Carbon black-based porous carbon structure and silicon-carbon composite comprising same

Abstract

The present invention relates to a carbon black-based porous carbon structure and a silicon-carbon composite comprising same, and more specifically, to: a porous carbon structure in which carbon black is used to control pore characteristics, and which can thus increase the content of silicon when applied to a silicon-carbon composite negative electrode active material for a secondary battery, and thereby increase the capacity of the secondary battery and prevent deterioration of lifespan characteristics; a carbon black-based porous carbon structure; and a silicon-carbon composite comprising same.

Description

Carbon black-based porous carbon structure and silicon-carbon composite containing the same

[0001] The present invention relates to a carbon black-based porous carbon structure and a silicon-carbon composite containing the same. More specifically, it relates to a porous carbon structure and a carbon black-based porous carbon structure and a silicon-carbon composite containing the same, which can increase the capacity of a secondary battery and prevent degradation of lifespan characteristics by increasing the silicon content when applied to a silicon-carbon composite negative electrode active material for a secondary battery by controlling pore characteristics using carbon black.

[0002] The performance improvement of secondary batteries is based on the components of the cathode material, anode active material, and electrolyte.

[0003] Among the above components, graphite-based materials, which are mainly used as negative electrode active materials, are commercially available due to their excellent electrochemical performance and low cost, but they have limitations in being applied to high-capacity secondary batteries because their theoretical capacity is limited to 370 mAh / g.

[0004] To overcome the aforementioned limitations, non-graphite cathode active materials such as silicon, tin, and germanium are emerging as alternative materials. Among them, silicon is gaining attention as a material to replace graphite because it has a theoretical capacity of 4,000 to 4,200 mAh / g, can store a very large amount of lithium per unit weight, and exhibits a high capacity nearly 10 times greater than that of graphite. However, there is a limitation in that, compared to its high theoretical capacity, a large volume expansion of about 300 to 400% occurs during the charge and discharge process, causing problems such as the destruction and pulverization of silicon particles and a decrease in electron conductivity with carbon additives and current collectors, which ultimately leads to capacity loss and reduced cycle life of the secondary battery.

[0005] As a method to mitigate the volume expansion of silicon, methods have been devised to control the properties of silicon particles and to manufacture silicon-carbon composites (Si-C composites) by mixing carbon-based materials, and applying said composites as negative electrode active materials for secondary batteries to improve the performance of secondary batteries is emerging as an important task.

[0006] A method using porous carbon structures has been proposed for the manufacture of such silicon-carbon composite negative electrode active materials. Porous carbon structures, including those described in Patent Document 1 (Korean Published Patent Application No. 10-2024-0093596), have been developed in a direction that reduces macropore volume while satisfying properties such as a micropore volume of 0.4 cm³ / g or more, or, as disclosed in Patent Document 2 (Korean Published Patent Application No. 10-2024-0059309), reduces pore volume even while having macropores. In particular, porous carbon structures having the above properties have generally been manufactured using activated carbon. While such porous carbon structures have the advantage of controlling silicon particle size to the nanoscale during silicon deposition or silicon impregnation, they have limitations in significantly increasing the silicon content to 60 wt% or more, making them insufficient for manufacturing negative electrode materials for high-capacity secondary batteries. Meanwhile, many negative electrode materials for secondary batteries with increased silicon content have been proposed, but even if high capacity can be achieved, there are limitations as porous carbon structures for secondary batteries that improve the lifespan retention rate of the secondary battery and are intended for stable and long-term use.

[0007] Therefore, it is still necessary to develop porous carbon structures for silicon-carbon composite anode active materials that can overcome the aforementioned limitations and achieve high capacity and excellent lifespan retention rates for secondary batteries.

[0008] In order to overcome the limitations of the aforementioned prior art, the objective of the present invention is to provide a carbon black-based porous carbon structure and a silicon-carbon composite containing the same, which, when applied to a silicon-carbon composite negative electrode active material, can increase the silicon content to 60 wt% or more and consequently improve the capacity, efficiency, and lifespan retention rate of a secondary battery by having pore characteristics such that the ratio of pores having an average size of 50 to 100 nm is 50% or more, the volume of pores having an average size of 50 to 100 nm is 0.5 cm³ / g or more, and the total pores (pores having a size of 350 nm or less) are 1.5 cm³ / g or more.

[0009] The objectives of the present invention are not limited to those mentioned above, and other objectives and advantages of the present invention not mentioned 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 objectives and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims.

[0010] To achieve the above objective, according to a first aspect of the present invention,

[0011] A first pore having an average pore size of 50 nm or less; a second pore having an average pore size greater than 50 nm and less than or equal to 100 nm; and a third pore having an average pore size greater than 100 nm and less than or equal to 350 nm; comprising,

[0012] Based on a total pore volume of 100 vol% obtained by summing the first, second, and third pores, the ratio of the second pore is 50 vol% or more, and

[0013] The pore volume of the second pore is 0.5 cm³ / g or more, and

[0014] A carbon black-based porous carbon structure having a total pore volume of 1.5 cm³ / g or more can be provided.

[0015] The pore volume of the first pore above may be 0.4 cm³ / g or less.

[0016] The sum of the pore volumes of the first pore and the second pore may be 0.6 cm³ / g or more.

[0017] The pore volume of the second pore mentioned above may be 1.0 cm³ / g or more.

[0018] The above porous carbon structure is,

[0019] (S1) A step of steam activating carbon black at a temperature of 800℃ or higher;

[0020] (S2) Step of grinding steam-activated carbon black;

[0021] (S3) A step of mixing the above-mentioned crushed carbon black with a binder;

[0022] (S4) A step of spray-drying the above mixture; and

[0023] (S5) The above-mentioned dried material may be obtained by sequentially carrying out the step of carbonizing it at a temperature of 500 to 1500°C.

[0024] According to a second aspect of the present invention, a silicon-carbon composite comprising a carbon black-based porous carbon structure according to a first aspect of the present invention can be provided.

[0025] Based on 100% by weight of the total weight of the silicon-carbon composite, the silicon content contained in the silicon-carbon composite may be 60% by weight or more.

[0026] According to a third aspect of the present invention, a negative electrode active material for a secondary battery comprising a silicon-carbon composite according to the second aspect of the present invention can be provided.

[0027] According to a fourth aspect of the present invention, a secondary battery comprising a negative electrode active material for a secondary battery comprising a silicon-carbon composite according to a second aspect of the present invention can be provided.

[0028] When a silicon-carbon composite comprising a porous carbon structure having pore characteristics such as a ratio of pores having an average size of 50 to 100 nm of 50% or more and a volume of pores having an average size of 50 to 100 nm of 0.5 cm³ / g or more, and a total pore (referring to all pores having a size of 350 nm or less) of 1.5 cm³ / g or more is used as a negative electrode active material, the capacity and efficiency of a secondary battery can be improved.

[0029] The porous carbon structure according to the present invention utilizes carbon black to control pore characteristics so that the ratio and pore volume of macropores having a size of 50 to 100 nm are satisfied within a certain range, and at the same time, pore uniformity can be increased, so that silicon can be uniformly deposited when applied to a silicon-carbon composite and the life retention rate of a secondary battery can be improved when applied as a negative electrode active material.

[0030] In addition to the effects described above, the effects of the present invention are described together with the details for implementing the invention below.

[0031] Figure 1 shows an SEM cross-sectional image (magnification: × 50,000) of a porous carbon structure of Example 1 of the present invention.

[0032] Figure 2 shows an SEM cross-sectional image (magnification: × 50,000) of a porous carbon structure of Example 2 of the present invention.

[0033] Figure 3 shows an SEM cross-sectional image (magnification: × 50,000) of a porous carbon structure of Comparative Example 1 of the present invention.

[0034] Figure 4 shows an SEM cross-sectional image (magnification: × 50,000) of a porous carbon structure of Comparative Example 2 of the present invention.

[0035] Figure 5 shows an SEM cross-sectional image (magnification: × 50,000) of a porous carbon structure of Comparative Example 3 of the present invention.

[0036] FIG. 6 shows a graph of the second pore distribution and the main peak of Example 1 and Comparative Examples 1 to 3 of the present invention.

[0037] Figure 7 shows an SEM image (magnification: × 50,000) of a silicon-carbon composite prepared by depositing silicon on a porous carbon structure of Example 1 of the present invention.

[0038] Figure 8 shows an SEM image (magnification: × 50,000) of a silicon-carbon composite prepared by depositing silicon on a porous carbon structure of Comparative Example 1 of the present invention.

[0039] Figure 9 shows an example conceptual diagram to explain the concept of void.

[0040] 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.

[0041] Where terms such as "comprising," "having," "consisting of," "arranging," or "having" are used for a component in this specification, other parts may be added unless "only" is used. Where a component is expressed in the singular, it includes cases where it is included in the plural unless specifically stated otherwise.

[0042] In this specification, micropore means that the average size of the pore is 2 nm or less, mesopore means that the average size of the pore is in the range of greater than 2 nm and less than or equal to 50 nm, and macropore means that the average size of the pore is in the range of greater than 50 nm and less than or equal to 350 nm.

[0043] In this specification, the porosity of micropores and mesopores was measured by the BET (Brunauer-Emmett-Teller) method (nitrogen adsorption / desorption method), and the porosity of macropores was measured by the mercury porosity measurement method.

[0044] In interpreting the components in this specification, they are interpreted to include an error range even if there is no separate explicit description.

[0045]

[0046] The present invention will be described in more detail below.

[0047]

[0048] silicon-carbon composite

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

[0050] A first pore having an average pore size of 50 nm or less; a second pore having an average pore size greater than 50 nm and less than or equal to 100 nm; and a third pore having an average pore size greater than 100 nm and less than or equal to 350 nm; comprising,

[0051] Based on a total pore volume of 100 vol% obtained by summing the first, second, and third pores, the ratio of the second pore is 50 vol% or more, and

[0052] The pore volume of the second pore is 0.5 cm³ / g or more, and

[0053] Total pore volume of 1.5 cm³ / g or more,

[0054] It is possible to provide a carbon black-based porous carbon structure.

[0055] The first pore of the silicon-carbon composite of the present invention has an average pore size of 50 nm or less, and includes micropores with an average pore size of 2 nm or less and mesopores with an average pore size of 2 nm to 50 nm.

[0056] In the present invention, silicon nanoparticles are impregnated or deposited into the first pores, which are micropores of a porous carbon structure, to form a silicon-carbon composite. Since the first pores increase the surface area of ​​the carbon structure, allowing for the inclusion of a large amount of silicon nanoparticles with high energy density, it is necessary to secure a certain amount or more, as this can contribute to the high capacity characteristics of the secondary battery as a negative electrode active material.

[0057] Meanwhile, if the first pores become too numerous, a surface remains unfilled with silicon, leading to the formation of a large amount of SEI (solid electrolyte interphase). This can cause a problem where the initial efficiency of the secondary battery decreases when applied as a negative electrode active material.

[0058] In this regard, it is preferable that the pore volume of the first pore be 0.15 to 0.4 cm³ / g. In the present invention, the pore volume of the first pore is measured by the nitrogen adsorption method and analyzed by density-functional theory (DFT).

[0059] The second pore of the silicon-carbon composite of the present invention is a macropore with an average pore size exceeding 50 nm, and in the present invention, a second pore having an average pore size of 50 nm to 100 nm is referred to as the second pore.

[0060] In the present invention, the second pore of the porous carbon structure is a relatively large pore, which can lower the diffusion resistance of the electrolyte of the secondary battery when applied as a negative electrode active material of a secondary battery, and can provide a space that allows for the smooth movement of lithium ions and mechanical damage during charging and discharging of silicon nanoparticles, thereby improving the stability of the negative electrode active material and the secondary battery.

[0061] In particular, the present invention is characterized by controlling the ratio and volume of the second pores to a higher level compared to the prior art, thereby increasing the amount of silicon deposited so that a silicon content of preferably 60 wt% or more, for example 70 wt% or more, for example 80 wt% or more can be achieved, and consequently, when applied as a negative electrode active material for a secondary battery, a high capacity of 2000 mA / h or more can be exhibited. In addition, by increasing the ratio of the second pores, spatial margin can be provided to prevent silicon expansion during charging and discharging of the secondary battery when applied as a negative electrode active material for a secondary battery, and this can contribute to improving the lifespan of the secondary battery.

[0062] In this regard, based on a total pore volume of 100 vol% including the first pore, the second pore, and the third pore, the proportion of the second pore may be 50 vol% or more, for example, 70 vol% or more, for example, 80 vol% or more. Additionally, the pore volume of the second pore may be 0.5 cm³ / g or more, for example, 0.8 cm³ / g or more, for example, 1.0 cm³ / g or more.

[0063] Meanwhile, if the second pores become too numerous, silicon fills the second pores and increases the size of the silicon particles, which may cause problems that lead to a decrease in the lifespan of the secondary battery; therefore, the pore volume of the second pores may be 2 cm³ / g or less, for example, 1.8 cm³ / g or less, for example, 1.5 cm³ / g or less, for example, 1.3 cm³ / g or less. In the present invention, the pore volume of the second pores is measured by the mercury pore measurement method.

[0064] According to one example of the present invention, the pore volume occupied by the first pore and the second pore within the porous carbon structure may be 0.6 cm³ / g or more, for example 1.0 cm³ / g or more, for example 1.5 cm³ / g or more, and the upper limit value may vary depending on the pore volume of the second pore described above. This is intended to provide sufficient pores within the porous carbon structure, thereby realizing the effects described above, including proper impregnation of silicon particles.

[0065] The porous carbon structure of the present invention is characterized by being manufactured using carbon black instead of activated carbon, unlike the prior art. Since porous carbon structures manufactured with activated carbon generally contain mostly micropores with an average pore size of 20 nm or less and exhibit conditions where the micropore volume is 0.4 cm³ / g or more, they are not suitable for manufacturing a porous carbon structure having pore characteristics for application to the high-performance silicon-carbon composite intended in the present invention (see FIG. 3).

[0066]

[0067] According to one example of the present invention, the porous carbon structure

[0068] (S1) A step of steam activating carbon black at a temperature of 800℃ or higher;

[0069] (S2) Step of grinding steam-activated carbon black;

[0070] (S3) A step of mixing the above-mentioned crushed carbon black with a binder;

[0071] (S4) A step of spray-drying the above mixture; and

[0072] (S5) The above-mentioned dried product may be obtained by sequentially carrying out the step of carbonizing it at a temperature of 500 to 1500°C, but is not necessarily limited thereto.

[0073] Thus, the method for manufacturing a porous carbon structure of the present invention may include the methods of (S1) to (S5) above.

[0074] In the above step (S1), steam activation is performed on the carbon black at a temperature of 800°C or higher. By doing so, the carbon within the carbon black is activated, increasing the pores and surface area, forming micropores with an average pore size of 50 nm or less, and allowing the pore volume to be controlled.

[0075] The carbon black resulting from step (S1) above may have a specific surface area (BET) of 300 to 1500 m² / g, for example 500 to 1200 m² / g, for example 800 to 1000 m² / g.

[0076] According to one example, the temperature of the steam activation may be 800 to 1200°C, for example, 900 to 1000°C. If the temperature is below the lower limit of the above temperature, there may be a problem that the reaction time increases significantly and it is difficult to provide a pore volume including micropores and mesopores intended in the present invention, and if the temperature exceeds the upper limit, there may be a problem that the inflow of impurities increases significantly due to the durability of the reactor (it is difficult to find a material for the reactor that has durability against temperatures exceeding 1200°C).

[0077] According to one example of the present invention, carbon black suitable for manufacturing the porous carbon structure may have an iodine absorption number (IA) of 100 mg / g or more, for example, 120 mg / g or more, for example, 140 mg / g or more, for example, 140 mg / g or more, and preferably 200 mg / g or less. When satisfying an iodine absorption number within this range, it is suitable for manufacturing a carbon structure having a desired pore size. Specifically, the iodine adsorption amount (IA) is a physical property value that typically represents the primary particle size (hereinafter "particle size") of carbon black. Since there is a tendency for the pore size to increase as the particle size increases, and conversely, for the pore size to decrease as the particle size decreases, it is important to use carbon black having an appropriate iodine adsorption amount value in order to meet the pore size targeted in the present invention. Therefore, from this perspective, it is preferable that the iodine adsorption amount value be 100 to 200 mg / g.

[0078] In addition, the carbon black may have an oil absorption number (OAN) of 100 ml / 100 g or more, for example, 120 ml / 100 g or more, for example, 140 ml / 100 g or more, for example, 160 ml / 100 g or more, for example, 180 ml / 100 g or more, preferably 300 ml / 100 g or less, and more preferably 250 ml / 100 g or less. When the oil absorption number within this range is satisfied, it is suitable for forming the desired pore volume. Specifically, the oil absorption number is a physical property indicating the degree of structural development of the carbon black; if the oil absorption number value is low, the degree of structural development is low, which tends to result in a lower pore volume when manufactured into a structure. Conversely, a high oil adsorption value promotes structural development of the carbon black, which can contribute to increasing the pore volume of the structure. Therefore, if the oil adsorption value of the carbon black is 100 ml / 100 g or less, there is insufficient void volume for silicon deposition during the chemical vapor deposition (CVD) process. On the other hand, if the oil adsorption value exceeds 300 ml / 100 g, it can have adverse effects, such as increasing the viscosity of the slurry during the subsequent cathode slurry preparation process, which clogs the nozzle during the subsequent spraying process, and causing problems by forming excessively large pores through the formation of internal microbubbles during the slurry preparation process. Additionally, if the oil adsorption value becomes too high, it can also cause problems by increasing the particle size when manufacturing the carbon structure.

[0079] According to one example, the above step (S1) can be performed under an inert gas such as nitrogen gas.

[0080]

[0081] In the above step (S2), a step of pulverizing the steam-activated carbon black is performed. According to one example, the pulverization in (S2) may be carried out using an instrument air (pneumatic, IA) method, and the pneumatic pressure may be formed at a condition of 5 bar or higher. The average particle size (D) of the pulverized carbon black 50 ) can be controlled to be 1 μm or less, for example, 0.5 μm or less, for example, 0.3 μm or less. Through such step (S2), micropores with an average pore size of 50 nm or less can be formed.

[0082]

[0083] In step (S3) above, the step of mixing the carbon black crushed in (S2) with a binder is carried out. The binder may be used without special restrictions as long as it has a high carbonization yield, but for example, pitch, phenolic resin, polyacrylonitrile resin, polyvinyl alcohol resin, etc., may be used. At this time, in order to achieve the pore characteristics intended in the present invention, when the total weight of the carbon black and binder is 100% by weight, it is preferable to mix the binder at 10% by weight or more, and for example, at 50% by weight or less. If the content of the binder is below the lower limit, it may be difficult to maintain the strength and shape of the carbon structure, and problems such as cracking may occur during the manufacture of the electrode plate; if it exceeds the upper limit, it may be difficult to impart the size and volume of the pores (micropores, mesopores, macropores) intended in the present invention to the carbon structure. By controlling the pore size and volume through the mixing of such step (S3), a porous carbon structure having the pore distribution and characteristics desired in the present invention can be manufactured.

[0084] According to one example, based on the combined amount of carbon black and binder, it is preferable that the solid content be 4 weight% or less. When preparing a slurry for a secondary battery negative electrode material, the viscosity varies depending on the solid content, and the viscosity acts as a factor affecting the particle size control of the structure when forming the negative electrode material using a spray drying method. The amount of carbon black used varies depending on the solid content, which in turn affects the carbon black content that can be included per unit particle of the carbon structure, and consequently, can affect the macropore volume of the manufactured carbon structure.

[0085]

[0086] In step (S4) above, a step of spray drying the mixture obtained in step (S3) above may be performed, and for example, the slurry input speed may be 50 to 200 g / min. By applying a spray drying method such as this, it is easy to manufacture spherical carbon structures, and consequently, it is advantageous to manufacture spherical cathode materials, and excellent particle size uniformity of the carbon structures can be achieved, for example, particle size uniformity satisfying a Span value of less than 1.2. At this time, by drying using nitrogen at high pressure (e.g., 0.5 to 4 bar) during spray drying, the average particle size (D 50 ) can be adjusted to a range of 4~10㎛.

[0087]

[0088] In the above step (S5), the above-mentioned dried material may be subjected to a step of carbonization or charring at a temperature of 500 to 1500°C. Through carbonization, a porous carbon structure in which a solid carbon structure is firmly formed can be obtained. Carbonization is a chemical process of incomplete combustion of a solid when treated with high heat. Such carbonization can remove hydrogen and oxygen from the solid through the action of heat, so that the residual product, char, consists mainly of carbon. More importantly, such carbonization can increase the conductivity required for a negative electrode active material for a secondary battery.

[0089] The above carbonization step can be performed under an inert gas such as nitrogen gas, and can be performed for, for example, for a time of 30 minutes or more.

[0090]

[0091] According to another aspect of the present invention, a silicon-carbon composite comprising a carbon black-based porous carbon structure according to one aspect of the present invention can be provided.

[0092] According to one example, the silicon content in the silicon-carbon composite of the present invention may be 60 weight% or more, for example 70 weight% or more, and 80 weight% or more, so that a negative electrode active material for a high-capacity secondary battery can be obtained.

[0093] According to one example, the average particle size of the silicon particles included in the silicon-carbon composite may be 1 nm to 100 nm, but is not limited thereto. In order to manufacture a negative electrode active material having a high capacity retention rate for a secondary battery, the silicon particle size must be reduced to suppress structural deformation of the silicon particles during charging and discharging of the secondary battery. Therefore, if the average particle size of the silicon nanoparticles exceeds 100 nm, there may be a problem in which the surface of the silicon particles cracks during charging and discharging, leading to a decrease in performance.

[0094] According to one example, the average particle size of the silicon-carbon composite of the present invention may be 4 μm to 8 μm. If the average particle size of the silicon-carbon composite particles is less than 4 μm, when applied as a negative electrode active material of a secondary battery, a large amount of SEI layer (Solid Electrolyte Interphase layer) is formed on the electrode surface during charging and discharging of the secondary battery, which may result in a decrease in initial efficiency. On the other hand, if the average particle size of the silicon-carbon composite particles is greater than 8 μm, when applied as a negative electrode active material of a secondary battery, there may be a problem in which the lifespan is reduced due to shrinkage and expansion of the silicon-carbon composite during charging and discharging of the secondary battery.

[0095]

[0096] The present invention will be explained in more detail below through examples and experimental examples. However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0097]

[0098] Preparation Example 1 - Preparation of a porous carbon structure

[0099] Carbon black (OCI, DC3501) was steam-activated at 950°C for 2 hours, and the specific surface area (BET) of the steam-activated carbon black was measured to be 820 m² / g. Pulverizing was performed using an pneumatic (IA) method under conditions of 6.5 bar, and the average particle size (D) of the pulverized carbon black 50The value was measured to be 0.15 μm (measured with PSA). Carbon black and a binder (carbon black:phenol resin = 55:45, weight ratio) were mixed in isopropyl alcohol (IPA). Then, spherical powder particles were formed by drying using a spray drying method (flow rate: 70 ml, N2 gas: 200 m³ / min). The spherical particles were carbonized at a temperature of 1000°C for 1 hour to prepare the porous carbon structure of Example 1. An SEM image of the prepared porous carbon structure is shown in Figure 1, and the pore properties were analyzed using BET (nitrogen adsorption method) and mercury pore method with a porosimeter (manufacturer: Micromeritics, model name: AutoPore IV).

[0100] The porous carbon structures of Example 2 and Comparative Examples 1 to 3 were each prepared in a manner similar to Example 1, using the carbon raw materials of Table 1 below, while controlling the pore properties differently as shown in Table 2 below, and SEM images of each porous carbon structure are shown in Figures 1 to 5.

[0101] In addition, to confirm the second pores with an average pore size greater than 50 nm and less than or equal to 100 nm among the macropores and their pore ratios for the porous carbon structures prepared in Examples 1 and 2 and Comparative Examples 1 to 3, the macropore distribution and the main peak of the pores were confirmed using a Prosimeter (Manufacturer: Micromeritics, Model: AutoPore IV), and the results are shown in Fig. 6. Fig. 6 represents the logarithm of the volume change of nitrogen infiltrated into the sample within a specific pore size range, where the vertical axis represents Log Differential Intrusion (cm²). 3 / g), the horizontal axis is Pore Size Diameter (nm). Cumulative Intrusion, that is, the accumulated amount of nitrogen intrusion (the total volume of nitrogen intruded per 1g of sample), is represented as a logarithmic derivative. It is expressed as a Log Differential Intrusion value to facilitate the identification of the pore size distribution and the dominant pore size when the pore size distribution spans a wide range. It is interpreted that the larger the peak value representing the Pore Size Diameter in Fig. 6, the more volume the corresponding pore size occupies.

[0102] Raw Material IA (mg / g) OAN (㎖ / 100g) Example 1 Carbon Black Cabot, LITX-HP125220 Example 2 Carbon Black OCI, DC3502144180 Comparative Example 1 Carbon Black OCI, DC2700G85154 Comparative Example 2 Carbon Black OCI, N3268272 Comparative Example 3 Carbon Black OCI, N234120125

[0103] BET Mercury Porosity Total Pores 1st Pores Volume (cm³ / g) Main Peak (nm) 2nd Pores Volume (cm³ / g) 2nd Pores Ratio (vol%) Total Pores Volume (cm³ / g) Example 1 0.35 7 21.0 58 21.6 8 Example 20.37 7 31.2 67 12.2 Comparative Example 10.36 134 0.1 21 11.3 2 Comparative Example 20.33 7 20.4 87 61.1 Comparative Example 30.35 66 0.4 67 01.0

[0104] Preparation Example 2 - Preparation of a Silicon-Carbon Composite

[0105] Approximately 5 g of the porous carbon structures of Example 1 and Comparative Examples 1 to 3 were placed on a crucible inside a reaction apparatus and heated to a temperature of 455°C. At atmospheric pressure, a mixed gas of monosilane gas and hydrogen gas (mixed in a ratio of monosilane gas : hydrogen mixed gas = 50 sccm : 450 sccm) was injected into the reaction apparatus heated to 455°C and reacted. After reacting for approximately 2 hours, the mixture was cooled to room temperature to obtain approximately 10 g of a grayish-black solid silicon-carbon composite deposited in the crucible.

[0106] A silicon-carbon composite was prepared by performing a chemical vapor deposition reaction at 455°C for 2 hours while flowing a mixed gas of acetylene gas and argon gas (acetylene gas : argon gas = C2H2 : Ar = 250 sccm : 250 sccm) over 2g of the above-mentioned silicon-carbon composite. An SEM image of the silicon-carbon composite of Example 1 is shown in Fig. 7, and an SEM image of the silicon-carbon composite of Comparative Example 1 is shown in Fig. 8.

[0107] The silicon content (unit: weight%) in the manufactured silicon-carbon composite was analyzed using an element analyzer (EA) and is shown in Table 3 below.

[0108] Experimental Example 1 - Half-Cell Test

[0109] The silicon-carbon composite prepared above was prepared as a negative electrode active material. Separately, conductive carbon black (Super P) and carbon nanotube conductive material (SWCNT) were mixed (Super P : SWCNT = 9 : 1 by weight ratio) to prepare a conductive material. Separately, sodium salt of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) were mixed (CMC : SBR = 3 : 7 by weight ratio) to prepare a binder. The negative electrode active material, conductive material, and binder prepared above were mixed using a sinker mixer (negative electrode active material : conductive material : binder = 8 : 1 : 1 by weight ratio) to obtain a negative electrode slurry.

[0110] The above cathode slurry was applied to a copper foil with a thickness of 18 μm and dried at 80°C for 1 hour. Then, after heat treatment in a vacuum oven at 100°C for 12 hours, it was punched to a 16 mm Ψ to manufacture a cathode plate.

[0111] The fabricated negative electrode plate was prepared as a coin cell using Li metal as the counter electrode, and its electrochemical characteristics were verified. Using the TOSCAT-3100 half-cell device, the charging and discharging conditions were set to charging CC / CV: 0.005V / 0.005C, discharging CC: 1.5V, and the rate limit: 0.1C. Charging and discharging were performed, and the initial charge capacity (ICC, mAh / g), initial discharge capacity (IDC, mAh / g), and initial efficiency (ICE, %) were measured. The results are shown in Table 2 below.

[0112] Si Content (Wt%) ICC (mAh / g) ICC (mAh / g) ICE (%) Example 1 75 264 124 339 2.1 Comparative Example 1 74 234 3216 39 2.3 Comparative Example 2 58 2248 208 29 2.6 Comparative Example 3 55 2232 202 09 0.5

[0113] As can be seen from Table 3 above, Example 1 and Comparative Example 1 had Si content that was nearly similar but slightly higher, and the capacity and efficiency were also nearly similar within the margin of error. However, Comparative Examples 2 and 3, in which the pore volume of the second pore was less than 1.0 cm³ / g, had a Si content of less than 60 wt%, and accordingly, the IDC value, which is an indicator of capacity, was lower than that of Example 1.

[0114] Experimental Example 2 - Coin Full-Cell Test

[0115] [Example 1]

[0116] A cathode material was prepared by mixing 8 wt% of the silicon-carbon composite of Example 1 prepared in Preparation Example 2 and 92 wt% of graphite by weight. Separately, a conductive material was prepared by mixing conductive carbon black (Super P) and carbon nanotube conductive material (SWCNT) (Super P : SWCNT = 9 : 1 by weight ratio). Separately, a binder was prepared by mixing CMC (sodium salt of carboxymethyl cellulose) and SBR (styrene-butadiene rubber) (CMC : SBR = 3 : 7 by weight ratio). The cathode material, conductive material, and binder prepared above were mixed using a sinker mixer (cathode material : conductive material : binder = 95.8 : 1 : 3.2 by weight ratio) to obtain a cathode slurry. The cathode slurry was coated onto a copper foil with a thickness of 18 μm and dried at 80°C for 1 hour. Then, after heat treatment in a vacuum oven at 100°C for 12 hours, a cathode plate was manufactured by punching it to a size of 16 mm Ψ.

[0117] The fabricated negative electrode plate was punched into a 14mm Ψ NCM811 positive plate and used as a counter electrode to form a coin full cell, and its electrochemical characteristics were verified. During the initial 1st and 2nd cycles (cycle formation), the charge CC / CV rate limit was set to 0.1C and the cut-off condition to 4.25V / 0.05C, while the discharge CC rate limit was set to 0.1C and the cut-off condition to 2.5V. From the 3rd cycle onwards, the rate limit was set to 0.5C, and 100 cycles were performed to measure the life characteristics; the results are shown in Table 4 below.

[0118] [Comparative Example 1]

[0119] The experiment was conducted in the same manner as Example 1 of Experimental Example 2, except that the negative electrode material was prepared by mixing 9 wt% of the silicon-carbon composite of Comparative Example 1 prepared in Preparation Example 2 and 91 wt% of graphite by weight.

[0120] [Comparative Example 2]

[0121] The experiment was conducted in the same manner as Example 1 of Experimental Example 2, except that the negative electrode material was prepared by mixing 9 wt% of the silicon-carbon composite of Comparative Example 2 prepared in Preparation Example 2 and 91 wt% of graphite by weight.

[0122] [Comparative Example 3]

[0123] The experiment was conducted in the same manner as Example 1 of Experimental Example 2, except that the negative electrode material was prepared by mixing 8.5 wt% of the silicon-carbon composite of Comparative Example 3 prepared in Preparation Example 2 and 91.5 wt% of graphite by weight.

[0124] Life retention rate (100 cycles) Example 192% Comparative Example 177% Comparative Example 282% Comparative Example 374%

[0125] As can be seen from the experimental results above, Example 1 and Comparative Example 1 had the same silicon loading (capacity) and similar capacities, but differed only in whether they satisfied the level intended by the present invention in terms of the pore volume and pore ratio of the second pore. However, as a result of the lifespan retention rate evaluation, it was confirmed that Example 1 showed a lifespan retention rate of 97%, which is significantly improved compared to the lifespan retention rate of Comparative Example 1 (77%). This is because the carbon structure of Comparative Example 1 had a low ratio of second pores at 11 vol%, which resulted in reduced uniformity when silicon was deposited by the CVD method and increased large voids (see Fig. 9) within the silicon-carbon composite, leading to a reduced lifespan. On the other hand, the carbon structure of Example 1 had a high ratio of second pores at 82 vol%, which resulted in improved uniformity when silicon was deposited by the CVD method. Consequently, large voids within the silicon-carbon composite were reduced, leading to a higher lifespan retention rate. This structural difference was also evident in the comparison of Figs. 7 and 8. Therefore, if the pore volume and pore ratio of the second pores intended for the present invention are not satisfied, when applied as a negative electrode material for a secondary battery, a reduction in lifespan may occur due to the collapse and erosion of the porous carbon structure of the negative electrode material during charging and discharging of the secondary battery. Meanwhile, Comparative Examples 2 and 3 have a ratio of the second pores similar to Example 1, but the pore volume of the second pores does not satisfy the requirement of being 0.5 cm³ / g or more, so it can be confirmed that the silicon content has decreased and the lifespan retention rate has decreased.

[0126]

[0127] Although the embodiments of this specification have been described in more detail with reference to the attached drawings, this specification is not necessarily limited to these embodiments and may be modified in various ways within the scope of the technical spirit of this specification. Accordingly, the embodiments disclosed in this specification are intended to explain, not limit, the technical spirit of this specification, and the scope of the technical spirit of this specification is not limited by these embodiments. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. The scope of protection of this specification shall be interpreted by the claims, and all technical spirits within an equivalent scope shall be interpreted as being included within the scope of rights of this specification.

Claims

1. A first pore having an average pore size of 50 nm or less; a second pore having an average pore size greater than 50 nm and less than or equal to 100 nm; and a third pore having an average pore size greater than 100 nm and less than or equal to 350 nm; comprising, Based on a total pore volume of 100 vol% obtained by summing the first, second, and third pores, the ratio of the second pore is 50 vol% or more, and The pore volume of the second pore is 0.5 cm³ / g or more, and Total pore volume of 1.5 cm³ / g or more, Carbon black-based porous carbon structure.

2. In Paragraph 1, The pore volume of the first pore is 0.4 cm³ / g or less, Carbon black-based porous carbon structure.

3. In Paragraph 2, The sum of the pore volumes of the first pore and the second pore is 0.6 cm³ / g or more, Carbon black-based porous carbon structure.

4. In Paragraph 1, The pore volume of the second pore is 1.0 cm³ / g or more, Silicon-carbon composite.

5. In Paragraph 1, The above porous carbon structure is, (S1) A step of steam activating carbon black at a temperature of 800℃ or higher; (S2) Step of grinding steam-activated carbon black; (S3) A step of mixing the above-mentioned crushed carbon black with a binder; (S4) A step of spray-drying the above mixture; and (S5) A step of carbonizing the above-mentioned dried material at a temperature of 500 to 1500°C; obtained by sequentially proceeding with the above-mentioned step, Carbon black-based porous carbon structure.

6. In Paragraph 5, The carbon black of step (S1) above satisfies an iodine absorption number (IA) of 100 mg / g or more and an oil absorption number (OAN) of 100 ml / 100 g or more, Carbon black-based porous carbon structure.

7. A porous carbon structure based on carbon black according to any one of claims 1 to 5, Silicon-carbon composite.

8. In Paragraph 7, Based on 100 weight% of the total weight of the silicon-carbon composite, the silicon content contained in the silicon-carbon composite is 60 weight% or more, Silicon-carbon composite.

9. A negative electrode active material for a secondary battery comprising a silicon-carbon composite according to either claim 7 or 8.

10. A secondary battery comprising a negative electrode active material for a secondary battery comprising a silicon-carbon composite according to either claim 7 or 8.

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