Gasket and electrochemical device

Abstract

Provided are a gasket having low water vapor permeability, and an electrochemical device using the same. The gasket includes polytetrafluoroethylene that exhibits non-melt formability, and has a water vapor permeability coefficient of 0.020 g / 1000 hr or less.

Description

Gasket and electrochemical device

[0001] The present disclosure relates to a gasket and an electrochemical device.

[0002] It is known that resins such as perfluoroalkoxyalkane (PFA) are used as sealing members (gaskets) for electrochemical devices such as lithium ion secondary batteries (see, for example, Patent Documents 1 to 4).

[0003] Japanese Patent Application Laid-Open No. 2017-174732 International Publication No. 2020 / 066050 International Publication No. 2014 / 049645 Japanese Patent Application Laid-Open No. 2021-141045

[0004] An object of the present disclosure is to provide a gasket with excellent low water vapor permeability and an electrochemical device using the same.

[0005] The present disclosure (1) is a gasket containing polytetrafluoroethylene exhibiting non-melt moldability and having a water vapor permeability coefficient of 0.020 g / 1000 hr or less.

[0006] The present disclosure (2) is the gasket according to the present disclosure (1), wherein the polytetrafluoroethylene is modified polytetrafluoroethylene.

[0007] The present disclosure (3) is the gasket according to the present disclosure (1) or (2), wherein the polytetrafluoroethylene is a modified polytetrafluoroethylene containing tetrafluoroethylene units and at least one modified monomer unit selected from the group consisting of perfluoro(alkyl vinyl ether) units and hexafluoropropylene units.

[0008] The present disclosure (4) is the gasket according to the present disclosure (2) or (3), wherein the modification amount of the modified polytetrafluoroethylene is 0.001 to 1.0 mass %.

[0009] The present disclosure (5) is a gasket of any combination with any of the present disclosures (1) to (4) having a specific gravity of 2.130 or more and 2.180 or less.

[0010] The present disclosure (6) is a gasket in any combination with any of the present disclosures (1) to (5) in contact with an electrolyte.

[0011] The present disclosure (7) is a gasket of any combination with any of the present disclosures (1) to (6) having a crystallinity of 35 to 60%.

[0012] The present disclosure (8) is a gasket of any combination with any of the present disclosures (1) to (7) having a scattering intensity of 800 to 1600.

[0013] The present disclosure (9) is an electrochemical device including a gasket in any combination with any of the present disclosures (1) to (8).

[0014] The present disclosure (10) is a gasket for an electrochemical device that contains polytetrafluoroethylene exhibiting non-melt moldability and has a specific gravity of 2.130 or more and 2.180 or less.

[0015] The present disclosure (11) is the gasket according to the present disclosure (10), which has a crystallinity of 65% or less and a scattering intensity of 800 or more.

[0016] The present disclosure (12) is a gasket for an electrochemical device, which contains polytetrafluoroethylene exhibiting non-melt moldability, has a crystallinity of 65% or less, and has a scattering intensity of 800 or more.

[0017] The present disclosure (13) is an electrochemical device including a gasket in any combination with any of the present disclosures (1) to (12) in which the polytetrafluoroethylene content is 99.9% by mass or more.

[0018] The present disclosure (14) is an electrochemical device comprising a gasket in any combination with any of the present disclosures (1) to (13) having a specific gravity of 2.140 to 2.170.

[0019] The present disclosure (15) is an electrochemical device including a gasket in any combination with any of the present disclosures (1) to (14), in which the polytetrafluoroethylene is a homopolymer of tetrafluoroethylene or a modified PTFE in which the content of modified monomer units is 0.01 to 0.10 mass% relative to all polymerized units.

[0020] According to the present disclosure, it is possible to provide a gasket with excellent low water vapor permeability, and an electrochemical device using the same.

[0021] 1 is a schematic cross-sectional view showing the configuration of a portion of an electrochemical device including a gasket. 2 is a schematic cross-sectional view of a permeation test jig used in a water vapor permeation test.

[0022] Conventionally, PFA and the like have been used as gaskets with excellent low water vapor permeability. On the other hand, polytetrafluoroethylene (PTFE) has been considered to have poor low water vapor permeability, although it has excellent chemical resistance and heat resistance. Surprisingly, it has been found that water vapor permeability can be reduced even when PTFE is used.

[0023] The present disclosure will be specifically described below.

[0024] The present disclosure provides a gasket (hereinafter also referred to as gasket (1) of the present disclosure) that contains non-melt-moldable PTFE and has a water vapor permeability coefficient of 0.020 g / 1000 hr or less.

[0025] In this specification, unless otherwise specified, the gasket (1) of the present disclosure, and the gasket (2) and gasket (3) of the present disclosure described below will be collectively referred to as the "gaskets of the present disclosure."

[0026] The gasket (1) of the present disclosure has the above-described configuration, and is excellent in low water vapor permeability. In addition, since it contains PTFE, it is also excellent in chemical resistance and heat resistance.

[0027] The gasket (1) of the present disclosure has a water vapor permeability coefficient of 0.020 g / 1000 hr or less, and in order to further improve low water vapor permeability, it is preferably 0.015 g / 1000 hr or less, more preferably 0.012 g / 1000 hr or less, even more preferably 0.010 g / 1000 hr or less, even more preferably 0.009 g / 1000 hr or less, even more preferably 0.008 g / 1000 hr or less, even more preferably 0.007 g / 1000 hr or less, even more preferably 0.006 g / 1000 hr or less, particularly preferably 0.004 g / 1000 hr or less, and may be 0.0001 g / 1000 hr or more.

[0028] The water vapor transmission coefficient is determined by measuring the mass of water that permeates a circular gasket having a rectangular cross section with an outer diameter Φ of 17.7 mm, an inner diameter Φ of 14.3 mm, and a thickness of 1.6 mmt, at a compression rate of 40% and under conditions of 80°C for 1,000 hours. The compression rate can be calculated using the following formula: Compression rate (%) = [(thickness of gasket before compression) - (thickness of gasket in compressed state)] / (thickness of gasket before compression) x 100. When measuring using a gasket attached to an electrochemical device, the gasket is removed from the attached state and heat-treated at 150°C for 24 hours, and the thickness of the gasket after that is taken as the thickness before the gasket is compressed, and then the measurement is performed by compressing it to the above compression rate. The water vapor permeability coefficient is a value measured at a compression rate of 40%, but in order to further improve low water vapor permeability, it is preferable to measure the value at a compression rate of 30%, more preferably at a compression rate of 25%, even more preferably at a compression rate of 20%, and even more preferably at a compression rate of 15%.

[0029] The present disclosure also provides a gasket for electrochemical devices (hereinafter also referred to as gasket (2) of the present disclosure) that contains non-melt-moldable PTFE and has a specific gravity of 2.130 or more and 2.180 or less.

[0030] The gasket (2) of the present disclosure has the above-described configuration, and is excellent in low water vapor permeability. In addition, since it contains PTFE, it is also excellent in chemical resistance and heat resistance.

[0031] The gasket (2) of the present disclosure has a specific gravity of 2.130 or more and 2.180 or less, but in order to further improve low water vapor permeability, it is preferably 2.175 or less, more preferably 2.170 or less, even more preferably 2.165 or less, even more preferably 2.160 or less, and preferably 2.135 or more, more preferably 2.140 or more. The specific gravity is measured by a water displacement method in accordance with ASTM D 792. The specific gravity of the gasket of the present disclosure may be measured before or after the water vapor permeability measurement.

[0032] The specific gravity of a gasket can be adjusted by the firing conditions during molding. Increasing the rate at which the temperature is lowered during firing of a gasket reduces the crystallinity and the specific gravity. A low specific gravity, i.e., a low degree of crystallinity, results in excellent low water vapor permeability. This is because a high specific gravity results in a high degree of crystallinity and a low proportion of molecular chains forming the amorphous portion, resulting in the presence of many tiny voids and a high amount of water vapor permeability in the amorphous portion. This is presumably because the gasket's low water vapor permeability is therefore impaired as a result.

[0033] The present disclosure also provides a gasket for an electrical device (hereinafter also referred to as gasket (3) of the present disclosure) that contains PTFE that exhibits non-melt moldability and has a crystallinity of 65% or less and a scattering intensity of 800 or more.

[0034] The gasket (3) of the present disclosure has the above-mentioned configuration, and is excellent in low water vapor permeability. In addition, since it contains PTFE, it is also excellent in chemical resistance and heat resistance.

[0035] The gasket (3) of the present disclosure has a crystallinity of 65% or less. To further improve low water vapor permeability, the crystallinity is preferably 62% or less, more preferably 60% or less, and even more preferably 58% or less. The lower limit is not particularly limited, but is preferably 30% or more, more preferably 35% or more, even more preferably 38% or more, and even more preferably 40% or more. The crystallinity is measured using an X-ray diffractometer (Ultima III, manufactured by Rigaku Corporation) under the following measurement conditions using a multiple peak separation method. A measurement sample having a thickness of 40 μm or more is placed in a sample holder, and the peaks of the crystalline and amorphous parts of the obtained diffraction spectrum are separated into independent peaks. The crystallinity is calculated by determining the integrated intensity (area) of each peak.

[0036] Measurement conditions

[0037] Gaskets with low crystallinity have excellent low water vapor permeability. While a higher degree of crystallinity would be expected to provide better low water vapor permeability, surprisingly, a lower degree of crystallinity was found to provide better low water vapor permeability. This is presumably because a higher degree of crystallinity reduces the proportion of molecular chains forming amorphous regions, resulting in the presence of numerous microvoids and increased water vapor permeability in the amorphous regions. This is thought to result in a deterioration in the gasket's low water vapor permeability. Crystallinity can be adjusted by adjusting the molding conditions of the PTFE used to form the gasket. Crystallinity can be measured on the gasket after molding or on a removed gasket. This is because there is almost no change in crystallinity before and after water vapor permeation measurement. After water vapor permeation measurement, the increased scattering intensity suggests the formation of pseudo-crystals, but the amount of pseudo-crystals formed is so small that it does not reflect a change in crystallinity.

[0038] The gasket (3) of the present disclosure has a scattering intensity of 800 or more. In order to further improve low water vapor permeability, the scattering intensity is preferably 850 or more, more preferably 900 or more, and even more preferably 1000 or more. The upper limit is not particularly limited, but is preferably 2000 or less, more preferably 1800 or less, even more preferably 1700 or less, even more preferably 1600 or less, and particularly preferably 1500 or less. The scattering intensity is measured using a small-angle X-ray diffractometer (RINT2500, manufactured by Rigaku Corporation) under the following measurement conditions, and the scattering vector q is 0.07 nm －１ The scattering intensity is defined as the scattering intensity when

[0039] Measurement conditions

[0040] The compression ratio at the time of installation can be estimated by measuring the scattering intensity in small-angle X-ray diffraction measurements of the gasket removed from the test jig after the water vapor permeation test. It is estimated that if the compression ratio is high, new pseudo-crystals are formed in the amorphous part of the PTFE that forms the gasket, and even after the test is completed and the compression is released, the scattering intensity increases due to the density difference between the newly formed pseudo-crystals and the amorphous part in the PTFE. Since a high degree of compression improves low water vapor permeability, measuring the scattering intensity of the gasket after installation indicates that the gasket has excellent low water vapor permeability.

[0041] In order to further improve the low water vapor permeability of the gasket (2) and the gasket (3) of the present disclosure, the water vapor permeability coefficient is preferably 0.010 g / 1000 hr or less, more preferably 0.009 g / 1000 hr or less, even more preferably 0.008 g / 1000 hr or less, even more preferably 0.007 g / 1000 hr or less, still more preferably 0.006 g / 1000 hr or less, particularly preferably 0.004 g / 1000 hr or less, and may be 0.0001 g / 1000 hr or more. As described above, the water vapor permeability coefficient is a value measured at a compression rate of 40%, but in order to further improve low water vapor permeability, it is preferable to measure the value at a compression rate of 30%, more preferably at a compression rate of 25%, even more preferably at a compression rate of 20%, and even more preferably at a compression rate of 15%.

[0042] In order to further improve the low water vapor permeability of the gasket (1) and the gasket (3) of the present disclosure, the specific gravity may be 2.185 or less, preferably 2.180 or less, more preferably 2.175 or less, even more preferably 2.170 or less, even more preferably 2.165 or less, and even more preferably 2.160 or less. The lower limit is not particularly limited, but the specific gravity may be 2.130 or more, preferably 2.135 or more, and more preferably 2.140 or more. The specific gravity is measured by a water displacement method in accordance with ASTM D 792. The specific gravity of the gasket of the present disclosure may be measured before or after the water vapor permeability measurement.

[0043] The gasket (1) and the gasket (2) of the present disclosure preferably have a crystallinity of 65% or less, more preferably 62% or less, even more preferably 60% or less, and even more preferably 58% or less. There is no particular lower limit, but the crystallinity is preferably 30% or more, more preferably 35% or more, even more preferably 38% or more, and even more preferably 40% or more. The crystallinity is measured by the method described above.

[0044] In order to further improve the low water vapor permeability of the gasket (1) and the gasket (2) of the present disclosure, the scattering intensity is preferably 800 or more, more preferably 850 or more, even more preferably 900 or more, and particularly preferably 1000 or more. There is no particular upper limit, but it is preferably 2000 or less, more preferably 1800 or less, even more preferably 1700 or less, even more preferably 1600 or less, and particularly preferably 1500 or less. The scattering intensity is measured by the method described above.

[0045] The PTFE in the gasket of the present disclosure exhibits non-melt-formability. In this specification, "non-melt-formability" means that the melt flow rate (MFR) is less than 0.10 g / 10 min, preferably less than 0.01 g / 10 min. The MFR is a value obtained in accordance with ASTM D1238 using a melt indexer, where the mass of polymer (g / 10 min) flows out of a nozzle with an inner diameter of 2.095 mm and a length of 8 mm at 372°C and a load of 5000 g (full load) per 10 minutes.

[0046] The PTFE may be a homopolymer of tetrafluoroethylene (TFE) or a modified PTFE. Modified PTFE is preferred because it has a lower water vapor permeability, and a homopolymer of tetrafluoroethylene or a modified PTFE in which the content of modified monomer units is 0.01 to 0.10% by mass relative to the total polymerized units is also preferred.

[0047] The modified PTFE preferably contains TFE units and 1.0% by mass or less of modified monomer units. The amount of TFE units may be 99.0% by mass or more. Alternatively, the modified PTFE may consist solely of TFE units and modified monomer units.

[0048] In order to further improve the low water vapor permeability of the modified PTFE, the content of the modified monomer unit (modification amount) is preferably in the range of 0.00001 to 1.0 mass% relative to the total polymerized units. The lower limit of the content of the modified monomer unit is more preferably 0.0001 mass%, even more preferably 0.001 mass%, even more preferably 0.005 mass%, and particularly preferably 0.010 mass%. The upper limit of the content of the modified monomer unit is preferably 0.90 mass%, more preferably 0.80 mass%, more preferably 0.50 mass%, even more preferably 0.40 mass%, even more preferably 0.30 mass%, even more preferably 0.20 mass%, and particularly preferably 0.10 mass%. In this specification, the modified monomer unit refers to a part of the molecular structure of PTFE that is derived from the modified monomer.

[0049] 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.

[0050] The above-mentioned modified monomer is not particularly limited as long as it can be copolymerized with TFE, and for example, can be listed perfluoroolefin such as hexafluoropropylene (HFP); hydrogen-containing fluoroolefin such as trifluoroethylene, vinylidene fluoride (VDF); perhaloolefin such as chlorotrifluoroethylene (CTFE); perfluorovinyl ether; perfluoroallyl ether; (perfluoroalkyl) ethylene, ethylene etc. In addition, the modified monomer used can be one kind or multiple kinds.

[0051] The perfluorovinyl ether is not particularly limited, and examples thereof include perfluorovinyl ethers represented by the following general formula (A): CF ２ =CF-ORf １ (A) (wherein, Rf １ represents a perfluoroorganic group. ) and perfluorounsaturated compounds represented by the following formula (I) 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.

[0052] 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.

[0053] 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.

[0054] The perfluorovinyl ether further includes a compound represented by the general formula (A) below, wherein Rf １is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, Rf １ is of the following formula:

[0055]

[0056] (wherein m represents 0 or an integer of 1 to 4), Rf １ is of the following formula:

[0057]

[0058] (wherein n represents an integer of 1 to 4).

[0059] The (perfluoroalkyl)ethylene [PFAE] is not particularly limited, and examples thereof include (perfluorobutyl)ethylene [PFBE] and (perfluorohexyl)ethylene.

[0060] Hydrogen-containing fluoroolefins include CH ２ =CF ２ , CFH=CH ２ , CFH=CF ２ , C.H. ２ =CFCF ３ , C.H. ２ = CHCF ３ , CHF=CHCF ３ (E form), CHF=CHCF ３ (Z-isomer), etc.

[0061] Examples of perfluoroallyl ethers include those represented by the general formula (B): CF ２ =CF-CF ２ -ORf ２ (B) (wherein, Rf ２ represents a perfluoroorganic group.

[0062] The above Rf ２ is preferably a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms. ２ =CF-CF ２ -O-CF ３ , C.F. ２ =CF-CF２ -O-C ２ F ５ , C.F. ２ =CF-CF ２ -O-C ３ F ７ , and CF ２ =CF-CF ２ -O-C ４ F ９ At least one selected from the group consisting of CF ２ =CF-CF ２ -O-C ２ F ５ , C.F. ２ =CF-CF ２ -O-C ３ F ７ , and CF ２ =CF-CF ２ -O-C ４ F ９ More preferably, at least one selected from the group consisting of CF ２ =CF-CF ２ -O-CF ２ CF ２ CF ３ is more preferred.

[0063] As the modified monomer, from the viewpoint of further improving low water vapor permeability, at least one selected from the group consisting of PAVE, PFAE, and HFP is preferred, at least one selected from the group consisting of PAVE and HFP is more preferred, PAVE is even more preferred, and perfluoro(propyl vinyl ether) [PPVE] is even more preferred.

[0064] The PTFE may have a core-shell structure. Examples of PTFE having a core-shell structure include modified PTFE particles containing a core of high molecular weight PTFE and a shell of lower molecular weight PTFE or modified PTFE. Examples of such modified PTFE include the PTFE described in JP-A-2005-527652.

[0065] In order to further improve the low water vapor permeability of the PTFE, the heat of crystallization measured by a differential scanning calorimeter (DSC) is preferably 25 J / g or more, more preferably 26 J / g or more, and even more preferably 27 J / g or more, and is preferably 33 J / g or less, more preferably 32 J / g or less, even more preferably 30 J / g or less, and particularly preferably 29 J / g or less. The heat of crystallization is measured by the following method. Approximately 3 mg of sample is precisely weighed and placed in a dedicated aluminum pan. Using an X-DSC7000 (manufactured by Hitachi High-Tech Science Corporation), the sample is heated to 380°C at a rate of 10°C / min under a nitrogen atmosphere, held for 1 minute, and then cooled to 250°C at a rate of 10°C / min to measure the heat of crystallization at the crystallization point. The value of the heat of crystallization is determined by drawing a line from 275° C. to 330° C. on the obtained DSC chart and determining the area enclosed by the line and the curve including the peak.

[0066] The gasket of the present disclosure may contain components other than the PTFE, but preferably consists essentially of the PTFE. This allows the effects of the PTFE to be significantly exhibited. "Consisting essentially of the PTFE" means that the PTFE content is 95.0% by mass or more relative to the gasket. The PTFE content is preferably 98.0% by mass or more relative to the gasket, 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 preferable that the gasket of the present disclosure consists essentially of the PTFE.

[0067] The gaskets of the present disclosure preferably exhibit non-melt formability.

[0068] In order to further improve the low water vapor permeability of the gasket of the present disclosure, the compression ratio when mounted is preferably 10% or more, more preferably 12% or more, even more preferably 17% or more, even more preferably 25% or more, and particularly preferably 35% or more, and is preferably 65% ​​or less, and more preferably 60% or less. The compression ratio can be calculated using the following formula: Compression ratio (%) = [(thickness of gasket before compression) - (thickness of gasket in compressed state)] / (thickness of gasket before compression) x 100. Note that when measuring using a gasket mounted on an electrochemical device, the gasket is removed from the mounted state and heat-treated at 150°C for 24 hours, and the thickness of the gasket after this is used to measure the compression ratio.

[0069] The gasket of the present disclosure can be produced by forming raw PTFE into a desired shape and sintering it. The form of the raw PTFE is not limited and may be a powder, a dispersion liquid, or the like, but is preferably a powder.

[0070] The standard specific gravity (SSG) of the raw PTFE is preferably 2.130 or more, more preferably 2.135 or more, even more preferably 2.140 or more, and preferably 2.180 or less, more preferably 2.175 or less, even more preferably 2.170 or less, even more preferably 2.165 or less, and particularly preferably 2.160 or less. The SSG is measured by the water displacement method according to ASTM D 792 using a sample molded in accordance with ASTM D 4895 89. By setting the SSG within the above range, the water vapor permeability coefficient can be easily set within the above range.

[0071] The raw material PTFE can be produced by emulsion polymerization or suspension polymerization, and is preferably produced by suspension polymerization.

[0072] Emulsion polymerization can be carried out by known method.For example, in the presence of anionic fluorine-containing surfactant and polymerization initiator, the emulsion polymerization of the monomers (TFE and optionally modified monomers) necessary for forming the above-mentioned PTFE is carried out in aqueous medium, thereby obtaining the aqueous dispersion liquid containing the above-mentioned PTFE particles (primary particles).In the above-mentioned emulsion polymerization, if necessary, chain transfer agent, buffer, pH adjuster, stabilizing aid, dispersion stabilizer, radical scavenger etc. can be used.

[0073] The resulting aqueous dispersion is coagulated to obtain a wet powder, which is then dried to obtain a powder of raw PTFE. Coagulation and drying can be carried out by known methods.

[0074] Suspension polymerization can be carried out, for example, by charging a reactor with a monomer such as TFE, an aqueous medium, and other additives as necessary, 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, additional monomers such as TFE, polymerization initiators, chain transfer agents, etc. may be added depending on the purpose.

[0075] The suspension-polymerized particles obtained may be washed and then pulverized, or the suspension-polymerized particles obtained may be pulverized while being washed, to produce pulverized particles.

[0076] The wet pulverized particles may be dehydrated and further dried. Drying is carried out for the purpose of removing moisture from the pulverized particles obtained by pulverization.

[0077] After the suspension polymerized particles are pulverized, the pulverized particles obtained may be classified by a known method such as air classification.

[0078] The resulting pulverized particles may be granulated by a known granulation method.

[0079] The physical properties of the resulting PTFE can be adjusted by adjusting the conditions of polymerization and post-treatment. For example, in emulsion polymerization, the endothermic peak temperature can be increased, the standard specific gravity can be lowered, and the melt viscosity can be increased by reducing the amount of polymerization initiator used, reducing the amount of chain transfer agent used, or using a radical scavenger. In post-treatment of emulsion polymerization, the decomposition temperature can be increased by setting the drying temperature to 150°C or higher. In suspension polymerization, the endothermic peak temperature can be increased, the standard specific gravity can be lowered, and the melt viscosity can be increased by reducing the amount of polymerization initiator used, reducing the amount of chain transfer agent used, or preferably not using it at all. In post-treatment, the decomposition temperature can be increased by performing washing or setting the drying temperature to 150°C or higher.

[0080] Regarding the method of molding raw PTFE, when using the powder obtained by emulsion polymerization, for example, raw PTFE powder and extrusion aid can be mixed, and paste extrusion molding can be carried out.Extrusion aid can be removed by drying.It is also preferable to compress the raw PTFE powder.

[0081] When the powder obtained by suspension polymerization is used, molding methods such as compression molding, ram extrusion molding, and isostatic pressing can be used. The PTFE molded body can be processed by machining such as cutting to produce a molded body having a desired shape. For example, a PTFE sheet can be obtained by cutting the PTFE molded body.

[0082] The calcination can be carried out, for example, by heating at a temperature of 350 to 380° C. for 0.5 to 50 hours.

[0083] The firing may include a section in which the temperature drop rate from 370°C to 250°C is 25°C / hr or more, and preferably includes a section in which the temperature drop rate is greater than 25°C / hr. The above section is preferably included in the cooling step after heating. The above temperature drop rate is more preferably 30°C / hr or more, even more preferably 45°C / hr or more, even more preferably 55°C / hr or more, and particularly preferably 65°C / hr or more. It is also preferable to cool (quench) by directly immersing in water. By setting the temperature drop rate within the above range, the water vapor permeability coefficient can be easily set within the above range. In addition, the heat of crystallization can also be easily set within the above range. When using raw PTFE with a relatively high molecular weight, it is preferable to set the temperature drop rate low.

[0084] The gasket of the present disclosure is a member used to prevent leakage of liquid or gas or intrusion of liquid or gas from the outside into an object (such as an apparatus) to which it is applied.

[0085] The shape of the gasket of the present disclosure is not particularly limited and may be, for example, an annular shape. Furthermore, the gasket of the present disclosure may have a shape such as a circle, an oval, or a rectangle with rounded corners in a plan view, and may have a through-hole in the center.

[0086] The gasket of the present disclosure has excellent low water vapor permeability and can be applied to any application requiring prevention of water leakage or intrusion, and is particularly suitable for use in electrochemical devices.

[0087] A mode of use of a gasket according to an embodiment of the present disclosure in an electrochemical device will be described with reference to the drawings.

[0088] 1, an electrochemical device 10 (e.g., a sealed prismatic secondary battery) includes an outer can (not shown) and a lid 1. An electric element (not shown), such as a power generator, is housed inside the outer can, and the opening of the outer can is hermetically sealed with the lid 1. An external terminal 2 (positive electrode terminal or negative electrode terminal) is provided on the lid 1, and externally generated electric power is supplied to the electric element via the external terminal 2 for storage, and also for supplying electric power to an external load.

[0089] A gasket 3 for sealing and insulation is provided between the external terminal 2 and the lid 1. The gasket 3 corresponds to the gasket of the present disclosure. An insulating plate 4 is provided on the lid 1 to electrically insulate the external terminal 2 from the lid 1. The external terminal 2 has a terminal head 21 having a rectangular block shape and a cylindrical shaft 22. The shaft 22 protrudes from the bottom surface of the terminal head 21 (the interior side of the electrochemical device).

[0090] As shown in FIG. 1 , the gasket 3 has a cylindrical portion 31 , a flange portion 32 that extends radially from one opening of the cylindrical portion 31 , and a side wall portion 33 that rises from the periphery of the flange portion 32 .

[0091] The cylindrical portion 31 is fitted onto the shaft portion 22 of the external terminal 2, and the inner peripheral surface of the cylindrical portion 31 abuts against the outer peripheral surface of the shaft portion 22. The cylindrical portion 31 is also inserted into the through hole of the lid 1, and the outer peripheral surface of the cylindrical portion 31 abuts against the inner peripheral surface of the through hole of the lid 1.

[0092] The flange portion 32 is sandwiched between the lid 1 and the external terminal 2 , with one contact surface of the flange portion 32 contacting the lower surface of the external terminal 2 and the other contact surface of the flange portion 32 contacting the surface of the lid 1 .

[0093] With the cylindrical portion 31 and flange portion 32 of the gasket 3 in a compressed state, the gasket 3 comes into contact with the external terminal 2 and the lid 1, thereby ensuring the hermeticity of the electrochemical device.

[0094] Examples of electrochemical devices to which the gasket of the present disclosure can be applied include batteries and capacitors. Examples of batteries 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.

[0095] The gasket of the present disclosure can be suitably used as a gasket for batteries, and can be particularly suitably used as a gasket for secondary batteries such as lithium ion batteries.

[0096] The secondary battery may be a secondary battery using an electrolytic solution or a solid-state 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.

[0097] The gasket of the present disclosure preferably contacts the electrolyte, i.e., has a contact surface with the electrolyte. Because the gasket of the present disclosure has excellent low water vapor permeability, when used in contact with the electrolyte, it can suppress the intrusion of water into the electrolyte. The electrolyte referred to here includes not only the electrolyte itself provided in the electrochemical device, but also substances derived from the electrolyte, and may be liquid, solid, or gas. The gas includes, for example, volatilized electrolytic solution and gas generated by decomposition of the electrolytic solution during charging and discharging.

[0098] The electrochemical device according to the present disclosure preferably includes a non-aqueous electrolyte. The gasket according to the present disclosure is preferably used in contact with the non-aqueous electrolyte, i.e., has a surface that comes into contact with the non-aqueous electrolyte.

[0099] The non-aqueous electrolyte may be prepared by dissolving a known electrolyte salt in a known organic solvent for dissolving electrolyte salts.

[0100] 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-based solvents such as fluoroethylene carbonate, fluoroether, and fluorinated carbonate can be used.

[0101] The electrolyte salt is, for example, LiClO４ , LiAsF ６ , LiBF ４ , LiPF ６ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ , LiCl, LiBr, CH ３ SO ３ Li, CF ３ SO ３ Li, cesium carbonate, etc. are listed, and LiPF is particularly preferred due to its good cycle characteristics. ６ , LiBF ４ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ Or a combination of these is preferred.

[0102] 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.

[0103] The solid electrolyte used in the solid secondary battery may be a sulfide-based solid electrolyte or an oxide-based solid electrolyte. In particular, the sulfide-based solid electrolyte has the advantage of being flexible.

[0104] The sulfide-based solid electrolyte is not particularly limited, and may be Li ２ S-P ２ S ５ , Li ２ S-P ２ S ３ , Li ２ S-P ２ S ３ -P ２ S ５ , Li ２ S-SiS ２ , LiI-Li ２ S-SiS ２ , LiI-Li ２ S-P ２ S ５, LiI-Li ２ S-P ２ O ５ , LiI-Li ３ P.O. ４ -P ２ S ５ , LiI-Li ２ S-SiS ２ -P ２ S ５ , Li ２ S-SiS ２ -Li ４ SiO ４ , Li ２ S-SiS ２ -Li ３ P.O. ４ , Li ３ P.S. ４ -Li ４ GeS ４ , Li ３．４ P ０．６ Si ０．４ S ４ , Li ３．２５ P ０．２５ Ge ０．７６ S ４ , Li ４－ｘ Ge １－ｘ P ｘ S ４ (x=0.6~0.8), Li ４＋ｙ Ge １－ｙ Ga ｙ S ４ (y=0.2-0.3), LiPSCl, LiCl, Li ７－ｘ－２ｙ P.S. ６－ｘ－ｙ Cl ｘ (0.8≦x≦1.7, 0<y≦-0.25x+0.5), Li １０ SnP ２ S １２ Any one selected from the above, or a mixture of two or more thereof, can be used.

[0105] 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.

[0106] 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.

[0107] Specific examples of the compound include Li ｘａ La ｙａ TiO ３ [xa=0.3~0.7, ya=0.3~0.7] (LLT), Li ｘｂ La ｙｂ Zr ｚｂ M ｂｂ ｍｂ O ｎｂ (M ｂｂ is at least one element selected from Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, where xb satisfies 5≦xb≦10, yb satisfies 1≦yb≦4, zb satisfies 1≦zb≦4, mb satisfies 0≦mb≦2, and nb satisfies 5≦nb≦20.), Li ｘｃ B ｙｃ M ｃｃ ｚｃ O ｎｃ (M 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 Oｚｇ (1≦xg≦3, 0<yg≦2, 1≦zg≦10), Li ３ BO ３ -Li ２ SO ４ , Li ２ Alumni ２ O ３ -P ２ O ５ , Li ２ O—SiO ２ , Li ６ BaLa ２ Ta ２ O １２ , Li ３ P.O. （４－３／２ｗ） N ｗ (w is w<1), Li having a LISICON (Lithium super ionic conductor) type crystal structure ３．５ Zn ０．２５ GeO ４ , La having a perovskite crystal structure ０．５１ Li ０．３４ TiO ２．９４ , La ０．５５ Li ０．３５ TiO ３ , LiTi having a NASICON (sodium super ionic conductor) type crystal structure ２ P ３ O １２ , Li １＋ｘｈ＋ｙｈ (Al, Ga) ｘｈ (Ti, Ge) ２－ｘｈ Si ｙｈ P ３－ｙｈ O １２ (where 0≦xh≦1, 0≦yh≦1), Li having a garnet-type crystal structure ７ La ３ Zr ２ O １２ Also, ceramic materials in which elements are substituted for LLZ are known. For example, Li ６．２４ La ３ Zr ２ Al ０．２４ O １１．９８ , Li ６．２５ Al ０．２５ La ３ Zr２ O １２ and Li substituted with Ta ６．６ La ３ Zr １．６ Ta ０．４ O １２ , Nb-substituted Li ６．７５ La ３ Zr １．７５ Nb ０．２５ O １２ Other examples include LLZ-based ceramic materials in which at least one element of Mg (magnesium) and A (A is at least one element selected from the group consisting of Ca (calcium), Sr (strontium), and Ba (barium)) is substituted for LLZ. Phosphorus compounds containing Li, P, and O are also desirable. For example, lithium phosphate (Li ３ P.O. ４ ), LiPON, LiPOD, in which some of the oxygen in lithium phosphate is replaced with nitrogen １ (D １ is at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc. １ ON (A １ is at least one selected from Si, B, Ge, Al, C, Ga, etc.) can also be preferably used. ２ O-Al ２ O ３ -SiO ２ -P ２ O ５ -TiO ２ -GeO ２ , Li ２ O-Al ２ O ３ -SiO ２ -P ２ O ５ -TiO ２ etc.

[0108] 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.

[0109] 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 ), NASICON type (Li １．３ Al ０．３ Ti １．７ (P.O. ４ ) ３ etc.), garnet type (Li ７ La ３ Zr ２ O １２ (LLZ), etc. Among these, garnet type is preferred.

[0110] The present disclosure also includes an electrochemical device including the gasket of the present disclosure.

[0111] 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.

[0112] The present disclosure will now be described in more detail with reference to examples, but the present disclosure is not limited to these examples.

[0113] Various physical properties were measured by the following methods.

[0114] <Content of modified monomer> The PPVE content was determined by press-molding a sample to prepare a thin film disk, measuring the infrared absorbance of the thin film disk by FT-IR, and determining the PPVE content at 995 cm －１ Absorbance at / 935 cm －１ The absorbance ratio was calculated by multiplying the absorbance ratio at 0.14.

[0115] <Standard Specific Gravity (SSG)> Using a sample molded in accordance with ASTM D4895 89, the standard specific gravity was measured by the water displacement method in accordance with ASTM D 792.

[0116] <Melt-moldability> According to ASTM D1238, the mass of polymer flowing out of a nozzle with an inner diameter of 2.095 mm and a length of 8 mm per 10 minutes (g / 10 min) was measured at 372°C and a load of 5000 g (total load) using a melt indexer. MFRs of 0.10 g / 10 min or more were deemed to be melt-moldable, while MFRs of less than 0.10 g / 10 min were deemed not to be melt-moldable (non-melt-moldable).

[0117] Gasket A Non-melt-moldable PTFE powder (modified PTFE containing 0.08% by mass of PPVE units obtained by suspension polymerization, SSG = 2.150) was compression molded under molding conditions of a pressure of 30 MPa and a retention time of 5 minutes, and the temperature was raised to 370°C at a rate of 50°C / hr in an electric furnace, followed by heat treatment at 370°C for 5.5 hours. Thereafter, the temperature was cooled to room temperature at a rate of 50°C / hr to obtain a circular gasket A with a square cross section having an inner diameter of Φ14.3 mm, an outer diameter of Φ17.7 mm, and a height of 1.6 mm.

[0118] Gasket B Annular gasket B was obtained in the same manner as gasket A, except that the heat-treated molded body was immersed in ice water to set the cooling rate at about 300° C. / hr.

[0119] Gasket C Annular gasket C was obtained in the same manner as gasket A, except that the cooling rate was 25° C. / hr.

[0120] Gasket D A circular gasket D was obtained in the same manner as in Gasket C, except that a TFE homopolymer (SSG=2.165) obtained by suspension polymerization was used as the non-melt-moldable PTFE powder.

[0121] Gasket E A circular gasket E was obtained in the same manner as in Gasket C, except that modified PTFE (PPVE content 0.08 mass%, SSG = 2.160) obtained by suspension polymerization was used as the non-melt-moldable PTFE powder.

[0122] The water vapor permeability coefficient of the obtained gasket was measured by the following method. After the water vapor permeability test, the gasket was removed from the test jig and the specific gravity, crystallinity, and scattering intensity of the gasket were measured. The results are shown in Table 1.

[0123] <Water Vapor Permeation Test> As shown in FIG. 2, 2 g of water 42 was placed in an aluminum alloy cup 41. A gasket 47 was inserted between the cup 41 and a gasket compression jig 43, and the lid 44 was tightened with bolts 45 to compress the gasket 47. A spacer 46 was placed between the lid 44 and the cup 41, and the compression rate of the gasket 47 was adjusted to 15% in Example 1 and Comparative Example 1, and 40% in Examples 2 to 4. The compression rate was calculated using the following formula: (Gasket compression rate (%)) = {1 - (Distance between the cup 41 and the gasket compression jig 43 (gasket placement portion)) / (Height of the gasket before compression)} × 100. The mass of the permeation test jig 40 obtained in this manner was measured. The permeation test jig 40 was placed in an electric furnace at 80°C, left for 1000 hours, removed, and left at room temperature for 2 hours, after which the mass was measured. The water vapor permeation coefficient was calculated using the following formula. This operation was repeated three times, and the average water vapor permeation coefficient was calculated. The average values ​​are shown in Table 1. Water vapor permeability coefficient (g / 1000 hr) = (mass of permeation test jig before heating) - (mass of permeation test jig after heating)

[0124] <Specific Gravity> Measured by the water displacement method in accordance with ASTM D 792.

[0125] <Crystallinity> The crystallinity was measured using an X-ray diffractometer (Ultima III, manufactured by Rigaku Corporation) under the following measurement conditions using a multiple peak separation method: A measurement sample having a thickness of 40 μm or more was placed on a sample holder, and the peaks of the crystalline and amorphous parts of the obtained diffraction spectrum were separated into independent peaks, and the crystallinity was calculated by determining the integrated intensity (area) of each peak.

[0126] Measurement conditions

[0127] <Scattering Intensity> The scattering intensity was measured using a small angle X-ray diffractometer (RINT2500, manufactured by Rigaku Corporation) under the following measurement conditions. －１The scattering intensity was determined as the case where

[0128] Measurement conditions

[0129]

[0130] 10: Electrochemical device 1: Lid 2: External terminal 21: Terminal head 22: Shaft 3: Gasket 31: Cylindrical portion 32: Flange portion 33: Side wall portion 4: Insulating plate 40: Permeation test jig 41: Cup 42: Water 43: Gasket compression jig 44: Lid 45: Bolt 46: Spacer 47: Gasket

Claims

1. A gasket containing polytetrafluoroethylene that exhibits non-melt moldability and has a water vapor permeability coefficient of 0.020 g / 1000 hr or less.

2. The gasket of claim 1, wherein said polytetrafluoroethylene is a modified polytetrafluoroethylene.

3. The gasket according to claim 2, wherein the polytetrafluoroethylene is a modified polytetrafluoroethylene containing tetrafluoroethylene units and at least one modified monomer unit selected from the group consisting of perfluoro(alkyl vinyl ether) units and hexafluoropropylene units.

4. The gasket according to claim 2 or 3, wherein the amount of modification of the modified polytetrafluoroethylene is 0.001 to 1.0% by mass.

5. The gasket according to any one of claims 1 to 4, which has a specific gravity of 2.130 or more and 2.180 or less.

6. The gasket according to any one of claims 1 to 5, which is in contact with an electrolyte.

7. The gasket according to any one of claims 1 to 6, wherein the crystallinity is 35 to 60%.

8. The gasket according to any one of claims 1 to 7, which has a scattering intensity of 800 to 1,600.

9. An electrochemical device comprising the gasket according to any one of claims 1 to 8.

10. A gasket for an electrochemical device, comprising polytetrafluoroethylene exhibiting non-melt moldability and having a specific gravity of 2.130 or more and 2.180 or less.

11. The gasket according to claim 10, which has a crystallinity of 65% or less and a scattering intensity of 800 or more.

12. A gasket for an electrochemical device, comprising polytetrafluoroethylene exhibiting non-melt moldability, having a crystallinity of 65% or less, and a scattering intensity of 800 or more.

13. A gasket according to any one of claims 1 to 12, wherein the polytetrafluoroethylene content is 99.9 mass % or more.

14. The gasket according to any one of claims 1 to 13, which has a specific gravity of 2.140 to 2.

170.

15. A gasket according to any one of claims 1 to 14, wherein the polytetrafluoroethylene is a homopolymer of tetrafluoroethylene, or a modified PTFE in which the content of modified monomer units is 0.01 to 0.10 mass% based on the total polymerized units.

Images