KR100555972B1 - Cathode active material and lithium secondary battery employing the same - Google Patents

Abstract

The present invention provides a cathode active material comprising a multiple doped lithium nickel cobalt oxide represented by Formula 1, a lithium manganese oxide represented by Formula 2, and a lithium secondary battery employing the same.

Li _x Ni _y Co _z M _n O ₂

Wherein M is Fe, Ga, Ge, Al, Ti, V, Cu, Zn, Mn, Si, P, Nb, Ta, Zr, Zn, Sn, Sb, Pt, In, Ag, Au, Bi, At least two selected from the group consisting of Pd, W and Nb, x is 0.5 to 1, y is 0.65 to 0.90, z is 0.05 to 0.30, n is 0.05 to 0.225,

Li _a Mn _2-b M1 _b O ₄

Wherein a is 0.98 to 1.02, b is 0 to 0.2, and M1 is at least one selected from the group consisting of Co, Cr and Ti. Cathode active material according to the present invention is excellent in capacity and cycle characteristics, can be suppressed irreversible loss and overcharge not only excellent safety, but also low manufacturing cost and excellent storage and cycle characteristics at high temperatures. Therefore, when the cathode active material is employed, it is possible to make a lithium secondary battery having a high capacity and excellent cycle life.

Description

Cathode active material and lithium secondary battery employing the same

1 is a view showing the results of X-ray diffraction analysis of the cathode active material according to Synthesis Example 3,

2 is an assembly schematic of a CR 2320 coin cell,

3 is a view showing the primary charge capacity characteristics of the cathode active material according to Synthesis Example 3,

4 is a view showing the primary charge capacity characteristics of the cathode active material according to Synthesis Example 4,

5 is a view showing the discharge capacity characteristics of the battery prepared according to Example 1.

<Explanation of symbols for the main parts of the drawings>

220 ... titanium mesh current collector 221 ... cathode active material layer

222 ... cathode casing 223 ... nickel mesh current collector

224 ... Lithium thin film anode 225 ... Celgard separator

The present invention relates to a cathode active material and a lithium secondary battery employing the same, and more particularly, a cathode active material made by mixing a multiple doped lithium nickel cobalt oxide and a lithium manganese oxide having a spinel structure, and a capacity and a cycle by employing the same. The present invention relates to a lithium secondary battery having excellent characteristics and improved safety and high temperature performance.

Lithium nickel oxide (LiNiO ₂ ) is widely used as a cathode active material for lithium secondary batteries together with lithium cobalt oxide (LiCoO ₂ ). Lithium nickel oxide is superior to lithium cobalt oxide in terms of initial capacity, but as the charge and discharge process is repeatedly performed, there is a problem in that capacity decreases rapidly due to disordering between lithium-nickel lattice positions.

As a solution for overcoming the above problems, studies have been actively conducted to replace a part of nickel element with another transition metal. As an example, a lithium composite oxide (LiNiCoO ₂ ) in which a part of nickel element is substituted with cobalt has been proposed.

By the way, this lithium composite oxide has the advantage that the cobalt provides structural stability and thermal stability, and the capacity, cycle characteristics and life characteristics compared to the case of lithium nickel oxide, but cobalt is more expensive than other metals. Therefore, many attempts have been made to reduce cobalt dependence and replace it with other cheap metal elements.

As a specific example of this effort, US Pat. No. 5,783,333 discloses a cathode comprising lithium nickel cobalt oxide represented by Li _x Ni _y Co _z M _n O ₂ . Wherein M is selected from aluminum (Al), titanium (Ti), tungsten (W), chromium (Cr), molybdenum (Mo), magnesium (Mg), tantalum (Ta) and silicon (Si), and Is 0 to 1, the sum of y + z + n is about 1, n is 0 to 0.25, y and z are greater than 0 and the z / y ratio is 0 to 1/3.

Therefore, the technical problem to be achieved by the present invention is to mix a lithium doped lithium nickel cobalt oxide and a lithium manganese oxide having a spinel structure to reduce the cost of irreversible loss, excellent safety, high capacity, high capacity and high-performance cathode active material To provide.

The technical problem to be achieved by the present invention relates to a lithium secondary battery having excellent safety, capacity, high temperature performance and cycle characteristics by employing the cathode active material.

In order to achieve the first technical problem, the present invention provides a cathode active material comprising a multiple doped lithium nickel cobalt oxide represented by Formula 1 and a lithium manganese oxide represented by Formula 2 or Formula 3.

<Formula 1>

Li _x Ni _y Co _z M _n O ₂

Wherein M is Fe, Ga, Ge, Al, Ti, V, Cu, Zn, Mn, Si, P, Nb, Ta, Zr, Zn, Sn, Sb, Pt, In, Ag, Au, Bi, At least two selected from the group consisting of Pd, W and Nb,

x is 0.5 to 1, y is 0.65 to 0.90, z is 0.05 to 0.30, n is 0.05 to 0.225,

<Formula 2>

Li _a Mn ₂ O ₄

Wherein a is 0.98 to 1.02.
<Formula 3>
Li _a Mn _2-b M1 _b O ₄
Wherein a is 0.98 to 1.02, 0 <b ≦ 0.2, and M1 is at least one selected from the group consisting of Co, Cr and Ti.

In the multiple doped lithium nickel cobalt oxide of Formula 1, M preferably includes Mn, Al, and Ga, or Al and Ga. And it is preferable that the lithium manganese oxide of Formula 2 or 3 is a manganese spinel compound containing at least one element of LiMn ₂ O ₄ , Co, Cr, Ti. And the mixed weight ratio of the multiple doped lithium nickel cobalt oxide of Formula 1 and the lithium manganese oxide of Formula 2 or 3 is preferably 90:10 to 30:70.

A second technical problem of the present invention includes a cathode active material comprising a multiple doped lithium nickel cobalt oxide represented by the formula (1) and a lithium manganese oxide represented by the formula (2) or (3), and captures lithium ions during discharge, charging A cathode that releases lithium ions upon loading;

An anode comprising homogeneous graphite particles, homogeneous non-graphite particles, or a mixture thereof, intercalating the chargeable lithium and deintercalating lithium upon discharge;

A separator inserted between the cathode and the anode; And

It has a conductivity with respect to lithium ions, and an electrolytic solution composed of a lithium salt and an organic solvent; made of a lithium secondary battery characterized in that it comprises a.

<Formula 1>

Li _x Ni _y Co _z M _n O ₂

Wherein M is Fe, Ga, Ge, Al, Ti, V, Cu, Zn, Mn, Si, P, Nb, Ta, Zr, Zn, Sn, Sb, Pt, In, Ag, Au, Bi, At least two selected from the group consisting of Pd, W and Nb,

x is 0.5 to 1, y is 0.65 to 0.90, z is 0.05 to 0.30, n is 0.05 to 0.225,
<Formula 2>
Li _a Mn ₂ O ₄
Wherein a is 0.98 to 1.02.
<Formula 3>
Li _a Mn _2-b M1 _b O ₄
Wherein a is 0.98 to 1.02, 0 <b ≦ 0.2, and M1 is at least one selected from the group consisting of Co, Cr and Ti.

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Hereinafter, the cathode active material according to the present invention will be described in more detail.

LiNi (Co, M ₁ , M ₂ , M ₃ ) O ₂ , a multiple-doped lithium nickel cobalt oxide of Formula 1, substitutes cobalt sites with multiple metal elements to retain the metals in cobalt and nickel sites. Improved safety, high capacity and very low manufacturing costs. As M ₁ , M ₂ , and M ₃ , it is preferable to use Mn, Al, and Ga, respectively, in terms of stability and capacity of the compound.

Meanwhile, the lithium manganese oxide represented by Formula 3 is represented by Li _a Mn _2-b M1 _b O ₄ , and in particular, the compound represented by Formula 2 or Formula 3 is one or more of LiMn ₂ O ₄ , Co, Cr, and Ti. It is preferable that it is a manganese spinel compound containing an element.

The lithium manganese oxide LiMn ₂ O ₄ is inexpensive and excellent in thermal safety, it is possible to make the electrode excellent in safety while maintaining high capacity characteristics. In addition, it is safer than LiNiO ₂ or LiCoO ₂ even in overcharging conditions and at high temperatures because the amount of energy and oxygen decreases during MnO ₂ decomposition. Thus, overcharged LiMn ₂ O ₄ electrodes generally do not cause dangerous decomposition reactions. At only 400 ° C., the decomposed MnO ₂ changes to Mn ₂ O ₃ , releasing oxygen.

Therefore, when the LiMn ₂ O ₄ is mixed with the multiple doped LiNiCoO ₂ , the capacity characteristics are excellent, the irreversible loss is small and the overcharge can be prevented, thereby increasing the safety, and the thermal safety and the cycle characteristics are excellent.

On the other hand, LiMn ₂ O ₄ has a reduced storage and cycle characteristics at a high temperature of about 45 ° C., which is due to the partial dissolution of manganese ions in the LiMn ₂ O ₄ compound by HF resulting from the reaction between the electrolyte support salt and excess water. Because. This manganese dissolution phenomenon is suppressed by the addition of multiple doped LiNiCoO ₂ to improve the stability of the structure. The effect of inhibiting manganese dissolution can be confirmed by the following experimental example.

LiNi _0.8 Co _0.2 O ₂ is mixed with electrolyte (1M LiPF ₆ EC / DEC) and LiMn ₂ O ₄ , completely sealed and stored at 80 ° C. for 10 days. Thereafter, HF and Mn concentrations were measured according to the ion-coupled plasma (ICP) and ion chromatography measurements. HF and Mn concentrations decreased with increasing weight percentage of LiNi _0.8 Co _0.2 O ₂ material. It can be seen that mixing doped LiNiO ₂ material with LiMn ₂ O ₄ with spinel structure reduces manganese dissolution.

In addition, mixing LiMn ₂ O ₄ with multiple doped LiNiCoO ₂ improves the high temperature performance of the cell, for example, the storage performance at high temperature. This effect can be confirmed by the following experimental example.

The storage performance at high temperatures in the case of a blend cathode and a graphite anode using a mixture of 80% of LiNi _0.8 Co _0.2 O ₂ and 20% of LiMn ₂ O ₄ as a cathode active material is investigated. As a result, the storage capacity of the battery (post-storage capacity / original capacity) is superior to that of LiNi _0.8 Co _0.2 O ₂ and LiMn ₂ O ₄ , respectively, as cathode active materials. Therefore, it can be seen that the multiple doped LiNiCoO ₂ compound serves as an additive to improve the high temperature performance.

And, multiple doped lithium nickel cobalt oxide is expensive to manufacture. However, by mixing this with LiMn ₂ O ₄ by changing its blending ratio to obtain a very increased LiNiCoO ₂ specific cost can be obtained a cathode active material having excellent capacity characteristics at a low manufacturing cost.

The mixed weight ratio of the multiple-doped lithium nickel cobalt oxide LiNiCoO ₂ of Formula 1 and the lithium nickel manganese oxide of Formula 2 is preferably 90:10 to 30:70, particularly preferably 50:50. If the mixed weight ratio of the multiple-doped lithium nickel botal oxide of Formula 1 and the lithium manganese oxide of Formula 2 is outside the above range, there is a problem in that the storage capacity characteristics are deteriorated.

Looking at the lithium secondary battery according to a preferred embodiment of the present invention employing a cathode active material according to the present invention and a method of manufacturing the same.

First, a cathode active material is obtained by mixing a multiple doped lithium nickel cobalt oxide represented by Chemical Formula 1 and a lithium manganese oxide represented by Chemical Formula 2 in a predetermined weight ratio, and a conductive material, a binder, and a solvent are mixed therein to prepare a cathode active material composition. Prepare. The cathode active material composition is coated and dried on a cathode current collector to form an active material layer to form a cathode. This cathode captures lithium ions upon discharge and releases lithium ions upon charge.

As the anode active material, a high-capacity, high lithium insertion reversibility and a high average discharge voltage are used. Examples of such materials are graphite carbon, non-graphite carbon, mixtures thereof. If necessary for such an anode active material, a binder is mixed and coated and dried on an anode current collector to produce an anode. The anode thus obtained intercalates lithium ions during charging and deintercalates lithium during discharge.

A separator is inserted between the cathode and the anode to form an electrode structure. At this time, the separator is impregnated with an electrolyte having conductivity to lithium ions.

The lithium secondary battery is completed by winding, folding or laminating the electrode structure into a case and sealing the electrode structure.

In the lithium secondary battery of the present invention, the electrolyte is composed of a lithium salt and a solvent. Organic solvents include propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane , 4-methyl 1,3-dioxolane, diethyl ether, sulfolane, acetonitrile, propionitrile, dimethyl carbonate, diethyl carbonate, anisole, methyl propionate, ethyl propionate, methyl acetate, n Propyl acetate, i-propyl acetate, n-butyl acetate, ethyl methyl carbonate and mixtures thereof. Preferably a mixture of ethylene carbonaneart, dimethyl carbonate and diethyl carbonate, a mixture of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate, a mixture of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate, ethylene carbonate, ethyl methyl carbonate, di It is to use a mixture of ethyl carbonate and dimethyl carbonate.

Examples of the lithium salt include LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, LiBr, CH ₃ SO At least one selected from ₃ Li and CF ₃ SO ₃ Li is used.

Hereinafter, the present invention will be described in detail with reference to the following synthesis examples and examples, but the present invention is not limited to the following examples and synthesis examples.

Synthesis Example 1 LiMn ₂ O ₄ Manufacture

A mixture of 0.25 mol of Li ₂ CO ₃ and 1 mol of MnCO ₃ was thoroughly mixed for 16 hours in a plastic container equipped with burundum grinding media. Subsequently, the mixture powder was sieved to collect only powder having a particle size of about 100 μm. The mixture powder was heated in air at 750 ° C. for 24 hours and cooled to room temperature.

The resulting product is ground to a particle size of 50 µm or less. Thereafter, grinding and reheating were repeated to obtain a LiMn ₂ O ₄ having a single phase.

Synthesis Example 2 _1.05 Mn ₂ O ₄ Manufacture

Li _1.05 Mn ₂ O ₄ was synthesized in the same manner as in Synthesis Example 1, except that the content of Li ₂ CO ₃ was 1.05 mol and the content of MnCO ₃ was 2.00 mol.

Since Li _1.05 Mn ₂ O ₄ is present in excess of lithium, the cycle characteristics are maintained well even when some of the lithium is lost during synthesis and during structural modification. Therefore, when Li _1.05 Mn ₂ O ₄ is used, the cycle characteristics are improved as compared with when LiMn ₂ O ₄ is used.

Synthesis Example 3 _0.65 Co _0.275 (Mn _0.025 Al _0.025 Ga _0.025 ) O ₂ Manufacture

A mixture of 1 mole LiOH, 0.65 mole NiO, 0.275 mole Co ₃ O ₄ , 0.025 mole MnCO _3, 0.025 mole Al ₂ O _{3 and} 0.025 mole Ga ₂ O ₃ was equipped with a Burundum grind ELD media Mix well for 16 hours in a plastic container. Subsequently, the mixture powder was sieved to collect only powder having a particle diameter of about 25 μm. The mixture powder was placed in an aluminum crucible and placed in a furnace, heated at 300 ° C. for at least 12 hours and at 500 ° C. for at least 19 hours under an oxygen gas atmosphere, and then cooled to room temperature.

Thereafter, the resultant was regrind and then reheated at 750 ° C. for 16 hours. Subsequently, this regrinding and reheating process was repeated several times to obtain LiNi _0.65 Co _0.275 (Mn _0.025 Al _0.025 Ga _0.025 ) O ₂ . An X-ray diffraction experiment of this compound was carried out, and the results are shown in FIG. 1. Referring to Figure 1, it was found that the compound has a single phase.

And the primary charging capacity of LiNi _0.65 Co _0.275 (Mn _0.025 Al _0.025 Ga _0.025 ) O ₂ according to Synthesis Example 3 in an overcharged state was investigated. At this time, the overcharge voltage was 4.7V. In order to measure the charge capacity of LiNi _0.6 Co _0.20 (Mn _0.05 Al _0.05 Ga _0.05 ) O ₂ according to Synthesis Example 3, a battery was manufactured according to the following method.

That is, 5 g of LiNi _0.65 Co _0.275 (Mn _0.025 Al _0.025 Ga _0.025 ) O ₂ prepared according to Synthesis Example 3 was mixed with 0.5 g of acetylene black and preheated and vacuum dried for 5 to 30 minutes with a stainless steel ball. Next, 0.4 g of polytetrafluoroethylene (PTFE) (Dupont) was added to the mixture to make a sheet. The sheet was cut to the appropriate size to make a cathode.

Lithium thin film was used as an anode, Celgard separator was used as a separator, titanium mesh was used as a cathode current collector, and nickel mesh was used as an anode current collector.

The cathode, anode and separator were used to assemble and seal a CR 2320 coin cell as shown in FIG. 2. In FIG. 2, reference numeral 20 denotes a titanium mesh (EXMET) current collector, 21 denotes a cathode active material layer, 22 denotes a stainless steel (SS304) cathode casing, and 23 denotes a nickel mesh (EXMET) current collector. 24 represents a lithium thin film anode, and 25 represents a Celgard separator.

LiPF ₆ (Grant Chemical) 1M (EC: DEC: DMC = 1: 1: 1 weight ratio) was used as an electrolyte.

3 illustrates the primary charge capacity characteristics of the cathode active material according to Synthesis Example 3 using the battery prepared as described above. Referring to this, it can be seen that the primary charge capacity of the compound is 200mAh / g.

Synthesis Example 4 LiNi _0.65 Co _0.20 (Mn _0.05 Al _0.05 Ga _0.05 ) O ₂ Manufacture

The same method as in Synthesis Example 3, except that the contents of NiO, Co ₃ O ₄ , MnCO ₃ , Al ₂ O ₃ and Ga ₂ O ₃ were changed to 0.65 mol, 0.2 mol, 0.05 mol, 0.05 mol and 0.05 mol, respectively. LiNi _0.65 Co _0.20 (Mn _0.05 Al _0.05 Ga _0.05 ) O ₂ was prepared in the same manner.

According to the same method as in Synthesis Example 3, the primary charging capacity of LiNi _0.65 Co _0.20 (Mn _0.05 Al _0.05 Ga _0.05 ) O ₂ prepared according to Synthesis Example 4 in the overcharged state was investigated. At this time, the overcharge voltage was 4.7V.

Figure 4 shows the primary charge capacity characteristics of the compound. Referring to this, the primary charge capacity of the compound was 215mAh / g, it was found that the charge capacity characteristics are excellent.

Example 1.

2.5 g of LiMn ₂ O ₄ prepared according to Synthesis Example 1 and 2.5 g of LiNi _0.65 Co _0.275 (Mn _0.025 Al _0.025 Ga _0.025 ) O ₂ prepared according to Synthesis Example 3, which were mixed at a 50:50 mixing weight ratio, were prepared using acetylene black 0.5. Pre-heated by mixing with g and vacuum dried for 5-30 minutes with stainless steel balls. Then, 0.4 g of PTFE (Dupont) was added to the mixture to make a sheet. The sheet was cut to the appropriate size to make a cathode.

Lithium thin film was used as an anode, Celgard separator was used as a separator, titanium mesh was used as a cathode current collector, and nickel mesh was used as an anode current collector.

The cathode, anode and separator were used to assemble and seal a CR 2320 coin cell as shown in FIG. 2. LiPF ₆ (Grant Chemical) 1M (EC: DEC: DMC = 1: 1: 1 weight ratio) was used as an electrolyte.

5 shows the primary discharge capacity characteristics of the battery. In Figure 2 the voltage cutoff range is 4.3-3.0V, the discharge capacity is measured at c / 5 rate (rate).

Referring to FIG. 5, the discharge capacity is about 135 mAh / g, when LiMn ₂ O ₄ is used (discharge capacity: 160 mAh / g) and when LiNi _0.65 Co _0.275 (Mn _0.025 Al _0.025 Ga _0.025 ) O ₂ is used (discharge It can be seen that it almost coincides with the average value of the capacity at the capacity: 115 mAh / g).

The cathode active material according to the present invention has excellent capacity and cycle characteristics, can suppress irreversible loss and overcharging, and thus has excellent safety and low manufacturing cost. It also has excellent storage and cycling characteristics at high temperatures. Therefore, when the cathode active material is employed, it is possible to make a lithium secondary battery having a high capacity and excellent cycle life.

Claims (16)

A cathode active material comprising multiple doped lithium nickel cobalt oxides represented by Formula 1 and lithium manganese oxides represented by Formula 2. <Formula 1> Li _x Ni _y Co _z M _n O ₂ Wherein M is Fe, Ga, Ge, Al, Ti, V, Cu, Zn, Mn, Si, P, Nb, Ta, Zr, Zn, Sn, Sb, Pt, In, Ag, Au, Bi, At least two selected from the group consisting of Pd, W and Nb, x is 0.5 to 1, y is 0.65 to 0.90, z is 0.05 to 0.30, n is 0.05 to 0.225, <Formula 2> Li _a Mn ₂ O ₄ Wherein a is 0.98 to 1.02. The cathode active material of claim 1, wherein a mixing ratio of the multiple doped lithium nickel cobalt oxide of Formula 1 and lithium manganese oxide of Formula 2 is 90:10 to 30:70 by weight. The cathode active material according to claim 1, wherein M in the multiple doped lithium nickel cobalt oxide of Chemical Formula 1 includes Mn, Al, and Ga. The cathode active material of claim 1, wherein M comprises Al and Ga in the multiple doped lithium nickel cobalt oxide of Chemical Formula 1. The cathode active material according to claim 1, wherein the lithium manganese oxide of Chemical Formula 2 is LiMn ₂ O ₄ . A cathode including a cathode active material comprising a multiple doped lithium nickel cobalt oxide represented by Formula 1 and a lithium manganese oxide represented by Formula 2, capturing lithium ions upon discharge and releasing lithium ions upon charge; An anode comprising homogeneous graphite particles, homogeneous non-graphite particles or mixtures thereof, intercalating lithium during charging and deintercalating lithium during discharge; A separator inserted between the cathode and the anode; And A lithium secondary battery having conductivity to lithium ions and comprising an electrolyte comprising a lithium salt and an organic solvent. <Formula 1> Li _x Ni _y Co _z M _n O ₂ Wherein M is Fe, Ga, Ge, Al, Ti, V, Cu, Zn, Mn, Si, P, Nb, Ta, Zr, Zn, Sn, Sb, Pt, In, Ag, Au, Bi, At least two selected from the group consisting of Pd, W and Nb, x is 0.5 to 1, y is 0.65 to 0.90, z is 0.05 to 0.30, n is 0.05 to 0.225, <Formula 2> Li _a Mn ₂ O ₄ Wherein a is 0.98 to 1.02. The lithium secondary battery of claim 6, wherein a mixing ratio of the multiple-doped lithium nickel cobalt oxide of Formula 1 and the lithium manganese oxide of Formula 2 is 90:10 to 30:70 by weight in the cathode active material. The lithium secondary battery of claim 6, wherein M in the multiple doped lithium nickel cobalt oxide of Chemical Formula 1 comprises Mn, Al, and Ga. The lithium secondary battery of claim 6, wherein M comprises Al and Ga in the multiple doped lithium nickel cobalt oxide of Chemical Formula 1. 8. The lithium secondary battery according to claim 6, wherein the lithium manganese oxide of Chemical Formula 2 is LiMn ₂ O ₄ . The organic solvent of claim 6, wherein the organic solvent is propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, or 2-methyltetrahydrofuran. , 1,3-dioxolane, 4-methyl 1,3-dioxolane, diethyl ether, sulfolane, acetonitrile, propionitrile, dimethyl carbonate, diethyl carbonate, anisole, methyl propionate, ethyl Lithium secondary battery, characterized in that selected from the group consisting of propionate, methyl acetate, n-propyl acetate, i-propyl acetate, n-butyl acetate, ethyl methyl carbonate and mixtures thereof. The method of claim 6, wherein the lithium salt is LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, A lithium secondary battery, characterized in that at least one selected from LiBr, CH ₃ SO ₃ Li and CF ₃ SO ₃ Li. A cathode active material comprising multiple doped lithium nickel cobalt oxides represented by Formula 1 and lithium manganese oxides represented by Formula 3. <Formula 1> Li _x Ni _y Co _z M _n O ₂ Wherein M is Fe, Ga, Ge, Al, Ti, V, Cu, Zn, Mn, Si, P, Nb, Ta, Zr, Zn, Sn, Sb, Pt, In, Ag, Au, Bi, At least two selected from the group consisting of Pd, W and Nb, x is 0.5 to 1, y is 0.65 to 0.90, z is 0.05 to 0.30, n is 0.05 to 0.225, <Formula 3> Li _a Mn _2-b M1 _b O ₄ Wherein a is 0.98 to 1.02, 0 <b ≦ 0.2, and M1 is at least one selected from the group consisting of Co, Cr and Ti. The method according to claim 1 or 13, wherein the cathode active material of Formula 1 is LiNi _0.65 Co _0.275 (Mn _0.025 Al _0.025 Ga _0.025 ) O ₂ , or LiNi _0.65 Co _0.20 (Mn _0.05 Al _0.05 Ga _0.05 ) O ₂ Cathode active material. A cathode comprising a cathode active material comprising a multiple doped lithium nickel cobalt oxide represented by Formula 1 and a lithium manganese oxide represented by Formula 3, capturing lithium ions upon discharge and releasing lithium ions upon charge; An anode comprising homogeneous graphite particles, homogeneous non-graphite particles or mixtures thereof, intercalating lithium during charging and deintercalating lithium during discharge; A separator inserted between the cathode and the anode; And A lithium secondary battery having conductivity to lithium ions and comprising an electrolyte comprising a lithium salt and an organic solvent. <Formula 1> Li _x Ni _y Co _z M _n O ₂ Wherein M is Fe, Ga, Ge, Al, Ti, V, Cu, Zn, Mn, Si, P, Nb, Ta, Zr, Zn, Sn, Sb, Pt, In, Ag, Au, Bi, At least two selected from the group consisting of Pd, W and Nb, x is 0.5 to 1, y is 0.65 to 0.90, z is 0.05 to 0.30, n is 0.05 to 0.225, <Formula 3> Li _a Mn _2-b M1 _b O ₄ Wherein a is 0.98 to 1.02, 0 <b ≦ 0.2, and M1 is at least one selected from the group consisting of Co, Cr and Ti. The method according to claim 6 or 15, wherein the cathode active material of Formula 1 is LiNi _0.65 Co _0.275 (Mn _0.025 Al _0.025 Ga _0.025 ) O ₂ , or LiNi _0.65 Co _0.20 (Mn _0.05 Al _0.05 Ga _0.05 ) O ₂ A lithium secondary battery.

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