JP2011216257A - Separator for nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a nonaqueous secondary battery which can enhance durability of a battery, in addition to a shutdown function and heat resistance.SOLUTION: The separator for a nonaqueous secondary battery, provided with a polyolefin porous base material, and a heat-resistant porous layer formed of heat-resistant resin and an inorganic filler and laminated on either or both faces of the porous base material, contains α-alumina of a purity of 99.9% or more as the inorganic filler.

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 represented by lithium ion secondary batteries are widely used as main power sources for portable electronic devices such as mobile phones and laptop computers. Lithium-ion secondary batteries have high energy density, high capacity, and high output, and this demand will continue to be strong. Ensuring safety is an important technical element from the viewpoint of meeting such demands.

  Conventionally, a polyolefin microporous film made of polyethylene or polypropylene has been used for a separator of a lithium ion secondary battery. Such a separator has a shutdown function (function of blocking the current by blocking the pores of the microporous membrane when the temperature of the battery rises), and plays a role in ensuring the safety of the lithium ion secondary battery. However, in the polyolefin microporous membrane, when the battery temperature further rises after the shutdown function is exhibited, the separator is melted (so-called meltdown). As a result, a short circuit occurs between the positive and negative electrodes inside the battery, and the battery is exposed to dangers such as smoke, ignition, and explosion. For this reason, in addition to the shutdown function, the separator is required to have sufficient heat resistance so that meltdown does not occur near the temperature at which the shutdown function operates.

  In this respect, a separator having a structure in which a porous layer made of a heat-resistant resin such as an aramid resin and ceramic powder such as α-alumina is laminated on a polyolefin microporous film has been known (for example, patents). Reference 1). Lithium ion secondary batteries using such separators have improved safety in high-temperature environments due to the contribution of improving the heat resistance of the separators, but on the other hand, the durability of the batteries such as cycle characteristics and storage characteristics is improved. May decrease.

  As one of the causes of the decrease in the durability, hydrogen fluoride (hereinafter referred to as HF as appropriate) present in a trace amount in the battery reacts with the ceramic powder, and the surface of the ceramic powder is fluorinated, and water is absorbed at that time. For example, the generated SEI (Solid Electrolyte Interface) film formed on the surface of the electrolyte or electrode may be decomposed by the water. When the electrolytic solution and the SEI film are decomposed in this manner, the internal resistance of the battery is increased, or lithium necessary for charging and discharging is deactivated, so that the durability of the battery is lowered. Further, when such a decomposition reaction occurs, gas is generated, which also reduces the durability of the battery. In addition, since a heat-resistant resin such as an aramid resin is generally a substance that easily adsorbs moisture, it can be said that the problem of decomposition reaction such as an electrolytic solution caused by moisture is more likely to occur.

  On the other hand, Patent Document 2 proposes a technique for improving gas generation in a battery with an inorganic filler. This technique mixes an inorganic powder gas absorbent in a separator and traps the generated gas with the gas absorbent. The structure is a separator made of a polyolefin microporous membrane and a gas absorbent.

  However, such a separator does not have sufficient heat resistance, and an inorganic filler that is a gas absorbent is mixed in a polyolefin microporous film that has a shutdown function, so that the shutdown function is significantly lowered. Therefore, although gas generation is apparently suppressed, there is a risk that safety may be reduced as compared with the case where a conventional polyolefin microporous membrane is applied.

Japanese Patent No. 3175730 JP 2008-146963 A

  An object of this invention is to provide the separator for non-aqueous secondary batteries which can improve the durability of a battery in addition to a shutdown function and heat 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 non-aqueous secondary battery separator comprising α-alumina having a purity of 99.9% or more as the inorganic filler.
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.

  ADVANTAGE OF THE INVENTION According to this invention, in addition to a shutdown function and heat resistance, the separator for non-aqueous secondary batteries which can improve battery durability can be provided. By using such a separator, a non-aqueous secondary battery excellent in safety and durability 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 includes α-alumina having a purity of 99.9% or more as the inorganic filler.

  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. In particular, since α-alumina with a purity of 99.9% or more is included as an inorganic filler, excellent heat resistance is obtained, and generation of water due to side reaction between hydrogen fluoride and the alumina surface is prevented, and gas generation is suppressed. In addition, a non-aqueous secondary battery having excellent durability 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.

[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. The porosity of the heat resistant porous layer is preferably in the range of 30 to 80%. Since the basis weight of the heat-resistant porous layer varies depending on the material used, it cannot be generally stated, but it is preferably approximately ² to 10 g / m ² .

[Inorganic filler]
In the present invention, as described above, the inorganic filler in the heat-resistant porous layer contains α-alumina having a purity of 99.9% or more. The inorganic filler only needs to contain 90% by weight or more of α-alumina having a purity of 99.9% or more, and the balance is an inorganic filler other than α-alumina having a purity of less than 99.9%, for example, Metal oxides such as titania, silica and zirconia, metal carbonates such as calcium carbonate, metal sulfates such as barium sulfate, metal phosphates such as calcium phosphate, metal hydroxides such as aluminum hydroxide and magnesium hydroxide, etc. Other inorganic fillers may be included.

  In the present invention, α-alumina having a purity of 99.9% or more is alumina containing 99.9% of an alumina component by weight and containing α crystals of alumina. Such alumina is not particularly limited in shape, and may be spherical, flat, indeterminate, or the like.

In general, α-alumina can be obtained by a method (so-called Bayer method) in which bauxite is used as a raw material, caustic soda is added to obtain sodium aluminate, this is decomposed to precipitate aluminum hydroxide, and further calcined at a high temperature. This Bayer alumina usually contains about 0.35 to 0.7% of Na component in terms of Na ₂ O. Since this Na component is often contained in the crystal lattice or in the crystal grain boundary, it is difficult to remove it by washing with water or pickling. In order to remove the Na component, a method of washing and baking aluminum hydroxide with acids, salts and phenols, adding and baking salts and silica to volatilize the Na component free from alumina, or soluble Na It can be obtained by a method of washing with a compound (see, for example, JP-A-8-12322). Such α-alumina is generally available as high purity alumina.

  In the present invention, the content of α-alumina in the heat resistant porous layer is preferably 50 to 95% by weight from the viewpoints of heat resistance, ion permeability and handling properties. The average particle diameter of α-alumina 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.

[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, and an inorganic filler is dispersed therein 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. 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 porous substrate. When forming a heat resistant porous layer on both surfaces of a polyolefin porous substrate, it is preferable from a viewpoint of shortening of a process to apply simultaneously on both surfaces of a substrate. 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

[Identification of α-alumina]
Identification of α-alumina was performed by X-ray diffraction measurement (manufactured by Rigaku Corporation: RAD-C).

[Purity measurement of α-alumina]
0.3 g of α-alumina was heat-treated in sulfuric acid at 230 ° C. for 60 hours, and the resulting solution was analyzed by inductively coupled plasma emission spectrometry (Thermo Fisher Scientific, Thermo iCAP 6500). Quantification was performed. Impurities were converted to weight as metal oxides, and the weight ratio excluding them was defined as the purity of α-alumina.

[Average particle diameter of α-alumina]
Measurement was performed using a laser diffraction particle size distribution measuring apparatus. Water was used as a dispersion medium, and a small amount of nonionic surfactant “Triton X-100” was used as a dispersant. The central particle size (D50) in the volume particle size distribution was taken as the average particle size.

[Gas generation]
A separator sample was cut out of 110 cm ^{2 and} vacuum-dried at 85 ° C. for 16 hours. This was put in an aluminum pack in an environment with a dew point of −60 ° C. or less, an electrolyte was further injected, the aluminum pack was sealed with a vacuum sealer, and a measurement cell was produced. Here, the electrolytic solution was 1M LiPF ₆ ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3/7 (weight ratio) (manufactured by Kishida Chemical Co., Ltd.). The measurement cell was stored at 85 ° C. for 3 days, and the appearance of the measurement cell after storage was visually observed. The cells in which no blistering was observed were assumed to have no gas generation (◯), and it was determined that gas was generated in the cells in which blistering was observed (×).

[Cycle characteristics]
Using the separators produced in the examples and comparative examples, non-aqueous secondary batteries were produced as follows.
89.5 parts by weight of lithium cobalt oxide (LiCoO ₂ ; manufactured by Nippon Chemical Industry Co., Ltd.), 4.5 parts by weight of acetylene black (manufactured by Denki Kagaku Co., Ltd .; trade name Denka Black), 6 polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd.) 6 These were kneaded using an N-methyl-2pyrrolidone solvent so as to be parts by weight to prepare a slurry. The obtained slurry was applied onto an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a thickness of 100 μm.
87 parts by weight of mesophase carbon microbeads (MCMB: Osaka Gas Chemical Co., Ltd.) powder, 3 parts by weight of acetylene black (manufactured by Denki Kagaku Kogyo; trade name Denka Black), 10 parts by weight of polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd.) Thus, these were knead | mixed using the N-methyl-2 pyrrolidone solvent, and the slurry was produced. The obtained slurry was applied onto a copper foil having a thickness of 18 μm, dried and pressed to obtain a negative electrode having a thickness of 90 μm.
The positive electrode and the negative electrode were opposed to each other through the separators prepared in the following examples and comparative examples. This was impregnated with an electrolytic solution and sealed in an exterior made of an aluminum laminate film to produce a non-aqueous secondary battery. Here, 1M LiPF ₆ ethylene carbonate / ethyl methyl carbonate (3/7 weight ratio) (manufactured by Kishida Chemical Co., Ltd.) was used as the electrolytic solution.
Each battery produced in this manner was charged and discharged by constant current / constant voltage charge of 1C 4.2V for 2 hours, constant current discharge of 1C and 2.75V cut-off, and the capacity at the first cycle was used as a reference. The capacity retention rate at the 100th cycle was determined, and this was used as an index of cycle characteristics as battery durability. The temperature at the time of measurement was 30 ° C.

[Example 1]
As polyethylene powder, GUR2126 (weight average molecular weight 41.50 million, melting point 141 ° C.) and GRX143 (weight average molecular weight 560,000, melting point 135 ° C.) manufactured by Ticona were used. A polyethylene solution was prepared by dissolving GUR2126 and GURX143 in a mixed solvent of liquid paraffin and decalin such that the polyethylene concentration was 30% by weight so that the ratio was 1: 9 (weight ratio). The composition of the polyethylene solution is polyethylene: liquid paraffin: decalin = 30: 45: 25 (weight ratio). This polyethylene solution was extruded from a die at 148 ° C., cooled in a water bath, and dried at 60 ° C. for 8 minutes and at 95 ° C. for 15 minutes to produce a gel tape (base tape). The base tape was stretched by biaxial stretching, which was sequentially performed with 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 obtained the polyethylene microporous film by annealing at 120 degreeC.

Next, Conex (registered trademark; manufactured by Teijin Techno Products), which is a meta-type wholly aromatic polyamide, and α-alumina (manufactured by High Purity Chemical Laboratory, ALO12PB) having an average particle diameter of 0.3 μm in a weight ratio of 25: A mixture of dimethylacetamide (DMAc) and tripropylene glycol (TPG) in a weight ratio of 50:50 so that the meta-type wholly aromatic polyamide concentration is 5.5% by weight. A slurry for coating was obtained by mixing with a solvent.
A pair of Meyer bars (count # 6) was confronted with a clearance of 20 μm. An appropriate amount of the above slurry for coating was placed on a Mayer bar, and the coating slurry was applied to both sides of the polyethylene microporous membrane by passing the polyethylene microporous membrane between a pair of Meyer bars. This was immersed in a coagulating liquid having a weight ratio of water: DMAc: TPG = 50: 25: 25 and 40 ° C. Next, washing with water and drying were performed to form heat-resistant porous layers on the front and back of the polyethylene microporous membrane, thereby obtaining a separator for a non-aqueous secondary battery of the present invention. Table 1 shows the properties (film thickness, basis weight, porosity, various physical properties of α-alumina, and gas expansion) of the obtained separator. The results of Example 2 and Comparative Example 1 below are also shown in Table 1.

[Example 2]
Under a nitrogen stream, 68.7 g of calcium chloride was added to 1000 g of NMP in a 5 L separable flask and dissolved at 100 ° C. After cooling to room temperature, 31.01 g of paraphenylenediamine 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 an NMP solution of 6% by weight of polyparaphenylene terephthalamide (hereinafter referred to as PPTA as appropriate).
NMP was added thereto to prepare a 1.5 wt% PPTA solution. To 100 parts by weight of this solution, 1.05 parts by weight of α-alumina 0.3 μm (manufactured by High-Purity Chemical Laboratory, ALO12PB) was added and dispersed by stirring.
This slurry was applied on the polyethylene microporous film obtained in Example 1 with a 0.3 mm doctor knife. 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. The separator was obtained by drying at 40 ° C. for 12 hours under vacuum.

[Comparative Example 1]
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 2 except that α-alumina (manufactured by Sumitomo Chemical Co., Ltd .; AM27) having a purity of 99.7% and an average particle diameter of 1 μm was used.

Claims (2)

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 non-aqueous secondary battery separator comprising α-alumina having a purity of 99.9% or more as the inorganic filler.   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.