JP2019033073A - Manufacturing method of separator for power storage element - Google Patents

Abstract

To provide a method for easily and economically manufacturing a separator for power storage element which improves ion permeability, has an excellent adhesion property and improves heat resistance and safety.SOLUTION: The present invention relates to a manufacturing method of a separator for power storage element including: forming coating by coating a surface of a porous substrate with a coating liquid containing polyamide imide (PAI) and a mixture solvent consisting of a rich solvent and a poor solvent with respect to PAI; and then forming a porous PAI layer having ion permeability by causing phase separation to occur within the coating while utilizing an action of the poor solvent residual in the coating when removing the solvent in the coating, thereby laminating and integrating an S layer and the porous PAI layer. In the manufacturing method of the separator for power storage element, the coating liquid has following features: (1) an amide-based solvent is contained as the rich solvent, (2) tripropylene glycol (TPG) is contained as the poor solvent, and (3) a filler is contained.SELECTED DRAWING: None

Description

The present invention relates to a method for manufacturing a separator for a storage element such as a lithium secondary battery, a lithium ion capacitor, a capacitor, and a capacitor.

When an internal short circuit or an external short circuit occurs due to battery damage or the like, a storage element such as a lithium secondary battery may generate a large current and generate abnormal heat. Therefore, it is important for lithium secondary batteries to prevent heat generation beyond a certain level and to ensure high safety. As a means for ensuring safety, a method in which a separator has a shutdown function for preventing heat generation by blocking the passage of ions between electrodes in the event of abnormal heat generation has been widely put into practical use.

For example, a porous polyolefin film is used as the separator having the shutdown function. The separator made of this porous film can shut down the passage of ions because the polyolefin melts and becomes nonporous at 110 to 160 ° C. during abnormal heat generation of the battery. However, since this polyolefin separator tends to shrink or break at a high temperature, in some cases, the positive electrode and the negative electrode may be in direct contact with each other to cause a short circuit, and abnormal heat generation due to the short circuit may not be suppressed.

As a method for solving such a problem, a porous layer made of a fluorine-based resin such as polyvinylidene fluoride is laminated on a porous substrate such as a porous polyolefin film (hereinafter sometimes abbreviated as “S layer”). Thus, a method for improving the shape stability at a high temperature has been proposed. In this laminated separator, since the heat resistance of the fluororesin itself constituting the heat resistant layer is low, the shape stability due to shrinkage at a high temperature is not always sufficient. Thus, a method has been proposed in which shape stability at high temperatures is secured by laminating a porous layer made of a heat-resistant resin such as polyimide or aramid on the S layer. For example, in Patent Documents 1 and 2, a solution containing a heat-resistant resin (for example, an aramid resin) and a good solvent (for example, an amide solvent) is applied to the surface of the S layer, and this is applied to the heat-resistant resin. A method has been proposed in which a porous layer is formed by dipping in a coagulation bath made of a poor solvent (for example, an alcohol solvent) to cause phase separation. Such a method using a coagulation liquid has a problem from the viewpoints of environmental compatibility, economy, and the like because a waste liquid containing the coagulation liquid is generated from the coagulation bath.

As a method for solving such a problem, Patent Document 3 discloses polyamideimide (PAI), an amide solvent (a good solvent for PAI), and an alcohol solvent such as diethylene glycol and decanol (a poor solvent for PAI). And a coating liquid containing filler is applied to the S layer and dried to form a porous PAI layer having ion permeability (hereinafter sometimes abbreviated as “P layer”). ing. However, a separator with a P layer obtained by using such a coating liquid cannot obtain sufficient ion permeability. Further, the adhesiveness between the S layer and the P layer is not sufficient, and there is a point that should be improved from the viewpoint of reliability.

JP 2005-209570 A JP 2010-50024 A JP 2006-59733 A

Accordingly, the present invention solves the above-described problems, and the present invention provides a separator for a storage element that has excellent ion permeability and good adhesion between an S layer and a P layer, simply and economically. The object is to provide a manufacturing method.

As a result of intensive studies to solve the above-mentioned problems, the present inventors applied a PAI coating liquid containing an amide solvent, tripropylene glycol (TPG), and filler to the surface of the S layer. The inventors have found that a heat-resistant separator having good ion permeability and adhesiveness can be produced by heating and drying to form a P layer and integrating the layers, and the present invention has been achieved.

The present invention has the following objects.

<1> A method for producing a separator for an electricity storage device, wherein a coating liquid containing PAI and a mixed solvent composed of a good solvent and a poor solvent for PAI is applied to the surface of the S layer, and the coating film After that, when the solvent in the coating film is removed, phase separation is caused in the coating film by utilizing the action of the poor solvent remaining in the coating film, and the P layer having ion permeability. In the method for manufacturing a storage element separator in which the S layer and the P layer are laminated and integrated by forming the layer, the coating liquid has the following characteristics.
(1) An amide solvent is contained as a good solvent.
(2) Contains TPG as a poor solvent.
(3) Contains filler.
<2> The method for producing a separator for an electricity storage element, wherein the filler is at least one selected from alumina and boehmite, and the average particle diameter is 0.02 μm or more and less than 1 μm.

By the method of the present invention, it is possible to easily and economically produce a heat-resistant separator for a storage element having excellent ion permeability and having good adhesion between the P layer and the S layer.

Hereinafter, the present invention will be described in detail.

In the method for producing a separator for an electricity storage device of the present invention, a coating liquid containing PAI is applied to the surface (both sides or one side) of the S layer to form a coating film, and then the solvent in the coating film is removed by heating. As a result, a P layer is formed and integrated with the S layer.

The S layer is a porous substrate having a structure having pores connected to the inside thereof, and allowing gas and liquid to pass from one surface to the other surface, and the substrate of the laminated porous film of the present invention It will be.

As the S layer, for example, a porous film made of polyolefin resin, polyethylene terephthalate, cellulose or the like, a nonwoven fabric, a woven fabric, or the like can be used. In these, the porous film which consists of polyolefin resin from a viewpoint of shutdown performance is preferable. As the polyolefin-based resin, homopolymers or copolymers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene can be used. These polyolefin resins can be used alone or in admixture of two or more.
Commercially available products can be used as the porous substrate used as the S layer.

The air permeability of the S layer is preferably 10 seconds / 100 cc or more and 700 seconds / 100 cc or less, more preferably 50 seconds / 100 cc or more and 300 seconds / 100 cc or less in terms of Gurley value (JIS standard P8117). . Although there is no restriction | limiting in the thickness of S layer, Usually, it is 5-50 micrometers. Air permeability is an index representing ion permeability, and the smaller this value, the greater the ion permeability.

In the method for manufacturing a separator for an electricity storage device of the present invention, a coating liquid containing PAI, an amide solvent, TPG, and filler is applied to the surface of the S layer to form a coating film. When the solvent in the coating film is removed, the effect of the poor solvent remaining in the coating film is used to cause phase separation in the coating film to form a porous PAI layer having good ion permeability.

The PAI that forms the P layer is a polymer obtained by performing a polycondensation reaction between a tricarboxylic acid component and a diamine component as raw materials.

The tricarboxylic acid component of PAI is an organic compound having three carboxyl groups (including derivatives thereof) and one or more aromatic rings per molecule, and at least two carboxyl groups among the three carboxyl groups The group is arranged at a position where an acid anhydride form can be formed.

Examples of the aromatic tricarboxylic acid component include a benzene tricarboxylic acid component and a naphthalene tricarboxylic acid component.

Specific examples of the benzenetricarboxylic acid component include, for example, trimellitic acid, hemimellitic acid, their anhydrides and their monochlorides.

Specific examples of the naphthalene tricarboxylic acid component include, for example, 1,2,3-naphthalene tricarboxylic acid, 1,6,7-naphthalene tricarboxylic acid, 1,4,5-naphthalene tricarboxylic acid, anhydrides thereof, and monochlorides thereof. Can be mentioned.

Of the aromatic tricarboxylic acid components, trimellitic acid and trimellitic anhydride chloride (TAC) are preferred.

A tricarboxylic acid component may be used independently and may be used in combination of 2 or more type.

Some of the tricarboxylic acid components are terephthalic acid, isophthalic acid, pyromellitic acid, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 3,3 ′, 4,4′-benzophenonetetracarboxylic acid. Those substituted with such components may be used.

The diamine component of PAI is an organic compound having two primary amino groups (including derivatives thereof) and one or more aromatic rings per molecule.

Specific examples of the aromatic diamine component include, for example, 4,4′-diaminodiphenyl ether (DADE), m-phenylenediamine (MDA), p-phenylenediamine, 4,4′-diphenylmethanediamine (DMA), 4,4 ′. -Diphenyl ether diamine, diphenyl sulfone-4,4'-diamine, diphenyl-4,4'-diamine, o-tolidine, 2,4-tolylenediamine, 2,6-tolylenediamine, xylylenediamine, naphthalenediamine, and These diisocyanate derivatives can be mentioned.

Of the aromatic diamine components, DADE, MDA and DMA are preferred.

An aromatic diamine component may be used independently and may be used in combination of 2 or more type.

PAI usually has a glass transition temperature of 200 ° C. or higher. As the glass transition temperature, a value measured by DSC (differential thermal analysis) is used.

The PAI coating liquid used in the present invention contains a mixed solvent composed of a good solvent and a poor solvent for PAI. Here, the good solvent is a solvent having a solubility in PAI at 25 ° C. of 1% by mass or more, and the poor solvent is a solvent having a solubility in PAI at 25 ° C. of less than 1% by mass. That is.

In the present invention, an amide solvent is used as the good solvent. Examples of amide solvents include N-methyl-2-pyrrolidone (NMP boiling point: 202 ° C.), N, N-dimethylformamide (boiling point: 153 ° C.), N, N-dimethylacetamide (DMAc boiling point: 166 ° C.). Can be mentioned. These amide solvents may be used alone or in combination of two or more. Among these, NMP is preferable.

The poor solvent used in the present invention needs to be TPG. By using TPG, unprecedented high ion permeability and adhesion to the S layer can be ensured. In addition, other alcohol solvents, ether solvents, ketone solvents and the like can be used by mixing with TPG as long as the effects of the present invention are not impaired.

The content of TPG (poor solvent) in the mixed solvent is preferably 1% by mass or more and less than 50% by mass, more preferably 5% by mass or more and 30% by mass or less, based on the total solvent mass. . By making the solvent composition as described above, when the coating film obtained from the PAI coating liquid is dried and solidified, phase separation occurs efficiently due to the action of TPG (poor solvent) remaining in the coating film, A P layer having good ion permeability can be obtained. In addition, about the PAI coating liquid which has such a solvent composition, Unexamined-Japanese-Patent No. 2006-222912 can be referred.

The coating liquid used in the method for manufacturing a separator for an electricity storage device of the present invention needs to contain filler in the PAI coating liquid. By doing in this way, the favorable ion permeability of the P layer formed and the adhesiveness with respect to S layer are securable. That is, good ion permeability and adhesiveness can be obtained by the surprising synergistic effect of the porous structure formed by the action of TPG and the porous structure formed by blending the filler. For example, diethylene glycol Such a synergistic effect cannot be obtained with other high-boiling alcohols such as triethylene glycol, dipropylene glycol, and decanol.

As the filler, an organic filler, an inorganic filler, a mixture thereof, and the like can be used. From the viewpoint of adhesion to the S layer, an inorganic filler is preferably used. Specific examples of the organic filler include, for example, styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, methyl acrylate alone, or a copolymer of two or more kinds, polytetrafluoroethylene, Examples thereof include a powder made of a polymer such as a fluororesin such as a tetrafluoroethylene-6 fluoropropylene copolymer, a tetrafluoroethylene-ethylene copolymer, and polyvinylidene fluoride. An organic filler can be used individually or in mixture of 2 or more types. Examples of inorganic fillers include powders made of inorganic substances such as metal oxides, metal nitrides, metal carbides, metal hydroxides, carbonates and sulfates. Specific examples include powders made of alumina, boehmite (aluminum oxide hydroxide), kaolin (aluminum silicate), silica, titanium dioxide, barium sulfate, calcium carbonate, and the like. An inorganic filler can be used individually or in mixture of 2 or more types. Among these inorganic fillers, alumina, boehmite, and a mixture thereof are preferable from the viewpoint of adhesion to the S layer.

There is no restriction | limiting in the shape of a filler, Particle | grains, such as substantially spherical shape, cube shape, plate shape, column shape, needle shape, whisker shape, fiber shape, can be used, and substantially spherical shape or cube shape is preferable.

Although there is no restriction | limiting in the average particle diameter of a filler, it is preferable that they are 0.01 micrometer or more and 2 micrometers or less, and it is more preferable that they are 0.02 micrometer or more and less than 1 micrometer. The average particle diameter can be measured by a measuring device based on the laser diffraction scattering method.

The surface of the filler may be treated with a surface treatment agent such as a surfactant or a silane coupler.

The filler content is preferably 80/20 to 10/90, more preferably 70/30 to 20/80, in terms of mass ratio to PAI solid content (PAI / filler).

1-50 mass% is preferable and, as for the PAI solid content density | concentration in a PAI coating liquid, 2-30 mass% is more preferable.

You may add well-known additives, such as various surfactant and a silane coupler, to a PAI coating liquid in the range which does not impair the effect of this invention as needed. Moreover, you may add other polymers other than PAI to a PAI coating liquid in the range which does not impair the effect of this invention as needed.

A PAI porous layer having good ion permeability can be formed by applying the PAI coating solution obtained as described above to the surface of the S layer and drying at 90 ° C. to 180 ° C. Although there is no restriction | limiting in the thickness of a PAI porous layer, It is preferable to set it as 1-20 micrometers, and it is more preferable to set it as 2-10 micrometers.

In applying the PAI coating solution, a method of continuous application by roll-to-roll or a method of applying in a sheet-like manner can be adopted, and any method may be used. As the coating device, a die coater, a multilayer die coater, a gravure coater, a comma coater, a reverse roll coater, a doctor blade coater, or the like can be used.

The air permeability of the laminated separator thus obtained is preferably 30 seconds / 100 cc or more and 500 seconds / 100 cc or less in terms of Gurley value (JIS standard P8117), preferably 50 seconds / 100 cc or more, 300 seconds / 100 cc. The following is more preferable. By doing in this way, favorable ion permeability is securable.

Further, the adhesive strength between the S layer and the P layer of the obtained laminated separator is preferably 0.5 N / cm or more, more preferably 0.7 N / cm or more, in the adhesive strength measurement method described later. preferable. By doing in this way, favorable adhesiveness is obtained and the reliability as an electrical storage element separator can be ensured.

As described above, a storage element separator having excellent ion permeability and adhesiveness can be easily manufactured by a simple process.

Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the examples.

The characteristics of the laminated separators obtained in the following examples and comparative examples were evaluated by the following methods.

(1) Ion permeability
The ion permeability was evaluated by measuring the air permeability based on JIS standard P8117.
(2) Adhesive properties One side of the P layer was reinforced with an adhesive tape, and then cut into a width of 25 mm to obtain a test sample. Evaluation was performed by measuring the adhesive strength between the S layer and the P layer by a peel method (peeling speed 100 mm / min, T-type peeling) using a Tensilon type tensile tester under the conditions of 23 ° C. and 50% RH. In addition, it measured over time in 100 mm from the measurement start to the measurement completion, the average value of the measured value was computed, and it converted into 1 cm width, and it was set as adhesive strength.

<Example 1>
A PAI solution was prepared in accordance with the description in JP-A-2006-222912. That is, a PAI powder (glass transition temperature 280 ° C.) obtained by copolymerizing TAC, DADE and MDA (copolymerization molar ratio: DADE / MDA = 7/3) is a mixed solvent composed of NMP and TPG. In (mass ratio NMP / TPG = 90/10), it melt | dissolved at 30 degreeC, and obtained the uniform PAI solution (A-1) whose solid content concentration of PAI is 13 mass%. The PAI coating liquid (L-1) was obtained by adding the said mixed solvent and commercially available substantially spherical alumina powder (average particle diameter: 0.5 micrometer) to A-1, and mixing with a ball mill. The solid content concentration of L-1 was 25% by mass, and the mass ratio of PAI to alumina was PAI / alumina = 40/60. L-1 is applied to both sides of a commercially available polyethylene separator having a thickness of 20 μm, an air permeability of 214 seconds / 100 cc, and a porosity of 45% by volume, and dried at 100 ° C. for 20 minutes to form a P layer having a thickness of 5 μm on both sides. A laminated separator (P-1) was obtained. Table 1 shows the results of evaluating the P-1 ion permeability and adhesive properties.

<Example 2>
A PAI coating liquid (L-2) was obtained in the same manner as in Example 1 except that the mass ratio of PAI to alumina was PAI / alumina = 30/70. Using L-2, in the same manner as in Example 1, a laminated separator (P-2) having a P layer having a thickness of 5 μm formed on both surfaces was obtained. Table 1 shows the results of evaluating the ion permeability and adhesive properties of P-2.

<Example 3>
A PAI coating liquid (L-3) was obtained in the same manner as in Example 1 except that the mass ratio of PAI and alumina was PAI / alumina = 50/50. Using L-3, a multilayer separator (P-3) in which a P layer having a thickness of 5 μm was formed on both surfaces was obtained in the same manner as in Example 1. Table 1 shows the results of evaluating the ion permeability and adhesive properties of P-3.

<Example 4>
A PAI coating liquid (L-4) was obtained in the same manner as in Example 1 except that the mass ratio of PAI and alumina was PAI / alumina = 60/40. Using L-4, a multilayer separator (P-4) in which a P layer having a thickness of 5 μm was formed on both surfaces was obtained in the same manner as in Example 1. Table 1 shows the evaluation results of ion permeability and adhesive properties of P-4.

<Example 5>
A PAI coating liquid (L-5) was obtained in the same manner as in Example 1 except that the mass ratio of the mixed solvent composed of NMP and TPG was changed to “NMP / TPG = 80/20”. Using L-5, a multilayer separator (P-5) in which a P layer having a thickness of 7 μm was formed on both surfaces was obtained in the same manner as in Example 1. Table 1 shows the evaluation results of ion permeability and adhesive properties of P-5.

<Example 6>
A PAI coating liquid (L-6) was obtained in the same manner as in Example 1 except that the mass ratio of the mixed solvent composed of NMP and TPG was changed to “NMP / TPG = 93/7”. Using L-6, a multilayer separator (P-6) in which a P layer having a thickness of 3 μm was formed on both sides in the same manner as in Example 1 was obtained. Table 1 shows the results of evaluating the ion permeability and adhesive properties of P-6.

<Example 7>
As a commercially available polyethylene separator, a P layer having a thickness of 5 μm was used in the same manner as in Example 1 except that a separator having a thickness of 16 μm, an air permeability of 156 seconds / 100 cc, and a porosity of 43 vol% was used. Obtained a laminated separator (P-7) formed on both sides. Table 1 shows the results of evaluating the ion permeability and adhesive properties of P-7.

<Example 8>
A PAI coating liquid (L-8) was obtained in the same manner as in Example 1 except that a substantially spherical alumina powder (commercially available product) having an average particle size of 0.2 μm was used as the filler. Using L-8, a multilayer separator (P-8) in which a P layer having a thickness of 3 μm was formed on both surfaces was obtained in the same manner as in Example 1. Table 1 shows the evaluation results of ion permeability and adhesive properties of P-8.

<Example 9>
A PAI coating liquid (L-9) was obtained in the same manner as in Example 1 except that cube-like boehmite powder (commercially available product) having an average particle size of 0.7 μm was used as the filler. Using L-9, a multilayer separator (P-9) in which a P layer having a thickness of 3 μm was formed on both surfaces in the same manner as in Example 1 was obtained. Table 1 shows the results of evaluating the ion permeability and adhesive properties of P-9.

<Example 10>
A PAI coating liquid (L-10) was obtained in the same manner as in Example 1 except that cube-like boehmite powder (commercially available product) having an average particle size of 0.7 μm was used as the filler. Using L-10, a multilayer separator (P-10) in which a P layer having a thickness of 3 μm was formed on both surfaces in the same manner as Example 1 was obtained. Table 1 shows the evaluation results of ion permeability and adhesive properties of P-10.

<Example 11>
A PAI coating liquid (L-11) was obtained in the same manner as in Example 1 except that a substantially spherical silica powder (commercially available product) having an average particle size of 0.5 μm was used as the filler. Using L-11, a multilayer separator (P-11) in which a P layer having a thickness of 3 μm was formed on both sides in the same manner as in Example 1 was obtained. Table 1 shows the evaluation results of ion permeability and adhesive properties of P-11.

<Comparative Example 1>
A PAI coating liquid (M-1) was obtained in the same manner as in Example 1 except that only NMP was used as a solvent for dissolving the PAI powder. Using M-1, a multilayer separator (R-1) in which P layers having a thickness of 5 μm were formed on both surfaces was obtained in the same manner as in Example 1. Table 1 shows the evaluation results of ion permeability and adhesive properties of R-1.

<Comparative example 2>
A PAI coating liquid (M-2) was obtained in the same manner as in Example 1 except that TPG was changed to ethylene glycol. Using M-2, a multilayer separator (R-2) in which a P layer having a thickness of 5 μm was formed on both sides in the same manner as Example 1 was obtained. Table 1 shows the results of evaluating the ion permeability and adhesive properties of R-2.

<Comparative Example 3>
A PAI coating liquid (M-3) was obtained in the same manner as in Example 1 except that TPG was changed to diethylene glycol. Using M-3, a multilayer separator (R-3) having a P layer having a thickness of 5 μm formed on both sides was obtained in the same manner as in Example 1. Table 1 shows the evaluation results of ion permeability and adhesive properties of R-3.

<Comparative example 4>
A PAI coating liquid (M-4) was obtained in the same manner as in Example 1 except that TPG was changed to triethylene glycol. Using M-4, in the same manner as in Example 1, a multilayer separator (R-4) in which P layers having a thickness of 5 μm were formed on both surfaces was obtained. Table 1 shows the evaluation results of ion permeability and adhesive properties of R-4.

<Comparative Example 5>
A PAI coating liquid (M-5) was obtained in the same manner as in Example 1 except that TPG was changed to decanol. Using M-5, in the same manner as in Example 1, a multilayer separator (R-5) in which P layers having a thickness of 5 μm were formed on both surfaces was obtained. Table 1 shows the evaluation results of R-5 ion permeability and adhesive properties.

<Comparative Example 6>
A PPG having a thickness of 5 μm was used in the same manner as in Example 1 except that TPG was dipropylene glycol, and a commercially available polyethylene separator having a thickness of 16 μm, an air permeability of 156 seconds / 100 cc, and a porosity of 43% by volume was used. A laminated separator (R-6) having layers formed on both sides was obtained. Table 1 shows the evaluation results of ion permeability and adhesive properties of R-6.

<Comparative Example 7>
Using the PAI solution (A-1) obtained in Example 1, a multilayer separator (R-7) in which a P layer having a thickness of 5 μm was formed on both surfaces was obtained in the same manner as in Example 1. Table 1 shows the results of evaluating the ion permeability and adhesive properties of R-7.

<Comparative Example 8>
A PAI coating liquid (M-8) was obtained in the same manner as in Example 1 except that TPG was decanol and glass powder (commercial product) having an average particle diameter of 1 μm was used as the filler. Using M-8, in the same manner as in Example 1, a multilayer separator (R-8) in which P layers having a thickness of 3 μm were formed on both surfaces was obtained. Table 1 shows the evaluation results of ion permeability and adhesive properties of P-8.

<Comparative Example 9>
PAI coating liquid (M-9) was obtained in the same manner as in Example 1 except that TPG was decanol and polytetrafluoroethylene (commercial product) having an average particle size of 0.3 μm was used as filler. . Using M-9, in the same manner as in Example 1, a multilayer separator (R-9) in which P layers having a thickness of 3 μm were formed on both surfaces was obtained. Table 1 shows the results of evaluating the ion permeability and adhesive properties of R-9.

As shown in the Examples and Comparative Examples, the separator for a storage element obtained by the production method of the present invention has a synergistic action by the poor solvent TPG and fillers such as alumina and boehmite in the P layer. Therefore, it can be seen that good ion permeability and adhesion of the separator in which the P layer is laminated and integrated can be secured. Moreover, according to the manufacturing method of this invention, a highly safe laminated separator can be manufactured with a simple process excellent in environmental compatibility.

The method for producing a separator for an electricity storage device of the present invention is excellent in environmental compatibility and economy. Moreover, the obtained laminated separator is excellent in ion permeability and adhesive properties. Therefore, it can be suitably used as a separator for an electricity storage element having excellent safety.

Claims (2)

A method for producing a separator for an electricity storage device, wherein a coating liquid containing polyamideimide (PAI) and a mixed solvent composed of a good solvent and a poor solvent for PAI is applied to the surface of a porous substrate. After forming the coating film and then removing the solvent in the coating film, it has ion permeability by causing phase separation in the coating film by utilizing the action of the poor solvent remaining in the coating film. In the method for producing a storage element separator in which a porous substrate and the porous PAI layer are laminated and integrated by forming a porous PAI layer, the coating liquid has the following characteristics. Production method.
(1) An amide solvent is contained as a good solvent.
(2) Contains tripropylene glycol (TPG) as a poor solvent.
(3) Contains filler. The method for producing a separator for an electricity storage element according to claim 1, wherein the filler is at least one selected from alumina and boehmite, and the average particle size is 0.02 µm or more and less than 1 µm.