Graphite Material, Negative Electrode Active Material for Li Secondary Battery and the Negative Electrode for Li Secondary Battery including the Same

Abstract

The graphite material according to the disclosure is a graphite material for a lithium secondary battery negative electrode material, and comprises an assembly of artificial graphite units, and has an aggregation rate defined by the following Equation 1 of 0.50 or less: (Equation 1) Aggregation rate = [1 / C - 1] × 100, where Equation 1, C is a convexity which is the ratio of the area of ​​a particle to the convex hull area in a captured image in which a three-dimensional particle is captured as a two-dimensional image, and is the convexity of a graphite material that belongs to a central size range of 0.9D50 to 1.1D50 based on a cumulative volume-based median diameter D50.

Description

Technology Field

[0001] The present invention relates to a graphite material, a negative electrode material for a lithium secondary battery, and a negative electrode for a lithium secondary battery comprising the same. Background Technology

[0002] As the market for electronic devices such as mobile phones, laptops, and PCs grows, the market for lithium-ion batteries, their power source, is also expanding rapidly. Furthermore, as interest in environmental issues grows and the demand for eco-friendly vehicles like electric cars increases, there is a growing trend of research into lithium-ion batteries capable of meeting various applications.

[0003] The negative electrode active material stores lithium ions during charging and significantly influences the battery's capacity, charging speed, and stability. Representative commercially used negative electrode active materials include graphite-based materials such as synthetic graphite and natural graphite. Among these, although synthetic graphite is more expensive than natural graphite, it is actively used as a negative electrode active material in medium and large-sized batteries due to its long lifespan, improved electrical conductivity, and excellent durability. However, the medium and large-sized battery sector requires not only long lifespan and stability but also enhanced high-rate performance; consequently, there is a demand for graphite-based negative electrode active materials with improved high-rate characteristics. Prior art literature

[0004] Republic of Korea Published Patent No. 10-2024-0105537 The problem to be solved

[0005] According to one embodiment of the present invention, a graphite material for a lithium secondary battery negative electrode having improved high rate characteristics can be provided.

[0006] The problems of the present invention are not limited to those described above. A person skilled in the art to which the present invention pertains will have no difficulty understanding additional problems of the present invention from the overall contents of this specification. means of solving the problem

[0007] A graphite material for a lithium secondary battery negative electrode according to one embodiment of the present invention comprises an assembly of artificial graphite units, and the assembly ratio defined by Formula 1 below is 0.50 or less.

[0008] (Equation 1)

[0009] Modulus of Assembly = [1 / C - 1] × 100

[0010] In Equation 1, C is the convexity, which is the ratio of the particle area to the convex hull area in a captured image of a 3D particle captured as a 2D image, and the cumulative volume-based median diameter D 50 Based on, 0.9D 50 to 1.1D 50 It is the curvature of a graphite material that falls within the central size range, which is the size range of .

[0011] In one specific example, the graphite material can satisfy Formula 2 below.

[0012] (Equation 2)

[0013] Second assembly factor / First assembly factor ≤ 5.00

[0014] In Equation 2, the first aggregation modulus is the aggregation modulus due to the curvature of the graphite material belonging to the center size range, and the second aggregation modulus is 1.2D 50 to 1.4D 50 It is the fineness modulus according to Equation 1 based on the curvature of the graphite material within the size range.

[0015] In one specific example, 1.2D 50 to 1.4D 50 The second fineness modulus according to Equation 1, which is the fineness modulus of the graphite material within the size range, may be 1.50 or less.

[0016] In one specific example, 1.5D 50 to 1.6D 50 The third fineness modulus according to Equation 1, which is the fineness modulus of the graphite material within the size range, may be 5.00 or less.

[0017] In one specific example, the graphite material may have a span of 1 or less.

[0018] In one embodiment, the D of the graphite material 50 It can be 8 to 25 μm.

[0019] In one embodiment, the artificial graphite unit may have a shape selected from one or more of a rod shape, a plate shape, and a flake shape.

[0020] In one embodiment, the assembly may further include amorphous graphite located at the boundary between the artificial graphite units.

[0021] In one embodiment, the assembly may contain 8 to 15 parts by weight of amorphous graphite based on 100 parts by weight of the artificial graphite unit.

[0022] In one embodiment, the graphite material is m 2 BET specific surface area (BET) in units of / g, D in units of μm 50 The ratio divided by (BET / D 50 ) may be 0.14 or less.

[0023] In one embodiment, the graphite material is 0.95 g / cm³ 3 It can have a tap density greater than or equal to the above.

[0024] In one embodiment, the artificial graphite unit assembled into the assembly has a cumulative volume median diameter D of the graphite material. 50 Based on, 0.4D 50 to 0.8D 50 It can have an average size.

[0025] Another embodiment of the present invention includes a negative electrode material for a lithium secondary battery comprising the aforementioned graphite material.

[0026] Another embodiment of the present invention includes a negative electrode for a lithium secondary battery comprising the aforementioned negative electrode material. Effects of the invention

[0027] A graphite material according to one embodiment can exhibit improved high-rate filling characteristics and high-rate output characteristics.

[0028] The various and beneficial advantages and effects of the present invention are not limited to those described above and will be more easily understood in the process of explaining specific embodiments of the present invention. Specific details for implementing the invention

[0029] Preferred embodiments of the present invention are described below. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0030] In addition, embodiments of the present invention are provided to more fully explain the present invention to those with average knowledge in the relevant technical field.

[0031] In describing the embodiments of the present invention, if it is determined that a detailed description of known technology related to the present invention may unnecessarily obscure the essence of the present invention, such detailed description will be omitted. Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intentions or conventions of the user or operator. Therefore, such definitions should be based on the content throughout this specification. The terms used in the detailed description are merely for describing the embodiments of the present invention and should not be limited in any way. Unless explicitly stated otherwise, expressions in the singular form include the meaning of the plural form.

[0032] In this description, expressions such as “include” or “equipped” are intended to refer to certain characteristics, numbers, steps, actions, elements, parts or combinations thereof, and should not be interpreted to exclude the existence or possibility of one or more other characteristics, numbers, steps, actions, elements, parts or combinations thereof other than those described.

[0033] Unless otherwise specifically defined in the specification of the present invention, % units mean weight %.

[0034] Additionally, throughout the specification, when it is said that one part is 'connected' to another part, this includes not only cases where they are 'directly connected,' but also cases where they are 'indirectly connected' with other elements in between.

[0035] The present invention will be described in detail below through each embodiment or example of the invention. It should be noted that each embodiment or example described in this specification is not limited to a single embodiment or example, but may also be combined with other embodiments or examples. Accordingly, the citation of claims in the patent claims is merely an example of an embodiment, and the technical concept of the present invention should not be interpreted as being limited only to a combination with the cited claims; rather, combinations with various claims are also included within the scope of the technical concept of the present invention.

[0036] The inventors have conducted long-term research to develop a graphite material with improved high-rate characteristics by assembling particulate artificial graphite. During the research process, it was discovered that the degree of artificial graphite assembling and the uniformity of assembling significantly affect the curvature of the assembly. Furthermore, it was found that the electrochemical properties of the graphite material, particularly its high-rate characteristics, change sensitively depending on the curvature of the assembly. Based on these findings, the inventors have filed the present invention.

[0037] The graphite material for a lithium secondary battery negative electrode according to the work includes an assembly of artificial graphite units, and the assembly ratio defined by Formula 1 below is 0.50 or less.

[0038] (Equation 1)

[0039] Modulus of Assembly = [1 / C - 1] × 100

[0040] In Equation 1, C is the convexity, which is the ratio of the particle area to the convex hull area in a captured image of a 3D particle captured as a 2D image, and the cumulative volume-based median diameter D 50 Based on, 0.9D 50 to 1.1D 50 It is the curvature of a graphite material that falls within the central size range, which is the size range of .

[0041] The aggregation modulus of Equation 1 is an indicator that indicates the degree of aggregation of artificial graphite monomers within the assembly and the uniformity of aggregation (crystallographic isotropy of the assembly). Specifically, a very low aggregation modulus of 0.50 or less means that the assembly is randomly and densely aggregated, has high crystallographic isotropy, and is a particulate form with a contour similar to a smooth curve such as a circle or an ellipse. In other words, as the value of the aggregation modulus increases, it may mean that the monomers are aggregated more unevenly and more loosely.

[0042] The graphite material may have a low agglomeration rate of 0.50 or less, specifically 0.05 to 0.50, more specifically 0.10 to 0.40, even more specifically 0.10 to 0.35, even more specifically 0.10 to 0.30, even more specifically 0.10 to 0.25, and even more specifically 0.10 to 0.20.

[0043] The curvature adopted in the assimilation rate of Equation 1 is not the curvature of the entire graphite material, but D, which is the median diameter based on the cumulative volume of the graphite material. 50 Based on, 0.9D 50 to 1.1D 50 It may be the curvature of a graphite material within the size range (hereinafter, center size range). The curvature in the center size range has minimized distortion and can represent the electrochemical properties of the graphite material.

[0044] Specifically, the curvature within the center size range is a value in which curvature distortion caused by unassembled artificial graphite monomers can be excluded, and also a value in which curvature distortion caused by aggregation between secondary particles or between secondary and primary particles, rather than the desired single particle shape, can be excluded, and it is a curvature that can represent the entire graphite material in terms of particle size distribution.

[0045] The graphite material can have improved high-rate characteristics by having the aforementioned low aggregate ratio based on the curvature in the center size range.

[0046] In one specific example, the graphite material can satisfy the following Formula 2.

[0047] (Equation 2)

[0048] Second assembly factor / First assembly factor ≤ 5.00

[0049] In Equation 2, the first aggregate modulus is the aggregate modulus due to the curvature of the graphite material within the center size range, and the second aggregate modulus is 1.2D 50 to 1.4D 50 It is the fineness modulus according to Equation 1 based on the curvature of the graphite material within the size range.

[0050] The ratio of the second aggregation modulus to the first aggregation modulus according to Equation 2 indicates short-range aggregation uniformity based on the size of the graphite material. That is, the center size range or D 50 It indicates the uniformity of the degree of agglomeration of the graphite material in a short range of sizes that are 1.2 to 1.4 times larger than.

[0051] As the size increases, it becomes difficult to assemble into a granular form having a contour similar to a smooth curve, so the aggregation rate may increase. The ratio of the second aggregation rate to the first aggregation rate may be 5.00 or less, specifically 1.00 to 5.00, more specifically 1.50 to 4.50, even more specifically 1.50 to 4.00, even more specifically 1.50 to 3.50, and even more specifically 1.5 to 3.0. The aforementioned ratio of the second aggregation rate to the first aggregation rate indicates that even if the size of the assembly increases, the assembly is maintained in a random and dense manner with high crystallographic isotropy.

[0052] As a practical example, the second assembly ratio may be 1.50 or less, specifically 0.30 to 1.50, more specifically 0.35 to 1.40, even more specifically 0.35 to 1.20, even more specifically 0.40 to 1.00, and even more specifically 0.40 to 0.80.

[0053] In reality, D of graphite material 90 1.5D, a size exceeding 50 to 1.6D 50 The third aggregation modulus, which is the aggregation modulus according to Equation 1 based on the curvature of the graphite material within the size range, is a value that can represent long-range aggregation uniformity based on the size of the graphite material. The graphite material according to one embodiment may have a third aggregation modulus of 5.00 or less, specifically 1.00 to 5.00, more specifically 1.50 to 4.50, even more specifically 1.50 to 4.00, and even more specifically 2.00 to 3.50. The statement that the graphite material satisfies the aforementioned ratio of the second aggregation modulus to the first aggregation modulus (or the second aggregation modulus) and the third aggregation modulus may mean that, on a volume basis, substantially most of the graphite material contains an aggregated structure that is randomly and densely aggregated and has high crystallographic isotropy, while simultaneously having low surface roughness.

[0054] When the graphite material has the aforementioned low aggregation rate within the center size range and satisfies short-range aggregation uniformity, it can have improved high-rate output characteristics and high-rate filling characteristics, and when it further satisfies long-range aggregation uniformity, it can have improved rheological properties along with even better high-rate characteristics.

[0055] In one embodiment, the artificial graphite monomer may be an artificial graphite primary particle, and the assembly may be a secondary particle containing the artificial graphite primary particle(s). In this case, the primary particle may refer to a single particle. In terms of assembly, the primary particle may refer to the original particle (A) when a heterogeneous particle (B) with a different shape, structure, or composition is formed from a particle (A). The secondary particle (assembly) may refer to a particle larger than the primary particle, formed by artificially aggregating, combining, or assembling two or more primary particles.

[0056] The synthetic graphite monomer may be in the form of particles having an anisotropic shape, and the anisotropic shape may be one or more shapes selected from rod shape, plate shape, and flake shape. Each shape may be defined based on the lengths in the directions of three orthogonal axes (x, y, z) with the center of the particle as the axis. A rod shape may be defined as such when the longest length (e.g., Lz) is at least 1.5 times the other two lengths (e.g., Lx and Ly), in a substantial example, between 1.5 and 5 times, and the ratio of the longer length to the shorter length among the other two lengths excluding the longest length (e.g., Lx / Ly) is at the level of 1 to 3. Accordingly, scale shape or rectangular shape, etc., may also belong to the rod shape. A plate shape and a flake shape can be defined as a plate or a flake shape when the ratio of the longest length (e.g., Lx) to the shortest length (e.g., Lz, corresponding to thickness) is at a level of 5 to 100, specifically 10 to 80, and the ratio of the longest length (e.g., Lx) to the second longest length (e.g., Ly) is at a level of 1 to 5. In this case, if the aforementioned definition of a plate or flake shape is satisfied and the difference between the thickness Tc at the center of the particle and the thickness Te at the edge (end) is within 0.1Tc, it can be defined as a plate, and if there is thickness non-uniformity at a level where the difference between Tc and Te exceeds 0.1Tc, it can be defined as a flake shape. As a practical example, the artificial graphite monomer may be plate-shaped or flake-shaped, or may have a mixture of plate-shaped and flake-shaped forms. Experimentally, the shape of the monomer can be determined using conventional shape observation equipment such as a scanning electron microscope.Here, the statement that the artificial graphite unit has a rod shape, a plate shape, and / or a flake shape should be interpreted as the assembly (graphite material) containing artificial graphite units of a rod shape, a plate shape, and / or a flake shape, and should not be interpreted as the assembly (graphite material) consisting only of artificial graphite units of a rod shape, a plate shape, and / or a flake shape.

[0057] The artificial graphite monomers assembled into an assembly have a cumulative volume median diameter D of the graphite material. 50 Based on, 0.4D 50 to 0.8D 50 The average size (diameter) of, specifically 0.5D 50 to 0.7D 50 It can have an average size of . In terms of manufacturing method, the aforementioned artificial graphite monomer is 0.5D 50 to 0.8D 50 A graphite material may be produced that satisfies a low aggregation rate in the center size range, short-range aggregation uniformity, and long-range aggregation uniformity, by assembling such a carbon material having a cumulative volume median diameter and a span value of 0.9 or more, and by assembling such a carbon material under the conditions described below.

[0058] In one embodiment, the assembly may further include amorphous graphite located at the boundary between artificial graphite units. In terms of manufacturing method, the amorphous graphite may be derived from a carbon precursor (carbon-based binder) used as a binder to assemble artificial graphite units, or it may be generated by the graphitization of the carbon precursor (carbon-based binder). Accordingly, the amorphous graphite is located in at least a portion of the space between the artificial graphite units contained in the assembly, thereby bonding the artificial graphite units together. In this case, the amorphous nature of the amorphous graphite refers to a shape that partially or entirely fills the space between the artificial graphite units; it is defined as amorphous merely because its shape varies depending on the shape of the space between the artificial graphite units and the degree to which it fills the space, and it does not exclude shapes that can be defined uniformly, such as a layer (for example, an interfacial layer between units). The assembly may contain 8 to 15, specifically 9 to 12 parts by weight of amorphous graphite based on 100 parts by weight of artificial graphite monomers.

[0059] In one embodiment, the span of the graphite material may be 1.0 or less, specifically 0.6 to 1.0, more specifically 0.6 to 0.9, and even more specifically 0.6 to 0.8. A small span value (narrow particle size distribution of the graphite material) is advantageous for improving electrode density and allows for the formation of uniform inter-particle voids when implementing the negative electrode active material layer.

[0060] In one embodiment, the cumulative volume median diameter (D) of the graphite material 50 ) may be 8 to 25 μm, specifically 10 to 20 μm, more specifically 10 to 18 μm, and even more specifically 12 to 18 μm, but is not necessarily limited thereto.

[0061] In one specific example, m 2 The BET specific surface area (BET) of the graphite material in units of / g is the cumulative volume median diameter (D) of the graphite material in units of μm.50 The ratio divided by ) (BET / D 50 ) may be 0.14 or less, specifically 0.07 to 0.14, more specifically 0.07 to 0.12, and even more specifically 0.07 to 0.10. Such low BET / D 50 The ratio may be due to the fact that the spaces between synthetic graphite monomers in the assembly and / or the micropores within the synthetic graphite monomers themselves are stably filled by amorphous graphite. The aforementioned low BET / D 50 The ratio is advantageous for suppressing side reactions and forming a thin and stable SEI (Solid Electrolyte Interface).

[0062] In one embodiment, the tap density of the graphite material is 0.95 g / cm³ 3 Above, specifically 0.95 to 1.20 g / cm³ 3 , more specifically 1.00 to 1.20 g / cm³ 3 It may be, but is not necessarily limited to this.

[0063] A method for manufacturing a graphite material for a lithium secondary battery negative electrode according to the disclosure thereof comprises D, which is the cumulative volume median diameter of the desired (previously designed) negative electrode material. 50 Based on (NEA), 0.5D 50 (NEA) to 0.8D 50 The method comprises the steps of: preparing a carbon material having a cumulative volume median diameter of (NEA) and a span value of 0.9 or more, specifically 0.9 to 1.5; preparing a first mixture by mixing the carbon material and the first carbon-based binder at a temperature of Ts-50°C to Ts-5°C based on the softening point Ts(°C) of the first carbon-based binder; preparing a second mixture by mixing the first mixture and the second carbon-based binder; preparing an intermediate in which the carbon material comprising the first carbon material and the second carbon material is assembled by applying mechanical force to the second mixture at a temperature above the softening point of the first carbon-based binder and the softening point of the second carbon-based binder; and preparing an assembly by graphitizing the prepared intermediate.

[0064] In one embodiment, the carbon material may be coke. Specifically, the carbon material may be green coke, calcined coke, or a combination thereof. As is well known, coke can be obtained through a coking reaction of coal-based / petroleum residue or coal-based / petroleum pitch, wherein the coke obtained through the coking reaction may be classified into green coke and calcined coke depending on whether or not calcination heat treatment is performed. More specifically, the carbon material may be petroleum-based isotropic coke, petroleum-based needle coke, coal-based isotropic coke, coal-based needle coke, pitch coke, or a combination thereof. In a substantial example, the step of preparing the carbon material may be a step of preparing coke having a cumulative volume median diameter of 4 to 20 μm, more substantially 6 to 12 μm, and a span value of 0.9 to 1.5.

[0065] The first carbon-based binder and the second carbon-based binder used for assembling carbon materials may each be carbon-based binders having a softening point. Representative examples of the first carbon-based binder and the second carbon-based binder include petroleum-based pitch, coal-based pitch, coal tar pitch, natural pitch, mesophase pitch, or mixtures thereof. The softening points of the first carbon-based binder and the second carbon-based binder may each be 100 to 300°C, specifically 200 to 280°C, wherein the softening point may be measured according to ASTM D 3104.

[0066] The first carbon-based binder and the second carbon-based binder may differ in size, and the first carbon-based binder may be a fine binder with a smaller size than the second carbon-based binder. As a practical example, the cumulative volume median diameter (D) of the first carbon-based binder 50 ) may be 0.5 to 3.0 μm, more specifically 0.5 to 1.5 μm, and the cumulative volume median diameter (D50) of the second carbon-based binder may be 4 to 10 μm, specifically 5 to 9 μm.

[0067] The mixing between the carbon material and the carbon-based binder may be a sequential mixing step comprising a pre-mixing step of first mixing a finer first carbon-based binder, a step of mixing the mixture produced by the pre-mixing in a heated state to produce a first mixture, and a step of mixing the first mixture with a second carbon-based binder to produce a second mixture. The pre-mixing step may be a step of producing a pre-mix by mixing the carbon material and the first carbon-based binder at room temperature. After the carbon material and the first carbon-based binder are mixed by the pre-mixing, a first mixing step may be performed by mixing the pre-mix at a temperature of Ts-50°C to Ts-5°C, specifically Ts-30°C to Ts-5°C, and more specifically Ts-15°C to Ts-5°C, based on the softening point Ts of the first carbon-based binder. At such temperatures, the carbon material and the first carbon-based binder are mechanically mixed, thereby producing a first mixture in which the carbon material and the first carbon-based binder are mixed together and partially bound and / or fused. After the mixing between the carbon material and the first carbon-based binder is performed, the first mixture and the second carbon-based binder are mixed at room temperature to produce a second mixture. At this time, the statement that mixing is performed at room temperature means that no artificial heat is applied from the outside, and does not exclude a state of spontaneous heating caused by frictional heat generated during mixing.

[0068] It is advantageous for the weight ratio of the first carbon-based binder to the second carbon-based binder contained in the second mixture to be 100:50 to 120, specifically 100:60 to 110, and for the weight ratio of the carbon material to the carbon-based binder (first carbon-based binder and second carbon-based binder) in the second mixture to be 100:10 to 20, specifically 100:13 to 18. The aforementioned sequential mixing can be performed so that the second mixture, in its final mixed state, satisfies these weight ratios.

[0069] Pre-mixing, primary mixing, and secondary mixing may each be performed using methods commonly used in the industry for uniformly mixing different powders, such as ball milling, mechanofusion milling, shaker milling, planetary milling, attritor milling, disk milling, shape milling, nauta milling, and nobilta milling. However, for primary mixing in a heated state, heating of the mixing device by a conventional heating element may be performed.

[0070] After the second mixture is prepared by sequential mixing, a step (assembly step) may be performed to prepare an assembled intermediate in which the carbon material is bound by the carbon-based binder and an intermediate is prepared by applying mechanical force while heating the second mixture to a temperature higher than Ts(H), based on Ts(H), which is the higher softening point among the two softening points of the two carbon-based binders (first carbon-based binder and second carbon-based binder). In terms of ensuring smooth fluidity of the carbon-based binder and suppressing modifications such as thermal decomposition, the assembly step may be performed at a temperature of Ts(H) + 10°C to Ts(H) + 600°C, specifically at a temperature of Ts(H) + 100°C to Ts(H) + 500°C, and more specifically at a temperature of Ts(H) + 300°C to Ts(H) + 500°C. The assembly step may be performed for 1 to 10 hours, but is not limited thereto. The assembly step is sufficient if it is performed using methods commonly used in the industry to assemble artificial graphite based on shear force, such as V-mixing, cone mixing, double cone mixing, planetary mixing, and kneading.

[0071] If necessary, after aggregation is performed by mechanical force based on shear force at a temperature of Ts(H) or higher, a disintegration step to break up the aggregation may be further performed. It is sufficient for the disintegration step to be performed using methods commonly used in the industry to break up the aggregation of fine particles, such as jet milling, air classifier milling, and roller milling.

[0072] The manufactured intermediate can be converted into an assembly through graphitization treatment, in which the carbon materials (carbon materials, first carbon-based binder and second carbon-based binder) contained in the intermediate are graphitized. Graphitization may be performed at 2500 to 3500°C, specifically 2800 to 3200°C, for 0.5 to 5 hours under an atmosphere of an inert gas (nitrogen, argon, helium, or a mixture thereof), but is not limited thereto.

[0073] If necessary, a preliminary carbonization treatment to remove volatile components contained in the intermediate prior to graphitization treatment may be performed, followed by graphitization treatment. The preliminary carbonization treatment may be performed at 800 to 1500°C, specifically 1000 to 1300°C, for 1 to 5 hours under an atmosphere of an inert gas (nitrogen, argon, helium, or a mixture thereof), but is not necessarily limited thereto. The heating rate during graphitization treatment and preliminary carbonization treatment may be at a level of 5 to 20°C / min independently of each other, but is not limited thereto.

[0074] If necessary, a disintegration step to break up the aggregation of the aggregates obtained by the graphitization treatment and a classification step to remove fines and / or coarse particles may be further performed. It is sufficient for the disintegration to be performed using methods commonly used in the industry to break up the aggregation of fine particles, such as jet milling, air classifier milling, and roller milling, and it is sufficient for the classification to be performed using methods commonly used in the industry to remove fines or coarse particles, such as sieving and / or air stream classification.

[0075] The present invention includes a negative electrode material for a lithium secondary battery containing the aforementioned graphite material.

[0076] The present invention includes a negative electrode material for a lithium secondary battery containing a graphite material manufactured by the aforementioned manufacturing method.

[0077] A cathode material according to one embodiment may include a graphite material in which the bare surface of the assembly is exposed. Alternatively, the cathode material may include the aforementioned graphite material in which a separate coating layer is not formed on the surface of the assembly (uncoated state).

[0078] A cathode material according to one embodiment may include the aforementioned graphite material and a surface layer covering part or all of the surface of the graphite material. Alternatively, the cathode material may include a core of graphite material and a shell (surface layer) of a heterogeneous material. The shell of the heterogeneous material may have a structure of a single shell of a single heterogeneous material, a single shell in which two or more heterogeneous materials are mixed, or a multilayer shell in which each of two or more heterogeneous materials forms a different shell. Such a shell of the heterogeneous material may form the surface of the cathode material.

[0079] The heterogeneous material may include amorphous carbon, graphene, carbon nanotubes, silicon-based materials, metal oxides, mixtures thereof, or composites thereof. Silicon-based materials may include metallic silicon, silicon oxide, silicon carbide, composite oxides of silicon and alkali to alkaline earth metals, mixtures thereof, or composites thereof, but are not limited thereto. Metal oxides may include lithium titanium oxide, iron oxide, titanium oxide, aluminum oxide, chromium oxide, zinc oxide, copper oxide, magnesium oxide, zirconium oxide, molybdenum oxide, vanadium oxide, niobium oxide, manganese oxide, vanadium oxide, cobalt oxide, nickel oxide, tantalum oxide, mixtures thereof, or composites thereof, but are not limited thereto. In one embodiment, the thickness of the shell (thickness of the surface layer) may be at the level of 1 to 50 nm, but is not necessarily limited thereto.

[0080] The present invention includes a negative electrode for a lithium secondary battery containing the negative electrode material described above.

[0081] The negative electrode according to the first disclosure is a negative electrode for a lithium secondary battery and comprises a current collector and a negative electrode active material layer located on at least one surface of the current collector and containing the negative electrode material (artificial graphite-based negative electrode material) described above.

[0082] The negative electrode active material layer may contain 95 to 99 weight percent of a negative electrode active material based on the total weight of the negative electrode active material layer. At this time, the negative electrode active material may contain the aforementioned negative electrode material alone or a heterogeneous negative electrode material together with the aforementioned negative electrode material (synthetic graphite-based negative electrode material). Examples of heterogeneous negative electrode materials include natural graphite-based negative electrode materials and / or silicon-based negative electrode materials (silicon, silicon oxide, silicon-silicon oxide composite, silicon-carbon composite, silicon alloy, etc.). When the negative electrode active material contains both the aforementioned negative electrode material (synthetic graphite-based negative electrode material) and the heterogeneous negative electrode material, the weight ratio of the aforementioned negative electrode material (synthetic graphite-based negative electrode material) to the heterogeneous negative electrode material may be 100:1 to 100, but is not necessarily limited thereto.

[0083] The negative electrode active material layer may further include an additive containing an organic binder together with the negative electrode active material, and if necessary, the additive may further include a conductive material. In terms of achieving stable fixation between negative electrode active materials and between the negative electrode active material and the current collector by the organic binder without damaging the conductivity and open pore structure within the negative electrode active material layer, the negative electrode active material layer may contain 1 to 5 weight% of an organic binder, substantially 1 to 3 weight% of an organic binder. Additionally, if the negative electrode active material layer further contains a conductive material, the negative electrode active material layer may contain 0.5 to 3 weight% of a conductive material, substantially 0.5 to 2 weight% of a conductive material, but is not limited thereto.

[0084] The organic binder is sufficient if it is a polymer binder commonly used in the field of lithium secondary batteries to bind particulate negative electrode active materials together and to bind the negative electrode active material to a current collector. Practical examples of organic binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or mixtures thereof.

[0085] The conductive material is sufficient if it is a conductive additive commonly used to improve the conductivity of the anode in the field of lithium secondary batteries. Specifically, the conductive material may include point conductive materials, linear conductive materials, planar conductive materials, or mixtures thereof. Examples of point conductive materials include conductive carbon materials such as carbon black, acetylene black, Ketjen black, channel black, Farness black, lamp black, thermal black, etc.; metal particles such as copper, nickel, aluminum, silver, etc.; conductive polymer particles; core-shell particles of a non-conductive core and a conductive shell; etc. Examples of linear conductive materials include carbon nanotubes, conductive carbon fibers, metal fibers, or conductive polymer fibers, etc. Examples of planar conductive materials include graphene or reduced graphene oxide, etc., but are not limited thereto. As a practical example, the conductive material may include carbon black, and as another practical example, the conductive material may include carbon black and carbon nanotubes.

[0086] The cathodic density (electrode density) of the cathode is 1.20 to 1.90 g / cm³. 3 Level, specifically 1.50 to 1.90 g / cm³ 3 It may be, but is not limited to this.

[0087] The current collector is sufficient to be a conventional conductive material used to ensure smooth current flow to the negative electrode active material layer in the field of lithium secondary batteries. The current collector may be in the form of a foil, porous foil, foam, mesh, nonwoven fabric, a non-conductive material with a conductive coating layer, or a combination thereof, but is not limited thereto. The material of the current collector is sufficient to have high conductivity without causing chemical changes within the battery. Practical examples of the current collector include copper, stainless steel, aluminum, nickel, titanium, or alloys thereof, but are not limited thereto. The current collector may have a conventional thickness, a practical example being 3 to 500 μm, but is not limited thereto.

[0088] The negative electrode may be manufactured using a method commonly used for manufacturing negative electrodes in the field of lithium secondary batteries. For example, the negative electrode may be manufactured by applying a slurry containing a negative electrode active material, a binder, a solvent, and, if necessary, a conductive material to at least one surface of a current collector, followed by drying and rolling, but is not limited thereto.

[0089] The solvent may be any solvent commonly used in the field of lithium secondary batteries for forming a slurry for manufacturing a negative electrode. For example, the solvent may be dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, dimethylformamide (DMF), water, or a mixture thereof, but is not limited thereto.

[0090] The application of the slurry may be any method commonly used in the field of lithium secondary batteries to form an active material layer using a slurry. As a practical example, the application of the slurry may be performed by slot die coating, Meyer bar coating, gravure coating, comma coating, roll coating, blade coating, bar coating, dipping coating, etc.

[0091] The present invention includes a lithium secondary battery comprising the aforementioned negative electrode.

[0092] A lithium secondary battery according to the first disclosure may include the aforementioned negative electrode, positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte. Specifically, the secondary battery may include a positive electrode comprising a positive current collector and a positive active material layer located on at least one surface of the positive current collector, the aforementioned negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte that conducts lithium ions. The positive active material or composition of the positive current collector and the positive active material layer, the solvent or electrolyte salt of the separator and the electrolyte, or the concentration of the electrolyte salt, etc., are sufficient if they are materials or compositions conventionally adopted in lithium secondary batteries. Furthermore, the secondary battery may further include an electrode assembly comprising a positive electrode, a negative electrode, and a separator, and a sealable battery container in which the electrolyte is housed.

[0093] Based on the type of separator and electrolyte, the lithium secondary battery may be a lithium-ion battery, a lithium-ion polymer battery, or a lithium-polymer battery, and based on the shape, it may be cylindrical, prismatic, coin-type, or pouch-type, but is not limited thereto.

[0094] The physical properties described in the detailed description and claims were measured according to the 'analysis and measurement methods' below.

[0095] Analysis and Measurement Methods

[0096] (D 50 )

[0097] 0.02–0.04 g of the analyte was suspended in water, and the prepared suspension was sonicated for 1 minute. Subsequently, the cumulative volumetric diameter distribution was measured using a conventional laser diffraction particle size distribution analyzer (Microtrac S3500). The median diameter D of the analyte 50 represents the diameter at the position where the cumulative volume is 50% in the cumulative volume diameter distribution. The span value is (D 90 -D 10 ) / D 50 It is defined as, and D 10 represents the diameter at the position where the cumulative volume is 10% in the cumulative volume diameter distribution, and D 90 represents the diameter at the position where the cumulative volume is 90% in the cumulative volume diameter distribution.

[0098] (Curvature)

[0099] Convexity was measured by ultrasonically dispersing 0.01 g of the analyte in 5 mL of ethanol and using a particle shape analyzer (Flowcam 8100, Fluid Imaging Technologies) commonly used for particle shape analysis. By using particle size scattergrams generated by conventional programs equipped with data processing and analysis software for the particle shape analyzer, such as visual spreadsheets, or by processing the measured raw data, the minimum size of the particle group (major particle group) used for calculating convexity was 0.9D 50 and the maximum size is 1.1D 50 A particle group was selected such that , the curvature of particles belonging to the major particle group was calculated, and the aggregate modulus (first aggregate modulus) was obtained according to Equation 1. Similarly, 1.2D 50 to 1.4D 50 A second fineness modulus is obtained using the curvature calculated from a group of particles belonging to the size range of , and 1.5D 50 A third aggregation rate was obtained using the aggregation calculated from a particle group belonging to a size range of 1.6D50. The aggregation of a material (first aggregation, second aggregation, or third aggregation) is the average of the aggregation values ​​(first aggregation, second aggregation, or third aggregation) for a particle group of a specific size range in each of 10 randomly collected samples.

[0100] As is well known, the convex hull area is the area defined by an elastic band that stretches around the particle contour in a 2D image of the 3D particle to be measured. The particle area is the actual area of ​​the particle. The curvature of each particle is defined by the ratio of the particle area in the captured image to the convex outer surface area.

[0101] (BET specific surface area)

[0102] After performing pretreatment by drying the analyte at a vacuum of 0.1 Torr or less and a temperature of 300°C for 1 hour, the BET specific surface area (m²) was calculated using the BET method from the nitrogen adsorption isotherm of the pretreated analyte. 2 / g) was calculated. The nitrogen adsorption-desorption isotherm was measured using a specific surface area measuring device (ASAP 2400, Micromeritics) with a specific surface area measuring device (ASAP 2400, Micromeritics) at a temperature of 77K using liquid nitrogen as the adsorbed nitrogen gas and a relative pressure (P / P0) measurement precision of 0.05.

[0103] (Tap density)

[0104] The tap density was measured by using a standard tap density measuring device (BEDENSI of Bettersize) based on ASTM B527, by placing 15g of the substance to be measured into a 50mL container and tapping 3000 times with a stroke length of 1.2cm (tapping speed = 250 times / min), and is the average value of the tap density measured twice on randomly collected samples.

[0105] (Half cell)

[0106] To evaluate the electrochemical properties of the assemblies prepared in the examples and comparative examples, a carbon coating layer was formed on each of the assemblies prepared in the examples and comparative examples, and a half cell was prepared using the assemblies as a cathode material. The carbon coating layer was formed by mixing 97 parts by weight of the assembly with 3 parts by weight of petroleum-based pitch having a softening point of 250°C, and then heat-treating the mixture at 1200°C for 5 hours in a nitrogen atmosphere.

[0107] Specifically, a slurry was prepared by adding the cathode material, styrene butadiene rubber, carboxymethylcellulose, and carbon black (super-P) to distilled water and mixing for 10 minutes so that the weight ratio of cathode material : carboxymethylcellulose (CMC) : styrene butadiene rubber (SBR) : conductive carbon black (super-P) is 95.6 : 1.1 : 2.3 : 1.0; then, the prepared slurry was applied to a copper (Cu) foil, dried, and rolled to obtain an electrode density of 1.55 g / cm³. 3 The cathode of was manufactured.

[0108] A coin-type 2032 half cell was fabricated using lithium foil as the counter electrode of the negative electrode. A porous polypropylene film was used as the separator, and a solution of LiPF6 dissolved at a concentration of 1 M in a mixed solvent with a volume ratio of ethylene carbonate (EC) and dimethyl carbonate (DMC) of 1:1 was used as the electrolyte.

[0109] Hereinafter, the manufactured half cell is collectively referred to as the half cell with the same number as the specific example number or comparative example number in which the assembly was manufactured. For example, the half cell manufactured using the assembly manufactured in Example 1 is collectively referred to as the half cell of Example 1.

[0110] (Electrochemical properties using a half-cell)

[0111] The electrochemical characteristics of the manufactured half cell were evaluated after the formation stage. In the formation charging stage, the cell was charged to 0.005 V with a constant current (CC) of 0.1 C and then charged from 0.005 V to 0.005 C with a constant voltage (CV). In the formation discharge stage, the cell was discharged to 1.5 V with a constant current (CC) of 0.1 C. The formation charging and formation discharge constituted one cycle, and three (three cycles) of charging and discharging were performed in the formation stage.

[0112] The discharge capacity in the third and final cycle of the three charge-discharge cycles performed during the fusion phase was calculated as the discharge capacity of the half cell.

[0113] After the formation phase was performed, to test the high-rate characteristics, voltage values ​​according to the resistance increase rate and state of charge (SOC) under rapid charging conditions were measured using HPPC (Hybrid Pulse Power Characterization).

[0114] Specifically, for the HPPC test, a fully charged half cell (SOC 100%) was discharged to SOC 50% at 0.1C, and then a charge / discharge pulse of 2.5C and 0.2 sec was applied at SOC 50% to calculate the resistance increase rate.

[0115] The voltage value according to the state of charge (SOC) was measured by charging a fully discharged half cell (SOC 0%) to 3.0C.

[0116] The present invention will be described in detail below through examples. However, it should be noted that the examples described below are intended merely to illustrate and embody the present invention and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the patent claims and matters reasonably inferred therefrom.

[0117] (Example 1)

[0118] D as carbon material 50 Coal-based needle-shaped green coke with a particle size of 10.5 μm and a span value of 1.1 was used. Petroleum-based pitch with a softening point of 250°C was used as the first carbon-based binder and the second carbon-based binder, wherein D of the first carbon-based binder 50 was 1.1 μm, and D of the second carbon-based binder 50 It was 6.3 μm.

[0119] A carbon material and a first carbon-based binder were mixed at room temperature (pre-mixed), and then the pre-mixed mixture was mixed at 240°C (first mixing) to prepare a first mixture. Subsequently, the first mixture and a second carbon-based binder were mixed at room temperature (second mixing) to prepare a second mixture. In the second mixture, the weight ratio of the carbon material to the carbon-based binder (first carbon-based binder and second carbon-based binder) was 100:16, and the weight ratio of the first carbon-based binder to the second carbon-based binder was 62.5:37.5.

[0120] The second mixture prepared using a cone mixer was granulated at a temperature of 600°C for 2 hours to produce an intermediate in the form of secondary particles.

[0121] Subsequently, the manufactured intermediate was subjected to total carbonization treatment in a nitrogen atmosphere at 1200°C for 3 hours, followed by graphitization treatment in a nitrogen atmosphere at 3000°C for 2 hours, and the treated material produced by the graphitization treatment was crushed and classified to obtain an aggregate.

[0122] (Example 2)

[0123] In Example 1, D 50 An assembly was obtained in the same manner as in Example 1, except that a petroleum-based pitch having a thickness of 0.7 μm and a softening point of 250°C was used as the first carbon-based binder, and the second mixture was prepared by performing pre-mixing, first mixing, and second mixing such that the weight ratio of the carbon material to the carbon-based binder (first carbon-based binder and second carbon-based binder) in the second mixture was 100:16 and the weight ratio of the first carbon-based binder to the second carbon-based binder was 50:50.

[0124] (Comparative Example 1)

[0125] An assembly was prepared in the same manner as in Example 1, except that the same carbon material and the same first carbon-based binder and second carbon-based binder as in Example 1 were used, and the carbon material, the first carbon-based binder, and the second carbon-based binder were all simply mixed together at room temperature to prepare a mixture, and then the prepared mixture was assembled to prepare an intermediate.

[0126] (Comparative Example 2)

[0127] D as carbon material 50 A coal-based needle green coke with a thickness of 10.5 μm and a span value of 1.1 was used, and a petroleum-based pitch with a D50 of 4 μm and a softening point of 250°C was used as a carbon-based binder. A mixture was prepared by mixing the carbon material and the carbon-based binder at room temperature so that the weight ratio of the carbon material to the carbon-based binder was 95:5, and then the prepared mixture was granulated for 5 hours to produce an intermediate, except that an intermediate was prepared in the same manner as in Example 1.

[0128] Cumulative volume median diameter (D) of the assemblies prepared in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 50 ), span value (span), BET specific surface area (m²) 2 / g) D 50 Ratio divided by (㎛) (BET / D 50 ) and tap density (TD) were measured and summarized in Table 1.

[0129] (Table 1)

[0130]

[0131] The first assembly rate, second assembly rate, and third assembly rate of the assemblies manufactured in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 are summarized in Table 2.

[0132] (Table 2)

[0133]

[0134] After forming a carbon coating layer on the assembly prepared in Example 1, Example 2, Comparative Example 1, and Comparative Example 2, the voltage difference (ΔV in Table 2) between the voltage at SOC 50% and the voltage at SOC 70%, and the increase rate of charging resistance (RC) and the increase rate of discharge resistance (RD) by HPPC were measured and summarized in Table 3 for the half cell prepared using the same as the cathode material under rapid charging conditions (3.0C).

[0135] (Table 3)

[0136]

[0137] As can be seen from Comparative Example 2 in Tables 2 and 3, when the assembly rate is low, a larger voltage drop occurs under high-speed charging conditions, and the resistance increase rate due to HPPC is also large, so the high-speed output characteristics are also degraded.

[0138] In addition, through Example 1 and Comparative Example 1 in Tables 2 and 3, it can be seen that even when the material composition of the final assembly (and cathode material) is substantially the same because the carbon material and carbon-based binder used in assembly have the same material and content, the high-rate characteristics are significantly affected by the uniformity of assembly according to the assembly ratio and size. As seen in Example 1, Example 2, Comparative Example 1, and Comparative Example 2, when the graphite material has a low assembly ratio, a low voltage drop occurs under high-speed charging conditions, and the resistance increase rate due to HPPC is also significantly lower, resulting in improved high-speed output characteristics. Furthermore, it can be seen that the high-rate characteristics are further improved when there is higher assembly uniformity with a lower assembly ratio.

[0139] The present invention is not limited to the embodiments described above but can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without altering the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

Claim 1 A graphite material for a lithium secondary battery negative electrode, comprising an assembly of artificial graphite monomers, having a span of 0.6 to 0.9, and having an aggregation modulus defined by the following Formula 1 of 0.50 or less. (Formula 1) Aggregation modulus = [1 / C - 1] × 100(wherein Equation 1, C is the convexity, which is the ratio of the particle area to the convex hull area in a captured image of a 3D particle captured as a 2D image, and the cumulative volume-based median diameter D 50 Based on, 0.9D 50 to 1.1D 50 It is the curvature of the graphite material belonging to the central size range, which is the size range of . Claim 2 A graphite material for a lithium secondary battery negative electrode according to claim 1, satisfying the following Equation 2. (Equation 2) (Second assembly ratio) / (First assembly ratio) ≤ 5.00 (wherein, the first assembly ratio is the assembly ratio due to the curvature of the graphite material belonging to the center size range, and the second assembly ratio is 1.2D 50 to 1.4D 50 It is the fineness modulus according to Equation 1 based on the curvature of the graphite material within the size range. Claim 3 In Article 1, 1.2D 50 to 1.4D 50 A graphite material for a lithium secondary battery negative electrode, wherein the second aggregation modulus according to Equation 1, which is the aggregation modulus based on the curvature of the graphite material within the size range, is 1.50 or less. Claim 4 In Paragraph 3, 1.5D 50 to 1.6D 50 A graphite material for a lithium secondary battery negative electrode, wherein the third aggregation modulus according to Equation 1, which is the aggregation modulus based on the curvature of the graphite material within the size range, is 5.00 or less. Claim 5 delete Claim 6 In claim 1, the above D 50 Graphite material for lithium secondary battery anode material, having a thickness of 8 to 25 μm. Claim 7 A graphite material for a lithium secondary battery negative electrode, wherein the artificial graphite unit is a shape selected from one or more of a rod shape, a plate shape, and a flake shape. Claim 8 A graphite material for a lithium secondary battery negative electrode, wherein the assembly further comprises amorphous graphite located at the boundary between the artificial graphite units in the first paragraph. Claim 9 In claim 8, the above assembly is a graphite material for a lithium secondary battery negative electrode, containing 8 to 15 parts by weight of amorphous graphite based on 100 parts by weight of the artificial graphite unit. Claim 10 In Article 1, m 2 BET specific surface area (BET) in units of / g, D in units of μm 50 The ratio divided by (BET / D 50 Graphite material for lithium secondary battery anode material having ) 0.14 or less. Claim 11 In claim 1, 0.95 g / cm² 3 Graphite material for a lithium secondary battery negative electrode having a tap density of the above. Claim 12 In claim 1, the artificial graphite unit assembled into the assembly has a cumulative volume median diameter D of the graphite material. 50 Based on, 0.4D 50 to 0.8D 50 Graphite material for lithium secondary battery anode material having an average size. Claim 13 A negative electrode material for a lithium secondary battery comprising a graphite material according to any one of claims 1 to 4 and claims 6 to 12. Claim 14 A negative electrode for a lithium secondary battery comprising a negative electrode material according to Clause 13.

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