JPH10194713A - Production of granular graphite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the melt foaming of a mesophase pitch in a heat-treating step and improve the production and operating efficiencies by heat-treating the mesophase pitch prepared by polymerizing a condensed polycyclic hydrocarbon or a substance containing the hydrocarbon in the presence of hydrogen fluoride-boron trifluoride in the presence of a specific compound and then carrying out the pulverizing and graphitizing treatments thereof. SOLUTION: A condensed polycyclic hydrocarbon or a substance containing the hydrocarbon is polymerized in the presence of hydrogen f1uoride-boron trifluoride to provide a mesophase pitch having >=170 deg.C melting point, >=70% optical anisotropic phase content and >=70% carbonization yield. The resultant mesophase pitch in an amount of 100 pts.wt. is then mixed with 5-40 pts.wt. one or more compounds selected from aromatic nitro compounds, quinone dioximes and nonmetallic salts of nitric acid, sulfuric acid (sulfurous acid), peroxosulfuric acid and peroxodisulfuric acid and the resultant mixture is heat- treated at 150-350 deg.C for 1-120min, then pulverized, heated at 800-1,600 deg.C in a nonoxoidizing atmosphere and graphitized to afford a granular graphite.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing highly crystalline granular graphite suitable for a negative electrode material for a lithium ion battery.

[0002]

2. Description of the Related Art With the remarkable progress of multimedia, lithium secondary batteries have been increasingly important as a key device supporting an advanced information society.
Lithium-ion batteries using carbon material for the negative electrode have been rapidly commercialized because of their cleanliness, high energy density, and excellent charge-discharge cycle characteristics. In order to cope with weight reduction, higher capacity is strongly required. In response to these demands, various carbon materials have been taken up as potential anode materials, and active research and development are underway. Natural graphite and mesocarbon microbeads (MC
MB) has received great attention as a practical electrode material.

Since natural graphite has excellent crystallinity and a very high true density, it is considered to be advantageous in increasing the packing density of the negative electrode and obtaining a high energy density. However, the shape is bulky because of its scale-like shape, and the coating property is reduced due to the generation of coating unevenness or the falling off of particles during electrode molding, so that it is difficult to secure a stable electrode structure, and the battery performance is poor. There is a problem that deterioration (especially reduction in cycle life) and internal short circuit are likely to occur.

[0004] On the other hand, MCMB is obtained by extracting and separating mesophase spherules generated from heat treatment of coal tar or petroleum heavy oil from the matrix pitch. A graphite powder applicable as a material is obtained (JP-A-7-145387).
issue). This graphite powder has an advantage that the electrode filling property can be enhanced because its shape is spherical. However, in the preparation of MCMB, a large amount of solvent is required for the extraction and separation operations from the matrix pitch, the yield of mesophase spheres relative to the raw material pitch is extremely low, and a constant quality is stably ensured. There is a problem that it is not easy to do so, and there is a strong demand for environmental and cost improvements. Furthermore, graphite derived from MCMB has a significantly lower crystallinity than natural graphite, so that it cannot be said that the level of battery performance is always satisfactory.

[0005]

DISCLOSURE OF THE INVENTION The present inventors have previously attempted to obtain a high energy density by enhancing the electrode filling property, and at the same time, secure a good electrode structure and extend the life of the charge / discharge cycle. Proposed a method for producing non-flaky graphite powder having high crystallinity (Japanese Patent Application No. 8-278012).
issue). That is, synthetic mesophase pitch obtained by polymerizing a condensed polycyclic hydrocarbon or a substance containing the same in the presence of hydrogen fluoride / boron trifluoride is used as a raw material, which is heat-treated in a non-oxidizing atmosphere and then pulverized. This is a method for producing granular graphite suitable as an electrode material by treating and graphitizing.

[0006] However, this method involves remarkable melting and foaming during the heat treatment process of the synthetic mesophase pitch.
Further improvements are required in terms of manufacturing efficiency and operability. That is, in the development of the negative electrode carbon material aiming at the high performance as described above, the further reduction in the price due to the efficiency of the production is an important factor for practical use. An object of the present invention is to perform heat treatment of synthetic mesophase pitch, pulverization, and graphitization to produce granular graphite suitable as a negative electrode material of a lithium ion battery, and to suppress intense melt foaming of mesophase pitch in the heat treatment step. It is an object of the present invention to provide a method for improving manufacturing efficiency and operability.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies with the aim of improving the heat treatment technology of synthetic mesophase pitch. As a result, a specific compound having a hardening action (viscosity increasing action) and a synthetic mesophase pitch have been obtained. The present inventors have found that, by reacting the above, remarkable foaming in the heat treatment step can be suppressed, and a graphite precursor can be efficiently prepared with good operability. That is, the present invention provides a mesophase pitch obtained by polymerizing a condensed polycyclic hydrocarbon or a substance containing the same in the presence of hydrogen fluoride / boron trifluoride to obtain an aromatic nitro compound, nitric acid, quinone dioxime or the like. , And nitric acid, nitrous acid,
One or two selected from non-metal salts of peroxonitrate, sulfuric acid, sulfurous acid, peroxosulfuric acid and peroxodisulfuric acid
This is a method for producing granular graphite, which comprises subjecting to a heat treatment in the presence of at least one species, followed by a pulverization treatment and a graphitization treatment.

[0008]

The raw material mesophase pitch used in the present invention is a mesophase pitch obtained by polymerization in the presence of a condensed polycyclic hydrocarbon or a substance containing the same, hydrogen fluoride / boron trifluoride, JP-A-1-1396
21, JP-A-1-254796 and JP-A-3-2
No. 23391, naphthalene, anthracene, methylnaphthalene, phenanthrene, acenaphthene, acenaphthylene, pyrene and the like, condensed polycyclic hydrocarbons having these skeletons, and mixtures thereof or pitches synthesized from substances containing these It is. This synthetic mesophase pitch is already commercially produced and has excellent features in terms of quality, price, chemical purity and the like.

The mesophase pitch preferably has a softening point by a flow tester method of 170 ° C. or more, an optically anisotropic phase content of 70% or more, and a carbonization yield of 70% or more. In the present invention, the term “optically anisotropic phase” refers to a method of polishing a cross section of a solidified pitch mass near a room temperature and rotating the sample or the orthogonal Nicols when observed under a reflective optical microscope under orthogonal Nicols. Means the portion where is observed, that is, the portion that is optically anisotropic, "optically anisotropic phase content"
Means the area fraction of this optically anisotropic phase when observed with a microscope. The “carbonization yield” means that the temperature of the mesophase pitch powder is raised in an inert gas atmosphere (10 ° C./m
in), a value when the temperature was maintained for 2 hours after reaching 600 ° C.

Compounds for suppressing foaming in the heat treatment step of the mesophase pitch according to the present invention include aromatic nitro compounds, nitric acid, quinone dioximes, nitric acid, nitrous acid, peroxonitrate, sulfuric acid, sulfurous acid, peroxosulfuric acid Non-metal salts of peroxodisulfuric acid are used. Specific examples of the aromatic nitro compound include dinitronaphthalene, (di) nitrobenzene, (di) nitrotoluene,
(Di) nitroxylene, (di) nitrophenol, and the like. Specific examples of quinone dioximes include p-quinone dioxime and p, p'-dibenzoylquinone dioxime. Examples of the nonmetal salts of nitric acid, nitrous acid, peroxonitrate, sulfuric acid, sulfurous acid, peroxosulfuric acid, and peroxodisulfuric acid include organic alkali salts such as ammonium salts and amine salts. If these metal salts are used, the metal component is taken into the mesophase pitch heat-treated product, so that the metal component easily remains as an impurity in the graphite powder even if it is graphitized, which is preferable for the physical properties as an electrode material. There may be no effect.

When the raw material mesophase pitch is heated in a state in which one or more selected from the above compounds and the raw material mesophase pitch are sufficiently mixed, the melt viscosity increases and the mesophase pitch is solidified (hardened). The quantitative relationship between the raw material mesophase pitch and the compound and the heat treatment conditions depend on the properties of the mesophase pitch and the type of the compound. Generally, 5 to 40 parts by weight of the compound is used for 100 parts by weight of the raw material mesophase pitch. Can be The method of mixing the raw material mesophase pitch with the compound is not particularly limited. The heat treatment temperature is generally in the range of 150 to 350C, and the heat treatment time is generally in the range of 1 to 120 minutes. After the completion of the curing treatment, a secondary heat treatment is performed at a temperature of 400 ° C. or more as necessary. The time of the second heat treatment is 1 to 240 minutes, preferably 10 to 120 minutes.

The mechanism for explaining the curing phenomenon of the mesophase pitch differs depending on the type of the coexisting compound. For example, when an aromatic nitro compound is allowed to coexist, it is considered that polycondensation of pitch constituent molecules is mainly promoted by a radical reaction. When nitric acid is used, it is considered that a nitro group is first introduced, and subsequently, a polymerization reaction is accelerated simultaneously with the denitration reaction to cause an increase in viscosity. On the other hand, in the presence of quinone dioximes, polymerization by crosslinking is thought to play a dominant role in increasing viscosity. The mechanism of the curing reaction differs depending on the type of the compound thus coexisted,
It is difficult to describe accurately.

When the mesophase pitch is heat-treated together with the compound having the above-mentioned hardening action, remarkable melting and foaming can be effectively suppressed, so that a remarkable improvement in volume efficiency, operability and reproducibility is achieved. Efficiency can be improved. In order to produce granular graphite, first, the mesophase pitch heat-treated product in which melt foaming is suppressed by the reaction with the compound functioning as a curing agent as described above is cooled to near room temperature and then pulverized. The pulverization conditions are selected so that the particle size of the powder is in the range of usually 1 to 50 μm, preferably 10 to 30 μm in average particle size (median diameter). As the pulverizer, an optimal model is appropriately selected from a jet mill, an impact pulverizer, and the like, and is not particularly limited. As the classifier, an optimal model is appropriately selected from a mechanical classifier, a wind classifier, and the like, and is not particularly limited. Next, the pulverized mesophase pitch heat-treated product is usually calcined before graphitization. However, the calcining step may be omitted and the graphitization treatment may be performed immediately after pulverization. Generally, the calcination is performed at 800 to 1600 ° C. in a non-oxidizing atmosphere. The graphitization treatment is performed at 1900 ° C. or more, preferably 240 ° C.
Performed at 0 ° C. or higher.

The granular graphite obtained by the method of the present invention has high crystallinity and excellent conductivity. If the granular graphite is used as a negative electrode material of a lithium ion battery, high conductivity and high density electrode molding can be performed, and a high energy density can be obtained. In addition, since a stable electrode structure can be secured, the charge / discharge efficiency is excellent and the cycle life is improved. U.S. Patent Nos. 2500208 and 25000020 include:
A method using an aromatic nitro compound as a polymerization accelerator such as tar pitch is described. However, these are all related to the production of carbon moldings composed of fillers such as coke and binders such as pitches, with the aim of improving the performance of binder components such as increasing the carbonization yield and improving operability. It is. Therefore, this is essentially different from the technical idea of the present invention in which a hardening agent is used for the purpose of preventing foaming in the heat treatment step of mesophase pitch in producing granular graphite.

[0015]

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited by these examples.

Example 1 Synthetic mesophase pitch obtained by polymerizing naphthalene in the presence of hydrogen fluoride / boron trifluoride (softening point: 255)
° C, optically anisotropic phase content: 100%, carbonization yield: 90
%) A homogeneous mixed powder of 80 parts by weight and 20 parts by weight of industrial dinitronaphthalene is supplied to a kneaded and heatable continuous reactor, heat-treated at 250 ° C. to complete a curing reaction, and then produced from a reactor outlet. The product was collected in the form of granules. The product was post-cured for 1 hour at 350 ° C. in a nitrogen atmosphere using an electric furnace. After cooling this to room temperature, it was pulverized by a ball mill to obtain an average particle size of 15
μm. The temperature of the powder was increased at a rate of 5 ° C./min in a nitrogen atmosphere. At this time, no adhesion between the particles was observed, and no crushing treatment was required. Then, under argon atmosphere, 3000
Graphitization was performed at ℃. When the crystal structure of the obtained granular graphite was examined by an X-ray diffraction method, the lattice constant C ₀ obtained from the (002) diffraction line was 0.6726 nm, and the crystallite size Lc was 100 nm or more.

Example 2 The same homogeneous powder of 82 parts by weight of mesophase pitch and 18 parts by weight of ammonium nitrate as in Example 1 was supplied to a kneaded and heatable continuous reactor, and heat-treated at 280 ° C. to complete the curing reaction. After that, the product was recovered in granular form from the reactor outlet. Further, the product was transferred to a carbonization furnace and subjected to a secondary heat treatment at 450 ° C. for 1 hour. At this time, vigorous foaming did not occur, and the adhesion between particles was slightly observed. The heat-treated product was pulverized with a ball mill to an average particle size of 14 μm, and then calcined under the same conditions as in Example 1. At this time, no fusion between the particles was observed. Subsequently, graphitization was carried out under the same conditions as in Example 1. According to the X-ray analysis of the granular graphite, the lattice constant C ₀ obtained from the (002) diffraction line was 0.6724 nm, and the crystallite size Lc was 100 nm or more.

Example 3 The same homogeneous mixed powder of 88 parts by weight of mesophase pitch and 12 parts by weight of ammonium hydrogen sulfate as in Example 1 was fed to a continuous reactor capable of kneading and heating, and heat-treated at 250 ° C. to carry out a curing reaction. After completion, the product was recovered in granular form from the reactor outlet. Further, the product was transferred to a carbonization furnace and subjected to a secondary heat treatment at 450 ° C. for 1 hour. At this time, foaming was significantly suppressed to the extent that a 1.5-fold volume expansion was observed. The heat-treated product was pulverized with a ball mill to an average particle size of 14 μm, and then calcined under the same conditions as in Example 1. At this time, no fusion between the particles was observed. Subsequently, graphitization was carried out under the same conditions as in Example 1. According to the X-ray analysis of the granular graphite, the lattice constant C obtained from the (002) diffraction line was 0.6723 nm, and the crystallite size Lc was 100 nm or more.

[0019]

According to the method of the present invention, when a synthetic mesophase pitch is heat-treated, a compound having a hardening action (polymerization accelerating action) is allowed to coexist with the heat-treated synthetic mesophase pitch. Since they can be effectively suppressed, the volume efficiency, operability, and reproducibility can be significantly improved. Therefore, according to the present invention, the process of producing granular graphite from synthetic mesophase pitch is greatly simplified, and graphite powder suitable for a negative electrode carbon material of a lithium ion battery can be industrially advantageously obtained. The significance is significant.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01M 4/04 H01M 4/04 A 4/58 4/58

Claims (1)

[Claims] 1. A mesophase pitch obtained by polymerizing a condensed polycyclic hydrocarbon or a substance containing the same in the presence of hydrogen fluoride / boron trifluoride, to obtain an aromatic nitro compound, nitric acid, quinone dioxime or the like. And heat treatment in the presence of one or more selected from nonmetal salts of nitric acid, nitrous acid, peroxonitrate, sulfuric acid, sulfurous acid, peroxosulfuric acid, and peroxodisulfuric acid, followed by pulverization and graphitization A method for producing granular graphite.