Silicon-carbon composite for anode material of secondary battery and preparing method of the same

Abstract

The present invention relates to a silicon-carbon composite for a secondary battery negative electrode material capable of improving the initial discharge capacity (IDC), initial efficiency (ICE), and lifespan characteristics of a secondary battery, and a method for manufacturing the same.

Description

Technology Field

[0001] The present invention relates to a silicon-carbon composite for a secondary battery negative electrode material capable of improving the initial discharge capacity (IDC), initial efficiency (ICE), and lifespan characteristics of a secondary battery, and a method for manufacturing the same. Background Technology

[0003] The performance improvement of secondary batteries is based on the components of the cathode, anode, and electrolyte.

[0004] Among the above components, graphite-based materials, which are mainly used as cathode materials, are commercially available due to their excellent electrochemical performance and low cost, but there are limitations to their application in high-capacity secondary batteries because their theoretical capacity is limited to 370 mAh / g.

[0005] To overcome the aforementioned limitations, non-graphite cathode materials such as silicon, tin, and germanium are emerging as alternative materials. Among them, silicon is receiving attention as a material to replace graphite because it has a theoretical capacity of 4,000 to 4,200 mAh / g and exhibits a high capacity nearly 10 times greater than that of graphite. However, despite its high theoretical capacity, it undergoes a large volume expansion of approximately 400% during the charging and discharging process, leading to structural destruction of the material and a short lifespan.

[0006] A method of manufacturing a composite by mixing carbon materials has been devised to mitigate the volume expansion of silicon, and applying the said composite as a negative electrode material for secondary batteries to improve the performance of secondary batteries is emerging as an important task.

[0007] For example, a method has been developed in which a slurry containing nano silicon (Nano Si) particles is formed into spherical powder particles, and then pitch is coated on the surface of the spherical powder particles as a carbon material. It is necessary to develop a high-quality silicon-carbon composite for secondary battery anode materials and a method for manufacturing the same, which can further improve the initial discharge capacity, initial efficiency, and lifespan characteristics of the secondary battery by controlling the properties of the composite using the nano silicon particles and pitch. The problem to be solved

[0009] The object of the present invention is to provide a secondary battery negative electrode material comprising a silicon-carbon composite prepared using a silicon-pitch composite comprising nano silicon particles and high softening point pitch, and a method for manufacturing the same.

[0010] Another objective of the present invention is to provide a negative electrode material for a secondary battery, a negative electrode material for a secondary battery including the same, and a secondary battery so as to improve the initial discharge capacity, initial efficiency, and lifespan characteristics of the secondary battery.

[0011] The objects of the present invention are not limited to those mentioned above, and other unmentioned objects and advantages of the present invention may be understood from the following description and will be more clearly understood by the embodiments of the present invention. Furthermore, it will be readily apparent that the objects and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims. means of solving the problem

[0013] According to one aspect of the present invention, a silicon-carbon composite for a secondary battery negative electrode material can be provided, which is formed from a silicon-pitch composite comprising nano silicon particles and a high softening point pitch, wherein the average particle size (D50) of the nano silicon particles is 150 nm or less, the softening point of the high softening point pitch is 200 to 300°C, and the average particle size (D50) of the high softening point pitch is 0.5 to 2 μm.

[0014] According to another aspect of the present invention,

[0015] (a) A step of mixing high softening point pitch with a softening point of 200~300℃ into a solvent, and then wet-grinding to produce a ground pitch slurry having an average pitch particle size (D50) of 0.5~2㎛;

[0016] (b) a step of mixing silicon particles with a solvent and then grinding them to produce a nano silicon particle slurry having an average particle size (D50) of 150 nm or less;

[0017] (c) a step of mixing the ground pitch slurry of step (a) and the nano silicon particle slurry of step (b) to form a pitch-silicon particle mixed slurry;

[0018] (d) drying the mixed slurry of the pitch-silicon particles to form spherical powder particles; and

[0019] (e) a step of carbonizing the spherical powder particles;

[0020] A method for manufacturing a silicon-carbon composite for a secondary battery negative electrode material, comprising

[0021] According to another aspect of the present invention, a negative electrode material for a secondary battery comprising a silicon-carbon composite manufactured using a silicon-pitch composite according to one aspect of the present invention can be provided. Effects of the invention

[0023] The silicon-carbon composite, which is a negative electrode material for a secondary battery according to the present invention, can have an optimized pore size and ratio within the composite, and thus can improve the initial discharge capacity, initial efficiency, and lifespan characteristics of a secondary battery manufactured by including the composite as a negative electrode material.

[0024] In addition to the effects described above, the specific effects of the present invention are described together with the specific details for implementing the invention below. Brief explanation of the drawing

[0026] FIG. 1 is a flowchart illustrating a method for manufacturing a secondary battery negative electrode material according to one embodiment of the present invention. Figures 2 and 3 are graphs analyzing the grinding pitch and the diameter of the nano silicon particles of Example 1, respectively. Figures 4 to 6 show SEM images of the silicon-carbon composite prepared in Example 1, respectively. Figure 7 is a graph analyzing the diameter of the grinding pitch of Comparative Example 1. Figure 8 shows SEM images of the silicon-carbon composite prepared in Comparative Example 1. Figure 9 shows SEM images of the silicon-carbon composite prepared in Example 2. Figure 10 shows SEM images of the silicon-carbon composite prepared in Comparative Example 2. FIG. 11 shows a graph regarding the life characteristics at 50 cycles of Examples 1 and 2 and Comparative Examples 1 and 2 (vertical axis: 50 cycle capacity, horizontal axis: number of cycles). Specific details for implementing the invention

[0027] The aforementioned objectives, features, and advantages are described in detail below with reference to the attached drawings, thereby enabling those skilled in the art to easily implement the technical concept of the present invention. In describing the present invention, detailed descriptions of known technologies related to the present invention are omitted if it is determined that such descriptions would unnecessarily obscure the essence of the invention. Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the attached drawings. In the drawings, the same reference numerals are used to indicate the same or similar components.

[0028] Details not described in this specification that can be sufficiently technically inferred by a person skilled in the art are to be omitted.

[0029] In the following, the statement that any configuration is placed on the "upper (or lower)" of a component or on the "upper (or lower)" of a component may mean not only that any configuration is placed in contact with the upper (or lower) surface of said component, but also that another configuration may be interposed between said component and any configuration placed on (or below) said component.

[0030] In addition, where it is stated that one component is "connected," "combined," or "connected" to another component, it should be understood that while the components may be directly connected or connected to each other, another component may be "interposed" between each component, or each component may be "connected," "combined," or "connected" through another component.

[0031] In this specification, “silicon-pitch composite” refers to a composite material formed by mixing silicon and pitch, and “silicon-carbon composite” may be described as a composite material in which pitch has been converted into carbon after performing a carbonization process on the silicon-pitch composite.

[0032] In this specification, “average particle size” may mean “D50” measured using a particle size analyzer (LS 13 320 Laser Diffraction Particle Size Analyzer; LS 13 320 Laser Diffraction Particle Size Analyzer; manufactured by BECKMAN COULTER), which was used to define and measure the size of the pitch particles, silicon particles, and the final silicon-carbon composite in the present invention.

[0033] In this specification, “average diameter” is used to define the size of the “pores” of the silicon-carbon composite of the present invention and may mean that it is measured according to <Measurement Method 2: Pore Size and Porosity> described below in this specification.

[0034] Hereinafter, a silicon-carbon composite for a secondary battery negative electrode material according to the present invention and a method for manufacturing the same will be described in detail.

[0036] Silicon-Carbon Composite for Secondary Battery Anode Material >

[0037] According to one embodiment of the present invention, a silicon-carbon composite that is a secondary battery negative electrode material may be formed as a silicon-pitch composite comprising nano silicon particles and high softening point pitch. In order to manufacture the silicon-carbon composite that is a secondary battery negative electrode material, a process is performed to carbonize the silicon-pitch composite, which is manufactured by forming spherical powder particles from a slurry prepared by mixing silicon particles and a pitch composite.

[0038] In the above carbonization process, silicon particles remain as a framework, and the high softening point pitch undergoes a volume (weight) reduction of 30–50% during carbonization, creating pores in the shape of the pitch before carbonization in the areas where the pitch existed, and becoming carbon. At this time, if the high softening point pitch is dissolved in a solvent to manufacture a composite, the pitch can be uniformly coated on the nano silicon particles before carbonization, resulting in a smaller amount of pores being created, and even after carbonization, the final pore size is small and the porosity is reduced.

[0039] As a result of diligent research, the inventors confirmed that by controlling the size of the pitch included in the silicon-pitch composite used to manufacture a secondary battery negative electrode material, and thereby controlling the size and ratio of pores generated in the composite, the performance of the battery can be further improved when the finally manufactured silicon-carbon composite is applied to a secondary battery as a negative electrode material, and thus completed the present invention.

[0040] Specifically, the silicon-carbon composite, which is a negative electrode material for a secondary battery according to the present invention, can be manufactured from a silicon-pitch composite comprising nano silicon particles and high softening point pitch. At this time, it is preferable that the average particle size (D50) of the nano silicon particles is 150 nm or less, and although there is no specific limit on the lower limit of the average particle size (D50), it is preferable that it be about 50 nm or more considering the nano silicon particles generally used in the art. The softening point of the high softening point pitch may be 200 to 300°C, and it is preferable that the average particle size (D50) of the high softening point pitch is 0.5 to 2 μm. If the pitch size is too small with an average particle size of less than 0.5 μm, the porosity of the silicon-carbon composite finally manufactured after carbonization becomes low, and if the pitch size is too large with an average particle size of more than 2 μm, there may be a problem in that the pores of the silicon-carbon composite finally manufactured after carbonization become too large.

[0041] In particular, the silicon-carbon composite of the present invention is characterized by including pores generated by carbonizing the high softening point pitch, and it has been experimentally confirmed that the average diameter of the pores is preferably 0.2 μm or more, and that this can be optimized for improving the performance of the secondary battery by applying it as a negative electrode material for a secondary battery. In addition, the pores are dependent on the size of the pitch in the silicon-pitch composite finally manufactured, and the average particle size (D50) of the silicon-carbon composite finally manufactured may be, for example, 3 to 10 μm, or for example, 6 to 10 μm.

[0042] It is preferable that the 'average diameter' of the above pores be 1 / 10 or less of the average particle size (D50) of the silicon-carbon composite finally manufactured, and the 'maximum diameter' of the above pores be 1 / 2 or less of the average particle size (D50) of the silicon-carbon composite. If these conditions are not satisfied, pores cannot be formed evenly around the silicon particles, and when applied as a negative electrode material for a secondary battery, silicon expansion during charging of the secondary battery cannot be efficiently controlled, and as a result, the efficiency and lifespan of the secondary battery may be reduced.

[0043] It was experimentally confirmed that the porosity of the pores of the silicon-carbon composite is preferably 20 to 50%, for example, and preferably 30 to 40%, and that when the porosity range is satisfied along with the pore size condition, it can be applied as a negative electrode material for a secondary battery and optimized for improving the performance of the secondary battery.

[0044] The surface area (BET) of the silicon-carbon composite is preferably, for example, 10 to 30 m² / g, preferably 15 to 30 m² / g, and preferably 18 to 25 m² / g. If the surface area (BET) is less than 10 m² / g, there may be a problem of low initial efficiency due to a small contact area with the electrolyte when applied to a secondary battery. If the surface area (BET) exceeds 30 m² / g, there may be a problem of a Solid Electrolyte Interphase Layer (SEI) being easily and extensively formed due to the increased contact area with the electrolyte when applied to a secondary battery, which causes the electrolyte to be consumed quickly and reduces the lifespan of the secondary battery.

[0045] The tap density of the silicon-carbon composite is preferably, for example, 0.5 to 1 g / cm², and preferably, for example, 0.5 to 0.8 g / cm². If the tap density is less than 0.5 g / cm², the energy density is lowered, which may cause a problem where the capacity of the battery is reduced relative to the same volume when applied to a secondary battery. If the tap density exceeds 1 g / cm², the porosity is lowered, which may cause a problem where there is insufficient space for the silicon to expand during charging and discharging of the secondary battery, thereby reducing the lifespan of the secondary battery.

[0046] In addition, since the above silicon-carbon composite can be used as a negative electrode material for a secondary battery, the present invention can provide a negative electrode material for a secondary battery comprising the above silicon-carbon composite and a secondary battery comprising the same.

[0048] < Method for manufacturing a silicon-carbon composite for secondary battery anode material >

[0049] According to another aspect of the present invention,

[0050] (a) A step of preparing a ground pitch slurry having an average particle size (D50) of 0.5 to 2 μm by mixing a high softening point pitch with a softening point of 200 to 300°C in a solvent and then wet-grinding it;

[0051] (b) a step of mixing silicon particles with a solvent and then grinding them to produce a nano silicon particle slurry having an average particle size (D50) of 150 nm or less;

[0052] (c) a step of mixing the ground pitch slurry of step (a) and the nano silicon particle slurry of step (b) to form a pitch-silicon particle mixed slurry;

[0053] (d) drying the mixed slurry of the pitch-silicon particles to form spherical powder particles; and

[0054] (e) a step of carbonizing the spherical powder particles;

[0055] A method for manufacturing a silicon-carbon composite for a secondary battery negative electrode material, comprising

[0056] At this time, it is preferable that the solvent be an insoluble solvent with respect to the high softening point pitch. If a solvent soluble with respect to the high softening point pitch is used, the pitch is completely dissolved in the solvent, which causes the density of the pitch particles and the coated pitch to become excessively high, making it difficult to achieve the pore size and porosity intended in the present invention. Specific examples of the insoluble solvent may include one or more selected from solvents such as ethanol, methanol, acetone, and isopropyl alcohol, but are not necessarily limited thereto.

[0058] The solid content in the mixed slurry of pitch-silicon particles formed in step (c) above may be, for example, 10 to 30 wt%, or for example, 15 to 20 wt%, and if the above range is not satisfied, there may be a problem in that spherical powder particles having the desired size and size distribution intended in the present invention cannot be obtained.

[0060] Step (d), which is a drying step for forming spherical powder particles from the silicon-containing slurry, may be performed, and the resulting product may be a silicon-pitch composite. In Step (d), the drying method is not particularly limited as long as spherical powder particles can be formed, but preferably, it can be performed by spray drying. Spray drying is a technique for producing a powder state by rapidly drying a material in a liquid state using hot air, and can be performed using spray dryer equipment comprising a sprayer that atomizes the material in a liquid state, a heater, and a dryer. Spray drying allows for controlling particle size and shape based on various conditions such as experimental conditions and liquid state, and is suitable for mass production. The average particle size of the spherical powder particles produced above can be selected according to the application of the cathode material used, but it is preferably, for example, 3 to 20 μm, and for example, 5 to 10 μm.

[0062] By performing step (e) of carbonizing the mixed slurry of the high softening point pitch and nano silicon particles, a silicon-carbon composite for a secondary battery negative electrode material can finally be obtained. For example, the carbonization can be performed under an inert gas atmosphere (e.g., nitrogen atmosphere) by raising the temperature to 1000 to 1100°C and maintaining it for about 1 hour, at which time the heating rate can be, for example, 5 to 10°C. Although increasing the carbonization temperature results in a higher effect of removing impurities and pitch, if the temperature exceeds 1100°C, there is a problem of SiC formation; therefore, it is preferable to carbonize at a temperature of 1000 to 1100°C.

[0064] In addition, the proportion of silicon nanoparticles in the solid after carbonization in step (e) above may be, for example, 50 to 90 wt%, for example, 60 to 80 wt%, or for example, 65 to 75 wt%. If the proportion of silicon nanoparticles in the solid is less than 50 wt%, there may be a problem of reduced capacity when applied as a negative electrode material for a secondary battery, and a problem of silicon-pitch composites sticking together during the carbonization process due to an increase in the proportion of pitch. If the proportion of silicon nanoparticles in the solid exceeds 90 wt%, the proportion of pitch becomes too low, which may result in poor adhesion (coating) of pitch to silicon particles. Consequently, when applied as a negative electrode material for a secondary battery, silicon particles are directly exposed to the electrolyte, causing the SEI layer to form rapidly and reducing the lifespan of the secondary battery.

[0065] The silicon-carbon composite manufactured by the method for manufacturing a silicon-carbon composite for a secondary battery negative electrode material as described above is the above Silicon-Carbon Composite for Secondary Battery Anode Material > It can have the same characteristics as those described in detail.

[0067] The structure and operation of the present invention will be described in more detail below through preferred embodiments. However, these are presented as preferred examples of the present invention and should not be interpreted in any way as limiting the present invention.

[0069] I. Preparation Example: Preparation of a Silicon-Carbon Composite

[0070] Example 1

[0071] 1) 530 g of high softening point pitch (HSPP, OCI, softening point 250°C) was mixed with 3,000 g of ethanol and stirred thoroughly for 1 hour. Then, Zr beads (average diameter 0.5 mm, 2 kg) were placed in a bead mill (UBM-1L, Nanointek) and milled at 3,000 rpm for 3 hours to prepare a ground pitch slurry. As shown in Fig. 2, the average diameter (D50) of the ground pitch of Example 1 was 0.921 μm.

[0072] 2) 600 g of silicon particles (OCI, maximum average particle size 100 μm or less), 2,700 g of ethanol, and 60 g of stearic acid were mixed and stirred thoroughly for 1 hour. Then, Zr beads (average diameter 0.5 mm, 2 kg) were placed in a bead mill (UBM-1L, Nanointec) and ground at 3000 rpm for 2 hours to make the average particle size of the silicon particles 2 μm or less. Then, Zr beads (average diameter 0.1 mm, 2 kg) were placed in a nano mill (NPM-1L, Nanointec) and ground at 3000 rpm for 4 hours to prepare a nano silicon particle slurry so that the average particle size of the silicon particles became 150 nm or less. As shown in Fig. 3, the average diameter (D50) of the nano silicon particles of Example 1 was 0.111 μm.

[0073] 3) 80g of the ground pitch slurry (weight of ground pitch only: 15g) and 100g of the nano silicon particle slurry prepared in 1) and 2) respectively were mixed using a homogenizer to prepare a pitch-silicon particle mixed slurry, and 110g of ethanol was added so that the solid content of the mixed slurry was 20 wt%.

[0074] 4) Using a spray dryer, spray drying was performed at 30 ml / min with an in-let air 100°C two-fluid nozzle (2.4 bar) to form liquid drops from the slurry prepared in 3), and then the solvent of the liquid drops was evaporated to obtain a silicon-pitch composite in the form of spherical powder particles with an average diameter of 3 to 10 μm.

[0075] 5) Subsequently, the temperature was raised to 1000–1100°C at a rate of 5°C under a nitrogen atmosphere and maintained for 1 hour to carbonize, thereby finally producing a silicon-carbon composite. At this time, the content of silicon nanoparticles in the solid was 70 wt%.

[0076] A cross-section of the silicon-carbon composite according to Example 1 was observed using SEM, and SEM images taken at different magnification ratios are shown in FIGS. 4 to 6.

[0078] Comparative Example 1

[0079] A silicon-carbon composite was prepared in the same manner as in Example 1 above, but the preparation of a completely ground pitch in a solvent when preparing the slurry in 1) above was replaced with 1') below, thereby producing a smaller average particle size of the ground pitch.

[0080] 1') 530 g of high softening point pitch (HSPP, OCI, softening point 250°C) was mixed with 3,000 g of ethanol and stirred thoroughly for 1 hour. Then, Zr beads (average diameter 0.5 mm, 2 kg) were placed in a bead mill (UBM-1L, Nanointec) and milled at 3,000 rpm for 3 hours. Subsequently, Zr beads (diameter 0.1 mm, 2 kg) were placed in a nano mill (NPM-1L, Nanointec) and milled at 3,000 rpm for 4 hours to prepare a ground pitch slurry such that the average particle size (D50) of the pitch particles was 0.5 μm or less. As a result of actual measurement, as shown in Fig. 7, the average particle size (D50) of the ground pitch of Comparative Example 1 was 0.182 It was μm.

[0081] A cross-section of the silicon-carbon composite according to Comparative Example 1 was observed using SEM, and the captured SEM image is shown in Fig. 8.

[0083] Example 2

[0084] A silicon-carbon composite was prepared in the same manner as in Example 1, except that the ground pitch slurry of Example 1 and the ground pitch slurry of Comparative Example 1 were mixed in 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).

[0085] A cross-section of the silicon-carbon composite according to Example 2 was observed using SEM, and the captured SEM image is shown in Fig. 9.

[0087] Comparative Example 2

[0088] A silicon-carbon composite was prepared in the same manner as in Example 1 above, but with a difference in that the slurry preparation in 3) was replaced with 3') to completely dissolve the pitch. Specifically, in Example 1, ethanol, an insoluble solvent for pitch, was used, while in Comparative Example 2, THF (tetrahydrofuran), a soluble solvent for pitch, was used. Accordingly, in Comparative Example 2, the silicon-carbon composite was prepared in a manner in which the pitch was completely dissolved in the solvent and then coated onto nano-silicon particles as it dried.

[0089] 3') 80g of the ground pitch slurry prepared in 1) above (the weight of the ground pitch alone is 15g) was completely dissolved in 150g of THF, and then 100g of the nano silicon particle slurry prepared in 2) above was added to it and mixed using a homogenizer to prepare a pitch-silicon particle mixed slurry, and the solid content of the mixed slurry was made to be 20 wt%.

[0090] The content of silicon nanoparticles in the final solid produced after processes 4) and 5) in Comparative Example 2 was 70 wt%.

[0091] A cross-section of the silicon-carbon composite according to Comparative Example 2 was observed using SEM, and the captured SEM image is shown in Fig. 10.

[0093] II. Experimental Example: Measurement of Surface Properties for Silicon-Carbon Composites

[0094] For the silicon-carbon composites of Examples 1 and 2 and Comparative Examples 1 and 2 prepared above, the surface area (BET), tap density, pore size, and porosity were measured and are shown in Table 1 below. At this time, the surface area (BET) was measured according to ASTM D-6556, and the measurement methods for other values ​​are described below.

[0096] < Measurement Method 1: Surface Area (BET) and Tap Density >

[0097] The surface area (BET) of the silicon-carbon composite was measured according to ASTM D-6556 using a specific surface area analyzer (Belsorp-max, manufactured by BEL Japan).

[0098] In addition, 30g of the sample was placed in a 100ml mess cylinder, and tapping was performed for 10 minutes using a tap density meter (JV2000, manufactured by Copley), the scale was read, and tapping was performed again for 10 minutes until the volume change was within 2%, thereby measuring the tap density.

[0100] < Measurement Method 2: Pore Size and Porosity >

[0101] Using the 'ImageJ' program, lines were drawn on the particles of the finally manufactured silicon-carbon composite in a cross-sectional SEM image (50,000x magnification) of the silicon-carbon composite, and the lengths of the pores of the silicon-carbon composite touching the lines were measured and recorded ("parts that are not cross-sectional, appearing empty or three-dimensional"). At least five lines were drawn at regular intervals so that they did not overlap. The average value of the measured pore lengths was taken as the pore size.

[0102] The porosity (%) was calculated as the percentage of the value obtained by dividing the 'total length of lines' drawn on the particles of the finally manufactured silicon-carbon composite by the 'total sum of measured pore lengths'.

[0104] < Measurement Method 3: Measurement of Average Particle Size (D50) of the Final Silicon-Carbon Composite >

[0105] The final manufactured silicon-carbon composite was used as a cathode material, and the average particle size D50 [㎛] of the composite was measured using a particle size analyzer, the 'LS 13 320 Laser Diffraction Particle Size Analyzer' (LS 13 320 Laser Diffraction Particle Size Analyzer, manufactured by BECKMAN COULTER, Inc.) and is shown in Table 1 below.

[0107] Surface area [㎡ / g] Tap density [g / cm³] Pore ​​size [㎛] Porosity[%] Average particle size of the final cathode material (D50) [㎛] Example 1 19.0 0.62 0.270 38.8 5.795 Example 2 23.2 0.61 0.225 35.9 5.410 Comparative Example 1 21.9 0.62 0.177 32.7 5.575 Comparative Example 2 7.8 0.64 0.083 7.3 6.139

[0109] As can be seen from Table 1 above, the silicon-carbon composites of Example 1 and Comparative Example 1, which have similar manufacturing methods and similar porosity, had similar surface area (BET) values, but in the case of Comparative Example 2, in which pitch was dissolved in a solvent and sphericalized, the pore size and porosity were too small, and the surface area (BET) value was also low.

[0110] In addition, it was found that the pore size was proportional to the pitch size, and the porosity was also proportional to the pitch size, but there was no significant difference. The tap density was approximately 0.62 g / cm³ when prepared with ground pitch, and in the case of Comparative Example 2, prepared by dissolving pitch in a solvent, the porosity was low and the tap density was measured to be a relatively high value of 0.64 g / cm³.

[0112] III. Half-Cell Test

[0113] To analyze the electrochemical characteristics of the negative electrode material for a secondary battery, the silicon-carbon composites prepared in Examples 1 and 2 and Comparative Examples 1 and 2, respectively, 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 prepared by casting a slurry, in which the active material, a conductive material (Super-P, Imerys Graphite & Carbon), and a binder were mixed in a weight ratio of 94:1:5, onto copper foil; in this case, a binder consisting of CMC and SBR mixed in a weight ratio of 3:7 was used. The fabricated negative electrode plate was converted into a coin cell using Li metal as the counter electrode, and its electrochemical characteristics were verified. The charge / discharge conditions were set as Charge CC / CV: 0.01V / 0.01C, Discharge CC: 1.5V, and the rate limit was 0.2C.

[0114] Using a half-cell device - TOSCAT-3100 equipment - the initial coulombic efficiency (ICE; discharge amount relative to initial charge amount), initial charge capacity (ICC; initial charge capacity), and initial discharge capacity (IDC; initial discharge capacity) were measured and are shown in Table 2 below.

[0115] In addition, the life characteristics (50-cycle capacity) at 50 cycles were measured and shown in Table 2 and Figure 11 below (vertical axis: 50-cycle capacity, horizontal axis: number of cycles).

[0116] In addition, the percentage (%) of the value obtained by dividing the 50-cycle capacity by the initial discharge capacity (IDC) is shown in Table 2 below. This indicates whether the life characteristics are maintained even after 50 cycles compared to the initial discharge capacity, and a higher value indicates superior life characteristics.

[0118] ICE (%) ICC (mAh / g) IDC (mAh / g) 50 Cycle specific capacity (mAh / g) 50-Cycle Cost / IDC (%) Example 1 85.8 2376 2038 685 33.6% Example 2 85.4 2533 2162 549 25.4% Comparative Example 1 84.8 2445 2074 366 17.7% Comparative Example 2 85.3 2362 2014 255 12.6%

[0120] As can be seen from Table 2 and Figure 11 above, it was found that when the silicon-carbon composite of Examples 1 and 2 according to the present invention is used as a negative electrode material, the performance of the battery, particularly the battery life characteristics, is superior compared to Comparative Examples 1 and 2.

[0122] Although the present invention has been described above with reference to the illustrated drawings, the present invention is not limited by the embodiments and drawings disclosed in this specification, and it is obvious that various modifications can be made by a person skilled in the art within the scope of the technical concept of the present invention. Furthermore, even if the effects of the configuration according to the present invention were not explicitly described while describing the embodiments of the present invention above, it is natural to acknowledge that the effects predictable by said configuration should also be recognized.

Claims

Claim 1 delete Claim 2 delete Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 delete Claim 7 delete Claim 8 (a) a step of preparing a ground pitch slurry having an average particle size (D50) of 0.5 to 2 μm by mixing high softening point pitch having a softening point of 200 to 300°C with a solvent and then wet-grinding the pitch; (b) a step of preparing a nano silicon particle slurry having an average particle size (D50) of 150 nm or less by mixing silicon particles with a solvent and then grinding them; (c) a step of forming a pitch-silicon particle mixed slurry by mixing the ground pitch slurry of step (a) and the nano silicon particle slurry of step (b); (d) a step of forming spherical powder particles by drying the pitch-silicon particle mixed slurry; and (e) a step of carbonizing the spherical powder particles; comprising a method for preparing a silicon-carbon composite for a secondary battery negative electrode material. Claim 9 A method for manufacturing a silicon-carbon composite for a secondary battery negative electrode material, wherein, in claim 8, the solvent is a solvent insoluble with respect to the high softening point pitch. Claim 10 A method for manufacturing a silicon-carbon composite for a secondary battery negative electrode material, wherein, in claim 9, the insoluble solvent comprises one or more selected from the group consisting of ethanol, methanol, acetone, and isopropyl alcohol. Claim 11 A method for manufacturing a silicon-carbon composite for a secondary battery negative electrode material according to claim 8, wherein the solid content in the mixed slurry of pitch-silicon particles formed in step (c) is 10 to 30 wt%. Claim 12 A method for manufacturing a silicon-carbon composite for a secondary battery negative electrode material, wherein, in claim 11, the ratio of silicon nanoparticles in the solid content after carbonization in step (d) is 50 to 90 wt%. Claim 13 A method for manufacturing a silicon-carbon composite for a secondary battery negative electrode material, wherein, in claim 8, the drying in step (d) is performed by spray drying. Claim 14 A method for manufacturing a silicon-carbon composite for a secondary battery negative electrode material, wherein, in claim 8, the carbonization is performed at a temperature of 1000 to 1100°C. Claim 15 A silicon-carbon composite for a secondary battery negative electrode material manufactured by a manufacturing method according to any one of claims 8 to 14, wherein the silicon-carbon composite for the negative electrode material comprises pores formed by carbonizing high softening point pitch, the average diameter of the pores is 0.2 μm or more and is 1 / 10 or less of the average particle size (D50) of the silicon-carbon composite, the maximum diameter of the pores is 1 / 2 or less of the average particle size (D50) of the silicon-carbon composite, and the average particle size (D50) of the silicon-carbon composite is 3 to 10 μm. Claim 16 A silicon-carbon composite for a secondary battery negative electrode material, wherein, in item 15, the porosity of the above pores is 30 to 50%.

Images