JP7496000B2 - Method for producing carbon precursor particles and carbonaceous material for secondary battery negative electrode - Google Patents

Description

The present invention relates to a method for producing carbon precursor particles and a method for producing a carbonaceous material for secondary battery negative electrodes using the carbon precursor particles.

In recent years, with growing concern about environmental issues, large secondary batteries with high energy density and excellent output characteristics are being installed in electric vehicles (xEVs) and other vehicles. Lithium-ion secondary batteries, which are non-aqueous solvent lithium secondary batteries, are used as secondary batteries for vehicles, and carbonaceous materials are used as negative electrode materials from the viewpoint of high capacity and durability.

Carbonaceous negative electrode materials are generally produced by calcining carbon precursor particles. Powdered oxidized pitch obtained by pulverizing oxidized pitch is used as the carbon precursor particles. The pitch melts when heated to form graphitizable carbon. On the other hand, when the pitch is oxidized, a crosslinked structure is formed, making it infusible to heat and a precursor of non-graphitizable carbon. The structure of the carbon precursor can be controlled by controlling the degree of oxidation of the pitch. The pitch is oxidized by heating in an oxidizing gas atmosphere. In this case, it is necessary to oxidize the pitch without melting it, and for this purpose precise temperature control is required while taking into consideration the oxidation rate, the temperature rise due to heat generated by oxidation, and the softening of the pitch.

When uniformly oxidizing pitch, the smaller the particle size, the more advantageous it is in terms of increasing the contact area between the particles and the oxidizing gas and diffusing the oxidizing gas uniformly to the inside of the particles. For this reason, it is possible to pulverize the pitch into powder form and then oxidize it. In industrial processes, a fluidized bed reactor is generally used to perform a uniform gas-solid reaction. When oxidizing powdered pitch using a fluidized bed reactor, it is necessary to uniformly fluidize the pitch in the fluidized bed. The smaller the particle size, the less the gas flow rate for forming the fluidized bed, and the more likely the gas in the bed is to drift and the flow is to become uneven. In areas where the flow is insufficient, the heat generated by oxidation is not sufficiently removed, and the temperature in the fluidized bed rises locally. As the temperature rises, the pitch melts, the particles fuse together, the particle size increases, and the flow of the particles becomes even more uneven. If these conditions progress, there is a problem that the heat removal in the fused particles becomes even more insufficient, which may lead to thermal runaway.

As a means for solving these problems, a method for preparing powdered oxidized pitch, as described in paragraph [0058] of Patent Document 1, has been known so far. In this preparation method, additives are added to petroleum- or coal-based pitch, the pitch is spheroidized to obtain a pitch compact containing the additives, and the additives are then extracted and removed from the pitch compact with a solvent to prepare spherical porous pitch. The porous pitch is then subjected to a heat oxidation (infusibility) treatment to obtain oxidized pitch, which is then pulverized to produce powdered oxidized pitch. This production method requires the preparation of spherical porous pitch from raw material pitch, and involves many complicated steps for this purpose.

Other methods of oxidizing powdered pitch to obtain oxidized pitch particles include, for example, a method using a rolling furnace disclosed in paragraph [0028] of Patent Document 2, and a method using a rotary furnace disclosed in paragraph [0049] of Patent Document 3. However, these methods of oxidizing pitch particles using rolling furnaces and rotary furnaces have the risk of fusing the particles together because the movement of the pitch particles in the furnace is slow. Furthermore, while the pitch particles are lifted along the side wall surface of the furnace as the furnace rotates, the oxidizing gas flowing through the furnace mainly flows near the center of the furnace, resulting in low contact efficiency between the pitch particles and the oxidizing gas.

Also, if the amount of pitch particles to be oxidized is small, they can be spread out on a flat plate and heated and oxidized in air to obtain powdered oxidized pitch. However, there is a limit to the size of the flat plate on which the pitch particles can be placed. Furthermore, if the layer of pitch particles is made thicker to increase the amount of processing, heat is stored in the particle layer due to the self-heating caused by the oxidation reaction, making it difficult to control the oxidation process and, depending on the conditions, there is a risk of thermal runaway and combustion.

For these reasons, a method was desired that could produce carbon precursor particles such as powdered oxidized pitch in a short period of time with fewer processing steps.

International Publication No. 2016/021736 Japanese Patent Application Laid-Open No. 10-32004 JP 2016-13948 A

The present invention aims to provide a method for producing carbon precursor particles by oxidizing organic particles, which can produce carbon precursor particles in a short period of time with fewer processing steps.

The inventors discovered that by using a reaction vessel having a stirring means equipped with a stirring blade and stirring the organic particles contained in the reaction vessel while introducing an oxidizing gas into the reaction vessel, the organic particles are oxidized in a short period of time, and carbon precursor particles can be efficiently produced, leading to the completion of the present invention. Specifically, the present invention includes the following aspects (1) to (6).

(1) A method for producing carbon precursor particles by oxidizing organic particles, comprising: using a reaction vessel having a stirring means equipped with a rotating shaft and a stirring blade attached to the rotating shaft, placing a raw material containing organic particles having an average particle size of 1 to 100 μm in the reaction vessel; introducing an oxidizing gas into the reaction vessel while stirring the raw material with the stirring means, thereby oxidizing the organic particles; and treating the raw material in the reaction vessel at a temperature of 150°C or higher during the oxidation treatment, while controlling the temperature so that the maximum temperature reached is 180 to 350°C.

(2) The method for producing carbon precursor particles described in (1) above, wherein the angle between the rotation axis of the agitator blade and the horizontal plane is greater than or equal to 60 degrees and less than or equal to 90 degrees.

(3) A method for producing carbon precursor particles described in (1) or (2), in which the inner surface of the reaction vessel and the surface of the stirring blade are separated, and the closest separation distance between the inner surface and the surface is 50 mm or less.

(4) A method for producing carbon precursor particles described in any of (1) to (3), wherein the organic matter of the organic particles is petroleum pitch or coal pitch.

(5) A method for producing carbon precursor particles described in any one of (1) to (4), wherein the carbon precursor particles are non-graphitizable carbon precursor particles.

(6) A method for producing a carbonaceous material for a secondary battery negative electrode, comprising the step of producing a carbonaceous material by heat-treating the carbon precursor particles described in any one of (1) to (5) in a non-oxidizing gas atmosphere at a temperature of 1000 to 1400°C.

According to the present invention, organic particles are oxidized, and carbon precursor particles can be produced in a short time with fewer processing steps, so that a manufacturing method for efficiently mass-producing the carbon precursor particles can be provided. The carbon precursor particles obtained by the manufacturing method of the present invention can be used as a raw material for producing carbonaceous materials for negative electrodes in nonaqueous electrolyte secondary batteries, solid state batteries, etc.

FIG. 2 is a diagram illustrating an example of a manufacturing apparatus according to the present embodiment.

The following is a detailed description of an embodiment of the present invention. The present invention is not limited to the following embodiment, and can be implemented with appropriate modifications within the scope of the object of the present invention. In this specification, the expression "X to Y" (X and Y are arbitrary numbers) means "X or more and Y or less."

1. Method for Producing Carbon Precursor Particles The present embodiment is a method for producing carbon precursor particles by oxidizing organic particles, and the features thereof include the following.
A reaction vessel having an agitation means including a rotating shaft and an agitation blade attached to the rotating shaft is used, and a raw material containing organic particles having an average particle size of 1 to 100 μm is placed in the reaction vessel.
An oxidizing gas is introduced into the reaction vessel while stirring the raw material with the stirring means, thereby oxidizing the organic particles.
In the oxidation treatment, the raw material in the reaction vessel is treated at a temperature of 150°C or higher, and the temperature is controlled so that the maximum temperature reached is 180 to 350°C.

<Organic particles>
The organic matter in the raw material organic particles can be, for example, petroleum pitch or coal pitch. The pitch can be pulverized to produce particulate pitch, which can be used as the raw material.

The raw material containing organic particles is placed in a reaction vessel and subjected to a specified oxidation treatment while being stirred. When the raw material containing organic particles is stirred and made to flow, the flow of the organic particles may be hindered by static electricity generated by friction between organic polymers. In addition to the organic particles, conductive fine particles such as carbon black may be mixed into the raw material to prevent the generation of static electricity. In this specification, the "raw material containing organic particles" may be simply referred to as "organic particles" or "raw material". The form in which the raw material is stored in the reaction vessel may also be referred to as a "particle layer".

The raw material charged and stored in the reaction vessel includes organic particles having an average particle diameter of 1 to 100 μm. The average particle diameter (μm) according to this embodiment refers to D _V50 (μm) at which the cumulative volume in the particle diameter distribution is 50%. In order to obtain carbon precursor particles, it is necessary to mix the organic particles with an oxidizing gas in the reaction vessel and diffuse oxygen into the organic particles. If the average particle diameter of the organic particles exceeds 100 μm, there is a risk that oxygen cannot be sufficiently diffused into the organic particles. The average particle diameter of the organic particles is preferably 100 μm or less, more preferably 50 μm or less, or 30 μm or less. If the average particle diameter is less than 1 μm, the organic particles are light and easily scattered by the oxidizing gas. In order to avoid the scattering, it is necessary to reduce the amount of oxidizing gas introduced, which results in a decrease in the efficiency of the oxidation treatment. The average particle diameter of the organic particles is preferably 1 μm or more, more preferably 2 μm or more, or 3 μm or more. Therefore, the average particle size of the organic particles to be oxidized is preferably 1 to 100 μm.

The organic matter constituting the organic particles is not particularly limited as long as it is a carbon precursor. Examples include petroleum-based pitch, coal-based pitch, thermoplastic resins (e.g., polyacrylonitrile, styrene/divinylbenzene copolymer, acrylonitrile/styrene/divinylbenzene copolymer), and thermosetting resins (e.g., polyimide, furan resin, phenolic resin, and cellulose resin).

A known particle manufacturing method can be used to prepare the organic particles. For example, petroleum-based or coal-based pitch can be crushed to form pitch particles having a predetermined average particle diameter D _V50 . The pulverizer used for pulverization is not particularly limited. For example, a jet mill, a rod mill, a vibrating ball mill, or a hammer mill can be used.

When organic particles are stirred and mixed, friction between the particles can generate static electricity, causing the organic particles to aggregate. In this case, conductive particles can be mixed into the organic particles. As conductive particles, carbon black or fine particles of carbonaceous materials are preferred.

<Reaction vessel>
The manufacturing method according to the present embodiment includes putting a raw material containing organic particles into a reaction vessel. In this specification, the word "put" may be written as "charged", and the raw material may be written as "charged raw material". The reaction vessel has a volume necessary for storing the raw material. The shape of the reaction vessel may be cylindrical, conical, spherical, or the like. Since the raw material in the vessel is caused to flow by the rotating stirring means, a structure having a curved surface on the inner surface of the vessel is preferable from the viewpoint of increasing the fluidity of the raw material and the stirring action of the stirring means. For example, in the case of a cylindrical or conical reaction vessel, the inner surface is composed of a curved side surface and a flat bottom surface. In the case of a spherical reaction vessel, it is composed of a curved inner surface. Since the raw material particles flow along the curved surface, retention of the raw material particles is suppressed.

When viewing a cross section of a reaction vessel, it is preferable that the shape of the inner surface in the cross section is a perfect circle. In this embodiment, the "cross section" of a reaction vessel means, in the case of a vessel having a bottom surface, a cross section at a position parallel to the bottom surface. In the case of a spherical vessel, the position of the cross section is not limited.

An example of a manufacturing apparatus using the manufacturing method according to this embodiment is shown in Figure 1. The manufacturing apparatus in Figure 1 includes a reaction vessel 1, an agitator 2, a chopper 3, a cooling water supply 4, a bag filter 5, and a gas exhaust pipe 6.

<Means for supplying and discharging the material to be treated into the reaction vessel>
The reaction vessel 1 is provided with a top lid 105, a discharge port 106 for the material to be treated, an observation window 107, and a gas inlet 108. The raw material 10 is supplied to the reaction vessel 1 by opening the top lid 105, and is stored in the reaction vessel 1. After the raw material 10 is subjected to a predetermined oxidation treatment, the material to be treated is discharged through the discharge port 106. When discharging the material to be treated, for example, the partition (not shown) installed between the side wall 103 of the reaction vessel and the discharge port 106 is opened, and then the stirring blade 202 is slowly rotated to discharge the material to be treated. The material to be treated that has adhered to the inner surface of the reaction vessel 1 can be collected by opening the top lid 105. The state of the raw material 10 in the reaction vessel 1 can be confirmed through the observation window 107 provided in the top lid 105.

<Stirring means>
The agitator 2 has a rotating shaft 201, an agitating blade 202 attached to the rotating shaft 201, and a motor 203 for driving the rotating shaft 201, and is a means for agitating and mixing the raw material 10 charged in the reaction vessel 1. Agitation flow 17 is formed by the rotation of the agitating blade 202, causing the raw material 10 to flow.

The reaction vessel has a stirring means therein, which includes a rotating shaft and a stirring blade attached to the rotating shaft. As shown in FIG. 1, the stirring blade 202 extends around the rotating shaft. In this specification, the outermost part of the stirring blade 202 is called the tip 204, and the part extending from the center of rotation to the tip that faces the bottom surface 102 of the reaction vessel is called the lower end 205. In order to prevent the stirring blade 202 from contacting the inner surface of the reaction vessel 1, it is necessary to separate the surface of the stirring blade 202 from the side surface 101 and bottom surface 102, which are the inner surface of the reaction vessel. Specifically, it is necessary to separate the surface of the tip 204 of the stirring blade from the side surface 101 of the reaction vessel, and the surface of the lower end 205 of the stirring blade from the bottom surface 102 of the reaction vessel by leaving a certain distance between them. On the other hand, if the distance is too large, the action of the stirring blade does not reach the raw material near the inner surface of the reaction vessel sufficiently, and the flow state of the raw material is insufficient. As a result, regions in which raw material particles remain in the reaction vessel are generated, which may result in partial fusion of particles without disintegrating particle agglomerates. When particles fuse to each other to form large fusion products, contact between each particle and the oxidizing gas is hindered, and carbon precursor particles of good quality cannot be obtained. From this perspective, the closest separation distance between the inner surface of the reaction vessel and the surface of the stirring blade is preferably set to 50 mm or less, and may be 30 mm or less.

The above-mentioned "inner surface" of the reaction vessel includes the side surface and bottom surface of the reaction vessel. In an embodiment in which the reaction vessel has a bottom surface, such as a cylindrical or conical shape, it is preferable to set the distance between the side surface or bottom surface of the reaction vessel and the end of the stirring blade within the above-mentioned range. In an embodiment in which the entire inner surface is a curved surface, such as a spherical vessel, it is preferable to set the distance between the end of the stirring blade and the inner surface of the vessel within the above-mentioned range.

The agitator according to this embodiment includes a rotating shaft and an agitator blade attached to the rotating shaft. The shape of the agitator blade is not particularly limited. Agitator blades of existing shapes can be used. For example, paddle blades with blades attached perpendicular to the rotating shaft, disk turbine blades, curved blades, Pfaudle blades, etc., or inclined paddle blades with an inclination angle on the blades or propeller blades, etc. can be selected. The rotating shaft is driven by a driving means such as a motor, and the agitator blades rotate, thereby agitating the raw materials charged in the reaction vessel. In addition, since organic particles of the raw materials tend to settle on the bottom surface of the reaction vessel, in order to sufficiently agitate the settled particle layer, it is preferable that the lower end of the agitator blade is parallel to the bottom surface as shown in FIG. 1.

Regarding the positioning of the agitator blades, it is preferable that when the reaction vessel is placed on a horizontal surface, the center of the height of the agitator blades is located below half the height of the vessel. Because the agitator blades rotate in the lower region of the reaction vessel, clumps of particles that have settled to the lower region can be efficiently broken down.

It is preferable that the rotating shaft of the agitator is shaped to pass through the center of the cross section of the reaction vessel and extend perpendicularly to the cross section. With such a shape, the agitator blade rotates at a certain distance from the inner surface of the reaction vessel, so that the raw material can be agitated uniformly throughout. As a result, a good mixing state in which the individual particles flow is maintained, so that the formation of aggregated lumps of particles in the particle layer is suppressed. Even if the particles are fused together or aggregated lumps of particles are formed, they are immediately broken down, so that thermal runaway caused by a chain reaction of particle fusion can be suppressed. In addition, since the flow state of the particles is maintained, the oxidizing gas comes into contact with the particles appropriately, and the oxidation process can be efficiently carried out.

In a configuration in which the reaction vessel is installed so that its bottom surface is parallel to the horizontal plane, the rotation axis extending perpendicular to the cross section of the reaction vessel is also arranged perpendicular to the horizontal plane, i.e., vertically. Therefore, the angle between the rotation axis and the horizontal plane is equivalent to 90 degrees. In this case, the direction of gravity on the raw material is approximately the same for the entire raw material during rotation, so the raw material can be made to flow homogeneously. In addition, clumps of particles that are agglomerated together are heavier than particles that are not agglomerated, so they settle during stirring and come into contact with the stirring blades located below. This allows the particle clumps to be efficiently broken down.

In addition, this embodiment is not limited to the form in which the reaction vessel is placed on a horizontal plane. Even if the reaction vessel is tilted so that the angle between the rotation axis of the agitator and the horizontal plane is less than 90 degrees, the rotation axis of the agitator means is held perpendicular to the cross section of the reaction vessel, so the agitator rotates while maintaining a certain distance between the inner surface of the reaction vessel. Therefore, the agitation action required to homogeneously flow the entire raw material is obtained. In addition, since the direction of gravity on the raw material does not change significantly during rotation, the lumps of particles settle downward and are broken down by the agitator, and good agitation efficiency is maintained. On the other hand, if the angle at which the reaction vessel is tilted is too large, the proportion of the agitator protruding outside the particle layer of the raw material increases, and the proportion of the raw material that comes into contact with the agitator decreases, resulting in a decrease in agitation efficiency. From the above, it is preferable that the angle between the rotation axis of the agitator and the horizontal plane is 60 degrees or more and 90 degrees or less. The lower limit of the angle may be 70 degrees or more or 80 degrees or more.

In addition, as a means to supplement the stirring means using the stirring blades, a chopper 3 with multiple chopper blades attached to a rotating shaft may be attached to the side of the reactor. The chopper 3 is a stirring means having a structure in which multiple chopper blades 302 are attached perpendicular to the rotating shaft 301. The rotating shaft 301 and chopper blades 302 are rotated by a motor 303, which is a driving means. The rotation of the chopper blades 302 has the effect of stirring the raw material 10 and breaking down clumps of particles, so it can be attached to supplement the stirring means 2 using the stirring blades 202. The chopper is effective in breaking down agglomerated particles.

<Oxidation Treatment Means>
The manufacturing method according to the present embodiment includes introducing an oxidizing gas into the reaction vessel while stirring the raw material with a stirring means, and performing an oxidation treatment of the organic particles. This oxidation treatment is a treatment for infusible the organic particles to obtain carbon precursor particles. By oxidizing the organic particles, carbon precursor particles having a high softening temperature and melting point can be obtained. When using such carbon precursor particles to produce a carbonaceous material by subsequent heat treatment, the softening and melting of the particles are suppressed, so that a carbonaceous material with a controlled structure can be obtained. In this infusible treatment, oxygen atoms taken into the organic material by the oxidation reaction act to crosslink the molecules of the organic material. Therefore, the oxygen content of the carbon precursor particles that have been subjected to the oxidation treatment can be measured to evaluate the degree of crosslinking. In this specification, this oxidation treatment is sometimes referred to as "infusible treatment".

The oxidizing gas is supplied to the raw material in the reaction vessel through a gas inlet provided in the reaction vessel. As shown in FIG. 1, in order to efficiently contact the oxidizing gas 11 with the raw material 10, the gas inlet 108 is preferably provided on the bottom wall 104 of the reaction vessel 1. The gas inlet 108 may be provided at multiple locations, or a gas dispersion device (not shown) such as a gas dispersion plate or a dispersion tube (sparger) may be provided on the bottom surface 102 of the reaction vessel, and the oxidizing gas 11 may be supplied to the raw material through the gas dispersion device. When the gas dispersion device is provided, it is necessary to separate the gas dispersion device from the surface of the lower end 205 of the stirring blade so that they do not come into contact with each other. Depending on the shape and structure of the reaction vessel 1, the gas inlet 108 may be provided on the side wall 103 of the reaction vessel. The organic particles of the raw material are contacted with the oxidizing gas while being stirred, so that each particle is uniformly oxidized.

When the oxidation process is to be completed, the introduction of the oxidizing gas 11 is stopped, and a non-oxidizing gas 12 such as nitrogen gas is introduced from the gas inlet 108. A cooled heating medium is introduced from the heating medium supply port 109 to cool the manufacturing apparatus including the reaction vessel and the workpiece.

The type of oxidizing gas is not particularly limited as long as it is a gas containing oxygen. For example, air can be used. Furthermore, oxygen gas can be diluted with air, an inert gas (e.g., nitrogen gas, a rare gas), etc.

The oxidation reaction in the oxidation treatment according to this embodiment tends to be rate-limited by the amount of oxygen gas introduced in the oxidizing gas. The amount of oxygen gas introduced is expressed as the product of the oxygen gas concentration in the oxidizing gas and the amount of oxidizing gas introduced. If the oxygen gas concentration is low, the amount of oxygen gas introduced into the raw material reaction system per unit time decreases, and the treatment time becomes longer, which is not preferable. Also, if the oxygen gas concentration is low, the heat required to maintain the chain oxidation reaction cannot be obtained, so it becomes necessary to heat the raw material from the outside as an auxiliary. Therefore, the oxygen gas concentration in the oxidizing gas is preferably 10% by volume or more, 18% by volume or more, or 25% by volume or more. On the other hand, if the oxygen gas concentration is too high, the oxidation reaction may proceed partially in the raw material, causing combustion or a non-uniform reaction, which is not preferable. Therefore, the oxygen gas concentration is preferably 90% by volume or less, 80% by volume or less, or 70% by volume or less.

The amount of oxidizing gas introduced can be appropriately selected depending on the amount of oxygen gas introduced, the amount of raw material charged, the time for oxidation treatment, etc. If the amount of oxygen gas introduced is too small, the treatment time increases and the treatment efficiency decreases. On the other hand, if the amount of oxidizing gas introduced is too large, the proportion of organic particles in the raw material that are scattered and captured in the bag filter increases, and the recovery rate of oxidized carbon precursor particles decreases. For example, the amount of oxidizing gas introduced per 1 kg of organic particles in the raw material can be adjusted in the range of 15 to 500 NL/kg/h.

<Temperature control>
As described above, the organic particles of the raw material stored in the reaction vessel are oxidized by the introduced oxidizing gas. In order to efficiently proceed with the oxidation reaction, it is preferable to treat the organic particles of the raw material in a high temperature range above a certain level. Therefore, it is necessary to heat the raw material to a predetermined temperature range. After the raw material reaches the predetermined temperature range, the oxidation reaction proceeds with the self-heating of the raw material, so there is no need to apply auxiliary heating from the outside except when the temperature falls below the predetermined temperature.

On the other hand, the oxidation reaction generates heat and accumulates it in the raw material particle layer, causing the temperature in the particle layer to rise. If the temperature is excessively high, the oxidation reaction will proceed vigorously, which may lead to thermal runaway, causing further oxidation heat generation and a rise in temperature.

In addition, the melting point of organic particles during oxidation treatment increases due to the oxidation reaction, and they can proceed to become infusible without softening or melting even in high-temperature oxidation reactions. However, if organic particles are exposed to high temperatures when the oxidation reaction is insufficient, some of the particles may melt and fuse together. Fused particles have a large particle size, so the oxygen of the oxidizing gas that comes into contact with them does not diffuse sufficiently to the inside of the particles, and infusibility by oxidation does not occur sufficiently, and the softening temperature and melting point of the particles are at low levels. Therefore, when the particles are fired in the firing process for producing a carbonaceous material, softening and melting occur, making it difficult to form a homogeneous carbonaceous material.

From the above viewpoints, in the manufacturing method according to this embodiment, it is preferable that in the oxidation treatment, the raw materials stored in the reaction vessel are treated at a temperature of 150°C or higher, and the temperature is controlled so that the maximum temperature reached is 180 to 350°C. The raw materials during the oxidation treatment are heated to a temperature range of 150°C or higher and oxidized. The above "maximum temperature reached" refers to the highest of the temperatures to which the raw materials are heated. If the raw materials during the oxidation treatment are treated at less than 150°C or the maximum temperature reached is less than 180°C, the oxidation reaction takes time and the treatment efficiency decreases. Depending on the treatment time, the particles are not sufficiently oxidized, and carbon precursor particles that are not sufficiently infusible are formed.

On the other hand, if the temperature of the raw material exceeds 350°C, the oxidation consumption becomes excessive, and the yield of the oxidation process decreases. Furthermore, if the oxidation of the particles progresses too rapidly, there is a risk of combustion. Therefore, it is economically disadvantageous and there is a risk that it may become difficult to carry out the oxidation process safely.

The raw materials can be heated from the inside of the reaction vessel or by heating the gas fed into the system. In addition, heat generated by the oxidation of the raw materials contributes to an increase in the temperature of the raw materials. Therefore, when heating the raw materials from outside the reaction vessel, it is preferable to maintain the raw materials within a specified temperature range while adjusting both the external heating and the heat generated by the oxidation of the raw materials.

In order to prevent the raw materials from overheating and to control the temperature, it is preferable to cool the system while the oxidation reaction of the raw materials is proceeding. One cooling method is, for example, spraying water on the raw materials and cooling them with the latent heat of vaporization of the water. After the oxidation process is completed, a method is used in which a non-oxidizing gas is introduced instead of the oxidizing gas to cool the raw materials. Nitrogen gas or an inert gas can be used as the non-oxidizing gas.

An example of temperature control in oxidation treatment is described below. After the raw materials are loaded into the reaction vessel, oxidizing gas is introduced while stirring. The raw materials in the reaction vessel are heated by external heating and oxidation heat. During this process, the temperature due to the external heating (hereinafter sometimes referred to as the "external temperature") and the temperature of the raw materials (hereinafter sometimes referred to as the "internal temperature") are monitored. The internal temperature can be made higher than the external temperature because oxidation heat is added to the external heating.

First, the external temperature is raised to a predetermined temperature (e.g., 160°C), and then the external temperature is maintained at the predetermined temperature. The internal temperature rises and becomes constant at a temperature lower than the external temperature. Next, the external temperature is further raised (e.g., by 10°C) and then maintained. This temperature maintenance operation is repeated during the period in which the internal temperature is maintained at a temperature lower than the external temperature. When the oxidation reaction of the raw material progresses, the oxidation heat generation increases, and the internal temperature exceeds the external temperature, the internal temperature is maintained so that the temperature difference between the external temperature and the internal temperature does not exceed a certain range (e.g., 10°C) while cooling the raw material by spraying water. After the oxidation heat generation at the maintained temperature decreases, the external temperature is again raised to a further predetermined temperature (e.g., 10°C). Then, similar to the above operation, the internal temperature is maintained while cooling the raw material so that the temperature difference does not exceed a certain range. This temperature maintenance operation is repeated, and the temperature is maintained until the oxidation heat generation ends at a predetermined maximum reached temperature (e.g., 240°C). The internal temperature is kept constant without the need for water spraying for cooling, and the end of the oxidation heat generation can be confirmed when the internal temperature becomes lower than the external temperature. The external temperature may be raised stepwise as described above, or may be raised continuously. The oxidation heat generation can be known from the temperature difference between the external and internal temperatures.

After the oxidation heat generation at the maximum temperature is completed, external heating is stopped and the introduction of the oxidizing gas is stopped. Next, a non-oxidizing gas such as nitrogen gas is introduced into the reaction vessel, and the raw materials are allowed to cool, then discharged from the reaction vessel and the carbon precursor particles are recovered.

The reaction time is not particularly limited. It can be set appropriately depending on the amount of raw material to be treated. The oxidation reaction is continued until the oxidation heat ends by maintaining the temperature at a predetermined maximum temperature, and the degree of oxidation of the organic particles can be controlled by controlling the maximum temperature.

<Heating means of the manufacturing equipment>
The example of the manufacturing apparatus shown in FIG. 1 further includes a supply port 109 and a discharge port 111 for a heating medium. The heating method using the heating medium 15 (hereinafter also referred to as "heat medium") is an example of external heating in which the raw material 10 is heated from the side wall 103 and the bottom wall 104 of the reaction vessel 1. A heat medium flow passage 110 is installed facing the side wall 103 and the bottom wall 104 of the reaction vessel 1, and the heat medium 15 at a predetermined temperature is supplied from the heat medium supply port 109 of the flow passage 110 and discharged from the heat medium discharge port 111. The raw material 10 in the reaction vessel is heated by heat transfer from the heat medium 15 through the side wall 103 and the bottom wall 104. The heat medium flow passage 110 may be attached to only one of the side wall 103 or the bottom wall 104. The heating medium is not particularly limited as long as it is a heat medium that can be used at the temperature of external heating. Mineral oil-based, synthetic, inorganic, and other heat mediums can be used. From the viewpoint of the applicable temperature range, a synthetic heat transfer medium is preferably used. The temperature of the raw material can be controlled by the supply amount and supply speed of the heat transfer medium.

As shown in FIG. 1, a first temperature measuring device 8 is installed in the pipe leading to the heat medium outlet 111 to measure the external temperature caused by the heat medium 15. A second temperature measuring device 7 is inserted into the raw material 10 through the side wall 103 of the reaction vessel 1 to measure the internal temperature of the raw material.

.
<Method of cooling raw materials>
The manufacturing apparatus is equipped with a cooling water supplying machine 4. The spray nozzle 401 is disposed near the upper part in the reaction vessel 1. In order to prevent the raw material 10 in the reaction vessel 1 from being overheated, the cooling water 13 stored in a storage vessel 404 installed outside the reaction vessel is supplied to the spray nozzle 401 by a pipe 402 and sprayed onto the raw material 10 through the spray nozzle 401. As an example of a control method for supplying the cooling water, as shown in FIG. 1, while monitoring the fluctuation of the cooling water 13 in the storage vessel 404 with a weight meter 403, the pressurizing air 406 adjusted by a pressure gauge 405 is introduced into the storage vessel 404, and the cooling water surface is pressed to supply the required amount of the cooling water 13 to the spray nozzle 401.

<Means for recovering scattered raw materials and means for measuring oxygen concentration in exhaust gas>
The manufacturing apparatus is provided with a bag filter 5, which is installed in the middle of a gas exhaust pipe 6 that exhausts the gas in the reaction vessel 1. Further, an inlet pipe for backwash air 14 is installed downstream of the bag filter 5, and an oxygen concentration meter 9 for measuring the oxygen concentration of the exhaust gas 16 is installed. The powder scattered upward from the particle layer of the raw material 10 during stirring is collected by the bag filter 5. By flowing the backwash air 14 into the bag filter 5, the collected powder can be returned to the reaction vessel 1 and reused. In addition, the oxygen concentration of the exhaust gas 16 is measured by the oxygen concentration meter 9. The oxygen concentration corresponds to the residual oxygen concentration consumed in the oxidation reaction. By detecting the residual oxygen concentration, the amount of the oxidation reaction can be known. If the residual oxygen concentration becomes high when the internal temperature is high, it is not preferable because there is a risk of a dust explosion. Specifically, the oxygen concentration in the exhaust gas at an internal temperature of 200° C. or higher is preferably 10% by volume or less, more preferably 5% by volume or less, and even more preferably 3% by volume or less.

<Supporting means for reaction vessel>
The reaction vessel 1 may be structured to be placed on a support stand 112. By adopting this structure, a space for installing the stirring means 2 below the reaction vessel 1 is formed.

<Carbon precursor particles>
The carbon precursor particles obtained by the manufacturing method according to the present embodiment are preferably non-graphitizable carbon precursor particles. The non-graphitizable carbon precursor particles are specified by the fact that the true density of the carbonaceous material obtained when the non-graphitizable carbon precursor particles are heat-treated in a nitrogen gas atmosphere at 1100°C for 1 hour is 1.70 g/cm3 or ^less . The non-graphitizable carbon precursor provides a non-graphitizable carbonaceous material by heat treatment, and provides a carbonaceous material for secondary battery negative electrodes having a high discharge capacity. Note that the "true density of the carbonaceous material" described in this specification means the true density determined by the butanol method.

The oxygen content of the carbon precursor particles obtained by the manufacturing method according to this embodiment is not particularly limited as long as the effects of the present invention can be obtained. The oxidation treatment is to make the organic particles infusible to obtain the carbon precursor particles. If the oxygen content is less than 3% by weight, the infusibility treatment is insufficient, and when the carbon precursor particles are heat-treated to produce a carbonaceous material, the particles may soften or fuse. As a result, the true density of the carbonaceous material may fluctuate, leading to a decrease in quality. Therefore, the oxygen content is preferably 3% by weight or more, more preferably 7% by weight or more. If the oxygen content is 7% by weight or more, a more uniform non-graphitizable carbonaceous material can be formed, and decomposition during carbonization is suppressed by oxygen crosslinking, contributing to an improvement in the carbonization yield.

<Carbonaceous material for negative electrode>
The carbon precursor particles obtained by the manufacturing method according to this embodiment are preferably applied to a manufacturing method of a carbonaceous material for a secondary battery negative electrode, which includes a step of main-calcining at a temperature of 1000 to 1400 ° C. in a non-oxidizing gas atmosphere, and the main-calcining temperature is more preferably 1050 to 1350 ° C., and even more preferably 1100 to 1300 ° C. The heat treatment step includes a calcination step. The calcination step includes (a) main-calcining the carbon precursor particles in a non-oxidizing gas atmosphere at 1000 to 1400 ° C., or (b) pre-calcining the carbon precursor particles in a non-oxidizing gas atmosphere at 400 to less than 1000 ° C., and then main-calcining in a non-oxidizing gas atmosphere at 1000 to 1400 ° C. In the calcination step for obtaining the carbonaceous material for a secondary battery negative electrode according to this embodiment, pre-calcination may be performed according to the operation (b) above, and then main calcination may be performed, or main calcination may be performed according to the operation (a) above without performing pre-calcination. The method may further include a step of performing heat treatment in a non-oxidizing gas atmosphere containing a hydrocarbon gas after the main sintering and coating with pyrolytic carbon.

In the method for producing a carbonaceous material for a secondary battery negative electrode, an alkali metal compound may be impregnated to the carbon precursor particles before the step of calcining the carbon precursor particles. By impregnating the alkali metal compound, a carbonaceous material exhibiting a high charge/discharge capacity is obtained. The alkali metal element is preferably sodium. The alkali metal element may be impregnated to the carbonaceous precursor in a metallic state. It may be impregnated as a compound containing an alkali metal element, such as a hydroxide, carbonate, hydrogen carbonate, or a halogen compound. The alkali metal compound is not limited. Hydroxides or carbonates are preferred because they have high permeability and can be uniformly impregnated into the carbonaceous precursor, and hydroxides are particularly preferred.

The upper limit of the true density of the carbonaceous material obtained when the carbon precursor particles according to this embodiment are heat-treated in a nitrogen gas atmosphere at 1100° C. for 1 hour is preferably 1.70 g/cm ³ or less, and may be 1.65 g/cm ³ or less, or 1.60 g/cm ³ or less. The lower limit of the true density of the carbonaceous material obtained when the carbon precursor particles are heat-treated in a nitrogen gas atmosphere at 1100° C. for 1 hour is preferably 1.40 g/cm ³ or more, and may be 1.45 g/cm ³ or more, or 1.50 g/cm ³ or more.

The present invention will be described in more detail below with reference to the following examples. The present invention is not limited to these examples.

The methods for measuring the average particle size and softening point of the organic particles used in this example are described below. The physical properties of the carbon precursor particles obtained by this manufacturing method were evaluated in terms of the presence or absence of fusion, the oxygen content, and the true density by the butanol method. The methods for measuring these are described below. The presence or absence of fusion in the carbon precursor particles was observed visually.

<Average particle size>
Three drops of a dispersant (a cationic surfactant "SN Wet 366" manufactured by San Nopco Ltd.) were added to approximately 0.1 g of the sample, and the dispersant was allowed to penetrate into the sample. Next, 30 mL of pure water was added, and the sample was dispersed in an ultrasonic cleaner for approximately 2 minutes. The particle size distribution in the particle size range of 0.02 to 2000 μm was then determined using a particle size distribution measuring device ("Microtrac MT3300II" manufactured by Microtrac Bell Co., Ltd.). Based on the obtained particle size distribution, the average particle size D _V50 (μm) at which the cumulative volume reached 50% was obtained.

<Softening point>
1.0 g of the sample that had passed through a sieve with 150 μm openings was placed in a flow tester ("CFT-500EX" manufactured by Shimadzu Corporation), and the softening point (°C) was measured under the conditions of a temperature rise rate of 6.0°C/min, a sample load pressure of 0.98 MPa, a die hole diameter of 1.0 mm, and a die length of 1.0 mm.

<Oxygen content>
The measurement was performed in accordance with the method specified in JIS M 8819. The mass percentages of carbon, hydrogen, and nitrogen in the sample obtained by elemental analysis using a CHN analyzer were subtracted from 100 to obtain the oxygen content (weight % (wt %)).

<True density by butanol method>
The true density (g/cm ³ ) was measured using butanol in accordance with the method defined in Japanese Industrial Standard JIS R7222:2017.

Example 1
The oxidation treatment for infusibility was carried out using the production apparatus shown in Fig. 1 as a reaction vessel. The production apparatus is equipped with a cylindrical reaction vessel having a diameter of 600 mm and an internal volume of 100 L. Furthermore, as described above, it is equipped with a stirring blade and a chopper, and is also equipped with an external heating means.

First, 30 kg of petroleum pitch with a softening point of 205°C and an average particle size of 20 μm was placed in the reaction vessel of the manufacturing equipment, and then the stirring blade was rotated at 200 rpm and the chopper at 1500 rpm, while air was introduced into the raw material as an oxidizing gas at a flow rate of 2000 NL/h (67 NL/kg/h) from the gas inlet at the bottom of the reaction vessel. The unit of the flow rate "NL/h" means normal liters per hour, and the unit "NL/kg/h" in parentheses means the flow rate per 1 kg of raw material. The scattered powder was collected with a bag filter and returned to the raw material. The external temperature was raised to 160°C, and the raw material was cooled by spraying water on it so that the temperature difference between the external temperature and the internal temperature did not exceed 10°C due to oxidation heat generation, while the temperature of the raw material was maintained. After the oxidation heat generation at the maintained temperature stopped, the external temperature was raised by 10°C, and the temperature maintenance operation of the raw material was repeated in the same manner as the above-mentioned maintenance operation. The temperature was then maintained until it reached the maximum temperature of 240° C. and the heat generated by oxidation was terminated. Thereafter, the introduction of air was stopped and external heating was stopped.

Nitrogen gas was then introduced into the raw material, which was allowed to cool, and the carbon precursor particles were then recovered. The time from when the internal temperature exceeded 150°C to when the oxidation heat generation at the maximum temperature of 240°C ended (hereinafter referred to as the "reaction time") was 14 hours. The residual oxygen concentration in the exhaust gas was 2.0 volume% (vol%) or less. No fusion of the obtained carbon precursor particles was observed. There was no softening or melting due to the heat treatment at 1100°C in a nitrogen atmosphere. The physical properties of the obtained carbon precursor particles are shown in Table 1.

Example 2
Carbon precursor particles were obtained in the same manner as in Example 1, except that the maximum temperature was 200° C. The reaction time was 5 hours. No fusion of the obtained carbon precursor particles was observed, and the particles did not soften or melt due to the subsequent heat treatment. The physical properties of the obtained carbon precursor particles are shown in Table 1.

Example 3
Carbon precursor particles were obtained in the same manner as in Example 1, except that the maximum temperature was 260° C. The reaction time was 18 hours. No fusion of the obtained carbon precursor particles was observed, and the particles did not soften or melt due to the subsequent heat treatment. The physical properties of the obtained carbon precursor particles are shown in Table 1.

Example 4
Carbon precursor particles were obtained in the same manner as in Example 1, except that a mixed gas having an oxygen content of 30 volume % (vol%), which was a mixture of air and oxygen gas, was used as the oxidizing gas, and the maximum temperature reached was 250°C. The reaction time was 13 hours. No fusion of the obtained carbon precursor particles was observed, and the particles did not soften or melt due to the subsequent heat treatment. The physical properties of the obtained carbon precursor particles are shown in Table 1.

Example 5
Carbon precursor particles were obtained in the same manner as in Example 1, except that the average particle size of the petroleum pitch was 40 μm, the flow rate of the oxidizing gas into the reaction system was 100 NL/kg/h, and the maximum temperature reached was 260° C. The reaction time was 15 hours. No fusion of the obtained carbon precursor particles was observed, and the subsequent heat treatment did not cause softening or melting. The physical properties of the obtained carbon precursor particles are shown in Table 1.

Example 6
Carbon precursor particles were obtained in the same manner as in Example 1, except that coal pitch with an average particle size of 23 μm was used instead of petroleum pitch, the flow rate of the oxidizing gas into the reaction system was 67 NL/kg/h, and the maximum temperature reached was 260° C. The reaction time was 15 hours. No fusion of the obtained carbon precursor particles was observed, and the subsequent heat treatment did not cause softening or melting. The physical properties of the obtained carbon precursor particles are shown in Table 1.

(Example 7)
In this example, particles of an AN/St/DVB copolymer were used as the organic particles. First, 45% by weight of acrylonitrile (AN), 41% by weight of styrene (St), and 13% by weight of divinylbenzene (DVB) were mixed, and 2,2'-azobis-2,4-dimethylvaleronitrile was further added to prepare a monomer mixture. This monomer mixture was added to an aqueous dispersion medium and dispersed by a homogenizer to form minute droplets of the monomer mixture. Next, polymerization was performed in a polymerization tank equipped with a stirrer to obtain a spherical AN/St/DVB copolymer having an average particle size (D _V50 ) of 17 μm.

In this example, carbon precursor particles were produced using a cylindrical vertical tubular furnace (diameter 100 mm) equipped with a distributor as a reaction vessel. 700 g of the above-mentioned AN/St/DVB copolymer obtained was charged into the vertical tubular furnace (diameter 100 mm), and then a stirring blade attached to a rotating shaft passing through the center of the cross section of the vertical tubular furnace was placed on the copolymer layer. Then, air was introduced into the copolymer layer from the bottom of the vertical tubular furnace at a flow rate of 180 NL/h (257 NL/kg/h), and the stirring blade was rotated at 50 to 100 rpm.

Using the same procedure as in Example 1, the temperature of the copolymer layer was raised while maintaining it, and maintained at 280°C for 1 hour. Thereafter, the introduction of air was stopped, and external heating was stopped. Nitrogen gas was then introduced into the copolymer layer, and the layer was allowed to cool, and the oxidized carbon precursor particles were recovered. No fusion of the obtained carbon precursor particles was observed, and the subsequent heat treatment did not result in softening or melting. The physical properties of the obtained carbon precursor particles are shown in Table 1.

(Comparative Example 1)
Carbon precursor particles were prepared in the same manner as in Example 1, except that stirring was not performed. However, in this comparative example, due to the occurrence of the channeling phenomenon, partial heat generation occurred in the petroleum pitch during heating, and fusion and melting occurred in the pitch particles. This made it difficult to continue the experiment. The channeling phenomenon refers to a phenomenon in which the flow path of gas flowing inside the particle layer is restricted to a local area, resulting in the uniform flow of the particle layer being hindered.

(Comparative Example 2)
Carbon precursor particles were obtained in the same manner as in Example 1, except that the maximum temperature reached was 160° C. The reaction time was 3 hours. No fusion of the obtained carbon precursor particles was observed. However, the particles were softened by the subsequent heat treatment, and therefore a carbonaceous material having the required physical properties could not be obtained. The physical properties of the obtained carbon precursor particles are shown in Table 1.

(Comparative Example 3)
A carbon precursor was obtained in the same manner as in Example 5, except that the average particle size of the petroleum pitch was 150 μm. No fusion of the obtained carbon precursor particles was observed, but foaming from within the particles was observed after the subsequent heat treatment. The physical properties of the obtained carbon precursor particles are shown in Table 1.

(Comparative Example 4)
The AN/St/DVB copolymer was infusible treated in the same manner as in Example 7, except that stirring with a stirring blade was not performed in the reaction vessel. Channeling was observed in the copolymer layer, causing partial heat generation, and fusing and melting of the copolymer. The physical properties of the obtained carbon precursor particles are shown in Table 1.

<Evaluation>
In Examples 1 to 7 within the scope of the present invention, no fusion was observed in the obtained carbon precursor particles. Furthermore, because the oxygen content was high, the obtained carbon precursor particles were sufficiently oxidized and infusible. In addition, in view of the true density of the carbonaceous material obtained by heat treatment at 1100°C, it was confirmed that non-graphitizable carbon precursor particles were obtained.

On the other hand, in Comparative Examples 1 and 4, stirring was not performed, so the particles fused together and the desired carbon precursor particles were not obtained. In Comparative Example 2, the maximum temperature reached was lower than the range of 180 to 350°C, so the oxygen content of the carbon precursor particles was low and sufficiently oxidized (infusible) carbon precursor particles were not obtained. As a result, the particles softened during the subsequent heat treatment.

In Comparative Example 3, the average particle size of the organic particles was large, exceeding the range of 1 to 100 μm, and foaming from within the particles was observed during subsequent heat treatment. If the average particle size of the organic particles is too large, oxygen cannot diffuse sufficiently into the interior of the organic particles, making it difficult to form a structure that is infusible throughout the entire particle. When particles with such a structure are heated, rapid decomposition occurs in the non-infusible parts, causing the surface of the particles to crack, which is thought to result in the foamed surface properties of Comparative Example 3.

<Battery performance evaluation>
An electrode was prepared from the carbonaceous material obtained by using the carbon precursor particles according to the present invention. A non-aqueous electrolyte secondary battery was prepared using the electrode, and the battery performance was measured. Each operation is described below in "(a) Preparation of electrode", "(b) Preparation of test battery", and "(c) Measurement of battery capacity". The battery performance was evaluated by the charge capacity (doped amount) and discharge capacity (undoped amount) of the carbonaceous material.

(a) Preparation of electrode NMP was added to 90% by weight of the obtained carbonaceous material and 10% by weight of polyvinylidene fluoride (Kureha Corporation) to form a paste, which was then uniformly applied onto copper foil. After drying, the coated electrode was punched out into a disk shape with a diameter of 15 mm, which was then pressed to prepare a test electrode.

(b) Preparation of Test Battery A lithium secondary battery was constructed using the test electrode obtained above and lithium metal as the counter electrode. Specifically, a stainless steel mesh disk was spot-welded to the outer lid of a coin-type battery can, and a 0.8 mm thick metallic lithium thin plate punched into a disk shape with a diameter of 15 mm was pressed to the stainless steel mesh disk in an Ar atmosphere to form an electrode (counter electrode).

The electrolyte used was a mixed solvent of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate in a volume ratio of 1:2:2 to which LiPF6 was added at a ratio of 1.5 mol/L. The separator was a borosilicate glass fiber microporous membrane with a diameter of 19 mm, and a polyethylene gasket was used. A 2016 size coin-type nonaqueous electrolyte solution lithium secondary battery was assembled in an Ar atmosphere to prepare a test lithium secondary battery.

(c) Measurement of battery capacity A charge/discharge test was performed using the above-mentioned test lithium secondary battery, and the battery capacity of the carbonaceous material electrode was measured at 45 ° C. The doping reaction was performed by constant current constant voltage charging. Constant current charging was performed at a current density of 0.5 mA / cm ² , and after the terminal voltage reached -5 mV, constant voltage charging was performed at a control voltage of -5 mV. The applied current was attenuated until the applied current reached 20 μA. The value obtained by dividing the amount of electricity at this time by the weight of the carbonaceous material used was defined as the charge capacity and expressed in Ah / kg units. Next, a current was similarly passed in the reverse direction to undo the lithium doped in the carbonaceous material. The undoping was performed at a current density of 0.5 mA / cm ² until the terminal potential reached 1.5 V. The value obtained by dividing the amount of electricity undoped at this time by the weight of the carbonaceous material of the electrode was defined as the discharge capacity (Ah / kg) per unit weight of the carbonaceous material.

(Example 8)
The carbon precursor particles prepared in Example 3 were impregnated with an aqueous sodium hydroxide solution. The solution was then dried in a nitrogen atmosphere to obtain a sodium hydroxide-impregnated carbon precursor impregnated with 10.0% by weight of sodium hydroxide relative to the carbon precursor particles. Next, 10 g of the carbon precursor was charged into a horizontal tubular furnace and pre-fired at 700°C in a nitrogen atmosphere for 1 hour. Then, the carbon precursor was fired at 1200°C for 1 hour in a nitrogen atmosphere with a flow rate of 10 L/min to obtain fired charcoal. Next, the fired charcoal was charged into a vertical tubular furnace made of quartz with a perforated plate, heated to 750°C in a nitrogen stream, and then held at 750°C. Next, hexane gas was introduced into the furnace so that the hexane gas concentration in the nitrogen gas was 30% by volume, and the mixture was held at 750°C for 30 minutes, after which the introduction of hexane gas was stopped and the mixture was allowed to cool to room temperature under a nitrogen stream. The average particle size of the obtained carbonaceous material was 19 μm, and the true density measured by the butanol method was 1.42 g/cm ³ .

According to the results of measuring the battery performance using the carbonaceous material of Example 8, the charge capacity was 593 Ah/kg and the discharge capacity was 541 Ah/kg. It was confirmed that the carbonaceous material obtained using the carbon precursor particles according to the present invention can provide a secondary battery having high charge capacity and discharge capacity.

REFERENCE SIGNS LIST 1 Reaction vessel 101 Side surface 102 Bottom surface 103 Side wall 104 Bottom wall 105 Top cover 106 Discharge port for treated object 107 Observation window 108 Gas inlet 109 Supply port for heating medium 110 Flow path for heating medium 111 Discharge port for heating medium 112 Support stand 2 Stirring means (stirrer)
201 Rotating shaft 202 Agitating blade 203 Motor 204 Tip of agitating blade 205 Lower end of agitating blade 3 Chopper 301 Rotating shaft 302 Chopper blade 303 Motor 4 Cooling water supply device 401 Spray nozzle 402 Cooling water piping 403 Weight scale 404 Cooling water storage container 405 Pressure measuring device 406 Pressurizing air 5 Bag filter 6 Gas exhaust piping 7 Second temperature measuring device 8 First temperature measuring device 9 Oxygen concentration measuring device 10 Raw material (organic particles)
11 Oxidizing gas (air)
12. Non-oxidizing gas (nitrogen gas)
13 Cooling water 14 Bag filter backwash air 15 Heating medium (heat medium)
16 Exhaust gas 17 Agitated flow

Claims (6)

1. A method for producing carbon precursor particles by oxidizing organic particles, comprising the steps of:
A reaction vessel having a stirring means including a rotating shaft and a stirring blade provided on the rotating shaft is used, and a raw material containing organic particles having an average particle diameter of 1 to 100 μm is placed in the reaction vessel;
introducing an oxidizing gas into the reaction vessel while stirring the raw material with the stirring means, thereby carrying out an oxidation treatment of the organic particles;
In the oxidation treatment, the raw material in the reaction vessel is treated at a temperature of 150° C. or higher, and the temperature is controlled so that the maximum temperature is 180 to 350° C.;
A method for producing carbon precursor particles, comprising: 2 . The method for producing carbon precursor particles according to claim 1 , wherein an angle between the rotation axis of the stirring blade and a horizontal plane is 60 degrees or more and 90 degrees or less. The method for producing carbon precursor particles according to claim 1 or 2, wherein the inner surface of the reaction vessel and the surface of the stirring blade are spaced apart, and the closest distance between the inner surface and the surface is 50 mm or less. The method for producing carbon precursor particles according to claim 1 , wherein the organic matter of the organic particles is petroleum pitch or coal pitch. The method for producing carbon precursor particles according to claim 1 , wherein the carbon precursor particles are non-graphitizable carbon precursor particles. A method for producing a carbonaceous material for a secondary battery negative electrode, comprising the step of heat-treating the carbon precursor particles according to claim 1 in a non-oxidizing gas atmosphere at a temperature of 1000 to 1400° C. to produce a carbonaceous material.

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