JP6855166B2 - Separator for power storage device and its manufacturing method - Google Patents

Description

The present invention relates to a separator for a power storage device and a method for manufacturing the same. More specifically, the present invention relates to a separator for a power storage device exhibiting excellent performance, and a method for easily manufacturing the separator with a small number of steps.

In the power storage device, a separator that insulates the positive electrode and the negative electrode, holds an electrolytic solution, and controls ionic conduction between the two electrodes is used. In recent years, with the increasing functionality and weight reduction of mobile devices and the electrification or hybridization of vehicles, high output densities and high capacity densities are required for power storage devices.
Polyolefin porous membranes are widely used as separator materials because they are excellent in electrical insulation, ion permeability, etc., and have an appropriate shutdown function. The shutdown function is a function that suppresses ion permeability to stop the progress of the electrochemical reaction when the device generates abnormal heat, and safely stops the abnormal reaction of the device. It is considered that the mechanism by which the porous polyolefin membrane has an excellent shutdown function is that the polyolefin melts due to abnormal heat generation and closes the pores in the separator. Since the polyolefin porous membrane is excellent in this shutdown function, it is applied as a separator in a power storage device as a drive power source in equipment that requires high output density and high capacity density, for example, an electric vehicle, a hybrid vehicle, and the like.

In a polyolefin porous membrane, a multilayer structure separator in which another layer is laminated on the porous membrane has been studied in order to improve various performances as a separator including a shutdown function. For example, Patent Documents 1 and 2 each describe a separator having a multilayer structure having an inorganic layer containing an inorganic filler on at least one side of a porous polyolefin membrane.

Japanese Unexamined Patent Publication No. 2014-097656 Japanese Unexamined Patent Publication No. 2014-078515 International Publication No. 2013/147071 International Publication No. 2015/1223222 Japanese Unexamined Patent Publication No. 2014-225410 JP-A-2009-76410

Both of the above-mentioned techniques of Patent Documents 1 and 2 can provide a separator satisfying a desired target, and are remarkable techniques showing a high contribution to the prior art. Many follow-up patent documents have been published that follow and imitate these technologies.
In the techniques of Patent Documents 1 and 2 and these mimicking techniques, in the production of a multilayer separator, a coating liquid containing a constituent material of an inorganic layer is applied onto a polyolefin porous film as a base material to form a coating film. After that, the coating film is usually heated and, in some cases, further compressed. Here, it is common to perform a corona discharge treatment on the base material prior to the application of the coating liquid.
This corona discharge treatment is performed for the purpose of improving the wettability of the surface of the base material and improving the chemical bonding force between the base material and the inorganic layer. If an attempt is made to coat and form an inorganic layer on the surface of a base material without performing a corona discharge treatment, poor wetting such as coating repellent may occur, and problems such as poor formation and peeling of the inorganic layer may occur.

In the corona discharge treatment, the surface of the base material is attacked by corona discharge to generate active species such as ionic species and radical species, and the active species react with oxygen, nitrogen, water, etc. in the ambient atmosphere to form a carbonyl group and carboxyl. This is a technique for modifying the surface of a base material by converting it into a group, a hydroxyl group, or the like. The treatment is invasive in that it cleaves the chemical bonds of the surface species of the base material to generate active species, and may damage the base material. For example, shape defects such as wrinkles and irregularities may occur on the surface of the base material, which may cause coating defects. Alternatively, the charge concentration of the discharge may occur in this poorly shaped region, causing structural defects such as voids and pinholes in the base material. Such a structural defect causes a withstand voltage defect of the separator. Further, it is necessary to keep the area around the discharge device for performing the corona discharge treatment extremely clean, and a small amount of dirt causes unevenness or local concentration of the discharge, which causes defects such as uneven coating and foreign matter defects.
Therefore, those skilled in the art strongly desire a multilayer separator which can be manufactured without corona discharge treatment and has excellent insulation, ion permeability, adhesion, shutdown property and the like.

In this regard, Patent Documents 3 to 5 describe separators containing a water-soluble (meth) acrylic resin having a carboxyl group-containing monomer unit of 27% by mass or more. However, these patent documents do not describe a porous layer containing a water-soluble (meth) acrylic resin having a carboxyl group-containing monomer unit of 2% by mass or more and less than 27% by mass.
When the present inventors examined the separator using the porous layer according to Patent Documents 3 to 5, the coating was performed when the polyolefin base material was not corona-treated before the coating liquid for the porous layer was applied. It was found that when the liquid was applied to the base material, there was repulsion of the coating liquid, and the peel strength between the base material / multi-layer layer and the heat shrinkage rate of the separator were inferior (see Comparative Examples 1 to 3 described later). ..

Patent Document 6 describes a separator having a porous layer containing a fluorine-based surfactant. This patent document does not describe a porous layer containing a water-soluble (meth) acrylic resin having a carboxyl group-containing monomer unit of 2% by mass or more and less than 27% by mass.
When the present inventors examined the separator using the porous layer according to Patent Document 6, when the polyolefin substrate was not corona-treated before the coating liquid for the porous layer was applied, the substrate / It was found that the peel strength between the polylayers was inferior (see Comparative Example 5 described later).

The present invention has been made based on such circumstances. An object of the present invention is that even when the polyolefin base material is not subjected to the corona treatment before the coating liquid for the porous layer is applied, when the coating liquid is applied to the base material, the coating liquid is used. A separator that has no repellency, has excellent peel strength between the substrate / multi-layer, and has excellent thermal stability, a power storage device that uses the separator and has excellent rate characteristics, and the separator with or without corona discharge treatment. It is to provide a method of easy manufacture.

The present invention achieves the above object by the following means.
[1] A layer composed of a porous base material layer and
It is characterized by having a water-soluble (meth) acrylic resin (b1) having a carboxyl group-containing monomer unit of 2% by mass or more and less than 27% by mass, and a B layer containing a first water-soluble polymer selected from salts thereof. Separator for power storage device.
[2] The separator for a power storage device according to [1], wherein the B layer further contains an inorganic filler.
[3] The power storage device according to [2], wherein the content ratio of the first water-soluble polymer in the B layer is 0.1 part by mass to 5 parts by mass with respect to 100 parts by mass of the inorganic filler. Separator.
[4] The power storage device according to any one of [1] to [3], wherein the first water-soluble polymer is an ammonium salt or a sodium salt of the water-soluble (meth) acrylic resin (b1). Separator for.

[5] The separator for a power storage device according to any one of [1] to [4], wherein the first water-soluble polymer is an ammonium salt of the water-soluble (meth) acrylic resin (b1).
[6] The B layer further contains a second water-soluble polymer selected from a water-soluble (meth) acrylic resin (b2) having a carboxyl group-containing monomer unit of 27% by mass or more and a salt thereof [1]. ] To [5]. The separator for a power storage device according to any one of the items.
[7] The separator for a power storage device according to [6], wherein the second water-soluble polymer is an ammonium salt of the water-soluble (meth) acrylic resin (b2).
[8] The separator for a power storage device according to any one of [1] to [7], wherein the B layer further contains a resin binder.
[9] The separator for a power storage device according to [8], wherein the resin binder is a water-insoluble acrylic (co) polymer.

[10] The separator for a power storage device according to [1], wherein the B layer does not contain an inorganic filler.
[11] The separator for a power storage device according to [10], wherein the first water-soluble polymer is an ammonium salt or a sodium salt of the water-soluble (meth) acrylic resin (b1).
[12] The separator for a power storage device according to [10] or [11], wherein the first water-soluble polymer is an ammonium salt of the water-soluble (meth) acrylic resin (b1).

[13] The B layer further contains a second water-soluble polymer selected from a water-soluble (meth) acrylic resin (b2) having a carboxyl group-containing monomer unit of 27% by mass or more and a salt thereof [10]. ] To [12]. The separator for a power storage device according to any one of the items.
[14] The separator for a power storage device according to [13], wherein the second water-soluble polymer is an ammonium salt of the water-soluble (meth) acrylic resin (b2).
[15] The separator for a power storage device according to any one of [10] to [14], wherein the B layer further contains a resin binder.
[16] The separator for a power storage device according to [15], wherein the amount of the first water-soluble polymer used is 0.5 parts by mass or more with respect to 100 parts by mass of the resin binder.
[17] The separator for a power storage device according to [15] or [16], wherein the resin binder is a water-insoluble acrylic (co) polymer.

[18] A single-layer or multi-layer base sheet containing at least a layer A composed of a porous base material layer is subjected to a corona discharge treatment or without a corona discharge treatment.
B containing a water-soluble (meth) acrylic resin (b1) having a carboxyl group-containing monomer unit of 2% by mass or more and less than 27% by mass and a first water-soluble polymer selected from salts thereof on the base material sheet. A method for manufacturing a separator for a power storage device, which comprises a step of forming a layer.
[19] The B layer further contains a second water-soluble polymer selected from a water-soluble (meth) acrylic resin (b2) having a carboxyl group-containing monomer unit of 27% by mass or more and a salt thereof [18]. ]. The method for manufacturing a separator for a power storage device.
[20] The method for manufacturing a power storage device separator according to [18], wherein the power storage device separator is the power storage device separator according to any one of claims 1 to 17.

According to the present invention, even when the polyolefin base material is not subjected to the corona treatment before the coating liquid for the porous layer is applied, the coating liquid is repelled when the coating liquid is applied to the base material. It is easy to manufacture a separator having excellent peel strength between a substrate / porous layer and having excellent thermal stability, a power storage device using the separator and having excellent rate characteristics, and the separator regardless of the presence or absence of corona discharge treatment. A method is provided.

The separator for a power storage device of the present invention has at least an A layer and a B layer. Hereinafter, the A layer and the B layer will be described in order.

<Layer A>
The layer A in the present invention is composed of a porous base material layer.
The A layer, which is a porous base material layer, preferably contains a polyolefin resin. It is preferable that the A layer contains a polyolefin resin from the viewpoint of effectively exhibiting the shutdown performance of the power storage device. The content ratio of the polyolefin resin in the layer A is preferably 50% by mass or more, more preferably 75% by mass or more, further preferably 80% by mass or more, and particularly preferably 90% or more. preferable. Particularly preferably, the layer A is substantially composed of only a polyolefin resin.
As the polyolefin resin constituting the A layer, for example, one or more polymers or copolymers selected from ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and the like. Can be mentioned.
As the polyolefin resin in the A layer, a polyolefin resin containing polypropylene is preferable from the viewpoint of improving the heat resistance of the separator. The three-dimensional structure of the polypropylene is arbitrary, and any of isotactics, syndiotactics, and tactics, and a mixture thereof can be used. Considering the balance between heat resistance and cost, it is preferable to use isotactic polypropylene.

Examples of the polyolefin resin containing polypropylene include polypropylene and
With one or more polymers or copolymers selected from ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, etc.
Can be mentioned as a mixture of. Considering the balance between the shutdown performance of the separator and the electrical characteristics, a mixture of polypropylene and polyethylene is more preferable. Examples of the polyethylene include low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene and the like. Of these, from the viewpoint of improving the strength of the separator, it is particularly preferable to use polyethylene having ^{a density of 0.93 g / cm 3 or more measured in accordance with JIS K 7112.}
The proportion of polypropylene used in the A layer is preferably 1 to 35% by mass, more preferably 3 to 20% by mass, still more preferably 4 to 10% by mass, from the viewpoint of achieving both heat resistance and shutdown performance of the separator. %.
The viscosity average molecular weight of the polyolefin resin is preferably 30,000 to 12 million, more preferably 50,000 to 2 million, and even more preferably 100,000 to 1,000,000. A molecular weight in this range is preferable from the viewpoint of moldability of layer A, thickness stability, and development of shutdown performance.

The layer A may contain other components in addition to the polyolefin resin as long as the effects of the present invention are not impaired. Examples of other components include antioxidants, metal soaps, ultraviolet absorbers, antistatic agents, colorants and the like. The content ratio of these other components is preferably 10% by mass or less, more preferably 5% by mass or less, as the mass ratio of the total of the other components to the total mass of the layer A.

Layer A has a porous structure. The porous structure provides excellent ionic conductivity, withstand voltage, and mechanical strength when incorporated into a power storage device.
The average pore size of the layer A is preferably 0.035 to 0.060 μm, more preferably 0.040 to 0.060 μm, and even more preferably 0.042 to 0.060 μm. The curvature ratio of the A layer is preferably 1.1 to 1.7, more preferably 1.15 to 1.67, and even more preferably 1.1 to 1.7. Number of holes A layer is preferably from 100 to 500 pieces / [mu] m ^2, is preferably from 120 to 450 pieces / [mu] m ^2, and further preferably from 140 to 400 pieces / [mu] m ^2. These average pore diameters, curvature ratios, and number of pores can be measured by the gas-liquid method.
From the viewpoint of moderate ionic conductivity and withstand voltage characteristics
The porosity of layer A is preferably 50-90%, more preferably 52-75%, and even more preferably 55-70%;
The thickness of the layer A is preferably 5 to 22 μm, more preferably 7 to 20 μm.

[Manufacturing method of layer A]
The A layer as described above can be produced by a known method or a method obtained by appropriately modifying it by a person skilled in the art.
For example, a method may be used in which the above-mentioned polyolefin resin or a mixture thereof is melt-kneaded with a plasticizer to obtain a polyolefin resin composition, the polyolefin resin composition is formed into a sheet, and then the plasticizer is extracted. ..
Examples of the plasticizer 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. The content ratio of the plasticizer in the polyolefin resin composition is preferably 30 to 80% by mass, more preferably 40 to 70% by mass, from the viewpoint of balancing sheet moldability and stretch resistance.

The melt kneading of the polyolefin resin composition can be performed by a known kneading device, for example, a dispenser, a kneader, a lab plast mill, a kneading roll, a Banbury mixer or the like. The kneading temperature and kneading time are appropriately set by those skilled in the art according to the composition of the polyolefin resin composition, the specific purpose of use of the separator, and the like.
The melt-kneaded polyolefin resin composition is formed into a sheet. Examples of molding include a method in which a melt-kneaded product is extruded through a T-die and then sandwiched between a pair of cooling rolls to form a sheet.
The molded sheet is preferably stretched. This stretching is preferably simultaneous biaxial stretching. The draw ratio is preferably in the range of 4 to 10 times in the MD direction, 4 to 10 times in the TD direction, and 20 to 100 times as the surface magnification from the viewpoint of the balance between film strength and productivity.

Then, by extracting and removing the plasticizer from the sheet-shaped polyolefin composition, the sheet can be made porous to form the A layer.
Examples of the extraction solvent include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorine halogenated solvents such as hydrofluoroether and hydrofluorocarbon; Alcohols such as ethanol and isopropanol; ethers such as dietyl ether and tetrahydrofuran; ketones such as acetone and methyl ethyl ketone can be mentioned.
In this way, the layer A according to the present invention can be produced.
The obtained layer A may be used as it is for the production of a separator, or may be further subjected to operations such as hydrophilization, cross-linking, and heat fixation, and then used for the production of a separator.

As the layer A in the present invention, a commercially available product may be used.
Examples of commercially available products that can be applied as the A layer in the present invention include CG2300, 2400, 2500, 3559, 5550, and 5559 manufactured by Celgard Co., Ltd. (all of the above are product names).
Ube Industries, Ltd. Yupore (product name);
Setira (product name) manufactured by Toray Battery Separator Film Co., Ltd .;
LP (product name) manufactured by Entek;
And so on.

<B layer>
The B layer in the present invention contains at least the first water-soluble polymer. The B layer can be, for example, a porous layer further containing an inorganic filler or an adhesive layer containing no inorganic filler. The porous layer includes a case where it is a non-adhesive porous layer having no adhesiveness to another layer and an adhesive porous layer having adhesiveness to another layer.
The B layer in the present invention preferably contains a second water-soluble polymer together with the first water-soluble polymer.

[First water-soluble polymer]
The first water-soluble polymer in the present invention is selected from a water-soluble (meth) acrylic resin (b1) having a carboxyl group-containing monomer unit of 2% by mass or more and less than 27% by mass and a salt thereof. The acid equivalent of the first water-soluble polymer is preferably 125 to 850 g / mol, more preferably 150 to 800 g / mol.
The first water-soluble polymer is selected from the group consisting of a copolymer of a monomer selected from a carboxyl group-containing monomer and a salt thereof, a (meth) acrylic acid ester, and other monomers used in some cases. It is preferable that the number is one or more.
Examples of the carboxyl group-containing monomer include (meth) acrylic acid, crotonic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid and the like. These may be used alone or in combination of two or more. As the carboxyl group-containing monomer, it is preferable to use (meth) acrylic acid or a salt thereof from the viewpoint of monomer availability and copolymerizability.
Examples of the counter cation used when the carboxyl group-containing monomer is used as a salt include alkali metal ions, alkaline earth metal ions, ammonium ions, and quaternary ammonium ions. Of these, ammonium ions or sodium ions are preferable from the viewpoint of increasing the peel strength between the base material / porous layer of the separator, and even if they remain in the final product, they have little adverse effect on the charge / discharge function of the device. From the viewpoint of, ammonium ion is more preferable.

Examples of the (meth) acrylic acid ester include an alkyl ester of (meth) acrylic acid, an aryl ester of (meth) acrylic acid, and an aralkyl ester of (meth) acrylic acid. Specific examples of these include, as alkyl esters of (meth) acrylic acid, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, (meth). Butyl acrylate (meth) t-butyl acrylate, cyclohexyl (meth) acrylate, etc.;
As aryl esters of (meth) acrylic acid, for example, phenyl (meth) acrylic acid, hydroxyphenyl (meth) acrylic acid and the like;
Examples of the aralkyl ester of (meth) acrylic acid include benzyl (meth) acrylic acid and the like.

Examples of the other monomer include aromatic vinyl compounds, conjugated diene, α-olefin and the like. Specific examples of these are
Examples of the aromatic vinyl compound include styrene, α-methylstyrene, vinyltoluene, vinylnaphthalene, vinylpyridine and the like;
As the conjugated diene, for example, butadiene, isoprene, chloroprene, etc.;
As α-olefins, for example, ethylene, propylene, 1-butene, 1-hexene and the like;
Each can be listed.

The content ratio of the polymerization unit derived from the carboxyl group-containing monomer or the salt thereof in the first water-soluble polymer is 2% by mass or more and less than 27% by mass. The first water-soluble polymer in which the content ratio of the polymerization unit derived from the carboxyl group-containing monomer or a salt thereof is within this range can sufficiently increase the surface tension of the coating liquid and the wettability with respect to the polyolefin substrate. It acts as a wetting agent that reduces it to the extent possible. Therefore, in this case, even when the polyolefin base material is not subjected to the corona treatment, the repelling of the coating liquid can be reduced when the coating liquid is applied to the base material.
In addition, the carboxyl group-containing unit has a high affinity with the filler because of its high polarity, while the low-polarity unit such as an acrylic acid ester has a high affinity with the base material, so that after the coating liquid is dried, the unit has a high affinity with the filler. , It is considered to work as a binder to increase the peel strength between the base material / multi-layer layer. Therefore, since the peel strength between the base material and the multi-layer is improved, it is difficult for a displacement between the heat-resistant porous layer and the base material to occur even when the separator is heated, and the heat shrinkability of the separator is reduced. Is considered to be good.
From the above viewpoint, the content ratio of the polymerization unit derived from the carboxyl group-containing monomer or a salt thereof is more preferably 3% by mass or more and 20% by mass or less.

The amount of the first water-soluble polymer used is as follows, depending on the presence or absence of the inorganic filler described later in the B layer.
When the B layer contains an inorganic filler, the amount of the first water-soluble polymer used is preferably 10 parts by mass or less, more preferably 0.1 parts by mass or more and 5 parts by mass or less, based on 100 parts by mass of the inorganic filler. .. Within this range, even if the polyolefin base material is not subjected to the corona discharge treatment, the coating liquid is not repelled and the peel strength between the porous layer and the base material is good. Further, within this range, the amount of increase (rate of change) in the air permeability of the separator is small when the polyolefin substrate is subjected to the corona discharge treatment and when it is not subjected to the corona discharge treatment, which is preferable.
When the B layer does not contain an inorganic filler, the amount of the first water-soluble polymer used is arbitrary. However, when the B layer contains a resin binder described later, the amount of the first water-soluble polymer used is preferably 0.5 parts by mass or more with respect to 100 parts by mass of the resin binder. Within this range, even when the polyolefin base material is not subjected to the corona discharge treatment, the coating liquid is not repelled and the peel strength between the adhesive layer and the base material is good. When the resin binder is used as a dispersion, the amount of the resin binder is calculated as a solid content conversion value.

The glass transition temperature Tg of the first water-soluble polymer is preferably -20 to 120 ° C, more preferably -10 to 100 ° C, and even more preferably 0 to 80 ° C. This glass transition temperature is a value measured at a heating rate of 10 ° C./min using a differential scanning calorimeter (DSC) in accordance with ASTM E1356-08.
For the first water-soluble polymer, the weight average molecular weight Mw in terms of sodium polyacrylate measured by gel permeation chromatography (GPC) is preferably 5,000 to 500,000 from the viewpoint of adhesive strength. More preferably, it is 7,000 to 200,000.

[Second water-soluble polymer]
The second water-soluble polymer that can be contained in the B layer in the present invention is selected from a water-soluble (meth) acrylic resin (b2) having a carboxyl group-containing monomer unit of 27% by mass or more and a salt thereof.
The second water-soluble polymer is a polymer of a monomer selected from (meth) acrylic acid and a salt thereof, a monomer selected from (meth) acrylic acid and a salt thereof, and a (meth) acrylic acid ester. It is preferable that the amount is one or more selected from the group consisting of a copolymer of the other monomers used in the above. Specific examples of the counter cation and the (meth) acrylic acid ester when the above-mentioned carboxyl group-containing monomer is used as a salt include the same species as exemplified for the above-mentioned first water-soluble polymer.

The (meth) acrylic acid ester in the second water-soluble polymer is made of (meth) acrylic acid from the viewpoint of setting the adhesion of the formed B layer to the A layer, the air permeability of the obtained separator, and the like within a preferable range. Alkyl esters are preferred, more preferably methyl (meth) acrylate, ethyl (meth) acrylate, or isopropyl (meth) acrylate, and particularly preferably methyl (meth) acrylate.
The content ratio of the polymerization unit derived from (meth) acrylic acid or a salt thereof in the second water-soluble polymer is preferably 50% by mass or more, more preferably 75% by mass or more, and 80% by mass or more. Is more preferable, and particularly preferably 90% by mass or more. The second water-soluble polymer having a content ratio of the polymerization unit derived from (meth) acrylic acid or a salt thereof in this range is excellent in solubility in an aqueous medium described later and dispersibility of an inorganic filler, and has excellent adhesion of the B layer and adhesion of the inorganic filler. The electrical characteristics of the separator will be excellent.
As the other monomer in the second water-soluble polymer, the same monomer as the above-mentioned monomer can be used as the other monomer in the first water-soluble polymer.
The second water-soluble polymer in the present invention is more preferably a polymer of a monomer selected from (meth) acrylic acid and a salt thereof, and particularly preferably ammonium poly (meth) acrylic acid.

Regarding the second water-soluble polymer, the weight average molecular weight Mw measured by the same method as that of the first water-soluble polymer is from 2,000 to 2,000 from the viewpoint that the dispersibility of the inorganic filler is good when present. It is preferably 20,000, more preferably 4,000 to 100,000.

[Manufacturing or obtaining a first water-soluble polymer and a second water-soluble polymer]
The first water-soluble polymer and the second water-soluble polymer as described above can be produced by a polymerization reaction using a known method or a method appropriately modified by those skilled in the art, respectively. .. When a salt of (meth) acrylic acid is used as a polymerization component in these polymers, it may be subjected to a polymerization reaction as (meth) acrylic acid and then used as a salt, or it may be polymerized as a (meth) acrylic acid salt. It may be subjected to a reaction. Solution polymerization using the same type of medium as the aqueous medium described later enables precise structure control, and it is preferable to obtain (meth) acrylate and then subject it to the polymerization reaction.

The first water-soluble polymer and the second water-soluble polymer may be obtained as commercial products, respectively.
Examples of commercially available products of the first water-soluble polymer include Julimer AT-210, Julimer ET-325, Julimer AT-510, Julimer AT-613, and the like (all manufactured by Toagosei Co., Ltd.).
Examples of commercially available second water-soluble polymers include SN Dispersant 5468 and SN Dispersant 5027 (all manufactured by San Nopco);
Aaron A6114, Aron A30SL, (all manufactured by Toagosei Co., Ltd.) and the like can be mentioned.

[Ratio of use of first water-soluble polymer and second water-soluble polymer]
The ratio of the first water-soluble polymer and the second water-soluble polymer used in the B layer of the separator of the present invention shall be 20 parts by mass or more as the ratio of the first water-soluble polymer used to the total of both. Is more preferable, 50% by mass or more is more preferable, and 75% by mass or more is further preferable. The first water-soluble polymer or the B layer containing both water-soluble polymers at such a usage ratio has high adhesiveness even when the A layer is not subjected to the corona discharge treatment. preferable.

[Perforated layer]
The B layer in the separator for a power storage device of the present invention can contain an inorganic filler together with the first water-soluble polymer (and optionally the second water-soluble polymer) as described above. Since the B layer containing the inorganic filler has a large number of pores and can hold the electrolytic solution in the pores, it can exert a function of ensuring the ionic conductivity of the obtained power storage element. .. The B layer as the porous layer may further contain a resin binder, a thickener, and the like in addition to the above components.
The porous layer includes a non-adhesive porous layer having no adhesiveness to other layers and an adhesive porous layer having adhesiveness to other layers. In the following explanation, the parts that are common to both of these will be explained together, and the parts that need to be considered separately will be given a special note to that effect.
In the B layer, which is a porous layer, the first water-soluble polymer and the second water-soluble polymer are considered to function as dispersants for improving and maintaining the dispersibility of the inorganic filler, respectively.

Examples of the inorganic filler that can be contained in the B layer, which is a porous layer, include oxide-based ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, itria, zinc oxide, and iron oxide; silicon nitride, titanium nitride, and nitride. Nitride-based ceramics such as boron; silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide oxide, potassium titanate, talc, kaolinite, decite, nacrite, halloysite, pyrophyllite, Examples thereof include ceramics such as montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica sand, and glass fiber. Of these, alumina, aluminum hydroxide oxide, kaolinite, dekite, nakrite, halloysite, pyrophyllite, etc. are preferable from the viewpoint of improving the heat resistance without adversely affecting the electrochemical properties of the obtained separator;
Aluminum hydroxide oxide, kaolin and the like are more preferable.

The average particle size of the inorganic filler is preferably 0.1 to 4.0 μm, more preferably 0.2 to 3.5 μm, and even more preferably 0.4 to 3.0 μm. By adjusting the average particle size of the inorganic filler within the above range, the heat resistance of the obtained separator, particularly the heat shrinkage, is excellent, which is preferable.
The amount of the inorganic filler in the B layer, which is a porous layer, is preferably 15 to 200 parts by mass with respect to 1 part by mass in total of the first water-soluble polymer and the second water-soluble polymer. It is more preferable that the amount is 20 to 100 parts by mass.
When the B layer is a porous layer, its thickness is preferably 0.1 to 50 μm, more preferably 0.5 to 15 μm, and even more preferably 1 to 10 μm.

-Resin binder-
When the B layer contains an inorganic filler, the B layer preferably further contains a resin binder.
This resin binder is preferably a resin that plays a role of binding inorganic fillers to each other and also plays a role of enhancing the adhesive force between the B layer and another layer.
As the type of resin binder, it is preferable to use a resin that is insoluble in the electrolytic solution of the power storage device when used as a separator and is electrochemically stable within the range of use of the power storage device.

Specific examples of the resin binder in the B layer, which is a porous layer, include the following 1) to 7).
1) Polyolefin: For example, polyethylene, polypropylene, ethylene propylene rubber, and modified products thereof;
2) Conjugate diene-based polymer: For example, styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride;
3) Acrylic (co) copolymer: For example, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer;
4) Polyvinyl alcohol-based resin: For example, polyvinyl alcohol, polyvinyl acetate;

5) Fluororesin: For example, vinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene Copolymers, hexafluoropropylene-tetrafluoroethylene copolymers, ethylene-tetrafluoroethylene copolymers;
6) Cellulose-based semi-synthetic polymer compound: For example, nonionic cellulosic semi-synthetic polymer compound, anionic cellulosic semi-synthetic polymer compound, cationic cellulosic semi-synthetic polymer compound;
7) Resins with a melting point and / or glass transition temperature of 180 ° C. or higher, or polymers that do not have a melting point but have a decomposition temperature of 200 ° C. or higher: for example, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamide. Imid, polyamide, polyester. In particular, from the viewpoint of durability, all aromatic polyamides, especially polymetaphenylene isophthalamide, are preferable.
Among these, the above 2) conjugated diene polymer and 5) fluororesin are preferable from the viewpoint of easy compatibility with the electrode, and the above 3) acrylic (co) polymer is preferable from the viewpoint of withstand voltage. From the viewpoint of suppressing heat shrinkage, the above 6) cellulosic semi-synthetic polymer compounds are preferable.

The above 2) 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, and substituted linear chain. Conjugated pentadienes, substitutions, side chain conjugated hexadiene and the like can be mentioned, and these may be used alone or in combination of two or more. Of these, 1,3-butadiene is particularly preferable.

The above 3) acrylic (co) polymer is a polymer or copolymer 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 the (meth) acrylic acid used in the above 3) acrylic (co) polymer include acrylic acid and methacrylic acid.
Examples of the (meth) acrylic acid ester used in the above 3) acrylic (co) polymer include, for example.
(Meta) Acrylic acid alkyl esters such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl amethacrylate, phenyl acrylate, phenyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate. ;
Epoxy group-containing (meth) acrylic acid esters such as glycidyl acrylate and glycidyl methacrylate; may be used alone or in combination of two or more.

The above-mentioned 2) conjugated diene-based polymer and 3) acrylic-based (co) polymer may be obtained by copolymerizing other monomers copolymerizable with these. Other copolymerizable monomers used include, for example, unsaturated carboxylic acid alkyl esters, aromatic vinyl-based monomers, vinyl cyanide-based monomers, and unsaturated monomers containing hydroxyalkyl groups. , Unsaturated carboxylic acid amide monomer, crotonic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid and the like, and these may be used alone or in combination of two or more. Good. Among the above, unsaturated carboxylic acid alkyl ester monomers are particularly preferable. Examples of the unsaturated carboxylic acid alkyl ester monomer include dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, and the like. It may be used alone or in combination of two or more.
The above 2) conjugated diene polymer may be obtained by copolymerizing the above (meth) acrylic compound as another monomer.

The content of the resin binder in the B layer, which is a porous layer, should be specially considered depending on whether the porous layer is an adhesive porous layer or a non-adhesive porous layer.
When the porous layer is a non-adhesive porous layer, the content of the resin binder is preferably 1% by mass to 15% by mass, preferably 2 to 10% by mass, when the inorganic filler is 100% by mass. Is more preferable. On the other hand, when the porous layer is an adhesive porous layer, the content of the resin binder is preferably 10% by mass to 50% by mass, preferably 20 to 40% by mass, when the inorganic filler is 100% by mass. It is more preferable to do so.

These resin binders may be either water-soluble or water-insoluble, except that 3) the acrylic (co) polymer is water-insoluble. However, 3) the acrylic (co) polymer is distinguished from the above-mentioned first and second water-soluble polymers in that it is water-insoluble.

[Adhesive layer]
When the B layer in the separator for a power storage device of the present invention does not contain an inorganic filler, the B layer can function as an adhesive layer that controls adhesion between the B layer and another layer. The B layer, which is an adhesive layer, contains the above-mentioned first water-soluble polymer (and optionally a second water-soluble polymer), but substantially does not contain an inorganic filler. The content ratio of the inorganic filler in the B layer, which is the adhesive layer, is preferably 5% by mass or less, more preferably 1% by mass or less, and particularly preferably no inorganic filler at all.

The B layer, which is an adhesive layer, preferably further contains a resin binder in both the first water-soluble polymer and, in some cases, the second water-soluble polymer.
As the resin binder in the B layer, which is the adhesive layer, the above 2) conjugated diene polymer is preferable from the viewpoint of easy compatibility with the electrode, and the above 3) acrylic (co) polymer is preferable from the viewpoint of withstand voltage. And 5) Fluororesin-containing resin is preferable. Particularly preferably, 3) an acrylic (co) polymer.

The resin binder in the B layer, which is the adhesive layer, is
A first resin binder showing a glass transition temperature in a region of less than 30 ° C.
A second resin binder showing a glass transition temperature in the region of 30 ° C. or higher,
It is preferable to use it as a mixture containing.

The glass transition temperature of the first resin binder showing a low glass transition temperature is preferably less than 30 ° C., more preferably 5 ° C. or lower, still more preferably −10 ° C. or lower. When the glass transition temperature is less than 30 ° C., it is preferable from the viewpoint of adhesion to the multilayer and adhesive strength.
The glass transition temperature of the second resin binder showing a high glass transition temperature is preferably 30 ° C. or higher, more preferably 45 ° C. or higher, still more preferably 70 ° C. or higher. When the glass transition temperature is 30 ° C. or higher, it is preferable from the viewpoint of stickiness and handleability of the outermost surface of the separator.

The content of the resin binder in the B layer, which is the adhesive layer, is preferably set according to the relationship with the A layer. Specifically, a preferable range is determined according to the contact area between the A layer and the B layer.
The content of the resin binder in an adhesive layer B layer, based on the contact area between the A layer and the B layer, 0.05 g / ^{m 2} or more 1.50 g / ^{m 2} or less, more preferably 0.07g It is / m ² or more and 1.00 g / m ² or less, and more preferably 0.10 g / m ² or more and 0.70 g / m ² or less. When the content of the resin binder and 0.05 g / m ² or more 1.50 g / m ² or less, the separator obtained, together with further improve the adhesion between the B layer and the substrate, the pores of the substrate It is preferable from the viewpoint of further suppressing a decrease in cycle characteristics (permeability) due to clogging.
When the resin binder is a mixture of the above-mentioned first resin binder and the second resin binder, the usage ratio of both is 2 to 50% by mass as the usage ratio of the first resin binder to the total of both. It is preferably 10 to 30% by mass, and more preferably 10 to 30% by mass.

When the B layer is an adhesive layer, its thickness is preferably 2.0 μm or less, more preferably 1.0 μm or less. Setting the average thickness of the B layer to 2.0 μm or less suppresses the decrease in permeability due to the polymer layer, and is effective in sticking the B layers to each other or between the B layer and the base material when the separator is stored as a roll. It is preferable from the viewpoint of suppressing the polymer.

[Method of forming layer B]
The separator for a power storage device of the present invention can be produced by forming a B layer on a single-layer or multi-layer base sheet including at least an A layer composed of a porous base material layer.
As the base material sheet, a single-layer sheet composed of the A layer itself may be used, or a multi-layer sheet having another layer in the A layer may be used. The other layer may be the B layer in the present invention, may be a layer other than the B layer, or may have both a B layer and a layer other than the B layer. .. The B layer and the layers other than the B layer may be only one layer, or at least one of them may be present in two or more layers.
The base sheet in the present invention is preferably a single-layer sheet composed of the A layer itself, or a single-layer sheet.
This is a case where the sheet is a multi-layered sheet having another layer in the A layer, and at least one of the outermost layers is the A layer. In these cases, the B layer is preferably formed in contact with the A layer of the base material sheet.

The B layer is preferably formed by a coating method or a transfer method.
In the coating method, a coating liquid containing each component of the B layer is applied onto the base sheet as described above to form a coating film, which is then heated, and if necessary, a further pressing step is performed. By forming the B layer on the A layer, the separator for the power storage device of the present invention can be obtained.

Prior to the above coating, the base sheet may or may not be subjected to the corona discharge treatment. However, since the B layer in the present invention can be efficiently formed without performing the corona discharge treatment, it accepts the risk of causing various inconveniences due to the corona discharge treatment as described above. There is no real benefit to dare to do this. Further, when the corona discharge treatment is not performed, the manufacturing cost is low and the air permeability of the obtained separator is excellent.
Therefore, it is preferable not to perform the corona discharge treatment on the base sheet prior to the coating.

A coating liquid containing each component of the B layer is applied to the base sheet as described above.
The medium of the coating liquid is preferably an aqueous medium from the viewpoint of solubility of the components in the B layer, particularly the first water-soluble polymer and the second water-soluble polymer. The aqueous medium can be water, or a mixture of water and a water-soluble organic solvent. Examples of the water-soluble organic solvent include alcohol, ether and the like. However, it is preferable to use water as the medium of the coating liquid because good coatability can be obtained and the influence on the operator and the environment is small.
The coating liquid is preferably prepared as an aqueous solution or an aqueous dispersion containing each component in the B layer in a predetermined ratio. It is more preferable that the coating liquid is prepared as an aqueous dispersion when forming a porous layer and as an aqueous solution when forming an adhesive layer. The solid content concentration of the coating liquid is preferably 15 to 70% by mass, more preferably 30 to 50% by mass.

Examples of the coating method include 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, a blade coater method, and a rod coater method. , Squeeze coater method, cast coater method, die coater method, screen printing method, spray coating method and the like can be adopted as appropriate.
By the above coating, the coating film formed on the base material is then heated to evaporate and remove the dispersion medium in the coating film, whereby a separator having a B layer formed on the base material can be obtained. .. The heating temperature at this time is preferably 90 ° C. or lower, more preferably 70 ° C. or lower.

The transcription method can be, for example, the following method.
First, a coating liquid containing each component of the B layer is applied onto an appropriate base film, and the low humidity zone and the high humidity zone are sequentially passed to gel the B layer component on the base film. A transfer film having a gelled B layer component layer is produced. Next, the B layer component layer of the transfer film is laminated on the A layer to form a laminated body, and then immersed in a coagulation bath to convert the B layer component into a porous layer or an adhesive layer. Then, by peeling the base film from the laminated body, a separator in which the B layer is laminated on the A layer can be obtained.

As the base film, for example, polyester (particularly polyethylene terephthalate), polyolefin (particularly polyethylene or polypropylene) or the like can be used. The preparation of the coating liquid and the coating of the coating liquid on the base film can be carried out in the same manner as described for the coating method, respectively.
The low humidity zone is preferably adjusted to, for example, an absolute humidity of 4 g / m ³ or less, preferably ^{a humidity of 3} g / m 3 or less, and a temperature of 20 ° C to 50 ° C. High humidity zones, for example, absolute humidity ^{6g / m 3 ~25g / m 3} , preferably it is preferably adjusted to a temperature of ^{8 g} / m 3 humidity to 15 g / ^{m 3,} and 20 ° C. to 50 ° C.. The transit time of each zone is preferably 3 seconds to 20 seconds for the low humidity zone and 3 seconds to 20 seconds for the high humidity zone.

As the coagulation bath, for example, it is preferable to use an aqueous solution of N-methylpyrrolidone or the like. The laminate after immersion in the coagulation bath is preferably washed with a suitable solvent such as water.
After that, the separator of the present invention can be obtained by peeling the base film from the laminate.

The separator obtained by the above step can be used as it is or after being pressed by a known method, preferably hot pressing, if necessary. In this arbitrary press, the press pressure is preferably 1 to 30 MPa, and the press time is preferably about 5 seconds to 30 minutes.

<Separator>
The separator for a power storage device of the present invention has the above-mentioned A layer and B layer.
As described above, the B layer can be, for example, a porous layer, an adhesive layer, or the like. A layer B as a porous layer and a layer B as an adhesive layer may be superposed on the layer A. The B layer may be formed on only one side of the A layer, or may be formed on both sides of the A layer. Two or more layers B may be formed on one side of the layer A. When the separator for a power storage device of the present invention has two or more B layers in total on one side or both sides of the A layer, one B layer and another B layer have the same composition. It may be present or it may have a different composition.

The separator for a power storage device in the present invention can have, for example, the following layer structure:
Layer A / Layer B, which is an adhesive layer,
B layer / A layer which is an adhesive layer / B layer which is an adhesive layer,
Layer A / Layer B, which is a non-adhesive porous layer,
A layer / B layer which is a non-adhesive porous layer / B layer which is an adhesive layer,
B layer which is an adhesive layer / A layer / B layer which is a non-adhesive porous layer / B layer which is an adhesive layer,
B layer / A layer which is a non-adhesive porous layer / B layer which is a non-adhesive porous layer,
B layer which is an adhesive layer / B layer which is a non-adhesive porous layer / A layer / B layer which is a non-adhesive porous layer / B layer which is an adhesive layer,
Layer A / Layer B, which is an adhesive porous layer,
B layer / A layer which is an adhesive porous layer / B layer which is an adhesive porous layer,
etc.

Even if the separator for a power storage device of the present invention has any of the above layer configurations, it is a case where the polyolefin base material of the A layer is not corona-treated before the coating liquid for the B layer is applied. However, there is no repelling of the coating liquid for the B layer, the peel strength between the A layer / B layer is excellent, and the power storage device using the separator is excellent in rate characteristics. As described above, the separator for a power storage device of the present invention can be produced by forming the B layer by a coating method or a transfer method without performing an invasive corona discharge treatment on the A layer. Therefore, the separator can avoid various inconveniences caused by the corona discharge treatment.

<Power storage device>
The separator of the present invention is suitably applied as a separator for a power storage device.
As long as the power storage device includes the separator of the present invention, the other configurations are not particularly limited, and may be the same as those conventionally known. The power storage device provided with the separator of the present invention is not particularly limited, and may be, for example, a battery such as a non-aqueous electrolyte battery, a capacitor, a capacitor, or the like.
Hereinafter, a preferred embodiment in the case where the power storage device is a non-aqueous electrolyte battery will be described.
The positive electrode, the negative electrode, and the non-aqueous electrolytic solution are not limited, and known ones can be used.

Examples of the positive electrode material include _{lithium-containing composite oxides such as LiCoO 2} , LiNiO ₂ , spinel-type LiMnO ₄ , and olivine-type LiFePO ₄ , and examples of the negative electrode material include graphite, non-graphitizable carbonaceous material, and easy-to-graphite. Carbon materials such as carbon dioxide and composite carbonaceous; silicon, tin, metallic lithium, various alloy materials and the like can be mentioned.
As the non-aqueous electrolytic solution, an electrolytic solution in which an electrolyte is dissolved in an organic solvent can be used, and as the organic solvent, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate and the like can be used. For example, lithium salts such as _{LiClO 4} , LiBF ₄ , and LiPF _{6 can be mentioned.}

The power storage device is not particularly limited, but is manufactured as follows, for example. That is, the separator of the present invention is produced as, for example, a vertically elongated separator having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m). Next, the separator is laminated together with the positive electrode and the negative electrode in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator to obtain a laminate. The laminate is then wound into a cylindrical or flat spiral to obtain a wound body. Then, the power storage device can be obtained by accommodating the wound body in the outer body and further undergoing steps such as injecting an electrolytic solution.
Further, in the above-mentioned power storage device, after forming a separator, a positive electrode, and a negative electrode into a flat plate shape, the positive electrode-separator-negative electrode-separator-positive electrode or the negative electrode-separator-positive electrode-separator-negative electrode is laminated in this order to obtain a laminated body. After that, it can be manufactured by accommodating it in the outer body and injecting an electrolytic solution into it.
As the exterior body, a battery can or a bag-shaped film can be used.

Hereinafter, the present invention will be specifically described by presenting examples.

<Measurement method and evaluation method>
The various measurements and evaluations described below were performed according to the following procedures.
[Evaluation of coatability (coating repellent)]
In the production of the separator described later, the state of the coating film immediately after the coating liquid was applied was visually observed, and the presence or absence of cissing and its degree were examined. The coatability was evaluated according to the following criteria.
If no repellency is seen: Workability "○" (good)
If repellent is seen: Workability "x" (defective)

[Peeling strength of porous layer]
The peel strength is the peel strength between the porous layer and the polyolefin porous base material or between the adhesive layer and the polyolefin porous base material, depending on the structure of the separator in each Example and Comparative Example. , Measured and evaluated by the following methods.
The peel strength was measured in an environment of 25 ° C. using a tensile tester (Autograph AG-IS) manufactured by Shimadzu Corporation.
The separator manufactured above is cut out to a size of 2.5 cm x 10 cm, the base material surface is fixed to a glass plate with double-sided tape (Nichiban Co., Ltd. Nystack NWBB-15), and 3M Co., Ltd. is placed on a porous layer or an adhesive layer. A cellophane tape (registered trademark) (Scotch 810-3-12) manufactured by Nichiban Co., Ltd. was attached. Peel off about 5 mm from the end of the attached tape, attach the tape side to the upper side (tensile side) of the tensile tester, and attach the base material side to the lower side (fixed side) of the tensile tester, and attach it to the surface of the porous layer. On the other hand, the integrated average load when pulled at a speed of 100 mm / min in the 180 ° direction was defined as the peel strength and evaluated according to the following criteria.
When the peel strength is 100 g / cm or more: Peel strength "○" (good)
When the peel strength is 50 g / cm or more and less than 100 g / cm: Peel strength "△" (possible)
When the peel strength is 10 g / cm or more and less than 50 g / cm: Peel strength "x" (defective)
When the peel strength is less than 10 g / cm: Peel strength "XX" (outside the problem)

[Peeling strength of adhesive layer]
A separator and a positive electrode current collector as an adherend (aluminum foil manufactured by Fuji Kako Paper Co., Ltd., thickness: 20 μm) were cut into 30 mm × 150 mm, respectively, and laminated to obtain a laminated body. Next, the laminate was sandwiched between Teflon (registered trademark) sheets (Nachias Corporation Naflon (trademark) PTFE sheet TOMBO-No. 9000) to obtain samples. Each of the obtained samples was pressed in the stacking direction for 3 minutes under the conditions of a temperature of 80 ° C. and a pressure of 10 MPa to obtain a test press.
The peel strength between the base material or separator of each test press and the positive electrode current collector obtained was based on JIS K6854-2 using Autograph AG-IS type (trademark) manufactured by Shimadzu Corporation. The tension was measured at a tensile speed of 200 mm / min. The adhesiveness with the electrode was evaluated according to the following evaluation criteria according to the value of the peel strength.
<Evaluation criteria>
○ (Allowable): 5 N / m or more and less than 9.8 N / m × (Defective): Less than 5 N / m

[Heat shrinkage rate]
A 12 cm × 12 cm square sample was cut out from the obtained separator. Two marks (four in total) were marked at 10 cm intervals in each of the MD direction and the TD direction of the sample.
The above sample was sandwiched between papers and allowed to stand in an oven at 150 ° C. for 60 minutes. After taking out the sample from the oven and cooling it, the length (cm) between the marks was measured, the heat shrinkage rate was calculated by the following formula, and the evaluation was made according to the following criteria.
Heat shrinkage rate (TD direction) (%) = (10-length between marks in the TD direction after heating (cm)) / 10 × 100
Heat shrinkage rate (MD direction) (%) = (10-length between marks in MD direction after heating (cm)) / 10 × 100
When the heat shrinkage rate is less than 5%: Heat shrinkage rate "○" (good)
When the heat shrinkage rate is 5% or more: Heat shrinkage rate "x" (defective)

<Manufacturing of base material>
[Manufacturing of Polyolefin Porous Base Material]
Production Example S1 (Production of Polyolefin Porous Base Material (S1))
47.5 parts by mass of polyethylene homopolymer having a viscosity average molecular weight of Mv 700,000 and
47.5 parts by mass of polyethylene homopolymer with Mv250,000 and
5 parts by mass of polypropylene homopolymer of Mv 400,000 was dry-blended in a tumbler blender to obtain a polymer mixture. To 99 parts by mass of the obtained polymer mixture, 1 part by mass of pentaerythrityl tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] as an antioxidant was added again in the tumbler blender. Dry blended with to give a polymer composition.
The obtained polymer composition was nitrogen-substituted and fed to a twin-screw extruder via a feeder in a nitrogen atmosphere. Further, liquid paraffin (kinematic viscosity at 37.78 ° C., 7.59 × ^10-5 m ² / s) was supplied to the cylinder portion of the twin-screw extruder via a plunger pump.
The feer and the plunger pump were adjusted so that the concentration of the resin composition in the extruded total mixture was 33% by mass and the concentration of the liquid paraffin was 67% by mass, and these were melt-kneaded. This melt kneading was performed under the conditions of a set temperature of 200 ° C., a screw rotation speed of 100 rpm, and a discharge rate of 12 kg / h.

The above-mentioned molten mixture was extruded and cast on a cooling roll having a surface temperature set to 25 ° C. via a T-die to obtain a gel sheet having a thickness of 1,600 μm.
The gel sheet was guided to a simultaneous biaxial tenter stretching machine and biaxially stretched under the conditions of an MD magnification of 7.0 times, a TD magnification of 6.1 times, and a set temperature of 121 ° C. to obtain a stretched sheet.
Next, the stretched sheet was led to a methyl ethyl ketone layer, and the stretched sheet was sufficiently immersed to extract and remove liquid paraffin, and then the methyl ethyl ketone was dried and removed to obtain a porous sheet.
The obtained perforated sheet was guided to a TD tenter and heat-fixed at a set temperature of 120 ° C. with a maximum TD magnification of 2.0 times and a relaxation rate of 0.9 times to achieve a film thickness of 12 μm, a porosity of 40%, and an air permeability. A polyolefin porous substrate (S1) having a puncture strength of 320 g at 150 seconds and 100 cc was obtained.

The viscosity average molecular weight Mv in the above is based on ASTM-D4020, and from the ultimate viscosity [η] measured at 135 ° C. in decalin, the following formula:
[Η] = k × Mva ^a
{In the formula, k = 6.77 and a = 0.67 for polyethylene, and k = 1.10 and a = 0.80 for polypropylene. } Is the value obtained by.
For the porosity, a sample of 10 cm × 10 cm square is cut out from a porous polyolefin membrane, the volume (cm ³ ) and mass (g) of the sample are measured, and the film density is 0.95 (g / cm ³ ), and the following formula is used. It is a value calculated by.
Porosity (%) = (volume-mass / membrane density) / volume x 100
As the air permeability, the value of the air permeability resistance measured by the Garley type air permeability meter GB2 (trademark) manufactured by Toyo Seiki Co., Ltd. was adopted in accordance with JIS P-8117.
For the puncture strength, a handy compression tester KES-G5 (trademark) manufactured by Katou Tech was used to fix the polyolefin porous substrate with a sample holder having an opening diameter of 11.3 mm, and then this fixed polyolefin. The value of the maximum piercing load (g) when a piercing test was performed on the central part of the porous substrate with a pin having a radius of curvature of 0.5 mm at the tip of the needle at a piercing speed of 2 mm / sec in an atmosphere of 25 ° C. Was adopted, and this was used as the piercing strength.

(Preparation of polyolefin porous substrate (S2))
CG2500 (dry type, made of PP, Celgard Co., Ltd.) was prepared as the polyolefin porous base material S2.

<Manufacturing of resin binder>
Production example P1
65 parts by mass of water and Aqualon KH10 (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., polyoxyethylene-1) were initially charged in a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer. -(Allyloxymethyl) alkyl ether sulfate ammonium salt: 100% solid content) 0.5 parts by mass was added. Next, 1.5 parts by mass (0.15 parts by mass in terms of solid content) of a 10% by mass aqueous solution of ammonium peroxodisulfate was added while maintaining the temperature in the reaction vessel at 80 ° C.
5 minutes after adding the aqueous solution of ammonium peroxodisulfate,
As the (meth) acrylic acid ester compound, 26.5 parts by mass of methyl methacrylate, 6 parts by mass of cyclohexyl methacrylate, 25 parts by mass of butyl acrylate, and 35 parts by mass of 2-ethylhexyl methacrylate;
As functional group-containing monomers, 1 part by mass of methacrylic acid, 1.5 parts by mass of acrylic acid, 3 parts by mass of glycidyl methacrylate, and 2 parts by mass of 2-hydroxyethyl methacrylate;
As an emulsifier, 150 parts by mass of aqualon KH10, 1.5 parts by mass of a 10% by mass aqueous solution of ammonium peroxodisulfate (0.15 parts by mass in terms of solid content), and 55 parts by mass of water. It was dropped from the dropping tank into the reaction vessel over a minute. During the dropping, the pH of the reaction system was maintained at 4 or less. After the addition of the emulsified mixture was completed, the temperature of the reaction vessel was maintained at 80 ° C., stirring was continued for 120 minutes, and then the mixture was cooled to room temperature.
After cooling, filtration is performed with a 200-mesh wire mesh to remove agglomerates, etc., and then the pH is adjusted to 8 with 25% by mass of ammonia water, and water is further added to dilute the pH to a concentration of 45% by mass. A latex containing an acrylic polymer (1) was obtained.

Production example P2
In a reaction vessel equipped with a stirrer, a reflux cooler, a dropping tank, and a thermometer, 70.4 parts by mass of ion-exchanged water and "Aqualon KH1025" (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) were initially charged. 0.125 parts by mass (solid content equivalent) of 25% by mass aqueous solution and 0.125 parts by mass (solid content equivalent) of "Adecaria Soap SR1025" (trade name, manufactured by ADEKA Co., Ltd., 25% by mass aqueous solution). The mixture was charged, the temperature inside the reaction vessel was raised to 80 ° C., and 0.15 parts by mass (in terms of solid content) of ammonium persulfate (2% by mass aqueous solution) was added while maintaining the temperature of 80 ° C.

5 minutes after adding the ammonium persulfate aqueous solution,
As the (meth) acrylic acid ester compound, 5.1 parts by mass of methyl methacrylate, 25 parts by mass of cyclohexyl methacrylate, 1 part by mass of n-butyl acrylate, 1 part by mass of n-butyl methacrylate, and 2-ethylhexyl acrylate 60. Mass part;
As functional group-containing monomers, 0.1 parts by mass of methacrylic acid, 0.1 parts by mass of acrylic acid, 2 parts by mass of 2-hydroxyethyl methacrylate, and 5 parts by mass of acrylamide;
As emulsifiers, "Aqualon KH1025" (trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., 25% by mass aqueous solution) 0.75 parts by mass (solid content conversion), "Adecaria Soap SR1025" (trade name, manufactured by ADEKA Corporation (25% by mass aqueous solution) 0.75 parts by mass (in terms of solid content), and 0.05 parts by mass of sodium p-styrene sulfonate;
As a cross-linking agent, 0.7 parts by mass of trimethylolpropane triacrylate;
A mixture of 0.15 parts by mass (solid content equivalent) of ammonium persulfate (2% by mass aqueous solution) as an initiator; and 52 parts by mass of ion-exchanged water was mixed with a homomixer for 5 minutes to prepare an emulsion. The obtained emulsion was added dropwise from the dropping tank to the reaction vessel over 150 minutes.

After the completion of dropping the emulsion, the temperature inside the reaction vessel was maintained at 80 ° C. for 90 minutes, and then cooled to room temperature to obtain an emulsion. Ammonia hydroxide aqueous solution (25% by mass aqueous solution) was added to the obtained emulsion to adjust the pH to 9.0 to obtain a latex containing an acrylic polymer (2A) having a concentration of 40% by mass.
As a result of observation with a transmission electron microscope (TEM), it was found that this acrylic polymer (2A) was spherical and monodisperse with a particle size of 160 nm. The glass transition temperature of the obtained acrylic polymer (2A) was −30 ° C.

Production example P3
In Production Example P2, a latex containing an acrylic polymer (2B) having a concentration of 40% by mass was obtained in the same manner as in Production Example P2 except that the components of the emulsion dropped into the reaction vessel were changed as follows. .. The glass transition temperature of the obtained acrylic polymer (2B) was 60 ° C.

[(Meta) acrylic acid ester compound]
Methyl methacrylate: 5 parts by mass,
Cyclohexyl methacrylate: 70 parts by mass,
N-Butyl methacrylate: 10 parts by mass, and 2-ethylhexyl acrylate: 11.8 parts by mass;
[Functional group-containing monomer]
Methacrylic acid: 1 part by mass,
Acrylic acid: 1 part by mass,
2-Hydroxyethyl methacrylate: 1 part by mass and acrylamide: 0.1 part by mass;
[emulsifier]
"Aqualon KH1025" (trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., 25% by mass aqueous solution) 0.75 parts by mass (solid content equivalent),
"Adecaria Soap SR1025" (trade name, manufactured by ADEKA Corporation, 25% by mass aqueous solution) 0.75 parts by mass (in terms of solid content), and 0.05 parts by mass of sodium p-styrene sulfonate;
[Crosslinking agent]
Trimethylolpropane triacrylate: 0.1 parts by mass;
[Initiator]
Ammonium persulfate (2% by mass aqueous solution): 0.15 parts by mass (in terms of solid content); and a mixture of 52 parts by mass of ion-exchanged water.

When evaluated in the same manner as in Production Example P2, the acrylic polymer (2B) had a spherical particle size of 160 nm and a monodisperse, and had a glass transition temperature of 60 ° C.

<Manufacturing of first water-soluble polymer>
Production example WS1 (Production of polymer E)
46 g of deionized water and 250 g of isopropyl alcohol were charged into a tank reactor equipped with a stirrer and a condenser and maintained at 80 ° C. To this reactor, 207 g of a 40 mass% ammonium methacrylate aqueous solution, 97 g of methyl acrylate, and 151 g of methyl methacrylate were mixed, and 330 g of a monomer and 60 g of a 15 mass% ammonium persulfate aqueous solution were added dropwise over 5 hours. .. After completion of the dropping, the reaction solution was held at 80 ° C. for 3 hours to obtain an aqueous solution containing the first water-soluble polymer E having a solid content concentration of 40% by mass and a pH of 7.
The weight average molecular weight (hereinafter referred to as "Mw") of the obtained polymer E was measured by gel permeation chromatography (GPC) under the following conditions.
Measuring device: HLC8020 system [manufactured by Tosoh Corporation]
Column: G4000PWxl, G3000PWxl, and G2500PWxl [manufactured by Tosoh Corporation] are connected in series and used. Eluent: 0.1M NaCl + phosphate buffer (pH 7)
Calibration curve: Prepared using sodium polyacrylate (manufactured by Sowa Kagaku) As a result of measurement, the Mw of polymer E was 10,000.

Production example WS2 (Production of polymer F)
In the above production example WS1 (production of polymer E),
Same as Production Example WS1 except that ammonium methacrylate was changed to sodium methacrylate, the amount of 40% by mass sodium methacrylate aqueous solution used was changed to 247 g, methyl acrylate was changed to 90 g, and methyl methacrylate was changed to 141 g. An aqueous solution containing the first water-soluble polymer F (Mw: 10,000) having a solid content concentration of 40% by mass and a pH of 7 was obtained.

Production example WS3 (Production of polymer G)
In the above production example WS1 (production of polymer E),
The solid content concentration was 40 in the same manner as in Production Example WS1, except that the amount of the aqueous ammonium methacrylate solution was changed to 247 g, the amount of methyl acrylate used was 90 g, and the amount of methyl methacrylate used was 141 g. An aqueous solution containing the first water-soluble polymer G (Mw: 11,000) having a mass% of pH and a pH of 7 was obtained.

In Examples 1 to 16 and Comparative Examples 1 to 6 below, a test was conducted on a mode in which the base sheet is coated without corona discharge treatment;
In Examples 17 to 21 and Reference Example 1, a test was conducted on a mode in which the base sheet is subjected to a corona discharge treatment and then coated.

Example 1 (However, Example 1 is Reference Example I).
<Preparation of coating liquid for porous layer>
100 parts by mass of aluminum hydroxide oxide particles (average particle size 1.0 μm) as an inorganic filler;
4. As the first water-soluble polymer, 4 parts by mass (1 part by mass as the solid content of the polymer A) of the aqueous solution of the polymer A (described later); and as the resin binder, the acrylic polymer (1) obtained in Production Example P1 above. 0 parts by mass;
Was uniformly dissolved or dispersed in 100 parts by mass of water to prepare a coating liquid for forming a porous layer.

<Manufacturing of separator>
The coating liquid prepared above was applied onto one side of the polyolefin porous film (S1) using a gravure coater so as to have a coating texture of 6.6 g / m ^2, and then dried at 60 ° C. to obtain the above. A multilayer separator was produced by forming a porous layer having a thickness of 4 μm on the porous polyolefin membrane. Here, at the time of coating, the polyolefin porous film as the base sheet was not subjected to the corona discharge treatment.

The separator produced above was evaluated in various ways according to the method described above. The evaluation results are shown in Table 2.

Example 2
In <Preparation of coating liquid for porous layer> of Example 1 above,
The amount of polymer A used as the first water-soluble polymer was changed to 0.1 parts by mass as a solid content conversion value.
As the second water-soluble polymer, 1 part by mass of the aqueous dispersion containing the following polymer H (0.4 parts by mass as the solid content of the polymer H) was further used, and the coating liquid was applied in the same manner as in Example 1. Was prepared, a separator was produced using the coating liquid, and various evaluations were performed. The evaluation results are shown in Table 2.

Examples 3 to 21, Comparative Examples 1 to 6, and Reference Example 1 (However, Examples 6 and 17 are Reference Examples VI and XVII, respectively).
In <Preparation of coating liquid for porous layer> of Example 2 above, the types and amounts of the inorganic filler, the first water-soluble polymer, and the second water-soluble polymer were changed as shown in Table 1, respectively. The coating liquid was adjusted, and in the <Manufacturing of Separator> of Example 1 above, the above coating liquid was used to form the type of the porous polyolefin film and the presence or absence of corona discharge treatment on the base sheet. Separator was produced in the same manner as in Example 1 except that the thickness of the porous layer was set as shown in Table 1, and various evaluations were performed.

In Examples 17 to 21 and Reference Example 1, a corona discharge device manufactured by Kasuga Electric Works Ltd. was used to discharge the polyolefin porous membrane as the base sheet under the condition of ^{a discharge amount of 50 W · min / m 2.} After the treatment, the coating liquid was applied.

The evaluation results are shown in Table 2.
The "F-based surfactant" used in Comparative Example 5 does not correspond to the "first water-soluble polymer" prescribed in the present invention, but for convenience of table preparation, the "first water-soluble polymer". Described in the column.

The "acid monomer ratio" in Table 1 represents the copolymerization ratio of the monomer having a carboxyl group in the polymer, and the "cation species" represents the type of counter cation of the carboxyl group of the monomer.
The abbreviations for each component in Table 1 have the following meanings.
[Base material (polyolefin porous membrane)]
S1: Polyolefin porous membrane (S1) obtained in the above synthesis example S1.
S2: Made by Cellguard, product name "CG2500",
[Inorganic filler]
Aluminum hydroxide: Average particle size 1.0 μm
Baked kaolin: average particle size 1.0 μm
Alumina: Average particle size 1.0 μm

[First water-soluble polymer]
Polymer A: manufactured by Toagosei Co., Ltd., trade name "Julimer AT-613", ammonium salt of water-soluble acrylic copolymer, ratio of carboxyl group-containing monomer unit = 10% by mass, Tg = 76 ° C, solid content concentration 25 wt%
Polymer B: manufactured by Toagosei Co., Ltd., trade name "Julimer AT-210", ammonium salt of water-soluble acrylic copolymer, ratio of carboxyl group-containing monomer unit = 10% by mass, Tg = -7.5 ° C, solid content concentration 30 wt%
Polymer C: manufactured by Toagosei Co., Ltd., trade name "Julimer ET-325", ammonium salt of water-soluble acrylic copolymer, ratio of carboxyl group-containing monomer unit = 5% by mass, Tg = 28 ° C, solid content concentration 30 wt%
Polymer D: manufactured by Toagosei Co., Ltd., trade name "Julimer AT-510", ammonium salt of water-soluble acrylic copolymer, ratio of carboxyl group-containing monomer unit = 10% by mass, Tg = 27.5 ° C, solid content concentration 30 wt %
Polymer E: Ratio of ammonium salt and carboxyl group-containing monomer unit of the water-soluble acrylic copolymer produced in Production Example WS1 = 25% by mass.
Polymer F: Ratio of sodium salt and carboxyl group-containing monomer unit of the water-soluble acrylic copolymer produced in Production Example WS2 = 10% by mass.
Polymer G: Ratio of ammonium salt and carboxyl group-containing monomer unit of the water-soluble acrylic copolymer produced in Production Example WS3 = 30% by mass.

[Second water-soluble polymer]
Polymer H: manufactured by San Nopco, trade name "SN Dispersant 5468", ammonium polyacrylate, solid content concentration 40 wt%
Polymer I: manufactured by Toagosei Co., Ltd., trade name "Aron A6114", copolymer of acrylic acid ester, solid content concentration 40 wt%
Polymer J: manufactured by San Nopco, trade name "SN Dispersant 5027", solid content concentration 20 wt%
[Resin binder]
P1: Acrylic polymer (1) obtained in Synthetic Example P1
[Other ingredients]
F-based surfactant: perfluorooctanesulfonic acid

Examples 22-26
The coating liquid was adjusted in the same manner as in Example 2 except that the types and amounts of the inorganic filler, the first water-soluble polymer, and the second water-soluble polymer were changed as shown in Table 3, respectively. Separators were prepared in the same manner as in Example 1 for each of the cases where the porous polyolefin substrate was corona-treated and the case where it was not treated.
Then, in the obtained separator, the rate of increase in air permeability represented by the following formula was determined. The results are shown in Table 3.
ΔAR (%) = {(AR1-AR2) / A0} × 100
AR0: Air permeability of polyolefin porous membrane substrate (seconds / 100 cc)
AR1: Air permeability (seconds / 100 cc) of a separator formed with a porous membrane after corona treatment on a polyolefin porous membrane base material.
AR2: Air permeability (seconds / 100 cc) of a separator in which a porous membrane is formed on a polyolefin porous membrane base material without corona treatment.
△ When AR is less than 30%: Small change in air permeability with or without corona treatment "◎" (extremely good)
△ When AR is 30% or more and less than 60%: Moderate change in air permeability with or without corona treatment “○” (good)
When the AR is 60% or more: The change in air permeability with or without corona treatment is large "△" (possible)

Example 27
<Preparation of coating liquid for adhesive layer>
As the resin binder, 20 parts by mass of the acrylic polymer 2A obtained in Production Example P2 and 80 parts by mass of the acrylic polymer 2B obtained in Production Example P3;
Was uniformly dissolved in 100 parts by mass of water to obtain a resin binder solution. To this solution, 4 parts by mass of an aqueous solution of polymer A as a first water-soluble polymer (1 part by mass as a solid content of polymer A, 5 parts by mass as a solid content of polymer A with respect to 100 parts by mass of acrylic polymer solid content) was added. , Uniformly mixed to obtain a coating solution for an adhesive layer.
<Manufacturing of separator>
The above coating liquid was applied to one side of the polyolefin porous base material S1 by a gravure coater without performing a corona discharge treatment, and then applied to the entire surface so as to have a coating ^{texture of 0.5 g / m 2, and then 50 ° C.} By heating and drying for 1 minute in the above, an adhesive layer having a layer thickness of 1 μm was formed on the porous polyolefin substrate, and a separator was obtained.
The separator produced above was evaluated in various ways according to the method described above. The evaluation results are shown in Table 5.

Example 28
In <Preparation of coating liquid for adhesive layer> of Example 27 above,
Further, as the second water-soluble polymer, the coating liquid was applied in the same manner as in Example 27, except that 1 part by mass of the aqueous dispersion containing the polymer H (0.4 parts by mass as the solid content of the polymer H) was used. It was prepared, and a separator was produced using the coating liquid and various evaluations were performed. The evaluation results are shown in Table 5.

Examples 29-35 and Comparative Examples 7 and 8
In Example 27, the type and amount of the first water-soluble polymer were changed as shown in Table 4 to prepare a coating liquid, and the coating liquid was used to prepare a porous polyolefin membrane. A separator was produced in the same manner as in Example 27, except that the types were as shown in Table 4.

Reference example 2
A separator was applied in the same manner as in Comparative Example 7, except that the base sheet was coated after being subjected to a corona discharge treatment of a discharge amount of 50 W · min / m ^{2 by a corona surface treatment device manufactured by Kasuga Electric Works.} Manufactured.

The evaluation results of Examples 29 to 35, Comparative Examples 7 and 8, and Reference Example 2 are shown in Table 4.
The meanings of abbreviations such as component names in Table 4 below are the same as those in Table 1.

Examples 36 and 37, and Reference Examples 3 and 4
<Battery evaluation>
The rate characteristics of the batteries manufactured using the separators obtained in Examples 2 and 27 and Reference Examples 1 and 2 were evaluated by the following procedure.
(1) Preparation of positive electrode 90.4 of nickel-manganese-cobalt composite oxide (NMC) (Ni: Mn: Co = 1: 1: 1 (element ratio), density 4.70 g / cm ³ ) was used as the positive electrode active material. Mass%, graphite powder (KS6) (density 2.26 g / cm ³ , number average particle diameter 6.5 μm) 1.6 mass% as conductive auxiliary material, and acetylene black powder (AB) (density 1.95 g / cm) ^{3. A} number average particle diameter of 48 nm) was mixed at a ratio of 3.8% by mass, and polyvinylidene 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-methyl. A slurry was prepared by dispersing in pyrrolidone (NMP). This slurry is 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 compression-molded using a roll press to obtain a positive electrode. Made. The amount of the positive electrode active material applied at this time was 109 g / m ² .

(2) Preparation of negative electrode As the 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 2.27 g / cm 3, number). Average particle size (6.5 μm) is 9.7% by mass, and carboxymethyl cellulose ammonium salt 1.4% by mass (solid content equivalent) (solid content concentration 1.83% by mass aqueous solution) and diene rubber latex 1.7 as a binder. A slurry was prepared by dispersing mass% (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 to be 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 prepare a negative electrode. The amount of the negative electrode active material applied at this time was 5.2 g / m ² .

_{(3) Preparation of non-aqueous electrolyte solution Non-aqueous solution is prepared by dissolving LiPF 6} as a solute in a mixed solvent of ethylene carbonate: ethyl methyl carbonate = 1: 2 (volume ratio) so as to have a concentration of 1.0 mol / L. An electrolytic solution was prepared.

(4) Battery Assembly The separators obtained in Examples 2 and 27 and Comparative Examples 1 and 7 were cut out into a circle of 24 mmφ, and the positive electrode and the negative electrode were cut out into a circle of 16 mmφ, respectively.
The negative electrode, the separator, and the positive electrode are stacked in this order so that the positive electrode and the active material surfaces of the negative electrode face each other, and roll-pressed under the conditions of 22.6 N / cm and 70 ° C. at a press speed of 2 m / min. , Contained in a stainless metal container with a lid. The container and the lid were insulated, and the container was in contact with the copper foil of the negative electrode and the lid was in contact with the aluminum foil of the positive electrode. A battery (simple battery) was assembled by injecting 0.4 ml of the non-aqueous electrolytic solution into this container and sealing the container.

(5) Evaluation of rate characteristics The simple battery assembled in (4) above 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 then holds 4.2 V. By the method of starting to throttle the current value from 3 mA, the first charge after the battery was made was performed for a total of 6 hours. After that, the battery was discharged to a battery voltage of 3.0 V at a current value of 3 mA.
Next, at 25 ° C., the battery is charged to a battery voltage of 4.2 V with a current value of 6 mA (about 1.0 C), and then the current value is started to be throttled from 6 mA so as to maintain 4.2 V for a total of 3 hours. It was charged. After that, the discharge capacity when discharged to a battery voltage of 3.0 V at a current value of 6 mA was defined as 1 C discharge capacity (mAh).
Further, at 25 ° C., the battery is charged to a battery voltage of 4.2 V with a current value of 6 mA (about 1.0 C), and then charged for a total of 3 hours by a method of holding 4.2 V and starting to throttle the current value from 6 mA. Was done. After that, the discharge capacity when the current value was variable and discharged to the battery voltage of 3.0 V was defined as the 2C discharge capacity (mAh).
The ratio of the discharge capacity of (2C) to the discharge capacity of (1C) was defined as the capacity retention rate (%), and the rate characteristics of the batteries manufactured using each separate were obtained. The results are shown in Table 5.

As can be understood from Table 5, the separator of the present invention in which the porous layer or the adhesive layer contains a water-soluble (meth) acrylic resin or a salt thereof was produced without subjecting the base sheet to a corona discharge treatment. Even in this case, it was confirmed that the rate characteristics were maintained at a high level and the battery characteristics were not impaired.

Claims (10)

A layer composed of a porous base material layer and
A first water-soluble polymer which is an ammonium salt or a sodium salt of a water-soluble (meth) acrylic resin (b1) having a carboxyl group-containing monomer unit of 2% by mass or more and 20% by mass or less (excluding 20% by mass). possess a B layer containing a carboxyl group-containing monomer units of 27 mass% or more with a water-soluble (meth) second water-soluble polymer selected from an acrylic resin (b2) and salts thereof, and
A separator for a power storage device, characterized in that the first water-soluble polymer does not contain acrylamide. The separator for a power storage device according to claim 1, wherein the B layer further contains an inorganic filler. The separator for a power storage device according to claim 1, wherein the B layer does not contain an inorganic filler. The separator for a power storage device according to claim 2, wherein the content ratio of the first water-soluble polymer in the B layer is 0.1 part by mass to 5 parts by mass with respect to 100 parts by mass of the inorganic filler. The B layer further contains a resin binder, the amount of the first water-soluble polymer used is 0.5 parts by mass or more with respect to 100 parts by mass of the resin binder, and the resin binder is water-insoluble. The separator for a power storage device according to any one of claims 1 to 4 , which is an acrylic (co) polymer. The following formula:
ΔAR (%) = {(AR1-AR2) / AR0} × 100
{In the formula, AR0: Air permeability of polyolefin porous membrane substrate (seconds / 100 cc)
AR1: Air permeability (seconds / 100 cc) of a separator for a power storage device in which a porous film is formed after corona treatment is performed on a polyolefin porous film base material.
AR2: Air permeability (seconds / 100 cc) of the separator for a power storage device in which a porous film is formed on a polyolefin porous film substrate without corona treatment.
The separator for a power storage device according to any one of claims 1 to 5 , wherein the rate of increase in air permeability represented by is less than 60%. The separator for a power storage device according to any one of claims 1 to 6 , which does not contain acrylamide. Any of claims 1 to 7 , wherein in the B layer, the ratio of the first water-soluble polymer to the total mass of the first water-soluble polymer and the second water-soluble polymer is 20% by mass or more. The separator for a power storage device according to item 1. After or without corona discharge treatment, a single-layer or multi-layer base sheet containing at least layer A composed of a porous base material layer is subjected to corona discharge treatment or without corona discharge treatment.
A water-soluble (meth) acrylic resin (b1) ammonium salt or sodium salt having a carboxyl group-containing monomer unit of 2% by mass or more and 20% by mass or less (excluding 20% by mass) on the base sheet. A layer B containing a first water-soluble polymer and a second water-soluble polymer selected from a water-soluble (meth) acrylic resin (b2) having a carboxyl group-containing monomer unit of 27% by mass or more and a salt thereof is formed. process only contains, and
A method for producing a separator for a power storage device, wherein the first water-soluble polymer does not contain acrylamide. The method for manufacturing a separator for a power storage device according to claim 9 , wherein the separator for a power storage device is the separator for a power storage device according to any one of claims 1 to 8.