JPH07145387A - Production of mesocarbon microbead - Google Patents

Abstract

PURPOSE:To obtain a mesocarbon microbead baked or graphitized with a good reproducibility at a low cost. CONSTITUTION:A mesocarbon microbead is baked to 120 deg.C) in the air and graphitized in an inert or nonoxidizing atmosphere at a temp. rise rate of 10 deg.C/hr to 1,000 deg.C, if necessary to 3,000 deg.C.

Description

Detailed Description of the Invention

[0001]

[Industrial application] Mesocarbon microbeads are optical anisotropy in which pitch polycyclic aromatic macromolecules formed in pitch when heat-treated at 350-450 ℃ A fine carbonaceous fine powder having a particle size of several to several tens of μm, which is obtained by separating mesophase spheroids exhibiting the above from the pitch matrix with an organic solvent. Mesocarbon microbeads have an intermediate property between coke and pitch, and have been put into practical use as a binderless high-density carbon material raw material. In recent years, mesocarbon microbeads have been directly fired and graphitized to form a conductive resin, etc. Attention has been paid to its use as an additive to carbon or as a carbon material for a negative electrode of a Li-ion secondary battery. The present invention relates to a method for producing a fired and graphitized mesocarbon microbead used as a conductive resin additive or a carbon material for a negative electrode of a Li-ion secondary battery.

[0002]

2. Description of the Related Art Generally, carbon materials are often used after being treated at a high temperature of 2000 ° C. or higher. In this high-temperature treatment, the carbon material usually reacts with oxygen and is oxidized and consumed.
It is carried out in an inert gas such as N ₂ or in a reducing atmosphere such as coke breeze. Since the mesocarbon microbeads have intermediate properties between coke and pitch, they are still chemically active, and they easily self-sinter without firing under pressure when graphitizing, and the mesocarbon microbeads are used as primary particles. There has been a problem that it is necessary to crush and to crush after graphitization to obtain beads, and this crushing process requires a great deal of labor because of strong fusion between particles.

On the other hand, as described above, in recent years, new applications have been developed which make use of the physical properties of the mesocarbon microbeads, and especially JP-A-4-115458 and JP-A-4-1-1.
88559, JP-A-4-190557, and JP-A-4-190557.
As shown in No. 332484 and the like, it became clear that a carbon material obtained by treating mesocarbon microbeads at a high temperature is suitable for a negative electrode of a lithium ion secondary battery, and an inexpensive high temperature treatment technique for mesocarbon microbeads becomes a problem. Has become.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a method for producing mesocarbon microbeads which are calcined or graphitized, which are inexpensive and excellent in reproducibility without impairing the original physical properties of mesocarbon microbeads. To do.

[0005]

[Means for Solving the Problems] That is, according to the present invention, after firing mesocarbon microbeads to 120 ° C. in air, they are further heated to 10 ° C. in an inert or non-oxidizing atmosphere.
1000 ° C at a heating rate of / hr or more, 30 if necessary
The present invention provides a method for producing mesocarbon microbeads, which comprises performing graphitization treatment up to 00 ° C. After firing in air, it is preferable to perform firing up to 600 ° C. at a temperature rising rate of 100 ° C./hr or less.

[0006]

The present invention will be described in more detail below. The reason why the mesocarbon microbeads have self-sintering properties, unlike cokes, is that they contain a relatively low molecular weight fraction in their constituent molecules. This low molecular weight fraction softens and melts in the region of 350 to 450 ° C. during firing and has a constant residual carbon rate, so that the mesocarbon microbeads are firmly bonded to each other. This adhesion depends on the firing rate according to the studies by the present inventors. Usually, a fast heating rate shifts the melting and evaporation of light components to the high temperature side, resulting in stronger adhesion.

However, as a matter of course, increasing the firing rate makes it difficult to crush the strongly bonded mesocarbon microbeads, resulting in an increase in manufacturing cost. The initial goal of high temperature treatment method cannot be achieved.

As a result of further diligent studies, the present inventors have found that
It was discovered that it is possible to significantly increase the subsequent firing rate by once reacting with oxygen in air in the low temperature region of 120 ° C. or lower during firing of the mesocarbon microbeads. Not to mention mesocarbon microbeads, it easily reacts with oxygen and burns in the air. However, the reaction in the temperature range of 120 ° C. or lower is slow and can be industrially sufficiently controlled. The mesocarbon microbeads exposed to the air at a temperature of 120 ° C. or lower make oxygen a heavy component of the low molecular weight fraction, which is a constituent thereof, and rapidly reduce the adhesive strength. At a temperature above 120 ° C., the oxidation reaction proceeds rapidly, making it difficult to control and burning the mesocarbon microbeads, as well as causing the destruction of the crystal structure. On the other hand, at a temperature of 40 ° C. or lower, the oxidation reaction is extremely slow and no effect can be obtained. Therefore, it is preferable to select a temperature of 40 ° C. or higher.

The mesocarbon microbeads that have been subjected to such an oxidation treatment in air have a reduced adhesive force between the mesocarbon microbeads without destroying the crystal structure, and then the firing rate is 10 ° C./hr or more, preferably Is 1
The firing rate of the carbon material, which is equal to or lower than 00 ° C./hr, is extremely fast, and it is possible to perform firing up to a temperature range of 1000 ° C. Furthermore, if necessary, 3000 ℃
It can be graphitized. The condition of 100 ° C./hr or less is preferably up to a temperature of around 600 ° C., and in a temperature range higher than this, it is possible to adopt a higher temperature rising rate. By adopting such a condition, conventionally, an extremely slow temperature rising rate of 1 to 3 ° C./hr is used to prevent fusion of mesocarbon microbeads to each other, and nevertheless, in the final step, It turned out that the complicated manufacturing process which requires a crushing operation is greatly simplified. The firing or graphitization treatment after the oxidation treatment in air is performed in an inert or non-oxidizing atmosphere as in the conventional case.

[0010]

EXAMPLES The present invention will be specifically described below based on examples. (Example 1) Coal tar containing 1.5% of free carbon (QI) was heat-treated at 450 ° C for 0.2 hr to generate mesophase microspheres. The heat-treated pitch was extracted using oil in tar (bp: 130 to 250 ° C.), the mesophase microspheres were separated and filtered from the pitch matrix, and sufficiently dried to remove the solvent to obtain mesocarbon microbeads. . About 15 kg of such mesocarbon microbeads was filled in a 15 L SUS firing tube, and while being blown with air, the mixture was treated at 100 ° C. for 2 minutes, then the air was changed to a nitrogen atmosphere, and 1000 ° C. at 20 ° C./hr. Bake to ℃. Then, using a graphitization furnace, high temperature treatment was performed up to 2800 ° C. at a rate of 500 ° C./hr to obtain a target graphitized product of mesocarbon microbeads. At this time, the mesocarbon microbeads remained as primary particles without being fused to each other. The graphitized mesocarbon microbeads have an average particle size of 1
At 2.1 μm, the lattice constant Co and the crystallite size Lc obtained from the (002) diffraction line of X-ray are 6.758, respectively.
It was Å, 376Å.

(Example 2) About 5 kg of mesocarbon microbeads obtained in the same manner as in Example 1 was added with 15 L of SUS.
It is filled in a baking tube made of steel and heated from room temperature (23 ° C) to a heating rate of 15
Baking was performed at a constant rate up to 1000 ° C at a rate of ° C / hr. At this time, air was flown through the firing tube up to 120 ° C, and when the temperature exceeded 120 ° C, the air was switched to nitrogen. After that, graphitization was performed under the same conditions as in Example 1 to obtain a graphitized mesocarbon microbead. At this time, the mesocarbon microbeads remained as primary particles without being fused to each other as in Example 1. The graphitized mesocarbon microbeads have an average particle size of 1
At 2.4 μm, the lattice constant Co and the crystallite size Lc obtained from the (002) diffraction line of X-ray are 6.753, respectively.
Å, 396Å, showing the same physical properties as in Example 1.

(Comparative Example 1) About 5 kg of mesocarbon microbeads obtained in the same manner as in Example 1 was mixed with 15 L of SUS.
It is filled in a baking tube made of steel and heated from room temperature (23 ° C) to a heating rate of 15
Baking was performed at a constant rate up to 1000 ° C at a rate of ° C / hr. At this time, nitrogen was flown into the firing tube up to 1000 ° C. The baked mesocarbon microbeads are firmly fused,
Obtained as a mass of about 5 kg. The calcined mesocarbon microbeads were graphitized under the same conditions as in Example 1. After crushing the graphitized mesocarbon microbeads with a crusher, the average particle size became 13.7 μm.
Also, the lattice constant C obtained from the (002) diffraction line of the X-ray
o and crystallite size Lc are 6.752Å and 38, respectively.
It was 6Å and had a crystal structure equivalent to that of the example.

[0013]

EFFECTS OF THE INVENTION According to the conventional method, self-sintering causes the mesocarbon microbeads to be firmly adhered to form a lump.
Although disintegration which requires a great deal of labor was required, the method of the present invention does not require such disintegration, and it is possible to produce calcined or graphitized mesocarbon microbeads at low cost, with good reproducibility. It can be suitably used for a conductive resin composition, a carbon material for a Li-ion secondary battery negative electrode, and the like.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitomi Hatano, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Technical Research Division (72) Inventor Takashi Oka Hara Kawasaki, Chuo-ku, Chiba 1st town Kawasaki Steel Co., Ltd. Technical Research Division

Claims (2)

[Claims] 1. Mesocarbon microbeads in air 1
Mesocarbon microbeads characterized by being calcined to 20 ° C. and then graphitized to 1000 ° C. at a temperature rising rate of 10 ° C./hr or more in an inert or non-oxidizing atmosphere, and to 3000 ° C. if necessary. Manufacturing method. 2. After firing in air, 100 up to 600 ° C.
The method for producing mesocarbon microbeads according to claim 1, wherein the mesocarbon microbeads are fired at a temperature rising rate of not more than ° C / hr.