KR100490613B1 - A positive active material for a lithium secondary battery and a method of preparing the same - Google Patents

Abstract

The present invention relates to a cathode active material for a lithium secondary battery and a method for manufacturing the same, wherein the cathode active material includes at least one compound selected from the group consisting of Chemical Formulas 1 to 4 and a metal oxide or a composite metal oxide layer formed on a surface of the compound. do.

[Formula 1]

Li _x Ni _1-y Mn _y F ₂

[Formula 2]

Li _x Ni _1-y Mn _y S ₂

[Formula 3]

Li _x Ni _1-yz Mn _y M _z O _2-a F _a

[Formula 4]

Li _x Ni _1-yz Mn _y M _z O _2-a S _a

Wherein M is Co, Mg, Fe, Sr, Ti, B, Si, Ga, Al, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, At least one element selected from the group consisting of Er, Tm, Yb, Lu, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, and Lr, and 0.95 ≤ x ≤ 1.1, 0 <y ≤ 0.99, 0 ≤ z ≤ 0.5, 0 ≤ a ≤ 0.5.)

Description

A positive electrode active material for a lithium secondary battery and a manufacturing method thereof {A POSITIVE ACTIVE MATERIAL FOR A LITHIUM SECONDARY BATTERY AND A METHOD OF PREPARING THE SAME}

[Industrial use]

The present invention relates to a positive electrode active material for a lithium secondary battery and a method of manufacturing the same, and more particularly, to a positive electrode active material for a lithium secondary battery excellent in electrochemical properties and a method of manufacturing the same.

[Prior art]

The lithium secondary battery uses a carbon material such as carbon or graphite as a negative electrode, a chacogenide compound as a positive electrode, a porous polypropylene / polyethylene as a separator, and a carbonate-based organic solvent as an electrolyte.

Representative examples of the chalcogenide compound used as the positive electrode include LiCoO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , LiNiO ₂ , LiNi _1-x Co _x O ₂ (0 <x <1). Among them, LiCoO ₂ has good electrical conductivity, has a high battery voltage of about 3.7V, excellent life characteristics, stability characteristics, and excellent discharge capacity of 160mAh / g, and is currently commercialized by Sony. Representative anode material. However, the price of LiCoO ₂ is expensive, the price of LiCoO ₂ occupies about 30% or more of the components (component) in the battery, there is a problem that the price competitiveness falls.

Mn-based electrode materials such as LiMn ₂ O ₄ and LiMnO ₂ are easy to synthesize, relatively inexpensive, have little pollution to the environment, and have a battery voltage of more than 3.9V, which is more attractive than LiCoO _2. Since it is about 120 mAh / g, which is about 20% or more smaller than LiCoO ₂ , there is a problem in manufacturing a relatively high capacity, flake battery. LiNiO ₂ is cheaper among the cathode active materials mentioned above, and has the highest discharge capacity of battery characteristics, but has a disadvantage of difficulty in synthesizing. In the case of LiNi _1-x Co _x O ₂ (o <x <1) powder, the discharge capacity was higher than that of LiCoO ₂ (200mAh / g), but the discharge potential was lowered and the life characteristics of the cycle progressed. It is relatively poor compared to the battery using LiCoO ₂ and is not commercialized due to incomplete safety.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a cathode active material for lithium secondary batteries having excellent electrochemical properties and low cost.

Another object of the present invention is to provide a cathode active material for a lithium secondary battery having excellent thermal stability.

Still another object of the present invention is to provide a method of manufacturing the cathode active material.

In order to achieve the above object, the present invention provides a cathode active material for a lithium secondary battery comprising at least one compound selected from the group consisting of Formulas 1 to 4 and a metal oxide or a composite metal oxide layer formed on the surface of the compound.

[Formula 1]

Li _x Ni _1-y Mn _y F ₂

[Formula 2]

Li _x Ni _1-y Mn _y S ₂

[Formula 3]

Li _x Ni _1-yz Mn _y M _z O _2-a F _a

[Formula 4]

Li _x Ni _1-yz Mn _y M _z O _2-a S _a

Wherein M is Co, Mg, Fe, Sr, Ti, B, Si, Ga, Al, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, At least one element selected from the group consisting of Er, Tm, Yb, Lu, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, and Lr, and 0.95 ≤ x ≤ 1.1, 0 <y ≤ 0.99, 0 ≤ z ≤ 0.5, 0 ≤ a ≤ 0.5.)

The present invention also comprises the steps of preparing a powder of at least one compound selected from the group consisting of Formula 1 to 4; Coating the powder with a metal alkoxide solution, metal salt organic solution or metal aqueous solution; And It provides a method for producing a cathode active material for a lithium secondary battery is selected from the metal oxide or composite metal oxide is coated with the metal alkoxide solution, metal salt organic solution or a metal aqueous solution is coated with a metal oxide or a composite metal oxide coating do.

The compound powder selected from the group consisting of Chemical Formulas 1 to 4 precipitates nickel salt and manganese salt by coprecipitation to prepare nickel manganese salt, and mixes the nickel manganese salt and lithium salt, followed by heat treatment. Are manufactured. In the precipitation step, a fluorine salt or a sulfur salt may be further added, and in the mixing step, a metal salt may be further added.

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

The positive electrode active material for a lithium secondary battery of the present invention uses Ni, Mn, which is relatively inexpensive compared to Co, and exhibits high discharge capacity of battery characteristics in order to replace LiCoO ₂ having excellent electrochemical properties but expensive. A LiNiMnO ₂ based active material that combines the advantages of inexpensive LiNiO _{2 and} the advantages of LiMnO ₄ with excellent battery voltage. In addition, the positive electrode active material of the present invention is an active material in which a metal oxide or a composite metal oxide layer is formed on a surface in order to improve discharge characteristics of a LiNiMnO ₂ based active material. In this way, the positive electrode active material of the present invention is LiCoO ₂ and the electrochemical properties may be the same one very low, replace LiCoO _2. In addition, when the positive electrode active material of the present invention is applied to a battery, it is possible to provide a lithium secondary battery that is very economically excellent in electrochemical properties (particularly, lifespan, high rate characteristics, discharge potential, power amount, and thermal stability).

The cathode active material of the present invention having such characteristics may be represented by the following Chemical Formulas 1 to 4.

[Formula 1]

Li _x Ni _1-y Mn _y F ₂

[Formula 2]

Li _x Ni _1-y Mn _y S ₂

[Formula 3]

Li _x Ni _1-yz Mn _y M _z O _2-a F _a

[Formula 4]

Li _x Ni _1-yz Mn _y M _z O _2-a S _a

Wherein M is Co, Mg, Fe, Sr, Ti, B, Si, Ga, Al, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, At least one element selected from the group consisting of Er, Tm, Yb, Lu, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, and Lr, and 0.95 ≤ x ≤ 1.1, 0 <y ≤ 0.99, 0 ≤ z ≤ 0.5, 0 ≤ a ≤ 0.5.)

The metal oxide is an oxide of a metal selected from the group consisting of Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B and As. It is a composite metal oxide formed by reaction of the metal contained in the positive electrode active material.

The thickness of the metal oxide or composite metal oxide layer is 1 to 100 nm, preferably 1 to 50 nm, and when the thickness of the oxide layer is less than 1 nm, the effect of coating the active material with an oxide does not appear and exceeds 100 nm. In this case, the oxide layer is too thick, which may interfere with the movement of lithium ions, which is undesirable.

The positive electrode active material of the above configuration can be prepared by the following method.

To prepare a compound powder selected from the group consisting of Chemical Formulas 1 to 4.

To prepare a compound powder selected from the group consisting of Chemical Formulas 1 to 4, first, nickel manganese salt is precipitated by coprecipitation to prepare nickel manganese salt. Nickel hydroxide, nickel nitrate or nickel acetate may be used as the nickel salt, and manganese acetate or manganese dioxide may be used as the manganese salt. The nickel salt and manganese salt are not limited thereto. It is also possible to precipitate fluorine salts or sulfur salts together. Manganese fluoride, lithium fluoride, or the like may be used as the fluorine salt, and manganese sulfide, lithium sulfide, or the like may be used as the sulfur salt. The fluorine salt and sulfur salt are not limited thereto.

The obtained nickel manganese salt and lithium salt are mixed. As the lithium salt, lithium nitrate, lithium acetate, lithium hydroxide, or the like may be used, but is not limited thereto. In this process, metal salts may be further added. As the metal, Co, Mg, Fe, Sr, Ti, B, Si, Ga, Al, Sc, Y, lanthanide element, actinium element, etc. may be used, and the lanthanide element is La, Ce, Pr, Any element included in the lanthanide of Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu can be used, and the actinides are Ac, Th, Pa, U, Np Any element included in the actinides of, Pu, Am, Cm, Bk, Cf, Es, Rm, Md, No or Lr can be used. Examples of the metal salt may be an oxide, nitrate salt, acetate salt or hydroxide of the metal. This mixing step may be carried out dry or may be carried out wet using an organic solvent as the mixing medium. As the organic solvent, alcohol or acetone such as ethanol can be used.

When the precursor, which is the prepared mixture, is first heat treated in a dry air blowing condition, a powder of a compound selected from the group consisting of Chemical Formulas 1 to 4 is prepared. The first heat treatment process is carried out in an oxidizing atmosphere at 200 to 900 ℃ for 1 to 20 hours. When the first heat treatment process is performed at a temperature lower than 200 ° C., the reaction between the compounds used is not sufficient, and when the temperature is higher than 900 ° C., an unstable structure is formed by evaporation of Li in the crystal structure. have. In addition, when the first heat treatment process is carried out for less than 1 hour, there is a problem that the crystallization does not occur, if the process is performed for more than 20 hours excessive crystallization or evaporation of Li in the crystal structure There is a problem in that an unstable structure is formed.

As the coating solution of the prepared powder, a metal alkoxide solution, metal salt organic solution or metal aqueous solution is used. As the metal used in preparing the coating solution, any one dissolved in alcohol, an organic solvent, or water may be used, and representative examples thereof include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As and the like, of which Al is preferred.

The metal alkoxide solution may be prepared by dissolving a metal or metal alkoxide in alcohol, or by refluxing the mixture. Methanol, ethanol or isopropanol may be used as the alcohol. The metal salt organic solution may be prepared by dissolving a metal salt in an organic solvent, or by refluxing the mixture. Organic solvents that can be used when preparing the metal salt organic solution include hexane, chloroform, tetrahydrofuran, ether, methylene chloride, acetone and the like. The aqueous metal solution is prepared by mixing a metal or metal oxide with respect to water, or by refluxing a mixture of water and the metal or metal oxide.

Representative examples of the Si alkoxide solution in the metal alkoxide solution include a tetraorthosilicate solution sold by Aldrich, and tetraethylorthosilicate prepared by dissolving the silicate in ethanol may be used. Representative examples of the metal aqueous solution include vanadium oxide and ammonium vanadate aqueous solution.

The amount of metal or metal alkoxide added in the preparation of the metal alkoxide solution is 0.1 to 20% by weight, preferably 0.1 to 10% by weight relative to the alcohol. Metal salt The amount of metal salt added in the preparation of the organic solution is 0.1 to 20% by weight, preferably 0.1 to 10% by weight relative to the organic solvent. The amount of metal or metal oxide added in the preparation of the aqueous metal solution is 0.1 to 20% by weight, preferably 0.1 to 10% by weight relative to water. When the concentration of the metal is lower than 0.1% by weight, there is no effect of coating a compound selected from the group consisting of the above formulas (1) to (4) with a metal alkoxide solution, a metal salt organic solution or a metal solution, and the concentration of the metal is 20% by weight. If it exceeds, the thickness of the coating layer becomes too thick, which is not preferable.

The at least one compound selected from the group consisting of the above formulas (1) to (4) is coated with a metal alkoxide solution, metal salt organic solution, or metal aqueous solution prepared as described above.

As the coating method, a general coating method such as sputtering, chemical vapor deposition (CVD), dip coating, which is an impregnation method, may be used, but powder, which is the simplest coating method, is simply dipped in the coating solution. It is preferable to use the dip coating method taken out.

The powder coated with the metal alkoxide solution, metal salt organic solution or metal aqueous solution is dried in air and then subjected to a second heat treatment. The secondary heat treatment process is carried out for 5 to 20 hours at 100 to 800 ℃ blowing blowing air (blowing). When the secondary heat treatment process is performed at a temperature below 100 ° C., a new metal oxide layer is not formed on the surface. When the secondary heat treatment process is performed at a temperature exceeding 800 ° C., the metal salt is formed in the crystal structure due to excessive reaction. There is a problem that is doped with. In addition, even when the secondary heat treatment process is performed for a time out of the above-described range, problems due to temperature conditions occur. In this process, a cathode active material selected from the group consisting of Chemical Formulas 1 to 4 having a metal oxide layer or a composite metal oxide layer formed on a surface thereof is formed. The composite metal oxide may be formed by reacting a metal alkoxide solution, a metal salt organic solution or a metal aqueous solution with a metal included in the active material.

The cathode active material of the present invention produced by the above-described method is a powder having a spherical shape, and exhibits a discharge capacity equal to or greater than LiCoO ₂ . In addition, LiCoO ₂ has a high manufacturing price due to the use of expensive Co ₃ O ₄ as a starting material (Co ₃ O _{4 in} the LiCoO ₂ production price of more than 70%), the positive electrode active material of the present invention By using these inexpensive nickel salts and manganese salts, the manufacturing cost can be significantly reduced. In addition, the positive electrode active material of the present invention has a metal oxide or a composite metal oxide layer formed on the surface thereof, it is possible to prevent the voltage drop at the end of discharge that may occur when the nickel manganese-based positive electrode active material is used in the battery. Therefore, the cathode active material of the present invention can replace LiCoO ₂ in terms of capacity and price.

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

(Example 1)

Nickel hydroxide and manganese hydroxide were precipitated in a molar ratio of 9: 1 by the coprecipitation method to prepare NiMnO (OH). LiOH was added to NiMnO (OH) and mixed in a mortar and pestle.

The precursor obtained as a mixture was first heat-treated at 700 ° C. for 20 hours under dry air blowing conditions to synthesize a powder for a positive electrode active material having a composition of LiNi _0.9 Mn _0.1 O ₂ . The size and shape of the particles were examined by SEM and the structure was confirmed by XRD. The powder was immersed in a 5 wt% Al-isopropoxide solution and stirred for about 10 minutes to uniformly coat the Al-isopropoxide solution on the powder surface. The powder coated with the Al-isopropoxide solution was dried in air for about 2 hours.

The Al- iso-propoxide solution is applied to the surface of LiNi _0.9 Mn _0.1 O ₂ powder, the dry air blowing condition, to heat treatment at 300 ℃ for 10 hours, the second having a Al ₂ O ₃ layer on the surface of LiNi _0.9 Mn _0.1 O ₂ Powders were synthesized.

After preparing the electrode plate at a weight ratio of polyvinylidene fluoride = 94/3/3 as a super P / binder with the prepared cathode active material / conductor, a 2016 type coin battery was manufactured to evaluate electrochemical properties. Lithium metal was used as a counter electrode, and a coin battery was constructed by using an electrolyte of 1M LiPF ₆ of ethylene carbonate and dimethyl carbonate (1/1 volume ratio) and a polyethylene separator.

(Example 2)

Nickel hydroxide and manganese hydroxide were mixed in a molar ratio of 7: 3, using 10% by weight of Al-isopropoxide solution, the first heat treatment was carried out at 750 ° C. for 12 hours, and the second heat treatment. Was carried out in the same manner as in Example 1 except that the reaction was carried out at 500 ° C. for 10 hours.

(Example 3)

Nickel hydroxide and manganese hydroxide were mixed in a molar ratio of 7: 3, using 10% by weight of Al-isopropoxide solution, the first heat treatment was performed at 700 ° C. for 12 hours, and the second heat treatment. Was carried out in the same manner as in Example 1 except that the reaction was carried out at 500 ° C. for 10 hours.

(Example 4)

Nickel hydroxide and manganese hydroxide are used at a 5: 5 molar ratio, 1.0 wt% Al-isopropoxide solution is used, the first heat treatment is carried out at 650 ° C. for 12 hours, and the second heat treatment. Was carried out in the same manner as in Example 1 except that the reaction was carried out at 700 ° C. for 10 hours.

(Example 5)

Nickel hydroxide and manganese hydroxide are used in a 1: 9 molar ratio, 1.0 wt% Al-isopropoxide solution is used, except that the first heat treatment is performed at 750 ° C. for 20 hours. It carried out similarly to Example 1.

(Example 6)

Nickel hydroxide and manganese hydroxide are used at a 5: 5 molar ratio, a 5.0% by weight tetraethylorthosilicate solution is used, the first heat treatment is performed at 650 ° C. for 12 hours, and the second heat treatment is 700 Except that was carried out for 10 hours at ℃ was carried out in the same manner as in Example 1.

(Example 7)

Nickel hydroxide and manganese hydroxide are used at a molar ratio of 7: 3, using 5.0% by weight of Mg methoxide solution, primary heat treatment at 750 ° C. for 12 hours, and secondary heat treatment at 750 ° C. The same procedure as in Example 1 was conducted except that the procedure was carried out for 10 hours.

(Comparative Example 1)

The same procedure as in Example 2 was conducted except that no Al-isopropoxide solution was used.

An SEM photograph of the active material prepared by the method of Example 2 is shown in FIG. 1A, and the SEM photograph shown in FIG. 1A is enlarged 10 times and shown in FIG. 1B. As shown in Figs. 1A and 1B, the active material produced by the method of Example 2 is almost spherical in shape and has a uniform shape. Since the shape of the active material manufactured as described above is almost spherical, the packing density may be increased in the electrode plate, thereby manufacturing a battery having a high capacity.

In addition, in order to examine the effect of the metal oxide layer on the charge and discharge characteristics, the initial charge and discharge characteristics of the battery of Example 2 and the battery of Comparative Example 1 was evaluated. Initial charge and discharge characteristics were evaluated by charging and discharging at 0.1 C at a charge and discharge potential of 4.3V-2.75V, and the results are shown in FIG. 2. As can be seen from FIG. 2, it can be seen that the battery (a) of Example 2 in which the metal oxide layer is formed on the surface of the discharge potential and the discharge capacity is superior to the battery (b) of Comparative Example 1 in which the metal oxide layer is not formed. . This seems to be able to increase the discharge potential and prevent the specific discharge capacity from decreasing as the shape of the active material surface changes due to the metal oxide layer formed on the surface. As described above, as the discharge potential and the discharge capacity increase, the total area (power amount) in the graph shown in FIG. 2 increases compared to the battery of Comparative Example 1, so that the battery of Example 2 is compared with that of Comparative Example 1. Can last longer than batteries.

In order to more clearly examine the effect of the metal oxide layer on the first discharge potential reduction, the specific discharge capacity when the total specific discharge capacity shown in FIG. 2 is converted to 100% is shown in FIG. 3. As shown in FIG. 3, the discharge potential of the battery (a) according to Example 2 in which the metal oxide layer was formed at 97% capacity was about 0.1 V than that of the battery (b) according to Comparative Example 1 in which the metal oxide layer was not formed. (About 3%) is excellent.

In addition, the charge and discharge cycle life characteristics of the battery of Example 2 and the battery of Comparative Example 1 were evaluated, and the results are shown in FIG. 4. As shown in FIG. 4, it can be seen that the battery (a) of Example 2 in which the metal oxide layer was formed on the surface of the charge and discharge cycle life characteristics was somewhat better than the battery (b) of Comparative Example 1 in which the metal oxide layer was not formed. have.

In order to examine the structural characteristics of the active material prepared by the present invention, the XRD of the cathode active material of Example 3 was measured and the results are shown in FIG. 5.

In addition, in order to examine the effect of the metal oxide layer on the thermal stability of the positive electrode active material, a battery using the battery of Example 2, Comparative Example 1 and LiNi _0.9 Co _0.1 Sr _0.002 O ₂ active material sold by Honjo After charging to 4.3V, DSC was measured and the results are shown in Figure 6 as (a), (b) and (c), respectively. As shown in FIG. 6, the battery (a) of Example 2 in which the metal oxide layer was formed was commercially available from Honjo and the battery (b) of Comparative Example 1 in which the exothermic peak was small while the metal oxide layer was not formed. LiNi _0.9 Co _0.1 Sr _0.002 O ₂ (c) it can be seen that the exothermic peak is large. These exothermic peaks decompose oxygen (Mn-O), which is bound to the metal at high temperatures, as the charged cathode active material has an unstable Li _1-x NiMnO ₄ structure, and when the decomposed oxygen reacts with the electrolyte It is caused by the heat generated. As the area of the exothermic peak is smaller, it means that the active material has a smaller reactivity with the electrolyte, and thus, it is understood that the active peak is stable. Therefore, since the exothermic peak appears small in the active material of Example 2, it can be seen that the active material is very stable.

In addition, to determine the effect of the metal oxide layer on the high rate (1C) charge and discharge characteristics of the positive electrode active material, the first charge and discharge characteristics of the battery of Example 2 and the battery of Comparative Example 1 and the charge and discharge characteristics after 50 cycles were measured. The results are shown in FIGS. 7 and 8, respectively. 7 and 8, a shows Example 2 and b shows Comparative Example 1. FIG. As shown in FIG. 7 and FIG. 8, it can be seen that the battery of Example 2 having the metal oxide layer was higher than the battery of Comparative Example 1 in which the metal oxide layer was not formed as well as the charge and discharge potential after 50 cycles. .

As described above, the positive electrode active material of the present invention can be economically produced, and the electrochemical property is a very excellent compound can replace the LiCoO ₂ which is excellent in battery characteristics but expensive. In addition, in the case of using the positive electrode active material of the present invention, improvement in power amount (Wh), improvement in life characteristics, stability, and the like are expected.

Figure 1a is a SEM photograph of the positive electrode active material of the present invention.

Figure 1b is a SEM photograph showing a magnified 10 times the SEM photograph of Figure 1a.

Figure 2 is a graph showing the first low-rate charge and discharge characteristics of the positive electrode active material and Comparative Example positive electrode active material according to an embodiment of the present invention.

3 is a graph showing the first discharge potential of the positive electrode active material and the positive electrode active material of the comparative example according to the embodiment of the present invention, respectively.

Figure 4 is a graph showing the charge and discharge life characteristics of the positive electrode active material and Comparative Example positive electrode active material according to an embodiment of the present invention.

Figure 5 is a graph showing the X-ray diffraction (XRD) results of the positive electrode active material of the present invention.

Figure 6 is a graph showing the differential scanning calorimetry (DSC) results of the positive electrode active material and the positive electrode active material according to an embodiment of the present invention.

7 is a graph showing the first high rate charge and discharge characteristics of the positive electrode active material and the positive electrode active material of Comparative Example according to the embodiment of the present invention.

8 is a graph showing charge and discharge characteristics after 50 cycles of the positive electrode active material according to an embodiment of the present invention and the positive electrode active material of Comparative Example.

Claims (10)

(delete) At least one compound selected from the group consisting of the following Chemical Formulas 1, 2, and 4 having a metal oxide or a complex metal oxide layer formed on a surface thereof, wherein the metal oxide is Mg, Al, Co, K, Na, Ca, Si, A positive electrode active material for a lithium secondary battery, which is an oxide of a metal selected from the group consisting of Ti, V, Sn, Ge, Ga, B, and As. [Formula 1] Li _x Ni _1-y Mn _y F ₂ [Formula 2] Li _x Ni _1-y Mn _y S ₂ [Formula 4] Li _x Ni _1-yz Mn _y M _z O _2-a S _a Wherein M is Co, Mg, Fe, Sr, Ti, B, Si, Ga, Al, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, At least one element selected from the group consisting of Er, Tm, Yb, Lu, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, and Lr, and 0.95 ≤ x ≤ 1.1, 0 <y ≤ 0.99, 0 ≤ z ≤ 0.5, 0 ≤ a ≤ 0.5.) The positive electrode active material of claim 2, wherein the oxide layer has a thickness of 1 to 100 nm. Preparing a powder of at least one compound selected from the group consisting of Formulas 1, 2 and 4; Coating the powder with a metal alkoxide solution, metal salt organic solution or metal aqueous solution; And Heat-treating the powder coated with the metal alkoxide solution, metal salt organic solution or metal aqueous solution; Metal oxides or composite metal oxides comprising a coating is selected from the following formulas 1, 2 and 4, wherein the metal oxide is Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, A method for producing a cathode active material for a lithium secondary battery, which is an oxide of a metal selected from the group consisting of Ga, B, and As. [Formula 1] Li _x Ni _1-y Mn _y F ₂ [Formula 2] Li _x Ni _1-y Mn _y S ₂ [Formula 4] Li _x Ni _1-yz Mn _y M _z O _2-a S _a Wherein M is Co, Mg, Fe, Sr, Ti, B, Si, Ga, Al, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, At least one element selected from the group consisting of Er, Tm, Yb, Lu, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, and Lr, and 0.95 ≤ x ≤ 1.1, 0 <y ≤ 0.99, 0 ≤ z ≤ 0.5, 0 ≤ a ≤ 0.5.) According to claim 4, wherein the step of preparing one or more compounds selected from the group consisting of Formula 1, 2 and 4 Preparing nickel manganese salt by precipitating nickel salt and manganese salt by a coprecipitation method; Mixing the nickel manganese salt with a lithium salt; And Primary heat treatment of the mixture Production method that is prepared by a method comprising. The method of claim 5, wherein fluorine salt or sulfur salt is further added in the nickel manganese salt manufacturing step. The method according to claim 5, wherein the metal salt is further added in the mixing step. The method of claim 5, wherein the first heat treatment is performed at 200 to 900 ° C. for 1 to 20 hours. The method of claim 5, wherein the primary heat treatment is performed in an oxidizing atmosphere. A metal oxide or a compound metal oxide layer is formed on the surface comprises a compound of formula 3, wherein the metal oxide is Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, And As positive electrode active material for a lithium secondary battery which is an oxide of a metal selected from the group consisting of. [Formula 3] Li _x Ni _1-yz Mn _y M _z O _2-a F _a Wherein M is Mg, Sr, Ti, Si, Al, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, At least one element selected from the group consisting of Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, and Lr, 0.95 ≦ x ≦ 1.1, 0 <y ≤ 0.99, 0 ≤ z ≤ 0.5, 0 ≤ a ≤ 0.5.)