Carbon-silicon composite and its manufacturing method

Abstract

The present invention relates to a carbon-silicon composite and a method for producing the same. One aspect of the present invention provides a carbon-silicon composite comprising a core containing a carbon material and silicon particles, and a shell formed on the surface of the core and containing amorphous carbon, wherein the silicon particles are uniformly distributed from the center of the core to the surface.

Description

[Technical Field]

[0001] The present invention relates to a carbon-silicon composite and a method for producing the same. [Background technology]

[0002] With the depletion of fossil fuels causing rising energy prices and growing concerns about environmental pollution, eco-friendly alternative energy sources are becoming an essential factor for future life. In particular, with the increasing technological development and demand for mobile devices, the demand for secondary batteries as an eco-friendly alternative energy source is rapidly increasing.

[0003] Among these, lithium secondary batteries have been widely commercialized and used due to their high energy density and working potential, long cycle life, and low self-discharge rate. Their applications are expected to expand from digital devices such as laptops and mobile phones to electric vehicles, hybrid vehicles, aerospace and aviation fields, and energy storage systems.

[0004] As a result, active research is being conducted to realize high-capacity lithium secondary batteries.

[0005] Conventional lithium metal was used as the negative electrode of lithium secondary batteries, but the risk of battery short circuit due to dendrite formation and the resulting explosion became an issue, leading to the emergence of carbon-based active materials, which allow reversible intercalation and deintercalation of lithium ions and maintain structural and electrical properties.

[0006] Although such carbon-based active materials offer many advantages in terms of energy density of lithium batteries, they have problems such as limitations on theoretical maximum capacity, safety issues, and reduced battery productivity due to the hydrophobicity of carbon-based compounds.

[0007] To solve this problem, silicon (Si) or silicon compounds were considered as high-capacity materials to replace carbon-based active materials, but most silicon anode materials have a problem in that the silicon volume expands by up to 300% upon lithium insertion, which destroys the anode and makes it impossible to demonstrate high cycle performance.

[0008] Furthermore, even when silicon or a silicon compound is added to a carbon-based active material, the silicon content is limited to a maximum of 10% due to the risk of electrode short-circuiting, cracking, and reduced lifespan caused by the swelling of silicon during charging and discharging, making it difficult to overcome the capacity limitation. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a carbon-silicon composite, which is an anode material for realizing a high-capacity lithium secondary battery, and which has a high content of silicon particles and can suppress volume expansion due to silicon, and a method for producing the same.

[0010] However, the problems to be solved by the present invention are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0011] One aspect of the present invention provides a carbon-silicon composite comprising a core containing a carbon material and silicon particles, and a shell formed on the surface of the core and containing amorphous carbon, crystalline carbon, or both, wherein the silicon particles are uniformly distributed from the center of the core to the surface.

[0012] According to one embodiment, the content of the silicon particles in the core may be 10% to 50% by weight.

[0013] According to one embodiment, the content ratio of the carbon material to the silicon particles may be 9:1 to 1:1.

[0014] According to one embodiment, the difference between the silicon particle content ratio in the portion of the core that is within 20% of the distance from the core center to the surface and the silicon particle content ratio in the portion other than 80% of the distance from the core center may be less than 5%.

[0015] According to one embodiment, the silicon particles may have a size of 20 nm to 100 nm.

[0016] According to one embodiment, the carbon material may include at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotube, graphene, and expanded graphite.

[0017] According to one embodiment, the shell may contain 40% to 60% by weight of crystalline carbon.

[0018] According to one embodiment, the carbon-silicon composite may have a size of 3 μm to 12 μm.

[0019] According to one embodiment, the porosity of the carbon-silicon composite may be 1% to 10%.

[0020] Another aspect of the present invention provides a method for producing a carbon-silicon composite, the method including the steps of: mixing a carbon material and silicon particles; applying a shear force to the mixed carbon material and silicon particles to form a core; applying a coating liquid containing amorphous carbon to a surface of the core to form a shell; and applying heat to the formed shell to crystallize part or all of the amorphous carbon.

[0021] According to one embodiment, the shear force may form pores within the carbon material, allowing the silicon particles to penetrate into the carbon material.

[0022] Another aspect of the present invention provides an electrode for a lithium ion battery, comprising the carbon-silicon composite or a carbon-silicon composite produced by the method for producing a carbon-silicon composite.

[0023] According to one embodiment, the volume expansion rate of the electrode is 50% or less, and the volume expansion rate may be measured by comparing the thickness of the electrode measured before charging and discharging with the thickness of the electrode measured after 100 cycles of discharge at a 0.5C rate.

[0024] According to one embodiment, the capacity of the electrode may be 600 mAh / g to 1680 mAh / g.

[0025] According to one embodiment, the initial coulombic efficiency of the electrode may be 80% or greater. [Effects of the Invention]

[0026] The carbon-silicon composite according to the present invention has a morphology including a core in which silicon particles are uniformly distributed throughout the carbon material and an amorphous carbon shell formed on the surface of the core, thereby suppressing silicon expansion, increasing the silicon content in the composite, and ensuring mechanical strength.

[0027] In addition, the method for producing a carbon-silicon composite according to the present invention can uniformly attach and distribute silicon particles within a carbon material by applying shear force, and can form pores within the carbon material, thereby increasing the silicon content within the composite through a simple process and forming a structure that can suppress expansion of the silicon particles.

[0028] Furthermore, the lithium ion battery electrode containing the carbon-silicon composite according to the present invention has a high silicon content, which allows for a high battery capacity, and has the effect of suppressing volume expansion of the electrode due to silicon swelling. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a graph showing an analysis of particle size distribution of a graphite-silicon composite according to an embodiment of the present invention. [Figure 2] 1 is an SEM image showing a cross section of a graphite-silicon composite according to an embodiment of the present invention and EDS analysis points. [Figure 3] 1 is a cross-sectional SEM image of a graphite-silicon composite according to an embodiment of the present invention. [Figure 4] 1 is an electron image of a graphite-silicon composite in an electrode formed from the graphite-silicon composite according to an embodiment of the present invention. [Figure 5] 1 is a layered EDS image of the graphite-silicon composite in an electrode formed from the graphite-silicon composite according to an embodiment of the present invention, where blue indicates silicon and red indicates carbon. [Figure 6] 1 is an EDS layered image showing silicon distribution in a graphite-silicon composite in an electrode formed of a graphite-silicon composite according to an embodiment of the present invention. [Figure 7] 1 is an EDS layered image showing the carbon distribution of the graphite-silicon composite in an electrode formed of the graphite-silicon composite according to an embodiment of the present invention. [Figure 8] 1 is a SEM image of an electrode formed of a graphite-silicon composite according to an embodiment of the present invention before and after charging and discharging. [Figure 9] 1 is a SEM image of an electrode formed of a graphite-silicon composite according to an embodiment of the present invention after charging and discharging. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. However, since various modifications can be made to the embodiments, the scope of the patent application is not limited or restricted by these embodiments. It should be understood that all modifications, equivalents, and alternatives to the embodiments are included in the scope of the patent.

[0031] The terms used in the examples are used merely for the purpose of explanation and should not be construed as limiting. A singular expression includes a plural expression unless the context clearly indicates otherwise. In this specification, the terms "comprise" or "have" and the like are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in this specification, and should be understood not to preclude the presence or possibility of addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0032] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which the embodiments belong. Terms defined in commonly used dictionaries, etc., should be interpreted as having a meaning consistent with the contextual meaning of the relevant art, and should not be interpreted as an ideal or overly formal meaning unless explicitly defined in this application.

[0033] Furthermore, when describing the embodiments, if it is determined that a detailed description of related publicly known technology may unnecessarily obscure the gist of the embodiments, the detailed description will be omitted.

[0034] The carbon-silicon composite and the method for producing the same of the present invention will be described in detail below with reference to examples and drawings, but the present invention is not limited to these examples and drawings.

[0035] One aspect of the present invention provides a carbon-silicon composite comprising a core containing a carbon material and silicon particles, and a shell formed on the surface of the core and containing amorphous carbon, crystalline carbon, or both, wherein the silicon particles are uniformly distributed from the center of the core to the surface.

[0036] The carbon-silicon composite according to the present invention has the effect of effectively suppressing volume expansion due to silicon while increasing the silicon content in the composite by uniformly dispersing silicon particles within the carbon material.

[0037] The silicon particles are uniformly distributed from the center of the core to the surface, and for example, the content ratio of the silicon particles to the carbon material is uniform from the center of the core to the surface.

[0038] According to one embodiment, the content of the silicon particles in the core may be 10% to 50% by weight.

[0039] Preferably, the content of the silicon particles may be 20% to 40% by weight.

[0040] If the content of the silicon particles is less than the above range, it may be difficult to achieve high capacity in a lithium-ion battery when used as an anode material. If the content of the silicon particles is more than the above range, the volume expansion rate of the electrode after charging and discharging the battery may increase by 50% or more.

[0041] According to one embodiment, the content ratio of the carbon material and the silicon particles may be 9:1 to 1:1.

[0042] Preferably, the content ratio of the carbon material to the silicon particles may be 4:1 to 3:2.

[0043] If the content ratio of the carbon material and the silicon particles is outside the above range, when the carbon-silicon composite is used as an anode material for a lithium ion battery, it may be difficult to achieve high battery capacity, and the volume expansion rate of the electrode after charging and discharging the battery may increase by 50% or more.

[0044] According to one embodiment, the difference between the silicon particle content ratio in the portion of the core that is within 20% of the distance from the core center to the surface and the silicon particle content ratio in the portion other than 80% of the distance from the core center may be less than 5%.

[0045] That is, the content ratio of silicon particles in the core is almost the same from the center to the surface of the core.

[0046] The carbon-silicon composite according to the present invention has a substantially uniform silicon particle content from the center of the core to the surface, making it possible to manufacture an electrode material with high capacity and excellent cycle characteristics.

[0047] According to one embodiment, the silicon particles may have a size of 20 nm to 100 nm.

[0048] The size may be a diameter, a radius, a maximum length, etc. depending on the shape of the particle.

[0049] If the size of the silicon particles is less than 20 nm, it may be difficult to achieve high capacity during electrode formation, and side reactions with the electrolyte may become more severe, resulting in reduced lifespan. If the size of the silicon particles is more than 100 nm, the expansion of the silicon may not be suppressed.

[0050] According to one embodiment, the carbon material may include at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotube, graphene, and expanded graphite. Preferably, the carbon material may include graphite.

[0051] According to one embodiment, the shell may have a thickness of 2 nm to 1 μm.

[0052] If the shell thickness is less than 2 nm, the stability of the carbon-silicon composite may be reduced, and if the thickness is more than 1 μm, the reaction with lithium during charge and discharge may be inhibited, making it difficult to expect high capacity during high-rate charge and discharge.

[0053] According to one embodiment, the shell may contain 40% to 60% by weight of crystalline carbon.

[0054] If the crystalline carbon content is less than 40 wt %, the mechanical strength of the carbon-silicon composite may be reduced, and if it exceeds 60 wt %, the composite may be destroyed due to volume expansion during charge and discharge, resulting in problems such as a decrease in capacity and a rapid decrease in cycle characteristics.

[0055] The amorphous carbon may be produced from a carbon precursor including sucrose, phenol resin, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, cellulose resin, styrene resin, polyimide resin, epoxy resin, or vinyl chloride resin, coal-based pitch, petroleum-based pitch, polyvinyl chloride, mesophase pitch, tar, block copolymer, polyol, and low-molecular-weight heavy oil, or a mixture thereof.

[0056] According to one embodiment, the carbon-silicon composite may have a size of 3 μm to 12 μm.

[0057] The size may be a diameter, a radius, a maximum length, etc. depending on the shape of the complex.

[0058] If the size of the carbon-silicon composite is less than 3 μm, the composite formation process may be difficult, the specific surface area may increase due to an increase in the differential, and the amount of binder required during electrode fabrication may increase, which may cause a decrease in capacity.

[0059] Furthermore, if the size of the carbon-silicon composite exceeds 12 μm, the electrode density may be reduced due to spaces between the composites when the electrode is formed.

[0060] According to one embodiment, the porosity of the carbon-silicon composite may be 1% to 10%, preferably 1% to 7%.

[0061] If the porosity of the carbon-silicon composite is less than 1%, the volume expansion suppression effect may be reduced due to insufficient formation of the pore structure, and if it exceeds 10%, the formation of excessive pores may increase the possibility of side reactions.

[0062] According to one embodiment, the porosity can be defined as follows:

[0063] Porosity = pore volume per unit mass / (specific volume + pore volume per unit mass)

[0064] The porosity may be measured by a BET method using an adsorption gas such as nitrogen, without any particular limitation.

[0065] The pores are formed inside the carbon-silicon composite and act as a buffer to reduce the volume expansion of silicon, thereby suppressing the volume expansion of the electrode.

[0066] Furthermore, the pores can be impregnated with a non-aqueous electrolyte, and lithium ions can be introduced into the inside of the negative electrode active material, which allows for efficient diffusion of lithium ions and enables high-rate charge / discharge.

[0067] The pores have a very fine average particle size and are uniformly distributed throughout the silicon particles. When the silicon particles are alloyed with lithium and expand in volume, the pores can expand while compressing their volume, without causing any significant change in appearance.

[0068] Another aspect of the present invention provides a method for producing a carbon-silicon composite, the method including the steps of: mixing a carbon material and silicon particles; applying a shear force to the mixed carbon material and silicon particles to form a core; applying a coating liquid containing amorphous carbon to a surface of the core to form a shell; and applying heat to the formed shell to crystallize part or all of the amorphous carbon.

[0069] The method for manufacturing a carbon-silicon composite according to the present invention allows silicon particles to be uniformly attached and distributed inside the carbon material by applying shear force, and can uniformly form pores inside the composite.

[0070] According to one embodiment, in the step of mixing the carbon material and silicon particles, the mixing may be overmixing, and the overmixing may be mixing in a milling process.

[0071] The milling process can be performed using one or more of a bead mill, a high energy ball mill, a planetary mill, a stirred ball mill, a vibration mill, a SPEX mill, a planetary mill, an attrition mill, a magneto-ball mill, and a vibration mill.

[0072] The step of applying shear force to the mixed carbon material and silicon particles to form cores can be performed using equipment capable of applying mechanical shear force, such as an equipment capable of applying shear force or a high-speed rotary mill.

[0073] According to one embodiment, the shear force forms pores within the carbon material, allowing the silicon particles to penetrate into the carbon material.

[0074] The pores can act as a buffer to suppress volume expansion due to swelling of the silicon particles, and the silicon particles can be physically bound to the interior of the carbon material by shear force.

[0075] The silicon particles physically bound within the carbon material will not separate from the carbon material unless a force corresponding to the applied shear force is applied, and can be uniformly distributed within the carbon-silicon composite.

[0076] Another aspect of the present invention provides an electrode for a lithium ion battery, comprising the carbon-silicon composite or a carbon-silicon composite produced by the method for producing a carbon-silicon composite.

[0077] According to one embodiment, the volume expansion rate of the electrode is 50% or less, and the volume expansion rate may be measured by comparing the thickness of the electrode measured before charging and discharging with the thickness of the electrode measured after 100 cycles of discharge at a 0.5C rate.

[0078] As an example, the thickness change can be measured by SEM image analysis, and the volume expansion rate of the electrode can be calculated using an equation such as:

[0079] Volume expansion rate = (electrode thickness after charge / discharge - electrode thickness before charge / discharge / electrode thickness before charge / discharge) x 100

[0080] According to one embodiment, the capacity of the electrode may be 600 mAh / g to 1680 mAh / g.

[0081] Preferably, the capacity of the electrode may be 850 mAh / g to 1500 mAh / g.

[0082] The capacity of the electrode corresponds to a capacity that can suppress the volume expansion rate to 20% or less while maximizing the silicon content.

[0083] According to one embodiment, the initial coulombic efficiency of the electrode may be 80% or greater.

[0084] For example, the initial coulombic efficiency of the electrode is determined by mixing the carbon-silicon composite, conductive material, and binder in a ratio of 90-6:2-3:6-8, and then applying the mixture to a copper foil with a loading mass of 3-10 mg / cm. 2 It can be coated with and measured at a rate of 0.1 to 0.5C.

[0085] According to one embodiment, the lithium ion battery electrode may be a lithium ion battery negative electrode.

[0086] The negative electrode may be prepared by a conventional method known in the art. For example, the negative electrode may be prepared by mixing and stirring a negative electrode slurry composition including the carbon-silicon composite, a binder, and additives such as a conductive material to prepare a negative electrode active material slurry, applying the slurry to a current collector, drying, and compressing the slurry.

[0087] The present invention will be described in more detail below with reference to examples and comparative examples.

[0088] However, the following examples are for illustrative purposes only and the scope of the present invention is not limited to the following examples. [Example]

[0089] Graphite (Tokai Carbon, BTR, etc.) was subjected to a mechanical grinding process and then mixed with silicon particles having diameters of 20 nm to 100 nm in a ratio of 7:3.

[0090] The mixture was subjected to shearing force in a high-speed mill to form a core in which silicon was uniformly distributed inside the graphite.

[0091] The surface of the formed core was coated with pitch to form a surface coating layer (shell), and the surface coating layer was heated to produce a graphite-silicon composite.

[0092] Experimental Example 1: Particle size distribution analysis of graphite-silicon composite A particle size distribution analysis was carried out on the graphite-silicon composite according to the example.

[0093] Referring to FIG. 1, it can be seen that the graphite-silicon composite according to the embodiment of the present invention exhibits a particle size distribution in which the range of D10 to D90 is 2.16 to 11.1 μm and D50 is 4.52 μm.

[0094] As mentioned above, if the size of the carbon-silicon composite is less than 3 μm, it may cause a decrease in capacity. Therefore, in the graphite-silicon composite according to the embodiment of the present invention, carbon-silicon composites having a size of less than 3 μm were screened out and not used.

[0095] Experimental Example 2: SEM-EDS analysis of graphite-silicon composite SEM-EDS analysis was carried out on the graphite-silicon composite according to the example.

[0096] SEM analysis was performed using a JEOL JSM-7600F, and the EDS measurement results at arbitrary points inside the composite are shown in Table 1.

[0097] [Table 1] 2 and 3 are SEM images showing EDS analysis points and a cross-sectional image of a graphite-silicon composite according to an embodiment of the present invention. The EDS analysis points in the SEM image of Fig. 2 correspond to point 1 (left), point 2 (center), and point 3 (right), respectively.

[0098] Referring to Table 1 and FIGS. 2 and 3, it can be seen that the graphite-silicon composite according to the embodiment of the present invention is formed of a core and an outer shell made of graphite and silicon, and that the silicon content is uniform from the center to the surface of the graphite-silicon composite.

[0099] Specifically, Figure 2 shows that the difference in silicon content ratio between point 2, which is the center of the carbon composite, and point 1, which is close to the surface, is only 3.68%, and Figure 3 shows that silicon particles are uniformly distributed inside the core, as indicated by the white dots.

[0100] Experimental Example 3: EDS analysis of an electrode made of graphite-silicon composite An electrode was formed using the graphite-silicon composite of the example, and then EDS analysis was carried out.

[0101] Table 2 shows the EDS measurement results for the inside of the electrode.

[0102] [Table 2] FIG. 4 is an electron image of a graphite-silicon composite within an electrode formed from a graphite-silicon composite according to an embodiment of the present invention.

[0103] FIG. 5 is an EDS layered image of the graphite-silicon composite in an electrode formed from the graphite-silicon composite according to an embodiment of the present invention, where blue represents silicon and red represents carbon.

[0104] FIG. 6 is an EDS layered image showing silicon distribution in a graphite-silicon composite within an electrode formed from a graphite-silicon composite according to an embodiment of the present invention.

[0105] FIG. 7 is an EDS layered image showing the carbon distribution of the graphite-silicon composite in an electrode formed from the graphite-silicon composite according to an embodiment of the present invention.

[0106] Referring to Table 2 and FIGS. 4 to 7, it can be seen that after the electrode is formed, the graphite-silicon composite in the electrode maintains a uniform silicon distribution and exhibits a silicon content of about 50%.

[0107] Experimental Example 4: Measurement of the volume expansion rate of an electrode made of graphite-silicon composite The thickness of the electrode formed using the graphite-silicon composite of the example and the thickness of the electrode after 100 cycles of discharge based on a 0.5C rate were measured by SEM image analysis to confirm the volume expansion rate.

[0108] At this time, the thickness was confirmed by measuring the length after cutting the cross section using FIB (Forced Ion Beam, TESCAN S9000G / OXFORD EDS Dual beam FIB (Ga LMIS)) and by SEM images.

[0109] FIG. 8 is a SEM image of an electrode formed of a graphite-silicon composite according to an embodiment of the present invention before and after charging and discharging.

[0110] FIG. 9 shows SEM images of an electrode formed of a graphite-silicon composite according to an embodiment of the present invention after charging and discharging.

[0111] 8 and 9, it can be seen that the thickness of the electrode before charge / discharge is about 35 μm, and the thickness of the electrode after 100 charge / discharge cycles is about 39 μm to 42 μm.

[0112] That is, the graphite-silicon composite according to the present invention exhibits a volume expansion rate of 10% to 20% after charge and discharge, which indicates that the volume expansion due to silicon is significantly suppressed.

[0113] Although the embodiments have been described above using limited drawings, those skilled in the art may apply various technical modifications and variations based on the above. For example, the described techniques may be performed in a different order than described, and / or the described components may be combined or combined in a different manner than described, or may be replaced or substituted with other components or equivalents, and still achieve suitable results. Therefore, other embodiments, other examples, and equivalents to the claims also fall within the scope of the following claims. The present disclosure also discloses the following exemplary embodiments. [Embodiment 1] a core comprising carbon material and silicon particles; and a shell formed on the surface of the core and comprising amorphous carbon, crystalline carbon, or both; The silicon particles are uniformly distributed from the center of the core to the surface. Carbon-silicon composite. [Embodiment 2] The content of the silicon particles in the core is 10% by weight to 50% by weight. 2. The carbon-silicon composite of embodiment 1. [Embodiment 3] The content ratio of the carbon material and the silicon particles is 9:1 to 1:1. 2. The carbon-silicon composite of embodiment 1. [Embodiment 4] the difference between the content ratio of silicon particles in a portion of the core within 20% of the distance from the core center to the surface and the content ratio of silicon particles in a portion other than 80% of the distance from the core center is less than 5%; 2. The carbon-silicon composite of embodiment 1. [Embodiment 5] The size of the silicon particles is 20 nm to 100 nm. 2. The carbon-silicon composite of embodiment 1. [Embodiment 6] The carbon material includes at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotube, graphene, and expanded graphite; 2. The carbon-silicon composite of embodiment 1. [Embodiment 7] The shell contains 40% by weight to 60% by weight of crystalline carbon. 2. The carbon-silicon composite of embodiment 1. [Embodiment 8] The size of the carbon-silicon composite is 3 μm to 12 μm. 2. The carbon-silicon composite of embodiment 1. [Embodiment 9] The porosity of the carbon-silicon composite is 1% to 10%. 2. The carbon-silicon composite of embodiment 1. [Embodiment 10] mixing a carbon material and silicon particles; applying a shear force to the mixed carbon material and silicon particles to form a core; forming a shell by applying a coating liquid containing amorphous carbon to the surface of the core; and and applying heat to the formed shell to crystallize some or all of the amorphous carbon. Method for producing carbon-silicon composites. [Embodiment 11] The shear force forms pores inside the carbon material, allowing the silicon particles to penetrate into the carbon material. 11. A method for producing a carbon-silicon composite according to embodiment 10. [Embodiment 12] 12. A carbon-silicon composite comprising the carbon-silicon composite of any one of embodiments 1 to 9 or the carbon-silicon composite produced by any one of embodiments 10 and 11. Electrodes for lithium-ion batteries. [Embodiment 13] The volume expansion rate of the electrode is 50% or less, The volume expansion rate is measured by comparing the thickness of the electrode measured before charging and discharging with the thickness of the electrode measured after 100 cycles of discharging at a 0.5C rate. 13. An electrode for a lithium ion battery according to embodiment 12. [Embodiment 14] The capacity of the electrode is 600mAh / g to 1680mAh / g. 13. An electrode for a lithium ion battery according to embodiment 12. [Embodiment 15] The initial coulomb efficiency of the electrode is 80% or more. 13. An electrode for a lithium ion battery according to embodiment 12.

Claims

1. mixing a carbon material and silicon particles; applying shear force to the mixed carbon material and silicon particles to form a core; applying pitch to the surface of the core to form a shell; and and applying heat to the formed shell to partially or completely crystallize the pitch; the difference between the content ratio of silicon particles in a portion of the core that is within 20% of the distance from the center of the core to the surface and the content ratio of silicon particles in a portion other than 80% of the distance from the center of the core is less than 5%; A method for producing a carbon-silicon composite.

2. The shear force forms pores inside the carbon material, allowing the silicon particles to penetrate into the carbon material. The method for producing the carbon-silicon composite according to claim 1.

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