Silicon carbon composite, negative electrode active material, negative electrode including negative electrode active material, and secondary battery including negative electrode

Abstract

The present invention is based on the Raman spectrum, which is obtained by measuring the ratio of the intensity of the D band to the intensity of the Si peak (B D / B Si ) or the ratio of the intensity of the G band to the intensity of the Si peak (B G / B Si ) are greater than 5 and less than 50, and the position of the Si peak is 495 cm -1 ~515cm -1 and a negative electrode active material, a negative electrode composition, a negative electrode, a lithium secondary battery, a battery module, and a battery pack, each of which includes the silicon carbon composite.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2023-0140497, filed with the Korean Intellectual Property Office on October 19, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a silicon carbon composite, an anode active material containing the same, an anode containing the anode active material, and a secondary battery containing the anode. [Background technology]

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

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

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

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

[0007] An object of one embodiment of the present invention is to provide a silicon carbon composite that has excellent capacity and / or efficiency characteristics and can be used as a high-energy density anode active material, an anode active material, an anode, and a lithium secondary battery. [Means for solving the problem]

[0008] In one embodiment of the present invention, the intensity of the Si peak in the Raman spectrum is Si , the intensity of the D band is B D , the intensity of the G band is B G Then, the ratio of the D band intensity to the Si peak intensity (B D / B Si ) or the ratio of the intensity of the G band to the intensity of the Si peak (B G / B Si ) are greater than 5 and less than 50, and the position of the Si peak is 495 cm -1 ~515cm -1 The silicon carbon composite is located between

[0009] According to one embodiment of the present invention, the silicon carbon composite according to the above-described embodiment has a Raman spectrum in which the ratio of the intensity of the D band to the intensity of the G band (B D / B G ) has a value greater than 1.3 and less than 1.7.

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

[0011] One embodiment of the present invention provides a negative electrode composition comprising a negative electrode active material according to the above-described embodiment.

[0012] One embodiment of the present invention provides a negative electrode comprising a negative electrode composition according to the above-described embodiment.

[0013] One embodiment of the present invention provides a lithium secondary battery comprising a negative electrode, a positive electrode, and a separator according to the above-described embodiment.

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

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

[0016] One embodiment of the present invention provides a battery pack including a battery module according to the above-described embodiment. [Effects of the Invention]

[0017] According to an embodiment of the present invention, a silicon-carbon composite having a ratio of the D-band or G-band peak intensity to the Si-peak intensity within a specific range and a Si-peak position within a specific range in a Raman spectrum is used as an anode active material, thereby providing a lithium secondary battery with improved capacity and / or efficiency. Furthermore, by satisfying these ranges, problems of process compatibility and gas generation of aqueous binders that occur with silicon-based active materials can be improved. [Brief explanation of the drawings]

[0018] [Figure 1] 1 shows spectra obtained by Raman analysis of negative electrodes using the silicon carbon composites of Examples 1 to 4. [Figure 2] 1 shows the spectra obtained by Raman analysis of the negative electrodes using SiO or silicon carbon composites of Comparative Examples 1 to 5. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be described in more detail below to facilitate understanding of the present invention. The present invention may be realized in various different forms and is not limited to the embodiments described herein. In this regard, the terms and words used in the specification and claims should not be interpreted in a limited manner to their ordinary or dictionary meanings, but should be interpreted in a manner that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their invention.

[0020] It should be understood that in this specification, terms such as "comprises," "provides," or "has" specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0021] Furthermore, when a part such as a layer exists "on" or "above" another part, it does not only mean that it is "directly above" that part, but also includes the case where there is another part between them. In contrast, when a part exists "directly above" another part, it means that there is no other part between them. Furthermore, when a part exists "on" or "above" a reference part, it means that it is located above or below the reference part, and does not necessarily mean that it is located "above" or "above" the direction opposite to gravity.

[0022] The terms and words used in this specification should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

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

[0024] Preferred embodiments of the present invention will be described in detail below. However, the embodiments of the present invention may be modified in various ways, and the scope of the present invention is not limited to the embodiments described below.

[0025] In this specification, a Raman spectrum can be obtained by taking 100 points on the surface of a sample, irradiating each point with a 532 nm laser, and then calculating the average value of the spectrum.

[0026] In the Raman spectrum, the D band is the band at 1350 cm -1 The D band is a band in which a peak exists near the D band. The D band occurs due to irregularities in the atomic arrangement within a crystal, and indicates disorder or structural instability within a material.

[0027] In the Raman spectrum, the G band is the band at 1600 cm -1 The G band is a band in which a peak exists around the 2 It refers to bonding and provides information about the crystalline structure of the material and the form of carbon bonding.

[0028] In the Raman spectrum, the Si peak occurs due to vibration of the Si crystal structure and is used as an indicator of the crystallinity, stress, and other structural properties of Si.

[0029] In the Raman spectrum, the D band peak is 1300 to 1370 cm -1 This means the point where the scattering intensity measured within the range is maximum and peaks that have a scattering intensity of 10% or more of that point, and does not include peaks that are less than 10% of the maximum scattering intensity within the D band.

[0030] In the Raman spectrum, the G band peak is 1580 to 1600 cm -1This refers to the point where the scattering intensity measured within the range is maximum and peaks that have a scattering intensity of 10% or more of that point, and does not include peaks that are less than 10% of the maximum scattering intensity within the G band.

[0031] In the Raman spectrum, the Si peak is a peak between 400 and 600 cm -1 This means the point where the scattering intensity measured within the range is maximum and any peaks having a scattering intensity of 10% or more of that point, and does not include peaks that are less than 10% of the maximum scattering intensity within the range.

[0032] In the Raman spectrum, peaks may overlap to form a shoulder peak, or two or more peaks may coexist.

[0033] If noise occurs in the Raman spectrum, a noise smoothing technique may be used to remove the noise so that only the main peak is observed.

[0034] In this specification, the peak intensity refers to the value obtained by deconvolving the Raman spectrum into individual peaks, fitting it to a Gaussian / Lorentzian model, and then integrating the area under the resulting Gaussian function graph.

[0035] In this specification, the D band peak intensity refers to the intensity of the D band peak at 1300 to 1370 cm -1 This means the value obtained by integrating the Gaussian function of the peaks located within the range.

[0036] In the Raman spectrum, the intensity of the G band peak is 1580 to 1600 cm -1 This means the value obtained by integrating the Gaussian function of the peaks located within the range.

[0037] In the Raman spectrum, the intensity of the Si peak is the intensity of the peak between 400 and 600 cm -1This means the value obtained by integrating the Gaussian function of the peaks located within the range.

[0038] Here, when at least one of the D band peak, the G band peak, and the Si peak includes two or more peaks, the intensity of the peak is calculated as the sum of the intensities of the two or more peaks.

[0039] In the Raman spectrum, the intensity of the Si peak is Si , the intensity of the D band is B D , the intensity of the G band is B G Then, the ratio of the D band intensity to the Si peak intensity (B D / B Si ) or the ratio of the intensity of the G band to the intensity of the Si peak (B G / B Si ) are more than 5 and less than 50, have the characteristics of high initial capacity and efficiency, and excellent cycle capacity retention rate.

[0040] According to one embodiment, the ratio of the intensity of the D band to the intensity of the Si peak (B D / B Si ) or the ratio of the intensity of the G band to the intensity of the Si peak (B G / B Si ) may be greater than 5 and less than 45, greater than 10 and less than 40, or greater than 15 and less than 35.

[0041] According to one embodiment, the position of the Si peak is 495 cm -1 ~515cm -1 When the Si peak is located lower than the above range, it may be located between 450 and 495 cm -1 If the Si peak is located higher than the above range, specifically at 520 cm, it means that silicon is present in an amorphous state, and it is highly reactive with the solvent, which may cause viscosity reduction and gas generation. -1 If located nearby, the silicon will exist in a crystalline state, which can reduce capacity, efficiency, and lifetime.

[0042] According to one embodiment, the ratio of the intensity of the D band to the intensity of the G band (B D / B G ) may be greater than 1.3 and less than 1.7, greater than 1.4 and less than 1.7, or greater than 1.4 and less than 1.6.

[0043] According to one embodiment, the intensity of the Si peak is determined by B Si , the intensity of the D band is B D , the intensity of the G band is B G Then, the ratio of the D band intensity to the Si peak intensity (B D / B Si ) and the ratio of the intensity of the G band to the intensity of the Si peak (B G / B Si ) may be more than 5 and less than 50.

[0044] According to another embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0045] According to one embodiment, the silicon carbon composite is a composite of Si and C, in which both Si and C (e.g., graphite) are present. In this specification, the silicon carbon composite can be expressed as Si / C. The silicon carbon composite may consist of unbonded Si and C, but may contain additional components as necessary. For example, the silicon carbon composite may or may not contain silicon carbide, which is expressed as SiC. When the silicon carbon composite contains silicon carbide, its content is 3 wt % or less. The silicon carbon composite may exist in a crystalline state, an amorphous state, or a mixture thereof. According to one example, the C in the silicon carbon composite may exist in an amorphous state.

[0046] According to one embodiment, the silicon carbon composite may be a particle having porous carbon-based particles and silicon provided in at least a portion of the interior and surface of the porous carbon-based particles; or a particle having porous silicon-based particles and carbon provided in at least a portion of the interior and surface of the porous silicon-based particles.

[0047] According to one embodiment, the silicon carbon composite is a particle having porous carbon particles and silicon provided in 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 may be further formed on the surface of the silicon carbon composite. The carbon layer imparts conductivity, thereby improving the initial efficiency, life characteristics, and capacity characteristics of the secondary battery. The total weight of the carbon layer may be 5 wt% to 40 wt% based on 100 wt% of the silicon carbon composite particles. The carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0048] According to one embodiment, the silicon carbon composite may be a particle having porous silicon-based particles and carbon provided in at least a portion of the interior and surface of the porous silicon-based particles. This can be formed by etching silicon oxide to form porous silicon-based particles, for example, a Si matrix, and then coating the silicon-based particles with carbon. The above description of the carbon layer may be applied to the carbon.

[0049] According to one embodiment, the silicon carbon composite has a specific surface area of ​​0.5 to 10 m by the BET method. 2 / g, and the pore volume is 0.005 to 0.03 cm 3 The silicon carbon composite may have a pore volume of 0.005 to 0.03 cm3 as measured by mercury penetration spectroscopy, and a pore size of 10 to 20 nm as measured by BET method. 3 / g.

[0050] According to one embodiment, the silicon carbon composite is 90 The particle size may be 5 to 15 μm, and D 50 The particle size may be 1 to 10 μm, and D min may be 1 to 3 μm, and D max In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 ) can be measured, for example, by using a laser diffraction method. The laser diffraction method is generally capable of measuring particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0051] One embodiment provides an active negative electrode material comprising a silicon carbon composite according to the above-described embodiment.

[0052] One embodiment provides a negative electrode composition including a negative electrode active material according to the above embodiment, a binder, and a conductive material.

[0053] According to one embodiment, the silicon carbon composite may be included in an amount of 0.1 to 10 parts by weight, for example, 1 to 10 parts by weight, based on 100 parts by weight of the negative electrode active material.

[0054] 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 90 parts by weight to 99.9 parts by weight, for example, 90 parts by weight to 99 parts by weight, based on 100 parts by weight of the negative electrode active material included in the negative electrode composition. The carbon-based active material may include at least one of natural graphite and artificial graphite. When the carbon-based active material includes both natural graphite and artificial graphite, the weight ratio of the artificial graphite to the natural graphite may be 1:9 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.

[0055] The natural graphite refers to graphite that is naturally occurring, and examples thereof include flake graphite, scaly graphite, and soil graphite. Natural graphite has the advantages of being abundant, inexpensive, having a high theoretical capacity and a high compressed density, and being able to achieve high output.

[0056] According to one example, the natural graphite may be spherical natural graphite, and may have a sphericity of 0.9 or more. According to one example, the natural graphite may be spherical natural graphite, and may have a tap density of 0.9 g / cc or more.

[0057] In this specification, sphericity may be the value obtained by dividing the circumference of a circle having the same area as the projected image by the perimeter of the projected image when a particle is projected. The sphericity can be determined from an SEM image or measured using a particle shape analyzer such as a Sysmex FPIA3000 manufactured by Malvern. The crystal size can also be confirmed by XRD analysis.

[0058] According to one embodiment of the present invention, the negative electrode composition further includes a binder and a conductive material, and the binder may be a water-based binder.

[0059] The binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0060] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0061] According to one embodiment, the aqueous binder may be contained 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 contained in an amount of 0.1 to 2 wt %, for example, about 1 wt %, based on the solid content of the negative electrode composition.

[0062] One embodiment of the present invention provides a negative electrode comprising a negative electrode composition according to the above-described embodiment.

[0063] Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer including the negative electrode composition according to the above-described embodiment.

[0064] The negative electrode active material layer may be formed by applying a negative electrode slurry containing the above-described negative electrode composition to at least one surface of a negative electrode current collector, followed by drying and rolling.

[0065] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that easily adsorbs carbon, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but is not limited thereto.

[0066] The negative electrode slurry may include a solvent for forming a negative electrode slurry. Specifically, the solvent for forming a negative electrode slurry may include at least one solvent selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate dispersion of components.

[0067] One embodiment of the present invention provides a lithium secondary battery comprising a negative electrode, a positive electrode, and a separator according to the above-described embodiment.

[0068] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

[0069] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0070] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMn 2-c3 Examples of lithium manganese composite oxides include, but are not limited to, LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, and LiMn2O4, where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and 0.01≦c3≦0.1, or Li2Mn3MO8, where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn. The positive electrode may be Li-metal.

[0071] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-described positive electrode active material.

[0072] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be any material that has electronic conductivity without causing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0073] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders may be used singly or in combination.

[0074] The separator separates the negative electrode and positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitation. It is particularly preferable that the separator exhibits low resistance to ion migration and has excellent electrolyte humidifying ability. Specifically, porous polymer films, such as those made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0075] The lithium secondary battery may further include an electrolyte, which may be used in manufacturing a lithium secondary battery, such as, but not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte.

[0076] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0077] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0078] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents, because they have a high dielectric constant and dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and therefore such cyclic carbonates can be more preferably used.

[0079] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3- , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0080] In addition to the constituent components of the electrolyte, the electrolyte may further include one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, in order to improve the life characteristics of the battery, suppress a decrease in battery capacity, and improve the discharge capacity of the battery.

[0081] According to another embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. [Example]

[0082] Hereinafter, the present specification will be described in detail with reference to examples in order to specifically explain the present specification. However, the examples according to the present specification may be modified into various other forms, and the scope of the present application should not be interpreted as being limited to the examples described below. The examples of the present application are provided to more completely explain the present specification to those skilled in the art.

[0083] Example 1 (1) Production of silicon carbon composite 1 The cellulose powder was placed in a tubular furnace, heated to 400°C at a rate of 4°C / min, and then heated under a nitrogen atmosphere for 2 hours. The furnace was then heated to 900°C at a rate of 4°C / min and then heated under a nitrogen atmosphere for 2 hours. The powder was mixed with sulfuric acid and nitric acid in a 3:1 volume ratio, stirred at 60°C for 2 hours, and centrifuged to obtain a precipitate. The resulting powder was washed five times with a 1:3 volume ratio mixture of ethanol and distilled water and then dried at 120°C for 12 hours. The carbonaceous 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 at least 12 hours. The porous carbon structure was placed in a horizontal furnace and a SiH4 / He=5 / 95 gas mixture was passed through at a flow rate of 50 ml / min at 700°C for 1 hour to produce a silicon carbon composite. The silicon carbon composite was then placed in an electric furnace and heat-treated at 800°C for 2 hours. The heat-treated silicon carbon composite was then placed in the furnace and reacted with methane at 700°C for 3 hours to produce a silicon carbon composite anode active material with a carbon layer on the surface.

[0084] (2) Manufacturing of the negative electrode A negative electrode slurry was prepared by mixing the above-prepared silicon carbon composite, natural graphite, and artificial graphite in a weight ratio of 10:15:75 as a negative electrode active material, the conductive material including carbon black and SWCNT, and the binder including carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) in a weight ratio of 95.3:1:3.6 with an appropriate amount of distilled water to achieve a total solids content of approximately 46 wt%.

[0085] The negative electrode slurry was applied to a Cu metal thin film with a thickness of 20 μm, and then dried in circulating air at 60° C. After rolling, it was dried in a vacuum oven at 130° C. for about a day, and then cut into 1.4875 cm 2 The negative electrode was then manufactured by punching out a circular piece.

[0086] (3) Secondary battery manufacturing 1.7671cm 2 A Li metal thin film punched into the shape of a square was used as the positive electrode. A porous polyethylene separator was placed between the positive and negative electrodes, and an electrolyte solution containing 1M LiPF6 dissolved therein and an additive made from a mixed solution of EMC (methyl ethyl carbonate) and EC (ethylene carbonate) in a 7:3 ratio was injected to fabricate a Li coin half cell.

[0087] Example 2 (1) Production of silicon carbon composite 2 D 50SiO2 particles with a diameter of 6 μm were placed in a horizontal tube and an inert atmosphere was created by flowing argon (Ar) gas at a rate of 1500 sccm for 1 hour. Then, with argon gas flowing at a rate of 150 sccm, the temperature was increased to 650°C at a rate of 10°C / min and maintained for 6 hours. The heat-treated SiO2 particles were removed from the tube and immersed in a 20% by weight HF aqueous solution and stirred at room temperature for 1 hour to remove the SiO2 phase. The porous silicon from which the SiO2 phase had been removed was washed twice with distilled water and twice with ethanol and then filtered under reduced pressure. The resulting porous silicon was dried in a vacuum oven at 600°C for 12 hours. The dried porous silicon was then placed in an electric furnace and immersed in a 9:1 volumetric argon / acetylene gas mixture at 600°C for 3 hours at 100 sccm to produce the final silicon-carbon composite.

[0088] (2) Manufacturing of anodes and secondary batteries An anode and a secondary battery were produced in the same manner as in Example 1, except that silicon carbon composite 2 was used as the silicon carbon composite.

[0089] Example 3 (1) Production of silicon carbon composite 3 D 50 Silicon carbon composites were produced in the same manner as silicon carbon composite 2, except that SiO of 4 μm was used.

[0090] (2) Manufacturing of anodes and secondary batteries An anode and a secondary battery were manufactured in the same manner as in Example 1, except that silicon carbon composite 3 was used as the silicon carbon composite.

[0091] Example 4 (1) Production of silicon carbon composite 4 Silicon carbon composites were prepared in the same manner as silicon carbon composite 2, except that the temperature was increased to 750°C at a rate of 10°C / min under an inert atmosphere and then maintained for 6 hours.

[0092] (2) Manufacturing of anodes and secondary batteries An anode and a secondary battery were produced in the same manner as in Example 1, except that silicon carbon composite 4 was used as the silicon carbon composite.

[0093] Comparative Example 1 (1) Metal-doped SiO x Manufacturing SiO, a mixture of Si and SiO2 in a 1:1 molar ratio, was placed in crucible 1 and heated to a sublimation temperature of 1400°C to evaporate. Metallic magnesium was evaporated separately by heating at 800°C. The crucible was then depressurized to 0.1 torr, and the raw materials were evaporated. The vapor mixture containing Mg was reacted for 6 hours and then solidified in a vacuum at 800°C. The silicon-based active material produced by this method was pulverized for 3 hours using a ball mill. Then, in an inert Ar atmosphere, methane was reacted at 0.1 torr and 1 L / min for 5 hours using a CVD apparatus to form a carbon layer on the surface of the silicon-based active material, producing a magnesium silicon oxide active material coated with a carbon layer (D of the produced active material). 50 :6μm).

[0094] (2) Manufacturing of anodes and secondary batteries As the negative electrode active material, metal-doped SiO obtained by the above process was used instead of silicon carbon composite. x A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that the above-mentioned was used.

[0095] Comparative Example 2 (1) Production of silicon carbon composite 5 A silicon carbon composite was manufactured in the same manner as in Silicon Carbon Composite 1, except that the heat treatment at 800°C in an electric furnace and the carbon coating process were not performed on the manufactured silicon carbon composite.

[0096] (2) Manufacturing of anodes and secondary batteries An anode and a secondary battery were produced in the same manner as in Example 1, except that silicon carbon composite 5 was used as the silicon carbon composite.

[0097] Comparative Example 3 (1) Production of silicon carbon composite 6 A silicon carbon composite was manufactured in the same manner as in Silicon Carbon Composite 1, except that the manufactured silicon carbon composite was not subjected to the heat treatment at 800° C. in an electric furnace.

[0098] (2) Manufacturing of anodes and secondary batteries An anode and a secondary battery were produced in the same manner as in Example 1, except that silicon carbon composite 6 was used as the silicon carbon composite.

[0099] Comparative Example 4 (1)SiO x Manufacturing A mixture of Si and SiO2 with a molar ratio of 1:1 was placed in an electric furnace and heat-treated at 1300°C for 6 hours in an Ar atmosphere to obtain SiO x The SiO obtained by the above method was x was ground for 3 hours using a ball mill.

[0100] Then, in an inert gas Ar atmosphere, a CVD device was used to react methane at 0.1 torr and 1 L / min for 5 hours at 900°C to form a carbon layer on the surface of the silicon-based active material, and SiO x / Manufacture carbon composites.

[0101] (2) Manufacturing of anodes and secondary batteries As the negative electrode active material, SiO obtained by the above process was used instead of silicon carbon composite. x A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that the above-mentioned was used.

[0102] Comparative Example 5 (1) Production of silicon carbon composite 7 Of the total mixture amount of 100 parts by weight, 35 parts by weight of silicon (Si, D50 40 parts by weight of pitch-based carbon and 25 parts by weight of flake graphite were mixed and dry milled at 2,000 rpm for 3 minutes, and then heat-treated in an argon (Ar) gas atmosphere at about 1,150°C for 4 hours to prepare a negative electrode active material.

[0103] (2) Manufacturing of anodes and secondary batteries An anode and a secondary battery were produced in the same manner as in Example 1, except that silicon carbon composite 7 was used as the silicon carbon composite.

[0104] The Raman spectrum analysis results of the negative electrode active materials prepared in the Examples and Comparative Examples are shown in FIGS. 1 and 2, and the positions and ratios of the D band peak, G band peak, and Si peak are shown in Table 1 below.

[0105] [Table 1]

[0106] The batteries manufactured in the examples and comparative examples were evaluated as follows, and the results are shown in Table 2 below.

[0107] <Particle size analysis> The particle size of the negative electrode active material was analyzed by laser diffraction particle size analysis using a Marlven device.

[0108] <Discharge capacity, initial efficiency, capacity retention rate> The first and second cycles were charged and discharged at 0.1 C, and from the third to the 299th cycles, they were charged and discharged at 0.5 C. The 300th cycle was completed in a charged state (with lithium in the anode).

[0109] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharge condition: CC (constant current) condition 1.5V

[0110] The discharge capacity (mAh / g) and initial efficiency (%) were calculated from the results of one charge / discharge. Specifically, the initial efficiency (%) was calculated as follows:

[0111] Initial efficiency (%) = (single discharge capacity / single charge capacity) x 100

[0112] The capacity retention rate was calculated as follows.

[0113] Capacity retention rate (%) = (299 discharge capacity / 1 discharge capacity) × 100

[0114] <Slurry viscosity change rate> To measure the viscosity change rate of the slurry, graphite, the negative electrode active material, carbon black, CMC, and PAA were mixed in a weight ratio of 77:20:1:1:1 to prepare a slurry. 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.

[0115] The shear viscosity change (%) was calculated using the following formula:

[0116] Shear viscosity change rate (%) = ((shear viscosity of slurry after 2 days - viscosity of slurry immediately after mixing) / viscosity of slurry immediately after mixing) × 100

[0117] [Table 2]

[0118] As shown in Table 2, B D / B Si or B G / B Si It can be confirmed that Examples 1 to 4, in which the ratio is in the range of more than 5 and less than 50, exhibit high capacity and efficiency, and there is little change in the viscosity change rate of the slurry and the volume change rate of the pouch.

[0119] Comparative Examples 1 and 4 are B D / B Si and B G / B Si This corresponds to the case where the ratio is less than 5, and the capacity efficiency and cycle capacity retention rate were lower than those of Examples 1 to 4. This is because the highly crystalline silicon caused a serious volume change during charge and discharge.

[0120] Comparative Examples 2 and 3 are B G / B Si or B D / B Si The ratio of is in the range of more than 5 and less than 50, but the Si peak is at 495 cm -1 ~515cm -1 This corresponds to the case where the value appears outside the range of . It was confirmed that Comparative Examples 2 and 3 had a low cycle capacity retention rate, a large viscosity change rate of the slurry, and a large volume change rate of the pouch due to gas generation. This is because the highly amorphous nature of silicon, which causes a decrease in viscosity and gas generation, makes it highly reactive with the solvent.

[0121] Comparative Example 5 is B D / B Si and B G / B Si When the ratio exceeds 50, it means that the carbon in the active material is crystalline and there are bonds in the crystalline structure, which can be seen to impede the charge transfer pathway, reduce the contribution of silicon to electrochemical performance, and reduce efficiency.

Claims

1. In a Raman spectrum, the ratio of the intensity of the D band to the intensity of the Si peak (B Ｄ / B Ｓｉ ) or the ratio of the intensity of the G band to the intensity of the Si peak (B Ｇ / B Ｓｉ ) is greater than 5 and less than 50, and the position of the Si peak is 495 cm －１ ~515cm －１ A silicon-carbon composite located in the middle position.

2. The ratio of the intensity of the D band to the intensity of the G band (B Ｄ / B Ｇ The silicon-carbon composite according to claim 1, wherein the ratio is greater than 1.3 and less than 1.

7.

3. The ratio of the intensity of the D band to the intensity of the Si peak (B Ｄ / B Ｓｉ ) and the ratio of the intensity of the G band to the intensity of the Si peak (B Ｇ / B Ｓｉ 2. The silicon carbon composite of claim 1, wherein σ is greater than 5 and less than 50.

4. The ratio of the intensity of the D band to the intensity of the Si peak (B Ｄ / B Ｓｉ ) or the ratio of the intensity of the G band to the intensity of the Si peak (B Ｇ / B Ｓｉ 2. The silicon carbon composite of claim 1, wherein σ is greater than 10 and less than 40.

5. The ratio of the intensity of the D band to the intensity of the G band (B Ｄ / B Ｇ 3. The silicon carbon composite of claim 2, wherein σ is greater than 1.4 and less than 1.

6.

6. The silicon carbon composite is Particles having porous carbon-based particles and silicon provided in at least a portion of the interior and surface of the porous carbon-based particles; or The silicon-carbon composite according to claim 1, comprising porous silicon-based particles and carbon provided in at least a portion of the interior and surface of the porous silicon-based particles.

7. A negative electrode active material comprising the silicon carbon composite according to any one of claims 1 to 6.

8. A negative electrode composition comprising the negative electrode active material according to claim 7, a binder, and a conductive material.

9. The negative electrode composition according to claim 8 , wherein the negative electrode active material further comprises a carbon-based active material.

10. The negative electrode composition according to claim 9, wherein the silicon-carbon composite is included in an amount of 0.1 parts by weight or more and 10 parts by weight or less, based on 100 parts by weight of the negative electrode active material.

11. The negative electrode composition according to claim 9 , wherein the carbon-based active material comprises artificial graphite and spheroidized natural graphite.

12. An anode comprising the anode composition of claim 8 .

13. A lithium secondary battery comprising the negative electrode of claim 12, a positive electrode, and a separator.

14. A battery module comprising the lithium secondary battery according to claim 13.

15. A battery pack comprising the lithium secondary battery according to claim 13.

16. A battery pack comprising the battery module according to claim 14.

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