JP5374705B2 - Method for producing SiOx - Google Patents

Description

  The present invention relates to a method for producing SiOx, and more particularly to a method for producing SiOx used for a negative electrode material of a lithium ion secondary battery.

  In recent years, with the remarkable development of portable electronic devices, communication devices, etc., there is a strong demand for the development of secondary batteries with a high energy density from the viewpoints of economy, miniaturization and weight reduction of the devices. Examples of such high energy density secondary batteries include nickel cadmium batteries, nickel metal hydride batteries, lithium ion secondary batteries, and polymer batteries. Among these, the lithium ion secondary battery has a high lifespan and a high capacity, and thus shows a high demand growth in the power supply market.

  FIG. 1 is a diagram illustrating a configuration example of a lithium ion secondary battery. As shown in FIG. 1, the lithium ion secondary battery maintains the electrical insulation between the positive electrode 1, the negative electrode 2, the separator 3 impregnated with the electrolyte, and the positive electrode 1 and the negative electrode 2 and seals the battery contents. It is comprised from the gasket 4, and lithium ion reciprocates between the positive electrode 1 and the negative electrode 2 through electrolyte solution by charging / discharging.

The positive electrode 1 includes a counter electrode case 1a, a counter electrode current collector 1b, and a counter electrode 1c. Lithium cobaltate (LiCoO ₃ ) and manganese spinel (LiMn ₂ O ₄ ) are mainly used for the counter electrode 1c. The negative electrode 2 is composed of a working electrode case 2a, a working electrode current collector 2b, and a working electrode 2c, and the negative electrode material used for the working electrode 2c is generally an active material capable of occluding and releasing lithium ions (negative electrode active material). And a conductive assistant and a binder.

  Conventionally, as a negative electrode active material of a lithium ion secondary battery, a composite oxide of lithium and boron, a composite oxide of lithium and a transition metal (V, Fe, Cr, Mo, Ni, etc.), Si, Ge, or Sn Compounds including nitrogen (N) and oxygen (O), Si particles whose surfaces are covered with a carbon layer by chemical vapor deposition, and the like have been proposed.

  However, all of these negative electrode active materials can improve the charge / discharge capacity and increase the energy density, but due to the formation of dendrites and passive compounds on the electrodes along with charge / discharge, the deterioration is significant, Or the expansion and contraction at the time of occlusion and release of lithium ions increase. Therefore, lithium ion secondary batteries using these negative electrode active materials are insufficient in sustainability of discharge capacity (hereinafter referred to as “cycle characteristics”) due to repeated charge and discharge. Further, the ratio of the discharge capacity to the charge capacity immediately after manufacture (discharge capacity / charge capacity; hereinafter referred to as “initial efficiency”) is not sufficient.

  In contrast, attempts have been made to use silicon oxide such as SiO as the negative electrode active material. Silicon oxide has a low electrode potential with respect to lithium (base), and does not deteriorate due to occlusion or release of lithium ions during charging / discharging, generation of irreversible substances, etc., and reversibly occludes lithium ions. Therefore, by using this silicon oxide as a negative electrode active material, a lithium ion secondary battery having high voltage, high energy density, and excellent charge / discharge characteristics (initial efficiency) and cycle characteristics can be obtained. Because it can be expected.

  For example, in Patent Document 1, a silicon oxide and lithium or a substance containing lithium are used as both electrodes, and they are opposed to each other in a non-aqueous electrolyte and are energized between the two electrodes to electrochemically store lithium ions. Lithium-containing silicon oxide or lithium-ion secondary battery production method using lithium-containing silicon oxide obtained by mixing and heating lithium or lithium with silicon or a silicon compound as a negative electrode active material Has been proposed. However, according to the study by the present inventors, in this lithium ion secondary battery, the irreversible capacity during the first charge / discharge is large (that is, the initial efficiency is not sufficient), and the cycle characteristics sufficiently reach the practical level. I cannot say that.

  In Patent Document 2, a silicon oxide gas generated by heating a raw material for generating silicon oxide gas (SiO gas) at 1100 to 1600 ° C. and silicon generated by heating metal silicon at 1800 to 2400 ° C. A method for producing SiOx by precipitating a mixed gas with a gas on the substrate surface to obtain SiOx (0.3 <x <0.9) has been proposed. By using this as a negative electrode active material, the initial charge / discharge efficiency is improved. (Corresponding to the above-mentioned “initial efficiency”) and a lithium ion secondary battery excellent in cycle characteristics can be obtained. However, this method is not practical because there are few containers (materials) that can sufficiently withstand the melt of metal silicon and the high-concentration silicon gas generated from it, and the cost is high. In addition, due to safety problems such as bumping when silicon is melted, it is difficult to increase the size of the manufacturing apparatus, and it is difficult to say that it is suitable for mass production.

Japanese Patent No. 2999741 Japanese Patent No. 42007055

  The present invention has been made in view of the above-described problems when using silicon oxide as a negative electrode active material, and is a silicon oxide (SiOx), in particular, a lithium ion secondary battery having excellent cycle characteristics and initial efficiency. It aims at providing the manufacturing method of SiOx which can be used suitably as a negative electrode active material of this.

  In order to solve the above-mentioned problems, the present inventors do not involve raw material treatment at a high temperature such as 1100 to 1600 ° C. or 1800 to 2400 ° C., which is employed in the method described in Patent Document 2 described above. The present inventors have repeatedly studied a method for producing SiOx by processing in a lower temperature region and an appropriate range of values of x in SiOx. As a result, SiOx (x <1) can be obtained by heat-treating silicon oxide (SiO) in an Ar atmosphere at 400 to 800 ° C. for a predetermined time and then etching (cleaning) with hydrofluoric acid (HF). I found out that there was.

This is described in detail later, by heat treatment under the Ar atmosphere, Si in the SiO are the enriched portion (Si-rich region) SiO ₂ is a enriched portion (SiO ₂ rich region) (In other words, the Si-rich region and the SiO ₂ -rich region are separated from the SiO), and subsequently washed with HF to dissolve and remove the SiO ₂ -rich region, so that silicon oxide as a raw material This is a knowledge obtained as a result of examination based on the idea of removing part of oxygen (O) in (SiO). The value of x in SiOx can be controlled by appropriately adjusting the temperature and time during the heat treatment.

The separation of the Si-rich region and the SiO ₂ -rich region can be performed not by heat treatment but also by pulverizing silicon oxide (SiO) with a planetary ball mill.

  Furthermore, as a result of investigating initial efficiency and cycle characteristics of the produced lithium ion secondary battery using the obtained SiOx as a negative electrode active material of a lithium ion secondary battery, the ideal value of x in SiOx is 0. It was found that 8 <x <0.95.

The present invention has been made on the basis of such knowledge, and the gist thereof is the following method for producing SiOx.
That is, a method for producing SiOx, comprising the following steps (1) and (2), wherein the value of x in the SiOx is controlled within a range of 0.8 <x <0.95. It is a manufacturing method of SiOx.
(1) Silicon oxide (SiO) is heat-treated at 400 to 800 ° C. for 2 hours or more in a non-oxidizing atmosphere.
(2) The silicon oxide after the heat treatment is washed with 0.5 to 10% by volume (hereinafter referred to as “%”) hydrofluoric acid.

In the method for producing SiOx of the present invention, instead of the heat treatment in the non-oxidizing atmosphere of the step (1), a pulverization treatment by a planetary ball mill may be performed.
In the method for producing SiOx of the present invention, the heat treatment temperature in the non-oxidizing atmosphere in the step (1) is preferably 600 to 700 ° C.

  According to the method for producing SiOx of the present invention, it is possible to produce SiOx having a predetermined x value by using silicon oxide (SiO) as a raw material and relatively easily without heat treatment at a high temperature. In particular, by using SiOx (0.8 <x <0.95) produced by the method of the present invention as a negative electrode active material of a lithium ion secondary battery, a lithium ion secondary having excellent cycle characteristics and initial efficiency. A battery can be manufactured.

It is a figure which shows the structural example of a lithium ion secondary battery. It is a figure which shows the structural example of the manufacturing apparatus of a silicon oxide. It is a figure which shows typically the micro state of the silicon oxide (SiO) after the heat processing in the non-oxidizing atmosphere implemented with the manufacturing method of this invention.

As described above, the method for producing SiOx of the present invention is a method for producing SiOx, which includes the following steps (1) and (2), and the value of x in the SiOx is 0.8 <x <0.95. It is the manufacturing method of SiOx characterized by controlling within the range.
(1) Silicon oxide (SiO) is heat-treated at 400 to 800 ° C. for 2 hours or more in a non-oxidizing atmosphere.
(2) The silicon oxide after the heat treatment is washed with 0.5 to 10% hydrofluoric acid.

  The silicon oxide (SiO) used as a raw material in the step (1) is not limited to a specific one. For example, silicon oxide (SiO) powder produced by an apparatus having the configuration described below may be used as a raw material.

  FIG. 2 is a diagram illustrating a configuration example of a silicon oxide manufacturing apparatus. This apparatus includes a vacuum chamber 5, a raw material chamber 6 disposed in the vacuum chamber 5, and a deposition chamber 7 disposed on the upper portion of the raw material chamber 6.

  The raw material chamber 6 is formed of a cylindrical body, and a cylindrical raw material container 8 and a heating source 9 surrounding the raw material container 8 are disposed at the center thereof. As the heating source 9, for example, an electric heater can be used.

  The deposition chamber 7 is configured by a cylindrical body arranged so that its axis coincides with the raw material container 8. A deposition base 10 made of stainless steel is provided on the inner peripheral surface of the deposition chamber 7 for vapor deposition of gaseous silicon oxide generated by sublimation in the raw material chamber 6.

  A vacuum device (not shown) for discharging atmospheric gas is connected to the vacuum chamber 5 that accommodates the raw material chamber 6 and the deposition chamber 7, and the gas is discharged in the direction of arrow A.

  When producing silicon oxide (SiO) used as a raw material in the production method of the present invention using the production apparatus shown in FIG. 2, equimolar amounts of silicon powder and silicon dioxide powder are mixed, granulated and dried. A mixed granulated raw material 11 is used. This mixed granulated raw material 11 is filled in the raw material container 8 and heated in an inert gas atmosphere or vacuum to generate (sublimate) SiO. Gaseous SiO generated by the sublimation rises from the raw material chamber 6 and enters the deposition chamber 7, is vapor-deposited on the surrounding deposition base 10, and is deposited as precipitated silicon oxide (SiO) 12. Thereafter, the deposited silicon oxide (SiO) 12 is removed from the deposited substrate 10 and pulverized to obtain a silicon oxide powder.

In the step (1), the silicon oxide (SiO) as a raw material is heat-treated in a non-oxidizing atmosphere at 400 to 800 ° C. because the silicon-rich (SiO) -rich region, the SiO ₂ -rich region, This is to separate them.

FIG. 3 is a diagram schematically showing a micro state of silicon oxide (SiO) after heat treatment in a non-oxidizing atmosphere performed in the step (1) in the production method of the present invention. As shown in FIG. 3, the disproportionation reaction proceeds by heat-treating silicon oxide (SiO) as a raw material at a predetermined temperature in a non-oxidizing atmosphere, and a silicon-rich region (FIG. 3 is labeled “Si”) and the SiO ₂ rich region (labeled “SiO ₂ ” in FIG. 3) is separated. At this time, the reaction is not allowed to proceed completely, and the heat treatment is finished in a state where unreacted SiO (indicated as “intermediate layer” in FIG. 3), the Si rich region, and the SiO ₂ rich region coexist.

When silicon oxide that has been subjected to such heat treatment is subjected to HF cleaning in the step (2) described below, the SiO ₂ rich region is selectively removed, so that the intermediate layer (SiO) and Si are removed. Microscopically mixed SiOx (x <1) can be obtained.

In that case, the abundance ratio of the intermediate layer (SiO), the Si-rich region, and the SiO ₂ -rich region changes depending on the progress of the reaction, and the value of x in the resulting SiOx (x <1) changes accordingly. By grasping in advance the relationship between x and the value of x in SiOx, the value of x in the resulting SiOx can be controlled. The x value of SiOx is calculated by, for example, quantifying O (oxygen) with an oxygen analyzer in a ceramic (melting method under an inert gas stream), and Si by quantifying the solution with SiOP and then ICP emission spectrometry. can do.

When the heat treatment temperature is less than 400 ° C., the reaction does not proceed easily, and separation between the Si-rich region and the SiO ₂ -rich region hardly occurs. On the other hand, when the heat treatment temperature exceeds 800 ° C., the reaction rate is too fast, and the value of x tends to be small, and it is difficult to properly control the value of x in SiOx.

The heat treatment temperature in the non-oxidizing atmosphere of the step (1) is preferably 600 to 700 ° C. Thereby, it is easy to obtain a state in which the Si rich region, the SiO ₂ rich region, and SiO are mixed, and the value of x in SiOx can be easily controlled.

The non-oxidizing atmosphere is usually an Ar atmosphere, but may be an N ₂ atmosphere or the like.

The heat treatment time at the predetermined temperature is 2 hours or more. If the heat treatment time is less than 2 hours, the degree of progress of the reaction is low, so that it is difficult to reach the state where the SiO, Si rich region and SiO ₂ rich region are mixed, and it is difficult to control the value of x in SiOx. The upper limit of the heat treatment time is not particularly defined, but if the heat treatment is performed for an excessively long time, the work efficiency is lowered.

In the step (2), the silicon oxide (SiO) after the heat treatment is washed with 0.5 to 10% hydrofluoric acid (HF). This is because the SiO ₂ rich region generated in SiO is dissolved and removed to partially remove oxygen (O) in silicon oxide (SiO). If the HF concentration is less than 0.5%, it takes a long time to dissolve and remove the SiO ₂ -rich region. If it exceeds 10%, it is difficult to control the value of x in SiOx because of the increase in dissolution rate accompanying the increase in concentration. There is also a risk of explosion due to the generation of SiH ₄ .

In the cleaning with HF, the SiO ₂ rich region is selectively dissolved, and the influence on the SiO or Si rich region is small. Accordingly, the cleaning time is not particularly limited, but is preferably about 5 to 30 minutes in consideration of work efficiency and the like. In addition, it is desirable to appropriately stir to promote dissolution.

  As described above, after heat-treating silicon oxide (SiO) in a non-oxidizing atmosphere, the silicon oxide (SiO) is washed with HF to remove a part of oxygen (O) in the silicon oxide (SiO), and SiOx (x <1 ). At that time, the value of x in SiOx is controlled within the range of 0.8 <x <0.95 when the SiOx is used as a negative electrode active material of a lithium ion secondary battery and excellent cycle characteristics and This is because a lithium ion secondary battery having initial efficiency can be manufactured. If the value of x is 0.8 or less, the cycle characteristics deteriorate. On the other hand, if the value of x is 0.95 or more, the initial efficiency is lowered.

The silicon oxide (SiOx; 0.8 <x <0.95) thus obtained is usually in the form of powder and suspended in HF, and is filtered and dried. For example, it is desirable to perform filtration for about 24 hours with a dryer set at 120 ° C. after filtration using an appropriate filter. Further, when this SiOx is used as a negative electrode active material of a lithium ion secondary battery, it is further pulverized and adjusted to an appropriate particle size (for example, D ₅₀ (about 50 μm in the integrated particle size distribution) at about 10 μm). .

  In the method for producing SiOx of the present invention, instead of the heat treatment in the non-oxidizing atmosphere of the step (1), a pulverization treatment by a planetary ball mill may be performed.

  A planetary ball mill generally includes a main shaft (revolving rotation shaft) that is rotated by a driving force of a motor, a revolving rotation arm that extends radially from the main shaft, and a rotation shaft that is inclined with respect to the main shaft at the tip of the arm. And a pulverization container (mill pot) mounted so as to be rotatable about the center.

When this planetary ball mill is used to treat silicon oxide (SiO) as the material to be crushed, the mill pot containing the material to be crushed and the grinding media ball is rotated while revolving, so the revolution centrifugal acceleration and the rotation centrifugal acceleration are measured in the mill pot. The material to be crushed and the grinding media ball can be applied to each other, and the material to be ground and the grinding media ball collide violently, and a strong impact force is applied to the material to be crushed. As a result, a high-pressure state is instantaneously generated, and the Si-rich region and the SiO ₂ -rich region are separated from the silicon oxide (SiO) as in the case where the above-described heat treatment is performed. It is inferred that a mixture of _two rich areas can be obtained.

  Regarding the processing conditions in the planetary ball mill, it is desirable to appropriately adjust the rotational speed of the main shaft (revolving rotation shaft): 10 to 60 rpm and the processing time: 5 to 60 minutes. When the rotational speed is less than 10 rpm, the impact force is small and separation cannot be performed. Similarly, when the processing time is less than 5 minutes, separation cannot be performed. On the other hand, when the rotational speed is 60 rpm or the treatment time exceeds 60 minutes, the particle size becomes too small and the amount of fine powder increases, so that it becomes difficult to control the separation reaction.

  According to the method for producing SiOx of the present invention, SiOx having a predetermined x value can be produced by a relatively easy process using silicon oxide (SiO) as a raw material. In particular, if SiOx (0.8 <x <0.95) produced by the method of the present invention is used as a negative electrode active material of a lithium ion secondary battery, the lithium ion secondary battery having excellent cycle characteristics and initial efficiency. Can be manufactured. Since the manufacturing method of the present invention does not involve heat treatment at high temperature when manufacturing SiOx, there are few restrictions on the selection of material for the device, and it is relatively easy to cope with the increase in size of the manufacturing device and is suitable for mass production. ing.

Example 1
Using a mixed granulation raw material in which equal amounts of silicon powder and silicon dioxide powder are mixed, granulated, and sublimated under reduced pressure using the apparatus having the configuration shown in FIG. SiO was deposited as silicon oxide (SiO) on a cooled precipitation substrate.

The granular SiO obtained by pulverizing this silicon oxide (SiO) to a particle size of 1 to 4 mm is heat-treated in an atmosphere furnace in an Ar atmosphere at 700 ° C. for 2 hours, then washed with HF to form SiOx, filtered After passing through a drying treatment, it was pulverized to obtain a SiOx powder having a D ₅₀ of 10 µm.

  Using this SiOx powder as a negative electrode active material, adding acetylene black and a binder as a conductive auxiliary agent to a negative electrode material, and producing a coin-shaped lithium ion secondary battery using Li foil for the positive electrode, Efficiency and cycle characteristics were investigated. In addition, the cycle characteristic in this case is a maintenance ratio with respect to the initial discharge capacity (discharge capacity immediately after manufacture) of the discharge capacity after repeating charging and discharging 100 times.

  In the initial efficiency and cycle characteristic investigation, the value of x in the SiOx powder was changed in the range of 0.86 to 0.97. Further, the concentration of HF used for cleaning after the heat treatment was set to 0.4%, 0.5%, or 10%. The x value of SiOx used in the investigation was obtained from the quantitative value of O (oxygen) by the oxygen analyzer in the ceramic and the quantitative value of Si by the ICP emission spectroscopic analysis method. I confirmed that there was.

  The survey results are shown in Table 1.

From the results shown in Table 1, when the value of x in SiOx is in the range of 0.8 to 0.95 (Invention Examples 1 and 2), the initial efficiency is 85% or more, and the cycle characteristics are also 85%. It can be seen that the above good values are maintained. From the results shown in Table 1, it is appropriate that the concentration of HF used for cleaning after the heat treatment be within the range of 0.5 to 10%. When the value of x in SiOx was 0.97 and the HF concentration was 0.4 (comparative example), both the initial efficiency and the cycle characteristics were greatly reduced as compared with Examples 1 and 2 of the present invention.
(Example 2)

The granular SiO used in Example 1 was treated with a planetary ball mill, washed with HF to form SiOx, filtered, dried, pulverized, and made into a ₅₀ μm SiOx powder with D ₅₀ . The processing conditions in the planetary ball mill were: the rotation speed of the main shaft (revolving rotation shaft): 12 rpm, the processing time: 20 minutes, and the HF concentration used for cleaning after the processing by the planetary ball mill was 10%. The value of x in the obtained SiOx powder was 0.91.

  Using this SiOx powder as the negative electrode active material, a lithium ion secondary battery was produced in the same manner as in Example 1, and the initial efficiency and cycle characteristics were investigated.

  The investigation results are shown in Table 1 as Example 3 of the present invention. From this result, it was confirmed that the effect equivalent to the case where heat treatment was performed at a predetermined temperature in a non-oxidizing atmosphere was obtained by treating with a planetary ball mill.

  According to the method for producing SiOx of the present invention, SiOx (0.8 <x <0.95) can be produced by relatively easy processing using silicon oxide (SiO) as a raw material. If this SiOx (0.8 <x <0.95) is used as the negative electrode active material of a lithium ion secondary battery, a lithium ion secondary battery having excellent cycle characteristics and initial efficiency can be produced. Therefore, the present invention can be suitably used in the manufacture of lithium ion secondary batteries.

1: positive electrode, 1a: counter electrode case, 1b: counter electrode current collector, 1c: counter electrode,
2: negative electrode, 2a: working electrode case, 2b: working music collector, 2c: working electrode,
3: separator, 4: gasket, 5: vacuum chamber, 6: raw material chamber,
7: Precipitation chamber, 8: Raw material container, 9: Mixed granulated raw material, 10: Heat source 11: Precipitation base, 12: Precipitated silicon oxide

Claims (3)

A method for producing SiOx, comprising:
A method for producing SiOx, comprising the following steps (1) and (2), wherein the value of x in the SiOx is controlled within a range of 0.8 <x <0.95.
(1) Silicon oxide (SiO) is heat-treated at 400 to 800 ° C. for 2 hours or more in a non-oxidizing atmosphere.
(2) The silicon oxide after the heat treatment is washed with 0.5 to 10% hydrofluoric acid.   2. The method for producing SiOx according to claim 1, wherein a grinding process using a planetary ball mill is performed instead of the heat treatment in a non-oxidizing atmosphere in the step (1).   The method for producing SiOx according to claim 1, wherein the heat treatment temperature in the non-oxidizing atmosphere in the step (1) is 600 to 700 ° C.

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