WO2025143677A1 - Carbon-silicon/carbon composite and method for producing same - Google Patents

Abstract

The present invention relates to: a carbon-silicon/carbon composite in which a silicon/carbon composite matrix is formed on the surface of and inside the pores of a porous carbon support having controlled pore properties; and a method for producing same. When the carbon-silicon/carbon composite according to an embodiment of the present invention is used as a negative electrode active material, the overall silicon size can be suppressed, and the formation of Crystal-Li_xSi_y (e.g., Li₁₅Si₄ or Li_3.75Si), which is an intermediate phase affecting battery performance degradation, can be suppressed to mitigate battery performance degradation during repeated charging and discharging.

Description

Carbon-silicon/carbon composite and its manufacturing method

The present invention relates to a carbon-silicon/carbon composite, and more particularly, to a carbon-silicon/carbon composite and a method for producing the same.

Carbon materials are materials made of carbon, one of the most common resources on Earth. Carbon materials are very light, strong, and have excellent electrical and thermal conductivity, making them a key material widely used in fields such as hydrogen cars, aviation, secondary batteries, and high-end consumer goods.

Carbon materials can be manufactured from various raw materials such as palm shell, polyacrylonitrile, rayon, and pitch. Among these, it is difficult to control the molecular weight and components of carbon materials manufactured from solid raw materials such as palm shell (Korean Patent Application Publication No. 10-2019-0093960).

On the other hand, pitch, a viscoelastic solid polymer extracted from crude oil or plants, has the advantages of high yield when converted into carbon materials, low cost of raw materials, and its molecular structure is closer to the graphite structure than other raw materials, which can reduce energy required for heat treatment (U.S. Patent Nos. 4,242,196 and 4,340,464).

In particular, pyrolysis fuel oil (PFO), naphtha cracking bottom oil (NCB), vacuum residue (VR), and fluid catalytic cracking decant oil (FCC-DO), which are obtained as by-products in the petroleum refining process, have a high content of aromatic compounds and a low content of impurities such as sulfur and nitrogen, and therefore pitch manufactured from them is attracting attention as a material for carbon materials.

Meanwhile, attempts are being made to use silicon-based negative electrode active materials to improve the capacity of secondary batteries. Silicon theoretically has a very high energy density, and is attracting attention as a next-generation battery negative electrode active material to replace graphite. However, it has the problem of very low mechanical stability, such as the volume increasing by up to 300% during charging and discharging, and the silicon, which is the negative electrode active material, is crushed as charging and discharging proceeds.

Accordingly, research has been conducted to solve these problems, but in the case of conventional negative active materials, there was a problem in that the phenomenon of fragmentation due to volume expansion was not sufficiently resolved.

[Prior art literature]

[Patent Document]

(Patent Document 0001) Republic of Korea Patent Application Publication No. 10-2019-0093960

(Patent Document 0002) U.S. Patent No. 4,242,196

(Patent Document 0003) U.S. Patent No. 4,340,464

An object of the present invention is to provide a carbon-silicon/carbon composite in which a silicon/carbon composite matrix is formed in the pores and/or surface of a porous carbon support having controlled pore characteristics.

Another object of the present invention is to provide a method for producing the carbon-silicon/carbon composite.

Another object of the present invention is to provide a negative electrode active material comprising the carbon-silicon/carbon composite.

The present invention provides a carbon-silicon/carbon composite including a porous carbon support having a volume ratio of mesopores having a pore size of 2 to 50 nm based on the total pore volume of 5 to 80%, and a silicon/carbon composite matrix disposed on the surface and inside the pores of the porous carbon support.

According to one embodiment of the present invention, the porous carbon support may have a BET specific surface area of 300 to 3,000 m2/g, a tap density of 0.05 to 0.5 g/㎖, and an average particle diameter of 1 to 20 ㎛.

Additionally, the content of silicon among the total weight of the carbon-silicon/carbon composite may be 20 to 70 wt%.

Additionally, the silicon/carbon composite matrix may be 10 to 90 wt% of the total weight of the carbon-silicon/carbon composite.

Additionally, the average size of the silicon crystals in the silicon/carbon composite matrix may be 10 nm or less.

Additionally, the carbon-silicon/carbon composite may have a c/a peak ratio of 0 to 1.5.

In addition, the present invention provides a method for producing a carbon-silicon/carbon composite, including a step of forming a silicon/carbon composite matrix on the surface and inside the pores of a porous carbon support to produce a carbon-silicon/carbon composite.

According to one embodiment of the present invention, before the step of manufacturing the carbon-silicon/carbon composite, the method may further include: (1) a step of synthesizing pitch by thermal decomposition and condensation polymerization of a petroleum-based raw material, (2) a step of solidifying and pelletizing the pitch to obtain a pellet-like pitch or solidifying, pelletizing, and pulverizing the pitch to obtain a powder-like pitch, (3) a step of stabilizing the pellet-like pitch or the powder-like pitch, (4) a step of carbonizing the stabilized pitch to obtain a carbonized body, and (5) a step of activating the carbonized body to obtain a porous carbon support.

In addition, the silicon/carbon composite matrix can be formed by composite CVD of a silicon source and a carbon source on the porous carbon support.

Additionally, the gas flow ratio of the silicon source and the carbon source can be 1:0.1 to 1:2.

In addition, the present invention provides a negative electrode active material comprising the carbon-silicon/carbon composite described above.

In addition, the present invention provides an all-solid-state battery including a solid electrolyte interphase (SEI) film including the carbon-silicon/carbon composite described above.

The carbon-silicon/carbon composite according to an embodiment of the present invention forms a silicon/carbon composite matrix in the pores and/or surface of a porous carbon support having a high ratio of mesopores among the total pores, thereby suppressing the overall silicon size when the carbon-silicon/carbon composite is used as an anode active material, and suppressing the formation of an intermediate phase Crystal-Li _x Si _y (e.g., Li ₁₅ Si ₄ or Li _3.75 Si) that affects battery performance deterioration, thereby alleviating battery performance deterioration during repeated charge/discharge.

In addition, the manufacturing method according to the embodiment of the present invention can easily manufacture a carbon-silicon/carbon composite having the above characteristics.

FIG. 1 is a SEM image of a carbon-silicon/carbon composite (Example 1) according to one embodiment of the present invention.

Figure 2 is a graph showing the electrochemical evaluation results (charge/discharge efficiency, ICE, and capacity retention rate) of Example 1, Example 2, and Comparative Example 1 of the present invention.

Figure 3 is a dQ/dV measurement graph of Example 1, Example 2, and Comparative Example 1 of the present invention.

FIG. 4 is an image showing the results of XRD analysis of a carbon-silicon/carbon composite (Example 1) according to one embodiment of the present invention.

Figure 5 is an image of the XRD analysis results according to heat treatment temperature (Examples 1-1 to 1-3) of a carbon-silicon/carbon composite (Example 1) according to a comparative example and an embodiment of the present invention.

The present invention is not limited to the contents disclosed below, and may be modified in various forms as long as the gist of the invention is not changed.

As used herein, the term “comprising” means that other components may be included unless otherwise specified.

All numbers and expressions expressing quantities of ingredients, reaction conditions, and the like described in this specification are to be understood as being modified in all cases by the term "about" unless otherwise stated.

The present invention will be described in more detail below.

Carbon-silicon/carbon composite

According to one embodiment of the present invention, a carbon-silicon/carbon composite is provided, which includes a porous carbon support having a volume ratio of mesopores having a pore size of 2 to 50 nm based on a total pore volume of 5 to 80%, and a silicon/carbon composite matrix disposed on a surface and inside the pores of the porous carbon support.

Hereinafter, each component of a carbon-silicon/carbon composite according to one embodiment of the present invention is described.

porous carbon support

A carbon-silicon/carbon composite according to an embodiment of the present invention comprises a porous carbon support.

The porous carbon support may have a volume ratio of mesopores having a pore size of 2 to 50 nm of 5 to 80%, preferably 30 to 60%, and more preferably 40 to 50%, based on the total pore volume. If the volume ratio of the mesopores of the porous carbon support is less than 5%, there may be too many micropores, so that a relatively large amount of silicon/carbon composite matrix may be formed on the outside of the particle, and if the volume ratio of the mesopores of the porous carbon support exceeds 80%, the hardness of the particle is insufficient, so that when an electrode is manufactured using the same, there is a concern that the structure of the electrode may collapse.

In addition, the porous carbon support may have a BET specific surface area of 300 to 3,000 m2/g. Preferably, the porous carbon support may have a BET specific surface area of 300 to 1,500 m2/g, more preferably, a BET specific surface area of 500 to 1,500 m2/g. When the BET specific surface area of the porous carbon support is less than 300 m2/g, there may be too many macropores and thus a lack of effective pores, and when the BET specific surface area of the porous carbon support exceeds 3,000 m2/g, there may be too many micropores and thus a relatively large amount of silicon/carbon composite matrix may be deposited on the outside of the particles.

In addition, the porous carbon support may have a tap density of 0.05 to 0.5 g/㎖. Preferably, the porous carbon support may have a tap density of 0.05 to 0.3 g/㎖, more preferably, a tap density of 0.1 to 0.3 g/㎖. When the tap density of the porous carbon support is less than 0.05 g/㎖, process control may be difficult during formation of a silicon/carbon composite matrix, which may result in a decrease in yield, and when the tap density of the porous carbon support exceeds 0.5 g/㎖, it may be difficult to uniformly form a matrix during formation of a silicon/carbon composite matrix.

And, the porous carbon support may have an average particle size of 1 to 20 ㎛. Preferably, the porous carbon support may have an average particle size of 3 to 20 ㎛, more preferably an average particle size of 3 to 10 ㎛. When the average particle size of the porous carbon support is less than 1 ㎛, the silicon/carbon composite matrix does not sufficiently penetrate into the pores and is formed in large amounts only on the outside of the particles, and when the average particle size of the porous carbon support exceeds 20 ㎛, it is difficult for the silicon/carbon composite matrix to sufficiently form within the pores.

Since the carbon-silicon/carbon composite according to an embodiment of the present invention includes a porous carbon support having the above characteristics, when this carbon-silicon/carbon composite is used as an anode active material, it has excellent electrical conductivity and can relieve stress due to volume expansion of silicon.

Silicon/carbon composite matrix

A carbon-silicon/carbon composite according to an embodiment of the present invention comprises a silicon/carbon composite matrix disposed on the surface and inside the pores of the porous carbon support.

In the present invention, the silicon/carbon composite matrix may mean a continuous phase (Si _x C _y ) in which a silicon portion formed by a Si-Si bond and a silicon carbide portion formed by a Si-C bond are mixed.

In a specific example of the present invention, as described below, a carbon-silicon/carbon composite can be obtained by performing composite CVD of a silicon source and a carbon source on a porous carbon support.

In a specific embodiment of the present invention, the silicon/carbon composite matrix may include crystalline silicon particles. At this time, the size of the silicon crystals may be on the nano level. Specifically, the average size of the silicon crystals in the silicon/carbon composite matrix may be 10 nm or less. Preferably, the average size of the silicon crystals in the silicon/carbon composite matrix may be 8 nm or less, 5 nm or less, 3 nm or less, or 1 nm or less. When the average size of the silicon crystals in the silicon/carbon composite matrix satisfies the above range, the size of the stress due to the volume expansion of silicon is reduced, so that the life characteristics of the negative electrode active material may be improved. Meanwhile, the fact that the average particle size of the silicon crystals satisfies the above range may be due to the fact that the Si-C bond is more preferred than the Si-Si bond.

Meanwhile, since the silicon/carbon composite matrix is included in the carbon-silicon/carbon composite, the silicon content in the total weight of the carbon-silicon/carbon composite may be 20 to 70 wt%, and preferably 25 to 65 wt%. If the silicon content in the total weight of the carbon-silicon/carbon composite is less than 20 wt%, the electric capacity may be reduced, and if it exceeds 70 wt%, the problem caused by the volume expansion of silicon during charge and discharge may not be solved, which may cause structural damage to the negative electrode material and deteriorate the cycle characteristics.

In addition, the silicon/carbon composite matrix may be 10 to 90 wt% of the total weight of the carbon-silicon/carbon composite, and preferably 15 to 85 wt%. If the silicon/carbon composite matrix is less than 10 wt% of the total weight of the carbon-silicon/carbon composite, the electric capacity may be reduced, and if it exceeds 90 wt%, a problem caused by volume expansion of silicon during charge and discharge may not be resolved, which may cause structural damage to the negative electrode material and deteriorate cycle characteristics.

Meanwhile, the silicon may be crystalline or amorphous, and preferably may be amorphous or a similar phase. When the silicon is crystalline, the smaller the crystallite size, the more dense the composite can be obtained, so that the strength of the matrix is strengthened and cracks can be prevented. Accordingly, the initial efficiency or cycle life characteristics of the secondary battery can be improved.

The above silicon may further include a silicon oxide compound. The silicon oxide compound may be represented by a general formula of SiO _x (0.5≤x≤2). Here, when the value of x is less than 0.5, expansion and contraction may increase during charge and discharge of the secondary battery, and the life characteristics may deteriorate, and when x exceeds 2, the initial efficiency of the secondary battery may decrease as the amount of inactive oxide increases.

The content of the silicon oxide compound in the silicon may be 50 wt% or less based on the total weight of the silicon. If the content of the silicon oxide compound in the silicon exceeds 50 wt%, the initial efficiency of the secondary battery may be reduced.

Meanwhile, the carbon-silicon/carbon composite may have a c/a peak ratio of 0 to 1.5, preferably 0 to 1.3, more preferably 0 to 1.2, even more preferably 0 to 1.18, and even more preferably 0 to 1.15. When the c/a peak ratio of the carbon-silicon/carbon composite satisfies the above range, it may be more advantageous in achieving the purpose of the present invention, such as having an effect of maintaining stable electrochemical performance during a life evaluation. At this time, the c/a peak ratio represents the peak ratio of crystal (c) and amorphous (a).

Method for producing carbon-silicon/carbon composites

A carbon-silicon/carbon composite according to one embodiment of the present invention is manufactured by a manufacturing method including a step of manufacturing a carbon-silicon/carbon composite by forming a silicon/carbon composite matrix on the surface and inside the pores of a porous carbon support.

Meanwhile, according to one embodiment of the present invention, prior to the step of manufacturing the carbon-silicon/carbon composite, the present invention may further include: (1) a step of synthesizing pitch by thermal decomposition and condensation polymerization of a petroleum-based raw material, (2) a step of solidifying and pelletizing the pitch to obtain a pellet-like pitch or solidifying, pelletizing, and pulverizing the pitch to obtain a powder-like pitch, (3) a step of stabilizing the pellet-like pitch or the powder-like pitch, (4) a step of carbonizing the stabilized pitch to obtain a carbonized body, and (5) a step of activating the carbonized body to obtain a porous carbon support.

Hereinafter, each step of a method for manufacturing a carbon-silicon/carbon composite according to one embodiment of the present invention is described.

(1) Step

In the above step (1), pitch can be synthesized by thermal decomposition and polycondensation of petroleum-based raw materials.

In a specific embodiment of the present invention, the petroleum raw material may include at least one selected from the group consisting of pyrolysis fuel oil (PFO), naphtha cracking residue (NCB), ethylene cracker bottom oil (EBO), vacuum residue (VR), de-asphalted oil (DAO), atmospheric residue (AR), fluid catalytic cracking (RFCC-DO) oil, residue fluid catalytic cracking decant oil (RFCC-DO), and heavy aromatic oil. In a preferred embodiment of the present invention, the petroleum raw material may include pyrolysis fuel oil.

In a specific embodiment of the present invention, the petroleum-based raw material may contain an aromatic compound in an amount of 10 to 90 wt%. Preferably, the petroleum-based raw material may contain an aromatic compound in an amount of 20 to 80 wt%, more preferably 30 to 70 wt%. When the content of the aromatic compound in the petroleum-based raw material satisfies the above range, even if the solid pitch pellets described below are stabilized, carbonized, and activated without separately pulverizing, a porous carbon support having controlled pore characteristics can be obtained.

In a specific embodiment of the present invention, the aromatic compound may be a compound having 1 to 4 aromatic rings. Specifically, the aromatic compound may include at least one selected from the group consisting of substituted or unsubstituted benzene, naphthalene, phenanthrene, indene, biphenyl, anthracene, tetralin, and fluorene. In this case, even if the solid pitch pellets described below are stabilized, carbonized, and activated without separately pulverizing, a porous carbon support having controlled pore characteristics can be obtained.

In a specific embodiment of the present invention, the thermal decomposition and polycondensation of the petroleum raw material can be performed at a temperature of 350 to 500°C. In a preferred specific embodiment of the present invention, the thermal decomposition and polycondensation of the petroleum raw material can be performed at a temperature of 400 to 500°C. In a more preferred specific embodiment of the present invention, the thermal decomposition and polycondensation of the petroleum raw material can be performed at a temperature of 430 to 470°C. When the temperature of the thermal decomposition and polycondensation of the petroleum raw material is 350 to 500°C, a pitch containing a large amount of relatively low molecular weight components can be manufactured, and in the activation process of step (5) described below, components having relatively small molecular weights are vaporized first, thereby sufficiently forming mesopores in the carbon support. If the thermal decomposition and polycondensation temperature of the petroleum-based raw material is less than 350°C, it is difficult to manufacture pitch that is solid at room temperature, and if this temperature exceeds 500°C, the pitch contains a lot of relatively high molecular weight components, making it difficult to manufacture a carbon support having mesopores.

In a specific embodiment of the present invention, the thermal decomposition and polycondensation of the petroleum raw material can be performed under an atmosphere of an oxidizing gas, an inert gas, or a mixture thereof. In a preferred specific embodiment of the present invention, the oxidizing gas can be oxygen, ozone, or a combination thereof, the inert gas can be nitrogen, helium, neon, argon, or a combination thereof, and the mixture thereof can be air, but is not particularly limited thereto.

When an oxidizing gas is used in the thermal decomposition and polycondensation of petroleum-based raw materials, a pitch having a high softening point can be manufactured, but it is difficult to perform the thermal decomposition and polycondensation at high temperatures. When an inert gas is used in the thermal decomposition and polycondensation of petroleum-based raw materials, thermal decomposition and polycondensation can be performed at high temperatures, but it is difficult to manufacture a pitch having a relatively high softening point. When a mixed gas of an oxidizing gas and an inert gas is used in the thermal decomposition and polycondensation of petroleum-based raw materials, thermal decomposition and polycondensation can be performed at a relatively high temperature to manufacture a pitch having a relatively high softening point.

In a specific embodiment of the present invention, the gas may be supplied at a flow rate of 10 to 800 ml/min during the thermal decomposition and polycondensation of the petroleum raw material. In a preferred specific embodiment of the present invention, the gas may be supplied at a flow rate of 100 to 500 ml/min during the thermal decomposition and polycondensation of the petroleum raw material. When the flow rate of the gas is less than 10 ml/min, the yield of the pitch increases, but the low molecular weight component increases too much, which is disadvantageous for the subsequent process (e.g., stabilization). When the flow rate of the gas exceeds 800 ml/min, the yield of the pitch may decrease.

In a specific embodiment of the present invention, the thermal decomposition and polycondensation of the petroleum raw material can be performed for 1 to 10 hours. In a preferred specific embodiment of the present invention, the thermal decomposition and polycondensation of the petroleum raw material can be performed for 2 to 8 hours. In a more preferred specific embodiment of the present invention, the thermal decomposition and polycondensation of the petroleum raw material can be performed for 2 to 7 hours. If the thermal decomposition and polycondensation time of the petroleum raw material is less than 1 hour, it is difficult to produce a pitch having a high softening point, and if the thermal decomposition and polycondensation time of the petroleum raw material exceeds 10 hours, an excessive amount of quinoline insoluble components may be generated.

In a specific embodiment of the present invention, the thermal decomposition and polycondensation of the petroleum-based raw material can be performed under stirring. The stirring conditions of the petroleum-based raw material are not particularly limited, but, for example, a stirrer rotating at 10 to 500 rpm can be used.

In a specific embodiment of the present invention, the pitch synthesized in step (1) may have a softening point of 200 to 350°C. In a preferred specific embodiment of the present invention, the pitch may have a softening point of 200 to 330°C. In a more preferred specific embodiment of the present invention, the pitch may have a softening point of 200 to 300°C. Since the pitch manufactured according to the present invention has a high softening point, when used as a precursor for manufacturing a carbon support, the stabilization process is easy, and a high yield can be obtained after carbonization and activation.

In a specific embodiment of the present invention, the yield of the pitch synthesized in step (1) may be 10 to 50 wt%. In a preferred specific embodiment of the present invention, the yield of the pitch may be 10 to 40 wt%. In a more preferred specific embodiment of the present invention, the yield of the pitch may be 20 to 30 wt%.

In a specific embodiment of the present invention, a step of pretreating a petroleum-based raw material may be performed before step (1) above. By removing low-boiling-point components contained in the petroleum-based raw material through the pretreating step, a pitch having a higher softening point can be manufactured.

In a specific embodiment of the present invention, the pretreatment step may be performed at a temperature equal to or lower than the thermal decomposition and polycondensation temperature of the petroleum-based raw material in step (1), but is not particularly limited to this condition. Specifically, the pretreatment step may be performed at 250 to 450°C, preferably 250 to 400°C, and more preferably 300 to 400°C.

In a specific embodiment of the present invention, the pretreatment step may be performed for a time equal to or shorter than the thermal decomposition and polycondensation time of the petroleum-based raw material in step (1), but is not particularly limited to this condition. Specifically, the pretreatment step may be performed for 1 to 8 hours, preferably 1 to 6 hours, and more preferably 1 to 5 hours.

In addition, in the step (2), the pitch can be solidified and pelletized to obtain a pellet-like pitch, or the pitch can be solidified, pelletized, and pulverized to obtain a powder-like pitch.

First, in the case of the pellet-shaped pitch, the pitch (liquid) obtained in the step (1) is solidified, for example, by extrusion and cooling, and is pelletized into a desired size to obtain a solid pitch pellet (pellet-shaped pitch). The process of extruding, cooling, and pelletizing the liquid pitch to obtain a solid pitch pellet can be performed using a commercialized device. For example, this process can be performed using a double belt cooler & flaker of IPCO, but is not particularly limited to this device.

(2) The pitch pellets (pellet-shaped pitch) obtained in step (2) have an average particle size of 1 to 30 mm, preferably 5 to 25 mm. When the average particle size of the pitch pellets (pellet-shaped pitch) is within this range, the pitch pellets (pellet-shaped pitch) can be used to manufacture a porous carbon support through stabilization, carbonization, and activation, which will be described later, without separately pulverizing them.

In addition, in the case of powdered pitch, the pitch pellets (pellet-shaped pitch) can be further crushed or pulverized and classified. Through crushing or pulverization, the pitch pellets (pellet-shaped pitch) can be further finely divided, and through classification, the particle size distribution of the pitch pellets (pellet-shaped pitch) can be made uniform. Here, the classification can be dry classification, wet classification, classification using a sieve, etc. By crushing or pulverizing and classification, a powdered pitch having an average particle size of 50 to 500 ㎛ can be obtained.

And, in step (3), a step of stabilizing the pellet-shaped pitch or powder-shaped pitch can be performed.

First, the pellet-shaped pitch or powder-shaped pitch obtained in step (2) is first oxidized to stabilize the carbon structure of the pitch.

In a specific embodiment of the present invention, the stabilization may be performed under an oxidizing gas atmosphere. In a preferred embodiment of the present invention, the stabilization may be performed under an air atmosphere, but is not particularly limited thereto.

In a specific embodiment of the present invention, the stabilization can be performed at a temperature of 100 to 500°C, preferably 150 to 300°C. When the stabilization is performed at this temperature, the carbon structure in the pellet-shaped pitch or the powder-shaped pitch changes from thermoplastic to thermosetting, so that the structure can be stably maintained during the subsequent carbonization process. At this time, the heating rate can be 2 to 10°C/min. If the heating rate is too slow, the productivity is poor, and if the heating rate is too fast, uniform stabilization treatment can be difficult.

In a specific embodiment of the present invention, the stabilization can be performed at a pressure of 0.1 to 10 bar, preferably 0.5 to 5 bar. When the stabilization is performed at this pressure, the structure of the carbon inside the pellet-shaped pitch or the powder-shaped pitch can be sufficiently stabilized.

In a specific embodiment of the present invention, the stabilization can be performed under conditions of a flow rate of an oxidizing gas, preferably air, of 0.1 to 500 ml/min, preferably 1 to 300 ml/min. When the stabilization is performed under these oxidizing gas flow rates, the structure of the carbon inside the pellet-shaped pitch or the powder-shaped pitch can be sufficiently stabilized.

In a specific embodiment of the present invention, the stabilization can be performed for a period of 1 to 10 hours, preferably 2 to 8 hours. When the stabilization is performed for this period of time, the structure of the carbon inside the pellet-shaped pitch or the powder-shaped pitch can be sufficiently stabilized.

And, in step (4), the stabilized pitch is carbonized to obtain a carbonized body. Through carbonization of the stabilized pitch, other functional groups included in the pitch are removed, and a carbonized body composed of substantially pure carbon can be obtained.

In a specific embodiment of the present invention, the carbonization may be performed under an inert gas atmosphere. In a preferred specific embodiment of the present invention, the carbonization may be performed under a nitrogen or argon atmosphere, but is not particularly limited thereto.

In a specific embodiment of the present invention, the carbonization may be performed at a temperature of more than 700°C and less than or equal to 1,000°C, preferably 800 to 900°C. If the temperature during carbonization is lower than this range, carbonization may not be sufficiently performed, and if the temperature during carbonization is higher than this range, the carbonization yield may decrease.

In a specific embodiment of the present invention, the carbonization can be performed under a flow rate condition of an inert gas, preferably nitrogen, of 0.1 to 30 ml/min, preferably 0.1 to 10 ml/min. When the carbonization is performed under this inert gas flow rate condition, the stabilized pitch can be sufficiently carbonized.

In a specific embodiment of the present invention, the carbonization can be performed for 0.5 to 5 hours, preferably 1 to 3 hours. When the carbonization is performed for this period of time, the stabilized pitch can be sufficiently carbonized.

And, in step (5), the carbonized body is activated to obtain a porous carbon support. By activating the carbonized body, pores are formed in the carbonized body, thereby obtaining a porous carbon support.

In a specific embodiment of the present invention, the activation of the carbonized body can be performed under an oxidizing gas atmosphere. In a preferred specific embodiment of the present invention, the activation of the carbonized body can be performed under a steam atmosphere, but is not particularly limited thereto.

In a specific example of the present invention, the activation of the carbonized body can be performed at a temperature of more than 700°C and less than or equal to 1,000°C, preferably 800 to 900°C. When the activation of the carbonized body is performed at this temperature, a porous carbon support in which micropores and mesopores are sufficiently formed can be obtained.

In a specific embodiment of the present invention, the activation of the carbonized body can be performed at a pressure of 0.1 to 10 bar, preferably 0.1 to 5 bar. When the activation of the carbonized body is performed at this pressure, a porous carbon support in which micropores and mesopores are sufficiently formed can be obtained.

In a specific example of the present invention, the activation of the carbonized body can be performed under a flow rate condition of an oxidizing gas, preferably steam, of 0.1 to 100 ml/min, preferably 0.1 to 50 ml/min. When the activation of the carbonized body is performed under this oxidizing gas flow rate condition, a porous carbon support in which micropores and mesopores are sufficiently formed can be obtained.

In a specific embodiment of the present invention, the activation of the carbonized body can be performed for 0.5 to 5 hours, preferably 1 to 3 hours. When the activation of the carbonized body is performed for this period of time, a porous carbon support in which micropores and mesopores are sufficiently formed can be obtained.

In a specific embodiment of the present invention, the stabilization, carbonization and activation of the above steps (3) to (5) can each be performed in a heating furnace using microwaves. In a preferred specific embodiment of the present invention, the stabilization, carbonization and activation of the above steps (3) to (5) can all be performed in a heating furnace using microwaves. A heating furnace using microwaves is preferred because it can increase the temperature of the pitch itself without increasing the external temperature of the pitch, but is not particularly limited thereto.

In a specific embodiment of the present invention, the above steps (3) to (5) can be performed continuously in one device. In a preferred specific embodiment of the present invention, the above steps (3) to (5) can be performed continuously in one rotary kiln, but are not particularly limited to this device. By performing the above steps (3) to (5) continuously in one device, optimization of the process can be achieved.

In a specific embodiment of the present invention, the porous carbon support obtained in step (5) can be further disintegrated or pulverized and classified. The porous carbon support can be further finely divided through disintegration or pulverization, and the particle size distribution of the porous carbon support can be made uniform through classification. Here, the classification can be dry classification, wet classification, classification using a sieve, etc. By the disintegration or pulverization and classification treatment, a porous carbon support powder having an average particle size of 1 to 20 ㎛, a BET specific surface area of 300 to 3,000 m2/g, and a tap density of 0.05 to 0.5 g/㎖ can be obtained. In addition, the porous carbon support powder has a volume ratio of mesopores having a pore size of 2 to 50 nm based on the total pore volume of 5 to 80%.

Meanwhile, in the case where the pitch in pellet form is stabilized, carbonized and activated without further pulverizing the pitch in the above step (2), a porous carbon support may be obtained, but is not limited to, by pulverizing (or further classifying) the carbon support to have an average particle size of 1 to 20 ㎛.

Next, a silicon/carbon composite matrix is formed on the surface and inside the pores of the porous carbon support to manufacture a carbon-silicon/carbon composite.

At this time, the formation of the silicon/carbon composite matrix can be performed using a device (e.g., a rotary kiln) and a method (e.g., chemical vapor deposition (CVD)) known in the technical field to which the present invention belongs. Specifically, a composite CVD can be performed by simultaneously supplying a silicon source and a carbon source to a porous carbon support to perform CVD, thereby forming a silicon/carbon composite matrix on the surface and inside the pores of the porous carbon support.

In a specific embodiment of the present invention, the silicon source may include at least one selected from silane (SiH ₄ ), dichlorosilane (SiH ₂ Cl ₂ ), silicon tetrafluoride (SiF ₄ ), silicon tetrachloride (SiCl ₄ ), methylsilane (CH ₃ SiH ₃ ), and disilane (Si ₂ H ₆ ), but is not particularly limited thereto.

Additionally, the carbon source may include at least one selected from the group consisting of methane, ethane, propane, butane, methanol, ethanol, propanol, propanediol, butanediol, ethylene, propylene, butylene, butadiene, cyclopentene, acetylene, benzene, toluene, xylene, ethylbenzene, naphthalene, anthracene, and dibutylhydroxytoluene, but is not particularly limited thereto.

In addition, the composite CVD can be performed at a temperature of 300 to 600° C., and preferably at a temperature of 450 to 550° C. In addition, the composite CVD can be performed at atmospheric pressure, and may be performed under a low vacuum of about 10 Torr, if necessary. In addition, the composite CVD can be supplied with a silicon source at a charging flow rate of 100 sccm to 1000 sccm based on a charging batch amount of 10 g to 100 g, and the silicon source and the carbon source can be supplied at a weight ratio of 1:0.1 to 2, and preferably at a weight ratio of 1:0.15 to 1:1.9.

If the weight ratio of the silicon source and the carbon source exceeds 1:2 (silicon source less than 1 and carbon source more than 2), SiCx may be formed relatively in large quantities, which may result in a decrease in electric capacity and a deterioration in cycle characteristics. In addition, if the weight ratio is less than 1:0.1 (silicon source more than 1 and carbon source less than 0.1), SiCx may be formed relatively in small quantities and Si may be formed relatively in large quantities, which may not resolve the problem caused by volume expansion of silicon during charge and discharge, which may result in structural damage to the negative electrode material.

Negative active material

According to another embodiment of the present invention, a negative active material comprising the carbon-silicon/carbon composite is provided.

The negative active material according to an embodiment of the present invention may include a carbon-silicon/carbon composite.

In addition, the negative electrode active material according to an embodiment of the present invention may additionally include a carbon-based negative electrode material, specifically a graphite-based negative electrode material, in addition to the carbon-silicon/carbon composite. For example, the negative electrode active material may be obtained by mixing the carbon-silicon/carbon composite according to an embodiment of the present invention and a carbon-based negative electrode material, for example, a graphite-based negative electrode material.

Here, the carbon-based negative electrode material may include at least one selected from the group consisting of, for example, natural graphite, artificial graphite, soft carbon, hard carbon, mesocarbon, carbon fibers, carbon nanotubes, pyrolytic carbons, cokes, organic polymer compound sintered bodies, and carbon black, but is not particularly limited thereto.

The content of the carbon-based negative electrode material in the negative electrode active material according to an embodiment of the present invention may be 2 to 80 wt%, preferably 5 to 70 wt%, and more preferably 30 to 70 wt%, based on the total weight of the negative electrode active material.

The negative active material according to an embodiment of the present invention can be effectively used in manufacturing a secondary battery, specifically, a negative electrode of a lithium secondary battery and a negative electrode of an all-solid-state battery.

All-solid-state battery

According to another embodiment of the present invention, an all-solid-state battery is provided comprising a solid electrolyte interphase (SEI) film including the carbon-silicon/carbon composite.

The above-described all-solid-state battery may be an all-solid-state battery including a cathode, an anode, and a solid electrolyte between the cathode and the anode, and the anode may include a cathode active material layer, and may include a solid electrolyte interphase (SEI) film including the carbon-silicon/carbon composite described above on at least a portion of cathode active material particles of the cathode active material layer.

Meanwhile, the above-described negative electrode active material particles may be carbon-based negative electrode materials, in which case the description may be similar to that described in the above-described negative electrode active material, and therefore, the related description will be omitted.

In addition, in addition to the negative active material particles and SEI film of the above-mentioned all-solid-state battery, the negative electrode configuration, positive electrode configuration, and solid electrolyte configuration can be applied to known configurations of all-solid-state batteries, and therefore the present invention does not specifically limit them.

Example

The present invention is described more specifically by the following examples. The following examples are intended only to illustrate the present invention, and the scope of the present invention is not limited thereto.

<Example 1>

300 g of petroleum residual oil (YNCC, HTC PFO (pyrolysis fuel oil)) was placed in a reactor equipped with a stirrer, and pyrolysis and polycondensation were performed at 450°C for 3 hours while supplying nitrogen at a flow rate of 100 ml/min. At this time, the stirrer was rotated at a speed of 200 rpm to mix the reactants (step (1)). The polymerized pitch was solidified and pelletized to obtain solid pitch pellets having an average particle size of 1 to 30 mm.

The solid pitch pellets obtained above were pulverized to manufacture pitch particles having an average particle size of 200 μm (step (2)), and then placed in a rotary kiln having three zones to sequentially perform stabilization (step (3)), carbonization (step (4)), and activation (step (5)). The conditions for stabilization, carbonization, and activation are as shown in Table 1 below.

The specific surface area of the carbon support was measured using Belsorp mini II according to ASTM D4820-93. The tap density of the carbon support was measured using a tap density analyzer (Electrolab, ETD-1020x) according to ASTM B527. The average particle size of the carbon support was measured using a particle size analyzer (Horiba, laser particle analyzer, LA-960V2) according to ASTM E112. The results are shown in Table 1.

step condition Standard example stabilization Temperature (℃) 300 Time (hr) 3 atmosphere air carbonization Temperature (℃) 900 Time (hr) 1 atmosphere nitrogen activate Temperature (℃) 900 Time (hr) 3 Water vapor flow rate (㎖/min) 200 Support properties Average particle size (㎛) 200 Specific surface area (㎡/g) 1409.1 Tap density (g/ml) 0.44

The porous carbon support of the reference example was pulverized with a pulverizer (NETZSCH, air jet mill) to obtain a fine powder of the porous carbon support having an average particle size of 7 ㎛. Next, 15 g of the fine powder of the porous carbon support was charged into a rotating CVD device, and the temperature was raised to 475°C in an inert atmosphere (N ₂ ), and then composite CVD was performed for 1 hour at a gas flow rate of SiH ₄ :C ₂ H ₄ = 450 sccm : 144 sccm (gas flow rate ratio of the silicon source and the carbon source 1 : 0.32) to form a silicon/carbon composite matrix on the surface and inside the pores of the porous carbon support, thereby manufacturing a carbon-silicon/carbon composite.

<Example 2>

The same procedure as in Example 1 was followed, but the gas flow rate of SiH ₄ :C ₂ H ₄ = 450 sccm : 144 sccm was changed to SiH ₄ :C ₂ H ₄ = 450 sccm : 108 sccm (gas flow rate ratio of the silicon source and the carbon source 1 : 0.24) to manufacture a carbon-silicon/carbon composite.

<Example 3>

The same procedure as Example 1 was followed, but the gas flow rate of SiH ₄ :C ₂ H ₄ = 450 sccm : 144 sccm was changed to the gas flow rate of SiH ₄ :C ₂ H ₄ = 150 sccm : 450 sccm (gas flow rate ratio of the silicon source and the carbon source of 1 : 3) to manufacture a carbon-silicon/carbon composite.

<Comparative example>

A carbon-silicon/carbon composite was manufactured by performing the same procedure as in Example 1, but without performing composite CVD, changing the deposition conditions to a gas flow rate of SiH ₄ of 450 sccm and a temperature of 475°C for 1 hour, and then a gas flow rate of C ₂ H ₄ : Ar = 100 sccm : 900 sccm and a temperature of 700°C for 1 hour.

<Experimental Example 1>

(1) Scanning electron microscope (SEM) analysis

The carbon-silicon/carbon composite manufactured according to Example 1 was observed using a scanning electron microscope (SEM). The results of the SEM analysis are shown in Fig. 1.

As a result, as shown in Fig. 1, it was confirmed that a uniform silicon/carbon composite matrix was formed on the surface and inside the pores of the porous carbon support.

(2) Electrochemical evaluation

Half coin cells were manufactured using the composites of Examples 1, 2, 3, and Comparative Examples, and then electrochemical evaluations were performed. The conditions for manufacturing the half coin cells are shown in Table 2, and the evaluation results are shown in Tables 3 to 4 and FIG. 2. In Table 2, AM, CM, and BM represent active material (carbon-silicon/carbon composite), conductor (Super P carbon black), and binder (styrene-butadiene rubber/carboxymethyl cellulose 5:5), respectively, and EC, EMC, DMC, FEC, VC, and PS represent ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, fluoroethylene carbonate, vinylene carbonate, and propane sultone, respectively.

Composition (AM:CM:BM) 8:1:1 Area capacity (mAh/㎠) 1 Electrolyte 1.3 M LiPF ₆ EC/EMC/DMC 3:5:2, FEC 10%, LiBF ₄ 0.2%, 0.5% VC, 1% PS Cut-off voltage (V) Formation: 0.005-1.5, Cycle test: 0.005-1.2 C-rate (C) Formation: 0.1-0.1, 0.005 V at 0.01 C cut-off (CV)

Sample Charging capacity (mAh/g) Discharge capacity (mAh/g) ICE(%) Example 1 2348 2007 85.5 Example 2 2335 2024 86.7 Example 3 1534 1031 67.2

Sample Cycle maintenance rate Example 1 72.4 Example 2 66.8 Comparative example 22.0

As can be confirmed from Tables 3 to 4 and FIG. 2 above, Examples 1 and 2 show a reversible capacity of about 2000 mAh/g, and it can be seen that the peak around 0.45 V representing the suSi phase is significantly lower, and it can be seen that a high CE of more than 99.6% is achieved after 25 cycles. In contrast, in the case of Example 3 (1:3) exceeding the range of the gas flow rate ratio of the silicon source and the carbon source in the composite CVD, it was confirmed that the electric capacity decreased and the ICE was low because carbon was more dominant than silicon in the composition of the silicon/carbon composite matrix, and it was confirmed that the cycle maintenance rate of the comparative example was significantly reduced because the composite matrix in which silicon and carbon were bonded to each other was not present.

(3) dq/dV measurement (c-LiSi phase related measurement)

For Example 1, Example 2 and Comparative Example 1, Formation (CC-CV) is performed under the conditions of 0.1C-0.1C, 0.005V/0.01C cut off (CV) using the C-rate calculated based on the amount of Si mounted in the cathode material, etc. Then, dQ/dV (d(Q-Qo)/dE) is derived using the collected data. In the present invention, dQ/dV is calculated and derived through the Analysis Process of EC-Lab. This is shown in Fig. 3.

As a result, the c/a peak ratio of Example 1 was derived as 0.66, the c/a peak ratio of Example 2 was derived as 0.64, and the c/a peak ratio of the comparative example was derived as 2.72. It was found that Example 1 and Example 2 formed less c-LiSi phase than Comparative Example 1, and therefore, it was expected that there would be an effect of maintaining stable electrochemical performance during the life evaluation.

(4) XRD analysis

For the carbon-silicon/carbon composite according to Example 1, XRD analysis was performed under the conditions below. This is shown in Fig. 4.

- Equipment: D-MAX 2200 (RIGAKU)

- Angle: 20~70°

- Sampling W.: 0.01

- X-Ray 40kV/30mA

- DivSlit: 1/2 deg.

- DivH.L.Slit: 10 mm

- SctSlit: 1/2 deg

- RecSlit : 0.15mm

As a result, it was confirmed that the carbon-silicon/carbon composite according to Example 1 did not have a crystalline peak of Si and no SiC peak.

<Examples 1-1 to 1-3>

The composite according to Example 1 was heat treated at temperatures of 600°C (Example 1-1), 700°C (Example 1-2), and 900°C (Example 1-3), respectively.

Experimental example 2

(1) XRD analysis

XRD analysis was performed on the composites according to Example 1, Examples 1-1 to 1-3, and Comparative Examples.

Specifically, XRD analysis was performed on the composite according to Example 1, the heat-treated composite according to Examples 1-1 to 1-3, and the comparative composite under the following conditions. This is shown in Fig. 5.

- Equipment: D-MAX 2200 (RIGAKU)

- Angle: 20~70°

- Sampling W.: 0.01

- X-Ray 40kV/30mA

- DivSlit: 1/2 deg.

- DivH.L.Slit: 10 mm

- SctSlit: 1/2 deg.

- RecSlit : 0.15mm

As a result, in the case of the comparative example, it can be seen that the crystalline Si (Si peak) was clearly observed due to the additional carbon coating at a temperature of 700℃, which resulted in poor results in the life evaluation as described above.

Additionally, in the case of the heat-treated composite, no distinct Si and SiC peaks were observed up to 700°C heat treatment, and a broad amorphous peak was observed between 28 and 32°C.

And, when heat-treated at 900℃, SiC(111), SiC(220) and Si(111) peaks were observed. At this time, when calculating the crystallite size through each peak, it was as follows.

- SiC(111): 1.1nm

- SiC(220): 2.4nm

- Si(111): 4.8nm

The above results confirm that a silicon-carbon composite matrix was formed on the porous carbon support and that the Si crystallite size was controlled through this.

Although one embodiment of the present invention has been described above, the spirit of the present invention is not limited to the embodiment presented in this specification, and those skilled in the art who understand the spirit of the present invention will be able to easily suggest other embodiments by adding, changing, deleting, or adding components within the scope of the same spirit, but this will also be considered to fall within the spirit of the present invention.

Claims (12)

A porous carbon support having a volume ratio of mesopores with a pore size of 2 to 50 nm of 5 to 80% based on the total pore volume; and A carbon-silicon/carbon composite comprising a silicon/carbon composite matrix disposed on the surface and inside the pores of the porous carbon support. In the first paragraph, the porous carbon support is, The BET surface area is 300 to 3,000 ㎡/g, The tap density is 0.05 to 0.5 g/㎖. Carbon-silicon/carbon composite with an average particle size of 1–20 ㎛. In the first paragraph, A carbon-silicon/carbon composite having a silicon content of 20 to 70 wt% of the total weight of the carbon-silicon/carbon composite. In the first paragraph, A carbon-silicon/carbon composite wherein the silicon/carbon composite matrix is 10 to 90 wt% of the total weight of the carbon-silicon/carbon composite. In the first paragraph, A carbon-silicon/carbon composite having an average size of silicon crystals in the silicon/carbon composite matrix of 10 nm or less. In the first paragraph, The above carbon-silicon/carbon composite is a carbon-silicon/carbon composite having a c/a peak ratio of 0 to 1.5. A method for producing a carbon-silicon/carbon composite, comprising: a step of forming a silicon/carbon composite matrix on the surface and inside the pores of a porous carbon support to produce a carbon-silicon/carbon composite; In Article 7, Before the step of manufacturing the above carbon-silicon/carbon composite, (1) A step of synthesizing pitch by thermal decomposition and condensation polymerization of petroleum-based raw materials; (2) a step of solidifying and pelletizing the pitch to obtain a pellet-like pitch, or solidifying, pelletizing and pulverizing the pitch to obtain a powder-like pitch; (3) A step of stabilizing the pellet-shaped pitch or powder-shaped pitch; (4) a step of carbonizing the stabilized pitch to obtain a carbonized body; and (5) A method for producing a carbon-silicon/carbon composite, further comprising: a step of activating the carbonized body to obtain a porous carbon support. In Article 7, The above silicon/carbon composite matrix is a method for manufacturing a carbon-silicon/carbon composite formed by composite CVD of a silicon source and a carbon source on the porous carbon support. In Article 9, A method for manufacturing a carbon-silicon/carbon composite, wherein the gas flow ratio of the silicon source and the carbon source is 1:0.1 to 1:2. A negative electrode active material comprising a carbon-silicon/carbon composite according to any one of claims 1 to 6. An all-solid-state battery comprising a SEI (Solid Electrolyte Interphase) film comprising a carbon-silicon/carbon composite according to any one of claims 1 to 6.

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