WO2022250169A1

WO2022250169A1 - PRODUCTION METHOD OF Si-C COMPOSITE

Info

Publication number: WO2022250169A1
Application number: PCT/JP2022/021957
Authority: WO
Inventors: 雅人藤田; 邦裕小島; 祐司伊藤; 浩文井上
Original assignee: 昭和電工株式会社
Priority date: 2021-05-28
Filing date: 2022-05-30
Publication date: 2022-12-01
Also published as: JPWO2022250169A1

Abstract

This method for producing a silicon-carbon composite involves passing a silane-containing gas into a reactor filled with porous carbon particles, pyrolyzing the silane in the silane-containing gas and precipitating the silicon in the pores of the porous carbon particles, wherein the reactor is provided with a silane-containing gas passage that leads from a silane-containing gas inlet to an exhaust gas outlet, the porous carbon particles are filled in the silane-containing gas passage, the reaction temperature in the silane-containing gas passage is 330°C-450°C, and has a temperature distribution that rises from the silane-containing gas inlet towards the exhaust gas outlet; defining the reaction temperature of the porous carbon particles in the silane-containing gas passage at the silane-containing gas inlet end as Tup, the reaction temperature at the midpoint between the silane-containing gas inlet end and the exhaust gas outlet end as Tmid, and the reaction temperature at the exhaust gas outlet end as Tdown, it holds that 0°C < Tmid – Tup ≤ 70°C and 0°C ≤ Tdown – Tmid ≤ 50°C.

Description

Method for producing Si—C composite

The present invention relates to a method for producing a Si—C composite (silicon-carbon composite).

Silicon is an attractive negative electrode material for lithium-ion secondary batteries due to its high capacity, but its volume change is large during charging and discharging, and its cycle characteristics are poor. As a technique for effectively using silicon as a negative electrode material for lithium ion secondary batteries, by depositing elemental silicon in the pores of a porous carbon material, as disclosed in Patent Document 1 (U.S. Pat. No. 1,045,4103), One method is to use it as a silicon-carbon (Si--C) composite.

By making the silicon-carbon composite have a structure as disclosed in Patent Document 2 (Japanese translation of PCT publication No. 2018-534720), silicon can be fixed at a single position. Porous carbon materials are also believed to play an important role as a framework for expansion/contraction as well as contributing to the overall electronic and ionic conduction capabilities of the composite particles.
For this reason, such a composite is considered to have much better cycle characteristics than when silicon is used alone as an active material.

In this method, a silicon-containing gas such as silane or disilane is applied to porous carbon particles with pores in a furnace maintained at a high temperature. Then, the silicon-containing gas is thermally decomposed on the surface of the porous carbon particles and in the pores, and silicon is produced there. At this time, since the porous carbon contains pores such as micropores, mesopores, and macropores, it is considered that silicon having the size of these pores or smaller than them is deposited. Although this is a chemical vapor deposition (CVD) method, it is also called chemical vapor infiltration (CVI) in the sense that silicon is infiltrated into a material called porous carbon particles.

U.S. Patent No. 10454103 Japanese translation of PCT publication No. 2018-534720

In the method of Patent Document 1, silicon may not precipitate uniformly over the entire porous carbon particles. Moreover, in the method of Patent Document 1, it may precipitate not only in the pores of the porous carbon, but also on the surface of the porous carbon particles and everywhere in the furnace.

The main object of the present invention is to provide a method for producing a Si--C composite that deposits silicon uniformly over the entire porous carbon particles.

In the method of Patent Document 1, the reason why silicon may not precipitate uniformly was thought to be that the treatment temperature was too high for silane gas. In addition, it was thought that the temperature at which precipitation occurs not only in the pores of the porous carbon but also on the surface of the porous carbon particles and everywhere in the furnace is included.

Prior to the decomposition of silane gas, adsorption of silane molecules to the solid surface occurs, and heat is generated at that time. For this reason, the reaction temperature varies depending on the location in the furnace, and it is thought that the concentration of silicon between the particles of the Si—C composite to be produced and the distribution of Si deposited on the outermost surface are uneven.

By forming a temperature gradient from upstream to downstream of the silane gas, the present inventors succeeded in eliminating variations in the silicon content in the Si—C composite and surface deposition Si depending on the location in the furnace. By performing chemical vapor infiltration (Si-CVI) of silicon at a lower temperature than before, the inventors succeeded in selectively depositing silicon in the pores of porous carbon particles, and completed the present invention.

The configuration of the present invention is as follows.
[1] Si—C, in which a silane-containing gas is passed through a reactor charged with porous carbon particles to thermally decompose silane in the silane-containing gas to deposit silicon in the pores of the porous carbon particles. A method for manufacturing a composite,
The reactor includes a silane-containing gas flow path from a silane-containing gas inlet to an exhaust gas outlet, and the porous carbon particles are loaded in the silane-containing gas flow path,
The reaction temperature in the silane-containing gas flow path is 330° C. or higher and 450° C. or lower, and has a temperature distribution that rises from the silane-containing gas inlet toward the exhaust gas outlet,
Tup is the reaction temperature at the silane-containing gas inlet side end of the porous carbon particles in the silane-containing gas flow passage, and the middle point between the silane-containing gas inlet side end and the exhaust gas outlet side end When the reaction temperature at Tmid and the reaction temperature at the exhaust gas outlet side end is Tdown,
0° C.<Tmid−Tup≦70° C. and 0° C.≦Tdown−Tmid≦50° C.
A method for producing a Si—C composite.

[2] The method for producing a Si-C composite according to [1], wherein the Tup is less than 400°C.

[3] The method for producing a Si--C composite according to [1] or [2], wherein the gauge pressure in the reactor during the reaction is -10 kPa to +10 kPa.

[4] The exhaust gas discharged from the exhaust gas outlet is sampled to monitor the composition of the exhaust gas, and from the mass flow rate of the silane gas at the reactor inlet and the concentration and reaction time of the silane gas in the exhaust gas at the reactor outlet, The method for producing a Si—C composite according to any one of [1] to [3], wherein the reaction amount is estimated.

[5] The method for producing a Si—C composite according to [4], wherein the filling rate of silicon into the pores is adjusted from the reaction amount and the pore volume.

[6] The step of obtaining a Si-C composite by the method for producing a Si-C composite according to any one of [1] to [5] (step (A)) is followed by forming an unsaturated bond. A method for producing a Si—C composite, comprising the step of contacting the Si—C composite with a gas containing hydrocarbons at 400° C. or lower (step (B)).

According to the present invention, it is possible to provide a method for producing a Si--C composite in which silicon is uniformly deposited over the entire porous carbon particles.

The contents of the present invention will be described in detail below. The description of the contents of the constituent elements described below may be made based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.
In the present specification, "to" indicating a numerical range is used to include the numerical values before and after it as lower and upper limits.
In this specification, a unit described either before or after "-" indicating a numerical range applies to all numerical values within that numerical range unless otherwise specified.
The term "step" in this specification includes not only independent steps, but also if the desired purpose of the step is achieved, even if it cannot be clearly distinguished from other steps.
In the present specification, a combination of two or more preferred aspects is a more preferred aspect.
In this specification, unless otherwise specified, the term "pores" includes both the inside of pores and the outside of pores on the surface of porous carbon particles.

In the present specification, the expression "the porous carbon particles contained in the porous carbon particles have similar silicon deposition patterns" does not mean that there is little variation in the silicon deposition patterns among the porous carbon particles. This means that there is little variation in the way silicon precipitates from the porous carbon particles among the products obtained, regardless of the sampling location of the product (Si—C composite).
In the method for producing a Si—C composite of the present invention (hereinafter sometimes simply referred to as “the production method of the present invention”), since it has the above configuration, regardless of the location of the raw material in the reactor, It is considered that the method of silicon deposition is similar in the contained porous carbon particles (hereinafter sometimes referred to as "silicon is uniformly deposited over the entire porous carbon particles"). Therefore, a Si—C composite with small variations in physical properties can be obtained regardless of the location of the raw material in the reactor. As a result, improvement in yield and scalability can be expected. In addition, since the production method of the present invention can easily obtain a Si—C composite with little silicon deposition on the surface of the porous carbon particles, it is possible to obtain a negative electrode material excellent in cycle characteristics and initial coulomb efficiency. Next, the method for producing the Si—C composite (that is, the silicon-carbon composite) of the present invention will be described in detail.
In the production method of the present invention, a silane-containing gas is passed through a reactor charged with porous carbon particles, silane in the silane-containing gas is thermally decomposed, and silicon is deposited in the pores of the porous carbon particles. Let

<1> Reactor The reactor is provided with a silane-containing gas flow path extending from the silane-containing gas inlet to the exhaust gas outlet. The porous carbon particles used in the production method of the present invention are loaded in the silane-containing gas flow passage.

In the production method of the present invention, the silane-containing gas is introduced into the silane-containing gas flow path from the silane-containing gas inlet of the reactor, and the silane-containing gas flow path is heated to thermally decompose silane in the silane-containing gas. As a result, silicon is deposited in the pores of the porous carbon particles loaded in the silane-containing gas flow passages to form a Si—C composite. The exhaust gas generated from the silane-containing gas by the reaction and the unreacted silane-containing gas are discharged from the exhaust gas outlet.

The reactor is preferably equipped with a heater capable of controlling a predetermined temperature at a predetermined point in the silane-containing gas flow passage. There is no particular limitation on the location where the heater is installed, and a plurality of heaters may be installed along the silane-containing gas flow path. For example, the reactor may have three heaters, or four or more heaters. The greater the number of heaters, the easier it is to control each location in the silane-containing gas flow path at a predetermined temperature.

The reactor is not limited to a stationary furnace, and may be a rotary furnace such as a rotary kiln. The shape of the reactor is not particularly limited as long as the above functions can be realized, and various shapes such as a straight tubular shape, a disk shape, and a spiral circular tubular shape can be appropriately selected.
Also, the shape of the silane-containing gas flow path and the like is appropriately determined according to the shape of the reactor. For example, when the reactor has a straight tube shape, the inner space of the straight tube serves as the silane-containing gas flow passage.
The size of the reactor is not particularly limited as long as the functions can be realized, and can be appropriately determined according to production scale and the like.

<2> Porous carbon particles The porous carbon particles used in the production method of the present invention preferably have a pore volume of 0.2 cm ³ /g or more. Since the porous carbon particles have a pore volume of 0.2 cm ³ /g or more, they can be impregnated with a sufficient amount of silicon, so that a sufficiently large specific capacity can be obtained as a negative electrode material for batteries. From this point of view, the pore volume of the porous carbon particles is more preferably 0.4 cm ³ /g or more, more preferably 0.6 cm ³ /g or more.

The porous carbon particles used in the production method of the present invention preferably have a pore volume of, for example, 2.2 cm ³ /g or less. When the pore volume of the porous carbon particles is 2.2 cm ³ /g or less, the volume change due to expansion/contraction during charge/discharge can be absorbed by the porous carbon particles as a carrier. From this point of view, the pore volume of the porous carbon particles is more preferably 2.0 cm ³ /g or less, more preferably 1.8 cm ³ /g or less.
The pore volume of porous carbon particles can be measured by a nitrogen adsorption test.

The porous carbon particles used in the production method of the present invention preferably have a BET specific surface area of 800 m ² /g or more. When the BET specific surface area of the porous carbon particles is 800 m ² /g or more, a large amount of silicon can be deposited mainly on the inner surfaces of the porous carbon particles, so that a sufficiently high specific capacity can be obtained as a negative electrode material. Obtainable. From this point of view, the BET specific surface area of the porous carbon particles is more preferably 900 m ² /g or more, more preferably 1000 m ² /g or more.

For the BET specific surface area, use the value calculated using the BET method from the adsorption isotherm obtained by nitrogen adsorption measurement. The data range of the adsorption isotherm used for calculation follows a known method.

The porous carbon particles used in the production method of the present invention preferably have a 50% particle diameter (hereinafter also referred to as “D _V50 ”) in volume-based cumulative particle size distribution of 2.0 μm or more. If the D _V50 of the porous carbon particles is 2.0 μm or more, the resulting Si—C composite has excellent handleability, can be easily prepared into a slurry having a viscosity and density suitable for coating, and can be used when forming an electrode. The density of the porous carbon particles is likely to increase. From this point of view, D _V50 is more preferably 3.0 μm or more, further preferably 4.0 μm or more.

D _V50 of the porous carbon particles is preferably 30.0 μm or less. If the D _V50 of the porous carbon particles is 30.0 μm or less, the diffusion length of lithium in each particle is short, so the rate characteristics of the lithium ion battery are excellent, and when the slurry is applied to the current collector, In addition, it is possible to suppress the occurrence of streaks due to the porous carbon particles and the occurrence of abnormal irregularities derived from the porous carbon particles. From this point of view, D _V50 is more preferably 25.0 μm or less, more preferably 20.0 μm or less.

D _V50 can be measured by laser diffraction. D _V10 and D _V90 refer to the 10% particle size and 90% particle size in the volume-based cumulative particle size distribution, respectively. D _V10 , D _V90 can also be measured by laser diffraction.
The porous carbon particles having the pore volume as described above, or additionally the BET specific surface area and particle size, may be purchased and used, or a known technique may be used to synthesize a resin, which is then carbonized and activated. It may be obtained by adjusting the particle size.

A well-known technique can be used for adjusting the particle size. As a method for adjusting the particle size, for example, a pulverizer such as a jet mill, a pin mill, or a vibration mill, or an air classifier can be used.
Even from the state of the Si—C composite, for example, by eluting silicon using an aqueous potassium hydroxide solution, the pore volume and BET specific surface area of the porous carbon particles used as the raw material, and the volume-based cumulative particle size distribution of 50 Physical properties such as % particle size and true density can be measured.

<3> Loading of Porous Carbon Particles Porous carbon particles are loaded into the silane-containing gas flow path of the reactor as described above. The method of filling the porous carbon is not particularly limited, and the sagger may be filled with the porous carbon particles, or the porous carbon particles may be placed on a structure such as a shelf. The porous carbon particles are preferably loaded into the silane-containing gas flow path with a uniform thickness from the silane-containing gas inlet toward the exhaust gas outlet. The amount of porous carbon particles to be charged (amount to be charged) is not particularly limited, and can be appropriately determined according to the size of the reactor, production scale, and the like.

<4> Silane-Containing Gas The silane-containing gas is introduced into the silane-containing gas flow path of the reactor, and undergoes a reaction to deposit silicon in the pores of the porous carbon particles (hereinafter also referred to as “Si-CVI reaction”). ).
The silane-containing gas is preferably silane gas or a mixed gas of silane gas and inert gas. The molar fraction of silane gas in the mixed gas is preferably 0.001-1. The inert gas contained in the mixed gas is not particularly limited, but is preferably nitrogen or argon.
The silane gas is represented by the general formula Si _n H _2n+2 and specifically includes monosilane (SiH ₄ ), disilane, trisilane, tetrasilane, etc. Monosilane is preferred.

In the production method of the present invention, before carrying out the Si-CVI reaction, it is preferable to flow an inert gas through the silane-containing gas flow path and raise the temperature to a predetermined reaction temperature, and then appropriately at the set temperature. You can keep warm.
The rate at which the temperature is raised is not particularly limited, and can be freely selected in consideration of productivity, damage to the furnace, and the like. When the temperature is raised to a predetermined reaction temperature, the gas may be switched from an inert gas to a reaction gas (silane-containing gas) when starting the Si-CVI reaction.

<5> Pressure during reaction In the production method of the present invention, the gauge pressure in the reactor during the Si-CVI reaction is preferably −10 kPa or more and +10 kPa or less. By performing the Si-CVI reaction in such a pressure range, silicon can be selectively deposited in the pores of the porous carbon, and silicon can be deposited on surfaces other than the pores of the porous carbon. can be suppressed.

<6> Gas Flow Rate of Silane-Containing Gas In the production method of the present invention, the gas flow rate of silane-containing gas is not particularly limited. It can be determined as appropriate according to the scale and the like.

<7> Temperature during Reaction In the manufacturing method of the present invention, the Si-CVI reaction takes place in the silane-containing gas flow path.
The reaction temperature in the silane-containing gas flow path is 330° C. or higher and 450° C. or lower. That is, in the silane-containing gas flow path, the Si-CVI reaction with respect to the porous carbon particles takes place in the range of 330°C or higher and 450°C or lower.

When the reaction temperature is 330°C or higher, the silane gas is adsorbed in the pores of the porous carbon particles, and decomposition can occur only at the temperature reached by the temperature rise due to the heat generated at that time. Therefore, silicon can be selectively deposited in the pores. From this point of view, the reaction temperature is preferably 340°C or higher, more preferably 350°C or higher.

If the reaction temperature is 450°C or lower, most of the silane gas will not decompose by itself, so it will hardly decompose outside the pores of the porous carbon particles. From this point of view, the reaction temperature is preferably 445°C or lower, more preferably 440°C or lower.

The reaction temperature in the silane-containing gas flow path has a temperature distribution that rises from the silane-containing gas inlet toward the exhaust gas outlet. That is, the reaction temperature in the silane-containing gas flow path has a temperature gradient, and the reaction temperature must rise within the range of 330° C. or higher and 450° C. or lower from the silane-containing gas inlet toward the exhaust gas outlet. Alternatively, there may be a portion at a constant temperature from the silane-containing gas inlet to the exhaust gas outlet.

Specifically, the reaction temperature at the silane-containing gas inlet side end of the porous carbon particles in the silane-containing gas flow passage (hereinafter also referred to as "upstream end") is Tup, and the silane-containing gas inlet side end is Tup. Tmid is the reaction temperature at the midpoint between the part and the exhaust gas outlet side end (hereinafter also referred to as the “intermediate portion”), and the reaction temperature at the exhaust gas outlet side end (hereinafter also referred to as the “downstream end”). is Tdown, the temperature is controlled so that the following equation holds.
0℃<Tmid−Tup≦70℃
0°C ≤ Tdown-Tmid ≤ 50°C

On the upstream end side, there is a large amount of unreacted silane gas and porous carbon particles, so there is a high probability that the silane gas will be adsorbed in the pores in the porous carbon particles, and therefore a lot of heat will be generated. By setting the reaction temperature Tup at the upstream end to be lower than the reaction temperature Tmid at the intermediate portion, the reaction activity on the upstream side and the midstream portion can be matched, and the physical properties of the product will be uniform. On the other hand, when Tup is lower than Tmid by more than 70° C., the thermal decomposition reaction of silane is not promoted and Si deposition is greatly suppressed.

The temperature difference between Tmid and Tup (Tmid-Tup) is preferably greater than 5°C, more preferably greater than 15°C. The temperature difference between Tmid and Tup (Tmid-Tup) is preferably 60°C or less, more preferably 50°C or less.

Further, by making the reaction temperature Tdown at the downstream end equal to or higher than the reaction temperature Tmid at the intermediate portion, it is possible to compensate for the disadvantage of the downstream side that the concentration of silane gas is lower than that at the midstream portion. On the other hand, when Tdown exceeds Tmid by more than 50° C., reactions in the downstream portion proceed locally, resulting in non-uniform loading.

The temperature difference between Tdown and Tmid (Tdown-Tmid) is preferably 0 to 45°C, more preferably 0 to 40°C.
In the production method of the present invention, the reaction temperature Tup at the upstream end is preferably less than 400°C. When Tup is less than 400° C., Tmid may be less than 400° C. or 400° C. or more as long as 0° C.<Tmid−Tup≦70° C., and Tdown as long as 0° C.≦Tdown−Tmid≦50° C. It may be below 400°C or above 400°C.

The temperature distribution as described above can be achieved, for example, by a heater installed on the silane-containing gas inlet side along the silane-containing gas flow path of the reactor (hereinafter also referred to as an "upstream heater"), and a heater installed on the exhaust gas outlet side. (hereinafter also referred to as “downstream heater”), and a heater installed between the upstream heater and the downstream heater (hereinafter also referred to as “midstream heater”). It can be obtained by setting the set temperature of the heater to be lower than the set temperatures of the midstream heater and the downstream heater, and setting the set temperature of the downstream heater to be the same as the set temperature of the midstream heater or higher than the set temperature of the midstream heater. can.

<8> Reaction time The time for the Si-CVI reaction is not particularly limited, and may be, for example, 1 second to 30 hours. The silicon content can be freely changed by adjusting the Si-CVI reaction time.

<9> Monitoring Amount of Silane Gas In the Si-CVI reaction in the production method of the present invention, when monosilane (SiH ₄ ) gas is used as the silane-containing gas, the reaction SiH ₄ →Si+2H ₂ occurs. From this reaction formula, the gas composition at the outlet can be monitored by sampling the exhaust gas discharged from the exhaust gas outlet and measuring the concentration of silane gas or hydrogen gas. If the mass flow rate of silane gas at the reactor inlet and the concentration of silane gas in the exhaust gas at the reactor outlet are known, the amount of silane gas used for deposition on the porous carbon particles per unit time can be determined. Based on this, the amount of silicon deposited on the porous carbon particles per unit time can also be calculated. By accumulating the obtained values over the reaction time, the total amount of silicon deposited on the porous carbon particles during the reaction, that is, the reaction amount can be estimated.
Also, if the flow rate of the silane gas introduced into the reactor is adjusted by the mass flow rate, the mass flow rate at the inlet of the reactor can be known. A method for measuring this may be gas chromatography or a gas detector, but a real-time composite gas mass spectrometer is preferable because it allows monitoring during the reaction.

<10> Adjustment of Filling Rate of Silicon in Pores of Porous Carbon Particles In the production method of the present invention, silicon can be selectively deposited in the pores of the porous carbon particles. Also, using the density of silicon, the total amount of silicon deposited on the porous carbon particles can be converted from a unit of mass to a unit of volume. From the pore volume of the porous carbon particles and the volume of the total amount of silicon deposited in the pores of the porous carbon particles by the above reaction, the filling rate of silicon in the pores of the porous carbon particles is obtained by the following equation. can be done. Although it is difficult to strictly distinguish between the silicon inside the pores of the porous carbon particles and the silicon outside the pores, it is difficult to measure and calculate the filling ratio obtained by the following equation. is the filling rate of silicon into the pores of

(Filling rate α) (%) = 100 x w _Si / (V _p x w _C x ρ _Si )
Here, w _Si is the total amount of silicon deposited on the porous carbon particles by the Si-CVI reaction [g], ρ _Si is the density of silicon [g/cm ³ ], and w _C is the mass of the porous carbon particles used [ g], V _p is the pore volume [cm ³ /g] of the porous carbon particles. Also, the unit of the filling rate α is %.
As the density of silicon, it is necessary to accurately use the density of amorphous silicon, but even if 2.3290 g/cm ³ which is the density of crystalline silicon is used, the filling rate (%) of silicon can be obtained with sufficient accuracy. can be estimated. By sampling, estimating the amount of deposited silicon, and calculating the fill factor while the reaction is running, the reaction can be stopped when the desired fill factor is obtained. In this way, the filling rate of silicon into the pores of the porous carbon particles can be adjusted from the reaction amount and the pore volume.

<11> Step (B)
In a method for producing a Si—C composite according to another embodiment of the present invention, the step of obtaining a Si—C composite by the method for producing Si—C described above (step (A)) is followed by The step (step (B)) of contacting the Si—C composite at 400° C. or lower with a gas containing a hydrocarbon having
In the present invention, not only the Si—C composite obtained in step (A), but also the Si—C composite obtained by performing steps (A) and (B) are produced according to the present invention. contained in the Si—C composite obtained by the method.
It is believed that in the above process, the Si—H groups on the surface of the Si—C composite react with hydrocarbons having unsaturated bonds to form a layer containing hydrocarbons on the surface of the Si—C composite. Therefore, after obtaining the Si—C composite obtained in the step (A), it is preferable to perform the step (B) while suppressing oxidation of the surface of the Si—C composite. Therefore, as long as the oxidation of the surface of the Si—C composite is suppressed, the embodiment of the present invention also includes another step or operation between step (A) and step (B).

As a method of suppressing oxidation, for example, after step (A), an inert gas such as helium, argon or nitrogen, or a reducing gas such as hydrogen is used to remove the unreacted silane-containing gas in step (A). A method of removing gas is mentioned.
The layer containing hydrocarbons may contain a substance obtained by reacting hydrocarbons with each other.

As the hydrocarbon gas having an unsaturated bond, a hydrocarbon gas having a double bond or a triple bond can be used. Hydrocarbons that have a low vapor pressure and hardly vaporize under normal pressure (101,325 pa) can be used by lowering the pressure below normal pressure.
Hydrocarbons preferably used include acetylene, ethylene, propylene and 1,3-butadiene, which are gases at normal pressure, with acetylene and ethylene being more preferred. In step (B), multiple types of hydrocarbons may be used. In addition, an inert gas such as helium or argon, or a reducing gas such as hydrogen may be mixed with the hydrocarbon.

Step (B) is a treatment of contacting the Si—C composite at 400° C. or less from the viewpoint of reacting the Si—H groups with the unsaturated bonds in the hydrocarbon. If the temperature at which the Si—C composite is contacted (hereinafter also referred to as “contact temperature”) is 400° C. or less, the decomposition of the Si—H group is likely to be suppressed, and the Si— on the surface of the Si—C composite Reaction of H groups with unsaturated bonds in hydrocarbons is more likely.

The contact temperature in the step (B) is not limited as long as it is a temperature at which the hydrocarbon having an unsaturated bond reacts on the surface of the Si—C composite. 100° C. or higher is preferable, and 150° C. or higher is more preferable.

The thickness of the hydrocarbon-containing layer formed on the surface of the Si—C composite may be as thick as a monomolecular layer of hydrocarbon, or as thick as several molecular layers. Some of the hydrocarbons may be decomposed. Even if some of the hydrocarbons are decomposed into carbon, the layer containing the hydrocarbons is preferably a thin film because it is a material with high resistance unlike ordinary coated carbon.
Therefore, it is preferable that the change in mass of the Si—C composite be small before and after the step (B). The mass of the Si—C composite before performing the step (B) is W _B, before, and the mass of the Si—C composite having a layer containing a hydrocarbon after performing the step (B) is W _B, after Then, the rate of increase in the mass of the Si—C composite due to step (B), ΔW _B , is given by the following equation.
ΔW _B (%) = 100 × (W _B, rear - W _B, front) / W _B, front ΔW _B is more preferably 1.0% or less, more preferably 0.5% or less. more preferred.

The effects of the step (B) hydrocarbon treatment include, for example, suppression of oxidation of silicon inside the Si—C composite over time, suppression of hydrogen generation during preparation of slurry for electrode coating, increase in initial coulomb efficiency in the battery, cycle improvement of characteristics. The presence of the protective layer on the surface of the Si--C composite can prevent oxygen and moisture from entering the interior of the Si--C composite.

In the production method of the present invention, after silicon is precipitated in the pores of the porous carbon particles to obtain the Si—C composite, the Si—C composite is brought into contact with an inert gas atmosphere containing oxygen, The silicon surface may be oxidized. Pure silicon, in particular, has high activity, so rapid deterioration can be suppressed by oxidizing the surface.

After deposition or oxidation of silicon, the surface of the Si--C composite may be coated separately. A specific example is a carbon coating. Methods of carbon coating include chemical vapor deposition (CVD (Chemical Vapor Deposition), etc.) and the like. Carbon coating by CVD is referred to herein as "C-CVD."

　The effects of the coating include, for example, suppressing the oxidation of silicon inside the Si—C composite over time, increasing the initial coulombic efficiency, and improving cycle characteristics. The presence of the coat layer on the surface of the Si—C composite can suppress the intrusion of oxygen and moisture into the interior of the Si—C composite.

<12> Evaluation of Product Uniformity According to the production method of the present invention, a Si—C composite in which silicon is uniformly deposited over the entire porous carbon particles is obtained.
This indicates that the physical properties of the Si—C composite obtained by the Si—CVI reaction for each product acquisition location in the reactor (hereinafter sometimes referred to as “sampling position”) It can be evaluated by comparing values. For example, first, the obtained powder (Si—C composite) is divided into three equal parts along the length in the gas introduction direction, and the part on the side of the silane-containing gas inlet (upstream part) and the part on the side of the silane-containing gas outlet. The product is sampled from each portion (downstream portion) and the portion (midstream portion) sandwiched between the upstream portion and the downstream portion, and the products are uniformly mixed and then analyzed or evaluated for the battery. , and compare whether the products of each part have similar physical property values or battery characteristics.
The physical properties of the Si—C composite and the method for measuring them will be described below.
Further, hereinafter, variation indicates the difference between the highest value and the lowest value among the analysis values for each sampling position. For example, among the values obtained by analyzing the upstream portion, midstream portion, and downstream portion of the Si—C composite obtained as described above, the difference between the highest value and the lowest value show.

(1) R value of Raman spectrum In general, the R value of Raman spectrum reflects the amount of defects contained in the crystal structure of carbon. Therefore, the R value of the Raman spectrum of the Si--C composite obtained by the production method of the present invention is information on the amount of defects contained in the crystal structure of the porous carbon particles in the Si--C composite.
The R value is the ratio (I _D /I _G ) of the peak intensity I _D near 1360 cm ⁻¹ and the peak intensity I _G near 1580 cm ⁻¹ in the Raman spectrum.
Here, the peak intensity is the height from the baseline to the peak apex after correcting the baseline.

The Si—C composite obtained by the production method of the present invention preferably has a Raman spectrum R value of 0.50 or more.
When the R value is 0.50 or more, the reaction resistance is sufficiently low, leading to an improvement in the rate characteristics of the battery. From this point of view, the R value is more preferably 0.70 or more, more preferably 0.80 or more.

The R value of the Raman spectrum of the Si—C composite obtained by the production method of the present invention is preferably less than 1.50. When the R value is less than 1.50, the carbon surface of the Si—C composite has few defects, so side reactions in the battery are reduced and the initial coulombic efficiency is improved. From this point of view, the R value is more preferably 1.40 or less, even more preferably 1.35 or less, and particularly preferably 1.30 or less.

(2) Peak of Silicon in Raman Spectrum The Si—C composite obtained by the production method of the present invention has a silicon-derived peak in the Raman spectrum, and the peak exists at 450 to 495 cm ⁻¹ . It is generally known that silicon having a peak in this wavenumber range is amorphous. In contrast, crystalline silicon is known to have a peak near 520 cm ⁻¹ in the Raman spectrum.
It is believed that amorphous silicon is formed in the Si—C composite obtained by the manufacturing method of the present invention. In the present invention, the peak intensity of amorphous silicon is denoted as I _Si .

(3) I _Si /I _G in Raman spectrum
_IG is the intensity of the aforementioned peak near 1580 cm ^-1 , and this peak originates from porous carbon particles in the Si—C composite.

The variation in the value of I _Si /I _G of the Raman spectrum of the Si—C composite due to the sampling position in the reactor is preferably 0.25 or less, more preferably 0.20 or less, and 0.10 or less. More preferred.
As will be described later, variations in the value of I _Si /I _G are thought to be due to variations in the amount of Si deposited on the surface, which is thought to lead to variations in the cycle characteristics of the battery.

The I _Si /I _G of the Raman spectrum of the Si—C composite obtained by the production method of the present invention is preferably 0.80 or less, more preferably 0.70 or less, and less than 0.30. is more preferred. The appearance of a silicon peak in the Raman spectrum indicates that silicon is deposited near the surface of the Si—C composite, and I _Si /I _G is 0.80 or less (more preferably 0 .70 or less, more preferably less than 0.30), it can be estimated that silicon is mainly deposited inside the pores of the porous carbon particles and is hardly precipitated on the surfaces of the porous carbon particles. can. This leads to improved cycle characteristics in that the silicon does not come into direct contact with the electrolyte and in that the expansion and contraction of the silicon are absorbed by the porous carbon particles.
From the same point of view, I _Si /I _G is more preferably 0.25 or less, and even more preferably 0.20 or less. Although the lower limit of I _Si /I _G is not particularly limited, I _Si /I _G is preferably 0.03 or more, more preferably 0.06 or more. When I _Si /I _G is 0.03 or more, it is presumed that a sufficient amount of silicon is deposited, and a sufficiently large specific capacitance can be obtained.

(4) Si content rate Si content rate is defined by the following formula. The unit is % by mass.
(Si content)=100×(mass of silicon contained in Si—C composite)/(mass of Si—C composite)
The variation in the Si content of the Si—C composite due to the sampling position in the reactor is preferably 9% by mass or less, more preferably 6% by mass or less, and 3% by mass. preferable. This is because variations in the Si content lead to variations in the capacity of the battery.

From the viewpoint of obtaining a sufficient specific capacity of the Si--C composite, the Si content of the Si--C composite obtained by the production method of the present invention is preferably 15% by mass or more. From this point of view, the Si content is more preferably 20% by mass or more, and even more preferably 25% by mass.

From the viewpoint of obtaining a lithium ion secondary battery negative electrode material with stable cycle characteristics, the Si content of the Si—C composite obtained by the production method of the present invention is preferably 85% by mass or less. From this point of view, the Si content is more preferably 75% by mass or less, and even more preferably 65% by mass or less. At this time, ideally, silicon should be present only in the pores of the porous carbon particles, but in reality, silicon may also be deposited on the outermost surfaces of the porous carbon particles. In addition, silicon may be deposited on the outermost surface of the porous carbon particles without completely filling the pore volume of the porous carbon particles with silicon.

The Si content can be obtained by subjecting the Si—C composite to fluorescent X-ray analysis using a fundamental parameter (FP) method.

(5) BET Specific Surface Area The Si—C composite obtained by the production method of the present invention is preferably one in which silicon is selectively deposited in pores of porous carbon particles. Since the pores of the raw material porous carbon particles are filled with silicon or the entrances of the pores are blocked with silicon, the BET specific surface area of the Si—C composite is the BET specific surface area of the porous carbon particles. less than As a result, it becomes a value suitable for use as a negative electrode material for a lithium ion secondary battery.

Variation in the BET specific surface area of the Si—C composite due to sampling positions in the reactor is preferably 30 m ² /g or less, more preferably 20 m ² /g or less, and 15 m ² /g or less. is more preferred.
When the variation in the BET specific surface area is 30 m ² /g or less, the extent of the side reactions becomes equal, so the variation in the initial coulombic efficiency is reduced.

The BET specific surface area of the Si—C composite obtained by the production method of the present invention is preferably 40 m ² /g or less. If it is 40 m ² /g or less, the decomposition reaction of the electrolytic solution, which is a side reaction, does not become remarkable, so the initial coulombic efficiency can be increased. From this point of view, the BET specific surface area is more preferably 20 m ² /g or less, more preferably 15 m ² /g or less.

The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[material]
The porous carbon particles used to obtain the Si—C composite are as follows.
Porous carbon particles 1: Porous carbon particles having a pore volume of 0.85 cm ³ /g, D _V10 of 6.9 μm, D _V50 of 14.4 μm, D _V90 of 26.2 μm, and a BET specific surface area of 1770 m ² /g Porous carbon particles 2: Porous carbon particles having a pore volume of 0.60 cm ³ /g, D _V10 of 5.3 μm, D _V50 of 10.7 μm, D _V90 of 19.6 μm, and a BET specific surface area of 1550 m ² /g Porous carbon particles 3: Pores Porous carbon particles having a volume of 1.1 cm ³ /g, D _V10 of 3.2 μm, D _V50 of 4.4 μm, D _V90 of 6.1 μm, and a BET specific surface area of 2100 m ² /g. went like

[Nitrogen adsorption test]
(Method)
A sample is placed in a sample cell (9 mm x 135 mm) so that the total surface area of the sample is 2 to 60 m ² , dried at 300°C under vacuum conditions for 1 hour, and then the weight of the sample is measured using the following method. rice field.
Apparatus: NOVA4200e (registered trademark) manufactured by Quantachrome Instruments
・Measurement gas: Nitrogen ・Set value of relative pressure in the measurement range: 0.005 to 0.995

(Method of calculation)
(Calculation method of BET specific surface area)
The BET specific surface area of the porous carbon material was calculated by the BET multipoint method from the adsorption isotherm data at a relative pressure of about 0.005 to less than 0.08.
The BET specific surface area of the composite particles was calculated by the BET multipoint method from the adsorption isotherm data at three points near relative pressures of 0.1, 0.2 and 0.3.

(Method for calculating pore volume)
The pore volume was obtained by calculating the adsorption amount at a relative pressure of 0.99 by linear approximation from the adsorption isotherm data at two points around the relative pressure of 0.99. At this time, calculations were made assuming that the liquid density of nitrogen is 0.808 g/cc, the volume of 1 mol of nitrogen in the standard state is 22.4133 L, and the atomic weight of nitrogen is 14.0067.

(Measurement setting relative pressure)
The set value of the relative pressure at the time of actual measurement is as follows.
0.005, 0.007, 0.010, 0.020, 0.050, 0.075, 0.100, 0.200, 0.300, 0.800, 0.900, 0.925, 0.950, 0.975, 0.990, 0.995

[Particle size distribution measurement]
1 cup of ultra-small spatula of porous carbon particles used in Examples and Comparative Examples, and 2 100-fold diluted solutions of nonionic surfactant (SARAYA Palm Detergent High Power) undiluted solution (32% by mass) Add dropwise water (15 mL) and sonicate for 3 minutes. This dispersion is put into a laser diffraction particle size distribution analyzer (model number: LMS-2000e) manufactured by Seishin Enterprise Co., Ltd., and the _volume -based cumulative particle size distribution is measured. The diameter D _V50 and 90% particle diameter D _V90 were determined.

[I _Si /I _G , R value (I _D /I _G ), and Si peak position]
The sample was placed on a glass preparation using a small spatula and spread evenly so that the underlying glass preparation was not exposed. The range over which the sample was spread was wider than the measurement range described later. This is to ensure that only the composite particles are spread within the measurement range. This sample was measured by the following method.
・Microscopic Raman spectrometer: manufactured by Horiba, Ltd., product name: LabRAM HR Evolution
・Excitation wavelength: 532 nm
・Exposure time: 10 seconds ・Number of integration times: 2 ・Diffraction grating: 300 lines/mm (600 nm)
・Measurement range: length 60 μm x width 60 μm
Number of points: Measurement was performed at 30 points with a longitudinal feed of 12 μm and a lateral feed of 15 μm, and the spectrum obtained by averaging them was obtained and the following analysis was performed.

(analysis method)
The intensity was defined as the height of the peak top from the baseline. From the measured spectrum, the ratio (ID/IG) of the peak intensity ID (derived from the amorphous component) near 1350 cm ^-1 to the peak intensity IG (derived from the graphite component) near 1600 cm ^-1 was calculated. This ratio (ID/IG) was measured at two points, and the average value was taken as the R value (ID/IG).

Also, the ratio (I _Si /I _G ) between the intensity ISi of the peak derived from amorphous silicon appearing at 450 to 495 cm ⁻¹ and the IG was calculated. This ratio (I _Si /I _G ) was measured at two points, and the average value was taken as I _Si /I _G .

[Measurement of Si content]
The Si content of the Si—C composites obtained in Examples and Comparative Examples was measured under the following conditions.
・Fluorescent X-ray device: Rigaku NEX CG
・Tube voltage: 50 kV
・Tube current: 1.00mA
・Sample cup: Φ32 12mL CH1530
・Sample weight: 2 to 4 g
・Sample height: 5 to 18 mm
The FP method was performed using analysis software attached to the apparatus.

[Example 1]
Si-CVI reaction was carried out using a reactor (manufactured by Koyo Thermo Systems Co., Ltd.) equipped with a horizontal tubular reaction tube. The inner diameter of the tubular reaction tube, the inside of which serves as a flow path for the silane-containing gas, was 7 cm. A heater having a length of 70 cm was installed in the tubular reaction tube, and the temperature was controlled for each of three zones obtained by dividing the heater into three equal parts. A graphite plate having a length of 30 cm was placed in the tubular reaction tube so that the center of the heater in the extending direction of the reaction tube coincided with the center of the graphite plate in the extending direction of the reaction tube. 35 g of porous carbon particles 1 as a raw material are placed on a graphite plate over a length of 20 cm in the extending direction of the reaction tube so that the center of the heater in the extending direction of the reaction tube coincides with the center of the porous carbon particles 1 in the extending direction of the reaction tube. It was set up as

With the heater, the reaction temperature at the silane-containing gas inlet side end (upstream end) of the porous carbon particles 1, the midpoint (middle part) between the silane-containing gas inlet side end and the exhaust gas outlet side end and the reaction temperature at the exhaust gas outlet side end (downstream end) were adjusted to 375° C., 400° C., and 410° C., respectively.

Argon gas was passed through the silane-containing gas flow path from the silane-containing gas inlet, and the temperature was raised and maintained in the argon gas atmosphere as described above. After that, the argon gas was switched to 100% monosilane gas at 130 sccm, and the monosilane gas was circulated from the silane-containing gas inlet to the silane-containing gas flow passage. The pressure in the reactor at this time was +1.6 kPa in gauge pressure. A Si-CVI reaction was carried out for 250 minutes, after which the monosilane gas was switched to argon gas, heating of the reactor was stopped, and the reactor was cooled to room temperature.

The powder (Si—C composite) obtained by this Si—CVI reaction was divided into three equal parts in the direction of elongation of the reaction tube. The portion (downstream portion) and the portion (midstream portion) sandwiched between the upstream portion and the downstream portion are each sampled and uniformly mixed, and then each portion is subjected to Raman spectroscopic analysis, fluorescent X-ray analysis, and nitrogen Adsorption measurements were performed to determine the R value, Si peak position, I _Si /I _G , Si content, and BET specific surface area, and the numerical values and variations thereof were compared. Table 1 shows the results.

-evaluation-
When the variation in I _Si /I _G is 0.25 or less and the variation in BET specific surface area is 30 m ² /g or less, regardless of where the raw materials are placed in the reactor, In the obtained Si—C composite, it can be determined that silicon is uniformly deposited over the entire porous carbon particles.
Further, when the value of I _Si /I _G is 0.80 or less, in the obtained Si—C composite, silicon is mainly deposited inside the pores of the porous carbon particles, and is deposited on the surfaces of the porous carbon particles. It can be judged that there is almost no precipitation.

As can be seen from the results shown in Table 1, in Example 1, variations in the physical properties of the Si—C composites obtained from the upstream portion, downstream portion, and midstream portion were very small. From this, it was found that silicon was deposited uniformly over the entire porous carbon particles. In addition, since I _Si /I _G is 0.20 or less, it was found that silicon was mainly deposited inside the pores of the porous carbon particles and was hardly deposited on the surfaces of the porous carbon particles. .
In the Si-CVI reaction, the temperature in the reactor is 375 to 410°C, and the reaction is performed at Tmid-Tup = 25°C and Tdown-Tmid = 10°C. A temperature gradient was applied. It can be seen that the obtained Si—C composite had silicon deposited uniformly over the entire porous carbon particle regardless of the sampling position.

[Examples 2-3 and Comparative Examples 1-4]
Si-CVI was performed in the same manner as in Example 1, except that the reaction temperature and silane treatment time at the upstream end, intermediate portion, and downstream end of the silane-containing gas flow passage were adjusted as shown in Table 1, respectively. -C conjugate was obtained. Physical property values were measured in the same manner as in Examples. Table 1 shows the results.

[Example 4]
Si--CVI reaction was carried out in the same manner as in Example 1 except that porous carbon particles 2 were used instead of porous carbon particles 1 and the silane treatment time was changed to obtain a Si--C composite. Physical property values were measured in the same manner as in Examples. Table 1 shows the results.

[Example 5]
Si--CVI reaction was carried out in the same manner as in Example 1 except that porous carbon particles 3 were used instead of porous carbon particles 1 and the silane treatment time was changed to obtain a Si--C composite. Physical property values were measured in the same manner as in Examples. Table 1 shows the results.

[Example 6]
Si—CVI reaction was carried out in the same manner as in Example 1 except that the pressure in the reactor was set to 200 kPa in gauge pressure and the silane treatment time was changed to obtain a Si—C composite. Physical property values were measured in the same manner as in Examples. Table 1 shows the results.

In Example 2, the temperature in the reactor was 375 to 395° C., Tmid−Tup=25° C., and Tdown−Tmid=0° C. Therefore, from the upstream side to the downstream side, halfway Although there were points with the same temperature, there was an upward temperature gradient as a whole. It was found that the physical property values of the obtained Si--C composites all showed little variation, and silicon was uniformly deposited over the entire porous carbon particles of the obtained Si--C composites.

In Example 3, the temperature in the reactor is 395 to 445 ° C., Tmid-Tup = 25 ° C., Tdown-Tmid = 25 ° C., so there is an upward temperature gradient from the upstream side to the downstream side. was attached. Tdown was relatively high. It was found that the physical property values of the obtained Si--C composites all showed little variation, and silicon was uniformly deposited over the entire porous carbon particles of the obtained Si--C composites.

In Example 4, the temperature in the reactor is 375 to 410 ° C., Tmid-Tup = 25 ° C., Tdown-Tmid = 10 ° C., so there is an upward temperature gradient from the upstream side to the downstream side. was attached. The pore volume of the porous carbon particles used was rather small, and the obtained Si content was somewhat small. It was found that the physical property values of the obtained Si--C composites all showed little variation, and silicon was uniformly deposited over the entire porous carbon particles of the obtained Si--C composites.

In Example 5, the temperature in the reactor is 375 to 410 ° C., Tmid-Tup = 25 ° C., Tdown-Tmid = 10 ° C., so there is an upward temperature gradient from the upstream side to the downstream side. was attached. The porous carbon particles used had a rather large pore volume, and the resulting Si content was also large. It was found that the physical property values of the obtained Si--C composites all showed little variation, and silicon was uniformly deposited over the entire porous carbon particles of the obtained Si--C composites.

In Example 6, the temperature in the reactor was 375 to 410 ° C., Tmid-Tup = 25 ° C., Tdown-Tmid = 10 ° C., so there was an upward temperature gradient from the upstream side to the downstream side. was attached. The value of the gauge pressure during the reaction was as high as +200 kPa, but the variations in the physical properties of the obtained Si—C composites were all small, and the obtained Si—C composites were homogeneously siliconized throughout the porous carbon particles. was found to precipitate.

In Comparative Example 1, the temperature in the reactor was 400° C., Tmid−Tup=0° C., and Tdown−Tmid=0° C. Therefore, there was no upward temperature gradient from the upstream side to the downstream side. rice field. As for the physical properties of the obtained Si--C composite, the variation in BET specific surface area was relatively large at 241.0.

In Comparative Example 2, the temperature in the reactor is 430 to 470° C., Tmid−Tup=20° C., and Tdown−Tmid=20° C. Therefore, there is an upward temperature gradient from the upstream side to the downstream side. However, the temperature at the downstream end was high, and silicon was deposited in various places near the downstream end in the furnace. In addition, the physical property values of the obtained Si--C composite had a relatively large variation in the value of I _Si /I _G of 0.46.

In Comparative Example 3, Tup=410° C., Tmid=400° C., Tdown=375° C., Tmid−Tup=−10° C., Tdown−Tmid=−25° C. Therefore, from the upstream portion to the downstream portion. , without an upward temperature gradient. The physical property values of the obtained Si--C composites had a large BET specific surface area variation of 314.

In Comparative Example 4, the temperature in the reactor was 300 to 350° C., Tmid−Tup=25° C., and Tdown−Tmid=25° C. Therefore, there was an upward temperature gradient from the upstream side toward the downstream side. However, the temperature from the upstream end to the intermediate part was low, and the decomposition of silane gas was slow. Therefore, silicon did not precipitate much even in the pores of the porous carbon particles, and the pores were not completely filled with silicon. The variation in values was also large at 379.

From these examples, by adopting the conditions within the scope of the production method according to the present invention, the Si—C composite produced in the Si—CVI reaction exhibits uniform physical properties regardless of the sampling position, and porous carbon particles It can be seen that silicon is deposited uniformly over the entire surface.

Claims

A silane-containing gas is passed through a reactor charged with porous carbon particles to thermally decompose silane in the silane-containing gas to deposit silicon in the pores of the porous carbon particles. A manufacturing method comprising:
The reactor includes a silane-containing gas flow path from a silane-containing gas inlet to an exhaust gas outlet, and the porous carbon particles are loaded in the silane-containing gas flow path,
The reaction temperature in the silane-containing gas flow path is 330° C. or higher and 450° C. or lower, and has a temperature distribution that rises from the silane-containing gas inlet toward the exhaust gas outlet,
Tup is the reaction temperature at the silane-containing gas inlet side end of the porous carbon particles in the silane-containing gas flow passage, and the middle point between the silane-containing gas inlet side end and the exhaust gas outlet side end When the reaction temperature at Tmid and the reaction temperature at the exhaust gas outlet side end is Tdown,
0° C.<Tmid−Tup≦70° C. and 0° C.≦Tdown−Tmid≦50° C.
A method for producing a Si—C composite.
The method for producing a Si—C composite according to claim 1, wherein the Tup is less than 400°C.
The method for producing a Si—C composite according to claim 1 or 2, wherein the gauge pressure in the reactor during the reaction is -10 kPa to +10 kPa.
The flue gas discharged from the flue gas outlet is sampled, the composition of the flue gas is monitored, and the reaction amount is estimated from the mass flow rate of the silane gas at the reactor inlet, the concentration of the silane gas in the flue gas at the reactor outlet, and the reaction time. The method for producing a Si—C composite according to any one of claims 1 to 3.
The method for producing a Si—C composite according to claim 4, wherein the filling rate of silicon into the pores is adjusted from the values of the reaction amount and the pore volume.
The step of obtaining a Si—C composite by the method for producing a Si—C composite according to any one of claims 1 to 5 (step (A)) is followed by a gas containing a hydrocarbon having an unsaturated bond. is brought into contact with the Si—C composite at 400° C. or lower (step (B)).