Negative electrode active material for secondary battery, method for manufacturing same, and negative electrode comprising same for secondary battery

Abstract

The present invention relates to a negative electrode active material for a secondary battery, comprising a silicon compound and a surface layer provided to cover at least a portion of the surface of the silicon compound, wherein the surface layer contains graphene and an organic compound, and the organic compound forms a catechol bond together with the silicon compound.

Description

Negative electrode active material for secondary batteries, method for manufacturing the same, and negative electrode for secondary batteries including the same

[0001] The present invention relates to a negative electrode active material for a secondary battery, a method for producing the same, and a negative electrode for a secondary battery including the same.

[0002] Lithium-ion secondary batteries (LIBs) are seeing increasing demand for energy storage devices such as portable electronic devices, electric vehicles, and energy storage systems, and their market is expanding significantly. Consequently, the need to improve the power density and energy density of LIBs is growing.

[0003] To improve the energy density of lithium-ion secondary batteries, various materials with higher theoretical capacities than graphite, which is commonly used as an anode material, are being studied, and among them, silicon materials are being studied as a substitute for graphite.

[0004] Silicon (Silicon) is attracting attention as a high-capacity anode material due to its high theoretical capacity (4200 mAh / g). However, the lifespan of secondary batteries is reduced due to large expansion (approximately 400%) when reacting with lithium ions, material pulverization during repeated charge / discharge, and unstable solid-electrolyte interface. Therefore, improvement is necessary for practical use. In addition, low electrical conductivity and initial coulombic efficiency of silicon are factors that hinder the implementation of high energy density of cells, so these must also be improved. Among silicon-based materials, silicon oxide (SiO x ) is attracting attention due to its improved volume expansion and lifespan compared to pure silicon materials, but has the disadvantages of reduced electrical conductivity and initial Coulomb efficiency.

[0005] Accordingly, various studies are being conducted to improve electrochemical characteristics and mechanical properties by applying silicon material as a cathode.

[0006] Prior patent: KR 10-1142534 (April 26, 2012)

[0007] The purpose of the present invention is to provide a negative electrode active material for a secondary battery having improved long-term cycle characteristics during a charge / discharge process, a method for producing the same, and a negative electrode for a secondary battery including the same.

[0008] In addition, another object of the present invention is to provide a negative electrode active material for a secondary battery having improved electrochemical performance by overcoming the problems of a secondary battery using a silicon compound as a negative electrode, a method for producing the same, and a negative electrode for a secondary battery including the same.

[0009] One embodiment of the present invention provides a negative electrode active material for a secondary battery, a method for manufacturing the same, and a secondary battery including the same.

[0010] In one embodiment, the negative electrode active material for the secondary battery includes a silicon compound; and a surface layer provided to cover at least a portion of the surface of the silicon compound; wherein the surface layer includes graphene and carbon, and the carbon can be formed by carbonizing an organic compound that forms a catechol bond with the silicon compound.

[0011] In one embodiment, the silicon compound is SiO x (0≤x<2), SiO containing lithium compound x (0≤x<2), and SiO containing magnesium compounds x (0≤x<2), silicon alloy (Si alloy), and silicon-carbon composite (Si-C composite).

[0012] In one embodiment, the average thickness of the surface layer may be 10 nm to 10 μm.

[0013] In one embodiment, the thickness of the surface layer may be 0.05% to 10% of the average radius of the negative electrode active material.

[0014] In one embodiment, the carbon in the silicon compound may be from 0.2 wt% to 20 wt%.

[0015] In one embodiment, the weight ratio of the organic compound to the silicon compound may be 1:0.1 to 0.8.

[0016] In one embodiment, the organic compound may include at least one selected from the group consisting of polydopamine, cellulose, polyphenylene, polypropylene, resin, tannic acid, lignan, catechin, flavonoid, phenolic acid, and stilbene.

[0017] In one embodiment, the organic compound comprises a polymer formed by polymerizing a monomer, wherein the monomer may include at least one of catechol, dopamine, dopamine hydrochloride, norepinephrine, L-dihydroxyphenylalanine, hydroxyphenolic acid, adrenaline, lignin monomer, ellagitannin, and pyrogall (1,2,3-benzenetriol).

[0018] In one embodiment, the temperature at which the organic compound is carbonized may be 300°C to 1500°C.

[0019] In one embodiment, the electrical conductivity of the silicon negative electrode material using the negative electrode active material may be 0.001 S / cm to 30 S / cm.

[0020] In one embodiment, the method for producing the negative electrode active material for a secondary battery may include a step of dispersing a monomer in a first solvent, adding a silicon compound to the first solvent, and stirring the prepared first dispersion solution to produce a silicon compound coated with an organic compound; a step of preparing a graphene dispersion solution in which graphene and a cationic surfactant are dispersed, and mixing the silicon compound coated with the organic compound with the graphene dispersion solution to produce a second dispersion solution; and a step of centrifuging the second dispersion solution to select a solid material.

[0021] In one embodiment, the monomer comprises at least one of catechol, dopamine, dopamine hydrochloride, norepinephrine, L-dihydroxyphenylalanine, hydroxyphenolic acid, adrenaline, lignin monomer, ellagitannin, and pyrogall (1,2,3-benzenetriol), and the silicone compound is SiO x (0≤x<2), SiO containing lithium compound x (0≤x<2), SiO containing magnesium compounds x (0≤x<2), may include at least one of a silicon alloy (Si alloy) and a silicon-carbon composite (Si-C composite).

[0022] In one embodiment, the monomer in the first solvent may be 0.05 wt% to 5 wt%, and the weight ratio of the monomer to the silicon compound may be 1:0.1 to 0.8.

[0023] In one embodiment, the organic compound may include at least one selected from the group consisting of polydopamine, cellulose, polyphenylene, polypropylene, resin, and tannic acid, lignan, catechin, flavonoid, phenolic acid, and stilbene.

[0024] In one embodiment, the graphene dispersion solution is prepared by dispersing graphene in a second solvent, adding the cationic surfactant, and physically stirring the cationic surfactant, and the surfactant is 0.05 wt% to 100 wt% with respect to the graphene, and the surfactant is cetyltrimethylammonium bromide (CTAB), alkyltrimethylammonium chlorides, dialkyl dimethyl ammonium chloride, benzalkonium chloride, didecyldimethylammonium chloride, 1,2-distearoyl-sn-glycero-3-phosphorylethanolamine-N-[methoxy(polyethylene glycol)] It may include at least one of polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), polyethylene glycol tert-octylphenyl ether (Triton X-100), and sodium dodecyl sulfate (SDS).

[0025] In one embodiment, in the step of preparing the second dispersion solution, the silicon compound coated with the organic compound is dispersed in a third solvent, and then the second dispersion solution is prepared by physical stirring with the graphene dispersion solution, and the concentration of graphene in the graphene dispersion solution is 0.1 wt% to 3 wt%, and the weight ratio of graphene to 100 wt% of the silicon compound may be 1 wt% to 10 wt%.

[0026] In one embodiment, the negative electrode active material for the secondary battery includes silicon oxide and a surface layer provided on the surface of the silicon oxide, and the surface layer includes graphene and carbon, and the step of preparing the second dispersion solution and the step of selecting the solid material are repeated at least once to increase the thickness of the surface layer.

[0027] In one embodiment, the step of selecting the solid material may further include a step of heat treating the solid material in an inert gas atmosphere at a temperature of 300° C. to 1500° C. for 0.5 to 24 hours.

[0028] In one embodiment, a secondary battery negative electrode is provided, which includes the negative electrode active material described above; graphite; a binder; and a conductive material, wherein the graphite is included in an amount of 30 to 95 parts by weight, the binder is included in an amount of 2 to 10 parts by weight, and the conductive material is included in an amount of 0 to 10 parts by weight, based on 100 parts by weight of the total of the negative electrode active material, graphite, binder, and conductive material.

[0029] According to the present invention as described above, it is possible to provide a negative electrode active material for a secondary battery, which can reduce the content of a conductive material and a binder, and has reduced volume expansion occurring during a charge / discharge process, a method for producing the same, and a negative electrode for a secondary battery including the same.

[0030] In addition, according to the present invention, by providing a surface layer of a silicon compound by a novel method, the conductivity between silicon compounds can be improved and the life characteristics of a secondary battery can be improved.

[0031] FIG. 1 is a schematic diagram illustrating a negative electrode active material for a secondary battery according to one embodiment of the present invention.

[0032] Figure 2 is a flow chart of a method for manufacturing a negative electrode active material for a secondary battery according to one embodiment of the present invention.

[0033] FIG. 3 is a schematic diagram illustrating a method for manufacturing a negative electrode active material according to one embodiment of the present invention.

[0034] Figure 4 shows graphene-coated SiO x This is an SEM image of .

[0035] Fig. 5 is SiO x This is an SEM image of a negative electrode material sequentially coated with polydopamine (PDA) and graphene (Gr).

[0036] Fig. 6 is SiO x , dopamine-coated SiO x and polydopamine-coated SiO x This is a diagram showing the FT-IR results.

[0037] Figure 7 is a graph showing the FT-IR results of the negative electrode active material before and after carbonization.

[0038] Figure 8 is a graph showing the Raman peak change of the negative electrode active material before and after carbonization.

[0039] Fig. 9 is SiO x, Graphene coated SiO x (SiO x +Gr) and polydopamine and graphene coated and carbonized SiO x (SiO x This is the result of measuring the electrical conductivity of +Gr+PAD.

[0040] Fig. 10 is SiO x , and the results of evaluating the electrochemical performance of a half-cell using a negative electrode active material according to an embodiment of the present invention as a negative electrode.

[0041] Fig. 11 is SiO x , and the results of evaluating the electrochemical performance of a half-cell using artificial graphite as a negative electrode by mixing it with a negative electrode active material according to an embodiment of the present invention.

[0042] Fig. 12 is SiO x And this is the result of TGA confirmation for the negative electrode active material according to the embodiment of the present invention.

[0043] Specific details of other embodiments are included in the detailed description and drawings.

[0044] The advantages and features of the present invention, and the methods for achieving them, will become clear with reference to the embodiments described in detail below together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms, and unless otherwise specified in the following description, all numbers, values, and / or expressions expressing components, reaction conditions, and contents of components in the present invention are to be understood as being modified in all cases by the term "about" because such numbers are approximations that reflect various uncertainties of measurement that occur in obtaining such values, among other things. In addition, when a numerical range is disclosed herein, such range is continuous and includes every value from the minimum value to the maximum value inclusive, unless otherwise indicated. Furthermore, when such a range refers to an integer, every integer from the minimum value to the maximum value inclusive, unless otherwise indicated, is included.

[0045] Additionally, when a range is described for a variable in the present invention, it will be understood that the variable includes all values ​​within the described range including the described endpoints of the range. For example, the range "5 to 10" will be understood to include the values ​​5, 6, 7, 8, 9, and 10, as well as any subranges such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, etc., and also any value between integers that fall within the described range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, and 6.5 to 9. For example, a range of "10% to 30%" would be understood to include all integers up to and including 30%, as well as any subranges such as 10% to 15%, 12% to 18%, 20% to 30%, etc., and any value between reasonable integers within the stated range, such as 10.5%, 15.5%, 25.5%, etc.

[0046] FIG. 1 is a schematic diagram illustrating a negative electrode active material for a secondary battery according to one embodiment of the present invention.

[0047] Referring to FIG. 1, a negative electrode active material (100) for a secondary battery according to the present invention may include a silicon compound (110); and a surface layer (120) provided to cover at least a portion of the surface of the silicon compound. The surface layer (120) may include graphene and carbon, and the carbon may be provided by carbonizing an organic compound that forms a catechol bond with the silicon compound (110).

[0048] The present invention is to improve a problem caused by volume expansion of a silicon compound material used as an anode active material (100) for a secondary battery, and by providing the surface layer (120) on the silicon compound (110), the conductivity of the silicon compound (110) can be improved, and the deterioration of long-term cycle characteristics of a secondary battery due to volume expansion can be solved. The surface layer (120) can improve the structural stability of the anode active material (100) for a secondary battery, and can be implemented by stably coating carbon and graphene on the silicon compound (110) using a novel method.

[0049] The above silicon compound (110) is SiO x (0≤x<2), SiO containing lithium compound x (0≤x<2), SiO containing magnesium compounds x (0≤x<2), silicon alloy (Si alloy), and silicon-carbon composite (Si-C composite).

[0050] For example, the silicon compound (110) is SiO containing the lithium compound. x (0≤x<2) Si or silicon oxide can contain lithium by a prelithiation method. Specifically, the prelithiation method includes a method of manufacturing a negative electrode after lithiating a silicon compound (110) by a physicochemical method or an electrochemical charging method.

[0051] SiO containing the above magnesium compound x (0≤x<2) may include MgSiO3 crystals and Mg2SiO4 crystals in silicon oxide.

[0052] The above silicon alloy may be represented as Si-M, where M may be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof. Specifically, the silicon alloy may be one selected from SiTiNi, SiAlMn, SiAlFe, SiFeCu, SiCuMn, SiMgAl, SiMgCu, and a combination thereof.

[0053] The above silicon-carbon composite may be a material formed of silicon and carbon through heat treatment or the like, wherein the carbon may be at least one of carbon, carbon nanotubes, and graphene.

[0054] The average thickness (t) of the surface layer (120) may be 10 nm to 10 μm. If the thickness (t) of the surface layer (120) is less than 10 nm, the effect of improving the volume expansion problem of the silicon compound (110) due to the surface layer is minimal, and if it exceeds 10 μm, the ion conductivity of the secondary battery may deteriorate. Specifically, the average thickness (t) of the surface layer (120) may be 10 nm to 5 μm, or 50 nm to 5 μm, or 100 nm to 5 μm, or 100 nm to 1 μm.

[0055] The average thickness (t) of the surface layer (120) may be provided in a length of 0.05% to 10% with respect to the average radius of the negative electrode active material (100). The negative electrode active material (100) may have a silicon compound (110) provided therein, and the surface layer (120) may be provided on the surface of the silicon compound (110). If the average thickness (t) of the surface layer (120) is less than 0.05% with respect to the average radius of the negative electrode active material (100), the surface layer (120) is difficult to be uniformly formed on the surface of the silicon compound (110), and if it exceeds 10%, the electrolyte is difficult to be uniformly impregnated into the silicon compound (110), and an unreacted region may be formed during the formation process by charge and discharge. Specifically, the average thickness (t) of the surface layer (120) may be 0.05% to 8%, or 0.1% to 8%, or 0.5% to 8%, or 1% to 8%, or 5% to 8% with respect to the average radius of the negative electrode active material (100).

[0056] The content of carbon in the silicon compound (110) may be included in a weight ratio of 0.2 wt% to 20 wt%, as evaluated by TGA. The surface layer (120) includes the graphene and carbon, and the carbon may be formed by carbonizing the organic compound. If the weight ratio of the carbon in the silicon compound (110) is less than 0.2 wt%, the effect of improving the conductivity of the negative electrode active material is minimal, and if it exceeds 20 wt%, the surface layer is not stably fixed, which is problematic. Specifically, the carbon in the silicon compound (110) may be 0.2 wt% to 15 wt%, or 0.2 wt% to 10 wt%, or 1 wt% to 10 wt%, or 1 wt% to 7 wt%.

[0057] The weight ratio of the organic compound to the silicon compound (110) may be 1: 0.1 to 0.8. The silicon compound (110) is provided in a particle form, and the organic compound may be coated on the silicon compound (110) in the particle form by a catechol bond. When the weight ratio of the organic compound to the silicon compound is less than 0.1, it is difficult to stably fix the graphene to the silicon compound (110), and when it is more than 0.8, a part where the organic compound clumps is formed, which may lower the electrical conductivity of the secondary battery. Specifically, when the silicon compound (110) is 1, the weight ratio of the organic compound may be 0.1 to 0.7, or 0.3 to 0.7, or 0.4 to 0.6.

[0058] The above organic compound may be selected from the group consisting of polydopamine, cellulose, polyphenylene, polypropylene, resin, tannic acid, lignan, catechin, flavonoid, phenolic acid and stilbene.

[0059] The organic compound may include a polymer formed by polymerizing a monomer. The monomer may include at least one of dopamine, dopamine hydrochloride, norepinephrine, L-dihydroxyphenylalanine, hydroxyphenolic acid, adrenaline, lignin monomer, ellagitannin, and pyrogall (1,2,3-benzenetriol).

[0060] When the organic compound is a polymer formed by polymerizing a monomer, the silicone compound (110) can be manufactured into an organic compound by coating the monomer and polymerizing the coated monomer. In the process of manufacturing the organic compound, the amine functional group of the organic compound and the silicone compound (110) can form a catechol bond through a covalent bond. Since the catechol bond forms a high bonding strength, graphene or the like can be stably fixed to the silicone compound (110).

[0061] The organic compound may include one or more catechol functional groups and an amine functional group that perform the catechol bond. The catechol functional group may be provided with a structure in which two hydroxyl groups (-OH) are adjacent to each other at the terminal of a benzene ring. The two hydroxyl groups of the organic compound may be bonded to the surface of the silicon compound and then oxidized to form a quinone. The quinone may form a catechol bond through a chain network formation reaction with an amine group.

[0062] Specifically, the monomer may include dopamine, and the organic compound may include polydopamine formed by polymerization of the dopamine. The dopamine is a substance having a molecular weight of approximately 153 Da and having catechol and amine functional groups, and after being provided on the surface of the silicon compound (110), a coating layer of polydopamine may be formed by oxidation of catechol amine contained in the dopamine. The polydopamine includes a catechol functional group, and the catechol functional group has redox ability, and thus, through the reduction ability of metal ions and specific adhesiveness, the graphene may be stably fixed to the surface of the silicon compound (110).

[0063] By adding the silicon compound (110) coated with the organic compound to the graphene dispersion solution, the graphene can be provided on the surface of the organic compound. The silicon compound provided with both the graphene and the organic compound can be heat-treated, and the organic compound can be carbonized and converted into carbon through the heat treatment.

[0064] The temperature for carbonizing the organic compound may be 300°C to 1500°C. If the temperature for carbonizing the organic compound is less than 300°C, the organic compound may not be carbonized uniformly, which may be problematic. If the temperature exceeds 1500°C, crystallization of silicon nanodomains may occur on the surface of the silicon compound, thereby deteriorating the structure and crystallinity of the silicon compound or forming silicon carbide. Specifically, the temperature for carbonizing the organic compound may be 300°C to 1200°C, or 300°C to 1000°C, or 500°C to 1500°C, or 500°C to 1200°C, or 700°C to 1500°C, or 700°C to 1100°C, or 700°C to 1000°C.

[0065] The negative electrode active material (100) for a secondary battery according to the present embodiment uses a silicon compound (110) as a main material and may include a surface layer (120) provided on the surface of the silicon compound (110). The surface layer (120) can induce slippage between the negative electrode active materials (100) when adjacent negative electrode active materials (100) collide with each other, thereby preventing problems such as the negative electrode active materials (100) colliding with each other and being destroyed.

[0066] Typically, as secondary batteries are charged and discharged, the volume of the silicon compound undergoes reversible and irreversible contraction and expansion, causing the silicon compound's position in the negative electrode to shift, causing the entire negative electrode to expand and reducing its conductivity. Furthermore, the negative electrode layer coated on the negative electrode plate may peel off, reducing electrical conductivity.

[0067] On the other hand, since the negative electrode active material (100) according to the present embodiment is provided with a surface layer (120), when the silicon compound (110) expands and contracts as charge and discharge are performed, slip is induced by the surface layer (120), thereby preventing the negative electrode active material (100) from being damaged. In addition, since the graphene provided in the surface layer (120) is provided by being directly or closely bonded to the negative electrode active material (100), it can act as a path for electron transfer, thereby effectively maintaining high ionic conductivity between neighboring negative electrode active materials (100). For example, the negative electrode active material (100) according to the present embodiment can improve the electrochemical performance of a secondary battery by alleviating the widening of the particle spacing, the decrease in electrical conductivity, etc. caused by the volume expansion of the silicon compound.

[0068] The electrical conductivity of a secondary battery using the above negative electrode active material (100) may be 0.01 S / cm to 30 S / cm.

[0069]

[0070] Figure 2 is a flow chart of a method for manufacturing a negative electrode active material for a secondary battery according to one embodiment of the present invention.

[0071] Referring to FIG. 2, the method for manufacturing the negative electrode active material for a secondary battery may include a step of dispersing a monomer in a first solvent, adding a silicon compound to the first solvent, and stirring the first dispersion solution to prepare a silicon compound coated with an organic compound; a step of preparing a graphene dispersion solution in which graphene and a cationic surfactant are dispersed, and mixing the silicon compound coated with the organic compound with the graphene dispersion solution to prepare a second dispersion solution; and a step of centrifuging the second dispersion solution to select a solid material.

[0072] The above solid material may include a silicon compound in the central portion and graphene and carbon in the surface portion. The surface portion may be stably fixed to the silicon compound to a predetermined thickness. The surface layer may be formed by providing an organic compound and graphene to the silicon compound, and then carbonizing the organic compound.

[0073] The above monomer may include at least one of dopamine, dopamine hydrochloride, norepinephrine, L-dihydroxyphenylalanine, hydroxyphenolic acid, adrenaline, lignin monomer, ellagitannin, and pyrogall (1,2,3-benzenetriol). The above silicone compound (110) may include SiO x (0≤x<2), SiO containing lithium compound x (0≤x<2), SiO containing magnesium compounds x (0≤x<2), silicon alloy (Si alloy), and silicon-carbon composite (Si-C composite).

[0074] The first solvent may include at least one of ultrapure water, N-methyl-2-pyrrolidone (NMP), methanol, ethanol, polypyrrolidone, isopropanol, acetone, petroleum ether, tetrahydrofuran, ethyl acetate, N,N-dimethylacetamide, N,N-dimethylformamide, n-hexane, and halogenated hydrocarbons.

[0075] Among the first solvents, the monomer may be present in an amount of 0.05 wt% to 5 wt%, and the weight ratio of the monomer to the silicon compound may be 1:0.1 to 0.8.

[0076] If the weight ratio of the monomer in the first solvent is less than 0.05 wt%, when coating the monomer on the silicone compound, the coating time increases, thereby lowering the process efficiency. If it exceeds 5 wt%, the viscosity of the first dispersion solution increases, making it difficult to uniformly disperse the silicone compound. Specifically, the monomer in the first solvent may be 0.1 wt% to 5 wt%, or 0.1 wt% to 3 wt%, or 0.5 wt% to 5 wt%, or 0.5 wt% to 3 wt%.

[0077] If the monomer is provided in the above silicone compound in an amount less than 0.1, the effect of the monomer is minimal, and if it exceeds 0.8, the dispersibility of the monomer is reduced, so that the surface layer may not be formed uniformly. By providing the monomer in the above-mentioned weight ratio with respect to the silicone compound, the monomer can be uniformly coated without lowering the electrical properties of the silicone compound. Specifically, the weight ratio of the monomer to the silicone compound may be 1: 0.1 to 0.7, or 1: 0.3 to 0.7, or 1: 0.3 to 0.6.

[0078] The first dispersion solution may be stirred for 0.5 to 24 hours to produce a silicone compound coated with an organic compound. If the time for stirring the first dispersion solution is less than 0.5 hours, the organic compound may not be stably coated on the surface of the silicone compound, which may be problematic. However, since 24 hours is sufficient, if the stirring time exceeds this, the process efficiency may be reduced, which may be problematic. By stirring the first dispersion solution for the aforementioned time, the monomer can be produced into an organic compound, and at the same time, the organic compound can be stably coated on the surface of the silicone compound.

[0079] The above graphene dispersion solution can be prepared by dispersing graphene in a second solvent, adding the cationic surfactant, and physically stirring.

[0080] The surfactants are cetyltrimethylammonium bromide (CTAB), alkyltrimethylammonium chlorides, dialkyl dimethyl ammonium chloride, benzalkonium chloride, didecyldimethylammonium chloride, 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)] (DSPE-mPEG), polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), polyethylene glycol-tert-octylphenyl ether. (polyethylene glycol tert-octylphenyl ether, Triton X-100), and sodium dodecyl sulfate (Sodium Dodecyl Sulfate, SDS).

[0081] The second solvent may include at least one of ultrapure water, N-methyl-2-pyrrolidone (NMP), methanol, ethanol, polypyrrolidone, isopropanol, acetone, petroleum ether, tetrahydrofuran, ethyl acetate, N,N-dimethylacetamide, N,N-dimethylformamide, n-hexane, and halogenated hydrocarbons.

[0082] The above graphene dispersion solution can be prepared by stirring graphene in the second solvent and then adding the cationic surfactant thereto. By sequentially adding graphene and the cationic surfactant to the second solvent, the graphene can be uniformly dispersed within the second solvent without clumping.

[0083] In addition, the surfactant may be 0.05 wt% to 100 wt% with respect to the graphene. If the surfactant is less than 0.05 wt% with respect to the graphene, a problem of the surface layer being detached from the silicon compound during the process of manufacturing a slurry may occur. In addition, the more the surfactant is added, the easier it is to form the surface layer, and since the surfactant is carbonized by subsequent heat treatment, a problem of side reactions does not occur. By providing the surfactant in the above-described range, the graphene can be stably dispersed in the second solvent. Specifically, the surfactant with respect to the graphene may be 0.05 wt% to 80 wt%, or 0.1 wt% to 80 wt%, or 0.1 wt% to 50 wt%.

[0084] In the step of preparing the second dispersion solution, the silicon compound coated with the organic compound is dispersed in a third solvent, and then the graphene dispersion solution is added thereto and physically stirred to prepare the second dispersion solution.

[0085] The concentration of graphene in the graphene dispersion solution may be 0.8 wt% to 2 wt%. If the concentration of graphene in the graphene dispersion solution is less than 0.8 wt%, it is difficult for the graphene to be uniformly coated on the surface of the silicon compound, and if it exceeds 2 wt%, problems such as graphene clumping in the graphene dispersion solution may occur.

[0086] The content of graphene with respect to 100 wt% of the silicon compound may be 1 wt% to 10 wt%. If the content of graphene is less than 1 wt%, the effect by graphene is insignificant, and if it exceeds 10 wt%, the capacity of the secondary battery may be reduced. The graphene with respect to the silicon compound is provided in the above-described weight ratio, thereby improving the conductivity of the silicon compound by the graphene and effectively improving the life characteristics of the secondary battery. Specifically, the graphene may be 1 wt% to 8 wt%, or 3 wt% to 8 wt%, or 4 wt% to 6 wt% with respect to 100 wt% of the silicon compound.

[0087] The above physical agitation may include one or more of ultrasonic mixing, mechanical mixing, and mixing using shear force.

[0088] The above ultrasonic mixing can be performed at 10 kHz to 80 kHz. During the ultrasonic mixing process, the graphene raw material can be pulverized and its size can be reduced. Specifically, the graphene raw material can be pulverized during the ultrasonic mixing process, and can be controlled to a predetermined size by performing the process at a time and frequency within the above-described range. If the frequency is less than 10 kHz, the graphene raw material is not pulverized to a desired size, and if it exceeds 80 kHz, the size of the pulverized graphene is too small to attach in a scale-like form on the surface of the silicon compound, which is problematic.

[0089] The above mechanical mixing can be accomplished by spinning at high speed, by applying pressure into the fluid, by spraying the fluid through small holes or gaps, or by causing the dispersed fluid to collide with the walls of the container.

[0090] Dispersion using the above shear force can be achieved by applying a shear force to the liquid while rotating two cylindrical rotating bodies and passing the fluid between the two rotating bodies.

[0091] The negative electrode active material for the secondary battery includes silicon oxide and a surface layer formed on the surface of the silicon oxide, and the surface layer includes graphene and carbon, and the carbon can be formed by carbonizing an organic compound that forms a catechol bond with the silicon compound. The step of preparing the second dispersion solution and the step of selecting the solid material can be repeated at least once to increase the thickness of the surface layer.

[0092] In the method for manufacturing a negative electrode active material for a secondary battery according to the present embodiment, the thickness of the surface layer can be easily controlled by controlling the number of repetitions of the step of manufacturing the second dispersion solution and the step of selecting the solid material.

[0093] In the method for manufacturing the negative electrode active material for the secondary battery, a step of heat treating in an inert gas atmosphere at a temperature of 300°C to 1500°C for 0.5 to 24 hours may be further included after the step of selecting the solid material. By the heat treatment, the organic compound of the surface layer is carbonized, thereby stably fixing the surface layer to the surface of the silicon compound. In addition, since the organic compound is carbonized and provided as carbon between the graphenes, electrical conductivity can be improved.

[0094] The first to third solvents may each include at least one of ethanol, ultrapure water, N-methyl-2-pyrrolidone (NMP), methanol, ethanol, polypyrrolidone, isopropanol, acetone, petroleum ether, tetrahydrofuran, ethyl acetate, N,N-dimethylacetamide, N,N-dimethylformamide, n-hexane, and halogenated hydrocarbons.

[0095] FIG. 3 is a schematic diagram illustrating a method for manufacturing a negative electrode active material according to one embodiment of the present invention.

[0096] Referring to Fig. 3, the negative electrode active material can be manufactured by coating an organic compound and graphene on a silicon compound, and then heat-treating to carbonize the organic compound to form a surface layer. The organic compound may be polydopamine, and the polydopamine may be formed by polymerizing dopamine as a monomer.

[0097] Specifically, the silicon compound (Si) can be coated with dopamine (DA) and polymerized to produce a silicon compound coated with polydopamine (PDA). The polydopamine can be stably fixed to the silicon compound by catechol bonding. The silicon compound coated with polydopamine can be added to a graphene dispersion solution and physically stirred, and graphene included in the graphene dispersion solution can be attached to the polydopamine. Subsequently, through heat treatment, the polydopamine can be carbonized to form carbon, and a surface layer composed of graphene and carbon can be formed on the surface of the silicon compound.

[0098] The surface layer provides a sliding effect to adjacent negative electrode active materials, so that even when the negative electrode active materials reversibly change in volume during the charge and discharge process, they slide against each other without being destroyed by applying physical force to the surrounding negative electrode active materials, thereby improving the life characteristics of the secondary battery. In addition, the graphene provided in the surface layer greatly improves the conductivity between adjacent negative electrode active materials due to increased electrical conductivity, and can provide a path for charge movement by connecting like a bridge in the empty space formed by displacement due to volume change of the negative electrode active materials.

[0099] According to another aspect of the present invention, the present invention comprises the above-described negative electrode active material; graphite; a binder; and a conductive material, and based on 100 parts by weight of the total of the negative electrode active material, graphite, binder, and conductive material, the graphite may be included in an amount of 30 to 95 parts by weight, the binder in an amount of 2 to 10 parts by weight, and the conductive material in an amount of 0 to 10 parts by weight.

[0100] In the present embodiment, the negative electrode for the secondary battery may be used by mixing the negative electrode active material having the silicon compound and the surface layer with graphite. In this case, the binder and conductive agent may be included in a lower content than in the case of using graphite alone or in the case of using a mixture of the silicon compound and graphite, and the conductive agent may not be included.

[0101] The above graphite may include natural graphite or artificial graphite.

[0102] The above natural graphite may be flake graphite, vein graphite, or amorphous graphite, and specifically, may be bulk graphite or vein graphite. In addition, more specifically, the above natural graphite may have a high tap density or bulk density because the contact area between particles increases, the bonding area increases, and thus the bonding strength is improved.

[0103] The above artificial graphite may be in the form of powder, flake, block, plate, or rod, and specifically, in order to exhibit the best output characteristics, the shorter the movement distance of lithium ions, the better, and in order to shorten the movement distance in the direction of the electrode, the crystal grain orientation of the artificial graphite may be isotropic.

[0104] In this embodiment, the graphite is included in the above-described range and mixed with the negative electrode active material, thereby further improving the capacity characteristics and life characteristics of the secondary battery through electrochemical, particle shape, and particle surface interactions with the negative electrode active material.

[0105] Typically, a negative electrode essentially contains a binder to bind particles together and a conductive agent to improve electrical conductivity. However, the binder and conductive agent relatively reduce the specific capacity of the negative electrode, and there is a problem that the production cost increases because the binder and conductive agent must be uniformly mixed with the negative electrode active material, graphite, etc. In addition, since the conductive agent exists as separate particles from the negative electrode active material, graphite, etc., the negative electrode active material, graphite, etc., which undergo volume expansion during the cycle, do not come into close contact with the conductive agent, which causes a problem of reduced electrical conductivity. This has been particularly problematic in the case of silicon compounds that undergo large volume expansion during the charge and discharge process.

[0106] The above binder may be provided in an amount of 2 to 10 parts by weight. The binder physically binds between the negative electrode active material and graphite, and between the negative electrode active material, graphite, and current collector. If the amount is less than 2 parts by weight, the function of the binder is not sufficient, and if it exceeds 10 parts by weight, unnecessary binder is used, which reduces the specific capacity of the secondary battery and improves the production cost.

[0107] The above binder may include at least one of styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), nitrile butadiene rubber (NBR), polyacrylamide (PAM), polyacrylonitrile (PAN), polyimide (PI), and polyamideimide (PAI).

[0108] The conductive material may be present in an amount of 0 to 10 parts by weight. That is, in the present embodiment, the conductive material may be omitted entirely, and even when the conductive material is used, the electrochemical characteristics and cycle characteristics of the secondary battery may be improved even when used in a lower amount than conventional methods, such as 10 parts by weight or less.

[0109] The conductive material may include carbon nanotubes, graphene, graphite, carbon black, or carbon fibers. For example, the conductive material may include carbon nanotubes, graphene, graphite such as natural graphite or artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, superp, toka black, and denka black, carbon fibers, and the like. More specifically, the conductive material may be carbon nanotubes or graphene.

[0110] The present invention is SiO x This can improve the problem of volume change inherent in materials. Specifically, this problem can be solved by imparting conductivity to the surface of silicon-based anode materials and forming a surface layer to improve volume, thereby ensuring structural stability within the electrode. Furthermore, performance can be enhanced by applying a carbonization process to the surface of silicon-based anode materials through the introduction of a carbon layer and graphene coating.

[0111] In addition, the negative electrode active material for a secondary battery according to the present invention can improve the conductivity of the negative electrode for a secondary battery by increasing the interlayer adhesion between the surface of the silicon compound and graphene, and forming a surface layer including graphene and carbon through final carbonization. In addition, the method for manufacturing the negative electrode active material for a secondary battery according to the present invention can improve process efficiency and productivity by using an aqueous graphene solution and a water-soluble polymer in consideration of the negative electrode aqueous process, thereby enabling an aqueous process rather than an organic solvent. In addition, since an aqueous process is possible, the use of organic solvents is reduced, so that the negative electrode active material for a secondary battery can be manufactured in an environmentally friendly manner.

[0112] Hereinafter, examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the scope of the present invention is not limited by the following examples.

[0113] 1. Manufacturing of negative electrode active material

[0114] Preparation of dopamine-silicon dispersion solution

[0115] At room temperature, 0.5 g of DA (dopamine hydrochloride) was dispersed in 50 ml of ethanol, and then the silicon material (SiO x ) 1g was added together with DA dispersed in ethanol and dispersed. The solution in which DA and silicone material were dispersed together was physically stirred at room temperature for 1 to 3 h to prepare a dopamine-silicon dispersion solution.

[0116] Polydopamine production

[0117] The dopamine-silicon dispersion solution was physically stirred for 12 h to form a polydopamine (PDA) layer on the surface of the silicon material. After stirring, the solution was filtered and distilled water was used to wash away any remaining impurities.

[0118] Preparation of graphene dispersion solution

[0119] Graphene (11 mg) was dispersed in 1000 mL of DI water to prepare a 1.1 wt% (11 mg / mL-water) dispersion. 1 wt% of a cationic surfactant was added to the 1.1 wt% graphene dispersion, and the dispersion was performed using a tip sonicator (BANDELIN, SONOPLUS HD 4200, pulse time 3 / 2 s, 20 kHz model amp 60%) for 1.5 h to reduce the size of the graphene and ensure uniform dispersion with the surfactant. Cetyltrimethylammonium bromide (CTAB) was used as the cationic surfactant.

[0120] SiO coated with graphene and carbon x manufacturing

[0121] 1 g of polydopamine (PDA)-coated silicone material and 1.5 g of ethanol were added together to a conical tube. The graphene dispersion solution was added so that the weight ratio of the polydopamine (PDA)-coated silicone material to the graphene dispersion solution was 1:2. The entire coating process was carried out at room temperature, and the mixture solution was mixed at 3000 rpm for 1 min using a vortex (Vortex, genie2) to perform the coating. Ethanol was additionally added to the conical tube to remove the residual graphene and impurities, excluding the coated silicone material. The amount of additional ethanol was 5 to 10 times the weight ratio of the graphene to the silicon material. Centrifugation (Hanil fleta 40p) was performed at 3000 rpm for 3 min to obtain the graphene-coated silicone material. At this time, the centrifugation speed was set to 500–4,000 rpm. The solid material obtained by centrifugation was dried in a vacuum oven using each prepared cathode and at 80°C for 4 h. The graphene repeat coating process was performed by repeating the above steps three times.

[0122] Polydopamine (PDA) coated between the silicon material surface and the graphene layer was carbonized, and heat treatment was performed to remove the surfactant remaining after coating. The heat treatment was performed by increasing the temperature from room temperature to 800 ℃ at a rate of 5 ℃ / min, and then performing the heat treatment for 2 h in an argon atmosphere to form SiO coated with graphene and carbon. x A negative electrode active material was manufactured.

[0123] graphene-coated SiO x

[0124] Silicon material (SiO x) was prepared so that 0.5 g of dopamine per 1 g of silicon material and graphene dispersion solution was prepared by adding the graphene dispersion solution prepared by the above method so that the ratio of silicon material and graphene dispersion solution was 1:2 to prepare a mixed solution. The process was carried out at room temperature, and the mixed solution was mixed for 1 min at 3000 rpm using a vortex (Vortex, genie2) to perform coating. In order to remove residual graphene and impurities, ethanol was additionally added to the conical tube from a minimum of 0 g to a maximum of approximately 30 g, and centrifugation (Hanil fleta 40p) was performed at 3000 rpm for 3 min. The solid material obtained by centrifugation was dried in a vacuum oven at 80 ℃ for 4 h to obtain graphene-coated SiO x A negative electrode active material was manufactured.

[0125] Cathode slurry manufacturing

[0126] A negative electrode slurry was prepared using the negative electrode active material manufactured according to the method described above.

[0127] When using only silicon as the negative electrode active material, the negative electrode slurry was prepared by adding DI water so that the composition ratio of silicon material, conductive material (carbon black), and binder (mixture of SBR:CMC in a weight ratio of 1:1) was 80:10:10 wt%.

[0128] When using a mixture of artificial graphite and silicon as an anode active material, the composition ratio of the anode active material, which is a mixture of silicon material and graphite, conductive material (carbon black) and binder (a mixture of SBR:CMC in a weight ratio of 1:1) was 94:3:3 wt%, and DI water was added to adjust the solid content to 45% to prepare a cathode slurry. At this time, the anode active material was used by mixing 20 wt% of silicon material and 80 wt% of graphite.

[0129] Half-cell manufacturing

[0130] Using the cathode slurry manufactured by the above-mentioned method, each manufactured cathode electrode had a density of 1.6 g / cm 3 A silicon-based negative electrode was used. CR2032 coin-type batteries (half-cells) were manufactured using a mixed solvent (ethylene carbonate: diethyl carbonate: dimethyl carbonate = 25:45:30 v%), 1% vinylene carbonate, and 1% LiPO2F2 as an electrolyte, and a polyethylene separator (W-SCOPE KOREA Co. Ltd., Korea). The CR2032 coin cells were subjected to three cycles at 0.1 C before performing charge and discharge cycles. In the case of a negative electrode composed solely of silicon material, 1 C is 1600 mAh / g, and in the case of a mixed negative electrode of silicon material and artificial graphite, it is 580 mAh / g.

[0131] 2. Evaluation of negative electrode active materials

[0132] Figure 4 shows graphene-coated SiO x is an SEM image of SiO. Fig. 5 is a SEM image of SiO x This is an SEM image of a negative electrode material sequentially coated with polydopamine (PDA) and graphene (Gr).

[0133] Figure 4 shows a negative electrode active material in which only graphene (Gr) is coated on SiOx, and Figure 5 shows a negative electrode active material in which both polydopamine (PDA) and graphene (Gr) are coated on SiOx and then carbonized.

[0134] Referring to Fig. 4, SiO x In Fig. 4, graphene is attached while maintaining a sheet shape, and graphene is entirely SiO by polydopamine. x It was confirmed that the coating was uniformly applied. It was confirmed that the coating was applied in a similar shape regardless of whether it was before or after the carbonization process of polydopamine by heat treatment. In other words, there was no significant difference in the surface morphology even when more polydopamine was included, and it was confirmed that there was no significant change before or after carbonization.

[0135] Fig. 6 is SiOx , dopamine-coated SiO x and polydopamine-coated SiO x This is a diagram showing the FT-IR results.

[0136] Referring to Fig. 6, SiO x , dopamine-coated SiO x , and SiO coated with polydopamine formed by polymerization of the above dopamine. x FT-IR of these coatings showed almost similar results. SiO x It was confirmed that the chemical structure and state did not change significantly.

[0137] Figure 7 is a graph showing the FT-IR results of the negative electrode active material before and after carbonization. Figure 8 is a graph showing the Raman peak changes of the negative electrode active material before and after carbonization.

[0138] In Fig. 7 and Fig. 8, SiO x After coating polydopamine and graphene, the carbonization process was performed by heat treatment from room temperature to 800℃ in an argon atmosphere, and the results were compared before and after. FT-IR showed no significant changes before and after carbonization. On the other hand, Raman peaks confirmed that the D and G band peaks were larger after carbonization. This is believed to be because polydopamine was converted to carbon during the carbonization process.

[0139] Fig. 9 is SiO x, Graphene coated SiO x (SiO x +Gr) and polydopamine and graphene coated and carbonized SiO x (SiO x This is the result of measuring the electrical conductivity of +Gr+PAD.

[0140] SiO x Compared to graphene-coated SiO x The electrical conductivity increased. In addition, graphene-coated SiOx and Polydopamine and graphene coated and carbonized SiO x When compared, it was confirmed that the electrical conductivity increased significantly when polydopamine was used and carbonization was performed compared to when only graphene was used.

[0141] Polydopamine itself does not affect electrical conductivity, but by fixing the graphene more firmly with polydopamine and performing carbonization here, it was confirmed that the electrical conductivity of the graphene greatly increases. The carbon material formed as a result of carbonization of polydopamine alone electrically connects neighboring graphene and at the same time, SiO x It was confirmed that it was stably fixed and increased the electrical conductivity.

[0142] Fig. 10 is SiO x , and the results of evaluating the electrochemical performance of a half-cell using a negative electrode active material according to an embodiment of the present invention as a negative electrode.

[0143] In Fig. 10, each SiO x Sole and SiO coated with polydopamine and graphene, which are negative active materials according to the present invention, and carbonized x were used as negative active materials, respectively. In the half-cell of Fig. 10, the composition of the negative electrode was 80 wt% of the negative active material, 10 wt% of the conductive agent (carbon black), and 10 wt% of the binder (SBR / CMC). After each went through the formation process at room temperature, 3 cycles were performed with 0.005-1.5 V charging and 0.1 C discharging to confirm.

[0144] SiO xIn the case of a single electrode, the capacity was found to decrease as charge and discharge were performed, whereas the negative electrode active material according to an embodiment of the present invention stably maintained the same capacity during three charge and discharge cycles. In addition, the results of confirming the life characteristics for 50 cycles also showed that the negative electrode active material according to an embodiment of the present invention stably maintained the capacity during the cycle, but SiO x The single negative electrode material exhibited a relatively low capacity, and it was confirmed that the capacity gradually decreased during the cycling process.

[0145] Fig. 11 is SiO x , and the results of evaluating the electrochemical performance of a half-cell using artificial graphite as a negative electrode by mixing it with a negative electrode active material according to an embodiment of the present invention.

[0146] In Fig. 11, the composition of the negative electrode was composed of 94 wt% of negative active material (20 wt% of silicon material, 80 wt% of artificial graphite), 3 wt% of conductive agent (carbon black), and 3 wt% of binder (SBR / CMC). The ratio of silicon and graphite was determined based on a capacity of 600 mAh / g. The electrode density of the negative electrode was 1.6 g / cc. After each formation process at room temperature, 3 cycles were performed with 0.005-1.5 V charge and 0.1 C discharge to confirm.

[0147] Referring to Fig. 11, SiO x In the case of mixing the negative active material according to the embodiment of the present invention with artificial graphite, it was confirmed that the capacity gradually decreased during the course of performing 3 cycles. On the other hand, in the case of mixing the negative active material according to the embodiment of the present invention with artificial graphite, it was confirmed that the capacity was stably exhibited during 3 cycles of charge and discharge. In addition, in the result of confirming the life characteristics continuously for 40 cycles, in the case of mixing the negative active material according to the embodiment of the present invention with artificial graphite, a high capacity was stably maintained during the course of performing the cycle, but in the case of SiO xIt was confirmed that the case of mixing artificial graphite and graphite showed a relatively low capacity.

[0148] The cathode manufactured according to this example demonstrated stable, high capacity and improved cycle characteristics. Furthermore, it was confirmed that these characteristics were effectively demonstrated even when mixed with graphite.

[0149] Fig. 12 is SiO x And this is the result of TGA confirmation for the negative electrode active material according to the embodiment of the present invention.

[0150] In Fig. 12, SiO x And the negative electrode active material according to the embodiment of the present invention was confirmed by measuring TGA (STA7300, Hitachi) twice each. In the negative electrode active material according to the embodiment of the present invention, the amount of graphene coating per 1 g of the active material was found to be about 5 wt%.

[0151] Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering its technical spirit or essential characteristics. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims below rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

Claims

1. Silicone compounds; and A surface layer provided to cover at least a portion of the surface of the silicon compound; The above surface layer comprises graphene and carbon, The above carbon is a negative electrode active material for a secondary battery formed by carbonizing an organic compound that forms a catechol bond with the above silicon compound.

2. In paragraph 1, The above silicon compound is SiO x (0≤x<2), SiO containing lithium compound x (0≤x<2), SiO containing magnesium compound x A negative electrode active material for a secondary battery comprising at least one of (0≤x<2), a silicon alloy (Si-alloy), and a silicon-carbon composite (Si-C composite).

3. In paragraph 1, A negative electrode active material for a secondary battery having an average thickness of the surface layer of 10 nm to 10 ㎛.

4. In paragraph 1, A negative electrode active material for a secondary battery, wherein the thickness of the surface layer is 0.05% to 10% of the average radius of the negative electrode active material.

5. In paragraph 1, A negative electrode active material for a secondary battery, wherein the carbon in the silicon compound is 0.2 wt% to 20 wt% in weight ratio.

6. In paragraph 1, A negative electrode active material for a secondary battery, wherein the organic compound to the silicon compound is in a weight ratio of 1:0.1 to 0.

8.

7. In paragraph 1, The organic compound is a negative electrode active material for a secondary battery, comprising at least one selected from the group consisting of polydopamine, cellulose, polyphenylene, polypropylene, resin, tannic acid, lignan, catechin, flavonoid, phenolic acid, and stilbene.

8. In paragraph 1, The above organic compound includes a polymer formed by polymerizing a monomer, The above monomer is a negative electrode active material for a secondary battery comprising at least one of catechol, dopamine, dopamine hydrochloride, norepinephrine, L-dihydroxyphenylalanine, hydroxyphenol acid, adrenaline, lignin monomer, ellagitannin, and pyrogallol.

9. In paragraph 1 A negative electrode active material for a secondary battery, wherein the temperature for carbonizing the organic compound is 300°C to 1500°C.

10. In paragraph 1 A negative electrode active material for a secondary battery, wherein the electrical conductivity of the secondary battery using the above negative electrode active material is 0.001 S / cm to 30 S / cm.

11. A step of dispersing a monomer in a first solvent, adding a silicone compound to the first solvent, and stirring the first dispersion solution to produce a silicone compound coated with an organic compound; A step of preparing a graphene dispersion solution in which graphene and a cationic surfactant are dispersed, and mixing a silicon compound coated with the organic compound with the graphene dispersion solution to prepare a second dispersion solution; and A method for producing a negative electrode active material for a secondary battery according to any one of claims 1 to 10, comprising the step of centrifuging the second dispersion solution to select a solid material.

12. In paragraph 11, The above monomer comprises at least one of catechol, dopamine, dopamine hydrochloride, norepinephrine, L-dihydroxyphenylalanine, hydroxyphenolic acid, adrenaline, lignin monomer, ellagitannin, and pyrogallol, The above silicon compound is SiO x (0≤x<2), SiO containing lithium compound x (0≤x<2), SiO containing magnesium compound x (0≤x<2), a method for manufacturing a negative electrode active material for a secondary battery, comprising at least one of a silicon alloy (Si-alloy) and a silicon-carbon composite (Si-C composite).

13. In paragraph 11, In the first solvent, the monomer is present in an amount of 0.05 wt% to 5 wt%, A method for manufacturing a negative electrode active material for a secondary battery, wherein the weight ratio of the monomer to the silicon compound is 1:0.1 to 0.

8.

14. In paragraph 11, A method for producing a negative electrode active material for a secondary battery, wherein the organic compound comprises at least one selected from the group consisting of polydopamine, cellulose, polyphenylene, polypropylene, resin, tannic acid, lignan, catechin, flavonoid, phenolic acid, and stilbene.

15. In paragraph 14, The above graphene dispersion solution is prepared by dispersing graphene in a second solvent, adding the cationic surfactant, and physically stirring. For the above graphene, the surfactant is 0.05 wt% to 100 wt%, The above surfactants are cetyltrimethylammonium bromide (CTAB), alkyltrimethylammonium chlorides, dialkyl dimethyl ammonium chloride, benzalkonium chloride, didecyldimethylammonium chloride, 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)] (DSPE-mPEG), polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), polyethylene glycol-tert-octylphenyl ether. A method for producing a negative electrode active material for a secondary battery, comprising at least one of (polyethylene glycol tert-octylphenyl ether), and sodium dodecyl sulfate (SDS).

16. In paragraph 15, In the step of preparing the second dispersion solution, The silicon compound coated with the organic compound is dispersed in a third solvent, and then a second dispersion solution is prepared by physical stirring with the graphene dispersion solution. The concentration of graphene in the above graphene dispersion solution is 0.1 wt% to 3 wt%, A method for producing a negative electrode active material for a secondary battery, wherein the graphene is present in a weight ratio of 1 wt% to 10 wt% relative to 100 wt% of the silicon compound.

17. In paragraph 11, The above secondary battery negative electrode active material comprises silicon oxide and a surface layer formed on the surface of the silicon oxide, and the surface layer comprises graphene and carbon. A method for producing a negative electrode active material for a secondary battery, wherein the step of producing the second dispersion solution and the step of selecting the solid material are repeated at least once to increase the thickness of the surface layer.

18. In paragraph 11, A method for producing a negative electrode active material for a secondary battery, further comprising a step of heat treating the solid material in an inert gas atmosphere at a temperature of 300° C. to 1500° C. for 0.5 to 24 hours after the step of selecting the solid material.

19. A negative electrode active material according to any one of clauses 1 to 10; graphite; a binder; and a conductive material; A secondary battery negative electrode, wherein the graphite is contained in an amount of 30 to 95 parts by weight, the binder is contained in an amount of 2 to 10 parts by weight, and the conductive material is contained in an amount of 0 to 10 parts by weight, based on 100 parts by weight of the total of the negative electrode active material, graphite, binder, and conductive material.

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