KR20100072160A - Anode active material for lithium secondary battery and lithium secondary battery containing the same for anode - Google Patents

Abstract

PURPOSE: A negative electrode active material of a lithium secondary battery is provided to obtain the high electrode density, and to improve the charge and discharge efficiency and the cycling ability of the battery. CONSTITUTION: A negative electrode active material of a lithium secondary battery contain the following: a first carbon material forming a coating layer including a carbon fiber and amorphous graphite on the surface of a graphite core formed with natural graphite, artificial graphite, and their compound; a second carbon material selected from the natural graphite, the artificial graphite, the amorphous coating graphite, plastic covering graphite, and amorphous carbon.

Description

Anode active material for lithium secondary battery and Lithium secondary battery containing the same for anode}

The present invention relates to a negative electrode active material for a lithium secondary battery and a lithium secondary battery comprising the same as a negative electrode, and more particularly, even when used at a high electrode density, a negative electrode for a lithium secondary battery capable of improving electrochemical characteristics due to mixing of carbon fibers. It relates to an active material and a lithium secondary battery comprising the same as a negative electrode.

Recently, the demand for secondary batteries, which are repeatedly charged and discharged with power sources such as PDAs, mobile phones, notebook computers, and portable electronic devices for electric communication, electric bicycles, and electric vehicles, is rapidly increasing. In particular, since the performance of products such as portable electronic devices and electric vehicles depends on the secondary battery, which is a key component, the demand for a high performance battery is very large. The characteristics required for the secondary battery have various aspects such as charge and discharge characteristics, lifespan, high rate characteristics, and stability at high temperatures. Lithium secondary batteries have the highest voltage and high energy density and are the most attracting attention.

Lithium secondary batteries are powered by oxidation and reduction reactions when lithium ions are inserted / desorbed from the positive electrode and the negative electrode while an organic or polymer electrolyte is charged between the negative electrode and the positive electrode made of an active material capable of inserting and removing lithium ions. To produce energy.

As a cathode active material of a lithium secondary battery, a chalcogenide compound is used. Examples thereof include a complex metal oxide such as LiCoO ₂ , LiMn ₂ O ₄ , or LiNi _{1- x} Co _x O ₂ (0 <x <1). It is used.

Lithium metal is used as a negative electrode active material of a lithium secondary battery. However, when lithium metal is used, a short circuit occurs due to the formation of dendrite, which may cause an explosion. Recently, lithium metal has been replaced with a carbon-based material instead of lithium metal. . As the carbon-based active material used as the negative electrode active material of the lithium secondary battery, crystalline carbon such as natural graphite and artificial graphite and amorphous carbon such as soft carbon and hard carbon are used.

Amorphous carbon has an advantage of large capacity, but has a problem of large irreversibility in charging and discharging.

As the crystalline carbon, natural graphite is typically used, and natural graphite has excellent initial capacity and a theoretical limit capacity of 372 mAh / g, which is relatively high, but has a problem of severe deterioration of life and low efficiency and cycle capacity. This problem is known to be due to the electrolyte decomposition reaction in the highly crystalline natural graphite edge portion.

In order to overcome this problem, the low-crystalline carbon is surface-treated (coated) on natural graphite and heat-treated at 1,000 ° C. or higher to coat low-crystalline carbide on the surface of natural graphite, thereby reducing the initial capacity but reducing the efficiency and cycle. A method of obtaining a negative electrode active material having improved capacity characteristics has been proposed.

In addition, in order to improve efficiency and cycle capacity characteristics, a method of obtaining a negative electrode active material surface-treated with natural graphite and mixed with other graphite has been proposed.

However, even if the surface treatment of low crystalline carbon or amorphous graphite to natural graphite can not implement a high electrode density of 1.7g / cc or more, there is a problem that the high capacity and cycle characteristics can not be sufficiently satisfied.

Accordingly, efforts to solve the above-mentioned problems of the prior art have been continued in the related art, and the present invention has been devised under such a technical background.

The present invention was devised to solve the above-mentioned problems of the prior art, and provides a negative active material for a lithium secondary battery and a lithium secondary battery including the same as a negative electrode, which can improve electrochemical properties even when used at a high electrode density. There is a purpose.

Other objects and advantages of the invention will be described below and will be appreciated by the embodiments of the invention. In addition, the objects and advantages of the present invention can be realized by the configuration and combination of configurations shown in the claims.

In order to achieve the above object, the negative electrode active material for a lithium secondary battery according to the present invention is a coating layer made of carbon fiber and amorphous graphite on the surface of any one graphite core selected from the group consisting of natural graphite, artificial graphite, and mixtures thereof. A formed first carbon material; At least one second carbon material selected from natural graphite, artificial graphite, amorphous coated graphite, resin coated graphite, and amorphous carbon is mixed with the first carbon material, and the first carbon material and the second carbon material have a weight ratio. To 95: 5 to 80:20.

The carbon fiber has a diameter of 1 to 1,000 nm, the carbon fiber is included in 0.5 to 5 parts by weight based on 100 parts by weight of the graphite core, the amorphous graphite is contained in 0.5 to 10 parts by weight based on 100 parts by weight of the graphite core. do.

In addition, according to another aspect of the present invention, there is provided a lithium secondary battery having a negative electrode including a negative electrode active material for a lithium secondary battery including at least any one of the above technical features.

According to the present invention, by uniformly dispersing carbon fibers in a graphite core and coating with amorphous graphite, by mixing at least one carbon material selected from natural graphite, artificial graphite, amorphous coated graphite, resin coated graphite and amorphous carbon, After manufacturing the electrode by using the negative electrode active material, it can prevent the fracture of the carbon particles during compression to realize a higher electrode density improved, even when used at a high electrode density is excellent in electrochemical properties such as charge and discharge efficiency and cycle characteristics A negative electrode active material can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings appended hereto illustrate preferred embodiments of the present invention, and the present invention is limited only to the matters described in such drawings as it serves to further understand the technical idea of the present invention together with the detailed description of the present invention. It should not be interpreted.
1 is a schematic process diagram of a method of manufacturing a negative active material for a lithium secondary battery according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the present specification and claims should not be construed as being limited to the common or dictionary meanings, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

The negative electrode active material for a lithium secondary battery according to a preferred embodiment of the present invention is a natural graphite, artificial graphite on a graphite core coated with carbon fiber and amorphous graphite in order to improve charge and discharge efficiency and cycle characteristics even when high electrode density is used. It is characterized by mixing at least one carbon material selected from graphite, amorphous coated graphite, resin coated graphite and amorphous carbon.

1 is a schematic process diagram of a method of manufacturing a negative active material for a lithium secondary battery according to the present invention.

Referring to FIG. 1, in the negative active material for a lithium secondary battery according to the present invention, carbon fiber and amorphous graphite are uniformly mixed after adding (S100) carbon fiber (Vapor Growth Carbon Fiber, VGCF) and amorphous graphite to a graphite core. The prepared mixture is heat-treated (S200) under any one of an oxidizing atmosphere, a reducing atmosphere, and a vacuum in a temperature range of 1,000 to 2,500 ° C. Here, the graphite core may be natural graphite, artificial graphite, and a mixture of the two, preferably spherical natural graphite.

In the heat treatment temperature range, the lower limit is less than the carbonization of the amorphous graphite and the specific surface area is not small, it is not preferable, if the upper limit is exceeded, it is not preferable because the sublimation of graphite may occur.

The carbon fiber preferably has a diameter of 1 to 1,000 nm, and preferably includes 0.5 to 5 parts by weight with respect to 100 parts by weight of the graphite core. When the carbon fiber is coated with amorphous graphite, even when a high electrode density is used, the conductive path of the electrode and the electrolyte solution penetration path are prevented from being damaged, and the conductivity of the electrode is improved to improve the electrical properties such as charge and discharge efficiency and cycle characteristics. Chemical properties are improved.

In the content limiting of the carbon fiber, when the lower limit is less than the lower limit, it is not preferable because the effect of adding carbon fiber, such as improved conductivity, is not preferable, and when the upper limit is exceeded, the carbon fibers are agglomerated with each other, making it difficult to disperse uniformly. .

The amorphous graphite is preferably included in 0.5 to 10 parts by weight based on 100 parts by weight of the graphite core.

In the limited content of the amorphous graphite, when the lower limit is less than the lower limit, it is not preferable because it does not inhibit the electrolyte decomposition reaction near the natural graphite edge, and when the upper limit is exceeded, the capacity decreases due to excessive coating of amorphous graphite. Is not desirable because it can occur.

On the other hand, the negative electrode active material for a lithium secondary battery according to the present invention is a natural carbon, artificial graphite, amorphous coated graphite, resin coated graphite and amorphous carbon in a graphite core (hereinafter referred to as the first carbon material) heat-treated by mixing carbon fiber and amorphous graphite One or more selected carbon materials (hereinafter referred to as the second carbon material) may be further mixed. (S300)

At this time, the first carbon material and the second carbon material is preferably mixed in a ratio of 95: 5 to 80:20 by weight ratio. When one or more carbon materials selected from natural graphite, artificial graphite, amorphous coated graphite, resin coated graphite, and amorphous carbon (ie, the second carbon material) are mixed with the first carbon material, even when a high electrode density is used, The conductivity can be further improved, and the particles can be prevented from being crushed to improve electrochemical properties such as charge and discharge efficiency and cycle characteristics.

In the limited mixing ratio of the first carbon material and the second carbon material, it is not preferable that the addition effect is difficult to appear when the lower limit is less than, and when the upper limit is exceeded, the characteristics of the first carbon material may be impaired. Not.

The present invention also provides a lithium secondary battery comprising a negative electrode active material for a lithium secondary battery in which the first carbon material and the second carbon material are mixed as a negative electrode.

The present invention is a secondary battery comprising a separator and an electrolyte interposed between the positive electrode, the negative electrode and the positive electrode, characterized in that it comprises a negative electrode active material for a lithium secondary battery according to the invention prepared by the above-described manufacturing method as a negative electrode do.

The method of manufacturing the secondary battery is a conventional method widely known in the art, and may be prepared by putting a porous separator between an anode and a cathode and putting an electrolyte therein.

As described above, the surface of the graphite core is coated with carbon fiber having a diameter of 1 to 1,000 nm and amorphous graphite and then mixed with another carbon material (that is, the second carbon material), thereby coating the carbon material coated with conventional amorphous graphite only. The electrode can be compressed to a higher electrode density, and the charge and discharge efficiency and cycle characteristics can be improved.

Hereinafter, the present invention will be described in more detail with reference to preferred examples (1 to 6) and comparative examples (1 to 3) in contrast thereto. However, embodiments according to the present invention can be modified in many different forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example  One

5% by weight of pitch and 2% by weight of carbon fiber (Vapor Growth Carbon Fiber, VGCF) dry mixed at high speed for about 10 minutes to prepare a mixture, the mixture was prepared at 1,100 ℃ and 2,200 ℃ 1 First and second firings were carried out for a time. Then, a classification and removal of fine powder produced a carbon material uniformly coated with pitch and carbon fibers.

50 weight% of spherical natural graphite which is uncoated to the said carbon material was added, and it mixed uniformly using the rotary mixer. 100 g of the negative electrode active material thus prepared was put into a 500 ml reactor, an aqueous solution of carboxymethyl cellulose (CMC) and an aqueous styrene-butadiene rubber (SBR) solution were added, kneaded using a mixer, and coated on a copper foil at a thickness of about 100 μm. It was. The resultant was then dried and molded through roll compression. The density per volume of the prepared electrode was set to 1.7 g / cm 3. In order to evaluate the electrode thus manufactured, a coin cell was manufactured and the charge and discharge efficiency and cycle characteristics were evaluated.

Example  2

A negative electrode active material was manufactured in the same manner as in Example 1, except that 50% by weight of spherical natural graphite coated on its entirety or part thereof with amorphous graphite was mixed with the carbon material.

Example  3

A negative electrode active material was manufactured in the same manner as in Example 1, except that 20 wt% of uneven coated natural graphite was mixed with the carbon material.

Example  4

A negative electrode active material was manufactured in the same manner as in Example 1, except that 30 wt% of spherical artificial graphite was mixed with the carbon material.

Example  5

A negative electrode active material was manufactured in the same manner as in Example 1, except that 30 wt% of plate-like artificial graphite was mixed with the carbon material.

Example  6

A negative electrode active material was prepared in the same manner as in Example 1, except that 15 wt% pitch and 2 wt% carbon fiber (VGCF) were used.

Comparative example  One

5% by weight of pitch and 2% by weight of carbon fiber (Vapor Growth Carbon Fiber, VGCF) dry mixed at high speed for about 10 minutes to prepare a mixture, the mixture was prepared at 1,100 ℃ and 2,200 ℃ 1 First and second firings were carried out for a time. Then, the negative electrode active material for lithium secondary batteries, which were classified and removed with fine powder, were coated with amorphous graphite.

100 g of the prepared negative active material was placed in a 500 ml reactor, an aqueous solution of carboxymethyl cellulose (CMC) and an aqueous styrene-butadiene rubber (SBR) solution were added, kneaded using a mixer, and coated on a copper foil at a thickness of about 100 μm. It was. The resultant was then dried and molded through roll compression. The density per volume of the prepared electrode was set to 1.7 g / cm 3. In order to evaluate the manufactured electrode, a coin cell was manufactured, and charge and discharge efficiency and cycle characteristics were evaluated.

Comparative example  2

A negative electrode active material was evaluated in the same manner as in Comparative Example 1, except that only 5 wt% pitch was mixed and coated on spherical natural graphite.

Comparative example  3

A negative electrode active material was evaluated in the same manner as in Comparative Example 2, except that 50 wt% of spherical natural graphite which was not coated was mixed.

Comparative example  4

The negative electrode active material was evaluated in the same manner as in Comparative Example 2, except that 20 wt% of uncoated spun natural graphite was mixed.

Charge / discharge characteristics were evaluated using the coin batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 4, and the results are shown in Table 1 below.

Battery characteristic evaluation

Charge and discharge tests were performed on the coin batteries prepared according to Examples 1 to 6 and Comparative Examples 1 to 4. The charge / discharge test regulates the potential in the range of 0 to 1.5V to charge until the charging current is 0.5V / cm 2 until it becomes 0.01V, and maintains the voltage of 0.01V until the charging current becomes 0.02mA / cm 2. Charging continued. The discharge current was discharged up to 1.5V at 0.5 mA / cm 2.

The experimental results are shown in Table 1 below, in which the charge and discharge efficiency indicates the ratio of the discharged capacity to the charged capacity.

1st Cycle Discharge Capacity
(mAh / g) 1st Cycle Efficiency (%) 30 Cycle capacity
% Retention Example 1 356.7 94.0 93.3 Example 2 355.3 94.2 94.5 Example 3 357.1 93.8 93.9 Example 4 356.4 93.9 94.1 Example 5 354.8 94.1 92.8 Example 6 355.9 93.8 93.3 Comparative Example 1 350.4 92.1 80.5 Comparative Example 2 347.5 91.0 75.1 Comparative Example 3 348.2 90.5 73.7 Comparative Example 4 347.1 90.8 74.1

As can be seen from Table 1, the overall charge and discharge efficiency even when the coin battery using the negative electrode active material according to the present invention used a higher electrode density than the coin cells of Comparative Examples 1 to 4 using the conventional negative electrode active material And cycle characteristics.

As described above, when the negative active material for the lithium secondary battery is manufactured according to the embodiments (1 to 6), the carbon fibers are uniformly dispersed, coated with amorphous graphite, and then mixed with other carbon materials. Electroconductivity of the electrode is improved by preventing the damage of the conductive path and electrolyte solution penetration path, and even higher electrode density can be realized by preventing the fracture of carbon particles, so that even when used at high electrode density, It can be seen that the same electrochemical properties are improved.

As described above, although the present invention has been described by way of limited embodiments and drawings, the present invention is not limited thereto and is intended by those skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of equivalents of the claims to be described.

Claims (5)

In the negative electrode active material for lithium secondary batteries,
A first carbon material having a coating layer made of carbon fibers and amorphous graphite formed on the surface of any one graphite core selected from the group consisting of natural graphite, artificial graphite, and mixtures thereof;
At least one second carbon material selected from natural graphite, artificial graphite, amorphous coated graphite, resin coated graphite and amorphous carbon is mixed with the first carbon material,
The first carbon material and the second carbon material is a lithium secondary battery negative electrode active material, characterized in that mixed in a ratio of 95: 5 to 80:20 by weight. The method of claim 1,
The carbon active material has a diameter of 1 to 1,000 nm, the negative electrode active material for lithium secondary batteries. The method of claim 2,
The carbon fiber is 0.5 to 5 parts by weight based on 100 parts by weight of the graphite core, the lithium secondary battery negative electrode active material. The method of claim 3, wherein
The amorphous graphite is 0.5 to 10 parts by weight based on 100 parts by weight of the graphite core, the lithium secondary battery negative electrode active material. The lithium secondary battery which has a negative electrode containing the negative electrode active material in any one of Claims 1-4.

Images