JP4518278B2 - Method for producing porous silicon oxide powder - Google Patents

Description

  The present invention relates to a raw material for producing ceramics, a raw material for film deposition for packaging, a raw material for producing organic silicon compounds, and a method for producing a porous silicon oxide powder useful as a negative electrode active material for a lithium ion secondary battery.

Silicon oxide is a known substance, and it is industrially useful to synthesize alkylhalosilanes that are chemically active (Gary N. Bokerman et al, USP 5051247 Silane products from silicon monolith with organic patent: Reference 1), and further attempts to synthesize siloxane directly (Peter L. Timms and William N. Rowlands, EPA 0406000A2 Polysiloxane oils and process for ther preparation: Patent Document 2), or reaction with magnesium at low temperature. (Fugle, in, E; Schubert, U, hem.Mater.1999,11,865-866: Non-Patent Document 1). There is also a report that the insertion and removal of lithium ions is facilitated by using SiO _x as a lithium ion secondary battery negative electrode active material (Japanese Patent Laid-Open No. 9-7638: Patent Document 3). The use as an active material is also expected to expand.

  In addition, the conventionally proposed silicon oxide powder is generally a fine powder for the purpose of enhancing the activity. For example, in Japanese Patent Publication No. 59-50601 (Patent Document 4), at least the surface is nitrided or carbonized. There is a description of oxidized amorphous SiO ultrafine powder having a particle size of 1 μm or less, and Japanese Patent Publication No. 4-81524 (Patent Document 5) discloses a method for producing ultrafine amorphous SiO powder of 0.1 μm or less. ing.

However, the above-mentioned ultrafine SiO powder has a large BET specific surface area and is highly active in performing various reactions, and is advantageous. However, since the particle diameter is as fine as 1 μm or less, it is inferior in handling properties and filling properties. There was a problem.
US Pat. No. 5,051,247 European Patent Application No. 0406000A2 Specification JP-A-9-7638 Japanese Patent Publication No.59-50601 Japanese Patent Publication No. 4-81524 Fugue, in, E; Schubert, U, Chem. Mater. 1999, 11, 865-866

  This invention is made | formed in view of the said situation, It aims at providing the manufacturing method of the porous silicon oxide powder which is highly active and excellent in handling property, and can be used usefully for the said use for this reason. .

  As a result of intensive studies to achieve the above object, the present inventors have produced a silicon oxide powder under specific production conditions to obtain a porous silicon oxide powder that has a high BET specific surface area but is not fine. By using this porous silicon oxide powder as various reaction raw materials, it has been found that it is as highly active as the above-mentioned ultrafine powder SiO, and that the handling and filling properties can be improved, and the present invention has been made. It is a thing.

Accordingly, in the present invention, mixed raw material powder containing at least silicon dioxide powder is heated in a temperature range of 1100 to 1600 ° C. under inert gas or reduced pressure to generate silicon oxide gas, and the silicon oxide gas is cooled on the surface of the substrate. In the method for producing silicon oxide powder to be deposited, the temperature of the substrate surface is 100 to 400 ° C., and the silicon oxide gas vapor concentration is 0.5 to 15 g / m ^3. Provided is a method for producing a porous silicon oxide powder having a diameter of ˜20 nm, a pore volume of 0.005 to 0.2 cm ³ / g, and a BET specific surface area of 5 to 300 m ² / g.
In this case, the silicon oxide powder is a silicon oxide powder represented by the general formula SiO _x , and the range of x is preferably 0.9 ≦ x ≦ 1.8. It is preferable that the measurement does not have a clear diffraction line.

  Since the silicon oxide powder of the present invention is highly active and excellent in handling properties, it can easily react with other elements and can sufficiently withstand industrial scale production.

Hereinafter, the present invention will be described in more detail.
The silicon oxide powder in the present invention has an average pore diameter of 0.5 to 20 nm, preferably 1.0 to 10 nm. If the average pore diameter is less than 0.5 nm, the BET specific surface area becomes too large, the proportion of silicon dioxide content due to surface oxidation becomes too large, and the purity of the silicon oxide decreases, resulting in a decrease in activity. To do. On the contrary, if the average pore diameter is larger than 20 nm, the BET specific surface area becomes small and the surface activity is lowered. Then, silicon oxide powder of the present invention, the pore volume of 0.005~0.2cm ³ / g, preferably 0.01~0.15cm ³ / g. If the pore volume is smaller than 0.005 cm ³ / g, the BET specific surface area becomes small and the activity decreases. Conversely, if the pore volume is larger than 0.2 cm ³ / g, the BET specific surface area becomes too large. Thus, the effect of surface oxidation is great, resulting in a decrease in surface activity. The silicon oxide powder of the present invention has a BET specific surface area of 5 to 300 m ² / g, preferably 10 to 200 m ² / g. When the BET specific surface area is less than 5 m ² / g, the surface activity is lowered and the reactivity with other elements is poor. On the other hand, if the BET specific surface area is larger than 300 m ² / g, the ratio of silicon dioxide content due to surface oxidation becomes too large and the purity of silicon oxide is lowered, resulting in a decrease in reactivity.

In the present invention, the average pore diameter and the pore volume are values measured by an N ₂ gas adsorption method by a constant volume method, for example, values measured by Tristar 3000 manufactured by Shimadzu Corporation. The specific surface area can be measured by the BET one-point method that is measured by the nitrogen gas adsorption amount.

The silicon oxide powder of the present invention is represented by the general formula SiO _x , and the range of x is preferably 0.9 to 1.8. When the range of x is smaller than 0.9, the metal silicon is substantially excessive, becomes crystalline and / or blocky, and does not contain active oxygen, which is not preferable. When the range of x is larger than 1.8, silicon dioxide is substantially formed and active silicon is not contained, which is not preferable. More preferably, the range of x is 0.9 to 1.6, more preferably 0.9 to 1.3.

  Furthermore, it is preferable that the porous silicon oxide powder of the present invention does not have a clear diffraction line in the X-ray diffraction measurement. If there is a clear diffraction line in the X-ray diffraction measurement, the activity of silicon may be significantly impaired.

The porous silicon oxide powder having the above physical properties is obtained by, for example, heating a mixed raw material powder containing silicon dioxide powder in a temperature range of 1100 to 1600 ° C. under an inert gas or reduced pressure to generate a silicon oxide gas, and a silicon oxide gas vapor concentration Can be produced by a method in which a silicon oxide gas of 0.5 to 15 g / cm ³ is deposited on the substrate surface cooled to 100 to 400 ° C.

  This production method will be described in more detail. In the production of the porous silicon oxide powder of the present invention, a mixture of silicon dioxide powder and powder for reducing it is used as a raw material. Specific reduction powders include metal silicon compounds and carbon-containing powders. Particularly, those using metal silicon powders are effective in terms of [1] increasing the reactivity and [2] increasing the yield. And is preferably used. In addition, although it does not specifically limit about the kind of metal silicon powder, The thing with high purity, such as semiconductor grade Si, ceramic grade Si, and chemical grade Si, is used suitably in order to raise the purity of the produced | generated silicon oxide powder.

The use ratio of the silicon dioxide powder and the powder for reducing it is not particularly limited. For example, metal silicon (Si) or carbon (C) is used as the metal powder for reduction, and these can be used for example. When used in a molar ratio of 1/1 to silicon powder, the reduction reaction proceeds according to the following formula, but is not limited to these reactions.
・ SiO ₂ + Si → 2SiO
・ SiO ₂ + C → SiO + CO

  In the present invention, the mixed raw material powder is heated and held at a temperature of 1100 to 1600 ° C., preferably 1200 to 1500 ° C., in a reaction chamber to generate silicon oxide gas. If the reaction temperature is less than 1100 ° C., the reaction is difficult to proceed and the productivity is reduced. Conversely, if the reaction temperature exceeds 1600 ° C., the mixed raw material powder is melted and the reactivity is lowered, Selection may be difficult.

In this silicon oxide gas generation step, particularly important for producing the porous silicon oxide powder having the physical properties of the present invention is that the generated silicon oxide gas vapor concentration is in the range of 0.5 to 15 g / m ³ . It is to be. When the generated silicon oxide gas vapor concentration is less than 0.5 g / m ³ , the silicon oxide obtained becomes a porous silicon oxide powder having a large pore diameter and a large pore volume, resulting in an excessively large BET specific surface area. The activity decreases due to the effect of surface oxidation. On the other hand, when the generated silicon oxide gas vapor concentration is higher than 15 g / m ³ , the resulting silicon oxide is silicon oxide having a small pore diameter and a small pore volume, and thus a small BET specific surface area, resulting in activity. descend. In this case, the silicon oxide gas vapor concentration is determined by the amount of raw material charged into the reaction chamber, the reaction temperature (silicon oxide gas generation rate), and the exhaust capacity (speed) of the vacuum pump, and can be controlled by appropriately selecting them. Is possible.

On the other hand, the atmosphere in the furnace is an inert gas or under reduced pressure, but it is desirable to carry out under reduced pressure because thermoreactive under reduced pressure has higher reactivity and enables low temperature reaction. Examples of the inert gas include non-oxidizing gases such as Ar, He, and H ₂ , and the degree of vacuum is 10 Torr (1330 Pa) or less [that is, 0 to 10 Torr (0 to 1330 Pa)], particularly 1 Torr. (133 Pa) [that is, 0 to 1 Torr (0 to 133 Pa)] or less is preferable.

In this case, the mixed raw material powder can be supplied to the reaction chamber at appropriate intervals or continuously by a raw material supply mechanism (feeder).
The silicon oxide gas generated in the reaction chamber is supplied to the deposition chamber via the transfer tube.

  In this case, the conveying tube is heated to 1000 ° C. and 1300 ° C. or less, preferably 1100 to 1200 ° C. and held. Here, the purpose of heating the transfer pipe is to prevent the deposition of silicon oxide vapor on the inner wall of the transfer pipe. When the temperature of the transfer pipe is 1000 ° C. or less, the silicon oxide vapor is deposited on and adhered to the inner wall of the transfer pipe. And stable continuous operation becomes impossible. Conversely, heating to a temperature exceeding 1300 ° C. not only shows no further effect, but also causes an increase in power cost.

A substrate cooled by a refrigerant is disposed in the deposition chamber, and the silicon oxide gas introduced into the deposition chamber comes into contact with the cooling substrate and is cooled, whereby silicon oxide powder is deposited on the substrate. . Here, it is important to control the temperature of the substrate surface to 100 to 500 ° C. When the temperature of the substrate surface is less than 100 ° C., the BET specific surface area becomes larger than 300 m ² / g, the ratio of inactive silicon dioxide increases due to surface oxidation, and the activity decreases. On the contrary, when the temperature of the substrate surface is higher than 500 ° C., the BET specific surface area becomes less than 5 m ² / g, and the activity decreases. The cause of the change in the BET specific surface area due to the substrate surface temperature is not clear, but by increasing the temperature of the substrate surface, the activity of the precipitate surface increases, resulting in densification by fusing, and the BET specific surface area is increased. Presumed to be reduced. Further, the temperature of the substrate surface is controlled by a combination of the temperature in the deposition chamber (heated by the deposition chamber heater), the type of refrigerant, and the flow rate. The type of the refrigerant is not particularly limited, but a liquid such as water or a heat medium, a gas such as air or nitrogen is used depending on the purpose. The type of the substrate is not particularly limited, but refractory metals such as SUS, molybdenum, and tungsten are preferably used in terms of workability.

  The silicon oxide powder deposited on the substrate is recovered by an appropriate means such as scraping. Further, the recovered silicon oxide powder can be pulverized by an appropriate means if necessary to obtain a desired particle size.

  As an apparatus used for the above method, for example, an apparatus as shown in FIG. 1 can be used. Here, in FIG. 1, 1 is a reaction furnace, and a muffle 2 is disposed in the reaction furnace 1. Inside the muffle 2 is a reaction chamber 3 in which a raw material container 5 for containing a mixed raw material powder 4 containing silicon dioxide powder is disposed. Further, a heater 6 is disposed so as to surround the muffle 2, and the mixed raw material powder 4 is heated by the heater 6. In addition, 7 is a heat insulating material.

  Further, 8 is a transfer pipe in which a heater 9 is embedded, 10 is a precipitation tank, and silicon oxide gas generated in the reaction chamber 3 passes through the transfer pipe 8 to the precipitation chamber 11 in the precipitation tank 10. be introduced. A substrate 12 is disposed in the deposition chamber 11. A cooling passage is formed in the base 12, and the base 12 is cooled by the refrigerant supplied to the refrigerant passage from the refrigerant introduction pipe 14, and the silicon oxide gas comes into contact with the cooling base 12 and is cooled. The silicon oxide powder is deposited on the substrate 12. A thermocouple 13 is embedded in the cooling base 12 so that the surface temperature of the cooling base 12 can be measured. The refrigerant is discharged through a refrigerant discharge pipe 15, and a heater 16 is disposed in the precipitation tank 10. Reference numeral 17 denotes a thermocouple for measuring the temperature in the deposition chamber 11. 18 is a vacuum pump.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited to the following Example.

[Example 1]
Silicon oxide powder was manufactured using the manufacturing apparatus shown in FIG. The raw material is a mixed powder obtained by mixing silicon dioxide powder (BET specific surface area = 200 m ² / g) and ceramic silicon metal powder (BET specific surface area = 3 m ² / g) in an equimolar ratio. 200 g was charged in a reactor having a volume of 6000 cm ³ . Next, the inside of the furnace was depressurized to 1 Torr or less using a vacuum pump 18 having an exhaust capacity of 30 m ³ / hr, and then the heater 6 was energized to raise and maintain the temperature at 1300 ° C. On the other hand, the conveyance tube 8 was heated and held at 1100 ° C. Next, the deposition chamber heater 16 was energized to set the temperature in the deposition chamber 11 to 900 ° C., and at the same time, 5.0 NL / min of water flowed into the SUS substrate 12 (surface area 200 cm ² ). The reaction completion time under these conditions was 3 hours, and the silicon oxide gas vapor concentration at this time was calculated as 2.1 g / cm ³ from the vacuum pump capability. The substrate surface temperature was 210 ° C. As a result of performing the above operation for 3 hours, black lump-shaped silicon oxide was deposited on the surface of the substrate 12. After collecting the massive precipitate, it was pulverized with a ball mill for 5 hours to produce a silicon oxide powder. The obtained silicon oxide powder has an average pore diameter of 4.5 nm, a pore volume of 0.05 cm ³ / g, a BET specific surface area of 60 m ² / g, and a general formula SiO _x (x = 1.05). It was an amorphous powder.

  Next, 10 g of the silicon oxide powder was heated to 1100 ° C. in nitrogen and held for 3 hours to produce a silicon nitride powder. The obtained silicon nitride powder was an α-type silicon nitride powder having a nitrogen content of 36.5%, and it was confirmed that the silicon oxide powder as a raw material was a very active powder.

[Examples 2 to 5, Comparative Examples 1 to 4]
A silicon oxide powder and a silicon nitride powder using this silicon oxide powder as a raw material were produced under the same conditions as in Example 1 except that the raw material charge amount, reaction temperature, reaction time, and substrate 12 surface temperature were the conditions shown in Table 1. . Table 1 shows the average pore diameter, pore volume, BET specific surface area, and x value of SiO _x of the obtained silicon oxide powder. On the other hand, the nitrogen content of the nitridation product subjected to the nitriding reaction under the same conditions as in Example 1 is shown in Table 1.

注：仕込み原料は、実施例１記載の二酸化珪素粉末とセラミックスグレード用金
属珪素粉末との等量モル混合物である。

Note: The charged raw material is an equimolar molar mixture of the silicon dioxide powder described in Example 1 and the ceramic grade metal silicon powder.

[Example 6]
100 parts by weight of the silicon oxide powder obtained in Example 1, 90 parts by weight of graphite as a conductive material, and 20 parts by weight of polyvinylidene fluoride (N-methylpyrrolidone solvent) as a binder are kneaded, and a part thereof is made of stainless steel. It applied to the mesh, pressure-bonded, and dried overnight in a vacuum dryer to obtain an electrode.
In order to evaluate the charge / discharge characteristics of the electrode obtained as described above, a lithium foil was used as the counter electrode, and lithium hexafluorophosphate was used as the non-aqueous electrolyte by using 1/1 of ethylene carbonate and 1,2-dimethoxyethane. A lithium ion secondary battery for evaluation using a non-aqueous electrolyte solution dissolved at a concentration of 1 mol / L in the mixed solution and a microporous polyethylene film having a thickness of 30 μm as a separator was prepared.
The prepared lithium ion secondary battery was allowed to stand overnight at room temperature, and then charged with a secondary battery charge / discharge tester (manufactured by Nagano Co., Ltd.) with a constant current of 0.5 mA / cm ² and a discharge final voltage of 0. A charge / discharge test was performed under the conditions of 003 V and a charge end voltage of 1.800 V.
As a result, it was confirmed that a high-capacity lithium ion secondary battery having an initial discharge capacity of 800 mAh / g was obtained.

[Comparative Example 5]
A lithium ion secondary battery was prepared in the same manner as in Example 6 except that the silicon oxide powder obtained in Comparative Example 1 was used, and a charge / discharge test was performed in the same manner as in Example 6.
As a result, the initial discharge capacity was 480 mAh / g, clearly inferior to Example 6 in terms of capacity.

It is a schematic sectional drawing which shows an example of the apparatus used for manufacture of the porous silicon oxide powder of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reaction furnace 2 Muffle 3 Reaction chamber 4 Mixed raw material powder 5 Raw material container 6 Heater 7 Heat insulating material 8 Transport pipe 9 Heater 10 Deposition tank 11 Deposition chamber 12 Base 13 Thermocouple 14 Refrigerant introduction pipe 15 Refrigerant discharge pipe 16 Heater 17 Thermocouple 18 Vacuum pump

Claims (3)

A mixed raw material powder containing at least silicon dioxide powder is heated in a temperature range of 1100 to 1600 ° C. under an inert gas or reduced pressure to generate silicon oxide gas, and the silicon oxide powder is deposited on the cooled substrate surface. In the production method, the temperature of the substrate surface is 100 to 400 ° C., the silicon oxide gas vapor concentration is 0.5 to 15 g / m ³ , and the average pore diameter is 0.5 to 20 nm, the pore volume A method for producing a porous silicon oxide powder having 0.005-0.2 cm ³ / g and a BET specific surface area of 5-300 m ² / g. The porous silicon oxide powder according to claim 1, wherein the silicon oxide powder is a silicon oxide powder represented by a general formula SiO _x , and a range of x is 0.9 ≦ x ≦ 1.8. Production method.   The method for producing a porous silicon oxide powder according to claim 1 or 2, wherein the silicon oxide powder does not have a clear diffraction line in X-ray diffraction measurement.

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