KR100453920B1 - Methods for the preparation of rounded-morphology graphite by coating with amorphous carbons - Google Patents

Abstract

The present invention relates to a spherical (rounded-morphology) graphite compound prepared in the form of a sphere by coating amorphous carbon on the surface of the graphite particles of irregular shape and a method for producing the same, in particular 10 weight of spherical spherical particles satisfying the following formula (1) It provides a spherical graphite compound coated with amorphous carbon containing more than%.

[Equation 1]

0.92 ≤ a / b ≤ 1

(Wherein a is the short diameter of the particle and b is the long diameter of the particle)

Description

Spherical Graphite Coated with Amorphous Carbon and a Method for Manufacturing the Same {METHODS FOR THE PREPARATION OF ROUNDED-MORPHOLOGY GRAPHITE BY COATING WITH AMORPHOUS CARBONS}

The present invention relates to spherical (rounded-morphology) graphite particles and a method of manufacturing the same by coating amorphous carbon on the surface of the graphite particles of irregular shape, in particular the particle size that can be used as a negative electrode active material of a lithium secondary battery of several to several tens of ㎛ A spherical graphite compound and a method for producing the same.

As the negative electrode material of the lithium secondary battery, a carbon-based material is mainly used, and the carbon-based material includes crystalline carbon and amorphous carbon. Crystalline carbon is typical of graphite carbon such as natural graphite and artificial graphite, and amorphous carbon is heat treated to non-graphitizable carbons (hard carbons) and pitch obtained by carbonizing a polymer resin. Graphitizable carbons (soft carbons). Among these, graphitized mesocarbon microbeads (manufactured by Osaka Gas Co., Japan, hereinafter referred to as 'g-MCMB'), which is a kind of artificial graphite, are most used.

Graphite, which is the crystalline carbon, has a low redox potential, excellent voltage flatness, constant discharge voltage during discharge, and excellent coulombic efficiency during the first cycle, thereby providing a high voltage battery when used as a negative electrode active material in a lithium secondary battery. . However, graphite has a large change in volume during charging and discharging, a large amount of irreversible reaction, and is subject to limitations in electrolyte during battery manufacture. In other words, when propylene carbonate, which is inexpensive and liquid at room temperature, is used, the crystalline graphite layer is peeled off by co-intercalation of the electrolyte, and thus lithium ion can not be properly inserted and desorbed. The initial efficiency of the active material decreases and the capacity of the battery decreases. Therefore, conventionally, expensive ethylene carbonate is mainly used as an electrolyte solution, which is solid at room temperature, has low ionic conductivity, and has low workability in manufacturing a battery.

On the other hand, when inexpensive natural graphite is applied to a battery, it has to undergo a grinding process, and thus, when the amorphous or plate-like crystalline carbon active material produced by the cumbersome grinding process is applied to the electrode plate as it is, its shape shows low tap density. In addition, when the active material is filled in the electrode plate and pressed, the amorphous active material particles are completely oriented so that a basal plane in which lithium ions are not inserted or removed is in contact with the electrolyte.

Natural graphite has such a low cost and large capacity that it can be used as a negative electrode active material of a lithium secondary battery, but there is a critical problem in that a low-cost propylene carbonate electrolyte cannot be used. Accordingly, various methods have been attempted to coat the graphite surface with amorphous carbon to be suitable as a negative electrode active material of a lithium secondary battery.

In this way, Korean Patent Publication No. 99-80594 discloses an amorphous carbon precursor or turbos having a thickness of 10 to 2000 mm 3 on the surface of carbon by dissolving an amorphous carbon precursor such as a phenol resin in an organic solvent and then mixing crystalline carbon such as graphite. The negative electrode active material for a lithium ion secondary battery including a carbon shell having a traverse structure and a lithium secondary battery using the same have been described. In addition, Korean Patent Publication No. 275,032 discloses the initial mixing and application of pitch to graphite carbon using physical or solvents, and in some cases induced and stabilized by induction of oxidation or meso layer formation, and finally heat treatment to form a double layer structure. Disclosed is a method for producing a negative electrode material. In addition, Korean Patent Laid-Open Publication No. 99-83662 describes a method of preparing a carbon material for a lithium battery negative electrode material by dissolving a carbonaceous raw material in an organic solvent, then coating the surface of the graphite powder and heat-treating in an inert atmosphere. In addition, Korean Patent Publication No. 2000-19113 discloses a positive electrode plate filled with a positive electrode active material, one or more crystalline carbon primary particles are coated with amorphous carbon, and the primary particles coated with the amorphous carbon are assembled to substantially A negative electrode plate filled with a negative electrode active material forming spherical secondary particles, a separator positioned between the positive electrode plate and the negative electrode plate, and an electrolyte solution in which lithium salt is impregnated in the positive electrode plate, negative electrode plate, and separator, dissolved in an organic solvent. Lithium-based secondary battery is described. However, all of the above methods do not require grinding by coating amorphous carbon on graphite, but the carbon particles produced after the coating do not form a uniform shape or are not spherical, and have to undergo a separate assembly process to produce a spherical shape. There is a problem.

In addition, Japanese Patent Application Laid-open No. Hei 10-29411 discloses a lithium secondary which graphitizes carbon or graphite powder having a ratio a / b of the long diameter a and the short diameter b of particles 1 ≦ a / b ≦ 3 and an average particle diameter of 1 to 30 μm. A graphite carbon material for a negative electrode active material of a battery and a method of manufacturing the same are disclosed. Japanese Patent Laid-Open No. 2000-294243 discloses a carbon powder for a negative electrode active material of a lithium secondary battery obtained by isotropically pressurizing a carbon powder and a method of manufacturing the same. Further, Japanese Patent Laid-Open No. 2001-89118 has a specific surface area of 0.3 to 2.0 m 2 / g, an aspect ratio of 1.1 to 5, a coarse surface density of 0.5 g / cm 3 or more, and multiple sets or combinations of flat particles. Graphite particles comprising a step of mixing a graphite particle having a shape, graphitizable aggregate or graphite and a graphitizable binder, and calcination of the mixture obtained by the above step and grinding the mixture to an average particle diameter of 10 to 100 µm. It describes the preparation method of.

However, since the shape of the surface of the graphite carbon or the graphite particles obtained in the above methods has an irregular shape and is not spherical, there is a problem in that a separate assembling process is required to produce a spherical shape.

In view of the problems in the prior art, an object of the present invention is to provide a spherical graphite compound by coating amorphous carbon on an irregularly shaped natural graphite surface having a size of several to several tens of micrometers.

Another object of the present invention is to provide a method for preparing the spherical graphite compound coated with the amorphous carbon.

Another object of the present invention is to provide a lithium secondary battery including the spherical graphite compound coated with amorphous carbon as a negative electrode active material.

Figure 1 is a scanning electron micrograph of 4,500 magnification for the "amorphous" carbon coated "spherical" graphite particles prepared in the present invention.

In order to achieve the above object, the present invention

In the spherical graphite compound coated with amorphous carbon,

It provides a spherical graphite compound coated with amorphous carbon comprising 10% by weight or more of spherical spherical particles satisfying Equation 1 below.

[Equation 1]

0.92 ≤ a / b ≤ 1

Wherein a is the short diameter of the particle and b is the long diameter of the particle.

In the manufacturing method of the spherical graphite compound coated with amorphous carbon,

a) graphite particles are dispersed in a solution in which a carbon precursor is dissolved in an organic solvent.

Removing the solvent to coat the carbon precursor on the graphite;

b) adding a hydrophobic inorganic material to the graphite coated with the carbon precursor of step a)

Carbonizing the mixture by heat treatment under an inert gas atmosphere; And

c) removing hydrophobic minerals by adding acid or alkali to the carbide of step b)

Steps to

It provides a manufacturing method comprising a.

In addition, the present invention provides a lithium secondary battery comprising a spherical graphite compound coated with amorphous carbon of the substrate as a negative electrode active material.

Hereinafter, the present invention will be described in detail.

The present invention is coated with amorphous carbon, which is inexpensive and has a large capacity, and is coated with amorphous carbon which can increase the amount of filling because the shape of the particles is close to a spherical shape. It is to provide a spherical graphite particles and a method of manufacturing the same. According to this method, the amorphous carbon precursor is coated on the graphite, followed by the addition of an inorganic material such as silica and heat treatment before the heat treatment to prepare the finally obtained graphite particles close to the spherical shape, and the amorphous carbon coated spherical graphite prepared by the above method. When the particles are used as a negative electrode active material in a lithium secondary battery, propylene carbonate can be used as an electrolyte, the filling amount can be increased, and the processability in the electrode manufacturing process is excellent, resulting in economical effects.

It is preferable that the amorphous carbon-coated spherical graphite compound of the present invention contains 10% by weight or more of spherical spherical particles satisfying Equation 1 below.

In addition, it is preferable that the remaining particles of the spherical graphite compound coated with amorphous carbon of the present invention include spherical spherical particles satisfying Equation 2 below.

[Equation 1]

0.92 ≤ a / b ≤ 1

[Equation 2]

0.1 ≤ a / b ≤ 0.92

Wherein a is the short diameter of the particle and b is the long diameter of the particle.

It is preferable that the spherical graphite compound coated with amorphous carbon of the present invention has an average particle diameter of 1 to 40 μm.

In addition, the method for producing the amorphous carbon-coated spherical graphite compound of the present invention will be described.

In the present invention, first, a) a carbon precursor is dissolved in a solvent, graphite particles are added and mixed, and then the solvent is removed to coat the carbon precursor on graphite.

Since the carbon precursor used in the present invention may be in a solid powder state that can be mixed with an inorganic substance, there is no particular limitation on the type of precursor, and preferably, resin, pitch or a mixture thereof is used.

In the present invention, the resin used as the carbon precursor is preferably a thermosetting synthetic resin. The thermosetting synthetic resin is a phenolics resin, a furan resin, an epoxy resin, a polyacrylonitrile resin, From the group consisting of polyimide resin, polybenzimidazoloe resin, polyphenylene resin, and biphenol resin, divinylbenzene styrene copolymer, and cellulose One or more selected may be used.

In the present invention, the pitch used as the carbon precursor may be petroleum pitch or coal pitch. It is preferable that the solvent is selected from one or more selected from the group consisting of acetone, tetrahydrofuran, and pyridine. As the graphite particles, it is preferable to use graphite powder of several to several tens of micrometers.

The mixing ratio of the graphite particles and the carbon precursor is preferably used by mixing in a weight ratio of 1: 0.01 to 10. In this case, when the mixing ratio of the carbon precursor to 1 part by weight of the graphite particles is less than the above range, the carbon precursor is not evenly coated on the graphite particles, and if the amount exceeds the above range, the capacity of the graphite to be implemented is too small.

At this time, the solvent removal is preferably dried under reduced pressure at a suitable temperature so that the solvent on the graphite surface coated with the carbon precursor is completely removed.

In addition, the present invention is b) adding a hydrophobic inorganic material to the carbon precursor coated graphite particles obtained in the above step by mixing and then performing a carbonization by heat treatment under an inert gas atmosphere.

The present invention can obtain graphite particles close to a spherical shape by adding an inorganic material whose surface is hydrophobically treated to graphite coated with a carbon precursor that is amorphous carbon. When the carbon is carbonized without introducing inorganic fine particles as in the prior art, agglomerated graphite particles are obtained. However, as in the present invention, when the surface of the inorganic fine particles is hydrophobized by mixing hydrophobic inorganic materials, carbonized particles which are close to a spherical shape rather than agglomerate form are obtained and do not require a grinding process. The hydrophobic inorganic material used in the present invention prevents agglomeration of carbon particles in the carbonization process by surrounding the carbon surface, and also provides a high surface tension when the particles shrink during the carbonization process to induce the particles to be spherical. Therefore, when the carbonized inorganic particles are introduced and carbonized, the hydrophobicity of the surface of the inorganic additive is very important for the production of spherical graphite particles.

As the hydrophobic inorganic material, silica, zeolite, alumina, titania (TiO ₂ ), ceria (CeO ₂ ), and the like, which are hydrophobically treated, may be used. In addition, other types of inorganic materials may be used as long as they are suitable for the configuration of the present invention in addition to those exemplified above. Among them, it is more preferable to use silica, which can be easily dissolved and removed by a weakly acidic or weakly alkaline solution, and is inexpensive and has a small particle size. Specific examples of the hydrophobic surface-treated silica include Cabosil (Cab-O-SIL TS-720, TS-610, TS-530, TS-500, TG-308F, TG-810G530, etc.). ) And Deggusa's aerosils (AEROSIL R972, R974, R812, R812S, R202). These inorganic substances may use a commercialized product, and may also use it synthetically.

For example, the method of synthesizing the hydrophobic inorganic material may include adding a general inorganic material having a non-hydrophobic surface and an organosilane surface treatment agent such as trimethylchlorosilane to a solvent such as toluene, and refluxing it under stirring to make the surface hydrophobic. You can easily get minerals.

In the present invention, the mixing ratio of the graphite particles coated with the carbon precursor, which is the amorphous carbon, and the inorganic material whose surface is hydrophobically treated is preferably mixed in a weight ratio of 100: 0.1 to 1000. At this time, it is difficult to produce spherical carbon when the amount of the hydrophobic inorganic substance added is less than 0.1 part by weight with respect to 100 parts by weight of the carbon precursor, and when the amount is more than 1000 parts by weight, it is difficult to obtain the effect as much as the added amount.

In the present invention, when the mixture made of the above ratio is carbonized by heat treatment under an inert gas (for example, argon, nitrogen, helium, etc.) atmosphere, graphite particles close to spherical shape are obtained. The heat treatment is preferably carried out at a temperature increase rate of 0.1 to 100 ℃ / min and carried out for 1 minute to 50 hours at 700 to 1500 ℃.

In addition, the present invention c) adding a acid or an alkali to the carbide obtained in the above step to remove the hydrophobic inorganic material to produce spherical graphite particles coated with amorphous carbon.

Spherical carbon prepared by the above process has to be removed because the inorganic particles are distributed on the surface portion. Therefore, the present invention removes inorganic substances by adding acid or alkali. In the case of silica, a hydrofluoric acid solution or an alkali solution can be used as a removal solvent. For example, in the case of using hydrofluoric acid, spherical graphite particles wrapped in silica may be removed by stirring in 20% to 50% hydrofluoric acid solution at room temperature for 30 minutes to 48 hours to dissolve the silica.

In addition, the spherical graphite particles coated with amorphous carbon may be used as a negative electrode active material of a lithium secondary battery.

According to the present invention, an electrode is formed to use spherical graphite particles coated with amorphous carbon as a lithium secondary battery negative active material. As an example of the method of forming the electrode, the amorphous carbon-coated spherical graphite particles and the binder prepared by the method described above are added to the dispersant and stirred in a weight ratio of 10: 0.5 to 2 to prepare a paste, and then, the current collector. It is applied to a metal material for compression, compressed and dried to produce a laminate electrode.

Representative examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), cellulose, and the like, and representative examples of the dispersant are isopropyl alcohol and N-methylpyrrolidone (NMP). , Acetone and the like.

The current collector metal material is a highly conductive metal, and any metal may be used as long as the paste of the material can be easily bonded. A representative example is a mesh or foil made of copper or nickel. Etc.

The method of evenly applying the paste of the electrode material to the metal material can be selected from known methods or performed by a new suitable method in consideration of the properties of the material. An example of this is to distribute the paste onto the current collector and then to distribute it evenly using a doctor blade or the like. In some cases, a method of distributing and dispersing in one process may be used. In addition, die casting, comma coating, screen printing, or the like may be selected, or may be molded on a separate substrate and bonded to the current collector by pressing or lamination. It may be.

An example of a method of drying the applied paste may include a process of drying in a vacuum oven at 50 to 200 ° C. for 1 to 3 days. In some cases, carbon black may be added in an amount of 5 to 20% by weight based on the total weight as the conductive material in order to further reduce the resistance of the electrode. Products commonly marketed as conductive materials include acetylene black series (Chevron Chemical Company or Gulf Oil Company), Ketjenblack EC series (Armak Company ), Vulcan XC-72 (manufactured by Cabot Company) and Super P (manufactured by MMM).

In the method of constructing a lithium secondary battery using the electrode manufactured by the above method, for example, the electrode is used as a cathode, LiCoO ₂ , LiNiO _2, LiMn ₂ O _4, etc. are used as an anode, and a separator is inserted therebetween. . The membrane blocks the internal short circuit of the two electrodes and impregnates the electrolyte, and materials that can be used include polymer, glassfiber mat, and kraft paper.Cellgard 2400, 2300 (Hoechest Celanese Corp.), polypropylene membrane (product of Ube Industries Ltd. or Pall RAI), etc. are mentioned.

The electrolyte is a system in which a lithium salt is dissolved in an organic solvent, and the lithium salt is LiClO ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiPF ₆ , LiSCN, and LiC (CF ₃ SO _{2 3} ) and the like, and the organic solvent is ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane (1,2- dimethoxyethane), 1,2-diethoxyethane, gamma-butyrolactone, tetrahydrofuran, tetrahydrofuran, 2-methyltetrahydrofuran, 1, 3-dioxene (1,3-dioxolane), 4-methyl-1,3-dioxene (4-methyl-1,3-dioxolane), diethyl ether, sulfolane and the like alone Or it can mix and use 2 or more types.

Hereinafter, the present invention will be described with reference to the following Examples and Comparative Examples. However, these examples are only for illustrating the present invention, and the present invention is not limited thereto.

Example 1

0.2 g of a phenol resin was dissolved in 0.1 L of acetone in a round-necked flask, and then 1 g of graphite carbon was mixed and sufficiently stirred for 2 hours. The solvent was removed while slowly depressurizing on a rotary evaporator. Thus obtained carbon particles and CAB-O-SIL TS-530 silica (fumed silica) surface-treated with hexamethyldisilazane were mixed in a mortar at a weight ratio of 10: 0.5, followed by argon gas. Spherical graphite particles coated with amorphous carbon were obtained by heating at an elevated temperature rate of 10 ° C./min under an atmosphere and heat-treating at 1000 ° C. for 1 hour. The spherical carbonaceous material and 48% hydrofluoric acid solution were placed in a reaction vessel made of Teflon, and the inorganic material was removed for two days, washed with ultrapure water, and dried in a vacuum oven at 120 ° C. for at least 12 hours. Scanning micrographs (magnification: 4,500) of the spherical graphite particles thus obtained are shown in FIG. 1. The ratio (a / b) of the short diameter a and the long diameter b of the spherical graphite particles was 0.93, and the average particle diameter was 23 µm.

Example 2

Spherical graphite particles coated with amorphous carbon were prepared in the same manner as in Example 1, except that 0.2 g pitch was dissolved in 0.1 L tetrahydrofuran. The ratio (a / b) of the short diameter a and the long diameter b of the spherical graphite particles was 0.94, and the average particle diameter was 20 µm.

Example 3

Spherical graphite particles coated with amorphous carbon were prepared in the same manner as in Example 1, except that CAB-O-SIL TS-720 dry silica whose surface was treated with polydimethylsiloxane was used. It was. The ratio (a / b) of the short diameter a and the long diameter b of the spherical graphite particles was 0.93, and the average particle diameter was 22 µm.

Example 4

Spherical graphite particles coated with amorphous carbon were prepared in the same manner as in Example 1, except that natural graphite was used as the graphite material. The ratio (a / b) of the short diameter a and the long diameter b of the spherical graphite particles was 0.92, and the average particle diameter was 26 µm.

Lithium secondary battery using spherical graphite particles coated with amorphous carbon as a negative electrode active material

Example 5

After preparing the paste by mixing the amorphous carbon coated spherical graphite particles prepared in Example 1 as a negative electrode active material and using a polytetrafluoroethylene (PTFE) as a binder in a weight ratio of 10: 0.5, a copper mesh zip A working electrode was prepared by attaching it to the whole, and the lithium secondary battery was manufactured using a negative electrode prepared by drying the same in a 120 ° C. vacuum oven for at least 12 hours.

As described above, in the present invention, the amorphous surface is finally obtained by a simple method by coating the graphite surface with an amorphous carbon precursor using an inexpensive and high capacity graphite material, and then adding a hydrophobic inorganic material such as silica and heat treatment. Carbon-coated graphite particles can be produced close to a sphere.

Claims (13)

delete delete delete In the manufacturing method of the spherical graphite compound coated with amorphous carbon, a) dispersing graphite particles in a solution in which a carbon precursor is dissolved in an organic solvent. Coating the carbon precursor on the graphite by removing the solvent after quenching; b) adding a hydrophobic inorganic material to the graphite particles coated with the carbon precursor of step a) Carbonizing the mixture by heat treatment under an inert gas atmosphere; And c) removing hydrophobic minerals by adding acid or alkali to the carbide of step b) Steps to Manufacturing method comprising a. The method of claim 1, The carbon precursor of step iii) is a resin, a pitch or a mixture thereof. The method of claim 5, wherein The resin is a phenol resin, furan resin, epoxy resin, polyacrylonitrile resin, polyimide resin, polybenzimidazoloe resin, polyphenylene ( A polyphenylene resin, and a thermosetting synthetic resin containing a biphenol resin, a divinylbenzene styrene copolymer, and a manufacturing method selected from the group consisting of cellulose. The method of claim 5, wherein The pitch is coal pitch or petroleum pitch. The method of claim 4, wherein The graphite particles and the carbon precursor of step a) is mixed in a weight ratio of 1: 0.01 to 10. The method of claim 4, wherein The hydrophobic inorganic material of step a) is selected from the group consisting of silica, zeolite, alumina, titania, and ceria whose surface is hydrophobically treated. The method of claim 4, wherein The hydrophobic inorganic material of a) step ii) is prepared by refluxing the inorganic material and the organosilane solution. The method of claim 4, wherein The a) step iii) the carbon precursor and the hydrophobic inorganic material of ii) is mixed in a weight ratio of 100: 0.1 to 1000. The method of claim 4, wherein The heat treatment of step b) is carried out for 1 minute to 50 hours at a temperature of 700 to 1500 ℃. delete