JPH10106528A - Manufacture of separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a separator, which can obtain a battery having high capacity, high output characteristic, excellent cycle characteristic and safety at a low cost, by expanding film forming solution on a support, and thereafter, making the film forming solution contact the lean solvent of the film forming material. SOLUTION: A solution, which is obtained by dissolving a film forming material in the rich solvent, is expanded on a support, and thereafter, the rich solvent in the expanded film is replaced with the lean solvent by a contact with the lean solvent of the film forming material, and the film forming material is deposited so as to form the expanded film into the fine porous film. Width of selection of the material, which is limited in the conventional manufacture of separator, is thereby widened so as to lower the cost, and since a film at a relatively large porosity can be obtained, and ion resistance is reduced so as to reduce the lowering of capacity at the time of high output discharge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a separator. By using the separator according to the present invention, it is possible to improve the capacity at the time of high-power discharge by improving the ion permeability and to select a low-cost material. In addition, the cost of the battery can be reduced by simplifying the manufacturing process, and a battery excellent in safety can be obtained.

[0002]

2. Description of the Related Art In recent years, with the spread of portable devices such as video cameras and notebook personal computers, demand for small and high capacity secondary batteries has been increasing. Most of the currently used secondary batteries are nickel-cadmium batteries or nickel-hydrogen batteries using an alkaline electrolyte, but the battery voltage is as low as about 1.2 V, and it is difficult to improve the energy density. Therefore, non-aqueous electrolyte secondary batteries such as lithium secondary batteries using lithium metal for the negative electrode and lithium ion secondary batteries have been developed. In these batteries, a porous separator is inserted between the positive and negative electrodes to prevent conduction between the positive and negative electrodes.

[0003] Specifically, Japanese Patent Application Laid-Open No. HEI 8-195220 discloses a method for producing a porous lithium ion conductive polymer membrane. It is described that a hole is formed. However, in order to obtain high ionic conductivity, an extremely large number of holes are required, and it is a practically impossible manufacturing method in consideration of film strength and cost.

[0004]

In the prior art such as the above-mentioned known example, the cost of the battery is largely increased due to the high price of the separator and the complicated manufacturing process. . Further, in terms of battery performance, there was a problem such as a decrease in capacity at the time of high-power discharge due to resistance to ion permeability. Furthermore, there was a problem in safety at the time of a destructive test such as a nail penetration test.

[0005]

SUMMARY OF THE INVENTION The present invention has the following arrangement to solve the above-mentioned problems.

"A method for producing a separator, comprising: spreading a film-forming solution on a support, and then contacting the solution with a poor solvent for the film-forming material."

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention can be used as a separator for various batteries and the like.
What kind of battery is used is not particularly limited. That is, conventionally, cellulose paper, nonwoven fabric, or the like has been used as a separator in a dry battery, and these can be replaced with these. In addition, a nickel-cadmium battery, a nickel-hydrogen battery, a lithium battery, a lithium-ion battery, and the like use a microporous film of polyvinyl chloride or a polyolefin-based (polypropylene, polyethylene, etc.) synthetic resin. Is also possible.

The form of the battery is not particularly limited, such as a square type, a cylindrical type, a card type, and a coin type.

Hereinafter, for convenience, a cylindrical lithium ion secondary battery using a microporous polyolefin-based synthetic resin film as a separator will be described in detail by way of example.

In the present invention, after the film-forming solution is spread on the support, the solution is brought into contact with the poor solvent of the film-forming material, whereby the good solvent and the poor solvent in the developed film are replaced. By making the spread film microporous by depositing a film-forming material, it was possible to widen the range of material selection limited by the above-described conventional method for producing a separator (cost reduction). . That is, it can be easily prepared by appropriately selecting a film-forming material, a good solvent, a poor solvent, development conditions (temperature, time, concentration, etc.), and contact conditions (temperature, time, concentration, etc.) between a good solvent and a poor solvent. can do.

[0011] The separator according to the present invention can be manufactured as an independent film and inserted between the positive electrode and the negative electrode when the electrode is wound, like the conventional separator. Further, since a film having a relatively large porosity can be obtained, the ionic resistance is reduced, and a decrease in capacity during high-power discharge can be reduced. Further, the separator according to the present invention has an advantage that a stretching step is not required for making the separator porous unlike the conventional separator.

In the case where the electrode using the separator of the present invention is used, the electrode active material is not particularly limited, but particularly when it is used as the negative electrode active material, a carbon body is often suitably used. The carbon body is not particularly limited, and is generally obtained by firing an organic substance, graphite, or the like. As the form of the carbon body, a powdered or fibrous carbon body is preferably used.
Powdered carbon includes natural graphite, artificial graphite, coke such as fluid coke, mesocarbon microbeads, polyacrylonitrile (PAN), polyvinyl alcohol, lignin, polyvinyl chloride, polyamide, polyimide, phenolic resin, and furfuryl alcohol resin. ,
Alternatively, fired resin such as a copolymer thereof, pitch such as coal or petroleum, fired cellulose, and the like may be used. Examples of the fibrous carbon body include a PAN-based carbon fiber obtained from PAN or a copolymer thereof, a pitch-based carbon fiber obtained from a pitch such as coal or petroleum, a cellulosic carbon fiber obtained from cellulose, and a gas of a low molecular weight organic substance. Examples thereof include vapor-grown carbon fibers obtained from, and in addition, carbon fibers obtained by firing the above-mentioned polyvinyl alcohol, lignin, polyvinyl chloride, polyamide, polyimide, phenol resin, and furfuryl alcohol resin. Absent.

[0013] Among them, a carbon body satisfying the characteristics is appropriately selected according to the characteristics of the electrode and the battery in which the carbon body is used. In the case where the carbon material is used for a negative electrode of a secondary battery using a non-aqueous electrolyte containing an alkali metal salt, a PAN-based carbon material, a pitch-based carbon material, and a vapor-grown carbon material are preferable. In particular, a PAN-based carbon body is preferably used in that the doping of an alkali metal ion, particularly, a lithium ion is good. The particle size of the powdered carbon body is
Preferably 0.1 to 100 μm is used, and more preferably 1 to 50 μm. The diameter of the carbon fiber should be determined so as to easily adopt each form, but preferably 1 to 1000 μm is used, more preferably 1 to 20 μm.
μm, particularly preferably 3 to 15 μm. It is also preferable to use several types of carbon fibers having different particle sizes. The average length of carbon fiber is 1m
m or less, more preferably 50 μm or less, and still more preferably 8 to 30 μm. Further, as a lower limit, a ratio of a fiber length to a fiber diameter (aspect ratio) is preferably 1 or more. When the thickness is 1 mm or more, there is a drawback that the coating property is deteriorated when a slurry is formed to form a sheet-like electrode, and when the electrode is used, a short circuit between the positive electrode and the negative electrode easily occurs. When the aspect ratio is 1 or less, during powdering, the active carbon surface is exposed by cleavage in the fiber direction, so that the cycle characteristics deteriorate. The average length of the fiber is determined by measuring the length of at least 20 carbon bodies in the fiber direction by microscopic observation such as SEM. To cut or crush carbon fiber to 1mm or less,
Various mills can be used. In addition to the carbon body, for example, compounds such as metal oxides and polyacenes, metal lithium and alloys thereof as shown in JP-A-7-235293 can be used as the negative electrode active material.

For the negative electrode, a metal such as copper or stainless steel can be used as a current collector in order to enhance the current collecting effect. The metal current collector is not particularly limited to a foil shape, a fiber shape, a mesh shape, and the like.For example, when a metal foil current collector is used, a sheet is formed by applying a slurry on the metal foil. A shaped electrode is produced. In order to further enhance the current collection effect on the sheet electrode, as a conductive agent,
It is preferable to add carbon black such as acetylene black and Ketjen black. Further, conductive powder such as carbon powder and metal powder may be added for the purpose of improving conductivity.

In the battery using the separator according to the present invention, as the positive electrode active material used for the positive electrode, artificial or natural graphite powder, inorganic compounds such as carbon fluoride, metal oxides, and organic polymer compounds are used. Can be In this case, when an inorganic compound such as a metal oxide is used as the positive electrode, a charge / discharge reaction occurs using doping and undoping of the cation. When an organic polymer compound is used, a charge / discharge reaction occurs due to doping and undoping of an anion.
As described above, various charge / discharge reaction modes are adopted depending on the substance, and these are appropriately selected according to the required positive electrode characteristics of the battery. Specifically, inorganic compounds such as transition metal oxides and transition metal chalcogens containing alkali metals, conjugated polymers such as polyacetylene, polyparaphenylene, polyphenylenevinylene, polyaniline, polypyrrole, and polythiophene, polymers having disulfide bonds, and the like And positive electrode active materials used in ordinary secondary batteries. Among these, in the case of a secondary battery using a non-aqueous electrolyte containing a lithium salt,
Transition metal oxides such as cobalt, manganese, nickel, molybdenum, vanadium, chromium, iron, copper, and titanium, and transition metal chalcogens are preferably used. In particular, Lix
CoO ₂ (0 <x ≦ 1.0), LixNiO ₂ (0 <x
≦ 1.0) or a lithium composite oxide in which part of these metal elements is replaced with an alkaline earth metal element and / or a transition metal element, or LixMnO ₂ (0 <x ≦ 1.
0), Li _x Mn ₂ O ₄ (0 <x ≦ 1.3) and the like are preferably used.

Similar to the negative electrode, a metal such as aluminum, nickel, stainless steel, or titanium can be used as the current collector for the positive electrode in order to enhance the current collecting effect. Also,
Like the negative electrode, carbon black such as acetylene black and Ketjen black is added as a conductive agent. Further, conductive powder such as carbon powder and metal powder may be added for the purpose of improving conductivity.

The method for producing the positive and negative electrodes is not particularly limited, but a paste obtained by kneading a binder, an active material, and a conductive agent with an organic solvent or water on the above-mentioned current collector is applied. It is dried, pressed and formed into a sheet. The solvent and the solid content concentration used for the pasting are not particularly limited, but are appropriately determined in consideration of the resin used, the coating method, the drying conditions, and the like. Also, in the paste, a surfactant for improving applicability, an antifoaming agent, a dispersant,
Various additives such as an ultraviolet absorber and a stabilizer for improving storage stability can be added.

The material of the separator according to the present invention includes:
As long as it is generally used as a separator, it can be used without any particular limitation. Specific separator materials include thermoplastic resins such as polypropylene (PP), polyethylene (PE), ethylene vinylene acetate (EVA), N-substituted maleimide resin, and poly 4-
Polyolefins such as methylpentene-1, polytetrafluoroethylene (PTFE), polystyrene, polyvinylcarbazole, polyvinylidene fluoride (PVD
F), copolymers of PVDF and propylene hexafluoride, halogen-containing systems such as polyvinyl chloride (PVC), celluloses such as lignin and carboxycellulose (CMC), and water-soluble polymers such as polyvinyl alcohol (PVA) Amides such as polyimides, polyimides and polyamides, imides, acryls such as polyacrylonitrile (PAN), polyacrylates and their copolymers, esters such as polycaprolactam, polyethylene terephthalate, and polybutylene terephthalate, and other poly Sulfone, polyester sulfone, polycarbonate, polyarylate, modified polyphenylene oxide, polyetheretherketone, silicone resin, polyacetal, and the like are used. In addition, as a thermosetting resin,
Phenoxy resin, epoxy resin and the like are used. Further, a mixture of a thermoplastic resin and a thermosetting resin, two or more kinds of thermoplastic resins, two or more kinds of thermosetting resins, and the like are also used. The thickness of the separator is preferably 200 μm or less, more preferably 50 μm or less, particularly preferably 25 μm to reduce the internal resistance of the battery.
It is as follows.

In the present invention, a solution obtained by dissolving a film-forming material in a good solvent is spread on a support, and is brought into contact with a poor solvent of the film-forming material, whereby the good solvent in the spread film is removed. The developing solvent is replaced with the poor solvent to precipitate the film-forming material, thereby making the spread film microporous. A method for manufacturing such a separator will be described in detail below with reference to specific examples.

The film-forming material is dissolved in an amount of about several to 20% by weight. Next, a support such as a metal plate or a Teflon plate that is stable to various solvents is dipped in the raw material solution for several seconds to 10 minutes, and pulled up by, for example, a dip method. If necessary, excess raw material solution adhering to the support is removed.
Alternatively, the film-forming solution is spread on the support using a coating apparatus such as a knife coater to form a spread film. The developed film prepared on the support by the above method is put together with the support in a poor solvent such as water, methanol, ethanol, acetone or hexane (one kind or a mixed solution of two or more kinds) for several minutes to several tens. By immersion for a minute, the good solvent and the poor solvent in the developed film on the support are replaced to make the developed film microporous. Thereafter, drying is performed at a temperature of about several tens to 200 ° C., and the microporous membrane is released from the support to obtain an independent membrane. Stretching or pressing can be performed if necessary, for example, to increase the film strength. In addition, the micropores of the separator membrane may be slightly deformed by these processes,
By selecting the processing conditions (pressure, temperature, etc.)
A film that does not impair the separator performance can be obtained. This manufacturing method is characterized in that it is relatively easy to control the thickness and porosity of the separator by appropriately selecting the manufacturing conditions.

A battery using the separator according to the present invention is:
An improvement in capacity during high-power discharge can be achieved by improving ion permeability. In addition, it is not necessary to use a conventional expensive separator, and the cost can be reduced. Further, it is also preferable to add a heat absorbing material, a flame retardant material, an antioxidant, and the like to the separator according to the present invention from the viewpoint of improving safety during a safety test (crush test, nail penetration test). The heat absorbing material is not limited, but preferably has a melting point of about 80 to 200 ° C. and does not dissolve in the electrolytic solution. For example, stearate, palmitate and the like are used. Although it is not limited as a flame retardant, the melting point is 200 ° C.
Those which do not dissolve in the electrolytic solution and have the above degree are preferably used, and for example, hexabromobenzene is used.
Further, as the antioxidant, an antioxidant which suppresses oxidation and does not dissolve in the electrolytic solution, for example, hindered amine or hindered phenol can be preferably used.

The electrolyte for a battery using the separator of the present invention is not particularly limited, and examples thereof include an acid or alkali aqueous solution and a non-aqueous solvent. Among these, propylene carbonate (PC), ethylene carbonate (EC), and γ are used as electrolytes for a secondary battery composed of a non-aqueous electrolyte containing the above-described alkali metal salt.
-Butyrolactone (BL), N-methylpyrrolidone (N
MP), acetonitrile (AN), N, N-dimethylformamide, dimethylsulfoxide, tetrahydrofuran (THF), 1,3-dioxolan, methyl formate,
Sulfolane, oxazolidone, thionyl chloride, 1,2-
Dimethoxyethane (DME), dimethyl carbonate (DMC), diethylene carbonate (DEC), dimethylimidazolidinone, a derivative thereof, a mixture of two or more thereof, and the like are preferably used.

The electrolyte contained in the electrolyte may be an alkali metal, especially lithium halide, perchlorate, thiocyanate, borofluoride, phosphorus fluoride, arsenic fluoride, aluminum fluoride, trifluoromethyl. Sulfates and the like are preferably used. Applications of the secondary battery using the separator of the present invention include a video camera, a personal computer,
Word processor, boombox, mobile phone, handy terminal,
It is widely applicable to portable small electronic devices such as CD players, MD players, electric shavers, liquid crystal televisions, toys, and portable electronic devices such as electric vehicles.

[0024]

EXAMPLES Specific embodiments of the present invention will be described below with reference to examples, but the present invention is not limited thereto.

Example 1 (1) Preparation of Film-Forming Solution NMP was added to PVDF (KF Polymer # 2300, manufactured by Kureha Chemical Co., Ltd.), and the mixture was completely dissolved by stirring. A containing NMP solution was prepared.

(2) Preparation of microporous membrane A Teflon plate is immersed in the solution prepared in (1), then pulled up by a dipping method, immersed in a methanol solution for 20 minutes,
Thereafter, drying was performed at 60 ° C. for 20 minutes. The developed film was released from the Teflon plate, slit to a width of 58 mm and a length of 550 mm,
A separator having a thickness of 20 μm was obtained. The thickness of the separator was observed with a scanning electron microscope (SEM).

(3) Measurement of Specific Resistance An electrolytic solution was prepared by dissolving LiPF ₆ at a ratio of 1 mol / L in a mixed solvent of equal volumes of PC and DMC. In this electrolyte, the nickel positive and negative electrodes and the separator prepared in (2) were arranged between the positive and negative electrodes, and the Cole-Cole plot was measured by the complex impedance method to determine the specific resistance. Was. The measurement was performed at 25 ° C. in a glove box under an argon atmosphere.

(4) Thermal analysis The separator prepared in (2) was converted to a thermal analyzer (SSC5200 / DSC2
The DSC temperature rise curve was measured using 20C (manufactured by Seiko Electronics Co., Ltd.), and the endothermic onset temperature due to the melting of the separator was measured. In the table, the temperature of the lowest endothermic peak is shown. The measurement was performed in a dry nitrogen atmosphere at a temperature rising rate of 5 ° C./min using a sealed aluminum container.

Example 2 A separator was prepared in the same manner as in Example 1 except that PSF was used instead of PVDF as the film-forming material, and the specific resistance and the endothermic onset temperature were determined.

Example 3 A separator was prepared in the same manner as in Example 1 except that 25% of PVDF was replaced with zinc stearate (reagent grade: manufactured by Wako Pure Chemical Industries, Ltd.). The temperatures were determined and are shown in Table 1.

Comparative Example 1 The specific resistance and endothermic initiation temperature of a commercially available polyethylene separator (Celgard # 2400 made by Hoechst, thickness 25 μm) were determined in the same manner as in Example 1, and are shown in Table 1.

[Table 1] Example 4 A separator was produced in the same manner as in Example 1 except that 10% of PVDF was replaced with hexabromobenzene (reagent: manufactured by Wako Pure Chemical Industries, Ltd.). The separator is 17
Even after the pores were closed at around 0 ° C., it had shape retention up to 320 ° C.

From Examples 1 and 2 and Comparative Example 1, it is expected that the separator according to the present invention has a small specific resistance and excellent high output characteristics. From Examples 1 and 3, it can be seen that the addition of zinc stearate lowers the endothermic onset temperature and improves safety. By appropriately selecting the heat absorbing material, the heat absorption starting temperature can be arbitrarily set without lowering the separator function such as specific resistance.

Also, from Example 4, even after the separator shuts down, even if the temperature inside the battery rises,
Up to ° C, it has a function to prevent direct contact between the positive and negative electrodes, and is considered to be highly safe.

[0034]

By using the separator according to the present invention, high capacity, high output characteristics and good cycle characteristics can be obtained.
A low-cost and highly safe battery can be provided.

Continued on the front page (72) Inventor Naoki Shimoyama 1-1-1, Sonoyama, Otsu-shi, Shiga Toray Industries, Inc. Shiga Plant (72) Inventor Yoshio Matsuda 1-1-1, Sonoyama, Otsu-shi, Shiga Toray, Inc. Company Shiga Office

Claims (9)

[Claims] (1) developing a film-forming solution on a support,
A method for producing a separator, comprising contacting the solution with a poor solvent for a film-forming material. 2. The method for producing a separator according to claim 1, wherein said contact means is immersed in said poor solvent. 3. The method according to claim 1, wherein the solution contains at least one selected from a heat absorbing material, a flame retardant material and an antioxidant. 4. The method for producing a separator according to claim 3, wherein said heat absorbing material is an organic compound containing zinc and / or manganese. 5. The method according to claim 3, wherein the flame retardant is a bromine-containing organic compound. 6. The method according to claim 3, wherein said antioxidant is a hindered amine organic compound. 7. The method for producing a separator according to claim 1, wherein said film-forming solution is a thermoplastic resin solution. 8. The method according to claim 7, wherein the thermoplastic resin is a fluorine-containing polymer and / or a sulfur-containing polymer. 9. The method according to claim 1, wherein the film-forming solution is a thermosetting resin solution.