KR102175126B1 - A cathode active material, method of preparing the same, and lithium secondary battery comprising a cathode comprising the cathode active material - Google Patents

Abstract

The present invention is a core comprising a lithium transition metal oxide; And a coating layer disposed on the surface of the core and including a transition metal, wherein the coating layer includes a concentration gradient region in which the concentration of the transition metal changes in the direction of the core from the surface to less than 150 nm, a method of manufacturing the same, And it relates to a lithium secondary battery including a positive electrode including the same.

Description

A cathode active material, method of preparing the same, and lithium secondary battery comprising a cathode comprising the cathode active material}

It relates to a positive electrode active material, a method for manufacturing the same, and a lithium secondary battery including a positive electrode including the positive electrode active material.

Since the lithium secondary battery was commercialized by Sony in 1991, demand has been rapidly increasing in various fields ranging from small home appliances such as mobile IT products to medium and large electric vehicles and energy storage systems. In particular, low-cost, high-energy cathode materials are essential for mid- to large-sized electric vehicles and energy storage systems. Cobalt, the main raw material of single crystal LiCoO ₂ (LCO), which is a cathode active material currently commercially available, is expensive.

So, LiNi _x Co _y Mn _z O ₂ (NCM, x+y+z=1) and LiNi _x Co _y Al _z O, in which a part of Co is substituted with another transition metal instead of LCO as a cathode active material for a mid- to large-sized secondary battery. ₂ (NCA, x+y+z=1), a Ni-based cathode active material is used, and these NCM and NCA-based cathode active materials have the advantage that the price of nickel as a raw material is low and has a high reversible capacity. The Ni-based cathode active material is prepared by mixing a transition metal compound precursor synthesized by a coprecipitation method with a lithium source and then synthesizing it in a solid state. However, the Ni-based cathode material synthesized in this way exists in the form of secondary particles in which small primary particles are agglomerated, and there is a problem that micro-crack occurs inside the secondary particles during a long-term charging/discharging process. The microcracks cause a side reaction between the new interface of the positive electrode active material and the electrolyte, and as a result, deterioration of battery performance such as degradation of stability due to gas generation and degradation of battery performance due to depletion of the electrolyte is caused. In addition, an increase in electrode density (>3.3g/cc) is required to realize a high energy density, which causes the collapse of secondary particles, causing electrolyte depletion due to side reactions with the electrolyte, causing a sharp decline in initial lifespan. Consequently, it means that the Ni-based cathode active material in the form of secondary particles synthesized by the conventional co-precipitation method cannot realize high energy density.

In order to solve the problems of the above-described secondary particle type Ni-based positive electrode active material, the development of a single-particle type Ni-based positive electrode active material has been recently made. The single crystal type Ni-based positive electrode active material does not cause particle collapse when the electrode density is increased (> 3.3g/cc) to realize high energy density, so it can realize excellent electrochemical performance. However, regardless of the shape of the particles, the Ni-based positive electrode active material may deteriorate battery stability due to structural and/or thermal instability due to unstable Ni ³⁺ and Ni ⁴⁺ ions during electrochemical evaluation. Therefore, in order to develop a high-energy lithium secondary battery, it is necessary to stabilize unstable Ni ions on the surface of the positive electrode active material together with the development of a single crystal Ni-based positive electrode active material.

In accordance with one aspect, a core comprising a lithium transition metal oxide; And a coating layer disposed on the surface of the core and including a transition metal, and comprising a concentration gradient region in which the concentration of a transition metal, for example, Mn or Co decreases in the direction of the core from the surface of the coating layer to less than 150 nm. Is to provide.

According to one aspect,

A core comprising a lithium transition metal oxide; And

A coating layer disposed on the surface of the core and including a transition metal;

Including,

The coating layer is provided with a positive electrode active material including a concentration gradient region in which the concentration of the transition metal changes in the direction of the core from the surface to less than 150 nm.

According to the other side,

Preparing a lithium transition metal oxide; And

There is provided a method of manufacturing a positive electrode active material comprising; providing a coating layer containing a transition metal on the surface of the lithium transition metal oxide.

According to another aspect,

A positive electrode including the positive electrode active material; cathode; And there is provided a lithium secondary battery including an electrolyte.

According to one aspect, by including a coating layer including a concentration gradient region on the surface of the lithium transition metal oxide, the content of unstable Ni ions on the surface of the active material particles is reduced, thereby improving structural/thermal stability, and improving high energy density and long life characteristics. Can have.

1 is a SEM photograph of a cathode active material prepared in Examples 1, 2, and Comparative Example 1.
2 is an average particle size distribution curve of the positive electrode active material prepared in Example 1, Example 2, and Comparative Example 1.
3 is a SEM photograph of the positive electrode active material prepared in Example 3, Example 4, and Comparative Example 2.
4 is an average particle size distribution curve of the positive electrode active material prepared in Example 3, Example 4, and Comparative Example 2.
5A is a high resolution transmission electron microscopy (HR-TEM) photograph and energy dispersive X-ray spectroscopy (EDX) graph of the positive electrode active material obtained in Comparative Example 1.
5B is a graph showing the ratio of the transition metal content by position to the positive electrode active material obtained in Comparative Example 1.
6A is a high resolution transmission electron microscopy (HR-TEM) photograph and energy dispersive X-ray spectroscopy (EDX) graph of the positive electrode active material obtained in Example 1.
6B is a graph showing the ratio of the transition metal content by position to the positive electrode active material obtained in Example 1. FIG.
7A is a high resolution transmission electron microscopy (HR-TEM) photograph and energy dispersive X-ray spectroscopy (EDX) graph of the positive electrode active material obtained in Example 2.
7B is a graph showing the ratio of the transition metal content by position to the positive electrode active material obtained in Example 2.
8A is a high resolution transmission electron microscopy (HR-TEM) photograph and energy dispersive X-ray spectroscopy (EDX) graph of the positive electrode active material obtained in Comparative Example 2.
8B is a graph showing the ratio of the transition metal content by position to the positive electrode active material obtained in Comparative Example 2.
9A is a high resolution transmission electron microscopy (HR-TEM) photograph and energy dispersive X-ray spectroscopy (EDX) graph of the positive electrode active material obtained in Example 3.
9B is a graph showing the ratio of the transition metal content by position to the positive electrode active material obtained in Example 3. FIG.
10A is a high resolution transmission electron microscopy (HR-TEM) photograph and energy dispersive X-ray spectroscopy (EDX) graph of the positive electrode active material obtained in Example 4.
10B is a graph showing the ratio of the transition metal content by position to the positive electrode active material obtained in Example 4.
11 is a graph showing capacity retention rates for 100 cycles of half cells prepared in Examples 5, 6, and 7;
12 is a graph showing capacity retention rates for 100 cycles of half cells prepared in Examples 7, 8 and Comparative Example 8. FIG.
13 is an initial charging and discharging curves of half-cells prepared in Examples 7, Comparative Examples 9, and 10.
14 is an initial charging and discharging curves of half-cells prepared in Example 8, Comparative Example 11, and Comparative Example 12.
15 is a schematic diagram of a lithium battery according to an exemplary embodiment.
<Explanation of symbols for major parts of drawings>
1: lithium battery 2: negative electrode
3: anode 4: separator
5: battery case 6: cap assembly

The present inventive concept described below may apply various transformations and may have various embodiments. Specific embodiments are illustrated in the drawings and will be described in detail in the detailed description. However, this is not intended to limit the present creative idea to a specific embodiment, it is to be understood as including all transformations, equivalents or substitutes included in the technical scope of the present creative idea.

The terms used below are only used to describe specific embodiments, and are not intended to limit the present inventive idea. Singular expressions include plural expressions unless the context clearly indicates otherwise. Hereinafter, terms such as "comprises" or "have" are intended to indicate the existence of features, numbers, steps, actions, components, parts, components, materials, or a combination thereof described in the specification. It is to be understood that the above other features, or the possibility of the presence or addition of numbers, steps, actions, components, parts, components, materials, or combinations thereof, are not excluded in advance. "/" used below may be interpreted as "and" or "or" depending on the situation.

In the drawings, the thickness is enlarged or reduced in order to clearly express various layers and regions. The same reference numerals are assigned to similar parts throughout the specification. Throughout the specification, when a part such as a layer, film, region, plate, etc. is said to be "on" or "on" another part, this includes not only the case directly above the other part, but also the case where there is another part in the middle. . Throughout the specification, terms such as first and second may be used to describe various components, but the components should not be limited by terms. The terms are used only for the purpose of distinguishing one component from another.

Hereinafter, a positive electrode active material according to exemplary embodiments, a method of manufacturing the same, and a lithium secondary battery including a positive electrode including the same will be described in more detail.

A positive electrode active material according to an embodiment includes a core comprising a lithium transition metal oxide; And a coating layer disposed on the surface of the core and including a transition metal, wherein the coating layer includes a concentration gradient region in which the concentration of the transition metal changes in the direction of the core from the surface to less than 150 nm.

As a cathode active material for a high-energy lithium secondary battery, a Ni-based cathode active material containing a high concentration of Ni ("high-nickel cathode active material") is attracting attention. High-nickel-based cathode active material has a higher capacity as the content of nickel among the transition metals constituting the cathode active material is higher than that of other transition metals, but structural instability due to unstable Ni ³⁺ and Ni ⁴⁺ ions on the surface of the cathode active material There is a limitation of having In order to solve such structural instability, various techniques for modifying the surface of a positive electrode active material have been studied.

In this regard, the inventors of the present invention completed the present invention in view of stabilizing unstable Ni ions by introducing a coating layer including a concentration gradient region having a transition metal concentration gradient on the surface of a high-nickel cathode active material. .

The positive electrode active material according to an aspect of the present invention includes a coating layer including a transition metal concentration gradient region, thereby improving structural and thermal stability, and as a result, a battery including such a positive electrode active material has a high energy density and long lifespan. Can have characteristics. In addition, by protecting the surface of the core particles by the coating layer, the active reaction area is reduced and the interfacial stability with the electrolyte is increased, so that the thermal stability of the electrode may be improved.

The coating layer includes Mn and/or Co, and the coating layer includes a concentration gradient in which the concentration of Mn or Co decreases from the surface of the coating layer toward the core. In other words, the concentration of Mn or Co is highest on the surface of the coating layer, and has a concentration gradient gradually decreasing from the surface toward the center of the core by 150 nm. By having such a concentration gradient, it is possible to introduce a coating layer containing a larger amount of Co or Mn on the surface than an active material having a concentration gradient from the surface of the active material to the center of the core, and as a result, a larger amount of unstable present on the surface. By stabilizing Ni ions, the stability of the active material can be improved.

When the coating layer includes a concentration gradient region, the concentration of unstable Ni ions present on the surface of the high-nickel-based positive electrode active material can be reduced. Therefore, the concentration of Ni may be the lowest on the surface of the coating layer, and the structural and thermal stability of the high-nickel cathode active material is improved.

The coating layer may include Mn and/or Co, and may include a concentration gradient region in which the concentration of Mn or Co decreases in the direction of the core from the surface of the coating layer to 100 nm or less. For example, from the surface of the coating layer to 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, or 50 nm or less, the concentration gradient region in which the concentration of Mn or Co decreases in the direction of the core may be included.

In the positive electrode active material, the concentration of the transition metal in the core is constant. For example, the coating layer of the positive electrode active material includes a transition metal concentration gradient region, and the concentration of the transition metal in the core is constant.

In addition, since the coating layer includes a concentration gradient region having a constant gradient of the transition metal concentration, there is no abrupt phase boundary region, and thus structural and thermal stability may be obtained.

The positive electrode active material according to an embodiment may contain a small amount of phosphorus (P) as a doping element.

The lithium transition metal oxide may be a compound represented by the following Formula 1:

<Formula 1>

Li _x P _y MO ₂

In Formula 1,

M is one or more transition metals,

0.98≤x≤1.02, 0<y<0.01

The M may include at least one transition metal selected from Ni, Co, Mn, Al, Mg, V, and Ti.

For example, the M may include one or more transition metals selected from Ni, Co, Mn, and Al, but is not limited thereto.

The x may be 0.99≦x≦1.02.

The y may be 0<y≤0.009, 0<y≤0.008, or 0<y≤0.007.

The lithium transition metal oxide may be a compound represented by Formula 2 below.

<Formula 2>

Li _x P _y Ni _1-z M1 _z O ₂

In Formula 2,

M1 is one or more transition metals selected from Co, Mn, Al, Mg, V, and Ti,

0.98≤x≤1.02, 0<y<0.01, 0<z<1

M1 includes one or more transition metals selected from Co, Mn, Al, Mg, V, and Ti, and may be 0<z≤0.5.

M1 includes one or more transition metals selected from Co, Mn, Al, Mg, V, and Ti, and may be 0<z≤0.4.

M1 includes at least one transition metal selected from Co, Mn, Al, Mg, V, and Ti, and may be 0<z≤0.3.

M1 includes at least one transition metal selected from Co, Mn, Al, Mg, V, and Ti, and may be 0<z≤0.2.

In Formula 2, x may be 0.99≦x≦1.02.

In Formula 2, y may be 0<y≤0.009, 0<y≤0.008, or 0<y≤0.007.

The positive electrode active material represented by Chemical Formula 2 does not replace other elements in the crystal structure of the nickel-based single crystal single-particle positive electrode active material, but has a structure in which a P element is doped in an empty tetrahedral position. Therefore, doping of the P element does not affect the stoichiometric value of Li or transition metals such as Ni and Co. As a result, the single crystal nickel-based positive electrode active material represented by Chemical Formula 2 may have a composition that deviates stoichiometrically through the introduction of the P element.

The positive electrode active material represented by Formula 2 may be doped with P of 0.007 mol% or less.

According to one embodiment, the P element may be located at a tetrahedral site in a layered structure of a single crystal. The tetrahedral site may be an empty site in the layered structure of the single crystal. Since the P element is located in the empty tetrahedron site, the amount of residual lithium is reduced. Without being bound by theory, it is possible to reduce the residual lithium by suppressing the release of Li due to the formation of oxygen defects in the crystal structure in the first heat treatment step at high temperature by partially replacing P in the empty tetrahedron site in the crystal structure. . The released Li may react with CO ₂ and moisture in the air at high temperature to form a residual lithium compound. However, P present in the empty tetrahedron in the structure stabilizes the oxygen framework in the anode structure, thereby reducing the residual lithium by suppressing the formation of oxygen defects at high temperatures.

According to one embodiment, the P element may exist inside a single crystal. For example, the P element is not present on the surface of the single crystal positive electrode active material, but may exist inside the single crystal positive electrode active material.

Since the P element is located at a tetrahedral site inside the single crystal, phase transition is alleviated during intercalation/deintercalation of lithium ions due to charge and discharge, thereby contributing to the phase stability of the positive electrode active material.

The lithium transition metal oxide may be a compound represented by Formula 3:

<Formula 3>

Li _x P _y Ni _1-α-z M1 _z M2 _α O ₂

In Formula 3,

M1 and M2 are each independently at least one transition metal selected from Co, Mn, Al, Mg, V, and Ti,

M1 and M2 are different from each other,

0.98≦x≦1.02, 0<y<0.01, 0<α<1, 0<z<1, and 0<α+z<1.

The lithium transition metal oxide may be a compound represented by Formula 4 below;

<Formula 4>

Li _x P _y Ni _1-α-z Co _z M2 _α O ₂

In Formula 4,

M2 is at least one transition metal selected from Mn, Al, Mg, V, and Ti,

0.98≦x≦1.02, 0<y<0.01, 0<α<1, 0<z<1, and 0<α+z≦0.5.

The lithium transition metal oxide may be a compound represented by any one of the following Formulas 5 to 7:

<Formula 5>

_{Li x 'P y' Ni 1} -α'-z 'Co z' Mn α 'O 2

<Formula 6>

Li _x'' P _y'' Ni _1-α''-z'' Co _z'' Al _α'' O ₂

<Formula 7>

Li _x''' P _y''' Ni _1-z''' Co _z''' O ₂

In Formulas 5 to 7,

0.98≤x'≤1.02, 0<y'<0.01, 0<α'≤0.3, and 0<z'≤0.3,

0.98≤x''≤1.02, 0<y''<0.01, 0<α''≤0.05, and 0<z''≤0.3,

0.98≤x'''≤1.02, 0<y'''<0.01, and 0<z'''≤0.2.

The average particle diameter (D50) of the positive electrode active material is 0.1 μm to 20 μm. The average particle diameter of the positive electrode active material is not limited to the above range, and includes arbitrary values selected from the above range. When the average particle diameter of the positive electrode active material falls within the above range, a predetermined energy density per volume may be achieved.

When the average particle diameter of the positive electrode active material exceeds 20 μm, the charge/discharge capacity rapidly decreases, and when it is less than 0.1 μm, it is difficult to obtain a desired energy density per volume.

The core is a single crystal. Here, a single crystal has a concept that is distinct from a single particle. A single particle refers to a particle formed of one particle regardless of the type and number of crystals therein, and a single crystal means that a single crystal is included in the particle. Since the core has a single crystal, the structural stability is very high.

The core is a single particle. Here, a single particle is a concept that is distinguished from a secondary particle that is an aggregate of a plurality of single particles. Since the positive electrode active material has a single particle shape, it is possible to prevent the particles from being broken even at a high electrode density. Accordingly, it is possible to realize a high energy density of the positive electrode active material. Since the core is a single particle, it is possible to achieve high energy density by preventing breakage during rolling, and it is possible to prevent deterioration in life due to breakage of the particles.

The concentration of Ni in the coating layer is less than the concentration of Ni in the core. As a result, the formation of an electrochemically inert phase formed by unstable Ni ions can be suppressed, and life stability can be improved. In addition, a stable positive electrode SEI layer can be formed by suppressing side reactions between Ni ions and an electrolyte on the surface of the positive electrode active material, thereby promoting diffusion of lithium ions.

Hereinafter, a method of manufacturing a cathode active material according to an aspect will be described in detail.

A method of manufacturing a positive electrode active material according to an embodiment comprises: preparing a lithium transition metal oxide; And providing a coating layer including a transition metal on the surface of the lithium transition metal oxide.

Preparing the lithium transition metal oxide includes mixing a molar equivalent of a Li-containing precursor, a P-containing precursor, and an M-containing precursor corresponding to the compound represented by Formula 1 below.

<Formula 1>

Li _x P _y MO ₂

In Formula 1,

M is one or more transition metals,

0.98≤x≤1.02, 0<y<0.01.

The mixing step is mixed by a dry mechanical mixing method. The mechanical mixing is to form a uniform mixture by pulverizing and mixing substances to be mixed by applying a mechanical force. Mechanical mixing is a mixing device such as a ball mill, a planetary mill, a stirred ball mill, a vibrating mill, etc. using chemically inert beads. It can be done using At this time, in order to maximize the mixing effect, alcohol such as ethanol and higher fatty acids such as stearic acid may be selectively added in small amounts.

The mechanical mixing is carried out in an oxidizing atmosphere, which is to prevent reduction of the transition metal in a transition metal source (eg, Ni compound), thereby realizing structural stability of the active material.

The Li-containing precursor may include lithium hydroxide, oxide, nitride, carbonate, or a combination thereof, but is not limited thereto. For example, the Li-containing precursor may be LiOH or Li ₂ CO ₃ .

The P-containing precursor includes all phosphorus-containing compounds capable of providing the P element. For example, the P-containing precursor may be NH ₄ HPO ₄ .

The M-containing precursor may include a transition metal hydroxide, oxide, nitride, carbonate, or a combination thereof, but is not limited thereto. For _{example, NiO, NiCO 3, MnO,} MnCO 3, CoO, CoCO 3, may be an AlO, AlCO _3, or a combination thereof.

After the mixing step, it may include a step of heat treatment. The heat treatment step may include a first heat treatment step and a second heat treatment step. The first heat treatment step and the second heat treatment step may be performed continuously or may have a rest period after the first heat treatment step. In addition, the first heat treatment step and the second heat treatment step may be performed in the same chamber or may be performed in different chambers.

The heat treatment temperature in the first heat treatment step may be higher than the heat treatment temperature in the second heat treatment step.

The first heat treatment step may be performed at a heat treatment temperature of 800°C to 1200°C. The heat treatment temperature may be, for example, 850°C to 1200°C, 860°C to 1200°C, 870°C to 1200°C, 880°C to 1200°C, 890°C to 1200°C, or 900°C to 1200°C, but limited thereto It does not, and includes all the ranges configured by selecting any two points within the range.

In the second heat treatment step, the heat treatment temperature may be performed at 700°C to 800°C. The heat treatment temperature is 710 ℃ to 800 ℃, 720 ℃ to 800 ℃, 730 ℃ to 800 ℃, 740 ℃ to 800 ℃, 750 ℃ to 800 ℃, 700 ℃ to 780 ℃, 700 ℃ to 760 ℃, 700 ℃ to 750 ℃, or 700 ℃ to 730 ℃ may be, but is not limited thereto, and includes all ranges configured by selecting any two points within the above range.

According to an embodiment, the heat treatment time in the first heat treatment step may be shorter than the heat treatment time in the second heat treatment step.

For example, the heat treatment time in the first heat treatment step may be 3 hours to 5 hours, 4 hours to 5 hours, or 3 hours to 4 hours, but is not limited thereto, and any two points within the above range are selected. It includes all the ranges constructed by this.

For example, the heat treatment time in the second heat treatment step may be 10 hours to 20 hours, 10 hours to 15 hours, but is not limited thereto, and includes all ranges configured by selecting any two points within the range. .

The first heat treatment step may include performing heat treatment at a heat treatment temperature of 800°C to 1200°C for 3 to 5 hours.

The second heat treatment step may include performing heat treatment at a heat treatment temperature of 700°C to 800°C for 10 to 20 hours.

In the first heat treatment step, the lithium transition metal oxide forms the positive electrode active material having a layered structure and at the same time causes the growth of particles, thereby forming a single crystal shape. In the first heat treatment step, the primary particles in the lithium transition metal oxide in the form of secondary particles rapidly grow and are fused to each other while revealing the inside of the primary particles as they cannot withstand the stress between the particles, so that the single crystal positive active material for secondary batteries is It is thought to be formed. The second heat treatment step increases the crystallinity of the layered structure generated in the first heat treatment step by performing heat treatment at a lower temperature in the first heat treatment step for a long time. Through the first and second heat treatment steps, a single phase, single crystal, and single particle nickel-based positive electrode active material may be obtained.

According to one embodiment, the lithium transition metal oxide manufactured by the above manufacturing method is a single crystal or a single particle, and the single crystal may have a layered structure. In addition, the average particle diameter of the lithium transition metal oxide may be 0.1㎛ to 20㎛.

In addition, the positive electrode active material prepared by the method of manufacturing the positive electrode active material was able to obtain a positive electrode active material in which P is partially located at the place of an empty tetrahedron in a single crystal structure, and through this, it is possible to obtain battery stability by suppressing phase transition during charging/discharging. And achieved long life

Providing the coating layer includes mixing the lithium transition metal oxide and the transition metal precursor, and performing heat treatment.

The transition metal precursor may be an oxide, hydroxide, nitride, carbonate, or a combination of Mn or Co.

After mixing the lithium transition metal oxide and the transition metal precursor, the heat treatment may be performed at a heat treatment temperature of 400° C. to 800° C. for a heat treatment time of 1 to 5 hours.

The heat treatment temperature is, for example, 400 ℃ to 750 ℃, 400 ℃ to 700 ℃, 400 ℃ to 650 ℃, 400 ℃ to 600 ℃, 450 ℃ to 800 ℃, 500 ℃ to 800 ℃, 550 ℃ to 800 ℃, Or it may be 600 ℃ to 800 ℃. Since the heat treatment is performed at a heat treatment temperature of 400° C. to 800° C., a concentration gradient of the transition metal can be formed in the coating layer while maintaining the crystal structure of the single crystal single particle lithium transition metal oxide.

The heat treatment time may be, for example, 1 to 4 hours, 1 to 3 hours, 2 to 5 hours, 2 to 4 hours, but is not limited thereto, and any time during which the coating layer can be sufficiently formed.

According to another aspect, a positive electrode including the positive electrode active material described above is provided.

According to another aspect, the anode; cathode; And there is provided a lithium secondary battery comprising; an electrolyte.

The positive electrode and a lithium secondary battery including the same may be manufactured by the following method.

First, the anode is prepared.

For example, a cathode active material composition in which the above-described cathode active material, conductive material, binder, and solvent are mixed is prepared. The positive electrode active material composition is directly coated on a metal current collector to prepare a positive electrode plate. Alternatively, the positive electrode active material composition may be cast on a separate support, and then a film peeled from the support may be laminated on a metal current collector to prepare a positive electrode plate. The anode is not limited to the shapes listed above, but may be in a shape other than the above shape.

Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon black; Conductive tubes such as carbon nanotubes; Conductive whiskers such as fluorocarbon, zinc oxide, and potassium titanate; Conductive metal oxides such as titanium oxide; And the like may be used, but are not limited thereto, and any material that can be used as a conductive material in the art may be used.

As the binder, vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene, mixtures thereof, metal salts, or styrene butadiene Rubber-based polymers and the like may be used, but are not limited thereto, and any one that can be used as a binder in the art may be used. As another example of the binder, lithium salt, sodium salt, calcium salt, or Na salt of the above-described polymer may be used.

As the solvent, N-methylpyrrolidone, acetone, or water may be used, but are not limited thereto, and any solvent that can be used in the art may be used.

The contents of the positive electrode active material, the conductive material, the binder, and the solvent are the levels commonly used in lithium batteries. One or more of the conductive material, the binder, and the solvent may be omitted depending on the use and configuration of the lithium battery.

Next, the cathode is prepared.

For example, an anode active material composition is prepared by mixing an anode active material, a conductive material, a binder, and a solvent. The negative electrode active material composition is directly coated and dried on a metal current collector having a thickness of 3 μm to 500 μm to prepare a negative electrode plate. Alternatively, after the negative active material composition is cast on a separate support, a film peeled from the support may be laminated on a metal current collector to prepare a negative electrode plate.

The negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes to the battery, and for example, copper, nickel, or copper surface-treated with carbon may be used.

The anode active material may be any material that can be used as an anode active material for lithium batteries in the art. For example, it may include at least one selected from the group consisting of lithium metal, a metal alloyable with lithium, a transition metal oxide, a non-transition metal oxide, and a carbon-based material.

For example, the metal alloyable with lithium is Si, Sn, Al, Ge, Pb, Bi, Sb Si-Y alloy (wherein Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth Element or a combination element thereof, not Si), Sn-Y alloy (the Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element, or a combination element thereof, not Sn ), etc. The element Y is Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, It may be Se, or Te.

For example, the transition metal oxide may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, or the like.

For example, the non-transition metal oxide may be SnO ₂ , SiO _x (0<x<2), or the like.

The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite such as amorphous, plate-shaped, flake, spherical or fibrous natural graphite or artificial graphite, and the amorphous carbon is soft carbon (low temperature calcined carbon) or hard carbon (hard carbon). carbon), mesophase pitch carbide, calcined coke, or the like.

In the negative electrode active material composition, the conductive material, the binder, and the solvent may be the same as those of the positive electrode active material composition.

The contents of the negative electrode active material, the conductive material, the binder, and the solvent are generally used in lithium batteries. One or more of the conductive material, the binder, and the solvent may be omitted depending on the use and configuration of the lithium battery.

Next, a separator to be inserted between the positive and negative electrodes is prepared.

Any of the separators can be used as long as they are commonly used in lithium batteries. Those having low resistance to ion migration of the electrolyte and excellent in the ability to impregnate the electrolyte may be used. The separator may be a single film or a multilayer film, for example, as selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), or a combination thereof. , It may be in the form of a non-woven fabric or a woven fabric. Further, a mixed multilayer film such as a polyethylene/polypropylene two-layer separator, a polyethylene/polypropylene/polyethylene three-layer separator, a polypropylene/polyethylene/polypropylene three-layer separator, and the like may be used. For example, a woundable separator such as polyethylene or polypropylene may be used for a lithium ion battery, and a separator having excellent organic electrolyte impregnation ability may be used for a lithium ion polymer battery. For example, the separator may be manufactured according to the following method.

A polymer resin, a filler, and a solvent are mixed to prepare a separator composition. The separator composition may be directly coated and dried on an electrode to form a separator. Alternatively, after the separator composition is cast and dried on a support, a separator film peeled off from the support may be laminated on an electrode to form a separator.

The polymer resin used for manufacturing the separator is not particularly limited, and all materials used for the bonding material of the electrode plate may be used. For example, vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or mixtures thereof may be used.

Next, the electrolyte is prepared.

For example, the electrolyte may be an organic electrolyte. In addition, the electrolyte may be a solid. For example, boron oxide, lithium oxynitride, etc. may be used, but the present invention is not limited thereto, and any solid electrolyte may be used as long as it can be used as a solid electrolyte in the art. The solid electrolyte may be formed on the negative electrode by a method such as sputtering.

For example, the organic electrolyte may be prepared by dissolving a lithium salt in an organic solvent.

The organic solvent may be used as long as it can be used as an organic solvent in the art. Cyclic carbonates, such as propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, and vinylene carbonate, for example; Chain carbonates such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate and dibutyl carbonate; Esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone; Ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, and 2-methyltetrahydrofuran; Nitriles such as acetonitrile; And amides such as dimethylformamide. These can be used alone or in combination of a plurality of them. For example, a solvent in which a cyclic carbonate and a chain carbonate are mixed can be used.

In addition, a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide and polyacrylonitrile with an electrolyte solution, or LiI, Li ₃ N, Li _x Ge _y P _z S _α , Li _x Ge _y P _z S _α X _δ ( Inorganic solid electrolytes such as X=F, Cl, Br) can be used.

The lithium salt may also be used as long as it can be used as a lithium salt in the art. For example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (where x,y are natural numbers), LiCl, LiI, or a mixture thereof.

As shown in FIG. 15, the lithium battery 1 includes a positive electrode 3, a negative electrode 2, and a separator 4. The positive electrode 3, the negative electrode 2 and the separator 4 described above are wound or folded to be accommodated in the battery case 5. Subsequently, an organic electrolyte is injected into the battery case 5 and sealed with a cap assembly 6 to complete the lithium battery 1. The battery case 5 may be a cylindrical shape, a square shape, a pouch type, a coin type, or a thin film type. For example, the lithium battery 1 may be a thin film type battery. The lithium battery 1 may be a lithium ion battery.

A separator may be disposed between the positive electrode and the negative electrode to form a battery structure. After the battery structure is stacked in a bi-cell structure, it is impregnated with an organic electrolyte, and the resulting product is accommodated in a pouch and sealed to complete a lithium ion polymer battery.

In addition, a plurality of battery structures are stacked to form a battery pack, and the battery pack can be used in all devices requiring high capacity and high output. For example, it can be used for laptop computers, smart phones, electric vehicles, and the like.

In addition, since the lithium battery has excellent life characteristics and high rate characteristics, it can be used in an electric vehicle (EV). For example, it can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). In addition, it can be used in a field requiring a large amount of power storage. For example, it can be used for electric bicycles, power tools, power storage systems, and the like.

The present invention will be described in more detail through the following Preparation Examples, Examples and Comparative Examples. However, the examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[Example]

(Synthesis of lithium transition metal oxide)

Manufacturing Example 1

100 g of Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ and 0.2 g of (NH ₄ ) ₂ HPO ₄ and 45.8 g of Li ₂ CO ₃ were mechanically mixed for about 15 minutes, followed by 4 hours at 1150°C and 10 at 780°C. A lithium transition metal oxide of single crystal LiP _0.007 Ni _0.5 Co _0.2 Mn _0.3 O ₂ was synthesized through time firing.

Manufacturing Example 2

100 g of Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ and 0.2 g of (NH ₄ ) ₂ HPO ₄ phosphate and 45.2 g of Li ₂ CO ₃ were mechanically mixed for about 15 minutes, and then at 1050°C for 4 hours and at 780°C. A lithium transition metal oxide of single crystal LiP _0.007 Ni _0.8 Co _0.1 Mn _0.1 O ₂ was synthesized through firing for 10 hours.

(Manufacture of positive electrode active material)

Example 1

0.5 g of cobalt acetate was dissolved in 30 g of ethanol, and then 30 g of LiP _0.007 Ni _0.5 Co _0.2 Mn _0.3 O ₂ lithium transition metal oxide obtained in Preparation Example 1 was added. After stirring for 30 minutes at 500 rpm for uniform dispersion of the lithium transition metal oxide, the ethanol solvent is evaporated at about 80 ^o C. The remaining powder was calcined at 750° C. for 3 hours to obtain a single crystal LiP _0.007 Ni _0.5 Co _0.2 Mn _0.3 O ₂ including a coating layer to which a Co concentration gradient was introduced.

Example 2

Synthesized in the same manner as in Example 1, except that 0.5 g of manganese acetate was used instead of 0.5 g of cobalt acetate, and a single crystal LiP including a coating layer into which the Mn concentration gradient was introduced _0.007 Ni _0.5 Co _0.2 Mn _0.3 O ₂ was obtained.

Example 3

After 0.5 g of cobalt acetate was dissolved in 30 g of ethanol, 30 g of a lithium transition metal oxide of single crystal LiP _0.007 Ni _0.8 Co _0.1 Mn _0.1 O ₂ obtained in Preparation Example 2 was added. After stirring for 30 minutes at 500 rpm for uniform dispersion of the lithium transition metal oxide, the ethanol solvent is evaporated at about 80 ^o C. The remaining powder was calcined at 750° C. for 3 hours to synthesize a single crystal LiP _0.007 Ni _0.8 Co _0.1 Mn _0.1 O ₂ including a coating layer to which a Co concentration gradient was introduced.

Example 4

Synthesized in the same manner as in Example 3, except that 0.5 g of manganese acetate was used instead of 0.5 g of cobalt acetate, and a single crystal LiP including a coating layer into which the Mn concentration gradient was introduced _0.007 Ni _0.8 Co _0.1 Mn _0.1 O ₂ was obtained.

Comparative Examples 1 and 2

The lithium transition metal oxide of single crystal LiP _0.007 Ni _0.5 Co _0.2 Mn _0.3 O _{2 and} the lithium transition metal oxide of single crystal LiP _0.007 Ni _0.8 Co _0.1 Mn _0.1 O _{2 obtained} in Preparation Examples 1 and 2 of Comparative Examples 1 and 2, respectively. It was used as a positive electrode active material.

Comparative Example 3

Synthesized in the same manner as in Example 3, except that the content of cobalt acetate was 1 g instead of 0.5 g, and a single crystal LiP including a coating layer having a Co concentration gradient region of 150 nm _0.007 Ni _0.8 Co _0.1 Mn _0.1 O ₂ Was synthesized.

Comparative Example 4

Synthesized in the same manner as in Example 3, except that the content of cobalt acetate was 1.5 g instead of 0.5 g, and a single crystal LiP including a coating layer having a Co concentration gradient region of 200 nm _0.007 Ni _0.8 Co _0.1 Mn _0.1 O ₂ was synthesized.

Comparative Example 5

Synthesized in the same manner as in Example 3, except that 1 g of manganese acetate was added instead of cobalt acetate, and a single crystal LiP _0.07 Ni _0.8 Co _0.1 Mn _0.1 O ₂ including a coating layer having a Mn concentration gradient region of 150 nm was synthesized. I did.

Comparative Example 6

Synthesized in the same manner as in Example 3, except that 1.5 g of manganese acetate was added instead of cobalt acetate, and a single crystal LiP _0.007 Ni _0.8 Co _0.1 Mn _0.1 O ₂ including a coating layer having a Mn concentration gradient region of 150 nm was prepared. Synthesized.

(Creation of Coin Cell)

Example 5

The cathode active material obtained in Example 1: the conductive material: the binder was mixed in a weight ratio of 94:3:3 to prepare a slurry. Here, carbon black was used as the conductive material, and polyvinylidene fluoride (PVdF) was dissolved in an N-methyl-2-pyrrolidone solvent and used as the binder.

The slurry was uniformly coated on an Al current collector and dried at 110° C. for 2 hours to prepare a positive electrode. The loading level of the electrode plate was 11.0 mg/cm ² and the electrode density was 3.6 g/cc.

Using the positive electrode thus prepared as a working electrode, a lithium foil used as a counter electrode, and the EC / EMC / DEC as a lithium salt in a mixed solvent in a volume ratio of 3/4/3 to the concentration of 1.3M LiPF ₆ A CR2032 half cell was fabricated according to a commonly known process using a liquid electrolyte added as possible.

Example 6 to 8

In place of the positive electrode active material obtained in Example 1, a half cell was manufactured in the same manner as in Example 5, except that the positive electrode active materials obtained in Examples 2 to 4 were used respectively.

Comparative example 7 to 12

A half cell was manufactured in the same manner as in Example 5, except that the positive electrode active material obtained in Comparative Examples 1 to 6 was used instead of the positive electrode active material obtained in Example 1.

Evaluation Example 1: Evaluation of particle size of positive electrode active material

SEM (Verios 460, FEI) photos were taken for the positive electrode active materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2, and the average particle size was measured (Cilas1090, Scinco), and the results are shown in FIGS. 1 to 4 . In addition, the size of the particle size is shown in Tables 1 and 2 below.

Referring to FIGS. 1 and 2, it can be confirmed through SEM photographs that the positive electrode active material of Examples 1 and 2 in which the coating layer was introduced and the positive electrode active material of Comparative Example 1 to which the coating layer was not introduced had no change in shape, and FIG. According to this, it can be seen that the change in the particle size distribution did not occur substantially, and thus it can be seen that the heat treatment for introducing the coating layer does not cause the growth of additional core particles. 3 and 4 in Examples 3 and 4, and Comparative Example 2, the same description as discussed in FIGS. 1 and 2 is possible.

D _min (㎛) D ₁₀ (㎛) D ₅₀ (㎛) D ₉₀ (㎛) D _max (㎛) Example 1 1.1 3.2 6.6 10.6 18.2 Example 2 1.1 3.3 6.5 10.4 18.4 Comparative Example 1 1.1 3.2 6.4 10.5 19.1

D _min (㎛) D ₁₀ (㎛) D ₅₀ (㎛) D ₉₀ (㎛) D _max (㎛) Example 3 1.2 4.1 7.6 11.2 20.8 Example 4 1.0 4.2 7.6 11.7 20.8 Comparative Example 2 1.1 4.0 7.5 11.4 18.8

Evaluation Example 2: Evaluation of the transition metal concentration on the surface of the positive electrode active material

The positive electrode active materials obtained in Examples 1 to 4 and Comparative Examples 1 and 2 were photographed using a high resolution transmission electron microscopy (HR-TEM), and energy dispersive x-ray spectroscopy (energy Dispersive X-ray spectroscopy (EDX)) analysis was performed. The results are shown in FIGS. 5 to 10.

Referring to FIGS. 5A and 5B and FIGS. 8A and 8B, it can be seen that the positive electrode active materials of Comparative Examples 1 and 2 that do not include a coating layer have a constant transition metal concentration.

6A, 6B, and 9a, 9b, the nickel-based positive electrode active material obtained in Examples 1 and 3 includes a coating layer having a Co concentration gradient, and is approximately from the surface of the positive electrode active material including the coating layer toward the center of the core. It can be seen that the concentration gradient of Co concentration decreases to 150 nm, and the concentration of all transition metals is kept constant inside the core. In addition, the positive electrode active materials of Examples 1 and 3, which are nickel-based positive electrode active materials, have a minimum concentration of Ni on the surface, and Comparative Example 1 not having a coating layer due to the introduction of a coating layer having a Co concentration gradient on the surface. It can be seen that the surface Ni concentration is reduced compared to (see FIGS. 5A and 5B).

7A, 7B and 10A, 10B, the nickel-based positive electrode active material obtained in Examples 2 and 4 includes a coating layer having a Mn concentration gradient, and from the surface of the positive electrode active material including the coating layer toward the center of the core. It can be seen that the concentration gradient of the Mn concentration decreases to about 150 nm, and the concentration of all transition metals is kept constant inside the core. In addition, the cathode active materials of Examples 2 and 4, which are nickel-based cathode active materials, have a minimum concentration of Ni on the surface, and comparative example 2 without a coating layer due to the introduction of a coating layer having a Mn concentration gradient on the surface ( 8a and 8b), it can be seen that the surface Ni concentration is decreased.

Evaluation Example 3: Room temperature life evaluation (1)

For the half-cells produced in Examples 5 to 6 and Comparative Example 7, after charging in CC mode to 4.45V at 0.5C at room temperature (25°C), charging in CV mode up to a current corresponding to 0.05C proceeds I did. Next, discharge was performed in CC mode to 3.0V at 1C, and this process was repeated a total of 100 times.

The capacity retention rate after 100 charging and discharging was calculated for the initial capacity, and the results are shown in Table 3 below. In addition, a graph showing the capacity retention rate according to the cycle is shown in FIG. 11.

After 100 charging/discharging
Capacity retention rate (%) Example 5 92.8 Example 6 98.7 Comparative Example 7 83.9

Referring to Table 3 and FIG. 11, the capacity retention rate after 100 charging/discharging is a comparison that does not include a concentration gradient region when the positive electrode active materials of Examples 5 and 6 including a coating layer including a concentration gradient region are included. Compared to Example 7, it showed a higher capacity retention rate of about 10% or more.

Evaluation Example 4: Room temperature life evaluation (2)

For the half-cells produced in Examples 7 to 8 and Comparative Example 8, charging in CC mode at room temperature (25°C) to 4.3V at 0.5C, and then charging in CV mode to a current corresponding to 0.05C Proceeded. Next, discharge was performed in CC mode to 3.0V at 1C, and this process was repeated a total of 100 times.

The capacity retention rate after 100 charging and discharging was calculated for the initial capacity, and the results are shown in Table 4 below. In addition, a graph showing the capacity retention rate according to the cycle is shown in FIG. 12.

After 100 charging/discharging
Capacity retention rate (%) Example 7 92.6 Example 8 94.1 Comparative Example 8 78.5

Referring to Table 4 and FIG. 12, the capacity retention rate after 100 charging/discharging is when the high-nickel cathode active materials of Examples 7 and 8 including coating layers including a concentration gradient region are included, the concentration gradient region is Compared to Comparative Example 8, which does not contain, it showed a higher capacity retention rate of about 14% or more.

Evaluation Example 5: Electrochemical evaluation (1)

For the half-cells produced in Example 7 and Comparative Examples 9 to 10, charged in CC mode at room temperature (25°C) to 4.3V at 0.5C, and then charged in CV mode to a current corresponding to 0.05C. Proceeded. Next, discharge was performed in CC mode to 3.0V at 1C to proceed with the initialization process.

The initial charge capacity and discharge capacity were measured, and the initial coulomb efficiency was measured and shown in Table 5 below. In addition, initial charge and discharge curves are shown in FIG. 13.

Initial charging capacity
(mAh/g) Initial discharge capacity
(mAh/g) Initial coulomb efficiency
(%) Example 7 223.1 203.2 91.0 Comparative Example 9 223.0 194.1 87.0 Comparative Example 10 225.2 193.5 85.9

Referring to Tables 5 and 13, it can be seen that the efficiency decreases when the Co concentration gradient region is 150 nm or more. Conceivably, when the concentration gradient region is 150 nm or more, it is considered that the Co concentration gradient region acts as a resistive layer of lithium ions, resulting in a decrease in efficiency.

Evaluation Example 6: Electrochemical Evaluation (2)

For the half-cells produced in Example 8 and Comparative Examples 11 to 12, charging in CC mode at room temperature (25°C) to 4.3V at 0.5C, and then charging in CV mode to a current corresponding to 0.05C Proceeded. Next, the initializing process was carried out by discharging in CC mode to 3.0V at 1C.

The initial charge capacity and discharge capacity were measured, and the initial coulomb efficiency was measured and shown in Table 6 below. In addition, the initial charge and discharge curves are shown in FIG. 14.

Initial charging capacity
(mAh/g) Initial discharge capacity
(mAh/g) Initial coulomb efficiency
(%) Example 8 222.3 201.7 90.7 Comparative Example 11 219.9 190.5 86.6 Comparative Example 12 220.2 190.3 86.4

Referring to Table 6 and FIG. 14, it can be seen that the efficiency decreases when the Mn concentration gradient region is 150 nm or more. It is conceivable that when the concentration gradient region is 150 nm or more, the Mn concentration gradient region acts as a resistive layer for lithium ions, resulting in a decrease in efficiency.

In the above, preferred embodiments according to the present invention have been described with reference to the drawings and embodiments, but these are only exemplary, and various modifications and other equivalent embodiments are possible from those of ordinary skill in the art. You will be able to understand. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims (19)

A core comprising a lithium transition metal oxide; And
A coating layer disposed on the surface of the core and including a transition metal;
Including,
The coating layer includes a concentration gradient region in which the concentration of the transition metal changes in the direction of the core from the surface to less than 150 nm,
The lithium transition metal oxide is a positive electrode active material represented by the following Formula 1:
<Formula 1>
Li _x P _y MO ₂
In Formula 1,
M is one or more transition metals,
0.98≤x≤1.02, 0<y<0.01. The method of claim 1,
The coating layer contains Mn and/or Co,
The coating layer includes a concentration gradient in which the concentration of Mn or Co decreases from the surface of the coating layer toward the core. The method of claim 1,
The coating layer contains Mn and/or Co,
A positive electrode active material comprising a concentration gradient region in which the concentration of Mn or Co decreases in the core direction from the surface of the coating layer to 100 nm or less. The method of claim 1,
The core has a constant concentration of a transition metal, a cathode active material. delete The method of claim 1,
The M is Ni, Co, Mn, Al, Mg, V, and including one or more transition metals selected from Ti, the positive electrode active material. The method of claim 1,
The lithium transition metal oxide is represented by the following formula (2), a positive electrode active material:
<Formula 2>
Li _x P _y Ni _1-z M1 _z O ₂
In Formula 2,
M1 is one or more transition metals selected from Co, Mn, Al, Mg, V, and Ti,
0.98≤x≤1.02, 0<y<0.01, 0<z<1 The method of claim 7,
0<z≤0.5, positive electrode active material. The method of claim 1,
The lithium transition metal oxide is represented by the following formula (3), a positive electrode active material:
<Formula 3>
Li _x P _y Ni _1-α-z M1 _z M2 _α O ₂
In Formula 3,
M1 and M2 are each independently at least one transition metal selected from Co, Mn, Al, Mg, V, and Ti,
M1 and M2 are different from each other,
0.98≤x≤1.02, 0<y<0.01, 0<α<1, 0<z<1, and 0<α+z<1 The method of claim 1,
The lithium transition metal oxide is represented by the following formula (4), a positive electrode active material;
<Formula 4>
Li _x P _y Ni _1-α-z Co _z M2 _α O ₂
In Formula 4,
M2 is at least one transition metal selected from Mn, Al, Mg, V, and Ti,
0.98≦x≦1.02, 0<y<0.01, 0<α<1, 0<z<1, and 0<α+z≦0.5. The method of claim 1,
The lithium transition metal oxide is represented by any one of the following Chemical Formulas 5 to 7, a cathode active material:
<Formula 5>
_{Li x 'P y' Ni 1} -α'-z 'Co z' Mn α 'O 2
<Formula 6>
Li _x'' P _y'' Ni _1-α''-z'' Co _z'' Al _α'' O ₂
<Formula 7>
Li _x''' P _y''' Ni _1-z''' Co _z''' O ₂
In Formulas 5 to 7,
0.98≤x'≤1.02, 0<y'<0.01, 0<α'≤0.3, and 0<z'≤0.3,
0.98≤x''≤1.02, 0<y''<0.01, 0<α''≤0.05, and 0<z''≤0.3,
0.98≤x'''≤1.02, 0<y'''<0.01, and 0<z'''≤0.2. The method of claim 1,
The positive electrode active material has an average particle diameter (D50) of 0.1 μm to 20 μm. The method of claim 1,
The core is a single crystal, a positive electrode active material. The method of claim 1,
The core is a single particle, a positive electrode active material. The method of claim 1,
The positive electrode active material in which the concentration of Ni in the coating layer is less than the concentration of Ni in the core. Preparing a lithium transition metal oxide; And
Providing a coating layer including a transition metal on the surface of the lithium transition metal oxide;
Including,
The lithium transition metal oxide is a method of manufacturing a positive electrode active material represented by the following Formula 1:
<Formula 1>
Li _x P _y MO ₂
In Formula 1,
M is one or more transition metals,
0.98≤x≤1.02, 0<y<0.01. The method of claim 16,
The step of providing the coating layer is:
Mixing the lithium transition metal oxide and the transition metal precursor, and comprising the step of heat treatment. The method of claim 17,
The heat treatment is carried out for 1 to 5 hours at a temperature of 400 ℃ to 800 ℃, the method for producing a positive electrode active material. Claims 1 to 4, and a positive electrode including the positive electrode active material according to any one of claims 6 to 15;
cathode; And
Electrolytes;
Lithium secondary battery comprising a.

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