JP4591010B2 - Porous membrane, method for producing the same, and lithium ion secondary battery using the same - Google Patents

Description

  The present invention relates to a polyamide-imide porous membrane that exhibits excellent shutdown temperature characteristics and high meltdown temperature characteristics as a separator for lithium ion secondary batteries that are required to improve safety, a method for producing the same, and lithium using the same The present invention relates to an ion secondary battery.

  In recent years, with the development of electronic portable devices, batteries with high energy density and high electromotive force have been developed. Among them, nonaqueous electrolyte batteries, particularly lithium ion secondary batteries, have been vigorously developed from the viewpoint of high electromotive force. One of the problems with such non-aqueous electrolyte batteries is the danger of using flammable organic solvents. When both electrodes of the battery are short-circuited and a decomposition reaction of the battery contents occurs, the contents are ejected due to a rapid temperature rise inside the battery. In order to solve such problems, there are currently attachment of a safety valve and provision of a shutdown function by a separator containing a meltable component.

  However, the safety valve is not an essential protective measure against a short circuit, but only relieves a sudden pressure increase inside the battery.

  On the other hand, the shutdown function of the separator uses a porous film made of a heat-meltable material. When the temperature inside the battery reaches a certain temperature due to a short circuit or the like, By blocking, the ionic conductivity is hindered and the battery reaction that causes heat generation is suppressed. As such a separator, a porous membrane of an olefin polymer material disclosed in Patent Documents 1 to 3 is disclosed. However, when such a heat-meltable material is used, even if the shutdown function works due to heat rise, if there is a further temperature rise, the film itself melts and the isolation between the electrodes, which is the original function, is impaired. End up. This is a phenomenon called meltdown, which is not preferable for a battery. It has been proposed to widen the range of the shutdown temperature as a remedy for such problems. For example, as disclosed in Patent Documents 4 to 7 and the like, it is a technique of laminating and coating a heat-meltable material on a porous film or a nonwoven fabric substrate. However, these preparation methods may be complicated and an insulation property at the time of shutdown is not necessarily obtained.

Japanese Patent No. 2642206 JP-A-6-212006 Japanese Patent Laid-Open No. 8-138643 Japanese Patent Publication No. 4-1692 JP-A-60-52 JP 61-232560 A Japanese Patent Laid-Open No. 10-6453

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an inexpensive separator that has excellent shutdown characteristics and melt-down characteristics, which are superior to conventional porous membrane separators, and is excellent in insulation. .

  As a result of intensive investigations to achieve the above object, the present invention is excellent in safety and cycle durability by using a porous polyamideimide resin film alone or in combination with other materials as a separator. It was found that a lithium ion secondary battery can be obtained. That is, this invention is the following porous membrane, its manufacturing method, and a lithium ion secondary battery using the same.

(1) A porous material comprising a polyamideimide resin layer having a glass transition temperature of 70 ° C. or higher and a logarithmic viscosity of 0.5 dl / g or higher, and having an overall absorbance of 700 nm or more and a film thickness of 5 to 100 μm. film.

(2) The porous film according to (1), wherein the isocyanate component of the polyamideimide resin contains at least one selected from the group consisting of o-tolidine diisocyanate, tolylene diisocyanate, and naphthalene diisocyanate.

(3) A part of the acid component of the polyamide-imide resin is at least one selected from the group consisting of dimer acid, polyalkylene glycol, polyester, and butadiene rubber containing any one of carboxyl group, hydroxyl group and amino group at the terminal. The porous membrane according to (1) or (2), which is a substituted copolymerized polyamideimide resin.

(4) The porous membrane according to any one of (1) to (3), which has an air permeability of 1 to 2000 sec / 100 cc Air.

(5) A composite porous membrane according to any one of (1) to (4), wherein a polyamide-imide resin layer and a polyolefin-based porous membrane are combined.

(6) A lithium ion secondary battery comprising the porous film according to any one of (1) to (5) interposed as a separator between a positive electrode and a negative electrode capable of inserting and extracting lithium ions.

(7) After applying or immersing the polyamideimide resin solution according to any one of (1) to (3) on a substrate, it is mixed with a solvent in which the polyamideimide resin is dissolved. A method for producing a porous membrane, which is charged into a solution which is a poor solvent and solidified.

(8) The method for producing a porous membrane according to (7), wherein a water-soluble additive is allowed to coexist in the polyamideimide resin solution.

(9) The method for producing a porous membrane according to (8), wherein the water-soluble additive is at least one selected from the group consisting of alcohol, polyethylene glycol and polyvinyl pyrrolidone.

(10) The method for producing a porous membrane according to any one of (7) to (9), wherein the poor solvent is water.

(11) The method for producing a porous membrane according to any one of (7) to (10), wherein a water-soluble additive is contained in a solution that is a poor solvent.

(12) The method for producing a porous membrane according to (11), wherein the water-soluble additive is at least one selected from the group consisting of an amide solvent, alcohol, polyethylene glycol and polyvinyl pyrrolidone.

(13) A polyamide-imide resin solution according to any one of (1) to (3) is applied or immersed on one or both surfaces of a polyolefin-based porous membrane, and then mixed with a solvent in which the polyamide-imide resin is dissolved. A method for producing a composite porous membrane, in which an imide resin is solidified by being put into a poor solvent.

  The present invention provides lithium ion excellent in balance between shutdown characteristics and meltdown characteristics by using a polyamideimide resin porous film having a specific structure or a composite porous film in which a polyamideimide resin porous film and a polyolefin film are laminated. A separator for a secondary battery can be provided.

The present invention will be described in detail below. The polyamideimide resin porous membrane used in the present invention is made of a polyamideimide resin having a glass transition temperature of 70 ° C. or higher, and has an absorbance at 700 nm of 0.5 or higher. As a result of intensive studies, the present inventors have confirmed that the absorbance is closely related to the structure of the polyamideimide resin porous membrane. For example, FIG. 1 shows a cross-sectional photograph of the one having a high absorbance, and vacancies are seen as a whole. Light is diffusely reflected by the holes, resulting in an increase in absorbance. On the other hand, a cross-sectional photograph of a low absorbance is as shown in FIG. The pores are larger than those in FIG. 1, but a dense layer is formed on the surface. When used as a separator, it was found that when a dense layer was formed on the surface, the passage of lithium ions was hindered and the separator did not function sufficiently. From the above, it was found that the absorbance is an important factor that can grasp the performance of the separator. The higher the absorbance, the more suitable for the separator, and preferably 1.0 or more, more preferably 1.5 or more, and most preferably 2.0 or more. Strictly speaking, the absorbance is affected by the thickness, but the influence is small when the film thickness of the present invention is in the range of 5 to 100 μm, and the absorbance dominates the characteristics as a separator.

  The production method of the polyamide-imide resin used in the present invention is an isocyanate method produced from an acid component and an isocyanate (amine) component, or an acid chloride method produced from an acid chloride (acid component) and an amine, and produced from an acid component and an amine component. However, the diisocyanate method is preferred from the viewpoint of production cost.

  In the present invention, it is desirable to use trimellitic anhydride (chloride) as the acid component used in the synthesis of the polyamideimide resin, but a part of it can be replaced with another polybasic acid or its anhydride. For example, tetracarboxylic acids such as pyromellitic acid, biphenyltetracarboxylic acid, biphenylsulfonetetracarboxylic acid, benzophenonetetracarboxylic acid, biphenylethertetracarboxylic acid, ethylene glycol bistrimellitate, propylene glycol bistrimellitate, and their anhydrides. Aliphatic dicarboxylic acids such as oxalic acid, adipic acid, malonic acid, sebacic acid, azelaic acid, dodecanedicarboxylic acid, dicarboxypolybutadiene, dicarboxypoly (acrylonitrile-butadiene) and dicarboxypoly (styrene-butadiene). Alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 4,4'-dicyclohexylmethane dicarboxylic acid, and dimer acid. Aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, diphenylsulfone dicarboxylic acid, diphenyl ether dicarboxylic acid, naphthalenedicarboxylic acid and the like can be mentioned. Among these, dicarboxypolybutadiene, dicarboxypoly (acrylonitrilebutadiene) and dicarboxypoly (styrene-butadiene) having a molecular weight of 1000 or more are preferable from the standpoint of shutdown characteristics.

  In addition, a urethane group can be introduced into the molecule by replacing part of the trimellitic acid compound with glycol. Examples of glycols include alkylene glycols such as ethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, and hexanediol, polyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol, and one or more of the above dicarboxylic acids. And polyesters having terminal hydroxyl groups synthesized from one or two or more of the above-mentioned glycols. Among these, polyethylene glycol and polyesters having terminal hydroxyl groups are preferred because of the shutdown effect. Moreover, these number average molecular weights are preferably 500 or more, and more preferably 1000 or more. The upper limit is not particularly limited, but is preferably less than 8000.

  It is also desirable to replace part of the acid component with at least one selected from the group consisting of dimer acid, polyalkylene ether, polyester and butadiene rubber containing any of carboxyl group, hydroxyl group and amino group at the end. It is preferable to replace 1 to 60 mol% of the components.

  As a diamine (diisocyanate) component used for the synthesis of the polyamideimide resin of the present invention, 4,4′-diphenylmethanediamine and these secondary isocyanates are essential components, but other components include ethylenediamine, propylenediamine, and hexamethylenediamine. Aliphatic diamines such as these, and these diisocyanates, 1,4-cyclohexanediamine, 1,3-cyclohexanediamine, isophorone diamine, alicyclic diamines such as 4,4′-dicyclohexylmethanediamine, and these diisocyanates, phenylenediamine, 4 , 4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl sulfone, benzidine, xylylenediamine, tolylenediamine, and the like. These diisocyanates and the like, reactivity among these, cost, tolidine in terms of electrolyte solution resistance, tolylenediamine, naphthalene diamine and its diisocyanates are preferred.

  The polyamideimide resin used in the present invention is stirred while heating at 60 to 200 ° C. in a polar solvent such as N, N′-dimethylformamide, N, N′-dimethylacetamide, N-methyl-2-pyrrolidone, and γ-butyrolactone. By doing so, it can be easily manufactured. In this case, amines such as triethylamine and diethylenetriamine, alkali metal salts such as sodium fluoride, potassium fluoride, cesium fluoride, sodium methoxide, and the like can be used as a catalyst as necessary.

  The polyamideimide resin used in the present invention preferably has a glass transition temperature of 70 ° C. or higher and a logarithmic viscosity of 0.5 dl / g or higher. When the glass transition temperature is 70 ° C. or lower, there is a shutdown effect, but the meltdown temperature is lowered, and when used for a separator, the positive electrode and the negative electrode may be short-circuited. On the other hand, if the logarithmic viscosity is less than 0.5 dl / g, the mechanical properties of the porous film may be deteriorated because the resin is brittle. As a result, the porous film is likely to crack when the porous film is processed or the battery is assembled, and the positive electrode and the negative electrode may be short-circuited.

  Next, a method for producing a polyamideimide porous membrane will be described. The production of the porous membrane of the present invention is not particularly limited, but after coating the polyamideimide polymerization solution on a substrate such as a polyester film to a predetermined thickness, or extruding the polymerization solution from a slit die into a film, It is preferable that the polyamideimide resin is mixed with a dissolving solvent, and the polyamideimide resin is solidified by being introduced into a solution which becomes a poor solvent.

  Since the solvent for dissolving the polyamide-imide resin is mainly amide solvents such as N-methyl-2-pyrrolidone, dimethylacetamide, N, N-dimethylformamide as described above, the substantial coagulation bath is mainly water. Into a solution. This coagulation bath can be mixed with other solvents miscible with water in order to adjust the coagulation rate, the pore size of the porous membrane and its distribution. Examples of such solvents include alcohols such as methanol, ethanol, propyl alcohol, ethylene glycol, propylene glycol, diethylene glycol, and polyethylene glycol, ketones such as acetone and methyl ethyl ketone, N, N-dimethylformamide, N, N-dimethylacetamide, Examples thereof include amide solvents such as N-methyl-2-pyrrolidone, and among these, glycols such as ethylene glycol and polyethylene glycol are preferable from the viewpoint of uniformity in the porous film having a pore size. Although there is no restriction | limiting in the addition amount, Preferably it is 5 parts to 500 parts with respect to 100 parts of water, More preferably, it is 10 parts to 400 parts, Most preferably, it is 20 parts to 300 parts.

The coagulation tank may be a single tank, but may be a multi-tank to adjust the coagulation rate, the pore diameter of the porous membrane and its distribution. At this time, it is preferable to change the concentration of the additive to water in each tank.
In addition, an additive may be used in the polyamideimide resin solution to adjust the coagulation rate, the pore size of the porous membrane, and the distribution thereof. For example, alcohols such as methanol, ethanol, propyl alcohol, ethylene glycol, propylene glycol, diethylene glycol, and polyethylene glycol; ketones such as acetone and methyl ethyl ketone; and water-soluble polymers such as polyethylene glycol and polyvinyl pyrrolidone. The addition amount is not limited, but is preferably 5 to 300 parts, more preferably 10 to 200 parts, and most preferably 20 to 100 parts with respect to 100 parts of the resin solution.

  The polyamideimide porous membrane may be a single layer or a laminate, but the total film thickness is 5 to 100 μm, preferably 10 to 70 μm, and more preferably 15 to 50 μm. If the film thickness is 5 μm or less, the film becomes weak and may break. On the other hand, if the film thickness exceeds 100 μm, the cycle characteristics deteriorate, which is not preferable. The porosity of the polyamide-imi porous film is preferably 30 to 90%. More preferably, it is 40 to 70%. When the porosity is 30% or less, the electric resistance of the film becomes high and it becomes difficult to flow a large current. On the other hand, if it is 80% or more, the film strength becomes weak. The air permeability, which is a measure of the pore diameter, is preferably 1 to 2000 sec / 100 cc Air measured by a method based on JIS-P8117. More preferably, it is 50-1500 sec / 100 cc Air, More preferably, it is 100-1000 sec / 100 cc Air. When the air permeability is 1 sec / 100 cc Aircc or less, the film strength is weak, and when it exceeds 2000 sec / 100 cc Air, the cycle characteristics may be deteriorated.

  The polyamideimide porous membrane thus produced exhibits excellent shutdown characteristics and meltdown characteristics even when used alone as a separator. In particular, the effect is remarkable in the case of a porous film made of a polyamide-imide resin in which butadiene rubber having an average molecular weight of 1000 or more, polyalkylene glycol, polyester or the like is copolymerized in a block shape.

  Another feature of the present invention is that a polyamide-imide porous membrane can be used in combination with a polyolefin-based porous membrane. The polyolefin-based porous membrane is a polyethylene or polypropylene film produced by, for example, the stretch opening method or the phase separation method described in 7th Polymer Material Forum (1998) Abstract 1 BIL09. When the polyamide-imide porous membrane and the polyolefin porous membrane are laminated, the polyamide-imide porous membrane is A, and the polyolefin-based porous membrane is B. A / B, A / B / A or B / A / B It becomes the composition of.

The production of these composite porous membranes is not particularly limited, but the following method is preferred.
(1) A polyamide-imide porous membrane and a polyolefin porous membrane are simply stacked.
(2) Using a polyolefin porous membrane as a support, impregnating or coating a polyamideimide resin solution on one side or both sides thereof, putting the solution in a coagulation bath in the same manner as described above, and coagulating it.
(3) Combine (1) and (2) above.

  In the case of these composite porous membranes, the total film thickness is 10 to 100 μm, preferably 15 to 70 μm. The porosity is 30 to 80%, and the air permeability is 1 to 2000 sec / 100 cc Air.

  The lithium ion secondary battery using the polyamideimide porous membrane of the present invention configured as described above as a separator exhibits the same battery performance as before, and obtains a safe battery excellent in shutdown characteristics and meltdown characteristics. Can do. The lithium ion secondary battery according to the present invention can be produced according to a conventional method except that the separator of the present invention is used.

  That is, a material containing lithium can be used as the positive electrode active material, a material that can store and release lithium as ions can be used as the negative electrode, and an organic solvent solution of an electrolyte composed of a compound containing lithium and fluorine can be used as the electrolytic solution.

  Specifically, lithium metal oxides such as lithium cobaltate and lithium manganate that can insert and remove lithium ions can be used as the positive electrode active material. A known active carbon, various cokes, carbon black, a binder, a solvent, and the like are blended into the positive electrode active material as a conductive agent, and this dispersion is applied to a current collector such as aluminum and dried to form a positive electrode material. Can do.

  Coke, graphite, amorphous carbon, etc. are used as the negative electrode active material, and these are applied to a current collector such as a copper foil with a dispersion composed of a binder and an organic solvent, and dried to form a negative electrode material. it can.

Examples of the electrolyte used for the electrolytic solution include LiClO ₄ , LiAsF ₆ , LiPF ₄ , LiBF ₄ , LiBr, LiCF ₃ SO ₃ , and the like. Examples of the organic solvent include propylene carbonate, ethylene carbonate, γ-butyrolactone, dimethyl One type or two or more types of carbonate, ethyl methyl carbonate, 1,2 dimethoxyethane, 1,2 diethoxyethane, tetrahydrofuran and the like are used.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited by these Examples.
In addition, the measured value in an Example was measured with the following method.

Logarithmic viscosity: A solution obtained by dissolving 0.5 g of polyamideimide resin in 100 ml of N-methyl-2-pyrrolidone was kept at 30 ° C. and measured using an Ubbelohde viscosity tube.

Glass transition temperature: The inflection point of the loss elastic modulus of dynamic viscoelasticity measured by applying a vibration of a frequency of 110 Hz to a polyamideimide film having a measurement width of 4 mm and a length of 15 mm, using a DVE-V4 rheospectr made by Rheology. The glass transition temperature was taken.

Film thickness: The polyamideimide porous film was measured with a SONY μ-meter.

Porosity: The average film thickness (At) and weight (Aw) of about 25 μm film (A) prepared by casting and drying from a polyamideimide resin solution were measured and coagulated in water from the same polyamideimide resin solution. The porosity was calculated from the average film thickness (Bt) of the porous film (B) thus prepared and the weight (Bw) of 10 cm □ by the following formula.
Porosity = [1- (Bw / Bt) / (Aw / At)] × 100 (%)

Shutdown temperature characteristics: A porous membrane filled with 1 mol / l of lithium tetrafluoroborate dissolved in propylene carbonate was used and measured at an AC frequency of 1 kHz, an AC amplitude of 100 mV, and a heating rate of 2 ° C./min. The temperature at which the rise in impedance value due to temperature rise once becomes 100 Ωcm ² is the shutdown start temperature, and the temperature at which the impedance value exceeds 1 kΩcm ² , then rises and decreases again to 1 kΩcm ² is the meltdown temperature. It was.

Absorbance: Absorbance at 700 nm was measured with a spectrophotometer (U-3210, manufactured by Hitachi, Ltd.).

[Example 1]
In a four-necked flask equipped with a thermometer, a condenser tube, and a nitrogen gas inlet tube, 1 mole of trimellitic anhydride, 0.2 mole of tolylene diisocyanate, 0.79 mole of 4,4′-diphenylmethane diisocyanate, 0 potassium fluoride 0.02 mol was charged with N-methyl-2-pyrrolidone so that the solid content concentration was 20%, stirred at 120 ° C. for 5 hours, and then N-methyl-2-pyrrolidone so that the solid content concentration was 15%. A polyamideimide resin was synthesized by diluting. The obtained polyamideimide resin had a logarithmic viscosity of 0.64 dl / g and a glass transition temperature of 295 ° C.
The varnish was applied to one side of a polyolefin porous membrane (25 μm) manufactured by Tonen Chemical Co., Ltd. so as to have a dry film thickness of 1 μm, immersed in water, coagulated, washed and dried. This composite porous membrane had a thickness of 26 μm, an air permeability of 620 sec / 100 cc, a shutdown temperature of 122 ° C., and a meltdown of 200 ° C. or higher. Absorbance was 2.5. Using this composite porous membrane as a separator, positive electrode using lithium cobaltate as a positive electrode active material, acetylene black as a conductive agent, polyvinylidene fluoride as a binder, negative electrode active material mixed with graphite and amorphous carbon, and polyvinylidene fluoride A coin-type battery was prepared by using a negative electrode with a binder and Sollite (manufactured by Mitsubishi Chemical) as an electrolytic solution, and the battery characteristics were evaluated. As a result, compared with a commercially available separator (polyolefin porous membrane manufactured by Tonen Chemical Co., Ltd .: 25 μm), the discharge capacity and cycle characteristics were almost the same.

[ Reference Example 2]
A polyamideimide resin was synthesized under the same conditions as in Example 1 except that 0.3 mol of o-tolidine isocyanate and 0.7 mol of tolylene diisocyanate were used as the isocyanate component of Example 1. The obtained polyamideimide resin had a logarithmic viscosity of 0.52 dl / g and a glass transition temperature of 310 ° C. A composite porous membrane was prepared from this polyamideimide resin solution by the same method as in Example 1. Absorbance was 2.7. The composite porous membrane had a thickness of 28 μm, an air permeability of 730 sec / 100 cc Air, a shutdown temperature of 123 ° C., and a meltdown temperature of 200 ° C. or higher.

[Example 3]
Example 1 except that 0.94 mol of trimellitic anhydride and 0.06 mol of poly (acrylonitrile-butadiene) copolymer of dicarboxylic acids at both ends (Hibe CTBN 1300 × 13 manufactured by Ube Industries) were used as the acid component of Example 1. 1 was synthesized under the same conditions as in 1. The obtained polyamideimide resin had a logarithmic viscosity of 0.62 dl / g and a glass transition temperature of 150 ° C. A composite porous membrane was prepared from this polyamideimide resin solution by the same method as in Example 1. The absorbance was 2.6. The composite porous membrane had a thickness of 28 μm, an air permeability of 650 sec / 100 cc Air, a shutdown temperature of 123 ° C., and a meltdown temperature of 165 ° C.

[Example 4]
A solution in which 20 parts of ethylene glycol was blended with 100 parts of the polyamideimide resin solution of Example 3 was applied to a 100 μm polyester film, immersed in water to solidify, washed with water, dried, peeled off from the polyester film, and removed from the polyesterimide porous film. A membrane was obtained. This porous membrane had a thickness of 30 μm, an absorbance of 3.2, a porosity of 67%, an air permeability of 5.3 sec / 100 cc Air, a shutdown temperature of 154 ° C., and a meltdown temperature of 172 ° C. or higher. Battery performance such as discharge capacity and cycle durability of a coin battery using this polyamideimide porous membrane as a separator in the same configuration as in Example 1 showed the same characteristics as the polyolefin porous membrane single separator.

[Example 5]
After immersing a polyolefin porous membrane (25 μm) manufactured by Tonen Chemical in a varnish in which 20 parts of polyethylene glycol # 400 was blended with 100 parts of the polyamideimide resin solution of Example 1, the dry film thicknesses were measured on both sides of the polyolefin porous film. It is scraped with a squeeze roll so as to be 1 μm, put into a coagulation bath having a water / polyethylene glycol (molecular weight 400) ratio of 70/30, coagulated, washed and dried to form a composite porous membrane of 3 layers having a thickness of 27 μm. Obtained. The composite porous membrane had an absorbance of 2.5, a shutdown temperature of 120 ° C, and a meltdown temperature of 200 ° C or higher. The battery performance such as the discharge capacity and cycle durability of the coin battery prepared by using the composite porous membrane as a separator and having the same structure as in Example 1 showed the same characteristics as the polyolefin porous membrane single separator.

[Example 6]
Discharge capacity and cycle endurance of a coin battery in which a composite membrane obtained by laminating a polyolefin porous membrane on the polyamideimide porous membrane side of the polyamideimide / polyolefin composite porous membrane prepared in Example 1 under the same conditions as in Example 1 The battery performance such as the property showed almost the same characteristics as the polyolefin porous membrane single separator.

[Comparative Example 1]
A polyamideimide resin was synthesized under the same conditions as in Example 1 except that TMA was 1.08 mol in Example 1. The obtained polyamideimide resin had a logarithmic viscosity of 0.33 dl / g, a glass transition temperature of 350 ° C., and an absorbance of 2.6. A porous membrane using this polyamideimide resin is fragile because of its low molecular weight, and is not suitable as a separator.

[Comparative Example 2]
Polyamide under the same conditions as in Example 1 except that the acid component was 0.15 mol trimellitic anhydride, 0.85 mol dimer acid, 0.5 mol naphthalene diisocyanate, and 0.49 mol 4,4'-diphenylmethane diisocyanate. An imide resin was synthesized. The obtained polyamideimide resin had a logarithmic viscosity of 0.64 dl / g and a glass transition temperature of 60 ° C. Using this polyamideimide resin solution, a porous membrane was prepared in the same manner as in Example 5. Absorbance was 2.3. This porous film had a good film thickness of 26 μm, porosity of 63%, and air permeability of 340 sec / 100 cc Air, but the shutdown temperature was 75 ° C. and the meltdown temperature was 95 ° C., which is low as a separator. Was insufficient.

[Comparative Example 3]
Using the same apparatus as in Example 1, 1 mol of trimellitic anhydride, 0.8 mol of o-tolidine diisocyanate, 0.2 mol of 2,4-tolylene diisocyanate, 0.01 mol of potassium fluoride and a solid content concentration of 20 %, Together with N-methyl-2-pyrrolidone, the mixture was stirred at 100 ° C. for 5 hours to synthesize a polyamideimide resin. The obtained polyamideimide resin had a logarithmic viscosity of 1.35 dl / g and a glass transition temperature of 310 ° C. A porous film having a thickness of 26 μm was produced in the same manner as in Example 1 using this polyamideimide resin solution. The absorbance was 0.2 and the air permeability was 2000 sec / 100 cc Air or more, which was unsuitable for a separator.

  The present invention provides lithium ion excellent in balance between shutdown characteristics and meltdown characteristics by using a polyamideimide resin porous film having a specific structure or a composite porous film in which a polyamideimide resin porous film and a polyolefin film are laminated. A separator for a secondary battery can be provided.

After the polyamideimide resin solution synthesized in Example 1 was applied to a PET film (E5100 manufactured by Toyobo Co., Ltd.) so as to have a porous film thickness of 80 μm, ion-exchanged water (each ionic property) more than 3000 times the resin solution weight. The porous film was removed from the PET film after 30 minutes, and further immersed in the same amount of water for 30 minutes. After repeating this operation 5 times, the adhered water was wiped off and dried at 25 ° C. for 24 hours. FIG. 1 is a scanning electron micrograph of the sample cross section. This corresponds to the embodiment of the present invention. After the polyamideimide resin solution synthesized in Comparative Example 3 was applied to a PET film (E5100 manufactured by Toyobo Co., Ltd.) so as to have a porous film thickness of 80 μm, ion-exchanged water (each ionic property) more than 3000 times the resin solution weight was applied. The porous film was removed from the PET film after 30 minutes, and further immersed in the same amount of water for 30 minutes. After repeating this operation 5 times, the adhered water was wiped off and dried at 25 ° C. for 24 hours. FIG. 2 is a scanning electron micrograph of the sample cross section. This corresponds to the comparative example of the present invention.

Claims (13)

A glass transition temperature of 70 ° C. or higher, a logarithmic viscosity of 0.5 dl / g or higher , a polyamideimide resin layer containing 4,4′-diphenylmethane diisocyanate as an essential component as an isocyanate component , and an overall absorbance at 700 nm There 2.0 or 3.2 or less, a lithium ion secondary battery separator having a thickness of a porous membrane of 5 to 100 [mu] m. Polyamideimide o- tolidine diisocyanate isocyanate component of the resin, tolylene diisocyanate and a lithium ion secondary battery separator according to claim 1, characterized in that it contains at least one of the group consisting of naphthalene diisocyanate. The separator for a lithium ion secondary battery according to claim 1, further comprising tolylene diisocyanate in the isocyanate component of the polyamideimide resin. Part of the acid component of the polyamide-imide resin was replaced with at least one selected from the group consisting of dimer acid, polyalkylene glycol, polyester, and butadiene-based rubber containing any of carboxyl, hydroxyl and amino groups at the terminal. The separator for a lithium ion secondary battery according to any one of claims 1 to 3, which is a copolymerized polyamideimide resin. Lithium ions in secondary battery separator, a polyamide-imide resin layer and a polyolefin porous film and a lithium ion secondary battery separator comprising a composite porous membrane, characterized in that it combines according to claim 1. A lithium ion secondary battery comprising the separator for a lithium ion secondary battery according to any one of claims 1 to 5 as a separator between a positive electrode and a negative electrode capable of inserting and extracting lithium ions. A glass transition temperature of 70 ° C. or higher, logarithmic viscosity of 0.5 dl / g or higher, and a solution containing a polyamideimide resin having 4,4′-diphenylmethane diisocyanate as an essential component as an isocyanate component was applied to or immersed in a substrate. 2. The method for producing a separator for a lithium ion secondary battery according to claim 1 , wherein the polyamideimide resin is mixed with a solvent in which the polyamideimide resin is dissolved, but the polyamideimide resin is solidified by being put into a poor solvent. . The method for producing a separator for a lithium ion secondary battery according to claim 7, wherein a water-soluble additive is allowed to coexist in the polyamideimide resin solution. The method for producing a separator for a lithium ion secondary battery according to claim 8, wherein the water-soluble additive is at least one selected from the group consisting of alcohol, polyethylene glycol and polyvinylpyrrolidone. The method for producing a separator for a lithium ion secondary battery according to any one of claims 7 to 9, wherein the poor solvent is water. The manufacturing method of the separator for lithium ion secondary batteries in any one of Claims 7-10 in which a water-soluble additive is contained in the solution which is a poor solvent. The method for producing a separator for a lithium ion secondary battery according to claim 11, wherein the water-soluble additive is at least one selected from the group consisting of an amide solvent, alcohol, polyethylene glycol, and polyvinylpyrrolidone. Polyamideimide resin having a glass transition temperature of 70 ° C. or higher, a logarithmic viscosity of 0.5 dl / g or higher, and 4,4′-diphenylmethane diisocyanate as an essential component on one or both sides of a polyolefin-based porous membrane after the solution is applied or dip including, but miscible with the solvent dissolving the polyamide-imide resin, polyamide-imide for the resin lithium ion according to claim 5 which solidified was put in a solution is a poor solvent A method for producing a separator for a secondary battery .