Silicon carbon composite, negative electrode composition, negative electrode, lithium secondary battery, battery module, battery pack, electric vehicle, and method for manufacturing silicon carbon composite

Abstract

The present invention relates to a silicon-carbon composite comprising silicon and carbon, wherein the silicon content is 40 to 60 parts by weight based on 100 parts by weight of the silicon-carbon composite, the carbon content ratio (C / Si) to silicon is 30 or more after 10 seconds of etching and 15 or less after 1,000 seconds of etching, as determined by XPS analysis under conditions where Ta2O5 is etched at a rate of 0.15 nm / s, and the oxygen content is 10 parts by weight or less based on 100 parts by weight of the silicon-carbon composite, as well as a negative electrode composition containing the same, a negative electrode, a lithium secondary battery, a battery module, a battery pack, an electric vehicle, and a method for manufacturing the silicon-carbon composite.

Description

[Technical Field]

[0001] This specification asserts the benefit as of the filing date of Korean Patent Application No. 10-2023-0167493, filed with the Korean Intellectual Property Office on November 28, 2023, and all content disclosed in the documents of said Korean Patent Application is incorporated herein.

[0002] The present invention relates to silicon carbon composites, negative electrode compositions, negative electrodes, lithium secondary batteries, battery modules, and battery packs. [Background technology]

[0003] Recently, with the rapid proliferation of battery-powered electronic devices such as mobile phones, laptops, electric vehicles, power tools, and vacuum cleaners, the demand for small, lightweight, yet relatively high-capacity and / or high-power rechargeable batteries has been rapidly increasing. In particular, lithium-ion batteries are attracting attention as power sources for electronic devices due to their light weight and high energy density. As a result, research and development efforts to improve the performance of lithium-ion batteries are actively underway. [Overview of the project] [Problems that the invention aims to solve]

[0004] While silicon-carbon composites offer superior initial capacity and energy efficiency compared to graphite or silicon oxide, they suffer from low stability during the anode manufacturing process using anode slurry or during storage of the anode slurry. Therefore, embodiments of the present invention provide a silicon-carbon composite, an anode composition containing the same, and an anode that can improve the phase stability of the slurry. Embodiments of the present invention also relate to lithium secondary batteries, battery modules, and battery packs containing the anode. [Means for solving the problem]

[0005] One embodiment of the present invention provides a silicon-carbon composite containing silicon and carbon, wherein the content of the silicon is 40 to 60 parts by weight based on 100 parts by weight of the silicon-carbon composite, and the content ratio of carbon to silicon (C / Si) is 30 or more after 10 seconds of etching and 15 or less after 1,000 seconds of etching under the condition that Ta2O5 is etched at a rate of 0.15 nm / s in XPS analysis, and the content of oxygen is 10 parts by weight or less based on 100 parts by weight of the silicon-carbon composite.

[0006] One embodiment of the present invention provides a silicon-carbon composite, wherein the content ratio of carbon to silicon (C / Si) is 30 or more in the region with a depth of 0 nm to 25 nm from the surface of the silicon-carbon composite and 15 or less in the region with a depth of 200 nm to 300 nm from the surface of the silicon-carbon composite.

[0007] One embodiment of the present invention provides a negative electrode composition containing the silicon-carbon composite.

[0008] One embodiment of the present invention provides a negative electrode for a lithium secondary battery, including a current collector; and a negative electrode active material layer provided on at least one surface of the current collector and containing the negative electrode composition.

[0009] One embodiment of the present invention provides a lithium secondary battery including the negative electrode; a separator; and a positive electrode.

[0010] One embodiment of the present invention provides a battery module including the lithium secondary battery.

[0011] One embodiment of the present invention provides a battery pack including the lithium secondary battery.

[0012] One embodiment of the present invention provides a battery pack including the battery module.

[0013] One embodiment of the present invention provides an electric vehicle including the battery pack.

[0014] One embodiment of the present invention provides a method for producing the silicon carbon composite. [Effects of the Invention]

[0015] A silicon-carbon composite according to one embodiment of the present invention contains a specific amount of silicon, and in XPS analysis, the carbon-to-silicon content ratio (C / Si) varies over time, and the oxygen-to-silicon content ratio falls within a specific range. This limits contact between Si and water, suppresses oxidation reactions, and reduces the amount of hydrogen gas generated, thereby providing excellent phase stability for the anode slurry and achieving high capacity and high efficiency of the anode.

[0016] The following drawings accompanying this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention that follows, serve to further illustrate the technical concept of the present invention. Therefore, the present invention should not be construed as being limited solely to what is depicted in these drawings. [Brief explanation of the drawing]

[0017] [Figure 1] These are drawings illustrating a battery pack including a battery cell according to one embodiment of the present invention. [Figure 2] This is a diagram illustrating an automobile including the battery pack shown in Figure 1. [Modes for carrying out the invention]

[0018] The following provides a more detailed explanation of this specification.

[0019] In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0020] In this specification, when one member is said to be "on top of" another member, this includes not only cases where one member is in contact with another member, but also cases where another member exists between the two members.

[0021] The terms and words used herein should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best explain their invention.

[0022] In this specification, singular expressions of terms include plural expressions unless the context clearly indicates otherwise.

[0023] In this specification, the average particle size D50 can be defined as the particle size at 50% of the cumulative volume in the particle size distribution curve (graph curve of the particle size distribution diagram). The average particle size D50 can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes from the submicron region to several millimeters, and can obtain highly reproducible and highly resolving results. The measurement of the average particle size can be confirmed using a Microtrac instrument (manufacturer: Microtrac, model name: S3500) with water and triton-X100 dispersant. Specifically, the average particle size of the positive electrode active material can be measured in the refractive index range of 1.5 to 1.7, and the negative electrode active material can be measured under conditions of a refractive index of 1.97 or 2.42. For example, particles can be dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer. After irradiating with ultrasound at approximately 28 kHz with an output of 60 W, a volume cumulative particle size distribution graph is obtained, and the size of the particle that accounts for 50% of the volume cumulative amount is determined to measure the particle size.

[0024] In a lithium-ion secondary battery, electrical energy is produced by oxidation and reduction reactions that occur when lithium ions are inserted into / deintercalated at the positive and negative electrodes, with an organic or polymer electrolyte filling the space between the positive and negative electrodes, which are made of an active material that allows for the insertion and deintercalation of lithium ions.

[0025] Graphite is primarily used as the negative electrode active material in lithium-ion batteries. However, graphite has a low capacity of 372 mAh / g per unit mass, making it difficult to increase the capacity of lithium-ion batteries. Therefore, to increase the energy density of lithium-ion batteries, non-carbon negative electrode materials with higher energy densities than graphite, such as silicon, tin, and their oxides, are being developed.

[0026] In this invention, a lithium secondary battery using a silicon-carbon composite as the negative electrode active material is provided with excellent phase stability of the negative electrode slurry by adjusting the composition of the silicon-carbon composite, and also provides a high-capacity and high-efficiency negative electrode.

[0027] Preferred embodiments of the present invention will be described in detail below. However, 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.

[0028] <Silicon-carbon composite> One embodiment of the present invention relates to a silicon-carbon composite.

[0029] A silicon-carbon composite according to one embodiment of the present invention is manufactured by the following method.

[0030] First, an appropriate specific surface area (for example, approximately 1850 m²) 2 / g~1900m 2 ( / g), appropriate pore volume (e.g., about 0.80 cm³) 3 / g~0.85cm 3An appropriate amount (e.g., about 0.9 g) of amorphous porous carbon scaffold having a silicon content of 0.5g / g is placed in a ceramic crucible and positioned in the center of a horizontal tube furnace. The furnace is then sealed, nitrogen gas is purged, and the furnace temperature is gradually increased (e.g., to 450°C to 500°C at about 10°C / min). Then, silane gas and hydrogen gas are allowed to remain at different flow rates for a predetermined time (e.g., about 60 to 90 minutes). As a result, a porous silicon-carbon composite having an appropriate silicon content (e.g., about 48 parts by weight) is produced. Subsequently, the furnace temperature is further increased (e.g., to 780°C to 900°C at 10°C / min), and propane gas is allowed to remain at different flow rates for a predetermined time (e.g., about 30 to 60 minutes) to produce a porous silicon-carbon composite having the properties required in this invention.

[0031] In the production of the porous silicon-carbon composite described above, the properties of the silicon-carbon composite required by the present invention can be obtained by adjusting parameters at each step, such as the specific surface area and / or amount of amorphous porous carbon scaffold, the method of raising the furnace temperature, and the flow rates and / or residence times of silane gas and hydrogen gas. Of course, the production process for the porous silicon-carbon composite is not limited to the production method described above, and any production method that can obtain the properties of the silicon-carbon composite required by the present invention may be used.

[0032] The silicon content in the silicon-carbon composite manufactured according to the aforementioned embodiment of the present invention is 40 to 60 parts by weight, for example, 45 to 55 parts by weight, based on 100 parts by weight of the silicon-carbon composite. When the silicon content is less than 40 parts by weight, the initial volume of the active material is not sufficiently high, and when it exceeds 60 parts by weight, it is difficult to form a structure in which hydrogen gas generation is suppressed, making it difficult to manufacture a silicon-carbon composite having a uniform Si distribution inside the carbon. Within the above range of silicon content, the volume and efficiency of the active material are appropriate, and gas generation in the slurry is easily suppressed.

[0033] The silicon content can be determined by first calculating the carbon (C) and oxygen (O) content of the silicon-carbon composite, and then calculating the silicon content in reverse. The carbon content can be analyzed using a CS analyzer (Bruker, G8 Galileo), and the oxygen content can be analyzed using an ONH analyzer (Bruker, G-4 ICARUS Series II).

[0034] The carbon content ratio (C / Si) to silicon, as determined by XPS analysis under conditions where Ta2O5 is etched at a rate of 0.15 nm / s, is 30 or higher after 10 seconds of etching and 15 or lower after 1,000 seconds of etching.

[0035] As described above, the carbon content ratio (C / Si) to silicon, when etched at a rate of 0.15 nm / s by Ta2O5, has the advantage that if it is 30 or higher after 10 seconds of etching in XPS analysis, the entire surface of the active material is uniformly coated with carbon, limiting contact with water, suppressing oxidation reactions, and reducing gas generation. If it is 15 or lower after 1,000 seconds of etching, the limitation of lithium movement due to the appropriate carbon layer thickness is not significant, there are no major problems with reactions with internal silicon, and the capacity efficiency is excellent. Here, XPS analysis can be performed under the following conditions.

[0036] -Equipment used: NEXSA G2, Thermo Fisher Scientific (device name ESCA-03) - Sample preparation: Press the powdered sample into the powder holder to create a mound, and flatten the measurement surface. -Measurement conditions: X-ray source: Monochromated Al Kα (1486.6 eV) X-ray spot size: 400 μm Etching conditions (sputter gun): monatomic Ar (energy: 1,000 eV, current: low, raster width: 2 mm) Charge compensation (flood gun): 0.3 V, 150 μA Survey scan:pass energy 200eV,energy step 1eV Narrow scan:pass energy 50eV,energy step 0.1eV Sensitivity factor (SF): Al THERMO1, Energy correction factor (ECF): TPP-2M Background subtraction: Smart

[0037] When performing quantitative analysis, the Si plasmon loss peak is not included.

[0038] The carbon content ratio (C / Si) to silicon is 30 or higher after 10 seconds of etching, under conditions where Ta2O5 is etched at a rate of 0.15 nm / s in XPS analysis. For example, it may be 35 or higher, 40 or higher, 45 or higher, or 50 or higher.

[0039] The carbon content ratio (C / Si) to silicon is 15 or less after 1,000 seconds of etching time, under conditions where Ta2O5 is etched at a rate of 0.15 nm / s in XPS analysis, and may be, for example, 12 or less or 10 or less.

[0040] The carbon content ratio (C / Si) to silicon is 100 or less after 10 seconds of etching, under conditions where Ta2O5 is etched at a rate of 0.15 nm / s in XPS analysis, and may be, for example, 80 or less, 70 or less, or 60 or less.

[0041] The carbon content ratio (C / Si) to silicon is 1 or greater after 1,000 seconds of etching, under conditions where Ta2O5 is etched at a rate of 0.15 nm / s in XPS analysis. For example, it may be 3 or greater, 4 or greater, 5 or greater, or 6 or greater.

[0042] The carbon content ratio (C / Si) to silicon is 30 or more in the region from 0 nm to 25 nm from the surface of the silicon-carbon composite, and 15 or less in the region from 200 nm to 300 nm from the surface of the silicon-carbon composite.

[0043] Since XPS analysis analyzes the components of a sample while etching it, as mentioned above, the analysis results after 1,000 seconds show analysis results from a region deeper than the surface of the sample compared to the analysis results after 10 seconds.

[0044] Specifically, the etching time of 10 seconds under the condition that the Ta2O5 is etched at a speed of 0.15 nm / s means the time it takes for the silicon-carbon composite surface to be etched to a depth of 0 nm to 25 nm, and for the XPS(C / Si) value of the silicon-carbon composite surface to be measured.

[0045] Furthermore, the etching time of 1,000 seconds under the condition that the Ta2O5 is etched at a speed of 0.15 nm / s means that the silicon-carbon composite surface is etched to a depth of 200 nm to 300 nm, and the XPS(C / Si) value of the region even deeper than the silicon-carbon composite surface is measured.

[0046] The depth from the surface of the silicon-carbon composite refers to the depth from the surface of the silicon-carbon composite toward the center.

[0047] The carbon content ratio (C / Si) to silicon is 30 or more in the region from 0 nm to 25 nm depth from the surface of the silicon-carbon composite, and may be, for example, 35 or more, 40 or more, 45 or more, or 50 or more.

[0048] The carbon content ratio (C / Si) to silicon is 15 or less in the region from the surface of the silicon-carbon composite to a depth of 200 nm to 300 nm, and may be, for example, 12 or less or 10 or less.

[0049] The carbon content ratio (C / Si) to silicon is 15 or less in the region from 0 nm to 25 nm depth from the surface of the silicon-carbon composite, and may be, for example, 12 or less or 10 or less.

[0050] The silicon-carbon composite has a depth of 200 nm to 300 nm from the surface, and the number of layers is 1 or greater in that region, for example, 3 or greater, 4 or greater, 5 or greater, or 6 or greater.

[0051] The oxygen content in the silicon-carbon composite is 10 parts by weight or less per 100 parts by weight of the silicon-carbon composite. When the oxygen content in the silicon-carbon composite is 10 parts by weight or less, it has the advantage of minimizing capacity degradation due to silicon oxidation, reducing lithium dissolution loss due to oxygen, and minimizing the decrease in the initial capacity and efficiency of the silicon-carbon composite.

[0052] The oxygen content of the silicon-carbon composite can be measured by an ONH analysis method.

[0053] The silicon-carbon content ratio, which has the silicon content, oxygen content, and a C / Si content ratio within a specific range based on the time course during XPS analysis, may vary depending on the carbonization conditions of the carbon structure (scaffold), the type of silane gas, the thermal decomposition conditions, and the carbon surface treatment conditions.

[0054] According to one embodiment of the present invention, the average particle size D50 of the silicon carbon composite is 1 μm to 20 μm, and may be, for example, 1.5 μm to 15 μm, or 3 μm to 10 μm. When the particle size is within the above range, the dispersibility of the active material is appropriate when manufacturing the slurry, and there is less problem of coating defects due to large particles when coating electrodes.

[0055] According to one embodiment, the specific surface area of the silicon-carbon composite is 20 m 2 / g or less, may be 15 m 2 / g or less, may be 10 m 2 / g or less, and may be 5 m 2 / g or less. The specific surface area of the silicon-carbon composite is 0.1 m 2 / g or more, may be 1 m 2 / g or more, may be 1.5 m 2 / g or more, may be 2 m 2 / g or more, or 3 m 2 / g or more. The specific surface area refers to the total specific surface area of the substrate measured by the BET method. The BET (Brunauer / Emmett / Teller) method is commonly used in the industry to determine the accessible surface area of a material by using an inert gas, such as nitrogen, to measure the amount of gas adsorbed on the material. For example, it can be measured by using a BET measuring device (BEL-SORP-MAX, Nippon Bell), removing the gas (degassing) at 200 °C for 8 hours, and performing N2 adsorption / desorption at 77 K.

[0056] According to one embodiment of the present invention, based on 100 parts by weight of the silicon-carbon composite, the total amount of carbon and silicon is 90 parts by weight to 100 parts by weight.

[0057] According to one example, the silicon-carbon composite may have a structure including a porous carbon structure and silicon provided inside and / or outside the porous carbon structure, or the composite may have a structure including a porous silicon structure and carbon provided inside and / or outside the porous silicon structure. The silicon-carbon composite does not need to be manufactured by a specific manufacturing method and may be manufactured by methods known in the art. For example, the manufacturing of the silicon-carbon composite may be performed by a method including the steps of manufacturing a porous carbon structure, for example, pyrolyzing a polymer to manufacture a porous carbon structure, and flowing silane gas through the porous carbon structure and pyrolyzing it at a high temperature to grow silicon inside and / or outside the porous carbon structure. Depending on the purpose, a step of modifying the surface layer with carbon or other components may be further performed. As another example, Si and SiO2 are co-evaporated to produce Si-containing SiO x After manufacturing an oxide (0 < x < 2), the oxide is chemically etched to manufacture a porous silicon structure, and through the process of heat-treating the porous silicon structure with carbon gas, a silicon-carbon composite can be manufactured.

[0058] <Negative electrode composition and negative electrode> The negative electrode composition according to one embodiment of the present invention includes a negative electrode active material including the silicon-carbon composite.

[0059] Also, a negative electrode according to one embodiment of the present invention includes a current collector; and a negative electrode active material layer provided on at least one surface of the current collector and including the negative electrode composition.

[0060] The negative electrode composition may further include an additional negative electrode active material.

[0061] As the additional negative electrode active material, a compound that allows for the reversible insertion and removal of lithium may be used. Specific examples include carbon-based active materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds that can alloy with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. β Examples include (0<β<2), SnO2, vanadium oxide, lithium titanate, lithium vanadium oxide, and other lithium-doped and dedoped metal oxides; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites, and one or more of these mixtures may be used.

[0062] Furthermore, low-crystalline carbon and high-crystalline carbon may be used as carbonaceous materials. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0063] The additional negative electrode active material may be a carbon-based active material, and may include, for example, graphite, specifically at least one of artificial graphite and natural graphite.

[0064] In one embodiment of the present invention, the weight ratio of the negative electrode active material and additional negative electrode active material contained in the negative electrode composition may be 1:99 to 99:1, specifically 10:90 to 90:10, for example, 5:95 to 50:50 or 10:90 to 30:70.

[0065] The negative electrode composition may further contain a binder and a conductive material, and optionally a thickening agent.

[0066] The negative electrode active material layer can be formed by applying a negative electrode composition, which includes a negative electrode active material, a binder, a conductive material, and optionally a thickener, to at least one surface of a current collector, followed by drying and rolling.

[0067] The negative electrode current collector is not particularly limited as long as it is conductive without inducing a chemical change in the battery. For example, the current collector can be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. Specifically, transition metals that adsorb carbon properly, such as copper and nickel, can be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but the thickness of the current collector is not limited thereto.

[0068] The binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, 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 the hydrogen atoms of these substances are substituted with Li, Na, or Ca, and may also contain a variety of copolymers thereof. For example, copolymers containing acrylamide and acrylonitrile.

[0069] The conductive material is not particularly limited as long as it is conductive without inducing a chemical change in the battery, and may be used for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives.

[0070] The aforementioned thickening agent may be carboxymethylcellulose (CMC), but is not limited thereto, and any other thickening agent used in the present art may be appropriately adopted.

[0071] In one embodiment of the present invention, the total negative electrode active material contained in the negative electrode composition may be in an amount of 60 to 99 parts by weight, specifically 70 to 98 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode composition.

[0072] In one embodiment of the present invention, the binder may be included in an amount of 0.5 to 30 parts by weight, specifically 1 to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode composition.

[0073] In one embodiment of the present invention, the conductive material may be included in an amount of 0.5 to 25 parts by weight, specifically 1 to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode composition.

[0074] In one embodiment of the present invention, the thickening agent may be included in an amount of 0.5 to 25 parts by weight, specifically 0.5 to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode composition.

[0075] A negative electrode composition according to one embodiment of the present invention may further contain a solvent for forming the negative electrode composition. Specifically, the solvent for forming the negative electrode composition may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate the dispersion of the components.

[0076] In one embodiment of the present invention, the solid content weight of the negative electrode composition may be 20 to 75 parts by weight, specifically 30 to 70 parts by weight, based on 100 parts by weight of the total negative electrode composition.

[0077] <Lithium-ion secondary battery> A lithium secondary battery according to one embodiment of the present invention may include a negative electrode according to the above-described embodiment. Specifically, the lithium secondary battery includes a negative electrode, a positive electrode, a separation membrane interposed between the positive and negative electrodes, and may additionally include an electrolyte. The negative electrode has been described above, so a detailed explanation will be omitted.

[0078] 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 containing the positive electrode active material.

[0079] In the positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0080] 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; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented as O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.5); chemical formula LiMn 2-c3 M c3Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 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); or LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., but are not limited to these. The positive electrode may be Li metal (Li-metal).

[0081] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0082] In this case, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitations as long as it does not cause chemical changes in the battery and has electronic conductivity. Specific examples include graphite such as natural graphite or 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 powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more may be used.

[0083] Furthermore, the positive electrode binder plays a role in improving adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these may be used.

[0084] The separation membrane separates the negative and positive electrodes and provides a pathway for lithium ions to move. Any membrane commonly used as a separation membrane in secondary batteries is generally acceptable, with no particular restrictions. Particular preference is for membranes that exhibit low resistance to ion movement in the electrolyte while maintaining excellent moisture-retaining capacity. Specifically, porous polymer films, such as those made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof, may be used. Alternatively, ordinary porous nonwoven fabrics, such as those made from high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separation membranes containing ceramic components or polymeric substances to ensure heat resistance or mechanical strength may be used, and these may be selectively used in single-layer or multi-layer structures.

[0085] Examples of the aforementioned electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0086] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0087] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate may be used.

[0088] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are suitable for use because they are high-viscosity organic solvents with high dielectric constants and readily dissociate lithium salts. Furthermore, by mixing such cyclic carbonates with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, an electrolyte with high electrical conductivity can be produced, making them even more suitable for use.

[0089] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte, 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 - You may use one or more selected from the group consisting of the following:

[0090] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0091] According to yet another embodiment of the present invention, a battery module and a battery pack including the lithium secondary battery as a unit cell are provided. Since the battery module and battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they 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.

[0092] Figure 1 is a diagram illustrating a battery pack 3 including a lithium secondary battery 1 according to one embodiment of the present invention.

[0093] Referring to Figure 1, a battery pack 3 according to one embodiment of the present invention includes a battery assembly in which a plurality of lithium secondary batteries 1 according to the above-described embodiment of the present invention are electrically connected, and a pack housing 2 that houses it. In the drawings of the present invention, for illustrative purposes, components such as busbars for electrical connection, cooling units, and power terminals have been omitted.

[0094] Figure 2 is a diagram illustrating the automobile 5 including the battery pack 3 shown in Figure 1.

[0095] Referring to Figure 2, the automobile 5 according to one embodiment of the present invention may be, for example, an electric vehicle, a hybrid vehicle, or a plug-in hybrid vehicle, and includes a battery pack 3 according to one embodiment of the present invention. The automobile 5 includes four-wheeled vehicles and two-wheeled vehicles. The automobile 5 operates by receiving electrodes from the battery pack 3 according to one embodiment of the present invention. [Examples]

[0096] The following are preferred embodiments to aid in understanding the present invention. However, these embodiments are merely illustrative of the description, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the description and the technical concept, and such variations and modifications naturally fall within the scope of the claims.

[0097] <Examples and Comparative Examples> Example 1 Specific surface area 1850m 2 / g~1900m 2 / g, pore volume 0.80 cm³ 3 / g~0.85cm 30.9 g of amorphous porous carbon scaffold containing 1 / g was placed in a ceramic crucible and positioned in the center of a horizontal tube furnace. After sealing the furnace and purging with nitrogen gas, the furnace temperature was increased to 450°C-500°C at a rate of 10°C / min, and then silane gas and hydrogen gas were retained at different flow rates for 60-90 minutes. Additionally, after increasing the furnace temperature to 780°C-900°C at a rate of 10°C / min, propane gas was retained at different flow rates for 30-60 minutes to produce porous silicon-carbon composites having the properties shown in Table 1.

[0098] Example 2 A porous silicon-carbon composite was produced in the same manner as in Example 1, except that the silane flow rate was increased so that the silicon content in the porous silicon-carbon composite was 52 parts by weight.

[0099] Comparative Example 1 A porous silicon-carbon composite was produced in the same manner as in Example 1, except that the silane flow rate and residence time were reduced so that the silicon content in the porous silicon-carbon composite was 38 parts by weight.

[0100] Comparative Example 2 A porous silicon-carbon composite was produced in the same manner as in Example 1, except that the primary heating temperature was increased and the silane flow rate and residence time were increased so that the silicon content in the porous silicon-carbon composite was 62 parts by weight.

[0101] Comparative Example 3 A porous silicon-carbon composite was manufactured in the same manner as in Example 1, except that the furnace temperature in the final stage of the manufacturing process was reduced and the residence time and flow rate of propane gas were lowered.

[0102] Comparative Example 4 A porous silicon-carbon composite was manufactured in the same manner as in Example 1, except that the furnace temperature in the final stage of the manufacturing process was increased, and the residence time and flow rate of the propane gas were increased.

[0103] Comparative Example 5 In the manufacturing process of the porous silicon-carbon composite, a porous silicon-carbon composite was produced in the same manner as in Example 1, except that a gas mixture of propane gas and CO2 gas was used.

[0104] The silicon content, oxygen content, and C / Si ratio of the silicon-carbon composites produced in the examples and comparative examples were measured by the following methods using XPS analysis, and the results are shown in Table 1.

[0105] - Oxygen content: The oxygen content of the complex was measured using an ONH analyzer.

[0106] -Silicon content: The carbon content was analyzed using a CS analyzer, and the oxygen content analyzed using an ONH analyzer was used to calculate the silicon content by subtracting it from the total weight of the silicon-carbon-oxygen composite.

[0107] - C / Si ratio by XPS analysis: Measured using the method described above with NEXSA G2 and Thermo Fisher Scientific (instrument name ESCA-03).

[0108] [Table 1]

[0109] Experimental Example 1 (Synthesis of Binder) In a reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet, acrylamide, acrylic acid, and acrylonitrile were mixed in a weight ratio of 60:30:10, a polymerization initiator (ammonium peroxodisulfate) was added, and the mixture was reacted at 75°C for 6 hours to produce an aqueous polymer.

[0110] Next, it was neutralized with an aqueous NaOH solution to produce a (meth)acrylic binder.

[0111] (Manufacturing of negative electrode slurry) A silicon-carbon composite manufactured in Example 1 was used as the negative electrode active material, and two types of conductive materials, particulate conductive material (SFG6L) and SWCNT (product name: Tuball OCSiAl), were used as conductive materials. The aqueous binder from Manufacturing Example 1 was used, and the materials were mixed in the ratio negative electrode active material:particulate conductive material:SWCNT:aqueous binder = 80:9.6:0.8:9.6 (based on weight ratio) to prepare the negative electrode composition.

[0112] A negative electrode slurry was prepared by adding water as a solvent, and the water content was adjusted considering coating properties, viscosity, and solid content. The viscosity of the resulting negative electrode slurry was adjusted to 8000 cps.

[0113] Experimental Example 2 and Comparative Experimental Examples 1-5 The negative electrode slurry was prepared in the same manner as in Experimental Example 1, except that the silicon carbon composites of Example 2 and Comparative Examples 1 to 5 were used instead of the silicon carbon composite of Example 1.

[0114] <Evaluation 1: Measurement of phase stability (viscosity change) of negative electrode slurry> 5g of active material or slurry was placed in a 9cm x 9cm pouch and sealed. The pouch was then stored in a constant temperature chamber at a high temperature (60°C) for 24 hours. After that, the gas inside the pouch was collected and the amount generated was measured by GC / MS.

[0115] <Evaluation 2: Battery Manufacturing and Battery Characterization> The negative electrode slurry was coated onto an 18 μm thick copper foil and dried to form a 50 μm thick electrode active material layer on one side of the copper foil. A test electrode (negative electrode) was then manufactured by punching a circular shape with a diameter of 14Φ (mm). A 0.3 mm thick metallic lithium foil was used as the positive electrode. A 0.1 mm thick porous polyethylene sheet was used as the separation membrane. As the electrolyte, a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1 was used, in which LiPF6 was dissolved as a lithium salt at a concentration of approximately 1 mol / L.

[0116] The negative electrode, positive electrode, separator membrane, and electrolyte were sealed in a stainless steel container to produce an evaluation coin cell with a thickness of 2 mm and a diameter of 32 mm. The coin cell was charged with a constant current of 0.05 C until the voltage reached 0.01 V, and then discharged with a constant voltage of 0.05 C until the voltage reached 1.5 V to determine the discharge capacity and initial efficiency. The results are shown in Table 2 below.

[0117] [Table 2]

[0118] As shown in the results in Table 2 above, the negative electrode slurries of Examples 1 and 2, and the lithium secondary batteries using them, in which the Si content of the silicon-carbon composite was within the target range of 40 to 60 parts by weight, the oxygen content was within the target range of 10 parts by weight or less, and the XPS C / Si content ratio at etching times of 10 seconds and 1000 seconds was controlled to a specific range (for example, 60 or more and 15 or less, respectively), not only generated little hydrogen gas but also exhibited excellent initial discharge capacity and initial efficiency. In contrast, in Comparative Example 1, where the Si content of the silicon-carbon composite was low at 38 parts by weight, the initial discharge capacity and initial efficiency were low. Furthermore, in Comparative Example 2, the Si content of the silicon-carbon composite was 62 parts by weight, exceeding the target range, and in Comparative Example 3, where the XPS C / Si content ratio at etching time of 10 seconds was 8, below the target range, the amount of gas generated was large, and the initial efficiency and initial discharge capacity were insufficient. Furthermore, in Comparative Example 4, the XPS C / Si ratio at an etching time of 1000 seconds was 17, which is within the target range of 15 or higher, and in Comparative Example 5, the oxygen content in the silicon-carbon composite was 12 parts by weight, which is within the target range of 10 parts by weight or higher, but the initial discharge capacity and initial efficiency were insufficient.

Claims

1. A silicon-carbon composite comprising silicon and carbon, The silicon content is 40 parts by weight or more and 60 parts by weight or less, based on 100 parts by weight of the silicon-carbon composite. The carbon content ratio (C / Si) to silicon is determined in XPS analysis by Ta ２ O ５ A silicon carbon composite in which, under conditions of etching at a speed of 0.15 nm / s, the oxygen content is 30 or more after 10 seconds of etching and 15 or less after 1,000 seconds of etching, and the oxygen content is 10 parts by weight or less based on 100 parts by weight of the silicon carbon composite.

2. The silicon-carbon composite according to claim 1, wherein the carbon content ratio (C / Si) to silicon is 30 or more in the region from 0 nm to 25 nm from the surface of the silicon-carbon composite, and 15 or less in the region from 200 nm to 300 nm from the surface of the silicon-carbon composite.

3. The silicon carbon composite according to claim 1, wherein the average particle size D50 of the silicon carbon composite is 1 μm or more and 20 μm or less.

4. The BET specific surface area of ​​the silicon-carbon composite is 20 m². ２ The silicon carbon composite according to claim 1, wherein the amount is less than or equal to / g.

5. A negative electrode composition for a lithium secondary battery, comprising a negative electrode active material containing a silicon carbon composite according to any one of claims 1 to 4.

6. The anode composition according to claim 5, further comprising a carbon-based active material.

7. The negative electrode composition according to claim 6, further comprising a binder and a conductive material.

8. Current collector; and A negative electrode active material layer provided on at least one surface of the current collector, comprising the negative electrode composition according to claim 5; The negative electrode, including the negative electrode.

9. The negative electrode according to claim 8; Separation membrane; and positive electrode; Lithium-ion batteries, including lithium-ion batteries.

10. A battery module comprising the lithium secondary battery described in claim 9.

11. A battery pack comprising the lithium secondary battery described in claim 9.

12. A battery pack comprising the battery module described in claim 10.

13. An electric vehicle comprising the battery pack described in claim 12.

14. A method for producing a silicon-carbon composite comprising silicon and carbon, The silicon content is approximately 40 parts by weight or more and 60 parts by weight or less, based on 100 parts by weight of the silicon-carbon composite. The carbon content ratio (C / Si) to silicon is determined in XPS analysis by Ta ２ O ５ A method for producing a silicon carbon composite, wherein, under conditions where the material is etched at a speed of 0.15 nm / s, the oxygen content is adjusted to be approximately 10 parts by weight or less after 10 seconds of etching and approximately 15 parts by weight or less after 1,000 seconds of etching, based on 100 parts by weight of the silicon carbon composite.

15. The method for producing a silicon carbon composite according to claim 14, wherein the carbon content ratio (C / Si) to silicon is adjusted to be about 30 or more in the region from 0 nm to 25 nm from the surface of the silicon carbon composite, and to about 15 or less in the region from 200 nm to 300 nm from the surface of the silicon carbon composite.

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