KR20170120314A - Composite of vanadium oxide, cathode for lithium secondary battery comprising the same and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a vanadium oxide composite, and more particularly, to a technique for applying a vanadium oxide composite having a structure in which a carbon nanotube (CNT) aggregate in a vanadium oxide matrix is dispersed to a cathode active material of a lithium secondary battery. According to the present invention, since the carbon nanotube (CNT) aggregate is used, the carbon nanotubes are easily dispersed in the vanadium oxide matrix, and the manufacturing process is simplified because there is no separate dispersion process. Such a vanadium oxide composite not only improves the electric conductivity but also can suppress the collapse of the electrode structure due to the elution of vanadium into the electrolyte during the charging and discharging processes.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a positive electrode for a lithium secondary battery comprising a vanadium oxide composite, a positive electrode for a lithium secondary battery comprising the same,

The present invention relates to a vanadium oxide composite, and more particularly, to a technique for applying a vanadium oxide composite having a structure in which a carbon nanotube (CNT) aggregate in a vanadium oxide matrix is dispersed to a cathode active material of a lithium secondary battery.

2. Description of the Related Art As technology development and demand for mobile devices have increased, demand for secondary batteries as energy sources has been rapidly increasing. In recent years, the use of secondary batteries as a power source for electric vehicles (EVs) and hybrid electric vehicles . Accordingly, a lot of research has been conducted on a secondary battery that can meet various demands, and in particular, there is a high demand for a lithium secondary battery having a high energy density, a high discharge voltage, and an output stability.

Lithium secondary battery technology has been applied to various fields at present through remarkable development. However, in view of capacity, safety, output, enlargement and miniaturization of batteries, various batteries capable of overcoming the limitations of current lithium secondary batteries have been studied . Metal-air batteries, which have a theoretical capacity in terms of capacity in comparison with current lithium secondary batteries, all solid batteries that do not have explosion risk in terms of safety, lithium secondary batteries in terms of output, (Na-S) or redox flow battery (RFB) in the aspect of enlargement, and a thin film battery in the aspect of miniaturization. Continuous research is underway in academia and industry.

Generally, a lithium secondary battery uses a metal oxide such as LiCoO ₂ as a cathode active material and a carbon material as a negative electrode active material, and a polyolefin-based porous separator is sandwiched between a cathode and an anode, and a non-aqueous electrolytic solution having a lithium salt such as LiPF ₆ Impregnated. However, LiCoO _{2, which} is used as a cathode active material in most commercial lithium secondary batteries, has a high operating voltage and a large capacity. However, due to the limit of the amount of resources, LiCoO ₂ is relatively expensive and has a charge / discharge current of about 150 mAh / g And the crystal structure is unstable at a voltage of 4.3 V or more, causing a reaction with the electrolytic solution, and there is a risk of ignition. Moreover, LiCoO ₂ has a disadvantage in that it exhibits a very large change in physical properties even when some parameters are changed on the manufacturing process.

One of the alternatives to this LiCoO ₂ is LiMn ₂ O ₄ . LiMn ₂ O ₄ has a lower capacity than LiCoO ₂ but has a low cost and no pollution factor.

Looking at the typical examples of the structure of LiCoO ₂ and LiMn ₂ O ₄ of the positive electrode active material, LiCoO ₂ has a layered structure (Layered structure), LiMn ₂ O ₄ has a spinel if (Spinel) structure. These two materials commonly have excellent performance as a battery when they have excellent crystallinity. Therefore, in order to crystallize the two materials, it is necessary to carry out the heat treatment process during the manufacture of the thin film or the post-process. Therefore, the fabrication of a battery using these two materials on a polymer (e.g., plastic) material for medical or special purposes is impossible up to now because the polymer material can not withstand the heat treatment temperature.

In order to solve the disadvantages of the two materials, vanadium oxide is proposed. The vanadium oxide has an advantage that it has very good electrode characteristics even in the amorphous state although the capacity is low. In the case of vanadium oxide, the synthesis of the vanadium oxide is relatively easy and the synthesis is possible at room temperature. The amorphous vanadium oxide synthesized at room temperature is superior to the crystalline vanadium oxide in its performance (for example, life or efficiency). Therefore, if vanadium oxide is used as a cathode active material, a room temperature process becomes possible, and it becomes possible to manufacture a secondary battery on a polymer material such as a plastic. For this reason, vanadium oxides by various chemical methods and vacuum thin film synthesis methods are expected to be highly applicable to cathode active materials of secondary batteries in the future.

However, a lithium secondary battery using vanadium oxide as a cathode active material has not yet been put into practical use, because the vanadium oxide anode does not exhibit sufficient charge / discharge characteristics.

Factors determining the performance of the battery include total energy storage capacity, instantaneous power density, and self-discharge rate. Particularly, in the case of the secondary battery, since the battery is repeatedly charged and discharged, the change in capacity due to the number of times of charge and discharge must be small. These characteristics are referred to as the cycle characteristics. These characteristics are due to the development of ultra-precision electronic and semiconductor engineering, and the life cycle of recently developed and produced electronic products (or parts) is extended, It is demanded desperately.

Korean Patent Laid-Open Publication No. 2004-0032421 entitled " Method for producing positive electrode plate for lithium secondary battery using vanadium pentoxide "

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made to solve the above problems and to solve the conventional problems. The present inventors have solved the problem caused by the low electric conductivity and the ion diffusion coefficient of vanadium oxide and have found that a cathode active material having excellent charge / discharge characteristics, The present invention has been completed.

Accordingly, an object of the present invention is to provide a vanadium oxide composite in which the electric conductivity is improved and the electrode structure is not collapsed by elution.

Another object of the present invention is to provide a positive electrode for a lithium secondary battery to which a vanadium oxide composite is applied as a positive electrode active material and a lithium secondary battery comprising the same.

It is still another object of the present invention to provide a method for producing the vanadium oxide composite.

In order to solve the above problems, the present invention provides a vanadium oxide composite having a structure in which a carbon nanotube aggregate is dispersed in a vanadium oxide matrix, a cathode to which the anode composite is applied, and a lithium secondary battery comprising the same.

According to the present invention, since the carbon nanotube (CNT) aggregate is used, the carbon nanotubes are easily dispersed in the vanadium oxide matrix, and the manufacturing process is simplified because there is no separate dispersion process. Such a vanadium oxide composite not only improves the electric conductivity but also can suppress the collapse of the electrode structure due to the elution of vanadium into the electrolyte during the charging and discharging processes.

1 is an SEM image of a vanadium oxide composite prepared according to an embodiment of the present invention.
FIG. 2 is a graph showing a capacity retention rate and efficiency characteristics of a lithium secondary battery manufactured according to Examples and Comparative Examples according to the progress of a cycle.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Vanadium oxide complex

The present invention discloses a vanadium oxide composite characterized in that a carbon nanotube (CNT) aggregate is dispersed in a vanadium oxide matrix.

The material based on vanadium oxide (Vanadium Oxide) is theoretically suitable as an electrode material due to the conversion of many oxidation states of vanadium having a high specific capacity. However, electric conductivity and ion diffusion coefficient There is a problem in that vanadium is eluted into the electrolytic solution and the electrode structure is collapsed.

Therefore, in order to complement the low electrical conductivity and ion diffusion coefficient of vanadium oxide and to prevent the collapse of the electrode structure during the charging and discharging processes, The purpose of the present invention is achieved by including tubes in the form of aggregates and matrixing them to form conductive structures.

Carbon nanotubes are substances in which the carbon atoms arranged in a hexagonal shape are in the form of a tube and have a diameter of 1 to 100 nm. Carbon nanotubes exhibit nonconductive, conductive, or semiconducting properties depending on their unique chirality. The carbon atoms are connected by a strong covalent bond, so tensile strength is about 100 times larger than steel, and excellent flexibility and elasticity , And is chemically stable.

Examples of such carbon nanotubes include single-walled carbon nanotubes (SWCNTs) composed of one layer and having a diameter of about 1 nm, double-walled carbon nanotubes composed of two layers and having a diameter of about 1.4 to 3 nm Walled carbon nanotube (DWCNT), and a multi-walled carbon nanotube (MWCNT) having a diameter of about 5 to 100 nm, which is composed of a plurality of pellets or more. Although all of the carbon nanotubes constituting the vanadium oxide composite of the present invention can be used without any particular limitation, it is preferable to apply aggregated aggregates (for example, a bundle type described below) of single wall or double wall carbon nanotubes , Multi-walled carbon nanotubes are themselves applicable.

That is, the term 'carbon nanotube aggregate' used in the present invention means aggregated forms of single wall or double wall carbon nanotubes or multiwall carbon nanotubes unless otherwise stated. When such aggregate-type carbon nanotubes are applied, there is no entanglement in the vanadium oxide matrix, so that they can be easily dispersed to omit a separate dispersion process, and also contribute to improve the electrical conductivity of the vanadium oxide composite, It is preferable for application as an active material.

The term 'Bundle' used in the present invention refers to a bundle or a rope shape in which a plurality of carbon nanotubes are arranged or intertwined in parallel, unless otherwise stated.

The carbon nanotubes according to the present invention can be fabricated by various methods such as arc-discharge, laser vaporization, plasma enhanced chemical vapor deposition, thermal chemical vapor deposition, vapor phase vapor deposition phase growth, electrolysis, Flame synthesis, and the like. For example, single-walled carbon nanotubes having a diameter of 1 nm or less can be grown at a high yield by a laser deposition method, and the grown single-walled carbon nanotubes are grown in the longitudinal direction, waals force to form a mass, and bundles are bundled to form a bundle-like aggregate.

Such a bundle-type carbon nanotube aggregate basically has a shape in which a plurality of carbon nanotube strands are bundled together to form a bundle, and each of the bundles has a straight, curved, or mixed shape. Also, bundles of bundled carbon nanotubes aggregated therein may also have a linear shape, a curved shape, or a mixture thereof. According to one embodiment, such a bundle-type carbon nanotube aggregate may have a thickness of 50 nm to 100 μm.

According to one embodiment, the carbon nanotube strands have an average particle diameter of 1 to 20 nm, and the bundle-type carbon nanotube aggregates have an average length of 1 to 1,000 μm, preferably 10 to 300 μm , And a bulk density in the range of 80 to 250 kg / m ³ , preferably 100 to 220 kg / m ³ . A bundle-type carbon nanotube aggregate having an average particle diameter, an average length and a bulk density in this range is a more favorable structure for improving the conductivity of the vanadium oxide matrix. The carbon nanotubes have a network structure in the vanadium oxide matrix. The carbon nanotubes having a longer length are more advantageous in forming such a network, and as a result, the frequency of inter-network contact is reduced, More than the other.

More specifically, a graphite tank in an oven at 1200 ° C is irradiated with a laser to vaporize the graphite. At this time, the oven can be filled with helium or argon gas to maintain the pressure at about 500 Torr. The carbon clusters vaporized in the graphite target are adsorbed and condensed in a Cu collector which is cooled at a low temperature, and thus the condensed material obtained is mixed with carbon nanotubes, carbon nanoparticles and carbon particles. When the target is made of pure graphite, multi-walled carbon nanotubes are synthesized in the condensed material. However, when graphite in which Co, Ni, Fe, Y, etc. are mixed in an appropriate ratio instead of pure graphite is used as a target, The nanotubes can be synthesized and form a bundle.

The vanadium oxide according to the present invention is represented by the following formula (1)

V _a O _b

(Provided that 1? A? 6 and 2? B? 13 in the above formula)

Depending on the oxidation number of the vanadium, for example, VO ₂ , V ₂ O ₅ , V ₃ O ₇ , V ₆ O ₁₃ Lt; / RTI > Although the vanadium oxide is not particularly limited, it is more preferable that amorphous is improved because the electron conductivity is improved and a high capacity lithium secondary battery can be produced.

Method for manufacturing vanadium oxide complex

Hereinafter, the vanadium oxide composite in which the carbon nanotube aggregates are dispersed in the vanadium oxide matrix will be described. First, when a vanadium oxide is added to an aqueous solution containing hydrogen peroxide (H ₂ O ₂ ) as a cathode active material and reacted, an oxygen (O ₂ ) gas is generated and a transparent aqueous solution, Sol (Sol) is formed. The following chemical formula 1 illustrates a chemical reaction in which vanadium pentoxide (V ₂ O ₅ ) is applied as a vanadium oxide according to an embodiment of the present invention.

(2)

V ₂ O ₅ + nH ₂ O ₂ ? V ₂ O _5? NH ₂ O (Sol) + n / 2 O ₂ (Gas)

In Formula 1, n is about 1.8, and there may be some errors. The mass ratio is not a reaction of H ₂ O to form a new compound, but H ₂ O in the structure of vanadium pentoxide (V ₂ O ₅ ). Therefore, it acts like a crystal, and the concentration of H ₂ O ₂ , It changes according to the condition.

When the generation of oxygen stops, wooly precipitate forms in the aqueous solution, and the precipitate expands over time to change into a reddish brown gel. Preferably, the sol is in a sol state before being converted into a gel. , A carbon nanotube (CNT) aggregate is added and uniformly mixed through a stirrer or the like. At this time, an additional sonication process is performed. Thereafter, heat treatment is performed using a box furnace at a temperature at which the CNT is not lost for moisture removal and oxidation.

Anode for lithium-ion batteries

The vanadium oxide composite in which the carbon nanotube aggregate is dispersed as described above can be applied as a cathode active material for a lithium secondary battery. According to the present invention, there is provided a cathode for a lithium secondary battery comprising the vanadium oxide composite.

As described above, the anode of the present invention can be produced by a conventional method known in the art using a vanadium oxide composite in which a carbon nanotube aggregate is dispersed as a cathode active material. For example, a slurry is prepared by dispersing and mixing the above-mentioned cathode active material, a binder, a conductive material or a filler as necessary in a dispersion medium (solvent) and applying the slurry to a cathode current collector, followed by drying and rolling, can do.

When a vanadium oxide composite in which a carbon nanotube aggregate is dispersed is used as a cathode active material according to the present invention, a desired viscosity can be obtained even with a small amount of solvent, and the amount of a solvent (for example, NMP) .

The binder is a component that assists in bonding between the positive electrode active material and the conductive material and bonding to the current collector. Examples of the binder include polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl (meth) acrylate, polyethyl (meth) acrylate, polytetrafluoroethylene ), Polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, -Butylene rubber, fluororubber, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, and The mixture can be used at least one member selected from the group consisting of, but is not limited thereto.

The binder is usually added in an amount of 1 to 50 parts by weight, more specifically 3 to 15 parts by weight based on 100 parts by weight of the total weight of the cathode material including the cathode active material. If the content of the binder is less than 1 part by weight, the adhesive force between the positive electrode active material and the current collector may be insufficient. If the amount of the binder is more than 50 parts by weight, the adhesive force may be improved, but the content of the positive electrode active material may be decreased.

When the carbon nanotube composite of the present invention is used as a cathode active material, it is not necessary to include a separate conductive material in the cathode material constituting the anode, because it is excellent in electrical conductivity itself. However, if necessary, It is possible.

The conductive material is not particularly limited as long as it does not cause side reactions in the internal environment of the lithium secondary battery and does not cause chemical change in the battery and has excellent electrical conductivity. Typically, graphite or conductive carbon may be used. For example, graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, black black, thermal black, channel black, furnace black, lamp black, and summer black; A carbon-based material whose crystal structure is graphene or graphite; Conductive fibers such as carbon fiber and metal fiber; Carbon fluoride; Metal powders such as aluminum and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; And polyphenylene derivatives may be used singly or in combination of two or more, but the present invention is not limited thereto.

The conductive material is usually added in an amount of 0.5 to 50 parts by weight, specifically 1 to 30 parts by weight based on 100 parts by weight of the total weight of the cathode material including the cathode active material. If the content of the conductive material is less than 0.5 parts by weight, the effect of improving electrical conductivity may not be expected or the electrochemical characteristics of the battery may deteriorate. If the content of the conductive material exceeds 50 parts by weight, the amount of the cathode active material And the capacity and the energy density may be lowered.

The method of incorporating the conductive material into the cathode material is not particularly limited, and conventional methods known in the art such as coating on the cathode active material can be used. In some cases, since the conductive second coating layer is added to the positive electrode active material, the addition of the conductive material as described above may be substituted.

The positive electrode material constituting the positive electrode of the present invention may optionally contain a filler as a component for suppressing the expansion of the positive electrode. Such a filler is not particularly limited as long as it can inhibit the expansion of the electrode without causing chemical change in the battery, and examples thereof include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers; Etc. may be used.

Examples of the dispersion medium include N-methyl-2-pyrrolidone (NMP), dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), ethanol, isopropanol, water and mixtures thereof.

The positive electrode current collector may be formed of a metal such as platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS) ), Molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO ₂ ), FTO (F doped SnO ₂ ) , A surface of aluminum (Al) or a stainless steel surface treated with carbon (C), nickel (Ni), titanium (Ti) or silver (Ag) may be used. The shape of the anode current collector may be in the form of a foil, a film, a sheet, a punched, a porous body, a foam or the like.

Lithium secondary battery

According to another aspect of the present invention, there is provided a lithium secondary battery including the positive electrode.

Generally, a lithium secondary battery is composed of a positive electrode composed of a positive electrode material and a current collector, a negative electrode composed of a negative electrode material and a current collector, and a separator intercepting electrical contact between the positive electrode and the negative electrode to move lithium ions, And an electrolytic solution for conduction of lithium ions is included.

The cathode can be produced by a conventional method known in the art. For example, a negative electrode may be prepared by dispersing and mixing a negative electrode active material, a conductive material, a binder, and a filler as necessary in a dispersion medium (solvent) to prepare a slurry, applying the dispersion to an anode current collector, and then drying and rolling.

As the negative electrode active material, lithium metal or a lithium alloy (for example, an alloy of lithium and a metal such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium or indium) may be used.

The negative electrode collector may be formed of at least one selected from the group consisting of Pt, Au, Pd, Ir, Ag, Ru, Ni, STS, ), Molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO ₂ ), FTO (F doped SnO ₂ ) (C), nickel (Ni), titanium (Ti), or silver (Ag) on the surface of copper, copper or stainless steel may be used. The anode current collector may be in the form of a foil, a film, a sheet, a punched, a porous body, a foam or the like.

The separation membrane is interposed between the positive electrode and the negative electrode to prevent a short circuit therebetween and to provide a movement path of lithium ions.

As the separation membrane, an olefin-based polymer such as polyethylene or polypropylene, glass fiber or the like may be used in the form of a sheet, a multilayer, a microporous film, a woven fabric and a nonwoven fabric, but is not limited thereto. On the other hand, when a solid electrolyte such as a polymer (for example, an organic solid electrolyte, an inorganic solid electrolyte or the like) is used as the electrolyte, the solid electrolyte may also serve as a separation membrane. Specifically, an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally in the range of 0.01 to 10 mu m, and the thickness may generally be in the range of 5 to 300 mu m.

As the electrolyte solution, carbonate, ester, ether, or ketone may be used alone or as a mixture of two or more of them as a non-aqueous liquid electrolyte (non-aqueous organic solvent), but the present invention is not limited thereto.

Examples of the solvent include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, Ethyl acetate, n-propyl acetate, phosphoric acid triester, dibutyl ether, N-methyl-2-pyrrolidinone, 1,2-dimethoxyethane, tetrahydroxyfurfurane (Franc), 2-methyltetrahydrofuran Dimethylformamide, dioxolane and derivatives thereof, acetonitrile, nitromethane, methyl formate, methyl acetate, trimethoxymethane, sulfolane, methyl sulfolane, 1,3-dioxolane, - dimethyl-2-imidazolidinone, methyl propionate, ethyl propionate and the like can be used but are not limited thereto It is not.

(Lithium salt-containing non-aqueous electrolyte solution), and the lithium salt may be a known one which is soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO _{4 , LiBF 4, LiB 10 Cl 10} , LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiPF 3 (CF 2 CF 3) 3, LiAlCl 4, CH 3 SO 3 Li, CF 3 SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylate lithium, lithium tetraphenylborate, imide, and the like, but not always limited thereto.

The above (non-aqueous) electrolytic solution may contain, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, Amide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, . In some cases, a halogen-containing solvent such as carbon tetrachloride, ethylene trifluoride or the like may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

The lithium secondary battery of the present invention can be produced by a conventional method in the art. For example, a porous separator may be placed between the anode and the cathode, and a non-aqueous electrolyte may be added.

The lithium secondary battery according to the present invention not only exhibits improved capacity characteristics (rapid capacity decrease prevention) under high-speed charge / discharge cycle conditions, but also excellent cycle characteristics, rate characteristics and life characteristics, The present invention can be suitably used as a unit cell of a battery module which is a power source of a medium and large-sized device.

In this respect, the present invention also provides a battery module in which two or more lithium secondary batteries are electrically connected (in series or in parallel). It is needless to say that the number of lithium secondary batteries included in the battery module may be variously controlled in consideration of the use and capacity of the battery module.

Further, the present invention provides a battery pack in which the battery module is electrically connected according to a conventional technique.

The battery module and the battery pack may include a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); Electric truck; Electric commercial vehicle; Or a power storage system, but is not limited thereto.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other 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 enable those skilled in the art to more fully understand the present invention.

< Example >

1. Carbon nanotubes ( CNT ) Aggregated vanadium oxide complex

1. 1 g of vanadium pentoxide (V ₂ O ₅ ) powder was stirred in 50 mL of an aqueous solution of 30 wt% hydrogen peroxide (H ₂ O ₂ ) and stored at room temperature for 24 hours to obtain vanadium pentoxide (V ₂ O ₅ ).

2. 0.2 g of the single-walled carbon nanotube (CNT) agglomerated as a bundle type was mixed with vanadium pentoxide (V ₂ O ₅ ) in the prepared sol state and stirred for 1 hour.

3. The mixed solution was washed with a bath type sonication at room temperature for 3 hours.

4. The mixture was centrifuged and washed, and water was removed at 70 ° C.

5. Heat treatment at 300 ° C for 5 hours in a box furnace.

The thus prepared vanadium oxide composite is shown in FIG. 1, and a bundle type carbon nanotube aggregate 10 included in the vanadium oxide matrix 20 can be identified.

2. Anode manufacturing

90 wt% of the vanadium oxide composite prepared above; And 10 wt% of PVDF as a binder were added to NMP together, and the slurry thus prepared was coated on an aluminum foil as a positive current collector, followed by rolling and drying to prepare a positive electrode for a lithium secondary battery. (Loading = 1.5 mAh / cm 2)

3. Lithium secondary battery manufacturing

A negative electrode for a lithium secondary battery was prepared using Li metal foil as an anode active material. (Loading = 30 mAh / cm 2)

A lithium-salt-containing nonaqueous electrolyte solution (1.0 M LiPF ₆ was mixed at a volume ratio of 1: 1 ethylene carbonate (EC): dimethyl carbonate (DMC)) in a volume ratio of 1: 1 with a porous polyethylene separator interposed between the prepared positive electrode and negative electrode. Dissolved in an organic solvent) was injected to prepare a coin cell type lithium secondary battery.

< Comparative Example >

A lithium secondary battery was produced in the same manner as in Example except that vanadium pentoxide (V ₂ O ₅ ) was used as the positive electrode active material.

<Experimental Example>

The capacity and efficiency (4.0 to 2.1 V) of each lithium secondary battery prepared according to the above Examples and Comparative Examples were tested for each discharge speed. The results are shown in FIG.

Referring to FIG. 2, the capacity retention ratio of the lithium secondary battery manufactured according to the example was significantly increased as compared with the lithium secondary battery manufactured according to the comparative example, and the efficiency was also improved. Life characteristics were improved.

The present invention can be effectively used particularly in the field of a cathode material of a lithium secondary battery.

10. Carbon nanotube aggregate
20. The vanadium oxide matrix

Claims (11)

Wherein the carbon nanotube (CNT) aggregate is dispersed in a vanadium oxide matrix.
The method according to claim 1,
Wherein the carbon nanotube aggregate is of a bundle type.
The method according to claim 1,
Wherein the carbon nanotube aggregate is in the form of a multi-walled carbon nanotube.
The method according to claim 1,
Wherein the carbon nanotube aggregate comprises 5 to 40 wt% based on the total weight of the vanadium oxide composite.
The method of claim 1, wherein
Wherein the vanadium oxide is represented by the following formula (1).

V _a O _b
(Provided that 1? A? 6 and 2? B? 13 in the above formula)
A positive electrode for a lithium secondary battery, comprising a vanadium oxide composite according to any one of claims 1 to 5 as a positive electrode active material.
The method according to claim 6,
The positive electrode for a lithium secondary battery according to claim 1, further comprising conductive carbon and a binder.
A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 6.
A method for producing a vanadium oxide composite,
I) adding vanadium oxide to hydrogen peroxide (H ₂ O ₂ ) and stirring to form a vanadium oxide in a sol state;
Ii) impregnating the carbon nanotube aggregate with vanadium oxide in a sol state;
Iii) subjecting the mixture of ii) to sonication;
Iv) centrifuging the mixture of iii) and washing; And
V) heat treating the mixture of iv);
&Lt; RTI ID = 0.0 &gt; 1, &lt; / RTI &gt;
10. The method of claim 9,
Wherein the carbon nanotube aggregate in step (ii) is contained in an amount of 5 to 40 wt% based on the total weight of the vanadium oxide composite.
10. The method of claim 9,
Wherein the heat treatment in the step (v) is performed at a temperature of 150 to 600 ° C for 3 to 24 hours.

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