WO2012098614A1 - Positive electrode for lithium ion secondary batteries, lithium ion secondary battery, method of producing a positive electrode for lithium ion secondary batteries, and vehicle - Google Patents

Positive electrode for lithium ion secondary batteries, lithium ion secondary battery, method of producing a positive electrode for lithium ion secondary batteries, and vehicle Download PDF

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Publication number
WO2012098614A1
WO2012098614A1 PCT/JP2011/006770 JP2011006770W WO2012098614A1 WO 2012098614 A1 WO2012098614 A1 WO 2012098614A1 JP 2011006770 W JP2011006770 W JP 2011006770W WO 2012098614 A1 WO2012098614 A1 WO 2012098614A1
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Prior art keywords
positive electrode
sulfur
lithium ion
ion secondary
secondary battery
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PCT/JP2011/006770
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French (fr)
Japanese (ja)
Inventor
琢寛 幸
敏勝 小島
妥絵 奥山
境　哲男
淳一 丹羽
晶 小島
正孝 仲西
一仁 川澄
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株式会社豊田自動織機
独立行政法人産業技術総合研究所
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Publication of WO2012098614A1 publication Critical patent/WO2012098614A1/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
    • H01M4/139—Processes of manufacture
    • H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • 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
    • H01M4/581—Chalcogenides or intercalation compounds thereof
    • H01M4/5815—Sulfides
    • 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 lithium ion secondary battery containing a sulfur-based positive electrode active material, a lithium ion secondary battery using the positive electrode, a method for producing the positive electrode, and a vehicle.
  • Lithium ion secondary batteries which are a type of non-aqueous electrolyte secondary battery, are batteries with large charge and discharge capacities, and are mainly used as batteries for portable electronic devices. In addition, lithium ion secondary batteries are also expected as batteries for electric vehicles.
  • a technology using sulfur as a positive electrode active material of a lithium ion secondary battery is known.
  • sulfur as a positive electrode active material
  • the charge and discharge capacity of the lithium ion secondary battery can be increased.
  • the charge and discharge capacity of a lithium ion secondary battery using sulfur as a positive electrode active material is about 6 times the charge and discharge capacity of a lithium ion secondary battery using a lithium cobaltate positive electrode material which is a general positive electrode material is there.
  • a compound of sulfur and lithium is formed during discharge.
  • the compound of sulfur and lithium is soluble in the non-aqueous electrolyte solution (for example, ethylene carbonate, dimethyl carbonate, etc.) of the lithium ion secondary battery.
  • a lithium ion secondary battery using sulfur as a positive electrode active material has a problem that when charge and discharge are repeated, the elution of the sulfur into the electrolytic solution gradually deteriorates and the battery capacity decreases.
  • cycle characteristics the characteristics of the lithium ion secondary battery in which the charge and discharge capacity decreases with repetition of charge and discharge are referred to as “cycle characteristics”.
  • the lithium ion secondary battery having a small decrease in charge and discharge capacity is excellent in cycle characteristics. Further, the lithium ion secondary battery having a large decrease in charge and discharge capacity is inferior in cycle characteristics.
  • Patent Document 1 introduces a technology that uses polysulfide carbon as a positive electrode active material.
  • This polysulfide carbon has carbon and sulfur as main components.
  • this polysulfurized carbon is one in which sulfur is added to a linear unsaturated polymer. It is considered that the carbon material can suppress the elution of sulfur into the electrolytic solution and improve the cycle characteristics of the lithium ion secondary battery.
  • the inventors of the present invention invented a positive electrode active material obtained by heat-treating a mixture of polyacrylonitrile and sulfur (see Patent Document 2).
  • the charge and discharge capacity of a lithium ion secondary battery using this positive electrode active material as a positive electrode is large, and a lithium ion secondary battery using this positive electrode active material as a positive electrode is excellent in cycle characteristics.
  • the positive electrode active material using the polyacrylonitrile or linear unsaturated polymer as the carbon material has a problem that the electrical resistance is high and the discharge rate characteristic (so-called C rate) is not sufficient. .
  • the present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a positive electrode and a lithium ion secondary battery which contain a sulfur-based positive electrode active material and can improve cycle characteristics and discharge rate characteristics of the lithium ion secondary battery. To aim.
  • the positive electrode for a lithium ion secondary battery of the present invention which solves the above problems, contains a sulfur-based positive electrode active material containing carbon (C) and sulfur (S), and a conductive material containing sulfur (S). At least a part of the conductive material is made of sulfide of at least one metal selected from the group consisting of a fourth period metal, a fifth period metal, a sixth period metal and a rare earth element.
  • the lithium ion secondary battery of the present invention for solving the above problems contains a sulfur-based positive electrode active material containing carbon (C) and sulfur (S), and a conductive material containing sulfur (S), At least a part of the conductive material is a positive electrode for a lithium ion secondary battery comprising a sulfide of at least one metal selected from the group consisting of a fourth period metal, a fifth period metal, a sixth period metal and a rare earth element It is characterized by Further, a vehicle according to the present invention for solving the above-mentioned problems is characterized in that the lithium ion secondary battery according to the present invention is mounted.
  • the first method for producing a positive electrode for a lithium ion secondary battery of the present invention is a lithium ion secondary battery containing a sulfur-based positive electrode active material containing carbon (C) and sulfur (S)
  • a method of manufacturing a positive electrode comprising a heat treatment step of heating a mixed material containing a carbon material, sulfur, and a conductive material containing sulfur, wherein the conductive material includes a fourth period metal, a fourth period metal, It is characterized in that it is a sulfide of at least one metal selected from the group consisting of a five period metal, a sixth period metal and a rare earth element.
  • a second method for producing a positive electrode for a lithium ion secondary battery of the present invention which solves the above-mentioned problems comprises: a positive electrode for a lithium ion secondary battery containing a sulfur-based positive electrode active material containing carbon (C) and sulfur (S) A heat treatment step of heating a mixed material containing a carbon material, sulfur, and a conductive material not containing sulfur, wherein the conductive material has a fourth period metal, the fifth It is characterized in that it is at least one metal selected from the group consisting of a periodic metal, a sixth periodic metal and a rare earth element.
  • the positive electrode of the present invention contains a sulfur-based positive electrode active material containing carbon (C) and sulfur (S), and a conductive material containing sulfur (S).
  • a lithium ion secondary battery using elemental sulfur as a positive electrode active material is inferior in cycle characteristics.
  • a sulfide of at least one metal selected from the group consisting of a fourth period metal, a fifth period metal, a sixth period metal and a rare earth element is blended.
  • the sulfides of these metals can exhibit high electric conductivity (conductivity) by themselves or can improve lithium ion conductivity of the positive electrode. Therefore, sulfides of these metals function as a conductive material. And the discharge rate characteristic can be improved by blending the sulfide of these metals in the positive electrode.
  • a conductive material is mix
  • the discharge rate characteristic is sufficiently It can be improved.
  • the positive electrode of the present invention can improve the cycle characteristics and the discharge rate characteristics of the lithium ion secondary battery by their cooperation. Similarly, the lithium ion secondary battery of the present invention is excellent in cycle characteristics and discharge rate characteristics. Furthermore, the lithium ion secondary battery of the present invention having these effects is suitable as a vehicle battery.
  • metal sulfide is used as the conductive material. Therefore, as described above, the conductive material and the positive electrode active material can be dispersed substantially uniformly, and the discharge rate characteristics can be improved.
  • the non-sulfurized metal is used in the manufacturing method of the 2nd positive electrode for lithium ion secondary batteries of this invention. Also in this case, since the conductive material is sulfided at the time of manufacture to exhibit high electrical conductivity or to improve lithium ion conductivity of the positive electrode, discharge rate characteristics are improved.
  • FIG. 15 is a graph showing the results of X-ray diffraction of the sulfur-based positive electrode active material-conductive material composite used for the positive electrode of Example 2.
  • FIG. FIG. 16 is a graph showing the results of X-ray diffraction of the sulfur-based positive electrode active material-conductive material composite used for the positive electrode of Example 4.
  • FIG. 15 is a graph showing the results of X-ray diffraction of the sulfur-based positive electrode active material-conductive material composite used for the positive electrode of Example 7.
  • FIG. FIG. 16 is a graph showing the results of X-ray diffraction of the sulfur-based positive electrode active material-conductive material composite used for the positive electrode of Example 9.
  • 5 is a graph showing the discharge rate characteristics (charge-discharge curve) of a lithium ion secondary battery using the positive electrode of Example 1.
  • 5 is a graph showing discharge rate characteristics (cycle characteristics) of a lithium ion secondary battery using the positive electrode of Example 1.
  • FIG. 5 is a graph showing the discharge rate characteristics (cycle characteristics) of a lithium ion secondary battery using the positive electrode of Example 2.
  • 15 is a graph showing the discharge rate characteristic (cycle characteristic) of the lithium ion secondary battery using the positive electrode of Example 3.
  • 15 is a graph showing the discharge rate characteristics (cycle characteristics) of a lithium ion secondary battery using the positive electrode of Example 4.
  • 15 is a graph showing the discharge rate characteristic (charge-discharge curve) of a lithium ion secondary battery using the positive electrode of Example 5.
  • It is a graph showing the discharge rate characteristic (cycle characteristic) of the lithium ion secondary battery using the positive electrode of Example 5.
  • It is a graph showing the discharge rate characteristic (charge-and-discharge curve) of the lithium ion secondary battery using the positive electrode of Example 6.
  • It is a graph showing the discharge rate characteristic (cycle characteristic) of the lithium ion secondary battery using the positive electrode of Example 6.
  • the positive electrode for a lithium ion secondary battery of the present invention contains a positive electrode active material and a conductive material.
  • the lithium ion secondary battery of the present invention is a battery using the positive electrode of the present invention.
  • the method for producing a positive electrode for a lithium ion secondary battery of the present invention comprises a heat treatment step of heating a mixed material containing a carbon material, sulfur, and a conductive material. A positive electrode containing an active material and a conductive material is manufactured. According to the production method of the present invention, the positive electrode of the present invention can be produced.
  • Conductive material that is, the material of the conductive material used when manufacturing the positive electrode of the present invention, at least one metal selected from the group consisting of the fourth period metal, the fifth period metal, the sixth period metal and the rare earth element Or its sulfide can be used.
  • the fourth period metal, the fifth period metal, and the sixth period metal in the present specification are according to the periodic table.
  • the fourth period metal refers to a metal included in the fourth period element in the periodic table.
  • the conductive material a material which exhibits high electric conductivity in the form of sulfide or which can greatly improve lithium ion conductivity of the positive electrode is preferable.
  • the conductive material is made of both the metal and the sulfide thereof, or only of the sulfide of the metal. These conductive materials are preferably rich in sulfides, and more preferably consist of sulfides alone.
  • the conductive material and the sulfur-based positive electrode active material can be easily conformed, and the conductive material and the positive electrode active material can be dispersed substantially uniformly.
  • the ratio of the metal and sulfur in the conductive material can be easily controlled to a desired range by using a sulfide as the conductive material.
  • TiS 2 , FeS 2 , Me 2 S 3 (wherein, Me is selected from Ti, La, Ce, Pr, Nd, Sm) It is a kind, MeS (in which Me is a kind selected from Ti, La, Ce, Pr, Nd and Sm), Me 3 S 4 (wherein Me is Ti, La, Ce, Pr and Nd) And Sm, Me x S y (wherein Me is Ti, Fe, V, Mn, Fe, Ni, Cu, Zn, Mo, Ag, Cd, In, Sn, Sb, Ta, It is 1 type chosen from W and Pb, and x and y are arbitrary integers.
  • conductive materials Ti, Fe, La, Ce, Pr, Nd, Sm, V, Mn, Fe, Ni, Cu, Zn, Mo, Ag, Cd, In, Sn, Sb, Ta, W, At least one selected from Pb may be used as it is or in the form of a sulfide such as the above-mentioned conductive material.
  • conductive material materials By using these conductive material materials, the electrical conductivity and / or lithium ion conductivity of the entire positive electrode can be improved, and the discharge rate characteristics of the lithium ion secondary battery can be improved. It is more preferable to use TiS z (in the formula, z is 0.1 to 2) in view of raw material cost, easiness of procurement and resource amount, and it is particularly preferable to use TiS 2 .
  • the compounding ratio of a carbon material such as polyacrylonitrile described later and the conductive material material is preferably 10: 0.5 to 10: 5 by mass ratio, and 10: 1 to 10: 3 More preferable. If the blending amount of the conductive material is too large, the amount of the positive electrode active material with respect to the entire positive electrode will be too small.
  • the conductive material is preferably in the form of powder.
  • the conductive material preferably has a particle diameter of 0.1 to 100 ⁇ m, more preferably 0.1 to 50 ⁇ m, and still more preferably 0.1 to 20 ⁇ m, as measured using an electron microscope or the like. .
  • the positive electrode active material used for the positive electrode of the present invention is a sulfur-based positive electrode active material containing carbon (C) and sulfur (S).
  • sulfur-based positive electrode active materials include those disclosed in the above-mentioned Patent Document 1 (using a linear unsaturated polymer as the carbon material) and those disclosed in the Patent Document 2 (carbon material) And those using various pitch-based carbon materials as the carbon material are preferably used.
  • a sulfur-based positive electrode active material using polyacrylonitrile as a carbon material is referred to as sulfur-modified polyacrylonitrile.
  • a sulfur-based positive electrode active material using a pitch-based carbon material as a carbon material is called a sulfur-modified pitch.
  • polyacrylonitrile is abbreviated as PAN if necessary.
  • Sulfur-modified polyacrylonitrile When polyacrylonitrile is used as the carbon material, the high capacity originally possessed by sulfur can be maintained, and the elution of sulfur into the electrolytic solution can be suppressed, so the cycle characteristics of the non-aqueous electrolyte secondary battery can be greatly improved. It is considered that this is because sulfur is not present as a single substance in the sulfur-based positive electrode active material but in a stable state in which it is combined with polyacrylonitrile. In the method of producing a sulfur-based positive electrode active material disclosed in Patent Document 2, sulfur is heat-treated together with polyacrylonitrile.
  • the polyacrylonitrile used as the carbon material is preferably in the form of powder, and the mass average molecular weight is preferably about 10 4 to 3 ⁇ 10 5 .
  • the particle diameter of polyacrylonitrile is preferably about 0.5 to 50 ⁇ m, more preferably about 1 to 10 ⁇ m, as observed by an electron microscope. If the molecular weight and particle size of polyacrylonitrile are within these ranges, the contact area between polyacrylonitrile and sulfur can be increased, and polyacrylonitrile and sulfur can be reacted with high reliability. Therefore, the elution of sulfur into the electrolyte can be suppressed more reliably.
  • the sulfur used for the sulfur-based positive electrode active material is also preferably in the form of powder.
  • the particle size of sulfur is not particularly limited, but when it is classified using a sieve, those which do not pass through a sieve with a sieve opening of 40 ⁇ m and which have a size within a 150 ⁇ m sieve are preferable. It is more preferable not to pass through a sieve with a sieve opening of 40 ⁇ m and in the size range of passing through a 100 ⁇ m sieve.
  • the compounding ratio of the polyacrylonitrile powder to the sulfur powder used for the sulfur-based positive electrode active material is not particularly limited, but it is preferably 1: 0.5 to 1:10 in mass ratio, 1: 0.5 to 1
  • the ratio is more preferably 7: 7, and more preferably 1: 2 to 1: 5.
  • Sulfur-modified polyacrylonitrile contains carbon, nitrogen, and sulfur as a result of elemental analysis, and may further contain small amounts of oxygen and hydrogen. Further, as shown in FIG. 1, as a result of X-ray diffraction of sulfur-modified polyacrylonitrile with CuK ⁇ rays, only a broad peak having a peak position near 25 ° was confirmed in the range of diffraction angle (2 ⁇ ) of 20 to 30 °. It was done.
  • X-ray diffraction measurement was performed using a powder X-ray diffractometer (manufactured by MAC Science, model number: M06XCE) using a CuK ⁇ ray. The measurement conditions were: voltage: 40 kV, current: 100 mA, scan rate: 4 ° / min, sampling: 0.02 °, number of integrations: 1 measurement range: diffraction angle (2 ⁇ ) 10 ° to 60 °.
  • the decrease in mass when the sulfur-modified polyacrylonitrile was heated from room temperature to 900 ° C. at a temperature rising rate of 20 ° C./min was measured by thermogravimetric analysis.
  • the reduction in mass of sulfur-modified polyacrylonitrile was 10% or less at 400 ° C.
  • a mixture of sulfur powder and polyacrylonitrile powder was heated under the same conditions.
  • the mass of the mixture decreased from around 120 ° C., and decreased rapidly and greatly at 200 ° C. or higher. This is considered to be based on the loss of sulfur.
  • sulfur-modified polyacrylonitrile it is considered that sulfur is not present as a single substance but is present in a state of being bonded to the ring-closed polyacrylonitrile.
  • FIG. 2 An example of a Raman spectrum of sulfur-modified polyacrylonitrile is shown in FIG.
  • the Raman spectrum shown in FIG. 2 there are major peak near 1331cm -1 of Raman shift, and, 1548cm -1 in the range of 200cm -1 ⁇ 1800cm -1, 939cm -1 , 479cm -1, 381cm -1, A peak is present around 317 cm -1 .
  • the peak of the above-mentioned Raman shift is observed at the same position even when the ratio of elemental sulfur to polyacrylonitrile is changed.
  • these peaks are characteristic of sulfur-modified polyacrylonitrile.
  • Each peak mentioned above exists in the range of about ⁇ 8 cm ⁇ 1 centered on the peak position mentioned above.
  • a "main peak” refers to the peak which peak height becomes the largest among all the peaks which appeared in the Raman spectrum.
  • the peaks of the Raman spectrum may change in number or the position of the peak top may be shifted depending on the wavelength of incident light or the difference in resolution. Therefore, when the Raman spectrum of the positive electrode of the present invention using sulfur-modified polyacrylonitrile as the positive electrode active material is measured, the same peak as the above peak or a peak slightly different in number or peak top position from the above peak is confirmed Be done.
  • the pitch-based carbon material is obtained by polycondensation of coal pitch, petroleum pitch, mesophase pitch (anisotropic pitch), asphalt, coal tar, coal tar pitch, condensed polycyclic aromatic hydrocarbon compound It refers to at least one selected from the group consisting of organic synthetic pitch, or organic synthetic pitch obtained by polycondensation of a heteroatom-containing fused polycyclic aromatic hydrocarbon compound. These are known as carbon materials containing fused polycyclic aromatics.
  • Coal tar which is a type of pitch-based carbon material, is a black viscous oily liquid obtained by high-temperature dry distillation (coal dry distillation) of coal.
  • Coal pitch can be obtained by refining and heat treating (polymerizing) coal tar.
  • Asphalt is a black-brown to black solid or semi-solid plastic material. Asphalt is roughly classified into those obtained as bottoms when vacuum distillation of petroleum (crude oil) is carried out and those which exist naturally. Asphalt is soluble in toluene, carbon disulfide and the like.
  • Petroleum pitch can be obtained by refining and heat treating (polymerizing) asphalt. The pitch is usually amorphous and optically isotropic (isotropic pitch).
  • anisotropic pitch mesophase pitch
  • Pitch is partially soluble in organic solvents such as benzene, toluene, carbon disulfide and the like.
  • the pitch-based carbon material is a mixture of various compounds and includes fused polycyclic aromatics as described above.
  • the fused polycyclic aromatic group contained in the pitch-based carbon material may be a single species or a plurality of species.
  • the main component of coal pitch which is a type of pitch-based carbon material, is a condensed polycyclic aromatic.
  • the fused polycyclic aromatic ring may contain nitrogen and sulfur in addition to carbon and hydrogen in the ring. Therefore, the main component of coal pitch is considered to be a mixture of a condensed polycyclic aromatic hydrocarbon consisting of only carbon and hydrogen and a heteroaromatic compound containing nitrogen, sulfur and the like in the condensed ring.
  • the particle size of the pitch-based carbon material is not particularly limited. Moreover, when using a pitch-based carbon material as a carbon material, the particle size of sulfur is not specifically limited, either.
  • the mixing ratio of the pitch-based carbon material to sulfur is also not particularly limited, but the mixing ratio of the pitch-based carbon material to sulfur in the mixed raw material is 1: 0.5 to 1:10 in mass ratio The ratio is preferably 1: 1 to 1: 7, more preferably 1: 2 to 1: 5.
  • Sulfur-modified pitch contains multiple types of polycyclic aromatic hydrocarbons.
  • the polycyclic aromatic hydrocarbon (PAH) referred to herein is selected from the group consisting of the various pitch-based carbon materials described above and various polycyclic aromatic hydrocarbons contained in the various pitch-based carbon materials described above. Refers to at least one carbon material.
  • the diffraction conditions are the same as the above-mentioned sulfur-modified polyacrylonitrile.
  • the main peak of single sulfur was present near 22 °, and the main peak of single coal pitch was present near 26 °.
  • the peak of the sulfur-modified pitch in which the blending ratio of coal pitch to sulfur was 1: 1 was a single peak and was present around 26 °.
  • the main peak of the sulfur-modified pitch in which the blending ratio of coal pitch to sulfur is 1: 5 and the main peak of the sulfur-modified pitch in which the blending ratio of coal pitch to sulfur is 1:10 was present at around 22 °.
  • Sulfur-modified pitch is excellent in heat stability.
  • the mass loss by thermogravimetric analysis when the sulfur-modified pitch is heated from room temperature to 550 ° C. at a heating rate of 10 ° C./min is about 25% at 550 ° C.
  • the mass loss of the coal pitch is about 30% at 550 ° C.
  • elemental sulfur the mass decreases gradually from around 170 ° C., and decreases sharply above 200 ° C.
  • Coal pitch also tends not to decrease in mass, and in the vicinity of 250 ° C. to 450 ° C., coal pitch tends to be less likely to decrease in weight than sulfur-modified pitch.
  • the sulfur-modified pitch tends to be less likely to lose mass than coal pitch.
  • FIG. 1 An example of a Raman spectrum of sulfur-modified pitch is shown in FIG.
  • this Raman spectrum is measured under the same conditions as the Raman spectrum of the sulfur-modified polyacrylonitrile described above.
  • the main peak is present near 1557cm -1 of Raman shift, and, 1371cm -1 in the range of 200cm -1 ⁇ 1800cm -1, 1049cm -1 , 994cm -1, 842cm -1 , 612cm -1, 412cm -1, 354cm -1, the peak respectively is present in the vicinity of 314 cm -1.
  • These peaks are observed at similar positions even when the ratio of elemental sulfur to pitch-based carbon material is changed, and is a peak that characterizes the sulfur-modified pitch.
  • the sulfur-modified pitch contains at least one of nitrogen, oxygen, and a sulfur compound as an impurity.
  • sulfur-based positive electrode active materials used in the positive electrode of the present invention include the above-mentioned polysulfur carbon, single sulfur, sulfur-modified polycyclic aromatic hydrocarbon, sulfur-modified rubber, plant materials such as coffee beans and seaweed, and sulfur. What was heat-treated, or these composites etc. can be mentioned. These sulfur-based positive electrode active materials have carbon skeletons derived from the various carbon materials described above.
  • polyacrylonitrile in terms of cycle characteristics and capacity
  • pitch-based carbon material in terms of cost.
  • sulfur-modified polyacrylonitrile and sulfur-modified pitch may be used in combination.
  • a mixed material obtained by mixing the above-described sulfur-based positive electrode active material (i.e., carbon material and sulfur) and the conductive material is heated.
  • the mixed material may be mixed by a general mixing device such as a mortar or a ball mill.
  • the mixed raw material one obtained by simply mixing sulfur, a carbon material and a conductive material may be used, but for example, the mixed raw material may be formed into a pellet and used.
  • the heat treatment step may be performed in a closed system or an open system, but in order to suppress the dissipation of sulfur vapor, the closed system is preferable.
  • the heat treatment step is not particularly limited as to the atmosphere, it is preferably performed in an atmosphere which does not prevent the bond between the carbon material and the sulfur (for example, an atmosphere containing no hydrogen or a non-oxidizing atmosphere).
  • an atmosphere which does not prevent the bond between the carbon material and the sulfur for example, an atmosphere containing no hydrogen or a non-oxidizing atmosphere.
  • hydrogen is present in the atmosphere, sulfur in the reaction system reacts with hydrogen to form hydrogen sulfide, which may result in loss of sulfur in the reaction system.
  • the non-oxidative atmosphere referred to here includes a reduced pressure state where the oxygen concentration is low to such an extent that the oxidation reaction does not proceed, an inert gas atmosphere such as nitrogen and argon, a sulfur gas atmosphere and the like.
  • the mixed raw material is placed in a container in which the sealing property is maintained to such an extent that the sulfur vapor is not dissipated. Then, the inside of the container may be decompressed or heated to an inert gas atmosphere. In addition, you may heat in the state vacuum-packed with the material (for example, aluminum laminate film etc.) which is hard to react with a sulfur raw material.
  • the packaged raw material is placed in a pressure container such as an autoclave containing water and heated so that the packaging material is not damaged by the generated sulfur vapor, and the generated steam is added from the outside of the packaging material It is preferable to press. According to this method, since the steam is pressurized by steam from the outside of the packaging material, the sulfur vapor prevents the packaging material from being blown and broken.
  • the heating time of the mixed raw material in the heat treatment step may be appropriately set according to the heating temperature, and is not particularly limited.
  • the above-described preferable heating temperature may be a temperature at which bonding between sulfur and the carbon material proceeds and the conductive material does not deteriorate.
  • the heating temperature is preferably 250 or more and 500 ° C. or less, more preferably 250 or more and 400 ° C. or less, and still more preferably 250 or more and 300 ° C. or less.
  • the heating temperature is preferably 200 ° C. to 600 ° C., more preferably 300 ° C. to 500 ° C., and 350 ° C. to 500 ° C. Is more preferred.
  • a pitch-based carbon material is used as the carbon material, at least a portion of the pitch-based carbon material and at least a portion of sulfur become liquid in the heat treatment step.
  • the contact area of the pitch-based carbon material and sulfur in the heat treatment step is large, the pitch-based carbon material and sulfur are sufficiently bonded, and the detachment of sulfur from the sulfur-based positive electrode active material is suppressed.
  • sulfur is preferably refluxed.
  • the mixed material may be heated so that a part of the mixed material becomes a gas and a part becomes a liquid.
  • the temperature of the mixed raw material may be a temperature higher than the temperature at which sulfur is vaporized.
  • vaporization refers to phase change of sulfur from liquid or solid to gas, which may be boiling, evaporation or sublimation.
  • the melting point of alpha sulfur is 112.8 ° C
  • the melting point of beta sulfur is 119.6 ° C
  • gamma sulfur monoclinic sulfur
  • the melting point of is 106.8 ° C.
  • the boiling point of sulfur is 444.7.degree.
  • the step of removing elemental sulfur from the object to be treated (sulfur-based positive electrode active material-carbon material composite) after the heat treatment step (elementary sulfur removing step)
  • the adverse effect of the above-mentioned elemental sulfur can be suppressed.
  • the object to be treated after the heat treatment step is heated at 200 ° C. to 250 ° C. while reducing pressure.
  • the object to be treated may be used as it is as a sulfur-based positive electrode active material.
  • the target after the single sulfur removing step may be used as the sulfur-based positive electrode active material.
  • the positive electrode of the present invention is manufactured by the above-described manufacturing method of the present invention, and contains a sulfur-based positive electrode active material and a conductive material.
  • the Raman spectrum of the positive electrode shows peaks derived from the sulfur-modified polyacrylonitrile shown in FIG.
  • the peak derived from the sulfur-modified pitch shown in FIG. 4 is observed together with other peaks.
  • the positive electrode can have the same structure as that of a general lithium ion secondary battery positive electrode except for the positive electrode active material and the conductive material.
  • the positive electrode of the present invention is a current collector comprising a mixture of a sulfur-based positive electrode active material and a conductive material (that is, an object to be treated obtained by the heat treatment step), a conductive additive, a binder, and a solvent. It can be manufactured by applying to Alternatively, the mixed raw material in which the sulfur powder, the carbon material powder and the conductive material powder are mixed may be filled in the current collector for the positive electrode and then heated (the heat treatment step may be performed).
  • a mixture of the sulfur-based positive electrode active material and the conductive material can be manufactured, and at the same time, the mixture and the current collector can be integrated without using a binder. If a binder is not used, the amount of positive electrode active material per positive electrode mass can be increased, and the capacity per positive electrode mass can be improved.
  • the positive electrode contains a conductive material.
  • the content ratio of the sulfur-based positive electrode active material to the conductive material in the positive electrode is preferably 10: 0.1 to 10: 5 by mass ratio, and more preferably 10: 0.3 to 10: 2 .
  • vapor grown carbon fiber As the conductive aid, vapor grown carbon fiber (VGCF), carbon powder, carbon black (CB), acetylene black (AB), ketjen black (KB), graphite, aluminum, titanium, etc.
  • VGCF vapor grown carbon fiber
  • CB carbon black
  • AB acetylene black
  • KB ketjen black
  • graphite aluminum, titanium, etc.
  • fine powder of metal stable at positive electrode potential is exemplified.
  • fine powder of metal stable at positive electrode potential is exemplified.
  • blend a conductive support agent depending on the kind and compounding quantity of a conductive material, it may not be necessary to mix
  • polyvinylidene fluoride PolyVinylidene DiFluoride: PVDF
  • PVDF polytetrafluoroethylene
  • SBR styrene-butadiene rubber
  • PI polyimide
  • PAI polyamidoimide
  • CMC carboxymethylcellulose
  • PVC vinyl (PVC), methacrylic resin (PMA), polyacrylonitrile (PAN), modified polyphenylene oxide (PPO), polyethylene oxide (PEO), polyethylene (PE), polypropylene (PP) and the like.
  • the solvent examples include N-methyl-2-pyrrolidone, N, N-dimethylformaldehyde, alcohol, water and the like.
  • These conductive aids, binders and solvents may be used in combination of two or more.
  • the compounding amount of these materials is not particularly limited, for example, it is preferable to mix about 20 to 100 parts by mass of the conductive aid and about 10 to 20 parts by mass of the binder with respect to 100 parts by mass of the sulfur-based positive electrode active material.
  • a mixture of the sulfur-based positive electrode active material of the present invention and the above-mentioned conductive additive and binder is kneaded with a mortar or press and made into a film, and the film-like mixture is collected with a press or the like.
  • the positive electrode for a lithium ion secondary battery of the present invention can also be produced by pressure bonding to a current collector.
  • What is generally used for the positive electrode for lithium ion secondary batteries may be used as a collector.
  • a current collector aluminum foil, aluminum mesh, punching aluminum sheet, aluminum expanded sheet, stainless steel foil, stainless steel mesh, punching stainless steel sheet, stainless steel expanded sheet, foamed nickel, nickel non-woven fabric, copper foil, copper mesh , A punched copper sheet, a copper expanded sheet, a titanium foil, a titanium mesh, a carbon non-woven fabric, a carbon woven fabric and the like.
  • a carbon nonwoven fabric / woven fabric current collector made of carbon having a high degree of graphitization is suitable as a current collector for a sulfur-based positive electrode active material because it does not contain hydrogen and has low reactivity with sulfur.
  • various pitches that is, by-products such as petroleum, coal, coal tar, etc.
  • lithium ion secondary battery (Lithium ion secondary battery)
  • a lithium ion secondary battery using the positive electrode of the present invention is simply abbreviated as a lithium ion secondary battery.
  • the positive electrode is as described above.
  • Electrode As a negative electrode material, elements which can be alloyed with lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Materials having at least one of Si, Ge, Sn, Pb, Sb, Bi and / or compounds thereof, known metallic lithium, carbon-based materials such as graphite, silicon-based materials such as silicon thin film, copper-tin and cobalt- Alloy materials such as tin can be used.
  • a carbon-based material, a silicon-based material, an alloy-based material or the like is used as the negative electrode material, for example, a material not containing lithium, for example, among the above-described negative electrode materials, short circuit between positive and negative electrodes due to generation of dendrite hardly occurs It is advantageous in point.
  • these negative electrode materials not containing lithium are used in combination with the positive electrode of the present invention, neither the positive electrode nor the negative electrode contains lithium. Therefore, a lithium pre-doping process is required in which lithium is inserted in advance into one or both of the negative electrode and the positive electrode.
  • a known method may be used as the lithium pre-doping method.
  • the electrolytic doping method is a method of forming a half cell using metallic lithium as a counter electrode and electrochemically doping lithium on a negative electrode.
  • the bonding pre-doping method is a method in which a metal lithium foil is bonded to an electrode, then left in an electrolytic solution, and lithium is inserted into the negative electrode using diffusion of lithium to the electrode.
  • the above-described electrolytic doping method can be used also in the case of pre-doping lithium to the positive electrode.
  • a negative electrode material not containing lithium it is particularly preferable to use a silicon-based material which is a high capacity negative electrode material, and among them, it is more preferable to use thin film silicon which has a thin electrode thickness and which is advantageous in capacity per volume. preferable.
  • Electrolyte As an electrolyte used for a lithium ion secondary battery, what melt
  • the organic solvent it is preferable to use at least one selected from non-aqueous solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl ether, gamma-butyrolactone and acetonitrile.
  • the electrolyte LiPF 6 , LiBF 4 , LiAsF 6 , LiCF 3 SO 3 , LiI, LiClO 4 or the like can be used.
  • the concentration of the electrolyte may be about 0.5 mol / l to 1.7 mol / l.
  • the electrolyte is not limited to liquid.
  • the electrolyte is in a solid state (for example, in the form of polymer gel).
  • a lithium ion secondary battery may be equipped with members, such as a separator, besides the negative electrode mentioned above, a positive electrode, and electrolyte.
  • the separator is interposed between the positive electrode and the negative electrode, allows movement of ions between the positive electrode and the negative electrode, and prevents an internal short circuit between the positive electrode and the negative electrode. If the lithium ion secondary battery is a closed type, the separator is also required to have a function of holding the electrolytic solution.
  • the separator it is preferable to use a thin, microporous or non-woven membrane made of polyethylene, polypropylene, polyacrylonitrile, aramid, polyimide, cellulose, glass or the like.
  • the shape of the lithium ion secondary battery is not particularly limited, and may be various shapes such as a cylindrical shape, a laminated shape, and a coin shape.
  • the positive electrode, the method for producing a positive electrode, and the lithium ion secondary battery of the present invention will be specifically described below.
  • Example 1 Mixed raw material As a sulfur powder, when it classified using a sieve, the thing used as a particle size of 50 micrometers or less was prepared.
  • As the polyacrylonitrile powder one having a particle diameter in the range of 0.2 ⁇ m to 2 ⁇ m as prepared by an electron microscope was prepared.
  • As a conductive material La 2 S 3 having a particle size of 50 ⁇ m or less when classified using a sieve was prepared.
  • the reaction device 1 comprises a reaction container 2, a lid 3, a thermocouple 4, an alumina protective tube 40, two alumina tubes (gas inlet tube 5, gas outlet tube 6), argon gas It has a piping 50, a gas tank 51 containing argon gas, a trap piping 60, a trap tank 62 containing an aqueous sodium hydroxide solution 61, an electric furnace 7, and a temperature controller 70 connected to the electric furnace.
  • reaction vessel 2 a bottomed cylindrical glass tube (made of quartz glass) was used.
  • the mixed raw material 9 was accommodated in the reaction container 2 in the heat treatment process mentioned later.
  • the opening of the reaction vessel 2 was closed by a glass lid 3 having three through holes.
  • An alumina protective tube 40 (alumina SSA-S, manufactured by Nikkato Co., Ltd.) containing a thermocouple 4 was attached to one of the through holes.
  • a gas introduction pipe 5 (alumina SSA-S, manufactured by Nikkato Co., Ltd.) was attached to the other one of the through holes.
  • a gas exhaust pipe 6 (alumina SSA-S, manufactured by Nikkato Co., Ltd.) was attached to the remaining one of the through holes.
  • the reaction vessel 2 had an outer diameter of 60 mm, an inner diameter of 50 mm, and a length of 300 mm.
  • the alumina protective tube 40 had an outer diameter of 4 mm, an inner diameter of 2 mm, and a length of 250 mm.
  • the gas introduction pipe 5 and the gas discharge pipe 6 had an outer diameter of 6 mm, an inner diameter of 4 mm, and a length of 150 mm.
  • the tips of the gas introduction pipe 5 and the gas discharge pipe 6 were exposed to the outside of the lid 3 (in the reaction vessel 2). The length of this exposed portion was 3 mm.
  • the tips of the gas introduction pipe 5 and the gas discharge pipe 6 become almost 100 ° C. or less in the heat treatment step described later. For this reason, the sulfur vapor generated in the heat treatment step does not flow out from the gas introduction pipe 5 and the gas discharge pipe 6 and is returned (refluxed) to the reaction vessel 2.
  • thermocouple 4 placed in the alumina protective tube 40 indirectly measured the temperature of the mixed raw material 9 in the reaction vessel 2.
  • the temperature measured by the thermocouple 4 was fed back to the temperature controller 70 of the electric furnace 7.
  • An argon gas pipe 50 was connected to the gas introduction pipe 5.
  • the argon gas pipe 50 was connected to a gas tank 51 containing argon gas.
  • One end of a trap pipe 60 was connected to the gas discharge pipe 6.
  • the other end of the trap pipe 60 was inserted into the sodium hydroxide aqueous solution 61 in the trap tank 62.
  • the trap pipe 60 and the trap tank 62 are traps of hydrogen sulfide gas generated in a heat treatment process described later.
  • the object to be treated after the heat treatment step was crushed in a mortar. Two grams of the ground material was placed in a glass tube oven and heated at 250 ° C. for 3 hours with vacuum suction. The temperature rising temperature at this time was 10 ° C./min.
  • the single sulfur remaining on the object to be treated after the heat treatment step is evaporated and removed, and a sulfur-based positive electrode active material-conductive material composite which does not contain (or almost does not contain) single sulfur is obtained.
  • Positive electrode A mixture of 3 mg of a sulfur-based positive electrode active material-conductive material composite, 2.7 mg of acetylene black and 0.3 mg of polytetrafluoroethylene (PTFE) in an agate mortar to form a film while adding an appropriate amount of hexane It knead
  • the whole amount of the positive electrode material was press-bonded to a 14 mm-diameter circular punched aluminum mesh (mesh roughness # 100) with a press, and dried overnight at 80 ° C. In this step, the positive electrode for a lithium ion secondary battery of Example 1 was obtained.
  • the conductive material in this positive electrode was La 2 S 3 , and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 0.6.
  • Negative Electrode As a negative electrode, metal lithium foil (disk-shaped 14 mm in diameter and 500 ⁇ m thick, made of Honjo Metal) was used.
  • Electrolyte As the electrolyte, a non-aqueous electrolyte in which LiPF 6 was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate was used. Ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1. The concentration of LiPF 6 in the electrolyte was 1.0 mol / l.
  • [4] Battery A coin battery was manufactured using the positive electrode and the negative electrode obtained in [1] and [2]. More specifically, in a dry room, a separator (Celgard 2400, 25 ⁇ m thick polypropylene microporous membrane) and a glass non-woven filter (440 ⁇ m thick, ADVANTEC, GA 100) between the positive electrode and the negative electrode in a dry room The electrode battery was used as an electrode battery.
  • the electrode battery was housed in a battery case (CR2032 type coin battery member manufactured by Takasen Co., Ltd.) consisting of a stainless steel container.
  • the electrolytic solution obtained in [3] was injected into the battery case.
  • the battery case was sealed with a caulking machine to obtain the lithium ion secondary battery of Example 1.
  • Example 2 The method of manufacturing the positive electrode of Example 2 is the same as the method of manufacturing the positive electrode of Example 1 except that a mixture of 5 g of sulfur powder, 1 g of polyacrylonitrile powder, and 0.3 g of conductive material powder is used as a mixed material. It is.
  • the mass ratio of polyacrylonitrile to the conductive material in the mixed raw material was 1: 0.3.
  • the conductive material in the positive electrode of Example 2 was La 2 S 3 as in Example 1, and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 1.8.
  • the lithium ion secondary battery of Example 2 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 2 is used.
  • Example 3 The method of manufacturing the positive electrode of Example 3 is the same as the method of manufacturing the positive electrode of Example 1 except that a mixture of 5 g of sulfur powder, 1 g of polyacrylonitrile powder, and 0.5 g of conductive material powder is used as the mixed raw material. It is. In the manufacturing method of Example 3, the mass ratio of polyacrylonitrile to the conductive material in the mixed raw material was 1: 0.5.
  • the conductive material in the positive electrode of Example 3 was La 2 S 3 as in Examples 1 and 2, and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 2.9. .
  • the lithium ion secondary battery of Example 3 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 3 is used.
  • Example 4 The manufacturing method of the positive electrode of Example 4 is an example except that a mixture of 5 g of sulfur powder, 1 g of polyacrylonitrile powder and 0.1 g of conductive material powder was used as the mixed material and TiS 2 was used as the mixed material. It is the same as the manufacturing method of the positive electrode of 1.
  • the mass ratio of polyacrylonitrile to the conductive material in the mixed raw material was 1: 0.1.
  • the conductive material in the positive electrode of Example 4 was TiS 2 , and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 0.6.
  • the lithium ion secondary battery of Example 4 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 4 is used.
  • Example 5 The manufacturing method of the positive electrode of Example 5 uses Sm 2 S 3 as the conductive material and uses a mixture of 5 g of sulfur powder, 1 g of polyacrylonitrile powder and 0.1 g of conductive material powder as the mixed raw material. It is the same as the method of manufacturing the positive electrode of Example 1. In the manufacturing method of Example 5, the mass ratio of polyacrylonitrile to the conductive material in the mixed raw material was 1: 0.1. The conductive material in the positive electrode of Example 5 was Sm 2 S 3 , and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 0.6. The lithium ion secondary battery of Example 5 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 5 is used.
  • Example 6 The manufacturing method of the positive electrode of Example 6 uses Ce 2 S 3 as the conductive material and uses a mixture of 5 g of sulfur powder, 1 g of polyacrylonitrile powder and 0.1 g of conductive material powder as mixed raw materials. It is the same as the method of manufacturing the positive electrode of Example 1. In the manufacturing method of Example 6, the mass ratio of polyacrylonitrile to the conductive material in the mixed raw material was 1: 0.1.
  • the conductive material in the positive electrode of Example 6 was Ce 2 S 3 , and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 0.6.
  • the lithium ion secondary battery of Example 6 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 6 is used.
  • Example 7 The manufacturing method of the positive electrode of Example 7 used a mixture of 5 g of sulfur powder, 1 g of polyacrylonitrile powder, and 0.1 g of conductive material material powder as a mixed raw material using unsulfurized Ti as a conductive material. It is the same as the method of manufacturing the positive electrode of Example 1. In the manufacturing method of Example 7, the mass ratio of polyacrylonitrile to the conductive material in the mixed raw material was 1: 0.1.
  • the conductive material in the positive electrode of Example 7 was TiS 2 , and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 0.6.
  • the lithium ion secondary battery of Example 7 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 7 was used.
  • Example 8 The method of manufacturing the positive electrode of Example 8 uses TiS 2 as the conductive material, 5 g of sulfur powder as the mixed raw material, 1 g of coal pitch powder (isotropic pitch, CAS number 65996-93-2) and 0 of the conductive material powder.
  • the method of manufacturing the positive electrode of Example 1 is the same as that of Example 1 except that the electrode is dried under a vacuum at 200 ° C. for 3 hours using a mixture with .1 g.
  • the mass ratio of the pitch-based carbon material to the conductive material in the mixed raw material was 1: 0.1.
  • the conductive material in the positive electrode of Example 8 was TiS 2 , and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 0.5.
  • the lithium ion secondary battery of Example 8 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 8 was used.
  • Example 9 The method of manufacturing the positive electrode of Example 9 is an example except that a mixture of 5 g of sulfur powder, 1 g of polyacrylonitrile powder and 0.1 g of conductive material powder is used as the mixed material and MoS 2 is used. It is the same as the manufacturing method of the positive electrode of 1.
  • the mass ratio of polyacrylonitrile to the conductive material in the mixed raw material was 1: 0.1.
  • the conductive material in the positive electrode of Example 9 was MoS 2 and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 0.6.
  • the lithium ion secondary battery of Example 9 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 9 is used.
  • the method of manufacturing the positive electrode of the comparative example is the same as the method of manufacturing the positive electrode of Example 1 except that the conductive material is not used.
  • the positive electrode of the comparative example is the same as the positive electrode of Example 1 except that the conductive material is not contained.
  • the lithium ion secondary battery of the comparative example is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of the comparative example was used.
  • the main diffraction peak positions of La 2 S 3 according to ASTM card are 24.7, 25.1, 26.9, 33.5, 37.2, 42.8 ° and so on.
  • the main diffraction peak positions of TiS 2 are 15.5, 34.2, 44.1, 53.9 ° and so on.
  • the main diffraction peak positions of Ti are 35.1, 38.4, 40.2, 53.0 degrees and so on.
  • the main diffraction peak positions of MoS 2 are 14.4, 32.7, 33.5, 35.9, 39.6, 44.2, 49.8, 56.0, 58.4 ° and so on.
  • the main diffraction peak positions of Fe are 44.7, 65.0, 82.3 ° and so on. As shown in FIG.
  • the diffraction angle (2 ⁇ ) is in the range of 20 to 30 °, around 25 ° A broad single peak is observed.
  • a peak derived from the conductive material appears. For example, as shown in FIGS. 6 and 7, when La 2 S 3 is used as the conductive material, peaks of La 2 S 3 appear around 24.7, 25.1, 33.5, and 37.2 °. This peak can be confirmed using the La 2 S 3 as conductive material (i.e. the positive electrode contains La 2 S 3 as conductive material). Further, as shown in FIG.
  • FIGS. 13 and 14 show the first embodiment
  • FIG. 15 shows the second embodiment
  • FIG. 16 shows the third embodiment
  • FIG. 17 shows the fourth embodiment
  • FIGS. 18 and 19 show the fifth embodiment
  • FIGS. , 23 is Example 7,
  • FIGS. 24, 25 are Example 8
  • FIGS. 26, 27 are Example 9, and
  • FIG. 28 is a lithium ion secondary battery of Comparative Example.
  • the graphs of FIGS. 13, 18, 20, 22, 24 are charge / discharge curves
  • the graphs of FIGS. 14-17, 19, 21, 23, 25, 27, 28 show cycle characteristics.
  • the discharge capacity at 2 C is 350 to 400 mAh / g, and the discharge capacity at 5 C is about 120 to 150 mAh / g Met.
  • the discharge capacity at 2 C is 500 mAh /
  • the discharge capacity at 5 C exceeding g also showed a very high value of about 250 mAh / g.
  • the discharge rate characteristics of the lithium ion secondary battery using the sulfur-based positive electrode active material can be improved by blending the conductive material with the positive electrode material. Furthermore, as shown in FIG. 14, the decrease in capacity was hardly observed even after 28 cycles (0.1 C) by using the sulfur-based positive electrode active material. From these results, it can be said that the positive electrode for a lithium ion secondary battery of the present invention in which the sulfur-based positive electrode active material and the conductive material are used in combination is excellent in discharge rate characteristics and cycle characteristics.
  • the lithium ion secondary battery of Example 1 blended with 0.1 parts by mass of the conductive material per 1 part by mass of polyacrylonitrile and the lithium of Example 2 blended with 0.3 parts by mass of the conductive material
  • the discharge rate characteristic is Example 1> Example 2 It was Example 3. This is because the capacity of the conductive material is lower than that of the sulfur-based positive electrode active material, or the conductive material is inactive as an active material of a lithium ion secondary battery, so a large amount of the conductive material is blended to make the positive electrode active.
  • the preferable blending ratio of the conductive material is in the range of 0.1 to 0.3 parts by mass of the conductive material with respect to 1 part by mass of the sulfur-based positive electrode active material. I understand that.
  • the lithium ion secondary battery of Example 4 using TiS 2 as the conductive material (FIG. 17)
  • the lithium ion secondary battery of Example 5 using Sm 2 S 3 as the conductive material (FIG. 19)
  • the discharge capacity at 2 C exceeded 500 mAh / g, and the discharge rate characteristics were excellent.
  • the discharge capacity at 2 C was about 500 mAh / g for the lithium ion secondary battery of Example 7 (FIG. 23) using Ti as the conductive material. From this result, it is understood that the discharge rate characteristics of the lithium ion secondary battery can be improved even if non-sulfide is used as the conductive material. It is considered that this is because unsulfided Ti reacts with sulfur in the heat treatment step to be sulfurized.
  • the lithium ion secondary battery of Example 4 (FIG. 17) using TiS 2 as the conductive material is more discharged than the lithium ion secondary battery (FIG. 23) of Example 7 using Ti as the conductive material. Excellent rate characteristics. From this result, it is understood that metal sulfide is more preferably used as the conductive material.
  • the lithium ion secondary battery of Example 8 using sulfur-modified pitch as a sulfur-based positive electrode active material is a lithium ion secondary battery of Example 4 using sulfur-modified polyacrylonitrile as a sulfur-based positive electrode active material.
  • the capacity itself is lower than that of the battery (FIG. 17)
  • the decrease in discharge capacity from 0.1 C to around 2.0 C is small by blending the conductive material. Therefore, even when using sulfur-modified pitch as the sulfur-based positive electrode active material, it is understood that the discharge rate characteristics can be enhanced by using the sulfur-based positive electrode active material and the conductive material in combination.
  • Lithium ion secondary batteries using sulfur-modified pitch as the positive electrode active material have less capacity and are inferior in cycle characteristics to lithium ion secondary batteries using sulfur-modified polyacrylonitrile as the positive electrode active material. It exhibits much better cycle characteristics as compared to lithium ion secondary batteries using elemental sulfur as the substance. Furthermore, in the lithium ion secondary battery (FIG. 27) of Example 9 in which MoS 2 as the conductive material is blended in the positive electrode material (specifically, the mixed raw material), the discharge capacity at 2 C exceeds 500 mAh / g, 5 C The discharge capacity also showed a very high value of about 200 mAh / g. From these results, it is understood that when MoS 2 is used as the conductive material, the discharge rate characteristics of the lithium ion secondary battery can be improved to the same extent as when La 2 S 3 is used as the conductive material.
  • the positive electrode of the present invention can improve the cycle characteristics and the discharge rate characteristics of the lithium ion secondary battery. Further, it can be seen that the lithium ion secondary battery of the present invention exhibits excellent cycle characteristics and discharge rate characteristics. Furthermore, according to the manufacturing method of the positive electrode of this invention, it turns out that the positive electrode which can improve the cycling characteristics and discharge rate characteristic of a lithium ion secondary battery can be manufactured.
  • Reactor 2 Reaction container 3: Lid 4: Thermocouple 5: Gas inlet pipe 6: Gas outlet pipe 7: Electric furnace

Abstract

Disclosed is a positive electrode containing a sulfur-based positive electrode active substance and capable of increasing discharge rate characteristics and the cycle characteristics of lithium ion secondary batteries. The positive electrode for lithium ion secondary batteries contains a sulfur-based positive electrode active substance which contains carbon (C) and sulfur (S), and a conductive material which contains sulfur (S), wherein at least one part of said conductive material is a sulfide of at least one metal selected from the group consisting of the fourth-period metals, fifth-period metals, sixth-period metals, and rare earth elements.

Description

リチウムイオン二次電池用正極、リチウムイオン二次電池およびリチウムイオン二次電池用正極の製造方法、ならびに車両Method of manufacturing positive electrode for lithium ion secondary battery, lithium ion secondary battery and positive electrode for lithium ion secondary battery, and vehicle
　本発明は、硫黄系正極活物質を含有するリチウムイオン二次電池用正極、この正極を用いたリチウムイオン二次電池、および、この正極を製造する方法、ならびに車両に関する。 The present invention relates to a positive electrode for a lithium ion secondary battery containing a sulfur-based positive electrode active material, a lithium ion secondary battery using the positive electrode, a method for producing the positive electrode, and a vehicle.
　非水電解質二次電池の一種であるリチウムイオン二次電池は、充放電容量の大きな電池であり、主として携帯電子機器用の電池として用いられている。また、リチウムイオン二次電池は、電気自動車用の電池としても期待されている。 Lithium ion secondary batteries, which are a type of non-aqueous electrolyte secondary battery, are batteries with large charge and discharge capacities, and are mainly used as batteries for portable electronic devices. In addition, lithium ion secondary batteries are also expected as batteries for electric vehicles.
　リチウムイオン二次電池の正極活物質としては、コバルトやニッケル等のレアメタルを含有するものが一般的である。しかし、これらの金属は流通量が少なく高価であるため、近年では、これらのレアメタルにかわる物質を用いた正極活物質が求められている。 As a positive electrode active material of a lithium ion secondary battery, what contains rare metals, such as cobalt and nickel, is common. However, since these metals have low flow rates and are expensive, in recent years, positive electrode active materials using materials that replace these rare metals are being sought.
　リチウムイオン二次電池の正極活物質として、硫黄を用いる技術が知られている。硫黄を正極活物質として用いることで、リチウムイオン二次電池の充放電容量を大きくできる。例えば、硫黄を正極活物質として用いたリチウムイオン二次電池の充放電容量は、一般的な正極材料であるコバルト酸リチウム正極材料を用いたリチウムイオン二次電池の充放電容量の約６倍である。 A technology using sulfur as a positive electrode active material of a lithium ion secondary battery is known. By using sulfur as a positive electrode active material, the charge and discharge capacity of the lithium ion secondary battery can be increased. For example, the charge and discharge capacity of a lithium ion secondary battery using sulfur as a positive electrode active material is about 6 times the charge and discharge capacity of a lithium ion secondary battery using a lithium cobaltate positive electrode material which is a general positive electrode material is there.
　しかし、正極活物質として単体硫黄を用いたリチウムイオン二次電池においては、放電時に硫黄とリチウムとの化合物が生成する。この硫黄とリチウムとの化合物は、リチウムイオン二次電池の非水系電解液（例えば、エチレンカーボネートやジメチルカーボネート等）に可溶である。このため、正極活物質として硫黄を用いたリチウムイオン二次電池は、充放電を繰り返すと、硫黄の電解液への溶出により次第に劣化し、電池容量が低下する問題がある。以下、充放電の繰り返しに伴って充放電容量が低下するリチウムイオン二次電池の特性を「サイクル特性」と呼ぶ。この充放電容量低下の小さいリチウムイオン二次電池はサイクル特性に優れる。また、この充放電容量低下の大きなリチウムイオン二次電池はサイクル特性に劣る。 However, in a lithium ion secondary battery using elemental sulfur as a positive electrode active material, a compound of sulfur and lithium is formed during discharge. The compound of sulfur and lithium is soluble in the non-aqueous electrolyte solution (for example, ethylene carbonate, dimethyl carbonate, etc.) of the lithium ion secondary battery. For this reason, a lithium ion secondary battery using sulfur as a positive electrode active material has a problem that when charge and discharge are repeated, the elution of the sulfur into the electrolytic solution gradually deteriorates and the battery capacity decreases. Hereinafter, the characteristics of the lithium ion secondary battery in which the charge and discharge capacity decreases with repetition of charge and discharge are referred to as “cycle characteristics”. The lithium ion secondary battery having a small decrease in charge and discharge capacity is excellent in cycle characteristics. Further, the lithium ion secondary battery having a large decrease in charge and discharge capacity is inferior in cycle characteristics.
　サイクル特性を向上させるため、硫黄を含む正極活物質（以下、硫黄系正極活物質と呼ぶ）に炭素材料を配合する技術が提案されている（例えば、特許文献１参照）。 In order to improve cycle characteristics, a technique has been proposed in which a carbon material is mixed with a positive electrode active material containing sulfur (hereinafter referred to as a sulfur-based positive electrode active material) (see, for example, Patent Document 1).
　特許文献１には、ポリ硫化カーボンを正極活物質として用いる技術が紹介されている。このポリ硫化カーボンは、炭素と硫黄とを主な構成要素とする。具体的には、このポリ硫化カーボンは直鎖状不飽和ポリマーに硫黄が付加されたものである。炭素材料によって電解液への硫黄の溶出を抑制でき、リチウムイオン二次電池のサイクル特性が向上すると考えられる。 Patent Document 1 introduces a technology that uses polysulfide carbon as a positive electrode active material. This polysulfide carbon has carbon and sulfur as main components. Specifically, this polysulfurized carbon is one in which sulfur is added to a linear unsaturated polymer. It is considered that the carbon material can suppress the elution of sulfur into the electrolytic solution and improve the cycle characteristics of the lithium ion secondary battery.
　本発明の発明者等は、ポリアクリロニトリルと硫黄との混合物を熱処理して得られる正極活物質を発明した（特許文献２参照）。この正極活物質を正極に用いたリチウムイオン二次電池の充放電容量は大きく、かつ、この正極活物質を正極に用いたリチウムイオン二次電池はサイクル特性に優れる。 The inventors of the present invention invented a positive electrode active material obtained by heat-treating a mixture of polyacrylonitrile and sulfur (see Patent Document 2). The charge and discharge capacity of a lithium ion secondary battery using this positive electrode active material as a positive electrode is large, and a lithium ion secondary battery using this positive electrode active material as a positive electrode is excellent in cycle characteristics.
　しかしその一方で、上述したポリアクリロニトリルや直鎖状不飽和ポリマーを炭素材料として用いた正極活物質は、電気的に高抵抗であり、放電レート特性（所謂Ｃレート）が充分でない問題があった。 However, on the other hand, the positive electrode active material using the polyacrylonitrile or linear unsaturated polymer as the carbon material has a problem that the electrical resistance is high and the discharge rate characteristic (so-called C rate) is not sufficient. .
特開２００２－１５４８１５号公報Japanese Patent Application Laid-Open No. 2002-154815 国際公開第２０１０／０４４４３７号WO 2010/044437
　本発明は上記事情に鑑みてなされたものであり、硫黄系正極活物質を含有しリチウムイオン二次電池のサイクル特性および放電レート特性を向上させ得る正極およびリチウムイオン二次電池を提供することを目的とする。 The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a positive electrode and a lithium ion secondary battery which contain a sulfur-based positive electrode active material and can improve cycle characteristics and discharge rate characteristics of the lithium ion secondary battery. To aim.
　上記課題を解決する本発明のリチウムイオン二次電池用正極は、炭素（Ｃ）および硫黄（Ｓ）を含有する硫黄系正極活物質と、硫黄（Ｓ）を含有する伝導材と、を含有し、該伝導材の少なくとも一部は、第４周期金属、第５周期金属、第６周期金属および希土類元素からなる群から選ばれる少なくとも一種の金属の硫化物からなることを特徴とする。 The positive electrode for a lithium ion secondary battery of the present invention, which solves the above problems, contains a sulfur-based positive electrode active material containing carbon (C) and sulfur (S), and a conductive material containing sulfur (S). At least a part of the conductive material is made of sulfide of at least one metal selected from the group consisting of a fourth period metal, a fifth period metal, a sixth period metal and a rare earth element.
　上記課題を解決する本発明のリチウムイオン二次電池は、炭素（Ｃ）と硫黄（Ｓ）とを含有する硫黄系正極活物質と、硫黄（Ｓ）を含有する伝導材と、を含有し、該伝導材の少なくとも一部は、第４周期金属、第５周期金属、第６周期金属および希土類元素からなる群から選ばれる少なくとも一種の金属の硫化物からなるリチウムイオン二次電池用正極を用いていることを特徴とする。また、上記課題を解決する本発明の車両は、本発明のリチウムイオン二次電池を搭載していることを特徴とする。 The lithium ion secondary battery of the present invention for solving the above problems contains a sulfur-based positive electrode active material containing carbon (C) and sulfur (S), and a conductive material containing sulfur (S), At least a part of the conductive material is a positive electrode for a lithium ion secondary battery comprising a sulfide of at least one metal selected from the group consisting of a fourth period metal, a fifth period metal, a sixth period metal and a rare earth element It is characterized by Further, a vehicle according to the present invention for solving the above-mentioned problems is characterized in that the lithium ion secondary battery according to the present invention is mounted.
　上記課題を解決する本発明の第１のリチウムイオン二次電池用正極の製造方法は、炭素（Ｃ）と硫黄（Ｓ）とを含有する硫黄系正極活物質を含有するリチウムイオン二次電池用正極を製造する方法であって、炭素材料と、硫黄と、硫黄を含有する伝導材材料と、を含有する混合原料を加熱する熱処理工程を含み、該伝導材材料は、第４周期金属、第５周期金属、第６周期金属および希土類元素からなる群から選ばれる少なくとも一種の金属の硫化物であることを特徴とする。 The first method for producing a positive electrode for a lithium ion secondary battery of the present invention, which solves the above problems, is a lithium ion secondary battery containing a sulfur-based positive electrode active material containing carbon (C) and sulfur (S) A method of manufacturing a positive electrode, comprising a heat treatment step of heating a mixed material containing a carbon material, sulfur, and a conductive material containing sulfur, wherein the conductive material includes a fourth period metal, a fourth period metal, It is characterized in that it is a sulfide of at least one metal selected from the group consisting of a five period metal, a sixth period metal and a rare earth element.
　上記課題を解決する本発明の第２のリチウムイオン二次電池用正極の製造方法は、炭素（Ｃ）および硫黄（Ｓ）を含有する硫黄系正極活物質を含有するリチウムイオン二次電池用正極を製造する方法であって、炭素材料と、硫黄と、硫黄を含有しない伝導材材料と、を含有する混合原料を加熱する熱処理工程を含み、該伝導材材料は、第４周期金属、第５周期金属、第６周期金属および希土類元素からなる群から選ばれる少なくとも一種の金属であることを特徴とする。 A second method for producing a positive electrode for a lithium ion secondary battery of the present invention which solves the above-mentioned problems comprises: a positive electrode for a lithium ion secondary battery containing a sulfur-based positive electrode active material containing carbon (C) and sulfur (S) A heat treatment step of heating a mixed material containing a carbon material, sulfur, and a conductive material not containing sulfur, wherein the conductive material has a fourth period metal, the fifth It is characterized in that it is at least one metal selected from the group consisting of a periodic metal, a sixth periodic metal and a rare earth element.
　本発明の正極は、炭素（Ｃ）および硫黄（Ｓ）を含有する硫黄系正極活物質と、硫黄（Ｓ）を含有する伝導材と、を含有する。単体硫黄を正極活物質として用いたリチウムイオン二次電池は、上述したように、サイクル特性に劣る。しかし、硫黄を含有する正極活物質に炭素材料を配合することで、硫黄の電解液への溶出を抑制でき、サイクル特性を向上させることができる。また本発明の正極には、第４周期金属、第５周期金属、第６周期金属および希土類元素からなる群から選ばれる少なくとも一種の金属の硫化物を配合している。これらの金属の硫化物は、自身が高い電気伝導度（導電率）を示すか、あるいは、正極のリチウムイオン伝導性を向上させ得る。このため、これらの金属の硫化物は伝導材として機能する。そして、これらの金属の硫化物を正極に配合することで、放電レート特性を向上させ得る。 The positive electrode of the present invention contains a sulfur-based positive electrode active material containing carbon (C) and sulfur (S), and a conductive material containing sulfur (S). As described above, a lithium ion secondary battery using elemental sulfur as a positive electrode active material is inferior in cycle characteristics. However, by mixing the carbon material with the positive electrode active material containing sulfur, elution of sulfur into the electrolytic solution can be suppressed, and cycle characteristics can be improved. Further, in the positive electrode of the present invention, a sulfide of at least one metal selected from the group consisting of a fourth period metal, a fifth period metal, a sixth period metal and a rare earth element is blended. The sulfides of these metals can exhibit high electric conductivity (conductivity) by themselves or can improve lithium ion conductivity of the positive electrode. Therefore, sulfides of these metals function as a conductive material. And the discharge rate characteristic can be improved by blending the sulfide of these metals in the positive electrode.
　なお、伝導材は硫黄系正極活物質とともに正極に配合されるため、硫黄系正極活物質に含まれる硫黄によって、正極の製造時および／または電池の充放電時に硫化する場合がある。このため、硫化物の状態で電気伝導度の低い材料や、硫化物の状態でリチウムイオン伝導性を向上させ得ない材料を伝導材として用いる場合には、放電レート特性を向上させ難い問題がある。しかし本発明においては、硫化物の状態で高い電気伝導度を示すか、硫化物の状態で正極のリチウムイオン伝導性を向上させ得るものを伝導材として用いているため、放電レート特性を充分に向上させ得る。 In addition, since a conductive material is mix | blended with a sulfur type positive electrode active material at a positive electrode, it may be sulfurated at the time of manufacture of a positive electrode, and / or charge / discharge of a battery with sulfur contained in a sulfur type positive electrode active material. For this reason, there is a problem that it is difficult to improve discharge rate characteristics when using a material having low electrical conductivity in the state of sulfide or a material which can not improve lithium ion conductivity in the state of sulfide as the conductive material . However, in the present invention, since a material which exhibits high electrical conductivity in the state of sulfide or which can improve lithium ion conductivity of the positive electrode in the state of sulfide is used as the conductive material, the discharge rate characteristic is sufficiently It can be improved.
　本発明の正極は、これらの協働によって、リチウムイオン二次電池のサイクル特性および放電レート特性を向上させ得る。同様に、本発明のリチウムイオン二次電池は、サイクル特性および放電レート特性に優れる。さらに、これらの効果をもつ本発明のリチウムイオン二次電池は、車両用バッテリとして好適である。 The positive electrode of the present invention can improve the cycle characteristics and the discharge rate characteristics of the lithium ion secondary battery by their cooperation. Similarly, the lithium ion secondary battery of the present invention is excellent in cycle characteristics and discharge rate characteristics. Furthermore, the lithium ion secondary battery of the present invention having these effects is suitable as a vehicle battery.
　本発明の第１のリチウムイオン二次電池用正極の製造方法においては、伝導材材料として金属硫化物を用いている。このため、上述したように、伝導材と正極活物質とを略均一に分散させることができ、放電レート特性を向上できる。なお、本発明の第２のリチウムイオン二次電池用正極の製造方法においては、未硫化の金属を用いている。この場合にも、製造時に伝導材材料が硫化して高い電気伝導度を示すか正極のリチウムイオン伝導性を向上させるため、放電レート特性が向上する。 In the first method for manufacturing a positive electrode for a lithium ion secondary battery of the present invention, metal sulfide is used as the conductive material. Therefore, as described above, the conductive material and the positive electrode active material can be dispersed substantially uniformly, and the discharge rate characteristics can be improved. In addition, in the manufacturing method of the 2nd positive electrode for lithium ion secondary batteries of this invention, the non-sulfurized metal is used. Also in this case, since the conductive material is sulfided at the time of manufacture to exhibit high electrical conductivity or to improve lithium ion conductivity of the positive electrode, discharge rate characteristics are improved.
硫黄変性ポリアクリロニトリルをＸ線回折した結果を表すグラフである。It is a graph showing the result of X-ray diffraction of sulfur modified polyacrylonitrile. 硫黄変性ポリアクリロニトリルをラマンスペクトル分析した結果を表すグラフである。It is a graph showing the result of having carried out the Raman spectrum analysis of sulfur modified polyacrylonitrile. 硫黄変性ピッチをＸ線回折した結果を表すグラフである。It is a graph showing the result of X-ray diffraction of sulfur-modified pitch. 硫黄変性ピッチをラマンスペクトル分析した結果を表すグラフである。It is a graph showing the result of having carried out Raman spectrum analysis of sulfur denaturation pitch. 実施例の正極の製造方法で用いた反応装置を模式的に表す説明図である。It is explanatory drawing which represents typically the reaction apparatus used by the manufacturing method of the positive electrode of an Example. 実施例１の正極に用いた硫黄系正極活物質－伝導材複合体をＸ線回折した結果を表すグラフである。7 is a graph showing the results of X-ray diffraction of the sulfur-based positive electrode active material-conductive material composite used for the positive electrode of Example 1. FIG. 実施例２の正極に用いた硫黄系正極活物質－伝導材複合体をＸ線回折した結果を表すグラフである。15 is a graph showing the results of X-ray diffraction of the sulfur-based positive electrode active material-conductive material composite used for the positive electrode of Example 2. FIG. 実施例４の正極に用いた硫黄系正極活物質－伝導材複合体をＸ線回折した結果を表すグラフである。FIG. 16 is a graph showing the results of X-ray diffraction of the sulfur-based positive electrode active material-conductive material composite used for the positive electrode of Example 4. FIG. 実施例７の正極に用いた硫黄系正極活物質－伝導材複合体をＸ線回折した結果を表すグラフである。15 is a graph showing the results of X-ray diffraction of the sulfur-based positive electrode active material-conductive material composite used for the positive electrode of Example 7. FIG. 実施例９の正極に用いた硫黄系正極活物質－伝導材複合体をＸ線回折した結果を表すグラフである。FIG. 16 is a graph showing the results of X-ray diffraction of the sulfur-based positive electrode active material-conductive material composite used for the positive electrode of Example 9. FIG. 比較例の正極に用いた硫黄系正極活物質をＸ線回折した結果を表すグラフである。It is a graph showing the result of having carried out the X-ray diffraction of the sulfur system positive electrode active material used for the positive electrode of the comparative example. 硫黄系正極活物質－伝導材（Ｆｅ）複合体をＸ線回折した結果を表すグラフである。It is a graph showing the result of having carried out the X-ray diffraction of the sulfur system positive electrode active material-conductivity material (Fe) complex. 実施例１の正極を用いたリチウムイオン二次電池の放電レート特性（充放電曲線）を表すグラフである。5 is a graph showing the discharge rate characteristics (charge-discharge curve) of a lithium ion secondary battery using the positive electrode of Example 1. 実施例１の正極を用いたリチウムイオン二次電池の放電レート特性（サイクル特性）を表すグラフである。5 is a graph showing discharge rate characteristics (cycle characteristics) of a lithium ion secondary battery using the positive electrode of Example 1. FIG. 実施例２の正極を用いたリチウムイオン二次電池の放電レート特性（サイクル特性）を表すグラフである。5 is a graph showing the discharge rate characteristics (cycle characteristics) of a lithium ion secondary battery using the positive electrode of Example 2. FIG. 実施例３の正極を用いたリチウムイオン二次電池の放電レート特性（サイクル特性）を表すグラフである。It is a graph showing the discharge rate characteristic (cycle characteristic) of the lithium ion secondary battery using the positive electrode of Example 3. 実施例４の正極を用いたリチウムイオン二次電池の放電レート特性（サイクル特性）を表すグラフである。15 is a graph showing the discharge rate characteristics (cycle characteristics) of a lithium ion secondary battery using the positive electrode of Example 4. 実施例５の正極を用いたリチウムイオン二次電池の放電レート特性（充放電曲線）を表すグラフである。15 is a graph showing the discharge rate characteristic (charge-discharge curve) of a lithium ion secondary battery using the positive electrode of Example 5. 実施例５の正極を用いたリチウムイオン二次電池の放電レート特性（サイクル特性）を表すグラフである。It is a graph showing the discharge rate characteristic (cycle characteristic) of the lithium ion secondary battery using the positive electrode of Example 5. 実施例６の正極を用いたリチウムイオン二次電池の放電レート特性（充放電曲線）を表すグラフである。It is a graph showing the discharge rate characteristic (charge-and-discharge curve) of the lithium ion secondary battery using the positive electrode of Example 6. 実施例６の正極を用いたリチウムイオン二次電池の放電レート特性（サイクル特性）を表すグラフである。It is a graph showing the discharge rate characteristic (cycle characteristic) of the lithium ion secondary battery using the positive electrode of Example 6. 実施例７の正極を用いたリチウムイオン二次電池の放電レート特性（充放電曲線）を表すグラフである。It is a graph showing the discharge rate characteristic (charge-and-discharge curve) of the lithium ion secondary battery using the positive electrode of Example 7. 実施例７の正極を用いたリチウムイオン二次電池の放電レート特性（サイクル特性）を表すグラフである。It is a graph showing the discharge rate characteristic (cycle characteristic) of the lithium ion secondary battery using the positive electrode of Example 7. 実施例８の正極を用いたリチウムイオン二次電池の放電レート特性（充放電曲線）を表すグラフである。It is a graph showing the discharge rate characteristic (charge-and-discharge curve) of the lithium ion secondary battery using the positive electrode of Example 8. 実施例８の正極を用いたリチウムイオン二次電池の放電レート特性（サイクル特性）を表すグラフである。It is a graph showing the discharge rate characteristic (cycle characteristic) of the lithium ion secondary battery using the positive electrode of Example 8. 実施例９の正極を用いたリチウムイオン二次電池の放電レート特性（充放電曲線）を表すグラフである。15 is a graph showing the discharge rate characteristics (charge / discharge curve) of a lithium ion secondary battery using the positive electrode of Example 9. 実施例９の正極を用いたリチウムイオン二次電池の放電レート特性（サイクル特性）を表すグラフである。15 is a graph showing the discharge rate characteristics (cycle characteristics) of a lithium ion secondary battery using the positive electrode of Example 9. 比較例の正極を用いたリチウムイオン二次電池の放電レート特性（サイクル特性）を表すグラフである。It is a graph showing the discharge rate characteristic (cycle characteristic) of the lithium ion secondary battery using the positive electrode of a comparative example.
　本発明のリチウムイオン二次電池用正極（以下、本発明の正極と呼ぶ）は、正極活物質と、伝導材とを含有する。本発明のリチウムイオン二次電池は、本発明の正極を用いた電池である。本発明のリチウムイオン二次電池用正極の製造方法（以下、本発明の製造方法と呼ぶ）は、炭素材料、硫黄、および、伝導材材料を含有する混合原料を加熱する熱処理工程を含み、正極活物質および伝導材を含有する正極を製造する。本発明の製造方法によると、本発明の正極を製造できる。 The positive electrode for a lithium ion secondary battery of the present invention (hereinafter referred to as the positive electrode of the present invention) contains a positive electrode active material and a conductive material. The lithium ion secondary battery of the present invention is a battery using the positive electrode of the present invention. The method for producing a positive electrode for a lithium ion secondary battery of the present invention (hereinafter referred to as the production method of the present invention) comprises a heat treatment step of heating a mixed material containing a carbon material, sulfur, and a conductive material. A positive electrode containing an active material and a conductive material is manufactured. According to the production method of the present invention, the positive electrode of the present invention can be produced.
　　〔伝導材材料〕
　伝導材材料、すなわち、本発明の正極を製造する際に用いる伝導材の材料としては、第４周期金属、第５周期金属、第６周期金属および希土類元素からなる群から選ばれる少なくとも一種の金属、またはその硫化物を用いることができる。なお、本明細書でいう第４周期金属、第５周期金属および第６周期金属とは、周期律表によるものである。例えば第４周期金属とは、周期律表における第４周期元素に含まれる金属を指す。伝導材材料としては、硫化物の状態で自身が高い電気伝導性を示すか、あるいは、正極のリチウムイオン伝導性を大きく向上させ得るものが好ましく、例えば、Ｔｉ、Ｆｅ、Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｓｍ、Ｖ、Ｍｎ、Ｆｅ、Ｎｉ、Ｃｕ、Ｚｎ、Ｍｏ、Ａｇ、Ｃｄ、Ｉｎ、Ｓｎ、Ｓｂ、Ｔａ、Ｗ、Ｐｂからなる群から選ばれる少なくとも一種、またはその硫化物であるのが好ましい。なお伝導材は、正極中においては、上記金属とその硫化物との両方からなるか、或いは、上記金属の硫化物のみからなる。これらの伝導材材料は硫化物を多く含むのが好ましく、硫化物のみからなるのがより好ましい。上記金属を硫化物の状態で正極に配合することで、伝導材と硫黄系正極活物質とがなじみ易くなり、伝導材と正極活物質とが略均一に分散するためである。また、伝導材材料として硫化物を用いることで、伝導材における上記金属と硫黄との比率を所望する範囲に容易に制御できる利点もある。 [Conductive material]
Conductive material, that is, the material of the conductive material used when manufacturing the positive electrode of the present invention, at least one metal selected from the group consisting of the fourth period metal, the fifth period metal, the sixth period metal and the rare earth element Or its sulfide can be used. The fourth period metal, the fifth period metal, and the sixth period metal in the present specification are according to the periodic table. For example, the fourth period metal refers to a metal included in the fourth period element in the periodic table. As the conductive material, a material which exhibits high electric conductivity in the form of sulfide or which can greatly improve lithium ion conductivity of the positive electrode is preferable. For example, Ti, Fe, La, Ce, Pr, At least one member selected from the group consisting of Nd, Sm, V, Mn, Fe, Ni, Cu, Zn, Mo, Ag, Cd, In, Sn, Sb, Ta, W, Pb, or a sulfide thereof preferable. In the positive electrode, the conductive material is made of both the metal and the sulfide thereof, or only of the sulfide of the metal. These conductive materials are preferably rich in sulfides, and more preferably consist of sulfides alone. By blending the metal in the form of a sulfide in the positive electrode, the conductive material and the sulfur-based positive electrode active material can be easily conformed, and the conductive material and the positive electrode active material can be dispersed substantially uniformly. Moreover, there is also an advantage that the ratio of the metal and sulfur in the conductive material can be easily controlled to a desired range by using a sulfide as the conductive material.
　詳しくは、電気伝導度および／またはリチウムイオン伝導性の高い伝導材としては、ＴｉＳ２、ＦｅＳ２、Ｍｅ２Ｓ３（式中、ＭｅはＴｉ、Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｓｍから選ばれる一種である）、ＭｅＳ（式中、ＭｅはＴｉ、Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｓｍから選ばれる一種である）、Ｍｅ３Ｓ４（式中、ＭｅはＴｉ、Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｓｍから選ばれる一種である）、ＭｅｘＳｙ（式中、ＭｅはＴｉ、Ｆｅ、Ｖ、Ｍｎ、Ｆｅ、Ｎｉ、Ｃｕ、Ｚｎ、Ｍｏ、Ａｇ、Ｃｄ、Ｉｎ、Ｓｎ、Ｓｂ、Ｔａ、Ｗ、Ｐｂから選ばれる一種であり、ｘ、ｙは任意の整数である）が挙げられる。この場合、伝導材材料としてはＴｉ、Ｆｅ、Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｓｍ、Ｖ、Ｍｎ、Ｆｅ、Ｎｉ、Ｃｕ、Ｚｎ、Ｍｏ、Ａｇ、Ｃｄ、Ｉｎ、Ｓｎ、Ｓｂ、Ｔａ、Ｗ、Ｐｂから選ばれる少なくとも一種を、そのまま、または、上記の伝導材のような硫化物の状態で用いれば良い。これらの伝導材材料を用いることで、正極全体の電気伝導度および／またはリチウムイオン伝導性を向上させることができ、リチウムイオン二次電池の放電レート特性を向上させ得る。なお、原料コストや調達のし易さ、資源量を鑑みると、ＴｉＳｚ（式中、ｚは０．１～２である）を用いるのがより好ましく、ＴｉＳ２を用いるのが特に好ましい。 Specifically, as a conductive material having high electric conductivity and / or lithium ion conductivity, TiS 2 , FeS 2 , Me 2 S 3 (wherein, Me is selected from Ti, La, Ce, Pr, Nd, Sm) It is a kind, MeS (in which Me is a kind selected from Ti, La, Ce, Pr, Nd and Sm), Me 3 S 4 (wherein Me is Ti, La, Ce, Pr and Nd) And Sm, Me x S y (wherein Me is Ti, Fe, V, Mn, Fe, Ni, Cu, Zn, Mo, Ag, Cd, In, Sn, Sb, Ta, It is 1 type chosen from W and Pb, and x and y are arbitrary integers. In this case, as conductive materials, Ti, Fe, La, Ce, Pr, Nd, Sm, V, Mn, Fe, Ni, Cu, Zn, Mo, Ag, Cd, In, Sn, Sb, Ta, W, At least one selected from Pb may be used as it is or in the form of a sulfide such as the above-mentioned conductive material. By using these conductive material materials, the electrical conductivity and / or lithium ion conductivity of the entire positive electrode can be improved, and the discharge rate characteristics of the lithium ion secondary battery can be improved. It is more preferable to use TiS z (in the formula, z is 0.1 to 2) in view of raw material cost, easiness of procurement and resource amount, and it is particularly preferable to use TiS 2 .
　後述するポリアクリロニトリル等の炭素材料と、伝導材材料と、の配合比は、質量比で、１０：０．５～１０：５であるのが好ましく、１０：１～１０：３であるのがより好ましい。伝導材材料の配合量が過大であれば、正極全体に対する正極活物質の量が過小になるためである。伝導材を硫黄系正極活物質中に略均一に分散させるためには、伝導材材料は粉末状であるのが好ましい。伝導材材料は、電子顕微鏡などを用いて測定した粒径が０．１～１００μｍであるのが好ましく、０．１～５０μｍであるのがより好ましく、０．１～２０μｍであるのがさらに好ましい。 The compounding ratio of a carbon material such as polyacrylonitrile described later and the conductive material material is preferably 10: 0.5 to 10: 5 by mass ratio, and 10: 1 to 10: 3 More preferable. If the blending amount of the conductive material is too large, the amount of the positive electrode active material with respect to the entire positive electrode will be too small. In order to disperse the conductive material substantially uniformly in the sulfur-based positive electrode active material, the conductive material is preferably in the form of powder. The conductive material preferably has a particle diameter of 0.1 to 100 μm, more preferably 0.1 to 50 μm, and still more preferably 0.1 to 20 μm, as measured using an electron microscope or the like. .
　　〔正極活物質〕
　本発明の正極に用いられる正極活物質は、炭素（Ｃ）および硫黄（Ｓ）を含有する硫黄系正極活物質である。硫黄系正極活物質としては、例えば、上記の特許文献１に開示されているもの（炭素材料として直鎖状不飽和ポリマーを用いたもの）や、特許文献２に開示されているもの（炭素材料としてポリアクリロニトリルを用いたもの）、その他炭素材料として各種のピッチ系炭素材料を用いたもの等が好ましく用いられる。以下、炭素材料としてポリアクリロニトリルを用いた硫黄系正極活物質を、硫黄変性ポリアクリロニトリルと呼ぶ。炭素材料としてピッチ系炭素材料を用いた硫黄系正極活物質を、硫黄変性ピッチと呼ぶ。さらに、必要に応じて、ポリアクリロニトリルをＰＡＮと略記する。 [Positive electrode active material]
The positive electrode active material used for the positive electrode of the present invention is a sulfur-based positive electrode active material containing carbon (C) and sulfur (S). Examples of sulfur-based positive electrode active materials include those disclosed in the above-mentioned Patent Document 1 (using a linear unsaturated polymer as the carbon material) and those disclosed in the Patent Document 2 (carbon material) And those using various pitch-based carbon materials as the carbon material are preferably used. Hereinafter, a sulfur-based positive electrode active material using polyacrylonitrile as a carbon material is referred to as sulfur-modified polyacrylonitrile. A sulfur-based positive electrode active material using a pitch-based carbon material as a carbon material is called a sulfur-modified pitch. Furthermore, polyacrylonitrile is abbreviated as PAN if necessary.
　　　〈硫黄変性ポリアクリロニトリル〉
　炭素材料としてポリアクリロニトリルを用いる場合、硫黄が本来有する高容量を維持でき、かつ、硫黄の電解液への溶出が抑制されるため、非水電解質二次電池のサイクル特性が大きく向上する。これは、硫黄系正極活物質中で硫黄が単体として存在するのでなくポリアクリロニトリルと結合した安定な状態で存在するためだと考えられる。特許文献２に開示されている硫黄系正極活物質の製造方法において、硫黄はポリアクリロニトリルとともに加熱処理されている。ポリアクリロニトリルを加熱すると、ポリアクリロニトリルが３次元的に架橋して縮合環（主として６員環）を形成しつつ閉環すると考えられる。このため硫黄は、閉環の進行したポリアクリロニトリルと結合した状態で硫黄系正極活物質中に存在していると考えられる。ポリアクリロニトリルと硫黄とが結合することで、硫黄の電解液への溶出を抑制でき、サイクル特性を向上させ得る。 Sulfur-modified polyacrylonitrile
When polyacrylonitrile is used as the carbon material, the high capacity originally possessed by sulfur can be maintained, and the elution of sulfur into the electrolytic solution can be suppressed, so the cycle characteristics of the non-aqueous electrolyte secondary battery can be greatly improved. It is considered that this is because sulfur is not present as a single substance in the sulfur-based positive electrode active material but in a stable state in which it is combined with polyacrylonitrile. In the method of producing a sulfur-based positive electrode active material disclosed in Patent Document 2, sulfur is heat-treated together with polyacrylonitrile. When polyacrylonitrile is heated, it is believed that polyacrylonitrile is three-dimensionally crosslinked to form a condensed ring (mainly a six-membered ring) to form a ring closure. For this reason, sulfur is considered to be present in the sulfur-based positive electrode active material in a state of being bonded to the ring-closed polyacrylonitrile. By combining polyacrylonitrile and sulfur, elution of the sulfur into the electrolytic solution can be suppressed, and cycle characteristics can be improved.
　炭素材料として用いるポリアクリロニトリルは、粉末状であるのが好ましく、質量平均分子量が１０４～３×１０５程度であるのが好ましい。また、ポリアクリロニトリルの粒径は、電子顕微鏡によって観察した際に、０．５～５０μm程度であるのが好ましく、１～１０μｍ程度であるのがより好ましい。ポリアクリロニトリルの分子量および粒径がこれらの範囲内であれば、ポリアクリロニトリルと硫黄との接触面積を大きくでき、ポリアクリロニトリルと硫黄とを信頼性高く反応させ得る。このため、電解液への硫黄の溶出をより信頼性高く抑制できる。 The polyacrylonitrile used as the carbon material is preferably in the form of powder, and the mass average molecular weight is preferably about 10 4 to 3 × 10 5 . The particle diameter of polyacrylonitrile is preferably about 0.5 to 50 μm, more preferably about 1 to 10 μm, as observed by an electron microscope. If the molecular weight and particle size of polyacrylonitrile are within these ranges, the contact area between polyacrylonitrile and sulfur can be increased, and polyacrylonitrile and sulfur can be reacted with high reliability. Therefore, the elution of sulfur into the electrolyte can be suppressed more reliably.
　硫黄系正極活物質に用いられる硫黄もまた、粉末状であるのが好ましい。硫黄の粒径については特に限定しないが、篩いを用いて分級した際に、篩目開き４０μｍの篩を通過せず、かつ、１５０μｍの篩を通過する大きさの範囲内にあるものが好ましく、篩目開き４０μｍの篩を通過せず、かつ、１００μｍの篩を通過する大きさの範囲内にあるものがより好ましい。 The sulfur used for the sulfur-based positive electrode active material is also preferably in the form of powder. The particle size of sulfur is not particularly limited, but when it is classified using a sieve, those which do not pass through a sieve with a sieve opening of 40 μm and which have a size within a 150 μm sieve are preferable. It is more preferable not to pass through a sieve with a sieve opening of 40 μm and in the size range of passing through a 100 μm sieve.
　硫黄系正極活物質に用いるポリアクリロニトリル粉末と硫黄粉末との配合比については特に限定しないが、質量比で、１：０．５～１：１０であるのが好ましく、１：０．５～１：７であるのがより好ましく、１：２～１：５であるのがさらに好ましい。 The compounding ratio of the polyacrylonitrile powder to the sulfur powder used for the sulfur-based positive electrode active material is not particularly limited, but it is preferably 1: 0.5 to 1:10 in mass ratio, 1: 0.5 to 1 The ratio is more preferably 7: 7, and more preferably 1: 2 to 1: 5.
　硫黄変性ポリアクリロニトリルは、元素分析の結果、炭素、窒素、及び硫黄を含み、更に、少量の酸素及び水素を含む場合もある。また、図１に示すように、硫黄変性ポリアクリロニトリルをＣｕＫα線によりＸ線回折した結果、回折角（２θ）２０～３０°の範囲では、２５°付近にピーク位置を有するブロードなピークのみが確認された。参考までに、Ｘ線回折は、粉末Ｘ線回折装置（ＭＡＣ　Ｓｃｉｅｎｃｅ社製、型番：Ｍ０６ＸＣＥ）により、ＣｕＫα線を用いてＸ線回折測定を行なった。測定条件は、電圧：４０ｋＶ、電流：１００ｍＡ、スキャン速度：４°/分、サンプリング：０．０２°、積算回数：１回、測定範囲：回折角（２θ）１０°～６０°であった。 Sulfur-modified polyacrylonitrile contains carbon, nitrogen, and sulfur as a result of elemental analysis, and may further contain small amounts of oxygen and hydrogen. Further, as shown in FIG. 1, as a result of X-ray diffraction of sulfur-modified polyacrylonitrile with CuKα rays, only a broad peak having a peak position near 25 ° was confirmed in the range of diffraction angle (2θ) of 20 to 30 °. It was done. For reference, X-ray diffraction measurement was performed using a powder X-ray diffractometer (manufactured by MAC Science, model number: M06XCE) using a CuKα ray. The measurement conditions were: voltage: 40 kV, current: 100 mA, scan rate: 4 ° / min, sampling: 0.02 °, number of integrations: 1 measurement range: diffraction angle (2θ) 10 ° to 60 °.
　さらに硫黄変性ポリアクリロニトリルを、室温から９００℃まで２０℃／分の昇温速度で加熱した際の質量の減少を熱重量分析により測定した。その結果、硫黄変性ポリアクリロニトリルの質量の減少は、４００℃時点で１０％以下であった。これに対して、硫黄粉末とポリアクリロニトリル粉末の混合物を同様の条件で加熱した。その結果、混合物の質量は１２０℃付近から減少し、２００℃以上になると急激にかつ大きく減少した。これは硫黄の消失に基づくものと考えられる。 Furthermore, the decrease in mass when the sulfur-modified polyacrylonitrile was heated from room temperature to 900 ° C. at a temperature rising rate of 20 ° C./min was measured by thermogravimetric analysis. As a result, the reduction in mass of sulfur-modified polyacrylonitrile was 10% or less at 400 ° C. On the other hand, a mixture of sulfur powder and polyacrylonitrile powder was heated under the same conditions. As a result, the mass of the mixture decreased from around 120 ° C., and decreased rapidly and greatly at 200 ° C. or higher. This is considered to be based on the loss of sulfur.
　すなわち、硫黄変性ポリアクリロニトリルにおいて、硫黄は単体としては存在せず、閉環の進行したポリアクリロニトリルと結合した状態で存在していると考えられる。 That is, in the sulfur-modified polyacrylonitrile, it is considered that sulfur is not present as a single substance but is present in a state of being bonded to the ring-closed polyacrylonitrile.
　硫黄変性ポリアクリロニトリルのラマンスペクトルの一例を図２に示す。図２に示すラマンスペクトルにおいて、ラマンシフトの１３３１ｃｍ－１付近に主ピークが存在し、かつ、２００ｃｍ－１～１８００ｃｍ－１の範囲で１５４８ｃｍ－１、９３９ｃｍ－１、４７９ｃｍ－１、３８１ｃｍ－１、３１７ｃｍ－１付近にピークが存在する。上記したラマンシフトのピークは、ポリアクリロニトリルに対する単体硫黄の比率を変更した場合にも同様の位置に観測される。このためこれらのピークは硫黄変性ポリアクリロニトリルを特徴づけるものである。上記した各ピークは、上記したピーク位置を中心として、ほぼ±８ｃｍ－１の範囲内に存在する。なお、本明細書において、「主ピーク」とは、ラマンスペクトルで現れた全てのピークのなかでピーク高さが最大となるピークを指す。 An example of a Raman spectrum of sulfur-modified polyacrylonitrile is shown in FIG. In the Raman spectrum shown in FIG. 2, there are major peak near 1331cm -1 of Raman shift, and, 1548cm -1 in the range of 200cm -1 ~ 1800cm -1, 939cm -1 , 479cm -1, 381cm -1, A peak is present around 317 cm -1 . The peak of the above-mentioned Raman shift is observed at the same position even when the ratio of elemental sulfur to polyacrylonitrile is changed. Thus, these peaks are characteristic of sulfur-modified polyacrylonitrile. Each peak mentioned above exists in the range of about ± 8 cm −1 centered on the peak position mentioned above. In addition, in this specification, a "main peak" refers to the peak which peak height becomes the largest among all the peaks which appeared in the Raman spectrum.
　参考までに、上記したラマンシフトは、日本分光社製　ＲＭＰ－３２０（励起波長λ＝５３２ｎｍ、グレーチング：１８００ｇｒ／ｍｍ、分解能：３ｃｍ－１）で測定したものである。なお、ラマンスペクトルのピークは、入射光の波長や分解能の違いなどにより、数が変化したり、ピークトップの位置がずれたりすることがある。したがって正極活物質として硫黄変性ポリアクリロニトリルを用いた本発明の正極のラマンスペクトルを測定すると、上記のピークと同じピーク、または、上記のピークとは数やピークトップの位置が僅かに異なるピークが確認される。 For reference, the above-mentioned Raman shift is measured by RMP-320 (excitation wavelength λ = 532 nm, grating: 1800 gr / mm, resolution: 3 cm −1 ) manufactured by JASCO Corporation. Note that the peaks of the Raman spectrum may change in number or the position of the peak top may be shifted depending on the wavelength of incident light or the difference in resolution. Therefore, when the Raman spectrum of the positive electrode of the present invention using sulfur-modified polyacrylonitrile as the positive electrode active material is measured, the same peak as the above peak or a peak slightly different in number or peak top position from the above peak is confirmed Be done.
　　　〈硫黄変性ピッチ〉
　本明細書において、ピッチ系炭素材料とは、石炭ピッチ、石油ピッチ、メソフェーズピッチ（異方性ピッチ）、アスファルト、コールタール、コールタールピッチ、縮合多環芳香族炭化水素化合物の重縮合で得られる有機合成ピッチ、またはヘテロ原子含有縮合多環芳香族炭化水素化合物の重縮合で得られる有機合成ピッチ、からなる群から選ばれる少なくとも一種を指す。これらは縮合多環芳香族を含む炭素材料として知られている。 Sulfur-modified pitch
In the present specification, the pitch-based carbon material is obtained by polycondensation of coal pitch, petroleum pitch, mesophase pitch (anisotropic pitch), asphalt, coal tar, coal tar pitch, condensed polycyclic aromatic hydrocarbon compound It refers to at least one selected from the group consisting of organic synthetic pitch, or organic synthetic pitch obtained by polycondensation of a heteroatom-containing fused polycyclic aromatic hydrocarbon compound. These are known as carbon materials containing fused polycyclic aromatics.
　ピッチ系炭素材料の一種であるコールタールは、石炭を高温乾留（石炭乾留）して得られる黒い粘稠な油状液体である。コールタールを精製・熱処理（重合）することで、石炭ピッチを得ることができる。アスファルトは、黒褐色ないし黒色の固体あるいは半固体の可塑性物質である。アスファルトは、石油（原油）を減圧蒸留したときに釜残として得られるものと、天然に存在するものとに大別される。アスファルトはトルエン、二硫化炭素等に可溶である。アスファルトを精製・熱処理（重合）することで、石油ピッチを得ることができる。ピッチは、通常、無定形であり光学的に等方性である（等方性ピッチ）。等方性ピッチを不活性雰囲気中で熱処理することで、光学的に異方性のピッチ（異方性ピッチ、メソフェーズピッチ）を得ることができる。ピッチは、ベンゼン、トルエン、二硫化炭素等の有機溶剤に部分的に可溶である。 Coal tar, which is a type of pitch-based carbon material, is a black viscous oily liquid obtained by high-temperature dry distillation (coal dry distillation) of coal. Coal pitch can be obtained by refining and heat treating (polymerizing) coal tar. Asphalt is a black-brown to black solid or semi-solid plastic material. Asphalt is roughly classified into those obtained as bottoms when vacuum distillation of petroleum (crude oil) is carried out and those which exist naturally. Asphalt is soluble in toluene, carbon disulfide and the like. Petroleum pitch can be obtained by refining and heat treating (polymerizing) asphalt. The pitch is usually amorphous and optically isotropic (isotropic pitch). By thermally processing the isotropic pitch in an inert atmosphere, it is possible to obtain an optically anisotropic pitch (anisotropic pitch, mesophase pitch). Pitch is partially soluble in organic solvents such as benzene, toluene, carbon disulfide and the like.
　ピッチ系炭素材料は様々な化合物の混合物であり、上述したように縮合多環芳香族を含む。ピッチ系炭素材料に含まれる縮合多環芳香族は、単一種であっても良いし、複数種であっても良い。例えば、ピッチ系炭素材料の一種である石炭ピッチの主成分は、縮合多環芳香族である。この縮合多環芳香族は、環の中に、炭素と水素以外にも、窒素や硫黄を含み得る。このため、石炭ピッチの主成分は、炭素と水素のみから成る縮合多環芳香族炭化水素と縮合環に窒素や硫黄等を含む複素芳香族化合物との混合物と考えられる。 The pitch-based carbon material is a mixture of various compounds and includes fused polycyclic aromatics as described above. The fused polycyclic aromatic group contained in the pitch-based carbon material may be a single species or a plurality of species. For example, the main component of coal pitch, which is a type of pitch-based carbon material, is a condensed polycyclic aromatic. The fused polycyclic aromatic ring may contain nitrogen and sulfur in addition to carbon and hydrogen in the ring. Therefore, the main component of coal pitch is considered to be a mixture of a condensed polycyclic aromatic hydrocarbon consisting of only carbon and hydrogen and a heteroaromatic compound containing nitrogen, sulfur and the like in the condensed ring.
　炭素材料としてピッチ系炭素材料を用いる場合にも、炭素材料としてポリアクリロニトリルを用いる場合と同様に、硫黄が本来有する高容量を維持できかつ硫黄の電解液への溶出が抑制されるため、サイクル特性が大きく向上する。これは、硫黄系正極活物質中で硫黄が単体として存在するのでなく、硫黄がピッチ系炭素材料のグラフェン層間に取り込まれているか、或いは、縮合多環芳香族の環に含まれる水素が硫黄に置換されてＣ－Ｓ結合となっているためだと推測される。 Even when using a pitch-based carbon material as the carbon material, as in the case of using polyacrylonitrile as the carbon material, the high capacity inherent in sulfur can be maintained and the elution of sulfur into the electrolytic solution is suppressed, so cycle characteristics Is greatly improved. This is because sulfur is not incorporated as a single substance in the sulfur-based positive electrode active material, but the sulfur is taken in between graphene layers of the pitch-based carbon material, or hydrogen contained in the condensed polycyclic aromatic ring is used as sulfur. It is guessed that it is because it is substituted and it becomes CS coupling | bonding.
　ピッチ系炭素材料の粒径は特に限定しない。また、炭素材料としてピッチ系炭素材料を用いる場合、硫黄の粒径もまた特に限定しない。ピッチ系炭素材料と硫黄との混合割合についてもまた特に限定しないが、混合原料中のピッチ系炭素材料と硫黄との配合比は、質量比で１：０．５～１：１０であるのが好ましく、１：１～１：７であるのがより好ましく、１：２～１：５であるのが特に好ましい。 The particle size of the pitch-based carbon material is not particularly limited. Moreover, when using a pitch-based carbon material as a carbon material, the particle size of sulfur is not specifically limited, either. The mixing ratio of the pitch-based carbon material to sulfur is also not particularly limited, but the mixing ratio of the pitch-based carbon material to sulfur in the mixed raw material is 1: 0.5 to 1:10 in mass ratio The ratio is preferably 1: 1 to 1: 7, more preferably 1: 2 to 1: 5.
　硫黄変性ピッチは、複数種の多環芳香族炭化水素を含む。ここでいう多環芳香族炭化水素（ＰＡＨ）とは、上述した各種ピッチ系炭素材料自体、および、上述した各種ピッチ系炭素材料に含まれる各種多環芳香族炭化水素、からなる群から選ばれる少なくとも一種の炭素材料を指す。 Sulfur-modified pitch contains multiple types of polycyclic aromatic hydrocarbons. The polycyclic aromatic hydrocarbon (PAH) referred to herein is selected from the group consisting of the various pitch-based carbon materials described above and various polycyclic aromatic hydrocarbons contained in the various pitch-based carbon materials described above. Refers to at least one carbon material.
　また、硫黄変性ピッチ（石炭ピッチ：硫黄＝１：１、１：５、１：１０）、単体石炭ピッチおよび単体硫黄をＣｕＫα線によりＸ線回折した。回折条件は上記の硫黄変性ポリアクリロニトリルと同じである。 In addition, sulfur-modified pitch (coal pitch: sulfur = 1: 1, 1: 5, 1:10), single coal pitch and single sulfur were subjected to X-ray diffraction with CuKα ray. The diffraction conditions are the same as the above-mentioned sulfur-modified polyacrylonitrile.
　図３に示すように、回折角（２θ）１０～６０°の範囲では、単体硫黄の主ピークは２２°付近に存在し、単体石炭ピッチの主ピークは２６°付近に存在した。石炭ピッチと硫黄との配合比が１：１である硫黄変性ピッチのピークは単一ピークであり、２６°付近に存在した。石炭ピッチと硫黄との配合比が１：５である硫黄変性ピッチ、および石炭ピッチと硫黄との配合比が１：１０である硫黄変性ピッチの主ピークは、２２°付近に存在した。 As shown in FIG. 3, in the diffraction angle (2θ) range of 10 ° to 60 °, the main peak of single sulfur was present near 22 °, and the main peak of single coal pitch was present near 26 °. The peak of the sulfur-modified pitch in which the blending ratio of coal pitch to sulfur was 1: 1 was a single peak and was present around 26 °. The main peak of the sulfur-modified pitch in which the blending ratio of coal pitch to sulfur is 1: 5 and the main peak of the sulfur-modified pitch in which the blending ratio of coal pitch to sulfur is 1:10 was present at around 22 °.
　硫黄変性ピッチは熱安定性に優れる。硫黄変性ピッチを、室温から５５０℃まで１０℃／分の昇温速度で加熱した際の熱重量分析による質量減少は５５０℃時点で２５％程度である。参考までに、石炭ピッチの質量減少は５５０℃時点で約３０％程度である。単体硫黄の場合、１７０℃付近から徐々に質量減少し、２００℃を超すと急激に減少する。石炭ピッチもまた質量減少し難く、２５０℃～４５０℃付近では石炭ピッチの方が硫黄変性ピッチより質量減少し難い傾向がある。４５０℃以上では石炭ピッチよりも硫黄変性ピッチの方が質量減少し難い傾向がある。 Sulfur-modified pitch is excellent in heat stability. The mass loss by thermogravimetric analysis when the sulfur-modified pitch is heated from room temperature to 550 ° C. at a heating rate of 10 ° C./min is about 25% at 550 ° C. For reference, the mass loss of the coal pitch is about 30% at 550 ° C. In the case of elemental sulfur, the mass decreases gradually from around 170 ° C., and decreases sharply above 200 ° C. Coal pitch also tends not to decrease in mass, and in the vicinity of 250 ° C. to 450 ° C., coal pitch tends to be less likely to decrease in weight than sulfur-modified pitch. At 450 ° C. or higher, the sulfur-modified pitch tends to be less likely to lose mass than coal pitch.
　硫黄変性ピッチのラマンスペクトルの一例を図４に示す。参考までに、このラマンスペクトルは、上述した硫黄変性ポリアクリロニトリルのラマンスペクトルと同じ条件で測定したものである。 An example of a Raman spectrum of sulfur-modified pitch is shown in FIG. For reference, this Raman spectrum is measured under the same conditions as the Raman spectrum of the sulfur-modified polyacrylonitrile described above.
　図４に示すラマンスペクトルにおいて、ラマンシフトの１５５７ｃｍ－１付近に主ピークが存在し、かつ、２００ｃｍ－１～１８００ｃｍ－１の範囲内で１３７１ｃｍ－１、１０４９ｃｍ－１、９９４ｃｍ－１、８４２ｃｍ－１、６１２ｃｍ－１、４１２ｃｍ－１、３５４ｃｍ－１、３１４ｃｍ－１付近にそれぞれピークが存在する。これらのピークは、ピッチ系炭素材料に対する単体硫黄の比率を変更した場合にも同様の位置に観測され、硫黄変性ピッチを特徴付けるピークである。正極活物質として硫黄変性ピッチを用いた本発明の正極のラマンスペクトルを測定すると、これらのピークと同じ、または、数やピークトップの位置が僅かに異なるピークが確認される。なお、硫黄変性ピッチのラマンスペクトルは、硫黄変性ポリアクリロニトリルのラマンスペクトルとは異なる。 In the Raman spectrum shown in FIG. 4, the main peak is present near 1557cm -1 of Raman shift, and, 1371cm -1 in the range of 200cm -1 ~ 1800cm -1, 1049cm -1 , 994cm -1, 842cm -1 , 612cm -1, 412cm -1, 354cm -1, the peak respectively is present in the vicinity of 314 cm -1. These peaks are observed at similar positions even when the ratio of elemental sulfur to pitch-based carbon material is changed, and is a peak that characterizes the sulfur-modified pitch. When the Raman spectrum of the positive electrode of the present invention using sulfur-modified pitch as the positive electrode active material is measured, a peak having the same or slightly different number or peak top position from these peaks is confirmed. The Raman spectrum of the sulfur-modified pitch is different from the Raman spectrum of the sulfur-modified polyacrylonitrile.
　硫黄変性ピッチを元素分析した結果、炭素、窒素、および硫黄が検出された。また、場合によっては、少量の酸素および水素が検出された。したがって、硫黄変性ピッチは、Ｃ、Ｓ以外に、窒素、酸素、硫黄化合物等の少なくとも一種を不純物として含有する。 As a result of elemental analysis of the sulfur-modified pitch, carbon, nitrogen and sulfur were detected. Also, in some cases small amounts of oxygen and hydrogen were detected. Therefore, in addition to C and S, the sulfur-modified pitch contains at least one of nitrogen, oxygen, and a sulfur compound as an impurity.
　　　〈その他の硫黄系正極活物質〉
　本発明の正極に用いられるその他の硫黄系正極活物質としては、上述したポリ硫化カーボン、単体硫黄、硫黄変性多環芳香族炭化水素、硫黄変性ゴム、コーヒー豆や海草等の植物原料と硫黄を熱処理したもの、又はこれらの複合体等を挙げることができる。これらの硫黄系正極活物質は、上述した各種の炭素材料に由来する炭素骨格を持つ。 <Other sulfur-based positive electrode active materials>
Other sulfur-based positive electrode active materials used in the positive electrode of the present invention include the above-mentioned polysulfur carbon, single sulfur, sulfur-modified polycyclic aromatic hydrocarbon, sulfur-modified rubber, plant materials such as coffee beans and seaweed, and sulfur. What was heat-treated, or these composites etc. can be mentioned. These sulfur-based positive electrode active materials have carbon skeletons derived from the various carbon materials described above.
　なお、正極活物質として硫黄変性ポリアクリロニトリルや硫黄変性ピッチを用いる場合には、正極活物質としてポリ硫化カーボンを用いる場合（正極活物質用の炭素材料として直鎖状不飽和ポリマーを用いる場合）に比べて、サイクル特性をさらに向上させることができる。これは、正極活物質としてポリ硫化カーボンを用いる場合には、放電時に硫黄とリチウムとが結合することにより、ポリ硫化カーボンに含まれる－ＣＳ－ＣＳ－結合や－Ｓ－Ｓ－結合が切断されて、ポリマーが切断されるためだと考えられる。したがって、本発明の正極の製造方法においては、炭素材料としてポリアクリロニトリルやピッチ系炭素材料を用いるのが好ましい。サイクル特性や容量の面ではポリアクリロニトリルを用いるのがより好ましく、コスト面ではピッチ系炭素材料を用いるのがより好ましい。また、炭素材料として、硫黄変性ポリアクリロニトリルと硫黄変性ピッチとを併用しても良い。 When using sulfur-modified polyacrylonitrile or sulfur-modified pitch as the positive electrode active material, using polysulfide carbon as the positive electrode active material (when using a linear unsaturated polymer as the carbon material for the positive electrode active material) In comparison, cycle characteristics can be further improved. This is because, when polysulfide carbon is used as the positive electrode active material, sulfur and lithium are combined at the time of discharge, whereby the -CS-CS- bond and -SS- bond contained in the polysulfide carbon are broken. It is believed that the polymer is cleaved. Therefore, in the method of manufacturing the positive electrode of the present invention, it is preferable to use polyacrylonitrile or a pitch-based carbon material as the carbon material. It is more preferable to use polyacrylonitrile in terms of cycle characteristics and capacity, and it is more preferable to use a pitch-based carbon material in terms of cost. Further, as the carbon material, sulfur-modified polyacrylonitrile and sulfur-modified pitch may be used in combination.
　（リチウムイオン二次電池用正極の製造方法）
　本発明の製造方法においては、上述した硫黄系正極活物質の材料（すなわち炭素材料および硫黄）と伝導材材料とを混合した混合材料を加熱する。混合材料は、乳鉢やボールミル等の一般的な混合装置で混合すれば良い。混合原料としては、硫黄と炭素材料と伝導材材料とを単に混合したものを用いても良いが、例えば、混合原料をペレット状に成形して用いても良い。 (Method of manufacturing positive electrode for lithium ion secondary battery)
In the manufacturing method of the present invention, a mixed material obtained by mixing the above-described sulfur-based positive electrode active material (i.e., carbon material and sulfur) and the conductive material is heated. The mixed material may be mixed by a general mixing device such as a mortar or a ball mill. As the mixed raw material, one obtained by simply mixing sulfur, a carbon material and a conductive material may be used, but for example, the mixed raw material may be formed into a pellet and used.
　熱処理工程において混合原料を加熱することで、混合原料に含まれる硫黄と炭素材料とが結合する。伝導材材料として未硫化の金属を用いる場合には、金属の硫化も生じる。熱処理工程は、密閉系でおこなっても良いし開放系でおこなっても良いが、硫黄蒸気の散逸を抑制するためには、密閉系で行うのが好ましい。また、熱処理工程を如何なる雰囲気で行うかについては特に問わないが、炭素材料と硫黄との結合を妨げない雰囲気（例えば、水素を含有しない雰囲気、非酸化性雰囲気）下で行うのが好ましい。例えば、雰囲気中に水素が存在すると、反応系中の硫黄が水素と反応して硫化水素となるため、反応系中の硫黄が失われる場合がある。また、特に炭素材料としてポリアクリロニトリルを用いる場合には、非酸化性雰囲気下で熱処理することで、ポリアクリロニトリルの閉環反応と同時に、蒸気状態の硫黄がポリアクリロニトリルと反応して、硫黄によって変性されたポリアクリロニトリルが得られると考えられる。ここでいう非酸化性雰囲気とは、酸化反応が進行しない程度の低酸素濃度とした減圧状態、窒素やアルゴン等の不活性ガス雰囲気、硫黄ガス雰囲気等を含む。 By heating the mixed raw material in the heat treatment step, sulfur contained in the mixed raw material and the carbon material are combined. When unsulfided metal is used as the conductive material, metal sulfidation also occurs. The heat treatment step may be performed in a closed system or an open system, but in order to suppress the dissipation of sulfur vapor, the closed system is preferable. Although the heat treatment step is not particularly limited as to the atmosphere, it is preferably performed in an atmosphere which does not prevent the bond between the carbon material and the sulfur (for example, an atmosphere containing no hydrogen or a non-oxidizing atmosphere). For example, when hydrogen is present in the atmosphere, sulfur in the reaction system reacts with hydrogen to form hydrogen sulfide, which may result in loss of sulfur in the reaction system. Further, particularly when using polyacrylonitrile as the carbon material, by heat treatment in a non-oxidative atmosphere, sulfur in the vapor state reacts with polyacrylonitrile simultaneously with the ring closure reaction of polyacrylonitrile and is modified by sulfur It is believed that polyacrylonitrile is obtained. The non-oxidative atmosphere referred to here includes a reduced pressure state where the oxygen concentration is low to such an extent that the oxidation reaction does not proceed, an inert gas atmosphere such as nitrogen and argon, a sulfur gas atmosphere and the like.
　熱処理工程を行う環境を密閉状態の非酸化性雰囲気とするための具体的な方法については特に限定はなく、例えば、硫黄蒸気が散逸しない程度の密閉性が保たれる容器中に混合原料を入れて、容器内を減圧または不活性ガス雰囲気にして加熱すれば良い。その他、混合原料を硫黄蒸気と反応し難い材料（例えばアルミニウムラミネートフィルム等）で真空包装した状態で加熱しても良い。この場合、発生した硫黄蒸気によって包装材料が破損しないように、例えば、水を入れたオートクレーブ等の耐圧容器中に、包装された原料を入れて加熱し、発生した水蒸気で包装材の外部から加圧することが好ましい。この方法によれば、包装材料の外部から水蒸気によって加圧されるので、硫黄蒸気によって包装材料が膨れて破損することが防止される。 There is no particular limitation on a specific method for making the environment in which the heat treatment process is performed a closed non-oxidizing atmosphere, for example, the mixed raw material is placed in a container in which the sealing property is maintained to such an extent that the sulfur vapor is not dissipated. Then, the inside of the container may be decompressed or heated to an inert gas atmosphere. In addition, you may heat in the state vacuum-packed with the material (for example, aluminum laminate film etc.) which is hard to react with a sulfur raw material. In this case, for example, the packaged raw material is placed in a pressure container such as an autoclave containing water and heated so that the packaging material is not damaged by the generated sulfur vapor, and the generated steam is added from the outside of the packaging material It is preferable to press. According to this method, since the steam is pressurized by steam from the outside of the packaging material, the sulfur vapor prevents the packaging material from being blown and broken.
　熱処理工程における混合原料の加熱時間は、加熱温度に応じて適宜設定すれば良く、特に限定しない。上述した好ましい加熱温度は、硫黄と炭素材料との結合が進行し、かつ、伝導材が変質しないような温度であれば良い。 The heating time of the mixed raw material in the heat treatment step may be appropriately set according to the heating temperature, and is not particularly limited. The above-described preferable heating temperature may be a temperature at which bonding between sulfur and the carbon material proceeds and the conductive material does not deteriorate.
　例えば、炭素材料としてポリアクリロニトリルを用いる場合、加熱温度は、２５０以上５００℃以下とすることが好ましく、２５０以上４００℃以下とすることがより好ましく、２５０以上３００℃以下とすることがさらに好ましい。また、炭素材料としてピッチ系炭素材料を用いる場合、加熱温度は、２００℃以上６００℃以下であるのが好ましく、３００℃以上５００℃以下であるのがより好ましく、３５０℃以上５００℃以下であるのがさらに好ましい。炭素材料としてピッチ系炭素材料を用いる場合には、熱処理工程においてピッチ系炭素材料の少なくとも一部と硫黄の少なくとも一部とが液体となる。換言すると、熱処理工程において、ピッチ系炭素材料の少なくとも一部と硫黄の少なくとも一部とは、液状で接触する。このため、熱処理工程におけるピッチ系炭素材料と硫黄との接触面積は大きく、ピッチ系炭素材料と硫黄とが充分に結合し、かつ硫黄系正極活物質からの硫黄の脱離が抑制される。 For example, when polyacrylonitrile is used as the carbon material, the heating temperature is preferably 250 or more and 500 ° C. or less, more preferably 250 or more and 400 ° C. or less, and still more preferably 250 or more and 300 ° C. or less. When using a pitch-based carbon material as the carbon material, the heating temperature is preferably 200 ° C. to 600 ° C., more preferably 300 ° C. to 500 ° C., and 350 ° C. to 500 ° C. Is more preferred. When a pitch-based carbon material is used as the carbon material, at least a portion of the pitch-based carbon material and at least a portion of sulfur become liquid in the heat treatment step. In other words, in the heat treatment step, at least a portion of the pitch-based carbon material and at least a portion of the sulfur contact in a liquid state. For this reason, the contact area of the pitch-based carbon material and sulfur in the heat treatment step is large, the pitch-based carbon material and sulfur are sufficiently bonded, and the detachment of sulfur from the sulfur-based positive electrode active material is suppressed.
　　熱処理工程においては、硫黄を還流するのが好ましい。この場合、混合原料の一部が気体となり、一部が液体となるように混合原料を加熱すれば良い。換言すると、混合原料の温度は、硫黄が気化する温度以上の温度であれば良い。ここで言う気化とは、硫黄が液体または固体から気体に相変化することを指し、沸騰、蒸発、昇華の何れによっても良い。参考までに、α硫黄（斜方硫黄、常温付近で最も安定な構造である）の融点は１１２．８℃、β硫黄（単斜硫黄）の融点は１１９．６℃、γ硫黄（単斜硫黄）の融点は１０６．８℃である。硫黄の沸点は４４４．７℃である。ところで、硫黄の蒸気圧は高いため、混合原料の温度が１５０℃以上になると、硫黄の蒸気の発生が目視でも確認できる。したがって、混合原料の温度が１５０℃以上であれば硫黄の還流は可能である。なお、熱処理工程において硫黄を還流する場合には、既知構造の還流装置を用いて硫黄を還流すれば良い。 In the heat treatment step, sulfur is preferably refluxed. In this case, the mixed material may be heated so that a part of the mixed material becomes a gas and a part becomes a liquid. In other words, the temperature of the mixed raw material may be a temperature higher than the temperature at which sulfur is vaporized. The term "vaporization" as used herein refers to phase change of sulfur from liquid or solid to gas, which may be boiling, evaporation or sublimation. For reference, the melting point of alpha sulfur (orthogonal sulfur, which is the most stable structure around normal temperature) is 112.8 ° C, the melting point of beta sulfur (monoclinic sulfur) is 119.6 ° C, gamma sulfur (monoclinic sulfur) The melting point of) is 106.8 ° C. The boiling point of sulfur is 444.7.degree. By the way, since the vapor pressure of sulfur is high, when the temperature of the mixed raw material reaches 150 ° C. or more, the generation of sulfur vapor can be visually confirmed. Therefore, if the temperature of the mixed raw material is 150 ° C. or more, sulfur reflux is possible. In addition, what is necessary is just to reflux sulfur using the reflux apparatus of known structure, when refluxing sulfur in a heat treatment process.
　なお、混合材料中の硫黄の配合量が過大である場合にも、熱処理工程において炭素材料に充分な量の硫黄を取り込むことができる。このため、炭素材料に対して硫黄を過大に配合する場合には、熱処理工程後の被処理体（硫黄系正極活物質－炭素材料複合体）から単体硫黄を除去する工程（単体硫黄除去工程）を行うことで、上述した単体硫黄による悪影響を抑制できる。詳しくは、混合原料中の炭素材料と硫黄との配合比を、質量比で１：２～１：１０とする場合、熱処理工程後の被処理体を減圧しつつ２００℃～２５０℃で加熱することで、炭素材料に充分な量の硫黄を取り込みつつ、残存する単体硫黄による悪影響を抑制できる。熱処理工程後の被処理体に単体硫黄除去工程を施さない場合には、この被処理体をそのまま硫黄系正極活物質として用いれば良い。また、熱処理工程後の被処理体に単体硫黄除去工程を施す場合には、単体硫黄除去工程後の被処理体を硫黄系正極活物質として用いれば良い。 Even in the case where the blending amount of sulfur in the mixed material is excessive, a sufficient amount of sulfur can be taken into the carbon material in the heat treatment step. For this reason, when sulfur is excessively blended to the carbon material, the step of removing elemental sulfur from the object to be treated (sulfur-based positive electrode active material-carbon material composite) after the heat treatment step (elementary sulfur removing step) By doing this, the adverse effect of the above-mentioned elemental sulfur can be suppressed. Specifically, when the blending ratio of carbon material to sulfur in the mixed raw material is 1: 2 to 1:10 in mass ratio, the object to be treated after the heat treatment step is heated at 200 ° C. to 250 ° C. while reducing pressure. Thus, it is possible to suppress the adverse effect of remaining single sulfur while incorporating a sufficient amount of sulfur into the carbon material. When the single sulfur removing step is not performed on the object to be treated after the heat treatment step, the object to be treated may be used as it is as a sulfur-based positive electrode active material. When the single sulfur removing step is performed on the target after the heat treatment step, the target after the single sulfur removing step may be used as the sulfur-based positive electrode active material.
　（リチウムイオン二次電池用正極）
　本発明の正極は、上述した本発明の製造方法で製造され、硫黄系正極活物質および伝導材を含有する。なお、本発明の正極が、硫黄変性ポリアクリロニトリルおよび／または硫黄変性ピッチを硫黄系正極活物質として含む場合、正極のラマンスペクトルには、図２に示す硫黄変性ポリアクリロニトリルに由来するピークおよび／または図４に示す硫黄変性ピッチに由来するピークが、他のピークとともに認められる。 (Positive electrode for lithium ion secondary battery)
The positive electrode of the present invention is manufactured by the above-described manufacturing method of the present invention, and contains a sulfur-based positive electrode active material and a conductive material. When the positive electrode of the present invention contains sulfur-modified polyacrylonitrile and / or sulfur-modified pitch as a sulfur-based positive electrode active material, the Raman spectrum of the positive electrode shows peaks derived from the sulfur-modified polyacrylonitrile shown in FIG. The peak derived from the sulfur-modified pitch shown in FIG. 4 is observed together with other peaks.
　正極は、正極活物質および伝導材以外は、一般的なリチウムイオン二次電池用正極と同様の構造にできる。例えば、本発明の正極は、硫黄系正極活物質と伝導材との混合物（すなわち熱処理工程により得られた被処理体）、導電助剤、バインダ、および溶媒を混合した正極材料を、集電体に塗布することによって製作できる。或いは、硫黄粉末、炭素材料粉末および伝導材材料粉末を混合した混合原料を、正極用集電体に充填した後に加熱する（熱処理工程を施す）こともできる。この方法によれば、硫黄系正極活物質と伝導材との混合物を製造すると同時に、バインダを用いることなく、この混合物と集電体とを一体化させることができる。バインダを用いなければ、正極質量あたり正極活物質の量を増大させることができ、正極質量当たりの容量を向上させることができる。 The positive electrode can have the same structure as that of a general lithium ion secondary battery positive electrode except for the positive electrode active material and the conductive material. For example, the positive electrode of the present invention is a current collector comprising a mixture of a sulfur-based positive electrode active material and a conductive material (that is, an object to be treated obtained by the heat treatment step), a conductive additive, a binder, and a solvent. It can be manufactured by applying to Alternatively, the mixed raw material in which the sulfur powder, the carbon material powder and the conductive material powder are mixed may be filled in the current collector for the positive electrode and then heated (the heat treatment step may be performed). According to this method, a mixture of the sulfur-based positive electrode active material and the conductive material can be manufactured, and at the same time, the mixture and the current collector can be integrated without using a binder. If a binder is not used, the amount of positive electrode active material per positive electrode mass can be increased, and the capacity per positive electrode mass can be improved.
　正極は伝導材を含む。正極における硫黄系正極活物質と伝導材との含有比は、質量比で、１０：０．１～１０：５であるのが好ましく、１０：０．３～１０：２であるのがより好ましい。 The positive electrode contains a conductive material. The content ratio of the sulfur-based positive electrode active material to the conductive material in the positive electrode is preferably 10: 0.1 to 10: 5 by mass ratio, and more preferably 10: 0.3 to 10: 2 .
　導電助剤としては、気相法炭素繊維（Ｖａｐｏｒ　Ｇｒｏｗｎ　Ｃａｒｂｏｎ　Ｆｉｂｅｒ：ＶＧＣＦ）、炭素粉末、カーボンブラック（ＣＢ）、アセチレンブラック（ＡＢ）、ケッチェンブラック（ＫＢ）、黒鉛、アルミニウムおよびチタン等の、正極電位において安定な金属の微粉末等が例示される。なお、伝導材の種類や配合量等によっては、導電助剤を配合しなくても良い場合もある。 As the conductive aid, vapor grown carbon fiber (VGCF), carbon powder, carbon black (CB), acetylene black (AB), ketjen black (KB), graphite, aluminum, titanium, etc. For example, fine powder of metal stable at positive electrode potential is exemplified. In addition, depending on the kind and compounding quantity of a conductive material, it may not be necessary to mix | blend a conductive support agent.
　バインダとしては、ポリフッ化ビニリデン（ＰｏｌｙＶｉｎｙｌｉｄｅｎｅ　ＤｉＦｌｕｏｒｉｄｅ：ＰＶＤＦ）、ポリ四フッ化エチレン（ＰＴＦＥ）、スチレン－ブタジエンゴム（ＳＢＲ）、ポリイミド（ＰＩ）、ポリアミドイミド（ＰＡＩ）、カルボキシメチルセルロース（ＣＭＣ）、ポリ塩化ビニル（ＰＶＣ）、メタクリル樹脂（ＰＭＡ）、ポリアクリロニトリル（ＰＡＮ）、変性ポリフェニレンオキシド（ＰＰＯ）、ポリエチレンオキシド（ＰＥＯ）、ポリエチレン（ＰＥ）、ポリプロピレン（ＰＰ）等が例示される。 As a binder, polyvinylidene fluoride (PolyVinylidene DiFluoride: PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyimide (PI), polyamidoimide (PAI), carboxymethylcellulose (CMC), polychlorinated Examples include vinyl (PVC), methacrylic resin (PMA), polyacrylonitrile (PAN), modified polyphenylene oxide (PPO), polyethylene oxide (PEO), polyethylene (PE), polypropylene (PP) and the like.
　溶媒としては、Ｎ－メチル－２－ピロリドン、Ｎ，Ｎ－ジメチルホルムアルデヒド、アルコール、水等が例示される。これら導電助剤、バインダおよび溶媒は、それぞれ複数種を混合して用いても良い。これらの材料の配合量は特に問わないが、例えば、硫黄系正極活物質１００質量部に対して、導電助剤２０～１００質量部程度、バインダ１０～２０質量部程度を配合するのが好ましい。また、その他の方法として、本発明の硫黄系正極活物質と上述した導電助剤およびバインダとの混合物を乳鉢やプレス機などで混練しかつフィルム状にし、フィルム状の混合物をプレス機等で集電体に圧着することで、本発明のリチウムイオン二次電池用正極を製造することもできる。 Examples of the solvent include N-methyl-2-pyrrolidone, N, N-dimethylformaldehyde, alcohol, water and the like. These conductive aids, binders and solvents may be used in combination of two or more. Although the compounding amount of these materials is not particularly limited, for example, it is preferable to mix about 20 to 100 parts by mass of the conductive aid and about 10 to 20 parts by mass of the binder with respect to 100 parts by mass of the sulfur-based positive electrode active material. Further, as another method, a mixture of the sulfur-based positive electrode active material of the present invention and the above-mentioned conductive additive and binder is kneaded with a mortar or press and made into a film, and the film-like mixture is collected with a press or the like. The positive electrode for a lithium ion secondary battery of the present invention can also be produced by pressure bonding to a current collector.
　集電体としては、リチウムイオン二次電池用正極に一般に用いられるものを使用すれば良い。例えば集電体としては、アルミニウム箔、アルミニウムメッシュ、パンチングアルミニウムシート、アルミニウムエキスパンドシート、ステンレススチール箔、ステンレススチールメッシュ、パンチングステンレススチールシート、ステンレススチールエキスパンドシート、発泡ニッケル、ニッケル不織布、銅箔、銅メッシュ、パンチング銅シート、銅エキスパンドシート、チタン箔、チタンメッシュ、カーボン不織布、カーボン織布等が例示される。このうち黒鉛化度の高いカーボンから成るカーボン不織布／織布集電体は、水素を含まず、硫黄との反応性が低いために、硫黄系正極活物質用の集電体として好適である。黒鉛化度の高い炭素繊維の原料としては、カーボン繊維の材料となる各種のピッチ（すなわち、石油、石炭、コールタールなどの副生成物）やポリアクリロニトリル繊維等を用いることができる。 What is generally used for the positive electrode for lithium ion secondary batteries may be used as a collector. For example, as a current collector, aluminum foil, aluminum mesh, punching aluminum sheet, aluminum expanded sheet, stainless steel foil, stainless steel mesh, punching stainless steel sheet, stainless steel expanded sheet, foamed nickel, nickel non-woven fabric, copper foil, copper mesh , A punched copper sheet, a copper expanded sheet, a titanium foil, a titanium mesh, a carbon non-woven fabric, a carbon woven fabric and the like. Among them, a carbon nonwoven fabric / woven fabric current collector made of carbon having a high degree of graphitization is suitable as a current collector for a sulfur-based positive electrode active material because it does not contain hydrogen and has low reactivity with sulfur. As a raw material of carbon fibers having a high degree of graphitization, various pitches (that is, by-products such as petroleum, coal, coal tar, etc.), polyacrylonitrile fibers, etc. can be used as materials of carbon fibers.
　（リチウムイオン二次電池）
　以下、本発明の正極を用いたリチウムイオン二次電池の構成について説明する。以下、本発明の正極を用いたリチウムイオン二次電池を単にリチウムイオン二次電池用と略する。なお、正極に関しては、上述したとおりである。 (Lithium ion secondary battery)
Hereinafter, the structure of the lithium ion secondary battery using the positive electrode of this invention is demonstrated. Hereinafter, a lithium ion secondary battery using the positive electrode of the present invention is simply abbreviated as a lithium ion secondary battery. The positive electrode is as described above.
　　〔負極〕
　負極材料としては、リチウムと合金化可能な元素であるＮａ、Ｋ、Ｒｂ、Ｃｓ、Ｆｒ、Ｂｅ、Ｍｇ、Ｃａ、Ｓｒ、Ｂａ、Ｒａ、Ｔｉ、Ａｇ、Ｚｎ、Ｃｄ、Ａｌ、Ｇａ、Ｉｎ、Ｓｉ、Ｇｅ、Ｓｎ、Ｐｂ、Ｓｂ、Ｂｉおよび／またはその化合物の少なくとも１種を有する材料、公知の金属リチウム、黒鉛などの炭素系材料、シリコン薄膜などのシリコン系材料、銅－錫やコバルト－錫などの合金系材料を使用できる。負極材料として、リチウムを含まない材料、例えば、上記した負極材料の内で、炭素系材料、シリコン系材料、合金系材料等を用いる場合には、デンドライドの発生による正負極間の短絡を生じ難い点で有利である。ただし、これらのリチウムを含まない負極材料を本発明の正極と組み合わせて用いる場合には、正極および負極が何れもリチウムを含まない。このため、負極および正極の何れか一方、または両方にあらかじめリチウムを挿入するリチウムプリドープ処理が必要となる。リチウムのプリドープ法としては公知の方法に従えば良い。例えば負極にリチウムをドープする方法としては、電解ドープ法、貼り付けプリドープ法等の方法が挙げられる。電解ドープ法は、対極に金属リチウムを用いて半電池を組み、負極に電気化学的にリチウムをドープする方法である。貼り付けプリドープ法は、金属リチウム箔を電極に貼り付けたあと電解液の中に放置し電極へのリチウムの拡散を利用して負極にリチウムを挿入する方法である。また、正極にリチウムをプリドープする場合にも、上記した電解ドープ法を利用することができる。 [Negative electrode]
As a negative electrode material, elements which can be alloyed with lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Materials having at least one of Si, Ge, Sn, Pb, Sb, Bi and / or compounds thereof, known metallic lithium, carbon-based materials such as graphite, silicon-based materials such as silicon thin film, copper-tin and cobalt- Alloy materials such as tin can be used. In the case where a carbon-based material, a silicon-based material, an alloy-based material or the like is used as the negative electrode material, for example, a material not containing lithium, for example, among the above-described negative electrode materials, short circuit between positive and negative electrodes due to generation of dendrite hardly occurs It is advantageous in point. However, when these negative electrode materials not containing lithium are used in combination with the positive electrode of the present invention, neither the positive electrode nor the negative electrode contains lithium. Therefore, a lithium pre-doping process is required in which lithium is inserted in advance into one or both of the negative electrode and the positive electrode. A known method may be used as the lithium pre-doping method. For example, as a method of doping lithium to the negative electrode, methods such as electrolytic doping method, sticking pre-doping method and the like can be mentioned. The electrolytic doping method is a method of forming a half cell using metallic lithium as a counter electrode and electrochemically doping lithium on a negative electrode. The bonding pre-doping method is a method in which a metal lithium foil is bonded to an electrode, then left in an electrolytic solution, and lithium is inserted into the negative electrode using diffusion of lithium to the electrode. In addition, the above-described electrolytic doping method can be used also in the case of pre-doping lithium to the positive electrode.
　リチウムを含まない負極材料としては、特に、高容量の負極材料であるシリコン系材料を用いるのが好ましく、その中でも電極厚さが薄くて体積当りの容量で有利となる薄膜シリコンを用いるのがより好ましい。 As a negative electrode material not containing lithium, it is particularly preferable to use a silicon-based material which is a high capacity negative electrode material, and among them, it is more preferable to use thin film silicon which has a thin electrode thickness and which is advantageous in capacity per volume. preferable.
　　〔電解質〕
　リチウムイオン二次電池に用いる電解質としては、有機溶媒に電解質（支持塩）であるアルカリ金属塩を溶解させたものを用いることができる。有機溶媒としては、エチレンカーボネート、プロピレンカーボネート、ジメチルカーボネート、ジエチルカーボネート、エチルメチルカーボネート、ジメチルエーテル、ガンマ－ブチロラクトン、アセトニトリル等の非水系溶媒から選ばれる少なくとも一種を用いるのが好ましい。電解質としては、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＡｓＦ６、ＬｉＣＦ３ＳＯ３、ＬｉＩ、ＬｉＣｌＯ４等を用いることができる。電解質の濃度は、０．５ｍｏｌ／ｌ～１．７ｍｏｌ／ｌ程度であれば良い。なお、電解質は液状に限定されない。例えば、リチウムイオン二次電池がリチウムポリマー二次電池である場合、電解質は固体状（例えば高分子ゲル状）をなす。 〔Electrolytes〕
As an electrolyte used for a lithium ion secondary battery, what melt | dissolved the alkali metal salt which is electrolyte (supporting salt) in the organic solvent can be used. As the organic solvent, it is preferable to use at least one selected from non-aqueous solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl ether, gamma-butyrolactone and acetonitrile. As the electrolyte, LiPF 6 , LiBF 4 , LiAsF 6 , LiCF 3 SO 3 , LiI, LiClO 4 or the like can be used. The concentration of the electrolyte may be about 0.5 mol / l to 1.7 mol / l. The electrolyte is not limited to liquid. For example, when the lithium ion secondary battery is a lithium polymer secondary battery, the electrolyte is in a solid state (for example, in the form of polymer gel).
　　〔その他〕
　リチウムイオン二次電池は、上述した負極、正極、電解質以外にも、セパレータ等の部材を備えても良い。セパレータは、正極と負極との間に介在し、正極と負極との間のイオンの移動を許容するとともに、正極と負極との内部短絡を防止する。リチウムイオン二次電池が密閉型であれば、セパレータには電解液を保持する機能も求められる。セパレータとしては、ポリエチレン、ポリプロピレン、ポリアクリロニトリル、アラミド、ポリイミド、セルロース、ガラス等を材料とする薄肉かつ微多孔性または不織布状の膜を用いるのが好ましい。リチウムイオン二次電池の形状は特に限定されず、円筒型、積層型、コイン型等、種々の形状にできる。 [Others]
A lithium ion secondary battery may be equipped with members, such as a separator, besides the negative electrode mentioned above, a positive electrode, and electrolyte. The separator is interposed between the positive electrode and the negative electrode, allows movement of ions between the positive electrode and the negative electrode, and prevents an internal short circuit between the positive electrode and the negative electrode. If the lithium ion secondary battery is a closed type, the separator is also required to have a function of holding the electrolytic solution. As the separator, it is preferable to use a thin, microporous or non-woven membrane made of polyethylene, polypropylene, polyacrylonitrile, aramid, polyimide, cellulose, glass or the like. The shape of the lithium ion secondary battery is not particularly limited, and may be various shapes such as a cylindrical shape, a laminated shape, and a coin shape.
　以下、本発明の正極、正極の製造方法およびリチウムイオン二次電池を具体的に説明する。 The positive electrode, the method for producing a positive electrode, and the lithium ion secondary battery of the present invention will be specifically described below.
　（実施例１）
　〔１〕混合原料
　硫黄粉末として、篩いを用いて分級した際に粒径５０μｍ以下となるものを準備した。ポリアクリロニトリル粉末として、電子顕微鏡で確認した場合に粒径が０．２μｍ～２μｍの範囲にあるものを準備した。伝導材材料として、篩を用いて分級した際に粒径５０μｍ以下であったＬａ２Ｓ３を準備した。 Example 1
[1] Mixed raw material As a sulfur powder, when it classified using a sieve, the thing used as a particle size of 50 micrometers or less was prepared. As the polyacrylonitrile powder, one having a particle diameter in the range of 0.2 μm to 2 μm as prepared by an electron microscope was prepared. As a conductive material, La 2 S 3 having a particle size of 50 μm or less when classified using a sieve was prepared.
　硫黄粉末５ｇとポリアクリロニトリル粉末１ｇと伝導材材料粉末０．１ｇと、を乳鉢で混合・粉砕して、混合原料を得た。 5 g of sulfur powder, 1 g of polyacrylonitrile powder and 0.1 g of conductive material powder were mixed and pulverized in a mortar to obtain a mixed raw material.
　〔２〕装置
　図５に示すように、反応装置１は、反応容器２、蓋３、熱電対４、アルミナ保護管４０、２つのアルミナ管（ガス導入管５、ガス排出管６）、アルゴンガス配管５０、アルゴンガスを収容したガスタンク５１、トラップ配管６０、水酸化ナトリウム水溶液６１を収容したトラップ槽６２、電気炉７、電気炉に接続されている温度コントローラ７０を持つ。 [2] Device As shown in FIG. 5, the reaction device 1 comprises a reaction container 2, a lid 3, a thermocouple 4, an alumina protective tube 40, two alumina tubes (gas inlet tube 5, gas outlet tube 6), argon gas It has a piping 50, a gas tank 51 containing argon gas, a trap piping 60, a trap tank 62 containing an aqueous sodium hydroxide solution 61, an electric furnace 7, and a temperature controller 70 connected to the electric furnace.
　反応容器２としては、有底筒状をなすガラス管（石英ガラス製）を用いた。後述する熱処理工程において、反応容器２には混合原料９を収容した。反応容器２の開口部は、３つの貫通孔を持つガラス製の蓋３で閉じた。貫通孔の１つには、熱電対４を収容したアルミナ保護管４０（アルミナＳＳＡ－Ｓ、株式会社ニッカトー製）を取り付けた。貫通孔の他の１つには、ガス導入管５（アルミナＳＳＡ－Ｓ、株式会社ニッカトー製）を取り付けた。貫通孔の残りの１つには、ガス排出管６（アルミナＳＳＡ－Ｓ、株式会社ニッカトー製）を取り付けた。なお、反応容器２は、外径６０ｍｍ、内径５０ｍｍ、長さ３００ｍｍであった。アルミナ保護管４０は、外径４ｍｍ、内径２ｍｍ、長さ２５０ｍｍであった。ガス導入管５およびガス排出管６は、外径６ｍｍ、内径４ｍｍ、長さ１５０ｍｍであった。ガス導入管５およびガス排出管６の先端は、蓋３の外部（反応容器２内）に露出した。この露出した部分の長さは３ｍｍであった。ガス導入管５およびガス排出管６の先端は、後述する熱処理工程においてほぼ１００℃以下となる。このため、熱処理工程において生じる硫黄蒸気は、ガス導入管５およびガス排出管６から流出せず、反応容器２に戻される（還流する）。 As the reaction vessel 2, a bottomed cylindrical glass tube (made of quartz glass) was used. The mixed raw material 9 was accommodated in the reaction container 2 in the heat treatment process mentioned later. The opening of the reaction vessel 2 was closed by a glass lid 3 having three through holes. An alumina protective tube 40 (alumina SSA-S, manufactured by Nikkato Co., Ltd.) containing a thermocouple 4 was attached to one of the through holes. A gas introduction pipe 5 (alumina SSA-S, manufactured by Nikkato Co., Ltd.) was attached to the other one of the through holes. A gas exhaust pipe 6 (alumina SSA-S, manufactured by Nikkato Co., Ltd.) was attached to the remaining one of the through holes. The reaction vessel 2 had an outer diameter of 60 mm, an inner diameter of 50 mm, and a length of 300 mm. The alumina protective tube 40 had an outer diameter of 4 mm, an inner diameter of 2 mm, and a length of 250 mm. The gas introduction pipe 5 and the gas discharge pipe 6 had an outer diameter of 6 mm, an inner diameter of 4 mm, and a length of 150 mm. The tips of the gas introduction pipe 5 and the gas discharge pipe 6 were exposed to the outside of the lid 3 (in the reaction vessel 2). The length of this exposed portion was 3 mm. The tips of the gas introduction pipe 5 and the gas discharge pipe 6 become almost 100 ° C. or less in the heat treatment step described later. For this reason, the sulfur vapor generated in the heat treatment step does not flow out from the gas introduction pipe 5 and the gas discharge pipe 6 and is returned (refluxed) to the reaction vessel 2.
　アルミナ保護管４０に入れた熱電対４の先端は、間接的に反応容器２中の混合原料９の温度を測定した。熱電対４で測定した温度は、電気炉７の温度コントローラ７０にフィードバックした。 The tip of the thermocouple 4 placed in the alumina protective tube 40 indirectly measured the temperature of the mixed raw material 9 in the reaction vessel 2. The temperature measured by the thermocouple 4 was fed back to the temperature controller 70 of the electric furnace 7.
　ガス導入管５にはアルゴンガス配管５０を接続した。アルゴンガス配管５０はアルゴンガスを収容したガスタンク５１に接続した。ガス排出管６にはトラップ配管６０の一端を接続した。トラップ配管６０の他端は、トラップ槽６２中の水酸化ナトリウム水溶液６１に挿入した。なお、トラップ配管６０およびトラップ槽６２は、後述する熱処理工程で生じる硫化水素ガスのトラップである。 An argon gas pipe 50 was connected to the gas introduction pipe 5. The argon gas pipe 50 was connected to a gas tank 51 containing argon gas. One end of a trap pipe 60 was connected to the gas discharge pipe 6. The other end of the trap pipe 60 was inserted into the sodium hydroxide aqueous solution 61 in the trap tank 62. The trap pipe 60 and the trap tank 62 are traps of hydrogen sulfide gas generated in a heat treatment process described later.
　〔３〕熱処理工程
　混合原料９を収容した反応容器２を、電気炉７（ルツボ炉、開口幅φ８０ｍｍ、加熱高さ１００ｍｍ）に収容した。このとき、ガス導入管５を介して反応容器２の内部にアルゴンを導入した。このときのアルゴンガスの流速は１００ｍｌ／分であった。アルゴンガスの導入開始１０分後に、アルゴンガスの導入を継続しつつ反応容器２中の混合原料９の加熱を開始した。このときの昇温速度は５℃／分であった。混合原料９が１００℃になった時点で、混合原料９の加熱を継続しつつアルゴンガスの導入を停止した。混合原料９が約２００℃になるとガスが発生した。混合原料９が３３０℃になった時点で加熱を停止した。加熱停止後、混合原料９の温度は３５０℃にまで上昇し、その後低下した。したがって、この熱処理工程において、混合原料９は３５０℃にまで加熱された。その後、混合原料９を自然冷却し、混合原料９が室温（約２５℃）にまで冷却された時点で反応容器２から生成物（すなわち、熱処理工程後の被処理体）を取り出した。なお、このときの加熱時間は３５０℃で約５分であり、硫黄は還流された。 [3] Heat Treatment Step The reaction vessel 2 containing the mixed raw material 9 was housed in an electric furnace 7 (crucible furnace, opening width φ 80 mm, heating height 100 mm). At this time, argon was introduced into the reaction vessel 2 through the gas introduction pipe 5. The flow rate of argon gas at this time was 100 ml / min. Ten minutes after the start of the introduction of the argon gas, heating of the mixed material 9 in the reaction vessel 2 was started while continuing the introduction of the argon gas. The temperature rising rate at this time was 5 ° C./min. When the mixed material 9 reached 100 ° C., the introduction of argon gas was stopped while continuing to heat the mixed material 9. When the mixed material 9 reached about 200 ° C., gas was generated. Heating was stopped when mixed material 9 reached 330 ° C. After the heating was stopped, the temperature of the mixed raw material 9 rose to 350 ° C. and then dropped. Therefore, the mixed raw material 9 was heated to 350 ° C. in this heat treatment step. Thereafter, the mixed raw material 9 was naturally cooled, and when the mixed raw material 9 was cooled to room temperature (about 25 ° C.), the product (that is, the object to be treated after the heat treatment step) was taken out from the reaction vessel 2. The heating time at this time was about 5 minutes at 350 ° C., and the sulfur was refluxed.
　〔４〕単体硫黄除去工程
　熱処理工程後の被処理体に残存する単体硫黄（遊離の硫黄）を除去するために、以下の工程をおこなった。 [4] Single Sulfur Removal Step In order to remove single sulfur (free sulfur) remaining on the object to be treated after the heat treatment step, the following steps were carried out.
　熱処理工程後の被処理体を乳鉢で粉砕した。粉砕物２ｇをガラスチューブオーブンに入れ、真空吸引しつつ２５０℃で３時間加熱した。このときの昇温温度は１０℃／分であった。この工程により、熱処理工程後の被処理体に残存する単体硫黄が蒸発・除去され、単体硫黄を含まない（または、ほぼ含まない）硫黄系正極活物質－伝導材複合体を得た。 The object to be treated after the heat treatment step was crushed in a mortar. Two grams of the ground material was placed in a glass tube oven and heated at 250 ° C. for 3 hours with vacuum suction. The temperature rising temperature at this time was 10 ° C./min. By this step, the single sulfur remaining on the object to be treated after the heat treatment step is evaporated and removed, and a sulfur-based positive electrode active material-conductive material composite which does not contain (or almost does not contain) single sulfur is obtained.
　〈リチウムイオン二次電池の製作〉
　〔１〕正極
　硫黄系正極活物質－伝導材複合体３ｍｇとアセチレンブラック２．７ｍｇとポリテトラフルオロエチレン（ＰＴＦＥ）０．３ｍｇとの混合物を、ヘキサンを適量加えつつ、メノウ製乳鉢でフィルム状になるまで混練し、フィルム状の正極材料を得た。この正極材料全量を、直径１４ｍｍの円形に打ち抜いたアルミニウムメッシュ（メッシュ粗さ＃１００）にプレス機で圧着し、８０℃で一晩乾燥した。この工程で、実施例１のリチウムイオン二次電池用正極を得た。なお、この正極における伝導材はＬａ２Ｓ３であり、硫黄系正極活物質と伝導材との含有比（質量比）は１０：０．６であった。 <Production of lithium ion secondary battery>
[1] Positive electrode A mixture of 3 mg of a sulfur-based positive electrode active material-conductive material composite, 2.7 mg of acetylene black and 0.3 mg of polytetrafluoroethylene (PTFE) in an agate mortar to form a film while adding an appropriate amount of hexane It knead | mixed until it became, and obtained the film-form positive electrode material. The whole amount of the positive electrode material was press-bonded to a 14 mm-diameter circular punched aluminum mesh (mesh roughness # 100) with a press, and dried overnight at 80 ° C. In this step, the positive electrode for a lithium ion secondary battery of Example 1 was obtained. The conductive material in this positive electrode was La 2 S 3 , and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 0.6.
　〔２〕負極
　負極としては、金属リチウム箔（直径１４ｍｍ、厚さ５００μｍの円盤状、本城金属製）を用いた。 [2] Negative Electrode As a negative electrode, metal lithium foil (disk-shaped 14 mm in diameter and 500 μm thick, made of Honjo Metal) was used.
　〔３〕電解液
　電解液としては、エチレンカーボネートとジエチルカーボネートとの混合溶媒に、ＬｉＰＦ６を溶解した非水電解質を用いた。エチレンカーボネートとジエチルカーボネートとは体積比１：１で混合した。電解液中のＬｉＰＦ６の濃度は、１．０ｍｏｌ／ｌであった。 [3] Electrolyte As the electrolyte, a non-aqueous electrolyte in which LiPF 6 was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate was used. Ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1. The concentration of LiPF 6 in the electrolyte was 1.0 mol / l.
　〔４〕電池
　〔１〕、〔２〕で得られた正極および負極を用いて、コイン電池を製作した。詳しくは、ドライルーム内で、セパレータ（Ｃｅｌｇａｒｄ社製Ｃｅｌｇａｒｄ２４００、厚さ２５μｍのポリプロピレン微孔質膜）と、ガラス不織布フィルタ（厚さ４４０μｍ、ＡＤＶＡＮＴＥＣ社製、ＧＡ１００）と、を正極と負極との間に挟装して、電極体電池とした。この電極体電池を、ステンレス容器からなる電池ケース（ＣＲ２０３２型コイン電池用部材、宝泉株式会社製）に収容した。電池ケースには〔３〕で得られた電解液を注入した。電池ケースをカシメ機で密閉して、実施例１のリチウムイオン二次電池を得た。 [4] Battery A coin battery was manufactured using the positive electrode and the negative electrode obtained in [1] and [2]. More specifically, in a dry room, a separator (Celgard 2400, 25 μm thick polypropylene microporous membrane) and a glass non-woven filter (440 μm thick, ADVANTEC, GA 100) between the positive electrode and the negative electrode in a dry room The electrode battery was used as an electrode battery. The electrode battery was housed in a battery case (CR2032 type coin battery member manufactured by Takasen Co., Ltd.) consisting of a stainless steel container. The electrolytic solution obtained in [3] was injected into the battery case. The battery case was sealed with a caulking machine to obtain the lithium ion secondary battery of Example 1.
　（実施例２）
　実施例２の正極の製造方法は、混合原料として、硫黄粉末５ｇとポリアクリロニトリル粉末１ｇと伝導材材料粉末０．３ｇとの混合物を用いたこと以外は、実施例１の正極の製造方法と同じである。実施例２の製造方法では、混合原料におけるポリアクリロニトリルと伝導材材料との質量比は１：０．３であった。また、実施例２の正極における伝導材は実施例１と同じＬａ２Ｓ３であり、硫黄系正極活物質と伝導材との含有比（質量比）は１０：１．８であった。実施例２のリチウムイオン二次電池は、実施例２の正極を用いたこと以外は実施例１のリチウムイオン二次電池と同じである。 (Example 2)
The method of manufacturing the positive electrode of Example 2 is the same as the method of manufacturing the positive electrode of Example 1 except that a mixture of 5 g of sulfur powder, 1 g of polyacrylonitrile powder, and 0.3 g of conductive material powder is used as a mixed material. It is. In the manufacturing method of Example 2, the mass ratio of polyacrylonitrile to the conductive material in the mixed raw material was 1: 0.3. The conductive material in the positive electrode of Example 2 was La 2 S 3 as in Example 1, and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 1.8. The lithium ion secondary battery of Example 2 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 2 is used.
　（実施例３）
　実施例３の正極の製造方法は、混合原料として、硫黄粉末５ｇとポリアクリロニトリル粉末１ｇと伝導材材料粉末０．５ｇとの混合物を用いたこと以外は、実施例１の正極の製造方法と同じである。実施例３の製造方法では、混合原料におけるポリアクリロニトリルと伝導材材料との質量比は１：０．５であった。また、実施例３の正極における伝導材は実施例１、２と同じＬａ２Ｓ３であり、硫黄系正極活物質と伝導材との含有比（質量比）は１０：２．９であった。実施例３のリチウムイオン二次電池は、実施例３の正極を用いたこと以外は実施例１のリチウムイオン二次電池と同じである。 (Example 3)
The method of manufacturing the positive electrode of Example 3 is the same as the method of manufacturing the positive electrode of Example 1 except that a mixture of 5 g of sulfur powder, 1 g of polyacrylonitrile powder, and 0.5 g of conductive material powder is used as the mixed raw material. It is. In the manufacturing method of Example 3, the mass ratio of polyacrylonitrile to the conductive material in the mixed raw material was 1: 0.5. The conductive material in the positive electrode of Example 3 was La 2 S 3 as in Examples 1 and 2, and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 2.9. . The lithium ion secondary battery of Example 3 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 3 is used.
　（実施例４）
　実施例４の正極の製造方法は、伝導材材料としてＴｉＳ２を用い、混合原料として硫黄粉末５ｇとポリアクリロニトリル粉末１ｇと伝導材材料粉末０．１ｇとの混合物を用いたこと以外は、実施例１の正極の製造方法と同じである。実施例４の製造方法では、混合原料におけるポリアクリロニトリルと伝導材材料との質量比は１：０．１であった。また、実施例４の正極における伝導材はＴｉＳ２であり、硫黄系正極活物質と伝導材との含有比（質量比）は１０：０．６であった。実施例４のリチウムイオン二次電池は、実施例４の正極を用いたこと以外は実施例１のリチウムイオン二次電池と同じである。 (Example 4)
The manufacturing method of the positive electrode of Example 4 is an example except that a mixture of 5 g of sulfur powder, 1 g of polyacrylonitrile powder and 0.1 g of conductive material powder was used as the mixed material and TiS 2 was used as the mixed material. It is the same as the manufacturing method of the positive electrode of 1. In the manufacturing method of Example 4, the mass ratio of polyacrylonitrile to the conductive material in the mixed raw material was 1: 0.1. The conductive material in the positive electrode of Example 4 was TiS 2 , and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 0.6. The lithium ion secondary battery of Example 4 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 4 is used.
　（実施例５）
　実施例５の正極の製造方法は、伝導材材料としてＳｍ２Ｓ３を用い、混合原料として硫黄粉末５ｇとポリアクリロニトリル粉末１ｇと伝導材材料粉末０．１ｇとの混合物を用いたこと以外は、実施例１の正極の製造方法と同じである。実施例５の製造方法では、混合原料におけるポリアクリロニトリルと伝導材材料との質量比は１：０．１であった。また、実施例５の正極における伝導材はＳｍ２Ｓ３であり、硫黄系正極活物質と伝導材との含有比（質量比）は１０：０．６であった。実施例５のリチウムイオン二次電池は、実施例５の正極を用いたこと以外は実施例１のリチウムイオン二次電池と同じである。 (Example 5)
The manufacturing method of the positive electrode of Example 5 uses Sm 2 S 3 as the conductive material and uses a mixture of 5 g of sulfur powder, 1 g of polyacrylonitrile powder and 0.1 g of conductive material powder as the mixed raw material. It is the same as the method of manufacturing the positive electrode of Example 1. In the manufacturing method of Example 5, the mass ratio of polyacrylonitrile to the conductive material in the mixed raw material was 1: 0.1. The conductive material in the positive electrode of Example 5 was Sm 2 S 3 , and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 0.6. The lithium ion secondary battery of Example 5 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 5 is used.
　（実施例６）
　実施例６の正極の製造方法は、伝導材材料としてＣｅ２Ｓ３を用い、混合原料として硫黄粉末５ｇとポリアクリロニトリル粉末１ｇと伝導材材料粉末０．１ｇとの混合物を用いたこと以外は、実施例１の正極の製造方法と同じである。実施例６の製造方法では、混合原料におけるポリアクリロニトリルと伝導材材料との質量比は１：０．１であった。また、実施例６の正極における伝導材はＣｅ２Ｓ３であり、硫黄系正極活物質と伝導材との含有比（質量比）は１０：０．６であった。実施例６のリチウムイオン二次電池は、実施例６の正極を用いたこと以外は実施例１のリチウムイオン二次電池と同じである。 (Example 6)
The manufacturing method of the positive electrode of Example 6 uses Ce 2 S 3 as the conductive material and uses a mixture of 5 g of sulfur powder, 1 g of polyacrylonitrile powder and 0.1 g of conductive material powder as mixed raw materials. It is the same as the method of manufacturing the positive electrode of Example 1. In the manufacturing method of Example 6, the mass ratio of polyacrylonitrile to the conductive material in the mixed raw material was 1: 0.1. The conductive material in the positive electrode of Example 6 was Ce 2 S 3 , and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 0.6. The lithium ion secondary battery of Example 6 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 6 is used.
　（実施例７）
　実施例７の正極の製造方法は、伝導材材料として未硫化のＴｉを用い、混合原料として硫黄粉末５ｇとポリアクリロニトリル粉末１ｇと伝導材材料粉末０．１ｇとの混合物を用いたこと以外は、実施例１の正極の製造方法と同じである。実施例７の製造方法では、混合原料におけるポリアクリロニトリルと伝導材材料との質量比は１：０．１であった。また、実施例７の正極における伝導材はＴｉＳ２であり、硫黄系正極活物質と伝導材との含有比（質量比）は１０：０．６であった。実施例７のリチウムイオン二次電池は、実施例７の正極を用いたこと以外は実施例１のリチウムイオン二次電池と同じである。 (Example 7)
The manufacturing method of the positive electrode of Example 7 used a mixture of 5 g of sulfur powder, 1 g of polyacrylonitrile powder, and 0.1 g of conductive material material powder as a mixed raw material using unsulfurized Ti as a conductive material. It is the same as the method of manufacturing the positive electrode of Example 1. In the manufacturing method of Example 7, the mass ratio of polyacrylonitrile to the conductive material in the mixed raw material was 1: 0.1. The conductive material in the positive electrode of Example 7 was TiS 2 , and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 0.6. The lithium ion secondary battery of Example 7 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 7 was used.
　（実施例８）
　実施例８の正極の製造方法は、伝導材材料としてＴｉＳ２を用い、混合原料として硫黄粉末５ｇと石炭ピッチ粉末（等方性ピッチ、ＣＡＳ番号６５９９６－９３－２）１ｇと伝導材材料粉末０．１ｇとの混合物を用い、電極を真空下、２００℃、３時間乾燥したこと以外は、実施例１の正極の製造方法と同じである。実施例８の製造方法では、混合原料におけるピッチ系炭素材料と伝導材材料との質量比は１：０．１であった。また、実施例８の正極における伝導材はＴｉＳ２であり、硫黄系正極活物質と伝導材との含有比（質量比）は１０：０．５であった。実施例８のリチウムイオン二次電池は、実施例８の正極を用いたこと以外は実施例１のリチウムイオン二次電池と同じである。 (Example 8)
The method of manufacturing the positive electrode of Example 8 uses TiS 2 as the conductive material, 5 g of sulfur powder as the mixed raw material, 1 g of coal pitch powder (isotropic pitch, CAS number 65996-93-2) and 0 of the conductive material powder. The method of manufacturing the positive electrode of Example 1 is the same as that of Example 1 except that the electrode is dried under a vacuum at 200 ° C. for 3 hours using a mixture with .1 g. In the manufacturing method of Example 8, the mass ratio of the pitch-based carbon material to the conductive material in the mixed raw material was 1: 0.1. The conductive material in the positive electrode of Example 8 was TiS 2 , and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 0.5. The lithium ion secondary battery of Example 8 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 8 was used.
　（実施例９）
　実施例９の正極の製造方法は、伝導材材料としてＭｏＳ２を用い、混合原料として硫黄粉末５ｇとポリアクリロニトリル粉末１ｇと伝導材材料粉末０．１ｇとの混合物を用いたこと以外は、実施例１の正極の製造方法と同じである。実施例９の製造方法では、混合原料におけるポリアクリロニトリルと伝導材材料との質量比は１：０．１であった。また、実施例９の正極における伝導材はＭｏＳ２であり、硫黄系正極活物質と伝導材との含有比（質量比）は１０：０．６であった。実施例９のリチウムイオン二次電池は、実施例９の正極を用いたこと以外は実施例１のリチウムイオン二次電池と同じである。 (Example 9)
The method of manufacturing the positive electrode of Example 9 is an example except that a mixture of 5 g of sulfur powder, 1 g of polyacrylonitrile powder and 0.1 g of conductive material powder is used as the mixed material and MoS 2 is used. It is the same as the manufacturing method of the positive electrode of 1. In the manufacturing method of Example 9, the mass ratio of polyacrylonitrile to the conductive material in the mixed raw material was 1: 0.1. The conductive material in the positive electrode of Example 9 was MoS 2 and the content ratio (mass ratio) of the sulfur-based positive electrode active material to the conductive material was 10: 0.6. The lithium ion secondary battery of Example 9 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of Example 9 is used.
　（比較例）
　比較例の正極の製造方法は、伝導材材料を用いなかったこと以外は実施例１の正極の製造方法と同じである。比較例の正極は伝導材を含まないこと以外は実施例１の正極と同じである。また、比較例のリチウムイオン二次電池は、比較例の正極を用いたこと以外は実施例１のリチウムイオン二次電池と同じである。 (Comparative example)
The method of manufacturing the positive electrode of the comparative example is the same as the method of manufacturing the positive electrode of Example 1 except that the conductive material is not used. The positive electrode of the comparative example is the same as the positive electrode of Example 1 except that the conductive material is not contained. Moreover, the lithium ion secondary battery of the comparative example is the same as the lithium ion secondary battery of Example 1 except that the positive electrode of the comparative example was used.
　〔Ｘ線回折による硫黄系正極活物質の分析〕
　実施例１～４、７、９の硫黄系正極活物質－伝導材複合体、および、比較例の硫黄系正極活物質について、Ｘ線回折分析を行った。装置として粉末Ｘ線回折装置（ＭＡＣ　Ｓｃｉｅｎｃｅ社製、Ｍ０６ＸＣＥ）を用いた。測定条件は、ＣｕＫα線、電圧：４０ｋＶ、電流：１００ｍＡ、スキャン速度：４°／分、サンプリング：０．０２°、積算回数：１回、回折角（２θ）：１０°～６０°であった。Ｘ線回折で得られた回折パターンを図６～１１に示す。 [Analysis of sulfur-based positive electrode active material by X-ray diffraction]
X-ray diffraction analysis was performed on the sulfur-based positive electrode active material-conductive material composites of Examples 1 to 4, 7 and 9 and the sulfur-based positive electrode active material of Comparative Example. As a device, a powder X-ray diffractometer (M06XCE manufactured by MAC Science) was used. Measurement conditions were: CuKα ray, voltage: 40 kV, current: 100 mA, scan rate: 4 ° / min, sampling: 0.02 °, number of integrations: 1 time, diffraction angle (2θ): 10 ° to 60 ° . The diffraction patterns obtained by X-ray diffraction are shown in FIGS.
　ＡＳＴＭカードによるＬａ２Ｓ３の主な回折ピーク位置は、２４．７、２５．１、２６．９、３３．５、３７．２、４２．８°等である。ＴｉＳ２の主な回折ピーク位置は、１５．５、３４．２、４４．１、５３．９°等である。Ｔｉの主な回折ピーク位置は、３５．１、３８．４、４０．２、５３．０°等である。ＭｏＳ２の主な回折ピーク位置は、１４．４、３２．７、３３．５、３５．９、３９．６、４４．２、４９．８、５６．０、５８．４°等である。Ｆｅの主な回折ピーク位置は、４４．７、６５．０、８２．３°等である。図１１に示すように、伝導材材料を配合せず炭素材料としてポリアクリロニトリルを用いた硫黄系正極活物質（比較例）では、回折角（２θ）２０～３０°の範囲で、２５°付近にブロードな単一ピークが認められる。これに対して、伝導材材料を配合した硫黄系正極活物質－伝導材複合体では、伝導材に由来するピークが現れる。例えば、図６、７に示すように伝導材材料としてＬａ２Ｓ３を用いた場合、２４．７、２５．１、３３．５、３７．２°付近にＬａ２Ｓ３のピークが現れる。このピークにより、伝導材材料としてＬａ２Ｓ３を用いたこと（すなわち正極が伝導材としてＬａ２Ｓ３を含むこと）を確認できる。また、図８に示すように伝導材材料としてＴｉＳ２を用いた場合、殆どピークが確認できなかった。図９に示すように、伝導材材料としてＴｉを用いた場合３５．１、３８．４、４０．２、５３．０°付近にＴｉのピークが現れる。このピークにより、伝導材材料としてＴｉを用いたことを確認できる。上記したように伝導材材料としてＴｉＯ２を用いた場合には、Ｘ線回折ではその存在を確認できないが、他の分析方法、例えばＩＣＰ元素分析や蛍光Ｘ線分析などの方法を用いればＴｉを検出できるため、Ｘ線回折でピークが確認されない場合にもＴｉＯ２の添加を推測できる。また、図１０に示すように、伝導材材料としてＭｏＳ２を用いた場合、１４．４、３２．７、３３．５、３５．９、３９．６、４４．２、４９．８、５６．０、５８．４°付近にＭｏＳ２のピークが現れる。このピークにより、伝導材材料としてＭｏＳ２を用いたこと（すなわち正極が伝導材としてＭｏＳ２を含むこと）を確認できる。参考までに、伝導材としてＦｅを用いた硫黄系正極活物質－伝導材複合体（ポリアクリロニトリル：Ｆｅ＝１：０．１）の回折パターンを図１２に示す。図１２に示すように、伝導材材料としてＦｅを用いた場合、２８．５、３３．０、３７．１、４０．８、４７．４、５６．３、５９．０°付近にＦｅＳ２のピークが現れる。このピークにより、伝導材材料としてＦｅを用いたこと（すなわち正極が伝導材としてＦｅＳ、ＦｅＳ２、Ｆｅ２Ｓ３の少なくとも一種を含むこと）を確認できる。 The main diffraction peak positions of La 2 S 3 according to ASTM card are 24.7, 25.1, 26.9, 33.5, 37.2, 42.8 ° and so on. The main diffraction peak positions of TiS 2 are 15.5, 34.2, 44.1, 53.9 ° and so on. The main diffraction peak positions of Ti are 35.1, 38.4, 40.2, 53.0 degrees and so on. The main diffraction peak positions of MoS 2 are 14.4, 32.7, 33.5, 35.9, 39.6, 44.2, 49.8, 56.0, 58.4 ° and so on. The main diffraction peak positions of Fe are 44.7, 65.0, 82.3 ° and so on. As shown in FIG. 11, in the sulfur-based positive electrode active material (comparative example) using polyacrylonitrile as the carbon material without blending the conductive material, the diffraction angle (2θ) is in the range of 20 to 30 °, around 25 ° A broad single peak is observed. In contrast, in the sulfur-based positive electrode active material-conductive material composite containing a conductive material, a peak derived from the conductive material appears. For example, as shown in FIGS. 6 and 7, when La 2 S 3 is used as the conductive material, peaks of La 2 S 3 appear around 24.7, 25.1, 33.5, and 37.2 °. This peak can be confirmed using the La 2 S 3 as conductive material (i.e. the positive electrode contains La 2 S 3 as conductive material). Further, as shown in FIG. 8, when TiS 2 was used as the conductive material, almost no peak could be confirmed. As shown in FIG. 9, when Ti is used as the conductive material, a Ti peak appears in the vicinity of 35.1, 38.4, 40.2, 53.0 °. From this peak, it can be confirmed that Ti was used as the conductive material. As described above, when TiO 2 is used as the conductive material, its presence can not be confirmed by X-ray diffraction, but if other analysis methods such as ICP elemental analysis or fluorescent X-ray analysis are used, Ti can be used. Since the detection is possible, the addition of TiO 2 can be inferred even when no peak is confirmed by X-ray diffraction. Further, as shown in FIG. 10, when MoS 2 is used as the conductive material, 14.4, 32.7, 33.5, 35.9, 39.6, 44.2, 49.8, 56. A peak of MoS 2 appears around 0, 58.4 °. This peak can be confirmed with MoS 2 as a conductive material (i.e. the positive electrode contains MoS 2 as conductive material). For reference, a diffraction pattern of a sulfur-based positive electrode active material-conductive material composite (polyacrylonitrile: Fe = 1: 0.1) using Fe as a conductive material is shown in FIG. As shown in FIG. 12, when Fe is used as the conductive material, FeS 2 at around 28.5, 33.0, 37.1, 40.8, 47.4, 56.3, and 59.0 °. A peak appears. From this peak, it can be confirmed that Fe is used as the conductive material (that is, the positive electrode contains at least one of FeS, FeS 2 and Fe 2 S 3 as the conductive material).
　〔放電レート特性試験〕
　実施例１～８および比較例のリチウムイオン二次電池の放電レート特性を測定した。詳しくは、各リチウムイオン二次電池に、正極活物質の１ｇあたりの電流値を、Ｃレートで０．１Ｃ、０．２Ｃ、０．５Ｃ、１Ｃ、２Ｃ・・・と変化させ、繰り返し充放電を行った。このときのカットオフ電圧は３．０Ｖ～１．０Ｖであった。温度は２５～３０℃であった。放電レート特性試験の結果を図１３～２８に示す。図１３、１４は実施例１、図１５は実施例２、図１６は実施例３、図１７は実施例４、図１８、１９は実施例５、図２０、２１は実施例６、図２２、２３は実施例７、図２４、２５は実施例８、図２６、２７は実施例９、図２８は比較例のリチウムイオン二次電池に関する。なお、このうち図１３、１８、２０、２２、２４のグラフは充放電曲線であり、図１４～１７、１９、２１、２３、２５、２７、２８のグラフはサイクル特性を表す。 [Discharge rate characteristic test]
The discharge rate characteristics of the lithium ion secondary batteries of Examples 1 to 8 and Comparative Example were measured. Specifically, the current value per 1 g of the positive electrode active material is changed to 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C,. Did. The cutoff voltage at this time was 3.0 V to 1.0 V. The temperature was 25-30 ° C. The results of the discharge rate characteristic test are shown in FIGS. 13 and 14 show the first embodiment, FIG. 15 shows the second embodiment, FIG. 16 shows the third embodiment, FIG. 17 shows the fourth embodiment, FIGS. 18 and 19 show the fifth embodiment, and FIGS. , 23 is Example 7, FIGS. 24, 25 are Example 8, FIGS. 26, 27 are Example 9, and FIG. 28 is a lithium ion secondary battery of Comparative Example. Among these, the graphs of FIGS. 13, 18, 20, 22, 24 are charge / discharge curves, and the graphs of FIGS. 14-17, 19, 21, 23, 25, 27, 28 show cycle characteristics.
　伝導材材料を配合しなかった比較例のリチウムイオン二次電池（図２８）では、２Ｃのときの放電容量が３５０～４００ｍＡｈ／ｇであり、５Ｃのときの放電容量は１２０～１５０ｍＡｈ／ｇ程度であった。これに対して、伝導材材料としてのＬａ２Ｓ３を正極材料（詳しくは混合原料）に配合した実施例１のリチウムイオン二次電池（図１４）では、２Ｃのときの放電容量が５００ｍＡｈ／ｇを超え、５Ｃのときの放電容量も２５０ｍＡｈ／ｇ程度と非常に高い値を示した。この結果から、正極材料に伝導材材料を配合することで、硫黄系正極活物質を用いたリチウムイオン二次電池の放電レート特性を向上させ得ることがわかる。さらに、図１４に示すように、硫黄系正極活物質を用いたことで、２８サイクル（０．１Ｃ）後にも容量低下が殆どみられなかった。これらの結果から、硫黄系正極活物質と伝導材材料とを併用した本発明のリチウムイオン二次電池用正極は放電レート特性とサイクル特性とに優れる、といえる。 In the lithium ion secondary battery (FIG. 28) of the comparative example in which the conductive material is not blended, the discharge capacity at 2 C is 350 to 400 mAh / g, and the discharge capacity at 5 C is about 120 to 150 mAh / g Met. On the other hand, in the lithium ion secondary battery (FIG. 14) of Example 1 in which La 2 S 3 as the conductive material is blended in the positive electrode material (specifically, the mixed raw material), the discharge capacity at 2 C is 500 mAh / The discharge capacity at 5 C exceeding g also showed a very high value of about 250 mAh / g. From this result, it is understood that the discharge rate characteristics of the lithium ion secondary battery using the sulfur-based positive electrode active material can be improved by blending the conductive material with the positive electrode material. Furthermore, as shown in FIG. 14, the decrease in capacity was hardly observed even after 28 cycles (0.1 C) by using the sulfur-based positive electrode active material. From these results, it can be said that the positive electrode for a lithium ion secondary battery of the present invention in which the sulfur-based positive electrode active material and the conductive material are used in combination is excellent in discharge rate characteristics and cycle characteristics.
　また、ポリアクリロニトリル１質量部に対して伝導材材料０．１質量部配合した実施例１のリチウムイオン二次電池（図１４）と、伝導材材料０．３質量部配合した実施例２のリチウムイオン二次電池（図１５）と、伝導材材料０．５質量部配合した実施例３のリチウムイオン二次電池（図１６）と、を比較すると、放電レート特性は実施例１＞実施例２＞実施例３であった。これは、伝導材の容量が硫黄系正極活物質よりも低容量であるか、または、伝導材がリチウムイオン二次電池の活物質として不活性であるため、伝導材を大量に配合し正極活物質の配合量がすくなくなることで、正極全体の容量が低下するためだと考えられる。そしてこの結果から、容量と出力のバランスを考慮すると、伝導材材料の好ましい配合割合は硫黄系正極活物質１質量部に対して伝導材材料０．１～０．３質量部となる範囲であることがわかる。 In addition, the lithium ion secondary battery of Example 1 (FIG. 14) blended with 0.1 parts by mass of the conductive material per 1 part by mass of polyacrylonitrile and the lithium of Example 2 blended with 0.3 parts by mass of the conductive material Comparing the ion secondary battery (FIG. 15) with the lithium ion secondary battery of Example 3 (FIG. 16) blended with 0.5 parts by mass of the conductive material, the discharge rate characteristic is Example 1> Example 2 It was Example 3. This is because the capacity of the conductive material is lower than that of the sulfur-based positive electrode active material, or the conductive material is inactive as an active material of a lithium ion secondary battery, so a large amount of the conductive material is blended to make the positive electrode active. This is considered to be because the capacity of the entire positive electrode is reduced because the compounding amount of the substance is too small. And from this result, in consideration of the balance of capacity and output, the preferable blending ratio of the conductive material is in the range of 0.1 to 0.3 parts by mass of the conductive material with respect to 1 part by mass of the sulfur-based positive electrode active material. I understand that.
　また、伝導材材料としてＴｉＳ２を用いた実施例４のリチウムイオン二次電池（図１７）、伝導材材料としてＳｍ２Ｓ３を用いた実施例５のリチウムイオン二次電池（図１９）、伝導材材料としてＣｅ２Ｓ３を用いた実施例６のリチウムイオン二次電池（図２１）の何れも、２Ｃのときの放電容量が５００ｍＡｈ／ｇを超え、放電レート特性に優れていた。 Also, the lithium ion secondary battery of Example 4 using TiS 2 as the conductive material (FIG. 17), the lithium ion secondary battery of Example 5 using Sm 2 S 3 as the conductive material (FIG. 19), In any of the lithium ion secondary batteries (FIG. 21) of Example 6 using Ce 2 S 3 as the conductive material, the discharge capacity at 2 C exceeded 500 mAh / g, and the discharge rate characteristics were excellent.
　また、伝導材材料としてＴｉを用いた実施例７のリチウムイオン二次電池（図２３）に関しても、２Ｃのときの放電容量が５００ｍＡｈ／ｇ程度であった。この結果から、伝導材材料として非硫化物を用いても、リチウムイオン二次電池の放電レート特性を向上させ得ることがわかる。これは、未硫化のＴｉが熱処理工程において硫黄と反応し硫化されるためだと考えられる。なお、伝導材材料としてＴｉＳ２を用いた実施例４のリチウムイオン二次電池（図１７）は、伝導材材料としてＴｉを用いた実施例７のリチウムイオン二次電池（図２３）よりも放電レート特性に優れる。この結果から、伝導材材料としては、金属硫化物がより好ましく用いられることがわかる。 In addition, the discharge capacity at 2 C was about 500 mAh / g for the lithium ion secondary battery of Example 7 (FIG. 23) using Ti as the conductive material. From this result, it is understood that the discharge rate characteristics of the lithium ion secondary battery can be improved even if non-sulfide is used as the conductive material. It is considered that this is because unsulfided Ti reacts with sulfur in the heat treatment step to be sulfurized. In addition, the lithium ion secondary battery of Example 4 (FIG. 17) using TiS 2 as the conductive material is more discharged than the lithium ion secondary battery (FIG. 23) of Example 7 using Ti as the conductive material. Excellent rate characteristics. From this result, it is understood that metal sulfide is more preferably used as the conductive material.
　さらに、硫黄系正極活物質として硫黄変性ピッチを用いた実施例８のリチウムイオン二次電池（図２５）は、硫黄系正極活物質として硫黄変性ポリアクリロニトリルを用いた実施例４のリチウムイオン二次電池（図１７）に比べると容量自体は低いが、伝導材材料を配合したことで０．１Ｃから２．０Ｃ付近までの放電容量低下は少ない。したがって、硫黄系正極活物質として硫黄変性ピッチを用いる場合にも、硫黄系正極活物質と伝導材材料とを併用することで放電レート特性を高め得ることがわかる。なお、正極活物質として硫黄変性ピッチを用いたリチウムイオン二次電池は、正極活物質として硫黄変性ポリアクリロニトリルを用いたリチウムイオン二次電池に比べると容量が少なくサイクル特性にも劣るが、正極活物質として単体硫黄を用いたリチウムイオン二次電池に比べると遙かに優れたサイクル特性を示す。さらに、伝導材材料としてのＭｏＳ２を正極材料（詳しくは混合原料）に配合した実施例９のリチウムイオン二次電池（図２７）では、２Ｃのときの放電容量が５００ｍＡｈ／ｇを超え、５Ｃのときの放電容量も２００ｍＡｈ／ｇ程度と非常に高い値を示した。この結果から、伝導材材料としてＭｏＳ２を用いる場合には、伝導材材料としてのＬａ２Ｓ３を用いる場合と同程度にリチウムイオン二次電池の放電レート特性を向上させ得ることがわかる。 Furthermore, the lithium ion secondary battery of Example 8 using sulfur-modified pitch as a sulfur-based positive electrode active material (FIG. 25) is a lithium ion secondary battery of Example 4 using sulfur-modified polyacrylonitrile as a sulfur-based positive electrode active material. Although the capacity itself is lower than that of the battery (FIG. 17), the decrease in discharge capacity from 0.1 C to around 2.0 C is small by blending the conductive material. Therefore, even when using sulfur-modified pitch as the sulfur-based positive electrode active material, it is understood that the discharge rate characteristics can be enhanced by using the sulfur-based positive electrode active material and the conductive material in combination. Lithium ion secondary batteries using sulfur-modified pitch as the positive electrode active material have less capacity and are inferior in cycle characteristics to lithium ion secondary batteries using sulfur-modified polyacrylonitrile as the positive electrode active material. It exhibits much better cycle characteristics as compared to lithium ion secondary batteries using elemental sulfur as the substance. Furthermore, in the lithium ion secondary battery (FIG. 27) of Example 9 in which MoS 2 as the conductive material is blended in the positive electrode material (specifically, the mixed raw material), the discharge capacity at 2 C exceeds 500 mAh / g, 5 C The discharge capacity also showed a very high value of about 200 mAh / g. From these results, it is understood that when MoS 2 is used as the conductive material, the discharge rate characteristics of the lithium ion secondary battery can be improved to the same extent as when La 2 S 3 is used as the conductive material.
　以上の結果から、本発明の正極は、リチウムイオン二次電池のサイクル特性および放電レート特性を向上させ得ることがわかる。また、本発明のリチウムイオン二次電池は優れたサイクル特性および放電レート特性を示すことがわかる。さらに、本発明の正極の製造方法によると、リチウムイオン二次電池のサイクル特性および放電レート特性を向上させ得る正極を製造できることがわかる。 From the above results, it is understood that the positive electrode of the present invention can improve the cycle characteristics and the discharge rate characteristics of the lithium ion secondary battery. Further, it can be seen that the lithium ion secondary battery of the present invention exhibits excellent cycle characteristics and discharge rate characteristics. Furthermore, according to the manufacturing method of the positive electrode of this invention, it turns out that the positive electrode which can improve the cycling characteristics and discharge rate characteristic of a lithium ion secondary battery can be manufactured.
１：反応装置　　　２：反応容器　　　３：蓋　　　４：熱電対
５：ガス導入管　　６：ガス排出管　　７：電気炉 1: Reactor 2: Reaction container 3: Lid 4: Thermocouple 5: Gas inlet pipe 6: Gas outlet pipe 7: Electric furnace

Claims (7)

  1. 　炭素（Ｃ）および硫黄（Ｓ）を含有する硫黄系正極活物質と、硫黄（Ｓ）を含有する伝導材と、を含有し、
    　該伝導材の少なくとも一部は、第４周期金属、第５周期金属、第６周期金属および希土類元素からなる群から選ばれる少なくとも一種の金属の硫化物からなることを特徴とするリチウムイオン二次電池用正極。     A sulfur-based positive electrode active material containing carbon (C) and sulfur (S), and a conductive material containing sulfur (S),
    At least a part of the conductive material is made of a sulfide of at least one metal selected from the group consisting of a fourth period metal, a fifth period metal, a sixth period metal and a rare earth element. Battery positive electrode.
  2. 　前記金属は、Ｔｉ、Ｆｅ、Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｓｍ、Ｖ、Ｍｎ、Ｎｉ、Ｃｕ、Ｚｎ、Ｍｏ、Ａｇ、Ｃｄ、Ｉｎ、Ｓｎ、Ｓｂ、Ｔａ、Ｗ、Ｐｂからなる群から選ばれる少なくとも一種である請求項１に記載のリチウムイオン二次電池用正極。 The metal is selected from the group consisting of Ti, Fe, La, Ce, Pr, Nd, Sm, V, Mn, Ni, Cu, Zn, Mo, Ag, Cd, In, Sn, Sb, Ta, W, Pb The positive electrode for a lithium ion secondary battery according to claim 1, which is at least one of
  3. 　前記金属の硫化物は、Ｌａ２Ｓ３、ＴｉＳ２、Ｓｍ２Ｓ３、Ｃｅ２Ｓ３、ＭｏＳ２からなる群から選ばれる少なくとも一種である請求項１または請求項２に記載のリチウムイオン二次電池用正極。 The lithium ion according to claim 1 or 2 , wherein the metal sulfide is at least one selected from the group consisting of La 2 S 3 , TiS 2 , Sm 2 S 3 , Ce 2 S 3 and MoS 2. Positive electrode for secondary battery.
  4. 　正極として、炭素（Ｃ）および硫黄（Ｓ）を含有する硫黄系正極活物質と、硫黄（Ｓ）を含有する伝導材と、を含有し、該伝導材の少なくとも一部は、第４周期金属、第５周期金属、第６周期金属および希土類元素からなる群から選ばれる少なくとも一種の金属の硫化物からなるリチウムイオン二次電池用正極を用いていることを特徴とするリチウムイオン二次電池。 A sulfur-based positive electrode active material containing carbon (C) and sulfur (S) as a positive electrode, and a conductive material containing sulfur (S), wherein at least a part of the conductive material is a fourth period metal A lithium ion secondary battery using a positive electrode for a lithium ion secondary battery comprising a sulfide of at least one metal selected from the group consisting of a fifth period metal, a sixth period metal and a rare earth element.
  5. 　炭素（Ｃ）および硫黄（Ｓ）を含有する硫黄系正極活物質を含有するリチウムイオン二次電池用正極を製造する方法であって、
    　炭素材料、硫黄、および、硫黄を含有する伝導材材料を含有する混合原料を加熱する熱処理工程を含み、
    　該伝導材材料は、第４周期金属、第５周期金属、第６周期金属および希土類元素からなる群から選ばれる少なくとも一種の金属の硫化物であることを特徴とするリチウムイオン二次電池用正極の製造方法。     A method for producing a positive electrode for a lithium ion secondary battery, comprising a sulfur-based positive electrode active material containing carbon (C) and sulfur (S),
    A heat treatment step of heating a mixed material containing a carbon material, sulfur, and a conductive material containing sulfur,
    The conductive material is a sulfide of at least one metal selected from the group consisting of a fourth period metal, a fifth period metal, a sixth period metal, and a rare earth element. A positive electrode for a lithium ion secondary battery Manufacturing method.
  6. 　炭素（Ｃ）および硫黄（Ｓ）を含有する硫黄系正極活物質を含有するリチウムイオン二次電池用正極を製造する方法であって、
    　炭素材料、硫黄、および、硫黄を含有しない伝導材材料を含有する混合原料を加熱する熱処理工程を含み、
    　該伝導材材料は、第４周期金属、第５周期金属、第６周期金属および希土類元素からなる群から選ばれる少なくとも一種の金属であることを特徴とするリチウムイオン二次電池用正極の製造方法。     A method for producing a positive electrode for a lithium ion secondary battery, comprising a sulfur-based positive electrode active material containing carbon (C) and sulfur (S),
    Including a heat treatment step of heating a mixed material containing a carbon material, sulfur, and a conductive material containing no sulfur,
    The method for manufacturing a positive electrode for a lithium ion secondary battery, wherein the conductive material is at least one metal selected from the group consisting of a fourth period metal, a fifth period metal, a sixth period metal, and a rare earth element. .
  7. 　請求項４に記載のリチウムイオン二次電池を搭載していることを特徴とする車両。 A vehicle comprising the lithium ion secondary battery according to claim 4.
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