JP6749001B2 - Graphite production method - Google Patents

Description

The present invention relates to a method for producing graphite.

Graphite is excellent in lubricity, conductivity, heat resistance, acid resistance and alkali resistance, and is useful as a structural material such as a refractory material, a heat insulating material for steelmaking, a conductive material for an electrode paste, a battery and the like. Particularly in recent years, graphite has become an important material supporting modern life as a negative electrode active material of a lithium ion secondary battery, and high crystallinity is required.

Such graphite is produced, for example, by adding an additive such as a surfactant or a plasticizer to a graphitizing raw material such as pitch or coke and heat-treating at a high temperature of 2000 to 2800° C. See Open 2014-19621).

Pitch and coke are a mixture of condensed polycyclic aromatic compounds composed of 5 to 10 aromatic rings and have high planarity. In the above conventional manufacturing method, artificial pitch having high crystallinity is obtained by using this pitch or coke as a graphitizing raw material. However, pitch and coke have high manufacturing costs, and it is difficult to provide inexpensive artificial graphite using them. On the other hand, a method using ashless coal, which can be inexpensively manufactured, as a graphitization raw material can be considered. However, ashless charcoal is a compound composed of 3 to 4 aromatic rings and is inferior in flatness to pitch and coke. Therefore, it is difficult to obtain highly crystalline graphite even if the ashless coal is directly subjected to high temperature heat treatment. As described above, it is difficult to inexpensively manufacture artificial graphite having high crystallinity by the conventional graphite manufacturing method.

JP, 2014-19621, A

The present invention has been made under the circumstances described above, and an object of the present invention is to provide a method for producing artificial graphite that has a relatively low production cost and high crystallinity.

The present inventors have found that artificial graphite with high crystallinity can be obtained by mixing graphite powder with high crystallinity into ashless coal that can be manufactured at low cost and then heat-treating it, and completed the present invention.

That is, the invention made to solve the above problems includes a step of mixing graphite powder with ashless coal and a step of heat-treating the mixture, and a surface of 002 surface of the graphite powder by an X-ray wide-angle diffraction method. The method for producing graphite is characterized in that the interval is 3.38 Å or less.

The graphite powder used in the method for producing the graphite has a crystal spacing of 002 planes of 3.38 Å or less according to the X-ray wide angle diffraction method, and has high crystallinity. In the method for producing graphite, it is considered that graphitization of ashless coal proceeds with the graphite powder having high crystallinity as a nucleus in the heat treatment step. Therefore, the crystallinity of ashless coal is improved and graphitization proceeds, and artificial graphite having high crystallinity can be obtained. In addition, since the graphite manufacturing method uses inexpensive ashless coal as the graphitization raw material, the manufacturing cost is relatively low.

The content of the graphite powder in the mixture is preferably 5% by mass or more and 50% by mass or less. By setting the content of the graphite powder within the above range, the production cost can be further reduced while maintaining the crystallinity of the produced graphite.

The particle diameter of 90% by mass of the graphite powder (D90 particle diameter) is preferably 50 μm or less. By setting the D90 particle size of the graphite powder to be the above upper limit or less, the crystallinity can be further enhanced.

The graphite powder may include crushed graphite obtained in the heat treatment step. In this way, by including the graphite powder obtained by crushing the graphite obtained in the heat treatment step in the graphite powder, the cost required for producing the graphite powder can be reduced, and thus the production cost of the graphite can be further reduced.

Here, ashless coal (Hyper-Coal, HPC) is a type of reformed coal obtained by reforming coal, and is a reformed coal obtained by removing ash and insoluble components from coal using a solvent as much as possible. Is. However, the ashless coal may contain ash as long as the fluidity and expandability of the ashless coal are not significantly impaired. Generally, coal contains 7% by mass or more and 20% by mass or less of ash, but ashless coal may contain about 2% by mass, and in some cases about 5% by mass. The "ash content" means a value measured according to JIS-M8812:2004.

In addition, “the particle diameter of 90% of the total mass” means that when all the particles are sieved by a metal net sieve specified in JIS-Z8801-1:2006, 90% by weight of all the particles are sieved. It means the value of the mesh size of the sieve that can pass through.

As described above, by using the graphite manufacturing method of the present invention, artificial graphite having relatively low manufacturing cost and high crystallinity can be manufactured.

It is a flow figure showing the manufacturing method of graphite of one embodiment of the present invention.

Hereinafter, an embodiment of the method for producing graphite according to the present invention will be described in detail.

As shown in FIG. 1, the graphite manufacturing method includes a mixing step S1 and a heat treatment step S2.

<ashless charcoal>
In the graphite manufacturing method, ashless coal is used as a graphitization raw material. This ashless coal can be obtained by various known production methods, for example, by removing the solvent from the solvent extract of coal. The manufacturing method for obtaining ashless coal by this solvent extraction includes, for example, a slurry heating step, a separation step, and an ashless coal recovery step.

(Slurry heating process)
In the slurry heating step, coal and solvent are mixed to prepare a slurry, which is heat-treated to extract a soluble component of coal (solvent-soluble component) in the solvent.

The type of raw coal for the ashless coal is not particularly limited, and various known coals such as bituminous coal, subbituminous coal, lignite, and lignite can be used. Among these, bituminous coal having a high extraction rate of ashless coal and less expensive low-grade coal (subbituminous coal or brown coal) are preferably used.

The solvent is not particularly limited as long as it dissolves coal, and for example, a bicyclic aromatic compound derived from coal is preferably used. This two-ring aromatic compound has a basic structure similar to that of a structural molecule of coal, and thus has a high affinity with coal and a relatively high extraction rate can be obtained. Examples of the bicyclic aromatic compound derived from coal include methylnaphthalene oil and naphthalene oil, which are distillation oils as by-product oils when coal is carbonized to produce coke.

As a minimum of coal concentration in the above-mentioned slurry based on anhydrous coal, 10 mass% is preferred and 13 mass% is more preferred. On the other hand, the upper limit of the coal concentration is preferably 25% by mass, more preferably 20% by mass. If the coal concentration is less than the lower limit, the elution amount of the solvent-soluble component becomes smaller than the amount of the slurry processed, and thus the ashless coal production efficiency may decrease. On the other hand, when the coal concentration exceeds the upper limit, the solvent-soluble component is likely to be saturated in the solvent, so that the elution rate of the solvent-soluble component may decrease.

The heating conditions of the slurry are not particularly limited, and may be, for example, a temperature of 350° C. or higher and 470° C. or lower, a pressure of 1 MPa or higher and 2 MPa or lower, and a heating time of 10 minutes or longer and 60 minutes or shorter.

(Separation process)
In the separation step, the slurry after the slurry heating step is separated into a liquid component containing a solvent-soluble component and a solid component containing a solvent-insoluble component. The solvent-insoluble component is an extraction residue that mainly contains ash and insoluble coal that are insoluble in the extraction solvent and further contains the extraction solvent.

The method for separating the slurry into a liquid content and a solid content is not particularly limited, and a known separation method such as a filtration method, a centrifugal separation method, or a gravity sedimentation method can be adopted. Among these, the gravity sedimentation method is preferable because it allows continuous treatment of a fluid, is low in cost, and is suitable for large-scale treatment. In the gravity settling method, a supernatant liquid that is a liquid component containing the coal component extracted in the solvent is separated in the upper part of the gravity settling tank, and the ash content and the coal component which are insoluble in the solvent as a solid component are separated in the lower part of the gravity settling tank. The containing solids concentrate is separated.

(Ashless coal recovery process)
In the ashless coal recovery step, the solvent is separated from the liquid content of the slurry obtained in the above separation step to recover ashless coal having an extremely low ash content.

The method for separating the solvent from the liquid component of the slurry is not particularly limited, and a general distillation method, an evaporation method (for example, a spray dry method) or the like can be used. By separating the solvent, ashless coal can be obtained from the liquid content. The separated and recovered solvent can be reused as a solvent in the slurry heating step.

<Mixing process>
In the mixing step S1, ashless coal is mixed with graphite powder.

The graphite powder has a crystal spacing of 002 planes (d002) of 3.38Å or less as measured by the X-ray wide-angle diffraction method, and has high crystallinity. In the method for producing graphite, by mixing the graphite powder having high crystallinity, crystallization of ashless coal is improved in the heat treatment step S2, and graphite having high crystallinity can be obtained. The reason why the crystallization of this ashless coal is improved is not always clear, but the graphitization of the ashless coal proceeds with the graphite powder having high crystallinity as a nucleus, and it easily occurs in the process of graphitizing the ashless coal. It is considered that the graphite powder having high crystallinity suppresses the occurrence of crystal strain due to expansion and contraction.

The graphite powder is not particularly limited as long as it has high crystallinity, that is, d002 is 3.38Å or less. For example, natural graphite, artificial graphite obtained by high-temperature treatment of pitch, coke, or the like, The graphite manufactured by the manufacturing method can be mentioned.

Above all, it is preferable to include, as the above-mentioned graphite powder, graphite manufactured by the method for manufacturing the graphite, that is, crushed graphite obtained in the heat treatment step described later. Since graphite produced by the graphite production method has high crystallinity, it can be used as the above graphite powder. When this graphite is used as graphite powder to produce graphite using expensive graphite such as natural graphite or artificial graphite obtained by subjecting pitch, coke, etc. to high temperature treatment, the following production is performed as described above. There is no need to use expensive graphite. Therefore, by crushing and using the graphite manufactured by the method for manufacturing the graphite as the graphite powder, the cost required for manufacturing the graphite powder can be reduced, and thus the manufacturing cost of the graphite can be further reduced.

The upper limit of the D90 particle size of the graphite powder is preferably 50 μm, more preferably 40 μm. When the D90 particle size of the graphite powder exceeds the above upper limit, the content of the graphite powder in the mixture of the ashless coal and the graphite powder is large when securing the number of nuclei necessary for promoting the graphitization of the ashless coal. It may become too large, and the effect of reducing the manufacturing cost may become insufficient. On the other hand, the lower limit of the D90 particle diameter of the graphite powder is not particularly limited, but is preferably 1 μm, more preferably 10 μm. If the D90 particle size of the graphite powder is less than the lower limit, the graphite powder does not sufficiently function as a nucleus for enhancing the crystallinity, and the effect of improving the crystallinity when graphitizing ashless coal cannot be sufficiently obtained. There is a risk.

As a minimum of content of the above-mentioned graphite powder in a mixture of ashless charcoal and graphite powder, 5 mass% is preferred, 15 mass% is more preferred, and 25 mass% is still more preferred. On the other hand, the upper limit of the content of the graphite powder is preferably 50% by mass, more preferably 40% by mass, and even more preferably 35% by mass. If the content of the graphite powder is less than the lower limit, the effect of improving the crystallinity when graphitizing the ashless coal may not be sufficiently obtained. On the contrary, when the content of the graphite powder exceeds the upper limit, the crystallinity-improving effect obtained with the increase of the graphite powder becomes small, and the cost-effectiveness may be insufficient.

A known device such as a ribbon mixer or a universal mixer can be used for mixing the ashless coal and the graphite powder.

<Heat treatment process>
In the heat treatment step S2, the mixture is heat treated. This heat treatment step S2 can be performed using a known graphitization furnace. Further, this heat treatment step S2 is preferably performed in an atmosphere of an inert gas such as nitrogen or argon.

The heat treatment step S2 includes a carbonization step and a graphitization step. Each step will be described below.

(Carbonization process)
In the carbonization step, the mixture is heated to remove volatile components, accelerate dehydration and thermal decomposition, and enhance the crystallinity of graphite obtained in the next graphitization step.

As a minimum of heating temperature in the above-mentioned carbonization process, 500 °C is preferred and 700 °C is more preferred. On the other hand, the upper limit of the heating temperature in the carbonization step is preferably 1500°C, more preferably 1000°C. If the heating temperature in the carbonization step is less than the above lower limit, the effect of improving the crystallinity of graphite may not be sufficiently obtained. On the contrary, when the heating temperature in the carbonization step exceeds the upper limit, graphitization may proceed in the carbonization step, and the crystallinity of graphite may not be sufficiently enhanced.

The heating time in the carbonization step may be, for example, 0.5 hours or more and 10 hours or less, depending on the heating temperature and the like. If the heating time is less than the lower limit, the effect of improving the crystallinity of graphite may not be sufficiently obtained. vice versa. When the heating time exceeds the upper limit, the crystallinity-improving effect obtained with an increase in heating time becomes small, and the cost effectiveness may be insufficient.

(Graphitization process)
In the graphitization step, graphite is obtained by heat-treating the mixture after the carbonization step at a high temperature.

As a minimum of heating temperature in the above-mentioned graphitization process, 2000 °C is preferred and 2500 °C is more preferred. On the other hand, the upper limit of the heating temperature in the graphitization step is preferably 3500°C, more preferably 3000°C. If the heating temperature in the graphitization step is less than the above lower limit, graphite with high crystallinity may not be obtained. On the other hand, if the heating temperature in the graphitization step exceeds the upper limit, the effect of improving the crystallinity obtained when the heating temperature rises becomes small, and the cost effectiveness may become insufficient.

The heating time in the graphitization step depends on the heating temperature and the like, but can be, for example, 0.5 hours or more and 10 hours or less. If the heating time is less than the lower limit, graphitization may be insufficient. On the other hand, if the heating time exceeds the upper limit, graphitization becomes difficult to proceed with the increase of the heating time, which may result in insufficient cost effectiveness.

<Graphite>
The graphite produced by the graphite production method has high crystallinity. As the upper limit of the interplanar spacing (d002) of the 002 plane of the above graphite by the X-ray wide angle diffraction method, 3.38Å is preferable, and 3.37Å is more preferable. When the above-mentioned d002 exceeds the above-mentioned upper limit, there is a possibility that it cannot be used as a negative electrode active material of a lithium ion secondary battery. On the other hand, the lower limit of d002 is not particularly limited, but can be set to, for example, 3.354Å which is the theoretical value of graphite. In addition, d002 can be adjusted by changing the content of the graphite powder mixed in the mixing step S1, for example.

And the peak intensity (peak intensity _{I D} of diamond-like carbon) in the range of 1300～1400Cm ^-1 measured by Raman spectrum of the graphite, the peak intensity (peak of graphitic carbon in the range of 1580～1620Cm ^-1 The upper limit of the intensity ratio I _D /I _G (R value) with respect to the intensity I _G ) is preferably 0.2, and more preferably 0.15. When the R value exceeds the upper limit, the crystallinity becomes insufficient and there is a possibility that the R value cannot be used as a negative electrode active material of a lithium ion secondary battery. On the other hand, the lower limit of the R value is not particularly limited, and the lower the better, the better, but it is generally 0.05. The smaller the R value, the higher the crystallinity. Further, the R value can be adjusted by, for example, changing the content of the graphite powder mixed in the mixing step S1.

<Advantages>
The graphite powder used in the method for producing the graphite has a crystal spacing of 002 planes of 3.38 Å or less according to the X-ray wide angle diffraction method, and has high crystallinity. In the method for producing graphite, it is considered that in the heat treatment step S2, the graphite powder having high crystallinity is used as a nucleus to promote graphitization of ashless coal. Therefore, the crystallinity of ashless coal is improved and graphitization proceeds, and artificial graphite having high crystallinity can be obtained. In addition, since the graphite manufacturing method uses inexpensive ashless coal as the graphitization raw material, the manufacturing cost is relatively low.

[Other Embodiments]
The method for producing graphite of the present invention is not limited to the above embodiment.

In the above embodiment, the case where the heat treatment step includes the carbonization step and the graphitization step has been described, but the carbonization step is not an essential step and can be omitted. Even if the carbonization step is omitted, graphite can be produced only by the graphitization step.

A crushing step may be provided before the graphitization step to crush the mixture. Graphite is used after being crushed to a predetermined size according to the application, but if crushing is performed after the graphitizing step, strain is likely to be introduced into the crystal structure. The crystallinity of can be maintained. The upper limit of the average particle size after crushing in the case of crushing depends on the use of graphite, but is preferably 100 μm, more preferably 50 μm.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

<Production of graphite>
Ashless coal was manufactured as a graphitization raw material by the method of removing the solvent from the solvent extract of coal. Two types of ashless coal were prepared: one using Indonesian sub-bituminous coal as the raw material coal, and one using Australian-produced bituminous coal.

With respect to each of the prepared two types of ashless coal, a mixture was prepared in which graphite powder was mixed in the content shown in Table 1. As the above graphite powder, commercially available natural graphite (“SP-20” manufactured by Nippon Graphite Co., Ltd.) was pulverized to have a D90 particle size of 50 μm or less. In Table 1, No. 1, and No. The content of No. 5 was 0% by mass, that is, no graphite powder was mixed.

Next, the above mixture was carbonized at 800° C. for 1 hour, and further graphitized at 2800° C. for 1 hour. 1-No. Graphite 8 was obtained.

<Evaluation>
The above No. 1-No. For graphite of No. 8, the interplanar spacing (d002) of the 002 plane by the X-ray wide-angle diffraction method and the intensity ratio I between the peak intensity I _D of diamond-like carbon and the peak intensity I _G of graphite-like carbon measured by Raman spectroscopy. _D / _IG (R value) was measured. The results are shown in Table 1.

From Table 1, No. manufactured by mixing graphite powder. 2 to No. 4 and No. 6-No. The graphite of No. 8 was No. 8 manufactured without mixing graphite powder. 1 and No. The crystallinity is higher than that of graphite of No. 5. That is, it can be seen that the crystallinity of graphite can be increased by mixing graphite powder for production.

Looking in more detail, no. No. with the graphite powder content of 30 mass% was used regardless of whether sub-bituminous coal or bituminous coal was used as the raw material coal. 3 and No. In the vicinity of 7, the effect of improving the crystallinity of graphite by mixing the graphite powder is saturated. That is, it can be seen that by setting the content of the graphite powder to 25% by mass or more and 35% by mass or less, graphite having high crystallinity can be obtained while reducing the manufacturing cost.

As described above, by using the graphite manufacturing method of the present invention, artificial graphite having relatively low manufacturing cost and high crystallinity can be manufactured. Therefore, the graphite produced by the method for producing graphite of the present invention can be suitably used as a material such as a negative electrode active material of a lithium ion secondary battery.

S1 mixing process S2 heat treatment process

Claims (3)

A step of mixing graphite powder with ashless coal,
A step of heat treating the above mixture,
Spacing of 002 surface by X-ray wide angle diffraction method of the graphite powder Ri der less 3.38 Å,
Method for producing a graphite, characterized in der Rukoto content of 50 mass% or more 5% by weight of the graphite powder in the mixture. The method for producing graphite according to claim 1, wherein a particle diameter of 90% by mass of the graphite powder is 50 μm or less. The method for producing graphite according to claim 1 or 2 , wherein the graphite powder contains crushed graphite obtained in the heat treatment step.

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