JP6394498B2 - Graphite-coated particles and method for producing the same - Google Patents

Description

  The present invention relates to graphite-coated particles having a high charge / discharge capacity and good cycle characteristics when used as a negative electrode material as a non-aqueous electrolyte secondary battery active material such as a lithium ion secondary battery, and a method for producing the same.

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 of using an oxide such as V, Si, B, Zr, Sn, or a composite oxide thereof as a negative electrode material (Patent Document 1: Japanese Patent Laid-Open No. Hei 5 -174818, Patent Document 2: JP-A-6-60867, etc., a method of applying a molten and quenched metal oxide as a negative electrode material (Patent Document 3: JP-A-10-294112), oxidation to a negative electrode material A method using silicon (Patent Document 4: Japanese Patent No. 2999741), a method using Si ₂ N ₂ O and Ge ₂ N ₂ O as negative electrode materials (Patent Document 5: Japanese Patent Laid-Open No. 11-102705), and the like are known. ing. Further, for the purpose of imparting conductivity to the negative electrode material, a method of carbonizing SiO with graphite and then carbonizing (Patent Document 6: Japanese Patent Laid-Open No. 2000-243396), a carbon layer is formed on the surface of silicon particles by chemical vapor deposition. (Patent Document 7: Japanese Patent Laid-Open No. 2000-215887), a method of coating a silicon oxide particle surface with a carbon layer by chemical vapor deposition (Patent Document 8: Japanese Patent Laid-Open No. 2002-42806), and lithium ions. As a method for coating the surface of a material that can be occluded and released with a graphite coating, there is a method (Patent Document 9: JP 2013-8654 A) performed in a continuous furnace such as a roller hearth kiln or a rotary kiln.

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 JP 2013-8654 A

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

  In particular, in Japanese Patent No. 2999741, silicon oxide is used as a negative electrode material for a lithium ion secondary battery to obtain a high-capacity electrode. However, as far as the present inventors see, the irreversible capacity at the time of initial charge / discharge is still present. There is room for improvement because the cycleability has not reached the practical level. Also, regarding the technique for imparting conductivity to the negative electrode material, in Japanese Patent Application Laid-Open No. 2000-243396, since it is a solid-solid fusion, a uniform carbon film is not formed and the conductivity is insufficient. There is a problem, and in the method of Japanese Patent Laid-Open No. 2000-215887, although a uniform carbon film can be formed, since Si is used as a negative electrode material, expansion / contraction at the time of lithium ion adsorption / desorption is too much. Is too large to be practically used as a result, and the cycle performance is lowered. Therefore, the charge amount must be limited to prevent this. In the method of Japanese Patent Application Laid-Open No. 2002-42806, although the improvement of cycle performance is confirmed due to insufficient deposition of fine silicon crystals, the structure of the carbon coating and the base material, When the number of cycles is repeated, there is a phenomenon that the capacity gradually decreases and then rapidly decreases after a certain number of times, which is still insufficient for a secondary battery. Moreover, in the method of JP2013-8654A, although productivity is increased, when the operation is performed for a long time, the heat transfer is reduced due to the adhesion of the material to the inner wall of the core tube, and the initial operation and the late operation are performed. There was a problem that quality variation occurred and operation stability was lowered.

  As a negative electrode material for non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, the charge / discharge capacity is expected to be several times that of graphite-based materials, which are currently mainstream. There has been a need for a method for improving the battery characteristics of silicon-based materials, which has been a major bottleneck in performance degradation due to charging and discharging.

As a result of intensive studies to achieve the above-mentioned object, the present inventors confirmed that a significant improvement in battery characteristics can be seen by coating the surface of a relatively high-capacity silicon-containing material with a graphite coating, At the same time, it was recognized that mere graphite coating could not meet the required characteristics of the market. Therefore, as a result of detailed studies aiming at further improvement in properties, the present inventors performed a graphite coating treatment with a rotary kiln under appropriate conditions, whereby a uniform graphite film was formed, and the obtained graphite-coated particles were

The present inventors have found that by using it as a negative electrode material for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, the characteristic level required by the market can be reached, and the present invention has been completed.

Accordingly, the present invention provides the following inventions.
[1]. A method for producing graphite-coated particles in which the surface of a silicon-containing material is coated with graphite, wherein the graphite-coating treatment is a CVD treatment using a rotary kiln apparatus, and silicon or a general formula SiOx (0.5 ≦ x <1. The silicon oxide represented by 5) is subjected to CVD treatment in an organic gas and / or steam at 500 to 1,300 ° C. at a graphite coating rate of 0.02 to 0.10 kg / hr · m ² per area inside the rotary kiln. it features a, the graphite coated particles, and the peak I _si of silicon appears at 500 cm ^-1 in the Raman spectrum, the intensity ratio I _si / I _G peak I _G of graphite appearing at 1,580cm ^-1 0~ 1 The method for producing the graphite-coated particles is 0.0 .
[2]. Production of graphite-coated particles according to [1], wherein the graphite-coated particles have an average particle diameter of 0.1 to 30 μm, a BET specific surface area of 0.3 to 30 m ² / g, and a coating carbon amount of 0.5 to 40% by mass. Method.
[3]. The method for producing graphite-coated particles according to [1] or [2] , wherein the rotary kiln apparatus is a batch-type rotary kiln apparatus.

  According to the production method including the CVD treatment using the rotary kiln of the present invention, when used as a negative electrode material for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, graphite having a high charge / discharge capacity and good cycle characteristics. Coated particles can be obtained.

Hereinafter, the present invention will be described in detail.
Production method of the present invention, the graphite coating process is a CVD process using a rotary kiln, a peak I _si of silicon appears at 500 cm ^-1 in the Raman spectrum, the intensity ratio of the peak I _G of graphite appearing on 1,580Cm ^-1 This is a method for producing graphite-coated particles having I _si / I _{G of 0} to 2.0.

First, the obtained graphite-coated particles will be described.
[Graphite-coated particles whose surface of silicon-containing material is coated with graphite]
What is coated with graphite is a silicon-containing material containing large-capacity silicon, and examples thereof include silicon, silicon oxide, silicon carbide, silicon nitride, silicon oxynitride, and mixtures thereof. Two or more species can be used in appropriate combination. Among these, silicon, silicon oxide represented by the general formula SiOx (0.5 ≦ x <1.5), particles having a structure in which fine particles of silicon are dispersed in a silicon-based compound, or a mixture thereof are preferable. The particles having a structure in which silicon fine particles are dispersed in a silicon-based compound can be obtained by using a general formula SiOx (0.5 ≦ x <1.5) as a starting material and performing a disproportionation reaction by heat treatment. The size of the silicon fine particles is preferably 1 to 500 nm. The size of the silicon fine particles can be obtained by measuring the crystallite size by X-ray diffraction / analysis. Examples of the silicon compound include silicon dioxide, silicon nitride, silicon carbide, and silicon oxynitride. Inert ones are preferred and silicon dioxide is preferred.

Graphite coated particles of the present invention, the peak I _si of silicon appears at 500 cm ^-1 in the Raman spectrum, the intensity ratio I _si / I _G peak I _G of graphite appearing on 1,580Cm ^-1 is in 0 to 2.0 is there. This ratio is an index of the uniformity of the graphite coating film, preferably 1.8 or less, and more preferably 1.0 or less. The strength ratio is an index indicating the ratio of the silicon in the silicon compound as the base material exposed to the surface, and is 0 when completely covered with graphite. When the strength ratio is larger than 2.0, the conductivity varies when used for the negative electrode material of a lithium ion secondary battery, and the battery characteristics are deteriorated.

  The physical properties of the graphite-coated particles are not particularly limited, but the average particle size is preferably from 0.1 to 30 μm, more preferably from 0.3 to 25 μm, still more preferably from 0.5 to 20 μm. If the average particle size is smaller than 0.1 μm, the purity decreases due to the effect of surface oxidation, and when used for a negative electrode material for a lithium ion secondary battery, the charge / discharge capacity decreases, the bulk density decreases, The charge / discharge capacity may be reduced. On the other hand, when it is larger than 30 μm, the amount of graphite deposited in the chemical vapor deposition treatment is reduced, and as a result, the cycle performance may be lowered when used for a negative electrode material for a lithium ion secondary battery. In addition, an average particle diameter can be represented by the weight average particle diameter in the particle size distribution measurement by a laser beam diffraction method.

BET specific surface area of the graphite coated particles, preferably 0.3~30m ² / g, more preferably 0.5~25m ² / g, more preferably 1.0~20m ² / g. When the BET specific surface area is less than 0.3 m ² / g, the surface activity becomes small, and as a result, when used as a negative electrode material for a non-aqueous electrolyte secondary battery, the charge / discharge capacity may be reduced. On the other hand, when the BET specific surface area exceeds 30 m ² / g, the amount of the binder at the time of electrode production increases, the capacity as an electrode decreases, and this is economically disadvantageous.

  The graphite coating amount is preferably 0.5 to 40% by mass, more preferably 2 to 30% by mass, and further preferably 2.5 to 20% by mass in the graphite-coated particles. When the graphite coating amount is less than 0.5% by mass, it is insufficient in terms of formation of a conductive film, and sufficient conductivity cannot be maintained. As a result, when used as a negative electrode material for a non-aqueous electrolyte secondary battery, May decrease. Conversely, even if the graphite coating amount exceeds 40% by mass, not only is the effect improved, but the proportion of graphite in the negative electrode material increases, and when used for the negative electrode material of a non-aqueous electrolyte secondary battery, charge / discharge Capacity decreases.

[Method for producing graphite-coated particles]
Next, the manufacturing method of the graphite covering particle in this invention is demonstrated. The production method of the present invention is characterized in that a graphite kiln is applied while rolling particles using a rotary kiln.

Specifically, silicon or silicon oxide represented by the general formula SiOx (0.5 ≦ x <1.5) is used in an organic gas and / or steam at 500 to 1,300 ° C. per area inside the rotary kiln. A method of performing CVD treatment at a graphite coating rate of 0.02 to 0.30 kg / hr · m ² can be mentioned.

  In the present invention, silicon oxide is a general term for amorphous silicon oxide obtained by cooling and precipitating silicon monoxide gas generated by heating a mixture of silicon dioxide and metal silicon. In the invention, the general formula SiOx (0.5 ≦ x <1.5) is used. x is preferably 1.0 ≦ x <1.3, and more preferably 1.0 ≦ x ≦ 1.2.

The average particle diameter of silicon or silicon oxide represented by the general formula SiOx (0.5 ≦ x <1.5) before carbon coating is preferably 0.1 to 30 μm, and more preferably 0.3 to 25 μm. Further, BET specific surface area is preferably 0.1~30m ² / g, more preferably 0.2~25m ² / g, more preferably 0.3 to 20 m ² / g. Graphite-coated particles having a desired average particle diameter and BET specific surface area when the average particle diameter and BET specific surface area of silicon and silicon oxide represented by the general formula SiOx (0.5 ≦ x <1.5) are outside the above ranges. May not be obtained.

  Specifically, the organic gas is rotated while rotating silicon or silicon oxide represented by the general formula SiOx (0.5 ≦ x <1.5) at 0.1 to 20 rpm, preferably 0.3 to 10 rpm. And / or CVD treatment at 500-1300 ° C. in steam.

  500-1300 degreeC is preferable and the process temperature which performs a graphite coating process has preferable 700-1200 degreeC. When the treatment temperature is lower than 500 ° C., a long time is required for the graphite coating treatment, and the productivity is lowered. On the other hand, when the treatment temperature exceeds 1,300 ° C., when the silicon oxide represented by the general formula SiOx (0.5 ≦ x <1.5) is coated with graphite, the disproportionation reaction proceeds excessively, When graphite-coated particles are used for a negative electrode material for a lithium ion secondary battery, the cycle characteristics may be deteriorated.

As an organic substance used as a raw material for generating an organic gas in the present invention, an organic substance that can be thermally decomposed at the above heat treatment temperature to generate carbon (graphite) is selected, particularly in a non-oxidizing atmosphere. For example, methane, ethane, A single or mixture of hydrocarbons such as ethylene, acetylene, propane, butane, butene, pentane, isobutane, hexane, benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone , Pyridine, anthracene, phenanthrene, and the like, and monocyclic to tricyclic aromatic hydrocarbons or a mixture thereof. Further, gas light oil, creosote oil, anthracene oil, and naphtha cracked tar oil obtained in the tar distillation step can be used alone or as a mixture. The atmosphere can also not particularly limited, mixed Ar, the non-oxidizing gas such as N _2, H _2, H _e in addition to the organic gas. Also, the pressure such as normal pressure and reduced pressure can be appropriately selected.

  While rotating non-oxidizing gas into the rotary kiln while rotating silicon or silicon oxide represented by the general formula SiOx (0.5 ≦ x <1.5), the temperature is raised to the above treatment temperature, and then organic matter Gas may be introduced.

What is important for obtaining the graphite-coated particles having the physical properties of the present invention is, for example, to keep the graphite coating speed within a certain range. As a result of various studies by the present inventors, by setting the graphite coating speed per area in the rotary kiln to 0.02 to 0.30 kg / hr · m ² , the silicon peak I _si appearing at 500 cm ⁻¹ in the Raman spectrum and , the intensity ratio I _si / I _G peak I _G of graphite appearing on 1,580Cm ^-1 is 0 to 2.0, it can be obtained graphite coated particles.

The graphite coating speed per area inside the rotary kiln is a value obtained by dividing the graphite coating amount per unit time by the area inside the rotary kiln, and is defined as the graphite coating speed when performing the graphite coating treatment using the rotary kiln. According to the knowledge of the present inventors, the physical properties of the present invention can be easily obtained by setting the graphite coating rate per area in the rotary kiln to 0.02 to 0.30 kg / hr · m ² . This range is preferably ^{0.03~0.28kg / hr · m 2, 0.03~0.10kg} / hr · m 2 is more preferable. If the graphite coating speed per area inside the rotary kiln is less than 0.02 kg / hr · m ² , it takes a long time for the graphite coating treatment, and the productivity decreases. On the other hand, if the graphite coating rate is higher than 0.30 kg / hr · m ² , the variation of the graphite coating film may increase.

  The rotary kiln apparatus is not particularly limited as long as it is a heating apparatus having a rotating mechanism, and a batch type, continuous type, etc. can be appropriately selected according to the purpose, but the batch type rotary kiln is more stable in quality and operation. From the viewpoint of In the case of a continuous rotary kiln, the area inside the rotary kiln means a graphite coating treatment zone.

  In the case of a batch type, the start of the unit time is the time when the graphite coating treatment starts, usually the time when the organic gas or vapor is introduced at the graphite coating treatment temperature, and the end is the time when the graphite coating treatment ends. Usually, it is the time when the organic gas or vapor is stopped. On the other hand, the initial stage in the case of the continuous type is the time when the raw material reaches the graphite coating treatment temperature, and the final stage is the time deviated from the graphite coating treatment temperature. The graphite coating rate per area in the rotary kiln can be controlled by the graphite coating processing temperature, time, amount charged, amount of organic substance generated gas, and the like. The unit time is selected so that the graphite coating speed falls within the above specific range, but is usually appropriately selected within the range of 0.5 to 30 hr.

[Negative electrode material for non-aqueous electrolyte secondary battery]
In the present invention, the above graphite-coated particles can be used as a negative electrode material as a negative electrode active material for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. Using the non-aqueous electrolyte secondary battery negative electrode material using this, a negative electrode can be produced and a lithium ion secondary battery can be produced.

  In addition, when producing a negative electrode using the said graphite covering particle | grains, electrically conductive agents, such as carbon, can be added. Also in this case, the kind of the conductive agent is not particularly limited, and any electronic conductive material that does not cause decomposition or alteration in the constituted battery may be used. Specifically, Al, Ti, Fe, Ni, Cu, Metal particles such as Zn, Ag, Sn, Si, metal fibers or natural carbon, artificial carbon, various coke particles, mesophase carbon, vapor-grown carbon fiber, pitch-based carbon fiber, PAN-based carbon fiber, various resin fired bodies Carbon such as can be used.

  The following method is mentioned as a preparation method of a negative electrode (molded object). A paste-like mixture is prepared by kneading the graphite-coated particles, 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]
The lithium ion secondary battery is characterized in that the graphite-coated particles are used as a negative electrode material for a non-aqueous electrolyte secondary battery as a non-aqueous electrolyte secondary battery negative electrode active material. Other positive electrodes, negative electrodes, electrolytes, The material such as the separator and the battery shape are not limited. For example, as the positive electrode active material, oxides of transition metals such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , V ₂ O ₆ , MnO ₂ , TiS ₂ , MoS ₂ , chalcogen compounds, and the like are used. As the electrolyte, for example, a non-aqueous solution containing a lithium salt such as lithium perchlorate is used, and as the non-aqueous solvent, propylene carbonate, ethylene carbonate, dimethoxyethane, γ-butyrolactone, 2-methyltetrahydrofuran or the like alone or in two types The above is used in combination. Various other non-aqueous electrolytes and solid electrolytes can also be used.

EXAMPLES Hereinafter, although an Example, a reference example, and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.

[Example 1]
1,000 g of silicon oxide powder represented by the general formula SiOx (x = 1.02) having an average particle diameter of 5 μm is charged into a batch type rotary kiln (inner diameter: 200 mmφ, length: 300 L, inner area: 0.188 m ² ). It is. Next, while rotating at a rotation speed of 1 rpm, nitrogen gas was introduced at 3 NL / min, and the temperature was raised and maintained at 1,000 ° C. at a temperature rising rate of 300 ° C./hr. Next, CH ₄ gas was added at an additional flow rate of 3 NL / min, and the graphite coating treatment was performed for 3 hours. After the treatment, the temperature was lowered to obtain about 1,050 g of black powder. The obtained black powder was graphite-coated particles having an average particle size = 5.1 μm, a BET specific surface area = 5.5 m ² / g, and a graphite coverage = 5.2% by mass (graphite coating amount = 55 g). Under this condition, the graphite coating rate per area in the rotary kiln is 0.10 kg / hr · m ² . This powder was subjected to microscopic Raman analysis (measured with a 532 nm green laser using Xplora PLUS manufactured by HORIBA). As a result, the Raman spectrum had Raman shifts of 500 cm ⁻¹ (I _si ) and 1,580 cm ⁻¹ ( I _G ) near the spectrum, I _si intensity = 47.3 counts, I _G intensity = 46.5 counts, and the intensity ratio I _si / I _G was 1.0.

[Battery evaluation]
Next, battery evaluation using the obtained conductive powder as a negative electrode active material was performed by the following method.
First, 10% by mass of polyimide is added to the obtained conductive powder, and further N-methylpyrrolidone is added to form a slurry. This slurry is applied to a copper foil having a thickness of 20 μm, dried at 80 ° C. for 1 hour, and then subjected to a roller press. The electrode was pressure-molded by the following, and this electrode was vacuum-dried at 350 ° C. for 1 hour, and then punched out to 2 cm ² to obtain a negative electrode.

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

The prepared lithium ion secondary battery was allowed to stand at room temperature overnight, and then charged with a secondary battery charge / discharge tester (manufactured by Nagano Co., Ltd.) until the test cell voltage reached 0 V at 0.5 mA / cm ² . Charging was performed at a constant current, and after reaching 0V, charging was performed by decreasing the current so as to keep the cell voltage at 0V. Then, charging was terminated when the current value fell below 40 μA / cm ² . Discharging was performed at a constant current of 0.5 mA / cm ² , and discharging was terminated when the cell voltage exceeded 2.0 V, and the discharge capacity was determined.

  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. As a result, the initial charge capacity is 1,880 mAh / g, the initial discharge capacity is 1,520 mAh / g, the initial charge / discharge efficiency is 80.9%, the 50th cycle discharge capacity is 1,400 mAh / g, and the cycle retention rate after 50 cycles is 92. It was confirmed that the lithium ion secondary battery had a high capacity of 1% and excellent initial charge / discharge efficiency and cycleability.

[Example 2]
The graphite coating treatment was performed under the same conditions as in Example 1 except that the amount charged was 500 g, the graphite coating treatment temperature was 950 ° C., and the treatment time was 5 hours.
The resulting black powder was graphite-coated particles having an average particle size = 5.1 μm, a BET specific surface area = 6.8 m ² / g, and a graphite coverage = 5.1% by mass (graphite coating amount = 27 g). Under these conditions, the graphite coating rate per area in the rotary kiln is 0.03 kg / hr · m ² . As a result of microscopic Raman analysis of this powder, the Raman spectrum has spectra near 500 cm ⁻¹ (I _si ) and 1,580 cm ⁻¹ (I _G ), and the I _si intensity = 42.1Counts, an I _G intensity = 55.8counts, the intensity ratio I _si / I _G was 0.8.

  As a result of battery evaluation of the graphite-coated particles in the same manner as in Example 1, the initial charge capacity was 1,910 mAh / g, the initial discharge capacity was 1,510 mAh / g, the initial charge / discharge efficiency was 79.1%, and the 50th cycle. The lithium ion secondary battery was confirmed to have a high discharge capacity of 1,400 mAh / g, a cycle retention of 92.7% after 50 cycles, and excellent initial charge / discharge efficiency and cycleability.

[Example 3]
The graphite coating treatment was performed under the same conditions as in Example 1 except that the amount of CH ₄ was 1 NL / min and the treatment time was 10 hours.
The obtained black powder was graphite-coated particles having an average particle size = 5.1 μm, a BET specific surface area = 6.3 m ² / g, and a graphite coverage = 4.9% by mass (graphite coating amount = 52 g). Under these conditions, the graphite coating rate per area in the rotary kiln is 0.03 kg / hr · m ² . As a result of microscopic Raman analysis of this powder, the Raman spectrum has spectra at Raman shifts near 500 cm ⁻¹ (I _si ) and 1,580 cm ⁻¹ (I _G ), and I _si intensity = 46.3 counts, I _G intensity = 54.5 counts, and the intensity ratio I _si / I _G was 0.8.

  As a result of battery evaluation of the graphite-coated particles in the same manner as in Example 1, the initial charge capacity was 1,890 mAh / g, the initial discharge capacity was 1,510 mAh / g, the initial charge / discharge efficiency was 79.9%, and the 50th cycle. The lithium ion secondary battery was confirmed to have a high discharge capacity of 1,400 mAh / g, a cycle retention of 92.7% after 50 cycles, and excellent initial charge / discharge efficiency and cycleability.

[ Reference Example 1 ]
The graphite coating treatment was performed under the same conditions as in Example 1 except that the amount of CH ₄ was 10 NL / min and the treatment time was 1 hour.
The obtained black powder was graphite-coated particles having an average particle size of 5.2 μm, a BET specific surface area of 4.8 m ² / g, and a graphite coverage of 4.8% by mass (graphite coating amount = 50 g). Under these conditions, the graphite coating rate per area in the rotary kiln is 0.27 kg / hr · m ² . As a result of microscopic Raman analysis of this powder, the Raman spectrum has spectra at Raman shifts near 500 cm ⁻¹ (I _si ) and 1,580 cm ⁻¹ (I _G ), and I _si intensity = 75.3counts, I _G intensity = 40.8counts, and the intensity ratio Isi / I _G was 1.8.

  As a result of battery evaluation of the graphite-coated particles in the same manner as in Example 1, the initial charge capacity was 1,850 mAh / g, the initial discharge capacity was 1,480 mAh / g, the initial charge / discharge efficiency was 80.0%, and the 50th cycle. It was confirmed that the lithium ion secondary battery had a high discharge capacity of 1,360 mAh / g, a cycle retention of 91.9% after 50 cycles, and excellent initial charge / discharge efficiency and cycleability.

[Example 4 ]
The graphite coating treatment was performed under the same conditions as in Example 1 except that the amount of CH ₄ was 1 NL / min and the treatment time was 15 hours.
The obtained black powder was graphite-coated particles having an average particle size = 5.1 μm, a BET specific surface area = 7.2 m ² / g, and a graphite coverage = 7.2% by mass (graphite coating amount = 78 g). Under these conditions, the graphite coating rate per area in the rotary kiln is 0.03 kg / hr · m ² . As a result of microscopic Raman analysis of this powder, the Raman spectrum has spectra at Raman shifts near 500 cm ⁻¹ (I _si ) and 1,580 cm ⁻¹ (I _G ), and I _si intensity = 0 counts, I _G intensity = 80.3 counts, and the intensity ratio I _si / I _G was 0.

  As a result of battery evaluation of the graphite-coated particles in the same manner as in Example 1, the initial charge capacity was 1,830 mAh / g, the initial discharge capacity was 1,460 mAh / g, the initial charge / discharge efficiency was 79.8%, and the 50th cycle. The lithium-ion secondary battery was confirmed to have a high capacity with a discharge capacity of 1,360 mAh / g, a cycle retention of 93.2% after 50 cycles, and excellent initial charge / discharge efficiency and cycleability.

[ Reference Example 2 ]
The graphite coating treatment was performed under the same conditions as in Example 1 except that the amount of CH ₄ was 8 NL / min and the treatment time was 1 hour.
The obtained black powder was graphite-coated particles having an average particle size = 5.1 μm, a BET specific surface area = 4.5 m ² / g, and a graphite coverage = 4.3% by mass (graphite coating amount = 45 g). Under this condition, the graphite coating rate per area in the rotary kiln is 0.24 kg / hr · m ² . As a result of microscopic Raman analysis of this powder, the Raman spectrum has spectra at Raman shifts near 500 cm ⁻¹ (I _si ) and 1,580 cm ⁻¹ (I _G ), and I _si intensity = 80.3 counts, I _G intensity = 40.1 counts, and the intensity ratio I _si / I _G was 2.0.

  As a result of battery evaluation of the graphite-coated particles in the same manner as in Example 1, the initial charge capacity was 1,860 mAh / g, the initial discharge capacity was 1,480 mAh / g, the initial charge / discharge efficiency was 79.6%, and the 50th cycle. It was confirmed that the lithium ion secondary battery had a discharge capacity of 1,350 mAh / g, a high capacity with a cycle retention of 91.2% after 50 cycles, and excellent initial charge / discharge efficiency and cycleability.

[Comparative Example 1]
The graphite coating treatment was performed under the same conditions as in Example 1 except that the amount of CH ₄ was 12 NL / min and the treatment time was 0.8 hours.
The obtained black powder is a graphite-coated particle having an average particle size = 5.2 μm, a BET specific surface area = 4.5 m ² / g, and a graphite coverage = 4.9% by mass (graphite coating amount = 52 g), and is coarse. Grain formation was seen. Under this condition, the graphite coating rate per area in the rotary kiln is 0.34 kg / hr · m ² . As a result of microscopic Raman analysis of this powder, the Raman spectrum has spectra near 500 cm ⁻¹ (I _si ) and 1,580 cm ⁻¹ (I _G ), and the I _si intensity = 82.5counts, I _G intensity = 36.6counts, and the intensity ratio I _si / I _G was 2.3.

  As a result of battery evaluation of the graphite-coated particles in the same manner as in Example 1, the initial charge capacity was 1,840 mAh / g, the initial discharge capacity was 1,450 mAh / g, the initial charge / discharge efficiency was 78.8%, and the 50th cycle. The discharge capacity was 1,300 mAh / g, the cycle retention after 50 cycles was 89.7%, and it was clearly a lithium ion secondary battery inferior in initial charge / discharge capacity and cycleability compared to the Examples.

[Comparative Example 2]
The graphite coating treatment was performed under the same conditions as in Example 1 except that the graphite coating treatment temperature was 1,100 ° C. and the treatment time was 0.5 hours.
The obtained black powder is a graphite-coated particle having an average particle size = 5.3 μm, a BET specific surface area = 4.3 m ² / g, and a graphite coverage = 5.5% by mass (graphite coating amount = 58 g), and is coarse. Grain formation was seen. Under this condition, the graphite coating rate per area in the rotary kiln is 0.62 kg / hr · m ² . As a result of microscopic Raman analysis of this powder, the Raman spectrum has spectra near 500 cm ⁻¹ (I _si ) and 1,580 cm ⁻¹ (I _G ), and the I _si intensity = 86.5 counts, I _G intensity = 32.6 counts, and the intensity ratio I _si / I _G was 2.7.

  As a result of battery evaluation of the graphite-coated particles in the same manner as in Example 1, the initial charge capacity was 1,780 mAh / g, the initial discharge capacity was 1,400 mAh / g, the initial charge / discharge efficiency was 78.7%, and the 50th cycle. The discharge capacity was 1,220 mAh / g, the cycle retention after 50 cycles was 87.1%, and clearly a lithium ion secondary battery inferior in initial charge / discharge capacity and cycleability compared to the Examples.

The results of Examples 1 to 4, Reference Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Tables 1 to 4.

Claims (3)

A method for producing graphite-coated particles in which the surface of a silicon-containing material is coated with graphite, wherein the graphite-coating treatment is a CVD treatment using a rotary kiln apparatus, and silicon or a general formula SiOx (0.5 ≦ x <1. The silicon oxide represented by 5) is subjected to CVD treatment in an organic gas and / or steam at 500 to 1,300 ° C. at a graphite coating rate of 0.02 to 0.10 kg / hr · m ² per area inside the rotary kiln. it features a, the graphite coated particles, and the peak I _si of silicon appears at 500 cm ^-1 in the Raman spectrum, the intensity ratio I _si / I _G peak I _G of graphite appearing at 1,580cm ^-1 0~ 1 The method for producing the graphite-coated particles is 0.0 . 2. The graphite-coated particles according to claim 1, wherein the graphite-coated particles have an average particle diameter of 0.1 to 30 [mu] m, a BET specific surface area of 0.3 to 30 m < ² > / g, and a coating carbon content of 0.5 to 40 mass%. Method. The method for producing graphite-coated particles according to claim 1 or 2 , wherein the rotary kiln device is a batch-type rotary kiln device.