JP2015095342A - Method for manufacturing negative electrode material for lithium ion secondary batteries, negative electrode material for lithium ion secondary batteries, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a method for manufacturing a negative electrode material for lithium ion secondary batteries high in initial charge/discharge efficiency and superior in cycle characteristics while holding the advantages of a silicon-based active material, such as a high battery capacity and a low volume expansion coefficient; a negative electrode material manufactured by the manufacturing method; and a lithium ion secondary battery including the negative electrode material.SOLUTION: A method for manufacturing a negative electrode material for lithium ion secondary batteries comprises: a deposition step for covering, by vapor deposition, particles of a silicon-based active material with a carbon coating formed by a carbon raw material. In the method, the deposition step is performed more than once, and the kind of the carbon raw material to use is changed for each deposition step at least once, whereby the carbon coating is formed with two or more kinds of carbon raw materials. In each deposition step, the carbon raw material is one selected from among three kinds of materials consisting of an aliphatic hydrocarbon, an aromatic hydrocarbon and a distillate produced in a tar distillation process; the selected material or a mixture thereof is used.

Description

  The present invention relates to a method for producing a negative electrode material for a lithium ion secondary battery, a negative electrode material for a lithium ion secondary battery, and a lithium ion 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 of using an oxide such as V, Si, B, Zr, or Sn and a composite oxide thereof as a negative electrode material (see Patent Documents 1 and 2) , A method of applying a melt-quenched metal oxide as a negative electrode material (see Patent Document 3), a method of using silicon oxide as a negative electrode material (see Patent Document 4), and Si ₂ N ₂ O and Ge ₂ N ₂ O as negative electrode materials There is known a method using the method (see Patent Document 5).

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

  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. 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 present inventors know, the irreversible capacity during the initial charge / discharge is still large. There is a problem that the cycle performance has 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. As a result, the battery cannot be put into practical use, and the cycle performance is degraded.
In the method of Patent Document 8, although improvement in cycle performance is confirmed, the number of cycles of charge / discharge 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.

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 method for producing a negative electrode material for a lithium ion secondary battery having high initial charge / discharge efficiency and excellent cycle characteristics while maintaining the advantages of a high battery capacity and a low volume expansion coefficient of a silicon-based active material, and the production thereof An object of the present invention is to provide a negative electrode material produced by the method and a lithium ion secondary battery including the negative electrode material.

  In order to achieve the above object, according to the present invention, a lithium ion having a vapor deposition step of coating the surface of particles of a silicon-based active material that absorbs and releases lithium ions with a carbon film using a carbon raw material by a vapor deposition method. A method for producing a negative electrode material for a secondary battery, wherein the vapor deposition step is performed twice or more, and the type of the carbon raw material used for each vapor deposition step is changed at least once, so that two or more types of the carbon Forming the carbon film using the raw material, and in each vapor deposition step, the type of the carbon raw material is selected from one of three types obtained from aliphatic hydrocarbons, aromatic hydrocarbons, and fractions obtained in the tar distillation step. The present invention also provides a method for producing a negative electrode material for a lithium ion secondary battery, characterized by using a single substance or a mixture of the selected types of substances.

  In this way, the vapor deposition process is divided into two or more processes, and at least two types of carbon raw materials are properly used in each vapor deposition process, thereby improving the characteristics as a negative electrode material such as productivity, battery capacity, initial charge / discharge efficiency, and cycle characteristics. Thus, a negative electrode material for a lithium ion secondary battery can be manufactured. Further, the production method of the present invention is not particularly complicated and simple, and can sufficiently withstand industrial scale production.

  At this time, the aliphatic hydrocarbon is preferably methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, hexane, propylene, or a mixture of at least two of these.

  The aromatic hydrocarbon may be benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, mesitylene, It is preferable to use a mixture of at least two.

  At this time, it is preferable that the fraction obtained in the tar distillation step is a simple gas gas oil, creosote oil, anthracene oil or naphtha cracked tar oil or a mixture of at least two of them.

  By selecting such materials from aliphatic hydrocarbons, aromatic hydrocarbons, and types of fractions obtained in the tar distillation step, a good carbon film can be deposited, battery capacity, initial charge. Discharge efficiency and cycle characteristics can be further improved.

In addition, the type of the carbon raw material used in each vapor deposition step is selected from the type of the aromatic hydrocarbon, and then selected from the type of the aliphatic hydrocarbon. Is preferably formed.
In this way, first, the conductivity is ensured by using an aromatic hydrocarbon in the previous vapor deposition process to efficiently increase the amount of carbon, and the aliphatic liquid is used in the subsequent vapor deposition process. By forming the surface state of the carbon film having good compatibility, it is possible to more reliably improve the productivity as a negative electrode material such as productivity, battery capacity, initial charge / discharge efficiency, and cycle characteristics.

At this time, in the said vapor deposition process, it is preferable to form a carbon film in the temperature range of 600-1200 degreeC.
If the carbon film is formed in such a temperature range, the silicon crystal enlargement of the silicon-based active material particles can be suppressed, so that the expansion of the silicon-based active material particles during charging can be suppressed. As a result, the characteristics as the negative electrode material, particularly the cycle characteristics can be improved more reliably.

The silicon-based active material particles include silicon particles, particles having a composite structure in which silicon fine particles are dispersed in a silicon-based compound, and an oxidation represented by a general formula SiO _x (0.5 ≦ x ≦ 1.6). One of the silicon particles or a mixture of two or more of these is preferable.
If these are used as particles of a silicon-based active material, a negative electrode material for a lithium ion secondary battery having higher initial charge / discharge efficiency, high capacity, and excellent cycle characteristics can be produced.

The present invention provides a negative electrode material for a lithium ion secondary battery produced by any one of the above-described methods for producing a negative electrode material for a lithium ion secondary battery.
If it is such, it will become a negative electrode material for lithium ion secondary batteries excellent in productivity, battery capacity, initial charge / discharge efficiency, and cycle characteristics.

Moreover, in the present invention, a lithium ion secondary battery using the negative electrode material for a lithium ion secondary battery produced by any one of the above-described methods for producing a negative electrode material for a lithium ion secondary battery. I will provide a.
If it is such, it will become a lithium ion secondary battery excellent in battery capacity, initial charge-and-discharge efficiency, and cycling characteristics.

  As described above, according to the present invention, a negative electrode material for a lithium ion secondary battery having a high capacity, high initial charge / discharge efficiency, and excellent cycle characteristics can be produced. The negative electrode material produced by the production method of the present invention is suitable for a lithium ion secondary battery, and the lithium ion secondary battery using this negative electrode material has high capacity, high initial charge / discharge efficiency, and excellent cycle characteristics. It will be a thing. Further, the present invention is not particularly complicated, is simple, and can sufficiently withstand industrial scale manufacturing.

  Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to this.

  As described above, production of a negative electrode material for a lithium ion secondary battery excellent in initial charge / discharge efficiency and cycle characteristics while maintaining the advantages of high battery capacity and low volume expansion coefficient of silicon-based active material used for the negative electrode material The development of the method was awaited.

Examples of the silicon-based active material used for the negative electrode material include silicon oxide. This silicon oxide can be expressed as SiO _x . In addition, silicon oxide has a structure in which nano-silicon of about several nanometers to several tens of nanometers is finely dispersed in silicon oxide as analyzed by X-ray diffraction. For this reason, the battery capacity is as high as 5 to 6 times per mass as compared with carbon, and further, the volume expansion during charging is small, and it is considered that the battery capacity is easy to use as a negative electrode active material.

  However, since silicon oxide is an insulator, it is necessary to provide conductivity by some means. As a method of imparting conductivity, there are a method of mixing silicon oxide particles and conductive particles such as graphite, a method of coating the surface of silicon oxide particles with a carbon film, and a method of combining both. For example, as a method of coating the surface of silicon oxide particles with a carbon film, a method of chemical vapor deposition (CVD) of the particles in an organic gas and / or vapor is suitable. Alternatively, it can be performed efficiently by introducing steam.

  Under such circumstances, the present inventors were able to confirm that the battery characteristics were significantly improved by coating the surface of the silicon-based active material that occludes and releases lithium ions with a carbon coating. At the same time, however, it was found that mere carbon coating could not meet the required characteristics of the market.

Therefore, the present inventors conducted detailed studies with the aim of further improving battery characteristics as a negative electrode material. As a result, it was found that the level of required characteristics in the market can be reached by controlling the coating state of the carbon coating to be coated within a specific range.
Specifically, it has been found that not only the amount of the carbon coating but also the uniformity and the quality of the carbon coating affect the conductivity. For example, even if a sufficient amount of carbon is obtained, if the carbon coating is uneven and the surface of the silicon oxide is partially exposed, or if the tar component remains due to insufficient graphitization, the portion Becomes insulative and adversely affects charge / discharge capacity and cycle characteristics.

  Various organic substances are listed as carbon raw materials for the formation of a carbon film by chemical vapor deposition, but the thermal decomposition temperature, vapor deposition rate, characteristics of the carbon film formed after vapor deposition, and the like vary greatly depending on the substance used. When using a material having a high deposition rate, the surface carbon film often cannot obtain sufficient uniformity. In addition, when using a substance that requires high temperature for thermal decomposition, the silicon crystal of the mother particle grows too much at the time of vapor deposition at high temperature, and there is a risk that the discharge efficiency and cycle characteristics will be lowered.

  The uniformity varies depending on the silicon crystal in the mother particle, the average particle diameter, and the amount of coated carbon, but 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.

  In order to fully graphitize the carbon coating and suppress the remaining tar component, the higher the temperature during vapor deposition, the more effectively the remaining tar component can be suppressed. Furthermore, if the temperature during vapor deposition is high, the vapor deposition rate increases and contributes to the improvement of productivity, but this leads to enlargement of nano-silicon finely dispersed in silicon oxide and causes a decrease in battery capacity and cycle characteristics. turn into. Moreover, although productivity will improve when a vapor deposition rate is large, it will become disadvantageous at the point of the uniformity of a film.

  Therefore, the present inventors have performed a vapor deposition step of forming a carbon film by chemical vapor deposition twice or more, and obtained two or more types of carbon raw materials, for example, carbon raw materials and surface characteristics for earning carbon in a short time. We find that it is possible to achieve both improvement in productivity and characteristics as negative electrode materials (battery capacity, initial charge / discharge efficiency, cycle characteristics) by properly using carbon materials for improvement in each vapor deposition step, The present invention has been completed.

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.
The present invention relates to a method for producing a negative electrode material for a lithium ion secondary battery comprising a conductive powder in which the surface of particles of a silicon-based active material that occludes and releases lithium ions is coated with a carbon coating, and a negative electrode produced by the method. And a lithium ion secondary battery using the negative electrode material.

  Next, although the manufacturing method of the negative electrode material for lithium ion secondary batteries of this invention is demonstrated in detail, of course, it is not limited to this.

  First, particles of a silicon-based active material that absorbs and releases lithium ions are prepared.

Here, as silicon active material particles that occlude and release lithium ions, silicon powder (silicon simple substance), particles having a composite structure in which silicon fine particles are dispersed in a silicon compound, a general formula SiO _x (0.5 ≦ 0.5) It is preferable to use any one of silicon oxide powders represented by x ≦ 1.6) or a mixture of two or more thereof.
Thus, as a powder made of a material capable of occluding and releasing lithium ions containing silicon, a silicon powder having features such as a high capacity and a low volume expansion coefficient upon repeated charge and discharge, One of particles having a composite structure in which silicon fine particles are dispersed in a silicon-based compound, silicon oxide powder represented by the general formula SiO _x (0.5 ≦ x ≦ 1.6), or two or more of these By using the mixture, it is possible to obtain a negative electrode material for a lithium ion secondary battery having higher initial charge / discharge efficiency, high capacity, and excellent cycleability.

The particles having a structure in which silicon fine particles (silicon nanoparticles) as one of the raw material powders are dispersed in a silicon-based compound (for example, silicon oxide) are, for example, a mixture of silicon fine particles and a silicon-based compound. The silicon oxide particles before disproportionation represented by the general formula SiO _x are heat-treated at a temperature of 400 ° C. or higher, preferably 800 to 1100 ° C. in an inert non-oxidizing atmosphere such as argon. However, it can be obtained by a method of 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.

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 SiO _x (0.5 ≦ x ≦ 1.6). Can be mentioned. The silicon oxide can be obtained by cooling and precipitating silicon monoxide gas generated by heating a mixture of silicon dioxide and metal silicon.

The physical properties of the particles having a structure in which silicon oxide particles and silicon nanoparticles before disproportionation are dispersed in silicon oxide can be appropriately selected depending on the intended composite particles.
For example, the average particle size is desirably 0.1 to 50 μm, the lower limit is more desirably 0.2 μm or more, and further desirably 0.5 μm or more. The upper limit is more desirably 30 μm or less, and further desirably 20 μm or less.
In addition, said average particle diameter is represented by the weight average particle diameter in the particle size distribution measurement by a laser beam diffraction method.

Further, BET specific surface area of the particles of silicon-based active material, 0.5 to 100 ² / g is desirable, and more desirably about 1-20 m ² / g.
If 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 lithium ion secondary battery negative electrode material, it can be set as the thing which does not have a possibility that battery capacity may fall.

  Then, carbon is chemically vapor-deposited in a predetermined temperature range in an organic gas and / or vapor atmosphere to the previously prepared silicon-based active material particles to form a carbon film to impart conductivity.

  In the present invention, in the process of forming the carbon film, the vapor deposition process is performed twice or more, and the type of the carbon raw material used for each vapor deposition process is changed at least once to use two or more carbon raw materials. Forming a carbon film. The kind of carbon raw material here is an aliphatic hydrocarbon, an aromatic hydrocarbon, or a fraction obtained in a tar distillation step. One type is selected from the three types of carbon raw materials, and a single substance or a mixture of the selected types of substances is used in each vapor deposition step. Each vapor deposition process does not necessarily need to be performed at the same temperature and pressure, and can be appropriately selected according to the characteristics of a substance that is a carbon raw material.

  Various organic substances are listed as carbon raw materials for the production of a carbon film by chemical vapor deposition. However, the thermal decomposition temperature, vapor deposition rate, and characteristics of the carbon film formed after vapor deposition may vary greatly depending on the substance used. Substances with a high deposition rate often have insufficient uniformity of the carbon coating on the surface, and charge / discharge efficiency and cycle characteristics deteriorate. On the other hand, when a high temperature is required for decomposition, the productivity is lowered, and further, the silicon crystal of the mother particle grows too much at the time of vapor deposition at a high temperature, leading to a decrease in charge / discharge efficiency and cycle characteristics. Therefore, as in the present invention, the vapor deposition process is performed twice or more, and the carbon material is appropriately used for each vapor deposition process, thereby improving the characteristics as a negative electrode material such as productivity, battery capacity, initial charge / discharge efficiency, and cycle characteristics. It becomes possible to produce a compatible negative electrode material for a lithium ion secondary battery. Further, the production method of the present invention is not particularly complicated and simple, and can sufficiently withstand industrial scale production.

  Moreover, you may perform the vapor deposition process of this carbon film under reduced pressure of 50 Pa-30000 Pa. In particular, in the case of a batch-type apparatus in which the vapor deposition apparatus is placed by allowing powder to stand, by performing the process under reduced pressure, carbon can be coated more uniformly, and battery characteristics can be improved.

At this time, it is preferable to form a carbon film in the temperature range of 600-1200 degreeC in a vapor deposition process.
If the carbon film is formed in such a temperature range, the silicon crystal enlargement of the silicon-based active material particles can be suppressed, so that the expansion of the silicon-based active material particles during charging can be suppressed. As a result, the battery capacity and cycle characteristics can be improved more reliably.

In the present invention, the substance used to generate the organic gas and / or vapor and used as the carbon raw material is thermally decomposed by heat treatment in the above-mentioned temperature range of 600 to 1200 ° C., particularly in a non-acidic atmosphere. Are preferably selected from the following:
For the type of aliphatic hydrocarbon, it is preferable to use methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, hexane, propylene alone or a mixture of at least two of these. .
Further, aromatic hydrocarbon types include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, and mesitylene. It is preferable to use a tricyclic aromatic hydrocarbon alone or a mixture of at least two of them.
Moreover, it is preferable to use the gas distillate obtained in the tar distillation step, gas gas oil, creosote oil, anthracene oil, naphtha cracked tar oil alone or a mixture of at least two of them.
By selecting these substances from the aliphatic hydrocarbons, aromatic hydrocarbons, and fractions obtained in the tar distillation process, and using them as carbon raw materials, the battery capacity, initial charge / discharge efficiency, and cycle characteristics can be improved. It can improve more reliably.

Furthermore, in the present invention, it is preferable to use the organic substance selected from the types of aromatic hydrocarbons, and then use the type of aliphatic hydrocarbons to form a carbon film.
Aromatic hydrocarbons have a high deposition rate even at relatively low temperatures. Moreover, since the carbon film formed by vapor deposition of aliphatic hydrocarbons hardly decomposes the electrolyte solution at the contact surface with the electrolyte solution, deterioration of battery characteristics can be suppressed. Therefore, in the vapor deposition step for coating the carbon coating, first, sufficient conductivity is ensured by using an aromatic hydrocarbon to efficiently increase the amount of carbon, and then by chemical vapor deposition of aliphatic hydrocarbon, By forming a surface state with good compatibility, productivity and battery characteristics can be improved more reliably.

The coating amount of the carbon coating in this case is not particularly limited, but the proportion of carbon is desirably 0.3 to 40% by mass with respect to the entire particles of the silicon-based silicon-coated material, 0.5 to 30% by mass is more desirable.
By setting the carbon coating amount to 0.3% by mass or more, it is possible to maintain sufficient conductivity, and it is possible to reliably achieve improvement in cycleability when used as a negative electrode of a nonaqueous electrolyte secondary battery. . 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.

  Moreover, the pressure of the vapor deposition process of a carbon film can be applied to both normal pressure and reduced pressure.

  Furthermore, as the apparatus used for the carbon film deposition process, generally known apparatuses such as a batch furnace, a continuous kiln such as a rotary kiln and a roller hearth kiln, and a fluidized bed furnace can be used.

A negative electrode material for a lithium ion secondary battery is manufactured by the method for manufacturing a negative electrode material for a lithium ion secondary battery as described above.
If manufactured by such a method, a negative electrode material for a lithium ion secondary battery that is superior in productivity, battery capacity, initial charge / discharge efficiency, and cycle characteristics is obtained.

[Lithium ion secondary battery]
In addition, the lithium ion secondary battery of the present invention is characterized in that it comprises a negative electrode using the above negative electrode material for lithium ion secondary batteries, and other materials such as positive electrode, electrolyte, separator, and battery shape are known. Can be used, and is not particularly limited.

Here, 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. 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 configured battery may be used.
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.

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

Example 1
100 g of SiO _x (x = 1.0) particles having an average particle diameter of 5 μm and a BET specific surface area of 3.5 m ² / g were laid on a tray so that the powder layer thickness was 10 mm, and charged in 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 the temperature in the furnace reached 900 ° C., toluene as an aromatic hydrocarbon was introduced into the furnace at 0.3 cc / min, and a vapor deposition step for forming a carbon film was performed for 4 hours. After the toluene was stopped, a vapor deposition step of venting methane gas, which is an aliphatic hydrocarbon, at 0.3 NL / min was performed for 3 hours. The furnace pressure at this time was 800 Pa. Thus, in Example 1, the vapor deposition step was performed twice, the type of carbon raw material used for each vapor deposition step was changed once, and two types (first using aromatic hydrocarbons and then fat A carbon film was formed using a carbon raw material of group hydrocarbon.

After the treatment, the temperature was lowered to obtain 106 g of black particles.
The obtained black particles were conductive particles having an average particle diameter of 5.2 μm, a BET specific surface area of 6.5 m ² / g, and a carbon coating amount of 4.8% by mass with respect to the black particles.

<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. Then, it punched out to 2 cm < ² > and set it as the negative electrode.

  In order to evaluate the charge / discharge characteristics of the obtained negative electrode, a lithium foil was used for the counter electrode, and lithium hexafluorophosphate was mixed with ethylene carbonate and diethyl carbonate in a 1/1 (volume ratio) mixture 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 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 / 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 the discharge was terminated when the cell voltage reached 1.4 V, 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, the initial charge capacity was 2150 mAh / g, the initial discharge capacity was 1656 mAh / g, and the initial charge / discharge efficiency (initial discharge capacity / initial charge capacity) was 77%. Further, the discharge capacity at the 50th cycle was 1573 mAh / g, and the cycle retention rate (capacity retention rate) after 50 cycles was 94%. From the above results, the lithium ion secondary battery using the negative electrode material for a lithium ion secondary battery of the present invention has a high battery capacity, and is a lithium ion secondary battery excellent in initial charge / discharge efficiency and cycleability. confirmed.

(Example 2)
The same SiO _x (x = 1.0) particles as in Example 1 were charged into a batch-type heating furnace.
Then, the pressure in the furnace was increased to 800 ° C. at a temperature increase rate of 200 ° C./hr while the pressure in the furnace was reduced by an oil rotary vacuum pump. Then, after the temperature in the furnace reached 800 ° C., mesitylene, which is an aromatic hydrocarbon, was flowed into the furnace at 0.3 cc / min, and a vapor deposition process for forming a carbon film was performed for 5 hours. After stopping the mesitylene, a vapor deposition step in which propylene gas, which is an aliphatic hydrocarbon, was vented at 0.3 NL / min was performed for 3 hours. The furnace pressure at this time was 800 Pa. Thus, in Example 2, the vapor deposition step was performed twice, the type of carbon raw material used for each vapor deposition step was changed once, and two types (first using aromatic hydrocarbons and then fat A carbon film was formed using a carbon raw material of group hydrocarbon.

After the treatment, the temperature was lowered to obtain 106 g of black particles.
The obtained black particles were conductive particles having an average particle diameter of 5.3 μm, a BET specific surface area of 4.0 m ² / g, and a carbon coating amount of 4.9% by mass with respect to the black particles.

<Battery evaluation>
Next, using this negative electrode material, a negative electrode was produced in the same manner as in Example 1, and in order to evaluate the charge / discharge characteristics of the obtained negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 1. Produced. And the battery evaluation of the produced lithium ion secondary battery was performed. The results are shown in Table 1.

  As a result, the initial charge capacity was 2225 mAh / g, the initial discharge capacity was 1691 mAh / g, and the initial charge / discharge efficiency (initial discharge capacity / initial charge capacity) was 76%. The discharge capacity at the 50th cycle was 1606 mAh / g, and the cycle retention rate (capacity retention rate) after 50 cycles was 95%. From the above results, the lithium ion secondary battery using the negative electrode material for a lithium ion secondary battery of the present invention has a high battery capacity, and is a lithium ion secondary battery excellent in initial charge / discharge efficiency and cycleability. confirmed.

(Example 3)
The same SiO _x (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 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 the temperature in the furnace reached 900 ° C., toluene as an aromatic hydrocarbon was flowed into the furnace at 0.3 cc / min, and a vapor deposition step for forming a carbon film was performed for 5 hours. After the toluene was stopped, the inside of the furnace was heated to 1000 ° C. at a temperature rising rate of 200 ° C./hr, and after reaching 1000 ° C., a vapor deposition step of aeration of methane gas as an aliphatic hydrocarbon at 0.3 NL / min was performed for 1 hour It was. The furnace pressure at this time was 800 Pa. Thus, in Example 3, the vapor deposition step was performed twice, the type of carbon raw material used for each vapor deposition step was changed once, and two types (first using aromatic hydrocarbons and then fat A carbon film was formed using a carbon raw material of group hydrocarbon.

After the treatment, the temperature was lowered to obtain 106 g of black particles.
The obtained black particles were conductive particles having an average particle diameter of 5.5 μm, a BET specific surface area of 6.5 m ² / g, and a carbon coating amount of 5.1% by mass with respect to the black particles.

<Battery evaluation>
Next, using this negative electrode material, a negative electrode was produced in the same manner as in Example 1, and in order to evaluate the charge / discharge characteristics of the obtained negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 1. Produced. And the battery evaluation of the produced lithium ion secondary battery was performed. The results are shown in Table 1.

  As a result, the initial charge capacity was 2096 mAh / g, the initial discharge capacity was 1635 mAh / g, and the initial charge / discharge efficiency was 78%. Further, the discharge capacity at the 50th cycle was 1504 mAh / g, and the cycle retention rate (capacity retention rate) after 50 cycles was 92%. From the above results, the lithium ion secondary battery using the negative electrode material for a lithium ion secondary battery of the present invention has a high battery capacity, and is a lithium ion secondary battery excellent in initial charge / discharge efficiency and cycleability. confirmed.

Example 4
The same SiO _x (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 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 the temperature in the furnace reached 900 ° C., toluene as an aromatic hydrocarbon was introduced into the furnace at 0.3 cc / min, and a vapor deposition step for forming a carbon film was performed for 5 hours. After stopping toluene, the inside of the furnace is heated up to 1000 ° C. at a heating rate of 200 ° C./hr, and after reaching 1000 ° C., gas gas oil, which is a fraction obtained in the tar distillation process, flows in at 0.2 cc / min. The process was performed for 1 hour. The furnace pressure at this time was 800 Pa. Thus, in Example 4, the vapor deposition step was performed twice, the type of carbon raw material used for each vapor deposition step was changed once, and two types (first using aromatic hydrocarbons and then tar) The carbon film using the carbon raw material of the fraction obtained in the distillation process was used.

After the treatment, the temperature was lowered to obtain 106 g of black particles.
The obtained black particles were conductive particles having an average particle diameter of 5.7 μm, a BET specific surface area of 4.1 m ² / g, and a carbon coating amount of 5.0 mass% with respect to the black particles.

<Battery evaluation>
Next, using this negative electrode material, a negative electrode was produced in the same manner as in Example 1, and in order to evaluate the charge / discharge characteristics of the obtained negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 1. Produced. And the battery evaluation of the produced lithium ion secondary battery was performed. The results are shown in Table 1.

  As a result, the initial charge capacity was 2129 mAh / g, the initial discharge capacity was 1640 mAh / g, and the initial charge / discharge efficiency was 77%. In addition, the discharge capacity at the 50th cycle was 1459 mAh / g, and the cycle retention rate (capacity retention rate) after 50 cycles was 89%. From the above results, the lithium ion secondary battery using the negative electrode material for a lithium ion secondary battery of the present invention has a high battery capacity, and is a lithium ion secondary battery excellent in initial charge / discharge efficiency and cycleability. confirmed.

(Example 5)
100 g of the same SiO _x (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. And after the temperature in a furnace reached to 900 degreeC, the vapor deposition process which ventilates methane gas which is an aliphatic hydrocarbon at 0.3 NL / min was performed for 3 hours. After stopping methane gas, toluene as an aromatic hydrocarbon was introduced at 0.3 cc / min, and a vapor deposition step for forming a carbon film was performed for 4 hours. In other words, in Example 5, the order was reversed from that in Example 1, and aliphatic hydrocarbons were used first, followed by aromatic hydrocarbons.

After the treatment, the temperature was lowered to obtain 107 g of black particles.
The obtained black particles were conductive particles having an average particle diameter of 5.2 μm, a BET specific surface area of 3.0 m ² / g, and a carbon coating amount of 5.1 mass% with respect to the black particles.

<Battery evaluation>
Next, using this negative electrode material, a negative electrode was produced in the same manner as in Example 1, and in order to evaluate the charge / discharge characteristics of the obtained negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 1. Produced. And the battery evaluation of the produced lithium ion secondary battery was performed. The results are shown in Table 1.

  As a result, the initial charge capacity was 2142 mAh / g, the initial discharge capacity was 1650 mAh / g, and the initial charge / discharge efficiency was 77%. Further, the discharge capacity at the 50th cycle was 1485 mAh / g, and the cycle retention rate (capacity retention rate) after 50 cycles was 90%. From the above results, the lithium ion secondary battery using the negative electrode material for a lithium ion secondary battery of the present invention has a high battery capacity, and is a lithium ion secondary battery excellent in initial charge / discharge efficiency and cycleability. confirmed.

(Comparative Example 1)
The same SiO _x (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 1100 ° C. while reducing the inside of the furnace with an oil rotary vacuum pump. After reaching 1100 ° C., methane gas, which is an aliphatic hydrocarbon, was introduced at 0.3 NL / min, and carbon coating treatment was performed for 5 hours. The furnace pressure at this time was 800 Pa. Thus, in the comparative example 1, the vapor deposition process was implemented only once and the carbon film which used one type of carbon raw material was formed.
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.

<Battery evaluation>
Next, using this negative electrode material, a negative electrode was produced in the same manner as in Example 1, and in order to evaluate the charge / discharge characteristics of the obtained negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 1. Produced. And the battery evaluation of the produced lithium ion secondary battery was performed. The results are shown in Table 1.

  As a result, the initial charge capacity was 2091 mAh / g, the initial discharge capacity was 1631 mAh / g, and the initial charge / discharge efficiency was 78%. In addition, the discharge capacity at the 50th cycle was 1402 mAh / g, and the cycle retention rate (capacity maintenance rate) after 50 cycles was 86%. From the above results, it was confirmed that the cycle characteristics were significantly inferior to those of the lithium ion secondary battery using the negative electrode material for a lithium ion secondary battery of the present invention.

(Comparative Example 2)
100 g of the same SiO _x (x = 1.0) particles as in Example 1 were charged in a batch 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 the temperature in a furnace reached 900 degreeC, toluene which is an aromatic hydrocarbon was flowed in into the furnace at 0.3 cc / min, and the carbon coating process for 4 hours was performed. After stopping toluene, benzene, which is an aromatic hydrocarbon, was aerated at 0.3 NL / min to perform carbon coating treatment for 2 hours. The furnace pressure at this time was 800 Pa. As described above, in Comparative Example 2, the vapor deposition process was performed twice, and without changing the type of the carbon raw material used for each vapor deposition process, one type of carbon raw material (both using aromatic hydrocarbons was used). A carbon film was formed using
After cooling, this powder was mixed and measured to find particles having a carbon coating amount of 5.3 mass%, an average particle size of 5.3 μm, and a BET specific surface area of 2.1 m ² / g.

<Battery evaluation>
Next, using this negative electrode material, a negative electrode was produced in the same manner as in Example 1, and in order to evaluate the charge / discharge characteristics of the obtained negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 1. Produced. And the battery evaluation of the produced lithium ion secondary battery was performed. The results are shown in Table 1.

  As a result, the initial charge capacity was 2155 mAh / g, the initial discharge capacity was 1660 mAh / g, and the initial charge / discharge efficiency was 77%. In addition, the discharge capacity at the 50th cycle was 1211 mAh / g, and the cycle retention rate (capacity retention rate) after 50 cycles was 73%. From the above results, it was confirmed that the cycle characteristics were significantly inferior to those of the lithium ion secondary battery using the negative electrode material for a lithium ion secondary battery of the present invention.

(Comparative Example 3)
100 g of the same SiO _x (x = 1.0) particles as in Example 1 were charged in a batch 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, methane gas was ventilated at 0.3 NL / min in the furnace, and the carbon coating process for 42 hours was performed. Thus, in the comparative example 3, the vapor deposition process was implemented only once and the carbon film which used one type of carbon raw material was formed.
When the powder was mixed and measured after cooling, the carbon coating amount was 4.7% by mass, but the productivity was very low compared to other examples and comparative examples.

<Battery evaluation>
Next, using this negative electrode material, a negative electrode was produced in the same manner as in Example 1, and in order to evaluate the charge / discharge characteristics of the obtained negative electrode, a lithium ion secondary battery was produced in the same manner as in Example 1. Produced. And the battery evaluation of the produced lithium ion secondary battery was performed. The results are shown in Table 1.

  As a result, the initial charge capacity was 2144 mAh / g, the initial discharge capacity was 1651 mAh / g, and the initial charge / discharge efficiency was 77%. Further, the discharge capacity at the 50th cycle was 1518 mAh / g, and the cycle retention rate (capacity retention rate) after 50 cycles was 92%. From the above results, in order to obtain the cycle characteristics equivalent to the lithium ion secondary battery using the negative electrode material for lithium ion secondary batteries of the present invention, the time required for the vapor deposition process (CVD time) is 42 hours, This confirmed that productivity would deteriorate significantly.

  Table 1 shows a list of carbon deposition steps and battery characteristics of Examples and Comparative Examples. The negative electrode material of Comparative Examples 1 and 2 is a lithium ion secondary battery that is clearly inferior in cycle characteristics as compared with the negative electrode material of Example 1-3. In Comparative Example 3, the battery characteristics are not inferior to the Examples, but the process It was confirmed that there were difficulties.

  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 (9)

A method for producing a negative electrode material for a lithium ion secondary battery, comprising a vapor deposition step of coating the surface of particles of a silicon-based active material that occludes and releases lithium ions with a carbon film using a carbon raw material by a vapor deposition method,
The vapor deposition step is performed twice or more, and the carbon film using two or more types of carbon raw materials is formed by changing the type of the carbon raw material used for each vapor deposition step at least once. In the process, the kind of the carbon raw material is selected from the three kinds of fractions obtained in the aliphatic hydrocarbon, the aromatic hydrocarbon, and the tar distillation process, and a simple substance or a mixture of the selected kinds of substances is selected. A method for producing a negative electrode material for a lithium ion secondary battery.   The aliphatic hydrocarbon is methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, hexane, propylene, or a mixture of at least two of these. The manufacturing method of the negative electrode material for lithium ion secondary batteries of 1.   The aromatic hydrocarbon is benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, mesitylene, or at least two of these. The method for producing a negative electrode material for a lithium ion secondary battery according to claim 1, wherein the mixture is a mixture of one or more.   The fraction obtained in the tar distillation step is gas light oil, creosote oil, anthracene oil, naphtha cracked tar oil or a mixture of at least two of them. 4. The method for producing a negative electrode material for a lithium ion secondary battery according to any one of 3 above.   The type of the carbon raw material used in each vapor deposition step is first selected from the type of the aromatic hydrocarbon, and then selected from the type of the aliphatic hydrocarbon to form the carbon film. The manufacturing method of the negative electrode material for lithium ion secondary batteries of any one of Claims 1-4 characterized by the above-mentioned.   The method for producing a negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 5, wherein in the vapor deposition step, a carbon film is formed in a temperature range of 600 to 1200 ° C. The silicon-based active material particles include silicon particles, particles having a composite structure in which silicon fine particles are dispersed in a silicon-based compound, and silicon oxide particles represented by the general formula SiO _x (0.5 ≦ x ≦ 1.6). The method for producing a negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 6, wherein any one of the above or a mixture of two or more thereof is used.   The negative electrode material for lithium ion secondary batteries manufactured with the manufacturing method of any one of Claim 1 to 7.   A lithium ion secondary battery comprising the negative electrode material for a lithium ion secondary battery according to claim 8.