JP2012033314A - Secondary battery separator, method of manufacturing the same, electrode with secondary battery separator, and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery separator having high output, safety and excellent cycle characteristic, a method of manufacturing the secondary battery separator and an electrode with the secondary battery separator, and to provide a secondary battery using the electrode with the secondary battery separator.SOLUTION: The secondary battery separator which includes nanofibers is characterized by being formed by annealing treatment on a coated film containing the nanofibers.

Description

  The present invention relates to a separator for a secondary battery, a manufacturing method thereof, an electrode with a separator for a secondary battery, and a secondary battery.

  Secondary batteries are widely used as power sources for devices such as household appliances and communication devices. In particular, portable devices using lithium ion secondary batteries are increasing because they have a high volumetric efficiency and are reduced in size and weight when installed in devices.

  On the other hand, large secondary batteries are being researched and developed in many fields related to energy and environmental issues, including electric vehicles, and are superior in terms of large capacity, high output, high voltage, and long-term storage. Applications of lithium ion secondary batteries, which are a type of non-aqueous electrolyte secondary battery, are expanding. It is important for such a large battery to have high output and high safety because of its use and energy storage.

  In the lithium ion secondary battery, a separator is interposed between the positive electrode and the negative electrode from the viewpoint of preventing an internal short circuit. Of course, the separator is required to have insulating properties due to its role. Moreover, it is necessary to have a microporous structure in order to provide air permeability as a lithium ion passage and a function of diffusing and holding the electrolyte.

  In order to ensure high output and safety, for example, the separator interposed between the positive electrode and the negative electrode is replaced with a heat-resistant fibrous material (nonwoven fabric) from the conventional polyolefin-based porous film. A technique is known (for example, refer to Patent Document 1).

  However, large batteries need to operate stably over a long period of time, and the above technique is still insufficient for stable operation. For example, the fibrous material (nonwoven fabric) is provided on a porous membrane. However, the thickness of the separator is increased, the high output characteristics are inferior, and further improvements are required (for example, see Patent Documents 2 and 3).

Special table 2010-500717 Special table 2010-500718 gazette JP 2010-44935 A

  The present invention has been made in view of the above circumstances, and its solution is to provide a separator for a secondary battery having high output, safety and excellent cycle characteristics, a method for producing the same, and an electrode with a separator for a secondary battery. That is. Moreover, it is providing the secondary battery using the said electrode with a separator for secondary batteries.

  The above-mentioned problem according to the present invention is solved by the following means.

  1. A separator for a secondary battery comprising a nanofiber, the separator being formed by subjecting a coating film containing the nanofiber to an annealing treatment.

  2. 2. The secondary battery separator according to claim 1, wherein the secondary battery separator has a crystallinity of 40 to 90%.

  3. 3. The secondary battery separator according to item 1 or 2, wherein the secondary battery separator contains nylon nanofibers and is subjected to a water vapor annealing treatment.

  4). A method for producing a separator for a secondary battery containing nanofibers, comprising a step of applying a dispersion containing the nanofibers, and a step of annealing the coating film formed in the step. A method for manufacturing a separator for a secondary battery.

  5. The method for manufacturing a separator for a secondary battery as described in the above item 4, wherein the annealing treatment is a water vapor annealing treatment.

  6). An electrode with a secondary battery separator, wherein the secondary battery separator according to any one of items 1 to 3 is formed on an electrode active material layer.

  7). A secondary battery comprising the secondary battery separator according to any one of the first to third aspects.

  By the above means of the present invention, it is possible to provide a separator for a secondary battery having high output, safety and excellent cycle characteristics, a production method thereof, and an electrode with a separator for a secondary battery. Moreover, the secondary battery using the said electrode with a separator for secondary batteries can be provided.

  The separator for a secondary battery of the present invention (hereinafter also simply referred to as “separator”) is a separator for a secondary battery containing nanofibers, and is formed by subjecting a coating film containing the nanofibers to an annealing treatment. It is characterized by that. This feature is a technical feature common to the inventions according to claims 1 to 7.

  As an embodiment of the present invention, it is preferable that the degree of crystallinity of the secondary battery separator is in the range of 40 to 90% from the viewpoint of the effect of the present invention. In addition, it is preferable that the secondary battery separator contains nylon nanofibers and is subjected to a water vapor annealing treatment.

  As a manufacturing method of the separator for secondary batteries containing nanofiber, it is a manufacturing method of the aspect which has the process of apply | coating the dispersion liquid containing the said nanofiber, and the process of annealing-treating the coating film formed at the said process. It needs to be. In this case, it is preferable that the annealing treatment is a water vapor annealing treatment.

  The separator for a secondary battery of the present invention can be suitably used for an electrode with a separator for a secondary battery in an aspect in which the separator for a secondary battery is formed on an electrode active material layer.

  Moreover, the separator for secondary batteries of this invention can be used suitably for the secondary battery of various aspects.

  Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In addition, in this application, "-" is used in the meaning which includes the numerical value described before and behind that as a lower limit and an upper limit.

[Secondary battery separator]
The separator for a secondary battery of the present invention is a separator for a secondary battery containing nanofibers, and is characterized in that an annealing treatment is performed after the separator is formed.

  Hereinafter, the components will be described in detail.

(Nanofiber)
The “nanofiber” as used in the present application is a resin fiber having a single yarn diameter of 10 to 250 nm, has an electrical insulation property, is electrochemically stable, and further contains an electrolyte solution described in detail below. If it is stable with respect to the solvent for dispersion | distribution used in the case of separator manufacture, there will be no restriction | limiting in particular.

  The “single yarn diameter” is the diameter of the single yarn forming the resin fiber aggregate, and can be determined by image observation using a transmission electron microscope, a scanning electron microscope, or the like.

  That is, a cross section of a single yarn (single fiber) or a single fiber bundle (fibrous aggregate) is observed with a transmission electron microscope (TEM; for example, H-7100FA type manufactured by Hitachi, Ltd.), and randomly within the same cross section. It can be determined by measuring the extracted 100 or more single fibers with the equivalent circle diameter and simply averaging them. That is, the diameter of a fiber cross-sectional photograph by TEM can be calculated using image processing software (for example, WINROOF), and a simple average value thereof can be obtained.

  For the measurement of the fiber length, a photograph in which a fine fibrous material was magnified about 2000 times by a scanning electron microscope (SEM; for example, S-4000 type manufactured by Hitachi, Ltd.) was taken, and then analysis of this photographic image was performed. Can be measured.

  The fineness of the nanofiber is preferably 0.0000005 dtex or more and 0.0005 dtex or less. More preferably, it is 0.0000001 dtex or more and 0.0001 dtex or less.

  Here, the fineness means the thickness of the nanofiber long fiber yarn. The unit tex means mass (number of grams) around 1000 meters long. The fineness can be measured using, for example, a motorcycle bro fineness measuring instrument DenierComputer DC-77A (manufactured by Search Co., Ltd.).

  As the resin component constituting the nanofiber, any resin component having fiber-forming ability may be used. For example, nylon 6, nylon 66, nylon 11, nylon 12, nylon 610, nylon 6T, nylon 6I, nylon 9T, nylon M5T, Polyamide such as nylon 612, nylon copolymer, polyethylene terephthalate, polyethylene terephthalate copolymer, polybutylene terephthalate, polybutylene terephthalate copolymer, polyolefin such as polyethylene, polypropylene, polymethylpentene, polychlorinated Vinyl polymers such as vinyl, polyvinylidene chloride, polytetrafluoroethylene, and polyvinylidene fluoride, polyurethane, polyacrylonitrile, polyglycolic acid, glycolic acid copolymer , Polylactic acid, aliphatic polyester polymers such as lactic acid copolymer, aliphatic polyester polymers such as coupleramide, tetramethylene adipamide, undecanamide, laurolactamide, hexamethylene adipamide, etc. Two or more kinds of resins such as aliphatic polyesteramide copolymers may be combined. Among these, polyamides of nylon copolymers such as nylon 6, nylon 11, nylon 12, nylon 66, nylon 610, nylon 6T, nylon 6I, nylon 9T, nylon M5T, nylon 612 and the like are preferably used in terms of heat resistance. It is done.

  The nanofiber according to the present invention is not particularly limited as long as it is a method capable of obtaining a fiber having a single yarn diameter of 10 to 250 nm from a resin. Can do. It can also be produced by the melt spinning method described in Japanese Patent No. 41841717.

(Formation of secondary battery separator)
The separator for a secondary battery of the present invention is a separator for a secondary battery containing nanofibers, and is characterized by being formed by subjecting a coating film containing the nanofibers to an annealing treatment.

  Therefore, as a manufacturing method of the separator for a secondary battery of the present invention, a manufacturing method of an embodiment having a step of applying a dispersion containing the nanofiber and a step of annealing the coating film formed in the above step. It needs to be.

(Coating process, drying process)
The coating film containing nanofibers according to the present invention (also referred to as “separator layer”) is a separator coating solution containing nanofibers dispersed therein, such as a plastic support such as polyethylene terephthalate or an aluminum foil. It is obtained by peeling off after applying and drying on a metal support, but it is more preferred to obtain by applying and drying on an active material layer of an electrode to be described later. The reason for showing good cycle characteristics by coating is not clear, but it may be because a robust film was formed by annealing when the entanglement between nanofibers was uniformed by applying it after forming a dispersion. Guessed. Furthermore, it seems that application and drying on the active material layer of the electrode improved the familiarity at the interface between the active material layer and the separator layer of the electrolytic solution, and further improved the rate characteristics.

  There is no particular limitation on the method for preparing the separator coating liquid containing nanofibers dispersed therein (hereinafter also referred to as “nanofiber dispersion liquid”), and is known in consideration of the physical and chemical properties of the suspension. An appropriate method may be selected from the distribution methods.

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

  5-50 mass% is preferable with respect to the whole dispersion liquid, and, as for the compounding quantity of the nanofiber in a nanofiber dispersion liquid, 10-40 mass% is especially preferable.

  The dispersion medium used for the nanofiber dispersion is not particularly limited as long as the dispersion can be prepared, but water, methanol, ethanol, butanol, propylene glycol methyl ether, dipropylene glycol methyl ether, propylene glycol methyl ether acetate, cyclohexanone. , Dioxane, dioxolane, acetone, methyl ethyl ketone, methyl isobutyl ketone, N-methyl-2-pyrrolidone, dimethyl sulfoxide, N, N-dimethylformamide, N, N-dimethylacetamide, γ-butyrolactone and the like. Of these, water is most preferred.

  In the nanofiber dispersion liquid, the following binders can be used to adjust the pore diameter described later. Examples of such binders include polysaccharides, thermoplastic resins, and polymers having rubber elasticity, such as starch, carboxymethylcellulose, cellulose, diacetylcellulose, methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, sodium alginate, polyacrylic acid. Water-soluble polymers such as sodium polyacrylate, polyvinylphenol, polyvinyl methyl ether, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylonitrile, polyacrylamide, polyhydroxy (meth) acrylate, styrene-maleic acid copolymer, polyvinyl chloride, polytetra Fluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride Ride-tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, polyvinyl acetal resin, methyl methacrylate, 2-ethylhexyl acrylate and other (meth) acrylic (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, fluororubber, polyethylene oxide, polyester polyurethane resin, polyether polyurethane resin, polycarbonate polyurethane Tan resins, polyester resins, phenolic resins, emulsion (latex) or a suspension such as an epoxy resin. Among these binders, polyacrylate ester 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. 5-30 mass% is preferable with respect to the whole dispersion liquid, and 10-20 mass% is especially preferable.

  There is no restriction | limiting in particular in the coating method of a nanofiber dispersion 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 in the nanofiber dispersion.

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

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

  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 (separator layer) and mechanical damage prevention, and the particularly preferred pressure is 200 to 550 kg / cm. cm.

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

  The porous membrane (separator layer) may have a predetermined thickness by a single press, or may be pressed 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.

(Annealing treatment)
“Annealing treatment” in the present invention means that the separator of the present invention is heat-treated at a temperature lower than the melting point (Tm) of the nanofiber polymer forming the separator but higher than the glass transition temperature (Tg). means.

  It is speculated that the annealing process promoted the crystallization of nanofibers, improving the strength and durability of the separator, and improving the safety and cycle characteristics.

  The melting points and glass transition points of typical polymers are shown below.

  Polymer (Tg, Tm): polyethylene (-20 ° C, 130 ° C), polypropylene (-20 ° C, 170 ° C), nylon 6 (47 ° C, 225 ° C), nylon 66 (49 ° C, 267 ° C), polyethylene terephthalate (68 ° C, 260 ° C), polyvinyl chloride (82 ° C, 180 ° C), polyvinylidene chloride (-18 ° C, 212 ° C), polytetrafluoroethylene (20 ° C, 320 ° C), polyvinylidene fluoride (-39 ° C, 210 ° C.).

  The annealing temperature varies depending on the nanofiber polymer to be used, but the crystallization can be adjusted between 40 ° C. and 200 ° C. and the treatment time between 10 seconds and 1000 seconds.

  The degree of crystallization of nanofibers can be expressed by the degree of crystallinity.

“Crystallinity” usually refers to the mass fraction of crystalline regions in a polymer. The crystallinity (Xc) is measured by using a differential scanning calorimeter (DSC) to measure the heat of fusion (ΔH) of the nanofiber of the secondary battery separator, and the crystallinity of the polymer material forming the nanofiber is 100. It can be determined by dividing by the heat of fusion (ΔH ₀ ) at% (Equation (1)).

Formula (1): Xc = (ΔH / ΔH ₀ ) × 100 (%)
In the present invention, the crystallinity is preferably 40 to 90%, more preferably 50 to 80% in terms of high output performance and cycle characteristics. Furthermore, in the present invention, a remarkable effect is exhibited in cycle characteristics by subjecting a separator formed by containing a nylon copolymer as nanofibers to water vapor annealing. Further, in the present invention, the nylon nanofiber refers to a nanofiber containing 50% by mass or more of nylon as a resin component and composed mainly of nylon.

  Here, “water vapor annealing treatment” means that the separator is exposed to heated water vapor, and not only heat treatment but also humidification treatment is performed simultaneously. The reason why this shows particularly good cycle characteristics is not clear, but the water vapor annealing treatment not only improves the crystallization of the polyamide and improves the strength and durability, but also has a water absorption capability and is incorporated in the battery. At that time, it is speculated that the removal of trace moisture existing inside the battery prevented deterioration due to residual moisture. In addition, it is preferable to dry below the glass transition temperature after the water vapor annealing treatment. For example, when using nylon 66 nanofibers, it is preferable that after forming the separator, annealing is performed with water vapor at 80 ° C. for 100 seconds, and then drying is performed at 45 ° C. for 120 minutes.

[electrode]
The electrode according to the present invention has an active material layer on a current collector. There are a positive electrode and a negative electrode as the electrode. The positive electrode has a positive electrode active material layer on the current collector, and the negative electrode has a negative electrode active material layer on the current collector.

  The positive electrode active material layer contains a positive electrode active material, and the negative electrode active material layer contains a negative electrode active material.

(Current collector)
As the current collector used in the electrode according to the present invention, a chemically stable electron conductor is used in the secondary battery.

  As a current collector that can be used for the positive electrode, in addition to a metal plate such as aluminum, stainless steel, nickel, and titanium, the surface of aluminum or stainless steel is treated with carbon, nickel, titanium, or silver. A coated alloy can be preferably used. 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.

(Active material layer)
(Positive electrode active material)
As the positive electrode active material used for the positive electrode, any of an inorganic active material, an organic active material, or a composite of both can be 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.

Examples of the metal oxide and double oxide that can be used as the positive electrode active material include Li _0.3 MnO ₂ , Li ₄ Mn ₅ O ₁₂ , V ₂ O ₅ , LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and 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 . 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, and 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, such as 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, vinylideneflora (Meth) acrylic such as do-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, fluororubber, polyethylene oxide, polyester polyurethane resin, polyether polyurethane resin, polycarbonate polyurethane 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.

Examples of the lithium salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiCF ₃ , CF ₂ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , A salt such as LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (CF ₃ CF ₂ CO) ₂ , or LiBOB can be used. In addition, these salts may be used individually by 1 type, and may use 2 or more types together.

  Aprotic organic solvents include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), cyclic carbonates such as vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl Linear carbonates such as carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2- Chain ethers such as diethoxyethane and 1-ethoxy-1-methoxyethane, cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, di Methylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2 -One or two or more kinds of aprotic organic solvents such as oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, etc. are mixed and used. A solution in which a lithium salt is dissolved in a solvent can be used.

(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 positive electrode active material layer and the negative electrode active material layer 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-described conductive auxiliary agent, 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. Among these, a blade method, a knife method, and an extrusion method are preferable. 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 in the range of 1 to 2000 μm on one side after drying.

  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.

  In the present invention, the separator layer and the active material layer may be formed at the same time. For example, a separator film 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.

[Secondary battery and manufacturing method]
The secondary battery of the present invention has a laminate structure having the positive electrode active material layer on one surface of the separator of the present invention and the negative electrode active material layer on the other surface, and the separator layer is a support described below. An electrolyte containing an electrolyte salt is cored.

  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.

[Electrolyte]
(Supporting electrolyte salt)
The supporting electrolyte salt is not particularly limited as long as the supporting electrolyte salt is dissolved in a solvent so that the solution has electrical conductivity. In the secondary battery according to the present invention, a salt that is dissolved in an organic solvent and has electrical conductivity is particularly preferable. Although there is no restriction | limiting in particular in such a salt, The salt which has a periodic table group I or II metal ion as a cation is mentioned, A lithium salt, sodium salt, and potassium salt are used especially preferable.

Examples of the anion of the supporting 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. 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 singly or in combination of two or more, but at least one of them preferably uses the same anion as the ionic liquid described above.

(Electrolyte solvent)
The solvent of the electrolytic solution is not particularly limited as long as it can dissolve the electrolyte salt and become an electrolyte.

  Examples of the electrolyte solution include carbonate compounds, heterocyclic compounds, ether compounds, chain ethers, nitrile compounds, esters, and aprotic polar substances.

  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.

  Examples of aprotic polar substances include dimethyl sulfoxide and sulfolane. Moreover, these electrolyte solution solvents may be used independently or may use 2 or more types together.

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

  The solvent 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 durability due to volatility.

  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 And salts having the bistrifluoromethanesulfonyl anion moiety as a bisfluorosulfonyl anion are preferred. Among them, 1-ethyl-2,3-dimethylimidazolium bisfluorosulfonyl salt is preferred in terms of ionic conductivity. Ku can be used.

  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.

  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)
According to the following method, separators SF-1-1 to SF-1-5, SF-2, SF-3, SF-4-1, SF-4-2, SF-5, SF-A-1, and SF -A-2 was produced.

(Preparation of separators SF-A-1 and SF-A-2)
A polymer solution was prepared by dissolving 10 g of polyethylene terephthalate in 95 g of dimethylacetamide (DMAc). The polymer solution was electrospun from a spinning nozzle to produce a polyethylene terephthalate nanofiber separator (SF-A-1) having a thickness of 20 μm. This separator had a crystallinity of 5%. A separator was formed in the same manner as SF-A-1, and was then annealed at 80 ° C. to produce a separator (SF-A-2) having a crystallinity of 60%.

(Preparation of separators SF-1-1 to SF-1-5)
It can be obtained by dissolving 10 parts of carboxymethylcellulose in 500 parts of water and then electrospinning in the same manner as separator SF-A, but slowly adding 50 parts of polyethylene terephthalate nanofibers cut to a fiber length of 10 mm to obtain a dispersion. Prepared. This dispersion was applied on a polyethylene terephthalate support having a thickness of 100 μm with a die coater so that the thickness after drying was 20 μm, and then dried by far infrared rays to peel from the support to form a separator at 80 ° C. An annealing treatment was performed to prepare a separator (SF-1-1) having a crystallinity of 35%. Similarly, the annealing conditions were changed to produce separators (SF-1-2 to SF-1-5) having the crystallinity shown in Table 1.

(Preparation of separators SF-2, SF-3, SF-4-1, SF-4-2)
A dispersion was prepared by dispersing 10 g of polypropylene fine powder (0.1 μm) in 95 g of dimethylacetamide (DMAc). A polypropylene nanofiber separator (SF-2) having a thickness of 20 μm and a crystallinity of 60% was produced in the same manner as SF-1-1 except that this dispersion was electrospun from a spinning nozzle.

  Nanofiber separators (SF-3, SF-4-1) shown in Table 1 were produced in the same manner except that nylon 6 and nylon 66 were used instead of polypropylene. After forming a nylon 66 nanofiber separator in the same manner as SF-4-1, annealing was performed with water vapor at 80 ° C. for 100 seconds, followed by drying at 45 ° C. for 120 minutes and nylon 66 nanofiber separator having a crystallinity of 60% ( SF-4-2) was produced.

(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.

(Preparation of separators SF-5, SF-6-1, SF-6-2)
After dissolving 10 parts of carboxymethyl cellulose in 500 parts of water, 50 parts of polyethylene terephthalate nanofibers obtained by electrospinning and cut to a fiber length of 10 mm were slowly added to prepare a dispersion. After applying this dispersion on both sides of the negative electrode prepared above with a die coater so that the thickness after drying is 20 μm, it is far infrared dried to form a separator integrated with the electrode, and annealed. A separator (SF-5) having a crystallinity of 60% was produced.

  A separator (SF-6-1) was produced in the same manner as described above except that nylon 66 nanofibers were used.

  A separator (SF-6-2) was produced in the same manner as described above except that the annealing treatment was changed to the water vapor annealing treatment.

(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 copolymer and N-methylpyrrolidone were 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.

(Manufacture of secondary batteries)
(Manufacture of secondary battery cell 1)
After ultrasonically welding current terminals (tabs) to the uncoated portions of the positive and negative electrodes, the separator (SF-A-1) is sandwiched between the positive and negative electrodes and wound with a winding machine. Was put into a cylindrical can. This was dried under reduced pressure, and in a dry source filled with dry air having an oxygen concentration of 10 ppm or less and a dew point of −60 ° C. or less, ethylene carbonate (EC) and diethyl carbonate (DEC) had a volume ratio of 3: 7. An electrolyte solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L was poured into the mixed solvent and sealed to manufacture the secondary battery cell 1.

(Manufacture of secondary battery cells 2-11)
Secondary battery cells 2 to 11 were obtained in the same manner as in the production example of the secondary battery cell 1 except that the separator was changed to the one described in Table 1.

(Manufacture of secondary battery cells 12-14)
A secondary battery cell 12 was manufactured in the same manner as the secondary battery cell 1 except that the positive electrode and the separator (SF-5) integrated with the negative electrode were used. Secondary battery cells 13 and 14 were produced in the same manner as above except that the separator was changed as shown in Table 1.

(Rate 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 2.0 to 4.0 V in an environment of 23 ° C. The capacity retention when charging / discharging at 0.2 C was evaluated by the following rank, and used as an output index. The higher the capacity retention rate, the better the secondary battery has rate characteristics.

◎: 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% (Heat resistance)
The obtained secondary battery cell was charged at a current (0.2 C) at a rate where charging / discharging was completed in 5 hours with respect to the theoretical capacity in a voltage range of 2.0 to 4.0 V in an environment of 23 ° C. Discharge was performed. These batteries were left in an environment of 120 ° C. for 1 hour, then returned to 23 ° C. and charged / discharged in the same manner. The capacity retention after the heat treatment was evaluated according to the following rank, and an output index: It was. The higher the capacity retention, the better the heat resistance and the safe secondary battery.

◎: Retains 90% or more capacity ○: Retains 80% or more and less than 90% capacity △: Retains 60% or more and less than 80% capacity ×: Short circuit after heat treatment, charge / discharge not possible (cycle characteristics) Evaluation of)
Under an environment of 23 ° C., charge / discharge is repeated at a current (1C) at a rate at which charging / discharging ends in 60 minutes with respect to the theoretical capacity in the voltage range of 2.0 to 4.0 V, respectively, and the capacity retention is 80 The number of times of charging / discharging was reduced to%. According to the number of possible cycles, the following rank was used as an index of cycle characteristics. In addition, it becomes a secondary battery with a high cycle characteristic, so that this cycle possible number is large.

◎: 3000 times or more ○: 1000 times to less than 3000 times Δ: 500 times to less than 1000 times ×: less than 500 times The evaluation results are shown in Table 1.

  From Table 1, it can be seen that the secondary battery using the separator of the present invention has high output, is safe and has high cycle characteristics.

Claims (7)

  A separator for a secondary battery comprising a nanofiber, the separator being formed by subjecting a coating film containing the nanofiber to an annealing treatment.   The secondary battery separator according to claim 1, wherein the degree of crystallinity of the secondary battery separator is within a range of 40 to 90%.   The separator for a secondary battery according to claim 1 or 2, wherein the separator for a secondary battery contains nylon nanofibers and is subjected to a water vapor annealing treatment.   A method for producing a separator for a secondary battery containing nanofibers, comprising a step of applying a dispersion containing the nanofibers, and a step of annealing the coating film formed in the step. A method for manufacturing a separator for a secondary battery.   The method for manufacturing a separator for a secondary battery according to claim 4, wherein the annealing treatment is a water vapor annealing treatment.   An electrode with a secondary battery separator, wherein the secondary battery separator according to any one of claims 1 to 3 is formed on an electrode active material layer.   A secondary battery comprising the separator for a secondary battery according to any one of claims 1 to 3.