KR101572454B1 - Cathode for Secondary Battery Having High Power and Lithium Secondary Battery Comprising the Same - Google Patents

Abstract

More particularly, the present invention relates to a positive electrode having a positive electrode active material, a conductive material and a binder coated on the current collector, wherein the positive electrode active material has an average A bimodal lithium-nickel-manganese-cobalt oxide and a monomodal-type olivine-type lithium transition metal phosphate each having a different particle size and different particle diameters, wherein the anode has a density of 1.0 mAh / cm ² To 1.8 mAh / cm < ² >, and a lithium secondary battery comprising the same.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an anode for a high-output secondary battery and a secondary battery including the same. ≪

More particularly, the present invention relates to a positive electrode having a positive electrode active material, a conductive material and a binder coated on the current collector, wherein the positive electrode active material has an average A bimodal lithium-nickel-manganese-cobalt oxide and a monomodal-type olivine-type lithium transition metal phosphate each having a different particle size and different particle diameters, wherein the anode has a density of 1.0 mAh / cm ² To 1.8 mAh / cm < ² >, and a lithium secondary battery comprising the same.

Among the components of the lithium secondary battery, the cathode active material plays an important role in determining the capacity and performance of the battery in the battery.

Lithium cobalt oxide (LiCoO ₂ ), which has excellent physical properties such as excellent cycle characteristics, is mainly used as a cathode active material. However, since cobalt used in LiCoO ₂ is a metal called a rare metal, There is an unstable problem in. In addition, LiCoO ₂ has a problem of high cost due to unstable supply of cobalt and increased demand of lithium secondary batteries.

In this background, studies on a cathode active material capable of replacing LiCoO ₂ have been progressing steadily, and studies have been made on a lithium-containing manganese oxide such as LiMnO ₂ , LiMn ₂ O _{4 having a} spinel crystal structure, and a lithium-containing nickel oxide (LiNiO ₂ ) It is difficult to apply LiNiO ₂ to an actual mass production process at a reasonable cost due to the characteristics of LiNiO ₂ in its production method and the disadvantage that lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ have poor cycle characteristics Lt; / RTI >

Recently, a method using a lithium-transition metal oxide or a lithium transition metal phosphate containing two or more transition metals among nickel (Ni), manganese (Mn), and cobalt (Co) In particular, studies on the use of three-component layered oxides of Ni, Mn, and Co have been carried out steadily.

However, the three-component oxide layer most representative of Li _{[Ni 1/3 Co 1/3 Mn 1/3]} O 2 is lost due to the instability of the lattice oxygen Ni ³⁺ or ⁴⁺ Ni existing in the crystal Ni ²⁺ And the lattice oxygen reacts with the electrolyte to change the surface property of the electrode or to increase the charge transfer impedance of the surface, thereby lowering the capacity or the high-rate characteristics. In order to solve the problem of unstability of the three-component layered oxide, there has been known a technique of mixing a metal oxide of a conventional olivine structure into the layered three-component cathode active material.

Particularly, LiFePO ₄ having an olivine structure using Fe has attracted much attention in the early stage due to stability of crystal structure and use of Fe at a low cost, and a mixture of LiFePO ₄ and the three-component layered oxide using this property has improved safety And was presented as a cathode active material.

However, when an electrode is formed using a cathode active material comprising a mixture of the three-component system layer oxide having a large particle diameter and the metal oxide of the olivine structure, an electrode having a high porosity is produced, and the three- The contact resistance between the active materials is higher than that in the case of the conventional method.

In order to solve this problem, an attempt has been made to reduce the electrical resistance by adding an excessive amount of conductive material. However, in this case, the active material ratio is relatively decreased and the energy density is remarkably reduced. In the rolling process, There is a problem that the lifetime characteristics of the battery are greatly deteriorated.

Therefore, in order to use a lithium secondary battery as a power source for an electric vehicle requiring a high output such as a hybrid electric vehicle (HEV) or a plug-in hybrid electric vehicle (PHEV) There is a high need for a technique that maintains a high output power and has excellent lifetime characteristics.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments and have found that a cathode active material including bimodal lithium nickel-manganese-cobalt oxide and olivine lithium transition metal phosphorus in a monomodal form The present inventors have found that a positive electrode having an energy per unit area in a specific range is produced at a desired level of energy density while exhibiting high output characteristics and improved lifetime characteristics without damaging the active material. It came.

Accordingly, the positive electrode according to the present invention is a positive electrode having a positive electrode active material, a conductive material and a binder coated on the current collector, wherein the positive electrode active material has a bimodal structure composed of small particles having different average particle diameters, Type lithium-nickel-manganese-cobalt oxide and a monomodal type olivine-type lithium transition metal phosphate, and the anode has an energy per unit area of 1.0 mAh / cm ² to 1.8 mAh / cm ² .

FIG. 1 is a partial schematic view of a cathode active material according to one embodiment of the present invention, and FIG. 2 is a SEM photograph. 1, the cathode active material 100 includes a bimodal lithium nickel-manganese-cobalt oxide 110, 120 having fine particles and an opposite particle having different average particle diameters, and a monomodal Manganese-cobalt oxide 120 of the major particle and lithium nickel-manganese-cobalt oxide 120 of the lithium nickel-manganese-cobalt oxide 110 of the minor particle are mixed with the lithium nickel- And is filled in the interstitial volume between the cargo 130 particles.

In this structure, the particle diameter of the lithium nickel-manganese-cobalt oxide 120 of the major particle is about two to three times larger than the particle diameter of the lithium nickel-manganese-cobalt oxide 110 of the minor particle, It can be confirmed that the particle diameter is about 3 to 4 times larger than the particle diameter of the lithium nickel-manganese-cobalt oxide 110 of the fine particles. However, the present invention is intended to exemplify the present invention and fall within the scope of the present invention within the particle diameter range according to the present invention.

In one specific example, the average particle size (D50) of the lithium nickel-manganese-cobalt oxide of the small particle is 2 to 6 占 퐉, and the average particle size (D50) of the lithium nickel- Lt; / RTI > At this time, the lithium nickel-manganese-cobalt oxide of the small particles and the large particles may be in an agglomerated structure, that is, in the form of agglomerates of fine powders.

In one specific example, the olivine-type lithium transition metal phosphate is composed of secondary particles having an average particle size (D50) of 10 to 40 mu m aggregated with primary particles having an average particle size (D50) of 100 to 300 nm .

The secondary particles can be formed by aggregation of primary particles by physical bonding such as van der Waals force rather than chemical bonding. In this case, the shape of the secondary particles collapses at least partially during the pressing process in the production of the electrode And the electric conductivity can be improved as a part of the primary particles is returned.

That is, high process efficiency, which is an advantage of secondary particles, can be ensured during the electrode process, and high electric conductivity and energy density, which are advantages of the primary particles after completion of the electrode process, can be obtained.

In one specific example, the porosity of the secondary particles can be from 15 to 40%, and in particular from 20 to 30%, so that the secondary particles can be returned to the primary particles upon electrode pressing .

When the porosity of the secondary particles is less than 15%, it is not preferable since the secondary particles can be refined only by applying a pressure higher than the pressure normally applied in the pressing process of the electrode, and when the porosity of the secondary particles is more than 40% There is a problem that handling is not easy.

The pores present in the secondary particles may be closed or open, and many pores may be formed in consideration of ease of return to the primary particles and uniform dispersion. The size of the pores may be 50 to 300 nm.

The shape of the secondary particles is not particularly limited, but may be spherical in one specific example in view of the tap density.

Specifically, the method for producing the secondary particles is prepared by drying and agglomerating a mixture of primary particles having a predetermined particle diameter, a binder and a solvent.

The primary particles may be contained in an amount of 5 to 20% by weight based on the weight of the solvent, and the binder may be included in an amount of 5 to 20% by weight based on the weight of the solvent. By controlling the ratio of the primary particles and the solvent, The internal porosity of the particles can be controlled. The solvent may be a polar solvent such as water or a nonpolar organic solvent. The binder may be dissolved in a polar solvent. Examples of the solvent include PVDF, PE-based polymers, saccharides such as sucrose, And coke, but the present invention is not limited thereto. The drying may be performed by a variety of methods known in the art such as spray drying, fluidized bed drying, and vibration drying. Specifically, spray drying may be used. More specifically, rotary spray drying may be used. Secondary particles can be produced in a spherical shape.

Meanwhile, in one specific example, the lithium nickel-manganese-cobalt oxide may be represented by the following formula (1).

Li _{1 + x} Ni _{1- (a + b + c)} Mn _a Co _b M _c O ₂ (1)

In this formula,

M is at least one element selected from the group consisting of Fe, Cr, Ti, Zn, V, Al, and Mg,

0.1? B? 0.4, 0? C? 0.2 and a + b + c <1.

As described above, the lithium transition metal oxide in which a part of nickel is substituted with another transition metal such as manganese or cobalt has a relatively high capacity and exhibits high cycle stability. However, since there is a problem such that excess gas is generated during the cycle, To solve this problem, in one specific example, the lithium nickel-manganese-cobalt oxide may be surface treated by reacting with a fluorine-containing polymer to form a coating layer, or by coating with a metal oxide.

Here, the fluorine-containing polymers, for example may be PVdF or PVdF-HFP, the metal oxide can be, for example, Al ₂ O _3.

In one specific example, the coating thickness may be, for example, 0.5 nm to 5 nm.

When the thickness of the coating layer is more than 5 nm, the amount of lithium nickel-manganese-cobalt oxide is relatively decreased and a desired capacity can not be obtained. When the thickness is less than 0.5 nm, the effect of suppressing gas generation can not be obtained.

In one specific example, the olivine-type lithium transition metal phosphate may be represented by the following formula (2).

Li _{1 + a '} M' (PO _{4 -b '} ) X _b' (2)

In this formula,

M 'is at least one selected from Fe, Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In,

X is at least one selected from F, S and N,

-0.5? A'? + 0.5, and 0? B'? 0.1.

In detail, M 'may be Fe _1-x' M '' _{x '} , where M "is at least one element selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, , Ce, In, Zn and Y, and 0? X? 0.5.

When the values of a ', b' and x 'are out of the above range, the conductivity may be lowered or the lithium transition metal phosphate may not be able to maintain the olivine structure, and the rate characteristic may deteriorate or the capacity may decrease It is not preferable. Also, in the above, x '= 0, and the metal component M''is an optional component, and in this case, it can be expressed as Li _{1 + a'} FePO ₄ . M &quot; is included, the stability of the olivine crystal structure can be improved and the electric conductivity can be improved. However, if the addition amount is more than 0.5, the capacity decrease may be caused, which is not preferable.

Preferred examples of the lithium transition metal phosphate having such a composition _{is, LiFePO 4, Li (Fe,} Mn) PO 4, Li (Fe, Co) PO 4, however, and the like _{Li (Fe, Ni) PO 4} , this limited But may be LiFePO _{4 in} detail.

The surface of the lithium transition metal phosphate may be coated with carbon to further improve electrical conductivity. The coating amount of the carbon may be 0.01 to 10 wt% based on the total weight of the lithium transition metal phosphate, In detail, it may be 0.03 to 7% by weight.

When the coating amount of the carbon is more than 10% by weight, the amount of the lithium transition metal phosphate may be decreased to decrease the capacity and the filling density of the electrode may be lowered. If the coating amount is less than 0.01% by weight, It is not preferable since conductivity is not obtained.

In addition, the carbon may be uniformly coated on the surface of the lithium transition metal phosphate to a thickness of 2 to 10 nm, and more specifically, may be coated with 3 to 7 nm. When the thickness is more than 10 nm, it may interfere with the occlusion and release of lithium ions. However, when the thickness is less than 2 nm, it is difficult to provide a uniform coating and does not provide desired electrical conductivity. I do not.

The carbon may be coated on the surface of the lithium transition metal phosphate in a physical bonding state or a chemical bonding state, and more specifically, may be coated in a chemical bonding state.

Generally, it is very difficult to chemically bond carbon to the surface of the metal oxide, so that the carbon can be chemically bonded via the hetero element. Such a hetero-element is an element which is not separated from the surface of the lithium-transition metal phosphate while being converted to a gas phase upon chemical bonding with oxygen and does not inhibit the action of the secondary battery including the lithium-transition metal phosphate, But it may be sulfur (S) in detail. At this time, the sulfur (S) may be derived from a precursor for the production of a lithium-transition metal phosphate or may be introduced by coating a lithium-containing metal phosphate with a sulfur-containing compound. The sulfur-containing compound may be one or more selected from the group consisting of sulfides, sulfites and sulfates.

According to the inventors of the present application, in the case of coating in a chemical bonding state as described above, not only can a high electrical conductivity be exhibited by a uniform coating, but also a phenomenon of separation due to a strong bonding force And it is possible to achieve a desired electric conductivity even in a small amount, and as a result, the electrode density can be improved.

The coating of the dissimilar materials on the surfaces of the lithium nickel-manganese-cobalt oxide and the lithium transition metal phosphate may be performed by a wet coating method or a dry coating method, and the wet coating method or the dry coating method is already known in the art Description thereof is omitted here.

In one specific example, the content of the oxides contained in the cathode active material may be 10 to 50 wt% based on the total weight of the cathode active material, and the lithium nickel-manganese-cobalt oxide of the lithium- The phosphorus content may be 10 to 40% by weight based on the total weight of the cathode active material, wherein the tap density of the cathode active material may be 0.5 to 3.0 g / cc.

When the content of the lithium nickel-manganese-cobalt oxide in the above-mentioned fine particles is less than 10% by weight, the filling density of the electrode is lowered. When the content is more than 50% by weight, A binder is required for connecting the particles, and it is not preferable because an electrode process is difficult.

When the content of the olivine-type lithium transition metal phosphate is less than 10% by weight, it is difficult to attain desired safety improvement and output assistance at the lower end of the SOC. When the content is more than 40% by weight, The content of the nickel-manganese-cobalt oxide is reduced and the desired output characteristics can not be obtained.

In this connection, the inventors of the present application have found that when the bimodal lithium-nickel-manganese-cobalt oxide and the monomodal lithium-transition metal phosphate are mixed at the weight ratio, The charging density of the electrode can be improved without damaging the active material, and the secondary battery including the lithium-nickel-manganese-cobalt oxide and the lithium- , It is confirmed that it has a high output performance and can secure energy density and lifetime characteristics at a desired level.

On the other hand, the cathode active material may be composed of bimodal lithium nickel-manganese-cobalt oxide and monomodal lithium transition metal phosphide according to the present invention, and may be composed of other lithium-containing transition metal oxides have.

Examples of the lithium-containing transition metal oxide include a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + y} Mn _2-y O ₄ (where y is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Formula _{LiNi 1-y M y O 2} ( where, the M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, y = 0.01 ~ 0.3 Im) Ni site type lithium nickel oxide which is represented by; Formula _{LiMn 2-y M y O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, y = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The positive electrode mixture according to the present invention may further include a conductive material and a binder in addition to the positive electrode active material, and may further include a filler and the like.

In one specific example, the conductive material may comprise from 2 to 7% by weight, based on the total weight of the cathode mix.

Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial 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.

The binder is a component that assists in binding of the active material to the conductive material and bonding to the current collector. In one specific example, the binder may be contained in an amount of 3 to 9% by weight based on the total weight of the positive electrode mixture.

Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, and various copolymers.

When the conductive material contains more than 8 wt% or the binder is contained in an amount of more than 9 wt%, the amount of the cathode active material is decreased and the capacity is decreased. When the conductive material is less than 2 wt% Is less than 3% by weight, the electrode process is difficult and causes a lot of problems and degrades lifetime performance.

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.

As described above, the positive electrode according to the present invention has an energy per unit area of 1.0 mAh / cm ² to 1.8 mAh / cm ^{2, and} the energy per unit area in this range is basically an anode loaded on the current collector Can be controlled by the amount of the active material.

However, when the energy density per unit area of the above range is achieved by simply controlling the amount of loading, the capacity drop of the battery is seriously deteriorated due to the excessively low energy density and the performance deterioration in the continuous charging / discharging process is significant. An ideal anode can be made by a particular combination of a bimodal form of lithium nickel-manganese-cobalt oxide, such as a bimodal form, and a monomodal form of olivinic lithium transition metal phosphorous.

The present invention also provides a high capacity lithium secondary battery comprising the positive electrode.

The lithium secondary battery may be composed of the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte containing a lithium salt, and may be manufactured by putting a porous separator between the positive electrode and the negative electrode by a conventional method known in the art, .

The cathode, the separator, the electrolyte, etc. are well known in the art and incorporated in the present invention, and a description thereof will be omitted herein.

The present invention also provides a battery pack comprising the lithium secondary battery as a unit battery.

In one specific example, the vehicle includes a hybrid electric vehicle (HEV) and a plug-in hybrid electric vehicle (PHEV). Lt; / RTI &gt;

As described above, the positive electrode according to the present invention uses a positive electrode active material including a bimodal lithium-nickel-manganese-cobalt oxide and a mono-modal olivine-type lithium transition metal phosphate, , It is possible to manufacture a positive electrode having a high packing density even at a low line pressure in the rolling process, thereby preventing the active material from being damaged, thereby providing a desired level of energy density and lifetime characteristics, It is effective.

1 is a partial schematic view of a cathode active material according to one embodiment of the present invention;
2 is a SEM photograph of a cathode active material according to one embodiment of the present invention;
3 is a graph showing the difference in electrode density according to Experimental Example 1;
4 is a graph showing a comparison of output characteristics of a lithium secondary battery according to Experimental Example 2. FIG.

Hereinafter, the present invention will be described with reference to Examples. However, the following Examples are intended to illustrate the present invention and the scope of the present invention is not limited thereto.

&Lt; Example 1 >

And LiFePO ₄ having a D50 of 15 ㎛, about 2 LiNi with a D50 of _{~ 6 ㎛ 0.45 Mn 0.35 Co 0.20} O 2 and LiNi about 10 ~ with a D50 of _{25 ㎛ 0.45 Mn 0.35 Co 0.20 O} 2 30:40 a: 30 to prepare a mixed cathode material.

The mixed cathode material thus prepared was mixed with Denka black as a conductive material and polyvinylidene fluoride as a binder in a weight ratio of 91.5: 3.5: 5, followed by addition of NMP (N-methyl pyrrolidone) to prepare a cathode mixture . The positive electrode slurry was applied to an aluminum current collector and dried in a vacuum oven at 120 DEG C to prepare a positive electrode. At this time, the energy density per unit area of the electrode is 1.5 mAh / cm ² .

&Lt; Example 2 >

LiNi _0.45 Mn _0.35 Co _0.20 O ₂ was mixed with PVdF in the manufacturing process of Example 1, and then heat-treated at a temperature of 150-600 ° C for 9 hours to obtain LiNi _0.45 Mn _0.35 Co _0.20 O ₂ was used as a positive electrode active material.

&Lt; Comparative Example 1 &

And LiFePO ₄ having a D50 of 15 ㎛ in the manufacturing process of Example 1, LiNi having a D50 of about _{2 ~ 6 ㎛ 0.45 Mn 0.35 Co} 0.20 O 2 and LiNi _0.45 with a D50 of about 10 ~ 25 ㎛ Mn _0.35 Co _0.20 O ₂ were mixed in a ratio of 30: 9: 61 in the same manner as in Example 1.

&Lt; Comparative Example 2 &

Except that LiFePO ₄ having a D50 of 15 μm and LiNi _0.45 Mn _0.35 Co _0.20 O ₂ having a D50 of about 10 to 25 μm were mixed at a ratio of 30:70 to prepare a cathode active material in the manufacturing process of Example 1 The positive electrode was prepared in the same manner as in Example 1.

<Experimental Example 1>

Electrode density measurement

The thickness of the coated anode was measured in each of Examples 1 and 2 and Comparative Examples 1 and 2, and the density of the electrode was calculated based on the thickness. The results are shown in FIG.

As can be seen from FIG. 3, it can be seen that the anodes of Examples 1 and 2 have a higher packing density as the electrode thickness after coating is thinner than that of the positive electrodes of Comparative Example 1 and Comparative Example 2, In the rolling process, high packing densities can be obtained even at a low line pressure, so that damage to the active material can be minimized.

<Experimental Example 2>

Evaluation of output characteristics

A porous polyethylene separator was interposed between the positive electrode and the reference negative electrode prepared in Examples 1 and 2 and Comparative Examples 1 and 2, and an electrolyte containing 1 M LiPF ₆ lithium salt was injected to prepare a full cell of a lithium secondary battery Respectively.

In order to confirm the effect of using the mixed cathode material, the batteries manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 were formulated at 4.2 V and the output change was measured in the entire SOC region. Respectively.

Referring to FIG. 4, it can be seen that the batteries using the positive electrodes of Examples 1 and 2 have superior output characteristics over the entire SOC period as compared with the batteries using the positive electrodes of Comparative Examples 1 and 2. The data shown in FIG. 4 is only one example, and the detailed output value according to the SOC will vary depending on the type of the battery cell, and therefore, the trend of the graph is more important than the detailed value.

&Lt; Comparative Example 3 &

Except that LiFePO ₄ having a D50 of 15 μm and LiNi _0.45 Mn _0.35 Co _0.20 O ₂ having a D50 of about 2 to 6 μm were mixed at a ratio of 30:70 to prepare a cathode active material in the manufacturing process of Example 1 The positive electrode was prepared in the same manner as in Example 1.

<Experimental Example 3>

Evaluation of life characteristics

Using the positive electrodes prepared in Examples 1 and 2 and Comparative Examples 1 to 3, a lithium secondary battery was manufactured as in Experimental Example 2, and the battery was charged and discharged in a voltage range of 2.7 to 4.2 V in a 45 ° C chamber, And the results are shown in Table 1 below.

Life characteristics
(300
Capacity in cycles,%) Example 1 93 Example 2 94 Comparative Example 1 89 Comparative Example 2 86 Comparative Example 3 88

Referring to Table 1, while the cells using the positive electrodes of Comparative Examples 1 to 3 exhibited a capacity retention rate of 90% or less in 300 execution cycles, the cells containing the positive electrodes of Example 1 and Example 2 exhibited 90% And the lifetime characteristics of the secondary battery according to the present invention are superior to those of the battery using the anode of Comparative Examples 1 to 3. [

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (20)

A positive electrode comprising a positive electrode active material, a conductive material and a binder,
The cathode active material includes a bimodal lithium nickel-manganese-cobalt oxide having the same chemical composition and different average particle sizes, and a monomodal type olivine-type lithium transition metal phosphate. and,
The anode has an energy per unit area of 1.0 mAh / cm ² to 1.8 mAh / cm ² ,
The lithium nickel-manganese-cobalt oxide of the fine particles is contained in an amount of 10% by weight to 50% by weight based on the total weight of the cathode active material,
Wherein the lithium nickel-manganese-cobalt oxide is represented by the following Formula 1, and the olivine-type lithium transition metal phosphate is represented by the following Formula 2:
Li _{1 + x} Ni _{1- (a + b + c)} Mn _a Co _b M _c O ₂ (1)
Li _{1 + a '} M' (PO _{4 -b '} ) X _b' (2)
In this formula,
M is at least one element selected from the group consisting of Fe, Cr, Ti, Zn, V, Al, and Mg,
B < 0.4, 0? C? 0.2 and a + b + c < 1,
M 'is at least one selected from Fe, Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In,
X is at least one selected from the group consisting of F, S and N, -0.5? A'? +0.5, and 0? B'0.1. delete The anode according to claim 1, wherein the olivine-type lithium transition metal phosphate is contained in an amount of 10 to 40% by weight based on the total weight of the cathode active material. The lithium-nickel-manganese-cobalt oxide according to claim 1, wherein the average particle size (D50) of the lithium nickel-manganese-cobalt oxide of the small particle is 2 to 6 占 퐉, . The anode according to claim 1, wherein the small particles and the major particles are aggregates of the fine powders. delete delete The method of claim 1, wherein M 'is Fe _1-x' M '' _x wherein M "is Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Ce, In, Zn and Y, and 0? X? 0.5). The anode according to claim 1, wherein the olivine-type lithium transition metal phosphate is LiFePO ₄ . The olivine-type lithium transition metal phosphate according to claim 1, wherein the olivine-type lithium transition metal phosphate is a mixture of secondary particles having an average particle size (D50) of 10 to 40 占 퐉 obtained by agglomerating primary particles having an average particle size (D50) Lt; / RTI &gt; 11. The anode according to claim 10, wherein the secondary particles are aggregated by physical bonding of primary particles. 11. The anode according to claim 10, wherein the secondary particles have a porosity of 15 to 40%. The positive electrode according to claim 10, wherein the size of the pores present in the secondary particles is 50 to 300 nm. 11. The anode according to claim 10, wherein the shape of the secondary particles is spherical. The positive electrode according to claim 1, wherein the conductive material is contained in an amount of 2 to 7 wt% based on the total weight of the positive electrode material mixture. The positive electrode according to claim 1, wherein the binder is contained in an amount of 3 to 9% by weight based on the total weight of the positive electrode material mixture. A high-output lithium secondary battery comprising the positive electrode according to claim 1. A battery pack comprising a lithium secondary battery according to claim 17 as a unit battery. A vehicle comprising the battery pack according to claim 18. The vehicle according to claim 19, wherein the vehicle is a hybrid electric vehicle (HEV) or a plug-in hybrid electric vehicle (PHEV).

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