sulfonic acid, phosphonic acid group or their salt at one or both ends. The PFPE acid or its salt may also have a different group at each end. For monofunctional PFPEs, the other end of the molecule is usually perfluorinated but may contain hydrogen or chlorine atoms. The PFPE acid or its salt has at least two ether oxygens, preferably at least four ether oxygens, and even more preferably at least six ether oxygens. Preferably, at least one of the fluorocarbon groups separating the ether oxygens, more preferably at least two of such fluorocarbon groups, has two or three carbon atoms. Even more preferably, at least 50% of the fluorocarbon groups separating the ether oxygens have 2 or 3 carbon atoms. Also preferably, the PFPE acid or salt thereof has a total of at least 15 carbon atoms, e.g., the preferred minimum value of n or n+m in the repeating unit structure is at least 5. Two or more of the PFPE acids or salts thereof having an acid group at one or both termini may be used in the manufacturing method of the present disclosure. The PFPE acid or salt thereof preferably has a number average molecular weight of less than 6000 g/mol.

The emulsion polymerization is preferably carried out with the addition of a radical scavenger or a decomposer of the polymerization initiator, since this can further increase the molecular weight of PTFE and improve the strength of the composite sheet. The radical scavenger or decomposer of the polymerization initiator is preferably added after the start of the polymerization reaction, preferably before 10% by mass or more, preferably 20% by mass or more of the total TFE consumed in the polymerization reaction is polymerized, and preferably before 50% by mass or less, preferably 40% by mass or less is polymerized. When depressurizing and repressurizing as described below are performed, it is preferable to add it after that.

The radical scavenger is a compound that does not have the ability to restart after addition or chain transfer to the free radical in the polymerization system. Specifically, a compound that easily undergoes a chain transfer reaction with a primary radical or a growing radical, and then generates a stable radical that does not react with a monomer, or a compound that easily undergoes an addition reaction with a primary radical or a growing radical, and generates a stable radical, is used.
Generally, the activity of what is called a chain transfer agent is characterized by the chain transfer constant and the reinitiation efficiency, and among chain transfer agents, those with a reinitiation efficiency of almost 0% are called radical scavengers.
The radical scavenger can be, for example, a compound whose chain transfer constant with TFE at the polymerization temperature is greater than the polymerization rate constant and whose reinitiation efficiency is substantially zero percent. The "reinitiation efficiency is substantially zero percent" means that the generated radicals turn the radical scavenger into stable radicals.
Preferably, the compound has a chain transfer constant (Cs) (=chain transfer rate constant (kc)/polymerization rate constant (kp)) with TFE at polymerization temperature of more than 0.1, and the above compound has a chain transfer constant (Cs) of more preferably 0.5 or more, even more preferably 1.0 or more, even more preferably 5.0 or more, and particularly preferably 10 or more.

The radical scavenger is preferably at least one selected from the group consisting of aromatic hydroxy compounds, aromatic amines, N,N-diethylhydroxylamine, quinone compounds, terpenes, thiocyanates, and cupric chloride (CuCl ₂ ).
Examples of the aromatic hydroxy compound include unsubstituted phenol, polyhydric phenol, salicylic acid, m- or p-salicylic acid, gallic acid, and naphthol.
The unsubstituted phenols include o-, m-, or p-nitrophenol, o-, m-, or p-aminophenol, p-nitrosophenol, etc. The polyhydric phenols include catechol, resorcinol, hydroquinone, pyrogallol, phloroglucinol, naphthresorcinol, etc.
Examples of aromatic amines include o-, m- or p-phenylenediamine, benzidine, and the like.
Examples of the quinone compound include o-, m- or p-benzoquinone, 1,4-naphthoquinone, alizarin, and the like.
Examples of thiocyanates include ammonium thiocyanate (NH ₄ SCN), potassium thiocyanate (KSCN), and sodium thiocyanate (NaSCN).
Of the above radical scavengers, aromatic hydroxy compounds are preferred, unsubstituted phenols or polyhydric phenols are more preferred, and hydroquinone is even more preferred.

The amount of the radical scavenger added is preferably an amount equivalent to 3 to 500% (molar basis) of the polymerization initiator concentration in order to appropriately reduce the standard specific gravity. A more preferred lower limit is 10% (molar basis), and even more preferred is 15% (molar basis). A more preferred upper limit is 400% (molar basis), and even more preferred is 300% (molar basis).

The decomposer for the polymerization initiator may be any compound capable of decomposing the polymerization initiator used, and is preferably at least one selected from the group consisting of sulfites, bisulfites, bromates, diimines, diimine salts, oxalic acid, oxalates, copper salts, and iron salts. Examples of the sulfites include sodium sulfite and ammonium sulfite. Examples of the copper salts include copper(II) sulfate, and examples of the iron salts include iron(II) sulfate.
The amount of the decomposition agent added is preferably an amount equivalent to 3 to 500% (molar basis) of the initiator concentration from the viewpoint of appropriately reducing the standard specific gravity. A more preferred lower limit is 10% (molar basis), and even more preferred is 15% (molar basis). A more preferred upper limit is 400% (molar basis), and even more preferred is 300% (molar basis).

The emulsion polymerization may be carried out in the presence of 5 to 500 ppm of dicarboxylic acid relative to the aqueous medium in order to reduce the amount of coagulation produced during polymerization, and is preferably carried out in the presence of 10 to 200 ppm of dicarboxylic acid. If the amount of dicarboxylic acid relative to the aqueous medium is too small, sufficient effects may not be obtained, and if the amount is too large, a chain transfer reaction may occur, resulting in a low molecular weight polymer. It is more preferable that the amount of dicarboxylic acid is 150 ppm or less. The dicarboxylic acid may be added before the start of the polymerization reaction or during the polymerization.

As the dicarboxylic acid, for example, those represented by the general formula: HOOCRCOOH (wherein R represents an alkylene group having 1 to 5 carbon atoms) are preferred, with succinic acid, malonic acid, glutaric acid, adipic acid, and pimelic acid being more preferred, and succinic acid being even more preferred.

In the above emulsion polymerization, polymerization temperature and polymerization pressure are appropriately determined according to the type of monomer used, the molecular weight of the PTFE to be targeted, and reaction rate.Usually, polymerization temperature is 5 to 150°C, preferably 10°C or higher, more preferably 30°C or higher, and even more preferably 50°C or higher.Moreover, it is more preferably 120°C or lower, and even more preferably 100°C or lower.
The polymerization pressure is 0.05 to 10 MPaG. The polymerization pressure is more preferably 0.3 MPaG or more, and even more preferably 0.5 MPaG or more. The polymerization pressure is more preferably 5.0 MPaG or less, and even more preferably 3.0 MPaG or less.

When VDF is used as the modified monomer, in the emulsion polymerization, the VDF concentration in the gas in the reactor at the start of polymerization (when the initiator is added) is preferably 0.001 mol% or more, more preferably 0.01 mol% or more, in order to easily obtain the above-mentioned physical properties. The above concentration may also be 15 mol% or less, preferably 6.0 mol% or less, more preferably 5.0 mol% or less, even more preferably 3.0 mol% or less, and particularly preferably 1.0 mol% or less. The above VDF concentration may be maintained until the end of the polymerization reaction, or depressurization may be performed during the reaction. It is preferable to charge VDF all at once before the start of polymerization, but a portion of it may be added continuously or intermittently after the start of polymerization.

When VDF is used as the modified monomer, it is preferable not to release the pressure in the emulsion polymerization after VDF is added to the polymerization vessel until the polymerization is completed. This allows VDF to remain in the system until the end of the polymerization, and the strength of the resulting composite sheet using PTFE can be further increased.

When HFP is used as the modified monomer, in the emulsion polymerization, the HFP concentration in the gas in the reactor at the start of polymerization (when the initiator is added) is preferably 0.01 to 3.0 mol % in order to easily obtain the above-mentioned physical properties. Furthermore, it is preferable that the HFP concentration in the gas in the reactor at the time when 40 mass % of the total TFE consumed in the polymerization reaction is polymerized is greater than 0 mol % and 0.2 mol % or less. It is preferable to maintain the above HFP concentration until the end of the polymerization reaction. HFP may be charged all at once before the start of polymerization, or a portion may be charged before the start of polymerization and added continuously or intermittently after the start of polymerization. By allowing HFP to remain until the end of the polymerization reaction, the extrusion pressure is reduced despite the high strength of the resulting composite sheet using PTFE.

When HFP is used as the modified monomer, in the above emulsion polymerization, it is preferable to release the pressure before polymerization of 5 to 40 mass% of the total TFE consumed in the polymerization reaction, and then re-pressurize the mixture using only TFE, in order to further improve the strength of the resulting composite sheet using PTFE.
The depressurization is preferably carried out so that the pressure inside the reactor is 0.2 MPaG or less, more preferably 0.1 MPaG or less, and even more preferably 0.05 MPaG or less. Also, it is preferably carried out so that the pressure inside the reactor is 0.0 MPaG or more.
The above pressure reduction and re-increase may be carried out several times. The pressure reduction may be carried out until the pressure is reduced using a vacuum pump.

When CTFE is used as the modified monomer, in the emulsion polymerization, the CTFE concentration in the gas in the reactor at the start of polymerization (when the initiator is added) is preferably 0.001 mol% or more, more preferably 0.01 mol% or more, in order to easily obtain the above-mentioned physical properties. The above concentration is also preferably 3.0 mol% or less, more preferably 1.0 mol% or less. The above CTFE concentration may be maintained until the end of the polymerization reaction, or depressurization may be performed midway. CTFE is preferably charged all at once before the start of polymerization, but a portion may be added continuously or intermittently after the start of polymerization.

When CTFE is used as the modified monomer, it is preferable not to release the pressure in the emulsion polymerization after the CTFE is charged into the polymerization vessel until the polymerization is completed. This allows the CTFE to remain in the system until the end of the polymerization, and the strength of the resulting composite sheet using PTFE can be further increased.

The mixing in step (A) can be carried out by a known method.

The coagulation in step (B) can be carried out by a known method.

In step (C), the drying is usually carried out by using a vacuum, high frequency, hot air, or other means while keeping the wet powder in a state where it is not very fluid, preferably in a stationary state. Friction between powders, especially at high temperatures, generally has an undesirable effect on fine powder-type PTFE. This is because particles made of this type of PTFE have the property of easily fibrillating even with a small shear force, losing the original stable particle structure.

In step (C), it is preferable to place the wet powder obtained in step (B) in a container with air permeability at the bottom and/or sides, and heat treat it at a temperature of 130 to 300°C for 2 hours or more. By carrying out heat treatment under such extremely limited conditions, the fluorine-containing compound having a molecular weight of 1000 or less can be efficiently removed together with water, and the content of the fluorine-containing compound and water can be kept within the above-mentioned range.

The temperature of the heat treatment in step (C) is preferably 140°C or higher, more preferably 150°C or higher, even more preferably 160°C or higher, even more preferably 180°C or higher, even more preferably 200°C or higher, particularly preferably 220°C or higher, and is preferably 280°C or lower, more preferably 250°C or lower, in order to more efficiently remove moisture and fluorine-containing compounds.

The time for the heat treatment in step (C) is preferably 5 hours or more, more preferably 10 hours or more, and even more preferably 15 hours or more, in order to more efficiently remove moisture and fluorine-containing compounds. There is no particular upper limit, but for example, it is preferably 100 hours, more preferably 50 hours, and even more preferably 30 hours.

The wind speed in step (C) is preferably 0.01 m/s or more, more preferably 0.03 m/s or more, even more preferably 0.05 m/s or more, and even more preferably 0.1 m/s or more, from the viewpoint of more efficiently removing moisture and fluorine-containing compounds. Also, from the viewpoint of suppressing scattering of powder, it is preferably 50 m/s or less, more preferably 30 m/s or less, and even more preferably 10 m/s or less.

The heat treatment in step (C) can be carried out using an electric furnace or a steam furnace. For example, it can be carried out using electric furnaces such as a parallel flow box type electric furnace, a ventilated box type electric furnace, a ventilated conveyor type electric furnace, a band electric furnace, a radiant conveyor type electric furnace, a fluidized bed electric furnace, a vacuum electric furnace, an agitator type electric furnace, an airflow type electric furnace, or a hot air circulation type electric furnace, or a steam furnace corresponding to the above (a device obtained by replacing the electric furnace in the device name of each electric furnace with a steam furnace). In terms of being able to remove moisture and fluorine-containing compounds more efficiently, a parallel flow box type electric furnace, a ventilated box type electric furnace, a ventilated conveyor type electric furnace, a band electric furnace, a fluidized bed electric furnace, a hot air circulation type electric furnace, or a steam furnace corresponding to the above (a device obtained by replacing the electric furnace in the device name of each electric furnace with a steam furnace) is preferred.

The heat treatment in step (C) is preferably carried out by placing the wet powder in a container having air permeability at its bottom and/or sides, in order to more efficiently remove moisture and the fluorine-containing compound. The container having air permeability at its bottom and/or sides may be any container that can withstand the heat treatment temperature, and is preferably made of a metal such as stainless steel.
As the container having breathability on the bottom and/or sides, a tray (bat) having breathability on the bottom and/or sides is preferable, and a tray whose bottom and/or sides are made of mesh (mesh tray) is more preferable.
The mesh is preferably either a woven mesh or a punched metal.
The mesh size is preferably 2000 μm or less (ASTM standard 10 mesh or more), more preferably 595 μm or less (30 mesh or more), even more preferably 297 μm or less (50 mesh or more), even more preferably 177 μm or less (80 mesh or more), particularly preferably 149 μm or less (100 mesh or more), and particularly preferably 74 μm or less (200 mesh or more). Also, 25 μm or more (500 mesh or less) is preferable.
When the mesh is a woven net, the weaving method may be, for example, plain weave, twill weave, plain tatami weave, or twill tatami weave.
When the mesh is a punched metal, the opening ratio is preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more, and is preferably 95% or less.

In step (C), the amount of the moist powder disposed is, from the viewpoint of more efficiently removing moisture and fluorine-containing compounds, preferably 10 g/ ^cm2 or less, more preferably 8 g/ ^cm2 or less, even more preferably 5 g/ ^cm2 or less, particularly preferably 3 g/ ^cm2 or less, and is preferably 0.01 g/ ^cm2 or more, more preferably 0.05 g/ ^cm2 or more, and even more preferably 0.1 g/ ^cm2 or more.

The moisture content of the moist powder to be heat-treated in step (C) 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 moist powder, in order to more efficiently remove moisture and fluorine-containing compounds, and is preferably 150% by mass or less, and more preferably 100% by mass or less.

The PTFE composition of the present disclosure is used in a battery binder. In the battery binder, the PTFE composition of the present disclosure may be used alone or in a mixture with other materials (e.g., polymers other than PTFE). However, it is preferable to use the PTFE composition of the present disclosure substantially alone, and it is more preferable to use it alone. Note that using the PTFE composition of the present disclosure substantially alone means that the amount of the PTFE composition in the battery binder is used within the range described below.

The present disclosure also provides a battery binder consisting essentially of a PTFE composition, the PTFE composition having endothermic peaks in a region (A) of 324°C or more and less than 333°C and a region (B) of 333°C or more and 350°C or less in differential scanning calorimetry (hereinafter also referred to as binder (1) of the present disclosure).

The present disclosure also provides a battery binder consisting essentially of a PTFE composition, the PTFE composition consisting essentially of PTFE (A) that exhibits melt flowability and PTFE (B) that does not exhibit melt flowability (hereinafter also referred to as binder (2) of the present disclosure).

In this specification, unless otherwise specified, binders (1) and (2) of the present disclosure are collectively referred to as "binders of the present disclosure."

The binder of the present disclosure contains a specific PTFE composition, so that even if it is kneaded for a long time with powder components of a battery such as an electrode active material and a solid electrolyte, agglomerates are unlikely to occur, and it can be mixed uniformly with the powder components. In addition, it is possible to obtain a mixture sheet having excellent strength and flexibility.
The binder of the present disclosure is also advantageous in terms of production process because it does not require the use of a large amount of a dispersion medium such as water or an organic solvent, and a wide range of electrode active materials and solid electrolytes can be selected for combination with the binder, and the process and cost involved in using a dispersion medium can be reduced.
Furthermore, since the binder of the present disclosure has excellent binding strength with the active material and the electrolyte, the amount of the binder used can be reduced.

The PTFE composition in the binder (1) of the present disclosure can be the same as the PTFE composition (1) of the present disclosure described above, and the preferred embodiments are also the same.

The PTFE composition in the binder (2) of the present disclosure can be the same as the PTFE composition (2) of the present disclosure described above, and the preferred embodiments are also the same.

The binder of the present disclosure is substantially composed of the PTFE composition. This allows the effect of the PTFE composition to be significantly exhibited. "Substantially composed of the PTFE composition" means that the content of the PTFE composition is 95.0% by mass or more relative to the binder.
The content of the PTFE composition relative to the binder is preferably 98.0% by mass or more, more preferably 99.0% by mass or more, even more preferably 99.5% by mass or more, particularly preferably 99.9% by mass or more, and most preferably 99.95% by mass or more.
It is also preferred that the binder of the present disclosure consists solely of the PTFE composition.

The binder of the present disclosure is preferably substantially free of organic solvent. This can reduce the steps and costs associated with the use of organic solvent. "Substantially free of organic solvent" means that the organic solvent content of the binder is 5% by mass or less.
The organic solvent content is preferably 3% by mass or less, more preferably 1% by mass or less, even more preferably 0.1% by mass or less, even more preferably 0.01% by mass or less, and particularly preferably 0.001% by mass or less.

The binder of the present disclosure is preferably in the form of a powder.

The binder of the present disclosure is used in batteries, and can be suitably used as a binder for secondary batteries such as lithium ion batteries.
The binders of the present disclosure may be used to fabricate battery components.
The binder of the present disclosure can be particularly suitably used as a binder for electrodes.
The binder of the present disclosure can also be suitably used as a binder in the solid electrolyte layer of a solid secondary battery.

The present disclosure also provides an electrode mixture containing the above-mentioned PTFE composition of the present disclosure or the binder of the present disclosure and an electrode active material. By using the electrode mixture of the present disclosure, an electrode can be obtained that can suppress gas generation inside a battery cell and deterioration of battery characteristics (e.g., decrease in capacity during high-temperature storage). In addition, a mixture sheet in which the powder components of the battery are uniformly dispersed and which has excellent strength and flexibility can be obtained. In addition, even with a small amount of binder, the electrode active material can be retained, so that more materials that improve battery characteristics, such as active materials and conductive assistants, can be added.

The above-mentioned electrode active materials include positive electrode active materials and negative electrode active materials.

The positive electrode active material is not particularly limited as long as it can electrochemically absorb and release alkali metal ions, but for example, a material containing an alkali metal and at least one transition metal is preferred. Specific examples include alkali metal-containing transition metal complex oxides and alkali metal-containing transition metal phosphate compounds. In particular, alkali metal-containing transition metal complex oxides that generate high voltage are preferred as the positive electrode active material. Examples of the alkali metal ions include lithium ions, sodium ions, potassium ions, and the like. In a preferred embodiment, the alkali metal ions may be lithium ions. That is, in this embodiment, the alkali metal ion secondary battery is a lithium ion secondary battery.

Examples of the alkali metal-containing transition metal composite oxide include:
Formula: M _a Mn _2-b M ¹ _b O ₄
(wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0.9≦a; 0≦b≦1.5; ^M1 is at least one metal selected from the group consisting of Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge),
Formula: MNi _1-c M ² _c O ₂
(wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0≦c≦0.5; ^M2 is at least one metal selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge), or
Formula: MCo _1-d M ³ _d O ₂
(wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0≦d≦0.5; ^M3 is at least one metal selected from the group consisting of Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge). In the above, M is preferably at least one metal selected from the group consisting of Li, Na, and K, more preferably Li or Na, and even more preferably Li.

Among _these , from the viewpoint of providing a secondary battery having high energy density and high output, _MCoO2 , _MMnO2 , _MNiO2 , _MMn2O4 , _{MNi0.8Co0.15Al0.05O2} , MNi1 _/ 3Co1/3Mn1 _{/ 3O2 , etc.} are preferred, and a compound represented by _{the following} general formula (3) is preferable.
MNi _h Co _i Mn _j M ⁵ _k O ₂ (3)
(In the formula, M is at least one metal selected from the group consisting of Li, Na, and K, M5 is at least one selected from the group consisting of Fe, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge, and (h+i+ ^j +k)=1.0, 0≦h≦1.0, 0≦i≦1.0, 0≦j≦1.5, and 0≦k≦0.2.)

The alkali metal-containing transition metal phosphate compound is, for example, a compound represented by the following general formula (4):
M _e M ⁴ _f (PO ₄ ) _g (4)
(wherein M is at least one metal selected from the group consisting of Li, Na and K, and ^M4 is at least one selected from the group consisting of V, Ti, Cr, Mn, Fe, Co, Ni and Cu, and 0.5≦e≦3, 1≦f≦2, 1≦g≦3). In the above, M is preferably at least one metal selected from the group consisting of Li, Na and K, more preferably Li or Na, and even more preferably Li.

The transition metal of the lithium-containing transition metal phosphate compound is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc., and specific examples thereof include iron phosphates such as _LiFePO4 , _Li3Fe2 ( _PO4 ) ₃ , and _LiFeP2O7 , _cobalt phosphates such as _LiCoPO4 , and lithium transition metal phosphate compounds in which a part of the transition metal atoms that constitute _the main part of the lithium transition metal phosphate compound is replaced with other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, and Si. The lithium-containing transition metal phosphate compound is preferably one having an olivine structure.

Other examples of the positive electrode active material include lithium-nickel-based composite oxides. The lithium-nickel-based composite oxides are represented by the following general formula (5):
Li _y Ni _1-x M _x O ₂ (5)
(wherein x is 0.01≦x≦0.7, y is 0.9≦y≦2.0, and M is a metal atom (excluding Li and Ni)) is preferred.

Other examples of the positive electrode active material include MFePO ₄ , MNi _0.8 Co _0.2 O ₂ , M _1.2 Fe _0.4 Mn _0.4 O ₂ , MNi _0.5 Mn _1.5 O ₂ , MV ₃ O ₆ , and M ₂ MnO ₃ . In particular, positive electrode active materials such as M ₂ MnO ₃ and MNi _0.5 Mn _1.5 O ₂ are preferred in that the crystal structure does not collapse even when the secondary battery is operated at a voltage exceeding 4.4 V or a voltage of 4.6 V or more. Therefore, electrochemical devices such as secondary batteries using positive electrode materials containing the above-mentioned positive electrode active materials are preferred because the remaining capacity is not easily reduced and the resistance increase rate is not easily changed even when stored at high temperatures, and the battery performance is not deteriorated even when operated at high voltages.

Other examples of the positive _electrode active material include a solid solution material _{of M2MnO3} and ^MM6O2 (wherein M is at least one metal selected from the group consisting of Li, Na, and K, and ^M6 is a transition metal such as Co, Ni, Mn, or Fe).

An example of the solid solution material is an alkali metal manganese oxide represented by the general formula Mx[Mn _{(1-y) M7y} ^] _Oz , where M in the formula is at least one metal selected from the group consisting of Li, Na, and K, and ^M7 is at least one metal element other than M and Mn, and contains, for example, one or more elements selected from the group consisting of Co, Ni, Fe, Ti, Mo, W, Cr, Zr, and Sn. The values of x, y, and z in the formula are in the ranges of 1<x<2, 0≦y<1, and 1.5<z<3. Among these, manganese _{-containing solid solution materials, such as Li1.2Mn0.5Co0.14Ni0.14O2, which are based on Li2MnO3 and contain LiNiO2 or LiCoO2 as a solid solution ,} are preferred because they can provide _an alkali metal ion secondary battery having a high energy density.

In addition, it is preferable to include lithium phosphate in the positive electrode active material, since this improves the continuous charging characteristics. There is no restriction on the use of lithium phosphate, but it is preferable to use a mixture of the positive electrode active material and lithium phosphate. The amount of lithium phosphate used is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, with respect to the total of the positive electrode active material and lithium phosphate, and is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less.

In addition, a material having a different composition may be attached to the surface of the positive electrode active material. Examples of surface-attached 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.

These surface-attaching substances can be attached to the surface of the positive electrode active material by, for example, dissolving or suspending them in a solvent, impregnating and adding them to the positive electrode active material, and drying them; dissolving or suspending a surface-attaching substance precursor in a solvent, impregnating and adding them to the positive electrode active material, and then reacting them by heating or the like; or adding them to a positive electrode active material precursor and simultaneously baking them. When attaching carbon, a method can also be used in which the carbonaceous material is mechanically attached later in the form of, for example, activated carbon.

The amount of the surface-attached substance is preferably 0.1 ppm or more, more preferably 1 ppm or more, and even more preferably 10 ppm or more, and preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less, by mass relative to the positive electrode active material. The surface-attached substance can suppress the oxidation reaction of the electrolyte on the surface of the positive electrode active material, thereby improving the battery life, but if the amount of attachment is too small, the effect is not fully manifested, and if it is too large, the movement of lithium ions is inhibited, which may increase resistance.

The shape of the particles of the positive electrode active material may be, as conventionally used, a block, polyhedron, sphere, oval sphere, plate, needle, column, etc. Primary particles may also aggregate to form secondary particles.

The tap density of the positive electrode active material is preferably 0.5 g/cm ³ or more, more preferably 0.8 g/cm ³ or more, and even more preferably 1.0 g/cm ³ or more. If the tap density of the positive electrode active material is below the lower limit, the amount of dispersion medium required during the formation of the positive electrode active material layer increases, and the amount of conductive material and binder required increases, so that the filling rate of the positive electrode active material in the positive electrode active material layer is restricted, and the battery capacity may be restricted. By using a complex oxide powder with a high tap density, a high-density positive electrode active material layer can be formed. The tap density is generally preferably as high as possible, and there is no particular upper limit, but if it is too high, the diffusion of lithium ions in the positive electrode active material layer using the electrolyte as a medium becomes rate-limiting, and the load characteristics may be easily deteriorated, so the upper limit is preferably 4.0 g/cm ³ or less, more preferably 3.7 g/cm ³ or less, and even more preferably 3.5 g/cm ³ or less.
The tap density is determined as the powder packing density (tap density) g/cm ³ when 5 to 10 g of the positive electrode active material powder is placed in a 10 ml glass measuring cylinder and tapped 200 times with a stroke of about 20 mm.

The median diameter d50 of the particles of the positive electrode active material (secondary particle diameter when primary particles are aggregated to form secondary particles) is preferably 0.3 μm or more, more preferably 0.5 μm or more, even more preferably 0.8 μm or more, and most preferably 1.0 μm or more, and is preferably 30 μm or less, more preferably 27 μm or less, even more preferably 25 μm or less, and most preferably 22 μm or less. If it is below the lower limit, a high tap density product may not be obtained, and if it exceeds the upper limit, it may take time for lithium to diffuse within the particles, resulting in problems such as a decrease in battery performance. Here, by mixing two or more of the above positive electrode active materials having different median diameters d50, the filling property during positive electrode production can be further improved.

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

In the case where the primary particles are aggregated to form secondary particles, the average primary particle diameter of the positive electrode active material is preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more, and the upper limit is preferably 5 μm or less, more preferably 4 μm or less, even more preferably 3 μm or less, and most preferably 2 μm or less. If the upper limit is exceeded, it is difficult to form spherical secondary particles, which may adversely affect the powder packing property or greatly reduce the specific surface area, and therefore the battery performance such as output characteristics may be likely to decrease. Conversely, if the lower limit is exceeded, problems such as poor reversibility of charge and discharge may occur due to underdeveloped crystals.
The average primary particle diameter is measured by observation using a scanning electron microscope (SEM). Specifically, in a photograph at a magnification of 10,000 times, the longest intercept value of a horizontal line at the left and right boundaries of a primary particle is determined for any 50 primary particles, and the average value is calculated.

The BET specific surface area of the positive electrode active material is preferably 0.1 ^m2 /g or more, more preferably 0.2 ^m2 /g or more, and even more preferably ^0.3 m2/g or more, and the upper limit is preferably ⁵⁰ m2/g or less, more preferably ⁴⁰ m2/g or less, and even more preferably 30 ^m2 /g or less. If the BET specific surface area is smaller than this range, the battery performance is likely to decrease, and if it is larger, it is difficult to increase the tap density, and problems may easily occur in the processability when forming the positive electrode active material layer.
The BET specific surface area is defined as a value measured by a nitrogen adsorption BET single-point method using a gas flow method, using a surface area meter (e.g., a fully automatic surface area measuring device manufactured by Ohkura Riken Co., Ltd.) after pre-drying a sample at 150° C. for 30 minutes under a nitrogen flow and then using a nitrogen/helium mixed gas accurately adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3.

When the secondary battery of the present disclosure is used as a large lithium-ion secondary battery for hybrid vehicles or distributed power sources, high output is required, so it is preferable that the particles of the positive electrode active material are mainly secondary particles. It is preferable that the particles of the positive electrode active material have an average secondary particle diameter of 40 μm or less and contain 0.5 to 7.0 volume % of fine particles with an average primary particle diameter of 1 μm or less. By containing fine particles with an average primary particle diameter of 1 μm or less, the contact area with the electrolyte is increased, and lithium ions can be diffused more quickly between the electrode mixture and the electrolyte, resulting in improved output performance of the battery.

The manufacturing method of the positive electrode active material is a general method for manufacturing inorganic compounds.In particular, various methods can be considered for manufacturing spherical or elliptical active materials, for example, the raw material of transition metal is dissolved or crushed and dispersed in a solvent such as water, and the pH is adjusted while stirring to prepare spherical precursors, which are then dried as necessary, and then LiOH, _Li2CO3 , _{LiNO3 ,} or other Li sources are added and calcined at high temperature to obtain active materials.

For the manufacture of the positive electrode, the positive electrode active material may be used alone, or two or more different compositions may be used in any combination or ratio. In this case, preferred combinations include a combination of _LiCoO2 and _a ternary system such as _{LiNi0.33Co0.33Mn0.33O2} , a combination of _LiCoO2 and _LiMn2O4 or a combination of LiFePO4 and _LiCoO2 or a combination of LiFePO4 _{and LiFePO2} or a combination of _LiFePO4 and _LiFePO2 or a combination of LiFePO4 and LiFePO2.

The content of the positive electrode active material is preferably 50 to 99.5% by mass of the positive electrode mixture, more preferably 80 to 99% by mass, in terms of high battery capacity. The content in the positive electrode active material layer is preferably 80% by mass or more, more preferably 82% by mass or more, and particularly preferably 84% by mass or more. The upper limit is preferably 99% by mass or less, more preferably 98% by mass or less. If the content of the positive electrode active material in the positive electrode active material layer is low, the electrical capacity may be insufficient. Conversely, if the content is too high, the strength of the positive electrode may be insufficient.

The negative electrode active material is not particularly limited, and examples thereof include lithium metal, artificial graphite, graphite carbon fiber, resin-sintered carbon, pyrolytic vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-sintered carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, and carbonaceous materials such as non-graphitizable carbon, silicon-containing compounds such as silicon and silicon alloys, and Li ₄ Ti ₅ O ₁₂ , or a mixture of two or more types. Among these, those containing at least a carbonaceous material and silicon-containing compounds can be particularly preferably used.

The negative electrode active material used in this disclosure preferably contains silicon as a constituent element. By using a material that contains silicon as a constituent element, a high-capacity battery can be produced.

As the silicon-containing material, silicon particles, particles having a structure in which fine silicon particles are dispersed in a silicon-based compound, silicon oxide particles represented by the general formula SiOx (0.5≦x≦1.6), or a mixture of these are preferred. By using these, a negative electrode mixture for lithium ion secondary batteries with higher initial charge/discharge efficiency, high capacity, and excellent cycle characteristics can be obtained.

In this disclosure, silicon oxide is a general term for amorphous silicon oxide, and silicon oxide before disproportionation is represented by the general formula SiOx (0.5≦x≦1.6). x is preferably 0.8≦x<1.6, and more preferably 0.8≦x<1.3. This silicon oxide can be obtained, for example, by heating a mixture of silicon dioxide and metallic silicon to produce silicon monoxide gas, which is then cooled and precipitated.

Particles having a structure in which silicon particles are dispersed in a silicon-based compound can be obtained, for example, by firing a mixture of silicon particles and a silicon-based compound, or by heat treating silicon oxide particles before disproportionation, represented by the general formula SiOx, in an inert, non-oxidizing atmosphere such as argon at a temperature of 400°C or higher, preferably 800 to 1,100°C, to carry out a disproportionation reaction. The material obtained by the latter method is particularly suitable because the silicon crystallites are uniformly dispersed. The size of the silicon nanoparticles can be made 1 to 100 nm by the above-mentioned disproportionation reaction. Note that the silicon oxide in the particles having a structure in which silicon nanoparticles are dispersed in silicon oxide is preferably silicon dioxide. Note that it is possible to confirm that silicon nanoparticles (crystals) are dispersed in amorphous silicon oxide using a transmission electron microscope.

The physical properties of the silicon-containing particles can be appropriately selected depending on the desired composite particles. For example, the average particle size is preferably 0.1 to 50 μm, with the lower limit being more preferably 0.2 μm or more, and even more preferably 0.5 μm or more. The upper limit is more preferably 30 μm or less, and even more preferably 20 μm or less. The above average particle size is represented by the weight average particle size in particle size distribution measurement by laser diffraction method.

The BET specific surface area is preferably 0.5 to 100 m ² /g, and more preferably 1 to 20 m ² /g. If the BET specific surface area is 0.5 m ² /g or more, there is no risk of the adhesiveness decreasing when processed into an electrode, resulting in a decrease in battery characteristics. If the BET specific surface area is 100 m ² /g or less, the proportion of silicon dioxide on the particle surface becomes large, and there is no risk of the battery capacity decreasing when used as a negative electrode material for a lithium ion secondary battery.

By coating the silicon-containing particles with carbon, electrical conductivity is imparted, and battery characteristics are improved. Methods for imparting electrical conductivity include mixing with electrically conductive particles such as graphite, coating the surfaces of the silicon-containing particles with a carbon coating, and a combination of both. The carbon coating method is preferred, and chemical vapor deposition (CVD) is even more preferred.

The content of the negative electrode active material is preferably 40% by mass or more in the electrode mixture, more preferably 50% by mass or more, and particularly preferably 60% by mass or more, in order to increase the capacity of the resulting electrode mixture. The upper limit is preferably 99% by mass or less, more preferably 98% by mass or less.

The electrode mixture of the present disclosure preferably further contains a conductive assistant.
Any known conductive material can be used as the conductive assistant. Specific examples include metal materials such as copper and nickel, graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, and carbon materials such as needle coke, carbon nanotubes, fullerene, and amorphous carbon such as VGCF. These may be used alone or in any combination and ratio of two or more.

The conductive assistant is used in an amount of usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more in the electrode mixture, and usually 50% by mass or less, preferably 30% by mass or less, more preferably 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. Conversely, if the content is higher than this range, the battery capacity may decrease.

The electrode mixture of the present disclosure may further contain a thermoplastic resin. Examples of the thermoplastic resin include polyvinylidene fluoride, polypropylene, polyethylene, polystyrene, polyethylene terephthalate, and polyethylene oxide. One type may be used alone, or two or more types may be used in any combination and ratio.

The ratio of the thermoplastic resin to the electrode active material is usually 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.10% by mass or more, and usually 3.0% by mass or less, preferably 2.5% by mass or less, more preferably 2.0% by mass or less. Adding the thermoplastic resin can improve the mechanical strength of the electrode. If the ratio exceeds this range, the ratio of the electrode active material in the electrode mixture decreases, which may cause problems such as a decrease in battery capacity or an increase in resistance between active materials.

In the electrode mixture of the present disclosure, the content of the binder may be 0.1% by mass or more, preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and may be 50% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 10% by mass or less, particularly preferably 5% by mass or less, and most preferably 3% by mass or less. If the proportion of the binder is too low, the electrode mixture active material cannot be sufficiently held, and the mechanical strength of the electrode mixture sheet may be insufficient, which may deteriorate the battery performance such as cycle characteristics. On the other hand, if the proportion is too high, it may lead to a decrease in battery capacity and conductivity. Since the binder of the present disclosure has excellent binding strength, even if the content is small, the electrode active material can be sufficiently held.

In the electrode mixture of the present disclosure, the binder component preferably consists essentially of the PTFE composition, and more preferably consists essentially of the PTFE composition. The binder component consisting essentially of the PTFE composition means that the content of the PTFE composition in the binder component constituting the electrode mixture is 95.0% by mass or more relative to the binder component. The content of the PTFE composition is preferably 98.0% by mass or more relative to the binder component, more preferably 99.0% by mass or more, even more preferably 99.5% by mass or more, particularly preferably 99.9% by mass or more, and most preferably 99.95% by mass or more.

The electrode mixture of the present disclosure is preferably in sheet form.

The electrode mixture of the present disclosure can be suitably used as an electrode mixture for secondary batteries. In particular, the electrode mixture of the present disclosure is suitable for lithium ion secondary batteries. When used in secondary batteries, the electrode mixture of the present disclosure is usually used in the form of a sheet.

The electrode mixture sheet preferably has a thickness of 300 μm or less, more preferably 250 μm or less, even more preferably 200 μm or less, even more preferably 180 μm or less, and particularly preferably 150 μm or less, and preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more.

The following is an example of a specific method for producing an electrode mixture sheet containing an electrode mixture. The electrode mixture sheet can be obtained by a production method including a step (1) of mixing a raw material composition containing an electrode active material, a binder, and, if necessary, a conductive assistant, a step (2) of forming the raw material composition obtained by the step (1) into a bulk form, and a step (3) of rolling the bulk raw material composition obtained by the step (2) into a sheet form.

At the stage where the raw material composition is mixed in the above step (1), the raw material composition is simply a mixture of the electrode active material, binder, etc., and exists in a state without a fixed shape. Specific mixing methods include mixing methods using a W-type mixer, V-type mixer, drum-type mixer, ribbon mixer, conical screw-type mixer, single-shaft kneader, twin-shaft kneader, mix muller, stirring mixer, planetary mixer, etc.

In the above step (1), the binder mixing conditions are preferably 3000 rpm or less. Preferably, it is 10 rpm or more, more preferably 15 rpm or more, and even more preferably 20 rpm or more, and is preferably 2000 rpm or less, more preferably 1500 rpm or less, and even more preferably 1000 rpm or less. If it is below the above range, mixing will take a long time, which will affect productivity. If it is above the above range, fibrillation will proceed excessively, and the electrode mixture sheet may have poor strength and flexibility.

In the above step (2), forming into a bulk shape means forming the raw material composition into a single mass. Specific methods for forming into a bulk shape include extrusion molding, press molding, and the like. In addition, the term "bulk shape" does not specify a particular shape, and may refer to a state in which the raw material composition is in the form of a single mass, and includes shapes such as rods, sheets, spheres, and cubes.

Specific rolling methods in the above step (3) include rolling using a roll press, a flat plate press, a calendar roll machine, etc.

It is also preferable to have a step (4) after step (3) in which a larger load is applied to the obtained rolled sheet to roll it into an even thinner sheet. It is also preferable to repeat step (4). In this way, the rolled sheet is not thinned all at once, but is rolled little by little in stages, thereby improving flexibility. The number of times step (4) is performed is preferably from 2 to 10 times, and more preferably from 3 to 9 times. Specific rolling methods include, for example, a method in which two or more rolls are rotated and the rolled sheet is passed between them to process it into a thinner sheet.

In addition, from the viewpoint of adjusting the fibril diameter, it is also preferable to have a step (5) after step (3) or step (4) in which the rolled sheet is roughly crushed, then remolded into a bulk shape and rolled into a sheet shape. It is also preferable to repeat step (5). The number of times of step (5) is preferably 1 to 12 times, and more preferably 2 to 11 times.

Specific methods for roughly crushing the rolled sheet and forming it into a bulk shape in step (5) include folding the sheet, forming it into a rod or thin sheet shape, chipping, etc. In this disclosure, "rough crushing" means changing the shape of the rolled sheet obtained in step (3) or step (4) into a different shape in order to roll it into a sheet shape in the next step, and also includes the case where the rolled sheet is simply folded.

Furthermore, step (4) may be performed after step (5), or may be performed repeatedly. Furthermore, uniaxial or biaxial stretching may be performed in steps (2), (3), (4), and (5). Furthermore, the fibril diameter can be adjusted by the degree of crushing in step (5).

In the above steps (3), (4) or (5), the rolling ratio is preferably 10% or more, more preferably 20% or more, and is preferably 80% or less, more preferably 65% or less, and even more preferably 50% or less. If it is below the above range, the number of rolling times increases, which takes time and affects productivity. If it is above the above range, fibrillation may proceed excessively, resulting in an electrode mixture sheet with poor strength and flexibility. The rolling ratio here refers to the reduction rate of the thickness of the sample after processing relative to the thickness before rolling. The sample before rolling may be a bulk-shaped raw material composition or a sheet-shaped raw material composition. The thickness of the sample refers to the thickness in the direction in which a load is applied during rolling.

The electrode mixture sheet is
Step (a): mixing a powder component and a binder to form an electrode mixture;
Step (b): calendaring or extruding the electrode mix to produce a sheet;
The mixing in step (a) is
(a1) homogenizing the powder components and the binder to form a powder;
The electrode mixture can also be suitably produced by a production method comprising the step (a2) of mixing the powdered raw material mixture obtained in the step (a1) to prepare an electrode mixture.

For example, PTFE has two transition temperatures at about 19°C and about 30°C. Below 19°C, PTFE can be easily mixed while still maintaining its shape. However, above 19°C, the PTFE particles become loosely structured and more sensitive to mechanical shear. At temperatures above 30°C, a greater degree of fibrillation occurs.

For this reason, it is preferred that the homogenization of (a1) is carried out at a temperature below 19°C, preferably between 0°C and 19°C.
That is, in such (a1), it is preferable to mix and homogenize while suppressing fibrillation.
The subsequent mixing step (a2) is preferably carried out at a temperature of 30° C. or higher to promote fibrillation.

The above step (a2) is preferably carried out at a temperature of from 30°C to 150°C, more preferably from 35°C to 120°C, even more preferably from 40°C to 80°C.
In one embodiment, the calendaring or extrusion of step (b) above is carried out at a temperature between 30°C and 150°C, preferably between 35°C and 120°C, more preferably between 40°C and 100°C.

The mixing in the above step (a) is preferably carried out while applying a shear force.
Specific examples of the mixing method include mixing methods using a W-type mixer, a V-type mixer, a drum mixer, a ribbon mixer, a conical screw mixer, a single-shaft kneader, a twin-shaft kneader, a mix muller, a stirring mixer, a planetary mixer, a Henschel mixer, a high-speed mixer, or the like.

The mixing conditions may be appropriately set by the number of rotations and the mixing time. For example, the number of rotations is preferably 15,000 rpm or less. It is preferably 10 rpm or more, more preferably 50 rpm or more, and even more preferably 100 rpm or more, and is preferably 12,000 rpm or less, more preferably 10,000 rpm or less, and even more preferably 8,000 rpm or less. If it is below the above range, it will take a long time to mix, which will affect productivity. If it is above the above range, fibrillation will proceed excessively, and the electrode mixture sheet may have poor strength.
The step (a1) is preferably carried out with a weaker shear force than the step (a2).
Moreover, it is desirable to carry out the step (a1) for a shorter time than the step (a2).

In the above step (a2), it is preferable that the raw material composition does not contain a liquid solvent, but a small amount of lubricant may be used. That is, a lubricant may be added to the powdered raw material mixture obtained in the above step (a1) to prepare a paste.

The above-mentioned lubricants are not particularly limited, and examples thereof include water, ether compounds, alcohols, ionic liquids, carbonates, aliphatic hydrocarbons (low polarity solvents such as heptane and xylene), isoparaffinic hydrocarbon compounds, and petroleum fractions (gasoline (C4-C10), naphtha (C4-C11), kerosene/paraffin (C10-C16), and mixtures thereof).

The lubricant preferably has a water content of 1000 ppm or less.
A moisture content of 1000 ppm or less is preferable in terms of reducing deterioration of the electrochemical device, and the moisture content is more preferably 500 ppm or less.

When using the above lubricants, it is particularly preferable that they are low polarity solvents such as butyl butyrate or ether compounds.

When the above-mentioned lubricant is used, the amount thereof may be 5.0 to 35.0 parts by weight, preferably 10.0 to 30.0 parts by weight, and more preferably 15.0 to 25.0 parts by weight, based on the total weight of the composition used in step (a1).

The raw material composition preferably does not substantially contain a liquid medium. In the conventional electrode mixture forming method, a solvent in which a binder is dissolved is used to prepare a slurry in which powder, which is an electrode mixture component, is dispersed, and the electrode mixture sheet is prepared by applying and drying the slurry. In this case, a solvent that disperses or dissolves the binder is used. However, the solvents that can dissolve the binder resins that have been commonly used in the past are limited to specific solvents such as N-methylpyrrolidone. Since the solvents have high polarity and require a drying process, the use of the solvents results in steps and costs. In addition, these react with electrolytes such as electrolytic solutions and solid electrolytes, deteriorating the electrolyte, and the remaining components during slurry preparation or after drying may cause a decrease in battery performance. In addition, the binder resins that can be dissolved in low-polarity solvents such as heptane are very limited, and the flash point is low, making handling difficult.

By using a powder binder with low moisture content instead of a solvent when forming the electrode mixture sheet, a battery with less electrolyte deterioration can be manufactured. Furthermore, in the above manufacturing method, an electrode mixture sheet containing a binder with a fine fiber structure can be manufactured, and by not producing a slurry, the burden on the manufacturing process can be reduced.

Step (b) is calendering or extrusion. Calendering and extrusion can be performed by a known method. By this, it is possible to form the electrode mixture sheet into a shape.
The step (b) preferably includes the steps of: (b1) forming the electrode mixture obtained in the step (a) into a bulk form; and (b2) calendaring or extrusion molding the bulk form of the electrode mixture.

Forming into a bulk form means forming the electrode mixture into a single mass.
Specific methods for forming the material into a bulk form include extrusion molding, press molding, and the like.
The term "bulk" does not specify a particular shape, but may refer to a state in which the material is in the form of a single mass, and includes shapes such as rods, sheets, spheres, and cubes. The size of the mass is preferably such that the diameter or the smallest side of the cross section is 10,000 μm or more, more preferably 20,000 μm or more.

Specific examples of the calendaring or extrusion molding method in step (b2) include rolling the electrode mixture using a roll press, a calendar roll machine, or the like.

The above step (b) is preferably carried out at 30 to 150°C. As mentioned above, PTFE has a glass transition temperature around 30°C, and therefore easily fibrillates at temperatures above 30°C. Therefore, it is preferable to carry out step (b) at such a temperature.

Calendaring or extrusion applies shear forces, which fibrillate the PTFE and form it into a shape.

It is also preferable to have a step (c) after the step (b) in which a larger load is applied to the obtained rolled sheet to roll it into a thinner sheet. It is also preferable to repeat the step (c). In this way, the rolled sheet is not thinned at once, but is rolled little by little in stages, thereby improving flexibility.
The number of times of the step (c) is preferably from 2 to 10, and more preferably from 3 to 9.
A specific rolling method includes, for example, a method in which a rolled sheet is passed between two or more rotating rolls to process it into a thinner sheet.

In addition, from the viewpoint of adjusting the sheet strength, it is also preferable to have a step (d) after step (b) or step (c) in which the rolled sheet is roughly crushed, then remolded into a bulk shape and rolled into a sheet shape. It is also preferable to repeat step (d). The number of times of step (d) is preferably 1 to 12 times, and more preferably 2 to 11 times.

Specific methods for roughly crushing the rolled sheet and forming it into a bulk shape in step (d) include folding the rolled sheet, forming it into a rod or thin sheet shape, chipping, etc. In this disclosure, "rough crushing" means changing the shape of the rolled sheet obtained in step (b) or step (c) into a different shape in order to roll it into a sheet shape in the next step, and also includes the case where the rolled sheet is simply folded.

Furthermore, step (c) may be carried out after step (d), or may be carried out repeatedly.
Moreover, uniaxial or biaxial stretching may be carried out in the steps (a), (b), (c) and (d).
Furthermore, the sheet strength can also be adjusted by the degree of coarse crushing in step (d).

In the above steps (b), (c) or (d), the rolling ratio is preferably 10% or more, more preferably 20% or more, and is preferably 80% or less, more preferably 65% or less, and even more preferably 50% or less. If it is below the above range, the number of rolling times increases and it takes time, which affects productivity. If it is above the above range, fibrillation may proceed excessively, resulting in an electrode mixture sheet with poor strength and flexibility.
The rolling ratio here refers to the reduction rate of the thickness of the sample after rolling to the thickness before rolling. The sample before rolling may be a bulk raw material composition or a sheet-like raw material composition. The thickness of the sample refers to the thickness in the direction in which a load is applied during rolling.
The above steps (c) and (d) are preferably carried out at 30° C. or higher, more preferably 60° C. or higher, and preferably 150° C. or lower.

The electrode mixture sheet can be used as an electrode mixture sheet for a secondary battery. It can be used for either a negative electrode or a positive electrode. In particular, the electrode mixture sheet is suitable for a lithium ion secondary battery.

The present disclosure also provides an electrode comprising the above-described PTFE composition of the present disclosure or the binder of the present disclosure, an electrode active material, and a current collector. The electrode of the present disclosure can suppress gas generation inside the battery cell and deterioration of battery characteristics (e.g., decrease in capacity during high-temperature storage). In addition, the powder components of the battery are uniformly dispersed, and the electrode has excellent strength and flexibility. Furthermore, even with a small amount of binder, the electrode active material can be retained, so that more materials that improve battery characteristics, such as active materials and conductive additives, can be added.

The electrode of the present disclosure may include the electrode mixture of the present disclosure described above (preferably an electrode mixture sheet) and a current collector.

The electrodes of the present disclosure may be positive or negative electrodes.

The positive electrode is preferably composed of a current collector and an electrode mixture sheet containing the positive electrode active material. Examples of materials for the positive electrode current collector include metals such as aluminum, titanium, tantalum, stainless steel, and nickel, or metal materials such as alloys thereof; and carbon materials such as carbon cloth and carbon paper. Among these, metal materials, particularly aluminum or its alloys, are preferred.

The shape of the current collector may be metal foil, metal cylinder, metal coil, metal plate, expanded metal, punched metal, foam metal, etc. for metal materials, or carbon plate, carbon thin film, carbon cylinder, etc. for carbon materials. Of these, metal foil is preferred. The metal foil may be appropriately formed into a mesh shape. The thickness of the metal foil is optional, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and is usually 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the metal foil is thinner than this range, the strength required as a current collector may be insufficient. Conversely, if the metal foil is thicker than this range, handling may be impaired.

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

The positive electrode may be manufactured by a conventional method. For example, the electrode mixture sheet and the current collector may be laminated with an adhesive and then vacuum dried.

The density of the positive electrode mixture sheet is preferably 2.80 g/cm ³ or more, more preferably 3.00 g/cm ³ or more, and even more preferably 3.20 g/cm ³ or more, and is preferably 3.80 g/cm ³ or less, more preferably 3.75 g/cm ³ or less, and even more preferably 3.70 g/cm ³ or less. If the density exceeds this range, cracks may easily occur in the sheet. If the density is below this range, the conductivity between the active materials may decrease, increasing the battery resistance and making it difficult to obtain high output.

The thickness of the positive electrode is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the mixture layer minus the metal foil thickness of the current collector is preferably 10 μm or more, more preferably 20 μm or more, as a lower limit on one side of the current collector, and is also preferably 500 μm or less, more preferably 450 μm or less.

The negative electrode is preferably composed of a current collector and an electrode mixture sheet containing the negative electrode active material. Examples of materials for the negative electrode current collector include metals such as copper, nickel, titanium, tantalum, and stainless steel, or metal materials such as alloys thereof; and carbon materials such as carbon cloth and carbon paper. Among these, metal materials, particularly copper, nickel, or alloys thereof, are preferred.

The shape of the current collector may be metal foil, metal cylinder, metal coil, metal plate, expanded metal, punched metal, foam metal, etc. for metal materials, or carbon plate, carbon thin film, carbon cylinder, etc. for carbon materials. Of these, metal foil is preferred. The metal foil may be appropriately formed into a mesh shape. The thickness of the metal foil is optional, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and is usually 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the metal foil is thinner than this range, the strength required as a current collector may be insufficient. Conversely, if the metal foil is thicker than this range, handling may be impaired.

The negative electrode may be manufactured by a conventional method. For example, the electrode mixture sheet and the current collector may be laminated with an adhesive and then vacuum dried.

The density of the negative electrode mixture is preferably 1.3 g/cm ³ or more, more preferably 1.4 g/cm ³ or more, and even more preferably 1.5 g/cm ³ or more, and is preferably 2.0 g/cm ³ or less, more preferably 1.9 g/cm ³ or less, and even more preferably 1.8 g/cm ³ or less. If it exceeds this range, cracks may easily occur in the sheet. If it is below this range, the conductivity between the active materials decreases, which increases the battery resistance and may prevent high output from being obtained.

The thickness of the negative electrode is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the mixture layer minus the metal foil thickness of the current collector is preferably 10 μm or more, more preferably 20 μm or more, as a lower limit on one side of the current collector, and is preferably 500 μm or less, more preferably 450 μm or less.

The present disclosure also provides a secondary battery having the electrode of the present disclosure described above.

The secondary battery of the present disclosure may be a secondary battery that uses an electrolyte solution or may be a solid-state secondary battery.
In this specification, the solid-state secondary battery may be a secondary battery containing a solid electrolyte, may be a semi-solid secondary battery containing a solid electrolyte and a liquid component as the electrolyte, or may be an all-solid-state secondary battery containing only a solid electrolyte as the electrolyte.

Secondary batteries using the above electrolyte can use electrolytes, separators, etc. that are used in known secondary batteries. These are described in detail below.

As the electrolyte, a non-aqueous electrolyte is preferably used. As the non-aqueous electrolyte, a solution in which a known electrolyte salt is dissolved in a known organic solvent for dissolving electrolyte salts can be used.

The organic solvent for dissolving the electrolyte salt is not particularly limited, but one or more of the following can be used: known hydrocarbon solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; and fluorine-based solvents such as fluoroethylene carbonate, fluoroether, and fluorinated carbonate.

Examples of electrolyte salts include _LiClO4 , _LiAsF6 , _LiBF4 , _LiPF6 , LiN( _SO2CF3 ) ₂ , _and LiN( _SO2C2F5 ) _{2. In} terms of good _cycle characteristics _{, LiPF6} , _LiBF4 , LiN( _SO2CF3 ) ₂ , LiN( _SO2C2F5 ) ₂ , or _combinations thereof are particularly preferred _.

The concentration of the electrolyte salt is preferably 0.8 mol/L or more, and more preferably 1.0 mol/L or more. The upper limit depends on the organic solvent used to dissolve the electrolyte salt, but is usually 1.5 mol/L.

The secondary battery using the above-mentioned electrolyte preferably further comprises a separator. The material and shape of the separator are not particularly limited as long as they are stable to the electrolyte and have excellent liquid retention, and any known separator can be used. In particular, it is preferable to use a material formed of a material stable to the electrolyte, such as resin, glass fiber, or inorganic material, and to use a porous sheet or nonwoven fabric-like material with excellent liquid retention.

As materials for the resin and glass fiber separator, for example, polyolefins such as polyethylene and polypropylene, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, glass filters, etc. can be used. These materials may be used alone or in any combination and ratio, such as polypropylene/polyethylene two-layer film and polypropylene/polyethylene/polypropylene three-layer film. Among them, the separator is preferably a porous sheet or nonwoven fabric made of polyolefins such as polyethylene and polypropylene, because of its good electrolyte permeability and shutdown effect.

The thickness of the separator is arbitrary, but is usually 1 μm or more, preferably 5 μm or more, more preferably 8 μm or more, and is usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less. If the separator is thinner than the above range, the insulating properties and mechanical strength may decrease. Furthermore, if the separator is thicker than the above range, not only may the battery performance such as rate characteristics decrease, but the energy density of the electrolyte battery as a whole may decrease.

On the other hand, inorganic materials include, for example, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate, and are used in particulate or fibrous form.

As for the form, a thin film shape such as a nonwoven fabric, a woven fabric, or a microporous film is used. In the thin film shape, a film with a pore size of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferably used. In addition to the above independent thin film shape, a separator can be used in which a composite porous layer containing the above inorganic particles is formed on the surface layer of the positive electrode and/or negative electrode using a resin binder. For example, a porous layer can be formed on both sides of the positive electrode using alumina particles with a 90% particle size of less than 1 μm and a fluororesin as a binder.

The material of the exterior case is not particularly limited as long as it is a substance that is stable against the electrolyte used. Specifically, metals such as nickel-plated steel sheet, stainless steel, aluminum or aluminum alloy, magnesium alloy, etc., or a laminate film of resin and aluminum foil (laminate film) can be used. From the viewpoint of weight reduction, metals such as aluminum or aluminum alloy, and laminate films are preferably used.

In the case of an exterior case using metals, the metals are welded together by laser welding, resistance welding, or ultrasonic welding to form a sealed structure, or the metals are used via a resin gasket to form a crimped structure. In the case of an exterior case using the above-mentioned laminate film, the resin layers are heat-sealed together to form a sealed structure. In order to improve the sealing properties, a resin different from the resin used in the laminate film may be interposed between the resin layers. In particular, when the resin layers are heat-sealed via a current collecting terminal to form a sealed structure, a bond is formed between the metal and the resin, so a resin having a polar group or a modified resin into which a polar group has been introduced is preferably used as the interposed resin.

The shape of the secondary battery using the above electrolyte is arbitrary, and examples of such shapes include cylindrical, square, laminated, coin, large, etc. The shapes and configurations of the positive electrode, negative electrode, and separator can be changed according to the shape of each battery.

The solid-state secondary battery is preferably an all-solid-state secondary battery. The solid-state secondary battery is preferably a lithium ion battery, and is also preferably a sulfide-based all-solid-state secondary battery.
The solid secondary battery preferably includes a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode.
In the solid secondary battery, the binder of the present disclosure may be used in the electrode layer or in the solid electrolyte layer.
A solid secondary battery mix (preferably a mix sheet) containing the binder and solid electrolyte of the present disclosure, and a solid electrolyte layer (preferably a solid electrolyte layer sheet) containing the binder and solid electrolyte of the present disclosure are also suitable aspects of the present disclosure.

The solid electrolyte used in the solid secondary battery mixture may be a sulfide-based solid electrolyte or an oxide-based solid electrolyte. In particular, when a sulfide-based solid electrolyte is used, it has the advantage of being flexible.

The sulfide-based solid electrolyte is not particularly limited, and examples thereof 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 Any one selected from -Li ₄ GeS ₄ , Li _3.4 P _0.6 Si _0.4 S ₄ , Li _3.25 P _0.25 Ge _0.76 S ₄ , Li _4-x Ge _1-x P _x S ₄ (x = 0.6 to 0.8), Li 4+ _y Ge _1-y Ga _y S ₄ (y = 0.2 to 0.3), LiPSCl, LiCl, Li 7 _-x-2y PS _6-x-y Cl _x (0.8≦x≦1.7, 0<y≦-0.25x+0.5), Li ₁₀ SnP ₂ S ₁₂ , etc., or a mixture of two or more kinds can be used.

The sulfide-based solid electrolyte preferably contains lithium. Sulfide-based solid electrolytes containing lithium are used in solid-state batteries that use lithium ions as a carrier, and are particularly preferred in terms of electrochemical devices with high energy density.

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

Specific examples of the compound include Li _xa La _ya TiO ₃ [xa=0.3 to 0.7, ya=0.3 to 0.7] (LLT), Li _xb La _yb Zr _zb M ^bb _mb O _nb (M ^bb is at least one element selected from the group consisting of Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, 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), and Li _xc B _yc M ^cc _zc O _nc (M ^cc is at least one element selected from C, S, Al, Si, Ga, Ge, In, and Sn, 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 of 0 or more and 0.1 or less, M ^ee represents a divalent metal atom, and D ^ee represents a halogen atom or a combination of two or more halogen atoms. ), Li _xf Si _yf O _zf (1≦xf≦5, 0<yf≦3, 1≦zf≦10), Li _xg S _yg O _zg (1≦xg≦3, 0<yg≦2, 1≦zg≦10), Li ₃ BO ₃ -Li ₂ SO ₄ , Li ₂ 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 (w is w<1), Li _3.5 Zn _{0.25 GeO 4 having a LISICON (lithium super ionic conductor) type crystal structure, La 3.5 Zn 0.25} GeO ₄ having a perovskite type crystal structure, _{0.51Li0.34TiO2.94} , _{La0.55Li0.35TiO3} , _LiTi2P3O12 having _a NASICON (sodium super ionic conductor) type crystal structure, Li1 _+xh+yh (Al _, Ga) _xh (Ti,Ge) _{2- xhSiyhP3 - yhO12 (} where 0≦xh≦ ₁ , ₀ ≦yh≦1 ₎ , _Li7La3Zr2O12 ( _LLZ ) having _{a garnet} type crystal structure, and the like. For example, _{Li6.24La3Zr2Al0.24O11.98 , Li6.25Al0.25La3Zr2O12 , Li6.6La3Zr1.6Ta0.4O12 ,} Li6.75La3Zr1.75Nb0.25O12, _etc. , in _which LLZ is partially substituted with Al _{, Li6.6La3Zr1.6Ta0.4O12} , Li6.75La3Zr1.75Nb0.25O12, _etc. , in which _{LLZ is partially} substituted with Ta, _etc. , can be mentioned. In addition, LLZ-based ceramic materials in which _at least _{one element} of Mg (magnesium) and A (A is at _{least one} element selected from the group consisting of Ca (calcium), Sr (strontium), and Ba (barium)) is substituted for LLZ can be mentioned. In addition, phosphorus compounds containing Li, P, and O are also desirable. Examples of the lithium phosphate include lithium phosphate (Li ₃ PO ₄ ), LiPON in which part of the oxygen in lithium phosphate is replaced with nitrogen, LiPOD ¹ (D ¹ is at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc.), etc. Also preferably usable is LiA ¹ ON (A ¹ is at least one selected from Si, B, Ge, Al, C, Ga, etc.). Specific examples include Li ₂ O-Al ₂ O ₃ -SiO ₂ -P ₂ O ₅ -TiO ₂ -GeO ₂ , Li ₂ O-Al ₂ O ₃ -SiO ₂ -P ₂ O ₅ -TiO ₂ , etc.

The oxide-based solid electrolyte preferably contains lithium. The oxide-based solid electrolyte containing lithium is used in solid-state batteries that use lithium ions as a carrier, and is particularly preferred in that it is an electrochemical device having a high energy density.

The oxide-based solid electrolyte is preferably an oxide having a crystalline structure. Oxides having a crystalline structure are particularly preferred in terms of good Li ion conductivity. Examples of oxides having a crystalline structure include perovskite type ( _{La0.51Li0.34TiO2.94 ,} etc.), NASICON type ( _{Li1.3Al0.3Ti1.7} ( _PO4 ) _{3 ,} etc. ₎ , and _garnet type ( _Li7La3Zr2O12 ( _LLZ ) _, etc.). Among them, NASICON type is preferred _.

The volume average particle diameter of the oxide-based solid electrolyte is not particularly limited, but is preferably 0.01 μm or more, and more preferably 0.03 μm or more. The upper limit is preferably 100 μm or less, and more preferably 50 μm or less. The average particle diameter of the oxide-based solid electrolyte particles is measured by the following procedure. The oxide-based solid electrolyte particles are diluted and adjusted to a 1 mass % dispersion in a 20 ml sample bottle using water (heptane in the case of a substance unstable in water). The diluted dispersion sample is irradiated with 1 kHz ultrasound for 10 minutes and used for testing immediately thereafter. Using this dispersion sample, data is taken 50 times using a laser diffraction/scattering particle size distribution measuring device LA-920 (manufactured by HORIBA) at a temperature of 25°C using a measurement quartz cell to obtain the volume average particle diameter. For other detailed conditions, etc., refer to the description of JIS Z8828:2013 "Particle size analysis - dynamic light scattering method" as necessary. Five samples are prepared for each level and the average value is used.

The solid secondary battery may include a separator between the positive electrode and the negative electrode. Examples of the separator 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 solid secondary battery may further include a battery case. The shape of the battery case is not particularly limited as long as it can accommodate the above-mentioned positive electrode, negative electrode, solid electrolyte layer, etc., but specific examples include a cylindrical type, a square type, a coin type, a laminate type, etc.

The above-mentioned solid-state secondary battery can be manufactured, for example, by stacking a positive electrode, a solid electrolyte layer sheet, and a negative electrode in that order and pressing them.

Although the embodiments have been described above, it will be understood that various changes in form and details are possible without departing from the spirit and scope of the claims.

The following examples will explain the present disclosure in more detail, but the present disclosure is not limited to these examples.

Various physical properties were measured using the following methods.

<Average primary particle size>
The PTFE aqueous dispersion is diluted with water until the solid content becomes 0.15% by mass, and the transmittance of the 550 nm projection light to the unit length of the obtained diluted latex and the number-based length average primary particle diameter determined by measuring the unidirectional diameter by a transmission electron microscope photograph are measured, and a calibration curve is prepared. Using this calibration curve, the average primary particle diameter is determined from the measured transmittance of the 550 nm projection light of each sample.
The average primary particle size was also measured by dynamic light scattering. In the dynamic light scattering method, a PTFE aqueous dispersion with a solid content concentration adjusted to about 1.0 mass% was prepared, and measurements were taken at 25°C and 70 times in total using an ELSZ-1000S (manufactured by Otsuka Electronics Co., Ltd.). The refractive index of the solvent (water) was 1.3328, and the viscosity of the solvent (water) was 0.8878 mPa·s.

<Polymer solids concentration>
1 g of the aqueous PTFE dispersion was dried in a blower dryer at 150° C. for 60 minutes, and the ratio of the mass of the heating residue to the mass (1 g) of the aqueous dispersion was expressed as a percentage and used.

<Melt fluidity>
According to ASTM D1238, the mass (g/10 min) of the polymer flowing out from a nozzle with an inner diameter of 2.095 mm and a length of 8 mm per 10 min was measured at 372° C. under a load of 5 kg using a melt indexer. A polymer having an MFR of 0.25 g/10 min or more was deemed to have melt fluidity, and a polymer having an MFR of less than 0.25 g/10 min was deemed not to have melt fluidity.

<Modifying Monomer Content>
The HFP content was determined by producing a thin film disk by press-molding the PTFE powder or composition, measuring the infrared absorbance of the thin film disk by FT-IR, and multiplying the ratio of the absorbance at 982 cm ^-1 to the absorbance at 935 cm ^-1 by 0.3.

<Standard specific gravity (SSG)>
Using samples molded in accordance with ASTM D4895 89, the measurement was performed by the water displacement method in accordance with ASTM D 792.

<Endothermic peak temperature>
The endothermic peak temperatures were determined as the temperatures corresponding to the respective minimum points in the regions (A) and (B) of the heat of fusion curve when a PTFE powder or composition that had not been heated to a temperature of 300° C. or higher was heated at a rate of 10° C./min using a differential scanning calorimeter [DSC].

<Endothermic peak intensity>
The minimum point of the heat of fusion curve in the measurement of the endothermic peak temperature was defined as (a), and the intersection point (b) between a line passing through the minimum point (a) and perpendicular to the horizontal axis (temperature) and a line connecting the points 300°C and 360°C on the heat of fusion curve was defined as (b). The distance between the minimum point (a) and the intersection point (b) was defined as the endothermic peak intensity.

<Endothermic peak intensity ratio>
The value obtained by dividing the endothermic peak intensity in the region (A) by the endothermic peak intensity in the region (B) was used.

<Can the paste be extruded?>
60 g of PTFE powder or composition and 12.3 g of hydrocarbon oil (trade name: Isopar G (registered trademark), manufactured by ExxonMobil Corporation) as an extrusion aid were mixed in a polyethylene container for 3 minutes. The mixture was filled into the cylinder of an extruder at room temperature (25±2°C), and a load of 0.47 MPa was applied to the piston inserted into the cylinder and held for 1 minute. Next, the mixture was extruded from the orifice at a ram speed of 20 mm/min. The ratio of the cross-sectional area of the cylinder to the cross-sectional area of the orifice was 200. At this time, the bead was evaluated as not extrudable if it could not be continuously extruded because it was torn, and the bead was evaluated as extrudable if it could be continuously extruded without being torn.

<Possibility of extension>
50 g of PTFE powder or composition and 10.25 g of hydrocarbon oil (trade name: Isopar E (registered trademark), manufactured by ExxonMobil Corporation) as an extrusion aid were mixed in a polyethylene container for 3 minutes. The mixture was filled into the cylinder of an extruder at room temperature (25±2° C.), and a load of 0.47 MPa was applied to the piston inserted into the cylinder and held for 1 minute. The mixture was then extruded from an orifice at a ram speed of 18 mm/min. The ratio of the cross-sectional area of the cylinder to the cross-sectional area of the orifice was 100.

The bead obtained by the above paste extrusion was dried at 230°C for 30 minutes to remove the lubricant. After drying, the bead was cut to an appropriate length and placed in an oven heated to 300°C. In the oven, it was stretched at a stretching speed of 100%/sec until it reached 25 times its length before the stretching test. Those that did not break during stretching were evaluated as being stretchable, and those that did break were evaluated as not being stretchable.

<Moisture content>
About 20 g of PTFE powder or composition was heated at 150° C. for 2 hours, the mass was measured before and after, and the mass was calculated according to the following formula. A sample was taken three times, and the average was calculated for each, and the average value was adopted.
Moisture content (mass%)=[(mass (g) of PTFE powder or composition before heating)−(mass (g) of PTFE powder or composition after heating)]/(mass (g) of PTFE powder or composition before heating)×100

A white solid A was obtained by the method described in Synthesis Example 1 of WO 2021/045228.

Synthesis Example 1
A 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature control jacket was charged with 3580 g of deionized water, 100 g of paraffin wax, and 5.4 g of white solid A, and the inside of the autoclave was replaced with nitrogen gas while heating to 70 ° C. to remove oxygen. After 0.06 g of HFP was injected with TFE, TFE was injected to make the system pressure 0.78 MPaG, and the system temperature was maintained at 70 ° C. while stirring. Next, an aqueous solution of 15.4 mg of ammonium persulfate dissolved in 20 g of water was injected 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 430 g of TFE was consumed from the start of polymerization, an aqueous solution of 18.0 mg of hydroquinone dissolved in 20 g of water as a radical scavenger was injected with TFE. The polymerization continued thereafter, and when the amount of polymerization of TFE reached about 1540 g from the start of polymerization, stirring and the supply of TFE were stopped, and the gas in the system was immediately released to normal pressure, and the polymerization reaction was terminated. The aqueous dispersion was taken out and cooled, and the paraffin wax was separated to obtain an aqueous PTFE dispersion. The average primary particle size of the obtained aqueous PTFE dispersion was 246 nm, and the solid content concentration was 29.8 mass%.

Production Example 1
The PTFE aqueous dispersion obtained in Synthesis Example 1 was diluted to a solids concentration of 13% by mass, and the PTFE was coagulated while stirring in a container, and then the water was separated by filtration to obtain a wet PTFE powder.
The obtained PTFE wet powder was placed on a stainless steel mesh tray, and the mesh tray was heat-treated in a hot air circulating electric furnace at 180° C. After 18 hours, the mesh tray was removed and air-cooled to obtain a PTFE powder.
The resulting PTFE powder did not exhibit melt flowability, and had an HFP content of 0.027 mass % and an SSG of 2.150.

Synthesis Example 2
A 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature control jacket was charged with 3480 g of deionized water, 100 g of paraffin wax, and 5.3 g of white solid A, and the inside of the autoclave was replaced with nitrogen gas while heating to 70 ° C. to remove oxygen. TFE was injected to make the system pressure 0.78 MPaG, and the system temperature was kept at 70 ° C. while stirring. Next, an aqueous solution of 15.0 mg of ammonium persulfate dissolved in 20 g of water was injected 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 400 g of TFE was consumed from the start of polymerization, an aqueous solution of 18.0 mg of hydroquinone dissolved in 20 g of water as a radical scavenger was injected with TFE. The polymerization continued thereafter, and when the amount of polymerization of TFE reached about 1200 g from the start of polymerization, stirring and the supply of TFE were stopped, and the gas in the system was immediately released to normal pressure, and the polymerization reaction was terminated. The aqueous dispersion was taken out and cooled, and the paraffin wax was separated to obtain an aqueous PTFE dispersion. The average primary particle size of the obtained aqueous PTFE dispersion was 310 nm, and the solid content concentration was 25.3 mass%.

Production Example 2
The PTFE aqueous dispersion obtained in Synthesis Example 2 was diluted to a solids concentration of 13% by mass, and the PTFE was coagulated while stirring in a container, and then the water was separated by filtration to obtain a wet PTFE powder.
The obtained PTFE wet powder was placed on a stainless steel mesh tray, and the mesh tray was heat-treated in a hot air circulating electric furnace at 180° C. After 20 hours, the mesh tray was removed and air-cooled to obtain a PTFE powder.
The resulting PTFE powder did not exhibit melt flowability and had an SSG of 2.156.

Synthesis Example 3
An aqueous dispersion of low molecular weight PTFE was obtained by the method described in Example 7 of WO 2009/020187. The average primary particle size of the obtained aqueous dispersion of low molecular weight PTFE was 180 nm, and the solid content concentration was 20.0 mass%.

Production Example 3
The aqueous dispersion of low molecular weight PTFE obtained in Synthesis Example 3 was coagulated by applying a strong mechanical shear force, and dried for 18 hours in a hot air circulation dryer at 160°C to obtain a low molecular weight PTFE powder.
The obtained low molecular weight PTFE powder exhibited melt flowability.

Preparation Example 1
The PTFE aqueous dispersion obtained in Synthesis Example 1 and the low molecular weight PTFE aqueous dispersion obtained in Synthesis Example 3 were mixed at a solid content mass ratio (Synthesis Example 1:Synthesis Example 3) of 90:10, then diluted to a solid content concentration of 13 mass%, vigorously stirred in a container equipped with a stirrer to solidify, and filtered from the water to obtain a PTFE wet powder. The obtained PTFE wet powder was placed on a stainless steel mesh tray (placement amount: 2.0 g/cm ² ), and the mesh tray was heat-treated in a hot air circulation type electric furnace at 180° C. After 18 hours, the mesh tray was removed and air-cooled, and then a PTFE composition 1 was obtained.
The resulting PTFE composition 1 had an HFP content of 0.024% by mass, an SSG of 2.184, endothermic peak temperatures of 328° C. and 343° C., an endothermic peak intensity ratio of 0.36, paste extrudability, stretchability, and a moisture content of 0.001% by mass.

Preparation Example 2
PTFE composition 2 was obtained in the same manner as in Preparation Example 1, except that the PTFE aqueous dispersion used was changed from Synthesis Example 1 to Synthesis Example 2, and the solid content mass ratio (Synthesis Example 2:Synthesis Example 3) was 98:2.
The resulting PTFE composition 2 had an SSG of 2.168. The endothermic peak temperatures were 328° C. and 344° C., the endothermic peak intensity ratio was 0.08, the paste was extrudable, and the stretchable material was capable of being stretched, and the moisture content was 0.000% by mass.

Preparation Example 3
A PTFE composition 3 was obtained in the same manner as in Preparation Example 2, except that the solid content mass ratio (Synthesis Example 2:Synthesis Example 3) was changed to 90:10.
The resulting PTFE composition 3 had an SSG of 2.194. The endothermic peak temperatures were 328° C. and 344° C., the endothermic peak intensity ratio was 0.27, the paste was extrudable, and the stretchable composition had a moisture content of 0.001% by mass.

Preparation Example 4
A PTFE composition 4 was obtained in the same manner as in Preparation Example 2, except that the solid content mass ratio (Synthesis Example 2:Synthesis Example 3) was changed to 75:25.
The resulting PTFE composition 4 had an SSG of 2.222. The endothermic peak temperatures were 327° C. and 343° C., the endothermic peak intensity ratio was 0.89, the paste was extrudable, and the stretchable material was capable of being stretched, and the moisture content was 0.001% by mass.

Preparation Example 5
A PTFE composition 5 was obtained in the same manner as in Preparation Example 2, except that the solid content mass ratio (Synthesis Example 2:Synthesis Example 3) was changed to 25:75.
The SSG of the obtained PTFE composition 5 was 2.274. The endothermic peak temperatures were 327° C. and 340° C., the endothermic peak intensity ratio was 5.3, the paste could not be extruded, the stretching was not possible, and the moisture content was 0.002% by mass.

Preparation Example 6
PTFE composition 6 was obtained in the same manner as in Preparation Example 3, except that the mesh tray was replaced with a flat tray (a tray with no air permeability at the bottom and sides), the drying temperature was changed from 180°C to 145°C, and the drying time was changed from 18 hours to 5 hours.
The resulting PTFE composition 6 had an SSG of 2.194. The endothermic peak temperatures were 328° C. and 344° C., the endothermic peak intensity ratio was 0.27, the paste was extrudable, and the moisture content was 0.156% by mass.

Preparation Example 7
The PTFE wet powder obtained in Production Example 2 was placed on a flat tray (a tray with no air permeability on the bottom and sides) and the flat tray was heat-treated in a hot air circulating electric furnace at 180° C. After 5 hours, the flat tray was removed and cooled in air, and then PTFE powder 7 was obtained.
The resulting PTFE powder 7 had an SSG of 2.156, an endothermic peak temperature of 345° C., was paste extrudable, and had a moisture content of 0.126% by mass.

Each of the PTFE compositions obtained above was evaluated using the following methods.

Evaluation of Electrolyte-Containing Batteries Preparation of mixture sheets and evaluation of the sheets and batteries of Examples 1 to 6 and Comparative Example 1 were carried out according to the following procedures.
<Preparation of Positive Electrode Mixture Sheet>
The active material and the conductive assistant were weighed, and the materials were put into a V-type mixer and mixed at 37 rpm for 10 minutes to obtain a mixture of the active material and the conductive assistant. Then, the weighed binder (PTFE powder or composition) was put into the mixture and thoroughly cooled in a thermostatic bath at 5 ° C. The mixture of the active material, the conductive assistant and the binder was put into a Henschel mixer and homogenized by processing at 1000 rpm for 3 minutes. Then, the mixture was sufficiently heated in a thermostatic bath at 50 ° C., and then processed for 4 minutes (32 rpm, heater 50 ° C., pressure 0.5 MPa) in a pressure kneader (D1-5: manufactured by Nippon Spindle Co., Ltd.) to promote fibrillation and obtain a bulk-like electrode mixture with cohesive properties. Then, the bulk-like electrode mixture was put into a Henschel mixer for re-pulverization, and the electrode mixture was obtained by processing at 300 rpm for 1 minute.
The electrode mixture was put into parallel metal rolls (temperature: 80° C., rotation speed: 1 m/min) and rolled to obtain an electrode mixture sheet. The obtained rolled sheet was again roughly crushed by folding in half, and the electrode mixture was put into metal rolls (temperature: 80° C., rotation speed: 1 m/min) and rolled to obtain an electrode mixture sheet with greater strength.
Thereafter, the electrode mixture sheet was placed in a roll press machine and the gap was adjusted to a final thickness of 90 μm.
Table 1 shows the material types and compositions.

ｄｅｎｋａ Ｌｉ－４００：デンカ社製カーボンブラック

Denka Li-400: Carbon black manufactured by Denka

<Evaluation of powder cohesiveness>
The electrode mixture before being put into the metal rolls arranged in parallel was used to sieve the mixture with a mesh size of 0.18 mm (JIS-Z8801). The mixture was sieved for 30 seconds, and when aggregates remained on the mesh, it was marked with "x", and when all of the aggregates passed through, it was marked with "o". The results are shown in Table 2.

<Measurement of strength of positive electrode mixture sheet>
The positive electrode mixture sheet was cut out to prepare a strip-shaped test piece having a width of 4 mm. A tensile tester (Shimadzu Corporation AGS-100NX) was used to measure at a speed of 100 mm/min. The distance between the chucks was 40 mm. Displacement was applied until breakage, and the maximum stress of the measured results was taken as the strength of each sample. Tests were performed with N=8, the average value was calculated, and the following three-level ranking was performed.
◯: 0.2 N/ ^mm2 or more △: 0.1 N/ ^mm2 or more ×: 0.1 N/ ^mm2 or less The coefficient of variation was also calculated to evaluate the variation.
The results are shown in Table 2.

<Flexibility evaluation of positive electrode mixture sheet (bending test)>
The prepared electrode mixture sheet was cut into a width of 4 cm and a length of 10 cm to prepare test pieces. Next, these test pieces were wrapped around a Φ2 mm round bar, and then the test pieces were visually inspected to confirm the presence or absence of damage such as scratches or cracks. No damage such as scratches or cracks was observed in Examples 1 to 6.

<Preparation of Positive Electrode>
The positive electrode mixture sheet was adhered to an aluminum foil having a thickness of 20 μm as follows.
The adhesive used was a slurry in which polyvinylidene fluoride (PVDF) was dissolved in N-methylpyrrolidone (NMP) and carbon black was dispersed in a ratio of 80: 20. The adhesive was applied to an aluminum foil and dried on a hot plate at 120°C for 15 minutes to form a current collector with an adhesive layer.
Thereafter, the positive electrode mixture sheet was placed on a current collector with an adhesive layer, and the positive electrode mixture sheet and the current collector were bonded together using a roll press machine heated to 100° C., cut into a desired size, and tabbed to form a positive electrode.

<Preparation of negative electrode>
To 98 parts by mass of a carbonaceous material (graphite), 1 part by mass of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose: 1% by mass) and 1 part by mass of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber: 50% by mass) were added as a thickener and binder, and mixed in a disperser to form a slurry. The obtained slurry was applied to a copper foil having a thickness of 10 μm, dried, and rolled in a press, cut to a desired size, and tabbed to form a negative electrode.

<Preparation of electrolyte>
As an organic solvent, a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC=30:70 (volume ratio)) was weighed into a sample bottle, and fluoroethylene carbonate (FEC) and vinylene carbonate (VC) were dissolved in the sample bottle at 1 mass% each to prepare a mixed solution. LiPF ₆ salt was mixed with this mixed solution at 23° C. so that the concentration in the electrolyte was 1.1 mol/L to obtain a nonaqueous electrolyte solution.

<Preparation of Aluminum Laminate Cell>
The positive electrode was opposed to the negative electrode via a 20 μm-thick microporous polyethylene film (separator), and the nonaqueous electrolyte obtained above was injected thereinto. After the nonaqueous electrolyte sufficiently permeated the separator and the like, the battery was sealed, precharged, and aged to prepare a lithium ion secondary battery.

<Evaluation of storage characteristics (remaining capacity rate, amount of gas generated)>
The lithium ion secondary battery produced above was charged at a constant current-constant voltage (hereinafter referred to as CC/CV charging) (0.1 C cut) at 25° C. up to 4.3 V at a current equivalent to 0.33 C, and then discharged to 3 V at a constant current of 0.33 C. This was counted as one cycle, and the initial discharge capacity was calculated from the discharge capacity at the third cycle.
The battery after the evaluation of the initial discharge capacity was again CC/CV charged (0.1C cut) to 4.3V at 25°C, and the volume of the battery was determined. After the volume of the battery was determined, the battery was stored at high temperature at 60°C for 30 days. After the high temperature storage, the battery was sufficiently cooled and then the volume of the battery was determined at 25°C, and the amount of gas generated was calculated from the difference in the volume of the battery before and after the storage test. The amount of gas generated was compared, with the amount of gas generated in Comparative Example 1 set to 100.
After determining the amount of gas generated, the battery was discharged at 0.33 C to 3 V at 25° C., and the remaining capacity was determined.
The ratio of the remaining capacity after high-temperature storage to the initial discharge capacity was calculated and this was taken as the remaining capacity rate (%).
(Residual capacity) / (Initial discharge capacity) x 100 = Remaining capacity rate (%)
The results are shown in Table 2.

Evaluation of Positive Electrode Mixture Sheets for Solid State Batteries Preparation and evaluation of the mixture sheets of Examples 7 to 12 and Comparative Example 2 were carried out according to the following procedures. The preparation and evaluation were carried out in an argon atmosphere.
<Preparation of Positive Electrode Mixture Sheet>
The active material and the conductive assistant were weighed, and the materials were put into a V-type mixer and mixed at 37 rpm for 10 minutes to obtain a mixture of the active material and the conductive assistant. Then, the weighed binder (PTFE powder or composition) and the solid electrolyte were put into the mixture, and the mixture was cooled sufficiently in a thermostatic bath at 5°C. The mixture of the active material, the conductive assistant, the binder, and the solid electrolyte was put into a Henschel mixer and homogenized by processing at 300 rpm for 3 minutes.
Thereafter, the mixture was sufficiently heated in a thermostatic bath at 40° C., and then treated in a Henschel mixer at 1000 rpm for 3 minutes to promote fibrillation, thereby obtaining an electrode mixture.
The electrode mixture was put into parallel metal rolls (temperature: 80° C., rotation speed: 1 m/min) and rolled to obtain an electrode mixture sheet. The obtained rolled sheet was again roughly crushed by folding in half, and the electrode mixture was put into metal rolls (temperature: 80° C., rotation speed: 1 m/min) and rolled to obtain an electrode mixture sheet with greater strength.
Thereafter, the electrode mixture sheet was placed in a roll press machine and the gap was adjusted to a final thickness of 150 μm.
Table 3 shows the material types and compositions.

ＳｕｐｅｒＰ Ｌｉ：Ｉｍｅｒｙｓ社製カーボンブラック

SuperP Li: Carbon black manufactured by Imerys

<Measurement of the strength of the positive electrode mixture sheet (tensile test)>
The positive electrode mixture sheet was cut out to prepare a rectangular test piece with a width of 8 mm. A tensile tester (Shimadzu Corporation AGS-100NX) was used to measure at 100 mm/min. The chuck distance was 30 mm. Displacement was applied until breakage, and the maximum stress of the measured results was taken as the strength of each sample. Tests were performed with N=8, the average value was calculated, and the following three-level ranking was performed.
◯: 0.2 N/ ^mm2 or more △: 0.1 N/ ^mm2 or more ×: 0.1 N/ ^mm2 or less The coefficient of variation was also calculated to evaluate the variation.
The results are shown in Table 4.

<Flexibility evaluation of positive electrode mixture sheet (bending test)>
The prepared positive electrode mixture sheet was cut into a width of 4 cm and a length of 10 cm to prepare test pieces. Next, these test pieces were wrapped around a Φ10 mm round bar, and the test pieces were visually inspected to confirm the presence or absence of damage such as scratches or cracks. If no damage was observed, a test was performed with a thinner Φ5 mm round bar to confirm damage. Again, if no damage was observed, a test was performed with a thinner Φ2 mm round bar to confirm damage. The results were classified into A to D.
A: No damage to Φ2 mm rod B: Damage to Φ2 mm rod C: Damage to Φ5 mm rod D: Damage to Φ10 mm rod The results are shown in Table 4.

Evaluation of Solid Electrolyte Mixture Sheets Preparation and evaluation of the mixture sheets of Examples 13 to 18 and Comparative Example 3 were carried out according to the following procedures. The preparation and evaluation were carried out in an argon atmosphere.

<Preparation of solid electrolyte mixture sheet>
The weighed binder (PTFE powder or composition) was sufficiently cooled in a thermostatic bath at 5° C., and then charged into a Henschel mixer and pulverized at 300 rpm for 2 minutes.
The crushed binder and solid electrolyte were each weighed and thoroughly cooled in a thermostatic bath at 5° C. The mixture was then placed in a Henschel mixer and homogenized by processing at 300 rpm for 1 minute.
Thereafter, the mixture was sufficiently heated in a thermostatic bath at 40° C., and then treated in a Henschel mixer at 1000 rpm for 1 minute to promote fibrillation, thereby obtaining an electrolyte mixture.
The electrode mixture was put into parallel metal rolls (temperature: 80° C., rotation speed: 1 m/min) and rolled to obtain an electrolyte mixture sheet. The rolled sheet obtained was again folded in half to be roughly crushed, and the electrolyte mixture was put into metal rolls (temperature: 80° C., rotation speed: 1 m/min) and rolled to obtain a stronger electrolyte mixture sheet.
Thereafter, the electrolyte mixture sheet was placed in a roll press machine and the gap was adjusted so that the final thickness of the electrolyte mixture sheet was 120 μm.
Table 5 shows the material types and compositions.

<Strength measurement of solid electrolyte mixture sheet (tensile test)>
The solid electrolyte mixture sheet was cut out to prepare a rectangular test piece with a width of 8 mm. A tensile tester (Shimadzu Corporation AGS-100NX) was used to measure at a speed of 100 mm/min. The chuck distance was 30 mm. Displacement was applied until breakage, and the maximum stress of the measured results was taken as the strength of each sample. Tests were performed with N=8, the average value was calculated, and the following three-level ranking was performed.
◯: 0.2 N/ ^mm2 or more △: 0.1 N/ ^mm2 or more ×: 0.1 N/ ^mm2 or less The coefficient of variation was also calculated to evaluate the variation.
The results are shown in Table 6.

<Flexibility evaluation of solid electrolyte mixture sheet (bending test)>
The prepared solid electrolyte mixture sheet was cut into a width of 4 cm and a length of 10 cm to prepare test pieces. Next, these test pieces were wrapped around a Φ10 mm round bar, and the test pieces were visually inspected to confirm the presence or absence of damage such as scratches or cracks. If no damage was observed, a test was performed using a thinner Φ5 mm round bar to confirm damage. Again, if no damage was observed, a test was performed using a thinner Φ2 mm round bar to confirm damage. The results were classified into A to D.
A: No damage to Φ2 mm rod B: Damage to Φ2 mm rod C: Damage to Φ5 mm rod D: Damage to Φ10 mm rod The results are shown in Table 6.

<Ionic Conductivity of Solid Electrolyte Mixture Sheet>
The solid electrolyte mixture sheet was cut to an appropriate size, and gold was vapor-deposited on both sides. The solid electrolyte mixture sheet was then punched into a circle of Φ10 mm with a punch, which was then placed in a pressure cell, the cell's screws were tightened with 8 N, and electrodes were removed from the top and bottom of the cell. A schematic diagram of the pressure cell used is shown in Figure 1.
The ionic conductivity of this sample was measured using an impedance device manufactured by Toyo Corporation under conditions of 25° C., AC amplitude modulation of 10 mV, and frequencies of 5×10 ⁶ to 0.1 Hz.
The results are shown in Table 6.

By using the PTFE composition of the present disclosure as a binder, it can be mixed uniformly with the powder components of the battery, improving the mechanical properties and uniformity of the composite sheet. In addition, it is possible to manufacture a battery that can maintain good battery properties.

1: Screw 2: Nut 3: Insulation sheet 4: Solid electrolyte mixture sheet 5: Gold vapor deposition 6: Upper electrode 7: Lower electrode

Claims (16)

A polytetrafluoroethylene composition for use in a battery binder, comprising:
A polytetrafluoroethylene composition having endothermic peaks in a region (A) of 324° C. or higher and lower than 333° C. and in a region (B) of 333° C. or higher and 350° C. or lower in differential scanning calorimetry. A battery binder consisting essentially of a polytetrafluoroethylene composition,
The polytetrafluoroethylene composition is a binder for batteries, which has endothermic peaks in a region (A) of 324° C. or higher and lower than 333° C. and in a region (B) of 333° C. or higher and 350° C. or lower in differential scanning calorimetry. The battery binder according to claim 2, wherein the polytetrafluoroethylene composition has an intensity ratio of the endothermic peak intensity in region (A) to the endothermic peak intensity in region (B) of 0.05 or more and 3.50 or less. The battery binder according to claim 2 or 3, wherein the polytetrafluoroethylene composition is paste extrudable. The battery binder according to claim 2 or 3, wherein the polytetrafluoroethylene composition is stretchable. The battery binder according to claim 2 or 3, wherein the polytetrafluoroethylene composition has a standard specific gravity of 2.250 or less. A polytetrafluoroethylene composition for use in a battery binder, comprising:
A polytetrafluoroethylene composition consisting essentially of polytetrafluoroethylene (A) exhibiting melt flowability and polytetrafluoroethylene (B) not exhibiting melt flowability. A battery binder consisting essentially of a polytetrafluoroethylene composition,
The polytetrafluoroethylene composition is a binder for batteries consisting essentially of polytetrafluoroethylene (A) exhibiting melt flowability and polytetrafluoroethylene (B) not exhibiting melt flowability. The battery binder according to claim 8, wherein the content of the polytetrafluoroethylene (A) in the polytetrafluoroethylene composition is 1% by mass or more and 50% by mass or less with respect to the polytetrafluoroethylene composition. The battery binder according to claim 2 or 8, wherein the polytetrafluoroethylene composition is a powder. The battery binder according to claim 2 or 8, wherein the polytetrafluoroethylene composition is substantially free of moisture. The battery binder according to claim 2 or 8, wherein the polytetrafluoroethylene composition is substantially free of fluorine-containing compounds having a molecular weight of 1000 or less. An electrode mixture comprising the polytetrafluoroethylene composition according to claim 1 or 7, or the battery binder according to any one of claims 2, 3, 8, and 9, and an electrode active material. The electrode mixture according to claim 13, which is a sheet. An electrode comprising the polytetrafluoroethylene composition according to claim 1 or 7, or the battery binder according to any one of claims 2, 3, 8, and 9, an electrode active material, and a current collector. A secondary battery comprising the electrode according to claim 15.

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