JPH103922A - Carbon or graphite powder for lithium battery negative electrode material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mathod for obtaining carbon powder and graphite powder having a small specific surface and a nearly spherical shape, and is suitable for lithium battery negative material, with a bulk mesophase as the starting raw material, by mass production inexpensively without trouble in environmental and safeyy aspects. SOLUTION: Bulk phase pitch; wherein mesophase quantity is 80wt.% or more, and a volatilization part is 25wt.% or less; is powdered into a means particle diameter of 3-20μm, and then is oxidized light, so that an oxygen containing ratio can be 2-8wt.%. This oxidized mesophase pitch is heated up to 30-50 deg.C, and a mold obtained by molding the resultant pitch under pressure, by an isotropic pressure molding method of a molding forming method oxidized as necessary, and then heated up to 600-3000 deg.C in an inert or own atmosphere to be carbonized or graphitized, and finally crushed and grain size uniformized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a carbon or graphite powder suitable as a material for a negative electrode of a lithium battery, and more specifically to a substantially spherical and small specific surface area manufactured from bulk mesophase pitch as a starting material under specific steps and processing conditions. The present invention relates to carbon or graphite powder and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, various carbon powders or graphite powders have been used as negative electrode materials for lithium batteries. recent years,
The most frequently used are mesocarbon microbeads having excellent conductivity, being close to spherical, and having excellent filling properties.

However, these mesocarbon microbeads are disclosed in, for example, Japanese Patent Application Laid-Open Nos.
As in the invention of No. 12208, since a large amount of solvent is used to separate beads from the matrix pitch during production, there is an environmental problem at the time of production.

Therefore, the present inventors have previously proposed a method for obtaining a carbon powder and a graphite powder having excellent spheroidity and excellent electrical conductivity without using a large amount of solvent in terms of environment and cost. Hei 6-36396 filed.

This application is characterized in that a surface layer is oxidized using a bulk mesophase pitch as a starting material and then subjected to a high-temperature heat treatment. The carbon powder having a nearly spherical shape and excellent conductivity without using a large amount of solvent is used. It is highly advantageous as a method for obtaining graphite powder.

However, in view of the properties of powders, particularly fine powders having a small particle size, there is no problem in terms of environment and the like when mass production is carried out, and carbon powder and graphite powder having excellent characteristics as a lithium battery negative electrode material. There is a need for a means to obtain That is, in general, when handling fine powder, it is necessary to consider the effects of scattering of dust on workers, contamination of the surrounding environment, and the danger of dust explosion.

As a countermeasure, pneumatic transportation using a pipeline is used for transporting and moving powder, and a reactor having a high degree of sealing is selected. In particular, when the powder is subjected to heat treatment, accompanied by flammable gas generation, and the reaction atmosphere is a special non-oxidizing atmosphere, the design of the reaction / processing apparatus is complicated, and the connection with the transport system is made. If this is the case, further devising will be required, resulting in higher costs.

In each of the processing steps, the fluidity of the powder,
It is necessary to devise an engineering solution to the change in particle size due to density, agglomeration, etc., and adhesion to the inner wall due to the generated gas. Considering such properties of the fine powder, a method of firing and graphitizing the raw material powder as it is from the beginning can be considered, but a method having advantages in terms of safety and cost is desired.

[0009]

SUMMARY OF THE INVENTION In view of the above problems, the present inventors have prepared a large amount of carbon powder and graphite powder having a small specific surface area, a substantially spherical shape, and suitable as a negative electrode material for a lithium battery using a bulk mesophase as a starting material. It is intended to provide a method that can be obtained at low cost in production without any problem in terms of environment and safety.

[0010]

In order to solve the above problems, the present inventors propose that the mesophase amount is 80 watts.
After pulverizing a bulk mesophase pitch of not less than t% and a volatile content of not more than 25 wt% to an average particle size of 3 to 20 μm, it is lightly oxidized so as to have an oxygen content of 2 to 8 wt%. The molded body obtained by pressure molding by the isotropic pressure molding method or the embedding molding method is subjected to post-oxidation treatment if necessary, and then 600 ° C. in an inert or self atmosphere.
This is a method for producing carbon or graphite powder for a negative electrode material of a lithium battery, wherein the powder is carbonized and / or graphitized by heating to about 3000 ° C., and then pulverized and sized.

That is, in the present invention, the bulk mesophase of the raw material is not slightly oxidized and then baked and graphitized as it is, but a molded body is first obtained, baked, graphitized, and crushed and sized. A substantially spherical carbon powder,
It is characterized by producing graphite powder. Hereinafter, the carbon powder, the graphite powder and the method for producing the same according to the present invention will be described in detail.

In the present invention, a bulk mesophase pitch having an amount of mesophase exhibiting optical anisotropy of 80% or more and a volatile content of 25% by weight or less in a visual field under a polarizing microscope is used as a starting material.

When the mesophase amount is less than 80%, there is a problem that the capacity of the battery becomes low, and when the volatile content exceeds 25%, it expands and deforms or breaks into small pieces during firing after molding in a later step. Is not preferred. The bulk mesophase pitch is used after being pulverized to an average particle diameter of 3 to 20 μm. When the particle size is 3 μm or less, the handling property of the powder is changed and it is difficult to handle the particles. When the particle size is 20 μm or more, the particle size distribution of the powder finally produced becomes wide and the yield at the time of sizing is lowered, which is not preferable.

Next, the above bulk mesophase pitch is lightly oxidized so that the oxygen content becomes 2 to 8% by weight. This oxidation treatment is an important step for pulverizing the compact later to obtain carbon powder and graphite powder of good quality.

That is, by lightly oxidizing,
Since the bulk mesophase pitch is infusibilized, the molded body is later calcined, graphitized, and crushed relatively easily from the particle boundary (hereinafter, grain boundary) portion of the powder when pulverized. The burden on the subsequent sizing step can be reduced, and the powder obtained can be nearly spherical, and the specific surface area can be as small as 4 m ² / g or less.

If the bulk mesophase pitch is formed without light oxidation treatment, fired, and graphitized, the pitch melts once, making it impossible to maintain the grain boundaries. It is difficult, and the burden on the subsequent sizing process is large.

The obtained carbon powder and graphite powder also have sharp edges, cannot be substantially spherical, and have a large number of minute irregularities on the fractured surface, which tends to increase the specific surface area.

In this case, if the body is excessively oxidized, a molded product may not be obtained.
A mild oxidation treatment is performed so as to be ８8 Wt%. After lightly oxidizing the bulk mesophase pitch as described above, pressure molding is performed. In this case, it is necessary that the molding method is die-molding or cold isostatic pressing.

This is because if the carbon powder or graphite powder finally obtained is to be substantially spherical, if a method with strong anisotropy such as lateral extrusion is used, it is flat and poor in packing. You can only get things. The molded body obtained by pressure molding as described above is post-oxidized as it is or after being subjected to post-oxidation treatment in a circulating hot air furnace, then packed in a calcining furnace or a graphitizing furnace, and calcined and carbonized in an inert or self atmosphere. Alternatively, it is graphitized.

The packing and unloading of the furnace at the time of carbonization and graphitization can be performed not in the form of powder but in the form of a compact, so that various containers required for handling the powder become unnecessary, leading to cost reduction. Furthermore, since it is processed as a molded body, the filling weight per unit volume is 3 to 4 times or more compared to the case where the powder is processed as it is, productivity is improved, and new equipment investment accompanying mass production is suppressed. It is possible.

The carbonized and graphitized compact is pulverized and sized. In this pulverization, for coarse pulverization and medium pulverization, a pulverization method using an impact force such as a jaw crusher, a hammer mill, or a roller mill may be used. However, in the final fine pulverization step, the BET specific surface area is 8 m ² / g or less. It is preferable to use a vertical jet mill that can secure a material having a smooth surface.

The carbon powder and graphite powder obtained as described above have the following characteristics. First, the shape is substantially spherical, with edgeless, rounded corners. The ratio a / b of the major axis a to the minor axis b of the particles is 1 ≦ a / b ≦ 3.

[0023] By having such a substantially spherical shape, when used as a battery, it is possible to provide an excellent filling property, handling property, and coating property after pasting. In addition, the surface is smooth without fine irregularities, and N ₂
BET specific surface area by gas adsorption is 8 m ² / g or less.

Further, the spectrum measured by laser Raman spectroscopy shows the lamination structure of the carbon net surface at 1580 cm ^-1.
The R value represented by the intensity ratio I ₁₃₆₀ / I ₁₅₈₀ of the peak near 1360 cm ⁻¹ indicating the turbostratic structure was 0.45 or less when the excitation wavelength was 5145 °, and the crystal structure was developed. Therefore, there is an effect that a high-capacity battery can be obtained.

[0025]

According to the present invention, it is possible to easily, inexpensively, and mass-produce substantially spherical carbon powder and graphite powder. That is, instead of powdering and carbonizing as it is, it is a method of first obtaining a compact, carbonizing and graphitizing, and pulverizing it. It can be done very easily without the need for any equipment or equipment, and the heat treatment amount per unit volume is 3 to 4 times or more.
The cost advantage is very high.

The carbon powder and graphite powder obtained according to the present invention have a substantially spherical shape, a smooth surface and a small specific surface area. Therefore, when used as a negative electrode material for a lithium battery, it has excellent filling properties, handling properties, and coating properties after pasting, and has a high merit in terms of battery capacity. As described above, the present invention is industrially extremely useful.

[0027]

[Examples and Comparative Examples]

Example 1 A bulk mesophase having a mesophase amount of 95 wt% showing optical anisotropy as observed by a polarizing microscope and a softening point of 300 ° C. and a volatile matter content of 18 wt% was converted to an average particle diameter of 10 μm.
m. The oxygen content of this raw material powder is 0.7w
t%. This was put into a tumbling drying furnace, and finally heat-treated at 250 ° C. in an air atmosphere to react with oxygen to obtain an oxygen content of 3.5 wt%. Then
A porous molded body having a bulk density of 1.0 g / cm ³ was obtained by cold isostatic pressing. Further, the porous molded body is heated at 1000 ° C.
, And then packed in an Acheson-type graphitization furnace for graphitization.

After firing at 1000 ° C. and after graphitization in an Acheson-type graphitization furnace, the compact did not collapse and no handling problems occurred. The bulk density of the porous formed body after graphitization was 1.4 g / cm ³ . This is subjected to coarse pulverization, medium pulverization, fine pulverization and further sizing to obtain an average particle diameter of 9.2 μm and a maximum particle diameter of 3 μm.
A graphite powder having a particle size of ² μm, a specific surface area of 2.3 m ² / g, a / b = 2, and an R value of 0.28 in Raman spectrophotometry was obtained.

[0029]

Example 2 A bulk mesophase pitch having a mesophase amount of 80 wt% showing optical anisotropy as observed by a polarizing microscope, a softening point of 350 ° C. and a volatile content of 24 wt% was pulverized to an average particle diameter of 7 μm. This raw material powder has an oxygen content of 1.4.
wt%. This is oxidized by the method of Example 1, and finally processed at 320 ° C. to reduce the oxygen content to 5.6 watts.
t%. Next, the bulk density was 0.8
g / cm ³ , and the molded body was placed in a hot-air circulating furnace and subjected to aging (post-oxidation).
The oxygen content was 9.3 wt%.

Thereafter, the molded body was directly packed in an Acheson-type graphitization furnace without firing and subjected to a graphitization treatment. The graphitized molded product was able to be removed from the furnace without any particular collapse, and had a bulk density of 1.38 g / cm ³ . Then, the particles are pulverized and sized to obtain an average particle diameter of 6.5.
μm, maximum particle diameter 30 μm, specific surface area 3.3 m ² / g,
A graphite powder having a / b = 1.8 and a laser Raman value R value of 0.40 was obtained.

[0031]

Comparative Example 1 The bulk mesophase pitch having an average particle size of 10 μm used in Example 1 was molded without being subjected to oxidation treatment, and the molded product having a bulk density of 1.0 g / cm ³ was fired at 1000 ° C. After the treatment, it expanded and expanded, the shape of the molded article was greatly deformed, and the pitch was once melted and carbonized, so that the initial grain boundaries could not be maintained, and finishing in the initial form was impossible .

[0032]

Comparative Example 2 Mesophase amount under a polarizing microscope: 60 wt
%, A softening point of 280 ° C. and a volatile content of 38 wt% were pulverized to a mean particle diameter of 10 μm. Its oxygen content was 1.2 wt%. This was oxidized in the same manner as in Example 1 and finally processed at 230 ° C. The oxygen content was 5.2 wt%. Cold isostatic pressing according to Example 1 and bulk density 0.8 g / cm
^When the porous body of No. ³ was obtained and baked at 1000 ° C., a large number of cracks were generated due to a large amount of volatile components (a component which does not easily undergo a cross-linking reaction even when subjected to oxidation treatment with a low molecular weight component). However, the fired product was divided into many small pieces.

[0033]

Example 3 A battery was prepared using the graphite powders obtained in Examples 1 and 2 in the following manner, and the characteristics were evaluated. Originally, the carbon material was used as the negative electrode. However, in this test, since lithium metal was used for the counter electrode, Li metal was used as the negative electrode, and the carbon material was evaluated as the positive electrode. The electrode was manufactured by kneading 90 parts by weight of the prepared carbon material and 10 parts by weight of polyvinylidene fluoride with N-methyl-2-pyrrolidone by using a three-roll mill, and forming a paste. Coated on top and dried.

First, at the stage up to this point, the applicability of the paste-like substance to the copper foil was examined by visual inspection and adhesion. As a result, both the handling property and the coating property were good. After drying, it was peeled off from the copper foil, punched out in a circular shape so as to have an area of 3 cm ² , and pressure-formed together with SUS steel to obtain a positive electrode. Li metal as the counter electrode and 1 as the electrolyte
A bipolar test cell was constructed using MLiCl ₄ -EC / DEC (volume ratio 1: 1), and a charge / discharge cycle test was performed at a constant current. The measurement conditions are a voltage range of 0 to 1.5 V, a current density of 0.1 A / cm ² , and a temperature of 30 ° C. The test results are summarized in Table 1.

[Table 1]

[0035]

Comparative Example 3 A mesophase pitch having a mesophase amount of 40%, a softening point of 280 ° C., and a volatile content of 25 wt% as observed under a polarizing microscope was treated in the same manner as in Example 1 to obtain an oxygen content of 3.3 wt%. The resulting mixture was formed by cold isostatic pressing and then pulverized to an average particle size of 10.2 μm and a maximum particle size of 3.
A graphite powder having a particle size of 5 μm, a specific surface area of 4.2 m ² / g, a / b = 2 and an R value of 0.49 was obtained. A test cell was prepared according to the method of Example 3 and a charge / discharge test was performed. As a result, the capacity was 270 mAh / g, which was lower than those of Examples 1 and 2. In addition, about application property, there was no problem similarly to Examples 1 and 2.

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Claims (3)

[Claims] 1. A bulk mesophase pitch having a mesophase amount of 80% by weight or more and a volatile content of 25% by weight or less is pulverized to an average particle diameter of 3 to 20 μm, and then lightly oxidized so as to have an oxygen content of 2 to 8% by weight. Treated, the bulk mesophase pitch is heated to 30 to 50 ° C., and a molded product obtained by pressure molding by an isotropic pressure molding method or a molding method is provided.
After oxidizing as required, carbonization or graphitization by heating to 600 ° C to 3000 ° C in an inert or self-atmosphere, pulverization and sizing is performed, Manufacturing method of graphite powder. 2. The BET specific surface area by N ₂ gas adsorption is 8 m ² / g or less, the shape of the powder particles is edgeless, the corners are rounded, and the ratio a / b of the major axis a to the minor axis b of the particles is 2. 1
The carbon or graphite powder of the electrode material for a lithium ion battery according to claim 1, wherein ≤a / b≤3. Represented by 3. A leather Raman spectroscopy peak intensity ratio of around 1360 cm ^-1 which shows a peak with turbostratic structure in the vicinity of 1580 cm ^-1 indicating the layered structure of carbon net plane in the spectrum in the measurement I ₁₃₆₀ / I ₁₅₈₀ R value is excitation wavelength 51
2. The carbon or graphite powder for an electrode material of a lithium ion battery according to claim 1, which has a value of 0.45 or less when 45 ° is used.