Negative active material precursor, negative active material comprising the same, method for preparing the same, and lithium secondary battery comprising the same

Abstract

The present embodiment relates to a negative active material precursor and a method of manufacturing the same. The negative active material precursor according to one embodiment of the present application can include: a stacked portion configured at a center portion of the negative active material precursor and stacked with graphite particles; and a pore portion configured with at least one or more between the center portion and a surface portion of the negative active material precursor, having an average particle diameter D50 of 10 to 18 µm, and satisfying the following Formula 1. <Formula 1> (D90-D10) / D50 ≤ 1.0 In the Formula 1, D10, D50, and D90 respectively represent particle diameters corresponding to 10, 50, and 90% in volume accumulation from the smaller side.

Description

Technical Field

[0001] This embodiment relates to a secondary battery, and more specifically to a negative electrode active material precursor, its preparation method, a negative electrode active material comprising the precursor, and a lithium secondary battery comprising the precursor. Background Technology

[0002] Lithium-ion rechargeable batteries typically consist of a positive electrode containing positive active material, a negative electrode containing negative active material, a separator, and an electrolyte. They are charged and discharged through the intercalation-decalation of lithium ions. These lithium-ion rechargeable batteries offer advantages such as high energy density, high electromotive force, and high capacity, and are therefore used in various fields.

[0003] Furthermore, improving high-temperature performance, such as high-temperature storage and high-temperature cycling characteristics, is a crucial issue to be addressed in lithium-ion batteries. For example, after coating the negative electrode active material onto the current collector and pressing it, a high total internal pore volume can lead to a significant decrease in the high-temperature performance of the negative electrode. Therefore, it is necessary to minimize the changes in electrode structure and total internal pore volume caused during electrode pressing, thereby improving high-temperature characteristics when developing negative electrode materials for lithium-ion batteries, such as those used in fast-charging batteries.

[0004] In addition, with the development and increasing demand for mobile device technology, the demand for secondary batteries as an energy source is rapidly increasing. Lithium secondary batteries with high energy density and operating potential, long cycle life and low self-discharge rate have been commercialized and widely used.

[0005] In addition, with increasing attention to environmental issues, there is growing interest in electric vehicles and hybrid electric vehicles because they can replace fossil fuel-powered cars such as gasoline and diesel vehicles, which are major contributors to air pollution. Furthermore, research is actively underway to use lithium-ion batteries as a power source for electric and hybrid electric vehicles.

[0006] In recent years, due to the rapid rise of EVs, expectations for lithium-ion batteries have been increasing, with greater demands for maintaining existing capacity and improving fast-charging characteristics. In improving fast charging, the role of the negative electrode active material responsible for storing lithium ions during charging has become increasingly important.

[0007] The negative electrode active material used is lithium metal negative electrode active material, carbon-based negative electrode active material, or silicon dioxide (SiO2). xMaterials such as [material name missing]. The carbon-based anode active material exhibits excellent capacity retention characteristics and efficiency. The potential of the carbon-based anode active material used as the anode in lithium secondary batteries is close to the electrode potential of lithium metal, thus the crystal structure changes less during the insertion and extraction of ionic lithium. Furthermore, the carbon-based anode active material can continuously and repeatedly undergo oxidation and reduction reactions in the electrode, resulting in high capacity and excellent lifespan for the lithium secondary battery.

[0008] Various forms of materials are used as carbon-based anode active materials, such as natural and artificial graphite as crystalline carbon materials, or hard and soft carbon as amorphous carbon materials. Among these carbon-based anode active materials, graphite-based anode active materials, which can improve the lifespan characteristics of lithium secondary batteries, are the most widely used due to their excellent reversibility. Compared to lithium, the discharge voltage of graphite-based anode active materials is as low as -0.2V; therefore, batteries using graphite-based active materials can exhibit a high discharge voltage of 3.6V, giving lithium secondary batteries a significant advantage in energy density.

[0009] Artificial graphite, as a crystalline carbon material, is formed by applying high heat energy above 2700°C to create a crystalline graphite structure. Therefore, it has a more stable crystalline structure than natural graphite. Even with repeated charging and discharging of lithium ions, the changes in the crystalline structure are minimal, resulting in a longer lifespan compared to natural graphite—approximately two to three times longer. Soft and hard carbons, as amorphous carbon materials with unstable crystalline structures, facilitate the entry and exit of lithium ions, improving charging and discharging speeds and making them suitable for electrodes requiring rapid charging. Therefore, considering the lifespan and output characteristics of the lithium-ion secondary battery to be used, these carbon materials are typically used in a mixture in a certain proportion.

[0010] Furthermore, existing negative electrode active material precursors have an internally coiled structure (e.g., a cabbage structure). Therefore, as the particles become larger, the load is concentrated on one side, leading to damage to the negative electrode active material precursor. In addition, due to the decreased adhesion between the electrodes, there is a problem of the negative electrode active material detaching from the Cu current collector. Summary of the Invention

[0011] Technical issues

[0012] The technical problem to be solved by the present invention is to provide a negative electrode active material precursor that maintains its negative electrode active material precursor structure even when subjected to a load.

[0013] Another technical problem to be solved by the present invention is to provide a negative electrode active material comprising a negative electrode active material precursor having the aforementioned advantages, and having excellent adhesion between electrodes.

[0014] Another technical problem to be solved by the present invention is to provide a lithium secondary battery that includes a negative electrode active material with the aforementioned advantages and prevents the current collector from falling off.

[0015] Another technical problem to be solved by the present invention is to provide a method for preparing a negative electrode active material precursor having the aforementioned advantages.

[0016] Technical solution

[0017] According to an embodiment of the present invention, a negative electrode active material precursor may comprise: a laminated portion disposed at the center of the negative electrode active material precursor and having graphite particles laminated thereon; and a porous portion disposed between the center portion and the surface portion of the negative electrode active material precursor, having at least one porous portion, an average particle size D50 of 10 to 18 μm, and satisfying the following formula 1.

[0018] <Formula 1>

[0019] (D90-D10) / D50 ≤ 1.0

[0020] In Equation 1, D10, D50 and D90 represent the particle size that accumulates from the smaller side to 10, 50 and 90% of the total volume, respectively.

[0021] In one embodiment, with the intermediate cross-section as a reference, the length of the pore portion relative to the diameter of the major axis can be more than 30%. In one embodiment, when the intermediate cross-section of the negative electrode active material precursor is cut, the area of ​​the laminated portion can be more than 20%.

[0022] In one embodiment, the specific surface area of ​​the negative electrode active material precursor can be 4 to 8 m². 2 / g. In one embodiment, the spheroidization rate of the negative electrode active material precursor can be above 0.71.

[0023] According to another embodiment of the present invention, a lithium secondary battery may include a negative electrode active material, comprising a negative electrode active material precursor, comprising: a stacked portion disposed at the center of the negative electrode active material precursor and having graphite particles stacked thereon; and a porous portion disposed between the center portion and the surface portion of the negative electrode active material precursor, having an average particle size D50 of 10 to 18 μm and satisfying the following formula 1.

[0024] <Formula 1>

[0025] (D90-D10) / D50 ≤ 1.0

[0026] In Equation 1, D10, D50 and D90 represent the particle size that accumulates from the smaller side to 10, 50 and 90% of the total volume, respectively.

[0027] In one embodiment, with the mid-section as a reference, the length of the pore portion relative to the diameter of the major axis can be more than 30%.

[0028] According to another embodiment of the present invention, a method for preparing a negative electrode active material precursor may include: a step of adjusting the purity of a graphite material, a step of pulverizing the graphite material, and a step of spheroidizing the pulverized graphite material. The spheroidizing step includes applying an external force to cause at least a portion of the carbon mesh surface of the graphite material to be wound. The step of pulverizing the graphite material includes adjusting the average particle size D50 to be 10 to 18 μm, and the graphite material satisfies the following formula 1.

[0029] In one embodiment, after the step of pulverizing the graphite material, a step of adjusting the particle size of the pulverized graphite material may be included. In one embodiment, the step of adjusting the purity of the graphite material can adjust the purity of the graphite material to 90% or more.

[0030] In one embodiment, the pulverizing step can be performed by at least one of physical impact and airflow impact. In one embodiment, the spheroidizing step can be performed by spheroidizing the pulverized particles using at least one of airflow method, granulation spheroidization method, and mechanical grinding method.

[0031] Invention Effects

[0032] According to one embodiment of the present invention, a precursor of a negative electrode active material can be provided for preparing a negative electrode material, which simultaneously includes a laminated portion and a porous portion, thereby having a discharge capacity derived from natural graphite.

[0033] In addition, according to another embodiment of the present invention, a negative electrode active material may be provided, which comprises a negative electrode active material precursor having the aforementioned advantages.

[0034] In addition, according to yet another embodiment of the present invention, a method for preparing a negative electrode active material precursor with the aforementioned advantages can be provided.

[0035] Another technical problem to be solved by the present invention is to provide a method for preparing a negative electrode active material precursor with the aforementioned advantages. Attached Figure Description

[0036] Figure 1a and Figure 1b A tissue photograph of a precursor of a negative electrode active material according to an embodiment of the present invention is shown.

[0037] Figure 2 This is a flowchart of a method for preparing a negative electrode active material precursor according to an embodiment of the present invention. Detailed Implementation

[0038] The terms "first," "second," "third," etc., are used to describe parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, and / or segment from another. Therefore, without departing from the scope of the invention, the first part, component, region, layer, and / or segment described below can also be described as a second part, component, region, layer, and / or segment.

[0039] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular forms used are intended to include the plural forms as well. It should also be understood that the term "comprising" as used in the specification can specifically refer to a feature, field, integer, step, action, element, and / or component, but does not exclude the presence or addition of other features, fields, integers, steps, actions, elements, and / or components.

[0040] If one part is described as being on top of another part, then other parts can exist directly on top of or in between the other part. When one part is described as being directly on top of another part, no other parts can exist in between.

[0041] Although not otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in dictionaries should be interpreted as having the same meaning as disclosed in relevant technical literature and herein, and should not be interpreted in an idealized or overly formal sense.

[0042] Embodiments of the present invention will be described in detail below. However, the following embodiments are merely examples, and the present invention is not limited to the following embodiments; the scope of the claims shall prevail.

[0043] Figure 1a and Figure 1b A negative electrode active material precursor is shown according to an embodiment of the present invention.

[0044] Reference Figure 1a and Figure 1b The negative electrode active material precursor 10 of the present invention may include a laminated portion 100 and a porous portion 200. In one embodiment, the negative electrode active material precursor may be a carbon-based material. The carbon-based material may be at least one of the following materials composed of amorphous carbon: artificial graphite, natural graphite, graphitized carbon fiber, graphitized mesophase carbon microspheres, petroleum coke, resin calcined body, carbon fiber, and pyrolytic carbon, preferably natural graphite. In one embodiment, the natural graphite may be in various shapes such as flakes, spheres, and blocks, for example, flake graphite.

[0045] The stacked portion 100 is formed by stacking the carbon-based materials and can be disposed in at least a portion of the negative electrode active material precursor 10. The stacked portion 100 refers to the stacked region, not the region spheroidized during the spheroidizing operation; for example, it is the stacked region rather than the region where the carbon mesh is wound. The stacked region is the portion that is beneficial to the actual capacity during subsequent electrode fabrication.

[0046] For example, the stacked portion 100 may be the carbon-based material stacked to penetrate the center (e.g., the middle region) of the negative electrode active material precursor 10, and the stacked portion 100 may be the carbon-based material stacked to penetrate a point offset from the center of the negative electrode active material precursor.

[0047] In one embodiment, when the negative electrode active material precursor 10 is cut at the mid-section, the area of ​​the stacked portion 100 can be 20% or more. Specifically, for the stacked portion 100, in the cross-section when the negative electrode active material precursor 10 is cut with the midpoint as a reference, the area occupied by the stacked portion 100 can be 20% or more of the total area. When the mid-section area of ​​the stacked portion 100 meets the above range, the carbon mesh will not be rolled up but stacked, which has the advantage of being beneficial to the actual capacity when preparing the electrode. If the mid-section area of ​​the stacked portion 100 does not meet the above range, it is difficult to exhibit the effects brought about by the above advantages.

[0048] In one embodiment, the carbon-based material may be, for example, a graphite mesh. The graphite mesh may be, for example, a hexagonal mesh. The carbon-based material may have a laminated structure formed by stacking layers.

[0049] In one embodiment, as a non-limiting example, the laminated structure can be stacked into an irregular laminated structure, a regular laminated structure, or a combination thereof. With the irregular laminated structure, the negative electrode active material precursor can readily adsorb and release lithium ions, and can absorb stresses caused by structural changes such as expansion and contraction due to lithium ion insertion / extraction and in-plane phase changes, thus exhibiting excellent durability. With the regular laminated structure, there is an advantage in ensuring excellent capacity density.

[0050] At least one pore portion 200 may be disposed between the laminated portion 100 and the surface portion of the negative electrode active material precursor 10. The pore portion 200 may be an internal pore formed by winding the laminated portion 100. The pore portion 200 may be a gap in carbonaceous material in a shape that winds more towards the surface portion of the negative electrode active material precursor 100 (e.g., a cabbage shape).

[0051] As a non-limiting example, the pore portion 200 can have a relatively long slit shape. The pore portion 200 can effectively buffer the volume expansion of the negative electrode active material precursor 10 during charging and discharging. The negative electrode active material prepared from the negative electrode active material precursor 10 is structurally stable, does not experience a decrease in lithium storage capacity, and can exhibit improved charge and discharge capacity and cycle life. Furthermore, the pore portion 200 has the advantage of reducing the external specific surface area.

[0052] In one embodiment, with the mid-section as a reference, the length of the pore portion 200 relative to the diameter of the major axis can be 30% or more. Specifically, the pore portion 200 can be a gap with a shape that, when the midpoint of the negative electrode active material precursor 10 is cut, has a length of 30% or more relative to the diameter of the major axis in the cross-section.

[0053] In one embodiment, the specific surface area of ​​the negative electrode active material precursor 10 can be 4 to 8 m². 2 / g. By meeting the specified range, the problem of decreased electrode adhesion during electrode preparation is prevented, resulting in excellent electrode adhesion.

[0054] In one embodiment, the spheroidization rate of the negative electrode active material precursor 10 can be 0.71 or higher. If the spheroidization rate is lower than the specified range, there is a possibility of providing non-reactive sites; therefore, the spheroidization rate can be 0.71 or higher.

[0055] In one embodiment, the average particle size D50 of the negative electrode active material precursor 10 can be 10 to 18 μm. The average particle size D50 can be the particle size accumulated from the smaller side to represent 50% of the total particle size. If the average particle size D50 of the negative electrode active material precursor 10 exceeds the lower limit of the range, the negative electrode active material precursor 10 is equivalent to micronized powder, thus resulting in a decrease in capacity and efficiency. If it exceeds the upper limit of the range, there is a decrease in efficiency due to a reduction in discharge capacity.

[0056] In one embodiment, the negative electrode active material precursor 10 can satisfy the following formula 1.

[0057] <Formula 1>

[0058] (D90-D10) / D50 ≤ 1.0

[0059] In Equation 1, D10, D50 and D90 represent the particle size that accumulates from the smaller side to 10, 50 and 90% of the total volume, respectively.

[0060] For the negative electrode active material precursor 10, satisfying the range of Formula 1 provides advantages such as excellent electrode adhesion and electrode processability. If the range of Formula 1 is exceeded, the specific surface area becomes higher, thus causing a decrease in electrode adhesion.

[0061] According to another embodiment of the present invention, the negative electrode active material may comprise a negative electrode active material precursor 10 and a coating consisting of a coating material on the negative electrode active material precursor 10. For the negative electrode active material precursor 10, the coating may be a commonly used material, provided that it does not contradict the foregoing FIG1.

[0062] As a non-limiting example, the coating may comprise amorphous carbon. In one embodiment, the coating may comprise at least one material selected from the group consisting of soft carbon and hard carbon. In one embodiment, the soft carbon may be at least one carbonaceous material selected from polyvinyl alcohol, polyvinyl chloride, coal tar pitch, petroleum tar pitch, mesophase pitch, and low molecular weight heavy oil that has been carbonized. In one embodiment, the hard carbon may be at least one carbonaceous material selected from sucrose, phenolic resin, furan resin, furfuryl alcohol, polyacrylonitrile, polyimide, epoxy resin, cellulose, styrene, citric acid, stearic acid, polyvinylidene fluoride, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, glucose, gelatin, sugars, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated ethylene-propylene-diene monomer (EPDM), and starch that has been carbonized.

[0063] The coating can promote the entry and exit of lithium ions or reduce the diffusion resistance of lithium ions, thereby helping to improve fast charging performance. Furthermore, the coating is disposed on the surface of the negative electrode active material precursor, thereby increasing the hardness of the negative electrode active material containing the coating, and thus improving the structural stability of the negative electrode active material, which can minimize structural changes during pressing.

[0064] According to another embodiment of the present invention, a lithium secondary battery is provided, which includes a negative electrode active material, said negative electrode active material comprising the aforementioned negative electrode active material precursor 10.

[0065] In one embodiment, the lithium secondary battery can effectively use a negative electrode active material for preparing lithium secondary batteries such as lithium-ion batteries, lithium-ion polymer batteries, or lithium polymer batteries, the lithium secondary battery comprising: a positive electrode comprising a positive electrode active material capable of lithium-ion intercalation and deintercalation; a negative electrode comprising the negative electrode active material prepared from the aforementioned negative electrode active material precursor 10; and an electrolyte.

[0066] In one embodiment, the lithium secondary battery may further include a separator disposed between the positive electrode and the negative electrode. The lithium secondary battery may be prepared by mixing a negative electrode active material prepared from the aforementioned negative electrode active material precursor 10, a binder, and optionally a conductive material to prepare a composition for forming a negative electrode active material layer, and then coating the composition onto a negative electrode current collector. As a non-limiting example, the negative electrode current collector may consist of copper foil, nickel foil, stainless steel, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0067] In one embodiment, the adhesive may be mixed to a weight percentage of 1 to 30% relative to the total amount of the composition used to form the negative electrode active material. As a non-limiting example, the adhesive may contain at least one of polyvinyl alcohol, carboxymethyl cellulose / styrene-butadiene rubber, hydroxypropyl cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or polypropylene.

[0068] In one embodiment, the conductive material may be mixed in a weight percentage of 0.1 to 30% relative to the total amount of the composition used to form the negative electrode active material. The conductive material may comprise any material that does not cause a chemical change in the battery and exhibits conductivity. Non-limiting examples include graphite such as natural and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking black; conductive fibers such as carbon fiber and metal fiber; metal powders such as fluorinated carbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives.

[0069] The lithium secondary battery prepared from the aforementioned negative electrode active material precursor 10 has an excellent buffering effect on the volume changes generated during charging and discharging. By including a negative electrode active material with excellent conductivity, it can have high charging and discharging capacity characteristics and excellent cycle characteristics.

[0070] Figure 2 This is a flowchart of a method for preparing a negative electrode active material precursor according to an embodiment of the present invention.

[0071] Reference Figure 2 According to another embodiment of the present invention, the preparation method of the negative electrode active material precursor 10 may include a step of adjusting the purity of the graphite material (S100), a step of pulverizing the graphite material (S200), and a step of spheroidizing the pulverized graphite material (S300). Without contradiction, the graphite material may refer to the aforementioned carbon-based materials in FIG1. ​​Specifically, the graphite material may be, for example, flake-like natural graphite. Furthermore, the characteristics of the negative electrode active material precursor 10 prepared by the above preparation method are shown in FIG1.

[0072] The step (S100) of adjusting the purity of the graphite material is to adjust the purity of the graphite material to 90% or higher. In one embodiment, the step (S100) of adjusting the purity of the graphite material can utilize the difference in specific gravity to adjust the purity. The specific gravity is the value of the solid density divided by the density of water. As a method of utilizing the difference in specific gravity, Archimedes' principle can be used, for example. Archimedes' principle determines the specific gravity of the graphite material by comparing the mass of the graphite material outside water with its mass in water. The purity of the graphite material can be controlled by this method. This is a non-limiting example, and various methods for measuring specific gravity can be used.

[0073] In one embodiment, if the purity of the graphite material is less than 90%, it will contain foreign matter other than carbon, such as ash, specifically foreign matter including Si, Al, S, etc., thus causing a decrease in the capacity and consequently a decrease in efficiency of the battery during fabrication. Therefore, by controlling the purity of the graphite material to above 90%, there are advantages in improving the capacity and efficiency during battery fabrication.

[0074] The step (S200) of pulverizing the graphite material may include applying an external force to pulverize the graphite material or to pulverize it into powder. In one embodiment, the pulverizing step (S200) may be performed by at least one of physical impact and airflow impact. As a non-limiting example, the physical impact may be performed by at least one of an air-classified mill, a Raymond mill, a vertical roller mill, a jaw crusher, a ball mill, a stirred ball mill, a hammer mill, and a pin mill. As a non-limiting example, the airflow impact may be performed by a jet mill.

[0075] In one embodiment, the step of pulverizing the graphite material (S200) may further include a step of adjusting the particle size of the graphite material. The particle size adjustment step can be performed using at least one of particle size separation, specific gravity difference separation, and magnetic separation. The particle size separation method separates particles based on their size or diameter, and may include various methods using sieves for separation. The specific gravity difference separation method separates particles considering the specific gravity difference of different materials; for example, it may use a specific solvent and separate particles based on the specific gravity of the particles corresponding to the specific solvent, and various specific gravity difference separation methods can be applied. The magnetic separation method can use a magnetic body to separate particles through contact with the magnetic body, and various magnetic separation methods can be applied.

[0076] In one embodiment, the step of adjusting the particle size of the graphite material may include adjusting the average particle size D50 to be 10 to 18 μm, and the graphite material satisfying Formula 1 below. A detailed description of the average particle size and Formula 1 below can be found in Figure 1.

[0077] <Formula 1>

[0078] (D90-D10) / D50 ≤ 1.0

[0079] In Equation 1, D10, D50 and D90 represent the particle size that accumulates from the smaller side to 10, 50 and 90% of the total volume, respectively.

[0080] In one embodiment, the step of adjusting the particle size of the graphite material can be performed to a particle size of less than 50 μm. If the particle size of the graphite material is greater than 50 μm, the two particles will stack, thus exceeding the ideal thickness of the active material on the electrode sheet. During pressure molding, the active material particles may break apart. Therefore, the particle size of the pulverized graphite material can be adjusted to less than 50 μm.

[0081] The step of spheroidizing the pulverized graphite material (S300) involves preparing the graphite material into spherical particles, which allows for adjustment of the filling density to achieve a high tap density. By spheroidizing the angular portions of the graphite material, it can be separated from or combined with the micro-powder. In one embodiment, the spheroidizing step (S300) can be performed using at least one of an airflow method, a granulation spheroidizing method, and a mechanical grinding method.

[0082] The airflow-based method can involve spheroidizing the negative electrode active material precursor by using centrifugal airflow through friction between the airflow and the wall surface. The granulation and spheroidization method is a method that simultaneously crushes and granulates, and can include dry methods that process the crushed particles using a blade mill, a multi-functional mixing mill, or a combination thereof, and wet methods utilizing spray drying. The mechanical grinding method can involve spheroidizing the negative electrode active material precursor by rotating two or more rollers that induce friction in the vertical direction.

[0083] In one embodiment, the spheroidizing step (S300) may include applying an external force to roll up at least a portion of the carbon mesh surface of the graphite material. Through the spheroidizing step (S300), not only can the aforementioned laminated portion 100 in FIG. 1 be formed, but also the porous portion 200 can be formed. For the graphite material, for example, the rolled-up portion of the carbon mesh surface can be maintained in a cabbage-like shape through physical surface contact.

[0084] Thus, the negative electrode active material precursor 10 prepared by applying external force to wind at least a portion of the carbon mesh of the graphite material has a wound structure to minimize side-effect sites on the surface, has certain pores 200 to maintain a buffering effect during charging and discharging, and may have a stacked portion 100 in the middle region of the negative electrode active material precursor 10, which is a portion of carbon materials such as graphite mesh stacked together. By distinguishing between the stacked portion 100 and the pores 200, the aforementioned method for preparing the negative electrode active material precursor can provide a negative electrode active material precursor 10 with a structure that facilitates the insertion and extraction of lithium particles, which are related to the capacity of lithium secondary batteries.

[0085] Embodiments of the present invention will be described in detail below to enable those skilled in the art to implement the invention. However, the present invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0086] <Example 1 and Comparative Example 1>

[0087] Table 1 below shows the results of electrode adhesion to copper foil based on the negative electrode active material precursors prepared according to Example 1 and Comparative Example 1. Example 1 is based on the aforementioned Figure 1 and... Figure 2 The embodiment of the negative electrode active material precursor 10 structure prepared in this invention differs from the negative electrode active material precursor 10 of this invention. The comparative example 1 does not contain the stacked portion 100 and has a conventional cabbage structure.

[0088] In Table 1 below, regarding electrode adhesion, after electrode preparation, the time point at which detachment occurred during drying in a vacuum oven at 100°C was measured to determine whether detachment had occurred within 12 hours. In Table 1 below, an electrode adhesion [hour] of 12 indicates that no detachment occurred. Detachment refers to the phenomenon of the negative electrode active material separating from the copper foil current collector.

[0089] Table 1

[0090]

[0091] As shown in Table 1 above, when comparing the similar particle size and (D90-D10) / D50 of Comparative Example 1 and Example 1, the specific surface area of ​​Example 1 is smaller. This indicates that Comparative Example 1 is due to excessive winding of the graphite mesh, unlike Example 1. Therefore, according to the structure of Example 1 based on the present invention, there are fewer internal pores and fewer external cracks, thus indicating fewer unnecessary side reaction sites such as electrolyte. By comparing Comparative Example 1 and Example 1, it can be confirmed that the electrode adhesion of the Example 1 is superior.

[0092] <Comparative Example 2 and Comparative Example 3>

[0093] See Table 2 below. Similar to Comparative Example 1 mentioned above, Comparative Examples 2 and 3 are existing negative electrode active material precursors. Unlike the present invention, they are for precursors that do not contain the stacked portion 100. Unlike Comparative Example 1, which only adjusted the particle size to confirm the specific surface area, electrode adhesion and adhesion.

[0094] Table 2

[0095]

[0096] As shown in Table 2 above, it can be confirmed that Comparative Example 2 has a larger D50, thus confirming a poorer electrode adhesion result. This can be attributed to the cabbage-like structure being rolled inside, resulting in a larger load on specific surfaces and damage to the structure of the negative electrode containing the negative electrode active material precursor. As shown in Table 2 above, Comparative Example 3 has a considerably larger (D90-D10) / D50, thus increasing the specific surface area, which confirms a decrease in electrode adhesion. Therefore, through Comparative Example 1 in Table 1 and Comparative Examples 2 and 3 in Table 2 above, it can be confirmed that the negative electrode active material precursor structure of the present invention, which simultaneously has a laminated portion and a porous portion, has excellent electrode adhesion and structural stability, thereby exhibiting excellent electrode processability.

[0097] <Comparative Examples 4 and 5>

[0098] See Table 3 below. Similar to Example 1, Comparative Examples 4 and 5 have the characteristics described in Figure 1 above. Figure 2The structure of the negative electrode active material precursor 10 prepared according to the present invention is shown, but the average particle size D50 or the value of (D90-D10) / D50 exceeds the range of the present invention, thus confirming that it exhibits poor performance.

[0099] Table 3

[0100]

[0101] Referring to Table 3 above, for Comparative Example 4, compared to Comparative Example 2 in Table 2 above, which has a similar particle size, although the electrode adhesion strength is 11 hours, it exhibits excellent electrode adhesion strength because the structure is undamaged. However, the electrode adhesion strength does not reach 12 hours, therefore, compared to Example 1, whose average particle size D50 falls within the scope of the present invention, it can be confirmed that it has poor adhesion strength. Referring to Table 3 above, for Comparative Example 5, compared to Comparative Example 3 in Table 2 above, which has a similar particle size, it can be confirmed that the electrode adhesion strength is slightly better, but because the value of (D90-D10) / D50 exceeds the range of the present invention, the specific surface area is higher, and it can be confirmed that the electrode adhesion strength is reduced.

[0102] As described above, Tables 2 and 3 confirm that by having a laminated portion in the central region of the negative electrode active material precursor as described in the present invention, and simultaneously including a portion of the laminated portion between the laminated portion and the surface portion, a graphite mesh portion formed by winding it to form a porous portion, a negative electrode active material precursor with excellent electrode adhesion and electrode processability can be provided. Furthermore, for the negative electrode active material precursor, D50 satisfies 18 μm or less and (D90-D10) / D50 value satisfies 1.00 or less, thereby providing a negative electrode active material precursor with even better electrode adhesion and electrode processability.

[0103] <Example 1-1, Example 1-2, Comparative Example 1-1 and Comparative Example 1-2>

[0104] See Table 4 below. The negative electrode active material precursors of Example 1 and Comparative Example 1 were subjected to a spheroidizing operation. For spheroidizing, the samples processed using a Hosokawa Micron mechanical fusion machine at 40% output for 10 minutes were named Example 1-1 and Comparative Example 1-1, while the samples further processed using the same process for 10 minutes were named Example 1-2 and Comparative Example 1-2.

[0105] For sphericity, the sample powder was dispersed in solvents such as ethanol using FlowCAM PV, and then optical images were obtained through Flowcell+ objectives, and the shape was analyzed using a dedicated algorithm.

[0106] In addition, in order to prepare a negative electrode using the negative electrode active material precursors of Comparative Example 1, Comparative Example 1-1, Comparative Example 1-2, Example 1, Example 1-1, and Example 1-2, a negative electrode active material was prepared by applying a shear force based on rapid rotation to petroleum asphalt with a softening point of 250°C, coating it at 2% relative to the weight of the parent material, and then heat-treating the coated particles at 1200°C for about 1 hour.

[0107] In addition, the negative electrode active material was prepared using the negative electrode active material precursors of Comparative Example 1, Comparative Example 1-1, Comparative Example 1-2, Example 1, Example 1-1, and Example 1-2. The negative electrode active material 97% by weight, the adhesive containing carboxymethyl cellulose and styrene-butadiene rubber 2% by weight, and the Super P conductive material 1% by weight were mixed in distilled water solvent to prepare a negative electrode active material slurry.

[0108] The negative electrode active material slurry was coated onto a copper (Cu) current collector, then dried at 100°C for 10 minutes and pressed in a roller press. It was then vacuum dried in a vacuum oven at 100°C for 12 hours to prepare the negative electrode. The electrode density of the vacuum-dried negative electrode was thus 1.5 to 1.7 g / cc.

[0109] Using the negative electrode prepared by the method described above and lithium metal as the opposite electrode, and an electrolyte consisting of 1 mole of LiPF6 solution dissolved in a 1:1 volume ratio of ethylene carbonate (EC):dimethyl carbonate (DMC), a 203 coin cell was fabricated using conventional methods. The capacity, initial efficiency, and capacity retention were then confirmed. Here, capacity retention indicates how much capacity is retained after 50 charge-discharge cycles.

[0110] Table 4

[0111]

[0112] As shown in Table 4 above, comparative examples 1-2, which underwent two rounds of spheroidization, confirm that as the spheroidization rate decreases, the (D90-D10) / D50 value based on particle size increases, resulting in pulverization rather than particle spheroidization. Furthermore, the examples confirm that as the spheroidization rate increases, the adhesion force also increases proportionally. Therefore, due to the structure of the negative electrode active material precursor of the present invention, it not only has excellent density and high hardness but also excellent electrode adhesion. In addition, due to the laminated structure with an intermediate region and the coiled-shaped pore portion between the laminated portion and the surface portion of the negative electrode active material precursor, a negative electrode active material precursor with flexibility due to elastic containment and a robust structure can be provided. Furthermore, the examples confirm that not only are the capacity and efficiency excellent, but the capacity retention rate also remains at a high level after 50 charge-discharge cycles.

[0113] This invention can be implemented in various ways and is not limited to the embodiments described above. Those skilled in the art will understand that the invention can be implemented in other specific ways without altering its technical concept or essential features. Therefore, it should be understood that the above embodiments are exemplary in all respects and not restrictive.

Claims

1. A precursor for a negative electrode active material, comprising: The stacked portion is located in the center of the negative electrode active material precursor and is stacked with graphite particles. A porous portion, having at least one disposed between the central portion and the surface portion of the negative electrode active material precursor. The average particle size D50 is 10 to 18 μm. And satisfy the following equation 1, <Formula 1> (D90-D10) / D50≤1.0 In Equation 1, D10, D50 and D90 represent the particle size that accumulates from the smaller side to 10, 50 and 90% of the total volume, respectively.

2. The negative electrode active material precursor according to claim 1, wherein, With the mid-section as a reference, the length of the pore portion relative to the diameter of the major axis is more than 30%.

3. The negative electrode active material precursor according to claim 1, wherein, When the negative electrode active material precursor is cut in the middle section, the area of ​​the stacked portion is more than 20%.

4. The negative electrode active material precursor according to claim 1, wherein, The specific surface area of ​​the negative electrode active material precursor is 4 to 8 m². 2 / g.

5. The negative electrode active material precursor according to claim 1, wherein, The spheroidization rate of the negative electrode active material precursor is above 0.

71.

6. A lithium secondary battery comprising a negative electrode active material, wherein, The negative electrode active material includes a negative electrode active material precursor. The negative electrode active material precursor comprises: The stacked portion is located in the center of the negative electrode active material precursor and is stacked with graphite particles. A porous portion, having at least one disposed between the central portion and the surface portion of the negative electrode active material precursor. The average particle size D50 is 10 to 18 μm. And satisfy the following equation 1, <Formula 1> (D90-D10) / D50≤1.0 In Equation 1, D10, D50 and D90 represent the particle size that accumulates from the smaller side to 10, 50 and 90% of the total volume, respectively.

7. The lithium secondary battery according to claim 6, wherein, With the mid-section as a reference, the length of the pore portion relative to the diameter of the major axis is more than 30%.

8. A method for preparing a precursor of a negative electrode active material, comprising: Steps for adjusting the purity of graphite materials; The step of pulverizing the graphite material; and The step of spheroidizing the pulverized graphite material. The spheroidizing step includes applying an external force to cause at least a portion of the carbon mesh surface of the graphite material to curl up. In the step of pulverizing the graphite material, the average particle size D50 is 10 to 18 μm. The steps to adjust the graphite material to satisfy the following formula 1 are as follows: <Formula 1> (D90-D10) / D50≤1.0 In Equation 1, D10, D50 and D90 represent the particle size that accumulates from the smaller side to 10, 50 and 90% of the total volume, respectively.

9. The method for preparing the negative electrode active material precursor according to claim 8, wherein, Following the step of pulverizing the graphite material, a step of adjusting the particle size of the pulverized graphite material is included.

10. The method for preparing the negative electrode active material precursor according to claim 8, wherein, The step of adjusting the purity of the graphite material is to adjust the purity of the graphite material to 90% or higher.

11. The method for preparing the negative electrode active material precursor according to claim 8, wherein, The pulverizing step is performed by at least one of physical impact and airflow impact.

12. The method for preparing the negative electrode active material precursor according to claim 8, wherein, The spheroidizing step involves spheroidizing the pulverized particles using at least one of the following methods: airflow method, granulation spheroidizing method, and mechanical grinding method.

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