JP2015149208A - Negative electrode material for lithium ion secondary batteries, manufacturing method thereof, negative electrode, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a negative electrode material which is suitable for a lithium ion secondary battery negative electrode, and superior in cycle characteristics while keeping an advantages of a silicon-containing material, e.g. a silicon oxide-based material, such as a high battery capacity and a low volume expansion coefficient; a method for manufacturing such a negative electrode material; a negative electrode arranged by use of such a negative electrode material; and a lithium ion secondary battery arranged by use thereof.SOLUTION: A negative electrode material for lithium ion secondary batteries comprises: coated particles which is capable of occluding and releasing lithium ions, and includes silicon-containing particles, and a carbon coating covering the surface of each silicon-containing particle, and of which the bvalue defined by JIS Z 8729 is 0.8-5.0.

Description

  The present invention relates to a negative electrode material for a lithium ion secondary battery and a manufacturing method that exhibit good cycle characteristics at a high capacity when used as a negative electrode active material for a lithium ion secondary battery, and a negative electrode and a lithium ion secondary battery using the same. The present invention relates to a secondary battery.

  In recent years, with the remarkable development of portable electronic devices, communication devices, etc., secondary batteries with high energy density are strongly demanded from the viewpoints of economy and downsizing and weight reduction of devices.

Conventionally, as a measure for increasing the capacity of this type of secondary battery, for example, a method using an oxide such as V, Si, B, Zr, Sn, or a composite oxide thereof as a negative electrode material (for example, Patent Documents 1 and 2). (See, for example, Patent Document 3), a method using silicon oxide as a negative electrode material (see, for example, Patent Document 4), and Si ₂ N ₂ O as a negative electrode material. And a method using Ge ₂ N ₂ O (see, for example, Patent Document 5).

  Further, for the purpose of imparting conductivity to the negative electrode material, a method of carbonizing SiO after graphite and mechanical alloying (for example, see Patent Document 6), a method of coating a carbon layer on the surface of silicon particles by a chemical vapor deposition method (for example, And Patent Document 7), and a method of coating the surface of silicon oxide particles with a carbon layer by chemical vapor deposition (for example, see Patent Document 8).

  However, in the above conventional method, although the charge / discharge capacity is increased and the energy density is increased, the cycle characteristics are insufficient or the required characteristics of the market are still insufficient, and are not always satisfactory. However, further improvement in energy density has been desired.

  In particular, Patent Document 4 uses silicon oxide as a negative electrode material for a lithium ion secondary battery to obtain a high-capacity electrode. However, as far as the inventors know, the irreversible capacity at the time of initial charge / discharge is still large. There is a problem that the cycle characteristics have not reached the practical level, and there is room for improvement.

Further, the technique of imparting conductivity to the negative electrode material also has a problem in Patent Document 6 that a uniform carbon film is not formed because of solid-solid fusion, and the conductivity is insufficient.
In the method of Patent Document 7, although a uniform carbon film can be formed, since Si is used as a negative electrode material, the expansion / contraction at the time of adsorption / desorption of lithium ions is too large. In order to prevent this, since it cannot endure practical use and cycle characteristics deteriorate, it is necessary to limit the amount of charge. In the method of Patent Document 8, although improvement in cycle characteristics is confirmed, the number of charge / discharge cycles is increased due to insufficient deposition of fine silicon crystals, integration of the carbon coating structure and the base material. As a result, there is a problem that the capacity gradually decreases and then rapidly decreases after a certain number of times, which is still insufficient for a secondary battery. From the above, while maintaining the advantages of high silicon oxide-based battery capacity and low volume expansion coefficient, negative electrode materials that are effective for lithium ion secondary batteries with high initial charge / discharge efficiency and excellent cycle characteristics, and their production The development of the method was awaited.

JP-A-5-174818 JP-A-6-60867 JP 10-294112 A Japanese Patent No. 2999741 JP-A-11-102705 JP 2000-243396 A JP 2000-215887 A JP 2002-42806 A

  The present invention provides a negative electrode material suitable for a negative electrode of a lithium ion secondary battery having a high capacity and excellent cycle characteristics while maintaining the advantage of a low volume expansion coefficient of a material containing silicon, for example, silicon oxide, and a method for producing the same. An object is to provide a negative electrode and a lithium ion secondary battery using the same.

The present inventor has found that not only the amount of carbon coating but also the film quality is important when particles containing silicon are coated with a carbon coating. Specifically, coated particles in which lithium ions can be occluded and released and the surfaces of silicon-containing particles are coated so that the b ^* value in JIS Z 8729 is in the range of 0.8 to 5.0. It has been found that a lithium ion secondary battery having a high capacity and excellent cycle characteristics can be obtained by using a negative electrode active material, and the present invention has been made.

Accordingly, the present invention provides the following negative electrode material for a lithium ion secondary battery and a method for producing the same, and the negative electrode and the lithium ion secondary battery.
[I]. Lithium ions can be occluded and released, and the surface of particles containing silicon is coated with a carbon film, and the lithium ion particles are made of coated particles having a b ^* value of 0.8 to 5.0 in JIS Z 8729. Negative electrode material for secondary batteries.
[II]. The negative electrode for lithium ion secondary batteries containing the negative electrode material for lithium ion secondary batteries as described in [I].
[III]. The lithium ion secondary battery which has a negative electrode for lithium ion secondary batteries as described in [II].
[IV]. (1) carbon-coated raw material gas, or (2) carbon-coated raw material in a temperature range of 600 to 1,200 ° C. in a carbon-coated raw material gas and vapor atmosphere, and occlude and release lithium ions. The method for producing a negative electrode material for a lithium ion secondary battery according to [I], wherein carbon is formed by chemical vapor deposition on the surface of particles containing silicon.

  According to the present invention, a lithium ion secondary battery having a high capacity and excellent cycle characteristics can be obtained. Further, the manufacturing method is not particularly complicated and simple, and can sufficiently withstand industrial scale production.

Hereinafter, the present invention will be described in detail.
[Anode material for lithium ion secondary battery]
The negative electrode material for a lithium ion secondary battery of the present invention can occlude and release lithium ions, the surface of particles containing silicon is coated with a carbon film, and the b ^* value in JIS Z 8729 is 0.8. Coated particles that are ˜5.0.

  As particles capable of inserting and extracting lithium ions and made of a silicon-containing material (hereinafter sometimes referred to as silicon-containing particles), silicon particles and silicon fine particles are dispersed in a silicon-based compound. Particles having a structure, silicon oxide particles represented by the general formula SiOx (0.5 ≦ x ≦ 1.6), or a mixture thereof are preferable. By using these, a negative electrode material for a lithium ion secondary battery having higher initial charge / discharge efficiency, high capacity, and excellent cycle characteristics can be obtained.

  Silicon oxide in the present invention is a general term for amorphous silicon oxide, and silicon oxide before disproportionation is represented by the general formula SiOx (0.5 ≦ x ≦ 1.6). x is preferably 0.8 ≦ x <1.6, and more preferably 0.8 ≦ x <1.3. This silicon oxide can be obtained, for example, by cooling and precipitating silicon monoxide gas generated by heating a mixture of silicon dioxide and metal silicon.

  Particles having a structure in which silicon fine particles are dispersed in a silicon-based compound are, for example, a method of firing a mixture of silicon fine particles and a silicon-based compound, or silicon oxide particles before disproportionation represented by the general formula SiOx Can be obtained by heat treatment at a temperature of 400 ° C. or higher, preferably 800 to 1,100 ° C. in an inert non-oxidizing atmosphere such as argon, and performing a disproportionation reaction. In particular, the material obtained by the latter method is suitable because silicon crystallites are uniformly dispersed. By the disproportionation reaction as described above, the size of the silicon nanoparticles can be set to 1 to 100 nm. Note that silicon dioxide in the particles having a structure in which silicon nanoparticles are dispersed in silicon oxide is preferably silicon dioxide. Note that it can be confirmed by transmission electron microscopy that silicon nanoparticles (crystals) are dispersed in amorphous silicon oxide.

  The physical properties of the particles containing silicon can be appropriately selected depending on the intended composite particles. For example, the average particle size is preferably 0.1 to 50 μm, the lower limit is more preferably 0.2 μm or more, and further preferably 0.5 μm or more. The upper limit is more preferably 30 μm or less, and further preferably 20 μm or less. In addition, the average particle diameter in this invention is represented by the weight average particle diameter in the particle size distribution measurement by a laser diffraction method.

BET specific surface area is preferably ^{0.5~100m 2 / g, 1~20m 2 /} g is more preferable. When the BET specific surface area is 0.5 m ² / g or more, there is no possibility that the adhesiveness when applied to the electrode is lowered and the battery characteristics are not lowered. Moreover, if it is 100 m < ² > / g or less, the ratio of the silicon dioxide on the particle | grain surface will become large, and when it uses as a negative electrode material for lithium ion secondary batteries, there is no possibility that a battery capacity may fall.

  Conductivity is imparted by coating the particles containing silicon with carbon to improve battery characteristics. Examples of a method for imparting conductivity include a method of mixing with conductive particles such as graphite, a method of coating the surface of the particles containing silicon with a carbon film, and a method of combining both. A method of coating with a film is preferable, and a method of chemical vapor deposition (CVD) is more preferable.

The color difference of the coated particles coated with the carbon coating has a b ^* value of 0.8 to 5.0 in JIS Z 8729. By setting it within this range, a lithium ion secondary battery having a high capacity and excellent cycle characteristics can be obtained. The b ^* value is preferably 0.9 to 4.0, more preferably 1.0 to 3.0, and particularly preferably 1.0 to 1.8. A method for obtaining coated particles having the above b ^* value range will be described below.

The average particle diameter of the coated particles coated with the carbon film is preferably 0.1 to 50 μm, more preferably 0.2 to 30 μm, further preferably 0.5 to 20 μm, and particularly preferably 2 to 10 μm. BET specific surface area is preferably from 0.5 to 100 ² / g, more preferably 1-20 m ² / g, more preferably 1~15m ² / g.

[Production method]
For example, as a method of chemical vapor deposition, the carbon coating material that can be pyrolyzed at 600 to 1,200 ° C. to generate carbon is pyrolyzed at 600 to 1,200 ° C. to form carbon on the particle surface. Can be formed by chemical vapor deposition. For example, in the above (1) carbon-coated raw material gas or (2) carbon-coated raw material gas and steam atmosphere, the carbon-coated raw material is thermally decomposed in a temperature range of 600 to 1,200 ° C., and the particle surface containing silicon And a method of chemical vapor deposition of carbon. Specifically, it can be carried out efficiently by introducing (1) a carbon-coated raw material gas or (2) a carbon-coated raw material gas and vapor into the reactor during the heat treatment. Note that as particles containing silicon, silicon particles, particles having a structure in which silicon fine particles are dispersed in a silicon-based compound, silicon oxide particles represented by a general formula SiOx (0.5 ≦ x ≦ 1.6), or these In the case of using a mixture of the above, the chemical vapor deposition temperature is 800 to 800 ° C. in terms of both productivity and the fact that if the treatment is carried out at a high temperature in the chemical vapor deposition step, the silicon crystal enlarges and the expansion during charging increases. 1,100 degreeC is preferable, 800-1,000 degreeC is more preferable, 900-1,000 degreeC is further more preferable.

  The pressure in the carbon coating forming step is applicable to both normal pressure and reduced pressure, and examples of reduced pressure include reduced pressure of 50 to 30,000 Pa. Moreover, generally known apparatuses, such as a continuous furnace, such as a batch furnace, a rotary kiln, and a roller hearth kiln, a fluidized bed, can be used for the apparatus used for the formation process of a carbon film. In particular, in the case of a batch furnace in which the vapor deposition apparatus is placed by allowing powder to stand, carbon can be more uniformly coated by performing the process under reduced pressure, and battery characteristics can be improved.

  The formation of carbon films by chemical vapor deposition includes various organic substances as described above as the carbon source, but the thermal decomposition temperature, vapor deposition rate, and characteristics of the carbon film formed after vapor deposition vary greatly depending on the materials used. There is a case. Substances with a high deposition rate often have insufficient uniformity of the carbon coating on the surface. On the other hand, substances that require a high temperature for decomposition cause excessive growth of silicon crystals of silicon-containing particles during deposition at a high temperature. There is a risk that the discharge efficiency and the cycle characteristics may be deteriorated.

As a method for obtaining coated particles having the above b ^* value range, it is important to use a specific component as a carbon coating raw material that can be pyrolyzed within the above temperature range to generate carbon, and to adjust the carbon coating amount. is there.

  Examples of the carbon raw material include a mixed gas in which the carbon-coated raw material contains methane, ethane, propane, or propylene and other gas components. By using methane, ethane, propane, or propylene as an essential component and a mixed gas containing other gas components, the lithium ion secondary battery has higher initial charge / discharge efficiency, high capacity, and excellent cycle characteristics. A negative electrode material is obtained. From the viewpoint of the production method, the higher the deposition rate, the higher the productivity, but it is disadvantageous in terms of the uniformity of the coating. The decomposition temperature varies depending on the type of organic matter used as the raw material for carbon deposition, and by combining the raw material for increasing the carbon content and the raw material for improving the surface characteristics, both productivity and characteristics as the negative electrode material can be achieved. Is possible. Examples of the raw material for improving the surface characteristics include methane, ethane, propane, and propylene, and examples of the raw material for increasing the carbon content include other gas components.

  The total amount of methane, ethane, propane or propylene in the mixed gas is preferably 60% by volume or more, and more preferably 85% by volume or more in the mixed gas. Although an upper limit is not specifically limited, 95 volume% or less may be sufficient and 90 volume% or less may be sufficient.

  Other gas components include hydrocarbons such as toluene, ethylene, acetylene, butane, butene, pentane, isobutane, hexane, benzene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone. 1- to 3-ring aromatic hydrocarbons such as pyridine, anthracene, and phenanthrene. These can be used singly or in appropriate combination of two or more. The total amount of other gas components is preferably 40% by volume or less, more preferably 15% by volume or less in the mixed gas. Although a minimum is not specifically limited, 5 volume% or more may be sufficient and 10 volume% or more may be sufficient.

  The methane, ethane, propane or propylene preferably contains two or more selected from the group consisting of methane, ethane, propane and propylene. In this case, other gas components may or may not be included.

  Furthermore, a mixed gas containing methane, ethane and propane is preferable. The total amount of methane, ethane, propane and propylene in the mixed gas is preferably 90% by volume or more, more preferably 95% by volume or more in the mixed gas. Although an upper limit may be 99.5 volume% or less, it is good also as 98 volume% or less. In particular, the amount of methane in the gas is preferably 80% by volume or more, and preferably 85 to 90% by volume. The amount of ethane in the gas is preferably 3 to 9% by volume, more preferably 4 to 8% by volume. The amount of propane in the gas is preferably 1 to 5% by volume, more preferably 2 to 4% by volume.

  Also in the case of a mixed gas containing two or more selected from the group consisting of methane, ethane, propane and propylene, other gas components may or may not be included. When other gas components are included, the total amount of the other gas components is preferably 0.5 to 10% by volume, more preferably 2 to 5% by volume in the mixed gas.

The coating amount of the carbon coating is preferably 1.0 to 40% by mass, and more preferably 1.0 to 30% by mass with respect to the entire carbon-coated particle. Although it depends on the particle diameter of the base material, by setting the carbon coating amount to 1.0% by mass or more, it is possible to maintain substantially sufficient conductivity. In order to make b ^* into a more suitable range and to improve cycling characteristics, the coating amount of the carbon film is more preferably 3 to 25% by mass. Further, if the carbon coating amount is 40% by mass or less, the improvement of the effect is not seen, and the proportion of carbon in the negative electrode material is increased so that the charge / discharge capacity is obtained when used as a negative electrode material for a lithium ion secondary battery. It is possible to reduce the possibility of occurrence of such a situation as much as possible.

  Furthermore, even if the carbon coverage is sufficient, if the coating is non-uniform and the silicon oxide surface is partially exposed, or if the tar component remains due to insufficient graphitization, that part will be insulated. And may adversely affect charge / discharge capacity and cycle characteristics. The uniformity can be confirmed by, for example, the crystal intensity ratio of silicon and graphite in Raman spectroscopic analysis. Similarly, graphitization of the carbon film can be confirmed by the ratio of carbon graphite to diamond crystal and the half-value width in Raman spectroscopic analysis.

  The higher the temperature during deposition, the more effective the graphitization of the carbon film and the suppression of tar formation. The higher the deposition rate, the higher the productivity, while the finely dispersed nano-particles in silicon oxide. This may lead to enlargement of silicon and may reduce battery capacity and cycle characteristics.

  When forming a carbon film by inflowing (venting) two or more organic gases in the process of forming the carbon film, it is not always necessary to perform the same at the same temperature and pressure. It is possible to select appropriately according to the situation.

[Negative electrode]
When producing a negative electrode using the said negative electrode material for lithium ion secondary batteries, conductive agents, such as carbon and graphite, can be added further. The type of the conductive agent is not particularly limited as long as it is an electron-conductive material that does not decompose or change in the configured battery. Specifically, metal particles such as Al, Ti, Fe, Ni, Cu, Zn, Ag, Sn, Si, metal fibers, natural graphite, artificial graphite, various coke particles, mesophase carbon, vapor grown carbon fiber, pitch Graphite such as carbon-based carbon fiber, PAN-based carbon fiber, and various resin fired bodies can be used.

Examples of the method for preparing the negative electrode (molded body) include the following methods.
A paste-like mixture is prepared by kneading a negative electrode material, if necessary, a conductive agent, and other additives such as a binder, with a solvent such as N-methylpyrrolidone or water. Apply to current collector sheet. In this case, as the current collector, any material that is usually used as a negative electrode current collector, such as a copper foil or a nickel foil, can be used without any particular limitation on thickness and surface treatment.
In addition, the shaping | molding method which shape | molds a mixture into a sheet form is not specifically limited, A well-known method can be used.

[Lithium ion secondary battery]
A lithium ion secondary battery is a lithium ion secondary battery having at least a positive electrode, a negative electrode, and a lithium ion conductive non-aqueous electrolyte. The negative electrode for a lithium ion secondary battery according to the present invention is used as the negative electrode. The material is used. The lithium ion secondary battery of the present invention is characterized in that it comprises a negative electrode using the negative electrode material composed of the above coated particles, and other positive electrode, electrolyte, separator, and other materials and battery shapes are used. There is no particular limitation. As described above, the negative electrode material of the present invention has good battery characteristics (charge / discharge capacity and cycle characteristics) when used as a negative electrode material for a lithium ion secondary battery, and is particularly excellent in cycle durability. .

As the positive electrode active material, oxides of transition metals such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , V ₂ O ₅ , MnO ₂ , TiS ₂ , MoS ₂ , lithium, chalcogen compounds, and the like are used.

  As the electrolyte, for example, a non-aqueous solution containing a lithium salt such as lithium hexafluorophosphate and lithium perchlorate is used. As the non-aqueous solvent, one or a combination of two or more of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethoxyethane, γ-butyrolactone, 2-methyltetrahydrofuran and the like are used. Various other non-aqueous electrolytes and solid electrolytes can also be used.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example. In the following examples, unless otherwise specified, “%” in the composition represents mass%, and the ratio represents mass ratio.

[Example 1]
SiOx (x = 1.0) particles having an average particle diameter of 5 μm were charged into a batch-type heating furnace.
Then, the inside of the furnace was heated to 900 ° C. at a temperature rising rate of 200 ° C./hr while the inside of the furnace was depressurized with an oil rotary vacuum pump. After reaching 900 ° C., natural gas (88.5% by volume of methane, 5% by volume of ethane, 2.5% by volume of propane) is introduced into the furnace at 0.3 L / min, and carbon coating treatment is performed for 100 hours. It was. The obtained black particles were conductive particles having an average particle size of 5.5 μm and a carbon coating amount of 5.1% by mass. Moreover, when this particle | grain was measured with the colorimetric color difference meter (Nippon Denshoku Industries Co., Ltd. product ZE-2000), b ^* value (yellowishness) was 1.06. A negative electrode and a lithium ion secondary battery were prepared by the following method, and the battery was evaluated.

<Battery evaluation>
Next, battery evaluation using the obtained particles as a negative electrode active material was performed by the following method.
First, 45% by mass of the obtained negative electrode material, 45% by mass of artificial graphite (average particle size 10 μm) and 10% by mass of polyimide were mixed, and N-methylpyrrolidone was further added to form a slurry.
This slurry was applied to a copper foil having a thickness of 12 μm, dried at 80 ° C. for 1 hour, then subjected to pressure molding by a roller press, and the electrode was vacuum-dried at 350 ° C. for 1 hour. Thereafter, it was punched into 2 cm ² to form a negative electrode.

  In order to evaluate the charge / discharge characteristics of the obtained negative electrode, a lithium foil was used for the counter electrode, lithium hexafluorophosphate was used as the non-aqueous electrolyte, and 1/1 (volume ratio) of ethylene carbonate and diethyl carbonate. A lithium ion secondary battery for evaluation using a non-aqueous electrolyte solution dissolved at a concentration of 1 mol / L in the mixed solution and a polyethylene microporous film having a thickness of 30 μm as a separator was produced.

The prepared lithium ion secondary battery is allowed to stand at room temperature overnight, and then charged with a secondary battery charge / discharge tester (manufactured by Nagano Co., Ltd.) until the voltage of the test cell reaches 0 V at 0.5 mA / cm ^2. After reaching 0V, the battery was charged by decreasing the current so as to keep the cell voltage at 0V. The charging was terminated when the current value fell below 40 μA / cm ² . The discharge was performed at a constant current of 0.5 mA / cm ² , and when the cell voltage reached 1.4 V, the discharge was terminated and the discharge capacity was determined.
The initial charge / discharge efficiency was calculated from the charge capacity (initial charge capacity) and the discharge capacity (initial discharge capacity) at this time. The above charge / discharge test was repeated, and a charge / discharge test after 50 cycles of the lithium ion secondary battery for evaluation was performed. The results are shown in Table 1.

  As a result, it was confirmed that the lithium ion secondary battery had an initial discharge capacity of 1,667 mAh / g, a high capacity with a discharge capacity retention rate of 94% after 50 cycles, and excellent cycle characteristics.

[Example 2]
The same SiOx (x = 1.0) particles g as in Example 1 were charged into a batch-type heating furnace.
Then, the inside of the furnace was heated to 900 ° C. at a temperature rising rate of 200 ° C./hr while the inside of the furnace was depressurized with an oil rotary vacuum pump. Then, after reaching 900 ° C., the household LP gas type 1 No. 2 (ethane + ethylene 5% by volume or less, propane + propylene 60% by volume to 80% by volume, butane + butylene 40% by volume or less) in the furnace is 0. It flowed in at 3 L / min and carbon coating treatment was performed for 8 hours. After the LP gas was stopped, the temperature was lowered to obtain 106 g of black particles.
The obtained black particles were conductive particles having an average particle size of 5.3 μm and a carbon coating amount of 4.9% by mass, and the b ^* value measured by a colorimetric color difference meter was 1.15. The same battery evaluation as in Example 1 was performed.

[Example 3]
100 g of the same SiOx (x = 1.0) particles as in Example 1 were laid on a tray so that the thickness of the powder layer was 10 mm, and charged into a batch-type heating furnace.
Then, the inside of the furnace was heated to 900 ° C. at a temperature rising rate of 200 ° C./hr while the inside of the furnace was depressurized with an oil rotary vacuum pump. After reaching 900 ° C., 0.1 L / min of methane and 0.2 cc / min of toluene are flown into the furnace (methane: 71% by volume, toluene: 29% by volume), and carbon coating treatment is performed for 7 hours. It was. After stopping methane and toluene, the inside of the furnace was cooled and cooled to obtain 106 g of black particles.

The obtained black particles are conductive particles having an average particle diameter of 5.2 μm, a BET specific surface area of 2.8 m ² / g, and a carbon coating amount of 4.8% by mass with respect to the black particles. ^{* The} value was 2.53. The same battery evaluation as in Example 1 was performed.

[Comparative Example 1]
The same SiOx (x = 1.0) particles as in Example 1 were charged into a batch-type heating furnace.
Then, the inside of the furnace was heated to 1,000 ° C. while reducing the inside of the furnace with an oil rotary vacuum pump. After reaching 1,000 ° C., methane gas was introduced at 0.3 NL / min, and carbon coating treatment was performed for 11 hours. In addition, the pressure reduction degree at this time was 800 Pa.
When this powder was mixed and measured, it was a particle having a carbon coating amount of 5.0% by mass, an average particle size of 5.3 μm, and a BET specific surface area of 5.1 m ² / g. The b ^* value measured by a colorimetric color difference meter was 0.76. The same battery evaluation as in Example 1 was performed.

[Comparative Example 2]
The same SiOx (x = 1.0) particles 100 g as in Example 1 were charged into a batch-type heating furnace.
While reducing the pressure inside the furnace with an oil rotary vacuum pump, the temperature inside the furnace was raised to 900 ° C. at a temperature rising rate of 200 ° C./hr. And after reaching 900 degreeC, toluene was flowed in into the furnace at 0.4 cc / min, and the carbon coating process for 5 hours was performed. After cooling, this powder was mixed and measured to find particles having a carbon coating amount of 4.8% by mass and an average particle size of 5.3 μm. The b ^* value of this particle was 0.69. The same battery evaluation as in Example 1 was performed.

[Comparative Example 3]
The same SiOx (x = 1.0) particles 100 g as in Example 1 were charged into a batch-type heating furnace.
While reducing the pressure inside the furnace with an oil rotary vacuum pump, the temperature inside the furnace was raised to 900 ° C. at a temperature rising rate of 200 ° C./hr. Then, after reaching 900 ° C., the same LP gas as in Example 2 was flowed into the furnace at 0.3 L / min, and carbon coating treatment was performed for 1 hour.
When this powder was mixed after cooling and measured, it was particles having a carbon coating amount of 0.8 mass% and an average particle size of 5.3 μm. The b * value of this particle was 5.9. The same battery evaluation as in Example 1 was performed.

  Table 1 shows carbon deposition processes and battery characteristics of Examples and Comparative Examples. While the examples of the present invention have high capacity and excellent cycle characteristics, and the initial charge and discharge efficiency is sufficient, the comparative example is a lithium ion secondary battery that is clearly inferior in cycle characteristics compared to the negative electrode material of the examples. It was confirmed that there was.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

Claims (8)

Lithium ions can be occluded and released, and the surface of particles containing silicon is coated with a carbon film, and the lithium ion particles are made of coated particles having a b ^* value of 0.8 to 5.0 in JIS Z 8729. Negative electrode material for secondary batteries.   The lithium ions can be occluded and released, and the silicon-containing particles are silicon particles, particles having a structure in which silicon fine particles are dispersed in a silicon-based compound, and a general formula SiOx (0.5 ≦ x ≦ 1.6). 2. The negative electrode material for a lithium ion secondary battery according to claim 1, which is a silicon oxide particle represented by the formula:   3. The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the carbon coating is a carbon coating formed by thermally decomposing a carbon coating raw material at 600 to 1,200 ° C. and chemically depositing carbon on the particle surface. .   The negative electrode material for a lithium ion secondary battery according to claim 3, wherein the carbon-coated raw material is a mixed gas containing methane, ethane, propane or propylene and other gas components.   The negative electrode material for a lithium ion secondary battery according to claim 3 or 4, wherein the carbon-coated raw material is a mixed gas containing two or more selected from the group consisting of methane, ethane, propane and propylene.   The negative electrode for lithium ion secondary batteries containing the negative electrode material for lithium ion secondary batteries of any one of Claims 1-5.   The lithium ion secondary battery which has a negative electrode for lithium ion secondary batteries of Claim 6.   (1) carbon-coated raw material gas, or (2) carbon-coated raw material in a temperature range of 600 to 1,200 ° C. in a carbon-coated raw material gas and vapor atmosphere, and occlude and release lithium ions. The method for producing a negative electrode material for a lithium ion secondary battery according to claim 1, wherein carbon is chemically deposited on the surface of particles containing silicon.