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

Abstract

To provide a separator for an electrochemical element with improved cycle characteristics, especially cycle characteristics at high rates.SOLUTION: The separator for electrochemical element according to the present disclosure includes: a polyolefin porous base material; and a porous layer on the polyolefin porous base material. When a cycle of applying a pressure of 70 MPa to the surface for 60 seconds, removing the load, and causing the separator to stand for 60 seconds is performed two times, the product of the compression rate in the first cycle and in the second cycle and the restoration rate is at least 850%2.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 equipped with a conventional separator such as the separator described in Patent Document 1 has room for improvement in terms of cycle characteristics, particularly cycle characteristics at high rates. One aspect of the present invention aims to provide a separator for an electrochemical element that can improve the cycle characteristics of the electrochemical element, particularly the cycle characteristics at high rates.

Means for Solving the Problems

[0006] As a result of the inventors' intensive research, it has been found that a separator with a large product of the recovery rate with respect to the compression amount in the first cycle and the recovery rate with respect to the compression amount in the second cycle when repeating twice a cycle consisting of applying a specific pressure and then releasing the pressure can achieve the above object, leading to the present invention.

[0007] The separator for an electrochemical element according to one aspect of the present invention includes a polyolefin porous base material and a porous layer laminated on the polyolefin porous base material, and when repeating twice a cycle consisting of applying a pressure of 70 MPa to the surface for 60 seconds and then releasing the pressure and leaving it for 60 seconds, the product of the recovery rate [%] with respect to the compression amount in the first cycle and the recovery rate [%] with respect to the compression amount in the second cycle is 850% 2 or more.

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, particularly the cycle characteristics at a high rate.

Mode for Carrying Out the Invention

[0009] 〔1. Separator for Electrochemical Element〕 The separator for an electrochemical element according to one embodiment of the present invention includes a polyolefin porous base material and a porous layer laminated on the polyolefin porous base material, and when repeating twice a cycle consisting of applying a pressure of 70 MPa to the surface for 60 seconds and then releasing the pressure and leaving it for 60 seconds, the product of the recovery rate [%] with respect to the compression amount in the first cycle and the recovery rate [%] with respect to the compression amount in the second cycle is 850% 2 or more.

[0010] Hereinafter, the "separator for an electrochemical element according to an embodiment of the present invention" is also simply referred to as "separator". The "polyolefin porous substrate" constituting the separator is also simply referred to as "porous substrate". The recovery rate [%] with respect to the compression amount in the first cycle when a cycle consisting of applying a pressure of 70 MPa to the surface for 60 seconds and then unloading and leaving it for 60 seconds is repeated twice is referred to as the "first recovery rate", and the recovery rate [%] with respect to the compression amount in the second cycle is referred to as the "second recovery rate". The product of the first recovery rate and the second recovery rate is referred to as the "product of the recovery rates".

[0011] In one embodiment of the present invention, "repeating a cycle consisting of applying a pressure of 70 MPa to the surface for 60 seconds and then unloading and leaving it for 60 seconds twice" means performing the operations shown in the following (a) to (h). (a) Perform an operation of applying a load of 70 MPa to the surface of the separator from the vertically upward direction. (b) Perform an operation of holding the load at 70 MPa for 60 seconds on the separator after performing the operation of (a). (c) Perform an operation of reducing the load on the separator after performing the operation of (b) until it becomes approximately 0 MPa. (d) Perform an operation of holding the load at approximately 0 MPa for 60 seconds on the separator after performing the operation of (c). (e) Perform the same operation as in (a) on the separator after performing the operation of (d). (f) Perform the same operation as in (b) on the separator after performing the operation of (e). (g) Perform the same operation as in (c) on the separator after performing the operation of (f). (h) Perform the same operation as in (d) on the separator after performing the operation of (g).

[0012] The specific method for performing the operations shown in (a) to (h) is not particularly limited, and for example, the methods described in the examples can be cited. Note that the operations shown in (a) to (h) are usually carried out under the condition of room temperature (about 25°C).

[0013] The "surface" in the operation of (a) means the surface on the porous layer side of the separator. In the case where the porous layer is laminated on both surfaces of the porous substrate in the separator, the "surface" may be the surface on either porous layer side of the separator.

[0014] The method for applying the load in the operation of (a) is not particularly limited, and examples include a method of pushing a flat platen into the surface of the separator, and a method of pressing the separator from the surface side using a press machine, etc.

[0015] The method for holding the load in the operation of (b) is not particularly limited. As the method for holding the load in the operation of (b), for example, when a flat platen is pushed into the surface to apply a load in the operation of (a), a method of fixing (holding) the position of the flat platen as it is in the state of being pushed into the surface can be cited. Also, as the method for holding the load in the operation of (b), for example, when the load is applied by the press in the operation of (a), a method of continuing the press while holding the load can be cited. The method of continuing the press while holding the load is specifically a method of carrying out the press under the conditions of a press pressure of 70 MPa and a press time of 60 seconds in the operation of 1. above.

[0016] The method for reducing the load in the operation (c) is not particularly limited. Examples of the method for reducing the load include, when a flat indenter is pushed into the surface to apply a load in the operation (a), pulling up the flat indenter from the surface. Further, examples of the method for reducing the load include, when the load is applied by the press in the operation (a), stopping (interrupting) the press and releasing the separator from the load.

[0017] "Approximately 0 MPa" in the operation (c) means 0 MPa or a pressure approximating 0 MPa. The exact value of the pressure approximating 0 MPa can be, for example, 1 mN.

[0018] The method for holding the load in the operation (d) is not particularly limited. Examples of the method for holding the load in the operation (d) include, when the flat indenter is pulled up from the surface to reduce the load in the operation (c), fixing the position of the flat indenter in the state of being pulled up from the surface as it is. Further, examples of the method for holding the load in the operation (d) include, when the press is interrupted to reduce the load in the operation (c), continuing the interruption of the press.

[0019] Here, the displacement amount of the indenter from the start of the operation (a) to the end of the operation (b) is defined as the compression amount in the first cycle. Hereinafter, the "compression amount in the first cycle" is referred to as the "first compression amount". Further, after the operation (b) is performed, the displacement amount of the indenter from the start of the operation (c) to the end of the operation (d) is defined as the restoration amount in the first cycle. Hereinafter, the "restoration amount in the first cycle" is referred to as the "first restoration amount". Using the first compression amount and the first restoration amount, the first restoration rate is calculated based on the following formula (1). First restoration rate [%] = (First restoration amount [μm] / First compression amount [μm]) × 100 ··· (1) After performing the operation of (d), the displacement amount of the pressure plate from the start of the operation of (e) to the end of the operation of (f) is defined as the compression amount in the second cycle. Hereinafter, the "compression amount in the second cycle" is referred to as the "second compression amount". Further, after performing the operation of (f), the displacement amount of the pressure plate from the start of the operation of (g) to the end of the operation of (h) is defined as the restoration amount in the second cycle. Hereinafter, the "restoration amount in the second cycle" is referred to as the "second restoration amount". Using the second compression amount and the second restoration amount, the second restoration rate is calculated based on the following formula (2). Second restoration rate [%] = (Second restoration amount [μm] / Second compression amount [μm]) × 100 ··· (2) Furthermore, using the first restoration rate and the second restoration rate, the product of the restoration rates is calculated based on the following formula (3). Product of restoration rates [% 2 = (First restoration rate [%]) × (Second restoration rate [%]) ··· (3) Note that the film thickness of the separator used when calculating the first compression amount, the first restoration amount, the second compression amount, and the second restoration amount means the film thickness at the location on the separator where the load is applied. The location where the load is applied is, for example, the location where the flat pressure plate is pushed into the surface to apply the load, or the directly pressed location when the load is applied by the press.

[0020] When a plurality of pressurization and unloading cycles are repeated for a conventional separator, the internal structure of the conventional separator is deformed by the pressurization in each cycle. Hereinafter, the "pressurization and unloading cycle" is also referred to as the "pressurization-unloading cycle". Due to the deformation of the internal structure, the conventional separator does not completely restore its shape during unloading in the pressurization-unloading cycle, and the restoration rate with respect to the compression amount in subsequent pressurization-unloading cycles decreases significantly, resulting in deterioration of its electrical characteristics. Hereinafter, the "restoration rate with respect to the compression amount" is also simply referred to as the "restoration rate". On the other hand, for the separator according to an embodiment of the present invention, the product of the restoration rates is 850%2 As described above, the first and second restoration rates are both large, which reflects that the first and second restoration rates are both large. From this, it can be understood that the separator has a small deformation of the internal structure due to pressurization in both the first and second cycles. Therefore, the separator has a property that the internal structure is not easily deformed by pressurization. Therefore, when the pressurization-unloading cycle is repeated multiple times, the degree to which the restoration rate relative to the compression amount in each pressurization-unloading cycle decreases as the repetition progresses is considered to be small. In other words, when the pressurization-unloading cycle is repeated three or more times, the separator is considered to have a large restoration rate in the third and subsequent pressurization-unloading cycles in addition to the restoration rates in the first and second pressurization-unloading cycles.

[0021] When the electrochemical element undergoes a charge / discharge cycle, the electrodes constituting the electrochemical element expand and contract. As the electrodes repeatedly expand and contract within the electrochemical element, a pressurization-unloading cycle is repeatedly generated for the separator constituting the electrochemical element.

[0022] In an electrochemical element, if the separator does not sufficiently follow the repeated expansion and contraction of the electrodes during repeated charge-discharge cycles, gaps may occur between the electrodes and the separator, increasing the resistance of the electrochemical element and deteriorating the cycle characteristics. Furthermore, when the charge-discharge cycles are performed at a high rate, the deterioration of the cycle characteristics due to the increase in resistance may become more noticeable.

[0023] On the one hand, when the separator according to an embodiment of the present invention repeatedly performs charge and discharge cycles in an electrochemical element including the separator, the recovery rate with respect to compression caused by the expansion and contraction of the electrode occurring during any charge and discharge among the repetitions is high. Further, due to the high recovery rate, the separator is less likely to undergo plastic deformation during the arbitrary charge and discharge cycles, and is more likely to deform in accordance with an external force applied later. Therefore, the separator is likely to follow the repeated expansion and contraction of the electrode resulting from charge and discharge cycles after the arbitrary charge and discharge cycle.

[0024] As described above, the separator can sufficiently follow the repeated expansion and contraction of the electrode. Therefore, the separator can prevent the deterioration of the above-described cycle characteristics that may occur when repeatedly performing charge and discharge cycles, particularly high-rate charge and discharge cycles, in the electrochemical element including the separator. Accordingly, the separator can improve the cycle characteristics of the electrochemical element including the separator, particularly the cycle characteristics at a high rate.

[0025] From the viewpoint of improving the cycle characteristics of the above-described electrochemical element, particularly the cycle characteristics at a high rate, the product of the recovery rates is preferably a large value. Specifically, the lower limit value of the product of the recovery rates is preferably 850% 2 or more, more preferably 900% 2 or more, and even more preferably 910% 2 or more. Note that the upper limit value of the product of the recovery rates is 10000% 2 or less, as described later, since the upper limits of both the first recovery rate and the second recovery rate are 100%.

[0026] From the perspective of controlling the product of the restoration rates to a large value and improving the cycle characteristics of the electrochemical element, particularly the cycle characteristics at high rates, the first restoration rate and the second restoration rate are preferably large values. Specifically, the lower limit of the first restoration rate is preferably 10% or more, more preferably 11% or more, and even more preferably 11.5% or more. Also, the lower limit of the second restoration rate is preferably 75% or more, more preferably 76% or more, and even more preferably 77% or more. Note that the upper limits of both the first restoration rate and the second restoration rate are 100%.

[0027] Also, when the first compression amount and the second compression amount are large, the separator is more likely to deform according to an external force and has excellent followability to the expansion of the electrode. As a result, the cycle characteristics of the electrochemical element, particularly the cycle characteristics at high rates, can be further improved. From the above perspective, the ratio [%] (hereinafter referred to as the "first compression rate") of the first compression amount to the film thickness before compression in the first cycle of the separator is preferably 30% or more, more preferably 35% or more. Also, the ratio [%] (hereinafter referred to as the "second compression rate") of the second compression amount to the film thickness before compression in the second cycle after the first cycle of the separator is preferably 5% or more, more preferably 7% or more.

[0028] When the first compression amount and the second compression amount are small, the separator is more excellent in terms of strength. From the above perspective, the first compression rate [%] is preferably 70% or less, more preferably 65% or less. Also, the second compression rate [%] is preferably 30% or less, more preferably 20% or less.

[0029] The separator includes a polyolefin porous base material and a porous layer laminated on the polyolefin porous base material. That is, the separator is a separator in which the porous layer and the polyolefin porous base material are laminated. The porous layer can be laminated on one or both surfaces of the polyolefin porous base material.

[0030] The separator may consist only of the porous layer and the porous base material, or layers different from the porous layer and the porous base material may be laminated as described later. The porous layer can be disposed between the porous base material and at least one of the positive electrode and the negative electrode as a member constituting the electrochemical element. The porous layer may be disposed between the porous base material and at least one of the positive electrode and the negative electrode so as to be in contact with them. The porous layer disposed between the porous base material and at least one of the positive electrode and the negative electrode may be one layer or two or more layers. The porous layer is preferably an insulating layer.

[0031] The porous layer usually contains a resin. The resin is not limited, and for example, it is a nitrogen-containing aromatic resin. A nitrogen-containing aromatic resin means an aromatic resin containing a nitrogen atom. An aromatic resin means a resin containing a structural unit having at least an aromatic group.

[0032] 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.

[0033] 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'-benz anilide terephthalamide), poly(paraphenylene-4,4'-biphenylene dicarboxamide), poly(paraphenylene-2,6-naphthalenedicarboxamide), poly(2-chloro-paraphenylene terephthalamide), para-phenylene terephthalamide / 2,6-dichloro para-phenylene terephthalamide copolymer, poly(4,4'-diphenylsulfonyl terephthalamide), para-phenylene terephthalamide / 4,4'-diphenylsulfonyl terephthalamide copolymer, 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].

[0034] 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 used.

[0035] 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.

[0036] The porous layer may contain a nitrogen-containing aromatic resin and a resin other than the nitrogen-containing aromatic resin. However, 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.

[0037] 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.

[0038] Examples of the polyester resin include aromatic polyesters such as polyarylate and liquid crystal polyesters.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] Examples of the water - soluble polymer include polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide, polymethacrylic acid, etc.

[0043] The porous layer can be a heat - resistant layer. The heat - resistant layer means a layer with 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 with 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.

[0044] The porous layer may contain a filler. The filler may be an inorganic filler or an organic filler. As the filler, a filler composed of 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.

[0045] The content of the filler in 100% by weight of the porous layer is preferably 0% by weight or more and less than 20% by weight, more preferably 0 to 15% by weight, even more preferably 0 to 10% by weight, and particularly preferably 0 to 5% by weight. That the content of the filler is 0% by weight means that the porous layer does not contain 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.

[0046] 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 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. 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 extracted 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.

[0047] 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 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. 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. In addition, an increase in the distance between the positive electrode and the negative electrode can also be suppressed, so that a decrease in the internal volume efficiency of the electrochemical element can be suppressed.

[0048] 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 one 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 the volume energy density of the electrochemical element can be increased.

[0049] 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 of the porous layer is preferably 1.0 μm or less, more preferably 0.5 μm or less. By setting the pore diameter of the pores to these sizes, the electrochemical element can obtain sufficient ion permeability.

[0050] The polyolefin porous substrate means a porous substrate mainly composed of a polyolefin resin. "Mainly composed of a polyolefin resin" means that the proportion of the polyolefin resin in the porous substrate is 50% by weight or more, preferably 90% by weight or more, and more preferably 95% by weight or more of the total materials constituting the porous substrate. The porous substrate 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 resulting 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 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, 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.

[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 that the weight energy density and the volume energy density of the electrochemical device can be increased, 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 preferred.

[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, more preferably 50 to 300 s / 100 mL. By having the above - mentioned air permeability, 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.

[0057] 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 holding 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.

[0058] 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.

[0059] The air permeability of the separator is preferably 30 to 1000 s / 100 mL, more preferably 50 to 800 s / 100 mL, and even more preferably 70 to 500 s / 100 mL. By having the air permeability, the separator can obtain sufficient ion permeability in the electrochemical device. The air permeability represents a value measured with a Wang Research air permeability tester in accordance with JIS P8117.

[0060] The separator may optionally include another functional layer different from the aforementioned 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.

[0061] The other functional layer may be provided on one or both sides of the separator. When the separator is provided with the aforementioned porous layers on both sides of the porous 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 aforementioned 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 may be provided as the outermost layer of the separator.

[0062] 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 may be provided on the surface of the separator that contacts the electrode. Examples of the component contributing to the adhesiveness included in the adhesive layer include acrylic resin and PVdF.

[0063] 〔2. Method for manufacturing separator for electrochemical element〕 A porous layer can be formed on a porous substrate using a coating liquid obtained by dissolving or dispersing a resin in a solvent, and the separator can be manufactured. Note that the solvent can also be said to be a dispersion medium for dispersing the resin. Examples of the resin include the aforementioned nitrogen-containing aromatic resin and resins other than the nitrogen-containing aromatic resin. Examples of the method for forming the coating liquid include a mechanical stirring method, an ultrasonic dispersion method, a high-pressure dispersion method, a media dispersion method, and the like.

[0064] Examples of the method for forming the separator include: a method of directly applying the coating liquid to the surface of the porous substrate and then removing the solvent; a method of applying the coating liquid to a suitable support, removing the solvent to form a porous layer, pressing the porous layer and the porous substrate together, and then peeling off the support; a method of applying the coating liquid to a suitable support, pressing the porous substrate onto the coated surface, peeling off the support, and then removing the solvent; and a method of performing dip coating by immersing the porous substrate in the coating liquid and then removing the solvent.

[0065] The solvent preferably has no adverse effect on the porous 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.

[0066] 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.

[0067] As a method for applying the coating liquid to the porous substrate, a conventionally known method can be adopted. Specifically, for example, a gravure coater method, a dip coater method, a bar coater method, a die coater method, and the like can be mentioned.

[0068] 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. Specific methods for applying moisture to the coating surface are not particularly limited, and examples include exposing to an atmosphere with high humidity, spraying water with a spray or the like, and spraying steam with a nozzle or the like.

[0069] The method for manufacturing the porous substrate is not particularly limited. For example, a sheet-like polyolefin resin composition is produced by kneading a polyolefin-based resin, a pore-forming agent such as an inorganic filler or a plasticizer, and optionally an antioxidant or the like, and then extruding. Then, the pore-forming agent 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-forming agent 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 the conditions shown in the following (i), a separator in which the product of the reduction rates is controlled within a range of 850% 2 or more can be manufactured. (i) Using a coating liquid with a low filler content or a coating liquid containing no filler as the coating liquid.

[0072] When the condition (i) is satisfied, a porous layer that does not contain the filler or contains a small amount of the filler, that is, a porous layer containing a large amount of resin, can be obtained. Here, the porous layer has a network structure composed of fibers made of resin. In the porous layer, when the network structure is maintained against an external force, the shape of the porous layer is retained, or even when the shape is deformed, a force acts to restore it to the original shape, and plastic deformation is suppressed. Further, when the porous layer contains a filler, the filler penetrates into the resin, so that the network structure is interrupted by the filler, and as a result, it is difficult to maintain the network structure when an external force is applied. Therefore, a porous layer with a high filler content is considered to be such that the network structure collapses against an external force, and its porous structure is likely to change irreversibly, and the degree of plastic deformation increases. On the other hand, in a porous layer that does not contain a filler or contains a small amount of a filler, there is no such interruption or the interruption is small, and the network structure is easily maintained even when an external force is applied. Therefore, a porous layer that does not contain a filler or contains a small amount of a filler is considered to have a small degree of plastic deformation because the network structure is maintained and deformed against an external force.

[0073] In addition to satisfying the condition (i), by satisfying one or more of the conditions (ii) to (iv) shown below, the product of the restoration rates can be preferably controlled to a value of 850% 2 or higher. (ii) The resin in the coating liquid contains two or more types of resins having different precipitation properties, or contains two or more components having different precipitation properties. (iii) When removing the solvent in the coating liquid to precipitate the porous layer, adjusting the precipitation time to a certain time or longer. (iv) As a precipitation method, changing the humidity of the precipitation layer over time.

[0074] After satisfying the condition (i), when the condition (ii) is satisfied, the product of the restoration rates is 850%2 The mechanism that can be preferably controlled within the above range is presumably the mechanism shown below. When the condition (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. Due to the compatibility relationship between the second resin or the second component and the solvent with the first resin or the first component that has precipitated first, it precipitates in the vicinity of the first resin or the first component that has precipitated first. By such uneven precipitation of the resin or component, a resin network structure that is easily maintained even when subjected to an external force can be sufficiently formed. Therefore, when the condition (ii) is satisfied, it is considered that the product of the restoration rates can be controlled to a value of 850% 2 or higher.

[0075] 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 types of components with different precipitation properties can be, for example, a resin with a wide molecular weight distribution. That is, by using one or more types of resins with a wide molecular weight distribution after satisfying the condition (i), a separator in which the product of the restoration rates is controlled to a value of 850% 2 or higher can be preferably manufactured.

[0076] Also, when the condition (iii) is satisfied after satisfying the condition shown in (i), by adjusting the precipitation time to a certain time or more, the time from when the resin that is easy to precipitate precipitates until the resin that is difficult to precipitate precipitates becomes longer. As a result, the fibers composed of the resin constituting the porous layer and the network structure composed of the fibers can be sufficiently formed. Therefore, by satisfying the above-mentioned conditions, the first restoration rate and the second restoration rate can be adjusted to high values, and the product of the restoration rates can be controlled to a value of 850% 2 or higher. Specifically, the precipitation time may be preferably adjusted to 5 seconds or more, more preferably 10 seconds or more.

[0077] Furthermore, when the condition (iv) is satisfied after satisfying the condition (i), by changing the humidity in the precipitation tank over time, the precipitation rates in the initial and later stages change, and by the same mechanism as when the condition (ii) is satisfied, the product of the restoration rates is 850% 2 or more, it is considered that a separator with a high value can be more preferably manufactured.

[0078] As described above, the porous layer obtained when the condition (i) is satisfied is considered to be less likely to undergo plastic deformation. Therefore, the porous layer is easily restored in shape against deformation by an external force, and the first restoration rate and the second restoration rate become high. As a result, the product of the restoration rates is 850% 2 or more, and it is considered that it can be controlled to a high value. In addition to the condition (i), when one or more of the conditions (ii) to (iv) are satisfied, the obtained porous layer has a higher first restoration rate and second restoration rate. As a result, the product of the restoration rates is 850% 2 or more, and it is considered that it can be more preferably controlled to a high value.

[0079] [3. Member for Electrochemical Element, Electrochemical Element] In a member for an electrochemical element according to an embodiment of the present invention, a positive electrode, the separator for an electrochemical element described above, and a negative electrode are arranged in this order. Further, an electrochemical element according to an embodiment of the present invention includes the separator for an electrochemical element described above.

[0080] 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.

[0081] For example, an electrochemical element member can be formed by arranging a positive electrode, the aforementioned separator, and a negative electrode in this order. Here, the porous layer can 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 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.

[0082] <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.

[0083] Examples of the positive electrode active material include materials capable of doping and undoping metal ions such as lithium ions or sodium ions. Specifically, 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.

[0084] 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 fibrous carbon materials such as graphitized carbon fibers and carbon nanotubes are used as the conductive agent, this proportion can be reduced.

[0085] As the binder, a thermoplastic resin can be used. Examples thereof include 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. Note that the binder also has a function as a thickener. These thermoplastic resins may be used as a mixture of two or more kinds. 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.

[0086] 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.

[0087] 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 it, and then pressing it to fix it to the positive electrode current collector.

[0088] 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; and amide solvents such as dimethylacetamide and NMP.

[0089] 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.

[0090] <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. The active material layer may further contain a conductive agent.

[0091] 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 potential lower than that of the positive electrode. Examples of carbonaceous materials include natural graphite, artificial graphite, cokes, carbon black, and pyrolytic carbons.

[0092] 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

[0093] 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

[0094] 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.

[0095] 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.

[0096] In addition, examples of metals that can be used as the negative electrode active material include lithium metal, silicon metal, and tin metal.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] <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.

[0103] 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 substituted 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 charged and discharged 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 negative electrode active material.

[0104] 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.

[0105] One embodiment of the present invention may include the following configuration. <1> A separator for an electrochemical element, comprising a porous polyolefin substrate and a porous layer laminated on the porous polyolefin substrate, and when repeating twice a cycle consisting of applying a pressure of 70 MPa to the surface for 60 seconds and then releasing the pressure and leaving it for 60 seconds, the product of the recovery rate [%] with respect to the compression amount in the first cycle and the recovery rate [%] with respect to the compression amount in the second cycle is 850% 2 or more. <2> The separator for an electrochemical element according to <1>, wherein the recovery rate with respect to the compression amount in the second cycle is 76% or more. <3> The separator for an electrochemical element according to <1> or <2>, wherein the recovery rate with respect to the compression amount in the first cycle is 10% or more. <4> The separator for an electrochemical element according to any one of <1> to <3>, wherein the porous layer contains an aramid resin. <5> The separator for an electrochemical element according to any one of <1> to <4>, further comprising an adhesive layer separately from the porous polyolefin substrate and the porous layer. <6> A member for an electrochemical element, in which a positive electrode, a separator for an electrochemical element according to any one of <1> to <5>, and a negative electrode are arranged in this order. <7> An electrochemical element including the separator for an electrochemical element according to any one of <1> to <5>. <8> The electrochemical element according to <7>, which is a secondary battery or a capacitor.

Example

[0106] An example of the present invention will be described below.

[0107] 〔Measurement and evaluation of physical properties〕 For the separators described in the examples and comparative examples, the physical properties were measured and evaluated by the methods shown below.

[0108] <Film thickness> The film thickness of the separator was measured using a high-precision digital length measuring instrument (manufactured by Mitutoyo Corporation). Specifically, each separator was cut into a square with a side length of 8 cm, and five-point measurements were taken within the range of the square. The film thickness of the separator before compression was determined from the average value of these five points.

[0109] Also, in the calculation of the first compression amount, the first restoration amount, the second compression amount, and the second restoration amount described below, the change amount of the film thickness of the separator accompanying compression or unloading was measured with respect to the location where the flat indenter was pushed in.

[0110] <The first compression amount, the first restoration rate, the second compression amount, the second restoration rate, the product of the restoration rates, the first compression rate, and the second compression rate> (Measurement of the film thickness before compression, the contact start point between the indenter and the separator, the indenter position after the first compression, the indenter position after the first restoration, and the indenter position after the second restoration) The film thickness of the separator before compression, the indenter position after the first compression, the indenter position after the first restoration, the indenter position after the second compression, and the indenter position after the second restoration were measured according to the following procedures 1. to 7. 1. The film thickness of the separator before compression was measured by the method described above. 2. The separator was cut out into a 1.5 cm square. The cut-out separator was adhered to the sample stage as a sample. 3. Using a micro-compression tester (MCT-510, manufactured by Shimadzu Corporation), a diamond flat indenter with a diameter of 50 μm was pushed into the surface of the sample. The pushing speed of the flat indenter was set to 1.0 mN / s. The indenter was pushed in until the load applied to the surface reached 138 mN (70 MPa). At this time, the position where the load began to rise was defined as the contact start point Z0 between the indenter and the separator. 4. Immediately after the load applied to the surface reached 70 MPa, the position of the flat indenter was fixed (held) in the state of being pushed into the surface for 60 seconds. The indenter position at this time was defined as the indenter position Z1 after the first compression. 5. The flat indenter was lifted from the surface until the load applied to the surface reached 1 mN (≈0 MPa). 6. Immediately after the load applied to the surface reached 1 mN (≈0 MPa), the flat indenter was lifted from the surface and fixed (held) in that state for 60 seconds. The position of the indenter at this time was defined as the indenter position Z2 after the first restoration. 7. For the sample on which the operation in 6. was performed, the same operations as in 3. to 6. were performed one more time. Here, the indenter position when the same operation as in 4. was performed was defined as the indenter position Z3 after the second compression. Also, the indenter position when the same operation as in 6. was performed was defined as the indenter position Z4 after the second restoration.

[0111] (Calculation of the first compression amount, the first restoration rate, the second compression amount, the second restoration rate, the product of the restoration rates, the first compression rate, and the second compression rate) The first compression amount was calculated by the following formula (4).

[0112] First compression amount = indenter position Z1 after the first compression - contact start point Z0 ··· (4) The first restoration amount was calculated by the following formula (5).

[0113] First restoration amount = indenter position Z1 after the first compression - indenter position Z2 after the first restoration ··· (5) The second compression amount was calculated by the following formula (6).

[0114] Second compression amount = indenter position Z3 after the second compression - indenter position Z2 after the first restoration ··· (6) The second restoration amount was calculated by the following formula (7).

[0115] Second restoration amount = indenter position Z3 after the second compression - indenter position Z4 after the second restoration ··· (7) Using the first compression amount and the first restoration amount, the first restoration rate [%] of the separator was calculated based on the following formula (1). First restoration rate [%] = (first restoration amount [μm] / first compression amount [μm]) × 100 ··· (1) Using the second compression amount and the second restoration amount, the second restoration rate [%] of the separator was calculated based on the following formula (2). Second restoration rate [%] = (Second restoration amount [μm] / Second compression amount [μm]) × 100 ··· (2) Using the first restoration rate [%] and the second restoration rate [%], the product of the restoration rates of the separator was calculated based on the following formula (3). Product of restoration rates [% 2 = (First restoration rate [%]) × (Second restoration rate [%]) ··· (3) Using the film thickness before compression and the first compression amount in the separator, the first compression rate of the separator was calculated based on the following formula (8). First compression rate [%] = (First compression amount [μm] / Film thickness before compression [μm]) × 100 ··· (8) Using the film thickness before compression, the first compression amount, the first restoration amount, and the second compression amount in the separator, the second compression rate of the separator was calculated based on the following formula (9). Second compression rate [%] = (Second compression amount [μm] / (Film thickness before compression [μm] - First compression amount [μm] + First restoration amount [μm]) × 100 ··· (9) <Cycle characteristics> (Fabrication of non-aqueous electrolyte secondary battery) A test non-aqueous electrolyte secondary battery incorporating a separator was fabricated as an electrochemical element according to the following procedure. 1. A positive electrode with a thickness of 49.9 μm, a density of 2.97 g / cm 3 , and a void volume of 24.4 μL was prepared. The positive electrode had a structure in which a positive electrode active material layer was laminated on a positive electrode current collector. The composition of the positive electrode active material layer was, by weight ratio, LiNi 0.78 Co 0.19 Al 0.03 O2: Conductive agent: Polyvinylidene fluoride = 92:4:4. Also, the positive electrode current collector was a conductor made of aluminum, and the conductive agent was acetylene black. 2. A thickness of 71.2 μm and a density of 1.45 g / cm 3, An anode with a void volume of 41.3 μL was prepared. The anode has a structure in which an anode active material layer is laminated on an anode current collector. The composition of the anode active material layer was artificial graphite: styrene-butadiene rubber: carboxymethyl cellulose = 96.5:2.0:1.5 by weight ratio. Also, the anode current collector was a conductor made of copper. The anode, separator, and cathode prepared in 3.2 were laminated in the order of the anode, the separator, and the cathode to produce a member for a non-aqueous electrolyte secondary battery. At this time, the anode and the separator were laminated so that the anode active material layer in the anode faced the surface of the separator on the polyolefin base material side. Also, the cathode and the separator were laminated so that the cathode active material layer in the cathode faced the surface of the separator on the porous layer side. The member for a non-aqueous electrolyte secondary battery prepared in 3 was stored in a bag in which an aluminum layer and a heat-sealing layer were laminated, and then a non-aqueous electrolyte was injected into the bag. The injection amount of the non-aqueous electrolyte was 230 μL. As the non-aqueous electrolyte, a non-aqueous electrolyte prepared by dissolving vinylene carbonate and LiPF6 in a mixed solvent so that the concentration of the vinylene carbonate was 1% by weight and the concentration of the LiPF6 was 1 mol / L was used. As the mixed solvent, a mixed solvent obtained by mixing ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate at a ratio of ethylene carbonate: ethyl methyl carbonate: diethyl carbonate = 3:5:2 (volume ratio) was used. While reducing the pressure inside the bag in which the member for a non-aqueous electrolyte secondary battery prepared in 4 was stored and the non-aqueous electrolyte was injected, the bag was heat-sealed. Thereby, a test non-aqueous electrolyte secondary battery was produced.

[0116] (Measurement of capacity retention rate) The discharge capacity of the produced test non-aqueous electrolyte secondary battery was measured according to the following procedure. 1. For the test non-aqueous electrolyte secondary battery, the first charge-discharge cycle was performed under the conditions of temperature: 25 °C, voltage range: 2.7 to 4.2 V, and current value: 0.1 C (during charging) or 0.2 C (during discharging). Here, 1 C is the current value for discharging the rated capacity based on the discharge capacity at the 1-hour rate in 1 hour. 2. For the test non-aqueous electrolyte secondary battery after performing the first charge-discharge cycle in 2.1., charge-discharge was performed 10 cycles at a temperature of 25 °C, a voltage range of 2.7 to 4.2 V, and a current value of 1 C (during charging) or 5 C (during discharging), and the test non-aqueous electrolyte secondary battery was aged. 3. For the test non-aqueous electrolyte secondary battery after aging in 2., charge-discharge was performed for 1 cycle at a temperature of 25 °C, a voltage range of 2.7 to 4.2 V, and a current value of 0.2 C (during charging) or 0.2 C (during discharging). Also, the discharge capacity in the 1 cycle of charge-discharge was measured. The measured discharge capacity was taken as the initial capacity (mAh). 4. For the test non-aqueous electrolyte secondary battery after performing 1 cycle of charge-discharge in 3., charge-discharge was performed 200 cycles under the conditions of temperature: 45 °C, voltage range: 2.7 to 4.2 V, and current value: 1 C (during charging) or 5 C (during discharging). The discharge capacity in the 200th cycle of charge-discharge among the 200 cycles of charge-discharge was measured. The measured discharge capacity in the 200th cycle of charge-discharge was taken as the discharge capacity (mAh) after 200 cycles. The value obtained by dividing the discharge capacity (mAh) after 200 cycles by the initial capacity (mAh) was taken as the capacity retention rate after 200 cycles.

[0117] [Synthesis Example 1: Synthesis of Resin A] Resin A (poly(4,4'-diphenylsulfonylterephthalamide)) was synthesized by 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 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 dichloride was added in three portions. 5. While maintaining the temperature of the obtained 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-phenylene terephthalamide)) 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 p-phenylenediamine was added and completely dissolved. 4. While maintaining the temperature of the solution at 25 ± 2 °C, a total of 24.24 g of terephthaloyl dichloride was added in three portions. 5. While maintaining the temperature of the obtained solution at 25 ± 2 °C, the solution was aged for 1 hour to obtain a solution containing Resin B.

[0119] [Example 1] A separator was prepared by laminating a porous layer with a weight ratio of resin A: resin B: alumina of 50:50:5 on a porous substrate. Specifically, the solutions obtained in Synthesis Examples 1 and 2 were mixed so that the weight ratio of resin A: resin B 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 a neutralized solution (1) was obtained. Then, alumina (average particle size: 13 nm) was added to the neutralized solution (1) so that the weight ratio of resin A: resin B: 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.

[0120] The coating solution (1) was applied to a polyethylene porous film (thickness: 10.3 μm, air permeability: 180 s / 100 mL), which is a porous substrate, and a porous layer (1) was deposited on the porous substrate in a deposition layer at 50 °C and 70% humidity. The deposition time was 10 seconds. Then, it was washed with water and dried to obtain a laminated separator in which a porous layer (1) was laminated on the porous substrate. The obtained laminated separator was designated as separator (1). The film thickness of separator (1) was 12.6 μm.

[0121] 〔Example 2〕 A separator having a porous layer containing no alumina and a weight ratio of resin A: resin B of 50:50 was manufactured. Specifically, the same operations as in Example 1 were performed except that alumina was not added to the neutralized solution (1), and a laminated separator in which a porous layer (2) was laminated on the porous substrate was obtained. The obtained laminated separator was designated as separator (2). The film thickness of separator (2) was 13.0 μm.

[0122] 〔Example 3〕 A separator having a porous layer that does not contain alumina and has a weight ratio of Resin A:Resin B of 70:30 was manufactured. Specifically, the same operations as in Example 2 were performed except that the solutions obtained in Synthesis Examples 1 and 2 were mixed so that the weight ratio of Resin A:Resin B was 70:30, and a laminated separator in which a porous layer (3) was laminated on a porous substrate was obtained. The obtained laminated separator was used as separator (3). The film thickness of separator (3) was 13.4 μm.

[0123] [Comparative Example 1] A separator having a porous layer with a weight ratio of Resin A:Resin B:Alumina of 50:50:100 was manufactured. Specifically, the same operations as in Example 1 were performed except that alumina was added to the neutralized solution (1) so that the weight ratio of Resin A:Resin B:Alumina was 50:50:100, and a laminated separator in which a porous layer (4) was laminated on a porous substrate was obtained. The obtained laminated separator was used as Comparative Separator (1). The film thickness of Comparative Separator (1) was 13.3 μm.

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

[0125] [Table 1]

[0126] As shown in Table 1, for Separators (1) to (3), the product of the recovery rates is 850% 2 or more. Therefore, Separators (1) to (3) correspond to the separator for an electrochemical element according to one embodiment of the present invention. On the other hand, for Comparative Separator (1), the product of the recovery rates is less than 850% 2 and does not correspond to the separator for an electrochemical element according to one embodiment of the present invention.

[0127] In addition, the non-aqueous electrolyte secondary battery including separators (1) to (3) has been shown to be superior in cycle characteristics, particularly in cycle characteristics at high rates, because the capacity retention rate after 200 cycles is higher than that of the non-aqueous electrolyte secondary battery including the comparative separator (1).

[0128] From the above, it has been found that the separator for an electrochemical element according to an embodiment of the present invention can improve the cycle characteristics of the electrochemical element including the separator for an electrochemical element, particularly the cycle characteristics at high rates.

Industrial Applicability

[0129] One aspect of the present invention can be used for an electrochemical element.

Claims

1. A separator for an electrochemical element, comprising a porous polyolefin substrate and a porous layer laminated on the porous polyolefin substrate, and The product of the recovery rate [%] with respect to the compression amount in the first cycle and the recovery rate [%] with respect to the compression amount in the second cycle when repeating twice a cycle consisting of applying a pressure of 70 MPa to the surface for 60 seconds and then releasing the pressure and leaving it for 60 seconds is 850% ２ or more, a separator for an electrochemical element.

2. The separator for an electrochemical element according to Claim 1, wherein the recovery rate with respect to the compression amount in the second cycle is 76% or more.

3. The separator for an electrochemical element according to Claim 1, wherein the recovery rate with respect to the compression amount in the first cycle is 10% or more.

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

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

6. A member for an electrochemical element, in which a positive electrode, the separator for an electrochemical element according to any one of Claims 1 to 5, and a negative electrode are arranged in this order.

7. An electrochemical element including the separator for an electrochemical element according to any one of Claims 1 to 5.

8. The electrochemical element according to Claim 7, which is a secondary battery or a capacitor.

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