KR20220036931A - Negative electrode material for rechargeable lithium battery, method for manufacturing the same, and rechargeable lithium battery including the same - Google Patents

Abstract

The present disclosure relates to a method for manufacturing a negative electrode active material for a lithium secondary battery, and a negative electrode active material for a lithium secondary battery manufactured therefrom, wherein the method includes the steps of: providing primary particles from a carbon raw material; inputting the primary particles and a binder into a continuous twin-shaft assembling device; manufacturing secondary particles by assembling the primary particles and the binder input in the continuous twin-shaft assembling device; and graphitizing the assembled secondary particles, and the carbon raw material has volatile content of 25 wt% or less.

Description

Anode active material for lithium secondary battery, manufacturing method thereof, and lithium secondary battery comprising same

The present disclosure relates to an anode active material for a lithium secondary battery and a method for manufacturing the same. Specifically, the present disclosure relates to an excellent negative active material for a lithium secondary battery by replacing the existing process and a method for manufacturing the same. In addition, the present disclosure relates to an anode for a lithium secondary battery including an excellent anode active material for a lithium secondary battery, and a lithium secondary battery including the same.

Since the graphite/carbon-based negative active material used as a negative electrode of a lithium secondary battery has a potential close to the electrode potential of lithium metal, the crystal structure change during insertion and desorption of ionic lithium is small, so continuous and repeated oxidation at the electrode By enabling the reduction reaction, the lithium secondary battery provided a basis for exhibiting high capacity and excellent lifespan.

As the carbon-based negative electrode active material, various types of materials such as natural graphite and artificial graphite, which are crystalline carbon-based materials, or hard carbon and soft carbon, which are amorphous carbon-based materials are used. Among them, a graphite-based active material that has excellent reversibility and can improve the lifespan characteristics of a lithium secondary battery is most widely used. Since the graphite-based active material has a low discharge voltage of -0.2 V compared to lithium, a battery using the graphite-based active material can exhibit a high discharge voltage of 3.6 V, providing many advantages in terms of energy density of lithium secondary batteries.

Artificial graphite, a crystalline carbon-based material, generates a crystal structure of graphite by applying high thermal energy of 2,700 ° C. . In general, artificial graphite-based negative electrode active material has a lifespan of 2-3 times longer than that of natural graphite.

Soft carbon and hard carbon, which are amorphous carbon-based materials in which the crystal structure is not stabilized, have a more smooth advance of lithium ions. Therefore, the charging/discharging speed can be increased, so that it can be used for an electrode requiring high-speed charging. Therefore, in consideration of the lifespan characteristics and output characteristics of the lithium secondary battery to be used, it is common to mix and use the carbon-based materials in a certain ratio with each other.

On the other hand, improving high-temperature performance (high-temperature storage characteristics and high-temperature cycle characteristics) in a lithium secondary battery is an important task to solve. If the total internal pore volume is high after the anode active material is applied to the current collector and rolled, the high-temperature performance of the anode is highly likely to be deteriorated. Therefore, it is necessary to improve the high-temperature characteristics of the lithium secondary battery by minimizing the change in the structure of the electrode and the change in the total internal pore volume that occurs during electrode rolling. In particular, when developing an anode material for a secondary battery for rapid charging, improvement of high-temperature characteristics is further demanded.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing, and among such secondary batteries, lithium secondary batteries exhibiting high energy density and operating potential, long cycle life, and low self-discharge rate. Batteries have been commercialized and widely used.

In addition, as interest in environmental problems grows, interest in electric vehicles and hybrid electric vehicles that can replace vehicles using fossil fuels such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, is increasing. Research for using a lithium secondary battery as a power source for electric vehicles, hybrid electric vehicles, etc. is being actively conducted.

A lithium secondary battery is generally composed of a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator, and an electrolyte, and is a secondary battery in which charging and discharging are performed by intercalation-decalation of lithium ions. Lithium secondary batteries have advantages of high energy density, high electromotive force, and high capacity, and thus are being applied to various fields.

A metal oxide such as LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ or LiCrO ₂ is used as a positive active material constituting the positive electrode of a lithium secondary battery, and as a negative active material constituting the negative electrode, metal lithium, graphite (graphite) ) or a carbon-based material such as activated carbon, or a material such as silicon oxide (SiOx) is used. Among the anode active materials, metallic lithium was mainly used in the beginning, but as the charging and discharging cycle proceeds, lithium atoms grow on the metallic lithium surface to damage the separator and damage the battery. Recently, carbon-based materials are mainly used. The graphite-based material exhibits excellent capacity retention characteristics and efficiency, and in the theoretical capacity value (eg, about 372 mAh/g for a LiC ₆ anode), until it achieves the theoretical characteristics of high energy and high power density required by the relevant market. It is still somewhat lacking.

In particular, due to the rapid rise of EV electric vehicles in recent years, the demand for lithium-ion secondary batteries is also rapidly increasing. However, in the case of the anode material process, various efforts have been made to overcome the technical limitations of the continuous manufacturing technology due to the limitations of the batchwise assembly process.

Accordingly, regarding the process of assembling secondary particles in a continuous manner (made as secondary particles by adding a binder such as coke + pitch, which is the primary particle), several anode material makers slightly modified the existing batching process to continue the vertical secondary particles. A method of feeding, dropping, and heat treatment was introduced, but a separate heat treatment was required, and there was a problem in that mixing was not performed before. This is because, in the direction from top to bottom, in the assembly method by air flow, the residence time cannot be long, so quality deterioration in the aspect of uniform mixing is inevitable. (i.e. not properly pitched properly adhered to the parent coke).

In particular, in the case of green coke, it is difficult to use because it has not undergone a calcination process (heat treatment of 1000 degrees or more) and has a high volatile matter (VM, volatile material) content of 5% or more. Heat treatment for the use of the coke is considered essential in order to reduce material cost repeatedly in the industry in recent years.

Even if a separate heat treatment is performed in the future, this negatively affects the assembly uniformity, and there is a problem in that the negative electrode material characteristics are inferior even after the subsequent graphitization process, so improvement is needed.

An object of the present disclosure is to provide a method for manufacturing a negative active material for a lithium secondary battery that replaces the conventional batch-type assembly process, and an excellent anode active material for a lithium secondary battery prepared therefrom. In addition, the present disclosure intends to provide an anode and a lithium secondary battery using an excellent anode active material.

The negative active material for a lithium secondary battery according to an exemplary embodiment of the present disclosure is a graphite material including secondary particles, wherein the secondary particles are an assembly of a plurality of primary particles, and the secondary particles have a sphericity of 0.85 based on a total particle diameter to 1.0.

The secondary particles may have a sphericity of 0.85 to 1.0 based on a partial particle diameter having an average of 5 to 15 μm.

The secondary particles may have a sphericity of 0.85 to 1.0 based on a partial particle diameter having an average of 15 to 25 μm.

The secondary particles may have a tap density of 0.8 to 1.2 g/cc.

A ratio ((D90-D10)/D50) of the difference between the D90 particle diameter and the D10 particle diameter to the D50 particle diameter of the secondary particles may be 1.4 or less.

A method of manufacturing a negative active material for a lithium secondary battery according to an embodiment of the present disclosure, the method comprising: providing primary particles from a carbon source; inputting the primary particles and the binder into a continuous twin-screw granulator; manufacturing secondary particles by assembling the primary particles and the binder input in the continuous twin-screw granulator; and graphitizing the assembled secondary particles; and, the carbon raw material may have a volatile content of 25 wt% or less.

The carbon raw material may be green coke.

The binder may have a pitch having a softening point of 200° C. or less.

inputting the primary particles and the binder into a continuous twin-screw granulator; It may further include the step of mixing the primary particles and the binder at room temperature before.

inputting the primary particles and the binder into a continuous twin-screw granulator; In the binder may be added in an amount of 10 to 20% by weight based on the weight of the primary particles.

The step of preparing secondary particles by assembling the primary particles and the binder input in the continuous twin-screw granulator; is at a point greater than 30% to less than 80% in the traveling direction with respect to the entire length of the twin-screw granulator, volatile matter using the exhaust gas It may include the step of removing.

Providing primary particles from the carbon raw material; may include grinding and grinding the carbon raw material.

The primary particles provided in the step of providing primary particles from the carbon source may have a particle size D50 of 5 to 14 μm.

In the step of assembling the primary particles and the binder introduced in the continuous twin-screw granulator to prepare secondary particles; the assembled secondary particles may have a sphericity of 0.85 to 1.0 based on the total particle diameter.

A lithium secondary battery according to an embodiment of the present disclosure includes a negative electrode including an anode active material for a lithium secondary battery prepared by any one of the above; anode; and an electrolyte solution.

According to one embodiment of the present disclosure, a negative active material may be provided using a continuous granulator.

In addition, according to one embodiment of the present disclosure, volatile matter can be effectively removed through the external exhaust pipe of the continuous granulator, so that low-quality coke having a high volatile content can be used.

In addition, according to one embodiment of the present disclosure, there is no need to go through a separate carbonization process due to an increase in the internal temperature of the continuous granulator.

In addition, according to one embodiment of the present disclosure, spheroidization is made inside the continuous granulator, and there is no need to go through a separate spherical process.

In addition, according to one embodiment of the present disclosure, an incidental process can be omitted by using a continuous granulator, which is useful in terms of process efficiency and cost reduction.

1 is a view of an anode active material prepared by the manufacturing method of an embodiment of the present disclosure with a scanning electron microscope (SEM).
2 is an observation of the negative active material prepared by a conventional manufacturing method with a scanning electron microscope (SEM).

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 only 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.

The terminology used herein is for the purpose of referring to specific embodiments only, and is not intended to limit the present invention. As used herein, the singular forms also include the plural forms unless the phrases clearly indicate the opposite. The meaning of "comprising," as used herein, specifies a particular characteristic, region, integer, step, operation, element and/or component, and includes the presence or absence of another characteristic, region, integer, step, operation, element and/or component. It does not exclude additions.

When a part is referred to as being “on” or “on” another part, it may be directly on or on the other part, or the other part may be involved in between. In contrast, when a part is referred to as being "directly above" another part, the other part is not interposed therebetween.

In addition, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

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 art to which the present invention belongs. Commonly used terms defined in the dictionary are additionally interpreted as having a meaning consistent with the related technical literature and the presently disclosed content, and unless defined, are not interpreted in an ideal or very formal meaning.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily implement them. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein.

The present disclosure intends to present a superior assembly through a continuous process that can replace the existing batch-type assembly process. In the case of this continuous assembly process, it is different from the existing assembly process using airflow because the assembly process is carried out in a closed space. This is a spheroidizing effect of coke (primary particles) through maximizing frictional force using a closed structure (which is an increase in internal temperature) and, in particular, when using a binder pitch with a low softening point, a separate carbonization process is not required. There are great advantages in

Hereinafter, each step will be described in detail.

The negative active material for a lithium secondary battery according to an exemplary embodiment of the present disclosure is a graphite material including secondary particles, wherein the secondary particles are an assembly of a plurality of primary particles, and the secondary particles have a sphericity of 0.85 based on a total particle diameter to 1.0. Specifically, the sphericity may be 0.88 to 1.0, more specifically, 0.91 to 1.0.

The secondary particles may have a sphericity of 0.85 to 1.0 based on a partial particle diameter having an average of 5 to 15 μm. Specifically, the sphericity may be 0.87 to 1.0, more specifically 0.93 to 1.0.

The secondary particles may have a sphericity of 0.85 to 1.0 based on a partial particle diameter having an average of 15 to 25 μm. Specifically, the sphericity may be 0.89 to 1.0, more specifically 0.90 to 1.0.

The closer the sphericity is to 1, the higher the tap density, and the fewer side reaction sites, the better the sphericity is.

The secondary particles may have a tap density of 0.8 to 1.2 g/cc. Specifically, the tap density may be 0.8 to 1.2 g/cc, more specifically 0.8 to 1.2 g/cc. In the case of a negative active material including a graphite material, the smaller the specific surface area and the larger the tap density, the better the battery characteristics when applied to a lithium secondary battery.

A ratio ((D90-D10)/D50) of the difference between the D90 particle diameter and the D10 particle diameter to the D50 particle diameter of the secondary particles may be 1.4 or less. The particle sizes of 10, D50, and D90 refer to particle sizes when particles of active material having various particle sizes are accumulated up to 10%, 50%, and 90% by volume, respectively.

Accordingly, when the ratio of the difference between the D90 particle diameter and the D10 particle diameter to the D50 particle diameter of the graphite material is too small, in order to industrially process a powder having a very small particle size deviation, the production yield may be greatly reduced and the cost may increase. In addition, since the porosity between the powders is relatively low, the wettability of the electrolyte decreases, which may cause a problem in that the ion conductivity in the electrode decreases, and it is difficult to construct an electrode having a high tap density.

On the other hand, if the ratio of the difference between the D90 and D10 particle diameters to the D50 particle diameter is too large, the total specific surface area due to fine powder increases, reducing the initial charge/discharge efficiency, and the viscosity of the slurry for electrode coating increases significantly, resulting in a uniform quality electrode There may be problems that are difficult to manufacture.

D10 of the secondary particles may be 6 to 9 μm, D50 may be 14 to 20 μm, and D90 may be 23 to 33 μm.

A method of manufacturing an anode active material according to an embodiment of the present disclosure includes providing primary particles from a carbon source; inputting the primary particles and the binder into a continuous twin-screw granulator; manufacturing secondary particles by assembling the primary particles and the binder input in the continuous twin-screw granulator; and graphitizing the assembled secondary particles; and, the carbon raw material may have a volatile content of 25 wt% or less. Since the method for manufacturing a negative active material according to an exemplary embodiment of the present disclosure is manufactured using a continuous twin-screw granulator, low-quality coke having a volatile content of up to 25% by weight can be used. Specifically, the carbon raw material may contain 4 to 25% by weight of volatile matter, more specifically 4 to 10% by weight.

The continuous twin-screw granulator is a method of assembling two closed horizontal square screws while rotating, and it is possible to obtain an assembly in a molded form through compression/expansion rather than coating of particles using an existing airflow. It tends to be assembled with a higher density, and frictional heat of about 200°C or more is generated through friction between particles in a closed rotation method inside. This makes it possible to assemble secondary particles without a separate carbonization process when using a coal-based pitch having a low softening point, so there is no need for a separate carbonization process.

The carbon raw material may be green coke. Specifically, when green coke is used, it is possible to provide an anode active material for a lithium secondary battery having a low expansion rate and excellent fast charging and discharging characteristics. In addition, when green coke is used, price competitiveness may be excellent because a separate heat treatment process is not performed to remove volatiles like calcined coke. For reference, a heat-treated product obtained by calcining or carbonizing green coke to remove volatiles is referred to as "calcined coke".

The binder may have a pitch having a softening point of 200° C. or less. Specifically, the softening point may be 80 to 200 ℃, more specifically 80 to 150 ℃ or less. When the softening point of the binder is too low, it is difficult to smoothly bond between primary particles and form secondary particles due to low binding force, and it is difficult to implement an economical manufacturing process due to a low carbonization yield. On the other hand, when the softening point is too high, the operating temperature of the equipment for melting the binder material is high, which increases the manufacturing cost of the equipment and may cause problems in that thermal denaturation and carbonization of some samples according to the use of high temperature proceed.

The pitch may be a coal-based raw material such as coal tar or a petroleum-based raw material-based material.

inputting the primary particles and the binder into a continuous twin-screw granulator; It may further include the step of mixing the primary particles and the binder at room temperature before. The primary particles and the binder may be added directly to the twin-screw granulator without prior mixing, or may be added by pre-mixing.

The step of mixing the primary particles and the binder at room temperature may be a step of mixing using a Hansel mixer or a V-mixer.

inputting the primary particles and the binder into a continuous twin-screw granulator; In , the binder may be added in an amount of 3 to 30% by weight based on the weight of the primary particles. Specifically, it may be added in an amount of 10 to 20% by weight, more specifically, 13 to 18% by weight.

When the content of the binder is too low, the binding effect is small and smooth secondary particle formation may not be achieved. In addition, since the binding force between the primary particles in the secondary particles is reduced, a problem of easily being pulverized during a powder treatment process such as pulverization may occur. On the other hand, when the content of the binder is too high, the capacity of the negative electrode material may be reduced because the content of graphite derived from the binder is relatively high. In addition, the high pore content generated during thermal decomposition may increase the specific surface area, thereby reducing battery efficiency.

The step of preparing secondary particles by assembling the primary particles and the binder input in the continuous twin-screw granulator; is at a point greater than 30% to less than 80% in the traveling direction with respect to the entire length of the twin-screw granulator, volatile matter using the exhaust gas It may include the step of removing. Specifically, the step of removing volatiles by using the exhaust gas may be performed at a point of 40 to 70%, more specifically, 50 to 60% in the moving direction. If volatile matter is removed at a point less than 30% from the moving direction, there is a problem that a lot of volatile matter remains in the final assembly. there may be If a large amount of volatile matter remains, the extruder is clogged and the process cannot proceed, or a separate heat treatment is required later to increase the process cost, or the electrochemical properties as a negative electrode active material after graphitization may be poor.

The exhaust gas may be any inert gas, for example, N ₂ , Ar, and He may be at least one selected from the group consisting of.

In addition, there may be two or more points at which volatile matter is removed using the exhaust gas, and at least one point is preferably located at a point that is more than 30% to less than 80% in the traveling direction with respect to the entire length of the twin-screw granulator.

Providing primary particles from the carbon raw material; may include grinding and grinding the carbon raw material.

First, in the step of pulverizing the carbon raw material, the pulverizer may use a jet-mill, a roller mill, or a general type continuous or batch pulverizer capable of performing air classification at the same time as pulverization. . However, the present invention is not limited thereto.

Thereafter, a step of grinding the pulverized carbon raw material may be performed. A grinding process is performed to reduce the roughness of the surface of the pulverized carbon raw material and the exposure of the fracture surface generated during pulverization, and to form spheronized particles. The grinding step may be performed at 1500 to 8000 rpm/min rotation speed. Specifically, the grinding process generally increases the sphericity of the pulverized particles to improve the packing density or tap density, which is the apparent density, and removes the pulverized region through additional air classification during the process. Thus, it can function to improve the particle size distribution more uniformly. The apparatus for the grinding process may use a general pulverizer or a modified pulverizer capable of improving the spheroidizing effect and finely classifying the particles. However, the present invention is not limited thereto.

The primary particles provided in the step of providing primary particles from the carbon source may have a particle size D50 of 5 to 14 μm. Specifically, the particle diameter (D50) of the primary particles may be 5.5 to 10㎛. Specifically, it may be 6 to 10 μm.

First, in the present specification, the D50 particle size refers to the particle size when the particles of the active material having various particle sizes distributed are accumulated up to 50% by volume. Specifically, when the particle diameter of the primary particles is too small, the particle diameter of the secondary particles to be prepared may be smaller than the intended purpose. In addition, since the specific surface area becomes excessively high, the amount of the binder added in the secondary particle manufacturing step may be increased. For this reason, it may be difficult to implement a high-capacity negative electrode material because the content of graphite derived from the binder is high. On the other hand, when the particle diameter of the primary particle is too large, the particle diameter of the secondary particle manufactured by using the particle diameter is excessively increased to decrease the tap density, so it may be difficult to form a high-density electrode. Accordingly, it may be difficult to realize high output during charging and discharging. In addition, the electrode orientation may increase, thereby increasing the electrode expansion rate during charging and discharging.

In the step of assembling the primary particles and the binder introduced in the continuous twin-screw granulator to prepare secondary particles; the assembled secondary particles may have a sphericity of 0.85 to 1.0 based on the total particle diameter.

The step of graphitizing the assembled secondary particles; may be carried out at a temperature of 2500 to 3200 ℃.

One embodiment of the present disclosure includes a negative electrode comprising a negative active material for a lithium secondary battery prepared by the above-described manufacturing method; anode; And it may provide a lithium secondary battery comprising an electrolyte.

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

Example

(1) Manufacturing and evaluation of negative electrode active materials

The secondary particles assembled by the conventional batch method and the secondary particles assembled by the continuous granulation method of the present invention were compared.

The coke used was two kinds of uncalcined petroleum-based green needle coke, and a commonly used commercial product was obtained and used. The pitch used as the binder is a coal-based material having a softening point of 100° C., and a commercially used commercially available product was obtained and used. The physical properties and mixing ratios of coke and binder are shown in Table 1 below.

cokes binder pitch Coke:Binder Ratio fair type particle size
D10 (μm) Particle size D50 (㎛) Particle size D90 (㎛) Tap density (g/cc) VMs (%) Petroleum Green Needle Coke A 3.1 5.8 12.7 0.6 8 Coal-based (softening point 100 degrees, D50: 5um) 100:13 Continuous (invention) Petroleum Green Needle Coke B 6.9 13.3 21.4 0.64 7.7 Coal-based (softening point 100 degrees) 100:13 Continuous (invention) Petroleum Green Needle Coke A 3.1 5.8 12.7 0.6 8 Coal-based (softening point 100 degrees) 100:13 Batch type (existing) Petroleum Green Needle Coke B 6.9 13.3 21.4 0.64 7.7 Coal-based (softening point 100 degrees) 100:13 Batch type (existing)

Examples 1 and 2 of Table 1 were assembled using a twin screw molding extruder (Kneader) rotating in opposite directions. The length of the screw shaft was 3.5 m, the rotation speed was 13 rpm, and the residence time was 27 minutes. The residence time refers to the time it takes for materials such as coke and binder to be put in and discharged into the assembled secondary particles. In addition, an external exhaust pipe for removing volatile matter (VM) using exhaust gas was installed at a point 2.1 m in the direction of travel with respect to the entire screw shaft length. The flue gas used at this time was nitrogen gas (N ₂ ). The feed green coke and binder were put into the hopper of the molding extruder without prior mixing. In addition, Examples 1 and 2 were evaluated as obtained by a screw molding machine, and a separate carbonization process was not performed. Comparative Examples 1 and 2 in Table 1 were assembled in the conventional batch method. The amount of feed put into the batch was 45 kg, and the processing time was 12 hours. Carbonized secondary particles were obtained by heat treatment at 800° C. for 3 hours while forming an airflow by rotating the blades in the vertical direction.

In the case of the continuous granulation of Examples 1 and 2, the production amount was 10 kg/h, and in the case of Comparative Examples 1 and 2, which are conventional batch types, the production amount was 4 kg/h, and in the case of continuous assembly, the production amount was It was found to be overwhelmingly excellent.

Table 2 below shows the results of evaluating the properties of the secondary particles assembled from Examples 1 and 2 and Comparative Examples 1 and 2.

cokes binder pitch Coke:Binder Ratio fair assembly type particle size
D10 (μm) Particle size D50 (㎛) Particle size D90 (㎛) Tap density (g/cc) VMs (%) Petroleum Green Needle Coke A Coal-based (softening point 100 degrees, D50: 5um) 100:13 Continuous (invention) 6.5 14.7 25.9 1.05 2.8 Petroleum Green Needle Coke B Coal-based (softening point 100 degrees) 100:13 Continuous (invention) 8.9 19.2 32.3 0.81 2.7 Petroleum Green Needle Coke A Coal-based (softening point 100 degrees) 100:13 Batch type (existing) 4.8 20.5 34.6 0.65 1.5 Petroleum Green Needle Coke B Coal-based (softening point 100 degrees) 100:13 Batch type (existing) 7.7 22.8 45.6 0.76 1.9

In the case of the secondary particles of Examples 1 and 2 assembled in a continuous manner, the tap density was improved compared to the secondary particles of Comparative Examples 1 and 2 assembled in a conventional batch manner. In addition, particle sizes D10, D50, The deviation between D90 is small in Examples 1 and 2 compared to Comparative Examples 1 and 2, indicating that the particle size distribution is narrow, that is, the particle size is more uniform. In particular, in the case of particle size D10, since there was no significant difference compared to the case of Comparative Examples 1 and 2, which are conventional batch types, compared to before assembly, it was found that local granulation was performed compared to the Example.

In terms of the amount of volatile matter (VM), it can be seen that Examples 1 and 2 satisfy the criteria for introduction to the graphitization process because the volatile matter does not exceed 4 wt%.

It can be seen that Examples 1 and 2 that did not go through the carbonization process and Comparative Examples 1 and 2 that had undergone the carbonization process showed no difference in the evaluation results. can

Thereafter, the secondary particles obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were graphitized at 2800° C. to prepare a negative electrode active material, and the discharge capacity in the third cycle of the half-cell including the negative electrode to which it was applied was evaluated did

In order to evaluate the discharge capacity, 97% by weight of the negative electrode active material of Examples 1 and 2 and Comparative Examples 1 and 2, 2% by weight of a binder containing carboxymethyl cellulose and styrene butadiene rubber, and 1% by weight of a carbon black conductive material in distilled water solvent Each negative active material slurry was prepared by mixing. The prepared slur was applied to a copper current collector, dried at 100° C. for 10 minutes, and compressed in a roll press. Thereafter, it was vacuum dried in a vacuum oven at 100° C. for 12 hours to prepare an electrode density of 1.5 to 1.7 g/cc.

As the electrolyte, 1 mol of LiPF ₆ solution was dissolved in a mixed solvent of ethylene carbonate (EC, Ethylene Carbonate): dimethyl carbonate (DMC, Dimethyl Carbonate) in a volume ratio of 1:1, and lithium metal was used as the positive electrode. , The negative electrode of Examples 1 to 2 and Comparative Examples 1 and 2 was evaluated using the negative electrode, respectively.

The evaluation results are shown in Table 3 below.

Electrochemical evaluation after graphitization Discharge capacity (mAh/g) efficiency(%) 354 92 356 93 353 92 358 91

As a result of the discharge capacity evaluation, it was confirmed that Examples 1 and 2, which were not subjected to a separate carbonization process using a continuous screw molding extruder, exhibited the same level of discharge capacity as Comparative Examples 1 and 2, which were subjected to a carbonization process. In particular, in the case of Examples 1 and 2, it was found that the effect of reducing the cost by omitting the carbonization process in that it exceeded the commercialization level of 350 mAh/g can be achieved by introducing a continuous screw molding extruder.

(2) Evaluation of sphericity

The sphericity of the active material obtained by graphitizing the secondary granulated particles of Examples 1 and 2 and Comparative Examples 1 and 2 was evaluated.

Sphericity was measured using a particle shape analyzer (Particle Image Analyzer, Model: FlowCAM 8100-B). The closer the sphericity is to 1, the closer the shape is to a smooth sphere, and the closer the negative electrode material is to the sphere, the higher the tap density and the fewer side reaction sites.

Table 4 below is a measurement of the sphericity of Examples 1 and 2 and Comparative Examples 1 and 2, and the sphericity for the total particle diameter, the sphericity for the partial particle diameter of 5 to 15 μm, and the sphericity for the partial particle diameter of 15 to 25 μm Each degree of sphericity was measured and shown.

cokes fair Standard deviation type Jeon Ik-kyung Partial particle size (5-15㎛) Partial particle size (15-25㎛) Petroleum Green Needle Coke A Continuous (invention) 0.91 (0.09) 0.93 (0.08) 0.90 (0.12) Petroleum Green Needle Coke B Continuous (invention) 0.88 (0.11) 0.87 (0.12) 0.89 (0.09) Petroleum Green Needle Coke A Batch type (existing) 0.72 (0.12) 0.75 (0.11) 0.70 (0.12) Petroleum Green Needle Coke B Batch type (existing) 0.75 (0.09) 0.84 (0.09) 0.83 (0.07)

In the case of Comparative Examples 1 and 2 subjected to batch carbonization, it was found that the degree of sphericity was inferior to that of Examples. In particular, Comparative Examples 1 and 2 were found to be very inferior in the degree of sphericity in the total particle size, because, in the case of batch production, local granulation occurs, and there are many fine powders of 5 μm or less. 1 and 2, it can be seen that FIG. 1 of the continuously manufactured embodiment has a spherical surface compared to FIG. 2, and FIG. 2 of the conventional batch type has fine powder scattered therein.

On the other hand, in the case of Examples 1 and 2 using a continuous screw molding extruder, the sphericity was excellently 0.85 or more. A spheroidization degree of 0.85 or higher is equivalent to the result of going through a separate spheronization process in the case of conventional batch assembly, which is accompanied by a spheroidization effect through the screw inside the continuous granulator, so there is no need for a separate spheronization operation existing in the existing process, It was found that the final assembly exhibited excellent sphericity even if the coke fed into the feed used a low grade with poor sphericity.

(3) volatile matter removal process test

In order to remove volatiles from the continuous screw molding extruder, the degree of volatile matter removal according to the position of the external exhaust pipe to remove volatiles (VM) using exhaust gas was tested.

When the direction in which the assembly is discharged from the inlet through which the feed is supplied to the continuous screw molding extruder was set as the traveling direction, the volatile matter removal efficiency was measured by installing external exhaust pipes at various positions. The volatile matter removal efficiency was measured by performing elemental analysis of the discharged assembly to measure the decrease in the volatile matter content.

An external exhaust pipe using N ₂ as an exhaust gas was installed at 30%, 50%, 70%, and 80% positions in the traveling direction relative to the overall length. The feed used was the same as in Example 1.

As a result, when the external exhaust pipe was installed at the 30% position in the traveling direction, the removal efficiency was 70% or less, the removal efficiency was 95% at the 50% position, and the removal efficiency was 96% at the 70% position. At the position of 80% in the direction of travel, the volatile matter could not be measured because the volatile matter had already not been released and accumulated inside and did not knead. That is, at the 80% position in the moving direction, the internal material became sticky and prevented the movement of the screw, making it impossible to obtain an assembly properly.

Therefore, it can be seen that when the external exhaust pipe is installed at a position of more than 30% to less than 80% of the total length in the feed direction, the volatile matter removal efficiency is high, so that low-grade coke with a volatile content of up to 25% can be used. However, it was found that even when the volatile matter is only 25.5%, the screw rotation is difficult even if there is an external exhaust pipe due to the excessive volatile matter.

The present invention is not limited to the embodiments, but can be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains can use other specific forms without changing the technical spirit or essential features of the present invention. It will be appreciated that this may be practiced. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (15)

Graphite material containing secondary particles,
The secondary particles are a plurality of primary particles assembled,
The secondary particles have a sphericity of 0.85 to 1.0 based on the total particle diameter,
The ratio of the difference between the D90 particle diameter and the D10 particle diameter to the D50 particle diameter of the secondary particles ((D90-D10)/D50) is 1.4 or less, the negative active material for a lithium secondary battery.
According to claim 1,
The secondary particles have an average degree of sphericity of 0.85 to 1.0 based on a partial particle diameter of 5 to 15 μm, an anode active material for a lithium secondary battery.
According to claim 1,
The secondary particles have a sphericity of 0.85 to 1.0 based on a partial particle diameter of 15 to 25 μm on average, A negative active material for a lithium secondary battery.
According to claim 1,
The secondary particles have a tap density of 0.8 to 1.2 g/cc, an anode active material for a lithium secondary battery.
According to claim 1,
D10 of the secondary particles is 6 to 9 μm, D50 is 14.7 to 20 μm, and D90 is 23 to 33 μm, a negative active material for a lithium secondary battery.
providing primary particles from a carbon source;
inputting the primary particles and the binder into a continuous twin-screw granulator;
manufacturing secondary particles by assembling the primary particles and the binder input in the continuous twin-screw granulator; and
Including; graphitizing the assembled secondary particles;
The carbon raw material has a volatile content of 25% by weight or less, and a method of manufacturing an anode active material for a lithium secondary battery.
7. The method of claim 6,
The carbon raw material is green coke, a method for producing a negative active material for a lithium secondary battery.
7. The method of claim 6,
The binder is a softening point of 200 ℃ or less pitch, a method of manufacturing a negative electrode active material for a lithium secondary battery.
7. The method of claim 6,
inputting the primary particles and the binder into a continuous twin-screw granulator; Before
A method of manufacturing a negative active material for a lithium secondary battery, further comprising the step of mixing the primary particles and the binder at room temperature.
10. The method of claim 6 or 9,
inputting the primary particles and the binder into a continuous twin-screw granulator; at
The binder is added in an amount of 10 to 20% by weight based on the weight of the primary particles, a method of manufacturing a negative active material for a lithium secondary battery.
7. The method of claim 6,
Preparing secondary particles by assembling the primary particles and the binder input in the continuous twin-screw granulator;
A method of manufacturing a negative active material for a lithium secondary battery, comprising the step of removing volatiles using exhaust gas at a point of more than 30% to less than 80% in the traveling direction with respect to the entire length of the twin-screw granulator.
7. The method of claim 6,
providing primary particles from the carbon source;
A method of manufacturing a negative active material for a lithium secondary battery, comprising the step of pulverizing and grinding the carbon raw material.
7. The method of claim 6,
In the step of providing primary particles from the carbon source
The provided primary particles have a particle size D50 of 5 to 14 μm, a method of manufacturing an anode active material for a lithium secondary battery.
7. The method of claim 6,
In the step of assembling the primary particles and the binder input in the continuous twin-screw granulator to prepare secondary particles;
The method of claim 1, wherein the assembled secondary particles have a sphericity of 0.85 to 1.0 based on a total particle diameter.
A negative electrode comprising an anode active material for a lithium secondary battery prepared according to any one of claims 6 to 14;
anode; and
A lithium secondary battery containing an electrolyte.

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