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

Abstract

To provide a separator for an electrochemical element which can improve the cycle characteristics of an electrochemical element.SOLUTION: The separator for an electrochemical element according to the present disclosure has a resin-containing porous layer, and the value represented by the following formula (1) is less than 0.05: the formula (1) is C / (A×B), in which A denotes the content [wt.%] of the resin in the porous layer and B denotes the gap ratio [%] of the porous layer, and C denotes the air permeability [sec / 100 mL] of the separator for electrochemical element.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 underway. 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] However, an electrochemical element including a separator in which a porous layer, which is a heat-resistant layer, is laminated on a conventional porous substrate such as the separator described in Patent Document 1 has room for improvement in terms of cycle characteristics. One aspect of the present invention aims to provide a separator for an electrochemical element capable of improving the cycle characteristics of the electrochemical element.

Means for Solving the Problems

[0006] In order to solve the above problems, as a result of intensive research by the present inventors, an electrochemical element including a porous layer and having a separator in which the resin ratio, porosity, and air permeability of the porous layer satisfy a specific relationship has been found to have excellent cycle characteristics.

[0007] A separator for an electrochemical element according to one aspect of the present invention includes a porous layer containing a resin, and a value represented by the following formula (1) is less than 0.05. C / (A×B)···(1) (In formula (1), A is the content [wt%] of the resin in the porous layer, B is the porosity [%] of the porous layer, and C is the air permeability [sec / 100mL] of the separator for the electrochemical element.)

Effect of the Invention

[0008] According to one aspect of the present invention, it is possible to provide a separator for an electrochemical element that can improve the cycle characteristics of the electrochemical element.

Mode for Carrying Out the Invention

[0009] The following describes one embodiment of the present invention, but the present invention is not limited thereto. Unless otherwise specified in this specification, "A~B" representing a numerical range means "A or more and B or less".

[0010] 〔1. Separator for Electrochemical Element〕 A separator for an electrochemical element according to one embodiment of the present invention includes a porous layer containing a resin, and a separator for an electrochemical element in which a value represented by the following formula (1) is less than 0.05. C / (A×B)···(1) (In formula (1), A is the content [wt%] of the resin in the porous layer, B is the porosity [%] of the porous layer, and C is the air permeability [sec / 100mL] of the separator for the electrochemical element.) Hereinafter, the "separator for an electrochemical element according to an embodiment of the present invention" is also simply referred to as "separator". Further, the "content of the resin in the porous layer" in this specification is the content of the resin with respect to the weight of the entire porous layer, in other words, the "content of the resin in 100% by weight of the porous layer".

[0011] The value represented by the formula (1) becomes small when A is large and / or B is large and / or C is small. The separator is controlled so that the value represented by the formula (1) is a small value less than 0.05. Therefore, the separator has a structure in which the content of the resin in the porous layer is large and / or the porosity of the porous layer is high and / or the air permeability is small. In this specification, the air permeability represents a value measured by the Gurley tester method in accordance with JIS P8117.

[0012] When the content of the resin in the porous layer is large, the adhesion to the electrode is high, and the porous layer and the separator including the porous layer have high followability with respect to the expansion and contraction of the electrode generated during operation. Here, in an electrochemical element, it is known that the growth of dendrites during operation is one of the causes of the deterioration of cycle characteristics. Also, it is known that the growth of dendrites occurs due to a local reaction in the plane direction of the electrode of cations such as Li + etc. Here, when the separator has high followability with respect to the expansion and contraction of the electrode, the reaction of cations occurs uniformly in the plane direction of the electrode during operation, and the local reaction of the cations in the plane direction of the electrode is suppressed. Therefore, when the content of the resin in the porous layer is large, the growth of dendrites is suppressed in an electrochemical element including the separator including the porous layer, and as a result, the cycle characteristics are improved.

[0013] When the porosity of the porous layer is high, the liquid retention property of the porous layer and the separator including the porous layer increases. The liquid retention property represents the property of retaining the electrolyte. Here, when the liquid retention property of the separator is high, in the electrochemical element including the separator, the occurrence of liquid depletion when repeating charge and discharge cycles, and the local occurrence in the plane direction of the cation electrode due to the liquid depletion are suppressed. As a result, even when the porosity of the porous layer is high, similar to the case where the resin content of the porous layer is large, dendrite growth is suppressed in the electrochemical element including the separator including the porous layer, and as a result, the cycle characteristics are improved.

[0014] When the air permeability of the separator is low, the resistance of the separator becomes low. Here, when the resistance of the separator is low, in the electrochemical element including the separator, overvoltage is less likely to occur when repeating charge and discharge cycles, and a decrease in battery performance due to damage caused by the overvoltage is less likely to occur. As a result, the cycle characteristics of the electrochemical element including the separator are improved.

[0015] As described above, the separator has a structure in which the resin content in the porous layer is large, and / or the porosity of the porous layer is high, and / or the air permeability is small, whereby the cycle characteristics of the electrochemical element including the separator can be improved.

[0016] From the viewpoint of more preferably improving the cycle characteristics of the electrochemical element including the separator, the value represented by the formula (1) is preferably a small value. Specifically, the value represented by the formula (1) is preferably 0.048 or less, more preferably 0.046 or less. Also, the value represented by the formula (1) may be 0.01 or more, or may be 0.02 or more.

[0017] It is preferable that the separator has a small value of the value represented by the following formula (2). C / A ··· (2) (In formula (2), A and C are the same as A and C in formula (1).) The fact that the value represented by the formula (2) is small means that the separator has a structure in which A is large and / or C is small. Therefore, when the value represented by the formula (2) is small, the value represented by the formula (1) is adjusted to a smaller value, and as a result, the cycle characteristics of the electrochemical element including the separator can be further improved. From the above viewpoints, the value represented by the formula (2) is preferably less than 3, more preferably 2.8 or less. Also, the value represented by the formula (2) may be 0.5 or more, or may be 1 or more.

[0018] It is preferable that the separator has a large value represented by the following formula (3). A × B ··· (3) (In the formula (3), A and B are the same as A and B in the formula (1).) The fact that the value represented by the formula (3) is large means that the separator has a structure in which A is large and / or B is large. Therefore, when the value represented by the formula (3) is large, the value represented by the formula (1) is adjusted to a smaller value, and as a result, the cycle characteristics of the electrochemical element including the separator can be further improved. From the above viewpoints, the value represented by the formula (3) is preferably more than 5200, more preferably 5500 or more, still more preferably more than 5500, and particularly preferably 5900 or more. Also, the value represented by the formula (3) may be 9000 or less, preferably 8000 or less.

[0019] From the viewpoint of adjusting the value represented by the formula (1) to a smaller value and further improving the cycle characteristics of the electrochemical element including the separator, it is preferable that A is larger. Also, from the same viewpoint, it is preferable that B is larger. Further, from the same viewpoint, it is preferable that C is smaller.

[0020] Specifically, the content of the resin in the porous layer, namely A, is preferably more than 80% by weight, more preferably 85% by weight or more, still more preferably 90% by weight or more, and even more preferably 95% by weight or more. Also, the content of the resin in the porous layer may be 100% by weight or less, or 99% by weight or less, based on the weight of the entire porous layer.

[0021] In addition, the porosity of the porous layer, namely B, is preferably 55% or more, more preferably 58% or more. Also, the porosity of the porous layer may be 90% or less, or 80% or less.

[0022] Furthermore, the air permeability of the separator, namely C, is preferably 320 sec / 100 mL or less, more preferably 300 sec / 100 mL or less, and still more preferably 280 sec / 100 mL or less. Also, the air permeability of the separator may be 10 sec / 100 mL or more, 25 sec / 100 mL or more, or 50 sec / 100 mL or more.

[0023] In one embodiment of the present invention, the porous layer can be disposed between the polyolefin porous substrate and at least one of the positive electrode and the negative electrode as a member constituting the electrochemical element. Hereinafter, the polyolefin porous substrate is also simply referred to as the "porous substrate". The porous layer may be disposed between the porous substrate 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 substrate 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.

[0024] The porous layer contains a resin. The resin is not limited, and examples thereof include nitrogen-containing resins and fluorine-containing resins. A nitrogen-containing resin means a resin containing a nitrogen atom (N), and a fluorine-containing resin means a resin containing a fluorine atom (F).

[0025] It can be said that the porous layer may itself be a self-supporting membrane. Therefore, one embodiment of the present invention includes a separator for an electrochemical element composed only of the porous layer.

[0026] The porous layer described in the present specification as a porous layer constituting a separator for an electrochemical element according to an embodiment of the present invention may be a porous layer for an electrochemical element, but the use of the porous layer is not limited thereto, and it may be used, for example, as a separation membrane, a base material, and a protective membrane.

[0027] As the nitrogen-containing resin, one or more selected from the group consisting of polyamide, polyamideimide, and polyimide are preferable. Further, the nitrogen-containing resin may be a nitrogen-containing aromatic resin. The nitrogen-containing aromatic resin means an aromatic resin containing a nitrogen atom. The aromatic resin means a resin containing at least a structural unit having an aromatic group. 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 includes an aramid resin.

[0028] Examples of aramid resins include para-aramid and meta-aramid, with para-aramid being preferred. Examples of para-aramid include poly(paraphenylene terephthalamide), poly(parabenzamide), poly(4,4'-benzylanilide terephthalamide), poly(paraphenylene-4,4'-biphenylene dicarboxamide), poly(paraphenylene-2,6-naphthalenedicarboxamide), poly(2-chloro-paraphenylene terephthalamide), a copolymer of paraphenylene terephthalamide / 2,6-dichloroparaphenylene terephthalamide, poly(4,4'-diphenylsulfonyl terephthalamide), a copolymer of paraphenylene terephthalamide / 4,4'-diphenylsulfonyl terephthalamide, and other para-aramids having a para-oriented or para-oriented-like structure. 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), etc. Poly(m-phenylene isophthalamide) is also referred to as poly[N,N'-(1,3-phenylene)isophthalamide].

[0029] Examples of fluorine-containing resins include polyvinylidene fluoride (PVdF), polytetrafluoroethylene, a copolymer of vinylidene fluoride / hexafluoropropylene, a copolymer of tetrafluoroethylene / hexafluoropropylene, a copolymer of tetrafluoroethylene / perfluoroalkyl vinyl ether, a copolymer of vinylidene fluoride / tetrafluoroethylene, a copolymer of vinylidene fluoride / trifluoroethylene, a copolymer of vinylidene fluoride / trichloroethylene, a copolymer of vinylidene fluoride / vinyl fluoride, a copolymer of vinylidene fluoride / hexafluoropropylene / tetrafluoroethylene, and a copolymer of ethylene / tetrafluoroethylene, etc. Among the above fluorine-containing resins, fluorine-containing rubbers with a glass transition temperature of 23°C or lower are also included.

[0030] The porous layer preferably contains at least one resin selected from the group consisting of polyamide, polyamideimide, polyimide, and polyvinylidene fluoride among the resins listed above, and more preferably contains an aramid resin as the polyamide.

[0031] 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. As described later, by using two or more types of resins having different precipitation properties as the resin, a porous layer constituting a separator in which the value represented by the formula (1) is less than 0.05 can be preferably prepared. 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. The two or more types of resins having different precipitation properties with respect to the solvent for dissolving the resin preferably 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-phenylene terephthalamide), poly(2-chloro-p-phenylene terephthalamide), poly(p-benzamide), and poly(4,4'-benzani lide terephthalamide) have a rigid structure. On the other hand, poly(4,4'-diphenylsulfonyl terephthalamide), p-phenylene terephthalamide / 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 a relatively similar structure, such as a combination of poly(p-phenylene terephthalamide) and poly(2-chloro-p-phenylene terephthalamide), may also be possible.

[0032] In addition, preferable examples of the resin other than two or more types of resins having different precipitation properties include one or more types of resins having a wide molecular weight distribution. As will be described later, even when one or more types of resins having a wide molecular weight distribution are used as the resin, a porous layer constituting a separator in which the value represented by the formula (1) is less than 0.05 can be suitably prepared.

[0033] Furthermore, even when one type of resin having a narrow molecular weight distribution other than the aforementioned preferable resin is used, by changing the humidity of the precipitation tank over time, as will be described later, a porous layer constituting a separator in which the value represented by the formula (1) is less than 0.05 can be suitably prepared.

[0034] 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.

[0035] 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 more than 0% by weight.

[0036] 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.

[0037] Examples of the polyester resin include aromatic polyesters such as polyarylate and liquid crystal polyester.

[0038] Examples of the rubbers include styrene-butadiene copolymer and its hydrogenated product, methacrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl acetate, and the like.

[0039] Examples of the resin having a melting point or a glass transition temperature of 180°C or higher include polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyetheramide, and polyetheretherketone.

[0040] Examples of the water-soluble polymer include polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide, polymethacrylic acid, and the like.

[0041] 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 a 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 is electrochemically stable within the operating range of the battery.

[0042] The porous layer may contain a filler. The filler can be an inorganic filler or an organic filler. As the filler, a filler composed of inorganic oxides 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.

[0043] The content of the filler in 100% by weight of the porous layer is preferably not less than 0% by weight and less than 20% by weight, more preferably 0 to 15% by weight, still 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.

[0044] The average particle size of the filler is preferably 1 μm or less, more preferably 800 nm or less, still more preferably 500 nm or less, still more preferably 100 nm or less, and still more preferably 50 nm or less. The lower limit value 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 spherical equivalent particle sizes of 50 fillers. Also, the spherical equivalent particle size of the filler is a value measured by a transmission electron microscope. An example of a specific measurement method is as follows. 1. Using a transmission electron microscope (TEM; JEOL Ltd., transmission electron microscope JEM-2100F), at an acceleration voltage of 200 kV, the imaging magnification uses a Gatan Imaging Filter and is taken at 10,000 times magnification. 2. For the obtained image, using image analysis software (ImageJ), trace the contour of the particles and measure the spherical equivalent particle size of the filler particles (primary particles). 3. Perform the above measurement on 50 filler particles randomly extracted. The arithmetic mean of the spherical equivalent particle sizes of the 50 filler particles is taken as the average particle size of the particles.

[0045] 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 element or the like can be sufficiently suppressed, and the amount of electrolyte retained in the porous layer becomes sufficient. Further, if the film thickness per layer of the porous layer is 5 μm or less, in the electrochemical element, 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 element can be suppressed. The film thickness per layer of the porous layer is not limited to the above range. For example, when used without being laminated on a substrate, it may be 0.3 to 35 μm, or may be 5.5 to 35 μm.

[0046] The weight per unit area 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 weight per unit area of each layer of the porous layer is preferably 0.15 g / m 2 or more, and more preferably 0.25 g / m 2 or more. The weight per unit area of each layer of the porous layer may be 0.3 g / m 2 or more, or may be 0.5 g / m 2 or more. The weight per unit area of each layer of the porous layer may be 30 g / m 2 or less, preferably 10 g / m 2 or less, and more preferably 5 g / m 2 or less. By setting the weight per unit area of the porous layer within these numerical ranges, the weight energy density and volume energy density of the electrochemical element can be increased.

[0047] The pore diameter of the pores in the porous layer is preferably 1.0 μm or less, and 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.

[0048] Specifically, the upper limit value of the air permeability of the porous layer is preferably 120 sec / 100 mL or less, more preferably 110 sec / 100 mL or less. Further, the lower limit value of the air permeability of the porous layer is a value exceeding 0 sec / 100 cc, and usually may be 10 sec / 100 cc or more, or may be 20 sec / 100 cc or more. The air permeability in the porous layer can be calculated, for example, by the method described in the examples.

[0049] In one embodiment of the present invention, the separator includes a polyolefin porous base material, and the porous layer is laminated on the polyolefin porous base material. That is, in one embodiment of the present invention, the separator is a separator in which the porous layer and the polyolefin porous base material are laminated. In this specification, such a separator is also referred to as a laminated separator. The porous layer can be laminated on one or both surfaces of the polyolefin porous base material.

[0050] The polyolefin porous base material means a porous base material mainly composed of a polyolefin resin. "Mainly composed of a polyolefin resin" means that the proportion of the polyolefin resin in the porous base material is 50% by weight or more, preferably 90% by weight or more, and more preferably 95% by weight or more of the entire material constituting the porous base material. The porous base material can be a polyolefin porous film.

[0051] 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.

[0052] 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.

[0053] 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 more preferable.

[0054] 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 circuits of the electrochemical element can be sufficiently prevented. On the other hand, if the film thickness of the porous substrate is 40 μm or less, an increase in the size of the electrochemical element can be prevented.

[0055] 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 element, 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 electrochemical element.

[0056] 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, the porous substrate can obtain sufficient ion permeability.

[0057] The porosity of the porous substrate is preferably 20 to 80% by volume, and more preferably 30 to 75% by volume, so as to increase the retention amount of the electrolyte 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, and 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.

[0058] The film thickness of the separator is preferably 5.5 to 45 μm, and 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.

[0059] The separator may contain, if necessary, another functional layer different from the above-mentioned porous substrate and porous layer (for example, heat-resistant layer) within a range not impairing the object of the present invention. Examples of the another functional layer include known porous layers such as an adhesive layer and a protective layer.

[0060] The another functional layer can be provided on one or both surfaces of the separator. When the separator is provided with the above-mentioned porous layers on both surfaces of the porous substrate, the another functional layer may be provided on the porous layers on both surfaces or on the porous layer on one surface. When the separator is provided with the above-mentioned porous layer on only one surface of the porous substrate, the another functional layer may be provided on the porous layer or on the surface of the porous substrate where the porous layer is not provided. The another functional layer can be provided as the outermost layer of the separator.

[0061] For example, the separator further includes an adhesive layer separately from the aforementioned porous substrate and porous layer. In the present 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.

[0062] [2. Method for manufacturing a separator for an electrochemical element] The porous layer can be formed using a coating liquid obtained by dissolving or dispersing a resin in a solvent. Incidentally, 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, and a media dispersion method.

[0063] Examples of the method for forming the porous layer include: a method of directly applying the coating liquid to the surface of the 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 substrate together, and then peeling off the support; a method of applying the coating liquid to a suitable support, pressing the substrate onto the coating surface, then peeling off the support, and then removing the solvent; and a method of performing dip coating by immersing the substrate in the coating liquid and then removing the solvent.

[0064] The solvent preferably has no adverse effect on the substrate, dissolves the resin uniformly and stably, and 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.

[0065] The coating liquid may contain a filler. The coating liquid may appropriately contain a dispersant, a plasticizer, a surfactant, a pH adjuster, and the like as components other than the resin and the filler.

[0066] As a method for applying the coating liquid to the 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.

[0067] When the coating liquid contains an aramid resin, the aramid resin can be precipitated by applying moisture to the coating surface. Thereby, a porous layer may be formed. The specific method for applying moisture to the coating surface is not particularly limited, and examples include exposing to an atmosphere with high humidity, spraying water by a spray or the like, and spraying steam with a nozzle or the like.

[0068] In particular, as a method for manufacturing the laminated separator, for example, in the method for manufacturing the porous layer described above, a method of using the aforementioned porous substrate as the substrate to which the coating liquid is applied can be mentioned.

[0069] The method for manufacturing the porous substrate is not particularly limited. For example, after 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, a sheet-like polyolefin resin composition is produced. Then, the pore former is removed from the sheet-like polyolefin resin composition with an appropriate solvent. Thereafter, the polyolefin resin composition from which the pore former has been removed is stretched to produce a porous substrate.

[0070] 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.

[0071] For example, by satisfying the conditions shown in the following (i) to (iii), a separator in which the value represented by the formula (1) is within the aforementioned range can be preferably manufactured. (i) As the coating liquid, use a coating liquid with a low filler content or a coating liquid that does not contain a filler. (ii) The resin in the coating liquid contains two or more types of resins with different precipitation properties, or contains two or more components with different precipitation properties. (iii) Shorten the precipitation time of the resin.

[0072] When the condition of (i) is satisfied, in the obtained porous layer, with respect to the total weight of the porous layer, the filler content [% by weight] decreases while the resin content [% by weight] increases. Therefore, by satisfying the condition of (i), the above-mentioned A can be increased.

[0073] On the other hand, when the condition of (i) is satisfied, that is, when the filler content is low or the filler is not contained, generally, it is known that the above-mentioned B, that is, the porosity of the porous layer, becomes small. However, the inventor has found that when the condition of (ii) is satisfied in addition to the condition of (i), the porosity of the porous layer increases. Although the mechanism is speculative, the following mechanism is considered. When the condition of (ii) is satisfied, in the precipitation process, 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 sufficient pore formation can be achieved without using a filler or by reducing the filler content compared to the conventional case. Therefore, by satisfying the condition of (ii) in addition to the condition of (i), based on the above mechanism, it is considered that the above-mentioned A can be increased and the above-mentioned B can also be increased.

[0074] Here, two or more types of resins with different precipitation properties can be, for example, two or more types of resins with different solubilities in the solvent in the coating liquid. Also, the precipitation property of the resin can vary depending on the molecular weight. Thus, a resin containing two or more components with different precipitation properties can be, for example, a resin with a broad molecular weight distribution. That is, by using one or more resins with a broad molecular weight distribution, a separator in which the value represented by the formula (1) is within the aforementioned range can be preferably manufactured.

[0075] Further, the present inventor has found that by satisfying the condition of (iii), that is, by shortening the precipitation time of the resin, the porosity of the porous layer can be increased and the air permeability values of the porous layer and the separator can be decreased. Although the mechanism is speculative, the following mechanism is considered. When the precipitation time of the resin is long, even after pores are formed at the initial stage of precipitation in the porous layer, the precipitation of the resin continues, and there is a possibility that the pores are blocked by the resin precipitated after the pore formation. Also, when the precipitation time of the resin is long, there is a possibility that the coating liquid enters the voids at the interface between the porous substrate and the porous layer of the porous substrate before precipitating the resin, and after entering the voids, the resin precipitates from the coating liquid. In that case, there is a possibility that the voids are blocked by the resin precipitated from the coating liquid that has entered the voids. On the other hand, when the condition of (iii) is satisfied, the aforementioned blockage of the pores and voids can be preferably prevented, and as a result, it is considered that the porosity in the porous layer can be increased and the air permeability values of the porous layer and the separator can be decreased. Therefore, by satisfying the condition of (iii), it is considered that B can be increased and C can be decreased.

[0076] Also, instead of satisfying the condition of (ii), it is considered that by satisfying the following condition of (iv), A can be increased and then B can also be increased. (iv) As the precipitation method, changing the humidity of the precipitation layer over time.

[0077] Here, by changing the humidity in the deposition tank over time, the deposition rates in the initial and later stages change, and it is considered that, by the same mechanism as in the case of satisfying the condition (i), after increasing the said A, the said B can also be increased.

[0078] As described above, by satisfying the conditions shown in (i) to (iii), the value represented by the formula (1) can be adjusted to a small value, and the separator for an electrochemical element according to one embodiment of the present invention can be preferably manufactured. Further, even when the condition (ii) is not satisfied, by satisfying the condition (iv) in addition to the conditions (i) and (iii), the separator for an electrochemical element according to one embodiment of the present invention can be preferably manufactured. Specifically, the case where one type of resin having a narrow molecular weight distribution is used can be cited as the case where the condition (ii) is not satisfied.

[0079] Further, when the separator is a laminated separator, by using a porous base material having a small air permeability value as the porous base material constituting the laminated separator, the air permeability value of the entire separator, that is, the said C can be made small. As a result, the value represented by the formula (1) can be adjusted to an even smaller value, and the separator for an electrochemical element according to one embodiment of the present invention can also be more preferably manufactured.

[0080] [3. Member for Electrochemical Element, Electrochemical Element] In the member for an electrochemical element according to one embodiment of the present invention, a positive electrode, the aforementioned separator for an electrochemical element, and a negative electrode are arranged in this order. Further, the electrochemical element according to one embodiment of the present invention includes the aforementioned separator for an electrochemical element.

[0081] Examples of the electrochemical element include secondary batteries and capacitors. Examples of the secondary battery include non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries. Examples of the capacitor 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, disk type, cylindrical type, or prismatic type such as a rectangular parallelepiped.

[0082] For example, an electrochemical element member can be formed by arranging a positive electrode, the separator described above, and a negative electrode in this order. Here, the porous layer may exist between the porous substrate and at least one of the positive electrode and the negative electrode. Next, the electrochemical element member is placed in a container that serves as a casing for the electrochemical element. Thereby, an electrochemical element can be manufactured. In the case of a non-aqueous electrolyte secondary battery, after filling the inside of the container with the non-aqueous electrolyte, it is sealed while reducing the pressure.

[0083] <Positive electrode> The positive electrode is not particularly limited as long as it is generally used as the 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.

[0084] 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 0.5 O2, LiFePO4, Li2FeP2O7, LiMnPO4, LiFeBO3, Li3V2(PO4)3, Li2CuO2, Li2FeSiO4, Li2MnSiO4, etc.

[0085] 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. The conductive agent may be used alone or in combination of two or more kinds. 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 using fibrous carbon materials such as graphitized carbon fibers and carbon nanotubes as the conductive agent, it is also possible to reduce this proportion.

[0086] 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, and 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 as a mixture of two or more kinds. By using a fluorine-based resin and a polyolefin resin as the binder, and setting the proportion of the fluorine-based 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.

[0087] 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.

[0088] 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, then coating the paste on the positive electrode current collector, drying, and then pressurizing to fix it to the positive electrode current collector.

[0089] 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, and the like.

[0090] Examples of the method for applying the paste of the positive electrode active material to the positive electrode current collector include, for example, slit die coating method, screen coating method, curtain coating method, knife coating method, gravure coating method, and electrostatic spraying method.

[0091] <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. The active material layer may further contain a conductive agent.

[0092] Examples of the negative electrode active material include materials capable of doping and de-doping 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 de-doping lithium ions at a lower potential than the positive electrode. Examples of the carbonaceous materials include natural graphite, artificial graphite, cokes, carbon black, and pyrolytic carbons.

[0093] Examples of the oxide that can be used as the negative electrode active material include silicon oxides represented by the formula SiO x (where x is a positive real number); titanium oxides represented by the formula TiO x (where x is a positive real number); vanadium oxides represented by the formula VO x (where x is a positive real number); iron oxides represented by the formula FeO such as Fe3O4, Fe2O3, and FeO xIron oxides represented by x (where x is a positive real number); tin oxides represented by x (where x is a positive real number); tungsten oxides represented by 12 Composite metal oxides containing lithium and titanium or vanadium such as Li4Ti5O

[0094] Sulfides that can be used as negative electrode active materials include Ti2S3, TiS2, TiS, etc., represented by x (where x is a positive real number); titanium sulfides represented by x (where x is a positive real number); vanadium sulfides represented by x (where x is a positive real number); iron sulfides represented by x (where x is a positive real number); molybdenum sulfides represented by x (where x is a positive real number); tin sulfides represented by x (where x is a positive real number); tungsten sulfides represented by x (where x is a positive real number); antimony sulfides represented by x (where x is a positive real number); selenium sulfides represented by

[0095] Nitrides that can be used as negative electrode active materials include Li3N, Li 3-x A x N (where A is either one or both of Ni and Co, and 0 < x < 3). Lithium-containing nitrides such as these can be mentioned.

[0096] 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.

[0097] In addition, examples of metals that can be used as the negative electrode active material include lithium metal, silicon metal, and tin metal.

[0098] 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, and Li-Sn-Ni; silicon alloys such as Si-Zn; tin alloys such as Sn-Mn, Sn-Co, Sn-Ni, Sn-Cu, and Sn-La; and alloys such as Cu2Sb and La3Ni2Sn7.

[0099] These metals and alloys are mainly used alone as electrodes after being processed into, for example, 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.

[0100] 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.

[0101] Examples of the method for manufacturing the negative electrode sheet include 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, then coating the paste on 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.

[0102] The negative electrode sheet may contain a binder if necessary. Examples of the binder include thermoplastic resins, and specifically, PVdF, thermoplastic polyimide, carboxymethyl cellulose, polyolefin resin, and the like can be mentioned.

[0103] <Non-aqueous electrolyte> The non-aqueous electrolyte is not particularly limited as long as it is generally a non-aqueous electrolyte used in an electrochemical device, for example, a non-aqueous electrolyte secondary battery. 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.

[0104] 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 a wide operating temperature range, is less likely to deteriorate even when charge and discharge are performed at a high current rate, is less likely to deteriorate even when used for a long time, and has many features such as 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.

[0105] 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.

[0106] One embodiment of the present invention may include the following configuration. <1>A separator for an electrochemical element, comprising a porous layer containing a resin, wherein the value represented by the following formula (1) is less than 0.05. C / (A×B)···(1) (In formula (1), A is the content [wt%] of the resin in the porous layer, B is the porosity [%] of the porous layer, and C is the air permeability [sec / 100mL] of the separator for the electrochemical element.) <2>The separator for an electrochemical element according to <1>, wherein the value represented by the following formula (2) is less than 3. C / A···(2) (In formula (2), A and C are the same as A and C in formula (1).) <3>The separator for an electrochemical element according to <1> or <2>, wherein the value represented by the following formula (3) is greater than 5200. A×B···(3) (In formula (3), A and B are the same as A and B in formula (1).) <4>The weight per unit area of the porous layer is 0.15 g / m 2 or more. 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 one or more resins selected from the group consisting of polyamide, polyamideimide, polyimide, and polyvinylidene fluoride. <6>The separator for an electrochemical element according to <5>, wherein the polyamide is an aramid resin. <7>Comprising a polyolefin porous substrate, The separator for an electrochemical element according to any one of <1> to <6>, wherein the porous layer is laminated on the polyolefin porous substrate. <8>The separator for an electrochemical element according to <7>, further comprising an adhesive layer separately from the polyolefin porous substrate and the porous layer. <9>A member for an electrochemical element, in which a positive electrode, the separator for an electrochemical element according to any one of <1> to <8>, and a negative electrode are arranged in this order. An electrochemical device comprising the separator for an electrochemical device according to any one of <10><1> to <8>. <11>The electrochemical device according to <10>, which is a secondary battery or a capacitor.

Example

[0107] One embodiment of the present invention will be described below.

[0108] 〔Measurement and evaluation of physical properties〕 For the porous layers and separators described in the examples and comparative examples, the measurement and evaluation of their physical properties were carried out by the methods shown below.

[0109] (Air permeability) In accordance with JIS P8117, the air permeability of the separator and the air permeability of the porous substrate were measured by the Gurley tester method.

[0110] Further, using the measured values of the air permeability of the separator and the air permeability of the porous substrate, the air permeability of the porous layer was calculated according to the following formula (4). Air permeability of porous layer [sec / 100mL] = Air permeability of separator [sec / 100mL] - Air permeability of porous film [sec / 100mL] ··· (4) Note that since the separator manufactured in Example 3 consists only of a porous layer, the "air permeability of the porous film" in the above formula (4) is "0", and the air permeability of the porous layer = the air permeability of the separator.

[0111] (Porosity of the porous layer) The porosity of the porous layer was calculated by the following procedure. 1. The parameters were defined as follows.

[0112] Constituent materials of the porous layer: a, b, c,..., n Weight ratio [wt%] of each constituent material in the porous layer: Wa, Wb, Wc,..., Wn True density of each constituent material [g / cm 3 : da, db, dc,..., dn Film thickness [cm] of the porous layer: t Areal density of the porous layer [g / cm 2 : Z 2. From the parameters defined in Step 1, the porosity ε [%] of the porous layer was calculated according to the following formula (5). ε [%] = [1 - {Z × (Wa / da + Wb / db + Wc / dc + … + Wn / dn) / t}] × 100 ··· (5) In addition, 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 X, the density described in Reference Document 1 shown below was adopted. As the true density of Resin Y, the density described in Reference Document 2 shown below was adopted. Reference Document 1: K Xiao et al., J. Mater. Sci. 27 (1992) 3065 Reference Document 2: Takashi Nomma, "Trends in the Development of Synthetic Fibers" Special Issue on the Characteristics and Applications of Aramid Fibers, Journal of the Fiber Society (Fiber and Industry), Vol. 56, No. 8, pp241 - 247, 2000 (Membrane thickness) In advance, the membrane thickness of the porous base material used in the examples and comparative examples was measured using a high-precision digital length measuring instrument (manufactured by Mitutoyo Corporation). Specifically, each of the porous base materials was cut into a square with a side length of 8 cm, and five-point measurements were performed within the range of the square, and the membrane thickness was determined from the average value of these five points.

[0113] Subsequently, for the separators manufactured in the examples and comparative examples, the membrane thickness of the separator was measured in the same manner as the method for measuring the membrane thickness of the porous base material.

[0114] Using the measured membrane thickness of the porous base material and the membrane thickness of the separator, the membrane thickness of the porous layer constituting the separator was calculated based on the following formula (7). Membrane thickness of the porous layer [μm] = Membrane thickness of the separator [μm] - Membrane thickness of the porous base material [μm] ··· (7) (Areal density of the porous layer) A sample of 8 cm × 8 cm square was cut out from the separator. The weight of this sample was measured and designated as W1 [g]. The areal density of the separator was calculated according to the following formula (7). Weight per unit area of the separator [g / m 2 = W1 [g] / (0.08 [m] × 0.08 [m]) ··· (7) Also, a square sample of 8 cm × 8 cm was cut out from the polyolefin porous film, which is a porous substrate before applying the coating liquid. The weight of this sample was measured and designated as W2 (g). The weight per unit area of the porous substrate was calculated according to the following formula (8). Weight per unit area of the porous substrate [g / m 2 = W2 [g] / (0.08 [m] × 0.08 [m]) ··· (8) Using the measured weight per unit area of the separator and the weight per unit area of the porous substrate, the weight per unit area of the porous layer was calculated according to the following formula (9). Weight per unit area of the porous layer [g / m 2 = Weight per unit area of the separator [g / m 2 - Weight per unit area of the porous film [g / m 2 ··· (9) (Cycle test) A cycle test was imposed according to the following procedure. 1. A laminate formed by laminating in order from above a spring, a spacer (thickness: 0.5 mm), a lithium metal (diameter: 15 mm, thickness: 0.5 mm, manufactured by Honjo Metal Co., Ltd.), two separators (diameter 17 mm, arranged so that both the porous layer and the lithium metal are in contact), a lithium metal (diameter: 15 mm, thickness: 0.5 mm, manufactured by Honjo Metal Co., Ltd.), and a spacer (thickness: 0.5 mm) was stored in a coin-type battery container. 2. 190 μL of a non-aqueous electrolyte was injected into the coin-type battery container storing the laminate. After vacuum impregnation, 85 μL of the non-aqueous electrolyte was further injected, and then the coin-type battery container was caulked and sealed to manufacture a coin-type battery. The composition of the non-aqueous electrolyte was a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate = 3:5:2 (volume ratio) in which LiPF6 was dissolved so that the concentration of the LiPF6 was 1 mol / L. 3. A constant current was passed through the coin-type battery to repeat the dissolution and precipitation of the lithium metal, and a cycle test was carried out. The test conditions of the cycle test were as follows: current density of the constant current: 1.0 mA / cm2 1. Charge time: 1 hour, capacity: 1.0 mAh / cm 2 2. Temperature: 25°C 4. The cycle test was terminated when the voltage of the coin-type battery reached the cut-off value (±0.5 V) or a short circuit occurred (the voltage became 0 V). The time [h] until the voltage reached the cut-off value (±0.5 V) was measured. Hereinafter, the measured time is referred to as the "cycle time".

[0115] [Synthesis Example 1: Synthesis of Resin X] Resin X (poly(4,4'-diphenylsulfonylterephthalamide)) was synthesized by the following procedure. 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'-diaminodiphenylsulfone was added at 100°C and completely dissolved. 4. The obtained 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. The obtained solution was aged for 1 hour while maintaining the temperature of the solution at 25 ± 2°C to obtain a solution containing Resin X.

[0116] [Synthesis Example 2: Synthesis of Resin Y] Resin Y (poly(p-phenyleneterephthalamide)) was synthesized by the following procedure. 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, the temperature of the solution was returned to room temperature. 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. While keeping the temperature of the resulting solution at 25 ± 2 °C, the solution was aged for 1 hour to obtain a solution containing resin Y.

[0117] 〔Example 1〕 A separator provided with a porous layer having a weight ratio of resin X: resin Y: alumina of 50:50:5 was manufactured. Specifically, the solutions obtained in Synthesis Examples 1 and 2 were mixed to obtain a mixture (1) so that the weight ratio of resin X: resin Y was 50:50. To 500 g of the obtained mixture (1), 11.68 g of calcium carbonate was added and stirred for 10 minutes to neutralize the solution and obtain a neutralized solution (1). Then, alumina (average particle size: 13 nm) was added to the neutralized solution (1) so that the weight ratio of resin X: resin Y: alumina was 50:50:5, further diluted with NMP, and defoamed 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.

[0118] The coating solution (1) was applied to a polyethylene porous film (thickness: 10.3 μm, air permeability: 180 s / 100 mL), and the porous layer (1) was deposited in a precipitation tank at 50 °C and 70% humidity. The precipitation time was 10 seconds. Then, it was washed with water and dried to obtain a laminated separator provided with the porous layer (1). The obtained laminated separator was designated as separator (1). The weight per unit area of the porous layer (1) was 1.1 g / m 2 It was.

[0119] 〔Example 2〕 A separator having a porous layer that does not contain alumina and has a weight ratio of resin X: resin Y of 50:50 was manufactured. Specifically, the same operations as in Example 1 were performed except that alumina (average particle size: 13 nm) was not added to the neutralizing solution (1), and a laminated separator having a porous layer (2) was obtained. The obtained laminated separator was designated as separator (2). The basis weight of the porous layer (2) was 1.5 g / m 2 was obtained.

[0120] [Example 3] A separator consisting only of a porous layer that does not contain alumina and has a weight ratio of resin X: resin Y of 90:10 was manufactured. Specifically, the solutions obtained in Synthesis Examples 1 and 2 were mixed to obtain a mixture (2) so that the weight ratio of resin X: resin Y was 90:10. To 500 g of the obtained mixture (2), 17.8 g of calcium carbonate was added and stirred for 10 minutes to neutralize the solution, and a neutralizing solution (2) was obtained. Then, the neutralizing solution (2) was diluted with NMP and defoamed under reduced pressure to prepare a slurry-like coating solution (2). The solid content concentration of the coating solution (2) was 6.0% by weight.

[0121] The coating solution (2) was applied to a release-treated PET film (thickness 75 μm), and a porous layer (3) was deposited by treating it in a deposition tank at 50 °C and a relative humidity of 70% for 5 minutes. Then, it was washed in a water washing tank and dried in a drying oven at 80 °C to obtain a laminate composed of the porous layer (3) and the PET film. Then, the PET film was peeled off from the laminate to obtain a porous membrane consisting only of the remaining porous layer (3). The obtained porous membrane itself was designated as separator (3). The porous layer (3) and the separator (3) were the same, and the basis weight was 12.5 g / m 2 was obtained.

[0122] [Comparative Example 1] The same operations as in Example 1 were performed except for the changes shown in the following (a) and (b) to obtain a laminated separator having a porous layer (4). The obtained laminated separator was designated as comparative separator (1). The basis weight of the porous layer (4) was 1.5 g / m 2 was obtained. (a) The precipitation time was changed from 10 seconds to 30 seconds. (b) The mode of adding alumina to the neutralizing solution (1) was changed so that the weight ratio of resin X: resin Y: alumina was 50:50:100.

[0123] [Comparative Example 2] The same operations as in Example 2 were performed except that the precipitation time was changed from 10 seconds to 30 seconds, and a laminated separator having a porous layer (5) was obtained. The obtained laminated separator was used as the comparative separator (2). The weight per unit area of the porous layer (5) was 1.7 g / m 2 and it was.

[0124] [Results] The production conditions of the examples and comparative examples, specifically, the weight ratios of the raw materials used, the precipitation time, and the evaluation results of the produced porous layers and separators are shown in Tables 1 and 2.

[0125] [Table 1]

[0126] [Table 2]

[0127] The separators (1) to (3) include a porous layer containing a resin, and as shown in Table 2, C / (A×B) is less than 0.05. Therefore, the separators (1) to (3) correspond to the separator for an electrochemical element according to an embodiment of the present invention.

[0128] The electrochemical elements provided with the separators (1) to (3) produced in Examples 1 and 2 have a longer cycle time than the electrochemical elements provided with the comparative separators (1) or (2) produced in Comparative Examples 1 and 2. Therefore, it is shown that the cycle characteristics of the electrochemical elements provided with the separators (1) to (3) are improved.

[0129] From the above, it has been found that the separator for an electrochemical device according to an embodiment of the present invention can improve the cycle characteristics of the electrochemical device.

Industrial Applicability

[0130] One aspect of the present invention can be used in an electrochemical device.

Claims

1. A separator for an electrochemical element, comprising a porous layer containing a resin, wherein a value represented by the following formula (1) is less than 0.

05. C / (A×B)...(1) (In formula (1), A is the content [wt %] of the resin in the porous layer, B is the porosity [%] of the porous layer, and C is the air permeability [sec / 100 mL] of the separator for electrochemical elements.)

2. The separator for an electrochemical element according to claim 1 , wherein the value represented by the following formula (2) is less than 3: C / A... (2) (In formula (2), A and C are the same as A and C in formula (1).)

3. The separator for an electrochemical element according to claim 1 , wherein the value represented by the following formula (3) is more than 5,200: A × B ... (3) (In formula (3), A and B are the same as A and B in formula (1).)

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

5. 2. The separator for an electrochemical element according to claim 1, wherein the porous layer contains one or more resins selected from the group consisting of polyamide, polyamideimide, polyimide, and polyvinylidene fluoride.

6. 6. The separator for an electrochemical element according to claim 5, wherein the polyamide is an aramid resin.

7. A polyolefin porous substrate is provided, The separator for an electrochemical element according to claim 1 , wherein the porous layer is laminated on a polyolefin porous substrate.

8. The separator for an electrochemical element according to claim 7 , further comprising an adhesive layer in addition to the polyolefin porous substrate and the porous layer.

9. A member for an electrochemical device comprising a positive electrode, the separator for an electrochemical device according to any one of claims 1 to 8, and a negative electrode arranged in this order.

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

11. The electrochemical device according to claim 10, which is a secondary battery or a capacitor.

Images