Negative electrode material for lithium secondary battery, and lithium secondary battery negative electrode comprising same

Abstract

Disclosed is a negative electrode material for a lithium secondary battery. The negative electrode material includes spherical natural graphite and a surface layer disposed on the surface of the spherical natural graphite and containing carbon. The ratio of AR(TL) to AR(AM), i.e., AR(TL) / AR(AM) is 4.0 or less, where AR(AM) is the area ratio occupied by voids on the particle surface in a scanning electron micrograph of the negative electrode material in the size range of D50 + 0.15D50 to D50 - 0.15D50 on the basis of D50 in a volumetric cumulative particle size distribution, and AR(TL) is the area ratio occupied by voids on the particle surface in a scanning electron micrograph of the low-temperature oxidation treated negative electrode material in the size range of D50 + 0.15D50 to D50 - 0.15D50 following a low-temperature oxidation treatment carried out under condition 1: air atmosphere, TL of 600°C, heat treatment at TL temperature for 2 hours, heating rate of 5°C / min, and cooling rate of 5°C / min.

Description

Anode material for lithium secondary batteries and anode of lithium secondary batteries containing the same

[0001] The present disclosure relates to a negative electrode material for a lithium secondary battery and a negative electrode of a lithium secondary battery including the same, and more particularly, to a natural graphite-based negative electrode material of a lithium secondary battery.

[0002] As the market for electronic devices such as mobile phones, laptops, and PCs grows, the market for lithium secondary batteries, the power sources for these devices, is also growing rapidly. Furthermore, growing concern over environmental issues has led to a surge in demand for eco-friendly vehicles like electric vehicles, leading to research into lithium secondary batteries that can meet a variety of applications.

[0003] Among the components that make up lithium secondary batteries, the anode active material stores lithium ions during charging and plays a crucial role in determining factors such as improved charging speed and battery capacity. Carbon-based active materials are representative examples of commercially used anode active materials. These can be divided into graphitic carbons, such as natural graphite or artificial graphite, and low-crystalline carbons, such as non-graphitizable or graphitizable carbons.

[0004] Among these, natural graphite is highly price competitive and has a higher capacity than artificial graphite, but it has a large irreversible reaction due to the exposed edge surface, the lithium ion diffusion path is limited due to the uniaxial orientation of the graphene layer plane, resulting in poor output characteristics, and it has the problem of low electrode density due to the ease of orientation in a plane on the current collector.

[0005] To address these issues, technologies are being developed to process natural graphite into a spherical shape and form a carbon coating on the spherical surface. However, heavy mechanical processing to improve sphericity causes significant damage to the natural graphite, which deteriorates its electrochemical properties.

[0006] According to one embodiment of the present invention, a high-quality natural graphite-based negative electrode material for a lithium secondary battery with minimal physical damage can be provided.

[0007] The objectives of the present invention are not limited to the above-described scope. Those skilled in the art will have no difficulty understanding the additional objectives of the present invention from the overall content of this specification.

[0008] According to one embodiment of the present invention, a negative electrode material for a lithium secondary battery comprises spherical natural graphite and a surface layer containing carbon located on the surface of the spherical natural graphite, and D in the volume cumulative particle size distribution 50 Based on , D 50 + 0.15D 50 Inland D 50 - 0.15D 50 In the scanning electron microscope observation images of the cathode material in the size range of , the area ratio AR(AM) occupied by the interstitial space on the particle surface is shown after low-temperature oxidation treatment according to the following condition 1. 50 + 0.15D 50 D50 - 0.15D 50 In the scanning electron microscope observation images of the low-temperature oxidation-treated cathode material in the size range, the ratio AR(TL) / AR(AM), which is the area ratio occupied by the interstitial space on the particle surface, is 4.0 or less.

[0009] Condition 1: Air atmosphere, TL of 600 ℃, heat treatment at TL temperature for 2 hours, heating rate of 5 ℃ / min and cooling rate of 5 ℃ / min

[0010] In one specific example, after high temperature oxidation treatment according to the following condition 2, the D 50 Based on D 50 + 0.15D 50 Inland D 50 - 0.15D 50In the scanning electron microscope observation image of a high-temperature oxidation-treated cathode material within the size range, the ratio AR(TH) / AR(AM), which is the area ratio occupied by the interstitial space on the particle surface divided by the AR(AM), may be 10.0 or less.

[0011] Condition 2: Air atmosphere, TH of 900 ℃, heat treatment at TH temperature for 1 hour, heating rate of 5 ℃ / min and cooling rate of 5 ℃ / min

[0012] In one specific example, the D 50 Based on D 50 + 0.15D 50 Inland D 50 - 0.15D 50 In a scanning electron microscope image of a high-temperature oxidation-treated single cathode particle within a size range, the uniformity within the particle, which is a standard deviation between the area ratio AR(TH_P) occupied by the interstitial space on the particle surface in each region, in four regions of the single cathode particle divided by an imaginary line connecting the centers of opposite sides of a rectangle in which the single cathode particle is positioned and each of the four sides is in contact with the single cathode particle, may be 3.5 or less.

[0013] In one specific example, the AR(TL) / AR(AM) may be 1.5 to 3.0.

[0014] In one specific example, the AR(TL) may be 2.5 to 6.0%.

[0015] In one specific example, the AR(TH) / AR(AM) may be 3.5 to 8.0.

[0016] In one specific example, the AR(TH) may be 6.5 to 12.0%.

[0017] In one specific example, the sphericity of the negative electrode material may be 0.90 or more.

[0018] In one specific example, based on the X-ray diffraction pattern of the cathode material, the maximum intensity I of the (110) peak110 The maximum intensity of the (004) peak I 004 The ratio divided by (I 110 / I 004 ) can be between 0.40 and 0.80.

[0019] In one specific example, the D 50 may be 10 to 25 μm.

[0020] In one specific example, the tap density of the negative electrode material is 0.8 to 1.2 g / cm 3 It could be.

[0021] In one specific example, the BET specific surface area of ​​the cathode material is 2.0 to 3.5 m 2 / g may be.

[0022] In one specific example, the spherical natural graphite may be in the form of particles in which natural graphite fragments are bonded and assembled.

[0023] In one specific example, the surface layer may be an amorphous carbon layer.

[0024] The present invention includes a negative electrode for a lithium secondary battery including the above-described negative electrode material.

[0025] The negative electrode material for a lithium secondary battery according to the invention can be a high-quality negative electrode material with low accumulated deformation and defect energy.

[0026] The various advantageous and beneficial effects of the present invention are not limited to the above-described contents, and will be more easily understood in the course of explaining specific embodiments of the present invention.

[0027] Figure 1 is a schematic diagram illustrating a specific method for dividing four regions in a high-temperature oxidation-treated single cathode material particle according to one specific example.

[0028] Figure 2 is a scanning electron microscope photograph of spherical natural graphite manufactured in Manufacturing Example 1.

[0029] Figure 3 is a representative particle image obtained after low-temperature oxidation treatment of the negative electrode material manufactured in Manufacturing Example 1.

[0030] Figure 4 is a representative particle image obtained after low-temperature oxidation treatment of the negative electrode material manufactured in Manufacturing Example 2.

[0031] Figure 5 is a diagram illustrating the process of calculating the gap space area ratio shown in black by defining the gap space from the representative particle image of Figure 3.

[0032] Figure 6 is a representative particle image of the negative electrode material particles of Manufacturing Example 1 subjected to high-temperature oxidation treatment.

[0033] Figure 7 is a diagram illustrating the process of calculating the gap space area ratio shown in black by defining the gap space from the representative particle image of Figure 6.

[0034] Figure 8 is a diagram illustrating a process of calculating the interstitial space area ratio for each region (AP1, AP2, AP3, AP4) of a particle to calculate the intra-particle uniformity from the representative particle image of Figure 6.

[0035] Figure 9 is a scanning electron microscope photograph of spheroidized natural graphite manufactured with ACM.

[0036] Hereinafter, preferred embodiments of the present invention will be described with reference to the attached drawings. However, the 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.

[0037] In addition, the embodiments of the present invention are provided to more completely explain the present invention to a person having average knowledge in the relevant technical field.

[0038] In addition, the attached drawing may have distorted and deformed parts during the conversion process for application, and may differ from the image used for actual measurement due to such distortion and deformation.

[0039] In describing the embodiments of the present invention, if a detailed description of a known technology related to the present invention is judged to unnecessarily obscure the gist of the present invention, such detailed description will be omitted. In addition, the terms described below are terms defined in consideration of their functions in the present invention, and these may vary depending on the intention or custom of the user or operator. Therefore, the definitions should be made based on the contents throughout this specification. The terminology used in the detailed description is only for the purpose of describing the embodiments of the present invention and should in no way be limiting. Unless clearly defined otherwise, expressions in the singular form include plural meanings.

[0040] In this description, expressions such as "including" or "having" are intended to indicate certain features, numbers, steps, operations, elements, portions or combinations thereof, and should not be construed to exclude the presence or possibility of one or more other features, numbers, steps, operations, elements, portions or combinations thereof other than those described.

[0041] Unless otherwise specified in the specification of the present invention, the % unit means weight %.

[0042] Additionally, throughout the specification, when we say that a part is 'connected' to another part, this includes not only cases where it is 'directly connected', but also cases where it is 'indirectly connected' with other elements in between.

[0043] Below, the present invention will be described in detail through each embodiment or example of the present 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 be combined with other embodiments or examples. Therefore, the citation of a claim in the patent claims is only an example of an embodiment, and the technical concept of the present invention should not be interpreted solely as a combination with the cited claim, and combinations with various claims also fall within the scope of the technical concept of the present invention.

[0044] The negative electrode material for a lithium secondary battery according to the invention comprises spherical natural graphite and a surface layer containing carbon located on the surface of the spherical natural graphite, and D in the volume cumulative particle size distribution 50 Based on , D 50 + 0.15D 50 Inland D 50 - 0.15D 50 In the scanning electron microscope observation images of the cathode material in the size range of , the area ratio AR(AM) occupied by the interstitial space on the particle surface is shown after low-temperature oxidation treatment according to the following condition 1. 50 + 0.15D 50 Inland D 50 - 0.15D 50 In the scanning electron microscope observation images of the low-temperature oxidation-treated cathode material in the size range, the ratio AR(TL) / AR(AM), which is the area ratio occupied by the interstitial space on the particle surface, is 4.0 or less.

[0045] Condition 1: Air atmosphere, TL of 600 ℃, heat treatment at TL temperature for 1 hour, heating rate of 5 ℃ / min and cooling rate of 5 ℃ / min

[0046] In condition 1, a low-temperature oxidation temperature (TL) of 600°C and a heat treatment time of 1 hour are conditions under which carbon contained in the surface layer of the negative electrode material is completely removed by reaction with oxygen, and high-energy accumulation regions containing a large number of defects and severely deformed spherical natural graphite of the negative electrode material can be removed by reaction with oxygen.

[0047] Accordingly, when low-temperature oxidation treatment is performed according to condition 1, carbon atoms in areas (high-energy accumulation areas) with high accumulated strain and defect energy in the spherical natural graphite of the negative electrode material react with oxygen to form carbon dioxide, and some of the planes forming the layer structure are decomposed, thereby creating gaps (empty spaces) between natural graphite fragments on the surface of the negative electrode material particles.

[0048] As described above, when subjected to low-temperature oxidation treatment according to Condition 1, the area ratio AR(TL) occupied by interstitial spaces on the entire surface of the negative electrode particle based on scanning electron microscope observation images can represent the degree of formation of high-energy accumulation regions in spherical natural graphite, and the distribution of interstitial spaces can represent the distribution of high-energy accumulation regions in spherical natural graphite.

[0049] The area ratio of the interstitial space (AR(TL), AR(AM), etc.) is D in the volume cumulative particle size distribution of the cathode material. 50 Based on , D 50 + 0.15D 50 Inland D 50 - 0.15D 50 It can be the area ratio of the gap space of the cathode material that falls within the size range of D. 50 If the area ratio of the interstitial space is calculated through an excessively small cathode material, the mechanical (physical) damage may be overestimated, and D 50 If the area ratio of the interstitial space is calculated through an excessively large cathode material, the mechanical (physical) damage may be underestimated. Therefore, D 50 + 0.15D 50 Inland D 50 - 0.15D50 By calculating the interstitial space from the scanning electron microscope image of the cathode material within the size range of , the degree of formation and distribution of high-energy accumulation regions within the cathode material, which can represent the cathode material with the corresponding sphericity without any distortion, can be quantitatively calculated. Hereinafter, D 50 + 0.15D 50 Inland D 50 - 0.15D 50 The size range is collectively called the center size range.

[0050] In one specific example, the ratio AR(TL) / AR(AM), which is obtained by dividing the area ratio AR(TL) occupied by the interstitial space on the particle surface in a scanning electron microscope observation image of a low-temperature oxidation-treated negative electrode material belonging to the center size range by the area ratio AR(AM) occupied by the interstitial space on the particle surface in a scanning electron microscope observation image of the negative electrode material belonging to the center size range, may be 4.0 or less, specifically 1.0 to 4.0, more specifically 1.5 to 3.5, even more specifically 1.5 to 3.0, even more specifically 2.0 to 2.8, and even more specifically 2.0 to 2.5.

[0051] An AR(TL) / AR(AM) of 4.0 or less, specifically 1.0 to 4.0, more specifically 1.5 to 3.5, even more specifically 1.5 to 3.0, even more specifically 2.0 to 2.8, and even more specifically 2.0 to 2.5, indicates that there are almost no locally concentrated highly damaged regions (high energy accumulation regions that are severely deformed and contain a large number of defects) in the anode material, particularly, the spherical natural graphite contained in the anode material.

[0052] In terms of manufacturing method, spherical natural graphite may be natural graphite whose shape is adjusted to a spherical shape through mechanical processing by applying mechanical forces such as impact compression, friction, and / or shear force to natural graphite having an anisotropic shape. The aforementioned low AR(TL) / AR(AM) value may indicate that sphericalization was achieved without significant local damage to the natural graphite during mechanical processing.

[0053] As a practical example, the AR(TL) of the cathode material may be from 2.5 to 6.0%, more substantially from 3.0 to 5.5%, even more substantially from 3.0 to 5.0%, even more substantially from 3.5 to 4.5%, and even more substantially from 3.8 to 4.4%.

[0054] As a practical example, the AR (AM) of the cathode material may be 0.1 to 2.0%, specifically 0.5 to 2.0%, more specifically 1.0 to 2.0%, and even more specifically 1.5 to 2.0%.

[0055] According to one specific example, the degree of formation and distribution of low-energy accumulation regions existing in the spherical natural graphite of the negative electrode material, substantially the negative electrode material, can be derived by high-temperature oxidation treatment according to the following condition 2.

[0056] Condition 2: Air atmosphere, TH of 900 ℃, heat treatment at TH temperature for 1 hour, heating rate of 5 ℃ / min and cooling rate of 5 ℃ / min

[0057] Similar to Condition 1, the high-temperature oxidation temperature (TH) of 900 ℃ and the heat treatment time of 1 hour in Condition 2 are also conditions under which all carbon contained in the surface layer of the negative electrode material is removed by reaction with oxygen.

[0058] While the low-temperature oxidation treatment according to condition 1 is a condition that can indicate the degree of formation and distribution of a high-energy accumulation region within the cathode material, the high-temperature oxidation treatment according to condition 2 is a condition that can indicate the degree of formation and distribution of parts (low-energy accumulation regions) with relatively small accumulated deformation and defect energy in the cathode material.

[0059] In detail, the high-temperature oxidation temperature (TH) of 900 ℃ and the heat treatment time of 1 hour in Condition 2 are conditions in which carbon atoms in areas (low-energy accumulation areas) with small strain and defect energy accumulated in the spherical natural graphite of the negative electrode material react with oxygen and are converted to carbon dioxide, and some of the planes forming the layer structure are decomposed, thereby removing the low-energy accumulation areas on the particle surface and creating interstitial spaces (empty spaces).

[0060] As described above, the interstitial space formed by the high-temperature oxidation treatment according to condition 2 can indicate the degree of formation and distribution of low-energy accumulation regions existing in the negative electrode material, specifically, the spherical natural graphite of the negative electrode material.

[0061] In one specific example, in a scanning electron microscope image of a cathode material subjected to high-temperature oxidation treatment according to condition 2 and belonging to the central size range, the ratio AR(TH) / AR(AM), which is obtained by dividing the area ratio AR(TH) occupied by the interstitial space on the particle surface by the area ratio AR(AM) occupied by the interstitial space on the particle surface in a scanning electron microscope image of the cathode material belonging to the central size range, may be 10.0 or less, specifically 3.0 to 10.0, more specifically 3.5 to 8.0, even more specifically 4.0 to 7.0, even more specifically 4.0 to 6.5, and even more specifically 4.5 to 6.0.

[0062] When subjected to high-temperature oxidation treatment according to Condition 2, an AR(TH) / AR(AM) value of 10.0 or less, specifically 3.0 to 10.0, more specifically 3.5 to 8.0, more specifically 4.0 to 7.0, more specifically 4.0 to 6.5, and even more specifically 4.5 to 6.0 may indicate that natural graphite is mild and spheroidized by rapid mechanical processing, and that low damage occurs to the spheroidal natural graphite.

[0063] As a practical example, the AR(TH) of the negative electrode material may be from 6.5 to 12.0%, more substantially from 6.5 to 11.0%, more substantially from 6.5 to 10.0%, more substantially from 7.0 to 9.5%, more substantially from 8.0 to 9.5%, and more substantially from 8.5 to 9.5%.

[0064] In one specific example, the distribution of interstitial spaces in a particle of a high-temperature oxidation-treated cathode material can indicate whether there is a local concentration of accumulated strain and defect energy in the cathode material, particularly in spherical natural graphite.

[0065] Fig. 1 is a schematic diagram illustrating a specific method for dividing four regions in a high-temperature oxidation-treated anode particle (A) according to one specific example. As shown in the example in Fig. 1, in a scanning electron microscope observation image, the high-temperature oxidation-treated anode particle (A) and an imaginary line (CL1, CL2) connecting the centers of opposite sides of a rectangle (SQ) each of which is in contact with the particle (A) and inside which the particle (A) is positioned can be divided into four regions (AP1, AP2, AP3, AP4).

[0066] The intra-particle uniformity, which is the standard deviation between the area ratio AR(TH_P) occupied by the interstitial space on the particle surface for each region (AP1, AP2, AP3, AP4), can represent the uniformity of deformation and defects in the negative electrode material particles.

[0067] In one specific example, the intra-particle uniformity of the high-temperature oxidation-treated negative electrode material particles may be 3.5 or less, specifically 0.5 to 3.5, more specifically 1.0 to 3.3, even more specifically 1.0 to 3.0, even more specifically 1.5 to 2.8, and even more specifically 2.0 to 2.5.

[0068] This low value of intra-particle uniformity may indicate that the low-energy storage region is evenly distributed throughout the cathode material, particularly the spherical natural graphite. In terms of manufacturing method, the aforementioned low value of intra-particle uniformity may indicate that the natural graphite has been mechanically processed uniformly across all directions and spheroidized.

[0069] As described above, the negative electrode material according to one embodiment may be a high-quality negative electrode material with low accumulated defects and strain energy. A high-quality negative electrode material with low accumulated defects and strain energy can reduce the electrical resistance within the negative electrode active material layer, suppress side reactions with the electrolyte, and prevent irreversible reactions and non-uniform volume changes at defects, thereby exhibiting improved cycle life.

[0070] In one specific example, the sphericity of the negative electrode material may be 0.90 or more, specifically 0.91 or more, and may be substantially 0.95 or less, more substantially 0.93 or less. The sphericity of the negative electrode material is the circumference (C) of a circle having the same area as the projected image (2D image) of the negative electrode material, which is a three-dimensional particle. ir ) is the perimeter of the projected image (P rj ) divided by the ratio (C) ir / P rj ) can be defined as follows.

[0071] As is well known, the high degree of sphericity in natural graphite spheroidized through mechanical processing is advantageous in that it can suppress volume expansion accompanying the insertion / de-insertion process of lithium ions, enables the manufacture of a high-density, uniform electrode (negative electrode) and an electrode (cathode) with excellent structural stability, and stably and uniformly forms empty spaces between particles into which an electrolyte can be impregnated.

[0072] Accordingly, in the case of a natural graphite-based negative electrode material used as a negative electrode material by forming a carbon coating layer on the surface of spheroidized natural graphite, it is common to perform hard mechanical processing for a longer period of time during spheroidization to improve the degree of spheroidization of the spheroidized natural graphite.

[0073] According to one specific example, the negative electrode material is a high-quality negative electrode material having low accumulated defects and strain energy as described above in terms of the ratio of AR(TL) / AR(AM), the ratio of AR(TH) / AR(AM) and / or the uniformity within the particle, and can have a remarkably high sphericity of 0.90 to 0.95, specifically 0.90 to 0.93, more specifically 0.91 to 0.93.

[0074] In one specific example, based on the X-ray diffraction pattern of the negative electrode material, the maximum intensity I of the (110) peak 110 The maximum intensity of the (004) peak I 004 The ratio divided by (I 110 / I 004 ) may be 0.40 to 0.80, specifically 0.50 to 0.80, more specifically 0.60 to 0.80. The cathode material may have the aforementioned high I 110 / I 004 By having a value, the edge direction of the graphite crystal of natural graphite in the negative electrode material is highly refractory, so that lithium ions can diffuse in all directions.

[0075] In one specific example, the cumulative volume-based median diameter (D) of the cathode material 50) may be 10 to 25 μm, specifically 10 to 20 μm, and more specifically 12 to 18 μm. The size of the negative electrode material is a size that is advantageous for high-density negative electrode, and when implemented as a negative electrode active material layer, a stable open pore structure can be formed within the active material layer, and a size that can prevent the viscosity of the slurry from increasing excessively during the electrode manufacturing process. The span of the negative electrode material may be 0.5 to 1.5, specifically 0.6 to 1.3, and more specifically 0.7 to 1.2, but is not limited thereto.

[0076] In one specific example, the tap density of the negative electrode material is 0.8 to 1.2 g / cm 3 , specifically 0.9 to 1.2 g / cm 3 This tap density of the cathode material can be advantageous in that it can increase the electrode energy density and improve electrical conductivity.

[0077] In one specific example, the BET specific surface area of ​​the cathode material is 2.0 to 3.5 m 2 / g can be 2.0 to 3.5 m 2 A BET surface area of ​​ / g level is advantageous in that it ensures a large contact area with the electrolyte and enables the penetration of lithium ions in all directions, while suppressing side reactions with the electrolyte.

[0078] As described above, the anode material may include spherical natural graphite and a surface layer containing carbon. Structurally, the anode material may have a core-shell structure, with the spherical natural graphite serving as the core and the carbon-containing surface layer serving as the shell. In terms of manufacturing method, the surface layer may be a coating layer containing carbon and coating the surface of the spherical natural graphite.

[0079] In one specific example, the spherical natural graphite may be a particle (secondary particle) in which natural graphite fragments are formed into bonds and assembled. Specifically, the spherical natural graphite may be a particle in which natural graphite fragments are formed into a spherical shape having a sphericity of 0.90 or higher, formed, folded, and / or assembled. In detail, the spherical natural graphite may be a natural graphite particle in which natural graphite fragments are formed into a cabbage shape and assembled, formed into a random shape and folded, and / or assembled, formed into a composite shape of a cabbage shape and a random shape. In this case, an example of a composite shape may include a shape in which the central region of the particle is randomly assembled and the surface region is formed into a cabbage shape.

[0080] In terms of the manufacturing method, the spherical natural graphite may be particles in which natural graphite fragments are formed into bonds, folds, and / or assembled by mechanical processing. That is, the spherical natural graphite may be natural graphite in which a mechanical force is applied to natural graphite having an anisotropic shape, such as a flake shape (mechanical processing), so that natural graphite fragments derived from the natural graphite having an anisotropic shape are folded, bent, joined, and / or assembled, and the shape is mechanically adjusted to a spherical shape. In this case, the spherical natural graphite may mean particles having a sphericity of 0.90 or more, specifically 0.91 or more, substantially 0.95 or less, and more substantially 0.93 or less.

[0081] The surface layer can cover at least the edges of natural graphite crystals exposed to the surface of the spherical natural graphite. As a practical example, the negative electrode material can include spherical natural graphite and a surface layer covering at least a portion of the spherical natural graphite. Since the spherical natural graphite is covered by the carbon-containing surface layer, the edges of the natural graphite contained in the spherical natural graphite can be prevented from being directly exposed to the surface of the negative electrode material, side reactions caused by the electrolyte can be suppressed, and irreversible reactions can be reduced.

[0082] In one embodiment, the surface layer may be a carbon layer, and the carbon layer may be an amorphous carbon layer (disordered carbon). The amorphous carbon layer may include soft carbon, hard carbon, or a mixture thereof. The thickness of the surface layer may be, but is not limited to, 5 to 200 nm, specifically 10 to 150 nm, and more specifically 10 to 50 nm.

[0083] The present invention provides a method for manufacturing the negative electrode material for a lithium secondary battery as described above.

[0084] A method for manufacturing a negative electrode material for a lithium secondary battery according to the present invention comprises the steps of S1) spheroidizing natural graphite particles (hereinafter, also collectively referred to as raw materials) having an anisotropic shape through mechanical processing; and S2) forming a surface layer containing carbon on the spheroidized natural graphite.

[0085] The anisotropic shape is defined as the size (length) l in the three axes (x, y, z) that are orthogonal to each other and have the center of the particle as the origin. x , l y and l z The longest length (e.g., l) x ) is the shortest length (e.g., l z ) can mean a shape with an aspect ratio of 2 or more, specifically 3 or more. At this time, experimentally l x , l y and l z can be measured through image observation, including observation with a conventional scanning electron microscope. Representative examples of anisotropic shapes include plate shapes and / or flake shapes. As a practical example, the raw material may be, but is not limited to, flaky natural graphite that can be easily and densely formed, folded, and / or assembled by mechanical processing.

[0086] The spheroidization process of step S1) may be mechanical processing of the raw material, and the mechanical processing may mean a process of applying a mechanical force to natural graphite (raw material) having an anisotropic shape to mechanically adjust its shape to a spherical shape.

[0087] The mechanical processing during spheroidization may be rotary processing using air currents. Rotary processing using air currents may refer to mechanical processing in which raw materials containing natural graphite are moved by a rotating air current, and mechanical forces such as shock compression, friction, and / or shear force are applied to the natural graphite.

[0088] In an advantageous example, the rotary processing using airflow may be batch processing. That is, the rotary processing using airflow may be performed in a batch manner. The fact that the rotary processing is performed in a batch manner means that the raw material is input, the mechanical processing of the raw material, and the production of spheroidized graphite are all completed within the same processing space. In other words, the term "batch processing" may mean that the raw material is input, the spheroidization of the raw material is initiated and completed within the same pre-defined processing space, and the spheroidized natural graphite is produced.

[0089] In a more advantageous example, spheroidization may be performed by batch processing using a batch-type device (batch-type spheroidization device) described below. By performing spheroidization by batch processing using the batch-type device described below, dense graphite (spherical natural graphite) with a high degree of spheroidization can be produced without causing localized or serious damage to the natural graphite.

[0090] In a batch device, a processing space may be defined by a spheroidizing case including a raw material inlet, a spheroidizing natural graphite outlet, and an air inlet formed at the bottom of the case, and the internal space of the spheroidizing case may correspond to the processing space. In the processing space where rotary processing using airflow is performed, a processing section including a rotating shaft and a rotating member coupled to the rotating shaft to generate a rotating airflow when rotated may be located. The rotating member may include a ring-shaped plate (a hollow circular plate). The rotating shaft may be located at the center of the ring-shaped plate, and the plate and the rotating shaft may be coupled to each other by a plurality of bar-shaped coupling members. Specifically, the rotating member may include a plurality of ring-shaped plates, more specifically, 2 to 5 ring-shaped plates, which are positioned to be spaced apart from each other in the axial direction of the rotating shaft. The ring-shaped plates may include hammers capable of applying a physical impact to the natural graphite. Specifically, each of the ring-shaped plates may be provided with a plurality of hammers spaced at regular intervals along the circumferential direction centered on the rotating shaft. The shape of the hammer may be an angular shape or a curved shape based on its cross-section. Representative examples of the angular shape include a triangle, a square, or a pentagon based on the cross-section, and representative examples of the curved shape include a circle, a truncated circle, an oval, or a truncated oval based on the cross-section, but are not limited thereto. In addition, the rotating shaft may further be provided with a circular plate located below the rotating member (below in the direction of gravity). By means of this circular plate, natural graphite can be easily introduced into the space between the rotating member (or hammer) and the inner surface (or liner) of the spheroidizer case. In addition, a plurality of liners spaced apart from each other may be provided on the inner surface of the spheroidizer case located at least outside the processing section.

[0091] When rotary machining is performed in a batch mode, fine particles can be removed during rotary machining using airflow. To this end, the processing space can be connected to a dust collector for removing fine particles within the processing space. The dust collector can have a fluid suction function through a typical fluid flow generating device such as a blower, and can suction and remove fine particles within the processing space. As a practical example, the dust collector can include a classifier connected to the processing space, and fine particles passing through the classifier can be suctioned out of the processing space and removed. The classifier can be an airflow classifier, and the airflow classifier can be a swirling airflow (centrifugal) classifier. As a practical example, the swirling airflow classifier can include a forced vortex classifier. Examples of forced vortex classifiers include, but are not limited to, a turboflex, a super separator, and a micro separator.

[0092] Spherification performed in a batch process using a batch device can be performed at a rotation speed of 800 to 3000 rpm, specifically 1000 to 2500 rpm, for 5 to 40 minutes.

[0093] When spheroidization is performed through batch processing using a batch device according to the example described above, the cumulative volume-based median diameter (D) of the raw material 50 ) can be on the order of tens of ㎛. Specifically, the D of the raw material 50 The size may be 15 to 40 ㎛, specifically 18 to 35 ㎛, and more specifically 18 to 30 ㎛, but is not necessarily limited thereto.

[0094] After manufacturing spherical natural graphite (cores) by spheroidization, a coating step can be performed to form a carbon-containing surface layer on the spherical natural graphite. This can form a carbon-containing surface layer that surrounds the spherical natural graphite.

[0095] Specifically, the coating step may include mixing and heating spherical natural graphite with a carbon precursor. The carbon precursor may be at least one selected from the group consisting of, but not limited to, isotropic pitch, anisotropic pitch, heavy oil, light oil, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), sucrose, phenol resin, furan resin, furfuryl alcohol, polyacrylonitrile, cellulose, styrene, polyimide, epoxy resin, and glucose.

[0096] The mixing between the spherical natural graphite and the carbon precursor may be mechanical mixing. For example, the mechanical mixing may be at least one selected from the group consisting of ball milling, mechanofusion milling, shaker milling, planetary milling, attritor milling, shape milling, nauta milling, nobilta milling, high speed mixing, paddle mixing, ribbon mixing, Henschel mixing, corn type mixing, homo mixing, and a stirrer, but is not limited thereto. If necessary, a solvent that dissolves the carbon precursor may be mixed together to perform the mechanical mixing, and independently, the mechanical mixing may be performed in a state where the carbon precursor is melted or softened by heating. At this time, heating may include frictional heat during mechanical mixing.

[0097] When mixing, the mixing ratio of the carbon precursor mixed with the spherical natural graphite may be any amount that allows the formation of a surface layer that stably covers the surface of the spherical natural graphite. As a specific example, the weight ratio of the spherical natural graphite to the carbon precursor may be 100:0.1 to 20, specifically 100:1 to 15, but is not limited thereto.

[0098] After mixing the spherical natural graphite with the carbon precursor, a heat treatment may be performed to carbonize the carbon precursor. The heat treatment for carbonization may be performed at a temperature of 600 to 1500°C in an atmosphere of hydrogen, nitrogen, argon, or a mixed gas thereof, but is not limited thereto.

[0099] If necessary, after the spheroidization step by mechanical processing and / or after coating, a step of removing fine particles and / or coarse particles contained in the powder by air classification and / or sieving classification of the powder recovered in the previous step may be further performed.

[0100] The present invention includes a negative electrode material for a lithium secondary battery manufactured by the above-described manufacturing method.

[0101] The present invention includes a negative electrode for a lithium secondary battery containing a negative electrode material (natural graphite-based negative electrode material) manufactured by the above-described manufacturing method.

[0102] The present invention includes a negative electrode for a lithium secondary battery containing the above-described negative electrode material (natural graphite-based negative electrode material).

[0103] The negative electrode according to the invention is a negative electrode for a lithium secondary battery, and includes a current collector and a negative electrode active material layer located on at least one surface of the current collector and containing the above-described negative electrode material (natural graphite-based negative electrode material).

[0104] The negative electrode active material layer may include 95 to 99 wt% of the 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 above-described negative electrode material (natural graphite-based negative electrode material) alone or a heterogeneous negative electrode material together with the above-described negative electrode material (natural graphite-based negative electrode material). Examples of the heterogeneous negative electrode material include an artificial graphite-based negative electrode material and / or a silicon-based (silicon, silicon oxide, silicon-silicon oxide composite, silicon-carbon composite, silicon alloy, etc.) negative electrode material. When the negative electrode active material contains both the above-described negative electrode material (natural graphite-based negative electrode material) and a heterogeneous negative electrode material, the weight ratio of the graphite-based negative electrode material: the heterogeneous negative electrode material may be 100:1 to 100, but is not necessarily limited thereto.

[0105] The negative electrode active material layer may further include an additive including an organic binder together with the negative electrode active material, and if necessary, the additive may further include a conductive material. In order to ensure stable fixation between the negative electrode active materials and between the negative electrode active material and the current collector by the organic binder, and to not damage the conductivity and open pore structure within the negative electrode active material layer, the negative electrode active material layer may contain 1 to 5 wt% of the organic binder, and substantially 1 to 3 wt% of the organic binder. In addition, when the negative electrode active material layer further contains a conductive material, the negative electrode active material layer may contain 0.5 to 3 wt% of the conductive material, and substantially 0.5 to 2 wt% of the conductive material, but is not limited thereto.

[0106] The organic binder may be a polymer binder commonly used in the lithium secondary battery field to bind particulate negative electrode active materials to each other and to bind the negative electrode active materials to a current collector. Practical examples of the organic binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or mixtures thereof.

[0107] The conductive agent may be any conductive additive commonly used to improve the conductivity of anodes in the lithium secondary battery field. Specifically, the conductive agent may include a dot-shaped conductive agent, a linear conductive agent, a planar conductive agent, or a mixture thereof. Dot-shaped conductive agents include conductive carbon materials such as carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, etc.; metal particles such as copper, nickel, aluminum, and silver; conductive polymer particles; core-shell particles with a non-conductive core and a conductive shell, etc. Linear conductive agents include carbon nanotubes, conductive carbon fibers, metal fibers, and conductive polymer fibers, etc. Planar conductive agents include graphene or reduced graphene oxide, but are not limited thereto. As a practical example, the conductive agent may include carbon black, and as another practical example, the conductive agent may include carbon black and carbon nanotubes.

[0108] The cathode density (electrode density) of the cathode is 1.20 to 1.90 g / cm 3 Level, specifically 1.50 to 1.90 g / cm 3 It may be, but is not limited to,

[0109] The current collector can be any conductive material commonly used in lithium secondary batteries to ensure smooth current flow to the anode active material layer. The current collector may be, but is not limited to, a foil, a porous foil, a foam, a mesh, a non-woven fabric, a non-conductive material having a conductive coating layer formed thereon, or a combination thereof. The current collector material may be any material having high conductivity that does not induce chemical changes within the battery. For example, the current collector may be, but is not limited to, copper, stainless steel, aluminum, nickel, titanium, or alloys thereof. The current collector may have a conventional thickness, for example, but is not limited to, a thickness of 3 to 500 μm.

[0110] The anode can be manufactured using any method commonly used for manufacturing anodes in the lithium secondary battery field. For example, the anode can be manufactured by applying a slurry containing an anode active material, a binder, a solvent, and, if necessary, a conductive agent to at least one surface of a current collector, followed by drying and rolling, but is not limited thereto.

[0111] In the lithium secondary battery field, the solvent may be any solvent commonly used in forming a slurry for the manufacture of anodes. Examples of solvents include, but are not limited to, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, dimethylformamide (DMF), water, or mixtures thereof.

[0112] The slurry may be applied using any method commonly used to form an active material layer using slurry in the lithium secondary battery field. For example, the slurry may be applied using slot die coating, Meyer bar coating, gravure coating, comma coating, roll coating, blade coating, bar coating, or dipping coating.

[0113] The present invention includes a lithium secondary battery including the above-described negative electrode.

[0114] A lithium secondary battery according to the present invention may include the above-described 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 including a positive electrode current collector and a positive electrode active material layer positioned on at least one surface of the positive electrode current collector, the above-described negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte that conducts lithium ions. The positive electrode current collector, the positive electrode active material or composition of the positive electrode active material layer, the solvent or electrolyte salt of the separator and the electrolyte, or the concentration of the electrolyte salt, may be any of materials or compositions commonly employed in lithium secondary batteries. In addition, the secondary battery may further include an electrode assembly including a positive electrode, a negative electrode, and a separator, and a sealable battery container in which an electrolyte is stored internally.

[0115] Lithium secondary batteries may be lithium ion batteries, lithium ion polymer batteries, or lithium polymer batteries based on the type of separator and electrolyte, and may be cylindrical, square, coin-shaped, or pouch-shaped, but are not limited thereto.

[0116] The properties described in the detailed description and claims are measured according to the 'Analysis and Measurement Method' below.

[0117] Analysis and Measurement Methods

[0118] (D 50 )

[0119] 0.01 g of the target substance was suspended in ethanol, and the prepared suspension was sonicated for 1 minute. Then, the cumulative volume diameter distribution was measured using a conventional laser diffraction particle size distribution measuring device (Microtrac S3500). The median diameter D of the target substance was 50 is the diameter at the location where the cumulative volume is 50% in the cumulative volume diameter distribution. The span value is (D 90 -D 10 ) / D 50 is defined as D 10 In the cumulative volume diameter distribution, D means the diameter at the location where the cumulative volume is 10%, and90 In the cumulative volume diameter distribution, it refers to the diameter at the location where the cumulative volume is 90%.

[0120] (Spherical shape)

[0121] Sphericity was measured using a particle shape analyzer (Flowcam 8100, Fluid Imaging Technologies) commonly used for particle shape analysis after ultrasonically dispersing 0.01 g of the analyte in 5 mL of ethanol.

[0122] (BET specific surface area)

[0123] After pretreatment by drying the target material for analysis at a vacuum of 0.1 Torr or less and a temperature of 300℃ for 1 hour, the BET specific surface area (m) was determined using the BET method from the nitrogen adsorption isotherm of the pretreated target material for analysis. 2 / g) was calculated. Nitrogen adsorption-desorption isotherms were measured using a surface area measuring device (ASAP 2400, Micromeritics) at a temperature of 77 K and a relative pressure (P / P0) measurement precision of 0.05 using nitrogen adsorbed gas, liquid nitrogen.

[0124] (tap density)

[0125] Tap density is measured by putting 15 g of the target material into a 50 mL container and tapping 3000 times (tapping speed = 284 times / min) with a stroke length of 1.2 cm using a conventional tap density measuring device (e.g., Autotap from Quantachrome) based on ASTM B527, and is the average value of the tap density measured twice for randomly collected samples.

[0126] (orientation)

[0127] An X-ray diffraction pattern of a target material is obtained using the θ-2θ method. Specifically, the X-ray diffraction pattern may be obtained using a conventional X-ray diffraction measuring device (e.g., RIGAKU, SmartLab SE) under the conditions of Cu Kα line, a scan step size of 0.03°, a scan speed of 0.05° / min, and a scan range of at least 2θ 75° to 80° and 2θ 53° to 56°. The scan range of 2θ 75° to 80° is a range for measuring a diffraction peak due to the (110) plane (hereinafter, (110) peak), and the scan range of 2θ 53° to 56° is a range for measuring a diffraction peak due to the (004) plane (hereinafter, (004) peak). XRD measurement (raw) data can be processed by removing noise (setting a baseline) using a standard program equipped with the XRD device as a data processing and analysis program, such as the Highscore program. In the orientation of the material to be measured, the intensity of the (110) peak (I 110 ) is the maximum intensity of the graphite (110) peak (maximum value of the peak), and the intensity of the (004) peak (I 004 ) is the maximum intensity (peak maximum) of the graphite (004) peak. The orientation of the material to be measured is the maximum intensity value of the (110) peak (I 110 ) is the maximum intensity value of the (004) peak (I 004 ) divided by the ratio (I) 110 / I 004 ) is defined as follows.

[0128] (Interstitial space area ratio and intraparticle uniformity)

[0129] The scanning electron microscope observation image (hereinafter, SEM image) used to calculate the interstitial space area ratio and intra-particle uniformity is an image obtained at ETH (acceleration voltage) 3 kV, WD (working distance) 4 to 10 mm, and scan speed 5 to 6, and has a magnification of 5000 to 10000 times and a resolution of 200 dpi or higher.

[0130] Scanning electron microscope observation to obtain SEM images from which interstitial space area ratio and intraparticle uniformity are calculated is performed by measuring the median diameter (D) of the target material (cathode material, low-temperature oxidation-treated cathode material, high-temperature oxidation-treated cathode material, etc.) 50 ) standard, D 50 - 0.15 D 50 Inland D 50 + 0.15 D 50 This is an SEM image obtained under the condition that there is at least one, specifically 1 to 2, intact particles (hereinafter, representative particles) that are not cut off by the edge of the image or covered by other particles in the obtained SEM image, and the observation is performed with particles (center particles) belonging to the size range as the object of observation.

[0131] In the SEM image obtained under the conditions described above, a representative particle image is obtained by removing the remaining image portion, leaving only one representative particle observed intact.

[0132] To calculate the interstitial space area, an image processing program is used to convert the representative particle image to an 8-bit grayscale (0-255), and then a threshold value is set between 55 and 65 to calculate the area occupied by the interstitial space (empty space) in the representative particle image. If necessary, the brightness or contrast of the representative particle image may be adjusted before setting the threshold value.

[0133] As a practical example, in the manufacturing example, only one representative particle that was observed intact in the SEM image at 3 kV ETH, 4.1 mm WD, scan speed 6, and 5000x was left, and the rest was removed to obtain a representative particle image (100 dpi, 10~15 cm x 10~15 cm). Then, the representative particle image was converted to 8-bit gray scale (0-255) without any separate brightness or contrast adjustment, and a threshold value of 62 was set to calculate the ratio (%) of the area occupied by the gap space in the total area of ​​one representative particle.

[0134] Intra-particle uniformity was determined by rotating the image so that the longest diameter crossing the center of the particle in the representative particle image is vertical, and then, similar to the schematic diagram in Fig. 1, a rectangle was set in which the representative particle and each of the four sides were in contact, and then, using an imaginary line (two imaginary lines) crossing the centers of two opposite sides of the rectangle, the representative particle was divided into four regions, and the interstitial space area ratio was calculated for each region in the same way as the interstitial space area ratio, and the standard deviation was obtained between the interstitial space area ratios for the four regions.

[0135] For each target material, 20 representative particle images were used to calculate the interstitial space area ratio (area occupied by interstitial space / area of ​​representative particle in representative particle image × 100, %) from each representative particle image, and the average was used as the interstitial space area ratio of the target material. For the intra-particle uniformity, the standard deviation of the interstitial space area ratio by four regions for each representative particle was calculated for each of the 20 representative particle images used to calculate the interstitial space area ratio, and the 20 standard deviation values ​​obtained from the 20 representative particle images were averaged, and this was taken as the intra-particle uniformity.

[0136] (Half cell)

[0137] A half cell is manufactured using the negative electrode material manufactured in the examples or comparative examples.

[0138] In detail, the weight ratio of negative electrode material: conductive carbon black (super-P): carboxymethyl cellulose (CMC): styrene butadiene rubber (SBR) was 96.6: 1.0: 1.1: 1.3, and the negative electrode active material, styrene butadiene rubber, carboxymethyl cellulose, and carbon black (super-P) were added to deionized water and mixed for 30 minutes to prepare a slurry, and the prepared slurry was applied to a copper (Cu) foil, dried, and rolled to obtain an electrode density of 1.55 g / cm. 3 The cathode is manufactured.

[0139] A coin-type 2032 half-cell is fabricated using lithium foil as the counter electrode. A porous polypropylene film is used as the separator, and the electrolyte is a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, vinylene carbonate (VC) is added at 0.5 wt%, fluoroethylene carbonate (FEC) is added at 10 wt%, and a solution containing LiPF6 dissolved at a concentration of 1 M is used.

[0140] (Electrochemical characteristics using half cells)

[0141] The manufactured half-cells are subjected to high-rate characteristics measurement after the Mars stage. During the Mars charge stage, the cells are charged to 0.005 V at a constant current (CC) of 0.1 C and then charged from 0.005 V to 0.005 C at a constant voltage (CV). During the Mars discharge stage, the cells are discharged to 1.5 V at a constant current (CC) of 0.1 C. The charge and discharge cycles are repeated three times during the Mars stage.

[0142] After the Mars step was performed, in order to test the cycle characteristics, the manufactured half-cell was repeatedly charged and discharged at 25°C, CC / CV, cut-off voltage 0.005 V to 1.5 V, 1 C-rate, and the ratio of the discharge capacity in the 50th cycle (C50) to the discharge capacity in the first cycle (C1) (C50 / C1*100, %) was calculated as the life characteristics.

[0143] To evaluate swelling, 30 charge-discharge cycles are performed under the same conditions as in the cycle characteristic test, then the half-cell is disassembled to recover the negative electrode, the recovered negative electrode is washed with diethyl carbonate and dried, and the thickness of the negative electrode before and after performing the charge-discharge cycle is calculated to calculate the swelling ratio (swelling ratio, {(t2-t1) / t1}×100, t1=thickness of the negative electrode immediately before performing the first charge-discharge cycle, t2=thickness of the negative electrode immediately after performing the 30th charge-discharge cycle).

[0144] In the manufacturing example, the mechanical processing of natural graphite was performed in a batch process using a batch spheroidizing device in which three ring-shaped plates equipped with a plurality of rectangular hammers are fixed to a rotating shaft at a distance from each other, a circular plate is fixed to the lowest point of the rotating shaft relative to the direction of gravity together with the ring-shaped plates, an air-flow classifier (classification point 3 ㎛) connected to a blower is positioned at the upper part of the spheroidizing device case for removing fine particles, and an air inlet is formed at the lower part of the case.

[0145] (Manufacturing Example 1)

[0146] Using a batch spheroidizing device, D 50 This 21.4 ㎛ flake natural graphite raw material was processed at 1800 rpm for 15 minutes, and then fine and coarse particles were removed through airflow classification and sieve classification to produce spherical natural graphite.

[0147] 100 parts by weight of the manufactured spherical natural graphite and 5 parts by weight of petroleum pitch having a softening point of 250°C were mixed with a stirrer for 10 minutes, and then the mixture was heat-treated at 1200°C for 5 hours to manufacture a negative electrode material.

[0148] D of the manufactured cathode material 50 The diameter was 15.4 ㎛, the span value was 0.96, the sphericity was 0.91, and the tap density was 0.94 g / cm 3 and the BET surface area was 3.2 m 2 / g was.

[0149] (Manufacturing Example 2)

[0150] In Manufacturing Example 1, a negative electrode material was manufactured in the same manner as in Manufacturing Example 1, except that processing was performed at 1900 rpm for 30 minutes. D of the manufactured negative electrode material 50 The diameter was 13.5 ㎛, the span value was 0.89, the sphericity was 0.92, and the tap density was 1.01 g / cm 3 It was.

[0151] Figure 2 is a scanning electron microscope photograph of spherical natural graphite manufactured in Manufacturing Example 1. As can be seen in Figure 2, it can be seen that natural graphite fragments derived from flaky natural graphite are bent and joined by mechanical processing to manufacture spherical natural graphite.

[0152] Figure 3 is a representative particle image obtained after the negative electrode material manufactured in Manufacturing Example 1 was subjected to low-temperature oxidation treatment, and Figure 4 is a representative particle image obtained after the negative electrode material manufactured in Manufacturing Example 2 was subjected to low-temperature oxidation treatment.

[0153] As shown in the examples of FIGS. 3 and 4, it can be seen that during low-temperature oxidation treatment, the amorphous carbon coating is removed, and at the same time, the high-energy accumulation regions that are severely deformed and contain a large number of defects in the spherical natural graphite are removed, and empty spaces are created on the particle surface.

[0154] Manufacturing Example 2 is an example in which, when manufacturing spherical natural graphite, processing was performed for a longer period of time at a faster rotation speed than Manufacturing Example 1, thereby manufacturing more severely damaged spherical natural graphite. In the case of the negative electrode material of Manufacturing Example 2, which has spherical natural graphite that has undergone more severe mechanical processing, it can be confirmed that a larger amount of interstitial space is formed than the negative electrode material of Manufacturing Example 1 even under the same low-temperature oxidation treatment conditions, and it can also be seen that the area occupied by the interstitial space has increased. In addition, the maximum intensity of the D band peak in the Raman spectrum of the spherical natural graphite before / after the low-temperature oxidation treatment, I D I is the maximum intensity of the G band peak G I divided by D / IG Through the values, it was confirmed that defects in natural graphite were reduced by low-temperature oxidation treatment, which is consistent with the results of Figs. 3 and 4.

[0155] Fig. 5 is a diagram illustrating a process of calculating the interstitial space area ratio shown in black by defining the interstitial space from the representative particle image of Fig. 3. The interstitial space area ratio of the low-temperature oxidation-treated single cathode material particles shown in Figs. 3 and 5 was 3.02%, and the interstitial space area ratio of the low-temperature oxidation-treated single cathode material particles shown in Fig. 4 was 5.89%.

[0156] FIG. 6 is a representative particle image of the negative electrode material particle of Manufacturing Example 1 subjected to high-temperature oxidation treatment, FIG. 7 is a drawing illustrating a process of calculating the gap space area ratio shown in black by defining the gap space from the representative particle image of FIG. 6, and FIG. 8 is a drawing illustrating a process of calculating the gap space area ratio for each region (AP1, AP2, AP3, AP4) of a particle to calculate the intra-particle uniformity from the representative particle image of FIG. 6.

[0157] As shown in examples shown in FIGS. 2 to 8, the interstitial space area ratio was calculated using 20 representative particle images of each of spherical natural graphite, anode material, low-temperature oxidation-treated anode material, and high-temperature oxidation-treated anode material, and the intra-particle uniformity of the high-temperature oxidation-treated anode material was calculated, and these results are summarized in Table 1.

[0158] AR(SNG) in Table 1 is the interstitial space area ratio of the spherical natural graphite manufactured in Manufacturing Example 1, AR(AM) in Table 1 is the interstitial space area ratio of the negative electrode material manufactured in Manufacturing Example 1, AR(TL) in Table 1 is the interstitial space area ratio of the negative electrode material of Manufacturing Example 1 subjected to low-temperature oxidation treatment, AR(TH) in Table 1 is the interstitial space area ratio of the negative electrode material of Manufacturing Example 1 subjected to high-temperature oxidation treatment, and uniformity in Table 1 is the intra-particle uniformity of the negative electrode material of Manufacturing Example 1 subjected to high-temperature oxidation treatment.

[0159] AR(SNG)AR(AM)AR(TL)AR(TH)Uniformity Manufacturing Example 11.87%1.80%4.13%9.25%2.33

[0160] As can be seen in Table 1, it can be seen that the anode material particles are uniformly processed throughout with a high sphericity of 0.91, and the intra-particle uniformity is 2.33, and the AR(TL) / AR(AM) is only 2.29 and the AR(TH) / AR(AM) is only 5.14, indicating that a high-quality anode material is manufactured with little accumulated defect energy within the anode material particles caused by mechanical processing. For comparison, 21 air classifying mills (ACMs) were connected in series so that the natural graphite discharged from the front-end ACM device was fed into the rear-end ACM device, and the flaky natural graphite was fed to continuously spheroidize the natural graphite. Afterwards, 100 parts by weight of the spheroidized natural graphite and 5 parts by weight of petroleum pitch having a softening point of 250°C were mixed with a stirrer for 10 minutes in the same manner as in Manufacturing Example 1, and then the mixture was heat-treated at 1200°C for 5 hours to manufacture the anode material (hereinafter, ACM anode material).

[0161] Figure 9 is a scanning electron microscope photograph of spheroidized natural graphite manufactured using ACM. As is well known, spheroidization using ACM is a method of spheroidizing flake graphite by passing it between a hammer and a protruding inner wall and applying shear stress therebetween. As can be seen in Figure 9, the measured spheroidization degree is approximately 0.87, which appears similar to a sphere at first glance. However, it can be seen that natural graphite closer to a plate shape than a sphere is manufactured due to spheroidization by shear stress. The interstitial space area ratio of the spheroidized natural graphite manufactured using ACM was 0.97%, which is lower than that of the spheroidized natural graphite manufactured in the manufacturing example. However, the interstitial space area ratio was 6.14% after low-temperature oxidation treatment, indicating that a large amount of defects and strain energy were accumulated in the spheroidized natural graphite due to severe mechanical processing.

[0162] The room temperature life characteristics (%) and swelling ratio (%) of the half-cell equipped with the negative electrode material manufactured in Manufacturing Example 1 and the half-cell equipped with the ACM negative electrode material are summarized in Table 2.

[0163] Manufacturing Example 1 ACM cathode material Room temperature life characteristics 92% 83% Swelling ratio (%) 21.1 27.4%

[0164] As can be seen from Table 2, the anode material of Manufacturing Example 1, which has a small amount of accumulated defect energy within the anode material particles, exhibits excellent room temperature life characteristics and lower swelling. The present invention is not limited to the examples, but can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains will understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential characteristics of the present invention. Therefore, it should be understood that the examples described above are illustrative in all respects and not restrictive.

Claims

Comprising spherical natural graphite and a surface layer containing carbon located on the surface of the spherical natural graphite, D in the volumetric cumulative particle size distribution 50 Based on , D 50 + 0.15D 50 Inland D 50 - 0.15D 50 In the scanning electron microscope observation images of the cathode material in the size range of , the area ratio AR(AM) occupied by the interstitial space on the particle surface is shown after low-temperature oxidation treatment according to the following condition 1. 50 + 0.15D 50 Inland D 50 - 0.15D 50 A negative electrode material for a lithium secondary battery, wherein the ratio AR(TL) / AR(AM), which is the area ratio of interstitial space occupied on the particle surface, is 4.0 or less in a scanning electron microscope observation image of a negative electrode material subjected to low-temperature oxidation within the size range of . Condition 1: Air atmosphere, TL of 600 ℃, heat treatment at TL temperature for 2 hours, heating rate of 5 ℃ / min and cooling rate of 5 ℃ / min In paragraph 1, After high temperature oxidation treatment according to the following condition 2, the above D 50 Based on D 50 + 0.15D 50 Inland D 50 - 0.15D 50 A lithium secondary battery negative electrode material having a ratio AR(TH) / AR(AM), which is obtained by dividing the area ratio AR(TH) occupied by interstitial space on the particle surface by the AR(AM) in a scanning electron microscope observation image of a high-temperature oxidation-treated negative electrode material within a size range, of 10.0 or less. Condition 2: Air atmosphere, TH of 900 ℃, heat treatment at TH temperature for 1 hour, heating rate of 5 ℃ / min and cooling rate of 5 ℃ / min In the second paragraph, Above D 50 Based on D 50 + 0.15D 50 Inland D 50 - 0.15D 50 A lithium secondary battery anode material, wherein in a scanning electron microscope observation image of a high-temperature oxidation-treated single cathode particle within a size range, the uniformity within the particle, which is a standard deviation between the area ratio AR(TH_P) occupied by interstitial spaces on the particle surface in each region, is 3.5 or less in four regions of the single cathode particle divided by an imaginary line connecting the centers of opposite sides of a rectangle in which the single cathode particle is located and each of the four sides is in contact with the single cathode particle. In paragraph 1, A negative electrode material for a lithium secondary battery, wherein the above AR(TL) / AR(AM) is 1.5 to 3.

0. In paragraph 4, The above AR(TL) is 2.5 to 6.0%, and is a negative electrode material for a lithium secondary battery. In the second paragraph, A negative electrode material for a lithium secondary battery, wherein the AR(TH) / AR(AM) is 3.5 to 8.

0. In paragraph 6, A negative electrode material for a lithium secondary battery, wherein the AR(TH) is 6.5 to 12.0%. In any one of claims 1 to 7, A negative electrode material for a lithium secondary battery, wherein the sphericity of the above negative electrode material is 0.90 or more. In any one of claims 1 to 7, Based on the X-ray diffraction pattern of the above cathode material, the maximum intensity of the (110) peak I 110 The maximum intensity of the (004) peak I 004 The ratio divided by (I 110 / I 004 ) is a negative electrode material for a lithium secondary battery, having a molecular weight of 0.40 to 0.

80. In any one of claims 1 to 7, Above D 50 A negative electrode material for a lithium secondary battery, having a diameter of 10 to 25 μm. In any one of claims 1 to 7, A negative electrode material for a lithium secondary battery, wherein the tap density of the above negative electrode material is 0.8 to 1.2 g / cm3. In any one of claims 1 to 7, The BET specific surface area of ​​the above cathode material is 2.0 to 3.5 m 2 / g, negative electrode material for lithium secondary batteries. In any one of claims 1 to 7, The above spherical natural graphite is a negative electrode material for a lithium secondary battery, which is a particle in which natural graphite fragments are bonded and assembled. In any one of claims 1 to 7, The above surface layer is a negative electrode material for a lithium secondary battery including an amorphous carbon layer. A negative electrode for a lithium secondary battery comprising a negative electrode material according to any one of claims 1 to 7.

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