KR100783293B1 - Cathode Active Material and Lithium Secondary Battery Containing the Same - Google Patents

Abstract

The present invention provides a high-output lithium secondary battery of a non-aqueous electrolyte having a long life at room temperature and high temperature even after repeated charging and discharging with a large current, and the lithium secondary battery includes lithium manganese spinel oxide and lithium nickel cobalt. It consists of a mixture of manganese composite oxides, and contains the positive electrode active material of the average particle diameter of 15 micrometers of at least 1 type of said oxide.

Description

Cathode Active Material and Lithium Secondary Battery Containing the Same

The present invention relates to a high output lithium secondary battery having a long life at room temperature and high temperature and excellent stability even after repeated charging and discharging with a large current.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is increasing rapidly. Recently, the use of secondary batteries as a power source for electric vehicles (EVs) and hybrid electric vehicles (HEVs) has been realized. have. Accordingly, many studies have been conducted on secondary batteries capable of meeting various needs, and in particular, there is a high demand for lithium secondary batteries having high energy density, high discharge voltage, and output stability.

In particular, lithium secondary batteries used in electric vehicles, such as high energy density and the ability to exhibit a large output in a short time, should be able to be used for more than 10 years under the harsh conditions that charge and discharge by a large current is repeated in a short time, It is inevitably required to have superior safety and long life characteristics than small lithium secondary batteries.

Lithium ion batteries used in conventional small batteries generally use a layered structure of lithium cobalt composite oxide for the positive electrode and a graphite-based material for the negative electrode. However, in the case of lithium cobalt composite oxide, cobalt is a major component. It is expensive and not suitable for electric vehicles in terms of safety. Therefore, a lithium manganese composite oxide having a spinel structure composed of manganese, which is inexpensive and has excellent safety, is suitable as a positive electrode of a lithium ion battery for an electric vehicle.

However, in the case of lithium manganese composite oxide, manganese is eluted into the electrolyte due to the influence of the electrolyte during high temperature and high current charge and discharge, and thus deteriorates the battery characteristics. In addition, since the capacity per unit weight is smaller than the conventional lithium cobalt composite oxide or lithium nickel composite oxide, there is a limit in increasing the capacity per weight of the battery, and the design of a battery that improves the power of the electric vehicle or the like must be performed in parallel. It can be put to practical use.

In order to compensate for each of these disadvantages, a study for producing an electrode with a mixed positive electrode active material has been attempted. For example, in Japanese Patent Application Publication No. 2003-0096214 and Japanese Patent Application Publication No. 2003-092108 of Sanyo Co., Ltd., lithium manganese composite oxide, lithium nickel cobalt manganese composite oxide and / or lithium in order to improve regenerative and output characteristics. A technique for mixing and using nickel manganese composite oxides is disclosed. However, there are still disadvantages of poor life characteristics of lithium manganese oxide and limitations in improving safety.

Accordingly, an object of the present invention is to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

That is, an object of the present invention is to provide a positive electrode active material for secondary batteries that can ensure safety and have a long life at room temperature and high temperature even when charging and discharging are repeated at a large current.

Still another object of the present invention is to provide a lithium secondary battery composed of a cathode including the cathode active material.

The cathode active material for a secondary battery according to the present invention comprises a mixture of a lithium manganese spinel oxide represented by the following Chemical Formula 1 and a lithium nickel cobalt manganese composite oxide represented by the following Chemical Formula 2, and includes at least one of the oxides. The average particle diameter is 15 µm or more.

[Formula 1]

Li _{1 + x} Mn ₂ O ₄

Where

0 ≦ x ≦ 0.2.

[Formula 2]

Li _{1 + y} Ni _b Mn _c Co _{1- (b + c)} O ₂

Where

0 ≤ y ≤ 0.1 and

0.2 ≦ b ≦ 0.7,

0.2 ≦ c ≦ 0.7,

b + c <1.

The present invention also provides a lithium secondary battery comprising a cathode, an anode, a separator, and an electrolyte including the cathode active material.

According to the present invention, the life characteristics of the battery are improved by using an oxide having an average particle diameter of 15 µm or more as the positive electrode active material. This is because decomposition of the electrolyte is suppressed as the particle size of the oxide increases, and the degree of dissolution of manganese into the electrolyte decreases. However, there is a limit in increasing the particle size in the production process of the oxide, and if the particles are too large, the efficiency of the battery to the weight is lowered, the average particle diameter of the oxide is preferably 15 to 30 ㎛.

As a preferred example, the average particle diameter of the lithium manganese spinel oxide of Formula 1 is 15 μm or more, and the average particle diameter of the manganese spinel oxide of Formula 1 and the average particle diameter of the lithium nickel cobalt manganese composite oxide of Formula 2 are each 15 μm. The case above is mentioned. That is, when the average particle diameter of the lithium manganese spinel oxide is 15 µm or more or the average particle diameter of both oxides is 15 µm or more, the life characteristics are further improved, and this fact can be confirmed through the following examples and comparative examples.

The average particle diameter of the oxide in the present invention preferably means a particle diameter when a plurality of particles aggregate to form one combination. The positive electrode active material tends to aggregate one oxide unit with each other according to the setting conditions of the manufacturing process to form one combination, and such agglomerated combination exhibits desirable active material properties by itself. Thus, the mean particle diameter of the oxide preferably means the particle diameter of such agglomerated combinations.

The particle size of the oxide unit may vary according to the method of preparing the oxide. In consideration of various properties as a cathode active material and a shape as an aggregated combination, in one preferred example, the oxide unit of the lithium manganese spinel oxide is It may have a particle diameter of 0.2 to 10 ㎛.

In addition, the particle diameter is closely related to the surface area, and when the oxide unit has a surface area of 0.1 to 1.0 m ² / g, it is possible to exhibit more excellent active material properties.

The lithium nickel cobalt manganese composite oxide, as shown in Formula 2, is a lithium oxide simultaneously containing nickel, manganese and cobalt elements, the safety of the positive electrode active material according to the present invention in combination with a lithium manganese spinel-based oxide And greatly improve the service life characteristics. The lithium nickel cobalt manganese composite oxide contains at least 0.2 mol or more of nickel and manganese, respectively, under conditions including cobalt, and preferably Li _{1 + z} Ni _1/3 Co _1/3 Mn _1/3 O ₂ and Li _{1 + z} Ni _0.4 Mn _0.4 Co _0.2 O ₂ may be mentioned, but is not limited thereto.

In the present invention, the mixing ratio of the two composite oxides is preferably 90:10 to 10:90, more preferably 90:10 to 30:70 based on the weight. Of the two composite oxides, if the content of the composite oxide of the formula (1) is too low, the safety of the battery occurs, on the contrary, if the content of the composite oxide of the formula (2) is too small, the desired life characteristics can not be obtained because Not. This fact can also be confirmed through the following examples and comparative examples.

The lithium manganese spinel oxide of Formula 1 may further improve the lifespan characteristics of the battery when its manganese is lithium manganese spinel oxide of Formula 3 substituted with some other metal.

[Formula 3]

Li _{1 + x} Mn _{2 - z} M _z O ₄

Where

M is a dihydric or trivalent metal oxide;

0 ≤ x ≤ 0.2 and

0 <z ≦ 0.2.

In the lithium manganese spinel oxide, Mn is substituted with dihydric or trivalent metal (M) in a predetermined range, and the metal (M) is preferably one species selected from Al and Mg, or both. Can be.

Since the oxidation number of the substituted metals is smaller than Mn, as the amount of the metal to be substituted increases, the average value of the oxidation number decreases and the oxidation number of Mn becomes relatively high, and consequently, dissolution of the Mn is suppressed. That is, as the amount of the metal (z) substituted in the lithium manganese spinel oxide of Formula 3 increases, the lifespan characteristics are improved. However, since the initial capacity is reduced accordingly, the maximum value of z is preferably 0.2 or less, which can improve the lifetime characteristics as much as possible and minimize the reduction of the initial capacity. More preferred z ranges from 0.01 to 0.2.

In the present invention, a method for preparing a lithium metal composite oxide such as lithium manganese spinel oxide of Formula 1, lithium nickel cobalt manganese composite oxide of Formula 2, and lithium manganese spinel oxide in which manganese of Formula 3 is substituted with a specific metal is known in the art. Since it is known, a description thereof is omitted herein.

Looking at the specific method of manufacturing a positive electrode including a positive electrode active material according to the present invention as follows.

First, a paste is prepared by adding and stirring a positive electrode active material of the present invention and a binder and a conductive agent in an amount of 1 to 20% by weight with respect to the positive electrode active material, and then applying it to a metal plate for current collector and compressing the paste. After drying, a laminate electrode can be prepared.

The positive electrode current collector is generally made to a thickness of 3 to 500 μm. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel The surface-treated with carbon, nickel, titanium, silver, etc. can be used for the surface. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), cellulose, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated Cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers, and the like. have.

The conductive agent is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive agent include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys 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. Specific examples of commercially available conductive agents include acetylene black Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, Ketjenblack, EC series (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal).

In some cases, a filler may be optionally added as a component that suppresses the expansion of the positive electrode. Such a filler is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefinic polymers such as polyethylene and polypropylene; Fibrous materials, such as glass fiber and carbon fiber, are used.

As the dispersion, isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and the like may be typically used.

The method of evenly applying the paste of the electrode material to the metal material can be selected from known methods or performed by a new suitable method in consideration of the properties of the material. For example, it is preferable to disperse the paste onto the current collector and then to disperse the paste uniformly using a doctor blade or the like. In some cases, a method of distributing and dispersing in one process may be used. In addition, die casting, comma coating, screen printing, or the like may be used. Alternatively, a separate substrate may be formed and then joined with a current collector by pressing or lamination. You can also

Drying of the paste applied on the metal plate is preferably dried for 1 to 3 days in a vacuum oven at 50 to 200 ℃.

The present invention also relates to a lithium secondary battery comprising the positive electrode as described above.

The lithium secondary battery of the present invention comprises an electrode assembly in which the positive electrode faces the negative electrode with a separator therebetween and a lithium salt-containing non-aqueous electrolyte.

For example, the negative electrode may be manufactured by coating and drying a negative electrode active material on a negative electrode current collector, and optionally further include components such as a conductive agent, a binder, and a filler as described above.

The negative electrode current collector is generally made to a thickness of 3 to 500 ㎛. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy, and the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The negative electrode active material may be, for example, carbon such as hardly graphitized carbon or graphite carbon; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _{1 - x} Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, 3 of the periodic table) Metal composite oxides such as a group element, halogen, 0 <x ≦ 1, 1 ≦ y ≦ 3, 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , and metal oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separator 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 from 0.01 to 10 ㎛ ㎛, thickness is generally 5 ~ 300 ㎛. As such a separator, for example, olefin polymers such as chemical resistance and hydrophobic polypropylene; Sheet or nonwoven fabric made of glass fiber or polyethylene; Kraft paper or the like is used. Typical examples currently on the market include Celgard series (Celgard ^R 2400, 2300 (manufactured by Hoechest Celanese Corp.), polypropylene separator (manufactured by Ube Industries Ltd. or Pall RAI), polyethylene series (Tonen or Entek), etc.).

In some cases, a gel polymer electrolyte may be coated on the separator to increase battery stability. Representative of such gel polymers are polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile and the like.

When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The said lithium salt containing non-aqueous electrolyte consists of a nonaqueous electrolyte and lithium. As the nonaqueous electrolyte, a nonaqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte, and the like are used.

As said non-aqueous electrolyte, N-methyl- 2-pyrrolidinone, a propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, for example , Gamma-butylo lactone, 1,2-dimethoxy ethane, 1,2-diethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, 4-methyl-1,3-dioxene, diethyl ether, formamide, dimethylformamide, dioxolon, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxolon Aprotic organic solvents such as derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used. Can be.

Examples of the organic solid electrolytes include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyedgetion lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluorides, Polymers containing ionic dissociating groups and the like can 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 , Nitrides, halides, sulfates and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

The lithium salt is a good material to dissolve 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, LiSCN, LiC (CF 3 SO 2) 3, (CF 3 SO 2) 2 NLi, chloro beam is lithium, lower aliphatic carboxylic acid lithium , 4-phenyl lithium borate, imide and the like can be used.

In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, etc. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, etc. It may be. In some cases, in order to impart nonflammability, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

Example 1

The average particle size of 19 ㎛ of Li _{1 + x} Mn ₂ O ₄ of the lithium manganese spinel oxide with a mean particle size of 17 ㎛ of _{Li 1 + z Ni 1/3} Co 1 / of ₃ Mn _1/3 O ₂ lithium nickel cobalt manganese complex An oxide was mixed in a weight ratio of 1: 1 to prepare a cathode active material. 5 wt% of carbon black and PVdF as a binder were mixed with the positive electrode active material, and the mixture was stirred with NMP as a solvent and then coated on aluminum foil as a metal current collector. This was dried in a vacuum oven at 120 ° C. for 2 hours or more to prepare a positive electrode.

An electrode assembly was prepared using a cathode and a porous separator made of polypropylene with MCMB artificial graphite coated on the anode and the copper foil. After inserting the electrode assembly into the pouch and connecting the lead wires, a solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1: 1, in which 1 M LiPF ₆ salt is dissolved, was injected into the electrolyte, and then sealed by lithium. A secondary battery was assembled.

The life characteristics of the lithium secondary battery were measured while charging and discharging in the 3.0 to 4.2 V voltage range, and the results are shown in Table 1 below.

Example 2

The average particle size of 19 ㎛ of Li _{1 + x} Mn ₂ O ₄ of the lithium manganese spinel oxide with a mean particle size of 9 ㎛ of _{Li 1 + z Ni 1/3} Co 1 / of ₃ Mn _1/3 O ₂ lithium nickel cobalt manganese complex A lithium secondary battery was assembled in the same manner as in Example 1 except that a positive electrode active material was prepared using an oxide, and the life characteristics thereof were measured while charging and discharging in the 3.0 to 4.2 V voltage region. The results are shown in Table 1 below.

Example 3

The average particle size of 15 ㎛ of Li _{1 + x} Mn ₂ O ₄ of the lithium manganese spinel oxide with a mean particle size of 17 ㎛ of _{Li 1 + z Ni 1/3} Co 1 / of ₃ Mn _1/3 O ₂ lithium nickel cobalt manganese complex A lithium secondary battery was assembled in the same manner as in Example 1 except that a positive electrode active material was prepared using an oxide, and the life characteristics thereof were measured while charging and discharging in the 3.0 to 4.2 V voltage region. The results are shown in Table 1 below.

Example 4

The average particle size of 15 ㎛ of Li _{1 + x} Mn ₂ O ₄ of the lithium manganese spinel oxide with a mean particle size of 9 ㎛ of _{Li 1 + z Ni 1/3} Co 1 / of ₃ Mn _1/3 O ₂ lithium nickel cobalt manganese complex A lithium secondary battery was assembled in the same manner as in Example 1 except that a positive electrode active material was prepared using an oxide, and the life characteristics thereof were measured while charging and discharging in the 3.0 to 4.2 V voltage region. The results are shown in Table 1 below.

Example 5

The average particle size of 10 ㎛ of Li _{1 + x} Mn ₂ O ₄ of the lithium manganese spinel oxide with a mean particle size of 17 ㎛ of _{Li 1 + z Ni 1/3} Co 1 / of ₃ Mn _1/3 O ₂ lithium nickel cobalt manganese complex A lithium secondary battery was assembled in the same manner as in Example 1 except that a positive electrode active material was prepared using an oxide, and the life characteristics thereof were measured while charging and discharging in the 3.0 to 4.2 V voltage region. The results are shown in Table 1 below.

Comparative Example 1

The average particle size of 10 ㎛ of Li _{1 + x} Mn ₂ O ₄ of the lithium manganese spinel oxide with a mean particle size of 9 ㎛ of _{Li 1 + z Ni 1/3} Co 1 / of ₃ Mn _1/3 O ₂ lithium nickel cobalt manganese complex A lithium secondary battery was assembled in the same manner as in Example 1 except that a positive electrode active material was prepared using an oxide, and the life characteristics thereof were measured while charging and discharging in the 3.0 to 4.2 V voltage region. The results are shown in Table 1 below.

TABLE 1

As shown in Table 1, it can be seen that the life characteristics are improved as the average particle size of the lithium manganese spinel oxide and the lithium nickel cobalt manganese composite oxide increases. When the average particle size of at least one of the two oxides is 15 ㎛ or more, even at 300 cycles, it expresses 70% or more of the initial capacity, and both oxides may express only 60% of the initial capacity when the average particle size is 15 μm or less. It can be seen that the life characteristics are very bad. In particular, when both oxides have an average particle size of 15 ㎛ or more it was confirmed that the life characteristics are further improved.

Example 6

The average particle size of 19 ㎛ of Li _{1 + x} Mn ₂ O ₄ of the lithium manganese spinel oxide with a mean particle size of 9 ㎛ of _{Li 1 + z Ni 1/3} Co 1 / of ₃ Mn _1/3 O ₂ lithium nickel cobalt manganese complex A lithium secondary battery was assembled in the same manner as in Example 1, except that the oxide was mixed in a weight ratio of 90:10 to fabricate a lithium secondary battery, and the charging and discharging was carried out in a 3.0 to 4.2 V voltage range. Was measured. The results are shown in Table 2 below.

Example 7

The average particle size of 19 ㎛ of Li _{1 + x} Mn ₂ O ₄ of the lithium manganese spinel oxide with a mean particle size of 9 ㎛ of _{Li 1 + z Ni 1/3} Co 1 / of ₃ Mn _1/3 O ₂ lithium nickel cobalt manganese complex Except that the positive electrode active material was prepared by mixing the oxide in a weight ratio of 70:30, the lithium secondary battery was assembled in the same manner as in Example 1, while charging and discharging in the 3.0 ~ 4.2 V voltage range, the life characteristics Was measured. The results are shown in Table 2 below.

Example 8

The average particle size of 19 ㎛ of Li _{1 + x} Mn ₂ O ₄ of the lithium manganese spinel oxide with a mean particle size of 9 ㎛ of _{Li 1 + z Ni 1/3} Co 1 / of ₃ Mn _1/3 O ₂ lithium nickel cobalt manganese complex A lithium secondary battery was assembled in the same manner as in Example 1 except that the positive electrode active material was prepared by mixing oxides in a weight ratio of 50:50 (1: 1) to charge and discharge in a 3.0 to 4.2 V voltage range. The lifetime characteristics were measured while proceeding. The results are shown in Table 2 below.

Example 9

The average particle size of 19 ㎛ of Li _{1 + x} Mn ₂ O ₄ of the lithium manganese spinel oxide with a mean particle size of 9 ㎛ of _{Li 1 + z Ni 1/3} Co 1 / of ₃ Mn _1/3 O ₂ lithium nickel cobalt manganese complex Except that the positive electrode active material was prepared by mixing the oxide in a weight ratio of 30:70, the lithium secondary battery was assembled in the same manner as in Example 1, and the charge and discharge in the 3.0 to 4.2 V voltage range, the life characteristics Was measured. The results are shown in Table 2 below.

Example 10

The average particle size of 19 ㎛ of Li _{1 + x} Mn ₂ O ₄ of the lithium manganese spinel oxide with a mean particle size of 9 ㎛ of _{Li 1 + z Ni 1/3} Co 1 / of ₃ Mn _1/3 O ₂ lithium nickel cobalt manganese complex Except that the positive electrode active material was prepared by mixing oxides in a weight ratio of 10:90, the lithium secondary battery was assembled in the same manner as in Example 1, and the lifespan characteristics were performed while charging and discharging in the 3.0 to 4.2 V voltage range. Was measured. The results are shown in Table 2 below.

Comparative Example 2

A lithium secondary battery was assembled in the same manner as in Example 1, except that a positive electrode active material was manufactured using only lithium manganese spinel oxide of Li _{1 + x} Mn ₂ O ₄ having an average particle size of 3.0 μm, to 3.0 to The life characteristics were measured while charging and discharging in the 4.2 V voltage region. The results are shown in Table 2 below.

Comparative Example 3

Have an average particle size of 9 ㎛ of _{Li 1 + z Ni 1/3} Co 1/3 Mn 1/3 O a positive electrode active material by using only a lithium nickel cobalt manganese composite oxide of ₂ was prepared it is as in Example 1, except that A lithium secondary battery was assembled in the same manner, and the life characteristics were measured while charging and discharging in the 3.0 to 4.2 V voltage range. The results are shown in Table 2 below.

TABLE 2

As shown in Table 2, when the lithium nickel cobalt manganese composite oxide having an average particle size of 9 μm is added to the lithium manganese spinel oxide having an average particle size of 19 μm, the lifespan begins to improve, and 30% may be added. It can be seen that the lifetime characteristic value represents the maximum value. However, when the content of the lithium nickel cobalt manganese composite oxide is too high, the safety of the battery is relatively low. Therefore, the lithium nickel cobalt manganese composite oxide is preferably used in an amount of 90% or less. In addition, it can be seen that the batteries of Examples 6 to 10 have better life characteristics than the batteries of Comparative Examples 2 and 3 including only one type of oxide as an active material.

Example 11

In place of Li _{1 + x} Mn ₂ O ₄ and Li _{1 + x} Mn _{1 .9} Al, except _{0 .1} O ₄ on the positive active material was prepared using a substituted lithium manganese oxide spinel of the point in Example 1, A lithium secondary battery was assembled in the same manner, and the life characteristics were measured while charging and discharging in the 3.0 to 4.2 V voltage range. The results are shown in Table 3 below.

Example 12

In place of _{Li 1 + x Mn 2 O 4} Li 1 + x Mn 1 .8 Al 0 .2 O 4 on the positive active material was prepared using a substituted lithium manganese oxide of spinel is as in Example 1, except that The lithium secondary battery was assembled in the same manner, and the life characteristics were measured while charging and discharging in the 3.0 to 4.2 V voltage range. The results are shown in Table 3 below.

Example 13

In place of Li _{1 + x} Mn ₂ O ₄ and Li _{1 + x} Mn _{1 .7} Al, except _{0 .3} O ₄ on the positive active material was prepared using a substituted lithium manganese oxide spinel of the point in Example 1, A lithium secondary battery was assembled in the same manner, and the life characteristics were measured while charging and discharging in the 3.0 to 4.2 V voltage range. The results are shown in Table 3 below.

Example 14

In place of Li _{1 + x} Mn ₂ O ₄ and Li _{1 + x} Mn _{1 .9} Mg, except _{0 .1} O ₄ on the positive active material was prepared using a substituted lithium manganese oxide spinel of the point in Example 1, A lithium secondary battery was assembled in the same manner, and the life characteristics were measured while charging and discharging in the 3.0 to 4.2 V voltage range. The results are shown in Table 3 below.

Example 15

In place of _{Li 1 + x Mn 2 O 4} Li 1 + x Mn 1 .8 Mg 0 .2 O 4 on the positive active material was prepared using a substituted lithium manganese oxide of spinel is as in Example 1, except that A lithium secondary battery was assembled in the same manner, and the life characteristics were measured while charging and discharging in the 3.0 to 4.2 V voltage range. The results are shown in Table 3 below.

Example 16

In place of Li _{1 + x} Mn ₂ O ₄ and Li _{1 + x} Mn _{1 .7} Mg, except _{0 .3} O ₄ on the positive active material by using a substituted lithium manganese oxide spinel was prepared in a point, Example 1 A lithium secondary battery was assembled in the same manner, and the life characteristics were measured while charging and discharging in the 3.0 to 4.2 V voltage range. The results are shown in Table 3 below.

TABLE 3

As shown in Table 3, in the composite oxide mixture of the positive electrode active material, by replacing the Mn site of the lithium manganese spinel oxide with Al or Mg, it can be seen that the life characteristics of the battery is further improved. In addition, it can be seen that the life characteristics are further improved as the amount of substitution is increased. However, when the substitution amount exceeds 0.2, it was confirmed that the initial dose decreases.

As described above, at least one of the lithium manganese spinel oxide and the lithium nickel cobalt manganese composite oxide according to the present invention uses a mixture having an average particle diameter of 15 μm or more as a positive electrode active material, which can ensure safety and provide high current short time charge and discharge. Can improve the service life under conditions.

Those skilled in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

Claims (15)

It is composed of a mixture of lithium manganese spinel oxide represented by the formula (1) and lithium nickel cobalt manganese composite oxide represented by the following formula 2, the mixing ratio of the lithium manganese spinel oxide and lithium nickel cobalt manganese composite oxide is 10: 10 by weight. 90 to 90:10, at least one of the oxides has an average particle diameter of 15 µm or more, and a charge / discharge potential of 3.0 to 4.2 V; Li _{1 + x} Mn ₂ O ₄ (1) Li _{1 + y} Ni _b Mn _c Co _{1- (b + c)} O ₂ (2) Where M is a divalent to trivalent metal 0 ≦ x ≦ 0.2, 0 ≦ y ≦ 0.1, 0.2 ≦ b ≦ 0.7, 0.2 <c <0.7 and b + c <1. The cathode active material of claim 1, wherein the lithium nickel cobalt manganese oxide of Chemical Formula 2 is Li _{1 + z} Ni _1/3 Co _1/3 Mn _1/3 O ₂ . The cathode active material of claim 1, wherein the lithium nickel cobalt manganese oxide of Chemical Formula 2 is Li _{1 + z} Ni _0.4 Mn _0.4 Co _0.2 O ₂ . The cathode active material for lithium secondary battery according to claim 1, wherein the average particle diameter is 15 to 30 µm. The cathode active material of claim 1, wherein the lithium manganese spinel oxide of Formula 1 has an average particle diameter of 15 µm or more. The cathode active material of claim 1, wherein an average particle diameter of the manganese spinel oxide of Formula 1 and an average particle diameter of the lithium nickel cobalt manganese composite oxide of Formula 2 are each 15 µm or more. The cathode active material of claim 1, wherein the oxide is an aggregation combination formed by aggregation of a plurality of oxide units. The cathode active material of claim 7, wherein the oxide unit of the lithium manganese spinel oxide of Chemical Formula 1 has a particle diameter of 0.2 μm to 10 μm. The cathode active material of claim 7, wherein the oxide unit has a surface area of 0.1 to 1.0 m ² / g. delete The cathode active material of claim 1, wherein the mixing ratio is 10:90 to 70:30. The cathode active material of claim 1, wherein the lithium manganese spinel oxide is a lithium manganese spinel oxide represented by the following Chemical Formula 3 in which manganese is partially substituted with another metal: Li_{One + x}Mn_{2 - z}M_zO₄ (3) Where M is a dihydric or trivalent metal oxide; 0 ≤ x ≤ 0.2 and 0 <z ≦ 0.2. The cathode active material for a lithium secondary battery according to claim 12, wherein M is one or both selected from Al and Mg. The cathode active material of claim 12, wherein z is 0.01 to 0.2. A lithium secondary battery comprising the cathode active material according to any one of claims 1 to 14.