Separator for electrochemical element, member for electrochemical element, and electrochemical element

Abstract

To provide a separator for an electrochemical element having an excellent resistance to heat when heat is applied on the separator from the outside.SOLUTION: The separator for an electrochemical element according to the present disclosure includes: a polyolefin porous base material; and a porous layer deposited on the polyolefin porous base material. The separator has a thermal diffusion rate of 0.04 mm2 / s at a maximum at the temperature of 25°C.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a separator for an electrochemical element, a member for an electrochemical element, and an electrochemical element.

Background Art

[0002] Electrochemical elements, such as non-aqueous electrolyte secondary batteries, particularly lithium-ion secondary batteries, are widely used as batteries for personal computers, mobile phones, portable information terminals, in-vehicle applications, etc., because of their high energy density.

[0003] As a member of the non-aqueous electrolyte secondary battery, the development of a separator with excellent heat resistance has been promoted. For example, as described in Patent Document 1, a separator in which a heat-resistant layer containing an aramid resin and inorganic particles is laminated on a porous substrate is known.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] On the other hand, when heat is applied from the outside to a conventional separator such as the separator described in Patent Document 1, the heat propagates not only to a part close to the heat source of the heat but also to the remaining part of the separator, and heat shrinkage and / or melting may occur in the entire separator. Therefore, there is room for improvement in the conventional separator in terms of suppressing or preventing heat shrinkage and / or melting in the entire separator when heat is applied from the outside, that is, from the viewpoint of heat resistance when heat is applied from the outside.

[0006] One aspect of the present invention aims to provide a separator for an electrochemical device that has excellent heat resistance when heat is applied from the outside.

Means for Solving the Problems

[0007] As a result of intensive research by the present inventors, it has been found that a separator having a low thermal diffusivity of a specific value or less has excellent heat resistance when heat is applied from the outside, and the present invention has been conceived.

[0008] The separator for an electrochemical device according to one aspect of the present invention includes a polyolefin porous substrate and a porous layer laminated on the polyolefin porous substrate, and has a thermal diffusivity at 25°C of 0.04 mm 2 / s or less.

Advantages of the Invention

[0009] According to one aspect of the present invention, it is possible to provide a separator for an electrochemical device that has excellent heat resistance when heat is applied from the outside.

Modes for Carrying Out the Invention

[0010] One embodiment of the present invention will be described below, but the present invention is not limited thereto. Unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more and B or less".

[0011] 〔1. Separator for Electrochemical Device〕 The separator for an electrochemical device according to one embodiment of the present invention includes a polyolefin porous substrate and a porous layer laminated on the polyolefin porous substrate, and has a thermal diffusivity at 25°C of 0.04 mm 2 / s or less.

[0012] Hereinafter, the "separator for an electrochemical element according to an embodiment of the present invention" is also simply referred to as "separator". Further, the "polyolefin porous base material" constituting the separator is also simply referred to as "porous base material". Furthermore, in this specification, the "thermal diffusivity at 25°C" is also simply referred to as "thermal diffusivity".

[0013] The separator according to an embodiment of the present invention has a low thermal diffusivity of 0.04 mm 2 / s or less at 25°C. The thermal diffusivity means the area where heat diffuses (moves) in the separator per unit time: 1 second (sec), and is a parameter representing the speed at which heat moves in the separator. Therefore, the separator is a separator in which heat hardly moves inside.

[0014] Therefore, when heat is applied to the separator from the outside, even if heat shrinkage and / or melting occur in a part of the separator close to the heat source of the heat, it is difficult for the heat to propagate to the remaining part of the separator. Therefore, even when heat is applied from the outside, it is considered that heat shrinkage and / or melting are suppressed or prevented in the entire separator. Note that examples of a part of the separator close to the heat source of the heat include the surface layer portion of the separator.

[0015] As described above, the separator is considered to have excellent heat resistance when heat is applied from the outside.

[0016] From the viewpoint of excellent heat resistance when heat is applied from the outside as described above, the lower the thermal diffusivity of the separator, the better. Specifically, the thermal diffusivity is preferably 0.040 mm 2 / s or less, more preferably 0.037 mm 2 / s or less, and even more preferably 0.035 mm 2 / s or less. Also, the thermal diffusivity may be 0.010 mm 2 / s or more, may be 0.020 mm 2 / s or more, or may be 0.025 mm 2It may also be above / s.

[0017] The thermal diffusivity is defined by the following formula (1). Thermal diffusivity [m 2 / s] = Thermal conductivity [J / m·s·K] / (Density [g / m 3 × Specific heat [J / g·K]) = Thermal conductivity [J / m·s·K] / Volumetric specific heat [J / m 3 ·K] ··· (1) From the above formula (1), it can be understood that in the separator, when the density and specific heat are large, the volumetric specific heat increases and the thermal diffusivity is controlled to a low value. Also, in the separator, when the thermal conductivity is small, it can be understood that the thermal diffusivity is controlled to a low value.

[0018] The separator has a porous structure with voids (pores). Since the weight of the void part is 0, the density of the separator can vary depending on its porosity, unlike the density of a material with a constant value. Specifically, the lower the porosity of the separator, the greater the tendency for the density of the separator to be larger.

[0019] The specific heat means the amount of heat (J) required to raise the temperature of a substance with a unit weight of 1 g by 1 °C (1 K). When a specific amount of heat is added, the more difficult it is for the temperature to rise, the larger the specific heat of the substance. Here, the separator usually contains resin and optionally contains a filler. Also, the inside of the voids in the separator is usually filled with air, and in the separator, the air content varies depending on the porosity. Furthermore, the specific heats of the resin, the filler, and the air are different from each other. Therefore, the specific heat can vary depending on the composition of the separator, that is, the resin content and the filler content, as well as the air content, that is, the porosity.

[0020] In addition, it is known that the specific heat of the porous structure can vary depending on the mode of pore distribution, for example, the size of each pore, the size (thickness) of the portion other than the pores, etc. Therefore, the specific heat of the separator can also vary depending on the mode of pore distribution, such as the size of each pore, the thickness of the resin portion, and the particle diameter of the filler, in addition to the composition.

[0021] As described above, by adjusting the composition such as the porosity, resin content, and filler content of the separator, as well as the mode of pore distribution, the density and specific heat of the separator can be adjusted to a suitable range. As a result, the thermal diffusivity of the separator can be controlled within a suitable range.

[0022] In addition, the thermal conductivity can vary depending on the type of material constituting the separator. Therefore, by appropriately selecting the material constituting the separator, that is, the raw material of the separator, the thermal conductivity of the separator can be adjusted, and as a result, the thermal conductivity can also be controlled within a suitable range.

[0023] The method for measuring the thermal diffusivity is not particularly limited, and a known method can be adopted. Preferably, the laser flash method can be adopted. Here, the laser flash method is a method compliant with JIS R 1611, and it is a method capable of directly measuring the thermal diffusivity without measuring the thermal conductivity. More specifically, the method described in the examples can be adopted as the laser flash method.

[0024] The separator includes a polyolefin porous base material and a porous layer laminated on the polyolefin porous base material. That is, the separator is a separator in which the porous layer and the polyolefin porous base material are laminated. The porous layer can be laminated on one or both surfaces of the polyolefin porous base material.

[0025] The separator may consist only of the porous layer and the porous base material, or layers different from the porous layer and the porous base material may be laminated as described later. The porous layer can be disposed between the porous base material and at least one of the positive electrode and the negative electrode as a member constituting the electrochemical element. The porous layer may be disposed between the porous base material and at least one of the positive electrode and the negative electrode so as to be in contact with them. The porous layer disposed between the porous base material and at least one of the positive electrode and the negative electrode may be one layer or two or more layers. The porous layer is preferably an insulating layer.

[0026] The porous layer usually contains a resin. The resin is not limited, for example, it is a nitrogen-containing aromatic resin. A nitrogen-containing aromatic resin means an aromatic resin containing a nitrogen atom. An aromatic resin means a resin containing a structural unit having at least an aromatic group.

[0027] Examples of the nitrogen-containing aromatic resin include aromatic polyamides such as wholly aromatic polyamide (aramid resin) and semi-aromatic polyamide, aromatic polyimide, aromatic polyamideimide, polybenzimidazole, aromatic polyurethane, and melamine resin. Among them, the nitrogen-containing aromatic resin preferably contains an aramid resin.

[0028] Examples of the aramid resin include para-aramid and meta-aramid, with para-aramid being preferred. Examples of para-aramid include para-oriented or para-oriented-like structured para-aramids such as poly(p-phenylene terephthalamide), poly(p-benzamide), poly(4,4'-benzani lide terephthalamide), poly(p-phenylene-4,4'-biphenylene dicarboxamide), poly(p-phenylene-2,6-naphthalenedicarboxamide), poly(2-chloro-p-phenylene terephthalamide), p-phenylene terephthalamide / 2,6-dichlorop-phenylene terephthalamide copolymer, poly(4,4'-diphenylsulfonyl terephthalamide), p-phenylene terephthalamide / 4,4'-diphenylsulfonyl terephthalamide copolymer. Examples of meta-aramid include poly(m-phenylene terephthalamide), poly(m-phenylene isophthalamide), poly(m-benzamide), poly(m-phenylene-4,4'-biphenylene dicarboxamide), poly(m-phenylene-2,6-naphthalenedicarboxamide). Poly(m-phenylene isophthalamide) is also referred to as poly[N,N'-(1,3-phenylene)isophthalamide].

[0029] The resin is not particularly limited, and preferably, it is two or more types of resins having different precipitation properties when forming the porous layer. Here, the two or more types of resins having different precipitation properties mean two or more types of resins having different solubilities in the solvent in the coating liquid used for forming the porous layer. The coating liquid is a liquid obtained by dissolving and / or dispersing the constituent material of the porous layer containing the resin in the resin. As the two or more types of resins having different precipitation properties with respect to the solvent for dissolving the resin, it is preferable to include, for example, two or more types of nitrogen-containing aromatic resins having different precipitation properties. As the two or more types of resins having different precipitation properties, it is preferable to combine resins having different structures, such as a resin having a rigid structure and a resin having flexibility. For example, poly(p-phenyleneterephthalamide), poly(2-chloro-p-phenyleneterephthalamide), poly(p-benzamide), and poly(4,4'-benzylanilide terephthalamide) have a rigid structure. On the other hand, poly(4,4'-diphenylsulfonyl terephthalamide), p-phenyleneterephthalamide / 4,4'-diphenylsulfonyl terephthalamide copolymer, and meta-aramid have flexibility. However, the combination of the two or more types of resins having different precipitation properties is not limited to these combinations. For example, a combination of resins having relatively similar structures, such as a combination of poly(p-phenyleneterephthalamide) and poly(2-chloro-p-phenyleneterephthalamide), may also be used.

[0030] In 100% by weight of the resin contained in the porous layer, 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. In 100% by weight of the resin contained in the porous layer, the nitrogen-containing aromatic resin may be 100% by weight or less, or less than 100% by weight. It is particularly preferable that the resin contained in the porous layer consists only of a nitrogen-containing aromatic resin.

[0031] The porous layer may contain a nitrogen-containing aromatic resin and a resin other than the nitrogen-containing aromatic resin, but in 100% by weight of the resin contained in the porous layer, the resin other than the nitrogen-containing aromatic resin is preferably less than 50% by weight, more preferably 30% by weight or less, and even more preferably 10% by weight or less. In 100% by weight of the resin contained in the porous layer, the resin other than the nitrogen-containing aromatic resin may be 0% by weight or more, or may be more than 0% by weight.

[0032] Examples of the resin other than the nitrogen-containing aromatic resin include polyolefin resins; (meth)acrylate resins; fluorine-containing resins; polyester resins; rubbers; resins having a melting point or glass transition temperature of 180°C or higher; water-soluble polymers; polycarbonate, polyacetal, and the like. In one embodiment, the resin contained in the porous layer can be a resin excluding polyester resins.

[0033] Examples of the polyester resin include aromatic polyesters such as polyarylate and liquid crystal polyesters.

[0034] Examples of the rubbers include styrene-butadiene copolymers and their hydrogenated products, methacrylic acid ester copolymers, acrylonitrile-acrylic acid ester copolymers, styrene-acrylic acid ester copolymers, ethylene propylene rubber, polyvinyl acetate, and the like.

[0035] Examples of the fluororesin 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, ethylene - tetrafluoroethylene copolymer, etc. Among the fluororesins, fluororubbers with a glass transition temperature of 23°C or lower are also included.

[0036] Examples of the resin with a melting point or glass transition temperature of 180°C or higher include polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyetheramide, polyetheretherketone, etc.

[0037] Examples of the water - soluble polymer include polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide, polymethacrylic acid, etc.

[0038] The porous layer can be a heat - resistant layer. The heat - resistant layer means a layer having a melting temperature higher than that of the base material. The resin contained in the porous layer can be a resin having heat resistance. The resin having heat resistance can be a resin having a melting point or glass transition temperature higher than that of the resin constituting the base material. The resin contained in the porous layer is preferably insoluble in the electrolyte of the electrochemical element and electrochemically stable within the operating range of the battery.

[0039] The porous layer may contain a filler. The filler may be an inorganic filler or an organic filler. As the filler, a filler composed of an inorganic oxide such as silica, calcium oxide, magnesium oxide, titanium oxide, alumina, mica, zeolite, aluminum hydroxide, or boehmite is preferable, a filler composed of calcium oxide, magnesium oxide, or alumina is more preferable, and a filler composed of alumina is even more preferable.

[0040] The content of the filler in 100% by weight of the porous layer is preferably 0% by weight or more and less than 20% by weight, more preferably 0 to 15% by weight, even more preferably 0 to 10% by weight, and particularly preferably 0 to 5% by weight. That the content of the filler is 0% by weight means that the porous layer does not contain the filler. From the viewpoint of ensuring ion permeability, the content of the filler in 100% by weight of the porous layer may exceed 0% by weight or may be 1% by weight or more. Here, the aforementioned preferable range of the content of the filler is less than the content of the filler in the conventional porous layer. Here, generally, it is known that the filler has a smaller specific heat than the resin constituting the porous layer. Therefore, since the content of the filler is less than that of the conventional porous layer, the specific heat of the separator becomes larger, and as a result, the thermal diffusivity becomes lower. Therefore, from the viewpoint of controlling the thermal diffusivity of the separator to a low value of 0.04 mm 2 / s or less, the content of the filler is preferably within the aforementioned range.

[0041] The average particle diameter of the filler is preferably 1 μm or less, more preferably 800 nm or less, more preferably 500 nm or less, more preferably 100 nm or less, and more preferably 50 nm or less. The lower limit value of the average particle diameter of the filler is not particularly limited, but can be, for example, 5 nm or more. Here, the average particle diameter of the filler is the average value of the spherical equivalent particle diameters of 50 fillers. Also, the spherical equivalent particle diameter of the filler is a value measured by a transmission electron microscope. Specific measurement methods are exemplified as follows. 1. Use a transmission electron microscope (TEM; JEOL Ltd., transmission electron microscope JEM - 2100F) to take pictures at an acceleration voltage of 200 kV and a magnification of 10,000 times using a Gatan Imaging Filter. 2. For the obtained images, use image analysis software (ImageJ) to trace the contours of the particles and measure the spherical equivalent particle sizes of the filler particles (primary particles). 3. Conduct the above - mentioned measurement for 50 randomly selected filler particles. Take the arithmetic mean of the spherical equivalent particle sizes of the 50 filler particles as the average particle size.

[0042] The film thickness per layer of the porous layer is preferably in the range of 0.15 μm to 5 μm, more preferably in the range of 0.25 μm to 5 μm, and even more preferably in the range of 0.35 μm to 3 μm from the viewpoints of ensuring adhesion to the electrode and high energy density. When the film thickness per layer of the porous layer is 0.15 μm or more, internal short - circuits due to damage of the electrochemical device can be sufficiently suppressed, and the amount of electrolyte retained in the porous layer becomes sufficient. Also, if the film thickness per layer of the porous layer is 5 μm or less, in the electrochemical device, the permeation resistance of metal ions is suppressed, so that deterioration of rate characteristics and cycle characteristics can be suppressed. Also, an increase in the distance between the positive electrode and the negative electrode can be suppressed, so that a decrease in the internal volume efficiency of the electrochemical device can be suppressed.

[0043] The areal weight of the porous layer, that is, the weight per unit area, can be appropriately determined in consideration of the strength, film thickness, weight, and handleability of the porous layer. The areal weight per layer of the porous layer is preferably 0.15 - 10 g / m 2 and more preferably 0.25 - 5 g / m 2 By setting the areal weight of the porous layer within these numerical ranges, the weight energy density and volume energy density of the electrochemical device can be increased.

[0044] The porosity of the porous layer is preferably 20 to 90% by volume, more preferably 30 to 80% by volume, so as to obtain sufficient ion permeability. Further, the pore diameter of the pores in the porous layer is preferably 1.0 μm or less, more preferably 0.5 μm or less. By setting the pore diameter of the pores to these sizes, the electrochemical element can obtain sufficient ion permeability.

[0045] The polyolefin porous substrate means a porous substrate mainly composed of a polyolefin resin. "Mainly composed of a polyolefin resin" means that the proportion of the polyolefin resin in the porous substrate is 50% by weight or more, preferably 90% by weight or more, more preferably 95% by weight or more of the total materials constituting the porous substrate. The porous substrate can be a polyolefin porous film.

[0046] The polyolefin resin preferably contains a high molecular weight component having a weight average molecular weight of 5×10 5 ~15×10 6 . In particular, it is more preferable that the polyolefin resin contains a high molecular weight component having a weight average molecular weight of 1,000,000 or more, because the strength of the obtained separator is improved.

[0047] The polyolefin resin is not particularly limited, and examples thereof include thermoplastic resins such as homopolymers or copolymers obtained by polymerizing monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, and 1-hexene. Examples of the homopolymer include polyethylene, polypropylene, and polybutene. Examples of the copolymer include an ethylene-propylene copolymer.

[0048] Among these, polyethylene is more preferable because it can prevent an excessive current from flowing through the separator at a lower temperature. Note that preventing the flow of this excessive current is also referred to as shutdown. Examples of the polyethylene include low-density polyethylene, high-density polyethylene, linear polyethylene (ethylene-α-olefin copolymer), and ultra-high molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more. Among these, ultra-high molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more is even more preferable.

[0049] The film thickness of the porous substrate is preferably 4 to 40 μm, and more preferably 5 to 20 μm. If the film thickness of the porous substrate is 4 μm or more, internal short circuit of the electrochemical device can be sufficiently prevented. On the other hand, if the film thickness of the porous substrate is 40 μm or less, enlargement of the electrochemical device can be prevented.

[0050] The weight per unit area of the porous substrate, that is, the weight per unit area can be appropriately determined in consideration of strength, film thickness, weight, and handleability. However, so as to increase the weight energy density and the volume energy density of the electrochemical device, the weight per unit area is preferably 4 to 20 g / m 2 and more preferably 4 to 12 g / m 2 and even more preferably 5 to 10 g / m 2 of the porous substrate, that is, the weight per unit area can be appropriately determined in consideration of strength, film thickness, weight, and handleability. However, so as to increase the weight energy density and the volume energy density of the electrochemical device, the weight per unit area is preferably 4 to 20 g / m

[0051] The porous substrate has a large number of interconnected pores inside, and it is possible to allow gas and liquid to pass from one surface to the other surface. The air permeability of the porous substrate is preferably 30 to 500 s / 100 mL, and more preferably 50 to 300 s / 100 mL. By having the above air permeability, sufficient ion permeability can be obtained. The air permeability represents a value measured with a King Research air permeability tester in accordance with JIS P8117.

[0052] The porosity of the porous substrate is preferably 20 to 90% by volume, more preferably 30 to 75% by volume, so as to increase the retention amount of the electrolytic solution and obtain a function of reliably preventing an excessive current from flowing at a lower temperature. The pore diameter of the pores of the porous substrate is preferably 0.3 μm or less, more preferably 0.14 μm or less, so as to obtain sufficient ion permeability and prevent particles from entering the positive electrode and the negative electrode.

[0053] The film thickness of the separator is preferably 5.5 to 45 μm, more preferably 6 to 25 μm. If the film thickness of the separator is 5.5 μm or more, internal short circuit of the electrochemical device can be sufficiently prevented. On the other hand, if the film thickness of the separator is 45 μm or less, enlargement of the electrochemical device can be prevented.

[0054] The air permeability of the separator is preferably 30 to 1000 s / 100 mL, more preferably 50 to 800 s / 100 mL, and even more preferably 70 to 500 s / 100 mL. By having the air permeability, the separator can obtain sufficient ion permeability in the electrochemical device. The air permeability represents a value measured by a King Research air permeability tester in accordance with JIS P8117.

[0055] As described above, generally, the lower the porosity of the separator, the greater the density of the separator tends to be. In particular, in separators with the same specific gravity of the constituent materials, the density of a separator with a lower porosity is greater than that of a separator with a higher porosity. Also, as described above, when the density of the separator is high, the volumetric specific heat of the separator increases, and the thermal diffusivity of the separator is controlled to a low value. Therefore, from the perspective of increasing the density of the separator to control the thermal diffusivity of the separator to a low value, it is preferable that the porosity of the separator is low. Also, generally, the specific heat of the air filling the pores is smaller than that of the resin constituting the porous layer. Therefore, when the porosity of the separator is low, the resin content in the porous layer increases and the air content decreases, so that the specific heat of the separator also increases, and as a result, the thermal diffusivity can be controlled to a low value. Therefore, from the perspective of suitably controlling the thermal diffusivity to a low value by increasing the specific heat, it is also preferable to control the porosity of the separator to a low value. Specifically, the upper limit value of the porosity of the separator is preferably 90% by volume or less, more preferably 70% by volume or less, and even more preferably 60% by volume or less. Also, when the porosity of the separator is equal to or greater than a specific value, it is considered that the ion permeability for functioning as the separator can be suitably ensured. Therefore, from the perspective of suitably ensuring the ion permeability of the separator described above, the lower limit value of the porosity of the separator is preferably 20% by volume or more, more preferably 30% by volume or more, and even more preferably 40% by volume or more.

[0056] Similar to the matters regarding the porosity described above, from the perspective of controlling the thermal diffusivity to a low value, it is preferable that the density of the separator is high. From the above perspective, the density of the separator is preferably 0.1 g / cm 3 or more, more preferably 0.2 g / cm 3 or more, and even more preferably 0.3 g / cm 3 or more. Also, the density of the separator is 1.5 g / cm 3It is preferably as follows, 1.0 g / cm 3 It is more preferably as follows, 0.8 g / cm 3 It is even more preferably as follows.

[0057] In addition, as shown in the examples and comparative examples of the present application, depending on the composition of the separator, even when the density is low, the thermal diffusivity may be low. Specifically, in a separator containing a substance with a large specific gravity and high thermal conductivity, by reducing the content of the substance, the density of the separator becomes small, the volumetric specific heat also becomes small, while the thermal conductivity becomes small. Therefore, in this case, the thermal diffusivity of the separator can be controlled to a low value. Examples of the substance with a large specific gravity and high thermal conductivity include fillers and the like.

[0058] The separator may optionally include another functional layer different from the aforementioned porous base material and porous layer (for example, heat-resistant layer) as long as the object of the present invention is not impaired. Examples of the other functional layer include known porous layers such as an adhesive layer and a protective layer.

[0059] The other functional layer can be provided on one or both sides of the separator. When the separator is provided with the aforementioned porous layers on both sides of the porous base material, the other functional layer may be provided on the porous layers on both sides or on the porous layer on one side. When the separator is provided with the aforementioned porous layer on only one side of the porous base material, the other functional layer may be provided on the porous layer or on the surface of the porous base material where the porous layer is not provided. The other functional layer can be provided as the outermost layer of the separator.

[0060] For example, the separator further includes an adhesive layer separately from the aforementioned porous base material and porous layer. In this specification, the adhesive layer means a porous layer having adhesiveness. The adhesive layer can be provided on the surface of the separator that contacts the electrode. Examples of the components contributing to the adhesiveness contained in the adhesive layer include acrylic resins and PVDF.

[0061] 〔2. Method for Manufacturing Separator for Electrochemical Element〕 A porous layer can be formed on a porous substrate using a coating liquid obtained by dissolving or dispersing a resin in a solvent. The solvent can also be said to be a dispersion medium for dispersing the resin. Examples of the resin include the aforementioned nitrogen-containing aromatic resin and resins other than the nitrogen-containing aromatic resin. Examples of the method for forming the coating liquid include a mechanical stirring method, an ultrasonic dispersion method, a high-pressure dispersion method, a media dispersion method, etc.

[0062] Examples of the method for forming the separator include: a method of directly applying the coating liquid to the surface of the porous substrate and then removing the solvent; a method of applying the coating liquid to a suitable support, removing the solvent to form a porous layer, pressing this porous layer and the porous substrate together, and then peeling off the support; a method of applying the coating liquid to a suitable support, pressing the porous substrate against the coating surface, then peeling off the support and then removing the solvent; and a method of performing dip coating by immersing the porous substrate in the coating liquid and then removing the solvent, etc.

[0063] The solvent preferably does not have an adverse effect on the porous substrate, uniformly and stably dissolves the resin, and uniformly and stably disperses the filler. Examples of the solvent include N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide, N,N-dimethylformamide, acetone, and water, etc.

[0064] The coating liquid may contain a filler. The coating liquid may appropriately contain a dispersant, a plasticizer, a surfactant, a pH adjuster, etc. as components other than the resin and the filler.

[0065] As a method for applying the coating liquid to the porous substrate, a conventionally known method can be adopted. Specifically, for example, a gravure coater method, a dip coater method, a bar coater method, a die coater method, etc. can be mentioned.

[0066] When the coating liquid contains an aramid resin, the aramid resin can be deposited by applying moisture to the coating surface. Thereby, a porous layer may be formed. Specific methods for applying moisture to the coating surface are not particularly limited, and examples include exposing to an atmosphere with high humidity, spraying water with a spray or the like, and spraying water vapor with a nozzle or the like.

[0067] The method for manufacturing the porous substrate is not particularly limited. For example, a sheet-like polyolefin resin composition is produced by kneading a polyolefin resin, a pore former such as an inorganic filler or a plasticizer, and optionally an antioxidant or the like, and then extruding. Then, the pore former is removed from the sheet-like polyolefin resin composition with an appropriate solvent. Thereafter, the porous substrate can be manufactured by stretching the polyolefin resin composition from which the pore former has been removed.

[0068] The inorganic filler is not particularly limited, and examples include inorganic fillers, specifically calcium carbonate and the like. The plasticizer is not particularly limited, and examples include low molecular weight hydrocarbons such as liquid paraffin.

[0069] For example, by using a coating liquid with a low filler content or a coating liquid without a filler as the coating liquid, a separator can be manufactured in which the thermal diffusivity is controlled to a low value of 0.04 mm 2 / s or less. Here, as described above, generally, it is known that the filler has a smaller specific heat than the resin constituting the porous layer. Therefore, the specific heat of the separator provided with the porous layer containing the filler is considered to increase when the content of the resin is large and the content of the filler is small or the filler is not contained. Therefore, by using a coating liquid with a low filler content or a coating liquid without a filler, the specific heat of the manufactured separator can be adjusted to a large value, and as a result, the thermal diffusivity of the separator can be controlled to 0.04 mm 2 / s or less.

[0070] Also, generally, when forming a porous layer using a coating liquid with a low filler content or no filler, it is known that the porosity of the formed porous layer becomes small. When the porosity of the porous layer is small, the density of the porous layer tends to increase. Therefore, by using a coating liquid with a low filler content or no filler, the density of the separator to be manufactured can be adjusted to a large value, and as a result, the thermal diffusivity of the separator can be controlled to 0.04 mm 2 / s or less.

[0071] On the other hand, when the porosity is excessively low, the ion permeability of the porous layer decreases, and the performance of the electrochemical device equipped with the separator may deteriorate. Therefore, it is considered preferable to ensure a certain degree of porosity in the porous layer. From the viewpoint of ensuring the aforementioned certain degree of porosity, as the resin in the coating liquid, it is preferable to adopt a method of using a resin containing two or more types of resins with different precipitation properties or a resin containing two or more components with different precipitation properties. Although the mechanism by which a certain degree of porosity can be ensured by the aforementioned method is speculative, the following mechanism is considered. According to the aforementioned method, in the process of precipitation, the resin or component with high precipitation property and easy precipitation (the first resin or the first component) precipitates first, while the resin or component with low precipitation property and difficult precipitation (the second resin or the second component) precipitates later. The second resin or the second component precipitates in the vicinity of the first resin or the first component that has precipitated earlier due to the compatibility relationship between the first resin or the first component and the solvent. By such uneven precipitation of the resin or the component, it is considered that a porous layer with sufficient pores and a certain degree of porosity can be formed without using a filler or by reducing the filler content compared to the conventional level.

[0072] In addition to using a coating liquid with a low filler content or no filler, by adjusting the solid content concentration of the coating liquid within a predetermined range, a separator with the thermal diffusivity controlled within a more suitable range can be manufactured. The solid content concentration of the coating liquid refers to the total concentration of the solid components in the coating liquid, such as resins and fillers. Specifically, by adjusting the solid content concentration of the coating liquid within a predetermined range, the porosity of the resulting porous layer and the separator provided with the porous layer can be controlled within the aforementioned preferable range. Therefore, by adjusting the solid content concentration of the coating liquid within a predetermined range, the density and specific heat of the manufactured separator can be adjusted within a suitable range, and as a result, it is considered that the thermal diffusivity of the separator can be controlled within a more suitable range.

[0073] For the reasons described above, the solid content in the coating liquid is specifically preferably 0.1% by weight to 10% by weight, more preferably 1% by weight to 8.0% by weight, and still more preferably 2.5% by weight to 6.0% by weight, based on the weight of the entire coating liquid.

[0074] Furthermore, in addition to using a coating liquid with a low filler content or no filler, by controlling the conditions for removing the solvent within a predetermined range, a separator with the thermal diffusivity controlled within a more suitable range can also be manufactured. Specifically, by controlling the conditions for removing the aforementioned solvent, a porous layer can be formed (precipitated) in which the mode of the pore size distribution, such as the size of each pore, the thickness of the resin part, and the particle diameter of the filler, is adjusted within a suitable range. As a result, a separator with the mode of the pore size distribution adjusted within a suitable range can be manufactured. Therefore, by controlling the conditions for removing the solvent within a predetermined range, the specific heat of the manufactured separator can be adjusted within a suitable range, and as a result, it is considered that the thermal diffusivity of the separator can be controlled within a more suitable range.

[0075] When removing the solvent, in other words, as the precipitation conditions of the porous layer, for example, precipitation time, precipitation temperature, precipitation humidity, etc. can be mentioned. The precipitation time means the time from the start of the operation to remove the solvent until the porous layer is formed (precipitated). The precipitation temperature and the precipitation humidity mean the temperature and humidity of the outside air (atmosphere) in contact with the coating liquid when removing the solvent to form (precipitate) the porous layer. The precipitation time is preferably from 1 second to 120 seconds, more preferably from 5 seconds to 90 seconds, and even more preferably from 10 seconds to 60 seconds. The precipitation temperature is preferably from 0°C to 100°C, more preferably from 10°C to 90°C, and even more preferably from 20°C to 80°C. The precipitation humidity is preferably from 20% to 100%, more preferably from 40% to 90%, and even more preferably from 50% to 80%.

[0076] [3. Member for Electrochemical Element, Electrochemical Element] The member for an electrochemical element according to an embodiment of the present invention is formed by arranging a positive electrode, the separator for an electrochemical element described above, and a negative electrode in this order. Further, the electrochemical element according to an embodiment of the present invention includes the separator for an electrochemical element described above.

[0077] The member for an electrochemical element and the electrochemical element include the separator for an electrochemical element according to an embodiment of the present invention, which is excellent in heat resistance when heat is applied from the outside. Therefore, the member for an electrochemical element has the effect of being usable for manufacturing an electrochemical element that is difficult to undergo thermal runaway. Further, the electrochemical element has the effect of being difficult to undergo thermal runaway.

[0078] Here, the thermal runaway means that the electrochemical element burns due to fire generated outside the electrochemical element. Specific examples of the thermal runaway include, in an apparatus including a member formed by assembling a plurality of electrochemical elements (cells), when some of the electrochemical elements ignite, the remaining electrochemical elements also burn due to the heat caused by the ignition, etc.

[0079] Examples of the electrochemical element include a secondary battery and a capacitor. Examples of the secondary battery include a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. Examples of the capacitor include an electric double layer capacitor. The shape of the non-aqueous electrolyte secondary battery is not particularly limited, and may be, for example, a thin plate (paper) type, a disk type, a cylindrical type, or a prismatic type such as a rectangular parallelepiped.

[0080] For example, a member for an electrochemical element can be formed by arranging a positive electrode, the above-described separator, and a negative electrode in this order. Here, the porous layer may be present between the porous substrate and at least one of the positive electrode and the negative electrode. Next, the member for the electrochemical element is placed in a container that serves as a housing for the electrochemical element. Thereby, an electrochemical element can be manufactured. In the case of a non-aqueous electrolyte secondary battery, after filling the container with the non-aqueous electrolyte, it is sealed while reducing the pressure.

[0081] <Positive electrode> The positive electrode is not particularly limited as long as it is generally used as a positive electrode of an electrochemical element. For example, as the positive electrode, 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. Note that the active material layer may further contain a conductive agent.

[0082] Examples of the positive electrode active material include materials capable of doping and undoping 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, LiNi x Mn y Co 1-x-y O2[0<x+y<1], LiNi x Co y Al 1-x-y O2[0<x+y<1], LiCr 0.5 Mn 0.5Examples include O2, LiFePO4, Li2FeP2O7, LiMnPO4, LiFeBO3, Li3V2(PO4)3, Li2CuO2, Li2FeSiO4, Li2MnSiO4, etc.

[0083] 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 fired organic polymer compounds. Only one type of the conductive agent may be used, or two or more types may be used in combination. The proportion of the conductive agent in the positive electrode mixture is preferably 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. When fibrous carbon materials such as graphitized carbon fibers and carbon nanotubes are used as the conductive agent, this proportion can be reduced.

[0084] As the binder, a thermoplastic resin can be used. For example, fluorine-based resins such as PVdF, polytetrafluoroethylene (PTFE), ethylene tetrafluoride - hexafluoropropylene - vinylidene fluoride copolymer, hexafluoropropylene - vinylidene fluoride copolymer, ethylene tetrafluoride - perfluorovinyl ether copolymer, acrylic resins, styrene - butadiene rubber, polyimide resins, and polyolefin resins can be mentioned. Note that the binder also has a function as a thickening agent. These thermoplastic resins may be used by mixing two or more of them. By using a fluorine resin and a polyolefin resin as the binder, and setting the proportion of the fluorine resin to 1% by mass or more and 10% by mass or less, and the proportion of the polyolefin resin to 0.1% by mass or more and 2% by mass or less with respect to the entire positive electrode mixture, a positive electrode mixture with high adhesion to the positive electrode current collector and high internal binding force within the positive electrode mixture can be obtained.

[0085] Examples of the positive electrode current collector include conductors such as Al, Ni, and stainless steel. Among them, Al is more preferable because it is easy to process into a thin film and is inexpensive.

[0086] Examples of the method for manufacturing the positive electrode sheet include a method of pressure-molding a positive electrode active material, a conductive agent, and a binder (positive electrode mixture) on a positive electrode current collector; a method of making the positive electrode mixture into a paste using an appropriate organic solvent, applying the paste to the positive electrode current collector, drying it, and then pressing it to adhere it to the positive electrode current collector, etc.

[0087] Examples of the organic solvent 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; amide solvents such as dimethylacetamide and NMP, etc.

[0088] Examples of the method for applying the paste of the positive electrode mixture to the positive electrode current collector include a slit die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method, and an electrostatic spraying method, etc.

[0089] <Negative electrode> The negative electrode is not particularly limited as long as it is generally used as the negative electrode of an electrochemical element. For example, as the negative electrode, 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. Note that the active material layer may further contain a conductive agent.

[0090] Examples of the negative electrode active material include materials capable of doping and undoping metal ions such as lithium ions or sodium ions. Examples of such materials include carbonaceous materials, chalcogen compounds (oxides, sulfides, etc.), nitrides, metals or alloys, and materials capable of doping and undoping lithium ions at a potential lower than that of the positive electrode. Examples of the carbonaceous materials include natural graphite, artificial graphite, cokes, carbon black, and pyrolytic carbons, etc.

[0091] Examples of the oxide that can be used as the negative electrode active material include SiO2, SiO, etc., of the formula SiO xSilicon oxide represented by (where x is a positive real number); titanium oxides such as TiO2 and TiO represented by (where x is a positive real number); x titanium oxides represented by (where x is a positive real number); vanadium oxides such as V2O5 and VO2 represented by (where x is a positive real number); x vanadium oxides represented by (where x is a positive real number); iron oxides such as Fe3O4, Fe2O3, and FeO represented by (where x is a positive real number); x iron oxides represented by (where x is a positive real number); tin oxides such as SnO2 and SnO represented by (where x is a positive real number); x tin oxides represented by (where x is a positive real number); tungsten oxides such as WO3 and WO2 represented by (where x is a positive real number); x tungsten oxides represented by (where x is a positive real number); composite metal oxides containing lithium and titanium or vanadium such as Li4Ti5O 12 and LiVO2 can be mentioned.

[0092] Sulfides that can be used as the negative electrode active material include titanium sulfides such as Ti2S3, TiS2, and TiS represented by TiS x titanium sulfides represented by (where x is a positive real number); vanadium sulfides such as V3S4, VS2, and VS represented by (where x is a positive real number); x vanadium sulfides represented by (where x is a positive real number); iron sulfides such as Fe3S4, FeS2, and FeS represented by (where x is a positive real number); x iron sulfides represented by (where x is a positive real number); molybdenum sulfides such as Mo2S3 and MoS2 represented by (where x is a positive real number); x molybdenum sulfides represented by (where x is a positive real number); tin sulfides such as SnS2 and SnS represented by (where x is a positive real number); x tin sulfides represented by (where x is a positive real number); tungsten sulfides such as WS2 represented by (where x is a positive real number); x tungsten sulfides represented by (where x is a positive real number); antimony sulfides such as Sb2S3 represented by (where x is a positive real number); x antimony sulfides represented by (where x is a positive real number); selenium sulfides such as Se5S3, SeS2, and SeS represented by (where x is a positive real number); x and selenium sulfides represented by (where x is a positive real number) can be mentioned.

[0093] Nitrides that can be used as the negative electrode active material include Li3N, Li 3-x A xExamples include lithium-containing nitrides such as N (where A is either or both of Ni and Co, and 0 < x < 3).

[0094] 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.

[0095] Examples of metals that can be used as the negative electrode active material include lithium metal, silicon metal, and tin metal.

[0096] Examples of alloys that can be used as the negative electrode active material include lithium alloys such as Li-Al, Li-Ni, Li-Si, Li-Sn, Li-Sn-Ni; silicon alloys such as Si-Zn; tin alloys such as Sn-Mn, Sn-Co, Sn-Ni, Sn-Cu, Sn-La; and alloys such as Cu2Sb, La3Ni2Sn7.

[0097] These metals and alloys are mainly used alone as electrodes, for example, after being processed into foil form. Among the above negative electrode active materials, carbonaceous materials mainly composed of graphite such as natural graphite and artificial graphite are preferably used. This is because the potential of the negative electrode hardly changes from the uncharged state to the fully charged state during charging (good potential flatness), the average discharge potential is low, and the capacity retention rate is high when repeatedly charged and discharged (good cycle characteristics). The shape of the carbonaceous material may be, for example, flaky like natural graphite, spherical like mesocarbon microbeads, fibrous like graphitized carbon fiber, or an aggregate of fine powder.

[0098] Examples of the negative electrode current collector include Cu, Ni, and stainless steel. Cu is more preferable because it is difficult to form an alloy with lithium and is easy to process into a thin film.

[0099] Examples of the method for manufacturing the negative electrode sheet include, for example, a method of pressure-molding the negative electrode active material on the negative electrode current collector; a method of making the negative electrode active material into a paste using an appropriate organic solvent, applying the paste to the negative electrode current collector, drying it, and then pressing it to adhere it to the negative electrode current collector; and the like. The paste preferably contains the aforementioned conductive agent and the binder.

[0100] The aforementioned negative electrode sheet may contain a binder as needed. Examples of the binder include thermoplastic resins, and specifically, PVdF, thermoplastic polyimide, carboxymethyl cellulose, polyolefin resin, and the like can be mentioned.

[0101] <Non-aqueous electrolyte> The non-aqueous electrolyte is not particularly limited as long as it is a non-aqueous electrolyte generally used in electrochemical elements, for example, non-aqueous electrolyte secondary batteries. As the non-aqueous electrolyte, for example, a non-aqueous electrolyte obtained by dissolving a lithium salt in an organic solvent can be used. Examples of the lithium salt 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 , LiBOB (where BOB is bis(oxalato)borate), LiFSI (where FSI is bis(fluorosulfonyl)imide), lithium salts of lower aliphatic carboxylic acids, LiAlCl4, and the like. The lithium salt may be used alone or in combination of two or more. Among them, as the electrolyte, it is preferable to use one containing at least one selected from the group consisting of LiPF6, LiAsF6, LiSbF6, LiBF4, LiCF3SO3, LiN(SO2CF3)2, and LiC(SO2CF3)3 containing fluorine.

[0102] Examples of the organic solvent 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; ethers such as 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran; esters 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-propane sultone; or solvents obtained by further introducing a fluoro group into these organic solvents (solvents in which one or more of the hydrogen atoms of the organic solvent are replaced with fluorine atoms). The organic solvent may be used alone or in combination of two or more. Among them, a mixed solvent containing carbonates is preferable, and a mixed solvent of a cyclic carbonate and an acyclic carbonate and a mixed solvent of a cyclic carbonate and ethers are more preferable. As the mixed solvent of a cyclic carbonate and an acyclic carbonate, a mixed solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is preferable. The electrolytic solution using such a mixed solvent has many features such as a wide operating temperature range, being hardly deteriorated even when charge and discharge are performed at a high current rate, being hardly deteriorated even when used for a long time, and being hardly decomposable even when a graphite material such as natural graphite or artificial graphite is used as the active material of the negative electrode.

[0103] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in 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.

[0104] One embodiment of the present invention may include the following configuration. <1>It comprises a polyolefin porous substrate and a porous layer laminated on the polyolefin porous substrate, and the thermal diffusivity at 25°C is 0.04 mm 2 / s or less, a separator for an electrochemical element. <2>The separator for an electrochemical element according to <1>, wherein the porosity is 20% or more and 90% or less. <3>The density is 0.1 g / cm 3 or more and 1.5 g / cm 3 or less, the separator for an electrochemical element according to <1> or <2>. <4>The weight per unit area of the porous layer is 0.15 g / m 2 or more and 10 g / m 2 or less, the separator for an electrochemical element according to any one of <1> to <3>. <5>The separator for an electrochemical element according to any one of <1> to <4>, wherein the porous layer contains an aramid resin. <6>Further comprising an adhesive layer separately from the polyolefin porous substrate and the porous layer, the separator for an electrochemical element according to any one of <1> to <5>. <7>A member for an electrochemical element in which a positive electrode, the separator for an electrochemical element according to any one of <1> to <6>, and a negative electrode are arranged in this order. <8>An electrochemical element comprising the separator for an electrochemical element according to any one of <1> to <6>. <9>The electrochemical element according to <8>, which is a secondary battery or a capacitor.

Example

[0105] One embodiment of the present invention will be described below.

[0106] 〔Measurement and evaluation of physical properties〕 For the porous layer and the separator described in the examples and comparative examples, the measurement and evaluation of their physical properties were carried out by the methods shown below.

[0107] <Film thickness> The film thickness of the separator was measured using a high-precision digital length measuring instrument (manufactured by Mitutoyo Corporation). Specifically, each separator was cut into a square with a side length of 8 cm, and five-point measurements were taken within the range of the square. The film thickness of the separator was determined from the average value of these five points.

[0108] <Thermal diffusivity> The separators of the examples and comparative examples were cut into circular test pieces with a diameter of 19.0 mm. After performing pre-treatment on the test pieces under the following conditions, the thermal diffusivity at 25 °C was measured using a laser flash apparatus (LFA467 HyperFlash manufactured by NETZSCH). The measured thermal diffusivity was taken as the thermal diffusivity of the separator [mm 2 / s].

[0109] (Conditions) Measurement method: Laser flash method Laser: Irradiation wavelength 1064 nm, pulse width 20 μm, voltage 150 V Detector: InSb (liquid nitrogen cooled) Pre-treatment: Coating by graphite spray on the surface of the test piece <Porosity> The porosity of the separator was calculated by the steps shown in 1. and 2. below. Step 1. Parameters were defined as follows.

[0110] Constituent materials of each layer: a, b, c,..., n Weight ratio [wt%] of each constituent material in each layer: Wa, Wb, Wc,..., Wn True density of each constituent material [g / cm 3 : da, db, dc,..., dn Film thickness of the separator [cm]: t Step 2. From the parameters defined in Step 1, the porosity ε [volume%] of the porous layer was calculated according to the following formula (2). ε [volume%] = [1 - {(Wa / da + Wb / db + Wc / dc +... + Wn / dn) / t}] × 100 ··· (2) Also, as the true density of the filler, the density described in the product information disclosed by the manufacturer was adopted. As the true density of resin A described later, the density described in Reference 1 shown below was adopted. As the true density of resin B described later, the density described in Reference 2 shown below was adopted. Reference 1: K Xiao et al., J. Mater. Sci. 27 (1992) 3065 Reference 2: Takashi Nomma, "Trends in the Development of Synthetic Fibers" Special Issue: Characteristics and Applications of Aramid Fibers, Journal of the Fiber Society (Fiber and Industry), Vol. 56, No. 8, pp. 241-247, 2000 <Areal weight of the porous layer> A square sample of 8 cm × 8 cm was cut out from the polyolefin porous film which is the porous substrate before applying the coating liquid. The weight of this sample was measured and designated as W1 (g). The areal weight of the porous substrate was calculated according to the following formula (3). Areal weight of the porous substrate [g / m 2 =W1 [g] / (0.08 [m] × 0.08 [m]) ··· (3) A square sample of 8 cm × 8 cm was cut out from the separator. The weight of this sample was measured and designated as W2 (g). The areal weight of the separator was calculated according to the following formula (4). Areal weight of the separator [g / m 2 =W2 [g] / (0.08 [m] × 0.08 [m]) ··· (4) Using the measured areal weight of the separator and the areal weight of the porous substrate, the areal weight of the porous layer was calculated according to the following formula (5). Areal weight of the porous layer [g / m 2 =Areal weight of the separator [g / m 2 -Areal weight of the porous film [g / m 2 ··· (5) <Density> By using the areal weight of the separator obtained by the above formula (4) and the film thickness, the density of the separator was calculated according to the following formula (6). Density of the separator [g / cm 3 =Areal weight of the separator [g / cm 2 / Thickness of separator film [cm] ··· (6) <Heating shape retention rate> The heating shape retention rate of the separator was measured by the following procedure. 1. The separator obtained in the example or comparative example was cut out into a square of 80 mm × 80 mm to obtain a sample. At this time, it was cut out so that each side of the square was parallel to either the MD direction or the TD direction. 2. For the sample cut out in 1., a line was drawn inside the outer periphery of 80 mm × 80 mm, and a square of 60 mm × 60 mm was drawn. At this time, the line was drawn so that each side of the square was parallel to either the MD direction or the TD direction of the sample. 3. After performing the operation in 2., the sample was sandwiched between papers, and the sample sandwiched between the papers was placed inside an oven heated to 130°C and left standing for 1 hour. 4. After standing for 1 hour in 3., the heated sample was taken out from the oven. The length of the line parallel to the MD direction in the square drawn on the taken-out sample: D MD [mm] was measured with a digital caliper. 5. Using the value of D MD [mm] measured in 4., based on the following formula (7), the degree of deformation in the MD direction was calculated as the heating shape retention rate. Heating shape retention rate [%] = (D MD [mm] / 60 [mm]) × 100 ··· (7) <Soldering iron test> The separator obtained in the example or comparative example was cut out into a size of 40 mm × 60 mm to prepare a soldering iron test sample. The soldering iron test sample was placed so as to cover the opening of an 80 mm × 80 mm metal sample stage having a longitudinal 20 mm × lateral 20 mm × depth 4 mm opening at the center. Note that the soldering iron test sample was placed with the surface corresponding to the surface on which the porous layer was provided in the separator facing upward.

[0111] Next, the short side of the soldering iron test sample was fixed to the metal sample stage using a polyimide adhesive tape made by Nitto Denko Corporation so as not to wrinkle. Subsequently, the metal sample stage with the soldering iron test sample fixed thereon was placed on a precision jack. Further, a soldering iron was installed above the precision jack using a clamp. As the tip of the soldering iron, RX-80HRT-B manufactured by Taiyo Electric Industry Co., Ltd. was used. The temperature of the tip was set to 450 °C. Then, the metal sample stage with the soldering iron test sample fixed thereon was raised using the precision jack until the tip penetrated the soldering iron test sample and then contacted the bottom of the opening of the metal sample stage. After 5 seconds had elapsed since the tip contacted the bottom of the opening of the metal sample stage, the metal sample stage with the soldering iron test sample fixed thereon was lowered using the precision jack. Thereby, a soldering iron test sample with a through hole formed therein was obtained. A photograph of the soldering iron test sample with the through hole formed therein was taken. At that time, a 1 cm line was drawn near the soldering iron test sample with the through hole formed therein so that the scale could be understood, and the soldering iron test sample with the through hole formed therein together with this 1 cm line was photographed. Next, using image analysis software Image J, a line was drawn along the shape of the through hole in the soldering iron test sample with the through hole formed therein, and the area of the through hole was calculated. As a result, when the area of the through hole was less than 0.1 cm 2 it was regarded as "test passed", and when the area of the through hole was 0.1 cm 2 or more it was regarded as "test failed".

[0112] [Synthesis Example 1: Synthesis of Resin A] Resin A (poly(4,4'-diphenylsulfonyl terephthalamide)) was synthesized by the following procedure. The true density of Resin A was 1.28 g / cm 3 at that time. 1. A 0.5 L separable flask equipped with a stirring blade, a thermometer, a nitrogen inlet tube, and a powder addition port was thoroughly dried. 2. 408.6 g of N-methylpyrrolidone was charged into the flask. Further, 31.4 g of calcium chloride (dried at 200 °C for 2 hours) was added, and the temperature was raised to 100 °C. 3. After the 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, a total of 25.88 g of terephthaloyl chloride was added in three portions. 5. While maintaining the temperature of the resulting solution at 25 ± 2 °C, the solution was aged for 1 hour to obtain a solution containing Resin A.

[0113] [Synthesis Example 2: Synthesis of Resin B] Resin B (poly(p-phenylene terephthalamide)) was synthesized by the following procedure. The true density of Resin B was 1.44 g / cm 3 . 1. A 0.5 L separable flask equipped with a stirring blade, thermometer, nitrogen inlet tube, and powder addition port was thoroughly dried. 2. 408.6 g of N-methylpyrrolidone was charged into the flask. Further, 31.4 g of calcium chloride (dried at 200 °C for 2 hours) was added, and the temperature was raised to 100 °C. 3. After the calcium chloride was completely dissolved, the temperature of the solution was returned to room temperature. Then, 13.20 g of p-phenylenediamine was added and completely dissolved. 4. While maintaining the temperature of the solution at 25 ± 2 °C, a total of 24.24 g of terephthaloyl chloride was added in three portions. 5. While maintaining the temperature of the resulting solution at 25 ± 2 °C, the solution was aged for 1 hour to obtain a solution containing Resin B.

[0114] [Example 1] A separator having a porous layer with a weight ratio of Resin A to Resin B of 50:50 was manufactured. Specifically, the solutions obtained in Synthesis Examples 1 and 2 were mixed so that the weight ratio of Resin A to Resin B would be 50:50. To 500 g of the resulting mixture (1), 11.68 g of calcium carbonate was added and stirred for 10 minutes to neutralize the solution, obtaining a neutralized solution (1). Then, it was diluted with NMP and degassed under reduced pressure to prepare a slurry-like coating solution (1). The solid content concentration of the coating solution (1) was 4.5% by weight.

[0115] The coating solution (1) was applied to a polyethylene porous film (thickness: 10.3 μm, air permeability: 180 s / 100 mL), and a porous layer (1) was deposited on the deposition layer at 50 °C and 70% humidity. The deposition time was 60 seconds. Then, it was washed with water and dried to obtain a laminated separator having the porous layer (1). The obtained laminated separator was designated as separator (1). The film thickness of separator (1) was 12.8 μm.

[0116] [Example 2] A separator having a porous layer with a weight ratio of Resin A to Resin B to alumina (average particle size: 13 nm) of 50:50:20 was manufactured. Specifically, except for the operations shown in the following (i) and (ii), the same operations as in Example 1 were performed to obtain a laminated separator having a porous layer (2). The obtained laminated separator was designated as separator (2). The film thickness of separator (2) was 12.8 μm. The true density of alumina was 3.27 g / cm 3 It was. (i) Instead of the coating solution (1), alumina (average particle size: 13 nm) was added to the neutralized solution (1) so that the weight ratio of Resin A to Resin B to alumina would be 50:50:20, further diluted with NMP, and degassed under reduced pressure to prepare a slurry-like coating solution (2). (ii) Instead of the coating solution (1), the coating solution (2) was applied to the polyethylene porous film.

[0117] [Example 3] A separator having a porous layer with a weight ratio of Resin A to Resin B of 30:70 was manufactured. Specifically, the same operations as in Example 1 were performed except for the operations shown in (iii) and (iv) below, and a laminated separator having a porous layer (3) was obtained. The obtained laminated separator was designated as separator (3). The film thickness of separator (3) was 11.5 μm. (iii) Instead of coating liquid (1), a neutralizing liquid (2) with a weight ratio of Resin A to Resin B of 30:70 was prepared, further diluted with NMP, and defoamed under reduced pressure to prepare a slurry-like coating liquid (3). Here, the neutralizing liquid (2) was prepared in the same manner as the method for preparing the neutralizing liquid (1), except that the solutions obtained in Synthesis Examples 1 and 2 were mixed so that the weight ratio of Resin A to Resin B was 30:70. (iv) Instead of coating liquid (1), coating liquid (3) was applied to the polyethylene porous film.

[0118] [Comparative Example 1] A separator having a porous layer with a weight ratio of Resin B to alumina (average particle size: 13 nm) of 100:100 was manufactured. Specifically, the same operations as in Example 1 were performed except for the operations shown in (v) to (vii) below, and a laminated separator having a porous layer (4) was obtained. The obtained laminated separator was designated as comparative separator (1). The film thickness of comparative separator (1) was 11.7 μm. (v) Instead of neutralizing liquid (1), 11.68 g of calcium carbonate was added to 500 g of the solution obtained in Synthesis Example 2 and stirred for 10 minutes to neutralize the solution, thereby obtaining a neutralizing liquid (3). (vi) Instead of coating liquid (1), neutralizing liquid (3) was diluted with NMP and defoamed under reduced pressure to prepare a slurry-like coating liquid (4). (vii) Instead of coating liquid (1), coating liquid (4) was applied to the polyethylene porous film.

[0119] [Results] The production conditions of the examples and comparative examples, specifically, the weight ratios of the raw materials used, and the evaluation results of the manufactured porous layers and separators are shown in Table 1.

[0120]

Table 1

[0121] As shown in Table 1, the separators (1) to (3) have a thermal diffusivity at 25°C of 0.04 mm 2 / s or less. Therefore, the separators (1) to (3) correspond to the separators for electrochemical elements according to one embodiment of the present invention. On the other hand, the comparative separator (1) has a thermal diffusivity at 25°C that exceeds 0.04 mm 2 / s and does not correspond to the separator for an electrochemical element according to one embodiment of the present invention.

[0122] In addition, the separators (1) to (3) have a higher heating shape retention rate and pass the soldering iron test as compared with the comparative separator (1). Therefore, the separators (1) to (3) are less likely to experience thermal shrinkage and / or melting throughout the separator, whether heat is applied from the outside or not. Accordingly, it has been found that the separators (1) to (3) have excellent heat resistance when heat is applied from the outside.

[0123] As shown in Table 1, the comparative separator (1) generally satisfies the conditions of "low porosity" and "high density", which are considered to result in a low thermal diffusivity, but the thermal diffusivity is high. This is presumably because the comparative separator (1) has a large specific gravity, contains a filler with high thermal conductivity, and has a high content of the filler. On the other hand, as compared with the comparative separator (1), the separators (1) to (3) have "high porosity" and "low density", but the thermal diffusivity is low. This is presumably because the separators (1) to (3) do not contain a filler with high thermal conductivity or have a low content of the filler, despite having a large specific gravity.

[0124] From the above, it was found that the separator for an electrochemical element according to one embodiment of the present invention is excellent in heat resistance when heat is applied from the outside.

Industrial Applicability

[0125] One aspect of the present invention can be used for an electrochemical element.

Claims

1. A separator for an electrochemical element, comprising a porous polyolefin substrate and a porous layer laminated on the porous polyolefin substrate, and The separator for an electrochemical element having a thermal diffusivity at 25°C of 0.04 mm ２ / s or less.

2. The separator for an electrochemical element according to claim 1, having a porosity of 20% by volume or more and 90% by volume or less.

3. The density is 0.1 g / cm ３ or more and 1.5 g / cm ３ or less. The separator for an electrochemical element according to claim 1.

4. The basis weight of the porous layer is 0.15 g / m ２ or more and 10 g / m ２ or less. The separator for an electrochemical element according to claim 1.

5. The separator for an electrochemical element according to claim 1, wherein the porous layer contains an aramid resin.

6. The separator for an electrochemical element according to claim 1, further comprising an adhesive layer separately from the porous polyolefin substrate and the porous layer.

7. A member for an electrochemical element, in which a positive electrode, the separator for an electrochemical element according to any one of claims 1 to 6, and a negative electrode are arranged in this order.

8. An electrochemical element including the separator for an electrochemical element according to any one of claims 1 to 6.

9. The electrochemical element according to claim 8, which is a secondary battery or a capacitor.

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