KR20010025881A - Negative active material for lithium secondary battery and method of preparing same - Google Patents

Abstract

PURPOSE: A negative active material for lithium secondary battery capable of forming an active layer on a current collector without pretreating the current collector is provided which reduces the cost of production and can increase a charge and discharge capacity. CONSTITUTION: This negative active material for lithium secondary battery comprises a core containing crystalline carbon; a first layer formed on the core and containing 0.01 to 10% by weight of a graphitized catalyst based on the total weight of the active material; and a second layer formed on the first layer and containing a quasi-crystalline carbon. In a process for producing the title compound, the carbon material containing an amorphous carbon precursor is graphitized at 2,000 to 3,000 deg.C.

Description

Negative active material for lithium secondary battery and manufacturing method thereof {NEGATIVE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY AND METHOD OF PREPARING SAME}

[Industrial use]

The present invention relates to a negative electrode active material for a lithium secondary battery and a method for manufacturing the same, and more particularly, to a negative electrode active material for a lithium secondary battery having a high capacity and excellent charge and discharge efficiency and a manufacturing method thereof.

[Prior art]

As the negative electrode active material of the lithium secondary battery, a carbon-based material is mainly used. Such carbonaceous materials include crystalline carbon and amorphous carbon. While amorphous carbon has a high discharge capacity, it has a disadvantage of high irreversible capacity, low charge and discharge efficiency, and excellent voltage flatness. Crystalline carbon has excellent voltage flatness, but has a disadvantage in that the electrolyte must be limited. Examples of such crystalline carbon include artificial graphite obtained by firing natural graphite and pitch at a high temperature of 2000 ° C. or higher. Among them, artificial side edge has a disadvantage of high charge and discharge efficiency but low capacity, and natural graphite has a disadvantage of low charge and discharge efficiency although relatively high charge and discharge capacity. Therefore, in order to manufacture a high capacity battery among such natural graphite and artificial graphite, natural graphite should be used, but since natural graphite has a very high reactivity with an electrolyte, there is a disadvantage in that the electrolyte must be used in a limited manner.

Therefore, in recent years, a method of mixing and using two kinds of carbons in order to take advantage of both crystalline carbon and amorphous carbon has been studied. Accordingly, by coating amorphous carbon on natural graphite or coke and heat treatment at about 1000 ℃ to prepare a material having the advantages of both amorphous carbon and crystalline carbon was used as a negative electrode material. However, this active material has a drawback due to the amorphous carbon layer is reflected in the negative electrode active material was halved the improvement effect of the characteristics.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a negative electrode active material for a lithium secondary battery having high capacity and excellent charge and discharge efficiency.

Another object of the present invention is to provide a negative electrode active material for a lithium secondary battery that can be used without limitation to the type of electrolyte.

Still another object of the present invention is to provide a method for producing the negative electrode active material for a lithium secondary battery.

1 is a cross-sectional view schematically showing the structure of a negative electrode active material for a lithium secondary battery of the present invention.

In order to achieve the above object, the present invention comprises a core containing crystalline carbon; A first layer formed on the core and comprising a graphitization catalyst element; And a second layer formed on the first layer and including a semicrystalline carbon.

The present invention also provides a method of coating a method comprising: coating amorphous or crystalline carbon with a graphitization catalyst element or a compound thereof; Coating amorphous or crystalline carbon coated with the graphitizing catalyst element or a compound thereof with an amorphous carbon precursor; And graphitizing a carbon material comprising the amorphous or crystalline carbon, a graphitization catalyst element formed on the carbon or a compound thereof, and an amorphous carbon precursor formed on the graphitization catalyst element or a compound thereof at 2000 to 3000 ° C. Provided is a method for producing a negative electrode active material for a lithium secondary battery.

Hereinafter, the present invention will be described in more detail.

The negative electrode active material of the present invention is a triple layer consisting of a core containing crystalline carbon, a first layer containing a graphitization catalyst element formed on the core, and a second layer containing semicrystalline carbon formed on the first layer. It is a negative electrode active material of the structure.

In the present invention, as the graphitization catalyst element, a transition metal, an alkali (earth) metal or a semimetal can be used, and preferably an alkali (earth) of transition metals Ca, Mg of Ni, Fe, Cr, Co, and Cu. Metals or semimetals of Si, B, Ti, Ga, Ge, Al can be used. As the compound of the graphitization catalyst element, any compound may be used as long as it includes the graphitization catalyst element. For example, the compound may be an oxide, a nitride, a sulfide, a hydroxide, or the like. The amount of graphitization catalyst element contained in the negative electrode active material of the present invention is 0.01 to 10% by weight of the total active material weight. When the content of the graphitization catalyst is less than 0.01% by weight, the effect of increasing the graphitization degree of the active material is insignificant, and when the content of the graphitization catalyst is more than 10% by weight, heterogeneous compounds are formed to prevent the movement of Li ions.

The method of manufacturing the negative electrode active material of the present invention having the above configuration is as follows.

Amorphous or crystalline carbon is coated with a graphitizing catalyst element or a compound thereof. As the graphitization catalyst element, a transition metal, an alkaline earth metal or a semimetal may be used. Preferably, transition earth metals such as Ni, Fe, Cr, Co, Cu, alkaline earth metals such as Mg, Si, B, Ti, Half metals of Ga, Ge or Al can be used. In addition, as the compound of the graphitization catalyst element, any kind of compound may be used as long as it contains the graphitization catalyst element. Examples thereof may include oxides, nitrides, sulfides, hydroxides, and the like.

The coating method may be a general coating method such as sputtering, chemical vapor deposition (CVD), dip coating, etc., but the simplest coating method is a dip coating method in which powder is simply dipped in a coating solution and then taken out. Preference is given to using. In the case of using the dip coating method, a compound of the graphitization catalyst element is prepared and used as a solution. The solution of the graphitizing catalytic element compound uses an organic solvent or an inorganic solvent according to the characteristics of the compound, and the concentration of the solution is adjusted in consideration of the solubility of the catalytic element compound. Examples of the organic solvent and the inorganic solvent may include ethanol, isopropyl alcohol, toluene, benzene, hexane, tetrahydrofuran, water and the like.

As the amorphous carbon, soft carbon (soft carbon) or hard carbon may be used. The soft carbon may be obtained by heat-treating coal-based pitch, petroleum-based pitch, tar, or low molecular weight heavy oil, and the hard carbon may be a phenol resin, naphthalene resin, polyvinyl alcohol resin, urethane resin, polyimide resin, furan It can obtain by heat-processing resin, a cellulose resin, an epoxy resin, polystyrene resin, etc.

As the crystalline carbon, amorphous, plate, flake, spherical or fibrous natural graphite or artificial graphite may be used alone or in combination of two or more.

Next, the amorphous or crystalline carbon coated with the obtained graphitization catalyst element or a compound thereof is coated with an amorphous carbon precursor. This coating method may be any of the general coating methods described above, but it is preferable to use a dip coating method. When using the dip coating method, an amorphous carbon precursor solution is used.

The amorphous carbon precursor solution is prepared by dissolving, melting, softening or dispersing the amorphous carbon precursor in a solvent. As the solvent, an organic solvent or an inorganic solvent may be used. Examples thereof include toluene, tetrahydrofuran, benzene, methanol, ethanol, hexane, cyclohexane, water, and the like. In some cases, a mixture thereof may be used. As the amorphous carbon precursor, resins such as phenol resin, naphthalene resin, polyvinyl alcohol resin, urethane resin, polyimide resin, furan resin, cellulose resin, epoxy resin, polystyrene resin, coal pitch, petroleum pitch, tar (tar) ) Or low molecular weight heavy oil. Of these, coal pitch and petroleum pitch are preferably used because they can exhibit a higher capacity and a smaller irreversible capacity. More preferably, an organic solvent soluble pitch obtained by dissolving a coal pitch or a petroleum pitch in an organic solvent such as toluene or tetrahydrofuran and extracting is used.

An amorphous or crystalline carbon core coated with a graphitizing catalyst element or a compound thereof and an amorphous carbon precursor is graphitized to heat at 2000 to 3000 ° C. to prepare a negative electrode active material for a lithium secondary battery. In this heat treatment step, the graphitization of the amorphous carbon on the surface proceeds and is converted into semicrystalline carbon, and only the transition metal and the semimetal remain in the graphitization catalyst compound to form the graphitization catalyst layer. The amorphous carbon of the core is also converted to crystalline carbon by performing the heat treatment step at a high temperature.

In the present invention, the graphitization catalyst element is diffused into the core because the activity of the atoms at a high temperature is increased, or in the thermodynamic aspect of the energy (Free energy) state is changed through a mechanism such as carbide formation (carbide formation) or carbide decomposition The crystallinity of the core can be increased to increase the amount of desorption / insertion of lithium ions, and a turbostratic structure can be formed in the amorphous second layer such as resin or pitch. As used herein, a turbostratic structure refers to a structure that exhibits extremely low crystallinity and small crystal size, similar to an amorphous structure, and exhibits a somewhat disordered orientation.

When the heat treatment step is performed at 2000 to 3000 ° C., an anode active material having I (110) / I (002), which is the ratio of the X-ray diffraction intensity of the (110) plane to the X-ray diffraction intensity of the (002) plane, is 0.04 or less. Lose. The smaller the X-ray diffraction intensity ratio, the higher the capacity, and the high capacity natural graphite has an X-ray diffraction intensity ratio of about 0.04 or less. Therefore, the negative electrode active material of the present invention can provide a battery having a high capacity.

The negative electrode active material produced by the above-described method has a three-layer structure as shown in FIG. 1, and includes a core 1, a first layer 2 including a graphitization catalyst element formed on the core, and a first layer 2 formed on the first layer. It consists of a second layer 3 comprising semicrystalline carbon. That is, since the negative electrode active material of the present invention is formed of a turbostratic structure having a semicrystalline carbon structure, the reactivity with the electrolyte is reduced. Accordingly, since the negative active material can reduce side reaction products generated by reacting with the electrolyte solution, the charging and discharging efficiency can be increased, and the electrolyte solution of the polycarbonate is not limited to any kind, and particularly excellent in low temperature characteristics, and dielectric constant (Dielectric It is possible to use a propylene carbonate that can dissolve a large amount of inorganic lithium salts because of the large constant. In addition, due to the graphitization catalyst element, since the crystallinity of the core is increased, the charge and discharge capacity can be increased.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only one preferred embodiment of the present invention and the present invention is not limited to the following examples.

(Example 1)

After soaking the carbon powder in a 5% aqueous boronic acid solution for about 30 minutes, the powder was separated from the boronic acid solution. The obtained boronic acid-coated carbon powder was dipped in a phenol resin solution for about 10 minutes, and then the powder was separated from the phenol resin solution. Carbonic acid powder coated with boronic acid and phenol resin was heat-treated in an inert atmosphere at 2800 ° C. to obtain a negative active material for a lithium secondary battery having high crystallinity.

(Example 2)

Except for using nickel nitrate instead of boronic acid it was carried out in the same manner as in Example 1.

(Example 3)

The same process as in Example 1 was carried out except that natural graphite powder was used instead of the carbon powder.

(Comparative Example 1)

Carbon powder was used as a negative electrode active material for a lithium secondary battery.

(Comparative Example 2)

Natural graphite powder was used as a negative electrode active material for a lithium secondary battery.

A slurry was prepared by mixing the negative active materials for the lithium secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2 with a polyvinylidene fluoride binder and an N-methylpyrrolidone solvent. This slurry was applied thinly to copper foil and dried to prepare a negative electrode. A 2016 type coin battery was manufactured using the prepared negative electrode, separator, and lithium metal as counter electrodes. At this time, a mixture of ethylene carbonate / dimethyl carbonate / propylene carbonate containing 1 mol LiPF ₆ was used as the electrolyte solution.

Discharge capacity and charge and discharge efficiency of the manufactured lithium secondary battery were measured and the results are shown in Table 1.

Discharge Capacity [mAh / g] Charge and discharge efficiency [%] Example 1 338 90.1 Example 2 316 89.2 Example 3 352 88.1 Comparative Example 1 280 53.0 Comparative Example 2 347 51.0

As shown in Table 1, the lithium secondary battery using the negative electrode active material of Example 1-3 can be seen that the discharge capacity is superior to the battery of Comparative Example 1-2. This is thought to be due to the increased crystallinity of the core of the negative electrode active material of Example 1-3 due to the graphitization catalyst element. In particular, it can be seen that the charge and discharge efficiency of the battery of Example 1-3 is much better than that of Comparative Example 1-2. This is thought to be due to the reduced reactivity with the electrolyte as the negative electrode active material of Example 1-3 has a surface of the turbostratic structure.

As described above, as the negative electrode active material for the lithium secondary battery includes the graphitization catalyst element, the crystallinity of the core of the negative electrode active material is increased, thereby increasing the charge and discharge capacity of the lithium secondary battery. In addition, the negative electrode active material for a lithium secondary battery of the present invention has a low reactivity with an electrolyte solution as the surface has a turbostratic structure. Therefore, even when a propylene carbonate electrolyte is used, the charge and discharge efficiency of the lithium secondary battery can be increased.

Claims (7)

A core comprising crystalline carbon; A first layer formed on the core and comprising a graphitization catalyst element; And A second layer formed over the first layer and comprising semicrystalline carbon A negative electrode active material for a lithium secondary battery comprising a. The method of claim 1, wherein the graphitization catalyst element is a transition metal selected from the group consisting of Ni, Fe, Cr, Co and Cu, alkaline earth metal of Ca or Mg, and Si, B, Ti, Ga, Ge and Al A negative electrode active material for a lithium secondary battery which is at least one element selected from the group consisting of semimetals selected from the group consisting of. The negative active material of claim 1, wherein the amount of the graphitization catalyst element is 0.01 to 10 wt% of the total weight of the active material. The negative active material of claim 1, wherein the negative active material has an I-110 / I (002) of 0.04 or less, which is an X-ray diffraction intensity ratio between the (002) plane and the (110) plane. The negative active material of claim 1, wherein the second layer has a turbostratic structure. Coating amorphous or crystalline carbon with a graphitization catalyst element or a compound thereof; Coating amorphous or crystalline carbon coated with the graphitizing catalyst element or a compound thereof with an amorphous carbon precursor; And Graphitizing a carbon material comprising the amorphous or crystalline carbon, a graphitization catalyst element or a compound formed on the carbon, and an amorphous carbon precursor formed on the catalyst element or a compound thereof at 2000 to 3000 ° C Method for producing a negative electrode active material for a lithium secondary battery comprising a. The method according to claim 6, wherein the graphitization catalyst element or a compound thereof is a transition metal selected from the group consisting of Ni, Fe, Cr, Co and Cu, alkaline earth metal of Ca or Mg, and Si, B, Ti, Ga, Ge And at least one element selected from the group consisting of semimetals selected from the group consisting of Al or compounds thereof.