US20180233749A1 - Hardly graphitizable carbonaceous material for nonaqueous electrolyte secondary batteries fully charged to be used, method for producing same, negative electrode material for nonaqueous electrolyte secondary batteries, and nonaqueous electrolyte secondary battery fully charged to be used - Google Patents

Hardly graphitizable carbonaceous material for nonaqueous electrolyte secondary batteries fully charged to be used, method for producing same, negative electrode material for nonaqueous electrolyte secondary batteries, and nonaqueous electrolyte secondary battery fully charged to be used Download PDF

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US20180233749A1
US20180233749A1 US15/749,972 US201615749972A US2018233749A1 US 20180233749 A1 US20180233749 A1 US 20180233749A1 US 201615749972 A US201615749972 A US 201615749972A US 2018233749 A1 US2018233749 A1 US 2018233749A1
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carbonaceous material
graphitizable carbonaceous
hardly graphitizable
nonaqueous electrolyte
electrolyte secondary
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Junji Fujioka
Jun-Sang Cho
Taketoshi Okuno
Hideharu Iwasaki
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Kuraray Co Ltd
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Kureha Corp
Kuraray Co Ltd
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Assigned to KUREHA CORPORATION, KURARAY CO., LTD. reassignment KUREHA CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: IWASAKI, HIDEHARU, OKUNO, TAKETOSHI, FUJIOKA, JUNJI, CHO, JUN-SANG
Publication of US20180233749A1 publication Critical patent/US20180233749A1/en
Assigned to KURARAY CO., LTD. reassignment KURARAY CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: KUREHA CORPORATION
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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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
    • C01P2002/86—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by NMR- or ESR-data
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/10—Solid density
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
    • 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
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/70—Energy storage systems for electromobility, e.g. batteries

Definitions

  • the present invention relates to a hardly graphitizable carbonaceous material suitable as a negative electrode material for nonaqueous electrolyte secondary batteries (for example, a lithium ion secondary battery) fully charged to be used and a method for producing the same, a negative electrode material for nonaqueous electrolyte secondary batteries, and a nonaqueous electrolyte secondary battery fully charged to be used.
  • a negative electrode material for nonaqueous electrolyte secondary batteries for example, a lithium ion secondary battery
  • the lithium ion secondary battery has hitherto been widely used for small mobile equipment such as a mobile phone and a notebook personal computer.
  • a hardly graphitizable carbonaceous material has been developed as a negative electrode material for lithium ion secondary batteries (Patent Document 1) and has also been used therefor because the hardly graphitizable carbonaceous material is capable of doping (charging) and dedoping (discharging) of lithium in an amount more than 372 mAh/g being the theoretical capacity of graphite and is also excellent in input-output characteristics, cycle durability, and low-temperature properties.
  • the hardly graphitizable carbonaceous material can be obtained from carbon sources such as petroleum pitch, coal pitch, phenol resins, and plants.
  • carbon sources such as petroleum pitch, coal pitch, phenol resins, and plants.
  • plants have been attracting attention because plants are raw materials that can be cultivated to be sustainedly stably supplied and are available inexpensively.
  • satisfactory charge-discharge capacity is expected because there are many fine pores in a carbonaceous material obtained by calcining a carbon raw material originating from plants (for example, Patent Document 1 and Patent Document 2).
  • charging of a lithium ion secondary battery is usually performed by a method (constant-current constant-voltage method) in which constant-current charging is performed (for example, at 0.5 mA/cm 2 ) until the electrical potential of a negative electrode terminal based on that of metallic lithium becomes a predetermined electrical potential of 0 mV or more, constant-voltage charging is performed after the electrical potential of the negative electrode terminal reached the predetermined electrical potential, and charging is completed when the current value is kept at a constant value (for example, at 20 ⁇ A) during a predetermined period of time.
  • the lithium ion secondary battery is not charged to be in a fully charged state even when there is still space to hold lithium ions in the negative electrode.
  • Patent Document 1 JP-A-H9-161801
  • Patent Document 2 JP-A-H10-21919
  • Patent Document 3 JP-A-2015-88354
  • Patent Document 4 JP-A-2001-15155
  • One object of the present invention is to provide a hardly graphitizable carbonaceous material used in a negative electrode material for nonaqueous electrolyte secondary batteries (for example, a lithium ion battery) having not only high charge capacity but also high charge-discharge efficiency and being fully charged to be used and a method for producing the same.
  • a negative electrode material for nonaqueous electrolyte secondary batteries comprising such a hardly graphitizable carbonaceous material, and a nonaqueous electrolyte secondary battery comprising such a negative electrode material for nonaqueous electrolyte secondary batteries and being fully charged to be used.
  • the present inventors have found out that the above-mentioned problems can be solved by using a hardly graphitizable carbonaceous material having an oxygen element content within a specific range in a negative electrode material for nonaqueous electrolyte secondary batteries fully charged to be used, and thus, the present invention has been completed.
  • the present invention includes the following preferred embodiments.
  • a hardly graphitizable carbonaceous material being a hardly graphitizable carbonaceous material for nonaqueous electrolyte secondary batteries fully charged to be used and having an oxygen element content of 0.25% by mass or less.
  • a method for producing the hardly graphitizable carbonaceous material according to any one of [1] to [7] mentioned above, comprising a step of subjecting a carbon precursor to an acid treatment and a step of calcining an acid-treated carbon precursor under an inert gas atmosphere at 1100° C. to 1400° C.
  • a negative electrode material for nonaqueous electrolyte secondary batteries comprising the hardly graphitizable carbonaceous material according to any one of [1] to [7] mentioned above.
  • a nonaqueous electrolyte secondary battery which comprises a negative electrode material for nonaqueous electrolyte secondary batteries comprising a hardly graphitizable carbonaceous material and which is fully charged to be used, wherein the hardly graphitizable carbonaceous material has an oxygen element content of 0.25% by mass or less.
  • nonaqueous electrolyte secondary battery When the hardly graphitizable carbonaceous material according to the present invention is used to produce a nonaqueous electrolyte secondary battery fully charged to be used, such a nonaqueous electrolyte secondary battery has not only extremely high charge capacity but also extremely high charge-discharge efficiency.
  • FIG. 1 shows an 7 Li nuclear-solid state NMR spectrum of the hardly graphitizable carbonaceous material prepared in Example 1.
  • FIG. 2 shows an 7 Li nuclear-solid state NMR spectrum of the carbonaceous material prepared in Comparative Example 2.
  • the hardly graphitizable carbonaceous material according to the present invention is a hardly graphitizable carbonaceous material for nonaqueous electrolyte secondary batteries fully charged to be used and has an oxygen element content of 0.25% by mass or less.
  • a nonaqueous electrolyte secondary battery being fully charged to be used refers to a nonaqueous electrolyte secondary battery being assembled with the use of a negative electrode comprising a hardly graphitizable carbonaceous material and a positive electrode comprising lithium, and allowing the negative electrode to be charged (doped) with lithium until just before precipitation of metallic lithium is confirmed by 7 Li nuclear-solid state NMR analysis; and usually means a nonaqueous electrolyte secondary battery being charged at a constant current value so as to have a charge capacity within the range of 580 to 700 mAh/g per unit mass of the negative electrode active material.
  • the charge capacity of a negative electrode at the time when the negative electrode is charged with lithium until just before precipitation of metallic lithium is confirmed by 7 Li nuclear-solid state NMR analysis is preferably set to 85 to 98%, further preferably set to 88 to 95%, and especially preferably set to 90 to 92% relative to a charge capacity at the time when lithium precipitation is confirmed.
  • the oxygen element content of the hardly graphitizable carbonaceous material according to the present invention is usually 0.25% by mass or less and preferably 0.24% by mass or less. It is further preferred that the hardly graphitizable carbonaceous material contains substantially no oxygen element.
  • containing substantially no oxygen element means having an oxygen element content equal to or less than 10 ⁇ 6 % by mass which is a detection limit of the elemental analysis method (inert gas fusion-thermal conductivity method) described below.
  • the oxygen element content is the above-mentioned value or less, the lowering in utilization efficiency of lithium ions, which is caused because lithium ions are consumed by a reaction of the lithium ion with oxygen, and the lowering in utilization efficiency of lithium ions, which is caused because moisture in the air is induced by oxygen and water is adsorbed by the hardly graphitizable carbonaceous material and hardly desorbed therefrom, can be suppressed.
  • a method of adjusting the oxygen element content to the above-mentioned value or less is not limited at all. For example, by subjecting a carbon precursor originating from plants to an acid treatment at a predetermined temperature, then, mixing an acid-treated carbon precursor with a volatile organic substance, and calcining the mixture under an inert gas atmosphere at a temperature of 1100° C. to 1400° C., the oxygen element content can be adjusted to the above-mentioned value or less.
  • the details of the measurement of the oxygen element content are as described in EXAMPLES.
  • a main resonance peak position of a chemical shift value observed by subjecting the hardly graphitizable carbonaceous material to 7 Li nuclear-solid state NMR analysis is preferably downfield by more than 115 ppm, more preferably downfield by more than 118 ppm, and especially preferably downfield by more than 120 ppm, from a peak position of lithium chloride.
  • the details of the 7 Li nuclear-solid state NMR analysis are as described in EXAMPLES.
  • a battery prepared with a hardly graphitizable carbonaceous material in which a main resonance peak position of a chemical shift value is downfield by more than 115 ppm from a peak position of lithium chloride, that is, the above-mentioned main resonance peak position is observed at the lower magnetic field side by more than 115 ppm means a battery prepared with the hardly graphitizable carbonaceous material having a large storage amount of clustered lithium atoms, that is, a battery having a high charge capacity.
  • the clustered lithium atoms occluded in a hardly graphitizable carbonaceous material are reversible lithium atoms that can be discharged (dedoped) therefrom, and a battery prepared with the hardly graphitizable carbonaceous material having a large storage amount of clustered lithium atoms means a battery having high charge-discharge efficiency calculated from “the discharge capacity/the charge capacity”.
  • Having high charge-discharge efficiency means having little loss of lithium in the negative electrode caused by a side reaction during the charge-discharge and the like.
  • a battery has little loss of lithium in the negative electrode, it becomes unnecessary to complement lithium for the negative electrode by using an excess amount of materials for the positive electrode, and the battery becomes advantageous from an aspect of capacity per volume of the battery or cost of the battery.
  • the hardly graphitizable carbonaceous material according to the present invention is derived from a phenol resin, a furan resin, pitch, tar, a carbon precursor originating from plants, or the like.
  • the hardly graphitizable carbonaceous material according to the present invention is preferably derived from a carbon precursor originating from plants.
  • a carbon precursor originating from plants means a substance before carbonization originating from plants or a substance after carbonization originating from plants (char derived from plants).
  • a plant as a raw material (hereinafter, sometimes referred to as “a plant raw material”) is not particularly limited.
  • coconut shell, coffee beans, tea leaves, sugarcane, fruits (for example, mandarine oranges and bananas), straws, rice husks, a broad-leaved tree, a needle-leaved tree and bamboo can be exemplified.
  • These exemplified plants include wastes after provided for its original purpose (for example, used tea leaves) and a portion of the plant raw material (for example, banana peels and mandarine orange peels). These plants can be used singly or in combination of two or more thereof. Of these plants, coconut shell, which is easily available abundantly, is preferred.
  • the coconut shell is not particularly limited. Examples thereof can include coconut shells of palm coconut (oil palm), coco palm, Salak, and sea coconut. These coconut shells can be used singly or in combination. Coco shells of coco palm and palm coconut, which are utilized as foodstuffs, raw material of a detergent, raw material of a biodiesel fuel oil, and the like and are biomass wastes generated in large quantities, are especially preferred.
  • a method of carbonizing the plant raw material that is, a method of producing the char derived from plants, is not particularly limited.
  • the method can be performed, for example, by subjecting the plant raw material to a heat treatment under an inert gas atmosphere at 300° C. or more (hereinafter, sometimes referred to as “temporary calcination”).
  • the plant raw material in the form of char (for example, coconut shell char) is also available.
  • the average face-to-face dimension d 002 of the (002) face calculated from the Bragg equation by a wide angle X-ray diffraction method of the hardly graphitizable carbonaceous material according to the present invention preferably falls within the range of 0.36 nm to 0.42 nm, more preferably falls within the range of 0.38 nm to 0.40 nm, and especially preferably falls within the range of 0.381 nm to 0.389 nm.
  • the average face-to-face dimension d 002 of the (002) face falls within the above-mentioned range, the lowering in input-output characteristics of a lithium ion battery caused by an electrical resistance made large at the time when lithium ions are inserted into the carbonaceous material or an electrical resistance made large at the time of output can be suppressed. Moreover, the lowering in stability of a battery material due to repeated expansion and shrinkage of the hardly graphitizable carbonaceous material can be suppressed. Furthermore, the lowering in effective capacity per volume caused by a volume of the hardly graphitizable carbonaceous material made large while a diffusion resistance of the lithium ion is made small can be avoided.
  • a carbon precursor giving a hardly graphitizable carbonaceous material may be calcined at a calcination temperature within the range of 1100 to 1400° C.
  • a method in which a carbon precursor is mixed with a thermally-decomposable resin such as polystyrene to be calcined can also be adopted.
  • the details of the measurement of the average face-to-face dimension d 002 are as described in EXAMPLES.
  • the specific surface area determined by a nitrogen adsorption BET three-point method of the hardly graphitizable carbonaceous material according to the present invention preferably falls within the range of 1 to 20 m 2 /g, more preferably falls within the range of 1.2 to 10 m 2 /g, and especially preferably falls within the range of 1.4 to 9.5 m 2 /g.
  • the specific surface area falls within the above-mentioned range, the number of micropores in the hardly graphitizable carbonaceous material can be sufficiently reduced by a calcination step described below, the moisture-absorption characteristics of the hardly graphitizable carbonaceous material can be sufficiently lowered, and in a nonaqueous electrolyte secondary battery produced with the use of the hardly graphitizable carbonaceous material, a lowering in utilization efficiency of lithium ions can be suppressed.
  • the specific surface area can be adjusted by controlling the temperature in a demineralization step described below. In this context, the details of the measurement of the specific surface area by a nitrogen adsorption BET three-point method are as described in EXAMPLES.
  • the true density by a butanol method of the hardly graphitizable carbonaceous material according to the present invention preferably falls within the range of 1.40 to 1.70 g/cm 3 , more preferably falls within the range of 1.42 to 1.65 g/cm 3 , and especially preferably falls within the range of 1.44 to 1.60 g/cm 3 .
  • the true density within the above-mentioned range can be attained, for example, by setting the calcination step temperature at the time of producing a hardly graphitizable carbonaceous material from the plant raw material to 1100 to 1400° C.
  • the details of the measurement of the true density ⁇ Bt are as described in EXAMPLES.
  • the potassium element content of the hardly graphitizable carbonaceous material according to the present invention is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, and further preferably 0.03% by mass or less. It is especially preferred that the hardly graphitizable carbonaceous material contains substantially no potassium element.
  • the iron element content of the hardly graphitizable carbonaceous material according to the present invention is preferably 0.02% by mass or less, more preferably 0.015% by mass or less, and further preferably 0.01% by mass or less.
  • the hardly graphitizable carbonaceous material contains substantially no iron element.
  • containing substantially no potassium element or substantially no iron element means having a potassium element content or an iron element content equal to or less than the detection limit value in the X-ray fluorescence analysis (for example, analysis using the “LAB CENTER XRF-1700” available from SHIMADZU CORPORATION) described below.
  • the potassium element content and the iron element content are equal to or less than the above-mentioned values, respectively, in a nonaqueous electrolyte secondary battery prepared with the hardly graphitizable carbonaceous material, a sufficient dedoping capacity and a satisfactory nondedoping capacity can be attained.
  • the moisture content of the hardly graphitizable carbonaceous material according to the present invention is preferably 10000 ppm or less, more preferably 9000 ppm or less, and especially preferably 8000 ppm or less.
  • the smaller the moisture content the amount of water that adsorbs to the hardly graphitizable carbonaceous material is reduced and the number of lithium ions that adsorb to the hardly graphitizable carbonaceous material is increased, which is preferable.
  • the smaller the moisture content self-discharge caused by a reaction of lithium ions with adsorbed water can be reduced, which is preferable.
  • the moisture content of the hardly graphitizable carbonaceous material can be reduced, for example, by reducing the number of oxygen atoms contained in a hardly graphitizable carbonaceous material.
  • the moisture content of the hardly graphitizable carbonaceous material can be measured, for example, by the use of a Karl Fischer moisture meter or the like. The details of the measurement of the moisture content are as described in EXAMPLES.
  • a method for producing the hardly graphitizable carbonaceous material according to the present invention comprises a step of subjecting a carbon precursor (for example, a carbon precursor originating from plants) to an acid treatment and a step of calcining an acid-treated carbon precursor under an inert gas atmosphere at 1100° C. to 1400° C.
  • a carbon precursor for example, a carbon precursor originating from plants
  • a carbon precursor refers to a phenol resin, a furan resin, pitch, tar, a carbon precursor originating from plants, or the like. In the present invention, it is preferred that the carbon precursor is a carbon precursor originating from plants.
  • a carbon precursor originating from plants means a substance before carbonization originating from plants or a substance after carbonization originating from plants (char derived from plants).
  • a plant as a raw material is not particularly limited. Such plants exemplified above can be used singly or in combination of two or more thereof. Of these, coconut shell, which is easily available abundantly, is preferred.
  • the coconut shell is not particularly limited. Such coconut shells exemplified above can be used singly or in combination.
  • coconut shells of coco palm and palm coconut which are utilized as foodstuffs, raw material of a detergent, raw material of a biodiesel fuel oil, and the like and are biomass wastes generated in large quantities, are especially preferred.
  • a method of carbonizing the plant raw material that is, a method of producing the char derived from plants, is not particularly limited.
  • the method can be performed by subjecting the plant raw material to a heat treatment under an inert gas atmosphere at 300° C. or more (hereinafter, sometimes referred to as “temporary calcination”).
  • the plant raw material in the form of char (for example, coconut shell char) is also available.
  • the plant raw material contains alkali metal elements (for example, potassium, sodium), alkaline earth metal elements (for example, magnesium, calcium), transition metal elements (for example, iron, copper), non-metallic elements (for example, phosphorus), and the like in large amounts.
  • alkali metal elements for example, potassium, sodium
  • alkaline earth metal elements for example, magnesium, calcium
  • transition metal elements for example, iron, copper
  • non-metallic elements for example, phosphorus
  • a method for producing the hardly graphitizable carbonaceous material according to the present invention comprises a step of subjecting a carbon precursor (for example, a carbon precursor originating from plants) to an acid treatment.
  • a carbon precursor for example, a carbon precursor originating from plants
  • subjecting a carbon precursor (for example, a carbon precursor originating from plants) to an acid treatment to lower the content of a metallic element and/or a non-metallic element in the carbon precursor also refers to demineralizing a carbon precursor.
  • a method for the acid treatment that is, a method for the demineralization
  • a method of exposing a carbon precursor to a high-temperature vapor phase containing a halogen compound such as hydrogen chloride to demineralize the carbon precursor vapor phase demineralization
  • a carbon precursor for example, a carbon precursor originating from plants
  • a carbon precursor is immersed in an aqueous organic acid solution to elute alkali metal elements, alkaline earth metal elements, and/or non-metallic elements to be removed from the carbon precursor into the aqueous organic acid solution.
  • a carbon precursor for example, a carbon precursor originating from plants
  • a necessary carbonaceous component is sometimes decomposed at the time of carbonization.
  • a carbon precursor containing a non-metallic element is not preferred because the non-metallic element such as phosphorus is liable to be oxidized to make the degree of oxidation on the surface of a carbonized product vary and to make characteristics of the carbonized product significantly vary.
  • phosphorus, calcium, and magnesium sometimes fail to be sufficiently removed.
  • the required time for the liquid phase demineralization and the remaining amount of a metallic element and/or a non-metallic element in a carbonized product after liquid phase demineralization greatly vary depending on the content of a metallic element and/or a non-metallic element in a carbonized product before liquid phase demineralization. Accordingly, it is preferred that a metallic element and/or a non-metallic element in a carbon precursor is sufficiently removed before carbonization to lower the content thereof. That is, it is preferred that, in liquid phase demineralization, a substance (for example, a substance originating from plants) before carbonization is used as “a carbon precursor (for example, a carbon precursor originating from plants)”.
  • the organic acid used in liquid phase demineralization does not contain any element acting as an impurity source such as phosphorus, sulfur, and a halogen.
  • an organic acid is advantageous because a carbonized product that can be suitably used as the carbon material is obtained even when a water washing process after liquid phase demineralization is omitted and a carbon precursor allowing an organic acid to remain therein is carbonized.
  • such an organic acid is advantageous because a waste liquid treatment for a waste liquid of the organic acid after use can be relatively easily performed without using a special apparatus.
  • organic acid examples include saturated carboxylic acids such as formic acid, acetic acid, propionic acid, oxalic acid, tartaric acid, and citric acid, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, and fumaric acid, and aromatic carboxylic acids such as benzoic acid, phthalic acid, and naphthoic acid. From the viewpoints of availability, corrosion due to the degree of acidity, and influence on human bodies, acetic acid, oxalic acid, and citric acid are preferred.
  • saturated carboxylic acids such as formic acid, acetic acid, propionic acid, oxalic acid, tartaric acid, and citric acid
  • unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, and fumaric acid
  • aromatic carboxylic acids such as benzoic acid, phthalic acid, and naphthoic acid. From the viewpoints of availability, corrosion due to the degree of acidity, and influence on human bodies,
  • an organic acid is mixed with an aqueous medium to be used as an aqueous organic acid solution.
  • the aqueous medium include water, a mixture of water and a water-soluble organic solvent, and the like.
  • the water-soluble organic solvent include alcohols such as methanol, ethanol, propylene glycol, and ethylene glycol.
  • the concentration of an acid in the aqueous organic acid solution is not particularly limited.
  • the acid concentration of an aqueous organic acid solution can be adjusted depending on the kind of the acid used to prepare the aqueous organic acid solution.
  • an aqueous organic acid solution with an acid concentration falling within the range of usually 0.001% by mass to 20% by mass, more preferably 0.01% by mass to 18% by mass, and especially preferably 0.02% by mass to 15% by mass, on the basis of the whole amount of the aqueous organic acid solution is usually used.
  • the pH of an aqueous organic acid solution is preferably 3.5 or less and more preferably 3 or less. In the case where the pH of an aqueous organic acid solution is not more than the above-mentioned value, the dissolution rate of a metallic element and/or a non-metallic element eluted into the aqueous organic acid solution is not lowered and the removal of a metallic element and/or a non-metallic element can be effectively performed.
  • the liquid temperature of an aqueous organic acid solution at the time of immersing a carbon precursor therein is not particularly limited.
  • the liquid temperature thereof falls within the range of preferably 45° C. to 120° C., more preferably 50° C. to 110° C., and especially preferably 60° C. to 100° C.
  • Such an aqueous organic acid solution is preferred because decomposition of the acid used is suppressed and an elution rate of a metallic element enabling a liquid phase demineralization treatment within a practical time period to be performed is attained as long as the liquid temperature of the aqueous organic acid solution at the time of immersing a carbon precursor therein falls within the above-mentioned range.
  • such an aqueous organic acid solution is preferred because a liquid phase demineralization treatment can be performed without using a special apparatus.
  • the time period during which a carbon precursor is immersed in an aqueous organic acid solution can be appropriately adjusted depending on the acid used.
  • the immersion time falls within the range of usually 1 to 100 hours, preferably 2 to 80 hours, and more preferably 2.5 to 50 hours.
  • the proportion of the mass of a carbon precursor to be immersed in an aqueous organic acid solution to the mass of the aqueous organic acid solution can be appropriately adjusted depending on the kind of the aqueous organic acid solution used, the concentration, the temperature, and the like and falls within the range of usually 0.1% by mass to 200% by mass, preferably 1% by mass to 150% by mass, and more preferably 1.5% by mass to 120% by mass.
  • a proportion is preferred because a metallic element and/or a non-metallic element eluted into an aqueous organic acid solution hardly precipitate from the aqueous organic acid solution and reattachment thereof to a carbon precursor is suppressed as long as the proportion falls within the above-mentioned range.
  • such a proportion is preferred in the point of an economic aspect because the volume efficiency becomes appropriate as long as the proportion falls within the above-mentioned range.
  • the atmosphere under which a liquid phase demineralization treatment is performed is not particularly limited and may vary depending on the method used for the immersion.
  • a liquid phase demineralization treatment is usually performed under an air atmosphere.
  • a series of these operations can be repeated preferably one time to five times and more preferably two times to four times to perform the liquid phase demineralization.
  • a washing step and/or a drying step can be performed as necessary.
  • a carbon precursor for example, a carbon precursor originating from plants
  • a heat treatment in a vapor phase containing a halogen compound.
  • the vapor phase demineralization is accompanied by a sudden thermal decomposition reaction of a carbon precursor at the time of the heat treatment, sometimes, the vapor phase demineralization efficiency can be lowered due to generation of thermally decomposed components, the inside of a heat treatment apparatus can be contaminated by the thermally decomposed components generated, and the thermally decomposed components can disturb safe operation.
  • a substance for example, a substance originating from plants
  • a carbon precursor for example, a carbon precursor originating from plants
  • the halogen compound used in a vapor phase demineralization treatment is not particularly restricted.
  • fluorine, chlorine, bromine, iodine, hydrogen fluoride, hydrogen chloride, hydrogen bromide, iodine bromide, chlorine fluoride (ClF), iodine chloride (ICl), iodine bromide (IBr), bromine chloride (BrCl), and a mixture thereof can be used.
  • Compounds that generate these halogen compounds by thermal decomposition or a mixture thereof can also be used. From the viewpoints of supply stability and stability of the halogen compound used, it is preferred that hydrogen chloride is used.
  • a halogen compound and an inert gas may be mixed to be used.
  • the inert gas is not particularly restricted as long as the inert gas does not react with a carbon component constituting a carbon precursor (for example, a carbon precursor originating from plants).
  • a carbon precursor for example, a carbon precursor originating from plants.
  • nitrogen, helium, argon, krypton, or a mixed gas thereof can be used. From the viewpoints of supply stability and economy, it is preferred that nitrogen is used.
  • the mixing ratio between a halogen compound and an inert gas is not particularly limited as long as sufficient demineralization can be attained.
  • the volume ratio of a halogen compound to an inert gas preferably falls within the range of 0.01 to 10.0% by volume, more preferably falls within the range of 0.05 to 8.0% by volume, and especially preferably falls within the range of 0.1 to 5.0% by volume.
  • the treatment temperature for a vapor phase demineralization treatment may vary depending on the kind of a carbon precursor (for example, a carbon precursor originating from plants) to be demineralized, from the viewpoint of attaining a desired oxygen element content and specific surface area
  • the vapor phase demineralization treatment can be performed at for example 500 to 950° C., preferably 600 to 940° C., more preferably 650 to 940° C., and especially preferably 850 to 930° C.
  • the demineralization temperature falls within the above-mentioned range, satisfactory demineralization efficiency can be attained to sufficiently demineralize the carbon precursor and activation by a halogen compound can be avoided.
  • the time period for the vapor phase demineralization is not particularly restricted. From the viewpoints of economic efficiency in reaction facilities and structure-preserving properties of a carbonaceous component, the time period for example falls within the range of 5 to 300 minutes, preferably falls within the range of 10 to 200 minutes, and more preferably falls within the range of 20 to 150 minutes.
  • the particle diameter of a carbon precursor (for example, a carbon precursor originating from plants) to be subjected to vapor phase demineralization is not particularly limited.
  • the lower limit of an average value of particle diameters is preferably 100 ⁇ m or more, more preferably 300 ⁇ m or more, and especially preferably 500 ⁇ m or more because it may become difficult for the vapor phase containing potassium and the like which are removed from a carbon precursor and the carbon precursor to be separated from each other in the case where the particle diameter is too small.
  • the upper limit of an average value of particle diameters is preferably 10000 ⁇ m or less, more preferably 8000 ⁇ m or less, and especially preferably 5000 ⁇ m or less. In this context, the details of the measurement of the particle diameter are as described in EXAMPLES.
  • An apparatus used in the vapor phase demineralization is not particularly limited as long as the apparatus enables the vapor phase containing a halogen compound to be heated and stirred together with a carbon precursor (for example, a carbon precursor originating from plants).
  • a carbon precursor for example, a carbon precursor originating from plants.
  • a fluidized bed or the like can be used and a continuous or batch-wise fluid layer distribution system can be adopted.
  • the supply volume (fluidization quantity) of the vapor phase is also not particularly limited.
  • the vapor phase is supplied at a rate of preferably 1 mL/minute or more, more preferably 5 mL/minute or more, and especially preferably 10 mL/minute or more, per 1 g of a carbon precursor (for example, a carbon precursor originating from plants).
  • a carbon precursor for example, a carbon precursor originating from plants.
  • a heat treatment in an inert gas atmosphere containing a halogen compound hereinafter, sometimes referred to as “a halogen heat treatment”
  • a heat treatment in an atmosphere containing no halogen compound hereinafter, sometimes referred to as “a vapor phase deacidification treatment”
  • the halogen heat treatment causes halogen elements to be contained in a carbon precursor (for example, a carbon precursor originating from plants)
  • halogen elements contained in the carbon precursor is removed by a vapor phase deacidification treatment.
  • a heat treatment in an inert gas atmosphere containing no halogen compound is performed at a temperature falling within the range of usually 500° C. to 940° C., preferably 600 to 940° C., more preferably 650 to 940° C., and especially preferably 850 to 930° C. It is preferred that this heat treatment is performed at a temperature equal to or higher than the treatment temperature for the preceding halogen heat treatment.
  • supply of the halogen compound can be cut off to perform a heat treatment as the vapor phase deacidification treatment.
  • the time period for the vapor phase deacidification treatment is also not particularly limited. The time period preferably falls within the range of 5 minutes to 300 minutes, more preferably falls within the range of 10 minutes to 200 minutes, and especially preferably falls within the range of 10 minutes to 100 minutes.
  • the acid treatment in the present invention is a treatment in which potassium, iron, and the like contained in a carbon precursor (for example, a carbon precursor originating from plants) are removed (a carbon precursor is demineralized).
  • a carbon precursor for example, a carbon precursor originating from plants
  • the potassium element content is reduced by the acid treatment preferably to 0.1% by mass or less, more preferably to 0.05% by mass or less, and further preferably to 0.03% by mass or less.
  • the potassium element content is reduced especially preferably to such a degree that the hardly graphitizable carbonaceous material contains substantially no potassium element.
  • the iron element content is reduced by the acid treatment preferably to 0.02% by mass or less, more preferably to 0.015% by mass or less, and further preferably to 0.01% by mass or less.
  • the iron element content is reduced especially preferably to such a degree that the hardly graphitizable carbonaceous material contains substantially no iron element.
  • containing substantially no potassium element or substantially no iron element means having a potassium element content or an iron element content equal to or less than the detection limit value in the X-ray fluorescence analysis (for example, analysis using the “LAB CENTER XRF-1700” available from SHIMADZU CORPORATION) described below.
  • the potassium element content and the iron element content are equal to or less than the above-mentioned values, respectively, a sufficient dedoping capacity and a satisfactory nondedoping capacity can be attained and a safety problem of the nonaqueous electrolyte secondary battery can be avoided.
  • the details of the measurement of the potassium element content and iron element content are as described in EXAMPLES.
  • a part of carbon components is removed while the carbon precursor is demineralized. Specifically, a part of carbon components is removed by the elution in the case of liquid phase demineralization and a part of carbon components is removed by the activation action of chlorine in the case of vapor phase demineralization.
  • a space from which a carbon component is removed plays a role of a storage site for clustered lithium atoms after a calcination step described below.
  • the acid treatment is performed at least one time.
  • the same or different acids may be used to perform the acid treatment two times or more.
  • a carbon precursor (for example, a carbon precursor originating from plants) to be subjected to an acid treatment is a substance (for example, a substance originating from plants) before carbonization or a substance (for example, a substance originating from plants) after carbonization.
  • a raw material for example, a plant raw material
  • a liquid phase demineralization treatment as an acid treatment.
  • a carbon precursor after the acid treatment is a carbon precursor not subjected to a carbonization treatment yet, that is, the case where a carbon precursor after the acid treatment is a carbon precursor prepared by subjecting a raw material (for example, a plant raw material) before carbonization to the acid treatment, subsequently, the carbon precursor is subjected to a carbonization treatment.
  • the carbonizing method is not particularly limited.
  • an acid-treated raw material for example, an acid-treated plant raw material
  • a heat treatment under an inert gas atmosphere at 300° C. or more (temporary calcination) to be carbonized.
  • a carbon precursor for example, a carbon precursor originating from plants
  • a carbon precursor for example, a carbon precursor originating from plants
  • a carbon precursor is pulverized so as to have an average particle diameter after a calcination step falling within, for example, the range of 3 to 30 ⁇ m from the viewpoint of coating properties at the time of preparing an electrode. That is, the hardly graphitizable carbonaceous material according to the present invention is adjusted so as to have an average particle diameter (Dv 50 ) falling within, for example, the range of 3 to 30 ⁇ m.
  • the average particle diameter of the hardly graphitizable carbonaceous material is 3 ⁇ m or more, a tendency that the amount of fine powder increases, the specific surface area increases, the reactivity with an electrolytic solution is heightened, the irreversible capacity being a capacity which is not dischargeable in spite of being charged into a battery increases, and the portion of useless capacity in a positive electrode increases can be suppressed.
  • voids to be formed between particles of the carbonaceous material can be sufficiently secured and satisfactory transfer of lithium ions in an electrolytic solution can be secured.
  • the average particle diameter (Dv 50 ) of the carbonaceous material of the present invention is preferably 3 ⁇ m or more, more preferably 4 ⁇ m or more, and especially preferably 5 ⁇ m or more.
  • the average particle diameter is 30 ⁇ m or less, such a carbonaceous material is preferred because the mean free path of lithium ions diffusing into the inside of a particle is shortened and the quick charge-discharge is possible.
  • enlarging the electrode area is of importance for enhancing the input-output characteristics, and for this reason, the coating thickness of an active material onto a current collecting plate is required to be thinned at the time of the electrode preparation.
  • the active material is required to have a small particle diameter.
  • the average particle diameter is preferably 30 ⁇ m or less, more preferably 19 ⁇ m or less, further preferably 17 ⁇ m or less, still further preferably 16 ⁇ m or less, and especially preferably 15 ⁇ m or less.
  • a carbon precursor for example, a carbon precursor originating from plants
  • a carbon precursor is shrunk by 0 to 20% or so. Therefore, in order to make the average particle diameter after calcination fall within the range of 3 to 30 ⁇ m, it is preferred that the average particle diameter of a carbon precursor is adjusted so as to be an average particle diameter larger by 0 to 20% or so than the desired average particle diameter after calcination.
  • the pulverization is performed so as to make the average particle diameter after pulverization fall within the range of preferably 3 to 36 ⁇ m, more preferably 3 to 22.8 ⁇ m, further preferably 3 to 20.4 ⁇ m, still further preferably 3 to 19.2 ⁇ m, and especially preferably 3 to 18 ⁇ m.
  • the pulverization step is not particularly limited in the sequence of steps. In view of the recovery (yield) of a carbon precursor in an acid treatment, it is preferred that the pulverization step is performed after an acid treatment and it is preferred that the pulverization step is performed before a calcination step from the viewpoint of sufficiently reducing the specific surface area of the carbonaceous material. However, the pulverization step may also be performed before an acid treatment or after a calcination step, and these cases are not eliminated.
  • a pulverizer used in the pulverization step is not particularly limited.
  • a jet mill, a ball mill, a hammer mill, a rod mill, or the like can be used.
  • a jet mill equipped with a classifying function is preferred.
  • classification can be performed after a pulverization step to remove fine powder.
  • a classification step enables the average particle diameter of the carbonaceous material to be more accurately adjusted. For example, it is possible to remove particles with a particle diameter of 1 ⁇ m or less.
  • the hardly graphitizable carbonaceous material according to the present invention has a content of particles with a particle diameter of 1 ⁇ m or less of 3% by volume or less.
  • pulverization and classification is simultaneously performed.
  • the content of particles with a particle diameter of 1 ⁇ m or less is preferably 3% by volume or less, more preferably 2.5% by volume or less, and especially preferably 2.0% by volume or less.
  • the classifying method is not particularly restricted. Examples thereof can include classification with a sieve, wet classification, and dry classification. Examples of a wet classifier can include a classifier utilizing the principle of gravity classification, inertial classification, hydraulic classification, centrifugal classification, or the like. Examples of a dry classifier can include a classifier utilizing the principle of sedimentary classification, mechanical classification, centrifugal classification, or the like.
  • a pulverization step and a classification step may be performed with the use of one apparatus.
  • a jet mill equipped with a dry classifying function can be used to perform a pulverization step and a classification step.
  • an apparatus equipped with a pulverizer and a classifier, both of which are constituted independently respectively, may be used. In this case, pulverization and classification can be sequentially performed, and moreover, pulverization and classification can be discontinuously performed.
  • a carbon precursor which has been subjected to an acid treatment and a carbonization treatment can be calcined to produce the hardly graphitizable carbonaceous material according to the present invention.
  • a calcination step is a step of elevating the atmosphere temperature from room temperature to a predetermined calcination temperature, and then, performing calcination at the calcination temperature.
  • the carbon precursor (a) may be calcined at a temperature of 1100 to 1400° C. (final calcination) or the carbon precursor (b) may be calcined at a temperature of 350 to less than 1100° C.
  • preliminary calcination preliminary calcination
  • final calcination further calcined at a temperature of 1100 to 1400° C.
  • a carbon precursor which has been subjected to an acid treatment and a carbonization treatment can be calcined at a temperature of 350 to less than 1100° C. to perform a preliminary calcination step in a method for producing the hardly graphitizable carbonaceous material according to the present invention.
  • the preliminary calcination temperature usually falls within the range of 350 to less than 1100° C. and preferably falls within the range of 400 to less than 1100° C.
  • the preliminary calcination can be performed according to a usual procedure for preliminary calcination. Specifically, the preliminary calcination can be performed in an inert gas atmosphere and examples of the inert gas can include nitrogen, argon, or the like. Moreover, the preliminary calcination can also be performed under reduced pressure, and for example, the preliminary calcination can be performed under a pressure of 10 KPa or less.
  • the time period for the preliminary calcination is not particularly limited, usually falls within the range of 0.5 to 10 hours, and preferably falls within the range of 1 to 5 hours.
  • a final calcination step in a method for producing the hardly graphitizable carbonaceous material according to the present invention can be performed according to a usual procedure for final calcination, and after the final calcination, a hardly graphitizable carbonaceous material is obtained.
  • the final calcination temperature usually falls within the range of 1100 to 1400° C., preferably falls within the range of 1200 to 1380° C., and more preferably falls within the range of 1250 to 1350° C.
  • the final calcination can be performed in an inert gas atmosphere and examples of the inert gas can include nitrogen, argon, or the like. Moreover, it is also possible to perform the final calcination in an inert gas atmosphere containing a halogen gas. Furthermore, it is also possible to perform the final calcination under reduced pressure, for example, under a pressure of 10 KPa or less.
  • the time period for the final calcination is not particularly limited, and the time period falls within the range of for example 0.05 to 10 hours, preferably 0.05 to 8 hours, and more preferably 0.05 to 6 hours.
  • the carbon precursor at the time of calcining a carbon precursor, can be mixed with a volatile organic substance to be calcined.
  • a volatile organic substance to be calcined By being mixed with a volatile organic substance to be calcined, a hardly graphitizable carbonaceous material obtained from the carbon precursor can have a specific surface area more suitable for a negative electrode material for lithium ion secondary batteries.
  • a volatile organic substance that can be used in the present invention is not particularly limited as long as the volatile organic substance is solid at an ambient temperature and has a residual carbon ratio of less than 5% by mass on the basis of the mass of a volatile organic substance before ashing in the case of being ashed at 800° C.
  • the content of volatile substances enabling the specific surface area to be decreased in a volatile organic substance is not particularly limited, the content thereof usually falls within the range of 1 to 20% by mass and preferably falls within the range of 3 to 15% by mass on the basis of the mass of the volatile organic substance.
  • the ambient temperature refers to 25° C.
  • Examples of the volatile organic substance can include a thermoplastic resin and a low molecular weight organic compound. More specifically, examples of the thermoplastic resin can include polystyrene, polyethylene, polypropylene, poly(meth)acrylic acid, a poly(meth)acrylic acid ester, or the like, and examples of the low molecular weight organic compound can include toluene, xylene, mesitylene, styrene, naphthalene, phenanthrene, anthracene, pyrene, or the like.
  • polystyrene, polyethylene, or polypropylene is preferred as the thermoplastic resin and naphthalene, phenanthrene, anthracene, or pyrene is preferred as the low molecular weight organic compound.
  • naphthalene, phenanthrene, anthracene, or pyrene is used.
  • the residual carbon ratio of the sample can be measured by quantitatively determining the carbon content of an intensively-heating residue obtained after a sample is intensively heated in an inert gas atmosphere.
  • a sample being intensively heated means about 1 g (the accurately weighed mass is defined as W 1 (g)) of a volatile organic substance being placed in a crucible, and the temperature of the crucible being elevated at a rate of 10° C./minute to 800° C. in an electric furnace with a nitrogen flow at a rate of 20 liters per 1 minute, and then, maintained for 1 hour at 800° C.
  • a residue thus obtained corresponds to an intensively-heating residue, and the mass thereof is defined as W 2 (g).
  • the intensively-heating residue is analyzed for the elemental analysis in accordance with a method stipulated in JIS M8819 to be measured for the mass proportion P 1 (%) of carbon.
  • the residual carbon ratio P 2 (%) is calculated from the following equation.
  • the carbon precursor and the volatile organic substance are mixed preferably at a mass ratio of 97:3 to 40:60.
  • This mixing ratio more preferably falls within the range of 95:5 to 60:40 and especially preferably falls within the range of 93:7 to 80:20.
  • the mixing of a carbon precursor and a volatile organic substance may be performed in a stage before or after pulverization of the carbon precursor.
  • the carbon precursor and the volatile organic substance can be simultaneously weighed and fed into a pulverizing apparatus to simultaneously perform pulverization and mixing.
  • a carbon precursor after pulverization is mixed with a volatile organic substance.
  • any mixing method may be adopted as long as the two are uniformly mixed.
  • a volatile organic substance is mixed in a particulate form, but the shape of particles and the particle diameter are not particularly limited.
  • the average particle diameter of the volatile organic substance preferably falls within the range of 0.1 to 2000 ⁇ m, more preferably falls within the range of 1 to 1000 ⁇ m, and especially preferably falls within the range of 2 to 600 ⁇ m.
  • the mixture of a carbon precursor and a volatile organic substance may contain an additional ingredient other than the carbon precursor and the volatile organic substance as long as effects on the hardly graphitizable carbonaceous material according to the present invention are exerted, that is, as long as the specific surface area of the hardly graphitizable carbonaceous material is decreased.
  • the mixture can further contain natural graphite, artificial graphite, a metal-based material, an alloy-based material, or an oxide-based material.
  • the content of the additional ingredient is not particularly limited and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, further preferably 20 parts by mass or less, and especially preferably 10 parts by mass or less, relative to 100 parts by mass of the mixture of a carbon precursor and a volatile organic substance.
  • the negative electrode material for nonaqueous electrolyte secondary batteries according to the present invention comprises the hardly graphitizable carbonaceous material according to the present invention.
  • anode electrode material containing the hardly graphitizable carbonaceous material according to the present invention can be produced.
  • a conductive additive can also be added to the electrode mixture, as necessary.
  • the conductive additive conductive carbon black, a vapor-grown carbon fiber (VGCF), a nanotube, and the like can be used.
  • the binding agent added can include PVDF (polyvinylidene fluoride), polytetrafluoroethylene, a mixture of SBR (styrene-butadiene-rubber) and CMC (carboxymethyl cellulose), and the like.
  • PVDF polyvinylidene fluoride
  • SBR styrene-butadiene-rubber
  • CMC carbboxymethyl cellulose
  • the addition amount of a binding agent varies with the kind of the binding agent used, with regard to a PVDF-based binding agent, the addition amount thereof preferably falls within the range of 3 to 13% by mass and more preferably falls within the range of 3 to 10% by mass on the basis of the whole mass of the hardly graphitizable carbonaceous material, the binding agent, and the conductive additive.
  • the addition amount of a binding agent fall within the above-mentioned range, problems that the electrical resistance of the resulting electrode becomes large, the internal resistance of a battery becomes large, the battery characteristics are lowered, and the electrical connection between two anode material particles and between an anode material particle and a current collecting plate becomes insufficient can be avoided.
  • a polar solvent such as N-methylpyrrolidone (NMP) may be preferably used.
  • NMP N-methylpyrrolidone
  • water may be preferably used as the solvent.
  • the binding agent to be blended with water as a solvent a mixture of plural binding agents such as a mixture of SBR and CMC is often used.
  • the addition amount of a solvent preferably falls within the range of 0.5 to 5% by mass and more preferably falls within the range of 1 to 4% by mass on the basis of the whole mass of the binding agent used.
  • one electrode active material layer may be formed only on one face thereof.
  • the thickness of the active material layer preferably falls within the range of 10 to 80 ⁇ m, more preferably falls within the range of 20 to 75 ⁇ m, and especially preferably falls within the range of 20 to 60 ⁇ m.
  • the nonaqueous electrolyte secondary battery according to the present invention comprises the negative electrode material for nonaqueous electrolyte secondary batteries according to the present invention.
  • a nonaqueous electrolyte secondary battery which is produced with a negative electrode material for nonaqueous electrolyte secondary batteries comprising the hardly graphitizable carbonaceous material according to the present invention and which is fully charged to be used shows not only high charge capacity but also high charge-discharge efficiency.
  • a negative electrode material for nonaqueous electrolyte secondary batteries no particular limitation is put on other constituent materials for a battery such as a positive electrode material, a separator, and an electrolytic solution. It is possible to use various materials which are used in or proposed for a conventional nonaqueous solvent secondary battery.
  • layered oxide-based composite metal chalcogen compounds represented by LiMO 2 , wherein M represents a metallic element: for example, LiCoO 2 , LiNiO 2 , LiMnO 2 , or LiNi x Co y Mo z O 2 (wherein, x, y, and z each represent a composition ratio)
  • olivine-based composite metal chalcogen compounds represented by LiMPO 4 , wherein M represents a metallic element: for example, LiFePO 4 or the like
  • spinel-based composite metal chalcogen compounds represented by LiM 2 O 4 , wherein M represents a metallic element: for example, LiMn 2 O 4 or the like
  • These chalcogen compounds may be mixed as necessary.
  • These positive electrode materials, together with an appropriate binder and a carbon material that imparts electrical conductivity to the electrode are molded and formed into a layer on an electrically conductive current collecting member to form a positive electrode.
  • a nonaqueous solvent type electrolytic solution combined with these positive and negative electrodes to be used is generally formed by dissolving an electrolyte in a nonaqueous solvent.
  • a nonaqueous solvent for example, one of organic solvents such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, diethoxyethane, ⁇ -butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, and 1,3-dioxolane can be used alone or two or more thereof can be used in combination.
  • LiClO 4 LiPF 6 , LiBF 4 , LiCF 3 SO 3 , LiAsF 6 , LiCl, LiBr, LiB(C 6 H 5 ) 4 , LiN(SO 3 CF 3 ) 2 , or the like may be used.
  • a nonaqueous electrolyte secondary battery is produced by opposing the positive electrode and the negative electrode which are formed as described above, as necessary with a liquid-permeable separator, composed of nonwoven fabric and other porous materials, interposed therebetween, and by immersing them in an electrolytic solution.
  • a permeable separator composed of nonwoven fabric and other porous materials, generally used in a secondary battery can be used.
  • a solid electrolyte composed of a polymer gel impregnated with an electrolytic solution can be used.
  • a nonaqueous electrolyte secondary battery fully charged to be used refers to a nonaqueous electrolyte secondary battery obtained by assembling the nonaqueous electrolyte secondary battery according to the present invention, and allowing its negative electrode to be charged (doped) with lithium until just before precipitation of metallic lithium is confirmed by 7 Li nuclear-solid state NMR analysis; and usually means a nonaqueous electrolyte secondary battery charged at a constant current value so as to have a charge capacity within the range of 580 to 700 mAbig per mass of the negative electrode active material.
  • the oxygen element content of the hardly graphitizable carbonaceous material is usually 0.25% by mass or less and preferably 0.24% by mass or less. It is further preferred that the hardly graphitizable carbonaceous material contains substantially no oxygen element.
  • containing substantially no oxygen element means having an oxygen element content equal to or less than 10 ⁇ 6 % by mass which is a detection limit of the elemental analysis method (inert gas fusion-thermal conductivity method) described below.
  • the oxygen element content is the above-mentioned value or less, the lowering in utilization efficiency of lithium ions can be suppressed.
  • a method of adjusting the oxygen element content is not limited at all. For example, by subjecting a carbon precursor originating from plants to an acid treatment at a predetermined temperature, then, mixing an acid-treated carbon precursor with a volatile organic substance, and calcining the mixture under an inert gas atmosphere at a temperature of 1100° C. to 1400° C., the oxygen element content can be adjusted.
  • the details of the measurement of the oxygen element content are as described in EXAMPLES.
  • a main resonance peak position of a chemical shift value observed by subjecting the hardly graphitizable carbonaceous material to 7 Li nuclear-solid state NMR analysis is preferably downfield by more than 115 ppm, more preferably downfield by more than 118 ppm, and especially preferably downfield by more than 120 ppm, from a peak position of lithium chloride.
  • the details of the 7 Li nuclear-solid state NMR analysis are as described in EXAMPLES.
  • a battery prepared with a hardly graphitizable carbonaceous material in which a main resonance peak position of a chemical shift value is downfield by more than 115 ppm from a peak position of lithium chloride means a battery having a high charge capacity and having high charge-discharge efficiency calculated from “the discharge capacity/the charge capacity”. Since the charge-discharge efficiency is high, the battery becomes advantageous from an aspect of capacity per volume of the battery or cost of the battery.
  • the hardly graphitizable carbonaceous material in the nonaqueous electrolyte secondary battery according to the present invention is derived from a phenol resin, a furan resin, pitch, tar, a carbon precursor originating from plants, or the like.
  • the hardly graphitizable carbonaceous material is preferably derived from a carbon precursor originating from plants.
  • a carbon precursor originating from plants means a substance before carbonization originating from plants or a substance after carbonization originating from plants (char derived from plants).
  • the plant raw material is not particularly limited. Such plants described above can be used singly or in combination of two or more thereof. Of these, coconut shell, which is easily available abundantly, is preferred.
  • the coconut shell is not particularly limited.
  • the coconut shells exemplified above can be used singly or in combination.
  • Coconut shells of coco palm and palm coconut which are utilized as foodstuffs, raw material of a detergent, raw material of a biodiesel fuel oil, and the like and are biomass wastes generated in large quantities, are especially preferred.
  • a method of carbonizing the plant raw material that is, a method of producing the char derived from plants, is not particularly limited.
  • the method can be performed, for example, by subjecting the plant raw material to a heat treatment under an inert gas atmosphere at 300° C. or more (hereinafter, sometimes referred to as “temporary calcination”).
  • the plant raw material in the form of char (for example, coconut shell char) is also available.
  • the average face-to-face dimension d 002 of the (002) face calculated from the Bragg equation by a wide angle X-ray diffraction method of the hardly graphitizable carbonaceous material in the nonaqueous electrolyte secondary battery according to the present invention preferably falls within the range of 0.36 nm to 0.42 nm, more preferably falls within the range of 0.38 nm to 0.40 nm, and especially preferably falls within the range of 0.381 nm to 0.389 nm.
  • a carbon precursor giving a hardly graphitizable carbonaceous material may be calcined at a calcination temperature within the range of 1100 to 1400° C.
  • the specific surface area determined by a nitrogen adsorption BET three-point method of the hardly graphitizable carbonaceous material in the nonaqueous electrolyte secondary battery according to the present invention preferably falls within the range of 1 to 20 m 2 /g, more preferably falls within the range of 1.2 to 10 m 2 /g, and especially preferably falls within the range of 1.4 to 9.5 m 2 /g.
  • the specific surface area falls within the above-mentioned range, the number of micropores in the hardly graphitizable carbonaceous material can be sufficiently reduced by a calcination step described below, the moisture-absorption characteristics of the hardly graphitizable carbonaceous material can be sufficiently lowered, and the lowering in utilization efficiency of lithium ions can be suppressed.
  • the specific surface area can be adjusted by controlling the temperature in a demineralization step described below. The details of the measurement of the specific surface area by a nitrogen adsorption BET three-point method are as described in EXAMPLES.
  • the true density by a butanol method of the hardly graphitizable carbonaceous material in the nonaqueous electrolyte secondary battery according to the present invention preferably falls within the range of 1.40 to 1.70 g/cm 3 , more preferably falls within the range of 1.42 to 1.65 g/cm 3 , and especially preferably falls within the range of 1.44 to 1.60 g/cm 3 .
  • the true density within the above-mentioned range can be attained, for example, by setting the calcination step temperature to 1100 to 1400° C.
  • the details of the measurement of the true density ⁇ Bt are as described in EXAMPLES.
  • the potassium element content of the hardly graphitizable carbonaceous material in the nonaqueous electrolyte secondary battery according to the present invention is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, and further preferably 0.03% by mass or less, and it is especially preferred that the hardly graphitizable carbonaceous material contains substantially no potassium element.
  • the iron element content of the hardly graphitizable carbonaceous material in the nonaqueous electrolyte secondary battery according to the present invention is preferably 0.02% by mass or less, more preferably 0.015% by mass or less, and further preferably 0.01% by mass or less, and it is especially preferred that the hardly graphitizable carbonaceous material contains substantially no iron element.
  • containing substantially no potassium element or substantially no iron element means having a potassium element content or an iron element content equal to or less than the detection limit value in the X-ray fluorescence analysis (for example, analysis using the “LAB CENTER XRF-1700” available from SHIMADZU CORPORATION) described below.
  • the potassium element content and the iron element content are equal to or less than the above-mentioned values, respectively, a sufficient dedoping capacity and a satisfactory nondedoping capacity can be attained and a safety problem of the nonaqueous electrolyte secondary battery can be avoided.
  • the details of the measurement of the potassium element content and iron element content are as described in EXAMPLES.
  • the moisture content of the hardly graphitizable carbonaceous material in the nonaqueous electrolyte secondary battery according to the present invention is preferably 10000 ppm or less, more preferably 9000 ppm or less, and especially preferably 8000 ppm or less.
  • the moisture content of the hardly graphitizable carbonaceous material can be reduced, for example, by reducing the number of oxygen atoms contained in a hardly graphitizable carbonaceous material.
  • the moisture content of the hardly graphitizable carbonaceous material can be measured, for example, with the use of a Karl Fischer moisture meter or the like. The details of the measurement of the moisture content are as described in EXAMPLES.
  • an Oxygen: inert gas fusion-Non Dispersive Infrared Ray absorption method (NDIR), a Nitrogen: inert gas fusion-Thermal Conductivity Detection method (TCD), and a Hydrogen: inert gas fusion-Non Dispersive Infrared Ray absorption method (NDIR) were adopted.
  • the calibration was performed by the use of an (Oxygen/Nitrogen) Ni capsule, TiH 2 (H standard sample), and SS-3 (N, O standard sample). The water content of a sample was measured at 250° C.
  • a negative electrode portion containing a hardly graphitizable carbonaceous material fully doped with lithium ions was taken out of a cell in a fully charged state, and the whole negative electrode portion from which the electrolyte was wiped off was placed into a sample tube for NMR.
  • “Nuclear magnetic resonance apparatus AVANCE 300” available from Bruker Corporation, 7 Li nuclear-solid state NMR analysis was performed. At the time of measurement, lithium chloride was adopted as a reference material and the peak position thereof was set to 0 ppm.
  • v m was determined by a three-point method utilizing nitrogen adsorption at a liquid nitrogen temperature to calculate the specific surface area of a sample according to the following equation.
  • v m represent's an adsorption amount (cm 3 /g) required for a monomolecular layer to be formed on the sample surface
  • v represents an actually measured adsorption amount (cm 3 /g)
  • p 0 represents a saturated vapor pressure
  • p represents an absolute pressure
  • c represents a constant (reflecting the heat of adsorption)
  • N represents Avogadro's number 6.022 ⁇ 10 23
  • a (nm 2 ) represents an area occupied by molecules of the adsorbate on the sample surface (molecular sectional area at the monolayer).
  • the amount of nitrogen adsorbed to a hardly graphitizable carbonaceous material at a liquid nitrogen temperature was measured in the following way.
  • a pulverized hardly graphitizable carbonaceous material with a particle diameter of about 5 to 50 ⁇ m was placed in a sample tube, the internal pressure of the sample tube in a state of being cooled to ⁇ 196° C. was once reduced, and then, the hardly graphitizable carbonaceous material was made to adsorb nitrogen (purity of 99.999%) at a desired relative pressure.
  • the amount of nitrogen adsorbed to a sample when the adsorption equilibrium is attained at each desired relative pressure was defined as the adsorption gas amount v.
  • the true density was measured by a butanol method.
  • a specific gravity bottle with a side tube having an internal volume of about 40 mL was accurately weighed for the mass (m 1 ).
  • a sample was placed into the bottle so that the sample flattened all over a bottom part of the bottle and the thickness of the sample becomes about 10 mm, after which the specific gravity bottle was accurately weighed for the mass (m 2 ).
  • 1-butanol was carefully added so that a depth from the bottom to the liquid level of 1-butanol became 20 mm or so.
  • the specific gravity bottle was taken out thereof, the outside surface was thoroughly wiped, and the contents were cooled to room temperature, after which the specific gravity bottle was accurately weighed for the mass (m 4 ).
  • the identical specific gravity bottle was filled only with 1-butanol and immersed in a constant-temperature water bath in the same manner as above to make the liquid level of 1-butanol coincide with the marked line, after which the specific gravity bottle was weighed for the mass (m 3 ).
  • the identical specific gravity bottle was filled only with distilled water prepared by being boiled just before use to remove dissolved gas and immersed in a constant-temperature water bath in the same manner as above to make the liquid level of distilled water coincide with the marked line, after which the specific gravity bottle was weighed for the mass (m 5 ).
  • the true density ⁇ Bt was calculated according to the following equation.
  • d represents the specific gravity (0.9946) of water at 30° C.
  • the potassium element content and the iron element content were measured in the following manner. Carbon samples containing predetermined amounts of the potassium element and the iron element were prepared beforehand, and with the use of an X-ray fluorescence spectroscopic analyzer, a calibration curve showing the relationship between the intensity of the potassium K ⁇ ray and the potassium element content and a calibration curve showing the relationship between the intensity of the iron K ⁇ ray and the iron element content were prepared. Then, a sample was measured for the intensities of the potassium K ⁇ ray and the iron K ⁇ ray in X-ray fluorescence analysis to determine the potassium element content and the iron element content by the use of the previously prepared calibration curves.
  • the X-ray fluorescence analysis was performed under the following condition.
  • a holder for the upper part irradiation system was used and the measurement area of the sample was set within the circumference of a diameter of 20 mm.
  • 0.5 g of the sample to be measured was placed in a polyethylene-made vessel with an inner diameter of 25 mm, the back side of the vessel was supported with a plankton net, and the measurement surface was covered with a polypropylene-made film to perform the measurement.
  • Conditions of an X-ray source were set to 40 kV and 60 mA.
  • LiF (200) was used as the dispersive crystal, a gas flow type proportional counter was used as a detector, and the sample was measured at a scanning speed of 8°/minute within the range of 90 to 140° as the value of 2 ⁇ .
  • a scintillation counter was used as a detector, and the sample was measured at a scanning speed of 8°/minute within the range of 56 to 60° as the value of 2 ⁇ .
  • the temperature of the crucible was elevated to 500° C. at 10° C./minute, maintained for 60 minutes, and then, cooled over a period of 6 hours.
  • the crucible was taken out thereof at 50° C. or less to obtain a carbonized product.
  • the obtained carbonized product was coarsely pulverized so as to have an average particle diameter of 10 ⁇ m using a ball mill, and then, pulverized using a compact jet mill (available from SEISHIN ENTERPRISE Co., Ltd., Co-Jet system ⁇ -mk III) and classified to obtain a carbon precursor with an average particle diameter of 9.0 ⁇ m.
  • the electrode corresponding to a negative electrode was used as a working electrode and metallic lithium was used as a counter electrode and a reference electrode.
  • Ethylene carbonate and methylethyl carbonate were mixed at a volume ratio of 3:7, and the obtained mixture was used as a solvent.
  • LiPF 6 was dissolved at a concentration of 1 mol/L, and the obtained solution was used as an electrolyte.
  • a sheet of glass fiber nonwoven fabric was used as a separator.
  • a coin cell was prepared under an argon atmosphere.
  • a predetermined capacity at which no metallic lithium was precipitated refers to an upper limit charge capacity (mAh/g) at which no precipitation of metallic lithium was observed by Li-NMR.
  • the hardly graphitizable carbonaceous material was subjected to 7 Li nuclear-solid state NMR analysis, and measured for the oxygen element content, the average face-to-face dimension d 002 of the (002) face, the specific surface area, the true density, the potassium element content and iron element content, and the moisture content.
  • the results are collected in Table 1 and the 7 Li nuclear-solid state NMR spectrum is shown in FIG. 1 .
  • coconut shell was crushed and dry-distilled at 500° C. to obtain coconut shell char with a particle diameter of 2.36 to 0.85 mm. While nitrogen gas containing hydrogen chloride gas in a content of 1% by volume was supplied at a flow rate of 10 L/minute to 100 g of the coconut shell char, the coconut shell char was subjected to a halogen heat treatment for 30 minutes at 870° C. Afterward, only the supply of hydrogen chloride gas was stopped. While nitrogen gas was supplied at a flow rate of 10 L/minute thereto, the coconut shell char was subjected to a vapor phase deacidification treatment for 30 minutes at 900° C. to obtain a carbon precursor.
  • the obtained carbon precursor was coarsely pulverized so as to have an average particle diameter of 10 ⁇ m using a ball mill, and then, pulverized using a compact jet mill (available from SEISHIN ENTERPRISE Co., Ltd., Co-Jet system ⁇ -mk III), and classified to obtain a carbon precursor with an average particle diameter of 9.6 ⁇ m.
  • the electrode corresponding to a negative electrode was used as a working electrode, and metallic lithium was used as a counter electrode and a reference electrode.
  • Ethylene carbonate and methylethyl carbonate were mixed at a volume ratio of 3:7, and the obtained mixture was used as a solvent.
  • LiPF 6 was dissolved at a concentration of 1 mol/L in this solvent, and the obtained solution was used as an electrolyte.
  • a sheet of glass fiber nonwoven fabric was used as a separator. In a glove box, a coin cell was prepared under an argon atmosphere.
  • a predetermined capacity at which no metallic lithium was precipitated refers to an upper limit charge capacity (mAh/g) at which no precipitation of metallic lithium was observed by Li-NMR.
  • the hardly graphitizable carbonaceous material was subjected to 7 Li nuclear-solid state NMR analysis, and measured for the oxygen element content, the average face-to-face dimension d 002 of the (002) face, the specific surface area, the true density, the potassium element content and iron element content, and the moisture content.
  • a hardly graphitizable carbonaceous material and a negative electrode which are similar to those in Example 2 were used to perform the following full-cell evaluation.
  • the obtained electrode was used as a positive electrode and metallic lithium was used as a counter electrode and a reference electrode.
  • Ethylene carbonate and methylethyl carbonate were mixed at a volume ratio of 3:7, and the obtained mixture was used as a solvent.
  • LiPF 6 was dissolved at a concentration of 1 mol/L in this solvent, and the obtained solution was used as an electrolyte.
  • a sheet of glass fiber nonwoven fabric was used as a separator. In a glove box, a coin cell was prepared under an argon atmosphere.
  • a cathode half cell of the above-mentioned constitution was subjected to a charge-discharge test.
  • Lithium dedoping from the positive electrode was performed at a rate of 15 mA/g relative to the mass of the active material until the potential becomes 4.2 V relative to the lithium potential, and the capacity attained at this time was defined as the charge capacity.
  • lithium doping to the positive electrode was performed at a rate of 15 mA/g relative to the mass of the active material until the potential becomes 3.0 V relative to the lithium potential, and the capacity attained at this time was defined as the discharge capacity.
  • the charge capacity attained and the discharge capacity attained were determined to be 174 mAh/g and 154 mAh/g, respectively, and the charge-discharge efficiency (initial charge-discharge efficiency) calculated as the percentage of the discharge capacity/the charge capacity was determined to be 88.5%.
  • a negative electrode mixture-applied face and a positive electrode mixture-applied face were opposed to each other with a separator composed of glass fiber nonwoven fabric interposed therebetween so that the positive electrode (with a diameter of 14 mm) did not protrude from the negative electrode face area with a diameter of 15 mm obtained in Example 2.
  • a ratio (anode capacity/cathode capacity) of an anode charge capacity (mAh) per opposing area to a cathode charge capacity (mAh) per opposing area was adjusted to be 1.
  • LiPF 6 was dissolved at a concentration of 1 mol/L in this solvent, and the obtained solution was used as an electrolyte.
  • a coin cell was prepared under an argon atmosphere.
  • a coin cell (full cell) of the above-mentioned constitution was subjected to a charge-discharge test. Charging was performed at a rate of 30 mA/g relative to the mass of the negative electrode active material until the potential becomes 4.2 V relative to the lithium potential, and the capacity attained at this time was defined as the charge capacity. Then, discharging was performed at a rate of 30 mA/g relative to the mass of the negative electrode active material until the potential becomes 2.0 V relative to the lithium potential, and the capacity attained at this time was defined as the discharge capacity.
  • TOSCAT charge-discharge testing device
  • the hardly graphitizable carbonaceous material was subjected to 7 Li nuclear-solid state NMR analysis, and measured for the oxygen element content, the average face-to-face dimension d 002 of the (002) face, the specific surface area, the true density, the potassium element content and iron element content, and the moisture content. The results are collected in Table 1.
  • the obtained carbonized product was coarsely pulverized so as to have an average particle diameter of 10 ⁇ m using a ball mill, and then, pulverized using a compact jet mill (available from SEISHIN ENTERPRISE Co., Ltd., Co-Jet system ⁇ -mk III) and classified to obtain a carbon precursor with an average particle diameter of 9.0 ⁇ m.
  • the operation in which 20 g of the carbon precursor thus obtained was immersed for 1 hour in 100 g of a 35% by mass aqueous hydrochloric acid solution and then washed for 1 hour with water at 80° C., was performed two times to perform demineralization.
  • the demineralized coconut shell was dried for 24 hours at 80° C. under a vacuum of 1 Torr.
  • the electrode corresponding to a negative electrode was used as a working electrode, and metallic lithium was used as a counter electrode and a reference electrode.
  • Ethylene carbonate and methylethyl carbonate were mixed at a volume ratio of 3:7, and the obtained mixture was used as a solvent.
  • LiPF 6 was dissolved at a concentration of 1 mol/L in this solvent, and the obtained solution was used as an electrolyte.
  • a sheet of glass fiber nonwoven fabric was used as a separator. In a glove box, a coin cell was prepared under an argon atmosphere.
  • a predetermined capacity at which no metallic lithium was precipitated refers to an upper limit charge capacity (mAh/g) at which no precipitation of metallic lithium was observed by Li-NMR.
  • the hardly graphitizable carbonaceous material was subjected to 7 Li nuclear-solid state NMR analysis, and measured for the oxygen element content, the average face-to-face dimension d 002 of the (002) face, the specific surface area, the true density, the potassium element content and iron element content, and the moisture content.
  • CARBOTRON PJ available from KUREHA CORPORATION
  • 6 parts by mass of PVDF (polyvinylidene fluoride), and 90 parts by mass of NMP (N-methylpyrrolidone) were mixed to obtain slurry.
  • the obtained slurry was applied onto a sheet of copper foil with a thickness of 14 ⁇ m, dried, and then, pressed to obtain an electrode with a thickness of 60 to 70 ⁇ m.
  • the obtained electrode was determined to have a density of 0.9 to 1.1 g/cm 3 .
  • the electrode corresponding to a negative electrode was used as a working electrode, and metallic lithium was used as a counter electrode and a reference electrode.
  • Ethylene carbonate and methylethyl carbonate were mixed at a volume ratio of 3:7, and the obtained mixture was used as a solvent.
  • LiPF 6 was dissolved at a concentration of 1 mol/L in this solvent, and the obtained solution was used as an electrolyte.
  • a sheet of glass fiber nonwoven fabric was used as a separator. In a glove box, a coin cell was prepared under an argon atmosphere.
  • a predetermined capacity at which no metallic lithium was precipitated refers to an upper limit charge capacity (mAh/g) at which no precipitation of metallic lithium was observed by Li-NMR.
  • the hardly graphitizable carbonaceous material was subjected to 7 Li nuclear-solid state NMR analysis, and measured for the oxygen element content, the average face-to-face dimension d 002 of the (002) face, the specific surface area, the true density, the potassium element content and iron element content, and the moisture content.
  • the results are collected in Table 1 and the 7 Li nuclear-solid state NMR spectrum is shown in FIG. 2 .
  • a nonaqueous electrolyte secondary battery comprising the hardly graphitizable carbonaceous material according to the present invention and being fully charged to be used has not only extremely high charge capacity but also extremely high charge-discharge efficiency. Accordingly, the nonaqueous electrolyte secondary battery can be used especially in the field of on-vehicle batteries for a vehicle such as a hybrid vehicle (HEY), an electric vehicle (EV), and the like.
  • a vehicle such as a hybrid vehicle (HEY), an electric vehicle (EV), and the like.

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