KR102117621B1 - Positive electrode active material for lithium secondary battery, method for preparing the same, and lithium secondary battery including the same - Google Patents

Abstract

The present invention is a positive electrode active material present in a concentration gradient in which nickel and manganese gradually change from the center of the particle to the surface, wherein the positive electrode active material has a central portion including a first lithium composite metal oxide having an average composition represented by Formula 1 below; And a surface portion including a second lithium composite metal oxide having an average composition represented by the following Chemical Formula 2, wherein the positive electrode active material has a positive peak at 235° C. or higher when the heat flow rate is measured by differential scanning calorimetry. An active material, a method for manufacturing the positive electrode active material, and a lithium secondary battery comprising the positive electrode active material are provided:
[Formula 1]
Li _1+x1 (Ni _a1 Mn _b1 Co _1-a1-b1-c1 Me _c1 )O _2-y1 A _y1
[Formula 2]
Li _1+x2 (Ni _a2 Mn _b2 Co _1-a2-b2-c2 Me _c2 )O _2-y2 A _y2
In Chemical Formulas 1 and 2, Me is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb , and at least one doping element selected from the group consisting of Mg, B and Mo, a is PO ₄ ^3-, NO ₄ ^- to ^{_{-, CO 3 2-, BO 3}} -, Cl -, Br -, I - and F At least one anion selected from the group consisting of, 0.8≤a1<1, 0<b1<0.2, 0<c1≤0.1, 0.8<a1+b1+c1<1, 0≤x1≤0.1, 0.0001<y1≤0.1 , 0.1≤a2<0.8, 0.1<b2<0.9, 0<c2≤0.1, and 0.2<a2+b2+c2<1, 0≤x2≤0.1, 0.0001<y2≤0.1.

Description

A cathode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery comprising the same {POSITIVE ELECTRODE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY, METHOD FOR PREPARING THE SAME, AND LITHIUM SECONDARY BATTERY INCLUDING THE SAME}

The present invention relates to a positive electrode active material for a lithium secondary battery, a method for manufacturing the positive electrode active material, and a lithium secondary battery comprising the positive electrode active material.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self-discharge rate have been commercialized and widely used.

Lithium transition metal composite oxides are used as a positive electrode active material for lithium secondary batteries, and lithium cobalt composite metal oxides such as LiCoO ₂ having high working voltage and excellent capacity characteristics are mainly used. However, LiCoO ₂ has very poor thermal properties due to destabilization of the crystal structure due to lithium. In addition, since LiCoO ₂ is expensive, there is a limit to use it in large quantities as a power source in fields such as electric vehicles.

As a positive electrode active material to replace this, various lithium transition metal oxides such as LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ or LiFePO ₄ , have been developed. Among them, LiNiO ₂ has an advantage of exhibiting high discharge capacity battery characteristics, but it is difficult to synthesize with a simple solid-phase reaction, and has low thermal stability and low cycle characteristics. Lithium manganese oxide such as LiMnO ₂ or LiMn ₂ O ₄ has the advantage of excellent thermal safety and low price, but has a problem of small capacity and low high temperature characteristics. In particular, in the case of LiMn ₂ O ₄ but a part commercialized in low-end products, there is a problem that occurs structure modification (Jahn-Teller distortion) due to the Mn ^{+ 3} during the charge and discharge whereby the life characteristics deteriorate. In addition, LiFePO ₄ is currently being researched for hybrid electric vehicles (HEV) due to its low price and excellent safety, but it is difficult to apply to other fields due to its low conductivity.

Due to such circumstances, the material that has recently been spotlighted as an alternative positive electrode active material for LiCoO ₂ is lithium nickel manganese cobalt oxide, Li(Ni _a Co _b Mn _c )O ₂ (At this time, a, b, and c are atomic fractions of the independent oxide composition elements, respectively, wherein 0<a<1, 0<b<1, 0<c<1, and a+b+c=1). This material is cheaper than LiCoO ₂ and has the advantage that it can be used for high capacity and high voltage, but has the disadvantages of poor rate capability and long life at high temperatures.

The lithium secondary battery using the positive electrode active material, as the charge and discharge are repeated, increases the interface resistance between the electrode and the electrolyte containing the active material, decomposes the electrolyte due to moisture or other effects in the battery, degrades the surface structure of the active material, and There is a problem in that the safety and lifespan characteristics of the battery are rapidly deteriorated due to an exothermic reaction accompanied by a sudden collapse of the structure, and this problem is particularly serious in high temperature and high voltage conditions.

In order to solve these problems, methods have been proposed to improve the structural stability and surface stability of the active material itself by doping or surface-treating the positive electrode active material, and to increase the interfacial stability between the electrolyte and the active material. This is not satisfactory.

Moreover, as the demand for high-capacity batteries has recently increased, the need for the development of a positive electrode active material that can improve the safety and life characteristics of the battery by securing the internal structure and surface stability of the active material particles is increasing.

Japanese Patent Publication No. 2009-140787 (published on June 25, 2009)

In order to solve the above problems, the first technical problem of the present invention is to provide a positive electrode active material for a lithium secondary battery capable of improving output characteristics, life characteristics and thermal stability.

The second technical problem of the present invention is to provide a method for manufacturing the positive electrode active material having improved output characteristics, life characteristics and thermal stability.

In addition, the third technical problem of the present invention is to provide a positive electrode and a lithium secondary battery comprising the positive electrode active material.

In one aspect, the present invention is a positive electrode active material present in a concentration gradient in which nickel and manganese gradually change from the center to the surface of the particle, and the positive electrode active material comprises a first lithium composite metal oxide having an average composition represented by Formula 1 below. Including the central portion; And a surface portion including a second lithium composite metal oxide having an average composition represented by the following Chemical Formula 2, wherein the positive electrode active material has a peak at 235° C. or higher when the heat flow rate is measured by differential scanning calorimetry, Provide a positive electrode active material:

[Formula 1]

Li _1+x1 (Ni _a1 Mn _b1 Co _1-a1-b1-c1 Me _c1 )O _2-y1 A _y1

[Formula 2]

Li _1+x2 (Ni _a2 Mn _b2 Co _1-a2-b2-c2 Me _c2 )O _2-y2 A _y2

In Chemical Formulas 1 and 2, Me is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb , and at least one doping element selected from the group consisting of Mg, B and Mo, a is PO ₄ ^3-, NO ₄ ^- to ^{_{-, CO 3 2-, BO 3}} -, Cl -, Br -, I - and F At least one anion selected from the group consisting of, 0.8≤a1<1, 0<b1<0.2, 0<c1≤0.1, 0.8<a1+b1+c1<1, 0≤x1≤0.1, 0.0001<y1≤ 0.1, 0.1≤a2<0.8, 0.1<b2≤0.9, 0<c2≤0.1, and 0.2<a2+b2+c2<1, 0≤x2≤0.1, 0.0001<y2≤0.1.

In another aspect, the present invention provides nickel, cobalt, manganese and doping elements Me (where Me is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo (including at least one or more selected from the group consisting of) containing a first metal-containing solution, and the first metal-containing solution to a different concentration Preparing a second metal-containing solution comprising nickel, cobalt, manganese and doping element Me; The first metal-containing solution and the second metal-containing solution such that the mixing ratio of the first metal-containing solution and the second metal-containing solution is gradually changed from 100% by volume: 0% by volume to 0% by volume: 100% by volume. Mixing, and adding an ammonium cation complex forming agent and an anion-containing basic compound to prepare a cathode active material precursor in which the nickel and manganese each independently exhibit a concentration gradient gradually changing from the center of the particle to the surface; Mixing and firing the positive electrode active material precursor and the lithium-containing raw material to synthesize a positive electrode active material; And, performing the heat treatment of the positive electrode active material in an oxygen atmosphere at 600 ℃ to 800 ℃; provides a method for producing a positive electrode active material comprising a.

In another aspect, the present invention provides a positive electrode for a lithium secondary battery including the positive electrode active material and a lithium secondary battery comprising the positive electrode.

The positive electrode active material according to the present invention can manufacture a positive electrode active material having increased structural stability and thermal stability by presenting a concentration gradient in which nickel and manganese gradually change from the center of the particle to the surface. In particular, by providing a positive electrode active material including a central portion having a high nickel content and a surface portion having a low nickel content, it is possible to manufacture a secondary battery exhibiting excellent capacity and improved output characteristics when applied to a secondary battery.

In addition, the positive electrode active material of the present invention can further improve the output characteristics of the battery to which it is applied by doping the doping element (Me) at the metal position of the lithium composite metal oxide. In addition, by partially displacing an anion at the oxygen position of the lithium composite metal oxide, it is possible to prevent the desorption of oxygen during charging and discharging of the lithium secondary battery, thereby providing a lithium secondary battery having high capacity and excellent lifespan characteristics.

1 is a graph showing the heat flux according to the temperature of the positive electrode active material prepared in Examples 1 to 2 and Comparative Examples 2 to 3 of the present invention.
2A and 2B are scanning electron microscope (SEM) photographs of the positive electrode active material prepared in Example 2 and Comparative Example 2 of the present invention, respectively.
Figure 3 is a graph showing the life characteristics according to the cycle at 4.25V of the lithium secondary battery prepared in Example 2 and Comparative Example 1 of the present invention.
Figure 4 is a comparative graph showing the life characteristics and resistance increase rate according to the cycle of the lithium secondary battery prepared in Example 1 and Comparative Example 3 of the present invention.
5 is a graph showing resistance characteristics according to a state of charge (SOC) according to Example 2 and Comparative Example 2 of the present invention.
6 is a graph showing the life characteristics of each lithium secondary battery prepared in Example 1 and Comparative Example 2 of the present invention at a cycle of 4.5V.

Hereinafter, the present invention will be described in more detail.

The terms or words used in the specification and claims should not be interpreted as being limited to ordinary or lexical meanings, and the inventor can appropriately define the concept of terms in order to explain his or her invention in the best way. Based on the principle that it should be interpreted as meanings and concepts consistent with the technical spirit of the present invention.

Normally, in the case of a positive electrode active material, cracks and collapses of the active material particles are likely to occur during coating and rolling during battery manufacturing, and cracks of the active material particles occur during battery charging and discharging to deteriorate life characteristics. In addition, in the positive electrode active material having a constant internal/external composition, when the nickel content is increased, positive electrode degeneration occurs on the surface due to side reactions on the surface. On the other hand, in the case of the positive electrode active material having a concentration gradient in which the content of the metal element in the active material particles gradually changes, structurally, the nickel content in the central portion is higher than the surface or the average composition, so that internal cracks have an internal stability when cracks occur in the positive active material particles There is a problem that becomes greatly vulnerable.

In order to solve this problem, in the present invention, in the positive electrode active material of a concentration gradient type having excellent structural stability by gradually changing the content of metal in the positive electrode active material particles, nickel having high capacity characteristics in the center of the positive electrode active material has a high content. Containing, the surface portion contains a relatively small amount of nickel, but by partially doping a part of the metal inside the positive electrode active material with a highly stable doping element, it is possible to improve the output characteristics, and to the oxygen site inside the positive electrode active material It provides a positive electrode active material that can prevent the desorption of oxygen in the process of charging and discharging by replacing anions.

Specifically, the positive electrode active material according to an embodiment of the present invention is a positive electrode active material present in a concentration gradient in which nickel and manganese gradually change from the center of the particle to the surface, and the positive electrode active material has an average composition represented by the following Chemical Formula 1 A central portion comprising a first lithium composite metal oxide; And a surface portion including a second lithium composite metal oxide having an average composition represented by the following Chemical Formula 2, wherein the positive electrode active material has a peak at 235° C. or higher when the heat flow rate is measured by differential scanning calorimetry, Provide a positive electrode active material:

[Formula 1]

Li _1+x1 (Ni _a1 Mn _b1 Co _1-a1-b1-c1 Me _c1 )O _2-y1 A _y1

[Formula 2]

Li _1+x2 (Ni _a2 Mn _b2 Co _1-a2-b2-c2 Me _c2 )O _2-y2 A _y2

In Chemical Formulas 1 and 2, Me is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb , and at least one doping element selected from the group consisting of Mg, B and Mo, a is PO ₄ ^3-, NO ₄ ^- to ^{_{-, CO 3 2-, BO 3}} -, Cl -, Br -, I - and F At least one anion selected from the group consisting of, 0.8≤a1<1, 0<b1<0.2, 0<c1≤0.1, 0.8<a1+b1+c1<1, 0≤x1≤0.1, 0.0001<y1≤0.1 And 0.1≤a2<0.8, 0.1<b2≤0.9, 0<c2≤0.1, and 0.2<a2+b2+c2<1, 0≤x2≤0.1, 0.0001<y2≤0.1.

The nickel and manganese contained in the positive electrode active material may be independently increased or decreased while exhibiting a gradually changing concentration gradient from the center of the positive electrode active material particle to the particle surface. At this time, the concentration gradient gradient of the metal element may be constant.

The nickel, cobalt and manganese contained in the positive electrode active material may each independently have one concentration gradient gradient value.

Specifically, the concentration of nickel contained in the positive electrode active material may decrease while having a concentration gradient gradually changing from the center of the positive electrode active material particle to the particle surface, wherein the gradient gradient of the nickel is the center of the positive electrode active material particle From to the surface can be constant. As described above, when the concentration of nickel is maintained at a high concentration at the center of the particles in the active material particles and includes a concentration gradient in which the concentration decreases toward the particle surface side, a decrease in capacity can be prevented while exhibiting thermal stability.

In addition, the concentration of manganese contained in the positive electrode active material may increase while having a concentration gradient gradually changing from the center of the active material particle to the particle surface, wherein the concentration gradient gradient of the manganese is from the center of the positive electrode active material particle to the surface. It can be constant. As described above, when the concentration of manganese is maintained at a low concentration in the center of the particles in the active material particles, and a concentration gradient in which the concentration increases toward the surface side is included, excellent thermal stability can be obtained without decreasing the capacity.

In addition, the concentration of cobalt contained in the positive electrode active material may be kept constant from the center of the active material particle to the particle surface by diffusion of cobalt when synthesizing the positive electrode active material.

In the present invention, the term'representing a gradually changing concentration gradient' means that the concentration of the metal exists as a concentration distribution continuously changing step by step in the entire particle or in a specific region. Specifically, the concentration distribution is a change in the metal concentration per 1 μm toward the surface in the particle, based on the total atomic weight of the metal contained in the active material particles, 0.1 atomic% to 30 atomic%, respectively, more specifically 0.1 There may be a difference of atomic% to 20 atomic%.

The positive electrode active material according to an embodiment of the present invention has a concentration gradient in which the concentration of the metal gradually changes depending on the position in the positive electrode active material particle as described above, so that there is no abrupt phase boundary region from the center to the surface. The crystal structure stabilizes and thermal stability increases. In addition, when the gradient of the concentration gradient of the metal is constant, the effect of improving the structural stability may be further improved, and by varying the concentration of each metal in the active material particles through the concentration gradient, the anode of the metal can be easily utilized. The effect of improving the battery performance of the active material can be further improved.

As described above, the positive electrode active material for a secondary battery according to an embodiment of the present invention includes particles of a lithium composite metal oxide present in a concentration gradient in which nickel and manganese gradually change from the particle center to the surface, and thus, when applied to a secondary battery, high capacity , High life and thermal stability, while performance degradation at high voltage can be minimized.

Specifically, the central portion includes a first lithium composite metal oxide having an average composition represented by Chemical Formula 1.

The central portion may contain nickel in an amount of 80 mol% or more and less than 100 mol%, preferably 90 mol% or more and less than 100 mol%, relative to the total mole of metal elements excluding lithium contained in the entire center. At this time, when the nickel is less than 80 mol%, there is a problem that the capacity of the positive electrode active material is reduced and thus cannot be applied to an electrochemical device requiring a high capacity.

The central portion may contain manganese in an amount greater than 0 mol% and less than 20 mol%, and preferably greater than 0 mol% and less than 5 mol% with respect to the total mole of metal elements excluding lithium contained in the entire center. At this time, when the manganese is 20 mol% or more, a problem may occur in expressing a high dose.

In addition, the content of cobalt included in the center may vary depending on the content of the nickel, manganese, and Me. When the content of the cobalt is too high, the cost of the raw material increases overall due to the high content of cobalt, and the reversible capacity There is a problem that this decreases somewhat, and when the content of cobalt is too low, it is difficult to achieve sufficient rate characteristics and high powder density of the battery at the same time. The cobalt contained in the center portion may be included in an amount greater than 0 mol% and less than 20 mol%, preferably 5 mol% or more and 10 mol% or less, based on the total moles of metal elements included in the entire center.

Meanwhile, the surface portion includes a second lithium composite metal oxide having an average composition represented by Chemical Formula 2.

The surface portion may be 10 mol% or more and less than 80 mol%, and preferably 60 mol% or more and less than 80 mol%, based on the total moles of metal elements excluding lithium contained in the entire surface portion of nickel. At this time, when the nickel is less than 10 mol%, there may be a problem that the average capacity of the positive electrode active material decreases, and when the nickel is 80 mol% or more, the stability required for the surface portion is not satisfied, so that the stability of the positive electrode active material It may degrade.

The surface portion may be greater than 10 mole% and less than 90 mole%, preferably 10 mole% or more and 20 mole% or less, based on the total moles of metal elements excluding lithium contained in the entire surface portion of manganese. At this time, when the manganese exceeds 90 mol%, a problem may occur in expressing a high dose.

In addition, the content of cobalt included in the surface part may vary depending on the content of the nickel, manganese, and Me, and may be kept constant throughout the center part and the entire surface part. The cobalt contained in the surface portion may be included in an amount greater than 0 mol% and less than 20 mol%, preferably 5 mol% or more and 15 mol% or less, based on the total moles of the metal elements included in the entire surface portion.

When forming a central portion with a first lithium composite metal oxide containing a large amount of nickel having a high capacity characteristics as described above, when forming a second lithium composite metal oxide having a low nickel content and excellent thermal stability on the surface of the central portion, as a surface portion, It is possible to provide a positive electrode active material having excellent output characteristics, life characteristics, and thermal stability.

Meanwhile, nickel, cobalt, or manganese included in the central portion and the surface portion may be doped by one or more doping elements Me. In the case of the positive electrode active material doped with such a doping element, the doping element may be uniformly included on the surface and inside of the positive electrode active material, thereby improving the structural stability of the positive electrode active material, thereby improving the lifespan characteristics and thermal stability.

The doping element Me may be used without particular limitation as long as it can contribute to improving the structural stability of the positive electrode active material, for example, W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, It may include at least one doping element selected from the group consisting of Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and preferably W. .

The Me, relative to the total moles of metal elements excluding lithium contained in the entire central portion and the surface portion, respectively, may be greater than 0 mole% and 10 mole% or less, preferably 0.05 mole% or more and 5 mole% or less. For example, when each of the Me and the central portion and the surface portion independently exceeds 10 mol%, lithium by-products may increase.

Oxygen (O ₂ ) included in the central portion and the surface portion may be substituted with one or more anions A. In the case of the positive electrode active material in which these anions are substituted, since the anion may be uniformly included on the surface and inside of the positive electrode active material, the secondary battery manufactured based on this exhibits excellent output characteristics and life characteristics, and exhibits high charging and discharging efficiency. You can.

That is, a specific anion uniformly contained in the surface and the inside of the positive electrode active material contributes to the improvement of ionic conductivity between grains, and induces crystal or crystal growth to be small, reducing structural changes when oxygen is generated in the activation step, and surface area Can increase the overall performance of the battery, such as rate characteristics.

And A is as long as they can contribute to increase the ionic conductivity between crystals can be used without particular limitation, for _{^{example, PO 4 3-, NO 4 -}} , CO 3 2-, BO 3 -, Cl -, Br -, I ^- and F ^- is at least one or more, preferably selected from the group consisting of PO ₄ ^3-, NO ₄ ^- it can include at least one or more selected from the group consisting of ^-, CO ₃ ^2-, BO ₃ ^- and F.

The A, with respect to the total moles of oxygen contained in the entire central portion and the surface portion, respectively, may be independently substituted with 0.01 mol% or more and 10 mol% or less, preferably 0.05 mol% or more and 5 mol% or less have. For example, A included in the central portion and the surface portion is each independently, when included in less than 0.01 mol%, the oxygen desorption prevention effect may be insignificant, and when included in more than 10 mol%, the positive electrode is prevented from crystallization of the positive electrode active material It can be difficult to improve the performance of the active material.

The average particle diameter (D ₅₀ ) of the positive electrode active material may be 4 μm to 20 μm, and preferably 6 μm to 15 μm. For example, when the average particle diameter of the positive electrode active material is less than 4 μm, high energy density cannot be achieved due to low rolling density, and when it exceeds 20 μm, it cannot be rolled below a certain thickness.

In the present specification, the average particle diameter (D ₅₀ ) may be defined as a particle size corresponding to 50% of the volume accumulation amount in the particle size distribution curve. The average particle diameter (D ₅₀ ) can be measured, for example, using a laser diffraction method. The laser diffraction method can generally measure a particle diameter of several mm from a submicron region, and can obtain high reproducibility and high resolution.

In addition, the positive electrode active material may further include a coating layer formed on the surface, and the coating layer may include at least one selected from the group consisting of B, Al, Hf, Nb, Ta, Mo, Si, Zn and Zr. have.

By blocking the contact between the positive electrode active material and the electrolyte contained in the lithium secondary battery by the coating layer to suppress the occurrence of side reactions, it is possible to improve the life characteristics, and also increase the filling density of the positive electrode active material.

The coating layer may be formed on the entire surface of the positive electrode active material, or may be partially formed. Specifically, when the coating layer is partially formed on the surface of the positive electrode active material, 20% or more to less than 100% of the total area of the positive electrode active material may be formed. When the area of the coating layer is less than 20%, the effect of improving life characteristics and filling density according to formation of the coating layer may be negligible.

In addition, the coating layer may be formed in a thickness ratio of 0.001 to 1 with respect to the average particle diameter of the positive electrode active material particles. If the thickness ratio of the coating layer to the particles of the positive electrode active material is less than 0.001, the effect of improving life characteristics and filling density according to the formation of the coating layer is insignificant, and when the thickness ratio exceeds 1, battery characteristics may be deteriorated. .

When the heat flux is measured by differential scanning calorimetry, the positive electrode active material may exhibit a peak in a temperature range of 235°C or higher, preferably 235°C to 250°C, more preferably 235°C to 240°C. For example, the heat flow rate is to measure the amount of heat released at this time while raising the positive electrode active material to 10° C./min using a differential scanning calorimeter (DSC). When the heat flow rate measured by differential scanning calorimetry of the positive electrode active material satisfies the above range, thermal stability of the positive electrode active material may be improved.

In addition, the crystal grains of the positive electrode active material may further include those having crystal orientation in a direction perpendicular to the C axis. When the crystal grains of the positive electrode active material have a crystal orientation in a direction perpendicular to the C axis, the mobility of lithium ions contained in the positive electrode active material is improved, the structural stability of the active material is increased, and when the battery is applied, initial capacity characteristics, output characteristics , Resistance characteristics and long life characteristics can be improved.

For example, the positive electrode active material particles have a structure in which at least one layer of an oxygen layer and a metal layer are layered and lithium ions are interposed between the layered body of the oxygen layer and the metal layer, and the C axis is such an anode. In the stacked structure of the active material particles, it means a direction perpendicular to the metal layer and the oxygen layer.

In addition, when the positive electrode active material has crystal orientation in one direction, intercalation and deintercalation of lithium ions during charging and discharging in the positive electrode active material having a laminated structure is facilitated, thereby improving the output characteristics of the lithium secondary battery. Can be.

The positive electrode active material may include less than 1% by weight of lithium by-products, but is not limited thereto. Specifically, the positive electrode active material may include a lithium by-product containing LiOH and Li ₂ CO ₃ less than 1% by weight. When the lithium by-product is 1% by weight or more in the positive electrode active material, the output characteristics of the lithium secondary battery may be deteriorated.

On the other hand, the method of manufacturing the positive electrode active material according to an embodiment of the present invention is nickel, cobalt, manganese and doping elements Me (where Me is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta , Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, including at least one or more selected from the group consisting of B) and Mo) 1 preparing a second metal-containing solution containing nickel, cobalt, manganese and doping elements Me at a different concentration from the metal-containing solution (step 1); The first metal-containing solution and the second metal-containing solution such that the mixing ratio of the first metal-containing solution and the second metal-containing solution is gradually changed from 100% by volume: 0% by volume to 0% by volume: 100% by volume. The step of preparing a positive electrode active material precursor exhibiting a concentration gradient in which the nickel and manganese are gradually changed from the center of the particle to the surface of the particles independently by adding an ammonium cation complex forming agent and an anion-containing basic compound at the same time (step) 2); Mixing and firing the positive electrode active material precursor and the lithium-containing raw material to synthesize a positive electrode active material (step 3); And performing heat treatment of the positive electrode active material in an oxygen atmosphere at 600°C to 800°C (step 4).

With respect to the method for manufacturing the positive electrode active material, all the contents described in the positive electrode active material described above can be applied.

First, nickel, cobalt, manganese and doping elements Me (where Me is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm , Ca, Ce, Nb, Mg, B and Mo (including at least one selected from the group consisting of) a first metal-containing solution and nickel, cobalt, manganese and A second metal-containing solution containing a doping element Me is prepared (step 1).

The first metal-containing solution is prepared by adding a nickel raw material, a cobalt raw material, a manganese raw material, and a raw material of Me to a mixture of an organic solvent (alcohol, etc.) and water that can be uniformly mixed with a solvent, specifically water or water. Alternatively, an aqueous solution containing each metal-containing raw material may be prepared and then mixed and used. At this time, when preparing the first metal-containing solution, the nickel, cobalt, manganese, and the respective metal raw materials are mixed so that the nickel is contained in an amount of 80 mol% or more and less than 100 mol% with respect to the total number of moles of Me.

The second metal-containing solution includes a nickel raw material, a cobalt raw material, a manganese raw material, and a raw material of a doping element Me, and may be prepared in the same manner as the first metal-containing solution. At this time, in the preparation of the second metal-containing solution, the nickel, cobalt, manganese, and the respective metal raw materials are mixed so that the nickel is contained in an amount of 10 mol% or more and less than 80 mol% with respect to the total number of moles of the doping element Me.

As the raw material of the nickel, cobalt, manganese, and doping elements Me, sulfates, nitrates, acetates, halides, hydroxides, or oxyhydroxides containing each metal element may be used, and may be dissolved in the above solvents such as water. If so, it can be used without particular limitation.

Specifically, the cobalt raw materials include Co(OH) ₂ , CoOOH, CoSO ₄ , Co(OCOCH ₃ ) ₂ ㆍ4H ₂ O, Co(NO ₃ ) ₂ ㆍ6H ₂ O or Co(SO ₄ ) ₂ ㆍ7H ₂ O and the like, and a mixture of one or more of them may be used.

In addition, Ni (OH) ₂ , NiO, NiOOH, NiCO ₃ 2Ni(OH) ₂ 4H ₂ O, NiC ₂ O ₂ 2H ₂ O, Ni(NO ₃ ) ₂ 6H ₂ O, NiSO ₄ , NiSO ₄ 6H ₂ O, fatty acid nickel salts or nickel halides, and mixtures of one or more of them may be used.

Further, as the raw material of the manganese, manganese oxides such as Mn ₂ O ₃ , MnO ₂ and Mn ₃ O ₄ ; Manganese salts such as MnCO ₃ , Mn(NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganese dicarboxylic acid, manganese citrate and manganese fatty acids; Oxyhydroxide, and manganese chloride, and mixtures of one or more of them may be used.

Subsequently, the first metal-containing solution and the second metal so that the mixing ratio of the first metal-containing solution and the second metal-containing solution is gradually changed from 100% by volume to 0% by volume to 0% by volume: 100% by volume. While mixing the containing solution, a co-precipitation reaction is performed by adding an ammonium cation complex forming agent and an anion-containing basic compound, and thus the cathode and the manganese precursors each independently exhibit a concentration gradient gradually changing from the center of the particle to the surface. Prepare (step 2).

Since the reaction (particle nucleation and particle growth) is performed in the state in which only the first metal-containing solution is present at the beginning of the cathode active material precursor manufacturing step, the first precursor particles have a composition of the first metal-containing solution. Since the second metal-containing solution is gradually mixed into the first metal-containing solution, the composition of the precursor particles is gradually changed to the composition of the second metal-containing solution in the outer direction from the center of the precursor particles. For example, the first metal-containing solution has a high nickel content, a low manganese content, and the second metal-containing solution has a lower nickel content and a higher manganese content than the first metal-containing solution. When it is reacted, the concentration of nickel decreases while having a continuous concentration gradient from the center of the active material particle to the particle surface direction, and the concentration of manganese has a continuous concentration gradient from the center of the particle to the particle surface direction. While increasing, cobalt can produce precursor particles in a form that is maintained at a constant concentration from the center of the particle to the particle surface.

Accordingly, by adjusting the composition of the first metal-containing solution and the second metal-containing solution, and adjusting the mixing speed and ratio, the metal element in the precursor has a desired composition in the desired direction from the center of the precursor particle to the surface direction. You can adjust the concentration gradient and its slope.

In addition, mixing of the first metal-containing solution and the second metal-containing solution is continuously performed, and by continuously supplying and reacting the second metal-containing solution as described above, from the center of the particle to the surface in one co-precipitation reaction process It is possible to obtain a precipitate in which the concentration of the metal has a continuous concentration gradient, wherein the concentration gradient of the metal in the resulting active material precursor and its slope depends on the composition and mixing supply ratio of the first metal-containing solution and the second metal-containing solution. Can be easily adjusted.

In addition, the concentration gradient of the metal element in the particle can be formed by controlling the reaction rate or reaction time. It is preferable to increase the reaction time and increase the reaction time in order to make a high-density state with a high concentration of a specific metal, and to shorten the reaction time and increase the reaction rate to make a low-density state with a low concentration of a specific metal. .

By controlling the supply amount and the reaction time of the second metal-containing solution to the first metal-containing solution, it is possible to control the size of the positive electrode active material particles and the thickness of the surface. Specifically, it may be desirable to appropriately control the supply amount and reaction time of the second metal-containing solution to have the particle size of the positive electrode active material as described above.

Meanwhile, the ammonium cation complex forming agent may be NH ₄ OH, (NH ₄ ) ₂ SO ₄ , NH ₄ NO ₃ , NH ₄ Cl, CH ₃ COONH ₄ , or NH ₄ CO ₃ , and a mixture of one or more of them Can be used. In addition, the ammonium cation-containing complex forming agent may be used in the form of an aqueous solution, and in this case, as a solvent, a mixture of water or an organic solvent (specifically alcohol, etc.) uniformly mixed with water and water may be used.

The ammonium cation-containing complex forming agent may be added in an amount to be a molar ratio of 0.5 to 1 with respect to 1 mol of the mixed solution obtained by mixing the first metal-containing solution and the second metal-containing solution. In general, the complexing agent containing ammonium cation reacts with a metal in a molar ratio of 1:1 or more to form a complex, but among the complexes formed, unreacted complexes that have not reacted with a basic aqueous solution are turned into intermediate products and recovered and reused as complex forming agents containing ammonium cation. Since it can be, in the present invention, the amount of the ammonium cation-containing complexing agent can be lowered than usual. As a result, the crystallinity of the positive electrode active material can be increased and stabilized.

The anion-containing basic compound is _{^{PO 4 3-, NO 4 -,}} CO 3 2-, BO 3 -, Cl -, Br -, I - and F ^- at least one anion selected from the group consisting of, preferably PO ₄ ^3- , NO ₄ ^- , CO ₃ ^2- , may include at least one anion selected from the group consisting of BO ₃ ^- and F ^- , the anion may include a state dissolved in a basic material.

The basic substance included in the anion-containing basic compound may be a hydroxide of an alkali metal or an alkaline earth metal such as NaOH, KOH or Ca(OH) ₂ or a hydrate thereof, and a mixture of one or more of them may be used. The anion-containing basic compound may also be used in the form of an aqueous solution, in which a mixture of water or an organic solvent (specifically, alcohol, etc.) uniformly mixed with water and water may be used as the solvent. At this time, the concentration of the anion-containing basic aqueous solution may be 2 M to 10 M, preferably 2 M to 8 M. When the concentration of the basic aqueous solution containing the anion is less than 2 M, the particle formation time becomes longer, the tap density decreases, and the yield of the coprecipitation reactant may decrease, and when it exceeds 10 M, the particles rapidly grow by rapid reaction. Therefore, it is difficult to form uniform particles and there is a possibility that the tap density is also lowered.

Oxygen position of the compound in which the anion contained in the anion-containing basic compound is represented by Formula 1 and Formula 2 by adding the anion-containing basic compound to the mixed solution in which the first metal-containing solution and the second metal-containing solution are mixed. It may be substituted with. By displacing the anion at the oxygen position, desorption of oxygen can be prevented during charging and discharging of the lithium secondary battery including the positive electrode active material.

In addition, the co-precipitation reaction may be performed under the conditions that the pH of the mixed first metal-containing solution and the second metal-containing solution is pH 10 to pH 13, specifically pH 10 to pH 12. When the co-precipitation reaction is performed in the above-described pH range, precursor particles can be produced without generating various oxides by side reactions due to a change in size of the precursor to be produced, particle splitting, or elution of metal ions from the precursor surface. Accordingly, the ammonium cation-containing complexing agent and the anion-containing basic compound may be used in a molar ratio of 1:10 to 1:2 to satisfy the above-described pH range.

In addition, the co-precipitation reaction may be performed at a temperature of 40°C to 70°C under an inert atmosphere such as nitrogen or argon. In addition, a stirring process may be selectively performed to increase the reaction speed during the reaction, wherein the stirring speed may be 100 rpm to 2,000 rpm.

Subsequently, the positive electrode active material precursor and the lithium-containing raw material are mixed and fired to synthesize a positive electrode active material (step 3).

The lithium-containing raw material can be used without particular limitations, for example, lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide, etc. It can be used, and is not particularly limited as long as it can be dissolved in water. Specifically, the lithium-containing raw material is Li ₂ CO ₃ , LiNO ₃ , LiNO ₂ , LiOH, LiOHㆍH ₂ O, LiH, LiF, LiCl, LiBr, LiI, CH ₃ COOLi, Li ₂ O, Li ₂ SO ₄ , CH ₃ COOLi, or at least one mixture selected from the group consisting of Li ₃ C ₆ H ₅ O ₇ may be used.

The amount of the lithium-containing raw material used may be determined according to the content of lithium and metal in the final positive electrode active material, specifically, lithium contained in the lithium-containing raw material and metal elements contained in the precursor for the positive electrode active material ( Ni, Co, Mn and Me) may be used in an amount such that the molar ratio (molar ratio of lithium/metal element) is 1.0 or more, preferably 1.03 to 1.20.

Firing the positive electrode active material precursor and the lithium-containing raw material may be performed by one-step or two-step firing.

For example, when the firing is performed using a one-step firing, the one-step firing is from 700°C to 1,000°C, preferably from 750°C to 850°C for 5 to 30 hours, more preferably from 20 hours to It can be carried out for 30 hours. When the positive electrode active material precursor and the lithium-containing raw material are performed at 700°C to 1,000°C as described above, repositioning of the molecules in the active material occurs, and accordingly, as the molecules are stabilized, thermal stability of the positive electrode active material may be improved. On the other hand, if the calcination temperature is less than 700°C and the calcination time is less than 5 hours, there is a concern that the discharge capacity per unit weight may be lowered, cycle characteristics may be lowered, and the operating voltage may be lowered due to the residual of unreacted raw materials. If it exceeds, and the firing time exceeds 30 hours, there is a fear that the discharge capacity per unit weight decreases, cycle characteristics decrease, and operation voltage decreases due to the formation of side reactants.

For example, when the firing is performed using a two-stage firing, the two-stage firing is heated from 25 °C to 400 °C at a heating rate of 2 °C/min to 5 °C/min and maintained for 7 to 12 hours. It includes a first firing and a second firing that is heated from 400°C to 800°C at a heating rate of 7°C/min to 10°C/min and maintained for 10 to 15 hours. More preferably, the first firing includes heating at 350° C. to 400° C. at a heating rate of 4° C./min to 5° C./min and maintaining it for 9 to 10 hours, and the second firing is 9° C. It includes heating at 700°C to 800°C at a heating rate of /min to 10°C/min and maintaining for 12 to 15 hours. When the positive electrode active material precursor and the lithium-containing raw material are fired in two stages as described above, the crystal grains of the positive electrode active material may have crystal orientation in a direction perpendicular to the C axis by slowing the temperature increase rate, and thus included in the positive electrode active material. The mobility of lithium ions is improved, and the structural stability of the active material is increased, so that initial capacity characteristics, output characteristics, resistance characteristics, and long-term life characteristics can be improved when the battery is applied. On the other hand, if the firing temperature and the temperature increase rate of the first firing and the second firing of the two-stage firing are out of the above range, the discharge capacity per unit weight decreases, the cycle characteristics and the operating voltage decrease due to the residual of unreacted raw materials. I have a concern.

In addition, the firing step may be performed under an oxidizing atmosphere such as air or oxygen, or a reducing atmosphere containing nitrogen or hydrogen. The diffusion reaction between particles can be sufficiently achieved through the firing process under such conditions, and the diffusion of metal occurs even at a portion where the internal metal concentration is constant, resulting in a positive electrode active material having a continuous metal concentration distribution from the center to the surface. Can be manufactured.

Meanwhile, when mixing the positive electrode active material precursor and the lithium-containing raw material, a sintering agent may be selectively added. The sintering agent is specifically a compound containing an ammonium ion, such as NH ₄ F, NH ₄ NO ₃ , or (NH ₄ ) ₂ SO ₄ ; Metal oxides such as B ₂ O ₃ or Bi ₂ O ₃ ; Or metal halides such as NiCl ₂ or CaCl _2, and mixtures of one or more of them may be used. The sintering agent may be used in an amount of 0.01 to 0.2 mol per 1 mol of the positive electrode active material precursor. If the content of the sintering agent is too low, less than 0.01 mol, the effect of improving the sintering properties of the positive electrode active material precursor may be insignificant, and if the content of the sintering agent is too high, exceeding 0.2 mol, the performance of the positive electrode active material is reduced due to excessive sintering agent. And the initial capacity of the battery may decrease during charging and discharging.

In addition, when mixing the positive electrode active material precursor and the lithium-containing raw material, a moisture removing agent may be optionally further added. Specifically, the water removal agent may include citric acid, tartaric acid, glycolic acid, or maleic acid, and a mixture of one or more of them may be used. The water removing agent may be used in an amount of 0.01 to 0.2 mol with respect to 1 mol of the positive electrode active material precursor.

In addition, it may further include the step of washing the synthesized positive electrode active material at a temperature of 15 ℃ or less.

The washing step is carried out at a temperature of 15° C. or less, preferably 5° C. to 15° C., more preferably 5° C. to less than 10° C. By washing the positive electrode active material in the temperature range, lithium by-products and unreacted anions present on the surface of the positive electrode active material can be effectively removed, thereby improving the life characteristics of the battery when applied to the secondary battery. On the other hand, when the water washing temperature exceeds 15°C, the lithium secondary battery may be overwashed, and in this case, life and capacity characteristics may be deteriorated.

Immediately after synthesis, the positive electrode active material may include lithium by-products including LiOH and Li ₂ CO ₃ in an amount of greater than 1.0% by weight and less than 3.0% by weight. At this time, by washing the positive electrode active material in a temperature range of 15 ℃ or less can effectively remove the lithium by-products present in the positive electrode active material. After the washing step, the positive electrode active material may include less than 1% by weight of lithium by-products including LiOH and Li ₂ CO ₃ , but is not limited thereto.

Lastly, the positive electrode active material is heat-treated at 600°C to 800°C under an oxygen atmosphere (step 5). The thermal stability of the positive electrode active material may be improved by performing heat treatment on the washed positive electrode active material at 600°C to 800°C, more preferably at 650°C to 750°C for 5 hours to 10 hours, and also the positive electrode active material Rearrangement of the metal elements occurs, lithium diffusion in the positive electrode active material proceeds, recrystallization of the positive electrode active material occurs, and the life characteristics can be further improved.

In addition, after the step of washing the positive electrode active material, before performing the heat treatment, if necessary, optionally consisting of B, Al, Hf, Nb, Ta, Mo, Si, Zn and Zr on the washed positive electrode active material The method may further include forming a coating layer by coating at least one selected from the group.

Specifically, the method for forming a coating layer on the positive electrode active material, a method of forming a coating layer on the surface of the active material can be used without particular limitation, for example, by applying the composition prepared by dispersing the metal in a solvent, After the surface treatment of the positive electrode active material using a conventional slurry coating method such as dipping and spraying, the coating layer may be formed on the surface of the positive electrode active material by heat treatment.

At least a solvent selected from the group consisting of water, alcohol having 1 to 8 carbon atoms, dimethyl sulfoxide (DMSO), N-methylpyrrolidone, acetone, and combinations thereof is used as a solvent capable of dispersing the metal to form the coating layer. One or more mixtures can be used.

In addition, the solvent may exhibit appropriate coating properties, and may be included in an amount that can be easily removed after heat treatment.

Subsequently, the heat treatment for forming the coating layer may be performed in a temperature range capable of removing the solvent contained in the composition, specifically, 200°C to 700°C, preferably 250°C to 400°C May be When the heat treatment temperature is less than 200°C, there is a fear of side reactions caused by residual solvents and deterioration of battery characteristics, and when the heat treatment temperature exceeds 700°C, there is a fear of side reactions caused by high temperature heat.

Meanwhile, according to another embodiment of the present invention, a positive electrode including the positive electrode active material is provided.

At this time, the positive electrode may be prepared by coating a positive electrode mixture comprising a positive electrode active material, a binder, a conductive material, and a solvent on the positive electrode current collector.

Since the positive electrode active material is the same as described above, a detailed description is omitted, and the rest of the configuration will be described in detail below.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , Surface treatment with nickel, titanium, silver, or the like can be used.

The positive electrode active material may be included in 80% to 99% by weight based on the total weight of each positive electrode mixture.

The binder is a component that assists in bonding the active material and the conductive material and the like to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the positive electrode mixture. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, and various copolymers.

The conductive material is usually added in 1 to 30% by weight based on the total weight of the positive electrode mixture.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder, 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 may be used. Specific examples of commercially available conductive materials include acetylene black-based Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc., Ketjenblack, EC Series (manufactured by Armak Company), Vulcan XC-72 (manufactured by Cabot Company) and Super P (manufactured by Timcal).

The solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that becomes a desirable viscosity when the positive electrode active material and optionally a binder and a conductive material are included. For example, the concentration of the solid content including the positive electrode active material and optionally a binder and a conductive material may be included to be 50% to 95% by weight, preferably 70% to 90% by weight.

According to another embodiment of the present invention, there is provided a lithium secondary battery comprising the positive electrode.

The lithium secondary battery specifically includes a positive electrode, a negative electrode located opposite to the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. In addition, the lithium secondary battery may further include a battery container for storing the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

Since the positive electrode is the same as described above, a detailed description is omitted, and the rest of the configuration will be described in detail below.

The negative electrode may be prepared by coating a negative electrode mixture containing a negative electrode active material, a binder, a conductive material, and a solvent on a negative electrode current collector, for example.

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

Examples of the negative electrode active material include natural graphite, artificial graphite, and carbonaceous materials; Lithium-containing titanium composite oxides (LTO), metals (Me) which are Si, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe; Alloys composed of the metals (Me); Oxides of the metals (Me); And at least one negative active material selected from the group consisting of a composite of the metals (Me) and carbon.

The negative electrode active material may be included in 80% to 99% by weight based on the total weight of the negative electrode mixture.

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is usually added at 1% to 30% by weight based on the total weight of the negative electrode mixture. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro Roethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber, and various copolymers thereof.

The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added at 1% to 20% by weight based on the total weight of the negative electrode mixture. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; Carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder, 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 may be used.

The solvent may include water or an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that becomes a desirable viscosity when the negative electrode active material and optionally a binder and a conductive material are included. For example, the concentration of the solid content including the negative electrode active material and optionally the binder and the conductive material may be included to be 50% to 95% by weight, preferably 70% to 90% by weight.

Further, as the separator, a conventional porous polymer film conventionally used as a separator, for example, polyolefin such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer and ethylene/methacrylate copolymer, etc. A porous polymer film made of a polymer based polymer may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a high melting point glass fiber, a polyethylene terephthalate fiber, or the like may be used, but is not limited thereto. It is not.

At this time, in order to secure heat resistance or mechanical strength, an organic/inorganic composite separator coated with an inorganic material may be used, or may be used in a single-layer or multi-layer structure.

The inorganic material may be used without being particularly limited as long as it is a material capable of uniformly controlling the pores of the organic-inorganic composite separator and improving heat resistance. For example, the inorganic material is, without limitation, SiO ₂ , Al ₂ O ₃ , TiO ₂ , BaTiO ₃ , Li ₂ O, LiF, LiOH, Li ₃ N, BaO, Na ₂ O, Li ₂ CO ₃ , CaCO ₃ , And at least one selected from the group consisting of LiAlO ₂ , SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO2, SiC and derivatives thereof and mixtures thereof.

The average diameter of the inorganic material may be 0.001 μm to 10 μm, and more specifically, 0.001 μm to 1 μm. If the average diameter of the inorganic material is within the above range, dispersibility in the coating solution is improved, and problems in the coating process can be minimized. In addition, not only can the physical properties of the final separation membrane be uniform, but also the inorganic particles are uniformly distributed in the pores of the nonwoven fabric to improve the mechanical properties of the nonwoven fabric, and the size of the pores of the organic/inorganic composite separation membrane can be easily adjusted. There is this.

The average diameter of the pores of the organic-inorganic composite separator may range from 0.001 μm to 10 μm, and more specifically, from 0.001 μm to 1 μm. When the average diameter of the pores of the organic-inorganic composite membrane is within the above range, the gas permeability and ionic conductivity can be controlled to a desired range. In addition, when manufacturing a battery using the organic-inorganic composite membrane, contact with the anode and the cathode The possibility of internal short circuit of the battery can be eliminated.

The porosity of the organic-inorganic composite membrane may be in the range of 30% to 90% by volume. When the porosity is within the above range, ion conductivity may be increased and mechanical strength may be excellent.

Further, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, and the like, which can be used in the manufacture of lithium secondary batteries. It does not work.

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent, methyl acetate (methyl acetate), ethyl acetate (ethyl acetate), γ-butyrolactone (γ-butyrolactone), ε-caprolactone (ε-caprolactone), such as ester solvents; Ether-based solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (ethylmethylcarbonate, EMC), ethylene carbonate (EC), propylene carbonate (propylene carbonate, PC) and other carbonate-based solvents; Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as R-CN (R is a straight-chain, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond aromatic ring or ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Alternatively, sulfolanes may be used. Of these, carbonate-based solvents are preferred, and cyclic carbonates (for example, ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and low-viscosity linear carbonate-based compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, the mixture of the cyclic carbonate and the chain carbonate in a volume ratio of about 1:1 to about 1:9 may be used to exhibit excellent electrolyte performance.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ and the like can be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can be effectively moved.

In addition to the electrolyte components, the electrolyte includes haloalkylene carbonate-based compounds such as difluoro ethylene carbonate, pyridine, and tree for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery. Ethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, or aluminum trichloride may also be included. At this time, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

As described above, the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, so portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles (hybrids) It is useful for electric vehicles, such as electric vehicles (HEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or battery pack includes a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); Alternatively, it can be used as a power supply for any one or more of medium and large-sized devices in a power storage system.

The appearance of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical, prismatic, pouch or coin type using a can.

The lithium secondary battery according to the present invention can be used not only for a battery cell used as a power source for a small device, but also as a unit battery for a medium-to-large battery module including a plurality of battery cells.

Hereinafter, examples will be described in detail to specifically describe the present invention. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

Example

Example  One

[ Cathode active material  Produce]

In a batch-type 5L reactor set at 60° C., NiSO ₄ , CoSO ₄ , MnSO ₄ and Na ₂ WO ₄ are watered in an amount such that the molar ratio of nickel:cobalt:manganese:tungsten is 98.77:0.63:0.57:0.03. To prepare a first metal-containing solution having a concentration of 2M, and further adding NiSO ₄ , CoSO ₄ , MnSO ₄ and Na ₂ WO ₄ to a molar ratio of nickel:cobalt:manganese:tungsten of 69.16:25.97:4.84:0.03 By mixing in water to prepare a second metal-containing solution of 2M concentration.

The container containing the first metal-containing solution and the container containing the second metal-containing solution were respectively connected to an in-line static mixer in a tube, and a reactor was connected to the outlet side of the static mixer. In addition, a 4 M NaOH solution to which 1 mol% of Na ₃ PO ₄ was added and an aqueous NH ₄ OH solution of 7% concentration were prepared and connected to each reactor. After adding 3 liters of deionized water to a co-precipitation reactor (capacity 5L), nitrogen gas was purged into the reactor at a rate of 2 L/min to remove dissolved oxygen in the water, and the reactor was composed of a non-oxidizing atmosphere. Thereafter, 100 mL of 4 M NaOH containing 1 mol% of Na ₃ PO ₄ was added, followed by stirring at a stirring speed of 1,100 rpm at a temperature of 60° C. to maintain pH 11.2.

Subsequently, the first metal-containing solution and the second metal-containing solution were mixed at a ratio of 100% by volume: 0% by volume to 0% by volume: 100% by volume. The resulting mixed metal solution was continuously introduced into the reactor at a rate of 5 m/s through the piping for the mixed solution, and a NaOH aqueous solution containing 1 mol% of Na ₃ PO ₄ was 180 mL/hr, and an NH ₄ OH aqueous solution was 10. The particles of nickel/manganese cobalt tungsten-based composite metal hydroxides were precipitated by coprecipitation reaction for 24 hours at a rate of mL/hr. The precipitated nickel manganese cobalt tungsten-based composite metal-containing hydroxide particles were separated and dried in an oven at 120° C. for 24 hours to prepare a precursor for a positive electrode active material.

The precursor obtained above is dry-mixed with Li ₂ CO ₃ (1.07 mol lithium carbonate relative to 1 mol of the precursor), and then heat-treated at 750° C. for 27 hours under an oxygen atmosphere to include a concentration gradient of metal elements in the active material particles. A positive electrode active material was prepared.

Specifically, the average by the above method a composition of _{Li 1.03 Ni 0.9124 Co 0.0722 Mn 0.0104} W 0.005 O 1.9955 (PO 4) is center, and an average composition represented by _{0.0045 Li 1.03 Ni 0.7626 Co 0.1046 Mn} 0.1278 W 0.005 (O 2) A positive electrode active material including a surface portion represented by _0.99775 (PO ₄ ) _0.0045 was prepared.

Subsequently, the positive electrode active material prepared above was washed with water at 9° C. and dried at 130° C. for 10 hours after water washing.

After the boron was coated by dry coating at 300° C. for 5 hours using boronic acid on the surface of the washed positive electrode active material, the positive electrode active material was heat treated at 700° C. under an oxygen atmosphere for 5 hours.

[Anode production]

The positive electrode active material, carbon black conductive material and polyvinylidene fluoride (PVDF) binder based on 100 parts by weight of N-methyl-2-pyrrolidone (NMP) as a solvent are mixed in a ratio of 96.5:1.5:2.0 (wt%) Thus, a positive electrode forming composition (viscosity: 5,000 mPas) was prepared, and applied to a positive electrode current collector (Al thin film) having a thickness of 100 μm, dried, and roll-pressed to prepare a positive electrode.

[Secondary Battery Manufacturing]

After interposing a polyethylene porous film between the positive electrode prepared by the above-described method and the Li metal as a counter electrode, 1 M lithium hexafluorophosphate (LiPF) in an organic solvent composed of ethylene carbonate/dimethyl carbonate (1:1 volume ratio). ₆ ) The electrolyte in which the dissolved electrolyte was poured is prepared to produce a coin-type half cell in a conventional manner.

Example  2

After the cathode active material precursor prepared in Example 1 was dry-mixed with Li ₂ CO ₃ (1.07 mol lithium carbonate relative to 1 mol of the precursor), and heated to 400° C. under an oxygen atmosphere at a heating rate of 5° C./min to 10° C. for 10 hours. It was maintained for a first firing, and then heated to 780°C at a heating rate of 10°C/min and maintained for 12 hours to perform a second firing to prepare a positive electrode active material, and was the same as in Example 1 above. A cathode active material, a cathode, and a secondary battery including the same were manufactured.

Comparative example

Comparative example  One

As a positive electrode active material, a positive electrode and a secondary battery including the same were prepared using a positive electrode active material represented by Li(Ni _0.88 Mn _0.09 Co _0.03 )(O ₂ ). At this time, the method of manufacturing the positive electrode and the secondary battery is the same as described in Example 1.

Comparative example  2

In a batch-type 5L reactor set at 60°C, water in an amount such that NiSO ₄ , CoSO ₄ , MnSO ₄ and Na ₂ WO ₄ is molar ratio of nickel:cobalt:manganese:tungsten is 98.77:0.63:0.57:0.03 To prepare a first metal-containing solution having a concentration of 2M, and further adding NiSO ₄ , CoSO ₄ , MnSO ₄ and Na ₂ WO ₄ to a molar ratio of nickel:cobalt:manganese:tungsten of 69.16:25.97:4.84:0.03 By mixing in water to prepare a second metal-containing solution of 2M concentration.

The container containing the first metal-containing solution and the container containing the second metal-containing solution were each connected to a co-precipitation reactor. In addition, a 4 M NaOH solution to which 1 mol% of Na ₃ PO ₄ was added and an aqueous NH ₄ OH solution of 7% concentration were prepared and connected to each reactor. After adding 3 L of deionized water to the co-precipitation reactor (capacity 5 L), nitrogen gas was purged to the reactor at a rate of 2 L/min to remove dissolved oxygen in the water and the inside of the reactor was formed in a non-oxidizing atmosphere. Thereafter, 100 mL of 4 M NaOH containing 1 mol% of Na ₃ PO ₄ was added, followed by stirring at a stirring speed of 1,100 rpm at a temperature of 60° C. to maintain pH 11.2.

The first metal-containing solution, NaOH solution, and NH ₄ OH aqueous solution were added to the coprecipitation reactor at 5 m/s, 180 mL/hr, and 10 mL/hr, respectively, and reacted for 12 hours to form a central portion of the positive electrode active material.

Subsequently, the second metal-containing solution, NaOH solution, and NH ₄ OH aqueous solution were added to the reactor at the same rate and reacted for 12 hours to prepare a positive electrode active material precursor having a surface formed on the surface of the center. A cathode and a secondary battery including the same were manufactured in the same manner as in Example 1, except that the precursor was used.

Comparative example  3

A positive electrode active material, a positive electrode, and a secondary battery including the same were prepared in the same manner as in Example 1, except that the prepared positive electrode active material was not heat treated in an oxygen atmosphere.

Experimental Example

Experimental Example  1: Thermal stability evaluation

Thermal stability was evaluated for the positive electrode active materials prepared in Examples 1 to 2 and Comparative Examples 2 to 3.

Specifically, the heat flux was measured while heating the positive electrode active materials prepared in Examples 1 to 2 and Comparative Examples 2 to 3 using a differential scanning calorimeter (DSC) at 10° C./min, and the results are shown in FIG. 1. Shown.

As shown in FIG. 1, the positive electrode active materials of Examples 1 to 2 were compared with the positive electrode active materials prepared in Comparative Example 3, and a heat flow peak appeared at a higher temperature, and the height of the heat flow peak was lower. Through this, the thermal stability of the positive electrode active material prepared by synthesizing the positive electrode active material as in Examples 1 to 2 and then heat-treated at a higher temperature than the positive electrode active material prepared without additional heat treatment under an oxygen atmosphere after synthesis as in Comparative Example 3 It was confirmed that it was more excellent. In addition, the positive electrode active materials prepared in Examples 1 to 2 of the present invention have a concentration gradient from the center of the particle to the surface, so that a sharp phase boundary region does not exist throughout the particle, thereby stabilizing the crystal structure, and thus the concentration. Thermal stability was further increased compared to Comparative Example 2 without a gradient.

Experimental Example  2: Synthesized Cathode active material  analysis

For the positive electrode active materials prepared in Example 2 and Comparative Example 2, crystal orientation was confirmed using a scanning electron microscope.

As a result of confirmation, as shown in FIG. 2A, the crystal grains of the positive electrode active material prepared in Example 2 showed crystal orientation in a direction perpendicular to the C axis, while the positive electrode active material prepared by the one-step firing of Comparative Example 2 shows FIG. 2B. As can be seen, it does not exhibit a specific orientation.

That is, it was confirmed that when the cathode active material precursor and Li ₂ CO ₃ were fired in two steps as in Example 2, a cathode active material having crystal orientation in a specific direction could be implemented.

Experimental Example  3: Life cycle evaluation

The lithium secondary batteries prepared in Example 2 and Comparative Example 1 were evaluated for life according to cycles, and the results are shown in FIG. 3.

Specifically, the lithium secondary battery having a battery capacity of 5 mAh prepared in Example 2 and Comparative Example 1 was charged at 25° C. to a constant current of 0.3 C at 4.25 V, and then charged at a constant voltage of 4.25 V, charging current When it reached 0.25 mA, charging was terminated. Thereafter, it was left for 10 minutes, and then discharged at a constant current of 0.3 C until 2.5 V was reached. The charging and discharging behavior was 1 cycle, and the capacity retention rate after 30 cycles of this cycle was measured.

As shown in FIG. 3, in the case of the lithium secondary battery of Example 2, while maintaining the capacity retention rate of about 95% while the cycle was repeated 30 times, the positive electrode active material had the same composition throughout the particles and did not exhibit a concentration gradient, The lithium secondary battery of Comparative Example 1 to which Li(Ni _0.88 Mn _0.09 Co _0.03 )O ₂ without anion substitution was applied exhibits a capacity retention rate of less than 80%, and the lithium secondary battery of Example 2 was used for the lithium secondary battery of Comparative Example 1. It was found that the cycle characteristics were excellent.

Experimental Example  4: Evaluation of resistance characteristics

The lithium secondary batteries prepared in Example 1 and Comparative Example 3 were evaluated for resistance characteristics and life characteristics, and the results are shown in FIG. 4.

Specifically, the lithium secondary battery having a battery capacity of 5 mAh prepared in Example 1 and Comparative Example 3 was charged at 25° C. to a constant current of 0.3 C at 4.25 V, and then left for 10 minutes, followed by 0.3 C constant current. And discharged until 2.5V.

First, the charge/discharge behavior was 1 cycle, and the capacity retention rate after repeating this cycle 30 times was measured. As shown in Figure 4, the lithium secondary battery prepared in Example 1 exhibited a capacity retention rate of 95% or more while the cycle was repeated 30 times. However, the lithium secondary battery of Comparative Example 3, which was prepared in the same manner as in Example 1, but did not perform additional heat treatment with oxygen after preparation of the active material, exhibited a capacity retention rate of less than 95% during the cycle of 30 cycles.

Subsequently, after charging and discharging the battery in the same manner as the capacity retention rate measurement, the charging and discharging behavior was 1 cycle, and after repeating this cycle 30 times, the rate of increase in resistance was measured based on the resistance measured at one discharge. .

As shown in Figure 4, in the case of the lithium secondary battery of Example 1, it was found that the resistance increase rate was improved compared to the lithium secondary battery of Comparative Example 3 while the cycle was repeated 30 times.

For the lithium secondary batteries prepared in Example 2 and Comparative Example 2, resistances at SOC 20%, 40%, 60%, 80%, and 100%, respectively, were measured. Specifically, the lithium secondary battery having a battery capacity of 5 mAh prepared in Example 2 and Comparative Example 2 was charged at 25° C. until 0.3C constant current became 4.25 V, and then, when 0.3 C constant current became 2.5 V Discharge was performed until and the resistance for each SOC was measured. The resistance measurement results for each SOC are shown in FIG. 5.

Referring to FIG. 5, the lithium secondary battery manufactured in Example 2 had the lowest resistance in all sections of SOC. The positive electrode active material of Example 2 not only has a concentration gradient in which nickel and manganese gradually change from the center of the particle to the surface, but also has a crystal orientation so that the structural stability of the active material is excellent, and the mobility of lithium ions contained in the active material Improved, the resistance is lower than the lithium secondary battery to which the active material of Comparative Example 2, which does not exhibit a concentration gradient and crystal orientation, is applied.

Experimental Example 5: At 4.5V  Life cycle evaluation

The lithium secondary batteries prepared in Example 1 and Comparative Example 2 were subjected to life evaluation according to cycles at high voltage (4.5 V), and the results are shown in FIG. 6.

Specifically, the lithium secondary battery having a battery capacity of 5 mAh prepared in Example 1 and Comparative Example 2 was charged at 25° C. until 0.5 V at a constant current of 0.5 C, and then left for 10 minutes, and then 0.1 C constant current. Was discharged until 2.5V. The charge/discharge behavior was 1 cycle, and after 50 cycles were repeated, the capacity retention rate of the battery after 50 cycles was measured.

As shown in FIG. 6, it was confirmed that the lithium secondary battery prepared in Example 1 exhibits an excellent capacity retention rate of 95% or more even after repeated charging and discharging of the battery 50 times at 4.5V. On the other hand, it was confirmed that the lithium secondary battery prepared in Comparative Example 2 had a lower capacity retention rate than that of Example 1 after repeated charging and discharging of the battery 50 times at 4.5V.

Claims (14)

It is a positive electrode active material that exists in a concentration gradient in which nickel and manganese gradually change from the center of the particle to the surface.
The positive electrode active material may include a central portion including a first lithium composite metal oxide having an average composition of Formula 1; And a surface portion including a second lithium composite metal oxide having an average composition represented by Chemical Formula 2 below.
The positive electrode active material has a peak at 235 °C or more when measuring the heat flow by differential scanning calorimetry, the positive electrode active material:
[Formula 1]
Li _1+x1 (Ni _a1 Mn _b1 Co _1-a1-b1-c1 Me _c1 )O _2-y1 A _y1
[Formula 2]
Li _1+x2 (Ni _a2 Mn _b2 Co _1-a2-b2-c2 Me _c2 )O _2-y2 A _y2
In Chemical Formulas 1 and 2,
Me is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo At least one doping element selected from the group consisting of,
A is PO ₄ ^3-, NO ₄ ^- and one or more anions selected from the group consisting of, ^-, CO ₃ ^2-, and BO ₃
0.8≤a1<1, 0<b1<0.2, 0<c1 ≤0.1, 0.8<a1+b1+c1<1, 0≤x1≤0.1, 0.0001<y1≤0.1,
0.1≤a2<0.8, 0.1<b2<0.9, 0<c2≤0.1, and 0.2<a2+b2+c2<1, 0≤x2≤0.1, 0.0001<y2≤0.1.
delete The method according to claim 1,
The grain of the positive electrode active material further comprises having a crystal orientation in a direction perpendicular to the C axis, the positive electrode active material.
The method according to claim 1,
The positive electrode active material, the positive electrode active material containing less than 1% by weight of lithium by-products.
The method according to claim 1,
A positive electrode active material further comprises a coating layer comprising at least one selected from the group consisting of B, Al, Hf, Nb, Ta, Mo, Si, Zn and Zr on the positive electrode active material.
The method according to claim 1,
The positive electrode active material has an average particle diameter (D ₅₀ ) of 4 μm to 20 μm.
Nickel, cobalt, manganese and doping elements Me (where Me is W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca , Containing at least one selected from the group consisting of Ce, Nb, Mg, B, and Mo), and nickel, cobalt, manganese, and doping at different concentrations from the first metal-containing solution. Preparing a second metal-containing solution containing the element Me;
The first metal-containing solution and the second metal-containing solution such that the mixing ratio of the first metal-containing solution and the second metal-containing solution is gradually changed from 100% by volume: 0% by volume to 0% by volume: 100% by volume. At the same time, the ammonium cation complexing agent, and an anion-containing basic compound to the mixture (wherein the anion is ^{_{PO 4 3-, NO 4 -,}} CO 3 2- , and BO ₃ ^- at least one anion being selected from the group consisting of a) By adding the nickel and manganese each independently preparing a positive electrode active material precursor exhibiting a concentration gradient gradually changing from the center of the particle to the surface;
Mixing the positive electrode active material precursor and a lithium-containing raw material and firing to synthesize a positive electrode active material; And,
A step of performing a heat treatment of the positive electrode active material at 600°C to 800°C under an oxygen atmosphere.
The method according to claim 7,
The firing of the positive electrode active material precursor and the lithium-containing raw material is carried out by one-step or two-step firing, a method for producing a positive electrode active material.
The method according to claim 8,
The one-step firing is to be carried out at 700 ℃ to 800 ℃, a method for producing a positive electrode active material.
The method according to claim 8,
The second-stage firing is a first firing to maintain the temperature from 25 ℃ to 400 ℃ at a heating rate of 2 ℃ / min to 5 ℃ / min; And a second firing to increase and maintain the temperature from 400°C to 800°C at a heating rate of 7°C/min to 10°C/min.
The method according to claim 7,
A method of manufacturing a positive electrode active material further comprising the step of washing the synthesized positive electrode active material at a temperature of 15° C. or less.
The method according to claim 7,
Further comprising the step of forming a coating layer comprising at least one selected from the group consisting of B, Al, Hf, Nb, Ta, Mo, Si, Zn and Zr on the positive electrode active material, the method of manufacturing a positive electrode active material.
The positive electrode for a lithium secondary battery comprising the positive electrode active material according to claim 1.
A lithium secondary battery comprising the positive electrode according to claim 13.

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