JP4843935B2 - Composite porous membrane, process for producing the same, and secondary battery using the same - Google Patents

Description

The present invention relates to a composite porous membrane exhibiting 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 ion using the same The present invention relates to a 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. As safeguards against the such problems, currently, the mounting of the safety valve, and the like shutdown imparted by a separator fusible components contained.

  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, by using a porous film using a thermally fusible material, when it reaches a certain temperature is the temperature of the battery due to short circuit, the hot melt material of the porous membrane By closing the hole, the ionic conductivity is hindered and the battery reaction that causes heat generation is suppressed. As such a separator, as shown in Patent Documents 1 to 3 and the like, a porous film of an olefin polymer material 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 production methods may be complicated . In addition, a sufficient 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. .

In order to achieve the above object, the present invention has been intensively studied, and as a result, a porous film of polyimide resin having a glass transition temperature and logarithmic viscosity in a specific range is formed in a geometric pattern on a porous substrate. It was found that a lithium ion secondary battery excellent in safety and cycle durability can be obtained by using the composite porous membrane as a separator. That is, the present invention is as follows (1) to (10) .

(1) A composite porous membrane used as a separator of a lithium ion secondary battery, which is composed only of a polyimide-based resin having a glass transition temperature of 70 ° C. or higher and a logarithmic viscosity of 0.5 dl / g or higher. A composite porous membrane comprising a porous substrate coated in a lattice pattern and a coverage of 10 to 90%.
(2) The composite porous membrane according to (1), wherein the porous substrate is a porous membrane made of polyethylene or polypropylene, or a nonwoven fabric.
(3) The composite porous membrane according to (1) or (2), wherein the polyimide resin is a polyamideimide resin whose acid component is mainly trimellitic anhydride.
(4) Polyimide-based resin further includes ethylene glycol anhydrobis trimellitate, propylene glycol anhydro bis trimellitate, pyromellitic acid anhydride, benzophenone tetracarboxylic acid anhydride, and biphenyl tetracarboxylic acid. The composite porous membrane according to (3), which is a polyamideimide resin using at least one or more members selected from the group consisting of acid anhydrides.
(5) The polyimide resin further comprises at least a part of the acid component of dimer acid, polyalkylene glycol, polyester, polycaprolactone and a butadiene rubber containing a carboxyl group, a hydroxyl group or an amino group at the terminal. The composite porous membrane according to (4), which is a copolymerized polyamideimide resin replaced with one kind.
(6) The composite porous membrane according to any one of (1) to (5), wherein the polyimide porous membrane has a thickness of 0.5 to 30 μm and the porous substrate has a thickness of 5 to 100 μm. .

(7) A method for producing a composite porous membrane used as a separator of a lithium ion secondary battery,
(I) A solute solution consisting only of a polyimide resin having a glass transition temperature of 70 ° C. or higher and a logarithmic viscosity of 0.5 dl / g or higher is applied to a porous film or non-woven fabric made of polyethylene or polypropylene. After applying in a grid pattern by gravure roll or screen printing method to 90%,
(II) It is miscible with the solvent in which the polyimide resin is dissolved, but for the polyimide resin, it is put into a solution that is a poor solvent and solidified.
A method for producing a composite porous membrane.
(8) The method for producing a composite porous membrane according to (7), wherein the polyimide resin is a polyamide-imide resin whose acid component is mainly trimellitic anhydride.
(9) Polyimide-based resin further includes ethylene glycol anhydrobis trimellitate, propylene glycol anhydro bis trimellitate, pyromellitic acid anhydride, benzophenone tetracarboxylic acid anhydride, and biphenyl tetracarboxylic acid. (8) The method for producing a composite porous membrane according to (8), which is a polyamide-imide resin using at least one of a group consisting of acid anhydrides.
(10) The polyimide resin further comprises at least a part of the acid component of dimer acid, polyalkylene glycol, polyester, polycaprolactone and a butadiene rubber containing a carboxyl group, a hydroxyl group or an amino group at the terminal. (9) The method for producing a composite porous membrane according to (9), wherein the composite porous imide resin is replaced with one type.

The present invention, shutdown properties and melt by using the composite porous membrane porous membrane of a polyimide resin is formed on the geometric shape on a porous substrate having a glass transition temperature and inherent viscosity in a specific range Rutotomoni well balanced down characteristics, can control the air permeability without using an excess of polyimide porous film can provide a lithium ion secondary battery separator that can suppress the curling of the composite porous membrane.

The present invention will be described in detail below.
Polyimide resin used in the present invention can be easily prepared by stirring at room temperature or under heating in a polar organic solvent such as polycarboxylic acid anhydride and diamine or a diisocyanate N- methyl-2-pyrrolidone .

The acid component used for the synthesis of the polyimide resin of the present invention is mainly trimellitic anhydride .
However , some or all of them can be replaced with other polybasic acids or their anhydrides. Examples of other polybasic acids or anhydrides thereof include pyromellitic acid, biphenyltetracarboxylic acid, biphenylsulfonetetracarboxylic acid, benzophenonetetracarboxylic acid, biphenylethertetracarboxylic acid, ethylene glycol anhydrobistrimellitate, propylene glycol a tetracarboxylic acid and their anhydrides, such as anhydroerythromycin bistrimellitate. Also, oxalic acid, adipic acid, malonic acid, sebacic acid, azelaic acid, dodecane dicarboxylic acid, dicarboxylate polybutadiene, dicarboxypoly (acrylonitrile - butadiene), aliphatic dicarboxylic acids such as dicarboxypoly (styrene-butadiene) 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 4,4′-dicyclohexylmethanedicarboxylic acid, alicyclic dicarboxylic acids such as dimer acid, terephthalic acid, isophthalic acid, diphenylsulfone dicarboxylic acid, diphenyl ether dicarboxylic acid Examples thereof include aromatic dicarboxylic acids such as acid and naphthalenedicarboxylic acid.
Among these, pyromellitic acid anhydride, benzophenone tetracarboxylic acid anhydride, biphenyl tetracarboxylic acid anhydride, ethylene glycol anhydrobistrimellitate, propylene glycol anhydrobistrimer in terms of reactivity, solubility, and price. Melitate is preferred. Also, from the viewpoint of electrolytic solution resistance among these, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid is not preferable. From the viewpoint of shutdown characteristics , dimer acid, dicarboxypolybutadiene having a molecular weight of 1000 or more, dicarboxypoly (acrylonitrilebutadiene), and dicarboxypoly (styrene-butadiene) are preferable.

In addition, a urethane group can be introduced into the molecule by replacing part of the acid component with glycol. The glycol, ethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, alkylene glycol such as hexane diol, polyethylene glycol, polypropylene glycol, one or two polyalkylene glycol and the dicarboxylic acid and polytetramethylene glycol or a polyester terminal hydroxyl groups synthesized from one or more of the above glycols Ru mentioned. Among these , polyethylene glycol and polyester having a terminal hydroxyl group are preferable 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.

When cyclohexanedicarboxylic acid is used as part of the acid component, it is preferable to replace 20 to 70 mol% of the acid component in order to improve solvent solubility and flexibility of the polyimide-based porous film. When a part of the acid component is replaced with at least one kind 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 terminal, Of these, it is preferable to replace 1 to 60 mol%.

Examples of the diamine (diisocyanate) component used for the synthesis of the polyimide resin of the present invention include aliphatic diamines such as ethylenediamine, propylenediamine, and hexamethylenediamine, and their diisocyanates, 1,4-cyclohexanediamine, and 1,3-cyclohexanediamine. Alicyclic diamines such as dicyclohexylmethane diamine, and diisocyanates thereof, m-phenylene diamine, p-phenylene diamine, 4,4′-diaminodiphenyl methane, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl sulfone, benzidine, 3,3'-dimethyl benzidine, xylylene diamine, and aromatic diamines and diisocyanates thereof such as naphthalene diamine like et be. Among these, diaminodiphenylmethane, 3,3′-dimethylbenzidine, isophoronediamine, dicyclohexylmethanediamine, and these diisocyanates are preferable from the viewpoint of reactivity, cost, and resistance to electrolytic solution.

  The polyimide 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 polyimide resin used in the present invention needs to have 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 less than 70 ° C., the meltdown temperature becomes low, and when used for a separator, the positive electrode and the negative electrode may be short-circuited. On the other hand, the upper limit is preferably less than 400 ° C. in consideration of workability and solvent solubility . If several pairs viscosity is less than 0.5 dl / g, as well as the risk that the positive electrode and the negative electrode cause a short circuit is increased, a polyimide porous film due to the low molecular weight may turn brittle by lowering the melting temperature. On the other hand , the upper limit of the logarithmic viscosity is preferably less than 2.0 dl / g in consideration of processability and solvent solubility.

  The porous substrate used in the present invention is not limited, but in order to provide a shutdown function when used for the separator of a lithium ion secondary battery which is the object of the present invention, a polyolefin-based porous material such as polyethylene or polypropylene is used. A membrane is preferred.

  Next, the manufacturing method of the composite porous membrane of a polyimide type porous membrane and a porous base material is demonstrated. A feature of the present invention resides in that a polyimide-based porous film is laminated on a porous substrate in a geometric pattern. By laminating in a geometric pattern, the air permeability can be controlled without excessive use of the polyimide-based porous film, and curling of the composite porous film can be suppressed.

In the present invention, the geometric pattern includes a stripe shape, a lattice shape, a polygonal shape such as a triangle or a quadrangle, a circle, an ellipse or the like alone or a combination thereof. It is not preferred. The ratio (coverage) that the geometric pattern portion covers the substrate is 10 to 90%, preferably 30 to 70%. This is because if the coverage is 10% or less, the effect of preventing meltdown when used in a lithium ion secondary battery is insufficient, and if it is 90% or more, the air permeability may be impaired.

Although there is no restriction | limiting in particular in the manufacturing method of the composite porous membrane of this invention, The following method is preferable.
(1) A polyimide-based resin solution is applied on a porous substrate by screen printing, and then a composite porous film is formed by a wet coagulation method.
(2) A polyimide-based resin solution is applied onto a porous substrate using a gravure roll engraved with a geometric pattern, and then a composite porous film is formed by a wet coagulation method.

Next, a method for producing a polyimide-based porous film by a wet coagulation method will be described. As described above, amide solvents such as N-methyl-2-pyrrolidone, dimethylacetamide, and N, N′-dimethylformamide are mainly used as solvents for dissolving the polyimide resin . In addition , alcohols such as methanol, ethanol, propyl alcohol, ethylene glycol, diethylene glycol, polyethylene glycol, and polypropylene glycol, and acetone are used to adjust the coagulation rate at the time of forming the polyimide-based porous film to adjust the pore size and pore size distribution. , as possible de be added, such as ketones such as methyl ethyl ketone. These additives, 5-300 parts of the polyimide resin solution 100 parts, preferably 10 to 200 parts, more preferably 20 to 100 parts.

After the above-mentioned polyimide resin solution is printed or coated in a gravure roll through design have been screen plate in geometric patterns on one or both sides of the multi-porous substrate, or engraved in a geometric pattern such as a polyolefin, polyimide A composite porous film is formed by mixing in a solvent of a resin and putting it in a coagulation bath that does not dissolve the polyimide resin.

Coagulating bath used in manufacturing the polyimide porous membrane of the present invention, a solution composed mainly of water is preferred. The coagulation bath can be mixed other solvent miscible with water in order to adjust the pore diameter and distribution thereof of the solidification rate and polyimide porous membrane. As such solvents, methanol, ethanol, propyl alcohol, ethylene glycol, propylene glycol, diethylene glycol, alcohols such as polyethylene glycol, ketones such as acetone and methyl ethyl ketone, N, N'-dimethylformamide, N, N' dimethylacetamide, Ru include amide-based solvents such as N- methyl-2-pyrrolidone. In terms of average one of pore size in the polyimide-based porous membrane Among these, ethylene glycol, glycol ethers and N- methyl-2-pyrrolidone and polyethylene glycol, N, N'-dimethylacetamide, N, N ' -Amide solvents such as dimethylformamide are preferred. The addition amount of these solvents, from 5 to 500 parts per 100 parts of water, preferably 10 to 400 parts, more preferably 20 to 300 parts.

  The film thickness of the polyimide-based porous film is 0.5 to 30 μm, preferably 1 to 20 μm, and more preferably 2 to 10 μm. When the film thickness is 0.5 μm or less, the effect of preventing meltdown is insufficient. Conversely, when the film thickness exceeds 30 μm, the cycle characteristics may deteriorate. The porosity of the polyimide-based 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 90% 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. When the air permeability is less than 1 sec / 100 cc Air, the film strength becomes weak, and when it exceeds 2000 sec / 100 cc Air, the internal resistance increases and the cycle durability becomes insufficient.

Further, as the porous substrate of the present invention, or a porous film of paper, plastic, non-woven fabric is preferably, suitable in particular porous film polyethylene or polypropylene non-woven fabric or paper making these filaments. The thickness of the porous substrate of the present invention is 5 to 100 μm, preferably 10 to 90 μm.

The lithium ion secondary battery using a composite porous membrane in which a polyimide-based porous membrane is combined in a geometric pattern on the porous base material of the present invention thus configured as a separator is the same battery performance as before. Demonstrate . According to the present invention , a safe battery excellent in shutdown characteristics and meltdown characteristics can be obtained. The lithium ion secondary battery according to the present invention can be produced according to a conventional method except that the composite membrane of the present invention is used as a separator.

Material containing lithium as a positive electrode active material, lithium absorption as a negative electrode as an ion, releasable material, as the electrolytic solution can be an organic solvent solution of an electrolyte composed of a compound containing lithium and fluorine.

  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 in the electrolytic solution include LiClO ₄ , LiAsF ₆ , LiPF ₄ , LiBF ₄ , LiBr, LiCF ₃ SO ₃ , and the organic solvents include propylene carbonate, ethylene carbonate, γ-butyrolactone, dimethyl carbonate. , Ethyl methyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran or the like is 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 polyimide resin in 100 ml of N-methyl-2-pyrrolidone was kept at 30 ° C. and measured using an Ubbelohde viscosity tube.

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

  Film thickness: measured with a SONY μ-meter.

Shutdown temperature characteristics: A composite porous membrane filled with a solution of 1 mol / l lithium tetrafluoroborate dissolved in propylene carbonate was measured at an AC frequency of 1 kHz, an AC amplitude of 100 mV, and a temperature increase 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.

[Example 1]
A four-necked flask equipped with a thermometer, a condenser tube, and a nitrogen gas inlet tube contains 1 mole of trimellitic anhydride (TMA), 1 mole of diphenylmethane diisocyanate (MDI), and 0.02 mole of potassium fluoride with a solid content of 25 % With N-methyl-2-pyrrolidone and stirred at 130 ° C. for 5 hours, and then cooled to room temperature. The obtained polyamideimide resin had a logarithmic viscosity of 0.68 dl / g and a glass transition temperature of 285 ° C.
A solution in which 20 parts of polyethylene glycol (number average molecular weight 400) is blended with 100 parts of this polyamideimide resin solution is placed on a polyethylene porous film having a thickness of 16 μm and a lattice pattern is arranged at an angle of 30 degrees on a 250 mesh stainless steel screen plate. The screen was printed and applied to a film thickness of 18 μm, immersed in water at 25 ° C. for about 3 minutes, fixed with a metal frame, and dried at 100 ° C. for 10 minutes. Coverage of the polyamideimide porous film 65%, air permeability of the obtained double if the porous membrane is 103sec / 100ccAir, the shutdown temperature is 120 ° C., meltdown temperature were 200 ° C. or higher. Using this porous membrane as a separator, a positive electrode using lithium cobaltate as a positive electrode active material, acetylene black as a conductive agent, polyvinylidene fluoride as a binder, a negative electrode active material mixed with graphite and amorphous carbon, and polyvinylidene fluoride A coin-type battery was fabricated using a negative electrode as a binder and Sollite (manufactured by Mitsubishi Chemical) as an electrolytic solution, and battery characteristics were evaluated. Commercial separator (Tonen Chemical Ltd.: 25.mu. m) discharge capacity as compared with, both the cycle characteristics exhibited almost the same performance.

[Example 2]
The acid component of Example 1 was TMA 0.9 mol, benzophenone tetracarboxylic acid anhydride 0.1 mol, diphenylmethane diisocyanate 1.0 mol, potassium fluoride 0.02 mol, N- The mixture was charged with methyl-2-pyrrolidone, allowed to cool at 100 ° C. for 3 hours, and then cooled to obtain a polyamideimide resin. This polyamideimide resin had a glass transition temperature of 300 ° C. and a logarithmic viscosity of 1.23 dl / g.
Using this polyamideimide resin solution, the air permeability of a composite porous membrane having a thickness of 20 μm produced by the same method as in Example 1 was 121 sec / 100 cc Air, the shutdown temperature was 120 ° C., and the meltdown temperature was 200 ° C. or higher. It was.

[Example 3]
Using the same apparatus as in Example 1, 0.74 mol of TMA, 0.2 mol of biphenyltetracarboxylic anhydride, 0.06 mol of polypropylene glycol having a molecular weight of 2000, 1.02 mol of isophorone diisocyanate, 0.02 mol of potassium fluoride were added. After charging with γ-butyrolactone so that the solid concentration is 50% and reacting at 180 ° C. for 5 hours, it is diluted with N, N′-dimethylacetamide so that the solid concentration is 25%. Synthesized. The obtained polyamideimide resin had a logarithmic viscosity of 0.63 dl / g and a glass transition temperature of 198 ° C.
A composite porous membrane was produced from this polyamideimide resin solution by the same method as in Example 1. This composite porous membrane had a thickness of 17 μm, an air permeability of 89 sec / 100 cc Air, a shutdown temperature of 122 ° C., and a meltdown temperature of 200 ° C. or higher.

[Example 4]
Using the same apparatus as in Example 1, 0.8 mol of TMA, 0.15 mol of pyromellitic anhydride, 0.05 mol of polycaprolactone (Placcel 220: molecular weight 2000 manufactured by Daicel Chemical Industries), 0.5 mol of isophorone diisocyanate (IPDI) , 0.5 mol of diphenylmethane-4,4′-diisocyanate and 0.02 mol of potassium fluoride were added together with N-methyl-2-pyrrolidone so that the solid concentration would be 50%, and reacted at 180 ° C. for about 5 hours. After that, it was diluted with N-methyl-2-pyrrolidone so that the solid content concentration was 25%. The obtained polyamideimide resin had a logarithmic viscosity of 0.71 dl / g and a glass transition temperature of 185 ° C.
A composite porous membrane was produced from this polyamideimide resin solution in the same manner as in Example 1. The composite porous membrane had a thickness of 18 μm, an air permeability of 67 sec / 100 cc Air, a shutdown temperature of 122 ° C., and a meltdown temperature of 200 ° C. or higher.

[Example 5]
Using the same apparatus as in Example 1, 1 mol of TMA, 0.7 mol of o-tolidine diisocyanate, 0.3 mol of MDI, and 0.02 mol of diazabicycloundecene were added so that the solid content concentration would be 30%. -Prepared together with dimethylformamide, reacted at 120 ° C for 5 hours, and then diluted with N, N'-dimethylformamide to a solid content concentration of 20%. The obtained polyamideimide resin had a logarithmic viscosity of 1.12 dl / g and a glass transition temperature of 305 ° C.
A composite porous membrane was produced in the same manner as in Example 1 using this polyamideimide resin solution. The porous film had a thickness of 17 μm, an air permeability of 95 seconds / 100 cc Air, a shutdown temperature of 122 ° C., and a meltdown temperature of 200 ° C. or higher.

[Example 6]
Using a solution in which 20 parts of polyethylene glycol (number average molecular weight 400) is blended with 100 parts of the polyamideimide resin solution of Example 1, a gravure having a spiral structure with an angle of 30 degrees and a groove width / line width of 0.3 mm / 0.3 mm After being applied to a polyethylene porous film using a roll, it is put into a coagulation bath having a water / N-methyl-2-pyrrolidone ratio of 70/30 (weight ratio), coagulated, washed and dried to form a composite porous material. A membrane was obtained. The composite porous membrane had a thickness of 22 μm, an air permeability of 132 seconds / 100 cc Air, a shutdown temperature of 120 ° C., and a meltdown temperature of 200 ° C. or higher. A battery performance such as discharge capacity and cycle durability of a coin battery manufactured using the composite porous membrane as a separator and having the same configuration as that of Example 1 showed good characteristics.

[Example 7]
A composite porous membrane was produced in the same manner as in Example 1 except that the polyethylene porous membrane used in Example 1 was changed to a polypropylene nonwoven fabric having a thickness of 15 μm. The composite porous membrane had a thickness of 18 μm, an air permeability of 86 seconds / 100 cc Air, a shutdown temperature of 165 ° C., and a meltdown temperature of 200 ° C. or higher.

[Comparative Example 1]
A polyamideimide resin was synthesized under the same conditions as in Example 1 except that TMA was changed to 1.07 mol in Example 2. The obtained polyamideimide resin had a logarithmic viscosity of 0.41 dl / g and a glass transition temperature of 295 ° C.
A polyimide-based porous film using this polyamide-imide resin is fragile because of its low molecular weight, and the coating film peeled off, making it unsuitable as a separator.

[Comparative Example 2]
Using the same apparatus as in Example 1, 0.15 mol of TMA, 0.85 mol of dimer acid, 1.02 mol of IPDI, and 0.02 mol of potassium fluoride were added so that the solid concentration was 50%. After charging with pyrrolidone and reacting at 180 ° C. for 5 hours, the solid content concentration was diluted to 25% with N-methyl-2-pyrrolidone while cooling. This polyamideimide resin had a logarithmic viscosity of 0.63 dl / g and a glass transition temperature of 53 ° C. Using this polyamide-imide resin solution, a composite porous membrane was prepared by printing on a polyethylene porous membrane in the same manner as in Example 1, and the battery characteristics were evaluated . However, meltdown and rapid shrinkage occurred at about 150 ° C. or less, and there was a problem in safety as a separator for a lithium ion secondary battery.

According to the present invention, by using a composite porous film in which a porous film of a polyimide resin having a glass transition temperature and a logarithmic viscosity in a specific range is laminated on a porous substrate in a geometric pattern , a shutdown characteristic and a melt Rutotomoni well balanced down characteristics, can control the air permeability without using an excess of polyimide porous film can provide a lithium ion secondary battery separator that can suppress the curling of the composite porous membrane.

Claims (10)

A composite porous membrane used as a separator for lithium ion secondary batteries, a polyimide porous film having a glass transition temperature of only polyimide resin is 70 ° C. or more and a logarithmic viscosity of 0.5 dl / g or higher, porous A composite porous membrane comprising a porous substrate coated in a lattice pattern and a coverage of 10 to 90% . Porous substrate, the composite porous membrane is a porous Makuma other consisting of polyethylene or polypropylene according to claim 1, characterized in that the non-woven fabric. The composite porous membrane according to claim 1 or 2, wherein the polyimide resin is a polyamide-imide resin whose acid component is mainly trimellitic anhydride. Polyimide-based resins are also part of the acid component such as ethylene glycol anhydrobis trimellitate , propylene glycol anhydro bis trimellitate, pyromellitic anhydride, benzophenone tetracarboxylic anhydride , and biphenyl tetracarboxylic anhydride The composite porous membrane according to claim 3 , wherein the composite porous membrane is a polyamide-imide resin using at least one member selected from the group consisting of: The polyimide resin is further at least one of its acid components selected from the group consisting of dimer acid, polyalkylene glycol, polyester , polycaprolactone , and butadiene rubber containing a carboxyl group, a hydroxyl group or an amino group at the terminal. 5. The composite porous membrane according to claim 4 , wherein the composite porous membrane is a substituted copolymer polyamideimide resin. The composite porous membrane according to any one of claims 1 to 5, wherein the polyimide-based porous membrane has a thickness of 0.5 to 30 µm, and the porous substrate has a thickness of 5 to 100 µm. A method for producing a composite porous membrane used as a separator of a lithium ion secondary battery,
(I) A solute solution consisting only of a polyimide resin having a glass transition temperature of 70 ° C. or higher and a logarithmic viscosity of 0.5 dl / g or higher is applied to a porous film or non-woven fabric made of polyethylene or polypropylene. After applying in a grid pattern by gravure roll or screen printing method to 90% ,
(II) It is miscible with the solvent in which the polyimide resin is dissolved, but for the polyimide resin, it is put into a solution that is a poor solvent and solidified .
A method for producing a composite porous membrane. The method for producing a composite porous membrane according to claim 7, wherein the polyimide resin is a polyamide-imide resin whose acid component is mainly trimellitic anhydride. Polyimide-based resins are also part of the acid component such as ethylene glycol anhydrobis trimellitate, propylene glycol anhydro bis trimellitate, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, and biphenyl tetracarboxylic anhydride The method for producing a composite porous membrane according to claim 8, wherein the composite porous membrane is a polyamide-imide resin using at least one or more members selected from the group consisting of: The polyimide resin is further at least one of its acid components selected from the group consisting of dimer acid, polyalkylene glycol, polyester, polycaprolactone, and butadiene rubber containing a carboxyl group, a hydroxyl group or an amino group at the terminal. The method for producing a composite porous membrane according to claim 9, wherein the method is a substituted copolymer polyamideimide resin.