Negative electrode slurry, negative electrode, and lithium secondary battery comprising silicon carbon composite

Abstract

The present invention relates to a negative electrode slurry, a negative electrode, a lithium secondary battery, a battery module, and a battery pack comprising: a silicon carbon composite having a pH of 6 to 8 and a silicon content of 40 parts by weight to 60 parts by weight with respect to 100 parts by weight in total of the silicon carbon composite; a cellulose-based binder; and a conductive material.

Description

Negative electrode slurry, negative electrode, and lithium secondary battery containing silicon carbon composite

[0001] This application claims the benefit of Korean Patent Application No. 10-2024-0013211 filed with the Korean Intellectual Property Office on January 29, 2024, the entire contents of which are incorporated herein by reference.

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

[0003] Due to the rapid increase in fossil fuel use, the demand for alternative or clean energy is increasing, and as part of this, the most actively researched field is power generation and storage using electrochemical reactions.

[0004] Secondary batteries are a prime example of electrochemical devices that utilize this electrochemical energy, and their applications are expanding. The 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 nature and high energy density. Accordingly, active research and development efforts are underway to improve the performance of lithium secondary batteries.

[0005] 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.

[0006] Graphite is mainly used as an anode active material in lithium secondary batteries, but because graphite has a low capacity per unit mass of 372 mAh / g, it is difficult to increase the capacity of lithium secondary batteries. Accordingly, non-carbonaceous anode materials with higher energy densities than graphite, such as silicon, tin, and their oxides, are being developed to increase the energy density of lithium secondary batteries. However, these non-carbonaceous anode materials have a large capacity, but low initial efficiency, which causes a large amount of lithium consumption during the initial charge and discharge, and a large irreversible capacity loss.

[0007] [Patent Document]

[0008] (Patent Document 1) Korean Patent Publication No. 10-2022-0089687 A

[0009] While silicon-carbon composites have 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 an anode slurry and an anode comprising a silicon-carbon composite capable of improving the phase stability of the anode slurry. Furthermore, embodiments of the present invention relate to a lithium secondary battery, a battery module, and a battery pack comprising the anode.

[0010] One embodiment of the present invention provides a cathode slurry comprising a silicon carbon composite having a pH of 6 to 8 and a silicon content of 40 to 60 parts by weight based on 100 parts by weight of the total silicon carbon composite; a cellulose-based binder; and a conductive material.

[0011] One embodiment of the present invention provides a cathode slurry in which, when the intensity value of the maximum peak in the 284 to 285.5 eV band region is set to 1 during XPS analysis of the surface of the silicon carbon composite, the intensity value of the maximum peak in the 288 to 289 eV band region is 0.1 or less.

[0012] One embodiment of the present invention provides a negative electrode including 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 slurry.

[0013] One embodiment of the present invention provides a lithium secondary battery including the negative electrode; a separator; and a positive electrode.

[0014] One embodiment of the present invention provides a battery module including the lithium secondary battery.

[0015] One embodiment of the present invention provides a battery pack including the lithium secondary battery.

[0016] One embodiment of the present invention provides a battery pack including the battery module.

[0017] According to one embodiment of the present invention, a negative electrode slurry includes a silicon-carbon composite having a specific pH while containing a specific amount of silicon, so that the change in the molecular weight of the cellulose-based binder due to the interaction between the cellulose-based binder and the negative electrode active material is small, the viscosity of the negative electrode slurry does not decrease, and thus a negative electrode slurry having excellent phase stability can be provided, and a uniform electrode can be manufactured.

[0018] Hereinafter, the present specification will be described in more detail.

[0019] 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.

[0020] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0021] 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.

[0022] 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.

[0023] In this specification, the C content in the negative active material particles can be analyzed using a CS analyzer (Bruker, G8 Galileo), and the O content can be analyzed using an ONH (Bruker, G-4 ICARUS SeriesII) analyzer.

[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). The average particle diameter can be measured using, for example, the laser diffraction method. The laser diffraction method can generally measure particle diameters from the submicron range to several millimeters, and can obtain results with high reproducibility and high resolution.

[0025] The above average particle size can be measured using a Microtrac device (manufacturer: Microtrac model number: S3500) using water and a triton-X100 dispersant. Specifically, the average particle size 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 size 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 the particles in a dispersion medium, the particles can be introduced into a commercially available laser diffraction particle size measuring device, irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, and then a volume cumulative particle size distribution graph can be obtained, and then the particle size corresponding to 50% of the volume cumulative amount can be measured.

[0026] In this specification, the specific surface area of ​​the negative active material particles can be measured by the BET (Brunauer-Emmett-Teller; BET) method. For example, it can be measured by the BET 6-point method using a porosimetry analyzer (Bell Japan Inc, Belsorp-±) and a nitrogen gas adsorption flow method.

[0027]

[0028] < Cathode slurry >

[0029] According to one embodiment of the present invention, a cathode slurry comprises a silicon carbon composite having a pH of 6 to 8 and a silicon content of 40 to 60 parts by weight based on 100 parts by weight of the total silicon carbon composite; a cellulose-based binder; and a conductive material.

[0030] The pH of the silicon carbon composite is 6 to 8. For example, the lower pH limit of the silicon carbon composite is 6, 6.1, 6.2, 6.3, 6.4, or 6.5, and the upper pH limit of the silicon carbon composite is 8, 7.9, 7.8, 7.7, or 7.6. When the pH of the silicon carbon composite is 6 to 8, the change in molecular weight due to the interaction between the binder and the negative electrode active material is small, the viscosity of the negative electrode slurry does not decrease, and a stable slurry can be manufactured. The pH of the silicon carbon composite can be measured by dispersing 10 g of the silicon carbon composite in 100 g of water.

[0031] The process for manufacturing the above silicon-carbon composite can be manufactured through various methods. For example, it can be manufactured through a step of manufacturing a carbon scaffold, a step of heat-treating with silane gas to grow silicon within the carbon, and a step of external surface treatment as needed. Furthermore, the pH of the silicon-carbon composite can vary depending on the raw materials, heat-treating atmosphere, or temperature used in each step. For example, a method of heat-treating by mixing butane gas and CO2, or a method of heat-treating by mixing butane gas and ammonia gas, can be mentioned.

[0032] In the case of the vapor deposition method, which is a general method for manufacturing the above silicon-carbon composite, a change in pH may occur due to oxidation or reduction reactions of the silicon-carbon composite itself even in a process that uses a solution, without using a solution. Therefore, the pH of the process solution and the pH of the silicon-carbon composite during the manufacturing process of the silicon-carbon composite are distinguished. The pH of the silicon-carbon composite can be measured by dispersing the silicon-carbon composite in water.

[0033] The pH of the above silicon-carbon composite varies depending on the degree of oxidation of the silicon-carbon composite, that is, the surface functional groups of carbon and the degree of oxidation of silicon. For example, if the pH of the silicon-carbon composite is 6, the amount of acidic functional groups is not large. As an example, the degree of oxidation of carbon is determined by the conditions of the manufacturing process of the silicon-carbon composite. Specifically, when the polymer resin is carbonized at high temperature, graphite without functional groups is more than neutral, but if the temperature is low, oxygen exists in some of the carbon. Alternatively, when the polymer resin is carbonized at high temperature under CO2 or water vapor instead of an inert atmosphere, the amount of oxygen in the carbon increases. In addition, the degree of oxidation of silicon varies depending on the temperature and atmosphere of the carbonization process. When the polymer resin is carbonized at high temperature under CO2 or water vapor instead of an inert atmosphere, some silicon is also oxidized.

[0034] Cellulosic binders such as CMC act as thickeners in the negative electrode slurry and are important in controlling the phase stability, i.e., viscosity, of the slurry. The molecular weight of the cellulose binder such as CMC tends to decrease due to the acidic functional groups of the silicon-carbon composite, which may lead to a decrease in the viscosity of the negative electrode slurry. If a decrease in the viscosity of the negative electrode slurry occurs, it may cause quality and production defects during coating, which may significantly affect the overall yield. Therefore, this can be controlled by selecting a method of covering the acidic portion of the silicon-carbon composite, for example, the portion containing the acidic functional group, with a carbon coating. That is, this phenomenon can be controlled depending on the amount or quality of the carbon coating, and this can be confirmed through the pH of the negative electrode slurry, the initial capacity and efficiency of the electrode, or XPS analysis, etc.

[0035] The silicon content in the silicon-carbon composite 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 40 parts by weight or more, the initial capacity is excellent, making it easy to increase the capacity of the electrode, and when the silicon content is 60 parts by weight or less, it is possible to manufacture a composite having a uniform silicon distribution. The silicon content in the silicon-carbon composite is obtained by calculating the C content and O content of the silicon-carbon composite, respectively, and then reversely calculating the silicon content. The C content can be analyzed using a CS analyzer (Bruker, G8 Galileo), and the O content can be analyzed using an ONH (Bruker, G-4 ICARUS SeriesII) analyzer.

[0036] According to one embodiment of the present invention, the content of O (oxygen) in the silicon carbon composite is 10 parts by weight or less based on 100 parts by weight of the total silicon carbon composite. Specifically, the content of oxygen in the silicon carbon composite is 10 parts by weight or less, 9 parts by weight or less, 8 parts by weight or less, 7 parts by weight or less, 6 parts by weight or less, or 5 parts by weight or less, and 0 parts by weight or more, 1 part by weight or more, 1.5 parts by weight or more, 1.6 parts by weight or more, 1.7 parts by weight or more, or 1.8 parts by weight or more. When the content of oxygen is 10 parts by weight or less based on 100 parts by weight of the silicon carbon composite, the capacity efficiency of the silicon carbon composite is excellent.

[0037] For example, 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.

[0038] 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 pyrolyzing a polymer to manufacture a porous carbon structure, 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 a Si-containing SiOx oxide (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.

[0039] According to one embodiment of the present invention, when the intensity value of the maximum peak in the 284 to 285.5 eV band region is set to 1 during XPS analysis of the surface of the silicon carbon composite, the intensity value of the maximum peak in the 288 to 289 eV band region is 0.1 or less. During the XPS analysis, the 284 to 289 band region includes -OH, C=O, and -COOH regions, and in this case, it may affect a decomposition reaction due to interaction with a cellulose-based binder.

[0040] In XPS analysis, the maximum peak intensity value refers to the maximum height of the peak, and refers to the maximum peak intensity value within a specific range regardless of whether the peaks overlap.

[0041] Specifically, when the intensity value of the maximum peak in the 284 to 285.5 eV band region is set to 1 during XPS analysis of the surface of the silicon carbon composite, the intensity value of the maximum peak in the 288 to 289 eV band region may be 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, 0.05 or less, 0.04 or less, or 0.03 or less. When the intensity value of the maximum peak in the 288 to 289 eV band region satisfies the above range, the decomposition reaction is suppressed by the interaction between the silicon carbon composite surface functional group and the cellulose-based binder, thereby suppressing the decrease in viscosity of the cellulose-based binder. Here, the XPS analysis may be performed under the following conditions.

[0042] - Equipment used: NEXSA G2, Thermo Fisher Scientific (Equipment name ESCA-03)

[0043] - Sample preparation: Press the powdered sample into the powder holder and make the measurement surface flat.

[0044] - Measurement conditions:

[0045] X-ray source: Monochromated Al Kα (1486.6 eV)

[0046] X-ray spot size: 400 ㎛

[0047] Etching conditions (sputtering gun): monatomic Ar (energy: 1,000 eV, current: low, raster width: 2 mm), 0.13 nm / s etching rate (based on Ta2O5, may vary depending on the sample)

[0048] Charge compensation (flood gun): 0.3 V, 150 ㎂

[0049] Survey scan: pass energy 200 eV, energy step 1 eV

[0050] Narrow scan: pass energy 50 eV, energy step 0.1 eV

[0051] Sensitivity factor (SF): Al THERMO1, Energy correction factor (ECF): TPP-2MBackground subtraction" Smart

[0052] The plasmon loss peak of Si is not included in the quantitative analysis.

[0053]

[0054] According to one embodiment of the present invention, the silicon carbon composite may include a carbon layer provided on at least a portion of the surface.

[0055] According to one embodiment of the present invention, the content of the carbon layer is 0.1 to 50 parts by weight based on 100 parts by weight of the total silicon carbon composite. Specifically, the carbon layer may be included in an amount of 0.1 to 30 parts by weight, 0.1 to 20 parts by weight, 0.5 to 15 parts by weight, or 1 to 10 parts by weight based on 100 parts by weight of the total silicon carbon composite.

[0056] When the above range is satisfied, the conductivity of the silicon carbon composite is improved, and the volume change of the silicon carbon composite during charging and discharging of the battery is easily suppressed, so that the life characteristics of the battery can be improved.

[0057] The above carbon layer can be formed by a chemical vapor deposition (CVD) method using at least one hydrocarbon gas selected from the group consisting of methane, ethane, propane, butane, and acetylene.

[0058] The above carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0059] The crystalline carbon can further improve the conductivity of the silicon carbon composite. The crystalline carbon can include at least one selected from the group consisting of fluorene, carbon nanotubes, and graphene.

[0060] The amorphous carbon can appropriately maintain the strength of the carbon layer, thereby suppressing expansion of the silicon-carbon composite. The amorphous carbon can be a carbon-based material formed using at least one carbide or hydrocarbon selected from the group consisting of tar, pitch, and other organic materials as a source for chemical vapor deposition.

[0061] The above-mentioned other organic carbonates may be carbonates of organic carbonates selected from sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or kedohexose and combinations thereof.

[0062] The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane, etc. The aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon may be benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, or phenanthrene, etc.

[0063] 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 average particle diameter of the silicon carbon composite is within the above range, the dispersibility of the active material is appropriate when preparing the slurry, the structural stability of the active material is ensured during charge and discharge, and the problem of coating defects due to large particles during electrode coating is reduced. In addition, the problem of the level of volume expansion / contraction also increasing as the particle diameter becomes excessively large can be prevented, and the problem of the initial efficiency decreasing as the particle diameter becomes excessively small can be prevented.

[0064] According to one embodiment of the present invention, 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 adsorption / desorption of nitrogen gas at 77K using BET measuring equipment (BEL-SORP-MAX, Nippon Bell).

[0065] The above negative electrode binder can play a role in improving the adhesion between negative electrode active material particles and the adhesive strength between the negative electrode active material particles and the negative electrode current collector.

[0066] According to one embodiment of the present invention, the negative electrode binder is a cellulose-based binder, and may include, for example, at least one selected from the group consisting of carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose, and may also include various copolymers thereof, or polymers having derivative structures. When the cellulose-based binder is used together with a silicon-carbon composite having a pH of 6 to 8 and a silicon content of 40 to 60 parts by weight based on 100 parts by weight of the total silicon-carbon composite, slurry phase stability is maintained and high-capacity electrode production is possible.

[0067] The above-mentioned negative electrode binder may be included in an amount of 0.5 to 20 parts by weight, specifically 1 to 15 parts by weight, based on 100 parts by weight of the total solid content of the above-mentioned negative electrode slurry.

[0068] 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.

[0069] The above-mentioned 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 slurry.

[0070] The above negative electrode slurry may further include an additional negative electrode active material.

[0071] 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.

[0072] In addition, low-crystalline carbon and high-crystalline carbon can be used as carbonaceous materials. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical or fibrous materials, 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.

[0073] According to one embodiment of the present invention, a negative electrode slurry further comprising a carbon-based active material is provided. That is, the additional negative electrode active material may be a carbon-based active material, for example, graphite, specifically, at least one of artificial graphite and natural graphite.

[0074] The weight ratio of the negative electrode active material and the additional negative electrode active material included in the above negative electrode slurry 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.

[0075] The total negative electrode active material included in the above negative electrode slurry 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 above negative electrode slurry.

[0076] The above cathode slurry may further include a thickener. The thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and any thickener used in the present technical field may be appropriately employed.

[0077] The above thickener may be included in an amount of 0.5 to 20 parts by weight, specifically 0.5 to 15 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0078] The above-described cathode slurry may further include a solvent for forming the cathode slurry. Specifically, the solvent for forming the cathode slurry 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.

[0079] In one embodiment of the present invention, the solid content weight of the cathode slurry 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 slurry.

[0080]

[0081] < Negative >

[0082] 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 slurry.

[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 negative electrode active material layer can be formed by applying a negative electrode slurry containing 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.

[0085]

[0086] <Lithium secondary battery>

[0087] 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. Since the anode has been described above, a detailed description thereof will be omitted.

[0088] 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.

[0089] 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 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0090] 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 c3Lithium 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.

[0091] 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.

[0092] 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.

[0093] In addition, the positive electrode binder plays a role of 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 include polyvinylidene fluoride (PVDF), polyvinylidene 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.

[0094] The positive electrode and the negative electrode can be manufactured according to a conventional method for manufacturing positive and negative electrodes, except that the positive and negative electrode active materials described above are used. Specifically, the slurry for forming an active material layer, which includes the active material and optionally a binder and a conductive material, is applied to a current collector, followed by drying and rolling. At this time, the types and contents of the positive and negative electrode active materials, binder, and conductive material are as described above. The solvent may be a solvent generally used in the relevant technical field, and examples thereof include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and water. One type alone or a mixture of two or more types thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the active material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity during subsequent coating for manufacturing the positive and negative electrodes. Additionally, in another method, the positive and negative electrodes may be manufactured by casting the slurry for forming the active material layer on a separate support, then peeling the film from the support and laminating the resulting film on a current collector.

[0095] The above separator separates the negative electrode and the positive electrode 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 having 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 an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0096] The above electrolyte may include, but is 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.

[0097] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] According to one embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell, a battery pack including the same, and a battery pack including the battery module are provided. The battery module and the battery pack include the lithium secondary battery having a 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.

[0103] 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.

[0104] < Manufacture of Silicon Carbon Composites >

[0105] Example 1-1

[0106] Specific surface area 1850 ~ 1900 m 2 / g, pore volume 0.80~0.85 cm 3 / g of an amorphous porous carbon scaffold 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 400 to 550°C at 10°C / min, and then the flow rates of silane gas and hydrogen gas were varied so that the silicon content was 48 parts by weight based on 100 parts by weight of the silicon carbon composite, and the furnace was maintained for 30 to 90 minutes. Additionally, the furnace temperature was increased from 780 to 900°C at 10°C / min, and then the flow rates of butane gas were varied so that the furnace was maintained for 30 to 60 minutes, thereby producing a silicon carbon composite having the characteristics shown in Table 1.

[0107]

[0108] Example 1-2

[0109] The same procedure as Example 1-1 was followed, except that the flow rate of silane gas was increased so that the silicon content in the silicon carbon composite was 51 parts by weight.

[0110]

[0111] Example 1-3

[0112] The process of manufacturing a silicon carbon composite was carried out in the same manner as in Example 1-1, except that the flow rate of silane gas was increased so that the silicon content was 49 parts by weight, and butane gas and CO2 were mixed and heat treated in the final stage of retaining butane gas.

[0113]

[0114] Comparative Example 1-1

[0115] The same procedure as Example 1-1 was followed, except that the final step of retaining butane gas was omitted during the silicon carbon composite manufacturing process.

[0116]

[0117] Comparative Example 1-2

[0118] The process of manufacturing a silicon carbon composite was carried out in the same manner as in Example 1-1, except that butane gas and ammonia gas were mixed and heat treated in the final step of retaining butane gas.

[0119]

[0120] Comparative Example 1-3

[0121] The same procedure as Example 1-1 was followed, except that the first heating temperature was lowered so that the silicon content in the silicon carbon composite was 37 parts by weight, and the flow rate and residence time of silane gas were reduced.

[0122]

[0123] Comparative Example 1-4

[0124] The same procedure as Example 1-1 was followed, except that the first heating temperature was lowered so that the silicon content in the silicon carbon composite was 62 parts by weight and the flow rate and residence time of silane gas were increased.

[0125]

[0126] < Evaluation 1: Measurement of the content of each component of the silicon carbon composite >

[0127] The pH, silicon content, and O (oxygen) content 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.

[0128] - pH:

[0129] After adding 10 g of silicon carbon composite to 100 g of aqueous solution and mixing with a homo mixer for 1 hour, the pH of the dispersion was measured.

[0130] - Silicon content:

[0131] The silicon content was calculated by estimating the weight excluding the C content analyzed by a CS analyzer (Bruker, G8 Galileo) and the O content analyzed by an ONH (Bruker, G-4 ICARUS SeriesII).

[0132] - O(oxygen) content:

[0133] O content was analyzed using an ONH (Bruker, G-4 ICARUS SeriesII) analyzer.

[0134]

[0135] < Evaluation 2: XPS analysis of the surface of the silicon carbon composite >

[0136] XPS analysis can be performed under the following conditions.

[0137] - Equipment used: NEXSA G2, Thermo Fisher Scientific (Equipment name ESCA-03)

[0138] - Sample preparation: Press the powdered sample into the powder holder and make the measurement surface flat.

[0139] - Measurement conditions:

[0140] X-ray source: Monochromated Al Kα (1486.6 eV)

[0141] Etching conditions (sputtering gun): monatomic Ar (energy: 1,000 eV, current: low, raster width: 2 mm), 0.13 nm / s etching rate (based on Ta2O5, may vary depending on the sample)

[0142] Charge compensation (flood gun): 0.3 V, 150 ㎂

[0143] Survey scan: pass energy 200 eV, energy step 1 eV

[0144] Narrow scan: pass energy 50 eV, energy step 0.1 eV

[0145] Sensitivity factor (SF): Al THERMO1, Energy correction factor (ECF): TPP-2MBackground subtraction" Smart

[0146]

[0147] When the intensity value of the maximum peak in the 284 to 285.5 eV band region was set to 1 during XPS analysis of the surface of the silicon carbon composite, the intensity value (maximum peak intensity value ratio) of the maximum peak in the 288 to 289 eV band region is shown in Table 1 below.

[0148]

[0149] pH Silicon content (based on 100 parts by weight of silicon-carbon composite) Oxygen content (based on 100 parts by weight of silicon-carbon composite) Ratio of intensity values ​​of maximum peak Example 1-16.8481.70.02 Example 1-27.6511.80.01 Example 1-36.649120.03 Comparative Example 1-15.3482.70.16 Comparative Example 1-210.3482.90.06 Comparative Example 1-36.8371.50.01 Comparative Example 1-45.6623.50.15

[0150]

[0151] < Manufacture of cathode slurry >

[0152] Example 2-1

[0153] The silicon carbon composite manufactured in Example 1-1 was used as the negative active material, two types of particle-type conductive material (SFG6L) and SWCNT (product name: Tuball OCSiAl) were used as the conductive material, and an aqueous binder (product name: Daicel 2200) was used as the cellulose-based binder. The negative active material: particle-type conductive material: SWCNT: cellulose-based binder were mixed in a ratio of 81:8.6:0.8:9.6 (based on weight ratio) to prepare a negative electrode composition, and water was added as a solvent to prepare a negative electrode slurry.

[0154]

[0155] Example 2-2

[0156] The same procedure as Example 2-1 was followed, except that the silicon carbon composite of Example 1-2 was used instead of the silicon carbon composite of Example 1-1.

[0157]

[0158] Example 2-3

[0159] The same procedure as Example 2-1 was followed, except that the silicon carbon composite of Example 1-3 was used instead of the silicon carbon composite of Example 1-1.

[0160]

[0161] Comparative Examples 2-1 to 2-4

[0162] The same procedure as Example 2-1 was followed, except that the silicon carbon composites of Comparative Examples 1-1 to 1-4 were used instead of the silicon carbon composite of Example 1-1.

[0163]

[0164] < Evaluation 3: Measurement of phase stability (viscosity change) of cathode slurry >

[0165] Using a TA rheometer, the shear viscosity was set to shear rat=2.5, and the viscosity after manufacturing the cathode slurry and the viscosity after 24 hours of standing were measured to measure the viscosity reduction rate compared to the initial viscosity.

[0166]

[0167] < Evaluation 4: Battery Manufacturing and Battery Characteristics Evaluation >

[0168] 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.

[0169] The above cathode, anode, separator, and electrolyte were sealed in a stainless steel container to manufacture a coin cell for evaluation with a thickness of 2 mm and a diameter of 32 mm.

[0170] The above coin cell was charged at a constant current of 0.05 C until the voltage reached 0.01 V, and then discharged at a constant current of 0.05 C until the voltage reached 1.0 V to confirm the discharge capacity and initial efficiency. The results are shown in Table 2 below.

[0171] Based on the results of one charge / discharge cycle, the initial efficiency (%) was derived using the following calculation formula.

[0172] Initial efficiency (%) = {Discharge capacity of negative active material (mAh / g) / Charge capacity of negative active material (mAh / g)}Х100

[0173]

[0174] Slurry phase stabilityViscosity reduction rate (%)Intensity value of maximum peakInitial efficiency (%)Initial discharge capacity (mAh / g)Example 2-150.03891850Example 2-220.01881900Example 2-320.02841500Comparative example 2-1800.16851730Comparative example 2-2700.03851720Comparative example 2-350.01881230Comparative example 2-4840.15841890

[0175]

[0176] According to Table 2 above, in the case of Comparative Example 2-1, when a negative electrode slurry was prepared using a silicon carbon composite (Comparative Example 1-1) that did not include a carbon layer and had a pH of less than 6 (pH 5.3), it was confirmed that the molecular weight of the cellulose-based binder changed significantly due to the interaction between the negative electrode binder and the negative electrode active material, and the viscosity of the negative electrode composition was greatly reduced due to the decrease in the viscosity of the binder.

[0177] In the case of Comparative Example 2-2, when a negative electrode slurry was manufactured using a silicon carbon composite (Comparative Example 1-2) having a pH exceeding 8 (pH 10.3), it was confirmed that the molecular weight of the cellulose-based binder changed significantly due to the interaction between the negative electrode binder and the negative electrode active material, and that the viscosity of the negative electrode slurry was significantly reduced due to the decrease in the viscosity of the binder.

[0178] In the case of Comparative Example 2-3, a silicon carbon composite (Comparative Example 1-3) having a silicon content of less than 40 parts by weight (37 parts by weight) was used to manufacture a cathode slurry, and it was confirmed that the initial capacity was insufficient, making it difficult to increase the capacity of the electrode.

[0179] In the case of Comparative Example 2-4, when a negative electrode slurry was manufactured using a silicon carbon composite (Comparative Example 1-4) having a silicon content exceeding 60 parts by weight (62 parts by weight), it was confirmed that the molecular weight of the cellulose-based binder changed significantly due to the interaction between the negative electrode binder and the negative electrode active material, gas was generated severely due to the oxidation reaction of silicon during the manufacture of the negative electrode slurry, the viscosity of the negative electrode slurry was greatly reduced, and it was not easy to increase the electrode capacity compared to the increase in the silicon content.

[0180] In the case of Example 2-3, when a negative electrode slurry was prepared using a silicon carbon composite (Example 1-3) having a pH of 6 to 8 (pH 6.6) and a silicon content of 40 to 60 parts by weight (51 parts by weight), the change in the molecular weight of the cellulose-based binder due to the interaction between the negative electrode binder and the negative electrode active material was small, and the viscosity reduction rate of the negative electrode slurry was small. However, it was confirmed that the lithium availability loss increased and the initial efficiency of the electrode decreased as the content of O (oxygen) exceeded 10 parts by weight (12 parts by weight) based on 100 parts by weight of the total silicon carbon composite.

Claims

1. A cathode slurry comprising a silicon carbon composite having a pH of 6 to 8 and a silicon content of 40 to 60 parts by weight based on 100 parts by weight of the total silicon carbon composite; a cellulose-based binder; and a conductive material.

2. In claim 1, a cathode slurry characterized in that when the intensity value of the maximum peak in the 284 to 285.5 eV band region is set to 1 during XPS analysis of the surface of the silicon carbon composite, the intensity value of the maximum peak in the 288 to 289 eV band region is 0.1 or less.

3. A cathode slurry according to claim 1, wherein the content of O (oxygen) in the silicon carbon composite is 10 parts by weight or less based on 100 parts by weight of the total silicon carbon composite.

4. In claim 1, the silicon carbon composite is a cathode slurry comprising a carbon layer provided on at least a portion of the surface.

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

6. In claim 1, the specific surface area of the silicon carbon composite is 20 m 2 / g or less cathode slurry.

7. In claim 1, a negative electrode slurry further comprising a carbon-based active material.

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 slurry according to any one of claims 1 to 7.

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 comprising a lithium secondary battery according to claim 9.

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