Negative electrode material for lithium secondary battery and method for manufacturing same

Abstract

A negative electrode material for a lithium secondary battery according to one embodiment comprises a core of spherical natural graphite and a surface layer containing carbon, wherein the negative electrode material has an activity defined as [SBET / D50]×P of 1.3 to 2.5, and an orientation index defined as I110 / I004×100 of 65 or more. Here, SBET is the BET specific surface area (m2 / g) of the negative electrode material, D50 is the cumulative volume-based median diameter (㎛) of the negative electrode material, P is the porosity (%) of the negative electrode material measured by a mercury intrusion method, I110 is the maximum intensity of a (110) peak in an X-ray diffraction pattern of the negative electrode material, and I004 is the maximum intensity of a (004) peak in the same X-ray diffraction pattern.

Description

Anode material for lithium secondary batteries and method for manufacturing the same

[0001] The present disclosure relates to an anode material for a lithium secondary battery and a method for manufacturing the same, and more particularly, to a natural graphite-based anode material for a lithium secondary battery and a method for manufacturing the same.

[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 solve these problems, a technology is being developed to improve the initial charge / discharge efficiency, electrode density, and high-rate characteristics by processing natural graphite into a spherical shape and forming a carbon coating layer on the surface of the spherical natural graphite. However, there is a need for technology development for a natural graphite-based negative electrode material with even improved high-rate output characteristics.

[0006] One aspect of the present invention is to provide a natural graphite-based negative electrode material having improved high-rate output characteristics and a method for manufacturing the same.

[0007] Another aspect of the present invention is to provide a natural graphite-based negative electrode material having improved immersion properties and a method for producing the same.

[0008] 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.

[0009] A method for manufacturing an anode material for a lithium secondary battery according to one embodiment of the present invention comprises the steps of isotropically pressing primary spheroidized natural graphite to produce pressed natural graphite; crushing the pressed natural graphite to produce crushed natural graphite; and re-spheroidizing the crushed natural graphite through mechanical processing to produce spherical natural graphite.

[0010] A manufacturing method according to one specific example may further include a step of manufacturing the first spheroidized natural graphite by spheroidizing natural graphite having an anisotropic shape before the isotropic pressing.

[0011] A manufacturing method according to one specific example may further include a step of forming a surface layer containing carbon on the spherical natural graphite after the re-sphericalization.

[0012] In one specific example, the spheroidization, the re-spheroidization, or each of the spheroidization and the re-spheroidization can be performed by rotary processing using airflow.

[0013] In one specific example, the rotary processing using the air flow can be performed by removing fine particles from the inside to the outside of the processing space where the rotary processing is performed.

[0014] In one embodiment, the isostatic pressing may include cold isostatic pressing (CIP) or hot isostatic pressing (HIP).

[0015] In one specific example, the pressure during the isotropic pressurization may be 100 to 500 MPa.

[0016] According to one embodiment of the present invention, a negative electrode material for a lithium secondary battery includes a core of spherical natural graphite and a surface layer containing carbon, has an activity defined by the following formula 1 of 1.3 to 2.5, and has an orientation index defined by the following formula 2 of 65 or more.

[0017] (Formula 1)

[0018] Activity = [S BET / D 50 ]×P

[0019] S in Equation 1 BET is the BET surface area (m) of the cathode material. 2 / g), and D 50 is the cumulative volume-based median diameter (㎛) of the cathode material, and P is the porosity (%) of the cathode material measured by mercury intrusion porosimetry.

[0020] (Formula 2)

[0021] Orientation index = I 110 / I 004 × 100

[0022] In Equation 2, I 110 is the maximum intensity of the (110) peak in the X-ray diffraction pattern of the cathode material, and I 004 is the maximum intensity of the (004) peak in the same X-ray diffraction pattern.

[0023] According to one specific example, the cathode material may have a curvature ratio of 10.0% to 13.0%, as defined by Equation 3 below.

[0024] (Formula 3)

[0025] Curvature ratio = [1 - 1 / R] × 100

[0026] In Equation 3, R is the roughness, which is the ratio of the perimeter (P) of the particle to the perimeter (CP) of the convex surface (P / CP), and is 0.8D. 50 1.2D 50 Roughness targeting a cathode material having the size of .

[0027] In one specific example, the S BET / D 50 can be 0.13 to 0.16.

[0028] In one specific example, the D 50 can be 10 to 25 μm.

[0029] In one specific example, the tap density of the negative electrode material is 1.00 to 1.30 g / cm 3 It could be.

[0030] In one specific example, the surface layer may be a carbon layer.

[0031] One embodiment of the present invention includes a negative electrode for a lithium secondary battery including the above-described negative electrode material.

[0032] The cathode material according to one specific example may have improved high-rate output characteristics.

[0033] The cathode material according to one embodiment may have improved electrolyte immersion properties.

[0034] 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.

[0035] Figure 1 is a scanning electron microscope photograph observing the shape of the negative electrode material manufactured in Comparative Example 1.

[0036] Figure 2 is a scanning electron microscope photograph observing the shape of the negative electrode material manufactured in Example 1.

[0037] 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.

[0038] 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.

[0039] The shape and size of elements in the drawing may be exaggerated for clearer explanation.

[0040] 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.

[0041] 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.

[0042] Unless otherwise specified in the specification of the present invention, the % unit means weight %.

[0043] 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.

[0044] 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.

[0045] The present inventors conducted a study on crystallographic isotropy through mechanical spheroidization of natural graphite and densification of graphite structure through isotropic pressing. In the process, it was confirmed that when natural graphite itself, which has an anisotropic shape (e.g., a flake shape) before mechanical spheroidization, is spheroidized by isotropic pressing, there is a limit to the improvement of crystallographic isotropy. Furthermore, when the spheroidized natural graphite is densified by isotropic pressing after mechanical spheroidization, it is possible to produce natural graphite with improved crystallographic isotropy and a dense structure. However, it was confirmed that the specific surface area of ​​the produced natural graphite is excessively low, which reduces the active area in contact with the electrolyte and reduces the wettability when implemented as an active material layer.

[0046] Accordingly, as a result of continuous research to solve the problems of low active area and low soakability, it was discovered that the main cause of low soakability is the particle shape of isotropically pressed natural graphite. In addition, it was discovered that even if the graphite structure has improved crystallographic isotropy during isotropic pressing, the surface of the particles mainly forms flat planar areas where the basal planes of graphite form the surface, inhibiting the penetration of lithium ions through the surface, which acts as a cause of reduced high-rate output characteristics along with a low specific surface area.

[0047] Based on these findings, the inventors of the present invention have established a technology for manufacturing spherical natural graphite having liquidity and a specific surface area comparable to mechanically spherical natural graphite, and wherein the mechanically spherical natural graphite has crystallographic isotropy and a curved surface comparable to isotropically pressed natural graphite, thereby completing the present invention.

[0048] A method for manufacturing a negative electrode material for a lithium secondary battery according to the present invention comprises the steps of isotropically pressing primary spheroidized natural graphite to produce pressed natural graphite; the step of crushing the pressed natural graphite to produce crushed natural graphite; and the step of re-spheroidizing the crushed natural graphite through mechanical processing.

[0049] The manufacturing method according to the present invention can significantly improve the crystallographic isotropy of natural graphite by isotropically pressing spheroidized natural graphite (primarily spheroidized natural graphite). In addition, by disintegrating the isotropically pressed natural graphite and then mechanically processing the disintegrated natural graphite to re-spheroidize it, the isotropic pressing can transform the macroscopically angular granular shape with a flat surface into a curved granular shape, essentially a curved spherical shape. In addition, by inducing an artificial spring back effect through the mechanical force applied to the natural graphite during the re-spheroidization process, a large number of channels through which an electrolyte can permeate through the particle surface can be created along with a change in the grain shape of the natural graphite. In terms of physical properties, the creation of channels through which an electrolyte can permeate can be represented by an increase in the specific surface area and an increase in the number of open pores.

[0050] As described above, by isotropically pressing and crushing the primary spheroidized natural graphite and then re-spheroidizing the natural graphite through mechanical processing, the advantages obtained by isotropic pressing and mechanical spheroidization of natural graphite are maintained, while the disadvantages caused by isotropic pressing are resolved. Thus, spherical natural graphite having excellent lyophilization properties, a specific surface area favorable for lithium diffusion (migration), and remarkably excellent crystallographic isotropy can be produced.

[0051] A manufacturing method according to one specific example may further include a step of manufacturing primary spheroidized natural graphite by spheroidizing natural graphite having an anisotropic shape before isotropic pressing.

[0052] A manufacturing method according to one specific example may further include a step of forming a surface layer containing carbon on the re-spheroidized natural graphite after re-spheroidization.

[0053] Hereinafter, in describing each step of the manufacturing method in detail, for clearer understanding and explanation, natural graphite having an anisotropic shape is referred to as the 'raw material', the spheroidization process of the raw material is referred to as the 'primary spheroidization' or the 'primary spheroidization process', the natural graphite obtained by spheroidization of the raw material (the aforementioned primary spheroidized natural graphite) is referred to as 'primary spheroidal graphite', the pressed natural graphite obtained by isotropic pressing of the primary spheroidal graphite is referred to as 'dense graphite', the natural graphite obtained by disintegrating dense graphite is referred to as 'disintegrated graphite', the spheroidization process of the disintegrated graphite is referred to as 're-spheroidization' or the 're-spheroidization process', the natural graphite obtained by re-spheroidization (re-spheroidized natural graphite) is referred to as the 'core' or 'spherical natural graphite', and the step of forming a surface layer may also be referred to as the 'coating step'.

[0054] First spherical stage

[0055] The raw material may be natural graphite particles having an anisotropic shape. The anisotropic shape is defined as the size (length) l in the three axes (x, y, z) directions, with 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.

[0056] The primary sphericalization process may be mechanical processing of the raw material, and mechanical processing may mean a process of applying mechanical force to natural graphite (raw material) having an anisotropic shape to mechanically adjust its shape to a sphere.

[0057] The primary spheroidization can be performed by a spheroidization method using mechanical processing commonly known in the secondary battery field. Representative examples of mechanical processing include Air Classifying milling, Spheronizing milling, Grinding milling, Mechanofusion milling, Planetary milling, Hybridization milling, Shape milling, and High speed milling. The mechanical processing can be performed under known conditions, for example, at a rotation speed of 500 to 4000 rpm, and can be performed for 5 to 60 minutes, but is not limited thereto.

[0058] In an advantageous example, the mechanical processing during the first sphericalization may be rotary processing using air currents. Rotary processing using air currents may refer to mechanical processing in which raw materials including natural graphite are moved by a rotating air current, and mechanical forces such as impact compression, friction, and / or shear force are applied to the natural graphite.

[0059] In a more advantageous example, the rotary processing using airflow may be a 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.

[0060] In a more advantageous example, the primary spheroidization may be batch processing using a batch-type device (batch-type spheroidization device) described below. Since the primary spheroidization is performed by batch processing using the batch-type device, the crystallographic isotropy of natural graphite can be significantly improved through the primary spheroidization and isotropic pressing, and dense graphite having a high degree of spheroidization can be produced. Specifically, when the degree of spheroidization of natural graphite produced by the primary spheroidization is low and the isotropy of the primary spheroidized natural graphite is low, the graphite may be deformed into a shape with increased anisotropy, such as a rectangular (elongated) shape or a disk shape, by isotropic pressing, compared to the primary spheroidized state, and there is a risk that the improvement in isotropy may be minimal. In addition, in the case of dense graphite having a highly anisotropic shape, such as a rectangular or disc shape, very harsh mechanical processing may be required for re-spheroidization, and there is a risk that during this harsh mechanical processing, the effect of isotropic pressing after the first spheroidization will disappear, leaving only the effect of re-spheroidization.

[0061] However, when primary spheroidization is performed through batch processing using the batch-type device described below, spheroidization can be achieved with excellent isotropy and in a manner that is substantially similar to a true sphere. Consequently, through subsequent isotropic pressing, isotropy is significantly improved compared to primary spheroidization, and dense graphite (disintegrated graphite) can be obtained in the form of square, angular particles.

[0062] The term "square angular particle" should not be interpreted as meaning an angular particle having flat faces in a square shape. The term "square angular particle" can be interpreted as having a flat surface area, with a minimum square that is a square or a pseudo-square that can be positioned inside the particle and that is in contact with the particle based on a two-dimensional image of the particle. In this case, the pseudo-square may mean that the ratio of the length of a relatively long side (L1) divided by the length of another relatively short side (L2) in the minimum square that is in contact with the particle and surrounds the particle (L1 / L2) is 1 to 1.6, specifically 1 to 1.4, and more specifically 1 to 1.2. Here, the L1 / L2 ratio may of course be an average value of values ​​measured for each disintegrated graphite particle for at least 100 or more, and substantially 500 to 20,000 disintegrated graphite particles. The flat surface areas that are formed into a flat shape by pressing can be positioned in different directions from the center of the sphere, specifically in 2 to 10 different directions (2 to 10 flat surface areas), specifically in 2 to 8 different directions (2 to 8 flat surface areas), and the flat surface areas can be recessed, protruded, and / or extended from the surrounding surface areas. In this case, it goes without saying that the area connecting the flat surface areas to each other (the corner area) can be a sharp corner where the flat surface areas directly meet, or can be a curved surface (a curved corner).

[0063] In a batch device, a processing space may be defined by a spheroidizing case that divides the inner and outer spaces, and the inner space of the spheroidizing case may correspond to the processing space. In the processing space where rotary processing using airflow is performed, a processing unit may be located, which includes a rotating shaft and a rotating member that is coupled to the rotating shaft and generates a rotating airflow when rotated. 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, two to three ring-shaped plates, that are positioned spaced apart from each other in the axial direction of the rotating shaft. The ring-shaped plates may include hammers that can apply a physical impact to 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, based on its cross-section, may be an angular shape or a curved shape. Representative examples of angular shapes include cross-sections, triangles, squares, and pentagons, and representative examples of curved shapes include cross-sections, circles, truncated circles, ovals, and truncated ovals, but are not limited thereto. In addition, the rotating shaft may further be provided with a circular plate located below the rotating member. This circular plate allows natural graphite to easily flow 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 processed portion.

[0064] 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 and removed outside the processing space. 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 turboplex, a super separator, and a micro separator.

[0065] The primary spheroidization performed in a batch process using a batch device can be performed at a rotation speed of 800 to 3000 rpm, specifically 1500 to 2500 rpm, for 5 to 40 minutes.

[0066] The primary spherical graphite manufactured by the batch process using the batch device described above may have a sphericity of 0.85 or more, specifically 0.87 or more, and in practice, the sphericity of the primary spherical graphite may be 0.91 or less, more practically 0.90 or less.

[0067] Advantageously, the primary spherical graphite has a density of 0.85 g / cm 3 More than 1.00 g / cm 3 It can have a tap density below. Tap density is a property that is affected by various factors such as the shape of the primary spherical graphite, surface characteristics, degree of assembly (construction), internal pore structure, and porosity. 0.85 g / cm 3Primary spherical graphite that does not reach the spherical shape may be in a state where spheroidization is not substantially completed, i.e., a large number of internal pores exist and the assembly and bonding between natural graphite fragments are not firmly formed. Such primary spherical graphite has low crystallographic isotropy and is at risk of being deformed into rectangular particles during isotropic pressing due to the wedge-shaped internal pores between graphite fragments. On the other hand, when the tap density is 1.00 g / cm 3 Beyond this, there is a risk that the degree of isotropic improvement due to isotropic pressing will be minimal due to excessively dense primary spherical graphite.

[0068] Accordingly, according to an advantageous example, by manufacturing primary spherical graphite satisfying the above-mentioned sphericity and tap density using a batch process using a batch device, and then isotropically pressing the same, a square dense graphite (and disintegrated graphite) having significantly improved isotropy can be manufactured.

[0069] The size of the raw material used for the first sphericalization may be any size that is commonly used in the sphericalization of natural graphite.

[0070] However, when spheroidization is performed through batch processing using a batch device according to the advantageous 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 silver may be 15 to 40 μm, specifically 18 to 35 μm, and more specifically 18 to 30 μm.

[0071] Isotropic pressurization stage

[0072] Isostatic pressing can be cold isostatic pressing (CIP) or hot isostatic pressing (HIP), and a practical example is cold isostatic pressing.

[0073] By isotropic pressing, the graphite tissue is densified and at the same time, dense graphite with remarkably high crystallographic isotropy and a square, angular particle shape can be produced. Pressure (P) during isotropic pressing t ) may be 100 to 500 MPa, specifically 150 to 400 MPa, and more specifically 200 to 350 MPa.

[0074] When pressurized isotropically, the preset pressure (P t ) is sufficient as the time required for the natural graphite fragments forming the primary spherical graphite to be deformed, the graphite tissue to be densified, and the crystallographic isotropy to be improved. Specifically, since the deformation of natural graphite fragments by pressing is instantaneous, the pressure (P) during isotropic pressing t ) is sufficient to ensure that the pressure applied from the surface to the interior of the primary spherical graphite is stably transmitted. As a practical example, the pressure (P t ) may be from 10 seconds to 20 minutes, specifically from 30 seconds to 15 minutes, and more specifically from 1 minute to 10 minutes, but is not limited thereto.

[0075] In isotropic pressurization, the pressurization up to the set pressure (P1) can be performed at a controlled pressurization rate. Specifically, in order to stably secure the orientation index improvement by isotropic pressurization, the pressurization can be performed at a pressurization rate of 10 to 100 MPa / min.

[0076] Disintegration stage

[0077] After isotropic pressing is performed, a crushing step can be performed to crush natural graphite particles that have been agglomerated by the pressing.

[0078] The disintegration step can be performed by applying physical impact. As a specific example, the disintegration step can be performed using equipment that utilizes physical impact, such as a jet mill, an air classifier mill (or air current classification mill), or a roller mill. Specifically, a jet mill disintegrates particles by colliding them with a high-pressure air stream, an air classifier disintegrates particles by using an air stream and classifies particles according to specific gravity, and a roller mill disintegrates particles by placing them between two or more rollers that rotate in opposite directions and compressing and crushing them.

[0079] For effective disintegration, the disintegration step may include a coarse crushing step and a fine crushing step. Specifically, the disintegration step may include a coarse crushing step of crushing natural graphite lumps agglomerated by isostatic pressing into coarse powder, a fine crushing step of crushing the coarse powder into fine powder, and a step of disintegrating the fine powder by applying physical impact.

[0080] As a practical example, the crushing step is to crush natural graphite lumps by isotropic pressing into a mass of 10 to 50 mm cumulative volume-based median diameter (D 50 ), with a cumulative volume-based median diameter (D) of 10 to 30 mm in detail 50 ) may be a step of grinding into a coarse powder. After the coarse grinding is performed, in the fine grinding step, the coarse powder is ground into a cumulative volume-based median diameter (D 50 ) can be pulverized into fine powder of less than 10 mm, and the fine powder can be pulverized into individual graphite particles (pulverized particles) by applying physical impact. However, this is only a specific pulverization condition for faster and more effective pulverization, and the present invention is not limited to the pulverization method. If necessary, after pulverization, further classification such as air classification and / or sieve classification can be performed to remove unpulverized agglomerated particles or fine particles that may be generated during pulverization.

[0081] Re-sphericization stage

[0082] After the disintegration step is performed, a step of re-spherifying the disintegrated graphite through mechanical processing (mechanical force) to produce spherical natural graphite can be performed.

[0083] Re-sphering can also be performed by a mechanical processing sphering method commonly known in the secondary battery field. Re-sphering can be performed independently of the primary sphering by one or more methods selected from the group consisting of Air Classifying milling, Spheronizing milling, Grinding milling, Mechanofusion milling, Planetary milling, Hybridization milling, Shape milling, and High speed milling, but is not limited thereto. Re-sphering can be performed independently of the primary sphering at a rotation speed of 500 to 4000 rpm, and can be performed for 5 to 60 minutes, but is not limited thereto.

[0084] In an advantageous example, re-sphericization may also be performed by rotary machining using airflow. In a more advantageous example, rotary machining using airflow for re-sphericization may also be performed in batch mode.

[0085] In a more advantageous example, the re-sphericization can be performed as a batch process using substantially the same batch apparatus (batch sphericization apparatus) as the primary sphericization.

[0086] The batch process using the aforementioned batch device is advantageous in that mechanical forces, including impact compression, friction, and / or shear, can be applied to the particles in all directions, thereby easily processing flat surface areas and edge areas into curved surfaces. In addition, the batch process using the aforementioned batch device is advantageous in that re-sphericization can be achieved in a shorter period of time using a weaker mechanical force, thereby preventing the formation of excessive open pores.

[0087] Resphericization performed in a batch process using a batch device can be performed under more relaxed conditions than the first sphericization, i.e., at lower rpm and for a shorter time than the first sphericization. Specifically, the resphericization can be performed at a rotation speed of 500 to 1800 rpm, specifically 800 to 1500 rpm, for 3 to 20 minutes.

[0088] The curvature of the flat surface area and the increase in open pores due to re-sphericization reduce the fraction of crystal planes of the crystallographic basal planes that overlap each other to form a macroscopic plane, thereby enabling omnidirectional diffusion of lithium ions and increasing the contact area with the electrolyte, thereby enabling smooth movement and diffusion of lithium ions to and / or from the particles.

[0089] Coating stage

[0090] After manufacturing spherical natural graphite (cores) by respheroidization, 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] The present invention includes a negative electrode material for a lithium secondary battery manufactured by the above-described manufacturing method.

[0096] cathode material

[0097] A negative electrode material for a lithium secondary battery according to the invention comprises a core of spherical natural graphite and a surface layer containing carbon, has an activity defined by the following formula 1 of 1.3 to 2.5, and has an orientation index defined by the following formula 2 of 65 or more.

[0098] (Formula 1)

[0099] Activity = [S BET / D 50 ]×P

[0100] S in Equation 1 BET is the BET surface area (m) of the cathode material. 2 / g), and D 50 is the cumulative volume-based median diameter (㎛) of the cathode material, and P is the porosity (%) of the cathode material measured by mercury intrusion porosimetry.

[0101] (Formula 2)

[0102] Orientation index = I 110 / I 004 × 100

[0103] In Equation 2, I 110is the maximum intensity of the (110) peak in the X-ray diffraction pattern of the cathode material, and I 004 is the maximum intensity of the (004) peak in the same X-ray diffraction pattern.

[0104] The activity in Equation 1 is an indicator of the active area of ​​the negative electrode material that can directly receive lithium ions when in contact with the electrolyte. The orientation index in Equation 2 is an indicator of the crystallographic isotropy of the negative electrode material.

[0105] The anode material has remarkably excellent crystallographic isotropy, with an orientation index of 65 or higher. This high isotropy can be achieved by mechanical spheroidization of natural graphite, advantageously mechanical spheroidization using the batch-type spheroidization device described above, and isotropic pressing of the spheroidized natural graphite. Specifically, the orientation index of the anode material may be 65 to 90, more specifically 70 to 90, and even more specifically 75 to 85.

[0106] The cathode material has the high isotropy mentioned above, and at the same time, [S BET / D 50 ]×P may be 1.3 to 2.5, specifically 1.6 to 2.5, more specifically 1.9 to 2.4, and even more specifically 2.0 to 2.3. This activity is a high activity that is not practically realized in isotropically pressed natural graphite.

[0107] As described above, the cathode material according to one embodiment exhibits enhanced activity and high crystallographic isotropy. This high activity and excellent isotropy are advantageous in that they can enhance the high-rate characteristics of the cathode material.

[0108] In one specific example, the BET surface area S of the cathode material BET (m 2 / g) is the cumulative volume-based median diameter D of the cathode material 50 S divided by (㎛) BET / D 50The S of the negative electrode material under a dense structure may be 0.13 to 0.16, specifically 0.14 to 0.16. BET / D 50 The value can be mainly determined by the surface roughness of the negative electrode active material. The curvature of the negative electrode particles increases the surface roughness, and the high surface roughness of the negative electrode material is advantageous because it enables the penetration of lithium ions in all directions. However, excessively high S BET / D 50 The value may cause side reactions with the electrolyte. BET / D 50 It is advantageous if the value is less than 0.16.

[0109] According to one specific example, the cathode material may have a curvature ratio of 10.0% to 13.0%, as defined by Equation 3 below.

[0110] (Formula 3)

[0111] Curvature ratio = [1 - 1 / R] × 100

[0112] In Equation 3, R is the roughness, which is the ratio of the perimeter (P) of the particle to the perimeter (CP) of the convex surface (P / CP), and is 0.8D. 50 1.2D 50 Roughness targeting a cathode material having the size of .

[0113] The curvature ratio, defined by Equation 3, is related to the shape of the negative electrode material particles. Specifically, as the flat surface area increases, the curvature ratio decreases, and as the curved surface area increases, the curvature ratio increases. As described above in the manufacturing method, the negative electrode material can have an increased curvature ratio by transforming the flat surface areas formed during isotropic pressing into curved surfaces through resphericization.

[0114] As described above, the curvature ratio is an indicator of the degree to which a flat surface is removed from the negative electrode material, i.e., the degree to which a curved surface is formed. The curvature ratio of the negative electrode material may be 10.0% to 13.0%, specifically 10.5% to 13.0%, more specifically 11.0% to 13.0%, and even more specifically 11.5% to 12.5%.

[0115] The roughness adopted in Equation 3 is not the roughness of the entire cathode material, but the median diameter D based on the cumulative volume of the cathode material. 50 Based on , 0.8D 50 1.2D 50 The roughness of the cathode material may fall within the size range of D 50 Standard 0.8D 50 1.2D 50 The roughness for particles falling within the size range is advantageous because it can represent the electrolyte immersion characteristics of the negative electrode material.

[0116] 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. A negative electrode material with a high degree of sphericity is advantageous for high densification. At this time, it was confirmed through a previous experiment that even when the square angular particles described above in the manufacturing method were re-sphericized, there was no significant difference in the degree of sphericity between the square angular particles and the re-sphericized particles. This means that the degree of sphericity is a property insensitive to the spherical particle shape of the negative electrode material.

[0117] 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 1.3, specifically 0.6 to 1.1, and more specifically 0.7 to 1.0, but is not limited thereto.

[0118] In one specific example, the negative electrode material has a density of 1.00 to 1.30 g / cm 3 , specifically 1.05 to 1.25 g / cm 3 , more specifically 1.10 to 1.25 g / cm 3 , more specifically 0.15 to 1.25 g / cm 3 of It can have a tap density. When the negative electrode material has the aforementioned tap density, it can have improved immersion properties and improved long-term life characteristics.

[0119] In the negative electrode material, the core, which is a spherical natural graphite, may be a secondary particle in which natural graphite fragments are formed into a spherical shape with a sphericity of 0.90 or higher, formed by folding, bending, and / or assembling them. Specifically, 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, or 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.

[0120] In detail, 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 (mechanical processing), so that natural graphite fragments (natural graphite crystals) derived from the natural graphite having an anisotropic shape are folded, bent, combined, 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.

[0121] Cumulative volume-based median diameter (D) of spherical natural graphite 50 ) may be 10 to 25 μm, specifically 10 to 20 μm, more specifically 12 to 18 μm, and the cumulative volume-based median diameter (D) of the negative electrode material 50 ) can be substantially identical.

[0122] As described above, the anode material may comprise a core of 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.

[0123] 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.

[0124] The surface layer may be a carbon layer, and the carbon layer may be a low-crystalline carbon layer (disordered carbon). The low-crystalline 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.

[0125] cathode

[0126] 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.

[0127] 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).

[0128] 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).

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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,

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] lithium secondary battery

[0139] The present invention includes a lithium secondary battery including the above-described negative electrode.

[0140] 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.

[0141] 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.

[0142] The properties described in the detailed description and claims are measured according to the 'Analysis and Measurement Method' below.

[0143] Analysis and Measurement Methods

[0144] (D 50 )

[0145] 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 D10 In the cumulative volume diameter distribution, D means the diameter at the location where the cumulative volume is 10%, and 90 In the cumulative volume diameter distribution, it refers to the diameter at the location where the cumulative volume is 90%.

[0146] (Spherical shape)

[0147] 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.

[0148] (asperity)

[0149] Roughness 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. Using a particle size scattergram generated by a typical program equipped with a particle shape analyzer as a data processing and analysis program, such as a visual spreadsheet, the minimum size of the particle group (main particle group) used for roughness measurement was 0.8D. 50 and the maximum size is 1.2D 50 By selecting a particle group to be , the roughness of particles belonging to the main particle group is calculated. The roughness of a material is the average value of the roughness values ​​for the main particle group of each of 10 randomly collected cathode material powder samples.

[0150] As is known, the convex hull is a surface defined by an elastic band that surrounds the three-dimensional particle to be measured in a 2D image captured by an imaginary elastic band that stretches around the particle outline. The convex perimeter of the convex hull is the perimeter of this convex hull, and the particle perimeter is the perimeter of the actual particle. The roughness is defined as the ratio of the particle perimeter in the captured image to the perimeter of the convex hull.

[0151] (BET specific surface area)

[0152] 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.

[0153] (tap density)

[0154] Tap density is measured using a conventional tap density measuring device (Quantachrome Autotap) based on ASTM B527 by putting 15 g of the target material into a 50 mL container and tapping 3000 times with a stroke length of 1.2 cm (tapping speed = 284 times / min), and is the average value of the tap density measured twice for randomly collected samples.

[0155] (orientation index)

[0156] An X-ray diffraction pattern of a target material is obtained using the θ-2θ method. Specifically, the X-ray diffraction pattern can be obtained using a conventional X-ray diffraction measuring device (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 index of the material to be measured, the intensity of the (110) peak (I 110 ) is the maximum intensity of the (110) peak (maximum value of the peak), and the intensity of the (004) peak (I 004 ) is the maximum intensity of the (004) peak (maximum value of the peak). The orientation index 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 × 100, %) is defined.

[0157] (porosity)

[0158] The porosity of the target material is measured by mercury porosimetry (also known as mercury intrusion). After pretreatment by drying the powdered negative active material at a temperature of 150℃ and a vacuum of 0.1 Torr or less for 12 hours, the porosity is measured using a conventional mercury porosimetry instrument (Autopore V 9620, Micromeritics). The measurement can be performed based on ASTM D 4284-83. When the pressure is increased to infiltrate mercury into the pores of the target material, the incremental pore volume (dV) through which mercury infiltrates at each pressure stage can be recorded. As is known, the applied pressure is proportional to the pore diameter (D Hg ) is converted to pore size distribution (dV / dlogD) from pore volume increment (dV). Hg ) can be obtained. cm 3 Porosity (P) in g o ) is D in the pore size distribution Hg The volume of pores in the size range of 3 nm to 2000 nm can be accumulated (the volume of mercury penetrated into pores in the size range of 3 nm to 2000 nm). The porosity (%) of the target material is obtained by calculating the density (D) for the apparent volume of the negative active material (the volume of the active material particle when mercury has not penetrated into the active material particle) using a mercury porosity measuring device (Autopore V 9620, Micromeritics). a ) and find the porosity (%) = D a × P o × It is calculated using the formula for 100.

[0159] (saliva)

[0160] The weight ratio of the target material (negative electrode material manufactured in the examples or comparative examples): conductive carbon black (super-P): carboxymethyl cellulose (CMC): styrene butadiene rubber (SBR) was 95.6: 1.0: 1.1: 2.3, and each material was added to deionized water and mixed for 10 minutes to prepare a slurry. The prepared slurry was applied to copper foil, dried, and rolled to obtain an electrode density of 1.55 g / cm. 3 Manufacture test electrodes.

[0161] A solution containing 1 M LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7 is used as the test electrolyte.

[0162] After dropping one drop of test electrolyte with a volume of 1 μL at five locations along the center line of the test electrode, the time taken for the test electrolyte to be completely absorbed into the test electrode at each location is measured, and the immersion time is calculated by averaging the time.

[0163] (Half cell)

[0164] A half cell is manufactured using the negative electrode material manufactured in the examples or comparative examples.

[0165] In detail, the weight ratio of negative electrode material: conductive carbon black (super-P): carboxymethyl cellulose (CMC): styrene butadiene rubber (SBR) was 95.6: 1.0: 1.1: 2.3, and the negative electrode active material, styrene butadiene rubber, carboxymethyl cellulose, and carbon black (super-P) were added to deionized water and mixed for 10 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.

[0166] 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 1.0 wt%, fluoroethylene carbonate (FEC) is added at 10 wt%, and a solution containing LiPF6 dissolved at a concentration of 1 M is used.

[0167] Hereinafter, the manufactured half-cells are collectively referred to as half-cells having the same number as the specific example number or comparative example number in which the negative electrode material was manufactured. For example, a half-cell manufactured using the negative electrode material manufactured in Example 1 is collectively referred to as the half-cell of Example 1.

[0168] (Electrochemical characteristics using half cells)

[0169] 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.

[0170] After the Mars step was performed, to test the high-rate characteristics, the cells were charged at 0.5C, 1.0C, or 3.0C to 0.005V / 0.005C under constant current / constant voltage (CC / CV) conditions at 25°C, and then discharged at 0.5C to 1.2V under constant current (CC) conditions. The charge capacity retention is the ratio (%) of the charged capacity at each C-rate divided by the charge capacity at 0.5C.

[0171] Hereinafter, the present invention will be described in detail through examples. However, it should be noted that the examples described below are intended only to illustrate and concretize the present invention and are not intended to limit the scope of the invention. This is because the scope of the invention is determined by the matters set forth in the patent claims and matters reasonably inferred therefrom.

[0172] In the embodiment, the mechanical processing of natural graphite was performed 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, and an air-flow classifier (classification point 2 μm) connected to a blower is positioned at the top of the spheroidizing device case for removing fine particles.

[0173] (Example)

[0174] Using a batch spheroidizing device, natural graphite (D 50 The raw material (24.1 μm) was spheroidized at 1900 rpm for 14 minutes to obtain the primary spheroidized natural graphite (D 50 17.2 μm, sphericity 0.89, span 1.30, tap density 0.90 g / cm 3 ) was manufactured.

[0175] Dense graphite was manufactured by filling the primary spherical natural graphite into a mold and then performing cold isostatic pressing. The cold isostatic pressing conditions were a pressurization rate of 50 MPa / min and a pressure of 300 MPa (P t ) and 5 minutes of isostatic pressing time (P t It was the approval time.

[0176] After cold isostatic pressing, the lumps were crushed to a size of 10 to 50 mm using a crusher to break up the particles that had clumped together, and then finely crushed to a size of 10 mm or less using a pin mill, and finally the particles were crushed using an air classifier to obtain crushed graphite crushed into individual particles.

[0177] For the crushed graphite, the same batch spheroidizing device was used to re-spheroidize the graphite at 1100 rpm for 15 minutes, and then air-classified and sieved to remove fine and coarse particles, thereby producing spherical natural graphite.

[0178] 100 parts by weight of the manufactured spherical natural graphite and 5 parts by weight of petroleum pitch with 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 in an inert atmosphere to manufacture a negative electrode material. D of the manufactured negative electrode material 50 The diameter was 14.7 ㎛, the span value was 0.81, and the sphericity was 0.92.

[0179] (Comparative Example 1)

[0180] A negative electrode material was manufactured in the same manner as in Example 1, except that the crushed graphite, which was crushed after cold isostatic pressing without performing re-sphericization, was mixed directly with petroleum pitch.

[0181] (Comparative Example 2)

[0182] A negative electrode material was manufactured in the same manner as in Example 1, except that the primary spheroidized natural graphite was directly re-spheroidized without performing cold isostatic pressing in Example 1, and the re-spheroidized natural graphite was mixed with petroleum pitch.

[0183] (Comparative Example 3)

[0184] In Example 1, a negative electrode material was manufactured in the same manner as in Example 1, except that the first spheroidized natural graphite was re-spheroidized under the conditions of Example 1, and then the re-spheroidized natural graphite was cold isostatically pressed under the conditions of Example 1, then crushed and mixed with petroleum pitch.

[0185] BET specific surface area (m) of the negative electrode material manufactured in the examples and comparative examples 2 / g) to D 50 (μm) divided by the ratio (S in Table 1) BET / D 50 ), S BET / D50 The activity according to Equation 1, which is the value obtained by multiplying the porosity (%), the orientation index of the negative electrode powder according to Equation 2, the curvature ratio (%) according to Equation 3, and the tap density (g / cm 3 ), and the immersion time (sec) are summarized in Table 1.

[0186] S BET / D 50 Activity Orientation Index Curvature Rate Tap Density Immersion Time Example 10.146 2.135 78.9 11.5% 1.17 17.4 Comparative Example 10.128 1.54 0 54.79.8% 1.144 1.6 Comparative Example 20.134 1.9 126 0.2 1 1.5% 1.17 24.3 Comparative Example 30.105 0.94 575.19.9% ​​1.203 8.8

[0187] As can be seen from the curvature ratio in Table 1 and the scanning electron microscope image of the negative electrode material manufactured in Comparative Example 1 in Fig. 1, when the negative electrode material is manufactured by the final process of cold isostatic pressing (and disintegration), macroscopically flat surface areas are formed on the natural graphite particles by cold isostatic pressing, and the curvature ratio of the negative electrode material is greatly reduced.

[0188] However, in the case where the first spherical natural graphite is cooled and isotropically pressed according to one specific example and then re-sphericalized, as shown in Fig. 2, which is a scanning electron microscope photograph of the negative electrode material manufactured in Example 1, it can be seen that the particle shape is adjusted to a curved surface, and a negative electrode material having significantly improved crystallographic isotropy and greatly increased activity is manufactured, as shown in Table 1.

[0189] In addition, as a result of testing the immersion property for the electrolyte using a test electrode substantially equivalent to the negative electrode that can be adopted for a secondary battery, it can be confirmed that the particle shape due to isotropic pressing is the main factor that inhibits the immersion property, as in Comparative Examples 1 and 3, and it can be seen that even when the curvature ratios are similar to each other, as in Example 1 and Comparative Example 2, the negative electrode material of the example with higher activity shows more improved immersion property.

[0190] Table 2 summarizes the charge capacity retention rates of half cells manufactured using the negative electrode materials manufactured in Examples and Comparative Examples. In Table 2, 1C is the ratio (%) of the charge capacity at 1C divided by the charge capacity at 0.5C, and 3C is the ratio of the charge capacity at 3C divided by the charge capacity at 0.5C.

[0191] Charging capacity retention rate (%) 0.5C1C3C Example 1 100% 79.6% 21.5% Comparative example 1 100% 72.3% 17.4% Comparative example 2 100% 77.7% 20.1% Comparative example 3 100% 78.2% 20.3%

[0192] Looking at Comparative Examples 1 and 2 in Table 2, it can be seen that the anode material of Comparative Example 1 has low crystallographic isotropy and flat surface areas along with low activity, resulting in the worst high-rate output characteristics. It can be seen that the anode material of Comparative Example 2 has improved crystallographic isotropy compared to Comparative Example 1, and its high-rate output characteristics are improved compared to Comparative Example 1 due to its curved surface and relatively high activity. Looking at Example 1 and Comparative Example 3, it can be seen that despite the fact that both Example 1 and Comparative Example 3 have very high crystallographic isotropy (orientation index) of 78.9 and 75.1, the high-rate output characteristics of the anode material of Comparative Example 3 are significantly worse than those of Example 1 due to its low activity and flat surfaces.

Claims

1. 1 A step of isotropically pressing spherical natural graphite to produce pressed natural graphite; A step of producing crushed natural graphite by crushing the pressurized natural graphite; and A step of manufacturing spherical natural graphite by re-spherifying the crushed natural graphite through mechanical processing; A method for manufacturing a negative electrode material for a lithium secondary battery, comprising:

2. In paragraph 1, The above manufacturing method, before the isotropic pressing, A method for manufacturing an anode material for a lithium secondary battery, further comprising a step of manufacturing the first spheroidized natural graphite by spheroidizing natural graphite having an anisotropic shape.

3. In paragraph 1, The above manufacturing method, after the above re-sphericization, A method for manufacturing a negative electrode material for a lithium secondary battery, further comprising a step of forming a surface layer containing carbon on the above spherical natural graphite.

4. In paragraph 2, A method for manufacturing a negative electrode material for a lithium secondary battery, wherein the above spheroidization, the above re-spheroidization, or each of the above spheroidization and re-spheroidization is performed by rotary processing using air current.

5. In paragraph 4, A method for manufacturing a negative electrode material for a lithium secondary battery, wherein fine particles are removed from the inside to the outside of a processing space where rotary processing using the above air current is performed.

6. In paragraph 1, A method for manufacturing a negative electrode material for a lithium secondary battery, wherein the above isostatic pressing includes cold isostatic pressing (CIP) or hot isostatic pressing (HIP).

7. In paragraph 6, A method for manufacturing a negative electrode material for a lithium secondary battery, wherein the pressure during the above isotropic pressurization is 100 to 500 MPa.

8. A negative electrode material for a lithium secondary battery, comprising a core of spherical natural graphite and a surface layer containing carbon, having an activity of 1.3 to 2.5 as defined by the following formula 1, and an orientation index of 65 or more as defined by the following formula 2. (Formula 1) Activity = [S BET / D 50 ]×P (S in Equation 1 BET is the BET surface area (m) of the cathode material. 2 / g), and D 50 is the cumulative volume-based median diameter (㎛) of the cathode material, and P is the porosity (%) of the cathode material measured by mercury porosimetry. (Formula 2) Orientation index = I 110 / I 004 × 100 (In Equation 2, I 110 is the maximum intensity of the (110) peak in the X-ray diffraction pattern of the cathode material, and I 004 is the maximum intensity of the (004) peak in the same X-ray diffraction pattern.

9. In paragraph 8, A negative electrode material for a lithium secondary battery, having a curvature ratio of 10.0 to 13.0%, as defined by the following equation 3. (Formula 3) Curvature ratio = [1 - 1 / R] × 100 (In Equation 3, R is the roughness, which is the ratio of the perimeter (P) of the particle to the perimeter (CP) of the convex surface (P / CP), and is 0.8D 50 1.2D 50 Roughness targeting a cathode material having the size of 10. In paragraph 8, S above BET / D 50 A negative electrode material for a lithium secondary battery having a molecular weight of 0.13 to 0.

16.

11. In paragraph 8, Above D 50 A negative electrode material for a lithium secondary battery, having a diameter of 10 to 25 μm.

12. In paragraph 8, The tap density of the above negative electrode material is 1.00 to 1.30 g / cm 3 In, a negative electrode material for lithium secondary batteries.

13. In paragraph 8, A negative electrode material for a lithium secondary battery, wherein the surface layer is a carbon layer.

14. A negative electrode for a lithium secondary battery comprising a negative electrode material according to any one of claims 8 to 13.

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