KR101941638B1 - Manufacturing method of cathode active material for a lithium secondary battery and cathode active material obtained thereby - Google Patents

Abstract

The present invention relates to a method for producing a precursor of a cathode active material, and more particularly, to a method for producing a precursor of a cathode shell, which is produced by a conventional build-up method by selectively removing only nickel present on the surface of a precursor, Fine control over the active material precursor or the cathode active material is possible.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for producing a cathode active material for a lithium secondary battery, and a cathode active material for a lithium secondary battery,

The present invention relates to a precursor of a cathode active material for a lithium secondary battery, and more particularly, to a method for producing a precursor of a cathode active material for a lithium secondary battery, a precursor for a cathode active material for a lithium secondary battery and a method for producing a cathode active material for a lithium secondary battery To a cathode active material for a lithium secondary battery.

In general, lithium-ion batteries have been used in a variety of fields since the discovery of the technology, through more research and development, nowadays, such as cell phones and means for storing energy in electric vehicles. Particularly, as electronic devices have become compact and portable, there has been a great increase in the demand for lightweight and high energy density lithium secondary batteries.

As representative cathode active material of the lithium secondary _{battery, LiCoO 2, LiMn 2 O 2} , LiNiO 2, LiNi 1-x Co x O 2 (0 <x <1) such as a lithium metal oxide, and, in the conventional LiCoO ₂ ilbyeondo of (Li [Ni, Co, Al] O ₃ ) and LiMnO ₄ and LiFePO ₄ are known at low cost.

Conventional LiCoO ₂ has attracted a great deal of attention due to its large storage capacity and excellent charge / discharge characteristics. However, Co, which is a rare metal used for this purpose, is unstable in terms of supply because the reserves are small in the world and production sites are concentrated in specific regions. And it is required to develop new materials.

In order to solve the above problems, research has been carried out in the direction of minimizing the amount of rare metals such as Co. As a result, LiNiO ₂ having a layered rock salt structure using Ni, Mn, Fe, LiNi ₂ O _{4 with a} spinel structure and LiFePO _{4 with an} olivine structure have been developed. However, since the NiO ₂ crystal structure is unstable, LiNiO ₂ alone can not be used, and it is difficult to synthesize a material having a pure layered structure. Because of the very good Ni ⁴⁺ ions, Li _x Ni _1-x O, which has a rocksalt structure, is transferred to Li _x Ni _1-x O and releases excess oxygen, so that it can not be commercialized due to its longevity and thermal instability.

In order to overcome this problem, a high-nickel-based lithium oxide has been proposed. However, since it also has a problem in high-temperature storage characteristics and life span, it still has limitations such as cycle characteristics, high-rate characteristics and thermal stability.

As a method for solving this problem, there has been developed a dual-layered cathode active material composed of a core composed of a high-content nickel-based cathode active material and a shell composed of a high-content manganese-based cathode active material having high stability characteristics (Patent Document 1) By adjusting the concentration of the precursors in the coprecipitation process carried out in each reactor to have different compositions, it is difficult and time-consuming to control the process, and substantially the primary particles still retain a large amount of nickel Ni rich) or manganese (Mn rich). Therefore, the stability of the Ni rich portion is still low.

It is an object of the present invention to provide a positive electrode active material precursor for a lithium secondary battery and a positive electrode active material for a lithium secondary battery capable of easily and simply controlling the metal composition of a center portion and a surface portion by introducing a wet leaching method, And a method for producing the same.

Another object of the present invention is to provide a positive electrode active material precursor for a lithium secondary battery and a positive electrode active material for a lithium secondary battery excellent in capacity and stability using the above-described manufacturing method.

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

The present invention provides a method for preparing a precursor of a cathode active material for a lithium secondary battery, comprising the steps of:

(I) preparing a coprecipitated compound represented by the following formula (I) by coprecipitation with a metal salt aqueous solution containing a nickel salt, a manganese salt and a cobalt salt, a chelating agent and a basic aqueous solution in a reactor; And

(II) adding a leaching solution to the coprecipitation compound to leach only a specific metal present on the surface of the coprecipitation compound.

[Chemical Formula 1]

Ni _x CoyMn _(1-xy) (OH) ₂

In the above formulas,

0.5? X? 0.75, 0.1? Y? 0.24, and 0.01? 1-x-y? 0.4.

The chelating agent is an aqueous ammonia solution (NH ₄ OH), ammonium sulfate _{((NH 4) 2 SO 4} ), ammonium nitrate (NH ₄ NO _3), first ammonium phosphate _{((NH 4) 2 HPO 4} ) , and mixtures thereof &Lt; / RTI &gt;

The molar ratio of the nickel salt, cobalt and manganese salt may be 0.5-0.85: 0.05-0.3: 0-0.45.

The specific metal may be (i) nickel or (ii) nickel and cobalt.

The leaching solution may be any one selected from the group consisting of an alkali leaching solution, an acid leaching solution, a polymer leaching solution, an organic solvent leaching solution, and a mixture of two or more of them.

The acid leaching solution may be a sulfuric acid solution.

The average surface thickness of the cathode active material precursor may be 10 nm to 1 탆.

The step (I) and the step (II) may all be carried out at 10 to 100 ° C.

In order to achieve the above other object, according to the present invention, And a surface portion formed so as to surround the center portion of the cathode active material precursor.

A center portion of the cathode active material precursor is represented by the following Formula 1a,

The surface portion of the cathode active material precursor is represented by the following Chemical Formula 2.

[Formula 1a]

Ni _x1 Co _y1 Mn _{(1-x1- y1 )} (OH) ₂

In the above formulas,

0.5? X1? 0.75, and 0.1? Y1? 0.24.

(2)

_{Ni x2 Co y2 Mn 1 -x2- y2} (OH) 2

In the above formulas,

0.0? X2? X1, and 0.0? Y2? Y1.

(I) the concentration of nickel or (ii) the concentration of nickel and cobalt may have a concentration gradient structure that decreases from the inside of the surface portion toward the outside of the surface portion.

The average diameter of the center portion of the cathode active material precursor may be 1 to 10 mu m and the average thickness of the surface portion of the cathode active material precursor may be 10 nm to 1 mu m.

The cathode active material precursor may have a layered structure in both the central portion and the surface portion.

The tap density of the cathode active material precursor may be 2.4 to 3 g / cm &lt; 3 &gt;.

The surface of the surface portion of the cathode active material precursor may have an uneven surface.

According to another aspect of the present invention, there is provided a method of manufacturing a cathode active material for a lithium secondary battery, comprising the steps of:

(I) preparing a coprecipitated compound represented by the following formula (I) by coprecipitation with a metal salt aqueous solution containing a nickel salt, a manganese salt and a cobalt salt, a chelating agent and a basic aqueous solution in a reactor;

II) adding a leaching solution to the coprecipitation compound to leach only a specific metal present on the surface of the coprecipitation compound; And

III) mixing the lithium salt with the cathode active material precursor, followed by firing.

[Chemical Formula 1]

Ni _x Co _y Mn _(1-xy) (OH) ₂

In the above formulas,

0.5? X? 0.75, and 0.1? Y? 0.24.

The specific metal may be (i) nickel or (ii) nickel and cobalt.

In the step (III), the heat treatment may be performed at 400 to 900 ° C.

According to another aspect of the present invention, And a surface portion formed to surround the center portion, wherein a center portion of the cathode active material precursor is represented by the following Formula 3, and a surface portion of the cathode active material precursor is represented by the following Formula 4: Thereby providing a cathode active material.

(3)

Li [Ni _{x 3} Co _{y 3} Mn _{(1-x 3-y 3 )} ] O ₂

In the above formulas,

0.5? X3? 0.75, and 0.1? Y3? 0.24.

[Chemical Formula 4]

Li [Ni _{x 4} Co _{y 4} Mn _{1 -x 4-y 4} ] O ₂

In the above formulas,

0.0? X4? X3, and 0.0? Y4? Y3.

The maximum exothermic peak temperature of the cathode active material measured according to the thermal stability evaluation method using a differential scanning calorimeter may be 265 ° C to 275 ° C.

The calorific value of the cathode active material measured according to the thermal stability evaluation method using a differential scanning calorimeter may be 350 to 385 W / g.

The lithium secondary battery includes the cathode active material.

When the lithium secondary battery is stored in a fully charged state at 60 to 90 ° C for 5 to 10 days and then charged and discharged in a voltage range of 2.5 to 4.3 V and at a room temperature for 10 to 100 cycles, retention may be 99.9 to 90%.

According to another aspect of the present invention, there is provided a battery module including the secondary battery as a unit cell.

According to another aspect of the present invention, there is provided a device using the battery module as a power source.

The device may be any one selected from an electric vehicle or a hybrid electric vehicle or a power storage device.

The present invention relates to a core shell structure manufactured by a conventional build-up method by selectively removing only nickel present on the surface of a precursor, which is a nano-sized primary particle, through a simple process. As compared with a cathode active material precursor or a cathode active material, Is possible.

In addition, the surface leaching process of the wet film can be easily applied to the washing process of the common co-production process currently in commercial use, which has a great advantage in the process cost.

In addition, the wet-based surface leaching process has no problems in use and size.

Further, when the cathode active material precursor formed through the manufacturing method of the present invention is mixed with and calcined with the lithium precursor to produce the final cathode active material, the center portion and the surface structure of the cathode active material precursor are maintained as they are, .

In addition, the positive electrode active material prepared using the positive electrode active material precursor of the present invention does not contain nickel at all on its surface, so that it is possible to achieve an effect of exhibiting a void capacity while increasing stability.

1A is a cross-sectional view illustrating the structure of a cathode active material precursor according to the present invention.
1B is a cross-sectional view illustrating a structure of a cathode active material according to the present invention.
FIG. 1C is a schematic process diagram of a cathode active material precursor according to the present invention. FIG.
2 is a photograph of the cathode active material precursor (a) prepared in Comparative Example 1 and the cathode active material precursor (b) prepared in Example 1 by a scanning electron microscope.
FIG. 3 is a photograph (a) of the cathode active material precursor prepared in Example 1 by an electron scanning microscope and FIG. 3 (b) is a graph showing the analysis of the metal composition according to the thickness through an electron probe microanalysis technique.
4 is a graph showing the high temperature storage cycle characteristics of the cathode active material (Wet Sek) prepared in Example 2 and the cathode active material (black) prepared in Comparative Example 2. FIG.
5 is a graph showing the results of evaluating the thermal stability of the positive electrode active material prepared in Example 2 (Wetting) and the positive electrode active material (black) prepared in Comparative Example 2 up to 4.3 V by means of differential scanning calorimetry (DSC) Fig.

Hereinafter, various aspects and various embodiments of the present invention will be described in more detail.

Development of a cathode active material having a core-shell structure has been developed in order to solve the problem that the stability is largely lowered due to exposure of nickel in the conventional cathode active material, and to achieve high stability and high capacity. A build-up method to control the input ratio of the transition metal in the process has been proposed. This is because it is difficult to control the process, and the core shell structure is still rich in nickel, I can not.

However, in the present invention, the present invention has been accomplished in order to achieve a high capacity of the positive electrode active material and to secure the stability of the positive electrode active material through an easy and simple process by recognizing the above-mentioned problems.

According to an aspect of the present invention, there is provided a method for manufacturing a cathode active material precursor including the following steps.

(I) preparing a coprecipitated compound represented by the following formula (I) by coprecipitation with a metal salt aqueous solution containing a nickel salt, a manganese salt and a cobalt salt, a chelating agent and a basic aqueous solution in a reactor; And

II) adding a leaching solution to the coprecipitation compound to leach only a specific metal present on the surface of the coprecipitation compound;

[Chemical Formula 1]

Ni _x CoyMn _(1-xy) (OH) ₂

In the above formulas,

0.5? X? 0.75, and 0.1? Y? 0.24.

FIG. 1C is a schematic process diagram of a cathode active material precursor according to the present invention. FIG.

First, I) a coprecipitated compound represented by the following Chemical Formula 1 is prepared by mixing a metal salt aqueous solution containing a nickel salt, a manganese salt and a cobalt salt, a chelating agent and a basic aqueous solution in a reactor and coprecipitating it.

The metal salts such as the nickel salts, manganese salts and cobalt salts are not particularly limited as long as they can be dissolved in water. Sulfates, nitrates, nitrates, halides, hydroxides and the like may be preferably used.

The molar ratio of the nickel salt, the cobalt salt and the manganese salt may be 0.5 to 0.85: 0.05 to 0.3: 0 to 0.45, preferably 0.5 to 0.75: 0.1 to 0.24 : 0.01 to 0.4 is preferable in view of the capacity of the cathode active material.

The chelating agent is an aqueous ammonia solution (NH ₄ OH), ammonium sulfate _{((NH 4) 2 SO 4} ), ammonium nitrate (NH ₄ NO _3), first ammonium phosphate _{((NH 4) 2 HPO 4} ) , and mixtures thereof &Lt; / RTI &gt;

The molar ratio of the chelating agent to the metal salt aqueous solution is preferably 0.2-0.5: 1. When the molar ratio of the chelating agent exceeds 0.5, the chelating agent reacts with the metal aqueous solution at a ratio of 1: 1, The chelating agent can be in a supersaturated state. If the chelating agent is less than 0.2, the crystallinity is lowered, and the degree of stabilization may be significantly lowered.

In addition, the basic solution is used to maintain the pH at 10.5 to 12, and NaOH, KOH, and a mixture thereof can be used.

The density of the coprecipitation compound can be controlled by adjusting the time of residence in the coprecipitation reactor in the above step, preferably 1 to 5 hours, and the tap density of the cathode active material precursor to be produced thereafter is 2.4 to 3 g / It is most preferable to hold it for 2 to 4 hours.

Thereafter, (II) the leaching solution is added to the coprecipitation compound to leach only the specific metal present on the surface of the coprecipitation compound. Through this process, the prepared cathode active material precursor particles have a concentration gradient structure in which the concentration of a specific metal decreases from the inside of the surface portion to the outside of the surface portion.

The leaching solution may be any one selected from the group consisting of an alkali leaching solution, an acid leaching solution, a polymer leaching solution, and an organic solvent leaching solution.

The specific metal is (i) nickel or (ii) nickel and cobalt. It may be suitably selected according to the leaching solution, preferably at least one selected from the group consisting of hydrochloric acid, nitric acid and sulfuric acid, and particularly preferably, when a sulfuric acid solution is used as the leaching solution, nickel and cobalt It can leach.

The alkali leaching solution may be sodium hydroxide.

The step (II) may be carried out under a condition that the solution is perfectly mixed.

The cathode active material precursor having the center portion 110 having an average diameter of 1 to 10 mu m and the surface portion 120 having an average thickness of 10 nm to 1 mu m can be produced through the production method of the cathode active material precursor The microcore-shell type microcrystalline cellulose microspheres of the present invention can be manufactured in a controlled manner.

In the cathode active material precursor, the average thickness of the surface portion 120 is 10 nm to 1 占 퐉, specifically, the specific metal is leached by the leaching solution within an average thickness of 10 nm to 1 占 퐉 of the surface portion 120 , And a region having a concentration gradient structure in a direction in which the specific metal decreases.

Also, the cathode active material precursor 100 having the double-layered structure defined by the surface portion 120 and the center portion 110 is manufactured through the above-described manufacturing process, and the cathode active material precursor 100, Since the core 120 and the central portion 110 have a layered structure, the charge and discharge reactivity is high and the high-rate characteristics of the battery can be improved.

The method of preparing the cathode active material precursor 100 is performed at a temperature of 10 to 100 ° C. The reason for increasing the temperature of the entire process of the cathode active material precursor is that the produced cathode active material precursor precipitates in a complex form at a low temperature, It is difficult to obtain a cathode active material precursor. Therefore, when the cathode active material is manufactured in a temperature range outside the above range, the density of the cathode active material precursor may be lowered.

The precursor of the cathode active material 100 is prepared by leaching a specific metal with a coprecipitation compound having a layered structure prepared by a coprecipitation method as a leaching solution. The precursor of the cathode active material thus prepared has a layered structure on both the surface and the center.

This is because the positive electrode active material composed of the center portion of the layered structure and the surface portion having another crystal structure excellent in structural stability has a problem of lowering the high capacity characteristics in order to reinforce the low structural stability of the layered structure and protect the reactivity of nickel However, a material having another crystal structure (for example, a spinel structure) having excellent structural stability is formed on the surface portion.

The cathode active material composed of the center portion and the surface portion having different crystal structures may have reinforced the structural stability but can not maintain excellent high capacity characteristics of the layered structure.

However, when the cathode active material precursor 100 is manufactured through the above-described manufacturing method proposed in the present invention, although the surface portion and the center portion have a layered structure, only the nickel or nickel and cobalt existing on the surface portion Through the simple process of leaching, the structural stability can be improved while maintaining the layered structure, and thus excellent high-capacity characteristics can be maintained.

In addition, when the oxidation number of Mn is +4 in the above formula (1), the structure transition (the Jahn-Teller effect) generated by the oxidation / reduction reaction of Mn when the positive electrode active material precursor of the layered structure is produced It is possible to improve the life characteristic by stabilizing the structure during charge and discharge. That is, in the present invention, it is preferable that the oxidation number of Ni is +2, the oxidation number of Mn is +4, and the oxidation number of Co is +3.

According to another aspect of the present invention, And a surface portion formed to surround the center portion. The structure of the cathode precursor is specifically shown in FIG. 1A.

1A, the cathode active material precursor is a spherical particle composed of a center portion 110 and a surface portion 120 formed to surround the center portion 110. The center portion 110 of the cathode active material precursor is represented by the following formula 1a, and the surface portion 120 of the cathode active material precursor may be represented by the following Chemical Formula 2.

[Formula 1a]

Ni _x1 Co _y1 Mn _{(1-x1- y1 )} (OH) ₂

In the above formulas,

0.5? X1? 0.75, and 0.1? Y1? 0.24.

(2)

_{Ni x2 Co y2 Mn 1 -x2- y2} (OH) 2

In the above formulas,

0.0? X2? X1, and 0.0? Y2? Y1.

The concentration of the nickel or (ii) the concentration of the nickel and the cobalt in the cathode active material precursor is lowered from the central portion 110 toward the surface portion 120, A density gradient structure is formed in the surface portion 120 of the surface portion 120 from the inner side 120a of the central portion 110 side of the surface portion 120 to the outer side 120b of the surface portion 120, The concentration of nickel or (ii) the concentration of nickel and cobalt is gradually lowered.

(I) the concentration of nickel or (ii) the concentration of nickel and cobalt is close to zero so that (i) the nickel or (ii) the nickel Nickel and the cobalt are exposed, the problem that the stability of the cathode active material precursor is lowered can be solved.

That is, the cathode active material precursor according to the present invention has a structure in which the surface portion 120 is formed with a layer made of a material having a crystal structure excellent in stability for improving structural stability, or is excellent in structural stability, When the cathode active material is manufactured using the same, the prepared cathode active material has excellent thermal stability, which can be confirmed by the following experimental example.

Whether the specific metal having a concentration gradient structure in the surface portion 120 is (i) the nickel or (ii) the nickel and cobalt can be appropriately selected according to the leaching solution used in the production of the cathode active material .

The average diameter D1 of the center portion 110 of the cathode active material precursor may be 1 to 10 占 퐉 and the average thickness D2 of the surface portion 120 of the cathode active material precursor may be 10 nm to 1 占 퐉, If the average diameter D1 of the center portion 110 of the cathode active material precursor is less than 1 占 퐉 or more than 10 占 퐉, the density of the electrode plate may be lowered or the specific surface area may be decreased.

Also, when the average thickness D2 of the surface portion 120 of the cathode active material precursor is less than 10 nm, the section having the concentration gradient structure becomes small, and the nickel present in the center portion 110 is exposed, And the lifetime characteristics are also deteriorated. When the average thickness (D2) exceeds 1 탆, there arises a problem that the electrochemical characteristics at a high capacity and a high rate are lowered.

It is preferable that the tap density of the cathode active material precursor is 2.4 to 3 g / cm 3. If the tap density is improved, the energy density of the battery is improved.

At this time, the tap density of the cathode active material precursor is the density of the entire active material precursor, including both the center portion 110 and the surface portion 120.

The tap density represents the density of the entire volume of the cathode active material precursor and can be measured by the following method. A mass (A) of a 100 cm &lt; 3 &gt; cell is measured, and a sample containing the porous material is naturally dropped into the cell using a mesh. Thereafter, the tap density can be obtained by measuring the mass (B) and the filling volume (D) after 200 times of tapping using a device equipped with a spacer and calculating the tap density by the following equation (1).

[Equation 1]

Tap density (g / cm3) = (B-A) / D

The surface of the surface portion 120 of the cathode active material precursor may have an uneven surface, which can exhibit high-capacity and high-rate electrochemical characteristics and maximize structural stability, thereby improving cycle characteristics and lifetime characteristics , And leaching solution from the surface portion (120) of the cathode active material precursor to leach and remove specific metals of nickel and / or cobalt.

The uneven surface of the surface portion 120 of the cathode active material 200 may be represented by a porous structure.

The cathode active material precursor is also in the form of a microcore-shell of a surface portion 120 having a center portion 110 having an average diameter of 1 to 10 mu m and an average thickness of 10 nm to 1 mu m which is superior to a conventional cathode active material precursor By controlling the particles having a remarkably fine size in the form of a core-shell, it has an excellent structural and thermal stability while having a specific porous surface structure due to leaching which can not be achieved in the conventional cathode active material precursor.

Another aspect of the present invention relates to a method for producing a cathode active material for a lithium secondary battery, comprising the steps of:

(I) preparing a coprecipitated compound represented by the following formula (I) by coprecipitation with a metal salt aqueous solution containing a nickel salt, a manganese salt and a cobalt salt, a chelating agent and a basic aqueous solution in a reactor;

II) adding a leaching solution to the coprecipitation compound to leach only a specific metal present on the surface of the coprecipitation compound; And

III) mixing the lithium salt with the cathode active material precursor, followed by firing.

[Chemical Formula 1]

Ni _x Co _y Mn _(1-xy) (OH) ₂

In the above formulas,

0.5? X? 0.75, and 0.1? Y? 0.24.

First, (I) a metal salt aqueous solution containing a nickel salt, a manganese salt and a cobalt salt, a chelating agent, and a basic aqueous solution are mixed in a reactor and coprecipitated to prepare a coprecipitated compound represented by the following formula (1).

The metal salts such as the nickel salts, manganese salts and cobalt salts are not particularly limited as long as they can be dissolved in water. Sulfates, nitrates, nitrates, halides, hydroxides and the like may be preferably used.

The molar ratio of the nickel salt, the cobalt salt and the manganese salt may be 0.5 to 0.85: 0.05 to 0.3: 0 to 0.45, preferably 0.5 to 0.75: 0.1 to 0.24 : 0.01 to 0.4 is preferable in view of the capacity of the cathode active material.

The chelating agent is an aqueous ammonia solution (NH ₄ OH), ammonium sulfate _{((NH 4) 2 SO 4} ), ammonium nitrate (NH ₄ NO _3), first ammonium phosphate _{((NH 4) 2 HPO 4} ) , and mixtures thereof &Lt; / RTI &gt;

The molar ratio of the chelating agent to the metal salt aqueous solution is preferably 0.2-0.5: 1. When the molar ratio of the chelating agent exceeds 0.5, the chelating agent reacts with the metal aqueous solution at a ratio of 1: 1, The chelating agent can be in a supersaturated state. If the chelating agent is less than 0.2, the crystallinity is lowered, and the degree of stabilization may be significantly lowered.

In addition, the basic solution is used to maintain the pH at 10.5 to 12, and NaOH, KOH, and a mixture thereof can be used.

The density of the coprecipitation compound can be controlled by adjusting the time of residence in the coprecipitation reactor in the above step, preferably 1 to 5 hours, and the tap density of the prepared cathode active material precursor is then 2.4 to 3 g / cm 3 It is most preferable to keep it for 2 to 4 hours.

At this time, the tap density of the cathode active material precursor 100 is the density of the entire active material precursor, including both the center portion 110 and the surface portion 120.

The tap density represents the density of the entire volume of the cathode active material precursor and can be measured by the following method. A mass (A) of a 100 cm &lt; 3 &gt; cell is measured, and a sample containing the porous material is naturally dropped into the cell using a mesh. Thereafter, the tap density can be obtained by measuring the mass (B) and the filling volume (D) after 200 times of tapping using a device equipped with a spacer and calculating the tap density by the following equation (1).

[Equation 1]

Tap density (g / cm3) = (B-A) / D

Thereafter, (II) the leaching solution is added to the coprecipitation compound to leach only the specific metal present on the surface of the coprecipitation compound. Through this process, the prepared cathode active material precursor particles have a concentration gradient structure in which the concentration of a specific metal decreases from the inside of the surface portion to the outside of the surface portion.

The leaching solution may be any one selected from the group consisting of an alkali leaching solution, an acid leaching solution, a polymer leaching solution, and an organic solvent leaching solution.

The specific metal is (i) nickel or (ii) nickel and cobalt. This can be appropriately selected depending on the leaching solution. Especially preferably, when the sulfuric acid solution is used as the leaching solution, nickel and cobalt can be leached out with a specific metal.

The alkali leaching solution may be sodium hydroxide.

The step (II) may be carried out under perfect mixing of the solution.

The positive electrode active material precursor has a center portion 110 and a surface portion 120 formed to surround the center portion 110, ).

The average thickness of the surface portion 120 is 10 nm to 1 占 퐉. Specifically, the specific metal is leached out by the leaching solution within an average thickness of 10 nm to 1 占 퐉 of the surface portion 120, It is also a region having a concentration gradient structure in the direction in which the metal decreases. By performing the leaching process in this manner, the surface portion 120 has the advantage of forming a specific porous structure and improving the structural and thermal stability characteristics.

Also, the cathode active material precursor 100 having the double-layered structure defined by the surface portion 120 and the center portion 110 is manufactured through the above-described manufacturing process, and the cathode active material precursor 100, Since the core 120 and the central portion 110 have a layered structure, the charge and discharge reactivity is high and the high-rate characteristics of the battery can be improved.

The method of preparing the cathode active material precursor 100 is performed at a temperature of 10 to 100 ° C. The reason for increasing the temperature of the entire process of the cathode active material precursor is that the produced cathode active material precursor 100 precipitates in a complex form at a low temperature , It is difficult to obtain the high-density cathode active material precursor 100. Therefore, when the cathode active material precursor 100 is manufactured in a temperature range outside the above range, the density of the cathode active material precursor 100 may be lowered.

Since the cathode active material precursor 100 is prepared by leaching a specific metal with a coprecipitation compound having a layered structure prepared by a coprecipitation method as a leaching solution, Structure.

The positive electrode active material, which has been prepared using the conventional positive electrode active material precursor and has a central portion of the layered structure and a surface portion having a different crystal structure with excellent structural stability, has a high capacity to reinforce the low structural stability of the layered structure, A material having another crystal structure (for example, a spinel structure) having excellent structural stability is formed on the surface portion in spite of the problem that the characteristics are deteriorated.

The cathode active material composed of the center portion and the surface portion having different crystal structures may have reinforced the structural stability but can not maintain excellent high capacity characteristics of the layered structure.

However, if the cathode active material precursor is prepared through the above-described manufacturing method proposed in the present invention and the cathode active material is obtained by using the same, both the surface portion 220 and the center portion 210 have a layered structure as shown in FIG. The structural stability can be improved while keeping the layered structure, so that the excellent high-capacity characteristics can be maintained.

In addition, when the oxidation number of Mn is +4 in the above formula (1), the structure transition (the Jahn-Teller effect) generated by the oxidation / reduction reaction of Mn when the positive electrode active material precursor of the layered structure is produced It is possible to improve the life characteristic by stabilizing the structure during charge and discharge. That is, in the present invention, it is preferable that the oxidation number of Ni is +2, the oxidation number of Mn is +4, and the oxidation number of Co is +3.

Finally, III) a lithium salt is mixed with the cathode active material precursor, followed by firing.

The lithium salt is not particularly limited as long as it is commonly used in the art, but it may preferably be LiOH.

In the step (III), the heat treatment may be performed at 400 to 900 ° C.

Due to the porous surface, the cathode active material precursor 100, which is fabricated to have a core-shell structure of layered structure and controlled to have a fine porous structure through simple, simple, and fast manufacturing processes described above, Even if the cathode active material 200 is manufactured by the above-described method, the core and shell portions including the core-shell structure have a layered structure, and the diffusion of lithium ions is maintained while maintaining the microstructure of the cathode active material precursor 100 It has excellent structural and thermal stability as well as excellent rate characteristics.

Yet another aspect of the present invention is directed to a lithographic apparatus comprising a central portion 210; And a surface portion 220 formed to surround the center portion 210. The center portion 210 of the cathode active material 200 is represented by the following Formula 3 and the cathode active material 200 ) Of the positive electrode active material for a lithium secondary battery is represented by the following formula (4).

(3)

Li [Ni _{x 3} Co _{y 3} Mn _{(1-x 3-y 3 )} ] O ₂

In the above formulas,

0.5? X3? 0.75, and 0.1? Y3? 0.24.

[Chemical Formula 4]

Li [Ni _{x 4} Co _{y 4} Mn _{1 -x 4-y 4} ] O ₂

In the above formulas,

0.0? X4? X3, and 0.0? Y4? Y3.

Since the cathode active material 200 is prepared by mixing the cathode active material precursor 100 with a lithium salt and sintering the same, the structure of the cathode active material precursor 100 is maintained as it is, 1b. &Lt; / RTI &gt;

That is, the cathode active material 200 has a central portion 210 as shown in FIG. 1B; And a surface portion 220 formed to surround the center portion 210. The center portion 210 of the positive electrode active material is represented by Formula 3 and the surface portion 220 of the positive electrode active material 220 ) Can be represented by the above formula (4).

In order to improve the high-capacity characteristics while maintaining the layered structure having the disadvantage that the structural stability is low, the positive electrode active material preferably has (i) the nickel Or (ii) the concentration of the nickel and the cobalt is made close to zero.

(I) the concentration of nickel or (ii) the concentration of nickel and cobalt in the cathode active material decreases from the central portion 210 toward the surface portion 220, A density gradient structure is formed in the surface portion 220 of the surface portion 220 from the inner side 220a of the central portion 210 of the surface portion 220 to the outer side 220b of the surface portion 220, Nickel or (ii) the concentration of nickel and cobalt is gradually lowered.

(I) the concentration of nickel or (ii) the concentration of nickel and cobalt is close to zero at a region near the outer side 220b of the surface portion 220, (i) the nickel or (ii) Nickel and the cobalt are exposed, the problem that the stability of the cathode active material precursor is lowered can be solved.

Whether the specific metal having the concentration gradient structure in the surface portion 220 is (i) the nickel or (ii) the nickel and the cobalt can be appropriately selected according to the leaching solution used in the production of the cathode active material .

The average diameter D1 of the center portion 210 of the cathode active material 200 may be 1 to 10 mu m and the average thickness D2 of the surface portion 220 of the cathode active material may be 10 nm to 1 mu m If the average diameter D1 of the center portion 210 of the cathode active material is less than 1 占 퐉 or more than 10 占 퐉, the density of the electrode plate may decrease or the specific surface area may decrease.

Also, when the average thickness D2 of the surface portion 220 of the cathode active material is less than 10 nm, the interval having the concentration gradient structure becomes small, and the nickel present in the center portion 210 is exposed, Life characteristics are deteriorated. When the average thickness (D2) exceeds 1 占 퐉, there arises a problem that the electrochemical characteristics at a high capacity and a high rate are lowered.

It is preferable that the tap density of the cathode active material 200 is 2.4 to 3 g / cm 3. If the tap density is improved, the energy density of the battery is improved.

The tap density represents the density of the total volume of the cathode active material and can be measured by the following method. A mass (A) of a 100 cm &lt; 3 &gt; cell is measured, and a sample containing the porous material is naturally dropped into the cell using a mesh. Thereafter, the tap density can be obtained by measuring the mass (B) and the filling volume (D) after 200 times of tapping using a device equipped with a spacer and calculating the tap density by the following equation (1).

[Equation 1]

Tap density (g / cm3) = (B-A) / D

However, the surface of the surface portion 220 of the cathode active material 200 has a relatively even surface compared to the surface of the surface portion 120 of the cathode active material precursor. However, the conventional cathode active material precursor The surface of the surface portion 220 has an uneven porous surface.

Due to such a structure, the cathode active material according to the present invention has an advantage of exhibiting a high capacity and a high electrochemical characteristic and at the same time maximizing the structural stability, thereby having improved cycle characteristics and life characteristics.

The maximum exothermic peak temperature of the cathode active material measured according to the thermal stability evaluation method using a differential scanning calorimeter may be 265 ° C to 275 ° C which is higher than that of the cathode active material of Comparative Example 2, And shows excellent thermal stability.

Also, in the case of the cathode active material of the conventional core-shell structure (Patent Document 1), the cathode active material of the present invention has an excellent thermal stability compared to the conventional cathode active material because it does not resist 251 캜 (10 캜 lower than the present invention) .

The calorific value of the cathode active material measured according to the thermal stability evaluation method using a differential scanning calorimeter may be 350 to 385 W / g, which is also an improved structure so that the cathode active material of the present invention has a remarkably excellent effect as compared with the conventional cathode active material Respectively.

Another aspect of the present invention relates to a lithium secondary battery comprising the cathode active material. For example, the lithium secondary battery may be a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery. The lithium secondary battery can be manufactured in various forms, such as a jelly-roll type, a stack type, a stack / folding type, and the like.

The lithium secondary battery comprises a cathode, a separator, and a cathode manufactured through the cathode active material, and the cathode may be manufactured by a conventional method known in the art.

The positive electrode may also be produced using the positive electrode active material of the present invention by a conventional method known in the art.

The lithium secondary battery according to the present invention provides a battery module including a unit cell, which can be used as a power source for a small-sized device, and is a middle- or large-sized battery module including a plurality of battery modules. Lt; / RTI &gt;

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape using a can, a rectangular pouch shape, a coin shape, or the like.

When the lithium secondary battery is stored in a fully charged state at 60 to 90 ° C for 5 to 10 days and then charged and discharged in a voltage range of 2.5 to 4.3 V and at a room temperature for 10 to 100 cycles, retention is 99.9% to 90%. The improvement of the cathode active material according to the present invention is remarkably superior in the lifetime characteristics and the high capacity characteristics.

That is, the lithium secondary battery according to the present invention can be used as a battery module by being included as a unit cell, and can also provide a device using the electric module as a power source.

Specific examples of the device include a power tool, a plug-in electric vehicle (PHEV), a hybrid electric vehicle (HEV), etc., which are powered by an electric motor Electric cars; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; And a power storage system.

Hereinafter, the present invention will be described in more detail with reference to Examples and the like, but the scope and content of the present invention can not be construed to be limited or limited by the following Examples. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the present invention as set forth in the following claims. It is natural that it belongs to the claims.

In addition, the experimental results presented below only show representative experimental results of the embodiments and the comparative examples, and the respective effects of various embodiments of the present invention which are not explicitly described below will be specifically described in the corresponding part.

Example  One.

_{Ni 0 .6 Co 0 .2 Mn 0} .2 (OH) to prepare a metallic aqueous solution for the production of _2, and supplies it to the co-precipitation reactor (volume: 4 L, 80 W output of the rotary motor).

In the coprecipitation reactor, distilled water was added to the coprecipitation reactor to feed nitrogen gas into the reactor at a rate of 0.5 liter / min to remove dissolved oxygen, the reactor was heated to 80 ° C, and then stirred at 1000 rpm .

Thereafter, the metal aqueous solution was administered to the coprecipitation reactor at a rate of 0.3 liter / hour, and the ammonia solution was continuously administered at 0.03 liter / hour.

To adjust the pH, a pH of 4.8 M in NaOH was fed to maintain the pH in the reactor at a constant value of 11, and a co-precipitation reaction was performed at an impeller speed of 1000 rpm in the coprecipitation reactor to obtain a precipitate.

The density of the coprecipitation compound can be controlled by controlling the residence time in the coprecipitation reactor, preferably about 1 to 5 hours. In this embodiment, the retention time of 3 hours The flow rate was adjusted to have

Filtering the co-precipitated compound obtained in the precipitate, and the thus obtained coprecipitated compound _{(Ni 0 .6 Co 0 .2 Mn} 0 .2 (OH) 2). A mixture of 4 L of water, the temperature rising rate of 5 ℃ / min (0.05M-2M), diluted amount), and then stirring the resultant solution. The nickel present on the surface of the coprecipitation compound was subjected to wet leaching perform the final lithium secondary battery precursor of the positive electrode active material by _{(Ni 0 .6 Co 0 .2 Mn} 0 .2 (OH) 2) to obtain a.

By the leaching process described above wherein the cathode active material for a lithium secondary battery, to the center _{(Ni 0 .6 Co 0 .2 Mn} 0 .2 (OH) 2) from the outer side surface of the _{(Ni 0.0 Co 0.0 Mn 0.2 (} OH) 2) It is a spherical particle with an inclined structure in which the nickel content gradually decreases. Specifically, it has a gradient structure in which the content of nickel gradually decreases from the inner surface of the surface portion (Ni _0.6 Co _0.2 Mn _0.2 (OH) ₂ ) to the outer surface of the surface portion (Ni _0.0 Co _0.0 Mn _0.2 (OH) ₂ ).

Example  2.

LiOH 占₂ 2O was mixed as a lithium salt in the precursor of the cathode active material for lithium secondary battery prepared in Example 1, and then heated at a rate of 2 占 폚 / min, maintained at 450 占 폚 for 5 hours, followed by 820 占 폚 For 10 hours to obtain a final cathode active material.

Comparative Example  One.

_{Ni 0 .6 Co 0 .2 Mn 0} .2 (OH) to prepare a metallic aqueous solution for the production of _2, and supplies the co-precipitation reactor (volume: 4 L, 80 W output of the motor rotation speed), this as a percentage.

In the coprecipitation reactor, distilled water was added to the coprecipitation reactor to feed the nitrogen gas to the reactor at a rate of 0.5 liter / min to remove dissolved oxygen, the reactor was heated to 80 ° C, and then stirred at 1000 rpm .

Thereafter, the metal aqueous solution was administered to the coprecipitation reactor at a rate of 0.3 liter / hour, and the ammonia solution was continuously administered at 0.03 liter / hour.

To adjust the pH, a pH of 4.8 M in NaOH was fed to maintain the pH in the reactor at a constant value of 11, and a co-precipitation reaction was performed at an impeller speed of 1000 rpm in the coprecipitation reactor to obtain a precipitate.

The density of the coprecipitation compound can be controlled by controlling the residence time in the coprecipitation reactor, preferably about 1 to 5 hours. In this embodiment, the retention time of 3 hours branches to control the flow rate of the precursor to obtain the _{(Ni 0 .6 Co 0 .2 Mn} 0 .2 (OH) 2) of the anode without the nickel and cobalt contents in between the center and the surface of the active material portion.

Comparative Example  2.

LiOH.H ₂ O as a lithium salt was mixed with the precursor of the cathode active material for lithium secondary battery prepared in Comparative Example 1, and then heated at a rate of 2 ° C / min, maintained at 450 ° C for 5 hours, then at 820 ° C For 10 hours to obtain a final cathode active material.

FIG. 2 is a photograph of the cathode active material precursor (a) prepared in Comparative Example 1 and the cathode active material precursor (b) prepared in Example 1 by a scanning electron microscope. Referring to FIG. 2, While the surface of the precursor was flat, the cathode active material precursor prepared in Example 1 had an average diameter of 1 to 10 mu m and had a spherical shape without surface smoothness.

Since nickel or cobalt or nickel and cobalt were simultaneously eluted by sulfuric acid, the surface of the positive electrode active material precursor of Example 1 has an uneven rough structure.

However, the cathode active material precursors of Example 1 and Comparative Example 1 have similar sizes.

FIG. 3 is a photograph (a) of the cathode active material precursor prepared in Example 1 by an electron scanning microscope and FIG. 3 (b) is a graph showing the analysis of the metal composition according to the thickness through an electron probe microanalysis technique.

The cathode active material precursor prepared in Example 1 was polished and photographed by a scanning electron microscope. As shown in FIG. 3, it can be confirmed that the cathode active material precursor is composed of a very dense core portion and a non-dense surface portion (shell) .

In addition, it can be confirmed that the average diameter of the center portion is 4.8 mu m, which indicates that the average diameter of the center portion of the cathode active material precursor according to the present invention is 1 to 10 mu m. Also, it was confirmed that the surface portion was 0.6 mu m, and the average thickness of the surface portion of the cathode active material precursor according to the present invention was found to be 10 nm to 1 mu m.

Referring to FIG. 3B, it can be seen that the concentration of nickel and cobalt is maintained up to 2.4 μm from the center of the core, and then a concentration gradient structure in which the composition of nickel and cobalt decreases at the surface portion is formed.

4 is a graph showing the high temperature storage cycle characteristics of the cathode active material (red) prepared in Example 2 and the cathode active material (black) prepared in Comparative Example 2. FIG.

To measure this, each of the electrodes prepared through the cathode active material prepared in Example 2 and Comparative Example 2 was used as a working electrode of a half-cell, and as a reference electrode or counter electrode, Lithium metal was used, and poly-propylene electrolyte was wetted as a separator.

The electrolyte solution used was a mixture of ethylene carbonate (EC) and ethyl-methyl carbonate (EMC) 3: 7 in which 1 M LiPF ₆ salt was dissolved.

The fabricated half cell was fabricated with Coin 2032 type. All processes in the cell assembly proceeded in a dry room where the relative humidity was always kept below 3%.

As shown in FIG. 4, the thus fabricated half-cell was charged / discharged for 3 cycles at a 0.5 C-rate and a 3.0 to 4.3 V cut-off voltage at room temperature, fully charged to 4.3 V, After storing the cell at 60 ° C, charge / discharge characteristics were measured again at 1C-rate for 50 cycles at room temperature.

The discharge capacity retention of the electrode using the cathode active material prepared in Example 2 was about 99.2%, whereas the discharge capacity retention capacity of the electrode using the cathode active material prepared from Comparative Example 2 was 74.2% It was confirmed that the cathode active material had a cycle characteristic that was 25% more stable than that of the conventional cathode active material.

5 shows the result of evaluating the thermal stability of the positive electrode active material (red) prepared in Example 2 and the positive electrode active material (black) prepared in Comparative Example 2 up to 4.3 V, followed by differential scanning calorimetry (DSC) Fig.

In Example 2 and Comparative Example 2, the cathode active material electrode charged up to 4.3 V was recovered, and the remaining LiPF6 salt remained on the electrode was washed with DMC and removed. The washed electrodes were vacuum-dried, and then the oxide on the electrode was scraped off and put into a stainless steel high-pressure capsule (3 g) filled with 3 mg of the active material and 3 ㎕ electrolyte to prevent the evaporation of the solvent The capsule was sealed.

All work was done in a glove box with oxygen and water vapor less than 0.1 ppm.

The cathode active material electrode of Example 2 was 268.8 占 폚 higher than the maximum exothermic peak temperature of the cathode active material electrode of Comparative Example 2, which was 260.1 占 폚.

In addition, the cathode active material electrode of Example 2 was 382.3 W / g, which is less than the heat generation amount of the cathode active material electrode of Comparative Example 2, which is 981.8 W / g.

Claims (24)

(I) preparing a coprecipitated compound represented by the following formula (I) by coprecipitation with a metal salt aqueous solution containing a nickel salt, a manganese salt and a cobalt salt, a chelating agent and a basic aqueous solution in a reactor; And
(II) adding a leaching solution to the coprecipitation compound to leach only (i) nickel or (ii) nickel and cobalt present on the surface of the coprecipitation compound to prepare a precursor of a cathode active material for a lithium secondary battery,
The positive electrode active material precursor for a lithium secondary battery includes: a center portion; And a surface portion formed to surround the center portion, wherein both the center portion and the surface portion are spherical particles having a layered structure,
Wherein the center of the cathode active material precursor is represented by the following Formula 1a, and the surface portion of the cathode active material precursor is represented by the following Formula 2,
(I) the concentration of nickel present in the surface portion of the positive electrode active material precursor or (ii) the concentration of nickel and cobalt in the surface portion of the positive electrode active material precursor has a concentration gradient structure that decreases from the inside of the surface portion toward the outside of the surface portion, Having a surface structure,
Wherein the leaching solution is any one selected from the group consisting of an alkali leaching solution, an acid leaching solution, a polymer leaching solution, an organic solvent leaching solution, and a mixture of two or more thereof.
[Chemical Formula 1]
Ni _x CoyMn _(1-xy) (OH) ₂
In the above formulas,
0.5? X? 0.75, and 0.1? Y? 0.24.
[Formula 1a]
Nix1Coy1Mn (1-x1-y1) (OH) 2
In the above formulas,
0.5? X1? 0.75, and 0.05? Y1? 0.24.
(2)
Nix2Coy2Mn1-x2-y2 (OH) 2
In the above formulas,
0.0? X2? X1, and 0.0? Y2? Y1. The method according to claim 1,
The chelating agents are aqueous ammonia (NH ₄ OH), ammonium sulfate _{((NH 4) 2 SO 4} ), ammonium nitrate (NH ₄ NO _3), first ammonium phosphate _{((NH 4) 2 HPO 4} ) and their Wherein the cathode active material precursor is one selected from the group consisting of a lithium salt, a lithium salt, and a mixture. The method according to claim 1,
Wherein the molar ratio of the nickel salt, cobalt and manganese salt is 0.5 to 0.85: 0.05 to 0.3: 0 to 0.45. delete delete The method according to claim 1,
Wherein the acid leaching solution is a sulfuric acid solution. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; The method according to claim 1,
Wherein the step (I) and the step (II) are all carried out at 10 to 100 ° C. center; And a surface portion formed to surround the center portion, wherein the cathode active material precursor is a spherical cathode active material precursor,
A center portion of the cathode active material precursor is represented by the following Formula 1a,
The surface portion of the cathode active material precursor is represented by the following Chemical Formula 2,
Wherein both the central portion and the surface portion have a layered structure,
(I) the concentration of nickel present in the surface portion of the positive electrode active material precursor or (ii) the concentration of nickel and cobalt in the surface portion of the positive electrode active material precursor has a concentration gradient structure that decreases from the inside of the surface portion toward the outside of the surface portion, Wherein the precursor of the positive electrode active material for lithium secondary batteries has a surface structure.
[Formula 1a]
Ni _x1 Co _y1 Mn _(1-x1-y1) (OH) ₂
In the above formulas,
0.5? X1? 0.75, and 0.05? Y1? 0.24.
(2)
Ni _x2 Co _y2 Mn _1-x2-y2 (OH) ₂
In the above formulas,
0.0? X2? X1, and 0.0? Y2? Y1. delete 9. The method of claim 8,
The average diameter of the center portion of the cathode active material precursor is 1 to 10 탆,
Wherein the cathode active material precursor has an average thickness of 10 nm to 1 占 퐉 on the surface portion of the cathode active material precursor. delete 9. The method of claim 8,
Wherein the tap density of the cathode active material precursor is 2.4 to 3 g / cm &lt; 3 &gt;. delete (I) preparing a coprecipitated compound represented by the following formula (I) by coprecipitation with a metal salt aqueous solution containing a nickel salt, a manganese salt and a cobalt salt, a chelating agent and a basic aqueous solution in a reactor;
(II) adding a leaching solution to the coprecipitation compound to produce (i) nickel or (ii) leaching only nickel and cobalt present on the surface of the coprecipitation compound to produce a cathode active material precursor; And
III) mixing the lithium salt with the cathode active material precursor, followed by calcination to produce a cathode active material for a lithium secondary battery,
The cathode active material for a lithium secondary battery includes a center portion; And a surface portion formed to surround the center portion, wherein both the center portion and the surface portion are spherical particles having a layered structure,
Wherein the center portion of the cathode active material is represented by the following Formula 3, the surface portion of the cathode active material is represented by the following Formula 4,
(I) the concentration of nickel present on the surface portion of the positive electrode active material, or (ii) the concentration of nickel and cobalt have a concentration gradient structure that decreases from the inside of the surface portion toward the outside of the surface portion, Structure,
Wherein the leaching solution is any one selected from the group consisting of an alkali leaching solution, an acid leaching solution, a polymer leaching solution, an organic solvent leaching solution, and a mixture of two or more of them.
[Chemical Formula 1]
Ni _x Co _y Mn _(1-xy) (OH) ₂
In the above formulas,
0.5? X? 0.75, and 0.1? Y? 0.24.
(3)
Li [Ni _{x 3} Co _{y 3} Mn _{(1-x 3-y 3)} ] O ₂
In the above formulas,
0.5? X3? 0.75, and 0.1? Y3? 0.24.
[Chemical Formula 4]
Li [Ni _{x 4} Co _{y 4} Mn _{1-x 4-y 4} ] O ₂
In the above formulas,
0.0? X4? X3, and 0.0? Y4? Y3. delete 15. The method of claim 14,
Wherein the heat treatment in step (III) is performed at 400 to 900 ° C. center; And a surface portion formed so as to surround the center portion, the spherical cathode active material according to Claim 14,
The center portion of the positive electrode active material is represented by the following Formula 3,
The surface portion of the positive electrode active material is represented by the following Formula 4,
Wherein both the central portion and the surface portion have a layered structure,
(I) the concentration of nickel present on the surface portion of the positive electrode active material, or (ii) the concentration of nickel and cobalt have a concentration gradient structure that decreases from the inside of the surface portion toward the outside of the surface portion, A positive electrode active material for a lithium secondary battery.
(3)
Li [Ni _{x 3} Co _{y 3} Mn _{(1-x 3-y 3)} ] O ₂
In the above formulas,
0.5? X3? 0.75, and 0.1? Y3? 0.24.
[Chemical Formula 4]
Li [Ni _{x 4} Co _{y 4} Mn _{1-x 4-y 4} ] O ₂
In the above formulas,
0.0? X4? X3, and 0.0? Y4? Y3. 18. The method of claim 17,
Wherein the maximum exothermic peak temperature of the cathode active material measured according to the thermal stability evaluation method using a differential scanning calorimeter is 265 ° C to 275 ° C. 18. The method of claim 17,
Wherein a calorific value of the positive electrode active material measured by a thermal stability evaluation method using a differential scanning calorimeter is 350 to 385 W / g. A lithium secondary battery comprising the cathode active material according to claim 17. 21. The method of claim 20,
When the lithium secondary battery is stored in a fully charged state at 60 to 90 ° C for 5 to 10 days and then charged and discharged in a voltage range of 2.5 to 4.3 V and at a room temperature for 10 to 100 cycles, retention is 99.9 to 90%. 20. A battery module comprising a secondary battery according to claim 20 as a unit cell. A device using the battery module according to claim 22 as a power source. 24. The method of claim 23,
Wherein the device is any one selected from an electric vehicle or a hybrid electric vehicle or a power storage device.

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