Anode active material for lithium secondary battery, and manufacturing method therefor

Abstract

The present invention relates to an anode active material for a lithium secondary battery, and a manufacturing method therefor. The anode active material for a lithium secondary battery comprises natural graphite and satisfies relation 1. <Relation 1> 2.23 ≤ [D90] / [D10] ≤ 2.37 (In relation 1, [D10] and [D90] mean particle diameters corresponding to 10% and 90% of the volume accumulation amount of an anode active material measured using a laser diffraction method).

Description

Negative active material for lithium secondary batteries and method for manufacturing the same

[0001] The present invention relates to a lithium secondary battery, and more particularly, to a negative electrode active material for a lithium secondary battery and a method for manufacturing the same.

[0002] Lithium secondary batteries generally consist of a positive electrode containing positive active material, a negative electrode containing negative active material, a separator, and an electrolyte, and charge and discharge are performed by intercalation and deintercalation of lithium ions. The lithium secondary batteries have the advantages of high energy density, high electromotive force, and high capacity, and are therefore applied in various fields.

[0003] Furthermore, improving high-temperature performance, such as high-temperature storage characteristics and high-temperature cycling characteristics, is a critical challenge in lithium secondary batteries. For example, if the negative electrode active material is applied to a current collector and rolled, there is a high possibility that the high-temperature performance of the negative electrode will be degraded if the total internal pore volume is high. Therefore, when developing negative electrode active materials for lithium secondary batteries, such as rapid-charge secondary batteries, it is necessary to minimize changes in electrode structure and total internal pore volume that occur during electrode rolling to improve high-temperature characteristics.

[0004] In addition, as technological development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing, and among secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life, and low self-discharge rate, are being commercialized and widely used.

[0005] In addition, as interest in environmental issues grows, interest in electric vehicles and hybrid electric vehicles that can replace vehicles that use fossil fuels, such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, is increasing, and research is actively being conducted to use lithium secondary batteries as a power source for the electric vehicles and hybrid electric vehicles.

[0006] Recently, with the rapid rise of electric vehicles (EVs), expectations for lithium secondary batteries have grown, and there is a growing demand for improved rapid charging characteristics while preserving existing capacity. The role of the cathode active material, which stores lithium ions during charging, is becoming increasingly important in improving rapid charging.

[0007] As a negative electrode active material for lithium ion secondary batteries used in conventional small batteries, graphite-based materials such as artificial graphite and natural graphite have been mainly used among carbon-based active materials that reversibly accept or supply lithium ions while maintaining structural and electrical properties and have chemical potentials that are almost similar to metallic lithium when lithium ions are inserted and removed.

[0008] Synthetic graphite has superior charge-discharge efficiency and less swelling during charge and discharge than natural graphite, resulting in superior cycle life. However, compared to natural graphite, it has lower reversible capacity, harder particles that make rolling difficult during electrode manufacturing, and minimal morphological change, hindering proper alignment. Furthermore, the requirement for 3,000°C graphitization heat treatment results in higher manufacturing costs.

[0009] Meanwhile, natural graphite is widely used as an anode active material because it is cheaper than artificial graphite, has a high reversible capacity, and exhibits similar electrochemical properties. However, natural graphite has a plate-like shape, resulting in a large surface area and exposed edges. This can lead to electrolyte penetration or decomposition reactions, which can cause peeling or destruction of the edges, resulting in significant irreversible reactions. Furthermore, the increased expansion rate can also lead to reduced long-term lifespan characteristics.

[0010] Furthermore, lithium metal, which has been considered as an anode material, boasts a very high energy density, enabling high capacity. However, it suffers from safety issues due to dendrite growth during repeated charging and discharging, as well as short cycle life. Furthermore, attempts have been made to use carbon nanotubes as an anode active material, but these have been criticized for their low productivity, high price, and low initial efficiency of less than 50%.

[0011] As another anode material, silicon, tin, or their alloys have been known to be able to reversibly store and release large amounts of lithium through a compound formation reaction with lithium, and much research has been conducted on this recently. For example, silicon is promising as a high-capacity anode material because its theoretical maximum capacity is approximately 4020 mAh / g (9800 mAh / cc, specific gravity 2.23), which is much higher than that of graphite-based materials. However, the above anode materials have the disadvantages of very large volume changes during charge and discharge and poor high-rate discharge characteristics.

[0012] Therefore, there is a need to improve the performance of cathode materials to achieve low expansion rate, a certain capacity, high output characteristics, and life characteristics.

[0013] In this regard, particularly in the case of natural graphite, pores reduce the density of the negative active material, making it difficult to manufacture high-density negative electrode plates. Furthermore, during the process of increasing the density of the negative active material layer on the current collector, the low-crystalline carbon coating breaks, exposing the graphite edges, which can lead to electrolyte-induced destruction and irreversible reactions.

[0014] Accordingly, various attempts are being made to develop cathode materials with excellent life characteristics by improving high-power characteristics and low-expansion capability, and there is a high need for technology that can fundamentally solve these problems while simultaneously realizing high-power characteristics and high energy density of cathode materials.

[0015] According to one embodiment of the present invention, a negative electrode active material for a lithium secondary battery is provided that can simultaneously implement high output characteristics and high energy density.

[0016] According to another embodiment of the present invention, a method for producing a negative electrode active material for a lithium secondary battery provides a method for producing a negative electrode active material having the above-described advantages.

[0017] According to one embodiment of the present invention, a negative active material for a lithium secondary battery includes natural graphite and satisfies the following equation 1.

[0018] <Formula 1>

[0019] 2.23 ≤ [D90] / [D10] ≤ 2.37

[0020] (In the above formula 1, [D10] and [D90] mean particle sizes corresponding to 10% and 90% of the cumulative volume of the negative active material measured using the laser diffraction method)

[0021] In one embodiment, the above formula 1 may be 2.26 to 2.36. Specifically, the average particle diameter (D50) of the negative active material may be 15.0 to 18.0 μm.

[0022] In one embodiment, the porosity measured by mercury intrusion porosimetry may be between 0.045 and 0.085 ml / g. In one embodiment, the porosity ratio measured by mercury intrusion porosimetry may be between 5.0 and 14.0%.

[0023] In one embodiment, a negative electrode active material for a lithium secondary battery may satisfy the following equation 2.

[0024] <Formula 2>

[0025] 0.50 ≤ [tap density (g / cm 3 )] / [BET specific surface area (m 2 / g)] ≤ 1.0

[0026] (The above [tab density (g / cm 3 )] and [BET surface area (m 2 / g)] is the tap density (g / cm) of the negative active material. 3 ) and the specific surface area)

[0027] In one embodiment, the negative active material for a lithium secondary battery has an orientation (I) in terms of XRD peak value 110 / I 004 ) satisfies the following equation 3.

[0028] <Formula 3>

[0029] 50.0 ≤ I 110 / I 004 ≤ 90.0

[0030] (In the above equation 3, I 004 is the peak intensity value on the 004 side, and I 110 refers to the peak intensity value on the 110 side)

[0031] In one embodiment, the negative active material for a lithium secondary battery has a density of 600 kg·f / cm 2 Pellet density of the bottom (g / cm) 3 ) can be between 1.50 and 1.85.

[0032] In one embodiment, a negative electrode active material for a lithium secondary battery may satisfy the following equation 4.

[0033] <Formula 4>

[0034] 0.100 ≤ (P1000-P600) / P400 ≤ 0.119

[0035] (In the above equation 4, P400, P600, and P1000 are 400, 600, and 1,000 kg·f / cm, respectively. 2 (means pellet density in )

[0036] According to another embodiment of the present invention, a method for manufacturing a negative electrode active material for a lithium secondary battery includes a step of spheroidizing natural graphite particles and a step of pressurizing the spheroidized natural graphite particles.

[0037] The negative active material can satisfy the following equation 1.

[0038] <Formula 1>

[0039] 2.23 ≤ [D90] / [D10] ≤ 2.37

[0040] (In the above formula 1, [D10] and [D90] mean particle sizes corresponding to 10% and 90% of the cumulative volume of the negative active material measured using the laser diffraction method)

[0041] In one embodiment, the step of spheroidizing the natural graphite may include a step of first spheroidizing the natural graphite particles, and a step of secondarily re-spheroidizing the first spheroidized natural graphite particles. In one embodiment, the step of pressing the spheroidized natural graphite particles may be performed through a cold isostatic press (CIP) method or a hot isostatic press (HIP) method.

[0042] In one embodiment, the step of pressurizing the spheroidized natural graphite particles may be applying a pressure of 250 MPa or more. In one embodiment, the step of spheroidizing the natural graphite particles may be adjusted so that the average particle diameter (D50) of the natural graphite particles is 14.0 to 18.0 μm.

[0043] In one embodiment, after the step of secondarily re-spheroidizing the primary spheroidized natural graphite particles, the method may further include a step of coating the re-spheroidized natural graphite particles with a low-crystalline carbon material.

[0044] According to one embodiment of the present invention, a negative electrode active material for a lithium secondary battery is formed by high-density spheroidization and cold isostatic pressing to form pores on the surface, thereby improving the mobility of lithium (Li) ions and making the crystal orientation more diversified, thereby providing a negative electrode active material capable of simultaneously realizing high output characteristics and high energy density.

[0045] According to another embodiment of the present invention, a method for manufacturing a negative electrode active material for a lithium secondary battery can provide a method for manufacturing a negative electrode active material having the above-described advantages by performing high-density spheroidization and cold isostatic pressing.

[0046] Figures 1a to 1d show SEM photographs of cross-sections of negative active materials according to examples and comparative examples of the present invention.

[0047] FIG. 2a and FIG. 2b are graphs of nitrogen porosity and mercury porosity according to examples and comparative examples of the present invention.

[0048] Figure 3 is a graph showing pellet density according to examples and comparative examples of the present invention.

[0049] Figures 4a and 4b are graphs showing room temperature life and high temperature life characteristics according to examples and comparative examples of the present invention.

[0050] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0051] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0052] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0053] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0054] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and the present invention is not limited thereto, and the present invention is defined solely by the scope of the claims set forth below.

[0055] According to one embodiment of the present invention, a negative electrode active material for a lithium secondary battery may include natural graphite. Specifically, the natural graphite may include spherical natural graphite that has undergone a spheroidization step, thereby providing a negative electrode active material for a lithium secondary battery with a high degree of spheroidization.

[0056] In one embodiment, the sphericity of the negative electrode active material for a lithium secondary battery may be 0.90 or greater. Specifically, the sphericity may be 0.925 or greater, and more specifically, 0.925 to 0.934. When the sphericity satisfies the above-described range, the density and orientation of the negative electrode active material may increase together, thereby improving the output characteristics and expansion characteristics of the negative electrode active material.

[0057] In one embodiment, a negative active material for a lithium secondary battery may satisfy the following equation 1.

[0058] <Formula 1>

[0059] 2.23 ≤ [D90] / [D10] ≤ 2.37

[0060] (In the above formula 1, [D10] and [D90] mean particle sizes corresponding to 10% and 90% of the cumulative volume of the negative active material measured using the laser diffraction method)

[0061]

[0062] The above equation 1 is a value obtained by dividing the particle size corresponding to 90% of the volume accumulation amount of the negative active material by the particle size corresponding to 10%, and may be an indicator of the particle size distribution according to the conditions of airflow classification and sieve classification in the manufacturing process of the negative active material. The above equation 1 may be 2.23 to 2.37. Specifically, the above equation 1 may be 2.23 to 2.36, and more specifically, 2.30 to 2.36.

[0063] If the above equation 1 exceeds the upper limit, the particle size ratio is relatively high, which causes a springback problem in the electrode. If the above equation 1 exceeds the lower limit, the amount classified increases, which causes a problem in the process yield.

[0064] In one embodiment, a particle size (D10) corresponding to 10% of the volume accumulation amount of the negative active material for a lithium secondary battery may be 8.5 to 15.0 μm. Specifically, the D10 may be 9.0 to 12.5 μm, and more specifically, 10.5 to 12.0 μm.

[0065] In one embodiment, the average particle diameter (D50), which is a particle diameter corresponding to 50% of the volume accumulation amount of the negative active material for a lithium secondary battery, may be 15.0 to 18.0 μm. Specifically, the average particle diameter (D50) may be 15.9 to 17.3 μm, and more specifically, 15.9 to 17.0 μm.

[0066] In one embodiment, the particle size (D90) corresponding to 90% of the volume accumulation amount of the negative active material for a lithium secondary battery may be 20.0 to 28.0 μm. Specifically, the D90 may be 21.0 to 27.0 μm, and more specifically, 23.0 to 26.5 μm.

[0067] If the above particle size exceeds the upper limit, the particle size ratio is relatively high, which causes springback problems in the electrode. If the above particle size exceeds the lower limit, the amount classified increases, which causes problems in process yield.

[0068] In one embodiment, the span value of the negative electrode active material for a lithium secondary battery may be 0.82 to 1.00. The span value is an indicator of the uniformity of the particles of the negative electrode active material, and may be a value calculated by (particle size (D90) corresponding to 90% of the volumetric accumulation amount of the negative electrode active material - particle size (D10) corresponding to 10% of the volumetric accumulation amount of the negative electrode active material) / particle size (D50) corresponding to 50% of the volumetric accumulation amount of the negative electrode active material. The span value may be 0.82 to 1.00, specifically 0.87 to 1.00, and more specifically 0.88 to 0.95.

[0069] If the above SPAN value exceeds the upper limit, the relative particle ratio increases, resulting in increased spring back of the electrode and uneven electrode manufacturing. If the above SPAN value exceeds the lower limit, the amount classified increases, resulting in problems with process yield.

[0070] In one embodiment, the pores (cm) of the negative electrode active material for a lithium secondary battery are determined by nitrogen adsorption. 2 / g) is 0.0025 to 0.0055 cm 2 / g. Specifically, the pores (cm) by the nitrogen adsorption method 2 / g) is 0.0025 to 0.0049 cm 2 / g, more specifically, 0.0025 to 0.0038 cm 2 / g, more specifically, 0.0025 to 0.0040 cm 2 / g could be.

[0071] If the porosity value obtained by the above nitrogen adsorption method exceeds the upper limit, there is a problem with high-temperature performance during charge and discharge. If the porosity value obtained by the above nitrogen adsorption method exceeds the lower limit, there is a problem in the electrode manufacturing process due to high hardness.

[0072] In one embodiment, the porosity of the negative active material for a lithium secondary battery measured by mercury porosimetry may be 0.045 to 0.085 ml / g. Specifically, the porosity measured by mercury porosimetry may be 0.050 to 0.079 ml / g, more specifically, 0.050 to 0.075 ml / g, and even more specifically, 0.052 to 0.060 ml / g.

[0073] If the porosity value measured by the above mercury intrusion method exceeds the upper limit, there is a problem with high-temperature performance during discharge. If the porosity value measured by the above mercury intrusion method exceeds the lower limit, there is a problem (due to high hardness during the electrode manufacturing process).

[0074] In one embodiment, the porosity ratio measured by mercury porosimetry may be from 5.0 to 14.0%. Specifically, the porosity ratio may be from 5.0 to 12.0%, more specifically from 6.0 to 10.0%, and even more specifically from 6.5 to 8.0%.

[0075] If the above pore ratio exceeds the upper limit, there will be problems with high-temperature performance during discharge. If the above pore ratio exceeds the lower limit, there will be problems in the electrode manufacturing process due to high hardness.

[0076] In one embodiment, a negative electrode active material for a lithium secondary battery may satisfy the following equation 2.

[0077] <Formula 2>

[0078] 0.50 ≤ [tap density (g / cm 3 )] / [BET specific surface area (m 2 / g)] ≤ 1.0

[0079] (The above [tab density (g / cm 3 )] and [BET surface area (m 2 / g)] is the tap density (g / cm) of the negative active material. 3 ) and the specific surface area)

[0080]

[0081] The above equation 2 refers to a value obtained by dividing the tap density of the negative active material by the BET specific surface area. The above equation 2 may be 0.50 to 1.0, specifically 0.60 to 1.0, and more specifically 0.70 to 0.90.

[0082] If the value of the above equation 2 exceeds the upper limit, the hardness increases, causing a problem in the electrode manufacturing process. If the value of the above equation 2 exceeds the lower limit, the roughness increases, causing a problem in side reactions.

[0083] In one embodiment, the negative active material has an orientation (I) in terms of XRD peak values. 110 / I 004 ) can satisfy the following equation 3.

[0084] <Formula 3>

[0085] 50.0 ≤ I 110 / I 004 ≤ 90.0

[0086] (In the above equation 2, I 004 is the peak intensity value on the 004 side, and I 110 refers to the peak intensity value on the 110 side)

[0087] The above orientation can be judged using JCPDS (ASTM) data as a standard data by X-ray diffraction, and means the value obtained by dividing the peak intensity value of the (110) plane by the peak intensity value of the (004) plane after measuring the (004) plane and (110) plane of the negative active material by XRD. The above equation 3 may be 65.0 to 90.0, specifically, 75.0 to 90.0, and more specifically, 80.0 to 88.5.

[0088] If the orientation exceeds the upper limit of the above range, the degree of processing required during the production of the active material increases, resulting in decreased yield and productivity. Furthermore, the roughness increases, necessitating surface area control. If the orientation exceeds the lower limit of the above range, swelling increases and charging characteristics deteriorate.

[0089] In one embodiment, the tap density (g / cm) of the negative electrode active material for a lithium secondary battery 3 ) is 1.10 g / cm 3 It can be ideal. Specifically, the tap density (g / cm 3 ) is 1.14 g / cm 3 Above, more specifically, 1.25 g / cm 3 It can be ideal. The more the tap density satisfies the aforementioned range, the better the electrochemical properties of the negative active material can be.

[0090] In one embodiment, the negative active material for a lithium secondary battery has a density of 400 kg·f / cm 2 Pellet density of the bottom (g / cm) 3 ) is 1.40 to 1.80 g / cm 3 It can be. Specifically, 400 kg·f / cm 2 Pellet density of the bottom (g / cm) 3 ) is 1.44 to 1.75 g / cm 3 , more specifically, 1.60 to 1.75 g / cm 3 , more specifically, 1.65 to 1.70 g / cm 3 It could be.

[0091] In one embodiment, the negative active material for a lithium secondary battery has a density of 600 kg·f / cm 2 Pellet density of the bottom (g / cm) 3 ) is 1.50 to 1.85 g / cm 3 It can be. Specifically, 600 kg·f / cm 2 Pellet density of the bottom (g / cm) 3 ) is 1.69 to 1.85 g / cm 3, more specifically, 1.70 to 1.85 g / cm 3 , more specifically, 1.75 to 1.80 g / cm 3 It could be.

[0092] In one embodiment, the negative active material for a lithium secondary battery has a density of 800 kg·f / cm 2 Pellet density of the bottom (g / cm) 3 ) is 1.60 to 1.95 g / cm 3 It can be. Specifically, 800 kg·f / cm 2 Pellet density of the bottom (g / cm) 3 ) is 1.68 to 1.90 g / cm 3 , more specifically, 1.72 to 1.85 g / cm 3 , more specifically, 1.75 to 1.80 g / cm 3 It could be.

[0093] In one embodiment, the negative active material for a lithium secondary battery has a density of 1000 kg·f / cm 2 Pellet density of the bottom (g / cm) 3 ) is 1.70 to 2.00 g / cm 3 It can be. Specifically, 800 kg·f / cm 2 Pellet density of the bottom (g / cm) 3 ) is 1.72 to 2.00 g / cm 3 , more specifically, 1.88 to 1.98 g / cm 3 , more specifically, 1.92 to 1.98 g / cm 3 It could be.

[0094] If the pellet density exceeds the upper limit, there is a problem of side reactions occurring when the structure collapses under applied pressure. If the pellet density exceeds the lower limit, there is a problem of low electrode density.

[0095] In one embodiment, a negative electrode active material for a lithium secondary battery may satisfy the following equation 4.

[0096] <Formula 4>

[0097] 0.100 ≤ (P1000-P600) / P400 ≤ 0.119

[0098] (In the above equation 4, P400, P600, and P1000 are 400, 600, and 1,000 kg·f / cm, respectively. 2 (means pellet density in )

[0099] The above equation 4 is 1000 kg·f / cm 2 Pellet density at 600 kg·f / cm 2 The difference in pellet density in 400 kg·f / cm 2 By pellet density value in , I mean a value. The value of the above formula 4 means 0.100 to 0.119, specifically, 0.101 to 0.118.

[0100] If the value of the above equation 4 exceeds the upper limit, there is a problem in that the electrode density is low, making it difficult to manufacture a high-energy-density electrode. If the value of the above equation 4 exceeds the lower limit, there is a problem in that a strong rolling process is required.

[0101] According to another embodiment of the present invention, a method for manufacturing an anode active material for a lithium secondary battery may include a step of spheroidizing natural graphite particles and a step of pressurizing the spheroidized natural graphite particles. By simultaneously including the spheroidizing step and the pressurizing step, the anode active material for a lithium secondary battery can minimize internal graphite porosity and increase particle density, thereby securing electrode manufacturing processability, and can provide an anode active material with minimized expansion rate and suppressed side reactions during repeated charge and discharge.

[0102] The step of spheroidizing the natural graphite particles may include a step of first spheroidizing the natural graphite particles and a step of secondarily respheroidizing the first spheroidized natural graphite particles.

[0103] The step of first spheroidizing the above natural graphite particles may be to spheroidize the plate-shaped graphite particles in order to use the spheroidized graphite material in the manufacture of a lithium secondary battery negative electrode active material. The step of first spheroidizing the above natural graphite particles may be to spheroidize the plate-shaped graphite particles using a general method for spheroidizing the plate-shaped graphite particles.

[0104] The step of secondary re-sphericizing the primary spheroidized natural graphite particles may be a step of further sphericizing the primary spheroidized natural graphite particles using a mechanical sphericization method. Through the additional re-sphericization, the degree of sphericity of the graphite material increases, and the properties of the negative electrode active material, such as tap density and orientation, are improved, thereby exhibiting improved effects such as suppressing expansion of the electrode. In this way, by performing high-density sphericization through the continuous processes of primary sphericization and secondary sphericization, the pores within the negative electrode active material can be minimized.

[0105] The above mechanical spheroidization method may utilize at least one of Air Classifying milling, Spheronizing milling, Grinding milling, Mechanofusion milling, Planetary milling, Hybridization milling, Shape milling, and High speed milling. By performing the above-described mechanical spheroidization method, the protruding portions of the primary spheroidized natural graphite particles are removed and compressed to spheroidize them, thereby improving the spheroidization degree and density of the negative electrode active material.

[0106] The above mechanical spheroidization method can be performed at a rotation speed of 500 to 4000 rpm. Specifically, the rotation speed can be 1000 to 3000 rpm, and more specifically, 1000 to 1500 rpm. When performed within the above range, cracking and destruction of the graphite raw material can be minimized.

[0107] In one embodiment, the step of spheroidizing natural graphite particles may be adjusted such that the average particle diameter (D50) of the natural graphite particles is 14.0 to 18.0 μm. Specifically, the average particle diameter (D50) of the natural graphite particles may be adjusted to 14.0 to 16.0 μm, and more specifically, to 14.0 to 15.0 μm.

[0108] Specifically, after the step of re-sphericizing the first spherical natural graphite particles, a particle size classification step may be further included. The particle size classification step may classify the natural graphite particles so that the average particle diameter (D50) is adjusted to the above-mentioned range. The particle size classification step may partially remove particles of 14.0 μm or less through airflow classification, and remove particles of 18.0 μm or more through sieve classification.

[0109] If the particle size classification step exceeds the lower limit, not only will the overall sphericity decrease due to the fine particles that are not spherical, but when applied as an anode active material, side reactions may increase, reducing efficiency. If the particle size classification step exceeds the upper limit, not only will it be difficult to control the orientation within the particles, but when applied as an anode active material, due to the increase in particle size, it will take time for lithium diffusion, which may lead to a problem of deterioration in input / output characteristics.

[0110] The step of pressurizing the spherical natural graphite particles may be a step of applying pressure to the spherical natural graphite particles. The step of pressurizing may be a step of reducing pores within the natural graphite particles to impart high density to the powder.

[0111] In one embodiment, the step of pressing the spheroidized natural graphite particles may be performed through a cold isostatic press (CIP) method or a hot isostatic press (HIP) method. Specifically, the pressing step may press the natural graphite particles through a cold isostatic press method.

[0112] In one embodiment, the step of pressurizing the spheroidized natural graphite particles may be a step of applying a pressure of 250 MPa or more. Specifically, the pressure may be 250 to 500 MPa, and more specifically, the pressure may be 300 to 350 MPa.

[0113] In one embodiment, the step of pressing the spherical natural graphite particles may include pressing for a time of 2 to 10 minutes. Specifically, the time may be 3 to 7 minutes.

[0114] If the pressurizing step exceeds the upper limit of the above time, there is a problem of the structure of the spherical graphite collapsing. If the pressurizing step exceeds the lower limit of the above time, there is a problem of difficulty in controlling the internal pores.

[0115] As pressure is applied within the aforementioned range, the reaction area between graphite and electrolyte is reduced, thereby suppressing side reactions and improving the battery's lifespan characteristics. As the graphite becomes denser, the tap density increases, and the pourability in high-density electrode plates can be improved. Specifically, volume expansion during cycling can be suppressed, similar to the suppression of graphite particle swelling.

[0116] After the step of spheroidizing natural graphite, a crushing step may be included. The crushing step may be a step of crushing the spheroidized natural graphite while controlling the particle size. In one embodiment, the crushing step may be controlled by physical impact. The physical impact may utilize equipment that utilizes physical impact, such as a jet mill, an air classifier mill (or air current classification mill), or a roller mill. The jet mill directly crushes particles by colliding high-pressure air current with particles, the air classifier crushes particles or classifies particles according to specific gravity by using air current, and the roller mill crushes particles by introducing, compressing, and crushing particles between two or more rollers that rotate in opposite directions.

[0117] In one embodiment, the crushing step may be a step of crushing the natural graphite particles to an average particle diameter (D50) of 13.0 to 17.0 μm. Specifically, the average particle diameter (D50) may be 13.5 to 15.0 μm.

[0118] If the average particle size of the natural graphite particles in the above-mentioned crushing step is outside the upper limit of the above-mentioned range, the coarse particle ratio is relatively high, which increases the spring back of the electrode, and there is a problem of unevenness in electrode manufacturing. If the average particle size of the natural graphite particles in the above-mentioned crushing step is outside the lower limit of the above-mentioned range, the fine particle ratio is relatively high, which increases the specific surface area of ​​the powder, and there is a problem of fairness in manufacturing the slurry.

[0119] In one embodiment, the crushing step after the pressurizing process may include a coarse crushing step and a fine crushing step. Including at least one crushing step allows for more precise control of the particle size of the graphite particles.

[0120] In one embodiment, the crushing step may crush the graphite lumps in a pressurized process to have an average particle size (D50) of 10 to 50 mm. Specifically, the average particle size (D50) may be crushed to 10 to 30 mm.

[0121] In one embodiment, the fine grinding step can grind the ground material that has undergone the coarse grinding step to an average size of 10 mm or less.

[0122] After the step of secondarily re-spheroidizing the first spheroidized natural graphite particles, a step of coating a low-crystalline carbon material on the re-spheroidized natural graphite particles may be further included. The low-crystalline carbon material may be at least one selected from the group consisting of petroleum pitch, coal pitch, mesophase 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.

[0123] In one embodiment, the low-crystalline carbon material may have a softening point of 200 to 270°C. Specifically, the softening point may be 240 to 260°C. If the softening point is outside the upper limit of the aforementioned range, there is a problem that the coking value is high and thus hardness increases. If the softening point is outside the lower limit of the aforementioned range, there is a problem that the coking value is low and thus specific surface area increases.

[0124] By coating the above-mentioned re-spheroidized natural graphite particles with a low-crystalline carbon material, when applying the negative electrode active material, side reactions due to the electrolyte are suppressed, irreversible reactions are reduced, and electrochemical characteristics are improved, which has the advantage of improving the properties.

[0125] In the coating layer forming step of coating a low-crystalline carbon material on the surface of the above-mentioned re-spheroidized graphite material, the content of the low-crystalline carbon material may be 0.1 to 20 parts by weight per 100 parts by weight of the re-spheroidized graphite material. When coated in the above-mentioned range of parts by weight, the graphite material and the low-crystalline carbon material can effectively form a bonding layer, and excellent life characteristics of the lithium secondary battery can be exhibited due to reduced side reactions and improved conductivity.

[0126] The step of forming a coating layer for coating a low-crystalline carbon material on the surface of the above-mentioned re-spheroidized graphite material forms the coating layer by a mechanical mixing method, and the mechanical mixing method 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, thinky mixing, homo mixing, and a stirrer.

[0127] The step of forming a coating layer by coating a low-crystalline carbon material on the surface of the above-mentioned re-spheroidized graphite material may further include a heat treatment step after mechanical mixing, and the heat treatment may be a step of heat treatment in an atmosphere of hydrogen, nitrogen, argon, or a mixed gas thereof at a temperature of 1,000 to 1,500°C. Specifically, the temperature may be 1,100 to 1,300°C.

[0128] According to another embodiment of the present invention, a lithium secondary battery may include a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a separator and an electrolyte positioned between the positive electrode and the negative electrode.

[0129] The above anode is LiCoO2, LiNiO2, LiNi x Mn y O2, Li 1+z Ni x Mn y Co 1-x-y O2, LiNi x Co y Al z Any one of the group consisting of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, LiFeO2, LiFePO4, and combinations thereof, wherein x is 0.3 to 0.8, y is 0.1 to 0.45, and z may independently be 0 to 0.2. The positive electrode may be more specifically LiFePO4, LiCoO2, NCM811, and NCM622.

[0130] The above negative electrode may use the negative electrode active material described above, or a negative electrode active material manufactured through a method for manufacturing a negative electrode active material.

[0131] The above separation membrane may be a conventional porous polymer film used as a separator in the past, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / propylene copolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, used alone or in a laminated manner, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc., may be used, and these are non-limiting examples.

[0132] In the above electrolyte, lithium salts that can be included as the electrolyte can be used without limitation as those commonly used in electrolytes for lithium secondary batteries, and for example, the anion of the lithium salt may be F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N -It can be any one selected from the group consisting of .

[0133] In the above electrolyte, as the organic solvent, those commonly used in electrolytes for lithium secondary batteries can be used without limitation, and representative examples thereof include one selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran, or a mixture of two or more thereof.

[0134] The above lithium secondary battery may be placed in a battery case. The battery case may be, as non-limiting examples, any one of a cylindrical shape using a can, a square shape, a pouch shape, and a coin shape.

[0135] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0136]

[0137] (Manufacture of negative active material)

[0138] <Example 1>

[0139] (1) Preparation of natural graphite powder

[0140] Primary spherical natural graphite powder with an average particle diameter (D50) of 16 ㎛ was prepared.

[0141]

[0142] (2) Cold Isostatic Pressing (CIP)

[0143] Afterwards, the spherical natural graphite powder was filled into a mold and a molded body was manufactured through a pressing process. The applied molding pressure was 300 MPa and the molding time was 5 minutes. Cold isostatic pressing was applied in the molding process.

[0144]

[0145] (3) Crushing stage

[0146] The molded sample is obtained as a graphite lump several tens of centimeters in size and is crushed into particles of 10 to 50 mm using a coarse crusher. The coarsely crushed graphite particles are then finely crushed through two processes: a pin mill to a particle size of 10 mm or less, and an air classifier to break up any remaining graphite particles.

[0147]

[0148] (4) Coating and heat treatment process

[0149] Pitch having a softening point of 250°C was mixed in an amount of 5 parts by weight based on 100 parts by weight of the pulverized sample. After mixing at 2,500 rpm for 10 minutes, heat treatment was performed at 1,200°C for 13 hours to obtain a negative electrode active material.

[0150]

[0151] (Manufacturing of cathode)

[0152] The negative active material powder, conductive material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener prepared by the above method were mixed in a mass ratio of Coin Half Cell (CHC) - 96.3:1:1.5:1.2 and Full Cell (FC) - 95.6:1.0:1.1:2.3, and water was added to prepare a negative active material slurry. The negative active material slurry was applied to a copper (Cu) foil current collector, and then dried and rolled to prepare each negative electrode. At this time, the loading of the negative electrode was CHC - 3.6 mAh / cm 2 , FC - 3.95 mAh / cm 2 It was manufactured as much as possible.

[0153] At this time, a separator made of a porous polypropylene film was inserted between the working electrode and the counter electrode, and as an electrolyte, a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 20:80 was used, in which vinylene carbonate (VC) was added at 0.5 wt% relative to the solvent, and 1.0 M concentration of LiPF6 was dissolved.

[0154]

[0155] <Example 2>

[0156] A negative active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a high-density spheroidization step was performed as follows. A detailed description of the high-density spheroidization step is as follows.

[0157]

[0158] (1)_1 High-density sphericalization stage

[0159] After preparing natural graphite powder, the natural graphite powder was subjected to secondary mechanical spheroidization treatment at 1,000 rpm for 15 minutes in a spheronizer, followed by air classification and sieve classification to remove fine and coarse particles, thereby producing high-density re-spheroidized natural graphite particles having an average particle diameter (D50) of 14.7 ㎛.

[0160]

[0161] <Comparative Example 1>

[0162] A negative active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the cold isostatic pressing (CIP) step was not performed.

[0163]

[0164] <Comparative Example 2>

[0165] A negative active material and a lithium secondary battery were manufactured in the same manner as in Example 2, except that the cold isostatic pressing (CIP) step was not performed.

[0166]

[0167] <Evaluation Example 1>: Properties of negative electrode active material

[0168] Table 1 below shows the properties of the negative electrode active materials of Examples 1 and 2 and Comparative Examples 1 and 2. The properties of the negative electrode active materials were measured by the following methods.

[0169] D10, D50, D90 (㎛): D10, D50, and D90 are particle sizes corresponding to 1%, 10%, 50%, 90%, and maximum values ​​of the volume accumulation amount of the negative active material measured using the Laser Diffraction Method, respectively.

[0170] Tap density (g / cm) 3 ): The tap density was measured using the AT-2 model of Quantachrome. After filling the test vessel with a sample volume of 20 ml, tapping was performed 3000 times, and the volume and weight of the sample were measured to obtain the ratio of weight per volume.

[0171] BET(m 2 / g): It refers to the total surface area of ​​the material per unit mass, and was measured using the BET method (Surface Area and Porosity Analyzer) (Micromeritics, ASAP2020).

[0172] Direction (I)110 / I 004 ): Using Bruker's XRD equipment, the XRD peak intensity values ​​of the 004 plane and 110 plane of the negative active material were measured, and then the peak intensity value of the 110 plane was divided by the peak intensity value of the 004 plane.

[0173] Nitrogen pores (cm) 3 / g): Using the equipment of Micrometics, ASAP2020, nitrogen was adsorbed on the sample and the pore size and volume were measured within the range of 150 nm or less.

[0174] Mercury Porosity (ml / g): The volume of mercury penetrating into the pores within the range of 3 nm to 2000 nm was measured using equipment from Micromeritics (Autopore V 9620).

[0175] Mercury porosity (%): (Measured by using equipment from Micromeritics (Autopore V 9620) by dividing the apparent density including the volume of pores by the density of the graphite volume, assuming the total volume to be 1, and subtracting the value from the total volume.

[0176] Pellet density (g / cm) 3 ):HanTech, Powder Resistivity Measurement System equipment is used to fill powder into an insulating mold, apply pressure, and analyze the change in characteristics at 400, 600, 800, and 1,000 kg·f / cm 3 Each was measured in .

[0177] Particle size distribution (㎛)D 90 / D 10 -(D90-D10) / D50 tab density [g / cm 3 ]BET(m 2 / g)Nitrogen pores (cm) 3 / g)Mercury pore (ml / g)Mercury pore (%)Tap density / BET orientation I 110 / I 004 D 10 D 50 D 90Example 111.417.325.82.260.831.142.220.00490.07612.00.5154.7Example 210.716.025.12.350.901.251.490.00340.0557.40.8486.8Comparative Example 110.717.325.62.390.861.092.870.00590.13415.10.3840.5Comparative Example 210.715.823.52.200.811.192.130.00390.08714.20.5660.2

[0178] Looking at Table 1 above, when comparing Examples 1 and 2 with Comparative Examples 1 and 2, it was confirmed that the particle size distribution, tap density, BET, nitrogen pores, mercury pores, orientation, and the range of D90 / D10 and tap density / BET formulas were included in the scope of the present invention. In addition, when comparing Examples 1 and 2, it was confirmed that Example 2 had a superior tap density, a lower specific surface area, and a lower porosity value due to nitrogen pores and mercury pores than Example 1. Figures 1a to 1d show SEM photographs of cross-sections of negative electrode active materials according to Examples and Comparative Examples of the present invention.

[0179] Figures 1a to 1d are SEM photographs of Example 1, Example 2, Comparative Example 1, and Comparative Example 2, respectively. Referring to Figures 1a to 1d, the porosity of the graphite cross-section can be confirmed. Looking at Figures 1a to 1d and Table 1 above, the values ​​for nitrogen pores decrease in the order of Comparative Example 1, Example 1, Comparative Example 2, and Example 2, and the values ​​for mercury pores decrease in the order of Comparative Example 1, Comparative Example 2, Example 1, and Example 2, confirming that the porosity is reduced through CIP.

[0180] FIG. 2a and FIG. 2b are graphs of nitrogen porosity and mercury porosity according to examples and comparative examples of the present invention.

[0181] Figure 2a shows a nitrogen porosity graph according to a gas adsorption method of an example and a comparative example of the present invention. Figure 2b shows a mercury porosity graph according to a mercury adsorption method of an example and a comparative example of the present invention.

[0182]

[0183] <Evaluation Example 2>: Pellet density of negative active material

[0184] Figure 3 is a graph showing pellet density according to examples and comparative examples of the present invention.

[0185] Table 2 below shows the pellet density of the negative active materials manufactured by Examples 1 and 2 and Comparative Examples 1 and 2.

[0186] Pellet density (g / cm) 3 )Formula 44006008001000(P1000-P600) / P400 * Classification [kg·f / cm 2 ]Example 11.441.551.641.720.118Example 21.681.771.861.950.107Comparative Example 11.351.471.571.650.133Comparative Example 21.581.671.771.860.120*P400, P600, P1000 are 400, 600, and 1,000 kg·f / cm, respectively. 2 Pellet density in

[0187] Looking at Table 2 and Figure 3 above, it can be confirmed that the examples are superior to the comparative examples in terms of pellet density. In addition, it was confirmed that the examples 1 and 2 fall within the scope of the present invention in terms of pellet density according to equation 4, but the comparative examples 1 and 2 do not fall within the scope of the present invention.

[0188] <Evaluation Example 3>: Electrochemical characteristics

[0189] Table 3 below shows the electrochemical characteristics of Coin Half Cells and Full Cells manufactured from the negative active materials manufactured in Examples 1 and 2 and Comparative Examples 1 and 2.

[0190] The measurement method for the above electrochemical properties is as follows.

[0191] Evaluation of Initial Capacity (mAh / g) and Initial Efficiency (%) of Coin Half Cells: After fabricating half cells of lithium secondary batteries, they were aged at 25°C for 48 hours and then subjected to charge-discharge tests. Using an electrochemical analyzer (WonATech), the initial capacity and efficiency were measured after three charge-discharge cycles under the conditions of 25°C, a potential range of 0.005 to 1.5 V, and a current density of 0.36 mA / cm2.

[0192]

[0193] Evaluation of Initial Capacity (mAh) and Initial Efficiency (%) of Full Cell: After manufacturing a lithium secondary battery, a charge / discharge test was conducted after aging at 25℃ for 30 hours. For the initial capacity evaluation, the capacity was designed to be 770 mAh based on 0.33C, and charged to 4.2 V with a constant current of 0.1C, then switched to constant voltage and charged until the end current reached 0.05C. After a rest time of 10 minutes after charging, the battery was discharged to 2.75 V with a constant current of 0.1C, using 770 mAh / g as the reference capacity.

[0194]

[0195] Evaluation of expansion rate (%): After discharging the coin cell, the cell was separated and the cathode thickness was measured using a Mitutoyo micrometer device.

[0196] Life characteristics (25 ℃ or 45 ℃): A constant current of 1 C was applied, and when the voltage reached 4.25 V, the constant voltage was maintained and the battery was charged until the current reached 0.05 C. After a 10-minute rest period, the battery was discharged by applying a constant current of 1 C until the voltage reached 2.5 V. The life evaluation was conducted at room temperature of 25 ℃ and at a high temperature of 45 ℃, respectively.

[0197] Coin Half CellFull CellDischarge Capacity[mAh / g]Initial Efficiency[%]Expansion Rate[%]Room Temperature Lifespan0.5C / 1C Cycle[%]High Temperature Lifespan0.5C / 0.5C Cycle[%]Example 1363.593.819.795.890.5Example 2360.293.919.497.492.0Comparative Example 1363.494.023.895.389.7Comparative Example 2360.493.521.595.890.0

[0198] Referring to Table 3 above, it was confirmed that Examples 1 and 2 were superior to Comparative Examples 1 and 2 in terms of electrochemical characteristics of the battery. Specifically, it was confirmed that Examples 1 and 2 were superior to Comparative Examples 1 and 2 in terms of discharge capacity and initial efficiency, had a lower expansion rate, and had superior room temperature life and high temperature life characteristics. FIGS. 4a and 4b are graphs showing room temperature life and high temperature life characteristics according to Examples and Comparative Examples of the present invention.

[0199] Figure 4a shows the characteristics of the examples and comparative examples at room temperature of 25°C, and Figure 4b shows the characteristics of the examples and comparative examples at a high temperature of 45°C. Referring to Figures 4a and 4b, when comparing Examples 1 and 2 with Comparative Examples 1 and 2, it can be confirmed that the lifespan characteristics of Examples 1 and 2 are superior. In addition, when comparing Examples 1 and 2, it was confirmed that the effect of Example 2, which went through the high-density spheroidization and cold isostatic pressing steps, was more superior.

[0200] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the following claims also fall within the scope of the present invention.

Claims

1. Contains natural graphite, A negative electrode active material for a lithium secondary battery satisfying the following equation 1. <Formula 1> 2.23 ≤ [D90] / [D10] ≤ 2.37 (In the above formula 1, [D10] and [D90] mean particle sizes corresponding to 10% and 90% of the cumulative volume of the negative active material measured using the laser diffraction method) 2. In paragraph 1, The above formula 1 is a negative active material for a lithium secondary battery having a molecular weight of 2.26 to 2.

36.

3. In paragraph 1, A negative electrode active material for a lithium secondary battery, wherein the average particle diameter (D50) of the negative electrode active material is 15.0 to 18.0 ㎛.

4. In paragraph 1, A negative active material for a lithium secondary battery having a porosity of 0.045 to 0.085 ml / g as measured by mercury porosimetry.

5. In paragraph 1, A negative active material for a lithium secondary battery having a porosity ratio of 5.0 to 14.0% as measured by mercury porosimetry.

6. In paragraph 1, A negative electrode active material for a lithium secondary battery satisfying the following equation 2. <Formula 2> 0.50 ≤ [tap density (g / cm 3 )] / [BET specific surface area (m 2 / g)] ≤ 1.0 (The above [tab density (g / cm 3 )] and [BET surface area (m 2 / g)] is the tap density (g / cm) of the negative active material. 3 ) and the specific surface area) 7. In paragraph 1, In terms of XRD peak values, the orientation (I 110 / I 004 ) is a negative electrode active material for a lithium secondary battery that satisfies the following equation 3. <Formula 3> 50.0 ≤ I 110 / I 004 ≤ 90.0 (In the above equation 3, I 004 is the peak intensity value on the 004 side, and I 110 refers to the peak intensity value on the 110 side) 8. In paragraph 1, 600 kg·f / cm 2 Pellet density of the bottom (g / cm) 3 ) is 1.50 to 1.

85.

9. In paragraph 1, A negative electrode active material for a lithium secondary battery satisfying the following equation 4. <Formula 4> 0.100 ≤ (P1000-P600) / P400 ≤ 0.119 (In the above equation 4, P400, P600, and P1000 are 400, 600, and 1,000 kg·f / cm, respectively. 2 (means pellet density in ) 10. Step of spheroidizing natural graphite particles; and Comprising a step of pressurizing the spherical natural graphite particles, A method for manufacturing a negative electrode active material for a lithium secondary battery satisfying the following equation 1. <Formula 1> 2.23 ≤ [D90] / [D10] ≤ 2.37 (In the above formula 1, [D10] and [D90] mean particle sizes corresponding to 10% and 90% of the cumulative volume of the negative active material measured using the laser diffraction method) 11. In paragraph 10, The step of spherizing the above natural graphite is A step of first spherizing the above natural graphite particles; and A method for producing a negative electrode active material for a lithium secondary battery, comprising a step of secondarily re-sphericizing the first spherical natural graphite particles.

12. In paragraph 10, A method for manufacturing a negative electrode active material for a lithium secondary battery, wherein the step of pressing the spherical natural graphite particles is performed through a cold isostatic press (CIP) method or a hot isostatic press (HIP) method.

13. In paragraph 12, A method for producing a negative electrode active material for a lithium secondary battery, wherein the step of pressing the spherical natural graphite particles is to apply a pressure of 250 MPa or more.

14. In paragraph 10, A method for producing a negative electrode active material for a lithium secondary battery, wherein the step of spheroidizing the natural graphite particles is performed to adjust the average particle diameter (D50) of the natural graphite particles to 14.0 to 18.0 ㎛.

15. In paragraph 10, A method for producing a negative electrode active material, further comprising, after the step of secondarily re-spheroidizing the first spheroidized natural graphite particles, a step of coating the re-spheroidized natural graphite particles with a low-crystalline carbon material.

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