JP2012033366A - Porous separator, lithium ion secondary battery, and method of manufacturing porous separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous separator contributing to a secondary battery having high output, heat resistance, and impact resistance, to provide a lithium ion secondary battery using the porous separator, and to provide a method of manufacturing the porous separator formed by applying.SOLUTION: The porous separator is characterized by being formed by using a coating liquid which contains an organic solvent-soluble polyimide resin and inorganic particulates.

Description

  The present invention relates to a porous separator, a lithium ion secondary battery using the same, and a method for producing the porous separator.

  In recent years, lithium-ion secondary batteries are required to have increased output for use in electric vehicles, and it is desired to increase the size of battery cells.

  In addition to output, the increase in size, in particular in electric vehicle applications, is subject to various vibrations, shocks, and heat storage for a long time during operation, which is more heat-resistant and safer than stationary applications such as power storage. A high one is required.

  The separator is required to have a sophisticated function of preventing a short circuit between the positive electrode and the negative electrode constituting the battery and not hindering the ionic conductivity of the electrolyte. In particular, it is fatal to cause a short circuit between electrodes due to deformation due to heat storage or impact, and various improvements have been made in recent years.

  In order to ensure high output and safety, a technology for directly forming a porous layer composed of insulating fine particles and a binder on the surface of the electrode active material layer (see Patent Document 1) has been developed. Heat resistance and handleability have been greatly improved with respect to separators made of a porous resin membrane (see Patent Document 2). And since the separator film thickness can be reduced by 50% or more, it has an advantage that a significant improvement in output can be achieved.

  However, in automotive applications, there is a need for a member that can maintain the function of the separator without being easily deformed even when exposed to high temperatures of about 300 ° C. or exposed to extreme vibrations and shocks. In fact, there is no member that can achieve both heat resistance and impact resistance.

Japanese Patent No. 3253632 JP-A-3-105851

  An object of the present invention is to provide a porous separator that contributes to a secondary battery that maintains high output and is excellent in heat resistance and impact resistance, a lithium ion secondary battery using the same, and a method for producing a porous separator by coating It is to provide.

  The above object of the present invention is achieved by the following means.

  1. A porous separator formed using a coating liquid containing an organic solvent-soluble polyimide resin and inorganic fine particles.

  2. 2. The porous separator according to 1 above, wherein the organic solvent-soluble polyimide resin is a block copolymerized polyimide resin obtained by dehydration condensation of tetracarboxylic dianhydride and diamine.

  3. A lithium ion secondary battery formed using the porous separator according to 1 or 2 above, comprising a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, and a non-aqueous electrolyte containing lithium ions A lithium ion secondary battery characterized by:

  4). 3. The method for producing a porous separator according to 1 or 2, wherein the porous separator is formed by coating on an active material layer of a positive electrode or a negative electrode of a lithium ion secondary battery.

  According to the present invention, it is possible to provide a porous separator that contributes to a secondary battery having high output, excellent heat resistance and impact resistance, a lithium ion secondary battery using the same, and a method for producing a porous separator by coating. did it.

  The best mode for carrying out the present invention will be described in detail below, but the present invention is not limited thereto.

  The present invention is characterized by using a porous separator containing an organic solvent-soluble polyimide resin and inorganic fine particles, which is directly formed on an active material layer of a positive electrode or a negative electrode by coating, maintaining a high output, and 300 A lithium ion secondary battery excellent in heat resistance and impact resistance can be obtained even at a high temperature of about ℃.

(Porous separator)
The porous separator of the present invention has at least one inorganic fine particle aggregate layer, and the fine particle aggregate contains the organic solvent-soluble polyimide resin of the present invention for bonding the fine particles as a binder, Further, at least one inorganic fine particle aggregate layer has a three-dimensional network void structure, whereby pores through which ions can pass are formed in the porous separator.

(Method for producing porous separator)
The porous separator according to the present invention is obtained by directly applying and drying a coating liquid composed of a dispersion containing a binder composed of a polyimide resin and inorganic fine particles on an active material layer of an electrode to be described later.

  There is no particular limitation on the method of preparing a separator coating liquid (hereinafter also referred to as a dispersion coating liquid) containing a binder made of polyimide resin and inorganic fine particles, and a known dispersion method considering the physical and chemical properties of the coating liquid. An appropriate method may be selected from the above.

  For example, when the viscosity of the dispersion is high, it is preferable to stir while vacuum degassing in order to prevent mixing of bubbles during stirring.

  The blending amount of the polyimide resin and the inorganic fine particles in the dispersion coating liquid is preferably 5% by mass to 50% by mass, and particularly preferably 10% by mass to 40% by mass with respect to the entire dispersion coating liquid.

  The dispersion medium used for dispersion is not particularly limited as long as a dispersion liquid can be prepared, but propylene glycol methyl ether, dipropylene glycol methyl ether, propylene glycol methyl ether acetate, cyclohexanone, dioxane, dioxolane, acetone, methyl ethyl ketone, methyl isobutyl. Examples include ketones, N-methyl-2-pyrrolidone, dimethyl sulfoxide, N, N-dimethylformamide, N, N-dimethylacetamide, and γ-butyrolactone. Of these, N-methyl-2-pyrrolidone is most preferred. In addition, the organic solvent which melt | dissolves the polyimide resin mentioned later used for this invention and the dispersion medium described here may be the same, and may differ.

  There is no restriction | limiting in particular in the coating method of a dispersion coating liquid, What is necessary is just to apply | coat and form a coating film using a conventionally well-known coating method. Examples of the coating method that can be preferably used include doctor blade coating, die coating, gravure coating, micro gravure coating, and roll coating.

  For drying the coating film, warm air, infrared rays, microwaves, or the like can be used. The drying temperature is preferably 60 ° C. or higher and 200 ° C. or lower, although it depends on the type of solvent used for the polyimide resin and the inorganic fine particle dispersion. Among them, the method of heating by infrared irradiation is a particularly preferable method in terms of heat resistance. The place to irradiate with infrared rays may be from the surface coated with the dispersion coating solution or from the back surface, but when irradiated with infrared rays from the back surface, it is absorbed or reflected by the current collector, and preferably the surface coated with the dispersion coating solution To drying by infrared irradiation. Examples of the infrared source include a normal infrared lamp, a xenon flash lamp, a xenon lamp, a xenon short arc lamp, a near infrared halogen heater, an infrared LED, an infrared laser, and the like. A xenon flash lamp, a xenon lamp, a near-infrared halogen heater, an infrared LED, a solid-state laser or a semiconductor laser emitting infrared light having a wavelength of 700 to 1500 nm is preferable. Further, another infrared source may be used as an auxiliary. As the far-infrared heater used as an infrared drying device, a panel-shaped, tubular, or lamp-shaped heater is used.

  The reason why the porous separator according to the present invention exhibits particularly good heat resistance and impact resistance is not clear, but in the process of drying the applied polyimide resin and the inorganic fine particle dispersion, particularly drying by infrared irradiation. In this case, since the entire temperature of the polyimide resin and the inorganic fine particle dispersion is uniformly increased in the thickness direction, the viscosity of the polyimide resin and the inorganic fine particle dispersion rises more uniformly over the whole, and the polyimide resin and the inorganic fine particles are more densely packed. It is presumed that a porous film (porous separator) having entanglement heat resistance is formed, and adhesion with the active material layer is more uniform and strong.

  The thickness of the coating film to be applied is not particularly limited, and the porous separator that is the produced porous film has sufficient mechanical strength and is a good ion when used as an electrode of a secondary battery. What is necessary is just to have conductivity.

  A preferable thickness of the porous separator is 2 μm to 40 μm after drying, and more preferably 4 μm to 30 μm. By forming the porous film so as to fall within the above range, a porous separator having sufficient mechanical strength and good ionic conductivity can be formed.

  The average pore diameter of the porous membrane is preferably 10 nm to 500 nm, more preferably 50 nm to 300 nm, from the viewpoints of output and heat resistance.

  The average pore size of the porous membrane (porous separator) can be measured by a nitrogen adsorption method using a pore size distribution measuring device (for example, OMISORP 100CX, manufactured by Beckman Coulter, Inc.). The adsorption-desorption isotherm of nitrogen is measured at −196 ° C., the pore diameter distribution is obtained using the adsorption isotherm (desorption side), and the average pore diameter can be calculated from the adsorption isotherm. In the present invention, since the electrode active material itself is also a porous film, the average pore diameter can be obtained by measuring only the electrode and taking the difference between the two.

  The average pore diameter can be adjusted by the type of polyimide resin used and the diameter of the inorganic fine particles, the concentration of the polyimide resin and the inorganic fine particle dispersion, the press work described below, and the like. In this invention, what gave roll press work can be used conveniently.

  Roll press processing is performed using a metal roll, an elastic roll, a heating roll, etc., for example. When performing the pressing, either a stereotaxic press or a constant pressure press may be performed. The pressure at the time of pressurization is preferably 100 to 700 kg / cm as a linear pressure from the viewpoint of the homogeneity of the porous membrane (porous separator) and mechanical damage prevention, and the particularly preferable pressure is 200 to 550 kg. / Cm.

  The gap between the pair of press rolls for rolling the porous separator is equal to or greater than the current collector thickness and smaller than the sum of the current collector thickness and the thickness of the electrode active material layer and the porous membrane (porous separator). It is preferable to adjust to.

  The porous separator may have a predetermined thickness by a single press, or may be pressed in several times for the purpose of improving homogeneity. Moreover, the temperature of a roll is not specifically limited, It heats and uses it to the temperature from room temperature to 200 degreeC. The pressing speed is preferably 0.1 to 50 m / min.

  In the present invention, the porous separator and the active material layer may be formed at the same time. For example, a porous separator and an active material layer can be formed simultaneously by forming a coating film by so-called multilayer coating and drying, which is a preferred embodiment in the present invention.

(Inorganic fine particles)
Examples of the inorganic fine particles include oxides [for example, Li ₂ O, BeO, B ₂ O ₃ , Na ₂ O, MgO, Al ₂ O ₃ , SiO ₂ , P ₂ O ₅ , CaO, Cr ₂ O ₃ , Fe ₂ O]. _3, ZnO, ZrO ₂ and TiO _2, etc.], zeolite _{[M 2 / n O · Al 2} O 3 · xSiO 2 · yH 2 O ( wherein, M is Na, K, metal atom such as Ca and Ba, n Is the number corresponding to the charge of the metal cation M ^{n +} , x and y are the number of moles of SiO ₂ and H ₂ O and 2 ≦ x ≦ 10, 2 ≦ y ≦)], nitrides (eg BN, AlN, Si ₃ N ₄ and Ba ₃ N ₂ etc.], silicon carbide (SiC), zircon (ZrSiO ₄ ), carbonates [eg MgCO ₃ and CaCO ₃ etc.], sulfates [eg CaSO ₄ and BaSO ₄ etc.] and These composites [for example, a kind of porcelain , Steatite (MgO · SiO ₂ ), forsterite (2MgO · SiO ₂ ), and cordierite (2MgO · 2Al ₂ O ₃ · 5SiO ₂ )].

  In general, it is preferable to use inorganic particles having high hardness. When such particles are used, the volume of the active material layer expands and the particles are not deformed even when pressure is applied to the separator. Therefore, a portion where the electrolyte can exist is always ensured, so that the ion conductivity is not lowered and the heat resistance of the battery is improved.

  The average particle size of the inorganic fine particles is preferably 5 nm to 100 μm, more preferably 5 nm to 10 μm, still more preferably 5 nm to 1 μm.

(Polyimide resin soluble in organic solvents)
The porous separator of the present invention includes an organic solvent-soluble polyimide resin that binds inorganic fine particles to each other.

  Preferable specific examples of the organic resin-soluble polyimide resin include blocks obtained by dehydration condensation of tetracarboxylic acid anhydride and diamine described in JP-A No. 2003-119285 and JP-A No. 2006-2163. Examples include copolymerized polyimide resins.

  The polyimide resin used in the present invention is soluble in an organic solvent, and the separator of the present invention is formed by coating. The organic solvent preferably has a boiling point of 30 ° C. or higher and 270 ° C. or lower at normal temperature and normal pressure.

  Preferable specific examples of the organic solvent include methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl n-hexyl ketone, diethyl ketone, diisopropyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone. , Acetylacetone, diacetone alcohol, cyclohexen-1-one, tetrahydrofuran, tetrahydropyran, anisole, phenetole, N-methylpyrrolidone (NMP), N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide and the like. .

  The polyimide resin of the present invention is preferably dissolved in an organic solvent in an amount of 10% by mass or more, and particularly preferably 40% by mass or more.

"Tetracarboxylic anhydride"
Examples of the tetracarboxylic acid anhydride include 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, 3,3 ', 4,4'-biphenyl ether tetracarboxylic dianhydride, 3,3', 4,4'-diphenylsulfone tetracarboxylic dianhydride, bicyclo (2,2,2) -oct-7-ene- 2,3,5,6-tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxylicoxyphenyl) hexafluoropropane dianhydride , Pyromellitic dianhydride, 5- (2,5-dioxotetrahydrofuryl) -3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, and these may be used alone or in two kinds It may be combined above.

"Diamine"
Examples of the diamine include silicone diamine, bis (3-aminopropyl) ether ethane, N, N-bis (3-aminopropyl) ether, 1,4-bis (3-aminopropyl) piperazine, isophorone diamine, 1 , 3'-bis (aminomethyl) cyclohexane, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane, 4,4'-methylenebis (cyclohexylamine), 4,4'- (or 3,4 ' -, 3,3'-, 2,4 '-) diamino-biphenyl ether, 4,4'-(or 3,4'-, 3,3 '-) diamino-diphenylmethane, 4,4'-(or 3,4'-, 3,3 '-) diamino-diphenylsulfone, 4,4'-(or 3,4'-, 3,3 '-) diamino-diphenyl sulfide, 2,4- ( 2,5-) diaminotoluene, 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 2,2-bis [4- (4-aminophenoxy) phenyl ] Propane, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone 4,4'-bis (4-aminophenoxy) biphenyl, 1,4-bis (4-aminophenoxy) benzene, 4,4'-diaminodiphenyl sulfide, 3,3'-diamino-4,4'-dihydroxy Biphenyl sulfone is mentioned, and these may be used alone or in combination of two or more.

"Production method"
The block copolymerized polyimide resin preferably used in the present invention is obtained by heating the above tetracarboxylic dianhydride and diamine in a ketone and / or ether solvent in the presence of an acid catalyst at 160 ° C. to 200 ° C. Next, tetracarboxylic dianhydride and / or diamine is added so that the molar ratio of total tetracarboxylic dianhydride and total diamine is 0.95 to 1.05. It is preferable to manufacture by the method of synthesize | combining a polymerization polyimide. The weight-average molecular weight of the block copolymerized polyimide is preferably 10,000 to 200,000 (measured by gel permeation chromatography and converted to standard polystyrene).

  Next, specific examples of particularly preferred organic solvent-soluble polyimide resins used in the present invention are listed, but the present invention is not limited to these.

"Concrete example"
BAPP: Polyimide resin described in Example 1 of JP-A-2003-119285 2BPDA + Si: Polyimide resin described in Example 2 of the same publication BCD + 2 isophoronediamine: Polyimide resin described in Example 3 of the same publication BPDA + 0.5Si + 0.5m-TPE + m− DADE: polyimide resin described in Example 4 of the same publication H-PMDA + 2m-BAPS: polyimide resin described in Example 5 of the same publication (lithium ion secondary battery)
The lithium ion secondary battery preferably used in the present invention includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, a non-aqueous electrolyte, and the porous separator of the present invention.

(Positive electrode and negative electrode)
The positive electrode preferably used in the present invention has a positive electrode active material on the current collector, and the negative electrode has a negative electrode active material on the current collector.

"Current collector"
As the current collector preferably used in the present invention, a chemically stable electron conductor in the secondary battery is used. Current collectors that can be used for the positive electrode include aluminum, stainless steel, nickel, titanium, and other metal plates, as well as aluminum or stainless steel surfaces treated with carbon, nickel, titanium, or silver. The alloy made into can be used preferably. Among these, aluminum and aluminum alloys can be used more preferably.

  The current collector used for the negative electrode is preferably copper, stainless steel, nickel, or titanium, and more preferably copper or a copper alloy.

  As the shape of the current collector, a film sheet is usually used, but a porous body, a foam, a molded body of a fiber group, and the like can also be used. Although it does not specifically limit as thickness of the said electrical power collector, 1-500 micrometers is preferable. Moreover, it is also preferable that the current collector surface is roughened by surface treatment.

(Positive electrode active material)
As the positive electrode active material, any of an inorganic active material, an organic active material, or a composite of both can be preferably used. Since the energy density of the battery is increased by using an inorganic active material or a composite of an inorganic active material and an organic active material, it can be particularly preferably used.

  Examples of inorganic active materials that can be preferably used include metal oxides, double oxides, phosphates, silicates, and borates.

As metal oxides and double oxides that can be used as the positive electrode active material, Li _0.3 MnO ₂ , Li ₄ Mn ₅ O ₁₂ , V ₂ O _5, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiFePO ₄ LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , Li _1.2 (Fe _0.5 Mn _0.5 ) _0.8 O ₂ , Li _1.2 (Fe _0.4 Mn _0.4 Ti _0.2 ) _0.8 O ₂ , Li _{1 + x} (Ni _0.5 Mn _0.5 ) _1-x O ₂ , LiNi _0.5 Mn _1.5 O ₄ , Li ₂ MnO ₃ , Li _0.76 Mn _{0 .5} 1Ti _0.49 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , Fe ₂ O _{3 and the} like. In these chemical formulas, x is in the range of 0-1.

Examples of phosphates, silicates, and borates that can be used as the positive electrode active material include LiFePO ₄ , LiCoPO ₄ , LiMnPO ₄ , Li ₂ MPO ₄ F (M = Fe, Mn), LiMn _0.875 Fe _{0. .125 PO 4, Li 2 FeSiO 4} , Li 2-x MSi 1-x P x O 4 (M = Fe, Mn), LiMBO 3 (M = Fe, Mn) and the like. In these chemical formulas, x is in the range of 0-1. Furthermore, metal fluorides such as FeF ₃ , Li ₃ FeF ₆ and Li ₂ TiF ₆ , metal sulfides such as Li ₂ FeS ₂ , TiS ₂ , MoS ₂ and FeS, and composite oxides of these compounds and lithium are also positive electrodes. It can be used as an active material.

  Examples of the organic active material include conductive polymers, sulfur-based positive electrode materials, and organic radical compounds.

  Examples of the conductive polymer that can be used as the positive electrode active material include polyacetylene, polyaniline, polypyrrole, polythiophene, and polyparaphenylene. Organic disulfide compound, organic sulfur compound DMcT (2,5-dimercapto-1,3,4-thiadiazole), benzoquinone compound PDBM (poly 2,5-dihydroxy-1,4-benzoquinone-3,6-methylene), carbon disulfide Sulfur-based positive electrode materials such as active sulfur, organic radical compounds, and the like are used.

The surface of the positive electrode active material is preferably coated with an inorganic oxide from the viewpoint of extending the battery life. As a method of coating the inorganic oxide, a method of coating the surface of the positive electrode active material is preferable, and as a method of coating, a method of coating using a surface modifying apparatus such as a hybridizer can be mentioned. Examples of inorganic oxides that can be used for the surface coating include magnesium oxide, silicon oxide, alumina, zirconia, titanium oxide oxide, barium titanate, calcium titanate, lead titanate, γ-LiAlO ₂ , LiTiO _{3, and the} like. In particular, it is preferable to coat with silicon oxide.

(Negative electrode active material)
The negative electrode active material is not particularly limited, and a known negative electrode active material can be used. Examples of the negative electrode active material that can be preferably used in the secondary battery of the present invention include graphite, a mixture of a tin alloy and a binder, a silicon thin film, and a lithium foil.

  The negative electrode active material of graphite or tin alloy and a binder can be obtained by mixing a powder such as graphite or tin alloy with a binder such as styrene butadiene rubber or polyvinylidene fluoride and drying the paste. The negative electrode active material of a silicon thin film can be obtained by physical vapor deposition (such as sputtering or vacuum vapor deposition) of a silicon thin film on a current collector. Although there is no restriction | limiting in particular in the thickness of the negative electrode active material layer of a silicon thin film, It is preferable that it is about 3-5 micrometers. As the negative electrode active material of the lithium foil, a current collector obtained by bonding a lithium foil having a thickness of 10 to 30 μm can be used. It is preferable to use a negative electrode active material composed of a silicon-based thin film negative electrode or a lithium metal negative electrode because the capacity can be increased and an electrode mixture is not essential.

"Active material layer additive"
The active material layer contains the positive electrode active material or the negative electrode active material, but preferably further contains a conductive agent and a binder. Other materials include filler, lithium salt, aprotic organic solvent, etc. May be.

  The conductive agent is not particularly limited as long as it is an electron conductive material that does not cause a chemical change in the configured secondary battery. As the conductive agent that can be preferably used in the present invention, one kind of conductive material selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder, metal fiber, polyphenylene derivative, and the like is used. Or a mixture of two or more. Among these, it is particularly preferable to use a mixture of graphite and acetylene black.

  As addition amount of a electrically conductive agent, 1-50 mass% is preferable and 2-30 mass% is more preferable. In the case of carbon or graphite, 2 to 15% by mass is particularly preferable.

  The binder is not particularly limited as long as it is a material that does not cause a chemical change in the constituted secondary battery. Examples of such a binder include polysaccharides, thermoplastic resins, and polymers having rubber elasticity.For example, starch, carboxymethyl cellulose, cellulose, diacetyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, sodium alginate, poly Water-soluble polymers such as acrylic acid, sodium polyacrylate, polyvinyl phenol, polyvinyl methyl ether, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylonitrile, polyacrylamide, polyhydroxy (meth) acrylate, styrene-maleic acid copolymer, polyvinyl chloride, Polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene furo (Meth) acrylic such as id-tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, polyvinyl acetal resin, methyl methacrylate, 2-ethylhexyl acrylate (Meth) acrylic acid ester copolymer containing acid ester, (meth) acrylic acid ester-acrylonitrile copolymer, polyvinyl ester copolymer containing vinyl ester such as vinyl acetate, styrene-butadiene copolymer, acrylonitrile -Butadiene copolymer, polybutadiene, neoprene rubber, fluoro rubber, polyethylene oxide, polyester polyurethane resin, polyether polyurethane resin, polycarbonate polyurethane Down resins, polyester resins, phenolic resins, emulsion (latex) or a suspension such as an epoxy resin.

  Among these binders, polyacrylate latex, carboxymethyl cellulose, polytetrafluoroethylene, and polyvinylidene fluoride are more preferable. The binder which can be used by this invention can be used individually by 1 type or in mixture of 2 or more types. When the amount of the binder added is small, the holding power and cohesive force of the electrode mixture are weakened. If the amount is too large, the electrode volume increases and the electrode unit volume or the capacity per unit mass decreases. For these reasons, the amount of the binder added is preferably 1 to 30% by mass, and more preferably 2 to 10% by mass.

  Any filler can be used as long as it is a fibrous material that does not cause a chemical change in the secondary battery of the present invention. Usually, olefin polymers such as polypropylene and polyethylene, fibers such as glass and carbon are used. Although the addition amount of a filler is not specifically limited, 0-30 mass% is preferable.

"Production method of electrode"
The secondary battery of the present invention can be applied to any shape such as a sheet type, a square type, and a cylinder type, and an optimal shape can be selected in accordance with the shape of the secondary battery used.

  The layer made of the positive electrode active material and the layer made of the negative electrode active material are provided on the current collector. The positive electrode active material layer and the negative electrode active material layer may be provided on one side or both sides of the current collector, and it is more preferable to use electrodes provided on both sides.

  There is no restriction | limiting in particular in the ratio of the magnitude | size of the negative electrode plate with respect to a positive electrode plate. The area of the positive electrode plate is preferably 0.9 to 1.1, particularly preferably 0.95 to 1.0, with respect to the area 1 of the negative electrode plate.

  The electrode is obtained by applying a coating solution containing an active material to the surface of a current collector, drying, and pressing to form an active material layer.

  As the coating solution, for example, a slurry-like coating solution containing a dispersion medium such as the above-mentioned conductive auxiliary agent, a binder, N-methyl-2-pyrrolidone (NMP), water, and toluene is used as necessary.

  Examples of the coating method include a reverse roll method, a direct roll method, a blade method, a knife method, an extrusion method, a curtain method, a gravure method, a bar method, a dip method, and a squeeze method. Of these, the blade method, knife method and extrusion method are preferred. Further, the coating speed is preferably 0.1 to 100 m / min. Under the present circumstances, the surface state of a favorable coating layer can be obtained by selecting the said coating method according to the solution physical property and drying property of a coating liquid. Application of the coating solution may be performed one side at a time or both sides simultaneously.

  Furthermore, the application of the coating solution may be continuous, intermittent or striped. The thickness, length and width of the active material layer are appropriately determined depending on the shape and size of the battery. The thickness of the active material layer is preferably such that the single-sided film thickness after drying is in the range of 1 to 2000 μm.

  The method for drying and dehydrating the active material layer formed by coating is not particularly limited, and a method in which hot air, vacuum, infrared rays, far infrared rays, electron beams and low-humidity air are used alone or in combination can be used. The drying temperature is preferably 80 to 350 ° C, more preferably 100 to 250 ° C. The formed active material layer is preferably pressure-bonded to increase the adhesion and the density of the active material layer. As a method for pressing the active material layer, a generally adopted method can be used, and a roll press method is particularly preferable. Although a press pressure is not specifically limited, 20-300 Mpa is preferable. The pressing speed is preferably 0.1 to 50 m / min, and the temperature during pressing is preferably room temperature to 200 ° C.

(Non-aqueous electrolyte)
The non-aqueous electrolyte preferably used in the present invention refers to a substance that dissolves in an organic medium and the solution exhibits ion conductivity.

  In this invention, the electrolyte salt containing Li ion is contained. As cations other than Li ions, metal ions of Group I or II of the Periodic Table can be included, and sodium salts and potassium salts are particularly preferably used.

Examples of the anion of the electrolyte salt include halide ions (I ⁻ , Cl ⁻ , Br ^{− and the} like), SCN ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , ClO ₄ ⁻ , SbF ₆ ⁻ , (FSO ₂ ) ₂ N ⁻ , ( ^{_{CF 3 SO 2) 2 N -}} , (CF 3 CF 2 SO 2) 2 N -, Ph 4 B -, (C 2 H 4 O 2) 2 B -, (CF 3 SO 2) 3 C -, CF 3 COO ⁻ , CF ₃ SO ₃ ⁻ , C ₆ F ₅ SO ₃ ^{— and the} like can be mentioned. Among these anions, SCN ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , ClO ₄ ⁻ , SbF ₆ ⁻ , (FSO ₂ ) ₂ N ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (CF ₃ CF ₂ SO ₂₎ ) ₂ N ⁻ , (CF ₃ SO ₂ ) ₃ C ⁻ , and CF ₃ SO ₃ ^— are more preferable.

Examples of the electrolyte salt that can be preferably used in the present invention include LiCF ₃ SO ₃ , LiPF ₆ , LiClO ₄ , LiI, LiBF ₄ , LiCF ₃ CO ₂ , LiSCN, LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ F ) ₂ , NaI, NaCF ₃ SO ₃ , NaClO ₄ , NaBF ₄ , NaAsF ₆ , KCF ₃ SO ₃ , KSCN, KPF ₆ , KClO ₄ , KAsF _{6 and the} like. More preferably, LiCF ₃ SO ₃ , LiPF ₆ , LiPF _n (C _k F _{(2k + 1)} ) _(6-n) (n = 1 to 5, k = 1 to 8), LiClO ₄ , LiI, LiBF ₄ , Examples include lithium salts such as LiCF ₃ CO ₂ , LiSCN, LiN (SO ₂ CF ₃ ) ₂ and LiN (SO ₂ F) ₂ , most preferably LiPF ₆ , LiBF ₄ , LiPF _n (C _k F _{(2k + 1)} ) _(6-n) , a lithium salt selected from LiN (SO ₂ CF ₃ ) ₂ and LiN (SO ₂ C ₂ F ₅ ) ₂ . These electrolyte salts may be used alone or in combination of two or more, but at least one of them preferably uses the same anion as the ionic liquid described above.

"Organic medium"
The organic medium used in the present invention is not particularly limited as long as it is a medium that does not deform / dissolve the separator, dissolves the electrolyte salt, and can be an electrolyte.

  Specific examples include carbonate compounds, heterocyclic compounds, ether compounds, chain ethers, nitrile compounds, and esters.

  Examples of the carbonate compound include ethylene carbonate, propylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Examples of the heterocyclic compound include 3-methyl-2-oxazolidinone. Examples of the ether compound include dioxane and diethyl ether. Examples of chain ethers include ethylene glycol dialkyl ether, propylene glycol dialkyl ether, polyethylene glycol dialkyl ether, and polypropylene glycol dialkyl ether. Examples of nitrile compounds include acetonitrile, glutarodinitrile, methoxyacetonitrile, propionitrile, and benzonitrile. Esters include carboxylic acid esters, phosphoric acid esters, and phosphonic acid esters. These organic media may be used alone or in combination of two or more.

  Among these organic media, ethylene carbonate, propylene carbonate, 3-methyl-2-oxazolidinone, acetonitrile, glutarodinitrile, methoxyacetonitrile, propionitrile, and benzonitrile can be particularly preferably used.

  The organic medium preferably has a boiling point of 200 ° C. or higher, more preferably 250 ° C. or higher, more preferably 270 ° C. or higher, from the viewpoint of improving heat resistance due to volatility. preferable.

  In the present invention, an ionic liquid can be used for the purpose of improving safety. The ionic liquid that can be used is not particularly limited as long as it has a very low melting point compared to a normal salt such as sodium chloride. The melting point of the ionic liquid used in the present invention is preferably 80 ° C. or less, more preferably 60 ° C. or less, and still more preferably 30 ° C. or less, so-called room temperature molten salt. Examples of the ionic liquid that can be preferably used in the present invention include alkyl ammonium salts, pyrrolidinium salts, piperidinium salts, imidazolium salts, pyridinium salts, sulfonium salts, and phosphonium salts. Particularly preferred is an imidazolium salt represented by the following general formula (1).

In the general formula (1), R ¹ and R ³ each independently represent an optionally substituted hydrocarbon group having 1 to 20 carbon atoms, and R ² , R ⁴ and R ⁵ are Each independently represents a hydroxyl group, amino group, nitro group, cyano group, carboxyl group, ether group, or hydrocarbon group having 1 to 10 carbon atoms which may have an aldehyde group or a hydrogen atom, and X is monovalent Specifically, chlorine, bromine, iodine, BF ₄ ⁻ , BF ₃ C ₂ F ₅ ⁻ , PF ₆ ⁻ , NO ₃ ⁻ , CF ₃ CO ₂ ⁻ , CF ₃ SO ₃ ⁻ , (FSO ₂₎ ) ₂ N ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (CF ₃ SO ₂ ) ₃ C ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ⁻ , AlCl ₄ ⁻ , Al ₂ Cl ₇ ^{− and the} like. .

  Specific examples of the compound represented by the general formula (1) include, for example, 1-isopropyl-2,3-dimethylimidazolium bistrifluoromethanesulfonyl salt, 1-ethyl-2,3-dimethylimidazolium bistrifluoromethanesulfonyl salt. 1-butyl-2,3-dimethylimidazolium bistrifluoromethanesulfonyl salt, 1-hexyl-2,3-dimethylimidazolium bistrifluoromethanesulfonyl salt, 1-octyl-2,3-dimethylimidazolium bistrifluoromethanesulfonyl Salts, and salts having the bistrifluoromethanesulfonyl anion moiety as bisfluorosulfonyl anions, among which 1-ethyl-2,3-dimethylimidazolium bisfluorosulfonyl salt is preferred in terms of ionic conductivity. It can be used properly.

  In the present invention, the amount of the supporting electrolyte salt in the electrolytic solution is preferably 5 to 40% by mass, and particularly preferably adjusted to be in the range of 10 to 30% by mass.

[Method for producing lithium ion secondary battery]
The lithium-ion secondary battery of the present invention has a laminate structure having the positive electrode active material layer on one surface of the separator according to the present invention and the negative electrode active material layer on the other surface, and is a porous separator. Impregnates an electrolytic solution containing a supporting electrolyte salt described below. The laminated structure is not limited to a single layered form, but a multi-layered structure having a plurality of laminated structures, a form in which layers stacked on both sides of a current collector are combined, and these are wound. A rotated form is mentioned. The application of the secondary battery of the present invention is not particularly limited. As an example, electronic devices include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, cordless phones, pagers, handy terminals, mobile faxes, mobile copy, mobile printers, headphone stereos, and video movies. , LCD TVs, handy cleaners, portable CDs, minidiscs, electric shavers, transceivers, electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, memory cards, and the like. Other consumer products include automobiles, electric vehicles, motors, lighting equipment, toys, game equipment, road conditioners, watches, strobes, cameras, medical equipment (such as pacemakers, hearing aids, and shoulder grinders). Furthermore, it can be used for various military use and space use. Moreover, it can also combine with a solar cell.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited at all by these Examples. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.
(Preparation of Separator Preparation Dispersion 1: Example 1 of Japanese Patent No. 3253632)
[Materials used]
Inorganic fine particles: α-Al ₂ O ₂ (particle A) having an average particle size of 0.5 μm
Resin binder: Fluoro rubber [trade name Miracron, manufactured by Asahi Kasei Corporation]
Solvent: Mixed solvent of ethyl acetate and ethyl cellosolve in a volume ratio of 1: 3 The above-mentioned milaflon was dissolved in a mixed solvent of ethyl acetate and ethyl cellosolve to prepare a 4.3 mass% milaflon solution, and α- Al ₂ O ₃ powder was mixed to obtain a slurry having a solid content of 45.3% by mass.

(Preparation of Separator Preparation Dispersion 2: Example 2 of Japanese Patent No. 3253632)
[Materials used]
Inorganic fine particles: α-Al ₂ O ₃ (particles B) having an average particle size of 1.0 μm
Resin binder: Polyvinylidene fluoride (PVDA) KF # 1100 [manufactured by Kureha Chemical Industry Co., Ltd.]
Solvent: 1-methyl-2-pyrrolidone (NMP)
The above α-Al ₂ O ₃ powder and PVDA powder are mixed at a mass ratio of 100: 5 while being in a powder state, and NMP is added thereto and further mixed to obtain a slurry having a solid content of 56.8% by mass. It was.

(Preparation of separator preparation dispersion 3: Example 4 of Japanese Patent No. 3253632)
[Materials used]
Inorganic fine particles: Zeolite having a molecular number ratio of SiO ₂ / Al ₂ O ₃ = 29 (particle C)
Resin binder: Polyvinylidene fluoride (PVDA) KF # 1100 [manufactured by Kureha Chemical Industry Co., Ltd.]
Solvent: 1-methyl-2-pyrrolidone (NMP)
The above zeolite powder and PVDA powder were mixed at a mass ratio of 100: 5 while being in a powder state, and NMP was added thereto and further mixed to obtain a slurry having a solid content of 55.0% by mass.

(Preparation of separator preparation dispersions 4 to 13: the present invention)
[Materials used]
Inorganic fine particles: α-Al ₂ O ₃ (particle A) having an average particle size of 1.0 μm
Resin binder: BAPP
Solvent: 1-methyl-2-pyrrolidone (NMP)
The above α-Al ₂ O ₃ powder and BAPP powder are mixed at a mass ratio of 100: 5 while being in a powder state, and NMP is added thereto and further mixed to obtain a slurry having a solid content of 56.8% by mass. It was. This is designated as a separator-preparing dispersion 4.

  In place of the preparation of the separator-preparing dispersion 4, the dispersion 5 is the same as the dispersion 4 except that the inorganic fine particles, the resin binder, the solvent, and the solid content ratio are changed to those described in Table 1. ~ 13 were made. Note that the solid content is changed to adjust the coating thickness.

(Production of electrodes)
A positive electrode and a negative electrode were produced according to the following method.

(Preparation of positive electrode)
To a powder obtained by mixing 90 parts of lithium iron phosphate (LiFePO ₄ ) and 6 parts of graphite powder, 4 parts of polyvinylidene fluoride (PVDA) KF # 1100 (manufactured by Kureha Chemical Industry Co., Ltd.) and 1-methyl- 2-Pyrrolidone was added to prepare a slurry. This slurry was applied to both surfaces of an aluminum foil having a thickness of 20 μm so that the thickness after drying was 100 μm. This positive electrode precursor was hot-air dried at 130 ° C. for 5 minutes and then roll-pressed to produce a positive electrode.

(Production of negative electrode)
A slurry was prepared by mixing 96 parts graphite, 2 parts styrene butadiene copolymer latex, 2 parts carboxymethylcellulose and water. This slurry was applied to both sides of a 15 μm thick copper foil so that the thickness after drying was 100 μm. The negative electrode precursor was hot-air dried at 130 ° C. for 5 minutes and then roll-pressed to produce a negative electrode.

(Production of lithium ion secondary battery cells 1 to 13)
The separator preparation dispersion 1 was applied to both surfaces of the negative electrode with a die coater so that the thickness after drying was 20 μm, and then dried with warm air at 130 ° C. to form a porous film (porous separator). An electrode for a secondary battery with an electrode separator was obtained.

Subsequently, current terminals (tabs) were ultrasonically welded to the uncoated portions of the positive electrode and the negative electrode, and then the positive electrode was stacked on the negative electrode, wound with a winding machine, and then put into a cylindrical can . This was dried under reduced pressure at 120 ° C., and ethylene carbonate (EC) and diethyl carbonate (DEC) were in a volume ratio of 3 in a dry can filled with dry air having an oxygen concentration of 10 ppm or less and a dew point of −60 ° C. or less. The electrolyte solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L was injected into the mixed solvent of No. 7 and sealed to manufacture the lithium ion secondary battery cell 1.

  In the production of the lithium ion secondary battery cell 1, the secondary battery cell shown in Table 1 was prepared in the same manner as in the production of the lithium ion secondary battery cell 1, except that the separator preparation dispersion 1 was changed to 2-13. 2 to 13 were produced.

(Evaluation of output characteristics)
The obtained secondary battery cell was charged / discharged at a current (5C) at a rate at which charging / discharging ended in 12 minutes with respect to the theoretical capacity in a voltage range of 2.0V to 4.0V in an environment of 23 ° C. The capacity retention when charging / discharging at 0.2 C was evaluated with the following rank.

◎: Holds a capacity of 95% or more ○: Holds a capacity of 90% or more and less than 95% △: Holds a capacity of 80% or more and less than 90% ×: Holds a capacity of less than 80% (Evaluation of heat resistance)
The obtained secondary battery cell was heated in a 300 ° C. constant temperature bath for 1 minute, allowed to cool naturally, and then at a voltage of 2.0 V to 4.0 V in a 23 ° C. environment with respect to the theoretical capacity. Then, charging / discharging was performed at a current (5C) at a rate at which charging / discharging ended in 12 minutes, and capacity retention when charging / discharging at 0.2C was evaluated in the following rank.

◎: Retains 90% or more capacity ○: Retains 85% or more and less than 90% capacity △: Retains 75% or more and less than 85% capacity x: Retains less than 75% capacity (Evaluation of impact resistance )
The obtained secondary battery cell was subjected to a vibration test in which vibration with a pulse width of 50 Hz was applied for 10 hours at 20G. The ratio of the discharge capacity after the vibration test to the discharge capacity before the vibration test as a percentage value was evaluated as the discharge capacity ratio in the following rank.

◎: Retains a capacity of 95% or more. ○: Retains a capacity of 90% or more and less than 95%. △: Retains a capacity of 80% or more and less than 90%. X: Retains a capacity of less than 80%. Show.

  From Table 1, it was found that the lithium ion secondary battery using the porous separator of the present invention maintained high output and was excellent in heat resistance and impact resistance.

Claims (4)

  A porous separator formed using a coating liquid containing an organic solvent-soluble polyimide resin and inorganic fine particles.   The porous separator according to claim 1, wherein the organic solvent-soluble polyimide resin is a block copolymerized polyimide resin obtained by dehydration condensation of tetracarboxylic dianhydride and diamine.   A lithium ion secondary battery formed using the porous separator according to claim 1, wherein a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, and a non-aqueous electrolyte containing lithium ions. A lithium ion secondary battery containing the lithium ion secondary battery.   The method for producing a porous separator according to claim 1, wherein the method is formed by coating on an active material layer of a positive electrode or a negative electrode of a lithium ion secondary battery.