Silicon-carbon composite, negative electrode active material, negative electrode, and secondary battery

Abstract

The present invention relates to a silicon-carbon composite, a negative electrode active material comprising the silicon-carbon composite, a negative electrode composition, a negative electrode, a lithium secondary battery, a battery module, and a battery pack, in the silicon-carbon composite, when etching is performed with an argon (Ar) ion beam at an energy of 1,000 eV for 5,000 seconds, followed by XPS analysis, the ratio of the Si element proportion measured by the Si 2p spectrum to the N element proportion measured by the N 1s spectrum is 35 to 200. 2p 1s The ratio of the Si element proportion measured by the Si 2p spectrum to the N element proportion measured by the N 1s spectrum is 35 to 200.​

Description

Technical Field

[0001] This application is based on and claims priority to Korean Patent Application No. 10-2024-0144985, filed with the Korean Intellectual Property Office on October 22, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0002] This application relates to a silicon-carbon composite, a negative electrode active material comprising the silicon-carbon composite, a negative electrode comprising the negative electrode active material, and a secondary battery comprising the negative electrode. Background Technology

[0003] With the rapid proliferation of battery-powered electronic devices such as mobile phones, laptops, electric vehicles, power tools, and vacuum cleaners in recent years, the demand for small, lightweight, yet relatively high-capacity and / or high-output rechargeable batteries is increasing rapidly. Lithium-ion batteries, with their light weight and high energy density, are attracting significant attention as power sources for electronic devices. Therefore, research and development efforts aimed at improving the performance of lithium-ion batteries are currently underway.

[0004] By innovating on the core materials (i.e. the main components of lithium secondary batteries), including positive electrode materials, negative electrode materials, separators, and electrolytes, the performance of lithium secondary batteries can be improved. Summary of the Invention

[0005] Technical issues

[0006] One embodiment of this disclosure provides a silicon-carbon composite, a negative electrode active material, a negative electrode, and a lithium secondary battery that can be used as a negative electrode active material with excellent capacity and / or efficiency characteristics and high energy density.

[0007] Technical means

[0008] One embodiment of this disclosure provides a silicon-carbon composite wherein, when etched for 5,000 seconds using an argon (Ar) ion beam at an energy of 1,000 eV, followed by XPS analysis, the silicon... 2p The Si ratio measured by the spectrum relative to N 1s The ratio of N measured by the spectrum is between 35 and 200.

[0009] One embodiment of this disclosure provides a negative electrode active material comprising the silicon-carbon composite according to the above embodiments.

[0010] One embodiment of this disclosure provides a negative electrode composition comprising the negative electrode active material according to the above embodiments.

[0011] One embodiment of this disclosure provides a negative electrode comprising the negative electrode composition according to the above embodiments.

[0012] One embodiment of this disclosure provides a lithium secondary battery comprising a negative electrode, a positive electrode, and a separator according to the above embodiment.

[0013] One embodiment of this disclosure provides a battery module that includes a lithium secondary battery according to the above embodiment.

[0014] One embodiment of this disclosure provides a battery pack that includes a battery module according to the above-described embodiment.

[0015] Technical effect

[0016] According to embodiments of this disclosure, a silicon-carbon composite is used as the negative electrode active material. In this silicon-carbon composite, when etched for 5,000 seconds using an argon (Ar) ion beam at an energy of 1,000 eV, followed by XPS analysis, the silicon... 2p The Si ratio measured by the spectrum relative to N 1s The ratio of N measured by the spectrum meets a specific value, thereby providing a lithium secondary battery with improved capacity and / or efficiency. Attached Figure Description

[0017] The following figures illustrate preferred embodiments of this disclosure, and, together with the detailed description provided below, are intended to further enhance the understanding of the technical essence of this disclosure. Therefore, this disclosure should not be construed as being limited to the matters depicted in these figures.

[0018] Figure 1 This is a schematic diagram illustrating a lithium secondary battery structure according to one embodiment of the present disclosure.

[0019] Figure 2 This is a schematic diagram showing the negative electrode of a lithium secondary battery according to one embodiment of the present disclosure.

[0020] Figure 3 This is a graph showing the spectrum obtained by XPS analysis after etching the silicon-carbon composites of Examples 1 to 4 for 5,000 seconds.

[0021] Figure 4 This is a graph showing the spectrum obtained by XPS analysis after etching the silicon-carbon composites of Comparative Examples 1 to 5 for 5,000 seconds.

[0022] Throughout the accompanying drawings, corresponding reference numerals denote corresponding elements. The drawings presented are for simplicity and clarity and are not necessarily drawn to scale. For example, to aid in understanding the various embodiments, the dimensions of some elements may be enlarged relative to others. Furthermore, common but easily understood elements that are useful or necessary in commercially viable embodiments are often not shown so as not to obstruct observation of these various embodiments. Detailed Implementation

[0023] This disclosure will be described in more detail below to aid in understanding it. This disclosure may be implemented in various different forms and is not limited to the embodiments described herein.

[0024] It should be understood that terms such as “comprising,” “including,” or “having” in this specification are intended to specify the presence of a feature, number, step, element, or combination thereof, but are not intended to exclude the possibility of the presence or addition of one or more other features, numbers, steps, elements, or combinations thereof.

[0025] Furthermore, when describing a part (such as a layer) as being "above" or "on top of" another part, this includes not only the case where it is "directly" "above" the other part, but also the case where other parts are interspersed in between. Conversely, when describing a part as being "directly" "above" another part, it means that no other parts are interspersed in between. Additionally, when describing a part as being "above" or "on top of" a reference part, it means that the part is located above or below the reference part, and does not necessarily mean that the part is located "above" or "on top of" the reference part in the opposite direction of gravity.

[0026] The terms or vocabulary used in this specification should not be construed as limited to their common or dictionary meanings, but should be interpreted based on the principle that the inventors can appropriately define the concepts of the terms to best describe the contents of this disclosure, and in accordance with the meanings and concepts consistent with the technical intent of this disclosure.

[0027] The singular expressions of terms used in this specification include the plural expressions, unless the context clearly indicates otherwise.

[0028] The embodiments of this disclosure will be described in detail below. However, the embodiments of this disclosure can be modified in various ways, and the scope of this disclosure is not limited to the embodiments described below.

[0029] Figure 1 This is a schematic diagram illustrating a lithium secondary battery structure according to one embodiment of the present disclosure.

[0030] Reference Figure 1According to one embodiment of the present disclosure, a lithium secondary battery 100 includes a positive electrode 110, a negative electrode 120, a separator 130 inserted between the positive electrode 110 and the negative electrode 120, an electrolyte 140, etc. In the lithium secondary battery 100, during charging, lithium ions move from the positive electrode 110 through the separator 130 to the negative electrode 120 (e.g., energy storage), and during discharging, lithium ions move from the negative electrode 120 through the separator 130 to the positive electrode 110, thereby generating electricity. In this process, the positive electrode 110 and the negative electrode 120 respectively play the role of releasing or accepting lithium ions, and utilize the electrochemical reaction in which electrons move through the wires connecting the positive electrode 110 and the negative electrode 120 to generate current, and lithium ions move between the positive electrode 110 and the negative electrode 120 through the electrolyte 140 to generate current.

[0031] The positive electrode 110 and negative electrode 120 of the lithium secondary battery 100 can each be manufactured by forming an active material layer containing positive electrode active material and negative electrode active material on a current collector, respectively. Typically, the positive electrode uses lithium-containing metal oxides (such as LiCoO2 and LiMn2O4) as the positive electrode active material, while the negative electrode uses lithium-free carbon-based active materials and silicon-based active materials as the negative electrode active materials.

[0032] Figure 2 This is a schematic diagram showing the negative electrode 120 of a lithium secondary battery 100 according to one embodiment of the present disclosure.

[0033] Reference Figure 2 According to one embodiment of the present disclosure, the negative electrode 120 of a lithium secondary battery 100 includes a current collector 122 and a negative electrode active material layer 124.

[0034] Batteries using graphite as the negative electrode active material can exhibit a high discharge voltage of 3.6V, but their low capacity limits their ability to improve energy density. On the other hand, silicon-based active materials, due to their high capacity and efficiency, are attracting considerable attention as next-generation negative electrode active materials. Therefore, there is a need to develop silicon-based active materials with high capacity or efficiency characteristics. For example, an active material comprising a silicon-carbon composite could be developed, wherein the silicon-carbon composite is composed of silicon with high capacity characteristics and lightweight carbon elements capable of mitigating silicon volume expansion.

[0035] On the other hand, silicon-carbon composite active materials with high capacity, high efficiency and long life may cause problems in slurry processability, and improving processability is important for the development of high energy density lithium secondary batteries.

[0036] This disclosure provides a silicon-carbon composite for use as a negative electrode active material in a lithium secondary battery 100 and a technique for manufacturing a negative electrode 120 using the same. The silicon-carbon composite can improve slurry processability while maintaining high capacity and high efficiency through the physical properties of porous carbon and the introduction of a surface coating.

[0037] According to one embodiment of this disclosure, a silicon-carbon composite is a silicon-carbon composite in which silicon and carbon (e.g., graphite) are respectively present. In this specification, a silicon-carbon composite may be represented as Si / C. The silicon-carbon composite may consist of unbonded silicon and carbon, but may further include other components as needed. For example, the silicon-carbon composite may or may not contain silicon carbide, denoted as SiC. When the silicon-carbon composite contains silicon carbide, its content is 3% by weight or less. The silicon-carbon composite may be in a crystalline, amorphous, or mixed state. In one example, the C in the silicon-carbon composite may be in an amorphous state.

[0038] According to one embodiment, the silicon-carbon composite comprises porous carbon particles and silicon particles disposed in at least a portion of the interior and surface of the porous carbon particles. The silicon can be formed by depositing silicon onto the porous carbon particles using a silane gas. If necessary, a carbon layer can be further formed on the surface of the silicon-carbon composite. The carbon layer can impart conductivity and enhance the initial efficiency, lifetime characteristics, and capacity characteristics of the secondary battery. Based on a total of 100% by weight of the silicon-carbon composite particles, the total weight of the carbon layer can be from about 5% by weight to 40% by weight. The carbon layer can comprise at least one of amorphous carbon and crystalline carbon. As used herein, the terms “about,” “approximately,” and “substantially” refer to a range or approximation of a value or degree of magnitude taking into account inherent manufacturing and material tolerances (e.g., ±5%).

[0039] According to one embodiment, the silicon-carbon composite may be particles comprising porous silicon particles and carbon disposed in at least a portion of the interior and surface of the porous silicon particles. This can be formed by etching silicon oxide to form silicon-based particles (e.g., a Si matrix) with a porous structure, followed by coating with carbon. The carbon can be as described above regarding carbon layers.

[0040] The negative electrode active material comprising the silicon-carbon composite according to embodiments of the present disclosure can be prepared by the following method.

[0041] First, the carbon-based particle precursor is placed in an electric furnace and heated for a predetermined time under a nitrogen atmosphere. Then, the resulting heated powder is mixed with a mixed solution, such as sulfuric acid and nitric acid, and stirred at a predetermined temperature for a predetermined time. The mixture is then centrifuged to obtain a precipitate. The obtained precipitate is dried to produce carbon-based particles.

[0042] Examples of carbon-based particle precursors may include natural polymers, synthetic polymers, and biomass, such as cellulose powder, polyacrylonitrile (PAN), phenolic resins, melamine resins, or coconut shells, but are not limited thereto, and may also use other materials available to those skilled in the art without limitation.

[0043] Subsequently, carbon-based particles are heated in a specific solvent under a specific atmosphere to obtain a porous carbon structure, which is then dried. The porous carbon structure is then treated under a specific atmosphere to prepare a silicon-carbon composite. The silicon-carbon composite is reacted with a specific gas (e.g., acetylene gas) in an electric furnace to prepare a silicon-carbon composite anode active material containing a carbon layer on its outermost surface.

[0044] In the silicon-carbon composite for negative electrode active materials prepared according to embodiments of this disclosure, when etched with an argon (Ar) ion beam and analyzed by X-ray photoelectron spectroscopy (XPS), the Si... 2p The Si ratio measured by the spectrum relative to N 1s The ratio of N measured by spectroscopy is approximately 35 to 200, and is based on a total content of 100 atomic% of Si, C, O, and N in the silicon-carbon composite, derived from N. 1s The proportion of N measured by the spectrum is approximately 0.35 atomic percent or more.

[0045] In this specification, X-ray photoelectron spectroscopy (XPS) is a technique for analyzing the surface chemical composition of materials, in which high-energy X-rays are used to irradiate the sample surface to measure the binding energy of photoelectrons emitted from surface atoms. This enables qualitative and quantitative analysis of elements and allows identification of the chemical state and environment of each element.

[0046] As described above, the method may further include a step of etching the surface of the silicon-carbon composite with an argon (Ar) ion beam prior to XPS analysis. By including the step of etching the surface of the silicon-carbon composite with an argon (Ar) ion beam, the surface layer of the sample (e.g., the carbon coating surrounding the silicon-carbon composite) can be removed to analyze the elemental distribution at deeper levels within the particles.

[0047] In one embodiment of this disclosure, the step of etching the surface of the silicon-carbon composite with an argon (Ar) ion beam can be performed for 5,000 seconds at an energy of approximately 1,000 eV. By etching at the aforementioned energy and time, the outermost carbon coating can be sufficiently removed to ensure data reliability and preserve the inherent properties of the sample, thereby preventing errors in resolving the chemical state of the sample.

[0048] In this specification, N obtained through XPS analysis 1s Spectrum and Si 2pThe spectra respectively correspond to the detected photoelectrons emitted from the 1s orbital of nitrogen atoms and the 2p orbital of silicon atoms, whereby the contents of nitrogen and silicon present on the surface of the negative electrode active material can be measured.

[0049] In this specification, XPS analysis is performed under the following conditions.

[0050] <XPS Analysis Conditions>

[0051] - X-ray source: Monochromatic Al Kα (1486.6eV)

[0052] - X-ray spot size: 400μm

[0053] - Sputter gun: Monatomic Ar (Energy: 1,000eV, Current: Low, Grating width: 2mm)

[0054] - Etch rate: 0.09nm / s for Ta₂O₅

[0055] - Operation mode: CAE (Constant Analyzer Energy) mode

[0056] - Full spectrum scan: Pass energy 200eV, energy step 1eV

[0057] - Narrow scan: Scan mode, pass energy 50eV, energy step 0.1eV

[0058] - Charge compensation: 0.1V 150μA

[0059] - SF: Al THERMO1

[0060] - ECF: TPP-2M

[0061] - Background subtraction: Smart

[0062] In one embodiment of the present disclosure, the depth profile of X-ray photoelectron spectroscopy (XPS) can be measured using a monochromatic Al Kα X-ray source at a rate of 0.09nm / s on a Ta₂O₅ sample.

[0063] In this specification, the peak intensity refers to a value obtained by deconvolving the Si 2p spectrum obtained through XPS analysis for each peak, fitting each peak with a "Gaussian / Lorentzian" model, and then integrating the area under the resulting Gaussian function graph.

[0064] In this specification, respective peaks may overlap and appear in the form of shoulder peaks, and more than two peaks may coexist.

[0065] In the present specification, in the case where peaks overlap or coexist, the intensity of a peak is calculated by adding the intensities of two or more peaks.

[0066] In the present specification, the element content ratio can be calculated according to Formula 1: [Formula 1]

[0067] In Formula 1, i represents the type of element to be measured, j represents the types of all elements measured by XPS. In addition, C i represents the element content ratio, A i represents the area corrected by taking into account the inelastic mean free path in the solid, and RSF i represents the relative sensitivity factor. For example, when peaks of A and B are detected by XPS, the peak areas are 1,000 and 500 respectively, and the RSF values are 0.8 and 1.2 respectively, the element content ratio of A can be calculated as: .

[0068] In the present specification, the XPS peak intensity of a specific element refers to the sum of all peaks appearing in the XPS spectrum of the element. For example, when Si 2p spectrum is observed by XPS, peaks representing various oxidation states (such as Si 0 , Si–C and Si x (0<x≤4)) will appear. However, when calculating the element content ratio of Si, the peak intensity of Si is determined as the sum of the intensities of all these peaks.

[0069] In one embodiment of the present specification, j may be any one of silicon, carbon, oxygen and nitrogen.

[0070] In one embodiment of the present disclosure, when the silicon-carbon composite is etched with an argon (Ar) ion beam at an energy of 1,000 eV for 5,000 seconds and then subjected to XPS analysis, the ratio of the Si proportion measured from the Si 2p spectrum to the N proportion measured from the N 1s spectrum may be about 35 to 200.

[0071] In the silicon-carbon composite according to the embodiment of the present disclosure, the lower limit of the ratio of the Si proportion to the N proportion may be about 35 or more, 37 or more, or 40 or more, and the upper limit may be about 200 or less, 150 or less, or 100 or less.

[0072] Secondary batteries using negative electrode active materials in which the Si-to-N ratio at the surface of the silicon-carbon composite meets the above-mentioned range exhibit excellent capacity, efficiency, and lifetime. For example, when the Si-to-N ratio at the surface of the silicon-carbon composite is within the above-mentioned range, the battery capacity and efficiency may increase, thereby improving the battery energy density and exhibiting excellent cycle performance and high-rate characteristics.

[0073] For example, amorphous silicon in an aqueous slurry phase can lead to unstable processability, but when N is doped within the above-mentioned proportion range to form a Si-N phase, stability during processing can be ensured, and the Si-N phase plays a role in buffering volume expansion during charge and discharge, thereby improving long-term life performance.

[0074] In one embodiment of this disclosure, when a silicon-carbon composite is etched using an argon (Ar) ion beam at an energy of 1,000 eV for 5,000 seconds, followed by XPS analysis, the total content of Si, C, O, and N in the silicon-carbon composite is 100 atomic%, based on N... 1s The proportion of N measured by the spectrum can be above approximately 0.35 atomic%. For example, the lower limit of the N proportion can be above approximately 0.35 atomic%, above 0.37 atomic%, or above 0.40 atomic%, and the upper limit can be below approximately 2 atomic%, below 1.5 atomic%, or below 1 atomic%.

[0075] When the proportion of N is within the above range, the battery energy density can be increased due to high capacity and high efficiency, and the cycle performance and high rate characteristics are excellent.

[0076] In one embodiment of this disclosure, when a silicon-carbon composite is etched using an argon (Ar) ion beam at an energy of 1,000 eV for 5,000 seconds, followed by XPS analysis, the silicon... 2p The proportion of Si measured by spectroscopy can be above approximately 20 atomic percent and below approximately 50 atomic percent. For example, the lower limit of the Si proportion can be above approximately 20 atomic percent, above approximately 25 atomic percent, or above approximately 28 atomic percent, and the upper limit can be below approximately 50 atomic percent, below approximately 40 atomic percent, or below approximately 35 atomic percent.

[0077] When the proportion of Si is kept within the above range, the capacity and efficiency can be increased, thereby improving the battery energy density and exhibiting excellent cycle performance and high rate characteristics.

[0078] In one embodiment of this specification, in order to satisfy the above-mentioned peak ratio in a silicon-carbon composite material obtained by depositing silicon on porous carbon, at least one of the following methods may be performed: a method for adjusting the mixing ratio of nitrogen source gas in the step of heating carbon-based powder, and a method for adjusting the mixing ratio using a silane / nitrogen source gas mixture in the step of depositing silicon.

[0079] In one embodiment of this specification, the nitrogen source gas may be nitrogen or ammonia, and may be, for example, nitrogen.

[0080] According to one embodiment, a heating step may be performed in which, after placing the carbon-based powder in a tube furnace and introducing nitrogen to form an inert atmosphere, the temperature is gradually increased to about 300°C to 500°C, and then further gradually heated to about 800°C to 1,000°C.

[0081] The powder obtained by heating can then be mixed with an acidic solvent, followed by centrifugation to obtain a precipitate. The precipitate is then neutralized in an alkaline solvent and dried to produce a porous carbon structure. In this case, the carbon particles can be heated in the alkaline solvent at a temperature of approximately 700°C to 900°C.

[0082] The porous carbon structure can then be placed in a horizontal electric furnace, and SiH4 / N2 gas can be introduced at approximately 500°C to 800°C to prepare the silicon-carbon composite. For example, the temperature can be approximately 550°C to 700°C, or approximately 550°C to 650°C.

[0083] At this point, the mixing ratio of SiH4 to N2 (SiH4 / N2) can be approximately 97:3 to 88:12, for example, approximately 95:5 to 90:10. The method may further include placing the silicon-carbon composite obtained in the above steps into an electric furnace for heat treatment, and introducing hydrocarbon gas at approximately 600°C to 800°C to form a carbon layer. According to one embodiment, the temperature can be approximately 550°C to 770°C, or 600°C to 700°C.

[0084] Alternatively, silicon-based powder can be placed in a horizontal tube, and argon gas can be introduced to create an inert atmosphere. The temperature can then be gradually increased to induce a disproportionation reaction. In this case, the heat treatment temperature can be from about 750°C to 1,200°C, for example, from about 800°C to 1,100°C.

[0085] Then the heat-treated SiO x Remove it from the tube, treat it with acid, and then stir to remove the SiO2 phase.

[0086] The obtained porous silicon can then be dried and subjected to chemical vapor deposition (CVD) using a hydrocarbon gas at approximately 550°C to 850°C to form a carbon layer. The hydrocarbon gas can be at least one selected from methane, ethane, propane, and acetylene.

[0087] Within the aforementioned deposition / coating temperature range, the carbon surface layer becomes uniform and silicon carbide is formed, thereby improving the processability of the water-based slurry.

[0088] In one embodiment of this specification, when carbon is combined with porous silicon, in order to satisfy the above-mentioned peak ratio, a hydrocarbon / nitrogen gas mixture can be mixed in a predetermined ratio during the CVD process for composite formation.

[0089] For example, the mixing ratio of hydrocarbons to nitrogen can be from about 97:3 to 88:12, such as from about 95:5 to 90:10.

[0090] According to one embodiment, the silicon-carbon composite exhibits a specific surface area of ​​about 0.5 m² / g to 10 m² / g and a pore volume of about 0.005 cm³ / g to 0.03 cm³ / g using the Brunol-Emmett-Teller (BET) method, with a pore size of about 1 nm to 20 nm as measured by the BET method. The pore volume of the silicon-carbon composite, as measured by mercury porosimetry, can be about 0.005 cm³ / g to 0.03 cm³ / g.

[0091] According to one embodiment, the silicon-carbon composite can exhibit a density of approximately 5 μm to 15 μm. 90 Particle size, approximately 1 μm to 10 μm D 50 Particle size, 1μm to 3μm D min and D of approximately 17μm to 23μm max In this specification, the average particle size (D) is... 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 For example, laser diffraction can be used for measurement. Laser diffraction can typically measure particle sizes from the submicron region to several millimeters, and provides highly repeatable and high-resolution results.

[0092] One embodiment provides a negative electrode active material comprising a silicon-carbon composite according to the above embodiment.

[0093] One embodiment provides a negative electrode composition comprising a negative electrode active material, a binder, and a conductive material according to the above embodiments.

[0094] According to one embodiment, based on 100 parts by weight of the negative electrode active material, the content of the silicon-carbon composite can be from about 0.1 parts by weight to 15 parts by weight, for example from about 0.1 parts by weight to 10 parts by weight, or from 1 part by weight to 8 parts by weight.

[0095] According to one embodiment, the negative electrode active material may further comprise a carbon-based active material. Based on a total of 100 parts by weight of the negative electrode active material contained in the negative electrode composition, the content of the carbon-based active material may be more than about 70 parts by weight and less than 99.9 parts by weight, for example, 85 parts by weight to 99 parts by weight. The carbon-based active material may comprise at least one of natural graphite and artificial graphite. When the carbon-based active material comprises both natural graphite and artificial graphite, the weight ratio of artificial graphite to natural graphite may be about 1:9 to 9:1, for example, about 3:7 to 7:3. For example, based on 100 parts by weight of the carbon-based active material, natural graphite may be about 10 parts by weight to 70 parts by weight, and artificial graphite may be about 30 parts by weight to 90 parts by weight.

[0096] Natural graphite refers to graphite that occurs naturally, including examples such as flake graphite, plate graphite, or amorphous graphite. Natural graphite has the advantages of abundant reserves, low price, high theoretical capacity and compaction density, and the ability to achieve high output.

[0097] In one example, spherical natural graphite with a sphericity of about 0.9 or higher can be used as natural graphite. In another example, the natural graphite can be spherical natural graphite with a tap density of about 0.9 g / cc or higher.

[0098] In this specification, sphericity can be a value obtained by dividing the circumference of a circle having the same area as the particle projection image by the circumference of the projection image. Sphericity can be obtained from scanning electron microscopy (SEM) images or measured using a particle shape analyzer such as the Sysmex FPIA 3000 (Malvern). Furthermore, crystal size can be confirmed by XRD analysis.

[0099] According to one embodiment of this disclosure, the negative electrode composition may further include a binder and a conductive material, and the binder may be an aqueous binder.

[0100] The adhesive may contain at least one selected from polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and substances obtained by replacing hydrogen in these substances with Li, Na, Ca, etc., and may also contain various copolymers thereof.

[0101] The conductive material is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. Examples of the conductive material may include: graphite, such as natural graphite and artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking black; conductive fibers, such as carbon fibers or metal fibers; conductive tubes, such as carbon nanotubes; metal powders, such as fluorocarbons, aluminum or nickel powder; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; or conductors, such as polyphenylene derivatives.

[0102] According to one embodiment, based on the solid components of the negative electrode composition, the content of the aqueous binder can be from about 1% to 5% by weight, for example, from about 3% to 4% by weight, and based on the solid components of the negative electrode composition, the content of the conductive material can be from about 0.1% to 2% by weight, for example, from about 1% by weight.

[0103] One embodiment of this disclosure provides a negative electrode 120 comprising the negative electrode composition according to the above embodiments.

[0104] For example, the negative electrode 120 may include a negative electrode current collector 122 and a negative electrode active material layer 124 disposed on at least one surface of the negative electrode current collector 122. The negative electrode active material layer 124 includes the negative electrode composition according to the above embodiments.

[0105] The negative electrode active material layer 124 can be formed by coating a negative electrode slurry containing the above-described negative electrode composition onto at least one surface of the negative electrode current collector 122, followed by drying and calendering.

[0106] The negative electrode current collector 122 is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, or surface-treated materials such as aluminum or stainless steel treated with carbon, nickel, titanium, silver, etc., can be used as the current collector 122. According to one embodiment, transition metals such as copper or nickel, which have good adsorption properties for carbon, can be used as the current collector 122. The thickness of the current collector 122 can be from about 6 μm to 20 μm, but is not limited thereto.

[0107] The negative electrode slurry may contain a solvent for forming the negative electrode slurry. For example, to facilitate the dispersion of the components, the solvent for forming the negative electrode slurry may contain at least one selected from distilled water, ethanol, methanol, and isopropanol, such as distilled water.

[0108] One embodiment of this disclosure provides a lithium secondary battery 100 comprising a negative electrode 120, a positive electrode 110, and a separator 130 according to the above embodiment.

[0109] The positive electrode 110 may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing positive electrode active material.

[0110] In the positive electrode 110, the positive electrode current collector is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or surface-treated materials such as aluminum or stainless steel treated with carbon, nickel, titanium, silver, etc., can be used as the positive electrode current collector. Furthermore, the positive electrode current collector can typically have a thickness of approximately 3 μm to 500 μm, and fine irregularities can be formed on its surface to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0111] The positive electrode active material can be any commonly used positive electrode active material. Examples of positive electrode active materials can include: layered compounds, such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; lithium iron oxides, such as LiFe3O4; lithium manganese oxides, such as those with the chemical formula Li 1+c1 Mn 2-c1 Those represented by O4 (0≤c1≤0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxides (Li2CuO2); vanadium oxides, such as LiV3O8, V2O5, and Cu2V2O7; Ni-site type lithium nickel oxides, such as LiNi 1-c2 M c2 O2 (where M is at least one selected from Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≤ c2 ≤ 0.3); lithium manganese composite oxides, such as those with the chemical formula LiM n2-c3 M c3 O2 (where M is at least one selected from Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01 ≤ c3 ≤ 0.1) or Li2M n3 MO8 (where M is at least one selected from Fe, Co, Ni, Cu and Zn); and LiMn2O4, but not limited to, in which a portion of the Li in the chemical formula is replaced by alkaline earth metal ions. The cathode 110 can be lithium metal.

[0112] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder in addition to the above-mentioned positive electrode active material.

[0113] Positive electrode conductive materials are used to impart conductivity to the electrode and can be used without particular restrictions, as long as they are electronically conductive and do not cause chemical changes in the battery. Examples of positive electrode conductive materials can include: graphite, such as natural and artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, and carbon fibers; metal powders or fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives. These can be used alone or as a mixture of two or more.

[0114] In addition, positive electrode binders are used to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Examples of positive electrode binders may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. These can be used alone or as a mixture of two or more.

[0115] Separator 130 separates the negative electrode 120 from the positive electrode 110 and provides a lithium-ion migration channel. It can be any separator commonly used in secondary batteries without particular limitation, as long as it has low electrolyte ion migration resistance and excellent electrolyte wettability. Examples of separators may include porous polymer membranes made of polyolefin polymers (such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers), or laminated structures of two or more layers thereof. Alternatively, conventional porous nonwoven fabrics, such as those made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0116] The lithium secondary battery 100 may also include an electrolyte 140. Examples of electrolytes may include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used to manufacture lithium secondary batteries.

[0117] According to one embodiment, electrolyte 140 may comprise a non-aqueous organic solvent and a metal salt.

[0118] Examples of the non-aqueous organic solvents may include aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0119] In carbonate-based organic solvents, cyclic carbonates (such as ethylene carbonate and propylene carbonate) exhibit high viscosity and high dielectric constant, thus readily dissociating lithium salts, and are therefore preferred for use. Electrolyte 140 with high conductivity can be prepared by mixing such cyclic carbonates with low-viscosity and low-dielectric-constant chain carbonates (such as dimethyl carbonate and diethyl carbonate) in appropriate proportions.

[0120] The metal salt may be a lithium salt, and the lithium salt may be a material that is readily soluble in non-aqueous electrolytes. For example, the lithium salt may contain one or more anions selected from the following: F - Cl - I - NO3 - N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N- .

[0121] In addition to the electrolyte components mentioned above, in order to achieve improved battery life characteristics, prevent battery capacity reduction, and improve battery discharge capacity, electrolyte 140 may also contain one or more additives, such as alkylene carbonate halide compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride.

[0122] According to another embodiment of this disclosure, a battery module comprising a lithium secondary battery 100 as a unit cell and a battery pack comprising the battery module are provided. Since the battery module and battery pack comprise secondary batteries with high capacity, high rate capability, and excellent cycle characteristics, they can be used as power sources for medium to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems.

[0123] Methods of implementing the invention

[0124] The embodiments described in this specification will be described in detail below. However, the embodiments according to this specification can be modified in various other forms, and the scope of this application should not be construed as limited to the embodiments described below. The embodiments of this application are provided to provide a more complete description of this specification to those skilled in the art.

[0125] <Example 1>

[0126] (1) Preparation of silicon-carbon composite 1

[0127] Cellulose powder was placed in a tube furnace and heated to 400°C at a rate of 4°C / min, followed by heating under a nitrogen atmosphere for 2 hours. Subsequently, the temperature of the tube furnace was increased to 900°C at a rate of 4°C / min, and the sample was further heated under a nitrogen atmosphere for 2 hours. The resulting powder was mixed with sulfuric acid and nitric acid in a volume ratio of 3:1, stirred at 60°C for 2 hours, and then centrifuged to obtain a precipitate. The obtained precipitate was washed five times in a mixed solvent of ethanol and distilled water in a volume ratio of 1:3, and then dried at 120°C for 12 hours. Carbon-based particles were placed in KOH solvent and heated at 800°C for 2 hours under a nitrogen atmosphere to obtain a porous carbon structure. The porous carbon structure was washed three times with distilled water and then dried at 120°C for more than 12 hours. The porous carbon structure was fractionated to achieve an average particle size (D...). 50The thickness was adjusted to 9 μm. The porous carbon structure was placed in a horizontal electric furnace, and a SiH4 / N2 (95 / 5) mixed gas was supplied at a flow rate of 50 ml / min for 1 hour at 650 °C to prepare a silicon-carbon composite. Subsequently, the silicon-carbon composite was placed in an electric furnace and reacted with acetylene gas at 600 °C for 3 hours, thereby preparing a silicon-carbon composite anode active material with a carbon layer on its outermost surface.

[0128] (2) Manufacturing of the negative electrode

[0129] A negative electrode slurry is prepared by mixing a negative electrode active material comprising the prepared silicon-carbon composite, natural graphite and artificial graphite (in a weight ratio of 10:15:75); a conductive material comprising carbon black and SWCNT; and a binder comprising carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in a weight ratio of 95.4:1:3.6 with an appropriate amount of distilled water to make the total solids content approximately 46% by weight.

[0130] The negative electrode slurry was coated onto a Cu metal foil with a thickness of approximately 15 µm and then dried in circulating air at 60 °C. Subsequently, after rolling, it was further dried in a vacuum oven at 130 °C for about one day, and then stamped to manufacture a circular negative electrode with an area of ​​1.4875 cm².

[0131] (3) Manufacturing of secondary batteries

[0132] A lithium (Li) metal foil stamped to an area of ​​1.7671 cm² is used as the positive electrode. A porous polyethylene membrane is inserted between the positive and negative electrodes, and an electrolyte is injected. The electrolyte contains additives and 1 M LiPF6 dissolved in a mixed solvent of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) in a volume ratio of 7:3. This produces a lithium coin half-cell.

[0133] <Example 2>

[0134] (1) Preparation of silicon-carbon composite 2

[0135] The silicon-carbon composite was prepared in the same manner as in Example 1, except that a mixed gas of SiH4 / N2=90 / 10 was introduced at a flow rate of 50 ml / min at 650°C for 1 hour.

[0136] (2) Manufacturing of negative electrode and secondary battery

[0137] Except for the use of silicon-carbon composite 2, the negative electrode and secondary battery were manufactured in the same manner as in Example 1.

[0138] <Example 3>

[0139] (1) Preparation of silicon-carbon composite 3

[0140] A silicon-carbon composite was prepared in the same manner as in Example 1, except that a mixed gas of SiH4 / N2=95 / 5 was introduced at a flow rate of 50 ml / min at 550°C for 1 hour.

[0141] (2) Production of Negative Electrode and Secondary Battery

[0142] A negative electrode and a secondary battery were produced in the same manner as in Example 1, except that silicon-carbon composite 3 was used.

[0143] <Example 4>

[0144] (1) Preparation of Silicon-Carbon Composite 4

[0145] D 50 SiO x (0<x≤1) was placed in a horizontal tube, and argon (Ar) was introduced at a flow rate of 1500 sccm for 1 hour to form an inert atmosphere. Then, argon was introduced at a flow rate of 150 sccm, the temperature was raised to 1,000°C at a rate of 10°C per minute and maintained for 6 hours to induce a disproportionation reaction. The heat-treated SiO x (0<x≤1) was taken out from the tube, immersed in a 20 wt% HF aqueous solution, and stirred at room temperature for 1 hour to remove the SiO2 phase. The obtained porous silicon was dried in a vacuum oven at 600°C for 12 hours. Thereafter, the dried porous silicon was subjected to a CVD treatment, in which a nitrogen / acetylene gas mixture at a volume ratio of 1:9 was introduced at a flow rate of 100 sccm at 600°C for 3 hours, thereby preparing the final silicon-carbon composite.

[0146] (2) Production of Negative Electrode and Secondary Battery

[0147] A negative electrode and a secondary battery were produced in the same manner as in Example 1, except that silicon-carbon composite 4 was used.

[0148] <Comparative Example 1>

[0149] (1) Preparation of Silicon-Carbon Composite 5

[0150] A silicon-carbon composite was prepared in the same manner as in Example 1, except that a mixed gas of SiH4 / N2=95 / 5 was introduced at a flow rate of 50 ml / min at 500°C for 1 hour.

[0151] (2) Production of Negative Electrode and Secondary Battery

[0152] A negative electrode and a secondary battery were produced in the same manner as in Example 1, except that silicon-carbon composite 5 was used.

[0153] <Comparative Example 2>

[0154] (1) Preparation of Silicon-Carbon Composite 6

[0155] The silicon-carbon composite was prepared in the same manner as in Example 1, except that a mixed gas of SiH4 / N2=99 / 1 was introduced at a flow rate of 50 ml / min at 650°C for 1 hour.

[0156] (2) Manufacturing of negative electrode and secondary battery

[0157] Except for the use of silicon-carbon composite 6, the negative electrode and secondary battery were manufactured in the same manner as in Example 1.

[0158] <Comparative Example 3>

[0159] (1) Preparation of silicon-carbon composite 7

[0160] The silicon-carbon composite was prepared in the same manner as in Example 4, except that a nitrogen / acetylene gas mixture with a volume ratio of 1:99 was introduced at a flow rate of 100 sccm at 750°C and reacted for 3 hours.

[0161] (2) Manufacturing of negative electrode and secondary battery

[0162] Except for the use of silicon-carbon composite 7, the negative electrode and secondary battery were manufactured in the same manner as in Example 1.

[0163] <Comparative Example 4>

[0164] (1) Preparation of silicon-carbon composite 8

[0165] The silicon-carbon composite was prepared in the same manner as in Example 1, except that a mixed gas of SiH4 / N2=95 / 5 was introduced at 750°C at a flow rate of 50 ml / min for 10 hours.

[0166] (2) Manufacturing of negative electrode and secondary battery

[0167] Except for the use of silicon-carbon composite 8, the negative electrode and secondary battery were manufactured in the same manner as in Example 1.

[0168] <Comparative Example 5>

[0169] (1) Preparation of silicon-carbon composite 9

[0170] Grinded Si particles and pulverized carbon were mixed at 40°C to prepare a silicon-carbon composite, which was then pulverized to an average particle size of 7 μm. The pulverized silicon-carbon composite was then reacted at 800°C with a nitrogen / acetylene gas mixture at a flow rate of 100 sccm and a volume ratio of 5:95 for 3 hours to prepare silicon-carbon composite 9.

[0171] (2) Manufacturing of negative electrode and secondary battery

[0172] Except for the use of silicon-carbon composite 9, the negative electrode and secondary battery were manufactured in the same manner as in Example 1.

[0173] The results of XPS analysis of the negative electrode active materials prepared in the above examples and comparative examples are as follows: Figure 3 , Figure 4 As shown in Table 1.

[0174] Figure 3 The spectrum obtained from the secondary battery in the example using XPS analysis is shown. Figure 4 The spectrum obtained from the secondary battery of the comparative example is shown using XPS analysis.

[0175] The relative sensitivity factor (RSF) used in the experiment is as follows.

[0176] RSF Si =0.9

[0177] RSF N =1.676

[0178] RSF C =1.0

[0179] RSF O =2.881

[0180] [Table 1]

[0181] The discharge capacity, initial efficiency, capacity retention rate, and slurry viscosity changes of the examples and comparative examples were measured, and the results are shown in Table 2 below.

[0182] <Discharge capacity, initial efficiency, capacity retention>

[0183] In the first and second cycles, the charge and discharge rates were 0.1C, and from the third to the 299th cycle, the rates were 0.5C. The 300th cycle was terminated in a charged state (i.e., lithium contained in the negative electrode).

[0184] Charging conditions: Constant current (CC) / Constant voltage (CV) (5mV / 0.005C current cutoff)

[0185] Discharge conditions: Constant current (CC) 1.5V

[0186] The discharge capacity (mAh / g) and initial efficiency (%) were obtained from the results of the first charge-discharge cycle. Specifically, the initial efficiency (%) was calculated as follows: Initial efficiency (%) = (First discharge capacity / First charge capacity) × 100 Capacity retention is obtained through the following calculation: Capacity retention rate (%) = (Capacity at the 299th discharge / Capacity at the 1st discharge) × 100 [Table 2]

[0187] As shown in Table 2, in Table 1, Si 2p The Si ratio measured by the spectrum relative to N 1s Examples 1 to 4, with N ratios of 35 to 200 as measured by spectral analysis, exhibited high discharge capacity and efficiency, and excellent capacity retention.

[0188] In contrast, Comparative Examples 1 to 5, which did not meet the above ratios, exhibited poor performance in terms of capacity, efficiency, and capacity retention. For example, in Comparative Examples 1, 2, and 4, although the silicon-carbon composite was prepared by depositing silane gas onto porous carbon, an excess of Si relative to N was deposited inside the silicon-carbon composite due to an improper mixing ratio of silane gas to nitrogen or an inappropriate deposition temperature, resulting in poor cycling performance and high-rate characteristics.

[0189] In Comparative Example 3, although the silicon-carbon composite was prepared by depositing acetylene gas onto porous silicon, low cycling performance was observed in Example 4, which prepared the silicon-carbon composite in a similar manner, due to the excessive deposition of Si relative to N inside the silicon-carbon composite.

[0190] In Comparative Example 5, it was confirmed that there was an excess of N relative to Si inside the silicon-carbon composite, resulting in a low Si ratio, which in turn led to reduced energy density and poor efficiency.

[0191] Although embodiments of the present disclosure have been described above with reference to examples, those skilled in the art or those with ordinary knowledge in the art will understand that various modifications and changes can be made within the scope of the technical features of the embodiments of the present disclosure described in the appended claims without departing from the scope of the present disclosure. Therefore, the technical scope of the embodiments of the present disclosure should not be limited by the detailed description in the specification, but should be defined by the scope of the appended claims.

Claims

1. A silicon-carbon composite, wherein, When etched for 5,000 seconds using an argon (Ar) ion beam at an energy of 1,000 eV, followed by XPS analysis, the Si... 2p The Si ratio measured by the spectrum relative to N 1s The ratio of N measured by the spectrum is between 35 and 200.

2. The silicon-carbon composite according to claim 1, wherein, Based on the total atomic content of Si, C, O, and N in the silicon-carbon composite being 100%, the N... 1s The proportion of N measured by the spectrum is above 0.35 atomic%.

3. The silicon-carbon composite according to claim 1, wherein, The silicon-carbon composite comprises porous carbon particles and silicon particles disposed in at least a portion of the interior and surface of the porous carbon particles; or comprises porous silicon particles and carbon particles disposed in at least a portion of the interior and surface of the porous silicon particles.

4. A negative electrode active material comprising a silicon-carbon composite according to any one of claims 1 to 3; and a carbon-based active material.

5. The negative electrode active material according to claim 4, wherein, Based on 100 parts by weight of the negative electrode active material, the content of the silicon-carbon composite is from 0.1 parts by weight to 15 parts by weight.

6. A negative electrode composition comprising the negative electrode active material, binder, and conductive material according to claim 4.

7. The negative electrode composition according to claim 6, wherein, Based on 100 parts by weight of the negative electrode active material, the content of the silicon-carbon composite is from 0.1 parts by weight to 15 parts by weight.

8. The negative electrode composition according to claim 6, wherein, The carbon-based active materials include artificial graphite and natural graphite.

9. A negative electrode comprising the negative electrode composition according to claim 6.

10. A lithium secondary battery comprising a negative electrode, a positive electrode, and a separator as described in claim 9.

11. A battery module comprising the lithium secondary battery according to claim 10.

12. A battery pack comprising the lithium secondary battery according to claim 10.

13. A battery pack comprising the battery module according to claim 11.

14. A lithium secondary battery, comprising: positive electrode; Negative electrode; and The membrane located between the positive electrode and the negative electrode in, The negative electrode includes a current collector and a layer of negative electrode active material formed on at least one surface of the current collector. The negative electrode active material layer comprises a negative electrode composition, which includes a negative electrode active material, a binder, and a conductive material. The negative electrode active material comprises a silicon-carbon composite, wherein, when etched with an argon (Ar) ion beam at an energy of 1,000 eV for 5,000 seconds and subsequently analyzed by XPS, the silicon-carbon composite exhibits high permeability due to the presence of silicon. 2p The Si ratio measured by the spectrum relative to N 1s The ratio of N measured by the spectrum is between 35 and 200.

15. The lithium secondary battery according to claim 14, wherein, Based on the total atomic percentage (100%) of Si, C, O, and N in the silicon-carbon composite, the N in the silicon-carbon composite is... 1s The proportion of N measured by the spectrum is above 0.35 atomic%.

16. The lithium secondary battery according to claim 14, wherein, The silicon-carbon composite comprises porous carbon particles and silicon particles disposed in at least a portion of the interior and surface of the porous carbon particles; or comprises porous silicon particles and carbon particles disposed in at least a portion of the interior and surface of the porous silicon particles.

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