Silicon-carbon composite for secondary battery anode material and manufacturing method thereof

Abstract

The present invention relates to a silicon-carbon composite for use as an anode material for secondary batteries, which can improve the initial discharge capacity (IDC), initial efficiency (ICE), and life characteristics of secondary batteries, and a manufacturing method thereof. More specifically, the present invention provides a silicon-carbon composite formed from a silicon-pitch composite containing nanosilicon particles and high softening point pitch, wherein the nanosilicon particles have an average particle size (D50) of 150 nm or less, the high softening point pitch has a softening point of 200 to 300°C, and the high softening point pitch has an average particle size (D50) of 0.5 to 2 μm, and an anode material for secondary batteries containing the silicon-carbon composite.

Description

[Technical Field]

[0001] The present invention relates to a silicon-carbon composite for use as an anode material for secondary batteries, which can improve the initial discharge capacity (IDC), initial efficiency (ICE) and life characteristics of secondary batteries, and a method for producing the same. [Background technology]

[0002] The improvement in the performance of secondary batteries is based on the components of the positive electrode material, negative electrode material, and electrolyte.

[0003] Among the above components, graphite-based materials, which are mainly used as anode materials, are commonly used commercially due to their excellent electrochemical properties and low cost. However, their theoretical capacity is limited to 370 mAh / g, which limits their application to high-capacity secondary batteries.

[0004] To overcome these limitations, non-graphite anode materials such as silicon, tin, and germanium have emerged as alternatives, with silicon attracting attention as a potential graphite replacement due to its theoretical capacity of 4000-4200mAh / g, roughly 10 times higher than that of graphite. However, despite its high theoretical capacity, silicon experiences a large volume expansion of approximately 400% during charging and discharging, which can lead to structural damage and a shorter lifespan.

[0005] One method for alleviating the volumetric expansion of silicon is to mix it with a carbon material to produce a composite. Applying this composite as a negative electrode material for secondary batteries to improve the performance of secondary batteries has become an important issue.

[0006] For example, a method has been developed in which a slurry containing nanosilicon (Nano Si) particles is formed from spherical powder particles, and then the surfaces of the spherical powder particles are coated with pitch as a carbon material. By adjusting the properties of the composite using the nanosilicon particles and pitch, it is possible to further improve the initial discharge capacity, initial efficiency, and life characteristics of secondary batteries. Therefore, there is a need to develop a high-quality silicon-carbon composite for use as a secondary battery anode material, and a manufacturing method thereof. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a secondary battery negative electrode material including a silicon-carbon composite produced using a silicon-pitch composite containing nanosilicon particles and high softening point pitch, and a method for producing the same.

[0008] Another object of the present invention is to provide the anode material for a secondary battery, an anode material for a secondary battery including the same, and a secondary battery, so that the initial discharge capacity, initial efficiency, and life characteristics of the secondary battery can be improved.

[0009] The technical object of the present invention is not limited to the above-mentioned objects, and other unmentioned objects and advantages of the present invention can be understood from the following description and can be more clearly understood from the examples of the present invention. Furthermore, it can be easily understood that the objects and advantages of the present invention can be achieved by the means and combinations thereof set forth in the claims. [Means for solving the problem]

[0010] According to one aspect of the present invention, there is provided a silicon-carbon composite for use as a secondary battery negative electrode material, which is formed from a silicon-pitch composite containing nanosilicon particles and high-softening point pitch, wherein the nanosilicon particles have an average particle size (D50) of 150 nm or less, the high-softening point pitch has a softening point of 200 to 300°C, and the high-softening point pitch has an average particle size (D50) of 0.5 to 2 μm.

[0011] According to another aspect of the present invention, (a) mixing a high-softening-point pitch having a softening point of 200 to 300°C with a solvent and then wet-pulverizing the mixture to prepare a pulverized pitch slurry having an average particle size (D50) of 0.5 to 2 μm; (b) mixing silicon particles with a solvent and then pulverizing the mixture to prepare a nanosilicon particle slurry having an average particle size (D50) of 150 nm or less; (c) mixing the ground pitch slurry of step (a) with the nanosilicon particle slurry of step (b) to form a pitch-silicon particle mixed slurry; (d) drying the pitch-silicon particle mixed slurry to form spherical powder particles; and (e) carbonizing the spherical powder particles; The present invention provides a method for producing a silicon-carbon composite for use as a secondary battery negative electrode material, comprising the steps of:

[0012] According to yet another aspect of the present invention, there is provided an anode material for a secondary battery, including a silicon-carbon composite manufactured using the silicon-pitch composite according to an aspect of the present invention. [Effects of the Invention]

[0013] The silicon-carbon composite, which is a secondary battery anode material according to the present invention, may have an optimized pore size and ratio within the composite, thereby improving the initial discharge capacity, initial efficiency, and lifespan characteristics of a secondary battery manufactured using the composite as an anode material.

[0014] The above-mentioned effects and specific effects of the present invention will be described in conjunction with the following description of the preferred embodiment of the invention. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a flowchart showing a method for producing a secondary battery negative electrode material according to one embodiment of the present invention. [Figure 2]1 is a graph showing an analysis of the diameter of the pulverized pitch of Example 1. [Figure 3] 1 is a graph showing the analysis of the diameter of nanosilicon particles in Example 1. [Figure 4] FIG. 1 is a SEM image of the silicon-carbon composite produced in Example 1. [Figure 5] FIG. 1 is a SEM image of the silicon-carbon composite produced in Example 1. [Figure 6] FIG. 1 is a SEM image of the silicon-carbon composite produced in Example 1. [Figure 7] 1 is a graph showing an analysis of the diameter of the pulverized pitch of Comparative Example 1. [Figure 8] FIG. 2 is a SEM image of the silicon-carbon composite produced in Comparative Example 1. [Figure 9] FIG. 2 shows an SEM image of the silicon-carbon composite produced in Example 2. [Figure 10] FIG. 1 shows an SEM image of the silicon-carbon composite produced in Comparative Example 2. [Figure 11] 1 is a graph showing the life characteristics at 50 cycles of Examples 1 and 2 and Comparative Examples 1 and 2 (vertical axis: specific capacity at 50 cycles, horizontal axis: number of cycles). DETAILED DESCRIPTION OF THE INVENTION

[0016] The above-mentioned objects, features, and advantages will be described in detail below with reference to the accompanying drawings, so that those skilled in the art can easily implement the technical concept of the present invention. In describing the present invention, if a detailed description of known technologies relating to the present invention is deemed to obscure the gist of the present invention, the detailed description will be omitted. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings are used to indicate the same or similar components.

[0017] Of the contents not described in this specification, explanations of those that can be sufficiently inferred from a technical standpoint by a person of ordinary skill in this technical field will be omitted.

[0018] Hereinafter, when an arbitrary configuration is arranged "on top (or bottom)" of a component or "above (or below)" a component, it means that the arbitrary configuration is not only arranged in contact with the upper surface (or lower surface) of the component, but also that other configurations may be interposed between the component and the arbitrary configuration arranged above (or below) the component.

[0019] Furthermore, when a component is described as being "coupled," "coupled," or "connected" to another component, it should be understood that the components may be directly coupled or connected to each other, but that other components may be "intervening" between the components, or that each component may be "coupled," "coupled," or "connected" via other components.

[0020] In this specification, the term "silicon-pitch composite" refers to a composite material in which silicon and pitch are mixed, and the term "silicon-carbon composite" can be described as referring to a composite material in which the pitch has been converted into carbon after the silicon-pitch composite has been subjected to a carbonization process.

[0021] The term "average particle size" as used herein may refer to "D50" measured using a particle size analyzer (LS13 320 Laser Diffraction Particle Size Analyzer; manufactured by BECKMAN COULTER), which is used to define and measure the sizes of the pitch particles, silicon particles, and the final silicon-carbon composite in the present invention.

[0022] The term "average diameter" as used herein is intended to define the size of the "pores" in the silicon-carbon composite of the present invention, and may refer to the size measured by <Measurement Method 2: Pore Size and Porosity> described below in this specification.

[0023] The silicon-carbon composite for use as a secondary battery negative electrode material according to the present invention and the method for producing the same will be described in detail below.

[0024] <Silicon-carbon composite for secondary battery anode material> According to one aspect of the present invention, a silicon-carbon composite serving as a secondary battery anode material may be formed from a silicon-pitch composite containing nanosilicon particles and high-softening-point pitch. To manufacture the silicon-carbon composite serving as a secondary battery anode material, a slurry is prepared by mixing silicon particles and a pitch composite, and the resulting silicon-pitch composite is then carbonized to form spherical powder particles.

[0025] Through the carbonization process, silicon particles remain as a skeleton, and the high softening point pitch undergoes a 30-50% volume (weight) reduction during carbonization, generating pores in the shape of the pitch before carbonization where the pitch was present, resulting in carbonization. If high softening point pitch is dissolved in a solvent to prepare a composite, the nanosilicon particles can be uniformly coated with pitch before carbonization, reducing the number of pores generated, resulting in small final pore sizes and low porosity after carbonization.

[0026] As a result of extensive research, the present inventors have found that by adjusting the pitch size contained in a silicon-pitch composite used to manufacture a secondary battery anode material, and thereby adjusting the size and proportion of pores generated in the composite, when the final silicon-carbon composite is applied to a secondary battery as an anode material, the battery performance can be further improved, and have completed the present invention.

[0027] Specifically, the silicon-carbon composite serving as a secondary battery anode material according to the present invention may be prepared from a silicon-pitch composite containing nanosilicon particles and high-softening-point pitch. The nanosilicon particles preferably have an average particle size (D50) of 150 nm or less. While the lower limit of the average particle size (D50) is not particularly limited, it is preferably about 50 nm or more, taking into account the nanosilicon particles typically used in this technical field. The high-softening-point pitch may have a softening point of 200 to 300°C, and the average particle size (D50) of the high-softening-point pitch may preferably be 0.5 to 2 μm. If the average particle size is less than 0.5 μm and the pitch size is too small, the porosity of the final silicon-carbon composite produced after carbonization may be low. However, if the average particle size exceeds 2 μm and the pitch size is too large, the pores of the final silicon-carbon composite may be too large.

[0028] In particular, the silicon-carbon composite of the present invention is characterized by containing pores formed by carbonization of the high softening point pitch, and it has been experimentally confirmed that the average diameter of the pores, preferably 0.2 μm or more, can be used as a negative electrode material for secondary batteries and optimized to improve secondary battery performance. Furthermore, the pores depend on the pitch size in the final silicon-pitch composite, and the average particle diameter (D50) of the final silicon-carbon composite may be, for example, 3 to 10 μm, or for example, 6 to 10 μm.

[0029] The "average diameter" of the pores is preferably 1 / 10 or less of the average particle size (D50) of the silicon-carbon composite to be finally produced, and the "maximum diameter" of the pores is preferably 1 / 2 or less of the average particle size (D50) of the silicon-carbon composite. If these conditions are not met, pores will not be formed uniformly around the silicon particles, and when used as an anode material for a secondary battery, expansion of the silicon cannot be efficiently controlled during charging of the secondary battery, which may reduce the efficiency and lifespan of the secondary battery.

[0030] The porosity of the pores in the silicon-carbon composite is preferably, for example, 20 to 50%, and more preferably, for example, 30 to 40%. It has been experimentally confirmed that when the pore size condition and the porosity range are satisfied, the silicon-carbon composite can be used as a negative electrode material for a secondary battery, and can be optimized to improve the performance of the secondary battery.

[0031] The surface area (BET) of the silicon-carbon composite is, for example, 10 to 30 m 2 / g, for example, 15 to 30m 2 / g, for example, 18 to 25 m 2 / g. The surface area (BET) is preferably 10 m 2 If the surface area (BET) is less than 30 m / g, the contact area with the electrolyte may be small when applied to a secondary battery, resulting in low initial efficiency. 2 If the porosity exceeds 1 / g, when applied to a secondary battery, the contact area with the electrolyte increases, which may result in the formation of a large amount of SEI (Solid Electrolyte Interphase Layer), which may lead to the rapid consumption of the electrolyte and shorten the life of the secondary battery.

[0032] The tap density of the silicon-carbon composite is, for example, 0.5 to 1 g / cm 2 For example, it is preferably 0.5 to 0.8 g / cm 2 Preferably, the tap density is 0.5 g / cm 2 If the tap density is less than 1 g / cm, the energy density is low, and when applied to a secondary battery, the battery capacity for the same volume is reduced. 2 If the thickness exceeds 1000 nm, the porosity will be low, and when applied to a secondary battery, there will be insufficient space for the silicon to expand during charging and discharging of the secondary battery, which may result in a reduced lifespan of the secondary battery.

[0033] Furthermore, since the silicon-carbon composite can be used as an anode material for secondary batteries, the present invention can provide an anode material for secondary batteries including the silicon-carbon composite, and a secondary battery including the same.

[0034] <Method of manufacturing silicon-carbon composite for secondary battery anode material> According to another aspect of the present invention, (a) mixing a high-softening-point pitch having a softening point of 200 to 300°C with a solvent and then wet-pulverizing the mixture to prepare a pulverized pitch slurry having an average particle size (D50) of 0.5 to 2 μm; (b) mixing silicon particles with a solvent and then pulverizing the mixture to prepare a nanosilicon particle slurry having an average particle size (D50) of 150 nm or less; (c) mixing the ground pitch slurry of step (a) with the nanosilicon particle slurry of step (b) to form a pitch-silicon particle mixed slurry; (d) drying the pitch-silicon particle mixed slurry to form spherical powder particles; and (e) carbonizing the spherical powder particles; The present invention provides a method for producing a silicon-carbon composite for use as a secondary battery negative electrode material, comprising the steps of:

[0035] In this case, the solvent is preferably insoluble in the high softening point pitch. If a solvent that dissolves the high softening point pitch is used, the pitch will be completely dissolved in the solvent, resulting in excessive density of the pitch particles and the pitch coated therewith, making it difficult to achieve the target pore size and porosity of the present invention. Specific examples of the insoluble solvent may include, but are not limited to, one or more solvents selected from ethanol, methanol, acetone, and isopropyl alcohol.

[0036] The solid content of the mixed slurry of pitch and silicon particles formed in step (c) may be, for example, 10 to 30 wt %, or may be, for example, 15 to 20 wt %. If the solid content does not satisfy the above range, there may be a problem in that the spherical powder particles having the desired size and size distribution intended in the present invention cannot be obtained.

[0037] Step (d), in which the silicon-containing slurry is dried to form spherical powder particles, may be carried out. The resulting product may be a silicon-pitch composite. In step (d), the drying method is not particularly limited as long as it can form spherical powder particles. However, spray drying is preferred. Spray drying is a technique for rapidly drying a liquid material with hot air to produce a powder. It can be carried out using a spray dryer equipped with a sprayer, heater, and dryer to atomize the liquid material. Spray drying allows for particle size and shape to be adjusted depending on various conditions, such as experimental conditions and liquid state, making it suitable for mass production. The average particle size of the spherical powder particles produced can be selected depending on the application of the negative electrode material, but is preferably 3 to 20 μm, and more preferably 5 to 10 μm.

[0038] The mixed slurry of the high-softening point pitch and nanosilicon particles is carbonized in step (e) to finally obtain a silicon-carbon composite for use as a secondary battery anode material. For example, the carbonization can be carried out in an inert gas atmosphere (e.g., a nitrogen atmosphere) by heating the mixture to a temperature of 1000-1100°C and maintaining the temperature for about one hour, with the heating rate being, for example, 5-10°C. While increasing the carbonization temperature further enhances the removal of impurities and pitch, temperatures above 1100°C can lead to the formation of SiC, so carbonization at a temperature of 1000-1100°C is preferred.

[0039] Furthermore, after carbonization in step (e), the proportion of silicon nanoparticles in the solid content may be, for example, 50 to 90 wt%, for example, 60 to 80 wt%, or 65 to 75 wt%. If the proportion of silicon nanoparticles in the solid content is less than 50 wt%, when used as an anode material for a secondary battery, the capacity may decrease and the increased proportion of pitch may cause entanglement of silicon-pitch composites during the carbonization process. If the proportion of silicon nanoparticles in the solid content exceeds 90 wt%, the pitch proportion may be too low, resulting in poor adhesion (coating) of the pitch to the silicon particles. As a result, when used as an anode material for a secondary battery, the silicon particles may be directly exposed to the electrolyte, causing the rapid formation of an SEI layer and shortening the lifespan of the secondary battery.

[0040] The silicon-carbon composite produced by the method for producing a silicon-carbon composite for use as a secondary battery negative electrode material as described above may have the same properties as those described in detail above for the <Silicon-carbon composite for use as a secondary battery negative electrode material>. [Example]

[0041] The present invention will be described in more detail below with reference to preferred embodiments thereof, which are presented as preferred examples of the present invention and are not to be construed as limiting the present invention in any way.

[0042] I. Manufacturing Example: Manufacturing of Silicon-Carbon Composite Example 1 1) 530 g of high softening point pitch (HSPP, OCI, softening point 250°C) was mixed with 3,000 g of ethanol and thoroughly stirred for 1 hour. Zr beads (average diameter 0.5 mm, 2 kg) were then placed in a bead mill (UBM-1L, Nanointec) and milled at 3,000 rpm for 3 hours to produce a ground pitch slurry. As shown in Figure 2, the average diameter (D50) of the ground pitch in Example 1 was 0.921 μm.

[0043] 2) 600 g of silicon particles (OCI, maximum particle size: 100 μm or less) were mixed with 2,700 g of ethanol and 60 g of stearic acid and thoroughly stirred for 1 hour. Zr beads (average diameter: 0.5 mm, 2 kg) were then placed in a bead mill (UBM-1L, Nano Intec) and milled at 3000 rpm for 2 hours to reduce the average particle size of the silicon particles to 2 μm or less. Zr beads (average diameter: 0.1 mm, 2 kg) were then placed in a nano mill (NPM-1L, Nano Intec) and milled at 3000 rpm for 4 hours to produce a nano silicon particle slurry with an average particle size of 150 nm or less. As shown in FIG. 3, the average diameter (D50) of the nano silicon particles in Example 1 was 0.111 μm.

[0044] 3) 80 g of the pulverized pitch slurry (weight of pulverized pitch alone: 15 g) prepared in 1) and 2) above and 100 g of the nanosilicon particle slurry were mixed using a homogenizer to prepare a pitch-silicon particle mixed slurry, and 110 g of ethanol was added to the mixed slurry so that the solid content of the mixed slurry became 20 wt %.

[0045] 4) Using a spray dryer, spray drying was carried out with an inlet air temperature of 100°C, a two-fluid nozzle (2.4 bar), and a pressure of 30 ml / min to form liquid droplets from the slurry prepared in 3), and the solvent in the droplets was evaporated to obtain a silicon-pitch composite, which was spherical powder particles with an average diameter of 3 to 10 μm.

[0046] 5) Then, the temperature was raised to 1000-1100°C at a rate of 5°C under a nitrogen atmosphere and maintained at that temperature for 1 hour for carbonization, finally producing a silicon-carbon composite. At this time, the content of silicon nanoparticles in the solid was 70 wt%.

[0047] The cross section of the silicon-carbon composite according to Example 1 was observed using an SEM, and SEM images taken at different magnifications are shown in FIGS.

[0048] Comparative Example 1 A silicon-carbon composite was produced in the same manner as in Example 1 above, but instead of mixing completely pulverized pitch with a solvent to produce a slurry in 1) above, the following 1') was used to produce a pulverized pitch with an even smaller average particle size.

[0049] 1') 530 g of high softening point pitch (HSPP, OCI, softening point 250°C) was mixed with 3,000 g of ethanol and thoroughly stirred for 1 hour. Zr beads (average diameter 0.5 mm, 2 kg) were then placed in a bead mill (UBM-1L, Nano Intec) and milled at 3,000 rpm for 3 hours. Zr beads (diameter 0.1 mm, 2 kg) were then placed in a nano mill (NPM-1L, Nano Intec) and milled at 3,000 rpm for 4 hours to produce a pulverized pitch slurry with an average particle size (D50) of 0.5 μm or less. The average particle size (D50) of the pulverized pitch of Comparative Example 1 was measured and found to be 0.182 μm, as shown in FIG. 7.

[0050] The cross section of the silicon-carbon composite according to Comparative Example 1 was observed using an SEM, and the SEM image taken is shown in FIG.

[0051] Example 2 A silicon-carbon composite was produced in the same manner as in Example 1 above, except that the pulverized pitch slurry of Example 1 and the pulverized pitch slurry of Comparative Example 1 were mixed at a 1:1 ratio. The pitch size of Example 2 was set to 0.5515 μm, which is the average value of the pitch size of Example 1 (0.921 μm) and the pitch size of Comparative Example 1 (0.182 μm).

[0052] The cross section of the silicon-carbon composite according to Example 2 was observed using an SEM, and the SEM image taken is shown in FIG.

[0053] Comparative Example 2 A silicon-carbon composite was produced in the same manner as in Example 1 above, except that the slurry produced in 3) above was replaced with 3') to completely dissolve the pitch. Specifically, ethanol, a solvent insoluble in pitch, was used in Example 1 above, while THF (tetrahydrofuran), a solvent soluble in pitch, was used in Comparative Example 2. Thus, in Comparative Example 2, the silicon-carbon composite was produced in such a way that the pitch was completely dissolved in the solvent, and then dried, coating the nanosilicon particles.

[0054] 3') 80 g of the ground pitch slurry (15 g of ground pitch alone) prepared in 1) above was dissolved completely in 150 g of THF, and then 100 g of the nanosilicon particle slurry prepared in 2) above was added thereto and mixed using a homogenizer to prepare a pitch-silicon particle mixed slurry, with the solid content of the mixed slurry being 20 wt%.

[0055] After steps 4) and 5) in Comparative Example 2, the content of silicon nanoparticles in the final solid content was 70 wt %.

[0056] The cross section of the silicon-carbon composite according to Comparative Example 2 was observed using an SEM, and the SEM image taken is shown in FIG.

[0057] II. Experimental Example: Measurement of Surface Properties for Silicon-Carbon Composites The surface area (BET), tap density, pore size, and porosity of the silicon-carbon composites of Examples 1 and 2 and Comparative Examples 1 and 2 were measured and are shown in Table 1. The surface area (BET) was measured according to ASTM D-6556, and the measurement methods for the other values are described below.

[0058] <Measurement Method 1: Surface Area (BET) and Tap Density> The surface area (BET) of the silicon-carbon composite was measured using a specific surface area analyzer (Belsorp-max, manufactured by BEL Japan) in accordance with ASTM D-6556.

[0059] In addition, 30 g of the sample was placed in a 100 ml mess cylinder and tapped for 10 minutes using a tap density measuring instrument (JV2000, manufactured by Copley). After reading the scale, the sample was tapped for another 10 minutes, and the tap density was measured repeatedly until the volume change was within 2%.

[0060] <Measurement method 2: Pore size and porosity> Lines were drawn on the cross-sectional SEM image (50,000x magnification) of the silicon-carbon composite using the "ImageJ" program, and the lengths of the pores in the silicon-carbon composite that touched the lines (pores were determined to be "parts that were not cross-sectional and appeared open or three-dimensional") were measured and recorded. Five or more lines were drawn, with the lines spaced at regular intervals so as not to overlap each other. The average of the measured pore lengths was taken as the pore size.

[0061] The porosity (%) was calculated as the percentage of the "total length of the lines" drawn on the particles of the finally produced silicon-carbon composite divided by the "total length of the measured pores."

[0062] <Measurement Method 3: Measurement of the average particle size (D50) of the final silicon-carbon composite> The final silicon-carbon composite was used as an anode material, and the average particle size D50 [μm] of the composite was measured using a particle size analyzer, LS 13 320 Laser Diffraction Particle Size Analyzer (manufactured by BECKMAN COULTER), and the results are shown in Table 1 below.

[0063] [Table 1]

[0064] As can be seen from Table 1 above, the silicon-carbon composites of Example 1 and Comparative Example 1, which were manufactured using similar methods and had similar porosities, had similar surface area (BET) values. However, in the case of Comparative Example 2, in which pitch was dissolved in a solvent and spherically formed, the pore size and porosity were too small, and the surface area (BET) value was also low.

[0065] It was also found that the pore size was proportional to the pitch size, and the porosity also appeared to be proportional to the pitch size, but there was no significant difference. The tap density was about 0.62 g / cm when produced with crushed pitch. 2 In the case of Comparative Example 2, which was produced by dissolving pitch in a solvent, the porosity was low and the tap density was 0.64 g / cm 2 was measured to be a relatively high value.

[0066] III. Half-Cell Test To analyze the electrochemical properties of the negative electrode material for secondary batteries, the silicon-carbon composites prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were used as negative electrode materials. A negative electrode plate was fabricated using the silicon-carbon composite powder as the active material. The negative electrode plate was fabricated by casting a slurry containing the active material, a conductive material (Super-P, Imerys Graphite & Carbon), and a binder in a weight ratio of 94:1:5 onto copper foil. The binder was a mixture of CMC and SBR in a weight ratio of 3:7. The fabricated negative electrode plate was fabricated into a coin cell using Li metal as the counter electrode, and the electrochemical properties were confirmed. The charge / discharge conditions were CC / CV: 0.01 V / 0.01 C for charge, CC: 1.5 V for discharge, and the rate limiting was 0.2 C.

[0067] Using a half-cell device TOSCAT-3100, the initial charge efficiency (ICE; the amount of discharge relative to the initial charge), initial charge capacity (ICC; the initial charge capacity), and initial discharge capacity (IDC; the initial discharge capacity) were measured and are shown in Table 2 below.

[0068] Furthermore, the life characteristics after 50 cycles (specific capacity at 50 cycles) were measured and are shown in Table 2 below and FIG. 11 (vertical axis: specific capacity at 50 cycles, horizontal axis: number of cycles).

[0069] In addition, the percentage (%) of the 50-cycle specific capacity divided by the initial discharge capacity (IDC) is shown in Table 2 below. This is to confirm whether the life characteristics are maintained even after 50 cycles compared to the initial discharge capacity, and the higher the value, the better the life characteristics.

[0070] [Table 2]

[0071] As can be seen from Table 2 and FIG. 11 above, when the silicon-carbon composites of Examples 1 and 2 according to the present invention were used as negative electrode materials, the battery performance, particularly the battery life characteristics, were found to be superior to those of Comparative Examples 1 and 2.

[0072] Although the present invention has been described above with reference to the illustrative drawings, the present invention is not limited to the embodiments and drawings disclosed in this specification, and various modifications may be made by those skilled in the art within the scope of the technical concept of the present invention. Furthermore, even if the effects of the configurations of the present invention are not explicitly described in the above-described embodiments of the present invention, it is natural that the effects that can be predicted by the configurations should also be recognized.

Claims

1. formed from a silicon-pitch composite comprising nanosilicon particles and high softening point pitch; The average particle size (D50) of the nanosilicon particles is 150 nm or less, The high softening point pitch has a softening point of 200 to 300°C and an average particle size (D50) of 0.5 to 2 µm. Silicon-carbon composite for secondary battery anode materials.

2. The high softening point pitch contains pores formed by carbonization, the average diameter of the pores is 0.2 μm or more and 1 / 10 or less of the average particle size (D50) of the silicon-carbon composite; the maximum diameter of the pores is equal to or less than half the average particle size (D50) of the silicon-carbon composite; The silicon-carbon composite has an average particle size (D50) of 3 to 10 μm. The silicon-carbon composite for use as a secondary battery negative electrode material according to claim 1.

3. The porosity of the pores is 20 to 50%. The silicon-carbon composite for use as a secondary battery negative electrode material according to claim 1.

4. Surface area (BET) is 10-30m ２ / g, and the tap density is 0.5 to 1 g / cm ２ That is, The silicon-carbon composite for use as a secondary battery negative electrode material according to claim 1.

5. The silicon-carbon composite has an average particle size (D50) of 6 to 10 μm. The silicon-carbon composite for use as a secondary battery negative electrode material according to claim 2.

6. A secondary battery negative electrode material comprising the silicon-carbon composite for a secondary battery negative electrode material according to any one of claims 1 to 5.

7. A secondary battery comprising the silicon-carbon composite for use as a secondary battery negative electrode material according to any one of claims 1 to 5.

8. (a) mixing a high softening point pitch having a softening point of 200 to 300°C with a solvent and then wet-pulverizing the mixture to prepare a pulverized pitch slurry having an average particle size (D50) of 0.5 to 2 μm; (b) mixing silicon particles with a solvent and then pulverizing the mixture to prepare a nanosilicon particle slurry having an average particle size (D50) of 150 nm or less; (c) mixing the ground pitch slurry of step (a) with the nanosilicon particle slurry of step (b) to form a pitch-silicon particle mixed slurry; (d) drying the pitch-silicon particle mixed slurry to form spherical powder particles; and (e) carbonizing the spherical powder particles; A method for producing silicon-carbon composites for use as negative electrode materials in secondary batteries.

9. The solvent is a solvent insoluble in the high softening point pitch. The method for producing a silicon-carbon composite for use as a secondary battery negative electrode material according to claim 8.

10. The insoluble solvent includes one or more selected from the group consisting of ethanol, methanol, acetone, and isopropyl alcohol. The method for producing a silicon-carbon composite for use as a secondary battery negative electrode material according to claim 9.

11. The solid content of the pitch-silicon particle mixed slurry formed in step (c) is 10 to 30 wt %. The method for producing a silicon-carbon composite for use as a secondary battery negative electrode material according to claim 8.

12. After the carbonization in step (d), the proportion of silicon nanoparticles in the solid content is 50 to 90 wt %. The method for producing the silicon-carbon composite for use as a secondary battery negative electrode material according to claim 11.

13. The drying in the step (d) is carried out by spray drying. The method for producing a silicon-carbon composite for use as a secondary battery negative electrode material according to claim 8.

14. The carbonization is carried out at a temperature of 1000 to 1100°C. The method for producing a silicon-carbon composite for use as a secondary battery negative electrode material according to claim 8.

15. A silicon-carbon composite for use as a secondary battery negative electrode material, produced by the method according to any one of claims 8 to 14, The silicon-carbon composite for a negative electrode material contains pores formed by carbonization of high softening point pitch, the average diameter of the pores is 0.2 μm or more and 1 / 10 or less of the average particle size (D50) of the silicon-carbon composite; the maximum diameter of the pores is equal to or less than half the average particle size (D50) of the silicon-carbon composite; The silicon-carbon composite has an average particle size (D50) of 3 to 10 μm. Silicon-carbon composite for secondary battery anode materials.

16. The porosity of the pores is 20 to 50%. The silicon-carbon composite for use as a secondary battery negative electrode material according to claim 15.

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