Fluoropolymer composition, binder for electrochemical device, electrode mixture, electrode, and secondary battery

Abstract

To provide: a fluoropolymer composition for use in a binder for an electrochemical device, which is capable of being uniformly mixed with the powder components of an electrochemical device and from which a mixture sheet having excellent strength and flexibility can be obtained; a binder for an electrochemical device using the composition; an electrode mixture; an electrode; and a secondary battery.SOLUTION: There is provided a fluoropolymer composition for use in a binder for an electrochemical device, the fluoropolymer composition containing a fluoropolymer. The fluoropolymer contains two or more tetrafluoroethylene polymers, and the fluoropolymer content is 90 mass% or more with respect to the fluoropolymer composition.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a fluorine-based polymer composition, a binder for an electrochemical device, an electrode mixture, an electrode, and a secondary battery. [Background technology]

[0002] Secondary batteries such as lithium-ion secondary batteries have high voltage, high energy density, low self-discharge, little memory effect, and the potential for ultra-lightweight design, and are therefore used in small, portable electrical and electronic devices such as notebook computers, mobile phones, smartphones, tablet computers, and ultrabooks, and are also being put into practical use as a wide range of power sources, including on-board power supplies for driving automobiles and large-scale stationary power supplies. There is a demand for even higher energy densities in secondary batteries, and further improvements in the properties of electrochemical devices are also required.

[0003] Patent Document 1 describes an energy storage device in which at least one of the cathode and the anode contains a polytetrafluoroethylene mixed binder material.

[0004] Patent Documents 2 to 6 describe the use of polytetrafluoroethylene as a binder for batteries.

[0005] Patent Document 7 describes the use of a mixture of polytetrafluoroethylene and polyvinylidene fluoride as a binder for batteries. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2017-517862 [Patent Document 2] International Publication No. 2021 / 181887 [Patent Document 3] International Publication No. 2021 / 181888 [Patent Document 4] International Publication No. 2021 / 192541 [Patent Document 5] International Publication No. 2022 / 138942 [Patent Document 6] International Publication No. 2022 / 138939 [Patent Document 7] International Publication No. 2022 / 234227 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present disclosure is to provide a fluorine-based polymer composition for binders for electrochemical devices that can be uniformly mixed with powder components of electrochemical devices and that can give a mixture sheet that is excellent in strength and flexibility, as well as a binder for electrochemical devices, an electrode mixture, an electrode, and a secondary battery that use the same. [Means for solving the problem]

[0008] The present disclosure (1) provides a fluorine-based polymer composition used as a binder for an electrochemical device, Contains a fluorine-based polymer, the fluorine-based polymer contains two or more types of tetrafluoroethylene-based polymers, The fluoropolymer composition has a content of the fluoropolymer of 90% by mass or more based on the fluoropolymer composition.

[0009] The present disclosure (2) provides a binder for electrochemical devices consisting essentially of a fluorine-based polymer composition, The fluoropolymer composition comprises a fluoropolymer, the fluorine-based polymer contains two or more types of tetrafluoroethylene-based polymers, The binder for electrochemical devices has a content of the fluoropolymer of 90% by mass or more relative to the fluoropolymer composition.

[0010] The present disclosure (3) is the binder for electrochemical devices according to the present disclosure (2), wherein the fluorine-based polymer composition contains a homopolymer of tetrafluoroethylene and a copolymer of a modified monomer and tetrafluoroethylene.

[0011] The present disclosure (4) is the binder for electrochemical devices according to the present disclosure (2) or (3), wherein the fluorine-based polymer composition contains two or more tetrafluoroethylene-based polymers having different standard specific gravities.

[0012] The present disclosure (5) is a binder for electrochemical devices in any combination with any of the present disclosures (2) to (4), wherein the fluorine-based polymer composition contains two or more paste-extrudable tetrafluoroethylene-based polymers.

[0013] The present disclosure (6) is a binder for electrochemical devices in any combination with any of the present disclosures (2) to (5), wherein the fluoropolymer composition contains two or more tetrafluoroethylene polymers having different extrusion pressures.

[0014] The present disclosure (7) is a binder for electrochemical devices in any combination with any of the present disclosures (2) to (6), wherein the fluorine-based polymer composition is paste-extrudable.

[0015] The present disclosure (8) is a binder for electrochemical devices in any combination with any of the present disclosures (2) to (7), wherein the fluorine-based polymer composition has an endothermic peak temperature of 320° C. or higher.

[0016] The present disclosure (9) is a binder for electrochemical devices in any combination with any of the present disclosures (2) to (8), in which the fluorine-based polymer composition is a powder.

[0017] The present disclosure (10) is a binder for electrochemical devices in any combination with any of the present disclosures (2) to (9), wherein the fluorine-based polymer composition is substantially free of moisture.

[0018] The present disclosure (11) is a binder for electrochemical devices in any combination with any of the present disclosures (2) to (10), wherein the fluorine-containing polymer composition is substantially free of a fluorine-containing compound having a molecular weight of 1,000 or less.

[0019] The present disclosure (12) is a binder for electrochemical devices in any combination with any of the present disclosures (2) to (11), wherein the fluorine-based polymer composition has an average aspect ratio of 2.5 or less.

[0020] The present disclosure (13) is an electrode mixture comprising a binder for electrochemical devices, which is the fluorine-based polymer composition according to the present disclosure (1) or any combination of the fluorine-based polymer composition with any of the present disclosures (2) to (12), and an electrode active material.

[0021] The present disclosure (14) is the electrode mixture according to the present disclosure (13), which is a sheet.

[0022] The present disclosure (15) is an electrode comprising a binder for electrochemical devices, which is the fluorine-based polymer composition according to the present disclosure (1) or any combination with any of the present disclosures (2) to (12), an electrode active material, and a current collector.

[0023] The present disclosure (16) is a secondary battery including the electrode according to the present disclosure (15). [Effects of the Invention]

[0024] According to the present disclosure, it is possible to provide a fluorine-based polymer composition for a binder for an electrochemical device, which can be uniformly mixed with a powder component of an electrochemical device and from which a mixture sheet excellent in strength and flexibility can be obtained, as well as a binder for an electrochemical device, an electrode mixture, an electrode, and a secondary battery using the same. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 2 is a schematic diagram of a cross section of a pressure cell used to measure the ionic conductivity of a solid electrolyte mixture sheet in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present disclosure will be specifically described below.

[0027] The present disclosure provides a fluoropolymer composition for use as a binder for an electrochemical device, the fluoropolymer composition comprising a fluoropolymer, the fluoropolymer comprising two or more types of tetrafluoroethylene-based polymers, and a content of the fluoropolymer in the fluoropolymer composition of 90 mass% or more.

[0028] The fluoropolymer composition of the present disclosure contains a predetermined amount of a fluoropolymer containing two or more types of tetrafluoroethylene (TFE)-based polymers, and therefore, compared to the case where only one type of TFE-based polymer is used, aggregates are less likely to form even when kneaded for a long period of time with powder components of electrochemical devices such as electrode active materials and solid electrolytes, and the fluoropolymer composition can be uniformly mixed with the powder components.Furthermore, a mixture sheet excellent in strength and flexibility can be obtained. The fluoropolymer composition of the present disclosure is 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 composition, and it can also reduce the number of steps and costs associated with the use of a dispersion medium. Furthermore, the fluoropolymer composition of the present disclosure has excellent binding strength with active materials and electrolytes, so that the amount used can be reduced.

[0029] The fluoropolymer composition of the present disclosure may contain the fluoropolymer in an amount of 90% by mass or more based on the fluoropolymer composition, but preferably consists essentially of the fluoropolymer, which allows the effects of the fluoropolymer to be significantly exhibited. "Consisting essentially of only the fluoropolymer" means that the total amount of the fluoropolymer is 95.0% by mass or more based on the fluoropolymer composition. The fluoropolymer preferably accounts for 98.0% by mass or more of the fluoropolymer composition, 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 fluoropolymer composition of the present disclosure consists solely of the above fluoropolymer.

[0030] The fluoropolymer may contain at least two or more TFE polymers, and may further contain a fluoropolymer other than the TFE polymer. Examples of the fluoropolymer other than the TFE polymer include vinylidene fluoride (VdF) polymers. Examples of the VdF polymer include VdF resins such as polyvinylidene fluoride (PVdF) and VdF / TFE copolymers (VT); and VdF elastomers such as VdF / HFP copolymers, VdF / TFE / HFP copolymers, and VdF / 2,3,3,3-tetrafluoropropylene copolymers.

[0031] The fluoropolymer may contain two types of TFE polymers, or may contain three or more types of TFE polymers, but preferably contains two types of TFE polymers.

[0032] The two or more types of TFE polymers may be, for example, two or more types of TFE polymers having different compositions and / or physical properties.

[0033] The fluoropolymer composition of the present disclosure can be mixed more uniformly with the powder components of an electrochemical device, and a composite sheet having even greater strength and flexibility can be obtained. Therefore, it is preferable to use two or more TFE polymers having different compositions as the two or more TFE polymers. Examples of TFE polymers having different compositions include TFE polymers that differ in the type of modifying monomer copolymerizable with TFE and / or the content of polymerized units based on the modifying monomer (hereinafter also referred to as "modifying monomer units").

[0034] The combination of two or more TFE polymers having different compositions may be, for example, a combination of a TFE homopolymer and a copolymer of a modifying monomer and TFE, a combination of two or more copolymers having different types of modifying monomers, or a combination of two or more copolymers having the same modifying monomer unit but different content ratios of the modifying monomer unit. The homopolymer of TFE refers to one in which the content of modified monomer units relative to all polymerized units is less than 0.0001% by mass. Furthermore, "the content ratio of the modified monomer unit is different" means that the difference in the content ratio (mass % value) of the modified monomer unit in all polymerized units is 0.005 or more. The difference in the content ratio is preferably 0.10 or more, more preferably 0.15 or more, even more preferably 0.20 or more, and is preferably 5.0 or less, more preferably 3.0 or less, even more preferably 1.0 or less, even more preferably 0.80 or less, even more preferably 0.60 or less, and particularly preferably 0.40 or less.

[0035] The content of the modified monomer unit in the copolymer of the modified monomer and TFE (hereinafter referred to as TFE copolymer) is preferably in the range of 0.0001 to 10 mass% based on the total polymerized units, since this allows for more uniform mixing with the powder components of the electrochemical device and allows for the production of a composite sheet with even greater strength and flexibility. The lower limit of the modified monomer unit content is preferably 0.001 mass%, more preferably 0.005 mass%, even more preferably 0.010 mass%, even more preferably 0.015 mass%, and particularly preferably 0.020 mass%. The upper limit of the modified monomer unit content is preferably 5.0 mass%, more preferably 3.0 mass%, even more preferably 1.0 mass%, even more preferably 0.80 mass%, even more preferably 0.60 mass%, even more preferably 0.50 mass%, even more preferably 0.40 mass%, even more preferably 0.30 mass%, and particularly preferably 0.20 mass%.

[0036] The TFE-based polymer is preferably polytetrafluoroethylene (PTFE). The PTFE includes a TFE homopolymer and a modified PTFE containing 99.0% by mass or more of TFE units and 1.0% by mass or less of modified monomer units. The modified PTFE may consist only of TFE units and modified monomer units.

[0037] The above combination is preferably a combination of a TFE homopolymer and a TFE copolymer, and more preferably a combination of a TFE homopolymer and a modified PTFE.

[0038] The mass ratio of the TFE homopolymer to the TFE copolymer (homopolymer / TFE copolymer) is preferably 1 / 99 or more, more preferably 5 / 95 or more, even more preferably 10 / 90 or more, even more preferably 15 / 85 or more, and particularly preferably 20 / 80 or more, and is preferably 99 / 1 or less, more preferably 95 / 5 or less, even more preferably 90 / 10 or less, even more preferably 85 / 15 or less, and particularly preferably 80 / 20 or less.

[0039] The mass ratio of the TFE homopolymer to the modified PTFE (homopolymer / modified PTFE) is preferably 1 / 99 or more, more preferably 5 / 95 or more, even more preferably 10 / 90 or more, even more preferably 15 / 85 or more, and particularly preferably 20 / 80 or more, and is preferably 99 / 1 or less, more preferably 95 / 5 or less, even more preferably 90 / 10 or less, even more preferably 85 / 15 or less, and particularly preferably 80 / 20 or less.

[0040] The modified PTFE contains TFE-based polymerized units (TFE units) and modified monomer units. The modified PTFE may contain 99.0% by mass or more of TFE units and 1.0% by mass or less of modified monomer units. Alternatively, the modified PTFE may consist only of TFE units and modified monomer units.

[0041] The modified PTFE can be more uniformly mixed with the powder components of the electrochemical device, and a composite sheet having even greater 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 modified monomer unit content is more preferably 0.001% by mass, even more preferably 0.010% by mass, and even more preferably 0.050% by mass. The upper limit of the modified monomer unit content is preferably 0.80% by mass, more preferably 0.60% by mass, and even more preferably 0.40% by mass. In this specification, the modified monomer unit means a part of the molecular structure of the TFE polymer that is derived from the modified monomer.

[0042] 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.

[0043] The modifying monomer is not particularly limited as long as it is copolymerizable 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 ether, perfluoroallyl ether, (perfluoroalkyl)ethylene, ethylene, etc. The modifying monomer used may be one type or multiple types.

[0044] The perfluorovinyl ether is not particularly limited, and examples thereof include perfluorovinyl ethers represented by the following general formula (A): CF2=CF-ORf1 (A) (In the formula, Rf 1 represents a perfluoroorganic group. ) and perfluorounsaturated compounds represented by the following formulas are included. In this specification, the "perfluoroorganic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. The perfluoroorganic group may have an ether oxygen.

[0045] The perfluorovinyl ether may be, for example, a compound represented by the general formula (A) in which Rf 1 is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5.

[0046] 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.

[0047] The perfluorovinyl ether further includes a compound represented by the general formula (A) in which Rf 1 is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, Rf 1 is the following formula:

[0048] [ka]

[0049] (wherein m represents 0 or an integer of 1 to 4), Rf 1 is the following formula:

[0050] [ka]

[0051] (wherein n represents an integer of 1 to 4).

[0052] The (perfluoroalkyl)ethylene [PFAE] is not particularly limited, and examples thereof include (perfluorobutyl)ethylene [PFBE] and (perfluorohexyl)ethylene.

[0053] Examples of perfluoroallyl ethers include those represented by the general formula (B): CF2=CF-CF2-ORf 2 (B) (In the formula, Rf 2 represents a perfluoroorganic group.

[0054] Above Rf 2 is preferably a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms. The perfluoroallyl ether is preferably at least one selected from the group consisting of CF2=CF-CF2-O-CF3, CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9, more preferably at least one selected from the group consisting of CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9, and even more preferably CF2=CF-CF2-O-CF2CF2CF3.

[0055] The modified monomer is represented by the following general formula (I): CX 1 X 2 =CX 3 X 4 (I) (In the formula, X 1 ~X 3 are each independently H or F. 4 is F, Cl, Rf or O-Rf. Rf is a perfluoro organic group.

[0056] Rf in general formula (I) 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.

[0057] 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 PPVE, even more preferably at least one selected from the group consisting of CTFE, HFP, and PPVE, and particularly preferably at least one selected from the group consisting of CTFE and HFP, in that it can be mixed more uniformly with the powder components of the electrochemical device and a composite sheet having even greater strength and flexibility can be obtained.

[0058] The fluoropolymer composition of the present disclosure preferably contains two or more TFE polymers having different standard specific gravities (SSG) as the two or more TFE polymers, since this allows the fluoropolymer composition to be more uniformly mixed with the powder components of an electrochemical device and allows a composite sheet having even greater strength and flexibility to be obtained.

[0059] "Different SSG" means that the difference in SSG is 0.005 or more. The difference in SSG is preferably 0.010 or more, more preferably 0.015 or more, even more preferably 0.020 or more, and is preferably 0.050 or less, more preferably 0.040 or less, even more preferably 0.030 or less.

[0060] The two or more TFE polymers having different SSGs may be a combination of a TFE polymer with a high SSG and a TFE polymer with a low SSG. The TFE-based polymer having a high SSG preferably has an SSG of 2.160 or more, more preferably 2.165 or more, and preferably 2.200 or less, more preferably 2.190 or less, even more preferably 2.185 or less, even more preferably 2.180 or less, and particularly preferably 2.175 or less. The TFE polymer having a low SSG preferably has an SSG of less than 2.160, more preferably 2.155 or less, and preferably 2.130 or more, more preferably 2.140 or more, and even more preferably 2.145 or more. The SSG is measured by the water displacement method in accordance with ASTM D 792 using a sample molded in accordance with ASTM D 4895.

[0061] The two or more TFE-based polymers with different SSGs may be TFE homopolymers or TFE copolymers, but it is preferable that at least the TFE-based polymer with a high SSG is a TFE copolymer, it is more preferable that at least the TFE-based polymer with a high SSG is a modified PTFE, it is even more preferable that both the TFE-based polymer with a high SSG and the TFE-based polymer with a low SSG are TFE copolymers, and it is even more preferable that both the TFE-based polymer with a high SSG and the TFE-based polymer with a low SSG are modified PTFE.

[0062] The mass ratio of the TFE-based polymer with a high SSG to the TFE-based polymer with a low SSG (high SSG / low SSG) is preferably 1 / 99 or more, more preferably 5 / 95 or more, even more preferably 10 / 90 or more, even more preferably 15 / 85 or more, and particularly preferably 20 / 80 or more, and is preferably 99 / 1 or less, more preferably 95 / 5 or less, even more preferably 90 / 10 or less, even more preferably 85 / 15 or less, and particularly preferably 80 / 20 or less.

[0063] The fluoropolymer composition of the present disclosure preferably contains two or more paste-extrudable TFE polymers as the two or more TFE polymers, since this allows the fluoropolymer composition to be more uniformly mixed with the powder components of an electrochemical device and allows a mixture sheet having even greater strength and flexibility to be obtained. Whether or not a TFE-based polymer can be paste-extruded is determined by the following method. 60 g of TFE-based polymer powder and 12.3 g of hydrocarbon oil (trade name: Isopar G (registered trademark), manufactured by ExxonMobil Corporation) serving 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 into the cylinder and maintained for 1 minute. The mixture is then extruded through 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, the mixture is judged to be unextrudable; if the bead can be extruded continuously without breaking, the mixture is judged to be extrudable.

[0064] The fluoropolymer composition of the present disclosure can be mixed more uniformly with powder components of an electrochemical device, and a mixture sheet having even greater strength and flexibility can be obtained. In this respect, the two or more TFE polymers preferably include two or more TFE polymers having different extrusion pressures, and more preferably include two or more PTFE polymers having different extrusion pressures.

[0065] "Different extrusion pressures" means that the difference in extrusion pressure is 5 MPa or more. The difference in extrusion pressure is preferably 10 MPa or more, more preferably 15 MPa or more, and even more preferably 20 MPa or more, and is preferably 35 MPa or less, more preferably 30 MPa or less, and even more preferably 25 MPa or less.

[0066] The two or more TFE polymers having different extrusion pressures may be a combination of a TFE polymer having a high extrusion pressure and a TFE polymer having a low extrusion pressure. The TFE-based polymer having a high extrusion pressure preferably has an extrusion pressure at a reduction ratio (RR) of 200 of 20 MPa or more, more preferably 25 MPa or more, and even more preferably 30 MPa or more, and preferably 70 MPa or less, more preferably 60 MPa or less, more preferably 50 MPa or less, and even more preferably 40 MPa or less. The TFE-based polymer having a low extrusion pressure preferably has an extrusion pressure at a reduction ratio (RR) of 200 of less than 20 MPa, more preferably 15 MPa or less, even more preferably 13 MPa or less, and even more preferably 12 MPa or less, and preferably 5 MPa or more, more preferably 8 MPa or more, and even more preferably 10 MPa or more. The extrusion pressure is measured by the following method. In the latter half of the extrusion operation of the above-mentioned paste extrusion, the load (N) when the pressure reaches an equilibrium state is divided by the cross-sectional area of ​​the cylinder, and the value is defined as the extrusion pressure (MPa).

[0067] The two or more TFE-based polymers having different extrusion pressures may be TFE homopolymers or TFE copolymers, but it is preferable that at least the TFE-based polymer having a low extrusion pressure is a TFE copolymer, more preferable that at least the TFE-based polymer having a low extrusion pressure is a modified PTFE, further preferable that both the TFE-based polymer having a high extrusion pressure and the TFE-based polymer having a low extrusion pressure are TFE copolymers, and it is particularly preferable that the TFE-based polymer having a high extrusion pressure and the TFE-based polymer having a low extrusion pressure are modified PTFE.

[0068] The two or more TFE polymers having different extrusion pressures are preferably two or more TFE polymers having different SSGs, and are also preferably a combination of a TFE polymer with a high SSG and a TFE polymer with a low SSG. In this case, the TFE polymer with a high extrusion pressure is preferably a TFE polymer with a low SSG, and the TFE polymer with a low extrusion pressure is preferably a TFE polymer with a high SSG.

[0069] The mass ratio of the TFE-based polymer with a high extrusion pressure to the TFE-based polymer with a low extrusion pressure (high extrusion pressure / low extrusion pressure) is preferably 1 / 99 or more, more preferably 5 / 95 or more, even more preferably 10 / 90 or more, even more preferably 15 / 85 or more, and particularly preferably 20 / 80 or more, and is preferably 99 / 1 or less, more preferably 95 / 5 or less, even more preferably 90 / 10 or less, even more preferably 85 / 15 or less, and particularly preferably 80 / 20 or less.

[0070] The TFE polymer in the fluoropolymer composition of the present disclosure may have a core-shell structure. Examples of TFE polymers having a core-shell structure include TFE copolymers containing a core of a high molecular weight TFE polymer and a shell of a lower molecular weight TFE polymer or TFE copolymer in particles, and modified PTFE is preferred. Examples of such modified PTFE include the PTFE described in JP-A-2005-527652.

[0071] The TFE-based polymer with a high SSG and a low extrusion pressure preferably have a core-shell structure, which allows for more uniform mixing with the powder components of the electrochemical device and provides a composite sheet with greater strength and flexibility.

[0072] In the core-shell structure, there is not necessarily a clear boundary between the core and the shell, and the TFE-based polymer constituting the core and the TFE-based polymer constituting the shell may be mixed near the boundary between the core and the shell.

[0073] The core in the core-shell structure is preferably a modified PTFE having polymerized units based on a modified monomer. The modifying monomer in the core is preferably at least one selected from the group consisting of fluoro(alkyl vinyl ether), vinyl heterocycle, and fluoroolefin, more preferably at least one selected from the group consisting of fluoro(alkyl vinyl ether) and fluoroolefin, even more preferably at least one selected from the group consisting of PAVE, HFP, and CTFE, even more preferably at least one selected from the group consisting of PAVE and CTFE, and particularly preferably CTFE. Moreover, the PAVE is preferably perfluoro(propyl vinyl ether) [PPVE].

[0074] The shell in the core-shell structure is preferably a TFE copolymer having polymerized units based on a modified monomer and / or a TFE copolymer obtained by polymerization using a chain transfer agent, and more preferably a modified PTFE. The modifying monomer in the shell is preferably at least one selected from the group consisting of fluoro(alkyl vinyl ether)s and fluoroolefins, more preferably at least one selected from the group consisting of PAVE, HFP, and CTFE, even more preferably at least one selected from the group consisting of HFP and CTFE, and even more preferably CTFE.

[0075] The chain transfer agent is not particularly limited as long as it reduces the molecular weight of the TFE-based polymer constituting the shell, and examples thereof include non-peroxide organic compounds such as water-soluble alcohols, hydrocarbons and fluorinated hydrocarbons, water-soluble organic peroxides such as disuccinic acid peroxide [DSP], and persulfates such as ammonium persulfate [APS] and potassium persulfate [KPS]. The chain transfer agent may contain at least one of a non-peroxide organic compound, a water-soluble organic peroxide, and a persulfate. In the chain transfer agent, one or more of each of the non-peroxide organic compound, the water-soluble organic peroxide, and the persulfate can be used.

[0076] The chain transfer agent is preferably at least one selected from the group consisting of water-soluble alcohols having 1 to 4 carbon atoms, hydrocarbons having 1 to 4 carbon atoms, and fluorohydrocarbons having 1 to 4 carbon atoms, in view of good dispersibility and uniformity in the reaction system, more preferably at least one selected from the group consisting of methane, ethane, n-butane, isobutane, methanol, HFC-134a, HFC-32, DSP, APS, and KPS, still more preferably methanol and / or isobutane, and particularly preferably methanol.

[0077] The total amount of the two or more TFE-based polymers 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 fluoropolymer.

[0078] The fluoropolymer composition of the present disclosure preferably consists essentially of the two or more TFE polymers. This allows the effects of the two or more TFE polymers to be significantly exhibited. "Consisting essentially of the two or more TFE polymers" means that the total amount of the two or more TFE polymers is 95.0% by mass or more relative to the fluoropolymer composition. The total amount of the two or more TFE polymers 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, based on the fluoropolymer composition. The fluoropolymer composition of the present disclosure preferably consists solely of the two or more TFE polymers described above, and more preferably consists solely of the two or more PTFEs described above.

[0079] The fluoropolymer composition of the present disclosure may contain a conductive aid. Any known conductive material can be used as the conductive additive. 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 materials may be used alone or in any combination and ratio of two or more.

[0080] When the fluoropolymer composition of the present disclosure contains the conductive additive, the content of the conductive additive is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, relative to the fluoropolymer composition, and the upper limit is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less.

[0081] The fluoropolymer composition of the present disclosure is preferably substantially free of water. This can suppress gas generation and deterioration of electrochemical device properties. Furthermore, it is advantageous in terms of production processes because it allows for a wide range of electrode active materials and solid electrolytes to be combined. Being substantially free of water means that the water content of the fluoropolymer composition is 0.010% by 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 fluoropolymer composition is measured before and after heating at 150°C for 2 hours, and the mass is calculated according to the following formula: A sample is taken three times, and the values ​​are calculated for each time, and the average value is calculated and used. Water content (mass%)=[(mass (g) of fluoropolymer composition before heating)−(mass (g) of fluoropolymer composition after heating)] / (mass (g) of fluoropolymer composition before heating)×100

[0082] The fluoropolymer composition of the present disclosure is preferably substantially free of 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 25 ppb by mass or less relative to the fluoropolymer 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 quantitation. The lower limit is not particularly limited, and may be an amount less than the lower limit of quantitation.

[0083] 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 sample, add 10 g (12.6 ml) of methanol, and ultrasonicate for 60 minutes to obtain an extract. The resulting extract is concentrated using an appropriate 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 a match with the structural formula of the candidate fluorine-containing compound is confirmed. Aqueous solutions with five or more levels of standard substance content are prepared, and LC / MS analysis is performed on each solution. The relationship between content and area relative to that content is plotted, and a calibration curve is drawn. Using the above calibration curve, the area of ​​the LC / MS chromatogram of the fluorine-containing compounds in the extract is converted to the content of the fluorine-containing compounds. The lower limit of quantification in this measurement method is 10 ppb by mass.

[0084] Examples of the fluorine-containing compound having a molecular weight of 1000 or less include a fluorine-containing compound having a hydrophilic group and 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 the TFE polymer. 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 is not added during polymerization, for example, a compound that is produced as a by-product during polymerization. When the fluorine-containing compound having a molecular weight of 1000 or less contains an anionic moiety and a cationic moiety, the fluorine-containing compound has a molecular weight of 1000 or less in the anionic moiety. The fluorine-containing compound having a molecular weight of 1000 or less does not include PTFE.

[0085] The hydrophilic group may be, for example, -COOM, -SO2M, or -SO3M, where -COOM, -SO3M (in each formula, M is H, a metal atom, NR 1 4. An optionally substituted imidazolium, an optionally substituted pyridinium, or an optionally substituted phosphonium, wherein R1 is H or an organic group.

[0086] As the fluorine-containing surfactant, a surfactant containing fluorine (anionic fluorine-containing surfactant) in which the molecular weight of the anionic part is 1000 or less can also be used. The "anionic part" means the part of the fluorine-containing surfactant excluding the cation. For example, F(CF2) n1 In the case of COOM, "F(CF2) n1 The "COO" part. 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. 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. Y 0 The anionic group may be -COOM, -SO2M, or -SO3M, and may be -COOM or -SO3M. M is H, metal atom, NR 1 4. An optionally substituted imidazolium, an optionally substituted pyridinium, or an optionally substituted phosphonium, wherein 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 As for H or C 1-10 may be an organic group of H or C 1-4 may be an organic group of H or C 1-4 The alkyl group may be: M is H, a metal atom, or NR 1 4, and 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 NH4. Above Rf n0 may be one in which 50% or more of H is substituted with fluorine.

[0087] The above fluorine-containing surfactant may be one type of fluorine-containing surfactant or a mixture containing two or more types of fluorine-containing surfactants.

[0088] 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)7COOM, F(CF2)5COOM, H(CF2)6COOM, H(CF2)7COOM, CF3O(CF2)3OCHFCF2COOM, C3F7OCF(CF3)CF2OCF(CF3)COOM, CF3CF2CF2OCF(CF3)COOM, CF3CF2OCF2CF2OCF2COOM, 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 [ka] (In each formula, M is H, metal atom, NR 14. An imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. 1 is H or an organic group. The fluoropolymer composition of the present disclosure is preferably substantially free of any of the fluorine-containing compounds represented by the above formulas.

[0089] In each of the above formulas, M is H, a metal atom, or NR 1 4, and 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 NH4. R 1 is H or C 1-10 may be an organic group of H or C 1-4 may be an organic group of H or C 1-4 The alkyl group may be:

[0090] When the fluoropolymer composition of the present disclosure is substantially free of any of the fluorine-containing compounds represented by the above formulas, gas generation and deterioration of electrochemical device properties can be further suppressed. "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 relative to the fluoropolymer 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 quantitation. The lower limit is not particularly limited, and may be an amount less than the lower limit of quantitation.

[0091] The fluoropolymer 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; M + represents a cation. It is also preferable that the composition is substantially free of a fluorine-containing compound represented by the formula (I). This makes it possible to further suppress gas generation and deterioration of the electrochemical device properties. The cation M in the above formula + The M constituting the above 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 relative to the fluoropolymer 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 quantitation. The lower limit is not particularly limited, and may be an amount less than the lower limit of quantitation.

[0092] The fluoropolymer composition of the present disclosure is preferably paste-extrudable, since it can be more uniformly mixed with the powder components of an electrochemical device and a mixture sheet having even greater strength and flexibility can be obtained. Whether or not a fluoropolymer composition can be paste-extruded is determined by the same method as described above for the TFE-based polymer.

[0093] The fluoropolymer composition of the present disclosure can be mixed more uniformly with the powder components of an electrochemical device, and a mixture sheet having even greater strength and flexibility can be obtained. In this respect, the endothermic peak temperature is preferably 320° C. or higher, more preferably 325° C. or higher, even more preferably 330° C. or higher, and even more preferably 333° C. or higher. The endothermic peak temperature is also preferably 350° C. or lower, more preferably 348° C. or lower, and even more preferably 346° C. or lower. The endothermic peak temperature is the temperature corresponding to the minimum point in the heat of fusion curve obtained by performing differential scanning calorimetry (DSC) at a heating rate of 2°C / min on a fluoropolymer composition that has not been heated to a temperature of 300°C or higher. When there are two or more minimum points in one melting peak, each of them is regarded as an endothermic peak temperature. When there are two or more endothermic peaks, it is preferable that all of them are within the above range.

[0094] The fluoropolymer composition of the present disclosure preferably has non-melt-processability, which 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, the composition does not easily flow even in the melting temperature range.

[0095] The fluoropolymer composition of the present disclosure can be mixed more uniformly with the powder components of an electrochemical device, and a composite sheet having even greater strength and flexibility can be obtained. In this respect, the standard specific gravity (SSG) of the fluoropolymer composition of the present disclosure is preferably 2.200 or less, more preferably 2.190 or less, even more preferably 2.180 or less, even more preferably 2.175 or less, and is preferably 2.130 or more, more preferably 2.140 or more, and even more preferably 2.150 or more. The SSG is measured by the water displacement method in accordance with ASTM D 792 using a sample molded in accordance with ASTM D 4895.

[0096] The fluoropolymer composition of the present disclosure can be more uniformly mixed with powder components of an electrochemical device, and a mixture sheet having even greater strength and flexibility can be obtained. In this respect, the extrusion pressure at a reduction ratio (RR) of 200 is preferably 10 MPa or more, more preferably 15 MPa or more, and is preferably 50 MPa or less, more preferably 40 MPa or less, and even more preferably 35 MPa or less. The extrusion pressure of the fluoropolymer composition at RR200 is measured by the same method as described above for the TFE-based polymer.

[0097] The fluoropolymer composition of the present disclosure is preferably stretchable, since it can be mixed more uniformly with the powder components of an electrochemical device and can provide a mixture sheet having even greater strength and flexibility. Whether or not a fluoropolymer composition can be stretched is determined by the following method. According to the description of JP 2002-201217 A, 21.7 g of lubricant (trade name: Isopar H (registered trademark), manufactured by ExxonMobil Corporation) was added to 100 g of a fluoropolymer composition and mixed for 3 minutes. The mixture was then left in a constant temperature bath at 25°C for 2 hours and then paste-extruded through an orifice (diameter 2.5 mm, land length 1.1 cm, entrance angle 30°) at 25°C under conditions of a reduction ratio (ratio of the cross-sectional area of ​​the die inlet to the cross-sectional area of ​​the outlet) of 100 and an extrusion speed of 51 cm / min to obtain a bead. The resulting bead was dried at 230°C for 30 minutes to remove the lubricant. The dried bead was cut to an appropriate length, clamped at each end so that the clamps were 3.8 cm apart, and heated to 300°C in an air-circulating oven. The clamps were then separated at a stretching rate of 1000% / s until a separation distance corresponding to a total stretch of 2400% was reached. "Total stretch" is the increase in length due to stretching relative to the bead length (100%) before the stretching test. If the bead does not break during stretching, it is judged to be stretchable, and if it breaks, it is judged to be unstretchable.

[0098] Whether or not the fluoropolymer composition is stretchable is preferably judged by the method described above, but can also be judged by the following method. 50 g of the fluoropolymer composition and 10.25 g of hydrocarbon oil (trade name: Isopar E®, ExxonMobil) used 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 maintained for 1 minute. The mixture was 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 was 100. The resulting beads were dried at 230°C for 30 minutes to remove the lubricant. The dried beads were cut to an appropriate length and placed in an oven heated to 300°C. They were stretched in the oven at a stretching speed of 100% / sec until the bead length was 25 times its original length. If no breakage occurred during stretching, the bead was deemed stretchable; if breakage occurred, the bead was deemed unstretchable.

[0099] The form of the fluoropolymer composition of the present disclosure is not limited, but is preferably a powder, since it can be mixed with the electrode active material and solid electrolyte without using a large amount of dispersion medium. The fluoropolymer composition may be in a form other than a powder, for example, a dispersion.

[0100] In terms of excellent powder flowability and excellent strength uniformity of a composite sheet, the fluoropolymer composition of the present disclosure preferably has an average aspect ratio of the powder of 2.5 or less, more preferably 2.0 or less, even more preferably 1.8 or less, and even more preferably 1.5 or less, and is preferably 1.0 or more, and more preferably 1.1 or more. The average aspect ratio of the powder is determined by spreading the powder thinly on a black paper surface with air without applying shear to the powder, observing the spread powder under a microscope, and averaging the ratio of the long diameter to the short diameter of 100 or more randomly selected powder particles.

[0101] The fluoropolymer 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 is 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 diameter is measured in accordance with JIS K 6891.

[0102] In view of excellent handleability, the fluoropolymer composition of the present disclosure preferably has an apparent density of 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 K 6892.

[0103] The fluoropolymer composition of the present disclosure can be produced by mixing two or more TFE polymers. The mixing method is not limited, and the two or more fluoropolymers may be mixed all in the form of powder, all in the form of aqueous dispersion, or mixed in the form of aqueous dispersion and powder. It is preferable to mix all in the form of aqueous dispersion, as this allows for more uniform mixing.

[0104] The fluorine-based polymer composition of the present disclosure can be suitably produced, for example, by a production method including a step (A) of mixing an aqueous dispersion of one type of TFE-based polymer with an aqueous dispersion of a TFE-based polymer different from the TFE-based polymer, a step (B) of coagulating the mixed aqueous dispersion to obtain a wet powder, and a step (C) of drying the wet powder.

[0105] The aqueous dispersion in step (A) can be produced, for example, by emulsion polymerization.

[0106] The emulsion polymerization can be carried out by a known method. For example, an aqueous dispersion containing particles (primary particles) of the TFE-based polymer can be obtained by emulsion polymerization of monomers (TFE and, if necessary, a modified monomer) necessary for constituting the TFE-based polymer 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 needed.

[0107] The aqueous dispersion may contain at least one of the above-mentioned fluorine-containing compounds.

[0108] The 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 other additives as necessary 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 initiator, chain transfer agent, the surfactant, etc. may be additionally added depending on the purpose.

[0109] 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, polymerization can also be initiated as a redox reaction in combination with a reducing agent or the like. The concentration of the polymerization initiator is determined appropriately depending on the type of monomer, the molecular weight of the target TFE-based polymer, and the reaction rate.

[0110] As the polymerization initiator, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator can be used.

[0111] The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, for example, dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and di-sec-butyl peroxydicarbonate, peroxyesters such as t-butyl peroxyisobutyrate and t-butyl peroxypivalate, dialkyl peroxides such as di-t-butyl peroxide, and the like. Also usable are 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-hexafluorobutyryl)peroxide, di(ω-chloro-decafluorohexanoyl)peroxide, di(ω-chloro-tetradecafluorooctanoyl)peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl-peroxide, di(dichloropentafluorobutanoyl)peroxide, di(trichlorooctafluorohexanoyl)peroxide, di(tetrachloroundecafluorooctanoyl)peroxide, di(pentachlorotetradecafluorodecanoyl)peroxide, and di(undecachlorodotriacontafluorodocosanoyl)peroxide.

[0112] 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, perborate, perchloric acid, perphosphoric acid, or percarbonate, 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 contained, and the amount used may be 0.1 to 20 times the amount of the peroxide.

[0113] 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 at the beginning of the polymerization in an amount (for example, several ppm relative to the water concentration) that does not significantly decrease the polymerization rate. The upper limit is a range in which the reaction temperature can be increased while removing heat from the equipment using the heat of polymerization reaction, and a more preferred upper limit is a range in which the heat of polymerization reaction can be removed from the equipment. 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.

[0114] For example, when polymerization is carried out at low temperatures below 30°C, it is preferable to use a redox initiator, which combines an oxidizing agent and a reducing agent, as the polymerization initiator. Examples of oxidizing agents include persulfates, organic peroxides, potassium permanganate, manganese triacetate, cerium ammonium nitrate, and bromates. Examples of reducing agents include sulfites, bisulfites, bromates, diimines, and oxalic acid. Examples of persulfates include ammonium persulfate and potassium persulfate. Examples of sulfites include sodium sulfite and ammonium sulfite. To increase the decomposition rate of the initiator, it is also preferable to add a copper salt or an iron salt to the redox initiator combination. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate.

[0115] As the redox initiator, it is preferred 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, persulfate, or bromic acid or a salt thereof, and the reducing agent is a dicarboxylic acid or a salt thereof.

[0116] 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 into a polymerization vessel in advance, 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 into a polymerization vessel and then 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.

[0117] 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 that is the salt is more preferably at least one selected from the group consisting of persulfates, permanganates, cerium (IV) salts, and bromates, further preferably permanganates, and particularly preferably potassium permanganate. Furthermore, the reducing agent which is the salt is more preferably at least one selected from the group consisting of oxalate, malonate, succinate, glutarate and bromate, further preferably oxalate, and particularly preferably ammonium oxalate.

[0118] Specifically, the redox initiator is preferably 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.

[0119] When a redox initiator is used, the oxidizing agent and the reducing agent may be added all at once at the beginning of the polymerization, or the reducing agent may be added all at once at the beginning of the polymerization and the oxidizing agent may be added continuously, or 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 the reducing agent may be added continuously.

[0120] When one of the redox polymerization initiators is added at the beginning of the polymerization and the other is added continuously, the rate of addition is preferably gradually reduced in order to obtain a TFE-based polymer having a low SSG, and further, the addition is preferably stopped midway through the polymerization, preferably before 20 to 40% by mass of the total TFE consumed in the polymerization reaction is consumed.

[0121] When a redox initiator is used 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, even more preferably 0.5 ppm or more, even more preferably 1 ppm or more, particularly preferably 5 ppm or more, particularly preferably 10 ppm or more, and preferably 10,000 ppm or less, more preferably 1,000 ppm or less, even 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, even more preferably 3 ppm or more, even more preferably 5 ppm or more, particularly preferably 10 ppm or more, and preferably 10,000 ppm or less, more preferably 1,000 ppm or less, even 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.

[0122] As the polymerization initiator, a water-soluble radical polymerization initiator and a redox initiator are preferred, since the above-mentioned properties can be easily obtained.

[0123] The aqueous medium is a reaction medium for polymerization 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 lower.

[0124] In the emulsion polymerization, a nucleating agent, a chain transfer agent, a buffer, a pH adjuster, a stabilizing aid, a dispersion stabilizer, a radical scavenger, a decomposing agent for the polymerization initiator, a dicarboxylic acid, etc. may be used, if necessary.

[0125] The emulsion polymerization is preferably carried out with the addition of a nucleating agent for the purpose of adjusting the particle size, and the nucleating agent is preferably added before the start of the polymerization reaction. As the nucleating agent, known agents can be used, and for example, at least one selected from the group consisting of fluoropolyethers, nonionic surfactants, and chain transfer agents is preferred, and a nonionic surfactant is more preferred.

[0126] 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 oxygen atoms in the main chain of the molecule are separated by saturated fluorocarbon groups having 1 to 3 carbon atoms. Two or more types of fluorocarbon groups may be present in the molecule. A typical structure has a repeating unit represented by the following formula: (-CFCF3-CF2-O-) n (-CF2-CF2-CF2-O-) n (-CF2-CF2-O-) n -(-CF2-O-) m (-CF2-CFCF3-O-) n -(-CF2-O-) m

[0127] 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 a salt thereof at one or both ends. The PFPE acid or its salt may also have a sulfonic acid or phosphonic acid group or a salt thereof 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 a hydrogen or chlorine atom. 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 2 or 3 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, for example, the preferred minimum value of n or n+m in the repeating unit structure above is at least 5. Two or more of the PFPE acids or salts thereof having acid groups at one or both termini can 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.

[0128] The emulsion polymerization is preferably carried out with the addition of a radical scavenger or a decomposer for the polymerization initiator, since this allows the TFE polymer to have a higher molecular weight and improves the strength of the mixture sheet.The radical scavenger or decomposer for 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 depressurization and repressurization are performed as described below, it is preferable to add it after that.

[0129] The radical scavenger is a compound that does not have the ability to restart after addition or chain transfer to a free radical in the polymerization system. Specifically, a compound that easily undergoes a chain transfer reaction with a primary radical or a propagating radical to generate a stable radical that does not subsequently react with the monomer, or a compound that easily undergoes an addition reaction with a primary radical or a propagating radical to generate 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, but among chain transfer agents, those with a reinitiation efficiency of almost 0% are called radical scavengers. The radical scavenger can also be described as 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. "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) with TFE at the polymerization temperature (=chain transfer rate constant (kc) / polymerization rate constant (kp)) of more than 0.1, and the 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.

[0130] The radical scavenger is preferably at least one selected from the group consisting of, for example, aromatic hydroxy compounds, aromatic amines, N,N-diethylhydroxylamine, quinone compounds, terpenes, thiocyanates, and cupric chloride (CuCl). Examples of aromatic hydroxy compounds include unsubstituted phenol, polyhydric phenol, salicylic acid, m- or p-salicylic acid, gallic acid, and naphthol. Examples of the unsubstituted phenol include o-, m-, or p-nitrophenol, o-, m-, or p-aminophenol, p-nitrosophenol, etc. Examples of the polyhydric phenol 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, and alizarin. Examples of thiocyanates include ammonium thiocyanate (NH4SCN), 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.

[0131] The amount of the radical scavenger added is preferably an amount equivalent to 3 to 500% (molar basis) of the polymerization 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).

[0132] The polymerization initiator decomposer 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 sulfites include sodium sulfite and ammonium sulfite. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate. The amount of the decomposing 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).

[0133] The emulsion polymerization may be carried out in the presence of 5 to 500 ppm of dicarboxylic acid relative to the aqueous medium, preferably 10 to 200 ppm, in order to reduce the amount of coagulation produced during polymerization. If the amount of dicarboxylic acid relative to the aqueous medium is too small, sufficient effects may not be obtained, while if the amount is too large, a chain transfer reaction may occur, resulting in a low molecular weight polymer. The amount of dicarboxylic acid is more preferably 150 ppm or less. The dicarboxylic acid may be added before the start of the polymerization reaction or during the polymerization.

[0134] The dicarboxylic acid is preferably, for example, one represented by the general formula: HOOCRCOOH (wherein R represents an alkylene group having 1 to 5 carbon atoms), more preferably succinic acid, malonic acid, glutaric acid, adipic acid, or pimelic acid, and even more preferably succinic acid.

[0135] In the emulsion polymerization, the polymerization temperature and polymerization pressure are appropriately determined depending on the type of monomer used, the molecular weight of the target TFE polymer, and the reaction rate. Usually, the 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. Also, the polymerization temperature 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.

[0136] When VDF is used as the modifying monomer, 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 in the emulsion polymerization. The 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 VDF concentration may be maintained until the end of the polymerization reaction, or pressure may be released during the reaction. VDF 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.

[0137] When VDF is used as the modifying monomer, it is preferable not to release the pressure in the emulsion polymerization after VDF is charged into the polymerization vessel until the polymerization is completed, which allows VDF to remain in the system until the end of the polymerization, thereby further increasing the strength of the resulting mixture sheet using the TFE-based polymer.

[0138] When HFP is used as the modifying monomer, 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 the emulsion polymerization, since this facilitates the attainment of the above-mentioned physical properties. Furthermore, the HFP concentration in the gas in the reactor at the time when 40 mass % of the total TFE consumed in the polymerization reaction has been polymerized is preferably greater than 0 mol % and 0.2 mol % or less. The above HFP concentration is preferably maintained thereafter 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 then 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 the TFE-based polymer.

[0139] When HFP is used as the modifying monomer, in the above emulsion polymerization, it is preferable to release the pressure before 5 to 40 mass% of the total TFE consumed in the polymerization reaction is polymerized, and then re-increase the pressure using only TFE, in order to further improve the strength of the resulting mixture sheet using the TFE-based polymer. The pressure reduction is preferably carried out so that the pressure inside the reactor becomes 0.2 MPaG or less, more preferably 0.1 MPaG or less, and even more preferably 0.05 MPaG or less, and is preferably carried out so that the pressure inside the reactor becomes 0.0 MPaG or more. The depressurization and re-pressurization may be repeated several times. The depressurization may be carried out until the pressure is reduced using a vacuum pump.

[0140] When CTFE is used as the modifying 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, since this facilitates the attainment of the above-mentioned physical properties. The concentration is also preferably 3.0 mol% or less, more preferably 1.0 mol% or less. The CTFE concentration may be maintained until the end of the polymerization reaction, or pressure may be released during the reaction. 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.

[0141] 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, which allows the CTFE to remain in the system until the end of the polymerization, and further increases the strength of the resulting mixture sheet using the TFE-based polymer.

[0142] The aqueous dispersion in step (A) can also be suitably produced by carrying out step (1a) of emulsion polymerizing TFE and a modifying monomer, in which the modifying monomer is charged into the reaction system at the initial stage of the polymerization reaction, and step (2a) of introducing a chain transfer agent and / or a modifying monomer into the reaction system after step (1a). According to this production method, an aqueous dispersion of the TFE-based polymer having a high SSG or a TFE-based polymer requiring a low extrusion pressure can be easily obtained, and a TFE-based polymer having a core-shell structure can be easily obtained.

[0143] Examples of the modifying monomer in step (1a) include fluoro(alkyl vinyl ethers) such as perfluoro(alkyl vinyl ether) [PAVE]; vinyl heterocycles such as perfluoro-2,2-dimethyl-1,3-dioxole [PDD]; and fluoroolefins such as hexafluoropropylene [HFP] and chlorotrifluoroethylene [CTFE]. One or more of these may be used. Among these, at least one selected from the group consisting of fluoro(alkyl vinyl ether)s and fluoroolefins is preferred, at least one selected from the group consisting of PAVE, HFP, and CTFE is more preferred, at least one selected from the group consisting of PAVE and CTFE is even more preferred, and CTFE is even more preferred. It is also preferable to use PAVE and HFP in combination as the modifying monomers in step (1a). The PAVE is preferably perfluoro(propyl vinyl ether) [PPVE].

[0144] The chain transfer agent used in step (2a) is not particularly limited as long as it reduces the molecular weight of the TFE polymer constituting the shell of the core-shell structure, and examples thereof include non-peroxide organic compounds such as water-soluble alcohols, hydrocarbons, and fluorinated hydrocarbons, water-soluble organic peroxides such as disuccinic acid peroxide [DSP], and persulfates such as ammonium persulfate [APS] and potassium persulfate [KPS]. The chain transfer agent may contain at least one of a non-peroxide organic compound, a water-soluble organic peroxide, and a persulfate. In the chain transfer agent, one or more of each of the non-peroxide organic compound, the water-soluble organic peroxide, and the persulfate can be used.

[0145] The chain transfer agent is preferably at least one selected from the group consisting of water-soluble alcohols having 1 to 4 carbon atoms, hydrocarbons having 1 to 4 carbon atoms, and fluorohydrocarbons having 1 to 4 carbon atoms, in view of good dispersibility and uniformity in the reaction system, more preferably at least one selected from the group consisting of methane, ethane, n-butane, isobutane, methanol, HFC-134a, HFC-32, DSP, APS, and KPS, still more preferably methanol and / or isobutane, and particularly preferably methanol.

[0146] The modifying monomer in step (2a) is preferably at least one selected from the group consisting of the above-mentioned fluoro(alkyl vinyl ether) and fluoroolefin, more preferably at least one selected from the group consisting of PAVE, HFP, and CTFE, even more preferably at least one selected from the group consisting of HFP and CTFE, and even more preferably CTFE.

[0147] In the step (2a), it is also preferable to use the chain transfer agent and the modifying monomer in combination.

[0148] When CTFE is used as the modifying monomer in step (1a), it is preferable to use CTFE as the modifying monomer in step (2a). When PAVE (and HFP) is used as the modifying monomer in step (1a), it is preferable to use methanol (and HFP as the modifying monomer) as the chain transfer agent in step (2a).

[0149] In the above step (1a), the polymerization reaction is preferably carried out until the conversion rate of TFE used in the entire emulsion polymerization process including step (1a) and step (2a) reaches 80% or more, preferably 80 to 97%, and more preferably 85 to 95%. In this specification, the above-mentioned "conversion rate" refers to the proportion of the amount of TFE consumed in the polymerization from the start of polymerization to a certain point during the polymerization, relative to the amount of TFE corresponding to the target amount of TFE units.

[0150] In the above step (1a) and step (2a), the reaction conditions can be appropriately set depending on the type of modifying agent used, the composition and yield of the target TFE polymer, and the like.

[0151] The emulsion polymerization can be carried out in an aqueous medium in the presence of an anionic fluorine-containing surfactant and a polymerization initiator. If necessary, a dispersion stabilizer or the like may be used. The anionic fluorine-containing surfactant can be present in an amount of 0.02 to 0.3% by mass of the aqueous medium.

[0152] Examples of the polymerization initiator include persulfates such as ammonium persulfate (APS), and water-soluble organic peroxides such as disuccinic acid peroxide (DSP). These polymerization initiators can be used alone or in combination of two or more. Among them, APS, DSP, etc. are preferred because they also act as chain transfer agents. The emulsion polymerization is preferably carried out in an amount of 0.0001 to 0.02 parts by mass of the polymerization initiator per 100 parts by mass of the aqueous medium.

[0153] As the aqueous medium, those mentioned above can be used.

[0154] The emulsion polymerization can be carried out at a polymerization temperature of 10 to 95°C, but is preferably carried out at a temperature of 60 to 90°C when a persulfate or a water-soluble organic peroxide is used as the polymerization initiator. The emulsion polymerization can be carried out usually at a pressure of 0.5 to 3.9 MPaG, preferably 0.6 to 3 MPaG. The emulsion polymerization can also be carried out by carrying out the reaction at a pressure of 0.5 MPaG or less at the initial stage of the polymerization, particularly until the TFE conversion rate reaches 15% or less of the total, and then maintaining the pressure at a level exceeding 0.5 MPaG; alternatively, the reaction pressure can be reduced, for example, to 0.1 MPaG or less during the formation of the core, and TFE is again supplied to carry out the reaction at a predetermined pressure.

[0155] The mixing in step (A) can be carried out by a known method.

[0156] The coagulation in step (B) can be carried out by a known method.

[0157] In step (C), the drying is usually carried out by using a vacuum, high frequency, hot air, or other means while the wet powder is kept in a state where it is not fluidized much, preferably kept stationary. Friction between powders, particularly at high temperatures, generally has an undesirable effect on fine powder-type TFE polymers. This is because particles made of this type of TFE polymer tend to easily fibrillate even with a small shear force, losing their original stable particle structure.

[0158] In step (C), the wet powder obtained in step (B) is preferably placed in a container having an air permeable bottom and / or sides, and heat-treated for 2 hours or more at a temperature of 130 to 300° C. By carrying out heat treatment under such extremely limited conditions, the fluorine-containing compound having a molecular weight of 1,000 or less can be efficiently removed together with water, and the contents of the fluorine-containing compound and water can be kept within the above-mentioned ranges.

[0159] 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, still 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.

[0160] 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, from the viewpoint of more efficiently removing moisture and fluorine-containing compounds. The upper limit is not particularly limited, but is, for example, preferably 100 hours, more preferably 50 hours, and even more preferably 30 hours.

[0161] The air velocity 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, and is preferably 50 m / s or less, more preferably 30 m / s or less, and even more preferably 10 m / s or less, from the viewpoint of suppressing scattering of powder.

[0162] 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 an electric furnace such as a parallel-flow box-type electric furnace, a ventilated box-type electric furnace, a ventilated conveyor-type electric furnace, a band furnace, a radiant conveyor-type electric furnace, a fluidized-bed electric furnace, a vacuum electric furnace, a stirring-type electric furnace, an airflow-type electric furnace, or a hot-air circulation electric furnace, or a steam furnace corresponding to the above (an apparatus obtained by replacing the electric furnace in the apparatus name of each electric furnace with 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 furnace, a fluidized-bed electric furnace, a hot-air circulation electric furnace, or a steam furnace corresponding to the above (an apparatus obtained by replacing the electric furnace in the apparatus name of each electric furnace with steam furnace) is preferred.

[0163] The heat treatment in step (C) is preferably carried out by placing the wet powder in a container whose bottom and / or sides are breathable, in order to more efficiently remove moisture and the fluorine-containing compound. The container whose bottom and / or sides are breathable may be any container that can withstand the heat treatment temperature, and is preferably made of a metal such as stainless steel. The container having breathable bottom and / or sides is preferably a tray (bat) having breathable bottom and / or sides, and more preferably a tray having a mesh bottom and / or sides (mesh tray). 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 preferred. 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 porosity is preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more, and is preferably 95% or less.

[0164] In step (C), the amount of the wet powder to be placed is preferably 10 g / cm 3 in order to more efficiently remove moisture and fluorine-containing compounds. 2 Preferably, it is 8 g / cm or less. 2 More preferably, it is 5 g / cm or less. 2 More preferably, it is 3 g / cm or less. 2 It is particularly preferable that the density is 0.01 g / cm or less. 2 It is preferable that the concentration is 0.05 g / cm or more. 2 More preferably, it is 0.1 g / cm or more. 2 More preferably, it is equal to or greater than this.

[0165] 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.

[0166] When the TFE polymers (A) and (B) are mixed in the form of powder, the composition can be produced, for example, by a production method including a step of obtaining the powdered TFE polymers (A) and (B) and a step of mixing the powdered TFE polymers (A) and (B).

[0167] The powdered TFE polymers (A) and (B) can be produced, for example, by a step of coagulating an aqueous dispersion of the TFE polymer (A) and an aqueous dispersion of the TFE polymer (B) to obtain wet powders, and a step of drying the wet powders. The aqueous dispersion of the TFE polymer (A) and the aqueous dispersion of the TFE polymer (B) can be produced, for example, by the method explained for the step (A) above. The coagulation of the aqueous dispersion and the drying of the wet powder can be carried out in the same manner as in the above steps (B) and (C).

[0168] The step of mixing the powdered TFE polymers (A) and (B) is preferably carried out by a mixing method that exerts a low shear force, since this can suppress fibrillation of the fluoropolymer composition, improve powder flowability, and improve the strength of the mixture sheet. Examples of mixing methods that exert a low shear force include airflow mixing and mixing using a V blender, which do not use stirring blades. When a mixing method using a normal stirring blade is used, the TFE-based polymer may become fibrillated, and the desired physical properties may not be obtained.

[0169] The fluoropolymer composition of the present disclosure can be obtained by mixing the fluoropolymer containing the two or more TFE polymers, together with a conductive additive or the like, as needed. The fluoropolymer composition of the present disclosure can be used as a binder for electrochemical devices and is mixed with an electrode active material or a solid electrolyte. In this way, by preparing the fluoropolymer composition of the present disclosure and then mixing it with an electrode active material or a solid electrolyte, the two or more TFE polymers are well dispersed in the fluoropolymer composition, and the binder function is significantly exhibited. In the binder for electrochemical devices, the fluoropolymer composition of the present disclosure may be used alone or in combination with other materials (e.g., polymers other than fluoropolymers), but it is preferable to use the fluoropolymer composition of the present disclosure substantially alone, and more preferably to use it alone. Note that using the fluoropolymer composition of the present disclosure substantially alone means that the amount of the fluoropolymer composition in the binder for electrochemical devices is used within the range described below.

[0170] The present disclosure also provides a binder for electrochemical devices consisting essentially of a fluoropolymer composition, wherein the fluoropolymer composition contains a fluoropolymer, and the fluoropolymer contains two or more types of TFE-based polymers, and the content of the fluoropolymer is 90 mass% or more relative to the fluoropolymer composition. The binder of the present disclosure contains a specific fluorine-based polymer composition, which makes it less likely to generate aggregates even when kneaded for a long period of time with powder components of electrochemical devices, such as electrode active materials and solid electrolytes, and allows for uniform mixing with the powder components. Furthermore, a composite sheet with excellent strength and flexibility can be obtained. The binder of the present disclosure is also advantageous in terms of production process, since 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 combined with it, and it can also reduce the number of steps and costs associated with the use of a dispersion medium. Furthermore, since the binder of the present disclosure has excellent binding strength with the active material and the electrolyte, the amount used can be reduced.

[0171] As the fluoropolymer composition in the binder of the present disclosure, the same fluoropolymer composition as the above-described fluoropolymer composition of the present disclosure can be used, and the preferred embodiments are also the same.

[0172] The binder of the present disclosure consists essentially of the fluoropolymer composition. This allows the effects of the fluoropolymer composition to be significantly exhibited. "Consisting essentially of the fluoropolymer composition" means that the content of the fluoropolymer composition is 95.0% by mass or more relative to the binder. The content of the fluoropolymer 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 above-mentioned fluoropolymer composition.

[0173] The binder of the present disclosure is preferably substantially free of organic solvents. This allows for reduction in the steps and costs associated with the use of organic solvents. "Substantially free of organic solvents" 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.

[0174] The binder of the present disclosure is preferably in the form of a powder.

[0175] The binders of the present disclosure are used in electrochemical devices such as batteries and capacitors. Examples of the battery include secondary batteries such as lithium ion batteries. The capacitor is not particularly limited, but is preferably an electrochemical capacitor. Examples of electrochemical capacitors include electric double layer capacitors, hybrid capacitors, and redox capacitors. Examples of hybrid capacitors include sodium ion capacitors, lithium ion capacitors, and magnesium ion capacitors. Among these, electric double layer capacitors are particularly preferred.

[0176] The binder of the present disclosure can be suitably used as a binder for batteries, and more suitably used as a binder for secondary batteries such as lithium ion batteries. The binders of the present disclosure may be used to fabricate electrochemical device components, preferably 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.

[0177] The present disclosure also provides an electrode mixture containing the fluoropolymer composition or binder of the present disclosure described above and an electrode active material. The use of the electrode mixture of the present disclosure allows the powder components of an electrochemical device to be uniformly dispersed, resulting in a mixture sheet with excellent strength and flexibility. Furthermore, because the electrode active material can be held in place even with a small amount of binder, it is possible to add more materials that improve the electrochemical device properties, such as active materials and conductive additives.

[0178] Examples of the electrode active material include a positive electrode active material and a negative electrode active material.

[0179] 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 composite oxides and alkali metal-containing transition metal phosphate compounds. Of these, alkali metal-containing transition metal composite oxides that generate high voltage are particularly preferred as the positive electrode active material. Examples of the alkali metal ions include lithium ions, sodium ions, and potassium ions. 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.

[0180] Examples of the alkali metal-containing transition metal composite oxide include: Formula:M a Mn 2-b M 1 b O4 (Wherein, M is at least one metal selected from the group consisting of Li, Na, and K; 0.9≦a; 0≦b≦1.5; M 1 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), alkali metal-manganese spinel composite oxides (such as lithium-manganese spinel composite oxides), Formula:MNi 1-c M 2 c O2 (Wherein, M is at least one metal selected from the group consisting of Li, Na, and K; 0≦c≦0.5; M 2 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 O2 (Wherein, M is at least one metal selected from the group consisting of Li, Na, and K; 0≦d≦0.5; M 3 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), and examples thereof include alkali metal-cobalt composite oxides (lithium-cobalt composite oxides, etc.). In the above, M is preferably one metal selected from the group consisting of Li, Na and K, more preferably Li or Na, and even more preferably Li.

[0181] Among these, MCoO2, MMnO2, MNiO2, MMn2O4, and MNi are the most popular because they can provide high energy density and high output secondary batteries. 0.8 Co 0.15 Al 0.05 O2 or MNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and the like are preferred, and a compound represented by the following general formula (3) is preferred. MNi h Co i Mn j M 5 k O2(3) (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K, and M 5 represents at least one element 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.

[0182] 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 (PO4) g (4) (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K, and M 4represents 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, and 1≦g≦3. In the above, M is preferably one metal selected from the group consisting of Li, Na, and K, more preferably Li or Na, and even more preferably Li. That is, the alkali metal-containing transition metal phosphate compound is preferably a lithium-containing transition metal phosphate compound.

[0183] The transition metal in the lithium-containing transition metal phosphate compound is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. Specific examples 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 portion of the transition metal atoms constituting the main components of these compounds have been substituted 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.

[0184] Other examples of the positive electrode active material include lithium-nickel composite oxides. The lithium-nickel composite oxides are represented by the following general formula (5): Li y Ni 1-x M x O2(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.

[0185] Other positive electrode active materials include MFePO4 and MNi 0.8 Co 0.2 O2, M 1.2 Fe 0.4 Mn 0.4 O2, MNi 0.5 Mn 1.5 O2, MV3O6, M2MnO3, etc. In particular, M2MnO3, MNi 0.5 Mn1.5 Positive electrode active materials such as O2 are preferable in that their crystal structures do not collapse even when the secondary battery is operated at a voltage exceeding 4.4 V or at a voltage of 4.6 V or higher. Therefore, an electrochemical device such as a secondary battery using a positive electrode material containing the positive electrode active material exemplified above is preferable because the residual capacity hardly decreases, the resistance increase rate hardly changes even when stored at a high temperature, and the battery performance does not deteriorate even when operated at a high voltage.

[0186] As other positive electrode active materials, solid solution materials such as M2MnO3 and M 6 O2 (where M is at least one metal selected from the group consisting of Li, Na, and K, and M 6 is a transition metal such as Co, Ni, Mn, Fe, etc.) can also be mentioned.

[0187] Examples of the solid solution material include, for example, an alkali metal manganate represented by the general formula Mx[Mn (1-y) M 7 y O z . Here, M in the formula is at least one metal selected from the group consisting of Li, Na, and K, and M 7 consists of at least one metal element other than M and Mn, and includes, for example, one or more elements selected from the group consisting of Co, Ni, Fe, Ti, Mo, W, Cr, Zr, and Sn. Also, 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 them, a manganese-containing solid solution material in which LiNiO2 or LiCoO2 is solid-dissolved based on Li2MnO3 such as Li 1.2 Mn 0.5 Co 0.14 Ni 0.14 O2 is preferable in that it can provide an alkali metal ion secondary battery having a high energy density.

[0188] Furthermore, it is preferable to include lithium phosphate in the positive electrode active material, since this improves continuous charging characteristics. Although there are no limitations on the use of lithium phosphate, it is preferable to use a mixture of the positive electrode active material and lithium phosphate. The amount of lithium phosphate used, based on the total of the positive electrode active material and lithium phosphate, 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, and is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less.

[0189] Alternatively, a substance having a different composition may be attached to the surface of the positive electrode active material, such as an oxide, such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, or bismuth oxide; a sulfate, such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, or aluminum sulfate; a carbonate, such as lithium carbonate, calcium carbonate, or magnesium carbonate; or carbon.

[0190] These surface-attaching substances can be attached to the surface of the positive electrode active material by, for example, a method of dissolving or suspending the substance in a solvent, impregnating the positive electrode active material, and then drying, a method of dissolving or suspending a surface-attaching substance precursor in a solvent, impregnating the positive electrode active material, and then reacting the surface-attaching substance by heating, or a method of adding the substance to a positive electrode active material precursor and simultaneously baking the surface-attaching substance, etc. When carbon is attached, a method of mechanically attaching the carbonaceous material in the form of, for example, activated carbon, etc., after the surface-attaching substance is also available.

[0191] The amount of the surface-attached substance is, by mass relative to the positive electrode active material, preferably 0.1 ppm or more as the lower limit, 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 as the upper limit. The surface-attached substance can suppress the oxidation reaction of the electrolyte on the surface of the positive electrode active material and improve the battery life, but if the amount of attachment is too small, the effect will not be fully exerted, and if it is too large, the movement of lithium ions is hindered, which may increase the resistance.

[0192] The shape of the particles of the positive electrode active material may be any of the conventional shapes such as block, polyhedron, sphere, oval sphere, plate, needle, column, etc. Furthermore, primary particles may aggregate to form secondary particles.

[0193] The tap density of the positive electrode active material is preferably 0.5 g / cm 3 More preferably, 0.8 g / cm 3 More preferably, 1.0 g / cm 3 That is all. If the tap density of the positive electrode active material is below the above lower limit, the amount of dispersion medium required when forming the positive electrode active material layer increases, and the amounts of conductive material and binder required also increase, which may restrict the filling rate of the positive electrode active material in the positive electrode active material layer and restrict the battery capacity. By using a composite oxide powder with a high tap density, a high-density positive electrode active material layer can be formed. Generally, the higher the tap density, the better, and there is no particular upper limit. However, if the tap density 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 reduced. Therefore, the upper limit is preferably 4.0 g / cm. 3 or less, more preferably 3.7 g / cm 3 More preferably 3.5 g / cm or less 3 The following is the result. The tap density is the powder packing density (tap density) in g / cm when 5 to 10 g of positive electrode active material powder is placed in a 10 ml glass measuring cylinder and tapped 200 times with a stroke of approximately 20 mm. 3 is required.

[0194] The median diameter d50 of the particles of the positive electrode active material (the secondary particle diameter when primary particles aggregate 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. Below the lower limit, a high tap density product may not be obtained. Above the upper limit, lithium diffusion within the particles takes too long, resulting in problems such as reduced battery performance. Mixing two or more of the above positive electrode active materials with different median diameters d50 can further improve the packing properties during positive electrode fabrication.

[0195] The median diameter d50 is measured using a known laser diffraction / scattering particle size distribution analyzer. When using a HORIBA LA-920 as the particle size distribution analyzer, the measurement is performed using a 0.1% by mass aqueous solution of sodium hexametaphosphate as the dispersion medium, and after ultrasonic dispersion for 5 minutes, the measurement is performed with a refractive index set to 1.24.

[0196] When primary particles aggregate 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, with an upper limit of 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 becomes difficult to form spherical secondary particles, which can adversely affect powder packing and significantly reduce the specific surface area, potentially resulting in a decrease in battery performance, such as output characteristics. Conversely, if the lower limit is exceeded, problems such as poor charge / discharge reversibility can 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 10,000x magnification, the longest intercepts of a horizontal line drawn between the left and right boundaries of a primary particle are determined for any 50 primary particles, and the average value is calculated.

[0197] The BET specific surface area of ​​the positive electrode active material is preferably 0.1 m 2 / g or more, more preferably 0.2m 2 / g or more, more preferably 0.3m 2 / g or more, and the upper limit is preferably 50m 2 / g or less, more preferably 40m 2 / g or less, more preferably 30m 2 If the BET specific surface area is smaller than this range, the battery performance is likely to decrease, whereas if it is larger, it becomes difficult to increase the tap density, which may easily cause problems in processability when forming the positive electrode active material layer. The BET specific surface area is defined as a value measured by a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.) using a nitrogen-helium mixed gas precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3, after which the sample is pre-dried at 150°C for 30 minutes under a nitrogen flow, by a nitrogen adsorption BET single-point method using a gas flow method.

[0198] When the secondary battery of the present disclosure is used as a large-scale 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. The particles of the positive electrode active material preferably have an average secondary particle size of 40 μm or less and contain 0.5 to 7.0 volume % of fine particles having an average primary particle size of 1 μm or less. The inclusion of fine particles having an average primary particle size of 1 μm or less increases the contact area with the electrolyte, allowing for faster diffusion of lithium ions between the electrode mixture and the electrolyte, resulting in improved battery output performance.

[0199] The cathode active material is produced by a method generally used for producing inorganic compounds. In particular, various methods are conceivable for producing spherical or oval-spherical active materials, such as dissolving or pulverizing and dispersing raw materials of transition metals in a solvent such as water, adjusting the pH while stirring, producing and recovering spherical precursors, drying them as necessary, adding a Li source such as LiOH, Li2CO3, or LiNO3, and baking them at high temperatures to obtain active materials.

[0200] For the production of a positive electrode, the above-mentioned positive electrode active materials may be used alone, or two or more of different compositions may be used in any combination or ratio. In this case, a preferred combination is LiCoO2 and LiNi 0.33 Co 0.33 Mn 0.33 Examples of such a combination include a combination with a ternary system such as O2, a combination of LiCoO2 and LiMn2O4 or a combination in which part of the Mn has been replaced with another transition metal, or a combination of LiFePO4 and LiCoO2 or a combination in which part of the Co has been replaced with another transition metal.

[0201] 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.

[0202] The negative electrode active material is not particularly limited, and examples thereof include lithium metal, artificial graphite, graphite carbon fiber, resin-baked carbon, pyrolytic vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-baked 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 Li4Ti5O 12Among them, those containing at least a carbonaceous material and silicon-containing compounds are particularly suitable.

[0203] The negative electrode active material used in the present disclosure preferably contains silicon as a constituent element, which allows the production of a high-capacity battery.

[0204] The silicon-containing material is preferably silicon particles, particles having a structure in which silicon fine particles are dispersed in a silicon-based compound, silicon oxide particles represented by the general formula SiOx (0.5≦x≦1.6), or a mixture thereof. By using these, a negative electrode mixture for a lithium ion secondary battery having higher initial charge / discharge efficiency, high capacity, and excellent cycle characteristics can be obtained.

[0205] In this disclosure, silicon oxide is a general term for amorphous silicon oxides, and silicon oxide before disproportionation is represented by the general formula SiOx (0.5≦x≦1.6). Preferably, x is 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.

[0206] Particles having a structure in which silicon nanoparticles are dispersed in a silicon-based compound can be obtained, for example, by calcining a mixture of silicon nanoparticles and a silicon-based compound, or by heat-treating undisproportionated silicon oxide particles represented by the general formula SiOx in an inert, non-oxidizing atmosphere such as argon at temperatures above 400°C, preferably 800 to 1,100°C, to carry out a disproportionation reaction. Materials obtained by the latter method are particularly suitable because the silicon crystallites are uniformly dispersed. The disproportionation reaction described above can reduce the size of silicon nanoparticles to 1 to 100 nm. The silicon oxide in particles having a structure in which silicon nanoparticles are dispersed in silicon oxide is preferably silicon dioxide. The dispersion of silicon nanoparticles (crystals) in amorphous silicon oxide can be confirmed using a transmission electron microscope.

[0207] 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 average particle size is expressed as the weight-average particle size measured by particle size distribution measurement using a laser diffraction method.

[0208] BET specific surface area is 0.5 to 100 m 2 / g is preferred, and 1 to 20m 2 / g is more preferable. 2 If the surface roughness is 100m / g or more, there is no risk of the adhesiveness decreasing when processed into an electrode, which may result in a decrease in the electrochemical device characteristics. 2 / g or less, the proportion of silicon dioxide on the particle surface is large, and there is no risk of a decrease in battery capacity when used as a negative electrode material for a lithium ion secondary battery.

[0209] The silicon-containing particles are coated with carbon to impart conductivity, resulting in improved electrochemical device properties. Methods for imparting conductivity include mixing the silicon-containing particles with conductive particles such as graphite, coating the surfaces of the silicon-containing particles with a carbon coating, and combining both methods. The carbon coating method is preferred, and chemical vapor deposition (CVD) is more preferred.

[0210] In order to increase the capacity of the resulting electrode mixture, the content of the negative electrode active material is preferably 40% by mass or more, more preferably 50% by mass or more, and particularly preferably 60% by mass or more, and the upper limit is preferably 99% by mass or less, more preferably 98% by mass or less.

[0211] The electrode mixture of the present disclosure preferably further contains a conductive auxiliary agent. The conductive auxiliary agent may be one contained in the fluoropolymer composition of the present disclosure, or may be one added separately from the fluoropolymer composition of the present disclosure.

[0212] The conductive additive is used in an amount of typically 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more, and typically 50% by mass or less, preferably 30% by mass or less, more preferably 15% by mass or less, in the electrode mixture. 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.

[0213] 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.

[0214] 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. On the other hand, 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 the active materials.

[0215] In the electrode mixture of the present disclosure, the binder content 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 binder content is too low, the electrode mixture active material may not be sufficiently retained, resulting in insufficient mechanical strength of the electrode mixture sheet and deterioration of battery performance such as cycle characteristics. On the other hand, if the binder content is too high, it may lead to a decrease in battery capacity and conductivity. Because the binder of the present disclosure has excellent binding strength, even a small content can sufficiently retain the electrode active material.

[0216] In the electrode mixture of the present disclosure, the binder component preferably consists essentially of the fluoropolymer composition, more preferably the fluoropolymer composition. The binder component consisting essentially of the fluoropolymer composition means that the content of the fluoropolymer 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 fluoropolymer composition 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 binder component.

[0217] The electrode mixture of the present disclosure is preferably in the form of a sheet.

[0218] 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.

[0219] 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, 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.

[0220] An example of a specific method for producing an electrode mixture sheet containing an electrode mixture is shown below. The electrode mixture sheet can be obtained by a production method including the steps of: (1) mixing a raw material composition containing an electrode active material, a binder, and, if necessary, a conductive additive; (2) forming the raw material composition obtained in the step (1) into a bulk; and (3) rolling the bulk raw material composition obtained in the step (2) into a sheet.

[0221] 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 formless state. Specific mixing methods include mixing methods using a W-type mixer, V-type mixer, drum mixer, ribbon mixer, conical screw mixer, single-screw kneader, twin-screw kneader, mix muller, stirring mixer, planetary mixer, etc.

[0222] In the above step (1), the binder mixing condition is preferably 3000 rpm or less. It is preferably 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 the mixing speed is below the above range, it will take a long time to mix, which will affect productivity. If the mixing speed is above the above range, fibrillation will proceed excessively, which may result in an electrode mixture sheet with poor strength and flexibility.

[0223] In the above step (2), forming into a bulk state refers to forming the raw material composition into a single mass. Specific methods for forming into a bulk state include extrusion molding, press molding, etc. Furthermore, the term "bulk state" 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, including rods, sheets, spheres, cubes, etc.

[0224] Specific examples of the rolling method in the above step (3) include rolling methods using a roll press, a plate press, a calender roll, or the like.

[0225] It is also preferable to include 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, by rolling the rolled sheet little by little in stages rather than thinning it all at once, flexibility is improved. 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 an even thinner sheet.

[0226] From the viewpoint of adjusting the fibril diameter, it is also preferable to include a step (5) after step (3) or step (4) in which the rolled sheet is crushed, re-formed into a bulk form, and rolled into a sheet. It is also preferable to repeat step (5). The number of times step (5) is performed is preferably from 1 to 12 times, more preferably from 2 to 11 times.

[0227] In step (5), specific methods for roughly crushing the rolled sheet and forming it into a bulk form include folding the sheet, forming it into a rod or thin sheet, chipping, etc. In the present disclosure, "rough crushing" means changing the form of the rolled sheet obtained in step (3) or (4) into a different form so that it can be rolled into a sheet in the next step, and also includes simply folding the rolled sheet.

[0228] Furthermore, step (4) may be performed after step (5), or may be repeated. 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).

[0229] In the above steps (3), (4), or (5), the rolling ratio is preferably 10% or more, more preferably 20% or more, and preferably 80% or less, more preferably 65% ​​or less, and even more preferably 50% or less. If the rolling ratio is below the above range, the number of rolling operations increases, which takes more time and affects productivity. If the rolling ratio 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 rate of reduction in thickness of the sample after rolling relative 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.

[0230] The electrode mixture sheet is Step (a): mixing powder components and a binder to form an electrode mixture; Step (b): Calendaring or extrusion molding the electrode mixture to produce a sheet; Including, The mixing in step (a) is (a1) homogenizing the powder components and the binder to form a powder; (a2) mixing the powdered raw material mixture obtained in step (a1) to prepare an electrode mixture; It can also be suitably produced by a production method comprising the steps of:

[0231] For example, PTFE has two transition temperatures at about 19°C and about 30°C. Below 19°C, PTFE can be easily mixed while maintaining its shape. However, above 19°C, the structure of the PTFE particles becomes loose and more sensitive to mechanical shear. At temperatures above 30°C, a greater degree of fibrillation occurs.

[0232] For this reason, the homogenization in (a1) is preferably carried out at a temperature of 19°C or lower, preferably 0 to 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.

[0233] The above step (a2) is carried out at a temperature of preferably 30°C to 150°C, more preferably 35°C to 120°C, and even more preferably 40°C to 80°C. In one embodiment, the calendering 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.

[0234] The mixing in the step (a) is preferably carried out while applying a shear force. Specific mixing methods include methods using a W-type mixer, V-type mixer, drum mixer, ribbon mixer, conical screw mixer, single-screw kneader, twin-screw kneader, Mix Muller, stirring mixer, planetary mixer, Henschel mixer, high-speed mixer, etc.

[0235] The mixing conditions may be set appropriately by adjusting the rotation speed and mixing time. For example, the rotation speed 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 the rotation speed is below the above range, mixing will take a long time, which will affect productivity. If the rotation speed is above the above range, fibrillation will proceed excessively, which may result in an electrode mixture sheet with poor strength. The step (a1) is preferably carried out with a weaker shear force than the step (a2). Furthermore, it is desirable that step (a1) be carried out for a shorter time than step (a2).

[0236] In the step (a2), the raw material composition preferably 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 step (a1) to prepare a paste.

[0237] The lubricant is not particularly limited, and examples thereof include water, ether compounds, alcohols, ionic liquids, carbonates, aliphatic hydrocarbons (low-polarity solvents such as heptane and xylene), isoparaffin hydrocarbon compounds, and petroleum fractions (gasoline (C4-C10), naphtha (C4-C11), kerosene / paraffin (C10-C16), and mixtures thereof).

[0238] The lubricant preferably has a water content of 1000 ppm or less. A water content of 1000 ppm or less is preferable in terms of reducing deterioration of the electrochemical device, and the water content is more preferably 500 ppm or less.

[0239] When the above-mentioned lubricant is used, it is particularly preferable that the lubricant is a solvent with low polarity such as butyl butyrate, or an ether compound.

[0240] When the above 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, more preferably 15.0 to 25.0 parts by weight, based on the total weight of the composition used in step (a1).

[0241] It is preferable that the raw material composition substantially does not contain a liquid medium. Conventional electrode mixture formation methods generally involve preparing a slurry in which powder electrode mixture components are dispersed using a solvent containing a binder, and then coating and drying the slurry to prepare an electrode mixture sheet. In this case, a solvent that disperses or dissolves the binder is used. However, solvents that can dissolve binder resins that have been commonly used in the past are limited to specific solvents such as N-methylpyrrolidone. Because of their high polarity and the drying process required, the use of solvents increases processing steps and costs. Furthermore, these solvents react with electrolytes, such as electrolytic solutions and solid electrolytes, degrading the electrolyte. Therefore, residual components during slurry preparation or after drying can cause a decrease in battery performance. Furthermore, low-polarity solvents such as heptane dissolve only a very limited number of binder resins, and their low flash points can make handling difficult.

[0242] By using a powder binder with low moisture content without using a solvent when forming the electrode mixture sheet, a battery with little electrolyte deterioration can be manufactured. Furthermore, in the manufacturing method described above, an electrode mixture sheet containing a binder with a fine fibrous structure can be manufactured, and by not preparing a slurry, the burden on the manufacturing process can be reduced.

[0243] Step (b) is calendering or extrusion. Calendering and extrusion can be performed by well-known methods. By doing so, the mixture can be formed into the shape of an electrode mixture sheet. Step (b) preferably includes: (b1) forming the electrode mixture obtained in step (a) into a bulk form; and (b2) calendering or extrusion-molding the bulk electrode mixture.

[0244] 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. Furthermore, the term "bulk" does not particularly specify a shape, but may refer to a state in which the material is in the form of a single mass, including rods, sheets, spheres, cubes, and the like. The size of the mass is preferably such that the diameter or the shortest side of the cross section is 10,000 μm or more, more preferably 20,000 μm or more.

[0245] Specific examples of the calendering or extrusion molding method in the step (b2) include a method in which the electrode mixture is rolled using a roll press, a calender roll, or the like.

[0246] 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 is easily fibrillated at temperatures above 30° C. Therefore, the step (b) is preferably carried out at such a temperature.

[0247] Then, calendering or extrusion applies shear force, which causes the PTFE to fibrillate and form.

[0248] It is also preferable to have a step (c) after step (b) 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 (c). In this way, by rolling the rolled sheet little by little in stages rather than thinning it all at once, flexibility is improved. The number of times step (c) is carried out is preferably 2 to 10 times, more preferably 3 to 9 times. A specific rolling method is, 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.

[0249] From the viewpoint of adjusting the sheet strength, it is also preferable to include a step (d) after step (b) or step (c) in which the rolled sheet is crushed, re-formed into a bulk form, and rolled into a sheet. It is also preferable to repeat step (d). The number of times step (d) is performed is preferably from 1 to 12 times, more preferably from 2 to 11 times.

[0250] In step (d), specific methods for crushing the rolled sheet and forming it into a bulk form include folding the rolled sheet, forming it into a rod or thin film sheet, chipping, etc. In the present disclosure, "crushing" means changing the form of the rolled sheet obtained in step (b) or (c) into a different form in order to roll it into a sheet in the next step, and also includes simply folding the rolled sheet.

[0251] 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 steps (a), (b), (c), and (d). Furthermore, the sheet strength can also be adjusted by the degree of crushing in step (d).

[0252] 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 the rolling ratio is below the above range, the number of rolling operations increases, which takes time and affects productivity. If the rolling ratio 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 relative 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 at 150° C. or lower.

[0253] 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. The electrode mixture sheet is particularly suitable for a lithium ion secondary battery.

[0254] The present disclosure also provides an electrode comprising the fluoropolymer 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 has uniformly dispersed powder components of an electrochemical device, and is therefore excellent in strength and flexibility. Furthermore, because the electrode active material can be held in place even with a small amount of binder, it is possible to add larger amounts of materials that improve electrochemical device properties, such as active materials and conductive additives.

[0255] The electrode of the present disclosure may include the above-described electrode mixture of the present disclosure (preferably an electrode mixture sheet) and a current collector.

[0256] The electrodes of the present disclosure may be positive electrodes or negative electrodes.

[0257] 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 alloys thereof; and carbon materials such as carbon cloth and carbon paper. Among these, metal materials, particularly aluminum or its alloys, are preferred.

[0258] Examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, expanded metal, punched metal, and foam metal for metal materials, and carbon plate, carbon thin film, and carbon cylinder for carbon materials. Of these, metal foil is preferred. The metal foil may be formed into a mesh shape as appropriate. The thickness of the metal foil is optional, but is usually 1 μm or more, preferably 3 μm or more, and more preferably 5 μm or more, and is usually 1 mm or less, preferably 100 μm or less, and 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.

[0259] In addition, it is also preferable that the surface of the current collector is coated with a conductive additive, from the viewpoint of reducing the electrical contact resistance between the current collector and the positive electrode active material layer. Examples of the conductive additive include carbon and precious metals such as gold, platinum, and silver.

[0260] The positive electrode may be produced by a conventional method, for example, by laminating the electrode mixture sheet and a current collector with an adhesive therebetween, followed by vacuum drying.

[0261] The density of the positive electrode mixture sheet is preferably 2.80 g / cm 3 More preferably, 3.00 g / cm 3 More preferably, 3.20 g / cm 3 or more, and preferably 3.80 g / cm 3 or less, more preferably 3.75 g / cm 3 More preferably, 3.70 g / cm or less 3 The range is as follows. If the temperature exceeds this range, cracks may easily occur within the sheet. If the temperature falls below this range, the conductivity between the active materials may decrease, increasing the battery resistance and making it difficult to obtain high output.

[0262] 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 thickness of the metal foil of the current collector is preferably 10 μm or more, more preferably 20 μm or more, as a lower limit, and is preferably 500 μm or less, more preferably 450 μm or less, on one side of the current collector.

[0263] 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 alloys thereof; and carbon materials such as carbon cloth and carbon paper. Among these, metal materials, particularly copper, nickel, and alloys thereof, are preferred.

[0264] Examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, expanded metal, punched metal, and foam metal for metal materials, and carbon plate, carbon thin film, and carbon cylinder for carbon materials. Of these, metal foil is preferred. The metal foil may be formed into a mesh shape as appropriate. The thickness of the metal foil is optional, but is usually 1 μm or more, preferably 3 μm or more, and more preferably 5 μm or more, and is usually 1 mm or less, preferably 100 μm or less, and 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.

[0265] The negative electrode may be produced by a conventional method, for example, by laminating the electrode mixture sheet and a current collector with an adhesive therebetween, followed by vacuum drying.

[0266] The density of the negative electrode mixture is preferably 1.3 g / cm 3 More preferably, 1.4 g / cm 3 More preferably, 1.5 g / cm 3 or more, and preferably 2.0 g / cm 3 or less, more preferably 1.9 g / cm 3 More preferably 1.8 g / cm or less 3The range is as follows. If the temperature exceeds this range, cracks may easily occur within the sheet. If the temperature falls below this range, the conductivity between the active materials may decrease, increasing the battery resistance and making it difficult to obtain high output.

[0267] 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 thickness of the metal foil of the current collector is preferably 10 μm or more, more preferably 20 μm or more, as a lower limit, and is preferably 500 μm or less, more preferably 450 μm or less, on one side of the current collector.

[0268] The present disclosure also provides a secondary battery comprising the electrode of the present disclosure described above.

[0269] The secondary battery of the present disclosure may be a secondary battery that uses an electrolyte solution or may be a solid secondary battery. In this specification, the solid-state secondary battery may be a secondary battery containing a solid electrolyte, and may be a semi-solid-state secondary battery containing a solid electrolyte and a liquid component as the electrolyte, or an all-solid-state secondary battery containing only a solid electrolyte as the electrolyte.

[0270] The secondary battery using the above-mentioned electrolyte solution can use the electrolyte solution, separator, etc. used in known secondary batteries, which will be described in detail below.

[0271] The electrolyte is preferably a non-aqueous electrolyte, which may be prepared by dissolving a known electrolyte salt in a known organic solvent for dissolving electrolyte salts.

[0272] The organic solvent for dissolving the electrolyte salt is not particularly limited, and one or more of 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-containing solvents such as fluoroethylene carbonate, fluoroethers, and fluorinated carbonates can be used.

[0273] Examples of electrolyte salts include LiClO4, LiAsF6, LiBF4, LiPF6, LiN(SO2CF3)2, and LiN(SO2C2F5)2, and LiPF6, LiBF4, LiN(SO2CF3)2, LiN(SO2C2F5)2, or combinations thereof are particularly preferred due to their favorable cycle characteristics.

[0274] The concentration of the electrolyte salt is preferably 0.8 mol / L or more, more preferably 1.0 mol / L or more. The upper limit is usually 1.5 mol / L, although it depends on the organic solvent used to dissolve the electrolyte salt.

[0275] A secondary battery using the above-mentioned electrolyte solution preferably further includes a separator. The material and shape of the separator are not particularly limited as long as it is stable to the electrolyte solution and has excellent liquid retention properties, and any known separator can be used. Among them, it is preferable to use a material that is stable to the electrolyte solution, such as resin, glass fiber, or inorganic material, and that is in the form of a porous sheet or nonwoven fabric with excellent liquid retention properties.

[0276] Examples of materials that can be used for the resin or glass fiber separator include polyolefins such as polyethylene and polypropylene, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, and glass filters. These materials may be used alone or in any combination and ratio, such as polypropylene / polyethylene two-layer films and polypropylene / polyethylene / polypropylene three-layer films. Among these, porous sheets or nonwoven fabrics made from polyolefins such as polyethylene and polypropylene are preferred for the separator, due to their excellent electrolyte permeability and shutdown effect.

[0277] The thickness of the separator is optional, but is usually 1 μm or more, preferably 5 μm or more, more preferably 8 μm or more, and 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 be reduced. On the other hand, if the separator is thicker than the above range, not only may the battery performance such as rate characteristics be reduced, but also the energy density of the entire electrolyte battery may be reduced.

[0278] 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 these are used in particulate or fibrous form.

[0279] As for the form, a thin film such as a nonwoven fabric, a woven fabric, or a microporous film is used. A thin 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-mentioned independent thin film, a separator can be used in which a composite porous layer containing the above-mentioned 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.

[0280] The material of the outer case is not particularly limited as long as it is stable against the electrolyte used. Specifically, metals such as nickel-plated steel sheet, stainless steel, aluminum or aluminum alloy, magnesium alloy, 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 film are preferably used.

[0281] Examples of exterior cases using metals include those in which metals are welded together to form a sealed, airtight structure by laser welding, resistance welding, or ultrasonic welding, or those in which the metals are used via a resin gasket to form a crimped structure. Examples of exterior cases using the above-mentioned laminate film include those in which resin layers are heat-sealed to form a sealed, airtight structure. In order to improve sealing properties, a resin different from the resin used in the laminate film may be interposed between the resin layers. In particular, when a sealed structure is formed by heat-sealing the resin layers via a current collecting terminal, 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, since the metal and the resin are bonded together.

[0282] The shape of the secondary battery using the above-mentioned electrolyte solution is arbitrary, and examples thereof include cylindrical, prismatic, 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.

[0283] The solid secondary battery is preferably an all-solid secondary battery, and is also preferably a lithium ion battery, and is also preferably a sulfide-based solid 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 mixture (preferably a mixture 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.

[0284] 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.

[0285] The sulfide-based solid electrolyte is not particularly limited and may be Li2S-P2S5, Li2S-P2S3, Li2S-P2S3-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, LiI-Li2S-SiS2-P2S5, Li2S-SiS2-Li4SiO4, Li2S-SiS2-Li3PO4, Li3PS4-Li4GeS4, Li 3.4 P 0.6 Si 0.4 S4, Li 3.25 P 0.25 Ge 0.76 S4, Li 4-x Ge 1-x P x S4(X=0.6~0.8), Li 4+y Ge 1-y Ga y S4(y=0.2~0.3), 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 SnP2S 12 Any one selected from the above, or a mixture of two or more thereof, can be used.

[0286] 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 having high energy density.

[0287] 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.

[0288] Specific examples of compounds include Li xa La ya TiO3 [xa=0.3~0.7, ya=0.3~0.7] (LLT), Li xb La yb Zrzb M bb mb O nb (M bb is at least one element selected from Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, where xb satisfies 5≦xb≦10, yb satisfies 1≦yb≦4, zb satisfies 1≦zb≦4, mb satisfies 0≦mb≦2, and nb satisfies 5≦nb≦20.), Li xc B yc M cc zc O nc (M cc is at least one element selected from C, S, Al, Si, Ga, Ge, In, and Sn, where xc satisfies 0≦xc≦5, yc satisfies 0≦yc≦1, zc satisfies 0≦zc≦1, and nc satisfies 0≦nc≦6.), Li xd (Al,Ga) yd (Ti,Ge) zd Si ad P md O nd (where 1≦xd≦3, 0≦yd≦2, 0≦zd≦2, 0≦ad≦2, 1≦md≦7, 3≦nd≦15), Li (3-2xe) M ee xe D ee O(xe represents a number between 0 and 0.1, and M ee represents a divalent metal atom. ee represents a halogen atom or a combination of two or more halogen atoms.) Li xf Si yf O zf (1≦xf≦5, 0 <yf≦3、1≦zf≦10)、Li xg S yg O zg (1≦xg≦3, 0 <yg≦2、1≦zg≦10)、Li3BO3-Li2SO4、Li2O-B2O3-P2O5、Li2O-SiO2、Li6BaLa2Ta2O 12 , LiPO (4-3 / 2w) N w (w<1), Li with LISICON (Lithium super ionic conductor) type crystal structure 3.5 Zn 0.25GeO4, La with perovskite crystal structure 0.51 Li 0.34 TiO 2.94 , La 0.55 Li 0.35 TiO3, LiTi2P3O with NASICON (sodium super ionic conductor) type crystal structure 12 , Li 1+xh+yh (Al,Ga) xh (Ti,Ge) 2-xh Si yh P 3-yh O 12 (where 0≦xh≦1, 0≦yh≦1), Li7La3Zr2O with a garnet-type crystal structure 12 (LLZ), etc. Ceramic materials in which elements are substituted for LLZ are also known. For example, Li 6.24 La3Zr2Al 0.24 O 11.98 , Li 6.25 Al 0.25 La3Zr2O 12 and Ta-substituted Li 6.6 La3Zr 1.6 Ta 0.4 O 12 , Nb-substituted Li 6.75 La3Zr 1.75 Nb 0.25 O 12 Other examples include LLZ-based ceramic materials in which at least one element, Mg (magnesium) or A (A is at least one element selected from the group consisting of Ca (calcium), Sr (strontium), and Ba (barium)), is substituted for LLZ. Phosphorus compounds containing Li, P, and O are also desirable. For example, lithium phosphate (Li3PO4), LiPON, LiPOD, and other lithium phosphates in which some of the oxygen in the lithium phosphate is substituted with nitrogen, are also desirable. 1 (D 1 is at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc. 1 ON(A 1is at least one selected from Si, B, Ge, Al, C, Ga, etc. Specific examples include Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2 and Li2O-Al2O3-SiO2-P2O5-TiO2.

[0289] The oxide-based solid electrolyte preferably contains lithium. The oxide-based solid electrolyte containing lithium is used in a solid-state battery that uses lithium ions as a carrier, and is particularly preferred in terms of electrochemical devices having a high energy density.

[0290] 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 (La 0.51 Li 0.34 TiO 2.94 etc.), NASICON type (Li 1.3 Al 0.3 Ti 1.7 (PO4)3, etc.), garnet type (Li7La3Zr2O 12 (LLZ), etc. Among these, NASICON type is preferred.

[0291] The volume-average particle size of the oxide-based solid electrolyte is not particularly limited, but is preferably 0.01 μm or greater, and more preferably 0.03 μm or greater. The upper limit is preferably 100 μm or less, and more preferably 50 μm or less. The average particle size of oxide-based solid electrolyte particles is measured using the following procedure: A 1% by mass dispersion of oxide-based solid electrolyte particles is prepared by diluting them with water (or heptane for water-unstable substances) in a 20 ml sample bottle. The diluted dispersion sample is irradiated with 1 kHz ultrasound for 10 minutes and immediately used for testing. Using this dispersion sample, a laser diffraction / scattering particle size analyzer LA-920 (manufactured by HORIBA) is used to acquire data 50 times at 25°C using a quartz measurement cell to obtain the volume-average particle size. For other detailed conditions, please refer to JIS Z 8828:2013, "Particle Size Analysis - Dynamic Light Scattering Method," as necessary. Five samples are prepared for each level, and the average value is used.

[0292] The solid secondary battery may include a separator between the positive electrode and the negative electrode, such as a porous membrane of polyethylene or polypropylene, or a nonwoven fabric made of a resin such as polypropylene, or a glass fiber nonwoven fabric.

[0293] 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 shape, a square shape, a coin shape, and a laminate shape.

[0294] The solid secondary battery can be produced, for example, by stacking a positive electrode, a solid electrolyte layer sheet, and a negative electrode in this order and pressing them together.

[0295] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims. [Example]

[0296] The present disclosure will now be described in more detail with reference to examples, but the present disclosure is not limited to these examples.

[0297] Various physical properties were measured by the following methods.

[0298] <Average primary particle diameter> The aqueous dispersion of fluoropolymer was diluted with water to a solid content of 0.15% by mass, and the transmittance of the diluted latex to a 550 nm incident light per unit length and the number-average primary particle diameter determined by measuring the unidirectional diameter using a transmission electron microscope were measured to prepare a calibration curve. Using this calibration curve, the average primary particle diameter was determined from the measured transmittance of the 550 nm incident light for each sample.

[0299] <Polymer solids concentration> 1 g of the aqueous fluoropolymer 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.

[0300] <Modified Monomer Content> The CTFE content was determined by press-molding a thin film disk from a fluoropolymer powder or composition, and measuring the infrared absorbance of the thin film disk using FT-IR. -1 Absorbance at / 2360cm -1 The absorbance ratio was calculated by multiplying the absorbance ratio at 0.58. The HFP content was determined by press-molding a thin film disk from a fluoropolymer powder or composition, and measuring the infrared absorbance of the thin film disk by FT-IR. -1 Absorbance at / 935cm -1 The absorbance ratio was calculated by multiplying the absorbance ratio by 0.3.

[0301] <Standard specific gravity (SSG)> Using samples molded in accordance with ASTM D4895 89, measurements were made by the water displacement method in accordance with ASTM D 792.

[0302] <Extrusion pressure> 60 g of fluoropolymer powder and 12.3 g of hydrocarbon oil (trade name: Isopar G (registered trademark), manufactured by ExxonMobil Corporation) serving 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 maintained for 1 minute. The mixture was then extruded through 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. The extrusion pressure (MPa) was determined by dividing the load (N) by the cross-sectional area of ​​the cylinder when the pressure reached equilibrium in the latter half of the extrusion operation.

[0303] <Endothermic peak temperature> The endothermic peak temperature was determined as the temperature corresponding to the minimum point on the heat of fusion curve when a fluoropolymer powder or composition that had not been heated to a temperature of 300° C. or higher was heated at a rate of 2° C. / min using a differential scanning calorimeter (DSC). When there were two or more minimum points, each was determined as the endothermic peak temperature.

[0304] <Paste extrusion availability> 60 g of a fluoropolymer powder or composition was mixed with 12.3 g of hydrocarbon oil (trade name: Isopar G (registered trademark), manufactured by ExxonMobil Corporation) as an extrusion aid 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 in the cylinder and maintained for 1 minute. The mixture was then extruded through 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. If the beads were torn and could not be continuously extruded, the mixture was judged to be unextrudable, and if the beads were not torn and could be continuously extruded, the mixture was judged to be extrudable.

[0305] <Moisture content> Approximately 20 g of a fluoropolymer powder or composition was heated at 150°C for 2 hours, and the mass was measured before and after, and calculated according to the following formula: A sample was taken three times, and the values ​​were calculated for each time, and the average value was calculated and used. Moisture content (mass%)=[(mass (g) of fluoropolymer powder or composition before heating)−(mass (g) of fluoropolymer powder or composition after heating)] / (mass (g) of fluoropolymer powder or composition before heating)×100

[0306] <Content of perfluoroether carboxylic acids A and B> 1 g of the fluoropolymer composition was weighed, 10 g (12.6 ml) of methanol was added, and the mixture was sonicated for 60 minutes to obtain an extract. The resulting extract was measured by LC / MS / MS. The fluorine-containing compounds in the extract were measured using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC / TQD). The measurement equipment configuration and LC-MS measurement conditions are shown in Table 1. Using aqueous solutions of fluorine-containing compounds with known concentrations, aqueous solutions with five or more levels of content were prepared, and LC / MS analysis of each level was performed. The relationship between the content and the area versus content was plotted to draw a calibration curve. Using the calibration curve, the area of ​​the LC / MS chromatogram of the fluorine-containing compounds in the extract was converted to the content of the fluorine-containing compounds. The lower detection limit for this measurement method is 10 ppb by mass. [Table 1]

[0307] <Average aspect ratio of powder> The fluoropolymer powder or composition was thinly spread on a black paper surface using air without applying shear to the powder, and observed under a microscope. The ratio of the major axis to the minor axis of 100 or more randomly selected particles was calculated as the average.

[0308] A white solid A (perfluoroethercarboxylic acid A ammonium salt) was obtained by the method described in Synthesis Example 1 of WO 2021 / 045228.

[0309] The following fluorine-containing surfactants with molecular weights of 1,000 or less were prepared. Perfluoroether carboxylic acid B ammonium salt: Fujifilm Wako Pure Chemical Industries, Ltd., Ammonium perfluoro(2-methyl-3-oxahexanoate), structural formula: CF3CF2CF2OCF(CF3)COONH4 The following hydrophilic monomers were prepared: Hydrophilic monomer: Ammonium 2,3,3,3-tetrafluoro-2-[(1,1,2-trifluoro-2-propenyl)oxy]- Propanoate, structural formula: CH2=CFCF2OCF(CF3)COONH4

[0310] 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. The autoclave was heated to 70°C and the atmosphere was purged with nitrogen gas to remove oxygen. 0.06 g of HFP was then injected using TFE, followed by TFE injection to adjust the system pressure to 0.78 MPaG. The system temperature was maintained at 70°C while stirring. Next, an aqueous solution containing 15.4 mg of ammonium persulfate dissolved in 20 g of water was injected using TFE to initiate the polymerization reaction. As the polymerization reaction progressed, the system pressure decreased, but additional TFE was added to maintain the system temperature at 70°C and the system pressure at 0.78 MPaG. When 430 g of TFE had been consumed from the start of polymerization, an aqueous solution of 18.0 mg of hydroquinone as a radical scavenger dissolved in 20 g of water was injected with TFE. The polymerization continued, and when the amount of TFE polymerized reached approximately 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 return to normal pressure, terminating the polymerization reaction. The aqueous dispersion was removed and cooled, and the paraffin wax was separated to obtain a fluoropolymer aqueous dispersion. The average primary particle size of the resulting fluoropolymer aqueous dispersion was 246 nm, and the solids concentration was 29.8 mass%.

[0311] Manufacturing Example 1 The aqueous fluoropolymer dispersion obtained in Synthesis Example 1 was diluted to a solids concentration of 13% by mass, and the fluoropolymer was coagulated while stirring in a container. The water was then filtered off to obtain a wet fluoropolymer powder. The obtained fluoropolymer 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 fluoropolymer powder. The resulting fluoropolymer powder had an HFP content of 0.027% by mass, an SSG of 2.150, and an extrusion pressure of 32.4 MPa.

[0312] Synthesis Example 2 A 6-liter stainless steel autoclave equipped with a stainless steel stirring blade and a temperature-control jacket was charged with 3,480 g of deionized water, 100 g of paraffin wax, and 5.3 g of white solid A. The autoclave was heated to 70°C and the atmosphere was purged with nitrogen gas to remove oxygen. TFE was introduced under pressure to adjust the system pressure to 0.78 MPaG, and the system temperature was maintained at 70°C while stirring. Next, an aqueous solution containing 15.0 mg of ammonium persulfate dissolved in 20 g of water was introduced under pressure with TFE to initiate the polymerization reaction. As the polymerization reaction progressed, the system pressure decreased, but additional TFE was added to maintain the system temperature at 70°C and the system pressure at 0.78 MPaG. When 400 g of TFE had been consumed from the start of polymerization, an aqueous solution of 18.0 mg of hydroquinone as a radical scavenger dissolved in 20 g of water was injected with TFE. The polymerization continued, and when the amount of TFE polymerized reached approximately 1,200 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, terminating the polymerization reaction. The aqueous dispersion was removed and cooled, and the paraffin wax was separated to obtain a fluoropolymer aqueous dispersion. The average primary particle size of the resulting fluoropolymer aqueous dispersion was 310 nm, and the solids concentration was 25.3% by mass.

[0313] Manufacturing Example 2 The aqueous fluoropolymer dispersion obtained in Synthesis Example 2 was diluted to a solids concentration of 13% by mass, and the fluoropolymer was coagulated while stirring in a container. The water was then filtered off to obtain a wet fluoropolymer powder. The obtained fluoropolymer 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 fluoropolymer powder. The resulting fluoropolymer powder had an SSG of 2.156 and an extrusion pressure of 31.2 MPa.

[0314] Synthesis Example 3 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. The autoclave was heated to 80°C and the atmosphere was purged with nitrogen gas to remove oxygen. After adding 1.20 g of CTFE, additional TFE was added to bring the system pressure to 0.78 MPaG. The system temperature was maintained at 80°C while stirring. Next, an aqueous solution of 360 mg of disuccinic acid peroxide in 20 g of water and an aqueous solution of 10 mg of ammonium persulfate in 20 g of water were added with TFE to initiate the polymerization reaction. As the polymerization reaction progressed, the system pressure decreased, but additional TFE was added to maintain the system temperature at 80°C and the system pressure at 0.78 MPaG. When 1530 g of TFE had been consumed (90% conversion) since the start of polymerization, 4.2 g of CTFE was added with TFE. The polymerization continued, and when the amount of TFE polymerized reached approximately 1700 g from the start of polymerization, stirring and the supply of TFE were stopped, and the gas in the system was immediately released to return to normal pressure, thereby terminating the polymerization reaction. The aqueous dispersion was removed and cooled, and the paraffin wax was separated to obtain an aqueous fluoropolymer dispersion. The average primary particle size of the resulting aqueous fluoropolymer dispersion was 241 nm, and the solids concentration was 32.0 mass%. The fluoropolymer particles obtained above had a core-shell structure.

[0315] Manufacturing Example 3 The aqueous fluoropolymer dispersion obtained in Synthesis Example 3 was diluted to a solids concentration of 13% by mass, vigorously stirred in a container to solidify, and then filtered to separate the water, yielding a wet fluoropolymer powder. The obtained wet fluoropolymer powder was placed on a stainless steel mesh tray, and the mesh tray was heat-treated in a hot air circulating electric furnace at 145° C. After 18 hours, the mesh tray was removed and air-cooled to obtain a fluoropolymer powder. The resulting fluoropolymer powder had a CTFE content of 0.23 mass %, an SSG of 2.170, and an extrusion pressure of 10.5 MPa.

[0316] Synthesis Example 4 A fluoropolymer aqueous dispersion was obtained in the same manner as in Synthesis Example 2, except that 5.3 g of white solid A was replaced with 15.75 g of perfluoroethercarboxylic acid B ammonium salt and 35 mg of hydrophilic monomer. The average primary particle size of the obtained fluoropolymer aqueous dispersion was 295 nm, and the solid content was 26.5 mass%.

[0317] Manufacturing Example 4 The fluoropolymer aqueous dispersion obtained in Synthesis Example 4 was treated in the same manner as in Production Example 2 to obtain a fluoropolymer powder. The resulting fluoropolymer powder had an SSG of 2.159 and an extrusion pressure of 32.5 MPa.

[0318] Synthesis Example 5 A fluoropolymer aqueous dispersion was obtained in the same manner as in Synthesis Example 3, except that 5.4 g of the white solid A was changed to 16 g of perfluoroethercarboxylic acid B ammonium salt and 30 mg of hydrophilic monomer. The average primary particle size of the obtained fluoropolymer aqueous dispersion was 245 nm, and the solid concentration was 31.8 mass%.

[0319] The fluoropolymer aqueous dispersion obtained in Synthesis Example 5 was treated in the same manner as in Production Example 3 to obtain a fluoropolymer powder. The resulting fluoropolymer powder had a CTFE content of 0.23 mass %, an SSG of 2.172, and an extrusion pressure of 10.8 MPa.

[0320] Preparation example 1 The fluoropolymer aqueous dispersions obtained in Synthesis Examples 1 and 3 were mixed in a solid content mass ratio (Synthesis Example 1:Synthesis Example 3) of 75:25, then diluted to a solid content concentration of 13 mass%, vigorously stirred in a container to cause coagulation, and then filtered to separate the water, yielding a fluoropolymer wet powder. The obtained fluoropolymer wet powder was placed on a stainless steel mesh tray (amount placed: 2.0 g / cm). 2 ) and the mesh tray was heat-treated in a hot air circulation electric furnace at 180° C. After 18 hours, the mesh tray was taken out and cooled in air, and then Fluorine-based polymer composition 1 was obtained. The resulting fluoropolymer composition 1 had a CTFE content of 0.06% by mass, an HFP content of 0.020% by mass, endothermic peak temperatures of 338°C and 343°C, was paste extrudable, a water content of 0.000% by mass, a perfluoroethercarboxylic acid A content of less than 10 ppb by mass, and an average aspect ratio of the powder of 1.1.

[0321] Preparation example 2 Fluorine-based polymer composition 2 was obtained in the same manner as in Preparation Example 1, except that the solid content mass ratio of the fluorine-based polymer aqueous dispersion was changed to 50:50. The resulting fluoropolymer composition 2 had a CTFE content of 0.10% by mass, an HFP content of 0.014% by mass, endothermic peak temperatures of 337°C and 343°C, was paste extrudable, had a water content of 0.000% by mass, a perfluoroethercarboxylic acid A content of less than 10 ppb by mass, and an average aspect ratio of the powder of 1.3.

[0322] Preparation example 3 Fluorine-based polymer composition 3 was obtained in the same manner as in Preparation Example 1, except that the solid content mass ratio of the fluorine-based polymer aqueous dispersion was changed to 25:75. The resulting fluoropolymer composition 3 had a CTFE content of 0.15% by mass, an HFP content of 0.007% by mass, an endothermic peak temperature of 336°C, a paste extrudability, a water content of 0.000% by mass, a perfluoroethercarboxylic acid A content of less than 10 ppb by mass, and an average aspect ratio of 1.3.

[0323] Preparation example 4 Fluorine-based polymer composition 4 was obtained in the same manner as in Preparation Example 2, except that the fluoropolymer aqueous dispersion used was changed from Synthesis Example 1 to Synthesis Example 2. The resulting fluoropolymer composition 4 had a CTFE content of 0.10% by mass, endothermic peak temperatures of 337°C and 343°C, was paste extrudable, had a water content of 0.000% by mass, a perfluoroethercarboxylic acid A content of less than 10 ppb by mass, and an average aspect ratio of the powder of 1.2.

[0324] Preparation example 5 Fluorine-based polymer composition 5 was obtained in the same manner as in Preparation Example 4, except that the mesh tray was replaced with a flat tray (a tray with no air permeability at the bottom or 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 fluoropolymer composition 5 had a CTFE content of 0.10% by mass, endothermic peak temperatures of 337°C and 343°C, was paste extrudable, had a water content of 0.121% by mass, and had an average powder aspect ratio of 1.3.

[0325] Preparation Example 6 The fluoropolymer aqueous dispersions obtained in Synthesis Examples 4 and 5 were mixed at a solids mass ratio (Synthesis Example 4:Synthesis Example 5) of 50:50, then diluted to a solids concentration of 13 mass%, vigorously stirred in a container equipped with a stirrer to coagulate, and filtered to obtain a fluoropolymer wet powder. The obtained fluoropolymer wet powder was placed on a stainless steel flat tray, and the flat tray was heat-treated in a hot air circulating electric furnace at 145°C. After 18 hours, the flat tray was removed and air-cooled to obtain fluoropolymer composition 6. The resulting fluoropolymer composition 6 had a CTFE content of 0.10% by mass, endothermic peak temperatures of 337°C and 343°C, was paste extrudable, had a water content of 0.016% by mass, a perfluoroethercarboxylic acid B content of 160 ppb by mass, and an average aspect ratio of the powder of 1.1.

[0326] Preparation Example 7 The fluoropolymer powders obtained in Production Examples 2 and 3 were mixed in a mass ratio (Production Example 2:Production Example 3) of 50:50 using a blender (Waring Blender 7012S, manufactured by Waring) at a stirring speed of 3100 rpm for 1 minute to obtain fluoropolymer composition 7. The CTFE content of the resulting fluoropolymer composition 7 was 0.10% by mass, the endothermic peak temperatures were 337°C and 343°C, the perfluoroethercarboxylic acid A content was less than 10 ppb by mass, and the average aspect ratio of the powder was 2.6.

[0327] Preparation Example 8 The wet powder obtained in Production Example 2 was placed on a flat tray and the flat tray was heat-treated in a hot air circulating electric furnace at 180° C. After 5 hours, the flat tray was taken out and air-cooled to obtain fluoropolymer powder 8. The resulting fluoropolymer powder 8 had an endothermic peak temperature of 344°C, was paste extrudable, had a water content of 0.126 mass %, and had an average aspect ratio of 1.2.

[0328] Each of the fluoropolymer powders or compositions obtained above was evaluated by the following methods.

[0329] Evaluation of electrolyte-containing batteries Mixture sheets of Examples 1 to 5, A1, A2 and Comparative Example 1 were prepared and the sheets and batteries were evaluated according to the following procedures. <Preparation of positive electrode mixture sheet> The active material and conductive additive were weighed, placed in a V-type mixer, and mixed at 37 rpm for 10 minutes to obtain a mixture of the active material and conductive additive. The weighed binder (fluorine-based polymer powder or composition) was then added to the mixture, which was then thoroughly cooled in a thermostatic chamber at 5°C. The mixture of the active material, conductive additive, and binder was then placed in a Henschel mixer and homogenized by mixing at 1000 rpm for 3 minutes. The mixture was then heated sufficiently in a 50°C thermostatic bath and then treated for 5 minutes in a pressure kneader (D1-5: manufactured by Nihon Spindle Co., Ltd.) (32 rpm, heater 50°C, pressure 0.5 MPa) to promote fibrillation and obtain a bulk electrode mixture with cohesive properties. The bulk electrode mixture was then placed in a Henschel mixer for re-pulverization and treated at 300 rpm for 1 minute to obtain an electrode mixture. The electrode mixture was placed between parallel metal rolls (temperature: 80°C, rotation speed: 1 m / min) and rolled to obtain an electrode mixture sheet. The rolled sheet was then roughly crushed by folding it in half again, and the electrode mixture was placed between metal rolls (temperature: 80°C, rotation speed: 1 m / min) and rolled to obtain a stronger electrode mixture sheet. The electrode mixture sheet was then placed in a roll press, and the gap was adjusted to a final thickness of 90 μm. Table 2 shows the material types and compositions.

[0330] [Table 2] Denka Li-400: Carbon black manufactured by Denka

[0331] <Evaluation of powder cohesion> The electrode mixture before being poured into the parallel metal rolls was sieved for 30 seconds through a sieve with 0.18 mm openings (JIS-Z8801). If any aggregates remained on the mesh, it was marked with an X, and if all of the aggregates passed through, it was marked with an O. The results are shown in Table 3.

[0332] <Measurement of the strength of the positive electrode mixture sheet> The positive electrode mixture sheet was cut out to prepare 4 mm wide strip-shaped test pieces. Measurements were performed using a tensile tester (AGS-100NX manufactured by Shimadzu Corporation) at a speed of 100 mm / min. The distance between chucks was 30 mm. Displacement was applied until fracture, and the maximum stress measured was taken as the strength of each sample. N=8 tests were performed, and the average value was calculated. Comparison was made with Comparative Example 1 set to 100%. The coefficient of variation was calculated to evaluate the variability. The results are shown in Table 3.

[0333] <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 rod, and then the test pieces were visually inspected to check for damage such as scratches or cracks. No damage such as scratches or cracks was observed in Examples 1 to 5, A1, and A2.

[0334] <Preparation of positive electrode> The positive electrode mixture sheet was adhered to a 20 μm aluminum foil in the following manner. The adhesive used was a slurry of polyvinylidene fluoride (PVDF) dissolved in N-methylpyrrolidone (NMP) and carbon black dispersed in a ratio of 80:20. The adhesive was applied to 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 heated to 100°C. The sheet was then cut to the desired size and tabbed to form a positive electrode.

[0335] <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 thickeners and binders, and the mixture was mixed in a disperser to form a slurry. The resulting slurry was applied to a 10 μm thick copper foil, dried, rolled in a press, cut to the desired size, and tabbed to form a negative electrode.

[0336] <Preparation of electrolyte> A mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC = 30:70 (volume ratio)) was weighed into a sample bottle as an organic solvent, and 1 mass% each of fluoroethylene carbonate (FEC) and vinylene carbonate (VC) was dissolved therein to prepare a mixed solution. LiPF6 salt was mixed with this mixed solution at 23°C so that the concentration in the electrolyte solution became 1.1 mol / L, to obtain a nonaqueous electrolyte solution.

[0337] <Fabrication of aluminum laminated cells> The positive electrode was placed opposite the negative electrode via a 20 μm-thick microporous polyethylene film (separator), and the nonaqueous electrolyte solution obtained above was poured into the battery. After the nonaqueous electrolyte solution had sufficiently permeated the separator and other components, the battery was sealed, pre-charged, and aged to prepare a lithium ion secondary battery.

[0338] <Evaluation of storage characteristics (remaining capacity rate, gas generation rate)> The lithium ion secondary battery produced above was charged at 25°C with a constant current and constant voltage (hereinafter referred to as CC / CV charging) (0.1C cut) to 4.3V at a current equivalent to 0.33C, and then discharged to 3V at a constant current of 0.33C. This was counted as one cycle, and the initial discharge capacity was calculated from the discharge capacity at the third cycle. After the evaluation of the initial discharge capacity, the battery was again CC / CV charged (0.1 C cut) to 4.3 V at 25°C, and the volume of the battery was determined by Archimedes' method. After determining the volume of the battery, it 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. The amount of gas generated was calculated from the difference in volume between 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 25° C. and 0.33 C to 3 V, and the remaining capacity was determined. The ratio of the remaining capacity after high-temperature storage to the initial discharge capacity was calculated and taken as the remaining capacity rate (%). (Residual capacity) / (Initial discharge capacity)×100=Remaining capacity rate (%) The results are shown in Table 3.

[0339] [Table 3]

[0340] Solid electrolyte mixture sheet evaluation The mixture sheets of Examples 6 to 10 and Comparative Example 2 were produced and evaluated according to the following procedures. The production and evaluation were carried out in an argon atmosphere.

[0341] <Preparation of solid electrolyte mixture sheet> The weighed binder (fluorine-based polymer powder or composition) was cooled sufficiently in a thermostatic bath at 5°C, and then placed in 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 mixing 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 placed between parallel metal rolls (temperature: 80°C, rotation speed: 1 m / min) and rolled to obtain an electrolyte mixture sheet. The rolled sheet was again folded in half to be roughly crushed, and the electrolyte mixture was placed between 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 would be 120 μm. Table 4 shows the material types and compositions.

[0342] [Table 4]

[0343] <Measurement of the strength of solid electrolyte mixture sheets (tensile test)> The solid electrolyte mixture sheet was cut out to prepare 4 mm wide strip-shaped test pieces. Measurements were made using a tensile tester (AGS-100NX manufactured by Shimadzu Corporation) at a speed of 100 mm / min. The distance between chucks was 30 mm. Displacement was applied until breakage, and the maximum stress measured was taken as the strength of each sample. N=8 tests were performed, and the average value was calculated. Comparison was made with Comparative Example 2 set at 100%. The results are shown in Table 5.

[0344] <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 rod, and the test pieces were visually inspected to check for damage such as scratches or cracks. If no damage was observed, a test was performed using a thinner Φ5 mm round rod to check for damage. Again, if no damage was observed, a test was performed using an even thinner Φ2 mm round rod to check for damage. The results were classified as A to D. A: No damage with Φ2mm rod B: Φ2mm rod damaged C: Φ5mm rod damaged D: Φ10mm rod damaged The results are shown in Table 5.

[0345] <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 out into a 10 mm diameter circle using a punch, which was then placed in a pressure cell. The cell's screws were then tightened to 8 N, and the electrodes were removed from the top and bottom of the cell. A schematic diagram of the cross section of the pressure cell used is shown in Figure 1. This sample was measured using an impedance device manufactured by Toyo Corporation at 25°C, AC amplitude modulation 10 mV, and a frequency of 5 x 10 6 The ionic conductivity was measured at a frequency of up to 0.1 Hz. The results are shown in Table 5.

[0346] [Table 5]

[0347] Evaluation of solid electrolyte positive electrode mixture sheet The mixture sheets of Examples B1 and B2 and Comparative Example 3 were prepared and evaluated according to the following procedures. The preparation and evaluation were carried out in an argon atmosphere.

[0348] <Preparation of solid electrolyte electrode mixture sheet> The active material and conductive additive were weighed, placed in a V-type mixer, and mixed at 37 rpm for 10 minutes to obtain a mixture of the active material and conductive additive. The weighed binder (fluorine-based polymer powder or composition) was then added to the mixture, thoroughly cooled in a thermostatic chamber at 5°C, and then placed in a Henschel mixer and processed at 2800 rpm for 10 minutes to disperse the mixture and fibrillate the TFE composition, obtaining a solid electrolyte electrode mixture. The electrode mixture was placed between parallel metal rolls (temperature: 80°C, rotation speed: 0.5 m / min) and rolled to obtain a solid electrolyte electrode mixture sheet. The rolled sheet obtained was again roughly crushed by folding it in half, and the solid electrolyte electrode mixture was placed between metal rolls (temperature: 80°C, rotation speed: 0.5 m / min) and rolled. This process promoted fibrillation, and a strong solid electrolyte electrode mixture sheet was obtained. The solid electrolyte electrode mixture sheet was then placed in a roll press and the thickness of the solid electrolyte electrode mixture sheet was adjusted to 150 μm. Table 6 shows the material types and compositions.

[0349] [Table 6] Denka Li-400: Carbon black manufactured by Denka

[0350] <Measurement of the strength of solid electrolyte electrode mixture sheets (tensile test)> The solid electrolyte mixture electrode sheet was cut out to prepare 4 mm wide strip-shaped test pieces. Measurements were performed using a tensile tester (AGS-100NX manufactured by Shimadzu Corporation) at a speed of 100 mm / min. The distance between chucks was 30 mm. Displacement was applied until fracture, and the maximum stress measured was taken as the strength of each sample. N=8 tests were performed, and the average value was calculated. Comparison was made with Comparative Example 3 set to 100%. The results are shown in Table 7.

[0351] <Flexibility evaluation of solid electrolyte mixture sheet (bending test)> The prepared solid electrolyte 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 rod, and the test pieces were visually inspected to check for damage such as scratches or cracks. If no damage was observed, a test was performed using a thinner Φ5 mm round rod to check for damage. Again, if no damage was observed, a test was performed using an even thinner Φ2 mm round rod to check for damage. The results were classified as A to D. A: No damage with Φ2mm rod B: Φ2mm rod damaged C: Φ5mm rod damaged D: Φ10mm rod damaged The results are shown in Table 7.

[0352] [Table 7] [Explanation of symbols]

[0353] 1:Screw 2: Nut 3: Insulation sheet 4: Solid electrolyte mixture sheet 5: Gold vapor deposition 6:Top electrode 7: Lower electrode

Claims

1. A fluorine-containing polymer composition used as a binder for an electrochemical device, comprising: Contains a fluorine-based polymer, the fluorine-based polymer contains two or more types of tetrafluoroethylene-based polymers, A fluoropolymer composition, wherein the content of the fluoropolymer is 90% by mass or more based on the fluoropolymer composition.

2. A binder for electrochemical devices consisting essentially of a fluorine-based polymer composition, The fluoropolymer composition comprises a fluoropolymer, the fluorine-based polymer contains two or more types of tetrafluoroethylene-based polymers, The binder for electrochemical devices, wherein the content of the fluorine-based polymer is 90 mass % or more based on the fluorine-based polymer composition.

3. 3. The binder for electrochemical devices according to claim 2, wherein the fluoropolymer composition comprises a homopolymer of tetrafluoroethylene and a copolymer of a modified monomer and tetrafluoroethylene.

4. 4. The binder for electrochemical devices according to claim 2, wherein the fluoropolymer composition comprises two or more tetrafluoroethylene polymers having different standard specific gravities.

5. 4. The binder for electrochemical devices according to claim 2, wherein the fluoropolymer composition comprises two or more paste-extrudable tetrafluoroethylene polymers.

6. 4. The binder for electrochemical devices according to claim 2, wherein the fluoropolymer composition comprises two or more tetrafluoroethylene polymers having different extrusion pressures.

7. 4. The binder for electrochemical devices according to claim 2, wherein the fluoropolymer composition is paste-extrudable.

8. 4. The binder for electrochemical devices according to claim 2, wherein the fluoropolymer composition has an endothermic peak temperature of 320° C. or higher.

9. 4. The binder for electrochemical devices according to claim 2, wherein the fluoropolymer composition is in the form of a powder.

10. 4. The binder for electrochemical devices according to claim 2, wherein the fluoropolymer composition is substantially free of water.

11. 4. The binder for electrochemical devices according to claim 2, wherein the fluorine-containing polymer composition is substantially free of fluorine-containing compounds having a molecular weight of 1,000 or less.

12. 4. The binder for electrochemical devices according to claim 2, wherein the fluoropolymer composition has an average aspect ratio of 2.5 or less.

13. An electrode mixture comprising the fluorine-containing polymer composition according to claim 1, the binder for electrochemical devices according to claim 2 or 3, and an electrode active material.

14. The electrode mixture according to claim 13, which is in the form of a sheet.

15. 4. An electrode comprising the fluoropolymer composition according to claim 1, the binder for electrochemical devices according to claim 2 or 3, an electrode active material, and a current collector.

16. A secondary battery comprising the electrode according to claim 15.

Images