KR20230094219A - Anode active material for lithium secondary battery and method of manufacturing thereof - Google Patents

Abstract

The present invention relates to a negative electrode active material for lithium secondary batteries and a manufacturing method thereof. The negative electrode active material for lithium secondary batteries according to one embodiment of the present invention, which is a negative electrode active material derived from coke, comprises: graphite particles; and a carbon coating layer disposed on the graphite particles, wherein the carbon coating layer contains 10 to 20 parts by weight based on 100 parts by weight of the graphite particles, the amount of fixed carbon in the carbon coating layer is 20% or more, the carbon coating layer is a coal tar-derived material, and the coal tar may have a quinoline insoluble content (QI) of less than 2 wt% with respect to the total weight% of the coal tar. According to the present invention, it is possible to manufacture a battery with excellent tap density, stability, and lifespan characteristics during electrode manufacturing without affecting the change in particle size of a negative electrode material.

Description

Negative active material for lithium secondary battery and manufacturing method thereof

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

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

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 as the carbon-based negative electrode active material. Among them, a graphite-based active material capable of improving the lifespan characteristics of a lithium secondary battery due to its excellent reversibility 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 the lithium secondary battery.

Since the artificial graphite, which is a crystalline material, creates a crystal structure of graphite by applying high thermal energy of 2,700 ° C. or more, it has a more stable crystal structure than natural graphite, so that the change in the crystal structure is small even after repeated charging and discharging of lithium ions, and thus has a relatively long lifespan. long. In general, artificial graphite-based negative active materials have a lifespan two to three times longer than natural graphite.

Soft carbon and hard carbon, which are amorphous carbon-based materials in which crystal structures are not stabilized, have characteristics in which lithium ions advance more smoothly. Accordingly, the charging and discharging rates can be increased, so that it can be used for electrodes requiring high-speed charging. In consideration of the lifespan characteristics and output characteristics of a lithium secondary battery to be used, it is common to mix the carbon-based materials with each other in a predetermined ratio.

On the other hand, improving high-temperature performance related to high-temperature storage characteristics and high-temperature cycle characteristics in lithium secondary batteries is one of the important challenges. After the negative electrode active material is applied to the current collector and rolled, if the internal total pore volume is high, the high-temperature performance of the negative electrode 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 generated during electrode rolling.

Specifically, when developing a negative electrode material for a secondary battery for rapid charging, improvement of the high-temperature characteristics is further required. As technology development and demand for mobile devices increase, demand for secondary batteries as an energy source is rapidly increasing. Among the secondary batteries, a lithium secondary battery having high energy density and operating potential, long cycle life, and low self-discharge rate has been commercialized and widely used.

In addition, as interest in environmental issues 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 into the use of lithium secondary batteries as a power source for the electric vehicles and hybrid electric vehicles is being actively conducted.

A lithium secondary battery is a secondary battery composed of a positive electrode including a general positive electrode active material, a negative electrode including a negative electrode active material, a separator, and an electrolyte, and is charged and discharged by intercalation and decalation of lithium ions. Lithium secondary batteries have advantages of high energy density, large electromotive force, and high capacity, and thus are 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 electrode active material constituting the positive electrode of a lithium secondary battery, and as a negative electrode 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 (SiO _x ) is used.

Among the negative electrode active materials, metal lithium was initially mainly used, but as the charge and discharge cycle progresses, lithium atoms grow on the surface of metal lithium to damage the separator and damage the battery. Recently, carbon-based materials are mainly used. Graphite-based materials exhibit excellent capacity retention characteristics and efficiency, and in theoretical capacity values, there is a problem in that they do not reach the theoretical characteristics of high energy and high power density required by the related market.

Recently, due to the rapid rise of electric vehicles, expectations for lithium secondary batteries are also increasing. While the capacity of the existing lithium secondary battery is preserved as it is, there is an increasing demand for improving rapid charging characteristics. The improvement of such rapid charging is mainly composed of carbon/graphite-based materials, which cannot play a role in the anode active material responsible for storing lithium ions during charging, so the formation of a stable SEI (Solid Electrolyte Interface) is important during charging. do. Accordingly, there is a need for research on an anode material with fast charging and life stability secured.

A technical problem to be solved by the present invention is to provide an anode material that secures rapid charging and lifetime stability when applied to a lithium secondary battery.

Another technical problem to be solved by the present invention is to provide a method for manufacturing an anode material having the above advantages.

According to an embodiment of the present invention, the negative active material is a negative active material derived from coke, includes graphite particles and a carbon coating layer disposed on the graphite particles, and includes at least one spherical particle among the graphite particles, The carbon coating layer is included in an amount of 10 to 20 parts by weight based on 100 parts by weight of the graphite particles, the fixed carbon content of the carbon coating layer is 20% or more, the carbon coating layer is a material derived from coal tar, and the coal tar has quinoline insoluble content (QI) It may be less than 2% by weight based on the total weight% of the coal tar. In one embodiment, the spherical particles may have a size distribution within 10 to 25% of the D90 of the negative electrode active material.

In one embodiment, the spherical particles may have a value represented by one peak in the particle size distribution of the negative electrode active material. In one embodiment, the d (002) spacing, which is the interplanar spacing of the graphite layers, may be 0.3354 to 0.3362 nm.

In one embodiment, the coal tar may have a fixed carbon content of 20% or more based on the total weight of the coal tar. In one embodiment, the fixed carbon content of the spherical graphite particles may be 99% or more.

In one embodiment, the particle size (D50) of the negative electrode active material may be 11 to 20 μm. In one embodiment, the tap density of the negative electrode active material may be 0.70 or more. In one embodiment, the coke may be derived from any one of coal-based, petroleum-based, or a combination thereof.

According to another embodiment of the present invention, a method for manufacturing an anode active material includes finely pulverizing coke particles, graphitizing the pulverized product, mixing the graphitized product with a binder, and carbonizing the mixed product. In the step of mixing the graphitized product with a binder, the binder further includes 10 to 20 parts by weight based on 100 parts by weight of coke, the fixed carbon content of the binder is 20% or more, and the binder It is a material derived from coal tar, and the binder may have a quinoline insoluble component (QI) of less than 2% by weight based on the total weight% of the coal tar.

In one embodiment, the step of pulverizing the coke particles may have an average particle diameter (D50) of 6 to 12 μm. In one embodiment, the step of graphitizing the pulverized product may be performed at 2,700 °C or higher.

In one embodiment, the step of carbonizing the mixed product may be performed at 800 °C or higher. In one embodiment, the volatile matter content of the coal-based or petroleum-based coke may be greater than 1%.

Since the negative electrode material according to an embodiment of the present invention includes a small amount of spherical particles, it is possible to manufacture a battery having excellent tap density, stability, and lifespan characteristics during electrode manufacturing without affecting the particle size change of the negative electrode material.

According to another embodiment of the present invention, the method for manufacturing an anode material provides a method for manufacturing an anode material having the above advantages, by mixing a cathode material composed of only graphitized single particles and a binder without a separate kneading process, thereby improving stability. And a battery with excellent lifespan characteristics can be manufactured.

1 shows a photograph of a structure of an anode active material for a lithium secondary battery according to an embodiment of the present invention.
2 is a flowchart of a method for manufacturing an anode active material according to an embodiment of the present invention.
3a and 3b show a photograph of a structure of an anode active material for a lithium secondary battery according to a comparative example of the present invention.

Terms such as first, second and third are used to describe, but are not limited to, various parts, components, regions, layers and/or sections. These terms are only used 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 only for referring to specific embodiments 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 particular characteristics, regions, integers, steps, operations, elements and/or components, and the presence or absence of other characteristics, regions, integers, steps, operations, elements and/or components. Additions are not excluded.

When a part is referred to as being “on” or “on” another part, it may be directly on or on the other part or may be followed by another part therebetween. In contrast, when a part is said to be “directly on” another part, there is no intervening part between them.

Although not defined differently, all terms including technical terms 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. Terms defined in commonly used dictionaries are additionally interpreted as having meanings consistent with related technical literature and currently disclosed content, and are not interpreted in ideal or very formal meanings unless defined.

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

1 shows a photograph of a structure of an anode active material for a lithium secondary battery according to an embodiment of the present invention.

Referring to FIG. 1, an anode active material for a lithium secondary battery according to an embodiment of the present invention is a cathode active material derived from coke, and includes graphite particles and a carbon coating layer disposed on the graphite particles. It includes at least one spherical particle among the particles. The coke may be at least one of coal-based coke, petroleum-based coke, or a combination thereof.

The graphite particles may be derived from the coke. The graphite particles may be artificial graphite obtained by processing and heat-treating the coke, which is a carbon body obtained by heat-treating an organic material such as coal or petroleum residue. Since the artificial graphite is not an assembled product, but is a single particle itself and is not assembled, the artificial graphite used as a raw material in manufacturing the negative electrode active material does not include a structure such as a soft carbon adhesive or a hard carbon adhesive.

At least one spherical particle among the graphite particles is included. In one embodiment, the size distribution of the spherical particles may be within a range of 10 to 25% of D90 based on the particle size distribution of the negative electrode active material. The D90 means a particle size when the particles of the active material in which various particle sizes are distributed are accumulated up to 90% in a region with a low volume ratio. If it is lower than the above range, it acts as a powder and there is a problem of lowering capacity and efficiency when applying the battery.

In one embodiment, the spherical particles may have a value represented by one peak in the particle size distribution of the negative electrode active material. The peak means the largest area on a normal distribution when measuring particle size, and the peak may be, for example, D50 or a median value. Specifically, the peak means a peak formed at the highest level by gathering a large number of particle sizes on a normal distribution.

When no peak is formed, there is a problem in that the spherical particles are not formed, and when two or more peaks are formed, the content of the spherical particles increases, thereby reducing the tap density during lithium secondary battery manufacturing. there is a problem with As such, the spherical particles have only one peak in the particle size distribution of the negative electrode active material, so it can be confirmed that they are included in a small amount that does not affect the particle size distribution of the negative electrode active material.

In one embodiment, the content of the spherical particles may range from 10 to 25% in the negative electrode active material. When the spherical particles include a content lower than the lower limit of the content range, there is a problem in that the advantages expressed by including the spherical particles are not expressed, and the spherical particles include a content higher than the upper limit of the content range In this case, as the number of spherical particles in the negative electrode active material increases excessively, there is a problem in that the tap density decreases. In one embodiment, the fixed carbon content of the spherical particles may be 99% or more.

The carbon coating layer disposed on the graphite particles may be obtained by sintering a binder. The binder may be a pitch, and the pitch may be a material based on a coal-based raw material such as coal tar or a petroleum-based raw material. The pitch may be well coated on the graphite particles. In one embodiment, the binder may be included in an amount of 10 to 20 parts by weight based on 100 parts by weight of the graphite particles. A detailed description thereof will be described later in the manufacturing method.

In one embodiment, the volatile matter content of the carbon coating layer may be 1% or more. In one embodiment, the carbon coating layer may be a material derived from coal tar. In one embodiment, the coal tar may contain less than 2% by weight of quinoline insoluble (QI) based on the total weight% of the coal tar. When the content of the quinoline insoluble content is high, there is a problem in that the electrode is deteriorated after being manufactured as a negative electrode material.

In one embodiment, the coal tar may have a fixed carbon content of 20% by weight or more based on the total weight% of the coal tar. Specifically, the fixed carbon content of the coal tar may be 20 to 30% by weight. When the amount of fixed carbon does not satisfy the above content, a problem of inferior secondary battery performance such as discharge capacity and battery efficiency may occur.

Specifically, when the amount of fixed carbon is excessively large, it is difficult to liquefy, and it is uneconomical in that a desired advantage cannot be obtained through liquid coating and a separate process is required. When the amount of fixed carbon is excessively small, the rotation rate of the mixer must be increased when mixing with artificial graphite to realize the function as a coating material, and as the rotation rate increases, the temperature inside the mixer and the mixture rises, resulting in deterioration of battery performance. there is

In one embodiment, the negative electrode active material may have a d ₍₀₀₂₎ spacing between graphite layers measured through XRD of 0.3354 to 0.3362 nm. The interplanar spacing of the graphite layers refers to the spacing between the carbons constituting the graphite in the graphite in which carbon is stacked. When the interplanar spacing of the graphite layers satisfies the above range, there is an advantage in that insertion and desorption of lithium ions moving along with charging and discharging of the lithium secondary battery proceed smoothly.

In one embodiment, the particle size (D50) of the negative electrode active material may be 11 to 20 μm. The D50 means the particle size when the particles of the active material in which various particle sizes are distributed are accumulated up to 50% in a region with a low volume ratio. If it is lower than the above range, there is a problem of capacity and efficiency deterioration with the spherical negative electrode (MCMB), and if it is higher than the above range, there is a problem of peeling from the current collector during electrode manufacturing.

In one embodiment, the tap density of the negative electrode active material may be 0.70 or more. As the tap density increases, higher density of the electrode layer and increase in energy density can be expected. When the tap density is lower than 0.70, electrode slurry properties deteriorate, making it difficult to manufacture a negative electrode material.

2 is a flowchart of a method for manufacturing an anode active material according to an embodiment of the present invention.

Referring to FIG. 2 , a method for manufacturing an anode active material according to an embodiment of the present invention includes pulverizing coke particles (S100), graphitizing the pulverized result (S200), and combining the graphitized result with a binder. It includes mixing (S300) and carbonizing the mixed resultant (S400). A detailed description of the coke particles and the negative electrode active material produced by the above steps is as described in detail with reference to FIG. 1 .

The step of pulverizing the coke particles (S100) is a step of crushing the coke particles finely. The pulverizing step is a non-limiting example, and various types of particle size control methods such as a jet mill, a pin mill, an air classifier mill, a Raymond mill, a jaw crusher, and a vertical roller mill may be utilized.

In one embodiment, in the step of pulverizing the coke particles (S100), the average particle diameter (D50) of the coke particles may be classified into 6 to 12 μm. When the average particle diameter is excessively small, there is a problem in that a large amount of the binder is required when granulating using a binder as a fine powder, and there is a problem in capacity reduction as the binder increases. If the average diameter is excessively large, there is a problem of power deterioration during battery manufacturing.

In the step of graphitizing the pulverized product (S200), coke particles may be graphitized using a graphitization furnace such as an Acheson furnace. In one embodiment, the step of graphitizing the pulverized product (S200) may be performed at a temperature of 2,700 °C or higher. When graphitization is performed at a temperature lower than the above temperature range, there is a problem in that excessive time is required for graphitization of the coke particles.

In one embodiment, the step of graphitizing the pulverized product may be performed in an inert atmosphere. The inert atmosphere may be implemented in an atmosphere such as nitrogen, argon, and helium, as non-limiting examples.

In the step of mixing the graphitized product with a binder (S300), 10 to 20 parts by weight of the binder may be added and mixed based on 100 parts by weight of the graphitized product. In one embodiment, the binder may be loaded in the mixing reactor above the graphitized product. This is to ensure that the binder can be spread and applied as uniformly as possible to the graphitized product.

As the binder is included in the range of parts by weight, spherical particles are formed in an appropriate range, and the tap density is excellent and stability can be obtained when manufacturing a lithium secondary battery.

When the binder is out of the upper limit of the range, the content of the spherical particles is excessively increased, resulting in a decrease in tap density during manufacture of a lithium secondary battery. When the binder is out of the lower limit of the range, there is a problem in that the content of the spherical particles is not formed within an appropriate range.

Carbonizing the mixed product (S400) is to carbonize the graphite particles on which the coating layer is formed by mixing with the binder. Carbonizing the mixed product (S400) may be performed at a temperature range of 1,000 °C to 1,200 °C. When the lower limit of the temperature range is exceeded, the volatile content removal rate is low, resulting in a lower quality of the final product, and when the upper limit of the temperature range is exceeded, unnecessary energy consumption occurs at a temperature close to graphitization in graphitization. there is

The carbonizing step (S400) may be performed after the graphitizing step (S200). By performing graphitization before carbonizing the coke particles, there is an advantage in that the output of the battery is excellent when manufacturing the battery. In addition, in the manufacturing method, there is a reduction in process and cost. On the other hand, when the graphitization step follows the carbonization step, there is a problem in that a yield is lowered due to loss (Loss) occurs.

As such, the anode active material prepared through the above steps includes at least one or more spherical graphite particles, and by including a small amount of the spherical graphite particles, the tap density is excellent, the discharge capacity is excellent, and the efficiency is excellent when manufacturing an electrode. It is possible to manufacture an excellent lithium secondary battery.

A lithium secondary battery according to another embodiment of the present invention includes a negative electrode including the negative active material for a lithium secondary battery or the negative active material prepared by the negative active material manufacturing method described above; anode; and electrolytes. Specifically, the lithium secondary battery may further include a separator disposed between the positive electrode and the negative electrode.

The negative electrode may be prepared by preparing a composition for forming a negative electrode active material layer by mixing the negative electrode active material prepared according to an embodiment of the present invention, a binder, and optionally a conductive material, and then applying the composition to the negative electrode current collector. . Copper foil may be used as the anode current collector.

The binder is polyvinyl alcohol, carboxymethylcellulose/styrene-butadiene rubber, hydroxypropylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene or poly Propylene or the like may be used, but is not limited thereto.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and specifically, graphite such as natural graphite and artificial graphite; carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used. The conductive material may be mixed in an amount of 0.1 wt % to 30 wt % based on the total amount of the composition for forming the negative electrode active material layer.

The positive electrode may be prepared by preparing a composition for forming a positive electrode active material layer by mixing a positive electrode active material, a binder, and optionally a conductive material, and then applying the composition to a positive electrode current collector. At this time, the binder and the conductive material are used in the same way as in the case of the negative electrode.

The anode is LiCoO ₂ , LiNiO ₂ , LiNi _x Mn _y O ₂ , Li _1+z Ni _x Mn _y Co _1-xy O ₂ , LiNi _x Co _y Al _z O ₂ , LiV ₂ O ₅ , LiTiS ₂ , LiMoS ₂ , LiMnO ₂ , LiCrO ₂ , LiMn ₂ O ₄ , LiFeO ₂ , LiFePO ₄ , and any one of the group consisting of combinations thereof, wherein x is 0.3 to 0.8, y is 0.1 to 0.45, and z is independently It can be 0 to 0.2. The positive electrode may be more specifically LiFePO ₄ , LiCoO ₂ , NCM811, and NCM622.

For the positive current collector, for example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver may be used. As the cathode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used.

As an electrolyte filled in the lithium secondary battery, a non-aqueous electrolyte or a known solid electrolyte may be used, and a lithium salt dissolved therein may be used. The lithium salt is, for example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiCl, and at least one selected from the group consisting of LiI may be used.

Examples of the solvent for the non-aqueous electrolyte include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; Chain carbonates, such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone; ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, and 2-methyltetrahydrofuran; nitriles such as acetonitrile; Amides such as dimethylformamide may be used, but are not limited thereto. These may be used singly or in combination of a plurality of them. In particular, a mixed solvent of a cyclic carbonate and a chain carbonate can be preferably used.

As the electrolyte, a gel polymer electrolyte obtained by impregnating an electrolyte solution into a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li ₃ N may be used. The separator may be made of chemically resistant and hydrophobic olefin-based polymers such as polypropylene; A sheet or non-woven fabric made of glass fiber, polyethylene, or the like may be used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may serve as a separation membrane.

Hereinafter, specific embodiments of the present invention will be described. However, the following examples are only specific examples of the present invention, but the present invention is not limited to the following examples.

<Manufacture of negative electrode active material>

Comparative Example 1

After heating coal-based needle coke (D10: 3 μm, D50: 8 μm, D90: 12 μm) at 2,800 ° C. for 1 hour and generating graphite particles, the fixed carbon content is 20% and the quinoline insoluble content 5 parts by weight of the liquid binder of less than 1.5% based on 100 parts by weight of the coal-based needle coke was added and mixed. The mixing step was carried out for 30 minutes. After the mixing step, the mixture was carbonized at 1,200 ° C. for more than 1 hour to obtain a negative electrode Ash was made.

Example 1

Compared to Comparative Example 1, the particle size of the coal-based needle coke was adjusted to D10: 4 μm, D50: 8 μm, and D90: 25 μm, and the liquid binder was added at 10 parts by weight based on 100 parts by weight of the coal-based needle coke. Other than that, it was carried out in the same manner as in Comparative Example 1.

Example 2

In contrast to Comparative Example 1, the particle size of the coal-based needle coke was adjusted to D10: 7 μm, D50: 14 μm, D90: 28 μm, and the liquid binder was added at 15 parts by weight based on 100 parts by weight of the coal-based needle coke. Other than that, it was carried out in the same manner as in Comparative Example 1.

Example 3

Compared to Comparative Example 1, the particle size of the coal-based needle coke was adjusted to D10: 8 μm, D50: 20 μm, D90: 34 μm, and the liquid binder was added in 20 parts by weight based on 100 parts by weight of the coal-based needle coke. Other than that, it was carried out in the same manner as in Comparative Example 1.

Comparative Example 2

Compared to Comparative Example 1, the particle size of the coal-based acicular coke was adjusted to D10: 12 μm, D50: 23 μm, and D90: 38 μm, and the liquid binder was added in 25 parts by weight based on 100 parts by weight of the coal-based needle coke. Other than that, it was carried out in the same manner as in Comparative Example 1.

Table 1 below shows the amount of binder input, particle size distribution, and the number of particle size peaks expressed, the presence or absence of formation of spherical particles, and the tap density of the negative electrode material XRD analysis of Comparative Examples 1 and 2 and Examples 1 to 3. At this time, the number of particle size peaks means that the spherical graphite particles have a D50 or Dmean value represented by one peak in the particle size distribution of the negative electrode active material, and means the peak formed with the highest particle size on a normal distribution. . Specifically, it means the highest, sharpest part.

number bookbinder
input
[%] Particle size distribution [μm] particle size peak Presence of spherical particles Spherical particle content [%] tap density
[g/cc] d(002) spacing
[nm] note D10 D50 D90 One 5 3 8 14 One X 0 0.55 0.3358 Comparative Example 1 2 10 4 11 25 One O One 0.72 0.3354 Example 1 3 15 7 14 28 One O One 0.98 0.3356 Example 2 4 20 8 20 34 One O One 1.12 0.3354 Example 3 5 25 12 23 38 2 O One 0.68 0.3364 Comparative Example 2

Figures 3a and 3b show a tissue picture according to a comparative example of the present invention.

3A and 3B show tissue photographs of Comparative Examples 1 and 2 in Table 1, respectively. Looking at Figure 3a, it can be seen that the content of spherical particles is insufficient, looking at Figure 3b, it can be seen that a large number of spherical particles are generated.

Looking again at Table 1, in the case of Comparative Example 1, it can be confirmed that the binder is not uniformly applied when considering the particle size distribution, compared to the state in which the coke particles are pulverized, and accordingly, the tap density is poor. You can check. In the case of Comparative Example 2, due to the spherical particle content, two XRD peaks were formed, and it could be confirmed that the tap density was poor.

Table 2 below shows the tap density when the fixed carbon content of the binder is less than 20% and the quinoline insoluble content is less than 1%. Table 2 below shows tap densities when the fixed carbon content of the binder was controlled to 19%, 16%, and 18%, respectively.

number of binder
Fixed carbon content [%] tap density
[g/cc] note One 19 0.67 Comparative Example 3 2 16 0.55 Comparative Example 4 3 18 0.64 Comparative Example 5

Looking at Table 2, it can be seen that when the fixed carbon content of the binder is less than 20%, the tap density is lower than 0.7 and is inferior.

Table 3 below shows particle size peaks, tap densities, and d (200) intervals when the coal-based needle cokes of Examples 1 to 3 in Table 1 were used when the quinoline insoluble content of the binder was 2%.

number of binder
input [%] particle size peak tap density
[g/cc] d(002) spacing
[nm] note One 10 3 0.69 0.3364 Comparative Example 6 2 15 2 0.46 0.3364 Comparative Example 7 3 20 4 0.57 0.3366 Comparative Example 8

Looking at Table 3, it can be seen that when the quinoline insoluble content of the binder does not satisfy the range of the present invention, the tap density is lowered, the electrode processability is inferior, and the degree of graphitization is also affected.

<Cathode manufacturing>

A negative electrode was manufactured by the following process for the negative electrode active material after carbonization. A negative active material slurry was prepared by mixing 97% by weight of the negative electrode active material, 2% by weight of a binder including carboxymethyl cellulose and styrene butadiene rubber, and 1% by weight of a Super P conductive material in a distilled water solvent. After applying the negative electrode active material slurry to a copper (Cu) current collector, it was dried at 100 ° C. for 10 minutes and compressed using a roll press. Thereafter, the negative electrode was prepared by vacuum drying in a vacuum oven at 100 °C for 12 hours.

After vacuum drying, the electrode density of the negative electrode was set to 1.5 to 1.7 g/cc.

<Manufacture of lithium secondary battery>

Lithium metal (Li-Metal) is used as the anode and counter electrode prepared by the above method, and the volume ratio of ethylene carbonate (EC, Ethylene Carbonate): dimethyl carbonate (DMC, Dimethyl Carbonate) is 1: 1 as the electrolyte. A solution obtained by dissolving 1 mol of LiPF ₆ in a mixed solvent was used.

Using each of the above components, a 2032 coin cell type half coin cell was manufactured according to a conventional manufacturing method.

Table 4 below shows the results of electrochemical evaluation by preparing negative electrode materials made of various base materials. At this time, as the binder, coal tar having a fixed carbon content of 18% and a quinoline insoluble content of less than 0.8% were used.

number parent material Binder Dosage
[%] Particle size distribution (㎛) particle size peak Presence of spherical particles tap density
[g/cc] Discharge capacity (3rd)
[mAh/g] Efficiency (1rd) note D10 D50 D90 One coal system
needle coke 14 5 16 28 One O 1.05 354 92 Example 4 2 petroleum
needle coke 14 3 16 31 One O 0.92 350 94 Example 5 3 Coal-based: Petroleum-based = 5:5 14 5 16 29 One O 0.97 352 91 Example 6 4 hard coal 14 6 15 28 One X 1.17 310 85 Comparative Example 9 5 MCMB 14 4 17 30 One O 1.11 330 94 Comparative Example 10 6 Phenol Resin
carbonized product 14 6 17 27 One X 1.14 290 88 Comparative Example 11

Looking at Table 4, it can be seen that Examples 4 to 6 are all included in the range of an optimal discharge capacity of 350 mAh/g or more and an optimal battery efficiency of 92% or more. In Comparative Example 9 and Comparative Example 11, it can be confirmed that the discharge capacity and the efficiency are inferior, and Comparative Example 10 can be confirmed to have spherical particles, but the spherical particles in this case can be confirmed to be MCMB. The present invention is not limited to the above embodiments and / or examples, but can be manufactured in various different forms, and those skilled in the art to which the present invention belongs may change the technical spirit or essential features of the present invention. It will be appreciated that it may be embodied in other specific forms without Therefore, it should be understood that implementations and/or examples described above are illustrative in all respects and not restrictive.

Claims (14)

As an anode active material derived from coke,
A carbon coating layer obtained by calcining graphite particles and a binder disposed on the graphite particles;
At least one spherical particle among the graphite particles,
The amount of the binder is 10 to 20 parts by weight based on 100 parts by weight of the graphite particles,
The fixed carbon content of the binder is 20% or more,
The binder is a material derived from coal tar,
The negative electrode active material in which the coal tar has a quinoline insoluble component (QI) of less than 2% by weight based on the total weight% of the coal tar.
According to claim 1,
The spherical particles have a size distribution within 10 to 25% compared to the D90 of the negative electrode active material.
According to claim 1,
The spherical particles have a value represented by one peak in the particle size distribution of the negative electrode active material.
According to claim 1,
The negative electrode active material wherein the d (002) spacing, which is the interplanar spacing of the graphite layers, is 0.3354 to 0.3362 nm.
According to claim 1,
The coal tar is a negative electrode active material for a lithium secondary battery having a fixed carbon content of 20% or more based on the total weight% of the coal tar.
According to claim 1,
A negative electrode active material wherein the fixed carbon content of the spherical graphite particles is 99% or more.
According to claim 1,
The negative electrode active material has a particle size (D50) of 11 to 20 μm.
According to claim 1,
A negative electrode active material having a tap density of 0.70 or more.
According to claim 1,
The coke is a negative electrode active material derived from any one of coal-based, petroleum-based, or a combination thereof.
Finely pulverizing coke particles;
Graphitizing the pulverized product;
mixing the graphitized product with a binder; and
Including the step of carbonizing the mixed result,
In the step of mixing the graphitized product with a binder, the binder further includes 10 to 20 parts by weight based on 100 parts by weight of coke,
The fixed carbon content of the binder is 20% or more,
The binder is a material derived from coal tar,
Wherein the binder has a quinoline insoluble content (QI) of less than 2% by weight based on the total weight% of the coal tar.
According to claim 10,
The step of finely pulverizing the coke particles has an average particle diameter (D50) of 6 to 12 μm.
According to claim 10,
The step of graphitizing the pulverized product is a negative electrode active material manufacturing method performed at 2,700 ℃ or more.
According to claim 10,
The step of carbonizing the mixed product is a negative electrode active material manufacturing method performed at 800 ℃ or more.
According to claim 10,
A method for producing a negative electrode active material in which the volatile matter content of coal-based or petroleum-based coke is 1% or more.

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