JP4586327B2 - Polyamideimide resin for secondary battery separator, separator using the resin, and secondary battery using the separator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polyamide-imide resin exhibiting excellent shutdown temperature characteristics and high meltdown temperature characteristics as a separator for lithium ion secondary batteries that are required to improve safety, and a separator using the resin, and The present invention relates to a secondary battery using the separator.
[0002]
[Prior art]
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. In such a non-aqueous electrolyte battery, a flammable organic solvent is usually used as an electrolyte. However, in the unlikely event that both electrodes of the battery are short-circuited and a decomposition reaction of the battery contents occurs, the contents may leak due to a rapid temperature rise inside the battery. At present, countermeasures against such problems include attaching a safety valve and providing a shutdown function with a separator containing a meltable component.
[0003]
However, the safety valve is not an essential protective measure against a short circuit, but only relieves a sudden pressure increase inside the battery.
[0004]
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, As a result, the ionic conductivity is hindered and the battery reaction causing heat generation is suppressed (see, for example, Patent Documents 1, 2, and 3). However, when such a heat-meltable material is used, even if the shutdown function works due to heat rise, the temperature rises further, and the film itself melts and the isolation between the electrodes, which is the original function, is impaired. . This is a phenomenon called meltdown, which is not preferable for a battery. As measures for improving such problems, it has been proposed to widen the range of the shutdown temperature (see, for example, Patent Documents 4, 5, and 6). These are techniques such as laminating and coating a heat-meltable material on a porous membrane 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.
[0005]
[Patent Document 1]
Japanese Patent No. 2642206 ([Claims])
[Patent Document 2]
JP-A-6-212006 ([Claims])
[Patent Document 3]
Japanese Patent Laid-Open No. 8-138643 ([Claims])
[Patent Document 4]
Japanese Patent Publication No. 4-1692 ([0010])
[Patent Document 5]
JP-A-60-52 (Page 2)
[Patent Document 6]
JP 61-232560 A (page 2)
[0006]
[Problems to be solved by the invention]
The present invention has been made in view of such circumstances, and is an inexpensive separator excellent in insulation and excellent in shutdown characteristics and meltdown characteristics in place of conventionally used porous membrane separators, and secondary using the same. An object is to provide a battery.
[0007]
[Means for Solving the Problems]
As a result of intensive studies 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. We have found that a secondary battery can be obtained. That is, this invention is the following polyamideimide resin for secondary battery separators, the separator using the resin, and the secondary battery using the separator.
[0008]
(1) A polyamideimide resin for a secondary battery separator having a logarithmic viscosity of 0.5 dl / g or more and a glass transition temperature of 100 ° C. or more.
[0009]
(2) The polyamideimide resin is copolymerized with one or more of butadiene rubber, polyalkylene ether and polyester having any of a carboxyl group, a hydroxyl group and an amino group at the terminal. Polyamideimide resin for secondary battery separator.
[0010]
(3) The polyamideimide resin for a secondary battery separator according to (1) or (2), wherein the diamine component of the polyamideimide resin has an o-tolidine structure.
[0011]
(4) A secondary battery separator using the polyamideimide resin according to any one of (1) to (3).
[0012]
(5) The separator for secondary batteries according to (4), wherein the polyamideimide resin forms a porous film having a porosity of 30 to 80%.
[0013]
(6) The secondary battery separator according to (5), wherein a porous olefin having a porosity of 30 to 80% is further laminated on the polyamideimide porous membrane.
[0014]
(7) The separator for secondary batteries according to any one of (4) to (6), wherein the film thickness is 5 to 100 μm.
[0015]
(8) The separator for secondary batteries according to any one of (4) to (7), wherein the air permeability is 1 to 2000 sec / 100 cc Air.
[0016]
(9) A secondary battery using the separator according to any one of (4) to (8).
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below. The polyamide-imide resin of the present invention is synthesized by an ordinary method such as an acid chloride method using trimellitic acid chloride and diamine or a diisocyanate method using trimellitic anhydride and diisocyanate, but the diisocyanate method is preferred from the viewpoint of production cost.
[0018]
The acid component used for the synthesis of the polyamideimide resin is preferably trimellitic anhydride (chloride), 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), 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 Aromatic dicarboxylic acids such as phosphoric acid, diphenylsulfone dicarboxylic acid, diphenyl ether dicarboxylic acid, naphthalene dicarboxylic acid and the like can be mentioned. Among these, it is preferable to copolymerize dicarboxypolybutadiene, dicarboxypoly (acrylonitrile-butadiene), and dicarboxypoly (styrene-butadiene) having a molecular weight of 1000 or more from the standpoint of shutdown characteristics. Their copolymerization amount is preferably 2 mol% or more when the total acid component is 100 mol%.
[0019]
In addition, a part of the trimellitic acid compound can be replaced 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 two of the aforementioned dicarboxylic acids. Examples include polyesters having terminal hydroxyl groups synthesized from the above and one or more of the above glycols. Among these, polyethylene glycol having a molecular weight of 1000 or more or polyesters having terminal hydroxyl groups are copolymerized due to a shutdown effect. It is preferable. Their copolymerization amount is preferably 2 mol% or more when the total acid component is 100 mol%.
[0020]
Examples of the diamine (diisocyanate) component used in the synthesis of the polyamideimide resin include aliphatic diamines such as ethylenediamine, propylenediamine, and hexamethylenediamine, and diisocyanates thereof, 1,4-cyclohexanediamine, 1,3-cyclohexanediamine, and isophoronediamine. Alicyclic diamines such as 4,4′-dicyclohexylmethanediamine and their diisocyanates, m-phenylenediamine, p-phenylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, 4,4 ′ -Aromatic diamines such as diaminodiphenylsulfone, benzidine, o-tolidine, 2,4-tolylenediamine, 2,6-tolylenediamine, xylylenediamine, and diisocyanates thereof. Among these, 4,4′-diaminodiphenylmethane, o-tolidinediamine and these diisocyanates are preferable from the viewpoint of reactivity, cost, and resistance to electrolytic solution, and the amount of copolymerization thereof is 100 mol% of all amine components. In this case, it is preferable that both components are 50 mol% or more, and it is more preferable in terms of film strength that o-tolidinediamine and these diisocyanates are copolymerized in an amount of 30 mol% or more.
[0021]
The polyamideimide resin of the present invention is stirred in a polar solvent such as N, N′-dimethylformamide, N, N′-dimethylacetamide, N-methyl-2-pyrrolidone, γ-butyrolactone while heating at 60 to 200 ° C. It can be manufactured easily. 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.
[0022]
The polyamideimide resin of the present invention preferably has a glass transition temperature of 100 ° C. or higher and a logarithmic viscosity of 0.5 dl / g or higher. When the glass transition temperature is 100 ° 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. Moreover, even if the logarithmic viscosity is less than 0.5 dl / g, the porous film becomes brittle because there is a similar possibility due to a decrease in melting temperature and the molecular weight is low.
[0023]
Next, a method for producing a polyamideimide porous membrane will be described. The production of the film of the present invention is not particularly limited, but after coating the polyamideimide polymerization solution on a base material such as a polyester film to a predetermined thickness, or extruding the polymerization solution from a slit die into a film shape, It is preferable to put into a solution containing the main component and solidify.
[0024]
In the coagulation bath, 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, The porosity can be controlled by using a water-miscible solvent such as an amide solvent such as N-methyl-2-pyrrolidone together with water. The film thickness of the polyamideimide porous membrane is 5 to 100 μm, preferably 10 to 70 μm, more preferably 15 to 50 μm. If the film thickness is 5 μm or less, the film becomes weak and may break. Conversely, when the film thickness exceeds 100 μm, the cycle characteristics may deteriorate. The porosity of the polyamide-imi porous film is preferably 30 to 80%. More preferably, it is 40 to 70%. If the porosity is less than 30%, the electrical resistance of the film is increased, and it may be difficult to flow a large current. On the other hand, if it exceeds 80%, the film strength may be weakened. Here, the porosity is measured by measuring the average film thickness (At) and 10 cm square weight (Aw) of a film (A) prepared by casting and drying from a polyamideimide resin solution. It is a value calculated by the following formula from the average film thickness (Bt) of the porous film (B) prepared by solidification and the weight (Bw) of 10 cm square. Both film thicknesses must be adjusted to around 25 μm in order to completely remove the solvent.
Porosity = [1- (Bw / Bt) / (Aw / At)] × 100 (%)
The air permeability, which is a measure of the pore diameter, is preferably 1 to 2000 sec / 100 cc Air measured by a method (Gurley tester method) based on JIS P-8117, and if the air permeability is 1 sec / 100 cc Aircc or less, the membrane If the strength becomes weak and exceeds 2000 sec / 100 cc Air, the cycle characteristics may be deteriorated.
[0025]
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 polyamideimide resin in which a butadiene rubber having a number average molecular weight of 1000 or more, polyalkylene glycol, polyester, or the like is copolymerized in a block shape.
[0026]
The polyamideimide porous membrane of the present invention can be used in combination with a polyolefin-based porous membrane. The polyolefin-based porous membrane is produced by stretching a polyethylene or polypropylene film by a stretch opening method or a phase separation method. The film thickness in the case of laminating the polyamideimide porous membrane and the polyolefin porous membrane is 5 to 100 μm, preferably 15 to 70 μm. The porosity is preferably 30 to 80% and the air permeability is preferably 1 to 2000 sec / 100 cc Air.
[0027]
Each of the laminated films may be formed by simply laminating a single layer film, or a composite film obtained by applying a polyamide-imide resin solution to a polyolefin porous membrane as a base material, and adding the solution to water for solidification.
[0028]
The secondary battery using the polyamideimide porous membrane of the present invention thus configured as a separator exhibits the same battery performance as before, and can provide a safe battery with excellent shutdown characteristics and meltdown characteristics. . Here, the ionic species is not particularly limited, but lithium ion is particularly preferable in terms of versatility. The secondary battery according to the present invention can be manufactured according to a conventional method except that the separator of the present invention is used.
[0029]
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.
[0030]
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.
[0031]
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.
[0032]
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.
[0033]
【Example】
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.
1. 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.
2. 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.
3. Film thickness: The polyamideimide porous film was measured with a micrometer (μ-Mate) manufactured by Sony.
4). Porosity: The average film thickness (At) and weight of 10 cm square (Aw) of an approximately 25 μm film (A) prepared by casting and drying from a polyamideimide resin solution were measured, and solidified in water from the same polyamideimide resin solution. The porosity was calculated from the average thickness (Bt) of the approximately 25 μm porous membrane (B) prepared and the weight (Bw) of 10 cm square by the following formula.
Porosity = [1- (Bw / Bt) / (Aw / At)] × 100 (%)
5). Shutdown temperature characteristics: Using a porous membrane filled with a solution of lithium 4-fluoroborate dissolved in propylene carbonate at 1 mol / l, measurement was performed 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.
[0034]
Reference 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 0.01 mole of potassium fluoride with a solid content of 20 %, Together with N-methyl-2-pyrrolidone, stirred at 120 ° C. for 1.5 hours, heated to 180 ° C. and further stirred for about 3 hours to synthesize a polyamideimide resin. The obtained polyamideimide resin had a logarithmic viscosity of 0.86 dl / g and a glass transition temperature of 290 ° C.
This polyamideimide resin solution was applied onto a 100 μm-thick polyester film, immersed in water at 25 ° C. for about 3 minutes, peeled off from the polyester film, fixed with a metal frame, and dried at 100 ° C. for 10 minutes. The film thickness of the obtained polyamideimide film was 27 μm, the porosity was 65%, and the air permeability was 3.4 sec / 100 cc Air. The shutdown temperature of this film was 167 ° C., and the meltdown temperature was 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 prepared using a negative electrode as a binder and Sollite (manufactured by Mitsubishi Chemical) as an electrolytic solution, and the battery characteristics were evaluated. Compared to a commercially available separator (Cell Guard manufactured by Tonen Chemical Co., Ltd .: 25 μ), the discharge capacity and cycle characteristics were almost equivalent.
[0035]
Reference example 2
Polyamideimide resin was used under the same conditions as in Reference Example 1 except that TMA was 0.9 mol in Reference Example 1 and 0.1 mol of dicarboxypoly (acrylonitrile-butadiene) rubber (Hiker CTBN 1300 × 13: molecular weight 3500 made by Ube Industries) was changed to 0.1 mol. Synthesized. The obtained polyamidoimide resin had a logarithmic viscosity of 0.65 dl / g and a glass transition temperature of 203 ° C. A porous membrane was prepared from this polyamideimide resin solution by the same method as in Reference Example 1. This porous film had a thickness of 25 μm, a porosity of 48%, an air permeability of 4.6 sec / 100 cc Air, a shutdown temperature of 142 ° C., and a meltdown temperature of 200 ° C. or more.
[0036]
Reference example 3
Using the same apparatus as in Reference Example 1, 0.94 mol of TMA, 0.06 mol of polypropylene glycol having a molecular weight of 2000, and 1.02 mol of isophorone diisocyanate were charged together with γ-butyrolactone so that the solid concentration would be 50%. After reacting for a period of time, a polyamide-imide resin was synthesized by diluting with N-methyl-2-pyrrolidone so that the solid concentration was 20%. The obtained polyamideimide resin had a logarithmic viscosity of 0.63 dl / g and a glass transition temperature of 198 ° C. A porous membrane was prepared from this polyamideimide resin solution by the same method as in Reference Example 1. This porous film had a thickness of 30 μm, a porosity of 55%, an air permeability of 4.1 sec / 100 cc Air, a shutdown temperature of 134 ° C., and a meltdown temperature of 200 ° C. or more.
[0037]
Reference example 4
Using the same apparatus as in Reference Example 1, 0.93 mol of TMA, 0.07 mol of polycaprolactone (Placcel 220: molecular weight 2000) manufactured by Daicel Chemical Industries, 1.02 mol of MDI, and 0.02 mol of potassium fluoride had a solid content concentration of 50%. Then, the mixture was charged with γ-butyrolactone so that the mixture was reacted at 200 ° C. for about 5 hours, and then diluted with N-methyl-2-pyrrolidone so that the solid content was 20%. The obtained polyamideimide resin had a logarithmic viscosity of 0.71 dl / g and a glass transition temperature of 175 ° C. A porous membrane was prepared from this polyamideimide resin solution in the same manner as in Reference Example 1. The porous film had a thickness of 22 μm, a porosity of 43%, an air permeability of 6.7 sec / 100 cc Air, a shutdown temperature of 128 ° C., and a meltdown temperature of 200 ° C. or more.
[0038]
Example 5
Using the same apparatus as in Reference Example 1, 0.5 mol of TMA, 0.5 mol of dimer acid, 0.5 mol of o-tolidine diisocyanate, and 0.5 mol of MDI were added so that the solid concentration was 30%. -Charged together with pyrrolidone and allowed to react at 120 ° C for 1.5 hours and at 180 ° C for 3 hours. The obtained polyamideimide resin had a logarithmic viscosity of 0.70 dl / g and a glass transition temperature of 153 ° C. A porous membrane was prepared from this polyamideimide resin solution by the same method as in Reference Example 1. This porous film had a thickness of 28 μm, a porosity of 55%, an air permeability of 4.1 sec / 100 cc Air, a shutdown temperature of 121 ° C., and a meltdown temperature of 186 ° C.
[0039]
Comparative Example 1
A polyamideimide resin was synthesized under the same conditions as in Reference Example 1 except that TMA was changed to 1.07 mol in Reference Example 1. The obtained polyamideimide resin had a logarithmic viscosity of 0.35 dl / g and a glass transition temperature of 285 ° C. A porous membrane using this polyamideimide resin is fragile because of its low molecular weight, and is not suitable as a separator.
[0040]
Comparative Example 2
Using the same apparatus as in Reference Example 1, 0.3 mol of TMA, 0.7 mol of dimer acid, and 1 mol of MDI were charged together with N-methyl-2-pyrrolidone so that the solid concentration would be 40%, and reacted at 180 ° C. for 4 hours. I let you. The obtained polyamideimide resin had a logarithmic viscosity of 0.63 dl / g and a glass transition temperature of 82 ° C. A porous film was prepared from this polyamideimide resin by the same method as in Reference Example 1. This porous film had a good film thickness of 23 μm, porosity of 67%, and air permeability of 3.4 sec / 100 cc Air, but the shutdown temperature was as low as 72 ° C. and the meltdown temperature was as low as 118 ° C. Safety was insufficient.
[0041]
【The invention's effect】
The separator for secondary batteries using the polyamide-imide resin of the present invention is an inexpensive separator that has better shutdown characteristics and meltdown characteristics and better insulation than conventional porous membrane separators. It is possible to provide a secondary battery exhibiting excellent performance and cycle durability.

Claims (8)

And a logarithmic viscosity of 0.5 dl / g or more, and the glass transition temperature of Ri der 100 ° C. or higher, with a polyamideimide resin having a o- tolidine structure diamine component, air permeability of at 1~2000sec / 100ccAir A secondary battery separator . The secondary battery according to claim 1, wherein the polyamide-imide resin is copolymerized with one or more of butadiene rubber, polyalkylene ether and polyester having any of a carboxyl group, a hydroxyl group and an amino group at the terminal. separator. The polyamidoimide resin in which 4,4'-diaminodiphenylmethane, o-tolidinediamine, and these diisocyanates are copolymerized at 50 mol% or more when the total amine component is 100 mol% is used. Secondary battery separator. The secondary battery separator according to any one of claims 1 to 3, wherein a polyamide-imide resin in which o-tolidinediamine and these diisocyanates are copolymerized at 30 mol% or more when the total amine component is 100 mol% is used. The separator for secondary batteries according to any one of claims 1 to 4 , wherein the polyamideimide resin forms a porous film having a porosity of 30 to 80%. The separator for a secondary battery according to any one of claims 1 to 5 , wherein a porous olefin having a porosity of 30 to 80% is further laminated on the polyamideimide porous membrane. The separator for a secondary battery according to any one of claims 1 to 6 , wherein the film thickness is 5 to 100 µm. Secondary battery using the separator according to any one of claims 1 to 7.