WO2006123811A1

WO2006123811A1 - Separator for lithium ion secondary battery and lithium ion secondary battery

Info

Publication number: WO2006123811A1
Application number: PCT/JP2006/310094
Authority: WO
Inventors: Satoshi Nishikawa; Hiroyuki Honmoto; Takahiro Daido; Hiroki Sano
Original assignee: Teijin Limited
Priority date: 2005-05-17
Filing date: 2006-05-16
Publication date: 2006-11-23
Also published as: JP4832430B2; CN101180751B; KR101340357B1; CN101180751A; KR20080019621A; JPWO2006123811A1

Abstract

Disclosed is a membrane as a separator for lithium ion secondary batteries wherein a porous layer mainly composed of an aromatic polyamide is formed on both sides of a nonwoven fabric. This separator has sufficiently high heat resistance and good handling properties, and is an effective measure against overcharging. Safety of a lithium ion secondary battery can be improved by using such a separator.

Description

Description Lithium-ion secondary battery separator and lithium-ion secondary battery Technical Field

The present invention relates to a separator used for a lithium ion secondary battery. In particular, it relates to a separator technology for the purpose of improving the safety of lithium ion secondary batteries. Background art

Lithium ion doping 'Lithium ion secondary batteries that obtain an electromotive force by undoping have a high energy density and are widely used as power sources for portable electronic devices such as mobile phones and laptop computers. In addition, it has been applied to power applications such as electric tools with higher output.

In recent years, interest in hybrid electric vehicles (HEV) has increased due to global environmental problems. Currently, nickel-metal hydride batteries are generally used as batteries, but lithium-ion secondary batteries have less memory effect than nickel-metal hydride batteries. It is considered as a power source for HEV because it is easy to use and has the advantages of being able to be downsized due to its high energy and high power density. When considering batteries used in HEVs, the requirements are naturally different from those of portable electronic devices. For example, in HEV, batteries are highly likely to be exposed to high temperatures, and ensuring safety in high-temperature environments is one of the very important characteristics. In this way, the characteristics required for batteries differ between portable electronic devices and HEVs, so the characteristics required for battery components naturally differ.

In current lithium ion secondary batteries, a polyethylene microporous membrane is used as a separator. This separator has a shutdown function and contributes to ensuring the safety of the battery. This shutdown function utilizes the fact that the microporous membrane melts and closes the pores due to heat, and is characterized by the thermal fuse temperature and short circuit temperature. heat The fuse temperature is the temperature at which the separator resistance begins to increase due to hole closure, and the showroom temperature is the temperature at which the separator breaks down and the separator resistance drops rapidly. Between this thermal fuse temperature and short circuit temperature, the separator resistance can shut out very high currents. This function is said to be effective for ensuring safety such as external short circuit.

In the case of HEV, a case where it is actively heated from the outside is assumed. When considering the shutdown function in such applications, thermal fuses can lead to performance degradation when exposed to high temperatures, and film breakage can lead to ignition due to an internal short circuit between the positive and negative electrodes. For this reason, separators with a shutdown function are not necessarily effective in HEV, and it is considered that separators with sufficient heat resistance are more suitable.

Several proposals have already been made for the construction of a separator with high heat resistance. For example, Japanese Patent No. 31 42693 has proposed a non-woven sheet made of highly heat-resistant fibers such as aromatic polyamide fibers. However, the shape of the non-woven fabric has a large opening. <To prevent the short circuit between the positive and negative electrodes and retain the electrolyte, the characteristics related to the nature of the separator are insufficient. However, it is very difficult to obtain a suitable separator for a lithium ion secondary battery at the current technical level, and it has not been put into practical use.

A porous film made of a polymer having high heat resistance such as aromatic polyamide has also been proposed in WO01 Z 01 9906 and the like. This system has sufficient heat resistance in terms of short-circuiting due to membrane breakage. However, in a case where heat is actively generated from the inside such as overcharging, the battery may catch fire due to a runaway reaction. There is a problem that the countermeasure becomes complicated. In addition, a porous membrane made of an aromatic polyamide has a problem that productivity is low from the viewpoint of strength.

A technique for providing a shutdown function to a porous film made of a polymer having high heat resistance as described above has also been proposed. For example, shut down in JP 2001-23602 A technique for coating a porous film made of a highly heat-resistant resin on a porous film having a function is disclosed. However, the resistance after the thermal fuse rises only about 10 times the resistance before the thermal fuse, and it is difficult to say that the shutdown function is sufficient to ensure the safety of the battery. Japanese Patent Laid-Open No. 10-6453 proposes a structure in which fine particles made of polyethylene are mixed in a porous film made of a heat resistant resin. Similarly, this system does not have a sufficient shutdown function.

WO01 Z067536 proposes a configuration in which a non-woven fabric made of highly heat-resistant fibers is coated with a porous layer made of a polyvinylidene fluoride copolymer. This specification describes technical elements that can prevent the overcharge prevention function by appropriately controlling the morphology of the separate evening. Further, a manufacturing method suitable for this morphology control is disclosed in Japanese Patent Laid-Open No. 2003-171 495. However, the polyvinylidene fluoride copolymer swollen in the electrolyte solution is not high in heat resistance and melts at high temperatures, so it is considered that the heat resistance of this system is ensured by the nonwoven fabric. Similar to the discussion in Japanese Patent No. 31 42693, there is a problem that the prevention of short-circuiting of the positive and negative electrodes with a non-woven fabric is not reliable.

Japanese Patent Application Laid-Open No. 10-324758 discloses a separator in which the surface and voids of a substrate made of fiber or pulp are covered with a porous pararamide polymer. Japanese Patent No. 31 75730 is a system in which ceramic is dispersed in a porous layer in addition to the system disclosed in JP-A-10-324758. In the method of manufacturing a separator described in these patent documents, a non-woven cloth is placed on a carrier sheet, and a paraamide polymer dope is applied from above, and the paraamide polymer is deposited in an appropriate humidity and temperature environment. A porous membrane is obtained by the method of In this method, porous para- amide polymer can not be coated substantially on both sides of the non-woven fabric, and apparently a single-sided coating. In addition, since the deposition rate differs on the front and back, the morphology of the porous layer on the front and back is also largely asymmetric. Such a separator with a significant difference between the front and the back is not practical because it is difficult to form an appropriate electrode-separator interface and there are problems in battery performance. In addition, curling and handling There is also a title. In addition, there is a problem that pararamid polymer is difficult to adjust and mold. Specifically, it is difficult to form the holes continuously, and since only very small holes are formed, sufficient ion permeability cannot be obtained. In addition, this technique has a problem that the manufacturing method is complicated. Disclosure of the invention

As mentioned above, a separator with high heat resistance utilizing a heat resistant resin such as aromatic polyamide has been proposed. This heat resistance is a feature that significantly improves the safety of lithium ion secondary batteries and produces them. At present, no separator structure with good performance has been found and has not been put into practical use. In the sufficiently high heat-resistant separator, the present inventors believe that what is lacking from the viewpoint of ensuring the safety of lithium-ion secondary batteries is an overcharge countermeasure that leads to a runaway reaction due to self-heating from the inside. Thought. Accordingly, an object of the present invention is to provide a separator having sufficiently high heat resistance << effective for overcharge countermeasures and good handling characteristics.

As a result of intensive studies on the above problems by the present inventors, it has been confirmed that a separator in which a porous layer mainly made of an aromatic polyamide is coated on both front and back surfaces of a nonwoven fabric is effective in ensuring the safety of a lithium ion secondary battery. The headline has led to the present invention. That is, the present invention provides a separator for a lithium ion secondary battery, characterized in that a porous layer mainly composed of a metaaromatic polyamide is formed on both front and back surfaces of a nonwoven fabric. The present invention also provides the following inventions.

1. Lithium ion secondary battery according to the invention, characterized in that the film thickness force of the separator << 15 to 40 jum, the Gurley value (JIS P81 17) force << 10 to 50 seconds Z 1 OOcc Separator for use.

2. A surfactant containing at least one selected from the group consisting of a cationic surfactant, an anionic surfactant, an amphoteric surfactant and a nonionic surfactant is attached to the porous layer. The lithium ion according to any one of the above invention and 1, wherein On-secondary battery separator.

3. The separator for a lithium ion secondary battery according to 2, wherein the surfactant is attached in an amount of 0.005-0.750 gZm ² .

4. The separator for a lithium ion secondary battery according to the above invention or any one of 1 to 3, wherein the nonwoven fabric is a nonwoven fabric mainly composed of polyethylene terephthalate.

5. The separator for a lithium ion secondary battery according to 4, wherein the weight of the porous layer mainly composed of metaaromatic polyamide is 4 to 10 gZm ² .

6. The separator for a lithium ion secondary battery according to the above invention or any one of 1 to 3, wherein the nonwoven fabric is a nonwoven fabric mainly composed of a metaaromatic polyamide.

7. The separator for a lithium ion secondary battery according to the above invention or any one of 1 to 3, wherein the non-woven fabric comprises metaaromatic polyamide short fibers and para aromatic polyamide pulp.

8. The separator for a lithium ion secondary battery according to the above invention or 1, wherein the metaaromatic polyamide is polymetaphenylene diisophthalamide.

9. The porous layer contains ceramic fine particles having an average particle size of 0.05-2 μm, and the ceramic fine particles are 30-80% by weight with respect to the weight of the porous material layer. The separator for a lithium ion secondary battery according to any one of the above inventions or 1 to 8.

1 0. A polymer solution mainly composed of a metaaromatic polyamide and a solvent that is a good solvent for the metaaromatic polyamide is applied to both front and back surfaces of the nonwoven fabric, and the coated nonwoven fabric is then applied to the metaaromatic polyamide. In contrast, a method for producing a separator for a lithium ion secondary battery, comprising coagulating in a mixed liquid mainly composed of a solvent that is a poor solvent and a solvent that is a good solvent, and then washing and drying.

1 1. In a lithium ion secondary battery having a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, and obtaining an electromotive force by doping and detaching lithium ions, the separator is made of non-woven fabric. A lithium ion secondary battery, characterized in that a porous layer mainly composed of a metaaromatic polyamide is formed on both front and back surfaces.

1 2. Lithium ion according to 1 1 characterized in that the film thickness force of the separator << 15 to 40 〃m, Gurley value (JIS P81 1 F) force << 10 to 50 seconds Z 1 OOcc Secondary battery.

1 3. A surfactant containing at least one selected from the group consisting of a cationic surfactant, an anionic surfactant, an amphoteric surfactant and a nonionic surfactant is attached to the porous layer. 11. The lithium-ion secondary battery according to any one of 1 1 and 1 2 above.

1 4. The separator for a lithium ion secondary battery according to 1 3, wherein the surfactant is attached in an amount of 0.005-0.750 gZm ² .

1 5. The lithium ion secondary battery according to any one of 1 1 to 14, wherein the nonwoven fabric is a nonwoven fabric mainly composed of polyethylene terephthalate.

1 6. The lithium ion secondary battery according to 15, wherein the weight of the porous layer mainly composed of metaaromatic polyamide is 4 to 10 gZm ² .

1 7. The lithium ion secondary battery according to 15, wherein the electrolyte of the electrolytic solution is mainly composed of LiPF ₆ and contains 0.5 to 5% by weight of vinylene carbonate or vinyl acetate with respect to the total weight of the solvent.

1 8. The lithium ion secondary battery according to any one of 1 1 to 14, wherein the nonwoven fabric is a nonwoven fabric mainly composed of a metaaromatic polyamide.

1 9. The lithium ion secondary battery according to any one of 1 1 to 18, wherein the metaaromatic polyamide is polymetaphenylene diisophthalamide. Brief Description of Drawings

Figure 1 shows the results of the overcharge test. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described.

[Separator]

The separator for a lithium ion secondary battery of the present invention is characterized in that a porous layer mainly made of a metaaromatic polyamide is formed on both the front and back surfaces of a nonwoven fabric. By using a nonwoven fabric, the strength and dimensional stability of the porous membrane made of aromatic polyamide can be improved, and the handling property and productivity can be improved.

Here, the porous layer mainly made of meta-aromatic polyamide is formed on the front and back surfaces of the nonwoven fabric. When the front and back surfaces of the separator are observed, the entire front and back surfaces are covered with the porous layer made of aromatic polyamide. The fibers that make up the nonwoven fabric are not visible. This can be easily observed with a scanning electron microscope (SEM). In a separator in which the fibers constituting the nonwoven fabric are exposed on one or both of the front and back surfaces, the bonding interface between the electrode and the separator becomes non-uniform, causing a problem in battery performance. This is due to insufficient electrolyte retention at the electrode Z separator interface, and as the cycle progresses, the electrolyte present at the electrode separator interface is depleted, causing cycle characteristics and cycle discharge characteristics. Becomes defective.

In the separator of the present invention, the layer formed on the surface of the nonwoven fabric is a porous layer made of metaaromatic polyamide. In the porous layer, it is necessary that pores are continuously formed, and the structure of this porous layer can be determined by using a galley value (JIS P81 17) as an index. The Gurley value of the seno << lator of the present invention is preferably 10 to 50 seconds. If the Gurley value is lower than 10 seconds Z1 00 cc, it is not preferable because there is a high probability that there will be a defect part where the re-pin hole where the nonwoven fabric forming fibers are exposed. On the other hand, if it is larger than 50 seconds Z 1 OOcc, the ion permeability is not sufficient, and the rate characteristics are deteriorated. Furthermore, it becomes difficult to obtain the overcharge prevention function described in the specification of WO01 Z067536, which is not preferable from the viewpoint of ensuring safety during overcharge.

In the separator of the present invention, the film thickness is preferably 15 to 40 Um. If the film thickness is less than 1 5, the function of preventing the short circuit inherent to the separator will be insufficient. Also thicker than 40 m If this is the case, there will be problems such as insufficient relay characteristics with high resistance due to ionic conduction, and insufficient battery energy density.

In order to realize the separator thickness as described above, the thickness of the nonwoven fabric is 10 to 39 mm, and the thickness of the porous layer made of the metaaromatic polyamide is about 1 to 10 mm in total. preferable. The substantial strength of the separator of the present invention is determined by the nonwoven fabric <<, if the nonwoven fabric thickness force is less than 10 // m, it is difficult to ensure sufficient strength as a lithium ion battery separator. On the other hand, if it is thicker than 39 im, it is difficult to make the separator thickness 40 m or less. Moreover, if the thickness of the porous layer is less than 1 m in total, it is difficult to substantially cover the entire surface of the nonwoven fabric. The porous layer is not preferable from the viewpoint of ensuring sufficient discharge performance when the ion conduction resistance of the separator is generally rate-determined and becomes thicker.

The non-woven fabric used in the separator of the present invention is preferably as fine as possible, and the fiber diameter is preferably fine in order to obtain such a non-woven fabric. From such a viewpoint, the fiber diameter of the fibers constituting the nonwoven fabric is preferably 10 m or less, and more preferably 5 m or less.

When forming a non-woven fabric, a binder for binding the main fibers to the main fibers is required. The binder for forming the nonwoven fabric is preferably fiber or pulp.

A known method can be applied to the method for producing the nonwoven fabric. Specific examples include a dry method, a water needle method, a wet papermaking method, a spunbond method, a melt blow method, and an electrospinning method. The wet papermaking method is particularly suitable in view of the thinning and uniformity of the openings.

The material constituting the nonwoven fabric is not particularly limited as long as it has sufficient heat resistance and resistance to an electrolytic solution, and specifically, polyester, aromatic polyamide, polysulfone, represented by polyethylene terephthalate (PET), Examples include polyethersulfone, polyph: i: dilensulfide, polyimide and the like. In particular, PET is preferable from the viewpoint of facilitating molding of finer fibers and high heat resistance. Also, from the viewpoint of high strength and high heat resistance, aromatic polyamid In particular, from the viewpoint of moldability, polymetaphenylene sophthalamide is preferred. Even if polyolefin fibers such as polyethylene and polypropylene are mixed within the range in which the heat resistance of the nonwoven fabric is not impaired in the nonwoven fabric, there is a case where safety is improved by adding a small amount of these materials. In this case, the amount of polyolefin fiber added is preferably 30% by weight or less based on the weight of the nonwoven fabric.

In particular, from the viewpoint of thin film and high strength, non-woven fabric using short fibers made of meta-aromatic polyamide and para-aromatic polyamide pulp is preferable. The nonwoven fabric can be combined with a metaaromatic polyamide that forms a porous layer and has a high affinity to obtain a high strength. Moreover, the nonwoven fabric of said structure is easy to make thin film.

In the separator of the present invention, the material for forming the porous layer is preferably metaaromatic polyamide. Aromatic polyamides include para-aromatic polyamides typified by polyparaphenylene terephthalamide and meta-aromatic polyamides typified by polymeta-phenylene isophthalamide. Isophthalamide is preferred. Since the para-aromatic polyamide has low solubility in a solvent and high viscosity even at a low concentration, it is very difficult to form the porous layer with sufficient strength and ion permeability. Specifically, only small pores are formed, and these are discontinuous, resulting in insufficient ion permeability. On the other hand, the metaaromatic polyamide is sufficiently dissolved in the solvent, and it is easy to prepare an appropriate polymer solution in terms of concentration and viscosity. Further, the pore diameter can be easily controlled and sufficient ion permeability can be ensured. In particular, in order to develop the overcharge prevention function of WO01 No. 06 7536, it is necessary to appropriately control the pore diameter of the porous layer. From the viewpoint of adding such a function, the metaaromatic polyamide is a paraffin. It is more suitable than aromatic polyamide.

The material for forming the porous layer is preferably a metaaromatic polyamide. Other materials are mixed in a category that does not impair the heat resistance and the structural control of the porous layer, which are the characteristics of a metaaromatic polyamide. It does n’t matter. Specifically, para aromatic polyamide, polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinylidene fluoride copolymer, polyacrylo Nido J, polymethyl methacrylate include polyethylene oxide, polypropylene oxide, polyvinyl pyrrolidone, etc. These components are preferably 30% by weight or less based on the meta-aromatic polyamide forming the porous layer. is there.

When PET is used for the nonwoven fabric, the weight of the metaaromatic polyamide forming the porous layer is preferably 4 to 10 gZm ² . When PET is used as a separator material for lithium ion secondary batteries, there is a problem with durability in special environments, but this durability can be remarkably improved by compounding with metaaromatic polyamide. it can. When the weight of the metaaromatic polyamide is less than 4 gZm ² , the durability is not improved sufficiently, which is not preferable. If the weight is greater than 1 Og Zm ^{2, the} problem of deteriorating ion permeability occurs.

When the metaaromatic polyamide in the present invention is dissolved in N-methyl-1-pyrrolidone, it is represented by the logarithmic viscosity of the following formula (1): 0.8 to 2.5 dlZg, preferably 1.0 to A polymer in the range of 2, 2 dlZ g is preferred. When the logarithmic viscosity is lower than 0.8 dlZg, sufficient mechanical strength cannot be obtained, and when the logarithmic viscosity exceeds 2.5 dlZg, it becomes difficult to obtain a stable polymer solution, which is preferable for forming a uniform porous layer. Absent.

Logarithmic viscosity (unit: dlZg) = ln (TZTO) ZC (1)

T: Flow time of capillary viscometer at 30 ° C in a solution of 0.5 g of metaaromatic polyamide dissolved in 100 ml of N-methizole 2-pyrrolidone

TO: N-methyl-2-pyrrolidone flow time at 30 ° C in capillary viscometer

C: Polymer concentration in polymer solution (gZdl)

In the separator of the present invention, one having a surfactant attached to the porous layer is also preferable from the viewpoint of antistatic. The surfactant is not particularly limited, and for example, a cationic, anionic, zwitterionic or nonionic surfactant can be used. Examples of cationic surfactants include higher amine halogenates, halogenated alkyl pyridines, and quaternary ammonium salts. Examples of anionic surfactants include higher fatty acid alkali salts, polyoxyethylene alkyl ether sulfonate esters, polyoxyethylene alkyl ether phosphonates, alkyl sulfates, alkyls. Examples include sulfonates, alkylaryl sulfonates, and sulfosuccinate esters. Examples of zwitterionic surfactants include alkylbetaine compounds, imidazoline compounds, alkylamine oxides, and bisoxyborate compounds. Nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl aryl ethers.

—Tells, glycerin fatty acid esters, polyoxyethylene sorbitan fatty acid esters, sorbitan fatty acid esters and the like.

In particular, cationic surfactants, anionic surfactants, and zwitterionic surfactants have a strong antistatic effect, so that the amount used can be kept low and it is desirable to use them. Also, by mixing these, the affinity between the aromatic amide and the surfactant can be increased, and the antistatic effect can be improved.

The amount of the surfactant is desirably 0.005 to 0.750 Zm ² . Sufficient antistatic effect is less than 0. 005gZ m ² can not be obtained, which may adversely affect the performance of the battery is more than 0. 750 g Roh m ^2. The amount of the surfactant was determined after the surfactant was applied and vacuum-dried at 90 ° C for 10 hours and then immersed in a surfactant-soluble solvent.

Analyze the mass difference of battery separators vacuum-dried at 0 ° C for 10 hours or extract components obtained by drying a solution extracted with a surfactant-soluble solvent by H-NMR or gas chromatography to measure mass. You can ask for it.

As a method for evaluating static electricity, the frictional voltage measurement method of JIS L 1 084 is used. It is preferable that the half-life of static electricity is 30 seconds or less by the frictional voltage measurement method. If the half-life is 30 seconds or more, the antistatic effect is not sufficient because the decay of static electricity is slow.

[Separator manufacturing method]

The separator for a lithium ion secondary battery of the present invention can be produced by various methods, and is not limited by the production method. For example, a method of pressing a meta-aromatic polyamide porous film on both sides of a nonwoven fabric by press working, and a method using a meta-aromatic polyamide on both surfaces of a nonwoven fabric. For example, there is a method in which a polymer solution is applied and the coating layer is subjected to microphase separation by any one of a dry method, a dry wet method, and a wet method.

In particular, a polymer solution mainly composed of a metaaromatic polyamide and a solvent that is a good solvent for the metaaromatic polyamide is applied to both front and back surfaces of the cloth, and then the coated non-woven fabric is applied to the metaaromatic polyamide. A production method (wet microphase separation method) in which the mixture is coagulated in a mixed liquid (coagulating liquid) mainly composed of a solvent that is a poor solvent and a solvent that is a good solvent, then washed with water and dried (wet microphase separation method) is preferable. By adopting this production method, the structural control of the porous layer of the metaaromatic polyamide porous layer becomes easy. Moreover, it is possible to manufacture a high-quality separator by eliminating the exposure of the non-woven fabric constituting fiber due to poor impregnation of the polymer solution by coating on both the front and back surfaces.

Specifically, the manufacturing apparatus and concept described in Patent Document 6 can be applied to the above manufacturing method. Specifically, as a coating method in which a polymer solution is applied to both the front and back surfaces of a nonwoven fabric, an excess polymer solution is supplied from both sides of the nonwoven fabric, and the nonwoven fabric is placed between a pair of opposed Meyer bars and dies. There is a method to measure by passing, and further, the porous layer solidified by immersing the nonwoven fabric coated with this polymer solution in the coagulation liquid so that both front and back surfaces are in contact with the coagulation liquid Molded on both sides.

In the production method, an amide solvent is suitable as the good solvent, and for example, dimethylacetamide, N-methyl-2-pyrrolidone and the like are preferable. Specific examples of the poor solvent include alcohols and water, and water is particularly preferable.

The polymer concentration of the polymer solution is largely determined depending on the type and degree of polymerization of the metaaromatic polyamide used. However, for example, when using polymetaphenylene isophthalamide, it is 5 to 20 weights. % Range is preferred.

When the polymer concentration is low, a separator with particularly excellent ion permeability can be obtained. However, since the viscosity of the high molecular solution is low, the productivity is not sufficient from the viewpoint of pinholes when applied to a nonwoven fabric. In order to obtain a polymer solution with particularly high ion permeability by reducing the polymer concentration, it is preferable to add ceramic fine particles to the polymer solution. It is. The addition of the ceramic fine particles increases the viscosity of the polymer solution, so that it can be easily applied to the nonwoven fabric even at a low polymer concentration.

Specific examples of the ceramic fine particles include silica, alumina, zirconia, magnesia, titanium; a, barium titanate, aluminum nitride, calcium oxide, calcium carbonate, lithium fluoride, lithium oxide, and the like. In particular, alumina, zirconia, and magnesia are suitable.

The average particle size of the ceramic fine particles is preferably 0.05 to 2 m, particularly preferably in the range of 0. "! To 1 mm. From the viewpoint of aggregation and the like, when the ceramic fine particles are 0.05 m or less, the handling property is good. In addition, when the length is 2 m or more, die streaks are more likely to occur during coating, and it is preferable. <No. Here, the average particle size can be measured by the laser diffraction measurement method. The average particle size in the present invention is the average particle size of primary particles.

The amount of the ceramic fine particles to be added is suitably determined in view of the polymer concentration of the polymer solution, but is generally a metaaromatic polyamide that forms the porous material (if other organic polymers are included, this is not the case). 30 to 80% by weight with respect to the weight of the ceramic fine particles. If the amount of ceramic fine particles is less than 30% by weight, a sufficient thickening effect cannot be obtained and the effect is insufficient. Also, if the amount of ceramic fine particles is larger than 80% by weight, problems such as powder falling off when molding the separator are not preferable.

The effect of addition of ceramic fine particles in this production method is particularly suitable when the polymer concentration in the polymer solution is 10% by weight or less.

In addition, the effect of adding ceramic fine particles is not limited to the effect of the above manufacturing method, but also has structural features as described below. Ceramic fine particles generally have higher heat resistance than metaaromatic polyamides, and even when the battery temperature rises to around 400 ° C where the metaaromatic polyamide thermally decomposes, the ceramic fine particles function as a separator. Furthermore, the ceramic fine particles also function as a lubricant and contribute to an antistatic effect or improved handling when static electricity is generated. A phase separation agent may be added to the polymer solution for the purpose of controlling the porous structure. The phase separation agent is a poor solvent for the metaaromatic polyamide and can be used as long as it is compatible with the coagulation liquid. Specifically, water and alcohols are suitable, and in particular, propylene glycol, ethylene glycol, diethylene glycol, tripropylene glycol, 1,3-butanediol, 1,4-butanediol, polyethylene glycol mono, including polymerization holiday. Polyhydric alcohols such as ethyl ether, methanol, ethanol and glycerin are preferably selected. The concentration of the phase separation agent in the polymer solution is suitably selected in the range of 0 to 40% by weight with respect to the mixture of the good solvent and the phase separation agent.

The coagulation liquid is preferably a mixed liquid of the aforementioned good solvent and poor solvent. Here, when the phase separation agent is applied to the polymer solution, it is preferable in terms of process management to mix the phase separation agent into the coagulation liquid at an appropriate ratio. Specifically, it is preferable that the ratio of the coagulating liquid matches the ratio of the good solvent and the phase separating agent in the polymer solution.

The ratio of the poor solvent in the coagulation bath is suitably selected from the range of 10 to 80% by weight when water is applied to the poor solvent.

The nonwoven fabric on which the solidified porous layer is formed is then transferred to a water washing step, and then the water is dried in the drying step to obtain the separator of the present invention. Here, as the drying step, a method of drying by contacting with a heating roll is preferably selected.

In the production method of the separator of the present invention, when the surfactant is adhered, the method is not particularly limited, but the surfactant is dissolved in a solvent, sprayed onto the porous film and dried, or the porous film is immersed. The method of drying etc. are mentioned.

[Lithium ion secondary battery]

In general, a lithium ion secondary battery has a structure in which a battery element in which a positive electrode and a negative electrode are opposed to each other with a separator interposed therebetween is impregnated with an electrolytic solution and sealed in an exterior. The lithium ion secondary battery of the present invention is characterized by the use of the separator of the present invention described above, and a known technique can be applied to other components, which are essentially limited to other components. It is not something. A negative electrode is generally used in which a layer formed from a negative electrode active material, a binder, and a conductive additive is coated on a current collector. This is prepared by adding a solvent to a negative electrode active material, a binder, and a conductive additive to knead to prepare a slurry, which is applied onto a current collector and dried and pressed. When the total weight of the negative electrode active material, the binder, and the conductive additive is 100%, the negative electrode active material is 80 to 98% by weight, the binder is 2 to 20% by weight, and the conductive auxiliary is 0 to 10% by weight. The range of is preferable. Examples of the negative electrode active material include carbon materials, silicon, and tin. Examples of the carbon material include those obtained by using, as a precursor, pitches that are easily graphitized, such as mesocarbon microbeads and microcarbon fibers, and those that are difficult to graphitize, such as phenol resin. Examples of the binder include polyvinylidene fluoride and carboxymethylcellulose. As the conductive aid, graphite powder, acetylene black, ketjen black, vapor grown carbon fiber, and the like are preferably used. The current collector is preferably copper foil, stainless steel, or the like.

As in the case of the negative electrode, a positive electrode in which a layer formed of a positive electrode active material, a binder, and a conductive additive is coated on a current collector is generally used. This is prepared by adding a solvent to a positive electrode active material, a binder, and a conductive aid, kneading to prepare a slurry, applying the slurry onto a current collector, and drying and pressing. When the total weight of the positive electrode active material, the binder, and the conductive additive is 100%, the positive electrode active material is 80 to 98% by weight, the binder is 2 to 20% by weight, and the conductive auxiliary is 0 to 10%. A range of weight percent is preferred. Examples of the positive electrode active material include LiCo0 ₂ , LiNi 0 ₂ , spinel type LiMn ₂ 0 ₄ , olivine type LiFeP0 _{4, and the} like, and those in which different elements are dissolved, and these may be used in combination. . As the binder, polyvinylidene fluoride is preferably used. As the conductive additive, graphite powder, acetylene black, ketjen black, vapor growth power, one-bon fiber, etc. are preferably used. For the current collector, aluminum foil, stainless steel or the like is suitable.

As the electrolytic solution, a non-aqueous electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent is used. As the lithium salt, LiPF ₆ , LiBF _4. , LiCI 0 _{4 and the} like are preferably used. Non-aqueous solvents are propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), Examples include jetyl carbonate (DEC) and ethyl methyl carbonate (EMC). These lithium salts and non-aqueous solvents may be used alone or in combination of two or more. The concentration of the lithium salt is preferably in the range of 0.5 to 2. OM. In addition, it is preferable to add vinylene carbonate (VC) or vinyl acetate (VA) to the electrolyte from the viewpoint of durability.

In the lithium ion secondary battery of the present invention, the battery element composed of the positive electrode, the negative electrode, and the separator is wound into a cylindrical or flat shape or a laminated structure and enclosed in an exterior. From the viewpoint of satisfactorily expressing the overcharge prevention function, it is preferable to have a folded structure, and it is particularly preferable to have a wound flat structure.

The exterior can be implemented in any form such as a metal case or an aluminum laminated film case.

【Example】

Hereinafter, the present invention will be described in detail by way of examples. However, the present invention is not limited to the following examples.

[Example 1]

PET staple fibers with a fineness of 0.2 "M dtex (average fiber diameter approx. 3.2 m) and PET short fibers with a fineness of 0.33 dtex (average fiber diameter approx. 5.5 m), and fineness of 0.22 dtex (average fiber diameter approx. 4. 5mm m) binder PET short fiber was blended at a weight ratio of 3Z2Z5, and weighed by wet papermaking method 1 2. 6 gZm ² was formed, 1 40 ° C was calendered, film thickness 1 An 8 mm PET non-woven fabric was obtained.

Polymetaphenylene isophthalamide (manufactured by Teijin Techno Products Ltd .; trade name Γ Cornex)) is 9% by weight in a mixed solvent of dimethylacetamide: tripropylene glycol = 85: 1 5 (weight ratio). And the polymer solution was prepared. This polymer solution was coated on both sides of the PET nonwoven fabric, and the coated material was solidified by immersing in a 30 ° C coagulation bath with a composition of dimethylacetamide: water = 55:45 (weight ratio) for 60 seconds. A membrane was obtained. This solidified film is washed with water in a 50 ° C. water bath for 10 minutes, and then dried to obtain the lithium ion of the present invention. A separator for a secondary battery was obtained. This is the separator 1 of the present invention. The separator 1 of the present invention had a film thickness of 21 mm, a basis weight of 14.7 gZm ² and a galley value (JIS P8117) of 23 seconds Z1 OOcc.

As a result of observing the front and back surfaces of this sample with a scanning electron microscope (SEM), exposure of fibers constituting the nonwoven fabric was not observed.

[Example 2]

Using polymetaphenylene isophthalamide short fibers with a fineness of 0.9dtex (average fiber diameter of about 10 m), weighed by dry method with a basis weight of 15. OgZm ² and calendered at 320 ° C. A 30 mm non-woven fabric was obtained.

Using the nonwoven fabric, a polymer solution was used in the same manner as in Example 1, and the lithium ion secondary battery separator of the present invention was obtained in the same manner. This is the separator 2 of the present invention. The present invention snorator 2 had a film thickness, a basis weight of 18.1 gZm ² and a Gurley value (JIS P8117) of 35 seconds Z1 OOcc.

[Comparative Example 1]

A nonwoven fabric similar to that in Example 1 was fixed on a PET film, and the polymer solution used in Example 1 was coated thereon. The film was immersed in the same coagulation liquid as in Example 1 to obtain a coagulated film. This coagulated film was washed with water in a 50 ° C. water bath for 10 minutes and then dried. Thereafter, the PET film was peeled off to obtain comparative separator 1. The comparative separator 1 has a film thickness of 20 mm, a basis weight of 13.9 gm ² , and a galley value (JIS P8117) 15¾Z100ccT fc "Dfc.

As a result of observing the front and back surfaces of this sample with a scanning electron microscope (SEM), exposure of fibers constituting the nonwoven fabric was significantly observed on the side that was in contact with the PET film.

[Comparative Example 2]

Blends PET short fibers with a fineness of 0.33dtex (average fiber diameter 5.5 / m) and PET fibers for binder with a fineness of 0.22dtex (average fiber diameter 4.5; Um) at a weight ratio of 6Z4, and has a basis weight of 12.OgZm ^The film was prepared in 2 and calendered at 200 ° C. to obtain a PET non-woven fabric having a thickness of 18 mm. Polyvinylidene fluoride copolymer: vinylidene fluoride: hexafluoropropylene: black trifluoroethylene = 95.5: 2.3: 2.2 (weight ratio), dimethylacetamide: tripropylene glycol = 70 The polymer solution was prepared by dissolving in a mixed solvent of 30 (weight ratio) to 12% by weight.

This polymer solution was coated on both sides of the PET nonwoven fabric, and the coated material was immersed in a coagulation bath of 30 ° C having a composition of dimethylacetamide: water = 55: 45 (weight ratio) for 60 seconds. A coagulated film was obtained. This coagulated film was washed with water in a 50 ° C. water bath for 10 minutes and then dried to obtain Comparative Separator 2. Comparative separator 2 has a film thickness 24〃 m, basis weight 1 7. 3GZm ^2, Gurley value (JI S P81 1 7) 1 2 seconds, 1 00 (^ Deatta.

[Heat resistance evaluation 1]

Each of the above separators 1 and 2 of the present invention, comparative separators 1 and 2, and a microporous membrane made of polypropylene that is a separator for commercially available lithium ion secondary batteries (manufactured by Celgard; trade name “Celguard # 2400”) is 1 Ocm each. Cut into X 1 Ocm. The electrolyte was placed in a 70cc sample bottle. Here, 1 M LiBF ₄ PCZEC (1 Z1 weight ratio) was used as the electrolyte. The cut separator was placed in the sample bottle and treated at 150 ° C. for 2 hours. Then, the separator was taken out from the sample bottle and the separator was observed. The results are shown in Table 1.

[Heat resistance evaluation 2]

Each of the above separators 1 and 2 of the present invention, comparative separators 1 and 2, and a microporous membrane made of polypropylene that is a separator for commercially available lithium ion secondary batteries (manufactured by Celgard; trade name “Celguard # 2400”) is 1 Ocm each. Cut into x 1 Ocm. This was fixed to a frame that could be fixed in four directions and heat-treated at 200 ° C for 30 minutes. The form and dimensions after heat treatment were measured. The results are shown in Table 1.

[Example 3]

Lithium cobaltate (LiCoO ₂ ; manufactured by Nippon Chemical Industry Co., Ltd.) powder 89.5 parts by weight, acetylene black 4.5 parts by weight, polyfluoride (using N-methyl-2-pyrrolidone solvent to be 6 parts by weight of bilidene) These were kneaded to prepare a slurry, and the resulting slurry had a thickness of 20 It was coated on a μm aluminum foil, dried and pressed to obtain a 100 μm positive electrode.

These are kneaded using N-methyl-2pyrrolidone solvent to 87 parts by weight of Mesophase Microbon beads (MCMB: Osaka Gas Chemical Co., Ltd.), 3 parts by weight of acetylene black, and 10 parts by weight of polyvinylidene fluoride. Thus, a slurry was prepared. The obtained slurry was applied onto a copper foil having a thickness of << 18 m, dried and pressed to obtain a 90 m negative electrode.

The positive electrode and the negative electrode were opposed to each other through the separator 1 of the present invention produced in Example 1. This was impregnated with an electrolytic solution and sealed in an outer package made of an aluminum laminate film to produce a lithium ion secondary battery of the present invention. Here, 1 M LiPF ₆ EC / EMC C3 Z7 weight ratio) was used as the electrolyte. This battery is referred to as “the battery of the present invention”!

[Comparative Example 3]

A lithium ion secondary battery was produced in the same manner as in Example 1 using Comparative Separator 1 as the separator. This lithium ion secondary battery is referred to as comparative battery 1.

[Comparative Example 4]

A lithium ion secondary battery was prepared in the same manner as in Example 1 using a polypropylene microporous membrane (Celgard; trade name “Celguard # 2400”), which is a commercially available lithium ion secondary battery separator. did. The secondary battery is referred to as Comparative Battery 2 for this lithium ion.

[Cycle test]

Inventive battery 1 and comparative batteries 1 and 2 were subjected to 100 cycles of 1 C, 4.2 V, constant current and constant voltage charging for 2 hours, and 1 C, 2.75 V constant current discharge. For each battery, (capacity maintenance ratio) = (discharge capacity at the 100th cycle) / (discharge capacity at the first cycle) was obtained. This is shown in Table 2. Only the comparative battery 1 using the comparative separator 1 in which the nonwoven fabric was exposed was significantly poor in cycle characteristics, and the inventive battery 1 using the separator 1 of the present invention coated on both sides is equivalent to a commercial separator. It is a characteristic.

[Overcharge test]

Inventive battery 1 and comparative battery 2 Constant current charging at 1 C for 10 hours (for original charging) On the other hand, an overcharge test in which 10 times the charge was performed was conducted. However, when the voltage reached 6V, the power reception was forcibly terminated. The overcharge characteristics were considered insufficient when charging was forcibly terminated 10 hours after the voltage reached 6V, and the overcharge characteristics were sufficient when it was not. The results of the overcharge test shown in FIG. 1 << the power of the present invention battery 1 using the separator of the present invention 1 is sufficient for overcharge characteristics <<, the comparative battery 2 using a commercially available separator is insufficient .

[Example 4]

Emargen 120 (manufactured by Kao; nonionic surfactant) was dissolved in methanol to prepare a 1% by weight solution. The separator 1 of the present invention produced in Example 1 was immersed in the surfactant methanol solution and dried to attach the surfactant to obtain the separator 3 of the present invention. Here, the amount of the surfactant adhering to the separator 3 of the present invention was 0.15 _g Zm ² .

[Example 5]

Electro stripper AC (made by Kao; amphoteric surfactant) was dissolved in methanol to prepare a 1% by weight solution. The separator 1 of the present invention produced in Example 1 was immersed in the surfactant methanol solution and dried to attach the surfactant, whereby the separator 4 of the present invention was obtained. Here, the amount of the surfactant attached to the separator 4 of the present invention was 0.02 gZm ² .

[Example 6]

Cotamine 60W (manufactured by Kao; cationic surfactant) was dissolved in methanol to prepare a 1% by weight solution. The separator 1 of the present invention produced in Example 1 was immersed in the surfactant methanol solution and dried to attach the surfactant, whereby a separator 5 of the present invention was obtained. Here, the amount of the surfactant adhered to the separator 5 of the present invention was 0.04 gZm ² .

[Example 7]

Electrosdritzba F (manufactured by Kao; anionic surfactant) was dissolved in methanol to prepare a 1 wt% solution. The separator 1 of the present invention prepared in Example 1 was immersed in the surfactant methanol solution and dried: Z was attached to the surfactant to obtain the separator 6 of the present invention. Here, the amount of the surfactant adhering to the separator 6 of the present invention is 0.10 gZm ² . [Measurement of charged voltage]

The charged voltage half-lives of the separators 1 and 3 to 6 of the present invention were measured using a static phone meter H-0110 (manufactured by Sisid electrostatic). The results are shown in Table 3. From Table 3, it can be seen that attaching a surfactant is effective in preventing static charge.

[Example 8]

Polymetaphenylene isophthalamide short fiber with a fineness of 0.9 dtex (average fiber diameter of about 10 jum) is used as the main fiber, pulp made of paraamide is used as the binder, and these are mixed in the main fiber binder (weight ratio). A wet papermaking method was used to form a film with a basis weight of 29.9 gZm ² and calendering to obtain an aramid nonwoven fabric (aramide paper) with a film thickness of 30 jw m. Polymetaphenylene isophthalamide (manufactured by Teijin Techno Products Co., Ltd .; trade name “Konex J”) is 9% by weight in a mixed solvent of dimethylacetamide: tripropylene glycol = 85: 1 5 (weight ratio) The polymer solution was coated on both sides of the aramid nonwoven fabric, and the coated product had a composition of dimethylacetamide: water = 60: 40 (weight ratio). The solidified film was immersed in a solidified bath at 40 ° C. for 60 seconds to obtain a solidified film, which was washed with water in a 30 ° C. water bath for 10 minutes and then dried to obtain the separator for the lithium ion secondary battery of the present invention. This was designated as the present separator 7. The present separator 7 had a film thickness of 39 m, a basis weight of 34.5 gZm ² , and a Gurley value (JIS P81 17) of 40 seconds Z1 OOcc. The weight of the porous layer made of isophthalamide is 4.6 gZ It was m ^2.

[Example 9]

PET short fibers with fineness of 0.1 1 dtex (average fiber defect 3.2 jum) and PET short fibers with fineness 0.33 dtex (average fiber diameter approx. 5.5 m), and fineness 0.22 dtex (average fiber diameter) About 4.5 ^ m) binder short PET fiber for 3Z2Z5 weight ratio, wet paper-making method to fabricate 1 3. OgZm ² film, calendered, 18 im thick PET A nonwoven was obtained. Using the PET nonwoven fabric, a separator for a lithium ion secondary battery of the present invention was obtained in the same manner as in Example 8. This is designated as separator 8 of the present invention. The separator 8 of the present invention had a film thickness of 29 ^ m, a basis weight of 18.3 gZm ² , and a gauge value (JIS P8 "7) of 28 seconds Z1 OOcc. A porous layer made of polymetaphenylene isophthalamide of weight was filed in the 5. 3gZm ^2.

[Example 1 ^]

In the same manner as in Example 9, the coating clearance was changed, the film thickness was 37 m, the basis weight was 22.1 g / m ² , and the galley value (JIS P81 1 7) was 32 seconds / 1 OOcc. 9 In addition, poly-polyethylene isophthalamide made of many? Weight of the L protein layer 9. 1 gZm ² der ivy.

[Example 1 1]

In the same manner as in Example 9, the coating clearance was changed, the film thickness was 22 m, the basis weight was 16.3 gZm ² , the Gurley value (JIS P81 1 7) was 32 seconds Z1 OOcc. The weight of the porous layer made of polymetaphenylene isophthalamide was 3.3 gZm ² .

[Example 1 2]

In the same manner as in Example 9, the coating clearance was changed, the film thickness was 24 mm, the basis weight was 17.3 gZm ² , the Gurley value (JIS P81 1 7) 32 seconds Z1 OOcc of the present invention separator 1 1 In addition, the weight of the porous layer made of polymetaphenylene isophthalamide was 4.3 gZm ² .

[Puncture strength measurement]

The puncture strength of the present separators 2, 7 to 11 was measured. The puncture strength was measured by setting a separator on a fixed frame of 11.3ΓΠΓΤΙΦ, pushing a needle with a tip radius of 0.5mm vertically into the center of the separator, and pushing the needle at a constant speed of 2mmZ seconds. The maximum load applied to the separator while moving the needle force << 5 mm was defined as the puncture strength. The results are shown in Table 4. When aramid materials are used as the nonwoven material, before and after coating The increase in puncture strength is large. Nonwoven fabric made of aramid material is effective in terms of obtaining a high-strength separator because it has a high affinity for polymetaphenylene isophthalamide forming the porous layer and provides a high reinforcing effect.

[Example 1 3 ~ "! 6]

The present invention batteries 2 to 5 were obtained in the same manner as in Example 3 using the separators 8 to 11 of the present invention obtained in Examples 9 to 12.

[Example 1 7-20]

This invention is the same as Example 3 except that the separators 8 to 11 of the present invention obtained in Examples 9 to 12 were used and 1 M LiPF ₆ ECZEMCZVC (29Z70Z1 weight ratio) was used as the electrolyte. Batteries 6-9 were obtained.

[Examples 21 to 24]

This invention is the same as Example 3 except that the separators 8-11 of the present invention obtained in Examples 9-12 are used and 1 M LiPF ₆ ECZEMCZVA (29Z70Z1 weight ratio) is used as the electrolyte. Batteries 10 0-13 were obtained.

[Comparative Example 5]

A battery was produced in the same manner as in Example 3 except that the PET nonwoven fabric produced in Example 9 was used as the separator. This battery is referred to as comparative battery 3.

[Battery durability evaluation]

Example 1 The inventive batteries 2 to 13 and the comparative battery 3 prepared in 3 to 24 were charged to 4.2 V and stored at 80 ° C. for 4 days. Thereafter, the battery was disassembled and the separator inside was taken out and observed. The results are shown in Table 5. Table 5 shows that when the amount of polymetaphenylene isophthalamide applied is appropriate, PET deterioration is sufficiently suppressed. It can also be seen that adding VC or VA to the electrolyte is effective in preventing this PET deterioration.

[Example 25]

PET short fibers with fineness of 0.1 1 dtex (average fiber diameter of about 3.2 m) and fineness of 0.33 dtex (average Wet paper making by blending PET short fibers with a fiber diameter of about 5.5 mm and PET short fibers for binder with a fineness of 0.22 dtex (average fiber diameter of about 4.5 mm) at a weight ratio of 3 2 to 5 According to the method, a fabric weight of 12.6 gZm ² was formed and calendered at 140 ° C to obtain a PET nonwoven fabric with a film thickness of 18 Um.

Polymetaphenylene isophthalamide (manufactured by Teijin Techno Products Co., Ltd .; trade name “Konex”) in a mixed solvent of dimethylacetamide: tripropylene glycol = 60: 30 (weight ratio) to be 6% by weight And the polymer solution was prepared. In this polymer solution, one alumina fine particle (SA-1 manufactured by Iwatani Chemical Industry Co., Ltd.) having an average particle size of 0.8 m was dispersed in the same weight part as poly (meta-phenylene isophthalamide) to prepare a coating slurry. This coating slurry was applied to both sides of the PET nonwoven fabric, and this coating was applied to a 40 ° C. coagulation bath having a composition of dimethylacetamide: water = 50 ′: 50 (weight ratio) for 60 seconds. A pulverized solidified film was obtained. This solidified film was washed with water in a 50 ° C. water bath for 10 minutes and then dried to obtain a separator for a lithium ion secondary battery of the present invention. This is designated as separator 1 of the present invention. The separator 1 of the present invention had a film thickness of 23 μm, a mesh size of 6.6 gZm ² , and a straight line (JIS Ρ81 1 7) for 20 seconds and 100 cc. As a result of visual observation of the separator 12 of the present invention, no pinhole was observed.

[Reference Example 1]

Polymetaph I diene isophthalamide (manufactured by Teijin Techno Products Co., Ltd .; trade name Γ Kohinex) is 6% by weight in a mixed solvent of dimethylacetamide: tripropylene glycol = 60:30 (weight ratio) Thus, a polymer solution was prepared.

This polymer solution was applied to both sides of the PET nonwoven fabric obtained in Example 25, and this coated product was coagulated at 40 ° C. having a composition of dimethylacetamide: water = 50: 50 (weight ratio). For 60 seconds to obtain a coagulated film. The solidified film was washed with water in a 50 ° C. water bath for 10 minutes, and then dried, so that the force and pinholes produced the separator of the present invention were frequently generated, and a sufficient product could not be obtained.

[Reference Example 2] The separator of the present invention was produced in the same manner as in Example 25 except that the amount of a-alumina fine particles was 10% by weight with respect to polymetaphenylene isophthalamide, but sufficient pinholes were generated and a sufficient product could be obtained. There wasn't.

[Reference Example 3]

a—Alumina fine particles lacked in the force coagulation / water washing process in which the separator of the present invention was produced in the same manner as in Example 25 except that the amount of fine alumina particles was 900% by weight with respect to polymetaphenylene isophthalamide. A separator with sufficient handleability could not be obtained.

[Membrane resistance measurement]

A measurement cell was prepared by impregnating an electrolyte into a separator, sandwiching the electrode in a pair of aluminum foil (size: 2 cm × 1.4 cm = 2.8 cm ² ), and enclosing it in an aluminum laminated film. Here, 1 M LiBF ₄ PCZEC (1 Z1 weight ratio) was used as the electrolyte. For each cell, the resistance of one, two, and three separators was measured by the AC impedance method, and from the inclination when this resistance was plotted against the number of separators, one separator was measured. Resistance was sought. The AC impedance measurement was performed using the 4-terminal method, with an amplitude of 1 OmV and a frequency of 1 OOkHz. The measurement temperature was 20 ° C.

The above membrane resistance measurements performed on the present invention the separator 1 and 1 2, film resistors is 6. 026ohrrv cm ^2, 5. was 21 1 ohrrv cm ^2.

From the measurement results of the membrane resistance, it can be seen that it is effective to reduce the concentration of polymetaphenylene isophthalamide in the polymer solution. However, when coating using such a polymer solution, as shown in Reference Examples 1 and 2, the viscosity is too low, and pinholes frequently occur and it is difficult to obtain a sufficient one. As described in Example 25, this problem can be solved by appropriately adding ceramic fine particles. However, as shown in Reference Example 3, if too much ceramic fine particles are added, it becomes difficult to obtain a sufficient coating film due to the problem of powder falling. 【table 1】

[Table 2]

Separator Half-life Second Separator of the invention 1 1600 Separator of the invention 3 12 Separator of the invention 4 15 Separator of the invention 5 8 Separator of the invention 6 20 [Table 4]

Night C: 1 M IiPFe EC EMC / VA (29/70/1 Brnt) [Industrial applicability]

Since the separator for a lithium ion secondary battery of the present invention has high heat resistance and is effective for overcharge countermeasures, the use of this separator can improve the safety of the lithium ion secondary battery. The lithium ion secondary battery of the present invention with the separator of the present invention is suitable for HEV applications that require safety and performance at high temperatures.

Claims

The scope of the claims

1. A separator for a lithium ion secondary battery, characterized in that a porous layer mainly composed of a metaaromatic polyamide is formed on both the front and back surfaces of a nonwoven fabric.

2. Lithium ion secondary according to claim 1, characterized in that the film thickness of the separator << 15 to 40, galley value ("15 P81 17) force << 10 to 50 seconds Z1 OOcc Battery separator.

3. A surfactant containing at least one selected from the group consisting of a cationic surfactant, an anionic surfactant, an amphoteric surfactant and a nonionic surfactant is attached to the porous layer. The separator for a lithium ion secondary battery according to any one of claims 1 and 2.

4. The separator for a lithium ion secondary battery according to claim 3, wherein the adhesion amount of the surfactant is 0.005-0.750 _g Zm ² .

5. The separator for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the nonwoven fabric is a nonwoven fabric mainly composed of polyethylene terephthalate.

6. The separator for a lithium ion secondary battery according to claim 5, wherein the weight of the porous layer mainly composed of metaaromatic polyamide is 4 to 10 gZm ² .

7. The separator for a lithium ion secondary battery according to claim 1, wherein the nonwoven fabric is a nonwoven fabric mainly composed of a metaaromatic polyamide.

8. The separator for a lithium ion secondary battery according to any one of claims 1 to 4, characterized in that the nonwoven fabric is composed of a meta-aromatic polyamide short fiber and a para-aromatic polyamide pulp.

9. The separator for a lithium ion secondary battery according to any one of claims 1 to 6, wherein the metaaromatic polyamide is polymetaphenylene diisophthalamide.

1 0. includes a ceramic particulate average porous layer particle diameter 0.5 from 05 to 2 jw m, the ceramic particles is in the 30 to 80 weight ^_0/0 by weight of the porous layer Features The separator for a lithium ion secondary battery according to any one of claims 1 to 9.

1 1. A polymer solution mainly composed of a metaaromatic polyamide and a solvent that is a good solvent for the metaaromatic polyamide is applied to both the front and back surfaces of the nonwoven fabric, and then the coated nonwoven fabric is applied to the metaaromatic polyamide. In contrast, a method for producing a separator for a lithium ion secondary battery, comprising coagulating in a mixed liquid mainly composed of a solvent that is a poor solvent and a solvent that is a good solvent, and then washing and drying.

1 2. In a lithium ion secondary battery that has a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, and obtains an electromotive force by doping and detaching lithium ions, the separator is mainly meta-aromatic on both sides of the nonwoven fabric. A lithium ion secondary battery characterized in that a porous layer made of an aromatic polyamide is formed.

1 3. Thickness force of the separator << 15 to 40 〃m, galley value (JIS P81 1 7) force << 1 0 to 50 seconds Z 1 OOcc Lithium ion secondary battery.

1 4. A surfactant containing at least one selected from the group consisting of a cationic surfactant, an anionic surfactant, an amphoteric surfactant and a nonionic surfactant is attached to the porous layer. The lithium ion secondary battery according to any one of claims 12 and 13.

1 5. The separator for a lithium ion secondary battery according to claim 14, wherein the adhesion amount of the surfactant is 0.005-0.750 gZm ² .

1 6. The lithium ion secondary battery according to any one of claims 12 to 15, wherein the nonwoven fabric is a nonwoven fabric mainly made of polyethylene terephthalate.

1 7. The lithium ion secondary battery according to claim 16, wherein the weight of the porous layer mainly composed of metaaromatic polyamide is 4 to 1 OgZm ² .

1 8. The non-aqueous electrolyte is composed of an electrolyte and a solvent that dissolves the electrolyte. The electrolyte is mainly composed of Li PF ₆ , and the solvent contains vinylene sulfonate or vinyl carbonate in a solvent weight of 0.5 to 5 The lithium ion secondary battery according to claim 16 (?), Next battery.

1 9. The lithium ion secondary battery according to any one of claims 12 to 15, wherein the nonwoven fabric is a nonwoven fabric mainly composed of a metaaromatic polyamide.

20. The lithium ion secondary battery according to any one of claims 12 to 19, characterized in that the aromatic polyamide is polymetaphenylene isophthalamide.