JP2018204057A - Carbon coating method - Google Patents

Abstract

To provide a carbon coating method capable of making uniform a carbon coating amount of a base material particle.SOLUTION: The present invention relates to a carbon coating method for base material particles P in which the base material particles P put in a reaction pipe 20 are heated up to a carbonization temperature of a carbon source gas G1 or higher in the presence of the carbon source gas G1, and a first mode in which the carbon source gas G1 is circulated from one end side to the other end side in a lengthwise direction of the reaction pipe 20 and a second mode in which the carbon source gas G1 is circulated from the other end side to the one end side of the reaction pipe 20 are carried out each once or more. A time tfor which the first mode is performed and a time tfor which the second mode is performed are so related that 0.5t≤t≤1.5t. The base material particles P are negative-electrode particles including a negative polarity active substance for lithium secondary battery.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a carbon coating method for base particles, which coats the base particles with carbon.

Techniques for performing carbon coating on various substrate particles are known.
For example, a silicon-containing negative electrode active material used as a negative electrode active material for a lithium ion secondary battery has a large theoretical capacity but is inferior in conductivity. For this reason, as a negative electrode material for a lithium ion secondary battery, a silicon-coated negative electrode active material obtained by carbon coating may be used.

  As a method of performing carbon coating on a silicon-containing negative electrode active material, it has been proposed to employ a chemical vapor deposition (CVD) method. Specifically, when a silicon-containing negative electrode active material as a base particle is accommodated in a reaction tube and the base particle is heated to a temperature higher than the carbonization temperature of the carbon source gas in the presence of the carbon source gas, The touched carbon source gas can be carbonized, and the surface of the substrate particles can be carbon coated.

  However, it is difficult to make the carbon coating amount of a large number of substrate particles present in the reaction tube uniform by simply performing the above carbon coating method. For example, Patent Document 1 mentions that the carrier gas supplied to the reaction tube together with the carbon source gas causes turbulent flow in the reaction tube. Patent Document 1 explains that the turbulent flow of the carrier gas causes uneven temperature in the reaction tube and the back flow of the carbon source gas, which makes it difficult to control the CVD and consequently causes variations in the film quality of the carbon coat. Has been. And the said patent document 1 introduces the technique which suppresses the turbulent flow of carrier gas by adjusting the blowing direction of the carrier gas to a reaction tube with a baffle plate etc.

JP 2006-138315 A

The inventor of the present invention has intensively studied to further improve the carbon coating method of the base particles.
This invention is made | formed in view of this situation, and it aims at providing the technique which can equalize the carbon coat amount of a base particle.

  The present inventor presumed the reason why the carbon coating amount of the substrate particles cannot be made uniform even by the carbon coating method introduced in Patent Document 1.

According to the carbon coating method introduced in Patent Document 1, by suppressing turbulent flow in the reaction tube, a carbon source gas in a plane perpendicular to the gas flow path of the reaction tube, that is, in the gas flow channel cross-sectional direction of the reaction tube It is possible to reduce unevenness. However, even with the carbon coating method of Patent Document 1, it is difficult to reduce the unevenness of the carbon source gas in the gas flow path direction of the reaction tube. As described above, since the carbon source gas is heated and carbonized in the reaction tube and is coated on the surface of the substrate particles, the carbon source gas concentration on the downstream side of the gas flow path of the reaction tube inevitably has to be the reaction tube. This is because the carbon source gas concentration on the upstream side of the gas flow path is less.
The inventor conducted further research based on this assumption and completed the present invention.

That is, the carbon coating method of the present invention comprises:
A method for coating the base particles, wherein the base particles contained in the reaction tube are heated in the presence of the carbon source gas to a temperature above the carbonization temperature of the carbon source gas,
A first mode in which the carbon source gas is circulated from one end side to the other end side in the longitudinal direction of the reaction tube;
And a second mode in which the carbon source gas is circulated from the other end side to the one end side of the reaction tube.

  According to the carbon coating method of the present invention, the carbon coating amount of the substrate particles can be made uniform.

It is explanatory drawing which represents typically the coating apparatus used for the carbon coating method of Example 1. FIG. It is explanatory drawing which represents typically a mode that the 1st aspect is implemented with the coating apparatus used for the carbon coating method of Example 1. FIG. It is explanatory drawing which represents typically a mode that the 2nd aspect is implemented with the coating apparatus used for the carbon coating method of Example 1. FIG.

  The best mode for carrying out the present invention will be described below. Unless otherwise specified, the numerical range “x to y” described in this specification includes the lower limit x and the upper limit y. The numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples. Furthermore, numerical values arbitrarily selected from the numerical value range can be used as upper and lower numerical values.

The carbon coating method of the present invention comprises:
A method for coating the base particles, wherein the base particles contained in the reaction tube are heated in the presence of the carbon source gas to a temperature above the carbonization temperature of the carbon source gas,
A first mode in which the carbon source gas is circulated from one end side to the other end side in the longitudinal direction of the reaction tube;
And a second mode in which the carbon source gas is circulated from the other end side to the one end side of the reaction tube.

  According to the conventional carbon coating method introduced in Patent Document 1 described above, the carbon source gas is circulated only in one direction with respect to the longitudinal direction of the reaction tube. This mode is natural if the carbon coating is performed based on the specifications of a very general rotary kiln type CVD apparatus. However, the present inventor has found that the distribution of the carbon source gas in only one direction is a factor that causes unevenness in the carbon coating amount of the substrate particles. And the method different from the specification of the conventional general CVD apparatus, that is, the first mode in which the carbon source gas is circulated from one end side to the other end side in the longitudinal direction of the reaction tube, and the other end side of the reaction tube The carbon coating amount on the base particles in the reaction tube can be made uniform over the entire length of the reaction tube by performing each of the second mode in which the carbon source gas is circulated from the first side toward the one end side at least once. I reached that.

  Hereinafter, details of the carbon coating method of the present invention will be described.

  The material, size, and shape of the reaction tube in the carbon coating method of the present invention are not particularly limited, and the reaction tube may or may not rotate. For example, a reaction furnace in a known CVD apparatus such as a hot wall type, a cold wall type, a horizontal type, a vertical type, etc., such as a fluidized bed reaction furnace, a rotary furnace, a tunnel furnace, a batch-type firing furnace, a rotary kiln, etc. You may use as a reaction tube in a carbon coat method. The heating method of the reaction tube is not particularly limited. For example, when a reaction furnace of a rotary kiln is used as a reaction tube, an external heating type rotary kiln may be selected, or an internal heating type rotary kiln is selected. Also good. However, in order to prevent the carbon source gas flowing through the reaction tube from burning, the inside of the reaction tube is preferably a non-oxidizing atmosphere, and, for example, compared to a gas combustion type internal heating rotary kiln, for example. It is more preferable to select a thermal rotary kiln.

In order to make the carbon coating amount of the base particles more uniform throughout the reaction tube, it is preferable to rotate the reaction tube during the carbon coating.
By performing the carbon coating while rotating the reaction tube, the carbon coating can be performed while the substrate particles are in a fluid state. By doing so, the entire outer surface of the substrate particles at various positions can be evenly contacted with the carbon source gas, and the carbon coat amount of the substrate particles is more uniform at various positions in the reaction tube. Can be.

  Further, by providing a baffle plate or the like inside the reaction tube, the base particles may be brought into contact with the carbon source gas while stirring. In this case, some of the substrate particles remain on the baffle plate and fall from a predetermined height as the reaction tube rotates. In this way, the base particles in the reaction tube are agitated, and when the base particles are partially dense in the reaction tube, some of the base particles are difficult to contact with the carbon source gas as they are. However, it is possible to move the substrate particles that are difficult to contact with the carbon source gas to a position where they are easily contacted with the carbon source gas. By doing so, the carbon coat amount of the base particles can be made more uniform throughout the reaction tube.

  By the way, when the carbon source gas is circulated only in one direction in the reaction tube as in the conventional carbon coating method, the base material particles are arranged at both ends in the flow direction of the carbon source gas, that is, in the longitudinal direction of the reaction tube. There is a difference in the amount of carbon coating. Hereinafter, as necessary, the “difference in the carbon coating amount of the base material particles occurring at both ends in the longitudinal direction of the reaction tube” is simply abbreviated as “coating amount difference”.

Assuming that the diameter of the reaction tube is constant, the longer the reaction tube is heated, the larger the coating amount difference becomes. According to the carbon coating method of the present invention, the first mode in which the carbon source gas is circulated from one end side to the other end side in the longitudinal direction of the reaction tube, and the carbon source gas from the other end side to the one end side of the reaction tube. The above-described coating amount difference can be reduced even if the heating length of the reaction tube is long by performing each of the second mode in which the liquid is circulated once or more. Such an effect of the carbon coating method of the present invention becomes more remarkable as the reaction tube is heated longer, assuming that the diameter of the reaction tube is constant.
In consideration of this, the relationship between the diameter φ of the reaction tube and the heating length L of the reaction tube is preferably L ≧ 2φ, more preferably L ≧ 3φ, and L ≧ 4φ. More preferably, L ≧ 5φ is particularly preferable. In addition, the heating length of the reaction tube means the length of the portion of the reaction tube that is heated to a temperature higher than the carbonization temperature of the carbon source gas during coating.

Further, the difference in the coating amount in the case where the carbon source gas is circulated only in one direction in the reaction tube becomes larger as the density of the base particles in the reaction tube is higher. According to the carbon coating method of the present invention, the difference in the coating amount can be reduced even when the density of the base particles in the reaction tube is high, and the effect becomes more remarkable when the density of the base particles in the reaction tube is high.
Considering this, the relationship between the heating volume C of the reaction tube and the volume V of the base particle is preferably 1.0C> V ≧ 0.05C, and 0.8C ≧ V ≧ 0.1C. It is more preferable that 0.7C ≧ V ≧ 0.3C. In addition, the heating volume of a reaction tube here means the volume of the part heated more than the carbonization temperature of carbon source gas at the time of a coating among reaction tubes. Further, the volume of the base particle refers to the bulk of the base particle, that is, the apparent volume of the base particle. The volume of the substrate particles can be measured with a measuring container such as a graduated cylinder. In order to obtain more accuracy, it is preferable to perform tapping as defined in the JIS Z 2512: 2012 metal powder-tap density measurement method when measuring the volume of the substrate particles.

In any case, the reaction tube has an inlet for introducing the carbon source gas toward one end side in the longitudinal direction toward the other end side in the longitudinal direction. Moreover, it has the inlet for introducing carbon gas toward the one end side of the said longitudinal direction in the other end side of the longitudinal direction of a reaction tube. Hereinafter, if necessary, one end in the longitudinal direction is simply abbreviated as one end, and the other end in the longitudinal direction is simply abbreviated as the other end. In addition, the inlet on one end of the reaction tube is referred to as a first inlet, and the inlet on the other end of the reaction tube is referred to as a second inlet. The first introduction port and the second introduction port may further serve as carrier gas introduction ports as necessary.
Furthermore, the reaction tube has a discharge port for discharging the carbon source gas on each of the one end side and the other end side. Hereinafter, as necessary, the discharge port on one end side is referred to as a first discharge port, and the discharge port on the other end side is referred to as a second discharge port. The first discharge port and the second discharge port may further serve as a carrier gas discharge port as necessary. Furthermore, if necessary, the first discharge port may also be used as the first introduction port, and the second discharge port may also be used as the second introduction port.

As described above, in the carbon coating method of the present invention, each of the first aspect and the second aspect is performed once or more. In the first aspect, the carbon source gas is introduced into the reaction tube through the first inlet, and the exhaust gas in the reaction tube is discharged through the second outlet. In the second mode, the carbon source gas is introduced into the reaction tube through the second introduction port, and the exhaust gas in the reaction tube is discharged through the first discharge port. Switching between the first mode and the second mode may be performed as appropriate, and the timing is not particularly limited, but the coating amount difference is reduced and the carbon coating amount of the substrate particles is made more uniform at various positions in the reaction tube. In order to achieve this, it is preferable that the first mode and the second mode are performed for the same amount of time. Specifically, when the time for performing the first aspect and _{t 1,} the time for performing the second embodiment and _{t 2,} the relationship between _{t 1} and _{t 2, 0.5t 1 ≦ t 2} ≦ 1.5t 1 is preferably at, more preferably from _{0.7t 1 ≦ t 2 ≦ 1.3t 1} , more preferably in the range of _{0.9t 1 ≦ t 2 ≦ 1.1t 1} , in t 1 = _{t 2} It is particularly preferred. Incidentally, t _1, t ₂ here, the time for performing a first aspect once means the time for performing the second embodiment once.

The first aspect and the second aspect may be performed once, but are preferably performed a plurality of times. In this case, the integrated value _{T 1} of the _{t 1,} the relationship between the integrated value _{T 2} of the _{t 2} also is preferably from _{0.5T 1 ≦ T 2 ≦ 1.5T 1} , 0.7T 1 ≦ T 2 ≦ 1.3 T is more preferably from _1, more preferably in the range of _{0.9T 1 ≦ T 2 ≦ 1.1T 1} , particularly preferably from T 1 = _{T 2.}

Further, in order to further reduce the coating amount difference, it is preferable that the first mode and the second mode are each performed for a certain length of time. Specifically, t ₁ and t ₂ are each independently preferably 2 minutes or longer, more preferably 5 minutes or longer, and even more preferably 10 minutes or longer. When the first mode and the second mode are performed a plurality of times, each first mode may be performed for the same time or may be performed for different times. The same applies to the second aspect.

  As the carbon source to be circulated in the reaction tube, those that can be pyrolyzed and carbonized by heating in a non-oxidizing atmosphere are used. For example, saturated fats such as methane, ethane, propane, butane, isobutane, pentane, and hexane are used. Hydrocarbons, unsaturated aliphatic hydrocarbons such as ethylene, propylene, acetylene, alcohols such as methanol, ethanol, propanol, butanol, benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, benzoic acid , One or a mixture selected from aromatic hydrocarbons such as salicylic acid, nitrobenzene, chlorobenzene, indene, benzofuran, pyridine, anthracene, phenanthrene, esters such as ethyl acetate, butyl acetate, amyl acetate, and fatty acids And the like.

These carbon sources may be passed through the reaction tube in a gaseous state, and may be introduced into the reaction tube while being heated to the carbonization temperature, or may be heated to the carbonization temperature within the reaction tube.
Further, the carbon source may be in a gaseous state at normal temperature or in a gaseous state in the vicinity of the carbonization temperature, but is preferably in a gaseous state at 100 ° C. or less, and 50 ° C. What becomes gaseous below is more preferable, and what becomes gaseous at normal temperature is still more preferable. This is because the process of gasifying the carbon source is easy or the process becomes unnecessary.
Specifically, the carbon source is preferably one or a mixture selected from methane, ethane, propane, butane, isobutane, ethylene, propylene, and acetylene.

These carbon source gases, that is, the carbon source gas may be supplied alone to the reaction tube, but are preferably supplied to the reaction tube together with the carrier gas. As the carrier gas, a general inert gas such as helium, nitrogen, or argon may be used.
The volume ratio of the carbon source gas to the carrier gas is preferably in the range of 1: 100 to 2: 1 and more preferably in the range of 1:10 to 1: 1 by volume.
If the volume ratio of the carbon source gas in the mixed gas of the carbon source gas and the carrier gas is large, a relatively thick carbon coat layer can be efficiently formed, but the carbon coat amount of the base material particles on the upstream side of the channel and the channel The difference from the carbon coating amount of the base particle on the downstream side tends to be large. By making the amount ratio of the carbon source gas and the carrier gas within an appropriate range, the carbon coat amount of the base material particles can be made more uniform throughout the reaction tube.

  The organic substance that can be used as the carbon source includes solid, liquid, and gaseous substances. In the carbon coating method of the present invention, the use of a gaseous carbon source makes it possible to obtain individual substrates. There is an advantage that the particles can be uniformly and thinly coated with carbon. In other words, when the carbon source gas is used, the coat layer formed on the surface of each base particle by the carbon coating is thinner and more uniform than when a solid or liquid carbon source is used. For example, when the base particle is porous or has a cavity communicating with the outside, the carbon source gas can be used to not only coat the outer surface of the base particle with carbon but also the inside of the base particle. There is an advantage that the surface can also be carbon coated.

  In the carbon coating method of the present invention, the substrate particles accommodated in the reaction tube are heated to the carbonization temperature of the carbon source gas or higher in the presence of the carbon source gas. Although the heating temperature at this time changes with kinds of carbon source gas, it is desirable to make it 50 degreeC or more higher than the temperature at which carbon source gas carbonizes. However, if the heating temperature is too high, free carbon (soot) may be generated in the system, so it is preferable to select conditions that do not generate free carbon (soot). The thickness of the formed carbon layer can be controlled by the processing time.

In the carbon coating method of the present invention, the material and size of the substrate particles to be carbon coated are not particularly limited. Therefore, according to the carbon coating method of the present invention, various substrate particles for use in various applications can be carbon coated. As an example of the substrate particles, a negative electrode active material for a lithium ion secondary battery can be given.
Examples of the average particle diameter of the base particles include 0.01 μm to 5000 μm, 0.05 μm to 1000 μm, and 0.1 μm to 100 μm. In addition, the average particle diameter as used in this specification means D50 at the time of measuring with a general laser diffraction scattering type particle size distribution measuring apparatus.
The carbon coating method of the present invention is particularly useful as a method for carbon coating a silicon-containing negative electrode active material.

Examples of the silicon-containing negative electrode active material include silicon-based materials such as silicon simple substance and SiO _x (0.3 ≦ x ≦ 1.6) which disproportionates to silicon simple substance and silicon dioxide. Furthermore, it is also preferable to use a silicon material disclosed in International Publication No. 2014/080608 as a silicon-based material. International Publication No. 2014/080608 discloses a silicon material having a structure in which a plurality of plate-like silicon bodies are laminated in the thickness direction. In International Publication No. 2014/080608, a layered silicon compound mainly composed of polysilane from which CaSi ₂ and acid have been removed by reacting CaSi ₂ is synthesized, and the layered silicon compound is heated at 300 ° C. or higher. It describes that a silicon material from which hydrogen has been released is manufactured, and a lithium ion secondary battery including the silicon material as an active material.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In addition, this invention is not limited by these Examples, In the range which does not deviate from a summary, it can change suitably and can implement. In addition, each component shown in the embodiment can be arbitrarily extracted and combined.

Example 1
The carbon coating method of Example 1 is an example in which negative electrode material particles, specifically, a particulate silicon-containing negative electrode active material is used as substrate particles, and propane is used as a carbon source gas. FIG. 1 is an explanatory view schematically showing a coating apparatus used in the carbon coating method of Example 1. FIG. FIG. 2 is an explanatory view schematically showing a state in which the first mode is implemented by the coating apparatus used in the carbon coating method of Example 1. FIG. FIG. 3 is an explanatory view schematically showing a state in which the second mode is implemented by the coating apparatus used in the carbon coating method of Example 1. Hereinafter, in the examples, “up”, “down”, “front”, and “rear” refer to the upper, lower, front, and rear shown in FIG.

(Coating equipment)
In the carbon coating method of Example 1, an external heating type rotary kiln was used as the coating apparatus 1. As shown in FIG. 1, the coating apparatus 1 includes a reaction tube 2, a heating unit 3, a first roll 41, a second roll 42, a driving unit 5, a carbon source gas container G1, a carrier gas container G2, and a gas introduction path unit 7. And a gas discharge path 8.

  The reaction tube 2 includes a main body 20, a first rotary joint 21, a second rotary joint 22, a first wheel 23, a second wheel 24, and a sprocket 25.

The main body 20 is made of quartz and has a cylindrical shape. The inside of the main body 20 corresponds to the inside of the reaction tube 2, and the inner diameter of the main body 20 corresponds to the diameter of the reaction tube 2. The longitudinal direction of the main body 20 means the axial direction of the main body 20. Furthermore, the length of the portion heated by the heating unit 3 described later in the length of the main body 20 in the longitudinal direction corresponds to the heating length of the reaction tube 2. The heating length of the reaction tube 2 can also be referred to as the length of the portion covered with the heating unit 3 in the length of the main body 20 in the longitudinal direction.
The main body 20 is disposed substantially horizontally with the longitudinal direction (that is, the axial direction) facing forward and backward. The relationship between the diameter φ of the reaction tube 2 and the heating length L of the reaction tube 2 is 5φ = L, which satisfies 2φ ≦ L.

  A first rotary joint 21 is attached to one end of the main body 20 in the longitudinal direction, and a second rotary joint 22 is attached to the other end of the main body 20 in the axial direction.

The first rotary joint 21 includes a first joint path portion 27 that communicates with the inside of the main body portion 20, and a first valve V <b> 1 that is attached to the first joint path portion 27. The first rotary joint 21 allows rotation of the main body 20 at the front end of the main body 20 and keeps communication between the inside of the main body 20 and the first joint path portion 27. Is hermetically sealed from the outside of the main body 20.
The first valve V1 is a three-way solenoid valve, and is connected to the first joint path portion 27, and a first gas introduction path portion 71 and a first gas discharge path portion 81 described later. The first valve V <b> 1 connects one of the first gas introduction path portion 71 and the first gas discharge path portion 81 to the first joint path portion 27 and blocks the other from the first joint path portion 27. A portion of the first valve V1 connected to the first gas introduction path portion 71 corresponds to the first introduction port described above. Moreover, the part connected to the 1st gas exhaust path part 81 among the 1st valves V1 is corresponded to the 1st exhaust port mentioned above.

The second rotary joint 22 includes a second joint path portion 28 that communicates with the inside of the main body portion 20, and a second valve V <b> 2 that is attached to the second joint path portion 28. The second rotary joint 22 allows rotation of the main body portion 20 at the rear end portion of the main body portion 20 and maintains communication between the inside of the main body portion 20 and the second joint path portion 28. The inside is hermetically sealed from the outside of the main body 20.
The second valve V2 is also a three-way electromagnetic valve, and is connected to the second joint path portion 28, and a second gas introduction path portion 72 and a second gas discharge path portion 82 described later. The second valve V <b> 2 connects one of the second gas introduction path part 72 and the second gas discharge path part 82 to the second joint path part 28 and blocks the other from the second joint path part 28. The part connected to the 2nd gas introduction path part 72 among the 2nd valves V2 is equivalent to the 2nd introduction port mentioned above. Moreover, the part connected to the 2nd gas discharge path | route part 82 among 2nd valves V2 is corresponded to the 2nd discharge port mentioned above.

The first wheel 23 and the second wheel 24 each have an annular shape that is provided coaxially with the main body portion 20 and protrudes from the outer peripheral surface of the main body portion 20. The first wheel 23 is located on the front end side of the main body portion 20, and the second wheel 24 is located on the rear end side of the main body portion. Therefore, the first wheel 23 and the second wheel 24 are separated from each other in the longitudinal direction of the main body 20.
Similarly to the first wheel 23 and the second wheel 24, the sprocket 25 is provided coaxially with the main body portion 20 and has an annular shape protruding from the outer peripheral surface of the main body portion 20. The sprocket 25 is located further to the rear end side of the main body 20 than the second wheel 24.

  The heating unit 3 is an electric furnace and covers the outside of the main body unit 20 between the first wheel 23 and the second wheel 24. The main body 20, and the base material particles and the carbon source gas inside the main body 20 are heated by the heating unit 3.

The first roll 41 is located below the first wheel 23 and is rotatable. The axial direction of the first wheel 23 and the axial direction of the first roll 41 are parallel, and the peripheral wall of the first roll 41 is in contact with the peripheral wall of the first wheel 23.
The second roll 42 is located below the second wheel 24 and is rotatable. The axial direction of the second wheel 24 and the axial direction of the second roll 42 are parallel, and the peripheral wall of the second roll 42 is in contact with the peripheral wall of the second wheel 24.
The first roll 41 and the second roll 42 support the main body 20 while allowing the main body 20 to rotate.

The drive unit 5 is a so-called pulley mechanism having a gear belt 50 and a drive source PS connected to the gear belt 50. The gear belt 50 meshes with the sprocket 25.
Note that the drive unit 5 is not limited to this, and may be constituted by, for example, a motor and a gear integrated with the rotation shaft of the motor.

The carbon source gas container G1 is a gas cylinder and contains propane gas. The outlet of the carbon source gas container G1 is branched into two. One outlet in the carbon source gas container G1 is referred to as a first carbon supply port co1, and the other outlet is referred to as a second carbon supply port co2.
The carrier gas container G2 is a gas cylinder and contains argon gas which is a non-oxidizing gas. The outlet of the carrier gas container G2 is also branched into two. One outlet in the carrier gas container G2 is referred to as a first carrier supply port io1, and the other outlet is referred to as a second carrier supply port io2.

The first gas introduction path 71 communicates the first carbon supply port co1, the first carrier supply port io1, and the first valve V1.
The second gas introduction path 72 communicates the second carbon supply port co2, the second carrier supply port io2, and the second valve V2.
The first gas discharge path 81 is connected to the first valve V1, and the second gas discharge path 82 is connected to the second valve V2. The first gas discharge path 81 and the second gas discharge path 82 communicate with the outside through a filter (not shown).

  Hereinafter, the carbon coating method of Example 1 will be described.

(Manufacture of substrate particles)
An aqueous HCl solution having a concentration of 36% by mass was cooled to 0 ° C. in an ice bath. In an argon gas stream, CaSi ₂ in an amount of 5.2 g was added to 100 mL of HCl aqueous solution and stirred. After confirming completion of foaming from the reaction solution, the obtained reaction solution was filtered, and the residue was washed with distilled water. Thereafter, the residue was further washed with acetone and vacuum dried to obtain a layered silicon compound.

The layered silicon compound was heat-treated at 900 ° C. for 1 hour in an argon gas atmosphere with an O ₂ content of 1% by volume or less to obtain a silicon material. X-ray diffraction measurement (XRD measurement) using CuKα rays was performed on this silicon material. From the obtained XRD chart, halo considered to be derived from Si fine particles was observed. For Si, the Si crystallite size calculated from Scherrer's equation using the half-value width of the diffraction peak on the Si (111) surface of the XRD chart was about 7 nm.

  Note that in the above heat treatment, the Si—H bond of the layered silicon compound is cut and hydrogen is released, so that the Si—Si bond is cut and recombined. Si-Si bond recombination occurs in the same layer and can occur between adjacent layers. A silicon material is obtained through the above steps. What grind | pulverized and grind | pulverized this silicon material was used for the following processes as base particle. When the obtained silicon material is observed with a scanning electron microscope, it can be seen that the silicon material has a structure in which a plurality of plate-like silicon bodies are laminated in the thickness direction. The details of the silicon material are disclosed in International Publication No. 2014/080608.

(Carbon coat)
In the carbon coating method of Example 1, the base particles are accommodated in the main body 20 of the coating apparatus 1, the main body 20 is rotated, and the heating unit 3 is heated to 860 ° C. for 20 minutes. The mode and the 20-minute second mode were alternately carried out for a total of 2 hours. This will be specifically described below.

[First embodiment]
In the first aspect, the heating unit 3, the driving unit 5, the first valve V1, and the second valve V2 were controlled as follows. In the carbon coating method of the first embodiment, these controls are performed manually. However, a controller for performing these controls may be provided in the coating apparatus.
The heating part 3 was heated to 860 ° C., and the main body part 20 covered with the heating part 3 was also heated to substantially the same temperature. In addition, the heating part 3 and the main-body part 20 were preheated before starting the 1st aspect, and reached said temperature.
The drive source PS of the drive unit 5 was rotationally driven, and the sprocket 25 was rotated via the gear belt 50 connected to the drive source PS. And the main-body part 20 integrated with the sprocket 25 also rotated. The rotation speed at this time was 1 rpm.

As shown in FIG. 2, the first valve V <b> 1 connects the first joint path portion 27 and the first gas introduction path portion 71, and connects the first joint path portion 27 and the first gas discharge path portion 81. Switched to shut off.
On the other hand, the second valve V2 connects the second joint path portion 28 and the second gas discharge path portion 82 and switches so as to block the connection between the second joint path portion 28 and the second gas introduction path portion 72. It was.

  Therefore, a mixed gas of propane gas, which is a carbon source gas, and argon gas, which is a carrier gas, is introduced into the main body portion 20 through the first joint path portion 27. The volume ratio of propane gas to argon gas in the mixed gas was 1: 4. The mixed gas circulated from the front side to the rear side of the main body 20 while contacting the base material particles p. The carbon source gas contained in the mixed gas was heated to the carbonization temperature, and the surface of the base particle p was carbon coated. Further, the mixed gas that reached the rear end of the main body 20 was discharged to the outside of the main body 20 through the second joint path portion 28 and further discharged to the outside through the second gas discharge path portion 82. This first aspect was continued for 20 minutes.

[Second embodiment]
20 minutes after the start of the first mode, the first mode was stopped and the second mode was started.
In the second mode, the heating unit 3, the drive unit 5, the first valve V1, and the second valve V2 were controlled as follows.
The heating unit 3 was subsequently heated to 860 ° C.
The drive source PS of the drive unit 5 was continuously rotated, and the main body unit 20 was also rotated. The rotation speed at this time was 1 rpm.

As shown in FIG. 3, the second valve V <b> 2 connects the second joint path portion 28 and the second gas introduction path portion 72, and connects the second joint path portion 28 and the second gas discharge path portion 82. Switched to shut off.
On the other hand, the first valve V1 connects the first joint path portion 27 and the first gas discharge path portion 81 and switches so as to block the connection between the first joint path portion 27 and the first gas introduction path portion 71. It was.

  Therefore, the mixed gas is introduced into the main body portion 20 through the second joint path portion 28. The mixed gas circulated from the rear side toward the front side inside the main body part 20 while contacting the base material particles p, and the surface of the base material particles p accommodated in the main body part 20 was coated with carbon. The mixed gas that reached the front end of the main body portion 20 was discharged to the outside of the main body portion 20 through the first joint path portion 27 and further discharged to the outside through the first gas discharge path portion 81. This second embodiment was also performed for 20 minutes.

  The coating material of Example 1 in which the base particle p was carbon-coated was obtained by alternately repeating the first aspect and the second aspect for a total of 2 hours. In addition, the coating material of Example 1 is a negative electrode material for lithium ion secondary batteries.

(Comparative Example 1)
The carbon coating method of Comparative Example 1 is the same as the carbon coating method of Example 1 except that the same coating apparatus as in Example 1 was used and only the first mode was continued for 2 hours. The coating material of Comparative Example 1 was obtained by the carbon coating method of Comparative Example 1.

(Evaluation example)
The following tests were conducted on the coating materials of Example 1 and Comparative Example 1.
The coating material coated with carbon on the front end side of the reaction tube and the coating material coated with carbon on the rear end side of the reaction tube were collected respectively, and each was analyzed using a carbon / sulfur analyzer manufactured by LECO Japan LLC. The carbon content of the coating material was measured. The results are shown in Table 1.

  In the coating material of Comparative Example 1 in which only the first embodiment was performed, the carbon coating amount of the base particles was remarkably non-uniform between one end side and the other end side in the longitudinal direction of the reaction tube. On the other hand, the coating material of Example 1 which performed the 1st aspect and the 2nd aspect was able to equalize the carbon coat amount of the base particle in the whole longitudinal direction of a reaction tube. From this result, the superiority of the present invention was confirmed.

DESCRIPTION OF SYMBOLS 1: Coat apparatus 2: Reaction tube 20: Main-body part 21: 1st rotary joint 22: 2nd rotary joint 23: 1st wheel 24: 2nd wheel 25: Sprocket
27: 1st joint path part 28: 2nd joint path part 3: Heating part 41: 1st roll 42: 2nd roll 5: Drive part 50: Gear belt 7: Gas introduction path part 71: 1st gas introduction path part 72 : Second gas introduction path section 8: gas discharge path section 81: first gas discharge path section 82: second gas discharge path section G1: carbon source gas container G2: carrier gas container PS: drive source V1: first valve V2 : Second valve co1: first carbon supply port co2: second carbon supply port io1: first carrier supply port io2: second carrier supply port p: base material particles

Claims (4)

A method for coating the base particles, wherein the base particles contained in the reaction tube are heated in the presence of the carbon source gas to a temperature above the carbonization temperature of the carbon source gas,
A first mode in which the carbon source gas is circulated from one end side to the other end side in the longitudinal direction of the reaction tube;
And a second mode in which the carbon source gas is circulated from the other end side to the one end side of the reaction tube. And the time t ₁ for performing the first embodiment, the relationship between the time t ₂ for performing the second embodiment,
The carbon coating method according to claim ₁ , wherein 0.5 t ₁ ≦ t ₂ ≦ 1.5 t ₁ .   The carbon coating method according to claim 1 or 2, wherein a relationship between a diameter φ of the reaction tube and a heating length L of the reaction tube satisfies 2φ ≦ L.   The carbon coating method according to any one of claims 1 to 3, wherein the base material particles are negative electrode material particles containing a negative electrode active material for a lithium ion secondary battery.