KR101500644B1 - Anode active material for secondary battery and method for preparing thereof and secondary battery containing the same for anode - Google Patents

Abstract

The method for manufacturing an anode material for a secondary battery according to the present invention comprises the steps of filling spherical graphite powder in a vessel and keeping the spherical graphite in a vacuum state; injecting a pitch solution into the vessel and stirring to prepare a pitch-graphite paste; Heating the pitch-graphite paste to a vacuum to volatilize the solvent to coat the spherical graphite with the pitch; and heat treating and carbonizing the spherical graphite coated with the pitch.

Description

[0001] The present invention relates to an anode active material for a secondary battery, and an anode active material for a secondary battery,

The present invention relates to an anode material for a secondary battery and a manufacturing method thereof, and more particularly, to an anode material having an excellent charging and discharging efficiency and an improved life span by uniformly forming a carbon coating layer on the inside and outside of the graphite particle by a pitch, .

2. Description of the Related Art In recent years, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, demand for secondary batteries that are small and lightweight and relatively high in capacity has been rapidly increasing. Particularly, the lithium secondary battery is light in weight and has a high energy density, and is attracting attention as a driving power source for portable devices. Accordingly, research and development efforts have been actively made to improve the performance of the lithium secondary battery.

At present, natural graphite and artificial graphite have been commercialized and applied mainly to an anode material of a lithium secondary battery. In particular, natural graphite anode materials are known to exhibit higher capacity than artificial graphite. Despite the advantages of such high capacity, natural graphite is known to have poor lifetime characteristics in artificial graphite. In particular, since natural graphite has mostly a plate shape, spheroidized natural graphite is mainly used for easiness of electrode manufacturing process, increase of packing density, and improvement of output characteristics.

However, it is known that the lifetime characteristics of natural graphite deteriorate during repeated charging and discharging due to defects of graphite structure and internal stress generated by the spheroidization process of natural graphite. This deterioration in the lifetime characteristics is particularly related to the decomposition of the electrolyte generated by the reaction of graphite and electrolyte and the formation of SEI (solid electrolyte interface) layer at the interface between graphite and electrolyte. The formation of a stable SEI is very important because the formed SEI layer serves as a protective film to prevent the degradation reaction of the electrolyte from progressing further.

Conventionally, a negative electrode material having a structure in which a pitch or a polymer resin is coated on the surface of graphite particles and a carbon layer is formed through heat treatment is applied to improve the lifetime characteristics of natural graphite. The carbon coating layer thus formed functions to coat the edges and joints of the surface of the natural graphite particles to control the reactivity of the graphite surface with the electrolyte and form a stable SEI layer.

Japanese Patent Application Laid-Open No. 2002-348109 discloses a carbon material-based negative electrode active material in which a carbide layer is coated in order to prevent the decomposition reaction of an electrolytic solution from being caused at an edge portion of a crystalline carbon material.

Korean Patent Laid-Open Publication No. 2009-34589 discloses a carbon material-based anode active material having a property value in which electrochemical characteristics are not deteriorated even if a carbide layer is formed at the edge portion of the core carbon material and the compression process is performed by defining physical parameters based on XRD measurement data .

However, as shown in Fig. 1, pore formed in the nodularization process of natural graphite is contained in the nodular graphite. There is a possibility that a new graphite-electrolyte interface is formed between the electrolyte and the graphite due to the pores inside the particles thus formed. Especially, in the process of forming the high density electrode, the structure is deformed in the process of pressing to the electrode, so that the graphite structure in which the carbide layer is not coated is exposed to the outside. This exposure of the internal graphite causes a side reaction between the uncontrolled graphite and the electrolyte, thereby increasing the irreversible reaction.

Therefore, it is necessary to form a uniform carbon coating layer on the graphite surface to the inside of the spherical natural graphite in order to secure the long-life characteristics under the conditions of high-density electrode production.

It is an object of the present invention to provide a negative electrode material for a secondary battery capable of forming a high density electrode having long life stability by forming a uniform carbon coating layer inside and outside the spheroidized natural graphite, And a manufacturing method thereof.

In order to accomplish the above object, a method of manufacturing an anode material for a secondary battery according to an embodiment of the present invention includes the steps of filling powdery spheroidal graphite in a container and then maintaining the powder in a vacuum state, injecting a pitch solution into the container, Graphite paste by heating the pitch-graphite paste in a vacuum state to volatilize the solvent to coat the pitch with spherical graphite, and carbonizing the spherical graphite coated with the pitch by heat treatment .

The solvent used in the pitch solution may be any one selected from tetrahydrofuran (THF) or tetrahydroperfuryl alcohol, quinoline, and pyridine.

The vacuum heating temperature of the pitch-graphite paste may be 70 to 100 ° C.

The heat treatment temperature in the carbonization step may be 1000 to 2000 ° C.

Also, the negative electrode material for a secondary battery according to an embodiment of the present invention is characterized in that a uniform carbon coating layer is formed on the inside and outside of the spheroidized natural graphite.

The carbon coating layer may be formed by a carbonization process of the pitch.

The carbon coating layer may have a pore size of 0.1 m < 2 > / g or less within 2 mu m or less.

According to the method for producing an anode material for a secondary battery according to the present invention, a uniform carbon coating layer is formed on the inside and the outside of the spheroidal graphite so that a stable SEI is formed both inside and outside by a compression process at the time of manufacturing a high density electrode. The present invention also provides a method of manufacturing an anode material. In addition, it is possible to manufacture a secondary battery having a high energy density and a long life.

1 is a cross-sectional photograph of naturally graphitized natural graphite.
2 is a transmission electron microscope (TEM) photograph of the anode material cross section according to Example 1. Fig.
3 is a transmission electron microscope (TEM) photograph of the anode material cross section according to Comparative Example 1. Fig.
4 is a transmission electron microscope (TEM) photograph of the anode material cross section according to Comparative Example 2. Fig.
Fig. 3 is a graph showing the results of evaluation of lifetime characteristics by repeated charging / discharging tests of Example 1, Comparative Example 1 and Comparative Example 2. Fig.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims. Like reference numerals refer to like elements throughout the specification.

Hereinafter, an anode material for a secondary battery according to an embodiment of the present invention and a method of manufacturing the same will be described.

A method for manufacturing an anode material for a secondary battery according to an embodiment of the present invention includes the steps of filling a spherical graphite powder in a vessel and keeping it in a vacuum state, injecting a pitch solution into the vessel, stirring the mixture to form a pitch- Coating the spheroidal graphite with the pitch by heating the pitch-graphite paste in a vacuum to volatilize the solvent, and heat treating and carbonizing the spheroidal graphite coated with the pitch.

First, the spheroidized natural graphite is filled in a container in a powder state, and then the container is closed and kept in a vacuum state. In the case of spheroidized natural graphite, as shown in FIG. 1, it may include pores therein. It is the core of the present invention to form a carbon coating layer on such pores. The reason why the container is maintained in a vacuum state is to form a state in which air that may be present in the pores is removed so that a coating layer can be formed in the interior of natural graphite by a pitch in a subsequent process.

In a vacuum vessel, inject the pitch solution in which the petroleum / coal pitch is dissolved in the solvent. As the solvent used herein, an organic solvent capable of well dispersing the pitch can be used, and the solvent can be any one selected from tetrahydrofuran (THF), tetrahydroperfuryl alcohol, quinoline, and pyridine.

The softening point of the pitch used at this time is preferably 70 to 100 ° C. If the softening point of the pitch is too high, the viscosity of the pitch may be too high to reduce fluidity and become difficult to suck into the pores of the graphite. If the softening point of the pitch is too low, it may be difficult to form a uniform carbon coating layer.

The injected pitch solution fills the inner pores of the spheroidized natural graphite and forms a pitch-graphite paste impregnated with the pitch solution to the surface.

The pitch-graphite face is subjected to vacuum heating to volatilize the contained solvent components. At this time, the vacuum heating temperature may be about 70-100 ° C. and sufficient heating is required so that all of the solvent can be volatilized. It may be heated for about 1 to 4 hours, and it is preferable to heat while continuing the stirring.

When the heating temperature is lower than 70 캜, it is difficult to secure the fluidity of the pitch due to heating below the softening point of the pitch. When the heating temperature exceeds 100 캜, it is difficult to uniformly coat the inner part of the pitch. There is a problem that the pores are formed due to the presence of the catalyst.

The spheroidized natural graphite in which the solvent is removed through vacuum heating has a structure in which the pitch is coated on the inside and the outside of the particle.

The pitch-coated spheroidal graphite is heat-treated and carbonized. The heat treatment is preferably performed in an inert atmosphere at 1000 to 2000 ° C.

When the heat treatment temperature is lower than 1000 ° C, heat-treated carbon material micropores may be formed and electrochemically irreversible reaction may be caused. When the heat treatment temperature is higher than 2000 ° C, graphitization proceeds, which increases the heat treatment cost in the process. Therefore, it is limited to the above range.

The anode material for a secondary battery manufactured by the above method has a carbon coating layer formed uniformly on the inside and outside of the spheroidized natural graphite, so that there is no graphite layer exposed during the production of a high density electrode by a compression process, The characteristics can be improved.

The negative electrode material for a secondary battery manufactured by the above-described method may be mixed with a conductive material, a binder, and an organic solvent to prepare an active material paste. Then, the active material paste may be applied to a metal current collector such as a copper foil, followed by drying, heat treatment and pressing to form an electrode (cathode) for a secondary battery.

The electrode for a secondary battery thus manufactured can be used for the production of a lithium secondary battery. That is, the metal current collector having the negative electrode active material according to the present invention bound to a predetermined thickness and the metal current collector having the Li-based transition metal compound bound to the predetermined thickness are opposed to each other with the separator interposed therebetween, and then the electrolyte for lithium secondary battery is impregnated into the separator. It is possible to manufacture a lithium secondary battery capable of repetitive charging and discharging.

The present invention relates to an anode material for a secondary battery, and when manufacturing an electrode for a secondary battery and a secondary battery including the same using the anode material according to the present invention, various methods known in the art to which the present invention pertains are applied . It is apparent that the kind of the secondary battery in which the anode material according to the present invention can be utilized is not limited to the lithium secondary battery.

Hereinafter, the present invention will be described in more detail with reference to Examples.

100 g of pitch having a softening point of 70 캜 was added to 100 ml of THF and stirred for 30 minutes to prepare a pitch solution. 1 kg of spheroidized natural graphite powder was placed in a reaction vessel and maintained in a vacuum state, and the prepared pitch solution was injected, followed by stirring for 30 minutes. The mixed pitch-graphite paste was held in a vacuum at 70 캜 for 2 hours to volatilize the solvent components. The graphite powder coated with dried pitch was then carbonized by heat treatment at 1100 ° C for 1 hour in an Ar gas atmosphere to produce an anode material.

≪ Comparative Example 1 &

The anode material was manufactured using the same process as in Example 1, except that the softening point of the pitch was 230 ° C.

≪ Comparative Example 2 &

As a general dry coating process, a pitch having a softening point of 230 ° C and a spherical natural graphite were dry-mixed and then mechanically mixed at a high speed for 10 minutes. After the pitch coating, And then carbonized by heat treatment for 1 hour to prepare an anode material.

The production conditions of the examples and comparative examples are shown in Table 1 below.

Pitch softening point
(° C) Coating method Pitch weight ratio (wt%) to graphite Weight ratio of pitch carbide to graphite (wt%) Example 1 70 Vacuum condition
Solution injection 10% 2% Comparative Example 1 230 Vacuum condition
Solution injection 10% 4% Comparative Example 2 230 Dry coating
(Mechanofusion) 6% 2%

In order to confirm whether or not a carbon coating layer was formed inside the spheroidized natural graphite, the inner cross section of Example 1, Comparative Example 1 and Comparative Example 2 was observed with a transmission electron microscope (TEM).

2 is a transmission electron microscope (TEM) photograph of the anode material cross section according to Example 1. Fig. As shown in FIG. 2, it was found that the pores inside the graphite particles disappeared and the carbon coating layer was formed.

3 and 4 are transmission electron microscope (TEM) photographs of negative electrode material cross sections according to Comparative Examples 1 and 2, respectively. In Comparative Example 1, it was confirmed that pores inside the graphite were reduced, but an uncoated portion was observed as compared with Example 1. In the case of Comparative Example 2, it was found that a carbon coating layer was formed only on the surface of the particles by the dry coating process and no coating layer was present in the pores inside.

The pore volume and the specific surface area were measured in order to indirectly confirm whether or not the pitch was coated inside the respective specimens, and the results are shown in Table 2 below. The mercury porosimeter was used to measure the internal pore volume of the powder of the anode material. In order to prevent the error between the particles, the volume of the pores having a size of 2 μm or less was measured.

Pore volume (ml / g) Specific surface area (m < 2 > / g) Tap density (g / cc) Example 1 0.08 1.9 1.1 Comparative Example 1 0.13 4.0 1.0 Comparative Example 2 0.13 2.5 1.0

It was found that the pore volume and the specific surface area of 2 탆 or less were lower than those of Comparative Examples 1 and 2 due to the effect of coating inside the particles in Example 1. In the case of one tap density, it was found that the pitch density was relatively high because of the presence of pitch carbide inside the particles.

In Comparative Example 1, the pore volume was similar to that of Comparative Example 2 in which only the particle surface was coated as the pitch could not penetrate into the particle. On the other hand, since the content of unevenly coated carbon was large on the particle surface, the specific surface area was higher than that of Comparative Example 2.

In order to evaluate the electrochemical properties of each specimen, life characteristics were evaluated by repeated charging and discharging tests under the following conditions.

- Electrode density: 1.8 g / cc

- Loading amount of active material: 9mg / ㎠

- Repeated charge / discharge condition: 2032 coin half cell test

· Charge: CC-CV, 0.5C, 0.01V, 1 / 10mA Cut-off @ 25 ℃ ± 2 ℃

· Discharge: CC, 0.5C, 1.5V Cut-off @ 25 ℃ ± 2 ℃

Fig. 3 is a graph showing the results of evaluation of lifetime characteristics by repeated charging / discharging tests of Example 1, Comparative Example 1 and Comparative Example 2. Fig.

It can be confirmed that the life characteristics of Example 1 are higher than those of Comparative Example 1 and Comparative Example 2. Also, in the case of Comparative Example 1, since the carbon content was increased with the formation of the uneven carbon coating layer, the lifetime characteristics were improved as compared with Comparative Example 2 produced through the dry coating process.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the exemplary embodiments or constructions. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. will be.

It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (7)

Filling spheroidal graphite powder in a vessel and keeping it in a vacuum state;
Injecting a pitch solution into the vessel and stirring the mixture to produce a pitch-graphite paste;
Heating the pitch-graphite paste in a vacuum to volatilize the solvent to coat the spheroid graphite with the pitch; And
Heat treating the pitch-coated spheroidal graphite to carbonize it;
A method for manufacturing an anode material for a secondary battery comprising The method of claim 1,
Wherein the solvent used in the pitch solution is any one selected from the group consisting of tetrahydrofuran (THF), tetrahydrofurfuryl alcohol, quinoline, and pyridine. The method of claim 1,
And the vacuum heating temperature of the pitch-graphite paste is 70 to 100 占 폚. In paragraph 3
Wherein the heat treatment temperature in the carbonization step is 1000 to 2000 占 폚. An anode material for a secondary battery produced according to any one of claims 1 to 4,
A uniform carbon coating layer is formed inside and outside the spheroidized natural graphite,
An anode material for a secondary battery, wherein the volume of pores having a size of 2 m or less in the anode material is 0.1 ml / g or less. The method of claim 5,
Wherein the carbon coating layer is formed by a carbonization process of the pitch. delete

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