JP5390336B2 - Negative electrode material for nonaqueous electrolyte secondary battery, method for producing negative electrode material for nonaqueous electrolyte secondary battery, negative electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a negative electrode material for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, a method for producing a negative electrode material for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte using the negative electrode material produced by this method The present invention relates to a negative electrode for a secondary battery and a non-aqueous electrolyte secondary battery.

In recent years, with the remarkable development of portable electronic devices, communication devices, etc., there is a strong demand for non-aqueous electrolyte secondary batteries with high energy density from the viewpoints of economy and downsizing and weight reduction of devices.
Conventionally, as a measure for increasing the capacity of this type of non-aqueous electrolyte secondary battery, for example, negative electrode materials such as oxides such as B, Ti, V, Mn, Co, Fe, Ni, Cr, Nb, and Mo and composites thereof A method using an oxide (see Patent Documents 1 and 2, etc.), a method using M _100-x Si _x (x ≧ 50 at%, M = Ni, Fe, Co, Mn) that has been melt-quenched and cooled as a negative electrode material (Patent Document 3) And a method using silicon oxide (see Patent Document 4), a method using Si ₂ N ₂ O, Ge ₂ N ₂ O, and Sn ₂ N ₂ O (see Patent Document 5), and the like.

Silicon shows the theoretical capacity (4200 mAh / g) which is much higher than the theoretical capacity of 372 mAh / g of the carbon material currently in practical use, and is the most expected material for miniaturization and high capacity of the battery. .
Various forms of silicon having different crystal structures are known depending on the production method. For example, a lithium ion secondary battery using single crystal silicon as a support for the negative electrode active material has been proposed (see Patent Document 6), and Li _x Si of single crystal silicon, polycrystalline silicon, and amorphous silicon (provided that , X is 0 to 5), and a lithium ion secondary battery using a lithium alloy has been proposed (see Patent Document 7). This is exemplified by Li _x Si using amorphous silicon, specifically, a pulverized product of crystalline silicon coated with amorphous silicon obtained by plasma decomposition of monosilane. However, 30 wt% of silicon and 55 wt% of graphite as a conductive agent were used, and the battery capacity of silicon could not be fully exhibited.

Further, for the purpose of imparting conductivity to the negative electrode material, a method of mechanically alloying a metal oxide such as silicon oxide and graphite, followed by carbonization (see Patent Document 8), and a Si particle surface by chemical vapor deposition A method of coating with a carbon layer (see Patent Document 9) and a method of coating the surface of silicon oxide particles with a carbon layer by chemical vapor deposition (see Patent Document 10) have been proposed.
However, the conductivity can be improved by providing a carbon layer on the particle surface, but the large volume change accompanying charging / discharging, which is a problem to be overcome by the silicon negative electrode, is mitigated, and the current collecting deterioration and cycle are associated with this. The deterioration of characteristics could not be prevented.

Therefore, in recent years, a method for suppressing the volume expansion by limiting the battery capacity utilization rate of silicon (see Patent Documents 9, 11, 12, 13, etc.), or the grain boundary of the polycrystalline particles is used as a buffer zone for volume change. Technology for rapidly cooling a silicon melt to which alumina is added (see Patent Document 14), polycrystalline particles made of a mixed phase polycrystal of α, β-FeSi ₂ (see Patent Document 15), and high-temperature plasticity of a single crystal silicon ingot Processing (see Patent Document 16) has been proposed.

  In addition, a method of reducing volume expansion by devising a laminated structure of silicon active materials has also been proposed. For example, a method of disposing silicon negative electrodes in two layers (see Patent Document 17), carbon, other metals, and oxides. A method of covering or encapsulating to suppress particle collapse (see Patent Document 18-24) and the like are disclosed. In addition, in a method in which silicon is directly grown in a vapor phase on a current collector, a method has been proposed in which the growth direction is controlled to suppress deterioration in cycle characteristics due to volume expansion (see Patent Document 25).

However, the method of improving the cycle characteristics of the negative electrode material by, for example, coating the silicon surface with carbon to make it conductive or coating with an amorphous metal layer can only exhibit about half of the original battery capacity of silicon. Therefore, further increase in capacity has been demanded.
In addition, with polycrystalline silicon having crystal grain boundaries, it is difficult to control the cooling rate by the proposed method, and it is difficult to reproduce stable physical properties.

On the other hand, silicon oxide can be expressed as SiO _x (where x is an oxide film and is slightly larger than the theoretical value of 1). However, in the analysis by X-ray diffraction, amorphous silicon of about several nm to several tens of nm is The structure is finely dispersed in silica. For this reason, although the battery capacity is small compared to silicon, the battery capacity is 5-6 times higher than the mass, and further, the volume expansion is small.
However, silicon oxide has a large irreversible capacity, and the initial efficiency is very low at about 70%. Therefore, when a battery is actually manufactured, the battery capacity of the positive electrode is excessively required, and the capacity increases by 5 to 6 times per active material. We could not expect an increase in battery capacity to meet the minute.

As described above, the practical problem of silicon oxide is that the initial efficiency is remarkably low, and methods for solving this include a method of replenishing the irreversible capacity and a method of suppressing the irreversible capacity. For example, it has been reported that a method of compensating for the irreversible capacity by doping Li metal in advance is effective. For example, in order to dope Li metal, a method of attaching a Li foil to the surface of the negative electrode active material (see Patent Document 26), a method of performing Li deposition on the surface of the negative electrode active material (see Patent Document 27), and the like are disclosed. .
However, it is difficult to obtain a Li thin body suitable for the initial efficiency of the silicon oxide negative electrode by attaching the Li foil, and the cost is high, and vapor deposition using Li vapor is not practical because the manufacturing process is complicated. It was.

On the other hand, a method for increasing the initial efficiency by increasing the mass ratio of Si irrespective of Li doping is disclosed.
One is a method in which silicon powder is added to silicon oxide powder to reduce the mass ratio of silicon oxide (see Patent Document 28), and the other is silicon by simultaneously generating and depositing silicon vapor in the production stage of silicon oxide. This is a method for obtaining a mixed solid of silicon oxide and silicon oxide (see Patent Document 29).
However, silicon has both high initial efficiency and battery capacity compared to silicon oxide, but is an active material that exhibits a volume expansion coefficient of 400% during charging, and even when added to a mixture of silicon oxide and carbon material. The volume expansion coefficient becomes very large. Furthermore, as a result, it was necessary to add 20% by mass or more of a carbon material to suppress the battery capacity to 1000 mAh / g. On the other hand, in the method of obtaining a mixed solid by simultaneously generating vapors of silicon and silicon oxide, since the vapor pressure of silicon is low, a manufacturing process at a high temperature exceeding 2000 ° C. is required, and there is a problem in operation.

Japanese Patent No. 3008228 Japanese Patent No. 3242751 Japanese Patent No. 3846661 Japanese Patent No. 2999741 Japanese Patent No. 3918311 Japanese Patent No. 2964732 Japanese Patent No. 3079343 JP 2000-243396 A JP 2000-215887 A JP 2002-42806 A JP 2000-173596 A Japanese Patent No. 3291260 JP 2005-317309 A JP 2003-109590 A JP 2004-185991 A JP 2004-303593 A JP 2005-190902 A JP 2005-235589 A JP 2006-216374 A JP 2006-236684 A JP 2006-339092 A Japanese Patent No. 3622629 JP 2002-75351 A Japanese Patent No. 3622631 JP 2006-338996 A Japanese Patent Laid-Open No. 11-086847 JP 2007-122992 A Japanese Patent No. 3982230 JP 2007-290919 A

As described above, even if the silicon-based active material is a single metal or an oxide thereof, each has a problem to be solved, which has been a problem in practical use.
Therefore, it is possible to sufficiently suppress the volume change associated with insertion and extraction of Li, to reduce the pulverization due to particle cracking, and to reduce the decrease in conductivity due to peeling from the current collector. Therefore, there has been a demand for a negative electrode active material that is particularly advantageous and that can be applied to applications in which repetitive cycle characteristics are particularly important, such as for mobile phones.

  The present invention has been made in view of the above problems, and solves the expansion of the electrode, which is a defect of silicon oxide, and the expansion of the battery due to gas generation, and is used for a negative electrode of a nonaqueous electrolyte secondary battery excellent in cycle characteristics. An object is to provide an effective negative electrode material, a method for producing a negative electrode material, a negative electrode for a nonaqueous electrolyte secondary battery using the negative electrode material produced by this method, and a nonaqueous electrolyte secondary battery.

In order to solve the above problems, the present invention provides a negative electrode material used for a negative electrode for a secondary battery using a nonaqueous electrolyte, the negative electrode material being on the surface of silicon oxide particles represented by the general formula SiO _x. A negative electrode material for a nonaqueous electrolyte secondary battery is provided, wherein the carbon film is coated with a carbon film, and the carbon film is subjected to a thermal plasma treatment.

  In such a negative electrode material, the ratio of high-strength, high-density, high-insulation carbon with diamond structure and carbon with electrically conductive graphite structure is strong, and electrode destruction due to expansion / contraction of electrode material during charge / discharge is strong Silicon oxide particles coated with a carbon coating in a proportion suitable to have a conductive network that is prevented and highly conductive. That is, a negative electrode material for a secondary battery using a non-aqueous electrolyte that has a high capacity and excellent cycle characteristics and is suitable for a negative electrode of, for example, a lithium ion secondary battery is provided.

In the present invention, there is provided a method for producing a negative electrode material for a secondary battery with a nonaqueous electrolyte, at least, a step of depositing carbon on the surface of the silicon oxide particles represented by the formula SiO _x, wherein A negative electrode for a nonaqueous electrolyte secondary battery, comprising: a step of performing a thermal plasma treatment on silicon oxide particles after carbon deposition; and a step of mixing the silicon oxide particles after the thermal plasma treatment and a binder. A method of manufacturing a material is provided.

In this manner, thermal plasma treatment is performed on the silicon oxide particles on which carbon is deposited.
As a result, the carbon material covering the surface of the silicon oxide particles has an appropriate ratio of the carbon material having a diamond structure and the carbon material having a graphite structure, and the characteristics of diamond having high strength, high density, and high insulation properties. In addition, the characteristics of graphite with electrical conductivity are optimized, and it is possible to strongly prevent electrode breakdown due to expansion / contraction of the electrode material during charge / discharge, and to produce a negative electrode active material having a highly conductive network. it can.
By using such a negative electrode material for a non-aqueous electrolyte secondary battery, it is possible to obtain a non-aqueous electrolyte secondary battery having excellent cycle characteristics while maintaining a high battery capacity with small deformation of the battery.

Here, it is preferable that the BET specific surface area of the silicon oxide particles after carbon deposition is 5 m ² / g or less.
Thus, by setting the BET specific surface area of the silicon oxide particles after carbon deposition to 5 m ² / g or less, carbon can be uniformly coated on the surface of the silicon oxide particles. When used as, a negative electrode material for a non-aqueous electrolyte secondary battery having high conductivity and excellent cycle characteristics can be produced.

The binder is preferably a polyimide resin.
Thus, by using a polyimide resin as the binder, it has excellent adhesion to a current collector such as a copper foil, has high initial charge / discharge efficiency, and can reduce volume changes during charge / discharge. Thus, a non-aqueous electrolyte secondary battery having good cycle characteristics and cycle efficiency by repetition can be manufactured.

The carbon deposition step is a step of chemically depositing carbon on the silicon oxide particles at a temperature of 600 to 1100 ° C. under a pressure of 50 to 30000 Pa, an organic gas and / or steam atmosphere, and the thermal plasma treatment. The step is preferably a step of putting the silicon oxide particles after carbon deposition into a thermal plasma atmosphere at a temperature of 5000 ° C. to 10000 ° C.
Thus, by setting the pressure of the processing atmosphere of the carbon vapor deposition process to 50 Pa or more, the battery characteristics can be improved and an excessive vacuum capacity is not required, thereby preventing an increase in apparatus cost and running cost. be able to. Moreover, by setting it as 30000 Pa or less, it can prevent that the powder specific resistance of a powder increases by reducing electroconductivity, and when it is used as a negative electrode material for nonaqueous electrolyte secondary batteries, the battery capacity decreases. Can be reliably prevented.
By setting the carbon vapor deposition temperature to 600 ° C. or higher, the vapor deposition treatment can be performed for a short time, and the yield can be improved. Moreover, by setting it as 1100 degrees C or less, possibility that particle | grains will melt | fuse and aggregate by a chemical vapor deposition process can be made small, and the danger that a conductive film will not be formed on the aggregation surface can be made small as much as possible. Therefore, when used as a negative electrode material for a lithium ion secondary battery, it is possible to eliminate the possibility that the cycle performance is lowered, and to obtain a negative electrode material for a non-aqueous electrolyte secondary battery with good cycle characteristics.
In addition, by introducing silicon oxide particles after carbon deposition into a thermal plasma atmosphere at a temperature of 5000 ° C. to 10,000 ° C., the diamond structure suitable for improving the battery characteristics of carbon in the carbon film covering the surface It can be made into the thing of the ratio of carbon and graphite structure carbon, and can be set as the negative electrode material for nonaqueous electrolyte secondary batteries excellent in the battery characteristic.
Therefore, it is possible to produce a negative electrode material for a non-aqueous electrolyte secondary battery that is further excellent in cycle characteristics while further reducing battery deformation and maintaining a high battery capacity.

And in this invention, it is a negative electrode containing the negative electrode material for nonaqueous electrolyte secondary batteries manufactured by the manufacturing method of the negative electrode material for nonaqueous electrolyte secondary batteries as described in this invention, Comprising: The volume after charge is before charge. The negative electrode for a non-aqueous electrolyte secondary battery is provided.
As described above, the negative electrode material for a non-aqueous electrolyte secondary battery manufactured by the manufacturing method of the present invention has a well-balanced ratio in which the surface of diamond-structured carbon and graphite-structured carbon can be improved compared to conventional materials. A negative electrode material comprising silicon oxide particles and a binder. Therefore, the negative electrode using such a negative electrode material for a non-aqueous electrolyte secondary battery has a volume expansion after charging suppressed as compared with the conventional case, and is less than twice that before charging.

In the present invention, a nonaqueous electrolyte secondary battery comprising at least the negative electrode for a nonaqueous electrolyte secondary battery according to the present invention, a positive electrode, a separator, and a nonaqueous electrolyte is provided. I will provide a.
As described above, the non-aqueous electrolyte secondary battery negative electrode of the present invention having excellent cycle characteristics while maintaining a high battery capacity with a small deformation of the battery, a positive electrode, a separator, and a non-aqueous electrolyte are provided. The water electrolyte secondary battery is a secondary battery that is extremely excellent in cycle characteristics even when charging and discharging are repeated, with less deformation of the battery and less decrease in battery capacity.

Here, the non-aqueous electrolyte secondary battery is preferably a lithium ion secondary battery.
As described above, the non-aqueous electrolyte secondary battery of the present invention is a secondary battery that is extremely excellent in cycle characteristics with little deformation and reduced capacity of the battery. Therefore, it is very suitable as a lithium ion secondary battery which has a strong demand for higher energy density in recent years.

  As described above, according to the present invention, the expansion of the electrode, which is a defect of silicon oxide, and the expansion of the battery due to gas generation are suppressed, and it is effective as a negative electrode for a nonaqueous electrolyte secondary battery excellent in cycle characteristics. A negative electrode material and the like are provided.

Hereinafter, the present invention will be described more specifically.
As described above, the development of a negative electrode material for a non-aqueous electrolyte secondary battery, which is small in deformation when used as a negative electrode of a battery and maintains a high battery capacity and excellent in cycle characteristics, has been awaited.

  Accordingly, the present inventor has found that the active material has a high initial charge / discharge efficiency, which exceeds the battery capacity of the carbon material, has a small battery expansion during operation, and overcomes the low initial charge / discharge efficiency, which is a drawback of silicon oxide. investigated.

As a result, it has been found that the above problems can be solved by using silicon oxide particles coated with a thermal plasma treated carbon film as an active material.
And by using a negative electrode material in which an appropriate amount of a binder is blended with this active material, the negative electrode material can be prevented from being destroyed or pulverized even if repeated expansion and contraction due to charging and discharging, and the conductivity of the electrode itself does not decrease. It turned out that the negative electrode material for nonaqueous electrolyte secondary batteries can be manufactured.
Furthermore, when this negative electrode material is used as a non-aqueous electrolyte secondary battery, it has been found that a non-aqueous electrolyte secondary battery with a small amount of gas generation and good cycle characteristics can be obtained, and the present invention has been made. .

Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto.
The negative electrode material used for the negative electrode for a secondary battery using the non-aqueous electrolyte of the present invention is one in which a carbon film is coated on the surface of silicon oxide particles represented by the general formula SiO _x and coated. The carbon film has been subjected to a thermal plasma treatment.

  In such negative electrode materials, the composition of the carbon film coated on the surface of silicon oxide particles is optimized for the characteristics of diamond with high strength, high density, and high insulation and the characteristics of graphite with electrical conductivity. The carbon material having a diamond structure and the carbon material having a graphite structure are in an appropriate ratio, and electrode destruction due to expansion / contraction of the electrode material during charge / discharge is strongly prevented, and the conductivity is high. A negative electrode material for a non-aqueous electrolyte secondary battery having a conductive network and a high capacity and excellent cycle characteristics.

Hereinafter, although the manufacturing method of the negative electrode material for nonaqueous electrolyte secondary batteries of this invention is demonstrated in detail, this invention is not limited to these.
First, depositing carbon on the surface of the silicon oxide particles represented by the formula SiO _x.

For this reason, first, silicon oxide particles represented by the general formula SiO _x are prepared.
Here, the silicon oxide in the present invention is an amorphous silicon oxide obtained by cooling and precipitating a silicon oxide gas generated by heating a mixture of silicon dioxide and metal silicon, and has a general formula SiO _x. It is represented by
The general physical properties and the like are not particularly limited, but the range of x is preferably 0.1 ≦ x <2.0, and more preferably 0.5 ≦ x ≦ 1.2.

As such a method for producing silicon oxide, for example, a silicon oxide gas obtained by heating a mixture of silicon dioxide and metal silicon under reduced pressure, preferably at 5 to 200 Pa, and 1000 to 1500 ° C. It can manufacture by making it precipitate at 1100 degreeC. In particular, it is important to keep the precipitation chamber at 500 to 1100 ° C, and more preferably 600 to 950 ° C.
Under this condition, crystalline silicon deposited in silicon oxide becomes nano-sized particles of several nm to several tens of nm, and thus the volume expansion during charge / discharge is very small. It can be suitably used for a negative electrode material of a secondary battery using an electrolyte.
On the other hand, when disproportionation occurs at high temperatures, silicon particles tend to increase and electrode expansion tends to increase. Therefore, it is desirable to use silicon oxide kept at the lowest possible temperature. As a standard, in solid-state NMR ( ²⁹ Si-DD / MAS) measurement, the ratio S ₋₈₄ / S _{−110 of} a broad signal area centered around ₋₁₁₀ ppm to a signal area around ₋₈₄ ppm is 0.5 <S _{−. It} is desirable that ₈₄ / S- ₁₁₀ <1.1.

Further, the silicon oxide is further pulverized into silicon oxide particles. The particle diameter is the particle diameter at the point where the cumulative curve becomes 10%, 50%, and 90% when the total curve is determined by the laser diffraction / scattering particle size distribution measurement method with the total volume of the particle being 100%. Are evaluated as 10% diameter, 50% diameter, and 90% diameter (μm), respectively. In the following, the particle diameter means a cumulative median diameter D ₅₀ (median diameter) of 50% diameter.
Silicon oxide particles to be prepared are the median diameter _{D 50} is preferably in the range of 0.1 to 20 [mu] m, 1 to 10 [mu] m is more preferable and more preferable. If the median diameter _{D 50} 0.1μm or more, can suppress the BET specific surface area is large ^{(10 m} 2 / g or more), also can be suppressed negative electrode film density is too small. Then, if the median diameter D ₅₀ is 20μm or less, it is possible to reliably prevent the possibility of causing a short circuit through the negative electrode film.

By the way, in order to make the silicon oxide particles have a predetermined particle diameter, a generally well-known pulverizer or classifier can be used.
As an example of a pulverizer, for example, a ball mill or a medium agitating mill that moves a pulverizing medium such as a ball or a bead and pulverizes a material to be crushed using an impact force, a frictional force, or a compressive force due to the kinetic energy is used. it can. It is also possible to use a roller mill that performs pulverization using the compressive force of the roller, or a jet mill that collides the object to be crushed with the lining material at high speed, collides particles with each other, and performs pulverization by the impact force of the impact. . And, hammer mill, pin mill, disk mill that pulverizes the material to be crushed using the impact force of the rotation of the rotor with fixed hammer, blade, pin, etc., colloid mill that uses shear force and high pressure wet counter collision type dispersion A machine “ultimizer” or the like can be used.
And this pulverization can be used for both wet and dry processes.

Further, since the particle size distribution is adjusted after pulverization, dry classification, wet classification, or sieving classification can be performed.
In dry classification, an air stream is mainly used, and dispersion, separation (separation of fine particles and coarse particles), collection (separation of solid and gas), and discharge are performed sequentially or simultaneously. Pre-treatment (adjustment of moisture, dispersibility, humidity, etc.) before classification so as not to reduce classification efficiency due to interference between particles, particle shape, air flow turbulence, velocity distribution, static electricity, etc. Or by adjusting the water content and oxygen concentration of the airflow used. In addition, a dry type in which a classifier is integrated is more preferable because pulverization and classification are performed at a time and a desired particle size distribution can be obtained.

And the vapor deposition process is performed with respect to the prepared silicon oxide particle, and carbon is vapor-deposited on the surface.
Thereby, conductivity can be imparted to the insulating silicon oxide.

And this carbon vapor deposition can be made into the process of carrying out the chemical vapor deposition of carbon on silicon oxide particle at the temperature of 600-1100 degreeC by the pressure of 50-30000 Pa, the atmosphere of organic substance gas, and / or a vapor | steam.
The pressure range is 50 to 30000 Pa under reduced pressure, more preferably 100 to 20000 Pa, and further preferably 1000 to 20000 Pa.
Thus, if the pressure of the processing atmosphere of carbon vapor deposition processing is 50 Pa or more, battery characteristics can be improved, excessive vacuum capacity is not required, and an increase in apparatus cost and running cost can be prevented. Moreover, if it is 30000 Pa or less, it can prevent that electrical conductivity falls and powder specific resistance increase, and when it is used as a negative electrode material for nonaqueous electrolyte secondary batteries, it is surely prevented that battery capacity falls. Is done.

The temperature range is preferably 600 to 1100 ° C, more preferably 800 to 1050 ° C.
If the processing temperature of carbon vapor deposition processing is 600 degreeC or more, vapor deposition processing will become a short time and a yield improvement can be achieved. Moreover, if it is 1100 degrees C or less, it can prevent that particle | grains fuse | melt and aggregate by a chemical vapor deposition process, and it can prevent that the location where a carbon membrane | film | coat is not formed generate | occur | produces. That is, it is possible to eliminate the possibility of a decrease in conductivity and a decrease in cycle performance, and it is possible to obtain a negative electrode material for a nonaqueous electrolyte secondary battery with good cycle characteristics.

  The treatment time is appropriately selected depending on the target carbon coating amount, treatment temperature, organic gas concentration (flow rate), introduction amount, etc., but usually 1 to 10 hours, particularly about 2 to 7 hours is economical. Is also efficient.

Here, the BET specific surface area of the silicon oxide particles after carbon deposition can be 5 m ² / g or less.
Thus, if the BET specific surface area of silicon oxide particles after carbon deposition is 5 m ² / g or less, carbon is uniformly coated on the surface, and when used as a negative electrode material, the conductivity is high. Thus, the negative electrode material for a non-aqueous electrolyte secondary battery having excellent cycle characteristics is obtained.

Although the amount of carbon coating is not particularly limited, the proportion of the carbon-coated silicon oxide particles in the total weight is preferably 1 to 30% by mass, and more preferably 5 to 20% by mass.
When the content is 1% by mass or more, variation in the carbon coating can be prevented and sufficient conductivity can be obtained. On the other hand, if the amount of carbon is 30% by mass or less, it is possible to prevent a decrease in the high battery capacity as silicon oxide due to an increase in the proportion of carbon, and the BET specific surface area exceeds 10 m ² / g. It is possible to reliably prevent the decomposition reaction from increasing and the battery from expanding due to gas generation or the like.

Further, as the organic substance used as a raw material for generating the organic gas in the present invention, an organic substance that can be thermally decomposed to generate carbon (graphite) is selected particularly in a non-acidic atmosphere.
For example, hydrocarbons such as methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, hexane, and cyclic hydrocarbons such as cyclopropane, cyclobutane, cyclopentane, cyclohexane, cyclohexene, alone or as a mixture, benzene, Examples thereof include 1 to 3 aromatic hydrocarbons such as toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, and mixtures thereof.
In addition, gas gas oil, creosote oil, anthracene oil, and naphtha cracked tar oil obtained in the tar distillation step can be used alone or as a mixture.

Next, thermal plasma treatment is performed on the silicon oxide particles after carbon deposition.
The plasma processing apparatus used for this thermal plasma processing is equipped with a powder supply apparatus that transports powder in a gas stream such as argon, and the powder can be introduced into the plasma atmosphere from the upper part of the reactor.
Further, it is desirable that the treatment be performed by putting it in a thermal plasma atmosphere using argon or argon / hydrogen as a source gas.
The treatment time is preferably about 1 second or less, but it is more desirable to carry out the treatment in a short time, whereby the disproportionation reaction of the internal silicon oxide particles can be suppressed.

When the carbon-coated silicon oxide particles after the thermal plasma treatment are subjected to Raman spectral analysis, they have scattering peaks at ₁₃₃₀ cm ⁻¹ and 1580 cm ⁻¹ , and their intensity ratio I ₁₃₃₀ / I ₁₅₈₀ is 0.5 <I ₁₃₃₀ / I ₁₅₈₀ <1.5.
Generally, carbon materials are divided into three allotropes, namely diamond, graphite (graphite), and amorphous carbon (amorphous carbon). Each of these carbon materials has characteristic physical properties. That is, diamond has high strength, high density, and high insulation, and graphite has excellent electrical conductivity.
If the Raman intensity is within the above range, the ratio of the carbon material having a diamond structure and the carbon material having a graphite structure in the carbon film covering the surface of the silicon oxide particles becomes an appropriate value. The characteristics are optimized, and as a result, the electrode material can be prevented from being destroyed due to the expansion and contraction of the electrode material during charging and discharging, and the negative electrode material has a conductive network.

In this thermal plasma treatment, silicon oxide particles after carbon deposition can be put into a thermal plasma atmosphere at a temperature of 2000 to 10000 ° C., particularly 5000 ° C. to 10000 ° C.
As a result, the ratio of diamond-structured carbon and graphite-structured carbon in the carbon film coated on the surface can be further prevented from electrode destruction due to expansion / contraction of the electrode material during charge / discharge, and a higher conductive network. This can be facilitated by a ratio suitable for the negative electrode material.
Therefore, it is possible to produce a negative electrode material for a non-aqueous electrolyte secondary battery that is further excellent in cycle characteristics while maintaining a high battery capacity with a smaller deformation of the battery.

There are various plasma generation conditions depending on the plasma torch to be used. In the present invention, it is desirable that the plasma contact time be 1 second or less, so that the amount of powder supply can be set high. Even with a throughput of about 2 kg per hour, a plasma torch with an output of about 35 kw can be selected.
The argon supply rate is desirably 50 to 200 L / min. However, if the supply amount is too large, the plasma state cannot be maintained, so 80 to 150 L / min is more desirable. The argon supply amount is preferably set to 1/20 to 1/5 L / min.
The reactor internal pressure is preferably 1 to 25 kPa, but the plasma becomes unstable when the reactor internal pressure increases, so that it is more preferably 1 to 15 kPa.
With the above supply rate and processing conditions, processing of 0.1 seconds or less is possible, processing in a shorter time is possible, and further disproportionation reaction of internal silicon oxide particles in thermal plasma processing Can be suppressed.

  The average particle diameter of the carbon-coated silicon oxide particles after the thermal plasma treatment is in the range of 0.1 to 50 μm, which is almost the same as that of the silicon oxide particles before the treatment, and more preferably 1 to 20 μm.

  Next, the silicon oxide particles after the thermal plasma treatment and the binder are mixed. Thereby, the negative electrode material for nonaqueous electrolyte secondary batteries is manufactured.

Here, a polyimide resin can be used as the binder, and an aromatic polyimide resin is more desirable.
By using a polyimide resin as a binder, it has excellent adhesion to the current collector, high initial charge / discharge efficiency, volume change during charge / discharge is alleviated, and cycle characteristics and efficiency due to repetition are excellent. A water electrolyte secondary battery is obtained.
In addition, the aromatic polyimide resin is excellent in solvent resistance and can strongly suppress separation from the current collector and separation of the active material. In addition, a binder can be used individually by 1 type or in combination of 2 or more types as appropriate.

Aromatic polyimide resins generally need to be poorly soluble in organic solvents, in particular not to swell or dissolve in the electrolyte, and generally only dissolve in high-boiling organic solvents such as cresol.
Therefore, when preparing the electrode paste, it is a precursor of polyimide and compared with various organic solvents such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, dioxolane. It is good to add in the state of a polyamic acid which is easy to dissolve, and heat-treat at a temperature of 300 ° C. or higher for a long time, thereby dehydrating and imidizing to form a binder.

  In this case, the aromatic polyimide resin has a basic skeleton composed of tetracarboxylic dianhydride and diamine. Specific examples thereof include pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride and biphenyltetra. Arocyclic tetracarboxylic dianhydrides such as aromatic tetracarboxylic dianhydrides such as carboxylic dianhydrides, cyclobutane tetracarboxylic dianhydrides, cyclopentane tetracarboxylic dianhydrides and cyclohexane tetracarboxylic dianhydrides And aliphatic tetracarboxylic dianhydrides such as butanetetracarboxylic dianhydride can be used alone or in combination of two or more.

  Examples of the diamine include p-phenylenediamine, m-phenylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, 2,2′-diaminodiphenylpropane, 4,4′-diaminodiphenylsulfone, 4,4′-diaminobenzophenone, 2,3-diaminonaphthalene, 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 4,4′-di (4- Aminophenoxy) diphenyl sulfone, aromatic diamines such as 2,2′-bis [4- (4-aminophenoxy) phenyl] propane, alicyclic diamines, aliphatic diamines, and the like are included, one kind alone or two kinds The above can be used in appropriate combination.

  As a method for synthesizing the polyamic acid intermediate, a solution polymerization method is usually used. Solvents used in the solution polymerization method include N, N′-dimethylformamide, N, N′-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, dimethyl sulfoxide, tetramethylurea, pyridine, dimethyl Examples include sulfone, hexamethylphosphoramide, and butyrolactone, which can be used alone or in appropriate combination of two or more.

  The reaction temperature is usually in the range of -20 to 150 ° C, but is preferably in the range of -5 to 100 ° C. Furthermore, in order to convert the polyamic acid intermediate into a polyimide resin, a method of dehydrating and ring-closing by heating is usually employed. The heating and dehydrating ring-closing temperature can be selected from 140 to 400 ° C, preferably 150 to 250 ° C. The time required for this dehydration and ring closure is 30 seconds to 10 hours, preferably 5 minutes to 5 hours, although it depends on the reaction temperature.

  Examples of such polyimide resin include polyimide resin powder and N-methylpyrrolidone solution of a polyimide precursor. For example, U-varnish A, U-varnish S, UIP-R, UIP-S (Ube) Kosan Co., Ltd.), KAYAFLEX KPI-121 (Nippon Kayaku Co., Ltd.), Rika Coat SN-20, PN-20, EN-20 (Shin Nihon Rika Co., Ltd.).

In addition to the carbon-coated silicon oxide particles subjected to thermal plasma treatment and the binder, a conductive agent such as graphite can be added to the negative electrode material of the nonaqueous electrolyte secondary battery.
In this case, the kind of the conductive agent is not particularly limited as long as it is an electron conductive material that does not cause decomposition or alteration in the configured battery. Specifically, metal powder and metal fibers such as Al, Ti, Fe, Ni, Cu, Zn, Ag, SnSi, natural graphite, artificial graphite, various coke powders, mesophase carbon, vapor grown carbon fiber, pitch-based carbon Fiber, PAN-based carbon fiber, graphite such as various resin fired bodies, and the like can be used.
Since these conductive agents are prepared by adding a dispersion of water or a solvent such as N-methyl-2-pyrrolidone in advance, an electrode paste uniformly attached and dispersed on silicon particles can be prepared. It is desirable to add as the solvent dispersion.
The conductive agent can be dispersed in the solvent using a known surfactant. The solvent used for the conductive agent is preferably the same as the solvent used for the binder.

  In addition to the binder, carboxymethyl cellulose, poly (sodium acrylate), other acrylic polymers or fatty acid esters may be added as a viscosity modifier.

Here, the blending amount of the carbon-coated silicon oxide particles with respect to the negative electrode material is desirably 50 to 98 mass%, more desirably 75 to 96 mass%, and particularly desirably 80 to 96 mass%.
And 1-20 mass% is suitable in a negative electrode material, and, as for the compounding quantity of a binder, 3-15 mass% is more desirable. If the amount of the binder is too small, the negative electrode active material may be separated. If the amount is too large, the porosity is reduced and the insulating film becomes thick, which may inhibit the movement of Li ions. For this reason, it is desirable to set it as 1-20 mass%.
Furthermore, the blending amount of the conductive agent is desirably 50% by mass or less in the negative electrode material (the battery capacity per negative electrode material is approximately 1000 mAHr / g or more), 1-30% by mass, and further 1-10% by mass. desirable. When the amount of the conductive agent is small, the conductivity of the negative electrode material may be poor, and the initial resistance tends to increase. On the other hand, an increase in the amount of conductive agent may lead to a decrease in battery capacity.

And suitable for dissolution and dispersion of binders such as N-methylpyrrolidone or water in the previously produced negative electrode material for non-aqueous electrolyte secondary battery, conductive agent as necessary, and other additives. A negative electrode for a non-aqueous electrolyte secondary battery can be produced by kneading a solvent into a paste-like mixture, applying the mixture to a sheet of a current collector, drying and pressing, and the like.
Such a negative electrode has a volume expansion after charging that is smaller than the conventional one, and is less than twice that before charging. Note that the measurement conditions when the volume (V2) after filling is less than twice the volume (V1) before filling, that is, (V2) / (V1) is less than 2, are the measurement conditions described in Example 1 described later. The value in the condition.
Here, the current collector in the present invention can be used without any limitation in thickness and surface treatment as long as it is a material usually used as a negative electrode current collector, such as a copper foil or a nickel foil. 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.

Furthermore, a non-aqueous electrolyte secondary battery provided with a negative electrode (molded body) for a non-aqueous electrolyte secondary battery, a positive electrode, a separator, and a non-aqueous electrolyte obtained in this manner can be manufactured, and in particular, a lithium ion secondary battery. A battery is preferred.
The nonaqueous electrolyte secondary battery is characterized in that the negative electrode material is used, and other materials such as the positive electrode, the separator, and the nonaqueous electrolyte solution, the battery shape, and the like are not limited.

Here, examples of the positive electrode active material include oxides or sulfides capable of inserting and extracting lithium ions, and these can be used singly or in appropriate combination of two or more.
Specifically, TiS ₂ , MoS ₂ , NbS ₂ , ZrS ₂ , VS ₂ , V ₂ O ₅ , MoO ₃ , Mg (V ₃ O ₈ ) ₂ or other metal sulfide or oxide not containing lithium, or Examples thereof include lithium and lithium composite oxide containing lithium, and composite metals such as NbSe ₂ are also used. Among these, in order to increase the energy density, a lithium composite oxide mainly composed of Li _p MetO ₂ is desirable. Met is preferably one or more of cobalt, nickel, iron and manganese, and p is usually a value in the range of 0.05 ≦ p ≦ 1.10.

Specific examples of the lithium composite _{oxide, LiCoO 2, LiNiO 2, LiFeO} 2, Li q Ni r Co 1-r O 2 ( where, the values of q and r is a charge-discharge state of the battery having the layer structure Generally, 0 <q <1, 0.7 <r ≦ 1), spinel-structured LiMn ₂ O _4, orthorhombic LiMnO _{2, and the} like. Furthermore, LiMet _s Mn _1-s O ₄ (0 <s <1) is also used as a substituted spinel manganese compound as a high-voltage compatible type, where Met is titanium, chromium, iron, cobalt, nickel, copper and zinc. Etc.

  The lithium composite oxide is obtained by, for example, grinding lithium carbonate, nitrate, oxide or hydroxide, and transition metal carbonate, nitrate, oxide or hydroxide according to a desired composition. It can prepare by mixing and baking at the temperature within the range of 600-1,000 degreeC in oxygen atmosphere.

  Furthermore, an organic substance can also be used as the positive electrode active material. Illustrative examples include polyacetylene, polypyrrole, polyparaphenylene, polyaniline, polythiophene, polyacene, polysulfide compounds and the like.

  The above positive electrode active material is kneaded together with the conductive agent and binder used for the negative electrode mixture and applied to the current collector, and can be formed into a positive electrode (molded body) by a known method.

  In addition, the separator used between the positive electrode and the negative electrode is not particularly limited as long as it is stable with respect to the electrolytic solution and has excellent liquid retention, but generally, polyolefins such as polyethylene and polypropylene, and their co-polymers. Examples thereof include porous sheets such as coalesced or aramid resin or non-woven fabrics. These may be used as a single layer or multiple layers, and ceramics such as metal oxide may be laminated on the surface. Moreover, porous glass, ceramics, etc. are also used.

Examples of the non-aqueous electrolyte include a non-aqueous electrolyte solution containing an electrolyte salt and a non-aqueous solvent.
Examples of the electrolyte salt include light metal salts. Examples of the light metal salts include alkali metal salts such as lithium salts, sodium salts, and potassium salts, alkaline earth metal salts such as magnesium salts and calcium salts, and aluminum salts. Can be used in appropriate combination. For example, in the case of a lithium salt, LiBF ₄ , LiClO ₄ , LiPF ₆ , LiAsF ₆ , CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, C ₄ F ₉ SO ₃ Li, CF ₃ CO ₂ Li, ( CF ₃ CO ₂ ) ₂ NLi, C ₆ F ₅ SO ₃ Li, C ₈ F ₁₇ SO ₃ Li, (C ₂ F ₅ SO ₂ ) ₂ NLi, (C ₄ F ₉ SO ₂ ) (CF ₃ SO ₂ ) NLi , (FSO ₂ C ₆ F ₄ ) (CF ₃ SO ₂ ) NLi, ((CF ₃ ) ₂ CHOSO ₂ ) ₂ NLi, (CF ₃ SO ₂ ) ₃ CLi, (3,5- (CF ₃ ) ₂ C ₆ F ₃ ) ₄ BLi, LiCF ₃ , LiAlCl ₄ or C ₄ BO ₈ Li.

  The concentration of the electrolyte salt in the nonaqueous electrolyte solution is preferably 0.5 to 2.0 mol / L from the viewpoint of electrical conductivity. The conductivity of the electrolyte at 25 ° C. is preferably 0.01 S / cm or more, and is adjusted according to the type or concentration of the electrolyte salt.

Furthermore, you may add various additives to a nonaqueous electrolyte solution as needed.
For example, vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 4-vinylethylene carbonate and the like for the purpose of improving cycle life, biphenyl, alkylbiphenyl, cyclohexylbenzene, t-butylbenzene, diphenyl ether for the purpose of preventing overcharge, Examples include benzofuran, various carbonate compounds for the purpose of deoxidation and dehydration, various carboxylic acid anhydrides, various nitrogen-containing compounds, and sulfur-containing compounds.

Examples of non-aqueous solvents include aprotic high dielectric constant solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, dipropyl carbonate, diethyl ether, Acetic acid esters such as tetrahydrofuran, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,3-dioxolane, sulfolane, methylsulfolane, acetonitrile, propionitrile, anisole, methyl acetate, or propionic acid esters Examples include aprotic low viscosity solvents. It is desirable to use these aprotic high dielectric constant solvents and aprotic low viscosity solvents in combination at an appropriate mixing ratio. Furthermore, ionic liquids using imidazolium, ammonium, and pyridinium type cations can be used. The counter anion is not particularly limited, and examples thereof include BF ₄ ⁻ , PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ^{− and the} like. The ionic liquid can be used by mixing with the non-aqueous electrolyte solvent described above.

  In addition, solid electrolytes, gel electrolytes, etc. can also be used as non-aqueous electrolytes, and include silicone gels, silicone polyether gels, acrylic gels, silicone acrylic gels, acrylonitrile gels, poly (vinylidene fluoride), etc. as polymer materials Is possible. These may be polymerized in advance or may be polymerized after injection. These can be used individually by 1 type or in combination of 2 or more types.

  The shape of the nonaqueous electrolyte secondary battery is arbitrary and is not particularly limited. In general, a coin type battery in which an electrode punched into a coin shape and a separator are stacked, and a square type or cylindrical type battery in which an electrode sheet and a separator are wound in a spiral shape are included.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.
Example 1
Mixed particles in which silicon dioxide particles (BET specific surface area = 200 m ² / g) and chemical grade metal silicon particles (BET specific surface area = 4 m ² / g) are mixed at an equimolar ratio are mixed at 1350 ° C. and 10 Pa in a high temperature reduced pressure atmosphere. After heat treatment, the generated silicon oxide gas was deposited on a SUS substrate maintained at 800 ° C.
Next, this precipitate was collected and then roughly crushed with a jaw crusher. This coarsely crushed material was pulverized using a jet mill (AFG-100 manufactured by Hosokawa Micron Corporation) at a rotation speed of 9000 rpm of a classifier, and silicon oxide particles (SiO _x : x: D ₅₀ = 7.6 μm, D ₉₀ = 11.9 μm). = 1.02) was recovered with a cyclone.

Further, the obtained silicon oxide particles were flowed in at a temperature of 1000 ° C./2000 Pa with CH ₄ gas at a flow rate of 0.5 NL / min in a vertical heating furnace while operating an oil rotary vacuum pump, and subjected to a carbon coating treatment for 8 hours. Went.
After completion of the operation, the system was cooled to collect black particles “A ′” having a carbon coating amount of 10% by mass. This particle was measured by solid-state NMR ( ²⁹ Si-DDMAS). The ratio of the signal area of broad silicon dioxide centered around −110 ppm to the signal area of diamond structure silicon around ₋₈₄ ppm (S ₋₈₄ / S). _-110) is 0.69, as a result of Raman analysis, Raman shift has a spectrum in the vicinity of 1330 cm ^-1 and 1580 cm ^-1, an intensity ratio _I 1330 _{/ I 1580} 1.1 met It was. At this time, the BET specific surface area was 6.0 m ² / g.

Next, the obtained black particles “A ′” were subjected to thermal plasma treatment. A part of the black particles “A ′” was stored separately for use in Comparative Example 1 described later.
Plasma generation conditions were an output of 12.5 kW, a pressure of 15 kPa, an argon supply rate of 120 L / min, and a hydrogen supply rate of 10 L / min. The obtained black particles “A ′” were supplied to the plasma reaction chamber at a rate of 25 g / min using 10 L / min argon as a carrier gas.

By screening the particles after the thermal plasma treatment, conductive particles having an average particle diameter of 7.2 μm and a carbon content of 5% (in black particles) could be obtained. This particle was measured by solid-state NMR ( ²⁹ Si-DDMAS). The ratio of the signal area of broad silicon dioxide centered around −110 ppm to the signal area of diamond structure silicon around ₋₈₄ ppm (S ₋₈₄ / S). _-110) is 0.72, as a result of Raman analysis, Raman shift has a spectrum in the vicinity of 1330 cm ^-1 and 1580 cm ^-1, an intensity ratio _I 1330 _{/ I 1580} 1.0 met It was. At this time, the BET specific surface area was 4.5 m ² / g.

Thereafter, 85% by mass of the carbon-coated silicon oxide particles subjected to thermal plasma treatment, and a polyimide resin U-varnish A (manufactured by Ube Industries) (solid content 18.1%) as a binder (solid content ratio: 15% by mass). In addition, it was diluted with N-methylpyrrolidone to form a slurry.
This slurry was applied to a copper foil having a thickness of 12 μm using a 50 μm doctor blade, dried under reduced pressure at 200 ° C. for 2 hours, and then subjected to pressure molding with a roller press at 60 ° C. to obtain a negative electrode molded body.

In order to confirm the usefulness as a negative electrode material, the charge / discharge capacity and the volume expansion coefficient were measured.
The negative electrode molded body obtained above is punched out into a disk shape of 2 cm ² , lithium foil as a counter electrode, and lithium bis (trifluoromethanesulfonyl) imide as a non-aqueous electrolyte in a 1/1 (volume ratio) mixture of ethylene carbonate and diethyl carbonate. 6 lithium ion secondary batteries for evaluation each using a non-aqueous electrolyte solution dissolved at a concentration of 1 mol / L and a 30 μm-thick polyethylene microporous film as a separator were prepared.

The prepared lithium ion secondary battery was allowed to stand at room temperature for 24 hours, two were immediately disassembled and measured for thickness, and the film thickness was measured in the electrolyte swelling state to determine the volume (V1). Note that the amount of increase in lithium due to the electrolyte and charging was not included.
The next two are charged with a constant current of 0.05 c until the voltage of the lithium ion secondary battery reaches 5 mV using a secondary battery charge / discharge test device (manufactured by Asuka Electronics Co., Ltd.). After reaching, the battery was charged by decreasing the current so as to keep the cell voltage at 5 mV. And charge was complete | finished when the electric current value fell below 0.02c. Note that c is a current value for charging the theoretical capacity of the negative electrode in one hour, and 1c = 15 mA.
After the end of charging, the previous two lithium ion secondary batteries were disassembled and the volume during charging was determined by measuring the thickness (V2). And the volume change rate after charge was computed by V2 / V1 from the result of said V1 and V2.
The remaining two were charged by the above method and then discharged at a constant current of 0.05 c until reaching 2000 mV, thereby calculating the charge / discharge capacity [mAh / g], and the initial charge / discharge efficiency (% ) The charge / discharge capacity is the capacity per active material excluding the binder, and the initial charge / discharge efficiency (%) is expressed as a percentage of the discharge capacity with respect to the charge capacity (discharge capacity / charge capacity × 100).

Next, in order to evaluate the cycle characteristics, a lithium ion secondary battery for evaluation was manufactured by the following method.
A laminate battery of 10 cm × 10 cm was produced by using lithium cobaltate / acetylene black / PVDF (= 94/2/4) for the positive electrode and combining the previously produced negative electrode.
The non-aqueous electrolyte uses a non-aqueous electrolyte solution in which lithium hexafluorophosphate is dissolved in a 1/1 (volume ratio) mixture of ethylene carbonate and diethyl carbonate at a concentration of 1 mol / L, and the separator is made of polyethylene having a thickness of 30 μm. A microporous film was used.

The produced laminated lithium ion secondary battery was left at room temperature for 2 nights.
Thereafter, using a secondary battery charge / discharge test apparatus (manufactured by Asuka Electronics Co., Ltd.), the battery is charged with a constant current of 380 mA (1 c on the positive electrode basis) until the voltage of the test cell reaches 4.2 V, and the voltage is set to 4.2 V. After that, the battery was charged by decreasing the current so as to keep the cell voltage at 4.2V. Then, charging was terminated when the current value fell below 40 mA. The discharge was performed at a constant current of 250 mA, and the discharge was terminated when the cell voltage reached 2.5V. The battery thickness after this was continued for 50 cycles was measured.
Further, the percentage of the discharge capacity at the 50th cycle with respect to the initial discharge capacity (discharge capacity at the 50th cycle / initial discharge capacity × 100) was calculated as the discharge capacity retention rate (%).
These results are shown in Table 1.

(Example 2)
Mixed particles in which silicon dioxide particles (BET specific surface area = 200 m ² / g) and chemical grade metal silicon particles (BET specific surface area = 4 m ² / g) are mixed at an equimolar ratio are mixed at 1350 ° C. and 10 Pa in a high temperature reduced pressure atmosphere. After heat treatment, the generated silicon oxide gas was deposited on a SUS substrate maintained at 800 ° C.
Next, this precipitate was collected and then roughly crushed with a jaw crusher. This coarsely crushed material was pulverized using a jet mill (AFG-100 manufactured by Hosokawa Micron Corporation) at a rotation speed of 9000 rpm of a classifier, and silicon oxide particles (SiO _x : x: D ₅₀ = 7.6 μm, D ₉₀ = 11.9 μm). = 1.02) was recovered with a cyclone.

Further, the obtained silicon oxide particles were infused with cyclohexane gas at 0.5 NL / min under a condition of 1000 ° C./2000 Pa while operating an oil rotary vacuum pump in a vertical heating furnace, and carbon coating treatment for 8 hours. Went.
After the operation, the system was cooled to collect black particles “B ′” having a carbon coating amount of 10% by mass. This particle was measured by solid-state NMR ( ²⁹ Si-DDMAS). The ratio of the signal area of broad silicon dioxide centered around −110 ppm to the signal area of diamond structure silicon around ₋₈₄ ppm (S ₋₈₄ / S). _-110) is 0.68, as a result of Raman analysis, Raman shift has a spectrum in the vicinity of 1330 cm ^-1 and 1580 cm ^-1, an intensity ratio _I 1330 _{/ I 1580} 1.0 met It was. At this time, the BET specific surface area was 2.5 m ² / g.

Next, the obtained black particles “B ′” were subjected to thermal plasma treatment.
Plasma generation conditions were an output of 12.5 kW, a pressure of 15 kPa, an argon supply rate of 120 L / min, and a hydrogen supply rate of 10 L / min. The obtained black particles “B ′” were supplied to the plasma reaction chamber at a rate of 25 g / min using 10 L / min argon as a carrier gas.

By screening the particles after the thermal plasma treatment, conductive particles having an average particle diameter of 7.2 μm and a carbon content of 5% (in black particles) could be obtained. This particle was measured by solid-state NMR ( ²⁹ Si-DDMAS). The ratio of the signal area of broad silicon dioxide centered around −110 ppm to the signal area of diamond structure silicon around ₋₈₄ ppm (S ₋₈₄ / S). _-110) is 0.71, as a result of Raman analysis, Raman shift has a spectrum in the vicinity of 1330 cm ^-1 and 1580 cm ^-1, an intensity ratio _I 1330 _{/ I 1580} is 0.99 met It was. At this time, the BET specific surface area was 2.2 m ² / g.

  Then, the negative electrode material for nonaqueous electrolyte secondary batteries and the evaluation lithium ion secondary battery were manufactured by the method similar to Example 1, and the same evaluation as Example 1 was performed. The results are shown in Table 1.

(Comparative Example 1)
A part of the carbon-coated silicon oxide particles [A ′] produced in Example 1 was taken out and mixed with a polyimide resin that had not been subjected to thermal plasma treatment, and a negative electrode material for a non-aqueous electrolyte secondary battery. A lithium ion secondary battery for evaluation was manufactured in the same manner as in Example 1 except that the evaluation was performed, and the same evaluation was performed. The results are shown in Table 1.

As shown in Table 1, the rate of change in the electrode volume due to charging is smaller in both Examples 1 and 2 than in Comparative Example 1, and the initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency are all evaluated in Comparative Example 1. As compared with the lithium ion secondary battery for use, it showed a good value, and it was found that the battery characteristics could be improved by modifying the surface carbon film by thermal plasma treatment.
In addition, the discharge capacity retention rate after 50 cycles is also 5% or more better than the case of using the carbon-coated silicon oxide particles of Comparative Example 1 in both Examples 1 and 2, and the cycle characteristics are also improved by the thermal plasma treatment. I found out that I was able to do it.
Furthermore, the negative electrode of Example 1 had an initial thickness of 2 mm and the thickness after 50 cycles of charge / discharge was 2.1 mm, whereas the negative electrode of Comparative Example 1 had increased to 2.5 mm. It was. That is, it was found that gas generation on the electrode surface of Example 1 was small.

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

Claims (8)

A negative electrode material used for a negative electrode for a secondary battery using a non-aqueous electrolyte,
The negative electrode material is a non-aqueous material characterized in that the surface of silicon oxide particles represented by the general formula SiO _x is coated with a carbon film, and the carbon film is subjected to a thermal plasma treatment. Negative electrode material for electrolyte secondary battery. A method for producing a negative electrode material for a secondary battery using a non-aqueous electrolyte,
at least,
Depositing carbon on the surface of the silicon oxide particles represented by the general formula SiO _x ;
Performing a thermal plasma treatment on the silicon oxide particles after carbon deposition;
A method for producing a negative electrode material for a non-aqueous electrolyte secondary battery, comprising a step of mixing the silicon oxide particles after the thermal plasma treatment and a binder. The method for producing a negative electrode material for a non-aqueous electrolyte secondary battery according to claim 2, wherein the silicon oxide particles after carbon deposition have a BET specific surface area of 5 m ² / g or less.   The method for producing a negative electrode material for a nonaqueous electrolyte secondary battery according to claim 2 or 3, wherein the binder is a polyimide resin. The carbon deposition step is a step of chemically vapor-depositing carbon on the silicon oxide particles at a temperature of 600 to 1100 ° C. under a pressure of 50 to 30000 Pa, an organic gas and / or steam atmosphere,
5. The process according to claim 2, wherein the thermal plasma treatment step is a step of introducing the silicon oxide particles after the carbon deposition into a thermal plasma atmosphere at a temperature of 5000 ° C. to 10,000 ° C. 5. The manufacturing method of the negative electrode material for nonaqueous electrolyte secondary batteries as described in a term.   A negative electrode comprising a negative electrode material for a nonaqueous electrolyte secondary battery produced by the method for producing a negative electrode material for a nonaqueous electrolyte secondary battery according to any one of claims 2 to 5, wherein A negative electrode for a nonaqueous electrolyte secondary battery, wherein the volume is less than twice that before charging.   A nonaqueous electrolyte secondary battery comprising at least the negative electrode for a nonaqueous electrolyte secondary battery according to claim 6, a positive electrode, a separator, and a nonaqueous electrolyte.   The nonaqueous electrolyte secondary battery according to claim 7, wherein the nonaqueous electrolyte secondary battery is a lithium ion secondary battery.