Silicon carbon composite, negative electrode active material, negative electrode composition, negative electrode, and lithium secondary battery

Abstract

The present invention provides 29 The present invention relates to a silicon-carbon composite having chemical shift values ​​of Peak A in the range of 20 ppm to -15 ppm, Peak B in the range of -20 ppm to -100 ppm, and Peak C in the range of -110 ppm to -140 ppm in a Si-MAS-NMR spectrum, as well as a negative electrode active material, a negative electrode composition, a negative electrode, a lithium secondary battery, a battery module, and a battery pack each containing the same.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2023-0136853, filed with the Korean Intellectual Property Office on October 13, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a silicon carbon composite, a negative electrode active material, a negative electrode composition, a negative electrode, and a lithium secondary battery. [Background technology]

[0003] In recent years, with the rapid spread of battery-powered electronic devices, such as mobile phones, laptops, and electric vehicles, as well as power tools and vacuum cleaners, the demand for secondary batteries that are small, lightweight, and have relatively high capacity and / or high output has been rapidly increasing. In particular, lithium secondary batteries, which are lightweight and have high energy density, have attracted attention as power sources for electronic devices. As a result, active research and development efforts are being made to improve the performance of lithium secondary batteries.

[0004] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, an electrolyte, an organic solvent, etc. The positive electrode and the negative electrode may each have an active material layer formed on a current collector, the active material layer including a positive electrode active material and a negative electrode active material. Generally, the positive electrode uses a lithium-containing metal oxide such as LiCoO2 or LiMn2O4 as the positive electrode active material, and the negative electrode uses a lithium-free carbon-based active material or a silicon-based active material as the negative electrode active material.

[0005] Batteries that use graphite as the negative electrode active material can exhibit a high discharge voltage of 3.6 V, but their capacity is low and there is a limit to how much energy density can be increased.

[0006] In contrast, silicon-based active materials have attracted attention as next-generation negative electrode active materials due to their high capacity and efficiency. Therefore, there is a demand for the development of silicon-based active materials with high capacity or efficiency characteristics. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of one embodiment of the present invention is to provide a silicon carbon composite that can be used as a negative electrode active material with excellent capacity and / or efficiency characteristics.

[0008] An object of one embodiment of the present invention is to provide a silicon carbon composite that is excellent in aqueous processability and can be used as a negative electrode active material with reduced gas generation.

[0009] An object of one embodiment of the present invention is to provide a silicon carbon composite that can be used as a negative electrode active material with excellent life characteristics.

[0010] An object of one embodiment of the present invention is to provide an anode active material, an anode composition, an anode, and a lithium secondary battery, each containing the silicon carbon composite. [Means for solving the problem]

[0011] One embodiment of the present invention comprises: 29 Provided is a silicon carbon composite having, in a Si-MAS-NMR spectrum, chemical shift values ​​of Peak A within a range of 20 ppm to -15 ppm, Peak B within a range of -20 ppm to -100 ppm, and Peak C within a range of -110 ppm to -140 ppm, and wherein the ratio of the sum of the intensities of Peak B and Peak C to the intensity of Peak A ((B+C) / A) is 1.3 or more and less than 4.

[0012] In one embodiment of the present invention, the silicon carbon composite may contain carbon, and the weight parts of the carbon may be 38 parts by weight to 50 parts by weight based on 100 parts by weight of the silicon carbon composite.

[0013] In one embodiment of the present invention, the silicon carbon composite may be a particle having porous silicon-based particles and carbon provided in at least a portion of the interior and surface of the porous silicon-based particles.

[0014] In one embodiment of the present invention, the silicon carbon composite may further include a carbon layer on the surface thereof, and the total weight of the carbon layer may be 5 wt % to 40 wt % based on 100 wt % of the silicon carbon composite particles.

[0015] In one embodiment of the present invention, the BET specific surface area of ​​the silicon carbon composite is 0.5 m 2 / g~10m 2 / g.

[0016] In one embodiment of the present invention, the pore volume of the silicon carbon composite is 0.005 m 3 / g~0.03cm 3 / g.

[0017] In one embodiment of the present invention, the pore size of the silicon carbon composite may be 10 nm to 20 nm.

[0018] In one embodiment of the present invention, the silicon carbon composite may have a D90 particle size of 5 μm to 15 μm, a D50 particle size of 1 μm to 10 μm, a Dmin of 1 μm to 3 μm, and a Dmax of 17 μm to 23 μm.

[0019] One embodiment of the present invention provides an active negative electrode material comprising a silicon carbon composite according to the above-described embodiment.

[0020] In one embodiment of the present invention, there is provided a negative electrode active material, wherein the silicon carbon composite is included in an amount of 0.1 to 14 parts by weight based on 100 parts by weight of the negative electrode active material.

[0021] In one embodiment of the present invention, the negative electrode active material may further include a carbon-based active material, and the carbon-based active material may be included in an amount of 86 parts by weight to 99.9 parts by weight based on 100 parts by weight of the negative electrode active material.

[0022] One embodiment of the present invention provides a negative electrode composition comprising a negative electrode active material according to the above-described embodiment, a binder, and a conductive material.

[0023] In one embodiment of the present invention, there is provided a negative electrode composition, wherein the negative electrode active material further comprises a carbon-based active material.

[0024] One embodiment of the present invention provides a negative electrode comprising a negative electrode composition according to the above-described embodiment.

[0025] One embodiment of the present invention provides a lithium secondary battery comprising a negative electrode, a positive electrode, and a separator according to the above-described embodiment.

[0026] One embodiment of the present invention provides a battery module including the lithium secondary battery according to the above-described embodiment.

[0027] One embodiment of the present invention provides a battery pack including the lithium secondary battery according to the above-described embodiment.

[0028] One embodiment of the present invention provides a battery pack including a battery module according to the above-described embodiment.

[0029] One embodiment of the present invention is a method for producing a silicon carbon composite, comprising the steps of: heat-treating a silicon oxide powder to perform a disproportionation reaction; etching the heat-treated silicon oxide powder with an etchant; pulverizing the etched silicon oxide powder to obtain porous silicon particles; and reacting the porous silicon particles with a carbon compound to form a carbon layer on the surface of the porous silicon particles,

[0030] The silicon carbon composite is 29The present invention provides a method for producing a silicon carbon composite, which has, in a Si-MAS-NMR spectrum, chemical shift values ​​of Peak A in the range of 20 ppm to -15 ppm, Peak B in the range of -20 ppm to -100 ppm, and Peak C in the range of -110 ppm to -140 ppm, and the ratio of the sum of the intensities of Peak B and Peak C to the intensity of Peak A ((B+C) / A) is 1.3 or more and less than 4. [Effects of the Invention]

[0031] According to an embodiment of the present invention, 29 By ensuring that the intensities of multiple chemical shift values ​​within a specific range in a Si-MAS-NMR spectrum are within a specific ratio, a lithium secondary battery with improved capacity and / or efficiency can be provided. Specifically, by ensuring that the intensity ratio between peaks within a specific range is within a specific range, the life characteristics and / or aqueous processability can be improved. When the intensity ratio is within the range according to an embodiment of the present invention, the higher the intensity, the better the capacity and efficiency. In addition, the aqueous processability is excellent because there is less change in phase stability (viscosity) in a negative electrode slurry containing a binder such as carboxymethyl cellulose (CMC) and less gas generation such as H2. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a graph showing the results of NMR analysis of the silicon carbon composite produced in Example 1. [Figure 2] 1 is a graph showing the results of NMR analysis of the silicon carbon composite produced in Example 2. [Figure 3] 1 is a graph showing the results of NMR analysis of the silicon carbon composite produced in Example 3. [Figure 4] 1 is a graph showing the results of NMR analysis of the silicon carbon composite produced in Example 4. [Figure 5] 1 is a graph showing the results of NMR analysis of the silicon carbon composites produced in Comparative Examples 1, 2, and 5. [Figure 6]10 is a graph showing the results of NMR analysis of the silicon carbon composite produced in Comparative Example 6. [Figure 7] 10 shows the results of waveform analysis based on the NMR analysis results of the silicon carbon composite of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention will be described in more detail below to facilitate understanding of the present invention. The present invention may be realized in various different forms and is not limited to the embodiments described herein. In this regard, the terms and words used in the specification and claims should not be interpreted in a limited manner to their ordinary or dictionary meanings, but should be interpreted in a manner that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their invention.

[0034] It should be understood that in this specification, terms such as "comprises," "provides," or "has" specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0035] Furthermore, when a part such as a layer exists "on" or "above" another part, it does not only mean that it is "directly above" that part, but also includes the case where there is another part between them. In contrast, when a part exists "directly above" another part, it means that there is no other part between them. Furthermore, when a part exists "on" or "above" a reference part, it means that it is located above or below the reference part, and does not necessarily mean that it is located "above" or "above" the direction opposite to gravity.

[0036] The terms and words used in this specification should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0037] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0038] Preferred embodiments of the present invention will be described in detail below. However, the embodiments of the present invention may be modified in various ways, and the scope of the present invention is not limited to the embodiments described below.

[0039] A silicon carbon composite according to one embodiment of the present invention comprises: 29 The Si-MAS-NMR spectrum has a chemical shift value of Peak A in the range of 20 ppm to -15 ppm, Peak B in the range of -20 ppm to -100 ppm, and Peak C in the range of -110 ppm to -140 ppm, and the ratio of the sum of the intensities of Peak B and Peak C to the intensity of Peak A ((B+C) / A) is 1.3 or more and less than 4. The ratio may be, for example, 1.3 or more and 3.5 or less. Here, when at least one of Peak A, Peak B, and Peak C contains two or more peaks, the intensity of the peak is calculated as the sum of the intensities of the two or more peaks when calculating the ratio. For example, when there are two Peak Bs, the intensity of Peak B is calculated as the sum of the intensities of the two Peak Bs when calculating the ratio.

[0040] In this specification, 29 The Si-MAS-NMR spectrum was measured using a solid 400 MHz WB (wide bore) NMR system, and the measurement can be performed under the following conditions. MAS(magic angle spinning)rate:14kHz Spectral frequency(sfo1):79.51MHz(29Si) Temperature: ambient temperature 29Si chemical shift reference:TMS(l)at 0ppm Pulse program: 1D Hahn-echo Spectral width (sw): 100kHz Acquisition time: 40 ms Carrier frequency(o1p)at -40ppm Pulse length(p1):3μs Recycle delay(d1):60s Number of scans: 1k~5k

[0041] The fitting model for analyzing the waveform measured by the above method was selected as "Gaussian / Lorentzian." The parameters used for the analysis consisted of peak amplitude, peak position, peak full width at half maximum (FWHM), and Gaussian / Lorentzian ratio (xG / (1-x)L), and fitting was performed after setting appropriate initial values. In this case, xG / (1-x)L was fixed at 0.3. The fitting conditions used were nParVar = 15, Step = 1, and Thresh = 0.001, and fitting was repeated until an appropriate convergence value was reached.

[0042] In this specification, 29 A peak in a Si-MAS-NMR spectrum means a peak having an intensity of 10% or more of the maximum peak intensity, and does not include peaks having an intensity less than 10% of the maximum peak intensity.

[0043] The aforementioned 29In a Si-MAS-NMR spectrum, Peak A, whose chemical shift value is in the range of 20 ppm to -15 ppm, represents the peak of silicon carbide (Si-C), in which silicon and carbon are covalently bonded, and Peak B, whose chemical shift value is in the range of -20 ppm to -100 ppm, may represent the peak of element Si itself or silicon oxide. The component represented by Peak B can be represented as SiOx (x is 0 or more and less than 2). For example, since Si itself is a material that exhibits a peak at or around -79 ppm, a material that exhibits Peak B at or around -89 ppm can be determined to be Si or SiOx.

[0044] The silicon carbon composite is 29 The Si-MAS-NMR spectrum further has a peak C within the chemical shift range of -110 ppm to -140 ppm. This peak C indicates the presence of SiO2. Peak C has technical significance in that it can improve the capacity characteristics of the battery by ensuring that the above-mentioned ratio (B+C) / A has a specific value.

[0045] The inventors have found that Peak B and Peak C are beneficial for battery capacity development, while Peak A contributes to improving aqueous processability. Furthermore, they have found that when the intensity ratio between these peaks is within a specific range, both the battery capacity and aqueous processability can be improved. In one example, the ratio of the sum of the intensities of Peak B and Peak C to the intensity of Peak A ((B+C) / A) is 1.3 or greater and less than 4. When the ratio is within this range, the battery exhibits excellent capacity and efficiency characteristics, and the silicon-based active material exhibits excellent discharge capacity. Furthermore, when the ratio is within this range, gas generation during aqueous processing is reduced, and decomposition of components such as cellulose-based binders used in aqueous processing is prevented, thereby maintaining phase stability and preventing a decrease in slurry viscosity.

[0046] According to one embodiment, the silicon carbon composite can be referred to as a Si / C-based active material. In this specification, the silicon carbon composite is a composite of Si and C, and is distinguished from silicon carbide itself, which is represented by SiC. Silicon carbide does not electrochemically react with lithium, and all performance characteristics, including lifespan, can be measured to be zero.

[0047] Herein, the silicon carbon composite is a composite of Si and C, and Si and C (e.g., graphite) are present. For example, the peaks of Si and C can be observed by elemental analysis such as XRD or NMR. Herein, the silicon carbon composite can be expressed as Si / C. The silicon carbon composite may contain additional components as needed. For example, the silicon carbon composite may contain silicon carbide, which is expressed as SiC. When the silicon carbon composite contains silicon carbide, its content is 3 wt % or less. The silicon carbon composite may exist in a crystalline state, an amorphous state, or a mixture thereof. According to one example, C in the silicon carbon composite may exist in an amorphous state.

[0048] According to one embodiment of the present invention, the carbon may be included in an amount of 38 to 50 parts by weight based on 100 parts by weight of the silicon carbon composite. Specifically, the carbon may be included in an amount of 38 to 45 parts by weight, or 38 to 43 parts by weight based on 100 parts by weight of the silicon carbon composite.

[0049] If the part by weight of the carbon is less than the above range, the silicon is more exposed on the surface of the silicon carbon composite, which increases the possibility of side reactions with water, resulting in poor aqueous processability. If the part by weight of the carbon is more than the above range, the part by weight of the silicon is relatively small, making it impossible to achieve the target capacity.

[0050] According to one embodiment, the silicon carbon composite may be a particle having porous silicon-based particles and carbon provided in at least a portion of the interior and surface of the porous silicon-based particles.

[0051] If necessary, a carbon layer may be further formed on the surface of the silicon carbon composite. The carbon layer may provide the electrical conductivity, thereby improving the initial efficiency, life characteristics, and capacity characteristics of the secondary battery. The total weight of the carbon layer may be 5 wt% to 40 wt% based on 100 wt% of the silicon carbon composite particles. The carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0052] According to one embodiment, the silicon carbon composite may be manufactured by the steps of: heat-treating silicon oxide powder to perform a disproportionation reaction; etching the heat-treated silicon oxide powder with an etchant; pulverizing the etched silicon oxide powder to obtain porous silicon particles; and reacting the porous silicon particles with a carbon compound to form a carbon layer on the surfaces of the porous silicon particles.

[0053] According to one embodiment, the silicon carbon composite may be a particle having porous silicon-based particles and carbon provided in at least a portion of the interior and surface of the porous silicon-based particles. This can be formed by etching silicon oxide to form porous silicon-based particles, for example, a Si matrix, and then coating the silicon-based particles with carbon. The above description of the carbon layer may be applied to the carbon.

[0054] According to one example, the porous silicon-based particles may be manufactured by a process of phase-separating silicon oxide (e.g., SiO) into Si and silicon dioxide (SiO2) through heat treatment, followed by etching with an etchant such as HF. When the silicon oxide is heat-treated, the size of the Si crystal grains corresponding to peak B can be controlled by a disproportionation reaction (900°C to 1400°C). This allows the ratio between peaks A, B, and C to be adjusted.

[0055] According to one embodiment, the silicon carbon composite has a specific surface area of ​​0.5 m as measured by the BET method. 2 / g~10m 2 / g and a pore volume of 0.005 cm 3 / g~0.03cm 3 The silicon carbon composite may have a pore volume of 0.005 cm3 or less as measured by mercury penetration method, and the pore size measured by BET method may be 10 nm to 20 nm. 3 / g~0.03cm 3 / g.

[0056] According to one embodiment, the silicon carbon composite may have a D90 particle size of 5 μm to 15 μm, a D50 particle size of 1 μm to 10 μm, a Dmin of 1 μm to 3 μm, and a Dmax of 17 μm to 23 μm. 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 ) can be measured, for example, by using a laser diffraction method. The laser diffraction method is generally capable of measuring particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0057] One embodiment provides an active negative electrode material comprising a silicon carbon composite according to the above-described embodiment.

[0058] One embodiment provides a negative electrode composition including a negative electrode active material according to the above embodiment, a binder, and a conductive material.

[0059] According to one embodiment, the silicon carbon composite may be included in an amount of 0.1 to 14 parts by weight, for example, 0.1 to 12 parts by weight, or 1 to 10 parts by weight, based on 100 parts by weight of the negative electrode active material.

[0060] According to one embodiment, the negative electrode active material may further include a carbon-based active material. The carbon-based active material may be included in an amount of 86 to 99.9 parts by weight, 88 to 99.9 parts by weight, for example, 90 to 99 parts by weight, based on 100 parts by weight of the negative electrode active material included in the negative electrode composition. The carbon-based active material may include at least one of natural graphite and artificial graphite. When the carbon-based active material includes both natural graphite and artificial graphite, the weight ratio of the artificial graphite to the natural graphite may be 1:99 to 99:1, for example, 1:9 to 9:1, or 3:7 to 7:3. For example, based on 100 parts by weight of the carbon-based active material, the natural graphite may be 10 to 70 parts by weight, and the artificial graphite may be 30 to 90 parts by weight.

[0061] The natural graphite refers to graphite that is naturally occurring, and examples thereof include flake graphite, scaly graphite, and soil graphite. Natural graphite has the advantages of being abundant, inexpensive, having a high theoretical capacity and a high compressed density, and being able to achieve high output.

[0062] According to one example, the natural graphite may be spherical natural graphite, and may have a sphericity of 0.9 or more. According to one example, the natural graphite may be spherical natural graphite, and may have a tap density of 0.9 g / cc or more.

[0063] In this specification, sphericity may be the value obtained by dividing the circumference of a circle having the same area as the projected image by the perimeter of the projected image when a particle is projected. The sphericity can be determined from an SEM image or measured using a particle shape analyzer such as a Sysmex FPIA3000 manufactured by Malvern. The crystal size can also be confirmed by XRD analysis.

[0064] According to one embodiment of the present invention, the negative electrode composition further includes a binder and a conductive material, and the binder may be a water-based binder.

[0065] The binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, 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, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0066] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0067] According to one embodiment, the aqueous binder may be contained in an amount of 1 wt % to 5 wt %, for example, about 3 wt % to 4 wt %, based on the solid content of the negative electrode composition, and the conductive material may be contained in an amount of 0.1 wt % to 2 wt %, for example, about 1 wt %, based on the solid content of the negative electrode composition.

[0068] One embodiment of the present invention provides a negative electrode comprising a negative electrode composition according to the above-described embodiment.

[0069] Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer including the negative electrode composition according to the above-described embodiment.

[0070] The negative electrode active material layer may be formed by applying a negative electrode slurry containing the above-described negative electrode composition to at least one surface of a negative electrode current collector, followed by drying and rolling.

[0071] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that easily adsorbs carbon, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but is not limited to this.

[0072] The negative electrode slurry may include a solvent for forming a negative electrode slurry. Specifically, the solvent for forming a negative electrode slurry may include at least one solvent selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate dispersion of components.

[0073] One embodiment of the present invention provides a lithium secondary battery comprising a negative electrode, a positive electrode, and a separator according to the above-described embodiment.

[0074] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

[0075] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0076] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMn 2-c3 Examples of lithium manganese composite oxides include, but are not limited to, LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, and Li3O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and 0.01≦c3≦0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn). The positive electrode may be Li metal.

[0077] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-described positive electrode active material.

[0078] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be any material that has electronic conductivity without causing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0079] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), vinylidene 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, and various copolymers thereof. These binders may be used singly or in combination.

[0080] The separator separates the negative electrode and positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitation. It is particularly preferable that the separator exhibits low resistance to ion migration and has excellent electrolyte humidifying ability. Specifically, porous polymer films, such as those made from 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, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0081] The lithium secondary battery may further include an electrolyte, which may be used in manufacturing a lithium secondary battery, such as, but not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte.

[0082] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0083] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene 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, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0084] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents, because they have a high dielectric constant and dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and therefore such cyclic carbonates can be more preferably used.

[0085] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be 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 - One or more selected from the group consisting of:

[0086] In addition to the constituent components of the electrolyte, the electrolyte may further include one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, in order to improve the life characteristics of the battery, suppress a decrease in battery capacity, and improve the discharge capacity of the battery.

[0087] According to another embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. [Example]

[0088] Hereinafter, the present specification will be described in detail with reference to examples in order to specifically explain the present specification. However, the examples according to the present specification may be modified into various other forms, and the scope of the present application should not be interpreted as being limited to the examples described below. The examples of the present application are provided to more completely explain the present specification to those skilled in the art.

[0089] Example 1 (1) Manufacturing of silicon carbon composites 20 g of SiOx (x = 0.9-1) powder was heat-treated at 1,200°C in an inert atmosphere of argon gas to cause disproportionation of SiO.

[0090] 10 g of the treated SiOx (x = 0.9-1) powder was dispersed in distilled water, and then 10 ml of a 30 wt% HF aqueous solution was gradually added while stirring at a speed of 500 rpm. The SiO powder obtained by the above process was etched for 2 hours. After the above manufacturing process, the powder was filtered or washed to make the pH neutral. After the powder was obtained, porous silicon was manufactured by drying it under vacuum at 130°C for 6 hours. Then, it was crushed in a mortar to a particle size of D50 4 μm-6 μm. In an inert gas Ar atmosphere, acetylene (C2H2) was added to 10 -1 A silicon carbon composite containing a carbon coating layer was produced by reacting the porous silicon at 720°C for approximately 5 hours at a flow rate of 1 L / min under torr, forming a carbon layer on the surface of the porous silicon. The NMR analysis results are shown in Figure 1. In Figure 1, peaks corresponding to peaks A, B, and C appear, and the (B+C) / A ratio was measured to be 3.3.

[0091] (2) Manufacturing of the negative electrode A negative electrode slurry was prepared by mixing the negative electrode active material containing the silicon carbon composite and graphite in a weight ratio of 9:91, the conductive material containing carbon black and SWCNT, and the binder containing carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) in a weight ratio of 95.3:1:3.6, and adding an appropriate amount of distilled water to achieve a total solids content of approximately 46 wt%.

[0092] The negative electrode slurry was applied to a Cu metal thin film with a thickness of 20 μm, and then dried in circulating air at 60° C. After rolling, it was dried in a vacuum oven at 130° C. for about a day, and then cut into 1.4875 cm 2 The negative electrode was then punched out into a circular shape.

[0093] (3) Secondary battery manufacturing 1.7671cm 2 A Li metal thin film punched into the shape of a square was used as the positive electrode. A porous polyethylene separator was placed between the positive and negative electrodes, and an electrolyte solution of 1M LiPF6 dissolved in a 7:3 mixture of EMC (ethyl methyl carbonate) and EC (ethylene carbonate) containing additives was injected to fabricate a Li coin half cell.

[0094] <Example 2> A silicon carbon composite was prepared in the same manner as in Example 1, except that the disproportionation temperature was 1,150°C and acetylene (C2H2) was flowed at 700°C to form the carbon layer. The NMR analysis results for the active material prepared by the method of Example 2 are shown in Figure 2. In Figure 2, peaks corresponding to peaks A, B, and C were observed, and the (B + C) / A ratio was determined to be 3.5.

[0095] Using the silicon carbon composite, a negative electrode and a secondary battery were produced in the same manner as in Example 1.

[0096] Figure 7 shows the results of waveform analysis of the NMR analysis results of Figure 2. The silicon carbon composite of Example 2 has peaks (1) to (6), of which (1) corresponds to peak A, (2), (4), (5), and (6) correspond to peak B, and (3) corresponds to peak C. When calculating the ratio (B+C) / A, B was calculated as the sum of the intensities of peaks (2), (4), (5), and (6).

[0097] Example 3 A silicon carbon composite was prepared in the same manner as in Example 1, except that the disproportionation temperature was 1,000°C and acetylene (C2H2) was flowed at 750°C to form the carbon layer. The NMR analysis results for the active material prepared by the method of Example 3 are shown in Figure 3. As shown in Figure 3, peaks corresponding to peaks A, B, and C were observed, and the (B + C) / A ratio was determined to be 2.1.

[0098] Using the silicon carbon composite, a negative electrode and a secondary battery were produced in the same manner as in Example 1.

[0099] Example 4 A silicon carbon composite was prepared in the same manner as in Example 1, except that the disproportionation temperature was 900°C and acetylene (C2H2) was flowed at 770°C to form a carbon layer. As shown in Figure 4, NMR analysis of the active material prepared by the method of Example 4 revealed peaks corresponding to peaks A, B, and C, and the (B+C) / A ratio was determined to be 1.4.

[0100] Using the silicon carbon composite, a negative electrode and a secondary battery were produced in the same manner as in Example 1.

[0101] <Comparative Example 1> (1) Manufacturing method of magnesium-containing silicon oxide Si and SiO2 were mixed in a 1:1 molar ratio in crucible No. 1, and then heated to a sublimation temperature of 1400°C. Metallic magnesium was separately heated and evaporated in crucible No. 2 between 600°C and 1000°C. Both crucibles were decompressed to a 0.1 torr level. The vapor mixture containing Mg obtained from crucibles No. 1 and No. 2 was reacted for 6 hours, and then solidified in a vacuum at 800°C. The silicon-based active material produced by the above method was pulverized using a ball mill for approximately 3 to 4 hours to produce particles with a D50 of 6 μm. Then, a CVD apparatus was used to pulverize the mixture with 10 methane (CH4) in an inert gas atmosphere of Ar. -1 The magnesium-containing silicon oxide was produced by reacting the particles with the silicon-based active material at a flow rate of 1 L / min for about 5 hours at torr, forming a carbon layer on the surface of the silicon-based active material.The Mg content in the powder was measured to be 8 wt% by ICP-MS analysis.

[0102] As shown in FIG. 5, the NMR analysis of the silicon oxide produced by this method showed peaks corresponding to peaks B and C, but not peak A. Since peak A did not exist, it was impossible to measure the ratio (B+C) / A.

[0103] A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that the silicon carbon composite and graphite were used as the negative electrode active material in a ratio of 15:85.

[0104] <Comparative Example 2> An active material was produced in the same manner as in Comparative Example 1, except that the metallic magnesium in crucible No. 2 was omitted. As shown in Figure 5, the NMR analysis of the silicon oxide produced by this method showed peaks corresponding to peaks B and C, but no peak A. Since peak A did not exist, it was impossible to measure the ratio of (B + C) / A.

[0105] A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that the silicon carbon composite and graphite were used as the negative electrode active material in a ratio of 12:88.

[0106] <Comparative Example 3> The same procedure as in Example 1 was carried out, except that the CVD carbon coating process using acetylene (C2H2) on porous silicon was carried out at a temperature of 900°C. NMR analysis of the silicon carbon composite produced in this manner revealed peaks corresponding to peaks A, B, and C, and the (B+C) / A ratio was determined to be 0.8.

[0107] Using the silicon carbon composite, a negative electrode and a secondary battery were produced in the same manner as in Example 1.

[0108] <Comparative Example 4> A mixture of silane at 1 L / min, acetylene at 3 L / min, and argon at 1 L / min was introduced into the deposition chamber of a fluidized bed reactor at a temperature of 700°C and a pressure of 1 atm. Silicon carbon composites were obtained from the collection chamber of the fluidized bed reactor. NMR analysis of the silicon carbon composite produced in this manner revealed peaks corresponding to peaks A, B, and C, confirming that the (B+C) / A ratio was 2.8.

[0109] A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that the silicon carbon composite and graphite were used as the negative electrode active material in a ratio of 11:89.

[0110] <Comparative Example 5> 1 kg of silicon powder and 1 kg of silica powder were placed in a vacuum reactor. A vacuum of less than 0.1 torr was first created, and the reactor was heated to 1400 °C to convert the raw materials into vapor. A benzene solution was then slowly passed through the reactor to rapidly vaporize the benzene, thoroughly mixing it with the silicon / silica mixture vapor. The vapor mixture was then cooled and deposited on a water-cooled substrate. The material was then pulverized to obtain silicon oxide with uniformly intercalated carbon atoms at the atomic level. The pulverized material was then carbon-coated by placing 1 kg of the material in a rotary furnace and heating it to 1000 °C under an argon protective gas atmosphere. Argon gas and an equal volume of propylene and methane mixed with the argon gas were then introduced in a 1:1 volume ratio for vapor-phase coating, where the volume ratio of propylene to methane was 2:3. The temperature was maintained for 1 hour, and the organic gas supply was shut off and the material was cooled to obtain silicon oxide. As shown in Figure 5, NMR analysis of the silicon-carbon composite thus produced revealed no peak corresponding to peak A, making it impossible to determine the (B+C) / A ratio.

[0111] A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that the silicon carbon composite and graphite were used as the negative electrode active material in a ratio of 12:88.

[0112] <Comparative Example 6> The same method as in Example 4 was used, except that the disproportionation temperature for the silicon-carbon composite was 1250°C and the CVD carbon coating process for the porous silicon using acetylene (C2H2) was performed at 650°C. The NMR analysis results for the active material prepared by the method of Comparative Example 6 are shown in Figure 6. Peaks corresponding to peaks A, B, and C were observed in Figure 6, and the (B + C) / A ratio was determined to be 1.1.

[0113] A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that the silicon carbon composite and graphite were used as the negative electrode active material in a ratio of 15:85.

[0114] The ratios between peaks identified by NMR analysis of the silicon-based active materials produced in the examples and comparative examples are shown in Table 1 below.

[0115] In addition, the C content, O content, and Si content of each example and comparative example were measured using a carbon-sulfur analyzer (CS analyzer) and an oxygen-nitrogen-hydrogen analyzer (ONH analyzer), and the percentage of graphite contained in the negative electrode active material are shown in Table 2 below.

[0116] [Battery performance evaluation] The manufactured batteries were charged and discharged to evaluate the discharge capacity, initial efficiency, and capacity retention rate, and the results are shown in Table 1 below.

[0117] The first and second cycles were charged and discharged at 0.1 C, and the third to 49th cycles were charged and discharged at 0.5 C. The 50th cycle was completed in a charged state (with lithium in the anode). Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharge condition: CC (constant current) condition 1.5V

[0118] The discharge capacity (mAh / g) and initial efficiency (%) were calculated from the results of one charge / discharge. Specifically, the initial efficiency (%) was calculated as follows: Initial efficiency (%) = (single discharge capacity / single charge capacity) x 100

[0119] The capacity retention rate was calculated as follows. Capacity retention rate (%) = (49 discharge capacity / 1 discharge capacity) × 100

[0120] [Evaluation of aqueous processability] 1) Evaluation of processability (Shear viscosity) characteristics As part of the processability evaluation, the shear viscosity change at a shear rate of 1 Hz was measured for the slurries produced in the examples and comparative examples, and the results are shown in Table 1. Specifically, the shear viscosity change (%) was calculated using the following formula. Change in shear viscosity (%) = ((shear viscosity of slurry after 48 hours - shear viscosity of slurry immediately after mixing) / shear viscosity of slurry immediately after mixing) × 100

[0121] 2) Time point of gas generation: 20 g of slurry is placed in a 10 x 15 cm aluminum pouch and vacuum sealed. The volume change is measured using Archimedes' principle, and the time point at which the volume change at 60°C is 2 mL or more is defined as the time point of gas generation.

[0122] [Table 1]

[0123] [Table 2]

[0124] In Examples 1 to 4, materials having peaks corresponding to Peaks A, B, and C and having peak ratios that fall within the range of the present invention were applied to batteries. As shown in Table 1, these materials had effects above a certain level in discharge capacity, initial efficiency, and capacity retention rate, and viscosity change and gas generation were below a certain level.

[0125] In contrast, Comparative Examples 1 to 3 and 5 failed to satisfy the peak ratio and therefore exhibited poor effects in terms of capacity and aqueous processability. Specifically, Comparative Examples 1, 2 and 5 did not produce an appropriate amount of SiC, and NMR analysis showed no A peak, resulting in poor aqueous processability due to reaction with the electrolyte. Comparative Example 3 produced excess SiC that could not contribute to capacity because the temperature during carbon coating layer formation was too high, resulting in poor cell performance.

[0126] Comparative Example 4 satisfied the peak ratio of the present invention, but the carbon content in the silicon carbon composite was too low, resulting in silicon exposure on the surface and a side reaction with water, making it poorly suited for aqueous processes.

[0127] In the case of Comparative Example 6, the peak ratio of the present invention was not satisfied, and it was confirmed that the negative electrode active material contained an excessive amount of silicon carbon composite, resulting in poor cycle performance and aqueous processability.

Claims

1. ２９ A silicon carbon composite having, in a Si-MAS-NMR spectrum, a peak A within a chemical shift value range of 20 ppm to −15 ppm, a peak B within a chemical shift value range of −20 ppm to −100 ppm, and a peak C within a chemical shift value range of −110 ppm to −140 ppm, wherein the ratio ((B+C) / A) of the sum of the intensities of peak B and peak C to the intensity of peak A is 1.3 or more and less than 4.

2. 2. The silicon carbon composite of claim 1, wherein the silicon carbon composite comprises carbon, and the carbon is contained in an amount of 38 to 50 parts by weight based on 100 parts by weight of the silicon carbon composite.

3. 2. The silicon carbon composite according to claim 1, wherein the silicon carbon composite is a particle having porous silicon-based particles and carbon provided in at least a portion of the interior and surface of the porous silicon-based particles.

4. 2. The silicon carbon composite of claim 1, further comprising a carbon layer on a surface of the silicon carbon composite, wherein the total weight of the carbon layer is 5 wt % to 40 wt % based on 100 wt % of the silicon carbon composite particles.

5. The BET specific surface area of ​​the silicon carbon composite is 0.5 m ２ / g to 10m ２ 2. The silicon carbon composite of claim 1, wherein the silicon carbon composite has a molecular weight of 1.001 or more.

6. The pore volume of the silicon carbon composite is 0.005 cm ３ / g to 0.03 cm ３ 2. The silicon carbon composite of claim 1, wherein the silicon carbon composite has a molecular weight of 1.001 or more.

7. 2. The silicon carbon composite of claim 1, wherein the pore size of the silicon carbon composite is 10 nm to 20 nm.

8. 2. The silicon carbon composite of claim 1, wherein the D90 particle size is from 5 μm to 15 μm, the D50 particle size is from 1 μm to 10 μm, the Dmin is from 1 μm to 3 μm, and the Dmax is from 17 μm to 23 μm.

9. A negative electrode active material comprising the silicon carbon composite according to claim 1 .

10. The negative electrode active material of claim 9, wherein the silicon carbon composite is included in an amount of 0.1 to 14 parts by weight based on 100 parts by weight of the negative electrode active material.

11. 10. The negative electrode active material of claim 9, further comprising a carbon-based active material, the carbon-based active material being present in an amount of 86 parts by weight to 99.9 parts by weight based on 100 parts by weight of the negative electrode active material.

12. A negative electrode composition comprising the negative electrode active material according to claim 9 , a binder, and a conductive material.

13. The negative electrode composition of claim 12 , wherein the negative electrode active material further comprises a carbon-based active material.

14. An anode comprising the anode composition of claim 12.

15. A lithium secondary battery comprising the negative electrode of claim 14, a positive electrode, and a separator.

16. A battery module comprising the lithium secondary battery according to claim 15.

17. A battery pack comprising the lithium secondary battery according to claim 15.

18. A battery pack comprising the battery module of claim 16.

19. heat-treating the silicon oxide powder to carry out a disproportionation reaction; etching the heat-treated silicon oxide powder with an etchant; grinding the etched silicon oxide powder to obtain porous silicon particles; and forming a carbon layer on the surface of the porous silicon particles by reacting the porous silicon particles with a carbon compound; A method for producing a silicon carbon composite, comprising: The silicon carbon composite is ２９ A method for producing a silicon carbon composite, wherein in a Si-MAS-NMR spectrum, the silicon carbon composite has a chemical shift value of Peak A in the range of 20 ppm to −15 ppm, a chemical shift value of Peak B in the range of −20 ppm to −100 ppm, and a chemical shift value of Peak C in the range of −110 ppm to −140 ppm, and the ratio of the sum of the intensities of Peak B and Peak C to the intensity of Peak A ((B+C) / A) is 1.3 or more and less than 4.

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