JP2011210435A - Separator for nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a nonaqueous secondary battery superior in thermal shrinkage under high temperatures, and having an excellent membrane resistance.SOLUTION: The separator for the nonaqueous secondary battery is formed containing a polyolefin porous base material, a heat resistant resin, and an inorganic filler, and has a heat-resistant porous layer laminated on one side or both sides of the porous base material. The porosity of the heat-resistant porous layer is 5% or more and less than 30%.

Description

  The present invention relates to a separator used for a non-aqueous secondary battery. Specifically, the present invention relates to a separator that improves the safety of a non-aqueous secondary battery.

  Non-aqueous secondary batteries typified by lithium ion secondary batteries are widely used as main power sources for portable electronic devices such as mobile phones and notebook computers. In such a lithium ion secondary battery, technological development has been advanced to achieve further higher energy density, higher capacity, and higher output, and this demand is expected to increase further in the future. In order to meet such demands, technology for ensuring a high level of battery safety has become even more important.

  Generally, a microporous film made of polyethylene or polypropylene is used for a separator of a lithium ion secondary battery. This separator has a function called a shutdown function for the purpose of ensuring the safety of the lithium ion secondary battery. This shutdown function refers to a function in which the resistance increases remarkably when the battery temperature rises and reaches a certain temperature. With this shutdown function, when the battery generates heat for some reason, the current can be cut off, further heat generation of the battery can be prevented, and smoke, fire, and explosion can be prevented. Such a shutdown function is based on the operating principle that the material constituting the separator is melted and deformed to close the holes of the separator. Therefore, in the case of a separator made of polyethylene, the shutdown function operates at around 140 ° C. near the melting point of polyethylene, and in the case of polypropylene, this function operates at about 165 ° C. This shutdown function preferably operates at a relatively low temperature from the viewpoint of ensuring the safety of the battery, and polyethylene is generally used for this reason.

  On the other hand, a separator of a lithium ion secondary battery is required to have sufficient heat resistance in addition to a shutdown function. The reason is as follows. In a conventional separator made of only a microporous membrane such as polyethylene, after the shutdown function is activated, the battery continues to be exposed to a temperature higher than the temperature at which the shutdown function is activated, so that the separator is melted (so-called meltdown). End up. This is natural when considering the principle of the shutdown function. As a result of this meltdown, a short circuit occurs inside the battery, and a large amount of heat is generated along with this, so that the battery is exposed to dangers of smoke, ignition, and explosion. For this reason, in addition to the shutdown function, the separator is required to have sufficient heat resistance that does not cause meltdown in the vicinity of the temperature at which the shutdown function operates.

  Here, conventionally, in order to impart both a shutdown function and heat resistance to the separator, a separator having a polyethylene microporous film coated with a porous layer made of a heat-resistant resin such as polyimide or aromatic polyamide has been proposed ( For example, see Patent Documents 1 and 2). In such a separator, the shutdown function operates in the vicinity of the melting point of polyethylene (about 140 ° C.), and the heat-resistant porous layer exhibits sufficient heat resistance, so that no melt down occurs at 180 ° C. or higher.

  However, this type of separator, which has been proposed in the past, does not have a sufficient heat shrinkage rate at 180 ° C., and there is a concern that a short circuit between the electrodes may occur due to film breakage or misalignment of the separator due to heat shrinkage. . In addition, it is conceivable to increase the thickness of the heat-resistant layer in order to suppress the thermal shrinkage of the separator, or to make the heat-resistant layer a dense structure, but this increases the film resistance, which decreases the battery characteristics. It is also a concern that

International Publication No. 2008/062727 Pamphlet International Publication No. 2008/156033 Pamphlet

  Accordingly, an object of the present invention is to provide a separator for a non-aqueous secondary battery that has an excellent heat shrinkage rate at a high temperature and has a good film resistance.

  As a result of intensive studies to solve the above problems, the present inventors have found that the problem can be solved by the following configuration, and have reached the present invention. That is, the present invention adopts the following configuration.

1. A separator for a non-aqueous secondary battery comprising a polyolefin porous substrate, a heat-resistant porous layer formed by including a heat-resistant resin and an inorganic filler, and laminated on one or both surfaces of the porous substrate. A separator for a non-aqueous secondary battery, wherein the heat-resistant porous layer has a porosity of 5% or more and less than 30%.
2. 2. The separator for a non-aqueous secondary battery according to 1 above, wherein the heat resistant resin is a meta-type wholly aromatic polyamide or para-type wholly aromatic polyamide.
3. 3. The separator for a non-aqueous secondary battery according to the above 1 or 2, wherein the inorganic filler is at least one selected from a metal oxide, a metal carbonate, a metal phosphate, and a metal hydroxide. .

  ADVANTAGE OF THE INVENTION According to this invention, the separator for non-aqueous secondary batteries which is excellent in the thermal contraction rate under high temperature and has favorable film | membrane resistance can be provided. A lithium ion secondary battery using such a separator can prevent a short circuit due to shrinkage of the separator, and a non-aqueous secondary battery excellent in safety can be obtained.

  Hereinafter, embodiments of the present invention will be sequentially described. In addition, these description and Examples illustrate this invention, and do not restrict | limit the scope of the present invention.

[Separator for non-aqueous secondary battery]
The separator for a non-aqueous secondary battery according to the present invention includes a polyolefin porous substrate, a heat resistant porous layer formed by including a heat resistant resin and an inorganic filler, and laminated on one or both surfaces of the porous substrate. The non-aqueous secondary battery separator is characterized in that the heat-resistant porous layer has a porosity of 5% or more and less than 30%.

  According to such a separator for a non-aqueous secondary battery of the present invention, the polyolefin porous substrate can provide a shutdown function, and the heat-resistant porous layer holds the polyolefin even at a temperature higher than the shutdown temperature. Melt down hardly occurs, and safety at high temperatures can be secured. Particularly, when the porosity of the heat-resistant porous layer is 5% or more and less than 30%, for example, the heat shrinkage rate is low even at a high temperature of about 180 degrees, and the membrane resistance is sufficient. It becomes. Therefore, according to the separator of the present invention, a non-aqueous secondary battery excellent in safety can be obtained.

The separator for a non-aqueous secondary battery of the present invention preferably has a total film thickness of 30 μm or less from the viewpoint of the energy density of the non-aqueous secondary battery. The Gurley value (JIS P8117) of the separator is preferably 100 to 500 sec / 100 cc from the viewpoint of improving the balance between mechanical strength and membrane resistance. The membrane resistance of the separator is preferably 1.5 to 10 ohm · cm ² from the viewpoint of load characteristics of the non-aqueous secondary battery. The heat shrinkage rate of the separator at 180 ° C. is preferably 5 to 20%.

[Polyolefin porous substrate]
The polyolefin porous substrate used in the separator of the present invention is particularly limited as long as it has a large number of pores or voids inside and has a porous structure in which these pores are connected to each other. It is not a thing. Examples of such a substrate include a microporous film, a nonwoven fabric, a paper-like sheet, and other sheets having a three-dimensional network structure. Among these, a microporous membrane is preferable from the viewpoint of handling properties and strength. In addition, the polyolefin porous substrate is heated to a predetermined temperature, so that the micropores in the microporous membrane are closed, and a shutdown function is exhibited.

  Examples of the polyolefin include polyethylene, polypropylene, and polymethylpentene. Among them, those containing 90% by weight or more of polyethylene are preferable from the viewpoint of obtaining good shutdown characteristics. As the polyethylene, for example, low density polyethylene, high density polyethylene, ultrahigh molecular weight polyethylene and the like are preferably used, and particularly, high density polyethylene and ultra high molecular weight polyethylene are suitable. Furthermore, polyethylene comprising a mixture of high density polyethylene and ultra high molecular weight polyethylene is preferred from the viewpoint of strength and moldability.

  The film thickness of the polyolefin porous substrate is preferably 5 to 25 μm from the viewpoint of the energy density, load characteristics, mechanical strength, and handling properties of the non-aqueous secondary battery. The porosity of the polyolefin porous substrate is preferably 30 to 60% from the viewpoints of permeability, mechanical strength, and handling properties. The Gurley value (JIS P8117) of the polyolefin porous substrate is preferably 50 to 500 sec / 100 cc from the viewpoint of obtaining a good balance between mechanical strength and membrane resistance.

[Heat-resistant porous layer]
In the present invention, examples of the heat-resistant porous layer include microporous film-like, non-woven fabric, paper-like, and other layers having a three-dimensional network-like porous structure. From the viewpoint of being obtained, the layer is preferably a microporous film. Here, the microporous film-like layer has a large number of micropores inside, and has a structure in which these micropores are connected. Gas or liquid can pass from one surface to the other. It says the layer that became.

  The heat-resistant resin used in the present invention is suitably a polymer having a melting point of 200 ° C. or higher, or a polymer having no melting point but having a decomposition temperature of 200 ° C. or higher. Preferable examples of such heat-resistant resins include at least one resin selected from the group consisting of wholly aromatic polyamides, polyimides, polyamideimides, polysulfones, polyketones, polyether ketones, polyether imides, and celluloses. In particular, from the viewpoint of durability, meta-type wholly aromatic polyamide or para-type wholly aromatic polyamide is preferable.

  In the present invention, the heat-resistant porous layer may be formed on both surfaces or one surface of the polyolefin microporous membrane. However, from the viewpoint of handling properties, durability, and the effect of suppressing heat shrinkage, it is preferable to form the heat-resistant porous layer on both surfaces of the substrate. preferable. In order to fix the heat-resistant porous layer on the substrate, a method in which the heat-resistant porous layer is directly formed on the substrate by a coating method is preferable. A technique of adhering the quality layer sheet on the base material using an adhesive or the like, a technique such as heat fusion or pressure bonding can also be employed.

  In the present invention, regarding the thickness of the heat resistant porous layer, when the heat resistant porous layer is formed on both surfaces of the substrate, the total thickness of the heat resistant porous layer may be 3 μm or more and 12 μm or less. Preferably, when the heat resistant porous layer is formed only on one side of the substrate, the thickness of the heat resistant porous layer is preferably 3 μm or more and 12 μm or less.

  In the present invention, the porosity of the heat resistant porous layer is 5% or more and less than 30%. If the porosity is less than 5%, there is a problem that the membrane resistance is high and cannot be used as a battery separator, which is not preferable. On the other hand, if the porosity is 30% or more, there is a problem that the thermal shrinkage rate is increased and the safety of the battery is impaired, which is not preferable.

  The method for controlling the porosity of the heat resistant porous layer to the above range is not particularly limited. For example, in the case of a method of using a meta-type wholly aromatic polyamide as a heat-resistant resin, dissolving it in a solvent and applying it to a substrate and then coagulating it, controlling the composition and temperature of the coagulation liquid, etc. It is done. In addition, for example, in the case of a method in which para-type wholly aromatic polyamide is used as a heat-resistant resin, and this is dissolved in a solvent and applied to a substrate and then precipitated, the polymer deposition conditions (humidity, temperature, etc.) are set. Control and the like. In this case, basically, the lower the humidity, the lower the deposition temperature, and the smaller the added amount of the inorganic filler, the smaller the porosity of the heat resistant porous layer.

  In the present invention, the heat resistant porous layer preferably contains an inorganic filler. The inorganic filler is not particularly limited, but for example, metal oxides such as alumina, titania, silica and zirconia, metal carbonates such as calcium carbonate, metal sulfates such as barium sulfate, metal phosphates such as calcium phosphate, water It is preferably at least one selected from metal hydroxides such as aluminum oxide and magnesium hydroxide.

  Especially, as an inorganic filler, what produces an endothermic reaction in 200-400 degreeC is preferable. As an inorganic filler which has such a characteristic, the thing which is an inorganic filler which consists of a metal hydroxide, a boron salt compound, or a clay mineral, for example, and produces an endothermic reaction at 200-400 degreeC is mentioned. Specific examples include aluminum hydroxide, magnesium hydroxide, calcium aluminate, dosonite, zinc borate and the like, and these can be used alone or in combination of two or more.

  In the present invention, the average particle diameter of the inorganic filler is preferably in the range of 0.1 to 2 μm from the viewpoint of short circuit resistance at high temperature, moldability, and the like. In the present invention, the content of the inorganic filler in the heat resistant porous layer is preferably 1 to 50% by weight from the viewpoint of controlling the porosity of the heat resistant porous layer.

[Method of manufacturing separator for non-aqueous secondary battery]
In the present invention, the method for producing a separator for a non-aqueous secondary battery is not particularly limited as long as the separator of the present invention having the above-described configuration can be produced. For example, it can be produced through the following steps (1) to (5). It is.

(1) Preparation of coating slurry A heat-resistant resin is dissolved in a solvent to prepare a coating slurry. The solvent is not particularly limited as long as it dissolves the heat-resistant resin, but specifically, a polar solvent is preferable, and examples thereof include N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethylsulfoxide. Moreover, the said solvent can add the solvent used as a poor solvent with respect to heat resistant resin in addition to these polar solvents. By applying such a poor solvent, a microphase separation structure is induced and the formation of a heat-resistant porous layer is facilitated. As the poor solvent, alcohols are preferable, and polyhydric alcohols such as glycol are particularly preferable. The concentration of the heat resistant resin in the coating slurry is preferably 4 to 9% by weight. Moreover, an inorganic filler is disperse | distributed to this as needed, and it is set as the slurry for coating. In dispersing the inorganic filler in the coating slurry, when the dispersibility of the inorganic filler is not preferable, a method of improving the dispersibility by surface-treating the inorganic filler with a silane coupling agent or the like is also applicable.

(2) Coating of slurry The slurry is coated on at least one surface of the polyolefin microporous membrane. When forming a heat-resistant porous layer on both surfaces of a polyolefin microporous film, it is preferable from a viewpoint of shortening of a process to apply simultaneously on both surfaces of a base material. Examples of the method for coating the slurry for coating include a knife coater method, a gravure coater method, a screen printing method, a Meyer bar method, a die coater method, a reverse roll coater method, an ink jet method, a spray method, and a roll coater method. . Among these, the reverse roll coater method is preferable from the viewpoint of uniformly forming a coating film. When applying simultaneously to both sides of the base material, for example, by passing the base material between a pair of Meyer bars, an excess coating slurry is applied to both sides of the base material, and this is applied to a pair of reverse roll coaters. There is a method of precise measurement by scraping off excess slurry in between.

(3) Solidification of slurry The base material on which the slurry is applied is treated with a coagulating liquid capable of coagulating the heat-resistant resin. By treating the substrate coated with the coating slurry in a coagulating liquid capable of coagulating the heat resistant resin or in a moist heat atmosphere, the heat resistant resin is coagulated to form a heat resistant porous layer. Form. As a method of treating with the coagulating liquid, a method of spraying the coagulating liquid on the substrate coated with the coating slurry, or a method of immersing the substrate in a bath (coagulating bath) containing the coagulating liquid. Alternatively, it may be deposited in an atmosphere of a predetermined humidity and temperature and then immersed in a coagulation bath to coagulate. Here, when installing a coagulation bath, it is preferable to install it below the coating apparatus. The coagulation liquid is not particularly limited as long as it can coagulate the heat-resistant resin, but water or a solution obtained by mixing an appropriate amount of water with the solvent used in the slurry is preferable. Here, the mixing amount of water is preferably 40 to 80% by weight with respect to the coagulation liquid. If the amount of water is less than 40% by weight, the time required for solidifying the heat-resistant resin may become long, or solidification may be insufficient. On the other hand, if the amount of water is more than 80% by weight, the cost for solvent recovery may increase, or the surface that contacts the coagulation liquid may become too solidified and the surface may not be sufficiently porous.

(4) Removal of coagulating liquid The coagulating liquid is removed by washing with water.

(5) Drying Dry and remove water from the sheet. Although there is no particular limitation on the drying method, the drying temperature is preferably 50 to 80 ° C. When a high drying temperature is applied, a method of contacting with a roll to prevent dimensional change due to heat shrinkage. It is preferable to apply.

[Non-aqueous secondary battery]
In the present invention, the non-aqueous secondary battery is a non-aqueous secondary battery that obtains an electromotive force by doping or dedoping lithium, and is characterized by using the separator described above. The type and configuration of the non-aqueous secondary battery to which the separator of the present invention is applied are not limited in any way, but an electrolytic solution is impregnated into a battery element in which a positive electrode, a separator, and a negative electrode are sequentially laminated, and this is applied to the exterior. Any configuration can be applied as long as it has a sealed structure.

  The negative electrode has a structure in which a negative electrode mixture composed of a negative electrode active material, a conductive additive and a binder is formed on a current collector. Examples of the negative electrode active material include materials capable of electrochemically doping lithium, and examples thereof include carbon materials, silicon, aluminum, tin, and wood alloys. Examples of the conductive assistant include carbon materials such as acetylene black and ketjen black. The binder is made of an organic polymer, and examples thereof include polyvinylidene fluoride and carboxymethyl cellulose. As the current collector, a copper foil, a stainless steel foil, a nickel foil, or the like can be used.

The positive electrode has a structure in which a positive electrode mixture composed of a positive electrode active material, a conductive additive and a binder is formed on a current collector. Examples of the positive electrode active material include lithium-containing transition metal oxides. Specifically, LiCoO ₂ , LiNiO ₂ , LiMn _0.5 Ni _0.5 O ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 Examples include O ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiCo _0.5 Ni _0.5 O ₂ , LiAl _0.25 Ni _0.75 O _{2, and the} like. Examples of the conductive assistant include carbon materials such as acetylene black and ketjen black. The binder is made of an organic polymer, and examples thereof include polyvinylidene fluoride. As the current collector, aluminum foil, stainless steel foil, titanium foil, or the like can be used.

The electrolytic solution has a structure in which a lithium salt is dissolved in a non-aqueous solvent. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO _{4 and the} like. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, vinylene carbonate, and the like. These may be used alone or in combination.

  Examples of the exterior material include a metal can or an aluminum laminate pack. The shape of the battery includes a square shape, a cylindrical shape, a coin shape, and the like, but the separator of the present invention can be suitably applied to any shape.

Examples of the present invention will be described below, but the present invention is not limited thereto.
Each value in this example was determined according to the following method.

[Film thickness]
The film thickness of the polyolefin microporous membrane and the separator for a non-aqueous secondary battery was determined by measuring 20 points with a contact-type film thickness meter (manufactured by Mitutoyo Corporation) and averaging them. Here, the contact terminal used was a cylindrical one having a bottom surface of 0.5 cm in diameter.

[Weighing]
The basis weight of the non-aqueous secondary battery separator is obtained by cutting a sample into 10 cm × 10 cm and measuring the weight. By dividing this weight by the area, the basis weight which is the weight per 1 m ² was obtained.

[Porosity]
The constituent materials are a, b, c..., N, and the weights of the constituent materials are Wa, Wb, Wc..., Wn (g · cm ² ), and their true densities are da, db, dc. g / cm ³ ), where the film thickness of the layer of interest is t (cm), the porosity ε (%) was obtained from the following equation.
ε = {1− (Wa / da + Wb / db + Wc / dc +... + Wn / dn) / t} × 100

[Membrane resistance]
A separator as a sample was cut into a size of 2.6 cm × 2.0 cm. The cut-out separator was immersed in a methanol solution in which 3% by weight of a nonionic surfactant (manufactured by Kao Corporation; Emulgen 210P) was dissolved and air-dried. A 20 μm thick aluminum foil was cut into 2.0 cm × 1.4 cm, and a lead tab was attached. Two aluminum foils were prepared, and a separator cut between the aluminum foils was sandwiched between the aluminum foils so that the aluminum foils were not short-circuited. As the electrolytic solution, a solution in which 1M LiBF ₄ was dissolved in a solvent in which propylene carbonate and ethylene carbonate were mixed at a weight ratio of 1: 1 was used, and the separator was impregnated with the electrolytic solution. This was sealed in an aluminum laminate pack under reduced pressure so that the tabs came out of the aluminum pack. Such cells were prepared so that there were one, two, and three separators in the aluminum foil, respectively. The cell was placed in a constant temperature bath at 20 ° C., and the resistance of the cell was measured by an AC impedance method at an amplitude of 10 mV and a frequency of 100 kHz. The measured resistance value of the cell was plotted against the number of separators, and this plot was linearly approximated to obtain the slope. The inclination was multiplied by the electrode area of 2.0 cm × 1.4 cm to determine the membrane resistance (ohm · cm ² ) per separator.

[Heat shrinkage]
A separator serving as a sample was cut into 18 cm (MD direction) × 6 cm (TD direction). On the line that bisects the TD direction, points (point A, point B) of 2 cm and 17 cm from the top were marked. In addition, points (points C and D) 1 cm and 5 cm from the left were marked on a line that bisects the MD direction. A clip was attached to this (the place where the clip is attached is within 2 cm in the upper part in the MD direction), and it was hung in an oven adjusted to 180 ° C. and heat-treated for 30 minutes under no tension. The length between the two points AB and the CD was measured before and after the heat treatment, and the thermal shrinkage rate was obtained from the following equation.
MD direction thermal shrinkage = {(AB length before heat treatment−AB length after heat treatment) / AB length before heat treatment} × 100
TD direction thermal contraction rate = {(length of CD before heat treatment−length of CD after heat treatment) / length of CD before heat treatment} × 100

[Example 1]
(1) Manufacture of a polyethylene porous membrane As polyethylene powder, GUR2126 (weight average molecular weight 4150,000, melting | fusing point 141 degreeC) and GURX143 (weight average molecular weight 560,000, melting | fusing point 135 degreeC) by a Ticona company were used. GUR2126 and GURX143 are made to be 1: 9 (weight ratio), and liquid paraffin (manufactured by Matsumura Oil Research Co., Ltd .; Smoyl P-350P; boiling point 480 ° C.) and decalin so that the polyethylene concentration becomes 30% by weight. A polyethylene solution was prepared by dissolving in a mixed solvent. The composition of this polyethylene solution was polyethylene: liquid paraffin: decalin = 30: 45: 25 (weight ratio).
This polyethylene solution was extruded from a die at 148 ° C. and cooled in a water bath to prepare a gel tape (base tape). The base tape was dried at 60 ° C. for 8 minutes and at 95 ° C. for 15 minutes, and then the base tape was stretched by biaxial stretching that was performed in the order of longitudinal stretching and lateral stretching. Here, the longitudinal stretching was 5.5 times, the stretching temperature was 90 ° C., the transverse stretching was 11.0 times the stretching ratio, and the stretching temperature was 105 ° C. After transverse stretching, heat setting was performed at 125 ° C. Next, this was immersed in a methylene chloride bath to extract liquid paraffin and decalin. Then, it dried at 50 degreeC and annealed at 120 degreeC, and obtained the polyethylene microporous film. The film thickness was 12 μm, the porosity was 37%, the Gurley value was 301 sec / 100 cc, and the film resistance was 2.6 ohm · cm ² .

(2) Production of polymetaphenylene isophthalamide When 160.5 g of isophthalic acid chloride was dissolved in 1120 ml of tetrahydrofuran and a solution of 85.2 g of metaphenylenediamine dissolved in 1120 ml of tetrahydrofuran was gradually added while stirring, A cloudy milky solution was obtained. Stirring was continued for about 5 minutes, and then an aqueous solution in which 167.6 g of sodium carbonate and 317 g of sodium chloride were dissolved in 3400 ml of water was rapidly added while stirring for 5 minutes. The reaction system increased in viscosity after a few seconds and then decreased again to obtain a white suspension. This was left standing, the separated transparent aqueous solution layer was removed, and 185.3 g of a white polymer of polymetaphenylene isophthalamide was obtained by filtration.

(3) Manufacture of separator The above-mentioned polymetaphenylene isophthalamide and an inorganic filler composed of magnesium hydroxide having an average particle size of 0.8 μm (manufactured by Kyowa Chemical Co., Ltd .; Kisuma 5) are adjusted so that the weight ratio is 90:10. These were mixed in a mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) in a weight ratio of 80:20 so that the polymetaphenylene isophthalamide concentration was 2% by weight. A slurry was obtained.
The slurry was applied on a polyethylene microporous membrane with a doctor knife having a clearance of 0.3 mm. And what was coated was immersed in the coagulating liquid which is 20 degreeC by water: DMAc: TPG = 50: 40: 10 by weight ratio. Next, washing and drying were performed. As a result, a separator for a non-aqueous secondary battery of the present invention in which a heat-resistant porous layer made of polymetaphenylene isophthalamide and magnesium hydroxide was formed on one surface of a polyethylene microporous membrane was obtained. The characteristics of the obtained separator are shown in Tables 1 and 2. The characteristics of the following Examples 2 to 4 and Comparative Examples 1 and 2 are also shown in Table 1 and Table 2 together.

[Example 2]
(1) Production of polyparaphenylene terephthalamide solution In a 5 L separable flask, 68.7 g of calcium chloride was added to 1000 g of NMP in a nitrogen stream, dissolved at 100 ° C., cooled to room temperature, and then paraphenylenediamine 31. 01 g was added and dissolved. To this, 56.80 g of terephthalic acid dichloride was added little by little and stirred so that the liquid temperature did not rise above 20 ° C. This solution was degassed to obtain a 6% by weight NMP solution of polyparaphenylene terephthalamide (PPTA).

(2) Manufacture of separator NMP was further added to said PPTA solution, and it adjusted to the 1.5 weight% PPTA solution. To 100 parts by weight of this solution, 1.05 parts by weight of α-alumina (manufactured by Daimei Chemical Co., Ltd., TM-5D) having an average particle diameter of 0.2 μm was added and dispersed by stirring. It apply | coated on the single side | surface of the polyethylene microporous film obtained in Example 1 with the doctor knife whose clearance is 0.3 mm. This was allowed to stand for 10 minutes in an atmosphere of 30 ° C. and 60% humidity, and then washed with running water at 25 ° C. for 6 hours. It was dried at 40 ° C. for 12 hours under vacuum. As a result, a separator for a non-aqueous secondary battery according to the present invention in which a heat-resistant porous layer made of polyparaphenylene isophthalamide and α-alumina was formed on one surface of a polyethylene microporous membrane was obtained.

[Example 3]
The polymetaphenylene isophthalamide obtained in Example 1 and an inorganic filler composed of barium sulfate having an average particle size of 0.3 μm (manufactured by Sakai Chemical Co., Ltd., B-30) were adjusted so as to have a weight ratio of 90:10. These were mixed in a mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) in a weight ratio of 60:40 so that the polymetaphenylene isophthalamide concentration was 2% by weight. A slurry was obtained.
It apply | coated on the single side | surface of the polyethylene microporous film obtained in Example 1 with the doctor knife whose clearance is 0.3 mm. And what was coated was immersed in the coagulating liquid which is 40 degreeC by water: DMAc: TPG = 50: 30: 20 by weight ratio. Next, washing and drying were performed. As a result, a separator for a non-aqueous secondary battery according to the present invention in which a heat-resistant porous layer made of polymetaphenylene isophthalamide and barium sulfate was formed on one surface of a polyethylene microporous membrane was obtained.

[Example 4]
The non-aqueous system of the present invention was the same as Example 1 except that the weight ratio of polymetaphenylene isophthalamide and calcium carbonate having an average particle size of 1 μm (Escalon # 2300, Hayashi Kasei Co., Ltd.) was 95: 5. A separator for a secondary battery was obtained.

[Comparative Example 1]
Non-aqueous system in the same manner as in Example 2 except that α-alumina was 0.26 parts by weight and that the sample was allowed to stand for 10 minutes in an atmosphere of 25 ° C. and 70% humidity after the PPTA solution was applied. A separator for a secondary battery was obtained.

[Comparative Example 2]
Non-aqueous system in the same manner as in Example 2 except that the α-alumina was 1.28 parts by weight and that it was allowed to stand at 35 ° C. and a humidity of 70% for 10 minutes after the PPTA solution was applied. A separator for a secondary battery was obtained.

Claims (3)

A separator for a non-aqueous secondary battery comprising a polyolefin porous substrate, a heat-resistant porous layer formed by including a heat-resistant resin and an inorganic filler, and laminated on one or both surfaces of the porous substrate. And
A nonaqueous secondary battery separator, wherein the heat-resistant porous layer has a porosity of 5% or more and less than 30%.   The separator for a non-aqueous secondary battery according to claim 1, wherein the heat resistant resin is a meta-type wholly aromatic polyamide or para-type wholly aromatic polyamide.   The non-aqueous system according to claim 1 or 2, wherein the inorganic filler is at least one selected from metal oxide, metal carbonate, metal sulfate, metal phosphate, and metal hydroxide. Secondary battery separator.