JP2012099385A - Electrode with heat-resistant porous layer, manufacturing method thereof, and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode with a heat-resistant porous layer having excellent high capacity, high output, and safety, and provide a secondary battery.SOLUTION: An electrode is used for a secondary battery and includes a heat-resistant porous layer between a positive electrode of which an active material layer is formed on a collector and a negative electrode of which an active material layer is formed on the collector. The electrode is formed by directly applying the heat-resistant porous layer on the active material layer of at least one of the positive electrode active material layer and the negative electrode active material layer, and the active material layer is surrounded by the collector.

Description

  The present invention relates to an electrode with a heat-resistant porous layer, a method for producing the same, 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 high 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. Further, it is necessary to have a porous structure in order to provide permeability for lithium ion passages and a function of diffusing and holding the electrolyte.

  For the separator, in order to ensure high output and safety, for example, a separator interposed between a positive electrode and a negative electrode is added to a conventional polyolefin-based porous film, and a heat-resistant inorganic filler and a membrane binder. There is known a technique of providing a porous film made of an electrode on an electrode (for example, see Patent Documents 1 to 5).

  However, although the heat resistance is improved with the above-mentioned technology, in electric vehicle applications, since it is mounted on a moving body called an automobile, it will receive various vibrations and impacts for a long time during operation, and vibration resistance is also good. Although it has become an important item, the above technology is still insufficient and further improvement is required.

JP 2004-273437 A JP 2005-174792 A JP 2005-222780 A Japanese Patent Laying-Open No. 2005-235508 JP 2006-66141 A

  This invention is made | formed in view of the said condition, The solution subject is providing a high capacity | capacitance, a high output, the electrode with a heat resistant porous layer excellent in safety | security, and a secondary battery.

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

  1. An electrode for use in a secondary battery having a heat-resistant porous layer between a positive electrode having an active material layer formed on a current collector and a negative electrode having an active material layer formed on the current collector. An electrode comprising: a material layer formed by direct coating on at least one of a positive electrode active material layer and a negative electrode active material layer, and surrounding the active material layer together with a current collector .

  2. 2. The electrode according to 1 above, wherein the content of the binder in the active material layer is less than 1% by mass of the entire active material layer.

  3. 3. The electrode according to 1 or 2 above, wherein a conductive layer is provided between the current collector and the active material layer.

  4). 4. The method for producing an electrode according to any one of 1 to 3, wherein an active material layer and a heat resistant porous layer, or a conductive layer, an active material layer and a heat resistant porous material are formed on the current collector. A method for producing an electrode, wherein the layers are formed by simultaneous coating and drying in this order.

  5. A secondary battery comprising the electrode according to any one of 1 to 3 above.

  By the above means of the present invention, it is possible to provide an electrode with a heat-resistant porous layer and a secondary battery excellent in safety with high capacity, high output.

It is a figure which shows the structure of the heat resistant porous layer of this invention which surrounded the electrode active material layer with the electrical power collector. It is a figure which shows the structure which has a conductive layer between the electrical power collector and the electrode active material layer of this invention, and the heat-resistant porous layer surrounded the electrode active material layer with the electrical power collector. It is a figure which shows the structure of the electrode in which the conventional porous layer was formed on the active material layer.

  The structure of the electrode of the present invention will be described with reference to the drawings.

  FIG. 3 is a diagram illustrating a configuration of an electrode in which a conventional porous layer is formed on an active material layer. An electrode active material layer is formed on the current collector 1, and a porous layer 3 is formed thereon.

  On the other hand, FIG. 1 is a view showing a configuration in which the heat-resistant porous layer of the present invention surrounds the electrode active material layer together with the current collector, and FIG. 2 shows a conductive layer between the current collector and the electrode active material layer. FIG. 3 is a diagram showing a configuration in which a heat-resistant porous layer surrounds an electrode active material layer together with a current collector.

  As shown in the figure, the present invention can improve durability against compression and vibration by surrounding the active material layer with the heat-resistant porous layer. Adhesives can be reduced, and the characteristics as a secondary battery can be improved.

  Hereinafter, the present invention will be described in more detail.

[Heat-resistant porous layer]
As shown in FIG. 1, the heat-resistant porous layer according to the present invention is formed on the surface of at least one of the positive electrode and the negative electrode, which will be described in detail below, with a current collector and a structure surrounding the active material layer. The The active material layer is surrounded and protected by a heat resistant porous layer and a current collector, reducing the amount of binder used to bind the active materials to form the active material layer. Or can be eliminated. This binder partially coats the surface of the active material and prevents the entry and exit of lithium ions. Therefore, the internal resistance is increased, the output is decreased, and a portion that does not allow lithium ions to pass completely is created to induce a decrease in capacity. It was. It is considered that this problem has been solved by the present invention.

  The heat-resistant porous layer according to the present invention only needs to hold the active material layer inside together with the current collector, have heat resistance, and the ability to pass lithium ions. It is preferably made of a binder.

(Inorganic oxide fine particles)
The composition of the oxide inorganic particles according to the present invention can be selected from known materials. Specifically, for example, silica (SiO ₂ ), alumina (Al ₂ O ₃ ), zirconium oxide ( ZrO ₂ ), zeolite, titanium oxide (TiO ₂ ), barium titanate (BaTiO ₃ ), strontium titanate (SrTiO ₃ ), calcium titanate (CaTiO ₃ ), aluminum borate, iron oxide, calcium carbonate, barium carbonate, Lead oxide, tin oxide, cerium oxide, calcium oxide, trimanganese tetroxide, magnesium oxide, niobium oxide, tantalum oxide, tungsten oxide, antimony oxide, aluminum phosphate, calcium silicate, zirconium silicate, ITO (Sn (tin) -containing oxide) _indium, In _{2 O 3),} titanium Examples include silicate, FSM16 (mesoporous silica), MCM41 (Mobile Crystalline Material 41, honeycomb-shaped mesoporous silica, manufactured by Mobil Corp.), montmorillonite, saponite, vermiculite, hydrotalcite, kaolinite, anelite, magadiite, keniaite, etc. These composite oxides can also be preferably used. Among the above oxide inorganic particles, neutral to acidic oxide inorganic particles are effective in terms of strength. For example, zirconium oxide, montmorillonite, saponite, vermiculite, hydrotalcite, kaolinite, kanemite, tin oxide, oxidation Tungsten, titanium oxide, aluminum phosphate, silica, zinc oxide, alumina and the like correspond to this, and particularly preferable oxide inorganic particles in the present invention are alumina particles or silica particles, which can be easily obtained industrially. .

The oxide inorganic particles according to the present invention can also have porosity. The porous oxide inorganic particles are oxide inorganic particles having innumerable fine voids on the surface or inside of the particles, and the specific surface area is preferably 500 to 1000 m ² / g. If the specific surface area is 500 m ² / g or more, when the heat-resistant porous layer of the present invention is applied to a separator of a lithium ion secondary battery, the lithium ion conductivity tends to be improved, which is preferable. Moreover, if the specific surface area is 1000 m ² / g or less, the strength of the heat-resistant porous layer tends to be improved, which is preferable. The specific surface area referred to in the present invention can be measured by a conventionally known mercury intrusion method or gas adsorption method (BET method). In the present invention, the BET method can be suitably used as a measuring method. it can. The BET method is a method in which a molecule having a known adsorption area (for example, N ₂ ) is adsorbed on the particle surface at the temperature of liquid nitrogen and the specific surface area of the sample is obtained from the adsorbed amount. In addition, as a pore diameter that is another index of porosity, it is preferable to have a pore diameter in the meso region. The meso region is a region of 2 to 50 nm to which Kelvin's capillary condensation theory can be applied. If it is larger than 2 nm, the ionic conductivity of the solid electrolyte tends to be improved, and if it is smaller than 50 nm, the strength of the solid electrolyte tends to be improved. The pore diameter is determined by analyzing the hysteresis pattern of the adsorption / desorption isotherm obtained by the gas adsorption method with a pore diameter distribution measuring device, or by obtaining the median diameter of the pore distribution, or by observation with a transmission electron microscope (TEM) It can ask for.

  As the oxide inorganic particles, for example, as described in JP-A-7-133105, the surface of the porous oxide inorganic particles is coated with silica or the like, and has a low refractive index nanometer-size composite oxidation. As described in JP-A-2001-233611, low-refractive-index nanometer-sized silica-based fine particles composed of silica and inorganic oxides other than silica and having cavities inside are also suitable. Yes.

  The average particle diameter of the oxide inorganic particles according to the present invention is preferably 1 nm to 200 nm. If the average particle size is 1 nm or more, when the heat-resistant porous layer of the present invention is applied to a separator of a lithium ion secondary battery, the lithium ion conductivity tends to be improved, and the average particle size is 200 nm or less. It is preferable because the strength of the heat-resistant porous layer tends to be improved.

  The average particle diameter of the oxide inorganic particles is a volume average value of the diameter (sphere converted particle diameter) when each oxide inorganic particle is converted to a sphere having the same volume, and this value can be obtained by observation with an electron microscope. . That is, it is obtained by measuring 200 or more diameters of porous inorganic fine particles within a certain visual field from electron microscope observation of oxide inorganic particles, obtaining a sphere equivalent particle diameter of each particle, and obtaining an average value thereof. Value.

  As the oxide inorganic particles according to the present invention, particles whose surface is modified with a coupling agent or the like can be used, and the surface modifying group is not particularly limited.

  Surface modification methods include a dry method in which alkoxysilane, chlorosilane, aluminum alkoxide, titanium alkoxide, etc. are directly sprayed onto the oxide inorganic particles and then heat-fixed, the particles are dispersed in a solution, and a surface treatment agent There is a wet method in which the surface treatment is performed by adding a nitrile, and a wet method in which particles are more uniformly dispersed is preferable. For example, particles treated by a wet method as described in JP-A-2007-264581 are suitable for the present invention because they have high dispersibility. In both the dry and wet processes, the coupling reaction can be promoted by hydrothermal treatment of the oxide inorganic particles in advance.

  The content of the oxide inorganic particles in the heat resistant porous layer of the present invention is not particularly limited, but is preferably 10% by mass or more and 95% by mass or less, more preferably 100% by mass with respect to the heat resistant porous layer. It is 50 mass% or more and 90 mass% or less. If it is 10 mass% or more, the lithium ion conductivity tends to be high, and if it is 95 mass% or less, it is preferable from the viewpoint that the mechanical strength of the heat-resistant porous layer tends to be high.

(Membrane binder)
Examples of the membrane binder according to the present invention 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, vinylidene fluoride (Meth) acrylic esters such as 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, (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 resin , Polyester resins, phenolic resins, emulsion (latex) or a suspension such as an epoxy resin. Of these, water-soluble polymers are preferable, and polyvinyl alcohol is more preferably used.

  The membrane binder according to the present invention may further contain a crosslinking agent for crosslinking the membrane binder for the purpose of improving the membrane strength.

  The content of the membrane binder in the heat resistant porous layer of the present invention is not particularly limited, but is preferably 1.0% by mass or more and 80% by mass or less with respect to 100% by mass of the heat resistant porous layer. Preferably they are 3.0 mass% or more and 60 mass% or less. If it is 1.0% by mass or more, the strength of the heat resistant porous layer is improved, and if it is 80% by mass or less, it is preferable from the viewpoint of improving the ionic conductivity of the electrolytic solution impregnated in the heat resistant porous layer. .

(Method for forming heat-resistant porous layer)
Subsequently, the formation method of the heat resistant porous layer of this invention is demonstrated.

  The heat-resistant porous layer of the present invention is formed by direct application on at least one of the positive electrode active material layer and the negative electrode active material layer, and not only the upper part of the active material layer but also, for example, as shown in FIG. In addition, the edge portion of the active material layer has a heat-resistant porous layer, has a shape like a lid, and is surrounded by a current collector.

  The thickness of the heat-resistant porous layer of the present invention is preferably 1 μm to 200 μm, more preferably 5 μm to 30 μm, in the portion above the electrode active material layer. If it is this range, the short circuit between positive and negative electrodes can be prevented, and a battery characteristic can be improved. The width of the edge portion of the electrode active material layer is preferably 0.5 mm to 10 mm, and more preferably 1 mm to 5 mm. If it is this range, an electrode active material layer can be protected and the short circuit between positive and negative electrodes can be prevented. Note that there are four edge portions of the electrode active material layer, and it is necessary to provide a heat-resistant porous layer on at least two opposite sides, but it is most preferable to provide them on all four sides.

  The method for forming the heat resistant porous layer of the present invention is not particularly limited, but a wet coating method is preferred. Specifically, the oxide inorganic particles according to the present invention, a film binder, and water or an organic solvent are mixed to prepare a slurry as a coating solution, and then the positive electrode active material is applied to the current collector metal foil. The structure after drying the slurry on the coated positive electrode plate or the negative electrode plate coated with the negative electrode active material on the current collector metal foil is as shown in FIG. 1 on the active material layer and the edge portion of the active material layer. A heat-resistant porous layer integrated with the electrode can be formed by adjusting the coating amount on each current collector.

  Water or an organic solvent that can be used in the above method may be any solvent that can uniformly disperse the oxide inorganic particles and a solvent that can stably dissolve or disperse the membrane binder used. 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 can be used. Various additives may be added to stabilize the coating solution or dispersion. Even if these additives are materials that can be removed by heating, when the heat-resistant porous layer of the present invention is applied to a lithium ion secondary battery, it is stably present at high temperatures and high voltages and inhibits battery reactions. If it is a material that does not, it may remain in the battery.

  The coating method using the coating solution is not particularly limited as long as it can be applied uniformly to a desired thickness. For example, screen printing, bar coater method, roll coater method, reverse coater method, gravure printing method, doctor blade method, die coater method, etc. can be mentioned, and the application type is necessary for continuous application, intermittent application, stripe application, etc. It can be used properly according to your needs.

  The drying method after coating is not particularly limited as long as the organic solvent contained in the coating solution can be removed. Various methods such as hot air drying, infrared drying, far-infrared drying, microwave drying, electron beam drying, vacuum drying, etc. A method can be selected as appropriate.

  The drying temperature is not particularly limited, but is preferably 50 to 400 ° C, more preferably 80 to 200 ° C.

[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 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 . 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.

  The average particle diameter of the positive electrode active material can be 0.001 μm to 10 μm. Of these, those having a thickness of 0.01 μm to 0.1 μm are preferable because higher output can be achieved.

(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 drying a paste mixed with powder such as graphite or tin alloy and a binder such as styrene butadiene rubber or polyvinylidene fluoride. 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 a conductive agent and a binder may be further added.

  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. If the amount of binder added is small, the retention and cohesive strength of the electrode mixture will be weak, but if too much, internal resistance will be prevented by reducing the capacity due to the increase in electrode volume and adhering to the active material surface due to adhesion to the active material surface. Output decreases with increase. For these reasons, it is preferable that the amount of the binder added is small or not, and the heat-resistant porous layer of the present invention surrounds the active material layer together with the current collector, thereby reducing the amount of the binder. It can be reduced as much as possible, and can be 0 to less than 1% by mass.

(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.

  In general, the ratio of the size of the negative electrode plate to the positive electrode plate is increased in consideration of safety so that metallic lithium is not generated on the negative electrode plate during charge and discharge. The area of the positive electrode plate is preferably 0.80 to 0.99, particularly preferably 0.90 to 0.98, relative 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 may be continuous, intermittent, or a combination thereof.

  As for the thickness of the preferable active material layer, it is preferable that the single-sided film thickness after drying is in the range of 1 to 200 μm.

[Conductive layer]
In the present invention, it is more preferable to have a conductive layer between the current collector and the active material layer as shown in FIG. It has been found that by providing the conductive layer, the electron transfer capability between the active material layer and the current collector is improved, the output is further improved, and the repeated charge / discharge resistance is also improved.

  The conductive layer in the present invention comprises a conductive agent and a binder. 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, 70-99 mass% is preferable, and 90-98 mass% is more 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 strength of the conductive layer 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 20% by mass, and more preferably 2 to 10% by mass.

  The thickness of the conductive layer is preferably in the range of 0.5 μm to 5 μm. This is because if the thickness is small, the effect of improving the electrical contact is small, and if the thickness is large, the amount of the active material that can be filled in the battery decreases, and the capacity density decreases.

  The conductive layer of the present invention may be formed independently after the electrode active material layer and the heat-resistant porous layer are formed alone, or after the conductive layer and the electrode active material layer are formed by simultaneous multilayer coating, the heat-resistant porous layer is formed. A layer may be formed.

  In the present invention, when an electrode active material layer and a heat-resistant porous layer or a conductive layer are provided, it is preferable to simultaneously apply a conductive layer, an electrode active material layer and a heat-resistant porous layer in this order.

[Simultaneous multilayer coating]
The simultaneous multilayer coating in the present invention is, for example, a method in which an electrode active material layer is applied on a current collector with a coater constituted by a single head (slot), and before the electrode active material layer is dried, it is applied to another coating machine. The current collector coated with the electrode active material is moved and stacked by applying a heat-resistant porous layer on the electrode active material layer (2-coater 2-head system). Installed in the same coater, each electrode is used to apply an electrode active material layer and a heat-resistant porous layer onto a current collector (one coater, two heads), and a single head with multiple flow paths A method of applying an electrode active material layer and a heat-resistant porous layer on a current collector (one coater / one head system) in one step by using an extrusion die. By extending these methods, the electrode active material layer and the multilayer heat-resistant porous layer can be simultaneously laminated.

  By applying these layers simultaneously so as to have the layer structure of the present invention, the binder in the electrode active material layer, which has been necessary in the past, can be eliminated, so that the capacity and output can be further increased. . Moreover, productivity can be improved by layering simultaneously, and an electrode-heat resistant porous layer laminate can be produced at low cost.

  These coatings may be performed on each side or on both sides simultaneously. Furthermore, the application may be continuous, intermittent, or a combination thereof.

  It is preferable to remove as much water as possible from the electrode having a heat-resistant porous layer formed by coating in the present invention before manufacturing a secondary battery. There is no restriction | limiting in particular as a drying and dehydration method, The method of combining hot air, a vacuum, infrared rays, far infrared rays, an electron beam, and low-humidity air individually or in combination can be used. The drying temperature is preferably 80 to 350 ° C, more preferably 100 to 250 ° C.

  As the electrode having a heat-resistant porous layer in the present invention, those subjected to roll press processing can be suitably used. 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 10 to 70 MPa in terms of linear pressure from the viewpoint of heat-resistant porous homogeneity and mechanical damage prevention, and a particularly preferred pressure is 20 to 55 MPa.

  The gap between the pair of press rolls for rolling the electrode having the heat resistant porous layer is equal to or greater than the current collector thickness, and the sum of the current collector thickness and the thickness of the conductive layer, electrode active material layer, and heat resistant porous layer. Is preferably adjusted to a small distance.

  The electrode having the heat resistant porous 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.

[Secondary battery and manufacturing method]
The secondary battery of the present invention includes the electrode having the heat-resistant porous layer of the present invention in at least one of the positive electrode and the negative electrode, has a laminate structure of the positive electrode and the negative electrode, and the heat-resistant porous layer is a supporting electrolyte described below Impregnated with electrolyte containing salt.

  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 represent a hydroxyl group, an amino group, a nitro group, a cyano group, a carboxyl group, an ether group or a hydrocarbon group or a hydrogen atom having 1 to 10 carbon atoms which may have an aldehyde group,, X ^- one 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 It is done.

  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 positive electrode S-1)
92 parts of lithium iron phosphate (LiFePO ₄ ) and 7 parts of graphite powder were mixed with 0.5 parts of acrylonitrile-butadiene copolymer latex, 0.5 parts of carboxymethylcellulose and water as a binder. Were mixed 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 50 μm. This was hot-air dried at 130 ° C. for 5 minutes and then roll-pressed to produce positive electrode S-1.

(Preparation of positive electrodes S-2, S-3)
27 parts of oxide inorganic particles (non-porous alumina average particle size 13 nm) were added to 70 parts of water, 3 parts of acetic acid was further added, and dispersed and mixed with a homogenizer at 5000 rpm for 30 minutes. Furthermore, 9 parts of polyvinyl alcohol (saponification degree 88%, average molecular weight 480,000) was added, and finally 40 parts of water was added and stirred to prepare a heat-resistant porous layer slurry having a nonvolatile content ratio of 26% by mass. This slurry was applied to the surface having the electrode active material layer before roll pressing, which was prepared in the same manner as the positive electrode S-1, so that the thickness after drying was 10 μm, and warm air was applied at 130 ° C. for 10 minutes. After drying, an electrode (positive electrode S-2) having a heat-resistant porous membrane was produced by roll pressing.

  A positive electrode S-3 was produced in the same manner as S-2 except that the amount of the electrode binder added was changed to 0.25 part of acrylonitrile-butadiene copolymer latex and 0.25 part of carboxymethylcellulose.

(Preparation of positive electrode S-4)
As shown in FIG. 1, the positive electrode active material layer was surrounded with the current collector so that the thickness after drying of the heat-resistant porous layer slurry of the positive electrode 3 was 10 μm and the width of the edge portion of the positive electrode active material layer was 2 mm. A positive electrode S-4 was prepared in the same manner as the positive electrode 3 except that it was coated and dried into a shape.

(Preparation of positive electrode S-5)
95 parts of acetylene black, 3 parts of styrene butadiene copolymer latex, 2 parts of carboxymethyl cellulose and water were mixed to prepare a slurry for the conductive layer. This slurry was applied to one side of an aluminum foil having a thickness of 20 μm so that the thickness after drying was 5 μm. This was dried with warm air at 130 ° C. for 5 minutes, and then a positive electrode active material layer and a heat-resistant porous layer were sequentially provided in the same manner as the positive electrode S-4 to produce the positive electrode S-5 shown in FIG. .

(Preparation of positive electrode S-6)
A positive electrode active material layer slurry prepared by mixing 92 parts of lithium iron phosphate (LiFePO ₄ ) and water and a slurry for a heat-resistant porous layer were coated and dried at the same time as in the positive electrode S-4, A positive electrode S-6 was produced.

(Preparation of positive electrode S-7)
The positive electrode S except that the slurry for the conductive layer, the slurry for the positive electrode active material layer prepared by mixing 92 parts of lithium iron phosphate (LiFePO ₄ ) and water, and the slurry for the heat-resistant porous layer are simultaneously applied and dried in this order. In the same manner as −5, a positive electrode S-7 was produced.

(Preparation of negative electrode F-1)
99 parts of graphite, 0.5 part of styrene-butadiene copolymer latex as a binder, 0.5 part of carboxymethylcellulose and water were mixed to prepare a slurry. This slurry was applied to both sides of a 15 μm thick copper foil so that the thickness after drying was 50 μm. This negative electrode precursor was hot-air dried at 130 ° C. for 5 minutes and then roll-pressed to prepare a negative electrode F-1.

(Preparation of negative electrode F-2)
27 parts of oxide inorganic particles (non-porous alumina average particle size 13 nm) were added to 70 parts of water, 3 parts of acetic acid was further added, and dispersed and mixed with a homogenizer at 5000 rpm for 30 minutes. Furthermore, 9 parts of polyvinyl alcohol (saponification degree 88%, average molecular weight 480,000) was added, and finally 40 parts of water was added and stirred to prepare a heat-resistant porous layer slurry having a nonvolatile content ratio of 26% by mass. The electrode before roll pressing was prepared in the same manner except that this slurry was changed to 0.25 part of styrene butadiene copolymer latex and 0.25 part of carboxymethyl cellulose in the negative electrode F-1. As shown in FIG. 1, the negative electrode active material layer is coated on the surface having the active material layer so as to surround the current collector so that the thickness after drying is 10 μm, and warm air is applied at 130 ° C. for 10 minutes. The electrode (negative electrode F-2) which has a heat-resistant porous membrane was produced by carrying out roll press after drying.

(Preparation of negative electrode F-3)
95 parts of acetylene black, 3 parts of styrene butadiene copolymer latex, 2 parts of carboxymethyl cellulose and water were mixed to prepare a slurry for the conductive layer. This slurry was applied to one side of a 20 μm thick copper foil so that the thickness after drying was 5 μm. After drying this with hot air at 130 ° C. for 5 minutes, in the same manner as the negative electrode F-2, a negative electrode active material layer and a heat-resistant porous layer were sequentially provided to form a negative electrode F-3 having the configuration shown in FIG. Produced.

(Preparation of negative electrode F-4)
A negative electrode F-4 was produced in the same manner as the negative electrode F-2, except that 99 parts of graphite and water were mixed and a negative electrode active material layer slurry and a heat-resistant porous layer slurry were simultaneously applied and dried. did.

(Preparation of negative electrode F-5)
A negative electrode active material layer slurry prepared by mixing 99 parts of graphite and water and a slurry for a heat-resistant porous layer and a slurry for a heat-resistant porous layer in the same manner as in the negative electrode F-3 A negative electrode F-5 was produced.

(Manufacture of secondary batteries)
(Manufacture of secondary battery cell 1)
After ultrasonically welding current terminals (tabs) to the uncoated portions of the positive electrode S-1 and the negative electrode F-1, a polyethylene film having a thickness of 25 μm is formed between the positive electrode S-1 and the negative electrode F-1. A separator (2400, manufactured by Celgard Inc.) was sandwiched, and an aluminum-deposited polyethylene laminate sheet was sandwiched from both sides, and heat sealed in three directions.

After drying this under reduced pressure, ethylene carbonate (EC) and diethyl carbonate (DEC) are in a volume ratio of 3: in a dry bath filled with dry air having an oxygen concentration of 10 ppm or less and a dew point of −60 ° C. or less. An electrolyte solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L was injected into the mixed solvent No. 7, and the remaining one direction was heat-sealed to produce a secondary battery cell 1.

(Manufacture of secondary battery cells 2 to 13)
Secondary battery cells 2 to 13 were obtained in the same manner as in the production example of the secondary battery cell 1 except that the electrodes described in Table 1 were used instead of the polyethylene separator.

(Evaluation of battery capacity)
Under an environment of 23 ° C., charging / discharging was repeated 5 times with a current (1.0 C) at a rate where charging / discharging was completed in 60 minutes with respect to the theoretical capacity in the voltage range of 2.0 to 4.0 V, respectively. The capacity retention rate was calculated for the second discharge capacity with respect to the theoretical capacity of 100%, and used as an index of battery capacity. Note that the higher the capacity retention rate, the higher the capacity of the secondary battery.

◎: Retains 90% or more capacity ○: Retains 85% or more and less than 90% capacity △: Retains 80% or more and less than 85% capacity x: Retains less than 80% capacity (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 discharge capacity at this time was evaluated according to the following rank, with the discharge capacity when charging / discharging at 0.2 C being 100%, 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 and discharged in the same manner. The discharge capacity retention before and after the heat treatment was evaluated in the following ranks, It was used as an index. The higher the capacity retention rate, the better the heat resistance and the safe secondary battery.

◎: Retains capacity of 90% or more. ○: Retains capacity of 80% or more and less than 90%. △: Retains capacity of 60 or more and less than 80%. Evaluation of)
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. The higher the discharge capacity ratio, the higher the vibration resistance.

◎: 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, the secondary battery using the electrode with the heat-resistant porous layer of the present invention can reduce the amount of the binder in the electrode active material layer, has high capacity, high output, and vibration resistance. It can be seen that it is high and has excellent durability.

DESCRIPTION OF SYMBOLS 1 Current collector 2 Electrode active material layer 3 Heat resistant porous layer 4 Conductive layer

Claims (5)

  An electrode for use in a secondary battery having a heat-resistant porous layer between a positive electrode having an active material layer formed on a current collector and a negative electrode having an active material layer formed on the current collector. An electrode comprising: a material layer formed by direct coating on at least one of a positive electrode active material layer and a negative electrode active material layer, and surrounding the active material layer together with a current collector .   The electrode according to claim 1, wherein the content of the binder in the active material layer is less than 1% by mass of the entire active material layer.   The electrode according to claim 1, further comprising a conductive layer between the current collector and the active material layer.   It is a manufacturing method of the electrode of any one of Claims 1-3, Comprising: On the said electrical power collector, an active material layer and a heat resistant porous layer, or a conductive layer, an active material layer, and a heat resistant porous A method for producing an electrode, comprising forming a porous layer by simultaneously applying and drying in this order.   A secondary battery comprising the electrode according to claim 1.

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