JP2005281100A - Method for manufacturing carbon material, negative electrode material for rechargeable lithium-ion battery, negative electrode for rechargeable lithium-ion battery, and rechargeable lithium-ion battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rechargeable lithium-ion battery which has high discharge capacity, a suppressed increase in irreversible capacity and is excellent in cycling characteristics, even when electrode density is made higher, and to provide a negative electrode, a negative electrode material for the same, and a method for manufacturing a carbon material for the same. <P>SOLUTION: In the method for manufacturing a carbon material, heat-treated pitch containing mesocarbon microspheres or a mixture of mesocarbon microspheres with fibrous, spherical or lumpy carbon is heat-treated at a high temperature after adjusting a content of volatile portions to 2.0-30 mass%. The negative electrode material and the negative electrode for a rechargeable lithium-ion battery includes the resulting carbon material. The rechargeable lithium-ion battery uses the negative electrode. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a carbon material production method, a negative electrode material for a lithium ion secondary battery, a negative electrode, and a lithium ion secondary battery excellent in charge / discharge characteristics and cycle characteristics.

  Lithium-ion secondary batteries have excellent features such as high operating voltage, large battery capacity, long cycle life, and low environmental pollution. Therefore, conventional nickel-cadmium batteries and nickel It is widely used in place of hydrogen batteries. Lithium ion secondary batteries have become practical because it was discovered that carbon materials with intercalated lithium ions could be a stable active material instead of lithium metal, which had a safety problem as a negative electrode material. This is due to the recognition of the role of carbon materials in the practical application and performance improvement of ion secondary batteries.

  With the recent increase in performance and functionality of portable electronic devices such as mobile phones and notebook computers, power consumption has increased, and further increase in capacity of lithium ion secondary batteries has been demanded. The capacity of the lithium ion secondary battery is particularly determined by the discharge capacity per mass of the carbon material for the negative electrode, but the discharge capacity per mass is the theoretical capacity 372 mAh of high-purity natural graphite among the carbon materials for the negative electrode. / g is the limit, and the problem is to increase the active material density of the negative electrode and improve the discharge capacity per volume.

  For example, Patent Document 1 introduces a technique for obtaining a high load discharge characteristic with a high discharge capacity using a carbon material having a low degree of orientation. However, it is only oriented when the electrode density is increased. In other words, the amount of the electrolyte in the electrode tends to decrease. Therefore, the amount of lithium ions around the negative electrode material is reduced, and the charge / discharge characteristics may be deteriorated. That is, since the carbon material itself is oriented by increasing the electrode density, the carbon edge surface is not in contact with the electrolytic solution, the charge / discharge characteristics are degraded, and the original discharge capacity cannot be obtained. there were.

  In addition, even in the case of carbon materials that are difficult to align, such as graphitized mesocarbon spheres, the void volume in the electrode is reduced, and the amount of electrolyte around the carbon material is reduced, thereby reducing the amount of lithium ions. There was a problem. Therefore, the electrolyte solution around the negative electrode material is secured by mixing the carbon material for negative electrode and carbon fine particles or carbon fibers such as carbon black. For example, when vapor-grown carbon fibers such as carbon nanotubes and graphite nanofibers that have been attracting attention in recent years are used, the amount of liquid absorption is excellent. However, since the vapor grown carbon fiber has a large specific surface area, there is a problem that the reactivity with the non-aqueous electrolyte used in the lithium ion secondary battery is high and the irreversible capacity is large. In order to use these carbon fibers as battery materials, it is necessary to perform heat treatment at a high temperature in order to remove impurities. However, since the bulk density is low, the amount of containers for heat treatment is limited, and the processing cost increases. There was a problem.

Patent Document 2 discloses a composition containing a resin such as a phenol resin on the surface of a minute carbon material having a particle size of several μm to several tens of μm such as mesocarbon microsphere carbonaceous material, graphite material, or coke powder. There has been proposed a method for producing a carbon material suitable for a negative electrode material for a lithium ion secondary battery to be deposited, mixed with fibrous carbon, and then heat-treated. However, this method is intended only to improve the conductivity of the carbonaceous powder, which is the negative electrode active material, and to the extent that it is possible to ensure the amount of electrolyte around the negative electrode material. It is difficult to attach fibers. As a result, when used as a negative electrode material for a lithium ion secondary battery, there has been a problem of insufficient discharge capacity.
JP-A-11-283622 No. 2003-226510

  Even if the electrode density is increased, the present invention can sufficiently secure voids in the electrode, exhibit high charge / discharge characteristics, and has a high discharge capacity per volume, a negative electrode for the same, and therefore It is an object to provide a method for producing a carbon material.

  In the present invention, mesocarbon spherules are mixed with at least one carbon selected from fibrous, spherical or massive carbon at a ratio of 0.1 to 10% by mass, and the volatile content of the mixture is set to 2. After adjusting to 0-30 mass%, it is a manufacturing method of the carbon material characterized by performing high temperature heat processing.

  In the present invention, mesocarbon spherules are mixed with at least one carbon selected from fibrous, spherical, or massive carbon at a ratio of 0.1 to 10% by mass, and the mixture is heat-treated to mix volatile matter. After adjusting content to 2.0-30 mass%, it is a manufacturing method of the carbon material characterized by performing high temperature heat processing.

  In the present invention, mesocarbon spherules are mixed with at least one carbon selected from fibrous, spherical or massive carbon at a ratio of 0.1 to 10% by mass in the presence of an organic solvent, It is a method for producing a carbon material, characterized in that an organic solvent is separated and removed, and the content of volatile components in the obtained mixture is adjusted to 2.0 to 30% by mass, followed by high-temperature heat treatment.

  In the present invention, mesocarbon spherules are mixed with at least one carbon selected from fibrous, spherical, or massive carbon in a proportion of 0.1 to 10% by mass in the presence of an organic solvent, An organic solvent is separated and removed, and the resulting mixture is heat-treated to adjust the content of volatile components to 2.0 to 30% by mass, followed by high-temperature heat treatment.

  In addition, the present invention provides a mesocarbon microsphere having at least one carbon selected from fibrous, spherical, or massive carbon as a heat treatment pitch containing mesocarbon microspheres produced by heat-treating a pitch containing free carbon. Mixed at a rate of 0.1 to 10% by mass, and then the pitch is separated and removed, and the volatile content of the obtained mixture is adjusted to 2.0 to 30% by mass, followed by high-temperature heat treatment. Is a method for producing a carbon material.

  In addition, the present invention provides a mesocarbon microsphere having at least one carbon selected from fibrous, spherical, or massive carbon as a heat treatment pitch containing mesocarbon microspheres produced by heat-treating a pitch containing free carbon. Mixed at a ratio of 0.1 to 10% by mass, and then the pitch was separated and removed, and the resulting mixture was heat treated to adjust the volatile content to 2.0 to 30% by mass. It is a manufacturing method of the carbon material characterized by heat-processing.

  In the method for producing a carbon material of the present invention, it is preferable that the carbon organic solvent dispersion is added to and mixed with the heat treatment pitch.

  In the method for producing a carbon material of the present invention, the heat treatment pitch is preferably added to and mixed with the carbon organic solvent dispersion.

  In the method for producing a carbon material of the present invention, an organic solvent is preferably added to and mixed with the mixture of the heat treatment pitch and the carbon.

  In the method for producing a carbon material of the present invention, the organic solvent is preferably oil obtained by tar distillation, toluene or tetrahydrofuran.

  Moreover, this invention is a negative electrode material for lithium ion secondary batteries containing the carbon material manufactured with the said any manufacturing method.

  Moreover, this invention is a negative electrode for lithium ion secondary batteries using the said negative electrode material for lithium ion secondary batteries.

  Moreover, this invention is a lithium ion secondary battery using the said negative electrode for lithium ion secondary batteries.

  Although the lithium ion secondary battery using the carbon material of the present invention uses a carbon material precursor to which carbon is added as a negative electrode, the holding power of the electrolyte is large, and the discharge capacity is high even at a high electrode density. Excellent charge / discharge characteristics such as irreversible capacity and cycle characteristics. Further, according to the method for producing a carbon material for a lithium ion secondary battery of the present invention, a sufficient gap can be secured in the electrode, and as a result, a lithium ion secondary battery having a high discharge capacity per volume can be obtained.

(Carbon material)
The carbon material of the present invention is a carbon containing a mesocarbon microsphere graphitized product obtained by heat-treating a mixture of mesocarbon microsphere and 0.1 to 10% by mass of carbon with respect to the mesocarbon microsphere. Material.
The size of the optically anisotropic mesocarbon microsphere graphitized material constituting the carbon material of the present invention is several μm to several tens of μm, preferably 10 to 70 μm. Its content is 1-50% by mass, preferably 15-40% by mass. In the carbon material of the present invention, the volatile component contained before the high temperature heat treatment does not remain.

(Pitch of raw material)
The pitch of the raw material of the present invention is a petroleum-based or coal-based tar pitch containing 0.01 to 2% by mass, preferably 0.3 to 0.9% by mass of free carbon, coal tar, tar light oil, Tar medium oil, tar heavy oil, naphthalene oil, anthracene oil, coal tar pitch, pitch oil, oxygen-crosslinked petroleum pitch, heavy oil and the like are preferred, and coal tar pitch and petroleum pitch are preferred.
When the raw material pitch is heat-treated at 350 to 1000 ° C., preferably 400 to 600 ° C., more preferably 400 to 450 ° C., mesocarbon microspheres are generated from free carbon. Accordingly, the small spheres are present in the pitch after the heat treatment in a proportion of 1 to 50% by mass, preferably 15 to 40% by mass.
The contents of free carbon and microspheres can be measured by a quinoline insoluble content determination method based on JIS K2425-1983.
In addition, mesocarbon microspheres previously separated from the pitch can be used as the raw material of the present invention.

(Fibrous, spherical or massive carbon)
Carbon acts to secure voids in the electrode, and is preferably graphitic, fibrous, spherical, or massive carbon. Scaly natural graphite is not preferred. Specifically, it is fibrous carbon such as carbon nanotubes, spherical carbon such as carbon black and fullerene, and bulk carbon such as artificial graphite. The carbon is preferably minute so that the maximum effect can be exhibited even if the ratio to the mesocarbon microspheres is small (hereinafter also referred to as microcarbon), and preferably smaller than the size of the mesocarbon microspheres. . The maximum length of the carbon is preferably 20 μm or less, more preferably 50 nm to 20 μm, and still more preferably 100 nm to 20 μm. If the size of the fine carbon exceeds 20 μm, it may not be sufficiently dispersed on the surface of the graphitized material of mesocarbon spherules. The shape must be fibrous, spherical, or massive. In the case of other shapes, the dispersion on the mesocarbon microsphere surface is not sufficient, and the formation of voids is insufficient.
The blending ratio of fine carbon to mesocarbon microspheres is 0.01 to 20% by mass, preferably 0.1 to 7% by mass.

(Manufacture of carbon materials)
The carbon material of the present invention is obtained by mixing a heat-treated pitch containing mesocarbon spherules produced by heat-treating a pitch containing free carbon and the fine carbon, and extracting and separating the pitch from the mixture. The mixture is directly or heat-treated (fired), and the volatile content is adjusted to 2.0 to 30% by mass with respect to the entire mixture, followed by high-temperature heat treatment.
Also, the mesocarbon microspheres separated in advance from the heat treatment pitch and the fine carbon are mixed, and the mixture is left as it is or heat-treated (fired), and the content of volatile components in the microspheres is reduced with respect to the entire small spheres. After adjusting to 2.0-30 mass%, it manufactures by carrying out high temperature heat processing.

There is no particular limitation on the method of mixing the mesocarbon microspheres containing the mesocarbon microspheres or the mesocarbon microspheres previously separated from the heat treatment pitch and the fine carbon, but when mixed in the presence of an organic solvent, a good mixed state can be obtained. This is preferable. For example, in the case of using a heat treatment pitch, specifically, a method (a) in which both the heat treatment pitch and the fine carbon are dispersed in an organic solvent and mixed, and the fine carbon is organically added to the heat treatment pitch containing mesocarbon microspheres. A method of adding and mixing a dispersion dispersed in a solvent (b), a method of adding a heat treatment pitch containing mesocarbon microspheres to a dispersion in which fine carbon is dispersed in an organic solvent (c) In addition, a method (d) in which an organic solvent is added to and mixed with a mixture of heat-treated pitch and fine carbon containing mesocarbon microspheres is preferable. The dispersion obtained by dispersing both the heat-treated pitch and the fine carbon in the organic solvent is not particularly limited as long as it has a concentration that allows a good dispersion state to be obtained by stirring and mixing.
The mixing is performed by heating to 50 to 300 ° C, preferably 100 to 200 ° C.
When using mesocarbon microspheres previously separated from the heat treatment pitch, the same method as described above is preferable. In the following description, the description in the case where the heat treatment pitch is used is also applicable to the mesocarbon microspheres unless otherwise specified, and thus the description may be omitted.

  The organic solvent is not particularly limited as long as it can disperse both mesocarbon microspheres and fine carbon well, but benzene, toluene, quinoline, tar oil, tar heavy oil, tar light oil, tetrahydrofuran and the like are used. Preference is given to oils obtained by tar distillation, such as tar middle oil, tar heavy oil, tar light oil and the like.

  As a result of the mixing by the above method, the small spheres and the minute carbons are well dispersed without being unevenly distributed in the matrix pitch. The dispersion state can be confirmed by observation with an optical microscope (magnification 100 to 500 times).

  It is preferable that the heat-treated pitch and fine carbon mixture containing mesocarbon microspheres is heated and held at 50 to 300 ° C, preferably 100 to 200 ° C. Thereby, the mixture is well dispersed. The holding time is not particularly limited, but is 1 to 90 minutes, preferably 10 to 60 minutes.

The pitch is extracted and separated from the heat-treated pitch containing the mesocarbon spherules and the mixture after the heating and holding of the fine carbon, and the extraction residue is filtered to separate and recover the mesocarbon spherules. The extraction / separation method is not particularly limited.
When an organic solvent is not used for mixing the heat-treated pitch containing the mesocarbon microspheres and the fine carbon, it is preferable to use the organic solvent for preparing the mixture as an extraction solvent.
Since the mesocarbon microspheres recovered by the extraction filtration contain a considerable amount of volatile components derived from the raw material pitch, organic solvent, etc., it is necessary to adjust the volatile content in the present invention. .
The content of the volatile component is adjusted by blowing a gas such as air or nitrogen to the mixture containing the recovered mesocarbon spherules or by heat treatment (firing). The content is adjusted to 2.0 to 30% by mass, preferably 3 to 20% by mass, more preferably 3 to 10% by mass with respect to the mesocarbon microspheres. This volatile matter is presumed to be effective in suppressing irreversible capacity derived from fine carbon by filling around the mesocarbon microspheres and forming a non-oxidizing atmosphere during high-temperature heat treatment exceeding 2000 ° C. . If it is less than 2.0% by mass, the formation of a non-oxidizing atmosphere is insufficient, and if it exceeds 30% by mass, it is excessive, and there is a possibility that small spheres are ejected or volatile components are ignited during high-temperature heat treatment. . The heat treatment (firing) temperature is not particularly limited, but is 50 to 800 ° C, preferably 100 to 500 ° C.

The mixture containing mesocarbon spherules with the volatile content adjusted is subjected to high-temperature heat treatment in a non-oxidizing atmosphere. By high-temperature heat treatment, the mesocarbon microspheres are carbonized, further graphitized, and highly crystallized. And a volatile matter will not be contained substantially.
The high-temperature heat treatment is preferably performed in a non-oxidizing atmosphere such as a vacuum, a nitrogen atmosphere, or an argon atmosphere. For example, it is preferably 2000 ° C. or higher, more preferably 2800 ° C. or higher, using a Tamman furnace or an Atchison furnace. More preferably, it is carried out at a temperature around 3000 ° C. By high-temperature heat treatment, highly crystalline graphitized mesocarbon spherules are obtained. Since this has no distortion in the crystal structure and lithium ions can enter the graphite structure, it can give a good result in increasing the discharge capacity.

The carbon material of the present invention thus obtained is prepared as a negative electrode mixture paste as a negative electrode material for a lithium-on secondary battery by the following method, and is further produced into a negative electrode and a lithium-on secondary battery.
The lithium ion secondary battery is essentially a battery mechanism in which lithium ions are occluded in the negative electrode during charge / discharge and are detached from the negative electrode during discharge. A lithium ion secondary battery usually has a negative electrode, a positive electrode, and a nonaqueous electrolyte as main battery components, and the positive and negative electrodes are each composed of a lithium ion carrier, and the nonaqueous solvent enters and exits between layers in the charge / discharge process. .
The lithium ion secondary battery of the present invention is not particularly limited except that the carbon material is used as the negative electrode material, and other battery components conform to the elements of a general lithium ion secondary battery.

The negative electrode material and the negative electrode using the carbon material can be produced in accordance with a normal production method. However, the carbon material can sufficiently draw out the performance of the carbon material and has high moldability to powder, and can be chemically and electrically produced. There is no limitation as long as it is a method capable of obtaining a chemically stable negative electrode.
For preparing the negative electrode, a negative electrode mixture paste obtained by adding a binder to the carbon material can be used. As the binder, those having chemical stability and electrochemical stability with respect to the electrolyte are preferably used. For example, fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene, polyethylene, polyvinyl alcohol, carboxy Methyl cellulose, styrene butadiene rubber or the like is used. These can also be used together.

In the present invention, by using the above carbon material as the negative electrode material, not only an organic solvent-based binder that dissolves or disperses in an organic solvent, but also a water-soluble and / or water-dispersible water-based binder can be used. A negative electrode exhibiting excellent charge / discharge characteristics and cycle characteristics can be obtained.
Among them, it is preferable to use an organic solvent-based binder such as polyvinylidene fluoride in order to achieve the object of the present invention and maximize the effect.
In general, the binder is preferably used at a ratio of about 0.5 to 20% by mass in the total amount of the negative electrode mixture.
Specifically, for example, the carbon material is adjusted to an appropriate particle size by classification and the like, and the negative electrode mixture is adjusted by mixing with the binder, and this negative electrode mixture is usually used on one side of the current collector or The negative electrode mixture layer can be formed by applying to both sides.

At this time, a normal solvent can be used, and the negative electrode mixture is dispersed in the solvent to form a paste, and then applied to the current collector and dried. Glued to. More specifically, for example, the carbon material and fluorine resin powder such as polytetrafluoroethylene may be mixed and kneaded in a solvent such as isopropyl alcohol and then applied. Further, the carbon material and a fluororesin such as polyvinylidene fluoride, or carboxymethyl cellulose, styrene butadiene rubber, etc. are mixed with a solvent such as N-methylpyrrolidone, dimethylformamide, water, alcohol and the like, and then applied. be able to.
The paste can be adjusted by stirring using a known stirrer, mixer, kneader, kneader or the like.
The coating thickness when applying the mixture of the carbon material and the binder to the current collector is suitably 10 to 200 μm. When the negative electrode mixture layer is formed and then pressure bonding such as pressurization is performed, the adhesive strength between the negative electrode mixture layer and the current collector can be further increased.

The carbon material of the present invention and resin powder such as polyethylene and polyvinyl alcohol can be dry-mixed and hot press molded in a mold to produce a negative electrode.
The shape of the current collector used for the negative electrode is not particularly limited, and examples thereof include a foil shape or a net shape such as a mesh or an expanded metal. Examples of the current collector include copper, stainless steel, and nickel. In the case of a foil, the current collector preferably has a thickness of about 5 to 20 μm.

As the positive electrode material (positive electrode active material), it is preferable to select a material capable of inserting and extracting a sufficient amount of lithium. Examples of such positive electrode active materials include lithium-containing transition metal oxides, transition metal chalcogenides, vanadium oxides (V ₂ O ₅ , V ₆ O ₁₃ , V ₂ O ₄ , V ₃ O _8, etc.) and lithium compounds. Lithium-containing compound of general formula M _X Mo ₆ S _8-Y (where X is a numerical value in the range of 0 ≦ X ≦ 4, Y is 0 ≦ Y ≦ 1, and M represents a metal such as a transition metal) A chevrel phase compound represented by the formula, activated carbon, activated carbon fiber and the like can be used.
The lithium-containing transition metal oxide is a composite oxide of lithium and a transition metal, and may be a solid solution of lithium and two or more transition metals. Specifically, the lithium-containing transition metal oxide is LiM (1) _1-X M (2) _X O ₂ (where X is a numerical value in the range of 0 ≦ X ≦ 1, M (1), M (2) represents at least one transition metal) or LIM (1) _2-Y M (2) _Y O ₄ (where Y is a numerical value in the range 0 ≦ Y ≦ 1, M (1), M (2) represents at least one transition metal).

Examples of the transition metal element represented by M include Co, Ni, Mn, Cr, Ti, V, Fe, Zn, Al, In, Sn, etc., preferably Co, Fe, Mn, Ti, Cr, V and Al are mentioned.
More specifically, as the lithium-containing transition metal oxide, LiCoO ₂ , Li _X Ni _Y M _1-Y O ₂ (M is a transition metal element excluding Ni, preferably Co, Fe, Mn, Ti, Cr, V , At least one selected from Al, 0.05 ≦ X ≦ 1.10, 0.5 ≦ Y ≦ 1.0), LiNiO ₂ , LiMnO ₂ , LiMn ₂ O _{4 and the} like.

  The lithium-containing transition metal oxide as described above, for example, uses Li, transition metal oxides or salts as starting materials, and mixes these starting materials according to the composition, and in a temperature range of 600 to 1000 ° C. in an oxygen atmosphere. It can be obtained by firing. Note that the starting materials are not limited to oxides or salts, and can be synthesized from hydroxides or the like.

In the present invention, the positive electrode active material may be used alone or in combination of two or more. For example, a carbon salt such as lithium carbonate can be added to the positive electrode.
In order to form a positive electrode with such a positive electrode material, for example, a positive electrode mixture comprising a positive electrode material, a binder, and a conductive agent for imparting conductivity to the electrode is applied to both sides of the current collector. An agent layer is formed. As the binder, any of those exemplified for the negative electrode can be used. As the conductive agent, for example, graphite particles are used.

  The shape of the current collector is not particularly limited, and a foil shape or a mesh shape such as a mesh or an expanded metal is used. For example, examples of the current collector include aluminum, stainless steel, and nickel. The thickness is preferably 10 to 40 μm.

Also in the case of the positive electrode, like the negative electrode, the positive electrode mixture is dispersed in a solvent to form a paste, and the paste-like positive electrode mixture is applied to a current collector and dried to form a positive electrode mixture layer. Alternatively, after forming the positive electrode material mixture, press bonding such as pressurization may be further performed. Thereby, the positive electrode mixture layer is uniformly and firmly bonded to the current collector.
In forming the negative electrode and the positive electrode as described above, conventionally known various additives such as a conductive agent and a binder can be appropriately used.

As the electrolyte used for the present invention can be used an electrolyte salt used in the conventional non-aqueous electrolyte solution, for example _{LiPF 6, LiBF 4, LiAsF 6} , LiClO 4, LiB (C 6 H 5), LiCl, LiBr, LiCF ₃ SO ₃ , LiCH ₃ SO ₃ , LiN (CF ₃ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ CH ₂ OSO ₂ ) ₂ , LiN (HCF ₂ CF ₂ CH ₂ OSO ₂ ) ₂ , LiN [(CF ₃ ) ₂ CHOSO ₂ ] ₂ , LiB [C ₆ H ₃ (CF ₃ ) ₂ ] ₄ , LiAlCl ₄ , LiSiF ₆ and other lithium salts can be used. In particular, LiPF6 and LiBrF4 are preferably used from the viewpoint of oxidation stability.
The electrolyte concentration in the electrolytic solution is preferably 0.1 to 5 mol / liter, and more preferably 0.5 to 3.0 mol / liter.

The non-aqueous electrolyte may be a liquid non-aqueous electrolyte or a polymer electrolyte such as a solid electrolyte or a gel electrolyte. In the former case, the non-aqueous electrolyte battery is configured as a so-called lithium ion battery, and in the latter case, the non-aqueous electrolyte battery is configured as a polymer electrolyte battery such as a polymer solid electrolyte battery or a polymer gel electrolyte battery.
In the case of a liquid nonaqueous electrolyte, the solvent is ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, 1,1- or 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltatrahydrofuran, γ-butyllactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, anisole, diethyl ether, sulfolane, methylsulfolane, acetonitrile, chloronitrile, propionitrile, trimethylborate Aprotic organic solvents such as tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, tetrahydrothiophene, dimethyl sulfoxide, 3-methyl-2-oxazolidone, ethylene glycol, dimethyl sulfite it can.

When the nonaqueous electrolyte is a polymer electrolyte such as a polymer solid electrolyte or a polymer electrolyte, the matrix polymer compound gelled with a plasticizer (nonaqueous electrolyte) is included. Fluorine polymers such as ether polymer compounds such as polyethylene oxide and cross-linked polymers thereof, polymethacrylate polymer compounds, polyacrylate polymer compounds, polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymers. Molecular compounds can be used alone or in combination.
Among these, it is preferable to use a fluorine-based polymer compound such as polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer from the viewpoint of redox stability.

  As the electrolyte salt and non-aqueous solvent constituting the plasticizer contained in these polymer solid electrolyte and polymer gel electrolyte, any of the above-mentioned ones can be used. In the case of a gel electrolyte, the electrolyte salt concentration in the non-aqueous electrolyte that is a plasticizer is preferably 0.1 to 5 mol / liter, and more preferably 0.5 to 2.0 mol / liter.

The method for producing such a solid electrolyte is not particularly limited. For example, a polymer compound that forms a matrix, a lithium salt, and a solvent are mixed, heated and melted, and an appropriate organic solvent for mixing is used. Method of evaporating the organic solvent for mixing after dissolving the molecular compound, lithium salt and solvent, and mixing the monomer, lithium salt and solvent, and irradiating them with ultraviolet rays, electron beams or molecular beams to form a polymer And the like.
Moreover, the addition ratio of the solvent in the solid electrolyte is preferably 10 to 90% by mass, and more preferably 30 to 80% by mass. When the content is 10 to 90% by mass, the electrical conductivity is high, the mechanical strength is high, and the film is easily formed.

A separator can also be used in the lithium ion secondary battery of the present invention.
Although it does not specifically limit as a separator, For example, a woven fabric, a nonwoven fabric, a synthetic resin microporous film, etc. are mentioned. In particular, a synthetic resin porous membrane is preferably used. Among these, a polyolefin-based microporous membrane is preferable in terms of thickness, membrane strength, and membrane resistance. Specifically, it is a microporous film made of polyethylene and polypropylene, or a microporous film in which these are combined.

In the lithium ion secondary battery of the present invention, a gel electrolyte can be used because of the high initial charge / discharge efficiency.
The gel electrolyte secondary battery is configured by laminating a negative electrode containing the carbon material of the present invention, a positive electrode, and a gel electrolyte in the order of, for example, a negative electrode, a gel electrolyte, and a positive electrode, and accommodating them in a battery exterior material. . In addition to this, a gel electrolyte may be further disposed outside the negative electrode and the positive electrode. In the gel electrolyte secondary battery using such a carbon material for the negative electrode, even when propylene carbonate is contained in the gel electrolyte and the carbon material powder has a small particle size that can sufficiently reduce the impedance, Irreversible capacity can be kept small. Therefore, a large discharge capacity is obtained and a high initial charge / discharge efficiency is obtained.

  Furthermore, the structure of the lithium ion secondary battery according to the present invention is arbitrary, and the shape and form thereof are not particularly limited, and can be arbitrarily selected from a cylindrical shape, a square shape, a coin shape, a button shape, and the like. be able to. In order to obtain a sealed nonaqueous electrolyte battery with higher safety, it is preferable to include a means for detecting an increase in the internal pressure of the battery and shutting off the current when there is an abnormality such as overcharging. In the case of a polymer solid electrolyte battery or a polymer gel electrolyte battery, a structure enclosed in a laminate film can also be used.

(Example 1)
A coal tar pitch containing 0.3% by mass of free carbon was heated at 400 to 460 ° C. to produce mesocarbon microspheres in the coal tar pitch.
Ultrafine carbon fibers having a diameter of 100 to 300 nm and a length of 2 to 10 μm were added to the heat treatment pitch at a ratio of 3% by mass with respect to mesocarbon microspheres. The obtained mixture was kept at 100 to 150 ° C. and stirred for 1 hour. The mixture after stirring was poured into a pressure filter, pressurized with nitrogen gas, the pitch was extracted with an organic solvent, and mesocarbon spherules were separated by filtration with ultrafine carbon fibers.
The obtained mesocarbon microspheres containing ultrafine carbon fibers were dried in a nitrogen atmosphere at 80 to 130 ° C. to remove oil, and then fired at 400 to 450 ° C. in a nitrogen atmosphere. The volatile content of the mixture containing the obtained mesocarbon microspheres was 6.0% by mass.
The volatile content was measured according to the method defined in JIS M8511-1976.
The carbon material was further graphitized at 2900 ° C. to obtain a carbon material comprising a graphitized product of spherical mesocarbon spherules having an average particle size of 30 μm. This contained no volatiles.

The carbon material was mixed with polyvinylidene fluoride (PVdF) as a binder at a mass ratio of 90:10, and PVdF was dissolved and kneaded with N-methylpyrrolidone to obtain a paste.
A negative electrode plate produced by applying this paste-like negative electrode mixture on one side of a copper foil as a current collector using a doctor blade applicator with a clearance of 200 μm was dried at 100 ° C. for 12 minutes, and the electrode density was 1 It pressed so that it might become 0.8-2.2 g / cm < ³ >, Then, it vacuum-dried at 130 degreeC all day and night.

Using a negative electrode plate having an electrode density of 2.08 g / cm ³ and a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are in a volume ratio of 1: 2, LiPF ₆ has a concentration of 1 mol / kg. An evaluation battery was produced using the non-aqueous electrolyte solution described above, using the counter electrode as a lithium foil, and a porous separator between the negative electrode plate and the lithium foil.

The structure and manufacturing method of a button-type secondary battery as an evaluation battery are described below.
As shown in FIG. 1, the evaluation battery 1 has an outer cup 1 and an outer can 3 that have a sealed structure that is caulked with an insulating gasket 6 at the periphery thereof, and in order from the inner surface of the outer can 3. A battery system in which a current collector 7a made of nickel net, a disc-shaped working electrode (negative electrode) 2 made of lithium foil, and a current collector 7b made of copper foil are laminated.
In this evaluation battery, a separator 5 impregnated with an electrolyte solution is sandwiched between a working electrode 2 in close contact with a current collector 7b and a counter electrode 4 in close contact with the current collector 7a, and then the working electrode 2 is attached. The counter electrode 4 is accommodated in the outer can 3 in the outer cup 1, the outer cup 1 and the outer can 3 are combined, and the periphery of the outer cup 1 and the outer can 3 is caulked and sealed with an insulating gasket 6. Made.

The evaluation battery was subjected to the following charge / discharge test at a temperature of 25 ° C.
Constant current charging was performed until the circuit voltage reached 0 mV at a current value of 0.9 mA, and switching to constant voltage charging was performed when the circuit voltage reached 0 mV, and charging was continued until the current value reached 20 μA. The charging capacity was determined from the amount of electricity applied during that time. Then, it rested for 120 minutes.
Next, constant current charging was performed at a current value of 0.9 mA until the circuit voltage reached 1.5 V, and the discharge capacity was determined from the amount of current supplied during this period. The charge capacity and discharge capacity were determined from the energization amount in the first cycle, and the irreversible capacity and initial discharge efficiency were calculated from the following equations.
Irreversible capacity = charge capacity-discharge capacity Initial charge / discharge efficiency (%) = (discharge capacity / charge capacity) × 100
In this test, the process of occluding lithium ions in the negative electrode mixture was charged, and the process of desorbing from the negative electrode mixture was discharge.
The evaluation battery had a discharge capacity of 355 mAh / g and an irreversible capacity of 18 mAh / g.
Table 1 shows the discharge capacity (mAh / g), irreversible capacity (mAh / g), and initial charge / discharge efficiency (%) per gram of the negative electrode mixture.

(Example 2)
A coal tar pitch containing 0.3% by mass of free carbon was heated at 400 to 460 ° C. to produce mesocarbon microspheres in the coal tar pitch. Tar oil (boiling point 180-300 ° C.) was added to the resulting coal tar pitch, and mesocarbon microspheres were extracted and separated from the pitch.
Ultrafine carbon fibers having a diameter of 100 to 300 nm and a length of 2 to 20 μm were added to tar oil containing the mesocarbon microspheres at a ratio of 3% by mass with respect to the mesocarbon microspheres. The resulting mixture was dispersed in tar oil and kept at 100-150 ° C. and stirred for 1 hour. The mixture after stirring was poured into a pressure filter, pressurized with nitrogen gas, tar oil was separated, and mesocarbon microspheres were separated together with ultrafine carbon fibers.
The obtained mesocarbon microspheres containing ultrafine carbon fibers were dried in a nitrogen atmosphere at 80 to 130 ° C. to remove oil, and then fired at 400 to 450 ° C. in a nitrogen atmosphere. The volatile content of the mixture containing the carbonized product of mesocarbon microspheres was 6.2% by mass.
The carbonized mesocarbon spherules were graphitized at 2900 ° C. to obtain a carbon material composed of spherical mesocarbon spherulites graphitized with an average particle size of 30 μm.

Using the carbon material, a paste and a negative electrode plate were produced under the same method and conditions as in Example 1.
Using a negative electrode plate having an electrode density of 2.05 g / cm ³ and a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are in a volume ratio of 1: 2, LiPF ₆ has a concentration of 1 mol / kg. An evaluation battery was prepared and evaluated by using the non-aqueous electrolyte solution, using the counter electrode as a lithium foil, and using a porous separator between the negative electrode plate and the lithium foil. As a result, the discharge capacity was 355 mAh / g and the irreversible capacity was 19 mAh / g.

(Example 3)
A coal tar pitch containing 0.3% by mass of free carbon was heated at 400 to 460 ° C. to produce mesocarbon microspheres in the coal tar pitch. Tar oil was added to the resulting coal tar pitch, the pitch was extracted and separated, and the mesocarbon microspheres were further separated by filtration.
Ultrafine carbon fibers having a diameter of 100 to 300 nm and a length of 2 to 20 μm were dispersed in toluene at a ratio of 3% by mass with respect to mesocarbon microspheres. The obtained dispersion was poured into the mesocarbon microspheres to obtain a mixture. The mixture was kept at 100 to 150 ° C. and stirred for 1 hour. The mixture after stirring was poured into a pressure filter, pressurized with nitrogen gas, toluene was separated, and mesocarbon microspheres were obtained together with ultrafine carbon fibers.
The obtained mesocarbon microspheres containing ultrafine carbon fibers were dried in a nitrogen atmosphere at 80 to 130 ° C. to remove oil, and then fired at 400 to 450 ° C. in a nitrogen atmosphere. The volatile content of the obtained mixture containing carbides of mesocarbon microspheres was 6.2% by mass.
The mesocarbon microsphere carbide was graphitized at 2900 ° C. to obtain a carbon material composed of spherical mesocarbon microsphere graphitized particles having an average particle diameter of 30 μm.

Using the carbon material, a paste and a negative electrode plate were produced under the same method and conditions as in Example 1.
Using a negative electrode plate having an electrode density of 2.06 g / cm ³ and a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are in a volume ratio of 1: 2, LiPF ₆ has a concentration of 1 mol / kg. An evaluation battery was prepared and evaluated by using the non-aqueous electrolyte solution, using the counter electrode as a lithium foil, and a negative separator and a lithium foil between the negative electrode plate and a porous separator. The discharge capacity was 354 mAh / g and the irreversible capacity was 18 mAh / g.

Example 4
A coal tar pitch containing 0.3% by mass of free carbon was heated at 400 to 460 ° C. to produce mesocarbon microspheres in the coal tar pitch. Tar oil was added to the resulting coal tar pitch, the pitch was extracted and separated, and the mesocarbon microspheres were further separated by filtration.
Ultrafine carbon fibers having a diameter of 100 to 300 nm and a length of 2 to 20 μm were dispersed in toluene at a ratio of 3% by mass with respect to the mass of mesocarbon microspheres. The mesocarbon microspheres were added to the obtained dispersion, and the mixture was kept at 100 to 150 ° C. and stirred for 1 hour. The obtained heated and held mixture was poured into a pressure filter, pressurized with nitrogen gas, toluene was separated, and mesocarbon microspheres were obtained together with ultrafine carbon fibers.
The obtained mesocarbon microspheres containing ultrafine carbon fibers were heated in a nitrogen atmosphere at 80 to 130 ° C. to dry and remove the oil. Then, it baked at 400-450 degreeC in nitrogen atmosphere. The volatile content of the obtained mixture containing carbides of mesocarbon microspheres was 5.4% by mass.
The carbonized mesocarbon spherules were graphitized at 2900 ° C. to obtain a carbon material made of spherical mesocarbon spherulites graphitized with an average particle size of 30 μm.

Using the carbon material, a paste and a negative electrode plate were produced under the same method and conditions as in Example 1.
Using a negative electrode plate having an electrode density of 2.06 g / cm ³ and a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are in a volume ratio of 1: 2, LiPF ₆ has a concentration of 1 mol / kg. Using the non-aqueous electrolyte solution, a counter battery was used as a lithium foil, and a test battery was prepared and evaluated through a porous separator between the test electrode and the lithium foil. The discharge capacity was 355 mAh / g and the irreversible capacity was 17 mAh / g.

(Example 5)
A coal tar pitch containing 0.3% by mass of free carbon was heated at 400 to 460 ° C. to produce mesocarbon microspheres in the coal tar pitch. To the coal tar pitch containing the mesocarbon spherules, tar oil was added, the pitch was extracted, and the mesocarbon spherules were separated by filtration.
Extra fine carbon fibers having a diameter of 100 to 300 nm and a length of 2 to 20 μm were added at a ratio of 3% by mass with respect to the mass of mesocarbon microspheres. To this mixture, tar oil was poured, heated to 100 to 150 ° C., and stirred for 1 hour. The heated mixture was poured into a pressure filter, pressurized with nitrogen gas, the tar oil was separated, and the mesocarbon microspheres were filtered and separated together with the ultrafine carbon fibers.
The mesocarbon microspheres containing ultrafine carbon fibers were heated in a nitrogen atmosphere at 80 to 130 ° C., and the oil was removed by drying. Then, it baked at 400-450 degreeC in nitrogen atmosphere. The volatile content of the obtained mixture containing carbides of mesocarbon microspheres was 4.8% by mass.
The carbonized mesocarbon spherules were graphitized at 2900 ° C. to obtain a carbon material made of spherical mesocarbon spherulites graphitized with an average particle size of 30 μm.

Using the carbon material, a paste and a negative electrode plate were produced under the same method and conditions as in Example 1.
Using a negative electrode plate having an electrode density of 2.05 g / cm ³ and a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are in a volume ratio of 1: 2, LiPF ₆ has a concentration of 1 mol / kg. Using the non-aqueous electrolyte solution, an evaluation battery was prepared and evaluated by using a lithium foil as a counter electrode and a porous separator between the test electrode and the lithium foil. The discharge capacity was 355 mAh / g and the irreversible capacity was 18 mAh / g.

(Comparative Example 1)
A coal tar pitch containing 0.3% by mass of free carbon was heated at 400 to 460 ° C. to produce mesocarbon microspheres in the coal tar pitch. To the obtained coal tar pitch, tar oil (boiling point 180 to 300 ° C.) was added, heated to 100 to 150 ° C. and stirred for 1 hour to obtain a slurry. The slurry was put into a pressure filter and pressurized with nitrogen gas, and the slurry was filtered to separate mesocarbon spherules.
The obtained mesocarbon microspheres (without ultrafine carbon fibers) were dried in a nitrogen atmosphere at 80 to 130 ° C. to remove oil, and then fired at 400 to 450 ° C. in a nitrogen atmosphere. The amount of volatile components in the mixture containing the carbides of the obtained mesocarbon microspheres was 5.0% by mass.
Subsequently, the small sphere carbonized product was graphitized at 2900 ° C. to obtain a carbon material made of a spherical mesocarbon small sphere graphitized product having an average particle size of 30 μm.

Using the carbon material, a paste and a negative electrode plate were produced under the same method and conditions as in Example 1.
Using a negative electrode plate having an electrode density of 2.03 g / cm ³ and a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are in a volume ratio of 1: 2, LiPF ₆ has a concentration of 1 mol / kg. An evaluation battery was prepared and evaluated by using the non-aqueous electrolyte solution, using the counter electrode as a lithium foil, and using a porous separator between the negative electrode plate and the lithium foil. As a result, the discharge capacity was 353 mAh / g, and the irreversible capacity was 20 mAh / g.

(Comparative Example 2)
A coal tar pitch containing 0.3% by mass of free carbon was heated at 400 to 460 ° C. to produce mesocarbon microspheres in the coal tar pitch. To the obtained coal tar pitch, an ultrafine carbon fiber having a diameter of 100 to 300 nm and a length of 2 to 20 μm was added at a ratio of 3% by mass with respect to the mesocarbon microspheres, and heated and maintained at 100 to 150 ° C. Stir for hours. Then, the mixture was put into a pressure filter, pressurized with nitrogen gas, the slurry was filtered, and mesocarbon microspheres were separated together with ultrafine carbon fibers.
The obtained mesocarbon microspheres containing ultrafine carbon fibers were dried in a nitrogen atmosphere at 80 to 130 ° C. to remove oil, and then fired at 400 to 450 ° C. in a nitrogen atmosphere. The volatile content of the mixture containing the carbides of the obtained mesocarbon microspheres was 1.8% by mass.
The carbonized mesocarbon spherules were graphitized at 2900 ° C. to obtain a carbon material made of spherical mesocarbon spherulites graphitized with an average particle size of 30 μm.

Using the carbon material, a paste and a negative electrode plate were produced under the same method and conditions as in Example 1.
Using a negative electrode plate having an electrode density of 2.00 g / cm ³ and a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are in a volume ratio of 1: 2, LiPF ₆ has a concentration of 1 mol / kg. An evaluation battery was prepared and evaluated by using the non-aqueous electrolyte solution, using the counter electrode as a lithium foil, and using a porous separator between the negative electrode plate and the lithium foil. As a result, the discharge capacity was 354 mAh / g and the irreversible capacity was 35 mAh / g.

Next, evaluation batteries of Examples 1 to 5 and Comparative Examples 1 and 2 were separately prepared, and changes in capacity retention rate (charge / discharge cycle characteristics) were evaluated.
Charging / discharging cycle characteristics are as follows: constant current charging at a current value of 4.0 mA until the circuit voltage reaches 0 mV, then switching to constant voltage charging, charging is continued until the current value reaches 20 μA, and then paused for 120 minutes did. Next, constant current discharge was performed at a current value of 4.0 mA until the circuit voltage reached 1.5V. This charge / discharge was repeated 100 cycles, and the capacity retention rate was determined from the obtained discharge capacity using the following equation. The results are shown in FIG.
Capacity maintenance rate (%) = (discharge capacity in each cycle / discharge capacity in the first cycle)
) × 100

  The capacity maintenance rate in the 100th cycle was 91 to 92% in Examples 1 to 5, but was as low as 83% in Comparative Example 1 (without ultrafine carbon fibers). In Comparative Example 2 (1.8% by mass with a low volatile content before high-temperature heat treatment), it was 89%. From this, it was found that when ultrafine carbon fibers were added, cycle characteristics were improved. In addition, as in Examples 1 to 5, when mesocarbon microspheres and ultrafine carbon fibers are mixed, the volatile content before high-temperature heat treatment is 2.0 to 30% by mass, and high-temperature heat treatment is combined, it is irreversible. It can be seen that the capacity is reduced. This is presumed to be because the volatile matter remaining in the mesocarbon microspheres is fused with the surface of the ultrafine carbon fiber, thereby reducing the reactivity of the active material with the electrolyte and reducing the irreversible capacity.

  Moreover, the relationship between the electrode density and discharge rate of the evaluation batteries of Examples 1 to 5 and Comparative Examples 1 and 2 is shown in FIG. Since Examples 1-5 and the comparative example 2 contain carbon fiber, it turns out that a discharge characteristic is excellent in a high-density area | region. In addition, the discharge rate was made into the ratio (%) with respect to the discharge capacity of the 1st cycle when the initial charge / discharge efficiency of the discharge capacity in the case of 2.5C was calculated | required. Here, C is a unit in which 1 C is assumed to be discharged in one hour. Therefore, 2.5 C corresponds to discharging with a current equal to discharging all the stored electric quantity in 0.4 hours.

  The carbon material of the present invention is suitable as a negative electrode material for a lithium ion secondary battery, and is used for a negative electrode for a lithium ion secondary battery and further for a lithium ion secondary battery. Moreover, it can also be utilized for a fuel cell etc. taking advantage of the feature.

It is sectional drawing of the evaluation battery for evaluating a charging / discharging characteristic. It is a graph which shows cycling characteristics. It is a graph which shows the relationship between an electrode density and a discharge rate (however, in the case of 2.5C).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exterior cup 2 Working electrode 3 Exterior can 4 Counter electrode 5 Electrolyte solution impregnation separator 6 Insulation gasket 7a, 7b Current collector

Claims (10)

  Mesocarbon spherules are mixed with at least one kind of carbon selected from fibrous, spherical or massive carbon at a ratio of 0.1 to 10% by mass, and the volatile content of the mixture is 2.0 to 30% by mass. %, And thereafter a high temperature heat treatment is performed.   Mesocarbon spherules are mixed with at least one kind of carbon selected from fibrous, spherical, or massive carbon at a ratio of 0.1 to 10% by mass, and the mixture is heat-treated to have a volatile content of 2.0. A method for producing a carbon material, characterized by performing high-temperature heat treatment after adjusting to -30% by mass.   Mesocarbon spherules are mixed with at least one carbon selected from fibrous, spherical or massive carbon in the proportion of 0.1 to 10% by mass in the presence of an organic solvent, and then the organic solvent is separated and removed. A method for producing a carbon material, comprising adjusting the content of a volatile component of the obtained mixture to 2.0 to 30% by mass and then performing a high-temperature heat treatment.   Mesocarbon spherules are mixed with at least one carbon selected from fibrous, spherical or massive carbon in the proportion of 0.1 to 10% by mass in the presence of an organic solvent, and then the organic solvent is separated and removed. A method for producing a carbon material, wherein the obtained mixture is heat-treated to adjust the content of volatile components to 2.0 to 30% by mass, and then subjected to high-temperature heat treatment.   The heat treatment pitch containing mesocarbon spherules produced by heat-treating the pitch containing free carbon contains at least one kind of carbon selected from fibrous, spherical, or massive carbons in a range of 0.1 to 0.1 mesocarbon spherules. Carbon material characterized in that it is mixed at a rate of 10% by mass, then the pitch is separated and removed, and the volatile content of the resulting mixture is adjusted to 2.0-30% by mass, followed by high-temperature heat treatment. Manufacturing method.   The heat treatment pitch containing mesocarbon spherules produced by heat-treating the pitch containing free carbon contains at least one kind of carbon selected from fibrous, spherical, or massive carbons in a range of 0.1 to 0.1 mesocarbon spherules. It is characterized by mixing at a rate of 10% by mass, then separating and removing the pitch, heat-treating the resulting mixture to adjust the volatile content to 2.0-30% by mass, and then heat treating at a high temperature. Carbon material manufacturing method.   The method for producing a carbon material according to claim 3 or 4, wherein the organic solvent is oil obtained by tar distillation, toluene or tetrahydrofuran.   The negative electrode material for lithium ion secondary batteries containing the carbon material manufactured with the manufacturing method of any one of Claims 1-7.   The negative electrode for lithium ion secondary batteries using the negative electrode material for lithium ion secondary batteries of Claim 8.   The lithium ion secondary battery using the negative electrode for lithium ion secondary batteries of Claim 9.

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