Silicon carbon composite, anode active material, anode, and secondary battery

Abstract

The present invention relates to a silicon carbon composite, an anode active material comprising same, an anode composition, an anode, a lithium secondary battery, a battery module, and a battery pack, wherein, in a Si2p spectrum obtained by XPS analysis, a ratio of the intensity of Six(0<x≤4) present at 100.5-105 eV to the intensity of a Si0 peak present at 99-100.5 eV is 0.1 to 0.9.

Description

Silicon carbon composites, negative electrode active materials, negative electrodes and secondary batteries

[0001] This application claims the benefit of Korean Patent Application No. 10-2024-0109007, filed with the Korean Intellectual Property Office on August 14, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a silicon carbon composite, a negative electrode active material including the same, a negative electrode including the negative electrode active material, and a secondary battery including the negative electrode.

[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. In particular, lithium secondary batteries, with their lightweight design and high energy density, are attracting significant attention as power sources for electronic devices. Accordingly, active research and development efforts are underway to improve the performance of lithium secondary batteries.

[0004] In general, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, an organic solvent, etc. In addition, an active material layer including a positive electrode active material and a negative electrode active material may be formed on a current collector on the positive electrode and the negative electrode, respectively. In general, a lithium-containing metal oxide such as LiCoO2 or LiMn2O4 is used as a positive electrode active material for the positive electrode, and a carbon-based active material or a silicon-based active material that does not contain lithium is used as an negative electrode active material for the negative electrode.

[0005] Batteries using graphite as a negative active material can exhibit a high discharge voltage of 3.6 V, but their low capacity limits their ability to increase energy density.

[0006] On the other hand, silicon-based active materials are attracting attention as next-generation cathode active materials due to their high capacity and efficiency. Therefore, the development of silicon-based active materials with high capacity or efficiency characteristics is required.

[0007] One embodiment of the present invention provides a silicon carbon composite, an anode active material, an anode, and a lithium secondary battery that have excellent capacity and / or efficiency characteristics and can be used as a high-energy-density anode active material.

[0008] Si obtained by XPS analysis of the present invention 2p In the spectrum, Si exists between 99 eV and 100.5 eV. 0 Si present at 100.5 eV to 105 eV compared to the intensity of the peak x (0 <x≤4) 피크의 강도의 비가 0.1 내지 0.9인 실리콘 카본 복합체를 제공한다.

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

[0010] One embodiment of the present invention provides a negative electrode composition comprising a negative electrode active material according to the above-described embodiment.

[0011] One embodiment of the present invention provides a cathode comprising a cathode composition according to the above-described embodiment.

[0012] One embodiment of the present invention provides a lithium secondary battery including a negative electrode, a positive electrode, and a separator according to the above-described embodiment.

[0013] One embodiment of the present invention provides a battery module including a lithium secondary battery according to the above-described embodiment.

[0014] One embodiment of the present invention provides a battery pack including a lithium secondary battery according to the above-described embodiment.

[0015] One embodiment of the present invention provides a battery pack including a battery module according to the above-described embodiment.

[0016] According to embodiments of the present invention, a lithium secondary battery with improved capacity and / or efficiency can be provided by using a silicon-carbon composite having a specific ratio of peaks within a specific range during XPS analysis as an anode active material. Furthermore, by satisfying the above range, problems with process suitability and gas generation of aqueous binders, which occur when using silicon-based active materials, can be improved.

[0017] Figure 1 shows the Si that appears when the silicon carbon composite of Example 1 is analyzed by XPS. 2p It shows a graph of the spectrum and the spectrum separated by Gaussian fitting.

[0018] Figure 2 shows the Si that appears when the silicon carbon composite of Example 2 is analyzed by XPS. 2p It shows a graph of the spectrum and the spectrum separated by Gaussian fitting.

[0019] Figure 3 shows the Si that appears when the silicon carbon composite of Example 3 is analyzed by XPS. 2p It shows a graph of the spectrum and the spectrum separated by Gaussian fitting.

[0020] Figure 4 shows the Si that appears when the silicon carbon composite of Example 4 is analyzed by XPS. 2p It shows a graph of the spectrum and the spectrum separated by Gaussian fitting.

[0021] Figure 5 shows the Si that appears when the silicon carbon composite of Comparative Example 1 is analyzed by XPS. 2p It shows a graph of the spectrum and the spectrum separated by Gaussian fitting.

[0022] Figure 6 shows the Si that appears when the silicon carbon composite of Comparative Example 2 is analyzed by XPS. 2pIt shows a graph of the spectrum and the spectrum separated by Gaussian fitting.

[0023] Figure 7 shows the Si that appears when the silicon carbon composite of Comparative Example 3 is analyzed by XPS. 2p It shows a graph of the spectrum and the spectrum separated by Gaussian fitting.

[0024] Figure 8 shows the Si that appears when the silicon carbon composite of Comparative Example 4 is analyzed by XPS. 2p It shows a graph of the spectrum and the spectrum separated by Gaussian fitting.

[0025] Figure 9 shows the Si that appears when the silicon carbon composite of Comparative Example 5 is analyzed by XPS. 2p It shows a graph of the spectrum and the spectrum separated by Gaussian fitting.

[0026] Figure 10 shows the Si that appears when the silicon carbon composite of Comparative Example 6 is analyzed by XPS. 2p It shows a graph of the spectrum and the spectrum separated by Gaussian fitting.

[0027] Figure 11 shows the Si that appears when the silicon carbon composite of Comparative Example 7 is analyzed by XPS. 2p It represents the spectrum.

[0028] Hereinafter, the present invention will be described in more detail to facilitate understanding. The present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0029] It should be understood that the terms “include,” “comprising,” or “having” used in this specification are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0030] Furthermore, when we say that a part of a layer or the like is "above" or "on" another part, this includes not only cases where it is "directly above" that part, but also cases where there is another part in between. Conversely, when we say that a part is "directly above" another part, it means that there is no other part in between. Furthermore, when we say that a part is "above" or "on" a reference part, it means that it is located above or below that reference part, and does not necessarily mean that it is located "above" or "on" in the direction opposite to gravity.

[0031] 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.

[0032] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0033] 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.

[0034] In this specification, X-ray photoelectron spectroscopy (XPS) is a technique for analyzing the surface chemical composition of a material. It measures the binding energy of photoelectrons emitted from surface atoms by irradiating the sample surface with high-energy X-rays. This enables qualitative and quantitative analysis of elements, and identifies the chemical state and environment of each element.

[0035] In this specification, Si obtained through XPS analysis 2p The spectrum detects photoelectrons emitted from the 2p orbital of silicon atoms, which allows the oxidation state of silicon present on the surface of the negative active material to be identified.

[0036] In this specification, XPS analysis is performed under the following conditions.

[0037] <XPS 분석 조건>

[0038] - X-ray source: Monochromated Al K α (1486.6 eV)

[0039] - X-ray spot size: 400 ㎛

[0040] - Sputtering gun: Monatomic Ar (energy: 1000 eV, current: low, raster width: 2mm)

[0041] - Etching rate: 0.09 nm / s for Ta2O5

[0042] - Operation Mode: CAE (Constant Analyzer Energy) mode

[0043] - Survey scan: pass energy 200 eV, energy step 1 eV

[0044] - Narrow scan: scanned mode, pass energy 50 eV, energy step 0.1 eV

[0045] - Charge compensation: 0.1V 150μA

[0046] - SF: Al THERMO1

[0047] - ECF: TPP-2M

[0048] - BG subtraction: Smart

[0049] In one embodiment of the present invention, the depth profile of the X-ray photoelectron spectroscopy (XPS) can be measured at 0.09 nm / s for up to 3000 seconds under an X-ray source of monochromated Al K α.

[0050] In this specification, the intensity of the peak refers to Si obtained through XPS analysis. 2p It refers to the value obtained by integrating the area under the Gaussian function graph obtained after deconvolving the spectrum by peak and fitting it with the 'Gaussan / Lorentzian' model.

[0051] In this specification, peaks may overlap and appear as shoulder peaks, and two or more peaks may coexist.

[0052] In this specification, when peaks overlap or coexist, the intensity of the corresponding peak is calculated as the sum of the intensities of two or more peaks when calculating the intensity.

[0053] A silicon carbon composite according to one embodiment of the present invention is obtained by XPS analysis. 2p In the spectrum, Si exists between 99 eV and 100.5 eV. 0 Si present at 100.5 eV to 105 eV compared to the intensity of the peak x (0 <x≤4) 피크의 강도의 비가 0.1 내지 0.9인 것을 특징으로 한다.

[0054] A silicon carbon composite according to one embodiment of the present invention is Si 0 The peak may exist between 99 eV and 100 eV.

[0055] The silicon carbon composite according to one embodiment of the present invention may have a ratio of the intensity of the peaks of 0.1 or more, 0.15 or more, 0.19 or more, and 0.9 or less, 0.7 or less, or 0.6 or less.

[0056] In this specification Si 0 and Si x (0 <x≤4)에서 0 또는 x는 Si의 산화 상태를 의미한다. Si 0 It refers to a state in which pure silicon is bonded to itself, and the Si atoms are not bonded to other atoms. Si x (0 <x≤4)에서 x는 실리콘 원자가 다른 원자, 예컨대 O 와 결합한 상태를 나타내며, 예를 들어 SiO2에서는 결정 구조 상 실리콘 원자 하나에 산소 원자 4개가 결합하였으므로 Si 4 can be expressed as

[0057] If the ratio is below the above range, the ratio of pure Si on the surface of the silicon carbon composite may be too high, which may result in a large volume change during charge and discharge, which may cause a decrease in life and capacity, and the possibility of side reactions with the aqueous binder may increase, which may worsen the aqueous processability. On the other hand, if the ratio exceeds the above range, the number of Si phases combined with oxygen on the surface of the negative active material increases, which may result in a large number of irreversible phases being generated during lithium insertion, resulting in low charge and discharge efficiency.

[0058] According to one embodiment, the silicon-carbon composite is a composite of Si and C, wherein Si and C (e.g., graphite) are present respectively. In the present specification, the silicon-carbon composite may be expressed as Si / C. The silicon-carbon composite may be composed of Si and C that are not bonded to each other, but may include additional components as needed. For example, the silicon-carbon composite may or may not include silicon carbide, expressed as SiC. When the silicon-carbon composite includes silicon carbide, the content thereof is 3 wt% or less. The silicon-carbon composite may exist in a crystalline, amorphous, or mixed state thereof. According to one example, C in the silicon-carbon composite may exist in an amorphous state.

[0059] According to one embodiment, the silicon carbon composite may be a porous carbon particle and a particle having silicon provided on at least a portion of the interior and surface of the porous carbon particle; or a porous silicon particle and a particle having carbon provided on at least a portion of the interior and surface of the porous silicon particle.

[0060] According to one embodiment, the silicon-carbon composite is a particle having porous carbon particles and silicon provided on at least a portion of the interior and surface of the porous carbon particles. The silicon can be formed by depositing silicon on the porous carbon particles using silane gas. If necessary, a carbon layer can be further formed on the surface of the silicon-carbon composite. By the carbon layer, the conductivity is provided, and the initial efficiency, life characteristics, and battery capacity characteristics of the secondary battery can be improved. The total weight of the carbon layer can be comprised in an amount of 2 wt% to 10 wt% based on a total of 100 wt% of the silicon-carbon composite particles. The carbon layer can include at least one of amorphous carbon and crystalline carbon.

[0061] According to one embodiment, the silicon-carbon composite may be a porous silicon particle and a particle having carbon provided on at least a portion of the interior and surface of the porous silicon particle. This may be formed by etching silicon oxide to form a porous silicon particle, such as a Si matrix, and then coating carbon. The description of the carbon layer described above may be applied to the carbon.

[0062] In one embodiment of the present specification, in order to satisfy the above peak ratio in a silicon carbon composite material by depositing silicon on porous carbon, a method of oxidizing the surface after silicon deposition and D 50 This can be done by at least one of two methods of controlling the particle size by classifying it to 5 to 15㎛.

[0063] For example, a step of placing carbon powder into a tubular furnace, flowing nitrogen gas to create an inert atmosphere, gradually increasing the temperature to heat at a temperature of 300°C to 500°C, and then gradually increasing the temperature again to heat at a temperature of 800°C to 1000°C can be performed.

[0064] Afterwards, the obtained powder is mixed with an acid solvent and centrifuged to obtain a precipitate. The obtained powder is neutralized in an alkaline solvent and then dried to obtain a porous carbon structure. At this time, the temperature at which the carbon particles are heated in the alkaline solvent may be 700°C to 900°C.

[0065] The above porous carbon structure can be placed in a horizontal furnace and SiH4 / He gas can be flowed at 600°C to 800°C to obtain a silicon carbon composite.

[0066] The method may further include a step of placing the silicon carbon composite obtained through the above process into an electric furnace and flowing oxygen gas at 300°C to 500°C to form an oxide layer.

[0067] The method may further include a step of placing the silicon carbon composite obtained through the above process into an electric furnace, heat-treating it, and then flowing hydrocarbon gas at 600°C to 800°C to form a carbon layer.

[0068] In one embodiment of the present specification, in the case of a method of complexing carbon into porous silicon, in order to satisfy the peak ratio, at least one of a method of lowering the heat treatment temperature for the disproportionation reaction and a method of lowering the temperature during the acid treatment process can be performed.

[0069] For example, silicon powder can be placed in a horizontal tube, argon gas can be flowed to create an inert atmosphere, and then the temperature can be gradually increased to induce a disproportionation reaction. The heat treatment temperature can be 500°C to 1100°C, and specifically 650°C to 950°C.

[0070] After this, the heat-treated SiO xAfter removing it from the tube, it can be placed in an HF solvent at 20°C to 60°C, and then treated with acid while lowering the temperature to 0°C to 10°C using a circulator, followed by stirring to remove the SiO2 phase.

[0071] After drying the porous silicon obtained above, a carbon layer can be formed by chemical vapor deposition (CVD) using a hydrocarbon gas at 550°C to 850°C. The hydrocarbon gas can be at least one hydrocarbon gas selected from the group consisting of methane, ethane, propane, and acetylene.

[0072] If the above deposition / coating temperature is lower than the above range, silicon carbide is not formed, resulting in poor aqueous slurry processability.

[0073] According to one embodiment, the silicon carbon composite has a surface area of ​​0.5 to 10 m by the BET method. 2 / g, and the pore volume can be 0.005 to 0.03 cm 3 / g, and the pore size by the BET method may be 1 to 20 nm. The silicon carbon composite has a pore volume of 0.005 to 0.03 cm as measured by the mercury penetration method. 3 / g could be.

[0074] According to one embodiment, the silicon carbon composite is D 90 The particle size can be 5 to 15 ㎛, D 50 The particle size can be 1 to 10 ㎛, D min This 1 to 3 μm, D max may be 17 to 23 ㎛. In this specification, the average particle diameter (D 50 ) can be defined as the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve. The average particle size (D 50) can be measured, for example, using 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.

[0075] One embodiment provides a negative electrode active material comprising a silicon carbon composite according to the above-described embodiments.

[0076] One embodiment provides a negative electrode composition including a negative electrode active material according to the above-described embodiment; a binder and a conductive material.

[0077] According to one embodiment, the silicon carbon composite may be included in an amount of 0.1 to 15 parts by weight based on 100 parts by weight of the negative electrode active material, for example, 0.1 to 10 parts by weight, or 1 to 10 parts by weight.

[0078] According to one embodiment, the negative electrode active material may further include a carbon-based active material. The carbon-based active material may be included in an amount of 85 parts by weight or more and 99.9 parts by weight or less, for example, 85 parts by weight to 99 parts by weight, based on 100 parts by weight of the total negative electrode active material included in the negative electrode composition. The carbon-based active material may include at least one of natural graphite and artificial graphite. When the carbon-based active material includes both natural graphite and artificial graphite, the weight ratio of the artificial graphite and the natural graphite may be 1:9 to 9:1, for example, 3:7 to 7:3. For example, based on 100 parts by weight of the carbon-based active material, the natural graphite may be 10 to 70 parts by weight; and the artificial graphite may be 30 to 90 parts by weight.

[0079] The above natural graphite refers to graphite that occurs naturally, and examples thereof include scaled graphite, scaly graphite, or soil graphite. The above natural graphite has the advantages of being abundant, low in price, having high theoretical capacity and compaction density, and being capable of realizing high output.

[0080] In one example, the natural graphite may be spheroidized natural graphite, and may have a spheroidization degree of 0.9 or more. In one example, the natural graphite is spheroidized natural graphite and may have a tap density of 0.9 g / cc or more.

[0081] In this specification, the degree of sphericity may be a value obtained by dividing the circumference of a circle having the same area as the projected image when the particle is projected by the perimeter of the projected image. The degree of sphericity may be obtained from an SEM image, or alternatively, may be measured using a particle shape analyzer, such as a Malvern sysmex FPIA3000. In addition, the crystal size can be confirmed through XRD analysis.

[0082] According to one embodiment of the present invention, the cathode composition further includes a binder and a conductive material, and the binder may be an aqueous binder.

[0083] 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 materials in which hydrogens of these are substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0084] 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.

[0085] According to one embodiment, the aqueous binder may be included in an amount of 1 to 5 wt%, for example, about 3 to 4 wt%, based on the solid content of the negative electrode composition, and the conductive material may be included in an amount of 0.1 to 2 wt%, for example, about 1 wt%, based on the solid content of the negative electrode composition.

[0086] One embodiment of the present invention provides a cathode comprising a cathode composition according to the above-described embodiments.

[0087] Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes the negative electrode composition according to the embodiment described above.

[0088] The above negative electrode active material layer can be formed by applying a negative electrode slurry containing the above-described negative electrode composition to at least one surface of a negative electrode current collector, drying, and rolling.

[0089] 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.

[0090] The above-described cathode slurry may 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.

[0091] One embodiment of the present invention provides a lithium secondary battery including a negative electrode, a positive electrode, and a separator according to the above-described embodiment.

[0092] 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.

[0093] 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.

[0094] 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≤0.3); 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); LiMn2O4, etc., in which a part 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.

[0095] 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.

[0096] 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.

[0097] 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), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, 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.

[0098] 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.

[0099] The above lithium secondary battery may additionally include an electrolyte. Examples of the 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.

[0100] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0101] 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.

[0102] 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 with high electrical conductivity can be produced, so that they can be used even more preferably.

[0103] 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.

[0104] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as, for example, a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, a cyclic ether, 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.

[0105] According to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the same are provided. The battery module and the battery pack include the 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.

[0106]

[0107] Hereinafter, examples will be provided to specifically explain the present specification. However, the embodiments described herein may be modified in various ways, and the scope of the present application is not limited to the embodiments described below. The embodiments of the present application are provided to more fully explain the present specification to those of ordinary skill in the art.

[0108]

[0109] <Example 1>

[0110] (1) Preparation of silicon carbon composite 1

[0111] Cellulose powder was placed in a tubular furnace, heated to 400°C at a rate of 4°C, and heated for 2 hours under a nitrogen atmosphere. Thereafter, the furnace was heated to 900°C at a rate of 4°C and heated for 2 hours under a nitrogen atmosphere. The powder was mixed with sulfuric acid and nitric acid in a volume ratio of 3:1, stirred at 60°C for 2 hours, and then centrifuged to obtain a precipitate. The obtained powder was washed five times with a solvent mixed with ethanol and distilled water in a volume ratio of 1:3, and dried at 120°C for 12 hours. The carbon particles were placed in a KOH solvent and heated at 800°C for 2 hours under a nitrogen atmosphere to obtain a porous carbon structure. The porous carbon structure was washed three times with distilled water, and then dried at 120°C for more than 12 hours. The porous carbon structure was classified to determine the average particle diameter (D 50 ) was made to be 9㎛. The porous carbon structure was placed in a horizontal furnace, and SiH4 / He=5 / 95 gas was flowed at a flow rate of 50 ml / min at 650°C for 1 hour to manufacture a silicon carbon composite. The silicon carbon composite was placed in the furnace, and the silicon surface was oxidized in an oxygen atmosphere at 400°C for 30 minutes. Thereafter, the oxidized silicon carbon composite was placed in the furnace, and acetylene gas was flowed at 600°C to react for 3 hours to manufacture a silicon carbon composite negative electrode active material including a carbon layer on the outermost surface.

[0112] (2) Manufacturing of cathode

[0113] An anode slurry was prepared by adding and mixing an appropriate amount of distilled water to a negative electrode active material comprising the above-mentioned silicon carbon composite, natural graphite, and artificial graphite in a weight ratio of 10:15:75; a conductive material comprising carbon black and SWCNT; and a binder comprising carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) in a weight ratio of 95.3:1:3.6 so that the total solid content was approximately 46 wt%.

[0114] The above cathode slurry was applied to a Cu metal thin film with a thickness of 20 μm and dried at a circulating air temperature of 60°C. Then, after rolling, it was dried in a vacuum oven at 130°C for about a day, and then 1.4875 cm 2 The cathode was manufactured by punching out a circular shape.

[0115] (3) Manufacturing of secondary batteries

[0116] 1.7671cm 2 A Li metal film formed by porous polyethylene was used as the anode. A porous polyethylene separator was placed between the anode and the cathode, and a 1 M LiPF6 electrolyte containing additives in a mixed solution of EMC (methyl ethyl carbonate) and EC (ethylene carbonate) in a mixing ratio of 7:3 was injected to manufacture a Li coin half-cell.

[0117]

[0118] <Example 2>

[0119] (1) Preparation of silicon carbon composite 2

[0120] A silicon carbon composite was manufactured in the same manner as in Example 1, except that an oxide layer was formed on the surface of the silicon carbon composite at 400°C for 1 hour in an oxygen atmosphere.

[0121] (2) Manufacturing of cathode and secondary batteries

[0122] It was manufactured in the same manner as Example 1 except that silicon carbon composite 2 was used.

[0123]

[0124] <Example 3>

[0125] (1) Preparation of silicon carbon composite 3

[0126] Average particle diameter (D 50 ) was manufactured in the same manner as Example 1, except that the particle size was sized to 6 μm.

[0127] (2) Manufacturing of cathode and secondary batteries

[0128] It was manufactured in the same manner as Example 1 except that silicon carbon composite 3 was used.

[0129]

[0130] <Example 4>

[0131] (1) Preparation of silicon carbon composite 4

[0132] D 50 This 6㎛ SiOx (0 <x≤1)를 수평식 튜브 (horizontal tube)에 넣은 후, 1500sccm의 속도로 아르곤(Ar) 가스를 1시간 동안 흘러줘서 비활성 분위기를 만들어주었다. 그리고 150sccm의 속도로 아르콘 가스를 흘러주었고, 10℃ / min의 속도로 온도를 1000℃까지 증가시킨 후 6시간 동안 유지하여 불균등 반응(disproportionation)을 유도하였다. 상기 열처리된 SiOx(0<x≤1)를 튜브에서 꺼낸 후, circulator를 이용하여 10℃로 낮춘 20 중량비의 HF 수용액에 침지시킨 후, 상온에서 1시간동안 교반하여 SiO2상을 제거하였다. 상기 얻어진 다공성 실리콘을 600℃진공 오븐에서 12시간 동안 건조하였다. 이후, 상기 건조된 다공성 실리콘을 CVD 장비를 이용하여 600℃에서 9:1 부피비로 혼합된 아르곤 / 아세틸렌 혼합 가스를 100sccm 속도로 3시간 흘러주어 최종 실리콘 카본 복합체를 제조하였다.

[0133] (2) Manufacturing of cathode and secondary batteries

[0134] It was manufactured in the same manner as Example 1 except that silicon carbon composite 4 was used.

[0135]

[0136] <Comparative Example 1>

[0137] (1) Preparation of silicon carbon composite 5

[0138] It was manufactured in the same manner as Example 1, except that an oxide layer was not formed on the surface of the silicon carbon composite in an oxygen atmosphere.

[0139] (2) Manufacturing of cathode and secondary batteries

[0140] It was manufactured in the same manner as Example 1 except that silicon carbon composite 5 was used.

[0141]

[0142] Comparative Example 2

[0143] (1) Preparation of silicon carbon composite 6

[0144] It was manufactured in the same manner as Example 1, except that an oxide layer was not formed on the surface of the silicon carbon composite in an oxygen atmosphere and acetylene gas was reacted at 700°C for 3 hours.

[0145] (2) Manufacturing of cathode and secondary batteries

[0146] It was manufactured in the same manner as Example 1, except that silicon carbon composite 6 was used.

[0147]

[0148] <Comparative Example 3>

[0149] (1) Preparation of silicon carbon composite 7

[0150] It was manufactured in the same manner as Example 1, except that an oxide layer was formed on the surface of the silicon carbon composite at 200°C for 15 minutes in an oxygen atmosphere.

[0151] (2) Manufacturing of cathode and secondary batteries

[0152] It was manufactured in the same manner as Example 1, except that silicon carbon composite 7 was used.

[0153]

[0154] Comparative Example 4

[0155] (1) Preparation of silicon carbon composite 8

[0156] A silicon carbon composite was manufactured in the same manner as in Example 1, except that an oxide layer was not formed on the surface of the silicon carbon composite in an oxygen atmosphere, acetylene gas was reacted at 700°C for 3 hours, and then immersed in hydrogen peroxide (H2O2) for 30 minutes.

[0157] (2) Manufacturing of cathode and secondary batteries

[0158] It was manufactured in the same manner as Example 1 except that silicon carbon composite 8 was used.

[0159]

[0160] Comparative Example 5

[0161] (1) Preparation of silicon carbon composite 9

[0162] The above heat-treated SiOx(0 <x≤1)를 튜브에서 꺼낸 후, 20 중량비의 HF 수용액에 침지시킨 후, 45℃에서 1시간동안 교반하여 SiO2상을 제거한 것을 제외하고 실시예 4와 동일한 방법으로 제조하였다.

[0163] (2) Manufacturing of cathode and secondary batteries

[0164] It was manufactured in the same manner as Example 1 except that silicon carbon composite 9 was used.

[0165]

[0166] Comparative Example 6

[0167] (1) Preparation of silicon carbon composite 10

[0168] It was manufactured in the same manner as Example 1, except that a surface oxide layer was formed in an oxygen atmosphere at 600°C for 1 hour.

[0169]

[0170] (2) Manufacturing of cathode and secondary batteries

[0171] It was manufactured in the same manner as Example 1 except that silicon carbon composite 10 was used.

[0172]

[0173] Comparative Example 7

[0174] (1) Preparation of silicon carbon composite 11

[0175] It was manufactured in the same manner as Example 1, except that an oxide layer was formed on the surface of the silicon carbon composite at 400°C for 4 hours in an oxygen atmosphere.

[0176]

[0177] (2) Manufacturing of cathode and secondary batteries

[0178] It was manufactured in the same manner as Example 1 except that silicon carbon composite 11 was used.

[0179]

[0180] The XPS analysis results of the negative electrode active materials manufactured in the above examples and comparative examples are shown in Figures 1 to 11 and Table 1 below.

[0181] Specifically, Si analyzed by XPS of each negative electrode active material as shown in Figs. 1 to 10 2p The spectrum was analyzed using Gaussian / Lorentzian fitting, and the Si obtained through waveform analysis 0 Peak and Si x (0 <x≤4) 피크의 면적을 적분하여 얻은 값으로 강도의 비를 계산하였다.

[0182] The bold lines in Figures 1 to 11 indicate Si before separation. 2pIt is a spectrum, and the spectrum of each peak after waveform separation is indicated by a thin line.

[0183] At this time, Si in Example 1 0 The peak intensity was normalized to 1.0, and the relative values ​​of the remaining peak intensities are listed in Table 1.

[0184] Si 0 Peak Si x (0 <x≤4) 피크Si 0 Peak intensity and Si x (0 <x≤4) 피크 강도의 비Position(eV)피크 강도Position(eV)피크 강도실시예 199.51.0101~102.50.110.11실시예 299.81.93100.5~1030.190.10실시예 399.80.89101~1030.530.60실시예 499.51.88101~1030.220.12비교예 199.52.11101~102.50.050.02비교예 299.51.82101~1020.050.03비교예 399.41.77101~1030.080.05비교예 499.62.24101~1030.080.04비교예 599.11.45101~1030.070.05비교예 699.21.15101~1045.95.13비교예 799.01.71101~1041.550.91

[0185]

[0186] The discharge capacity, initial efficiency, capacity retention rate, and slurry viscosity change rate of the above examples and comparative examples were measured and are listed in Table 2 below.

[0187] <Discharge capacity, initial efficiency, capacity retention rate>

[0188] The 1st and 2nd cycles were charged and discharged at 0.1C, and from the 3rd to the 299th cycles, the charging and discharging was performed at 0.5C. The 300th cycle was terminated in a charged state (with lithium in the negative electrode).

[0189] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off)

[0190] Discharge conditions: CC (constant current) condition 1.5 V

[0191] Based on the results of a single charge / discharge cycle, the discharge capacity (mAh / g) and initial efficiency (%) were derived. Specifically, the initial efficiency (%) was derived using the following calculation.

[0192] Initial efficiency (%) = (1-time discharge capacity / 1-time charge capacity) × 100

[0193] The capacity retention rate was derived by the following calculations.

[0194] Capacity retention rate (%) = (299 discharge capacity / 1 discharge capacity) × 100

[0195]

[0196] <Slurry viscosity change rate>

[0197] To measure the change in slurry viscosity, a slurry was prepared by mixing graphite: the above-described negative active material: carbon black: CMC: PAA in a weight ratio of 77: 20: 1: 1: 1. The shear viscosity of the prepared slurry was measured at a shear rate of 1 Hz, and the change over time was measured and compared.

[0198] The change in shear viscosity (%) was derived using the following formula.

[0199] Change in shear viscosity (%) = ((shear viscosity of slurry after 2 days - viscosity of slurry immediately after mixing) / viscosity of slurry immediately after mixing) × 100

[0200]

[0201] Total discharge capacity (mAh / g) Initial efficiency (%) Capacity retention (%) Slurry viscosity change (%, after 2 days) Pouch volume change (%, @40℃, after 2 days) Example 150 292.08 9.0-2.51 Example 250 391.88 8.9-1.10 Example 349 89 1.58 8.1-0.40 Example 449 091.68 8.6-3.11.5 Comparative Example 148 591.08 4.4-41.68 Comparative Example 249 590.68 4.7-35.37 Comparative Example 349 490.18 5.8-30.66 Comparative Example 449 290.88 5.5-26.86 Comparative Example 548889.983.8-20.14Comparative example 647986.181.3-4.92.5Comparative example 746884.279.6-1.21

[0202] As shown in Table 2 above, Examples 1 to 4, in which the ratio of the peak of Six to the peak of Si0 in Table 1 satisfies 0.1 to 0.9, exhibited high capacity and efficiency, and it was confirmed that there was little change in the slurry viscosity change rate and pouch volume change rate.

[0203] Comparative examples 1 to 5 are experimental data when an oxide layer is not formed on the surface of a silicon carbon composite or is not sufficiently formed, and when analyzed by XPS, Si 0 Si for peak rain x The peak ratio was very small. This is because the silicon on the surface was not oxidized to an appropriate amount, so Si on the surface 0 It was confirmed that the aqueous slurry processability was poor and that a large volume expansion occurred because the silicon in the state was exposed and unstable, and could react with water to generate hydrogen gas.

[0204] Comparative examples 6 and 7 are Si 0 Si for peak rain x The peak ratio was large, which was due to the excessive generation of SiOx through the surface oxidation process at high temperature, which resulted in a decrease in initial efficiency and low electrical conductivity.

Claims

1. Si obtained by XPS analysis 2p In the spectrum, Si exists between 99 eV and 100.5 eV. 0 Si present at 100.5 eV to 105 eV compared to the intensity of the peak x (0 <x≤4) 피크의 강도의 비가 0.1 내지 0.9인 실리콘 카본 복합체.

2. In claim 1, the Si 0 Silicon carbon complex with peaks between 99 eV and 100 eV.

3. In claim 1, the silicon-carbon composite is a silicon-carbon composite comprising porous carbon particles and particles having silicon provided on at least a portion of the interior and surface of the porous carbon particles; or porous silicon particles and particles having carbon provided on at least a portion of the interior and surface of the porous silicon particles.

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

5. In claim 4, the negative electrode active material further comprises a carbon-based active material.

6. In claim 5, the negative electrode active material comprises artificial graphite and natural graphite.

7. In claim 4, the negative electrode active material is comprised of 0.1 to 10 parts by weight of the silicon carbon composite based on 100 parts by weight of the negative electrode active material.

8. A negative electrode composition comprising a negative electrode active material according to claim 4; a binder and a conductive material.

9. A cathode comprising a cathode composition according to claim 8.

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

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

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

13. A battery pack comprising the battery module of claim 11.

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