KR100433626B1 - Method of synthesizing amorphous vanadium oxides, lithium secondary batteries comprising the same, and method of manufacturing the same - Google Patents

Abstract

A method for synthesizing an amorphous vanadium oxide using an NH ₄ VO ₃ precursor, a lithium secondary battery obtained therefrom, and a method for producing the same are disclosed. In the method for synthesizing amorphous vanadium oxide according to the present invention, the NH ₄ VO ₃ precursor is dissolved in water to prepare an NH ₄ VO ₃ solution. By adding an acid to the NH ₄ VO ₃ solution to form an amorphous vanadium oxide by acidification (acidification) to the NH ₄ VO ₃ solution. The amorphous vanadium oxide is separated from the NH ₄ VO ₃ solution. The electrode of the lithium secondary battery according to the present invention is constructed by using the amorphous vanadium oxide synthesized in this manner as an active material.

Description

Method of synthesizing amorphous vanadium oxides, lithium secondary batteries comprising the same, and method of manufacturing the same

The present invention relates to a method for producing an active material that can be used in a lithium secondary battery, a lithium secondary battery and a method for producing the same, and in particular, a method for synthesizing an amorphous vanadium oxide, a lithium secondary battery comprising an amorphous vanadium oxide obtained from the method, and The manufacturing method is related.

Currently, commercially available lithium secondary batteries have an operating voltage of about 3.6V. However, due to the development of electronic devices, the development of new secondary batteries with low operating voltage and higher capacity is expected. LiMnO ₂ , V ₂ O ₅ , and the like are expected as positive electrode materials that can be employed in next-generation secondary batteries. Of these, since V ₂ O ₅ does not contain lithium, it cannot be used in a conventional lithium secondary battery using carbon as a negative electrode, but can be used in a system using lithium metal. In fact, research and development in V ₂ O ₅ that can be used as a positive electrode material of a lithium secondary battery for an electric vehicle is underway.

V ₂ O ₅ has been the subject of much research for the last century and its focus has been crystalline vanadium oxide (cV ₂ O ₅ ). However, it has been found that cV ₂ O ₅ has a reversible capacity range for lithium of only 1 mole per mole of V ₂ O ₅ , and beyond this voltage range, the capacity decreases through an irreversible phase shift. For this reason, it has recently been converted to the study of amorphous vanadium oxide (aV ₂ O ₅ ) which does not undergo phase transition.

As a method of synthesizing aV ₂ O ₅ according to the prior art, there is a method of using an amorphous former (glass former). Among them, aV ₂ O ₅ / P ₂ O ₅ in which P ₂ O ₅ was used as an amorphous inducer showed high capacity and excellent cycle characteristics. However, this material has a process problem because it easily absorbs moisture in the atmosphere and requires rapid quenching during the synthesis process. In order to solve this problem, a synthesis method by the sol-gel method has been proposed. According to the synthesis method by the sol-gel method, (1) V ₂ O ₅ solution is synthesized by adding water, (2) vanadium alkoxide is reacted with water, or (3) metavanadate solution ( aV ₂ O ₅ can be synthesized by passing the metavanadate solution through a cation exchange resin. The third of these methods is in the spotlight. According to this method, NaVO ₃ is dissolved in ultrapure water, and then acidified by passing through an ion exchange resin to convert to gel state through polymerization. Here, the gel is dried immediately, XROgel (XRG, xerogel), the surface tension through the exchange of solvents to reduce the breakage of the pores, while being synthesized in the form (ARG-like) similar to the airgel (ARG, aerogel) or Supercritical fluids can be used to convert the aerogels.

As described above, in the conventional method of synthesizing aV ₂ O ₅ by the sol-gel method using NaVO ₃ as a starting material, a cation exchange resin is used for acidification. That is, sodium ions dissolved in water are acidified by exchange with hydrogen ions in the ion exchange resin, and the acidified vanadium solution is converted into a gel form through inorganic polymerization. In this method, there is a problem in mass production because of the use of ion exchange resin, and because of the use of NaVO ₃ as a precursor, sodium remains in the product as an impurity, which may impair the characteristics of the battery when used as a battery material. have. Therefore, it is necessary to use a precursor capable of reducing impurities, and development of a process capable of synthesizing aV ₂ O ₅ without using an ion exchange resin is required.

An object of the present invention is to solve the problems in the prior art as described above, and to provide a method for synthesizing amorphous vanadium oxide without fear of contamination by impurities and capable of mass production.

Another object of the present invention is to provide a lithium secondary battery having an electrode made of a material which is free from contamination by impurities and which can improve electrochemical properties of the battery.

Still another object of the present invention is to provide a method for producing a lithium secondary battery having an electrode made of a material which is free from contamination by impurities and which can improve electrochemical characteristics of the battery.

1 is a flowchart for explaining a method for synthesizing an amorphous vanadium oxide according to the present invention.

2 is an X-ray diffraction analysis result of the amorphous vanadium oxide synthesized by the method according to the present invention.

Figure 3 is a graph showing the capacity per weight according to the number of charge and discharge of the electrode using the amorphous vanadium oxide synthesized by the method according to the invention as an active material.

Figure 4 is a graph showing the results of the fast charge and discharge experiment of the electrode using the amorphous vanadium oxide doped with silver synthesized by the method according to the present invention as an active material.

Figure 5 is a graph showing the capacity per weight according to the number of charge and discharge of each electrode using the amorphous vanadium oxide doped with silver and copper synthesized by the method according to the present invention as an active material.

In order to achieve the above object, in the synthesis method of the amorphous vanadium oxide according to the present invention, the NH ₄ VO ₃ precursor is dissolved in water to prepare a NH ₄ VO ₃ solution. By adding an acid to the NH ₄ VO ₃ solution to form an amorphous vanadium oxide by acidification (acidification) to the NH ₄ VO ₃ solution. The amorphous vanadium oxide is separated from the NH ₄ VO ₃ solution.

In the synthesis of the amorphous vanadium oxide according to the present invention, the concentration of the NH ₄ VO ₃ precursor in the NH ₄ VO ₃ solution is preferably set to 0.05 ~ 0.5M. The step of preparing the NH ₄ VO ₃ solution is carried out at a temperature of 50 ~ 200 ℃. In the step of forming the amorphous vanadium oxide, an acid is added to the NH ₄ VO ₃ solution so that the pH of the NH ₄ VO ₃ solution becomes 0-4. The acid may for example consist of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid or boric acid. The acid can be used as having a purity of 5 to 70%.

In the method for synthesizing amorphous vanadium oxide according to the present invention, the separating of the amorphous vanadium oxide may include precipitating the amorphous vanadium oxide in the acidified NH ₄ VO ₃ solution, and filtering the amorphous vanadium oxide. It may include.

Preferably, forming the amorphous vanadium oxide comprises completely vaporizing NH ₃ generated from the acidified NH ₄ VO ₃ solution.

After the step of forming the amorphous vanadium oxide in order to obtain an amorphous vanadium oxide doped with a metal by the addition of acid to the NH ₄ VO ₃ solution was acidified with the NH ₄ VO ₃ solution, and in the resulting acidified with NH ₄ VO ₃ solution Add metal powder. Here, the metal powder is added so that the metal is doped in a concentration of 0.01 to 0.5M based on V ₂ O ₅ 1M in the amorphous vanadium oxide doped with the metal.

In addition, in the method for synthesizing amorphous vanadium oxide according to the present invention, after forming the amorphous vanadium oxide, adding and stirring water to the amorphous vanadium oxide to form a gel-like amorphous vanadium oxide, and Drying the gel-shaped amorphous vanadium oxide may further comprise forming a porous amorphous vanadium oxide having a larger specific surface area than the amorphous vanadium oxide. In the step of forming the porous amorphous vanadium oxide, the amorphous vanadium oxide on the gel is dried by a solvent exchange method or a method using a supercritical fluid.

In the method of synthesizing an amorphous vanadium oxide according to the present invention, after the step of separating the amorphous vanadium oxide, may further comprise the step of drying the separated amorphous vanadium oxide. Here, an oven may be used to dry the separated amorphous vanadium oxide, or may be performed by a solvent exchange method or a method using a supercritical fluid.

In order to achieve the above another object, the lithium secondary battery according to the present invention includes an electrode made of amorphous vanadium oxide obtained from the method having the features as described above.

In order to achieve the above another object, in the method of manufacturing a lithium secondary battery according to the present invention, a mixture of amorphous vanadium oxide, a conductive material, and a binder is prepared by the method having the characteristics as described above. The mixture is mixed with a dispersant to prepare a paste. The paste is applied to a metal current collector. The paste-coated metal current collector is compressed and dried to form a laminate electrode. The amorphous vanadium oxide may be made of amorphous vanadium oxide doped with copper or silver.

The method for producing amorphous vanadium oxide according to the present invention can be carried out by a simple method, and can be usefully applied to mass production of amorphous vanadium oxide since the contamination by impurities of the product can be reduced. The lithium secondary battery according to the present invention may exhibit excellent electrochemical characteristics at high charge and discharge with high density of the active material.

Next, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a flowchart for explaining a method for synthesizing an amorphous vanadium oxide according to the present invention.

Referring to FIG. 1, in step 10, NH ₄ VO ₃ precursor is first dissolved in water to prepare an NH ₄ VO ₃ solution. In order to completely dissolve the NH ₄ VO ₃ in water, the step of preparing the NH ₄ VO ₃ solution is performed at a high temperature of about 50-200 ° C. The concentration of precursor NH ₄ VO ₃ affects the shape, specific surface area, charge and discharge capacity of the battery, and the like, of the final composite amorphous vanadium oxide. Therefore, the NH ₄ VO ₃ solution is preferably formed to have a concentration of about 0.05 to 0.5M. In addition, when the NH ₃ generated in the NH ₄ VO ₃ solution preparation step is vaporized and removed, impurity NH ₄ V ₃ O ₈ may be avoided.

In step 20, by adding an acid to the NH ₄ VO ₃ solution by acidification (acidification) to the NH ₄ VO ₃ solution to form an amorphous vanadium oxide. The amorphous vanadium oxide is formed in the form of a precipitate. As the acid to be added here, any acid may be used, and for example, nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid or boric acid may be used. The concentration of the acid added in step 20 determines the crystallinity of the vanadium oxide synthesized. Preferably, the amount of acid added in step 20 is adjusted so that the pH of the NH ₄ VO ₃ solution is 0-4. The acid used at this time may be used to have a purity of 5 to 70%.

In step 30, the amorphous vanadium oxide is separated from the NH ₄ VO ₃ solution. In order to separate the amorphous vanadium oxide from the NH ₄ VO ₃ solution, the amorphous vanadium oxide is precipitated, filtered and dried. As an example of a method of drying the amorphous vanadium oxide, a precipitate composed of amorphous vanadium oxide is dried in an oven maintained at a temperature in the range of 80 to 120 ° C. As another example of drying the amorphous vanadium oxide, a solvent exchange method or a method using a supercritical fluid may be used. In the case of using these drying methods, an amorphous vanadium oxide having a large specific surface area can be synthesized. In the case of using the solvent exchange method, water contained in the pores is first substituted with a polar solvent and then replaced with a nonpolar solvent and dried. The polar solvents usable herein include acetone, methanol, ethanol, and the like, and non-polar solvents include hexane and pentane. In the drying method using a supercritical fluid, a sample exchanged with a nonpolar solvent by a solvent exchange method is placed in a high-pressure reaction vessel (autoclave), and then extracted under critical temperature and pressure using carbon dioxide as a solvent, and amorphous vanadium oxide having a large specific surface area. Can be synthesized.

In step 20, to obtain an amorphous vanadium oxide doped with metal, a metal powder, for example, copper powder or silver powder, to be doped is added to the acidified NH ₄ VO ₃ solution, and when the reaction of these metal powders is finished Stir until. At this time, the metal powder is preferably added so that the metal is doped in a concentration of 0.01 to 0.5M based on V ₂ O ₅ 1M in the amorphous vanadium oxide doped with the metal.

After amorphous vanadium oxide is obtained in the form of a precipitate in step 20, water is added to the precipitate and stirred to switch to a gel state. The gel-like amorphous vanadium oxide is dried by a solvent exchange method or a method using a supercritical fluid to synthesize an amorphous vanadium oxide having a larger specific surface area.

In order to actually apply the amorphous vanadium oxide synthesized by the method according to the present invention to a battery, the amorphous vanadium oxide obtained by the above-described method is used as an active material, and the conductive material and the adhesion between the material and the current collector to impart electrical conductivity thereto The mixture is prepared with a binder to enable this. Based on the total weight of the mixture, the conductive material is mixed in an amount of about 5 to 30% by weight, and the binder is mixed in an amount of about 1 to 10% by weight. Thereafter, the mixture is mixed with a dispersant to prepare a paste, which is then applied to a metal current collector. Thereafter, the paste-coated metal current collector is compressed and dried to prepare a laminate electrode.

Carbon black may be used as the conductive material. A commercially available product can be used as the conductive material. These commercially available products include, for example, acetylene black series (Chevron Chemical Company or Gulf Oil Company, etc.), Ketjen Black EC series (Armak Company). Products), Vulcan XC-72 (manufactured by Cabot Company), and Super P (manufactured by MMM). Representative examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF) and its copolymers, cellulose, and the like, and representative examples of the dispersant are isopropyl alcohol and N-methylpyrrolidone. (NMP), acetone and the like.

The metal current collector is made of a highly conductive metal. The metal current collector is made of a metal to which the paste can be easily bonded, and any metal may be used as long as it is not reactive in the voltage range of the battery. Representative examples include meshes, foils, and the like, such as aluminum or stainless steel.

The method of applying the paste to the metal current collector may be selected from known methods or carried out by a new suitable method in consideration of the properties of the material. For example, the paste may be distributed on the metal current collector, and then uniformly dispersed using a doctor blade or the like. In some cases, a method of performing the above distribution and dispersion process in one process may be used. In addition, die casting, comma coating, screen printing, or the like may be selected. Alternatively, the paste may be molded on a separate substrate and then bonded to the metal current collector by pressing or lamination.

In order to dry the paste applied to the metal current collector, it is dried for about 1 to 3 days in a vacuum oven maintained at about 50 to 200 ° C, for example.

In order to construct a lithium secondary battery using the electrode manufactured by the above-described method, the electrode is used as a positive electrode, a metal lithium or an alloy-based material is used as a negative electrode, and a separator is inserted therebetween. The separator serves to block internal short circuits of the two electrodes and impregnate the electrolyte. Materials that can be used as the separator include a polymer, glass fiber mat, kraft paper, etc. Typical examples of commercially available Celgard series (Celgard 2400, 2300; Hoechest Celanese Corp.), polypropylene membrane (polypropylene membrane; Ube Industries) Ltd. or Pall RAI Co., Ltd.).

The electrolyte is a system in which lithium salt is dissolved in an organic solvent. LiClO ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiPF ₆ , LiSCN, LiC (CF ₃ SO ₂ ) ₃ , and the like may be used as the lithium salt. In addition, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMMC), 1,2-dimethoxyethane (1) as the organic solvent. , 2-dimethoxyethane), 1,2-diethoxyethane, gamma-butyrolactone, tetrahydrofuran, tetrahydrofuran, 2-methyltetrahydrofuran , 1,3-dioxoene (1,3-dioxolane), 4-methyl-1,3-dioxoene (4-methyl-1,3-dioxolane), diethylether, sulfolene ) Etc. can be used 1 type or in mixture of 2 or more types.

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

Example 1

Synthesis of Amorphous Vanadium Oxide

In this example, amorphous vanadium oxides were synthesized by varying the concentration of NH ₄ VO ₃ used as a precursor. Specifically, the precursor NH ₄ VO ₃ is dissolved in water to prepare solutions having concentrations of 0.09M, 0.14M, 0.20M, 0.26M and 0.30M, respectively, and each solution obtained has a purity of about 66%. The eggplant was added with concentrated nitric acid at a temperature of 100 ° C. to acidify each solution to precipitate amorphous vanadium oxide. In the presence of precipitated amorphous vanadium oxide in each solution, the pH of each solution was measured between 0.7 and 1.4, depending on the concentration of the precursor, and continued to heat for 10 minutes to remove NO _x gas from the added nitric acid. Was added. The synthesized vanadium oxide was filtered several times using ultrapure water, then dried in a vacuum oven maintained at 100 ° C. for 24 hours and ground. FIG. 2 is an X-ray diffraction analysis result of amorphous vanadium oxide synthesized from precursors having different concentrations as described above.

Example 2

Synthesis of Porous Amorphous Vanadium Oxide by Solvent Exchange Method

Among the precipitates consisting of amorphous vanadium oxide obtained in Example 1, the precipitate obtained from a solution having a concentration of NH ₄ VO ₃ of 0.2 M was washed with ultrapure water, and then acetone was added several times to exchange water with acetone. Stir for 24 hours after exchange to completely exchange water with acetone. In the same manner, hexane was added several times to the vanadium oxide precipitate exchanged with acetone and washed. It was stirred for 24 hours to completely exchange the acetone with hexane. The amorphous vanadium oxide in which the solvent was replaced with hexane was dried at room temperature for 24 hours, and then dried in a vacuum oven maintained at 100 ° C. for 24 hours to prepare a porous amorphous vanadium oxide having a specific surface area of 105 m ² / g.

Example 3

Synthesis of Porous Amorphous Vanadium Oxide by Drying Method Using Supercritical Fluids

In the precipitates consisting of amorphous vanadium oxide obtained in Example 1, the precipitate obtained from the solution having a concentration of NH ₄ VO ₃ of 0.2 M was washed and filtered with ultrapure water, and then physically stirred for 48 hours by adding ultrapure water to gel vanadium. Oxides were synthesized. The acetone was added and washed several times to exchange water with acetone. Stir for 24 hours to completely exchange water with acetone. The sample completely exchanged with acetone was placed in a high pressure reaction vessel (autoclave), and then the solvent was extracted at a critical temperature and pressure (32 ° C., 1200 psi) using carbon dioxide as a solvent, and the porous amorphous vanadium oxide having a specific surface area of 168 m ² / g. Was synthesized.

Example 4

Synthesis of Amorphous Vanadium Oxide Doped with Silver

0.9 g of precursor NH ₄ VO ₃ was added to an ultrapure water solvent and dissolved completely by heating to 100 ° C. to prepare a 0.2 M NH ₄ VO ₃ solution, and concentrated nitric acid was added to the solution in the same manner as in Example 1 to form amorphous vanadium oxide. Was synthesized. 0.1 g of micron-sized silver powder was added to the obtained amorphous vanadium oxide precipitate, followed by stirring for 5 days. The added silver powder was not doped at all but only 50%, and the rest was dissolved in nitric acid in the liquid phase to have a blue color. Inductively coupled plasma (ICP) analysis was performed to confirm the doped amount, and it was confirmed that Ag _0.20 V ₂ O ₅ was synthesized. Thereafter, the powder was prepared by washing with ultrapure water and drying in a vacuum oven maintained at 100 ° C.

Example 5

Synthesis of Amorphous Vanadium Oxide Doped with Copper

0.9 g of precursor NH ₄ VO ₃ was added to an ultrapure water solvent and dissolved completely by heating to 100 ° C. to prepare a 0.2 M NH ₄ VO ₃ solution, and concentrated nitric acid was added to the solution in the same manner as in Example 1 to form amorphous vanadium oxide. Was synthesized. 0.12 g of micron-sized copper powder was added to the obtained precipitate, followed by stirring for 5 days. All of the added copper powder was doped without doping, only 13%, and the rest was dissolved in nitric acid in the liquid phase to give a bluish color. ICP analysis to confirm the doped amount was confirmed that the Cu _0.06 V ₂ O ₅ was synthesized. Thereafter, the mixture was washed with ultrapure water and dried in a vacuum oven maintained at 100 ° C to prepare a powder.

Example 6

Fabrication of Lithium Secondary Battery Using Amorphous Vanadium Oxide as Positive Electrode Active Material

0.9 g of precursor NH ₄ VO ₃ was added to an ultrapure water solvent and dissolved completely by heating to 100 ° C. to prepare a 0.2 M NH ₄ VO ₃ solution, and concentrated nitric acid was added to the solution in the same manner as in Example 1 to form amorphous vanadium oxide. Was synthesized. Thus prepared amorphous vanadium oxide as an active material, Ketjen Black EC as a conductive material, polytetrafluoroethylene (PTFE) as a binder and mixed them in a weight ratio of 7: 2: 1 to prepare a paste. It was. Thereafter, the obtained paste was pasted to a stainless steel mesh current collector to prepare a working electrode, which was dried in a vacuum oven maintained at 120 ° C. for at least 10 hours. Using a lithium metal foil as the counter electrode and the reference electrode in a dry box in an argon atmosphere, and using a 1 molar concentration LiClO ₄ / EC: DEC (volume ratio 1: 1) as an electrolyte, a beaker type 3-pole cell was used. It prepared, and the constant current experiment and the cyclic scanning voltammetry experiment were performed at 25 degreeC. 3 is a graph showing the capacity per weight according to the number of charge and discharge cycles obtained when charging and discharging an electrode using amorphous vanadium oxide synthesized from 0.2M NH ₄ VO _{3 at} a current density of 0.2 mA / cm ² .

Example 7

Fabrication of lithium secondary battery using amorphous vanadium oxide doped with metal as positive electrode active material

An amorphous vanadium oxide doped with silver prepared in Example 4 and an amorphous vanadium oxide doped with copper in Example 5, respectively, were used as active materials, and Ketjen Black EC was used as a conductive material, and as a binder. Using polytetrafluoroethylene (PTFE), they were mixed at a weight ratio of 7: 2: 1, respectively, to prepare two kinds of pastes. The obtained two kinds of pastes were pasted to a stainless steel mesh current collector to prepare working electrodes, and these were dried in a vacuum oven maintained at 120 ° C. for at least 10 hours. Using a lithium metal foil as the counter electrode and the reference electrode in a dry box in an argon atmosphere, and using a 1 molar concentration LiClO ₄ / EC: DEC (volume ratio 1: 1) as an electrolyte, a beaker type 3-pole cell was used. It was prepared, and the constant current experiment, the cyclic scanning voltammetry, the fast charge and discharge experiments were performed at 25 ℃. 4 is a graph showing the results of a high-speed charge-discharge experiment by varying the current density of the electrode using the amorphous vanadium oxide doped with silver as an active material, Figure 5 is a case of using the amorphous vanadium oxide doped with silver as an active material, copper In the case of using the amorphous vanadium oxide doped with an active material, it is a graph showing the capacity per weight according to the number of charge and discharge obtained when the electrode prepared using each active material charged and discharged at a current density of 1 mA / cm ² .

In the method for preparing amorphous vanadium oxide according to the present invention, amorphous vanadium oxide is prepared using NH ₄ VO ₃ precursor. The method for producing amorphous vanadium oxide according to the present invention can be carried out by a simpler method than the sol-gel method using an ion exchange resin. In addition, amorphous vanadium oxide can be synthesized by a method without using a rapid cooling method and without using a glass former or an ion exchange resin. Therefore, it is possible to reduce the removal, drying, grinding, etc. of impurities generated when using an ion exchange resin, and to reduce contamination by impurities of the product, and thus can be usefully applied to mass production of amorphous vanadium oxide. According to the method for preparing amorphous vanadium oxide according to the present invention, not only porous amorphous vanadium oxide but also amorphous vanadium oxide doped with a metal may be prepared. Amorphous vanadium oxides synthesized by the process according to the invention are electrochemically stable and exhibit good anode properties. Therefore, the lithium secondary battery according to the present invention, which is composed of an electrode using amorphous vanadium oxide synthesized by the method according to the present invention, may exhibit excellent electrochemical characteristics at high charge and discharge with high density of the active material.

The present invention has been described in detail with reference to preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications can be made by those skilled in the art within the scope of the technical idea of the present invention. Do.

Claims (20)

Dissolving the NH ₄ VO ₃ precursor in water to prepare an NH ₄ VO ₃ solution, Forming an amorphous vanadium oxide by acidifying the NH ₄ VO ₃ solution by adding an acid to the NH ₄ VO ₃ solution such that the pH of the NH ₄ VO ₃ solution is 0-4; And separating the amorphous vanadium oxide from the NH ₄ VO ₃ solution. The method of claim 1, wherein the NH ₄ VO ₃ solution, the concentration of the NH ₄ VO ₃ precursor synthesis of the amorphous vanadium oxide, characterized in that 0.05 ~ 0.5M. The method of claim 1, wherein the preparing of the NH ₄ VO ₃ solution is performed at a temperature of 50 ° C. to 200 ° C. 6. delete The method of claim 1, wherein the acid in the forming of the amorphous vanadium oxide comprises nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, or boric acid. The method of claim 1, wherein the separating the amorphous vanadium oxide is Precipitating the amorphous vanadium oxide in the acidified NH ₄ VO ₃ solution, Method for synthesizing the amorphous vanadium oxide, characterized in that it comprises the step of filtering the amorphous vanadium oxide. The method of claim 1, wherein the acid added to the NH ₄ VO ₃ solution in the step of forming the amorphous vanadium oxide has a purity of 5 to 70%. The method of claim 1, wherein forming the amorphous vanadium oxide comprises completely vaporizing NH ₃ generated from the acidified NH ₄ VO ₃ solution. The method of claim 1, wherein the forming of the amorphous vanadium oxide comprises acidifying the NH ₄ VO ₃ solution by adding an acid to the NH ₄ VO ₃ solution to obtain an amorphous vanadium oxide doped with a metal, and then obtaining the acidified solution. A method for synthesizing an amorphous vanadium oxide, wherein a metal powder made of copper or silver is added to an NH ₄ VO ₃ solution. delete 10. The synthesis of amorphous vanadium oxide according to claim 9, wherein the metal powder is added such that the metal is doped in an amorphous vanadium oxide doped with the metal at a concentration of 0.01 to 0.5 M based on V ₂ O ₅ 1M. Way. The method of claim 1 or 9, wherein after forming the amorphous vanadium oxide, Adding water to the amorphous vanadium oxide and stirring to form amorphous vanadium oxide on a gel; Drying the gel-like amorphous vanadium oxide to form a porous amorphous vanadium oxide having a larger specific surface area than the amorphous vanadium oxide. The method of claim 12, wherein in the forming of the porous amorphous vanadium oxide, the gel-like amorphous vanadium oxide is dried by a solvent exchange method or a method using a supercritical fluid. 10. The method of claim 1 or 9, further comprising, after separating the amorphous vanadium oxide, drying the separated amorphous vanadium oxide. The method for synthesizing amorphous vanadium oxide according to claim 14, wherein the separated amorphous vanadium oxide is dried at a temperature of 80 ° C. to 120 ° C. using an oven. The method for synthesizing amorphous vanadium oxide according to claim 14, wherein the separated amorphous vanadium oxide is dried by a solvent exchange method or a method using a supercritical fluid. A lithium secondary battery comprising an electrode made of amorphous vanadium oxide prepared by the method according to claim 1. A lithium secondary battery comprising an electrode made of amorphous vanadium oxide prepared by the method according to claim 12. Preparing a mixture of amorphous vanadium oxide prepared by the method according to claim 1 or 9, a conductive material and a binder; Mixing the mixture with a dispersant to prepare a paste, Applying the paste to a metal current collector; Compressing and drying the paste-coated metal current collector to form a laminate-shaped electrode, characterized in that it comprises a lithium secondary battery. 20. The method of claim 19, wherein the amorphous vanadium oxide is an amorphous vanadium oxide doped with copper or silver.