JP5368030B2 - Nonaqueous secondary battery separator, method for producing the same, and nonaqueous secondary battery - Google Patents

Nonaqueous secondary battery separator, method for producing the same, and nonaqueous secondary battery Download PDF

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JP5368030B2
JP5368030B2 JP2008215208A JP2008215208A JP5368030B2 JP 5368030 B2 JP5368030 B2 JP 5368030B2 JP 2008215208 A JP2008215208 A JP 2008215208A JP 2008215208 A JP2008215208 A JP 2008215208A JP 5368030 B2 JP5368030 B2 JP 5368030B2
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aqueous secondary
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JP2010050024A (en
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淳弘 大塚
聡 西川
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帝人株式会社
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50Manufacturing or production processes characterised by the final manufactured product
    • Y02P70/54Manufacturing of lithium-ion, lead-acid or alkaline secondary batteries

Description

  The present invention relates to a separator for a non-aqueous secondary battery that improves battery characteristics, a manufacturing method thereof, and a non-aqueous secondary battery.

  Lithium ion secondary batteries that use non-aqueous electrolytes are widely used as the main power source for portable electronic devices such as mobile phones and laptop computers because of their high capacity and high energy density. These batteries have a structure in which a separator made of an electrically insulative porous film is sandwiched between positive and negative electrodes, and the storage and discharge of lithium ions in the electrolyte flow between the electrodes. Is made.

  The basic characteristics of the separator are required to have electrical insulation between the electrodes, permeability of ions in the electrolyte, mechanical strength, etc., but the characteristics vary greatly depending on the separator material, manufacturing method, post-treatment, etc. To do.

  As a manufacturing method of a separator, there are roughly a dry process and a wet process. The dry process is a method of obtaining a porous film by dissolving a polymer such as a polyolefin resin, extruding it into a film, annealing, and stretching. On the other hand, the wet process is a method of obtaining a porous film by mixing a hydrocarbon solvent or other low molecular solvent and a polymer such as a polyolefin resin, processing it into a sheet, and removing the solvent.

  In addition, a separator having a laminated structure of different polymers is also known for improving battery safety. In order to manufacture this separator having a laminated structure, a method of coating a different polymer on a substrate such as polyolefin may be used.

  When producing a laminated separator by the method by coating, the coating solution is used by mixing a solvent that dissolves the polymer and, in some cases, a solvent that becomes a poor solvent for the polymer, washing with water after coating, In general, the solvent is removed by a drying step or the like. For example, a method disclosed in Patent Document 1 is known.

In Patent Document 1, a coating liquid using dimethylacetamide as a solvent for dissolving a polymer and tripropylene glycol as a solvent to be a poor solvent is coated on a polyethylene substrate, coagulated with a coagulating liquid, washed with water, and dried. Is going.
JP 2005-209570 A

  Here, in non-aqueous secondary batteries, it is known that if a large amount of impurities are mixed in materials such as electrodes, electrolytes, and separators, battery characteristics such as discharge characteristics are adversely affected. Therefore, it is necessary to appropriately manage the coating solvent remaining in the separator and the residual solvent present in the electrolyte so that the battery characteristics are not adversely affected.

However, as in the above-mentioned Patent Document 1, although the conventional technical document describes that the solvent is removed after the coating process, since there was no knowledge about the residual solvent, the residual solvent in the separator is not described. It was.
Therefore, an object of the present invention is to provide a separator having good battery characteristics by appropriately managing the residual solvent and the like of the separator.

In order to solve the above problems, the present invention employs the following configuration.
(1) A separator for a non-aqueous secondary battery comprising an electrically insulating breathable substrate and a porous layer laminated on one or both sides of the substrate, the breathable substrate or the porous A solvent that is contained in the porous layer and is a poor solvent for the polymer that forms the porous layer is contained in an amount of 0.001 to 3% by weight based on the weight of the separator. Separator for non-aqueous secondary battery.
(2) The nonaqueous secondary battery separator according to (1), wherein the solvent is contained in an amount of 0.001 to 1.5% by weight or less based on the weight of the separator.
(3) The nonaqueous secondary battery separator according to (1) or (2), wherein the solvent is one or more solvents selected from alcohols and polyhydric alcohols. .
(4) The non-aqueous system according to any one of (1) to (3), wherein the breathable substrate is a substrate formed of a thermoplastic resin and having pores or voids therein. Secondary battery separator.
(5) The above polymer (1), wherein the polymer is one or more polymers selected from aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide. The separator for non-aqueous secondary batteries according to any one of) to (4).
(6) The method for producing a separator for a non-aqueous secondary battery according to (1), wherein (i) a polymer for forming the porous layer is prepared by using a solvent for dissolving the polymer and the polymer In a solution containing a solvent that is a poor solvent to prepare a coating solution, and (ii) a step of applying the coating solution to one or both sides of the breathable substrate, iii) a step of immersing the substrate after the coating step in a coagulation bath to solidify the polymer; (iv) a step of washing the substrate after the coagulation step with water; and (v) a substrate after the water washing step. And a step of drying the material. A method for producing a separator for a non-aqueous secondary battery.
(7) The method for producing a separator for a non-aqueous secondary battery according to (1) above, wherein (i) a polymer for forming the porous layer, a solvent for dissolving the polymer, and the polymer (Ii) a step of applying the coating solution to one or both sides of the breathable substrate, and (ii) a step of dissolving in a solution containing a solvent that is a poor solvent. and iii) drying the substrate after the coating step, volatilizing the solvent, and solidifying the polymer, and a method for producing a separator for a non-aqueous secondary battery.
(8) A non-aqueous secondary battery that obtains an electromotive force by doping and dedoping lithium, and includes a positive electrode, a negative electrode, a separator disposed between these electrodes, and an electrolytic solution. A non-aqueous secondary battery using the separator for a non-aqueous secondary battery according to any one of (1) to (5) as the separator.
(9) A non-aqueous secondary battery for obtaining an electromotive force by doping and dedoping of lithium, comprising a positive electrode, a negative electrode, a separator disposed between these electrodes, and an electrolytic solution The separator includes an electrically insulating air-permeable base material and a porous layer formed on one or both surfaces of the base material by a coating method, and the electrolyte layer includes the porous layer. A non-aqueous secondary battery comprising 0.001 to 0.15% by weight of a solvent which is a poor solvent for the polymer to be formed, based on the weight of the electrolytic solution.

  According to the present invention, since the residual solvent concentration in the separator or the residual solvent concentration present in the electrolyte is controlled within an appropriate range, the adverse effect of the residual solvent on the battery characteristics can be solved, and the initial charge can be reduced. A battery having good discharge characteristics and the like can be provided.

[Separator for non-aqueous secondary battery]
The present invention is a separator for a non-aqueous secondary battery comprising an electrically insulating breathable substrate and a porous layer laminated on one or both sides of the substrate, the breathable substrate or A solvent that is contained in the porous layer and that is a poor solvent for the polymer that forms the porous layer is contained in an amount of 0.001 to 3% by weight based on the weight of the separator. This is a separator for a non-aqueous secondary battery.

  In the present invention, it is important that a solvent which is a poor solvent for the polymer forming the porous layer is contained in an amount of 0.001 to 3% by weight based on the weight of the separator. This is because, when adjusted within such a range, a battery having good initial charge / discharge characteristics and small self-discharge can be obtained. When the solvent is contained in the separator in an amount of more than 3% by weight, a film that deteriorates battery characteristics is formed on the electrode surface. However, if it is within the range of 3% by weight or less, a good film that does not deteriorate the performance is obtained. A battery having good initial charge / discharge characteristics can be obtained. Also, if the solvent concentration in the separator is less than 0.001% by weight, a good film will not be formed, resulting in a battery with a large self-discharge amount, but within a range of 0.001% by weight or more. Thus, a battery having a small self-discharge amount can be obtained without causing such a phenomenon.

  In the present invention, the solvent concentration is preferably 0.001 to 1.5% by weight. In such a range, in addition to the above good initial charge / discharge characteristics and self-discharge characteristics, a battery having further excellent impedance characteristics can be obtained.

  In the present invention, the residual solvent in the separator may be contained in the gas permeable substrate or the porous layer. That is, this is because the residual solvent exists only in the breathable substrate, the residual solvent exists only in the porous layer, and the residual solvent exists in both the breathable substrate and the porous layer. It is meant to include any of the states.

  In the present invention, the solvent that is a poor solvent for the polymer is one or two or more solvents selected from alcohols and polyhydric alcohols. Specific examples of alcohols include methanol, ethanol, propanol, isopropyl alcohol, and 1-butanol. Examples of polyhydric alcohols include ethylene glycol, tripropylene glycol, and glycerin.

  In the present invention, the air permeable substrate means a substrate having pores or voids therein. Examples of such a substrate include a microporous membrane, a nonwoven fabric, a paper-like sheet, and other sheets having a three-dimensional network structure, and a microporous membrane is particularly preferable. A microporous membrane means a membrane that has a large number of micropores inside and has a structure in which these micropores are connected, allowing gas or liquid to pass from one surface to the other. To do. Moreover, although the organic material or inorganic material which has electrical insulation can be used for the material which comprises this base material, it is preferable to use a thermoplastic resin from a viewpoint which provides a shutdown function to a base material. Here, the shutdown function is a function that prevents the movement of the battery and prevents thermal runaway of the battery by melting the thermoplastic resin and closing the hole of the breathable base material when the battery temperature is raised. Means. As the thermoplastic resin, a thermoplastic resin having a melting point of less than 200 ° C. is suitable, preferably a polyolefin, and particularly preferably polyethylene. The polyethylene is not particularly limited, but high-density polyethylene or a mixture of high-density polyethylene and ultrahigh molecular weight polyethylene is suitable. For example, in addition to polyethylene, other polyolefins such as polypropylene and polymethylpentene may be mixed and used.

  The thickness of the breathable substrate is preferably 5 μm or more and 18 μm or less. If the thickness of the breathable substrate is less than 5 μm, mechanical properties such as tensile strength and puncture strength will be insufficient, and if the thickness of the breathable substrate is greater than 18 μm, it will be difficult to achieve an appropriate separator thickness. It is not preferable.

  The air-permeable base material preferably has a porosity of 20 to 60%. If the porosity of the air-permeable substrate is less than 20%, the membrane resistance of the entire separator becomes too high, and the output of the battery is remarkably lowered. On the other hand, if it exceeds 60%, the shutdown characteristic is remarkably deteriorated.

  The Gurley value (JIS P8117) of the breathable substrate is preferably 10 sec / 100 cc or more and 500 sec / 100 cc or less. When the Gurley value of the air-permeable base material is higher than 500 sec / 100 cc, the ion permeability is insufficient and the problem that the resistance of the separator increases is caused. When the Gurley value of the air-permeable base material is lower than 10 sec / 100 cc, the shutdown function is remarkably lowered. The puncture strength of the breathable substrate is preferably 10 g or more.

  In the present invention, the porous layer can use various polymers depending on the function to be imparted to the separator, but particularly from the viewpoint of imparting heat resistance, aromatic polyamide, polyimide, polyethersulfone, polysulfone, It is preferably formed of one or more heat resistant polymers selected from polyether ketone and polyether imide. In addition, an inorganic filler such as a metal oxide or a metal hydroxide may be added to the porous layer, and such an effect that the heat resistance is further improved by adding such an inorganic filler.

  The porous layer may be formed on at least one surface of the base material, but it is more preferable to form the porous layer on both the front and back surfaces from the viewpoints of handling properties, durability, and the effect of suppressing heat shrinkage. When the porous layer is a heat resistant porous layer, when the heat resistant porous layer is formed on both surfaces of the substrate, the total thickness of the heat resistant porous layer is 3 μm or more and 12 μm. Or when the heat-resistant porous layer is formed only on one side of the substrate, the heat-resistant porous layer preferably has a thickness of 3 μm or more and 12 μm or less. In any case, when the total thickness of the heat-resistant porous layer is less than 3 μm, sufficient heat resistance, particularly a heat shrinkage suppressing effect cannot be obtained. On the other hand, when the total thickness of the heat-resistant porous layer exceeds 12 μm, it is difficult to realize an appropriate separator thickness. The porosity of the heat resistant porous layer is preferably in the range of 50 to 90%. If the porosity of the heat-resistant porous layer exceeds 90%, the heat resistance tends to be insufficient, and if it is lower than 50%, the cycle characteristics, storage characteristics, and discharge characteristics tend to decrease, such being undesirable.

[Method for producing separator for non-aqueous secondary battery]
Although the manufacturing method of the non-aqueous secondary battery separator of this invention is not specifically limited, For example, it is possible to manufacture through the following processes (i)-(v). That is, (i) a polymer for forming the porous layer is dissolved in a solution containing a solvent that dissolves the polymer and a solvent that is a poor solvent for the polymer, and a coating solution is obtained. A step of producing, (ii) a step of applying the coating liquid to one or both sides of the breathable substrate, and (iii) immersing the substrate after the application step in a coagulation bath to coagulate the polymer. And (iv) a step of washing the substrate after the coagulation step with water, and (v) a step of drying the substrate after the step of washing with water.

  For example, when an aromatic polyamide obtained from an aromatic dicarboxylic acid and an aromatic diamine is used as the polymer, in the step (i), the aromatic dicarboxylic acid and the aromatic diamine are produced with respect to the resulting polyamide. By reacting in an organic solvent which is a good solvent to produce an aromatic polyamide (solution polymerization), an aromatic polyamide solution that directly becomes a coating solution can be produced.

  In addition, when polymetaphenylene isophthalamide is used as the polymer, for example, in the step (i), isophthalic acid chloride and metaphenylenediamine are converted into organic solvents that are not good solvents for the polyamide to be formed, such as tetra It is convenient to produce polymetaphenylene isophthalamide by the so-called interfacial polymerization method, in which it is reacted in hydrofuran to form a solution or dispersion, which is contacted with an aqueous solution of an acid acceptor such as sodium carbonate to complete the reaction. It is.

  In the step (i), the solvent (good solvent) for dissolving the polymer is not particularly limited, but specifically, a polar solvent is preferable, for example, N-methylpyrrolidone, dimethylacetamide, dimethylformamide, dimethylsulfoxide and the like. Is mentioned. The solvent to be the poor solvent is as described above, but by applying such a solvent, a microphase separation structure is induced, and the formation of a porous layer facilitates the formation of a porous layer.

In the step (ii), the polymer coating solution is applied to at least one surface of the breathable substrate. In the present invention, it is preferable to apply to both surfaces of the breathable substrate. The polymer concentration of the coating solution is preferably 4 to 9% by weight, and the coating amount on the substrate is preferably about 20 to 40 g / m 2 . Examples of the coating method include knife coater method, gravure coater method, screen printing method, Mayer bar method, die coater method, reverse roll coater method, ink jet method, spray method, roll coater method and the like. From the viewpoint of uniformly applying the coating film, the reverse roll coater method is particularly suitable. More specifically, for example, when the coating liquid is applied to both surfaces of the breathable base material, the coating liquid is excessively applied to both surfaces of the base material through a pair of Meyer bars, A method of precise measurement by passing through a reverse roll coater and scraping off an excessive coating liquid can be mentioned.

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

  The step (iv) is to remove the coagulating liquid by washing with respect to the separator immersed in the coagulating liquid. For example, the step (iv) is performed by immersing the separator in a water washing bath. At this time, the longer the immersion time, the lower the concentration of the solvent remaining in the separator.

  In the step (v), the separator after the water washing step is dried. The drying method is not particularly limited, but the drying temperature is suitably 40 to 80 ° C. When a high drying temperature is applied, a method of contacting the roll to prevent a dimensional change due to heat shrinkage occurs. It is preferable to apply.

  In addition, the manufacturing method of the separator for non-aqueous secondary batteries of this invention is not limited to the wet process mentioned above, For example, following (i)-(iii) may be implemented. That is, (i) a polymer for forming the porous layer is dissolved in a solution containing a solvent that dissolves the polymer and a solvent that is a poor solvent for the polymer, A step of producing, (ii) a step of applying the coating liquid to one or both sides of the breathable substrate, and (iii) drying the substrate after the application step to volatilize the solvent, Solidifying the molecule. In such a method, the solvent for dissolving the polymer and the solvent that is a poor solvent for the polymer can be the same as those in the wet process described above.

[Non-aqueous secondary battery]
The non-aqueous secondary battery of the present invention is a non-aqueous secondary battery that obtains an electromotive force by doping and dedoping lithium, and among these non-aqueous secondary batteries, a lithium ion secondary battery is preferable.

  Specifically, the non-aqueous secondary battery of the present invention includes a positive electrode, a negative electrode, a separator disposed between these electrodes, and an electrolytic solution, and such a battery element is provided on the exterior. It is enclosed.

  The non-aqueous secondary battery of the present invention is characterized in that the separator for non-aqueous secondary batteries of the present invention described above is used as the separator. With such a battery, as described above, it is possible to obtain good battery characteristics such that the residual solvent does not adversely affect the battery characteristics, the initial charge / discharge characteristics are good, and the self-discharge is small. .

  Further, in the non-aqueous secondary battery of the present invention, even when the above-described separator for non-aqueous secondary battery is not used, as the separator, an electrically insulating air-permeable base and one or both sides of this base In the electrolyte solution, a solvent which is a poor solvent for the polymer forming the porous layer is added to the weight of the electrolyte solution. It may be contained in an amount of 0.001 to 0.15% by weight. Even with such a battery, the above-described good battery characteristics can be obtained. In addition, the solvent which is said poor solvent may be added in electrolyte solution as an additive.

  The negative electrode has a structure in which a negative electrode mixture composed of a negative electrode active material, a conductive additive, and a binder is formed on a current collector (copper foil, stainless steel foil, nickel foil, etc.). As the negative electrode active material, a material capable of electrochemically doping lithium, for example, a carbon material, silicon, aluminum, tin, or the like is used.

The positive electrode has a structure in which a positive electrode mixture composed of a positive electrode active material, a conductive additive, and a binder is formed on a current collector. Examples of the positive electrode active material include lithium-containing transition metal oxides such as LiCoO 2 , LiNiO 2 , LiMn 0.5 Ni 0.5 O 2 , LiCo 1/3 Ni 1/3 Mn 1/3 O 2 , LiMn 2 O. 4 and LiFePO 4 are used.

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

  Examples of the exterior material include a metal can or an aluminum laminate pack. The shape of the battery includes a square shape, a cylindrical shape, a coin shape, and the like, but the separator of the present invention can be suitably applied to any shape.

The test methods in the examples of the present invention are as follows.
[Measurement of poor solvent concentration in separator]
10 ml of N-methyl-2-pyrrolidone was added to a separator (0.1 g, 8.3 × 10 −3 m 2 ), immersed for 24 hours, and then subjected to ultrasonic treatment for 30 minutes. Extracted with methyl-2-pyrrolidone. Then, the poor solvent concentration contained per separator weight was determined by GC-MS (Agilent 6890 / 5973-GC / MS).

[Measurement of charge / discharge characteristics]
In order to evaluate the charge / discharge characteristics of the battery, a non-aqueous secondary battery was produced as follows.
1) Positive electrode 6 wt% PVdF so that the lithium cobalt oxide (LiCoO 2 , Nippon Chemical Industry Co., Ltd.) powder 89.5 parts by weight, acetylene black 4.5 parts by weight and PVdF dry weight 6 parts by weight A positive electrode paste was prepared using the NMP solution. The obtained paste was applied onto an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a thickness of 97 μm.
2) Negative electrode 6 wt% PVdF so that the dry weight of mesophase carbon microbeads (MCMB, manufactured by Osaka Gas Chemical Co., Inc.) powder 87 parts by weight, acetylene black 3 parts by weight and PVdF 10 parts by weight as the negative electrode active material. An NMP solution was used to prepare a negative electrode agent paste. The obtained paste was applied onto a copper foil having a thickness of 18 μm, dried and pressed to prepare a negative electrode having a thickness of 90 μm.
3) electrolytic solution of ethylene carbonate and ethyl methyl carbonate of 3: a mixed solution with 7 weight ratio, were used as LiPF 6 was dissolved at a 1 mol / L.
4) Trial manufacture of non-aqueous secondary battery Separator (2.6 cm × 2.2 cm) in which the positive electrode (2 cm × 1.4 cm) and the negative electrode (2.2 cm × 1.6 cm) were prepared in the following examples and comparative examples It was made to face through. This was impregnated with the above electrolytic solution (0.15 to 0.21 g) and sealed in an exterior made of an aluminum laminate film to produce a non-aqueous secondary battery.
5) Charging / discharging characteristics Using a charging / discharging measuring device (HJ-101SM6 manufactured by Hokuto Denko Co., Ltd.), the charging / discharging characteristics of the non-aqueous secondary battery manufactured by the above method were examined. In the measurement, the battery was charged at 1.6 mA / h to 4.2 V, and then discharged at 1.6 mA / h to 2.75 V, which was defined as one cycle. The initial charge / discharge characteristics indicate the charge / discharge characteristics of the first cycle.

[Measurement of impedance characteristics]
After continuously measuring the charge / discharge characteristics for 5 cycles (after 5 cycles of charge / discharge), an AC impedance measuring device (SI1260, SI1287 manufactured by Toyo Technica Co., Ltd.) is used for a non-aqueous secondary battery charged to 4.2V. It was used and measured by the AC impedance method under conditions of an amplitude of 10 mV and a frequency of 0.1 to 100,000 Hz.

[Durability test]
After continuously measuring the charge / discharge characteristics for 5 cycles (after 5 cycles of charge / discharge), the non-aqueous secondary battery charged to 4.2 V was stored at 80 ° C. for 3 days using a heating and drying furnace. The voltage of the non-aqueous secondary battery was measured, and the voltage drop that occurred before and after storage was investigated. And since the self-discharge was so small that a voltage drop was small, it evaluated that favorable durability was shown.

[Measurement of poor solvent concentration in electrolyte]
About the electrolytic solution obtained by disassembling the non-aqueous secondary battery produced by the above method, the concentration of the poor solvent contained per electrolytic solution weight is obtained using GC-MS (Agilent 6890 / 5973-GC / MS). It was.

[Example 1]
1) Production of polymetaphenylene isophthalamide Into a reaction vessel equipped with a thermometer, a stirrer, and a raw material inlet, 753 g of NMP having a moisture content of 100 ppm or less was placed. In this NMP, 85.2 g of metaphenylenediamine and 0.5 g of aniline were added. Was dissolved and cooled to 0 ° C. To this cooled diamine solution, 160.5 g of isophthalic acid chloride was gradually added with stirring to react. This reaction increased the temperature of the solution to 70 ° C. After the change in viscosity stopped, 58.4 g of calcium hydroxide powder was added and stirred for another 40 minutes to complete the reaction, and the polymerization solution was taken out and reprecipitated in water to obtain 184.0 g of polymetaphenylene isophthalamide. .

2) Production of polyethylene microporous membrane As polyethylene powder, GUR2126 (weight average molecular weight 4150,000, melting point 141 ° C) and GURX143 (weight average molecular weight 560,000, melting point 135 ° C) manufactured by Ticona were used. GUR2126 and GURX143 are made to be 1: 9 (weight ratio), and liquid paraffin (manufactured by Matsumura Oil Research Co., Ltd .; Smoyl P-350P; boiling point 480 ° C.) and decalin so that the polyethylene concentration becomes 30% by weight. A polyethylene solution was prepared by dissolving in a mixed solvent. The composition of this polyethylene solution was polyethylene: liquid paraffin: decalin = 30: 45: 25 (weight ratio).

  This polyethylene solution was extruded from a die at 148 ° C. and cooled in a water bath to prepare a gel tape (base tape). The base tape was dried at 60 ° C. for 8 minutes and at 95 ° C. for 15 minutes, and then the base tape was stretched by biaxial stretching that was performed in the order of longitudinal stretching and lateral stretching. Here, the longitudinal stretching was 5.5 times, the stretching temperature was 90 ° C., the transverse stretching was 11.0 times the stretching ratio, and the stretching temperature was 105 ° C. After transverse stretching, heat setting was performed at 125 ° C. Next, this was immersed in a methylene chloride bath to extract liquid paraffin and decalin. Then, it dried at 50 degreeC and annealed at 120 degreeC, and obtained the polyethylene microporous film.

3) Manufacture of non-aqueous secondary battery separator Using the polymetaphenylene isophthalamide obtained above and a polyethylene porous membrane, and using an inorganic filler in combination with this, the separator for non-aqueous secondary battery of the present invention is manufactured. did.

  Specifically, the inorganic filler made of polymetaphenylene isophthalamide and aluminum hydroxide having an average particle size of 0.8 μm (made by Showa Denko KK; H-43M) is adjusted to a weight ratio of 25:75. These were mixed in a mixed solvent in which dimethylacetamide (DMAc) and tripropylene glycol (TPG) as a poor solvent had a weight ratio of 50:50 so that the polymetaphenylene isophthalamide concentration was 5.5% by weight. A slurry for coating was obtained.

  An appropriate amount of the above slurry for coating was placed on a Mayer bar, and the coating slurry was applied to both sides of the polyethylene microporous membrane by passing the polyethylene microporous membrane between a pair of Meyer bars. This was immersed in a coagulation liquid having a weight ratio of water: DMAc: TPG = 50: 25: 25 and 40 ° C. Thereafter, the obtained film was immersed in a water washing tank having a water temperature of 40 ° C. for 23 minutes and then dried. This obtained the separator for non-aqueous secondary batteries of this invention.

[Example 2]
A non-aqueous secondary battery separator of the present invention was obtained in the same manner as in Example 1 except that the washing time was changed to 9 minutes.

[Example 3]
A non-aqueous secondary battery separator of the present invention was obtained in the same manner as in Example 1 except that the washing time was changed to 6 minutes.

[Example 4]
A separator for a non-aqueous secondary battery of the present invention was obtained in the same manner as in Example 1 except that the poor solvent used in the coating slurry and the coagulation liquid was changed from tripropylene glycol to ethylene glycol.

[Example 5]
A separator for a non-aqueous secondary battery of the present invention was obtained in the same manner as in Example 1 except that the poor solvent used in the coating slurry and the coagulation liquid was changed from tripropylene glycol to methanol.

[Example 6]
A separator for a non-aqueous secondary battery of the present invention was obtained in the same manner as in Example 1 except that the poor solvent used in the coating slurry and the coagulating liquid was changed from tripropylene glycol to isopropyl alcohol.

[Comparative Example 1]
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1 except that the washing time was changed to 3 minutes.

[Comparative Example 2]
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1 except that the washing time was changed to 120 minutes.

(1) Poor solvent concentration in the separator Table 1 shows the results of measuring the poor solvent concentration for each of the separators of Examples 1 to 6 and Comparative Examples 1 and 2 produced as described above. From the results in Table 1, it can be seen that the longer the washing time, the lower the solvent concentration. In Table 1, since Comparative Example 2 was below the detection limit concentration, it was expressed as “<0.002.”

(2) Concentration of poor solvent in electrolytic solution For each separator of Examples 1 to 6 and Comparative Examples 1 and 2 prepared as described above, a non-aqueous secondary battery was prepared and included in the electrolytic solution. The results of measuring the amount of poor solvent are shown in Table 1. In Table 1, since Comparative Example 2 was below the detection limit concentration, it was expressed as “<0.002”.

(3) Evaluation / Durability Test of Initial Charge / Discharge Characteristics Regarding the separators of Examples 1 to 6 and Comparative Examples 1 and 2 produced as described above, the charge capacity, the discharge capacity, and the initial charge / discharge efficiency were determined. The measured results are shown in Table 2. Table 2 also shows the voltage drop obtained by the durability test.

  From Table 2, it can be evaluated that the initial charge and discharge characteristics of Examples 1 to 6 are equally excellent, but Comparative Example 1 is inferior in discharge capacity and efficiency as compared with other Examples. Moreover, although the voltage drop of Examples 1-6 is small and can be evaluated that it is equally excellent, it turns out that the voltage drop of the comparative example 2 is large and inferior compared with another Example. From these results, it can be seen that when the concentration of the poor solvent in the separator is 0.001 to 3% by weight, a battery having good initial charge / discharge characteristics and durability can be obtained.

(4) Evaluation of impedance characteristic Next, the result of having measured the impedance characteristic about each separator of Examples 1-3 and Comparative Examples 1 and 2 is shown in FIG.
As can be seen from FIG. 1, Examples 1 and 2 can be evaluated as having excellent impedance characteristics of the same level, but Example 3 is inferior in impedance characteristics to Examples 1 and 2. Furthermore, it can be seen that the impedance characteristics of Comparative Example 1 are inferior to those of Example 3. In addition, although illustration is abbreviate | omitted, the impedance characteristic comparable as Examples 1 and 2 was acquired also about Examples 4-6.

From the above, it can be seen that when the poor solvent concentration in the separator is 0.001 to 1.5% by weight, a battery having excellent impedance characteristics in addition to good initial charge / discharge characteristics can be obtained.
Moreover, when the above results are compared with the poor solvent concentration in the electrolytic solution, if the poor solvent concentration is 0.001 to 0.15% by weight in the electrolytic solution, the initial charge / discharge characteristics, durability, and impedance characteristics are It turns out that it is favorable.

It is the graph which showed the impedance characteristic of the Example and comparative example of this invention.

Claims (5)

  1. A separator for a non-aqueous secondary battery comprising an electrically insulating air-permeable base material and a porous layer laminated on one or both surfaces of the base material,
    The solvent, which is contained in the gas-permeable base material or the porous layer and is a poor solvent for the polymer forming the porous layer, is 0.07 to 2.48 weight based on the weight of the separator. % Is included,
    The solvent, alcohols, and Ri one or more solvents der selected from polyhydric alcohols,
    The air-permeable base material is a microporous membrane formed of a thermoplastic resin, and is a separator for a non-aqueous secondary battery.
  2.   The separator for a non-aqueous secondary battery according to claim 1, wherein the solvent is contained in an amount of 0.07 to 1.23% by weight based on the weight of the separator.
  3.   3. The polymer according to claim 1, wherein the polymer is one or more polymers selected from aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide. The separator for non-aqueous secondary batteries as described.
  4.   A non-aqueous secondary battery that obtains an electromotive force by doping and dedoping lithium,
      A positive electrode, a negative electrode, a separator disposed between these electrodes, and an electrolyte,
      The non-aqueous secondary battery separator according to any one of claims 1 to 3 is used as the separator.
      A non-aqueous secondary battery.
  5.   A non-aqueous secondary battery that obtains an electromotive force by doping and dedoping lithium,
      A positive electrode, a negative electrode, a separator disposed between these electrodes, and an electrolyte,
      The separator includes an electrically insulating air-permeable base and a porous layer formed by a coating method on one or both sides of the base,
      In the electrolytic solution, a solvent that is a poor solvent for the polymer that forms the porous layer is contained in an amount of 0.003 to 0.095% by weight based on the weight of the electrolytic solution,
      The solvent is one or more solvents selected from alcohols and polyhydric alcohols,
      The non-aqueous secondary battery, wherein the air permeable substrate is a microporous film formed of a thermoplastic resin.
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