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; a negative electrode composition, a negative electrode, a lithium secondary battery, a battery module, a battery pack, and an electric vehicle comprising same; and a method for manufacturing the silicon carbon composite, wherein the silicon carbon composite comprises silicon and carbon, the content of silicon is 40 to 60 parts by weight with respect to 100 parts by weight of the silicon carbon composite, the content ratio (C / Si) of carbon to silicon is 30 or more after 10 seconds of etching time under the condition of Ta2O5 being etched at a rate of 0.15 nm / s during XPS analysis and is less than or equal to 15 after 1,000 seconds of etching time, and the oxygen content is less than or equal to 10 parts by weight with respect to 100 parts by weight of the silicon carbon composite.

Description

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

[0001] This specification claims the benefit of Korean Patent Application No. 10-2023-0167493 filed with the Korean Intellectual Property Office on November 28, 2023, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to a silicon carbon composite, a negative electrode composition, a negative electrode, a lithium secondary battery, a battery module, and a battery pack.

[0003] The recent rapid proliferation of battery-powered electronic devices, including mobile phones, laptops, electric vehicles, power tools, and vacuum cleaners, has led to a rapid increase in demand for compact, lightweight, and relatively high-capacity and / or high-output secondary batteries. Lithium secondary batteries, in particular, are attracting attention as power sources for electronic devices due to their lightweight design and high energy density. Accordingly, active research and development efforts are underway to improve the performance of lithium secondary batteries.

[0004] While silicon-carbon composites exhibit superior initial capacity and energy efficiency compared to graphite or silicon oxide, they suffer from low phase 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 capable of improving the phase stability of a slurry, and an anode composition and anode comprising the same. Furthermore, embodiments of the present invention relate to a lithium secondary battery, a battery module, and a battery pack comprising the anode.

[0005] One embodiment of the present invention provides a silicon-carbon composite including 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-to-silicon content ratio (C / Si) is 30 or more after 10 seconds of etching time and 15 or less after 1,000 seconds of etching time under the condition that Ta2O5 is etched at a rate of 0.15 nm / s during XPS analysis, and the silicon-carbon composite has an oxygen content of 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 in which the content ratio of carbon to silicon (C / Si) is 30 or more in a region of 0 nm to 25 nm in depth from the surface of the silicon-carbon composite, and 15 or less in a region of 200 nm to 300 nm in depth from the surface of the silicon-carbon composite.

[0007] One embodiment of the present invention provides a cathode composition comprising the silicon carbon composite.

[0008] One embodiment of the present invention provides a negative electrode for a lithium secondary battery, comprising: 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.

[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.

[0015] The silicon carbon composite according to one embodiment of the present invention includes a specific amount of silicon, and at the same time, the content ratio of carbon to silicon (C / Si) varies with time during XPS analysis, and the content ratio of oxygen to silicon is within a specific range, thereby limiting contact between Si and water and suppressing oxidation reactions to reduce the amount of hydrogen gas generated, thereby providing excellent phase stability of the cathode slurry and achieving high capacity and high efficiency of the cathode.

[0016] The following drawings attached to this specification illustrate preferred embodiments of the present invention, and together with the detailed description of the invention described below, serve to further understand the technical idea of ​​the present invention, and therefore, the present invention should not be interpreted as being limited to matters described in such drawings.

[0017] FIG. 1 is a drawing for explaining a battery pack including a battery cell according to one embodiment of the present invention.

[0018] FIG. 2 is a drawing for explaining a vehicle including the battery pack of FIG. 1.

[0019] Hereinafter, the present specification will be described in more detail.

[0020] In this specification, when a part is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0021] In this specification, when it is said that a member is located “on” another member, this includes not only cases where the member is in contact with the other member, but also cases where another member exists between the two members.

[0022] The terms and words used in this specification should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0023] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0024] In this specification, the average particle diameter D50 can be defined as the particle diameter corresponding to 50% of the volume accumulation amount in the particle size distribution curve (graph curve of particle size distribution) of particles. The average particle diameter can be measured using, for example, a laser diffraction method. The laser diffraction method can generally measure particle diameters from the submicron range to several mm, and can obtain results with high reproducibility and high resolution. The measurement of the average particle diameter can be confirmed using a Microtrac device (manufacturer: Microtrac model name: S3500) using water and a triton-X100 dispersant. Specifically, the average particle diameter of the positive electrode active material can be measured in the range of a refractive index of 1.5 to 1.7, and the average particle diameter of the negative electrode active material can be measured under the condition of a refractive index of 1.97 or 2.42. For example, after dispersing particles in a dispersion medium, the particles can be measured by introducing them into a commercially available laser diffraction particle size measuring device, irradiating them with ultrasonic waves of approximately 28 kHz at an output of 60 W, obtaining a volume-cumulative particle size distribution graph, and then calculating the particle size corresponding to 50% of the volume-cumulative amount.

[0025]

[0026] Lithium secondary batteries produce electrical energy through oxidation and reduction reactions when lithium ions are inserted / deintercalated between the positive and negative electrodes, which are made of active materials capable of intercalating and deintercalating lithium ions, while charging an organic electrolyte or polymer electrolyte between them.

[0027] Graphite is primarily used as an anode active material in lithium secondary batteries. However, graphite has a low capacity per unit mass of 372 mAh / g, making it difficult to achieve high capacity in lithium secondary batteries. Therefore, to increase the energy density of lithium secondary batteries, non-carbonaceous anode materials with higher energy densities than graphite, such as silicon, tin, and their oxides, are being developed.

[0028] In the present invention, in a lithium secondary battery using a silicon carbon composite as an anode active material, the composition of the silicon carbon composite is controlled to provide excellent phase stability of the anode slurry, and also to provide a high-capacity and high-efficiency anode.

[0029]

[0030] Hereinafter, preferred embodiments of the present invention will be described in detail. 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.

[0031]

[0032] <Silicon Carbon Composite>

[0033] One embodiment of the present invention relates to a silicon carbon composite.

[0034] A silicon carbon composite according to one embodiment of the present invention is manufactured by the following method.

[0035] First, a suitable surface area (e.g., about 1850 m 2 / g ~ 1900 m 2 / g), with an appropriate pore volume (e.g., about 0.80 cm3 / g ~ 0.85 cm 3 An appropriate amount (e.g., about 0.9 g) of amorphous porous carbon scanfold having a silicon content of / g) is placed in a ceramic crucible and placed in the center of a horizontal tube furnace. The furnace is then sealed and purged with nitrogen gas, and the furnace temperature is gradually increased (e.g., increased to 450 to 500°C at a rate of about 10°C / min), followed by varying the flow rates of silane gas and hydrogen gas while maintaining the temperature for a predetermined period of 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. Thereafter, the furnace temperature is additionally increased (e.g., increased to 780 to 900°C at a rate of 10°C / min), and propane gas is maintained for a predetermined period of time (e.g., about 30 to 60 minutes) while varying the flow rates, thereby producing a porous silicon carbon composite having the properties required in the present invention.

[0036] In the production of the porous silicon carbon composite described above, the parameters in each process, such as the specific surface area and / or amount of the amorphous porous carbon scanfold, the method of increasing the temperature of the furnace, the flow rate and / or residence time of the silane gas and hydrogen gas, etc., can be controlled to obtain the properties of the silicon carbon composite required in the present invention. Of course, the production process of the porous silicon carbon composite is not limited to the production method described above, and any production method capable of obtaining the properties of the silicon carbon composite required in the present invention can be used.

[0037] The silicon content in the silicon carbon composite manufactured according to one embodiment of the present invention described above 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 capacity 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, and it is difficult to manufacture a silicon carbon composite having a uniform Si distribution within the carbon. Within the above silicon content range, the capacity and efficiency of the active material are appropriate, and it is easy to suppress gas generation in the slurry.

[0038] The silicon content can be calculated by calculating the silicon content inversely by calculating the C content and O content of the silicon carbon composite, respectively. The C content can be analyzed using a CS analyzer (Bruker, G8 Galileo), and the O content can be analyzed using an ONH analyzer (Bruker, G-4 ICARUS SeriesII).

[0039] The content ratio of carbon to silicon (C / Si) is 30 or more after 10 seconds of etching under the condition that Ta2O5 is etched at a rate of 0.15 nm / s during XPS analysis, and 15 or less after 1,000 seconds of etching.

[0040] As described above, when the content ratio of carbon to silicon (C / Si) is 30 or more after 10 seconds of etching time when analyzing XPS under the condition that Ta2O5 is etched at a rate of 0.15 nm / s, there is an advantage that a carbon coating is evenly formed over the entire surface of the active material, limiting contact with water and suppressing oxidation reactions, thereby reducing the amount of gas generated. In addition, when the content ratio is 15 or less after 1,000 seconds of etching time, there is no significant restriction on lithium movement due to an appropriate carbon layer thickness, and there is no significant problem in reacting with internal silicon, so there is an advantage of excellent capacity efficiency. Here, XPS analysis can be performed under the following conditions.

[0041] - Equipment used: NEXSA G2, Thermo Fisher Scientific (Equipment name ESCA-03)

[0042] - Sample preparation: Press the powdered sample into the powder holder and make the measurement surface flat.

[0043] - Measurement conditions:

[0044] X-ray source: Monochromated Al Kα (1486.6 eV)

[0045] X-ray spot size: 400 ㎛

[0046] Etching conditions (sputtering gun): monatomic Ar (energy: 1,000 eV, current: low, raster width: 2 mm) Charge compensation (flood gun): 0.3 V, 150 ㎂

[0047] Survey scan: pass energy 200 eV, energy step 1 eV

[0048] Narrow scan: pass energy 50 eV, energy step 0.1 eV

[0049] Sensitivity factor (SF): Al THERMO1, Energy correction factor (ECF): TPP-2M

[0050] Background subtraction: Smart

[0051] The plasmon loss peak of Si is not included in the quantitative analysis.

[0052] The content ratio of carbon to silicon (C / Si) is 30 or more after 10 seconds of etching under the condition that Ta2O5 is etched at a rate of 0.15 nm / s during XPS analysis, and may be, for example, 35 or more, 40 or more, 45 or more, or 50 or more.

[0053] The content ratio of carbon to silicon (C / Si) is 15 or less after 1,000 seconds of etching under the condition that Ta2O5 is etched at a rate of 0.15 nm / s during XPS analysis, and may be, for example, 12 or less or 10 or less.

[0054] The content ratio of carbon to silicon (C / Si) is 100 or less after 10 seconds of etching under the condition that Ta2O5 is etched at a rate of 0.15 nm / s during XPS analysis, and may be, for example, 80 or less, 70 or less, or 60 or less.

[0055] The content ratio of carbon to silicon (C / Si) is 1 or more after 1,000 seconds of etching under the condition that Ta2O5 is etched at a rate of 0.15 nm / s during XPS analysis, and may be, for example, 3 or more, 4 or more, 5 or more, or 6 or more.

[0056] The content ratio of carbon to silicon (C / Si) is 30 or more in a region of 0 nm to 25 nm in depth from the surface of the silicon carbon composite, and 15 or less in a region of 200 nm to 300 nm in depth from the surface of the silicon carbon composite.

[0057] Since XPS analysis analyzes components while etching a sample, the analysis results after 1,000 seconds show analysis results from a deeper area from the surface of the sample compared to the analysis results after 10 seconds as shown above.

[0058] Specifically, the etching time of 10 seconds under the condition that the above Ta2O5 is etched at a rate of 0.15 nm / s means the time for etching from the surface of the silicon carbon composite to a depth of 0 nm to 25 nm and measuring the XPS (C / Si) value of the surface of the silicon carbon composite.

[0059] In addition, the etching time of 1,000 seconds under the condition that the above Ta2O5 is etched at a rate of 0.15 nm / s means the time for etching to a depth of 200 nm to 300 nm from the surface of the silicon carbon composite and for measuring the XPS (C / Si) value of a deeper region from the surface of the silicon carbon composite.

[0060] The depth from the surface of the above silicon carbon composite means the depth from the surface of the silicon carbon composite toward the center.

[0061] The content ratio of carbon to silicon (C / Si) is 30 or more in a region of 0 nm to 25 nm in 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.

[0062] The depth from the surface of the silicon carbon composite may be 15 or less in a region of 200 nm to 300 nm, for example, 12 or less or 10 or less.

[0063] The content ratio of carbon to silicon (C / Si) is 15 or less in a region of 0 nm to 25 nm in depth from the surface of the silicon carbon composite, and may be, for example, 12 or less or 10 or less.

[0064] The depth from the surface of the silicon carbon composite may be 1 or more in the range of 200 nm to 300 nm, for example, 3 or more, 4 or more, 5 or more, or 6 or more.

[0065] The oxygen content in the above 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, there is an advantage in that capacity degradation due to silicon oxidation is minimized, and lithium availability loss due to oxygen is small, thereby minimizing the decrease in initial capacity and efficiency of the silicon-carbon composite.

[0066] The oxygen content of the above silicon carbon composite can be measured by the ONH analysis method.

[0067] The silicon carbon content ratio having a silicon content, oxygen content, and C / Si content ratio within a specific range over time during XPS analysis as described above 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.

[0068] According to one embodiment of the present invention, the average particle diameter D50 of the silicon carbon composite is 1 ㎛ to 20 ㎛, for example, 1.5 ㎛ to 15 ㎛, or 3 ㎛ to 10 ㎛. When the particle diameter is within the above range, the dispersibility of the active material is appropriate when preparing a slurry, and the problem of coating defects due to large particles during electrode coating is reduced.

[0069] According to one embodiment, the specific surface area of ​​the silicon carbon composite is 20 m 2 / g or less, and 15 m 2 / g may be less than 10 m 2 / g can be less than 5 m 2 / g or less. The specific surface area of ​​the silicon carbon composite is 0.1 m 2 / g or more, 1 m 2 / g may be more than 1.5 m 2 / g can be more than 2 m 2 / g or more or 3 m 2 / g or more. The above specific surface area refers to the total specific surface area of ​​the substrate measured by the BET technique. The BET (Brunauer / Emmett / Teller) technique is commonly used in the art 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, the measurement can be performed by degassing at 200°C for 8 hours and performing N2 adsorption / desorption at 77K using BET measuring equipment (BEL-SORP-MAX, Nippon Bell).

[0070] According to one embodiment of the present invention, the total amount of carbon and silicon is 90 to 100 parts by weight based on 100 parts by weight of the silicon carbon composite.

[0071] 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 a method known in the art. For example, the manufacturing of the silicon-carbon composite may be performed by a method including a step of manufacturing a porous carbon structure, for example, a step of manufacturing a porous carbon structure by pyrolyzing a polymer, and a step of flowing silane gas into the porous carbon structure and pyrolyzing it at a high temperature to grow silicon inside and / or outside the porous carbon structure, and a step of modifying the surface layer with carbon or another component depending on the purpose may be additionally performed. In addition, as another example, Si and SiO2 are simultaneously deposited to form Si-containing SiO. xOxide (0) <x<2)을 제조한 후 산화물을 화학적으로 에칭하여 다공성 실리콘 구조체를 제조하고, 다공성 실리콘 구조체에 탄소가스로 열처리 공정을 거쳐 실리콘 카본 복합체를 제조할 수 있다.

[0072]

[0073] <Cathode composition and cathode>

[0074] A negative electrode composition according to one embodiment of the present invention includes a negative electrode active material including the silicon carbon composite.

[0075] In addition, 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.

[0076] The above negative electrode composition may further include an additional negative electrode active material.

[0077] As the above-mentioned additional negative electrode active material, a compound capable of reversible intercalation and deintercalation 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 capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO β (0 < β < 2), metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, lithium titanium oxide, and lithium vanadium oxide; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used.

[0078] In addition, low-crystalline carbon and high-crystalline carbon can be used as carbonaceous materials. Soft carbon and hard carbon are representative examples of low-crystalline carbon, and high-crystalline carbon is representative examples of high-crystalline carbon, such as natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical or fibrous shapes, 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.

[0079] The above additional negative active material may be a carbon-based active material, for example, graphite, specifically at least one of artificial graphite and natural graphite.

[0080] In one embodiment of the present invention, the weight ratio of the negative electrode active material and the additional negative electrode active material included in the negative electrode composition may be 1:99 to 99:1, and specifically, 10:90 to 90:10, for example, 5:95 to 50:50 or 10:90 to 30:70.

[0081] The above cathode composition may further include a binder and a conductive material, and may further include a thickener as needed.

[0082] The above negative electrode active material layer can be formed by applying a negative electrode composition including a negative electrode active material, a binder, a conductive material, and, if necessary, a thickener to at least one surface of a current collector, and drying and rolling.

[0083] The negative current collector may be any conductive material that does not cause chemical changes in the battery, and is not particularly limited thereto. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that readily absorbs carbon, such as copper or nickel, may be used as the current collector. The current collector may have a thickness of 6 μm to 20 μm, but the thickness of the current collector is not limited thereto.

[0084] The above 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, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and substances in which hydrogens thereof are substituted with Li, Na, Ca, etc., and may also include various copolymers thereof, for example, copolymers containing acrylamide and acrylonitrile.

[0085] The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, paneth black, lamp black, and thermal black; conductive fibers such as carbon fiber or metal fiber; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0086] The above thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and any thickener used in the present technical field may be appropriately employed.

[0087] In one embodiment of the present invention, the total negative electrode active material included in the negative electrode composition may be included 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.

[0088] 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.

[0089] 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.

[0090] In one embodiment of the present invention, the thickener 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.

[0091] The cathode composition according to one embodiment of the present invention may further include a solvent for forming the cathode composition. Specifically, the solvent for forming the cathode 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 dispersion of the components.

[0092] In one embodiment of the present invention, the solid content weight of the cathode composition may be 20 parts by weight to 75 parts by weight, specifically 30 parts by weight to 70 parts by weight, based on 100 parts by weight of the total cathode composition.

[0093]

[0094] Lithium secondary battery

[0095] A lithium secondary battery according to one embodiment of the present invention may include the anode according to the aforementioned embodiment. Specifically, the lithium secondary battery includes a cathode, a cathode, a separator interposed between the cathode and the anode, and may additionally include an electrolyte. As the anode has been described above, a detailed description thereof will be omitted.

[0096] The above 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.

[0097] In the above positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 ㎛, and fine unevenness may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0098] The above 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), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound having 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 by O2 (wherein, M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤c2≤0.5); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxide represented by O2 (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≤c3≤0.1) or Li2Mn3MO8 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); or LiMn2O4 in which a portion of Li in the chemical formula is replaced with an alkaline earth metal ion; but is not limited thereto. The positive electrode may be Li-metal.

[0099] The above-described positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the positive electrode active material described above.

[0100] At this time, the positive electrode conductive material is used to provide conductivity to the electrode, and in the battery to be constructed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. 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, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of these may be used alone or a mixture of two or more may be used.

[0101] In addition, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesiveness between the positive electrode active material and the positive electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof.

[0102] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. Any separator commonly used in secondary batteries can be used without any particular restrictions, and in particular, one that has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. In addition, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. can also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure.

[0103] Examples of the above 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.

[0104] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0105] As the above non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrropionate, ethyl propionate, etc. can be used.

[0106] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and thus can be preferably used because they easily dissociate lithium salts. In addition, when low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed and used in an appropriate ratio with these cyclic carbonates, an electrolyte having high electrical conductivity can be produced, so that they can be used even more preferably.

[0107] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, for example, the anion of the lithium salt is 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 may be used.

[0108] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as, for example, difluoroethylene carbonate and other haloalkylene carbonate compounds, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery.

[0109] According to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided. The battery module and the battery pack include the lithium secondary battery having high capacity, high rate characteristics, and cycle characteristics, and thus can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0110] FIG. 1 is a drawing for explaining a battery pack (3) including a lithium secondary battery (1) according to one embodiment of the present invention.

[0111] Referring to FIG. 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 one embodiment of the present invention are electrically connected, and a pack housing (2) that accommodates the battery assembly. In the drawing of the present invention, components such as bus bars, cooling units, and power terminals for electrical connection are omitted for convenience of illustration.

[0112] FIG. 2 is a drawing for explaining a vehicle (5) including the battery pack (3) of FIG. 1.

[0113] Referring to FIG. 2, a vehicle (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 vehicle (5) includes a four-wheeled vehicle and a two-wheeled vehicle. The vehicle (5) operates by receiving power from the battery pack (3) according to one embodiment of the present invention.

[0114] Hereinafter, preferred embodiments are presented to help understand the present invention, but the above embodiments are only illustrative of the present disclosure, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0115]

[0116] <Examples and Comparative Examples>

[0117] Example 1

[0118] Specific surface area 1850 m 2 / g ~ 1900 m 2 / g, pore volume 0.80 cm 3 / g ~ 0.85 cm 3 / g of amorphous porous carbon scanfold (0.9 g) was placed in a ceramic crucible and placed in the center of a horizontal tube furnace. After sealing the furnace and purging with nitrogen gas, the furnace temperature was increased from 450°C to 500°C at a rate of 10°C / min, and then silane gas and hydrogen gas were allowed to remain for 60 to 90 minutes at different flow rates. Additionally, the furnace temperature was increased from 780°C to 900°C at a rate of 10°C / min, and then propane gas was allowed to remain for 30 to 60 minutes at different flow rates to produce a porous silicon carbon composite having the characteristics shown in Table 1.

[0119]

[0120] Example 2

[0121] A porous silicon carbon composite was manufactured 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.

[0122]

[0123] Comparative Example 1

[0124] A porous silicon carbon composite was manufactured 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.

[0125]

[0126] Comparative Example 2

[0127] A porous silicon carbon composite was manufactured in the same manner as in Example 1, except that the first heating temperature was increased so that the silicon content in the porous silicon carbon composite was 62 parts by weight, and the silane flow rate and residence time were increased.

[0128]

[0129] Comparative Example 3

[0130] A porous silicon carbon composite was manufactured in the same manner as in Example 1, except that the furnace temperature in the final step of the porous silicon carbon composite manufacturing process was lowered and the residence time and flow rate of propane gas were reduced.

[0131]

[0132] Comparative Example 4

[0133] A porous silicon carbon composite was manufactured in the same manner as in Example 1, except that the furnace temperature in the final step of the porous silicon carbon composite manufacturing process was increased and the residence time and flow rate of propane gas were increased.

[0134]

[0135] Comparative Example 5

[0136] A porous silicon carbon composite was manufactured using the same method as Example 1, except that a gas mixture of propane gas and CO2 gas was used during the manufacturing process of the porous silicon carbon composite.

[0137]

[0138] The silicon content, oxygen content, and C / Si ratio by XPS analysis of the silicon carbon composites manufactured in the examples and comparative examples were measured by the following methods, and the results are shown in Table 1.

[0139] - Oxygen content: The oxygen content of the complex was measured using an ONH analyzer.

[0140] - Silicon content: The silicon content was calculated by analyzing the C content using a CS analyzer and subtracting the O content analyzed using an ONH analyzer from the total weight of the silicon carbon oxygen complex.

[0141] - C / Si ratio by XPS analysis: Measured using the method described above using NEXSA G2, Thermo Fisher Scientific (equipment name ESCA-03).

[0142]

[0143] Silicon content (based on 100 parts by weight of silicon-carbon composite) C / Si (after 10 seconds of XPS analysis) C / Si (after 1,000 seconds of XPS analysis) Oxygen content (based on 100 parts by weight of silicon-carbon composite) Example 14850101.8 Example 2524561.8 Comparative example 13854141.5 Comparative example 2623531.6 Comparative example 34981.21.5 Comparative example 44454171.6 Comparative example 54652912

[0144] Experimental Example 1 (Binder Synthesis)

[0145] In a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet pipe, acrylamide, acrylic acid, and acrylonitrile were mixed in a weight ratio of 60:30:10, a polymerization initiator (ammonium persulfate) was added, and the mixture was reacted at 75°C for 6 hours to produce a polymer in an aqueous solution.

[0146] Next, a (meth)acrylic binder was prepared by neutralizing with an aqueous NaOH solution.

[0147] (Cathode slurry manufacturing)

[0148] The silicon carbon composite manufactured in Experimental Example 1 was used as the negative active material, and two types of particle-type conductive material (SFG6L) and SWCNT (product name: Tuball OCSiAl) were used as the conductive material, and the aqueous binder of Manufacturing Example 1 was used. The negative active material: particle-type conductive material: SWCNT: aqueous binder = 80:9.6:0.8:9.6 (based on weight ratio) was mixed to prepare a negative electrode composition.

[0149] A cathode slurry was prepared by adding water as a solvent, wherein the water content was adjusted taking into account the coating properties, viscosity, and solid content. The viscosity of the obtained cathode slurry was adjusted to 8000 cps.

[0150]

[0151] Experimental Example 2 and Comparative Experimental Examples 1 to 5

[0152] A cathode 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.

[0153]

[0154] <Evaluation 1: Measurement of phase stability (viscosity change) of cathode slurry>

[0155] 5g of active material or slurry was placed in a 9cmx9cm pouch, sealed, and stored in a constant temperature chamber at high temperature (60℃) for 24 hours. The gas inside the pouch was captured and the amount generated was measured using GC / MS.

[0156]

[0157] <Evaluation 2: Battery Manufacturing and Battery Characteristics Evaluation>

[0158] The above-mentioned negative electrode slurry was coated on a copper foil having a thickness of 18 μm and dried, and an electrode active material layer having a thickness of 50 μm was formed on one side of the copper foil, which was then punched into a circle having a diameter of 14 Φ (mm) to manufacture a test electrode (negative electrode). A metallic lithium foil having a thickness of 0.3 mm was used as the positive electrode. A porous polyethylene sheet having a thickness of 0.1 mm was used as the separator. In addition, as the electrolyte, LiPF6 was dissolved as a lithium salt at a concentration of about 1 mol / L in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1:1.

[0159] The above cathode, anode, separator, and electrolyte were sealed in a stainless steel container to manufacture a coin cell for evaluation, 2 mm thick and 32 mm in diameter. The coin cell was charged at a constant current of 0.05 C until the voltage reached 0.01 V, and discharged at a constant current of 0.05 C until the voltage reached 1.5 V, to obtain the discharge capacity and initial efficiency. The results are shown in Table 2 below.

[0160]

[0161] Slurry phase stability (H2 gas generation, μL) Initial discharge capacity (mAh / g) Initial efficiency (%) Experimental example 1 20 18 50 89 Experimental example 2 24 19 00 88 Comparative experiment example 1 12 12 5 0 83 Comparative experiment example 2 14 00 18 10 84 Comparative experiment example 3 18 5 00 17 10 86 Comparative experiment example 4 10 14 00 83 Comparative experiment example 5 30 14 00 82

[0162] As can be seen from the results in Table 2 above, the negative electrode slurries of Examples 1 and 2 and the lithium secondary batteries using the same, 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 (e.g., 60 or more and 15 or less, respectively), produced little hydrogen gas and exhibited excellent initial discharge capacity and initial efficiency. In contrast, when the Si content of the silicon nanocomposite of Comparative Example 1 was as low as 38 parts by weight, the initial discharge capacity and initial efficiency were low. In addition, Comparative Example 2 is a case where the Si content of the silicon nanocomposite exceeded the target range at 62 parts by weight, and Comparative Example 3 is a case where the XPS C / Si content ratio at etching times of 10 seconds was 8, which was below the target range, and the gas production was large and the initial efficiency and initial discharge capacity were not sufficient. In addition, in Comparative Example 4, the XPS C / Si ratio at an etching time of 1000 seconds was 17, which was 15 or more, which was the target range, and in Comparative Example 5, the oxygen content in the silicon carbon composite was 12 parts by weight, which was 10 parts by weight or more, which was the target range, and the initial discharge capacity and initial efficiency were not sufficient.

Claims

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

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

3. A silicon carbon composite according to claim 1, wherein the average particle diameter D50 of the silicon carbon composite is 1 ㎛ to 20 ㎛.

4. In claim 1, the BET surface area of ​​the silicon carbon composite is 20 m 2 / g or less silicon carbon composite.

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

6. A negative electrode composition according to claim 5, wherein the negative electrode active material further includes a carbon-based active material.

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

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

9. A lithium secondary battery comprising a negative electrode according to claim 8; a separator; and a positive electrode.

10. A battery module including a lithium secondary battery according to claim 9.

11. A battery pack including a lithium secondary battery according to claim 9.

12. A battery pack comprising a battery module according to claim 10.

13. An electric vehicle comprising a battery pack according to claim 12.

14. A method for producing a silicon carbon composite containing silicon and carbon, The content of the silicon is about 40 to 60 parts by weight based on 100 parts by weight of the silicon carbon composite. The content ratio of carbon to silicon (C / Si) was Ta in XPS analysis. 2 O 5 A method for producing a silicon carbon composite, wherein the oxygen content is controlled to be about 30 or more after 10 seconds of etching, and about 15 or less after 1,000 seconds of etching under conditions in which the silicon carbon composite is etched at a rate of 0.15 nm / s, and the oxygen content is controlled to be about 10 parts by weight or less based on 100 parts by weight of the silicon carbon composite.

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

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