Method for producing siO powder and spherical particulate siO powder

Abstract

The present invention relates to a method for producing SiO powder and spherical particulate SiO powder. The present invention aims to efficiently and economically produce a SiO powder that is spherical and particulate without corners and has a small particle diameter, and that also has a low degree of contamination caused by impurities. A mixture of Si and SiO2, which are raw materials for generating SiO gas, is charged into a crucible. The mixture inside the crucible is heated under reduced pressure to generate SiO gas. The generated SiO gas is deposited on a deposition substrate that is rotated on the crucible. When the SiO deposit deposited on the deposition substrate is scraped by a blade, the tip of the blade is separated from the surface of the deposition substrate to leave a part of the SiO deposit deposited on the deposition substrate on the deposition substrate, while the remaining SiO deposit is scraped by the blade and recovered as SiO powder.

Description

[0001] This application is a divisional application of the invention patent application filed on August 26, 2019, with application number 201980056749.9 and invention title "Method for manufacturing SiO powder and spherical granular SiO powder". Technical Field

[0002] This invention relates to a method for manufacturing SiO powder used as a negative electrode material in lithium-ion secondary batteries, and to spherical granular SiO powder. Background Technology

[0003] As is well known, SiO has a large electrical capacity and is an excellent anode material for lithium-ion secondary batteries. This SiO-based anode material is produced by coating a slurry obtained by mixing SiO powder, conductive additives, and a binder onto a current collector made of copper foil or similar material and then drying it, thereby creating a thin-film anode. The SiO powder used here is obtained by cooling and heating a mixture of silicon dioxide and silicon to generate SiO gas, causing it to precipitate, and then pulverizing the resulting gas.

[0004] The advantage of SiO powder produced using this precipitation method is that it contains many amorphous components, which reduces the coefficient of thermal expansion and improves battery characteristics such as cycle performance. In particular, patent documents 1-3 report highly rounded SiO powder without sharp edges, which is effective in improving battery characteristics.

[0005] However, it is not easy to manufacture angular, spherical SiO powder on an industrial scale economically. This is because the SiO gas produced by heating a mixture of silicon dioxide and silicon and then precipitating it is broken into angular, non-spherical particles after being pulverized. This results in significant losses during the process of selecting angular, spherical particles, which in turn greatly reduces the yield.

[0006] To address this issue, reference 1 uses an airflow-based jet mill or cyclone mill for fine grinding, while reference 3 uses a ball mill. However, increased grinding costs are unavoidable, and the yield remains low. Additionally, reference 2 proposes a technique that causes particles to collide with each other, but this still cannot prevent increased grinding costs.

[0007] In addition to these issues, there is a fundamental problem: the finer the grinding, the greater the contact between the grinding container and the grinding medium, and the higher the frequency of contact. Therefore, the higher the degree of contamination caused by impurities in the resulting particles.

[0008] In addition, as one of the methods for manufacturing SiO powder industrially at low cost, patent documents 4 and 5 have proposed a technique in which SiO gas generated by heating a mixture of silicon dioxide and silicon is deposited on a cooled precipitation substrate, and the deposited precipitate is mechanically scraped off and recovered from the precipitation substrate with a blade.

[0009] According to this technology, SiO powder can be directly and continuously manufactured from SiO precipitates deposited on a precipitation matrix. Particularly, as described in Patent Document 5, when a rotating body is used as the precipitation matrix, particularly high production efficiency can be achieved. However, the SiO powder scraped from the precipitation matrix will become flaky particles, making it impossible to directly and continuously manufacture spherical particles without sharp edges. Furthermore, the flaky particles also suffer from an increased particle size.

[0010] Patent Document 1: Japanese Patent Application Publication No. 2014-225347

[0011] Patent Document 2: Re-presentation of WO 2015 / 004834

[0012] Patent Document 3: Japanese Patent Application Publication No. 2017-92009

[0013] Patent Document 4: Japanese Patent Application Publication No. 2001-220123

[0014] Patent Document 5: Japanese Patent Publication No. 2016-519046 Summary of the Invention

[0015] The purpose of this invention is to provide a method for manufacturing SiO powder that can efficiently and economically produce spherical particles of SiO powder with small particle size and low contamination caused by impurities, as well as the spherical particle-shaped SiO powder.

[0016] From the aforementioned objective, particularly the viewpoint of reducing the degree of contamination caused by impurities in the manufactured SiO powder, the inventors have focused on a technique for mechanically scraping SiO precipitates deposited on a cooled precipitate substrate from the substrate using a blade. According to this technique, it is anticipated that the blade will only come into contact with the SiO precipitates during scraping, thus reducing the chance of contamination caused by impurities and lowering the degree of contamination. However, in this scraping technique, in addition to the quantity, contamination caused by impurities inevitably occurs in the SiO powder along with the mechanical scraping of the blade.

[0017] Therefore, the inventors believe that when mechanically scraping precipitates from a substrate using a blade, contamination caused by impurities is not only due to the contact between the precipitate and the blade, but also to the intermetallic contact between the cooled precipitate and the blade. Thus, they pioneered a method for scraping precipitates from the substrate by separating the blade from the substrate, and conducted various experimental studies. The results showed that compared to scraping precipitates from the substrate by contacting the blade, this method not only suppressed contamination caused by impurities, but also produced precipitates scraped by the blade that were small, spherical particles without sharp edges, which could be directly and efficiently recovered from the substrate.

[0018] In other words, a portion of the SiO precipitates deposited on the cooled precipitation substrate remain on the precipitation substrate, and the remaining SiO precipitates are directly scraped off.

[0019] Furthermore, the SiO powder obtained in this way does not simply have highly spherical particles, but rather a composite sphere, like that of a cauliflower, with multiple smaller spherical satellites integrally combined on a larger spherical core. Both the outer surfaces of the core and the satellites are relatively smooth (see [reference]). Figure 2 Moreover, this special composite spherical particle shape is difficult to identify using the roundness and BET specific surface area commonly used to identify the particle shape of active materials used in batteries. On the other hand, based on fractal dimension analysis, this special composite spherical shape can be quantitatively identified, and SiO powder composed of this special composite spherical particles has been found to have the following excellent properties as a negative electrode active material, or as an intermediate material for use as a negative electrode active material after further crushing.

[0020] In other words, unlike the case of SiO precipitation, it does not produce fine powder and has a relatively small diameter relative to the spherical core, being a composite sphere formed by multiple spherical satellites, making it easy to handle (difficult to drift or adhere). Due to a moderately increased specific surface area and reduced expansion caused by Li insertion through the voids, it exhibits characteristics of both primary and secondary particles, primarily improving recyclability. Even when used after pulverization, it can be easily separated at the junction (neck), resulting in good pulverization and saving energy required for pulverization.

[0021] This invention was developed based on these findings. The method for manufacturing SiO powder involves depositing SiO gas onto a cooled precipitation substrate. When scraping the SiO precipitates from the substrate with a blade, the blade separates from the substrate. A portion of the SiO precipitates remains on the substrate, while the remainder is scraped off and recovered. In other words, of the two surfaces of the SiO precipitates deposited on the substrate, the contact side surface, which is in contact with the substrate, remains in contact with the substrate surface, and only the opposite, non-contact side surface is scraped off for recovery.

[0022] In practice, by maintaining a constant distance from the substrate to the blade and repeatedly scraping at a constant cycle, a constant thickness of SiO precipitate remains on the substrate, upon which new SiO precipitate is deposited. The process of scraping off the SiO precipitate can be repeated. From an efficiency point of view, a drum-shaped rotating substrate is preferred, but even a flat substrate can recover SiO powder by repeatedly scraping it with a blade at a constant cycle.

[0023] In the SiO powder manufacturing method of the present invention, when scraping the SiO precipitates deposited on the precipitation substrate, the blade used as the scraping tool does not come into contact with the surface of the precipitation substrate. As a result, the SiO precipitates deposited on the precipitation substrate, as highly rounded SiO powder without sharp edges, can be directly recovered from the precipitation substrate, and the particle size of this SiO powder is small, with a very low degree of contamination caused by impurities. The reason for this is believed to be as follows.

[0024] When SiO precipitates are scraped off the substrate using a blade, a portion of the deposited SiO precipitates remain on the substrate. New SiO precipitates are deposited on top of this residual SiO precipitate, and these are scraped off and recovered in the next cycle. That is, a certain amount of SiO precipitates remain on the substrate, and new SiO precipitates are directly deposited on top of this residual SiO precipitate, repeating this process of scraping off new SiO precipitates. At this point, the surface of the residual SiO precipitates on the substrate is in a slightly rough state because it also includes attached fine powder after scraping. It is believed that by depositing new SiO precipitates on this slightly rough surface, the slight roughness of the surface becomes the starting point, and the newly deposited SiO precipitates will become spherical. By scraping off this aggregate of newly deposited fine spherical SiO precipitates with a blade, highly rounded fine SiO powder without sharp edges is obtained. By avoiding contact between the substrate and the blade, the degree of contamination of the SiO powder caused by impurities is also reduced.

[0025] When all the SiO precipitates deposited on the substrate are scraped off, the resulting powder will not be spherical but rather flaky, as the precipitates will be scraped off literally. Furthermore, even when SiO precipitates are deposited on top of residual SiO precipitates on the substrate, if the time between deposition and scraping becomes very long, the newly deposited SiO precipitates will integrate with the underlying residual precipitates, resulting in a flaky powder.

[0026] From this perspective, in the SiO powder manufacturing method of the present invention, the deposition rate of SiO precipitates on the substrate is defined as the growth rate d (μm / min) and the scraping cycle n (min). -1 The d / n (μm) factor in the relationship between the SiO powder and the precipitated matrix is ​​very important. This is a factor that has a significant impact on the properties (particle size and shape) of the SiO powder recovered by scraping from the precipitated matrix, and is preferably 0.5 to 20 μm, more preferably 0.5 to 15 μm, and particularly preferably 1 to 10 μm.

[0027] That is, when the value of d / n (μm) becomes too small, no new SiO precipitates will be deposited on the residual SiO precipitates. As the SiO powder obtained by scraping becomes micronized, not only does the processing performance deteriorate, but the specific surface area of ​​the SiO powder also becomes too large. On the other hand, when the value of d / n (μm) becomes too large, new SiO precipitates are excessively deposited on the residual SiO precipitates. During this period, they will become integrated with the residual SiO precipitates, thereby causing the SiO powder obtained by scraping to become flaky.

[0028] Besides d / n (μm), the distance g (mm) from the precipitate matrix to the blade is important. This determines the thickness of the SiO precipitate layer remaining on the precipitate matrix. If the layer thickness is too small, the SiO precipitate layer remaining on the precipitate matrix will be very thin, posing a risk that the SiO powder generated during scraping will become flake-like. Conversely, if the layer thickness is too large, more SiO precipitate will remain on the precipitate matrix because it is not scraped off, thus deteriorating the yield. From these points, the distance g (mm) from the precipitate matrix to the blade is preferably 0.1 to 3 mm, more preferably 0.5 to 2.5 mm, and particularly preferably 0.5 to 2 mm.

[0029] The material of the blade can affect the contamination of the product powder with impurities. From the viewpoint of suppressing this effect, the material is preferably stainless steel or ceramic, and particularly preferably ceramic.

[0030] As a pre-processing step, a mixture of Si and SiO2 is used as the raw material for generating SiO gas. This raw material needs to be heated under reduced pressure in a reaction chamber to generate SiO gas. Furthermore, the SiO gas needs to be condensed / precipitated and deposited on a cooled substrate. If the pressure in the reaction chamber is too high, the reaction to generate SiO gas from the raw material will be difficult to occur. Therefore, the pressure is preferably 10 Pa or less, more preferably 7 Pa or less, and particularly preferably 5 Pa or less.

[0031] The temperature t1 (°C) within the reaction chamber affects the reaction rate of SiO. When the temperature is too low, the reaction rate is slow; when the temperature is too high, the raw materials melt, reducing the reaction area and also slowing the reaction rate. Furthermore, damage to the crucible is also a concern. From this perspective, the temperature t1 (°C) within the reaction chamber is preferably 1000~1600°C, more preferably 1100~1500°C, and particularly preferably 1100~1400°C.

[0032] The temperature t2 of the precipitation matrix affects the crystallinity of the SiO precipitates (aggregates of spherical powders) deposited on the residual SiO precipitates on the precipitation matrix. When the temperature is too low, the SiO microstructure becomes too sparse, and the specific surface area increases. On the other hand, when the temperature is too high, disproportionation (homogenization) occurs. From this viewpoint, the temperature t2 is preferably below 800°C, more preferably 150°C to 750°C, and particularly preferably 150°C to 650°C.

[0033] Heat treatment of the SiO powder recovered by scraping with a blade increases the density of the structure, thereby reducing the specific surface area and improving battery performance as a negative electrode material. Specifically, when incorporated into a battery as an active material, the initial efficiency can be improved by reducing the amount of SEI film grown on the surface of the SiO powder particles. Furthermore, cycling characteristics can be improved by coating the SiO powder with conductive carbon.

[0034] The heat treatment atmosphere is preferably an inactive gas atmosphere to suppress oxidation. From the perspective of optimizing crystallinity, the heat treatment temperature t3 (°C) is preferably 500~900°C, more preferably 550~850°C, and particularly preferably 600~850°C. When the heat treatment temperature t3 (°C) is too low, the microstructure of the powder becomes too sparse, and the specific surface area increases; when the heat treatment temperature t3 (°C) is too high, disproportionation occurs. Expressed as the weight ratio of carbon to the total mass of the powder, the coating amount of conductive carbon is preferably 0.5~20 wt%. When this coating amount is too small, the effect of improving cycle characteristics by increasing conductivity is insufficient; when this coating amount is too large, the proportion of SiO decreases, and the effect of improving capacity is insufficient.

[0035] Furthermore, as raw materials for SiO gas generation, not only mixtures of Si and SiO2 can be used, but also mixtures obtained by adding materials containing other elements to the mixture. By using raw materials containing other elements, in addition to obtaining spherical powders without sharp edges, it is also possible to manufacture SiO powders doped with other elements. Materials containing other elements can be, for example, metal silicates or metal oxides such as lithium silicate, magnesium silicate, aluminum silicate, lithium oxide, magnesium oxide, and aluminum oxide, or materials such as phosphorus and boric acid used as so-called dopants. In this case, by adjusting the elemental ratio of the main component of the mixture of Si, SiO2, and lithium silicate, Li-doped SiO powder with the desired Li concentration can be obtained.

[0036] Furthermore, the spherical SiO powder of the present invention not only has high sphericity, but also, for 20 randomly selected particles, when performing fractal dimension analysis by frequency division method on the cross-section with the largest cross-sectional area, the average fractal dimension D of the 20 particles is 1.03 or more and 1.50 or less. The sphericity is preferably 0.8 or more.

[0037] As a specific fractal dimension analysis method, after fabricating composite material electrodes or performing resin filling, a cross-section is created using the FIB method. For each cross-section of 20 randomly selected particles before charging / discharging from the field of view observed by SEM, a fractal dimension analysis based on the frequency division method is performed. That is, after fabricating composite material electrodes using SiO powder, a 3D-SEM image is obtained for the range of 20 particles including SiO. After generating three-dimensional reconstructed images of the 20 particles, image analysis software is used to calculate the area of ​​each XY cross-section, and for each particle, the fractal dimension is calculated for the XY cross-section image with the largest area.

[0038] In 3D-SEM, depth information can be continuously obtained by sample preparation in the FIB, SEM observation, and repeating sample preparation at approximately 100 nm intervals (obtaining approximately 400 SEM images). Furthermore, by taking into account the platform tilt angle of the FIB to correct for the obtained continuous SEM images, and after confirming the continuous observation of a series of SEM images in the depth direction, a three-dimensional reconstructed image can be obtained by overlaying the image sequence simply by performing alignment (straightening) of the continuous SEM images.

[0039] For each SiO particle (20 particles) extracted by the 3D-SEM, after calculating the area of ​​the XY section (FIB processing direction) using Avizo 9.7.0 image analysis software manufactured by Thermo Fisher Scientific, the fractal dimension based on the frequency division method can be calculated using Image-Pro10 manufactured by Nippon Roper.

[0040] As is well known, the fractal dimension based on the frequency division method is a method of approximating the contour line with broken lines of characteristic length, thereby obtaining the fractal dimension. When the number of line segments required to approximate the contour line of the projected particle image with a set of line segments of length r is set as N(r), then N(r) = a·r -D In this context, D represents the fractal dimension (a is the coefficient).

[0041] In particles with uneven surfaces, if the length r of the line segment is set to be small, then when r is large, the small unevenness of the particle surface that is not represented can be approximated by a broken line, and N(r) increases beyond the portion of r that is reduced. This increase is represented by the fractal dimension D, which can show the complexity of the unevenness on the surface of a composite spherical particle, such as cauliflower, in which multiple smaller spherical parts (satellites) are integrally combined on a larger spherical part (core) that forms the core, i.e., the particle shape.

[0042] Roundness and BET specific surface area are well-known factors for representing the shape of active material particles used in batteries. However, in the case of composite spheres where multiple small spherical satellites are integrally combined on a larger spherical core, roundness cannot accurately reflect the morphological characteristics. Furthermore, when using BET specific surface area, the influence of surface roughness and micropores, which are microscopic shapes, significantly dominates compared to the simplicity of the macroscopic shape; there is no difference between particles obtained from pulverized blocky SiO and the aforementioned composite spheres. On the other hand, the fractal dimension D of the frequency division method is not affected by the microscopic surface area factor and can accurately reflect the morphological characteristics of the composite spheres.

[0043] When performing fractal dimension analysis based on the frequency division method on 20 randomly selected particles in each cross-section with the largest cross-sectional area, if the average fractal dimension D of the 20 particles, Dfi, is less than 1.03, the overall shape is too simple and the desired effect for composite spherical particles cannot be obtained. Conversely, when the average Dfi exceeds 1.50, the junctions connecting the spherical core and spherical satellites become more numerous and thinner, making the particles prone to breakage due to volume changes accompanying charging / discharging. As a result, cycling characteristics deteriorate. Furthermore, the emergence of new linear surfaces due to particle breakage leads to side reactions with the electrolyte, further reducing initial efficiency. Particularly preferred is an average fractal dimension D, Dfi, of 1.05 or higher and 1.50 or lower.

[0044] In the spherical granular SiO powder of this invention, the magnification ratio is crucial when calculating the fractal dimension. This magnification ratio is set to a value where the cross-sectional area of ​​the particle used for calculating the fractal dimension occupies 20-90% of the field of view. This is because if this is not done, the shape of the complex contour will not be visible, and the fractal dimension of the appearance will be lower. On the other hand, if the cross-section with the largest area does not fall within the 20-90% range of the field of view, the particle will be excluded from the target for calculating the fractal dimension.

[0045] In the SiO powder manufacturing method of the present invention, a portion of the SiO precipitates deposited on the cooled precipitation substrate remain on the precipitation substrate. The remaining SiO precipitates are directly scraped off and recovered. This not only allows for the efficient and economical production of SiO powder with low levels of contamination caused by impurities, but also for the efficient and economical production of SiO powder with high roundness and small particle size, free of sharp edges. By using SiO powder as the negative electrode material of lithium-ion secondary batteries, the battery performance of lithium-ion secondary batteries can be effectively improved.

[0046] Furthermore, the spherical granular SiO powder of the present invention can effectively improve the battery performance when used as a negative electrode material for lithium-ion secondary batteries by macroscopically quantifying and rationally managing the morphological characteristics of the special powder particles through the fractal dimension D based on the frequency division method.

[0047] Furthermore, the spherical SiO powder of the present invention can be further pulverized and used as an intermediate for the negative electrode active material. Since the pulverization is excellent at this time, it will help reduce pulverization energy and production costs. Attached Figure Description

[0048] Figure 1 This is a schematic diagram illustrating an example of a SiO powder manufacturing apparatus used in the SiO powder manufacturing method of the present invention.

[0049] Figure 2A microscope image of SiO powder produced by the method of the present invention;

[0050] Figure 3 Microscopic photographs of SiO powder manufactured using existing methods for comparison;

[0051] Figure 4 Microscopic photograph of SiO powder produced by existing methods after pulverization;

[0052] Figure 5A This is a three-dimensional reconstructed image of the SiO powder particles of the present invention;

[0053] Figure 5B Cross-sectional images of the same powder particles;

[0054] Figure 6A A three-dimensional reconstructed image of existing SiO powder particles;

[0055] Figure 6B Cross-sectional images of the same powder particles;

[0056] Figure 7 A graph showing the relationship between the roundness and cycle characteristics of the same powder particles;

[0057] Figure 8 A graph showing the relationship between the fractal dimension Dfi and the cyclic properties of the same powder;

[0058] Figure 9 A graph showing the relationship between the fractal dimension Dfi of the same powder particles and the time required for pulverization (pulverization). Detailed Implementation

[0059] The embodiments of the present invention will now be described.

[0060] The method for manufacturing SiO powder in this embodiment includes: a SiO gas generation step, in which SiO gas is generated; a SiO precipitation step, in which the generated SiO gas is condensed and deposited on a cooled precipitation substrate; and a SiO powder recovery step, in which the SiO precipitates deposited on the precipitation substrate are scraped off by a blade and recovered as SiO powder. These steps are performed simultaneously in parallel, and the SiO powder recovery step among these steps has significant characteristics.

[0061] like Figure 1As shown, the SiO powder manufacturing apparatus used in the SiO powder manufacturing method of this embodiment includes: a furnace body 1, a crucible 2 disposed in the furnace body 1, a heater 3 surrounding the crucible 2 to heat the inside of the crucible 2, an insulating material 4 that retains the upper opening of the crucible 2 and covers the crucible 2 and the heater 3, a precipitation substrate 5 composed of a drum-shaped rotating body disposed on the upper opening of the crucible 2, a blade 7 disposed from the front side of the precipitation substrate 5 toward the precipitation substrate 5 in order to scrape the SiO precipitates deposited on the outer peripheral surface of the precipitation substrate 5, and a SiO powder receiving tray 8 disposed below the blade 7.

[0062] To produce SiO powder, firstly, a mixture of materials such as Si and SiO2, which serves as the raw material 9 for generating SiO gas, is placed in a crucible 2, which is the reaction chamber. Then, the internal pressure of the furnace body 1 is reduced, while the inside of the crucible 2 is heated by a heater 3. As described above, the pressure inside the furnace body 1 is preferably 10 Pa or less, more preferably 7 Pa or less, and particularly preferably 5 Pa or less. Furthermore, the heating temperature inside the crucible 2, i.e., the temperature t1 within the reaction chamber, is preferably 1000–1600 °C, more preferably 1100–1500 °C, and particularly preferably 1100–1400 °C.

[0063] By reducing the pressure and heating inside crucible 2, SiO gas will be generated from the SiO gas generating material 9 in crucible 2. This is the SiO gas generation process.

[0064] At this time, the precipitation substrate 5, composed of a drum-shaped rotating body, is rotating on top of crucible 2. The temperature t2 of the precipitation substrate 5 is set lower than t1 in the reaction chamber, and more specifically, it is set lower than the condensation temperature of SiO gas. As described above, this temperature t2 is preferably 800°C or lower, more preferably 150°C or higher and 750°C or lower, and particularly preferably 150°C or higher and 650°C or lower. Thus, the SiO gas generated by the SiO gas generating raw material 9 in crucible 2 will condense and deposit on the surface of the precipitation substrate 5. This is the SiO precipitation process.

[0065] Meanwhile, the blade 7 faces the rotating precipitation substrate 5 from the front side. It is important that the tip of the blade 7 does not come into contact with the surface of the precipitation substrate 5. The distance between the surface of the precipitation substrate 5 and the tip of the blade 7 is ensured to be a predetermined distance g (gap). As described above, this distance g (gap) is preferably 0.1 to 3 mm, more preferably 0.5 to 2.5 mm, and particularly preferably 0.5 to 2 mm.

[0066] Thus, the SiO precipitate 10 deposited on the surface of the precipitate substrate 5 is scraped off by the blade 7 and recovered as SiO powder 11 in the receiving tray 8. However, since the tip of the blade 7 is in contact with the surface of the precipitate substrate 5, and the distance between the surface of the precipitate substrate 5 and the tip of the blade 7 is ensured to be a predetermined distance g (gap), contamination from impurities caused by direct contact between the precipitate substrate 5 and the blade 7 is prevented in the recovered SiO powder 11, and the SiO powder 11 becomes a high-quality powder with small particle size and spherical particles without sharp edges. The reason for this is as described above.

[0067] This is the SiO powder recovery process, which is carried out simultaneously with the SiO gas generation process and the SiO precipitation process to continuously produce the aforementioned high-quality SiO powder.

[0068] The SiO powder recovery process is analyzed by focusing on specific positions along the circumference of the precipitate substrate 5, with the scraping position based on the blade 7 as the starting point. More specifically, when the specific position reaches the scraping position, the previously deposited SiO precipitates 10 are scraped off, leaving a specified thickness of SiO precipitates 10 remaining on the surface of the precipitate substrate 5. Then, SiO precipitates 10 continue to deposit on this surface until the next specific position reaches the scraping position, at which point the newly deposited SiO precipitates 10 are scraped off, and this process is repeated. In other words, a constant thickness of SiO precipitates 10 continuously remains on the surface of the precipitate substrate 5, and newly deposited SiO precipitates 10 are scraped off by the blade 7. The deposition rate of SiO precipitates 10 per unit time is the growth rate d (μm / min), and the rotational speed of the precipitate substrate 5 per unit time is the scraping cycle n (min). -1 ).

[0069] As described above, the growth rate d (μm / min) and scraping cycle n (min) of SiO precipitate 10 -1 The relationship between d / n (μm) has a significant impact on the properties (particle size, shape) of the recovered SiO powder.

[0070] Furthermore, the SiO powder obtained in this way is not simply a spherical particle with high sphericity, but a composite spherical particle, like cauliflower, with multiple small spherical satellite parts integrally combined on a larger spherical core. The particle shape is represented by the average value Dfi of the fractal dimension D of the 20 particles, which is 1.03 or higher and 1.50 or lower, particularly 1.05 or higher and 1.50 or lower. As described above, it exhibits excellent recyclability and pulverability. Additionally, from the viewpoint of near-spherical powder particles, its sphericity is preferably 0.8 or higher, as mentioned above.

[0071] Regarding the median particle size, the preferred particle size of SiO particles is 0.5~30 μm. If the particle size is too small, the influence of electrolyte decomposition reactions on the particle surface will increase, leading to a decrease in coulombic efficiency and a reduction in processing performance due to increased cohesion or decreased packing density. If the particle size is too large, the electrode expansion during Li adsorption will be greater, resulting in a decrease in cycle characteristics.

[0072] [Example]

[0073] Next, the results of actually manufacturing SiO powder using the above apparatus and steps will be described. The precipitation matrix, consisting of a drum-shaped rotating body, is made of stainless steel and cooled with oil, and the blades are also made of stainless steel.

[0074] (Example 1-1)

[0075] A mixture of Si and SiO2 (Si:O = 1:1), used as the raw material for SiO gas generation, is loaded into a crucible serving as the reaction chamber. After the crucible is positioned in the furnace, the furnace pressure is reduced to 1 Pa, and the inside of the crucible is heated to 1300°C to generate SiO gas. Simultaneously, the temperature of the precipitation substrate above the rotating crucible is controlled at 150°C, and the crucible is rotated to cause SiO gas to condense / precipitate on the surface of the precipitation substrate.

[0076] At this point, the growth rate d of the SiO precipitates on the surface of the substrate, i.e., the film formation rate, is 4.8 μm / min. By adjusting the rotation speed of the substrate, the scraping cycle n is set to 2.4 min. -1 The ratio d / n between the two is set to 2. Additionally, the distance g from the surface of the precipitated matrix to the tip of the blade is set to 0.5 mm.

[0077] At the scraping position of the blade, SiO precipitates are scraped off by leaving a 0.5 mm thick SiO precipitate layer, and SiO powder is recovered, thereby continuously producing SiO powder. Among the produced SiO powder, micro-powder with a particle size of less than 45 μm is evaluated as active material by sieving.

[0078] In addition, the production capacity per unit length of SiO powder precipitated matrix (g / (hr·m)), yield (weight of recovered SiO / weight reduction of raw material) and micro powder recovery rate (weight of recovered SiO residue on 45μm sieve / weight of recovered SiO) were investigated.

[0079] The particle shape of the manufactured SiO powder was investigated by roundness (circumference of a circle with equal projected area / circumference of a particle). The method for measuring roundness is shown in Table 1.

[0080] [Table 1]

[0081]

[0082] Next, SiO micro powder with a thickness of less than 45 μm, which is the final powder product, is used as the negative electrode active material to fabricate the negative electrode of the lithium-ion secondary battery. Specifically, a slurry is prepared by mixing SiO powder, Ketjen black, and a polyimide precursor as a non-aqueous solvent binder at a mass ratio of 85:5:10, and further adding NMP (n-methylpyrrolidone) and mixing thoroughly. Then, the slurry is coated onto a copper foil with a thickness of 40 μm, pre-dried at 80°C for 15 minutes, stamped to a diameter of 11 mm, and then subjected to acylation treatment to form the negative electrode.

[0083] Furthermore, the fabricated negative electrode is used to manufacture a lithium-ion secondary battery. Specifically, lithium foil is used as the counter electrode in the secondary battery. The electrolyte is a solution obtained by dissolving LiPF6 (lithium hexafluorophosphate) at a ratio of 1 mol / L in a solution obtained by mixing ethylene carbonate and diethyl carbonate in a 1:1 volume ratio. Then, a 20 μm thick porous membrane made of polyethylene is used as the separator to fabricate a button cell.

[0084] The fabricated lithium-ion secondary batteries were subjected to charge / discharge tests using a secondary battery charge / discharge test apparatus (manufactured by Nagano Co., Ltd.). Table 2 shows the test conditions used in the charge / discharge tests. Through these tests, the initial charge capacity, initial discharge capacity, the ratio of the initial discharge capacity to the initial charge capacity (initial coulombic efficiency), and the ratio of the 50th discharge capacity to the initial discharge capacity (capacity retention after 50 cycles) were determined.

[0085] [Table 2]

[0086]

[0087] In order to evaluate the particle shape of SiO powder, in addition to the roundness measurement mentioned above, 3D-SEM images of the negative electrode and fractal analysis of the cross-section of SiO particles were obtained by the following methods.

[0088] (1) 3D-SEM images obtained for the electrodes.

[0089] Sample preparation and observation apparatus: Helios G4 manufactured by FEI

[0090] FIB processing conditions: Accelerating voltage 30kV

[0091] SEM observation conditions: accelerating voltage 2kV, secondary electron image.

[0092] Processing area: Approximately 40μm (width) × Approximately 40μm (height)

[0093] Image stride: 100nm

[0094] Number of images: Approximately 400

[0095] Sample tilt: 52°

[0096] (2) Sample processing, SEM observation, and sample processing via FIB were repeated at intervals of approximately 100 nm (resulting in approximately 400 SEM images), thereby continuously obtaining thickness information of approximately 40 μm in the depth direction. Furthermore, the obtained continuous SEM images were corrected considering the platform tilt angle of the FIB. After confirming the series of continuously observed SEM images in the depth direction, alignment of the continuous SEM images was performed, and a three-dimensional reconstructed image was obtained by overlaying the image sequence. The observation range was selected to include 20 particles in the observed field of view.

[0097] (3) Then, perform fractal dimension analysis as follows.

[0098] Software used: Manufactured by Thermo Fisher Scientific

[0099] Avizo 9.7.0

[0100] Image-Pro10 manufactured by Nippon Roper

[0101] Image analysis method: For each SiO particle (20 particles) extracted by the 3D-SEM, the area of ​​the XY section (FIB processing direction) was calculated using Avizo 9.7.0. For each particle, the fractal dimension D of each particle was calculated from the XY section image with the largest area using Image-Pro 10, and the average value was compared.

[0102] In addition to these measurements, considering the further pulverization of the SiO powder and its use as an active material, the pulverability was investigated by the following method.

[0103] (1) The particle size distribution of the residue obtained by sieving the recovered powder through a sieve with a sieve aperture of 45 μm was measured to determine the median particle size D50 (hereinafter referred to as the average particle size) on a volume basis. The particle size distribution was measured using a laser diffraction type particle size distribution measuring device. In this embodiment, a Mastersizer2000 manufactured by Malvern was used. Isopropanol was used as the solvent.

[0104] (2) Using a dry mill, the powder remaining after sieving through a 45 μm sieve was pulverized to an average particle size of 5 μm. The apparatus used was a Nippon Coke MA1D dry mill, with zirconia balls of 5 mm in diameter and a rotation speed of 300 rpm. The time required to reach the desired particle size (5 μm) was measured.

[0105] Table 3 shows the results of various surveys on the specifications, productivity, battery performance, and pulverability of the manufactured SiO powder, as well as the manufacturing conditions of the SiO powder.

[0106] (Examples 1-2)

[0107] In Example 1-1, the rotational speed of the precipitated matrix was reduced to decrease the scraping cycle n from 2.4 min. -1 Change 0.24min -1 Therefore, d / n was changed from 2 to 20. Other manufacturing conditions and testing methods were the same as in Examples 1-1. The various investigation results are shown in Table 3 together with the manufacturing conditions of SiO powder.

[0108] (Examples 1-3)

[0109] In Example 1-1, the rotational speed of the precipitated matrix was increased to reduce the scraping cycle n from 2.4 min. -1 Change to 48min -1 This changes d / n from 2 to 0.1. Other manufacturing conditions and testing methods are the same as in Examples 1-1. The various investigation results, along with the manufacturing conditions of the SiO powder, are shown in Table 3.

[0110] (Example 2)

[0111] In Example 1-1, the distance g between the surface of the precipitated matrix and the tip of the blade was changed from 0.5 mm to 1 mm. Other manufacturing conditions and testing methods were the same as in Example 1-1. The various findings, along with the manufacturing conditions of the SiO powder, are shown in Table 3.

[0112] (Example 2-i)

[0113] In Example 2, the final product (SiO micro powder) was heat-treated. Specifically, the final product (SiO micro powder) was placed in an aluminum crucible and heated in an electric furnace at 850°C for 2 hours in an inert gas atmosphere (Ar gas atmosphere). Other conditions were the same as in Example 2. The various findings, along with the manufacturing conditions of the SiO powder, are shown in Table 3.

[0114] (Example 2-ii)

[0115] In Example 2-i, the heat-treated final product (SiO micro powder) was coated with conductive carbon (C coating). Specifically, the heat-treated powder was loaded into a rotary kiln and carbon coating was performed by thermal CVD using a mixture of argon and propane as the carbon source. The carbon coating amount (the weight ratio of C in the total powder) was 2 wt%. Other conditions were the same as in Example 2-i. The various findings, along with the manufacturing conditions of the SiO powder, are shown in Table 3.

[0116] (Example 3)

[0117] In Example 2, the distance g between the surface of the precipitated matrix and the tip of the blade was changed from 1 mm to 3 mm. Other manufacturing conditions and testing methods were the same as in Example 2. The various findings, along with the manufacturing conditions of the SiO powder, are shown in Table 3.

[0118] (Example 4)

[0119] In Example 3, the precipitation temperature of the matrix was changed from 150°C to 500°C. This resulted in a decrease in the film formation rate from 4.8 μm / min to 4.5 μm / min, and a decrease in d / n from 2 to 1.88. Other manufacturing conditions and testing methods were the same as in Example 3. The various findings, along with the manufacturing conditions of the SiO powder, are shown in Table 3.

[0120] (Example 5)

[0121] In Example 1, the mixture of Si and SiO2 (Si:O = 1:1) was changed to a mixture of Si, SiO2, and lithium silicate (Li:Si:O = 0.1:1:1) as the raw material for SiO gas generation. Additionally, the distance g between the surface of the deposited matrix and the tip of the blade was changed from 0.5 mm to 0.1 mm. Other manufacturing conditions and testing methods were the same as in Examples 1-1. Various investigation results, along with the manufacturing conditions of the SiO powder, are shown in Table 3.

[0122] (Example 5-i)

[0123] In Example 5, the final product (SiO micro powder) was heat-treated. Specifically, the final product (SiO micro powder) was placed in an aluminum crucible and heated in an electric furnace at 850°C for 2 hours in an inert gas atmosphere (Ar gas atmosphere). Other conditions were the same as in Example 5. The various findings, along with the manufacturing conditions of the SiO powder, are shown in Table 3.

[0124] (Example 5-ii)

[0125] In Example 5-i, the heat-treated final product (SiO micro powder) was coated with conductive carbon (C coating). Specifically, the heat-treated powder was loaded into a rotary kiln and carbon coating was performed by thermal CVD using a mixture of argon and propane as the carbon source. The carbon coating amount (weight ratio of C element in the total powder) was 2 wt%. Other conditions were the same as in Example 5-i. The various findings, along with the manufacturing conditions of the SiO powder, are shown in Table 3.

[0126] (Example 6)

[0127] In Example 5, the mixture of Si and SiO2 with lithium silicate (Li:Si:O = 0.1:1:1) was changed to a mixture of Si and SiO2 with MgO (Mg:Si:O = 0.1:1:1) as the raw material for SiO gas generation. Other manufacturing conditions and testing methods were the same as in Example 5. The various investigation results, along with the manufacturing conditions of the SiO powder, are shown in Table 3.

[0128] (Example 7)

[0129] In Example 1-1, the rotational speed of the precipitated matrix was slowed down to reduce the scraping cycle n from 2.4 min. -1 Change to 0.08min -1 This changes the d / n ratio from 2 to 60. Other manufacturing conditions and testing methods are the same as in Examples 1-1. The various investigation results, along with the manufacturing conditions of the SiO powder, are shown in Table 3.

[0130] (Comparative Example 1)

[0131] In Example 1-1, the distance g between the surface of the precipitated matrix and the tip of the blade was changed from 0.5 mm to 0 mm. That is, the surface of the precipitated matrix was brought into contact with the tip of the blade. Other manufacturing conditions and testing methods were the same as in Example 1-1. The various investigation results are shown in Table 3 along with the manufacturing conditions of the SiO powder.

[0132] (Comparative Example 2)

[0133] In Example 7, the distance g between the surface of the precipitated matrix and the tip of the blade is changed from 0.5 mm to 0 mm. That is, in Example 1-1, the rotational speed of the precipitated matrix is ​​slowed down to reduce the scraping cycle n from 2.4 min. -1 Change to 0.08min -1 This changed d / n from 2 to 60, and brought the surface of the precipitated matrix into contact with the tip of the blade. Other manufacturing conditions and testing methods were the same as in Example 7 or Examples 1-1. The various findings, along with the manufacturing conditions of the SiO powder, are shown in Table 3.

[0134] [Table 3]

[0135]

[0136] As can be seen from Table 3, in the embodiments of the present invention where the blade tip separates from the surface of the deposited substrate, the capacity retention rate after fifty cycles, a characteristic of battery performance, is improved compared to the comparative example where the blade tip is in contact with the surface of the deposited substrate. This is likely due to the reduction of contamination caused by impurities in the SiO powder resulting from the contact between the blade tip and the surface of the deposited substrate in the embodiments of the present invention.

[0137] Furthermore, in Comparative Examples 1 and 2, the SiO powder particles were flaky with a sphericity of less than 0.8, while in the embodiments of the present invention, the SiO powder particles had a sphericity of 0.8 or higher, and except for Example 7, all had a sphericity of 0.9 or higher, being exceptionally spherical. Microscopic photographs of the SiO powder (recovered powder before sieving) produced in Examples 1-1 are shown below. Figure 2 In addition, a microscopic photograph of the SiO powder (recycled powder before sieving) produced in Comparative Example 1 is shown below. Figure 3 The state of the powder after pulverization is shown in the figure. Figure 4 middle.

[0138] It can be seen that the SiO powder produced in Examples 1-1 is a spherical granular powder without sharp edges. Furthermore, it can be seen in more detail that it grows into a composite spherical shape, similar to cauliflower, where multiple small spherical satellite portions are integrally combined on a larger spherical core. On the other hand, the SiO powder produced in Comparative Example 1 is clearly flaky. Even when pulverized, it does not become the spherical granular powder without sharp edges produced in Examples 1-1.

[0139] The roundness of the particles in Example 7 is lower than that in the other examples, and the shape is almost spherical granular. This is because the rotation speed of the precipitated matrix is ​​relatively slow, resulting in an extremely short scraping cycle n of 0.08 min. -1 Furthermore, due to the extended time between scraping and the next scraping, the new SiO precipitates deposited on the residual SiO precipitates move forward as a whole with the next residual SiO precipitates. The SiO powder obtained by scraping will become flake-like and be peeled off from the precipitate matrix in two forms: spherical particles and larger flakes. However, as mentioned above, spherical particles can be recovered by sieving, and the spherical particles have a higher sphericity than the comparative example.

[0140] Furthermore, in the embodiments other than Example 7, since spherical particles without sharp edges were obtained, the initial efficiency of the battery performance was significantly improved compared to the comparative example and Example 7. Additionally, the micron powder recovery rate in SiO powder manufacturing was high. This means that micronization was already underway during the scraping and recovery stage using a blade.

[0141] In Examples 2, 2-i, 2-ii and Examples 3 and 4, the yield was slightly lower than in the other examples, and the spacing between the surface of the precipitated matrix and the tip of the blade was not necessarily optimal.

[0142] Furthermore, as shown in Examples 2-i and 2-ii and Examples 5-i and 5-ii, heat treatment of the recovered SiO powder is effective in improving initial efficiency, and coating with conductive carbon is effective in improving capacity retention after fifty cycles. Particularly in Example 4, despite neither heat treatment of the SiO powder nor coating with conductive carbon, both initial efficiency and capacity retention after fifty cycles were relatively high. This is likely because although the deposition temperature of the substrate is higher than other temperatures and the film formation rate is suppressed, the structure of the SiO precipitates tends to be denser, which is reflected in the battery evaluation. Although heat treatment of the recovered SiO powder also densifies the structure (Example 2-i), the battery performance of Example 4 is improved compared to that. This is because, after recovery, less oxygen is absorbed when heated in a non-atmospheric state compared to heating after atmospheric exposure.

[0143] In addition, as shown in Examples 5 and 6, Li doping and Mg doping caused by the presence of doping sources in the raw materials are effective in improving battery performance, and heat treatment and coating with conductive carbon are also effective in improving battery performance (Examples 5-i and 5-ii).

[0144] Furthermore, when evaluating the particle shape in the examples and comparative examples by the average fractal dimension Dfi of the 20 particles, in the example, it was in the range of 1.03 or higher and 1.50 or lower, while in the comparative example, it was less than 1.03. A three-dimensional reconstructed image of a particle from the SiO powder obtained in Examples 1-1 is shown below. Figure 5A Its cross-sectional image is shown in Figure 5B The fractal dimension D of this cross-sectional image is 1.055. Additionally, a three-dimensional reconstructed image of a particle in the SiO powder obtained in Comparative Example 1-1 is shown below. Figure 6A Its cross-sectional image is shown in Figure 6B The fractal dimension D of this cross-sectional image is 1.017, which is significantly different from the SiO particles obtained in Example 1-1.

[0145] Furthermore, the relationship between roundness and capacity retention (cycle characteristics) after fifty cycles in the embodiments and comparative examples is shown in... Figure 7 Furthermore, the relationship between the average fractal dimension D, Dfi, in the examples and comparative examples, and the capacity retention rate (cycling characteristics) after fifty cycles is shown in the figure. Figure 8 .

[0146] from Figure 7 As can be seen, embodiments with high roundness will show improved capacity retention, but the correlation is not monotonic and is difficult to control through roundness. In contrast, from... Figure 8 It can be seen that the fractal dimension D exhibits a strong correlation with the capacity retention rate, and the capacity retention rate can be controlled by the fractal dimension D. This is because the fractal dimension D accurately reflects the morphological characteristics of composite spherical particles, such as those found in cauliflower, which have multiple small spherical satellite parts integrally combined on a larger spherical core.

[0147] Furthermore, the relationship between the average fractal dimension D, Dfi, and the time required for pulverization (pulverization) in the examples and comparative examples is shown in the figure. Figure 9 As can be clearly seen from the figure, the pulverization rate increases with the increase of the average fractal dimension Dfi, which also indicates that the fractal dimension D is effective in quantitatively evaluating the characteristics of composite spherical particles such as cauliflower.

[0148] Furthermore, in this invention, SiO does not refer to SiO2. x (x=1). This means SiO in a broad sense, including substances doped with other elements. If expressed as a chemical formula, it would be M. y SiO x Where 0.5 ≤ x ≤ 1.5, 0 ≤ y ≤ 1. When x, representing the ratio of the atomic weight of O to the atomic weight of Si, is less than 0.5, then SiO... x It would be too close to Si, which would increase its reactivity with oxygen and reduce safety. On the other hand, when x is greater than 1.5, the initial efficiency decreases, and the battery performance also deteriorates.

[0149] Regarding x and y, it is preferable to further satisfy 0.05 ≤ y / x ≤ 1. When y / x is less than 0.05, the effect of M doping will be very weak, while when it is greater than 1, the stability may decrease.

[0150] In the above-described embodiments and comparative examples, the amounts of Si, O, and Li or Mg in the obtained SiO powder were measured. For Si, Li, and Mg, the amounts were measured by ICP emission spectroscopy analysis. For O, the amounts were measured using a LECO TC-436 spectrometer via gas fusion-infrared absorption spectrometry (GFA). The O / Si, Li / O, and Mg / O ratios for each example are also shown in Table 3.

[0151] Symbol Explanation

[0152] 1 Furnace body

[0153] 2. Crucible

[0154] 3 heaters

[0155] 4. Thermal insulation materials

[0156] 5. Precipitated matrix

[0157] 7 blades

[0158] 8. Taking over

[0159] 9 SiO gas generation raw materials

[0160] 10 SiO precipitates

[0161] 11 SiO powder

Claims

1. A spherical granular SiO powder, Composite electrodes are fabricated using SiO powder. Obtain 3D-SEM images, Generate 3D reconstructed images of 20 randomly selected particles. For each particle, a fractal dimension analysis was performed on the cross-section with the largest area. The average value of the fractal dimension D calculated through the fractal dimension analysis, Dfi, is greater than 1.03 and less than 1.

50.

2. The spherical granular SiO powder according to claim 1, wherein the SiO powder is used as a negative electrode active material.

3. The spherical granular SiO powder according to claim 1, wherein, The roundness of the powder particles is 0.8 or higher.

4. The spherical granular SiO powder according to claim 1, wherein, It is doped with elements M other than Si and O.

5. The spherical granular SiO powder according to claim 4, wherein, The molar ratio of element M to O in the SiO powder is 0.05 ≤ M / O ≤ 1.

6. The spherical granular SiO powder according to claim 5, wherein, M is selected from Li, Mg, Al, P and B.

7. The spherical granular SiO powder according to claim 1, wherein, The particle size of the SiO powder is 0.5–30 μm, based on the median particle size.

8. The spherical granular SiO powder according to claim 1, wherein, At least a portion of the particles constituting the SiO powder are covered with a conductive carbon film.

9. The spherical granular SiO powder according to claim 8, wherein, The amount of conductive carbon film formed is expressed as the weight ratio of carbon to the total mass of SiO powder, ranging from 0.5 to 20 wt%.

Images