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

Abstract

To provide a separator for an electrochemical element excellent in wettability to an electrolyte.SOLUTION: A separator for an electrochemical element includes a porous layer having a maximum average pore area / minimum average pore area of 1.80 or more or a maximum average pore diameter / minimum average pore diameter of 1.25 or more in six divided regions obtained by dividing a cross section passing through a center and parallel to a thickness direction into six equal parts using a straight line perpendicular to the thickness direction.SELECTED DRAWING: Figure 1

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 disclosed 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, the conventional separators as described above had room for improvement from the viewpoint of wettability with the electrolyte. One aspect of the present invention aims to provide a separator for an electrochemical element having excellent wettability with the electrolyte.

Means for Solving the Problems

[0006] As a result of intensive studies by the present inventors to solve the above problems, it has been found that a separator for an electrochemical element having excellent wettability with the electrolyte can be realized by distributing the pore area or pore diameter in the porous layer to be somewhat non-uniform in the thickness direction.

[0007] The separator for an electrochemical element according to one aspect of the present invention includes a porous layer, and the ratio of the maximum average pore area to the minimum average pore area among the average pore areas in each of the six divided regions obtained by dividing a cross section parallel to the thickness direction passing through the center of the porous layer into six equal parts using a straight line perpendicular to the thickness direction is 1.80 or more. The separator for an electrochemical element according to another aspect of the present invention includes a porous layer, and the ratio of the maximum average pore diameter to the minimum average pore diameter among the average pore diameters in each of the six divided regions obtained by dividing a cross section parallel to the thickness direction passing through the center of the porous layer into six equal parts using a straight line perpendicular to the thickness direction is 1.25 or more.

Advantages of the Invention

[0008] According to one aspect of the present invention, it is possible to provide a separator for an electrochemical element that is excellent in wettability with an electrolytic solution.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

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 Element〕 The separator for an electrochemical element according to one embodiment of the present invention includes a porous layer, and the ratio of the maximum average pore area to the minimum average pore area among the average pore areas in each of six divided regions obtained by dividing a cross-section parallel to the thickness direction passing through the center of the porous layer into six equal parts using a straight line perpendicular to the thickness direction is 1.80 or more. The porous layer is provided. Further, the separator for an electrochemical element according to another embodiment of the present invention includes a porous layer, and the ratio of the maximum average pore diameter to the minimum average pore diameter among the average pore diameters in each of six divided regions obtained by dividing a cross-section parallel to the thickness direction passing through the center of the porous layer into six equal parts using a straight line perpendicular to the thickness direction is 1.25 or more. The porous layer is provided. Hereinafter, the separator for an electrochemical element according to one embodiment of the present invention and the separator for an electrochemical element according to another embodiment of the present invention are collectively referred to simply as "separator".

[0012] Hereinafter, the ratio of the maximum average pore area to the minimum average pore area, that is, the ratio of the maximum average pore area / the minimum average pore area is also referred to as the "ratio of average pore areas". Further, the ratio of the maximum average pore diameter to the minimum average pore diameter, that is, the ratio of the maximum average pore diameter / the minimum average pore diameter is also referred to as the "ratio of average pore diameters". Note that the separator may have a ratio of average pore areas of 1.80 or more and a ratio of average pore diameters of 1.25 or more. Further, "dividing a cross-section parallel to the thickness direction passing through the center into six equal parts using a straight line perpendicular to the thickness direction" in the present invention means dividing the cross-section of the porous layer obtained by cutting the porous layer in a direction perpendicular to the surface of the porous layer so as to pass through the center of the porous layer into six equal parts in the thickness direction using a straight line parallel to the in-plane direction.

[0013] Here, refer to FIG. 1. FIG. 1 is a schematic diagram showing an example of six divided regions in a porous layer according to an embodiment of the present invention. The vertical direction in FIG. 1 is the thickness direction of the porous layer 1. Further, FIG. 1 is a cross-section parallel to the thickness direction passing through the center of the porous layer, and more specifically, it is a schematic diagram showing an aspect of the cross-section of the porous layer obtained by cutting the porous layer in a direction perpendicular to the surface of the porous layer so as to pass through the center of the porous layer. The divided region refers to each region represented by member numbers "2" to "7" obtained by equally dividing the porous layer 1 in the thickness direction as shown in FIG. 1.

[0014] Also, in the porous layer 1 of FIG. 1, the divided regions 2 to 7 each have different diameters and densities of the existing pores 8, that is, different average pore diameters and pore densities. Hereinafter, the "diameter of the pore" is also referred to as the "pore diameter". More specifically, the average pore diameter and pore density in the divided region 2 are the smallest, and the average pore diameter and pore density in the divided region 7 are the largest. In this case, the average pore area and average pore diameter in the divided region 2 become the "smallest average pore area" and the "smallest average pore diameter", and the average pore area and average pore diameter in the divided region 7 become the "largest average pore area" and the "largest average pore diameter". In this specification, the "pore diameter" means the diameter of a circle when the pore is regarded as a circle having the same area as the pore, and is a value calculated based on the following formula (1). S = π×(d / 2) 2 ···(1) (In formula (1), S: pore area [nm 2 , d: pore diameter [nm].) Furthermore, among the divided regions 2 to 7, the surface on the opposite side of the interface with the divided region 3 in the divided region 2 and the surface on the opposite side of the interface with the divided region 6 in the divided region 7 are defined as the outermost surfaces of the porous layer 1. In other words, the divided regions 2 and 7 include the outermost surfaces of the porous layer 1. In this specification, among the two outermost surfaces, the outermost surface with a smaller average pore area of the included divided region is also referred to as the "first outermost surface", and the other outermost surface is also referred to as the "second outermost surface". Specifically, the divided region 2 with a smaller average pore area corresponds to the divided region including the first outermost surface, and the divided region 7 with a larger average pore area corresponds to the divided region including the second outermost surface. Also, in this specification, "the divided region is located on the outermost surface" means that the divided region includes the first outermost surface or the second outermost surface. Specifically, it means that the divided region is at the position of the divided region 2 or the divided region 7.

[0015] In addition, in one embodiment of the present invention, the average pore diameter and the average pore area can be measured by the methods shown in the following (i) to (iii). (i) The porous layer is cut in a direction perpendicular to the surface of the porous layer so as to pass through the center of the porous layer, and the cross-section of the porous layer thus obtained is observed using a scanning electron microscope (SEM) to acquire an SEM image. (ii) In the SEM image, the pore part and the part other than the pores are binarized for two-dimensional quantitative analysis, and the pore area and pore diameter of each pore that is two-dimensionally independent are measured. (iii) After the SEM image is divided into six parts using a straight line parallel to the in-plane direction to form six divided regions, based on the pore area and pore diameter of each pore belonging to each divided region, the average pore diameter and the average pore area in each divided region are calculated. Also, when pores exist across a plurality of divided regions, the divided region where the centroid of the pore exists is taken as the divided region to which the pore belongs, and the average pore diameter and the average pore area are calculated. More specifically, the average pore diameter and the average pore area can be measured by the method described in the examples.

[0016] The fact that the ratio of the average pore area is 1.80 or more means that among the six divided regions, there are a divided region with a large average pore area and a divided region with a small average pore area. Also, the fact that the ratio of the average pore diameter is 1.25 or more means that among the six divided regions, there are a divided region with a large average pore diameter and a divided region with a small average pore diameter.

[0017] For the wetting of the porous layer, that is, the penetration of the electrolytic solution into the porous layer, the following two mechanisms shown in (A) and (B) coexist. (A) A macro process in which the electrolytic solution spreads over the entire porous layer (B) A micro process in which the electrolytic solution that has spread over the entire porous layer penetrates into the pores in the porous layer Here, in the porous layer according to an embodiment of the present invention, there are a divided region with a large average pore area and / or average pore diameter and a divided region with a small average pore area and / or average pore diameter. In other words, in the porous layer, there are pores with large pore diameters and pores with small pore diameters, and the pore diameter distribution in the pores in the porous layer is wide.

[0018] Further, when the pore diameter distribution is wide and there are pores with large pore diameters in the porous layer, since the propagation of the liquid is fast in the pores with large pore diameters, the speed at which the macro process (A) proceeds is improved. When the pore diameter distribution is wide, the probability of the existence of pores with small pore diameters in the porous layer is improved, and the speed at which the micro process (B) proceeds decreases. However, in the entire porous layer, the process of the penetration of the electrolytic solution is a process in which the macro process (A) is rate-determining rather than the micro process (B). Therefore, in the entire porous layer according to an embodiment of the present invention, the speed of the macro process (A) is improved, and as a result, the electrolytic solution easily penetrates in the thickness direction.

[0019] As described above, the separator includes a porous layer through which the electrolytic solution easily penetrates in the thickness direction. As a result, the wettability with respect to the electrolytic solution is improved. The improvement in the wettability of the separator with respect to the electrolytic solution leads to an improvement in the injectability of the electrolytic solution during battery manufacturing and an improvement in the amount of the electrolytic solution retained due to the volume expansion and contraction of the electrodes during charging and discharging of the battery. Therefore, it is presumed that the injection time of the electrolytic solution during battery manufacturing becomes short, the productivity of the battery is improved, and the battery performance such as cycle characteristics is improved because the amount of the electrolytic solution retained during battery operation is large.

[0020] From the viewpoint of improving the wettability described above, the lower limit value of the ratio of the average pore areas is preferably 1.85 or more, more preferably 2.00 or more. From the viewpoint of ensuring a predetermined strength, the upper limit value of the ratio of the average pore areas is preferably 4.50 or less, more preferably 3.00 or less.

[0021] From the viewpoint of improving the wettability described above, the lower limit value of the ratio of the average pore diameters is preferably 1.27 or more, more preferably 1.30 or more. From the viewpoint of ensuring a predetermined strength, the upper limit value of the ratio of the average pore diameters is preferably 2.20 or less, more preferably 1.90 or less.

[0022] From the viewpoint of improving the wettability of the porous layer and the separator, the lower limit value of the average pore area in the entire porous layer is preferably 0.5×10 3 nm 2 or more, more preferably 1.0×10 3 nm 2 or more. Further, from the viewpoint of improving the strength of the porous layer and the separator and suppressing internal short circuits, the upper limit value of the average pore area in the entire porous layer is preferably 2.0×10 4 nm 2 or less, more preferably 1.0×10 4 nm 2 or less.

[0023] From the viewpoint of improving the wettability of the porous layer and the separator, the lower limit of the average pore diameter in the entire porous layer is preferably 20 nm or more, more preferably 30 nm or more. Also, from the viewpoint of improving the strength of the porous layer and the separator and suppressing internal short circuits, the upper limit of the average pore diameter in the entire porous layer is preferably 150 nm or less, more preferably 100 nm or less.

[0024] In the cross-section, the number of pores per 1 μm 2 is preferably 30 or more, more preferably 40 or more. Also, the number of pores per 1 μm 2 is preferably 150 or less, more preferably 100 or less. The number of pores per 1 μm 2 is a parameter representing the pore density in the entire porous layer. The number of pores per 1 μm 2 When the number of pores per 1 μm is 30 or more, since the pore density in the entire porous layer is high, the wettability of the porous layer can be further improved. As a result, the wettability of the separator can be further improved. Also, when the number of pores per 1 μm 2 is 150 or less, since there are many portions other than pores such as resin portions in the entire porous layer, the strength of the porous layer can be more suitably ensured. As a result, the strength of the separator can be more suitably ensured. Also, in an electrochemical element including the porous layer or the separator, internal short circuits can be suppressed. The cross-section can be, for example, a cross-section parallel to the MD direction or the TD direction. The number of pores per 1 μm 2 can be measured by the method described in the examples.

[0025] In the porous layer, it is preferable that the divided region having the minimum average pore area among the six divided regions is located on the outermost surface of the porous layer. In other words, among the average pore diameters of each of the six divided regions, it is preferable that the average pore area of the divided region including the first outermost surface is the smallest. In this case, in the porous layer and the separator, the proportion occupied by the resin portion, which is the portion other than pores, in the divided region including the first outermost surface is large. Therefore, the resin constituting the porous layer is densely arranged on the first outermost surface. Here, the electrolytic solution penetrates into the porous layer along the resin. Therefore, when the average pore area of the divided region including the first outermost surface is the smallest, in addition to the above-described penetration of the electrolytic solution in the thickness direction, the wettability in the direction perpendicular to the thickness direction can also be improved. As a result, in the porous layer and the separator, the wettability in both the thickness direction and the direction perpendicular to the thickness can be improved. Further, it is more preferable that the average pore area or the average pore diameter of the divided region close to the second outermost surface is the largest among the average pore areas or the average pore diameters in each of the six divided regions, in terms of the fact that the electrolytic solution penetrates more easily and the wettability is further improved. The divided region close to the second outermost surface is, for example, in the porous layer 1 shown in FIG. 1, the divided region 7 including the second outermost surface, or the divided region 6 adjacent to the divided region 7.

[0026] In one embodiment of the present invention, the porous layer can be disposed between a polyolefin porous base material and at least one of a positive electrode and a negative electrode as a member constituting an electrochemical element. Hereinafter, the polyolefin porous base material is also simply referred to as "porous base material". 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.

[0027] The porous layer usually contains a resin. The resin is not limited, for example, it can be 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.

[0028] 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, melamine resin, etc. Among them, the nitrogen-containing aromatic resin preferably includes an aramid resin.

[0029] Examples of the aramid resin include para-aramid and meta-aramid, and para-aramid is preferred. Examples of para-aramid include para-oriented or para-oriented-like structured para-aramids such as poly(p-phenyleneterephthalamide), poly(p-benzamide), poly(4,4'-benzylanilide terephthalamide), poly(p-phenylene-4,4'-biphenylenedicarboxamide), poly(p-phenylene-2,6-naphthalenedicarboxamide), poly(2-chloro-p-phenyleneterephthalamide), p-phenyleneterephthalamide / 2,6-dichlorop-phenyleneterephthalamide copolymer, poly(4,4'-diphenylsulfonyl terephthalamide), p-phenyleneterephthalamide / 4,4'-diphenylsulfonyl terephthalamide copolymer. Examples of meta-aramid include poly(m-phenyleneterephthalamide), poly(m-phenyleneisophthalamide), poly(m-benzamide), poly(m-phenylene-4,4'-biphenylenedicarboxamide), poly(m-phenylene-2,6-naphthalenedicarboxamide), etc. Poly(m-phenyleneisophthalamide) is also referred to as poly[N,N'-(1,3-phenylene)isophthalamide].

[0030] 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-phenylene terephthalamide), poly(2-chloro-p-phenylene terephthalamide), poly(p-benzamide), and poly(4,4'-benzylanilide 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 relatively similar structures, such as a combination of poly(p-phenylene terephthalamide) and poly(2-chloro-p-phenylene terephthalamide), may also be possible.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] Examples of the polyester resin include aromatic polyesters such as polyarylate and liquid crystal polyesters.

[0035] 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.

[0036] 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 above fluororesins, fluororubbers with a glass transition temperature of 23°C or lower are also included.

[0037] 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, and polyetheretherketone, etc.

[0038] Examples of the water - soluble polymer include polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide, polymethacrylic acid, etc.

[0039] 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.

[0040] The porous layer may contain a filler. The filler may be an inorganic filler or an organic filler. Preferred fillers include fillers composed of inorganic oxides such as silica, calcium oxide, magnesium oxide, titanium oxide, alumina, mica, zeolite, aluminum hydroxide, or boehmite. Fillers composed of calcium oxide, magnesium oxide, or alumina are more preferred, and fillers composed of alumina are even more preferred.

[0041] 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. When the content of the filler is 0% by weight, it means that the porous layer does not contain a 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.

[0042] The average particle size 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 even 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. The spherical equivalent particle size of the filler is a value measured by a transmission electron microscope. A specific measurement method is exemplified 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 randomly selected filler particles. The arithmetic mean of the spherical equivalent particle sizes of the 50 filler particles is taken as the average particle size of the particles.

[0043] 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 circuit due to breakage of the electrochemical element or the like can be sufficiently suppressed, and the amount of the electrolytic solution 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 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.

[0044] 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 to 10 g / m 2 and more preferably 0.25 to 5 g / m 2 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.

[0045] The upper limit value of the air permeability of the porous layer is preferably 150 sec / 100 cc or less, more preferably 120 sec / 100 cc or less, from the viewpoint of obtaining sufficient ion permeability. The 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 represents a value measured with a Kawaguchi type air permeability tester in accordance with JIS P8117.

[0046] 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 device can obtain sufficient ion permeability.

[0047] In one embodiment of the present invention, the separator includes a polyolefin porous substrate, and the porous layer is laminated on the polyolefin porous substrate. That is, in one embodiment of the present invention, the separator is a separator in which the porous layer and the polyolefin porous substrate are laminated. In this specification, such a separator is also referred to as a laminated separator. The porous layer can be laminated on one side or both sides of the polyolefin porous substrate.

[0048] When the separator is a laminated separator, it is preferable that the porous layer is laminated on the porous substrate such that the second outermost surface of the porous layer faces the porous substrate side. Further, in the laminated separator, it is more preferable that the average pore area and / or the average pore diameter of the divided region closest to the second outermost surface among the six divided regions in the porous layer are large. Furthermore, it is particularly preferable to have a configuration in which the average pore area and / or the average pore diameter of the divided region closest to the second outermost surface are the maximum values among the average pore area and / or the average pore diameter in each of the six divided regions. By having the above-described preferable configuration, in the laminated separator, the electrolytic solution can easily penetrate through the porous layer and the porous substrate, and becomes more wettable. As a result, the wettability of the entire laminated separator is further improved.

[0049] 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 total materials constituting the porous base material. The porous base material can be a polyolefin porous film.

[0050] 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 resulting separator is improved.

[0051] 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.

[0052] 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.

[0053] The film thickness of the porous substrate is preferably 4 to 40 μm, 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.

[0054] 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 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 is even more preferable.

[0055] 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 upper limit value of the air permeability of the porous substrate is preferably 200 sec / 100cc or less, more preferably 180 sec / 100cc or less. The lower limit value of the air permeability of the porous substrate is preferably 30 sec / 100cc or more, more preferably 50 sec / 100cc or more. By having the air permeability within the above range, sufficient ion permeability can be obtained. The air permeability represents a value measured by a King - type air permeability tester in accordance with JIS P8117.

[0056] The porosity of the porous substrate is preferably 20 to 80% by volume, 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, 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.

[0057] 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.

[0058] The upper limit value of the air permeability of the separator is preferably 430 sec / 100cc or less, more preferably 350 sec / 100cc or less, still more preferably 330 sec / 100cc or less, and particularly preferably 300 sec / 100cc or less. The lower limit value of the air permeability of the separator is preferably 30 sec / 100cc or more, more preferably 50 sec / 100cc or more, still more preferably 70 sec / 100cc or more. By having the air permeability within the above range, the separator can obtain sufficient ion permeability in the electrochemical device. The air permeability represents a value measured by a Wangyan type air permeability tester in accordance with JIS P8117.

[0059] The separator may optionally contain another functional layer different from the above-mentioned porous substrate and porous layer (e.g., 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.

[0060] The other functional layer can be provided on one or both sides of the separator. When the separator is provided with the above-mentioned porous layers on both sides of the porous substrate, 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 above-mentioned porous layer on only one side of the porous substrate, the other 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 other 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 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 resin, PVdF, and the like.

[0062] A porous layer can be formed using a coating liquid obtained by dissolving or dispersing a resin in a solvent. It can also be said that the solvent is 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, and the like.

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

[0064] The solvent preferably does not have an adverse effect on the base material, 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, but 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 above-mentioned 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 porous substrate can be manufactured by stretching the polyolefin resin composition from which the pore former has been removed.

[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 one or more conditions selected from the group consisting of the following (a) to (d), a porous layer and a separator in which the ratio of the average pore area and / or the ratio of the average pore diameter are controlled within the above-mentioned range can be manufactured. In addition to one or more conditions selected from the group consisting of the following (a) to (d), the condition of the following (e) may be satisfied. (a) Using, as the coating liquid, a coating liquid containing two or more types of resins having different solubilities in the solvent in the coating liquid. (b) Using, as the coating liquid, a coating liquid containing a resin having a wide molecular weight distribution. (c) Making the precipitation time of the resin long. (d) As a precipitation method, changing the humidity of the precipitation layer over time. (e) Using, as the coating liquid, a coating liquid having a low filler content or containing no filler.

[0072] Although it is speculative, in the case of (a), the following mechanism is considered. When there is a difference in the ease of dissolution (precipitability) of two or more types of resins, in the process of precipitation, the resin that is difficult to dissolve (the first resin) precipitates first, while the resin that is easy to dissolve (the second resin) precipitates later. By using a coating liquid containing a plurality of resins with a difference in precipitation rate, the outermost surface of the formed porous layer is mainly composed of the first resin that is easy to precipitate and precipitates first. Also, the inside of the porous layer is mainly composed of the second resin that is difficult to precipitate and precipitates later. Therefore, there is a difference in the resin structure between the outermost surface and the inside of the porous material. As a result, it is considered that a pore distribution that satisfies the ratio of the average pore area and / or the ratio of the average pore diameter described above occurs.

[0073] (b) In the case of using a coating liquid containing a resin having a wide molecular weight distribution, a difference in precipitability occurs between the low molecular weight component and the high molecular weight component, and it is considered that a pore distribution that satisfies the ratio of the average pore area and / or the ratio of the average pore diameter described above occurs by the same mechanism as in the case of (a).

[0074] In the case of (c), by setting the precipitation time to be long, after the easily precipitable resin that constitutes the outermost surface precipitates, the time until the hardly precipitable resin that constitutes the inside of the porous layer precipitates becomes long, and it is considered that a pore distribution that satisfies the ratio of the average pore area and / or the ratio of the average pore diameter described above is generated. Note that the easily precipitable resin is, for example, a high molecular weight component, and the hardly precipitable resin is, for example, a low molecular weight component.

[0075] In the case of (d), by changing the humidity in the precipitation tank over time, the precipitation rate in the initial and later stages changes, and it is considered that a pore distribution that satisfies the ratio of the average pore area and / or the ratio of the average pore diameter described above is generated. By selecting whether the humidity change is in the increasing direction or the decreasing direction, it is considered that the magnitude of the average pore area with respect to the thickness direction can be reversed.

[0076] In the case of (e), the filler is used as a resin pore former, and by using the filler, uniform pores are generated at a high density regardless of the precipitation property of the resin. Therefore, by reducing the filler content or using a coating liquid that does not contain the filler, it is considered that a pore distribution that satisfies the ratio of the average pore area and / or the ratio of the average pore diameter described above is generated.

[0077] [3. Member for Electrochemical Element, Electrochemical Element] The member for an electrochemical element according to one embodiment of the present invention is configured such that a positive electrode, the separator for an electrochemical element described above, and a negative electrode are arranged in this order. Further, the electrochemical element according to one embodiment of the present invention includes the separator for an electrochemical element described above.

[0078] 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.

[0079] For example, a member for an electrochemical element can be formed by arranging a positive electrode, the aforementioned separator, and a negative electrode in this order. Here, the porous layer can 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 the housing of 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.

[0080] <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.

[0081] 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.

[0082] 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. 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.

[0083] 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. 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.

[0084] 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 easily processed into a thin film and is inexpensive. 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, coating the paste on the positive electrode current collector, drying it, and then pressing it to adhere it to the positive electrode current collector.

[0085] 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.

[0086] Examples of the method for applying the paste of the positive electrode active material to the positive electrode current collector include slit die coating method, screen coating method, curtain coating method, knife coating method, gravure coating method, and electrostatic spraying method, and the like.

[0087] <Negative electrode> The negative electrode is not particularly limited as long as it is generally used as the negative electrode of an electrochemical device. 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.

[0088] 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.

[0089] 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 xIron oxides represented by (where x is a positive real number); Tin oxides represented by SnO such as SnO2 and SnO x Tin oxides represented by (where x is a positive real number); Tungsten oxides represented by WO such as WO3 and WO2 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.

[0090] Sulfides that can be used as negative electrode active materials include TiS such as Ti2S3, TiS2, and TiS x Titanium sulfides represented by (where x is a positive real number); Vanadium sulfides represented by VS such as V3S4, VS2, and VS x Vanadium sulfides represented by (where x is a positive real number); Iron sulfides represented by FeS such as Fe3S4, FeS2, and FeS x Iron sulfides represented by (where x is a positive real number); Molybdenum sulfides represented by MoS such as Mo2S3 and MoS2 x Molybdenum sulfides represented by (where x is a positive real number); Tin sulfides represented by SnS such as SnS2 and SnS x Tin sulfides represented by (where x is a positive real number); Tungsten sulfides represented by WS such as WS2 x Tungsten sulfides represented by (where x is a positive real number); Antimony sulfides represented by SbS such as Sb2S3 x Antimony sulfides represented by (where x is a positive real number); Selenium sulfides represented by SeS such as Se5S3, SeS2, and SeS x and selenium sulfides represented by (where x is a positive real number) can be mentioned.

[0091] Nitrides that can be used as negative electrode active materials include Li3N, Li 3-x A x N (where A is either Ni or Co or both, and 0 < x < 3). Lithium-containing nitrides such as this can be mentioned.

[0092] 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.

[0093] In addition, examples of metals that can be used as the negative electrode active material include lithium metal, silicon metal, and tin metal.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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, 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.

[0098] The negative electrode sheet may contain a binder as required. Examples of the binder include thermoplastic resins, and specifically, PVdF, thermoplastic polyimide, carboxymethyl cellulose, polyolefin resin, and the like can be mentioned.

[0099] <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 lower aliphatic carboxylate salts, 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.

[0100] 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 a solvent obtained by further introducing a fluoro group into these organic solvents (a solvent 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 hardly deteriorated even when charge and discharge are performed at a high current rate, is hardly deteriorated 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.

[0101] 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.

[0102] One embodiment of the present invention may include the following configuration. <1>A separator for an electrochemical element, comprising a porous layer, wherein the ratio of the maximum average pore area to the minimum average pore area among the average pore areas in each of six divided regions obtained by dividing a cross-section parallel to the thickness direction passing through the center of the porous layer into six equal parts using a straight line perpendicular to the thickness direction is 1.80 or more. <2>A separator for an electrochemical element, comprising a porous layer, wherein the ratio of the maximum average pore diameter to the minimum average pore diameter among the average pore diameters in each of six divided regions obtained by dividing a cross-section parallel to the thickness direction passing through the center of the porous layer into six equal parts using a straight line perpendicular to the thickness direction is 1.25 or more. <3>The separator for an electrochemical element according to <1> or <2>, wherein the film thickness of the porous layer is 0.15 to 5 μm. <4>The weight per unit area of the porous layer is 0.15 to 10 g / m 2 The separator for an electrochemical element according to any one of <1> to <3>. <5>The number of pores per 1 μm 2 in the cross-section is 30 or more, and the separator for an electrochemical element according to any one of <1> to <4>. <6>The separator for an electrochemical element according to any one of <1> to <5>, wherein the divided region having the minimum average pore area among the six divided regions is located on the outermost surface of the porous layer. <7>The separator for an electrochemical element according to any one of <1> to <6>, wherein the air permeability of the porous layer is 150 sec / 100 cc or less. <8>The separator for an electrochemical element according to any one of <1> to <7>, wherein the porous layer contains an aramid resin. <9>A separator for an electrochemical element, comprising a polyolefin porous substrate, wherein the porous layer is laminated on the polyolefin porous substrate, and the separator for an electrochemical element according to any one of <1> to <8>. <10>The separator for an electrochemical element according to <9>, further comprising an adhesive layer separately from the polyolefin porous substrate and the porous layer. <11>The separator for an electrochemical element according to <9> or <10>, wherein the air permeability is 330 sec / 100 cc or less. <12>An electrochemical element member in which a positive electrode, a separator for an electrochemical element described in any one of <1> to <11>, and a negative electrode are arranged in this order. <13>An electrochemical element including the separator for an electrochemical element described in any one of <1> to <11>. <14>The electrochemical element according to <13>, which is a secondary battery or a capacitor.

Example

[0103] One embodiment of the present invention will be described below.

[0104] 〔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.

[0105] <Average pore area, average pore diameter, and pore number density of the porous layer> The separators produced in the examples and comparative examples were used as measurement samples. The measurement sample was cut by the ion milling method (IB-19520 (manufactured by JEOL Ltd.)) in a direction parallel to MD and perpendicular to the surface passing through the center of the measurement sample, and the cut surface was vapor-deposited with osmium (Os), and a cross-sectional image was obtained by observing with a scanning electron microscope (SEM, S-4800 (manufactured by Hitachi High-Technologies Corporation)). In this way, more than 10 cross-sectional images were obtained.

[0106] The processing conditions by the ion milling method and the observation conditions using SEM are shown below. (Processing conditions by the ion milling method) ·Acceleration voltage: 4.5 kV ·Processing time: 8 h ·Processing temperature: -100 °C or lower (Observation conditions using SEM) ·Acceleration voltage: 0.8 kV ·Working distance (WD): 3 mm ·Probe current: High ·Condenser lens 1: 1 · Condenser lens 2:1 · Emission current: 20 μA · Backscattered electron image · Image resolution: 9.92 nm / pix For the cross-sectional image, two-dimensional quantitative analysis of pores was performed using software from Lattic System Engineering Co., Ltd. (TRI / 3D-BON-FCS: 2D particle analysis option), and the pore area and pore diameter of the pores in the porous layer of the separator were calculated.

[0107] Specifically, for the two-dimensional quantitative analysis, the porous layer was extracted from the cross-sectional image, and an image in which the pores and the solid portion in the porous layer were binarized was obtained. Next, for the image, a process of identifying and labeling two-dimensionally isolated pores was performed. The number of the labeled pores was 10,000 or more.

[0108] The area of the porous layer extracted from the cross-sectional image and the number of the pores labeled in the process were determined, and the pore number density [pieces / μm 2 was calculated.

[0109] The pore area S of each pore constituting all the pores labeled in the process was determined, and the pore diameter d of each pore was calculated from the above formula (1). Next, for the cross-sectional image of the porous layer, that is, the image, as shown in FIG. 1, it was divided into six in the direction parallel to the in-plane direction with respect to the thickness direction of the porous layer to form six divided regions. Then, based on the pore area S and the pore diameter d of each pore constituting all the pores in each divided region, which are measured for the pores whose centroids are included in each divided region, the average pore area and the average pore diameter in each divided region were calculated.

[0110] Based on the maximum value and the minimum value of the average pore area and the average pore diameter in each divided region, the "ratio of average pore areas" and the "ratio of average pore diameters" were calculated. Also, based on the pore area S and the pore diameter d of each selected pore in the entire porous layer, the average pore area and the average pore diameter in the entire porous layer were calculated.

[0111] <Air permeability of the separator> The separator was cut into a square with a size of 60 mm × 60 mm and used as a sample for measuring the air permeability of the separator. The sample for measuring the air permeability of the separator was placed in a digital Wangyan type air permeability tester EGO1 manufactured by Asahi Seiko Co., Ltd., and the air permeability of the separator was measured to obtain the air permeability of the separator (unit: s / 100 mL).

[0112] <Film thickness> In advance, the film thickness of the porous base materials 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 film thickness was determined from the average value of these five points.

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

[0114] Using the measured film thickness of the porous base material and the film thickness of the separator, the film thickness of the porous layer constituting the separator was calculated based on the following formula (2). Film thickness of the porous layer [μm] = Film thickness of the separator [μm] - Film thickness of the porous base material [μm] ··· (2) <Wettability> The wettability of the separators manufactured in the examples and comparative examples was evaluated by the following method. (1) The separator was cut out to a size of 2.7 cm × 4.5 cm. (2) The separator was placed on a stainless steel plate with the porous layer on the upper surface, and both ends in the short side direction of the separator were fixed with Kapton tape. The stainless steel plate has a depression with a length of 2 cm, a width of 3 cm, and a depth of 3 mm at the center, and the separator was arranged so as to straddle the depression so that the separator in the test part does not contact the stainless steel plate. (3) Using a micropipette, 2 μL of propylene carbonate (manufactured by Fujifilm Wako Pure Chemical Corporation, hereinafter referred to as "PC") was dropped onto the separator. (4) After leaving it for 5 minutes, a photograph of the separator was taken from above. (5) For the obtained photograph, wettability evaluation was performed using analysis software (Image J).

[0115] Hereinafter, with reference to FIG. 2, a specific method for evaluating the wettability will be described. FIG. 2 is a diagram showing an example of the obtained photograph. As shown in FIG. 2, in the photograph, a region 10 where PC penetrated both the porous layer and the polyolefin porous substrate (hereinafter referred to as the "first region") and a region 20 where PC penetrated only the porous layer (hereinafter referred to as the "second region") were observed. In FIG. 2, the area A of the first region 10 was calculated. Next, in addition to the first region 10, an area B including the second region 20 that spreads outside the first region 10 was calculated. Here, the area B corresponds to the sum of the areas of the first region 10 and the second region 20. Then, the wettability of the separator was evaluated by the ratio (area B / area A) calculated by dividing the area B by the area A. Hereinafter, the ratio (area B / area A) is referred to as the "wet area ratio". Note that the first region 10 is a region near the location where the PC droplet 30 was dropped and has a dark color. The second region 20 is a region far from the location where the PC droplet 30 was dropped and has a light color. Specifically, it is the region between the broken line in FIG. 2 and the outer peripheral portion of the first region 10.

[0116] The fact that the "wet area ratio" is small means that most of the PC dropped onto the separator penetrated the entire thickness direction of the porous layer, passed through the porous layer, and penetrated to the porous substrate. On the other hand, the fact that the "wet area ratio" is large means that most of the PC dropped onto the separator did not penetrate the entire thickness direction of the porous layer, remained inside the porous layer, and did not penetrate to the porous substrate. Therefore, the fact that the "wet area ratio" is small indicates that the separator has excellent wettability to the electrolyte.

[0117] [Synthesis Example 1: Synthesis of Resin A] Resin A (poly(4,4'-diphenylsulfonylterephthalamide)) was synthesized according to the following procedure. 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, 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 terephthalic acid dichloride 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.

[0118] [Synthesis Example 2: Synthesis of Resin B] Resin B (poly(p-phenyleneterephthalamide)) was synthesized according to the following procedure. 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 terephthalic acid dichloride 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.

[0119] [Comparative Synthesis Example 1: Synthesis of Resin C] Resin C (a block copolymer in which block 1 accounts for 50% of the whole molecule and block 2 accounts for 50% of the whole molecule) was synthesized according to the following procedure. Block 1 consists of poly(4,4'-diphenylsulfonyl terephthalamide). Block 2 consists of poly(p-phenylene terephthalamide). 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. 420 g of N-methylpyrrolidone was charged into the flask. Further, 27.27 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, 20.34 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 16.54 g of terephthalic acid dichloride was added in three portions and reacted for 1 hour. Thereby, block 1 was synthesized. 5. 8.87 g of 1,4-phenylenediamine was added to the resulting solution and dissolved over 30 minutes. 6. While maintaining the temperature of the solution at 25 ± 2 °C, a total of 16.46 g of terephthalic acid dichloride was added in three portions and reacted for 1 hour. Thereby, block 2 was extended on both sides of block 1. 7. 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 C.

[0120] [Example 1] A porous layer with a weight ratio of Resin A:Resin B of 90:10 was prepared. Specifically, the solutions obtained in Synthesis Examples 1 and 2 were mixed so that the weight ratio of Resin A:Resin B was 90:10. To 500 g of the resulting mixture (1), 17.27 g of calcium carbonate was added and stirred for 10 minutes to neutralize the solution, and a neutralized solution (1) was obtained. 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.

[0121] The coating liquid (1) was applied to a polyethylene porous film (thickness: 10.3 μm, air permeability: 180 sec / 100 cc). The application was carried out using a coating bar under the condition of a clearance of 100 μm. The polyethylene porous film coated with the coating liquid (1) was placed inside a deposition tank under the conditions of 50 °C and 70% humidity and left for a deposition time of 60 seconds. Thereby, a porous layer (1) was deposited on the polyethylene porous film. Thereafter, the laminate composed of the deposited porous layer (1) and the polyethylene porous film was washed with water and dried to obtain a separator (1) provided with the porous layer (1). The film thickness of the separator (1) was 13.0 μm.

[0122] [Example 2] The same operations as in Example 1 were carried out except that the solutions obtained in Synthesis Examples 1 and 2 were mixed so that the weight ratio of Resin A: Resin B was 50:50, and a separator (2) provided with a porous layer (2) was obtained. The film thickness of the separator (2) was 12.8 μm.

[0123] [Example 3] The same operations as in Example 2 were carried out except that the deposition time was 30 seconds, and a separator (3) provided with a porous layer (3) was obtained. The film thickness of the separator (3) was 13.1 μm.

[0124] [Example 4] The same operations as in Example 3 were carried out except that the clearance of the coating bar was changed to 70 μm to reduce the film thickness of the porous layer, and a separator (4) provided with a porous layer (4) was obtained. The film thickness of the separator (4) was 11.9 μm.

[0125] [Example 5] The same operations as in Example 2 were carried out except that the deposition time was 15 seconds, and a separator (5) provided with a porous layer (5) was obtained. The film thickness of the separator (5) was 13.1 μm.

[0126] [Example 6] The same operations as in Example 5 were carried out except that the clearance of the coating bar was changed to 70 μm to reduce the film thickness of the porous layer, and a separator (6) having a porous layer (6) was obtained. The film thickness of the separator (6) was 12.0 μm.

[0127] 〔Example 7〕 The same operations as in Example 2 were carried out except that the precipitation time was set to 10 seconds, and a separator (7) having a porous layer (7) was obtained. The film thickness of the separator (7) was 13.0 μm.

[0128] 〔Example 8〕 The same operations as in Example 7 were carried out except that the clearance of the coating bar was changed to 70 μm to reduce the film thickness of the porous layer, and a laminated separator (8) having a porous layer (8) was obtained. The film thickness of the separator (8) was 12.0 μm.

[0129] 〔Example 9〕 The same operations as in Example 7 were carried out except that the solutions obtained in Synthesis Examples 1 and 2 were mixed so that the weight ratio of Resin A: Resin B was 40:60, and the film thickness of the polyethylene porous film was changed to 8.3 μm, and a separator (9) having a porous layer (9) was obtained. The film thickness of the separator (9) was 9.6 μm.

[0130] 〔Example 10〕 The same operations as in Example 7 were carried out except that the solutions obtained in Synthesis Examples 1 and 2 were mixed so that the weight ratio of Resin A: Resin B was 30:70, and the film thickness of the polyethylene porous film was changed to 8.3 μm, and a separator (10) having a porous layer (10) was obtained. The film thickness of the separator (10) was 9.8 μm.

[0131] 〔Example 11〕 Separator (11) having a porous layer (11) was obtained by performing the same operations as in Example 7, except that the solutions obtained in Synthesis Examples 1 and 2 were mixed so that the weight ratio of Resin A: Resin B was 10:90, and the film thickness of the polyethylene porous film was changed to 8.3 μm. The film thickness of the separator (11) was 9.2 μm.

[0132] [Example 12] The same operations as in Example 7 were performed, except that a mixture (2) obtained by mixing the solutions obtained in Synthesis Examples 1 and 2 and the alumina was used so that the weight ratio of Resin A: Resin B: alumina (average particle size: 13 nm) was 50:50:20 instead of the mixture (1). As a result, a separator (12) having a porous layer (12) was obtained. The film thickness of the separator (12) was 14.3 μm.

[0133] [Example 13] The same operations as in Example 3 were performed, except that a mixture (3) obtained by mixing the solutions obtained in Synthesis Examples 1 and 2 and the alumina was used so that the weight ratio of Resin A: Resin B: alumina (average particle size: 13 nm) was 50:50:50 instead of the mixture (1). As a result, a separator (13) having a porous layer (13) was obtained. The film thickness of the separator (13) was 13.0 μm.

[0134] [Example 14] The same operations as in Example 3 were performed, except that a mixture (4) obtained by mixing the solutions obtained in Synthesis Examples 1 and 2 and the alumina was used so that the weight ratio of Resin A: Resin B: alumina (average particle size: 13 nm) was 50:50:80 instead of the mixture (1). As a result, a separator (14) having a porous layer (14) was obtained. The film thickness of the separator (14) was 13.4 μm.

[0135] [Comparative Example 1] Instead of the mixture (1), a mixture (5) was prepared by mixing the solutions obtained in Synthesis Examples 1 and 2 and the alumina such that the weight ratio of Resin A: Resin B: alumina (average particle size: 13 nm) was 50:50:100. The same operations as in Example 7 were performed except for using this mixture (5). A separator (12) having a porous layer (12) was obtained. The membrane thickness of the separator (12) was 13.9 μm.

[0136] 〔Comparative Example 2〕 Instead of the mixture (1), a mixture (6) was prepared by mixing the solution obtained in Comparative Synthesis Example 1 and the alumina such that the weight ratio of Resin C: alumina (average particle size: 13 nm) was 100:100. The same operations as in Example 7 were performed except for using this mixture (6). A separator (13) having a porous layer (13) was obtained. The membrane thickness of the separator (13) was 12.8 μm.

[0137] 〔Results〕 Table 1 shows the production conditions of the examples and comparative examples, specifically, the weight ratios of the raw materials used, the precipitation times, and the evaluation results of the produced porous layers and separators.

[0138]

Table 1

[0139] As shown in Table 1, the porous layers (1) to (11) have a ratio of average pore area of 1.80 or more. Also, the porous layers (1) to (11) have a ratio of average pore diameter of 1.25 or more. Therefore, the porous layers (1) to (11) and the separators (1) to (11) correspond to the porous layer according to one embodiment of the present invention and the separator for an electrochemical element according to one embodiment of the present invention.

[0140] The separators (1) to (11) have a smaller wetting area ratio than the separators (12) and (13) produced in Comparative Examples 1 and 2. Therefore, it is shown that the porous layers (1) to (11) constituting the separators (1) to (11) are excellent in wettability with the electrolyte, and the separators (1) to (11) are also excellent in wettability with the electrolyte.

[0141] From the above, it was found that both the separator for an electrochemical element according to an embodiment of the present invention and the porous layer according to an embodiment of the present invention are excellent in wettability with an electrolytic solution.

Industrial Applicability

[0142] One aspect of the present invention can be used in an electrochemical element.

Explanation of Signs

[0143] 1 Porous layer 2 Division region 3 Division region 4 Division region 5 Division region 6 Division region 7 Division region 8 Pore

Claims

1. Comprising a porous layer, The ratio of the maximum average pore area to the minimum average pore area among the average pore areas in each of the six divided regions obtained by dividing a cross-section parallel to the thickness direction passing through the center of the porous layer into six equal parts using a straight line perpendicular to the thickness direction is 1.80 or more, a separator for an electrochemical element.

2. Comprising a porous layer, The ratio of the maximum average pore diameter to the minimum average pore diameter among the average pore diameters in each of the six divided regions obtained by dividing a cross-section parallel to the thickness direction passing through the center of the porous layer into six equal parts using a straight line perpendicular to the thickness direction is 1.25 or more, a separator for an electrochemical element.

3. The separator for an electrochemical element according to claim 1 or 2, wherein the film thickness of the porous layer is 0.15 to 5 μm.

4. The basis weight of the porous layer is 0.15 to 10 g / m ２ The separator for an electrochemical element according to claim 1 or 2, wherein the basis weight is as defined above.

5. In the cross-section, the number of pores per 1 μm ２ The separator for an electrochemical element according to claim 1 or 2, wherein the number of pores per 1 μm is 30 or more.

6. The separator for an electrochemical element according to claim 1 or 2, wherein the divided region having the minimum average pore area among the six divided regions is located on the outermost surface of the porous layer.

7. The separator for an electrochemical element according to claim 1 or 2, wherein the air permeability of the porous layer is 150 sec / 100 cc or less.

8. The separator for an electrochemical element according to claim 1 or 2, wherein the porous layer contains an aramid resin.

9. Comprising a polyolefin porous substrate, The separator for an electrochemical element according to claim 1 or 2, wherein the porous layer is laminated on the polyolefin porous substrate.

10. The separator for an electrochemical element according to claim 9, further comprising an adhesive layer separately from the polyolefin porous substrate and the porous layer.

11. The separator for an electrochemical element according to claim 9, wherein the air permeability is 330 sec / 100 cc or less.

12. A member for an electrochemical element in which a positive electrode, the separator for an electrochemical element according to claim 1 or 2, and a negative electrode are arranged in this order.

13. An electrochemical element comprising the separator for an electrochemical element according to claim 1 or 2.

14. The electrochemical element according to claim 13, which is a secondary battery or a capacitor.

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