JP2017084707A - Method for manufacturing carbonaceous material for nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a carbonaceous material (i.e. carbonaceous material for a nonaqueous electrolyte secondary battery) used for a negative electrode of a nonaqueous electrolyte secondary battery (e.g. a lithium ion secondary battery), which shows good charge/discharge capacity and a low resistance, and has a satisfying resistance against the degradation owing to oxidation.SOLUTION: A method for manufacturing a carbonaceous material for a nonaqueous electrolyte secondary battery comprises: a sintering step for sintering a carbon precursor or a mixture of the carbon precursor and a volatile organic material at 800-1400°C under an inert gas atmosphere to obtain a carbonaceous material; and a later pulverizing step and/or later classification step for regulating, by pulverization and/or classification, a specific surface area of the carbonaceous material, which is determined according to a nitrogen absorption BET three-point method within a range of 20-75 m/g.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a carbonaceous material suitable for a negative electrode of a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery.

  Lithium ion secondary batteries are widely used in small portable devices such as mobile phones and laptop computers. As a negative electrode material for a lithium ion secondary battery, non-graphitizable carbon capable of doping (charging) and dedoping (discharging) lithium in an amount exceeding the theoretical capacity of 372 mAh / g of graphite has been developed (for example, Patent Document 1). ), Have been used.

  The non-graphitizable carbon can be obtained using, for example, petroleum pitch, coal pitch, phenol resin, or plant as a carbon source. Among these carbon sources, plants are attracting attention because they are raw materials that can be continuously and stably supplied by cultivation and can be obtained at low cost. Moreover, since the carbonaceous material obtained by baking a plant-derived carbon raw material has many pores, a favorable charge / discharge capacity is expected (for example, Patent Document 1 and Patent Document 2).

  On the other hand, in recent years, due to increasing interest in environmental problems, development of lithium ion secondary batteries for in-vehicle applications has been promoted and is being put to practical use.

JP-A-9-161801 JP-A-10-21919

  In particular, carbonaceous materials used in lithium-ion secondary batteries for automotive applications are required to have good charge / discharge capacity as well as resistance to oxidative degradation, and low resistance is required in order to further demonstrate battery output characteristics. It is done.

  Accordingly, an object of the present invention is to provide a carbonaceous material used for a negative electrode of a nonaqueous electrolyte secondary battery (for example, a lithium ion secondary battery) that exhibits a low resistance as well as a good charge / discharge capacity and has a good resistance to oxidative degradation. It is providing the manufacturing method of (carbonaceous material for nonaqueous electrolyte secondary batteries).

The present inventors have found that the above object can be achieved by the production method of the present invention described below.
That is, the present invention includes the following preferred embodiments.
[1] A carbon precursor or a mixture of the carbon precursor and a volatile organic substance is calcined in an inert gas atmosphere at 800 to 1400 ° C. to obtain a carbonaceous material, and nitrogen is obtained by grinding and / or classification. A method for producing a carbonaceous material for a non-aqueous electrolyte secondary battery, comprising a post-grinding step and / or a post-classification step of adjusting the specific surface area of the carbonaceous material obtained by the adsorption BET three-point method to ²⁰ to 75 m ² / g .
[2] including a pre-grinding step and / or a pre-classification step of adjusting the specific surface area of the carbon precursor obtained by the nitrogen adsorption BET three-point method to 100 to 800 m ² / g by pulverization and / or classification [1] ] Method.
[3] The method according to [1] or [2], wherein the carbon precursor is derived from a plant.
[4] The method according to any one of [1] to [3], wherein the volatile organic substance is in a solid state at room temperature and has a residual carbon ratio of less than 5% by mass.
[5] The carbonaceous material has an average interplanar spacing d ₀₀₂ of (002) plane calculated using the Bragg equation by wide-angle X-ray diffraction method in the range of 0.36 to 0.42 nm, and has a nitrogen element content. The method according to any one of [1] to [4], wherein the content is 0.5% by mass or less, the oxygen element content is 2.5% by mass or less, and the average particle diameter is 1 to 4 μm by a laser scattering method. .
[6] The method according to any one of [1] to [5], wherein the carbonaceous material has a potassium element content of 0.1% by mass or less and an iron element content of 0.02% by mass or less.
[7] The method according to any one of [1] to [6], wherein the carbonaceous material has a true density obtained by a butanol method of 1.4 to 1.7 g / cm ³ .

  According to the carbonaceous material obtained by the production method of the present invention, a nonaqueous electrolyte secondary battery using the carbonaceous material has a good resistance to oxidative degradation, a low resistance as well as a good charge / discharge capacity.

  The following is an explanation of an embodiment of the present invention, and is not intended to limit the present invention to the following embodiment. In addition, in this specification, normal temperature refers to 25 degreeC.

The method for producing a carbonaceous material for a non-aqueous electrolyte secondary battery according to the present invention includes the following steps:
A calcining step of obtaining a carbonaceous material by calcining a carbon precursor or a mixture of the carbon precursor and a volatile organic substance in an inert gas atmosphere at 800 to 1400 ° C .; and nitrogen adsorption BET 3 points by grinding and / or classification It includes a post-grinding step and / or a post-classification step of adjusting the specific surface area of the carbonaceous material obtained by the method to ²⁰ to 75 m ² / g.

The method for producing a carbonaceous material of the present invention includes the following steps:
A pre-grinding step and / or a pre-classification step may be included in which the specific surface area of the carbon precursor determined by the nitrogen adsorption BET three-point method is adjusted to 100 to 800 m ² / g by pulverization and / or classification.

  A carbon precursor is a precursor of a carbonaceous material that supplies a carbon component when producing a carbonaceous material, and is produced using a plant-derived carbon material (hereinafter also referred to as “plant-derived char”) as a raw material. can do. In addition, char generally indicates a powder-like solid rich in carbon that is not melt-softened, which is obtained when coal is heated, but here it is rich in carbon that is not melt-softened obtained by heating organic matter. Also shown is a powdered solid. When the carbon precursor is derived from a plant, it is advantageous in terms of environment and economy from the viewpoint of carbon neutral and easy availability.

  There are no particular restrictions on the plant (hereinafter also referred to as “plant material”) that is the raw material for char derived from plants. For example, coconut shells, coconut beans, tea leaves, sugar cane, fruits (for example, mandarin oranges, bananas), cocoons, shells, hardwoods, conifers, and bamboo can be exemplified. Examples of this include waste (for example, used tea leaves) after being used for the original use, or part of plant materials (for example, bananas and tangerine peels). These plants can be used alone or in combination of two or more. Among these plants, coconut shells are preferred because they are easily available in large quantities and industrially advantageous.

  The coconut shell is not particularly limited, and examples thereof include palm palm (oil palm), coconut palm, salak, and palm palm. These coconut shells can be used alone or in combination. Coconut palm and palm palm coconut shells, which are biomass wastes that are used as foods, detergent raw materials, biodiesel oil raw materials and the like and are generated in large quantities, are particularly preferred.

  The method for producing char from the plant raw material is not particularly limited. For example, the char is produced by heat-treating the plant raw material in an inert gas atmosphere at 300 ° C. or higher (hereinafter also referred to as “temporary firing”). be able to.

  It can also be obtained in the form of char (eg, coconut shell char).

  Since the produced carbonaceous material produced from plant-derived char can be doped with a large amount of active material, it is basically suitable as a negative electrode material for a non-aqueous electrolyte secondary battery. However, plant-derived char contains a large amount of metal elements contained in plants. For example, coconut shell char contains about 0.3% by mass of potassium element and about 0.1% by mass of iron element. If a carbonaceous material containing a large amount of such metal elements is used as the negative electrode, it may adversely affect the electrochemical characteristics and safety of the nonaqueous electrolyte secondary battery.

  The plant-derived char also contains alkali metals other than potassium (for example, sodium), alkaline earth metals (for example, magnesium, calcium), transition metals (for example, iron, copper) and other metals. If the carbonaceous material contains these metals, impurities may elute into the electrolyte during dedoping from the negative electrode of the non-aqueous electrolyte secondary battery, which may adversely affect battery performance and harm safety. is there.

  Furthermore, it has been confirmed by the inventors that the pores of the carbonaceous material are blocked by ash, which may adversely affect the charge / discharge capacity of the battery.

  Therefore, the production method of the present invention may include a decalcification step of decalcifying a carbon material, for example, plant-derived char to obtain a carbon precursor. Such ash (alkali metal, alkaline earth metal, transition metal, and other elements) contained in plant-derived char is deashed prior to the firing step to obtain the carbonaceous material. Ash content can be reduced. The deashing method is not particularly limited. For example, a method (liquid phase deashing) in which a metal component is extracted and deashed using acid water containing a mineral acid such as hydrochloric acid or sulfuric acid, or an organic acid such as acetic acid or formic acid, hydrogen chloride A method of deashing by exposing to a high temperature gas phase containing a halogen compound such as (gas phase deashing) can be used. Although not intended to limit the deashing method to be applied, gas phase deashing that is preferable in that no drying process is required after deashing will be described below. The decalcified plant-derived char is hereinafter also referred to as “plant-derived char carbon precursor”.

  As the gas phase decalcification, it is preferable to heat-treat the plant-derived char in a gas phase containing a halogen compound. The halogen compound is not particularly limited. For example, fluorine, chlorine, bromine, iodine, hydrogen fluoride, hydrogen chloride, hydrogen bromide, iodine bromide, chlorine fluoride (ClF), iodine chloride (ICl), iodine bromide ( IBr) and bromine chloride (BrCl). A compound that generates these halogen compounds by thermal decomposition, or a mixture thereof can also be used. From the viewpoint of the stability of the halogen compound used and its supply stability, hydrogen chloride is preferred.

  The vapor phase deashing may be used by mixing a halogen compound and an inert gas. The inert gas is not particularly limited as long as it is a gas that does not react with the carbon component constituting the plant-derived char. For example, nitrogen, helium, argon and krypton, and mixed gas thereof can be mentioned. From the viewpoint of supply stability and economy, nitrogen is preferred.

  In the gas phase deashing, the mixing ratio of the halogen compound and the inert gas is not limited as long as sufficient deashing can be achieved. For example, safety, economy, and persistence in carbon From the viewpoint, the amount of the halogen compound with respect to the inert gas is preferably 0.01 to 10% by volume, more preferably 0.05 to 8% by volume, and further preferably 0.1 to 5% by volume.

  The temperature of the vapor phase demineralization may be changed depending on the plant-derived char which is the object of demineralization, but from the viewpoint of obtaining a desired nitrogen element content and oxygen element content, for example, 500 to 950 ° C., preferably 600 to 940. C., more preferably 650 to 940.degree. C., still more preferably 850 to 930.degree. When the deashing temperature is equal to or higher than the above lower limit, the deashing efficiency is good and sufficient deashing is possible. Activation by a halogen compound can be suppressed as a deashing temperature is below the said upper limit.

  The time for vapor phase decalcification is not particularly limited, but is, for example, 5 to 300 minutes, preferably 10 to 200 minutes, from the viewpoint of the economic efficiency of the reaction equipment and the structure retention of the carbon content, More preferably, it is 20 to 150 minutes.

  The vapor phase decalcification in the present embodiment is to remove potassium and iron contained in plant-derived char. The potassium element content contained in the carbon precursor obtained after vapor phase deashing is preferably 0.1% by mass or less, from the viewpoint of increasing the dedoping capacity and decreasing the non-dedoping capacity, and 0.05% by mass. The following is more preferable, and 0.03% by mass or less is more preferable. The iron element content contained in the carbon precursor obtained after vapor phase deashing is preferably 0.02% by mass or less, from the viewpoint of increasing the dedoping capacity and from the viewpoint of decreasing the undoping capacity, and 0.015% by mass. The following is more preferable, and 0.01% by mass or less is more preferable. When the content of potassium element or iron element contained in the carbon precursor is increased, the dedoping capacity may be reduced in the nonaqueous electrolyte secondary battery using the obtained carbonaceous material. Also, the undedoped capacity may increase. Furthermore, a short circuit may occur when these metal elements are eluted and re-deposited in the electrolytic solution, which may cause a serious problem in the safety of the nonaqueous electrolyte secondary battery. It is particularly preferred that the plant-derived char carbon precursor after vapor phase decalcification does not substantially contain potassium element and iron element. Details of the measurement of the content of potassium element and iron element are as described in Examples, and a fluorescent X-ray analyzer (for example, “LAB CENTER XRF-1700” manufactured by Shimadzu Corporation) can be used. In addition, the potassium element content and the iron element content contained in the carbon precursor are usually 0% by mass or more.

  The particle diameter of the plant-derived char that is subject to vapor phase demineralization is not particularly limited. However, if the particle diameter is too small, the gas phase containing removed potassium and the like and the plant-derived char Since it may be difficult to separate, the lower limit of the average particle diameter (D50) is preferably 100 μm or more, more preferably 300 μm or more, and even more preferably 500 μm or more. In addition, the upper limit of the average value of the particle diameter is preferably 10,000 μm or less, more preferably 8000 μm or less, and even more preferably 5000 μm or less from the viewpoint of fluidity in a mixed gas stream. Here, the details of the measurement of the particle diameter are as described in the examples. For example, a particle size distribution measuring instrument (for example, “SALD-3000S” manufactured by Shimadzu Corporation, “Micro” manufactured by Nikkiso Co., Ltd.) can be used. Track MT 3000 ") can be used.

  The apparatus used for vapor phase demineralization is not particularly limited as long as it can be heated while mixing plant-derived char and a vapor phase containing a halogen compound. For example, using a fluidized furnace, a continuous type or a batch type in-bed flow method using a fluidized bed or the like can be used. The supply amount (flow rate) of the gas phase is not particularly limited, but from the viewpoint of fluidity in the mixed gas stream, for example, preferably 1 ml / min or more, more preferably 5 ml / min or more, per 1 g of plant-derived char. Preferably, a gas phase of 10 ml / min or more is supplied.

  In vapor phase deashing, after heat treatment in an inert gas atmosphere containing a halogen compound (hereinafter also referred to as “halogen heat treatment”), further heat treatment in the absence of a halogen compound (hereinafter referred to as “gas phase deoxidation treatment”). It is preferable to carry out. Since halogen is contained in the plant-derived char by the halogen heat treatment, it is preferable to remove the halogen contained in the plant-derived char by gas phase deoxidation treatment. Specifically, the gas-phase deoxidation treatment is performed in an inert gas atmosphere not containing a halogen compound, for example, 500 ° C. to 940 ° C., preferably 600 to 940 ° C., more preferably 650 to 940 ° C., and further preferably 850. The heat treatment is performed at a temperature of ˜930 ° C. The heat treatment temperature is preferably the same as or higher than the temperature of the first heat treatment. For example, after the halogen heat treatment, the halogen can be removed by shutting off the supply of the halogen compound and performing the heat treatment. The time for the vapor phase deoxidation treatment is not particularly limited, but is preferably 5 minutes to 300 minutes, more preferably 10 minutes to 200 minutes, and further preferably 10 minutes to 100 minutes. .

  The average particle diameter of the carbon precursor is adjusted through a pre-grinding step and / or a pre-classification step as necessary. The pre-grinding step and / or the pre-classification step is preferably performed after the deashing step.

In the present embodiment, the specific surface area before milling step and / or carbon precursor before and after classification step is preferably 100~800m ² / g, more preferably 200-700 ² / g, for example 200 600 m ² / g. It is preferable to perform the pre-grinding step and / or the pre-classification step so that a carbon precursor having a specific surface area in the above range is obtained. If the specific surface area is too small, the fine pores of the carbonaceous material may not be sufficiently reduced even after the firing step described later, and the hygroscopicity of the carbonaceous material may be difficult to decrease. When water is present in the carbonaceous material, the generation of acid accompanying the hydrolysis of the electrolyte and the generation of gas due to the electrolysis of water may cause problems. Further, the oxidation of the carbonaceous material proceeds under an air atmosphere, and the battery performance may change greatly. If the specific surface area becomes too large, the specific surface area of the carbonaceous material will not be reduced even after the firing step described later, and the utilization efficiency of lithium ions in the nonaqueous electrolyte secondary battery may be reduced. The specific surface area of the carbon precursor can also be adjusted by controlling the temperature of vapor phase demineralization. In the present specification, the specific surface area means a specific surface area (BET specific surface area) determined by a BET method (nitrogen adsorption BET three-point method). Specifically, it can measure using the method mentioned later.

  In the pre-grinding step and / or the pre-classifying step, the carbon precursor is pulverized and / or classified so that the average particle size (D50) of the carbon precursor is in the range of 5 to 800 μm before the firing step. It is preferable from the viewpoint of uniformity during firing. That is, the average particle diameter (D50) of the carbon precursor of the present embodiment is adjusted to be in the range of, for example, 5 to 800 μm. If a carbon precursor having an average particle size within the above range is obtained, only the pre-grinding step or the pre-classification step may be performed, or both the pre-grinding step and the pre-classification step may be performed. When the average particle diameter is 5 μm or more, the fine powder is less likely to be scattered in the firing furnace at the time of firing, the recovery rate of the produced carbonaceous material is excellent, and the load on the apparatus can be further suppressed. On the other hand, when the average particle size is 800 μm or less, the process of gas emitted from the particles during firing is not likely to be long, and the uniformity of the inside and outside of the carbonaceous material is good. From such a viewpoint, the average particle diameter is preferably 800 μm or less, more preferably 700 μm or less, further preferably 600 μm or less, particularly preferably 500 μm or less, and most preferably 400 μm or less. .

  By performing the pre-grinding step and / or the pre-classification step, and further performing the post-grinding step and / or the post-classification step, the particles whose particle size is adjusted by the pre-grinding are supplied, so that the post-grindability is stabilized, Not only the particle size distribution can be easily adjusted, but also the recovery rate can be improved by stabilizing the particle size distribution. Further, the post-classification facilitates firing the particle size distribution to a desired distribution.

  The crusher used for the pre-crushing process is not particularly limited, and for example, a jet mill, a ball mill, a bead mill, a hammer mill, or a rod mill can be used. From the viewpoint of grinding efficiency, a method of grinding in the presence of a grinding media such as a ball mill or a bead mill is preferred. From the viewpoint of equipment load, the use of a ball mill is preferred.

  In one embodiment of the present invention, the pre-classification step can be performed after the pre-grinding step. By the pre-classification step after the pre-grinding step, the average particle size of the carbonaceous material can be adjusted more accurately. For example, coarse particles having a particle diameter of 800 μm or more can be removed.

  The classification method is not particularly limited, and examples thereof include classification using a sieve, wet classification, and dry classification. As the wet classifier, for example, a classifier using principles such as gravity classification, inertia classification, hydraulic classification, centrifugal classification, and the like can be given. Examples of the dry classifier include a classifier using a principle such as sedimentation classification, mechanical classification, and centrifugal classification.

  In one embodiment of the present invention, the method for producing a carbonaceous material according to the present embodiment includes firing a carbon precursor or a mixture of the carbon precursor and a volatile organic substance in an inert gas atmosphere at 800 to 1400 ° C. Including a step of obtaining a carbonaceous material (hereinafter also referred to as a “firing step”). By including the firing step, the obtained nonaqueous electrolyte secondary battery using the carbonaceous material has a good resistance to oxidative degradation as well as a good discharge capacity. In addition, it is preferable to implement a baking process after a decalcification process, and it is preferable to implement after a deashing process, a pre-grinding process, and a pre-classification process as needed.

  The carbonaceous material of the present embodiment is obtained by firing the carbon precursor or a mixture of the carbon precursor and a volatile organic substance. By mixing and firing a carbon precursor and a volatile organic substance, the specific surface area of the obtained carbonaceous material can be reduced, and the specific surface area suitable for a negative electrode material for a non-aqueous electrolyte secondary battery is set. Can do. Furthermore, the amount of carbon dioxide adsorbed on the carbonaceous material can be adjusted.

  The mechanism by which the specific surface area of the carbonaceous material is reduced by mixing and firing the carbon precursor and the volatile organic substance has not been elucidated in detail, but can be considered as follows. However, the present invention is not limited by the following description. It is thought that a carbonaceous film obtained by heat treatment of volatile organic substances is formed on the surface of plant-derived char carbon precursors by mixing and firing plant-derived char carbon precursors and volatile organic substances. It is done. This carbonaceous coating reduces the specific surface area of the carbonaceous material produced from plant-derived char carbon precursors and suppresses the formation reaction of a coating called SEI (Solid Electrolyte Interphase) due to the reaction between the carbonaceous material and lithium. Therefore, it can be expected to reduce the irreversible capacity. Moreover, since the produced carbonaceous film can also dope and dedope lithium, the effect of increasing the capacity can be expected.

  Examples of volatile organic materials include thermoplastic resins and low molecular organic compounds. Specifically, examples of the thermoplastic resin include polystyrene, polyethylene, polypropylene, poly (meth) acrylic acid, poly (meth) acrylic acid ester, and the like. In this specification, (meth) acryl is a generic term for acrylic and methacrylic. Examples of the low molecular organic compound include toluene, xylene, mesitylene, styrene, naphthalene, phenanthrene, anthracene, and pyrene. Since those which do not oxidize and activate the surface of the carbon precursor when volatilized at the firing temperature and thermally decomposed are preferable, polystyrene, polyethylene and polypropylene are preferable as the thermoplastic resin. The low molecular weight organic compound preferably has low volatility at room temperature from the viewpoint of safety, and naphthalene, phenanthrene, anthracene, pyrene and the like are preferable.

  In one embodiment of the present invention, examples of the thermoplastic resin include olefin-based resins, styrene-based resins, and (meth) acrylic acid-based resins. Examples of the olefin resin include polyethylene, polypropylene, a random copolymer of ethylene and propylene, and a block copolymer of ethylene and propylene. Examples of the styrenic resin include polystyrene, poly (α-methylstyrene), a copolymer of styrene and (meth) acrylic acid alkyl ester (the alkyl group has 1 to 12, preferably 1 to 6 carbon atoms). be able to. Examples of the (meth) acrylic resin include polyacrylic acid, polymethacrylic acid, and (meth) acrylic acid alkyl ester polymers (the alkyl group has 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms). it can.

  In one embodiment of the present invention, for example, a hydrocarbon compound having 1 to 20 carbon atoms can be used as the low molecular organic compound. Carbon number of a hydrocarbon compound becomes like this. Preferably it is 2-18, More preferably, it is 3-16. The hydrocarbon compound may be a saturated hydrocarbon compound or an unsaturated hydrocarbon compound, and may be a chain hydrocarbon compound or a cyclic hydrocarbon compound. In the case of an unsaturated hydrocarbon compound, the unsaturated bond may be a double bond or a triple bond, and the number of unsaturated bonds contained in one molecule is not particularly limited. For example, the chain hydrocarbon compound is an aliphatic hydrocarbon compound, and can include a linear or branched alkane, alkene, or alkyne. Examples of the cyclic hydrocarbon compound include alicyclic hydrocarbon compounds (for example, cycloalkane, cycloalkene, cycloalkyne) and aromatic hydrocarbon compounds. Specifically, examples of the aliphatic hydrocarbon compound include methane, ethane, propane, butane, pentane, hexane, octane, nonane, decane, ethylene, propylene, butene, pentene, hexene and acetylene. Examples of the alicyclic hydrocarbon compound include cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclopropane, cyclopentene, cyclohexene, cycloheptene, cyclooctene, decalin, norbornene, methylcyclohexane, and norbornadiene. Further, aromatic hydrocarbon compounds include benzene, toluene, xylene, mesitylene, cumene, butylbenzene, styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, vinylxylene, p- Examples thereof include monocyclic aromatic compounds such as tert-butylstyrene and ethylstyrene, and condensed polycyclic aromatic compounds having 3 to 6 rings such as naphthalene, phenanthrene, anthracene and pyrene, preferably condensed polycyclic aromatic compounds. A compound, more preferably naphthalene, phenanthrene, anthracene or pyrene. Here, the hydrocarbon compound may have an arbitrary substituent. The substituent is not particularly limited, and for example, an alkyl group having 1 to 4 carbon atoms (preferably an alkyl group having 1 to 2 carbon atoms) or an alkenyl group having 2 to 4 carbon atoms (preferably alkenyl having 2 carbon atoms). Group) and a cycloalkyl group having 3 to 8 carbon atoms (preferably a cycloalkyl group having 3 to 6 carbon atoms).

  The volatile organic material is preferably in a solid state at room temperature from the viewpoint of easy mixing and uniform dispersion, for example, a thermoplastic resin that is solid at room temperature such as polystyrene, polyethylene, or polypropylene, or naphthalene, phenanthrene, anthracene, or A low molecular organic compound that is solid at room temperature, such as pyrene, is more preferable. Since those which volatilize and do not oxidize the surface of the plant-derived char carbon precursor when pyrolyzed at the firing temperature are preferred, the thermoplastic resin is preferably an olefin resin and a styrene resin, polystyrene, More preferred are polyethylene and polypropylene. The low molecular weight organic compound is preferably a hydrocarbon compound having 1 to 20 carbon atoms, more preferably a condensed polycyclic aromatic compound, and more preferably naphthalene, phenanthrene, and anthracene, because it is preferable from the viewpoint of safety that the volatility is low at room temperature. Or pyrene is more preferable. Furthermore, from the viewpoint of easy mixing with the carbon precursor, a thermoplastic resin is preferable, an olefin resin and a styrene resin are more preferable, polystyrene, polyethylene, and polypropylene are further preferable, and polystyrene and polyethylene are particularly preferable.

  The volatile organic substance is an organic substance having a residual carbon ratio of preferably less than 5% by mass, more preferably less than 3% by mass, from the viewpoint of stable operation of the baking equipment. The residual coal rate in the present invention is preferably the residual coal rate when ashing at 800 ° C. The volatile organic substance is preferably one that generates a volatile substance (for example, hydrocarbon gas or tar component) that can reduce the specific surface area of the carbon precursor produced from plant-derived char. Further, from the viewpoint of maintaining the properties of the carbonaceous material produced after firing, the residual carbon ratio is preferably less than 5% by mass. When the residual carbon ratio is less than 5%, it is difficult to produce carbonaceous materials having locally different properties.

The residual carbon ratio can be measured by quantifying the carbon content of the ignition residue after the sample is ignited in an inert gas. Intense heat means that about 1 g of volatile organic substances (this exact mass is W ₁ (g)) is placed in a crucible and 20 liters of nitrogen is allowed to flow for 1 minute while the crucible is placed in an electric furnace at 10 ° C./min. The temperature is raised from room temperature to 800 ° C. at a rate of temperature rise of 1, and then ignited at 800 ° C. for 1 hour. Let the residue at this time be an ignition residue, and let the mass be W ₂ (g).

Next, the ignition residue is subjected to elemental analysis in accordance with the method defined in JIS M8819, and the carbon mass ratio P ₁ (%) is measured. The residual carbon ratio P ₂ (mass%) can be calculated by the following formula (I).

  When the carbon precursor and the volatile organic substance are mixed, the mass ratio of the carbon precursor and the volatile organic substance in the mixture is not particularly limited, but preferably the mass ratio of the carbon precursor and the volatile organic substance. Is 97: 3 to 40:60. The mass ratio of the carbon precursor and the volatile organic substance is more preferably 95: 5 to 60:40, and still more preferably 93: 7 to 80:20. For example, when the volatile organic substance is 3 parts by mass or more, the specific surface area can be sufficiently reduced. Further, when the volatile organic substance is 60 parts by mass or less, the effect of reducing the specific surface area is not saturated and it is difficult to consume the volatile organic substance excessively, which is industrially advantageous.

  Mixing of the carbon precursor and the volatile organic substance that is liquid or solid at room temperature may be performed at any stage before the pre-grinding process or after the pre-grinding process.

  When mixing the carbon precursor with the volatile organic substance before the pre-grinding step, the carbon precursor and the liquid or solid volatile organic substance at room temperature are weighed and mixed simultaneously by supplying to the grinding device. Can be performed simultaneously. In addition, when using volatile organic substances that are gases at normal temperature, non-oxidizing gas containing gaseous volatile organic substances is circulated in a heat treatment apparatus containing char-carbon precursors derived from plants and thermally decomposed, and then derived from plants. It is possible to use a method of mixing with the char carbon precursor.

  In the case of mixing after the pre-grinding step, a known mixing method can be used as long as the mixing method is a method in which both are uniformly mixed. When the volatile organic substance is solid at room temperature, it is preferably mixed in the form of particles, but the shape and particle diameter of the particles are not particularly limited. From the viewpoint of uniformly dispersing the volatile organic substance in the pulverized carbon precursor, the average particle size of the volatile organic substance is preferably 0.1 to 2000 μm, more preferably 1 to 1000 μm, and still more preferably 2 to 600 μm. .

  The carbon precursor or mixture described above may contain other components other than the carbon precursor and the volatile organic substance. For example, natural graphite, artificial graphite, metal-based material, alloy-based material, or oxide-based material can be included. The content of the other components is not particularly limited, but is preferably 50 parts by mass or less, more preferably 100 parts by mass with respect to 100 parts by mass of the carbon precursor or the mixture of the carbon precursor and the volatile organic substance. Is 30 parts by mass or less, more preferably 20 parts by mass or less, and most preferably 10 parts by mass or less.

  In the firing step in the production method of the present embodiment, the carbon precursor or a mixture of the carbon precursor and volatile organic material is preferably fired at 800 to 1400 ° C.

The firing process
(A) The pulverized carbon precursor or mixture may be baked at 800 to 1400 ° C. to perform a main baking,
(B) The pulverized carbon precursor or mixture may be pre-baked at 350 ° C. or higher and lower than 800 ° C., and then subjected to main baking at 800 to 1400 ° C.

  When the firing step (a) is performed, it is considered that the carbon precursor is covered with the tar component and the hydrocarbon-based gas in the main firing step. In the case of carrying out the firing step (b), it is considered that the carbon precursor is coated with the tar component and hydrocarbon gas in the preliminary firing step.

  Hereinafter, as an embodiment of the present invention, an example of the pre-baking and main baking procedures will be described, but the present invention is not limited thereto.

(Preliminary firing)
The preliminary firing step in the present embodiment can be performed, for example, by firing the pulverized carbon precursor or mixture at 350 ° C. or more and less than 800 ° C. Volatile components (for example, CO ₂ , CO, CH ₄ , H _2, etc.) and tar components can be removed by the preliminary firing step. Generation | occurrence | production of the volatile matter and the tar component in the main baking process implemented after a preliminary baking process can be reduced, and the burden of a baking apparatus can be reduced.

  The pre-baking step is preferably performed at 350 ° C. or higher, more preferably 400 ° C. or higher. The pre-baking step can be performed according to a normal pre-baking procedure. Specifically, the pre-baking can be performed in an inert gas atmosphere. Examples of the inert gas include nitrogen and argon. Further, the pre-baking may be performed under reduced pressure, for example, 10 kPa or less. The pre-baking time is not particularly limited, but can be carried out in the range of 0.5 to 10 hours, for example, and more preferably 1 to 5 hours.

(Main firing)
The main baking step can be performed according to a normal main baking procedure. By performing the main baking, the carbonaceous material in the present invention can be obtained.

  The specific temperature of the main firing step is 800 to 1400 ° C, preferably 1000 to 1350 ° C, and more preferably 1100 to 1300 ° C. The main firing is performed in an inert gas atmosphere. Examples of the inert gas include nitrogen, argon, and the like, and the main calcination can be performed in an inert gas containing a halogen gas. Moreover, this baking process can also be performed under reduced pressure, for example, it is also possible to implement at 10 kPa or less. Although the time which implements this baking process is not specifically limited, For example, it can carry out in 0.05 to 10 hours, 0.05 to 8 hours are preferable and 0.05 to 6 hours are more preferable.

Next, a post-grinding step and / or a post-classification step of adjusting the specific surface area of the fired product (carbonaceous material) obtained by the above firing step to ²⁰ to 75 m ² / g by pulverization and / or classification. The average particle diameter of the fired product (carbonaceous material) can be adjusted by a post-grinding step and / or a post-classification step after the firing step. In the present invention, it is preferable to perform a post-grinding step and / or a post-classification step after the firing step from the viewpoint of process control such that fine powder does not scatter during firing, and the obtained carbonaceous material is used as a non-aqueous electrolyte secondary battery. When used, the production method of the present invention includes a post-grinding step and / or a post-classification step after the firing step, so that the effective surface area in contact with the electrolytic solution of the obtained carbonaceous material is improved and low resistance is brought about. Can do.

The specific surface area of the carbonaceous material obtained by the present invention ^is 20m ² / g~75m 2 / g, preferably ^{22m 2} / ^g~73m 2 / g, more preferably ^{24m 2} / ^g~71m 2 / g, more preferably ^{26m 2} / ^g~70m 2 / g, for example ^{26m 2} / ^g~60m 2 / g, further ^{26m 2} / ^g~50m 2 / g. It is preferable to perform a post-pulverization step and / or a post-classification step so that a carbon precursor having a specific surface area in the above range is obtained. When the specific surface area is too small, the amount of lithium ions adsorbed on the carbonaceous material is decreased, and the charge capacity of the nonaqueous electrolyte secondary battery may be decreased. When the specific surface area is too high, lithium ions react and are consumed on the surface of the carbonaceous material, so that the utilization efficiency of lithium ions is lowered.

  Other methods for adjusting the specific surface area to the above range are not limited at all, but, for example, a method of adjusting the firing temperature and firing time of the carbon precursor that gives the carbonaceous material can be used. That is, if the firing temperature is increased or the firing time is increased, the specific surface area tends to decrease. Therefore, the firing temperature and the firing time may be adjusted so that the specific surface area in the above range can be obtained. Moreover, you may use the method of mixing and baking with a volatile organic substance. As described above, it is considered that a carbonaceous film obtained by heat treatment of a volatile organic substance is formed on the surface of the carbon precursor by mixing and firing the carbon precursor and the volatile organic substance. . And it is thought by this carbonaceous film that the specific surface area of the carbonaceous material obtained from the carbon precursor reduces. Therefore, it can adjust to said range of the specific surface area of a carbonaceous material by adjusting the quantity of the volatile organic substance to mix.

  The specific surface area of the carbonaceous material obtained by the present invention is preferably in the range of 1 to 4 [mu] m from the viewpoint of coatability during electrode production. That is, the average particle diameter (D50) of the carbonaceous material of the present embodiment is adjusted to be in the range of 1 to 4 μm, for example. If a carbonaceous material having an average particle diameter within the above range is obtained, only the post-grinding step or the post-classification step may be performed, or both the post-grinding step and the post-classification step may be performed. If the average particle size is less than 1 μm, the fine powder increases, the specific surface area increases, the reactivity with the electrolyte increases, the irreversible capacity that does not discharge even when charged increases, and the capacity of the positive electrode is wasted May increase. Moreover, when a negative electrode is manufactured using the obtained carbonaceous material, the space | gap formed between carbonaceous materials will become small and the movement of the lithium ion in electrolyte solution may be suppressed. The average particle diameter (D50) of the carbonaceous material obtained by the present invention is preferably 1 μm or more, more preferably 1.5 μm or more, and even more preferably 1.7 μm or more. On the other hand, when the average particle diameter is 4 μm or less, the lithium ion diffusion free path in the particles is small, and rapid charge / discharge is possible. Further, in the lithium ion secondary battery, it is important to increase the electrode area for improving the input / output characteristics. For this reason, it is necessary to reduce the thickness of the active material applied to the current collector plate during electrode fabrication. In order to reduce the coating thickness, it is necessary to reduce the particle diameter of the active material. From such a viewpoint, the average particle size is 4 μm or less, preferably 3.5 μm or less, more preferably 3.3 μm or less, still more preferably 3.1 μm or less, and most preferably 2.9 μm. It is as follows.

  The pulverization apparatus used in the post-pulverization step is not particularly limited, and for example, a jet mill, a ball mill, a bead mill, a hammer mill, or a rod mill can be used. From the viewpoint of pulverization efficiency, the method of pulverization by contact between particles such as a jet mill has a long pulverization time and the volume efficiency decreases. Therefore, the method of pulverization in the presence of pulverization media such as a ball mill and a bead mill is preferable. From the viewpoint of avoiding contamination from the media, it is preferable to use a bead mill.

  By the post-classification step, it becomes possible to adjust the average particle size of the carbonaceous material more accurately. For example, it becomes possible to remove particles having a particle size of 0.5 μm or less and coarse particles.

  The classification method is not particularly limited, and examples thereof include classification using a sieve, wet classification, and dry classification. As the wet classifier, for example, a classifier using principles such as gravity classification, inertia classification, hydraulic classification, centrifugal classification, and the like can be given. Examples of the dry classifier include a classifier using a principle such as sedimentation classification, mechanical classification, and centrifugal classification.

The carbonaceous material obtained by the present invention has an (002) plane average plane distance d ₀₀₂ calculated from the wide angle X-ray diffraction method using the Bragg equation, preferably 0.36 nm to 0.42 nm, and more preferably. Is 0.38 nm to 0.4 nm, more preferably 0.382 nm to 0.396 nm. When the average spacing d ₀₀₂ of (002) plane is too small, there is the resistance when the lithium ions are inserted into the carbon material increases, there is the resistance increases at the time of output, the lithium ion Input / output characteristics as a secondary battery may deteriorate. In addition, since the carbonaceous material repeatedly expands and contracts, the stability as the battery material may be impaired. If the average interplanar spacing _d002 is too large, the diffusion resistance of lithium ions will be small, but the volume of the carbonaceous material will be large, and the effective capacity per volume may be small.

  The method for adjusting the average interplanar spacing to the above range is not limited at all. For example, the firing temperature of the carbon precursor that gives the carbonaceous material may be in the range of 800 to 1400 ° C. Moreover, it is also possible to use a method of mixing and baking with a thermally decomposable resin such as polystyrene.

The content of nitrogen element contained in the carbonaceous material obtained according to the present invention is preferably as low as possible. However, it is usually preferably 0.5% by mass or less, more preferably 0.48% by mass or less in the analytical value obtained by elemental analysis. More preferably 0.45% by weight or less, particularly preferably 0.4% by weight or less, particularly preferably 0.35% by weight or less, very preferably 0.3% by weight or less, very preferably 0.25% by weight. Hereinafter, it is most preferably 0.2% by mass or less, for example 0.18% by mass or less. More preferably, the carbonaceous material contains substantially no nitrogen element. Here, “substantially not contained” means that it is 10 ⁻⁶ mass% or less, which is the detection limit of an elemental analysis method (inert gas melting-thermal conductivity method) described later. If the nitrogen element content is too high, lithium ions and nitrogen react to consume lithium ions, which not only reduces the utilization efficiency of lithium ions, but may also react with oxygen in the air during storage .

  The method for adjusting the nitrogen element content to the above range is not limited at all. For example, a gas phase is a method including a step of heat-treating plant-derived char at 500 ° C. to 940 ° C. in an inert gas atmosphere containing a halogen compound. The nitrogen element content can be adjusted to the above range by deashing or by mixing and baking the plant-derived char with the volatile organic substance.

The content of oxygen element contained in the carbonaceous material obtained in the present embodiment is preferably as low as possible. However, it is usually preferably 2.5% by mass or less, more preferably 2.3% by mass in the analytical value obtained by elemental analysis. Hereinafter, it is more preferably 2% by mass or less. More preferably, the carbonaceous material contains substantially no oxygen element. Here, “substantially not contained” means that it is 10 ⁻⁶ mass% or less, which is the detection limit of an elemental analysis method (inert gas melting-thermal conductivity method) described later. If the oxygen element content is too high, lithium ions react with oxygen to consume lithium ions, thereby reducing the utilization efficiency of lithium ions. In addition to attracting oxygen and moisture in the air and increasing the probability of reacting with carbonaceous materials, the utilization efficiency of lithium ions may be reduced, such as not easily desorbing when water is adsorbed. .
The method for adjusting the oxygen element content to the above range is not limited at all. For example, the gas phase is a method including a step of heat-treating plant-derived char at 500 ° C. to 940 ° C. in an inert gas atmosphere containing a halogen compound. By decalcifying or mixing and baking plant-derived char with volatile organic substances, the oxygen element content can be adjusted to the above range.

  The potassium element content contained in the carbonaceous material obtained in the present embodiment is preferably 0.1% by mass or less, and 0.05% by mass or less from the viewpoint of increasing the dedoping capacity and decreasing the non-dedoping capacity. Is more preferably 0.03% by mass or less, particularly preferably 0.01% by mass or less, and particularly preferably 0.005% by mass or less. The iron element content contained in the carbonaceous material obtained in the present embodiment is preferably 0.02% by mass or less, preferably 0.015% by mass or less from the viewpoint of increasing the dedoping capacity and decreasing the non-dedoping capacity. Is more preferably 0.01% by mass or less, particularly preferably 0.006% by mass or less, and particularly preferably 0.004% by mass or less. When the content of potassium element and / or iron element contained in the carbonaceous material is less than or equal to the above upper limit value, in the nonaqueous electrolyte secondary battery using this carbonaceous material, the dedoping capacity is increased, and the non-desorption capacity is increased. The doping capacity tends to be small. Furthermore, when the content of potassium element and / or iron element contained in the carbonaceous material is less than or equal to the above upper limit, it is possible to suppress the occurrence of a short circuit due to the elution of these metal elements into the electrolyte solution and reprecipitation. Therefore, the safety of the nonaqueous electrolyte secondary battery can be ensured. It is particularly preferable that the carbonaceous material does not substantially contain potassium element and iron element. The content of potassium element and iron element can be measured as described above. In addition, the potassium element content and the iron element content contained in the carbonaceous material are usually 0% by mass or more. The potassium element content and iron element content contained in the carbonaceous material tend to decrease as the potassium element content and iron element content contained in the carbon precursor decrease.

From the viewpoint of increasing the capacity per mass in the battery, the carbonaceous material obtained by the present invention preferably has a true density ρ _Bt by the butanol method of 1.4 to 1.7 g / cm ³ , 1.65 g / cm ³ is more preferable, and 1.44 to 1.6 g / cm ³ is more preferable. The plant-derived char carbon precursor having such a true density ρ _Bt can be produced, for example, by firing a plant raw material at 800 to 1400 ° C. Here, the details of the measurement of the true density ρ _Bt are as described in the examples, and the true density ρ _Bt can be measured by the butanol method according to the method defined in JIS R 7212.

  The carbonaceous material obtained by the present invention preferably has an Lc (carbon hexagonal network layer direction) of 3 nm or less, particularly from the viewpoint of repetitive characteristics in lithium doping and dedoping required for automotive applications and the like. Lc is more preferably 0.5 to 2 nm. When Lc exceeds 3 nm, carbon hexagonal network surfaces are stacked in multiple layers, and volume expansion and contraction accompanying lithium doping and dedoping may increase. Therefore, the carbon structure is destroyed by volume expansion and contraction, lithium doping / dedoping is interrupted, and the repeated characteristics may be deteriorated. Here, the details of the measurement of Lc are as described in Examples, and can be obtained by the X-ray diffraction method using Scherrer's equation.

  Further, the moisture absorption of the carbonaceous material obtained by the present invention is preferably 15,000 ppm or less, more preferably 14,000 ppm or less, and further preferably 8,000 ppm or less. The smaller the amount of moisture absorption, the more the moisture adsorbed on the carbonaceous material decreases, and the more lithium ions adsorbed on the carbonaceous material increase. Further, it is preferable that the amount of moisture absorption is small because the self-discharge due to the reaction between the adsorbed moisture and the nitrogen atom of the carbonaceous material and the reaction between the adsorbed moisture and lithium ion can be reduced. The moisture absorption amount of the carbonaceous material can be reduced by reducing the amount of nitrogen atoms and oxygen atoms contained in the carbonaceous material, for example. The amount of moisture absorption of the carbonaceous material can be measured using, for example, a Karl Fischer.

(Negative electrode for non-aqueous electrolyte secondary battery)
The carbonaceous material obtained by the production method of the present invention can be used as a carbonaceous material for a nonaqueous electrolyte secondary battery, for example, a negative electrode (electrode) for a nonaqueous electrolyte secondary battery. Below, the manufacturing method of the negative electrode for nonaqueous electrolyte secondary batteries is described concretely. A negative electrode (electrode) for a non-aqueous electrolyte secondary battery is obtained by adding a binder (binder) to the carbonaceous material obtained according to the present invention, adding an appropriate amount of an appropriate solvent, kneading to obtain an electrode mixture, It can be manufactured by applying pressure to a current collector plate made of, etc., after applying and drying.

  By using the carbonaceous material obtained by the present invention, an electrode having high conductivity can be produced without adding a conductive auxiliary. For the purpose of imparting higher conductivity, a conductive aid can be added as necessary when preparing the electrode mixture. As the conductive assistant, conductive carbon black, vapor grown carbon fiber (VGCF), nanotube, or the like can be used. The amount of conductive auxiliary agent added varies depending on the type of conductive auxiliary agent used, but if the amount added is too small, the expected conductivity may not be obtained, and if too large, the dispersion in the electrode mixture will be poor. May be. From such a viewpoint, the preferable ratio of the conductive auxiliary agent to be added is 0.5 to 10% by mass (where the amount of active material (carbonaceous material) + the amount of binder + the amount of conductive auxiliary agent = 100% by mass). More preferably, it is 0.5-7 mass%, Most preferably, it is 0.5-5 mass%. The binder is not particularly limited as long as it does not react with an electrolytic solution such as PVDF (polyvinylidene fluoride), polytetrafluoroethylene, and a mixture of SBR (styrene-butadiene rubber) and CMC (carboxymethylcellulose). Among them, PVDF is preferable because PVDF attached to the surface of the active material hardly inhibits lithium ion migration and obtains favorable input / output characteristics. In order to dissolve PVDF and form a slurry, a polar solvent such as N-methylpyrrolidone (NMP) is preferably used, but an aqueous emulsion such as SBR or CMC can also be dissolved in water. When the amount of the binder added is too large, the resistance of the obtained electrode increases, so that the internal resistance of the battery increases and the battery performance may be deteriorated. Moreover, when there is too little addition amount of a binder, the coupling | bonding between the particle | grains of a negative electrode material and a collector plate may become inadequate. Although the preferable addition amount of a binder changes also with the kind of binder to be used, for example in a PVDF-type binder, it is preferably 3-13 mass%, More preferably, it is 3-10 mass%. On the other hand, in a binder using water as a solvent, a mixture of a plurality of binders such as a mixture of SBR and CMC is often used, and the total amount of all binders used is preferably 0.5 to 5% by mass, Preferably it is 1-4 mass%.

  The electrode active material layer is basically formed on both sides of the current collector plate, but may be formed on one side as necessary. The thicker the electrode active material layer, the fewer current collector plates, separators, and the like, which is preferable for increasing the capacity. However, since the larger the electrode area facing the counter electrode is, the more advantageous the input / output characteristics are. Therefore, if the electrode active material layer is too thick, the input / output characteristics may deteriorate. The thickness of the active material layer (per one side) is preferably 10 to 80 μm, more preferably 20 to 75 μm, and further preferably 20 to 60 μm, from the viewpoint of output during battery discharge.

(Non-aqueous electrolyte secondary battery)
By using the negative electrode for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery can be provided. The non-aqueous electrolyte secondary battery has a good resistance to oxidative degradation as well as a good discharge capacity. The nonaqueous electrolyte secondary battery including the carbonaceous material obtained by the present invention has a good resistance to oxidative deterioration, suppresses an increase in irreversible capacity due to the inactivation of lithium ions, and improves the charge / discharge efficiency. Can be kept high. The nonaqueous electrolyte secondary battery using the negative electrode (electrode) for nonaqueous electrolyte secondary batteries using the carbonaceous material obtained by the present invention exhibits excellent output characteristics and excellent cycle characteristics.

  When a negative electrode for a non-aqueous electrolyte secondary battery is formed using the carbonaceous material obtained by the present invention, other materials constituting the battery such as a positive electrode material, a separator, and an electrolytic solution are not particularly limited, Various materials conventionally used or proposed as nonaqueous electrolyte secondary batteries can be used.

For example, as the positive electrode material, a layered oxide system (represented as LiMO ₂ , where M is a metal: for example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , or LiNi _x Co _y Mo _z O ₂ (where x, y , Z represents a composition ratio)), olivine system (represented by LiMPO ₄ , M is a metal: for example LiFePO _4, etc.), spinel system (represented by LiM ₂ O ₄ , M is a metal: for example LiMn ₂ O _4, etc. ) Is preferable, and these chalcogen compounds may be mixed as necessary. These positive electrode materials are molded together with a suitable binder and a carbon material for imparting conductivity to the electrode, and a positive electrode is formed by forming a layer on a conductive current collector.

The nonaqueous solvent electrolyte used in combination with these positive electrode and negative electrode is generally formed by dissolving an electrolyte in a nonaqueous solvent. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, diethoxyethane, γ-butyllactone, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, and 1,3-dioxolane. Can be used singly or in combination of two or more. As the electrolyte, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiCl, LiBr, LiB (C ₆ H ₅ ) ₄ , or LiN (SO ₃ CF ₃ ) ₂ is used.

  In nonaqueous electrolyte secondary batteries, the positive electrode and the negative electrode formed as described above are generally immersed in an electrolytic solution so that they face each other through a liquid-permeable separator made of a nonwoven fabric, other porous materials, or the like as necessary. Is formed. As the separator, a non-woven fabric usually used for a secondary battery or a permeable separator made of another porous material can be used. Alternatively, a solid electrolyte made of a polymer gel impregnated with an electrolytic solution can be used instead of or together with the separator.

  The carbonaceous material obtained by the present invention is suitable as a carbonaceous material for a battery (typically a non-aqueous electrolyte secondary battery for driving a vehicle) mounted on a vehicle such as an automobile. In the present invention, the vehicle can be a target such as a vehicle that is usually known as an electric vehicle or a hybrid vehicle with a fuel cell or an internal combustion engine. And an electric drive mechanism that is driven by power supply from the power supply device, and a control device that controls the electric drive mechanism. The vehicle may further include a power generation brake and a regenerative brake, and may include a mechanism that converts energy generated by braking into electricity and charges the nonaqueous electrolyte secondary battery.

  EXAMPLES Hereinafter, the present invention will be specifically described by way of examples, but these do not limit the scope of the present invention. In addition, although the measuring method of the physical-property value of a carbonaceous material is described below, the physical-property value described in this specification including an Example is based on the value calculated | required by the following method.

(Specific surface area measurement by nitrogen adsorption BET three-point method)
An approximate expression (formula (II)) derived from the BET formula is shown below.

Using the above approximate equation, _vm was determined by a three-point method by nitrogen adsorption at liquid nitrogen temperature, and the specific surface area of the sample was calculated by the following equation (III).

In this case, _{v m} adsorption amount necessary to form a monomolecular layer on the surface of the sample ^(cm 3 / g), v adsorption amount is measured _{^{(cm 3 / g), p}} 0 is saturation vapor pressure, p is Absolute pressure, c is a constant (reflecting heat of adsorption), N is Avogadro's number 6.022 × 10 ²³ , and a (nm ² ) is an area occupied by the adsorbate molecule on the sample surface (molecular occupation cross-sectional area).

  Specifically, the amount of nitrogen adsorbed on the sample at the liquid nitrogen temperature was measured using “BELL Sorb Mini” manufactured by BELL, Japan. The sample is filled in the sample tube, and once the pressure is reduced to −196 ° C., the pressure is once reduced, and then nitrogen (purity 99.999%) is adsorbed to the sample at a desired relative pressure. The amount of nitrogen adsorbed on the sample when the equilibrium pressure was reached at each desired relative pressure was defined as the amount of adsorbed gas v.

(Measurement of average interplanar spacing d ₀₀₂ using Bragg equation by wide angle X-ray diffraction method)
Using “MiniFlexII manufactured by Rigaku Corporation”, an X-ray diffraction pattern was obtained using a CuKα ray filled with a carbonaceous material powder in a sample holder and monochromated by a Ni filter as a radiation source. The peak position of the diffraction pattern is obtained by the barycentric method (a method of obtaining the barycentric position of the diffraction line and obtaining the peak position by the corresponding 2θ value), and using the diffraction peak on the (111) plane of the high-purity silicon powder for standard materials. Corrected. The wavelength λ of the CuKα ray was 0.15418 nm, and d ₀₀₂ was calculated according to the Bragg formula (formula (IV)) described below.

(Elemental analysis)
Elemental analysis was performed using an oxygen / nitrogen / hydrogen analyzer EMGA-930 manufactured by HORIBA, Ltd.
The detection method of the apparatus is as follows: oxygen: inert gas melting-non-dispersive infrared absorption method (NDIR), nitrogen: inert gas melting-thermal conductivity method (TCD), hydrogen: inert gas melting-non-dispersing infrared ray It is an absorption method (NDIR), and calibration is carried out with (oxygen / nitrogen) Ni capsules, TiH ₂ (H standard sample), SS-3 (N, O standard sample). A sample of 20 mg whose moisture content was measured was weighed into a Ni capsule and measured after degassing in the analyzer for 30 seconds. In the test, three samples were analyzed, and the average value was used as the analysis value.

(Measurement of residual coal rate)
The residual carbon ratio was measured by quantifying the carbon content of the ignition residue after the sample was ignited in an inert gas. The strong heat is obtained by putting about 1 g of volatile organic substances (this exact mass is W ₁ (g)) into the crucible and flowing the crucible in an electric furnace at 10 ° C./min while flowing 20 liters of nitrogen per minute. The temperature was raised from room temperature to 800 ° C. at a rate of temperature rise, and then ignited at 800 ° C. for 1 hour. The remnants of this time and Tsuyonetsu residue was its mass W ₂ and _(g).

Next, the ignition residue was subjected to elemental analysis in accordance with the method defined in JIS M8819, and the carbon mass ratio P ₁ (%) was measured. The residual carbon ratio P ₂ (mass%) was calculated by the above formula (I).

(Measurement of true density by butanol method)
The true density ρ _Bt was measured by the butanol method according to the method defined in JIS R 7212. The mass (m ₁ ) of a specific gravity bottle with a side tube having an internal volume of about 40 mL was accurately measured. Next, the sample was put flat on the bottom so as to have a thickness of about 10 mm, and the mass (m ₂ ) was accurately measured. To this, 1-butanol was gently added to a depth of about 20 mm from the bottom. Next, light vibration was applied to the specific gravity bottle, and it was confirmed that large bubbles were not generated. Then, the bottle was placed in a vacuum desiccator and gradually evacuated to 2.0 to 2.7 kPa. After maintaining the pressure for 20 minutes or more and removing bubbles, remove the specific gravity bottle, fill with 1-butanol, plug it, and put it in a constant temperature water bath (adjusted to 30 ± 0.03 ° C.) 15 Immerse it for more than one minute and adjust the 1-butanol liquid level to the marked line. Next, this was taken out, wiped out well, cooled to room temperature, and then the mass (m ₄ ) was accurately measured. Next, the same specific gravity bottle was filled with only 1-butanol, immersed in a constant temperature water bath in the same manner as described above, and the mass (m ₃ ) was measured after aligning the marked lines. Moreover, distilled water excluding the gas which had been boiled and dissolved immediately before use was taken in a specific gravity bottle, immersed in a constant temperature water bath in the same manner as described above, and the mass (m ₅ ) was measured after aligning the marked lines. The true density ρ _Bt was calculated by the following formula (V). At this time, d is the specific gravity of water at 30 ° C. (0.9946).

(Average particle size measurement by laser scattering method)
The average particle size (particle size distribution) of plant-derived char and carbonaceous material was measured by the following method. The sample was put into an aqueous solution containing 0.3% by mass of a surfactant (“Toriton X100” manufactured by Wako Pure Chemical Industries, Ltd.), treated with an ultrasonic cleaner for 10 minutes or more, and dispersed in the aqueous solution. The particle size distribution was measured using this dispersion. The particle size distribution measurement was performed using a particle size / particle size distribution measuring instrument (“Microtrack MT3000” manufactured by Nikkiso Co., Ltd.). D50 is the particle diameter at which the cumulative volume is 50%, and this value was used as the average particle diameter.

(Metal content measurement)
The measuring method of potassium element content and iron element content was measured by the following method. A carbon sample containing a predetermined potassium element and iron element is prepared in advance, and using a fluorescent X-ray analyzer, the relationship between the intensity of potassium Kα ray and the potassium element content, and the intensity of iron Kα ray and iron element content A calibration curve for the relationship was created. Next, the intensity of potassium Kα ray and iron Kα ray in the fluorescent X-ray analysis was measured for the sample, and the potassium element content and the iron element content were determined from the calibration curve prepared previously. The fluorescent X-ray analysis was performed using LAB CENTER XRF-1700 manufactured by Shimadzu Corporation under the following conditions. Using the upper irradiation system holder, the sample measurement area was within the circumference of 20 mm in diameter. The sample to be measured was placed by placing 0.5 g of the sample to be measured in a polyethylene container having an inner diameter of 25 mm, pressing the back with a plankton net, and covering the measurement surface with a polypropylene film for measurement. The X-ray source was set to 40 kV and 60 mA. For potassium, LiF (200) was used for the spectroscopic crystal and a gas flow proportional coefficient tube was used for the detector, and 2θ was measured in the range of 90 to 140 ° at a scanning speed of 8 ° / min. For iron, LiF (200) was used for the spectroscopic crystal, and a scintillation counter was used for the detector, and 2θ was measured in the range of 56 to 60 ° at a scanning speed of 8 ° / min.

(Measurement of moisture absorption)
10 g of the sample was put in a sample tube, pre-dried at 120 ° C. under reduced pressure of 133 Pa for 2 hours, transferred to a glass petri dish having a diameter of 50 mm, and exposed to a constant temperature and humidity chamber at 25 ° C. and a humidity of 50% for a predetermined time. . Thereafter, 1 g of the sample was weighed and heated to 250 ° C. by Karl Fischer (manufactured by Mitsubishi Chemical Analytech Co., Ltd.), and the moisture absorption was measured under a nitrogen stream.

(Preparation Example 1)
The coconut shell was crushed and dry-distilled at 500 ° C. to obtain coconut shell char having a particle size of 2.360 to 0.850 mm (containing 98% by mass of particles having a particle size of 2.360 to 0.850 mm). A vapor phase deashing process was performed for 50 minutes at 900 ° C. while supplying nitrogen gas containing 1% by volume of hydrogen chloride gas at a flow rate of 10 L / min to 100 g of this coconut shell char. Thereafter, only the supply of hydrogen chloride gas was stopped, and while supplying nitrogen gas at a flow rate of 10 L / min, vapor phase deoxidation treatment was further performed at 900 ° C. for 30 minutes to obtain a carbon precursor.
The obtained carbon precursor was pulverized by using a dry ball mill (SDA5 manufactured by Ashizawa Finetech Co., Ltd.) under the conditions of a bead diameter of 3 mmφ, a bead filling rate of 75%, and a raw material feed amount of 1.63 kg / Hr. A carbon precursor (1) having a diameter of 5.5 μm and a specific surface area of 467 m ² / g was obtained.

(Preparation Example 2)
Carbon having an average particle diameter of 2.5 μm and a specific surface area of 467 m ² / g in the same manner as in Preparation Example 1 except that the bead diameter is 3 mmφ, the bead filling rate is 75%, and the raw material feed amount is crushed under the conditions of 1 kg / Hr. A precursor (2) was obtained.

Example 1
9.1 g of the carbon precursor (1) prepared in Preparation Example 1 and 0.9 g of polystyrene (manufactured by Sekisui Chemicals Co., Ltd., average particle diameter of 400 μm, residual carbon ratio of 1.2% by mass) were mixed. 10 g of this mixture was placed in a graphite sheath (length 100 mm, width 100 mm, height 50 mm), and 1290 ° C. at a heating rate of 60 ° C. per minute under a 5 L / min nitrogen flow rate in a high-speed heating furnace manufactured by Motoyama Co., Ltd. Then, the temperature was maintained for 23 minutes, and then naturally cooled. After confirming that the furnace temperature had dropped to 100 ° C. or less, the carbonaceous material was taken out of the furnace. The mass of the recovered carbonaceous material was 8.1 g, and the recovery rate relative to the carbon precursor was 81%.

  The obtained carbonaceous material was put into an 80 mL zirconia container filled with zirconia beads having a bead diameter of 5 mm using a dry ball mill (Fritsch P-6), and rotated at 400 rpm for 5 minutes. The process of stopping for 1 minute was repeated 15 times to obtain a carbonaceous material (1) having an average particle size of 2.9 μm. Table 1 shows the physical properties of the obtained carbonaceous material (1).

(Example 2)
10 g of the carbon precursor (1) prepared in Preparation Example 1 was placed in a graphite sheath (length 100 mm, width 100 mm, height 50 mm), and in a high-speed heating furnace manufactured by Motoyama Co., Ltd. under a nitrogen flow rate of 5 L / min. The temperature was raised to 1290 ° C. at a rate of 60 ° C. per minute, then held for 23 minutes, and then naturally cooled. After confirming that the furnace temperature had dropped to 100 ° C. or less, the carbonaceous material was taken out of the furnace. The mass of the recovered carbonaceous material was 9.1 g, and the recovery rate relative to the carbon precursor was 91%.

  The obtained carbonaceous material was placed in an 80 mL zirconia container filled with zirconia beads having a bead diameter of 5 mm using a ball mill (P-6 manufactured by Fritsch) and rotated for 1 minute after rotating at 400 rpm. The carbonaceous material (2) was obtained by pulverizing by repeating the process of stopping for 15 minutes 15 times. Table 1 shows the physical properties of the obtained carbonaceous material (2).

(Comparative Example 1)
A carbonaceous material (3) was obtained in the same manner as in Example 1 except that the carbon precursor (1) prepared in Preparation Example 1 was not pulverized after firing. Table 1 shows the physical properties of the carbonaceous material (3) obtained.

(Comparative Example 2)
A carbonaceous material (4) was obtained in the same manner as in Example 1, except that the number of repetitions of the process of stopping for 1 minute after rotating for 5 minutes with a dry ball mill was changed to 20. Table 1 shows the physical properties of the obtained carbonaceous material (4).

(Comparative Example 3)
A carbonaceous material (5) was obtained in the same manner as in Example 2 except that the carbon precursor (1) prepared in Preparation Example 1 was not pulverized after firing. Table 1 shows the physical properties of the carbonaceous material (5) obtained.

(Comparative Example 4)
A carbonaceous material (6) was obtained in the same manner as in Example 2 except that the carbon precursor (2) prepared in Preparation Example 2 was used instead of the carbon precursor (1). Table 1 shows the physical properties of the carbonaceous material (6) obtained.

(Production of electrodes)
Using the carbonaceous materials (1) to (6) obtained in Examples 1 and 2 and Comparative Examples 1 to 4, electrodes (negative electrodes) were produced according to the following procedure.

92 parts by mass of the prepared carbonaceous material, 2 parts by mass of acetylene black, 6 parts by mass of PVDF (polyvinylidene fluoride) and 90 parts by mass of NMP (N-methylpyrrolidone) were mixed to obtain a slurry. The obtained slurry was applied to a copper foil having a thickness of 14 μm, dried and pressed to obtain electrodes (1) to (6) having a thickness of 60 μm. The density of the obtained electrodes (1) to (6) was 0.9 to 1.1 g / cm ³ .

(Production of lithium ion secondary battery)
Each of the electrodes (1) to (6) produced above was used as a working electrode, and metallic lithium was used as a counter electrode and a reference electrode. As a solvent, a mixture of ethylene carbonate and methyl ethyl carbonate (volume ratio 3: 7) was used. In this solvent, 1 mol / L of LiPF ₆ was dissolved and used as an electrolyte. A glass fiber nonwoven fabric was used for the separator. Each coin cell was produced in a glove box under an argon atmosphere.

(Measurement of charge capacity, discharge capacity, charge / discharge efficiency and initial DC resistance)
About the lithium ion secondary battery of the said structure, the charge / discharge test was done using the charge / discharge test apparatus (the Toyo System Co., Ltd. make, "TOSCAT"). The initial DC resistance was a resistance value generated when 0.5 mA was passed for 3 seconds. Lithium was doped at a rate of 70 mA / g with respect to the mass of the active material, and was doped until 1 mV with respect to the lithium potential. Further, a constant voltage of 1 mV with respect to the lithium potential was applied for 8 hours to complete the doping. The capacity (mAh / g) at this time was defined as the charge capacity. Next, dedoping was performed at a rate of 70 mA / g with respect to the mass of the active material until 2.5 V with respect to the lithium potential, and the capacity discharged at this time was defined as the discharge capacity. The percentage of discharge capacity / charge capacity was defined as charge / discharge efficiency (charge / discharge efficiency), which was used as an index of the utilization efficiency of lithium ions in the battery. The obtained battery performance is shown in Table 2.

In the lithium ion secondary battery produced using the carbonaceous material obtained in Examples 1 and 2, a high charge capacity and discharge capacity can be obtained at the same time, the charge / discharge efficiency is excellent, and the initial DC resistance is low. became. On the other hand, in Comparative Examples 1 and 3 in which pulverization was not performed after the firing step, the charge capacity and charge / discharge efficiency were low, and the initial DC resistance was high. In Comparative Example 2 including a post-grinding step in which the specific surface area of the carbonaceous material was ground to 80 m ² / g, the charge / discharge efficiency was low. Furthermore, although the specific surface area was 42 m ² / g, Comparative Example 4 in which pulverization was not performed after the firing step resulted in a high initial DC resistance.
As described above, the carbon used for the negative electrode of a non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) that exhibits a low resistance as well as a good resistance to oxidative degradation along with a good charge / discharge capacity by the production method of the present invention. It is clear that a porous material (a carbonaceous material for a non-aqueous electrolyte secondary battery) can be provided.

Claims (7)

A carbon precursor or a mixture of the carbon precursor and a volatile organic substance is calcined in an inert gas atmosphere at 800 to 1400 ° C. to obtain a carbonaceous material, and pulverized and / or classified to give 3 points of nitrogen adsorption BET A method for producing a carbonaceous material for a non-aqueous electrolyte secondary battery, comprising a post-grinding step and / or a post-classifying step of adjusting the specific surface area of the carbonaceous material obtained by the method to ²⁰ to 75 m ² / g. 2. The method according to claim 1, comprising a pre-grinding step and / or a pre-classifying step of adjusting the specific surface area of the carbon precursor determined by the nitrogen adsorption BET three-point method to 100 to 800 m ² / g by pulverization and / or classification. Method.   The method according to claim 1, wherein the carbon precursor is derived from a plant.   The method according to any one of claims 1 to 3, wherein the volatile organic substance is in a solid state at room temperature and has a residual carbon ratio of less than 5 mass%. The carbonaceous material has an average interplanar spacing d ₀₀₂ of (002) plane calculated using the Bragg equation by wide-angle X-ray diffraction method in the range of 0.36 to 0.42 nm and a nitrogen element content of 0.5. The method according to any one of claims 1 to 4, wherein the content is not more than mass%, the oxygen element content is not more than 2.5 mass%, and the average particle size by laser scattering method is 1 to 4 µm.   The said carbonaceous material is a method of any one of Claims 1-5 whose potassium element content is 0.1 mass% or less and whose iron element content is 0.02 mass% or less. The said carbonaceous material is the method of any one of Claims 1-6 whose true density calculated | required by the butanol method is 1.4-1.7 g / cm < ³ >.