JP2017027852A - Separator for power storage element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator material excellent in both adhesion to an electrode and ion permeability, and capable of manufacturing a battery having excellent battery characteristics in a short process time.SOLUTION: In a separator for a power storage element including a polyolefin porous base material, and a thermoplastic polymer layer placed on at least one side of the porous base material, the peel strength between the separator for a power storage element and an electrode is 0.147 N/cm or more, when the separator for a power storage element and the electrode are superposed and roll pressed at a press speed of 2 m/min., and the value obtained by subtracting the air permeability of the porous base material from that of the separator for a power storage element is 100 seconds or less.SELECTED DRAWING: None

Description

  The present invention relates to a separator for a storage element.

In recent years, development of power storage elements represented by lithium ion secondary batteries has been actively conducted. Usually, a power storage element is provided with a microporous film (separator) between positive and negative electrodes. Such a separator has a function of preventing direct contact between the positive and negative electrodes and allowing ions to permeate through the electrolytic solution held in the micropores.
In order to improve the cycle characteristics or safety of the nonaqueous electrolyte battery, improvement of the separator has been studied.

For example, Patent Document 1 aims to improve battery safety and suppress performance degradation by improving separator adhesion and preventing film peeling. The patent publication discloses a separator using styrene-butadiene rubber as an adhesive layer, and it is described that the separator is excellent in adhesion to electrodes and other members.
Patent Document 2 discloses a separator partially coated with a gel polymer as a separator for reducing battery resistance and improving battery power.
Patent Document 3 aims to provide a separator with a low thermal shrinkage rate even at high temperatures by increasing the efficiency of battery manufacture by increasing the adhesion of the separator. It is described that a separator formed by supporting a partially crosslinked adhesive on a substrate porous film achieves the above object.

Patent Document 4 discloses a porous membrane (separator) for a secondary battery that includes a polymer particle binder having a core-shell structure and non-conductive particles with respect to a separator that has high strength and is less likely to crack.
Patent Document 5 discloses a separator for a lithium secondary battery that has excellent heat resistance and improved battery safety, and includes a separator having a coating layer containing a binder having a specific glass transition temperature and organic particles. .
Patent Document 6 discloses a separator having an adhesive layer containing polymer particles having a specific core-shell structure.

Patent Documents 7 to 10 are intended to provide a lithium secondary battery excellent in high-temperature storage characteristics and charge / discharge cycle characteristics, and have a resin porous layer (I) mainly composed of a resin having a specific melting point, and a heat resistant temperature. A separator having a resin porous layer (II) containing a high filler and a resin binder is disclosed.
Patent document 11 relates to a separator whose adhesion is not impaired even in the presence of an electrolytic solution, and discloses a separator having a porous layer made of an insulating resin containing two types of adhesive resins having different gelation degrees. The separator is described as having high ionic conductivity over a wide temperature range.
Patent Documents 12 to 14 relate to a technique for providing a separator having high adhesiveness in a short process time. Each of these patent documents discloses a separator having an adhesive layer containing a polymer particle binder having a specific core-shell structure.

Special table 2008-521964 JP-T-2006-525624 JP 2004-342572 A International Publication No. 2011/040474 JP2013-251259A International Publication No. 2013/047853 JP 2014-170752 A JP 2014-026986 A JP 2011-0504502 A JP 2011-023186 A JP 2005-056800 A International Publication No. 2013/141140 International Publication No. 2013/146515 International Publication No. 2013/151144

In Patent Document 1, only the adhesion of the separator is evaluated in the example, and battery performance such as cycle characteristics is not verified at all. In Examples of Patent Documents 2 to 4, verification according to actual use of the battery is not performed.
In recent years, cost reduction and improvement in product yield in the battery manufacturing process have been screamed more strongly than ever before. Therefore, in the field of separators, in addition to the fact that the above-mentioned practical characteristics have been sufficiently verified, there is a demand to achieve both a reduction in process time and an improvement in separator adhesion at a high level. It is growing.
However, Patent Documents 5 and 6 do not consider the adhesiveness of the separator.

Patent Documents 6 to 12 are intended to provide a separator with high adhesiveness. However, in patent document 6, in the Examples, verification based on actual use of the battery is not performed. In patent documents 7-10, after forming resin porous layer (II) on resin porous layer (I), after performing press for 1 minute at 80 ° C, adhesiveness of a separator is evaluated. ;
In Patent Document 11, the formation of a porous layer made of an insulating resin is performed by a method of standing for 1 hour in a thermostatic chamber;
There is no recognition that there is a need to shorten the process time in the manufacture of separators.

Patent Documents 12 to 14 have a field of view similar to the present invention in that one of the purposes is to provide a separator having high adhesiveness in a short process time. However, in the examples of these patent documents, a time of 10 seconds is adopted as the press time in the production of the battery, and the effect of shortening the process time is insufficient.
The present invention has been made in view of the above situation. An object of the present invention is to provide a separator material for a storage element that can produce a battery having excellent battery characteristics in a short process time, and is excellent in both adhesion and adhesion to an electrode and ion permeability. With the goal.

The present invention for achieving the above object is as follows.
[1]
A separator for an electricity storage device comprising a polyolefin porous substrate, and a thermoplastic polymer layer disposed on at least one surface of the porous substrate,
The peel strength between the electricity storage element separator and the electrode when the electricity storage element separator and the electrode are overlapped and roll pressed at a pressing speed of 2 m / min is 0.147 N / cm or more, and The value obtained by subtracting the air permeability of the porous substrate from the air permeability of the electricity storage element separator is 100 seconds / 100 cc or less.
[2]
The thermoplastic polymer contained in the thermoplastic polymer layer is a particulate thermoplastic polymer, and using the Voronoi polygonal area (Si) obtained by Voronoi division of the particulate thermoplastic polymer, :
{Wherein Si is the actual value of the area of the Voronoi polygon, m is the average value of the area of the Voronoi polygon, and n is the total number of Voronoi polygons}. The storage device separator according to [1], wherein the dispersion (σ ² ) is 0.01 or more and 0.7 or less.
[3]
[1] or [2], wherein the surface coverage of the thermoplastic polymer layer is 5 to 80% with respect to the area of the surface of the polyolefin porous substrate on which the thermoplastic polymer layer is disposed. The separator for electrical storage elements described in 1.
[4]
[1] to [3] A storage element separator according to any one of
A positive electrode;
A negative electrode,
It is comprised from these, The laminated body characterized by the above-mentioned.
[5]
A wound body obtained by winding the laminated body according to [4].
[6]
[1] to [3] A storage element separator according to any one of
A positive electrode;
A negative electrode,
An electrolyte,
A secondary battery comprising:
[7]
[1] to [3] A storage element separator according to any one of
An electrode having an active material layer formed on at least one surface of the current collector and the current collector;
A method for manufacturing a power storage element, comprising a step of pressing for 1 second or less by superimposing the two.

  ADVANTAGE OF THE INVENTION According to this invention, the electrical storage element which is excellent in a battery characteristic can be manufactured in a short process time, and the separator for electrical storage elements which is excellent in both the adhesiveness with an electrode and ion permeability is provided. The electrical storage element separator can be suitably used as a separator of a lithium ion secondary battery, for example.

FIG. 1 shows an example of a photograph observing the surface of the polymer layer. FIG. 2 shows an example of a result of automatically specifying a thermoplastic polymer included in the observation visual field of FIG. 1 using image processing software. FIG. 3 shows an example of a result obtained by performing Voronoi division on the plurality of particles identified in FIG. 2 to obtain a Voronoi polygon. FIG. 4 shows an example of a result of automatically calculating the area of the Voronoi polygon obtained in FIG. 3 using image processing software. FIG. 5 shows an example of a method for setting one section composed of 19 views out of 95 views for observing the thermoplastic polymer particles arranged on the separator. FIG. 6 shows an example of a method for setting five sections including 95 visual fields for observing thermoplastic polymer particles arranged on a separator.

<Separator for power storage element>
The separator for an electricity storage device of the present invention includes a polyolefin porous substrate and a thermoplastic polymer layer disposed on at least one surface of the porous substrate. This electricity storage element separator may consist of only a polyolefin porous substrate and a thermoplastic polymer layer, or may further include a filler porous layer. When the separator for electrical storage elements of this invention has a filler porous layer, this filler porous layer is arrange | positioned at the single side | surface or both surfaces of a polyolefin porous base material. When the thermoplastic polymer layer is disposed on the surface having the filler porous layer, the mutual positional relationship between these is arbitrary, but the filler porous layer and the thermoplastic polymer layer may be laminated in this order on the polyolefin porous substrate. preferable.
Preferred embodiments of each member constituting the electricity storage element separator of the present invention and a method for producing the electricity storage element separator will be described in detail below.

[Polyolefin porous substrate]
Although it does not specifically limit as a polyolefin porous substrate in this embodiment, For example, the porous membrane comprised from the polyolefin resin composition containing polyolefin is mentioned, It is a porous membrane which has polyolefin resin as a main component. preferable. The content of the polyolefin resin in the polyolefin porous substrate in the present embodiment is not particularly limited, but from the viewpoint of shutdown performance when used as a separator for a power storage element, 50 mass of all components constituting the porous substrate. It is preferable that it is a porous film which consists of a polyolefin resin composition which polyolefin resin occupies% -100 mass%. The proportion of the polyolefin resin is more preferably 60% by mass or more and 100% by mass or less, and further preferably 70% by mass or more and 100% by mass or less.

The polyolefin resin is not particularly limited, and may be a polyolefin resin used for normal extrusion, injection, inflation, blow molding, and the like, and includes ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and Homopolymers and copolymers such as 1-octene, multistage polymers and the like can be used. In addition, polyolefins selected from the group consisting of these homopolymers and copolymers and multistage polymers can be used alone or in admixture.
Representative examples of the polyolefin resin are not particularly limited, but for example, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene Random copolymer, polybutene, ethylene propylene rubber and the like can be mentioned.
As a material for the polyolefin porous substrate used as a separator for an electricity storage device, it is preferable to use a resin mainly composed of high-density polyethylene because it has a low melting point and a high strength.

In order to improve the heat resistance of the polyolefin porous substrate, it is more preferable to use a porous film made of a resin composition containing polypropylene and a polyolefin resin other than polypropylene.
Here, the three-dimensional structure of polypropylene is not limited, and any of isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene may be used.
The ratio of polypropylene to the total polyolefin in the polyolefin resin composition is not particularly limited, but is preferably 1 to 35% by mass, more preferably 3 to 20% by mass from the viewpoint of achieving both heat resistance and a good shutdown function. %, More preferably 4 to 10% by mass.

  In this case, the polyolefin resin other than polypropylene is not limited. For example, homopolymers of olefin hydrocarbons such as ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene or the like Mention may be made of copolymers. Specifically, examples of the polyolefin resin other than polypropylene include polyethylene, polybutene, and ethylene-propylene random copolymer.

From the viewpoint of shutdown characteristics in which the pores of the polyolefin porous substrate are blocked by heat melting, polyolefin resins other than polypropylene include low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, etc. It is preferable to use polyethylene. Among these, from the viewpoint of strength, it is more preferable to use polyethylene having a density measured according to JIS K 7112 of 0.93 g / cm ³ or more.

  The viscosity average molecular weight of the polyolefin resin constituting the polyolefin porous substrate is not particularly limited, but is preferably 30,000 or more and 12 million or less, more preferably 50,000 or more and less than 2 million, and still more preferably 100,000. More than 1 million. A viscosity average molecular weight of 30,000 or more is preferable because the melt tension during melt molding increases, moldability is improved, and the strength tends to increase due to entanglement between polymers. On the other hand, when the viscosity average molecular weight is 12 million or less, it is easy to uniformly melt and knead, and it tends to be excellent in sheet formability, particularly thickness stability, which is preferable. Furthermore, when the viscosity average molecular weight is less than 1,000,000, it is preferable because pores are likely to be blocked when the temperature rises and a good shutdown function tends to be obtained.

For example, instead of using a polyolefin having a viscosity average molecular weight of less than 1 million alone, a mixture of a polyolefin having a viscosity average molecular weight of 2 million and a polyolefin having a viscosity average molecular weight of 270,000, the mixture having a viscosity average molecular weight of less than 1 million It may be used.
The polyolefin porous substrate in the present embodiment can contain any additive. Such additives are not particularly limited, and include, for example, polymers other than polyolefins; inorganic particles; antioxidants such as phenols, phosphoruss, and sulfurs; metal soaps such as calcium stearate and zinc stearate; Agents; light stabilizers; antistatic agents; antifogging agents; colored pigments and the like.
The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and still more preferably 5 parts by mass or less with respect to 100 parts by mass of the polyolefin resin composition.

The porosity of the polyolefin porous substrate in the present embodiment is not particularly limited, but is preferably 20% or more, more preferably 35% or more, preferably 90% or less, preferably 80% or less. Setting the porosity to 20% or more is preferable from the viewpoint of securing the permeability of the separator. On the other hand, setting the porosity to 90% or less is preferable from the viewpoint of securing the puncture strength. Here, the porosity is calculated, for example, from the volume (cm ³ ), mass (g), and membrane density (g / cm ³ ) of the polyolefin porous substrate sample:
Porosity = (volume−mass / film density) / volume × 100
It can ask for. Here, in the case of a polyolefin porous substrate made of, for example, polyethylene, the film density can be calculated assuming 0.95 (g / cm ³ ). The porosity can be adjusted by changing the draw ratio of the polyolefin porous substrate.

  The air permeability of the polyolefin porous substrate in the present embodiment is not particularly limited, but is preferably 10 seconds / 100 cc or more, more preferably 50 seconds / 100 cc or more, preferably 1,000 seconds / 100 cc or less, more Preferably, it is 500 seconds / 100 cc or less. The air permeability is preferably 10 seconds / 100 cc or more from the viewpoint of suppressing self-discharge of the electricity storage device. On the other hand, setting the air permeability to 1,000 seconds / 100 cc or less is preferable from the viewpoint of obtaining good charge / discharge characteristics. Here, the air permeability is an air resistance measured in accordance with JIS P-8117. The air permeability can be adjusted by changing the stretching temperature and / or stretching ratio of the porous substrate.

  The average pore diameter of the polyolefin porous substrate in the present embodiment is preferably 0.15 μm or less, more preferably 0.1 μm or less, and the lower limit is preferably 0.01 μm or more. Setting the average pore size to 0.15 μm or less is preferable from the viewpoint of suppressing self-discharge of the electricity storage device and suppressing capacity reduction. The average pore diameter can be adjusted by changing the draw ratio when producing a polyolefin porous substrate.

The puncture strength of the polyolefin porous substrate in the present embodiment is not particularly limited, but is preferably 200 g / 20 μm or more, more preferably 300 g / 20 μm or more, preferably 2,000 g / 20 μm or less, more preferably 1, 000 g / 20 μm or less. It is preferable that the puncture strength is 200 g / 20 μm or more from the viewpoint of suppressing film breakage due to the dropped active material or the like during battery winding, and from the viewpoint of suppressing the concern of short-circuiting due to expansion and contraction of the electrode accompanying charge / discharge. . On the other hand, a puncture strength of 2,000 g / 20 μm or less is preferable from the viewpoint of reducing width shrinkage due to orientation relaxation during heating. The puncture strength is measured by the method described in Examples below.
The puncture strength can be adjusted by adjusting the draw ratio and / or the draw temperature of the polyolefin porous substrate.

  The film thickness of the polyolefin porous substrate in the present embodiment is not particularly limited, but is preferably 2 μm or more, more preferably 5 μm or more, preferably 100 μm or less, more preferably 60 μm or less, and even more preferably 50 μm or less. . The film thickness of 2 μm or more is preferable from the viewpoint of improving mechanical strength. On the other hand, it is preferable to set the film thickness to 100 μm or less because the occupied volume of the separator in the battery is reduced, which tends to be advantageous in increasing the capacity of the battery.

[Filler porous layer]
The filler porous layer includes an inorganic filler and a resin binder.
(Inorganic filler)
The inorganic filler used in the filler porous layer is not particularly limited, but preferably has a melting point of 200 ° C. or higher, high electrical insulation, and electrochemically stable in the range of use of the lithium ion secondary battery. .
The inorganic filler is not particularly limited. For example, oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide and iron oxide; nitrides such as silicon nitride, titanium nitride and boron nitride Ceramics: silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide oxide, potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, Acerite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica sand and other ceramics; glass fiber and the like. These may be used alone or in combination.

Among these, from the viewpoint of improving the electrochemical stability and the heat resistance of the separator, aluminum oxide compounds such as alumina and aluminum hydroxide oxide; and ion exchange such as kaolinite, dickite, nacrite, halloysite, and pyrophyllite. An aluminum silicate compound having no function is preferred. As the aluminum oxide compound, aluminum hydroxide oxide (AlO (OH)) is particularly preferable. As the aluminum silicate compound having no ion exchange ability, kaolin mainly composed of kaolin mineral is more preferable because it is inexpensive and easily available. Known kaolins include wet kaolin and calcined kaolin obtained by calcining this. In the present invention, calcined kaolin is particularly preferred. The calcined kaolin is particularly preferable from the viewpoint of electrochemical stability because crystal water is released during the calcining process and impurities are also removed.

  The average particle size of the inorganic filler is preferably more than 0.01 μm and not more than 4.0 μm, more preferably more than 0.2 μm and not more than 3.5 μm, more than 0.4 μm and 3.0 μm. More preferably, it is as follows. Adjusting the average particle size of the inorganic filler to the above range is preferable from the viewpoint of suppressing thermal shrinkage at high temperature even when the filler porous layer is thin (for example, 7 μm or less). Examples of the method for adjusting the particle size and distribution of the inorganic filler include a method of reducing the particle size by pulverizing the inorganic filler using an appropriate pulverizer such as a ball mill, a bead mill, or a jet mill. .

  Examples of the shape of the inorganic filler include a plate shape, a scale shape, a needle shape, a columnar shape, a spherical shape, a polyhedral shape, and a lump shape. A plurality of inorganic fillers having these shapes may be used in combination.

  The proportion of the inorganic filler in the filler porous layer can be appropriately determined from the viewpoints of the binding properties of the inorganic filler, the permeability of the separator, and the heat resistance. The proportion of the inorganic filler in the filler porous layer is preferably 20% by mass or more and less than 100% by mass, more preferably 50% by mass or more and 99.99% by mass or less, and further preferably 80% by mass or more and 99.9% by mass. % Or less, particularly preferably 90% by mass or more and 99% by mass or less.

(Resin binder)
The type of resin binder contained in the filler porous layer is not particularly limited, but is insoluble in the electrolyte solution of the lithium ion secondary battery and is electrochemically stable in the usage range of the lithium ion secondary battery. It is preferable to use a resin binder.
Specific examples of such a resin binder include, for example, polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, ethylene -Fluorine-containing rubber such as tetrafluoroethylene copolymer; styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride, methacrylic acid Rubbers such as ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate Cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose; polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, polyester, etc., melting point and / or glass transition temperature of 180 ° C. or higher And the like.

  A resin latex binder is preferably used as the resin binder. When a resin latex binder is used as the resin binder, the separator having the filler porous layer containing the binder and the inorganic filler binds the resin binder onto the porous film through a step of applying the resin binder solution onto the substrate. Compared with the separator made to make it, it has the tendency for ion permeability to fall easily and to provide an electrical storage element with a high output characteristic. Furthermore, the power storage element having the separator has a smooth shutdown characteristic even when the temperature rise during abnormal heat generation is fast, and tends to provide high safety.

  As the resin latex binder, from the viewpoint of improving electrochemical stability and binding properties, aliphatic conjugated diene monomers and unsaturated carboxylic acid monomers, and other monomers copolymerizable therewith Those obtained by copolymerizing are preferred. There is no particular limitation on the polymerization method in this case. Emulsion polymerization is preferred. There is no restriction | limiting in particular as a method of emulsion polymerization, A conventionally well-known method can be used. The method for adding the monomer and other components is not particularly limited, and any one of a batch addition method, a divided addition method, and a continuous addition method can be adopted. Either step polymerization or multistage polymerization of three or more steps can be employed.

The average particle size of the resin binder is preferably 50 to 500 nm, more preferably 60 to 460 nm, and still more preferably 80 to 250 nm. When the average particle size of the resin binder is 50 nm or more, the separator including the filler porous layer containing the binder and the inorganic filler is less likely to have low ion permeability and easily provides a storage element with high output characteristics. Furthermore, even when the temperature rises rapidly during abnormal heat generation, it is easy to obtain a power storage element that exhibits smooth shutdown characteristics and has high safety. When the average particle size of the resin binder is 500 nm or less, good binding properties are exhibited, and when a multilayer porous film is formed, heat shrinkage is good and the safety tends to be excellent.
The average particle diameter of the resin binder can be controlled by adjusting the polymerization time, polymerization temperature, raw material composition ratio, raw material charging order, pH, and the like.

The layer thickness of the filler porous layer is preferably 1 μm or more from the viewpoint of improving heat resistance and insulation, and is preferably 50 μm or less from the viewpoint of increasing the capacity and permeability of the battery.
Layer density of the filler porous layer is preferably from 0.5 to 2.0 g / cm ^3, more preferably 0.7~1.5cm ^3. When the layer density of the filler porous layer is 0.5 g / cm ³ or more, the thermal contraction rate at high temperature tends to be good, and when it is 2.0 g / cm ³ or less, the air permeability tends to decrease. It is in.

Examples of the method for forming the porous filler layer include a method of applying a coating liquid containing an inorganic filler and a resin binder on at least one surface of a substrate. In this case, the coating liquid may contain a solvent, a dispersant, and the like in order to improve dispersion stability and coating property.
The method for applying the coating liquid to the substrate is not particularly limited as long as the required layer thickness and coating area can be realized. The filler raw material containing the resin binder and the polymer base material may be laminated and extruded by a co-extrusion method, or may be bonded after the base material and the filler porous film are individually produced.

[Thermoplastic polymer layer]
The thermoplastic polymer layer in the present embodiment is disposed on at least one side of the polyolefin porous substrate as described above.
The thermoplastic polymer layer may be disposed on the entire surface of the polyolefin porous substrate, or may be disposed only on a part of the surface of the substrate. In order to show high ion permeability in the obtained battery, it is preferable to dispose the thermoplastic polymer layer only on a part of the surface of the polyolefin porous substrate.
In this embodiment, the area ratio of the thermoplastic polymer layer to the total area of the surface on which the thermoplastic polymer layer is disposed in the surface of the polyolefin porous substrate is not particularly limited, but is 80% or less, 75% or less. Or 70%, and the area ratio is preferably 5% or more, 10% or more, or 15% or more. More preferably, the area ratio is 20% or more and 60% or less. This area ratio is measured by observing the thermoplastic polymer layer forming surface of the obtained separator with an SEM.

When the thermoplastic polymer layer is arranged only on a part of the surface of the polyolefin porous substrate, the arrangement pattern includes, for example, a dot shape, a stripe shape, a lattice shape, a stripe shape, a turtle shell shape, a random shape, and the like. Arbitrary patterns such as combinations can be used.
The thickness of the thermoplastic polymer layer disposed on the polyolefin porous substrate is preferably 0.01 to 5 μm, more preferably 0.1 to 3 μm, more preferably 0.1 to 1 μm per side. More preferably.

[Voronoi division]
Voronoi obtained by Voronoi division of particulate thermoplastic polymer (hereinafter also referred to as "thermoplastic polymer particles") placed on the separator substrate to improve the high-temperature storage characteristics in addition to the rigidity of the electricity storage device The dispersion (σ ² ) of the polygonal area (s _i ) is preferably 0.01 or more and 0.7 or less.

  Voronoi division refers to dividing a plurality of points (mother points) arranged at arbitrary positions in a certain distance space according to which mother point is closer to other points in the same space. . A diagram including the region thus obtained is called a Voronoi diagram. In general, in the Voronoi diagram, the boundary lines of a plurality of regions become a part of the bisector of each generating point, and each region forms a polygon (Voronoi polygon).

When observing the separator surface with a specific visual field, one thermoplastic polymer particle is regarded as one circle having an average diameter (l) in the observation visual field. A perpendicular bisector is drawn between a plurality of adjacent thermoplastic polymer particles, and a polygon surrounded by the perpendicular bisector for each particle is referred to as a “Voronoi polygon”.
The variance (σ ² ) of the area (s _i ) of the Voronoi polygon is:
{Wherein s _i is the actual value of the area of the Voronoi polygon, m is the average value of the actual area of the Voronoi polygon, and n is the total number of Voronoi polygons}
Is a value calculated by. It is assumed that a region that is not closed when Voronoi division is performed in the observation field is not subject to calculation of the above formula. Examples of the non-closed region include a region obtained by performing Voronoi division on the particle when the particle is present at the boundary of the observation field and the entire particle is not observed.
Therefore, in an image obtained by photographing at least a part of the separator surface, it is preferable to confirm whether or not the entire particle is observed at the edge of the image.

In this embodiment, the dispersion (σ ² ) of the area (s _i ) of the Voronoi polygon is an index indicating the level of variation in the arrangement of the thermoplastic polymer particles on the substrate. This dispersion (σ ² ) is considered to represent the distribution or aggregation state on the coated surface of the thermoplastic polymer particles. When the dispersion (σ ² ) of the area (s _i ) of the Voronoi polygon is 0.01 or more, it can be evaluated that the thermoplastic polymer particles are appropriately aggregated and disposed on the separator surface. Therefore, in this case, the adhesiveness between the electrode and the separator tends to be sufficient. If the dispersion (σ ² ) is 0.7 or less, it can be evaluated that the thermoplastic polymer particles are not excessively aggregated on the separator surface. Therefore, in this case, the ion resistance on the separator surface is uniform, lithium ions do not concentrate on a specific region of the surface, and the generation of metallic lithium is suppressed, so the high-temperature storage characteristics of the electricity storage device tend to be excellent It is in. The value of this dispersion (σ ² ) is preferably 0.01 or more and 0.6 or less, more preferably 0.01 or more and 0.5 or less, and 0.1 or more and 0.4 or less. Is more preferable, and 0.1 to 0.35 is particularly preferable.

In order to know the area density of the thermoplastic polymer particles and the dispersion (σ ² ) of the area (s _i ) of the Voronoi polygon obtained by performing Voronoi division on the thermoplastic polymer particles, the surface of the separator is observed. The observation means is appropriately selected depending on the size or distribution state of the thermoplastic polymer particles coated on the separator, and any method can be adopted. For example, an electron microscope, an atomic force microscope, an optical microscope, a differential interference microscope, or the like can be used. Among these, when dealing with the distribution state of the dispersed particles as in the present embodiment, it is preferable to use an electron microscope or an atomic force microscope.

  Within the observation field, an average observation field of the polymer layer coated on the separator surface should be ensured. Further, the projected area in the observation field should be adjusted as appropriate so that the average distribution state of the dispersed particles can be grasped. For example, the number of dispersed particles employed as a calculation target is preferably about 80 to 200 / field of view. This observation visual field can be obtained by observing the polymer layer with a preset observation means and magnification. For example, FIG. 1 is an example of a photograph in which the surface of the polymer layer is observed with a scanning electron microscope as the observation means and a magnification of 10,000. FIG. 1 clearly captures the state in which thermoplastic polymer particles having a particle diameter of about 500 nm are dispersed on the surface of the polymer layer. Thus, by grasping the state in which the thermoplastic polymer particles are dispersed on the surface of the polymer layer, the dispersion state of the thermoplastic polymer particles can be analyzed by Voronoi division.

  In observation using a scanning electron microscope, an appropriate magnification is set for analysis by Voronoi division according to the particle size of the thermoplastic polymer particles. Specifically, the magnification is set such that the number of thermoplastic polymer particles observed in one visual field is preferably 40 to 300, more preferably 60 to 240, and still more preferably 80 to 200. . Thus, analysis by Voronoi division can be performed appropriately. For example, if the particle size is about 500 nm, it is appropriate to set the magnification to 10,000 times. If the particle size is about 200 nm, setting the magnification to about 30,000 times is suitable for analysis by Voronoi division. Is appropriate.

  The thermoplastic polymer particles included in the observation field obtained by the above observation method are specified. For example, the thermoplastic polymer particles are identified from the observation field with the naked eye or using image processing software. FIG. 2 is an example showing a result of automatically specifying the thermoplastic polymer particles included in the observation visual field of FIG. 1 using image processing software. By identifying the thermoplastic polymer particles in a preset method and magnification field of view, the total number of particles, the diameter of each particle, and the projected area of each particle are calculated (see also FIG. 3 below). In that case, it is preferable to specify only particles that are entirely contained within the observation field.

  The above-defined Voronoi division can be performed on the thermoplastic polymer particles specified in a specific field of view on the separator surface. Specifically, the surface of the coated film after the thermoplastic polymer is coated on the separator surface is photographed to obtain an image. A Voronoi polygon can be drawn by performing the Voronoi division by regarding the thermoplastic polymer particles specified in the obtained image as a circle having an average diameter (l). For example, Voronoi polygons may be drawn manually or using image processing software. Then, the area of the drawn Voronoi polygon is calculated.

  For example, FIG. 3 is an example of a result obtained by performing Voronoi division on the plurality of thermoplastic polymer particles specified in FIG. 2 to obtain a Voronoi polygon. FIG. 4 shows the result of automatically calculating the number and area of Voronoi polygons corresponding to the closed region in the Voronoi polygon shown in FIG. 3 using image processing software.

By the above observation method and image processing method, the projected area in the viewing field is determined, and the total number of thermoplastic polymer particles, the projected area, and the Voronoi polygonal area in the viewing field are obtained. Then, according to the above definition, it can be calculated for the thermoplastic polymer particles in the visual field, the area density, and Voronoi dispersion polygonal area (s _i) a (sigma ^2).
However, the distribution of the thermoplastic polymer particles may vary depending on the observation field. Therefore, as the area density and the variance (σ ² ), it is preferable to employ an average value of values calculated for a plurality of observation fields. The number of fields of view is preferably 3 or more.

It is particularly preferable to employ an average value of values calculated for 95 visual fields determined as follows.
i) Each measurement field: an image taken with a scanning electron microscope ii) Field setting method:
a) Set the field of view of the starting point,
b) Nine visual fields consisting of regions sequentially adjacent in the horizontal direction with respect to the visual field of the starting point, nine visual fields consisting of regions adjacent in the vertical direction, and the visual field of the starting point 19 Set the field of view,
c) setting the area defined by the 19 fields of view as the starting section;
d) Set four sections consisting of regions that are sequentially adjacent to each other in the uniaxial direction at intervals of 10 mm with respect to the starting section.
e) For each of the four sections, set 19 fields of view at positions similar to 19 fields in the starting section, and f) All 95 fields in the four sections and the starting section (19 fields × 5 Section) is set as the measurement field of view.
Each of the measurement visual fields is preferably a captured image that is captured by setting the magnification so that the number of thermoplastic polymer particles observed in one visual field is 80 to 200.

Hereinafter, a preferred method for setting 95 fields of view according to the present embodiment will be described with reference to the drawings.
i) As described above, it is preferable to employ an image captured by a scanning electron microscope with a magnification of 10,000 times as described above. For example, the image shown in FIG. FIG. 5 is a diagram schematically showing a part of an image of thermoplastic polymer particles on a base material, which is imaged with a scanning electron microscope with a magnification of 10,000 times.
In the image of FIG. 5, first, the visual field (10) of the starting point is set. Since one field of view is composed of images taken with a scanning electron microscope with a magnification of 10,000 times, the scale of one field of view is about 10 μm × 10 μm, and a field of view suitable for Voronoi division evaluation based on thermoplastic polymer particles is provided. Configure. Next, nine visual fields (1 to 9) that are sequentially adjacent to the starting visual field (10) in the lateral direction (X-axis direction) are set. Each of these visual fields (1 to 9) is made up of captured images having the same magnification as that of the starting visual field (10), and is sequentially set in one direction with a common side and one side. Next, nine visual fields (11 to 19) which are sequentially adjacent to the starting visual field (10) in the vertical direction are set. Each of these visual fields (11 to 19) is composed of the same area as the starting visual field (10), and is sequentially set in one direction with one side shared by an adjacent area.

Subsequently, the region defined by the 19 fields of view is set as the starting section (I). Since the starting section (I) is composed of a square area having two sides, the upper side of the visual fields 1 to 10 and the right side of the visual fields 10 to 19 in FIG. 5, the scale of one section is about 100 μm × 100 μm. The dispersion calculated from the 19 fields of view constituting the section (I) can be evaluated as a value more accurately representing the state of the separator surface.
In this embodiment, in order to further accurately evaluate the state of the separator surface, the evaluation is performed by providing five sections equivalent to the above-described one section. Specifically, refer to FIG. FIG. 6 is an overall image of an image of the thermoplastic polymer particles on the substrate shown in FIG. In FIG. 6, four sections (II to V) that are sequentially adjacent to each other in the uniaxial direction at intervals of 10 mm are set with respect to the section (I) of the starting point. Each of these four sections consists of the same area as the starting section (I).
Next, for each of these four sections (II to V), 19 fields of view are set at positions similar to the 19 fields of view in the starting section (I). Then, all 95 fields (19 fields × 5 fields) in the four sections (II to V) and the field (I) of the starting point are set as observation fields of the thermoplastic polymer particles on the substrate.

The observation of the separator surface is preferably performed on a region of the separator surface that is not involved in ion conduction. For example, it is possible to observe a separator that has just been manufactured and is not yet incorporated into a storage element. When the electricity storage element is in use or after use, the so-called “ear” portion of the separator (a region near the outer edge of the separator and not involved in ion conduction) may be observed. This is a preferred aspect in the present embodiment.
As understood from the above evaluation method, when 95 visual fields are to be observed, a separator piece having a length of about 40 mm is to be measured, and therefore, the dispersion state of the thermoplastic polymer on the separator surface can be accurately evaluated.

The fact that thermoplastic polymer particles can be subjected to Voronoi division as described above means that in the polymer layer formed on the substrate, the thermoplastic polymer particles do not substantially overlap and exist as single layer particles. It shows that. For example, when thermoplastic polymers overlap in a polymer layer several times, the concept of area occupied by a single particle cannot be established, and Voronoi division cannot be performed.
The separator in the present embodiment is arranged such that the thermoplastic polymer particles in the polymer layer formed on the substrate do not substantially overlap, and the above-described area density and dispersion (σ ² ) However, it is preferable that each is adjusted to the above-mentioned range.

The means for adjusting the area density and dispersion (σ ² ) of the thermoplastic polymer to the above range is not limited, but for example, the thermoplastic polymer content in the coating liquid applied to the substrate, the coating It can be adjusted by changing the coating amount of the working liquid, the coating method, and the coating conditions. More specifically, the viscosity of the thermoplastic polymer solution is adjusted to be high, and the thermoplastic polymer is dispersed and arranged in the above range by applying a shearing force to the coated surface of the porous film. be able to.

The presence form (pattern) of the polymer layer on the base material is not particularly limited, but it is preferable that the thermoplastic polymer particles exist in a mutually dispersed state over the entire surface of the base material so as to satisfy the above dispersion. . The thermoplastic polymer particles may form clusters in a part of the region, but it is necessary that the particles are dispersed to the extent that the dispersion range is satisfied as a whole. The polymer particles may be stacked in a part of the region, but it is necessary that the particles are dispersed to the extent that the dispersion range is satisfied as a whole.
When the polymer layer is present in a pattern on the substrate, the above-described area density and dispersion (σ ² ) are preferably evaluated using an image obtained by photographing a region where the polymer layer is present.

[Thermoplastic polymer]
The structure of the thermoplastic polymer used in the present embodiment is not particularly limited. It is preferably in the form of particles. The particulate thermoplastic polymer has, for example, a single layer structure;
A structure composed of a particulate thermoplastic polymer and a polymer surrounding at least a portion of the particulate thermoplastic polymer;
A laminated structure and the like can be mentioned.
In the thermoplastic polymer layer, at least a part of the thermoplastic polymer present on the outermost surface of the electricity storage device separator is preferably a particulate thermoplastic polymer. By having such a structure, it is excellent in the adhesiveness of a separator and an electrode, and ion permeability, and it is effective in shortening the process time at the time of battery preparation, and improving a battery characteristic.
The particulate thermoplastic polymer may be a particle having a single composition, a particle having a mixture of a plurality of compositions, a particle having a core-shell structure, or two types. A state where the above thermoplastic polymers are blended may be used.
Here, the particulate form refers to a state in which each thermoplastic polymer has a contour in measurement with a scanning electron microscope (SEM). The particles may have an arbitrary shape such as an elongated shape, a spherical shape, or a polygonal shape.

The thermoplastic polymer is preferably in a state where a plurality of polymers are blended. In particular, a polymer having a glass transition temperature of less than 20 ° C. is blended from the viewpoints of wettability to the polyolefin microporous membrane, binding property between the polyolefin microporous membrane and the thermoplastic polymer layer, and adhesion to the electrode. Preferably;
From the viewpoint of blocking resistance and ion permeability, it is preferable that a polymer having a glass transition temperature of 20 ° C. or higher is also blended. As a mixing ratio in the case of blending, a ratio of a polymer having a glass transition temperature in a region of 20 ° C. or more and a polymer having a glass transition temperature in a region of less than 20 ° C. is 0.1: 99.9 to 99.99. The range is preferably 9: 0.1, more preferably 5:95 to 95: 5, still more preferably 50:50 to 95: 5, and particularly preferably 60:40 to 95: 5. It is.

The particulate thermoplastic polymer preferably has a core-shell structure. The core-shell structure is a polymer having a dual structure with a core polymer belonging to the central portion and a shell polymer belonging to the outer shell portion. The core polymer and the shell polymer may have the same composition or different compositions. However, in order to maximize the effects of the present invention, it is preferable to make the two compositions different.
In the case of the core-shell structure, the adhesiveness and compatibility with other materials such as electrodes and polyolefin microporous membranes can be adjusted by changing the shell polymer, and by adjusting the core polymer, for example, adhesion to the electrode during hot pressing Can increase the sex. Furthermore, the presence of the core polymer suppresses the collapse of the polymer particle shape after hot pressing. As a result, the blockage of the pores of the polyolefin substrate by the thermoplastic polymer is minimized, and the ion permeability is not deteriorated.

The glass transition temperature Tg of the thermoplastic polymer used in the present embodiment is preferably in the range of −10 ° C. to 100 ° C. from the viewpoint of adhesion to the electrode and ion permeability, and is 0 ° C. to 40 ° C. More preferably, it is in the range.
The glass transition temperature in this embodiment is determined from a DSC curve obtained by differential scanning calorimetry (DSC). Specifically, the temperature at the intersection of a straight line obtained by extending the baseline on the low temperature side in the DSC curve to the high temperature side and the tangent at the inflection point of the stepwise change portion of the glass transition may be adopted as the glass transition temperature. it can. In more detail, the method described in an Example can be referred.

Although it does not specifically limit as a thermoplastic polymer used by this embodiment, For example,
Polyolefin resins such as polyethylene, polypropylene and α-polyolefin;
Fluoropolymers such as polyvinylidene fluoride and polytetrafluoroethylene or copolymers containing these;
Diene polymers containing conjugated dienes such as butadiene and isoprene as monomer units, copolymers containing them, or hydrides thereof;
An acrylic polymer containing acrylic acid ester, methacrylic acid ester or the like as a monomer unit, a copolymer containing these, or a hydride thereof;
Rubbers such as ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate;
Cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose;
Examples thereof include particles made of resins such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester: and a mixture of a plurality of these.

Of the thermoplastic polymers, diene polymers, acrylic polymers, or fluorine polymers are preferable because they are excellent in binding properties, strength, and flexibility with the electrode active material.
Although a diene polymer is not specifically limited, For example, it is a polymer containing the monomer unit obtained by superposing | polymerizing the conjugated diene monomer which has two conjugated double bonds, such as butadiene and isoprene. Although it does not specifically limit as a diene polymer, For example, the copolymer of the homopolymer of a conjugated diene and the monomer copolymerizable with a conjugated diene is mentioned. The conjugated diene monomer is not particularly limited. For example, 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 1,3-pentadiene, 2 -Methyl-1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl-1,3-octadiene, 3-butyl-1,3-octadiene and the like. The monomer copolymerizable with the conjugated diene is not particularly limited. For example, (meth) acrylate monomer, α, β-unsaturated nitrile compound, unsaturated carboxylic acid compound, styrene monomer, halogen atom-containing monomer, vinyl ester Examples include compounds, vinyl ether compounds, vinyl ketone compounds, heterocyclic ring-containing vinyl compounds, (meth) acrylic acid ester compounds, hydroxyalkyl group-containing compounds, amide monomers, and the like.

  The acrylic polymer is not particularly limited, but is preferably a polymer containing a monomer unit obtained by polymerizing a (meth) acrylic acid ester monomer. Although it does not specifically limit as (meth) acrylic acid ester monomer, For example, alkyl (meth) acrylic acid alkyl ester, hydroxy group containing (meth) acrylate, amino group containing (meth) acrylate, epoxy group containing (meth) acrylate, etc. Is mentioned. The ratio of the monomer units obtained by polymerizing the (meth) acrylic acid ester monomer is not particularly limited, but is, for example, 40% by mass or more, preferably 50% by mass or more, more preferably, based on the total mass of the acrylic polymer. Is 60% by mass or more.

  Examples of the acrylic polymer include a homopolymer of a (meth) acrylic acid ester monomer or a copolymer of a (meth) acrylic acid ester monomer and a monomer copolymerizable with the (meth) acrylic acid ester monomer. Examples of the monomer copolymerizable with the (meth) acrylic acid ester monomer include the compounds listed above as monomers copolymerizable with the diene monomer.

  Although it does not specifically limit as a fluorine-type polymer, For example, the homopolymer of vinylidene fluoride and the copolymer with the monomer copolymerizable with vinylidene fluoride are mentioned. Fluoropolymers are preferred from the viewpoint of electrochemical stability. Although it does not specifically limit as a monomer copolymerizable with vinylidene fluoride, For example, a fluorine-containing ethylenically unsaturated compound, a fluorine-free ethylenically unsaturated compound, a fluorine-free diene compound, etc. are mentioned. Among the fluorine-based polymers, a homopolymer of vinylidene fluoride, a vinylidene fluoride / tetrafluoroethylene copolymer, a vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer, and the like are preferable.

As the thermoplastic polymer used in the present embodiment, the use of an acrylic polymer has excellent binding properties, strength, and flexibility with the electrode active material, and the resulting separator has ion permeability. Since it will be excellent, it is especially preferable.
As this acrylic polymer,
(Meth) acrylic acid alkyl ester,
An acid monomer;
A functional group-containing monomer;
Optionally an aromatic ring-containing monomer;
Optionally a crosslinkable monomer;
It is particularly preferable that a copolymer of the above can be produced because it is possible to produce a separator that is particularly excellent in the balance between adhesion to an electrode and ion permeability.

As the (meth) acrylic acid alkyl ester, for example,
Methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, hexyl ( (Meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, lauryl (meth) acrylate, n-tetradecyl (meth) acrylate, (Meth) acrylic acid chain alkyl esters such as stearyl (meth) acrylate;
(Meth) acrylic acid cyclic alkyl esters such as cyclohexyl (meth) acrylate;
Etc.

Examples of the acid monomer include:
Unsaturated monocarboxylic acids such as (meth) acrylic acid and pentenoic acid;
Unsaturated dicarboxylic acids such as itaconic acid, maleic acid, fumaric acid;
Etc.

As the functional group-containing monomer, for example,
Hydroxy group-containing monomers such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, pentenol;
Amino group-containing monomers such as 2-aminoethyl methacrylate;
Amide group-containing monomers such as (meth) acrylamide and N-methylol (meth) acrylamide;
Cyano group-containing monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-cyanoethyl acrylate;
Epoxy group-containing monomers such as glycidyl (meth) acrylate and (meth) acrylic acid 3,4-epoxycyclohexyl;
Etc.

As the aromatic ring-containing monomer, for example,
Aromatic vinyl compounds such as styrene, α-methylstyrene, vinylnaphthalene;
Aromatic ring-containing (meth) acrylic acid ester compounds such as phenyl (meth) acrylate and benzyl (meth) acrylate;
Etc.

Examples of the crosslinkable monomer include trimethylolpropane triacrylate.
The acrylic polymer as the thermoplastic polymer in the present embodiment preferably has the following monomer composition. The following is a preferable content ratio of each monomer unit based on the total mass of the acrylic polymer.
(Meth) acrylic acid alkyl ester: preferably 50 to 99.9% by mass, more preferably 60 to 99.9% by mass, particularly preferably 80 to 99.9% by mass
Acid monomer: preferably 0.1 to 20% by mass, more preferably 0.1 to 10% by mass, particularly preferably 0.1 to 5% by mass
Functional group-containing monomer: preferably 0.1 to 20% by mass, more preferably 1 to 20% by mass, particularly preferably 1 to 10% by mass
Aromatic ring-containing monomer: Preferably it is 10% by mass or less, more preferably 5% by mass or less, and particularly preferably no aromatic ring-containing monomer is used.
Crosslinkable monomer: Preferably it is 10 mass% or less, More preferably, it is 0.01-5 mass%, Most preferably, it is 0.1-3 mass%

The thermoplastic polymer in this embodiment is preferably particles having a core-shell structure.
More preferably, the core has a core-shell structure in which the glass transition temperature Tg (core) of the core is higher than the glass transition temperature Tg (shell) of the shell. The difference between Tg (core) and Tg (shell) (Tg (core) −Tg (shell) value) is preferably 10 ° C. or more, more preferably 20 to 150 ° C., and even more preferably 30 to 30 ° C. 100 ° C.
The preferable ranges of Tg (core) and Tg (shell) in the particles having a core-shell structure are as follows, provided that the relationship of Tg (core)> Tg (shell) is satisfied.
Tg (core): preferably 0 to 200 ° C, more preferably 20 to 150 ° C, still more preferably 30 to 120 ° C
Tg (shell): Preferably it is -50-100 degreeC, More preferably, it is -10-60 degreeC, More preferably, it is 0-40 degreeC
In the method for producing an electricity storage element described later, when pressing is performed on a laminate of separators and electrodes or a wound body of the laminate, the Tg (shell) is preferably lower than the press temperature. In this case, the difference between the press temperature and Tg (shell) (press temperature−Tg (shell) is preferably 30 ° C. or higher, and more preferably 50 ° C. or higher.

The thermoplastic polymer in the present embodiment is preferably a particle having a core-shell structure in which at least one of the core and the shell, preferably both of them are made of an acrylic polymer. In a particularly preferred form, both the core and the shell are (meth) acrylic acid alkyl esters,
An acid monomer;
A functional group-containing monomer;
Optionally an aromatic ring-containing monomer;
Optionally a crosslinkable monomer;
In the case of particles having a core-shell structure, which is a copolymer of As these monomers, the same compounds as those exemplified above can be used.

The composition ratio of each monomer in the core in this case is as follows as a preferable content ratio of each monomer unit based on the total mass of the core.
(Meth) acrylic acid alkyl ester: preferably 50 to 99.9% by mass, more preferably 60 to 99.9% by mass, particularly preferably 80 to 99.9% by mass
Acid monomer: preferably 0.1 to 20% by mass, more preferably 1 to 15% by mass, particularly preferably 3 to 10% by mass
Functional group-containing monomer: preferably 0.1 to 20% by mass, more preferably 1 to 15% by mass, particularly preferably 1 to 10% by mass
Aromatic ring-containing monomer: Preferably it is 10% by mass or less, more preferably 5% by mass or less, and particularly preferably no aromatic ring-containing monomer is used.
Crosslinkable monomer: Preferably it is 10 mass% or less, More preferably, it is 0.01-5 mass%, Most preferably, it is 0.1-3 mass%

The constituent ratio of each monomer in the shell is as follows as a preferable content ratio of each monomer unit based on the total mass of the shell.
(Meth) acrylic acid alkyl ester: preferably 50 to 99.99% by mass, more preferably 60 to 99.95% by mass, particularly preferably 80 to 99.9% by mass
Acid monomer: preferably 0.01 to 20% by weight, more preferably 0.05 to 10% by weight, particularly preferably 0.1 to 5% by weight
Functional group-containing monomer: preferably 0.1 to 20% by mass, more preferably 1 to 20% by mass, particularly preferably 1 to 10% by mass
Aromatic ring-containing monomer: Preferably it is 10% by mass or less, more preferably 5% by mass or less, and particularly preferably no aromatic ring-containing monomer is used.
Crosslinkable monomer: Preferably it is 10 mass% or less, More preferably, it is 0.01-5 mass%, Most preferably, it is 0.1-3 mass%

In this Embodiment, the glass transition temperature Tg of a thermoplastic polymer can be suitably adjusted by changing the monomer component used when manufacturing a thermoplastic polymer and the input ratio of each monomer, for example. That is, for each monomer used in the production of the thermoplastic polymer, from the generally indicated Tg of the homopolymer (for example, described in “A WILEY-INTERSCIENCE PUBLICATION”) and the blending ratio of the monomers, An outline of the glass transition temperature can be estimated. For example, a copolymer with a high proportion of monomers such as methyl methacrylate, acrylonitrile, methacrylic acid, etc., that gives a homopolymer with a Tg of about 100 ° C. has a high Tg;
For example, a copolymer having a high ratio of monomers such as n-butyl acrylate and 2-ethylhexyl acrylate, which give a homopolymer having a Tg of about -50 ° C., has a low Tg.
Moreover, Tg of a copolymer is following numerical formula (1):
1 / Tg = W1 / Tg1 + W2 / Tg2 +... + Wi / Tgi +... Wn / Tgn (1)
{In Formula (1), Tg (K) is the Tg of the copolymer, Tgi (K) is the Tg of the homopolymer of each monomer i, and Wi is the mass fraction of each monomer. } Can also be approximated by the formula of FOX represented by:
However, as the glass transition temperature Tg of the thermoplastic polymer in this embodiment, a value measured by the method using the DSC is adopted.

When the thermoplastic polymer in the present embodiment is a particle having a core-shell structure, the ratio of the core to the shell is preferably 1 to 50% by mass as the mass ratio of the core to the whole particle, and 5 to 20 More preferably, it is mass%.
When the ratio of the core to the shell is in the above range, the adhesion of the shell polymer having a lower Tg effectively functions when adhering to the electrode. In addition, the presence of the core polymer having a higher Tg suppresses the collapse of the polymer particle shape after hot pressing, so that blockage of the pores of the polyolefin substrate by the thermoplastic polymer is minimized, and ion permeability is reduced. There is nothing.

  The average particle size of the particulate thermoplastic polymer is preferably 10 nm to 2,000 nm, more preferably 50 nm to 1,500 nm, still more preferably 100 nm to 1,000 nm, particularly preferably 130 nm to 800 nm, and particularly preferably. It is 150-800 nm, Most preferably, it is 200-750 nm. Setting the average particle size to 10 nm or more means that the size of the particulate thermoplastic polymer is such that it does not enter the pores of the substrate when the particulate thermoplastic polymer is applied to the substrate including at least the porous film. Means to be secured. Therefore, in this case, it is preferable from the viewpoint of improving the adhesion between the electrode and the separator and the cycle characteristics of the electricity storage device. In addition, when the average particle diameter is 2,000 nm or less, an amount of the particulate thermoplastic polymer necessary for achieving both the adhesion between the electrode and the separator and the cycle characteristics of the electricity storage device is formed on the substrate. It is preferable from the viewpoint of coating. The average particle size of the particulate thermoplastic polymer can be measured according to the method described in the following examples.

  The particulate thermoplastic polymer as described above can be produced by a known polymerization method except that the monomer as described above is used. As a polymerization method, for example, an appropriate method such as solution polymerization, emulsion polymerization, bulk polymerization or the like can be employed. However, the thermoplastic polymer emulsion obtained by emulsion polymerization is preferably used as the coating solution as it is, preferably by emulsion polymerization in that the thermoplastic polymer layer in this embodiment can be easily formed by a coating method. Because it is possible.

[Optional ingredients]
The thermoplastic polymer layer in the present embodiment may contain only the thermoplastic polymer as described above, or may contain other optional components.
Examples of the optional component that can be used here include a binder, an inorganic filler, and a water-soluble polymer.

<Method for producing separator for power storage element>
[Method for producing polyolefin porous substrate]
The method for producing the polyolefin porous substrate in the present embodiment is not particularly limited, and a known production method can be adopted. For example, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded and formed into a sheet shape, optionally stretched and then made porous by extracting the plasticizer, and a polyolefin resin composition is melt-kneaded to obtain a high draw rate. After extruding at a ratio, the polyolefin crystal interface is peeled off by heat treatment and stretching, the polyolefin resin composition and the inorganic filler are melt-kneaded and molded on a sheet, and then the polyolefin and inorganic filler are stretched And a method of making the structure porous by removing the solvent at the same time as solidifying the polyolefin by dissolving it in a poor solvent for the polyolefin after dissolving the polyolefin resin composition.

Hereinafter, as an example of a method for producing a polyolefin porous substrate, a method for melt-kneading a polyolefin resin composition and a plasticizer to form a sheet and then extracting the plasticizer will be described.
First, a polyolefin resin composition and a plasticizer are melt-kneaded. As the melt-kneading method, for example, polyolefin resin and other additives as required may be added to a resin kneading apparatus such as an extruder, kneader, lab plast mill, kneading roll, Banbury mixer, etc. A method of introducing a plasticizer at a ratio of kneading and kneading. At this time, it is preferable that the polyolefin resin, other additives, and the plasticizer are pre-kneaded in advance at a predetermined ratio using a Henschel mixer or the like before being added to the resin kneading apparatus. More preferably, only a part of the plasticizer is added in the pre-kneading, and the remaining plasticizer is kneaded while side-feeding the resin kneading apparatus.

  As the plasticizer, a non-volatile solvent capable of forming a uniform solution at a melting point or higher of the polyolefin can be used. Specific examples of such a non-volatile solvent include hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; higher alcohols such as oleyl alcohol and stearyl alcohol. Of these, liquid paraffin is preferred.

  The ratio of the polyolefin resin composition and the plasticizer is not particularly limited as long as they can be uniformly melt-kneaded and formed into a sheet shape. For example, the mass fraction of the plasticizer in the composition comprising the polyolefin resin composition and the plasticizer is preferably 30 to 80 mass%, more preferably 40 to 70 mass%. By setting the mass fraction of the plasticizer within this range, it is preferable from the viewpoint of achieving both melt tension during melt molding and formability of a uniform and fine pore structure.

  Next, the melt-kneaded product is formed into a sheet shape. As a method for producing a sheet-like molded product, for example, a melt-kneaded product is extruded into a sheet shape via a T-die or the like, and brought into contact with a heat conductor to cool to a temperature sufficiently lower than the crystallization temperature of the resin component. And then solidify. As the heat conductor used for cooling and solidification, metal, water, air, plasticizer itself, and the like can be used, but a metal roll is preferable because of high heat conduction efficiency. In this case, it is more preferable that the metal roll is sandwiched between the rolls, since the efficiency of heat conduction is further increased, the sheet is oriented and the film strength is increased, and the surface smoothness of the sheet is also improved. The die lip interval when extruding from a T-die into a sheet is preferably from 400 μm to 3,000 μm, and more preferably from 500 μm to 2,500 μm.

  It is preferable to subsequently stretch the sheet-like molded body thus obtained. As the stretching treatment, either uniaxial stretching or biaxial stretching can be suitably used. Biaxial stretching is preferred from the viewpoint of the strength of the resulting porous substrate. When the sheet-like molded body is stretched at a high magnification in the biaxial direction, the molecules are oriented in the plane direction, and the porous substrate finally obtained is difficult to tear and has high puncture strength. Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple stretching. Simultaneous biaxial stretching is preferred from the viewpoints of improvement of puncture strength, uniformity of stretching, and shutdown property.

  The draw ratio is preferably in the range of 20 times to 100 times, more preferably in the range of 25 times to 50 times in terms of surface magnification. The stretching ratio in each axial direction is preferably in the range of 4 to 10 times in the MD direction, preferably in the range of 4 to 10 times in the TD direction, 5 to 8 times in the MD direction, and 5 times in the TD direction. More preferably, it is in the range of 8 times or less. By setting the total area magnification within this range, it is preferable in that sufficient strength can be imparted, film breakage in the stretching step can be prevented, and high productivity can be obtained.

  The sheet-like molded body obtained as described above may be further rolled. Rolling can be performed, for example, by a pressing method using a double belt press or the like. Rolling can particularly increase the orientation of the surface layer portion. The rolling surface magnification is preferably greater than 1 and 3 or less, more preferably greater than 1 and 2 or less. By setting the rolling magnification within this range, it is preferable in that the film strength of the porous substrate finally obtained can be increased and a uniform porous structure can be formed in the film thickness direction.

  Next, the plasticizer is removed from the sheet-like molded body to obtain a porous substrate. As a method for removing the plasticizer, for example, a method of extracting the plasticizer by immersing the sheet-like molded body in an extraction solvent and sufficiently drying it can be mentioned. The method for extracting the plasticizer may be either a batch type or a continuous type. In order to suppress the shrinkage of the porous substrate, it is preferable to constrain the end of the sheet-like molded body during a series of steps of immersion and drying. Further, the residual amount of plasticizer in the porous substrate is preferably less than 1% by mass.

  As the extraction solvent, it is preferable to use a solvent that is a poor solvent for the polyolefin resin and a good solvent for the plasticizer and has a boiling point lower than the melting point of the polyolefin resin. Examples of such an extraction solvent include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorine such as hydrofluoroether and hydrofluorocarbon. Halogenated solvents; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered and reused by an operation such as distillation.

  In order to suppress the shrinkage of the porous substrate, a heat treatment such as heat fixation or heat relaxation may be performed after the stretching step or after the formation of the porous substrate. The porous substrate may be subjected to a post-treatment such as a hydrophilic treatment with a surfactant or the like, or a crosslinking treatment with ionizing radiation or the like.

[Method of arranging thermoplastic polymer layer]
A thermoplastic polymer layer is disposed on at least one surface of the polyolefin porous substrate produced as described above. The method for disposing the thermoplastic polymer on the polyolefin porous substrate is not particularly limited, and examples thereof include a method of applying a coating liquid containing the thermoplastic polymer to the polyolefin porous substrate.

As the coating solution, a dispersion in which a thermoplastic polymer is dispersed in a solvent that does not dissolve the polymer can be preferably used. Particularly preferred is a case where a thermoplastic polymer is synthesized by emulsion polymerization, and an emulsion obtained by the emulsion polymerization is used as it is as a coating solution.
As content of the thermoplastic polymer in a coating liquid, as a mass ratio of the thermoplastic polymer with respect to the whole quantity of this coating liquid, 1-40 mass% is preferable, 5-30 mass% is more preferable, 5-20 mass% is Further preferred.

  The method for applying a coating solution containing a thermoplastic polymer on a polyolefin porous substrate is not particularly limited as long as a desired coating pattern, coating film thickness, and coating area can be realized. For example, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast Examples thereof include a coater method, a die coater method, a screen printing method, a spray coating method, and an ink jet coating method. Among these, the gravure coater method or the spray coating method is preferable from the viewpoint that the degree of freedom of the coating shape of the thermoplastic polymer is high and a preferable area ratio can be easily obtained.

  As a medium for the coating solution, it is preferable to use a poor solvent for a thermoplastic polymer. As such a medium, water or a mixed solvent composed of water and a water-soluble organic medium is preferable. Although it does not specifically limit as a water-soluble organic medium, For example, ethanol, methanol, etc. can be mentioned.

  Prior to coating, it is preferable to perform a surface treatment on the surface of the polyolefin porous substrate because the coating solution can be easily applied and the adhesion between the polyolefin porous substrate and the thermoplastic polymer is improved. Examples of the surface treatment method include a corona discharge treatment method, a plasma treatment method, a mechanical surface roughening method, a solvent treatment method, an acid treatment method, and an ultraviolet oxidation method.

  The method for removing the solvent from the coating film after coating is not particularly limited as long as it does not adversely affect the porous substrate and the polymer layer. For example, a method of drying at a temperature below its melting point while fixing a polyolefin porous substrate, a method of drying under reduced pressure at a low temperature, and dipping in a poor solvent for a thermoplastic polymer to solidify the thermoplastic polymer into particles The method of extracting a solvent simultaneously is mentioned.

<Physical properties of separator for power storage element>
The separator for an electricity storage device of this embodiment has a peel strength of 0.147 N / cm or more between the separator for the electricity storage device and the electrode when roll pressing is performed at a press speed of 2 m / min with the electrode overlapped with the electrode. It is. The peel strength is preferably 0.196 N / cm or more, and more preferably 0.294 N / cm or more. By setting the peel strength within this range, it is possible to suppress press back when a wound body composed of an electrode and a separator is press molded. In addition, it is possible to prevent peeling and positional deviation after press-molding a laminated body composed of a sheet-like electrode and a sheet-like separator. Therefore, it is preferable because the yield reduction in the battery assembly process can be suppressed and the production process time can be shortened.
The peel strength is measured by a commercially available tensile tester after a separator for a power storage element is overlapped with an electrode and roll-pressed at a press speed of 2 m / min under conditions of a linear pressure of 22.6 N / cm and 70 ° C. 180 ° peel strength value. It is appropriate to measure the tensile test sample with a width of 15 mm and a tensile speed of 300 mm / min.

The electrode used for the measurement of the peel strength may be either a positive electrode or a negative electrode, but it is appropriate to use a positive electrode in order to properly grasp the effect of the separator for an electricity storage device of this embodiment. . In particular, a positive electrode for a lithium ion secondary battery in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector is disposed so that the positive electrode active material layer faces the thermoplastic polymer layer forming surface of the separator. It is appropriate to measure after overlapping and roll pressing as described above.
This positive electrode for a lithium ion secondary battery will be described later.

The air permeability of the electricity storage device separator of the present embodiment is preferably 10 to 10,000 seconds / 100 cc, more preferably 10 to 1,000 seconds / 100 cc, and further preferably 50 to 500 seconds / 100 cc. It is.
Thus, the separator for electrical storage elements of this embodiment shows very large air permeability. Accordingly, when the separator is applied to a lithium ion secondary battery, a large ion permeability is exhibited.
As described above, the separator for an electricity storage device of the present embodiment includes a polyolefin porous substrate and a thermoplastic polymer layer disposed on the porous substrate. Here, it is characteristic that the air permeability originally possessed by the polyolefin porous substrate used as a raw material is less damaged by the arrangement of the thermoplastic polymer layer. Specifically, it is preferable that the value obtained by subtracting the air permeability of the porous base material used as the raw material from the air permeability of the separator of the present embodiment is 100 seconds / 100 cc or less. This value is more preferably 70 seconds / 100 cc or less, and still more preferably 50/100 cc or less. On the other hand, since an appropriate amount of the thermoplastic polymer layer is disposed on the raw porous substrate so that the obtained separator exhibits high adhesiveness, the above value is 5 seconds / 100 cc or more. Preferably there is.
This air permeability is the air resistance measured according to JIS P-8117, similar to the air permeability of the polyolefin porous substrate.

<Storage element>
The separator for an electricity storage device of this embodiment can be suitably applied as a separator for an electricity storage device by combining this with a positive electrode, a negative electrode, and a non-aqueous electrolyte. An example of the electricity storage element is a lithium ion secondary battery.
When manufacturing a lithium ion secondary battery using the separator of this embodiment, there is no limitation in a positive electrode, a negative electrode, and a non-aqueous electrolyte, Each can use a well-known thing.
As the positive electrode, a positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector can be suitably used. As the positive electrode current collector, for example, an aluminum foil or the like;
Examples of the positive electrode active material include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel type LiMnO ₄ , and olivine type LiFePO ₄ ;
Each can be mentioned. In addition to the positive electrode active material, the positive electrode active material layer may include a binder, a conductive material, and the like.

As the negative electrode, a positive electrode in which a negative electrode active material layer containing a negative electrode active material is formed on a negative electrode current collector can be suitably used. As the negative electrode current collector, for example, copper foil or the like;
Examples of the negative electrode active material include carbon materials such as graphite, non-graphitizable carbonaceous, graphitizable carbonaceous, and composite carbon bodies; silicon, tin, metallic lithium, various alloy materials, and the like;
Each can be mentioned.

The nonaqueous electrolytic solution is not particularly limited, but an electrolytic solution in which an electrolyte is dissolved in an organic solvent can be used. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiBF ₄ , and LiPF ₆ .

The method for producing the electricity storage device using the electricity storage device separator of the present embodiment is not particularly limited. For example, the following method can be illustrated.
The separator of this embodiment is manufactured as a vertically long separator having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4,000 m (preferably 1,000 to 4,000 m). Laminated in the order of positive electrode-separator-negative electrode-separator, or negative electrode-separator-positive electrode-separator, wound into a circular or flat spiral shape to obtain a wound body, and the wound body is housed in a battery can, Furthermore, it can manufacture by inject | pouring electrolyte solution. Alternatively, it is manufactured by a method in which a laminate composed of a sheet-like separator and an electrode, or a wound body obtained by folding an electrode and a separator is placed in a battery container (for example, an aluminum film) and an electrolyte is injected. May be.

At this time, it is preferable to press the laminated body or the wound body. In particular,
A separator for a storage element of the present embodiment;
An electrode having an active material layer formed on at least one surface of the current collector and the current collector;
Can be exemplified by a method in which the former thermoplastic polymer layer and the active material layer are overlapped and pressed for 1 second or less. The pressing temperature is preferably, for example, 50 ° C. or higher as a temperature at which adhesiveness can be effectively expressed. Further, the press temperature is preferably lower than the melting point of the polyolefin porous substrate, and more preferably 100 ° C. or less, in order to suppress clogging of the separator holes and heat shrinkage due to hot pressing. Furthermore, it is preferable to set it as 60-80 degreeC. The pressing time is preferably 0.01 to 1 second, and more preferably 0.01 to 0.5 second. By setting the pressing time within the above range, the time required for battery production is significantly shortened compared with the method in the prior art, so that battery productivity can be significantly increased.

In order to perform the above press, a known press apparatus can be appropriately selected and used. However, in order to effectively realize a very short press in the method of the present embodiment, it is preferable to use a roll press.
Specifically, the roll temperature is set to the above preferable temperature, the roll speed is preferably set to 0.1 to 20 m / min, more preferably set to 0.5 to 10 m / min, and roll pressing is performed.

  Since the lithium ion secondary battery manufactured as described above includes a separator that has both strong adhesiveness and high ionic conductivity, it exhibits excellent battery characteristics (particularly rate characteristics) and at high temperatures. Excellent long-term storage stability and long-term continuous operation resistance.

The physical properties in the following experimental examples were evaluated by the following methods.
(1) Porosity A 10 cm × 10 cm square sample was cut from a polyolefin porous substrate, and its volume (cm ³ ) and mass (g) were determined. Using these values, the density of the porous substrate was 0.95 (g / cm ³ ), and the porosity was expressed by the following formula:
Porosity (%) = (1−mass / volume / 0.95) × 100
Calculated by
(2) Air permeability (sec / 100cc)
Based on JIS P-8117, the air resistance measured by the Gurley type air permeability meter G-B2 (trademark) manufactured by Toyo Seiki Co., Ltd. was defined as the air permeability.

(3) Difference in air permeability The air permeability of the electricity storage element separator and the polyolefin porous substrate used as the raw material were measured by the method of (2) above, and the air permeability of the electricity storage element separator ( AR (A) (second / 100 cc)) and the air permeability of the polyolefin porous substrate (AR (B) (second / 100 cc)) (AR (A) -AR (B) (second / 100 cc)) Asked. This value was evaluated according to the following criteria.
◎ (Excellent): When AR (A) -AR (B) is 50 seconds / 100 cc or less ○ (Good): AR (A) -AR (B) exceeds 50 seconds / 100 cc and 100 seconds / 100 cc or less X (defect): AR (A) -AR (B) exceeds 100 seconds / 100cc

(4) Puncture strength (g)
Using a handy compression tester KES-G5 (trademark) manufactured by Kato Tech, a polyolefin porous substrate was fixed with a sample holder having a diameter of 11.3 mm at the opening. Next, a maximum piercing load is obtained by performing a piercing test in a 25 ° C. atmosphere at a piercing speed of 2 mm / sec. As a result, a puncture strength (g) was obtained.

(5) Rate characteristics a. Production of positive electrode 90.4% by mass of nickel, manganese, cobalt composite oxide (NMC) (Ni: Mn: Co = 1: 1: 1 (element ratio), density 4.70 g / cm ³ ) as a positive electrode active material, 1.6% by mass of graphite powder (KS6) (density 2.26 g / cm ³ , number average particle diameter 6.5 μm) and acetylene black powder (AB) (density 1.95 g / cm ³ , number average) as conductive aids 3.8% by mass of particle diameter 48 nm) and polyvinylidene fluoride (PVDF) (density 1.75 g / cm ³ ) as a binder at a ratio of 4.2% by mass, and these are mixed with N-methylpyrrolidone (NMP). A slurry was prepared by dispersing in the slurry. This slurry was applied to one side of a 20 μm-thick aluminum foil serving as a positive electrode current collector using a die coater, dried at 130 ° C. for 3 minutes, and then subjected to compression molding using a roll press to obtain a positive electrode. Produced. The coating amount of the positive electrode active material at this time was 109 g / m ² .

b. Graphite powder A as prepared negative active material of the negative electrode (density 2.23 g / cm ^3, number average particle diameter 12.7 [mu] m) 87.6% by weight and graphite powder B (density 2.27 g / cm ^3, number average particle diameter 6.5 μm) is 9.7% by mass, and the ammonium salt of carboxymethyl cellulose as a binder is 1.4% by mass (in terms of solid content) (solid content concentration is 1.83% by mass aqueous solution) and the diene rubber latex is 1.7% by mass ( (Solid content conversion) (solid content concentration 40 mass% aqueous solution) was dispersed in purified water to prepare a slurry. This slurry was applied to one side of a 12 μm thick copper foil serving as a negative electrode current collector with a die coater, dried at 120 ° C. for 3 minutes, and then compression molded with a roll press to produce a negative electrode. The coating amount of the negative electrode active material at this time was 5.2 g / m ² .

c. Preparation of non-aqueous electrolyte solution By dissolving LiPF ₆ as a solute in a mixed solvent of ethylene carbonate: ethyl methyl carbonate = 1: 2 (volume ratio) to a concentration of 1.0 mol / L, a non-aqueous electrolyte solution was prepared. Prepared.
d. Battery assembly The separator for a storage element obtained in each Example and Comparative Example was cut into a circle of 24 mmφ, and the positive electrode and the negative electrode were each cut into a circle of 16 mmφ. The negative electrode, the separator, and the positive electrode were stacked in this order so that the positive electrode and the active material surface of the negative electrode face each other, and roll-pressed at a linear pressure of 2.3 kg / cm, a roll speed of 2 m / min, and a press temperature described in Table 5. Then, it was housed in a stainless steel container with a lid. The container and the lid were insulated, and the container was in contact with the negative electrode copper foil and the lid was in contact with the positive electrode aluminum foil. A battery was assembled by injecting 0.4 ml of the non-aqueous electrolyte into the container and sealing it.

e. Evaluation of rate characteristics d. After charging the simple battery assembled in step 3 at 25 ° C. to a battery voltage of 4.2 V at a current value of 3 mA (about 0.5 C), the current value starts to be reduced from 3 mA so as to maintain 4.2 V. The first charge after the battery was made was performed for a total of about 6 hours. Thereafter, the battery was discharged to a battery voltage of 3.0 V at a current value of 3 mA.
Next, after charging to a battery voltage of 4.2 V at a current value of 6 mA (about 1.0 C) at 25 ° C., the current value starts to be reduced from 6 mA so as to hold 4.2 V, so that a total of about 3 Charged for hours. Thereafter, the discharge capacity when discharging to a battery voltage of 3.0 V at a current value of 6 mA was defined as 1 C discharge capacity (mAh).
Next, after charging to a battery voltage of 4.2 V at a current value of 6 mA (about 1.0 C) at 25 ° C., the current value starts to be reduced from 6 mA so as to hold 4.2 V, so that a total of about 3 Charged for hours. Thereafter, the discharge capacity when discharged to a battery voltage of 3.0 V at a current value of 12 mA (about 2.0 C) was defined as 2 C discharge capacity (mAh).
Then, the ratio of the 2C discharge capacity to the 1C discharge capacity was calculated, and this value was used as the rate characteristic.
Rate characteristic (%) = (2C discharge capacity / 1C discharge capacity) × 100
The evaluation criteria for rate characteristics (%) were as follows.
○ (Good): Rate characteristic is 90% or more × (Bad): Rate characteristic is less than 90%

(6) Peel strength The separator for electrical storage elements obtained in each Example and Comparative Example,
The positive electrode as the adherend (produced in the same manner as the above (5) a) was cut into a rectangular shape having a width of 15 mm and a length of 60 mm, respectively.
After superposing the separator so that the thermoplastic polymer particle layer of the separator and the active material layer of the positive electrode face each other to obtain a laminate, the laminate was roll-pressed under the following conditions.
Linear pressure: 22.6 N / cm
Temperature: 70 ° C
Press speed: 2m / min

About the laminated body after press, 180 ° at a peeling speed of 300 mm / min by a method in which an electrode is fixed, a separator is gripped and pulled by using force gauge ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd. A peel test was performed to examine the peel strength. At this time, the average value of the peel strength in a peel test for 40 mm in length performed under the above conditions was adopted as the peel strength, and evaluation was performed according to the following criteria.
◎ (excellent): peel strength 0.196 N / cm or more ○ (good): peel strength 0.147 N / cm or more and less than 0.196 N / cm x (defect): peel strength less than 0.147 N / cm Comparative Examples 1 to 5 In addition to the evaluation of the laminate by the roll press method under the above conditions,
The peel strength of the laminate subjected to hot pressing at 70 ° C. and 60 seconds instead of the roll press was also measured.

(7) Battery failure rate (productivity)
A five-layer laminate comprising positive electrode / separator / negative electrode / separator / positive electrode was prepared and roll-pressed under the same conditions as in (5) above.
When the end of the laminate after pressing was picked up and lifted, it was observed whether or not the laminate was peeled off. When this test is performed three times and no layered product is peeled off (when the defect rate is 0%), “○ (productivity is good)” and when one layered product is peeled off (When the defect rate was 33% or more) was evaluated as “× (productivity failure)”.

(8) High-temperature storage characteristics The high-temperature storage specific evaluation was performed using the simple battery assembled as described in (5) ad above.
A method in which the battery is charged to a battery voltage of 4.2 V at a current value of 3 mA (about 0.5 C) at 25 ° C., and the current value starts to be reduced from 3 mA so as to maintain 4.2 V after reaching the battery voltage. The battery was charged for a total of 6 hours. Thereafter, the battery was discharged to a battery voltage of 3.0 V at a current value of 3 mA.
Next, in a 25 ° C. atmosphere, the battery voltage is charged to 4.2 V at a current value of 6 mA (about 1.0 C), and after reaching the voltage value, the current value starts to be reduced from 6 mA so as to maintain 4.2 V. The battery was charged for 3 hours. The discharge capacity when discharging to a battery voltage of 3.0 V at a current value of 6 mA was defined as A (mAh).
Next, in a 25 ° C. atmosphere, the battery voltage is charged to 4.2 V at a current value of 6 mA (about 1.0 C), and after reaching the voltage value, the current value starts to be reduced from 6 mA so as to maintain 4.2 V. The battery was charged for 3 hours. The cell held in a charged state was held in a 60 ° C. atmosphere for 7 days. Thereafter, the cell was taken out and discharged to a battery voltage of 3.0 V at a current value of 6 mA in an atmosphere of 25 ° C. Next, in a 25 ° C. atmosphere, the battery voltage is charged to 4.2 V at a current value of 6 mA (about 1.0 C), and after reaching the voltage value, the current value starts to be reduced from 6 mA so as to maintain 4.2 V. The battery was charged for 3 hours. Furthermore, the discharge capacity when discharging to a battery voltage of 3.0 V at a current value of 6 mA was defined as B (mAh).
Then, using the ratio of B to A, the high temperature storage characteristics were evaluated according to the following criteria.
A (good): When the ratio of the discharge capacity B to the discharge capacity A is 70% or more B (allowable): When the ratio of the discharge capacity B to the discharge capacity A is less than 70%

(9) Viscosity average molecular weight Mv
Based on ASRM-D4020, the intrinsic viscosity [η] at 135 ° C. was determined in a decalin solvent. Using this [η] value, the viscosity average molecular weight Mv was calculated from the relationship of the following mathematical formula.
In the case of polyethylene: [η] = 0.00068 × Mv 0.67
In the case of polypropylene: [η] = 1.10 × Mv0.80

(10) Observation method of polymer layer (Voronoi division)
i) Evaluation using 3 fields of view Using a scanning electron microscope S-4800 (manufactured by Hitachi High-Technologies Corporation), the surface of the polymer layer on the separator is 3 times at 10,000 or 30,000 times depending on the particle size of the polymer particles. I took a picture with two fields of view. Area density, dispersion (σ ² ) of Voronoi polygon area (s _i ), and projected area (c _i ) and area of Voronoi polygon (s _i ) for the granular thermoplastic polymer included in these three fields of view (C _i / s _i ) was obtained as an average value of three fields of view. Here, area density, Voronoi polygon area (s _i ) variance (σ ² ), and ratio (c _i / s _i ) are image processing software “A image kun” (registered trademark; manufactured by Asahi Kasei Engineering Corporation). ) Automatically calculated. Further, when Voronoi division was performed in the observation field of view, the region that was not closed was not considered as an object for calculating the area of the Voronoi polygon.

ii) Evaluation using 95 visual fields Using a scanning electron microscope S-4800 (manufactured by Hitachi High-Technologies Corporation), the surface of the polymer layer on the separator is photographed at a magnification of 10,000 or 30,000, depending on the particle size of the polymer particles. I took a picture. Using the obtained image, a 5-compartment 95 visual field was set as described above. The area density, the Voronoi polygon area density, the Voronoi polygon area (s _i ) variance (σ ² ), and the projected area (c _i ) and Voronoi for the granular thermoplastic polymer included in these 95 fields of view A ratio (c _i / s _i ) to the polygonal area (s _i ) was obtained as an average value of 95 fields in the same manner as i).

<Manufacture of polyolefin porous substrate>
Production example A
45 parts by mass of a homopolymer high-density polyethylene having an Mv of 700,000,
45 parts by mass of a homopolymer high-density polyethylene having an Mv of 300,000,
5 parts by mass of a homopolymer polypropylene having an Mv of 400,000,
Was dry blended using a tumbler blender.
1 part by mass of tetrakis- [methylene- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane as an antioxidant was added to 99 parts by mass of the obtained polyolefin mixture, and again a tumbler blender. Was used for dry blending to obtain a mixture.
The obtained mixture was supplied to the twin screw extruder by a feeder under a nitrogen atmosphere.
Further, liquid paraffin (kinematic viscosity at 37.78 ° C .: 7.59 × 10 ⁻⁵ m ² / s) was injected into the extruder cylinder by a plunger pump.
The operating conditions of the feeder and the pump were adjusted so that the ratio of liquid paraffin in the total mixture to be extruded was 65 parts by mass and the polymer concentration was 35 parts by mass.

Next, they are melt-kneaded while being heated to 230 ° C. in a twin-screw extruder, and the obtained melt-kneaded product is extruded through a T-die onto a cooling roll controlled at a surface temperature of 80 ° C. A sheet-like molded product was obtained by bringing into contact with a cooling roll and molding by cooling.
This sheet was stretched by a simultaneous biaxial stretching machine at a temperature of 112 ° C. and a magnification of 7 × 6.4. Thereafter, the stretched product was immersed in methylene chloride, and the liquid paraffin was extracted and dried, and then dried, and further stretched twice in the transverse direction at a temperature of 130 ° C. using a tenter stretching machine.
Thereafter, the stretched sheet was relaxed by about 10% in the width direction and heat-treated to obtain a polyolefin porous substrate A.

Production example B
The following materials:
6.4 parts by mass of SiO ₂ “DM10C” (trademark, manufactured by Tokuyama Corporation)
12.2 parts by mass of high density polyethylene having a viscosity average molecular weight of 700,000,
12.2 parts by mass of high-density polyethylene having a viscosity average molecular weight of 250,000,
1.3 parts by mass of homopolypropylene having a viscosity average molecular weight of 400,000
Liquid paraffin 37.1 parts by mass as a plasticizer, and pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] 0.3 parts by mass as an antioxidant The raw material of the polyolefin 1st microporous layer was prepared by premixing addition with a super mixer.
The following ingredients:
10.8 parts by mass of high density polyethylene having a viscosity average molecular weight of 700,000, 10.8 parts by mass of high density polyethylene having a viscosity average molecular weight of 250,000,
1.1 parts by weight of homopolypropylene having a viscosity average molecular weight of 400,000
As plasticizer, liquid paraffin 46.3 parts by mass, and as antioxidant, pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] 0.3 part by mass Were premixed with a super mixer to prepare a raw material for the polyolefin second microporous layer.

Each of the above raw materials was supplied to two twin-screw co-directional screw extruder feed ports by a feeder. At this time, liquid paraffin was side-fed to the twin screw extruder cylinder so that the amount ratio of the plasticizer in the total mixture extruded by melt kneading together with each raw material was 60% by mass.
The melt kneading conditions in the extruder are as follows.
Raw material for the first microporous layer Setting temperature: 200 ° C
Screw rotation speed: 100rpm
Discharge rate: 5kg / h
Raw material for the second microporous layer Setting temperature: 200 ° C
Screw rotation speed: 120rpm
Discharge rate: 16kg / h

Subsequently, the melt-kneaded material was extruded between a pair of rolls controlled at a surface temperature of 30 ° C. through a gear pump set at a temperature of 220 ° C., a conduit, and a T-die capable of co-extrusion of two types and three layers. A sheet-like composition having a first layer made of the raw material of the first microporous layer as a surface layer was obtained. Thereafter, a polyolefin porous substrate B was obtained by performing the same operations as in Production Example A, except that the stretching temperature and the relaxation rate were adjusted.
The obtained polyolefin porous substrate B was evaluated in the same manner as in Production Example A by the above method. The evaluation results are shown in Table 1.

Production Example C
The following ingredients:
95 parts by mass of Mv2.5 × 10 ⁵ high density polyethylene,
5 parts by mass of Mv 4.0 × 10 ⁵ polypropylene, and tetrakis [methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane 0.1 mass as an antioxidant A first resin composition constituting the first microporous layer was prepared by mixing parts.
The following ingredients:
44.8 parts by mass of SiO ₂ having a primary particle size of 15 nm (81% by mass as a proportion of the total amount of resin and inorganic particles),
Mv 7.0 × 10 ⁵ high-density polyethylene resin 10.4 parts by mass (19% by mass as a proportion of the total amount of resin and inorganic particles),
As a plasticizer, 44.8 parts by mass of liquid paraffin,
As an antioxidant, 0.1 part by mass of tetrakis [methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane,
Was premixed with a Henschel mixer to prepare a second resin composition constituting the second microporous layer.

Said 1st resin composition and 2nd resin composition were supplied to the feed screw port of 2 units | sets of 2 axis | shafts same direction screws with the feeder. Moreover, the amount ratio of the plasticizer in the total mixture of the first microporous layer extruded by melt kneading is 65% by mass, and the ratio of the amount of plasticizer in the total mixture of the second microporous layer extruded by melt kneading The liquid paraffin was side-fed to a twin-screw extruder cylinder so that the ratio was 60% by mass. The melt kneading conditions in the extruder are as follows.
Raw material for the first microporous layer Setting temperature: 200 ° C
Screw rotation speed: 20rpm
Discharge rate: 8kg / h
Raw material for the second microporous layer Setting temperature: 200 ° C
Screw rotation speed: 150rpm
Discharge rate: 14kg / h

Subsequently, the melt-kneaded material is extruded onto a pair of rolls controlled at a surface temperature of 30 ° C. through a gear pump set at a temperature of 200 ° C., a conduit, and a T-die capable of co-extrusion of two types and three layers. The sheet is cooled by a roll having a surface temperature of 80 ° C., and the first microporous layer made of the first resin composition becomes the surface layer, and the second microporous layer made of the second resin composition becomes the intermediate layer. A composition was obtained. Next, the sheet-like composition was continuously introduced into a simultaneous biaxial tenter and subjected to simultaneous biaxial stretching under the conditions of 7 times in the longitudinal direction and 6 times in the transverse direction. At this time, the set temperature of the simultaneous biaxial tenter was 123 ° C. Next, the stretched sheet was introduced into an extraction tank and sufficiently immersed in methylene chloride to extract and remove liquid paraffin, and then methylene chloride was dried. Furthermore, the polyolefin porous substrate C was obtained by conducting the heat setting by guiding the sheet to a horizontal tenter.
The properties of the resulting polyolefin porous substrate C are shown in Table 1.

Production Example D
In the same manner as in Production Example A, a polyolefin porous substrate A was produced.
Next, aluminum hydroxide oxide (average particle size 1.0 μm) 96.0 parts by mass, acrylic latex (solid content concentration 40%, average particle size 145 nm, minimum film formation temperature 0 ° C. or less) 4.0 parts by mass, and A coating solution was prepared by uniformly dispersing 1.0 part by mass of an aqueous solution of ammonium polycarboxylate (SN Dispersant 5468 manufactured by San Nopco) in 100 parts by mass of water. Subsequently, the coating solution was applied to the surface of the polyolefin porous substrate A using a gravure coater. Then, it dried at 60 degreeC and removed water. Thus, a polyolefin porous substrate D was obtained by forming an aluminum hydroxide oxide layer (inorganic filler porous layer) with a thickness of 2 μm on the polyolefin porous substrate A.

Production Example E
In the same manner as in Production Example A, a polyolefin porous substrate A was produced.
Next, Production Example D except that the amount of aluminum hydroxide oxide (average particle size 1.0 μm) was 80.0 parts by mass, the amount of acrylic latex was 20.0 parts by mass, and the coating thickness was 3 μm. A polyolefin porous substrate E was obtained by forming an aluminum hydroxide oxide layer on the polyolefin porous substrate A in the same manner as described above.

  Table 1 shows the porosity, air permeability, and puncture strength measured by the above-described methods for each of the substrates A to E obtained above.

<Synthesis of thermoplastic polymer particles>
Synthesis examples A to H
(Manufacture of core)
Into a reaction vessel equipped with a stirrer, reflux condenser, dropping tank and thermometer, 70.4 parts by mass of ion-exchanged water and “AQUALON KH1025” (registered trademark, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., 25) (Mass% aqueous solution) 0.5 part by mass and "Adekaria soap SR1025" (registered trademark, manufactured by ADEKA Corporation, 25 mass% aqueous solution) 0.5 part by mass are added, and the internal temperature of the reaction vessel is set to 80 ° C. The temperature was raised, and 7.5 parts by mass of ammonium persulfate (2% by mass aqueous solution) was added while maintaining the temperature at 80 ° C.
Separately from the above, the monomer described in the “Emulsion 1” column of Table 2 and other raw materials used were mixed for 5 minutes with a homomixer to prepare Emulsion 1.
The above emulsion 1 was dropped into the reaction vessel. Specifically, 5 minutes after adding the ammonium persulfate aqueous solution to the reaction vessel, dropping of the emulsion 1 from the dropping tank into the reaction vessel was started, and the entire amount was dropped over 150 minutes.
After completion of the dropwise addition of the emulsion 1, the reaction vessel internal temperature was maintained at 80 ° C. for 90 minutes, and then cooled to room temperature to obtain an emulsion. An aqueous solution of ammonium hydroxide (25% by mass aqueous solution) was added to the obtained emulsion to adjust the pH to 9.0, whereby an emulsion containing 40% by mass of core particles was obtained.

(Manufacture of shell (manufacture of thermoplastic polymer particles))
The emulsion containing the core particles obtained above is used as a seed polymer, and in the presence of the seed polymer, the second stage polymerization is performed as follows to synthesize a shell portion, thereby producing a heat having a core / shell structure. Plastic polymer particles were produced.
Into a reaction vessel equipped with a stirrer, reflux condenser, dripping tank, and thermometer, ion exchange water, seed polymer emulsion, and emulsifier are charged as an initial charge, and the temperature in the reaction vessel is kept at 30 ° C. A 2% by weight aqueous solution of the agent was added.
Separately from the above, the monomer described in the “Emulsion 2” column of Table 3 and other raw materials used were mixed for 5 minutes with a homomixer to prepare Emulsion 2.
The above emulsion 2 was dropped into the reaction vessel. Specifically, 5 minutes after adding the initiator to the reaction vessel, dropping of the emulsion 2 from the dropping tank into the reaction vessel was started, and the entire amount was dropped over 150 minutes. In this state, stirring was continued for another 30 minutes to allow the seed polymer to absorb the monomer.
Next, while maintaining the pH of the reaction system at 4 or less, the temperature of the reaction vessel was raised to 80 ° C., and stirring was continued for 120 minutes, and then cooled to room temperature.
After cooling, the mixture was filtered through a 200-mesh wire mesh to remove aggregates and the like, thereby obtaining emulsions containing thermoplastic polymer particles A to H, respectively.
The obtained emulsion was filtered, and 25% by mass of ammonia water and water were added to adjust the pH = 8 and the solid content = 40% by mass before use.
In Synthesis Examples G and H, the emulsions each containing single-layered particles were adjusted to pH = 8 and the solid content = 40% by mass before being used.

(Measurement of glass transition temperature)
The glass transition temperatures of the core particles and the thermoplastic polymer particles were measured by the following method using the core particles and the thermoplastic polymer particles obtained as described above as samples. The glass transition temperature of the shell part is the same as that of the above-mentioned “Manufacture of shell part (manufacture of thermoplastic polymer particles)” except that no seed polymer is used to obtain polymer particles having the same composition as the shell part. Then, the measurement was performed by the following method using the particles as a sample. The measurement results are shown in Table 4.

About 17 mg of the sample was packed in an aluminum container for measurement, and a DSC curve and a DDSC curve in a nitrogen atmosphere were obtained with a DSC measuring apparatus (manufactured by Shimadzu Corporation, DSC 6220). The measurement conditions were as follows.
First stage temperature increase program: Start at 70 ° C., increase temperature at a rate of 15 ° C. per minute. Maintained for 5 minutes after reaching 110 ° C.
Second stage temperature drop program: temperature drop from 110 ° C. at a rate of 40 ° C. per minute. Maintained for 5 minutes after reaching -50 ° C.
Third stage temperature increase program: Temperature is increased from -50 ° C to 130 ° C at a rate of 15 ° C per minute. DSC and DDSC data are acquired at the third stage of temperature rise.
The intersection of the base line (the straight line obtained by extending the base line in the obtained DSC curve to the high temperature side) and the tangent at the inflection point (the point where the upward convex curve changes to the downward convex curve) is defined as the glass transition temperature ( Tg).

(Measurement of particle diameter)
The average particle size of the thermoplastic polymer particles was measured using a particle size measuring device (Nikkiso Co., Ltd., Microtrac UPA150). As the measurement conditions, the loading index = 0.15 to 0.3, the measurement time was 300 seconds, and the numerical value of the 50% particle diameter in the obtained data was described as the particle diameter.

Abbreviations of used raw materials described in Table 2 and Table 3 have the following meanings, respectively.
(emulsifier)
KH1025: Aqualon KH1025, trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., 25% by mass aqueous solution SR1025: Adekaria soap SR1025, trade name, manufactured by ADEKA Co., Ltd., 25% by mass aqueous solution,
NaSS: Sodium p-styrene sulfonate (initiator)
APS: ammonium persulfate (2% by weight aqueous solution)

(monomer)
MMA: Methyl methacrylate BA: n-butyl acrylate CHMA: cyclohexyl methacrylate EHA: 2-ethylhexyl acrylate MAA: methacrylic acid AA: acrylic acid HEMA: 2-hydroxyethyl methacrylate AM: acrylamide (crosslinking agent)
A-TMPT: trimethylolpropane triacrylate

Example 1
An emulsion containing the thermoplastic polymer particles A obtained in Synthesis Example A above,
An emulsion containing the thermoplastic polymer particles H obtained in Synthesis Example H;
Were mixed so that the blending amount of the polymer particles H with respect to the total of the polymer particles A and the polymer particles H was 10% by mass to obtain a mixed solution. A coating solution was obtained by diluting this mixed solution 4 times (by mass) with water.
The coating solution is applied to the entire surface of the polyolefin porous substrate A obtained in Production Example A so that the coating area ratio is 60% and the coating weight is 0.5 g / m ² by a gravure coater. did. Next, by heating at 50 ° C. for 1 minute and drying, a thermoplastic polymer particle layer was formed on the polyolefin porous substrate to obtain a separator for a storage element.
Using this separator, a lithium ion secondary battery was assembled and evaluated as described above.
The evaluation results are shown in Table 5.

Examples 2 to 10 and Comparative Examples 1 to 5
In Example 1 above, the types of the polyolefin porous substrate and the thermoplastic polymer particles, the blending amount of the polymer particles H in the coating liquid, the coating method, the coating shape, the coating area, and the coating weight, A separator was produced in the same manner as in Example 1 except that it was as described in Table 5 or 6, and a lithium ion secondary battery was assembled and evaluated using the separator.
The evaluation results are shown in Tables 5 and 6.
In Comparative Example 5, a polyolefin porous substrate that does not form a thermoplastic polymer particle layer was used as a separator as it was.

Claims (7)

A separator for an electricity storage device comprising a polyolefin porous substrate, and a thermoplastic polymer layer disposed on at least one surface of the porous substrate,
The peel strength between the electricity storage element separator and the electrode when the electricity storage element separator and the electrode are overlapped and roll pressed at a pressing speed of 2 m / min is 0.147 N / cm or more, and The value obtained by subtracting the air permeability of the porous substrate from the air permeability of the electricity storage element separator is 100 seconds / 100 cc or less. The thermoplastic polymer contained in the thermoplastic polymer layer is a particulate thermoplastic polymer, and using the Voronoi polygonal area (Si) obtained by Voronoi division of the particulate thermoplastic polymer, :
{Wherein Si is the actual value of the area of the Voronoi polygon, m is the average value of the area of the Voronoi polygon, and n is the total number of Voronoi polygons}. The electrical storage device separator according to claim 1, wherein the dispersion (σ ² ) is 0.01 or more and 0.7 or less.   The surface coverage of the said thermoplastic polymer layer is 5 to 80% with respect to the area of the surface where the said thermoplastic polymer layer is arrange | positioned among the said polyolefin porous base materials. The separator for electrical storage elements. The separator for an electricity storage element according to any one of claims 1 to 3,
A positive electrode;
A negative electrode,
It is comprised from these, The laminated body characterized by the above-mentioned.   A wound body obtained by winding the laminate according to claim 4. The separator for an electricity storage element according to any one of claims 1 to 3,
A positive electrode;
A negative electrode,
An electrolyte,
A secondary battery comprising: The separator for an electricity storage element according to any one of claims 1 to 3,
An electrode having an active material layer formed on at least one surface of the current collector and the current collector;
A method for manufacturing a power storage element, comprising a step of pressing for 1 second or less by superimposing the two.