KR101762480B1 - Positive electrode material for lithium secondary battery and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a cathode active material for a lithium secondary battery and a method for producing the same, and more particularly, to a cathode active material for a lithium secondary battery, which comprises mixing a cobalt oxide, a Li-containing compound and a compound providing a +4 valent transition metal cation; Heat-treating the mixture at 100 to 110 캜; And a step of pulverizing the heat-treated mixture to select a powder having a uniform particle size distribution, thereby producing a cathode active material which is stable in a high-voltage region and has improved rate characteristics, and a method for producing a cathode for a lithium secondary battery produced by such a method Thereby providing an active material.

Description

TECHNICAL FIELD The present invention relates to a cathode active material for a lithium secondary battery, and a cathode 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 producing the same, more specifically, to a cathode active material for a lithium secondary battery which is stable in a high voltage region and has improved rate characteristics, and a method for manufacturing the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density and voltage, a long cycle life, and a low self discharge rate are widely used.

In particular, lithium secondary batteries used in electric vehicles have high energy density and high output in a short time, and are superior in safety and long life time than conventional small lithium secondary batteries so that they can be used for more than 10 years under harsh conditions Is inevitably required.

Lithium cobalt oxide (LiCoO ₂ ) having a layered structure with high rate characteristics and reproducibility and very small variations in performance has been commercialized as a cathode for a lithium secondary battery used in an electric vehicle, And is being commercialized.

Since LiCoO ₂ is superior in physical properties such as cycle characteristics and better cycle characteristics than LiNiO ₂ and LiMn ₂ O ₄ , cobalt (Co) is eluted at a high voltage or at a high temperature environment due to high unit cost of cobalt as raw material. There is a disadvantage that a lot of cost is used for management and process control.

In order to solve such a problem, there have been known techniques for replacing a part of cobalt with a metal element or surface-treating a surface of LiCoO _{2 with} a metal oxide such as Al ₂ O ₃ , Mg ₂ O, TiO ₂ or the like.

However, when replacing a part of cobalt with other metal elements or coating a metal oxide on the surface of the lithium cobalt oxide, there is a decrease in specific capacity due to the addition of a material not directly involved in charge / There is a problem that conductivity is lowered.

On the other hand, general LiCoO ₂ has two structures depending on the heat treatment temperature. For example, when synthesized by a solid phase reaction method at 800 ° C. or higher, layered LiCoO ₂ is formed, and at about 400 ° C., a spinel Li ₂ CO ₂ O ₄ structure is formed. It is known that the Li ₂ CO ₂ O ₄ structure synthesized at a low temperature is deteriorated in electrochemical characteristics due to defects in the crystal and low crystallinity, and LiCoO ₂ synthesized at a high temperature is used as a typical cathode active material . However, even in the case of LiCoO ₂ produced by the solid-phase reaction method, since the lithium ion has to move two-dimensionally, the rate characteristic is not as high as about 92%.

Accordingly, there is a high need for a technique capable of improving high-voltage lifetime characteristics and rate characteristics while fundamentally solving various problems of LiCoO ₂ .

In order to solve the above-mentioned problems, the present invention provides a method for producing a cathode active material having improved rate characteristics by adding Mn element at the time of synthesizing LiCoO ₂ , and a method for producing a cathode active material for a lithium secondary battery produced by such a method do.

The present invention also provides a positive electrode for a secondary battery comprising the positive electrode active material for a lithium secondary battery.

Specifically, in one embodiment of the present invention

Cobalt oxide, a Li-containing compound and a compound providing a +4 valence transition metal cation by a solid-phase reaction method; Heat-treating the mixture synthesized from the mixing step at 100 to 110 ° C; And pulverizing the heat-treated mixture to select a powder having a uniform particle size distribution. The present invention also provides a method for producing a cathode active material for a lithium secondary battery.

Further, in the present invention, as the cathode active material produced by the above method,

1. A lithium secondary battery comprising: a first cathode active material composed of a lithium transition metal oxide represented by Formula 1; And a second cathode active material composed of lithium manganese oxide having a layered structure represented by the following general formula (2): < EMI ID = 2.0 >

[Chemical Formula 1]

LiM'O ₂

(2)

Li ₂ MnO ₃

In the above formula, M 'is at least one metal element selected from the group consisting of Ni and Co.

In this case, the cathode active material may further include a third cathode active material composed of lithium cobalt oxide represented by Formula 3 below.

(3)

Li _{1 - x} CoO ₂

In the above formula, x is 0 < x < 1.

Further, in the present invention, the positive electrode collector; And a positive electrode active material of the present invention applied on the positive electrode current collector.

INDUSTRIAL APPLICABILITY As described above, according to the present invention, structural safety can be ensured by replacing a part or the whole of a cobalt element with a Mn element by injecting a Mn element together at the time of LiCoO ₂ synthesis, so that it is stable even in a high voltage range, A cathode active material for an improved lithium secondary battery and a positive electrode for a lithium secondary battery including the same can be manufactured.

Hereinafter, the present invention will be described in detail. Herein, terms and words used in the present specification and claims should not be construed to be limited to ordinary or dictionary meanings, and the inventor may appropriately define the concept of the term to describe its own invention in the best way. It should be construed as meaning and concept consistent with the technical idea of the present invention.

LiCoO _{2, which} is typically used for a cathode active material for a lithium secondary battery, is a single component type active material having a rhombohedral structure (R 3 m). When Li is present in Li _x CoO ₂ of 0.5 or more (x> 0.5), it becomes irreversible because the phase transition occurs to some monoclinic structure in the state where the O 3 -type layer structure and the P 3 -type layer structure are mixed. Therefore, in LiCoO _2, only about 50% or less of lithium ions are reversibly intercalated-deintercalated. In CoO ₂ in which lithium ions are completely eliminated, an irreversible phase transition occurs in a hexagonal structure of O 1 layered structure. When the overcharge occurs at about 4.5V, the Co oxidation number increases and the O-Co-O bond length decreases and the lattice constant a of the xy plane decreases by about 0.3%. However, due to the repulsive force between CoO ₂ and CoO ₂ layer, 2% or more, so that the volume expands as a whole.

In the present invention, by controlling the nature of this LiCoO ₂ and LiCoO ₂ to provide the improved stability and rate characteristics in the high voltage area of 4.4V.

That is, in order to solve the above problems, in one embodiment of the present invention

Cobalt oxide, a Li-containing compound and a compound providing a +4 valence transition metal cation by a solid-phase reaction method; Heat-treating the mixture synthesized from the mixing step at 100 to 110 ° C; And pulverizing the heat-treated mixture to select a powder having a uniform particle size distribution. The present invention also provides a method for producing a cathode active material for a lithium secondary battery.

At this time, in the method of the present invention, the cobalt oxide and the Li-containing compound are not particularly limited as long as they are materials conventionally used in the production of a cathode active material. Specifically, examples of the cobalt oxide include Co ₃ O ₄ that maintains a stable phase in the air, and typical examples of the Li-containing compound include Li ₂ O ₃ .

In addition, in the method of the present invention, the compound providing the +4-valent transition metal cation is not particularly limited as long as it is a substance having physical properties to maintain a stable phase in the air, and a typical example thereof is Mn ₃ O ₄ .

In the method of the present invention, the mixing ratio (molar ratio) of the cobalt oxide: Li-containing compound: +4-transition metal cation providing compound is 1: 1 to 5: 0.001 to 0.007 , Specifically 1: 2.3175: 0.005. At this time, the mixing ratio of Mn ₃ O ₄ based on Li ₂ O ₃ may be 1: 1,000 to 10,000 ppm, specifically 3000 ppm. If it is more than 10,000 ppm, there arises a disadvantage that Mn can form another oxide during firing, and when it is less than 1,000 ppm, it does not exhibit a high rate characteristic.

In the present invention, the mixing step is preferably performed by paste-mixing at room temperature.

Further, in the present invention, heat treatment may be performed at a high temperature of 1000 占 폚 or higher, specifically 1090 占 폚 for 10 to 12 hours for Mn doping.

In addition, in the method of the present invention, the heat-treated mixture is pulverized, and powders having a particle size distribution of 12 to 20 μm are selected to obtain the cathode active material of the present invention.

Further, in another embodiment of the present invention

As the cathode active material produced by the method of the present invention,

1. A lithium secondary battery comprising: a first cathode active material composed of a lithium transition metal oxide represented by Formula 1; And a second cathode active material composed of lithium manganese oxide having a layered structure represented by the following general formula (2): &lt; EMI ID = 2.0 &gt;

[Chemical Formula 1]

LiM'O ₂

(2)

Li ₂ MnO ₃

In the above formula, M 'is at least one metal element selected from the group consisting of Ni and Co.

In this case, the cathode active material may further include a third cathode active material consisting of lithium cobalt oxide having a spinel-like structure represented by Formula 3 below.

 (3)

Li _{1 - x} CoO ₂

In the above formula, x is 0 < x < 1.

That is, in the cathode active material, the second cathode active material represented by Formula 2 is mostly present on the surface, and the third cathode active material represented by Formula 3 is also present on the surface.

Specifically, in the cathode active material, the lithium transition metal oxide represented by Chemical Formula 1 is preferably LiCoO ₂ , and the lithium manganese oxide of the layered structure is preferably Li ₂ MnO ₃ .

In the cathode active material, the lithium transition metal oxide represented by Formula 1: the lithium manganese oxide represented by Formula 2, specifically, the lithium element contained in the lithium transition metal oxide represented by Formula 1: lithium represented by Formula 2 The molar ratio of manganese contained in the manganese oxide may be limited to 1: 0.3 to 3. If, Mn is a molar ratio of less than 0.3, and may not be able to form the Li ₂ MnO ₃ on the surface, when the three or more the higher the possibility of other manganese compound to the outside without the Li ₂ MnO ₃ produced inside the cathode active material for the active material is formed.

In the cathode active material for a lithium secondary battery, the lithium manganese oxide having a layered structure represented by Formula 2 and the lithium cobalt oxide represented by Formula 3 are preferably present on the surface of the cathode active material.

In particular, the cathode active material for a lithium secondary battery is characterized in that electrochemical activity is exhibited at a voltage of 4.4 V or more.

In general, the Mn element tends to exist on the surface side of the compound structure (for example, substitution with Co). Accordingly, when the Mn element is added together during the LiCoO ₂ synthesis as in the method of the present invention, a flower pattern in which six Mn elements are present around the Li element, A positive electrode active material made of a Li-Li dumbbell structure can be formed. Furthermore, when a flower pattern or a Li-Li dumbbell structure is formed on the surface of a compound structure, there is a high possibility that a Li deficient layer is formed around these structures. The Li-deficient layer forms a different phase from LiCoO ₂ in general. For example, in general LiCoO ₂ , the direction in which Li ions can move is limited to a two-dimensional plane, whereas in the case of a Li-deficient layer (Li _{1 - x} CoO ₂ ) , Li ions can move more easily and quickly. Therefore, the cathode active material of the present invention has a low c-axis change in lattice constant relative to LiCoO ₂ during charging and discharging, and can secure structural stability, so that the cathode active material can be stabilized in a high voltage region and the rate characteristic can be improved.

Further, in another embodiment of the present invention

Anode collector; And

And a positive electrode active material of the present invention applied on the positive electrode current collector. The anode may optionally include a conductive material, a binder, a filler, and the like.

At this time, the conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture containing the cathode active material.

Such a conductive material is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery, and includes, for example, graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. Concrete examples of commercially available conductive materials include acetylene black series such as Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc.), Ketjenblack, EC (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal).

The binder is a component which assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene Ethylene, propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers, and the like.

The filler is optionally used as a component for suppressing the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing any chemical change in the battery. Examples of the filler include olefin-based polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The present invention provides a positive electrode for a secondary battery, which is prepared by coating a slurry prepared by mixing the positive electrode material mixture with a solvent such as N-methylpyrrolidone (NMP), and then drying and rolling the positive electrode current collector.

The cathode current collector is generally made to have a thickness of 3 to 500 mu m. Such a positive electrode collector is not particularly limited as long as it has conductivity without causing chemical change to the battery, and may be formed on the surface of stainless steel, aluminum, nickel, titanium, sintered carbon or aluminum or stainless steel Carbon, nickel, titanium, silver, or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

In still another embodiment of the present invention, there is provided a lithium secondary battery including the positive electrode. Specifically, the lithium secondary battery comprises the positive electrode and the negative electrode, a separator, and a lithium-containing non-aqueous electrolyte.

The negative electrode is prepared, for example, by applying a negative electrode mixture containing a negative electrode active material on a negative electrode collector and then drying the same. The negative electrode mixture may contain a conductive material, a binder, a filler or the like &Lt; / RTI &gt;

Examples of the negative electrode active material include carbon and graphite materials such as natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotube, fullerene and activated carbon; Metals such as Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt and Ti which can be alloyed with lithium and compounds containing these elements; Complexes of metals and their compounds and carbon and graphite materials; Lithium-containing nitrides, and the like. Among them, a carbon-based active material, a silicon-based active material, a tin-based active material, or a silicon-carbon based active material is more preferable, and these may be used singly or in combination of two or more.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m, and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing nonaqueous electrolyte solution is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, a nonaqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ Nitrides, halides, sulfates and the like of Li such as SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution may be mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexaphosphoric triamide, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

Such a secondary battery includes a plurality of battery cells used as a power source for a middle- or large-sized device requiring high temperature stability, long cycle characteristics, and high rate characteristics, And may be suitably used as a unit cell in a middle- or large-sized battery module.

Preferred examples of the above medium to large devices include a power tool that is powered by an electric motor and moves; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; Power storage devices, and the like, but the present invention is not limited thereto.

In the foregoing detailed description of the present invention, specific examples have been described. However, various modifications are possible within the scope of the present invention. The technical spirit of the present invention should not be limited to the embodiments of the present invention but should be determined by the claims and equivalents thereof.

Example

Example

Li ₂ CO ₃ , Co ₃ O _4, and Mn ₃ O ₄ were mixed so that the molar ratio of Co to Li and Mn was 1: 2.3175: 0.005. Next, the mixture was heat-treated at 1090 ° C. for 10 hours to synthesize a cathode active material composed of LiCoO ₂ and Li ₂ MnO ₃ stabilized in a layered structure. After synthesizing the cathode active material, the synthesized cathode active material was pulverized, classified and dried for measurement of density characteristics.

Next, 100 g of the positive electrode active material composed of LiCoO ₂ and Li ₂ MnO ₃ was placed in a 500 ml reactor, N-methylpyrrolidone (NMP), a conductive material (carbon black) and a binder (PVDF) And the mixture was kneaded to synthesize a positive electrode mixture. Then, the positive electrode mixture was compressed and dried on an aluminum foil to prepare a positive electrode.

Next, the prepared positive electrode and lithium foil were used as a counter electrode, a porous polyethylene film (thickness: 25 mu m) was used as a separator, and 1 mol of LiPF ₆ A coin cell was prepared according to a conventional manufacturing process of a lithium battery using a non-aqueous electrolyte consisting of ethylene carbonate: dimethyl carbonate = 1: 1 (volume ratio) mixed solvent.

Comparative Example

Li ₂ CO ₃ and Co ₃ O ₄ were mixed so that the molar ratio of Li and Co was 1.025: 1, and the first and second heat treatments were conducted under the same heat treatment conditions as in Example 1 to synthesize a LiCoO ₂ active material.

Next, MnO ₂ was added to the LiCoO ₂ active material, mixed with a ball mill together with a zirconia ball, and then subjected to first and second heat treatment. After completion of the reaction, the synthesized cathode active material was pulverized, classified and dried for measurement of the density characteristics, and then the density of the compacted state was measured under certain conditions.

Next, 100 g of the positive electrode active material composed of LiCoO ₂ and Li ₂ MnO ₃ was placed in a 500 ml reactor, N-methylpyrrolidone (NMP), a conductive material (carbon black) and a binder (PVDF) And the mixture was kneaded to synthesize a positive electrode mixture. Then, the positive electrode mixture was compressed and dried on an aluminum foil to prepare a positive electrode.

Next, the prepared positive electrode and lithium foil were used as a counter electrode, a porous polyethylene film (thickness: 25 mu m) was used as a separator, and 1 mol of LiPF ₆ A coin cell was prepared according to a conventional manufacturing process of a lithium battery using a non-aqueous electrolyte consisting of ethylene carbonate: dimethyl carbonate = 1: 1 (volume ratio) mixed solvent.

Experimental Example 1. Discharge Capacity

The discharge capacities of the coin cells prepared in the above Examples and Comparative Examples were evaluated and shown in the following table. The charging / discharging characteristics of these coin cells were examined and are shown in Table 1.

The discharge capacity of the coin half cell manufactured in each of the examples and the comparative examples was charged at a rate of 0.1 C (C-rate) in the first cycle until the voltage became 4.4 V, and then, at a constant voltage of 4.4 V The battery was further charged until the current reached 0.05C. Thereafter, it was rested for 10 minutes. Subsequently, each of the coin half cells was discharged at a rate of 0.1 C until the voltage reached 3.0 V, and the discharge capacity at that time was evaluated. The "C" is a discharge rate of the cell, which means a value obtained by dividing the total capacity of the cell by the total discharge time.

The coin half cells prepared in each of the examples and comparative examples were charged at a constant current (0.1 C) and a constant voltage (4.4 V, 0.05 C cut-off), rested for 10 minutes, C, 2.0C) until the voltage reached 2.5 V, thereby evaluating the high-rate discharge characteristics of each coin half cell. The high rate discharge characteristics in the coin half cell are shown in the following table.

At this time, the high rate discharge characteristic can be calculated by the following equation (1).

(%) = (Discharge capacity when the cell is discharged at 2.0 C) / (discharge capacity when the cell is discharged at the rate of 0.1 C) * 100

1 ^st Charge
(mAh / g) 1 ^st Discharge
(mAh / g) Efficiency
(%) 0.1C Capacity
(mAh / g) 1C Capacity
(mAh / g) 2C Capacity
(mAh / g) 1C Rate
(%) 2C Rate
(%) 4.40V Example 179.9 176.3 98.0 176.1 170.8 166.0 97.0 94.2 Comparative Example 177.7 172.4 97.0 172.4 163.7 158.9 94.9 92.2

From the above table, it was found that the discharging capacity of the positive electrode and the discharging capacity per unit volume in the coin cell of the Example were improved as compared with the comparative example. In addition, the coin cell of the example exhibited a higher rate discharge characteristic than the comparative example. Here, the 'high rate discharge characteristic' means that the rate of decrease of the normalized capacity (that is, the capacity retention rate) with the increase of the discharge rate (C-rate) is small.

Thus, when the Mn element is added together during the LiCoO ₂ synthesis, the structural stability can be ensured by reducing the change of the c-axis compared with the case where the Mn element is added separately during the synthesis of the lithium cobalt oxide, Thereby providing a cathode active material having improved characteristics and a lithium secondary battery including the same.

Claims (17)

Cobalt oxide, a Li-containing compound and a compound providing a +4 valence transition metal cation by a solid-phase reaction method;
Heat-treating the mixture synthesized from the mixing step; And
And pulverizing the heat-treated mixture to select a powder having a uniform particle size distribution,
The mixing ratio (molar ratio) of the compound providing the cobalt oxide: Li-containing compound: +4 valence transition metal cation is 1: 1 to 5: 0.001 to 0.005 based on Co, Li and Mn elements,
Wherein the heat treatment is performed at 1000 ° C. or more for 10 to 12 hours. The method according to claim 1,
Wherein the cobalt oxide is Co ₃ O _{4. The} method for producing a cathode active material for a lithium secondary battery according to claim ₁ , wherein the cobalt oxide is Co ₃ O ₄ . The method according to claim 1,
Wherein the Li-containing compound is Li ₂ O ₃ . The method according to claim 1,
Wherein the compound providing the +4 valence transition metal cation is Mn ₃ O ₄ . delete The method according to claim 1,
Wherein the mixing ratio (molar ratio) of the cobalt oxide: Li-containing compound: +4-transition metal cation providing compound is 1: 2.3175: 0.005 based on Co, Li and Mn elements. Way. The method according to claim 1,
Wherein the heat treatment is performed at 1090 캜 for 10 to 12 hours. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; A positive electrode active material produced by the method of claim 1,
1. A lithium secondary battery comprising: a first cathode active material composed of a lithium transition metal oxide represented by Formula 1; And a lithium manganese oxide having a layered structure represented by the following formula (2).
[Chemical Formula 1]
LiM'O ₂
(2)
Li ₂ MnO ₃
In the above formula, M 'is at least one metal element selected from the group consisting of Ni and Co. The method of claim 8,
Wherein the lithium transition metal oxide is LiCoO ₂ . The method of claim 8,
Wherein the layered lithium manganese oxide is Li ₂ MnO ₃ . The method of claim 8,
Wherein the cathode active material further comprises a third cathode active material composed of lithium cobalt oxide represented by the following formula (3).
(3)
Li _{1 - x} CoO ₂
In the above formula, x is 0 < x < 1. The method of claim 8,
Wherein the molar ratio of the lithium element contained in the lithium transition metal oxide represented by the formula (1): manganese contained in the lithium manganese oxide represented by the formula (2) is 1: 0.3 to 3. The method according to claim 8 or 11,
Wherein the second cathode active material represented by Formula 2 and the third cathode active material represented by Formula 3 are present on the surface of the cathode active material. The method of claim 8,
Wherein the positive electrode active material for a lithium secondary battery exhibits electrochemical activity at a voltage of 4.4 V or higher. Anode collector; And
The positive electrode for a lithium secondary battery according to claim 8, comprising the positive electrode active material coated on the positive electrode collector. 16. The method of claim 15,
Wherein the anode further comprises a binder and a conductive material. The anode according to claim 15,
cathode,
A separator interposed between the anode and the cathode, and
A lithium secondary battery comprising a nonaqueous electrolyte solution containing a lithium salt.