WO2012086186A1 - Électrode positive pour accumulateurs secondaires à électrolyte non aqueux et accumulateur secondaire à électrolyte non aqueux - Google Patents

Électrode positive pour accumulateurs secondaires à électrolyte non aqueux et accumulateur secondaire à électrolyte non aqueux Download PDF

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WO2012086186A1
WO2012086186A1 PCT/JP2011/007118 JP2011007118W WO2012086186A1 WO 2012086186 A1 WO2012086186 A1 WO 2012086186A1 JP 2011007118 W JP2011007118 W JP 2011007118W WO 2012086186 A1 WO2012086186 A1 WO 2012086186A1
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positive electrode
active material
conductive material
electrode active
electrolyte secondary
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PCT/JP2011/007118
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English (en)
Japanese (ja)
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卓也 廣部
俊文 名木野
藤原　勲
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パナソニック株式会社
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Priority claimed from JP2010283986A external-priority patent/JP2014041698A/ja
Priority claimed from JP2011031601A external-priority patent/JP2014041699A/ja
Application filed by パナソニック株式会社 filed Critical パナソニック株式会社
Publication of WO2012086186A1 publication Critical patent/WO2012086186A1/fr

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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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • 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
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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 positive electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery, and specifically relates to an improvement in a distribution state of a conductive material in a positive electrode used for a non-aqueous electrolyte secondary battery.
  • non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries have been used as power sources in various applications including portable electronic devices.
  • a lithium ion secondary battery an active material such as a carbonaceous material capable of inserting and extracting lithium is used for the negative electrode, and a composite oxide of transition metal and lithium such as LiCoO 2 is used as the active material for the positive electrode. Therefore, the battery voltage and discharge capacity are high.
  • electronic devices and communication devices have become multifunctional, and accordingly, a battery having a higher capacity is desired.
  • the positive electrode and the negative electrode are each coated with, for example, a slurry containing an active material and other constituent materials such as a conductive material and a binder, dried, and applied. It is produced by compressing to a predetermined thickness using a pressure roll or the like.
  • the capacity of the battery can be increased by reducing the ratio of other constituent materials such as a conductive material and a binder and increasing the ratio of the active material.
  • the binder When the binder is reduced, depending on the type of the binder, the viscosity of the slurry is lowered, and problems such as sedimentation of constituent components are likely to occur. In addition, since the binder is likely to be unevenly distributed, the adhesion between the mixture layer and the current collector is reduced, and the active material is likely to fall off or the mixture layer is peeled off.
  • the sheet resistance including the interface resistance with the body also increases. And battery capacity may fall by volume resistance and sheet resistance rising.
  • Patent Documents 1 and 2 although the dissolution and dispersion of the binder may be improved to some extent, it is difficult to suppress the aggregation and uneven distribution of the conductive material, and the ratio of the maximum available capacity to the charge capacity ( Hereinafter, it is difficult to increase the maximum utilization rate.
  • An object of the present invention is to provide a positive electrode for a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery using the same, by suppressing the increase in resistance by optimizing the distribution state of the conductive material and increasing the capacity of the battery. It is to provide a battery.
  • One aspect of the present invention includes a positive electrode current collector, a positive electrode active material, a conductive material, and a binder, and includes a positive electrode mixture layer attached to a surface of the positive electrode current collector. , Adhered to the surface of the positive electrode active material particles, dispersed so as to form a neck between the positive electrode active material particles, charged at a rate of 0.3 C at 25 ° C., and at a rate of 0.2 C
  • the present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery in which the ratio of the discharge capacity (that is, the maximum available capacity) to the charge capacity of the positive electrode active material is 95% or more when discharged.
  • Nonaqueous electrolyte secondary battery comprising: the positive electrode for a nonaqueous electrolyte secondary battery; a negative electrode including a negative electrode active material; a separator disposed between the positive electrode and the negative electrode; and a nonaqueous electrolyte.
  • a nonaqueous electrolyte secondary battery comprising: the positive electrode for a nonaqueous electrolyte secondary battery; a negative electrode including a negative electrode active material; a separator disposed between the positive electrode and the negative electrode; and a nonaqueous electrolyte.
  • the active material density of the positive electrode can be increased, a high capacity non-aqueous electrolyte secondary battery can be provided.
  • FIG. 6 is a schematic diagram schematically showing a distribution state of a conductive material in a positive electrode for a nonaqueous electrolyte secondary battery in Comparative Example 5.
  • FIG. 6 is a schematic diagram schematically showing a distribution state of a conductive material in a positive electrode for a nonaqueous electrolyte secondary battery in Comparative Example 6.
  • FIG. It is a perspective view of the L-shaped nickel plate used for the short circuit test of an Example.
  • the positive electrode for a non-aqueous electrolyte secondary battery of the present invention includes a positive electrode current collector, a positive electrode active material, a conductive material, and a binder, and includes a positive electrode mixture layer attached to the surface of the positive electrode current collector.
  • the conductive material particles are dispersed on the surface of the positive electrode active material particles so as to form a neck between the positive electrode active material particles.
  • the ratio of the maximum capacity that can be used to the charge capacity of the positive electrode active material (the maximum utilization rate of the positive electrode active material) is 95% or more.
  • FIG. 7 is a schematic view schematically showing a distribution state of a conductive material in a conventional positive electrode for a nonaqueous electrolyte secondary battery.
  • the positive electrode includes a positive electrode current collector 1 and a positive electrode mixture layer attached to the surface thereof.
  • the positive electrode mixture layer includes positive electrode active material particles 2, conductive material particles 3, and a binder (not shown).
  • the conductive material particles 3 exist between the positive electrode active material particles 2 and between the positive electrode active material particles 2 and the positive electrode current collector 1, but are aggregated. Therefore, the distance between the adjacent positive electrode active material particles 2 and between the positive electrode active material particles 2 and the positive electrode current collector 1 cannot be reduced, and a relatively large gap is formed therebetween. Due to the formation of such voids and the aggregation of the conductive material particles 3, the conductivity of the positive electrode tends to decrease.
  • the volume resistance in the positive electrode mixture layer tends to increase, and the maximum utilization rate of the positive electrode active material decreases.
  • FIG. 1 is a schematic view schematically showing a distribution state of a conductive material in a positive electrode for a nonaqueous electrolyte secondary battery according to an embodiment of the present invention.
  • FIG. 1 is an enlarged view of a main part of a positive electrode current collector 1 and a positive electrode mixture layer 5 existing in the vicinity thereof.
  • the positive electrode 6 includes a positive electrode current collector 1 and a positive electrode mixture layer 5 attached to the surface thereof.
  • the positive electrode mixture layer 5 includes positive electrode active material particles 2, conductive material particles 3, and a binder (not shown). )including.
  • the conductive material particles 3 are attached to the surface of the positive electrode active material particles 2 and dispersed so as to form a neck between the positive electrode active material particles 2.
  • the neck is formed of an aggregate of a small amount of conductive material particles 3.
  • the aggregate of the conductive material particles 3 is a thin layer. Also, the same neck as described above is formed between the positive electrode active material particles 2 and the positive electrode current collector 1.
  • the distance between the adjacent positive electrode active material particles 2 is close, and the distance between the positive electrode active material particles 2 and the positive electrode current collector 1 is also close. That is, in the positive electrode mixture layer 5, the positive electrode active material particles 2 are densely packed, and voids formed between the positive electrode active material particles 2 and between the positive electrode active material particles and the positive electrode current collector 1 are Relatively small.
  • the positive electrode active material particles and / or the positive electrode active material particles and the positive electrode current collector are electrically connected through the neck formed of the aggregate of the conductive material particles as described above. Can be made.
  • the size of the agglomerates is small compared to the conventional one. Then, between the positive electrode active material particles or between the positive electrode active material particles and the positive electrode current collector, the aggregate of the conductive material particles forms a junction having a low resistance.
  • the conductive material particles 3 adhere to the surface of the positive electrode active material particles 2 and are distributed in an aggregated state so that adjacent conductive material particles 3 come into contact with each other to form a thin layer.
  • the conductive material particles 3 can exist in a conductive state. For this reason, in the positive electrode mixture layer, aggregates of conductive material particles having a small size are distributed in a more dispersed state than in the past. Therefore, even if the ratio of the conductive material particles 3 is small, the positive electrode active material particles 2 can be efficiently electrically connected to each other, and the positive electrode active material particles 2 and the positive electrode current collector 1 can be efficiently electrically connected.
  • the positive electrode active material particles and the positive electrode active material particles and the positive electrode current collector are electrically connected via the aggregates of the conductive material particles.
  • the average number of collections increases.
  • SEM scanning electron microscope
  • the conductive material By optimizing the distribution state of the conductive material as described above, even if the proportion of the conductive material is reduced, it is possible to suppress a decrease in conductivity and an increase in the volume resistance of the positive electrode. it can. Moreover, since conductivity can be ensured only by using a small amount of a conductive material, the active material density in the positive electrode can be increased, and the maximum utilization rate of the positive electrode active material can be improved. As a result, in the nonaqueous electrolyte secondary battery using such a positive electrode, the battery capacity can be increased.
  • the maximum utilization rate is 95% or more, preferably 95.4% or more, more preferably 96% or more or 96.5% or more.
  • the upper limit of the maximum capacity ratio is not particularly limited, but is 99% or less, for example.
  • Examples of conductive materials include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fiber such as carbon fiber (carbon nanotube, etc.), etc. Can be illustrated. These electroconductivity can be used individually by 1 type or in combination of 2 or more types. Such conductivity is easily distributed in a thin layer on the surface of the positive electrode active material particles, which is advantageous for ensuring conductivity in the positive electrode active material layer.
  • the average primary particle size of the conductive material such as carbon black is, for example, 10 to 50 nm, preferably 20 to 50 nm, and more preferably 25 to 45 nm. When the average primary particle size is in such a range, it is easy to distribute the conductive material particles in a thin layer at the junction between the positive electrode active material particles, which is advantageous for ensuring the conductivity in the positive electrode active material layer. .
  • the average fiber diameter of a fibrous conductive material such as carbon fiber (carbon nanotube or the like) is, for example, 1 to 100 nm, preferably 2 to 50 nm, and more preferably 5 to 20 nm.
  • the average fiber length is, for example, 0.01 to 100 ⁇ m, preferably 0.1 to 10 ⁇ m, more preferably 0.2 to 8 ⁇ m, or 0.5 to 5 ⁇ m.
  • BET specific surface area of the conductive material for example, 320 m less than 2 / g exceed 40 m 2 / g, preferably 45 ⁇ 310m 2 / g, more preferably 50 ⁇ 300 meters 2 / g.
  • the BET specific surface area of the conductive material may be, for example, 150 to 310 m 2 / g or 200 to 300 m 2 / g for carbon nanotubes, depending on the type of conductive material.
  • the maximum utilization factor of the positive electrode active material can be increased.
  • the bulk density of the conductive material can be maintained in an appropriate range, and the active material density can be increased. Therefore, it is possible to more effectively suppress a decrease in battery capacity by suppressing a decrease in discharge characteristics.
  • the mass ratio of the conductive material can be selected, for example, from the range of 0.05 to 2 parts by mass per 100 parts by mass of the positive electrode active material, preferably more than 0.05 parts by mass and 1.4%. Less than 1 part by mass or 0.1 to 1.3 parts by mass, more preferably 0.2 to 1 part by mass or 0.2 to 0.5 parts by mass.
  • the conductive material particles, between the positive electrode active material particles, between the positive electrode active material particles and the positive electrode current collector even if the mass ratio of the conductive material is small in this way. It is advantageous in securing the electrical conductivity between them.
  • the mass ratio of the conductive material can be reduced, the ratio of the positive electrode active material can be relatively increased, and the capacity of the battery can be further increased.
  • binder examples include fluorine resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE); acrylic resins such as polymethyl acrylate and ethylene-methyl methacrylate copolymer; styrene-butadiene rubber ( And rubber-like materials such as SBR), butadiene rubber, isoprene rubber, acrylic rubber, ethylene-propylene-diene copolymer (EPDM) or modified products thereof (such as rubber having an acrylate unit or rubber-like polymer).
  • binders can be used singly or in combination of two or more.
  • the binder may contain an acrylate monomer or an acrylate oligomer into which a reactive functional group is introduced.
  • the binder is preferably one that dissolves in the dispersion medium contained in the positive electrode slurry.
  • the binder preferably contains a fluororesin, in particular, a homopolymer (PVDF) or copolymer (that is, a modified product of polyvinylidene fluoride) containing vinylidene fluoride as a constituent monomer.
  • a fluororesin in particular, a homopolymer (PVDF) or copolymer (that is, a modified product of polyvinylidene fluoride) containing vinylidene fluoride as a constituent monomer.
  • the copolymer include a copolymer of vinylidene fluoride and an olefin and / or a fluorinated olefin.
  • the content rate of the vinylidene fluoride unit in a copolymer is 60 mass% or more, for example.
  • the weight average molecular weight of the binder such as fluororesin can be appropriately selected from the range of 400,000 to 2 million, for example, preferably exceeding 500,000 (preferably 550,000) and less than 1.7 million, preferably 600,000 to More preferably, it is 1.5 million.
  • the weight average molecular weight of the binder is in such a range, even if the mass ratio of the binder is small, it is easy to impart an appropriate viscosity to the positive electrode slurry for forming the positive electrode mixture layer. This is advantageous because it is easy to ensure adhesion between the layer and the positive electrode current collector, and to easily suppress the aggregation of the binder.
  • the mass ratio of the binder in the positive electrode mixture layer can be selected, for example, from the range of 0.3 to 2 parts by mass per 100 parts by mass of the positive electrode active material, and 0.3 parts by mass (preferably 0.35 parts by mass). And less than 1.4 parts by mass, and more preferably 0.4 to 1.3 parts by mass.
  • the mass ratio of the binder is in such a range, it is easy to ensure an appropriate adhesion between the positive electrode mixture layer and the positive electrode current collector, and the active material density can be increased, and the battery is high. Easy to secure capacity.
  • a preferred positive electrode active material is a lithium-containing composite oxide.
  • the lithium-containing composite oxide includes a transition metal element, and a part of the transition metal element may be replaced with a different element.
  • the transition metal element include Sc, Y, Mn, Fe, Co, Ni, Cu, and Cr. Among these transition metal elements, Mn, Co, Ni and the like are preferable.
  • Examples of the different elements include Na, Mg, Ti, Zn, Al, Pb, Sb, and B. Of these different elements, Mg, Al, and the like are preferable.
  • a transition metal element and a different element can be used individually by 1 type or in combination of 2 or more types, respectively. By using such a lithium-containing composite oxide, it is possible to increase the capacity of the non-aqueous electrolyte secondary battery, and it is easy to ensure safety, which is advantageous.
  • the crystal structure of the lithium-containing composite oxide is not particularly limited, and may be a layered structure, a spinel structure, an olivine structure, or the like.
  • lithium-containing composite oxide examples include lithium cobaltate Li x CoO 2 , lithium manganate Li x MnO 2 , lithium nickelate or its modified product Li x Ni y M 1-y O 2 , lithium cobaltate modified product Li x Co z Me 1-z O n, lithium manganate modified products, and the like Li x Mn 2 O 4.
  • M represents at least one element selected from the group consisting of Co, Mn, Cr, Fe, Mg, Ti, and Al.
  • Me represents at least one element selected from the group consisting of Sc, Y, Mn, Cr, Fe, Cu, Na, Mg, Ti, Zn, Al, Pb, Sb, and B.
  • x, y, and z are 0.95 ⁇ x ⁇ 1.1, 0.3 ⁇ y ⁇ 1, and 0 ⁇ z ⁇ 1, respectively.
  • a lithium containing complex oxide can be used individually by 1 type or in combination of 2 or more types.
  • the element M preferably contains Co and / or Mn, and may further contain Mg, Al, Ti and the like.
  • Z is preferably 0.2 ⁇ z ⁇ 0.9, more preferably 0.25 ⁇ z ⁇ 0.8.
  • the element Me preferably contains Mn, Cr and / or Fe, and may further contain Mg, Ti, Zn and / or Al.
  • the average particle diameter (D50) of the lithium-containing composite oxide can be selected, for example, from the range of 1 to 50 ⁇ m, preferably 5 to 50 ⁇ m, more preferably 5 to 40 ⁇ m.
  • the average particle diameter (D50) is a median diameter in a volume-based particle size distribution.
  • the average particle diameter can be determined using, for example, a laser diffraction / scattering particle distribution measuring apparatus (LA-920) manufactured by Horiba, Ltd.
  • the positive electrode active material layer is obtained by applying a positive electrode slurry containing a positive electrode active material, a conductive material, a binder and a dispersion medium to the surface of the positive electrode current collector, and removing the dispersion medium by drying.
  • the positive electrode slurry is obtained by (a) preparing a conductive material paste by dispersing a conductive material in a dispersion medium, and then kneading the conductive material paste with the positive electrode active material and the binder, or (b ) After mixing the positive electrode active material and the conductive material to adhere the conductive material particles to the surface of the positive electrode active material particles, the positive electrode active material with the conductive material attached is kneaded with the binder and the dispersion medium. Is preferably obtained.
  • the conductive material particles can be attached to the surface of the positive electrode active material particles in a thin layer state as shown in FIG. It can be distributed at the junctions between the active material particles and the positive electrode current collector. Therefore, even if the mass ratio of the conductive material particles is small, it is easy to ensure the conductivity in the positive electrode active material layer. Moreover, a positive electrode slurry having an appropriate viscosity can be obtained.
  • the conductive material paste may be prepared by dispersing the conductive material in a dispersion medium in the presence of a dispersant.
  • a dispersion medium may be added when the positive electrode active material having conductive material particles attached to the surface thereof, the binder, and the dispersion medium are kneaded.
  • the concentration of the conductive material in the conductive material paste depends on the BET specific surface area of the conductive material, but can be selected, for example, from 1 to 50% by mass, preferably from 1 to 30% by mass.
  • the concentration of the conductive material in the conductive material paste is, for example, 10 to 30% by mass or 15 to 25% by mass. May be.
  • the concentration of the conductive material in the conductive material paste may be 1 to 10% by mass or 1 to 8% by mass, for example. Good.
  • the conductive material Since the conductive material easily aggregates, it is pulverized by a known pulverizer such as a bead mill, alone or with a dispersion medium, to an appropriate average particle size before being mixed with other components, and appropriately dispersed. It may be. At that time, it is advantageous to add a dispersant because re-aggregation of the conductive material can be suppressed and an appropriate average particle size can be maintained.
  • a known disperser or kneader such as a planetary mixer or a double arm kneader can be used.
  • dispersion medium examples include water, alcohols such as ethanol, ethers such as tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), or a mixed solvent thereof.
  • water dispersible or hydrophilic polymers such as cellulose derivatives such as methylcellulose, ethylcellulose, and hydroxyethylcellulose can be used in addition to polyvinylpyrrolidone. These dispersants can be used singly or in combination of two or more.
  • the ratio of the dispersant is, for example, 0.1 to 10 parts by mass, preferably 0.5 to 2 parts by mass with respect to 100 parts by mass of the conductive material.
  • the conductive material paste or the positive electrode slurry may further contain a known thickener as necessary.
  • the positive electrode slurry can be applied to the surface of the positive electrode current collector by a known application method such as a die coater.
  • the positive electrode slurry may be applied to one surface of the positive electrode current collector, or may be applied to both surfaces.
  • Examples of the material of the positive electrode current collector include aluminum, aluminum alloy, nickel, and nickel alloy.
  • As the positive electrode current collector a sheet-like one can be used, and it may be non-porous or porous having a plurality of through holes.
  • As the non-porous current collector a metal foil, a metal sheet, or the like can be used.
  • Examples of the porous current collector include a metal mesh body, a punching sheet, a metal sheet having a through hole, and an expanded metal.
  • the thickness of the positive electrode current collector is, for example, 3 to 50 ⁇ m, preferably 5 to 30 ⁇ m.
  • the coating film of the positive electrode slurry applied to the surface of the positive electrode current collector is dried and then compressed to a predetermined thickness to form a positive electrode mixture layer.
  • the thickness of the positive electrode mixture layer is, for example, 30 to 100 ⁇ m, preferably 50 to 90 ⁇ m.
  • Drying of the coating film may be, for example, natural drying or may be performed under heating by blowing hot air on the coating film.
  • the present inventors investigated the influence of the physical properties of the positive electrode mixture layer formed on the surface of the positive electrode current collector on the battery characteristics, and found that not only the volume resistance of the positive electrode mixture layer but also the sheet resistance was reduced. The present inventors have found that the charge / discharge cycle characteristics can be further improved.
  • the positive electrode mixture layer of the non-aqueous electrolyte secondary battery if the ratio of the conductive material and the binder is extremely small, if an internal short circuit occurs due to a defect or the like, a large amount is generated between the positive electrode mixture layer and the positive electrode current collector. A short circuit current flows. Thereby, Joule heat is generated, and safety may be impaired.
  • the positive electrode mixture layer when not only the volume resistance but also the area resistance is controlled to an appropriate range, when an internal short circuit occurs, the positive electrode mixture layer and It was found that a large amount of short-circuit current could flow between the positive electrode current collector and the charge / discharge cycle characteristics could be improved by suppressing the deterioration of the positive electrode.
  • the resistance between the positive electrode mixture layer and the positive electrode current collector is controlled within an appropriate range.
  • the ratio of the average conductive material particles distributed at the junction points between the positive electrode active material particles is larger than the ratio of the average conductive material particles distributed at the junction points between the positive electrode active material particles and the positive electrode current collector. Try to increase the ratio.
  • the dispersion state of the conductive material in such a manner will be described with reference to FIG.
  • FIG. 2 is a schematic view schematically showing a distribution state of the conductive material in the positive electrode for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention.
  • the conductive material particles 3 form a thin layer at the junction between the positive electrode active material particles 2 and the junction between the positive electrode active material particles 2 and the positive electrode current collector 1. Is unevenly distributed.
  • the adjacent positive electrode active material particles 2 and the positive electrode active material particles 2 and the positive electrode current collector 1 are electrically connected to each other by the conductive material particles 3.
  • the ratio of the conductive material particles 3 b present at the junction between the positive electrode active material particles 2 is the ratio of the conductive material particles 3 a present at the junction between the positive electrode active material particles 2 and the positive electrode current collector 1. More than that. Therefore, the resistance between the positive electrode active material particles and the positive electrode current collector can be slightly increased, and even when an internal short circuit occurs, a large amount of short circuits between the positive electrode active material particles and the positive electrode current collector. Current flow can be suppressed. As a result, it is possible to improve charge / discharge cycle characteristics and safety while maintaining a high battery capacity.
  • Sheet resistance of the positive electrode mixture layer is, for example, be selected from the range of 0.1 ⁇ 1.6 ⁇ ⁇ cm 2, preferably less than 1.6 ⁇ ⁇ cm 2 beyond the 0.1 ⁇ ⁇ cm 2, 0 More preferably, it is 15 to 1.55 ⁇ ⁇ cm 2 or 0.2 to 1.5 ⁇ ⁇ cm 2 .
  • the sheet resistance is in such a range, it is more advantageous in achieving both battery capacity and high charge / discharge cycle characteristics and safety.
  • FIG. 3 is a schematic diagram of an apparatus for measuring the sheet resistance of the positive electrode.
  • two positive electrodes 17 and 18 are overlapped and sandwiched between two copper plates 19 and 20 having a thickness of 2 mm. And these laminated bodies are measured in the state pressed from both sides with the press apparatus 16.
  • FIG. 3 is a schematic diagram of an apparatus for measuring the sheet resistance of the positive electrode.
  • two positive electrodes 17 and 18 are overlapped and sandwiched between two copper plates 19 and 20 having a thickness of 2 mm. And these laminated bodies are measured in the state pressed from both sides with the press apparatus 16.
  • the positive electrodes 17 and 18 have positive electrode current collectors 17a and 18a, respectively, and a positive electrode mixture layer formed on both surfaces.
  • the positive electrodes 17 and 18 those obtained by cutting out a positive electrode taken out from a precharged nonaqueous electrolyte secondary battery into a predetermined size, for example, 20 mm ⁇ 20 mm can be used.
  • One end of a lead wire is connected to each of the positive electrode current collectors 17a and 18a, and the other end is connected to a terminal of a resistance measuring device for measuring sheet resistance.
  • One end of a lead wire is connected to each of the copper plates sandwiching the positive electrodes 17 and 18, and the other end is connected to a terminal of the resistance measuring device.
  • the positive electrodes 17 and 18 are pressed together with the copper plates 19 and 20 at a pressure of 50 kgf / cm 2 (about 490 Pa) by the press device 16, and the sheet resistance at this time is measured.
  • the sheet resistance is measured by a direct current four-terminal method.
  • the distribution state of the conductive material in the positive electrode mixture layer is changed, and the positive electrode active material particles and The ratio of the conductive material particles present at the junction with the positive electrode current collector can be relatively reduced.
  • the mass ratio of the conductive material of the layer B formed on the surface of the layer A rather than the layer A formed on the surface of the positive electrode current collector You may increase. Further, a positive electrode active material having a smaller average particle diameter may be used in the layer B formed on the surface of the layer A than the layer A formed on the surface of the positive electrode current collector. Moreover, you may combine these methods.
  • a mass ratio R A of the conductive material in the layer A formed on the surface of the positive electrode current collector, the ratio R A / R B of the mass ratio R B of the conductive material in the layer B is formed on the surface of the layer A, For example, it is 1/10 to 1/2, preferably 1/5 to 1/3.
  • layer A when a positive electrode active material having an average particle size larger than that of layer B is used, the surface area is large, so the mass ratio of the conductive material particles present at the junction between the positive electrode active material particles and the positive electrode current collector is It can be relatively less.
  • FIG. 4 is a schematic diagram schematically showing a distribution state of the conductive material in the positive electrode for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention.
  • the positive electrode mixture layer is formed on the surface of the positive electrode current collector 1 and includes the layer A including the positive electrode active material particles 2 a and the surface of the layer A, and more than the positive electrode active material particles 2 a.
  • layer B including positive electrode active material particles 2b having a small average particle diameter.
  • Layer A and layer B include conductive material particles 3 and a binder (not shown) in addition to positive electrode active material particles 2a and 2b, respectively.
  • the positive electrode active material particles 2a have a large surface area, the conductive material on the surface of the positive electrode active material particles 2a compared to layer B even if the mass ratio of the conductive material particles 3 is the same as that of the layer B.
  • the distribution state of the particles 3 becomes rough. Therefore, the mass ratio of the conductive material particles 3 a existing at the junction between the positive electrode active material particles 2 a and the positive electrode current collector 1 is inevitably small.
  • the average particle diameter (D50) of the positive electrode active material in the layer A formed on the surface of the positive electrode current collector is, for example, 12 to 50 ⁇ m, preferably 15 to 30 ⁇ m. Further, the average particle size D A of the positive electrode active material contained in the layer A, the ratio D A / D B between the average particle size D B of the positive electrode active material contained in the layer B, for example, 5 / 1-1. 5/1, preferably 3/1 to 1.7 / 1.
  • the distribution state of the conductive material can also be changed by adjusting the drying conditions of the coating film of the positive electrode slurry.
  • the coating film of the positive electrode slurry applied to the surface of the positive electrode current collector can be dried under conditions such that the vaporization rate of the dispersion medium is, for example, 0.1 to 5 g / m 2 ⁇ s.
  • the vaporization rate is preferably 1 to 5 g / m 2 ⁇ s. Under such conditions, when the coating film is dried and the dispersion medium is removed, migration occurs in which the conductive material particles move to the surface side of the positive electrode mixture layer, and the mass ratio of the conductive material present in the vicinity of the positive electrode current collector is determined. It can be reduced relatively.
  • the drying temperature may be, for example, 80 to 220 ° C., preferably 100 to 200 ° C.
  • the nonaqueous electrolyte secondary battery of the present invention includes the above positive electrode, a negative electrode including a negative electrode active material, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte.
  • a cylindrical lithium ion secondary battery according to an embodiment of the present invention will be described as an example with reference to FIG.
  • FIG. 5 is a partially cutaway perspective view schematically showing a cylindrical lithium ion secondary battery.
  • the cylindrical lithium ion secondary battery includes an electrode group 11, a predetermined amount of non-aqueous electrolyte (not shown), and a bottomed cylindrical battery case 12 that accommodates them.
  • the electrode group 11 is formed by spirally winding a laminate including the positive electrode 6 described above, a negative electrode 7 containing a negative electrode active material, and a separator 8 disposed therebetween.
  • a positive electrode lead 10 is connected, and a negative electrode lead 9 is connected to the negative electrode 7.
  • an insulating plate 13 is disposed between the electrode group 11 and the inner bottom of the battery case 12, and the negative electrode lead 9 led out from the lower part of the electrode group 11 is connected to the inside of the battery case 12. Connected to the bottom. Further, the positive electrode lead 10 led out from the upper part of the electrode group 11 is connected to the lower surface of the sealing plate 14 having the sealing gasket 15 attached to the peripheral edge. And the sealing board 14 is arrange
  • the negative electrode includes a negative electrode active material.
  • the negative electrode usually includes a negative electrode current collector and a negative electrode active material layer attached to the surface of the negative electrode current collector.
  • the form and thickness of the negative electrode current collector can be selected from those similar to those exemplified as the positive electrode current collector.
  • the thickness of the negative electrode current collector is preferably 5 to 25 ⁇ m.
  • Examples of the material for the negative electrode current collector include metals such as copper and nickel, alloys thereof, and stainless steel.
  • Examples of the negative electrode active material include various materials capable of reversibly occluding and releasing lithium ions, such as materials having a graphite-type crystal structure; non-graphitic carbon materials such as low-temperature calcined carbon; silicon; silicon oxide, silicide, and the like Examples include silicon-containing compounds; tin; tin-containing oxides; lithium alloys containing Sn, Al, Zn and / or Mg. Examples of the material having a graphite-type crystal structure include carbon materials such as natural graphite, artificial graphite, non-graphitizable carbon, and graphitizable carbon. These negative electrode active materials may be used singly or in combination of two or more. A preferred negative electrode active material is graphite.
  • the negative electrode may be formed by depositing the negative electrode active material on the surface of the negative electrode current collector by a vapor phase method such as vacuum vapor deposition or sputtering.
  • the negative electrode slurry containing the negative electrode active material may be applied, dried, and compressed.
  • the negative electrode active material layer can be formed on one or both surfaces of the negative electrode current collector.
  • the negative electrode slurry usually contains a binder, and, if necessary, a conductive material and a thickener in addition to the negative electrode active material.
  • the negative electrode slurry can be prepared by mixing these components together with a dispersion medium. Similar to the positive electrode slurry, the constituent components can be mixed using a known disperser or kneader.
  • the binder the same binder as in the positive electrode can be used. From the viewpoint of improving the acceptability of lithium ions, it is preferable to use SBR and a modified product thereof.
  • the mass ratio of the binder is, for example, 0.1 to 5 parts by mass, preferably 0.2 to 4 parts by mass, per 100 parts by mass of the negative electrode active material.
  • the same conductive material as that in the positive electrode can be used.
  • the mass ratio of the conductive material is, for example, 0.1 to 10 parts by mass per 100 parts by mass of the negative electrode active material.
  • the thickener examples include cellulose derivatives such as methyl cellulose, hydroxymethyl cellulose, carboxymethyl cellulose (CMC) and ethyl cellulose; poly C 2-4 alkylene glycol such as polyethylene glycol; polyvinyl alcohol (PVA) and the like. It is preferable to use SBR as a binder or a modified product thereof in combination with a cellulose derivative such as CMC as a thickener.
  • the mass ratio of the thickener is, for example, 0.1 to 10 parts by mass, preferably 0.2 to 5 parts by mass with respect to 100 parts by mass of the negative electrode active material.
  • the dispersion medium the dispersion medium exemplified for the positive electrode can be used.
  • the thickness of the negative electrode active material layer can be appropriately selected from the range of 10 to 100 ⁇ m, for example.
  • the well-known porous insulator used with a nonaqueous electrolyte secondary battery can be used, For example, a resin-made microporous film, a nonwoven fabric, etc. are mentioned.
  • the resin constituting the separator include olefin resins such as polyethylene and polypropylene; polyamide; polyamideimide; polyimide and the like.
  • the separator may be a laminate of a plurality of microporous films or a laminate of a nonwoven fabric and a microporous film.
  • the thickness of the separator can be appropriately selected from the range of 10 to 100 ⁇ m, for example. In the case of a microporous film, the thickness may be 10 to 25 ⁇ m.
  • the non-aqueous electrolyte includes a lithium salt as an electrolyte salt and a non-aqueous solvent.
  • the lithium salt include LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiCF 3 SO 3 , LiN (SO 2 CF 3 ) 2 , LiN (SO 2 C 2 F 5 ) 2 , LiC (SO 2 CF 3 3 ).
  • a lithium salt can be used individually by 1 type or in combination of 2 or more types.
  • the concentration of the lithium salt in the nonaqueous electrolyte is, for example, 0.5 to 1.5 mol / L.
  • non-aqueous solvents examples include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC); chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC); ⁇ -butyrolactone, Examples thereof include cyclic carboxylic acid esters such as ⁇ -valerolactone.
  • cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC); chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC); ⁇ -butyrolactone, Examples thereof include cyclic carboxylic acid esters such as ⁇ -valerolactone.
  • the nonaqueous electrolyte may further contain a known additive.
  • additives include cyclic carbonates having a C ⁇ C bond such as vinylene carbonate (VC) and vinyl ethylene carbonate (VEC) or substituted products thereof; aromatics such as cyclohexylbenzene (CHB), biphenyl, and diphenyl ether. Group compounds or substituted products thereof; sultone compounds such as propane sultone may be contained.
  • the electrode group can be formed by winding a positive electrode, a negative electrode, and a separator disposed between both electrodes so as to insulate them.
  • the electrode group is not limited to a wound one, but may be a laminated one or a zigzag folded one.
  • the shape of the electrode group may be, for example, a cylindrical shape or a flat shape, respectively, depending on the shape of the target nonaqueous electrolyte secondary battery.
  • the shape of the nonaqueous electrolyte secondary battery may be a cylindrical shape, a rectangular shape, or the like. Moreover, it is not limited to these, A coin-type battery, a laminate-type battery, etc. may be sufficient.
  • steel plate aluminum, aluminum alloy (alloy containing a trace amount of metal such as manganese, copper, etc.) can be used.
  • Example 1 The cylindrical lithium ion secondary battery shown in FIG. 5 was produced by the following procedure. (1) Production of positive electrode Acetylene black (average primary particle size 30 nm, BET specific surface area 100 m 2 / g) as a conductive material and an appropriate amount of NMP as a dispersion medium are mixed in a bead mill, and acetylene black is mixed in NMP. Dispersed. To the obtained mixture, polyvinylpyrrolidone as a dispersant was added and stirred to prepare a conductive material paste. The amount of NMP was adjusted so that the concentration of acetylene black in the conductive material paste was 10% by mass.
  • a positive electrode slurry was prepared by stirring and kneading 0.8 parts by mass of PVDF (weight average molecular weight: 1,000,000) as a binder with a suitable amount of NMP in a double-arm kneader.
  • the positive electrode slurry was intermittently applied to both surfaces of a positive electrode current collector made of an aluminum foil (thickness: 15 ⁇ m). After drying the coating film, the mixture layer was pressed so that the thickness of the mixture layer per side was 70 ⁇ m. Next, slitting was performed to a specified width of the cylindrical lithium ion secondary battery, and the positive electrode 6 was produced. A positive electrode lead 10 was connected to a portion of the positive electrode 6 where the positive electrode current collector was exposed, and a positive electrode protective tape was attached so as to cover the positive electrode lead 10.
  • the negative electrode slurry was intermittently applied to both sides of a negative electrode current collector (thickness 10 ⁇ m) made of copper foil and dried. The dried coating film was pressed so that the thickness of the mixture layer per side became 80 ⁇ m. Next, slitting was performed to a width defined by the cylindrical lithium ion secondary battery, and the negative electrode 7 was produced. A negative electrode lead 9 was connected to a portion of the negative electrode 7 where the negative electrode current collector was exposed, and a negative electrode protective tape was attached so as to cover the negative electrode lead 9.
  • the cylindrical lithium ion secondary battery shown in FIG. 5 was produced using the positive electrode and negative electrode produced in the above (1) and (2) and a polyethylene microporous film having a thickness of 20 ⁇ m as the separator 8. .
  • the nominal capacity of the cylindrical lithium ion secondary battery was 3.0 Ah.
  • LiPF 6 and VC were dissolved in a mixed solvent in which EC, DMC, and EMC were mixed at a volume ratio of 1: 1: 1.
  • the concentration of LiPF 6 is 1 mol / L, the ratio of the VC, the mixed solvent 100 parts by weight, was 3 parts by weight.
  • Comparative Example 1 Except for preparing the conductive material paste, acetylene black was directly stirred and kneaded with a positive electrode active material, a binder and NMP as a dispersion medium in a double-arm kneader, as in Example 1. A positive electrode slurry was prepared. A positive electrode was produced in the same manner as in Example 1 except that the obtained positive electrode slurry was used. A cylindrical lithium ion secondary battery was produced in the same manner as in Example 1 except that the obtained positive electrode was used.
  • Adhesive strength was measured by a 90 degree peel strength test in accordance with JIS-C6481-1995. Specifically, the positive electrode mixture layer formed on the surface of the positive electrode current collector is fixed with a double-sided tape, and one end of the positive electrode current collector is 50 mm per minute in a direction perpendicular to the positive electrode mixture layer. It pulled at a speed and peeled off about 30 mm continuously. The load at this time was measured. The same measurement was performed 3 times, the average value was calculated
  • Example 1 and Comparative Example 1 are shown in Table 1 together with the active material density in the positive electrode mixture layer.
  • the maximum utilization rate of the positive electrode active material was lower than that in Example 1. This is because the conductive material particles are excessively aggregated between the positive electrode active material particles and between the positive electrode active material particles and the positive electrode current collector, so that the volume resistance at the positive electrode is increased. Conceivable. In addition, since the fall of the maximum utilization factor of a positive electrode active material also affects battery capacity, it is thought that the fall of battery capacity became remarkable as mentioned above.
  • Comparative Example 1 the adhesion of the positive electrode mixture layer was also reduced as compared with Example 1. In Comparative Example 1, it is considered that the binding force was reduced because the distance between the particles was increased due to excessive aggregation of the conductive material particles. In contrast to the results of Comparative Example 1, it is considered that in Example 1, the aggregation of the conductive material particles was suppressed, so that the active material density, the maximum utilization rate of the positive electrode active material, and the battery capacity were high.
  • Examples 2 to 4 and Comparative Example 2 A positive electrode slurry was prepared in the same manner as in Example 1 except that the amount of the conductive material added to 100 parts by mass of the positive electrode active material was changed to the values shown in Table 2.
  • a positive electrode was produced in the same manner as in Example 1 except that the obtained positive electrode slurry was used.
  • a cylindrical lithium ion secondary battery was produced in the same manner as in Example 1 except that the obtained positive electrode was used. Evaluation similar to Example 1 was performed using the obtained battery. The results are shown in Table 2.
  • Comparative Example 2 in which the amount of conductive material added is 0.05 parts by mass, the maximum utilization factor of the positive electrode active material is reduced, although the active material density is high. This is presumably because the volume resistance of the positive electrode increased due to the lack of conductive material in the positive electrode. Moreover, it is thought that the battery capacity was reduced in Comparative Example 2 due to the reduction in the maximum utilization rate of the positive electrode active material.
  • Example 2 where the addition amount of the conductive material is 0.1 parts by mass, the maximum utilization factor of the positive electrode active material is high, and a high battery capacity is obtained.
  • the conductive material is preferably used at a rate exceeding 0.05 parts by mass, and more preferably at a rate of 0.1 parts by mass or more with respect to 100 parts by mass of the positive electrode active material.
  • Example 3 in which the addition amount of the conductive material is 1.3 parts by mass, the active material density is slightly lower than in Example 2, but the maximum utilization rate and battery capacity of the positive electrode active material are relatively high. Is obtained.
  • Example 4 where the addition amount of the conductive material was 1.4 parts by mass, the maximum utilization rate of the positive electrode active material was high, but the active material density was slightly reduced, the battery capacity was reduced, and the adhesion was also low. Therefore, the conductive material is preferably used at a ratio of less than 1.4 parts by mass, and more preferably at a ratio of 1.3 parts by mass or less, with respect to 100 parts by mass of the positive electrode active material.
  • Example 5 to 7 and Comparative Example 3 A positive electrode slurry was prepared in the same manner as in Example 1 except that the conductive material acetylene black was changed to acetylene black having a BET specific surface area shown in Table 3. A positive electrode was produced in the same manner as in Example 1 except that the obtained positive electrode slurry was used. A cylindrical lithium ion secondary battery was produced in the same manner as in Example 1 except that the obtained positive electrode was used. Evaluation similar to Example 1 was performed using the obtained battery. The results are shown in Table 3.
  • Example 5 using a conductive material having a BET specific surface area of 50 m 2 / g, high results were obtained for both the active material density, the maximum utilization rate of the positive electrode active material, and the battery capacity.
  • Example 6 using a conductive material having a BET specific surface area of 300 m 2 / g, the maximum utilization factor and battery capacity of the positive electrode active material are high although the active material density is slightly low.
  • Example 7 using a conductive material having a BET specific surface area of 320 m 2 / g, although the maximum utilization factor of the positive electrode active material is high, the bulk density of the conductive material is decreased, and the active material density is decreased. Battery capacity is low. Therefore, it is preferable to use a conductive material having a BET specific surface area of more than 40 m 2 / g and less than 320 m 2 / g, more preferably 50 to 300 m 2 / g.
  • Examples 8 to 10 and Comparative Example 4 A positive electrode slurry was prepared in the same manner as in Example 1 except that the addition amount of PVDF as a binder was changed to the value shown in Table 4 with respect to 100 parts by mass of the positive electrode active material.
  • a positive electrode was produced in the same manner as in Example 1 except that the obtained positive electrode slurry was used.
  • a cylindrical lithium ion secondary battery was produced in the same manner as in Example 1 except that the obtained positive electrode was used. Evaluation similar to Example 1 was performed using the obtained battery. The results are shown in Table 4.
  • Example 8 As is apparent from Table 4, in Examples 8 to 10 in which the amount of the binder added was 0.35 to 1.3 parts by mass, the active material density, the maximum utilization factor, the maximum utilization factor of the positive electrode active material, and the battery capacity Both were high. However, in Example 8, the adhesive force was low. In Comparative Example 4 in which the addition amount of the binder was 1.4 parts by mass, the maximum utilization factor and the active material density of the positive electrode active material were slightly reduced and the battery capacity was also reduced, although the adhesion was high.
  • the adhesion is preferably 2 N / m or more. Therefore, from the viewpoint of the balance between the maximum utilization factor, the active material density and the battery capacity, and the adhesion, the ratio of the binder to 100 parts by mass of the positive electrode active material exceeds 0.35 parts by mass and is 1.4 parts by mass.
  • the amount is preferably less than parts, more preferably 0.4 to 1.3 parts by weight.
  • Examples 11-14 A positive electrode slurry was prepared in the same manner as in Example 1 except that the weight average molecular weight of PVDF as a binder was changed to the values shown in Table 5.
  • a positive electrode was produced in the same manner as in Example 1 except that the obtained positive electrode slurry was used.
  • a cylindrical lithium ion secondary battery was produced in the same manner as in Example 1 except that the obtained positive electrode was used. Evaluation similar to Example 1 was performed using the obtained battery. The results are shown in Table 5.
  • Example 13 using a binder having a weight average molecular weight of 1,500,000, high results were obtained in all of adhesion, active material density, maximum utilization rate of positive electrode active material, and battery capacity.
  • Example 14 using a binder having a weight average molecular weight of 1.7 million, the adhesion and the maximum utilization rate of the positive electrode active material are high, but the binder is difficult to dissolve and the degree of aggregation of the constituent components increases. The active material density and battery capacity were slightly reduced. From the viewpoint of the balance between the active material density, battery capacity, and adhesion, the weight average molecular weight of the binder is preferably more than 550,000 and less than 1.7 million, and preferably 600,000 to 1,500,000. More preferred.
  • acetylene black is used as the conductive material.
  • the present invention is not limited to this, and the same effect can be obtained with other carbon black, graphite, and / or carbon fiber.
  • PVDF was used as a binder, not only this but the same effect is acquired also when another binder is used.
  • Example 15 The lithium ion secondary battery shown in FIG. 5 was produced according to the following procedure.
  • a conductive material paste was prepared by stirring and kneading with a kneader.
  • the usage-amount of NMP was adjusted so that the density
  • a positive electrode slurry was prepared by stirring and kneading 1 part by mass of PVDF (weight average molecular weight: 680,000) as a dressing material together with an appropriate amount of NMP in a double-arm kneader.
  • the positive electrode slurry was intermittently applied to both surfaces of a positive electrode current collector made of an aluminum foil (thickness: 15 ⁇ m).
  • the obtained coating film was dried at a drying rate of 1.2 g / m 2 ⁇ s (dispersion rate of the dispersion medium).
  • the mixture layer was pressed so that the thickness of the mixture layer per side was 70 ⁇ m.
  • slitting was performed to a specified width of the cylindrical lithium ion secondary battery, and the positive electrode 6 was produced.
  • a positive electrode lead 10 was connected to a portion of the positive electrode 6 where the positive electrode current collector was exposed, and a positive electrode protective tape was attached so as to cover the positive electrode lead 10.
  • Example 16 1 part by mass of acetylene black as a conductive agent is added to 100 parts by mass of lithium nickelate (average particle diameter (D50): 10 ⁇ m) as a positive electrode active material, and dry-mixed by a double-arm kneader.
  • conductive material particles were adhered to the surface of the positive electrode active material particles.
  • the positive electrode active material particles having conductive material particles adhered to the surface and 1 part by mass of PVDF as a binder with respect to 100 parts by mass of the positive electrode active material are stirred together with an appropriate amount of NMP in a double-arm kneader.
  • a positive electrode slurry was prepared by kneading.
  • a positive electrode was produced in the same manner as in Example 15 except that the obtained positive electrode slurry was used.
  • the distribution state of the conductive material in the positive electrode was almost the same as in Example 15.
  • a cylindrical lithium ion secondary battery was produced in the same manner as in Example 1 except that the obtained positive electrode was used and the same negative electrode and separator as in Example 1 were used.
  • Example 17 (1) Production of positive electrode A positive electrode slurry (first positive electrode slurry) in the same manner as in step (1) of Example 15 except that the ratio of the conductive material to 100 parts by mass of the positive electrode active material was 0.4 parts by mass. ) was prepared. Moreover, the positive electrode slurry prepared similarly to the process (1) of Example 15 was used as the second positive electrode slurry.
  • the 1st positive electrode slurry was apply
  • the obtained coating film was dried at a drying rate of 1.2 g / m 2 ⁇ s (dispersion rate of the dispersion medium).
  • the second positive electrode slurry was applied to the surface of the dried coating film, and the obtained coating film was dried at a drying rate (dispersion rate of the dispersion medium) of 0.8 g / m 2 ⁇ s.
  • the mixture layer was pressed so that the thickness of the mixture layer per side was 70 ⁇ m.
  • slitting was performed to produce a positive electrode, a positive electrode lead was connected, and a positive electrode protective tape was attached.
  • the dispersion state of the conductive material in the obtained positive electrode was similar to that in Example 15, but was located at a junction point between the positive electrode current collector and the positive electrode active material particles as compared with the state in Example 15.
  • the proportion of conductive material particles was even smaller, as shown in FIG. This is presumably because the transfer of the conductive material particles to the coating film surface became conspicuous at the time of drying because the content of the conductive agent in the coating film of the first slurry was small and the thickness was small.
  • Example 18 (1) Production of Positive Electrode A positive electrode slurry (first positive electrode slurry) was prepared in the same manner as in Step (1) of Example 17 except that lithium nickel oxide having an average particle diameter (D50) of 20 ⁇ m was used as the positive electrode active material. Prepared.
  • a positive electrode was produced in the same manner as in Example 17 except that the first positive electrode slurry was intermittently applied so that the thickness after pressing was 20 ⁇ m.
  • the connection of the positive electrode lead and the application of the positive electrode protective tape were performed in the same manner as in Example 17.
  • the dispersion state of the conductive material in the obtained positive electrode was similar to that in Example 17. However, since the particle diameter of the positive electrode active material particles in contact with the positive electrode current collector is large, the ratio of the conductive material particles located at the junction point between the positive electrode current collector and the positive electrode active material particles is more than that in the state of Example 17. The state was as shown in FIG.
  • Comparative Example 5 Acetylene black was directly stirred and kneaded with a positive electrode active material, a binder, and NMP as a dispersion medium in a double-arm kneader without preparing a conductive material paste, as in Example 15. A positive electrode slurry was prepared. A positive electrode was produced in the same manner as in Example 1 except that the obtained positive electrode slurry was used.
  • the dispersed state of the conductive material in the obtained positive electrode is an aggregated state, a state where it is not in contact with the positive electrode active material particles or the adjacent conductive material particles, or only one positive electrode active material particle.
  • the conductive material particles are present in the positive electrode in a state of low conductivity with the adjacent conductive material particles and / or the positive electrode active material particles. Also, a relatively large number of conductive material particles were present on the surface of the positive electrode current collector.
  • a cylindrical lithium ion secondary battery was produced in the same manner as in Example 1 except that the positive electrode obtained was used.
  • Comparative Example 6 Without preparing a conductive material paste, acetylene black was directly stirred and kneaded with a positive electrode active material, a binder and NMP as a dispersion medium in a double-arm kneader, and 100 parts by mass of the positive electrode active material, A positive electrode slurry was prepared in the same manner as in Comparative Example 5, except that the ratio of the conductive material was changed to 3 parts by mass and the ratio of the binder was changed to 3 parts by mass. A positive electrode was produced in the same manner as in Comparative Example 5, except that the obtained positive electrode slurry was used.
  • the conductive material in the obtained positive electrode had a greater degree of aggregation than Comparative Example 5. Since the conductive material particles are present in an aggregated state between the positive electrode active material particles and between the positive electrode active material particles and the positive electrode current collector, the filling property of the positive electrode active material is lowered and the active material density is increased. Is difficult. There were also many conductive material particles that were not in contact with the positive electrode active material particles and / or the adjacent conductive material particles. That is, many conductive material particles existed in the positive electrode in a state of low conductivity with the adjacent conductive material particles and / or positive electrode active material particles. Moreover, the ratio of the electrically conductive material which exists in the surface of a positive electrode electrical power collector was also large.
  • a cylindrical lithium ion secondary battery was produced in the same manner as in Example 1 except that the positive electrode obtained was used.
  • the maximum utilization factor, sheet resistance, battery capacity and capacity retention rate of the positive electrode active material were evaluated, and a short circuit test was performed.
  • the sheet resistance was measured by the method described above, and the maximum utilization factor and battery capacity of the positive electrode active material were evaluated in the same manner as in Example 1.
  • the capacity retention rate measurement and the short-circuit test were performed by the following methods.
  • (G) Short circuit test The short circuit of the battery was evaluated by a foreign matter mixing test as described below. 100 cells of each of the lithium ion secondary batteries of Examples and Comparative Examples were prepared. Each lithium ion secondary battery is charged with a constant current of 1.45 A until the voltage reaches 4.25 V, and then charged with a constant voltage until the current reaches 50 mA. The group was removed.
  • a nickel plate having a thickness of “a” of 0.1 mm, a length of 2 mm, and a width of “b” is bent at an arbitrary point in the length direction, and the cross-sectional shape in the length direction as shown in FIG. A nickel plate 23 was formed.
  • the L-shaped nickel plate 23 is placed between the positive electrode and the separator located on the outermost periphery of the electrode group so that the height direction of the nickel plate 23 is perpendicular to the surfaces of the positive electrode and the separator (in other words, The nickel plate 23 was disposed so that the thickness direction thereof was parallel to the surfaces of the positive electrode and the separator.
  • the electrode group was accommodated again in the battery case, and the lithium ion secondary battery was pressed at a pressure of 800 N / cm 2 . And in the lithium ion secondary battery after a press, the resistance of a cell was measured and it was judged that the thing whose resistance became low was short-circuited. A similar test was performed on 100 cells, and short circuit was evaluated by the number of shorted cells in 100 cells (number of shorted cells / 100 cells).
  • the distribution state of the conductive material is optimized, an increase in volume resistance is suppressed, and the maximum utilization factor of the positive electrode active material can be increased.
  • the density and battery capacity can be improved. Moreover, it is possible to achieve both high battery capacity, high charge / discharge cycle characteristics, and high safety.
  • the positive electrode and the nonaqueous electrolyte secondary battery using the positive electrode are used in various applications, for example, a power source for driving a motor in a hybrid electric vehicle (particularly for a plug-in hybrid vehicle), a mobile phone, a notebook personal computer, It is useful for applications such as a driving power source in various portable electronic devices such as a video camcorder, and a large power source in a household power storage device.

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Abstract

La présente invention concerne : une électrode positive pour accumulateurs secondaires à électrolyte non aqueux, dans laquelle l'état de distribution d'un matériau électroconducteur est optimisé afin d'empêcher une augmentation de la résistivité et d'augmenter la capacité de l'accumulateur ; et un accumulateur secondaire à électrolyte non aqueux équipé de l'électrode positive. L'électrode positive pour accumulateurs secondaires à électrolyte non aqueux comprend un collecteur de courant d'électrode positive et une couche de mélange d'électrode positive contenant un matériau actif d'électrode positive, un matériau électroconducteur et un liant, laquelle couche adhère à la surface du collecteur de courant d'électrode positive. Les particules du matériau électroconducteur sont dispersées de telle sorte que les particules du matériau électroconducteur sont fixées sur les surfaces de particules du matériau actif d'électrode positive pour former un col qui constitue un agrégat en forme de couche mince, qui est composé d'une petite quantité des particules du matériau électroconducteur, entre les particules du matériau actif d'électrode positive. Le rapport de la capacité maximale applicable à la capacité de charge du matériau actif d'électrode positive est de 95 % ou plus pour un chargement à un taux de 0,3 C et un déchargement à un taux de 0,2 C à 25°C.
PCT/JP2011/007118 2010-12-21 2011-12-20 Électrode positive pour accumulateurs secondaires à électrolyte non aqueux et accumulateur secondaire à électrolyte non aqueux WO2012086186A1 (fr)

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JP2010283986A JP2014041698A (ja) 2010-12-21 2010-12-21 非水系二次電池用正極板およびこれを用いた非水系二次電池
JP2010-283986 2010-12-21
JP2011031601A JP2014041699A (ja) 2011-02-17 2011-02-17 非水系二次電池用正極板およびこれを用いた非水系二次電池
JP2011-031601 2011-02-17

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JP2014238944A (ja) * 2013-06-06 2014-12-18 日立化成株式会社 リチウムイオン二次電池用の正極及びその製造方法
CN105895911A (zh) * 2015-02-18 2016-08-24 株式会社杰士汤浅国际 铅蓄电池
WO2019244907A1 (fr) * 2018-06-20 2019-12-26 ヤマハ発動機株式会社 Électrode positive de batterie secondaire à électrolyte non aqueux et batterie secondaire à électrolyte non aqueux
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JP2014238944A (ja) * 2013-06-06 2014-12-18 日立化成株式会社 リチウムイオン二次電池用の正極及びその製造方法
CN105895911A (zh) * 2015-02-18 2016-08-24 株式会社杰士汤浅国际 铅蓄电池
WO2019244907A1 (fr) * 2018-06-20 2019-12-26 ヤマハ発動機株式会社 Électrode positive de batterie secondaire à électrolyte non aqueux et batterie secondaire à électrolyte non aqueux
WO2019244282A1 (fr) * 2018-06-20 2019-12-26 ヤマハ発動機株式会社 Électrode positive de batterie secondaire à électrolyte non aqueux et batterie secondaire à électrolyte non aqueux
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US11998888B2 (en) 2018-07-17 2024-06-04 Toyota Jidosha Kabushiki Kaisha Particle aggregate manufacturing method, electrode plate manufacturing method, and particle aggregate

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