JP2009231281A - Nonaqueous electrolyte battery separator and nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator, obtained by forming a heat resistant porous layer made of heat resistant polymers such as aromatic aramid by wet coating method on one side or both sides of a fine porous film made of thermoplastic resins represented by polyolefin, excellent in processablity of the heat resistant polymers, formation of the porous layer, as well as its heat resistance and shutdown properties. <P>SOLUTION: A nonaqueous electrolyte battery separator, includes: a fine porous film, mainly made of thermoplastic resins, having shutdown properties; and a heat resistant porous layer, mainly made of heat resistant polymers, laid on one side or both sides of the fine porous film, wherein the heat resistant porous layer includes an inorganic filler having a specific range of uniformity and particle side distribution. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nonaqueous electrolyte battery separator with improved quality and safety, and a nonaqueous electrolyte secondary battery using the same.

  Nonaqueous electrolyte batteries, particularly nonaqueous electrolyte secondary batteries represented by lithium ion secondary batteries, have high energy density and are widely used as the main power source for portable electronic devices such as mobile phones and laptop computers. . This lithium ion secondary battery is required to have a higher energy density, but ensuring safety is a technical issue. The role of the separator is important in ensuring the safety of the lithium ion secondary battery, and from the viewpoint of having a shutdown function, polyolefins, particularly polyethylene microporous membranes are currently used. Here, the shutdown function refers to a function of blocking pores in the microporous membrane when the temperature of the battery rises, and blocking the current, and has a function of preventing thermal runaway of the battery.

  On the other hand, lithium ion secondary batteries have been increased in energy density year by year, and heat resistance has been required in addition to a shutdown function to ensure safety. However, the shutdown function is contrary to heat resistance because the operating principle is to close the hole by melting polyethylene. For this reason, after the shutdown function is activated, the battery may continue to be exposed to a temperature higher than the temperature at which the shutdown function is activated, whereby the separator may be melted (so-called meltdown). As a result of this meltdown, a short circuit occurs inside the battery, and as a result, a large amount of heat is generated, 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 that does not cause meltdown in the vicinity of the temperature at which the shutdown function operates.

  In this regard, conventionally, in order to achieve both heat resistance and a shutdown function, one surface or both surfaces (front and back surfaces) of the polyolefin microporous film are coated with a heat resistant porous layer, or a nonwoven fabric made of heat resistant fibers is laminated. The technology is proposed. For example, a nonaqueous electrolyte battery separator is known in which a heat-resistant porous layer made of a heat-resistant polymer such as aromatic aramid is laminated on one side or both sides of a polyethylene microporous membrane by a wet coating method (Patent Documents 1 to 3). 4).

  Such a non-aqueous electrolyte battery separator operates with a shutdown function near the melting point of polyethylene (about 140 ° C), and the heat-resistant porous layer exhibits sufficient heat resistance, so that meltdown occurs even at 200 ° C or higher. Therefore, it exhibits excellent heat resistance and shutdown function. In particular, as in Patent Document 4, a type of separator in which an inorganic filler such as ceramic powder is mixed in the heat-resistant porous layer can be expected to further improve the heat resistance.

  However, in the type of separator as in Patent Document 4, depending on how the inorganic filler is applied, problems arise in the processability of the heat resistant polymer and the coating characteristics of the coating liquid containing the heat resistant resin and the inorganic filler. May end up. In such a case, the porous structure of the heat-resistant porous layer or the interface structure between the heat-resistant porous layer and the polyolefin microporous film is greatly affected, and the battery characteristics are also greatly affected. I will give it. However, until now, focusing on the heat resistance and flame retardancy of separators for non-aqueous electrolyte batteries, and further on the workability of heat-resistant polymers and the coating properties of coating solutions, the quality of separators has been sufficiently improved. It can be said that the proposed proposal has never been made.

JP 2002-355938 A JP 2005-209570 A JP 2005-285385 A Japanese Patent No. 3175730

  Therefore, in the present invention, a heat-resistant porous layer made of a heat-resistant polymer such as an aromatic aramid is formed by wet coating on one or both sides of a microporous film made of a thermoplastic resin typified by polyolefin. In obtaining a non-aqueous electrolyte battery separator, an object is to provide a separator that is excellent in heat-resistant polymer workability and porous layer formability, and excellent in heat resistance and shutdown function.

In order to solve the above problems, the present invention employs the following configuration.
1. A non-aqueous solution comprising a microporous film mainly formed of a thermoplastic resin and having a shutdown function, and a heat-resistant porous layer formed mainly of a heat-resistant polymer and laminated on one or both surfaces of the microporous film. It is an electrolyte battery separator, The inorganic filler which satisfies the following (a) and (b) is contained in the said heat resistant porous layer, The nonaqueous electrolyte battery separator characterized by the above-mentioned.
(A) 0.01 ≦ d50 ≦ 20 (μm)
(B) 0 <α ≦ 2
(However, d50 represents the average particle diameter (μm) of 50% by weight cumulatively calculated from the small particle side in the particle size distribution in the laser diffraction method. Α indicates the uniformity of the inorganic filler, and α = (d90 -D10) / d50, d90 represents the average particle diameter (μm) of 90% by weight of cumulative particle size calculated from the small particle side in the particle size distribution in the laser diffraction method, and d10 represents the particle size in the laser diffraction method. (In the distribution, an average particle diameter (μm) of 10% by weight of the cumulative weight from the small particle side is represented.)
2. 2. The nonaqueous electrolyte battery separator according to 1 above, wherein the inorganic filler satisfies the following (c) and (d).
(C) 0.1 ≦ d50 ≦ 2 (μm)
(D) 0 <α ≦ 1
(However, the definition of d50 and α is the same as 1.)
3. 3. The non-aqueous electrolyte battery separator according to claim 1 or 2, wherein the heat-resistant porous layer contains an inorganic filler in a weight fraction of 50% by weight to 95% by weight.
4). 4. The separator for a non-aqueous electrolyte battery according to any one of 1 to 3, wherein the inorganic filler is made of a metal hydroxide.
5. 5. The separator for a non-aqueous electrolyte battery according to claim 4, wherein the metal hydroxide is aluminum hydroxide.
6). 4. The separator for a non-aqueous electrolyte battery according to any one of 1 to 3, wherein the inorganic filler is a porous filler.
7). 7. The separator for a non-aqueous electrolyte battery according to 6 above, wherein the porous filler is activated alumina.
8). 1 to 7 above, wherein the heat-resistant polymer is one or more selected from the group consisting of aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide. The nonaqueous electrolyte battery separator according to any one of the preceding claims.
9. 9. The nonaqueous electrolyte battery separator according to 8 above, wherein the heat resistant polymer is polymetaphenylene isophthalamide.
10. 10. The nonaqueous electrolyte battery separator according to any one of 1 to 9 above, wherein the thermoplastic resin is a thermoplastic resin mainly composed of polyolefin.
11. 11. The nonaqueous electrolyte battery separator according to any one of the above 1 to 10, wherein the nonaqueous electrolyte battery separator is a lithium ion secondary battery separator.
12 A non-aqueous electrolyte secondary battery that obtains an electromotive force by doping and dedoping lithium, wherein the non-aqueous electrolyte battery separator according to any one of 1 to 11 is used. battery.

  ADVANTAGE OF THE INVENTION According to this invention, while being excellent in the workability of a heat resistant polymer and the formation property of a porous layer, the separator excellent in heat resistance and a shutdown function can be provided. Therefore, a nonaqueous electrolyte secondary battery excellent in safety and durability can be provided by using such a nonaqueous electrolyte battery separator.

It is an image figure showing a GPC curve typically.

[Nonaqueous electrolyte battery separator]
The present invention comprises a microporous film mainly formed of a thermoplastic resin and having a shutdown function, and a heat-resistant porous layer formed mainly of a heat-resistant polymer and laminated on one or both surfaces of the microporous film. A non-aqueous electrolyte battery separator, wherein the heat-resistant porous layer includes an inorganic filler that satisfies the following (a) and (b): .
(A) 0.01 ≦ d50 ≦ 20 (μm)
(B) 0 <α ≦ 2
Preferably, the following expressions (c) and (d) are satisfied.
(C) 0.1 ≦ d50 ≦ 2 (μm)
(D) 0 <α ≦ 1
However, in the above formula, d50 represents an average particle diameter (μm) of a cumulative weight of 50% by weight calculated from the small particle side in the particle size distribution in the laser diffraction method. α indicates the uniformity of the inorganic filler and is represented by α = (d90−d10) / d50. d90 represents an average particle diameter (μm) of 90% by weight of the cumulative weight calculated from the small particle side in the particle size distribution in the laser diffraction method, and d10 represents the weight calculated from the small particle side in the particle size distribution in the laser diffraction method. The average particle diameter (μm) of 10% by weight is represented.

(Inorganic filler)
In the present invention, by using the inorganic filler having the particle size distribution described above, the dispersibility of the inorganic filler in the coating liquid is improved, and the processability of the heat-resistant polymer and the formability of the porous layer can be improved. it can. In addition, in the inorganic filler having the particle size distribution described above, since the inorganic fillers having different particle sizes are contained in the heat-resistant porous layer, the packing density of the inorganic filler is increased, and the function of the inorganic filler (for example, heat resistance characteristics). Etc.) to the maximum extent possible. In addition, particles having a small diameter contribute to pore formation, so that a favorable porous structure can be formed. On the other hand, particles having a large diameter appear on the surface of the heat-resistant porous layer, so that the slipperiness of the separator is improved. It is possible to obtain the effects as described above.

  In addition, when the value of d50 is less than 0.01 μm, the dispersibility of the slurry is poor, so that the coating property is poor, and dense and fine through-holes cannot be formed uniformly. If the value of d50 exceeds 20 μm, it becomes close to the thickness of the heat-resistant porous layer, the film-forming property is not good, the streaks are easily formed, and it is difficult to apply thinly. On the other hand, if α is 0, the particle diameter becomes uniform, and the effect of the present invention cannot be obtained. When α exceeds 2, coarse or extremely small particles may be contained, and the fixability of the heat-resistant porous layer to the microporous film may be deteriorated.

  In the nonaqueous electrolyte battery separator of the present invention, examples of the inorganic filler (inorganic fine particles) contained in the heat-resistant porous layer include metal hydroxide, metal oxide, metal nitride, carbonate, sulfate, clay mineral, Or what combined these 2 or more types etc. can be used suitably. Specific examples of the metal hydroxide include aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, nickel hydroxide, boron hydroxide, boehmite and the like. Specific examples of the metal oxide include aluminum oxide, titanium oxide, zinc oxide, silicon oxide, yttrium oxide, cerium oxide, tin oxide, and iron oxide. Specific examples of the metal nitride include aluminum nitride, boron nitride, and titanium nitride. Specific examples of the carbonate include calcium carbonate, magnesium carbonate, barium carbonate and the like. Specific examples of the sulfate include barium sulfate and calcium sulfate. Specific examples of the clay mineral include calcium silicate, talc, mica, montmorillonite, hydrotalcite, bentonite, zeolite, sepiolite, kaolin, hectorite, saponite, stevensite, beidellite and the like.

  The present invention is preferably a metal hydroxide among the inorganic fillers described above. This is because such metal hydroxide functions effectively in making the non-aqueous electrolyte battery separator flame-retardant. That is, when a metal hydroxide is heated, a dehydration reaction occurs and becomes an oxide, and water is released. Furthermore, this dehydration reaction is a reaction with a large endotherm. By releasing water during the dehydration reaction and the endothermic reaction, a flame retardant effect is obtained. In addition, an electrolyte that is flammable to release water is diluted with water and is effective not only for the separator but also for the electrolyte, and is effective in making the battery itself flame-retardant. Furthermore, the metal hydroxide is preferable from the viewpoint of handleability. In addition, since the metal hydroxide is softer than the metal oxide such as alumina, the problem with the separator described in the conventional patent document 4, that is, the solid metal oxide filler contained in the separator is used at the time of manufacture. There is no problem with handling such that parts used in each process are worn.

  Such a metal hydroxide is preferably one that causes a dehydration reaction by heating at 200 ° C. to 400 ° C., and more preferably in the range of 250 ° C. to 350 ° C. In the nonaqueous electrolyte battery, heat generation due to the decomposition of the positive electrode is considered to be the most dangerous, and this decomposition occurs in the vicinity of 300 ° C. Therefore, when the generation temperature of the metal hydroxide dehydration reaction is in the range of 200 ° C. to 400 ° C., it is particularly effective in preventing the heat generation of the nonaqueous electrolyte battery. At 200 ° C. or higher, the negative electrode almost loses its activity, so that it does not react with the generated water to cause an exothermic reaction and is safe. Further, when the exothermic reaction temperature of the metal hydroxide exceeds 400 ° C., it is not preferable because the heat generation of the nonaqueous electrolyte battery may not be suitably prevented. In this respect, aluminum hydroxide undergoes a dehydration reaction in the temperature range of 250 to 300 ° C., and magnesium oxide undergoes a dehydration reaction in the temperature range of 350 to 400 ° C. Therefore, in the present invention, at least one of aluminum hydroxide and magnesium hydroxide is used. It is preferable to use one of them.

  In particular, aluminum hydroxide (dehydration reaction temperature: 250 to 300 ° C.) is most preferable as an inorganic filler in view of effectively utilizing the endothermic reaction accompanying dehydration. Furthermore, when aluminum hydroxide is applied, it also exhibits better characteristics than other metal hydroxides such as magnesium hydroxide in terms of shutdown characteristics. Specifically, in the measurement of shutdown characteristics, a resistance increase of about 10 times is observed at a temperature slightly exceeding 100 ° C., which has the effect of lowering the shutdown temperature. This behavior functions effectively in ensuring the safety of the battery. To do. Although an essential shutdown is observed in the vicinity of the melting point of polyethylene, there is also an effect of increasing the degree of resistance increase at this time. This behavior is effective when a thinner polyethylene microporous membrane is applied to the substrate.

  In the separator configuration of the present invention, the heat-resistant porous layer has a function of imparting heat resistance to the separator. By adding an inorganic filler to this layer, the heat-resistant porous layer is heat resistant from the viewpoint of short circuit prevention at high temperatures and dimensional stability. The heat resistance of the porous layer can be further improved. In general, a separator coated with a heat-resistant porous layer tends to be strongly charged with static electricity, and handling properties are often not preferable from such a viewpoint. Here, when a metal hydroxide such as aluminum hydroxide or magnesium hydroxide is added to the heat-resistant porous layer, the charged charge decays quickly, so that the charge can be kept at a low level. Improved. For these reasons, it is preferable to add an inorganic filler made of a metal hydroxide into the heat resistant porous layer.

  In non-aqueous electrolyte batteries, hydrogen fluoride (hereinafter referred to as HF) is a factor that impairs the positive electrode active material and lowers durability, but aluminum hydroxide and magnesium hydroxide have the function of adsorbing and co-precipitating HF. Therefore, the HF concentration in the electrolytic solution can be maintained at a low level, and the durability of the nonaqueous secondary battery can be improved by using a separator including such a metal hydroxide filler. From this point of view, aluminum hydroxide and magnesium hydroxide are preferable as the inorganic filler.

  When the inorganic filler is a metal hydroxide, as a subcomponent or impurity other than the metal hydroxide, at least one of a metal oxide, a hydrate of metal oxide, and adhering moisture is used as an inorganic component. It is preferable to contain 10% by weight or less of the whole filler. With such a content of subcomponents or the like, the obtained separator or battery characteristics are not particularly adversely affected. Here, the hydrate of a metal oxide means a combined product of a metal oxide and a water molecule, and the adhering moisture means moisture adhering to an inorganic filler. In addition, it is substantially difficult to obtain a metal hydroxide having a content of the subcomponent or impurity of less than 0.001% by weight.

  On the other hand, it is also preferable to use a porous filler as the inorganic filler in the present invention. This is because, when such a porous filler is used, it is possible to solve the problem of battery durability reduction due to factors such as gas generation. That is, in a system to which an inorganic filler is applied, the decomposition of the SEI film formed on the electrolytic solution or the electrode surface is accelerated by the reaction of moisture and HF present in a minute amount in the battery with the surface of the inorganic filler. As a result, gas may be generated in the battery to reduce the durability of the battery. In particular, since the heat-resistant resin constituting the heat-resistant porous layer is generally a substance that easily adsorbs moisture, the heat-resistant porous layer is likely to contain a relatively large amount of moisture, and the above-mentioned problem of lowering durability Can be said to occur easily. However, if a porous filler is used as the inorganic filler, the generated gas can be trapped by the porous filler. For this reason, it becomes possible to significantly improve the durability of the battery.

In particular, the porous filler is preferably a specific surface area of 40~3000m ² / g, more preferably if 40~1000m ² / g, more preferably if 40~500m ² / g, 150~500m ² / g is particularly preferable. If such a porous filler is used, the activity of moisture and HF present in a minute amount in the battery can be significantly reduced, and gas generation due to decomposition of the electrolyte can be suppressed. Therefore, the durability of the battery can be further improved. In addition, it is not preferable that the specific surface area is less than 40 m ² / g because the activity of moisture and HF cannot be sufficiently reduced. On the other hand, if it is greater than 3000 m ² / g, it is difficult to form the porous layer, and the strength of the porous layer may be significantly reduced. Here, the specific surface area is obtained by analyzing the adsorption isotherm measured by the nitrogen gas adsorption method using the BET equation.

  The porous filler is preferably composed of mesopores of 50 nm or less or micropores of 2 nm or less, and particularly preferably has a structure in which micropores of 2 nm or less are developed. In this case, the above-described effect of reducing the activity of moisture and HF is easily exhibited.

As such a porous filler, for example, a porous filler obtained by heat-treating a metal hydroxide such as zeolite, activated carbon, activated alumina, porous silica, magnesium hydroxide or aluminum hydroxide can be suitably used. Of these, activated alumina is preferred. Here, the activated alumina refers to a porous filler whose formula is represented by Al ₂ O ₃ .xH ₂ O (x can take a value of 0 or more and 3 or less). The surface of the activated alumina is amorphous Al ₂ O ₃ , γ-Al ₂ O ₃ , χ-Al ₂ O ₃ , gibbsite-like Al (OH) ₃ , boehmite-like Al ₂ O ₃ .H ₂ O, etc. It is preferable to have a structure, and it is particularly preferable that the porous structure is formed of these surface structures from the viewpoint of reducing the activity of moisture and HF. In addition, since the porous filler is generally softer than a dense metal oxide filler such as α-alumina, it is related to the handling property that the parts used in each process at the time of production are worn by the porous filler. There is no problem.
In addition, as an inorganic filler, you may mix and use the porous filler mentioned above and a non-porous filler in a suitable ratio.

  In the present invention, the content of the inorganic filler in the heat-resistant porous layer is preferably 50 to 95% by weight, and more preferably 70 to 85% by weight. When the content of the inorganic filler is in such a range, the inorganic filler is sufficiently compatible with the heat-resistant polymer and the dispersibility is improved. In addition, when the heat-resistant porous layer is formed by solidification in water due to the action of the inorganic filler, it is difficult for the low-molecular weight polymer of the heat-resistant polymer to flow out into the coagulation liquid, so that suitable pore formation is possible. For this reason, the air permeability is improved and the film resistance is further reduced.

(Heat resistant polymer)
The heat-resistant polymer 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. Specifically, one or more selected from the group consisting of aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide are preferable. In particular, wholly aromatic polyamides are preferable from the viewpoint of durability, and meta-type wholly aromatic polyamides are preferable from the viewpoint of easily forming a porous layer and excellent redox resistance. Of these, polymetaphenylene isophthalamide is preferred.

The heat-resistant polymer has a molecular weight distribution Mw / Mn of 5 ≦ Mw / Mn ≦ 100 and a weight average molecular weight Mw of 8.0 × 10 ³ or more and 1.0 × 10 ⁶ or less. preferable. This is because when such a heat-resistant polymer is used, a better heat-resistant porous layer can be formed when the heat-resistant porous layer is formed on the microporous film by a wet coating method. That is, as described above, the heat-resistant polymer having a wide molecular weight distribution contains many low molecular weight substances, so that the processability of the coating liquid in which the polymer is dissolved is improved. For this reason, it becomes easy to form a heat resistant porous layer with few defects and a uniform film thickness. In addition, since the coating can be performed well without applying a strong coating pressure, the air permeability at the interface between the heat-resistant porous layer and the microporous membrane can be obtained without causing clogging of the surface pores of the microporous membrane. Can be prevented from falling. Further, when the coating liquid is applied onto the microporous film and immersed in the coagulation liquid, the polymer in the coating film becomes easy to move, so that favorable pore formation is possible. Furthermore, since the familiarity between the low molecular weight substance and the inorganic filler is good, the inorganic filler that contributes to pore formation can be prevented from falling off. As a result, a good heat-resistant porous layer having uniform fine pores is easily formed. Therefore, a separator having excellent ion permeability and good contact with the electrode can be obtained. In addition, when the molecular weight distribution of the heat resistant polymer is less than 5, the processability is poor, and when it exceeds 100, the heat resistance of the heat resistant porous layer is lowered, which is not preferable. Moreover, when the weight average molecular weight of the heat-resistant polymer is less than 8.0 × 10 ³ , the heat-resistant porous layer tends to become brittle, and when it exceeds 1.0 × 10 ⁶ , processing is difficult.

  Also, when a heat-resistant polymer containing a low molecular weight polymer having a molecular weight of 8000 or less is contained in an amount of 1% by weight to 15% by weight, preferably 3% by weight to 10% by weight, the same as above Since a heat-resistant porous layer can be formed, this can be said to be a preferred embodiment. When the content of the low molecular weight polymer is less than 1% by weight, the processability of the heat-resistant polymer or the coating property of the coating liquid is poor, and the content exceeding 15% by weight is not preferable because the heat resistance is poor. A polymer having a molecular weight exceeding 8000 is no longer a low molecular weight polymer and hardly contributes to the effect of improving the processability of the heat-resistant polymer or the coating property of the coating liquid.

Furthermore, when an aromatic polyamide is used as the heat-resistant polymer, the end group concentration ratio of the aromatic polyamide is preferably [COOX] / [NH ₂ ] ≧ 1. Here, X represents hydrogen, an alkali metal, or an alkaline earth metal. For example, a terminal carboxyl group such as COONa has an effect of renewing and removing a malignant film formed on the negative electrode side of the battery. For this reason, when an aromatic polyamide having more terminal carboxyl groups than terminal amine groups is used, a discharge capacity is stable over a long period of time, and a nonaqueous electrolyte secondary battery having excellent cycle characteristics can be obtained.

  Further, the impurities in the heat-resistant polymer preferably contain 1000 ppm or less of one or more selected from the group consisting of alkali metals, alkaline earth metals, transition metals, halogens, and silicon. Specific examples of typical substances include Na or Li as an alkali metal, Mg or Ca as an alkaline earth metal, Fe as a transition metal, and chlorine as a halogen. These substances may affect the battery characteristics of the nonaqueous electrolyte battery. However, if the content in the heat-resistant polymer is in the range of 1000 ppm or less, these effects can be avoided. Note that it is practically difficult to obtain a heat-resistant polymer having an impurity content lower than 0.1 ppm.

(Heat resistant porous layer)
In the present invention, the heat-resistant porous layer has a large number of micropores inside and has a structure in which these micropores are connected, and gas or liquid can pass from one surface to the other. It means the layer that became. In addition, the heat-resistant porous layer only needs to be mainly composed of about 90% by weight or more of the heat-resistant polymer and the inorganic filler, and about 10% by weight or less of the other that does not affect the battery characteristics. Ingredients may be included.

  Such a heat-resistant porous layer may be formed on at least one surface of the microporous membrane, but it is more preferable that the heat-resistant porous layer is formed on both the front and back surfaces from the viewpoint of handling properties, durability, and the effect of suppressing heat shrinkage.

  When the heat-resistant porous layer is formed on both sides of the microporous membrane, the total thickness of the heat-resistant porous layer is preferably 3 μm or more and 12 μm or less, and the heat-resistant porous layer is on one side of the microporous membrane. In the case where only the heat-resistant porous layer is formed, the thickness of the heat-resistant porous layer is preferably 3 μm or more and 12 μm or less. In any case, when the total thickness of the heat-resistant porous layer is less than 3 μm, sufficient heat resistance, particularly a heat shrinkage suppressing effect cannot be obtained. On the other hand, when the total thickness of the heat-resistant porous layer exceeds 12 μm, it becomes difficult to achieve an appropriate separator thickness.

  The porosity of the heat resistant porous layer is preferably in the range of 60 to 90%. If the porosity of the heat-resistant porous layer exceeds 90%, the heat resistance tends to be insufficient, and if it is lower than 60%, the cycle characteristics, storage characteristics, and discharge characteristics tend to be lowered, which is not preferable.

(Microporous membrane)
The microporous membrane in the present invention has a structure in which a large number of micropores are connected and these micropores are connected, and gas or liquid can pass from one surface to the other. Means a membrane. Such a microporous membrane exhibits a shutdown function in which a part of the thermoplastic resin is melted when the temperature of the battery rises, and the pores of the microporous membrane are closed to block the current. The microporous membrane may be mainly composed of a thermoplastic resin in an amount of about 90% by weight or more, and may contain about 10% by weight or less of other components that do not affect the battery characteristics. good.

  As the thermoplastic resin used for the microporous membrane, a thermoplastic resin having a melting point of less than 200 ° C. is suitable, preferably polyolefin, and particularly preferably polyethylene. Although it does not specifically limit as polyethylene, A high density polyethylene and the mixture of a high density polyethylene and ultra high molecular weight polyethylene are suitable. The molecular weight of polyethylene is preferably 100,000 to 10,000,000 in terms of weight average molecular weight, and particularly preferably a polyethylene composition containing at least 1% by weight of ultrahigh molecular weight polyethylene having a weight average molecular weight of 1,000,000 or more. In addition, as the thermoplastic resin, a mixture of other polyolefins such as polypropylene and polymethylpentene in addition to polyethylene may be used. Further, the microporous film may be configured not only as a single layer of polyethylene microporous film but also as a laminate of two or more layers of, for example, a polyethylene microporous film and a polypropylene microporous film.

  The film thickness of the microporous film is preferably 5 μm or more and 18 μm or less. If the thickness of the microporous film is less than 5 μm, mechanical properties such as tensile strength and puncture strength are insufficient, and if the thickness of the microporous film is more than 18 μm, it is difficult to achieve an appropriate separator thickness. . The puncture strength of the microporous membrane is preferably 10 g or more.

  The porosity of the microporous membrane is preferably 20 to 60%. When the porosity of the microporous membrane is less than 20%, the membrane resistance of the separator becomes too high, and the output of the battery is remarkably lowered, which is not preferable. On the other hand, if it exceeds 60%, the shutdown characteristic is remarkably deteriorated.

  The Gurley value (JIS P8117), which is an index of air permeability of the microporous membrane, is preferably 10 to 500 sec / 100 cc or less. If the Gurley value of the microporous membrane is higher than 500 sec / 100 cc, the ion permeability is insufficient and the resistance of the separator increases. When the Gurley value of the microporous film is lower than 10 sec / 100 cc, the shutdown function is remarkably deteriorated. Furthermore, the Gurley value per unit thickness of the microporous membrane is preferably 10 seconds / 100 cc · μm or more. When the Gurley value per unit thickness is lower than 10 seconds / 100 cc · μm, clogging of the polyolefin microporous film occurs at the interface between the heat-resistant porous layer and the microporous film, and the membrane resistance increases remarkably. This is not preferable because there is a risk that the shutdown characteristics may be significantly lowered.

The microporous membrane has a Gurley value (JIS P8117) of X seconds / 100 cc and Y / X = 1 when the membrane resistance when the polyolefin microporous membrane is impregnated with an electrolyte is Yohm · cm ^2. What becomes * 10 ^{< -3} > ^-1 * 10 ^<-2 > ohm * cm ^{< 2} > / (second / 100cc) is preferable. Here, the Gurley value X is given by Equation 1 below.
X = K (τ ² · L) / (ε · d) (Equation 1)
In Equation 1, K is a proportional constant derived from measurement, τ is a curvature, L is a film thickness, ε is a porosity, and d is an average pore diameter. The film resistance Y is given by the following equation 2.
Y = ρ · τ ² · L / ε (Expression 2)
In Equation 2, ρ is the specific resistance of the electrolyte impregnated in the separator. From the above formulas 1 and 2, Y / X is expressed as the following formula 3.
Y / X = (ρ / K) · d (Formula 3)

Accordingly, Y / X is a parameter proportional to the pore diameter d of the polyolefin microporous membrane. That is, the range of Y / X means a preferable range of the pore diameter d of the microporous membrane. Here, the range of Y / X is that the membrane resistance Y is set at 20 ° C. using an electrolytic solution in which 1M LiBF ₄ is dissolved in a solvent in which propylene carbonate and ethylene carbonate are mixed at a weight ratio of 1: 1. It was obtained by measuring. The specific resistance ρ of the electrolyte at 20 ° C. is 2.66 × 10 ² ohm · cm at 20 ° C., and K is 0.0778 sec / 100 cc. Therefore, ρ / K = 3.4 × 10 ³ Calculated as ohm · cm / (seconds / 100 cc). Therefore, a preferable average pore diameter d based on the above Y / X range is calculated as 3.0 to 30 nm. In addition, when Y / X is smaller than 1 × 10 ⁻³ ohm · cm ² / (second / 100 cc), impregnation with the electrolytic solution becomes difficult, which may cause problems in application as a separator. When Y / X is greater than 1 × 10 ⁻² ohm · cm ² / (sec / 100 cc), the heat resistant porous layer induces clogging at the interface between the heat resistant porous layer and the microporous membrane, Problems such as an increase in the membrane resistance of the separator and a significant decrease in shutdown characteristics may occur.

(Physical properties of the nonaqueous electrolyte battery separator as a whole)
The Gurley value (JIS P8117) of the nonaqueous electrolyte battery separator is preferably 10 to 1000 sec / 100 cc, and more preferably 100 to 400 sec / 100 cc. When the Gurley value of the nonaqueous electrolyte battery separator is less than 10 sec / 100 cc, the Gurley value of the microporous membrane is too low, and the deterioration of the shutdown function is extremely impractical. On the other hand, if the Gurley value exceeds 1000 sec / 100 cc, the ion permeability becomes insufficient, and the membrane resistance of the separator increases, resulting in a problem that the output of the battery is reduced.

Membrane resistance of the nonaqueous electrolyte battery separator is preferably from 0.5~10ohm · cm ^2, and still more it is preferable that is 1~5ohm · cm ^2. The puncture strength is preferably 10 to 1000 g, and more preferably 200 to 600 g. The heat shrinkage rate is preferably 30% or less in both the MD direction and the TD direction. The term “heat shrinkage” as used herein refers to the rate of decrease in sample size when a sample is heat treated at 175 ° C. without tension. The oxygen index is preferably 19% or more. The withstand voltage half-life is preferably 30 minutes or less.

  The film thickness of the nonaqueous electrolyte battery separator of the present invention is preferably 30 μm or less, more preferably 20 μm or less. When the thickness of the separator exceeds 30 μm, the energy density and output characteristics of a battery to which the separator is applied are lowered, which is not preferable.

[Method for producing non-aqueous electrolyte battery separator]
Although the manufacturing method of the nonaqueous electrolyte battery separator of this invention is not specifically limited, For example, it is possible to manufacture through the following processes (i)-(iv). That is, (i) a step of dispersing an inorganic filler satisfying the above (a) and (b) in a water-soluble organic solvent solution of a heat-resistant polymer to prepare a slurry for coating; and (ii) obtained. (Iii) a step of solidifying the heat-resistant polymer on the coated microporous membrane using a coagulating liquid; and (iv) a step of coating the slurry for coating on one side or both sides of the microporous membrane; And a step of washing and drying the microporous membrane after the coagulation step.

  For example, when an aromatic polyamide obtained from an aromatic dicarboxylic acid and an aromatic diamine is used as the heat-resistant polymer, in the step (i), the aromatic dicarboxylic acid and the aromatic diamine are converted into a polyamide to be produced. On the other hand, an aromatic polyamide can be produced by reacting in an organic solvent which is a good solvent (solution polymerization), and a coating solution can be produced directly.

  For example, when polymetaphenylene isophthalamide is used, in the step (i), isophthalic acid chloride and metaphenylenediamine are reacted in an organic solvent that is not a good solvent for the resulting polyamide, for example, tetrahydrofuran. It is convenient to produce polymetaphenylene isophthalamide by a so-called interfacial polymerization method in which a solution or dispersion is prepared and contacted with an aqueous solution of an acid acceptor such as sodium carbonate to complete the reaction.

  In any of the above cases, preferably, 50 to 95% by weight of an inorganic filler is dispersed in a water-soluble organic solvent solution of a heat-resistant polymer to prepare a coating slurry (coating liquid). good. When the dispersibility of the inorganic filler is not good, a method of improving the dispersibility by surface-treating the inorganic filler with a silane coupling agent or the like is also applicable. And what is necessary is just to apply the obtained slurry for coating to the single side | surface or both surfaces of the said microporous film.

  In the step (i), the water-soluble organic solvent (solvent) that is a good solvent for the heat-resistant polymer is not particularly limited, but specifically, a polar solvent is preferable, for example, N-methylpyrrolidone, dimethylacetamide, Examples thereof include dimethylformamide and dimethyl sulfoxide. In addition, a solvent that becomes a poor solvent for the heat-resistant polymer may be mixed with these polar solvents. By applying such a 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.

In step (ii), a heat-resistant polymer coating solution is applied to at least one surface of the microporous membrane. In the present invention, it is preferable to apply on both surfaces of the microporous membrane. The concentration of the coating solution is preferably 4 to 9% by weight, and the coating amount on the microporous membrane is preferably about ² to 3 g / m ² . Examples of the coating method include knife coater method, gravure coater method, screen printing method, Mayer bar method, die coater method, reverse roll coater method, ink jet method, spray method, roll coater method and the like. From the viewpoint of uniformly applying the coating film, the reverse roll coater method is particularly suitable. More specifically, for example, in the case of applying a heat-resistant polymer coating solution on both sides of a polyethylene microporous membrane, an excessive coating solution is applied to both sides of the polyethylene microporous membrane through a pair of Meyer bars. There is a method in which the liquid is applied and precisely measured by passing it between a pair of reverse roll coaters and scraping off the excess coating liquid.

  In the step (iii), the heat-resistant polymer on the coated microporous film is coagulated using a coagulating liquid to form a porous layer. Examples of the coagulation method include a method of spraying a coagulation liquid with a spray and a method of immersing in a bath (coagulation bath) containing the coagulation liquid. The coagulating liquid is not particularly limited as long as it can coagulate the heat-resistant polymer, but water or an organic solvent used for the coating liquid is preferably mixed with an appropriate amount. Here, the mixing amount of water is preferably 40 to 80% by weight with respect to the coagulation liquid. When the amount of water is less than 40% by weight, there arises a problem that the time required for solidifying the heat-resistant resin becomes long or the solidification becomes insufficient. On the other hand, if the amount is more than 80% by weight, there arises a problem that the cost for solvent recovery becomes high, or the surface that comes into contact with the coagulating liquid is too rapidly solidified to make the surface sufficiently porous.

  Step (iv) is a step of removing the coagulating liquid from the obtained separator by washing with water, and then drying, following step (iii). The drying method is not particularly limited, but a drying temperature of 50 to 80 ° C. is appropriate. When a high drying temperature is applied, a method of contacting with a roll in order to prevent a dimensional change due to heat shrinkage occurs. It is preferable to apply.

[Nonaqueous electrolyte battery]
As long as the nonaqueous electrolyte battery separator has the above-described configuration, the nonaqueous electrolyte battery separator of the present invention can be applied to any known nonaqueous electrolyte battery, and is excellent in safety and battery characteristics. A battery is obtained.

  The applied nonaqueous electrolyte battery may be a primary battery or a secondary battery, and the type and configuration of the nonaqueous electrolyte battery are not limited in any way. It can be suitably applied to a non-aqueous electrolyte secondary battery that obtains an electromotive force by doping and dedoping. Among these, application to a lithium ion secondary battery is preferable.

  In general, a nonaqueous electrolyte secondary battery refers to a battery element in which a battery element in which a negative electrode and a positive electrode face each other with a separator interposed therebetween is impregnated with an electrolytic solution and sealed in an exterior.

  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 (copper foil, stainless steel foil, nickel foil, etc.). As the negative electrode active material, a material capable of electrochemically doping lithium, for example, a carbon material, silicon, aluminum, or tin is 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 such as LiCoO ₂ , LiNiO ₂ , LiMn _0.5 Ni _0.5 O ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiMn ₂ O. ₄ and LiFePO ₄ are used.

The electrolytic solution has a configuration in which a lithium salt, for example, LiPF ₆ , LiBF ₄ , or LiClO ₄ is dissolved in a non-aqueous solvent. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, and vinylene carbonate.

  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.

Hereinafter, the present invention will be described in detail by way of examples.
<1. Measurement method>
Various measurement methods in the present invention are as follows.
[Average particle size and particle size distribution of inorganic filler]
Measurement was performed using a laser diffraction particle size distribution analyzer (manufactured by Sysmex Corporation, Mastersizer 2000). Water was used as a dispersion medium, and a small amount of a nonionic surfactant Triton · X-100 was used as a dispersant. In addition, d50 represents an average particle diameter (μm) of cumulative weight 50% by weight calculated from the small particle side in the particle size distribution in the laser diffraction method, and d90 represents an average particle diameter (μm) of cumulative weight 90% by weight. , D10 represents an average particle diameter (μm) of 10% by weight. α was determined by α = (d90−d10) / d50.

[Molecular weight and molecular weight distribution of heat-resistant polymers]
1% by weight of the polymer was dissolved in a solution obtained by dissolving 0.01 mol / L of LiCl in DMF, and GPC measurement was performed using this as a measurement sample to calculate the molecular weight distribution. For the measurement, Shimadzu Chromatopack C-R4A and a GPC column (GPC / KD-802, manufactured by Showa Denko KK) were used and measured at a detection wavelength of 280 nm. As a reference, a polystyrene molecular weight standard was used. For the separator in which the microporous membrane and the heat resistant porous layer are combined, first, 1 g of the composite separator is sampled, and the sample is added to 20 g of DMF in which 0.01 mol / L of LiCl is dissolved. At 80 ° C., only aramid was dissolved to obtain a measurement sample. As shown in FIG. 1, the content (% by weight) of the low molecular weight polymer in the heat resistant polymer is a value S1 obtained by integrating the GPC curve in the section from molecular weight 0 to 8.0 × 10 ^3. Divided by the value S2 integrated over the interval from molecular weight 0 to 1.0 × 10 ⁶ and multiplied by 100. The molecular weight distribution (MWD) referred to here is represented by the ratio of the weight average molecular weight (Mw) and the number average molecular weight (Mn) determined by GPC, and is determined by MWD = Mw / Mn. In addition, a weight average molecular weight (Mw) and a number average molecular weight (Mn) are calculated in the whole area | region from molecular weight 0 to 1.0 * 10 < ⁶ >.

[Impurity content in heat-resistant polymer]
A sample polymer is mixed with ammonium sulfate, sulfuric acid, nitric acid and perchloric acid, wet-decomposed at about 300 ° C for 9 hours, diluted with distilled water, and an ICP emission analyzer (JY170 ULTRACE) manufactured by Rigaku Corporation. Used for qualitative and quantitative determination. By this method, the contents of alkali metal, alkaline earth metal, transition metal and silicon were measured.
In addition, the sample polymer is combusted by an automatic sample combustion apparatus AQF-100 (manufactured by Dia Instruments Co., Ltd.), and the generated gas is absorbed in 30 ppm of hydrogen peroxide water to be ion chromatograph (ICS-1500, manufactured by Dionex Co., Ltd.) Qualitative and quantitative determination of halogens was performed with a column (IonPacAG12A / AS12A).

[Film thickness]
The sample was measured at 20 points with a contact-type film thickness meter (manufactured by Mitutoyo Corp.) and averaged. Here, the contact terminal used was a cylindrical one having a bottom surface of 0.5 cm in diameter, and measurement was performed under such a condition that a load of 1.2 kg / cm ² was applied to the contact terminal.

[Gurley value]
The Gurley value (second / 100 cc) was measured according to JIS P8117.

[End group concentration of aromatic polyamide]
Using a DMF solution containing 1% by weight of polymer and 0.05% by weight of lithium chloride as a measurement sample, measurement was performed at a detection wavelength of 280 nm using Shimadzu Chromatopack C-R4A and an ODS (OctaDecylSilyl) column. The polymer to be evaluated was collected from the polymer after polymer production or from the heat-resistant layer incorporated in the composite separator. As a method of measuring the molecular weight distribution of aramid from the heat-resistant layer incorporated in the composite separator, first, 1 g of the composite separator is sampled, and the sample is added to 20 g of DMF in which 0.01 mol / L of LiCl is dissolved. Only aramid was dissolved at 0 ° C. to obtain a measurement sample.

[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 by the following formula 4.
ε = {1− (Wa / da + Wb / db + Wc / dc +... + Wn / dn) / t} × 100 (Equation 4)

[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.

[Friction characteristics]
Evaluation was performed using a card friction tester manufactured by Toyo Seiki Co., Ltd. A sample was attached to a 1 kg weight (76 mm square) and placed on a SUS stage. This was slid 10 cm at a speed of 90 cm / min. Then, the sample surface on the side that was in contact with the SUS stage was observed to confirm whether it was black. When it was black, it was determined that the SUS of the stage material was polished, and it was determined as x. Moreover, when it was not black, it judged that SUS was not grind | polished and determined as (circle).

[Fixability of heat-resistant porous layer]
The obtained separator was rolled up and stored at room temperature for one month. Then, it canceled again, the surface state of the heat resistant porous layer was observed visually, and the presence or absence of the lack of a heat resistant porous layer was observed. When no omission was observed, it was judged as “good”. Moreover, when the lack was observed, it determined with x.

[Shutdown characteristics (SD characteristics)]
First, the separator is punched to Φ19 mm, dipped in a 3% by weight methanol solution of a nonionic surfactant (manufactured by Kao Corporation; Emulgen 210P), and air-dried. Then, the separator was impregnated with the electrolytic solution and sandwiched between SUS plates (Φ15.5 mm). Here, 1 M LiBF ₄ propylene carbonate / ethylene carbonate (1/1 weight ratio) was used as the electrolytic solution. This was enclosed in a 2032 type coin cell. I took the lead from the coin cell, put a thermocouple, and put it in the oven. The cell resistance was measured by raising the temperature at a rate of temperature increase of 1.6 ° C./min and simultaneously applying alternating current with an amplitude of 10 mV and a frequency of 1 kHz.
In the above measurement, when the resistance value was 10 ³ ohm · cm ² or more in the range of 135 to 150 ° C., the SD characteristic was evaluated as “good”, and otherwise, the SD characteristic was evaluated as “x”.

[Heat-resistant]
In the evaluation of the above SD characteristics, if the resistance value continues to maintain a level of 1.0 × 10 ³ ohm · cm ² or higher even at a temperature of 150 to 190 ° C. after the shutdown function is exhibited, Was not generated and the heat resistance was excellent, and therefore, the heat resistance was judged to be good (◯). On the other hand, when the resistance value at 150 to 190 ° C. was lower than 1.0 × 10 ³ ohm · cm ² , the heat resistance was judged to be poor (×).

[Cycle characteristics]
Using the separators shown in the following examples and comparative examples, lithium ion secondary batteries were prepared as follows, and their cycle characteristics were evaluated.

1) Positive electrode 6 wt% PVdF so that the lithium cobalt oxide (LiCoO ₂ , Nippon Chemical Industry Co., Ltd.) powder 89.5 parts by weight, acetylene black 4.5 parts by weight and PVdF dry weight 6 parts by weight A positive electrode paste was prepared using the NMP solution. The obtained paste was applied onto an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a thickness of 97 μm.

2) Negative electrode 6 wt% PVdF so that the dry weight of mesophase carbon microbeads (MCMB, manufactured by Osaka Gas Chemical Co., Inc.) powder 87 parts by weight, acetylene black 3 parts by weight and PVdF 10 parts by weight as the negative electrode active material. An NMP solution was used to prepare a negative electrode agent paste. The obtained paste was applied onto a copper foil having a thickness of 18 μm, dried and pressed to prepare a negative electrode having a thickness of 90 μm.

3) electrolytic solution of ethylene carbonate and ethyl methyl carbonate of 3: a mixed solution with 7 weight ratio, were used as LiPF ₆ was dissolved at a 1 mol / L.

4) Trial production of lithium ion secondary battery Separator (2.6 cm × 2.2 cm) in which the positive electrode (2 cm × 1.4 cm) and the negative electrode (2.2 cm × 1.6 cm) were prepared in the following examples and comparative examples It was made to face through. This was impregnated with the above electrolytic solution (0.15 to 0.19 g) and sealed in an exterior made of an aluminum laminate film to produce a lithium ion secondary battery.

5) Cycle test About the produced lithium ion secondary battery, charging / discharging measurement apparatus (HJ-101SM6 by Hokuto Denko Co., Ltd.) was used, and charging / discharging was repeated 100 cycles. The battery was charged up to 4.2 V at 6 mA / h, and was discharged up to 2.75 V at 1.6 mA / h). Then, the cycle characteristics were calculated from the discharge capacity at the first cycle and the discharge capacity at the 100th cycle by the following formula 5.
Cycle characteristics (%) = (discharge capacity at the 100th cycle) / (discharge capacity at the first cycle) × 100 (Equation 5)
When the cycle characteristic was 80% or more, it was evaluated as good (◯), and when it was less than 80%, it was judged as defective (×).

<2. Study on molecular weight distribution of inorganic filler>
First, the effect of the molecular weight distribution of the inorganic filler was examined.
[Example 1]
1) Production of polymetaphenylene isophthalamide When 160.5 g of isophthalic acid chloride was dissolved in 1120 ml of tetrahydrofuran and stirred, a solution of 85.2 g of metaphenylenediamine in 1120 ml of tetrahydrofuran was gradually added as a trickle and became cloudy. A milky white 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.

2) Manufacture of polyethylene porous film 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) made from Ticona 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 .

3) Production of Nonaqueous Electrolyte Battery Separator The polymetaphenylene isophthalamide obtained above and a polyethylene porous membrane were used, and an inorganic filler was used in combination with this to produce the nonaqueous electrolyte battery separator of the present invention.
Specifically, an inorganic filler composed of polymetaphenylene isophthalamide and aluminum hydroxide (Showa Denko KK; H-43M) was adjusted to a weight ratio of 25:75. Dimethylacetamide (DMAc) and tripropylene glycol (TPG) were mixed in a mixed solvent having a weight ratio of 50:50 so that the amide concentration was 5.5% by weight to obtain a coating slurry. The inorganic filler had a particle size distribution in the laser diffraction method of d90 of 1.05, d50 of 0.75, and d10 of 0.38. Further, in the inorganic filler, water 0.3% SiO ₂ 0.01% _Fe 2 _{O 3} is 0.01%, was included Na ₂ O 0.34%.

A pair of Meyer bars (count # 6) was opposed to each other with a clearance of 20 μm. An appropriate amount of the above slurry for coating was placed on a Mayer bar, a polyethylene microporous membrane was passed between a pair of Mayer bars, and the coating slurry was coated on both sides of the polyethylene microporous membrane. And what was coated was immersed in the coagulating liquid which is 40 degreeC by water: DMAc: TPG = 50: 25: 25 by weight ratio. Next, washing with water and drying were performed to form heat-resistant porous layers on both surfaces (front and back surfaces) of the polyethylene microporous membrane, thereby obtaining the nonaqueous electrolyte battery separator of the present invention.
The characteristics of the obtained nonaqueous electrolyte battery separator were analyzed, and the evaluation results are shown in Table 1. The evaluation results of the following Examples 2 and 3 and Comparative Examples 1 and 2 are also shown in Table 1.

[Example 2]
The particle size distribution in the laser diffraction method is the same as that in Example 1 except that d90 is 1.07, d50 is 1.02, and d10 is 0.50 aluminum hydroxide (Showa Denko KK; H-42M). The separator for non-aqueous secondary batteries of this invention was obtained by this method. In this inorganic filler, moisture was 0.23%, SiO ₂ was 0.01%, Fe ₂ O ₃ was 0.01%, and Na ₂ O was 0.33%.

[Example 3]
Aluminum hydroxide (manufactured by Showa Denko; H-43M) was heat-treated at 280 ° C. to obtain activated alumina (porous filler) having an average particle diameter of 0.8 μm and a specific surface area of 400 m ² / g. A separator for a non-aqueous secondary battery of the present invention was obtained in the same manner as in Example 1 except that this activated alumina was used as an inorganic filler. In the inorganic filler, SiO ₂ is 0.01%, _Fe 2 _{O 3} is 0.01%, was included Na ₂ O 0.34%.

[Comparative Example 1]
The particle size distribution in the laser diffraction method is the same as that of Example 1 except that d90 is 22.0, d50 is 8.0, and d10 is 1.50 aluminum hydroxide (Showa Denko; H-32). Thus, a separator for a non-aqueous secondary battery was obtained.

[Comparative Example 2]
The particle size distribution in the laser diffraction method is the same as that of Example 1 except that d90 is 58.0, d50 is 23.0, and d10 is 5.10 aluminum hydroxide (Showa Denko KK; H-21). Thus, a separator for a non-aqueous secondary battery was obtained.

<2. Study on molecular weight of heat-resistant resin>
Next, effects such as the molecular weight of the heat resistant resin were examined.
[Example 4]
A separator for a non-aqueous secondary battery of the present invention was obtained in the same manner as in Example 3. The separator had physical properties of a heat-resistant porous layer having a porosity of 71%, a Gurley value of 309 seconds / 100 cc, a membrane resistance of 2.7 ohm · cm ² , and an overall film thickness of 20 μm. In addition, the molecular weight distribution Mw / Mn of the polymer in Example 3 was 6, the weight average molecular weight Mw was 1.5 × 10 ⁵ , and the content of the low molecular weight substance having a molecular weight of 8000 or less was 3.4% by weight. Further, the sodium content in this polymer was 100 ppm, the iron content was 2 ppm, the silicon content was 3 ppm, the magnesium content was 3 ppm, and the chlorine content was 80 ppm.

[Example 5]
A white polymer of polymetaphenylene isophthalamide in the same manner as in Example 1 except that a solution in which 160.5 g of isophthalic acid chloride was dissolved in 1120 ml of tetrahydrofuran and a solution in which 83.9 g of metaphenylenediamine was dissolved in 1120 ml of tetrahydrofuran were used. 185.0 g was obtained. This polymetaphenylene isophthalamide had a molecular weight distribution Mw / Mn of 10, a weight average molecular weight Mw of 2.0 × 10 ⁵ , and a content of a low molecular weight compound having a molecular weight of 8000 or less was 3.0% by weight.

A non-aqueous secondary battery separator of the present invention was obtained in the same manner as in Example 3 except that the polymetaphenylene isophthalamide thus obtained was used. The separator had physical properties of a heat-resistant porous layer having a porosity of 66%, a Gurley value of 318 seconds / 100 cc, a membrane resistance of 2.9 ohm · cm ² , and an overall film thickness of 20 μm.

[Example 6]
In a reaction vessel equipped with a thermometer, a stirrer, and a raw material inlet, 753 g of NMP having a moisture content of 100 ppm or less was placed, 85.5 g of metaphenylenediamine was dissolved in this NMP, and cooled to 0 ° C. To this cooled diamine solution, 160.5 g of isophthalic acid chloride was gradually added with stirring to react. This reaction increased the temperature of the solution to 70 ° C. After the change in viscosity stopped, 58.4 g of calcium hydroxide powder was added and stirred for another 40 minutes to complete the reaction, and the polymerization solution was taken out and reprecipitated in water to obtain 184.0 g of polymetaphenylene isophthalamide. . The molecular weight distribution Mw / Mn of this polymer was 4, the weight average molecular weight Mw was 1.0 × 10 ⁵ , and the content of low molecular weight substances having a molecular weight of 8,000 or less was 0.8% by weight. Further, the calcium content in this polymer was 120 ppm, and the chlorine content was 198 ppm.

A non-aqueous secondary battery separator of the present invention was obtained in the same manner as in Example 3 except that the polymetaphenylene isophthalamide thus obtained was used. The properties of the separator obtained were as follows: the porosity of the heat-resistant porous layer was 70%, the Gurley value was 400 seconds / 100 cc, the membrane resistance was 4.9 ohm · cm ² , and the average film thickness was 20 μm.
The above results are summarized in Table 3. In addition, when the GPC measurement of the polymetaphenylene isophthalamide was implemented about the separator of Examples 4-6, molecular weight distribution Mw / Mn and the weight average molecular weight Mw were equivalent to the polymer before application | coating.

As can be seen from the results in Table 3, it can be seen that the separators of Examples 4 and 5 are superior to the separator of Example 6 in air permeability and membrane resistance. Accordingly, a heat-resistant resin having a molecular weight distribution Mw / Mn of 5 ≦ Mw / Mn ≦ 100 and a weight average molecular weight Mw of 8.0 × 10 ³ or more and 1.0 × 10 ⁶ or less is used. It can also be seen that it is preferable to use a polymer containing 1% by weight to 15% by weight of a low molecular weight polymer having a molecular weight of 8000 or less. It can also be seen that there is no problem in cycle characteristics when the content of impurities in the polymer is 1000 ppm or less.

<3. Study on Polyamide End Group Concentration Ratio>
Next, the influence of the terminal group concentration ratio of the wholly aromatic polyamide was examined.
[Example 7]
When 160.5 g of isophthalic acid chloride was dissolved in 1120 ml of tetrahydrofuran and a solution of 84.9 g of metaphenylenediamine in 1120 ml of tetrahydrofuran was gradually added as a trickle while stirring, a milky white solution that became cloudy 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. The end group concentration ratio of this polyamide was [COOX] / [NH ₂ ] = 2.2. And the separator for non-aqueous secondary batteries of this invention was obtained by the method similar to Example 3 except having used the polymetaphenylene isophthalamide obtained as mentioned above.
Cycle characteristics were evaluated using this separator. Table 4 shows the measurement results of the discharge capacity at the 100th cycle.

[Example 8]
In a reaction vessel equipped with a thermometer, a stirrer, and a raw material inlet, 753 g of NMP having a moisture content of 100 ppm or less was placed, 84.9 g of metaphenylenediamine was dissolved in this NMP, and cooled to 0 ° C. To this cooled diamine solution, 160.5 g of isophthalic acid chloride was gradually added with stirring to react. This reaction increased the temperature of the solution to 70 ° C. After the change in viscosity stopped, 58.4 g of calcium hydroxide powder was added and stirred for another 40 minutes to complete the reaction, and the polymerization solution was taken out and reprecipitated in water to obtain 184.0 g of polymetaphenylene isophthalamide. . The end group concentration ratio of this polyamide was [COOX] / [NH ₂ ] = 2.1. And the separator for non-aqueous secondary batteries of this invention was obtained by the method similar to Example 3 except having used the polymetaphenylene isophthalamide obtained in this way.
Cycle characteristics were evaluated using this separator. Table 4 shows the measurement results of the discharge capacity at the 100th cycle.

[Example 9]
Except for using 86.4 g of metaphenylenediamine, 16.4 g of a white polymer of polymetaphenyleneisophthalamide was obtained in the same manner as in Example 7. The terminal group concentration ratio of the polyamide was [COOX] / [NH ₂ ] = 0.8. And the separator for non-aqueous secondary batteries of this invention was obtained by the method similar to Example 3 except having used the polymetaphenylene isophthalamide obtained in this way.
Cycle characteristics were evaluated using this separator. Table 4 shows the measurement results of the discharge capacity at the 100th cycle.

As can be seen from Table 4 above, it can be seen that Examples 7 and 8 are superior to Example 9 in charge and discharge characteristics after 100 cycles. From this, it can be seen that when aromatic polyamide is used as the heat resistant resin, the terminal group concentration ratio of the aromatic polyamide is preferably [COOX] / [NH ₂ ] ≧ 1.

Claims (12)

A non-aqueous solution comprising a microporous film mainly formed of a thermoplastic resin and having a shutdown function, and a heat-resistant porous layer formed mainly of a heat-resistant polymer and laminated on one or both surfaces of the microporous film. An electrolyte battery separator,
The non-aqueous electrolyte battery separator, wherein the heat-resistant porous layer contains an inorganic filler that satisfies the following (a) and (b).
(A) 0.01 ≦ d50 ≦ 20 (μm)
(B) 0 <α ≦ 2
(However, d50 represents the average particle diameter (μm) of 50% by weight cumulatively calculated from the small particle side in the particle size distribution in the laser diffraction method. Α indicates the uniformity of the inorganic filler, and α = (d90 -D10) / d50, d90 represents the average particle diameter (μm) of 90% by weight of cumulative particle size calculated from the small particle side in the particle size distribution in the laser diffraction method, and d10 represents the particle size in the laser diffraction method. (In the distribution, an average particle diameter (μm) of 10% by weight of the cumulative weight from the small particle side is represented.) The non-aqueous electrolyte battery separator according to claim 1, wherein the inorganic filler satisfies the following (c) and (d).
(C) 0.1 ≦ d50 ≦ 2 (μm)
(D) 0 <α ≦ 1
(However, the definitions of d50 and α are the same as in claim 1.) The non-aqueous electrolyte battery separator according to claim 1, wherein the heat-resistant porous layer contains an inorganic filler in a weight fraction of 50 wt% or more and 95 wt% or less. The said inorganic filler consists of metal hydroxides. The separator for nonaqueous electrolyte batteries of any one of Claims 1-3 characterized by the above-mentioned. The separator for a nonaqueous electrolyte battery according to claim 4, wherein the metal hydroxide is aluminum hydroxide. The non-aqueous electrolyte battery separator according to claim 1, wherein the inorganic filler is a porous filler. The separator for a nonaqueous electrolyte battery according to claim 6, wherein the porous filler is activated alumina. The heat-resistant polymer is one or more selected from the group consisting of aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide. The nonaqueous electrolyte battery separator according to any one of the above. The non-aqueous electrolyte battery separator according to claim 8, wherein the heat-resistant polymer is polymetaphenylene isophthalamide. The non-aqueous electrolyte battery separator according to claim 1, wherein the thermoplastic resin is a thermoplastic resin mainly composed of polyolefin. The nonaqueous electrolyte battery separator according to any one of claims 1 to 10, wherein the nonaqueous electrolyte battery separator is a separator for a lithium ion secondary battery. A non-aqueous electrolyte secondary battery that obtains an electromotive force by doping or dedoping lithium,
A non-aqueous electrolyte secondary battery using the non-aqueous electrolyte battery separator according to claim 1.

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