JP7034842B2 - Multi-layer separator - Google Patents

Description

The present invention relates to a multilayer separator for a power storage device used as a power generation element of a power storage device (hereinafter, also simply referred to as a "battery"), and further relates to a battery using the multilayer separator.

Conventionally, in a power storage device, an electrolytic solution is impregnated into a power generation element having a separator interposed between a positive electrode plate and a negative electrode plate. Generally, a separator having a porous layer containing a polyolefin resin is used because the separator is required to have ion permeability and safety such as a shutdown function. Further, from the viewpoint of electrical insulation, heat resistance, cycle characteristics, etc. during thermal runaway, a multilayer separator in which a resin porous layer and a porous layer containing an inorganic filler and its binder are laminated is also being studied (Patent Document 1). ~ 4).

Patent Document 1 describes that the cycle characteristics or trickle characteristics are good when the lithium (Li) ion diffusion coefficient of the polyolefin resin porous membrane constituting one layer of the multilayer separator is within a specific range. .. Patent Document 1 does not mention the ion diffusion coefficient of the layer other than the polyolefin resin porous membrane in the multilayer separator or the ion diffusion property at the interface of the multilayer separator.

Patent Document 2 attempts to improve the device output characteristics by adjusting the porosity of the heat-resistant fine particle-containing layer of the multilayer separator to 55% or more, but in addition to the room for improvement, the porosity There are concerns about reliability such as storage characteristics and lithium dendrite resistance due to the increase in the number of particles.

Patent Document 3 attempts to improve the output characteristics by reducing the binder ratio of the heat-resistant porous layer to 7% by volume or less, but in addition to the unclear lower limit of the binder ratio, binding There is a concern that short circuit or deterioration of cycle characteristics may occur due to deterioration of properties.

In Patent Document 4, the ion permeability is controlled by controlling the ratio of the binder resin permeating into the inside of the polyolefin porous film in the film in which the heat-resistant layer containing the binder resin and the filler is laminated on the surface of the polyolefin porous film. However, it is unclear how the ion permeability at the interface between the film and the heat-resistant layer specifically affects the output characteristics.

Japanese Unexamined Patent Publication No. 2016-7633 Japanese Unexamined Patent Publication No. 2011-100602 International Publication No. 2012/005152 Japanese Unexamined Patent Publication No. 2013-46998

The conventional multilayer separator has heat resistance due to the heat-resistant filler-containing layer, but the output characteristics and storage characteristics in the power storage device have not been studied or there is room for improvement. Further, although some conventional multi-layer separators are designed to suppress an increase in air permeability, the air permeability merely represents the gas permeability of the entire multi-layer structure, and is used in the multi-layer separator. However, it is not necessarily related to the device output characteristics. In addition, some of the conventional multilayer separators are designed to suppress the increase in resistance at the interface between the layers by controlling the structure of one layer as the base material, but the suppression of the increase in resistance is not sufficient. ..
Therefore, an object of the present invention is to provide a multilayer separator for a power storage device that has both output characteristics and storage characteristics.

The above problems are solved by the following technical means.
[1]
A multilayer separator for a power storage device including a porous layer A containing a polyolefin resin and a porous layer B containing inorganic particles.
The ion diffusion coefficient of the porous layer B is set to D (B) in the pulsed magnetic field gradient NMR measurement of the fluoride ion of the multilayer separator for a power storage device, and 100 ms in the exchange NMR measurement of the fluoride ion of the multilayer separator for a power storage device. When the ion permeability (%) between the porous layer A and the porous layer B at the mixing time is r (AB), r (AB) and D (B) have the following relational expression:
r (AB) / D (B)> 7.0 × 10 ¹¹
1 × ^10-11 <D (B) <1 × ^10-10
A multi-layer separator for power storage devices that meets the requirements.
[2]
When the ion diffusion coefficient of the porous layer A is D (A) in the pulsed magnetic field gradient NMR measurement of the fluoride ion of the multilayer separator for a power storage device, D (A) is the following relational expression:
8 × ^10-11 <D (A) <1 × ^10-9
The multilayer separator for a power storage device according to [1], which satisfies the above conditions.
[3]
The relational expression between r (AB) and D (B) is as follows:
r (AB) / D (B) ≤ 5.0 × 10 ¹²
The multilayer separator for a power storage device according to [1] or [2], which satisfies the above conditions.
[4]
In the exchange NMR measurement of the fluoride ion of the multilayer separator for a power storage device, the following formula:
S (% / ms) = {(Ion transmittance r (AB) at mixing time 100 ms)-(Ion transmittance r (AB) at mixing time 20 ms)} / (100-20)
When the value S calculated by the above is the ion transmission index S (AB), S (AB) and the ion diffusion coefficient D (B) have the following relational expression:
S (AB) / D (B)> 4.0 × 10 ⁹
The multilayer separator for a power storage device according to any one of [1] to [3], which satisfies the above conditions.
[5]
The S (AB) and the D (B) have the following relational expression:
S (AB) / D (B) ≤ 3.5 × 10 ¹⁰
The multilayer separator for a power storage device according to [4], which satisfies the above conditions.
[6]
A multilayer separator for a power storage device including a porous layer A containing a polyolefin resin and a porous layer B containing inorganic particles.
The ion diffusion coefficient of the porous layer B is set to D (B) in the pulsed magnetic field gradient NMR measurement of the fluoride ion of the multilayer separator for a power storage device, and the following is performed in the exchange NMR measurement of the fluoride ion of the multilayer separator for a power storage device. formula:
S (% / ms) = {(Ion transmittance r (AB) between the porous layer A and the porous layer B at the mixing time of 100 ms)-(Ions between the porous layer A and the porous layer B at the mixing time of 20 ms) Transmittance r (AB))} / (100-20)
When the value S calculated by the above is the ion permeation index S (AB), S (AB) and D (B) are the following relational expressions:
S (AB) / D (B)> 4.0 × 10 ⁹
1 × ^10-11 <D (B) <1 × ^10-10
A multi-layer separator for power storage devices that meets the requirements.
[7]
The S (AB) and the D (B) have the following relational expression:
S (AB) / D (B) ≤ 3.5 × 10 ¹⁰
The multilayer separator for a power storage device according to [6], which satisfies the above conditions.

According to the present invention, it is possible to provide a multilayer separator for a power storage device having both output characteristics and storage characteristics, and a power storage device using the same.

FIG. 1 is a schematic diagram for explaining the ion diffusion behavior in a multilayer separator for a power storage device including a porous layer A containing a polyolefin resin and a porous layer B containing inorganic particles. FIG. 2 is an example of a fluoride ion exchange NMR spectrum in the multilayer separator for a power storage device shown in FIG. 1, and FIG. 2A shows a case where the mixing time is 100 ms, and FIG. 2A is shown in FIG. (B) represents the case where the mixing time is 20 ms. FIG. 3 is slice data at the peak maximum value of the porous layer A shown in FIG. 2A, and shows how to obtain the areas of diagonal peaks and intersecting peaks.

Hereinafter, embodiments of the present invention (hereinafter referred to as “the present embodiment”) will be described in detail, but the present invention is not limited to the present embodiment. In the present specification, the upper limit value and the lower limit value of each numerical range can be arbitrarily combined.

<Multilayer separator>
The multilayer separator according to the present embodiment includes a porous layer A containing a polyolefin resin and a porous layer B containing inorganic particles.

[Ion diffusion coefficient of each layer and multi-layer ion transmission rate or multi-layer ion transmission index]
The multilayer separator according to the first embodiment has the ion diffusion coefficient of the porous layer B as D (B) in the pulsed magnetic field gradient NMR measurement of the fluoride ion, and has a mixing time of 100 ms in the exchange NMR measurement of the fluoride ion. When the ion permeability (%) between the porous layer A and the porous layer B is r (AB), r (AB) and D (B) have the following relational expression:
r (AB) / D (B)> 7.0 × 10 ¹¹
1 × ^10-11 <D (B) <1 × ^10-10
Meet. A multilayer separator satisfying the relationship of r (AB) / D (B)> 7.0 × ^{10 11} and 1 × ^10-11 <D (B) <1 × 10-10 is an ion diffusion of a layer containing inorganic particles. It has a novel and unique configuration in which the ion permeability between the porous layers A and B is remarkably excellent, although the property or permeability is equal to or inferior to that of the conventional separator, whereby the output characteristics and storage of the power storage device are achieved. Both characteristics are compatible.

From the viewpoint of further improving the output characteristics and the storage characteristics, r (AB) / D (B) is preferably 8.5 × 10 ¹¹ or more, more preferably 1.0 × 10 ¹² or more or 1.5 × 10 ¹² or more and / or D (B) is preferably 3.2 × 10 ^-11 or more and less than 1 × 10 ^-10 , more preferably 4.0 × 10 ^-11 or more and less than 1 × 10 ^-10 . .. The upper limit of r (AB) / D (B) can be 5.0 × 10 ¹² or less from the viewpoint of the balance between the output characteristic and the storage characteristic.
The exchange NMR measurement of the multilayer separator and the pulsed magnetic field gradient NMR measurement will be described in detail in the items of Examples.

The multilayer separator according to the second embodiment has the ion diffusion coefficient of the porous layer B as D (B) in the pulsed magnetic field gradient NMR measurement of the fluoride ion, and the following formula:
S (% / ms) = {(Ion transmittance r (AB) between the porous layer A and the porous layer B at the mixing time of 100 ms)-(Ions between the porous layer A and the porous layer B at the mixing time of 20 ms) Transmittance r (AB))} / (100-20)
When the value S calculated by the above is the ion permeation index S (AB), S (AB) and D (B) are the following relational expressions:
S (AB) / D (B)> 4.0 × 10 ⁹
1 × ^10-11 <D (B) <1 × ^10-10
Meet. The multilayer separator satisfying the relationship of S (AB) / D (B)> 4.0 × 10 ⁹ and 1 × 10 ^-11 <D (B) <1 × 10 ^-10 is an ion diffusion of the layer containing the inorganic particles. It has a novel and unique configuration in which the ion permeability between the porous layers A and B is remarkably excellent, although the property or permeability is equal to or inferior to that of the conventional separator, whereby the output characteristics and storage of the power storage device are achieved. Both characteristics are compatible.

From the viewpoint of further improving output characteristics and storage characteristics, S (AB) / D (B) is preferably 4.8 × 10 ⁹ or more, more preferably 9.4 × 10 ⁹ or more or 1.0 × 10. ¹⁰ or more and / or D (B) is preferably 3.2 × 10 ^-11 or more and less than 1 × 10 ^-10 , more preferably 4.0 × 10 ^-11 or more and less than 1 × 10 ^-10 . .. The upper limit of S (AB) / D (B) can be 3.5 × 10 ¹⁰ or less from the viewpoint of the balance between the output characteristic and the storage characteristic.

The multilayer separator according to the third embodiment has the following relational expression in which r (AB), S (AB) and D (B) are used in the pulsed magnetic field gradient NMR measurement of the fluoride ion and the exchange NMR measurement of the fluoride ion. :
r (AB) / D (B)> 7.0 × 10 ¹¹
S (AB) / D (B)> 4.0 × 10 ⁹
1 × ^10-11 <D (B) <1 × ^10-10
Meet.
The components of the multilayer separator common to the first, second and third embodiments will be described below.

From the viewpoint of achieving both output characteristics and storage characteristics, when the ion diffusion coefficient of the porous layer A is D (A) in the pulsed magnetic field gradient NMR measurement of the fluoride ion of the multilayer separator for a power storage device, D (A) is as follows. Relational expression:
8 × ^10-11 <D (A) <1 × ^10-9
It is preferable to satisfy. It is more preferable that D (A) is 9.3 × ^10-11 or more and less than 1 × ^10-9 .

Controlling D (A), D (B), r (AB) / D (B) and S (AB) / D (B) within the numerical ranges described above is, for example, with the porous layer A. By arranging an appropriate amount of a binder for inorganic particles near the interface of B, more specifically, it can be realized by appropriately adjusting the following means (i) or (ii):
(I) In the slurry for forming the porous layer B, in addition to the inorganic particles, an ionic binder and a soluble and non-ionic dispersant and / or an additive are used to segregate the binder and uniformly disperse the binder. To ensure proper ion permeation at the interface.
(Ii) When the slurry solvent does not permeate the coated substrate on the surface of the multilayer separator, the solvent volatilizes last from the outermost surface of the coated surface, so that the substrate side is particularly used when a particulate insoluble binder is used. A porous layer B is formed on the temporary support or film from the viewpoint that sedimentation and / or segregation is likely to occur in the temporary support or the film is less likely to be blocked by the binder on the outermost surface than the substrate / coating interface, and then the porous layer is formed. B is transferred to the porous layer A. Thereby, the ion permeation at the interface is not impaired.

[Laminate structure]
In the present embodiment, the multilayer separator has the following laminated structure:
Porous layer A / Porous layer B
Porous layer B / Porous layer A / Porous layer B
Porous layer A / Porous layer B / Porous layer A
And / or may include repetition of any of the laminated structures.

[Poor layer A]
The porous layer A is a layer containing a polyolefin resin. It is preferable that the polyolefin resin occupies 50% by mass or more and 100% by mass or less of the porous layer A. The proportion of the polyolefin resin in the porous layer A 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.

From the viewpoint of molding processability, the viscosity average molecular weight of the polyolefin used for the resin is preferably 1,000 or more, more preferably 2,000 or more, still more preferably 5,000 or more, and the upper limit is preferably 12. It is less than 1,000,000, preferably less than 2,000,000, more preferably less than 1,000,000.

The polyolefin resin is not particularly limited, and is a homopolymer obtained by using, for example, ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and the like as monomers, and a homopolymer and a homoweight. Examples thereof include coalescence or a multi-stage polymer. Further, these polyolefin resins may be used alone or in combination of two or more.
Of these, polyethylene, polypropylene, copolymers thereof, and mixtures thereof are preferable from the viewpoint of the shutdown characteristics of the separator for a power storage device.

Specific examples of polyethylene include low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ultra-high molecular weight polyethylene, and the like.
Specific examples of polypropylene include isotactic polypropylene, syndiotactic polypropylene, atactic polypropylene, and the like.
Specific examples of the copolymer include ethylene-propylene random copolymer, ethylene propylene rubber and the like.

Any additive can be contained in the porous layer A. Additives include polymers other than polyolefin resins, such as fluororesins, fluororubbers, other rubbers, polyimides and precursors thereof; inorganic fillers; antioxidants; metal soaps; UV absorbers; light. Stabilizers; antistatic agents; antifogging agents; coloring pigments and the like can be mentioned. The total amount of these additives added is preferably 20 parts by mass or less with respect to 100 parts by mass of the polyolefin resin from the viewpoint of improving shutdown performance and the like, more preferably 10 parts by mass or less, still more preferably 5 parts by mass. It is less than a part.

[Poor layer B]
The porous layer B is a layer containing inorganic particles. It is preferable that the inorganic particles occupy 50% by mass or more and 100% by mass or less of the porous layer B. The proportion of the inorganic particles in the porous layer B 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.

If desired, the porous layer B may contain a binder resin that binds the inorganic particles to each other, and a dispersant that disperses the inorganic particles in the binder resin.
Examples of the inorganic particles include oxide-based ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, itria, zinc oxide, and iron oxide; nitride-based ceramics such as silicon nitride, titanium nitride, and boron nitride; Silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, barium sulfate, aluminum hydroxide, aluminum hydroxide, aluminum hydroxide, potassium titanate, talc, kaolinite, dekite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, Ceramics such as amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, silicate soil, and silica sand; as well as glass fiber and the like. The inorganic particles may be used alone or in combination of two or more.
Examples of the binder resin here include 1) a conjugated diene-based polymer, 2) an acrylic-based polymer, 3) a polyvinyl alcohol-based resin, and 4) a fluororesin. The binder resin may be in the form of a soluble resin or an insoluble latex, but is preferably an insoluble latex. Further, an ionic functional group or a non-ionic functional group may be contained in the binder resin structure, but an ionic functional group such as a carboxylic acid, a carboxylate, a sulfonic acid, a sulfonate, a phosphoric acid, or a phosphate. Is preferably contained.

1) The conjugated diene-based polymer is a polymer containing a conjugated diene compound as a monomer unit. Examples of the conjugated diene compound include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chlor-1,3-butadiene, styrene-butadiene, and the like. Examples thereof include substituted linear conjugated pentadiene, substituted and side chain conjugated hexadiene, and these may be used alone or in combination of two or more. Of these, 1,3-butadiene is preferable.

2) The acrylic polymer is a polymer containing a (meth) acrylic compound as a monomer unit. The (meth) acrylic compound refers to at least one selected from the group consisting of (meth) acrylic acid and (meth) acrylic acid ester.
Examples of such a compound include a compound represented by the following formula (P1).
CH ₂ = CR ^Y1 -COO- ^RY2 (P1)
{In the formula, ^RY1 represents a hydrogen atom or a methyl group, and ^RY2 represents a hydrogen atom or a monovalent hydrocarbon group. }
When ^RY2 is a hydrogen atom, even if the ionic carboxyl group is replaced with a basic compound such as lithium hydroxide, sodium hydroxide or ammonia after polymerization, the hydrogen ion is replaced with lithium ion, sodium ion, ammonium ion or the like. good.
When ^RY2 is a monovalent hydrocarbon group, it may have a substituent and / or may have a heteroatom in the chain. Examples of the monovalent hydrocarbon group include a linear or branched chain alkyl group, a cycloalkyl group, and an aryl group.
As a chain alkyl group which is a kind of ^RY2 , more specifically, a methyl group, an ethyl group, an n-propyl group, and a chain alkyl group having 1 to 3 carbon atoms, which is an isopropyl group; n- Examples thereof include chain alkyl groups having 4 or more carbon atoms such as a butyl group, an isobutyl group, a t-butyl group, an n-hexyl group, a 2-ethylhexyl group, and a lauryl group. Moreover, as an aryl group which is one kind of ^RY2 , for example, a phenyl group can be mentioned.
Examples of the substituent of the monovalent hydrocarbon group include a hydroxyl group and a phenyl group, and examples of the hetero atom in the chain include a halogen atom and an oxygen atom.
Examples of such (meth) acrylic compounds include (meth) acrylic acid, chain alkyl (meth) acrylate, cycloalkyl (meth) acrylate, (meth) acrylate having a hydroxyl group, and phenyl group-containing (meth) acrylate. Can be mentioned. The (meth) acrylic compound may be used alone or in combination of two or more.

3) Examples of the polyvinyl alcohol-based resin include polyvinyl alcohol and polyvinyl acetate.

4) Examples of the fluororesin include polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene. Examples thereof include copolymers.

The dispersant referred to here is one that adsorbs to the surface of inorganic particles in a slurry and stabilizes the inorganic particles by electrostatic repulsion or the like. For example, a polycarboxylate, a sulfonate, a polyoxyether, or a surfactant. And so on.

<Manufacturing method and physical properties of multilayer separator>
The multilayer separator according to the present embodiment can be produced, for example, by the following method I or II.

[Method I: Slurry coating]
Method I is the following step:
(Ia) A step of forming a polyolefin resin film as the porous layer A by melt-kneading and extruding the composition A containing the polyolefin resin and the plasticizer, and then stretching and extracting the plasticizer; and (Ib) the inorganic particles and A slurry containing a solvent, an ionic binder, and a soluble and nonionic dispersant and / or an additive is applied to at least one surface of the porous layer A, and the solvent is volatilized by drying to volatilize the porous layer B. Steps to form;
including.

[Method II: Transfer]
Method II has the following steps:
(IIa) A step of forming a polyolefin resin film as the porous layer A by melt-kneading and extruding the composition A containing the polyolefin resin and the plasticizer, and then stretching and extracting the plasticizer;
(IIb) A step of coating a support film with a slurry containing inorganic particles, a resin binder, water or an aqueous solvent, and optionally a flow adjuster or surface tension adjuster of the slurry to form a porous layer B. And (IIc) the step of transferring the porous layer B from the support film to at least one side of the porous layer A;
including.
In order to carry out Step IIb and Step IIc, it is preferable to select the support film so that the porous layer B has more adhesiveness to the porous layer A than the support film.

The step Ia of the method I or the step IIa of the method II can be performed according to a method for producing a polyolefin resin porous single-layer film using a conventional plasticizer. The composition A may further contain a solvent, additives and the like, if desired. Further, a solvent may be used at the time of extracting the plasticizer.

As a method for melt-kneading the composition A, for example, a polyolefin resin and, if necessary, other additives are put into a resin kneading device such as an extruder, a kneader, a laboplast mill, a kneading roll, and a Banbury mixer to heat the resin component. Examples thereof include a method of introducing a plasticizer at an arbitrary ratio while melting and kneading. At this time, it is preferable to pre-knead the polyolefin resin, other additives and the plasticizer at a predetermined ratio using a Henschel mixer or the like before putting them into the resin kneading apparatus. By using such a kneading method, the dispersibility of the plasticizer is enhanced, and when the sheet-shaped molded product of the resin composition and the melt-kneaded plasticizer is stretched in a later step, the film is not broken and the magnification is high. It tends to be able to be stretched with.
Examples of the method for preparing the inorganic particle-containing slurry include a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloidal mill, an attritor, a roll mill, a high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and stirring. Examples include a mechanical stirring method using blades and the like.

The step Ib of the method I or the step IIb of the method II may be, for example, a gravure coater method, a small diameter gravure coater method, a reverse roll coater method, a transfer roll coater method, a kiss coater method, a dip coater method, a knife coater method, an air doctor coater method, and the like. It can be performed by a blade coater method, a rod coater method, a squeeze coater method, a cast coater method, a die coater method, a screen printing method, a spray coating method, or the like.

By method I or II, r (AB) / D (B)> 7.0 × 10 ¹¹ and S (AB) / D (B)> 4.0 × 10 ⁹ and 1 × ^10-11 <D (B) A multilayer separator for a power storage device satisfying the relationship of <1 × 10 ⁻¹⁰ can be obtained. The porous layer B can be formed on one side or both sides of the porous layer A in light of its use.

The polyolefin resins, inorganic particles, binder resins, dispersants and additives that can be used in Method I or II are as described above. The plasticizer that can be used in Method I or II is, for example, liquid paraffin. Solvents that can be used in Method I or II are, for example, N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, water, ethanol, toluene, hot xylene, hexane and the like. The aqueous solvent may be a mixture of water and a hydrophilic solvent such as alcohol.

In step IIb of Method II, the resin binder used is preferably acrylic latex, and the surface tension modifier used is preferably an aqueous solution of polycarboxylate and / or an aqueous solution of aliphatic polyether. ..

The additive used in Method I or II is preferably one that can be removed during solvent removal or plasticizer extraction, but is electrochemically stable when the power storage device is used, does not inhibit the battery reaction, and is 200. If it is stable up to about ° C., it may remain in the power storage device (or the separator in the power storage device).

The puncture strength of the multilayer separator is preferably 100 gf or more, more preferably 150 gf or more, still more preferably 200 gf or more, preferably 600 gf or less, more preferably 550 gf or less, still more preferably 500 gf or less. Adjusting the puncture strength to 100 gf or more is preferable from the viewpoint of suppressing film breakage due to the active material or the like that has fallen off during the production of the power storage device, and also reduces the concern of short circuit due to expansion and contraction of the electrode due to charge and discharge. It is also preferable from the viewpoint. On the other hand, adjusting the puncture strength to 600 gf or less is preferable from the viewpoint of reducing shrinkage due to relaxation of orientation during heating.

The final film thickness (total thickness) of the multilayer separator is preferably 2 μm or more and 200 μm or less, more preferably 5 μm or more and 100 μm or less, and further preferably 7 μm or more and 30 μm from the viewpoint of balancing mechanical strength and high rate. It is as follows. When the film thickness is 2 μm or more, the mechanical strength tends to be sufficient, and when the film thickness is 200 μm or less, the occupied volume of the separator is reduced, which tends to be advantageous in terms of increasing the capacity of the battery.
The final thickness of the porous layer B containing the inorganic particles is preferably 1.0 μm or more, more preferably 1.2 μm or more, still more preferably 1.5 μm or more, and 1.8 μm from the viewpoint of heat resistance or insulating property. The above, or 2.0 μm or more, is preferably 50 μm or less, more preferably 20 μm or less, still more preferably 10 μm or less or 7 μm or less from the viewpoint of improving ion permeability and output characteristics.

The lower limit of the air permeability of the multilayer separator is preferably 10 seconds / 100 ml or more, more preferably 20 seconds / 100 ml or more, still more preferably 30 seconds / 100 ml or more, and particularly preferably 50 seconds / 100 ml or more. On the other hand, the upper limit of the air permeability is preferably 650 seconds / 100 ml or less, more preferably 500 seconds / 100 ml or less, still more preferably 450 seconds / 100 ml or less, and particularly preferably 400 seconds / 100 ml or less. Setting the air permeability to 10 seconds / 100 ml or more is suitable from the viewpoint of suppressing self-discharge when the separator is used in the battery. On the other hand, setting the air permeability to 650 seconds / 100 ml or less is preferable from the viewpoint of obtaining good charge / discharge characteristics.

<Power storage device>
The power storage device according to another embodiment of the present invention includes a positive electrode, the multilayer separator described above, a negative electrode, and optionally an electrolytic solution.
Specific examples of the power storage device include a lithium battery, a lithium secondary battery, a lithium ion secondary battery, a sodium secondary battery, a sodium ion secondary battery, a magnesium secondary battery, a magnesium ion secondary battery, and a calcium secondary battery. , Calcium ion secondary battery, Aluminum secondary battery, Aluminum ion secondary battery, Nickel hydrogen battery, Nickel cadmium battery, Electric double layer capacitor, Lithium ion capacitor, Redox flow battery, Lithium sulfur battery, Lithium air battery, Zinc air battery And so on. Among these, from the viewpoint of practicality, a lithium battery, a lithium secondary battery, a lithium ion secondary battery, a nickel hydrogen battery, or a lithium ion capacitor is preferable, and a lithium ion secondary battery is more preferable.

In the power storage device, for example, a positive electrode and a negative electrode are superposed via the multilayer separator according to the present embodiment and wound as necessary to form a laminated electrode body or a wound electrode body, and then the exterior thereof is attached. It is loaded into the body, the positive and negative electrodes are connected to the positive and negative terminals of the exterior body via a lead body, and a non-aqueous electrolyte solution containing a non-aqueous solvent such as a chain or cyclic carbonate and an electrolyte such as a lithium salt is further applied. It can be produced by sealing the exterior body after injecting it into the exterior body.

Next, the present embodiment will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples as long as the gist thereof is not exceeded. The physical characteristics or cell characteristics in the examples were measured or evaluated by the following methods.

[Viscosity average molecular weight (Mv)]
Based on ASTM-D4020, the ultimate viscosity [η] (dl / g) at 135 ° C. in a decalin solvent is determined. The Mv of polyethylene was calculated by the following formula.
[Η] = 6.77 × 10 ^-4 Mv ^0.67
For polypropylene, Mv was calculated by the following formula.
[Η] = 1.10 × 10 ^-4 Mv ^0.80

[Thickness (μm)]
The film thickness of the sample was measured with a dial gauge (PEACOCK No. 25 (trademark) manufactured by Ozaki Seisakusho). A sample of MD 10 mm × TD 10 mm was cut out from the porous membrane, and the thickness of 9 points (3 points × 3 points) was measured in a grid pattern. The average value of the obtained measured values was calculated as the film thickness (μm) or the layer thickness.
The thickness of each single layer obtained in this example and the comparative example was measured in the state of the single layer obtained in each manufacturing process. In the case of the laminated state, it was calculated by subtracting the measured single layer value. For those in which the state of a single layer cannot be obtained by coextrusion, the thickness of each layer was calculated from the cross-sectional SEM.

[Air permeability (seconds / 100 ml)]
The measurement was performed using a Garley type air permeability meter (GB2 (trademark) manufactured by Toyo Seiki Co., Ltd.) conforming to JIS P-8117.

[Puncture strength (gf)]
Using a handy compression tester "KES-G5" (manufactured by Kato Tech Co., Ltd.), the microporous membrane was fixed with a sample holder having an opening diameter of 11.3 mm. A piercing test was performed on the central part of the fixed microporous membrane under the conditions of a radius of curvature of the needle tip of 0.5 mm and a piercing speed of 2 mm / sec in an atmosphere of 25 ° C. to pierce as the maximum piercing load. The intensity (gf) was measured.

[NMR]
<Measurement of fluoride ion diffusion coefficient D by magnetic field gradient NMR method>
1. 1. Sample preparation The separator was hollowed out to a diameter of 4 mmφ, laminated in the thickness direction, and introduced into an NMR tube so as to have a height of 5 mm. As the NMR tube, a micro sample tube manufactured by Shigemi was used. A mixture (volume ratio 1: 2) of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) of 1M lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) as an electrolytic solution is added to the NMR tube, and a separator is added to the electrolytic solution. Was soaked overnight to remove excess electrolytic solution other than the electrolytic solution impregnated in the separator, and the obtained sample was used for measurement.

2. 2. Measurement conditions Equipment: JNM-ECA400 (manufactured by JEOL Ltd.)
Observation nucleus: ¹⁹ F
Measurement frequency: 372.5 MHz
Lock solvent: None Measurement temperature: 30 ° C
Pulse sequence: bpp_led_dosy_pfg
Δ: 20 ms
δ: 0.3 ms to 0.6 ms

In the magnetic field gradient NMR measurement method, the observed peak height is E, the peak height when no magnetic field gradient pulse is applied is E ₀ , the nuclear gyromagnetic ratio is γ (T ^-1 · s ^-1 ), and the magnetic field gradient intensity is defined. When g (T · m ^-1 ), the pulsed field gradient pulse application time is δ (s), the diffusion time is Δ (s), and the self-diffusion coefficient is D (m ² · s ^-1 ), the following equation holds.
Ln (E / E ₀ ) = D × γ ² × g ² × δ ² × (Δ−δ / 3)
Fix Δ and δ and change g by 10 points or more in the range from 0 to Ln (E / E ₀ ) ≦ -3, and change Ln (E / E ₀ ) on the Y axis, γ ² × g ² × δ ² . The diffusion coefficient D was calculated from the slope of a straight line plotted with x (Δ−δ / 3) as the X axis.
Fluoride ion peaks impregnated in the porous layer A containing the polyolefin resin and the porous layer B containing the inorganic particles are observed in the NMR spectrum at -90 ppm to -70 ppm, and the peaks observed on the high magnetic field side are the porous layer A and the low. The peak observed on the magnetic field side was defined as the porous layer B. From the peak heights of the porous layer A and the porous layer B, the diffusion coefficient D of the fluoride ions contained in the porous layer A and the porous layer B was obtained.

<Measurement of Fluoride Ion Permeability r and Permeation Index S by Exchange NMR Method>
1. 1. Sample preparation The separator was hollowed out to a diameter of 4 mmφ, laminated in the thickness direction, and introduced into an NMR tube so as to have a height of 5 mm. However, the porous layer B containing the inorganic particles does not overlap with the porous layer A, but is always laminated so that the porous layers B overlap with each other. As the NMR tube, a micro sample tube manufactured by Shigemi was used. A 1M LiTFSI EC and MEC mixture (volume ratio 1: 2) solution as an electrolytic solution is added to the NMR tube, the separator is immersed in the electrolytic solution overnight, and a surplus electrolytic solution other than the electrolytic solution impregnated in the separator is added. It was removed and the obtained sample was used for measurement.

2. 2. Measurement conditions Equipment: JNM-ECS400 (manufactured by JEOL Ltd.)
Observation nucleus: ¹⁹ F
Measurement frequency: 376.2 MHz
Lock solvent: None Measurement temperature: 30 ° C
Pulse sequence: nosy_phase
Number of direct observation axis points: 1024
Number of indirect observation axis points: 256
Mixing time: 20 ms, 100 ms

In the exchange NMR measurement, the transmittance r and the transmission index S of the fluoride ion between the layers of the porous layer A containing the polyolefin resin and the porous layer B containing the inorganic particles were determined.

Measurement of Ion Permeability r (AB) Exchange NMR measurement was performed with a mixing time of 100 ms, and the transmittance r (AB) of fluoride ions moving from the porous layer A to the porous layer B was determined as follows.
FIG. 1 is a schematic diagram for explaining the ion diffusion behavior in a multilayer separator for a power storage device including a porous layer A containing a polyolefin resin and a porous layer B containing inorganic particles. In FIG. 1, the diffusion behavior of the fluoride ion impregnated in the porous layer A 1, the diffusion behavior of the fluoride ion impregnated in the porous layer B 2, and the diffusion of the fluoride ion transferred from the porous layer A to the porous layer B are shown. The behavior 3 and the diffusion behavior 4 of the fluoride ion transferred from the porous layer B to the porous layer A are shown.
With reference to FIG. 2A, which is an example of an exchange NMR spectrum at a mixing time of 100 ms, the high magnetic field side of the peaks observed at -90 ppm to -70 ppm of the direct observation axis is impregnated into the porous layer A. The fluoride ion peak and the low magnetic field side were defined as the fluoride ion peak impregnated in the porous layer B, and slice data (FIG. 3) was obtained at the maximum peak value of the porous layer A.
The peak position of the porous layer A in the slice data (FIG. 3) is a diagonal peak (representing the fluoride ion impregnated in the porous layer A and corresponding to the ion diffusion behavior 1 shown in the schematic diagram of FIG. 1). The peak position of the porous layer B is a crossed peak (representing a fluoride ion that has moved from the porous layer A to the porous layer B, and corresponds to the ion diffusion behavior 3 shown in the schematic diagram of FIG. 1).
The following formula:
Crossed peak area / (diagonal peak area + crossed peak area) x 100
The value (%) obtained from the above was taken as the ion transmittance r (AB).
When the peaks were close to each other, the diagonal peak and the crossed peak were separated from each other by a perpendicular line drawn directly from the extreme value between the peaks to the observation axis, and the respective areas were obtained.

Measurement of ion transmission index S (AB) Exchange NMR measurements were performed at 20 ms (for example, in the case of FIG. 2 (b)) and 100 ms (for example, in the case of FIG. 2 (a)) for the mixing time, and the mixing time was 20 ms and 100 ms. The ion transmittance r (AB) was calculated for each of the data. The rate of change S (% / ms) of the ion transmittance r (AB) when the mixing time is 20 ms and 100 ms is expressed by the following formula:
S = (Ion transmittance r (AB) at 100 ms)-(Ion transmittance r (AB) at 20 ms) / (100-20)
The ion permeation index S (AB) was calculated as described above.

[Battery characteristics]
a. Preparation of positive electrode Nickel, manganese, cobalt composite oxide (NMC) (Ni: Mn: Co = 1: 1: 1 (element ratio), density 4.70 g / cm ³ , mass density 175 mAh / g) as the positive electrode active material. 90.4% by mass, 1.6% by mass of graphite powder (KS6) (density 2.26 g / cm ³ , number average particle diameter 6.5 μm) as a conductive auxiliary material and 1.6% by mass of acetylene black powder (AB) (density 1.95 g). ( ³ , number average particle size 48 nm) was mixed at a ratio of 3.8% by mass, and vinylidene fluoride (PVDF) (density 1.75 g / cm ³ ) as a binder was mixed at a ratio of 4.2% by mass, and these were mixed with N. -Slurries were prepared by dispersing in methylpyrrolidone (NMP). 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 rolled using a roll press machine. The amount of the positive electrode active material applied at this time was 109 g / m ² .

b. Preparation of negative electrode As negative electrode active material, graphite powder A (density 2.23 g / cm ³ , number average particle diameter 12.7 μm) was added to 87.6% by mass and graphite powder B (density 2.27 g / cm ³ , number average particle diameter). 9.7% by mass (6.5 μm), 1.4% by mass (solid content equivalent) of ammonium salt of carboxymethyl cellulose (solid content concentration 1.83% by mass aqueous solution) and 1.7% by mass (diene rubber-based latex) as a binder. A slurry was prepared by dispersing (in terms of solid content) (solid content concentration 40% by mass aqueous solution) in purified water. This slurry was applied to one side of a copper foil having a thickness of 12 μm as a negative electrode current collector with a die coater, dried at 120 ° C. for 3 minutes, and then rolled using a roll press machine. The amount of the negative electrode active material applied at this time was 52 g / m ² .

c. Preparation of non-aqueous electrolyte solution LiPF ₆ was added to 1 mol / L in a mixed solvent (Lithium Battery Grade manufactured by Kishida Chemical Co., Ltd.) in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 2. It was dissolved so as to become. As an additive, 2 wt% of vinylene carbonate (VC) and 0.5 wt% of propane sultone (PS) were added to obtain a non-aqueous electrolyte electrolyte.

d. Battery assembly The separator is punched into a circle with a diameter of 24 mm, and item a. The positive electrode produced in step 1 was punched into a circle with an area of 2.00 cm ² and item b. The negative electrode produced in 1 was punched into a circle having an area of 2.05 cm ² .
The negative electrode, the separator, and the positive electrode are stacked in this order from the bottom in the vertical direction so that the active material surfaces of the positive electrode and the negative electrode face each other, and are stored in a stainless metal container with an aluminum lid. The container and the lid are insulated, and the container is in contact with the copper foil of the negative electrode and the lid is in contact with the aluminum foil of the positive electrode. The above-mentioned non-aqueous electrolytic solution was injected into this container and sealed to assemble a simple battery having a capacity of 3 mAh.

e1. Evaluation items of output characteristics d. The battery obtained in 1. is charged with a constant current of 0.3C in an environment of 25 ° C., reaches 4.2V, is charged with a constant voltage of 4.2V, and has a constant current of 0.3C. It was discharged to 0V. The total of charging time at a constant current and charging time at a constant voltage was set to 8 hours. Note that 1C is a current value at which the battery is discharged in one hour.
Next, the simple battery was charged with a constant current of 0.3 C, reached 4.2 V, charged with a constant voltage of 4.2 V, and discharged to 3.0 V with a constant current of 0.3 C. The total of the charging time at a constant current and the charging time at a constant voltage was 5 hours, and the capacity when discharged at a constant current of 0.3C was 0.3C discharge capacity (mAh).
Next, the simple battery was charged with a constant current of 0.3 C, reached 4.2 V, then charged with a constant voltage of 4.2 V, and discharged to 3.0 V with a constant current of 10 C. The total of charging time at a constant current and charging time at a constant voltage was 5 hours, and the capacity when discharged at a constant current of 10C was 10C discharge capacity (mAh).
The ratio of the 10C discharge capacity to the 0.3C discharge capacity was calculated from the following formula, and this value was used as the output characteristic.
Output characteristics (%) = (10C discharge capacity / 0.3C discharge capacity) x 100
The obtained output characteristics were evaluated according to the following criteria.
A: Output characteristics are over 60% B: Output characteristics are over 50% and 60% or less C: Output characteristics are over 40% and 50% or less D: Output characteristics are over 23% and 40% or less E: Output characteristics are , 23% or less

[Characteristics stored at 50 ° C]
e2. Evaluation of storage characteristics The battery after measuring the output characteristics with 10C discharge is charged with a constant current of 0.3C in an environment of 25 ° C, and after reaching 4.35V, it is charged with a constant voltage of 4.35V. Then, it was discharged to 3.0V with a constant current of 0.3C. The total of the charging time at the constant current and the charging time at the constant voltage was set to 5 hours, and this cycle was performed three times. The third discharge capacity was defined as the discharge capacity before storage.
Next, the battery was charged with a constant current of 0.3 C, reached 4.35 V, charged with a constant voltage of 4.35 V, and then the battery was stored in a constant temperature bath at 50 ° C. for 10 days. Then, the battery was allowed to stand in an environment of 25 ° C., and after the battery surface temperature was in the range of 25 ± 3 ° C., the battery was discharged to 3.0 V with a constant current of 0.3 C. The discharge capacity at that time was defined as the remaining capacity after storage at 50 ° C.
The 50 ° C. storage characteristics were calculated from the following formula.
50 ° C storage characteristics (%) = (residual capacity after storage at 50 ° C / discharge capacity before storage) x 100
The obtained 50 ° C. storage characteristics were evaluated according to the following criteria.
A: Preservation characteristics are over 80% B: Preservation characteristics are over 70% and 80% or less C: Preservation characteristics are over 60% and over 70% D: Preservation characteristics are over 60%

<Manufacturing of microporous membrane (A)>
Production Example A-1
47.5 parts by mass of homopolymer high-density polyethylene with a viscosity average molecular weight (Mv) of 700,000, 47.5 parts by mass of homopolymer high-density polyethylene with an Mv of 300,000, and 400,000 parts of Mv. 5 parts by mass of polyethylene of a homopolymer was dry-blended with a tumbler blender. To 99 parts by mass of the obtained polyolefin mixture, add 1 part by mass of tetrakis- [methylene- (3', 5'-di-t-butyl-4'-hydroxyphenyl) propionate] methane as an antioxidant, and tumbler blender again. The mixture was obtained by dry blending with.

The resulting mixture was fed by a feeder to the feed port of a twin-screw co-screw extruder. In addition, liquid paraffin "Smoyl P-350P" (manufactured by Matsumura Petroleum Research Institute Co., Ltd.) is added so that the ratio of the amount of liquid paraffin to the total mixture (100 parts by mass) extruded by melt-kneading is 67 parts by mass. Side-fed to the shaft extruder cylinder. The set temperature was 160 ° C. for the kneaded portion and 180 ° C. for the T-die. Subsequently, the melt-kneaded product was extruded into a sheet from a T-die and cooled with a cooling roll controlled to a surface temperature of 70 ° C. to obtain a sheet-shaped polyolefin resin composition having a thickness of 1260 μm. Next, they were continuously guided to a simultaneous biaxial tenter, and simultaneous biaxial stretching was performed 7 times in the vertical direction and 6.4 times in the horizontal direction. The stretching set temperature at this time was 120 ° C. Next, it was guided to a methylene chloride tank and sufficiently immersed in methylene chloride to extract and remove liquid paraffin. After that, after drying methylene chloride, it was further guided to a transverse tenter and stretched 1.75 times in the lateral direction, and then the final outlet was set to a relaxation rate of 14.3% so as to be 1.50 times (relaxation rate = (1). .75-1.5) /1.75 × 100 = 14.3%), the microporous polyolefin membrane was wound. The set temperature of the transversely stretched portion was 125 ° C., and the set temperature of the relaxation portion was 130 ° C.

Production Example A-2
High-density polyethylene with a viscosity average molecular weight (Mv) of 270,000 is 16.8 parts by mass, ultra-high molecular weight polyethylene with an Mv of 2 million is 11.2 parts by mass, and silica "RX200" with an average primary particle size of 12 nm (Nippon Aerodil (Nippon Aerodil) 7 parts by mass of (manufactured by Matsumura Co., Ltd.), 7 parts by mass of liquid paraffin "Smoyl P-350P" (manufactured by Matsumura Petroleum Research Institute Co., Ltd.) as a plasticizer, and tetrakis- [methylene- (3', 5') as an antioxidant. -Di-t-butyl-4'-hydroxyphenyl) propionate] 0.1 part by mass of methane was added and premixed with a super mixer.

The resulting mixture was fed by a feeder to the feed port of a twin-screw co-screw extruder. Further, the liquid paraffin was side-fed to the twin-screw extruder cylinder so that the ratio of the amount of liquid paraffin to the total mixture (100 parts by mass) extruded by melt-kneading was 65 parts by mass. The set temperature was 160 ° C for the kneaded portion and 230 ° C for the T die. Subsequently, the melt-kneaded product was extruded into a sheet from a T-die and cooled with a cooling roll controlled to a surface temperature of 70 ° C. to obtain a sheet-shaped polyolefin resin composition having a thickness of 1260 μm. Next, they were continuously guided to a simultaneous biaxial tenter, and simultaneous biaxial stretching was performed 7 times in the vertical direction and 6.4 times in the horizontal direction. The stretching set temperature at this time was 122 ° C. Next, it was guided to a methylene chloride tank and sufficiently immersed in methylene chloride to extract and remove liquid paraffin. After that, methylene chloride was dried. Further, after being guided to the lateral tenter and stretched 1.8 times in the lateral direction, the relaxation rate was set to 16.7% so that the final outlet became 1.5 times (relaxation rate = (1.8-1.5) / 1. 8 × 100 = 16.7%), the inorganic-containing polyolefin microporous membrane was wound. The set temperature of the transversely stretched portion was 130 ° C., and the set temperature of the relaxation portion was 135 ° C.

<Manufacturing of paint containing inorganic particles>
Paint A
95.0 parts by mass of aluminum hydroxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by mass (solid content equivalent) of ammonium polycarboxylate aqueous solution (SN Disper manufactured by San Nopco Ltd.) as an ionic dispersant. Santo 5468 (solid content concentration 40%) was uniformly dispersed in 100 parts by mass of water to prepare a dispersion. The obtained dispersion was crushed by a bead mill (cell volume 200 cc, zirconia bead diameter 0.1 mm, filling amount 80%), and the particle size distribution of the inorganic particles was adjusted to D50 = 1.0 μm. Acrylic latex (solid content concentration 40%, average particle size 145 nm, minimum film formation temperature 0 ° C. or less, constituent monomer) of 4.6 parts by mass (solid content equivalent) as an insoluble ionic binder in a dispersion liquid with adjusted particle size distribution. : Butyl acrylate, 2-ethylhexyl acrylate, methacrylic acid) was added to prepare paint A.

Paint B
85.0 parts by mass of aluminum hydroxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by mass (solid content equivalent) of ammonium polycarboxylate aqueous solution (SN Disper manufactured by San Nopco Ltd.) as an ionic dispersant. Santo 5468 (solid content concentration 40%) was uniformly dispersed in 100 parts by mass of water to prepare a dispersion. The obtained dispersion was crushed by a bead mill (cell volume 200 cc, zirconia bead diameter 0.1 mm, filling amount 80%), and the particle size distribution of the inorganic particles was adjusted to D50 = 1.0 μm. Acrylic latex (solid content concentration 40%, average particle size 145 nm, minimum film formation temperature 0 ° C. or less, constituent monomer) of 14.6 parts by mass (solid content equivalent) as an insoluble ionic binder in a dispersion liquid with adjusted particle size distribution. : Butyl acrylate, 2-ethylhexyl acrylate, methacrylic acid) was added to prepare paint B.

Paint C
80.0 parts by mass of aluminum hydroxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by mass (solid content equivalent) of ammonium polycarboxylate aqueous solution (SN Disper manufactured by San Nopco Ltd.) as an ionic dispersant. Santo 5468 (solid content concentration 40%) was uniformly dispersed in 100 parts by mass of water to prepare a dispersion. The obtained dispersion was crushed by a bead mill (cell volume 200 cc, zirconia bead diameter 0.1 mm, filling amount 80%), and the particle size distribution of the inorganic particles was adjusted to D50 = 1.0 μm. Acrylic latex (solid content concentration 40%, average particle size 145 nm, minimum film formation temperature 0 ° C. or less, constituent monomer) of 4.6 parts by mass (solid content equivalent) as an insoluble ionic binder in a dispersion liquid with adjusted particle size distribution. : Butyl acrylate, 2-ethylhexyl acrylate, methacrylic acid) and 15.0 parts by weight of sodium carboxymethyl cellulose (Dycel 1220) as an ionic flow conditioner were added to prepare paint C.

Paint D
97.0 parts by mass of aluminum hydroxide (average particle size 1.4 μm) as inorganic particles and 3.0 parts by mass (solid content equivalent) of ammonium polycarboxylate aqueous solution (SN Disper manufactured by San Nopco Ltd.) as an ionic dispersant. Santo 5468 (solid content concentration 40%) was uniformly dispersed in 100 parts by mass of water to prepare a dispersion. The obtained dispersion was crushed by a bead mill (cell volume 200 cc, zirconia bead diameter 0.1 mm, filling amount 80%), and the particle size distribution of the inorganic particles was adjusted to D50 = 1.0 μm. Paint D was produced.

Paint E
91.0 parts by mass of aluminum hydroxide (average particle size 1.4 μm) as inorganic particles and 1.0 part by mass (solid content equivalent) of an aliphatic polyether aqueous solution (San Nopco Ltd. E) as a nonionic dispersant. -D057, solid content concentration 40%) was uniformly dispersed in 100 parts by mass of water to prepare a dispersion liquid. The obtained dispersion was crushed by a bead mill (cell volume 200 cc, zirconia bead diameter 0.1 mm, filling amount 80%), and the particle size distribution of the inorganic particles was adjusted to D50 = 1.0 μm. Acrylic latex (solid content concentration 40%, average particle size 145 nm, minimum film formation temperature 0 ° C. or less, constituent monomer) of 5.0 parts by mass (solid content equivalent) as an insoluble ionic binder in a dispersion liquid with adjusted particle size distribution. : Butyl acrylate, 2-ethylhexyl acrylate, methacrylic acid) and 3.0% by weight of hydroxyethyl cellulose (SP-200 manufactured by Dycel) as a nonionic flow conditioner were added to prepare paint E.

Paint F
78.0 parts by mass of aluminum hydroxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by mass (solid content equivalent) of ammonium polycarboxylate aqueous solution (SN Disper manufactured by Sannopco) as an ionic dispersant. Santo 5468, solid content concentration 40%) and 0.6 parts by mass (solid content equivalent) of an aliphatic polyether aqueous solution (E-D057 manufactured by Sannopco, solid content concentration 40%, static surface tension) as a surface tension adjuster. A dispersion was prepared by uniformly dispersing 35 mN / m (0.1% by mass aqueous solution, 25 ° C.) in 100 parts by mass of water. The obtained dispersion was crushed by a bead mill (cell volume 200 cc, zirconia bead diameter 0.1 mm, filling amount 80%), and the particle size distribution of the inorganic particles was adjusted to D50 = 1.0 μm. Acrylic latex (solid content concentration 40%, average particle size 145 nm, minimum film formation temperature 0 ° C. or less, constituent monomer) of 4.0 parts by mass (solid content equivalent) as an insoluble ionic binder in a dispersion liquid with adjusted particle size distribution. : Butyl acrylate, 2-ethylhexyl acrylate, methacrylic acid) and 17.0 parts by mass (solid content equivalent) acrylic latex (solid content concentration 23%, average particle size 450 nm, glass transition temperature 55 ° C., constituent monomers) as organic particles. : Cyclohexyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate) was added to prepare paint F.

[Example 1-3, Comparative Example 1-5]
Separator was produced according to the substrate, paint, coating method, layer structure, separator manufacturing method, etc. shown in Table 1, and the above physical characteristics or cell characteristics were measured or evaluated. The measurement / evaluation results are also shown in Table 1.

[Paint coating on porous layer substrate]
The porous layer base material is fed out from a feeder, the surface is continuously subjected to corona discharge treatment, the paint is applied using a gravure reverse coater, and then dried in a dryer at 60 ° C. to remove water. I rolled it up. In the case of double-sided coating, the back surface of the porous layer base material was also coated in the same manner to prepare a multilayer separator.

[Transcription of Example 3]
The above paint F was applied to a surface-treated PET film (Toyobo Ester E5100, manufactured by Toyobo Co., Ltd.) using a gravure reverse coater. Subsequently, the coating layer was dried in a dryer at 60 ° C. to remove water and wound up. Next, the coating layer and the porous film A-1 are fed out, the coating layer and the porous film A-1 are laminated using a heating roll at 40 ° C., and then the PET film is peeled off to form the coating film. Transferred onto the surface of A-1 to obtain a multilayer separator.

1 Diffusion behavior of fluoride ions impregnated in porous layer A 2 Diffusion behavior of fluoride ions impregnated in porous layer B 3 Diffusion behavior of fluoride ions transferred from porous layer A to porous layer B 4 From porous layer B Diffusion behavior of fluoride ions transferred to the porous layer A

Claims (7)

A multilayer separator for a power storage device including a porous layer A containing a polyolefin resin and a porous layer B containing inorganic particles.
The ion diffusion coefficient of the porous layer B is set to D (B) in the pulsed magnetic field gradient NMR measurement of the fluoride ion of the multilayer separator for a power storage device, and 100 ms in the exchange NMR measurement of the fluoride ion of the multilayer separator for a power storage device. When the ion permeability (%) between the porous layer A and the porous layer B at the mixing time is r (AB), r (AB) and D (B) have the following relational expression:
r (AB) / D (B)> 7.0 × 10 ¹¹
1 × ^10-11 <D (B) <1 × ^10-10
A multi-layer separator for power storage devices that meets the requirements. When the ion diffusion coefficient of the porous layer A is D (A) in the pulsed magnetic field gradient NMR measurement of the fluoride ion of the multilayer separator for a power storage device, D (A) is the following relational expression:
8 × ^10-11 <D (A) <1 × ^10-9
The multilayer separator for a power storage device according to claim 1. The relational expression between r (AB) and D (B) is as follows:
r (AB) / D (B) ≤ 5.0 × 10 ¹²
The multilayer separator for a power storage device according to claim 1 or 2, which satisfies the above conditions. In the exchange NMR measurement of the fluoride ion of the multilayer separator for a power storage device, the following formula:
S (% / ms) = {(Ion transmittance r (AB) at mixing time 100 ms)-(Ion transmittance r (AB) at mixing time 20 ms)} / (100-20)
When the value S calculated by the above is the ion transmission index S (AB), S (AB) and the ion diffusion coefficient D (B) have the following relational expression:
S (AB) / D (B)> 4.0 × 10 ⁹
The multilayer separator for a power storage device according to any one of claims 1 to 3, which satisfies the above conditions. The S (AB) and the D (B) have the following relational expression:
S (AB) / D (B) ≤ 3.5 × 10 ¹⁰
The multilayer separator for a power storage device according to claim 4. A multilayer separator for a power storage device including a porous layer A containing a polyolefin resin and a porous layer B containing inorganic particles.
The ion diffusion coefficient of the porous layer B is set to D (B) in the pulsed magnetic field gradient NMR measurement of the fluoride ion of the multilayer separator for a power storage device, and the following is performed in the exchange NMR measurement of the fluoride ion of the multilayer separator for a power storage device. formula:
S (% / ms) = {(Ion transmittance r (AB) between the porous layer A and the porous layer B at the mixing time of 100 ms)-(Ions between the porous layer A and the porous layer B at the mixing time of 20 ms) Transmittance r (AB))} / (100-20)
When the value S calculated by the above is the ion permeation index S (AB), S (AB) and D (B) are the following relational expressions:
S (AB) / D (B)> 4.0 × 10 ⁹
1 × ^10-11 <D (B) <1 × ^10-10
A multi-layer separator for power storage devices that meets the requirements. The S (AB) and the D (B) have the following relational expression:
S (AB) / D (B) ≤ 3.5 × 10 ¹⁰
The multilayer separator for a power storage device according to claim 6.

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