KR20190057530A - Positive electrode active material for lithium secondary battery and method for preparing the same - Google Patents

Abstract

Disclosed are a positive electrode active material for a lithium secondary battery, which can enhance the lifetime characteristics of a battery by doping vanadium oxide with magnesium ions; and a method for manufacturing the positive electrode active material. The positive electrode active material for a lithium secondary battery comprises a compound represented by chemical formula 1, in which a part of vanadium of vanadium oxide is doped with magnesium ions. In the chemical formula 1: Mg_aV_bO_c, wherein 0.01 <= a <= 0.05, 1 <= b <= 6, and 2 <= c <= 13.

Description

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery,

The present invention relates to a cathode active material for a lithium secondary battery and a method for manufacturing the same, and more particularly, to a cathode active material for a lithium secondary battery capable of improving life characteristics of a battery by doping magnesium oxide with vanadium oxide will be.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Recently, the use of a secondary battery as a power source for an electric vehicle (EV), a hybrid electric vehicle (HEV) and the like has been realized. Accordingly, a lot of research has been conducted on a secondary battery that can meet various demands, and in particular, a demand for a lithium secondary battery having a high energy density, a discharge voltage, and an output stability is high, .

The lithium secondary battery technology has been applied to various fields through recent remarkable development. However, various batteries capable of overcoming the limitations of current lithium secondary batteries have been studied from the viewpoints of capacity, safety, output, enlargement and miniaturization of batteries have. 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, A supercapacitor having excellent output characteristics compared to a sodium-sulfur (Na-S) battery or a redox flow battery (RFB) in terms of enlargement and a thin film battery 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. Furthermore, 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 a heat treatment process during the manufacture of the thin film or a 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.

Vanadium oxide has been proposed to solve the disadvantages of these materials. 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 feasible, and it becomes possible to manufacture a secondary battery on a polymer material such as plastic.

Particularly, vanadium pentoxide having a layered structure (V ₂ O ₅ ) is a high-capacity cathode material containing no lithium and exhibits a theoretical capacity of 290 mAh / g during a two-electron reaction. The vanadium oxide has advantages of high capacity and high energy density Lt; / RTI &gt; However, when vanadium oxide is used as the positive electrode active material, there is a problem that the lithium ion diffusion coefficient is low and vanadium is eluted into the electrolytic solution, and the lifetime of the battery is reduced. Accordingly, in the related art, research and development of an improved cathode active material using vanadium oxide has been spurred, but a clear alternative has not yet been established.

Accordingly, an object of the present invention is to provide a positive electrode active material for a lithium secondary battery and a method for producing the same, which can improve life characteristics of a battery by doping magnesium oxide with vanadium oxide.

In order to accomplish the above object, the present invention provides a cathode active material for a lithium secondary battery, comprising a compound of the formula (1) wherein a part of vanadium of vanadium oxide is doped with magnesium ions.

[Chemical Formula 1]

Mg _a V _b O _c

In the above formula (1), 0.01? A? 0.05, 1? B? 6, and 2? C?

The present invention also relates to a method for producing a water-soluble polymer comprising the steps of: a) reacting a water-soluble magnesium compound, vanadium oxide and an organic acid in the presence of a solvent; And b) drying and heat-treating the reactant. The present invention also provides a method for producing a cathode active material for a lithium secondary battery.

According to the cathode active material for a lithium secondary battery and the method for producing the same according to the present invention, vanadium oxide is doped with magnesium ions to inhibit dissolution of vanadium in the electrolyte, thereby improving life characteristics of the battery.

1 is a graph showing lifetime characteristics of a lithium secondary battery manufactured according to an embodiment and a comparative example of the present invention.
2 is data obtained by XRD analysis of a cathode active material prepared according to one embodiment of the present invention and a comparative example.
3 is data for comparing vanadium elution amounts of a lithium secondary battery manufactured according to one embodiment of the present invention and a comparative example.

Hereinafter, the present invention will be described in detail.

The cathode active material for a lithium secondary battery according to the present invention comprises a compound of the following formula 1 in which a vanadium part of vanadium oxide is doped with magnesium ions.

[Chemical Formula 1]

Mg _a V _b O _c

In the above formula (1), 0.01? A? 0.05, 1? B? 6, and 2? C?

Vanadium oxide (Vanadium oxide) has excellent electrode characteristics even in the amorphous state (in particular, it is suitable as an electrode material because it has a theoretically high specific capacity in the case of vanadium pentoxide (V ₂ O ₅ )), And can be synthesized at room temperature, and has attracted attention as a cathode material (precisely, a cathode active material) of a next-generation lithium secondary battery. However, when vanadium oxide is used as the cathode active material, the ion diffusion coefficient is low, and vanadium is eluted into the electrolytic solution, thereby decreasing the lifetime of the battery. In order to solve such a problem, the present invention is a method for producing a vanadium oxide by doping or substituting a part of vanadium in a vanadium oxide with a magnesium ion.

The magnesium ion (Mg ²⁺ ) can be substituted with vanadium in various forms of vanadium oxide. When vanadium oxide is used as the cathode active material, lithium ions are introduced into the vanadium oxide having a bipyramid form. Even if magnesium ions are doped into the vanadium, there is almost no change in the vanadium oxide structure, The diffusion coefficient of the lithium ion is rapidly changed, thereby improving the lifetime characteristics of the battery. For example, when magnesium ions are doped, the vanadium pentavalent is converted into tetravalent vanadium to increase the electrical conductivity, and the MO6 octahedron (octahedral octahedron with the number of coordination numbers 6 including metal and oxygen) formed on the skeleton of Mg _X V ₂ O ₅ , Dimensional characteristics of the material, thereby suppressing the deformation of the material structure during the electrochemical cycle.

On the other hand, since vanadium, which is a transition metal, can have various oxidized water, various kinds of vanadium oxides having various ratios of vanadium and oxygen exist. Accordingly, the vanadium oxide (or vanadium oxide precursor) may be a compound represented by the following general formula (2), a salt thereof, or a mixture thereof, or a compound containing a vanadium atom and an oxygen atom. On the other hand, examples of the salt of the compound represented by the following formula (2) include ammonium metavanadate (NH ₄ VO ₃ ) and the like.

(2)

V _d O _e

In Formula 2, 1? D? 6 and 2? E? 13.

Although the type of the vanadium oxide used as the cathode active material is not limited in this way, vanadium pentoxide (V ₂ O ₅ ) may be preferable in view of the stability of the structure, and the vanadium pentoxide (V ₂ O ₅ ) bipyramidal form of orthorhombic crystal system, which has the structure of Pmmn space group. The cathode active material is substituted with magnesium ions of vanadium in a proportion of 0.5 to 4%, preferably 0.5 to 2.5% based on the number of atoms of vanadium. When vanadium of less than 0.5% is substituted with magnesium ion, the vanadium dissolution suppression effect due to the substitution of magnesium ion may be insignificant. When vanadium exceeding 4% is substituted with magnesium ion, the effect of reducing the capacity and improving the life characteristics is insignificant .

The positive electrode active material (which is vanadium oxide substituted with magnesium ion) can be applied to a positive electrode material for a lithium secondary battery. In this case, the positive electrode active material is used in an amount of 50 to 90 parts by weight, preferably 60 to 90 parts by weight, May be included in the cathode material in an amount of 80 parts by weight. If the content of the positive electrode active material is less than 50 parts by weight based on 100 parts by weight of the total weight of the positive electrode material, the electrochemical characteristics of the positive electrode active material are deteriorated. If the amount exceeds 90 parts by weight, And it may be difficult to manufacture an efficient battery. In addition, the cathode material for the lithium secondary battery further includes a binder and a conductive material, in addition to the cathode active material, which is vanadium oxide substituted with the magnesium ion.

The binder contained in the cathode material is a component that assists in bonding of the cathode active material and the conductive material and bonding to the collector, and examples thereof include polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene (Meth) acrylate, polyethyl (meth) acrylate, polytetrafluoroethylene, polytetrafluoroethylene, polytetrafluoroethylene, polytetrafluoroethylene, copolymers (PVdF / HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, Butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, liquor, polyvinylpyrrolidone, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, polyvinyl chloride, polyacrylonitrile, Epoxidized EPDM rubber, styrene-butylene rubber, fluororubber, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, But at least one member selected from the group consisting of cellulose production in the Woods, and mixtures thereof can be used, is not limited thereto.

The binder is usually added in an amount of 1 to 50 parts by weight, preferably 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.

The conductive material included in the cathode 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 is used Graphite such as natural graphite, artificial graphite and the like; 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, preferably 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. Further, if necessary, 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.

The positive electrode material of the present invention can be prepared by dispersing and mixing the positive electrode active material, the binder and the conductive material in a dispersion medium (solvent) to form a slurry, applying the slurry on the positive electrode current collector, and then drying and rolling. N-methyl-2-pyrrolidone (DMF), dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), ethanol, isopropanol, water and mixtures thereof may be used as the dispersion medium.

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.

The present invention also provides a lithium secondary battery comprising a positive electrode according to the above-described contents. Generally, a lithium secondary battery is composed of a positive electrode made of a positive electrode material and a current collector, a negative electrode made of a negative electrode material and a current collector, and a separator for blocking electrical contact between the positive electrode and the negative electrode and moving lithium ions, And an electrolytic solution for conduction of lithium ions. The negative electrode may be manufactured according to 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, coating the dispersion on an anode current collector, followed by 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 from 0.01 to 10 mu m, and the thickness generally ranges from 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 any known lithium salt which is soluble in a non-aqueous liquid electrolyte, for example, LiFSI, 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, ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylate lithium, lithium 4-phenylborate, imide, and the like. The (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, . If necessary, 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). The amount of the lithium secondary battery included in the battery module may be variously adjusted 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.

Next, a method for producing a cathode active material for a lithium secondary battery according to the present invention will be described. The method for producing the cathode active material for a lithium secondary battery includes the steps of: a) reacting a water-soluble magnesium compound, vanadium oxide and an organic acid in the presence of a solvent; and b) drying and heat-treating the reactant.

The mixing weight ratio of the vanadium oxide (precursor), the organic acid, and the magnesium compound (magnesium ion precursor) may be 20 to 55:40 to 75: 0.4 to 5. The magnesium-based compound is a water-soluble compound capable of dissolving magnesium ions in a solvent such as distilled water. The magnesium-based compound is not particularly limited as long as it can be reacted with any type of vanadium oxide to produce vanadium oxide substituted with magnesium ions. . Examples of such water-soluble magnesium compounds include water-soluble magnesium compounds known in the art such as magnesium nitrate (Mg (NO ₃ ) ₂ .6H ₂ O). Examples of the vanadium oxide may be replaced with the above-mentioned organic acid. Examples of the organic acid include common organic acids such as citric acid, oxalic acid, tannic acid, and mixtures thereof. Examples of the organic acid include citric acid Use is preferred.

The reaction (including mixing and dissolution) in step a) may be carried out by a conventional stirring method such as stirring at a temperature of 60 to 90 ° C, preferably 70 to 80 ° C, and the solvent may be distilled water Water, and the like. The drying process in step b) is a process for removing all or part of the solvent in the resulting mixture. The drying method is not particularly limited and may be a general method commonly used in the art. In addition, the heat treatment process in the step b) is a process for removing a solvent remaining in the dried mixture and for forming an appropriate vanadium oxide structure. The heat treatment is carried out in an air atmosphere at 350 to 650 ° C, preferably 450 to 550 ° C For example, by heating or the like in a furnace for 1 to 10 hours, preferably 4 to 8 hours. On the other hand, in the heat treatment process, when the temperature is out of the above temperature range, it is difficult to keep the structure of the vanadium oxide constant due to oxidation and thermal deformation, and when it exceeds the time range, the lithium ion diffusion path ion diffusion pathway is prolonged and an inefficient structure can be formed in the de-insertion of lithium ions.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention. It is of course also within the scope of the appended claims.

[Example 1]

Preparation of cathode active material

First, 500 ml of distilled water was added at a mixing weight ratio of ammonium citrate: ammonium metavanadate (vanadium oxide precursor): magnesium nitrate (magnesium ion precursor) at a weight ratio of 55: 43: 2, and the mixture was stirred at 80 ° C. Subsequently, the stirred mixture was dried at a temperature of 120 DEG C, and then heat-treated for 6 hours in a 500 DEG C heating furnace under an air atmosphere to obtain a vanadium oxide (Mg _0.05 V _1.95 O ₅ ) substituted with magnesium ions To prepare a cathode active material.

Preparation of positive electrode for lithium secondary battery

The prepared cathode active material, polyvinylidene fluoride (PVdF) as a binder and super-P as a conductive material were mixed at a weight ratio of 8: 1: 1 to prepare a cathode material, which was then dispersed in an NMP solvent, Lt; RTI ID = 0.0 &gt; 500 &lt; / RTI &gt; After coating, the substrate was dried in a vacuum oven at about 120 캜 for about 13 hours to prepare a positive electrode.

Manufacture of lithium secondary battery

After the prepared positive electrode was positioned to face the negative electrode, a polyethylene separator was interposed between the positive electrode and the lithium metal negative electrode. Subsequently, an electrolytic solution in which LiFSI was dissolved in a dimethyl ether solvent at a concentration of 4 M was injected into the case to prepare a coin cell.

[Example 2]

The magnesium ions are substituted with vanadium oxide Mg _0.05 V _1.95 O ₅ instead of Mg _0.01 V _1.99 O to _5, except that such that and are performed in the same manner as in Example 1, the positive electrode active material, a positive electrode and a lithium secondary battery (coin cell) .

[Comparative Example 1]

A positive electrode active material, a positive electrode and a lithium secondary battery (coin cell) were prepared in the same manner as in Example 1 except that magnesium nitrate was not used in the production of the positive electrode active material.

[Comparative Example 2]

The magnesium ions are substituted with vanadium oxide Mg _0.05 V _1.95 O ₅ instead of Mg _0.1 V _1.9 O ₅ is one, and is in the same way as in Example 1, the positive electrode active material, a positive electrode and a lithium secondary battery (coin cell), except that .

[Experimental Example 1] Evaluation of battery capacity and life characteristics

Charging / discharging (charging: 0.2 C, discharging: 0.5 C) was repeatedly performed on the coin cell (4.0 to 2.1 V) manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 to evaluate the life characteristics of the battery The specific capacity according to each cycle was measured, and the result is shown in Fig. 1 (Mg content is analyzed by ICP). FIG. 1 is a graph showing lifetime characteristics of a lithium secondary battery manufactured according to an embodiment and a comparative example of the present invention, wherein 'Mg-V ₂ O ₅ (Mg: 0.05) 'Corresponds to Comparative Example 1, and' Mg-V ₂ O ₅ (Mg: 0.1) 'corresponds to Comparative Example 2. As shown in FIG. 1, the battery of Example 1 including vanadium oxide in which magnesium ions were substituted according to the present invention is a battery of Comparative Example 1 containing only vanadium oxide, a battery of magnesium oxide having a magnesium ion value of 0.1 It was confirmed that the charge / discharge capacity and the life span maintenance ratio were improved as compared with Comparative Example 2. On the other hand, although not shown in FIG. 1, the results of Example 2 were also confirmed to be very similar to those of Example 1.

[Experimental Example 2] XRD analysis

The cathode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were subjected to XRD analysis. The results are shown in FIG. FIG. 2 is data obtained by XRD analysis of a cathode active material prepared according to one embodiment of the present invention and Comparative Example, wherein 'Mg _0.05 V _1.95 O ₅ ' corresponds to Example 1 and 'Ref.' Corresponds to Comparative Example 1 , And 'Mg _0.1 V _1.9 O ₅ ' corresponds to Comparative Example 2. As shown in Fig. 2, the magnesium-vanadium oxide composite peak (peak, dotted circle) appears in the case of the comparative example 2, but the peak does not appear in the case of the example 1. From this, It was confirmed that the magnesium ion was substituted into the vanadium oxide structure (that is, when a different crystal peak appears, it means that the corresponding part is not substituted in the vanadium oxide structure or is difficult to be substituted). This means that when magnesium is added in an excessive amount, the non-substituted magnesium produces a compound different from the vanadium oxide, and thus the initial capacity decreases and the electrical characteristics deteriorate because it can not participate in the battery activity. On the other hand, although not shown in FIG. 2, the results of Example 2 were also confirmed to be very similar to those of Example 1.

[Experimental Example 3] Evaluation of vanadium leaching amount of battery

The amount of vanadium elution per hour during the charging / discharging of the battery was evaluated using the coin cell (4.0 to 2.1 V) prepared in Example 1 and Comparative Example 1, and the results are shown in FIG. FIG. 3 is a graph for comparing the amount of vanadium elution of a lithium secondary battery manufactured according to an embodiment of the present invention and a comparative example. As shown in FIG. 3, It was confirmed that the amount of vanadium leached into the electrolytic solution was reduced by about 30% as compared with the battery of Comparative Example 1 in which only the vanadium oxide was used as the cathode active material.

Claims (12)

A cathode active material for a lithium secondary battery, comprising a compound of the following formula (1) wherein a part of vanadium of vanadium oxide is doped with magnesium ions.
[Chemical Formula 1]
Mg _a V _b O _c
In the above formula (1), 0.01? A? 0.05, 1? B? 6, and 2? C? The positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material has a vanadium content of 0.5 to 4% based on the number of atoms of vanadium. The cathode active material for a lithium secondary battery according to claim 1, wherein the vanadium oxide is selected from the group consisting of a compound represented by the following formula (2), a salt thereof, and a mixture thereof.
(2)
V _d O _e
In Formula 2, 1? D? 6 and 2? E? 13. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material is contained in an amount of 50 to 90 parts by weight based on 100 parts by weight of the positive electrode material. a) reacting a water-soluble magnesium compound, vanadium oxide and an organic acid in the presence of a solvent; And
b) drying and heat-treating the reactant. &lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; The method of claim 5, wherein the magnesium compound is magnesium nitrate (Mg (NO ₃ ) ₂ .6H ₂ O). [Claim 6] The method according to claim 5, wherein the vanadium oxide is a compound represented by the following formula (2), a salt thereof, or a mixture thereof.
(2)
V _d O _e
In Formula 2, 1? D? 6 and 2? E? 13. The method of claim 7, wherein the salt of the compound represented by Formula 2 is ammonium metavanadate (NH ₄ VO ₃ ). The method of claim 5, wherein the organic acid is selected from the group consisting of citric acid, oxalic acid, tannic acid, and mixtures thereof. [6] The method of claim 5, wherein the mixing weight ratio of the vanadium oxide, the organic acid, and the magnesium compound is 20 to 55:40 to 75: 0.4 to 5. [6] The method of claim 5, wherein the reaction is performed at a temperature of 60 to 90 [deg.] C. [6] The method of claim 5, wherein the heat treatment is performed at a temperature of 350 to 650 DEG C for 1 to 10 hours under air atmosphere.

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