Negative electrode active material for lithium secondary battery

Abstract

The present invention relates to a negative electrode active material comprising a carbon-based material and a silicon-based material, the carbon-based material having a property of adjusting the viscosity of a slurry, thereby enabling excellent electrode coating quality. The lithium secondary battery comprising the negative electrode active material of the present invention has high capacity characteristics while effectively preventing electrical isolation and peeling phenomena due to volume expansion of silicon, and can achieve excellent lifespan characteristics at low temperatures.

Description

Technical Field

[0001] The present invention relates to a negative electrode active material for a lithium secondary battery, a negative electrode including the negative electrode active material, and a lithium secondary battery. Background Art

[0002] In a lithium secondary battery, the negative electrode material serves to store and release lithium ions from the positive electrode so that current flows through an external circuit. During charging, lithium ions move from the positive electrode to the negative electrode and enter between the layers of graphite, which is the material of the negative electrode material, causing the graphite to expand and resulting in an increase in volume. That is, the expansion of graphite causes a structural change over time, which becomes a cause of a decrease in battery capacity. In recent years, the battery industry has been competing to develop next-generation negative electrode materials to meet the demand for high-capacity batteries in the era.

[0003] Currently, graphite stacked in a regular layered structure is mainly used as the negative electrode material, and it is roughly divided into natural graphite and artificial graphite. Natural graphite used to be the most stable and inexpensive material that could store lithium ions, but due to the expansion problem during use, the structural stability has gradually decreased. Therefore, the use ratio of artificial graphite that improves this problem is gradually increasing. Artificial graphite is made by high-temperature heat treatment at 3000 °C or higher. Compared with natural graphite, artificial graphite has higher crystallinity and a more uniform structure, so it has higher stability. However, due to additional manufacturing processes, such as processing petroleum-based asphalt or coal tar raw materials to produce needle coke, and aggregating and heating the crushed needle coke, etc., it is expensive.

[0004] In addition, silicon negative electrode materials have properties of higher capacity and higher power than graphite-based negative electrode materials, so they have attracted much attention as next-generation materials. Each 6 carbon atoms in graphite store 1 lithium ion, but silicon has a structure that stores 15 lithium ions per 4 atoms. Therefore, the unit energy capacity of the silicon-based negative electrode material is about 10 times higher than that of graphite. However, in the case of silicon negative electrode materials, when charging and discharging are repeated, the volume easily expands, resulting in a decrease in charge-discharge efficiency. To improve the volume expansion problem of this silicon negative electrode material, the silicon negative electrode material is utilized in the form of adding 4 - 5% to the graphite-based negative electrode material. Summary of the Invention

[0005] (I) Technical Problems to be Solved

[0006] According to one aspect of the present invention, a negative electrode active material can be provided, which can improve the increase in slurry viscosity during the manufacturing process of the negative electrode, and thus can achieve excellent electrode coating quality.

[0007] According to one aspect of the present invention, a negative electrode can be provided, which has a high capacity and at the same time alleviates the volume expansion caused by charging and discharging of the secondary battery, and thus has long-life characteristics.

[0008] According to one aspect of the present invention, a lithium secondary battery including a negative electrode having the above advantages can be provided, and it can be widely applied to the field of green technologies, such as electric vehicles, battery charging stations, other battery-utilizing solar power generation and wind power generation, etc.

[0009] (II) Technical Solution

[0010] The negative electrode active material according to the present invention may include a carbon-based material and a silicon-based material that satisfy the following formula 1.

[0011] [Formula 1]

[0012] 0.9 ≤ D A50 / D B50 ≤ 1.1

[0013] (wherein the D A50 and the D B50 are respectively the 50th percentile of the volume-weighted distribution of the carbon-based material diameter measured by two-dimensional perspective method and laser diffraction method.)

[0014] In the negative electrode active material according to one embodiment, the carbon-based material may be artificial graphite or natural graphite.

[0015] In the negative electrode active material according to one embodiment, the carbon-based material may be coated with pitch carbon, soft carbon, hard carbon, heavy oil, heavy fuel oil, phenols, mesophase pitch carbide, calcined coke, carbon fiber or a mixture thereof.

[0016] In the negative electrode active material according to one embodiment, the silicon-based material may include a silicon-based material selected from Si, SiOx (0 < x < 2), metal-doped SiOx (0 < x < 2) and silicon-carbon composites.

[0017] In the negative electrode active material according to one embodiment, the content of the silicon-based material may be 0.5 - 30 parts by weight relative to 100 parts by weight of the carbon-based material.

[0018] The method for manufacturing a negative electrode according to the present invention may include a coating step of depositing a negative electrode active material slurry on a current collector and then drying it, wherein the negative electrode active material slurry includes the negative electrode active material according to one embodiment of the present invention and a conductive material.

[0019] In the method for manufacturing a negative electrode according to one embodiment, the conductive material may be carbon nanotubes.

[0020] In the method for manufacturing a negative electrode according to one embodiment, the viscosity of the negative electrode active material slurry may be 2000 - 10000 cP.

[0021] In the method for manufacturing a negative electrode according to an embodiment, the solid content of the negative electrode active material slurry may be 10-70 parts by weight relative to a total of 100 parts by weight.

[0022] In the method for manufacturing a negative electrode according to an embodiment, the die head pressure in the coating step may be 0.05-20 psi.

[0023] In the method for manufacturing a negative electrode according to an embodiment, the negative electrode active material slurry may further contain carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), or a mixture thereof.

[0024] The lithium secondary battery of the present invention may include: a positive electrode; a negative electrode manufactured by the method for manufacturing a negative electrode of the present invention; and a separator disposed between the positive electrode and the negative electrode.

[0025] (III) Beneficial effects

[0026] The negative electrode active material according to an embodiment of the present invention can adjust the viscosity of the slurry during the manufacturing process of the negative electrode, thereby achieving excellent electrode coating quality.

[0027] The negative electrode active material according to an embodiment of the present invention and the negative electrode containing the negative electrode active material can have high-capacity characteristics according to the silicon content, and at the same time, can suppress the electrical isolation and peeling phenomena caused by the volume expansion of silicon.

[0028] The lithium secondary battery according to an embodiment of the present invention can achieve excellent life characteristics. Detailed description

[0029] Hereinafter, the present invention will be described in detail. However, this is merely exemplary, and the present invention is not limited to the specific embodiments described exemplarily. Unless otherwise defined, the terms used in this specification should be interpreted as those commonly understood by those skilled in the art.

[0030] Unless otherwise specifically stated herein, the singular forms used in this specification may also include the plural forms.

[0031] In addition, the numerical ranges used in this specification include the lower limit value and the upper limit value and all values within the range, the increments logically derived from the form and width of the defined range, all values defined therein, and all possible combinations of the upper and lower limits of the numerical ranges defined in different forms from each other. In the specification of the present invention, unless otherwise specifically defined, values outside the numerical range that may be generated due to experimental errors or rounding of values are also included in the defined numerical range.

[0032] In this specification, terms such as "comprising", "including", "having", and "possessing" indicate the presence of features or components described in the specification, and unless otherwise specified, do not preclude the possibility of adding one or more other features or components in advance.

[0033] As the demand for large and medium-sized secondary batteries such as secondary batteries for electric vehicles (EVs) and secondary batteries for energy storage systems (ESSs) is expected to increase rapidly, the necessity of developing high-capacity secondary batteries is also increasing. As part of this, for the practical application of a silicon-based composite anode material that exhibits high-capacity characteristics, a technology is needed to improve the problem of deterioration in electrode coating quality caused by the addition of a conductive material, which is added to alleviate volume expansion occurring during charge and discharge of the secondary battery.

[0034] The anode active material of the present invention can adjust the viscosity and solid content of the slurry during the manufacture of the anode, and thus can improve the adhesion between electrode fracture and the active material. Therefore, it is possible to suppress electrical isolation and peeling phenomena caused by volume expansion of silicon occurring during charge and discharge of the secondary battery, and to improve life characteristics and charge and discharge characteristics at low temperatures.

[0035] Specifically, the present invention provides an anode active material comprising a carbon-based material and a silicon-based material that satisfy the following formula 1.

[0036] [Formula 1]

[0037] 0.9 ≤ D A50 / D B50 ≤ 1.1

[0038] (wherein D A50 and D B50 are the 50th percentiles of the volume-weighted distribution of the carbon-based material diameter measured by two-dimensional perspective method and laser diffraction method, respectively.)

[0039] In the above formula, when D A50 / D B50 is in the range of 0.9 or more and 1.1 or less, the carbon-based material can achieve excellent sphericity. Specifically, it can be 0.9 < D A50 / D B50 < 1.1. At this time, the anode active material has the characteristic of not excessively increasing the viscosity of the slurry, so that the viscosity can be reduced without changing the amount of solids in the slurry. Therefore, it is not only beneficial to electrode coating, but also can improve life characteristics and low-temperature performance.

[0040] In addition, when D A50 / D B50When the value is less than 0.9 or exceeds 1.1, the slurry formed during the negative electrode coating cannot be formed uniformly, and due to the reduction of the solid content of the slurry, the surface tension decreases, which may result in an uneven coating. In addition, during the coating drying step, a large amount of solvent in the coating is lost, resulting in a large volume change, which may lead to electrode breakage and a decrease in the adhesion between the active materials.

[0041] The D of the particles A50 It can be measured using a particle shape analyzer. Specifically, a particle shape analyzer can be used to capture a two-dimensional (2D) image of the particles, and the diameter of the analyzed particles can be measured using the captured two-dimensional image.

[0042] For example, the D of the particles A50 can be the value of the 50th percentile after measuring the diameters of the particles in about 10,000 two-dimensional images captured using an image analysis program.

[0043] For example, the D of the particles A50 can be measured as follows: Disperse the particle sample, observe it with the high-resolution image sensor of the particle shape analyzer, capture the two-dimensional image of the particles and analyze it. Alternatively, the diameter of the particles can be measured as follows: After preparing a solution by mixing the particles with a water or ethanol solvent, capture the two-dimensional image of the secondary particles dispersed in the solvent using a dynamic camera and analyze it.

[0044] The sample can be prepared by dropping 1 mm 3 of the particle sample onto a glass sample plate and applying a gas pressure of 3 bar for dispersion. Alternatively, for example, the sample can be prepared by mixing and dispersing 1 mm 3 of the particle sample with an ethanol solvent and then inserting it between two glass sample plates.

[0045] For example, the particle shape analyzer can use Mastersizer, Morphologi G3 or Morphologi 4 of Malvern company, Sync, Camsizer-X2 of Microtrac company, etc.

[0046] The laser diffraction method can generally measure particle sizes ranging from the submicron region to several millimeters, and can obtain results with high reproducibility and high resolution. Specifically, the carbon-based material powder is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Mastersizer 3000 of Malvern Instruments Ltd.). By measuring the difference in the diffraction pattern according to the particle size when the particles pass through the laser beam, the particle size distribution can be calculated. At this time, D can be measured by calculating the particle diameter at the position where the cumulative distribution of the number of particles according to the particle size in the measuring device reaches 50%. B50 。

[0047] Specifically, D measured by the two-dimensional perspective method A50 can represent the diameter after replacing the area of the carbon-based material particles with a circle, and D measured by the laser diffraction method B50 can represent the diameter after replacing the area of the carbon-based material particles with a sphere.

[0048] The carbon-based material in the negative electrode active material according to an embodiment of the present invention may be crystalline carbon, amorphous carbon, a carbon composite, carbon fiber, or the like.

[0049] Examples of the amorphous carbon may include hard carbon, soft carbon, coke, mesocarbon microbead (MCMB), mesophase pitch-based carbon fiber (MPCF), and the like.

[0050] Examples of the crystalline carbon may include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and the like.

[0051] Specifically, the carbon-based material in the negative electrode active material according to an embodiment of the present invention may be artificial graphite or natural graphite.

[0052] The carbon-based material in the negative electrode active material according to an embodiment of the present invention may be coated with pitch carbon, soft carbon, hard carbon, heavy oil, heavy oil, phenol, mesophase pitch carbide, calcined coke, carbon fiber, or a mixture thereof. Specifically, it may be coated with pitch carbon, hard carbon, heavy oil, heavy oil, or phenol. Therefore, the surface of the carbon-based material particles can have higher hydrophobicity, so that the viscosity of the slurry can be appropriately adjusted during the manufacture of the negative electrode, and the negative electrode coating quality can be further improved.

[0053] The silicon-based material according to an embodiment of the present invention may include a silicon-based material selected from Si, SiOx (0 < x < 2), metal-doped SiOx (0 < x < 2), and silicon-carbon composites. The metal may include lithium and / or magnesium, and the metal-doped SiOx (0 < x < 2) may include metal silicate. Specifically, in the silicon-based material SiOx, the range of x may be 0.2 < x < 1.8, and more specifically, the range of x may be 0.5 < x < 1.5.

[0054] In the negative electrode active material according to an embodiment of the present invention, the content of the silicon-based material may be 0.5 - 30 parts by weight, specifically, 0.5 - 15 parts by weight or 0.5 - 9 parts by weight, and more specifically, 0.5 - 5 parts by weight, relative to 100 parts by weight of the carbon-based material.

[0055] The present invention provides a method for manufacturing a negative electrode, and the method for manufacturing the negative electrode includes a coating step of depositing a negative electrode active material slurry on a current collector and then drying it, wherein the negative electrode active material slurry includes a negative electrode active material and a conductive material according to an embodiment of the present invention.

[0056] The method for manufacturing the negative electrode can improve the problems of increased dynamic viscosity of the slurry and reduced solids content of the slurry caused by the simultaneous inclusion of the silicon-based active material and the conductive material, and can improve electrode breakage and the reduction of the adhesion between the active materials, thereby enabling the manufacture of a negative electrode having excellent life characteristics and low-temperature performance.

[0057] The negative electrode active material slurry can be prepared by mixing a negative electrode active material and a conductive material according to an embodiment of the present invention in a solvent. Specifically, non-limiting examples of the solvent may include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, tert-butanol, etc.

[0058] Non-limiting examples of the current collector may include copper foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper, a polymer substrate coated with a conductive metal, etc. The negative electrode current collector is not limited thereto, but for example, the negative electrode current collector may be 10 - 50 μm.

[0059] The coating step can be carried out by methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc., and is not limited thereto.

[0060] The negative electrode active material slurry contains a conductive material, thereby improving the swelling problem of the silicon-based negative electrode material with high resistance. Specifically, the conductive material is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), carbon fiber, etc. and / or metal-based conductive materials including perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc. Specifically, the conductive material may be carbon nanotubes.

[0061] In addition, the negative electrode active material slurry may further contain a binder. The binder serves to bond the negative electrode active material particles well to each other and bond the negative electrode active material well to the current collector. Representative examples of the binder may be, for example, polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) copolymer, carboxymethyl cellulose (CMC), polyacrylonitrile, polymethyl methacrylate, nitrile rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR). Specifically, it may be carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), or a mixture thereof.

[0062] In the method for manufacturing a negative electrode according to an embodiment of the present invention, the viscosity of the negative electrode active material slurry may be 2000 - 10000 cP. Specifically, it may be 3000 - 8000 cP. More specifically, it may be 4000 - 6500 cP. Further specifically, it may be 4000 - 6000 cP. When the viscosity of the slurry exceeds 6500 cP, the solids in the slurry cannot be sufficiently dispersed, so that a uniform slurry cannot be formed, and an excessive die pressure is required during electrode coating, which may cause problems of reducing the productivity of the process. When the viscosity of the slurry is lower than 2000 cP, an uneven coating may be formed.

[0063] In the method for manufacturing a negative electrode according to an embodiment of the present invention, the solid content of the negative electrode active material slurry may be 10-70 parts by weight relative to a total of 100 parts by weight. Specifically, it may be 20-65 parts by weight, and more specifically, it may be 30-60 parts by weight. In the present invention, the "solid content" refers to the solute or solid substance in a solution, and in the present invention, the solid content may refer to substances such as negative electrode active materials and conductive materials.

[0064] In the coating step of the method for manufacturing a negative electrode according to an embodiment of the present invention, the die head pressure may be 0.05-20 psi. Specifically, it may be 0.1-15 psi, and more specifically, it may be 0.1-10 psi. According to the method for manufacturing a negative electrode of the present invention, by adjusting the viscosity of the slurry, a high die head pressure is not required during electrode coating, and thus excellent productivity can be achieved in the process.

[0065] The present invention provides a lithium secondary battery, which includes a positive electrode, a negative electrode according to an embodiment of the present invention, and a separator disposed between the positive electrode and the negative electrode.

[0066] The positive electrode may include a positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the positive electrode current collector.

[0067] The positive electrode current collector may include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The positive electrode current collector is not limited thereto. For example, the positive electrode current collector may be 10-50 μm.

[0068] The positive electrode mixture layer may include a positive electrode active material. The positive electrode active material may include a compound capable of reversibly inserting and extracting lithium ions.

[0069] According to an exemplary embodiment, the positive electrode active material may include a lithium-nickel metal oxide. The lithium-nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0070] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or a crystal structure represented by the following Chemical Formula 1.

[0071] [Chemical Formula 1]

[0072] Li x Ni a M b O 2+z

[0073] In Chemical Formula 1, it may be 0.9 ≤ x ≤ 1.2, 0.6 ≤ a ≤ 0.99, 0.01 ≤ b ≤ 0.4, -0.5 ≤ z ≤ 0.1. As described above, M may include Co, Mn, and / or Al.

[0074] The chemical structure represented by Chemical Formula 1 represents the bonding relationship included in the layered structure or crystal structure of the positive electrode active material, and does not exclude other additional elements. For example, M may include Co and / or Mn, and Co and / or Mn may be provided together with Ni as the main active element of the positive electrode active material. Chemical Formula 1 is provided to represent the bonding relationship of the main active element, and it should be understood that Chemical Formula 1 is a formula including the introduction and substitution of additional elements.

[0075] In one embodiment, in addition to the main active element, an auxiliary element for enhancing the chemical stability of the positive electrode active material or the layered structure / crystal structure may be further included. The auxiliary element may be mixed into the layered structure / crystal structure together to form a bond, and it should be understood that this situation is also included within the scope of the chemical structure represented by Chemical Formula 1.

[0076] The auxiliary element may include at least one of, for example, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr. The auxiliary element may act as an auxiliary active element that contributes to the capacity / power activity of the positive electrode active material together with Co or Mn, such as Al.

[0077] For example, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or crystal structure represented by the following Chemical Formula 1-1.

[0078] [Chemical Formula 1-1]

[0079] Li x Ni a M 1b1 M 2b2 O 2+z

[0080] In Chemical Formula 1-1, M1 may include Co, Mn, and / or Al. M2 may include the above-mentioned auxiliary elements. In Chemical Formula 1-1, it may be 0.9 ≤ x ≤ 1.2, 0.6 ≤ a ≤ 0.99, 0.01 ≤ b1 + b2 ≤ 0.4, -0.5 ≤ z ≤ 0.1.

[0081] The positive electrode active material may further include a coating element or a doping element. For example, an element substantially the same as or similar to the above-described auxiliary element may be used as the coating element or the doping element. For example, one or a combination of two or more of the above elements may be used as the coating element or the doping element.

[0082] The coating element or the doping element may be present on the surface of the lithium-nickel metal oxide particles or penetrate through the surface of the lithium-nickel metal oxide particles and be included in the bonding structure represented by Chemical Formula 1 or Chemical Formula 1-1.

[0083] The positive electrode active material may include a nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, an NCM-based lithium oxide with an increased nickel content may be used.

[0084] Ni may be provided as a transition metal related to the power and capacity of the lithium secondary battery. Therefore, as described above, by using a high-content (high-nickel (High-Ni)) composition in the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0085] However, as the Ni content increases, the long-term storage stability and life stability of the positive electrode or the secondary battery may be relatively reduced, and side reactions with the electrolyte may also increase. However, according to an exemplary embodiment, conductivity can be maintained by including Co, and life stability and capacity retention characteristics can be improved by Mn.

[0086] In the NCM-based lithium oxide, the content of Ni (for example, the mole fraction of Ni in the total moles of nickel, cobalt, and manganese) may be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0087] In some embodiments, the positive electrode active material may further include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (for example, LiFePO4).

[0088] In some embodiments, the positive electrode active material may include, for example, a manganese-rich (Mn-rich)-based active material having a chemical structure or crystal structure represented by Chemical Formula 2, a lithium-rich layered oxide (LLO) / over-lithiated oxide (OLO)-based active material, or a cobalt-less-based active material.

[0089] [Chemical Formula 2]

[0090] p[Li2MnO3]·(1-p)[Li q JO2]

[0091] In Chemical Formula 2, 0 < p < 1 and 0.9 ≤ q ≤ 1.2 may be satisfied, and J may include at least one element selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0092] The separator may be configured to prevent a short circuit between the positive electrode and the negative electrode and allow the flow of ions. According to an embodiment, the thickness of the separator may be 10 μm to 20 μm, but the present invention is not limited thereto.

[0093] For example, the separator may include a porous polymer film or a porous nonwoven fabric. The porous polymer film may include polyolefin-based polymers such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers. The porous nonwoven fabric may include glass fibers having a high melting point, polyethylene terephthalate fibers, and the like. The separator may further include a ceramic-based material. For example, inorganic particles may be coated on or dispersed in the polymer film to improve heat resistance.

[0094] The separator may have a single-layer or multi-layer structure including the above polymer film and / or nonwoven fabric.

[0095] The lithium secondary battery may further include an electrolyte solution in which a lithium salt is dissolved, and according to an exemplary embodiment, the electrolyte solution may use a non-aqueous electrolyte solution.

[0096] The non-aqueous electrolyte solution may include a lithium salt as an electrolyte and an organic solvent. The lithium salt may be represented by, for example, Li + X - As the anion (X - ) of the lithium salt, F - , Cl - , Br - , 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 - etc.

[0097] The organic solvent may contain an organic compound that has sufficient solubility for the lithium salt and the additive and is non-reactive in the battery. As the organic solvent, at least one of, for example, carbonate-based solvents, ester-based solvents, ether-based solvents, ketone-based solvents, alcohol-based solvents, and aprotic solvents may be included. As the organic solvent, for example, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), ethyl fluoroacetate (FEA), ethyl difluoroacetate (DFEA), ethyl trifluoroacetate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfite may be used. These may be used alone or in combination of two or more.

[0098] The non-aqueous electrolyte may further contain an additive. The additive may contain, for example, cyclic carbonate-based compounds, fluorine-substituted carbonate-based compounds, sultone-based compounds, cyclic sulfate-based compounds, cyclic sulfite-based compounds, phosphate-based compounds, and borate-based compounds.

[0099] The cyclic carbonate-based compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0100] The fluorine-substituted carbonate-based compound may include fluoroethylenecarbonate (FEC), etc.

[0101] The sultone-based compound may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0102] The cyclic sulfate-based compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0103] The cyclic sulfite-based compound may include Ethylene sulfite, Butylene sulfite, etc.

[0104] The phosphate-based compound may include Lithium difluoro bis-oxalato phosphate, Lithium difluoro phosphate, etc.

[0105] The borate-based compound may include Lithium bis(oxalate) borate, etc.

[0106] Hereinafter, with reference to specific experimental examples, the embodiments of the present invention will be further described. The examples and comparative examples included in the experimental examples are only used to illustrate the present invention and do not limit the claims. Various changes and modifications can be made to the examples within the scope and technical concept of the present invention, which are obvious to those skilled in the art. Such variations and modifications are naturally within the scope of the claims.

[0107] D A50 / D B50 Measurement method

[0108] 1. Measurement method of D A50 (Two-dimensional perspective method)

[0109] 1) Prepare a graphite powder sample and dry it at 100 °C for more than 12 hours.

[0110] 2) Pressurize and disperse the dried sample using a Camsizer-X2 (Microtrac) and drop it vertically.

[0111] 3) Measure the two-dimensional image of the particles horizontally using a high-resolution dynamic camera.

[0112] 4) Statistically process the two-dimensional image using the built-in software of each measuring instrument, perform a volume-weighted distribution of the particle diameters, and define the value of the 50th percentile as D A50 。

[0113] 2. Method for measuring D B50 (Laser diffraction method)

[0114] 1) Prepare a graphite powder sample and dry it at 100 °C for more than 12 hours.

[0115] 2) Mix the dried sample with 1 g of an ethanol solution and then apply ultrasonic waves for 5 minutes for dispersion.

[0116] 3) Place the dispersed solution in a laser particle size analyzer Mastersizer3000 (Malvern) and measure the particle size distribution.

[0117] 4) In the particle size distribution, perform a volume-weighted distribution of the particle diameters and define the value of the 50th percentile as D B50 。

[0118] [Examples 1 to 10]

[0119] Mix graphite (92.20%), SiOx (0 < x < 2) (5%), carbon nanotubes (CNT) (0.1% (added in a 0.4 wt% solution)), carboxymethyl cellulose (CMC) (1.2%), and styrene-butadiene rubber (SBR) (1.5%) having the characteristics shown in Table 1 below to prepare a negative electrode material slurry.

[0120] Preparation of secondary particles

[0121] Prepare 100 g of artificial graphite powder in the form of primary particles and pitch, and mix them in a ratio of 90:10 to obtain a mixture. The pitch used has a softening point of 200 - 280 °C, a carbonization yield of 50 - 80%, and a quinoline insoluble content of less than 1%. Calcinate the mixture at a temperature of 600 °C for 10 hours to obtain secondary particles aggregated from the primary particles. Use an air classifying mill to screen and classify the secondary particles to obtain graphite secondary particles that meet the characteristics shown in Table 1 below.

[0122] Coating of Graphite

[0123] For the coated graphite, use pitch as the coating agent and calcine it at 1000 °C to obtain particles coated with amorphous carbon. Do this in such a way that the content of the carbon coating meets 1 wt% of the total weight of the graphite-based active material.

[0124] Manufacture of Lithium Secondary Battery

[0125] Coat the negative electrode active material slurry on one side of a copper foil (current collector, thickness: 10 μm) to form a negative electrode active material layer, and manufacture a negative electrode including this negative electrode active material layer. The loading amount of the negative electrode active material is 13 mg / cm based on one side 2 , and the density of the mixture is 1.7 g / cubic centimeter (cc).

[0126] Insert a polyethylene (PE) separator between the obtained negative electrode and the lithium metal positive electrode, and then inject an electrolyte containing 1 wt% of FEC, 1.0 M LiPF6, and a mixed solvent of EC:EMC:DEC = 25:45:30 to obtain a CR2016 coin-type battery. Let the assembled coin-type battery stand at room temperature for 24 hours to obtain a half-cell.

[0127] [Comparative Examples 1 to 6]

[0128] Manufacture a lithium secondary battery by the same method as in the example, except that the characteristics of the graphite contained in the negative electrode active material are the values shown in Table 1 below.

[0129] [Table 1]

[0130]

[0131] [Evaluation Example]

[0132] Evaluation 1. Evaluation of Slurry Viscosity

[0133] During the manufacturing processes of the embodiments and comparative examples, the viscosity of the negative electrode material slurry was measured and shown in Table 2 below. The viscosity of the slurry was measured using an advanced Peltier temperature control system and a Discovery HR-30 rheometer from TA Instruments.

[0134] Evaluation 2. Room temperature life characteristics

[0135] At room temperature (25 °C), under the C-rate condition of 0.5C charge / 0.5C discharge, the life characteristics of the lithium secondary batteries manufactured in the embodiments and comparative examples were evaluated. Specifically, the lithium secondary batteries of the embodiments and comparative examples were charged at 0.5C to 0.005V under constant current / constant voltage (CC / CV) conditions and discharged at 0.5C to 1.5V, and the discharge capacity was measured. According to the measurement method of the initial discharge capacity, 500 charge and discharge cycles were performed, the discharge capacity (C2) at the 500th cycle was measured, and the capacity retention rate was calculated by dividing the discharge capacity (C2) at the 500th cycle by the highest discharge capacity value (C1) in the initial 10 cycles, and the results are shown in Table 2 below (capacity retention rate (%) = C2 / C1 × 100).

[0136] Evaluation 3. Low temperature life characteristics

[0137] The embodiments and comparative examples were evaluated by the same method as in Evaluation 2, except that in the evaluation method of the room temperature life characteristics, the temperature was changed to -10 °C, and the results are shown in Table 2 below.

[0138] [Table 2]

[0139]

[0140] As shown in Table 2 above, in the embodiments where the D A50 / D B50 value is 0.9 or more and 1.1 or less, compared with the comparative examples where the D A50 / D B50 value is not within the range of 0.9 or more and 1.1 or less, the viscosity of the slurry is at least 5174 cP and at most 5988 cP, showing a viscosity suitable for forming a coating. On the other hand, in the case of the comparative examples, the viscosity of the slurry exceeds 6500 cP, indicating that the viscosity of the slurry is too high.

[0141] Therefore, when confirming the capacity retention rate at room temperature and the capacity retention rate at low temperature, it can be confirmed that, in the case of the embodiment, the capacity retention rate is shown to be 80 - 93% at room temperature, and even at low temperature, the capacity retention rate does not decrease significantly and remains above 80%. On the other hand, in the case of the comparative example, the capacity retention rate at room temperature and the capacity retention rate at low temperature are both 61 - 79%, and it is confirmed that the capacity retention rate is significantly lower compared to the embodiment.

[0142] It is thus considered that the carbon-based material of the present invention can not only improve the electrode coating quality by appropriately adjusting the viscosity of the slurry, but also improve the capacity retention rate and life characteristics of the battery.

[0143] The content described above is merely an example of applying the principle of the present invention, and other configurations may be further included without departing from the scope of the present invention.

Claims

1. A negative electrode active material comprising a carbon-based material and a silicon-based material satisfying the following formula 1, [Formula 1] 0.9≤D A50 / D B50 ≤1.1 The D A50 and the D B50 are the 50th percentiles of the volume-weighted distribution of carbon-based material diameters measured by two-dimensional perspective and laser diffraction, respectively.

2. The negative electrode active material according to claim 1, wherein The carbon-based substance is artificial graphite or natural graphite.

3. The negative electrode active material according to claim 1, wherein The carbon-based substance is coated with pitch carbon, soft carbon, hard carbon, heavy oil, heavy oil, phenols, mesophase pitch carbide, calcined coke, carbon fiber, or a mixture thereof.

4. The negative electrode active material according to claim 1, wherein The silicon-based material comprises a silicon-based material selected from Si, SiOx, metal-doped SiOx and a silicon-carbon composite, wherein: <x<2。 5. The negative electrode active material according to claim 1, wherein The content of the silicon-based substance is 0.5-30 parts by weight relative to 100 parts by weight of the carbon-based substance.

6. A method for manufacturing a negative electrode, comprising a coating step of depositing a negative electrode active material slurry on a current collector and then drying it, in, The negative electrode active material slurry includes the negative electrode active material according to any one of claims 1 to 5 and a conductive material.

7. The method for manufacturing a negative electrode according to claim 6, wherein: The conductive material is carbon nanotubes.

8. The method for manufacturing a negative electrode according to claim 6, wherein: The viscosity of the negative electrode active material slurry is 2000-10000 cP.

9. The method for manufacturing a negative electrode according to claim 6, wherein: The solid content of the negative electrode active material slurry is 10-70 parts by weight relative to 100 parts by weight of the total.

10. The method for manufacturing a negative electrode according to claim 6, wherein: The die pressure during the coating step was 0.05-20 psi.

11. The method for manufacturing a negative electrode according to claim 6, wherein: The negative electrode active material slurry further includes carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR) or a mixture thereof.

12. A lithium secondary battery comprising: positive electrode; A negative electrode, wherein the negative electrode is manufactured by the method for manufacturing a negative electrode according to claim 6; as well as A separator is disposed between the positive electrode and the negative electrode.

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