WO2013021443A1 - Non-aqueous electrolyte rechargeable battery - Google Patents

Non-aqueous electrolyte rechargeable battery Download PDF

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Publication number
WO2013021443A1
WO2013021443A1 PCT/JP2011/068019 JP2011068019W WO2013021443A1 WO 2013021443 A1 WO2013021443 A1 WO 2013021443A1 JP 2011068019 W JP2011068019 W JP 2011068019W WO 2013021443 A1 WO2013021443 A1 WO 2013021443A1
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Prior art keywords
negative electrode
graphite particles
mass
battery
parts
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PCT/JP2011/068019
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French (fr)
Japanese (ja)
Inventor
山田　直毅
博行 戸城
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日立ビークルエナジー株式会社
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Priority to JP2013527766A priority Critical patent/JP5736049B2/en
Priority to PCT/JP2011/068019 priority patent/WO2013021443A1/en
Publication of WO2013021443A1 publication Critical patent/WO2013021443A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a non-aqueous electrolyte secondary battery.
  • lithium ion secondary batteries have been applied to electronic devices such as notebook PCs and digital cameras that are driven at a relatively low voltage of 12 V or less. Under these conditions of use, it is assumed that the battery is used at a lower power than the battery capacity, and the characteristic required for the lithium ion secondary battery is that it has a larger capacity than other systems.
  • lithium-ion secondary batteries for in-vehicle use must have large capacity and high output. To achieve a large capacity, it is necessary to provide a larger amount of active material, and to achieve a high output, it is necessary to improve the input / output performance of the battery.
  • lithium-ion secondary batteries for in-vehicle use are easily assumed to be used for a long period of time, and the number of charge / discharge cycles increases. It is essential to be good.
  • the negative electrode contains a conductive material composed of graphite particles and scaly graphite, and a non-aqueous solution having excellent discharge load characteristics due to the presence of a recess not formed on the surface of the negative electrode.
  • An electrolyte secondary battery has been proposed.
  • Patent Document 2 for the purpose of improving the input / output performance of the battery, that is, reducing the electric resistance of the battery, carboxymethyl cellulose is used as the first binder as the binder component contained in the positive electrode.
  • a structure comprising a polyethylene oxide in a two-binding material has been proposed.
  • the type of binder component is defined as polyethylene oxide
  • the composition is different from that of a conventionally used rubber binder such as styrene butadiene rubber, members constituting other batteries, particularly electrolyte solution
  • a conventionally used rubber binder such as styrene butadiene rubber
  • members constituting other batteries particularly electrolyte solution
  • electrolyte solution there remains a possibility that some constraints will arise on. The reason for this is that, according to the study by the present inventors, low molecular weight components and the like generated during the synthesis of polyethylene oxide may be dissolved in the electrolytic solution, and the solubility of polyethylene oxide in the electrolytic solution needs to be considered. Conceivable.
  • the present invention has been made to solve the above-described problems, and its object is to suppress non-aqueous electrolysis that suppresses battery capacity deterioration with respect to charge / discharge cycles and suppresses an increase in electrical resistance in current input / output. It is to provide a liquid secondary battery.
  • the nonaqueous electrolyte secondary battery of the present invention that solves the above-mentioned problems is characterized in that the negative electrode mixture layer has scaly graphite particles and polyhedral graphite particles whose surfaces are coated with amorphous carbon.
  • the present embodiment is not limited to the following contents and does not depart from the gist thereof. Any change can be made within the range.
  • a nonaqueous electrolyte secondary battery that is, a lithium ion secondary battery
  • the battery according to this embodiment will be described.
  • the battery according to this embodiment is not limited to a non-aqueous electrolyte secondary battery, and the electrode of the battery according to this embodiment can be applied to any battery.
  • FIG. 1 is a schematic perspective view of the internal structure of a non-aqueous electrolyte secondary battery according to an embodiment (first embodiment) of the present invention.
  • the non-aqueous electrolyte secondary battery according to the first embodiment shown in FIG. 2 includes a battery container 1, a gasket 2, an upper lid 3, an upper lid case 4, a positive current collector plate 5, and a negative current collector plate 6.
  • the electrode group 8 and the positive electrode lead 9 are included.
  • the battery container 1 contains a positive electrode current collector plate 5, a negative electrode current collector plate 6, an electrode group 8, a positive electrode lead 9, and a non-aqueous electrolyte (not shown).
  • the battery container 1 has a cylindrical shape, but may have a rectangular shape. Further, as the material of the battery container 1, it is preferable to use a metal that is not corroded by the stored nonaqueous electrolytic solution, and nickel-plated iron or the like is used.
  • the gasket 2 is provided between the battery case 1 and the upper lid case 4.
  • the battery container 1 is sealed by the gasket 2 and the battery container 1 is electrically insulated from the upper lid 3 and the upper lid case 4.
  • a known sealing member such as an elastic resin such as polypropylene (PP) or tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA) can be used.
  • the upper lid 3 is an external terminal for taking out the electric power obtained from the battery, specifically, a positive external terminal.
  • the upper lid case 4 is integrally formed of the same material as the upper lid 3, and the upper lid 3 and the upper lid case 4 are electrically connected. As the material of the upper lid 3 and the upper lid case 4, a conductive metal can be used. The upper lid case 4 and the positive electrode current collector plate 5 are electrically connected via a positive electrode lead 9 made of metal.
  • the positive electrode current collector plate 5 and the negative electrode current collector plate 6 are electrically connected to a positive electrode tab 12 and a negative electrode tab 13 described later, respectively. This electrical connection can be performed by, for example, ultrasonic welding.
  • a hole is provided in the central portion of the positive electrode current collector plate 5 and the negative electrode current collector plate 6, and an axial center 7 (described later) is fitted into the hole, whereby the positive electrode current collector plate 5 and the negative electrode current collector plate.
  • the electric plate 6 is fixed with respect to the shaft center 7.
  • a conductive metal is used as a material for the positive electrode current collector plate 5 and the negative electrode current collector plate 6.
  • the negative electrode current collector plate 6 is electrically connected to the bottom of the battery case 1, and the bottom of the battery case 1 functions as a terminal for taking out the electric power obtained by the battery, specifically, a negative electrode external terminal. ing. Therefore, the bottom part and the side part of the battery container 1 are insulated from each other by an insulator (not shown).
  • the shaft center 7 is located at the center of the electrode group 8, and the positive electrode 14 and the negative electrode 15 are wound with a separator 18 interposed therebetween. Further, the upper and lower end portions of the shaft center 7 penetrate the positive electrode current collector plate 5 and the negative electrode current collector plate 6.
  • the shape of the shaft center is arbitrary, but a hollow cylinder is used in the first embodiment.
  • a resin or the like that does not have conductivity or has extremely low conductivity can be used.
  • the electrode group 8 is configured by winding a separator between the positive electrode 14 and the negative electrode 15 in a cylindrical shape, and the positive electrodes 14 and the negative electrodes 15 are alternately stacked.
  • the positive electrode 14 has a positive electrode current collector and a positive electrode mixture layer 16 provided on both surfaces of the positive electrode current collector, and the negative electrode 15 is formed on both surfaces of the negative electrode current collector and the negative electrode current collector.
  • the negative electrode mixture layer 17 is provided.
  • a separator 18 is provided on the outermost periphery of the electrode group 8.
  • the electrode group 8 is fixed to the separator 18 provided on the outermost periphery by a winding member 19 so that the winding of the electrode group 8 cannot be unwound.
  • a positive electrode tab 12 is provided above the positive electrode 14, and a negative electrode tab 13 is provided below the negative electrode 15.
  • the positive electrode current collector and the positive electrode tab 12 of the positive electrode 14 are made of a metal such as aluminum.
  • the positive electrode mixture layer 16 is formed by applying a slurry-like positive electrode mixture containing a positive electrode active material, a conductive material, and a binder component on both surfaces of the positive electrode current collector, and then drying and pressing the mixture.
  • the negative electrode current collector and the negative electrode tab 13 of the negative electrode 15 are made of a metal such as copper.
  • the negative electrode mixture layer 17 is formed by applying a slurry-like negative electrode mixture containing a negative electrode active material and a binder component on both sides of the negative electrode current collector, followed by drying and pressing.
  • the separator 18 is porous and has an insulating property, and any known separator that can be used for a lithium ion secondary battery can be used.
  • the nonaqueous electrolyte secondary battery according to the present embodiment can be charged from the outside of the battery container 1 or discharged to the outside of the battery container 1 by having the configuration described above and shown in FIG. That is, for example, when the battery is discharged, electrons generated at the negative electrode 15 of the electrode group 8 are taken out through the negative electrode tab 13, the negative electrode current collector plate 6, and the bottom of the battery container 1 in this order. On the other hand, electrons reach the positive electrode 14 of the electrode group 8 from the outside through the upper lid 3, the upper lid case 4, the positive electrode lead 9 and the positive electrode tab 12.
  • Negative electrode [Negative electrode active material]
  • the negative electrode active material is one that occludes and releases lithium ions in the non-aqueous electrolyte that the battery normally has, and also occludes and releases electrons.
  • the negative electrode active material has scaly graphite particles and polyhedral graphite particles whose surfaces are coated with amorphous carbon. According to the present invention, graphite particles having an average particle size of 1 ⁇ m or more and 50 ⁇ m or less can be suitably used.
  • the average particle diameter may be appropriately selected according to the thickness of the negative electrode to be produced.
  • the scaly graphite particles preferably have an average particle diameter of 5 ⁇ m to 50 ⁇ m, and more preferably 10 ⁇ m to 30 ⁇ m.
  • the polyhedral graphite particles preferably have an average particle size of 1 ⁇ m to 50 ⁇ m, and more preferably 5 ⁇ m to 15 ⁇ m.
  • the average particle diameter of the graphite particles exceeds 50 ⁇ m, the size of one particle is large with respect to the thickness of the mixture layer to be produced, and the thickness is likely to fluctuate. Handling becomes complicated and productivity is remarkably inferior.
  • the average particle diameter in this invention is a particle size of the integrated value 50% in the particle size distribution calculated
  • DCR direct current resistance component
  • the scaly graphite particles are a large number of flat graphites and / or aggregates thereof, and have a large surface area per weight. For this reason, there are many sites where lithium ions can be inserted and desorbed, and the resistance during insertion and desorption can be reduced, which can contribute to a reduction in electrical resistance. For this reason, it can be said that the use of scaly graphite particles is essential from the viewpoint of reducing the electric resistance of the battery.
  • the scaly graphite particles are aggregates of fine scaly structures, the contact area between the fine structures is small, and they are relatively brittle with respect to expansion and contraction due to repeated charge and discharge, and the inter-particles Contact is often blocked. That is, the reduction in charge / discharge capacity tends to be quick, and it can be said that there is a problem in the cycle characteristics of a battery using scaly graphite.
  • the polyhedral graphite particles have few voids inside the particles, and the surface area per weight with respect to the average particle diameter, that is, the specific surface area is small.
  • the electrical resistance increases.
  • polyhedral graphite particles are relatively strong in expansion and contraction, and are less likely to block contact between particles, so the charge / discharge capacity tends to decrease slowly and cycle characteristics are low. It can be said that it is relatively good.
  • the positive electrode and the negative electrode for lithium ion secondary batteries it is essential to press the mixture layer on the current collector (metal foil) to a certain density in order to impart desired battery performance.
  • the negative electrode scaly graphite has a relatively brittle structure, and since there are many voids in the particles, it is relatively easy to compress the particles, which is advantageous for adjusting the density.
  • Graphite has a high chemical activity on the surface, and may react with the electrolyte components to gradually change the electrolyte composition.
  • the change in the electrolyte composition is likely to deteriorate the battery performance.
  • the reaction with the electrolyte component can be suppressed by providing a coating layer on the surface of the graphite particles.
  • the method for forming the coating layer include attaching the material of the coating layer to the surface of the graphite powder and sintering it to form an amorphous carbon layer. It is desirable that the graphite powder of the present invention (flaky graphite particles and polyhedral graphite particles) also form a coating layer on the surface.
  • fine plate-like graphite particles which are single particles or those obtained by combining a plurality of particles, are referred to as scaly graphite particles.
  • the fine plate-like graphite particles can be arbitrarily selected in size according to the required performance, and the particle surface may be coated.
  • the surface coating can be realized by, for example, a method of forming an amorphous carbon film on the surface of the graphite particles. Since the basic unit is in the form of a fine plate in this way, the scaly graphite particles have a large number of voids formed between the particles or in the composite particles, and these voids are formed by a scanning electron microscope. (SEM) or the like can be used for easy observation.
  • SEM scanning electron microscope
  • the polyhedral graphite particles of the present invention have a polyhedral shape, almost no voids are observed in the particles, and each takes the form of an independent particle.
  • the shape may be partially spherical due to process conditions or the like, but most of the shape becomes a polyhedral shape due to irregular contact with particles or production equipment. At that time, it is conceivable that a gap is rarely generated due to a crack caused by a contact impact, but it is not intended to positively hold the gap.
  • the shape of the polyhedral graphite particle in this invention differs in a strict meaning from a geometric polyhedron.
  • the polyhedral shape in the present invention indicates a state in which the surface of the particle is flat or has a shape in which one or both of a flat portion having a slight unevenness are mixed. Most of the shape of this plane or planar portion is an irregular polygonal shape.
  • the outline of each particle is basically indefinite, and does not show a uniform shape to a certain extent, such as a spherical particle. It can be easily observed using a scanning electron microscope (SEM) or the like that it is polyhedral and almost no voids are observed inside, like the above-mentioned scaly graphite particles.
  • SEM scanning electron microscope
  • the polyhedral graphite particles are desirably coated on the surface, and polyhedral graphite having an amorphous carbon film is preferable.
  • the negative electrode active material of the negative electrode mixture layer by using a mixture of scaly graphite particles and polyhedral graphite particles, electrical resistance and cycle Achieving compatibility with characteristics.
  • the negative electrode mixture layer contains scaly graphite particles having an average particle diameter of 1 ⁇ m or more and 50 ⁇ m or less and polyhedral graphite particles as a negative electrode active material.
  • the surface of the polyhedral graphite particles is coated with amorphous carbon, and more preferably, the surface of the scaly graphite particles is coated with amorphous carbon.
  • the ratio of the scaly graphite particles and the polyhedral graphite particles to the total amount of the active material is preferably such that the scaly graphite particles are 60 parts by mass or more and 90 parts by mass or less, and the polyhedral graphite particles are 10 parts by mass or more and 40 parts by mass or less, More preferably, the scaly graphite particles are 65 parts by mass or more and 80 parts by mass or less, and the polyhedral graphite particles are 15 parts by mass or more and 20 parts by mass or less, and more preferably, the scaly graphite particles are 65 parts by mass or more and 75 parts by mass or less. And polyhedral graphite particles are 25 mass parts or more and 35 mass parts or less.
  • the number of scale-like graphite particles is less than 60 parts by mass and the number of polyhedral graphite particles is more than 40 parts by mass, the electric resistance of the battery increases and the density adjustment of the negative electrode mixture layer becomes difficult.
  • the scale-like graphite particles are more than 90 parts by mass and the polyhedral graphite particles are less than 10 parts by mass, the cycle characteristics are deteriorated.
  • the mechanism by which the cycle characteristics are improved by setting the scaly graphite particles and polyhedral graphite particles to a preferable mixing ratio is considered as follows.
  • the scaly graphite particles have a relatively low resistance during charging / discharging, but have a characteristic that they are partially broken by the stress of expansion / contraction during charging / discharging. For this reason, when the scaly graphite particles are used alone, the destruction portion due to repeated charge and discharge is expanded. The broken portion is a part of the graphite particles that are not electrically conductive. However, when this ratio is increased, the proportion of the graphite particles that are relatively electrically secured is decreased. This leads to a decrease in the total amount of lithium ions that can be inserted and desorbed, that is, the capacity of the electrode. That is, the cycle characteristics are deteriorated.
  • the polyhedral graphite particles that are relatively resistant to destruction by repeated charge and discharge are arranged so as to contact the scaly graphite particles, the scaly graphite particles themselves are destroyed, but the contacting polyhedrons Electrical conduction is ensured by using the graphite particles as a bypass. That is, the portion where the electrical conductivity is impaired by the scaly graphite particles alone is continuously secured by contact with the polyhedral graphite particles, and can be used for charging and discharging. Accordingly, it is possible to prevent a decrease in the total amount of lithium ions that can be inserted and desorbed, suppress a decrease in electrode capacity, prevent deterioration of cycle characteristics, and extend the life of the battery.
  • polyhedral graphite particles in an amount sufficiently contacting the scaly graphite particles are essential. At the same time, the polyhedral graphite particles are required to be stronger against expansion and contraction due to repeated charge and discharge.
  • the ratio of the graphite particles is preferably 60 parts by mass or more and 90 parts by mass or less of scaly graphite particles and 10 parts by mass or more and 40 parts by mass or less of polyhedral graphite particles, more preferably
  • the scaly graphite particles are 65 parts by mass or more and 80 parts by mass or less
  • the polyhedral graphite particles are 15 parts by mass or more and 20 parts by mass or less
  • the scaly graphite particles are 65 parts by mass or more and 75 parts by mass or less and the polyhedral graphite.
  • the particles are 25 parts by mass or more and 35 parts by mass or less.
  • the surfaces of the polyhedral graphite particles in the present invention are coated with amorphous carbon or the like.
  • Spherical graphite particles tend to have few points of contact with other particles due to their shape. From the viewpoint of ensuring conduction between graphite particles, it is more preferable that there are many contact points with other particles.
  • the polyhedral graphite particles are indefinite, and it can be expected that more contact points can be obtained between the adjacent graphite particles than the spherical graphite particles, and the probability of ensuring conduction between the graphite particles is maintained. Will be higher.
  • the polyhedral graphite particles have a plurality of planar portions and / or planar portions, projecting portions are generated at the borders between them. It can be easily imagined that stronger contact can be obtained in the compression process (described later) when producing a negative electrode when the protrusions are in a positional relationship that penetrates into adjacent graphite particles. From this viewpoint, it can be said that the shape is more preferable.
  • the negative electrode of the non-aqueous electrolyte secondary battery according to the present embodiment includes a binder that holds an active material on the current collector in the mixture layer, that is, a binder component, a rubber binder and carboxymethyl cellulose (hereinafter referred to as CMC). Abbreviated).
  • CMC carboxymethyl cellulose
  • these are essential for securing the binding property between the active materials.
  • a film is formed on the surface of the active material graphite particles, and lithium ions are inserted. Inhibits detachment.
  • the total content of CMC and the rubber binder in the entire negative electrode mixture layer occupies 2.4 parts by mass or more, an increase in electric resistance of the battery due to the presence of an excessive binder component was confirmed. Moreover, when it is less than 2.00 parts by mass, sufficient binding force cannot be obtained, the adhesion of the negative electrode mixture layer to the current collector becomes poor, and charging and discharging may be difficult due to insufficient conduction. Is expensive. Therefore, the total content of CMC and rubber binder with respect to the entire negative electrode mixture layer is preferably 2.05 parts by mass or more and 2.35 parts by mass or less, more preferably 2.10 parts by mass or more and 2.30 parts by mass or less. More preferably, it is 2.15 parts by mass or more and 2.25 parts by mass or less. When the content exceeds 2.35 parts by mass, the DCR of the battery increases.
  • a negative electrode mixture containing both scaly graphite particles and polyhedral graphite particles is particularly applied.
  • Polyhedral graphite particles tend to require a larger amount of binder component than scale-like graphite particles.
  • the detailed cause is unknown, it is presumed that the scaly graphite particles have many irregularities on the surface, and friction between the particles is likely to occur, so that sufficient binding can be secured even with a small amount of binder component.
  • the binder component that is, the rubber binder and the CMC
  • the binder component is not seen when the negative electrode is cut and the mixture layer is not peeled off from the cut portion.
  • the total content is 2.00 parts by mass, the mixture layer is peeled off from the cut portion when the electrode is similarly cut.
  • the tendency of such a mixture layer to peel off is due to a decrease in the binding force between the current collector and the negative electrode mixture layer.
  • the battery is particularly important. Application becomes difficult.
  • the binder component is preferably contained within the above range.
  • the type of rubber binder is arbitrary as long as the effects of the present invention are not significantly impaired, but synthetic rubber is preferred from the viewpoint of easy control of physical properties and few impurities.
  • synthetic rubbers include, for example, styrene-butadiene copolymer rubber (hereinafter abbreviated as SBR) and modified products thereof, acrylonitrile-butadiene copolymer rubber and modified products thereof, acrylic rubber and modified products thereof. And fluororubber.
  • SBR styrene-butadiene copolymer rubber
  • a rubber binder may consist only of 1 type, and may comprise 2 or more types in arbitrary ratios and combinations.
  • the negative electrode binder according to the present embodiment may include a binder other than the rubber binder.
  • a binder other than the rubber binder those having arbitrary physical properties can be used as long as the effects of the present invention are not significantly impaired. Examples thereof include polyvinylidene fluoride (PVDF).
  • PVDF polyvinylidene fluoride
  • 1 type of binders other than a rubber binder may be contained independently, and 2 or more types may be contained by arbitrary ratios and combinations.
  • Positive electrode [Positive electrode active material]
  • the positive electrode active material occludes and releases lithium ions in the non-aqueous electrolyte solution that the non-aqueous electrolyte secondary battery normally has, and takes in electrons.
  • the physical properties and types of the positive electrode active material are arbitrary as long as the effects of the present invention are not significantly impaired. Therefore, a positive electrode active material having any known physical property that is preferably used for a non-aqueous electrolyte secondary battery may be used.
  • lithium oxide or the like can be mentioned as a suitable material.
  • Specific examples of such lithium oxide include lithium cobalt oxide, lithium manganate, lithium nickelate, lithium iron phosphate, and lithium composite oxide (that is, two or more selected from the group consisting of cobalt, nickel, and manganese).
  • Lithium oxide containing the above metal and the like.
  • a positive electrode active material may be used individually by 1 type, and may be used 2 or more types by arbitrary ratios and combinations.
  • binders As the positive electrode according to the present embodiment, those having arbitrary physical properties can be used as long as the effects of the present invention are not significantly impaired. Examples thereof include a rubber binder similar to the negative electrode binder, and polyvinylidene fluoride (PVDF). In addition, 1 type of binders other than a rubber binder may be contained independently, and 2 or more types may be contained by arbitrary ratios and combinations.
  • the electrode according to the present embodiment includes a binder component, but other components that can be included in addition to the binder component are optional as long as the effects of the present invention are not significantly impaired.
  • the electrode according to the present embodiment usually includes a current collector in addition to the above mixture layer, and in particular, the positive electrode further includes a conductive material.
  • the thickness of the current collector is usually 5 ⁇ m or more, preferably 10 ⁇ m or more, and the upper limit is usually 30 ⁇ m or less, preferably 20 ⁇ m or less. If the thickness of the current collector is too thin, the strength of the electrode will decrease, and the electrode may be easily damaged. If it is too thick, the flexibility of the electrode will be impaired, and there will be restrictions on the battery manufacturing method in the subsequent process May occur.
  • the type of the current collector is arbitrary as long as the effect of the present invention is not significantly impaired, but usually a conductive material is used.
  • a conductive material for example, copper is suitably used for the negative electrode, and aluminum or the like is suitably used for the positive electrode.
  • One type of current collector may be used alone, or two or more types may be used in any ratio and combination.
  • the shape of the current collector is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually a foil shape.
  • the conductive material assists the exchange of electrons between the current collector and the active material.
  • the physical properties and types of the conductive material usually included in the electrode according to this embodiment are arbitrary as long as the effects of the present invention are not significantly impaired. Therefore, a conductive material having any known physical property that is suitably used for a non-aqueous electrolyte secondary battery may be used.
  • a conductive material examples include acetylene black and graphite.
  • a conductive material may be used individually by 1 type, and may be used 2 or more types by arbitrary ratios and combinations.
  • Non-aqueous electrolyte The battery according to this embodiment usually has a non-aqueous electrolyte in addition to the binder.
  • a nonaqueous electrolytic solution is not particularly limited as long as it can occlude and release lithium ions with respect to the active material.
  • the non-aqueous electrolyte usually consists of a non-aqueous solvent and a non-aqueous electrolyte.
  • Any nonaqueous solvent may be used as long as the effects of the present invention are not significantly impaired.
  • a carbonate solvent is preferable.
  • Specific examples of the carbonate solvent include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), and chain carbonates such as dimethyl carbonate (DMC) and methyl ethyl carbonate (MEC).
  • a non-aqueous solvent may be used individually by 1 type, and may be used 2 or more types by arbitrary ratios and combinations.
  • any nonaqueous electrolyte contained in the nonaqueous electrolytic solution can be used as long as the effects of the present invention are not significantly impaired.
  • a lithium salt is particularly suitable.
  • Specific examples of such a lithium salt include lithium fluorophosphate (LiPF 6 ), lithium fluoroborate (LiBF 4 ), and the like.
  • a non-aqueous electrolyte may also be used individually by 1 type, and may use 2 or more types by arbitrary ratios and combinations.
  • the battery according to the present embodiment can be manufactured by any known method as long as it has the above-described configuration.
  • the manufacturing method of the battery which concerns on this embodiment is given as an example, the manufacturing method of the electric potential which concerns on this embodiment is not limited to the method as described below.
  • the electrode (positive electrode and negative electrode) according to the present embodiment is, for example, applied to a current collector by applying an electrode mixture composed of an active material, a binder, a conductive material, a dispersion medium, and other components as necessary, and then dried. It can produce by doing.
  • the binder used was the one described in “[1-2. Negative electrode binder] of [1-2. Negative electrode]” and “[Positive electrode binder] of [1-3. Positive electrode]”, and a current collector,
  • the active material and the conductive material those described above in “[1-3. Other components]” can be used.
  • the amount of each component in the electrode mixture is the same as the amount of each component contained in the electrode after drying [1-2. Negative electrode] and [1-3. What is necessary is just to adjust suitably so that it may be what was described in the positive electrode].
  • SBR that can be suitably used as a rubber binder contained in the electrode according to the present embodiment can be usually produced by copolymerizing styrene and butadiene.
  • SBR may be synthesized in a system to which a copolymerizable component is appropriately added.
  • Tg glass transition temperature
  • components such as acrylonitrile and 2-vinylpyridine can be used as copolymerizable components.
  • the electrode mixture contains a dispersed liquid.
  • the type of the dispersion medium usually contained in the electrode mixture is arbitrary as long as the effects of the present invention are not significantly impaired.
  • NMP N-methylpyrrolidone
  • a dispersion medium may be used individually by 1 type, and may use 2 or more types by arbitrary ratios and combinations.
  • the amount of the dispersion medium in the electrode mixture is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 20% by weight or more, preferably 30% by weight or more, more preferably 40%, based on the total amount of the electrode mixture.
  • the upper limit is usually 70% by weight or less, preferably 65% by weight or less, more preferably 60% by weight or less. If the amount of the dispersion medium is too small, each component contained in the electrode mixture may not be properly dispersed, and each component may be unevenly distributed on the current collector. It may take too much.
  • Examples of other components included in the electrode mixture as needed include surfactants, antifoaming materials, thickeners, and the like.
  • the electrode mixture contains a surfactant
  • the dispersion stability of the rubber binder contained in the electrode mixture can be improved.
  • coating the electrode mixture containing the said surfactant can be suppressed because an electrode mixture contains an antifoamer.
  • an electrode mixture contains a thickener, the viscosity of an electrode mixture can be made into a desired thing, and application
  • surfactants include sodium n-dodecyl sulfate and the like, and one surfactant may be used alone, or two or more surfactants may be used in any ratio and combination.
  • specific examples of the antifoaming agent include n-octanol, polysiloxane and the like, and one type of antifoaming agent may be used alone, or two or more types may be used in any ratio and combination.
  • specific examples of the thickener include carboxymethyl cellulose (CMC) and the like, and one thickener may be used alone, or two or more thickeners may be used in any ratio and combination.
  • the above-mentioned active material, binder, conductive material, dispersion medium and other components as required can be mixed by any known method to produce an electrode mixture. Any mixing method can be used as long as each component can be uniformly dispersed in the dispersion medium and the effects of the present invention are not significantly impaired.
  • the solid content of the prepared electrode mixture is arbitrary as long as the effects of the present invention are not significantly impaired, but is usually 35% by weight or more, preferably 45% by weight or more, more preferably 50% by weight or more, and the upper limit thereof. Is usually 70% by weight or less, preferably 65% by weight or less, more preferably 60% by weight or less. If the solid content is too small, it may take too much time for the coating and drying process when forming the electrode, and if it is too large, the coating property may be lowered. The solid content can be measured by a method of heating and drying the electrode mixture.
  • the viscosity of the electrode mixture is arbitrary as long as the effects of the present invention are not significantly impaired, but usually 0.5 Pa ⁇ s or more, preferably 1 Pa ⁇ s or more, and the upper limit is usually 100 Pa ⁇ s or less.
  • the pressure is preferably 10 Pa ⁇ s or less. If the viscosity is too small, it may flow in the coating and drying step, and a uniform electrode mixture layer may not be obtained. If it is too large, coating may be difficult.
  • the viscosity can be measured using a measuring device such as a viscometer according to JIS Z 8803.
  • the coating method for applying the prepared electrode mixture to the current collector is arbitrary as long as the effects of the present invention are not significantly impaired.
  • Specific examples of the application method include a roll coating method and a slit die coating method.
  • coating may be performed only by 1 type of methods, and may be performed combining arbitrary 2 or more types of methods.
  • coating may be performed only once, for example, it may dry after apply
  • the application amount when applying the electrode mixture to the electrode is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 10 g / m 2 or more, preferably 20 g / m 2 or more with respect to the one-side surface area of the electrode. More preferably, it is 30 g / m 2 , and the upper limit is usually 500 g / m 2 or less, preferably 350 g / m 2 or less, more preferably 200 g / m 2 or less. If the amount of the electrode mixture is too small, it may be difficult to apply for electrode preparation. If it is too much, the prepared electrode will become more rigid and difficult to handle in the battery assembly process. there is a possibility.
  • drying method after applying the electrode mixture to the current collector is optional as long as the effects of the present invention are not significantly impaired.
  • the drying time is not particularly limited, and it may be dried to such an extent that the active material contained in the electrode mixture can be sufficiently fixed to the current collector.
  • the mixture layer can be brought to a desired density by compressing (pressing) the produced current collector having the electrode mixture layer.
  • compressing pressing
  • the negative electrode active materials contained in the mixture layer come into contact with each other, and current can be input and output, whereby the active material can be used.
  • the compression step is not particularly limited as long as the purpose of the previous period is achieved, but the roll press method is preferable from the viewpoint of productivity. Moreover, you may heat suitably.
  • non-aqueous electrolyte included in the battery according to the present embodiment can also be produced by an arbitrary method as long as the effects of the present invention are not significantly impaired.
  • the nonaqueous electrolyte described in [Nonaqueous Electrolyte] can be dissolved in a nonaqueous solvent so as to have a desired concentration to produce a nonaqueous electrolyte.
  • the large current in the present invention means the amount of current that can be discharged from the upper limit voltage to the lower limit voltage by discharging in less than 1 hour with respect to the initial discharge capacity of the battery to be produced. For example, for a battery with a capacity of 10 Ah, the amount of current that can be discharged in one hour from a fully charged state to a discharged state is 10 A, which is called 1 CA, but a larger amount of current is a large current.
  • the effect of the graphite particle mixing ratio on the discharge capacity retention rate at the 1000th cycle in the charge / discharge cycle was investigated.
  • the negative electrode active material, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC, number average polymerization degree 1500, etherification degree 0.7) are mixed so as to be 98: 1: 1.
  • a battery was produced by the method described below. As shown in FIG. 3, it was confirmed that the discharge capacity retention rate tended to improve as the ratio of the polyhedral graphite particles increased as compared with the case where the flaky graphite particles alone were used as the negative electrode active material.
  • the negative electrode mixture layer tends to be exfoliated from the current collector, particularly when the ratio of the polyhedral graphite particles exceeds 40 parts by mass. It was remarkable and it was difficult to produce a battery.
  • Example 1 Scale-like graphite particles having an average particle diameter of 20.5 ⁇ m and a specific surface area of 3.9 ⁇ 10 3 m 2 / kg, and polyhedral graphite particles having an average particle diameter of 5.4 ⁇ m and a specific surface area of 2.5 ⁇ 10 3 m 2 / kg Styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC, number average polymerization degree 1500, etherification degree 0.7) are 68.46: 29.34: 1.1: 1.1 in weight ratio.
  • SBR Styrene butadiene rubber
  • CMC carboxymethyl cellulose
  • the viscosity was measured using a conical plate viscometer according to JIS Z 8803. Then, the prepared electrode mixture paint is applied to the surface of a copper foil having a thickness of 10 ⁇ m by a roll coating method so that the coating amount is 90 g / m 2, and is sufficiently dried, and further pressed, A negative electrode having a density of 1.5 g / cm 3 was produced.
  • Example 2 A negative electrode was produced in the same manner as in Example 1 except that the content of each component in the electrode mixture was 68.53: 29.37: 1.05: 1.05 by weight.
  • the produced negative electrode mixture paint had a solid content of 50% by weight and a viscosity of 1.7 Pa ⁇ s.
  • Example 3 A negative electrode was produced in the same manner as in Example 1 except that the content of each component in the electrode mixture was 68.53: 29.37: 1: 1.1 by weight.
  • the produced negative electrode mixture paint had a solid content of 50% by weight and a viscosity of 1.7 Pa ⁇ s.
  • Example 4 A negative electrode was produced in the same manner as in Example 1 except that the content of each component in the electrode mixture was 68.53: 29.37: 1.1: 1 by weight.
  • the produced negative electrode mixture paint had a solid content of 50% by weight and a viscosity of 1.6 Pa ⁇ s.
  • Example 5 A negative electrode was produced in the same manner as in Example 1 except that the content of each component in the electrode mixture was 68.53: 29.37: 1.2: 1 by weight.
  • the produced negative electrode mixture paint had a solid content of 50% by weight and a viscosity of 1.7 Pa ⁇ s.
  • Example 1 A negative electrode was produced in the same manner as in Example 1 except that the content of each component in the electrode mixture was 98: 0: 1: 1 by weight, that is, the total amount of graphite particles was scaly graphite particles. did.
  • the produced electrode mixture paint had a solid content of 50% by weight and a viscosity of 2.0 Pa ⁇ s.
  • Example 2 A negative electrode was produced in the same manner as in Example 1 except that the content of each component in the electrode mixture was 68.6: 29.4: 1: 1 by weight.
  • the produced electrode mixture paint had a solid content of 50% by weight and a viscosity of 1.6 Pa ⁇ s.
  • Example 3 A negative electrode was produced in the same manner as in Example 1 except that the content of each component in the electrode mixture was 68.32: 29.28: 1.2: 1.2 by weight ratio.
  • the produced electrode mixture paint had a solid content of 50% by weight and a viscosity of 2.2 Pa ⁇ s.
  • a positive electrode active material lithium manganate
  • a positive electrode conductive agent mixture of graphite and acetylene black
  • a binder polyvinylidene fluoride
  • a slurry of the positive electrode mixture was prepared by dispersing.
  • the produced electrode mixture had a solid content of 60% by weight and a viscosity of 12 Pa ⁇ s. The viscosity was measured by the same method as that for the negative electrode.
  • the prepared electrode mixture was applied to the surface of an aluminum foil having a thickness of 15 ⁇ m by a roll coating method so that the coating amount was 200 g / m 2 , sufficiently dried, further pressed, and the mixture density Produced a positive electrode of 3.0 g / cm 3 .
  • a wound group was produced in which the positive electrode and the negative electrode produced by the above method were wound in a spiral shape through a separator (thickness 25 ⁇ m, width 58 mm) made of a polyethylene porous film. This wound group was inserted into a battery can together with an insulator made of polyethylene. Thereafter, the negative electrode tab was welded to the bottom surface of the battery can, and the positive electrode tab was welded to the positive electrode terminal.
  • FIG. 5 shows a schematic diagram (front view) of the produced nonaqueous electrolyte secondary battery.
  • the left half of FIG. 5 is a schematic view (front view) of a cross section of the nonaqueous electrolyte secondary battery.
  • the positive electrode terminal in FIG. 5 also serves as a sealing lid for the nonaqueous electrolyte secondary battery, and is equipped with a cleavage valve that cleaves to release the pressure inside the battery when the pressure inside the battery rises.
  • the conditions for the charge / discharge evaluation were charging by a constant current-constant voltage method, and termination conditions were an upper limit voltage of 4.1 V and a lower limit current of 20 mA. Further, the discharge was a constant current method, and the termination condition was a lower limit voltage of 2.7V.
  • the initial charge capacity of the batteries averaged 1420 mAh, the initial efficiency averaged 88%, and the battery capacity before evaluation averaged 1249 mAh. Then, the output characteristic in 25 degreeC of the battery charged to SOC (State of Charge) 100% was evaluated.
  • the DCR was calculated from the pre-discharge voltage and the voltage 10 seconds after the start of discharge, assuming that the current value was three conditions of 300 mA, 600 mA, and 1200 mA.
  • the charge / discharge cycle evaluation was performed using two each of the produced batteries. Charging was performed under constant current and constant voltage conditions with a current value of 3A, an upper limit voltage of 4.1V, and a current lower limit of 20mA, and discharging was performed under constant current conditions of a current value of 3A and a lower limit voltage of 2.7V. Furthermore, there was no downtime, that is, a condition was set such that discharging was started immediately at the end of charging, and charging was started immediately at the end of discharging.
  • Table 1 summarizes the composition of the negative electrode mixture, the degree of the mixture layer peeling from the cut surface when the negative electrode was cut, and the DCR and cycle characteristics of the batteries produced in Examples 1 and 2 and Comparative Examples 1 to 3.
  • the cycle characteristics were evaluated by the discharge capacity maintenance rate by inputting and outputting a current of 3 A for both charge and discharge, continuously charging and discharging with an upper limit voltage of 4.1 V and a lower limit voltage of 2.7 V.
  • the discharge capacity retention rate was evaluated in terms of a ratio, with the discharge capacity at 1000 cycles of Comparative Example 1 being 100.
  • Example 1 As shown in Table 1, the negative electrodes produced in Examples and Comparative Examples were each aligned to a width of 56 mm and cut using scissors. The number of cuts was 30 times, the cut length was 1680 mm in total, and peeling of the mixture layer from the cut surface was visually observed. In Examples 1, 2, 4 and 5, no clear peeling was observed. In Comparative Example 1 in which only the scaly graphite particles were used as the active material, no clear peeling was observed. On the other hand, in Comparative Example 2 in which the total amount of binder components was the same as that in Comparative Example 1, many peelings were observed. Moreover, although the tendency which peels off a little also in Example 3 was seen, the remarkable peeling did not arise. In Comparative Example 3 having the largest binder component content, no peeling was observed.
  • the negative electrode which mixed scaly graphite, polyhedral graphite, CMC, and SBR so that it might become 98.0: 0: 1: 1 by weight ratio was used.
  • the total content of the binder components in the mixture layer is 2.1% by mass or more and 2.3% by mass or less.
  • the technique of Comparative Example 1 which is a conventional technique (that is, an electrode containing only scaly graphite as a negative electrode active material), or a binder component content of 2.4% by mass in the mixture layer is compared.
  • the binder component content is an optimal ratio with respect to the active material amount, the durability with respect to the charge / discharge cycle is also improved.
  • the polyhedral graphite particles that are relatively resistant to destruction by repeated charge and discharge are arranged so as to contact the scaly graphite particles. Even if part of the scaly graphite particles is destroyed by the discharge and the fractured part that is not electrically conductive expands, electrical conduction is ensured with the polyhedral graphite particles in contact as a detour, and charging and discharging continue. Be available.
  • the battery having excellent cycle characteristics in the present invention can be suitably used for applications that require large current input / output over a long period of time, particularly for automobiles, railways, and the like.

Abstract

The issue of the present invention is to provide a battery in which capacity degradation of the battery has been suppressed with respect to a high-current charge/discharge cycle. The non-aqueous electrolyte rechargeable battery of the present invention is a non-aqueous electrolyte rechargeable battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte. In this non-aqueous electrolyte rechargeable battery, the negative electrode has a negative electrode compound layer containing as negative-electrode active materials scaly graphite particles, and polyhedral graphite particles whose surface has been coated with amorphous carbon. Of the total amount of active materials contained in the negative electrode compound layer, the scaly graphite particles are preferably from 60 parts by mass or more to 90 parts by mass or less, the polyhedral graphite particles are preferably from 10 parts by mass or more to 40 parts by mass or less, and the surface of the scaly graphite particles is preferably coated with amorphous carbon. Also, the binder component in the negative electrode compound layer is preferably from 2.05 parts by mass or more to 2.35 parts by mass or less of the total compound layer.

Description

非水電解液二次電池Non-aqueous electrolyte secondary battery
　本発明は、非水電解液二次電池に関する。 The present invention relates to a non-aqueous electrolyte secondary battery.
　地球温暖化等の環境問題の顕在化により、例えば乗り物の排気ガスに由来する二酸化炭素の排出量削減が求められている。このような要求に対し、電気エネルギーを動力とする鉄道及び自動車等の減速時に生じるエネルギーを回生し、動力の一部として使用するハイブリッド鉄道及びハイブリッド自動車等の開発が急ピッチで進められている。そして、上記の鉄道及び自動車等の動力源として通常搭載される電池として、電極でのリチウムイオンの吸蔵放出反応を利用したリチウムイオン二次電池（即ち非水電解液二次電池）が注目されている。また、太陽光発電又は風力発電等で発電した電力を蓄え、電力系統に供給する用途にもリチウムイオン二次電池も注目されている。 With the emergence of environmental problems such as global warming, for example, reduction of emissions of carbon dioxide derived from vehicle exhaust gas is required. In response to such demands, the development of hybrid railways and hybrid cars that regenerate energy generated during deceleration of railways and automobiles powered by electric energy and that are used as part of the power is being promoted at a rapid pace. As a battery normally mounted as a power source for the above-mentioned railways and automobiles, a lithium ion secondary battery (that is, a non-aqueous electrolyte secondary battery) using a lithium ion storage / release reaction at an electrode attracts attention. Yes. In addition, lithium ion secondary batteries are also attracting attention for applications in which electric power generated by solar power generation or wind power generation is stored and supplied to an electric power system.
　リチウムイオン二次電池はこれまで、多くがノートＰＣ、デジタルカメラ等、１２Ｖ以下の比較的低電圧で駆動される電子機器に適用されてきた。これらの使用条件では電池容量に比較して小電力での使用を前提としており、リチウムイオン二次電池に要求される特性は、他の方式と比較して大容量であることであった。 Many lithium ion secondary batteries have been applied to electronic devices such as notebook PCs and digital cameras that are driven at a relatively low voltage of 12 V or less. Under these conditions of use, it is assumed that the battery is used at a lower power than the battery capacity, and the characteristic required for the lithium ion secondary battery is that it has a larger capacity than other systems.
　車載用途向けのリチウムイオン二次電池は、小型電子機器向けとは異なり、大容量でありかつ高出力であることが必須である。大容量の達成には、より大量の活物質を具備する必要があり、また高出力の達成には、電池の入出力性能を向上する必要がある。 リ チ ウ ム Unlike small electronic devices, lithium-ion secondary batteries for in-vehicle use must have large capacity and high output. To achieve a large capacity, it is necessary to provide a larger amount of active material, and to achieve a high output, it is necessary to improve the input / output performance of the battery.
　さらに、車載用途向けのリチウムイオン二次電池は、長期間に渡り使用されることが容易に想定され、充放電の回数が多くなることから、充放電のサイクル回数に対する耐久性、すなわちサイクル特性が良好であることが必須である。 Furthermore, lithium-ion secondary batteries for in-vehicle use are easily assumed to be used for a long period of time, and the number of charge / discharge cycles increases. It is essential to be good.
　そこで、たとえば特許文献１には、負極が黒鉛質粒子と鱗片状黒鉛からなる導電材料を含有し、かつ負極表面に造孔処理によらない凹部が存在することにより放電負荷特性に優れた非水電解質二次電池が提案されている。 Thus, for example, in Patent Document 1, the negative electrode contains a conductive material composed of graphite particles and scaly graphite, and a non-aqueous solution having excellent discharge load characteristics due to the presence of a recess not formed on the surface of the negative electrode. An electrolyte secondary battery has been proposed.
　また、たとえば特許文献２には、電池の入出力性能の向上、すなわち電池の電気抵抗を低減することを目的に、正極に含有されるバインダ成分として、第１結着材にカルボキシメチルセルロースを、第２結着材にポリエチレンオキサイドを備える構造が提案されている。 Further, for example, in Patent Document 2, for the purpose of improving the input / output performance of the battery, that is, reducing the electric resistance of the battery, carboxymethyl cellulose is used as the first binder as the binder component contained in the positive electrode. A structure comprising a polyethylene oxide in a two-binding material has been proposed.
特許第４５８５２２９号公報Japanese Patent No. 4585229 特開２０１１－３５１１号公報JP 2011-3511 A
　しかしながら、特許文献１に記載の方法においては、負極に鱗片状黒鉛からなる導電材料が含有されており、相対的に黒鉛質粒子の比率が低下する。特許文献１の負極構成では、負極の充電容量は黒鉛質粒子の含有量に比例するため、負極の重量当たりの充電容量を低下させ、結果的に電池容量が低下する。 However, in the method described in Patent Document 1, a conductive material made of flaky graphite is contained in the negative electrode, and the ratio of graphitic particles is relatively reduced. In the negative electrode configuration of Patent Document 1, since the charge capacity of the negative electrode is proportional to the content of the graphite particles, the charge capacity per weight of the negative electrode is reduced, resulting in a decrease in battery capacity.
　また、特許文献２では、バインダ成分の種類がポリエチレンオキサイドに規定されており、従来用いられているスチレンブタジエンゴム等のゴムバインダとは組成が異なることから、他の電池を構成する部材、特に電解液についてある程度の制約が生じる可能性が残される。その理由としては、本発明者らの検討によると、ポリエチレンオキサイドの合成時に生じる低分子量成分等が、電解液中に溶解する場合があり、電解液に対するポリエチレンオキサイドの溶解度を考慮する必要が生じると考えられる。 Further, in Patent Document 2, the type of binder component is defined as polyethylene oxide, and since the composition is different from that of a conventionally used rubber binder such as styrene butadiene rubber, members constituting other batteries, particularly electrolyte solution There remains a possibility that some constraints will arise on. The reason for this is that, according to the study by the present inventors, low molecular weight components and the like generated during the synthesis of polyethylene oxide may be dissolved in the electrolytic solution, and the solubility of polyethylene oxide in the electrolytic solution needs to be considered. Conceivable.
　このように、特許文献１に記載の方法においては、車載用途向け電池に対する要求の一つである容量の確保が困難となる可能性がある。 Thus, in the method described in Patent Document 1, it may be difficult to ensure the capacity, which is one of the requirements for the battery for in-vehicle use.
　また、特許文献２に記載の方法においては、バインダの組成に由来する電解液組成の制限が生じる可能性がある。 Moreover, in the method described in Patent Document 2, there is a possibility that restriction of the electrolyte composition derived from the binder composition may occur.
　本発明は上記の課題を解決するべくなされたものであり、その目的は、充放電サイクルに対して電池の容量劣化を抑制し、かつ電流の入出力における電気抵抗の上昇を抑制した非水電解液二次電池を提供することである。 The present invention has been made to solve the above-described problems, and its object is to suppress non-aqueous electrolysis that suppresses battery capacity deterioration with respect to charge / discharge cycles and suppresses an increase in electrical resistance in current input / output. It is to provide a liquid secondary battery.
　上記課題を解決する本発明の非水電解液二次電池は、負極合剤層が、鱗片状黒鉛粒子と、表面が非晶質炭素により被覆されている多面体状黒鉛粒子とを有することを特徴とする。 The nonaqueous electrolyte secondary battery of the present invention that solves the above-mentioned problems is characterized in that the negative electrode mixture layer has scaly graphite particles and polyhedral graphite particles whose surfaces are coated with amorphous carbon. And
　本発明によれば、大電流での充放電に対して電池の容量劣化を抑制した電池を提供することができる。なお、上記した以外の課題、構成及び効果は、以下の実施形態の説明により明らかにされる。 According to the present invention, it is possible to provide a battery that suppresses battery capacity deterioration against charging / discharging with a large current. Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.
本発明の一実施形態に係る電池の内部構造の模式的な斜視図。The typical perspective view of the internal structure of the battery which concerns on one Embodiment of this invention. 本発明の実施形態に係る電池が有する電極における、バインダ成分と活物質との相対的な位置関係を模式的に示した図。The figure which showed typically the relative positional relationship of the binder component and active material in the electrode which the battery which concerns on embodiment of this invention has. 負極活物質中の多面体状黒鉛粉末比率と1000サイクル充放電後の電池の放電容量維持率の関係を示すグラフ。The graph which shows the relationship between the polyhedral graphite powder ratio in a negative electrode active material, and the discharge capacity maintenance factor of the battery after 1000 cycles charging / discharging. 負極合剤のバインダ成分含有量と電池のＤＣＲとの関係を示すグラフ。The graph which shows the relationship between binder component content of a negative mix, and DCR of a battery. 本発明の性能確認に用いた電池構造の模式図。The schematic diagram of the battery structure used for the performance confirmation of this invention.
　以下、本発明を実施するための形態（以下、適宜「本実施形態」と言う。）を詳細に説明するが、本実施形態は以下の内容に限定されるものではなく、その要旨を逸脱しない範囲内で任意に変更して実施することができる。 Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment” as appropriate) will be described in detail, but the present embodiment is not limited to the following contents and does not depart from the gist thereof. Any change can be made within the range.
　また、以下の記載においては、電池の具体例として非水電解液二次電池（即ちリチウムイオン二次電池）を挙げて、本実施形態に係る電池の説明を行う。ただし、本実施形態に係る電池は非水電解液二次電池に限定されるものではなく、本実施形態に係る電池が有する電極は任意の電池に適用することができる。 Further, in the following description, a nonaqueous electrolyte secondary battery (that is, a lithium ion secondary battery) is cited as a specific example of the battery, and the battery according to this embodiment will be described. However, the battery according to this embodiment is not limited to a non-aqueous electrolyte secondary battery, and the electrode of the battery according to this embodiment can be applied to any battery.
　図１は、本発明の一実施形態（第一実施形態）に係る非水電解液二次電池の内部構造の模式的な斜視図である。図２に示す第一実施形態に係る非水電解液二次電池は、電池容器１と、ガスケット２と、上蓋３と、上蓋ケース４と、正極集電板５と、負極集電板６と、電極群８と、正極リード９とを有する。 FIG. 1 is a schematic perspective view of the internal structure of a non-aqueous electrolyte secondary battery according to an embodiment (first embodiment) of the present invention. The non-aqueous electrolyte secondary battery according to the first embodiment shown in FIG. 2 includes a battery container 1, a gasket 2, an upper lid 3, an upper lid case 4, a positive current collector plate 5, and a negative current collector plate 6. The electrode group 8 and the positive electrode lead 9 are included.
　電池容器１は、正極集電板５、負極集電板６、電極群８、正極リード９及び非水電解液（図示しない。）を収納するものである。本実施形態に係る電池において、電池容器１は円筒形状となっているが、角形形状であってもよい。また、電池容器１の材質としては、収納される非水電解液により腐食されない金属を用いることが好まく、ニッケルメッキされた鉄材等が使用される。 The battery container 1 contains a positive electrode current collector plate 5, a negative electrode current collector plate 6, an electrode group 8, a positive electrode lead 9, and a non-aqueous electrolyte (not shown). In the battery according to this embodiment, the battery container 1 has a cylindrical shape, but may have a rectangular shape. Further, as the material of the battery container 1, it is preferable to use a metal that is not corroded by the stored nonaqueous electrolytic solution, and nickel-plated iron or the like is used.
　ガスケット２は、電池容器１と上蓋ケース４との間に設けられるものである。ガスケット２により、電池容器１が密封され、かつ、電池容器１と上蓋３及び上蓋ケース４とが電気的に絶縁されたものとなる。ガスケット２の材質は、例えばポリプロピレン（ＰＰ）、テトラフルオロエチレン・パーフルオロアルキルビニルエーテル共重合体（ＰＦＡ）などの弾性樹脂等の公知の封止部材を用いることができる。 The gasket 2 is provided between the battery case 1 and the upper lid case 4. The battery container 1 is sealed by the gasket 2 and the battery container 1 is electrically insulated from the upper lid 3 and the upper lid case 4. As the material of the gasket 2, a known sealing member such as an elastic resin such as polypropylene (PP) or tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA) can be used.
　上蓋３は、電池により得られた電力を外部に取り出す外部端子、具体的には正極外部端子である。 The upper lid 3 is an external terminal for taking out the electric power obtained from the battery, specifically, a positive external terminal.
　上蓋ケース４は、上蓋３と同一の材質により一体となって形成され、上蓋３と上蓋ケース４とは電気的に導通されたものとなっている。上蓋３及び上蓋ケース４の材質としては、導電性を有する金属を用いることができる。また、上蓋ケース４と正極集電板５とは、金属からなる正極リード９を介して電気的に接続されている。 The upper lid case 4 is integrally formed of the same material as the upper lid 3, and the upper lid 3 and the upper lid case 4 are electrically connected. As the material of the upper lid 3 and the upper lid case 4, a conductive metal can be used. The upper lid case 4 and the positive electrode current collector plate 5 are electrically connected via a positive electrode lead 9 made of metal.
　正極集電板５及び負極集電板６は、それぞれ、後述する正極タブ１２及び負極タブ１３と電気的に接続されている。この電気的な接続は、例えば超音波溶接等により行うことができる。また、正極集電板５及び負極集電板６の中央部には孔が設けられており、軸心７（後述する。）が当該孔に嵌められることにより、正極集電板５及び負極集電板６を軸心７に対して固定している。正極集電板５及び負極集電板６の材質としては、導電性を有する金属が用いられる。 The positive electrode current collector plate 5 and the negative electrode current collector plate 6 are electrically connected to a positive electrode tab 12 and a negative electrode tab 13 described later, respectively. This electrical connection can be performed by, for example, ultrasonic welding. In addition, a hole is provided in the central portion of the positive electrode current collector plate 5 and the negative electrode current collector plate 6, and an axial center 7 (described later) is fitted into the hole, whereby the positive electrode current collector plate 5 and the negative electrode current collector plate. The electric plate 6 is fixed with respect to the shaft center 7. As a material for the positive electrode current collector plate 5 and the negative electrode current collector plate 6, a conductive metal is used.
　また、負極集電板６は、電池容器１の底部と電気的に接続され、電池容器１の底部が電池にて得られた電力を外部に取り出す端子、具体的には負極外部端子として機能している。従って、電池容器１の底部と側面部とは、絶縁体（図示しない。）で相互に絶縁されたものとなっている。 The negative electrode current collector plate 6 is electrically connected to the bottom of the battery case 1, and the bottom of the battery case 1 functions as a terminal for taking out the electric power obtained by the battery, specifically, a negative electrode external terminal. ing. Therefore, the bottom part and the side part of the battery container 1 are insulated from each other by an insulator (not shown).
　軸心７は、電極群８の中心部に位置するものであり、正極電極１４と負極電極１５を、間にセパレータ１８を介在させて捲回させるものである。また、軸心７の上下端部においては、正極集電板５及び負極集電板６を貫通したものとなっている。軸心の形状は任意であるが、第一実施形態においては中空状の円柱を用いている。また、その材質としては、導電性を有さない、若しくは導電性が著しく低い例えば樹脂等を用いることができる。 The shaft center 7 is located at the center of the electrode group 8, and the positive electrode 14 and the negative electrode 15 are wound with a separator 18 interposed therebetween. Further, the upper and lower end portions of the shaft center 7 penetrate the positive electrode current collector plate 5 and the negative electrode current collector plate 6. The shape of the shaft center is arbitrary, but a hollow cylinder is used in the first embodiment. As the material, for example, a resin or the like that does not have conductivity or has extremely low conductivity can be used.
　電極群８は、正極電極１４と負極電極１５との間にセパレータを介在させて円筒状に捲回することによって構成されており、正極電極１４と負極電極１５とが交互に積層されている。正極電極１４は、正極集電体と、正極集電体の両面に設けられた正極合剤層１６を有しており、負極電極１５は、負極集電体と、負極集電体の両面に設けられた負極合剤層１７を有している。 The electrode group 8 is configured by winding a separator between the positive electrode 14 and the negative electrode 15 in a cylindrical shape, and the positive electrodes 14 and the negative electrodes 15 are alternately stacked. The positive electrode 14 has a positive electrode current collector and a positive electrode mixture layer 16 provided on both surfaces of the positive electrode current collector, and the negative electrode 15 is formed on both surfaces of the negative electrode current collector and the negative electrode current collector. The negative electrode mixture layer 17 is provided.
　電極群８の最外周には、セパレータ１８が設けられている。電極群８は、その最外周の設けられたセパレータ１８に対して捲回部材１９により固定され、電極群８の捲回が解けないようになっている。また、正極電極１４の上部には正極タブ１２が設けられ、さらに負極電極１５の下部には負極タブ１３が設けられている。 A separator 18 is provided on the outermost periphery of the electrode group 8. The electrode group 8 is fixed to the separator 18 provided on the outermost periphery by a winding member 19 so that the winding of the electrode group 8 cannot be unwound. Further, a positive electrode tab 12 is provided above the positive electrode 14, and a negative electrode tab 13 is provided below the negative electrode 15.
　正極電極１４の正極集電体と正極タブ１２は、アルミニウム等の金属からなるものである。正極合剤層１６は、正極活物質、導電材、バインダ成分を含むスラリー状の正極合剤を、正極集電体の両面に塗布した後に乾燥させてプレスすることによって形成される。 The positive electrode current collector and the positive electrode tab 12 of the positive electrode 14 are made of a metal such as aluminum. The positive electrode mixture layer 16 is formed by applying a slurry-like positive electrode mixture containing a positive electrode active material, a conductive material, and a binder component on both surfaces of the positive electrode current collector, and then drying and pressing the mixture.
　負極電極１５の負極集電体と負極タブ１３は、銅等の金属からなるものである。負極合剤層１７は、負極活物質、バインダ成分を含むスラリー状の負極合剤を、負極集電体の両面に塗布した後に乾燥させてプレスすることによって形成される。 The negative electrode current collector and the negative electrode tab 13 of the negative electrode 15 are made of a metal such as copper. The negative electrode mixture layer 17 is formed by applying a slurry-like negative electrode mixture containing a negative electrode active material and a binder component on both sides of the negative electrode current collector, followed by drying and pressing.
　セパレータ１８は、多孔質かつ絶縁性を有するものであり、リチウムイオン二次電池に用いることができる、公知の任意のセパレータを用いることができる。 The separator 18 is porous and has an insulating property, and any known separator that can be used for a lithium ion secondary battery can be used.
　本実施形態に係る非水電解液二次電池は、上記及び図１に示す構成を有することにより、電池容器１の外部から充電、若しくは電池容器１の外部へ放電することができる。即ち、例えば電池の放電時には、電極群８の負極電極１５にて発生した電子は、負極タブ１３、負極集電板６及び電池容器１の底部をこの順で経由して外部に取り出される。一方で、上蓋３、上蓋ケース４、正極リード９及び正極タブ１２を介して、外部から電極群８の正極電極１４に電子が到達するようになっている。 The nonaqueous electrolyte secondary battery according to the present embodiment can be charged from the outside of the battery container 1 or discharged to the outside of the battery container 1 by having the configuration described above and shown in FIG. That is, for example, when the battery is discharged, electrons generated at the negative electrode 15 of the electrode group 8 are taken out through the negative electrode tab 13, the negative electrode current collector plate 6, and the bottom of the battery container 1 in this order. On the other hand, electrons reach the positive electrode 14 of the electrode group 8 from the outside through the upper lid 3, the upper lid case 4, the positive electrode lead 9 and the positive electrode tab 12.
［１．電池の構成］
［１－１．負極電極］
〔負極活物質〕
　負極活物質は、電池が通常有する非水電解液中のリチウムイオンを吸蔵放出するものであり、併せて電子を吸蔵放出するものである。負極活物質は、鱗片状黒鉛粒子と、表面が非晶質炭素により被覆されている多面体状黒鉛粒子とを有している。本発明によれば、平均粒径１μｍ以上５０μｍ以下の黒鉛粒子が好適に用いることができる。 [1. Battery configuration]
[1-1. Negative electrode]
[Negative electrode active material]
The negative electrode active material is one that occludes and releases lithium ions in the non-aqueous electrolyte that the battery normally has, and also occludes and releases electrons. The negative electrode active material has scaly graphite particles and polyhedral graphite particles whose surfaces are coated with amorphous carbon. According to the present invention, graphite particles having an average particle size of 1 μm or more and 50 μm or less can be suitably used.
　平均粒径は、作製する負極の厚さに応じて適宜選択すれば良く、鱗片状黒鉛粒子は、平均粒径５μｍ以上５０μｍ以下が好ましく、１０μｍ以上３０μｍ以下がより好ましい。また、多面体状黒鉛粒子は、平均粒径１μｍ以上５０μｍ以下が好ましく、５μｍ以上１５μｍ以下がより好ましい。黒鉛粒子の平均粒径が５０μｍを超えると、作製される合剤層の厚さに対して粒子一個の大きさが大きく、厚さの変動を生じやすく、１μｍを下回ると微粉末である黒鉛の取り扱いが煩雑となり、生産性が著しく劣る。 The average particle diameter may be appropriately selected according to the thickness of the negative electrode to be produced. The scaly graphite particles preferably have an average particle diameter of 5 μm to 50 μm, and more preferably 10 μm to 30 μm. The polyhedral graphite particles preferably have an average particle size of 1 μm to 50 μm, and more preferably 5 μm to 15 μm. When the average particle diameter of the graphite particles exceeds 50 μm, the size of one particle is large with respect to the thickness of the mixture layer to be produced, and the thickness is likely to fluctuate. Handling becomes complicated and productivity is remarkably inferior.
　なお、本発明における平均粒径とは、レーザー回折式粒度分布測定装置を用いて求められる粒度分布における積算値５０％の粒度である。 In addition, the average particle diameter in this invention is a particle size of the integrated value 50% in the particle size distribution calculated | required using a laser diffraction type particle size distribution measuring apparatus.
　黒鉛を負極活物質として用いるリチウムイオン二次電池では、充電時には黒鉛に対するリチウムイオン挿入により黒鉛が膨張し、放電時には黒鉛からのリチウムイオン脱離により黒鉛が収縮する。このため、繰り返し充放電を行うことで、黒鉛は、膨張収縮を繰り返し、物理的に破壊される。そして、充放電のために十分な電流を流すことができない部位が増加して、リチウムイオンの挿入脱離がなされる部位が減少し、結果的に電池の充放電容量が低下することが知られている。 In a lithium ion secondary battery using graphite as a negative electrode active material, graphite expands due to lithium ion insertion into the graphite during charging, and shrinks due to lithium ion desorption from the graphite during discharging. For this reason, by repeatedly charging and discharging, graphite repeatedly expands and contracts and is physically destroyed. It is known that the number of sites where sufficient current cannot flow for charging / discharging increases, the number of sites where lithium ions are inserted and desorbed decreases, and as a result, the charge / discharge capacity of the battery decreases. ing.
　電池には、直流抵抗成分（ＤＣＲ）が生じるため、電流が流れる際には抵抗により発熱が生じる。鉄道及び自動車等の動力源や、太陽光発電又は風力発電等で発電した電力を蓄えるための電池は、大電流の入出力が生じるために、抵抗による発熱が考慮される必要がある。 Since a direct current resistance component (DCR) is generated in the battery, heat is generated by the resistance when a current flows. A battery for storing power generated by power sources such as railways and automobiles, solar power generation, wind power generation, and the like needs to take into account heat generation due to resistance because input / output of a large current occurs.
　負極について、電池の電気抵抗の低減を図る場合、活物質の黒鉛に鱗片状黒鉛を適用することが有効である。鱗片状黒鉛粒子は、多数の平板状黒鉛及び又はそれらの集合体であり、重量当たりの表面積が大きい。このため、リチウムイオンの挿入脱離が可能な部位が多く、挿入脱離の際の抵抗が低減されることで電気抵抗の低減に貢献できる。このため、電池の電気抵抗低減の観点からは、鱗片状黒鉛粒子の使用が必須であると言える。 For the negative electrode, when reducing the electric resistance of the battery, it is effective to apply scaly graphite to the active material graphite. The scaly graphite particles are a large number of flat graphites and / or aggregates thereof, and have a large surface area per weight. For this reason, there are many sites where lithium ions can be inserted and desorbed, and the resistance during insertion and desorption can be reduced, which can contribute to a reduction in electrical resistance. For this reason, it can be said that the use of scaly graphite particles is essential from the viewpoint of reducing the electric resistance of the battery.
　しかしながら、鱗片状黒鉛粒子は、微細な鱗片状の構造の集合体であることから、微細な構造間での接触面積が少なく、繰り返し充放電に伴う膨張収縮に対して比較的脆く、粒子間の接触が遮断されることが多い。すなわち充放電容量の低下が早い傾向にあることが多く、鱗片状黒鉛を用いた電池のサイクル特性には問題があると言える。 However, since the scaly graphite particles are aggregates of fine scaly structures, the contact area between the fine structures is small, and they are relatively brittle with respect to expansion and contraction due to repeated charge and discharge, and the inter-particles Contact is often blocked. That is, the reduction in charge / discharge capacity tends to be quick, and it can be said that there is a problem in the cycle characteristics of a battery using scaly graphite.
　これに対して、多面体状黒鉛粒子は、粒子内部に空隙が乏しく、平均粒径に対する重量当たりの表面積、すなわち比表面積が小さいことから、リチウムイオンの挿入脱離が可能な部位が少なく、相対的に電気抵抗が高くなる。 On the other hand, the polyhedral graphite particles have few voids inside the particles, and the surface area per weight with respect to the average particle diameter, that is, the specific surface area is small. The electrical resistance increases.
　しかし、鱗片状黒鉛粒子とは異なり、多面体状黒鉛粒子は、膨張収縮には比較的強固であり、粒子間の接触遮断が生じにくいため、充放電容量の低下が遅い傾向があり、サイクル特性が比較的良好であると言える。 However, unlike scaly graphite particles, polyhedral graphite particles are relatively strong in expansion and contraction, and are less likely to block contact between particles, so the charge / discharge capacity tends to decrease slowly and cycle characteristics are low. It can be said that it is relatively good.
　加えて、リチウムイオン二次電池用正極及び負極は、集電体（金属箔）上の合剤層をプレスして一定の密度とすることが、所望の電池性能を付与するために必須である。負極については、鱗片状黒鉛は比較的脆い構造であり、その粒子中にも多数の空隙があることから、粒子を圧縮することが比較的容易であり、密度の調節に有利である。対して多面体状黒鉛粒子はそれ以上粒子を圧縮することは困難であり、合剤層の密度調節が非常に困難である。 In addition, for the positive electrode and the negative electrode for lithium ion secondary batteries, it is essential to press the mixture layer on the current collector (metal foil) to a certain density in order to impart desired battery performance. . As for the negative electrode, scaly graphite has a relatively brittle structure, and since there are many voids in the particles, it is relatively easy to compress the particles, which is advantageous for adjusting the density. On the other hand, it is difficult for the polyhedral graphite particles to further compress the particles, and it is very difficult to adjust the density of the mixture layer.
　黒鉛は、表面の化学的な活性が高く、電解液成分と反応して徐々に電解液組成を変化させる恐れがある。電解液組成の変化は電池性能を悪化させる可能性が高い。これに対し、黒鉛粒子の表面に被覆層を設けることで、電解液成分との反応を抑制することができる。被覆層形成の方法としては、黒鉛粉末表面に、被覆層の材料を付着させ、焼結させて非晶質炭素層を形成する等が挙げられる。本発明の黒鉛粉末（鱗片状黒鉛粒子と多面体状黒鉛粒子）も、表面に被覆層を形成することが望ましい。 Graphite has a high chemical activity on the surface, and may react with the electrolyte components to gradually change the electrolyte composition. The change in the electrolyte composition is likely to deteriorate the battery performance. In contrast, the reaction with the electrolyte component can be suppressed by providing a coating layer on the surface of the graphite particles. Examples of the method for forming the coating layer include attaching the material of the coating layer to the surface of the graphite powder and sintering it to form an amorphous carbon layer. It is desirable that the graphite powder of the present invention (flaky graphite particles and polyhedral graphite particles) also form a coating layer on the surface.
　なお、本発明では、微細な板状の黒鉛粒子を、単独か、若しくは複数を複合させてより大きな粒子状としたものを鱗片状黒鉛粒子と呼ぶ。微細な板状の黒鉛粒子は、求める性能に応じて大きさを任意に選ぶことができ、かつ、粒子表面の被覆処理を行っていても良い。表面の被覆は、例えば黒鉛粒子の表面に不定形炭素の被膜を形成する等の手法により実現できる。このように基本単位が微細な板状であることから、鱗片状黒鉛粒子は、粒子間、もしくは複合させて得られた粒子中に、空隙が多数形成されており、この空隙は走査型電子顕微鏡（ＳＥＭ）等を用いて容易に観察することができる。 In the present invention, fine plate-like graphite particles, which are single particles or those obtained by combining a plurality of particles, are referred to as scaly graphite particles. The fine plate-like graphite particles can be arbitrarily selected in size according to the required performance, and the particle surface may be coated. The surface coating can be realized by, for example, a method of forming an amorphous carbon film on the surface of the graphite particles. Since the basic unit is in the form of a fine plate in this way, the scaly graphite particles have a large number of voids formed between the particles or in the composite particles, and these voids are formed by a scanning electron microscope. (SEM) or the like can be used for easy observation.
　また、本発明の多面体状黒鉛粒子とは、外形が多面体形状を有しており、粒子中に空隙がほぼ見られず、それぞれが独立した１個の粒子の形式を取っており、特に前記鱗片状黒鉛粒子のような、複数の粒子を複合させたものではない黒鉛粒子をいう。製造の際、プロセスの条件等により部分的に球状となる可能性も考えられるが、大部分は粒子同士若しくは製造装置と不規則に接触することにより多面体状の形状となる。その際、接触の衝撃により割れが生じることで、稀に空隙が発生することも考えられるが、積極的に空隙を保持することは目的とされない。 In addition, the polyhedral graphite particles of the present invention have a polyhedral shape, almost no voids are observed in the particles, and each takes the form of an independent particle. A graphite particle that is not a composite of a plurality of particles, such as a graphite particle. During production, there is a possibility that the shape may be partially spherical due to process conditions or the like, but most of the shape becomes a polyhedral shape due to irregular contact with particles or production equipment. At that time, it is conceivable that a gap is rarely generated due to a crack caused by a contact impact, but it is not intended to positively hold the gap.
　なお、便宜的に多面体状と呼称するが、本発明での多面体状黒鉛粒子の形状は、幾何学的な多面体とは厳密な意味で異なる。本発明における多面体状とは、粒子の表面が平面か又は、若干の凹凸を有する平面状の部分のいずれか一方、もしくは両方が複数混在した形状を取った状態を示している。この平面もしくは平面状の部分の形状は、大部分がいびつな多角形状である。さらに、各々の粒子の輪郭は基本的に不定形であり、例えば球状粒子の様に、或る程度一様な形状を示すものではない。このような多面体状であり、かつ内部に空隙がほぼ見られないことは、前記の鱗片状黒鉛粒子と同様、走査型電子顕微鏡（ＳＥＭ）等を用いて容易に観察することができる。 In addition, although it calls a polyhedral shape for convenience, the shape of the polyhedral graphite particle in this invention differs in a strict meaning from a geometric polyhedron. The polyhedral shape in the present invention indicates a state in which the surface of the particle is flat or has a shape in which one or both of a flat portion having a slight unevenness are mixed. Most of the shape of this plane or planar portion is an irregular polygonal shape. Furthermore, the outline of each particle is basically indefinite, and does not show a uniform shape to a certain extent, such as a spherical particle. It can be easily observed using a scanning electron microscope (SEM) or the like that it is polyhedral and almost no voids are observed inside, like the above-mentioned scaly graphite particles.
　多面体状黒鉛粒子も、表面を被覆することが望ましく、不定形炭素の被膜を形成した多面体状黒鉛が好適である。 The polyhedral graphite particles are desirably coated on the surface, and polyhedral graphite having an amorphous carbon film is preferable.
　これらの相反する特性変化及び要求事項を勘案し、本発明では、負極合剤層の負極活物質として、鱗片状黒鉛粒子と多面体状黒鉛粒子とを混合して使用することで、電気抵抗とサイクル特性との両立を図った。 In consideration of these contradictory property changes and requirements, in the present invention, as the negative electrode active material of the negative electrode mixture layer, by using a mixture of scaly graphite particles and polyhedral graphite particles, electrical resistance and cycle Achieving compatibility with characteristics.
　すなわち、負極合剤層は、負極活物質として、平均粒径１μｍ以上５０μｍ以下の鱗片状黒鉛粒子と、多面体状黒鉛粒子とを含有する。そして、好ましくは、多面体状黒鉛粒子は、その表面が非晶質炭素により被覆されており、より好ましくは、鱗片状黒鉛粒子も、その表面が非晶質炭素により被覆されている。 That is, the negative electrode mixture layer contains scaly graphite particles having an average particle diameter of 1 μm or more and 50 μm or less and polyhedral graphite particles as a negative electrode active material. Preferably, the surface of the polyhedral graphite particles is coated with amorphous carbon, and more preferably, the surface of the scaly graphite particles is coated with amorphous carbon.
　鱗片状黒鉛粒子及び多面体状黒鉛粒子の活物質総量に対する割合は、好ましくは鱗片状黒鉛粒子が６０質量部以上９０質量部以下でかつ多面体状黒鉛粒子が１０質量部以上４０質量部以下であり、より好ましくは鱗片状黒鉛粒子が６５質量部以上８０質量部以下でかつ多面体状黒鉛粒子が１５質量部以上２０質量部以下、さらに好ましくは、鱗片状黒鉛粒子が６５質量部以上７５質量部以下でかつ多面体状黒鉛粒子が２５質量部以上３５質量部以下である。 The ratio of the scaly graphite particles and the polyhedral graphite particles to the total amount of the active material is preferably such that the scaly graphite particles are 60 parts by mass or more and 90 parts by mass or less, and the polyhedral graphite particles are 10 parts by mass or more and 40 parts by mass or less, More preferably, the scaly graphite particles are 65 parts by mass or more and 80 parts by mass or less, and the polyhedral graphite particles are 15 parts by mass or more and 20 parts by mass or less, and more preferably, the scaly graphite particles are 65 parts by mass or more and 75 parts by mass or less. And polyhedral graphite particles are 25 mass parts or more and 35 mass parts or less.
　鱗片状黒鉛粒子が６０質量部よりも少なく多面体状黒鉛粒子が４０質量部よりも多い場合には電池の電気抵抗が上昇し、かつ負極合剤層の密度調節が困難となる。また、鱗片状黒鉛粒子が９０質量部よりも多く多面体状黒鉛粒子が１０質量部よりも少ない場合にはサイクル特性が悪化する。 When the number of scale-like graphite particles is less than 60 parts by mass and the number of polyhedral graphite particles is more than 40 parts by mass, the electric resistance of the battery increases and the density adjustment of the negative electrode mixture layer becomes difficult. In addition, when the scale-like graphite particles are more than 90 parts by mass and the polyhedral graphite particles are less than 10 parts by mass, the cycle characteristics are deteriorated.
　鱗片状黒鉛粒子と多面体状黒鉛粒子を、好ましい範囲の混合比率とすることによりサイクル特性が向上するメカニズムは以下のように考える。 The mechanism by which the cycle characteristics are improved by setting the scaly graphite particles and polyhedral graphite particles to a preferable mixing ratio is considered as follows.
　前述の通り鱗片状黒鉛粒子は、充放電の際の抵抗が比較的低い反面、充放電の際の膨張収縮の応力により部分的に破壊しやすい特徴を有する。そのため、鱗片状黒鉛粒子を単独で使用すると、繰り返し充放電による破壊部分が拡大する。破壊部分とは、電気的に導通されていない黒鉛粒子の一部であるが、この割合が上昇することで、相対的に電気的な導通が確保された黒鉛粒子の割合が低下する。このことは、挿入脱離可能なリチウムイオンの総量、すなわち電極の容量の低下につながる。すなわち、サイクル特性が悪化することを意味している。 As described above, the scaly graphite particles have a relatively low resistance during charging / discharging, but have a characteristic that they are partially broken by the stress of expansion / contraction during charging / discharging. For this reason, when the scaly graphite particles are used alone, the destruction portion due to repeated charge and discharge is expanded. The broken portion is a part of the graphite particles that are not electrically conductive. However, when this ratio is increased, the proportion of the graphite particles that are relatively electrically secured is decreased. This leads to a decrease in the total amount of lithium ions that can be inserted and desorbed, that is, the capacity of the electrode. That is, the cycle characteristics are deteriorated.
　これに対し、繰り返し充放電による破壊に比較的耐性のある多面体状黒鉛粒子が、鱗片状黒鉛粒子に接触するように配置されれば、鱗片状黒鉛粒子の粒子自体は破壊するものの、接触する多面体状黒鉛粒子を迂回路として使用して電気的な導通が確保される。すなわち、鱗片状黒鉛粒子単独では導通が損なわれる部位が、多面体状黒鉛粒子との接触により、引き続き導通が確保され、充放電に利用可能となる。したがって、挿入脱離可能なリチウムイオンの総量の低下を防ぎ、電極の容量低下を抑制でき、サイクル特性の悪化を防ぎ、電池として長寿命化が図れる。 On the other hand, if the polyhedral graphite particles that are relatively resistant to destruction by repeated charge and discharge are arranged so as to contact the scaly graphite particles, the scaly graphite particles themselves are destroyed, but the contacting polyhedrons Electrical conduction is ensured by using the graphite particles as a bypass. That is, the portion where the electrical conductivity is impaired by the scaly graphite particles alone is continuously secured by contact with the polyhedral graphite particles, and can be used for charging and discharging. Accordingly, it is possible to prevent a decrease in the total amount of lithium ions that can be inserted and desorbed, suppress a decrease in electrode capacity, prevent deterioration of cycle characteristics, and extend the life of the battery.
　このような効果が十分発揮されるためには、鱗片状黒鉛粒子に十分接触する量の多面体状黒鉛粒子が必須である。同時に、多面体状黒鉛粒子には繰り返し充放電による膨張収縮に対して、より強固であることも必須とされる。 In order for such an effect to be sufficiently exhibited, polyhedral graphite particles in an amount sufficiently contacting the scaly graphite particles are essential. At the same time, the polyhedral graphite particles are required to be stronger against expansion and contraction due to repeated charge and discharge.
　これらの条件を満たすために、黒鉛粒子の比率は、好ましくは鱗片状黒鉛粒子が６０質量部以上９０質量部以下でかつ多面体状黒鉛粒子が１０質量部以上４０質量部以下であり、より好ましくは鱗片状黒鉛粒子が６５質量部以上８０質量部以下でかつ多面体状黒鉛粒子が１５質量部以上２０質量部以下、さらに好ましくは鱗片状黒鉛粒子が６５質量部以上７５質量部以下でかつ多面体状黒鉛粒子が２５質量部以上３５質量部以下である。 In order to satisfy these conditions, the ratio of the graphite particles is preferably 60 parts by mass or more and 90 parts by mass or less of scaly graphite particles and 10 parts by mass or more and 40 parts by mass or less of polyhedral graphite particles, more preferably The scaly graphite particles are 65 parts by mass or more and 80 parts by mass or less, and the polyhedral graphite particles are 15 parts by mass or more and 20 parts by mass or less, more preferably the scaly graphite particles are 65 parts by mass or more and 75 parts by mass or less and the polyhedral graphite. The particles are 25 parts by mass or more and 35 parts by mass or less.
　そして、より強固な多面体状黒鉛粒子が必須であることから、本発明における多面体状黒鉛粒子は、非晶質炭素等により表面が被覆されていることがより好適である。 And since stronger polyhedral graphite particles are essential, it is more preferable that the surfaces of the polyhedral graphite particles in the present invention are coated with amorphous carbon or the like.
　なお、本発明の多面体状黒鉛粒子の代わりに球状黒鉛粒子を用いた場合には、上記した本発明の効果を奏することはできない。球状黒鉛粒子は、その形状に起因して他の粒子との接触点が少ない傾向にある。黒鉛粒子間の導通確保の観点からは、他の粒子との接触点が多いことがより好ましい。この点において、多面体状黒鉛粒子は、不定形であり、隣接する黒鉛粒子との間に、球状黒鉛粒子より多い接触点を得られることが期待でき、黒鉛粒子間の導通確保が保たれる確率が高くなると考えられる。また、多面体状黒鉛粒子は、複数の平面部分及び又は平面状部分を有することから、それらの接する境界には突起状の部分が生じる。突起状の部分が隣接する黒鉛粒子に貫入するような位置関係にある場合、負極を作製する際の圧縮工程（後述する）において、より強固な接触を得られることは容易に想像でき、導通確保の観点から、より好ましい形状であると言える。 In addition, when spherical graphite particles are used instead of the polyhedral graphite particles of the present invention, the above-described effects of the present invention cannot be achieved. Spherical graphite particles tend to have few points of contact with other particles due to their shape. From the viewpoint of ensuring conduction between graphite particles, it is more preferable that there are many contact points with other particles. In this respect, the polyhedral graphite particles are indefinite, and it can be expected that more contact points can be obtained between the adjacent graphite particles than the spherical graphite particles, and the probability of ensuring conduction between the graphite particles is maintained. Will be higher. In addition, since the polyhedral graphite particles have a plurality of planar portions and / or planar portions, projecting portions are generated at the borders between them. It can be easily imagined that stronger contact can be obtained in the compression process (described later) when producing a negative electrode when the protrusions are in a positional relationship that penetrates into adjacent graphite particles. From this viewpoint, it can be said that the shape is more preferable.
〔負極バインダ〕
　本実施形態に係る非水電解液二次電池が有する負極は、その合剤層中に、集電体上に活物質を保持する結着材、すなわちバインダ成分として、ゴムバインダとカルボキシメチルセルロース（以下ＣＭＣと略す）とを含有する。これらは集電体と活物質の他、活物質同士の結着性確保にも必須であるが、過剰量の含有は、活物質である黒鉛粒子の表面に被膜を形成し、リチウムイオンの挿入脱離を阻害する。本発明者らの検討では、負極合剤層全体におけるＣＭＣとゴムバインダの含有量が、合計２．４質量部以上を占める場合、過剰なバインダ成分の存在による電池の電気抵抗上昇が確認された。また、２．００質量部を下回る場合、十分な結着力が得られず、負極合剤層の集電体への密着性が乏しくなり、導通不十分のために充放電が困難となる可能性が高い。これらのことから、負極合剤層全体に対するＣＭＣとゴムバインダの合計含有量は、好ましくは２．０５質量部以上２．３５質量部以下、より好ましくは２．１０質量部以上２．３０質量部以下、さらに好ましくは２．１５質量部以上２．２５質量部以下である。該含有量が２．３５質量部を超える場合、電池のＤＣＲが上昇する。 [Negative electrode binder]
The negative electrode of the non-aqueous electrolyte secondary battery according to the present embodiment includes a binder that holds an active material on the current collector in the mixture layer, that is, a binder component, a rubber binder and carboxymethyl cellulose (hereinafter referred to as CMC). Abbreviated). In addition to the current collector and the active material, these are essential for securing the binding property between the active materials. However, when the content is excessive, a film is formed on the surface of the active material graphite particles, and lithium ions are inserted. Inhibits detachment. In the study by the present inventors, when the total content of CMC and the rubber binder in the entire negative electrode mixture layer occupies 2.4 parts by mass or more, an increase in electric resistance of the battery due to the presence of an excessive binder component was confirmed. Moreover, when it is less than 2.00 parts by mass, sufficient binding force cannot be obtained, the adhesion of the negative electrode mixture layer to the current collector becomes poor, and charging and discharging may be difficult due to insufficient conduction. Is expensive. Therefore, the total content of CMC and rubber binder with respect to the entire negative electrode mixture layer is preferably 2.05 parts by mass or more and 2.35 parts by mass or less, more preferably 2.10 parts by mass or more and 2.30 parts by mass or less. More preferably, it is 2.15 parts by mass or more and 2.25 parts by mass or less. When the content exceeds 2.35 parts by mass, the DCR of the battery increases.
　本発明では、特に鱗片状黒鉛粒子と多面体状黒鉛粒子とを併せて含有する負極合剤を適用している。多面体状黒鉛粒子は、鱗片状黒鉛粒子と比較して必要なバインダ成分量が多い傾向がある。この詳細な原因は不明であるが、鱗片状黒鉛粒子は表面の凹凸が多く、粒子同士の摩擦が生じやすいため、少量のバインダ成分でも十分な結着を確保できるためであると推察する。 In the present invention, a negative electrode mixture containing both scaly graphite particles and polyhedral graphite particles is particularly applied. Polyhedral graphite particles tend to require a larger amount of binder component than scale-like graphite particles. Although the detailed cause is unknown, it is presumed that the scaly graphite particles have many irregularities on the surface, and friction between the particles is likely to occur, so that sufficient binding can be secured even with a small amount of binder component.
　このため、鱗片状黒鉛粒子のみを含有する負極合剤では、負極合剤層全体に対してバインダ成分、すなわちゴムバインダとＣＭＣの含有量が合計で２．００質量部であれば十分な結着が見られ、負極を切断する際に、切断部分からの合剤層剥落は見られないのに対し、本発明の鱗片状黒鉛粒子と多面体状黒鉛粒子とを併せて含有する負極では、前記バインダ成分の含有量が合計で２．００質量部の場合、同様に電極を切断すると切断部分からの合剤層の剥落が見られる。 For this reason, in the negative electrode mixture containing only scaly graphite particles, sufficient binding is obtained if the total content of the binder component, that is, the rubber binder and the CMC, is 2.00 parts by mass with respect to the entire negative electrode mixture layer. In the negative electrode containing both the scaly graphite particles and the polyhedral graphite particles of the present invention, the binder component is not seen when the negative electrode is cut and the mixture layer is not peeled off from the cut portion. When the total content is 2.00 parts by mass, the mixture layer is peeled off from the cut portion when the electrode is similarly cut.
　このような合剤層の剥落が見られる傾向は、集電体と負極合剤層との結着力の低下によるものであり、車載用等の、長期に渡る信頼性が特に重要な電池への適用は困難となる。このことを勘案し検討を進めた結果、本発明では、上記の範囲でのバインダ成分の含有が好ましいことを見出している。 The tendency of such a mixture layer to peel off is due to a decrease in the binding force between the current collector and the negative electrode mixture layer. For long-term reliability such as in-vehicle use, the battery is particularly important. Application becomes difficult. As a result of studying this in consideration, the present invention has found that the binder component is preferably contained within the above range.
　ゴムバインダの種類としては、本発明の効果を著しく損なわない限り任意であるが、物性の制御を行いやすく、また、不純物が少ないという観点から、合成ゴムが好ましい。このような合成ゴムの具体的な種類としては、例えばスチレン－ブタジエン共重合体ゴム（以下ＳＢＲと略す）及びその変性体、アクリロニトリル－ブタジエン共重合体ゴム及びその変性体、アクリルゴム及びその変性体、フッ素ゴム等が挙げられる。ゴムバインダは、１種のみからなってもよく、２種以上を任意の比率及び組み合わせてなってもよい。 The type of rubber binder is arbitrary as long as the effects of the present invention are not significantly impaired, but synthetic rubber is preferred from the viewpoint of easy control of physical properties and few impurities. Specific examples of such synthetic rubbers include, for example, styrene-butadiene copolymer rubber (hereinafter abbreviated as SBR) and modified products thereof, acrylonitrile-butadiene copolymer rubber and modified products thereof, acrylic rubber and modified products thereof. And fluororubber. A rubber binder may consist only of 1 type, and may comprise 2 or more types in arbitrary ratios and combinations.
　上記のものの中でも、電池が通常有する非水電解液及びリチウムイオン等に対する優れた化学的安定性、並びに当該電池の通常の使用温度である－３０℃以上５０℃以下における温度変化に対して弾性率の変化が少ないという観点から、本実施形態に係る電極に含まれるゴムバインダとしては、ＳＢＲが好ましい。 Among the above, excellent chemical stability with respect to the non-aqueous electrolyte and lithium ions normally possessed by the battery, and elastic modulus against temperature change at −30 ° C. to 50 ° C., which is the normal use temperature of the battery SBR is preferable as the rubber binder included in the electrode according to the present embodiment from the viewpoint that there is little change in the thickness.
　また、本実施形態に係る負極バインダは、ゴムバインダ以外のバインダを含んでもよい。このようなゴムバインダ以外のバインダとしては、本発明の効果を著しく損なわない限り任意の物性を有するものを用いることができるが、例えばポリフッ化ビニリデン（ＰＶＤＦ）等が挙げられる。なお、ゴムバインダ以外のバインダは、１種が単独で含まれてもよく、２種以上が任意の比率及び組み合わせで含まれてもよい。 Moreover, the negative electrode binder according to the present embodiment may include a binder other than the rubber binder. As such a binder other than the rubber binder, those having arbitrary physical properties can be used as long as the effects of the present invention are not significantly impaired. Examples thereof include polyvinylidene fluoride (PVDF). In addition, 1 type of binders other than a rubber binder may be contained independently, and 2 or more types may be contained by arbitrary ratios and combinations.
 [１－２．正極電極]
〔正極活物質〕
　正極活物質は、非水電解液二次電池が通常有する非水電解液中のリチウムイオンを吸蔵放出するものであり、電子を取り込むものである。正極活物質の物性及び種類は、本発明の効果を著しく損なわない限り任意である。従って、非水電解液二次電池に好適に用いられる、公知の任意の物性を有する正極活物質を用いればよい。 [1-2. Positive electrode]
[Positive electrode active material]
The positive electrode active material occludes and releases lithium ions in the non-aqueous electrolyte solution that the non-aqueous electrolyte secondary battery normally has, and takes in electrons. The physical properties and types of the positive electrode active material are arbitrary as long as the effects of the present invention are not significantly impaired. Therefore, a positive electrode active material having any known physical property that is preferably used for a non-aqueous electrolyte secondary battery may be used.
　正極活物質としては、リチウム酸化物等が好適なものとして挙げられる。このようなリチウム酸化物の具体例としては、コバルト酸リチウム，マンガン酸リチウム，ニッケル酸リチウム，リン酸鉄リチウム，リチウム複合酸化物（即ち、コバルト，ニッケル，マンガンからなる群より選ばれる２種以上の金属を含むリチウム酸化物）等が挙げられる。正極活物質は、１種を単独で用いてもよく、２種以上を任意の比率及び組み合わせで用いてもよい。 As the positive electrode active material, lithium oxide or the like can be mentioned as a suitable material. Specific examples of such lithium oxide include lithium cobalt oxide, lithium manganate, lithium nickelate, lithium iron phosphate, and lithium composite oxide (that is, two or more selected from the group consisting of cobalt, nickel, and manganese). Lithium oxide containing the above metal) and the like. A positive electrode active material may be used individually by 1 type, and may be used 2 or more types by arbitrary ratios and combinations.
〔正極バインダ〕
　本実施形態に係る正極は、本発明の効果を著しく損なわない限り任意の物性を有するものを用いることができるが、例えば負極バインダ同様のゴムバインダ、及びポリフッ化ビニリデン（ＰＶＤＦ）等が挙げられる。なお、ゴムバインダ以外のバインダは、１種が単独で含まれてもよく、２種以上が任意の比率及び組み合わせで含まれてもよい。 [Positive electrode binder]
As the positive electrode according to the present embodiment, those having arbitrary physical properties can be used as long as the effects of the present invention are not significantly impaired. Examples thereof include a rubber binder similar to the negative electrode binder, and polyvinylidene fluoride (PVDF). In addition, 1 type of binders other than a rubber binder may be contained independently, and 2 or more types may be contained by arbitrary ratios and combinations.
［１－３．その他の成分］
　本実施形態に係る電極は、バインダ成分を含むものであるが、バインダ成分以外に含まれ得るその他の成分は、本発明の効果を著しく損なわない限り任意である。ただし、本実施形態に係る電極は、上記合剤層の他に、通常は集電体を含み、特に正極は、さらに導電材を含有する。 [1-3. Other ingredients]
The electrode according to the present embodiment includes a binder component, but other components that can be included in addition to the binder component are optional as long as the effects of the present invention are not significantly impaired. However, the electrode according to the present embodiment usually includes a current collector in addition to the above mixture layer, and in particular, the positive electrode further includes a conductive material.
〔集電体〕
　本実施形態に係る負極及び正極に通常含まれる集電体の物性及び種類については、本発明の効果を著しく損なわない限り任意である。例えば、集電体の厚さは、通常５μｍ以上、好ましくは１０μｍ以上、また、その上限は、通常３０μｍ以下、好ましくは２０μｍ以下である。集電体の厚さが薄すぎる場合、電極の強度が低下し、電極が容易に破損する可能性があり、厚すぎる場合、電極の柔軟性が損なわれ、後工程での電池作製方法について制約が生じる可能性がある。 [Current collector]
About the physical property and kind of the electrical power collector normally contained in the negative electrode and positive electrode which concern on this embodiment, unless the effect of this invention is impaired remarkably, it is arbitrary. For example, the thickness of the current collector is usually 5 μm or more, preferably 10 μm or more, and the upper limit is usually 30 μm or less, preferably 20 μm or less. If the thickness of the current collector is too thin, the strength of the electrode will decrease, and the electrode may be easily damaged. If it is too thick, the flexibility of the electrode will be impaired, and there will be restrictions on the battery manufacturing method in the subsequent process May occur.
　また、集電体の種類も本発明の効果を著しく損なわない限り任意であるが、通常は導電性を有するものを用いる。このような導電性を有する集電体としては、例えば負極に対しては銅、正極に対してはアルミニウム等が好適に用いられる。なお、集電体は、１種が単独であってもよく、２種以上が任意の比率及び組み合わせで用いられてもよい。 Further, the type of the current collector is arbitrary as long as the effect of the present invention is not significantly impaired, but usually a conductive material is used. As the current collector having such conductivity, for example, copper is suitably used for the negative electrode, and aluminum or the like is suitably used for the positive electrode. One type of current collector may be used alone, or two or more types may be used in any ratio and combination.
　また、集電体の形状も、本発明の効果を著しく損なわない限り任意であるが、通常は箔状である。 Further, the shape of the current collector is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually a foil shape.
〔導電材〕
　導電材は、上記集電体と上記活物質との間での電子の授受を補助するものである。本実施形態に係る電極に通常含まれる導電材の物性及び種類は、本発明の効果を著しく損なわない限り任意である。従って、非水電解液二次電池に好適に用いられる、公知の任意の物性を有する導電材を用いればよい。 [Conductive material]
The conductive material assists the exchange of electrons between the current collector and the active material. The physical properties and types of the conductive material usually included in the electrode according to this embodiment are arbitrary as long as the effects of the present invention are not significantly impaired. Therefore, a conductive material having any known physical property that is suitably used for a non-aqueous electrolyte secondary battery may be used.
　このような導電材の具体例としては、アセチレンブラック、黒鉛等が挙げられる。導電材は、１種を単独で用いてもよく、２種以上を任意の比率及び組み合わせで用いてもよい。 Specific examples of such a conductive material include acetylene black and graphite. A conductive material may be used individually by 1 type, and may be used 2 or more types by arbitrary ratios and combinations.
［１－４．非水電解液］
　本実施形態に係る電池は、上記バインダの他に、通常は非水電解液を有する。このような非水電解液は、リチウムイオンを上記活物質に対して吸蔵放出できるものであれば特に制限されない。 [1-4. Non-aqueous electrolyte]
The battery according to this embodiment usually has a non-aqueous electrolyte in addition to the binder. Such a nonaqueous electrolytic solution is not particularly limited as long as it can occlude and release lithium ions with respect to the active material.
　非水電解液は、通常は、非水溶媒と非水電解質とからなるものである。非水溶媒としては、本発明の効果を著しく損なわない限り任意であるが、例えば、カーボネート溶媒が好適なものとして挙げられる。カーボネート溶媒の具体例としては、エチレンカーボネート（ＥＣ），プロピレンカーボネート（ＰＣ）等の環状カーボネート、ジメチルカーボネート（ＤＭＣ），メチルエチルカーボネート（ＭＥＣ）等の鎖状カーボネート等が挙げられる。非水溶媒は１種を単独で用いてもよく、２種以上を任意の比率及び組み合わせで用いてもよい。 The non-aqueous electrolyte usually consists of a non-aqueous solvent and a non-aqueous electrolyte. Any nonaqueous solvent may be used as long as the effects of the present invention are not significantly impaired. For example, a carbonate solvent is preferable. Specific examples of the carbonate solvent include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), and chain carbonates such as dimethyl carbonate (DMC) and methyl ethyl carbonate (MEC). A non-aqueous solvent may be used individually by 1 type, and may be used 2 or more types by arbitrary ratios and combinations.
　また、非水電解液に含まれる非水電解質としても、本発明の効果を著しく損なわない限り、任意のものを用いることができる。このような非水電解質の具体例としては、リチウム塩が特に好適である。このようなリチウム塩の具体例としては、フッ化リン酸リチウム（ＬｉＰＦ６）、フッ化ホウ酸リチウム（ＬｉＢＦ４）等が挙げられる。なお、非水電解質も、１種を単独で用いてもよく、２種以上を任意の比率及び組み合わせで用いてもよい。 Further, any nonaqueous electrolyte contained in the nonaqueous electrolytic solution can be used as long as the effects of the present invention are not significantly impaired. As a specific example of such a nonaqueous electrolyte, a lithium salt is particularly suitable. Specific examples of such a lithium salt include lithium fluorophosphate (LiPF 6 ), lithium fluoroborate (LiBF 4 ), and the like. In addition, a non-aqueous electrolyte may also be used individually by 1 type, and may use 2 or more types by arbitrary ratios and combinations.
［２．電池の製造方法］
　本実施形態に係る電池は、上記の構成を有する限り、公知の任意の方法で製造することができる。以下、本実施形態に係る電池の製造方法を一例を挙げて説明するが、本実施形態に係る電位の製造方法は、以下に記載の方法に限定されるものではない。 [2. Battery Manufacturing Method]
The battery according to the present embodiment can be manufactured by any known method as long as it has the above-described configuration. Hereinafter, although the manufacturing method of the battery which concerns on this embodiment is given as an example, the manufacturing method of the electric potential which concerns on this embodiment is not limited to the method as described below.
［２－１．電極の製造方法］
　本実施形態に係る電極（正極電極及び負極電極）は、例えば、集電体に、活物質、バインダ、導電材、分散媒及び必要に応じてその他の成分からなる電極合剤を塗布し、乾燥することにより作製することができる。なお、バインダは、上記「［１－２．負極電極］の〔負極バインダ〕」及び「［１－３．正極電極］の〔正極バインダ〕」において説明したものを用い、さらに、集電体、活物質及び導電材は、上記「［１－３．その他の成分］」において説明したものを用いることができる。また、電極合剤中の各成分の量も、乾燥後の電極に含まれる各成分の量が上記［１－２．負極電極］及び［１－３．正極電極］において記載したものとなるように、適宜調整すればよい。 [2-1. Electrode manufacturing method]
The electrode (positive electrode and negative electrode) according to the present embodiment is, for example, applied to a current collector by applying an electrode mixture composed of an active material, a binder, a conductive material, a dispersion medium, and other components as necessary, and then dried. It can produce by doing. The binder used was the one described in “[1-2. Negative electrode binder] of [1-2. Negative electrode]” and “[Positive electrode binder] of [1-3. Positive electrode]”, and a current collector, As the active material and the conductive material, those described above in “[1-3. Other components]” can be used. Further, the amount of each component in the electrode mixture is the same as the amount of each component contained in the electrode after drying [1-2. Negative electrode] and [1-3. What is necessary is just to adjust suitably so that it may be what was described in the positive electrode].
　本実施形態に係る電極に含まれるゴムバインダとして好適に用いることができるＳＢＲは、通常はスチレンとブタジエンとを共重合させることにより製造することができる。ただし、ＳＢＲに所望の物性を有させる観点から、共重合可能成分を適宜追加した系でＳＢＲを合成してもよい。例えば、ＳＢＲのガラス転移温度（Ｔｇ）を所望のものとするためには、これらの原料比率を変更することで対応できる。高Ｔｇとする場合にはスチレンの比率を高め、また低Ｔｇとする場合にはブタジエンの比率を高めることが有効である。 SBR that can be suitably used as a rubber binder contained in the electrode according to the present embodiment can be usually produced by copolymerizing styrene and butadiene. However, from the viewpoint of imparting desired physical properties to SBR, SBR may be synthesized in a system to which a copolymerizable component is appropriately added. For example, in order to make the glass transition temperature (Tg) of SBR desired, it can be coped with by changing the ratio of these raw materials. It is effective to increase the ratio of styrene when the Tg is high, and to increase the ratio of butadiene when the Tg is low.
　また例えばＳＢＲの耐薬品性又は耐水性を向上させるためにアクリロニトリル、２－ビニルピリジン等の成分を共重合可能成分として用いることができる。 For example, in order to improve the chemical resistance or water resistance of SBR, components such as acrylonitrile and 2-vinylpyridine can be used as copolymerizable components.
　また、ＳＢＲは、通常は水中に分散された状態で保管されているため、分散された液体を通常は上記電極合剤に含有させることが好ましい。 In addition, since SBR is usually stored in a state of being dispersed in water, it is preferable that the electrode mixture contains a dispersed liquid.
　電極合剤に通常含まれる分散媒の種類としては、本発明の効果を著しく損なわない限り任意であるが、例えばＮ－メチルピロリドン（ＮＭＰ）、水等を用いることができる。分散媒は１種を単独で用いてもよく、２種以上を任意の比率及び組み合わせで用いてもよい。電極合剤における分散媒の量は、本発明の効果を著しく損なわない限り任意であるが、電極合剤の全量に対して、通常２０重量％以上、好ましくは３０重量％以上、より好ましくは４０重量％以上、また、その上限は、通常７０重量％以下、好ましくは６５重量％以下、より好ましくは６０重量％以下である。分散媒の量が少なすぎる場合、電極合剤に含まれる各成分を適切に分散できずに集電体上で各成分が偏在する可能性があり、多すぎる場合、塗布後の乾燥に時間がかかりすぎる可能性がある。 The type of the dispersion medium usually contained in the electrode mixture is arbitrary as long as the effects of the present invention are not significantly impaired. For example, N-methylpyrrolidone (NMP), water, and the like can be used. A dispersion medium may be used individually by 1 type, and may use 2 or more types by arbitrary ratios and combinations. The amount of the dispersion medium in the electrode mixture is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 20% by weight or more, preferably 30% by weight or more, more preferably 40%, based on the total amount of the electrode mixture. The upper limit is usually 70% by weight or less, preferably 65% by weight or less, more preferably 60% by weight or less. If the amount of the dispersion medium is too small, each component contained in the electrode mixture may not be properly dispersed, and each component may be unevenly distributed on the current collector. It may take too much.
　電極合剤に必要に応じて含まれるその他の成分としては、例えば界面活性剤、消泡材、増粘剤等が挙げられる。電極合剤が界面活性剤を含有することにより、電極合剤に含まれるゴムバインダの分散安定性を向上させることができる。また、電極合剤が消泡剤を含有することにより、上記界面活性剤を含有させた電極合剤を塗布する際の泡立ちを抑制することができる。さらに、電極合剤が増粘剤を含有することにより、電極合剤の粘度を所望のものとすることができ、集電体への電極合剤の塗布が容易になる。 Examples of other components included in the electrode mixture as needed include surfactants, antifoaming materials, thickeners, and the like. When the electrode mixture contains a surfactant, the dispersion stability of the rubber binder contained in the electrode mixture can be improved. Moreover, foaming at the time of apply | coating the electrode mixture containing the said surfactant can be suppressed because an electrode mixture contains an antifoamer. Furthermore, when an electrode mixture contains a thickener, the viscosity of an electrode mixture can be made into a desired thing, and application | coating of the electrode mixture to an electrical power collector becomes easy.
　このような界面活性剤の具体例としては、ｎ－ドデシル硫酸ナトリウム等が挙げられ、界面活性剤は１種を単独で用いてもよく、２種以上を任意の比率及び組み合わせで用いてもよい。また、消泡剤の具体例としては、ｎ－オクタノール、ポリシロキサン等が挙げられ、消泡剤も１種を単独で用いてもよく、２種以上を任意の比率及び組み合わせで用いてもよい。さらに、増粘剤の具体例としては、カルボキシメチルセルロース（ＣＭＣ）等が挙げられ、増粘剤も１種を単独で用いてもよく、２種以上を任意の比率及び組み合わせで用いてもよい。 Specific examples of such surfactants include sodium n-dodecyl sulfate and the like, and one surfactant may be used alone, or two or more surfactants may be used in any ratio and combination. . Further, specific examples of the antifoaming agent include n-octanol, polysiloxane and the like, and one type of antifoaming agent may be used alone, or two or more types may be used in any ratio and combination. . Furthermore, specific examples of the thickener include carboxymethyl cellulose (CMC) and the like, and one thickener may be used alone, or two or more thickeners may be used in any ratio and combination.
　上記の、活物質、バインダ、導電材、分散媒及び必要に応じてその他の成分を、公知の任意の方法により混合して、電極合剤を作製することができる。混合方法としては、各成分を均一に分散媒中に分散させることができ、本発明の効果を著しく損なわない限り任意である。 The above-mentioned active material, binder, conductive material, dispersion medium and other components as required can be mixed by any known method to produce an electrode mixture. Any mixing method can be used as long as each component can be uniformly dispersed in the dispersion medium and the effects of the present invention are not significantly impaired.
　作製した電極合剤の固形分率は、本発明の効果を著しく損なわない限り任意であるが、通常３５重量％以上、好ましくは４５重量％以上、より好ましくは５０重量％以上、また、その上限は、通常７０重量％以下、好ましくは６５重量％以下、より好ましくは６０重量％以下である。固形分率が小さすぎる場合、電極作成時、塗布乾燥の工程に時間がかかりすぎる可能性があり、大きすぎる場合、塗布性が低くなる可能性がある。なお、固形分率は、電極合剤の加熱乾燥の方法により測定することができる。 The solid content of the prepared electrode mixture is arbitrary as long as the effects of the present invention are not significantly impaired, but is usually 35% by weight or more, preferably 45% by weight or more, more preferably 50% by weight or more, and the upper limit thereof. Is usually 70% by weight or less, preferably 65% by weight or less, more preferably 60% by weight or less. If the solid content is too small, it may take too much time for the coating and drying process when forming the electrode, and if it is too large, the coating property may be lowered. The solid content can be measured by a method of heating and drying the electrode mixture.
　また、電極合剤の粘度は、本発明の効果を著しく損なわない限り任意であるが、通常０．５Ｐａ・ｓ以上、好ましくは１Ｐａ・ｓ以上、また、その上限は、通常１００Ｐａ・ｓ以下、好ましくは１０Ｐａ・ｓ以下である。粘度が小さすぎる場合、塗布乾燥の工程で流動し、均一な電極合剤層が得られない可能性があり、大きすぎる場合、塗布が困難となる可能性がある。なお、粘度は、ＪＩＳ　Ｚ　８８０３準拠の粘度計等の測定装置を用いて測定することができる。 Further, the viscosity of the electrode mixture is arbitrary as long as the effects of the present invention are not significantly impaired, but usually 0.5 Pa · s or more, preferably 1 Pa · s or more, and the upper limit is usually 100 Pa · s or less. The pressure is preferably 10 Pa · s or less. If the viscosity is too small, it may flow in the coating and drying step, and a uniform electrode mixture layer may not be obtained. If it is too large, coating may be difficult. The viscosity can be measured using a measuring device such as a viscometer according to JIS Z 8803.
　作製した電極合剤を集電体に塗布する際の塗布方法は、本発明の効果を著しく損なわない限り任意である。具体的な塗布方法としては、例えばロール塗工法、スリットダイ塗工法等が挙げられる。なお、塗布は１種の方法のみによって行ってもよく、２種以上の方法を任意に組み合わせて行ってもよい。また、塗布は、１回のみ行ってもよく、例えば１回塗布した後乾燥させ、さらにその上に電極合剤を塗布してもよい。 The coating method for applying the prepared electrode mixture to the current collector is arbitrary as long as the effects of the present invention are not significantly impaired. Specific examples of the application method include a roll coating method and a slit die coating method. In addition, application | coating may be performed only by 1 type of methods, and may be performed combining arbitrary 2 or more types of methods. Moreover, application | coating may be performed only once, for example, it may dry after apply | coating once, and may apply | coat an electrode mixture on it further.
　電極合剤を電極に塗布する際の塗布量は、本発明の効果を著しく損なわない限り任意であるが、電極の片側表面積に対して、通常１０ｇ／ｍ２以上、好ましくは２０ｇ／ｍ２以上、より好ましくは３０ｇ／ｍ２、また、その上限は、通常５００ｇ／ｍ２以下、好ましくは３５０ｇ／ｍ２以下、より好ましくは２００ｇ／ｍ２以下である。電極合剤の量が少なすぎる場合、電極作製のための塗布が困難となる可能性があり、多すぎる場合、作製した電極が剛直となる傾向を強め、電池組み立て工程での取り回しが困難となる可能性がある。 The application amount when applying the electrode mixture to the electrode is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 10 g / m 2 or more, preferably 20 g / m 2 or more with respect to the one-side surface area of the electrode. More preferably, it is 30 g / m 2 , and the upper limit is usually 500 g / m 2 or less, preferably 350 g / m 2 or less, more preferably 200 g / m 2 or less. If the amount of the electrode mixture is too small, it may be difficult to apply for electrode preparation. If it is too much, the prepared electrode will become more rigid and difficult to handle in the battery assembly process. there is a possibility.
　また、電極合剤を集電体に塗布した後の乾燥方法も、本発明の効果を著しく損なわない限り任意である。また、乾燥時間も特に制限されず、電極合剤に含まれる活物質等を集電体に十分に固定できる程度まで乾燥すればよい。 Also, the drying method after applying the electrode mixture to the current collector is optional as long as the effects of the present invention are not significantly impaired. Also, the drying time is not particularly limited, and it may be dried to such an extent that the active material contained in the electrode mixture can be sufficiently fixed to the current collector.
　作製した、電極合剤層を有する集電体に対して圧縮（プレス）を行うことで、合剤層を所望の密度とすることができる。適切な圧縮を行うことにより、合剤層に含有される負極活物質同士が接触し、電流の入出力が可能となることで、活物質を使用することができる。圧縮の工程は、前期の目的が達成されれば特に制限はないが、生産性の観点からはロールプレス法が好ましい。また、適宜加熱してもよい。 The mixture layer can be brought to a desired density by compressing (pressing) the produced current collector having the electrode mixture layer. By performing appropriate compression, the negative electrode active materials contained in the mixture layer come into contact with each other, and current can be input and output, whereby the active material can be used. The compression step is not particularly limited as long as the purpose of the previous period is achieved, but the roll press method is preferable from the viewpoint of productivity. Moreover, you may heat suitably.
　また、本実施形態に係る電池が有する非水電解液も、本発明の効果を著しく損なわない限り、任意の方法で作製することができる。例えば、上記［１－４．非水電解液］において説明した非水電解質を、所望の濃度となるように非水溶媒に溶解させて非水電解液を作製するこができる。 Further, the non-aqueous electrolyte included in the battery according to the present embodiment can also be produced by an arbitrary method as long as the effects of the present invention are not significantly impaired. For example, [1-4. The nonaqueous electrolyte described in [Nonaqueous Electrolyte] can be dissolved in a nonaqueous solvent so as to have a desired concentration to produce a nonaqueous electrolyte.
　以上のように作製した、電極及び非水電解液を組み合わせ、所望の電池を製造すればよい。 What is necessary is just to manufacture a desired battery by combining the electrode and the non-aqueous electrolyte produced as described above.
［２．電池の評価］
［２－１．大電流の定義］
　本発明における大電流とは、作製される電池の当初の放電容量に対して１時間未満の放電により上限の電圧から下限の電圧まで放電できる電流量を意味している。例えば、容量１０Ａｈの電池について、満充電状態から放電状態まで１時間で放電できる電流量は１０Ａであり、これを１ＣＡと呼ぶが、これ以上の電流量を大電流としている。 [2. Battery evaluation]
[2-1. Definition of large current]
The large current in the present invention means the amount of current that can be discharged from the upper limit voltage to the lower limit voltage by discharging in less than 1 hour with respect to the initial discharge capacity of the battery to be produced. For example, for a battery with a capacity of 10 Ah, the amount of current that can be discharged in one hour from a fully charged state to a discharged state is 10 A, which is called 1 CA, but a larger amount of current is a large current.
　以下、実施例を挙げて本実施形態をより詳細に説明するが、本実施形態は以下の実施例に限定されるものではなく、その要旨を逸脱しない範囲内で任意に変更して実施することができる。 Hereinafter, the present embodiment will be described in more detail with reference to examples. However, the present embodiment is not limited to the following examples, and may be arbitrarily modified without departing from the scope of the present invention. Can do.
　黒鉛粒子混合比率が充放電サイクルにおける１０００サイクル時点での放電容量維持率へ及ぼす影響を調査した。負極活物質、スチレンブタジエンゴム（ＳＢＲ）、及びカルボキシメチルセルロース（ＣＭＣ，数平均重合度１５００、エーテル化度０．７）とを、９８：１：１となるように混合し、その他の部材等は後述の方法で電池を作製した。図３に示す通り、鱗片状黒鉛粒子単独で負極活物質とした場合と比較し、多面体状黒鉛粒子の比率が増加するにつれ、放電容量維持率は改善する傾向が確認された。但し、多面体状黒鉛粒子を混合することにより、負極合剤層の集電体からの剥落が顕著となる傾向が有り、特に多面体状黒鉛粒子の比率が４０質量部を超えると、その傾向がより顕著であり、電池の作製が困難であった。 The effect of the graphite particle mixing ratio on the discharge capacity retention rate at the 1000th cycle in the charge / discharge cycle was investigated. The negative electrode active material, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC, number average polymerization degree 1500, etherification degree 0.7) are mixed so as to be 98: 1: 1. A battery was produced by the method described below. As shown in FIG. 3, it was confirmed that the discharge capacity retention rate tended to improve as the ratio of the polyhedral graphite particles increased as compared with the case where the flaky graphite particles alone were used as the negative electrode active material. However, when the polyhedral graphite particles are mixed, the negative electrode mixture layer tends to be exfoliated from the current collector, particularly when the ratio of the polyhedral graphite particles exceeds 40 parts by mass. It was remarkable and it was difficult to produce a battery.
〔実施例１〕
　平均粒径２０．５μｍ、比表面積３．９×１０３ ｍ２／ｋｇの鱗片状黒鉛粒子と、平均粒径５．４μｍ、比表面積２．５×１０３ ｍ２／ｋｇの多面体状黒鉛粒子、スチレンブタジエンゴム（ＳＢＲ）、及びカルボキシメチルセルロース（ＣＭＣ，数平均重合度１５００、エーテル化度０．７）とを、重量比で６８．４６：２９．３４：１．１：１．１となるように混合し、水１Ｌに分散させて負極合剤塗料を作製した。作製した合剤塗料の固形分率は５０重量％、粘度は１．８Ｐａ・ｓであった。なお、粘度は、ＪＩＳ　Ｚ　８８０３準拠の円錐平板型粘度計を用いて測定した。そして、作製した電極合剤塗料を、厚さ１０μｍの銅箔の表面に、塗布量が９０ｇ／ｍ２となるようにロール塗工法により塗布して十分に乾燥させ、さらにプレスを施し、合剤密度が１．５ｇ／ｃｍ３の負極を作製した。 [Example 1]
Scale-like graphite particles having an average particle diameter of 20.5 μm and a specific surface area of 3.9 × 10 3 m 2 / kg, and polyhedral graphite particles having an average particle diameter of 5.4 μm and a specific surface area of 2.5 × 10 3 m 2 / kg Styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC, number average polymerization degree 1500, etherification degree 0.7) are 68.46: 29.34: 1.1: 1.1 in weight ratio. The mixture was mixed and dispersed in 1 L of water to prepare a negative electrode mixture paint. The prepared mixture paint had a solid content of 50% by weight and a viscosity of 1.8 Pa · s. The viscosity was measured using a conical plate viscometer according to JIS Z 8803. Then, the prepared electrode mixture paint is applied to the surface of a copper foil having a thickness of 10 μm by a roll coating method so that the coating amount is 90 g / m 2, and is sufficiently dried, and further pressed, A negative electrode having a density of 1.5 g / cm 3 was produced.
〔実施例２〕
　電極合剤における各成分の含有量を、重量比で６８．５３：２９．３７：１．０５：１．０５としたこと以外は実施例１と同様にして負極を作製した。作製した負極合剤塗料の固形分率は５０重量％、粘度は１．７Ｐａ・ｓであった。 [Example 2]
A negative electrode was produced in the same manner as in Example 1 except that the content of each component in the electrode mixture was 68.53: 29.37: 1.05: 1.05 by weight. The produced negative electrode mixture paint had a solid content of 50% by weight and a viscosity of 1.7 Pa · s.
〔実施例３〕
　電極合剤における各成分の含有量を、重量比で６８．５３：２９．３７：１：１．１としたこと以外は実施例１と同様にして負極を作製した。作製した負極合剤塗料の固形分率は５０重量％、粘度は１．７Ｐａ・ｓであった。 Example 3
A negative electrode was produced in the same manner as in Example 1 except that the content of each component in the electrode mixture was 68.53: 29.37: 1: 1.1 by weight. The produced negative electrode mixture paint had a solid content of 50% by weight and a viscosity of 1.7 Pa · s.
〔実施例４〕
　電極合剤における各成分の含有量を、重量比で６８．５３：２９．３７：１．１：１としたこと以外は実施例１と同様にして負極を作製した。作製した負極合剤塗料の固形分率は５０重量％、粘度は１．６Ｐａ・ｓであった。 Example 4
A negative electrode was produced in the same manner as in Example 1 except that the content of each component in the electrode mixture was 68.53: 29.37: 1.1: 1 by weight. The produced negative electrode mixture paint had a solid content of 50% by weight and a viscosity of 1.6 Pa · s.
〔実施例５〕
　電極合剤における各成分の含有量を、重量比で６８．５３：２９．３７：１．２：１としたこと以外は実施例１と同様にして負極を作製した。作製した負極合剤塗料の固形分率は５０重量％、粘度は１．７Ｐａ・ｓであった。 Example 5
A negative electrode was produced in the same manner as in Example 1 except that the content of each component in the electrode mixture was 68.53: 29.37: 1.2: 1 by weight. The produced negative electrode mixture paint had a solid content of 50% by weight and a viscosity of 1.7 Pa · s.
〔比較例１〕
　電極合剤における各成分の含有量を、重量比で９８：０：１：１としたこと、すなわち黒鉛粒子の全量を鱗片状黒鉛粒子とした以外は、実施例１と同様にして負極を作製した。作製した電極合剤塗料の固形分率は５０重量％、粘度は２．０Ｐａ・ｓであった。 [Comparative Example 1]
A negative electrode was produced in the same manner as in Example 1 except that the content of each component in the electrode mixture was 98: 0: 1: 1 by weight, that is, the total amount of graphite particles was scaly graphite particles. did. The produced electrode mixture paint had a solid content of 50% by weight and a viscosity of 2.0 Pa · s.
〔比較例２〕
　電極合剤における各成分の含有量を、重量比で６８．６：２９．４：１：１としたこと以外は、実施例１と同様にして負極を作製した。作製した電極合剤塗料の固形分率は５０重量％、粘度は１．６Ｐａ・ｓであった。 [Comparative Example 2]
A negative electrode was produced in the same manner as in Example 1 except that the content of each component in the electrode mixture was 68.6: 29.4: 1: 1 by weight. The produced electrode mixture paint had a solid content of 50% by weight and a viscosity of 1.6 Pa · s.
〔比較例３〕
　電極合剤における各成分の含有量を、重量比で６８．３２：２９．２８：１．２：１．２としたこと以外は、実施例１と同様にして負極を作製した。作製した電極合剤塗料の固形分率は５０重量％、粘度は２．２Ｐａ・ｓであった。 [Comparative Example 3]
A negative electrode was produced in the same manner as in Example 1 except that the content of each component in the electrode mixture was 68.32: 29.28: 1.2: 1.2 by weight ratio. The produced electrode mixture paint had a solid content of 50% by weight and a viscosity of 2.2 Pa · s.
〔正極電極の作製〕
　正極活物質(マンガン酸リチウム)と、正極導電剤（黒鉛とアセチレンブラックとの混合物）と、バインダ（ポリフッ化ビニリデン）とを、質量比で９０：６:４となるように混合し、ＮＭＰに分散させて正極合剤のスラリーを作製した。作製した電極合剤の固形分率は６０重量％、粘度は１２Ｐａ・ｓであった。なお、粘度は負極と同様の方法にて測定した。そして、作製した電極合剤を、厚さ１５μｍのアルミニウム箔の表面に、塗布量が２００ｇ/ｍ２となるようにロール塗工法により塗布して十分に乾燥させ、さらにプレスを施し、合剤密度が３．０ｇ／ｃｍ３の正極を作製した。 [Production of positive electrode]
A positive electrode active material (lithium manganate), a positive electrode conductive agent (mixture of graphite and acetylene black), and a binder (polyvinylidene fluoride) are mixed at a mass ratio of 90: 6: 4 and mixed with NMP. A slurry of the positive electrode mixture was prepared by dispersing. The produced electrode mixture had a solid content of 60% by weight and a viscosity of 12 Pa · s. The viscosity was measured by the same method as that for the negative electrode. Then, the prepared electrode mixture was applied to the surface of an aluminum foil having a thickness of 15 μm by a roll coating method so that the coating amount was 200 g / m 2 , sufficiently dried, further pressed, and the mixture density Produced a positive electrode of 3.0 g / cm 3 .
　次に、電極の性能検証用に、非水電解液二次電池を作製した。上記の方法により作製した正極電極と負極電極とを、ポリエチレン多孔膜からなるセパレータ（厚さ２５μｍ、幅５８ｍｍ）を介して渦巻き状に捲回した捲回群を作製した。この捲回群を、ポリエチレンからなるインシュレータとともに電池缶に挿入した。その後、負極タブを電池缶の底面に溶接し、正極タブを正極端子と溶接した。その後、電池缶に非水電解液（ＥＣ，ＤＭＣ，ＤＥＣの体積比で１：１：１の混合溶媒に１．２モル／リットルのＬｉＰＦ6を溶解させたもの）を注入し、正極端子を電池缶にかしめて密閉し、直径１８ｍｍ、長さ６５ｍｍの円筒形の非水電解質二次電池とした。作製した非水電解質二次電池の模式図（正面図）を図５に示す。図５の左側半分は、非水電解質二次電池の断面の模式図（正面図）である。なお、図５中の正極端子は、非水電解質二次電池の密閉蓋を兼ねており、電池内の圧力が上昇すると開裂して電池内部の圧力を開放する開裂弁が備え付けられている。 Next, a non-aqueous electrolyte secondary battery was fabricated for electrode performance verification. A wound group was produced in which the positive electrode and the negative electrode produced by the above method were wound in a spiral shape through a separator (thickness 25 μm, width 58 mm) made of a polyethylene porous film. This wound group was inserted into a battery can together with an insulator made of polyethylene. Thereafter, the negative electrode tab was welded to the bottom surface of the battery can, and the positive electrode tab was welded to the positive electrode terminal. Thereafter, a non-aqueous electrolyte (1.2 mol / liter LiPF 6 dissolved in a 1: 1: 1 mixed solvent by volume ratio of EC, DMC, and DEC) is injected into the battery can, and the positive electrode terminal is inserted. The battery can was caulked and sealed to obtain a cylindrical nonaqueous electrolyte secondary battery having a diameter of 18 mm and a length of 65 mm. FIG. 5 shows a schematic diagram (front view) of the produced nonaqueous electrolyte secondary battery. The left half of FIG. 5 is a schematic view (front view) of a cross section of the nonaqueous electrolyte secondary battery. The positive electrode terminal in FIG. 5 also serves as a sealing lid for the nonaqueous electrolyte secondary battery, and is equipped with a cleavage valve that cleaves to release the pressure inside the battery when the pressure inside the battery rises.
　同様の電池を１０本作製し、電池の容量を確認した。充放電評価時の条件は、充電は定電流－定電圧方式により行い終止条件は上限電圧４．１Ｖかつ下限電流２０ｍＡとした。また、放電は定電流方式とし、終止条件は下限電圧２．７Ｖとした。電池の初回充電容量は平均１４２０ｍＡｈ、初期効率は平均８８％であり、評価前の電池容量は平均１２４９ｍＡｈであった。その後、ＳＯＣ（Ｓｔａｔｅ　ｏｆ　Ｃｈａｒｇｅ）１００％に充電した電池の２５℃における出力特性を評価した。電流値を３００ｍＡ、６００ｍＡ、１２００ｍＡの３条件とし、放電前電圧と、放電開始１０秒後の電圧からそれぞれのＤＣＲを算出した。 10 pieces of the same battery were produced and the capacity of the battery was confirmed. The conditions for the charge / discharge evaluation were charging by a constant current-constant voltage method, and termination conditions were an upper limit voltage of 4.1 V and a lower limit current of 20 mA. Further, the discharge was a constant current method, and the termination condition was a lower limit voltage of 2.7V. The initial charge capacity of the batteries averaged 1420 mAh, the initial efficiency averaged 88%, and the battery capacity before evaluation averaged 1249 mAh. Then, the output characteristic in 25 degreeC of the battery charged to SOC (State of Charge) 100% was evaluated. The DCR was calculated from the pre-discharge voltage and the voltage 10 seconds after the start of discharge, assuming that the current value was three conditions of 300 mA, 600 mA, and 1200 mA.
　作製した電池を各々２本ずつ使用して、充放電サイクル評価を行った。充電は電流値３Ａ、上限電圧４．１Ｖ、電流下限２０ｍＡの定電流定電圧条件とし、放電は電流値３Ａ、下限電圧２．７Ｖの定電流条件とした。さらに、休止時間は無し、すなわち充電終了時点で速やかに放電を開始し、放電終了時点でも速やかに充電を開始する条件とした。 The charge / discharge cycle evaluation was performed using two each of the produced batteries. Charging was performed under constant current and constant voltage conditions with a current value of 3A, an upper limit voltage of 4.1V, and a current lower limit of 20mA, and discharging was performed under constant current conditions of a current value of 3A and a lower limit voltage of 2.7V. Furthermore, there was no downtime, that is, a condition was set such that discharging was started immediately at the end of charging, and charging was started immediately at the end of discharging.
　実施例１及び２並びに比較例１～３における、負極合剤の組成及び負極切断時の切断面からの合剤層剥落の程度、及び作製した電池のＤＣＲ、サイクル特性を表１にまとめた。サイクル特性は、充放電とも３Ａの電流を入出力し、上限電圧４．１Ｖ、下限電圧２．７Ｖとして連続的に充放電を繰り返し、放電容量維持率により評価した。放電容量維持率は、比較例１の１０００サイクル時点での放電容量を１００として、比率で評価した。
Figure JPOXMLDOC01-appb-T000001
 Table 1 summarizes the composition of the negative electrode mixture, the degree of the mixture layer peeling from the cut surface when the negative electrode was cut, and the DCR and cycle characteristics of the batteries produced in Examples 1 and 2 and Comparative Examples 1 to 3. The cycle characteristics were evaluated by the discharge capacity maintenance rate by inputting and outputting a current of 3 A for both charge and discharge, continuously charging and discharging with an upper limit voltage of 4.1 V and a lower limit voltage of 2.7 V. The discharge capacity retention rate was evaluated in terms of a ratio, with the discharge capacity at 1000 cycles of Comparative Example 1 being 100.
Figure JPOXMLDOC01-appb-T000001
　表１に示す通り、実施例及び比較例により作製した負極をそれぞれ５６ｍｍ幅に揃え、鋏を用いて切断した。切断した回数は３０回、切断長さは、延べ１６８０ｍｍとし、切断面からの合剤層の剥落を目視により観察した。実施例１、２、４及び５では、明確な剥落は見られなかった。鱗片状黒鉛粒子のみを活物質に使用した比較例１でも明確な剥落は見られなかった。これらに対し、バインダ成分の合計が比較例１と同量含有されている比較例２では、剥落が多数見られた。また、実施例３でも若干剥落する傾向が見られたが、顕著な剥落は生じなかった。バインダ成分含有量が最も多い比較例３では、剥落は見られなかった。 As shown in Table 1, the negative electrodes produced in Examples and Comparative Examples were each aligned to a width of 56 mm and cut using scissors. The number of cuts was 30 times, the cut length was 1680 mm in total, and peeling of the mixture layer from the cut surface was visually observed. In Examples 1, 2, 4 and 5, no clear peeling was observed. In Comparative Example 1 in which only the scaly graphite particles were used as the active material, no clear peeling was observed. On the other hand, in Comparative Example 2 in which the total amount of binder components was the same as that in Comparative Example 1, many peelings were observed. Moreover, although the tendency which peels off a little also in Example 3 was seen, the remarkable peeling did not arise. In Comparative Example 3 having the largest binder component content, no peeling was observed.
　表１及び図４に示すように、ＳＢＲ及びＣＭＣの含有量が２．４質量部の比較例３では、ＤＣＲが増大していることが確認された。バインダ成分の含有量が過剰となり、活物質表面を被覆したために、リチウムイオンの挿入脱離の抵抗が増大したことが原因であると推察される。 As shown in Table 1 and FIG. 4, it was confirmed that DCR was increased in Comparative Example 3 in which the contents of SBR and CMC were 2.4 parts by mass. It is surmised that the content of the binder component is excessive and the surface of the active material is coated, so that the resistance to insertion / extraction of lithium ions is increased.
　表１に示すように、鱗片状黒鉛と多面体状黒鉛を混合した実施例１～５及び比較例２，３の１０００サイクル後放電容量維持率は、黒鉛粒子が鱗片状黒鉛単独である比較例１よりも高く、鱗片状黒鉛と多面体状黒鉛の混合が容量維持率向上に寄与することが確認された。 As shown in Table 1, the discharge capacity retention rate after 1000 cycles of Examples 1 to 5 and Comparative Examples 2 and 3 in which flaky graphite and polyhedral graphite were mixed is Comparative Example 1 in which the graphite particles are flaky graphite alone. It was confirmed that the mixture of flake graphite and polyhedral graphite contributed to the capacity retention rate improvement.
　また、表１及び図５に示すように、鱗片状黒鉛と、多面体状黒鉛、ＣＭＣ、及びＳＢＲとを、重量比で９８．０：０：１：１となるように混合した負極を用いた電池（比較例１）と、鱗片状黒鉛と、多面体状黒鉛、ＣＭＣ、及びＳＢＲとを、重量比で６８．６：２９．４：１：１となるように混合した負極を用いた電池（比較例２）を比較すると、比較例１では電極切断時の剥落が見られないのに対し、比較例２では多数の剥落が見られた。しかしながら、ＤＣＲは比較例２の方が低く、二種類の黒鉛を混合することによるＤＣＲ低減が確認された。多面体状黒鉛の含有により、集電体と合剤層との導通がより確保され、結果的に電池全体での電気抵抗が低減されたものと推察される。 Moreover, as shown in Table 1 and FIG. 5, the negative electrode which mixed scaly graphite, polyhedral graphite, CMC, and SBR so that it might become 98.0: 0: 1: 1 by weight ratio was used. A battery using a negative electrode in which a battery (Comparative Example 1), flake graphite, polyhedral graphite, CMC, and SBR were mixed at a weight ratio of 68.6: 29.4: 1: 1 ( When comparing Comparative Example 2), in Comparative Example 1, no peeling at the time of electrode cutting was seen, whereas in Comparative Example 2, many peelings were seen. However, the DCR was lower in Comparative Example 2, and it was confirmed that DCR was reduced by mixing two types of graphite. It is presumed that the inclusion of the polyhedral graphite ensures the electrical connection between the current collector and the mixture layer, and as a result, the electrical resistance of the entire battery is reduced.
　以上のように、鱗片状黒鉛と多面体状黒鉛の、二種類の黒鉛粒子を含んだ負極において、合剤層中におけるバインダ成分の含有量が、合計２．１質量％以上２．３質量％以下である場合、負極切断時の合剤層剥落が抑制され、かつ該負極を用いて作製されるリチウムイオン二次電池のＤＣＲが特に低減されることがわかった。従って、従来の技術である比較例１の技術（即ち、負極活物質として鱗片状黒鉛のみを含有させた電極）、又はバインダ成分の含有量が、合剤層中に２．４質量％の比較例３の技術と比較して、ＤＣＲが低い電池を達成することが可能となる。同時に、前記のバインダ成分含有量は活物質量に対して最適な比率となることから、充放電サイクルについての耐久性も向上する。 As described above, in the negative electrode containing two types of graphite particles, flaky graphite and polyhedral graphite, the total content of the binder components in the mixture layer is 2.1% by mass or more and 2.3% by mass or less. In this case, it was found that peeling of the mixture layer during cutting of the negative electrode was suppressed, and the DCR of the lithium ion secondary battery produced using the negative electrode was particularly reduced. Therefore, the technique of Comparative Example 1 which is a conventional technique (that is, an electrode containing only scaly graphite as a negative electrode active material), or a binder component content of 2.4% by mass in the mixture layer is compared. Compared to the technique of Example 3, it is possible to achieve a battery with a low DCR. At the same time, since the binder component content is an optimal ratio with respect to the active material amount, the durability with respect to the charge / discharge cycle is also improved.
　上記した本発明の非水電解液二次電池によれば、繰り返し充放電による破壊に比較的耐性のある多面体状黒鉛粒子が、鱗片状黒鉛粒子に接触するように配置されているので、繰り返し充放電により鱗片状黒鉛粒子の一部が破壊されて電気的に導通されていない破壊部分が拡大しても、接触する多面体状黒鉛粒子を迂回路として電気的な導通が確保され、引き続き充放電に利用可能となる。したがって、挿入脱離可能なリチウムイオンの総量の低下を防ぎ、電極の容量低下を抑制でき、サイクル特性の悪化を防ぎ、非水電解液二次電池の長寿命化を図ることができる。 According to the nonaqueous electrolyte secondary battery of the present invention described above, the polyhedral graphite particles that are relatively resistant to destruction by repeated charge and discharge are arranged so as to contact the scaly graphite particles. Even if part of the scaly graphite particles is destroyed by the discharge and the fractured part that is not electrically conductive expands, electrical conduction is ensured with the polyhedral graphite particles in contact as a detour, and charging and discharging continue. Be available. Accordingly, it is possible to prevent a decrease in the total amount of lithium ions that can be inserted and desorbed, to suppress a decrease in electrode capacity, to prevent deterioration in cycle characteristics, and to extend the life of the nonaqueous electrolyte secondary battery.
　なお、本発明は、上述の実施の形態の内容に限定されるものではなく、本発明の趣旨を逸脱しない範囲で種々の変更が可能である。 It should be noted that the present invention is not limited to the contents of the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
　本発明におけるサイクル特性に優れる電池は、長期間に渡り大電流の入出力が必要な用途、特に自動車、鉄道用等の用途に好適に用いることができる。 The battery having excellent cycle characteristics in the present invention can be suitably used for applications that require large current input / output over a long period of time, particularly for automobiles, railways, and the like.
１　電池容器
２　ガスケット
３　上蓋
４　上蓋ケース
５　正極集電板
６　負極集電板
７　軸心
８　電極群
９　正極リード
１２　正極タブ
１３　負極タブ
１４　正極電極
１５　負極電極
１６　正極合剤層
１７　負極合剤層
１８　セパレータ
１９　捲回部材
２１ａ　活物質（鱗片状黒鉛粉末）
２１ｂ　活物質（多面体状黒鉛粉末）
２２　バインダ
２３　カルボキシメチルセルロース DESCRIPTION OF SYMBOLS 1 Battery container 2 Gasket 3 Upper cover 4 Upper cover case 5 Positive electrode current collecting plate 6 Negative electrode current collecting plate 7 Axis 8 Electrode group 9 Positive electrode lead 12 Positive electrode tab 13 Negative electrode tab 14 Positive electrode 15 Negative electrode 16 Positive electrode mixture layer 17 Negative electrode mixture Layer 18 Separator 19 Winding member 21a Active material (flaky graphite powder)
21b Active material (polyhedral graphite powder)
22 Binder 23 Carboxymethylcellulose

Claims (5)

  1. 　正極と、負極と、非水電解液とを有する非水電解液二次電池であって、
    　前記負極は、鱗片状黒鉛粒子と、表面が非晶質炭素により被覆されている多面体状黒鉛粒子を負極活物質として含有する負極合剤層を有することを特徴とする非水電解液二次電池。     A non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte,
    The negative electrode has a negative electrode mixture layer containing scaly graphite particles and polyhedral graphite particles whose surfaces are coated with amorphous carbon as a negative electrode active material. .
  2. 　前記負極合剤層に含有される活物質総量のうち、前記鱗片状黒鉛粒子が６０質量部以上９０質量部以下、前記多面体状黒鉛粒子が１０質量部以上４０質量部以下であることを特徴とする請求項１に記載の非水電解液二次電池。 Of the total amount of active material contained in the negative electrode mixture layer, the scaly graphite particles are 60 parts by mass or more and 90 parts by mass or less, and the polyhedral graphite particles are 10 parts by mass or more and 40 parts by mass or less. The non-aqueous electrolyte secondary battery according to claim 1.
  3. 　前記鱗片状黒鉛粒子の表面が非晶質炭素により被覆されていることを特徴とする請求項２に記載の非水電解液二次電池。 The nonaqueous electrolyte secondary battery according to claim 2, wherein the surface of the scaly graphite particles is coated with amorphous carbon.
  4. 　前記負極合剤層に含有されるバインダ成分が、前記負極合剤層全体の２．０５質量部以上２．３５質量部以下であることを特徴とする請求項１に記載の非水電解液二次電池。 2. The nonaqueous electrolyte solution according to claim 1, wherein the binder component contained in the negative electrode mixture layer is 2.05 parts by mass or more and 2.35 parts by mass or less of the entire negative electrode mixture layer. Next battery.
  5. 　前記負極合剤層のバインダ成分としてゴムバインダ及びカルボキシメチルセルロースを含有することを特徴とする、請求項４記載の非水電解液二次電池。 The non-aqueous electrolyte secondary battery according to claim 4, comprising a rubber binder and carboxymethyl cellulose as a binder component of the negative electrode mixture layer.
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