Carbon-silicon / carbon composite and method for producing the same

Abstract

The present invention relates to a carbon-silicon / carbon composite in which a silicon / carbon composite matrix is ​​formed on the surface and inside the pores of a porous carbon support having controlled porosity characteristics, and a method for producing the same. When a carbon-silicon / carbon composite according to an embodiment of the present invention is used as a negative electrode active material, it exhibits excellent electrical conductivity and can alleviate stress caused by the volume expansion of silicon.

Description

Technical Field

[0001] The present invention relates to a carbon-silicon / carbon composite, and more particularly, to a carbon-silicon / carbon composite and a method for manufacturing the same.

Background Art

[0002] In recent years, due to the development of the information and communication industry, the demand for electronic devices has increased rapidly. As the electric vehicle market has become active, the demand for batteries used in these electronic devices and electric vehicles has also increased significantly.

[0003] Secondary batteries, such as lithium secondary batteries and all-solid-state batteries containing liquid electrolytes, have a high energy density and a low self-discharge rate when not in use, and are thus most widely used for such applications. Secondary batteries generally consist of a positive electrode, a negative electrode, and an electrolyte (liquid or solid), etc. As the negative electrode active material of secondary batteries, carbon-based materials such as graphite are widely used.

[0004] In recent years, attempts have been 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 has attracted attention as a next-generation battery negative electrode active material to replace graphite. However, during charge and discharge, it reacts with lithium and its volume increases by up to about 300%, and silicon, which is the negative electrode active material, is crushed as the charge and discharge progresses, and thus has a problem of very poor mechanical stability.

[0005] To solve such problems, a composite obtained by forming a silicon layer on a porous carbon support excellent in electrical conductivity has been proposed. However, since conventional carbon supports mainly have micropores, when chemical vapor deposition (CVD) or the like is carried out in subsequent processes, there is a problem that deposition cannot be well performed up to the deep pores, the crystals of silicon formed on the carbon support are large, and the crushing phenomenon due to volume expansion cannot be sufficiently eliminated.

Summary of the Invention

Problems to be Solved by the Invention

[0006] The object of the present invention is to provide a carbon-silicon / carbon composite in which a silicon / carbon composite matrix is ​​formed on the pores and / or surface of a porous carbon support having controlled porosity properties.

[0007] Another object of the present invention is to provide a method for producing the carbon-silicon / carbon composite.

[0008] Another object of the present invention is to provide a negative electrode active material containing the carbon-silicon / carbon composite. [Means for solving the problem]

[0009] The present invention provides a carbon-silicon / carbon composite comprising a porous carbon support and a silicon / carbon composite matrix disposed on the surface and inside the pores of the porous carbon support.

[0010] According to one embodiment of the present invention, the porous carbon support may have a volume ratio of 10 to 80% of mesopores, which have a pore size of 2 to 50 nm, based on the total pore volume.

[0011] Furthermore, the porous carbon support has a BET specific surface area of ​​300 to 3,000 m². 2 The density may be / g, the tap density may be 0.05 to 0.5 g / ml, and the average particle size may be 1 to 20 μm.

[0012] The silicon / carbon composite matrix may contain silicon and carbon in a weight ratio of 1:2 to 1:0.1.

[0013] Furthermore, the silicon / carbon composite matrix may be 10 to 90% by weight of the total weight of the carbon-silicon / carbon composite.

[0014] Furthermore, the material may further include a carbon layer formed on the silicon / carbon composite matrix.

[0015] Furthermore, the present invention provides a method for producing a carbon-silicon / carbon composite, comprising the steps of (1) forming silicon on the surface and inside the pores of a porous carbon support to obtain a carbon-silicon composite, and (2) heat-treating the carbon-silicon composite.

[0016] According to one embodiment of the present invention, the heat treatment step can be carried out by heat treating the carbon-silicon composite at a temperature of 800 to 1,000°C to convert some of the Si-Si bonds of silicon into Si-C bonds.

[0017] Furthermore, the heat treatment step can be carried out by forming a carbon layer on the carbon-silicon composite at a temperature of 800 to 1,000°C while converting some of the Si-Si bonds of silicon to Si-C bonds.

[0018] Furthermore, the present invention provides a negative electrode active material comprising the carbon-silicon / carbon composite described above, and a carbon-based negative electrode material.

[0019] Furthermore, the present invention provides an all-solid-state battery that includes an SEI (Solid Electrolyte Interphase) film containing the carbon-silicon / carbon composite described above. [Effects of the Invention]

[0020] In the carbon-silicon / carbon composite according to an embodiment of the present invention, a silicon / carbon composite matrix is ​​formed in the pores and / or on the surface of a porous carbon support with a high proportion of mesopores within the overall pores. When this carbon-silicon / carbon composite is used as a negative electrode active material, it exhibits excellent electrical conductivity, relieves stress due to the volume expansion of silicon, and achieves excellent capacity retention.

[0021] Furthermore, the manufacturing method according to an embodiment of the present invention can easily produce carbon-silicon / carbon composites having the above-mentioned characteristics. [Brief explanation of the drawing]

[0022] [Figure 1] Figure 1 shows the X-ray diffraction analysis results of the composite particles of the reference example, Examples 1 to 2, and Comparative Example 1. [Figure 2] Figure 2 shows the X-ray diffraction analysis results by heat treatment temperature for confirming the conversion of the Si-Si bond to the Si-C bond in the carbon-silicon composite. [Figure 3] Figures 3 and 4 show the electrochemical analysis results of the batteries manufactured using the composites of the reference example, Examples 1 to 2, and Comparative Example 1. [Figure 4] Figures 3 and 4 show the electrochemical analysis results of the batteries manufactured using the composites of the reference example, Examples 1 to 2, and Comparative Example 1.

Mode for Carrying Out the Invention

[0023] The present invention is not limited to the content disclosed below, and can be modified into various forms as long as the gist of the invention is not changed.

[0024] In this specification, "including" means that other components can be further included unless otherwise specified.

[0025] All numbers and expressions indicating the amounts of the components described in this specification, reaction conditions, etc. should be understood to be modified by the term "about" in all cases unless the opposite description is given.

[0026] Hereinafter, the present invention will be described more specifically.

[0027] <Carbon-silicon / carbon composite> According to an embodiment of the present invention, a carbon-silicon / carbon composite including a porous carbon support and a silicon / carbon composite matrix disposed on the surface and inside the pores of the porous carbon support is provided.

[0028] The following describes each component of the carbon-silicon / carbon composite according to one embodiment of the present invention.

[0029] Porous carbon support An embodiment of the present invention, a carbon-silicon / carbon composite, includes a porous carbon support.

[0030] The porous carbon support has a volume ratio of mesopores (pores with a size of 2 to 50 nm) of 10 to 80% of the total pore volume, preferably 30 to 60%, and more preferably 40 to 50%. If the volume ratio of mesopores in the porous carbon support is less than 10%, there may be too many fine pores, potentially leading to a relatively large amount of silicon being deposited on the outside. If the volume ratio of mesopores in the porous carbon support exceeds 80%, the particle hardness may be insufficient, and if used to manufacture electrodes, the electrode structure may collapse.

[0031] Furthermore, the porous carbon support may have an average particle size of 1 to 20 μm. Preferably, the porous carbon support may have an average particle size of 3 to 20 μm, and more preferably, an average particle size of 3 to 10 μm. If the average particle size of the porous carbon support is less than 1 μm, the silicon supply source cannot penetrate sufficiently into the pores and is deposited mostly only on the outside of the particles. If the average particle size of the porous carbon support exceeds 20 μm, it is difficult for the silicon supply source to be deposited sufficiently into the pores.

[0032] Furthermore, porous carbon supports are 300-3,000 m 2 It may have a BET specific surface area of ​​300 to 1,500 m² / g. Preferably, the porous carbon support is 300 to 1,500 m². 2 BET specific surface area per g, more preferably 500 to 1,500 m² 2 It may have a BET specific surface area of ​​300 m² / g. The BET specific surface area of ​​the porous carbon support is 300 m². 2 If the value is less than / g, there may be too many macropores and insufficient effective pores, and the BET specific surface area of ​​the porous carbon support is 3,000 m². 2If the value exceeds / g, there are many micropores, and a large amount of silicon source can be deposited on the outside of the particle.

[0033] Furthermore, the porous carbon support may have a tap density of 0.05 to 0.5 g / ml. Preferably, the porous carbon support may have a tap density of 0.05 to 0.3 g / ml, and more preferably, a tap density of 0.1 to 0.3 g / ml. If the tap density of the porous carbon support is less than 0.05 g / ml, process control may be difficult during the deposition of the silicon source, potentially leading to a decrease in yield. If the tap density of the porous carbon support exceeds 0.5 g / ml, uniform coating may become difficult during the deposition of the silicon source.

[0034] The carbon-silicon / carbon composite according to an embodiment of the present invention includes a porous carbon support having the above-mentioned properties. When such a carbon-silicon / carbon composite is used as a negative electrode active material, it exhibits excellent electrical conductivity and can alleviate stress caused by the volume expansion of silicon.

[0035] Silicon / carbon composite matrix An embodiment of the present invention, the carbon-silicon / carbon composite, includes a silicon / carbon composite matrix disposed on the surface and inside the pores of a porous carbon support.

[0036] In the present invention, the silicon / carbon composite matrix may mean a continuous phase in which silicon portions formed by Si-Si bonds and silicon carbide portions formed by Si-C bonds are mixed.

[0037] In a specific example of the present invention, as described later, silicon is formed on a porous carbon support to obtain a carbon-silicon composite, and then a silicon / carbon composite matrix can be obtained by heat-treating it at a temperature of 800 to 1,000°C to convert some of the Si-Si bonds of the silicon into Si-C bonds.

[0038] In another specific example of the present invention, as described later, after forming silicon on a porous carbon support to obtain a carbon-silicon composite, a silicon / carbon composite matrix can be obtained by forming a carbon layer on the carbon-silicon composite at a temperature of 800 to 1,000°C while converting some of the Si-Si bonds of silicon to Si-C bonds.

[0039] In a specific example of the present invention, the silicon / carbon composite matrix may contain crystalline silicon particles. In this case, the size of the silicon crystals may be at the nanoscale. 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.

[0040] When the average size of silicon crystals in the silicon / carbon composite matrix satisfies the aforementioned range, the magnitude of stress due to the volume expansion of silicon decreases, which can improve the lifetime characteristics of the negative electrode active material.

[0041] On the other hand, the silicon / carbon composite matrix can contain silicon and carbon in a weight ratio of 1:2 to 1:0.1, preferably in a weight ratio of 1:1.9 to 1:0.15. If the weight ratio of silicon and carbon is less than 1:2 (less than 1 part silicon, more than 2 parts carbon), it may not be possible to solve the problem caused by the volume expansion of silicon during charging and discharging, potentially leading to structural damage to the negative electrode material and a decrease in cycle characteristics. If the weight ratio exceeds 1:0.1 (more than 1 part silicon, less than 0.1 parts carbon), the capacitance may decrease.

[0042] On the other hand, the silicon / carbon composite matrix may be 10 to 90% by weight, preferably 15 to 85% by weight, of the total weight of the carbon-silicon / carbon composite. If the silicon / carbon composite matrix is ​​less than 10% by weight of the total weight of the carbon-silicon / carbon composite, the electrical capacity may decrease, and if it exceeds 90% by weight, it may not be able to solve the problems caused by the volume expansion of silicon during charging and discharging, potentially causing structural damage to the negative electrode material and degrading the cycle characteristics.

[0043] Carbon layer According to another embodiment of the present invention, the carbon-silicon / carbon composite may further include a carbon layer formed on the silicon / carbon composite matrix.

[0044] If the carbon-silicon / carbon composite further includes a carbon layer, even better electrical conductivity can be ensured and its specific surface area can be appropriately adjusted. Therefore, when this composite is used as the negative electrode active material for a secondary battery, the capacity retention rate of the secondary battery can be further improved.

[0045] The electrical conductivity of the negative electrode active material is a crucial factor in facilitating electron transfer during electrochemical reactions. If the carbon content in the carbon-silicon / carbon composite used as the negative electrode active material is insufficient, the electrical conductivity of the negative electrode active material may be inadequate. Therefore, by further including a carbon layer on the silicon / carbon composite matrix, the charge / discharge capacity, initial charge efficiency, and capacity retention rate of the secondary battery can be improved, resulting in even better electrical conductivity, suppressing side reactions of the electrolyte, and further enhancing the performance of the secondary battery.

[0046] In this case, the thickness of the carbon layer may be 1 nm to 1 μm, preferably 3 to 150 nm, and more preferably 5 to 100 nm. When the thickness of the carbon layer is within this range, it is possible to suppress the decrease in the capacity of the secondary battery while obtaining the effect of improving conductivity.

[0047] The carbon layer may contain one or more selected from graphene, carbon nanotubes, carbon nanofibers, and graphite. Specifically, the carbon layer may contain graphene and may further contain graphite, but is not particularly limited to these.

[0048] <Method for manufacturing carbon-silicon / carbon composites> A carbon-silicon / carbon composite according to one embodiment of the present invention is manufactured by a manufacturing method comprising (1) forming silicon on the surface and inside the pores of a porous carbon support to obtain a carbon-silicon composite, and (2) heat-treating the carbon-silicon composite.

[0049] The following describes each step of the method for producing a carbon-silicon / carbon composite according to one embodiment of the present invention.

[0050] Step (1) In step (1) above, silicon is formed on the surface and inside the pores of a porous carbon support to produce a carbon-silicon composite.

[0051] In specific examples of the present invention, the step of forming silicon on the surface and inside the pores of a porous carbon support can be carried out using apparatus (e.g., a rotary kiln) and methods (e.g., chemical vapor deposition; CVD) known in the art to which the present invention belongs. Specifically, a silicon source can be supplied to the porous carbon support, and CVD can be performed to form silicon on the surface and inside the pores of the porous carbon support.

[0052] In specific examples of the present invention, the silicon source may include, but is not limited to, at least one selected from silane (SiH4), dichlorosilane (SiH2Cl2), silicon tetrafluoride (SiF4), silicon tetrachloride (SiCl4), methylsilane (CH3SiH3), and disilane (Si2H6).

[0053] CVD of the silicon source can be carried out at temperatures of 300 to 700°C. For example, CVD of the silicon source can be carried out at temperatures of 400 to 600°C, 400 to 500°C, or 400 to 450°C, but is not particularly limited to this range. Furthermore, CVD can be carried out at atmospheric pressure and may be carried out under a low vacuum of about 10 Torr if necessary. In addition, the deposition may be carried out in a silane (SiH4) gas atmosphere of 50 sccm to 500 sccm, for example.

[0054] Step (2) In step (2) above, the carbon-silicon composite is heat-treated.

[0055] According to one embodiment of the present invention, the heat treatment step can be carried out by heat treating the carbon-silicon composite at a temperature of 800 to 1,000°C to convert some of the Si-Si bonds of silicon into Si-C bonds.

[0056] In this case, the heat treatment step can be carried out at a temperature of 800 to 1,000°C, preferably 800 to 950°C, more preferably 850 to 950°C, and even more preferably 900 to 950°C. When the carbon-silicon composite is heat-treated at this temperature, some of the Si-Si bonds in the silicon layer can be converted to Si-C bonds to form a silicon / carbon composite matrix.

[0057] The heat treatment time can be appropriately adjusted by the heat treatment temperature, the pressure during heat treatment, and the desired carbon-silicon content ratio. For example, the reaction time may be 10 to 120 minutes, more specifically 30 to 90 minutes, or more specifically 30 to 50 minutes, but is not particularly limited to this range.

[0058] In specific examples of the present invention, the heat treatment of the carbon-silicon composite may be carried out in an inert gas atmosphere. In preferred examples of the present invention, the heat treatment of the carbon-silicon composite may be carried out in a nitrogen or argon atmosphere, but is not particularly limited thereto.

[0059] A carbon-silicon / carbon composite having a silicon / carbon composite matrix can be produced through the aforementioned heat treatment of the carbon-silicon composite.

[0060] Furthermore, according to another embodiment of the present invention, the heat treatment step can be carried out by converting some of the Si-Si bonds of silicon to Si-C bonds while forming a carbon layer on the carbon-silicon composite at a temperature of 800 to 1,000°C.

[0061] The step of forming a carbon layer on the particle surface of the carbon-silicon composite can be carried out using apparatus and methods known in the art to which the present invention belongs, such as chemical pyrolysis deposition, but is not particularly limited thereto.

[0062] In this case, the step of forming the carbon layer can be carried out by heat-treating the carbon-silicon composite at a temperature of 800 to 1,000°C in the presence of a gaseous carbon source. Preferably, the heat treatment of the carbon-silicon composite in the presence of a gaseous carbon source can be carried out at a temperature of 800 to 950°C, more preferably 850 to 950°C. When the carbon-silicon composite is heat-treated at this temperature in the presence of a gaseous carbon source, some of the Si-Si bonds in the silicon layer can be converted to Si-C bonds to form a silicon / carbon composite matrix.

[0063] In preferred examples of the present invention, the carbon source may include, but is not limited to, 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.

[0064] When forming a carbon layer on the particle surface of a carbon-silicon composite, the process can be carried out in the presence of at least one inert gas selected from the group consisting of hydrogen, nitrogen, helium, and argon, in addition to the carbon source.

[0065] The reaction time (heat treatment time) for forming the carbon layer can be appropriately adjusted depending on the heat treatment temperature, the pressure during heat treatment, the composition of the gas mixture, and the desired amount of carbon coating. For example, the reaction time may be 10 to 120 minutes, more specifically 20 to 90 minutes, or more specifically 30 to 60 minutes, but is not particularly limited to this range.

[0066] In a specific example of the present invention, when forming a carbon layer on the particle surface of a carbon-silicon composite, this can be carried out by mixing a solution in which a carbon source is dispersed in a solvent as needed with the carbon-silicon composite, followed by drying and heat treatment at a temperature of 800 to 1,000°C.

[0067] In a preferred example of the present invention, the carbon source may be selected from the group consisting of pitch, hydrocarbons, and petroleum products. More specifically, the pitch may be petroleum pitch, coal pitch, or a mixture thereof; the hydrocarbon may be furfuryl alcohol or a phenolic resin; and the petroleum product may be pyrolysis fuel oil (PFO), naphtha cracking bottom oil (NCB), ethylene cracker bottom oil (EBO), vacuum residue (VR), de-asphalted oil (DAO), atmospheric residue (AR), fluid catalytic cracking decant oil (FCC-DO), RFCC-DO (residue fluid catalytic cracking decant oil), or heavy aromatic oil. The solvent may be tetrahydrofuran (THF) or an alcohol.

[0068] By performing heat treatment while forming the carbon layer, a carbon-silicon / carbon composite containing a carbon layer on a silicon / carbon composite matrix can be manufactured.

[0069] Pre-steps On the other hand, according to one embodiment of the present invention, the method for producing the carbon-silicon / carbon composite may further include, before step (1), the steps of (a) synthesizing pitch by thermal decomposition and condensation polymerization of petroleum-based raw materials, (b) solidifying and pulverizing the pitch to obtain pellets or powdered pitch, (c) stabilizing the pitch, (d) carbonizing the stabilized pitch to obtain a carbide, and (e) activating the carbide to obtain a porous carbon support.

[0070] In step (a), pitch can be synthesized by thermal decomposition and condensation polymerization of petroleum-based raw materials.

[0071] In specific examples of the present invention, the petroleum-based raw material may include at least one selected from the group consisting of pyrolytic fuel oil (PFO), naphtha cracking residue oil (NCB), ethylene cracker bottom oil (EBO), vacuum residue oil (VR), de-asphalted oil (DAO), atmospheric residue (AR), fluid catalytic cracking oil (RFCC-DO), RFCC-DO (residue fluid catalytic cracking decant oil), and heavy aromatic oil. In preferred examples of the present invention, the petroleum-based raw material may include pyrolytic fuel oil.

[0072] In a specific example of the present invention, the petroleum-based raw material may contain aromatic compounds in an amount of 10 to 90% by weight. Preferably, the petroleum-based raw material may contain aromatic compounds in an amount of 20 to 80% by weight, and more preferably 30 to 70% by weight. When the content of aromatic compounds in the petroleum-based raw material satisfies the above range, a porous carbon support having controlled porosity can be obtained by stabilizing, carbonizing, and activating the solid pitch pellets described later without further pulverization.

[0073] In specific examples 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, a porous carbon support with controlled porosity can be obtained by stabilizing, carbonizing, and activating the solid pitch pellets described later without further grinding.

[0074] In specific examples of the present invention, the thermal decomposition and polymerization of petroleum-based raw materials can be carried out at a temperature of 350 to 500°C. In preferred examples of the present invention, the thermal decomposition and polymerization of petroleum-based raw materials can be carried out at a temperature of 400 to 500°C. In even more preferred examples of the present invention, the thermal decomposition and polymerization of petroleum-based raw materials can be carried out at a temperature of 430 to 470°C. When the thermal decomposition and polymerization temperature of the petroleum-based raw materials is 350 to 500°C, a pitch containing a relatively large amount of low molecular weight components can be produced, and in the activation process of step (e) described later, the relatively small molecular weight components vaporize first, allowing sufficient pores to be formed in the carbon support. If the thermal decomposition and polymerization temperature of the petroleum-based raw materials is less than 350°C, it is difficult to produce a pitch that is solid at room temperature, and if this temperature exceeds 500°C, the pitch contains a relatively large amount of high molecular weight components, making it difficult to produce a carbon support with pores.

[0075] In specific examples of the present invention, the thermal decomposition and condensation polymerization of petroleum-based raw materials can be carried out under an atmosphere of an oxidizing gas, an inert gas, or a mixture thereof. In preferred examples of the present invention, the oxidizing gas may be oxygen, ozone, or a combination thereof, the inert gas may be nitrogen, helium, neon, argon, or a combination thereof, and the mixture thereof may be air, but is not particularly limited thereto.

[0076] When using an oxidizing gas during the thermal decomposition and polymerization of petroleum-based raw materials, a pitch with a high softening point can be produced, but it is difficult to carry out thermal decomposition and polymerization at high temperatures. When using an inert gas during the thermal decomposition and polymerization of petroleum-based raw materials, thermal decomposition and polymerization can be carried out at high temperatures, but it is difficult to produce a pitch with a relatively high softening point. When using a mixture of an oxidizing gas and an inert gas during the thermal decomposition and polymerization of petroleum-based raw materials, thermal decomposition and polymerization can be carried out at relatively high temperatures, and a pitch with a relatively high softening point can be produced.

[0077] In a specific example of the present invention, during the thermal decomposition and condensation polymerization of petroleum-based raw materials, the gas may be supplied at a flow rate of 10 to 800 ml / min. In a preferred specific example of the present invention, during the thermal decomposition and condensation polymerization of petroleum-based raw materials, the gas may be supplied at a flow rate of 100 to 500 ml / min. If the gas flow rate is less than 10 ml / min, the pitch yield will be high, but there will be too many low molecular weight components, which will be disadvantageous for subsequent processes (e.g., stabilization). If the gas flow rate exceeds 800 ml / min, the pitch yield may be low.

[0078] In specific examples of the present invention, the thermal decomposition and polymerization of petroleum-based raw materials can be carried out for 1 to 10 hours. In preferred examples of the present invention, the thermal decomposition and polymerization of petroleum-based raw materials can be carried out for 2 to 8 hours. In even more preferred examples of the present invention, the thermal decomposition and polymerization of petroleum-based raw materials can be carried out for 2 to 7 hours. If the thermal decomposition and polymerization of petroleum-based raw materials time is less than 1 hour, it is difficult to produce pitch with a high softening point, and if the thermal decomposition and polymerization of petroleum-based raw materials time exceeds 10 hours, excessive quinoline-insoluble components may be generated.

[0079] In a specific example of the present invention, the thermal decomposition and condensation polymerization of petroleum-based raw materials can be carried out under stirring. The stirring conditions for the petroleum-based raw materials are not particularly limited, but for example, a stirrer rotating at 10 to 500 rpm can be used.

[0080] In a specific example of the present invention, the pitch synthesized in step (a) may have a softening point of 200 to 350°C. In a preferred example of the present invention, the pitch may have a softening point of 200 to 330°C. In a more preferred example of the present invention, the pitch may have a softening point of 200 to 300°C. The high softening point of the pitch produced by the present invention makes the stabilization process easier when used as a precursor for producing carbon supports, and high yields can be obtained after carbonization and activation.

[0081] In a specific example of the present invention, the yield of the pitch synthesized in step (a) may be 10 to 50% by weight. In a preferred example of the present invention, the yield of the pitch may be 10 to 40% by weight. In a more preferred example of the present invention, the yield of the pitch may be 20 to 30% by weight.

[0082] In a specific example of the present invention, a step of pre-treating the petroleum-based raw material may be performed before step (a). By removing low-boiling-point components contained in the petroleum-based raw material through the pre-treatment step, a pitch having a higher softening point can be produced.

[0083] In specific examples of the present invention, the pretreatment step may be carried out at the same temperature as or lower than the thermal decomposition and condensation polymerization temperature of the petroleum-based raw material in step (a), but is not particularly limited to this condition. Specifically, the pretreatment step may be carried out at 250 to 450°C, preferably 250 to 400°C, and more preferably 300 to 400°C.

[0084] In specific examples of the present invention, the pretreatment step can be carried out for the same or shorter time as the thermal decomposition and condensation polymerization time of the petroleum-based raw material in step (a), but is not particularly limited to this condition. Specifically, the pretreatment step can be carried out for 1 to 8 hours, preferably 1 to 6 hours, and more preferably 1 to 5 hours.

[0085] In addition, in step (b), the pitch can be solidified and pulverized to obtain pellets or powdered pitch.

[0086] The liquid pitch obtained in step (a) is solidified, for example, by extrusion and cooling, and then pelletized to the desired size to obtain solid pitch pellets. The process of extruding, cooling, and pelletizing liquid pitch to obtain solid pitch pellets can be carried out using commercially available equipment. For example, this process can be carried out using IPCO's double belt cooler and flaker, but is not limited to this equipment.

[0087] The pitch pellets obtained in step (b) have an average particle size of 1 to 30 mm, preferably 5 to 25 mm. When the average particle size of the pitch pellets is within this range, a porous carbon support can be produced through stabilization, carbonization, and activation described later, without further grinding of the pitch pellets.

[0088] However, if necessary, the pitch pellets obtained in step (b) can be further crushed, pulverized, and classified. Through crushing or pulverization, the pitch pellets can be further pulverized, and through classification, the particle size distribution of the pitch pellets can be made uniform. Here, dry classification, wet classification, or sieving classification can be used. Through crushing or pulverization and classification, powdered pitch with an average particle size of 50 to 500 μm can be obtained.

[0089] Then, in step (c), the step of stabilizing the pitch can be performed.

[0090] First, the pitch obtained in step (b) is subjected to primary oxidation to stabilize the carbon structure of the pitch.

[0091] In specific examples of the present invention, pitch stabilization may be carried out under an oxidizing gas atmosphere. In preferred examples of the present invention, pitch stabilization may be carried out under an air atmosphere, but is not particularly limited thereto.

[0092] In a specific example of the present invention, pitch stabilization can be carried out at a temperature of 100 to 500°C, preferably 150 to 300°C. When pitch stabilization is carried out at this temperature, the carbon structure in the pitch changes from thermoplastic to thermosetting, and thereafter, this structure can be stably maintained during the carbonization process. At this time, the heating rate may be 2 to 10°C / min. If the heating rate is too slow, productivity will be poor, and if the heating rate is too fast, it may be difficult to perform a uniform stabilization process.

[0093] In a specific example of the present invention, the pitch stabilization can be performed at a pressure of 0.1 to 10 bar, preferably 0.5 to 5 bar. When the pitch stabilization is performed at this pressure, the structure can be sufficiently stabilized all the way to the carbon atoms deep within the pitch.

[0094] In a specific example of the present invention, pitch stabilization can be carried out under conditions of an oxidizing gas flow rate of 0.1 to 500 ml / min, preferably 1 to 300 ml / min, preferably air. When pitch stabilization is carried out under these oxidizing gas flow rate conditions, the structure can be sufficiently stabilized all the way to the carbon atoms deep within the pitch.

[0095] In a specific example of the present invention, pitch stabilization can be carried out for a period of 1 to 10 hours, preferably 2 to 8 hours. When pitch stabilization is carried out for this period of time, the structure can be sufficiently stabilized all the way to the carbon atoms deep within the pitch.

[0096] Then, in step (d), the stabilized pitch is carbonized to obtain a carbide. Through the carbonization of the pitch, other functional groups contained in the pitch are removed, and a carbide consisting of substantially pure carbon is obtained.

[0097] In specific examples of the present invention, pitch carbonization may be carried out under an inert gas atmosphere. In preferred examples of the present invention, pitch carbonization may be carried out under a nitrogen or argon atmosphere, but is not particularly limited thereto.

[0098] In a specific example of the present invention, the carbonization of pitch can be carried out at a temperature greater than 700°C but less than or equal to 1,000°C, preferably between 800°C and 900°C. If the temperature is lower than this range during pitch carbonization, carbonization may not be sufficient, and if the temperature is higher than this range, the carbonization yield may decrease.

[0099] In a specific example of the present invention, pitch carbonization can be carried out under conditions of an inert gas flow rate of 0.1 to 30 ml / min, preferably 0.1 to 10 ml / min, preferably nitrogen. When pitch carbonization is carried out under these inert gas flow rate conditions, the pitch can be sufficiently carbonized.

[0100] In a specific example of the present invention, the carbonization of the pitch may be carried out for 0.5 to 5 hours, preferably 1 to 3 hours. When the carbonization of the pitch is carried out for this period of time, the pitch can be sufficiently carbonized.

[0101] Then, in step (e), the carbide (carbonized pitch) is activated to obtain a porous carbon support. The porous carbon support can be obtained by forming pores in the pitch pellet through the activation of the carbide.

[0102] In specific examples of the present invention, the activation of the carbide can be carried out under an oxidizing gas atmosphere. In preferred examples of the present invention, the activation of the carbide can be carried out under a water vapor atmosphere, but is not particularly limited thereto.

[0103] In a specific example of the present invention, the activation of the carbide can be carried out at a temperature greater than 700°C but less than or equal to 1,000°C, preferably 800 to 900°C. When the activation of the carbide is carried out at this temperature, a porous carbon support can be obtained in which micropores and mesopores are sufficiently formed.

[0104] In a specific example of the present invention, the activation of the carbide can be carried out at a pressure of 0.1 to 10 bar, preferably 0.1 to 5 bar. When the activation of the carbide is carried out at this pressure, a porous carbon support with sufficiently formed fine pores and medium pores can be obtained.

[0105] In a specific example of the present invention, the activation of the carbide can be carried out under conditions of an oxidizing gas flow rate of 0.1 to 100 ml / min, preferably 0.1 to 50 ml / min, preferably water vapor. When the activation of the carbide is carried out under these oxidizing gas flow rate conditions, a porous carbon support with sufficiently formed fine pores and medium pores can be obtained.

[0106] In a specific example of the present invention, the activation of the carbide can be carried out for 0.5 to 5 hours, preferably 1 to 3 hours. When the activation of the carbide is carried out for this period of time, a porous carbon support with sufficiently formed micropores and medium pores can be obtained.

[0107] In specific examples of the present invention, the stabilization, carbonization, and activation in steps (c) to (e) can each be carried out in a microwave-powered heating furnace. In preferred examples of the present invention, the stabilization, carbonization, and activation in steps (c) to (e) can all be carried out in a microwave-powered heating furnace. A microwave-powered heating furnace is preferred because it can raise the temperature of the pitch itself without raising the external temperature of the pitch, but the invention is not particularly limited thereto.

[0108] In a specific example of the present invention, steps (c) to (e) can be carried out continuously in a single apparatus. In a preferred example of the present invention, steps (c) to (e) can be carried out continuously in a single rotary kiln, but the apparatus is not particularly limited to this. By carrying out steps (c) to (e) continuously in a single apparatus, process optimization can be achieved.

[0109] In a specific example of the present invention, the porous carbon support obtained in step (e) can be further crushed or pulverized and classified. Through crushing or pulverization, the porous carbon support can be further pulverized, and through classification, the particle size distribution of the porous carbon support can be made uniform. Here, classification can be performed using dry classification, wet classification, or sieving classification. Through crushing or pulverization and classification, an average particle size of 1 to 20 μm and 300 to 3,000 μm can be achieved. 2 A porous carbon support powder having a BET specific surface area of ​​0.05 g / ml and a tap density of 0.05 to 0.5 g / ml can be obtained. Furthermore, the porous carbon support powder may have a volume percentage of mesopores (pores with a size of 2 to 50 nm) of 10 to 80% based on the total pore volume.

[0110] On the other hand, if a porous carbon support is obtained by stabilizing, carbonizing, and activating the pitch in step (b) without further grinding, this carbon support can be ground (or further classified) to have an average particle size of 1 to 20 μm, but is not limited thereto.

[0111] In the method for producing carbon-silicon / carbon composites according to an embodiment of the present invention, the obtained carbon-silicon / carbon composite can be crushed or pulverized and classified. Through crushing or pulverization, the porous carbon support can be further pulverized, and through classification, the particle size distribution of the composite can be made uniform. Here, the classification can be dry classification, wet classification, or classification using a sieve.

[0112] <Negative electrode active material> In yet another embodiment of the present invention, a negative electrode active material comprising a carbon-silicon / carbon composite is provided.

[0113] The negative electrode active material according to an embodiment of the present invention may include a carbon-silicon / carbon composite.

[0114] Furthermore, the negative electrode active material according to the embodiment of the present invention may further 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 the embodiment of the present invention with a carbon-based negative electrode material, such as a graphite-based negative electrode material.

[0115] Here, the carbon-based anode material may include, but is not limited to, at least one selected from the group consisting of, for example, natural graphite, artificial graphite, soft carbon, hard carbon, mesocarbon, carbon fiber, carbon nanotubes, pyrolysis carbons, cokes, calcined organic polymer compounds, and carbon black.

[0116] The content of the carbon-based anode material in the anode active material according to the embodiment of the present invention may be 2 to 80% by weight, preferably 5 to 70% by weight, and more preferably 30 to 70% by weight, based on the total weight of the anode active material.

[0117] The negative electrode active material according to an embodiment of the present invention can be effectively used to manufacture secondary batteries, specifically the negative electrode of a secondary battery and the negative electrode of an all-solid-state battery.

[0118] <All-solid-state battery> In yet another embodiment of the present invention, an all-solid-state battery is provided that includes a Solid Electrolyte Interphase (SEI) film containing the carbon-silicon / carbon composite.

[0119] The all-solid-state battery may be an all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte between the positive electrode and the negative electrode, wherein the negative electrode may include a negative electrode active material layer, and at least a portion of the negative electrode active material particles of the negative electrode active material layer may include an SEI (Solid Electrolyte Interphase) film containing the carbon-silicon / carbon composite described above.

[0120] On the other hand, the negative electrode active material particles may be carbon-based negative electrode materials, and in this case, the content may be the same as that described above regarding the negative electrode active material, so the relevant explanation will be omitted.

[0121] Furthermore, in addition to the negative electrode active material particles and SEI film of the all-solid-state battery, the negative electrode configuration, positive electrode configuration, and solid electrolyte configuration can be those of known all-solid-state batteries, and therefore, the present invention does not particularly limit these. [Examples]

[0122] The present invention will be described more specifically below with reference to examples. The following examples are for illustrative purposes only, and the scope of the present invention is not limited thereto.

[0123] Examples 1-2 and Comparative Example 1 300 g of petroleum-based residual oil (YNCC, HTC PFO (pyrolytic fuel oil)) was placed in a reactor equipped with a stirrer, and thermal decomposition and condensation polymerization were carried out at 450°C for 3 hours while supplying nitrogen at a flow rate of 100 ml / min. During this time, the stirrer was rotated at a speed of 200 rpm to mix the reactants. The polymerized pitch was solidified and pelletized to obtain solid pitch pellets with an average particle size of 1 to 30 mm.

[0124] The solid pitch pellets obtained above were crushed to produce pitch particles with an average particle size of 200 μm. These particles were then fed into a rotary kiln with three sections for sequential stabilization, carbonization, and activation. The conditions for stabilization, carbonization, and activation are shown in Table 1 below.

[0125] The specific surface area of ​​the carbon support was measured using a Belsorp mini II according to the ASTM D4820-93 method. The tap density of the carbon support was measured using a tap density analyzer (Electrolab, ETD-1020x) according to the ASTM B527 method. The average particle size of the carbon support was measured using a particle size analyzer (Horiba, laser particle analyzer, LA-960V2) according to the ASTM E112 method. The results are shown in Table 1.

[0126] [Table 1]

[0127] A porous carbon support from a reference example was pulverized using a pulverizer (Netch, air jet mill) to obtain a fine powder of porous carbon support with an average particle size of 7 μm. Next, 15 g of this fine powder of porous carbon support was placed in a rotary kiln, and silane (SiH4) gas was injected to form a silicon layer on the porous carbon support. The silicon layer formation conditions and the physical properties of the carbon support after silicon layer formation are shown in Table 2 below.

[0128] [Table 2]

[0129] The carbon-silicon composite obtained above was placed in a rotary kiln and heat-treated at 900°C in an argon atmosphere for 30 minutes (Example 1). The same carbon-silicon composite was also placed in a rotary kiln and heat-treated at 900°C (Example 2) and 700°C (Comparative Example 1) in the presence of ethylene for 30 minutes to form a carbon layer.

[0130] Test example (1) X-ray diffraction analysis X-ray diffraction analysis was performed on the particles of the above-mentioned standard example, Examples 1-2, and Comparative Example 1 under the following conditions, and the results are shown in Figure 1. - Equipment: D-MAX 2200 (RIGAKU) - Angle: 20~70° - Sampling W.:0.01 - X-Ray 40kV / 30mA - DivSlit:1 / 2deg. - DivH.L.Slit: 10mm - SctSlit: 1 / 2deg. - RecSlit: 0.15mm

[0131] As can be seen from Figure 1, Si-C bonds were not formed in the carbon-silicon composite of the reference example and the carbon-silicon-carbon composite of Comparative Example 1. In contrast, it was confirmed that Si-C bonds were formed in the carbon-silicon / carbon composite of Example 1 and the carbon-silicon / carbon-carbon composite of Example 2.

[0132] Furthermore, as can be seen in Figure 2, the observation of a SiC peak at temperatures above 850°C clarifies why no SiC peak was observed in Comparative Example 1, where the heat treatment temperature was 700°C, in Figure 1. It also clarifies that a SiC peak was observed in Examples 1 and 2, where the heat treatment temperature was 900°C, in Figure 1.

[0133] (2) Electrochemical evaluation Half-coin cells were manufactured using the composites of the standard example, Example 2, and Comparative Example 1, and then electrochemical evaluations were performed. The manufacturing conditions for the half-coin cells are shown in Table 3, and the evaluation results are shown in Tables 4-5 and Figures 3-4. In Table 3, AM, CM, and BM represent the active material (porous carbon support with silane deposition), conductor (Super P carbon black), and binder (styrene-butadiene rubber / carboxymethylcellulose 5:5), respectively, while EC, EMC, DMC, FEC, VC, and PS represent ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, fluoroethylene carbonate, vinylene carbonate, and propanesultone, respectively.

[0134] [Table 3]

[0135] [Table 4]

[0136] [Table 5]

[0137] As can be seen from Tables 4-5 and Figures 3-4, in the case of half-coin cells manufactured from the composite of the examples, although the silicon content decreased and the capacity decreased, the cycle retention rate was significantly better than that of the reference example and comparative example.

Claims

1. Porous carbon supports; 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.

2. The carbon-silicon / carbon composite according to claim 1, wherein the porous carbon support has a volume ratio of 10 to 80% of mesopores, which have a pore size of 2 to 50 nm, based on the total pore volume.

3. The porous carbon support has a BET specific surface area of ​​300 to 3,000 m². ２ The carbon-silicon / carbon composite according to claim 1, wherein the density is 0.05 to 0.5 g / ml, the tap density is 0.05 to 0.5 g / ml, and the average particle size is 1 to 20 μm.

4. The carbon-silicon / carbon composite according to claim 1, wherein the silicon / carbon composite matrix contains silicon and carbon in a weight ratio of 1:2 to 1:0.

1.

5. The carbon-silicon / carbon composite according to claim 1, wherein the silicon / carbon composite matrix is ​​10 to 90% by weight of the total weight of the carbon-silicon / carbon composite.

6. The carbon-silicon / carbon composite according to claim 1, further comprising: a carbon layer formed on the silicon / carbon composite matrix;

7. (1) The step of forming silicon on the surface and inside the pores of a porous carbon support to obtain a carbon-silicon composite; and (2) A method for producing a carbon-silicon / carbon composite, comprising the step of heat-treating the carbon-silicon composite.

8. The method for producing a carbon-silicon / carbon composite according to claim 7, wherein the heat treatment step is carried out by heat treating the carbon-silicon composite at a temperature of 800 to 1,000°C to convert some of the Si-Si bonds of silicon into Si-C bonds.

9. The method for producing a carbon-silicon / carbon composite according to claim 7, wherein the heat treatment step is carried out by converting some of the Si-Si bonds of silicon to Si-C bonds while forming a carbon layer on the carbon-silicon composite at a temperature of 800 to 1,000°C.

10. The carbon-silicon / carbon composite according to any one of claims 1 to 6; and A negative electrode active material containing carbon-based negative electrode material.

11. A solid-state battery comprising a Solid Electrolyte Interphase (SEI) film containing a carbon-silicon / carbon composite according to any one of claims 1 to 6.

Images