WO2025183333A1 - Silicon negative electrode material comprising secondary particles formed by aggregating primary particles, and method for manufacturing same - Google Patents

Abstract

The present invention relates to a silicon negative electrode material comprising silicon secondary particles formed by aggregating silicon primary particles, wherein the silicon negative electrode material has a bridge connecting adjacent silicon primary particles in the silicon secondary particles.

Description

Silicon negative electrode material comprising secondary particles formed by agglomeration of primary particles and method for manufacturing the same

The present invention relates to a silicon negative electrode material including secondary particles formed by agglomeration of primary particles and a method for manufacturing the same.

Lithium secondary batteries are widely used in a wide range of applications, from portable electronic devices to electric vehicles, due to their high energy density, long lifespan, and high voltage. Previously, research to increase the capacity of lithium secondary batteries primarily focused on cathode active materials. However, as capacity enhancement through cathode active materials has reached its limits, research on anode active materials has recently become increasingly active. In particular, interest is growing in silicon anode materials, which have a theoretical capacity approximately 10 times higher than that of graphite, the traditional anode material.

Silicon anode materials possess a theoretical capacity approximately 10 times higher than that of graphite (approximately 4,200 mAh/g), making them a promising anode material for lithium secondary batteries. However, silicon anode materials suffer from a serious problem: their volume expands by more than 300% during charging and discharging, hindering their commercialization. This volume expansion during charging and discharging causes the silicon particles to become finer, leading to the continuous destruction and rebuilding of the surface Solid Electrolyte Interphase (SEI), which increases lithium consumption and shortens the battery's lifespan.

Therefore, new research and technological development to overcome these problems are necessary to improve the performance of silicon anode materials.

One object of the present invention according to the first embodiment is to provide a silicon negative electrode material including silicon secondary particles formed by agglomeration of silicon primary particles, and having a bridge connecting adjacent silicon primary particles within the silicon secondary particles.

In addition, another object of the present invention according to the first embodiment is to provide a method for manufacturing a silicon anode material, which can form silicon primary particles by pulverizing silicon raw material powder in a one-step process, and form silicon secondary particles by agglomerating the formed silicon primary particles and having bridges connecting adjacent silicon primary particles.

One object of the present invention according to the second embodiment is to provide a silicon anode material comprising silicon secondary particles formed by agglomeration of silicon primary particles and a conductive material, wherein the silicon secondary particles have a bridge connecting adjacent silicon primary particles, and the conductive material provides an electrical conduction path, thereby solving the problem of low conductivity, which is a disadvantage of conventional silicon anode materials.

In addition, another object of the present invention according to the second embodiment is to provide a method for manufacturing a silicon anode material, which can form silicon primary particles by pulverizing a conductive material and silicon raw material powder, and coagulating the formed silicon primary particles and the pulverized conductive material, thereby forming silicon secondary particles having a bridge connecting adjacent silicon primary particles.

One object of the present invention according to the third embodiment is to provide a silicon anode material comprising silicon secondary particles formed by agglomeration of silicon primary particles and silicon oxide particles, wherein the silicon secondary particles have bridges connecting adjacent silicon primary particles, and the silicon oxide particles can improve long-life stability.

In addition, another object of the present invention according to the third embodiment is to provide a method for manufacturing a silicon anode material capable of forming silicon primary particles by crushing silicon oxide particles and silicon raw material powder, agglomerating the formed silicon primary particles and the crushed silicon oxide particles, and forming silicon secondary particles having bridges connecting adjacent silicon primary particles.

Meanwhile, other unspecified purposes of the present invention will be additionally considered within the scope that can be easily inferred from the detailed description and effects thereof below.

To achieve the purpose proposed above, we propose solutions in various embodiments as follows.

The solution for the first embodiment is as follows.

A silicon anode material according to one embodiment of the present invention includes silicon secondary particles formed by agglomeration of silicon primary particles, and has a bridge connecting adjacent silicon primary particles within the silicon secondary particles.

In one embodiment, the bridge may be formed by cold welding.

In one embodiment, a carbon coating layer may be formed on the surface of the silicon secondary particle.

In one embodiment, the carbon coating layer may be crystalline carbon or amorphous carbon. Crystalline carbon has relatively high conductivity compared to amorphous carbon, and for example, the crystalline carbon may be at least one selected from the group consisting of artificial graphite, natural graphite, and graphene. The amorphous carbon may be at least one selected from the group consisting of hard carbon, soft carbon, petroleum pitch, coal pitch, mesophase pitch, and calcined coke.

In one embodiment, the silicon secondary particles may be such that the silicon primary particles are more densely aggregated from the periphery to the center.

A method for manufacturing a silicon anode material according to another embodiment of the present invention comprises: using a milling machine to pulverize silicon raw material powder to form silicon primary particles, while simultaneously agglomerating the silicon primary particles to form silicon secondary particles; and forming bridges connecting adjacent silicon primary particles within the silicon secondary particles by heat and pressure generated during the pulverization process of the silicon primary particles.

In another embodiment, the grinding of the silicon raw material powder and the formation of silicon secondary particles can be performed in an air atmosphere.

In another embodiment, the grinding of the silicon raw material powder and the formation of silicon secondary particles can be performed in an inert gas atmosphere.

In another embodiment, the milling machine may be at least one selected from the group consisting of a planetary mill, an attrition mill, and a beads mill.

In another embodiment, the grinding of the silicon raw material powder can be performed in the presence of a milling ball.

In another embodiment, the grinding of the silicon raw material powder can be performed at 1 to 6000 rpm for 1 second to 60 hours.

In another embodiment, after forming the silicon secondary particles, a step of forming a carbon coating layer on the surface of the silicon secondary particles may be further included.

The solution for the second embodiment is as follows.

A silicon anode material according to one embodiment of the present invention includes silicon secondary particles formed by agglomeration of silicon primary particles and a conductive material, and has a bridge connecting adjacent silicon primary particles within the silicon secondary particles.

In one embodiment, the conductive material may be at least one selected from the group consisting of graphene, carbon nanotubes, carbon nanofibers, graphite, and graphite-like material.

In one embodiment, the conductive material may be included in an amount of 1 to 15 wt% based on the silicon secondary particles.

In one embodiment, a carbon coating layer may be formed on the surface of the silicon secondary particle.

In one embodiment, the carbon coating layer may be crystalline carbon or amorphous carbon. Crystalline carbon has relatively high conductivity compared to amorphous carbon, and for example, the crystalline carbon may be at least one selected from the group consisting of artificial graphite, natural graphite, and graphene. The amorphous carbon may be at least one selected from the group consisting of hard carbon, soft carbon, petroleum pitch, coal pitch, mesophase pitch, and calcined coke.

In one embodiment, pores may also be formed in the central portion of the silicon secondary particle.

A method for manufacturing a silicon anode material according to another embodiment of the present invention comprises: using a milling machine to pulverize a conductive material and silicon raw material powder to form silicon primary particles; simultaneously, agglomerating the silicon primary particles and the pulverized conductive material to form silicon secondary particles; and forming bridges connecting adjacent silicon primary particles within the silicon secondary particles by heat and pressure generated during the pulverization process of the silicon primary particles.

In another embodiment, the conductive material may be at least one selected from the group consisting of graphene, carbon nanotubes, carbon nanofibers, graphite, and graphite-like material.

In another embodiment, the conductive material may be included in an amount of 1 to 15 wt% based on the silicon secondary particles.

In another embodiment, the grinding of the silicon raw material powder and the formation of silicon secondary particles can be performed in an air atmosphere.

In another embodiment, the milling machine may be at least one selected from the group consisting of a planetary mill, an attrition mill, and a beads mill.

In another embodiment, the grinding of the silicon raw material powder can be performed in the presence of a milling ball.

In another embodiment, the grinding of the silicon raw material powder can be performed at 1 to 6000 rpm for 1 second to 60 hours.

In another embodiment, after forming the silicon secondary particles, a step of forming a carbon coating layer on the surface of the silicon secondary particles may be further included.

The solution for the third embodiment is as follows.

A silicon anode material according to one embodiment of the present invention includes silicon primary particles and silicon secondary particles formed by agglomeration of silicon oxide SiO _x (where 0<X≤2) particles, and has a bridge connecting adjacent silicon primary particles within the silicon secondary particles.

In one embodiment, the content of the silicon oxide particles may be 2 to 50 wt% based on the silicon secondary particles.

In one embodiment, a carbon coating layer may be formed on the surface of the silicon secondary particle.

In one embodiment, the carbon coating layer may be crystalline carbon or amorphous carbon. Crystalline carbon has relatively high conductivity compared to amorphous carbon, and for example, the crystalline carbon may be at least one selected from the group consisting of artificial graphite, natural graphite, and graphene. The amorphous carbon may be at least one selected from the group consisting of hard carbon, soft carbon, petroleum pitch, coal pitch, mesophase pitch, and calcined coke.

According to another embodiment of the present invention, a method for manufacturing a silicon anode material comprises: using a milling machine to pulverize silicon raw material powder and silicon oxide SiO _x (wherein 0<X≤2) particles to form silicon primary particles; simultaneously, agglomerating the silicon primary particles and the pulverized silicon oxide to form silicon secondary particles; and forming bridges connecting adjacent silicon primary particles within the silicon secondary particles by heat and pressure generated during the pulverization process of the silicon primary particles.

In another embodiment, the content of the silicon oxide particles may be 2 to 50 wt% based on the silicon secondary particles.

In another embodiment, the grinding of the silicon raw material powder and the formation of silicon secondary particles can be performed in an air atmosphere.

In another embodiment, the milling machine may be at least one selected from the group consisting of a planetary mill, an attrition mill, and a beads mill.

In another embodiment, the grinding of the silicon raw material powder can be performed in the presence of a milling ball.

In another embodiment, the grinding of the silicon raw material powder can be performed at 1 to 6000 rpm for 1 second to 60 hours.

In another embodiment, after forming the silicon secondary particles, a step of forming a carbon coating layer on the surface of the silicon secondary particles may be further included.

The invention according to the first embodiment has the following effects.

A silicon anode material of a first embodiment includes silicon secondary particles formed by agglomeration of silicon primary particles, and has bridges connecting adjacent silicon primary particles within the silicon secondary particles. The silicon anode material of the first embodiment has excellent durability by dispersing stress caused by repeated volume expansion and contraction of the silicon secondary particles during the charge and discharge process of a secondary battery due to pores formed by agglomeration of the silicon primary particles. In particular, the silicon anode material of the first embodiment can prevent micronization by maintaining the bridges connecting adjacent silicon primary particles within the silicon secondary particles even when the repeated volume expansion and contraction of the silicon secondary particles occurs during the charge and discharge process of a secondary battery. Meanwhile, the method for manufacturing the silicon anode material of the first embodiment is very simple because the pulverization of silicon raw material powder and the formation of silicon secondary particles are performed in a single process, and is an environmentally friendly process because no organic solvent is used.

The invention according to the second embodiment has the following effects. For reference, the invention according to the second embodiment also has the effects of the first embodiment, and any duplicate explanations thereof will be omitted.

The silicon anode material of the second embodiment solves the problem of low conductivity, which is a shortcoming of conventional silicon anode materials, by providing an electrical conduction path with a conductive material aggregated together with silicon primary particles. Meanwhile, the method for manufacturing the silicon anode material of the second embodiment has the effect of inducing amorphousness of silicon primary particles by mixing a conductive material during the process of grinding silicon raw material powder and forming silicon secondary particles, and forming an internal porous structure in the central portion of the silicon secondary particles.

The invention according to the third embodiment has the following effects. For reference, the invention according to the second embodiment also has the effects of the first embodiment, and any duplicate explanations thereof will be omitted.

The silicon anode material of the third embodiment comprises silicon oxide particles aggregated with silicon primary particles, which serve as a buffer to suppress the repetitive volume expansion and contraction of the silicon secondary particles during the charge and discharge process of the secondary battery. In addition, during the repeated charge and discharge process of the silicon oxide particle secondary battery, silicon particles having a size of several to several tens of nanometers are formed inside, thereby developing capacity. Accordingly, the silicon anode material of the third embodiment can improve the long-life characteristics of the secondary battery.

The first through third embodiments described above can be combined with each other, and when combined, each can have its own unique effects. Furthermore, even if an effect is not explicitly mentioned herein, it should be noted that the effects and potential effects described in the following specification, expected by the technical features of the present invention, are treated as if they were described in the specification of the present invention.

Figure 1 is a schematic flow chart of a method for manufacturing a silicon negative electrode material of the present invention.

FIG. 2 is an electron microscope photograph of silicon secondary particles included in the silicon negative electrode material of the present invention, including (a) an electron microscope photograph of micron silicon before the pulverization-welding process and (b) an electron microscope photograph of silicon particles after the pulverization-welding process.

Figure 3 is a scanning electron microscope image of silicon secondary particles included in the silicon negative electrode material of the present invention, and shows silicon primary particles and bridges connecting them.

FIG. 4 is an electron microscope photograph of a cross-section of a silicon particle after a grinding-welding process according to a method for manufacturing a silicon anode material of the present invention, including (a) an electron microscope photograph of a cross-section of a silicon particle, (b) an electron microscope photograph of a central portion of a silicon particle, and (c) an electron microscope photograph of an edge of a silicon particle.

Figure 5 shows the results of BET analysis of silicon raw material powder (Bare Si) and silicon secondary particles (BMSi).

FIG. 6 is an electron microscope photograph of silicon particles after a grinding-welding process according to a method for manufacturing a silicon anode material of the present invention, showing (left) a case where the grinding-welding process was performed in an inert gas (Ar) atmosphere and (right) a case where the grinding-welding process was performed in an air atmosphere.

Figure 7 shows the results of particle size (D50) analysis according to the time (500 to 1500 min) of the grinding-welding process according to the method for manufacturing a silicon negative electrode material of the present invention.

Figure 8 is an electron microscope photograph after forming a carbon coating layer (graphene) on a silicon secondary particle included in the silicon negative electrode material of the present invention, including (a) an electron microscope photograph of the entire surface and (b) an electron microscope photograph of a cross-section.

Figure 9 is an electron microscope photograph of a carbon coating layer according to the carbon precursor reaction time of the chemical vapor deposition method used in the silicon anode material of the present invention.

Figure 10 shows the results of Raman spectroscopy measurements of silicon secondary particles coated with a carbon coating layer (graphene), with (top) the results when the carbon precursor reaction time is 4 hours and (bottom) the results when the carbon precursor reaction time is 1 hour.

Figure 11 shows the results of measuring the discharge capacity according to the number of repeated charge and discharge cycles of a lithium-ion negative electrode half-cell using a negative electrode material controlled to a capacity of 500 mAh/g by mixing graphite with silicon secondary particles (BMSi@Gr) coated with a carbon coating layer (graphene).

Figure 12 shows the Coulombic efficiency according to the number of repeated charge/discharge cycles of a lithium-ion negative electrode half-cell using a negative electrode material controlled to a capacity of 500 mAh/g by mixing graphite with silicon secondary particles (BMSi@Gr) coated with a carbon coating layer (graphene).

Figure 13 is an electron microscope photograph of the surface of a silicon secondary particle coated with a carbon coating layer (pitch shell).

Figure 14 is a schematic diagram of a silicon secondary particle formed by mixing silicon primary particles and pulverized conductive material.

FIG. 15 is an electron microscope photograph of a silicon secondary particle included in a silicon negative electrode material of the present invention, and relates to a silicon secondary particle formed by mixing silicon primary particles and a pulverized conductive material.

Fig. 16 is an electron microscope photograph of a cross-section of a silicon secondary particle included in a silicon negative electrode material of the present invention, and relates to a silicon secondary particle formed by mixing silicon primary particles and a pulverized conductive material.

Fig. 17 is XRD data of a cross-section of a silicon secondary particle included in a silicon negative electrode material of the present invention, and relates to a silicon secondary particle formed by mixing silicon primary particles and a pulverized conductive material.

Fig. 18 is an electron microscope photograph of a cross-section of a silicon secondary particle included in a silicon negative electrode material of the present invention, in which a carbon coating layer (pitch) is formed on a silicon secondary particle formed by mixing silicon primary particles and a pulverized conductive material.

Figure 19 shows the capacity and coulombic efficiency according to the number of repeated charge/discharge cycles of a lithium ion negative electrode half-cell using a negative electrode material that was mixed with graphite and controlled to a capacity of 500 mAh/g, and formed by mixing silicon primary particles and pulverized conductive materials (BMSi-G@Gr, Example 2-2) coated with a carbon coating layer (pitch).

Figure 20 illustrates Nyquist plots of Example 2-1, Comparative Example 2-1, and Comparative Example 2-2.

Figure 21 shows the capacity and coulombic efficiency according to the number of repeated charge/discharge cycles of a lithium ion negative electrode half-cell using a negative electrode material including silicon secondary particles (BMSi-G@Gr, Example 2-3) coated with a carbon coating layer (pitch) and formed by mixing silicon primary particles and pulverized conductive materials, and shows the capacity and coulombic efficiency according to the number of repeated charge/discharge cycles of the negative electrode half-cell according to the pitch ratio (red graph BMSi-G: Pitch = 1:1, purple graph BMSi-G: Pitch = 1:0.8, blue graph BMSi-G: Pitch = 1:0.6).

Fig. 22 is an electron microscope photograph of a silicon secondary particle included in a silicon negative electrode material of the present invention, and relates to a silicon secondary particle formed by mixing silicon primary particles and pulverized silicon oxide particles.

Fig. 23 is an electron microscope photograph of a cross-section of a silicon secondary particle included in a silicon negative electrode material of the present invention, and relates to a silicon secondary particle formed by mixing silicon primary particles and pulverized silicon oxide particles.

Figure 24 shows the capacity and coulombic efficiency measured according to the number of repeated charge and discharge cycles of a lithium ion negative electrode half-cell using a negative electrode material including silicon secondary particles formed by mixing silicon primary particles and pulverized silicon oxide particles.

Figure 25 shows the XRD measurement results of silicon secondary particles formed by mixing silicon primary particles and pulverized silicon oxide particles according to the pulverization time (when the weight ratio of silicon raw material powder and silicon oxide particles is 20:1).

Figure 26 shows the XRD measurement results of silicon secondary particles formed by mixing silicon primary particles and pulverized silicon oxide particles according to the pulverization time (when the weight ratio of silicon raw material powder and silicon oxide particles is 1:1).

Figure 27 shows the capacity and coulombic efficiency according to the number of repeated charge and discharge cycles of a lithium ion negative electrode half-cell using a negative electrode material including silicon secondary particles (BMSi-SOx@Pitch, Example 3-3) coated with a carbon coating layer (pitch) and formed by mixing silicon primary particles and pulverized silicon oxide particles.

It is to be understood that the attached drawings are provided for reference only to help understand the technical concept of the present invention, and the scope of the present invention is not limited thereby.

Hereinafter, with reference to the drawings, the configuration of the present invention, guided by various embodiments thereof, and the effects resulting from such configurations will be examined. In describing the present invention, detailed descriptions of related, well-known functions that are obvious to those skilled in the art and that may unnecessarily obscure the gist of the present invention will be omitted.

In this patent document, micro silicon means silicon having an average particle size range of several to several hundred micrometers, and nano silicon means silicon having an average particle size of several to several hundred nanometers.

The present invention relates to a silicon anode material comprising secondary particles formed by agglomeration of primary particles, and a method for manufacturing the same. For clarity, various embodiments are described separately below, but the embodiments can be combined with each other.

First, let's look at the first embodiment.

Figure 1 is a schematic flow chart of a method for manufacturing a silicon negative electrode material of the present invention.

The silicon anode material of the present invention includes silicon secondary particles formed by agglomeration of silicon primary particles, and has a bridge connecting adjacent silicon primary particles within the silicon secondary particles.

Here, the silicon primary particles may be formed by milling silicon raw material powder using a milling machine. Submicron and micro silicon powders can be used as the silicon raw material powder, and when silicon raw material powder is milled, nano silicon is formed, and this nano silicon is the silicon primary particle.

However, in the present invention, in the process of pulverizing silicon raw material powder, not only silicon primary particles are formed, but silicon secondary particles having a size of several to several tens of micrometers are formed by agglomerating silicon primary particles having a size of several to several hundred nanometers (see Fig. 2), and bridges connecting adjacent silicon primary particles are formed within the silicon secondary particles by heat and pressure generated during the process of pulverizing the silicon primary particles. As shown in Fig. 3, it can be confirmed that adjacent silicon primary particles are not simply in contact, but bridges are formed by cold welding.

The method for manufacturing the silicon anode material of the invention may use a ball mill such as a planetary mill, an attrition mill, or a bead mill. Silicon raw material powder and milling balls are placed together in a container, and milling can be performed at 1 to 6,000 rpm for 1 second to 60 hours in an air atmosphere or an inert gas atmosphere. The speed and time of the milling can be adjusted to control the size of the silicon primary particles and silicon secondary particles, and to form bridges. Milling balls made of carbon steel, stainless steel, zirconium dioxide, or the like, having a diameter of 0.3 to 100 cm, can be used. The inert gas can be at least one selected from the group consisting of helium, neon, argon, krypton, and xenon.

In the silicon anode material of the present invention, a three-dimensional network is formed by connecting silicon primary particles to some or all of adjacent silicon primary particles by bridges, and thus the silicon secondary particles have a porous structure.

In particular, in the case of the first embodiment, as shown in Fig. 5, the silicon secondary particles may be densely aggregated from the outer periphery to the center. In other words, pores are mainly formed on the outer side of the silicon secondary particles.

During the charge and discharge process of a secondary battery, the silicon anode material undergoes repeated volume expansion and contraction. The porous structure formed within the silicon secondary particles disperses the stress resulting from this expansion and contraction. Furthermore, the porous structure formed within the silicon secondary particles facilitates the movement of lithium and electrons through the pores, thereby enhancing high-speed charge and discharge efficiency.

Meanwhile, repeated volume expansion and contraction of the silicon anode material during the charge and discharge process of the secondary battery causes the silicon anode material to become undifferentiated. In particular, the problem of undifferentiation is more serious in silicon secondary particles formed by agglomeration of silicon primary particles, as in the present invention. However, in the silicon anode material of the present invention, the silicon primary particles are connected to adjacent silicon primary particles by bridges, so that the silicon anode material is robust against the problem of undifferentiation even when it undergoes volume expansion and contraction during the charge and discharge process of the secondary battery.

After forming the silicon secondary particles, a step of coating the silicon secondary particles with a carbon coating layer can be performed. Once the carbon coating layer is formed, the pores of the silicon secondary particles are filled with the carbon coating layer, and the carbon coating layer can act as a buffer to suppress volume expansion and contraction of the silicon anode material during the charge and discharge process of the secondary battery.

The carbon coating layer may be crystalline carbon or amorphous carbon. Crystalline carbon has relatively high conductivity compared to amorphous carbon, and for example, the crystalline carbon may be at least one selected from the group consisting of artificial graphite, natural graphite, and graphene. The amorphous carbon may be at least one selected from the group consisting of hard carbon, soft carbon, petroleum pitch, coal pitch, mesophase pitch, and calcined coke.

Additionally, the carbon coating layer may be composed of a primary coating layer and a secondary coating layer that covers the surface of the silicon secondary particle on which the primary coating layer is formed. The primary coating layer may be crystalline carbon or amorphous carbon, and the secondary coating layer may be crystalline carbon or amorphous carbon. The primary coating layer and the secondary coating layer may be of the same material or different materials.

A carbon coating layer composed of crystalline carbon can be formed through a chemical vapor deposition reaction. The chemical vapor deposition reaction includes a temperature-raising step, a constant temperature step, and a temperature-lowering step. The temperature-raising step can be performed in an atmosphere of hydrogen, nitrogen, argon, etc., the gas flow rate can be 10 to 300 mL/min, and the temperature-raising rate can be 1 to 100°C. The constant temperature can be 600 to 1500°C, and the constant temperature time can be 1 to 1000 min. The temperature-lowering step is performed in an atmosphere of an inert gas such as nitrogen or argon, the gas flow rate can be 10 to 300 mL/min, the temperature-lowering rate can be 1 to 100°C, and natural cooling can be performed after the temperature-lowering step.

A carbon coating layer composed of amorphous carbon can be formed using an amorphous carbon heat treatment reaction process. Heat treatment is performed by mixing silicon secondary particles with at least one amorphous carbon particle selected from the group consisting of hard carbon, soft carbon, petroleum pitch, coal pitch, mesophase pitch, and calcined coke. There are two main mixing methods: wet or dry. For wet coating, the pitch is dissolved in an organic solvent, mixed with the silicon secondary particles, and then dried. The organic solvent can be at least one of acetone, ethanol, tetrahydrofuran (THF), toluene, n-hexane, or quinoline. For dry mixing, the silicon secondary particles and amorphous carbon particles are placed in a mixer and mixed at a speed of 100 to 7,000 RPM for a processing time of 10 seconds to 1 hour. Once the amorphous carbon particles are coated or mixed with the silicon secondary particles, heat treatment is performed. High-temperature heat treatment includes a temperature-raising step, a constant temperature step, and a temperature-lowering step. The temperature-raising step is performed in an atmosphere such as nitrogen or argon, the gas flow rate is 10 to 300 mL/min, and the temperature-raising rate is 1 to 100°C. The constant temperature is 100 to 1500°C, and the constant temperature time is 1 to 1000 min. The temperature-lowering step is performed in an inert gas atmosphere such as nitrogen or argon, the gas flow rate is 10 to 300 mL/min, the temperature-lowering rate is 1 to 100°C, and natural cooling is performed after the temperature-lowering step.

Example 1-1

5 g of silicon raw material powder and 100 g of SUS milling balls were placed in a planetary milling container and milled at 300 rpm for 500 minutes in air. The milled sample was taken out of the container and separated from the balls to obtain a silicon anode material sample.

Example 1-2

5 g of silicon raw material powder and 100 g of SUS milling balls were placed in a planetary milling container and milled at 300 rpm for 500 minutes in an inert gas (Ar) atmosphere. The milled sample was taken out of the container and separated from the balls to obtain a silicon anode material sample.

Example 1-3

5 g of silicon raw material powder and 100 g of SUS milling balls were placed in a planetary milling container and milled at 300 rpm for 750 minutes in air. The milled sample was taken out of the container and separated from the balls to obtain a silicon anode material sample.

Example 1-4

A chemical vapor deposition reaction was used to form a carbon coating layer on the silicon secondary particle (BMSi) produced in Example 1-1. A tube furnace was used, and the furnace atmosphere was maintained as an inert atmosphere with argon gas during heating, and then heat treatment was performed at 1000 degrees for 1 hour in a methane (CH ₄ ) gas atmosphere.

Example 1-5

A pitch heat treatment reaction was used to form a pitch shell coating layer on the surface of the silicon secondary particles (BMSi) manufactured in Example 1-4. The silicon secondary particles and pitch particles were mixed in a solvent (THF) and then heat treated. The heat treatment was performed using a tube furnace, and the furnace atmosphere was maintained as an inert atmosphere with argon gas from the temperature rise to the heat treatment. The heat treatment of the pitch-coated silicon secondary particles (BMSi) was performed in two stages, more specifically, heat treatment was performed at 300°C for 2 hours and at 1000°C for 1 hour.

Example 1-6

A chemical vapor deposition reaction was used to form a carbon coating layer on the silicon secondary particles (BMSi) produced in Example 1-2. A tube furnace was used, and the furnace atmosphere was maintained as an inert atmosphere with argon gas during heating, and then heat treatment was performed at 1000 degrees for 1 hour in a methane (CH ₄ ) gas atmosphere.

Comparative Example 1-1

5g of silicon raw material powder and 100g of SUS milling balls were placed in a planetary milling machine container and milled at 300 rpm for 1250 minutes in the air. The milled sample was taken out of the container and separated from the balls to obtain a silicon anode sample. A carbon coating layer was formed on the surface of the manufactured silicon anode material. A chemical vapor deposition reaction was used to form the carbon coating layer. A tube furnace was used, and the furnace atmosphere was made inert with argon gas during heating, and then heat treatment was performed at 1000 degrees for 1 hour in a methane (CH ₄ ) gas atmosphere.

Comparative Example 1-2

5g of silicon raw material powder and 100g of SUS milling balls were placed in a planetary milling machine container and milled at 300 rpm for 1500 minutes in the air. The milled sample was taken out of the container and separated from the balls to obtain a silicon anode sample. A carbon coating layer was formed on the surface of the manufactured silicon anode material. A chemical vapor deposition reaction was used to form the carbon coating layer. A tube furnace was used, and the atmosphere inside the furnace was made inert with argon gas during heating, and then heat treatment was performed at 1000 degrees for 1 hour in a methane (CH ₄ ) gas atmosphere.

Experimental Example 1

FIG. 2 is an electron microscope photograph of silicon secondary particles included in the silicon anode material of Example 1-1, including (a) an electron microscope photograph of micron silicon before the pulverization-welding process and (b) an electron microscope photograph of silicon particles after the pulverization-welding process, FIG. 3 is an electron microscope photograph of silicon secondary particles included in the silicon anode material of Example 1-1, observing silicon primary particles and bridges connecting them, and FIG. 4 is an electron microscope photograph of a cross-section of silicon particles after the pulverization-welding process according to the method for manufacturing the silicon anode material of Example 1-1, including (a) an electron microscope photograph of a cross-section of silicon particles, (b) an electron microscope photograph of a central portion of silicon particles, and (c) an electron microscope photograph of an edge of silicon particles.

As shown in Fig. 2, silicon secondary particles are formed in a spherical shape. Silicon primary particles have a particle size of several to several hundred nanometers. These nano-sized silicon primary particles aggregate to form silicon secondary particles, which have a particle size of several to several tens of micrometers.

In addition, as can be seen in Fig. 3, adjacent silicon primary particles are connected to each other by bridges. That is, no binder or the like was added to bind the silicon primary particles together other than the silicon raw material powder and milling balls, and without any separate heat treatment, bridges were formed between the silicon primary particles by cold welding due to the heat and pressure generated during the milling process of the silicon raw material powder.

Meanwhile, as shown in Figure 4, pores are formed as silicon primary particles aggregate. At this time, silicon secondary particles are formed as the silicon primary particles aggregate more densely from the periphery to the center. In other words, pores are mainly distributed on the periphery of silicon secondary particles.

Figure 5 shows the results of BET analysis of silicon raw material powder (Bare Si) and silicon secondary particles (BMSi) of Example 1-1. As seen in Figure 5, the silicon secondary particles of Example 1-1 have a significantly larger specific surface area than the silicon raw material powder, confirming that pores were formed in the silicon secondary particles.

FIG. 6 is an electron microscope photograph of silicon particles after a grinding-welding process according to a method for manufacturing a silicon anode material of the present invention, showing (left) a case where the grinding-welding process was performed in an inert gas (Ar) atmosphere (Example 1-2) and (right) a case where the grinding-welding process was performed in an air atmosphere (Example 1-1).

Comparing Examples 1-1 and 1-2, in which grinding-welding was performed in an inert gas atmosphere, it can be confirmed that silicon primary particles were aggregated even when grinding-welding was performed in an inert gas atmosphere.

Figure 7 shows the results of particle size (D50) analysis according to the time (500 to 1500 min) of the grinding-welding process according to the method for manufacturing a silicon negative electrode material of the present invention, and the results are summarized in Table 1.

condition Milling time (min.) D ₅₀ (μm) Example 1-1 500 5.29 Example 1-3 750 3.61 Comparative Example 1-1 1250 3.72 Comparative Example 1-2 1500 3.81

As shown in Table 1, particle size is controlled by milling time. As the milling time increases, the particle size ( _D50 ) decreases, converging to 3.6 to 3.8 μm for the silicon secondary particles. Furthermore, as shown in Fig. 7, spheroidization becomes less effective as the milling time increases. Therefore, a milling time of 300 to 1,000 minutes is preferable based on 300 rpm. However, it should be noted that the milling time may vary depending on the milling speed.

Figure 8 is an electron microscope photograph of a silicon secondary particle included in a silicon anode material of Example 1-4 after forming a carbon coating layer (graphene), including (a) an electron microscope photograph of the entire surface and (b) a cross-sectional electron microscope photograph.

As can be seen in Fig. 8, it can be confirmed that graphene was formed on the surface of the silicon secondary particle by chemical vapor deposition. In particular, when chemical vapor deposition was used, it can be seen that graphene was uniformly grown not only on the surface and external pores of the silicon secondary particle but also in the internal pores. Therefore, a three-dimensional conductive network is formed inside the silicon secondary particle by the carbon coating layer. In addition, the carbon coating layer filled in the pores acts as a buffer to suppress the volume expansion-contraction behavior of the silicon anode material during the charge-discharge process of the secondary battery.

FIG. 9 is an electron microscope photograph of a carbon coating layer according to the carbon precursor reaction time of the chemical vapor deposition method used in the silicon anode material of the present invention, and FIG. 10 is a Raman spectroscopy measurement result of a silicon secondary particle coated with a carbon coating layer (graphene), showing the measurement results when (top) the carbon precursor reaction time is 4 hours and (bottom) the carbon precursor reaction time is 1 hour.

As shown in Figure 9, the shape of the carbon coating layer varies depending on the carbon precursor reaction time of the chemical vapor deposition method, and as the reaction time increases, the thickness and length of the graphene increase. Furthermore, as shown in Figure 10, the Raman spectroscopy measurement results also showed excellent crystallinity.

Fig. 11 shows the results of measuring the discharge capacity according to the number of repeated charge/discharge cycles of a lithium-ion negative electrode half-cell using a negative electrode material mixed with graphite and controlled to a capacity of 500 mAh/g in a silicon secondary particle (BMSi@Gr) coated with a carbon coating layer (graphene), and Fig. 12 shows the results of measuring the coulombic efficiency according to the number of repeated charge/discharge cycles of a lithium-ion negative electrode half-cell using a negative electrode material mixed with graphite and controlled to a capacity of 500 mAh/g in a silicon secondary particle (BMSi@Gr) coated with a carbon coating layer (graphene). Table 2 below summarizes the discharge capacity and coulombic efficiency.

volume
(mAh/g) ICE
(%) Retention
(%, @40cycle) Comparative Example 1-1 547 87.0 76.1 Comparative Example 1-2 541 87.3 95.3 Example 1-4 546 85.9 95.4 Example 1-6 529 82.0 93.4

Referring to FIGS. 11 and 12 and Table 1, the discharge capacity according to the number of silicon charge/discharge cycles of Example 1-4 was maintained more stably, and high Coulombic efficiency was shown. In addition, even in the case of Example 1-6, where the grinding-welding process was performed in an inert gas atmosphere, high capacity retention and Coulombic efficiency were shown. This means that the technology proposed in the present invention can solve the problem of volume expansion-contraction, which is a chronic problem of silicon anode materials, and can provide long-life characteristics. In the case of Comparative Example 1-1, the capacity tended to decrease as the cycle progressed, and in the case of Comparative Example 1-2, there was a problem of low Coulombic efficiency.

Figure 13 is an electron microscope photograph of the surface of a silicon secondary particle coated with a carbon coating layer (pitch shell) of Example 1-5.

Referring to Figure 13, it can be seen that a peach shell is smoothly coated on a silicon secondary particle having a graphene coating layer, filling the porous structure of the surface. When a peach shell coating layer is formed in this way, the surface pores are filled, reducing the specific surface area and preventing excessive inflow of electrolyte.

Next, let's examine the second embodiment. It should be noted that some parts that overlap with the first embodiment may be omitted.

Figure 14 is a schematic diagram of a silicon secondary particle formed by mixing silicon primary particles and pulverized conductive material.

In the second embodiment, the silicon anode material is produced by milling silicon raw material powder while the silicon raw material powder and conductive material are added together.

Accordingly, the silicon anode material of the second embodiment includes silicon secondary particles formed by agglomeration of silicon primary particles and conductive materials, and has a bridge connecting adjacent silicon primary particles within the silicon secondary particles.

The conductive material may be at least one selected from the group consisting of graphene, carbon nanotubes, carbon nanofibers, graphite, and earth graphite, and the conductive material may be included in an amount of 1 to 15 wt% based on the silicon secondary particles.

In carrying out the method for manufacturing a silicon anode material of the present invention, silicon raw material powder is pulverized in the presence of a conductive material to form silicon primary particles and then silicon secondary particles are assembled. During this process, the addition of a conductive material (particularly, a carbon-based conductive material) results in the formation of pores in the central portion of the silicon secondary particles at a level similar to that of the peripheral portion, unlike the first embodiment.

Meanwhile, the conductive material coagulated within the silicon secondary particles with the silicon primary particles provides an electrical conduction path, thereby resolving the low conductivity problem of conventional silicon anode materials without the need for a separate carbon coating layer. This suggests that the conductivity issue can be resolved without a separate carbon coating layer, but this does not preclude the formation of an additional carbon coating layer.

Example 2-1

Example 2-1 4.8 g of silicon raw material powder and 0.2 g of graphene powder were placed together with 100 g of SUS balls in a planetary milling container and milled at 300 rpm for 500 minutes in the air. The milled sample was taken out of the container and separated from the balls to obtain a silicon anode material sample.

Example 2-2

A carbon coating layer was formed on the silicon secondary particles (BMSi-G) manufactured in Example 2-1. A tube furnace was used to form the carbon coating layer. The furnace atmosphere was maintained as an inert atmosphere with argon gas from the temperature rise to the heat treatment. 1 g of the silicon secondary particles (BMSi-G) of Example 2-1 and 0.7 g of petroleum pitch were mixed using a spherical coater and then heat treated. The heat treatment of the pitch-coated silicon secondary particles (BMSi-G@Pitch) was performed in two stages: at 300 degrees for 2 hours and at 1000 degrees for 1 hour.

Example 2-3

A carbon coating layer was formed on the silicon secondary particles (BMSi-G) manufactured in Example 2-1. A tube furnace was used to form the carbon coating layer. The furnace atmosphere was maintained as an inert atmosphere with argon gas from the heating to the heat treatment. 1 g of the silicon secondary particles (BMSi-G) of Example 2-1 and 1, 0.8, and 0.6 g of petroleum pitch were each dissolved in tetrahydrofuran (THF), mixed, and then heat-treated. The heat treatment of the pitch-coated silicon secondary particles (BMSi-G@Pitch) was performed in two stages: at 300 degrees for 2 hours and at 1000 degrees for 1 hour.

Comparative Example 2-1

Bare silicone was used.

Comparative Example 2-2

5 g of silicon raw material powder and 100 g of SUS milling balls were placed in a planetary milling container and milled at 300 rpm for 500 minutes in air. The milled sample was taken out of the container and separated from the balls to obtain a silicon anode material sample.

Next, the manufactured silicon secondary particles (BMSi) were coated with a carbon coating layer (pitch). 1 g of the manufactured silicon secondary particles (BMSi) and 0.7 g of petroleum pitch were mixed using a spherical coater and then heat-treated. The heat treatment of the pitch-coated silicon secondary particles (BMSi @Pitch) was performed in two stages: at 300°C for 2 hours and at 1000°C for 1 hour.

Experimental Example 2

FIG. 15 is an electron microscope photograph of a silicon secondary particle included in a silicon negative electrode material of Example 2-1, and relates to a silicon secondary particle formed by mixing silicon primary particles and a pulverized conductive material, and FIG. 16 is an electron microscope photograph of a cross-section of a silicon secondary particle included in a silicon negative electrode material of Example 2-1, and relates to a silicon secondary particle formed by mixing silicon primary particles and a pulverized conductive material.

As shown in Fig. 15, silicon secondary particles are formed in a spherical shape. Silicon primary particles have a particle size of several to several hundred nanometers. These nano-sized silicon primary particles and pulverized conductive materials aggregate to form silicon secondary particles, which have a particle size of several to several tens of micrometers.

Meanwhile, as seen in Fig. 16, pores are formed as the silicon primary particles aggregate. At this time, it can be confirmed that the silicon secondary particles of Example 2-1 have pores developed even in the central portion, unlike the silicon secondary particles of Example 1-1.

Figure 17 is XRD data of a cross-section of a silicon secondary particle included in a silicon negative electrode material of the present invention, and is the result of measuring the silicon secondary particle by forming it in the same manner as Example 2-1 but changing the content of a conductive material (graphene).

Referring to Figure 17, it can be seen that as the proportion of the conductive material (graphene) increases, the crystalline state of silicon changes to an amorphous state. That is, the conductive material (graphene) induces amorphousness of the particles when the silicon raw material powder is pulverized and induces the formation of a porous structure in the central portion.

Fig. 18 is an electron microscope photograph of a cross-section of a silicon secondary particle included in a silicon negative electrode material of Example 2-2, and relates to a carbon coating layer (pitch) formed on a silicon secondary particle formed by mixing silicon primary particles and a pulverized conductive material.

Referring to Figure 18, it can be confirmed that the outer and central pores formed by the silicon primary particles and the pulverized conductive material are evenly filled with pitch. The pore-filled pitch enhances the conductivity of the silicon secondary particles and acts as a protective layer.

Figure 19 shows the capacity and coulombic efficiency according to the number of repeated charge/discharge cycles of a lithium ion negative electrode half-cell using a negative electrode material that was mixed with graphite and controlled to a capacity of 500 mAh/g, and formed by mixing silicon primary particles and pulverized conductive materials (BMSi-G@Gr, Example 2-2) coated with a carbon coating layer (pitch).

Referring to Fig. 19, it can be confirmed that when a conductive material is incorporated into the interior of a silicon secondary particle to impart conductivity, the discharge capacity is maintained very stably according to the number of charge/discharge cycles, and at the same time, high Coulombic efficiency is exhibited. This means that the technology proposed in the present invention can solve the problem of volume expansion and contraction, which is a chronic problem of silicon anode materials, and can achieve long-term life characteristics.

Figure 20 shows Nyquist plots after 10 cycles of Example 2-1, Comparative Example 2-1, and Comparative Example 2-2.

Referring to FIG. 20, it can be seen that Example 2-1, in which silicon primary particles and pulverized conductive material (graphene) are aggregated to form silicon secondary particles, has a lower resistance value than Comparative Examples 2-1 and 2-2.

Figure 21 shows the capacity and coulombic efficiency according to the number of repeated charge/discharge cycles of a lithium ion negative electrode half-cell using a negative electrode material including silicon secondary particles (BMSi-G@Gr, Example 2-3) coated with a carbon coating layer (pitch) and formed by mixing silicon primary particles and pulverized conductive materials, and shows the capacity and coulombic efficiency according to the number of repeated charge/discharge cycles of the negative electrode half-cell according to the pitch ratio (red graph BMSi-G: Pitch = 1:1, purple graph BMSi-G: Pitch = 1:0.8, blue graph BMSi-G: Pitch = 1:0.6).

Referring to Figure 21, as the pitch amount decreases, the capacity increases. However, Coulomb efficiency is unrelated to the pitch amount. Therefore, in the present invention, the capacity can be controlled by adjusting the pitch amount.

Next, let's examine the third embodiment. It should be noted that some parts that overlap with the first embodiment may be omitted.

In the silicon anode material of the third embodiment, the milling process of the silicon raw material powder is performed in a state where the silicon raw material powder and silicon oxide SiO _x (where 0<X≤2) particles are input together.

Accordingly, the silicon anode material of the third embodiment includes silicon secondary particles formed by agglomeration of silicon primary particles and silicon oxide particles, and has a bridge connecting adjacent silicon primary particles within the silicon secondary particles.

The content of the silicon oxide particles may be 2 to 50 wt% based on the silicon secondary particles.

The silicon anode material of the third embodiment comprises silicon oxide particles aggregated with silicon primary particles, which serve as a buffer to suppress the repetitive volume expansion and contraction of the silicon secondary particles during the charge and discharge process of the secondary battery. In addition, during the repeated charge and discharge process of the silicon oxide particle secondary battery, silicon particles having a size of several to several tens of nanometers are formed inside, thereby developing capacity. Accordingly, the silicon anode material of the third embodiment can improve the long-life characteristics of the secondary battery.

Example 3-1

4.8 g of silicon raw material powder and 0.2 g of SiO ₂ (D ₅₀ ~ 1 μm) were placed in a planetary milling vessel with 100 g of SUS balls in the air and milled at 300 rpm for 250 minutes. The milled sample was taken out of the vessel and separated from the balls to obtain a silicon anode material sample.

Example 3-2

4.8 g of silicon raw material powder and 0.2 g of SiO ₂ (D ₅₀ ~ 1 μm) were placed in a planetary milling vessel with 100 g of SUS balls in the air and milled at 300 rpm for 750 minutes. The milled sample was taken out of the vessel and separated from the balls to obtain a silicon anode material sample.

Example 3-3

4.76 g of silicon raw material powder and 0.24 g of SiO ₂ (D ₅₀ ~ 1 μm) were placed in a planetary milling vessel with 100 g of SUS balls in the air and milled at 300 rpm for 500, 750, 1000, and 1250 minutes. The milled sample was taken out of the vessel and separated from the balls to obtain a silicon anode material sample.

Example 3-4

2.5 g of silicon raw material powder and 2.5 g of SiO ₂ (D ₅₀ ~ 1 μm) were placed in a planetary milling vessel with 100 g of SUS balls in the air and milled at 300 rpm for 500, 750, 1000, and 1250 minutes. The milled sample was taken out of the vessel and separated from the balls to obtain a silicon anode material sample.

Example 3-5

4.5 g of silicon raw material powder and 0.5 g of SiOx (0<X<2) were placed in a planetary milling vessel with 100 g of SUS balls in the air and milled at 300 rpm for 500 min. The milled sample was taken out of the vessel and separated from the balls to obtain a sample. A tube furnace was used to carbon-coat the secondary particles (BMSi-SOx) milled with silicon powder and SiOx (0<X<2), and the furnace atmosphere was kept inert with argon gas from the temperature rising to the heat treatment. 1 g of the secondary particles (BMSi-SOx) milled with silicon and SiOx (0<X<2) and 0.7 g of petroleum pitch were mixed using a spherical coater and then heat treated. The heat treatment of the secondary particles (BMSi-SOx@Pitch) milled together with pitch-coated silicon and SiOx (0<X<2) was performed in two steps: at 300°C for 2 hours and at 1000°C for 1 hour.

Comparative Example 3-1

4.55 g of silicon raw material powder and 0.35 g of SiOx (0<X<2) were placed in a planetary milling vessel with 100 g of SUS balls in the air and milled at 300 rpm for 500 min. The milled sample was taken out of the vessel and separated from the balls to obtain a sample. A tube furnace was used to carbon-coat the secondary particles (BMSi-SOx) milled with silicon powder and SiOx (0<X<2), and the furnace atmosphere was kept inert with argon gas from the temperature rising to the heat treatment. 1 g of the secondary particles (BMSi-SOx) milled with silicon and SiOx (0<X<2) and 0.7 g of petroleum pitch were mixed using a spherical coater and then heat treated. The heat treatment of the secondary particles (BMSi-SOx@Pitch) milled together with pitch-coated silicon and SiOx (0<X<2) was performed in two steps: at 300°C for 2 hours and at 1000°C for 1 hour.

Comparative Example 3-2

4.8 g of silicon raw material powder and 0.2 g of SiOx (0<X<2) were placed in a planetary milling vessel with 100 g of SUS balls in the air and milled at 300 rpm for 500 min. The milled sample was taken out of the vessel and separated from the balls to obtain a sample. A tube furnace was used to carbon-coat the secondary particles (BMSi-SOx) milled with silicon powder and SiOx (0<X<2), and the furnace atmosphere was kept inert with argon gas from the temperature rising to the heat treatment. 1 g of the secondary particles (BMSi-SOx) milled with silicon and SiOx (0<X<2) and 0.7 g of petroleum pitch were mixed using a spherical coater and then heat treated. The heat treatment of the secondary particles (BMSi-SOx@Pitch) milled together with pitch-coated silicon and SiOx (0<X<2) was performed in two steps: at 300°C for 2 hours and at 1000°C for 1 hour.

Experimental Example 3

FIG. 22 is an electron microscope photograph of a silicon secondary particle included in a silicon anode material of the present invention, and relates to a silicon secondary particle formed by mixing silicon primary particles and pulverized silicon oxide particles, and FIG. 23 is an electron microscope photograph of a cross-section of a silicon secondary particle included in a silicon anode material of the present invention, and relates to a silicon secondary particle formed by mixing silicon primary particles and pulverized silicon oxide particles.

As shown in Fig. 22, silicon secondary particles are formed in a spherical shape. Silicon primary particles have a particle size of several to several hundred nanometers. These nano-sized silicon primary particles and pulverized silicon oxide particles aggregate to form silicon secondary particles, which have a particle size of several to several tens of micrometers.

Meanwhile, as shown in Figure 23, pores are formed as the silicon primary particles aggregate. At this time, the silicon oxide particles are larger than the silicon primary particles. The size of the silicon oxide particles can range from tens to hundreds of nanometers.

Figure 24 shows the capacity and coulombic efficiency measured according to the number of repeated charge/discharge cycles of a lithium ion negative electrode half-cell using a negative electrode material including silicon secondary particles of Examples 3-1 and 3-2.

Referring to Fig. 24, in the case of Example 3-2, which has a long milling time, the capacity is expressed by about 250 mAh/g more than in Example 3-1, and the long-life efficiency is also higher than in Example 3-1.

Fig. 25 shows the XRD measurement results of silicon secondary particles formed by mixing silicon primary particles and pulverized silicon oxide particles according to the pulverization time (when the weight ratio of silicon raw material powder and silicon oxide particles is 20:1), and Fig. 26 shows the XRD measurement results of silicon secondary particles formed by mixing silicon primary particles and pulverized silicon oxide particles according to the pulverization time (when the weight ratio of silicon raw material powder and silicon oxide particles is 1:1). Fig. 25 relates to Example 3-3, and Fig. 26 relates to Example 3-4.

Referring to FIGS. 25 and 26, it can be seen that when silicon and SiO ₂ (D ₅₀ ~ 1 μm) are milled together, the XRD results vary depending on the ratio of the heterogeneous materials. As the ratio of SiO ₂ (D ₅₀ ~ 1 μm) powder increases and the milling time increases, the full width at half maximum (FWHM) of the silicon crystal increases, which means that the crystal domain decreases. As the crystal domain decreases, it is advantageous for the longevity efficiency of the silicon anode material.

Figure 27 shows the capacity and coulombic efficiency measured according to the number of repeated charge and discharge cycles of a lithium ion negative electrode half-cell using a negative electrode material including silicon secondary particles (BMSi-SOx@Pitch, Example 3-5) coated with a carbon coating layer (pitch) and formed by mixing silicon primary particles and pulverized silicon oxide particles.

As can be seen in Fig. 27, the silicon anode material of Example 3-5 has a higher capacity retention rate and better Coulombic efficiency than Comparative Examples 3-1 and 3-2.

The scope of protection of the present invention is not limited to the description and expression of the embodiments explicitly described above. Furthermore, it should be noted that the scope of protection of the present invention may not be limited by obvious modifications or substitutions within the technical field to which the present invention pertains.

Claims (14)

A silicon anode material comprising silicon secondary particles formed by agglomeration of silicon primary particles, wherein the silicon secondary particles have bridges connecting adjacent silicon primary particles. In the first paragraph, The above silicon secondary particles are silicon negative electrode materials formed by coagulating the silicon primary particles and a conductive material. In the second paragraph, The above conductive material is a silicon anode material selected from the group consisting of graphene, carbon nanotubes, carbon nanofibers, graphite, and graphite. In the first paragraph, The above silicon secondary particles are silicon negative electrode materials formed by coagulating silicon primary particles and silicon oxide SiO _x (where 0<X≤2) particles. In the first paragraph, The above bridge is a silicon anode material formed by cold welding. In the first paragraph, A silicon anode material having a carbon coating layer formed on the surface of the above silicon secondary particle. In paragraph 6, The above carbon coating layer is a silicon anode material which is crystalline carbon or amorphous carbon. A method for manufacturing a silicon anode material, wherein silicon primary particles are formed by crushing silicon raw material powder using a milling machine, and at the same time, the silicon primary particles are aggregated to form silicon secondary particles, and bridges connecting adjacent silicon primary particles are formed within the silicon secondary particles by heat and pressure generated during the crushing process of the silicon primary particles. In paragraph 8, A method for manufacturing a silicon anode material, wherein the crushing of silicon raw material powder and the formation of silicon secondary particles are performed in an air atmosphere. In paragraph 8, A method for manufacturing a silicon anode material, wherein the crushing of silicon raw material powder and the formation of silicon secondary particles are performed in an inert gas atmosphere. In paragraph 8, A method for manufacturing a silicon anode material, comprising mixing the silicon raw material powder and the conductive material and then grinding the mixture of the silicon raw material powder and the conductive material using a milling machine. In paragraph 8, A method for manufacturing a silicon anode material, comprising mixing the above silicon raw material powder and silicon oxide SiO _x (provided that 0<X≤2) particles and then grinding the mixture of the silicon raw material powder and silicon oxide SiO _x (provided that 0<X≤2) particles using a milling machine. In paragraph 8, A method for manufacturing a silicon anode material, wherein the above silicon raw material powder is ground at 1 to 6000 rpm for 1 second to 60 hours. In paragraph 8, A method for manufacturing a silicon negative electrode material, further comprising the step of forming a carbon coating layer on the surface of the silicon secondary particles after forming the silicon secondary particles.