WO2018088020A1 - Method for producing silicon material - Google Patents

Abstract

Provided is a production method capable of producing a silicon material at excellent yield. This method for producing a silicon material includes a first heating step of performing heating, in the presence of both CaSi₂ and a halogen-containing polymer, at a temperature greater than or equal to the temperature at which decomposition gas of the halogen-containing polymer is generated and lower than the carbonization temperature of the halogen-containing polymer. The method for producing a silicon material is characterized by using a heating furnace which includes a first space in which the halogen-containing polymer is disposed, a second space in which the CaSi₂ is disposed, and a ceramic portion which divides the first space and the second space and has a through hole through which the decomposition gas can pass, the second space being provided in a flow channel of the decomposition gas generated from the halogen-containing polymer in the first space.

Description

Method for producing silicon material

The present invention relates to a method for manufacturing a silicon material.

Silicon is known to be used as a component of semiconductors, solar cells, secondary batteries, etc. Therefore, research on silicon is actively conducted.

For example, Patent Document 1 describes a silicon composite in which silicon oxide is coated with carbon by thermal CVD, and a lithium ion secondary battery including the silicon composite as a negative electrode active material.

Moreover, the present inventors synthesized a layered silicon compound mainly composed of polysilane obtained by reacting CaSi ₂ and an acid to remove Ca in Patent Document 2, and heating the layered silicon compound at 300 ° C. or higher. In this report, a silicon material from which hydrogen is released is manufactured, and a lithium ion secondary battery including the silicon material as an active material is reported.

Furthermore, the inventors synthesized a layered silicon compound mainly composed of polysilane obtained by reacting CaSi ₂ and an acid to remove Ca in Patent Document 3, and heating the layered silicon compound at 300 ° C. or higher. To produce a silicon material from which hydrogen has been released, and to produce a carbon-silicon composite in which the silicon material is coated with carbon, and a lithium ion secondary battery comprising the composite as an active material. Reporting.

Then, the present inventors have reported in Patent Document 4 a method for synthesizing a one-pot carbon-coated silicon material using CaSi ₂ and a halogen-containing polymer.

Japanese Patent No. 3952180 International Publication No. 2014/080608 International Publication No. 2015/114692 International Publication No. 2016/031146

The one-pot synthesis method of a carbon-coated silicon material using CaSi ₂ and a halogen-containing polymer specifically disclosed in Patent Document 4 is a method in which a reaction is allowed to proceed with CaSi ₂ and a halogen-containing polymer in contact (Example 1). ) And CaSi ₂ and the halogen-containing polymer in a non-contact state (Example 2). And, as evaluated in Evaluation Example 3 of Patent Document 4, it can be said that the method of allowing the reaction to proceed with CaSi ₂ and the halogen-containing polymer in a non-contact state can suppress local heat generation, and is therefore easy to control the reaction. .

When the present inventor made a study on a method for allowing the reaction to proceed in a non-contact state between CaSi ₂ and the halogen-containing polymer, it was found that there was room for improvement in terms of yield.

The present invention has been made in view of such circumstances, and an object thereof is to provide a production method capable of producing a silicon material with an excellent yield.

The inventor considered the manufacturing method of Patent Document 4. In the one-pot synthesis method of carbon-coated silicon material using CaSi ₂ and a halogen-containing polymer, first, the halogen-containing polymer is decomposed by heating to generate a decomposition gas, and the decomposition gas and CaSi ₂ come into contact with each other. By doing so, the reaction is started. Here, in the method disclosed in Example 2 of Patent Document 4, since the flow path of the decomposition gas generated by the decomposition of the halogen-containing polymer is not determined, the contact between the decomposition gas and CaSi ₂ is not necessarily sufficient. Conceivable. Therefore, the present inventor directed to arrange CaSi ₂ on the flow path of the decomposition gas generated by the decomposition of the halogen-containing polymer.

Further, Patent Document 4 specifically disclosed a one-pot synthesis method of carbon-coated silicon material using CaSi ₂ and a halogen-containing polymer. However, by appropriately controlling the heating temperature, The inventor has demonstrated that a coated silicon material and a silicon material not coated with carbon can be made separately. And this inventor completed this invention.

That is, the method for producing a silicon material according to the present invention includes:
Including the first heating step of heating at a temperature higher than the decomposition gas generation temperature of the halogen-containing polymer and lower than the carbonization temperature in the presence of CaSi ₂ and the halogen-containing polymer;
Ceramics comprising a first space in which the halogen-containing polymer is disposed, a second space in which the CaSi ₂ is disposed, the first space and the second space, and a through hole through which the decomposition gas can pass. And a heating furnace in which the second space is provided in the flow path of the decomposition gas generated from the halogen-containing polymer in the first space.

In the method for producing a silicon material of the present invention, the yield of the silicon material is improved by using a specific heating furnace.

1 is a schematic diagram of a heating furnace used in Example 1. FIG. 3 is a schematic diagram of a heating furnace used in Comparative Example 1. FIG. 4 is a SEM image of a cross section of a negative electrode of Example 4. It is the SEM image which expanded the SEM image of FIG. 10 is a SEM image of a cross section of a negative electrode of Comparative Example 4.

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. A new 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 any one of the numerical ranges described above can be used as the upper and lower numerical values of the new numerical range.

The method for producing a silicon material of the present invention (hereinafter, the silicon material produced by the method for producing a silicon material of the present invention may be referred to as “the silicon material of the present invention”) in the presence of CaSi ₂ and a halogen-containing polymer. A first heating step of heating at a temperature higher than the decomposition gas generation temperature of the halogen-containing polymer and less than the carbonization temperature, a first space in which the halogen-containing polymer is arranged, and a second space in which the CaSi ₂ is arranged, A ceramic portion that divides the first space and the second space and has a through hole through which the cracked gas can pass, and the cracked gas generated from the halogen-containing polymer in the first space A heating furnace in which the second space is provided in the flow path is used.

The reaction mechanism of the first heating step when polyvinyl chloride is employed as the halogen-containing polymer will be described below.

First, polyvinyl chloride is decomposed by heating to release hydrogen chloride.
-(CH ₂ CHCl) n- → nHCl +-(CH = CH) n-

Next, CaSi ₂ acts with the released hydrogen chloride to form a layered silicon compound represented by Si ₆ H ₆ .
3CaSi ₂ + 6HCl → Si ₆ H ₆ + 3CaCl ₂

And since it is under heating conditions, hydrogen of Si ₆ H ₆ is released and silicon is obtained.
Si ₆ H ₆ → 6Si + 3H ₂ ↑

Moreover, a carbon covering silicon material can be manufactured by performing the 2nd heating process heated at the temperature more than the carbonization temperature of a halogen-containing polymer after the 1st heating process in the manufacturing method of the silicon material of this invention.
That is, the carbon-coated silicon material produced by the method for producing a carbon-coated silicon material of the present invention is referred to as “the carbon-coated silicon material of the present invention, unless otherwise specified”. Is sometimes referred to as “silicon material”.) Includes a second heating step of heating at a temperature equal to or higher than the carbonization temperature of the halogen-containing polymer after the first heating step in the method for producing a silicon material of the present invention. To do. Hereinafter, the manufacturing method of the silicon material of the present invention and the manufacturing method of the carbon-coated silicon material of the present invention may be collectively referred to as “the manufacturing method of the present invention”.
Following the reaction mechanism of the first heating step, the reaction mechanism of the second heating step is as follows.

(CH = CH) n, which is a decomposition product of polyvinyl chloride, is carbonized under heating conditions higher than its carbonization temperature. At that time, since silicon and (CH = CH) n carbide coexist, a carbon-coated silicon material in which silicon and carbon are integrated is obtained.
Si + (CH═CH) n → carbon-coated Si + nH ₂ ↑

Hereinafter, the production method of the present invention will be described in detail.
CaSi ₂ generally has a structure in which a Ca layer and a Si layer are stacked. CaSi ₂ may be synthesized by a known production method, or a commercially available one may be adopted. CaSi ₂ used in the production method of the present invention is preferably pulverized in advance. The preferred average particle diameter of CaSi ₂ can be exemplified by the range of 0.1 to 50 μm, more preferably within the range of 0.3 to 20 μm, still more preferably within the range of 0.5 to 10 μm, particularly preferably 1 to A range of 5 μm can be exemplified. Incidentally, the average particle diameter in the present specification means a D ₅₀ as measured by conventional laser diffraction type particle size distribution measuring apparatus.

By crushing CaSi ₂ in advance, the first heating step and, if necessary, the second heating step can be performed on CaSi _{2 having} a large surface area, so that the desired reaction proceeds smoothly. I can expect. Further, in the manufacturing method of the present invention, the silicon material or the carbon-coated silicon material of the present invention is manufactured with the shape of CaSi ₂ substantially maintained, so the silicon material of the present invention or the carbon-coated silicon material itself is pulverized. There is no need to do. Furthermore, the aspect ratio of the particles of the silicon material or the carbon-coated silicon material of the present invention is increased by previously pulverizing CaSi ₂ . Here, the aspect ratio is a value of the minor axis / major axis when the particles of the silicon material or the carbon-coated silicon material of the present invention are observed. The long diameter means the longest diameter of the particles of the silicon material or the carbon-coated silicon material of the present invention, and the short diameter means the longest diameter among the diameters orthogonal to the longest diameter. As will be described later, the silicon material or carbon-coated silicon material of the present invention has a structure in which a plurality of plate-like silicon bodies are laminated in the thickness direction. When the silicon material is pulverized, the bonded portions of the layers in the laminated structure are broken, and flat particles having a small aspect ratio are manufactured.

The aspect ratio r in the particles of the silicon material or carbon-coated silicon material of the present invention is preferably 0.8 ≦ r ≦ 1. As the aspect ratio approaches 1, the powder characteristics such as fluidity of the silicon material or the carbon-coated silicon material of the present invention improve, so the handling of the silicon material or carbon-coated silicon material of the present invention in the manufacturing process becomes easier. In addition, when the silicon material or the carbon-coated silicon material of the present invention is used as a negative electrode active material of a power storage device, suitable charge / discharge can be expected.

The halogen-containing polymer may be any polymer that contains halogen in its chemical structure. The reason is as follows. Under the heating conditions of the method for producing a silicon material of the present invention, hydrohalic acid and / or halogen molecules are released from the halogen-containing polymer. Then, the negatively charged halogen constituting the hydrohalic acid or the halogen molecule reacts with Ca of CaSi ₂ . That is, in the case of a halogen-containing polymer, it becomes a source of minus-charged halogen, and a desired reaction proceeds. When CaSi ₂ reacts with hydrohalic acid, Si ₆ H ₆ and calcium halide are produced, and when CaSi ₂ reacts with a halogen molecule, silicon halide and calcium halide are produced. .

As a halogen-containing polymer, what has a monomer unit of General formula (1) can be mentioned.
General formula (1)

In General Formula (1), R ¹ is a trivalent or higher hydrocarbon group, X is independently halogen, and n is an integer of 1 or more.

Hydrocarbons include saturated hydrocarbons and unsaturated hydrocarbons. Saturated hydrocarbons include chain saturated hydrocarbons and cyclic saturated hydrocarbons. The unsaturated hydrocarbon includes a chain unsaturated hydrocarbon and a cyclic unsaturated hydrocarbon.

Among the chemical structures of R ^1, the chemical structure that is the main chain of the monomer unit (chemical structure including carbon involved in the polymerization reaction) is a chain saturated hydrocarbon, a cyclic saturated hydrocarbon, a chain unsaturated hydrocarbon, a cyclic Any of unsaturated hydrocarbons may be used. Specific examples of the chemical structure that becomes the main chain of the monomer unit include CH, CH ₂ —CH, CH═CH, a cyclohexane ring, and a benzene ring.

Among the chemical structures of R ^1, the chemical structure bonded to the main chain of the monomer unit (hereinafter sometimes referred to as a sub-chain) is hydrogen, chain saturated hydrocarbon, cyclic saturated hydrocarbon, chain unsaturated hydrocarbon. Any of cyclic unsaturated hydrocarbons may be used. Moreover, hydrogen of each hydrocarbon may be substituted with another element or another hydrocarbon.

X is any of fluorine, chlorine, bromine and iodine. When n is 2 or more, each X may be the same type or other types. X may be directly bonded to the carbon that is the main chain of the monomer unit, or may be bonded to the carbon of the sub-chain. The upper limit of n is determined by the chemical structure of R ¹ .

The halogen-containing polymer may be composed of only a single type of monomer unit of general formula (1), or may be composed of a plurality of types of monomer units of general formula (1). May be. Moreover, the halogen-containing polymer may be composed of a monomer unit of the general formula (1) and a monomer unit having another chemical structure.

Here, if a halogen-containing polymer having a high halogen mass% is employed, it is considered that the desired reaction proceeds more efficiently. Therefore, the halogen-containing polymer is composed only of the monomer unit of the general formula (1). preferable.

The molecular weight of the halogen-containing polymer is preferably in the range of 1,000 to 1,000,000, more preferably in the range of 1,000 to 500,000, and still more preferably in the range of 3,000 to 100,000. In terms of the degree of polymerization of the halogen-containing polymer, it is preferably in the range of 50,000 to 100,000, more preferably in the range of 100,000 to 50,000, and still more preferably in the range of 100 to 10,000.

A suitable thing is shown by the following general formula (2) among the monomer units of General formula (1).
General formula (2)

In the general formula (2), R ² , R ³ and R ⁴ are each independently selected from a monovalent hydrocarbon group, a halogen-substituted hydrocarbon group, hydrogen and halogen, and X is a halogen.

The hydrocarbon and halogen are as described in the general formula (1). Preferred hydrocarbons in the general formula (2) include alkyl groups having 1 to 6 carbon atoms, vinyl groups, and phenyl groups.

As described above, since it is considered that the halogen-containing polymer has a high halogen mass%, it is preferable that R ² , R ³ and R ⁴ of the monomer unit of the general formula (2) are independently hydrogen or halogen.

Particularly suitable halogen-containing polymers include polyvinylidene fluoride, polyvinyl fluoride, polyvinylidene chloride, and polyvinyl chloride.

The amount of CaSi ₂ and halogen-containing polymer used will be described. It is preferable to use a halogen-containing polymer in an amount such that the molar ratio of halogen is 2 or more with respect to Ca of CaSi ₂ to be used.

In the method for producing a silicon material of the present invention, the heating temperature in the first heating step is a temperature not lower than the decomposition gas generation temperature of the halogen-containing polymer and lower than the carbonization temperature. Here, for example, polyvinyl chloride, which is one embodiment of the halogen-containing polymer, may start the dehydrochlorination reaction from around 100 ° C., or desorb at about 210 to 300 ° C. under normal conditions. It is known to initiate a hydrogen chloride reaction, and generally organic compounds are carbonized from around 400 ° C. Therefore, the heating temperature in the first heating step can be exemplified by a range of 100 to 400 ° C., preferably a range of 210 to 380 ° C., more preferably a range of 230 to 360 ° C., and a range of 250 to 350 ° C. Even more preferable.

The heating temperature in the second heating step in the method for producing a carbon-coated silicon material of the present invention is a temperature equal to or higher than the carbonization temperature of the halogen-containing polymer. As described above, organic compounds generally carbonize from around 400 ° C. Here, the higher the heating temperature in the second heating step, the higher the conductivity of the carbide film. On the other hand, if the heating temperature in the second heating step is too high, there is a concern about the generation of by-products such as silicon carbide.
Further, a structure peculiar to a silicon material considered to be derived from the Si layer in the raw material CaSi ₂ is considered to be very advantageous when the silicon material is used as the negative electrode active material of the power storage device. The melting point of silicon is 1414 ° C. Therefore, in order to maintain the structure peculiar to the silicon material, the heating temperature in the second heating step needs to be lower than the melting point of silicon.
From the above viewpoint, the heating temperature in the second heating step is preferably within a range of 400 to 1400 ° C., more preferably within a range of 500 to 1100 ° C., further preferably within a range of 600 to 1000 ° C., and 700 to 950 It is particularly preferably within the range of ° C, and most preferably within the range of 800 to 900 ° C.

Depending on the heating temperature of the first heating step and the second heating step, the ratio of amorphous silicon and silicon crystallites contained in the silicon material or the carbon-coated silicon material, and the size of the silicon crystallites can also be adjusted. The shape and size of the nano-level layer containing amorphous silicon and silicon crystallites contained in the manufactured silicon material or carbon-coated silicon material can also be prepared.

The size of the silicon crystallite is preferably in the range of 0.5 nm to 300 nm, more preferably in the range of 1 nm to 100 nm, still more preferably in the range of 1 nm to 50 nm, and particularly preferably in the range of 1 nm to 10 nm. In addition, the size of the silicon crystallite was obtained by performing X-ray diffraction measurement (XRD measurement) on a silicon material or a carbon-coated silicon material, and using the half width of the diffraction peak on the Si (111) surface of the obtained XRD chart. Calculated from Scherrer's equation.

By the manufacturing method of the present invention, a silicon material or a carbon-coated silicon material having a structure in which a plurality of plate-like silicon bodies are laminated in the thickness direction can be obtained. This structure can be confirmed by observation with a scanning electron microscope or the like. In consideration of using the silicon material or carbon-coated silicon material of the present invention as an active material of a lithium ion secondary battery, the plate-like silicon body is thick for efficient insertion and desorption reaction of lithium ions. Is preferably in the range of 10 nm to 100 nm, more preferably in the range of 20 nm to 50 nm. The length of the plate-like silicon body in the longitudinal direction is preferably in the range of 0.1 μm to 50 μm. The plate-like silicon body preferably has (length in the longitudinal direction) / (thickness) in the range of 2 to 1000.

The production method of the present invention is preferably carried out in an inert gas atmosphere such as argon, helium, nitrogen gas.

Next, the heating furnace will be described. The heating furnace divides the first space in which the halogen-containing polymer is arranged, the second space in which CaSi ₂ is arranged, the first space and the second space, and has a through-hole through which a decomposition gas of the halogen-containing polymer can pass. And a second space is provided in the flow path of the decomposition gas generated from the halogen-containing polymer in the first space. Due to this structure of the heating furnace, the decomposition gas generated from the halogen-containing polymer can be brought into contact with CaSi ₂ without waste, so that a desired reaction proceeds suitably.

Specific examples of the heating furnace include a high frequency induction heating furnace, an electric furnace, an arc furnace, and a gas furnace.

The first space and the second space in the heating furnace may be formed by arranging a ceramic portion inside the heating furnace. Moreover, you may install in the heating furnace the reaction chamber provided with the 1st chamber provided with 1st space, the 2nd chamber provided with 2nd space, and the ceramic part.

Materials for the reaction chamber include refractory metals such as molybdenum, tungsten, tantalum or niobium, or alumina, zirconia, silicon nitride, aluminum nitride, silicon carbide, cordierite, mullite, steatite, calcia, magnesia, sialon, quartz Ceramics such as Vycor are good.

The reaction chamber may be sealable, may be provided with a ventilation part, and may be provided with a valve that opens and closes according to the internal pressure. When the first heating step and the second heating step are performed, the first space in the reaction chamber preferably has a structure in which there are no ventilation portions and on-off valves other than the ceramic portion. On the other hand, the second space in the reaction chamber preferably has a structure in which a ventilation portion other than the ceramic portion and an on-off valve are present.

The ceramic part divides the first space and the second space to suppress direct contact between the halogen-containing polymer and CaSi ₂ , and through holes in the ceramic part are generated from the halogen-containing polymer in the first space. It becomes a passage for the cracked gas to be guided and guides the cracked gas to the second space. Examples of the open porosity of the ceramic portion include a range of 30 to 80% and a range of 35 to 75%. The open porosity can be measured by a method defined in JIS R 1634, JIS R 2205, JIS A 1509-3, or the like.

Examples of the material of the ceramic part include alumina, zirconia, silicon nitride, aluminum nitride, silicon carbide, cordierite, mullite, steatite, calcia, magnesia, sialon, quartz and Vycor.

Regarding the arrangement of the first space, the second space, and the ceramic portion, it is preferable that the ceramic portion is arranged as a first space in the lower portion, a second space in the upper portion, and a partition between the first space and the second space. With this arrangement, as the cracked gas generated in the first space rises, it naturally passes through the through hole of the ceramic portion, reaches the second space, and comes into contact with CaSi _{2 in} the second space. Can do. Of course, in this arrangement, the diameter of the through hole of the ceramic portion is preferably smaller than the particle diameter of CaSi ₂ .

The silicon material or the carbon-coated silicon material obtained by the production method of the present invention may be pulverized or classified to form particles having a certain particle size distribution. As a preferable particle size distribution of the silicon material or the carbon-coated silicon material when measured with a general laser diffraction particle size distribution measuring apparatus, it can be exemplified that the average particle diameter (D ₅₀ ) is in the range of 1 to 30 μm. More preferably, the average particle diameter (D ₅₀ ) is in the range of 1 to 10 μm.

The silicon material or the carbon-coated silicon material obtained by the production method of the present invention is preferably subjected to a cleaning step of cleaning with a solvent having a relative dielectric constant of 5 or more. The cleaning step is a step of removing unnecessary components adhering to the silicon material or the carbon-coated silicon material by cleaning with a solvent having a relative dielectric constant of 5 or more (hereinafter sometimes referred to as “cleaning solvent”). is there. This step is mainly intended to remove salts that can be dissolved in a washing solvent such as calcium halide. For example, when polyvinyl chloride is used as the halogen-containing polymer, it is presumed that CaCl ₂ remains in the silicon material or the carbon-coated silicon material. Therefore, by cleaning the silicon material or the carbon-coated silicon material with a cleaning solvent, unnecessary components including CaCl ₂ can be dissolved and removed in the cleaning solvent. The cleaning step may be a method in which a silicon material or a carbon-coated silicon material is immersed in a cleaning solvent, or a method in which the silicon material or the carbon-coated silicon material is exposed to a cleaning solvent.

As the washing solvent, a solvent having a higher relative dielectric constant is preferable from the viewpoint of ease of dissolution of the salt, and a solvent having a relative dielectric constant of 10 or more or 15 or more can be presented as a more preferable one. The range of the relative dielectric constant of the cleaning solvent is preferably within the range of 5 to 90, more preferably within the range of 10 to 90, and even more preferably within the range of 15 to 90. In addition, as the cleaning solvent, a single solvent may be used, or a mixed solvent of a plurality of solvents may be used.

Specific examples of the washing solvent include water, methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, sec-butanol, tert-butanol, ethylene glycol, glycerin, and N-methyl-2-pyrrolidone. N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, acetonitrile, ethylene carbonate, propylene carbonate, benzyl alcohol, phenol, pyridine, tetrahydrofuran, acetone, ethyl acetate, and dichloromethane. Of these specific solvent chemical structures, a part or all of hydrogen substituted with fluorine may be employed as the cleaning solvent. The water as the washing solvent is preferably distilled water, reverse osmosis membrane permeated water, or deionized water.

For reference, the dielectric constants of various solvents are shown in Table 1.

As the washing solvent, water, methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, sec-butanol, tert-butanol, and acetone are particularly preferable.

When a mixed solvent of a plurality of solvents is used as the washing solvent, the other solvent is preferably 1 to 100 parts by volume, more preferably 2 to 50 parts by volume, further preferably 5 to 30 parts by volume with respect to 100 parts by volume of water. It is advisable to employ a mixed solvent mixed at a ratio of parts. By using a mixed solvent as the cleaning solvent, the dispersibility and affinity of the silicon material or the carbon-coated silicon material with respect to the cleaning solvent may be improved, and as a result, unnecessary components are preferably eluted in the cleaning solvent.

After the cleaning step, it is preferable to remove the cleaning solvent from the silicon material or the carbon-coated silicon material by filtration and drying.

The cleaning process may be repeated multiple times. In that case, the washing solvent may be changed. For example, water with an extremely high relative dielectric constant is selected as the cleaning solvent in the first cleaning process, and water is efficiently removed by using ethanol or acetone with low boiling point that is compatible with water as the next cleaning solvent. In addition, the cleaning solvent can be easily prevented from remaining.

The drying step after the washing step is preferably performed in a reduced pressure environment, and more preferably at a temperature equal to or higher than the boiling point of the washing solvent. The temperature is preferably 80 ° C to 110 ° C.

The silicon material or carbon-coated silicon material of the present invention is manufactured through the manufacturing method of the present invention as described above. Here, you may perform the carbon coating process coat | covered with carbon with respect to the silicon material or carbon covering silicon material obtained with the manufacturing method of this invention as a process separate from the 2nd heating process mentioned above. Moreover, you may perform the carbon removal process which removes at least one part carbon of the carbon covering silicon material after a 2nd heating process before a carbon covering process so that it may mention later.

As the carbon coating process, a conventional known technique may be applied. For example, a so-called thermal CVD method in which the material is carbonized by bringing the material into contact with an organic gas under heating in a non-oxidizing atmosphere and carbonizing the organic gas may be applied.

As the organic substance gas, a gas obtained by vaporizing an organic substance, a gas obtained by sublimating an organic substance, or an organic vapor can be used. In addition, organic substances that generate organic gases include those that can be thermally decomposed and carbonized by heating in a non-oxidizing atmosphere, for example, saturated fats such as methane, ethane, propane, butane, isobutane, pentane, and hexane. 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, coumarone, pyridine, anthracene, phenanthrene, esters such as ethyl acetate, butyl acetate, amyl acetate, and fatty acids Thing, and the like. The organic substance is preferably a saturated aliphatic hydrocarbon such as propane.

The treatment temperature in the carbon coating step varies depending on the type of organic substance, but it is preferable to set it at a temperature higher by 50 ° C. than the temperature at which the organic substance gas is thermally decomposed. However, when the temperature is too high or the organic gas concentration is too high, so-called soot is generated, so it is preferable to select a condition that does not generate soot. The thickness of the carbon layer to be formed can be controlled by the amount of organic matter and the processing time.

It is desirable to perform the carbon coating process while the material is in a fluid state. By doing in this way, the whole surface of material can be made to contact organic substance gas, and a uniform carbon layer can be formed. There are various methods such as using a fluidized bed to bring the material into a fluid state, but it is preferable to contact the material with an organic gas while stirring the material. For example, when a rotary furnace having a baffle plate is used, the material remaining on the baffle plate is stirred by dropping from a predetermined height as the rotary furnace rotates. At that time, the material comes into contact with the organic gas in a stirred state, and a carbon layer is formed on the surface of the material. Therefore, a uniform carbon layer can be formed on the entire material. Similarly, the first heating step and the second heating step are preferably performed with the material in a fluidized state if possible.

The carbon-coated silicon material of the present invention obtained by performing the second heating step and the carbon coating step is in a state where the carbon coating is performed by two kinds of methods. Such a carbon-coated silicon material of the present invention is in a state in which a coating state that has been insufficient with one carbon coating method is complemented with another carbon coating method. Therefore, it is considered that the secondary battery including the carbon-coated silicon material of the present invention as a negative electrode active material has favorable battery characteristics.

As the carbon removal step, the carbon-coated silicon material after the second heating step may be heated in the presence of oxygen to remove carbon as carbon dioxide or carbon monoxide. In the carbon removal step, a part or all of the carbon of the carbon-coated silicon material can be removed. Examples of the heating temperature include 350 to 650 ° C.

In the carbon removal step, it can be expected that impurities contained in the carbon-coated silicon material are also removed at the same time. For this reason, it is speculated that the carbon-coated silicon material of the present invention produced by being subjected to the carbon coating step after the carbon removal step is a more suitable material.

The carbon-coated silicon material of the present invention contains carbon and silicon as essential components. When the carbon-coated silicon material of the present invention is 100, carbon is preferably contained within a range of 1 to 30% by mass, more preferably within a range of 3 to 20% by mass. More preferably, it is contained within the range of mass%. When the carbon-coated silicon material of the present invention is 100, silicon is preferably contained in the range of 50 to 99% by mass, more preferably in the range of 60 to 97% by mass, and 65 to 95%. More preferably, it is contained within the range of mass%.

The silicon material or carbon-coated silicon material of the present invention may contain impurities derived from raw materials such as Ca and halogen, and inevitable impurities. Examples of the abundance (% by mass) of such impurities include the following ranges.
Ca: 0 to 5% by mass, 0 to 3% by mass, 0 to 2% by mass, 0.1 to 3% by mass, 0.5 to 2% by mass
Halogen: 0 to 10% by mass, 0.001 to 6% by mass

The silicon material or carbon-coated silicon material of the present invention preferably has a cavity inside. When the silicon material or carbon-coated silicon material of the present invention is used as an active material for a lithium ion secondary battery, the cavity expands when the insertion or desorption reaction of lithium ions occurs. And presumed to play a role in buffering contraction.

The silicon material or carbon-coated silicon material obtained by the production method of the present invention can be used as a negative electrode active material for a secondary battery such as a lithium ion secondary battery. Hereinafter, a lithium ion secondary battery will be described as an example of a secondary battery. The lithium ion secondary battery of the present invention comprises the silicon material or the carbon-coated silicon material of the present invention as a negative electrode active material. Specifically, the lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode including the silicon material or the carbon-coated silicon material of the present invention as a negative electrode active material, an electrolytic solution, and a separator.

The positive electrode has a current collector and a positive electrode active material layer bound to the surface of the current collector.

The current collector refers to a chemically inert electronic conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery. As the current collector, at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel, etc. Metal materials can be exemplified. The current collector may be covered with a known protective layer. What collected the surface of the electrical power collector by the well-known method may be used as an electrical power collector.

The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 1 μm to 100 μm.

The positive electrode active material layer contains a positive electrode active material and, if necessary, a conductive additive and / or a binder.

As the positive electrode active material, the layered compound Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, At least one element selected from Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, 1.7 ≦ f ≦ 3 ), Li ₂ MnO ₃ . Further, as a positive electrode active material, a solid solution composed of a spinel such as LiMn ₂ O ₄ and a mixture of a spinel and a layered compound, LiMPO ₄ , LiMVO ₄ or Li ₂ MSiO ₄ (wherein M is Co, Ni, Mn, And a polyanionic compound represented by (selected from at least one of Fe). Furthermore, as the positive electrode active material, tavorite compound (the M a transition metal) LiMPO ₄ F, such as LiFePO ₄ F represented by, Limbo ₃ such LiFeBO ₃ (M is a transition metal) include borate-based compound represented by be able to. Any metal oxide used as the positive electrode active material may have the above-described composition formula as a basic composition, and those obtained by substituting the metal elements contained in the basic composition with other metal elements can also be used as the positive electrode active material. . Further, as a positive electrode active material, a positive electrode active material that does not contain lithium ions that contribute to charge / discharge, for example, sulfur alone, a compound in which sulfur and carbon are combined, a metal sulfide such as TiS ₂ , V ₂ O ₅ , MnO ₂ and other oxides, polyaniline and anthraquinone, compounds containing these aromatics in the chemical structure, conjugated materials such as conjugated diacetate-based organic substances, and other known materials can also be used. Further, a compound having a stable radical such as nitroxide, nitronyl nitroxide, galvinoxyl, phenoxyl, etc. may be adopted as the positive electrode active material. When using a positive electrode active material that does not contain lithium, it is necessary to add ions to the positive electrode and / or the negative electrode in advance by a known method. Here, in order to add the ion, a metal or a compound containing the ion may be used.

Conductive aid is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be added arbitrarily when the electrode conductivity is insufficient, and may not be added when the electrode conductivity is sufficiently excellent. The conductive auxiliary agent may be any chemically inert electronic high conductor, such as carbon black, graphite, vapor grown carbon fiber (Vapor Grown Carbon Fiber), and various metal particles. The Examples of the carbon black include acetylene black, ketjen black (registered trademark), furnace black, and channel black. These conductive assistants can be added to the active material layer alone or in combination of two or more.

The blending ratio of the conductive auxiliary in the active material layer is preferably, in mass ratio, active material: conductive auxiliary = 1: 0.005 to 1: 0.5, and 1: 0.01 to 1: 0. .2 is more preferable, and 1: 0.03 to 1: 0.1 is more preferable. This is because if the amount of the conductive auxiliary is too small, an efficient conductive path cannot be formed, and if the amount of the conductive auxiliary is too large, the moldability of the active material layer is deteriorated and the energy density of the electrode is lowered.

The binder serves to hold the active material and the conductive auxiliary agent on the surface of the current collector and maintain the conductive network in the electrode. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, poly ( Examples thereof include acrylic resins such as (meth) acrylic acid, styrene-butadiene rubber (SBR), and carboxymethylcellulose. These binders may be used singly or in plural.

The blending ratio of the binder in the active material layer is preferably a mass ratio of active material: binder = 1: 0.001 to 1: 0.3, and 1: 0.005 to 1: 0. .2 is more preferable, and 1: 0.01 to 1: 0.15 is even more preferable. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.

The negative electrode has a current collector and a negative electrode active material layer bound to the surface of the current collector. What is necessary is just to employ | adopt suitably what was demonstrated with the positive electrode about a collector. The negative electrode active material layer includes a negative electrode active material and, if necessary, a conductive additive and / or a binder.

The negative electrode active material may be any material as long as it contains the silicon material or carbon-coated silicon material of the present invention, and may employ only the silicon material or carbon-coated silicon material of the present invention, or the silicon material or carbon of the present invention. A covering silicon material and a known negative electrode active material may be used in combination.

What is necessary is just to employ | adopt suitably suitably what was demonstrated with the positive electrode with the same mixture ratio about the conductive support agent and binder used for a negative electrode.

In order to form an active material layer on the surface of the current collector, a current collecting method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method can be used. An active material may be applied to the surface of the body. Specifically, an active material, a solvent, and, if necessary, a binder and / or a conductive aid are mixed to prepare a slurry. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. The slurry is applied to the surface of the current collector and then dried. In order to increase the electrode density, the dried product may be compressed.

The electrolytic solution contains a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent.

As the non-aqueous solvent, cyclic esters, chain esters, ethers and the like can be used. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, fluorinated ethylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, ethyl methyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. As the non-aqueous solvent, a compound in which part or all of hydrogen in the chemical structure of the specific solvent is substituted with fluorine may be employed.

Examples of the electrolyte include lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ .

As an electrolytic solution, 0.5 mol / L to 1.7 mol of a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3 in} a nonaqueous solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and diethyl carbonate. A solution dissolved at a concentration of about / L can be exemplified.

The separator separates the positive electrode and the negative electrode and allows lithium ions to pass while preventing a short circuit due to contact between the two electrodes. As separators, natural resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polymer), polyester, polyacrylonitrile, etc., polysaccharides such as cellulose, amylose, fibroin, keratin, lignin, suberin, etc. Examples thereof include porous bodies, nonwoven fabrics, and woven fabrics using one or more electrically insulating materials such as polymers and ceramics. The separator may have a multilayer structure.

Next, a method for manufacturing a lithium ion secondary battery will be described.

A separator is sandwiched between the positive electrode and the negative electrode as necessary to form an electrode body. The electrode body may be any of a stacked type in which a positive electrode, a separator and a negative electrode are stacked, or a wound type in which a positive electrode, a separator and a negative electrode are stacked. After connecting the current collector of the positive electrode and the current collector of the negative electrode to the positive electrode terminal and the negative electrode terminal that communicate with the outside using a current collecting lead or the like, an electrolyte is added to the electrode body, and the lithium ion secondary battery Good. Moreover, the lithium ion secondary battery of this invention should just be charged / discharged in the voltage range suitable for the kind of active material contained in an electrode.

The shape of the lithium ion secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape can be adopted.

The lithium ion secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy from a lithium ion secondary battery for all or a part of its power source, and may be, for example, an electric vehicle or a hybrid vehicle. When a lithium ion secondary battery is mounted on a vehicle, a plurality of lithium ion secondary batteries may be connected in series to form an assembled battery. Examples of devices equipped with lithium ion secondary batteries include various home appliances driven by batteries such as personal computers and portable communication devices, office devices, and industrial devices in addition to vehicles. Furthermore, the lithium ion secondary battery of the present invention includes wind power generation, solar power generation, hydroelectric power generation and other power system power storage devices and power smoothing devices, power supplies for ships and / or auxiliary power supply sources, aircraft, Power supply for spacecraft and / or auxiliary equipment, auxiliary power supply for vehicles that do not use electricity as a power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, You may use for the electrical storage apparatus which stores temporarily the electric power required for charge in the charging station for electric vehicles.

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 more specifically with reference to examples and comparative examples. In addition, this invention is not limited by these Examples.

Example 1
As shown in FIG. 1, the carbon-coated silicon material of Example 1 was manufactured using a heating furnace 10 in which the reaction chamber 1 was arranged. The reaction chamber 1 is a ceramic pot and the heating furnace 10 is an electric furnace.
Specifically, 1.6 g of polyvinyl chloride 2 (degree of polymerization 1100) was placed at the bottom of the reaction chamber 1. In order not to touch the polyvinyl chloride 2, a plate-shaped ceramic part 3 having a through hole 8 and an open porosity of 40% was disposed on the top of the polyvinyl chloride 2. 1 g of CaSi ₂ powder 4 was placed on the ceramic part 3. Then, not to touch the CaSi ₂ powder 4, the top of CaSi ₂ powder 4 was placed the lid 5 made of ceramic. A gap exists between the upper end of the reaction chamber 1 and the lid 5. In the reaction chamber 1, the through hole 8 of the ceramic part 3 serves as a passage that connects the first space 6 and the second space 7.
The reaction chamber 1 with the lid 5 as described above was placed in the heating furnace 10. As a result, the heating furnace 10 includes a first space 6 in which the polyvinyl chloride 2 that is a halogen-containing polymer is disposed, a second space 7 in which the CaSi ₂ powder 4 is disposed, and the first space 6 and the second space 7. The ceramic part 3 which comprises the through-hole 8 which partitions and the decomposition gas of the polyvinyl chloride 2 can pass through is provided.

In an argon atmosphere, the temperature of the electric furnace was increased to 900 ° C. at a rate of 5 ° C./min, and maintained at 900 ° C. for 1 hour. This heating condition corresponds to the first heating step and the second heating step. The reaction product was washed with water, then with acetone, and then dried under reduced pressure to obtain a black carbon-coated silicon material of Example 1.

(Example 2)
A black carbon-coated silicon material of Example 2 was obtained in the same manner as in Example 1 except that 24 g of polyvinyl chloride and 15 g of CaSi ₂ powder were used.

(Comparative Example 1)
A black carbon-coated silicon material of Comparative Example 1 was obtained in the same manner as in Example 1 except that the heating furnace 20 of FIG. 2 was used instead of the heating furnace 10 of FIG.
Specifically, 1 g of CaSi ₂ powder 4 was put in a first crucible 11 made of alumina, and the first crucible 11 was placed in a second crucible 12 made of alumina larger than this. 1.6 g of polyvinyl chloride 2 (degree of polymerization 1100) was put in the second crucible 12 made of alumina, and the lid 13 was put on the second crucible 12. The second crucible 12 with the lid 13 was placed in a heating furnace 20 as an electric furnace. There is a gap between the second crucible 12 and the lid 13.
Thereafter, a black carbon-coated silicon material of Comparative Example 1 was obtained in the same manner as in Example 1.

(Comparative Example 2)
A black carbon-coated silicon material of Comparative Example 2 was obtained in the same manner as in Comparative Example 1, except that 24 g of polyvinyl chloride and 15 g of CaSi ₂ powder were used.

(Evaluation example 1)
The carbon-coated silicon materials of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were subjected to X-ray diffraction measurement using a powder X-ray diffractometer. In any X-ray diffraction chart of the carbon-coated silicon material, a peak derived from Si was confirmed, and a peak derived from the raw material CaSi ₂ was remarkably small. Further, fluorescent X-ray analysis was performed on each carbon-coated silicon material. Table 2 shows the results of the yield in terms of Si from the obtained quantitative results of Si.

Even if the amount of CaSi ₂ charged is 1 g or 15 g, the yield of the example using the heating furnace 10 is superior. It was confirmed that the production method of the present invention is a method with excellent yield.

(Example 3)
The black carbon-coated silicon of Example 3 was used in the same manner as in Example 1 except that a plate-like ceramic part having an open porosity of 71% was used instead of the plate-like ceramic part having an open porosity of 40%. Obtained material.

(Comparative Example 3)
The carbon-coated silicon material of Comparative Example 3 was prepared in the same manner as in Example 1 except that a plate-like ceramic part having an open porosity of 0% was used instead of the plate-like ceramic part having an open porosity of 40%. Obtained.

(Evaluation example 2)
The carbon-coated silicon materials of Example 1, Example 3, and Comparative Example 3 were subjected to X-ray diffraction measurement using a powder X-ray diffractometer. In the X-ray diffraction charts of the carbon-coated silicon materials of Example 1 and Example 3, a peak derived from the raw material CaSi ₂ was hardly observed, and a peak derived from Si was confirmed, but the carbon of Comparative Example 3 was observed. In the X-ray diffraction chart of the coated silicon material, a peak derived from the raw material CaSi ₂ was clearly observed. From this result, it can be said that it is preferable to employ a ceramic portion having a certain degree of open porosity.

Example 4
CaSi ₂ was pulverized using a jet mill to produce CaSi ₂ powder having an average particle size of 2.18 μm. 2 g of the above CaSi ₂ powder and 3.6 g of polyvinyl chloride (degree of polymerization 1100) were placed in the reaction chamber in the same manner as in Example 1.
Under an argon atmosphere, the electric furnace was heated to 300 ° C. at a rate of 5 ° C./min and maintained at 300 ° C. for 30 minutes. This heating condition corresponds to the first heating step. The reaction product was washed with water and then dried under reduced pressure to obtain the silicon material of Example 4.

45 parts by mass of the silicon material of Example 4 as the negative electrode active material, 40 parts by mass of natural graphite as the negative electrode active material, 5 parts by mass of acetylene black as the conductive additive, 10 parts by mass of polyamideimide as the binder, N-methyl-2- Pyrrolidone was mixed to prepare a slurry. The slurry was applied to the surface of an electrolytic copper foil having a thickness of about 20 μm as a current collector using a doctor blade and dried to form a negative electrode active material layer on the copper foil. Thereafter, the current collector and the negative electrode active material layer were firmly and closely joined by a roll press. This was vacuum dried at 200 ° C. for 2 hours to produce a negative electrode of Example 4.

(Comparative Example 4)
Using CaSi ₂ that was not pulverized by a jet mill, a silicon material and a negative electrode of Comparative Example 4 were produced as follows.
CaSi ₂ was added to concentrated hydrochloric acid in an ice bath and stirred under an argon atmosphere. After confirming the completion of foaming from the reaction solution, the reaction solution was warmed to room temperature, the resulting reaction solution was filtered, the residue was washed with distilled water, washed with ethanol, vacuum dried and layered. A silicon compound was obtained. The layered silicon compound was heated up to 900 ° C. at a rate of 5 ° C./min in an argon gas atmosphere, and a heat treatment was performed for 1 hour at 900 ° C. to obtain a silicon material. The silicon material of the comparative example 4 whose average particle diameter is 3 micrometers was manufactured by grind | pulverizing the silicon material using the jet mill.
A negative electrode of Comparative Example 4 was produced in the same manner as in Example 4 except that the silicon material of Comparative Example 4 was used instead of the silicon material of Example 4.

(Evaluation example 3)
The silicon material of Example 4 and the silicon material of Comparative Example 4 were subjected to an image analysis particle size distribution analyzer (trade name: IF-200 nano, Jusco International Co., Ltd.) to perform image analysis of particles, and the average value of the aspect ratio was calculated. Calculated. The average value of the aspect ratio of the silicon material of Example 4 was 0.842, and the average value of the aspect ratio of the silicon material of Comparative Example 4 was 0.758. It can be said that the silicon material of Example 4 has a shape closer to a sphere.

(Evaluation example 4)
The cross sections of the negative electrode of Example 4 and the negative electrode of Comparative Example 4 were observed with a scanning electron microscope (SEM). The SEM image of the cross section of the negative electrode of Example 4 is shown in FIG. 3, and the enlarged SEM image is shown in FIG. Moreover, the SEM image of the cross section of the negative electrode of the comparative example 4 is shown in FIG. The light-colored portions in FIGS. 3 to 5 are silicon materials. From the SEM images of FIGS. 3 to 5, it can be seen that the silicon material of Example 4 has a shape closer to a sphere.

Claims (7)

1. Including the first heating step of heating at a temperature higher than the decomposition gas generation temperature of the halogen-containing polymer and lower than the carbonization temperature in the presence of CaSi ₂ and the halogen-containing polymer;
   Ceramics comprising a first space in which the halogen-containing polymer is disposed, a second space in which the CaSi ₂ is disposed, the first space and the second space, and a through hole through which the decomposition gas can pass. And a heating furnace in which the second space is provided in the flow path of the decomposition gas generated from the halogen-containing polymer in the first space. .
2. The method for producing a silicon material according to claim 1, further comprising a crushing step of crushing the CaSi ₂ before the first heating step.
3. 3. The method for producing a silicon material according to claim 1, wherein an open porosity of the ceramic portion is in a range of 30 to 80%.
4. The method for producing a silicon material according to any one of claims 1 to 3, wherein the halogen-containing polymer has a monomer unit represented by the following general formula (1).
   General formula (1)
   

   

   In General Formula (1), R ¹ is a trivalent or higher hydrocarbon group, X is independently halogen, and n is an integer of 1 or more.
5. The method for producing a silicon material according to any one of claims 1 to 4, wherein the halogen-containing polymer has a monomer unit represented by the following general formula (2).
   General formula (2)
   

   

   In the general formula (2), R ² , R ³ and R ⁴ are each independently selected from a monovalent hydrocarbon group, a halogen-substituted hydrocarbon group, hydrogen and halogen, and X is a halogen.
6. 6. The method for producing a silicon material according to claim 1, wherein an aspect ratio of the silicon material is 0.8 or more.
7. After the first heating step in the production method according to any one of claims 1 to 6,
   A method for producing a carbon-coated silicon material, comprising a second heating step of heating at a temperature equal to or higher than the carbonization temperature of the halogen-containing polymer.

Images