Porous membrane, separator for electrochemical device, member for electrochemical device, and electrochemical device

Abstract

To provide a porous membrane reusable after being used as a separator for an electrochemical device.SOLUTION: The porous membrane according to the present disclosure contains a first resin and a second resin. The first resin and the second resin each have a pyrolysis temperature of 300°C or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a porous membrane, a separator for an electrochemical device, a member for an electrochemical device, and an electrochemical device. [Background technology]

[0002] Electrochemical devices such as non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, have high energy densities and are therefore widely used as batteries for personal computers, mobile phones, personal digital assistants, and vehicle-mounted devices.

[0003] As a component of such non-aqueous electrolyte secondary batteries, separators with excellent heat resistance have been developed. For example, as disclosed in Patent Document 1, a separator is known in which a heat-resistant layer containing an aramid resin and inorganic particles is laminated on a porous substrate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 176421 Summary of the Invention [Problem to be solved by the invention]

[0005] However, it is difficult to remove and reuse the separators of the above-mentioned conventional techniques after use of the electrochemical element.

[0006] An object of one aspect of the present invention is to provide a porous membrane that can be reused after being used as a separator for an electrochemical device. [Means for solving the problem]

[0007] In order to solve the above problems, a porous membrane according to one aspect of the present invention comprises: A porous membrane comprising a first resin and a second resin, The first resin and the second resin both have a thermal decomposition temperature of 300° C. or higher. [Effects of the Invention]

[0008] According to one aspect of the present invention, there is provided a porous membrane that can be reused after use as a separator for an electrochemical device. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the present invention will be described below, but the present invention is not limited thereto. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more and B or less."

[0010] [1. Porous membrane] A porous film according to one embodiment of the present invention includes a first resin and a second resin. The first resin and the second resin are heat-resistant resins, each with a thermal decomposition temperature of 300°C or higher. In this specification, the thermal decomposition temperature is defined as the temperature at which a mass loss during heating exceeds 5%. Therefore, the first resin and the second resin have a mass loss of 5% or less at 300°C. The thermal decomposition temperatures of the first resin and the second resin may be 350°C or higher or 400°C or higher.

[0011] According to findings from the research of the present inventors, after use as a separator in an electrochemical element (such as a secondary battery), the pores in the porous membrane are blocked, which is thought to be due to components derived from the electrolyte solution, etc. This blocking material is thermally decomposed by heating, and therefore the porous membrane can be reused if it is heated at a temperature that does not thermally decompose the blocking material but does not thermally decompose the resin that forms the porous membrane.

[0012] However, many conventional porous membranes used as separators contain polyolefin films, making such a recycling method unfeasible. This is because polyolefin films have a shutdown function, and when heated to around 200°C, the polyolefin resin melts and clogs the pores. Therefore, in one embodiment of the porous membrane of the present invention, the above-mentioned problem is solved by incorporating heat-resistant resins, namely, first and second resins, into the material, thereby opening up the way for separator recycling.

[0013] The porous film may contain components other than the first resin and the second resin. Such components are preferably heat-resistant components. For example, the porous film may further contain one or more substances (such as a heat-resistant resin different from the first resin and the second resin, inorganic particles, etc.) whose thermal decomposition temperature is 300°C or higher. The thermal decomposition temperature of this substance may be 350°C or higher or 400°C or higher.

[0014] The porous membrane preferably has a low content of non-heat-resistant components. This configuration makes it easier to prevent the pores of the porous membrane from being blocked by molten non-heat-resistant components when the porous membrane is heated. In one embodiment, the content of resin in the porous membrane having a thermal decomposition temperature of less than 300°C is 5% by weight or less, 3% by weight or less, or 1% by weight or less, assuming that the weight of the porous membrane is 100% by weight. In one embodiment, the porous membrane does not contain a resin having a thermal decomposition temperature of less than 300°C.

[0015] The porous membrane preferably has a low content of components other than resin (such as inorganic particles). This configuration facilitates the regeneration process of the porous membrane by heating. In one embodiment, the content of components other than resin in the porous membrane is 5% by weight or less, 3% by weight or less, or 1% by weight or less, assuming that the weight of the porous membrane is 100% by weight. In one embodiment, the porous membrane does not contain components other than resin.

[0016] In one embodiment, the porous membrane is a single layer. In one embodiment, the porous membrane does not include two or more layers with different compositions, or is not in contact with a layer with a different composition in the thickness direction. In one embodiment, the porous membrane does not include a layer containing a resin as a main component (e.g., a layer in which resin accounts for 30 wt % or more, 50 wt % or more, 70 wt % or more, or 90 wt % or more of the total weight of the layer), or is not in contact with such a layer in the thickness direction. This configuration eliminates the need to stack multiple layers, thereby simplifying the manufacturing process. Note that the porous membrane can be used as a separator for an electrochemical device, and in this regard, it can be stacked with other components (such as the positive and negative electrodes of a secondary battery). Therefore, it is not necessarily understood that the porous membrane included in the electrochemical device component described below is not a single layer.

[0017] In one embodiment, the porous membrane does not contain or consist of fabric. As used herein, fabric refers to an article made of fibers, including woven fabrics, knitted fabrics, and nonwoven fabrics. In one embodiment, the porous membrane does not contain or consist of nonwoven fabric. Nonwoven fabric refers to an article formed by collecting unidirectionally or randomly oriented fibers, chemically or physically bonding the fibers, and processing them into a sheet. This manufacturing method is significantly different from, for example, the manufacturing method disclosed in the examples of the present application, in which a resin is precipitated from a solvent.

[0018] As mentioned above, the porous membrane may be any membrane other than a nonwoven fabric. The porous membrane may have a smoother surface than a nonwoven fabric. For example, the porous membrane may have a surface with a surface roughness of 0.1 μm or less. In this specification, surface roughness refers to the arithmetic mean height (Sa) defined in ISO 25178. A surface roughness of 0.1 μm or less is preferable from the viewpoint of improving adhesion to the electrode. The surface roughness is more preferably 0.05 μm or less, and even more preferably 0.02 μm or less. The lower limit of the surface roughness is not particularly limited, and may be 0.005 μm or more.

[0019] The porous film contains a first resin and a second resin, and therefore contains two or more types of resin. The reason for this configuration is to promote the formation of pores during film formation. The estimated mechanism is as follows: When a film is formed using only one type of resin, the solidification of the resin proceeds uniformly, making it difficult to form pores. On the other hand, when a film is formed using two or more types of resin, localized deviations in the solidification process occur, making it easier to form pores. In terms of a film formation method in which resins are precipitated from a solution, two or more types of resins have different solubilities. Therefore, when the less soluble first resin precipitates first, the more soluble second resin precipitates next to the precipitated first resin (the same applies when the solubilities of the first and second resins are reversed). Because of this estimated mechanism, it is preferable that the first and second resins be resins with different solubilities in solvents.

[0020] In one embodiment, both the first resin and the second resin are nitrogen-containing resins. In this specification, nitrogen-containing resin refers to a resin containing nitrogen atoms. Examples of nitrogen-containing resins include polyamide, polyimide, polyamideimide, polybenzimidazole, polyurethane, and melamine resin. In one embodiment, both the first resin and the second resin are selected from the group consisting of polyamide, polyimide, and polyamideimide. In this case, the first resin and the second resin may be selected from the same category. For example, both the first resin and the second resin may be polyamide.

[0021] The first resin and the second resin may be a nitrogen-containing aromatic resin. An aromatic resin refers to a resin containing at least a structural unit having an aromatic group. Examples of the nitrogen-containing aromatic resin include aromatic polyamides such as fully aromatic polyamides (aramid resins) and semi-aromatic polyamides, aromatic polyimides, aromatic polyamideimides, polybenzimidazole, aromatic polyurethanes, and melamine resins. Among these, from the viewpoint of heat resistance, the first resin and the second resin are preferably aramid resins.

[0022] Examples of aramid resins include para-aramid and meta-aramid, with para-aramid being preferred. Examples of para-aramid include para-oriented or para-oriented para-aramids having a structure similar to the para-oriented type, such as poly(paraphenylene terephthalamide), poly(parabenzamide), poly(4,4'-benzanilide terephthalamide), poly(paraphenylene-4,4'-biphenylenedicarboxylic acid amide), poly(paraphenylene-2,6-naphthalenedicarboxylic acid amide), poly(2-chloro-paraphenylene terephthalamide), paraphenylene terephthalamide / 2,6-dichloroparaphenylene terephthalamide copolymer, poly(4,4'-diphenylsulfonyl terephthalamide), paraphenylene terephthalamide / 4,4'-diphenylsulfonyl terephthalamide copolymer, and paraphenylene terephthalamide / 3,4'-oxydiphenylene terephthalamide copolymer. Examples of meta-aramids include poly(metaphenylene terephthalamide), poly(metaphenylene isophthalamide), poly(metabenzamide), poly(metaphenylene-4,4'-biphenylenedicarboxylic acid amide), and poly(metaphenylene-2,6-naphthalenedicarboxylic acid amide).

[0023] As mentioned above, to promote the formation of porous structures, it is preferable to combine the first and second resins with resins that differ in solubility in a solvent. For example, it is preferable to combine resins with different structures, such as a resin with a rigid structure and a resin with flexibility. For example, poly(paraphenylene terephthalamide), poly(2-chloro-paraphenylene terephthalamide), poly(parabenzamide), and poly(4,4'-benzanilide terephthalamide) have rigid structures. On the other hand, poly(4,4'-diphenylsulfonyl terephthalamide), paraphenylene terephthalamide / 4,4'-diphenylsulfonyl terephthalamide copolymer, and meta-aramid have flexibility. However, the combination of two or more nitrogen-containing aromatic resins is not limited to these combinations.

[0024] Of the 100% by weight of resin contained in the porous membrane, the nitrogen-containing aromatic resin is preferably more than 50% by weight, more preferably 70% by weight or more, and even more preferably 90% by weight or more. Of the 100% by weight of resin contained in the porous membrane, the nitrogen-containing aromatic resin may be 100% by weight or less, or may be less than 100% by weight. It is particularly preferable that the resin contained in the porous membrane consists solely of the nitrogen-containing aromatic resin.

[0025] The porous membrane may contain a nitrogen-containing aromatic resin and a resin other than the nitrogen-containing aromatic resin, but the resin other than the nitrogen-containing aromatic resin is preferably less than 50 wt%, more preferably 30 wt% or less, and even more preferably 10 wt% or less of 100 wt% of the resin contained in the porous membrane. The resin other than the nitrogen-containing aromatic resin may be 0 wt% or more, or may exceed 0 wt% of 100 wt% of the resin contained in the porous membrane.

[0026] Examples of resins other than nitrogen-containing aromatic resins include polyolefin resins, (meth)acrylate resins, fluorine-containing resins, polyester resins, rubbers, resins with a melting point or glass transition temperature of 180°C or higher, water-soluble polymers, polycarbonate, polyacetal, etc. In one embodiment, the resin contained in the porous membrane may be a resin other than polyester resins.

[0027] Examples of polyester resins include aromatic polyesters such as polyarylates and liquid crystal polyesters.

[0028] Examples of rubbers include styrene-butadiene copolymers and hydrogenated products thereof, methacrylic acid ester copolymers, acrylonitrile-acrylic acid ester copolymers, styrene-acrylic acid ester copolymers, ethylene propylene rubber, and polyvinyl acetate.

[0029] Examples of fluorine-containing resins include polyvinylidene fluoride (PVdF), polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-trichloroethylene copolymer, vinylidene fluoride-vinyl fluoride copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer, as well as fluorine-containing rubbers having a glass transition temperature of 23°C or lower among the above-mentioned fluorine-containing resins.

[0030] Examples of resins having a melting point or glass transition temperature of 180° C. or higher include polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyetheramide, and polyetheretherketone.

[0031] Examples of the water-soluble polymer include polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide, and polymethacrylic acid.

[0032] The porous membrane may or may not contain a filler. The filler may be an inorganic filler or an organic filler. As the filler, a filler made of an inorganic oxide such as silica, calcium oxide, magnesium oxide, magnesium hydroxide, titanium oxide, alumina, mica, zeolite, aluminum hydroxide, or boehmite is preferred, a filler made of calcium oxide, magnesium oxide, or alumina is more preferred, and a filler made of alumina is even more preferred.

[0033] The content of the filler in 100% by weight of the porous film is preferably 0 to 50% by weight, more preferably 0 to 30% by weight, and may be 0% by weight or more but less than 20% by weight, may be 0 to 15% by weight, may be 0 to 10% by weight, or may be 0 to 5% by weight. A filler content of 0% by weight means that the porous film does not contain a filler. The content of the filler in 100% by weight of the porous film may be more than 0% by weight or may be 1% by weight or more. In particular, from the viewpoint of strength, the content of the inorganic filler in 100% by weight of the porous film is preferably 0 to 50% by weight.

[0034] The average particle size of the filler is preferably 1 μm or less, more preferably 800 nm or less, even more preferably 500 nm or less, particularly preferably 100 nm or less, and most preferably 50 nm or less. The lower limit of the average particle size of the filler is not particularly limited, but can be, for example, 5 nm or more. Here, the average particle size of the filler is the average value of the equivalent sphere diameters of 50 filler particles. The equivalent sphere diameter of the filler is a value measured using a transmission electron microscope. Specific examples of measurement methods are as follows. 1. Using a transmission electron microscope (TEM; JEOL Ltd., JEM-2100F), images are taken at an accelerating voltage of 200 kV and a magnification of 10,000x using a Gatan Imaging Filter. 2. Using image analysis software (ImageJ), trace the particle contours of the obtained image and measure the spherical equivalent particle size of the filler particles (primary particles). 3. The above measurement is carried out on 50 randomly selected filler particles. The arithmetic mean of the spherical equivalent particle diameters of the 50 filler particles is taken as the average particle diameter of the particles.

[0035] The porous membrane may contain additives as long as they do not impair the effects of the present invention. Examples of additives include paper strength agents. The addition of paper strength agents can improve the mechanical strength of the porous membrane. Examples of paper strength agents include adipic acid-diethylenetriamine-epichlorohydrin resin and diallylamine hydrochloride-acrylamide copolymer.

[0036] The thickness of the porous membrane is preferably 0.3 to 35 μm, more preferably 5.5 to 35 μm, from the viewpoint of ensuring adhesion to the electrodes and high energy density. When the thickness of the porous membrane is 0.3 μm or more, internal short circuits due to breakage of the electrochemical device can be sufficiently suppressed, and the porous membrane can retain a sufficient amount of electrolyte. Furthermore, when the thickness of the porous membrane is 35 μm or less, the permeation resistance of metal ions in the electrochemical device can be suppressed, thereby suppressing deterioration in rate characteristics and cycle characteristics. Furthermore, an increase in the distance between the positive electrode and the negative electrode can be suppressed, thereby suppressing a decrease in the internal volume efficiency of the electrochemical device.

[0037] The basis weight of the porous membrane, i.e., the weight per unit area, can be appropriately determined in consideration of the strength, thickness, weight and handling properties of the porous membrane. The basis weight of the porous membrane is 0.3 to 30 g / m 2 It is preferable that the density is 0.5 to 10 g / m 2 By setting the basis weight of the porous film within these numerical ranges, it is possible to increase the weight energy density and volume energy density of the electrochemical device.

[0038] The porosity of the porous membrane is preferably 20 to 90% by volume, more preferably 30 to 80% by volume, so as to obtain sufficient ion permeability.

[0039] The air permeability of the porous membrane is preferably 150 sec / 100 cc or less, more preferably 120 sec / 100 cc or less, from the viewpoint of obtaining sufficient ion permeability. The air permeability of the porous membrane is a value exceeding 0 sec / 100 cc or more, and may usually be 10 sec / 100 cc or more, or even 20 sec / 100 cc or more. The air permeability is a value measured using an Oken air permeability tester in accordance with JIS P8117.

[0040] The heat shrinkage of the porous film at 300°C is preferably 1% or less, more preferably 0.5% or less, and even more preferably 0.3% or less. In this specification, the heat shrinkage is a parameter that represents heat resistance, and is calculated based on the degree to which the area of ​​a square drawn on the surface of the porous film shrinks after heating (calculated using the formula: "(area before heating - area after heating) / area before heating"). For more specific examples of the measurement method, see the examples of this application.

[0041] The porous membrane can be disposed between a positive electrode and a negative electrode as a component of an electrochemical device. The porous membrane may be disposed on the active material layer of at least one of the positive electrode and the negative electrode. The porous membrane may be disposed between the positive electrode and the negative electrode so as to be in contact with them. The porous membrane is preferably an insulating membrane.

[0042] 2. Method for producing porous membrane A porous film can be formed using a coating liquid obtained by dissolving or dispersing a first resin and a second resin in a solvent. The solvent can also be considered a dispersion medium for dispersing the resin. Examples of methods for forming the coating liquid include mechanical stirring, ultrasonic dispersion, high-pressure dispersion, and media dispersion.

[0043] As a method for forming a porous film, for example, a coating liquid is applied to a suitable support, a resin is precipitated, and then the solvent is removed to form a porous film, and the porous film is peeled off from the support. It is also preferable to set the resin precipitation time to a relatively long time. For example, the treatment time in the precipitation tank may be 3 minutes or more, 5 minutes or more, or 10 minutes or more.

[0044] The solvent is preferably one that does not adversely affect the support, dissolves the resin uniformly and stably, and, if necessary, disperses the filler uniformly and stably. Examples of the solvent include N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide, N,N-dimethylformamide, acetone, and water.

[0045] The coating liquid may contain a filler. The coating liquid may also contain, as appropriate, components other than the resin and the filler, such as a dispersant, a plasticizer, a surfactant, and a pH adjuster.

[0046] The coating liquid can be applied to the support by a conventionally known method, and specific examples thereof include a gravure coater method, a dip coater method, a bar coater method, and a die coater method.

[0047] When the coating liquid contains an aramid resin, the aramid resin can be precipitated by adding moisture to the coating surface. This may form a porous film. Specific methods for adding moisture to the coating surface include, but are not limited to, exposing the surface to a humid atmosphere, spraying water onto the surface with a spray or the like, and spraying water vapor onto the surface with a nozzle or the like.

[0048] [3. Separators for electrochemical elements, electrochemical element components, electrochemical elements] A separator for an electrochemical element according to one embodiment of the present invention includes the porous membrane described above. Hereinafter, the separator for an electrochemical element will also be simply referred to as a "separator." The separator may consist solely of the porous membrane described above.

[0049] An electrochemical device member according to one embodiment of the present invention comprises a positive electrode, the above-described separator for an electrochemical device, and a negative electrode arranged in this order. An electrochemical device according to one embodiment of the present invention includes the above-described separator for an electrochemical device.

[0050] Examples of electrochemical elements include secondary batteries and capacitors. Examples of secondary batteries include non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries. Examples of capacitors include electric double layer capacitors. The shape of the non-aqueous electrolyte secondary battery is not particularly limited, and may be a thin plate (paper) type, a disk type, a cylinder type, a prismatic type such as a rectangular parallelepiped, or the like.

[0051] For example, a member for an electrochemical device can be formed by arranging a positive electrode, the separator described above, and a negative electrode in this order. The member for an electrochemical device is then placed in a container that will serve as the housing for the electrochemical device. This completes the manufacture of an electrochemical device. In the case of a nonaqueous electrolyte secondary battery, the container is filled with the nonaqueous electrolyte and then sealed under reduced pressure.

[0052] <Positive electrode> The positive electrode is not particularly limited as long as it is generally used as a positive electrode for an electrochemical element. For example, a positive electrode sheet having a structure in which an active material layer containing a positive electrode active material and a binder is formed on a positive electrode current collector can be used as the positive electrode. The active material layer may further contain a conductive agent.

[0053] The positive electrode active material may be, for example, a material capable of doping and dedoping metal ions such as lithium ions or sodium ions. Specific examples of such materials include lithium-containing composite metal oxides containing lithium (Li) and at least one transition metal selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, and Al. Examples of such lithium-containing composite metal oxides include LiCoO2, LiNiO2, LiMn2O4, Li2MnO3, and LiNi x Mn y Co1-x-y O2[0 <x+y<1]、LiNi x Co y Al 1-x-y O2[0 <x+y<1]、LiCr 0.5 Mn 0.5 Examples include O2, LiFePO4, Li2FeP2O7, LiMnPO4, LiFeBO3, Li3V2(PO4)3, Li2CuO2, Li2FeSiO4, and Li2MnSiO4.

[0054] Examples of the conductive agent include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black (e.g., acetylene black), pyrolytic carbons, fibrous carbon materials, and baked organic polymer compounds. The conductive agent may be used alone or in combination of two or more. The proportion of the conductive agent in the positive electrode mixture is preferably 5 to 20 parts by mass per 100 parts by mass of the positive electrode active material. When a fibrous carbon material such as graphitized carbon fiber or carbon nanotubes is used as the conductive agent, this proportion can be reduced.

[0055] Thermoplastic resins can be used as the binder. Examples include fluororesins such as PVdF, polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymers, hexafluoropropylene-vinylidene fluoride copolymers, and tetrafluoroethylene-perfluorovinyl ether copolymers; acrylic resins; styrene-butadiene rubber; polyimide resins; and polyolefin resins. The binder also functions as a thickener. Two or more of these thermoplastic resins may be mixed. By using a fluororesin and a polyolefin resin as binders and setting the ratio of the fluororesin to the total positive electrode mixture to 1% by mass or more and 10% by mass or less and the ratio of the polyolefin resin to 0.1% by mass or more and 2% by mass or less, a positive electrode mixture with high adhesion to the positive electrode current collector and high internal bonding strength can be obtained.

[0056] Examples of the positive electrode current collector include conductors such as Al, Ni, stainless steel, etc. Among these, Al is more preferred because it can be easily processed into a thin film and is inexpensive.

[0057] Examples of methods for producing a positive electrode sheet include a method of pressurizing a positive electrode active material, a conductive agent, and a binder (positive electrode mixture) onto a positive electrode current collector; a method of forming the positive electrode mixture into a paste using an appropriate organic solvent, applying the paste to a positive electrode current collector, drying it, and then pressurizing it to adhere it to the positive electrode current collector.

[0058] Examples of organic solvents that can be used in the above method include amine solvents such as N,N-dimethylaminopropylamine and diethylenetriamine; ether solvents such as tetrahydrofuran; ketone solvents such as methyl ethyl ketone; ester solvents such as methyl acetate; and amide solvents such as dimethylacetamide and NMP.

[0059] Examples of methods for applying the positive electrode mixture paste to the positive electrode current collector include slit die coating, screen coating, curtain coating, knife coating, gravure coating, and electrostatic spraying.

[0060] <Negative electrode> The negative electrode is not particularly limited as long as it is generally used as a negative electrode for an electrochemical element. For example, a negative electrode sheet having a structure in which an active material layer containing a negative electrode active material and a binder is formed on a negative electrode current collector can be used as the negative electrode. The active material layer may further contain a conductive agent.

[0061] Examples of the negative electrode active material include materials that can be doped and dedoped with metal ions such as lithium ions or sodium ions. Examples of such materials include carbonaceous materials, chalcogen compounds (oxides, sulfides, etc.), nitrides, metals, and alloys that can be doped and dedoped with lithium ions at a lower potential than the positive electrode. Examples of carbonaceous materials include natural graphite, artificial graphite, cokes, carbon black, and pyrolytic carbons.

[0062] Oxides that can be used as negative electrode active materials include SiO2, SiO, and the like, which are compounds of the formula SiO x (where x is a positive real number); oxides of silicon such as TiO2 and TiO with the formula TiO x (where x is a positive real number); oxides of titanium, such as V2O5 and VO2, with the formula VO x (where x is a positive real number) oxides of vanadium; Fe3O4, Fe2O3, FeO, etc., with the formula FeO x (where x is a positive real number) Iron oxides such as SnO2 and SnO with the formula SnO x (where x is a positive real number); tin oxides such as WO3 and WO2 with the formula WO x (where x is a positive real number) is the oxide of tungsten; Li4Ti5O 12 and composite metal oxides containing lithium, such as LiVO2, and titanium or vanadium.

[0063] Sulfides that can be used as negative electrode active materials include Ti2S3, TiS2, TiS, and other sulfides with the formula TiS x (where x is a positive real number); titanium sulfides such as V3S4, VS2, and VS, with the formula VS x (where x is a positive real number) Vanadium sulfides such as Fe3S4, FeS2, and FeS, with the formula FeS x (where x is a positive real number) Iron sulfides such as Mo2S3 and MoS2 with the formula MoS x (where x is a positive real number) Molybdenum sulfides such as SnS2 and SnS with the formula SnS x (where x is a positive real number); tin sulfides such as WS2 with the formula WS x (where x is a positive real number) tungsten sulfides such as Sb2S3 with the formula SbS x (where x is a positive real number) Antimony sulfides such as Se5S3, SeS2, and SeS with the formula SeS x (where x is a positive real number) and selenium sulfide.

[0064] As nitrides that can be used as the negative electrode active material, Li3N, Li 3-x A x lithium-containing nitrides such as N (where A is either or both of Ni and Co, and where 0 < x < 3).

[0065] These carbonaceous materials, oxides, sulfides, and nitrides may be used alone or in combination of two or more. Also, these carbonaceous materials, oxides, sulfides, and nitrides may be either crystalline or amorphous.

[0066] [[ID=​​​​​​​​​​​​​​​​Examples of methods for producing a negative electrode sheet include a method of press-molding a negative electrode active material onto a negative electrode current collector, a method of forming a paste of a negative electrode active material using an appropriate organic solvent, applying the paste to a negative electrode current collector, drying, and then pressing to adhere it to the negative electrode current collector, etc. The paste preferably contains the conductive agent and the binder described above.

[0071] The negative electrode sheet may contain a binder as needed. Examples of the binder include thermoplastic resins, such as PVdF, thermoplastic polyimide, carboxymethyl cellulose, and polyolefin resins.

[0072] <Nonaqueous electrolyte> The non-aqueous electrolyte is not particularly limited as long as it is a non-aqueous electrolyte generally used in electrochemical elements, such as non-aqueous electrolyte secondary batteries. For example, a non-aqueous electrolyte obtained by dissolving a lithium salt in an organic solvent can be used as the non-aqueous electrolyte. Examples of lithium salts include LiClO4, LiPF6, LiAsF6, LiSbF6, LiBF4, LiCF3SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiN(SO2C2F5)2, LiN(SO2CF3)(COCF3), Li(C4F9SO3), Li2B 10 Cl 10 Examples of the lithium salt include LiBOB (here, BOB stands for bis(oxalato)borate), LiFSI (here, FSI stands for bis(fluorosulfonyl)imide), lithium salts of lower aliphatic carboxylic acids, and LiAlCl4. The lithium salts may be used alone or in combination of two or more. Among these, it is preferable to use an electrolyte containing at least one fluorine-containing material selected from the group consisting of LiPF6, LiAsF6, LiSbF6, LiBF4, LiCF3SO3, LiN(SO2CF3)2, and LiC(SO2CF3)3.

[0073] Examples of organic solvents include carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-di(methoxycarbonyloxy)ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of suitable organic solvents include ethers such as methyl formate, methyl acetate, and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; amides such as N,N-dimethylformamide and N,N-dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, and 1,3-propanesultone; and solvents obtained by further introducing fluoro groups into these organic solvents (solvents in which one or more hydrogen atoms in the organic solvent are substituted with fluorine atoms). These organic solvents may be used alone or in combination. Among these, mixed solvents containing carbonates are preferred, with mixed solvents of cyclic carbonates and acyclic carbonates and mixed solvents of cyclic carbonates and ethers being more preferred. Mixed solvents of cyclic carbonates and acyclic carbonates are preferably mixed solvents containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. An electrolyte solution using such a mixed solvent has many advantages, including a wide operating temperature range, resistance to deterioration even when charged and discharged at a high current rate, resistance to deterioration even when used for a long period of time, and resistance to decomposition even when a graphite material such as natural graphite or artificial graphite is used as the active material of the negative electrode.

[0074] [4. Method for Reusing Porous Membranes] By removing the blockage of the pores, the porous membrane can be reused as a separator for an electrochemical device, etc. Therefore, one aspect of the present invention also includes the above-mentioned method for reusing the porous membrane. The reused porous membrane tends to have a lower air permeability (Gurley value) because the blockage of the pores is removed.

[0075] An example of a method for removing blockages in a porous membrane is heating the porous membrane. This is because heating the porous membrane at a high temperature above a certain level can cause the blockages that clog the pores to thermally decompose. The lower limit of the heating temperature can be 150°C or higher, 170°C or higher, 200°C or higher, 250°C or higher, or 300°C or higher. The upper limit of the heating temperature is usually below the thermal decomposition temperature of the first resin and the second resin, and can be, for example, 400°C or lower, 350°C or lower, or 300°C or lower. When heating the porous membrane, it is preferable to heat it while applying a load or tension to the porous membrane in order to reduce shrinkage of the porous membrane.

[0076] Another example of a method for removing blockages in a porous membrane is washing the porous membrane. This is because washing the porous layer can wash away blockages that have blocked the pores. Examples of cleaning solutions include water and organic solvents. After washing the porous membrane, the porous membrane may be dried to remove the cleaning solution.

[0077] The above-mentioned heating and washing may be combined. For example, the porous membrane may be washed and then heated. Alternatively, the porous membrane may be heated and then washed. After washing, it is preferable to dry the porous membrane, but in the case of reuse treatment in the former process, heating may also serve as drying.

[0078] [5. Summary] The present invention includes the following aspects. <1> A porous membrane comprising a first resin and a second resin, The first resin and the second resin both have a thermal decomposition temperature of 300°C or higher. Porous membrane. <2> It is a single layer, <1> The porous membrane according to claim 1. <3> The first resin and the second resin are both selected from the group consisting of polyamide, polyimide, and polyamideimide. <1> Or the porous membrane according to <2>. <4> The first resin and the second resin are both aramid resins. <3> The porous membrane according to claim 1. <5> When the weight of the porous film is 100% by weight, the content of the resin having a thermal decomposition temperature of less than 300°C is 5% by weight or less. <1> ~ <4> The porous membrane according to any one of the preceding items. <6> When the weight of the porous membrane is 100% by weight, the content of components other than the resin is 5% by weight or less. <1> ~ <5> The porous membrane according to any one of the preceding items. <7> The heat shrinkage rate of the porous film at 300°C is 1% or less. <1> ~ <6> The porous membrane according to any one of the preceding items. <8> <1> ~ <7> The porous membrane according to any one of the above items is provided. Separators for electrochemical elements. <9> A positive electrode and <8> and a negative electrode arranged in this order. Components for electrochemical elements. <10> <8> The separator for an electrochemical element according to claim 1, Electrochemical element. <11> a secondary battery or a capacitor; <10> The electrochemical element according to claim 1.

[0079] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Example]

[0080] An embodiment of the present invention will now be described.

[0081] [Evaluation method] (Air permeability) The air permeability of the porous membrane cut into a size of 60 mm x 60 mm was measured in accordance with JIS P8117 using a digital Oken type air permeability tester EGO1 manufactured by Asahi Seiko Co., Ltd. The measured value was expressed as a Gurley value (sec / 100cc).

[0082] (Air permeability after recycling) A test non-aqueous electrolyte secondary battery incorporating the porous membrane as a separator was subjected to a cycle test. After that, the non-aqueous electrolyte secondary battery was disassembled, the porous membrane was removed, and the electrolyte and its decomposition products were removed by treating it under any of the following conditions 1 to 3. The air permeability of the porous membrane after the treatment was measured by the above-mentioned method. Condition 1: Heated on a hot plate at 150°C for 60 minutes. A weight was placed on the separator to prevent it from shrinking. Condition 2: Heated on a hot plate at 200°C for 60 minutes. A weight was placed on the separator to prevent it from shrinking. Condition 3: Heated on a hot plate at 300°C for 15 minutes. A weight was placed on the separator to prevent it from shrinking.

[0083] The cycle test procedure is as follows. 1. (Positive electrode) Thickness: 49.9 μm, Density: 2.97 g / cm 3 The positive electrode active material layer was composed of, by weight, LiNi 0.78 Co 0.19 Al 0.03 The ratio of O2:conductive agent:polyvinylidene fluoride was 92:4:4. 2. (Negative electrode) Thickness: 71.2 μm, Density: 1.45 g / cm 3 A negative electrode material having a void volume of 41.3 μL was prepared. The composition of the negative electrode active material layer was artificial graphite:styrene butadiene rubber:carboxymethyl cellulose=96.5:2.0:1.5 in weight ratio. 3. A negative electrode, a separator (porous film), and a positive electrode were laminated in this order to prepare a member for a non-aqueous electrolyte secondary battery. 4. The nonaqueous electrolyte secondary battery components were placed in a bag formed by laminating an aluminum layer and a heat-seal layer, and a nonaqueous electrolyte was poured into the bag. The amount of nonaqueous electrolyte poured was 2.8 times the total void volume of the electrodes and separator. The nonaqueous electrolyte was prepared by dissolving vinylene carbonate to a concentration of 1 wt % and LiPF6 to a concentration of 1 mol / L in a mixed solvent of ethylene carbonate: ethyl methyl carbonate: diethyl carbonate = 3:5:2 (volume ratio). 5. The bag was heat-sealed while the pressure inside the bag was reduced, thereby completing a non-aqueous electrolyte secondary battery for testing. 6. One initial charge / discharge cycle was performed under the following conditions: temperature: 25°C, voltage range: 2.7 to 4.2 V, current value: 0.1 C (charging) or 0.2 C (discharging). Here, 1 C is the current value at which the rated capacity based on the hourly rate of discharge capacity is discharged in 1 hour. 7. The non-aqueous electrolyte secondary battery was aged by performing 10 cycles of charge and discharge under the conditions of a temperature of 25°C, a voltage range of 2.7 to 4.2 V, and a current value of 1 C (when charging) or 5 C (when discharging). 8. 200 charge / discharge cycles were performed under the following conditions: temperature: 45°C, voltage range: 2.7 to 4.2V, current value: 1C (when charging) or 5C (when discharging).

[0084] (surface roughness) The non-contact surface roughness measuring device used was the "LEXT 3D MEASURING LASER MICROSCOPE OLS4100" manufactured by OLYMPUS Corp. The measurement conditions were as follows, and when the surface roughness differed between the front and back sides, the smaller value was used as the surface roughness of the sample. Objective lens: 100x Wavelength filter: 405nm Photography: After adjusting the focus using color photography, the upper and lower limits of brightness in the film thickness direction were manually adjusted using laser observation before photography. Measurement: After correcting the tilt using image correction, the surface roughness was calculated. Cutoff: None.

[0085] (heat shrinkage rate) The measurement was carried out according to the following procedure. 1. The porous membrane was cut into an 8cm x 8cm square. 2. A 6cm x 6cm square is drawn on the surface of the square sample. The area of ​​this square (36cm 2 ) was taken as the area before heating. 3. The sample was sandwiched between pieces of paper and placed in an oven heated to 150°C or 300°C. It was left in this state for 1 hour. 4. Measure the length of each side of the square drawn in step 2 with a digital caliper and mark each as L A and L B L A ×L B The value of was taken as the area after heating. 5. The value of "(area before heating - area after heating) / area before heating" was taken as the heat shrinkage rate.

[0086] (pyrolysis temperature) The measurement device used was a "TG / DTA6200" manufactured by Hitachi High-Tech Science Co., Ltd. The specific procedure is as follows. 1. The measurement sample (porous membrane) and the reference sample (aluminum oxide) were placed on an aluminum pan. 2. The measurement sample and the reference sample were placed in the measurement device, and the temperature was raised from 30 to 500°C at a rate of 10°C / min in a nitrogen atmosphere. 3. The mass loss of the porous film was measured as the temperature increased, and the temperature at which the mass loss exceeded 5% was defined as the thermal decomposition temperature. Therefore, if the mass loss of a porous film was 5% or less at 300°C, the thermal decomposition temperature of the porous film was determined to be 300°C or higher.

[0087] [Synthesis Example 1: Synthesis of Resin A] Resin A (poly(4,4'-diphenylsulfonyl terephthalamide)) was synthesized according to the following procedure. 1. A 0.5 L separable flask equipped with a stirring blade, a thermometer, a nitrogen inlet, and a powder addition port was thoroughly dried. 2. 408.6 g of NMP was charged into a flask. 31.4 g of calcium chloride was added, and the temperature was raised to 100°C. The calcium chloride was dried at 200°C for 2 hours before being added. 3. After calcium chloride was completely dissolved, 31.97 g of 4,4'-diaminodiphenyl sulfone was added at 100°C and completely dissolved. 4. The resulting solution was cooled to room temperature. While maintaining the temperature of the solution at 25±2°C, 26.14 g of terephthalic acid dichloride in total was added in three portions. 5. The temperature of the obtained solution was maintained at 25±2°C and the solution was aged for 1 hour to obtain a solution containing Resin A. The thermal decomposition temperature of Resin A was above the measurement limit of DSC (500°C or higher).

[0088] [Synthesis Example 2: Synthesis of Resin B] Resin B (poly(paraphenylene terephthalamide)) was synthesized according to the following procedure. 1. A 0.5 L separable flask equipped with a stirring blade, a thermometer, a nitrogen inlet, and a powder addition port was thoroughly dried. 2. 408.6 g of NMP was charged into a flask. 31.4 g of calcium chloride was added, and the temperature was raised to 100°C. The calcium chloride was dried at 200°C for 2 hours before being added. 3. After calcium chloride was completely dissolved, the solution was allowed to return to room temperature, and then 13.20 g of paraphenylenediamine was added and completely dissolved. 4. While maintaining the temperature of the solution at 25±2°C, a total of 24.24 g of terephthalic acid dichloride was added in three portions. 5. The temperature of the obtained solution was maintained at 25±2°C, and the solution was aged for 1 hour to obtain a solution containing Resin B. The thermal decomposition temperature of Resin B was above the measurement limit of DSC (500°C or higher).

[0089] [Example 1] The solutions obtained in Synthesis Examples 1 and 2 were mixed so that the weight ratio of resin A to resin B was 90:10 to obtain a mixture (1). 3.55 g of calcium carbonate was added to 100 g of the obtained mixture (1) and the mixture was stirred for 10 minutes to neutralize the solution, obtaining a neutralized liquid (1). The neutralized liquid (1) was then diluted with NMP and degassed under reduced pressure to prepare a slurry coating liquid (1). The solids concentration of the coating liquid (1) was 6.0 wt%.

[0090] The coating liquid (1) was applied to a release-treated PET film (75 μm thick) and treated in a deposition tank at 50°C and 70% relative humidity for 5 minutes to deposit a porous layer (1). The film was then washed with water in a water washing tank and dried in a drying oven at 80°C. After drying, the PET film was peeled off from the porous layer (1) to obtain a porous film (1). The physical properties of the resulting porous film (1) are shown in Table 1.

[0091] [Example 2] A porous membrane (2) was obtained in the same manner as in Example 1, except that the treatment was carried out in a precipitation tank at 50°C and a relative humidity of 70% for 15 minutes. The physical properties of the obtained porous membrane (2) are shown in Table 1.

[0092] [Comparative Example 1] The solution containing Resin B prepared in Synthesis Example 2 was mixed with alumina (average particle size: 13 nm) so that the weight ratio of Resin B:alumina was 50:50. 2.30 g of calcium carbonate was added to 100 g of the resulting mixture (3) and stirred for 10 minutes to neutralize the solution, obtaining a neutralized liquid (3). The neutralized liquid (3) was then diluted with NMP and degassed under reduced pressure to prepare a slurry coating liquid (3). The solids concentration of the coating liquid (3) was 4.5 wt %.

[0093] The coating liquid (3) was applied to a polyethylene porous film (thickness: 10.3 μm, air permeability: 180 s / 100 mL) and treated in an oven at 50°C and a relative humidity of 70% for 1 minute to precipitate a porous layer (3). The film was then washed with water and dried to obtain a porous membrane (3) comprising a porous layer (3) on a polyethylene porous film. The thickness of the obtained porous membrane (3) was 13.1 μm. Other physical properties of the porous membrane (3) are shown in Table 1.

[0094] [Evaluation results] The evaluation results are shown in Table 1. [Table 1]

[0095] As can be seen from Table 1, the porous membranes according to the examples had a certain degree of low Gurley value after heating. This suggests that the porous membranes according to the examples can be reused after being used as separators by subjecting them to appropriate treatment such as heating or washing.

[0096] In addition, Table 1 shows that the porous membranes according to the examples have low air resistance and excellent ion permeability even before being used as separators. Furthermore, Table 1 shows that the porous membranes according to the examples have low heat shrinkage and excellent heat resistance. These characteristics are preferable when using the porous membranes according to the examples as separators.

[0097] On the other hand, the porous membrane according to the comparative example contained a polyethylene porous film. Therefore, when heat-treated under condition 1, the Gurley fabric was extremely high, reaching the upper limit of measurement. This is thought to be because the pores of the polyethylene porous film contained in the porous membrane (3) were blocked by heating. Such porous membranes cannot be reused even after heat treatment. Furthermore, because the polyethylene porous film melts at around 200°C, it could not be treated under conditions 2 and 3. [Industrial Applicability]

[0098] One aspect of the present invention can be used in an electrochemical device.

Claims

1. A porous membrane comprising a first resin and a second resin, The first resin and the second resin both have a thermal decomposition temperature of 300°C or higher. Porous membrane.

2. It is a single layer, The porous membrane of claim 1.

3. The first resin and the second resin are both selected from the group consisting of polyamide, polyimide, and polyamideimide. The porous membrane of claim 1.

4. The first resin and the second resin are both aramid resins. The porous membrane of claim 3.

5. When the weight of the porous membrane is 100% by weight, the content of the resin having a thermal decomposition temperature of less than 300°C is 5% by weight or less. The porous membrane of claim 1.

6. When the weight of the porous membrane is 100% by weight, the content of components other than the resin is 5% by weight or less. The porous membrane of claim 1.

7. The heat shrinkage rate of the porous film at 300 ° C. is 1% or less. The porous membrane of claim 1.

8. A porous membrane according to any one of claims 1 to 7 is provided. Separators for electrochemical elements.

9. A separator for an electrochemical element according to claim 8, comprising a positive electrode, the separator for an electrochemical element according to claim 8, and a negative electrode arranged in this order. Components for electrochemical elements.

10. The separator for an electrochemical element according to claim 8 is provided. Electrochemical element.

11. a secondary battery or a capacitor; The electrochemical device according to claim 10.

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