KR100444141B1 - Anode active materials for lithium secondary battery, anode plates and secondary battery using them - Google Patents

Abstract

The present invention relates to a negative electrode active material for a lithium secondary battery, a negative electrode plate and a secondary battery using the same, and in detail, iron oxide (γ-ferrite) and / or nickel oxide fine particles having an average particle diameter of 20 to 80 nm prepared by colloidal dispersion and freeze-dried. After reducing in a reducing atmosphere of 400 to 700 ℃ using a basic catalyst, and mixed with hydrogen in the catalyst surface of the mobile phase and / or fixed bed using carbon monoxide and / or hydrocarbon as the raw material gas gas phase at 640 to 700 ℃ The multi-layered carbon nanotubes produced by decomposition are used as negative electrode active materials for lithium secondary batteries.

In the present invention, the highly crystalline multilayer carbon nanotubes used as the negative electrode active material express high graphitization and high charge / discharge capacity without separate graphitization and high purity treatment, and are charged due to high crystallinity in the case of lithium ion storage / removal characteristics. 0.3 V vs. discharge It has the effect of showing a high capacity under Li / Li ⁺ .

Description

Negative active material for lithium secondary battery, negative electrode plate and secondary battery using same {Anode active materials for lithium secondary battery, anode plates and secondary battery using them}

The present invention relates to a negative electrode active material for a lithium secondary battery, a negative electrode plate and a secondary battery using the same, and more specifically, to a high-crystalline graphitized multi-walled carbon nanotubes (highly graphitized multi-walled carbon nanotubes) prepared according to the method of the present invention lithium secondary Provided is a technique for use as a negative electrode active material for batteries.

The locking chair type secondary battery, unlike the secondary battery using metal lithium, exhibits more than 80% of its initial capacity even after 500 cycles based on the excellent cycle stability of the graphite-based carbon material used as the negative electrode. It is a kind of high performance secondary battery.

Currently, carbon materials are limited and used as negative electrode active materials of lithium secondary batteries. Among these, the graphite-based carbon material is 0.3 V vs. owing to its excellent crystallinity. It is suitable as a negative electrode material for a high performance secondary battery because of its advantage of having a flat portion of a potential expressed below Li / Li ⁺ ( Carbon , 38 , 1261).

In order to use the graphite-based carbon material as a negative electrode material for batteries, in the case of artificial graphite, graphitizable precusors should be manufactured by graphitizing at a high temperature of 2400 ° C. or higher, and remain even in the case of conventional high crystalline natural graphite. In order to remove impurities, high-purity treatment using a halogen gas has to be performed, resulting in a high manufacturing cost.

Accordingly, an object of the present invention is to eliminate such problems of the prior art, and is a method for producing a low-cost, high-crystalline carbon material, a graphitized carbon material in spite of being a material produced only at a low heat treatment temperature of 700 ℃ or less Better crystallinity and 0.3 V vs. It is to provide a negative electrode active material for a lithium secondary battery having a lithium ion storage and removal performance of less than Li / Li ⁺ .

Another object of the present invention is to provide a graphite-based negative electrode active material without undergoing the graphitization and high purity treatment, which is essential for the production of a conventional graphite-based negative electrode active material, and the surface of the carbon hexagon mask surface of the carbon material manufactured under the manufacturing conditions of 1400 ℃ or less distance between the initial investment and production cost extremely (d ₀₀₂₎ is 0.3400 to nm less than, the method which can be obtained a highly-crystallized carbon material, a specific surface area of 100 m or less ² / g, and accordingly it takes to produce a graphitizable carbon material It can be lowered to provide a negative active material for a lithium secondary battery that can significantly reduce the manufacturing cost.

1 is a high-resolution transmission electron micrograph of carbon nanotubes as a negative electrode active material for a lithium secondary battery prepared according to Example 1;

2 is a CuKα wide-angle X-ray diffraction pattern of carbon nanotubes as a negative electrode active material for a lithium secondary battery prepared according to Example 1;

3 is a lithium ion removal characteristics according to Example 5 and Comparative Examples 1 to 3;

4 is a discharge cycle stability according to the fifth embodiment.

The negative electrode active material for lithium secondary battery of the present invention for achieving the above object,

Prepared by colloidal dispersion, iron oxide (γ-ferrite) and / or nickel oxide fine particles having an average particle diameter of 20 to 80 nm and freeze-dried were reduced in a reducing atmosphere of 400 to 700 ° C. using carbon monoxide and / or hydrocarbon. It is characterized in that the raw material gas is mixed with hydrogen at the surface of the catalyst in the mobile phase and / or fixed bed to produce a gas phase decomposition at 640 ~ 700 ℃ on the catalyst surface.

Accordingly, the present invention uses a chemical vapor growth method of growing carbon filaments by decomposing hydrocarbons such as ethylene on a catalyst by using lyophilized ultrafine iron oxide and / or nickel oxide as a base catalyst by colloidal dispersion. method) to manufacture a multi-layer nano-carbon tube that can be used as a negative electrode active material for lithium secondary batteries.

As used herein, the term "base catalyst" refers to iron oxide and / or nickel oxide before reduction, and "catalyst" refers to iron oxide and / or nickel oxide after reduction. The gas phase decomposition reaction of the present invention mainly refers to a reaction occurring in the catalyst, but is a concept including a reaction of some basic catalysts not subjected to reduction treatment.

The ultrafine iron oxide and / or nickel oxide particles have a very limited condensation between particles, so that each particle acts as a reaction point. It is used by lyophilization while maintaining the The contents of the nickel oxide fine particles can be found in some documents (Shinwawa, surface, 32-3, 35, 1994, etc.).

The ultrafine basic catalyst is reduced in a reducing atmosphere. The reducing atmosphere may use a mixed gas of hydrogen and nitrogen, a mixed gas of hydrogen and argon, a mixed gas of hydrogen and helium, and the like. The content of hydrogen in the mixed gas is preferably 2 to 50% by volume. When the content of hydrogen is small, it is difficult to cause a reduction reaction, and when there is a large amount, there is a risk of explosion.

The temperature of the reduction treatment is usually 400 to 700 ° C., if the temperature is 400 ° C. or less, the reaction may not be easily initiated and a long time is required for the treatment. If the temperature is 700 ° C. or more, aggregation of fine particles may occur. The time of the reduction treatment can be varied by various conditions such as the reduction treatment temperature, which takes about 0.5 to 24 hours. As one specific example, a method of reducing the ultrafine basic catalyst at 550 ° C. for 2 hours using a hydrogen-helium mixed gas may be mentioned.

Looking at the specific example of the reduction process, the ultra-fine iron oxide and / or nickel oxide fine particles are placed in the center of a horizontal or vertical furnace equipped with a quartz tube having an inner diameter of 1 to 25 cm in a ceramic boat or crucible, and then hydrogen After adjusting the mixing ratio of helium to 1: 50 to 1: 2 and flowing at a flow rate of 0.1 to 10 cm / sec, the temperature is raised to 400 to 900 ℃, and reduced at 400 to 550 ℃ for 10 minutes to 4 hours. Here, the more preferable inner diameter of the quartz tube is 3 to 15 cm, if the inner diameter is too small, the output is small, if the inner diameter is too large there is a problem that the uniformity (Uniform zone) can not be formed wide, the degree of crystallinity falls. More preferred flow rate is 2 to 6 cm / sec, if the flow rate is too small or too large, there is a problem that the yield and crystallinity of the product is poor.

In the source gas, hydrocarbons are unsaturated and / or saturated hydrocarbons composed of hydrogen and carbon, each having 1 to 4 carbon atoms such as acetylene (C ₂ H ₂ ), methane (CH ₄ ), ethylene (C ₂ H ₄ ), and ethane ( C ₂ H ₆ ), propylene (C ₃ H ₆ ), propane (C ₃ H ₈ ), butane (C ₄ H ₁₀ ), butylene (C ₄ H ₈ ), butadiene (C ₄ H ₆ ) and its isomers One or more than one selected from the group consisting of can be used. Such hydrocarbons may be used in a single form or in a mixture with an inert gas such as Ar, He or the like.

The mixing ratio of source gas and hydrogen gas is preferably 10 to 95%, more preferably 20 to 90%. If the proportion of the source gas is less than 10%, the amount of carbon nanotubes produced is not economical, and if it is more than 95%, the reaction is terminated early and is not economical either.

The temperature of the gas phase decomposition is preferably 640 to 700 ° C, more preferably 650 to 680 ° C. If the gas phase decomposition temperature is 640 ° C or less, the crystallinity is inferior, if it is 700 ° C or more, other microstructured carbon material may be made. The time of gas phase decomposition can be changed by various conditions such as the temperature of gas phase decomposition, and it takes about 10 minutes to 10 hours. As one specific example, the carbon monoxide-hydrogen mixed gas may be reacted at a reaction temperature of 650 ° C. for 1.5 hours.

As described above, the carbon nanotubes grown from the ultrafine particles or the reducing bodies thereof are replaced with helium gas, cooled to room temperature, and finally, the multilayer carbon nanotubes are recovered.

The high crystalline carbon nanotubes thus prepared have a lower specific surface area than conventional carbon nanotubes, and have relatively high crystallinity and electrical conductivity and 0.0 to 0.3 V vs. It is excellent in charge / discharge specific amount in Li / Li ⁺ and has optimum conditions as a negative electrode active material for lithium secondary batteries. Moreover, since the workability at the time of making an electrode mixture for electrode manufacture is superior to the case where the conventional flake graphite material is used, it is excellent in cycling stability.

The present invention also relates to a negative electrode plate for a lithium transfer battery using such a negative electrode active material.

Looking at the manufacturing example of the negative electrode plate for a lithium secondary battery according to the present invention,

The active material, organic polymer and / or oligomeric binder, conductive polymer and / or carbon conductive material of the multilayer carbon nanotubes are dispersed or dissolved in a solvent to form a dough or slurry, which is then metal foil. Or by applying to a grid.

The binder is 0.0 ~ 3.0 V vs. Preferred are polymers which do not decompose in the potential band between Li / Li ⁺ and are excellent in chemical stability and binding properties. More specifically, ethylene propylene diene monomer (ethylene-propylene diene monomer), tetraethylene glycol diacrylate (tetra (ethylene glycol) diacrylate), polydimethylsiloxane (polydimethylsiloxane), ethylene-ethyl acrylate (ethylacrylate) copolymer, Ethylene-vinylacetate copolymer, polyvinylidene difluoride, vinylidene difluoride-hexafluoropropylene copolymer, vinylidene difluoride-maleic anhydride ( maleic anhydride copolymer, polyvinylchloride, polymethylmethacrylate, polymethacrylate, cellulose triacetate, polyurethane, polysulfone, polyether polyether, polyethyleneoxide, polyisobutylene, polybutyldiene (po lybutyldiene, polyvinylalcohol, polyacrylonitrile, polyimide, polyvinyl formal, acrylonitrilebutyldiene rubber, styrenebutadiene rubber (Styrene-Butadiene-Rubber), one or two or more mixtures or two or more copolymers selected from the group consisting of oligomers and polysilicones thereof are particularly preferred.

Since the said conductive material is used for the purpose of improving the ion and / or electron conductivity of an electrode, there is no restriction | limiting in particular in the shape, A spherical shape, a fibrous form, plate shape, etc. can be used. More specifically, the granular materials include carbon blacks, thermal blacks, furnace blacks, mesocarbon microbeads and spherical graphite, and the fibrous materials include vapor phase. Growth carbon fibers, fibrous nanocarbon, carbon nanotubes, and the like, the plate material is natural graphite, it may be used by mixing one or more of these materials. More preferably, carbon black, smalmal black, furnace black, mesocarbon microbeads, vapor-grown carbon fibers, fibrous nanocarbons, carbon nanotubes, or a mixture of one or two or more thereof are used.

When making the negative plate, in order to make a uniform phase and obtain a viscosity suitable for processing, organic solvents and / or water are used as a solvent and / or a dispersion medium to make dough and / or slurry suitable for application. Depending on manufacturing scale and manufacturing conditions (drying temperature, coating and laminating speed, etc.), preferred solvents include N-methylpyrrolidinone, dimethylformamide and dimethylacetamide. (dimethylacetamide), hexamethylphosphoramide, tetrahydrofuran, acetonitrile, cyclohexanone, chloroform, dichloromethane, dimethylsulfoxide, acetone, dioxene and various ketones Can be mentioned. When making dough or slurry, grinding or milling may be performed to control the porosity of the final electrode plate, and the porosity may be 50% or less as measured by the BET method and the image analysis method. It is suitable, and may include a thermocompression process during the manufacturing of the electrode plate to control the porosity.

The present invention also relates to a lithium secondary battery using such a negative electrode plate. The construction of the lithium secondary battery and a manufacturing method thereof are well known in the art, and thus a detailed description thereof will be omitted.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples thereof, but the scope of the present invention is not limited thereto.

Example 1

50 mg of ultrafine iron oxide (γ-ferrite, γ-Fe ₃ O ₄ ) fine particles (γ-ferrite, γ-Fe ₃ O ₄ ) particles prepared by colloidal dispersion and freeze-dried with an average particle diameter of about 40 nm were placed in a ceramic boat. It was placed at the center of a horizontal furnace equipped with a 10 cm inner diameter quartz tube, and heated to 550 ° C. while flowing a hydrogen-helium mixed gas having a mixing ratio of 20% by volume of hydrogen at a flow rate of 2 to 4 cm / sec. Thereafter, reduction treatment was performed at 550 ° C. for 2 hours.

Then, a carbon monoxide-hydrogen mixed gas having a carbon monoxide mixing ratio of 80% was reacted at 650 ° C. for 1.5 hours at a flow rate of 200 ml / min to prepare multilayer carbon nanotubes, and after the reaction was completed, the atmosphere was replaced with helium gas. After cooling to room temperature, nanotubes grown from the iron oxide catalyst particles were recovered from the ceramic boat. The weight of the recovered carbon nanotubes was 1024 mg.

A photograph taken of the multilayer carbon nanotubes prepared above with a high resolution transmission electron microscope (x9,000,000 times) is shown in FIG. 1. From the photograph of FIG. 1, it can be seen that the multilayer carbon nanotubes according to the present invention have an average diameter of 25 nm and have an advanced graphite crystal layer surface.

In addition, the carbon nanotubes prepared above were subjected to powder graphite crystallite analysis using a wide-angle X-ray diffractometer using a light source of CuKα (學 進 法, 大谷 彬 郞, 炭素 纖維, 附錄, 講 談 社, 東京, 1984, (Japanese)) 2 shows the results of irradiating the diffraction pattern to 5 to 90 ° under the conditions of 40 Hz and 30 Hz. It can be seen that the average interplanar distance (d ₀₀₂ ) of the multilayer carbon nanotubes calculated from the wide-angle X-ray diffraction pattern (hereinafter referred to as "XRD pattern") of FIG. 2 shows very high graphitization (high crystallinity) of 0.3380 nm. . The specific surface area measured by BET N ₂ adsorption method was 86 m 2 / g.

Example 2

Except for using acetylene (C ₂ H ₂ ) in place of the carbon monoxide as a raw material gas was a multi-layered carbon nanotubes were prepared in the same manner as in Example 1. The manufactured and recovered carbon nanotubes weighed 824 mg, and the XRD pattern of the produced carbon nanotubes was similar to that of FIG. 2, and the average interplanar distance (d ₀₀₂ ) of the carbon nanotubes calculated from the XRD patterns was found to be 0.3390 nm. It can be seen that qualitative. The specific surface area measured by the BET N ₂ adsorption method was 72 m 2 / g.

Example 3

The multilayer carbon nanotubes were manufactured in the same manner as in Example 1, except that the mixing ratio of carbon monoxide was 20% instead of 80%. The weight of the manufactured and recovered carbon nanotubes was 340 mg, and the XRD pattern of the produced nanotubes was similar to that of FIG. 2, and the average interplanar distance (d ₀₀₂ ) of the nanotubes calculated from the XRD patterns was 0.3390 nm. Able to know. The specific surface area measured by BET N ₂ adsorption method was 54 m 2 / g.

Example 4

The multilayer carbon nanotubes were manufactured in the same manner as in Example 1, except that ultrafine nickel oxide fine particles were used instead of the ultrafine iron oxide. The weight of the manufactured and recovered carbon nanotubes was 530 mg, and the XRD pattern of the produced nanotubes was similar to that of FIG. 2, and the average interplanar distance (d ₀₀₂ ) of the nanotubes calculated by the school method from the XRD pattern was 0.3398 nm. It can be seen that it corresponds to a relatively high crystallinity. In addition, the specific surface area measured by the BET N ₂ adsorption method was 38 m 2 / g.

The contents of the charge and discharge experiments after preparing the negative electrode plate using the multilayer carbon nanotubes prepared according to the present invention as an active material which is a negative electrode material for a lithium secondary battery are described in the following examples.

Example 5

A negative electrode plate was prepared by mixing the multilayer carbon nanotubes prepared in Example 1 as an active material of the negative electrode plate and PVdF as a binder in a ratio of 93: 7 (weight ratio). The negative electrode plate thus prepared was charged and discharged at a current density of 50 mAg ^-1 using a solution in which LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate at a concentration ratio of 1 M as an electrolyte. It was done. The result is shown in Figure 3 as 'A', as can be seen in Figure 3, the negative electrode active material according to the present invention is 0.0 ~ 0.3 V vs. It can be seen that the crystallinity is comparable to that of natural graphite and artificial graphite prepared at 3000 ° C by showing a distinct stage behavior between Li / Li ⁺ .

In addition, 120 charge / discharge experiments were performed on the negative electrode plate prepared as described above by making a coin cell half cell at a current rate of C / 5 in a 1.35 M LiPF ₆ / EC + PC solvent. As can be seen in Figure 4, the material does not deteriorate even after 110 cycles it can be seen that excellent cycle stability.

Example 6

Except that the multilayer carbon nanotubes prepared in Example 1 as the active material of the negative electrode plate, the multilayer carbon nanotubes prepared in Example 1 as the conductive material, and PVdF in the ratio of 86: 7: 7: A negative electrode plate was manufactured in the same manner as in Example 5, and the charge and discharge experiments were conducted. As a result, almost the same results as in Example 5 were obtained.

In order to compare with the method according to the present invention, a comparative experiment by various methods was performed.

Comparative Example 1

Charge and discharge experiments were carried out by fabricating a negative electrode plate in the same manner as in Example 5 except that brazilian natural graphites were used as active materials instead of the multilayer carbon nanotubes according to the present invention. The results are shown as 'B' in FIG.

Comparative Example 2

Charge and discharge experiments were carried out by preparing a negative electrode plate in the same manner as in Example 5 except that commercially available mesophase pitch-based carbon fibers (MCF) were used as an active material instead of multilayer carbon nanotubes according to the present invention. It was done. The results are shown as 'C' in FIG.

Comparative Example 3

Charge and discharge experiments were carried out by preparing a negative electrode plate in the same manner as in Example 5 except that commercially available graphitized MCMBs (mesocarbon microbeads) manufactured by Osaka Gas Co., Ltd. were used instead of the multilayer carbon nanotubes according to the present invention. It was. The results are shown as 'D' in FIG.

Referring to FIG. 3, which shows the results of Example 5 and Comparative Examples 1 to 3, it is compared with conventional active materials (Comparative Examples 1 to 3) which can obtain high crystallinity only by heat treatment in an inert atmosphere of 3000 ° C. or higher. Thus, the multilayer carbon nanotube active material (Example 5) of the present invention prepared at a low temperature (1000 ° C. or less) was 0.0 to 0.3 V vs. It can be seen that it shows excellent crystallinity by showing stage behavior below Li / Li.

Those skilled in the art to which the present invention pertains can make various applications and modifications within the scope of the present invention based on the above contents.

Unlike the conventional graphite-based carbon material, the negative electrode active material for a lithium secondary battery according to the present invention is the only high crystalline carbon raw material that can be manufactured without undergoing high-cost graphitization and high purity treatment, and has a high graphitization property that can be produced at low cost. Since it is a carbon material, there is an effect that can greatly contribute to the production of secondary batteries of low production cost.

Claims (6)

Prepared by colloidal dispersion, iron oxide (γ-ferrite) and / or nickel oxide fine particles having a freeze-dried average particle diameter of 20 to 80 nm are used as a basic catalyst, and then reduced in a reducing atmosphere of 400 to 700 ° C., followed by carbon monoxide and / or hydrocarbons. is a to and mixed with the hydrogen from the catalyst surface of the mobile phase and / or stationary phase with the source gas, and prepared by decomposition gas phase at 640 to 700 ℃ from the catalyst surface, the surface of the carbon hexagonal mangmyeon of the produced carbon material, spacing (d ₀₀₂₎ 0.3400 nm The negative electrode active material for lithium secondary batteries which is less than and is a highly crystalline carbon material whose specific surface area is 100 m <2> / g or less. The method of claim 1, wherein the reducing atmosphere is a mixed gas of hydrogen and nitrogen, a mixed gas of hydrogen and argon, or a mixed gas of hydrogen and helium, characterized in that the content of hydrogen in the mixed gas is 2 to 50% by volume. A negative electrode active material for a lithium secondary battery. The method of claim 1, wherein in the source gas, the hydrocarbon is an unsaturated and / or saturated hydrocarbon composed of hydrogen and carbon, acetylene (C ₂ H ₂ ), methane (CH ₄ ), ethylene (C ₂ ) having 1 to 4 carbon atoms H ₄ ), ethane (C ₂ H ₆ ), propylene (C ₃ H ₆ ), propane (C ₃ H ₈ ), butane (C ₄ H ₁₀ ), butylene (C ₄ H ₈ ), butadiene (C ₄ H ₆ ) and one or more selected from the group consisting of isomers thereof, The mixing ratio of source gas and hydrogen gas is a negative electrode active material for lithium secondary battery, characterized in that the ratio of the source gas per volume is 10 to 95%. The negative electrode active material of claim 1, wherein the gas phase decomposition temperature is 650 to 680 ° C. The negative electrode plate for lithium secondary batteries using the negative electrode active material of Claims 1-4. A lithium secondary battery using the negative electrode plate according to claim 5.